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Ischemia-Induced Interleukin6 as a Potential Endogenous Neuroprotective Cytokine Against NMDA Receptor-Mediated Excitoxicity in the Brain
Abstract
In the brain, the expression of the pleiotropic cytokine interleukin-6 (IL-6) is enhanced in various chronic or acute central nervous system disorders. However, the significance of IL-6 production in such neuropathologic states remains controversial. The present study investigated the role of IL-6 after cerebral ischemia. First, the authors showed that focal cerebral ischemia in rats early up-regulated the expression of IL-6 mRNA, without affecting the transcription of its receptors (IL-6Rα and gp130). Similarly, the striatal injection of N-methyl-D-aspartate (NMDA) in rats, a paradigm of excitotoxic injury, activated the expression of IL-6 mRNA. The involvement of glutamatergic receptor activation was further investigated by incubating cortical neurons with NMDA or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA). NMDA and ionomycin (a calcium ionophore) up-regulated IL-6 mRNA, suggesting that neurons may produce IL-6 in response to the calcium influx mediated through NMDA receptors. The potential role of IL-6 during ischemic/excitotoxic insults was then studied by testing the effect of IL-6 against apoptotic or excitotoxic challenges in cortical cultures. IL-6 did not prevent serum deprivation- or staurosporine-induced apoptotic neuronal death, or AMPA/kainate-mediated excitotoxicity. However, in both mixed and pure neuronal cultures, IL-6 dose-dependently protected neurons against NMDA toxicity. This effect was blocked by a competitive inhibitor of IL-6. Overall, the results suggest that the up-regulation of IL-6 induced by cerebral ischemia could represent an endogenous neuroprotective mechanism against NMDA receptor-mediated injury.
... Interleukin-6 (IL-6) is a pleiotropic cytokine, which has been extensively investigated in a variety of diseases (Kishimoto, 1989;Wolf et al., 2014), including ischemic stroke where its role is still disputed (Jung et al., 2011;Loddick et al., 1998;Matsuda et al., 1996;Suzuki et al., 2009). A number of studies have shown an increase in IL-6 expression acutely in the brain after experimental stroke (Suzuki et al., 2009;Erta et al., 2012) while IL-6 receptor (IL-6R) expression has been reported to remain unchanged (Ali et al., 2000;Vollenweider et al., 2003) or increase at later time points (Gertz et al., 2012). Clinical studies show that IL-6 levels in serum and cerebrospinal fluid (CSF) increase significantly within the first 24 h after stroke and that IL-6 levels correlate with final infarct size and mortality (Beridze et al., 2011;Fassbender et al., 1994;Smith et al., 2004). ...
... Ischemia-induced upregulation of IL-6 has been suggested to represent an endogenous neuroprotective mechanism against Nmethyl-D-aspartate (NMDA) receptor-mediated injury (Ali et al., 2000). Furthermore, it appears that IL-6 produced in brain cells promotes post-stroke angiogenesis thereby improving long-term outcome after stroke (Gertz et al., 2012). ...
... From previous studies we know that IL-6 is significantly elevated after different types of cerebral ischemia but with variation in peak expression time varying from 6 h to 7 days depending on the type of ischemia (Ali et al., 2000;Herrmann et al., 2003;Clark et al., 1999;Nakamachi et al., 2012). Up-regulation of IL-6 after cerebral ischemia can represent endogenous neuroprotective mechanisms (Gertz et al., 2012;Yamashita et al., 2005). ...
Interleukin-6 (IL-6) is a pleiotropic cytokine with neuroprotective properties. Still, the therapeutic potential of IL-6 after experimental stroke has not yet been investigated in a clinically relevant way. Here, we investigated the therapeutic use of intravenously administered IL-6 and the soluble IL-6 receptor (sIL-6R) alone or in combination, early after permanent middle cerebral artery occlusion (pMCAo) in mice. IL-6 did not affect the infarct volume in C57BL/6 mice, at neither 24 nor 72 h after pMCAo but reduced the infarct volume in IL-6 knockout mice at 24 h after pMCAo. Assessment of post-stroke behavior showed an improved grip strength after a single IL-6 injection and also improved rotarod endurance after two injections, in C57BL/6 mice at 24 h. An improved grip strength and a better preservation of sensory functions was also observed in IL-6 treated IL-6 knockout mice 24 h after pMCAo. Co-administration of IL-6 and sIL-6R increased the infarct volume, the number of infiltrating polymorphonuclear leukocytes and impaired the rotarod endurance of C57BL/6 mice 24 h after pMCAo. IL-6 administration to naïve C57BL/6 mice lead after 45 minutes to increased plasma-levels of CXCL1 and IL-10, whereas IL-6 administration to C57BL/6 mice lead to a reduction in the ischemia-induced increase in IL-6 and CXCL1 at both mRNA and protein level in brain, and of IL-6 and CXCL1 in serum. We also investigated the expression of IL-6 and IL-6R after pMCAo and found that cortical neurons upregulated IL-6 mRNA and protein, and also upregulated the IL-6R after pMCAo. In conclusion, the results show a complex but potentially beneficial effect of intravenously administered IL-6 in experimental stroke.
... During the maturation period, the gene expression of gp130 remained stable, while the expression of IL-6R increased. Previous studies have reported similar findings for IL-6-related receptors at the mRNA level in hESC-derived neural progenitors and at both the mRNA and protein levels in mouse cortical neurons (Ali et al., 2000;Hagman et al., 2019). Furthermore, the expression of gp130 and IL-6R was confirmed at the protein level, although gp130 levels were reduced and IL-6R levels increased in the late maturation stage. ...
... The exact role of IL-6 in epilepsy is not known, but in vitro studies with neuronal cultures have revealed that it plays a crucial role in neuroprotection and neurogenesis (Sulistio et al., 2018;Ali et al., 2000;Ma et al., 2015). Moreover, IL-6 has been shown to support the morphological and electrophysiological maturation of hiPSC-derived neurons detected with the patch clamp technique (Sulistio et al., 2018). ...
Human pluripotent stem cell (hPSC)-derived neural cultures have attracted interest for modeling epilepsy and seizure-like activity in vitro. Clinical and experimental evidence have shown that the multifunctional inflammatory cytokine interleukin (IL)-6 plays a significant role in epilepsy. However, the role of IL-6 in neuronal networks remains unclear. In this study, we modelled seizure-like activity in hPSC-derived cortical neurons using kainic acid (KA) and explored the effects of IL-6 and its counterpart, hyper-IL-6 (H-IL-6), a fusion protein consisting of IL-6 and its soluble receptor, IL-6R. In the seizure-like model, functionally mature neuronal networks responded to KA induction with an increased bursting phenotype at the single electrode level, while network level bursts decreased. The IL-6 receptors, IL6R and gp130, were expressed in hPSC-derived cortical neurons, and the gene expression of IL6R increased during maturation. Furthermore, the expression of IL-6R increased not only after IL-6 and H-IL-6 treatment but also after KA treatment. Stimulation with IL-6 or H-IL-6 was not toxic to the neurons and cytokine pretreatment did not independently modulate neuronal network activity or KA-induced seizures. Furthermore, the increased expression of IL-6R in response to IL-6, H-IL-6 and KA implies that neurons can respond through both classical and trans-signaling pathways. Acute treatment with IL-6 and H-IL-6 did not alter functional activity, suggesting that IL-6 does not affect the induction or modulation of newly induced seizures in healthy cultures. Overall, we propose this model as a useful tool to study seizure-like activity in neuronal networks in vitro.
... Furthermore, the clinical documentation that smaller infarcts translate into better neurological outcome [2,127] emphasizes the importance of infarct volume reduction, ideally in conjunction with improved functional recovery, as an important outcome in experimental stroke research. The size of ischemic damage is typically presented as: 1-total infarct volume ('direct infarct volume' given in mm 3 ), or 2-percentage of infarcted tissue in the ipsilateral hemisphere, corrected for edema formation and infarct resorption ('indirect infarct volume') (for details see [140]). Infarct volumes given as percentages and corrected for edema/resorption remain largely constant from 24 h to 24 weeks [140]. ...
... IL-6 is expressed in the normal CNS, where it influences neuronal homeostasis by acting as a neurotrophic factor via the classical signaling pathway (reviewed by [147]). Ischemic stroke in mice and rats leads to a significant increase in the levels of IL-6 from 6 to 12 h ( Fig. 1 and 2c), and in both IL-6R and gp130 from 3 days [3,70]. IL-6 has been shown to be neuroprotective in experimental stroke [192] although this is still debated [29]. ...
Inflammation is currently considered a prime target for the development of new stroke therapies. In the acute phase of ischemic stroke, microglia are activated and then circulating immune cells invade the peri-infarct and infarct core. Resident and infiltrating cells together orchestrate the post-stroke inflammatory response, communicating with each other and the ischemic neurons, through soluble and membrane-bound signaling molecules, including cytokines. Inflammation can be both detrimental and beneficial at particular stages after a stroke. While it can contribute to expansion of the infarct, it is also responsible for infarct resolution, and influences remodeling and repair. Several pre-clinical and clinical proof-of-concept studies have suggested the effectiveness of pharmacological interventions that target inflammation post-stroke. Experimental evidence shows that targeting certain inflammatory cytokines, such as tumor necrosis factor, interleukin (IL)-1, IL-6, and IL-10, holds promise. However, as these cytokines possess non-redundant protective and immunoregulatory functions, their neutralization or augmentation carries a risk of unwanted side effects, and clinical translation is, therefore, challenging. This review summarizes the cell biology of the post-stroke inflammatory response and discusses pharmacological interventions targeting inflammation in the acute phase after a stroke that may be used alone or in combination with recanalization therapies. Development of next-generation immune therapies should ideally aim at selectively neutralizing pathogenic immune signaling, enhancing tissue preservation, promoting neurological recovery and leaving normal function intact.
... Upregulated in serum and CSF within 24 h, newborns (Aly et al., 2006;Chiesa et al., 2003;Jenkins et al., 2012;Savman et al., 1998) Upregulated in lesioned brain at 3 h after HI, P7 rats (Hagberg et al., 1996;Li et al., 2014) 1) Induces nonspecific cell death and reduces the neuronal differentiation and accumulation (Monje et al., 2003); 2) promote HI-induced neuronal apoptosis ; 3) protects neurons against apoptosis by reducing N-methyl-Daspartate toxicity (Ali et al., 2000;Fang et al., 2013;Liu et al., 2011); 4) enhances astrocyte survival through IL-6/STAT3 signaling (Gu et al., 2016). ...
... IL-6 has the anti-inflammatory actions by inhibiting the synthesis of TNF-a and IL-1b, as well as by stimulating the production of their endogenous antagonists. Moreover, several studies have linked IL-6 to neuron protection against apoptosis by reducing N-methyl-D-aspartate toxicity (Ali et al., 2000;Fang et al., 2013;Liu et al., 2011). In human neonates with perinatal asphyxia, the levels of IL-6 are significantly higher and show a biphasic pattern with early and delayed peaks (Jenkins et al., 2012). ...
Perinatal hypoxia-ischemia remains the primary cause of acute neonatal brain injury, leading to a high mortality rate and long-term neurological deficits, such as behavioral, social, attentional, cognitive and functional motor deficits. An ever-increasing body of evidence shows that the immune response to acute cerebral hypoxia-ischemia is a major contributor to the pathophysiology of neonatal brain injury. Hypoxia-ischemia provokes an intravascular inflammatory cascade that is further augmented by the activation of resident immune cells and the cerebral infiltration of peripheral immune cells response to cellular damages in the brain parenchyma. This prolonged and/or inappropriate neuroinflammation leads to secondary brain tissue injury. Yet, the long-term effects of immune activation, especially the adaptive immune response, on the hypoxic-ischemic brain still remain unclear. The focus of this review is to summarize recent advances in the understanding of post-hypoxic-ischemic neuroinflammation triggered by the innate and adaptive immune responses and to discuss how these mechanisms modulate the brain vulnerability to injury. A greater understanding of the reciprocal interactions between the hypoxic-ischemic brain and the immune system will open new avenues for potential immunomodulatory therapy in the treatment of neonatal brain injury.
... Though this drug has shown an efficacy greater than clozapine in this network meta-analysis, this is the result of only one study included in this analysis and not known to be used in clinical practice yet. There are two main hypotheses to explain the escitalopram augmentation in schizophrenia, firstly, escitalopram increases firing rate and burst firing of dopamine neurons in the ventral tegmental area, potentiates cortical NMDA receptor-mediated transmission which may contribute to their ability to improve negative symptoms and cognitive dysfunction in schizophrenia [65]; secondly, impairments in NMDA receptor-mediated signaling and exposure to psychological and physical stressors enhance the production and release of pro-inflammatory cytokines such as IL-6 and high serum levels of IL-6 in schizophrenic patients correlate with symptom severity [66]. The previous study by Ding et al. reported a significant decrease in IL-6 level by escitalopram in schizophrenia and change in IL-6 level was associated with negative and cognitive symptoms [23]. ...
Objective:
The present network meta-analysis (NMA) was conducted to compare and generate evidence for the most efficacious treatment among available pharmacological interventions for treatment-resistant schizophrenia (TRS).
Methods:
Reviewers extracted data from 47 studies screened from PubMed/MEDLINE, Embase, Cochrane databases and clinical trial registries fulfilling the eligibility criteria. Random effects Bayesian NMA was done with non-informative priors. Network geometry was visualized, and node splitting was done for the closed triangles. Standardized mean difference and 95% credible interval(95%CrI) were reported for the reduction in symptom severity scores. The probability of each intervention for each rank was plotted. Meta-regression was done for the duration of the therapy.
Results:
Augmentation of antipsychotics with escitalopram (SMD: -1.7[95%CrI: -2.8, -0.70]), glycine (SMD: -1.2 [95%CrI: -2.2, -0.28]) and Yokukansan (SMD: -1.3 [95%CrI: -2.4, -0.24]) shows a statistically significant reduction in symptom severity when compared to clozapine. As per surface under cumulative ranking curve analysis, escitalopram in combination with antipsychotics appeared to be the best intervention with moderate certainty of evidence. There was no significant effect of the duration of therapy on the treatment effects.
Conclusion:
Escitalopram augmentation of antipsychotics appears to be the most efficacious treatment with moderate certainty of evidence among the available pharmacological interventions.
Prospero registration:
CRD42022380292.
... An example of this is vascular endothelial growth factor A (VEGFA) which causes permeability of the blood-brain barrier, thereby worsening brain edema in the early phase, yet is a potent inducer of angiogenesis at later phases (reviewed in [14]). Similarly, the pro-inflammatory cytokine interleukin (IL)-6 propels the immune response at early stages of stroke but contributes to neuroprotection and neurogenesis during stroke recovery [15][16][17]. Different therapeutic approaches to regulate the inflammatory response, the levels of growth factors, or other signaling molecules released in response to stroke, have been tested in animal models. Translation into human therapy has, however, been challenged by the intricacy and temporal changes in the signaling cascades these therapies aim to affect. ...
Stroke is the main cause for acquired disabilities. Pharmaceutical or mechanical removal of the thrombus is the cornerstone of stroke treatment but can only be administered to a subset of patients and within a narrow time window. Novel treatment options are therefore required. Here we induced stroke by permanent occlusion of the distal medial cerebral artery of wild-type mice and knockout mice for the lactate receptor hydroxycarboxylic acid receptor 1 (HCA1). At 24 h and 48 h after stroke induction, we injected L-lactate intraperitoneal. The resulting atrophy was measured in Nissl-stained brain sections, and capillary density and neurogenesis were measured after immunolabeling and confocal imaging. In wild-type mice, L-lactate treatment resulted in an HCA1-dependent reduction in the lesion volume accompanied by enhanced angiogenesis. In HCA1 knockout mice, on the other hand, there was no increase in angiogenesis and no reduction in lesion volume in response to L-lactate treatment. Nevertheless, the lesion volumes in HCA1 knockout mice—regardless of L-lactate treatment—were smaller than in control mice, indicating a multifactorial role of HCA1 in stroke. Our findings suggest that L-lactate administered 24 h and 48 h after stroke is protective in stroke. This represents a time window where no effective treatment options are currently available.
... In addition to IL-1β and TNF-α, IL-6 is also a pleiotropic cytokine that is involved in stroke, but its function is still controversial. Although accumulating evidence suggests that the inhibition of IL-6 can exert a protective effect on the brain, studies by Ali et al. showed that ischemia-induced IL-6 was an endogenous cytokine that exerted neuroprotective effects against NMDA receptor-mediated injury [50,51]. Notably, microglia are involved in phagocytosis and chemotaxis in addition to regulating neuroinflammation [52]. ...
Background
Emerging evidence has shown that myeloid cells that infiltrate into the peri-infarct region may influence the progression of ischemic stroke by interacting with microglia. Properdin, which is typically secreted by immune cells such as neutrophils, monocytes, and T cells, has been found to possess damage-associated molecular patterns (DAMPs) properties and can perform functions unrelated to the complement pathway. However, the role of properdin in modulating microglia-mediated post-stroke neuroinflammation remains unclear.
Methods
Global and conditional (myeloid-specific) properdin-knockout mice were subjected to transient middle cerebral artery occlusion (tMCAO). Histopathological and behavioral tests were performed to assess ischemic brain injury in mice. Single-cell RNA sequencing and immunofluorescence staining were applied to explore the source and the expression level of properdin. The transcriptomic profile of properdin-activated primary microglia was depicted by transcriptome sequencing. Lentivirus was used for macrophage-inducible C-type lectin (Mincle) silencing in microglia. Conditioned medium from primary microglia was administered to primary cortex neurons to determine the neurotoxicity of microglia. A series of cellular and molecular biological techniques were used to evaluate the proinflammatory response, neuronal death, protein–protein interactions, and related signaling pathways, etc.
Results
The level of properdin was significantly increased, and brain-infiltrating neutrophils and macrophages were the main sources of properdin in the ischemic brain. Global and conditional myeloid knockout of properdin attenuated microglial overactivation and inflammatory responses at the acute stage of tMCAO in mice. Accordingly, treatment with recombinant properdin enhanced the production of proinflammatory cytokines and augmented microglia-potentiated neuronal death in primary culture. Mechanistically, recombinant properdin served as a novel ligand that activated Mincle receptors on microglia and downstream pathways to drive primary microglia-induced inflammatory responses. Intriguingly, properdin can directly bind to the microglial Mincle receptor to exert the above effects, while Mincle knockdown limits properdin-mediated microglial inflammation.
Conclusion
Properdin is a new medium by which infiltrating peripheral myeloid cells communicate with microglia, further activate microglia, and exacerbate brain injury in the ischemic brain, suggesting that targeted disruption of the interaction between properdin and Mincle on microglia or inhibition of their downstream signaling may improve the prognosis of ischemic stroke.
... As a B-cell differentiation factor (BSF-2) originally identified in 1985 [5], interleukin-6 (IL-6) was found to play a significant role in the central nervous system [6]. Patients with various neurological disorders such as brain cancer, Parkinson's disease [7], multiple sclerosis (MS), Alzheimer's disease (AD), and brain ischemia are often associated with high expression and secretion of IL-6 [8][9][10][11][12]. However, levels of IL-6 in cerebrospinal fluid after craniotomy were much higher than in other diseases. ...
We monitored CSF (cerebrospinal fluid) for Th1/Th2 inflammatory cytokines in a patient with unexplained postoperative disturbance of consciousness after craniotomy and found that the level of IL-6 (interleukin-6) concentrations was extremely high, meeting the traditional criteria for an inflammatory cytokine storm. Subsequently, the cerebrospinal fluid specimens of several patients were tested, and it was found that IL-6 levels were increased in different degrees after craniotomy. Previous studies have focused more on mild and long-term IL-6 elevation, but less on the effects of this short-term IL-6 inflammatory cytokine storm. Cerebrospinal fluid rich in IL-6 may play a significant role in patients after craniotomy. The objective is to explore the degree of IL-6 elevation and the incidence of IL-6 inflammatory cytokine storm in patients after craniotomy, as well as the effect of IL-6 elevation on the brain. In this study, the levels and clinical manifestations of inflammatory factors in cerebrospinal fluid after craniotomy were statistically classified, and the underlying mechanisms were discussed preliminarily. CSF specimens of patients after craniotomy were collected, IL-6 level was measured at 1, 5, and 10 days after operation, and cognitive function was analyzed at 1, 10, and 180 days after surgery. Craniotomy mouse model, cerebrospinal fluid of patients with the appearance of IL-6 storm after craniotomy, and IL-6 at the same concentration stimulation model were established. Behavioral tests, fluorescence in situ hybridization (FISH), pathological means, western blot, and ELISA (enzyme-linked immune-sorbent assay) were performed for verification. CSF from patients after craniotomy caused disturbance of consciousness in mice, affected neuronal damage in the hypothalamus, activation of microglia in the hypothalamus, and decreased expression of barrier proteins in the hypothalamus and brain. The large amount of interleukin-6 in CSF after craniotomy was found to be mainly derived from astrocytes. The IL-6 level in CSF after craniotomy correlated inversely with patients’ performance in MoCA test. High levels of IL-6 in the cerebrospinal fluid derived from astrocytes after craniotomy may lead to disruption of the brain-cerebrospinal fluid barrier, most notably around the hypothalamus, which might result in inflammatory activation of microglia to damage the hypothalamic neurons and impaired cognitive function/more gradual cognitive repairment in patients after craniotomy with the appearance of IL-6 storm.
... Conversely, GM-CSF stimulates microglial IL-6 but not astrocytes. Glutamate-mediated membrane depolarization is one of the main mechanisms for neuronal upregulation of IL-6 [103,104]. ...
Poor outcomes in Subarachnoid Hemorrhage (SAH) are in part due to a unique form of secondary neurological injury known as Delayed Cerebral Ischemia (DCI). DCI is characterized by new neurological insults that continue to occur beyond 72 h after the onset of the hemorrhage. Historically, it was thought to be a consequence of hypoperfusion in the setting of vasospasm. However, DCI was found to occur even in the absence of radiographic evidence of vasospasm. More recent evidence indicates that catastrophic ionic disruptions known as Cortical Spreading Depolarizations (CSD) may be the culprits of DCI. CSDs occur in otherwise healthy brain tissue even without demonstrable vasospasm. Furthermore, CSDs often trigger a complex interplay of neuroinflammation, microthrombi formation, and vasoconstriction. CSDs may therefore represent measurable and modifiable prognostic factors in the prevention and treatment of DCI. Although Ketamine and Nimodipine have shown promise in the treatment and prevention of CSDs in SAH, further research is needed to determine the therapeutic potential of these as well as other agents.
... IL-6 can penetrate the BBB or be produced intrathecally; IL-6 mRNA is upregulated in the hippocampus and cerebral cortex of NPSLE patients [108]. Additionally, neuronal production of IL-6 can be induced by prolonged NMDAR activation which may result from autoantibodies or from increased levels of quinolinic acid [109,110]. ...
Neuropsychiatric lupus (NPSLE) is a debilitating manifestation of SLE which occurs in a majority of SLE patients and has a variety of clinical manifestations. In the central nervous system, NPSLE may result from ischemia or penetration of inflammatory mediators and neurotoxic antibodies through the blood brain barrier (BBB). Here we focus on cognitive dysfunction (CD) as an NPSLE manifestation; it is common, underdiagnosed, and without specific therapy.
For a very long time, clinicians ignored cognitive dysfunction and researchers who might be interested in the question struggled to find an approach to understanding mechanisms for this manifestation. Recent years, however, propelled by a more patient-centric approach to disease, have seen remarkable progress in our understanding of CD pathogenesis. This has been enabled through the use of novel imaging modalities and numerous mouse models. Overall, these studies point to a pivotal role of an impaired BBB and microglial activation in leading to neuronal injury. These insights suggest potential therapeutic modalities and make possible clinical trials for cognitive impairment.
... Although some cytokines aggravate cerebral damage, other cytokines, such as interleukin-10 (IL-10), a neurotrophic cytokine containing neurons and glia, exert a neuroprotective role during stroke [8]. Published work validated the protective mechanism of IL-10 towards cortical neurons via the activation of PI-3 kinase and STAT-3 pathways [9]. Preexisting interleukin-10 in cerebral arteries showed mitigation of brain damage induced by ischemic brain injury following MCAO [10]. ...
Inflammation is dominant in the pathogenesis of ischemic stroke (IS). Alpha-ketoglutarate (AKG), according to previous studies, has demonstrated a variety of pharmacological effects such as antioxidation and inhibitive inflammation activities. However, whether AKG ameliorates cerebral ischemic injury, as well as the underlying molecular events, is still unclear. Therefore, the effect and underlying mechanisms of AKG on ischemic brain injury should be identified. The study established a cerebral ischemia-reperfusion (I/R) model in mice as well as an oxygen-glucose deprivation/reperfusion (OGD/R) model in SH-SY5Y cells, respectively. It was observed that AKG markedly suppressed infarction volume and neuronal injuries and improved the neurological score in vivo. Moreover, AKG reduced the inflammatory response and lowered the expression of proinflammatory cytokines. In vitro, AKG treatment strongly inhibited OGD/R-induced neuronal injury and the proinflammatory factors. It was also found that the increased SOD and GSH levels, as well as the lower ROS levels, showed that AKG reduced oxidative stress in OGD/R-treated SY-SY5Y cells. Mechanistically, AKG largely promoted IL-10 expression in ischemic brain injury and OGD/R-induced neuronal injury. Furthermore, IL-10 silencing neutralized the protective effect of AKG on inflammation. Notably, it was discovered that AKG could upregulate IL-10 expression by promoting the translocation of c-Fos from the cytoplasm to the nucleus. The results indicated that AKG demonstrated neuroprotection on cerebral ischemia while inhibiting inflammation through c-Fos/IL-10/stat3 pathway.
... Under pathological conditions, IL-6 levels dramatically increase in the CNS and may be neuroprotective. For instance, microglial IL-6 prevents neuronal loss of neural progenitor cells during herpes simplex virus type 1 infection (113), and endogenous upregulation of IL-6 in response to cerebral ischemia is neuroprotective against excitotoxicity (114). However, elevated IL-6 levels in the fetal brain after maternal immune activation is a key mediator of transcriptional and behavioral alterations in the adult offspring brain (115,116). ...
Central nervous system (CNS) infections occur more commonly in young children than in adults and pose unique challenges in the developing brain. This review builds on the distinct vulnerabilities in children's peripheral immune system (outlined in part 1 of this review series) and focuses on how the developing brain responds once a CNS infection occurs. Although the protective blood-brain barrier (BBB) matures early, pathogens enter the CNS and initiate a localized innate immune response with release of cytokines and chemokines to recruit peripheral immune cells that contribute to the inflammatory cascade. This immune response is initiated by the resident brain cells, microglia and astrocytes, which are not only integral to fighting the infection but also have important roles during normal brain development. Additionally, cytokines and other immune mediators such as matrix metalloproteinases from neurons, glia, and endothelial cells not only play a role in BBB permeability and peripheral cell recruitment, but also in brain maturation. Consequently, these immune modulators and the activation of microglia and astrocytes during infection adversely impact normal neurodevelopment. Perturbations to normal brain development manifest as neurodevelopmental and neurocognitive impairments common among children who survive CNS infections and are often permanent. In part 2 of the review series, we broadly summarize the unique challenges CNS infections create in a developing brain and explore the interaction of regulators of neurodevelopment and CNS immune response as part of the neuro-immune axis.
... IL-6 may also play a neuroprotective role. For example, against N-methyl-D-aspartic acid receptor-mediated brain excitatory toxicity (Ali et al., 2000). ...
Subarachnoid hemorrhage (SAH) has a high mortality rate and causes long-term disability in many patients, often associated with cognitive impairment. However, the pathogenesis of delayed brain dysfunction after SAH is not fully understood. A growing body of evidence suggests that neuroinflammation and oxidative stress play a negative role in neurofunctional deficits. Red blood cells and hemoglobin, immune cells, proinflammatory cytokines, and peroxidases are directly or indirectly involved in the regulation of neuroinflammation and oxidative stress in the central nervous system after SAH. This review explores the role of various cellular and acellular components in secondary inflammation and oxidative stress after SAH, and aims to provide new ideas for clinical treatment to improve the prognosis of SAH.
... Nonetheless, IL-6 is emerging as an important mediator of neurogenesis and aids in long-term functional recovery after ischemic stroke. IL-6 alleviates glutamate excitotoxicity as well as ischemia in the brain [141,2,105,140]. IL-6 treatment improves infarct volumes and neurological scores, reduces neuronal death as well as IL-1β and TNF-α expression, and increases brain blood barrier integrity [113,65]and neural stem transplantation of IL-6 preconditioned cells promotes survival in mice subjected to ischemic stroke [217]. ...
The pleiotropic cytokine interleukin-6 (IL-6) is emerging as a molecule with both beneficial and destructive potentials. It can exert opposing actions triggering either neuron survival after injury or causing neurodegeneration and cell death in neurodegenerative or neuropathic disorders. Importantly, neurons respond differently to IL-6 and this critically depends on their environment and whether they are located in the peripheral or the central nervous system. In addition to its hub regulator role in inflammation, IL-6 is recently emerging as an important regulator of neuron function in health and disease, offering exciting possibilities for more mechanistic insight into the pathogenesis of mental, neurodegenerative and pain disorders and for developing novel therapies for diseases with neuroimmune and neurogenic pathogenic components.
... Based on this expression analysis, we subjected Slack WT and KO mice to an in vivo model of intrastriatal NMDA microinjection, allowing us to directly assess whether the presence or absence of endogenous Slack channels affects the extent of NMDA-triggered neuronal damage. [77][78][79][80] Importantly, in this in vivo model, interactions between Slack expression in GABAergic neurons and potentially other efferent/afferent striatal neurons can be examined in their physiological and pathophysiological context and therefore in the presence of all neuroprotective and neurotoxic mediators. These include growth factors, inflammatory cytokines, NO, and neuropeptides that are released from activated astrocytes or microglia to contribute to the outcome. ...
The neuronal Na⁺‐activated K⁺ channel Slack (aka Slo2.2, KNa1.1, or Kcnt1) has been implicated in setting and maintaining the resting membrane potential and defining excitability and firing patterns, as well as in the generation of the slow afterhyperpolarization following bursts of action potentials. Slack activity increases significantly under conditions of high intracellular Na⁺ levels, suggesting this channel may exert important pathophysiological functions. To address these putative roles, we studied whether Slack K⁺ channels contribute to pathological changes and excitotoxic cell death caused by glutamatergic overstimulation of Ca²⁺‐ and Na⁺‐permeable N‐methyl‐D‐aspartic acid receptors (NMDAR). Slack‐deficient (Slack KO) and wild‐type (WT) mice were subjected to intrastriatal microinjections of the NMDAR agonist NMDA. NMDA‐induced brain lesions were significantly increased in Slack KO vs WT mice, suggesting that the lack of Slack renders neurons particularly susceptible to excitotoxicity. Accordingly, excessive neuronal cell death was seen in Slack‐deficient primary cerebellar granule cell (CGC) cultures exposed to glutamate and NMDA. Differences in neuronal survival between WT and Slack KO CGCs were largely abolished by the NMDAR antagonist MK‐801, but not by NBQX, a potent and highly selective competitive antagonist of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA)‐type ionotropic glutamate receptors. Interestingly, NMDAR‐evoked Ca²⁺ signals did not differ with regard to Slack genotype in CGCs. However, real‐time monitoring of K⁺ following NMDAR activation revealed a significant contribution of this channel to the intracellular drop in K⁺. Finally, TrkB and TrkC neurotrophin receptor transcript levels were elevated in NMDA‐exposed Slack‐proficient CGCs, suggesting a mechanism by which this K⁺ channel contributes to the activation of the extracellular‐signal‐regulated kinase (Erk) pathway and thereby to neuroprotection. Combined, our findings suggest that Slack‐dependent K⁺ signals oppose the NMDAR‐mediated excitotoxic neuronal injury by promoting pro‐survival signaling via the BDNF/TrkB and Erk axis.
... It has been demonstrated that IL-6 is neuroprotective in cerebral ischemia [40][41][42][43], so it is plausible that exercise-induced IL-6 release contributes to the protection against ischemic stroke. In vivo administration of 50 ng IL-6 reduced cerebral infarction, restored SOD-2 expression via IL-6R-STAT3 pathway, and blocked the oxidation and dissociation of IL-6R and gp130 [40]. ...
There is a growing body of evidence showing the importance of physical activity against acute ischemic events in various organs. Ischemia/reperfusion injury (I/R) is characterized by tissue damage as a result of restriction and subsequent restoration of blood supply to an organ. Oxidative stress due to increased reactive oxygen species formation and/or insufficient antioxidant defense is considered to play an important role in I/R. Physical activity not only decreases the general risk factors for ischemia but also confers direct anti-ischemic protection via myokine production. Myokines are skeletal muscle-derived cytokines, representing multifunctional communication channels between the contracting skeletal muscle and other organs through an endocrine manner. In this review, we discuss the most prominent members of the myokines (i.e., brain-derived neurotrophic factor (BDNF), cathepsin B, decorin, fibroblast growth factors-2 and-21, follistatin, follistatin-like, insulin-like growth factor-1; interleukin-6, interleukin-7, interleukin-15, irisin, leukemia inhibitory factor, meteorin-like, myonectin, musclin, myostatin, and osteoglycin) with a particular interest in their potential influence on reactive oxygen and nitrogen species formation or antioxidant capacity. A better understanding of the mechanism of action of myokines and particularly their participation in the regulation of oxidative stress may widen their possible therapeutic use and, thereby, may support the fight against I/R.
... Production of IL-1β is induced by TNF-α, which shares many of its activities, including its ability to induce IL-6 production (Clark et al. 2010). Some studies have reported that IL-6 protects neurons against various types of damage (Ali et al. 2000;Yamashita et al. 2005). It has been hypothesized that the pathophysiology of the cytokine storm is attributable to the excessive production of proinflammatory cytokines that induce vascular endothelial cell dysfunction, resulting in the deterioration of vascular permeability. ...
The pathogenesis of virus-associated acute encephalopathy (VAE) involves brain edema caused by disruption of the blood–brain barrier (BBB). We aimed to develop an in vitro VAE model using an in vitro BBB model, to evaluate the dynamics of vascular dysfunction caused by tumor necrosis factor (TNF)-α. A co-culture model, consisting of Transwell®-grown human brain microvascular endothelial cells and pericytes, was treated with serially diluted TNF-α. Transendothelial electrical resistance (TER) was measured using cellZscope®. A permeability assay, using fluorescein isothiocyanate-conjugated sodium or dextran, was performed. Changes in claudin-5 localization and expression after TNF-α treatment were observed using immunofluorescence staining and western blot analysis. The TER decreased and permeability increased after TNF-α treatment; recovery time was dependent on TNF-α concentration. Claudin-5 was delocalized after TNF-α treatment and recovered in a TNF-α concentration-dependent manner. The expression of claudin-5 decreased 24 h after the TNF-α treatment and completely recovered 48 h after TNF-α treatment. Claudin-5 delocalization was likely associated with vascular hyperpermeability. To conclude, we evaluated vascular endothelial cell permeability and injury in VAE using an in vitro BBB model treated with TNF-α. This system can be useful for developing novel therapeutic strategies for VAE and designing treatments that target vascular permeability.
... With regard to the CNS, Suzuki et al. demonstrated that IL-6 plays a protective role in the early stage of brain injury. Intracerebroventricular injection of rhIL-6 dramatically reduces ischaemic brain damage measured 24 hours after middle cerebral artery occlusion [13,14,15]. ...
Background: Malignant ventricular arrhythmia is one of the main reason of death in acute myocardial infarction. In recent years, more and more attention has been paid to the mechanism of its pathogenesis. In this study we investigated the changes of inflammatory factors in the paraventricular nucleus during acute myocardial infarction and its effect on ventricular stability. Methods : The rats were divided into control group, myocardial infarction group and drug-administered group to observe how interleukin-6 and its downstream GP130-STAT3 pathway in paraventricular nucleus effect the ventricular stability . All data are expressed as the mean ± SEM. One-way ANOVA was used for comparison between groups, and the LSD test was used for comparison between two groups. p
... With regard to the CNS, Suzuki et al. demonstrated that IL-6 plays a protective role in the early stage of brain injury. Intracerebroventricular injection of rhIL-6 dramatically reduces ischaemic brain damage measured 24 hours after middle cerebral artery occlusion [13,14,15]. ...
Background: Malignant ventricular arrhythmias are the most common cause of death in acute myocardial infarction. Recent studies have revealed direct paraventricular nucleus (PVN) involvement in occurrence of ventricular arrhythmias (VAs)，however, the mechanisms are incompletely understood. In this study we investigated the changes of Interleukin-6 (IL-6)-glycorprotein130-STAT3 pathway in the PVN during acute myocardial infarction and its effect on ventricular stability. Methods: The rats were divided into control group, myocardial infarction group, and paraventricular injected anti-IL-6 antibody group and paraventricular injected SC144 group to observe how interleukin-6 and its downstream glycoprotein130-STAT3 pathway in paraventricular nucleus effect the ventricular stability. Left anterior descending coronary artery was ligated to make myocardial infarction. After that, anti-Interleukin-6 antibody and SC144 were injected into the paraventricular. All data are expressed as the mean ± SEM and were analyzed by ANOVA by a post-hoc LSD test. p
... With regard to the CNS, Suzuki et al. demonstrated that IL-6 plays a protective role in the early stage of brain injury. Intracerebroventricular injection of rhIL-6 dramatically reduces ischaemic brain damage measured 24 hours after middle cerebral artery occlusion [13,14,15]. ...
Background: Malignant ventricular arrhythmia (VA) is the most common cause of death associated with acute myocardial infarction (MI). Recent studies have revealed direct involvement of the paraventricular nucleus (PVN) in the occurrence of VA. However, the underlying mechanisms remain incompletely understood. In this study, we investigated changes in the interleukin-6 (IL-6)-glycoprotein 130-signal transducer and activator of transcription 3 (STAT3) pathway in the PVN during acute MI and the effects of this pathway on ventricular stability. Methods: Rats were divided into a control group, a MI group, a PVN-injected anti-IL-6 antibody group and a PVN-injected SC144 group to observe how IL-6 and its downstream glycoprotein 130-STAT3 pathway in the PVN affect ventricular stability. The left anterior descending coronary artery was ligated to induce MI. After that, an anti-IL-6 antibody and SC144 were injected into the PVNs of rats. All data are expressed as the mean ± SE and were analysed by ANOVA with a post hoc LSD test. p<0.05 was considered to indicate statistical significance. Results: After MI, the concentration of the inflammatory factor IL-6 increased, and its downstream glycoprotein 130-STAT3 pathway was activated in the PVN. After injection of MI rat PVNs with the anti-IL-6 antibody or glycoprotein 130 inhibitor (SC144), glutamate levels increased and γ-aminobutyric acid (GABA) levels decreased in the PVN. Plasma norepinephrine concentrations also increased after treatment, which increased the vulnerability to VA. Conclusions: In summary, IL-6 in the PVN exerts a protective effect in MI rats, and the glycoprotein 130-STAT3 pathway plays a key role in this process. We anticipate that our findings will provide new ideas for the prevention and treatment of arrhythmia after MI.
... With regard to the CNS, Suzuki et al. demonstrated that IL-6 plays a protective role in the early stage of brain injury. Intracerebroventricular injection of rhIL-6 dramatically reduces ischaemic brain damage measured 24 hours after middle cerebral artery occlusion [13,14,15]. ...
Background: Malignant ventricular arrhythmia (VA) is the most common cause of death associated with acute myocardial infarction (MI). Recent studies have revealed direct involvement of the paraventricular nucleus (PVN) in the occurrence of VA. However, the underlying mechanisms remain incompletely understood. In this study, we investigated changes in the interleukin-6 (IL-6)-glycoprotein 130-signal transducer and activator of transcription 3 (STAT3) pathway in the PVN during acute MI and the effects of this pathway on ventricular stability. Methods: Rats were divided into a control group, a MI group, a PVN-injected anti-IL-6 antibody group and a PVN-injected SC144 group to observe how IL-6 and its downstream glycoprotein 130-STAT3 pathway in the PVN affect ventricular stability. The left anterior descending coronary artery was ligated to induce MI. After that, an anti-IL-6 antibody and SC144 were injected into the PVNs of rats. All data are expressed as the mean ± SE and were analysed by ANOVA with a post hoc LSD test. p<0.05 was considered to indicate statistical significance. Results: After MI, the concentration of the inflammatory factor IL-6 increased, and its downstream glycoprotein 130-STAT3 pathway was activated in the PVN. After injection of MI rat PVNs with the anti-IL-6 antibody or glycoprotein 130 inhibitor (SC144), glutamate levels increased and γ-aminobutyric acid (GABA) levels decreased in the PVN. Plasma norepinephrine concentrations also increased after treatment, which increased the vulnerability to VA. Conclusions: In summary, IL-6 in the PVN exerts a protective effect in MI rats, and the glycoprotein 130-STAT3 pathway plays a key role in this process. We anticipate that our findings will provide new ideas for the prevention and treatment of arrhythmia after MI.
... With regard to the CNS, Suzuki et al. demonstrated that IL-6 plays a protective role in the early stage of brain injury. Intracerebroventricular injection of rhIL-6 dramatically reduces ischaemic brain damage measured 24 h after middle cerebral artery occlusion [13][14][15]. ...
Background:
Malignant ventricular arrhythmia (VA) is the most common cause of death associated with acute myocardial infarction (MI). Recent studies have revealed direct involvement of the paraventricular nucleus (PVN) in the occurrence of VA. However, the underlying mechanisms remain incompletely understood. In this study, we investigated changes in the interleukin-6 (IL-6)-glycoprotein 130-signal transducer and activator of transcription 3 (STAT3) pathway in the PVN during acute MI and the effects of this pathway on ventricular stability.
Methods:
Rats were divided into a control group, a MI group, a PVN-injected anti-IL-6 antibody group and a PVN-injected SC144 group to observe how IL-6 and its downstream glycoprotein 130-STAT3 pathway in the PVN affect ventricular stability. The left anterior descending coronary artery was ligated to induce MI. After that, an anti-IL-6 antibody and SC144 were injected into the PVNs of rats. All data are expressed as the mean ± SE and were analysed by ANOVA with a post hoc LSD test. p < 0.05 was considered to indicate statistical significance.
Results:
After MI, the concentration of the inflammatory factor IL-6 increased, and its downstream glycoprotein 130-STAT3 pathway was activated in the PVN. After injection of MI rat PVNs with the anti-IL-6 antibody or glycoprotein 130 inhibitor (SC144), glutamate levels increased and γ-aminobutyric acid (GABA) levels decreased in the PVN. Plasma norepinephrine concentrations also increased after treatment, which increased the vulnerability to VA.
Conclusions:
In summary, IL-6 in the PVN exerts a protective effect in MI rats, and the glycoprotein 130-STAT3 pathway plays a key role in this process. We anticipate that our findings will provide new ideas for the prevention and treatment of arrhythmia after MI.
... In vitro, ischemia alters the expression of miRNAs associated with CXCL12 regulation, leading to increased CXCL12 expression and release from astrocytes (Shin et al., 2014). In addition, acting on microglial cells, CXCL12 activates signaling pathways that trigger the release of IL-6 (Lu et al., 2009), which has neuroprotective properties in ischemia (Loddick et al., 1998;Ali et al., 2000;Ohtaki et al., 2006). ...
In the CNS, chemokines and chemokine receptors are involved in pleiotropic physiological and pathological activities. Several evidences demonstrated that chemokine signaling in the CNS plays key homeostatic roles and, being expressed on neurons, glia and endothelial cells, chemokines mediate the bidirectional cross-talk among parenchymal cells. An efficient communication between neurons and glia is crucial to establish and maintain a healthy brain environment which ensures normal functionality. Glial cells behave as active sensors of environmental changes induced by neuronal activity or detrimental insults, supporting and exerting neuroprotective activities. In this review we summarize the evidence that chemokines (CXCL12, CX3CL1, CXCL16 and CCL2) modulate neuroprotective processes upon different noxious stimuli and participate to orchestrate neurons-microglia-astrocytes action to preserve and limit brain damage. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.
... IL-8, were unaffected. The secretion of IL-6 is increased by NMDA receptor activation [47]. TNF-α is also related to NMDA receptor activation and blocking this receptor decreased the transcription of the chemokine in a nerve lesion model [48]. ...
Purpose
Intra- and intercellular redox-signaling processes where found responsible in various physiological and pathological processes with cellular thiol groups as important signal transducers. Using cold atmospheric plasma (CAP), a similar oxidation pattern of thiol groups can be achieved. Hence, it must be clarified which role extracellular thiol groups play in mediating CAP effects and whether or not the effects of short-lived reactive species can be preserved in a molecule like cysteine.
Methods
Physiological buffer solutions containing the amino acid cysteine were treated by an MHz argon plasma jet with molecular gas admixtures (kINPen) and transferred to cultured human keratinocytes. Cell proliferation, migratory activity, and metabolism were investigated. High-resolution mass spectrometry was used to estimate the impact of plasma generated species on thiol groups.
Results
While treated physiologic cysteine concentrations showed no impact on cell behavior, artificially high concentrations decreased proliferation, migration and lactate secretion. GSH levels inside cells were stabilized.
Conclusion
Extracellular thiol groups scavenge plasma-generated species and form a multitude of covalent modifications. Unexpectedly, human keratinocytes show only small functional consequences for treated physiologic cysteine concentrations. Results for high concentrated cysteine solutions indicate an improved cytostatic/cytotoxic impact by plasma treatment suggesting a potential application as a “preserving agent” of the chemical energy of plasma-derived species.
... In particular, IL-6 is a bi-functional cytokine, both performing as a pro-inflammatory mediator [24] and an anti-inflammatory myokine. [25] It has been suggested that increased IL-6 release could represent a neuroprotective reaction against excitotoxic damage [26], as observed in an ALS animal model. [6] IL-6 has a complex action on cell metabolism. ...
Background:
IL-6 is an inflammatory cytokine that is a possible factor in progression of the disease. We have investigated venous blood levels of IL-6 in controls and ALS patients in relation to clinical staging and respiratory function.
Methods:
We studied 82 patients with ALS and 43 age and gender-matched healthy control subjects. Blood was drawn at the same time of day in the mornings to avoid diurnal variation. IL-6 levels were estimated according to a fixed protocol. Clinical measures included ALSFRS-R, vital capacity, and mean bilateral phrenic nerve CMAP amplitude. A multi-regression data analysis was used in addition to conventional statistical methods.
Results:
IL-6 levels were positively correlated with increasing age in the control group. In ALS patients mean IL-6 levels were raised but the levels were markedly variable from case to case and did not reach significance (p 0.1). In addition to age effects reduction in phrenic nerve CMAP amplitude was correlated with increased IL-6 levels (p 0.026).
Conclusions:
IL-6 levels were physiologically influenced by aging in controls and by respiratory dysfunction in ALS. There was marked variability in levels from case to case, which might be related to respiratory factors, which cause pulmonary inflammation.
... IL-6 is expressed in the normal CNS, where it influences neuronal homeostasis by acting as a neurotrophic factor via the classical signaling pathway (reviewed by [147]). Ischemic stroke in mice and rats leads to a significant increase in the levels of IL-6 from 6 to 12 h ( Fig. 1 and 2c), and in both IL-6R and gp130 from 3 days [3,70]. IL-6 has been shown to be neuroprotective in experimental stroke [192] although this is still debated [29]. ...
... IL-1b increases excitatory transmission through an increase in surface expression of GluR1, but IL-6 and IL-10 do not produce these receptor changes (Stellwagen et al., 2005). However, IL-6 may downregulate NMDA receptor function or expression (Ali et al., 2000;Pizzi et al., 2004). Increasing evidence has demonstrated that TNFa regulates synaptic activity via AMPA receptor trafficking and astrocyte glutamate release. ...
Addiction is a chronic relapsing disorder, characterized by the compulsion to seek and take drugs despite negative consequences. It is extremely damaging and costly, accounting for $740 billion annually in the United States resulting from healthcare, crime, and lost work productivity (Birnbaum et al., 2011; CDC 2017; Xu et al., 2014). There is also an immeasurable cost in the loss of life and immense individual suffering. In order to find effective therapies for addiction, we must identify effective targets for treatment by understanding the complex mechanisms that are fundamental to this impenetrable disorder. Critical, well‐defined changes to the brain that underlie these behavioral stereotypes have been identified (Koob & Volkow, 2010). Although evidence has implicated both neurons and glia in mechanisms that contribute to these addictive behaviors, the largest body of work has focused on understanding neuronal mechanisms of addiction.
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... [61][62][63] However, in this study, we focused on the expression of cytokine genes in the blood cells that might respond differently to disease conditions as compared to affected tissues. Additionally, some studies have indicated that IL-1β and IL-6 expression have neuroprotective roles, [64][65][66] and therefore a decrease in their expression below the normal levels could result in neural injury and apoptosis. Because of the multifactorial nature of the diseases studied in this research, it is possible that the same disease in different individuals is resulted from the impairment of different signaling pathways or environmental factors. ...
Background: Neurodegenerative disorders (NDs) are categorized as multifactorial conditions with different molecular and environmental causes. Disturbance of important signaling pathways, such as energy metabolism and inflammation induced by environmental agents, is involved in the pathophysiology of NDs. It has been proposed that changes in the lifestyle and nutrition (metabolism) during mid-life could trigger and accumulate cellular and molecular damages resulting in NDs during aging.
Methods: In order to test the hypothesis, we investigated the expression level of two energy metabolism-related [forkhead box O1 (FOXO1) and forkhead box O3 (FOXO3A)] and two pro-inflammatory cytokines [interleukin 1β (IL-1β) and IL-6] genes, using quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR). Furthermore, changes in the ionic concentration of three essential heavy metals [iron (Fe), copper (Cu), and zinc (Zn)] by atomic absorption spectroscopy in patients with NDs, depression, obesity, and diabetes type II, were evaluated and compared with the results of normal individuals.
Results: More than half of the participants in obesity, depression, and ND groups had significant up-regulation of FOXO1 and FOXO3A, down-regulation of IL-1β and IL-6, and higher levels of Fe and Cu in their blood. This pattern of gene expression was not repeated in diabetic patients.
Conclusion: It could be concluded that individuals affected with different levels of obesity and depression have increased the risk of developing NDs later in life, probably through changes in energy metabolism, inflammatory pathways, and ionic concentrations.
... Moreover, it is worth mentioning that other mechanisms could be involved in the neuroprotective effects of IL-6; indeed, it was found to facilitate the concentration-and time-dependent upregulation of adenosine A1 receptor mRNA and signaling [73] and adenosine has been shown to exert a powerful anticonvulsant effect [74]. In addition, in vitro studies showed that IL-6 is able to protect against glutamate-and NMDA-induced excitotoxicity [75,76]. ...
Seizure-triggered maladaptive neural plasticity and neuroinflammation occur during the latent period as a key underlying event in epilepsy chronicization. Previously, we showed that α-tocopherol (α-T) reduces hippocampal neuroglial activation and neurodegeneration in the rat model of kainic acid (KA)-induced status epilepticus (SE). These findings allowed us to postulate an antiepileptogenic potential for α-T in hippocampal excitotoxicity, in line with clinical evidence showing that α-T improves seizure control in drug-resistant patients. To explore neurobiological correlates of the α-T antiepileptogenic role, rats were injected with such vitamin during the latent period starting right after KA-induced SE, and the effects on circuitry excitability, neuroinflammation, neuronal death, and microRNA (miRNA) expression were investigated in the hippocampus. Results show that in α-T-treated epileptic rats, (1) the number of population spikes elicited by pyramidal neurons, as well as the latency to the onset of epileptiform-like network activity recover to control levels; (2) neuronal death is almost prevented; (3) down-regulation of claudin, a blood–brain barrier protein, is fully reversed; (4) neuroinflammation processes are quenched (as indicated by the decrease of TNF-α, IL-1β, GFAP, IBA-1, and increase of IL-6); (5) miR-146a, miR-124, and miR-126 expression is coherently modulated in hippocampus and serum by α-T. These findings support the potential of a timely intervention with α-T in clinical management of SE to reduce epileptogenesis, thus preventing chronic epilepsy development. In addition, we suggest that the analysis of miRNA levels in serum could provide clinicians with a tool to evaluate disease evolution and the efficacy of α-T therapy in SE.
... IL-6 plays a pivotal role in the normal homeostasis of neuronal tissue, and its absence leads to reduced glial activation in traumatic brain injury [18,31]. On the other hand, a rapid increase in expression and secretion of IL-6 is observed in various neurological diseases, for example Alzheimer's and Parkinson's disease [5], brain cancer [21], multiple sclerosis [11,23] and brain ischemia [1]. In our study the level of IL-6 was significantly lower in patients with arrested and with brain atrophy hydrocephalus compared to the group with active iNPH. ...
Cytokines are widely known mediators of inflammation accompanying many neurodegenerative disorders including normal pressure hydrocephalus (NPH). NPH is caused by impaired cerebrospinal fluid (CSF) absorption and treated by surgical shunt insertion. The early diagnosis of NPH is difficult because of various manifestations of the disease. One of the most promising research directions is biochemical CSF analysis. The aim of this study was to determine the CSF levels of cytokines. The levels of various cytokines (IL-6, IL-8, IL-12, IL-10 and TNF-α) were measured in patients with idiopathic active normal pressure hydrocephalus, arrested hydrocephalus and hydrocephalus with brain atrophy compared to controls. Our study showed that the concentrations of IL-6 and IL-8 were significantly elevated in the group with idiopathic active hydrocephalus compared to control patients. Moreover, we observed that the levels of IL-6 and IL-8 in the group with idiopathic active hydrocephalus were significantly higher compared to patients with arrested hydrocephalus and hydrocephalus with brain atrophy.
... IL-6 is part of the family of IL-6-type cytokines that are involved in the regulation of the acute-phase response to injury and infection [45]. Despite the ambivalent roles of IL-6 between inflammatory and neurotrophic aspects, its neuroprotective effect after ischemic brain injury has been reported in several studies [37,38,46]. Moreover, mesenchymal stem cell-induced neuronal recovery and immune modulation are reportedly mediated by the secretion of IL-6 and VEGF [25]. ...
Objectives
Recent evidence shows that stem cells exert neuroprotective effect through the secretion of immune modulatory, neurotrophic factors. We aimed to assess the neuroprotective effect of selected recombinant factors (RFs) detected in human adipose stem cell (hASC)-conditioned medium (CM), in a rat ischemic stroke model.
Methods
Ischemic stroke was induced in Sprague-Dawley rats using 2 h transient middle cerebral artery occlusion (MCAO). One hour after reperfusion, the vehicle (Dulbecco’s modified Eagle medium; DMEM), concentrated CM, and selected RFs mixed with DMEM were administered intracerebroventricularly to each group (N = 14, 15, and 16, respectively). Rats were sacrificed 24 h after MCAO.
Results
IL-6, VEGF, HGF, and BDNF were detected in hASC-CM. At 24 h post-MCAO, the CM and RF groups both showed significantly better sensorimotor neurological test scores than the control group. The infarct volume was significantly lower in both the CM and RF groups than in the control group. The number of TUNEL-positive apoptotic cells was reduced, whereas HSP70 expression was enhanced in the peri-infarct area in both the CM and RF groups. Moreover, hASC-CM and RFs reduced IκB phosphorylation and influenced bcl-2 and bax protein expression.
Conclusions
Our results suggest that RFs, selected from hASC-CM, may exert a neuroprotective effect in an ischemic stroke rat model that is comparable to the neuroprotective effect of full hASC-CM. The therapeutic effects of the RFs may be mediated by an anti-inflammatory mechanism and cell apoptosis inhibition. Hence, treatment with RFs can be considered a feasible substitute for stem cell therapy after stroke.
... Mounting evidence suggest that the neuroprotective action observed in several types of brain injury (in vivo and in vitro) is mediated via leukemia inhibitory factor and ciliary neurotrophic factor (94)(95)(96). This positive response is consistent with an improvement in neuronal cell survival after NMDA treatment and with protection against apoptosis (95,97,98). In the neonatal brain, IL-6 appears transiently several hours after the insult (99) and blocking its action protects the injured brain (79). ...
Neonatal hypoxia-ischemia (HI) is one of the major causes of death and/or lifelong neurobehavioral and cognitive dysfunction. Undoubtedly, brain damage following HI insult is a complex process with multiple contributing mechanisms and pathways resulting in both early and delayed injury. It is increasingly recognized that one of the leading pathogenic factors of neonatal brain damage is inflammation, induced by activation of the central and peripheral immune system. Immune responses are induced within minutes and can expand for weeks and even months after the insult. Both activated intrinsic (glia) and infiltrating cells (mast cells, monocytes/macrophages) produce soluble inflammatory molecules such as cytokines, chemokines, reactive oxygen, and nitrogen species, which are thought to be pivotal mediators of persistent neuronal injury. This manuscript provides a brief summary of the current knowledge concerning the specific contribution of different cell types and soluble factors to injury of the developing brain caused by neonatal HI. Finally, we discuss the potential forthcoming treatments aimed at targeting inflammation and then attenuation of damaging effects caused by neonatal HI.
... Moreover, injection of IL-6 reduces the volume of induced brain infarcts in rats and protects against N-methyl-D-aspartate-induced toxicity in cortical, striatal, and retinal neurons. 17 According to our experiments, IL-6 is decreased in cortical neurons after exposure to oxygen deprivation (by 90% approximately, P<0.001) it is not significant to be prevented by NP (p>0.05). ...
... While in female albino mice, CGP 55845 caused an increase in inflammation, which was the sign of poor recovery. An increase in IL-6 levels observed in present studies are supported by several investigations following cerebral ischemia in rodents (Hill et al., 1999;Orzylowska et al., 1999;Suzuki et al., 1999a, b;Ali et al., 2000;Block et al., 2000;Legos et al., 2000). Taupin et al., (1993) had reported an increase in IL-6 expression in both hemispheres after mechanical brain injury in rat brain. ...
Interleukin (IL) 6 and 18 plays an important role in inflammatory response following hypoxia ischemia encephalopathy (HIE). Present study was designed to demonstrate the effect of two GABAB receptor antagonists (CGP 35348 and 55845), respectively, on the serum IL6 and IL 18 concentrations in albino mice. Albino mice pups (of both genders) were subjected to Murine model of hypoxia-ischemia encephalopathy on postnatal day 10 (right common carotid artery was ligated followed by 8% hypoxia for 25 minutes). After neonatal brain damage and following weaning, mice were divided in three groups, in gender specific manner, and fed on normal rodent diet till they were 13 week old. At this time point, group 1 received intraperitonial saline solution (control group), group 2 was supplemented with CGP 35348 (1mg/ml solvent/Kg body weight) and group 3 with CGP 55845 (1mg/ml solvent/Kg body weight), intraperitonially, for 12 days and IL 6 and 18 concentrations were determined in serum by ELISA. It was observed that CGP 35348 supplementation resulted in reduced interlukin-6 and interlukin-18 concentrations in male albino mice. While CGP 55845 supplementation increased IL-6 and IL-18 concentrations in female albino mice following HIE. Our results are indicating that GABAB receptor antagonist's supplementation affects IL concentrations in albino mice in a gender specific manner following neonatal brain damage and can be further explored for the treatments of hypoxia ischemia associated neurological ailments.
... In mild amounts, IL-6 enhances the differentiation and survival of neuron cells [49]. IL-6 has also been found to have neuroprotective effects in neurons exposed to glutamate excitotoxicity [50,51]. MCP-1, one of the chemokines, serves to regulate microglial movement, and protect human neurons and astrocyte damage against different stimuli. ...
Although, titanium dioxide nanoparticles (TiO2NPs) are nanomaterials commonly used in consumer products, little is known about their hazardous effects, especially on central nervous systems. To examine this issue, ALT astrocyte-like, BV-2 microglia and differentiated N2a neuroblastoma cells were exposed to 6 nm of 100% anatase TiO2NPs. A lipopolysaccharide (LPS) was pre-treated to activate glial cells before NP treatment for mimicking NP exposure under brain injury. We found that ALT and BV-2 cells took up more NPs than N2a cells and caused lower cell viability. TiO2NPs induced IL-1β in the three cell lines and IL-6 in N2a. LPS-activated BV-2 took up more TiO2NPs than normal BV-2 and released more intra/extracellular reactive oxygen species (ROS), IL-1β, IL-6 and MCP-1 than did activated BV-2. Involvement of clathrin- and caveolae-dependent endocytosis in ALT and clathrin-dependent endocytosis and phagocytosis in BV-2 both had a slow NP translocation rate to lysosome, which may cause slow ROS production (after 24 h). Although TiO2NPs did not directly cause N2a viability loss, by indirect NP exposure to the bottom chamber of LPS-activated BV-2 in the Transwell system, they caused late apoptosis and loss of cell viability in the upper N2a chamber due to H2O2 and/or TNF-α release from BV-2. However, none of the adverse effects in N2a or BV-2 cells was observed when TiO2NPs were exposed to ALT-N2a or ALT-BV-2 co-culture. These results demonstrate that neuron damage can result from TiO2NP-mediated ROS and/or cytokines release from microglia, but not from astrocytes.
Нейровоспаление играет важную роль в эпилептогенезе, однако большинство исследований этого процесса выполняется на фармакологических моделях эпилепсии, в то время как данные по неинвазивным, в том числе генетическим, моделям практически отсутствуют. У крыс линии Крушинского-Молодкиной (КМ) с высокой генетической предрасположенностью к аудиогенной эпилепсии, АЭ (интенсивный судорожный припадок в ответ на действие звука), и у контрольной линии «0» (не предрасположенной к АЭ) в ткани дорзального стриатума и в стволе мозга определяли уровни ряда провоспалительных цитокинов с помощью мультиплексного иммунофлуоресцентного анализа (MILLIPLEX map Kit). Фоновые уровни интерлейкинов IL-1β, IL-6 и фактора некроза опухолей (TNF-α) в дорсальном стриатуме крыс КМ были достоверно ниже, чем у крыс «0» (на 32,31, 27,84 и 38,87%, р р р р р р < 0,01). Таким образом, различия между фоновыми уровнями цитокинов и таковыми после действия звука были разными у крыс, различавшихся по предрасположенности к АЭ, что позволяет предположить участие цитокинов, в частности, провоспалительных факторов, в патофизиологии эпилепсии.
Stroke is a leading cause of mortality and morbidity with a paucity of effective pharmacological treatments. We have previously identified insulin-regulated aminopeptidase (IRAP) as a potential target for the development of a new class of drugs for the treatment of stroke, as global deletion of this gene in mice significantly protected against ischemic damage. In the current study, we demonstrate that small molecular weight IRAP inhibitors reduce infarct volume and improve neurological outcome in a hypertensive animal model of ischemic stroke. The effects of two structurally distinct IRAP inhibitors (HFI419 or SJM164) were investigated in a model of stroke where the middle cerebral artery was transiently occluded with endothelin-1 in the conscious spontaneously hypertensive rat. IRAP inhibitor was administered into the lateral ventricle at 2 or 6 h after stroke, with subsequent doses delivered at 24, 48 and 70 h post-stroke. Functional outcomes were assessed prior to drug treatment, and on day 1 and 3 post-stroke. Histological analyses and neuroinflammatory cytokine profiling were conducted at 72 and 24 h post-stroke respectively. IRAP inhibitor treatment following stroke significantly reduced infarct volume and improved neurological and motor deficits. These protective effects were maintained even when the therapeutic window was extended to 6 h. Examination of the cellular architecture at 72 h post-stroke demonstrated that IRAP expression was upregulated in CD11b positive cells and activated astrocytes. Furthermore, IRAP inhibitor treatment significantly increased gene expression for interleukin 6 and C–C motif chemokine ligand 2 in the ischemic core. This study provides proof-of-principle that selective inhibition of IRAP activity with two structurally distinct IRAP inhibitors reduces infarct volume and improves functional outcome even when the first dose is administered 6 h post-stroke. This is the first direct evidence that IRAP inhibitors are a class of drug with potential use in the treatment of ischemic stroke.
Neuroinflammation plays an important role in epileptogenesis, however, most studies are performed using pharmacological models of epilepsy, while there are only few data available for non-invasive, including genetic, models. The levels of a number of pro-inflammatory cytokines were examined in the Krushinsky-Molodkina (KM) rat strain with high audiogenic epilepsy (AE) proneness (intense tonic seizure fit in response to loud sound) and in the control strain "0" (not predisposed to AE) using multiplex immunofluorescence magnetic assay (MILLIPLEX map Kit). Cytokine levels were determined in the dorsal striatum tissue and in the brain stem. Background levels of IL-1β, IL-6, and TNF-α in the dorsal striatum of the KM rats were significantly lower than in the rats "0" (by 32.31, 27.84, and 38.87%, respectively, p < 0.05, 0.05, and 0.01), whereas no inter-strain differences in the levels of these metabolites were detected in the brain stem in the "background" state. Four hours after sound exposure, the TNF-α level in the dorsal striatum of the KM rats was significantly lower (by 38.34%, p < 0.01) than in the "0" rats. In the KM rats, the dorsal striatal levels of IL-1β and IL-6 were significantly higher after the sound exposure and subsequent seizure fit, compared to the background (35.29 and 50.21% increase, p < 0.05, 0.01, respectively). In the background state the IL-2 level in the KM rats was not detected, whereas after audiogenic seizures its level was 14.01 pg/ml (significant difference, p < 0.01). In the KM rats the brain stem levels of IL-1β and TNF-α after audiogenic seizures were significantly lower than in the background (13.23 and 23.44% decrease, respectively, p < 0.05). In the rats of the "0" strain, the levels of cytokines in the dorsal striatum after the action of sound (which did not induce AE seizures) were not different from those of the background, while in the brain stem of the "0" strain the levels of IL-1β were lower than in the background (40.28%, p < 0.01). Thus, the differences between the background levels of cytokines and those after the action of sound were different in the rats with different proneness to AE. These data suggest involvement of the analyzed cytokines in pathophysiology of the seizure state, namely in AE seizures.
Introduction: We monitored CSF (cerebrospinal fluid) for Th1/Th2 inflammatory cytokines in a patient with unexplained postoperative disturbance of consciousness after craniotomy and found that the level of IL-6 (Interleukin-6) concentrations was extremely high, meeting the traditional criteria for an inflammatory cytokine storm. Subsequently, the cerebrospinal fluid specimens of several patients were tested, and it was found that IL-6 levels were increased in different degrees after craniotomy. Previous studies have focused more on mild and long-term IL-6 elevation, but less on the effects of this short-term IL-6 inflammatory cytokine storm. Cerebrospinal fluid rich in IL-6 may play a significant role in patients after craniotomy.
Objective: To explore the degree of IL-6 elevation and the incidence of IL-6 inflammatory cytokine storm in patients after craniotomy, as well as the effect of IL-6 elevation on brain. In this study, the levels and clinical manifestations of inflammatory factors in cerebrospinal fluid after craniotomy were statistically classified, and the underlying mechanisms were discussed preliminarily.
Methods: CSF specimens of patients after craniotomy were collected, IL-6 level was measured at 1, 5 and 10 days after operation, and cognitive function was analyzed at 1, 10 and 180 days after surgery. Craniotomy mouse model, cerebrospinal fluid of patients with the appearance of IL-6 storm after craniotomy and IL-6 at the same concentration stimulation model were established. Behavioral tests, fluorescence in situ hybridization (FISH), pathological means, western blot, Elisa (enzyme-linked immune-sorbent assay) were performed for verification.
Results: CSF from patients after craniotomy caused disturbance of consciousness in mice, affected neuronal damage in the hypothalamus, activation of microglia in the hypothalamus, and decreased expression of barrier proteins in the hypothalamus and brain. The large amount of interleukin-6 in CSF after craniotomy was found to be mainly derived from astrocytes. The IL-6 level in CSF after craniotomy correlated inversely with patients’ performance in MoCA test.
Conclusion: High levels of IL-6 in the cerebrospinal fluid derived from astrocytes after craniotomy may lead to disruption of the brain-cerebrospinal fluid barrier, most notably around the hypothalamus, which might result in inflammatory activation of microglia to damage the hypothalamic neurons and impaired cognitive function/more gradual cognitive repairment in patients after craniotomy with the appearance of IL-6 storm.
Interleukin-6 (IL-6) is a major cytokine that promotes anti- and pro-inflammatory outcomes by activating the membrane IL-6 receptor (IL-6R) or the soluble IL-6 receptor (sIL-6R). IL-6R and sIL-6R signaling engage the JAK1/2/3 targets and the downstream transcription of STAT1 and STAT3 family. In the brain, physiological IL-6 signaling preserves neurogenesis, neuronal differentiation, and neuroprotection against tissue injury, but IL-6 has been proposed as a biomarker for poor prognosis in several mental pathologies such as depressive disorders, schizophrenia, bipolar disorder, and autism. Physiological or pathological outcomes of IL-6 are related to its pleiotropic effects in the brain by microglia, astrocytes, neurons, and endothelial cells, and also by peripheral infiltrating macrophages or T lymphocytes. Notably, definition of anti- or pro-inflammatory profiles by IL-6 signaling in the brain are sensitive to the levels, cellular source, and targets of the IL-6 itself, as well as IL-6 receptor signaling, and its activation/inhibition ratio. We propose that a mutual IL-6 crosstalk between microglia, astrocytes, neurons, and endothelial cells defines the anti- and pro-inflammatory outcomes in the brain, modulating brain function. This review will describe the cellular, molecular and context-dependent signaling pathways that define anti- or pro-inflammatory profiles setting by IL-6 during physiological or pathological outcomes in the brain.
Astrocytes are essential in maintaining normal brain functions such as blood brain barrier (BBB) homeostasis and synapse formation as the most abundant cell type in the central nervous system (CNS). After the stroke, astrocytes are known as reactive astrocytes (RAs) because they are stimulated by various damage-associated molecular patterns (DAMPs) and cytokines, resulting in significant changes in their reactivity, gene expression, and functional characteristics. RAs perform multiple functions after stroke. The inflammatory response of RAs may aggravate neuro-inflammation and release toxic factors to exert neurological damage. However, RAs also reduce excitotoxicity and release neurotrophies to promote neuroprotection. Furthermore, RAs contribute to angiogenesis and axonal remodeling to promote neurological recovery. Therefore, RAs’ biphasic roles and mechanisms make them an effective target for functional recovery after the stroke. In this review, we summarized the dynamic functional changes and internal molecular mechanisms of RAs, as well as their therapeutic potential and strategies, in order to comprehensively understand the role of RAs in the outcome of stroke disease and provide a new direction for the clinical treatment of stroke.
The role of increased brain inflammation in the development of neurodegenerative diseases is unclear. Here, we have compared cytokine changes in normal aging, motor neurone disease (MND), and Alzheimer's disease (AD). After an initial analysis, six candidate cytokines, interleukin (IL)‐ 4, 5, 6, 10, macrophage inhibitory protein (MIP)‐1α, and fibroblast growth factor (FGF)‐2, showing greatest changes were assayed in postmortem frozen human superior frontal gyri (n = 12) of AD patients, aging and young adult controls along with the precentral gyrus (n = 12) of MND patients. Healthy aging was associated with decreased anti‐inflammatory IL‐10 and FGF‐2 levels. AD prefrontal cortex was associated with increased levels of IL‐4, IL‐5, and FGF‐2, with the largest increase seen for FGF‐2. Notwithstanding differences in the specific frontal lobe gyrus sampled, MND patients’ primary motor cortex (precentral gyrus) was associated with increased levels of IL‐5, IL‐6, IL‐10, and FGF‐2 compared to the aging prefrontal cortex (superior frontal gyrus). Immunocytochemistry showed that FGF‐2 is expressed in neurons, astrocytes, and microglia in normal aging prefrontal cortex, AD prefrontal cortex, and MND motor cortex. We report that healthy aging and age‐related neurodegenerative diseases have different cortical inflammatory signatures that are characterized by increased levels of anti‐inflammatory cytokines and call into question the view that increased inflammation underlies the development of age‐related neurodegenerative diseases. Normal brain aging is associated with decreased anti‐inflammatory cytokine levels IL‐10 and FGF‐2, whereas several cytokines are elevated in Alzheimer's disease (AD) and MND. In particular, fibroblast growth factor‐2 is elevated almost 10‐fold in AD compared to controls and MND.
Poststroke hyperglycemia and inflammation have been implicated in the pathogenesis of stroke. Janus Kinase 2 (Jak2), a catalytic signaling component for cytokine receptors such as Interleukin-6 (IL-6), has inflammatory and metabolic properties. This study aimed to investigate the roles of Jak2 in poststroke inflammation and metabolic abnormality in a rat model of permanent cerebral ischemia. Pretreatment with Jak2 inhibitor AG490 ameliorated neurological deficit, brain infarction, edema, oxidative stress, inflammation, caspase-3 activation, and Zonula Occludens-1 (ZO-1) reduction. Moreover, in injured cortical tissues, Tumor Necrosis Factor-α, IL-1β, and IL-6 levels were reduced with concurrent decreased NF-κB p65 phosphorylation, Signal Transducers and Activators of Transcription 3 phosphorylation, Ubiquitin Protein Ligase E3 Component N-Recognin 1 expression, and Matrix Metalloproteinase activity. In the in vitro study on bEnd.3 endothelial cells, AG490 diminished IL-6-induced endothelial barrier disruption by decreasing ZO-1 decline. Metabolically, administration of AG490 lowered fasting glucose, with improvements in glucose intolerance, plasma-free fatty acids, and plasma C Reactive Proteins. In conclusion, AG490 improved the inflammation and oxidative stress of neuronal, hepatic, and muscle tissues of stroke rats as well as impairing insulin signaling in the liver and skeletal muscles. Therefore, Jak2 blockades may have benefits for combating poststroke central and peripheral inflammation, and metabolic abnormalities.
Excitotoxic events underlying ischaemic and traumatic brain injuries activate degenerative and protective pathways, particularly in the hippocampus. To understand opposing pathways that determine the brain's response to excitotoxicity, we used hippocampal explants, thereby eliminating systemic variables during a precise protocol of excitatory stimulation. N-methyl-d-aspartate (NMDA) was applied for 20 min and total RNA isolated one and 24 h later for neurobiology-specific microarrays. Distinct groups of genes exhibited early vs. delayed induction, with 63 genes exclusively reduced 24-h post-insult. Egr-1 and NOR-1 displayed biphasic transcriptional modulation: early induction followed by delayed suppression. Opposing events of NMDA-induced genes linked to pathogenesis and cell survival constituted the early expression signature. Delayed degenerative indicators (up-regulated pathogenic genes, down-regulated pro-survival genes) and opposing compensatory responses (down-regulated pathogenic genes, up-regulated pro-survival genes) generated networks with temporal gene profiles mirroring coexpression network clustering. We then used the expression profiles to test whether NF-κB, a potent transcription factor implicated in both degenerative and protective pathways, is involved in the opposing responses. The NF-κB inhibitor MG-132 indeed altered NMDA-mediated transcriptional changes, revealing components of opposing expression signatures that converge on the single response element. Overall, this study identified counteracting avenues among the distinct responses to excitotoxicity, thereby suggesting multi-target treatment strategies and implications for predictive medicine.
The deregulation of the inflammatory cytokine interleukin (IL)-6 has been associated to a variety of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). The aim of this work was to analyze the variation of IL-6 levels in blood and damaged tissues during the course of the disease. We studied IL-6 protein expression in spinal cord, extensor digital longus (EDL) muscle and soleus (SOL) muscle of the SOD1G93A animal model at four stages of the disease by western blot. Concurrently, we analyzed IL-6 gene and protein expression in blood of ALS patients, healthy subjects and patients with other neuropathies through RTqPCR and ELISA. The results revealed different expression patterns depending on both the tissue analyzed and the stage of the disease, showing increasing IL-6 levels in EDL muscle over time. Moreover, lower IL-6 levels in blood were found in ALS patients. The decreased levels of IL-6 in blood from ALS patients could suggest that IL-6 might not be the main pro-inflammatory biomarker in the last stages in whole blood. In contrast, IL-6 may play a main role in fast glycolytic muscle fibers associated with muscle atrophy, suggesting that modulation of IL-6 in this tissue could be a potential target for anti-inflammatory therapies in ALS.
White matter damage is a component of most human stroke and usually accounts for at least half of the lesion volume. Subcortical white matter stroke (WMS) accounts for 25% of all strokes and causes severe motor and cognitive dysfunction. The adult brain has a very limited ability to repair white matter damage. Pathological analysis shows that demyelination or myelin loss is the main feature of white matter injury and plays an important role in long-term sensorimotor and cognitive dysfunction. This suggests that demyelination is a major therapeutic target for ischemic stroke injury. An acute inflammatory reaction is triggered by brain ischemia, which is accompanied by cytokine production. The production of cytokines is an important factor affecting demyelination and myelin regeneration. Different cytokines have different effects on myelin damage and myelin regeneration. Exploring the role of cytokines in demyelination and remyelination after stroke and the underlying molecular mechanisms of demyelination and myelin regeneration after ischemic injury is very important for the development of rehabilitation treatment strategies. This review focuses on recent findings on the effects of cytokines on myelin damage and remyelination as well as the progress of research on the role of cytokines in ischemic stroke prognosis to provide a new treatment approach for amelioration of white matter damage after stroke.
Stroke is a major public health problem and ranks third most common cause of death in adults worldwide. Thrombolysis with recombinant tissue plasminogen activator and endovascular thrombectomy are the main revascularization therapies for acute ischemic stroke. However, ischemia-reperfusion injury, mainly caused by oxidative/nitrosative stress injury, after revascularization therapy can result in worsening outcomes. For better clinical prognosis, more and more studies have focused on the pharmaceutical neuroprotective therapies against free radical damage. The impact of vitamin C (ascorbic acid) on oxidative stress-related diseases is moderate because of its limited oral bioavailability and rapid clearance. However, recent evidence of the clinical benefit of parenteral vitamin C administration has emerged, especially in critical care. In this study we demonstrated that parenteral administration of vitamin C significantly improved neurological deficits and reduced brain infarction and brain edema by attenuating the transient middle cerebral artery occlusion (tMCAO)-induced nitrosative stress, inflammatory responses, and the resultant disruptions of blood brain barrier and cerebral neuronal apoptosis. These results suggest that parenteral administration of vitamin C has potential as an adjuvant agent with intravenous thrombolysis or endovascular thrombectomy in acute treatment of ischemic stroke.
Cytokines have been implicated in a variety of neurodegenerative conditions including Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), prion diseases, and others. Many investigators have attributed a negative role to cytokines in neurodegenerative disease, hypothesizing that cytokine-induced inflammatory processes result in toxicity to nerve cells. Indeed, there is substantial evidence from cell culture and animal studies that cytokines can have direct or indirect neurotoxic effects. Recently, however, there has been increasing awareness that some processes mediated by cytokines may be potentially beneficial to the compromised neuron This chapter will review the evidence for cytokine-induced neurotoxicity as well as possible protective effects in neurodegeneration.
Recent studies show that the cytokine interleukin-6 (IL-6) is expressed at elevated levels in the CNS in several disease states and contributes to the neuropathological process. The mechanisms through which IL-6 exerts its CNS effects are primarily unknown. We have investigated the pathophysiological effects of IL-6 on developing CNS neurons using a culture model system and a chronic treatment paradigm. Here, we show, using current- and voltage-clamp recordings, that chronic IL-6 treatment of developing cerebellar granule neurons increases the membrane and current response to NMDA and that these effects are the primary mechanism through which IL-6 produces an enhanced calcium signal to NMDA. We also show that calcium influx through voltage-sensitive calcium channels contributes to the enhanced calcium signal to NMDA in the IL-6-treated neurons in a developmentally regulated manner and that the membrane depolarization to NMDA is more sensitive to the NMDA receptor antagonist ifenprodil in the IL-6-treated neurons compared with control neurons at a late developmental stage, consistent with a larger proportion of NMDA receptors containing the NMDAR2B subunit in the IL-6-treated neurons. Additional studies show that IL-6 treatment reduces the number of granule neurons in culture and enhances neurotoxicity involving NMDA receptors. These results support a pathological role for IL-6 in the CNS and indicate that NMDA receptor-mediated functions are likely to play a critical role in neuropathological changes observed in CNS diseases associated with elevated CNS levels of IL-6.
The expression of interleukin-6 (IL-6) mRNA in the focal ischemic rat cortex was studied by means of Northern hybridization. IL-6 mRNA was induced after permanent occlusion of the middle cerebral artery, reached a significant level at 3 h, and peaked at 12 h, i.e., ~ 10-fold increase in the ischemic zone compared with the nonischemic cortex or sham-operated controls. The increased IL-6 mRNA was elevated for at least 24 h. Low levels of IL-6 mRNA were detected in sham-operated rats or in the contralateral nonischemic cortex. The expression of c-fos and zif268 mRNAs, two early response genes, was rapid (increased by 1 h postischemia) and transient (returned to basal levels by 24 and 12 h, respectively), clearly having different kinetic patterns from that of IL-6 mRNA. The early response kinetic pattern of c-fos and zif268 mRNAs in focal ischemia suggests their transcriptional regulatory roles in response to ischemic insult, while the delayed induction pattern of IL-6 mRNA suggests a role for this pleiotropic cytokine in the inflammatory response to the focal ischemic damage of the brain.Keywords: c-fos; Focal brain ischemia; Inflammation; Interleukin-6; Stroke; zif268
Staurosporine, a nonselective protein kinase inhibitor, has been shown to induce apoptosis in several different nonneuronal cell types. We tested the hypothesis that staurosporine would also induce apoptosis in central neurons. Exposure of murine cortical cell cultures to 30-100 nM staurosporine induced concentration-dependent selective neuronal degeneration over the following day; at higher concentrations, staurosporine damaged glial cells as well. Staurosporine-induced neuronal death was accompanied by cell body shrinkage, chromatin condensation, and DNA laddering. In contrast, NMDA-induced neuronal death was accompanied by acute cell body swelling without DNA laddering. Staurosporine-induced neuronal death, unlike excitotoxic death, was markedly attenuated by the protein synthesis inhibitor cycloheximide; this protective effect was not reversed by a glutathione synthesis inhibitor, buthionine sulfoximine. Interestingly, the glial cell death induced by 1 μM staurosporine was markedly potentiated by cycloheximide. Staurosporine-induced neuronal death was not accompanied by an increase in intracellular free Ca2+ and was attenuated by 30 mM K+; this protective effect of high K+ was blocked by nimodipine or Co2+. Present data suggest that staurosporine can induce apoptosis in cultured cortical neurons and that this apoptosis can be blocked by raising intracellular Ca2+ or by blocking protein synthesis. Staurosporine exposure may be useful as a model for studying central neuronal apoptosis in vitro.
Two species of the cDNAs encoding murine IL-6-R (one is abnormal and the other authentic) have been cloned from a plasmacytoma cell line, P3U1, and BALB/c mouse spleen cDNA libraries. In the cDNA encoding the abnormal IL-6-R, the region corresponding to an intracytoplasmic domain was replaced with a part of the long terminal repeat of the intracisternal A particle gene (IAP-LTR). The authentic IL-6-R consists of 460 amino acids with the domain of the Ig superfamily. The overall homology between murine and human IL-6-R was 69 and 54% at DNA and protein levels, respectively. The extracellular domain after the Ig-like domain of murine IL-6-R was found to have an homology with those of murine erythropoietin R, human IL-2-R beta chain, murine IL-4-R, and human granulocyte-macrophage CSF-R, as in the case of human IL-6-R, and these receptors have been classified as members of the IL receptor family. In P3U1 cells, the expression of the mRNA encoding abnormal IL-6-R was much higher than that of the mRNA encoding authentic IL-6-R. An IL-6-dependent human T cell line, KT-3, which did not respond to murine IL-6, acquired the responsiveness to murine IL-6 when transfected with the cDNA encoding abnormal IL-6-R, indicating that abnormal IL-6-R lacking a normal cytoplasmic domain can function. Since IL-6 functions as a potent growth factor for murine plasmacytomas, over-expression of abnormal IL-6-R may function as a positive selection element for the development of certain plasmacytomas.
We have developed an experimental paradigm to study the mechanism by which nerve growth factor (NGF) allows the survival of sympathetic neurons. Dissociated sympathetic neurons from embryonic day-21 rats were grown in vitro for 7 d in the presence of NGF. Neurons were then deprived of trophic support by adding anti-NGF antiserum, causing them to die between 24 and 48 h later. Ultrastructural changes included disruption of neurites, followed by cell body changes characterized by an accumulation of lipid droplets, changes in the nuclear membrane, and dilation of the rough endoplasmic reticulum. No primary alterations of mitochondria or lysosomes were observed. The death of NGF-deprived neurons was characterized biochemically by assessing [35S]methionine incorporation into TCA precipitable protein and by measuring the release of the cytosolic enzyme adenylate kinase into the culture medium. Methionine incorporation began to decrease approximately 18 h post-deprivation and was maximally depressed by 36 h. Adenylate kinase began to appear in the culture medium approximately 30 h after deprivation, reaching a maximum by 54 h. The death of NGF-deprived neurons was entirely prevented by inhibiting protein or RNA synthesis. Cycloheximide, puromycin, anisomycin, actinomycin-D, and dichlorobenzimidazole riboside all prevented neuronal death subsequent to NGF deprivation as assessed by the above morphologic and biochemical criteria. The fact that sympathetic neurons must synthesize protein and RNA to die when deprived of NGF indicates that NGF, and presumably other neurotrophic factors, maintains neuronal survival by suppressing an endogenous, active death program.
N-Methyl-D-aspartate (NMDA) receptor-mediated neurotoxicity may depend, in part, on the generation of nitric oxide (NO.) and superoxide anion (O2.-), which react to form peroxynitrite (OONO-). This form of neurotoxicity is thought to contribute to a final common pathway of injury in a wide variety of acute and chronic neurologic disorders, including focal ischemia, trauma, epilepsy, Huntington disease, Alzheimer disease, amyotrophic lateral scelerosis, AIDS dementia, and other neurodegenerative diseases. Here, we report that exposure of cortical neurons to relatively short durations or low concentrations of NMDA, S-nitrosocysteine, or 3-morpholinosydnonimine, which generate low levels of peroxynitrite, induces a delayed form of neurotoxicity predominated by apoptotic features. Pretreatment with superoxide dismutase and catalase to scavenge O2.- partially prevents the apoptotic process triggered by S-nitrosocysteine or 3-morpholinosydnonimine. In contrast, intense exposure to high concentrations of NMDA or peroxynitrite induces necrotic cell damage characterized by acute swelling and lysis, which cannot be ameliorated by superoxide dismutase and catalase. Thus, depending on the intensity of the initial insult, NMDA or nitric oxide/superoxide can result in either apoptotic or necrotic neuronal cell damage.
To elucidate mechanisms underlying neuroprotective properties of astrocytes in brain ischemia, production of neurotrophic mediators was studied in astrocytes exposed to hypoxia/reoxygenation (H/R). Rat astrocytes subjected to H/R released increased amounts of interleukin (IL) 6 in a time-dependent manner, whereas levels of tumor necrosis factor and IL-1 remained undetectable. IL-6 transcripts were induced in hypoxia and the early phase of reoxygenation, whereas synthesis and release of IL-6 antigen/activity occurred during reoxygenation. Elevated levels of IL-6 mRNA were due, at least in part, to increased transcription, as shown by nuclear runoff analysis. The mechanism stimulating synthesis and release of IL-6 antigen by astrocytes was probably production of reactive oxygen intermediates (ROIs), which occurred within 15-20 minutes after placing hypoxia cultures back into normoxia, as the inhibitor diphenyl iodonium inhibited the burst of ROIs and subsequent IL-6 generation (blockade of nitric oxide formation had no effect on ROI generation or IL-6 production). Enhanced IL-6 generation was also observed in human astrocytoma cultures exposed to H/R. Survival of differentiated PC12 cells exposed to H/R was potentiated by conditioned medium from H/R astrocytes, an effect blocked by neutralizing anti-IL-6 antibody. In a gerbil model of brain ischemia, IL-6 activity was lower in the hippocampus, an area sensitive to ischemia, compared with IL-6 activity in the cortex, an area more resistant to ischemia. IL-6 antigen, demonstrated immunohistochemically, was increased in astrocytes from ischemic regions of gerbil brain. These data suggest that H/R enhances transcription of IL-6, resulting in increased translation and release of IL-6 antigen after the burst of ROI generated early during reoxygenation. Release of IL-6 from astrocytes could exert a paracrine neurotrophic effect in brain ischemia.
Transforming growth factor-beta 1 (TGF-beta 1) has been shown to be an injury-related peptide growth factor within the mammalian central nervous system. We tested whether TGF-beta 1 has the capacity to protect rat neocortical neurons against excitotoxic damage in vitro and mouse neocortex against ischemic injury in vivo. After 14 days in vitro, cultured neurons from rat cerebral cortex were exposed to 1 mM L-glutamate in serum-free culture medium. The cultures received TGF-beta 1 immediately after the addition of glutamate. Eighteen hours later, the cell viability of the cultures was determined using trypan blue exclusion. TGF-beta 1 (1-10 ng/ml) significantly reduced the excitotoxic neuronal damage in a concentration-dependent manner. In vivo, male NMRI mice were subjected to a permanent occlusion of the left middle cerebral artery by microbipolar electrocoagulation. After 48 h, the animals received a transcardiac injection of carbon black. The area of ischemia (devoid of carbon) was restricted to the neocortex and its size was determined planimetrically by means of an image-analyzing system. The treatment with TGF-beta 1 (1 microgram/kg i.c.v.) at 6, 4, or 2 h prior to vessel occlusion reduced the area of ischemia by 5.3, 10.0, and 9.6%, respectively. The effect of the treatment with TGF-beta 1 was statistically significant (p < 0.05 by two-way ANOVA). The present in vitro and in vivo data suggest that TGF-beta 1 has the capacity to diminish the deleterious consequences of an excitotoxic or ischemic insult.
To develop a simple, relatively noninvasive small-animal model of reversible regional cerebral ischemia, we tested various methods of inducing infarction in the territory of the right middle cerebral artery (MCA) by extracranial vascular occlusion in rats. In preliminary studies, 60 rats were anesthetized with ketamine and different combinations of vessels were occluded; blood pressure and arterial blood gases were monitored. Neurologic deficit, mortality rate, gross pathology, and in some instances, electroencephalogram and histochemical staining results were evaluated in all surviving rats. The principal procedure consisted of introducing a 4-0 nylon intraluminal suture into the cervical internal carotid artery (ICA) and advancing it intracranially to block blood flow into the MCA; collateral blood flow was reduced by interrupting all branches of the external carotid artery (ECA) and all extracranial branches of the ICA. In some groups of rats, bilateral vertebral or contralateral carotid artery occlusion was also performed. India ink perfusion studies in 20 rats documented blockage of MCA blood flow in 14 rats subjected to permanent occlusion and the restoration of blood flow to the MCA territory in six rats after withdrawal of the suture from the ICA. The best method of MCA occlusion was then selected for further confirmatory studies, including histologic examination, in five additional groups of rats anesthetized with halothane. Seven of eight rats that underwent permanent occlusion of the MCA had resolving moderately severe neurologic deficits (Grade 2 of 4) and unilateral infarcts averaging 37.6 +/- 5.5% of the coronal sectional area at 72 hours after the onset of occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)
We have developed an experimental paradigm to study the mechanism by which nerve growth factor (NGF) allows the survival of sympathetic neurons. Dissociated sympathetic neurons from embryonic day-21 rats were grown in vitro for 7 d in the presence of NGF. Neurons were then deprived of trophic support by adding anti-NGF antiserum, causing them to die between 24 and 48 h later. Ultrastructural changes included disruption of neurites, followed by cell body changes characterized by an accumulation of lipid droplets, changes in the nuclear membrane, and dilation of the rough endoplasmic reticulum. No primary alterations of mitochondria or lysosomes were observed. The death of NGF-deprived neurons was characterized biochemically by assessing [35S]methionine incorporation into TCA precipitable protein and by measuring the release of the cytosolic enzyme adenylate kinase into the culture medium. Methionine incorporation began to decrease approximately 18 h post-deprivation and was maximally depressed by 36 h. Adenylate kinase began to appear in the culture medium approximately 30 h after deprivation, reaching a maximum by 54 h. The death of NGF-deprived neurons was entirely prevented by inhibiting protein or RNA synthesis. Cycloheximide, puromycin, anisomycin, actinomycin-D, and dichlorobenzimidazole riboside all prevented neuronal death subsequent to NGF deprivation as assessed by the above morphologic and biochemical criteria. The fact that sympathetic neurons must synthesize protein and RNA to die when deprived of NGF indicates that NGF, and presumably other neurotrophic factors, maintains neuronal survival by suppressing an endogenous, active death program.
To elucidate mechanisms underlying neuroprotective properties of astrocytes in brain ischemia, production of neurotrophic mediators was studied in astrocytes exposed to hypoxia/reoxygenation (H/R). Rat astrocytes subjected to H/R released increased amounts of interleukin (IL) 6 in a time-dependent manner, whereas levels of tumor necrosis factor and IL-1 remained undetectable. IL-6 transcripts were induced in hypoxia and the early phase of reoxygenation, whereas synthesis and release of IL-6 antigen/activity occurred during reoxygenation. Elevated levels of IL-6 mRNA were due, at least in part, to increased transcription, as shown by nuclear runoff analysis. The mechanism stimulating synthesis and release of IL-6 antigen by astrocytes was probably production of reactive oxygen intermediates (ROIs), which occurred within 15-20 minutes after placing hypoxia cultures back into normoxia, as the inhibitor diphenyl iodonium inhibited the burst of ROIs and subsequent IL-6 generation (blockade of nitric oxide formation had no effect on ROI generation or IL-6 production). Enhanced IL-6 generation was also observed in human astrocytoma cultures exposed to H/R. Survival of differentiated PC12 cells exposed to H/R was potentiated by conditioned medium from H/R astrocytes, an effect blocked by neutralizing anti-IL-6 antibody. In a gerbil model of brain ischemia, IL-6 activity was lower in the hippocampus, an area sensitive to ischemia, compared with IL-6 activity in the cortex, an area more resistant to ischemia. IL-6 antigen, demonstrated immunohistochemically, was increased in astrocytes from ischemic regions of gerbil brain. These data suggest that H/R enhances transcription of IL-6, resulting in increased translation and release of IL-6 antigen after the burst of ROI generated early during reoxygenation. Release of IL-6 from astrocytes could exert a paracrine neurotrophic effect in brain ischemia.
: Cytokines are powerfu1 mediators of biologic responses in the CNS and may contribute to cellular injury in pathophysiologic states. In order to better understand the actions of cytokines in the intact mammalian CNS, a transgenic approach was employed that targeted the expression of different cytokines to astrocytes in mice. Fusion gene constructs consisting of a GFAP expression vector into which was inserted the DNA encoding the cytokines interleukin-6 (IL-6), IL-3, or TNF-α were used to generate transgenic mice. Expression of the transgene-encoded cytokines in astrocytes was confirmed at both the RNA and protein levels. Transgenic mice were subject to multilevel analysis to determine the extent of structural and functional CNS alterations. Transgenic mice exhibited distinct adult-onset, chronic-progressive neurological disorders that correlated with the level and anatomic distribution of transgene-encoded cytokine expression. The principal findings were neurodegeneration and cognitive decline due to IL-6 expression, macrophage/microglial-mediated primary demyelination with motor disease resulting from IL-3 expression, and lymphocytic meningoencephalomyelitis with paralysis induced by TNF-α expression. These transgenic models (1) indicate that expression of cytokines per se in the intact CNS is pathogenic, with cytokine-specific neural cell injury leading to unique functional deficits; (2) recapitulate many of the structural and functional changes seen in human inflammatory neurological disorders; (3) provide a valuable tool for advancing our understanding of the CNS pathobiology of cytokines; and (4) offer a unique resource for the development and testing of therapies aimed at abrogating the harmful actions of these important mediators.
Measurement of lactate dehydrogenase (LDH) activity released to the extracellular bathing media has been found to be a simple yet quantitative method for assessing glutamate mediated central neuronal cell injury in cortical cell culture. Extracellular LDH is both chemically and biologically stable; the magnitude of LDH efflux in the cultures correlates in a linear fashion with the number of neurons damaged by glutamate exposure.
We examined the effect of interleukin-6 (human recombinant) on glutamate-induced neuronal death of cultured 20-day fetal rat hippocampal neurons. After 7 days in culture, the hippocampal neurons were markedly degenerated by the addition of L-glutamate and also N-methyl-D-aspartate. The neuronal death was prevented by the addition of MK801, a potent N-methyl-D-aspartate antagonist. Interleukin-6 at the concentration of 50 ng/ml has a significant preventive effect on the glutamate-induced neuronal death. Basic fibroblast growth factor at the concentration of 100 ng/ml gave also significant protective effect on hippocampal neurons, but nerve growth factor was ineffective in preventing the toxicity. It has been postulated that glutamate plays an important role in the pathogenesis of neuronal death such as ischemia and the various neurological diseases. Interleukin-6 might have somewhat physiological or pathological role in these events.
When stimulated with antigen, B cells are influenced by T cells to proliferate and differentiate into antibody-forming cells. Since it was reported1,2 that soluble factors could replace certain functions of helper T cells in the antibody response, several different kinds of lymphokines and monokines have been reported in B-cell growth and differentiation3,4. Among these, human B-cell differentiation factor (BCDF or BSF-2) has been shown to induce the final maturation of B cells into immunoglobulin-secreting cells5-8. BSF-2 was purified to homogeneity9 and its partial NH2-terminal amino-acid sequence was determined10. These studies indicated that BSF-2 is functionally and structurally unlike other known proteins. Here, we report the molecular cloning, structural analysis and functional expression of the cDNA encoding human BSF-2. The primary sequence of BSF-2 deduced from the cDNA reveals that BSF-2 is a novel interleukin consisting of 184 amino acids.
Various studies describe increased concentrations of transforming growth factor-β (TGF-β) in brain tissue after acute brain injury. However, the role of endogenously produced TGF-β after brain damage to the CNS remains to be clearly established. Here, the authors examine the influence of TGF-β produced after an episode of cerebral ischemia by injecting a soluble TGF-β type II receptor fused with the Fc region of a human immunoglobulin (TβRIIs-Fc). First, this molecular construct was characterized as a selective antagonist of TGF-β. Then, the authors tested its ability to reverse the effect of TGF-β1 on excitotoxic cell death in murine cortical cell cultures. The addition of 1 μg/mL of TβRIIs-Fc to the exposure medium antagonized the neuroprotective activity of TGF-β1 in N-methyl-D-aspartate (NMDA)-induced excitotoxic cell death. These results are consistent with the hypothesis that TGF-β1 exerts a negative modulatory action on NMDA receptor-mediated excitotoxicity. To determine the role of TGF-β1 produced in response to brain damage, the authors used a model of an excitotoxic lesion induced by the intrastriatal injection of 75 nmol of NMDA in the presence of 1.5 μg of TβRIIs-Fc. The intrastriatal injection of NMDA was demonstrated to induce an early upregulation of the expression of TGF-β1 mRNA. Furthermore, when added to the excitotoxin, TβRIIs-Fc increased (by 2.2-fold, P < 0.05) the lesion size. These observations were strengthened by the fact that an intracortical injection of TβRIIs-Fc in rats subjected to a 30-minute reversible cerebral focal ischemia aggravated the volume of infarction. In the group injected with the TGF-β1 antagonist, a 3.5-fold increase was measured in the infarction size (43.3 ± 9.5 versus 152.8 ± 46.3 mm3; P < 0.05). In conclusion, by antagonizing the influence of TGF-β in brain tissue subjected to excitotoxic or ischemic lesion, the authors markedly exacerbated the resulting extent of necrosis. These results suggest that, in response to such insults, brain tissue responds by the synthesis of a neuroprotective cytokine, TGF-β1, which is involved in the limitation of the extent of the injury. The pharmacologic potentiation of this endogenous defensive mechanism might represent an alternative and novel strategy for the therapy of hypoxic-ischemic cerebral injury.Keywords: TGF-β; Excitotoxicity; Ischemia; Cytokine
Although interleukin-6 (IL-6) has various neuroprotective effects against cerebral ischemia, the topographic distribution and cellular source of IL-6 after cerebral ischemia remain unclear. In the current study, the localization of IL-6 protein was immunohistochemically examined in rats after 3.5, 12, 24, and 48 hours of reperfusion after 1.5 hours of middle cerebral artery occlusion. Middle cerebral artery occlusion was induced by the intraluminal suture method. The specificity of the anti-IL-6 antibody used in the current study was confirmed by Western blot analysis and an immunoabsorption test. To identify the cellular source, lectin histochemical study and immunohistochemical study with microtubule-associated protein-2, ED1, and glial fibrillary acidic protein also were carried out. The sham group did not show any clear IL-6 immunoreactivity. After 3.5 hours of reperfusion, IL-6 immunoreactivity was first detected on the reperfused side, and it was upregulated, especially in the periinfarct region, after 24 hours of reperfusion. Also, IL-6 was expressed after 3.5 hours of reperfusion in the contralateral cerebral cortex and bilateral hippocampi. Double staining showed that the cells containing IL-6 were neurons and round-type microglia, not astrocytes. The current findings suggest that IL-6 expression in ischemically threatened neurons and reactive microglia is closely associated with brain tissue neuroprotective mechanisms against cerebral ischemia.Keywords: Focal ischemia; Immunohistochemistry; Interleukin-6; Microglia; Neuron; Rats
Excitotoxicity refers to the ability of glutamate or related excitatory amino acids to mediate the death of central neurons under certain conditions, for example, after intense exposure. Such excitotoxic neuronal death may contribute to the pathogenesis of brain or spinal cord injury associated with several human disease states. Excitotoxicity has substantial cellular specificity and, in most cases, is mediated by glutamate receptors. On average, NMDA receptors activation may be able to trigger lethal injury more rapidly than AMPA or kainate receptor activation, perhaps reflecting a greater ability to induce calcium influx and subsequent cellular calcium overload. It is possible that excitotoxic death may share some mechanisms with other forms of neuronal death. © 1992 John Wiley & Sons, Inc.
Interleukin-6 (IL-6) has been shown to have potent neurotrophic activity on peripheral and central neurons in vitro. However, it remains to be determined whether or not IL-6 rescues hippocampal CA1 neurons from lethal ischemia and prevents ischemia-induced learning disability. In the present in vivo study, we infused IL-6 continuously for 7 days into the lateral ventricle of gerbil starting 2 h before 3-min forebrain ischemia. IL-6 infusion prevented the occurrence of ischemia-induced learning disability in a dose-dependent manner as revealed by a step-down passive avoidance task. Subsequent light and electron microscopic examinations showed that pyramidal neurons in the CA1 region of the hippocampus as well as synapses within the strata moleculare, radiatum and oriens of the region were significantly more numerous in gerbils infused with IL-6 than in those receiving vehicle infusion. These findings suggest that IL-6 has a trophic effect on ischemic hippocampal neurons.
Interleukin-6 (IL-6) is known to differentiate the rat pheochromocytoma cell line PC12 to neuron-like cells. We examined the effect of IL-6 on the death of PC 12 cells. IL-6 significantly blocked the death of PC12 cells by serum deprivation. The protective effect of IL-6 was increased by preincubation of PC12 with IL-6 for 20 hr before serum deprivation. The inhibition of protein synthesis by cycloheximide had no effect on the protective effect of IL-6 on the serum deprivation-induced cell death. IL-6 also inhibited the death of PC12 cells induced by addition of the calcium ionophore A23187 to the culture medium. Specific in situ labeling of DNA cleavage was observed in PC12 cells subjected to both serum deprivation and A23187 for 24 hr. IL-6 inhibited DNA fragmentation in PC12 cells following serum deprivation. These results suggest that the death of PC12 cells induced by serum deprivation or by the addition of calcium ionophore is apoptosis, and that IL-6 blocks apoptosis of PC12 cells.
Markedly increased interleukin-6 (IL-6) mRNA levels occur in experimental cerebral ischemia, although the protein production and cellular sources of IL-6 remain unclear. We examined the cellular localization of IL-6 protein in gerbil brain following transient forebrain ischemia employing immunohistochemistry and Western blot analysis. The ischemia/recirculation groups revealed distinct IL-6 immunoreactivity predominantly in cortical and hippocampal neurons after 3 hours to 3 days recirculation. At 12 h recirculation, the IL-6 expression declined specifically in the hippocampus CA1. Microglia, but not activated astrocytes, also expressed IL-6 immunoreactivity. The sham group showed no apparent immunoreactivity. IL-6 protein may thus be expressed mainly in neurons following transient forebrain ischemia. Its transient decline in the CA1 at 12 h recirculation could reflect the specific vulnerability of this region.
The effects of transient global ischemia using bilateral carotid artery occlusion on regional cytokine levels in gerbil brain were investigated using enzyme-linked immunoassay techniques. Brain concentrations of interleukin-6 (IL-6), interleukin-lβ (IL-1β), and tumor necrosis factor-α (TNF-α) were increased during the early recirculation period (<6 h) after 10 min of ischemia, with lesser degrees of elevation following only 5 min of ischemia. TNF-α levels in the hippocampus and striatum were significantly increased as early as 1 h after recirculation, declining sharply to control levels by 12 h, then transiently increasing at 24 h. Elevated levels of IL-lβ and IL-6 were not seen until 3–6 h post-occlusion. No significant increases in cytokine concentrations were observed in the cerebellum or thalamus. These results suggest that regionally selective increases in cytokines may be involved in the pathophysiological changes in hippocampus and striatum following transient cerebral ischemia.
Interleukin-1 (IL-1) has been implicated in chronic and acute cerebral neuropathologies. IL-1 receptor antagonist (IL-1ra), a naturally occurring protein that binds to IL-1 receptors without inducing signal transduction, blocks several actions of IL-1. IL-1ra acts at the local level and it also circulates in the bloodstream. We now report evidence for a biological function of IL-1ra in the brain as an endogenous neuroprotective molecule. Cerebral expression of IL-1ra mRNA is induced rapidly by focal cerebral ischemia in rats, and inhibition of the action of IL-1ra, by passive immunoneutralization, markedly enhances ischemic damage. To our knowledge this is the first report of an action of endogenous IL-1ra in the brain. Control of IL-1ra expression or action may therefore provide a useful therapeutic strategy to limit acute neurodegeneration.
Ten years have passed since the molecular cloning of interleukin 6 (IL-6) in 1986. IL-6 is a typical cytokine, exhibiting functional pleiotropy and redundancy. IL-6 is involved in the immune response, inflammation, and hematopoiesis. The IL-6 receptor consists of an IL-6 binding alpha chain and a signal transducer, gp130, which is shared among the receptors for the IL-6 related cytokine subfamily. The sharing of a receptor subunit is a general feature of cytokine receptors and provides the molecular basis for the functional redundancy of cytokines. JAK tyrosine kinase is a key molecule that can initiate multiple signal-transduction pathways by inducing the tyrosine-phosphorylation of the cytokine receptor, gp130 in the case of IL-6, on which several signaling molecules are recruited, including STAT, a signal transducer and activator of transcription, and SHP-2, which links to the Ras-MAP kinase pathway. JAK can also directly activate signaling molecules such as STAT and Tec. These multiple signal-transduction pathways intimately regulate the expression of several genes including c-myc, c-myb, junB, IRF1, egr-1, and bcl-2, leading to the induction of cell growth, differentiation, and survival. The deregulated expression of IL-6 and its receptor is involved in a variety of diseases.
Interleukin-6 (IL-6, human recombinant) promoted the survival of catecholaminergic neurons from fetal and postnatal rat midbrains as assessed by an immunohistochemical staining for tyrosine hydroxylase (TH) in culture using a chemically defined medium. The maximal dose of IL-6 for the cell survival of postnatal P15 rat mesencephalic TH-positive neurons in culture for 7 days was 50 ng/ml. The survival-promoting effects on P15 cultures were observed both in high- and low-density cultures. The survival effect of IL-6 on the cultured P15 TH-positive neurons was significant for only 4-15 days in vitro. However, the viable number of TH-positive neurons with IL-6 was less than that of the control at early points in the culture process (1-2 days in vitro). Continuous presentation of IL-6 was required for promoting survival. The optimal dose of IL-6 for the survival of fetal E16 midbrain TH-positive neurons was 5 ng/ml, and the survival promoting effect was less than that for the P15 cultures. The maximal dose of IL-6 for the survival of P2 TH-positive neurons was 5 ng/ml and that of P8 was 50 ng/ml, indicating that the response of rat mesencephalic TH-positive neurons to IL-6 changes during the first postnatal week.
The potential neuroprotective effects of IL-6 against the excitotoxic neuronal loss induced by N-methyl-D-aspartate (NMDA) have been studied. Infusion into the rat striatum of excitotoxic amounts (250 nmol) of NMDA resulted in a 45% decrease in striatal choline acetyl transferase activity (ChAT; a marker of cholinergic neurons) and glutamate decarboxylase (GAD, a marker of GABAergic neurons) at 2 days post-injection. Co-infusion of 10 U of IL-6 reduced the loss of ChAT activity to 21% but failed to prevent the loss of GAD activity. IL-6 per se, up to the dose of 500 U, failed to affect ChAT or GAD activities. The in vivo effects of IL-6 are not mediated by a direct antagonism of NMDA toxicity, since IL-6 (up to a concentration of 500 and 5000 U/ml, respectively) did not antagonize either the increase in cyclic GMP levels resulting from NMDA receptor activation in cerebellar slices or the glutamate-induced release of lactate dehydrogenase, an index of neurotoxicity, by cultured cortical neurons. These results suggest that the increase in IL-6 levels observed in experimental brain lesions may play a role in the protection and regeneration of cholinergic neurons.
In order to locate the receptor-binding region of human interleukin-6 (IL-6), twelve peptide fragments were prepared by digestion of IL-6 with lysylendopeptidase. A significant activity of the receptor-binding was observed only for a peptide Ile88-Lys121, although the activity was estimated at 10(4)-fold less than that of intact IL-6. Solution structure of the peptide Ile88-Lys121 was analyzed by using two-dimensional nuclear magnetic resonance (NMR) spectroscopy. The results indicate the presence of alpha-helices in the regions Leu93-Phe106 and Glu110-Ser119. On the basis of the NMR data, we also prepared two peptides. Four-fold less binding activity than that of the peptide Ile88-Lys121 was observed for the peptide Ile88-Arg105, but no activity for the peptide Glu110-Lys121. These results suggest that the helical peptide Ile88-Arg105 composes a part of the receptor-binding region.
The IL-6R system comprises two functionally different chains: a ligand binding-chain (IL-6R) and a non-ligand-binding but signal-transducing chain (gp130). gp130 associates with the IL-6-IL-6R complex, resulting in the formation of high-affinity IL-6 binding sites, and transduces the signal. A cDNA for murine gp130 has been cloned from the cDNA library of murine macrophages by using a human gp130 cDNA as a probe. The overall homology with human gp130 was 76.8% at the protein level. The extracellular region of murine gp130, as observed in human gp130, comprises 6 U of a fibronectin type III module and part of this region of approximately 200 amino acids has typical features of a cytokine receptor family. Cloned murine gp130 could transduce the growth signal in a murine IL-3-dependent cell line in response to a complex of IL-6 and soluble IL-6R. Two species of murine gp130 mRNA (7 and 10 kb) were expressed in almost all the cell lines. These transcripts were also ubiquitously expressed in murine tissues, embryonic stem cells, and embryos as early as day 6 of gestation. Administration of IL-6 in mouse caused up-regulation of the gp130 mRNA levels in several tissues. Both gp130 and IL-6R mRNA in liver were up-regulated in vivo by IL-6.
To develop a simple, relatively noninvasive small-animal model of reversible regional cerebral ischemia, we tested various methods of inducing infarction in the territory of the right middle cerebral artery (MCA) by extracranial vascular occlusion in rats. In preliminary studies, 60 rats were anesthetized with ketamine and different combinations of vessels were occluded; blood pressure and arterial blood gases were monitored. Neurologic deficit, mortality rate, gross pathology, and in some instances, electroencephalogram and histochemical staining results were evaluated in all surviving rats. The principal procedure consisted of introducing a 4-0 nylon intraluminal suture into the cervical internal carotid artery (ICA) and advancing it intracranially to block blood flow into the MCA; collateral blood flow was reduced by interrupting all branches of the external carotid artery (ECA) and all extracranial branches of the ICA. In some groups of rats, bilateral vertebral or contralateral carotid artery occlusion was also performed. India ink perfusion studies in 20 rats documented blockage of MCA blood flow in 14 rats subjected to permanent occlusion and the restoration of blood flow to the MCA territory in six rats after withdrawal of the suture from the ICA. The best method of MCA occlusion was then selected for further confirmatory studies, including histologic examination, in five additional groups of rats anesthetized with halothane. Seven of eight rats that underwent permanent occlusion of the MCA had resolving moderately severe neurologic deficits (Grade 2 of 4) and unilateral infarcts averaging 37.6 +/- 5.5% of the coronal sectional area at 72 hours after the onset of occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)
Measurement of lactate dehydrogenase (LDH) activity released to the extracellular bathing media has been found to be a simple yet quantitative method for assessing glutamate mediated central neuronal cell injury in cortical cell culture. Extracellular LDH is both chemically and biologically stable; the magnitude of LDH efflux in the cultures correlates in a linear fashion with the number of neurons damaged by glutamate exposure.
Excitatory amino acids act via receptor subtypes in the mammalian central nervous system (CNS). The receptor selectively activated by N-methyl-D-aspartic acid (NMDA) has been best characterized using voltage-clamp and single-channel recording; the results suggest that NMDA receptors gate channels that are permeable to Na+, K+ and other monovalent cations. Various experiments suggest that Ca2+ flux is also associated with the activation of excitatory amino-acid receptors on vertebrate neurones. Whether Ca2+ enters through voltage-dependent Ca2+ channels or through excitatory amino-acid-activated channels of one or more subtype is unclear. Mg2+ can be used to distinguish NMDA-receptor-activated channels from voltage-dependent Ca2+ channels, because at micromolar concentrations Mg2+ has little effect on voltage-dependent Ca2+ channels while it enters and blocks NMDA receptor channels. Marked differences in the potency of other divalent cations acting as Ca2+ channel blockers compared with their action as NMDA antagonists also distinguish the NMDA channel from voltage-sensitive Ca2+ channels. However, we now directly demonstrate that excitatory amino acids acting at NMDA receptors on spinal cord neurones increase the intracellular Ca2+ activity, measured using the indicator dye arsenazo III, and that this is the result of Ca2+ influx through NMDA receptor channels. Kainic acid (KA), which acts at another subtype of excitatory amino-acid receptor, was much less effective in triggering increases in intracellular free Ca2+.
Interleukin 6 (IL-6) refers to the gene product that was characterized initially as beta 2 interferon/26-kDa protein produced by human fibroblasts and later was found to be identical to B-cell stimulatory factor 2, hybridoma/plasmacytoma growth factor, and probably hepatocyte-stimulating factor. Using the human IL-6 cDNA as a probe, we have isolated functional cDNA clones from mouse bone marrow stromal cell cDNA libraries. Sequence analysis of the mouse cDNA insert revealed significant homology between the human and mouse IL-6 cDNA clones both at the level of nucleotide (65%) and deduced amino acid (41%) sequences. The NH2-terminal sequence of the deduced protein is identical to a partial NH2-terminal sequence determined previously for a hybridoma/plasmacytoma growth factor and a plasmacytoma growth factor isolated from mouse T cells and macrophages, respectively. The mRNA for mouse IL-6 is expressed in IL-1-treated stromal cells and in activated T-cell and macrophage cell lines. Supernatants from COS-7 monkey cells transfected with the cDNA clone have plasmacytoma growth factor, hepatocyte-stimulating factor, and colony-stimulating factor activities, as well as the ability to support the growth of a factor-dependent myeloid cell line, thus revealing an additional biological activity for IL-6.
We have previously demonstrated that stroke influences systemic immune responses. The aim of the present study was to investigate patterns of local inflammatory response as a consequence of acute stroke.
Thirty stroke patients were studied prospectively on days 0 to 3, 7 to 9, 21 to 26, and after day 90 with clinical evaluations, radiological assessments, and analysis of serum and cerebrospinal fluid cytokine levels.
Significantly increased levels of interleukin-6 (IL-6) in cerebrospinal fluid (P < .001) were observed in virtually all patients studied compared with healthy control subjects. This increase was observed during the whole observation period but was significantly more pronounced within the first days after stroke onset, with a peak level on days 2 and 3. This initial increase was significantly correlated (r = .65, P = .002) with the volume of infarct measured by MRI 2 to 3 months later. Serum levels of IL-6 in stroke patients were significantly lower than cerebrospinal fluid levels of IL-6 (P = .013) and did not display any significant correlation to the size of the brain lesion. Also, increase in intrathecal but not systemic production of IL-1 beta was observed early during the stroke. Only minor increases of cerebrospinal fluid interferon-gamma levels were observed in two patients.
Our study demonstrates an intrathecal production of IL-6 and IL-1 beta in patients with stroke, supporting the notion of localized inflammatory response to acute brain lesion. In addition, the significant correlation between early intrathecal production of IL-6 and the subsequent size of the brain lesion can be used as a prognostic tool, predicting the size of the brain damage before it is possible to accurately visualize it with radiological methods.
We examined the effect of interleukin-6 (human recombinant) on glutamate-induced neuronal death of cultured 20-day fetal rat hippocampal neurons. After 7 days in culture, the hippocampal neurons were markedly degenerated by the addition of L-glutamate and also N-methyl-D-aspartate. The neuronal death was prevented by the addition of MK801, a potent N-methyl-D-aspartate antagonist. Interleukin-6 at the concentration of 50 ng/ml has a significant preventive effect on the glutamate-induced neuronal death. Basic fibroblast growth factor at the concentration of 100 ng/ml gave also significant protective effect on hippocampal neurons, but nerve growth factor was ineffective in preventing the toxicity. It has been postulated that glutamate plays an important role in the pathogenesis of neuronal death such as ischemia and the various neurological diseases. Interleukin-6 might have somewhat physiological or pathological role in these events.
The release of the proinflammatory cytokines IL-1 beta, IL-6, TNF-alpha and soluble TNF-receptors p55 and p75 in peripheral blood was serially determined in 19 patients with acute cerebral ischemia. Only patients admitted within 4 h following onset of symptoms were studied. In contrast to serum levels of IL-1 beta, TNF-alpha and TNF-receptors, which did not exhibit a significant response, IL-6 showed a significant increase of serum levels already within the first hours following onset of disease and reached a plateau at 10 h until day 3 and returned to baseline by day 7. The increase of levels of this cytokine was significantly (P < 0.05) correlated with increasing volumes of brain lesion and was also significantly (P < 0.005) associated with poor functional and neurological outcome. The increase of levels of IL-6 despite a considerable dilution in peripheral blood shown in this preliminary study suggests an early inflammatory response in ischemic brain lesion.
Using RT-PCR, the development profile of interleukin-6 (IL-6) and its receptor (IL-6R) mRNAs in rat brain was investigated. Our results indicate that IL-6 and IL-6R mRNAs are coexpressed and are developmentally regulated in a tissue-specific manner. Highest levels of both transcripts were detected in the adult hippocampus. Most pronounced developmental changes of IL-6 message levels were observed in the rat striatum increasing up to 8-fold. By contrast, in all other regions such as neocortex, hippocampus, cerebellum and pons/medulla oblongata only minor changes (2- to 3-fold) in IL-6 expression were seen. In most tissues IL-6 mRNA levels peaked at day 20. Marked induction of the receptor message levels was detected in the striatum, hippocampus and neocortex (8- to 10-fold) whereas no changes were observed in the cerebellum and the pons/medulla oblongata. The expression pattern of both genes in various brain areas during postnatal development strongly supports the concept of IL-6 as a candidate for a new neurotrophic factor.
The distribution of interleukin 6 (IL-6) mRNA and IL-6 receptor (IL-6R) mRNA in the brain of adult male rats was studied at the light microscope level by in situ hybridization histochemistry using 35S-labelled oligonucleotides. The transcripts of both genes were localized in the pyramidal neurons and in the granular neurons of the hippocampus, in neurons of the habenular nucleus as well as in the dorsomedial and ventromedial hypothalamus, in the piriform cortex, in scattered neurons of the cortex and in granular cells of the cerebellum. The medial preoptic nucleus and the anterior tip of the lateral ventricle contained mRNA encoding IL-6 and its receptor. Moreover, white matter areas, such as the internal capsule, which consist of only fibres and glial cells, were found to have autoradiographic signals above background. The mRNAs for IL-6 and IL-6R in hippocampus and cerebellum are not different, as shown by Northern blot analyses of RNA isolated from these tissues. We postulate that the cytokine IL-6 is expressed constitutively in discrete regions of the CNS and that it is involved in the mechanisms coordinating metabolic, behavioural and neuroendocrine changes not only during illness but also under normal physiological conditions. Our results suggest that IL-6 mRNA and IL-6R mRNA are colocalized, thus supporting a role of the cytokine in autocrine and paracrine communication.
The effects of transient global ischemia using bilateral carotid artery occlusion on regional cytokine levels in gerbil brain were investigated using enzyme-linked immunoassay techniques. Brain concentrations of interleukin-6 (IL-6), interleukin-1 beta (IL-1 beta), and tumor necrosis factor-alpha (TNF-alpha) were increased during the early recirculation period ( < 6 h) after 10 min of ischemia, with lesser degrees of elevation following only 5 min of ischemia. TNF-alpha levels in the hippocampus and striatum were significantly increased as early as 1 h after recirculation, declining sharply to control levels by 12 h, then transiently increasing at 24 h. Elevated levels of IL-1 beta and IL-6 were not seen until 3-6 h post-occlusion. No significant increases in cytokine concentrations were observed in the cerebellum or thalamus. These results suggest that regionally selective increases in cytokines may be involved in the pathophysiological changes in hippocampus and striatum following transient cerebral ischemia.
Cytokines are involved in nerve regeneration by modulating the synthesis of neurotrophic factors. The role played by interleukin-6 (IL-6) in promoting nerve growth factor (NGF) after brain injury was investigated by monitoring the release of IL-6 and NGF in ventricular cerebrospinal fluid (CSF) of 22 patients with severe traumatic brain injuries. IL-6 was found in the CSF of all individuals and remained elevated for the whole study period. NGF appeared in the CSF if IL-6 levels reached high concentrations and was often detected simultaneously with or following an IL-6 peak. The amounts of NGF correlated with the severity of the injury, as indicated by the clinical outcome of the patients. The functional relationship of IL-6 and NGF was investigated utilizing cultured mouse astrocytes. The CSF of 8 patients containing IL-6 induced NGF production in astrocytes, whereas control CSF without IL-6 had no effect. The induction of NGF was inhibited up to 100% by adding anti-IL-6 antibodies. These results were corroborated when astrocytes were exposed to recombinant IL-6 at different concentrations resulting in NGF production. Thus, the production of IL-6 within the injured brain may likely contribute to the release of neurotrophic factors by astrocytes.
Growing evidence suggests that aberrant production of inflammatory cytokines within the central nervous system (CNS) contributes to the development of pathological conditions. To test the cause-effect relationship between the overproduction of interleukin-6 (IL-6) in the CNS and the onset of neuropathological changes, we have generated transgenic mice in which human IL-6 expression has been targeted to the neurons by using the rat neuron-specific enolase promoter. These mice develop reactive astrocytosis and an increase in ramified microglial cells but do not show histological or behavioural signs of neuron damage at the light microscope level. We thus conclude that a constant release of human IL-6 by neuronal subpopulations in mice is sufficient to activate cells potentially capable of modulating the local immune response, but at the same time is compatible with normal neuron functions.
Injury of the central nervous system leads to a highly reproducible activation of neurons, astrocytes and microglia, which plays an important role in the posttraumatic repair of the damaged neural tissue. Recent work on proinflammatory cytokines has begun to shed light on the molecular mechanisms that direct and control this repair process. Here we summarize data on the regulation of these cytokines, which led to the identification of the macrophage colony-stimulating factor and interleukin-6 as key factors in microglial and astrocyte activation.
The localization of gp130, the signal transducing receptor component used in common for interleukin (IL)-6, IL-11, ciliary neurotrophic factor (CNTF), LIF and OSM, in the rat brain was demonstrated by immunohistochemistry using an antibody specific to gp130. The gp130 immunoreactivity was observed in both glial and neuronal cells. Two distinct neuronal staining patterns were observed. The first showed neuropil staining, observed mainly in telencephalic structures including the hippocampus, cerebral cortex and caudate-putamen. The second pattern was observed on the cytoplasmic membrane of neuronal somata and was found primarily in the lower brainstem, in the large neurons of the reticular formation, and in spinal and cranial motor neurons. Electron-microscopic analysis revealed that both types of gp130 immunoreactivity were primarily associated with the cytoplasmic membrane and were not localized exactly at synaptic sites. Further, gp130 immunoreactivity was also observed in the oligodendrocytes and subependymal zone. These widespread but characteristic patterns of gp130 immunoreactivity overlap well with those of IL-6 receptor and CNTF alpha chains, suggesting a role of cytokines and growth factors such as IL-6 and CNTF via gp130 in certain specific regions of the brain.
Interleukin-6 (IL-6) has been shown to have potent neurotrophic activity on peripheral and central neurons in vitro. However, it remains to be determined whether or not IL-6 rescues hippocampal CA1 neurons from lethal ischemia and prevents ischemia-induced learning disability. In the present in vivo study, we infused IL-6 continuously for 7 days into the lateral ventricle of gerbil starting 2 h before 3-min forebrain ischemia. IL-6 infusion prevented the occurrence of ischemia-induced learning disability in a dose-dependent manner as revealed by a step-down passive avoidance task. Subsequent light and electron microscopic examinations showed that pyramidal neurons in the CA1 region of the hippocampus as well as synapses within the strata moleculare, radiatum and oriens of the region were significantly more numerous in gerbils infused with IL-6 than in those receiving vehicle infusion. These findings suggest that IL-6 has a trophic effect on ischemic hippocampal neurons.
Hypoxic-ischemic neuronal death has long been considered to represent necrosis, but it now appears that many brain neurons undergo apoptosis after either global or focal ischemic insults. This event is probably substantially distinct from ischemia-triggered excitotoxicity, which tends to produce necrosis. While many questions remain unanswered, the concept of ischemic apoptosis has raised exciting prospects of combining anti-apoptotic with anti-excitotoxic treatments to achieve heightened therapeutic benefits in the brains of patients traumatized by cardiac arrest or stroke.
The cytokine interleukin-6 (IL-6) is an important mediator of inflammatory and immune responses in the periphery. IL-6 is produced in the periphery and acts systemically to induce growth and differentiation of cells in the immune and hematopoietic systems and to induce and coordinate the different elements of the acute-phase response. In addition to these peripheral actions, recent studies indicate that IL-6 is also produced within the central nervous system (CNS) and may play an important role in a variety of CNS functions such as cell-to-cell signaling, coordination of neuroimmune responses, protection of neurons from insult, as well as neuronal differentiation, growth and survival. IL-6 may also contribute to the etiology of neuropathological disorders. Elevated levels of IL-6 in the CNS are found in several neurological disorders including AIDS dementia complex, Alzheimer's disease, multiple sclerosis, systemic lupus erythematosus, CNS trauma, and viral and bacterial meningitis. Moreover, several studies have shown that chronic overexpression of IL-6 in transgenic mice can lead to significant neuroanatomical and neurophysiological changes in the CNS similar to that commonly observed in various neurological diseases. Thus, it appears that IL-6 may play a role in both physiological and pathophysiological processes in the CNS.