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![Reactive astrocytes show hypertrophy of their cellular processes but stay within their tiled domains. A: expression of GFAP, which forms bundles of intermediate filaments (green) in astrocytes in unchallenged mouse hippocampus (left) and in partially deafferented hippocampus (molecular layer of the dentate gyrus) 4 days after entorhinal cortex lesion that triggers astrocyte activation and reactive gliosis in the hippocampus. The processes of reactive astrocytes show distinct hypertrophy. [From Wilhelmsson et al. (260).] B: schematic drawing of astrocyte response to injury. The main cellular processes of reactive astrocytes get thicker (and thus visible over a greater distance; compare the circles); however, reactive astrocytes stay within their tiled domains. [From Wilhelmsson et al. (260).] C: examples of the functions of astrocytes in healthy CNS and at the early and late stages of neurological diseases.](profile/Milos-Pekny/publication/266625661/figure/fig7/AS:667691975180288@1536201580035/Reactive-astrocytes-show-hypertrophy-of-their-cellular-processes-but-stay-within-their.png)
Reactive astrocytes show hypertrophy of their cellular processes but stay within their tiled domains. A: expression of GFAP, which forms bundles of intermediate filaments (green) in astrocytes in unchallenged mouse hippocampus (left) and in partially deafferented hippocampus (molecular layer of the dentate gyrus) 4 days after entorhinal cortex lesion that triggers astrocyte activation and reactive gliosis in the hippocampus. The processes of reactive astrocytes show distinct hypertrophy. [From Wilhelmsson et al. (260).] B: schematic drawing of astrocyte response to injury. The main cellular processes of reactive astrocytes get thicker (and thus visible over a greater distance; compare the circles); however, reactive astrocytes stay within their tiled domains. [From Wilhelmsson et al. (260).] C: examples of the functions of astrocytes in healthy CNS and at the early and late stages of neurological diseases.
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Astrocytes are the most abundant cells in the central nervous system (CNS) that provide nutrients, recycle neurotransmitters, as well as fulfill a wide range of other homeostasis maintaining functions. During the past two decades, astrocytes emerged also as increasingly important regulators of neuronal functions including the generation of new nerv...
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Context 1
... / Vim / mice show reduced reactive gliosis and glial scar formation, a slower healing process with increased loss of neuronal synapses after neurotrauma (172, 262), and decreased resistance of the CNS tissue to severe me- chanical stresses (142,243). While astrocytes around the CNS lesion in GFAP / Vim / mice are comparable to those of wild-type mice with respect to their number and the volume they access (262), they do not develop the typical reactive phenotype characterized by the thickening (hypertrophy) of their main cellular processes (260, 262) (FIGURE 8, A AND B). This shows that IF upregulation is an important part of astrocyte activation and reactive astrogliosis, albeit not their proliferation in response to traumatic brain injury, and suggests a positive role for reactive astrocytes in the acute phase of neurotrauma (175, 176). ...
Citations
... Mesaconate pretreatment even slightly reduced the percentage of CD68 + microglia compared to PBS pretreatment, though without statistical signi cance (Fig. 3I). While microglia are recognized as the brain's primary immune cells, research has also highlighted astrocytes' signi cant role in immune responses and regulation, and both glial cells seem to in uence each other (44,45). In response to neuroin ammation, astrocytes undergo astrogliosis, marked by an increase in glial brillary acidic protein (GFAP) expression (46). ...
Despite advances in antimicrobial and anti-inflammatory treatment, inflammation and its consequences remain a major challenge in the field of medicine. Inflammatory reactions can lead to life-threatening conditions such as septic shock, while chronic inflammation has the potential to worsen the condition of body tissues and ultimately lead to significant impairment of their functionality. Although the central nervous system has long been considered immune privileged to peripheral immune responses, recent research has shown that strong immune responses in the periphery also affect the brain, leading to reactive microglia, which belong to the innate immune system and reside in the brain, and neuroinflammation. The inflammatory response is primarily a protective mechanism to defend against pathogens and tissue damage. However, excessive and chronic inflammation can have negative effects on neuronal structure and function. Neuroinflammation underlies the pathogenesis of many neurological and neurodegenerative diseases and can accelerate their progression. Consequently, targeting inflammatory signaling pathways offers potential therapeutic strategies for various neuropathological conditions, particularly Parkinson’s and Alzheimer’s disease, by curbing inflammation. Here the blood-brain barrier is a major barrier for potential therapeutic strategies, therefore it would be highly advantageous to foster and utilize brain innate anti-inflammatory mechanisms. The tricarboxylic acid cycle-derived metabolite itaconate is highly upregulated in activated macrophages and has been shown to act as an immunomodulator with anti-inflammatory and antimicrobial functions. Mesaconate, an isomer of itaconate, similarly reduces the inflammatory response in macrophages. Nevertheless, most studies have focused on its esterified forms and its peripheral effects, while its influence on the CNS remained largely unexplored. Therefore, this study investigated the immunomodulatory and therapeutic potential of endogenously synthesized itaconate and its isomer mesaconate in lipopolysaccharide (LPS)-induced neuroinflammatory processes. Our results show that both itaconate and mesaconate reduce LPS-induced neuroinflammation, as evidenced by lower levels of inflammatory mediators, reduced microglial reactivity and a rescue of synaptic plasticity, the cellular correlate of learning and memory processes in the brain. Overall, this study emphasizes that both itaconate and mesaconate have therapeutic potential for neuroinflammatory processes in the brain and are of remarkable importance due to their endogenous origin and production, which usually leads to high tolerance.
... In a healthy central nervous system (CNS), astrocytes participate in neural/synaptic development, blood flow regulation, ion, and neurotransmitter balance, blood-brain barrier (BBB) formation, and synaptic function (Barres, 2008;Pereira & Furlan, 2010;Santello et al., 2019;Schummers et al., 2008;Simard & Nedergaard, 2004). Under normal conditions, astrocytes exist in a 'naïve' state with diverse morphology but can also be activated to undergo complex changes to their structural-functional properties in a process known as reactive astrogliosis (Pekny & Pekna, 2014;Sofroniew, 2015;Verkhratsky, Ho, et al., 2019). Reactive astrogliosis is part of the CNS's response to injury, stress, and disease (Santello et al., 2019; ...
... The copyright holder for this preprint (which this version posted June 1, 2024. ; https://doi.org/10.1101/2024.05.31.596856 doi: bioRxiv preprint Verkhratsky, Ho, et al., 2019) that can exert both protective and pathological activity depending on the type and extent of astrocyte stimulation (Pekny & Pekna, 2014;Verkhratsky, Ho, et al., 2019). Astrogliosis is characterized by a variable degree of morphological and functional changes to astrocytes (Santello et al., 2019;Verkhratsky, Ho, et al., 2019) and can be visualized and measured morphologically and biochemically. ...
A better understanding of nicotine neurobiology is needed to reduce or prevent chronic addiction, ameliorate the detrimental effects of nicotine withdrawal, and increase successful cessation of use. Nicotine binds and activates two astrocyte-expressed nicotinic acetylcholine receptors (nAChRs), α4β2 and α7. We recently found that Protein kinase B-β (Pkb-β or Akt2) expression is restricted to astrocytes in mice and humans. To determine if AKT2 plays a role in astrocytic nicotinic responses, we generated astrocyte-specific Akt2 conditional knockout (cKO) and full Akt2 KO mice for in vivo and in vitro experiments. For in vivo studies, we examined mice exposed to chronic nicotine for two weeks in drinking water (200 μg/mL) and following acute nicotine challenge (0.09, 0.2 mg/kg) after 24 hrs. Our in vitro studies used cultured mouse astrocytes to measure nicotine-dependent astrocytic responses. We validated our approaches using lipopolysaccharide (LPS) exposure inducing astrogliosis. Sholl analysis was used to measure glial fibrillary acidic protein responses in astrocytes. Our data show that wild-type (WT) mice exhibit increased astrocyte morphological complexity during acute nicotine exposure, with decreasing complexity during chronic nicotine use, whereas Akt2 cKO mice showed increased astrocyte morphology complexity. In culture, we found that 100μM nicotine was sufficient for morphological changes and blocking α7 or α4β2 nAChRs prevented observed morphologic changes. Finally, we performed conditioned place preference (CPP) in Akt2 cKO mice and found that astrocytic AKT2 deficiency reduced nicotine preference compared to controls. These findings show the importance of nAChRs and Akt2 signaling in the astrocytic response to nicotine.
... Various stimuli, however, may induce profound alterations in the morphology and gene expression pattern of central glia, resulting in the formation of reactive astrocytes and reactive microglia (Pekny and Pekna, 2014;Liddelow and Barres, 2017;Wolf et al., 2017;Gao et al., 2023). ...
... 2023; Liu et al., 2023). The broad neurochemical repertoire of glial cells to influence neuronal and non-neuronal functions proved to be a double-edged sword, since reactive astrocytes and microglia profoundly change their expression profile and the composition of the released gliotransmitters (Pekny and Pekna, 2014;Bachiller et al., 2018;Bennett and Viaene, 2021;Escartin et al., 2021;Hasel et al., 2021;Woodburn et al., 2021). An appropriate set of gliotransmitters seems inevitable in maintaining neural functions, but substances released by reactive glia can be disadvantageous or even harmful for neural networks. ...
The endogenous cannabinoid 2-arachidonoylglycerol (2-AG) influences neurotransmission in the central nervous system mainly by activating type 1 cannabinoid receptor (CB1). Following its release, 2-AG is broken down by hydrolases to yield arachidonic acid, which may subsequently be metabolized by cyclooxygenase-2 (COX-2). COX-2 converts arachidonic acid and also 2-AG into prostanoids, well-known inflammatory and pro-nociceptive mediators. Here, using immunohistochemical and biochemical methods and pharmacological manipulations, we found that reactive spinal astrocytes and microglia increase the expression of COX-2 and the production of prostaglandin E2 when exposed to 2-AG. Both 2-AG and PGE2 evoke calcium transients in spinal astrocytes, but PGE2 showed 30% more efficacy and 55 times more potency than 2-AG. Unstimulated spinal dorsal horn astrocytes responded to 2-AG with calcium transients mainly through the activation of CB1. 2-AG induced exaggerated calcium transients in reactive astrocytes, but this increase in the frequency and area under the curve of calcium signals was only partially dependent on CB1. Instead, aberrant calcium transients were almost completely abolished by COX-2 inhibition. Our results suggest that both reactive spinal astrocytes and microglia perform an endocannabinoid-prostanoid switch to produce PGE2 at the expense of 2-AG. PGE2 in turn is responsible for the induction of aberrant astroglial calcium signals which, together with PGE2 production may play role in the development and maintenance of spinal neuroinflammation-associated disturbances such as central sensitization.
... Reactive gliosis is a dynamic glial cell response to all forms of central nervous system (CNS) disruption, including aging, inflammation, trauma, infection, and neurodegeneration (Allen et al., 2023;Burda & Sofroniew, 2014). Although a term occasionally applied to all glia, gliosis is most often defined as a constitutive and evolutionarily conserved astrocytic response characterized by cell hypertrophy, transcriptional regulation, and functional changes (Pekny & Pekna, 2014;Zamanian et al., 2012). Most commonly, it is detected by the up-regulation of glial fibrillary acidic (GFAP) protein and/ or vimentin (Eng & Ghirnikar, 1994;Wilhelmsson et al., 2019)-intermediate filaments thought to confer resilience in response to stress (Wilhelmsson et al., 2019). ...
Ependymal cells form a specialized brain–cerebrospinal fluid (CSF) interface and regulate local CSF microcirculation. It is becoming increasingly recognized that ependymal cells assume a reactive state in response to aging and disease, including conditions involving hypoxia, hydrocephalus, neurodegeneration, and neuroinflammation. Yet what transcriptional signatures govern these reactive states and whether this reactivity shares any similarities with classical descriptions of glial reactivity (i.e., in astrocytes) remain largely unexplored. Using single‐cell transcriptomics, we interrogated this phenomenon by directly comparing the reactive ependymal cell transcriptome to the reactive astrocyte transcriptome using a well‐established model of autoimmune‐mediated neuroinflammation (MOG35‐55 EAE). In doing so, we unveiled core glial reactivity‐associated genes that defined the reactive ependymal cell and astrocyte response to MOG35‐55 EAE. Interestingly, known reactive astrocyte genes from other CNS injury/disease contexts were also up‐regulated by MOG35‐55 EAE ependymal cells, suggesting that this state may be conserved in response to a variety of pathologies. We were also able to recapitulate features of the reactive ependymal cell state acutely using a classic neuroinflammatory cocktail (IFNγ/LPS) both in vitro and in vivo. Taken together, by comparing reactive ependymal cells and astrocytes, we identified a conserved signature underlying glial reactivity that was present in several neuroinflammatory contexts. Future work will explore the mechanisms driving ependymal reactivity and assess downstream functional consequences. image
... This results in the generation of reactive oxygen species (ROS) and free radicals [26,27], highly reactive compounds that cause oxidative harm to lipids, proteins, and DNA in brain cells, increasing neuronal damage [28,29]. Ischemic brain injury triggers a series of processes characterized by the activation of microglia [30][31][32], astrocytes [33][34][35], and immune cells that infiltrate the brain [36]. The inflammatory reaction triggers the release of cytokines, chemokines, and other substances that promote neuroinflammation and cause more tissue harm [37]. ...
Ischemic stroke triggers a complex cascade of cellular and molecular events leading to neuronal damage and tissue injury. This review explores the potential therapeutic avenues targeting cellular signaling pathways implicated in stroke pathophysiology. Specifically, it focuses on the articles that highlight the roles of RhoA/ROCK and mTOR signaling pathways in ischemic brain injury and their therapeutic implications. The RhoA/ROCK pathway modulates various cellular processes, including cytoskeletal dynamics and inflammation, while mTOR signaling regulates cell growth, proliferation, and autophagy. Preclinical studies have demonstrated the neuroprotective effects of targeting these pathways in stroke models, offering insights into potential treatment strategies. However, challenges such as off-target effects and the need for tissue-specific targeting remain. Furthermore, emerging evidence suggests the therapeutic potential of MSC secretome in stroke treatment, highlighting the importance of exploring alternative approaches. Future research directions include elucidating the precise mechanisms of action, optimizing treatment protocols, and translating preclinical findings into clinical practice for improved stroke outcomes.
... They also become reactive in response to a variety of disease processes in the brain including ischemic stroke and neurodegeneration, [17][18][19] during which they undergo characteristic morphological and functional changes, including the upregulation of a specific cytoskeletal protein, glial fibrillary acidic protein (GFAP), in a process termed reactive astrogliosis. [17][18][19][20] As such, elevated GFAP level is commonly used as a marker of reactive astrogliosis in human clinical studies. Higher GFAP levels have been reported in the cerebrospinal fluid of patients with AD and other non-AD neurodegenerative diseases. ...
INTRODUCTION
While elevated blood glial fibrillary acidic protein (GFAP) has been associated with brain amyloid pathology, whether this association occurs in populations with high cerebral small vessel disease (CSVD) concomitance remains unclear.
METHODS
Using a Singapore‐based cohort of cognitively impaired subjects, we assessed associations between plasma GFAP and neuroimaging measures of brain amyloid and CSVD, including white matter hyperintensities (WMH). We also examined the diagnostic performance of plasma GFAP in detecting brain amyloid beta positivity (Aβ+).
RESULTS
When stratified by WMH status, elevated brain amyloid was associated with higher plasma GFAP only in the WMH– group ( β = 0.383; P < 0.001). The diagnostic performance of plasma GFAP in identifying Aβ+ was significantly higher in the WMH– group (area under the curve [AUC] = 0.896) than in the WMH+ group (AUC = 0.712, P = 0.008).
DISCUSSION
The biomarker utility of plasma GFAP in detecting brain amyloid pathology is dependent on the severity of concomitant WMH.
Highlight
Glial fibrillary acidic protein (GFAP)’s association with brain amyloid is unclear in populations with high cerebral small vessel disease (CSVD).
Plasma GFAP was measured in a cohort with CSVD and brain amyloid.
Plasma GFAP was better in detecting amyloid in patients with low CSVD versus high CSVD.
Biomarker utility of GFAP in detecting brain amyloid depends on the severity of CSVD.
... Reactive astrocytes undergo profound functional changes, including increased proliferation and migration towards the site of injury [15,19]. These injury-induced phenotypic changes of mature astrocytes are also recognized in astrocyte precursors during CNS development [18,19,55], but the underlining molecular mechanisms are not well understood. ...
Astrocytes are the main homeostatic cells in the central nervous system, with the unique ability to transform from quiescent into a reactive state in response to pathological conditions by reacquiring some precursor properties. This process is known as reactive astrogliosis, a compensatory response that mediates tissue damage and recovery. Although it is well known that SOX transcription factors drive the expression of phenotype-specific genetic programs during neurodevelopment, their roles in mature astrocytes have not been studied extensively. We focused on the transcription factors SOX2 and SOX9, shown to be re-expressed in reactive astrocytes, in order to study the reactivation-related functional properties of astrocytes mediated by those proteins. We performed an initial screening of SOX2 and SOX9 expression after sensorimotor cortex ablation injury in rats and conducted gain-of-function studies in vitro using astrocytes derived from the human NT2/D1 cell line. Our results revealed the direct involvement of SOX2 in the reacquisition of proliferation in mature NT2/D1-derived astrocytes, while SOX9 overexpression increased migratory potential and glutamate uptake in these cells. Our results imply that modulation of SOX gene expression may change the functional properties of astrocytes, which holds promise for the discovery of potential therapeutic targets in the development of novel strategies for tissue regeneration and recovery.
... ASTs are increasingly recognized as partaking in complex homeostatic mechanisms critical for regulating neuronal plasticity following CNS insults [39]. Depending on the context and type of injury, reactive astrocytes respond with diverse morphological, proliferative and functional changes collectively known as astrogliosis, which results in both pathogenic and protective effects [40]. There is also growing interest in how astrogliosis might in some contexts be protective and help to limit the spread of the injury. ...
Methylene blue (MB) was found to exert neuroprotective effect on different brain diseases, such as ischemic stroke. This study assessed the MB effects on ischemia induced brain edema and its role in the inhibition of aquaporin 4 (AQP4) and metabotropic glutamate receptor 5 (mGluR5) expression. Rats were exposed 1 h transient middle cerebral artery occlusion (tMCAO), and MB was injected intravenously following reperfusion (3 mg/kg). Magnetic resonance imaging (MRI) and 2,3,5-triphenyltetrazolium chloride (TTC) staining was performed 48 h after the onset of tMCAO to evaluate the brain infarction and edema. Brain tissues injuries as well as the glial fibrillary acidic protein (GFAP), AQP4 and mGluR5 expressions were detected. Oxygen and glucose deprivation/reoxygenation (OGD/R) was performed on primary astrocytes (ASTs) to induce cell swelling. MB was administered at the beginning of reoxygenation, and the perimeter of ASTs was measured by GFAP immunofluorescent staining. 3,5-dihydroxyphenylglycine (DHPG) and fenobam were given at 24 h before OGD to examine their effects on MB functions on AST swelling and AQP4 expression. MB remarkably decreased the volumes of T2WI and ADC lesions, as well as the cerebral swelling. Consistently, MB treatment significantly decreased GFAP, mGluR5 and AQP4 expression at 48 h after stroke. In the cultivated primary ASTs, OGD/R and DHPG significantly increased ASTs volume as well as AQP4 expression, which was reversed by MB and fenobam treatment. The obtained results highlight that MB decreases the post-ischemic brain swelling by regulating the activation of AQP4 and mGluR5, suggesting potential applications of MB on clinical ischemic stroke treatment.
... We have shown that Fg dose-dependently increased the activation of astrocytes [15,16]. Astrogliosis is a reaction of astrocytes due to an injury or pathological process in the CNS, with the hallmark characteristic of upregulation in GFAP [38]. In the current study, we found that the astrogliosis resulting from TBI was greatly reduced during hypofibrinogenemia. ...
... They regulate synaptic transmission and modulate synaptic plasticity, long-term potentiation, and memory formation [43]. In the current study, we are the first to show that a decrease in blood levels of Fg caused a significant reduction in GFAP expression (one of the markers of astrocyte activation) [38]. These results suggest that lowered circulating Fg during TBI may result in a decrease in neurodegeneration and in the STM changes seen in previous studies [10,14,18,22]. ...
Vascular contribution to cognitive impairment and dementia (VCID) is a term referring to all types of cerebrovascular and cardiovascular disease-related cognitive decline, spanning many neuroinflammatory diseases including traumatic brain injury (TBI). This becomes particularly important during mild-to-moderate TBI (m-mTBI), which is characterized by short-term memory (STM) decline. Enhanced cerebrovascular permeability for proteins is typically observed during m-mTBI. We have previously shown that an increase in the blood content of fibrinogen (Fg) during m-mTBI results in enhanced cerebrovascular permeability. Primarily extravasated via a transcellular pathway, Fg can deposit into the parenchyma and exacerbate inflammatory reactions that can lead to neurodegeneration, resulting in cognitive impairment. In the current study, we investigated the effect of a chronic reduction in Fg concentration in blood on cerebrovascular permeability and the interactions of extravasated Fg with astrocytes and neurons. Cortical contusion injury (CCI) was used to generate m-mTBI in transgenic mice with a deleted Fg γ chain (Fg γ+/−), resulting in a low blood content of Fg, and in control C57BL/6J wild-type (WT) mice. Cerebrovascular permeability was tested in vivo. Interactions of Fg with astrocytes and neurons and the expression of neuronal nuclear factor-кB (NF-кB) were assessed via immunohistochemistry. The results showed that 14 days after CCI, there was less cerebrovascular permeability, lower extravascular deposition of Fg, less activation of astrocytes, less colocalization of Fg with neurons, and lower expression of neuronal pro-inflammatory NF-кB in Fg γ+/− mice compared to that found in WT mice. Combined, our data provide strong evidence that increased Fg extravasation, and its resultant extravascular deposition, triggers astrocyte activation and leads to potential interactions of Fg with neurons, resulting in the overexpression of neuronal NF-кB. These effects suggest that reduced blood levels of Fg can be beneficial in mitigating the STM reduction seen in m-mTBI.
... In the present results, the 31 kD isoform demonstrates an even more promising outcome, since reactive astrogliosis was downregulated by 60%. Such a decrease indicates a lower probability of glial scar formation in the gray/white matter interface, which is considered critical for the regrowth of the sectioned axons towards the reimplanted roots [59][60][61]. One possible explanation for such a decrease in astroglial response is the presence of FGF receptors (FGFR) in such cells. ...
Background
Spinal ventral root avulsion results in massive motoneuron degeneration with poor prognosis and high costs. In this study, we compared different isoforms of basic fibroblast growth factor 2 (FGF2), overexpressed in stably transfected Human embryonic stem cells (hESCs), following motor root avulsion and repair with a heterologous fibrin biopolymer (HFB).
Methods
In the present work, hESCs bioengineered to overexpress 18, 23, and 31 kD isoforms of FGF2, were used in combination with reimplantation of the avulsed roots using HFB. Statistical analysis was conducted using GraphPad Prism software with one-way or two-way ANOVA, followed by Tukey’s or Dunnett’s multiple comparison tests. Significance was set at *p < 0.05, **p < 0.01, ***p < 0.001, and ****p < 0.0001.
Results
For the first set of experiments, rats underwent avulsion of the ventral roots with local administration of HFB and engraftment of hESCs expressing the above-mentioned FGF2 isoforms. Analysis of motoneuron survival, glial reaction, and synaptic coverage, two weeks after the lesion, indicated that therapy with hESCs overexpressing 31 kD FGF2 was the most effective. Consequently, the second set of experiments was performed with that isoform, so that ventral root avulsion was followed by direct spinal cord reimplantation. Motoneuron survival, glial reaction, synaptic coverage, and gene expression were analyzed 2 weeks post-lesion; while the functional recovery was evaluated by the walking track test and von Frey test for 12 weeks. We showed that engraftment of hESCs led to significant neuroprotection, coupled with immunomodulation, attenuation of astrogliosis, and preservation of inputs to the rescued motoneurons. Behaviorally, the 31 kD FGF2 - hESC therapy enhanced both motor and sensory recovery.
Conclusion
Transgenic hESCs were an effective delivery platform for neurotrophic factors, rescuing axotomized motoneurons and modulating glial response after proximal spinal cord root injury, while the 31 kD isoform of FGF2 showed superior regenerative properties over other isoforms in addition to the significant functional recovery.
