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Representative zymosan-induced cavities, inflammation, and proteoglycan upregulation at 3 d after microinjection in vivo. Astrocyte GFAP staining ( A) and vimentin intermediate filament staining ( B) demarcate the astrocyte-free cavity that is filled with activated macrophages and microglia ( C). These inflammatory infiltrates are associated with increases in proteoglycans ( D), especially at the borders of the developing cavity (arrows; A, C, D). Scale bar, 225 m.
Source publication
Post-traumatic cystic cavitation, in which the size and severity of a CNS injury progress from a small area of direct trauma to a greatly enlarged secondary injury surrounded by glial scar tissue, is a poorly understood complication of damage to the brain and spinal cord. Using minimally invasive techniques to avoid primary physical injury, this st...
Contexts in source publication
Context 1
... large inflammation-induced cavities that developed 3 d after zymosan injection were devoid of astrocyte GFAP staining (Fig. 5A) and vimentin staining (Fig. 5B) and were filled with dense accumulations of activated macrophages and microglia (Fig. 5C) that were closely associated with areas of tissue dem- onstrating increased levels of chondroitin sulfate proteoglycans (Fig. 5D), particularly at the borders of the developing cavities (Fig. 5A,D, arrows). The ...
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... large inflammation-induced cavities that developed 3 d after zymosan injection were devoid of astrocyte GFAP staining (Fig. 5A) and vimentin staining (Fig. 5B) and were filled with dense accumulations of activated macrophages and microglia (Fig. 5C) that were closely associated with areas of tissue dem- onstrating increased levels of chondroitin sulfate proteoglycans (Fig. 5D), particularly at the borders of the developing cavities (Fig. 5A,D, arrows). The astrocyte-free cavities, which ...
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... large inflammation-induced cavities that developed 3 d after zymosan injection were devoid of astrocyte GFAP staining (Fig. 5A) and vimentin staining (Fig. 5B) and were filled with dense accumulations of activated macrophages and microglia (Fig. 5C) that were closely associated with areas of tissue dem- onstrating increased levels of chondroitin sulfate proteoglycans (Fig. 5D), particularly at the borders of the developing cavities (Fig. 5A,D, arrows). The astrocyte-free cavities, which persisted at 1 week after injection (Fig. 6 A), contained high levels of proteo- glycan ...
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... cavities that developed 3 d after zymosan injection were devoid of astrocyte GFAP staining (Fig. 5A) and vimentin staining (Fig. 5B) and were filled with dense accumulations of activated macrophages and microglia (Fig. 5C) that were closely associated with areas of tissue dem- onstrating increased levels of chondroitin sulfate proteoglycans (Fig. 5D), particularly at the borders of the developing cavities (Fig. 5A,D, arrows). The astrocyte-free cavities, which persisted at 1 week after injection (Fig. 6 A), contained high levels of proteo- glycan immunoreactivity inside and at the borders of the cavities (Fig. 6 A,B, white arrowheads). At 1 and 2 weeks after zymosan injection, ...
Context 5
... of astrocyte GFAP staining (Fig. 5A) and vimentin staining (Fig. 5B) and were filled with dense accumulations of activated macrophages and microglia (Fig. 5C) that were closely associated with areas of tissue dem- onstrating increased levels of chondroitin sulfate proteoglycans (Fig. 5D), particularly at the borders of the developing cavities (Fig. 5A,D, arrows). The astrocyte-free cavities, which persisted at 1 week after injection (Fig. 6 A), contained high levels of proteo- glycan immunoreactivity inside and at the borders of the cavities (Fig. 6 A,B, white arrowheads). At 1 and 2 weeks after zymosan injection, increases in proteoglycans were found immediately surrounding structures ...
Context 6
... in vivo inflammatory events are associated with increases in proteoglycan production (Figs. 5, 6), we looked for similar increases in chondroitin sulfate proteoglycans in our in vitro model of progressive cavitation. Astrocytes alone, astrocytes with zymosan alone, astrocytes with nonactivated macrophages (Fig. 12 A), and astrocytes with nonactivated macrophage-conditioned media exhibited uniform low levels of proteoglycan ...
Context 7
... increases previously described surrounding cavities in vivo (Figs. 5, 6) (MacLaren, 1996;Fitch and Silver, 1997a) were also demonstrated in vitro by astrocytes stimulated to change their motility and morphological characteristics in coculture with acti- vated macrophages or conditioned media. This heterogeneous increase in chondroitin sulfate proteoglycan may be related to the astrocyte migration and ...
Citations
... Zymosan is a yeast cell wall extract, which can stimulate inflammation in the nervous system [41][42][43]. We used zymosan to induce inflammation in the sciatic nerve in an attempt to condition the nerve. ...
Background
Since the 1990s, evidence has accumulated that macrophages promote peripheral nerve regeneration and are required for enhancing regeneration in the conditioning lesion (CL) response. After a sciatic nerve injury, macrophages accumulate in the injury site, the nerve distal to that site, and the axotomized dorsal root ganglia (DRGs). In the peripheral nervous system, as in other tissues, the macrophage response is derived from both resident macrophages and recruited monocyte-derived macrophages (MDMs). Unresolved questions are: at which sites do macrophages enhance nerve regeneration, and is a particular population needed.
Methods
Ccr2 knock-out (KO) and Ccr2gfp/gfp knock-in/KO mice were used to prevent MDM recruitment. Using these strains in a sciatic CL paradigm, we examined the necessity of MDMs and residents for CL-enhanced regeneration in vivo and characterized injury-induced nerve inflammation. CL paradigm variants, including the addition of pharmacological macrophage depletion methods, tested the role of various macrophage populations in initiating or sustaining the CL response. In vivo regeneration, measured from bilateral proximal test lesions (TLs) after 2 d, and macrophages were quantified by immunofluorescent staining.
Results
Peripheral CL-enhanced regeneration was equivalent between crush and transection CLs and was sustained for 28 days in both Ccr2 KO and WT mice despite MDM depletion. Similarly, the central CL response measured in dorsal roots was unchanged in Ccr2 KO mice. Macrophages at both the TL and CL, but not between them, stained for the pro-regenerative marker, arginase 1. TL macrophages were primarily CCR2-dependent MDMs and nearly absent in Ccr2 KO and Ccr2gfp/gfp KO mice. However, there were only slightly fewer Arg1⁺ macrophages in CCR2 null CLs than controls due to resident macrophage compensation. Zymosan injection into an intact WT sciatic nerve recruited Arg1⁺ macrophages but did not enhance regeneration. Finally, clodronate injection into Ccr2gfp KO CLs dramatically reduced CL macrophages. Combined with the Ccr2gfp KO background, depleting MDMs and TL macrophages, and a transection CL, physically removing the distal nerve environment, nearly all macrophages in the nerve were removed, yet CL-enhanced regeneration was not impaired.
Conclusions
Macrophages in the sciatic nerve are neither necessary nor sufficient to produce a CL response.
... To test whether collagen I repels axons and astrocytes in vivo, we evaluated the state of the neuropil after stereotactic injection of collagen I into the ventral horn at level T10 of the spinal cord. Unlike lipopolysaccharide and various growth or inflammatory factors tested before 42 , we noticed that the signals for β -tubulin III and GFAP were conspicuously absent in areas where collagen I was present, indicating few or no neurons and astrocytes existed. By contrast, an intense accumulation of Iba-1 + microglia/macrophages was observed within the vicinity of collagen I deposits, coinciding with a substantial production of CSPGs (Fig. 1g). ...
Although axotomized neurons retain the ability to initiate the formation of growth cones and attempt to regenerate after spinal cord injury, the scar area formed as a result of the lesion in most adult mammals contains a variety of reactive cells that elaborate multiple extracellular matrix and enzyme components that are not suitable for regrowth 1,2 . Newly migrating axons in the vicinity of the scar utilize upregulated LAR family receptor protein tyrosine phosphatases, such as PTPσ, to associate with extracellular chondroitin sulphate proteoglycans (CSPGs), which have been discovered to tightly entrap the regrowing axon tip and transform it into a dystrophic non-growing endball. The scar is comprised of two compartments, one in the lesion penumbra, the glial scar, composed of reactive microglia, astrocytes and OPCs; and the other in the lesion epicenter, the fibrotic scar, which is made up of fibroblasts, pericytes, endothelial cells and inflammatory cells. While the fibrotic scar is known to be strongly inhibitory, even more so than the glial scar, the molecular determinants that curtail axon elongation through the injury core are largely uncharacterized. Here, we show that one sole member of the entire family of collagens, collagen I, creates an especially potent inducer of endball formation and regeneration failure. The inhibitory signaling is mediated by mechanosensitive ion channels and RhoA activation. Staggered systemic administration of two blood-brain barrier permeable-FDA approved drugs, aspirin and pirfenidone, reduced fibroblast incursion into the complete lesion and dramatically decreased collagen I, as well as CSPG deposition which were accompanied by axonal growth and considerable functional recovery. The anatomical substrate for robust axonal regeneration was provided by laminin producing GFAP ⁺ and NG2 ⁺ bridging cells that spanned the wound. Our results reveal a collagen I-mechanotransduction axis that regulates axonal regrowth in spinal cord injury and raise a promising strategy for rapid clinical application.
... The initiation of posttraumatic cystic cavitation has been demonstrated to occur when peripheral macrophages and resident microglia infiltrate and become activated after SCI. 32 In the present investigation, the occurrence of cystic cavitation was almost non-existent in instances where durotomy was employed, potentially due to a significant hindrance in the buildup of macrophages at the injury site. Extensive infiltration of macrophages occurred in the SCI + laminectomy group, potentially leading to the development of sizable cystic cavities at the site of injury. ...
Currently, there is a lack of effective treatments for spinal cord injury (SCI), a debilitating medical condition associated with enduring paralysis and irreversible neuronal damage. Extradural decompression of osseous as well as soft tissue components has historically been the principal objective of surgical procedures. Nevertheless, this particular surgical procedure fails to tackle the intradural compressive alterations that contribute to secondary SCI. Here, we propose an early intrathecal decompression strategy and evaluate its role on function outcome, tissue sparing, inflammation, and tissue stiffness after SCI. Durotomy surgery significantly promoted recovery of hindlimb locomotor function in an open‐field test. Radiological analysis suggested that lesion size and tissue edema were significantly reduced in animals that received durotomy. Relative to the group with laminectomy alone, the animals treated with a durotomy had decreased cavitation, scar formation, and inflammatory responses at 4 weeks after SCI. An examination of the mechanical properties revealed that durotomy facilitated an expeditious restoration of the injured tissue's elastic rigidity. In general, early decompressive durotomy could serve as a significant strategy to mitigate the impairments caused by secondary injury and establish a more conducive microenvironment for prospective cellular or biomaterial transplantation.
... The two cell types then work together to cordon off the site from any nearby healthy tissue. In vivo, glial scarring takes place over the course of several weeks (Fitch et al., 1999;Tran et al., 2022). Given our experimental design and timecourse, we are only able to model an early response that is consistent with the glial scarring process and not the glial scar itself. ...
Neural interfacing devices interact with the central nervous system to alleviate functional deficits arising from disease or injury. This often entails the use of invasive microelectrode implants that elicit inflammatory responses from glial cells and leads to loss of device function. Previous work focused on improving implant biocompatibility by modifying electrode composition; here, we investigated the direct effects of electrical stimulation on glial cells at the electrode interface. A high-throughput in vitro system that assesses primary glial cell response to biphasic stimulation waveforms at 0 mA, 0.15 mA, and 1.5 mA was developed and optimized. Primary mixed glial cell cultures were generated from heterozygous CX3CR-1+/EGFP mice, electrically stimulated for 4 h/day over 3 days using 75 μm platinum-iridium microelectrodes, and biomarker immunofluorescence was measured. Electrodes were then imaged on a scanning electron microscope to assess sustained electrode damage. Fluorescence and electron microscopy analyses suggest varying degrees of localized responses for each biomarker assayed (Hoescht, EGFP, GFAP, and IL-1β), a result that expands on comparable in vivo models. This system allows for the comparison of a breadth of electrical stimulation parameters, and opens another avenue through which neural interfacing device developers can improve biocompatibility and longevity of electrodes in tissue.
... By joining the two ends of the ependymal bulb, cavitylike structures were formed in the grey matter. These cavity-like structures are seen only in the grey matter lined by ependymal cells and may not be the same as a fluid-filled astrocyte-lined cavity existing in the white matter in mammalian SCI (Balentine, 1978a(Balentine, , 1978bFitch et al., 1999;Renault-Mihara et al., 2008). ...
... Notably, brain inflammation in TBI patients has still been identified after a long time of being injury, leading to a persistent cognitive dysfunction (102). Neuronal survival and function are closely associated with inflammatory factors (103,104). Therefore, targeting neuroinflammation may be important for improving TBI prognosis. It is reported that some miRNAs such as miR-21, miR-146, miR-155 and miR-223 could be induced by inflammatory stimuli. ...
MicroRNAs (miRNAs) are small non-coding RNAs with the unique ability to degrade or block specific RNAs and regulate many cellular processes. Neuroinflammation plays the pivotal role in the occurrence and development of multiple central nervous system (CNS) diseases. The ability of miRNAs to enhance or restrict neuroinflammatory signaling pathways in CNS diseases is an emerging and important research area, including neurodegenerative diseases, stroke, and traumatic brain injury (TBI). In this review, we summarize the roles and regulatory mechanisms of recently identified miRNAs involved in neuroinflammation-mediated CNS diseases, aiming to explore and provide a better understanding and direction for the treatment of CNS diseases.
... The secondary injury is a multicascade of pathomechanisms occurring in the hours, days, and weeks following the primary injury and not only involves the site of the initial primary injury but also spreads to adjacent tissue. These events include alterations in electrolytes; production of ROSs; apoptosis and necrosis; increases in inflammatory factors such as tumor necrosis factor (TNF)-α, cytokines (IL-1α and IL-1β), and transforming growth factor (TGF)-α; the release of nitric oxide and glutamate; glial scar formation (gliosis) of astrocytes; significant increases in the frequency of chemokines; human growth-regulated oncogene/keratinocyte chemoattractant (GRO/KC); and macrophage inflammatory protein-1(MIP-1α) [28][29][30]. ...
Spinal cord injury (SCI) is an irreversible disease resulting in partial or total loss of sensory and motor function. The pathophysiology of SCI is characterized by an initial primary injury phase followed by a secondary phase in which reactive oxygen species (ROSs) and associated oxidative stress play hallmark roles. Physical exercise is an indispensable means of promoting psychophysical well-being and improving quality of life. It positively influences the neuromuscular, cardiovascular, respiratory, and immune systems. Moreover, exercise may provide a mechanism to regulate the variation and equilibrium between pro-oxidants and antioxidants. After a brief overview of spinal cord anatomy and the different types of spinal cord injury, the purpose of this review is to investigate the evidence regarding the effect of exercise on oxidative stress among individuals with SCI.
... Finally, we asked whether single-cell techniques could provide insights into the molecular mechanisms of pharmacotherapies for SCI. To address this question, we profiled the spinal cord of mice treated with three of the most extensively investigated clinical and experimental interventions: methylprednisolone [70][71][72] , minocycline [73][74][75][76] , and chondroitinase ABC (ChABC) [77][78][79][80][81][82][83][84] . ...
... We found that laminins (Lama1, Lama2, Lama4, Lama5) were expressed primarily by VLMCs, identifying these cells as a target to upregulate the expression of axon growthsupporting molecules for spinal cord repair ( Supplementary Fig. 15a-d). A second example comes from the family of chondroitin sulfate proteoglycans (CSPGs), which are known to play contrasting roles in inhibiting or supporting axon growth 15,63,[77][78][79]136 . Among inhibitory CSPGs, we found that OPCs are responsible for the expression of Acan, Vcan, and Ncan, whereas astrocytes were the dominant producers of Bcan ( Supplementary Fig. 15e-h). ...
Here, we introduce the Tabulae Paralytica - a compilation of four atlases of spinal cord injury (SCI) comprising a single-nucleus transcriptome atlas of half a million cells; a multiome atlas pairing transcriptomic and epigenomic measurements within the same nuclei; and two spatial transcriptomic atlases of the injured spinal cord spanning four spatial and temporal dimensions. We integrated these atlases into a common framework to dissect the molecular logic that governs the responses to injury within the spinal cord. The Tabulae Paralytica exposed new biological principles that dictate the consequences of SCI, including conserved and divergent neuronal responses to injury; the priming of specific neuronal subpopulations to become circuit-reorganizing neurons after injury; an inherent trade-off between neuronal stress responses and the activation of circuit reorganization programs; the necessity of reestablishing a tripartite neuroprotective barrier between immune-privileged and extra-neural environments after SCI; and a catastrophic failure to form this barrier in old mice. We leveraged the Tabulae Paralytica to develop a rejuvenative gene therapy that reestablished this tripartite barrier, and restored the natural recovery of walking after paralysis in old mice. The Tabulae Paralytica provides an unprecedented window into the pathobiology of SCI, while establishing a framework for integrating multimodal, genome-scale measurements in four dimensions to study biology and medicine.
... It has been established that neurons at the injury site undergo apoptosis and necrosis after SCI and are further damaged due to inflammation, and whether neurons can be regenerated determines the success or failure of spinal cord function recovery [32]. Our study demonstrated that neuron-derived exosomes could effectively promote neurite outgrowth and the survival of neurons 3 days after SCI, with more neurons observed 42 days after SCI in mice. ...
During spinal cord injury (SCI), the homeostasis of the cellular microenvironment in the injured area is seriously disrupted, which makes it extremely difficult for injured neurons with regenerative ability to repair, emphasizing the importance of restoring the cellular microenvironment at the injury site. Neurons interact closely with other nerve cells in the central nervous system (CNS) and regulate these cells. However, the specific mechanisms by which neurons modulate the cellular microenvironment remain unclear. Exosomes were isolated from the primary neurons, and their effects on astrocytes, microglia, oligodendrocyte progenitor cells (OPCs), neurons, and neural stem cells were investigated by quantifying the expression of related proteins and mRNA. A mouse SCI model was established, and neuron-derived exosomes were injected into the mice by the caudal vein to observe the recovery of motor function in mice and the changes in the nerve cells in the lesion area. Neuron-derived exosomes could reverse the activation of microglia and astrocytes and promote the maturation of OPCs in vivo and in vitro. In addition, neuron-derived exosomes promoted neurite outgrowth of neurons and the differentiation of neural stem cells into neurons. Moreover, our experiments showed that neuron-derived exosomes enhanced motor function recovery and nerve regeneration in mice with SCI. Our findings highlight that neuron-derived exosomes could promote the repair of the injured spinal cord by regulating the cellular microenvironment of neurons and could be a promising treatment for spinal cord injury.
... Astrogliosis is activated after TBIs forming a glial scar in and around the injury site [26][27][28][29] . Significantly, uninjured tissue around the injury site is also undergo astrogliosis, and the process of glial scarring consequently extends beyond the injury site [30] . According to the fact that glial scarring restricts regeneration after injury, several studies have considered whether limiting astrogliosis after injury, with specific focus on limiting deposition, could potentially stimulate regeneration [23,27,[31][32][33][34] . ...
Abstract
Background: This study proposes that the glial scar adjacent to the penetrating brain injuries is
active in stabilizing the surrounding uninjured tissue by limiting the inflammatory response to the
injury site. The study showed that tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6), a well known anti-inflammatory molecule, is present within the glial scar. The current study investigated
the role of TSG-6 within the glial scar using TSG-6 null and littermate control rat subjected to
penetrating brain injuries.
Results: The study outcomes display that rat lacking TSG-6 has a more severe inflammatory
response after injury, which was correlated with an enlarged area of astrogliosis beyond the injury
site.
Conclusion: The study results provide clue that TSG-6 has an anti-inflammatory role within the
glial scar.
Keywords: TSG-6, Astrocytes, Glial scar, Inflammation and glycosaminoglycans.
