The role of S100B/RAGE-enhanced ADAM17 activation in endothelial glycocalyx shedding after traumatic brain injury

Berberine decreases S100B generation to regulate gut vascular barrier permeability in mice with burn injury

Context: Berberine (BBR) can regulate enteric glial cells (EGCs) and the gut vascular barrier (GVB).Objective: To explore whether BBR regulates GVB permeability via the S100B pathway.Materials and methods: GVB hyperpermeability in C57BL/6J mice was induced by burns or S100B enema. BBR (25 or 50 mg/kg/d, 3 d) was gavaged preburn. S100B monoclonal antibody (S100BmAb) was i.v. injected postburn. Mouse intestinal microvascular endothelial cells (MIMECs) were treated with S100B, S100B plus BBR, or Z-IETD-FMK. GVB permeability was assayed by FITC-dextran, S100B by ELISA, caspase-8, β-catenin, occludin and PV-1 by immunoblot.Results: Burns elevated S100B in serum and in colonic mucosa to a peak (147.00 ± 4.95 ng/mL and 160.30 ± 8.50 ng/mg, respectively) at 36 h postburn, but BBR decreased burns-induced S100B in serum (126.20 ± 6.30 or 90.60 ± 3.78 ng/mL) and in mucosa (125.80 ± 12.40 or 91.20 ± 8.54 ng/mg). Burns raised GVB permeability (serum FITC-dextran 111.40 ± 8.56 pg/mL) at 48 h postburn, but BBR reduced GVB permeability (serum FITC-dextran 89.20 ± 6.98 or 68.60 ± 5.50 ng/mL). S100B enema (1 μM) aggravated burns-raised GVB permeability (142.80 ± 8.07 pg/mL) and PV-1, but the effect of S100B was antagonized by BBR. Z-IETD-FMK (5 μM) increased S100B-induced permeability to FITC-dextran (205.80 ± 9.70 to 263.80 ± 11.04 AUs) while reducing β-catenin in MIMECs. BBR (5 μM) reduced S100B-induced permeability (104.20 ± 9.65 AUs) and increased caspase-8, β-catenin and occludin.Discussion and conclusion: BBR decreases burns-induced GVB hyperpermeability via modulating S100B/caspase-8/β-catenin pathway and may involve EGCs.

Antibody-labeled gold nanoparticle based resonance Rayleigh scattering detection of S100B

Traumatic brain injury (TBI) is a sudden brain injury due to an external force that causes a large number of deaths and permanent disabilities every year. S100B has been recognized as a potential objective quantitative biomarker for screening the prognosis of TBI and severe head injury. In this article, an anti-S100B monoclonal antibody was immobilized on cysteamine (Cy) functionalized gold nanoparticles (AuNPs) by EDC-NHS chemistry, which enabled S100B resonance Rayleigh scattering (RRS) detection based on antibody-labeled gold nanoparticles. The prepared conjugates were characterized by ultraviolet-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Based on the specific binding of the antibody and antigen, the RRS intensities at 381 nm and 541 nm wavelengths were significantly enhanced, and thus a dual wavelength overlapping resonance Rayleigh scattering (DWO-RRS) method was established. The scattering intensity of the two overlapping peaks was proportional to the concentration of S100B in the range of 0.05-4.5 ng mL-1 with a detection limit of 0.002 ng mL-1. The proposed DWO-RRS method is time-saving, simple, sensitive, and can be used to determine the concentration of S100B in human serum with satisfactory results, which has a promising application in the early diagnosis of TBI.

1,25(OH)2D3 supplementation alleviates gut-vascular barrier disruption via inhibition of S100B/ADAM10 pathway

Gut-vascular barrier (GVB) is the second barrier in mucosa to control systemic dissemination of gut bacteria. Severe burns induce enteroglial cells to produce S100B and endothelial cells to generate ADAM10 and cause vitamin D3 insufficiency/deficiency and GVB disruption. It is not clear whether vitamin D3 supplementation attenuates GVB damage via regulation of S100B/ADAM10 pathway. Here, GVB disruption was induced by 30% of total body surface area scalds. Rats were treated with 1,25(OH)2D3 (0.05, 0.5 or 5 μg/kg) or S100B monoclonal antibody (S100BmAb, 10 μg/kg) or GI254023X (ADAM10 inhibitor, 100 mg/kg). Rat enteric glial cell-line CRL2690 and rat intestinal microvascular endothelial cells (RIMECs) were treated with S100B (5 μM) or plus 1,25(OH)2D3 (0.05, 0.5 or 5 μM) or GI254023X (5 μM). S100B, TNF-α, 25(OH)D3 and 1,25(OH)2D3 in serum and gut mucosa were determined by enzyme-linked immunosorbent assay. The endothelial permeability was measured using FITC-dextran 70 kDa. ADAM10 and β-catenin expression was assayed by Western blot. The results showed that 1,25(OH)2D3 and 25(OH)D3 concentration in serum reduced whereas TNF-α and S100B in serum and gut mucosa increased in burned rats. S100BmAb, GI254023X and 1,25(OH)2D3 treatment lowered burns-increased GVB permeability. 1,25(OH)2D3 also decreased S100B concentration in serum and gut mucosa. 1,25(OH)2D3 inhibited S100B release from TNF-α-treated CRL2690 and raised β-catenin while decreasing ADAM10 protein in S100B-treated RIMECs. 1,25(OH)2D3 and GI254023X also decreased the endothelial permeability of S100B-treated RIMECs. Collectively, these findings provide evidence that severe burns lower serum 25(OH)D3 and 1,25(OH)2D3 concentration. 1,25(OH)2D3 supplementation alleviates burns-elicited GVB disruption via inhibition of S100B/ADAM10 signaling.

THE NEUROENDOTHELIAL AXIS IN TRAUMATIC BRAIN INJURY: MECHANISMS OF MULTIORGAN DYSFUNCTION, NOVEL THERAPIES, AND FUTURE DIRECTIONS

ABSTRACT

Severe traumatic brain injury (TBI) often initiates a systemic inflammatory response syndrome, which can potentially culminate into multiorgan dysfunction. A central player in this cascade is endotheliopathy, caused by perturbations in homeostatic mechanisms governed by endothelial cells due to injury-induced coagulopathy, heightened sympathoadrenal response, complement activation, and proinflammatory cytokine release. Unique to TBI is the potential disruption of the blood-brain barrier, which may expose neuronal antigens to the peripheral immune system and permit neuroinflammatory mediators to enter systemic circulation, propagating endotheliopathy systemically. This review aims to provide comprehensive insights into the "neuroendothelial axis" underlying endothelial dysfunction after TBI, identify potential diagnostic and prognostic biomarkers, and explore therapeutic strategies targeting these interactions, with the ultimate goal of improving patient outcomes after severe TBI.

CLINICAL VALUE OF SYNDECAN-1 LEVELS IN TRAUMA BRAIN INJURY: A META-ANALYSIS

ABSTRACT

Background: Traumatic brain injury (TBI) is a head trauma usually associated with death and endothelial glycocalyx damage. Syndecan-1 (SDC-1)-a biomarker of glycocalyx degradation-has rarely been reported in meta-analyses to determine the clinical prognostic value in TBI patients. Methods: We looked into PubMed, EMBASE, Cochrane Library, and Web of Science databases from January 1, 1990, to May 1, 2023, to identify eligible studies. A meta-analysis was conducted using RevMan 5.4 and Stata 16.0 with the search terms "SDC-1" and "traumatic brain injury." Results: The present study included five studies with a total of 640 enrolled patients included. Syndecan-1 concentrations were higher in the isotrauma TBI group than in the non-TBI group (standardized mean difference [SMD] = 0.52; 95% CI: 0.03-1.00; P = 0.04). Subgroup analysis revealed statistical significance when comparing the SDC-1 level of multitrauma TBI (TBI + other injuries) group with the isotrauma TBI group (SMD = 0.74; 95% CI: 0.42-1.05; P < 0.001), and the SDC-1 level of the TBI coagulopathy (+) group (TBI with early coagulopathy) with the TBI coagulopathy (-) group (SMD = 1.75; 95% CI: 0.41-3.10; P = 0.01). Isotrauma TBI patients with higher SDC-1 level were at a higher risk of 30-day in-hospital mortality (odds ratio = 3.32; 95% CI: 1.67-6.60; P = 0.0006). Conclusion: This meta-analysis suggests that SDC-1 could be a biomarker of endotheliopathy and coagulopathy in TBI, as it was increased in isotrauma TBI patients and was higher in multitrauma TBI patients. There is a need for additional research into the use of SDC-1 as a prognostic biomarker in TBI, especially in isotrauma TBI patients.

A role for decorin in improving motor deficits after traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of death and disability due to injury worldwide. Extracellular matrix (ECM) remodeling is known to significantly contribute to TBI pathophysiology. Glycosaminoglycans, which are long-chain, variably sulfated polysaccharides abundant within the ECM, have previously been shown to be substantially altered after TBI. In this study, we sought to delineate the dynamics of glycosaminoglycan alterations after TBI and discover the precise biologic processes responsible for observed glycosaminoglycan changes after injury. We performed state-of-the art mass spectrometry on brain tissues isolated from mice after TBI or craniotomy-alone. We observed dynamic changes in glycosaminoglycans at Day 1 and 7 post-TBI, with heparan sulfate, chondroitin sulfate, and hyaluronan remaining significantly increased after a week vis-à-vis craniotomy-alone tissues. We did not observe appreciable changes in circulating glycosaminoglycans in mice after experimental TBI compared to craniotomy-alone nor in patients with TBI and severe polytrauma compared to control patients with mild injuries, suggesting increases in injury site glycosaminoglycans are driven by local synthesis. We subsequently performed an unbiased whole genome transcriptomics analysis on mouse brain tissues 7 days post-TBI and discovered a significant induction of hyaluronan synthase 2, glypican-3, and decorin. The functional role of decorin after injury was further examined through multimodal behavioral testing comparing wild-type and Dcn-/- mice. We discovered that genetic ablation of Dcn led to an overall negative effect of TBI on function, exacerbating motor impairments after TBI. Collectively, our results provide a spatiotemporal characterization of post-TBI glycosaminoglycan alterations in the brain ECM and support an important adaptive role for decorin upregulation after TBI.

How S100B crosses brain barriers and why it is considered a peripheral marker of brain injury

S100B is a 21-kDa protein that is produced and secreted by astrocytes and widely used as a marker of brain injury in clinical and experimental studies. The majority of these studies are based on measurements in blood serum, assuming an associated increase in cerebrospinal fluid and a rupture of the blood-brain barrier (BBB). Moreover, extracerebral sources of S100B are often underestimated. Herein, we will review these interpretations and discuss the routes by which S100B, produced by astrocytes, reaches the circulatory system. We discuss the concept of S100B as an alarmin and its dual activity as an inflammatory and neurotrophic molecule. Furthermore, we emphasize the lack of data supporting the idea that S100B acts as a marker of BBB rupture, and the need to include the glymphatic system in the interpretations of serum changes of S100B. The review is also dedicated to valorizing extracerebral sources of S100B, particularly adipocytes. Furthermore, S100B per se may have direct and indirect modulating roles in brain barriers: on the tight junctions that regulate paracellular transport; on the expression of its receptor, RAGE, which is involved in transcellular protein transport; and on aquaporin-4, a key protein in the glymphatic system that is responsible for the clearance of extracellular proteins from the central nervous system. We hope that the data on S100B, discussed here, will be useful and that it will translate into further health benefits in medical practice.

Resuscitating the Endothelial Glycocalyx in Trauma and Hemorrhagic Shock

The endothelium is lined by a protective mesh of proteins and carbohydrates called the endothelial glycocalyx (EG). This layer creates a negatively charged gel-like barrier between the vascular environment and the surface of the endothelial cell. When intact the EG serves multiple functions, including mechanotransduction, cell signaling, regulation of permeability and fluid exchange across the microvasculature, and management of cell-cell interactions. In trauma and/or hemorrhagic shock, the glycocalyx is broken down, resulting in the shedding of its individual components. The shedding of the EG is associated with increased systemic inflammation, microvascular permeability, and flow-induced vasodilation, leading to further physiologic derangements. Animal and human studies have shown that the greater the severity of the injury, the greater the degree of shedding, which is associated with poor patient outcomes. Additional studies have shown that prioritizing certain resuscitation fluids, such as plasma, cryoprecipitate, and whole blood over crystalloid shows improved outcomes in hemorrhaging patients, potentially through a decrease in EG shedding impacting downstream signaling. The purpose of the following paragraphs is to briefly describe the EG, review the impact of EG shedding and hemorrhagic shock, and begin entertaining the notion of directed resuscitation. Directed resuscitation emphasizes transitioning from macroscopic 1:1 resuscitation to efforts that focus on minimizing EG shedding and maximizing its reconstitution.

RAGE Inhibitors in Neurodegenerative Diseases

Nonenzymatic reactions of reducing sugars with primary amino groups of amino acids, proteins, and nucleic acids, followed by oxidative degradations would lead to the formation of advanced glycation endproducts (AGEs). The AGEs exert multifactorial effects on cell damage leading to the onset of neurological disorders. The interaction of AGEs with the receptors for advanced glycation endproducts (RAGE) contribute to the activation of intracellular signaling and the expression of the pro-inflammatory transcription factors and various inflammatory cytokines. This inflammatory signaling cascade is associated with various neurological diseases, including Alzheimer's disease (AD), secondary effects of traumatic brain injury (TBI), amyotrophic lateral sclerosis (ALS), and diabetic neuropathy, and other AGE-related diseases, including diabetes and atherosclerosis. Furthermore, the imbalance of gut microbiota and intestinal inflammation are also associated with endothelial dysfunction, disrupted blood-brain barrier (BBB) and thereby the onset and progression of AD and other neurological diseases. AGEs and RAGE play an important role in altering the gut microbiota composition and thereby increase the gut permeability and affect the modulation of the immune-related cytokines. The inhibition of the AGE-RAGE interactions, through small molecule-based therapeutics, prevents the inflammatory cascade of events associated with AGE-RAGE interactions, and thereby attenuates the disease progression. Some of the RAGE antagonists, such as Azeliragon, are currently in clinical development for treating neurological diseases, including AD, although currently there have been no FDA-approved therapeutics based on the RAGE antagonists. This review outlines the AGE-RAGE interactions as a leading cause of the onset of neurological diseases and the current efforts on developing therapeutics for neurological diseases based on the RAGE antagonists.

S100B, Actor and Biomarker of Mild Traumatic Brain Injury

Mild traumatic brain injury (mTBI) accounts for approximately 80% of all TBI cases and is a growing source of morbidity and mortality worldwide. To improve the management of children and adults with mTBI, a series of candidate biomarkers have been investigated in recent years. In this context, the measurement of blood biomarkers in the acute phase after a traumatic event helps reduce unnecessary CT scans and hospitalizations. In athletes, improved management of sports-related concussions is also sought to ensure athletes’ safety. S100B protein has emerged as the most widely studied and used biomarker for clinical decision making in patients with mTBI. In addition to its use as a diagnostic biomarker, S100B plays an active role in the molecular pathogenic processes accompanying acute brain injury. This review describes S100B protein as a diagnostic tool as well as a potential therapeutic target in patients with mTBI.

POLYDATIN AMELIORATES TRAUMATIC BRAIN INJURY-INDUCED SECONDARY BRAIN INJURY BY INHIBITING NLRP3-INDUCED NEUROINFLAMMATION ASSOCIATED WITH SOD2 ACETYLATION

ABSTRACT

Traumatic brain injury (TBI) is a kind of disease with high morbidity, mortality, and disability, and its pathogenesis is still unclear. Research shows that nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) activation in neurons and astrocytes is involved in neuroinflammatory cascades after TBI. What is more, polydatin (PD) has been shown to have a protective effect on TBI-induced neuroinflammation, but the mechanisms remain unclear. Here, we speculated that PD could alleviate TBI-induced neuroinflammatory damage through the superoxide dismutase (SOD2)-NLRP3 signal pathway, and SOD2 might regulate NLRP3 inflammasome activation. The model of lateral fluid percussion for in vivo and cell stretching injury for in vitro were established to mimic TBI. NLRP3 chemical inhibitor MCC950, SOD2 inhibitor 2-methoxyestradiol, and PD were administered immediately after TBI. As a result, the expression of SOD2 acetylation (SOD2 Ac-K122), NLRP3, and cleaved caspase-1 were increased after TBI both in vivo and in vitro , and using SOD2 inhibitor 2-methoxyestradiol significantly promoted SOD2 Ac-K122, NLRP3, and cleaved caspase-1 expression, as well as exacerbated mitochondrial ROS (mtROS) accumulation and mitochondrial membrane potential (MMP) collapse in PC12 cells. However, using NLRP3 inhibitor MCC950 significantly inhibited cleaved caspase-1 activation after TBI both in vivo and in vitro ; meanwhile, MCC950 inhibited mtROS accumulation and MMP collapse after TBI. More importantly, PD could inhibit the level of SOD2 Ac-K122, NLRP3, and cleaved caspase-1 and promote the expression of SOD2 after TBI both in vivo and in vitro. Polydatin also inhibited mtROS accumulation and MMP collapse after stretching injury. These results indicated that PD inhibited SOD2 acetylation to alleviate NLRP3 inflammasome activation, thus acting a protective role against TBI neuroinflammation.

Neuroinflammation of traumatic brain injury: Roles of extracellular vesicles

Traumatic brain injury (TBI) is a major cause of neurological disorder or death, with a heavy burden on individuals and families. While sustained primary insult leads to damage, subsequent secondary events are considered key pathophysiological characteristics post-TBI, and the inflammatory response is a prominent contributor to the secondary cascade. Neuroinflammation is a multifaceted physiological response and exerts both positive and negative effects on TBI. Extracellular vesicles (EVs), as messengers for intercellular communication, are involved in biological and pathological processes in central nervous system (CNS) diseases and injuries. The number and characteristics of EVs and their cargo in the CNS and peripheral circulation undergo tremendous changes in response to TBI, and these EVs regulate neuroinflammatory reactions by activating prominent receptors on receptor cells or delivering pro- or anti-inflammatory cargo to receptor cells. The purpose of this review is to discuss the possible neuroinflammatory mechanisms of EVs and loading in the context of TBI. Furthermore, we summarize the potential role of diverse types of cell-derived EVs in inflammation following TBI.

Alterations in heparan sulfate proteoglycan synthesis and sulfation and the impact on vascular endothelial function

The glycocalyx attached to the apical surface of vascular endothelial cells is a rich network of proteoglycans, glycosaminoglycans, and glycoproteins with instrumental roles in vascular homeostasis. Given their molecular complexity and ability to interact with the intra- and extracellular environment, heparan sulfate proteoglycans uniquely contribute to the glycocalyx's role in regulating endothelial permeability, mechanosignaling, and ligand recognition by cognate cell surface receptors. Much attention has recently been devoted to the enzymatic shedding of heparan sulfate proteoglycans from the endothelial glycocalyx and its impact on vascular function. However, other molecular modifications to heparan sulfate proteoglycans are possible and may have equal or complementary clinical significance. In this narrative review, we focus on putative mechanisms driving non-proteolytic changes in heparan sulfate proteoglycan expression and alterations in the sulfation of heparan sulfate side chains within the endothelial glycocalyx. We then discuss how these specific changes to the endothelial glycocalyx impact endothelial cell function and highlight therapeutic strategies to target or potentially reverse these pathologic changes.

Immunomodulatory role of metalloproteinase ADAM17 in tumor development

ADAM17 is a member of the a disintegrin and metalloproteinase (ADAM) family of transmembrane proteases involved in the shedding of some cell membrane proteins and regulating various signaling pathways. More than 90 substrates are regulated by ADAM17, some of which are closely relevant to tumor formation and development. Besides, ADAM17 is also responsible for immune regulation and its substrate-mediated signal transduction. Recently, ADAM17 has been considered as a major target for the treatment of tumors and yet its immunomodulatory roles and mechanisms remain unclear. In this paper, we summarized the recent understanding of structure and several regulatory roles of ADAM17. Importantly, we highlighted the immunomodulatory roles of ADAM17 in tumor development, as well as small molecule inhibitors and monoclonal antibodies targeting ADAM17.

Antioxidant-based neuroprotective effect of dimethylsulfoxide against induced traumatic brain injury in a rats model

Traumatic brain injury (TBI) has been the result of neurological deficit and oxidative stress. This study evaluated the antioxidative neuroprotective property and learning and memory-enhancing effects of dimethyl sulfoxide (DMSO) in a rat model after the induction of TBI. 21 albino rats with 7 rats per group were used in this study. Group I was induced with TBI and treated with DMSO at 67.5 mg/kg orally once daily which started 30 min after the induction of TBI and lasted 21 days. Group II was induced with TBI but not treated while Group III was neither induced with TBI nor treated. Assessment of behavioral function (Learning and memory, anxiety and motor function), the level of an antioxidant enzymes and their gene expression (superoxide dismutase, catalase, glutathione peroxidase), the biomarkers of oxidative stress (malondialdehyde) and S100B levels as well as brain tissues histological studies were conducted. Administration of DMSO to rats with induced TBI has improved learning and memory, locomotor function and decreased anxiety in Group I compared to Group II. Moreover, the level of S100B was significantly (p < 0.05) lower in Group I compared to Group II. Treatment with DMSO also decreased lipid peroxidation significantly (p < 0.05) compared to Group II. There exists a significant (p < 0.05) increase in CAT, SOD, and GPX activities in Group I compared to Group II. Therefore, DMSO has demonstrated a potential antioxidative neuroprotective effect through its ability to increase the level of antioxidant enzymes which they quench and inhibit the formation of ROS, thereby improving cognitive functions.

Tanshinone IIA reduces AQP4 expression and astrocyte swelling after OGD/R by inhibiting the HMGB1/RAGE/NF-κB/IL-6 pro-inflammatory axis

This study aimed to investigate the role of tanshinone IIA (TSO IIA) in astrocytic swelling caused by ischemia–reperfusion-like injury in an in vitro model and the molecular mechanisms underlying this effect. Primary brain astrocytes were cultured under conditions of glucose and oxygen deprivation and reoxygenation (OGD/R). The study explored the effects of TSO IIA treatment on cell swelling and injury and the protein levels of aquaporin 4 (AQP4) in the plasma membrane. It then examined the involvement of the high-mobility group box protein 1 (HMGB1)/receptors for advanced-glycation end products (RAGE)/nuclear factor-kappa B (NF-κB)/interleukin-6 (IL-6) pro-inflammatory axis in TSO IIA-mediated protection. The treatment with TSO IIA alleviated OGD/R-induced astrocytic swelling and the overclustering of AQP4 protein in the plasma membrane. In addition, TSO IIA significantly reduced the overexpression of HMGB1 and the high levels of the NF-κB protein in the nucleus and of the IL-6 protein in the cytoplasm and extracellular media induced by OGD/R. The combination of TSO IIA and recombinant HMGB1 reversed these effects. The inhibition of the RAGE, the receptor of HMGB1, induced results similar to those of TSO IIA. In addition, exogenous IL-6 reversed TSO IIA-mediated effect on AQP4 overclustering and cell swelling. TSO IIA significantly reduced astrocyte swelling after OGD/R injury in vitro, via blocking the activation of the HMGB1/RAGE/NF-κB/IL-6 pro-inflammatory axis and thereby decreasing the expression of AQP4 in the plasma membrane.

Proteoglycans and Glycosaminoglycans in Central Nervous System Injury

The brain and spinal cord constitute the central nervous system (CNS), which when injured, can be exceedingly devastating. The mechanistic roles of proteoglycans (PGs) and their glycosaminoglycan (GAG) side chains in such injuries have been extensively studied. CNS injury immediately alters endothelial and extracellular matrix (ECM) PGs and GAGs. Subsequently, these alterations contribute to acute injury, post-injury fibrosis, and post-injury repair. These effects are central to the pathophysiology of CNS injury. This review focuses on the importance of PGs and GAGs in multiple forms of injury including traumatic brain injury, spinal cord injury, and stroke. We highlight the causes and consequences of degradation of the PG and GAG-enriched endothelial glycocalyx in early injury and discuss the pleiotropic roles of PGs in neuroinflammation. We subsequently evaluate the dualistic effects of PGs on recovery: both PG/GAG-mediated inhibition and facilitation of repair. We then report promising therapeutic strategies that may prove effective for repair of CNS injury including PG receptor inhibition, delivery of endogenous, pro-repair PGs and GAGs, and direct degradation of pathologic GAGs. Last, we discuss importance of two PG- and GAG-containing ECM structures (synapses and perineuronal nets) in CNS injury and recovery.