Collagen matrix in spinal cord injury

Effects of duroplasty with bovine pericardium on fibrosis and extent of spinal cord injury: An experimental study in pigs

INTRODUCTION

Traumatic spinal cord injury (SCI) leads to increased intraspinal pressure that can be prevented by durotomy and duroplasty. The aim of the study was to evaluate fibrosis and neural damage in a porcine model of SCI after duroplasty and application of hyaluronic acid (HA) in the tissue cavity.

MATERIALS AND METHODS

Experimental study. We created a porcine SCI model by durotomy and spinal cord hemisection of a cervical segment (1cm). Six pigs (Sus scrofa domestica) were used to evaluate three surgical scenarios: (1)control injury with dural reparative microsurgery, (2)duroplasty using bovine pericardium (BPD), and (3)previous method plus HA applied at the lesion. Animals were sacrificed one-month post-injury to assess fibrotic responses and neural tissue damage using conventional histological and immunohistochemical methods.

RESULTS

In the control case, dural suture prevented invasion of the lesion by extradural connective tissue, and the dura mater showed a 1-mm thickening in the perilesional area. The bovine pericardium patch blocked the entrance of extradural connective tissue, decreased dura-mater tension, and satisfactorily integrated within the receptor tissue. However, it also enhanced subdural and perilesional fibrosis, which was not inhibited by filling the lesion cavity with low- or high-molecular-weight HA.

CONCLUSIONS

Duroplasty prevents collapse of the dura-mater over the spinal cord tissue, as well as invasion of the lesion by extramedullary fibrotic tissue, without creating additional neural damage. Nevertheless, it enhances the fibrotic response in the spinal cord lesion and the perilesional area. Additional antifibrotic strategies are needed to facilitate spinal cord repair.

[Translated article] Effects of duroplasty with bovine pericardium on fibrosis and extent of spinal cord injury: An experimental study in pigs

INTRODUCTION

Traumatic spinal cord injury (SCI) leads to increased intraspinal pressure that can be prevented by durotomy and duroplasty. The aim of the study was to evaluate fibrosis and neural damage in a porcine model of SCI after duroplasty and application of hyaluronic acid (HA) in the tissue cavity.

MATERIALS AND METHODS

Experimental study. We created a porcine SCI model by durotomy and spinal cord hemisection of a cervical segment (1cm). Six pigs (Sus scrofa domestica) were used to evaluate three surgical scenarios: (1) control injury with dural reparative microsurgery, (2) duroplasty using bovine pericardium (BPD), and (3) previous method plus HA applied at the lesion. Animals were sacrificed one-month post-injury to assess fibrotic responses and neural tissue damage using conventional histological and immunohistochemical methods.

RESULTS

In the control case, dural suture prevented invasion of the lesion by extradural connective tissue, and the dura mater showed a 1-mm thickening in the perilesional area. The bovine pericardium patch blocked the entrance of extradural connective tissue, decreased dura-mater tension, and satisfactorily integrated within the receptor tissue. However, it also enhanced subdural and perilesional fibrosis, which was not inhibited by filling the lesion cavity with low- or high-molecular-weight HA.

CONCLUSIONS

Duroplasty prevents collapse of the dura-mater over the spinal cord tissue, as well as invasion of the lesion by extramedullary fibrotic tissue, without creating additional neural damage. Nevertheless, it enhances the fibrotic response in the spinal cord lesion and the perilesional area. Additional antifibrotic strategies are needed to facilitate spinal cord repair.

The Role of Vitamins in Spinal Cord Injury: Mechanisms and Benefits

Spinal cord injury (SCI) is a common neurological disease worldwide, often resulting in a substantial decrease in quality of life, disability, and in severe cases, even death. Unfortunately, there is currently no effective treatment for this disease. Nevertheless, current basic and clinical evidence suggests that vitamins, with their antioxidant properties and biological functions, may play a valuable role in improving the quality of life for individuals with SCI. They can promote overall health and facilitate the healing process. In this review, we discuss the mechanisms and therapeutic potential of vitamins in the treatment of SCI.

Cellular and Transcriptional Response of Human Astrocytes to Hybrid Protein Materials

Collagen is a major component of the tissue matrix, and soybean can regulate the tissue immune response. Both materials have been used to fabricate biomaterials for tissue repair. In this study, adult and fetal human astrocytes were grown in a soy protein isolate (SPI)-collagen hybrid gel or on the surface of a cross-linked SPI-collagen membrane. Hybrid materials reduced the cell proliferation rate compared to materials generated by collagen alone. However, the hybrid materials did not significantly change the cell motility compared to the control collagen material. RNA-sequencing (RNA-Seq) analysis showed downregulated genes in the cell cycle pathway, including CCNA2, CCNB1, CCNB2, CCND1, CCND2, and CDK1, which may explain lower cell proliferation in the hybrid material. This study also revealed the downregulation of genes encoding extracellular matrix (ECM) components, including HSPG2, LUM, SDC2, COL4A1, COL4A5, COL4A6, and FN1, as well as genes encoding chemokines, including CCL2, CXCL1, CXCL2, CX3CL1, CXCL3, and LIF, for adult human astrocytes grown on the hybrid membrane compared with those grown on the control collagen membrane. The study explored the cellular and transcriptional responses of human astrocytes to the hybrid material and indicated a potential beneficial function of the material in the application of neural repair.

Collagen I is a critical organizer of scarring and CNS regeneration failure

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.

Collagen in the central nervous system: contributions to neurodegeneration and promise as a therapeutic target

The extracellular matrix is a richly bioactive composition of substrates that provides biophysical stability, facilitates intercellular signaling, and both reflects and governs the physiological status of the local microenvironment. The matrix in the central nervous system (CNS) is far from simply an inert scaffold for mechanical support, instead conducting an active role in homeostasis and providing broad capacity for adaptation and remodeling in response to stress that otherwise would challenge equilibrium between neuronal, glial, and vascular elements. A major constituent is collagen, whose characteristic triple helical structure renders mechanical and biochemical stability to enable bidirectional crosstalk between matrix and resident cells. Multiple members of the collagen superfamily are critical to neuronal maturation and circuit formation, axon guidance, and synaptogenesis in the brain. In mature tissue, collagen interacts with other fibrous proteins and glycoproteins to sustain a three-dimensional medium through which complex networks of cells can communicate. While critical for matrix scaffolding, collagen in the CNS is also highly dynamic, with multiple binding sites for partnering matrix proteins, cell-surface receptors, and other ligands. These interactions are emerging as critical mediators of CNS disease and injury, particularly regarding changes in matrix stiffness, astrocyte recruitment and reactivity, and pro-inflammatory signaling in local microenvironments. Changes in the structure and/or deposition of collagen impact cellular signaling and tissue biomechanics in the brain, which in turn can alter cellular responses including antigenicity, angiogenesis, gliosis, and recruitment of immune-related cells. These factors, each involving matrix collagen, contribute to the limited capacity for regeneration of CNS tissue. Emerging therapeutics that attempt to rebuild the matrix using peptide fragments, including collagen-enriched scaffolds and mimetics, hold great potential to promote neural repair and regeneration. Recent evidence from our group and others indicates that repairing protease-degraded collagen helices with mimetic peptides helps restore CNS tissue and promote neuronal survival in a broad spectrum of degenerative conditions. Restoration likely involves bolstering matrix stiffness to reduce the potential for astrocyte reactivity and local inflammation as well as repairing inhibitory binding sites for immune-signaling ligands. Facilitating repair rather than endogenous replacement of collagen degraded by disease or injury may represent the next frontier in developing therapies based on protection, repair, and regeneration of neurons in the central nervous system.

Clinical Observation of Various Types of Idiopathic Hypertrophic Cranial Pachymeningitis

BACKGROUND

To assist doctors in making better treatment decisions and improve patient prognosis, it is important to determine which therapy modalities are suitable for various forms of idiopathic hypertrophic cranial pachymeningitis (IHCP).

METHODS

All cases were received from the hospital medical record system, and some follow-up information was gathered through telephone follow-up.

RESULTS

A total of 26 patients, 14 men and 12 women, with ages ranging from 20 to 73 years and a mean of 47.42 years, were included in the research. Regular types were less likely to recur than irregular and nodular types, focal types were less likely to recur than diffuse types, and corticosteroid-refractory types were more likely to recur than corticosteroid-sensitive types.

CONCLUSIONS

The extent and shape of the lesion and susceptibility to corticosteroids are potential factors that could influence recurrence. Futhermore, this paper also proposes the fibroblasts as a new therapeutic target which may improve the quality of prognostic survival of patients.

Small leucine-rich proteoglycans inhibit CNS regeneration by modifying the structural and mechanical properties of the lesion environment

Extracellular matrix (ECM) deposition after central nervous system (CNS) injury leads to inhibitory scarring in humans and other mammals, whereas it facilitates axon regeneration in the zebrafish. However, the molecular basis of these different fates is not understood. Here, we identify small leucine-rich proteoglycans (SLRPs) as a contributing factor to regeneration failure in mammals. We demonstrate that the SLRPs chondroadherin, fibromodulin, lumican, and prolargin are enriched in rodent and human but not zebrafish CNS lesions. Targeting SLRPs to the zebrafish injury ECM inhibits axon regeneration and functional recovery. Mechanistically, we find that SLRPs confer mechano-structural properties to the lesion environment that are adverse to axon growth. Our study reveals SLRPs as inhibitory ECM factors that impair axon regeneration by modifying tissue mechanics and structure, and identifies their enrichment as a feature of human brain and spinal cord lesions. These findings imply that SLRPs may be targets for therapeutic strategies to promote CNS regeneration.

Organization of collagen fibers and tissue hardening: Markers of fibrotic scarring after spinal cord injury in mice revealed by multiphoton-atomic force microscopy imaging

Spinal cord injury is a dramatic disease leading to severe motor, sensitive and autonomic impairments. After injury the axonal regeneration is partly inhibited by the glial scar, acting as a physical and chemical barrier. The scarring process involves microglia, astrocytes and extracellular matrix components, such as collagen, constructing the fibrotic component of the scar. To investigate the role of collagen, we used a multimodal label-free imaging approach combining multiphoton and atomic force microscopy. The second harmonic generation signal exhibited by fibrillar collagen enabled to specifically monitor it as a biomarker of the lesion. An increase in collagen density and the formation of more tortuous fibers over time after injury are observed. Nano-mechanical investigations revealed a noticeable hardening of the injured area, correlated with collagen fibers' formation. These observations indicate the concomitance of important structural and mechanical modifications during the fibrotic scar evolution.

Electrospun decellularized extracellular matrix scaffolds promote the regeneration of injured neurons

Traumatic injury to the spinal cord (SCI) causes the transection of neurons, formation of a lesion cavity, and remodeling of the microenvironment by excessive extracellular matrix (ECM) deposition and scar formation leading to a regeneration-prohibiting environment. Electrospun fiber scaffolds have been shown to simulate the ECM and increase neural alignment and neurite outgrowth contributing to a growth-permissive matrix. In this work, electrospun ECM-like fibers providing biochemical and topological cues are implemented into a scaffold to represent an oriented biomaterial suitable for the alignment and migration of neural cells in order to improve spinal cord regeneration. The successfully decellularized spinal cord ECM (dECM), with no visible cell nuclei and dsDNA content < 50 ng/mg tissue, showed preserved ECM components, such as glycosaminoglycans and collagens. Serving as the biomaterial for 3D printer-assisted electrospinning, highly aligned and randomly distributed dECM fiber scaffolds (< 1 µm fiber diameter) were fabricated. The scaffolds were cytocompatible and supported the viability of a human neural cell line (SH-SY5Y) for 14 days. Cells were selectively differentiated into neurons, as confirmed by immunolabeling of specific cell markers (ChAT, Tubulin ß), and followed the orientation given by the dECM scaffolds. After generating a lesion site on the cell-scaffold model, cell migration was observed and compared to reference poly-ε-caprolactone fiber scaffolds. The aligned dECM fiber scaffold promoted the fastest and most efficient lesion closure, indicating superior cell guiding capabilities of dECM-based scaffolds. The strategy of combining decellularized tissues with controlled deposition of fibers to optimize biochemical and topographical cues opens the way for clinically relevant central nervous system scaffolding solutions.

Tackling the glial scar in spinal cord regeneration: new discoveries and future directions

Axonal regeneration and functional recovery are poor after spinal cord injury (SCI), typified by the formation of an injury scar. While this scar was traditionally believed to be primarily responsible for axonal regeneration failure, current knowledge takes a more holistic approach that considers the intrinsic growth capacity of axons. Targeting the SCI scar has also not reproducibly yielded nearly the same efficacy in animal models compared to these neuron-directed approaches. These results suggest that the major reason behind central nervous system (CNS) regeneration failure is not the injury scar but a failure to stimulate axon growth adequately. These findings raise questions about whether targeting neuroinflammation and glial scarring still constitute viable translational avenues. We provide a comprehensive review of the dual role of neuroinflammation and scarring after SCI and how future research can produce therapeutic strategies targeting the hurdles to axonal regeneration posed by these processes without compromising neuroprotection.

Deletion of Transglutaminase 2 from Mouse Astrocytes Significantly Improves Their Ability to Promote Neurite Outgrowth on an Inhibitory Matrix

Astrocytes are the primary support cells of the central nervous system (CNS) that help maintain the energetic requirements and homeostatic environment of neurons. CNS injury causes astrocytes to take on reactive phenotypes with an altered overall function that can range from supportive to harmful for recovering neurons. The characterization of reactive astrocyte populations is a rapidly developing field, and the underlying factors and signaling pathways governing which type of reactive phenotype that astrocytes take on are poorly understood. Our previous studies suggest that transglutaminase 2 (TG2) has an important role in determining the astrocytic response to injury. Selectively deleting TG2 from astrocytes improves functional outcomes after CNS injury and causes widespread changes in gene regulation, which is associated with its nuclear localization. To begin to understand how TG2 impacts astrocytic function, we used a neuron-astrocyte co-culture paradigm to compare the effects of TG2-/- and wild-type (WT) mouse astrocytes on neurite outgrowth and synapse formation. Neurons were grown on a control substrate or an injury-simulating matrix comprised of inhibitory chondroitin sulfate proteoglycans (CSPGs). Compared to WT astrocytes, TG2-/- astrocytes supported neurite outgrowth to a significantly greater extent only on the CSPG matrix, while synapse formation assays showed mixed results depending on the pre- and post-synaptic markers analyzed. We hypothesize that TG2 regulates the supportive functions of astrocytes in injury conditions by modulating gene expression through interactions with transcription factors and transcription complexes. Based on the results of a previous yeast two-hybrid screen for TG2 interactors, we further investigated the interaction of TG2 with Zbtb7a, a ubiquitously expressed transcription factor. Co-immunoprecipitation and colocalization analyses confirmed the interaction of TG2 and Zbtb7a in the nucleus of astrocytes. Overexpression or knockdown of Zbtb7a levels in WT and TG2-/- astrocytes revealed that Zbtb7a robustly influenced astrocytic morphology and the ability of astrocytes to support neuronal outgrowth, which was significantly modulated by the presence of TG2. These findings support our hypothesis that astrocytic TG2 acts as a transcriptional regulator to influence astrocytic function, with greater influence under injury conditions that increase its expression, and Zbtb7a likely contributes to the overall effects observed with astrocytic TG2 deletion.

Delayed inhibition of collagen deposition by targeting bone morphogenetic protein 1 promotes recovery after spinal cord injury

Fibrotic scars appear after spinal cord injury (SCI) and are mainly composed of fibroblasts and excess extracellular matrix (ECM), including different types of collagen. The temporal and spatial distribution and role of excess collagens and ECM after SCI are not yet fully understood. Here, we identified that the procollagen type I C-terminal propeptide (PICP), a marker of collagen type I deposition, and bone morphogenetic protein 1 (BMP1), a secreted procollagen c-proteinase (PCP) for type I collagen maturation, were significantly elevatedin cerebrospinal fluid of patients with SCI compared with healthy controls, and were associated with spinal cord compression and neurological symptoms. We revealed the deposition of type I collagen in the area damaged by SCI in mice and confirmed that BMP1 was the only expressed PCP and induced collagen deposition. Furthermore, transforming growth factor-β (TGF-β), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) can activate the expression of BMP1. However, inhibition of BMP1 at the acute phase eliminated fibrotic scars in the damaged area and inhibited activation and enrichment of astrocytes, which made the damage difficult to repair and increased hematoma. Unexpectedly, knockdown of Bmp1 by adeno-associated virus or the inhibition of BMP1 biological function by specific inhibitors and monoclonal antibodies at different time points after injury led to distinct therapeutic effects. Only delayed inhibition of BMP1 improved axonal regeneration and myelin repair at the subacute stage post-injury, and led to the recovery of motor function, suggesting that scarring had a dual effect. Early inhibition of the scarring was not conducive to limiting inflammation, while excessive scar formation inhibited the growth of axons. After SCI, the collagen deposition indicators increased in both human cerebrospinal fluid and mouse spinal cord. Therefore, suppression of BMP1 during the subacute phase improves nerve function after SCI and is a potential target for scar reduction.

Deletion of transglutaminase 2 from astrocytes significantly improves their ability to promote neurite outgrowth on an inhibitory matrix

Astrocytes are the primary support cells of the central nervous system (CNS) that help maintain the energetic requirements and homeostatic environment of neurons. CNS injury causes astrocytes to take on reactive phenotypes with altered overall function that can range from supportive to harmful for recovering neurons. The characterization of reactive astrocyte populations is a rapidly developing field, and the underlying factors and signaling pathways governing which type of reactive phenotype that astrocytes take on is poorly understood. Our previous studies suggest that transglutaminase 2 (TG2) has an important role in determining the astrocytic response to injury. TG2 is upregulated in astrocytes across multiple injury models, and selectively deleting TG2 from astrocytes improves functional outcomes after CNS injury and causes widespread changes in gene regulation, which is associated with its nuclear localization. The underlying molecular mechanisms by which TG2 causes these functional changes are unknown, and its interactions in the nucleus of astrocytes has not yet been described. To begin to understand how TG2 impacts astrocytic function, we used a neuron-astrocyte co-culture paradigm to compare the effects of TG2-/- and wild type (WT) astrocytes on neurite outgrowth and synapse formation. We assayed neurons on both a growth-supportive substrate and an injury-simulating matrix comprised of inhibitory chondroitin sulfate proteoglycans (CSPGs). Compared to WT astrocytes, TG2-/- astrocytes supported neurite outgrowth to a significantly greater extent only on the CSPG matrix, while synapse formation assays showed mixed results depending on the pre- and post-synaptic markers analyzed. We hypothesize that TG2 regulates the supportive functions of astrocytes in injury conditions by modulating the expression of a wide range of genes through interactions with transcription factors and transcription complexes. Based on results of a previous yeast two-hybrid screen for TG2 interactors, we further investigated the interaction of TG2 with Zbtb7a, a ubiquitously expressed transcription factor. Coimmunoprecipitation and colocalization analyses confirmed the interaction of TG2 and Zbtb7a in the nucleus of astrocytes. Genetic overexpression or knockdown of Zbtb7a levels in TG2-/- and WT astrocytes revealed that Zbtb7a robustly influenced astrocytic morphology and the ability of astrocytes to support neuronal outgrowth, which was significantly modulated by the presence of TG2. These findings support our hypothesis that astrocytic TG2 acts as a transcriptional regulator to influence astrocytic function, with greater influence under injury conditions that increase its expression, and Zbtb7a likely contributes to the overall effects observed with astrocytic TG2 deletion.

Remodeling Microenvironment for Endogenous Repair through Precise Modulation of Chondroitin Sulfate Proteoglycans Following Spinal Cord Injury

The fluid-filled cystic cavity sealed by a dense scar developed following traumatic spinal cord injury (SCI) has been a major obstacle to neural regeneration and functional recovery. Here the transected lesion is bridged using a functional self-assembling peptide (F-SAP) hydrogel loaded with membrane-permeable intracellular sigma peptide (ISP) and intracellular LAR peptide (ILP), targeted at perturbing chondroitin sulfate proteoglycan (CSPG) inhibitory signaling. As compared to F-SAP hydrogel loaded with chondroitinase ABC, the F-SAP+ISP/ILP promotes a beneficial anti-inflammatory response via manipulation of microglia/macrophages infiltration and assembly of extracellular matrix (ECM) molecules into fibrotic matrix rather than scarring tissues. The remodeled ECM creates a permissive environment that supports axon regrowth and the formation of synaptic connections with neurons derived from endogenous neural stem cells. The remodeled networks contribute to functional recovery, as demonstrated by improved hind limb movements and electrophysiological properties. This work proposes a unique mechanism that ECM remodeling induced by CSPG-manipulation-based anti-inflammation can construct a permissive environment for neural regeneration, and shed light on the advancement of manipulation of cascading cellular and molecular events potential for endogenous repair of SCI.

The optimal transplantation strategy of umbilical cord mesenchymal stem cells in spinal cord injury: a systematic review and network meta-analysis based on animal studies

Objective

Umbilical cord mesenchymal stem cells (UCMSCs) have great potential in the treatment of spinal cord injury. However, the specific therapeutic effect and optimal transplantation strategy are still unclear. Therefore, exploring the optimal treatment strategy of UCMSCs in animal studies by systematic review can provide reference for the development of animal studies and clinical research in the future.

Methods

Databases of PubMed, Ovid-Embase, Web of Science, CNKI, WanFang, VIP, and CBM were searched for the literature in February 11, 2022. Two independent reviewers performed the literature search, identification, screening, quality assessment, and data extraction.

Results and Discussion

A total of 40 animal studies were included for combined analysis. In different subgroups, the results of traditional meta-analysis and network meta-analysis were consistent, that is, the therapeutic effect of high-dose (≥ 1 × 10⁶) transplantation of UCMSCs was significantly better than that of low dose (< 1 × 10⁶), the therapeutic effect of local transplantation of UCMSCs was significantly better than that of intravenous transplantation, and the therapeutic effect of subacute transplantation of UCMSCs was significantly better than that of acute and chronic transplantation. However, in view of the inherent risk of bias and limited internal and external validity of the current animal studies, more high-quality, direct comparison studies are needed to further explore the optimal transplantation strategy for UCMSCs in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03103-8.

Fibrotic Scar in CNS Injuries: From the Cellular Origins of Fibroblasts to the Molecular Processes of Fibrotic Scar Formation

Central nervous system (CNS) trauma activates a persistent repair response that leads to fibrotic scar formation within the lesion. This scarring is similar to other organ fibrosis in many ways; however, the unique features of the CNS differentiate it from other organs. In this review, we discuss fibrotic scar formation in CNS trauma, including the cellular origins of fibroblasts, the mechanism of fibrotic scar formation following an injury, as well as the implication of the fibrotic scar in CNS tissue remodeling and regeneration. While discussing the shared features of CNS fibrotic scar and fibrosis outside the CNS, we highlight their differences and discuss therapeutic targets that may enhance regeneration in the CNS.

5-Fluorouracil reduces the fibrotic scar via inhibiting matrix metalloproteinase 9 and stabilizing microtubules after spinal cord injury

AIMS

Fibrotic scars composed of a dense extracellular matrix are the major obstacles for axonal regeneration. Previous studies have reported that antitumor drugs promote neurofunctional recovery.

METHODS

We investigated the effects of 5-fluorouracil (5-FU), a classical antitumor drug with a high therapeutic index, on fibrotic scar formation, axonal regeneration, and functional recovery after spinal cord injury (SCI).

RESULTS

5-FU administration after hemisection SCI improved hind limb sensorimotor function of the ipsilateral hind paws. 5-FU application also significantly reduced the fibrotic scar formation labeled with aggrecan and fibronectin-positive components, Iba1⁺ /CD11b⁺ macrophages/microglia, vimentin, chondroitin sulfate proteoglycan 4 (NG2/CSPG4), and platelet-derived growth factor receptor beta (PDGFRβ)⁺ pericytes. Moreover, 5-FU treatment promoted stromal cells apoptosis and inhibited fibroblast proliferation and migration by abrogating the polarity of these cells and reducing matrix metalloproteinase 9 expression and promoted axonal growth of spinal neurons via the neuron-specific protein doublecortin-like kinase 1 (DCLK1). Therefore, 5-FU administration impedes the formation of fibrotic scars and promotes axonal regeneration to further restore sensorimotor function after SCI.

Chondroitinase ABC Administration Facilitates Serotonergic Innervation of Motoneurons in Rats With Complete Spinal Cord Transection

Chondroitinase ABC (ChABC) is an enzyme that degrades glycosaminoglycan side-chains of chondroitin sulfate (CS-GAG) from the chondroitin sulfate proteoglycan (CSPG) core protein. Previous studies demonstrated that the administration of ChABC after spinal cord injury promotes nerve regeneration by removing CS-GAGs from the lesion site and promotes the plasticity of spinal neurons by removing CS-GAGs from the perineuronal nets (PNNs). These effects of ChABC might enhance the regeneration and sprouting of descending axons, leading to the recovery of motor function. Anatomical evidence, indicating that the regenerated axons innervate spinal motoneurons caudal to the lesion site, however, has been lacking. In the present study, we investigated whether descending axons pass through the lesion site and innervate the lumbar motoneurons after ChABC administration in rats with complete spinal cord transection (CST) at the thoracic level. At 3 weeks after CST, 5-hydroxytryptamine (5-HT) fibers were observed to enter the lesion in ChABC-treated rats, but not saline-treated rats. In addition, 92% of motoneurons in the ventral horn of the fifth lumbar segment (L5) in saline-treated rats, and 38% of those in ChABC-treated rats were surrounded by chondroitin sulfate-A (CS-A) positive structures. At 8 weeks after CST, many 5-HT fibers were observed in the ventral horn of the L5, where they terminated in the motoneurons in ChABC-treated rats, but not in saline-treated rats. In total, 54% of motoneurons in the L5 ventral horn in saline-treated rats and 39% of those in ChABC-treated rats were surrounded by CS-A-positive structures. ChABC-treated rats had a Basso, Beattie, and Bresnahan (BBB) motor score of 3.8 at 2 weeks, 7.1 at 3 weeks, and 10.3 at 8 weeks after CST. These observations suggest that ChABC administration to the lesion site immediately after CST may promote the regeneration of descending 5-HT axons through the lesion site and their termination on motoneurons at the level of caudal to the lesion site. ChABC administration might facilitate reinnervation by degrading CS-GAGs around motoneurons. Motor function of the lower limbs was significantly improved in ChABC-treated rats even before the 5-HT axons terminated on the motoneurons, suggesting that other mechanisms may also contribute to the motor function recovery.

Hydrogels in Spinal Cord Injury Repair: A Review

Traffic accidents and falling objects are responsible for most spinal cord injuries (SCIs). SCI is characterized by high disability and tends to occur among the young, seriously affecting patients' lives and quality of life. The key aims of repairing SCI include preventing secondary nerve injury, inhibiting glial scarring and inflammatory response, and promoting nerve regeneration. Hydrogels have good biocompatibility and degradability, low immunogenicity, and easy-to-adjust mechanical properties. While providing structural scaffolds for tissues, hydrogels can also be used as slow-release carriers in neural tissue engineering to promote cell proliferation, migration, and differentiation, as well as accelerate the repair of damaged tissue. This review discusses the characteristics of hydrogels and their advantages as delivery vehicles, as well as expounds on the progress made in hydrogel therapy (alone or combined with cells and molecules) to repair SCI. In addition, we discuss the prospects of hydrogels in clinical research and provide new ideas for the treatment of SCI.

Intraocular Delivery of a Collagen Mimetic Peptide Repairs Retinal Ganglion Cell Axons in Chronic and Acute Injury Models

Vision loss through the degeneration of retinal ganglion cell (RGC) axons occurs in both chronic and acute conditions that target the optic nerve. These include glaucoma, in which sensitivity to intraocular pressure (IOP) causes early RGC axonal dysfunction, and optic nerve trauma, which causes rapid axon degeneration from the site of injury. In each case, degeneration is irreversible, necessitating new therapeutics that protect, repair, and regenerate RGC axons. Recently, we demonstrated the reparative capacity of using collagen mimetic peptides (CMPs) to heal fragmented collagen in the neuronal extracellular milieu. This was an important step in the development of neuronal-based therapies since neurodegeneration involves matrix metalloproteinase (MMP)-mediated remodeling of the collagen-rich environment in which neurons and their axons exist. We found that intraocular delivery of a CMP comprising single-strand fractions of triple helix human type I collagen prevented early RGC axon dysfunction in an inducible glaucoma model. Additionally, CMPs also promoted neurite outgrowth from dorsal root ganglia, challenged in vitro by partial digestion of collagen. Here, we compared the ability of a CMP sequence to protect RGC axons in both inducible glaucoma and optic nerve crush. A three-week +40% elevation in IOP caused a 67% degradation in anterograde transport to the superior colliculus, the primary retinal projection target in rodents. We found that a single intravitreal injection of CMP during the period of IOP elevation significantly reduced this degradation. The same CMP delivered shortly after optic nerve crush promoted significant axonal recovery during the two-week period following injury. Together, these findings support a novel protective and reparative role for the use of CMPs in both chronic and acute conditions affecting the survival of RGC axons in the optic projection to the brain.

Study of the Therapeutic Efficiency of Transduced Olfactory Ensheathing Cells in Spinal Cord Cysts

Posttraumatic spinal cord cysts are difficult to treat with medication and surgery. Gene-cell therapy is a promising area of treatment for such patients. However, optimal gene-cell construct for this therapy has not been developed. We investigated the therapeutic efficiency of human olfactory ensheathing cells (OECs) transduced by adenoviral vector encoding the mature form of brain-derived neurotrophic factor (mBDNF) in spinal cord cysts. The adenoviral vectors Ad5/35-CAG-mBDNF and Ad5/35-CAG-Fluc were constructed. Spinal cysts were modeled in female Wistar rats. We selected animals at the early and intermediate stages of recovery with scores to 13 according to the Basso, Beattie and Bresnahan (BBB) scale. The efficiency of therapy was evaluated by BBB tests. No cytotoxicity was detected using the Resazurin/AlamarBlue assay for both vectors at multiplicity of infection (MOIs) of 1, 5, and 25. There was an increase in the proliferation of cells treated with Ad5/35-CAG-mBDNF at MOIs of 5 and 25. The hind limb mobility after the transplantation of Ad5/35-CAG-mBDNF- and Ad5/35-CAG-Fluc-transduced human OECs and nontransduced OECs had approximately the same tendency to improve. Cyst reduction was observed with the transplantation of all the samples. Although Ad5/35-CAG-mBDNF-transduced OECs had high BDNF expression levels in vitro, these cells lacked positive effect in vivo because they did not exhibit significant effect concerning functional test when comparing the groups that received the same numbers of OECs. The therapeutic efficiency of transduced OECs appears to be due to the cell component. The autological and tissue-specific human OECs are promising for the personalized cell therapy. It is extremely important to test new gene-cell constructs based on these cells for further clinical use.

The role of neural stem cells in regulating glial scar formation and repair

Glial scars are a common pathological occurrence in a variety of central nervous system (CNS) diseases and injuries. They are caused after severe damage and consist of reactive glia that form a barrier around the damaged tissue that leads to a non-permissive microenvironment which prevents proper endogenous regeneration. While there are a number of therapies that are able to address some components of disease, there are none that provide regenerative properties. Within the past decade, neural stem cells (NSCs) have been heavily studied due to their potent anti-inflammatory and reparative capabilities in disease and injury. Exogenously applied NSCs have been found to aid in glial scar healing by reducing inflammation and providing cell replacement. However, endogenous NSCs have also been found to contribute to the reactive environment by different means. Further understanding how NSCs can be leveraged to aid in the resolution of the glial scar is imperative in the use of these cells as regenerative therapies. To do so, humanised 3D model systems have been developed to study the development and maintenance of the glial scar. Herein, we explore the current work on endogenous and exogenous NSCs in the glial scar as well as the novel 3D stem cell–based technologies being used to model this pathology in a dish.

[Inhibition of TGF-β promotes functional recovery of spinal cord injury in mice by reducing fibronectin deposition]

OBJECTIVE

To investigate the effect of transforming growth factor (TGF-β) inhibition on functional recovery of spinal cord injury in mice.

METHODS

Twelve mice were divided into treatment group, control group and sham-operated group (n=4). The mice in the treatment group were subjected to hemisection of the spinal cord and received intraperitoneal injection of TGF-β neutralizing antibody (1D11) 3 times a week (25 μL each time), and those in control group were injected with the vehicle antibody (13C4) following spinal cord hemisection. The sham-operated mice underwent sham operation to expose the spinal cord without hemisection. Four weeks later, the heart of the mice was perfused and 1-2 cm of the spinal cord spanning the injury site was harvested. Immunofluorescence staining of FSP1, fibronectin, and PGP9.5 was performed to assess fibroblast recruitment in the injury area, fibronectin deposition, and neurological recovery. For further verification of the results, we used a mouse model of spinal cord clamp injury to observe the survival of axons and distribution of astrocytes by detecting expressions of 5-HT and GFAP with immunofluorescence assay.

RESULTS

In the hemisection injury model, fibroblasts recruitment and fibronectin deposition in the injured area was significantly reduced and the neurological function was improved in 1D11 treatment group as compared with those in 13C4-treated group (P < 0.05). In the spinal cord clamp injury model, treatment with 1D11, as compared with the 13C4, resulted in significantly increased number of 5-HT-positive axons with extended axonal length and obviously increased the number of GFAP-positive astrocytes in the injured area (P < 0.05).

CONCLUSION

Inhibiting TGF-β after spinal cord injury can reduce the recruitment of fibroblasts and fibronectin deposition to promote recovery of neurological function and repair of the injured spinal cord in mice.

Inhibition of TGF-β repairs spinal cord injury by attenuating EphrinB2 expressing through inducing miR-484 from fibroblast

Spinal cord injury (SCI) can lead to severe loss of motor and sensory function with high disability and mortality. The effective treatment of SCI remains unknown. Here we find systemic injection of TGF-β neutralizing antibody induces the protection of axon growth, survival of neurons, and functional recovery, whereas erythropoietin-producing hepatoma interactor B2 (EphrinB2) expression and fibroblasts distribution are attenuated. Knockout of TGF-β type II receptor in fibroblasts can also decrease EphrinB2 expression and improve spinal cord injury recovery. Moreover, miR-488 was confirmed to be the most upregulated gene related to EphrinB2 releasing in fibroblasts after SCI and miR-488 initiates EphrinB2 expression and physical barrier building through MAPK signaling after SCI. Our study points toward elevated levels of active TGF-β as inducer and promoters of fibroblasts distribution, fibrotic scar formation, and EphrinB2 expression, and deletion of global TGF-β or the receptor of TGF-β in Col1α2 lineage fibroblasts significantly improve functional recovery after SCI, which suggest that TGF-β might be a therapeutic target in SCI.

Neurogenesis after Spinal Cord Injury: State of the Art

Neurogenesis in the adult state is the process of new neuron formation. This relatively infrequent phenomenon comprises four stages: cell proliferation, cell migration, differentiation, and the integration of these cells into an existing circuit. Recent reports suggest that neurogenesis can be found in different regions of the Central Nervous System (CNS), including the spinal cord (SC). This process can be observed in physiological settings; however, it is more evident in pathological conditions. After spinal cord injury (SCI), the activation of microglial cells and certain cytokines have shown to exert different modulatory effects depending on the presence of inflammation and on the specific region of the injury site. In these conditions, microglial cells and cytokines are considered to play an important role in the regulation of neurogenesis after SCI. The purpose of this article is to present an overview on neural progenitor cells and neurogenic and non-neurogenic zones as well as the cellular and molecular regulation of neurogenesis. Additionally, we will briefly describe the recent advances in the knowledge of neurogenesis after SCI.

Collagen-based scaffolds: An auspicious tool to support repair, recovery, and regeneration post spinal cord injury

Spinal cord injury (SCI) is a perplexing traumatic disease that habitually gives ride to permanent disability, motor, and sensory impairment. Despite the existence of several therapeutic approaches for the injured motor or sensory neurons, they can't promote axonal regeneration. Whether prepared by conventional or rapid prototyping techniques, scaffolds can be applied to refurbish the continuity of the injured site, by creating a suitable environment for tissue repair, axonal regeneration, and vascularization. Collagen is a multi-sourced protein, found in animals skin, tendons, cartilage, bones, and human placenta, in addition to marine biomass. Collagen is highly abundant in the extracellular matrix and is known for its biocompatibility, biodegradability, porous structure, good permeability, low immunogenicity and thus is extensively applied in the pharmaceutical, cosmetic, and food industries as well as the tissue engineering field. Collagen in scaffolds is usually functionalized with different ligands and factors such as, stem cells, embryonic or human cells to augment its binding specificity and activity. The review summarizes the significance of collagen-based scaffolds and their influence on regeneration, repair and recovery of spinal cord injuries.

Time-Course Changes of Extracellular Matrix Encoding Genes Expression Level in the Spinal Cord Following Contusion Injury-A Data-Driven Approach

The involvement of the extracellular matrix (ECM) in lesion evolution and functional outcome is well recognized in spinal cord injury. Most attention has been dedicated to the “core” area of the lesion and scar formation, while only scattered reports consider ECM modification based on the temporal evolution and the segments adjacent to the lesion. In this study, we investigated the expression profile of 100 genes encoding for ECM proteins at 1, 8 and 45 days post-injury, in the spinal cord segments rostral and caudal to the lesion and in the scar segment, in a rat model. During both the active lesion phases and the lesion stabilization, we observed an asymmetric gene expression induced by the injury, with a higher regulation in the rostral segment of genes involved in ECM remodeling, adhesion and cell migration. Using bioinformatic approaches, the metalloproteases inhibitor Timp1 and the hyaluronan receptor Cd44 emerged as the hub genes at all post-lesion times. Results from the bioinformatic gene expression analysis were then confirmed at protein level by tissue analysis and by cell culture using primary astrocytes. These results indicated that ECM regulation also takes place outside of the lesion area in spinal cord injury.

A bioactive injectable self-healing anti-inflammatory hydrogel with ultralong extracellular vesicles release synergistically enhances motor functional recovery of spinal cord injury

The repair and motor functional recovery after spinal cord injury (SCI) remains a worldwide challenge. The inflammatory microenvironment is one of main obstacles on inhibiting the recovery of SCI. Using mesenchymal stem cells (MSCs) derived extracellular vesicles to replace MSCs transplantation and mimic cell paracrine secretions provides a potential strategy for microenvironment regulation. However, the effective preservation and controlled release of extracellular vesicles in the injured spinal cord tissue are still not satisfied. Herein, we fabricated an injectable adhesive anti-inflammatory F127-polycitrate-polyethyleneimine hydrogel (FE) with sustainable and long term extracellular vesicle release (FE@EVs) for improving motor functional recovery after SCI. The orthotopic injection of FE@EVs hydrogel could encapsulate extracellular vesicles on the injured spinal cord, thereby synergistically induce efficient integrated regulation through suppressing fibrotic scar formation, reducing inflammatory reaction, promoting remyelination and axonal regeneration. This study showed that combining extracellular vesicles into bioactive multifunctional hydrogel should have great potential in achieving satisfactory locomotor recovery of central nervous system diseases.

•

The novel FE hydrogel was designed for encapsulating the extracellular vesicles (FE@EVs).

•

FE hydrogel exert the capabilities of temperature-responsive, injectable, adhesive and biocompatible.

•

FE hydrogel with sustainable and long-term extracellular vesicle release for improving motor functional recovery after SCI.

•

FE@EVs plays a vital role in pathological process of spinal cord injury in rats.

Physiological and immunological changes in the brain associated with lethal eastern equine encephalitis virus in macaques

Aerosol exposure to eastern equine encephalitis virus (EEEV) can trigger a lethal viral encephalitis in cynomolgus macaques which resembles severe human disease. Biomarkers indicative of central nervous system (CNS) infection by the virus and lethal outcome of disease would be useful in evaluating potential medical countermeasures, especially for therapeutic compounds. To meet requirements of the Animal Rule, a better understanding of the pathophysiology of EEEV-mediated disease in cynomolgus macaques is needed. In this study, macaques given a lethal dose of clone-derived EEEV strain V105 developed a fever between 2-3 days post infection (dpi) and succumbed to the disease by 6 dpi. At the peak of the febrile phase, there was a significant increase in the delta electroencephalography (EEG) power band associated with deep sleep as well as a sharp rise in intracranial pressure (ICP). Viremia peaked early after infection and was largely absent by the onset of fever. Granulocytosis and elevated plasma levels of IP-10 were found early after infection. At necropsy, there was a one hundred- to one thousand-fold increase in expression of traumatic brain injury genes (LIF, MMP-9) as well as inflammatory cytokines and chemokines (IFN-γ, IP-10, MCP-1, IL-8, IL-6) in the brain tissues. Phenotypic analysis of leukocytes entering the brain identified cells as primarily lymphoid (T, B, NK cells) with lower levels of infiltrating macrophages and activated microglia. Massive amounts of infectious virus were found in the brains of lethally-infected macaques. While no infectious virus was found in surviving macaques, quantitative PCR did find evidence of viral genomes in the brains of several survivors. These data are consistent with an overwhelming viral infection in the CNS coupled with a tremendous inflammatory response to the infection that may contribute to the disease outcome. Physiological monitoring of EEG and ICP represent novel methods for assessing efficacy of vaccines or therapeutics in the cynomolgus macaque model of EEEV encephalitis.

A switch in pdgfrb+ cell-derived ECM composition prevents inhibitory scarring and promotes axon regeneration in the zebrafish spinal cord

In mammals, perivascular cell-derived scarring after spinal cord injury impedes axonal regrowth. In contrast, the extracellular matrix (ECM) in the spinal lesion site of zebrafish is permissive and required for axon regeneration. However, the cellular mechanisms underlying this interspecies difference have not been investigated. Here, we show that an injury to the zebrafish spinal cord triggers recruitment of pdgfrb⁺ myoseptal and perivascular cells in a PDGFR signaling-dependent manner. Interference with pdgfrb⁺ cell recruitment or depletion of pdgfrb⁺ cells inhibits axonal regrowth and recovery of locomotor function. Transcriptional profiling and functional experiments reveal that pdgfrb⁺ cells upregulate expression of axon growth-promoting ECM genes (cthrc1a and col12a1a/b) and concomitantly reduce synthesis of matrix molecules that are detrimental to regeneration (lum and mfap2). Our data demonstrate that a switch in ECM composition is critical for axon regeneration after spinal cord injury and identify the cellular source and components of the growth-promoting lesion ECM.

The therapeutic potential of targeting exchange protein directly activated by cyclic adenosine 3',5'-monophosphate (Epac) for central nervous system trauma

Millions of people worldwide are affected by traumatic spinal cord injury, which usually results in permanent sensorimotor disability. Damage to the spinal cord leads to a series of detrimental events including ischaemia, haemorrhage and neuroinflammation, which over time result in further neural tissue loss. Eventually, at chronic stages of traumatic spinal cord injury, the formation of a glial scar, cystic cavitation and the presence of numerous inhibitory molecules act as physical and chemical barriers to axonal regrowth. This is further hindered by a lack of intrinsic regrowth ability of adult neurons in the central nervous system. The intracellular signalling molecule, cyclic adenosine 3′,5′-monophosphate (cAMP), is known to play many important roles in the central nervous system, and elevating its levels as shown to improve axonal regeneration outcomes following traumatic spinal cord injury in animal models. However, therapies directly targeting cAMP have not found their way into the clinic, as cAMP is ubiquitously present in all cell types and its manipulation may have additional deleterious effects. A downstream effector of cAMP, exchange protein directly activated by cAMP 2 (Epac2), is mainly expressed in the adult central nervous system, and its activation has been shown to mediate the positive effects of cAMP on axonal guidance and regeneration. Recently, using ex vivo modelling of traumatic spinal cord injury, Epac2 activation was found to profoundly modulate the post-lesion environment, such as decreasing the activation of astrocytes and microglia. Pilot data with Epac2 activation also suggested functional improvement assessed by in vivo models of traumatic spinal cord injury. Therefore, targeting Epac2 in traumatic spinal cord injury could represent a novel strategy in traumatic spinal cord injury repair, and future work is needed to fully establish its therapeutic potential.

Dissecting the Dual Role of the Glial Scar and Scar-Forming Astrocytes in Spinal Cord Injury

Recovery from spinal cord injury (SCI) remains an unsolved problem. As a major component of the SCI lesion, the glial scar is primarily composed of scar-forming astrocytes and plays a crucial role in spinal cord regeneration. In recent years, it has become increasingly accepted that the glial scar plays a dual role in SCI recovery. However, the underlying mechanisms of this dual role are complex and need further clarification. This dual role also makes it difficult to manipulate the glial scar for therapeutic purposes. Here, we briefly discuss glial scar formation and some representative components associated with scar-forming astrocytes. Then, we analyze the dual role of the glial scar in a dynamic perspective with special attention to scar-forming astrocytes to explore the underlying mechanisms of this dual role. Finally, taking the dual role of the glial scar into account, we provide several pieces of advice on novel therapeutic strategies targeting the glial scar and scar-forming astrocytes.

Design of hydrogel-based scaffolds for the treatment of spinal cord injuries

Hydrogel-based scaffold design approaches for the treatment of spinal cord injuries.

Molecular and histologic outcomes following spinal cord injury in spiny mice, Acomys cahirinus

The spiny mouse (Acomys cahirinus) appears to be unique among mammals by showing little scarring or fibrosis after skin or muscle injury, but the Acomys response to spinal cord injury (SCI) is unknown. We tested the hypothesis that Acomys would have molecular and immunohistochemical evidence of reduced spinal inflammation and fibrosis following SCI as compared to C57BL/6 mice (Mus), which similar to all mammals studied to date exhibits spinal scarring following SCI. Initial experiments used two pathway-focused RT-PCR gene arrays ("wound healing" and "neurogenesis") to evaluate tissue samples from the C2-C6 spinal cord 3 days after a C3/C4 hemi-crush injury (C3Hc). Based on the gene array results, specific genes were selected for RT-qPCR evaluation using species-specific primers. The results supported our hypothesis by showing increased inflammation and fibrosis related gene expression (Serpine 1, Plau, and Timp1) in Mus as compared to Acomys (p < .05). RT-qPCR also showed enhanced stem cell and axonal guidance related gene expression (Bmp2, GDNF, and Shh) in Acomys compared to Mus (p < .05). Immunohistochemical evaluation of the spinal lesion at 4 weeks postinjury indicated less collagen IV immunostaining in Acomys (p < .05). Glial fibrillary acidic protein (GFAP) and ionized calcium binding adaptor molecule 1(IBA1) immunostaining indicated morphological differences in the appearance of astrocytes and macrophages/microglia in Acomys. Collectively, the molecular and histologic results support the hypothesis that Acomys has reduced spinal inflammation and fibrosis following SCI. We suggest that Acomys may be a useful comparative model to study adaptive responses to SCI.

Extracellular Vesicles Can Deliver Anti-inflammatory and Anti-scarring Activities of Mesenchymal Stromal Cells After Spinal Cord Injury

Spinal cord injury is characterized by initial neural tissue disruption that triggers secondary damage and extensive non-resolving inflammation, which aggravates loss of function and hinders recovery. The early onset of inflammation following traumatic spinal cord injury underscores the importance of acute intervention after the initial trauma. Injections of mesenchymal stromal cells (MSCs) can reduce inflammation following spinal cord injury. We asked if extracellular vesicles (EVs) can substitute the anti-inflammatory and anti-scarring activities of their parental MSCs in a rat model of contusion spinal cord injury. We report that MSC-EVs were as potent as the parental intact cells in reducing the level of neuroinflammation for up to 2 weeks post-injury. Acute application of EVs after spinal cord injury was shown to robustly decrease the expression of pro-inflammatory cytokines in the spinal cord parenchyma in the very early phase of secondary damage. Moreover, the anti-scarring impact of MSC-EVs was even more efficient than the parental cells. We therefore conclude that anti-inflammatory and anti-scarring activities of MSC application can be mediated by their secreted EVs. In light of their substantial safety and druggability advantages, EVs may have a high potential in early therapeutic treatment following traumatic spinal cord injury.

PTEN modulates neurites outgrowth and neuron apoptosis involving the PI3K/Akt/mTOR signaling pathway

The present study aimed to explore the role of the PTEN/Akt/mTOR signaling pathway in the neurite outgrowth and apoptosis of cortical neurons. Cortical neurons were seeded on or adjacent to chondroitin sulfate proteoglycans. The length, number and crossing behavior of the neurites were calculated. Immunohistochemical staining and TUNEL data were analyzed. Neurites treated with PTEN inhibitor exhibited significant enhancements in elongation, initiation and crossing abilities when they encountered chondroitin sulfate proteoglycans in vitro. These effects disappeared when the PTEN/Akt/mTOR signaling pathway was blocked. Neurons exhibited significant enhancements in survival ability following PTEN inhibition. The present study demonstrated that PTEN inhibition can promote axonal elongation and initiation in cerebral cortical neurons, as well as the ability to cross the chondroitin sulfate proteoglycan border. In addition, PTEN inhibition is useful for protecting the neuron from apoptosis. The PTEN/Akt/mTOR signaling pathway is an important signaling pathway.

Moving beyond the glial scar for spinal cord repair

Traumatic spinal cord injury results in severe and irreversible loss of function. The injury triggers a complex cascade of inflammatory and pathological processes, culminating in formation of a scar. While traditionally referred to as a glial scar, the spinal injury scar in fact comprises multiple cellular and extracellular components. This multidimensional nature should be considered when aiming to understand the role of scarring in limiting tissue repair and recovery. In this Review we discuss recent advances in understanding the composition and phenotypic characteristics of the spinal injury scar, the oversimplification of defining the scar in binary terms as good or bad, and the development of therapeutic approaches to target scar components to enable improved functional outcome after spinal cord injury.

Delayed Effects of Acute Reperfusion on Vascular Remodeling and Late-Phase Functional Recovery After Stroke

Tissue perfusion is a necessary condition for vessel survival that can be compromised under ischemic conditions. Following stroke, delayed effects of early brain reperfusion on the vascular substrate necessary for remodeling, perfusion and maintenance of proper peri-lesional hemodynamics are unknown. Such aspects of ischemic injury progression may be critical for neurological recovery in stroke patients. This study aims to describe the impact of early, non-thrombolytic reperfusion on the vascular brain component and its potential contribution to tissue remodeling and long-term functional recovery beyond the acute phase after stroke in 3-month-old male C57bl/6 mice. Permanent (pMCAO) and transient (60 min, tMCAO) brain ischemia mouse models were used for characterizing the effect of early, non-thrombolytic reperfusion on the brain vasculature. Analysis of different vascular parameters (vessel density, proliferation, degeneration and perfusion) revealed that, while early middle cerebral artery recanalization was not sufficient to prevent sub-acute vascular degeneration within the ischemic brain regions, brain reperfusion promoted a secondary wave of vascular remodeling in the peri-lesional regions, which led to improved perfusion of the ischemic boundaries and late-phase neurological recovery. This study concluded that acute, non-thrombolytic artery recanalization following stroke favors late-phase vascular remodeling and improves peri-lesional perfusion, contributing to secondary functional recovery.

Regionally specified human pluripotent stem cell-derived astrocytes exhibit different molecular signatures and functional properties

Astrocytes display diverse morphologies in different regions of the central nervous system. Whether astrocyte diversity is attributable to developmental processes and bears functional consequences, especially in humans, is unknown. RNA-seq of human pluripotent stem cell-derived regional astrocytes revealed distinct transcript profiles, suggesting differential functional properties. This was confirmed by differential calcium signaling as well as effects on neurite growth and blood-brain barrier formation. Distinct transcriptional profiles and functional properties of human astrocytes generated from regionally specified neural progenitors under the same conditions strongly implicate the developmental impact on astrocyte diversity. These findings provide a rationale for renewed examination of regional astrocytes and their role in the pathogenesis of psychiatric and neurological disorders.

The influence of microenvironment and extracellular matrix molecules in driving neural stem cell fate within biomaterials

Transplantation of stem cells is a promising potential therapy for central nervous system disease and injury. The capacity for self-renewal, proliferation of progenitor cells, and multi-lineage potential underscores the need for controlling stem cell fate. Furthermore, transplantation within a hostile environment can lead to significant cell death and limited therapeutic potential. Tissue-engineered materials have been developed to both regulate stem cell fate, increase transplanted cell viability, and improve therapeutic outcomes. Traditionally, regulation of stem cell differentiation has been driven through soluble signals, such as growth factors. While these signals are important, insoluble factors from the local microenvironment or extracellular matrix (ECM) molecules also contribute to stem cell activity and fate. Understanding the microenvironment factors that influence stem cell fate, such as mechanical properties, topography, and presentation of specific ECM ligands, is necessary for designing improved biomaterials. Here we review some of the microenvironment factors that regulate stem cell fate and how they can be incorporated into biomaterials as part of potential CNS therapies.

PDGFR-β-Positive Perivascular Adventitial Cells Expressing Nestin Contribute to Fibrotic Scar Formation in the Striatum of 3-NP Intoxicated Rats

Perivascular cells expressing platelet-derived growth factor receptor beta (PDGFR-β) have recently been implicated in fibrotic scar formation after acute brain injury, but their precise identity and detailed morphological characteristics remain elusive. This study sought to characterize and define the cellular phenotype of vascular-associated cells expressing PDGFR-β in the striatum of rats treated with the mitochondrial toxin 3-nitropropionic acid (3-NP). In the control striatum, PDGFR-β-positive cells were invariably localized on the abluminal side of smooth muscle cells of larger caliber vessels, and demonstrated morphological features typical of perivascular fibroblasts. PDGFR-β expression increased and expanded to almost all vessels, including microvessels in the lesion core, at 7 days after 3-NP injection. The cells expressing PDGFR-β had ultrastructural features of fibroblasts undergoing active collagen synthesis: large euchromatic nuclei with a prominent nucleolus, well-developed rough endoplasmic reticulum (rER) with dilated cisterns and extracellular collagen fibrils. By 14 days, PDGFR-β-positive cells had somata located at a distance from the vasculature, and their highly ramified, slender processes overlapped with those from other cells, thus forming a plexus of processes in the extravascular space of the lesion core. In addition, their ultrastructural morphology and spatial correlation with activated microglia/macrophages were elaborated by three-dimensional reconstruction. Using a correlative light- and electron-microscopy technique, we found that the intermediate filament proteins nestin and vimentin were induced in PDGFRβ-positive fibroblasts in the lesion core. Collectively, our data suggest that perivascular PDGFR-β-positive fibroblasts are distinct from other vascular cell types, including pericytes and contribute to fibrotic scar formation in the lesion core after acute brain injury. Nestin and vimentin play critical roles in the structural dynamics of these reactive fibroblasts.

Label-free multiphoton microscopy reveals relevant tissue changes induced by alginate hydrogel implantation in rat spinal cord injury

The development of therapies promoting recovery after spinal cord injury is a challenge. Alginate hydrogels offer the possibility to develop biocompatible implants with mechanical properties tailored to the nervous tissue, which could provide a permissive environment for tissue repair. Here, the effects of non-functionalized soft calcium alginate hydrogel were investigated in a rat model of thoracic spinal cord hemisection and compared to lesioned untreated controls. Open field locomotion tests were employed to evaluate functional recovery. Tissue analysis was performed with label-free multiphoton microscopy using a multimodal approach that combines coherent anti-Stokes Raman scattering to visualize axonal structures, two-photon fluorescence to visualize inflammation, second harmonic generation to visualize collagenous scarring. Treated animals recovered hindlimb function significantly better than controls. Multiphoton microscopy revealed that the implant influenced the injury-induced tissue response, leading to decreased inflammation, reduced scarring with different morphology and increased presence of axons. Demyelination of contralateral white matter near the lesion was prevented. Reduced chronic inflammation and increased amount of axons in the lesion correlated with improved hindlimb functions, being thus relevant for locomotion recovery. In conclusion, non-functionalized hydrogel improved functional outcome after spinal cord injury in rats. Furthermore, label-free multiphoton microscopy qualified as suitable technique for regeneration studies.

Spinal Cord Injury Scarring and Inflammation: Therapies Targeting Glial and Inflammatory Responses

Deficits in neuronal function are a hallmark of spinal cord injury (SCI) and therapeutic efforts are often focused on central nervous system (CNS) axon regeneration. However, secondary injury responses by astrocytes, microglia, pericytes, endothelial cells, Schwann cells, fibroblasts, meningeal cells, and other glia not only potentiate SCI damage but also facilitate endogenous repair. Due to their profound impact on the progression of SCI, glial cells and modification of the glial scar are focuses of SCI therapeutic research. Within and around the glial scar, cells deposit extracellular matrix (ECM) proteins that affect axon growth such as chondroitin sulfate proteoglycans (CSPGs), laminin, collagen, and fibronectin. This dense deposition of material, i.e., the fibrotic scar, is another barrier to endogenous repair and is a target of SCI therapies. Infiltrating neutrophils and monocytes are recruited to the injury site through glial chemokine and cytokine release and subsequent upregulation of chemotactic cellular adhesion molecules and selectins on endothelial cells. These peripheral immune cells, along with endogenous microglia, drive a robust inflammatory response to injury with heterogeneous reparative and pathological properties and are targeted for therapeutic modification. Here, we review the role of glial and inflammatory cells after SCI and the therapeutic strategies that aim to replace, dampen, or alter their activity to modulate SCI scarring and inflammation and improve injury outcomes.

MicroRNA-21a-5p promotes fibrosis in spinal fibroblasts after mechanical trauma

Traumatic spinal cord injury (SCI) causes permanent disability to at least 180,000 people per year worldwide. Early regulation of spinal fibroblast proliferation may inhibit fibrotic scar formation, allowing the creation of a favorable environment for neuronal regeneration and thereby enhancing recovery from traumatic SCIs. In this study, we aimed to identify the role of microRNA-21a-5p (miR-21a-5p) in regulating spinal fibroblasts after mechanical trauma and to investigate the dysregulation of miR-21a-5p in the pathological process of spinal SCI. We investigated the differential expression of microRNAs in primary spinal fibroblasts after mechanical trauma and found that the expression of miR-21a-5p was higher in spinal fibroblasts after scratch damage (SD). In addition, mouse spinal fibroblasts were transfected with miR-21a-5p mimics/inhibitor, and the role of miR-21a-5p in spinal fibrogenic activation was analyzed. These experiments demonstrated that miR-21a-5p overexpression promoted fibrogenic activity in spinal fibroblasts after mechanical trauma, as well as enhancing proliferation and attenuating apoptosis in spinal fibroblasts. Finally, the potential role of miR-21a-5p in regulating the Smad signaling pathway was examined. MiR-21a-5p activated the Smad signaling pathway by enhancing Smad2/3 phosphorylation. These results suggest that miR-21a-5p promotes spinal fibrosis after mechanical trauma. Based on these findings, we propose a close relationship between miR-21a-5p and spinal fibrosis, providing a new potential therapeutic target for SCI.

Fibronectin EDA forms the chronic fibrotic scar after contusive spinal cord injury

Gliosis and fibrosis after spinal cord injury (SCI) lead to formation of a scar that is an impediment to axonal regeneration. Fibrotic scarring is characterized by the accumulation of fibronectin, collagen, and fibroblasts at the lesion site. The mechanisms regulating fibrotic scarring after SCI and its effects on axonal elongation and functional recovery are not well understood. In this study, we examined the effects of eliminating an isoform of fibronectin containing the Extra Domain A domain (FnEDA) on both fibrosis and on functional recovery after contusion SCI using male and female FnEDA-null mice. Eliminating FnEDA did not reduce the acute fibrotic response but markedly diminished chronic fibrotic scarring after SCI. Glial scarring was unchanged after SCI in FnEDA-null mice. We found that FnEDA was important for the long-term stability of the assembled fibronectin matrix during both the subacute and chronic phases of SCI. Motor functional recovery was significantly improved, and there were increased numbers of axons in the lesion site compared to wildtype mice, suggesting that the chronic fibrotic response is detrimental to recovery. Our data provide insight into the mechanisms of fibrosis after SCI and suggest that disruption of fibronectin matrix stability by targeting FnEDA represents a potential therapeutic strategy for promoting recovery after SCI.

Role of proteoglycans in neuro-inflammation and central nervous system fibrosis

Fibrosis is defined as the thickening and scarring of connective tissue, usually as a consequence of tissue damage. The central nervous system (CNS) is special in the sense that fibrogenic cells are restricted to vascular and meningeal areas. Inflammation and the disruption of the blood-brain barrier can lead to the infiltration of fibroblasts and trigger fibrotic response. While the initial function of the fibrotic tissue is to restore the blood-brain barrier and to limit the site of injury, it also demolishes the structure of extracellular matrix and impedes the healing process by producing inhibitory molecules and forming a physical and biochemical barrier that prevents axon regeneration. As a major constituent in the extracellular matrix, proteoglycans participate in the neuro-inflammation, modulating the fibrotic process. In this review, we will discuss the pathophysiology of fibrosis during acute injuries of the CNS, as well as during chronic neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease, multiple sclerosis and age-related neurodegeneration with focus on the functional roles of proteoglycans.

MicroRNA-21-5p mediates TGF-β-regulated fibrogenic activation of spinal fibroblasts and the formation of fibrotic scars after spinal cord injury

Little regeneration of transected axons occurs after the damage caused by traumatic spinal cord injury (SCI), and unidirectional and irreversible fibrotic scars are thought to be the main chemical and physical obstacle for axonal regrowth in SCI pathology. We previously demonstrated that microRNA (miR)-21-5p and transforming growth factor (TGF)-β1, a central pathological mediator of fibrotic diseases, were significantly up-regulated in the lesion epicenter after SCI. Here, we found that TGF-β1 enhanced miR-21-5p expression in primary spinal fibroblasts, and regulated the expression of fibrosis-related genes. The overexpression of miR-21-5p promoted the pro-fibrogenic activity of TGF-β1 in spinal fibroblasts, while miR-21-5p knockdown attenuated this activity. We identified Smad7 as a target gene of miR-21-5p, suggesting a potential mechanism for the role of miR-21-5p in spinal fibrosis through regulating Smad7 expression. Furthermore, miR-21-5p knockdown in a mouse model significantly improved motor functional recovery after spinal cord injury. These data demonstrate that miR-21-5p functions in an amplifying circuit to enhance TGF-β signaling events in the activation of spinal fibroblasts and suggest that miR-21-5p is a potential therapeutic target in the treatment of fibrotic scar formation after SCI.