Scar-mediated inhibition and CSPG receptors in the CNS

Internalization of PEI-based complexes in transient transfection of HEK293 cells is triggered by coalescence of membrane heparan sulfate proteoglycans like Glypican-4

Polymer-cationic mediated gene delivery is a well-stablished strategy of transient gene expression (TGE) in mammalian cell cultures. Nonetheless, its industrial implementation is hindered by the phenomenon known as cell density effect (CDE) that limits the cell density at which cultures can be efficiently transfected. The rise in personalized medicine and multiple cell and gene therapy approaches based on TGE, make more relevant to understand how to circumvent the CDE. A rational study upon DNA/PEI complex formation, stability and delivery during transfection of HEK293 cell cultures has been conducted, providing insights on the mechanisms for polyplexes uptake at low cell density and disruption at high cell density. DNA/PEI polyplexes were physiochemically characterized by coupling X-ray spectroscopy, confocal microscopy, cryo-transmission electron microscopy (TEM) and nuclear magnetic resonance (NMR). Our results showed that the ionic strength of polyplexes significantly increased upon their addition to exhausted media. This was reverted by depleting extracellular vesicles (EVs) from the media. The increase in ionic strength led to polyplex aggregation and prevented efficient cell transfection which could be counterbalanced by implementing a simple media replacement (MR) step before transfection. Inhibiting and labeling specific cell-surface proteoglycans (PGs) species revealed different roles of PGs in polyplexes uptake. Importantly, the polyplexes uptake process seemed to be triggered by a coalescence phenomenon of HSPG like glypican-4 around polyplex entry points. Ultimately, this study provides new insights into PEI-based cell transfection methodologies, enabling to enhance transient transfection and mitigate the cell density effect (CDE).

Chondroitin sulfate proteoglycans mRNA expression and degradation in the zebra finch following traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of fatality and disability worldwide. From minutes to months following damage, injury can result in a complex pathophysiology that can lead to temporary or permanent deficits including an array of neurodegenerative symptoms. These changes can include behavioral dysregulation, memory dysfunctions, and mood changes including depression. The nature and severity of impairments resulting from TBIs vary widely given the range of injury type, location, and extent of brain tissue involved. In response to the injury, the brain induces structural and functional changes to promote repair and minimize injury size. Despite its high prevalence, effective treatment strategies for TBI are limited. PNNs are part of the neuronal extracellular matrix (ECM) that mediate synaptic stabilization in the adult brain and thus neuroplasticity. They are associated mostly with inhibitory GABAergic interneurons and are thought to be responsible for maintaining the excitatory/inhibitory balance of the brain. The major structural components of PNNs include multiple chondroitin sulfate proteoglycans (CSPGs) as well as other structural proteins. Here we examine the effects of injury on CSPG expression, specifically around the changes in the side change moieties. To investigate CSPG expression following injury, adult male and female zebra finches received either a bilateral penetrating, or no injury and qPCR analysis and immunohistochemistry for components of the CSPGs were examined at 1- or 7-days post-injury. Next, to determine if CSPGs and thus PNNs should be a target for therapeutic intervention, CSPG side chains were degraded at the time of injury with chondroitinase ABC (ChABC) CSPGs moieties were examined. Additionally, GABA receptor mRNA and aromatase mRNA expression was quantified following CSPG degradation as they have been implicated in neuronal survival and neurogenesis. Our data indicate the CSPG moieties change following injury, potentially allowing for a brief period of synaptic reorganization, and that treatments that target CSPG side chains are successful in further targeting this brief critical period by decreasing GABA mRNA receptor expression, but also decreasing aromatase expression.

Molars to Medicine: A Focused Review on the Pre-Clinical Investigation and Treatment of Secondary Degeneration following Spinal Cord Injury Using Dental Stem Cells

Spinal cord injury (SCI) can result in the permanent loss of mobility, sensation, and autonomic function. Secondary degeneration after SCI both initiates and propagates a hostile microenvironment that is resistant to natural repair mechanisms. Consequently, exogenous stem cells have been investigated as a potential therapy for repairing and recovering damaged cells after SCI and other CNS disorders. This focused review highlights the contributions of mesenchymal (MSCs) and dental stem cells (DSCs) in attenuating various secondary injury sequelae through paracrine and cell-to-cell communication mechanisms following SCI and other types of neurotrauma. These mechanistic events include vascular dysfunction, oxidative stress, excitotoxicity, apoptosis and cell loss, neuroinflammation, and structural deficits. The review of studies that directly compare MSC and DSC capabilities also reveals the superior capabilities of DSC in reducing the effects of secondary injury and promoting a favorable microenvironment conducive to repair and regeneration. This review concludes with a discussion of the current limitations and proposes improvements in the future assessment of stem cell therapy through the reporting of the effects of DSC viability and DSC efficacy in attenuating secondary damage after SCI.

Stroke and Neurogenesis: Bridging Clinical Observations to New Mechanistic Insights from Animal Models

Stroke was the 2nd leading cause of death and a major cause of morbidity. Unfortunately, there are limited means to promote neurological recovery post-stroke, but research has unearthed potential targets for therapies to encourage post-stroke neurogenesis and neuroplasticity. The occurrence of neurogenesis in adult mammalian brains, including humans, was not widely accepted until the 1990s. Now, adult neurogenesis has been extensively studied in human and mouse neurogenic brain niches, of which the subventricular zone of the lateral ventricles and subgranular zone of the dentate gyrus are best studied. Numerous other niches are under investigation for neurogenic potential. This review offers a basic overview to stroke in the clinical setting, a focused summary of recent and foundational research literature on cortical neurogenesis and post-stroke brain plasticity, and insights regarding how the meninges and choroid plexus have emerged as key players in neurogenesis and neuroplasticity in the context of focal cerebral ischemia disrupting the anterior circulation. The choroid plexus and meninges are vital as they are integral sites for neuroimmune interactions, glymphatic perfusion, and niche signaling pertinent to neural stem cells and neurogenesis. Modulating neuroimmune interactions with a focus on astrocyte activity, potentially through manipulation of the choroid plexus and meningeal niches, may reduce the exacerbation of stroke by inflammatory mediators and create an environment conducive to neurorecovery. Furthermore, addressing impaired glymphatic perfusion after ischemic stroke likely supports a neurogenic environment by clearing out inflammatory mediators, neurotoxic metabolites, and other accumulated waste. The meninges and choroid plexus also contribute more directly to promoting neurogenesis: the meninges are thought to harbor neural stem cells and are a niche amenable to neural stem/progenitor cell migration. Additionally, the choroid plexus has secretory functions that directly influences stem cells through signaling mechanisms and growth factor actions. More research to better understand the functions of the meninges and choroid plexus may lead to novel approaches for stimulating neuronal recovery after ischemic stroke.

Corticospinal tract: a new hope for the treatment of post-stroke spasticity

Stroke is the third leading cause of death and disability worldwide. Post-stroke spasticity (PSS) is the most common complication of stroke but represents only one of the many manifestations of upper motor neuron syndrome. As an upper motor neuron, the corticospinal tract (CST) is the only direct descending motor pathway that innervates the spinal motor neurons and is closely related to the recovery of limb function in patients with PSS. Therefore, promoting axonal remodeling in the CST may help identify new therapeutic strategies for PSS. In this review, we outline the pathological mechanisms of PSS, specifically their relationship with CST, and therapeutic strategies for axonal regeneration of the CST after stroke. We found it to be closely associated with astroglial scarring produced by astrocyte activation and its secretion of neurotrophic factors, mainly after the onset of cerebral ischemia. We hope that this review offers insight into the relationship between CST and PSS and provides a basis for further studies.

Combined RhoA morpholino and ChABC treatment protects identified lamprey neurons from retrograde apoptosis after spinal cord injury

Previously, we reported that RhoA knockdown by morpholino antisense oligonucleotides (MOs), and enzymatic digestion of chondroitin sulfate proteoglycans (CSPGs) at the site of injury with chondroitinase ABC (ChABC), each can reduce retrograde neuronal apoptosis after spinal cord transection in the lamprey. To elucidate the mechanisms in neuronal survival and axon regeneration, we have investigated whether these two effects are additive in vivo. We used lampreys as a spinal cord injury model. MOs were used to knockdown RhoA and Chondroitinase ABC (ChABC) was used to digest CSPGs in vivo. Retrograde labeling, fluorochrome-labeled inhibitor of caspase activity (FLICA), immunohistochemistry, and western blots were performed to assess axonal regeneration, neuronal apoptotic signaling and Akt activation. Four treatment combinations were evaluated at 2-, 4-, and 10-weeks post-transection: (1) Control MO plus enzyme buffer (Ctrl); (2) control MO plus ChABC; (3) RhoA MO plus enzyme buffer (RhoA MO); and (4) RhoA MO plus ChABC (RhoA MO + ChABC). Consistent with our previous findings, at 4-weeks post-transection, there was less caspase activation in the ChABC and RhoA MO groups than in the Ctrl group. Moreover, the RhoA MO plus ChABC group had the best protective effect on identified reticulospinal (RS) neurons among the four treatment combinations. At 2 weeks post-transection, when axons have retracted maximally in the rostral stump and are beginning to regenerate back toward the lesion, the axon tips in the three treatment groups each were closer to the transection than those in the Ctr MO plus enzyme buffer group. Long-term axon regeneration also was evaluated for the large, individually identified RS neurons at 10 weeks post-transection by retrograde labeling. The percent regenerated axons in the RhoA MO plus ChABC group was greater than that in any of the other groups. Akt phosphorylation levels at threonine 308 was quantified in the identified RS neurons by western blots and immunofluorescence. The RhoA MO plus ChABC treatment enhanced pAkt-308 phosphorylation more than any of the other treatment groups. Although some of the effects of CSPGs are mediated through RhoA activation, some growth-inhibiting mechanisms of RhoA and CSPGs are independent of each other, so combinatorial therapies may be warranted.

Lateral olfactory tract usher substance (LOTUS), an endogenous Nogo receptor antagonist, ameliorates disease progression in amyotrophic lateral sclerosis model mice

Nogo-Nogo receptor 1 (NgR1) signaling is significantly implicated in neurodegeneration in amyotrophic lateral sclerosis (ALS). We previously showed that lateral olfactory tract usher substance (LOTUS) is an endogenous antagonist of NgR1 that prevents all myelin-associated inhibitors (MAIs), including Nogo, from binding to NgR1. Here we investigated the role of LOTUS in ALS pathogenesis by analyzing G93A-mutated human superoxide dismutase 1 (SOD1) transgenic (Tg) mice, as an ALS model, as well as newly generated LOTUS-overexpressing SOD1 Tg mice. We examined expression profiles of LOTUS and MAIs and compared motor functions and survival periods in these mice. We also investigated motor neuron survival, glial proliferation in the lumbar spinal cord, and neuromuscular junction (NMJ) morphology. We analyzed downstream molecules of NgR1 signaling such as ROCK2, LIMK1, cofilin, and ataxin-2, and also neurotrophins. In addition, we investigated LOTUS protein levels in the ventral horn of ALS patients. We found significantly decreased LOTUS expression in both SOD1 Tg mice and ALS patients. LOTUS overexpression in SOD1 Tg mice increased lifespan and improved motor function, in association with prevention of motor neuron loss, reduced gliosis, increased NMJ innervation, maintenance of cofilin phosphorylation dynamics, decreased levels of ataxin-2, and increased levels of brain-derived neurotrophic factor (BDNF). Reduced LOTUS expression may enhance neurodegeneration in SOD1 Tg mice and ALS patients by activating NgR1 signaling, and in this study LOTUS overexpression significantly ameliorated ALS pathogenesis. LOTUS might serve as a promising therapeutic target for ALS.

3D collagen porous scaffold carrying PLGA-PTX/SDF-1α recruits and promotes neural stem cell differentiation for spinal cord injury repair

Spinal Cord Injury (SCI), one of the major factors of disability, can cause irreversible motor and sensory impairment. There are no effective therapeutic drugs and technologies available in domestic or foreign countries currently. Neural stem cells (NSCs), with the potential for multidirectional differentiation, are a potential treatment for SCI. However, it has been demonstrated that NSCs primarily differentiated into astrocytes rather than neurons due to the inflammatory microenvironment, and the current challenge remains to direct the differentiation of NSCs into neurons in the lesion site. It was reported that the microtubule-stabilizing agent paclitaxel (PTX) was able to promote the differentiation of NSCs into neurons rather than astrocytes after SCI. SDF-1α can recruit NSCs and thus guide the migration of stem cells. In this study, we developed a functional collagen scaffold by loading SDF-1α and nanoparticle-encapsulated PLGA-PTX into a 3D collagen porous scaffold, allowing for slow release of PTX. When the functional scaffolds were implanted into the injury site, it provided a neural regeneration conduit channel for the migration of NSCs and neuronal differentiation. Neural regeneration promoted the recovery of motor function and reduced glial scar formation after SCI. In conclusion, a 3D collagen porous scaffold combined with PLGA-PTX and SDF-1α is a promising therapeutic strategy for SCI repair.

Building a pathway to recovery: Targeting ECM remodeling in CNS injuries

Extracellular matrix (ECM) is a complex and dynamic network of proteoglycans, proteins, and other macromolecules that surrounds cells in tissues. The ECM provides structural support to cells and plays a critical role in regulating various cellular functions. ECM remodeling is a dynamic process involving the breakdown and reconstruction of the ECM. This process occurs naturally during tissue growth, wound healing, and tissue repair. However, in the context of central nervous system (CNS) injuries, dysregulated ECM remodeling can lead to the formation of fibrotic and glial scars. CNS injuries encompass various traumatic events, including concussions and fractures. Following CNS trauma, the formation of glial and fibrotic scars becomes prominent. Glial scars primarily consist of reactive astrocytes, while fibrotic scars are characterized by an abundance of ECM proteins. ECM remodeling plays a pivotal and tightly regulated role in the development of these scars after spinal cord and brain injuries. Various factors like ECM components, ECM remodeling enzymes, cell surface receptors of ECM molecules, and downstream pathways of ECM molecules are responsible for the remodeling of the ECM. The aim of this review article is to explore the changes in ECM during normal physiological conditions and following CNS injuries. Additionally, we discuss various approaches that target various factors responsible for ECM remodeling, with a focus on promoting axon regeneration and functional recovery after CNS injuries. By targeting ECM remodeling, it may be possible to enhance axonal regeneration and facilitate functional recovery after CNS injuries.

Astrogliosis and associated CSPG upregulation adversely affect dendritogenesis, spinogenesis and synaptic activity in the cerebellum of a double-hit rat model of protein malnutrition (PMN) and lipopolysaccharide (LPS) induced bacterial infection

The extracellular matrix (ECM) plays a vital role in growth, guidance and survival of neurons in the central nervous system (CNS). The chondroitin sulphate proteoglycans (CSPGs) are a type of ECM proteins that are crucial for CNS homeostasis. The major goal of this study was to uncover the effects of astroglial activation and associated intensified expression of CSPGs on dendritogenesis, spinogenesis as well as on synaptic activity in cerebellum following protein malnutrition (PMN) and lipopolysaccharide (LPS) induced bacterial infection. Female Wistar albino rats (3 months old) were switched to control (20% protein) or low protein (LP, 8% protein) diet for 15 days followed by breeding. A set of pups born to control/LP mothers and maintained on respective diets throughout the experimental period constituted the control and LP groups, while a separate set of both control and LP group pups exposed to bacterial infection by a single intraperitoneal injection of LPS (0.3 mg/ kg body weight) on postnatal day-9 (P-9) constituted control+LPS and LP+LPS groups respectively. The consequences of astrogliosis induced CSPG upregulation on cerebellar cytoarchitecture and synaptic activity were studied using standard immunohistochemical and histological tools on P-21 and 6 months of age. The results revealed reactive astrogliosis and associated CSPG upregulation in a double-hit model of PMN and LPS induced bacterial infection resulted in disrupted dendritogenesis, reduced postsynaptic density protein (PSD-95) levels and a deleterious impact on normal spine growth. Such alterations frequently have the potential to cause synaptic dysregulation and inhibition of plasticity both during development as well as adulthood. At the light of our results, we can envision that upregulation of CSPGs in PMN and LPS co-challenged individuals might emerge as an important modulator of brain circuitry and a major causative factor for many neurological disorders.

NgR1 is an NK cell inhibitory receptor that destabilizes the immunological synapse

The formation of an immunological synapse (IS) is essential for natural killer (NK) cells to eliminate target cells. Despite an advanced understanding of the characteristics of the IS and its formation processes, the mechanisms that regulate its stability via the cytoskeleton are unclear. Here, we show that Nogo receptor 1 (NgR1) has an important function in modulating NK cell-mediated killing by destabilization of IS formation. NgR1 deficiency or blockade resulted in improved tumor control of NK cells by enhancing NK-to-target cell contact stability and regulating F-actin dynamics during IS formation. Patients with tumors expressing abundant NgR1 ligand had poor prognosis despite high levels of NK cell infiltration. Thus, our study identifies NgR1 as an immune checkpoint in IS formation and indicates a potential approach to improve the cytolytic function of NK cells in cancer immunotherapy.

Paclitaxel-incorporated nanoparticles improve functional recovery after spinal cord injury

As a worldwide medical problem, spinal cord injury has no clear and effective treatment to improve its prognosis. Hence, new treatment strategies for spinal cord injury with good therapeutic efficacy have been actively pursued. As a new drug loading system, acetal dextran nanoparticles (SAD) have good biocompatibility and biodegradability. Therefore, we designed spermine-functionalized acetal-dextran (SAD) nanoparticles and encapsulated paclitaxel (PCL) into them. This design can ensure the sustained release of paclitaxel in the injured area for 4 days and promote the extension of nerve processes in vitro. In our experiment, we found that paclitaxel-loaded SAD nanoparticles (PCL@SAD) decreased the level of chondroitin sulfate proteoglycan in the rat spinal cord injury model, which reduced the scar repair of the injured site and changed the inhibitory environment after spinal cord injury. This reveals that PCL@SAD can effectively protect the injured spinal cord and ultimately improve the functional recovery of the injured spinal cord. One single injection of PCL@SAD shows better therapeutic effect than that of PCL. This study opens an exciting perspective toward the application of neuroprotective PCL@SAD for the treatment of severe neurological diseases.

The Composition and Cellular Sources of CSPGs in the Glial Scar After Spinal Cord Injury in the Lamprey

Axon regrowth after spinal cord injury (SCI) is inhibited by several types of inhibitory extracellular molecules in the central nervous system (CNS), including chondroitin sulfate proteoglycans (CSPGs), which also are components of perineuronal nets (PNNs). The axons of lampreys regenerate following SCI, even though their spinal cords contain CSPGs, and their neurons are enwrapped by PNNs. Previously, we showed that by 2 weeks after spinal cord transection in the lamprey, expression of CSPGs increased in the lesion site, and thereafter, decreased to pre-injury levels by 10 weeks. Enzymatic digestion of CSPGs in the lesion site with chondroitinase ABC (ChABC) enhanced axonal regeneration after SCI and reduced retrograde neuronal death. Lecticans (aggrecan, versican, neurocan, and brevican) are the major CSPG family in the CNS. Previously, we cloned a cDNA fragment that lies in the most conserved link-domain of the lamprey lecticans and found that lectican mRNAs are expressed widely in lamprey glia and neurons. Because of the lack of strict one-to-one orthology with the jawed vertebrate lecticans, the four lamprey lecticans were named simply A, B, C, and D. Using probes that distinguish these four lecticans, we now show that they all are expressed in glia and neurons but at different levels. Expression levels are relatively high in embryonic and early larval stages, gradually decrease, and are upregulated again in adults. Reductions of lecticans B and D are greater than those of A and C. Levels of mRNAs for lecticans B and D increased dramatically after SCI. Lectican D remained upregulated for at least 10 weeks. Multiple cells, including glia, neurons, ependymal cells and microglia/macrophages, expressed lectican mRNAs in the peripheral zone and lesion center after SCI. Thus, as in mammals, lamprey lecticans may be involved in axon guidance and neuroplasticity early in development. Moreover, neurons, glia, ependymal cells, and microglia/macrophages, are responsible for the increase in CSPGs during the formation of the glial scar after SCI.

Effect of Sulfation on the Conformational Dynamics of Dermatan Sulfate Glycosaminoglycan: A Gaussian Accelerated Molecular Dynamics Study

Glycosaminoglycans (GAGs) are anionic biopolymers present on cell surfaces as a part of proteoglycans. The biological activities of GAGs depend on the sulfation pattern. In our study, we have considered three octadecasaccharide dermatan sulfate (DS) chains with increasing order of sulfation (dp6s, dp7s, and dp12s) to illuminate the role of sulfation on the GAG units and its chain conformation through 10 μs-long Gaussian accelerated molecular dynamics simulations. DS is composed of repeating disaccharide units of iduronic acid (IdoA) and N-acetylgalactosamine (N-GalNAc). Here, N-GalNAc is linked to IdoA via β(1-4), while IdoA is linked to N-GalNAc through α(1-3). With the increase in sulfation, the DS structure becomes more rigid and linear, as is evident from the distribution of root-mean-square deviations (RMSDs) and end-to-end distances. The tetrasaccharide linker region of the main chain shows a rigid conformation in terms of the glycosidic linkage. We have observed that upon sulfation (i.e., dp12s), the ring flip between two chair forms vanished for IdoA. The dynamic cross-correlation analysis reveals that the anticorrelation motions in dp12s are reduced significantly compared to dp6s or dp7s. An increase in sulfation generates relatively more stable hydrogen-bond networks, including water bridging with the neighboring monosaccharides. Despite the favorable linear structures of the GAG chains, our study also predicts few significant bendings related to the different puckering states, which may play a notable role in the function of the DS. The relation between the global conformation with the micro-level parameters such as puckering and water-mediated hydrogen bonds shapes the overall conformational space of GAGs. Overall, atomistic details of the DS chain provided in this study will help understand their functional and mechanical roles, besides developing new biomaterials.

Low-Molecular Weight Protamine Overcomes Chondroitin Sulfate Inhibition of Neural Regeneration

Protamine is an arginine-rich peptide that replaces histones in the DNA-protein complex during spermatogenesis. Protamine is clinically used in cardiopulmonary bypass surgery to neutralize the effects of heparin that is required during the treatment. Here we demonstrate that protamine and its 14–22 amino acid long fragments overcome the neurite outgrowth inhibition by chondroitin sulfate proteoglycans (CSPGs) that are generally regarded as major inhibitors of regenerative neurite growth after injuries of the adult central nervous system (CNS). Since the full-length protamine was found to have toxic effects on neuronal cells we used the in vitro neurite outgrowth assay to select a protamine fragment that retains the activity to overcome the neurite outgrowth inhibition on CSPG substrate and ended up in the 14 amino acid fragment, low-molecular weight protamine (LMWP). In contrast to the full-length protamine, LMWP displays very low or no toxicity in our assays in vitro and in vivo. We therefore started studies on LMWP as a possible drug lead in treatment of CNS injuries, such as the spinal cord injury (SCI). LMWP mimicks HB-GAM (heparin-binding growth-associated molecule; pleiotrophin) in that it overcomes the CSPG inhibition on neurite outgrowth in primary CNS neurons in vitro and inhibits binding of protein tyrosine phosphatase (PTP) sigma, an inhibitory receptor in neurite outgrowth, to its CSPG ligand. Furthermore, the chondroitin sulfate (CS) chains of the cell matrix even enhance the LMWP-induced neurite outgrowth on CSPG substrate. In vivo studies using the hemisection and hemicontusion SCI models in mice at the cervical level C5 revealed that LMWP enhances recovery when administered through intracerebroventricular or systemic route. We suggest that LMWP is a promising drug lead to develop therapies for CNS injuries.

Heparin-Binding Growth-Associated Molecule (Pleiotrophin) Affects Sensory Signaling and Selected Motor Functions in Mouse Model of Anatomically Incomplete Cervical Spinal Cord Injury

Heparin-binding growth-associated molecule (pleiotrophin) is a neurite outgrowth-promoting secretory protein that lines developing fiber tracts in juvenile CNS (central nervous system). Previously, we have shown that heparin-binding growth-associated molecule (HB-GAM) reverses the CSPG (chondroitin sulfate proteoglycan) inhibition on neurite outgrowth in the culture medium of primary CNS neurons and enhances axon growth through the injured spinal cord in mice demonstrated by two-photon imaging. In this study, we have started studies on the possible role of HB-GAM in enhancing functional recovery after incomplete spinal cord injury (SCI) using cervical lateral hemisection and hemicontusion mouse models. In vivo imaging of blood-oxygen-level-dependent (BOLD) signals associated with functional activity in the somatosensory cortex was used to assess the sensory functions during vibrotactile hind paw stimulation. The signal displays an exaggerated response in animals with lateral hemisection that recovers to the level seen in the sham-operated mice by injection of HB-GAM to the trauma site. The effect of HB-GAM treatment on sensory-motor functions was assessed by performance in demanding behavioral tests requiring integration of afferent and efferent signaling with central coordination. Administration of HB-GAM either by direct injection into the trauma site or by intrathecal injection improves the climbing abilities in animals with cervical hemisection and in addition enhances the grip strength in animals with lateral hemicontusion without affecting the spontaneous locomotor activity. Recovery of sensory signaling in the sensorimotor cortex by HB-GAM to the level of sham-operated mice may contribute to the improvement of skilled locomotion requiring integration of spatiotemporal signals in the somatosensory cortex.

Astrocytes in the Traumatic Brain Injury: the Good and the Bad

Astrocytes control many processes of the nervous system in health and disease, and respond to injury quickly. Astrocytes produce neuroprotective factors in the injured brain to clear cellular debris and to orchestrate neurorestorative processes that are beneficial for neurological recovery after traumatic brain injury (TBI). However, astrocytes also become dysregulated and produce cytotoxic mediators that hinder CNS repair by induction of neuronal dysfunction and cell death. Hence, we discuss the potential role of astrocytes in neuropathological processes such as neuroinflammation, neurogenesis, synaptogenesis and blood-brain barrier repair after TBI. Thus, an improved understanding of the dual role of astrocytes may advance our knowledge of post-brain injury recovery, and provide opportunities for the development of novel therapeutic strategies for TBI.

A DAMP-scavenging, IL-10-releasing hydrogel promotes neural regeneration and motor function recovery after spinal cord injury

Spinal cord injury (SCI) creates an inflammatory microenvironment characterized by damage-associated molecular patterns (DAMPs) and immune cell activation that exacerbate secondary damage and impair neurological recovery. Here we develop an immunoregulatory hydrogel scaffold for treating SCI that scavenges DAMPs and slowly releases the anti-inflammatory cytokine interleukin-10 (IL-10). We created this dual-functional scaffold by modifying a photocrosslinked gelatin hydrogel with the cationic, DAMP-binding polymer poly (amidoamine) and with IL-10, and compared the therapeutic activity of this scaffold with that of gelatin-only, gelatin + poly (amidoamine), and gelatin + IL-10 scaffolds in vitro and in vivo. In vitro, the dual-functional scaffold scavenged anionic DAMPs and exhibited sustained release of IL-10, reduced the proinflammatory responses of macrophages and microglia, and enhanced the neurogenic differentiation of neural stem cells. In a complete transection SCI mouse model, the injected dual-functional scaffold suppressed proinflammatory cytokine production, promoted the M2 macrophage/microglia phenotype, and led to neural regeneration and axon growth without scar formation to a greater extent than the single-function or control scaffolds. This DAMP-scavenging, IL-10-releasing scaffold provides a new strategy for promoting neural regeneration and motor function recovery following severe SCI.

The spatial arrangement of cells in a 3D-printed biomimetic spinal cord promotes directional differentiation and repairs the motor function after spinal cord injury

Spinal cord injury is a permanent destructive disease that causes devastating neurologic deficits and disability. Long-term complications are associated with low prognosis, mortality, and decreased quality of life. The functional recovery depends on the regeneration of neurons and the growth of medullated axons. Single treatment strategies, including cell transplantation, cannot adapt to a changeable microenvironment. Patients with spinal cord injuries need more effective, long-term, and stable treatment options. Therefore, we investigated the benefit of a combined-tissue engineering strategy by loading homologous bone mesenchymal stem cells (BMSCs) and Schwann cells in three-dimensional (3D) scaffolds. We placed BMSCs and Rat Schwann cells (RSCs) in specific spatial arrangements using cell gravity and the diffusion effect to promote the formation of intercellular connections and cell-directed differentiation. This novel bioengineering system allowed us to control multiple factors, including cell types, cell relative position, and axon growth direction in the scaffold. Our system facilitated motor function recovery by enhancing tissue mimicry and allowing the reconstruction of medullated axons. This new 3D-integrated printing platform is multi-function and can simulate biomimetic tissue using different types of materials and multi-cells scaffolds. We believe that this study can help promote the clinical development and application of 3D printing in the field of regenerative medicine.

The Neuroprotective Role of Reactive Astrocytes after Central Nervous System Injury

Reactive astrocytes have traditionally been viewed as a significant contributor to secondary neuronal damage and repair inhibition after central nervous system (CNS) injury attributed, in large part, to their roles in glial scarring. However, more recent transcriptional evidence has uncovered the vast diversity in reactive astrocyte identity and functions that comprises both neuroprotective and -toxic characteristics. Additionally, the capacity of reactive astrocytes to shift between these activation states demonstrates a high level of environment-dependent plasticity that drives the interplay between neuroprotection and -toxicity after CNS injury. These recent findings have spawned a new field of research that seeks to identify and categorize the function of these discrete subpopulations in the context of neurotrauma, as well as identify their regulators. Therefore, this review will discuss the major and most recent advances in this field of research, with a primary emphasis on neuroprotection. This review will also discuss the major pitfalls present in the field, with a particular focus on model species and their impact on the development of novel therapies.

Neutrophil, Extracellular Matrix Components, and Their Interlinked Action in Promoting Secondary Pathogenesis After Spinal Cord Injury

Secondary pathogenesis following primary mechanical damage to the spinal cord is believed to be the ultimate reason for the limitation of currently available therapies. Precisely, the complex cascade of secondary events-mediated scar formation is the sole hurdle in the recovery process due to its inhibitory effect on axonal regeneration, plasticity, and remyelination. Neutrophils initiate this secondary injury along with other extracellular matrix components such as matrix metalloproteinase (MMPs), and chondroitin sulfate proteoglycans (CSPGs). Together, they mediate inflammation, necrosis, apoptosis, lesion, and scar formation at the injury site. Activated neutrophil releases several proteases, cytokines, and chemokines that cause complete tissue destruction. Thus, neutrophil activation and infiltration in the acute phase of injury act as a roadmap for inducing tissue destruction. MMPs, are extracellular proteolytic enzymes that degrade the ECM proteins, increases vascular permeability, and are predominantly released by neutrophils. These MMPs, in turn, cleave NG2 proteoglycan, a subtype of CSPG, into the active form. This active or shed form is involved in both the fibrotic as well as glial scar formation. Since neutrophils and ECM components are closely associated with each other in pathological conditions. Herein, we emphasize the interaction of neutrophils and their influence on ECM protein expression during the acute and chronic phases to identify a promising targets for designing a therapeutic approach in spinal cord injury.

Strategies to neutralize RhoA/ROCK pathway after spinal cord injury

Regeneration is bungled following CNS injuries, including spinal cord injury (SCI). Inherent decay of permissive conditions restricts the regrowth of the mature CNS after an injury. Hypertrophic scarring, insignificant intrinsic axon-growth activity, and axon-growth inhibitory molecules such as myelin inhibitors and scar inhibitors constitute a significant hindrance to spinal cord repair. Besides these molecules, a combined absence of various mechanisms responsible for axonal regeneration is the main reason behind the dereliction of the adult CNS to regenerate. The neutralization of specific inhibitors/proteins by stymieing antibodies or encouraging enzymatic degradation results in improved axon regeneration. Previous efforts to induce regeneration after SCI have stimulated axonal development in or near lesion sites, but not beyond them. Several pathways are responsible for the axonal growth obstruction after a CNS injury, including SCI. Herein, we summarize the axonal, glial, and intrinsic factor which impedes the regeneration. We have also discussed the methods to stabilize microtubules and through this to maintain the proper cytoskeletal dynamics of growth cone as disorganized microtubules lead to the failure of axonal regeneration. Moreover, we primarily focus on diverse inhibitors of axonal growth and molecular approaches to counteract them and their downstream intracellular signaling through the RhoA/ROCK pathway.

Scar tissue removal-activated endogenous neural stem cells aid Taxol-modified collagen scaffolds in repairing chronic long-distance transected spinal cord injury

Scar tissue removal combined with biomaterial implantation is considered an effective measure to repair chronic transected spinal cord injury (SCI). However, whether more scar tissue removal surgeries could affect the treatment effects of biomaterial implantation still needs to be explored. In this study, we performed the first scar tissue removal surgery in the 3^rd month and the second in the 6^th month after completely removing 1 cm of spinal tissue in canines. We found that Taxol-modified linear ordered collagen scaffold (LOCS + Taxol) implantation could promote axonal regeneration, neurogenesis, and electrophysiological and functional recovery only in canines at the first scar tissue removal surgery, but not in canines at the second scar tissue removal surgery. Interestingly, we found that more endogenous neural stem cells (NSCs) around the injured site could be activated in canines with the first rather than the second scar tissue removal. Furthermore, we demonstrated that Taxol could promote the neuronal differentiation of NSCs in the myelin inhibition microenvironment through the p38 MAPK signaling pathway in vitro. Therefore, we speculated that endogenous NSC activation by the first scar tissue removal surgery and its further differentiation into neurons induced by Taxol may contribute to functional recovery in canines. Together, LOCS + Taxol implantation in combination with the first scar tissue removal provides a promising therapy for chronic long-distance transected SCI repair with the help of scar tissue removal activated endogenous NSCs.

Running Promotes Transformation of Brain Astrocytes Into Neuroprotective Reactive Astrocytes and Synaptic Formation by Targeting Gpc6 Through the STAT3 Pathway

Ischemic stroke is caused by cerebral ischemia upon the blockage of an artery, which results in a high disability rate. Little is known regarding the mechanism of astrocyte function in cerebral ischemia. We aimed to determine the effects of running on the transformation of astrocytes, and subsequent synapse formation. A study of middle cerebral artery occlusion (MCAO) after running in vivo showed that running can promote the transformation of astrocytes toward the neuroprotective phenotype. Our findings of oxygen-glucose deprived astrocytes in vitro after running revealed that these astrocytes transformed into the neuroprotective phenotype, and that the expression of STAT3 and Gpc6 was increased. We confirmed that mechanistically, running can target Gpc6 through the STAT3 pathway and then regulate the number of synapses. We concluded that running promotes synapse proliferation by polarizing astrocytes toward the neuroprotective phenotype and ultimately leads to nerve regeneration.

Chondroitinase ABC Promotes Axon Regeneration and Reduces Retrograde Apoptosis Signaling in Lamprey

Paralysis following spinal cord injury (SCI) is due to failure of axonal regeneration. It is believed that axon growth is inhibited by the presence of several types of inhibitory molecules in central nervous system (CNS), including the chondroitin sulfate proteoglycans (CSPGs). Many studies have shown that digestion of CSPGs with chondroitinase ABC (ChABC) can enhance axon growth and functional recovery after SCI. However, due to the complexity of the mammalian CNS, it is still unclear whether this involves true regeneration or only collateral sprouting by uninjured axons, whether it affects the expression of CSPG receptors such as protein tyrosine phosphatase sigma (PTPσ), and whether it influences retrograde neuronal apoptosis after SCI. In the present study, we assessed the roles of CSPGs in the regeneration of spinal-projecting axons from brainstem neurons, and in the process of retrograde neuronal apoptosis. Using the fluorochrome-labeled inhibitor of caspase activity (FLICA) method, apoptotic signaling was seen primarily in those large, individually identified reticulospinal (RS) neurons that are known to be “bad-regenerators.” Compared to uninjured controls, the number of all RS neurons showing polycaspase activity increased significantly at 2, 4, 8, and 11 weeks post-transection (post-TX). ChABC application to a fresh TX site reduced the number of polycaspase-positive RS neurons at 2 and 11 weeks post-TX, and also reduced the number of active caspase 3-positive RS neurons at 4 weeks post-TX, which confirmed the beneficial role of ChABC treatment in retrograde apoptotic signaling. ChABC treatment also greatly promoted axonal regeneration at 10 weeks post-TX. Correspondingly, PTPσ mRNA expression was reduced in the perikaryon. Previously, PTPσ mRNA expression was shown to correlate with neuronal apoptotic signaling at 2 and 10 weeks post-TX. In the present study, this correlation persisted after ChABC treatment, which suggests that PTPσ may be involved more generally in signaling axotomy-induced retrograde neuronal apoptosis. Moreover, ChABC treatment caused Akt activation (pAkt-308) to be greatly enhanced in brain post-TX, which was further confirmed in individually identified RS neurons. Thus, CSPG digestion not only enhances axon regeneration after SCI, but also inhibits retrograde RS neuronal apoptosis signaling, possibly by reducing PTPσ expression and enhancing Akt activation.

Intravenous Administration of Heat Shock-Treated MSCs Can Improve Neuroprotection and Neuroregeneration in Canine Spinal Cord Injury Model

Simple Summary

Mesenchymal stem cells (MSCs), which are found in connective tissues, can be used to treat spinal cord injury (SCI) in dogs. These stem cells have the ability to repair damaged tissues and can be transplanted into the injured area. While this is considered a promising treatment, the transplanted cells often do not survive in the injured spinal cord. In this study, we found that heat shock treatment, i.e., exposure to high temperatures, increased the efficacy of MSC treatment for SCI.

Abstract

Transplantation of mesenchymal stem cells (MSCs) is a promising treatment for spinal cord injury (SCI). However, many transplanted cells die within a few days, eventually limiting the efficacy of cellular therapy. To overcome this problem, we focused on the potential of heat shock (HS) proteins in facilitating recovery from cell damage and protecting against cytotoxicity. PCR results showed that the expression of neurotrophic factor, anti-inflammatory, stemness, and homing genes increased in HS-treated MSCs. We investigated whether HS-treated MSCs could promote recovery of hindlimb function in an acute canine SCI model. We compared the effects of intravenous transplantation with (i) lactated Ringer’s solution as a control, (ii) green fluorescent protein-expressing MSCs (MSCs-GFP), and (iii) GFP-expressing and HS-treated MSCs (MSCs-GFP-HS). Spinal cords were harvested at four weeks and used for Western blot and histopathological analyses. The MSCs-GFP-HS group showed significant improvements in hindlimb function from weeks 3 and 4 compared with the other groups. This group also showed higher expression of neural markers, fewer intervening fibrotic changes, and pronounced myelination. These results suggest that induction of an HS response in MSCs could promote neural sparing. In conclusion, transplantation of HS-treated MSCs could improve neuroprotection and neuroregeneration in acute SCI.

Glial Metabolic Rewiring Promotes Axon Regeneration and Functional Recovery in the Central Nervous System

Axons in the mature central nervous system (CNS) fail to regenerate after axotomy, partly due to the inhibitory environment constituted by reactive glial cells producing astrocytic scars, chondroitin sulfate proteoglycans, and myelin debris. We investigated this inhibitory milieu, showing that it is reversible and depends on glial metabolic status. We show that glia can be reprogrammed to promote morphological and functional regeneration after CNS injury in Drosophila via increased glycolysis. This enhancement is mediated by the glia derived metabolites: L-lactate and L-2-hydroxyglutarate (L-2HG). Genetically/pharmacologically increasing or reducing their bioactivity promoted or impeded CNS axon regeneration. L-lactate and L-2HG from glia acted on neuronal metabotropic GABA_B receptors to boost cAMP signaling. Local application of L-lactate to injured spinal cord promoted corticospinal tract axon regeneration, leading to behavioral recovery in adult mice. Our findings revealed a metabolic switch to circumvent the inhibition of glia while amplifying their beneficial effects for treating CNS injuries.

LAR inhibitory peptide promotes recovery of diaphragm function and multiple forms of respiratory neural circuit plasticity after cervical spinal cord injury

Chondroitin sulfate proteoglycans (CSPGs), up-regulated in and around the lesion after traumatic spinal cord injury (SCI), are key extracellular matrix inhibitory molecules that limit axon growth and consequent recovery of function. CSPG-mediated inhibition occurs via interactions with axonal receptors, including leukocyte common antigen- related (LAR) phosphatase. We tested the effects of a novel LAR inhibitory peptide in rats after hemisection at cervical level 2, a SCI model in which bulbospinal inspiratory neural circuitry originating in the medullary rostral ventral respiratory group (rVRG) becomes disconnected from phrenic motor neuron (PhMN) targets in cervical spinal cord, resulting in persistent partial-to-complete diaphragm paralysis. LAR peptide was delivered by a soaked gelfoam, which was placed directly over the injury site immediately after C2 hemisection and replaced at 1 week post-injury. Axotomized rVRG axons originating in ipsilateral medulla or spared rVRG fibers originating in contralateral medulla were separately assessed by anterograde tracing via AAV2-mCherry injection into rVRG. At 8 weeks post-hemisection, LAR peptide significantly improved ipsilateral hemidiaphragm function, as assessed in vivo with electromyography recordings. LAR peptide promoted robust regeneration of ipsilateral-originating rVRG axons into and through the lesion site and into intact caudal spinal cord to reach PhMNs located at C3-C5 levels. Furthermore, regenerating rVRG axons re-established putative monosynaptic connections with their PhMNs targets. In addition, LAR peptide stimulated robust sprouting of both modulatory serotonergic axons and contralateral-originating rVRG fibers within the PhMN pool ipsilateral/ caudal to the hemisection. Our study demonstrates that targeting LAR-based axon growth inhibition promotes multiple forms of respiratory neural circuit plasticity and provides a new peptide-based therapeutic strategy to ameliorate the devastating respiratory consequences of SCI.

Neural Cadherin Plays Distinct Roles for Neuronal Survival and Axon Growth under Different Regenerative Conditions

Growing axons in the CNS often migrate along specific pathways to reach their targets. During embryonic development, this migration is guided by different types of cell adhesion molecules (CAMs) present on the surface of glial cells or other neurons, including the neural cadherin (NCAD). Axons in the adult CNS can be stimulated to regenerate, and travel long distances. Crucially, however, while a few axons are guided effectively through the injured nerve under certain conditions, most axons never migrate properly. The molecular underpinnings of the variable growth, and the glial CAMs that are responsible for CNS axon regeneration remain unclear. Here we used optic nerve crush to demonstrate that NCAD plays multifaceted functions in facilitating CNS axon regeneration. Astrocyte-specific deletion of NCAD dramatically decreases regeneration induced by phosphatase and tensin homolog (PTEN) ablation in retinal ganglion cells (RGCs). Consistent with NCAD’s tendency to act as homodimers, deletion of NCAD in RGCs also reduces regeneration. Deletion of NCAD in astrocytes neither alters RGCs’ mammalian target of rapamycin complex 1 (mTORC1) activity nor lesion size, two factors known to affect regeneration. Unexpectedly, however, we find that NCAD deletion in RGCs reduces PTEN-deletion-induced RGC survival. We further show that NCAD deletion, in either astrocytes or RGCs, has negligible effects on the regeneration induced by ciliary neurotrophic factor (CNTF), suggesting that other CAMs are critical under this regenerative condition. Consistent with this notion, CNTF induces expression various integrins known to mediate cell adhesion. Together, our study reveals multilayered functions of NCAD and a molecular basis of variability in guided axon growth.

PTEN-silencing combined with ChABC-overexpression in adipose-derived stem cells promotes functional recovery of spinal cord injury in rats

The efficiency of cell therapy after spinal cord injury (SCI) depend on the survival of transplanted cells. However, sterile microenvironment and glial scar hyperplasia extremely reduce their numbers. Our previous study found overexpression of ChABC gene is positively correlated to migration ability. Expression of PTEN gene is closely associated with proliferation. However, whether manipulation of PTEN and ChABC on adipose-derived mesenchymal stem cells (ADSCs) promote motor recovery is unknown. This study aimed to promote hindlimb function recovery in SCI rats by enhancing proliferation and migration ability of ADSCs, transiently silencing expression of PTEN following overexpression of ChABC (double-gene modified ADSCs, DG-ADSCs). After PTEN silencing, we observed strong proliferation and accelerated G1-S transition in DG-ADSCs using CCK8 assay and flow cytometry. In addition, we demonstrated that migration numbers of DG-ADSCs were higher than control group using Transwell assay. The protein and mRNA levels of MAP2 and βⅢ-tubulin in DG-ADSCs were increased compared with ADSCs. These results were further confirmed in SCI rats. Increased survival cells and reduction of glial scars were quantitatively analyzed in DG-ADSCs groups, which is definitely correlated to function recovery. Recovery of motor function was observed in DG-ADSCs treatment rats using BBB score, which emphasized that improved viability of transplanted cells and reduction of glial scars were an effective strategy for enhancing recovery of neurological function after SCI.

Chondroitin sulfate proteoglycans: key modulators of neuronal plasticity, long-term memory, neurodegenerative, and psychiatric disorders

The chondroitin sulfate proteoglycans (CSPGs) are large groups of heterogenous proteoglycans that are mainly expressed by reactive astrocytes in the central nervous system (CNS). They share similar core proteins and are post-transcriptionally modified by chondroitin sulfate glycosaminoglycans. CSPGs are the major components of the perineuronal nets (PNN) that regulate the opening and closure of the critical period. Mounting reports have documented the crucial roles of CSPGs in restricting neuronal plasticity, axonal growth, and pathfinding during development as well as axonal regeneration after CNS injury. Moreover, CSPGs and PNNs modulate long-term memory, which impairments frequently happened in several neurodegenerative and psychiatric disorders. This review will shortly introduce the expression patterns of CSPGs during development and after injury, the PNNs constitutions, the roles of CSPGs and PNNs in axonal regrowth, discuss the most recently identified roles of CSPGs and PNNs in mediating long-term memory and their correlation with brain disorders, and finally, propose a short perspective of future investigations. Hopefully, further explorations may validate the therapeutic potentials of PNNs and CSPGs.

Reelin Counteracts Chondroitin Sulfate Proteoglycan-Mediated Cortical Dendrite Growth Inhibition

Disruptions in neuronal dendrite development alter brain circuitry and are associated with debilitating neurological disorders. Nascent apical dendrites of cortical excitatory neurons project into the marginal zone (MZ), a cell-sparse layer characterized by intense chondroitin sulfate proteoglycan (CSPG) expression. Paradoxically, CSPGs are known to broadly inhibit neurite growth and regeneration. This raises the possibility that the growing apical dendrite is somehow insensitive to CSPG-mediated neurite growth inhibition. To test this, developing cortical neurons were challenged with both soluble CSPGs and CSPG-positive stripe substrates in vitro. Soluble CSPGs inhibited dendritic growth and cortical dendrites respected CSPG stripe boundaries, effects that could be counteracted by prior CSPG inactivation by chondroitinase. Importantly, addition of Reelin, an extracellular signaling protein highly expressed in the MZ, partially rescued dendritic growth in the presence of CSPGs. High-resolution confocal imaging revealed that the CSPG-enriched areas of the MZ spatially correspond with the areas of reduced dendritic density in the Reelin null (reeler) cortex compared with controls. Chondroitinase injections into reeler explants resulted in increased dendritic growth into the MZ, recovering to near wild-type levels. Activation of the serine threonine kinase Akt is required for Reelin-dependent dendritic growth and we find that CSPGs induce Akt dephosphorylation, an effect that can be counteracted by Reelin addition. In contrast, CSPG application had no effect on the cytoplasmic adaptor Dab1, which is rapidly phosphorylated in response to Reelin and is upstream of Akt. These findings suggest CSPGs do inhibit cortical dendritic growth, but this effect can be counteracted by Reelin signaling.

Neurocan Contributes to Perineuronal Net Development

Perineuronal nets (PNs) are matrix molecule assemblies surrounding neuronal somata, dendrites and axon initial segments in a lattice-like appearance. PN molecules are involved in many structural and physiological processes during development and in adulthood, suggesting a crucial role in normal brain function. Neurocan, as one of the main PN proteoglycans, is suggested to control important developmental processes of neuronal tissue. This statement relies on thorough and excellent experimental work mainly conducted in reduced systems, such as cell cultures. However, previous data collected in neurocan-deficient mice do not seem to support neurocan's role in development since brain development in general and the formation of PNs especially in the hippocampus were reported to be undisturbed in neurocan-deficient mice. Here, we aim to re-address the role of neurocan in developmental processes by investigating the influence of neurocan on PN formation in the medial nucleus of the trapezoid body, a PN-enriched nucleus in the auditory brainstem, using neurocan-deficient mice. Immunohistochemical and biochemical analyses demonstrate that neurocan controls the regulation of PN development by influencing mRNA and protein quantity of various PN molecules. Resulting alterations in PN fine structure are critical for PN function as estimated by reduced amount of GAD65/67 and prolongation of synaptic transmission delay of calyx of Held synapses. Thus, neurocan contributes to proper PN formation and synapse physiology in the MNTB.

Advances in the Signaling Pathways Downstream of Glial-Scar Axon Growth Inhibitors

Axon growth inhibitors generated by reactive glial scars play an important role in failure of axon regeneration after CNS injury in mature mammals. Among the inhibitory factors, chondroitin sulfate proteoglycans (CSPGs) are potent suppressors of axon regeneration and are important molecular targets for designing effective therapies for traumatic brain injury or spinal cord injury (SCI). CSPGs bind with high affinity to several transmembrane receptors, including two members of the leukocyte common antigen related (LAR) subfamily of receptor protein tyrosine phosphatases (RPTPs). Recent studies demonstrate that multiple intracellular signaling pathways downstream of these two RPTPs mediate the growth-inhibitory actions of CSPGs. A better understanding of these signaling pathways may facilitate development of new and effective therapies for CNS disorders characterized by axonal disconnections. This review will focus on recent advances in the downstream signaling pathways of scar-mediated inhibition and their potential as the molecular targets for CNS repair.

MiR-615 Regulates NSC Differentiation In Vitro and Contributes to Spinal Cord Injury Repair by Targeting LINGO-1

LINGO-1(LRR and Ig domain-containing NOGO receptor interacting protein 1) is a viable target for spinal cord injury (SCI) repair due to its potent negative regulation in neuron survival and axonal regeneration. Although promising, the intracellular mechanism underlying LINGO-1 regulation is unclear. Here, we identified miR-615 as a potential microRNA (miRNA) that directly targets LINGO-1 by binding its 3'-untranslated region (3'-UTR) and caused the translation inhibition of LINGO-1. MiR-615 negatively regulated LINGO-1 during neural stem cell (NSC) differentiation and facilitated its neuronal differentiation in vitro. Interestingly, compared to the control, neurons differentiated from miR-615-treated NSCs were immature with short processes. Further results showed LINGO-1/epidermal growth factor receptor (EGFR) signaling may be involved in this process, as blockade of EGFR using specific antagonist resulted in mature neurons with long processes. Furthermore, intrathecal administration of miR-615 agomir in SCI rats effectively knocked down LINGO-1, increased neuronal survival, enhanced axonal extension and myelination, and improved recovery of hindlimbs motor functions. This work thus uncovers miR-615 as an effective miRNA that regulates LINGO-1 in NSC and SCI animals, and suggests miR-615 as a potential therapeutic target for traumatic central nervous system (CNS) injury.

Upregulating Lin28a Promotes Axon Regeneration in Adult Mice with Optic Nerve and Spinal Cord Injury

Severed CNS axons fail to regenerate in adult mammals and there are no effective regenerative strategies to treat patients with CNS injuries. Several genes, including phosphatase and tensin homolog (PTEN) and Krüppel-like factors, regulate intrinsic growth capacity of mature neurons. The Lin28 gene is essential for cell development and pluripotency in worms and mammals. In this study, we evaluated the role of Lin28a in regulating regenerative capacity of diverse populations of CNS neurons in adult mammals. Using a neuron-specific Thy1 promoter, we generated transgenic mice that overexpress Lin28a protein in multiple populations of projection neurons, including corticospinal tracts and retinal ganglion cells. We demonstrate that upregulation of Lin28a in transgenic mice induces significant long distance regeneration of both corticospinal axons and the optic nerve in adult mice. Importantly, overexpression of Lin28a by post-injury treatment with adeno-associated virus type 2 (AAV2) vector stimulates dramatic regeneration of descending spinal tracts and optic nerve axons after lesions. Upregulation of Lin28a also enhances activity of the Akt signaling pathway in mature CNS neurons. Therefore, Lin28a is critical for regulating growth capacity of multiple CNS neurons and may become an important molecular target for treating CNS injuries.

Chondroitin sulfate proteoglycan represses neural stem/progenitor cells migration via PTPσ/α-actinin4 signaling pathway

Neural stem/progenitor cells (NSPCs) are a promising candidate for the cell-replacement therapy after central nervous system (CNS) injury. However, the short of sufficient NSPCs migration and integration into the lesions is an essential challenge for cell-based therapy after CNS injury due to the disturbance of local environmental homeostasis. Chondroitin sulfate proteoglycan (CSPG) is obviously accumulated at the lesions and destroyed local homeostasis after CNS injury. The previous study has demonstrated that the CSPG is a dominating ingredient inhibiting axonal regrowth of newly born neurons after CNS injury. NSPCs, a strain of special neural subtypes, hold the capacity of leading processes formation to regulate NSPCs migration, which has the same mechanism as axonal regrowth. Hence, it is worth investigating the effect of CSPG on NSPCs migration and its underlying mechanism. Here, different concentration of CSPG was used to evaluate its effect on NSPCs migration. The results showed that the CSPG suppressed NSPCs migration in a dose-dependent manner from 10 to 80 µg/mL with phase-contrast microscopy after 24 hours. Meanwhile, transwell assays were performed to certify the above results. Our data indicated that the 40 µg/mL CSPG obviously suppressed NSPCs migration via decreasing filopodia formation using immunofluorescence staining. Furthermore, data indicated that the 40 µg/mL CSPG upregulated protein tyrosine phosphatase receptor σ (PTPσ) expression and decreased α-actinin4 (ACTN4) expression through immunofluorescence, reverse transcription polymerase chain reaction, and Western blot assays. While the inhibitory effect was attenuated using PTPσ-specific small interfering RNA. In addition, data demonstrated that the 40 µg/mL CSPG facilitated NSPCs differentiation into glial fibrillary acidic protein-positive cells and inhibited NSPCs directing into MAP2- and MBP-positive cells. Collectively, these data demonstrated that the CSPG suppressed NSPCs migration through PTPσ/ACTN4 signaling pathway. Meanwhile, CSPG facilitated NSPCs differentiation into astrocytes and inhibited NSPCs directing into neurons and oligodendrocytes.

Docking software performance in protein-glycosaminoglycan systems

We present a benchmarking study for protein-glycosaminoglycan systems with eight docking programs: Dock, rDock, ClusPro, PLANTS, HADDOCK, Hex, SwissDock and ATTRACT. We used a non-redundant representative dataset of 28 protein-glycosaminoglycan complexes with experimentally available structures, where a glycosaminoglycan ligand was longer than a trimer. Overall, the ligand binding poses could be correctly predicted in many cases by the tested docking programs, however the ranks of the docking poses are often poorly assigned. Our results suggest that Dock program performs best in terms of the pose placement, has the most suitable scoring function, and its performance did not depend on the ligand size. This suggests that the implementation of the electrostatics as well as the shape complementarity procedure in Dock are the most suitable for docking glycosaminoglycan ligands. We also analyzed how free energy patterns of the benchmarking complexes affect the performance of the evaluated docking software.

Study on the pathological and biomedical characteristics of spinal cord injury by confocal Raman microspectral imaging

Confocal Raman microspectral imaging (CRMI) in combination with multivariate analysis was used to study pathological progression after spinal cord injury (SCI). By establishing moderate contusion in rat models, ex vivo longitudinal spinal cord tissue sections were prepared for microspectroscopic analysis. Comparative studies were then performed to determine the pathological distinctions among before injury (BI), one day post-injury (1 DPI), seven days post-injury (7 DPI), and 14 days post-injury (14 DPI) groups. Multivariate analysis algorithms, including K-mean cluster analysis (KCA) and principal component analysis (PCA), were conducted to highlight biochemical and structural variations after tissue damage. It is confirmed that typical spectral features and profiles can illustrate some fundamental and significant pathological processes post-injury, such as neuron apoptosis, hemorrhage, demyelination, and chondroitin sulfate proteoglycans (CSPGs) upregulation. Further, by establishing spectra-structure correlations, the reconstructed spectral images revealed some minute and important morphological characteristics following tissue injury, such as glial scar formation surrounding the cavity structure. The observed spectral phenomena also provide a detailed view on relevant pathobiological factors, which are involved in the spread of secondary damage after traumatic spinal cord injury. Our findings not only provide a spectral perspective to the well-known cellular mechanisms underlying SCI, but further provide a sound basis for developing real-time Raman methodologies to evaluate the prognostic factors and therapeutic results of SCI.

Oleoylethanolamide inhibits glial activation via moudulating PPARα and promotes motor function recovery after brain ischemia

Glial activation and scar formation impede the neurological function recovery after cerebral ischemia. Oleoylethanolamide (OEA), a bioactive lipid mediator, shows neuroprotection against acute brain ischemia, however, its long-term effect, especially on glial scar formation, has not been characterized. In this research, we investigate the effect of OEA on glial activation and scar formation after cerebral ischemia in vitro and in vivo experiments. Glial scar formation in vitro model was induced by transforming growth factor β1 (TGF-β1) in C6 glial cell culture, and experiment model in vivo was induced by middle cerebral artery occlusion (MCAO) in mice. The protein expressions of the markers of glial activation (S100β, GFAP, or pSmads) and glial scar (neurocan) were detected by Western blot and/or immunofluorescence staining; To evaluate the role of PPARɑ in the effect of OEA on glial activation, the PPARɑ antagonist GW6471 was used. Behavior tests were used to assay the effect of OEA on motor function recovery 14 days after brain ischemia in mice. Our results show that OEA (10-50 μM) concentration-dependently inhibited the upregulation of S100β, GFAP, pSmads and neurocan induced by TGF-β1 in C6 glial cells. At the same time, OEA promoted the protein expression and nuclear transportation of PPARɑ in glial cells. PPARα antagonist GW6471 abolished the effect of OEA on glial activation. In addition, we found that delay administration of OEA inhibited the astrocyte activation and promoted the recovery of motor function after brain ischemia in mice. These results indicate that OEA may be developed into a new candidate for attenuating astrocytic scar formation and improving motor function after ischemic stroke.

Reactive astrocytes in multiple sclerosis impair neuronal outgrowth through TRPM7-mediated chondroitin sulfate proteoglycan production

Multiple sclerosis (MS) is a chronic inflammatory disorder of the central nervous system (CNS), characterized by inflammation‐mediated demyelination, axonal injury and neurodegeneration. The mechanisms underlying impaired neuronal function are not fully understood, but evidence is accumulating that the presence of the gliotic scar produced by reactive astrocytes play a critical role in these detrimental processes. Here, we identified astrocytic Transient Receptor Potential cation channel, subfamily M, member 7 (TRPM7), a Ca²⁺‐permeable nonselective cation channel, as a novel player in the formation of a gliotic scar. TRPM7 was found to be highly expressed in reactive astrocytes within well‐characterized MS lesions and upregulated in primary astrocytes under chronic inflammatory conditions. TRPM7 overexpressing astrocytes impaired neuronal outgrowth in vitro by increasing the production of chondroitin sulfate proteoglycans, a key component of the gliotic scar. These findings indicate that astrocytic TRPM7 is a critical regulator of the formation of a gliotic scar and provide a novel mechanism by which reactive astrocytes affect neuronal outgrowth.

Exosomes Derived from Bone Mesenchymal Stem Cells Repair Traumatic Spinal Cord Injury by Suppressing the Activation of A1 Neurotoxic Reactive Astrocytes

Mesenchymal stem cell (MSC) transplantation is now considered as an effective treatment strategy for traumatic spinal cord injury (SCI). However, several key issues remain unresolved, including low survival rates, cell dedifferentiation, and tumor formation. Recent studies have demonstrated that the therapeutic effect of transplanted stem cells is primarily paracrine mediated. Exosomes are an important paracrine factor that can be used as a direct therapeutic agent. However, there are few reports on the application of exosomes derived from bone MSCs (BMSCs-Exos) in treating SCI. In this study, we demonstrated that BMSCs-Exos possessed robust proangiogenic properties, attenuated neuronal cells apoptosis, suppressed glial scar formation, attenuated lesion size, suppressed inflammation, promoted axonal regeneration, and eventually improved functional behavioral recovery effects after traumatic SCI. Briefly, lesion size was decreased by nearly 60%, neuronal apoptosis was attenuated by nearly 70%, glial scar formation was reduced by nearly 75%, average blood vessel density was increased by nearly 60%, and axonal regeneration was increased by almost 80% at day 28 after SCI in the BMSC-Exos group compared to the control group. Using a series of in vitro functional assays, we also confirmed that treatment with BSMCs-Exos significantly enhanced human umbilical vein endothelial cell proliferation, migration, and angiogenic tubule formation, attenuated neuronal cells apoptosis, and suppressed nitric oxide release in microglia. Moreover, our study demonstrated that administration of BMSCs-Exos suppressed inflammation efficiently after traumatic SCI and suppressed activation of A1 neurotoxic reactive astrocytes. In conclusion, our study suggested that the application of BMSCs-Exos may be a promising strategy for traumatic SCI.

Astrocyte activation and reactive gliosis-A new target in stroke?

Stroke is an acute insult to the central nervous system (CNS) that triggers a sequence of responses in the acute, subacute as well as later stages, with prominent involvement of astrocytes. Astrocyte activation and reactive gliosis in the acute stage of stroke limit the tissue damage and contribute to the restoration of homeostasis. Astrocytes also control many aspects of neural plasticity that is the basis for functional recovery. Here, we discuss the concept of intermediate filaments (nanofilaments) and the complement system as two handles on the astrocyte responses to injury that both present attractive opportunities for novel treatment strategies modulating astrocyte functions and reactive gliosis.

Dextran-based biodegradable nanoparticles: an alternative and convenient strategy for treatment of traumatic spinal cord injury

Introduction

After traumatic spinal cord injury (SCI), an inhibitory environment that contains chondroitin sulfate proteoglycans (CSPGs) is formed that prevents axonal regeneration and growth.

Materials and methods

As previously reported, local administration of Taxol^® at a low concentration has shown promising abilities to promote axonal regeneration and downregulate inhibitory molecules after acute SCI. However, the application of an invasive miniosmotic pump to deliver Taxol and the Cremophor-related toxicity caused by Taxol limits the administration of Taxol.

Results

In this study, the sustained release of paclitaxel (PTX) for 7 days was achieved by incorporating PTX into acetalated dextran (Ac-DEX) nanoparticles, and the prepared PTX-loaded Ac-DEX (PTX@Ac-DEX) nanoparticles promoted neurite extension in the presence of CSPGs. In a rat SCI model, both PTX@Ac-DEX and Taxol enhanced neural regeneration, inhibited CSPGs, protected the injured spinal cord, and improved locomotor recovery. Because of the sustained release of PTX, single administration of PTX@Ac-DEX showed equal therapeutic effect with Taxol, which need to be administered for seven days using a surgically implanted miniosmotic pump.

Conclusion

Overall, this study provides an effective and convenient strategy for SCI therapy, which can improve neurite extension across an inhibitory environment and avoid Cremophor-related toxicity caused by Taxol.

Comparison of subacute and chronic scar tissues after complete spinal cord transection

Traditional views consider scar tissue formed in the lesion epicenter after severe spinal cord injury (SCI) as both a physical barrier and chemical impediment for axonal regeneration. Recently, a controversial opinion suggested that astrocyte scar formation aids rather than prevents axonal regeneration in the CNS. Here, following complete transection of the thoracic spinal cord (T8) in rats, we found that scar tissue showed greater growth factor expression at 2 weeks than 8 weeks post-SCI. Further, tandem mass tag (TMT)-based quantitative proteomic analysis revealed that the components of scar tissue formed in the subacute phase are quite different from that formed in the chronic phase. We also found significantly increased axonal regrowth of sensory axons into the lesion center after chronically formed scar tissue was removed. This indicates that scar tissue formed at the chronic phase actually inhibits axonal regeneration, and that chronic removal of scar tissue may have clinical significance and benefit for SCI repair. Taken together, our study suggests that the features and roles of subacute and chronic scar tissues formed post-SCI is different and scar tissue-targeted strategies for spinal cord regeneration cannot be generalized.

An in vitro study of non-aligned or aligned electrospun poly(methyl methacrylate) nanofibers as primary rat astrocytes-loading scaffold

After spinal cord injury (SCI), functional regeneration of neurites is hard to achieve due to the existence of glial scar, meanwhile astrocytes are believed important for post injury neuroregeneration, therefore how to handle the contradictory roles of astrocytes remains a problem for better neurogenesis. In this report, aligned electrospun poly(methyl methacrylate) (PMMA) nanofibers were assessed as an astrocytes-loading scaffold in vitro. We found that cell adherence and cell expansion of astrocytes could be supported by PMMA nanofibers, which topographic features could obviously influence the growth manner of astrocytes, and cells on aligned nanofibers finally formed longer and highly aligned processes along the axis of substrate fibers compared with cells cultured on film and non-aligned nanofibers. Regarding the relationship between astrocytes and substratum nanofibers, different topographic feature of substrate nanofibers showed varying degree of impact on cell expansion. On non-aligned nanofibers astrocytes expanded along the orientation of nanofibers early, while on aligned nanofibers astrocytes complied with the cues of nanofibers gradually with time. The results strengthen the rationale that aligned nanofibers could serve as the candidate of implantable scaffold after SCI, and it may relieve the stress of proliferated astrocytes by manipulating the growth pattern of astrocytes through its topographic features.