Dissecting spinal cord regeneration

Thrombin induces morphological and inflammatory astrocytic responses via activation of PAR1 receptor

Spinal cord injury (SCI) will result in the significant elevation of thrombin production at lesion site via either breakage of blood-spinal cord barrier or upregulated expression within nerve cells. Thrombin-induced activation of the protease activated receptors (PARs) evokes various pathological effects that deteriorate the functional outcomes of the injured cord. The cellular consequences of thrombin action on the astrocytes, as well as the underlying mechanism are not fully elucidated by far. In the present study, SCI model of rats was established by contusion, and primary astrocytes were isolated for culture from newborn rats. The expression levels of thrombin and PAR1 receptor at lesion sites of the spinal cord were determined. The primary astrocytes cultured in vitro were stimulated with different concentration of thrombin, and the resultant morphological changes, inflammatory astrocytic responses, as well as PAR1-activated signal pathway of astrocytes were accordingly examined using various agonists or antagonists of the receptor. Thrombin was found to reverse astrocytic stellation, promote proliferation but inhibit migration of astrocytes. Furthermore, the serine protease was shown to facilitate inflammatory response of astrocytes through regulation of MAPKs/NFκB pathway. Our results have provided the morphological evidence of astrocytic reactivity in response to thrombin stimulation and its neuroinflammatory effects following SCI, which will be indicative for the fundamental insights of thrombin-induced neuropathology.

Fibrinogen regulates lesion border-forming reactive astrocyte properties after vascular damage

Reactive astrocytes at the border of damaged neuronal tissue organize into a barrier surrounding the fibrotic lesion core, separating this central region of inflammation and fibrosis from healthy tissue. Astrocytes are essential to form the border and for wound repair but interfere with neuronal regeneration. However, the mechanisms driving these astrocytes during central nervous system (CNS) disease are unknown. Here we show that blood-derived fibrinogen is enriched at the interface of lesion border-forming elongated astrocytes after cortical brain injury. Anticoagulant treatment depleting fibrinogen reduces astrocyte reactivity, extracellular matrix deposition and inflammation with no change in the spread of inflammation, whereas inhibiting fibrinogen conversion into fibrin did not significantly alter astrocyte reactivity, but changed the deposition of astrocyte extracellular matrix. RNA sequencing of fluorescence-activated cell sorting-isolated astrocytes of fibrinogen-depleted mice after cortical injury revealed repressed gene expression signatures associated with astrocyte reactivity, extracellular matrix deposition and immune-response regulation, as well as increased gene expression signatures associated with astrocyte metabolism and astrocyte-neuron communication. Systemic pharmacologic depletion of fibrinogen resulted in the absence of elongated, border-forming astrocytes and increased the survival of neurons in the lesion core after cortical injury. These results identify fibrinogen as a critical trigger for lesion border-forming astrocyte properties in CNS disease.

Axon Regeneration: A Subcellular Extension in Multiple Dimensions

Axons are a unique cellular structure that allows for the communication between neurons. Axon damage compromises neuronal communications and often leads to functional deficits. Thus, developing strategies that promote effective axon regeneration for functional restoration is highly desirable. One fruitful approach is to dissect the regenerative mechanisms used by some types of neurons in both mammalian and nonmammalian systems that exhibit spontaneous regenerative capacity. Additionally, numerous efforts have been devoted to deciphering the barriers that prevent successful axon regeneration in the most regeneration-refractory system-the adult mammalian central nervous system. As a result, several regeneration-promoting strategies have been developed, but significant limitations remain. This review is aimed to summarize historic progression and current understanding of this exciting yet incomplete endeavor.

Human spinal cord in vitro differentiation pace is initially maintained in heterologous embryonic environments

Species-specific differentiation pace in vitro indicates that some aspects of neural differentiation are governed by cell intrinsic properties. Here we describe a novel in vitro human neural-rosette assay that recapitulates dorsal spinal cord differentiation but proceeds more rapidly than in the human embryo, suggesting that it lacks endogenous signalling dynamics. To test whether in vitro conditions represent an intrinsic differentiation pace, human iPSC-derived neural rosettes were challenged by grafting into the faster differentiating chicken embryonic neural tube iso-chronically, or hetero-chronically into older embryos. In both contexts in vitro differentiation pace was initially unchanged, while long-term analysis revealed iso-chronic slowed and hetero-chronic conditions promoted human neural differentiation. Moreover, hetero-chronic conditions did not alter the human neural differentiation programme, which progressed to neurogenesis, while the host embryo advanced into gliogenesis. This study demonstrates that intrinsic properties limit human differentiation pace, and that timely extrinsic signals are required for progression through an intrinsic human neural differentiation programme.

Aldehyde-methacrylate-hyaluronan profited hydrogel system integrating aligned and viscoelastic cues for neurogenesis

Either oriented architecture or viscoelasticity is pivotal to neurogenesis, thus, native neural extracellular matrix derived-hyaluronan hydrogels with nano-orientation and viscoelasticity recapitulated might be instructive for neurogenesis, however it is still unexploited. Herein, based on aldehyde-methacrylate difunctionalized hyaluronan, by integrating imine kinetic modulation and microfluidic biofabrication, we construct a hydrogel system with orthogonal viscoelasticity and nano-topography. We then find the positive synergy effects of matrix nano-orientation and viscoelasticity not only on neurites outgrowth and elongation of neural cells, but also on neuronal differentiation of stem cells. Moreover, by implanting viscoelastic and nano-aligned hydrogels into lesion sites, we demonstrate the enhanced repair of spinal cord injury, including ameliorated pathological microenvironment, facilitated endogenous neurogenesis and functional axons regeneration as well as motor function restoration. This work supplies universal platform for preparing neuronal inducing hyaluronan-based hydrogels which might serve as promising therapeutic strategies for nerve injury.

Strategies for effective neural circuit reconstruction after spinal cord injury: use of stem cells and biomaterials

Spinal cord injury (SCI), a serious disease of the central nervous system, often with irreversible loss of motor or sensory functions. Failure of axon connection and inhibition of microenvironment after SCI severely hinder the regeneration of damaged tissue and neuron function. Therefore, the new perspective of treatment of spinal cord injury is the reconstruction of neural circuit. Stem cells are a kind of cells with differentiation potential. They reconstruct local circulation by differentiating into neurons to replace damaged cells. It can also secrete various factors to regulate the host microenvironment and play a therapeutic role. Biomaterials can fill the cavity at the site of spinal cord injury, load therapeutic drugs, provide adsorption sites for transplanted cells and play a bridging role. In this review, the therapeutic role of stem cells and biomaterials is discussed, together with their properties, advantages, limitations, and future perspectives, providing a reference for basic and clinical research on SCI treatment.

Maltol Promotes Mitophagy and Inhibits Oxidative Stress via the Nrf2/PINK1/Parkin Pathway after Spinal Cord Injury

Spinal cord injury (SCI), a fatal disease in the central nervous system, is characteristic of weak neuronal regeneration ability and complex pathological progress. Activation of oxidative stress (OS) and apoptosis-mediated cell death significantly contributes to the progression of SCI. Current evidence suggests that maltol exerts natural antioxidative properties via obstructing OS and apoptosis. However, the significant effect of maltol on SCI treatment has never been evaluated yet. In our current study, we explored maltol administration that could trigger the expression of Nrf2 and promote the retranslocation of Nrf2 from the cytosol to the nucleus, which can subsequently obstruct OS signal and apoptosis-mediated neuronal cell death after SCI. Furthermore, we found that maltol treatment enhances PINK1/Parkin-mediated mitophagy in PC12 cells, facilitating the recovery of mitochondrial functions. Our findings propose that maltol could be a promising therapeutic candidate for the treatment and management of SCI.

The Role of Biomaterials in Peripheral Nerve and Spinal Cord Injury: A Review

Peripheral nerve and spinal cord injuries are potentially devastating traumatic conditions with major consequences for patients’ lives. Severe cases of these conditions are currently incurable. In both the peripheral nerves and the spinal cord, disruption and degeneration of axons is the main cause of neurological deficits. Biomaterials offer experimental solutions to improve these conditions. They can be engineered as scaffolds that mimic the nerve tissue extracellular matrix and, upon implantation, encourage axonal regeneration. Furthermore, biomaterial scaffolds can be designed to deliver therapeutic agents to the lesion site. This article presents the principles and recent advances in the use of biomaterials for axonal regeneration and nervous system repair.

Melatonin Synergizes With Methylprednisolone to Ameliorate Acute Spinal Cord Injury

Methylprednisolone (MP) is the drug of choice for treating spinal cord injury (SCI), but the aggressive dosage regimen used often results in adverse side effects. Therefore, MP should be combined with other drugs to lower the required dose. Melatonin is effective in alleviating nerve damage and inhibiting axonal degeneration. The combination of melatonin and half-dose methylprednisolone (HMP) for spinal cord injury treatment has never been reported. In this study, we established a rat model of T9 spinal cord injury by the Allen's method and assessed the synergistic therapeutic effects of melatonin and HMP by factorial design. Our results demonstrated that melatonin could synergize with HMP to ameliorate acute SCI through PI3K-AKT1 pathway. Combining melatonin with HMP significantly reduced the standard-dose of methylprednisolone and limited its adverse reactions, representing a promising option for treating acute SCI.

Reactive Astrocytes in Central Nervous System Injury: Subgroup and Potential Therapy

Traumatic central nervous system (CNS) injury, which includes both traumatic brain injury (TBI) and spinal cord injury (SCI), is associated with irreversible loss of neurological function and high medical care costs. Currently, no effective treatment exists to improve the prognosis of patients. Astrocytes comprise the largest population of glial cells in the CNS and, with the advancements in the field of neurology, are increasingly recognized as having key functions in both the brain and the spinal cord. When stimulated by disease or injury, astrocytes become activated and undergo a series of changes, including alterations in gene expression, hypertrophy, the loss of inherent functions, and the acquisition of new ones. Studies have shown that astrocytes are highly heterogeneous with respect to their gene expression profiles, and this heterogeneity accounts for their observed context-dependent phenotypic diversity. In the inured CNS, activated astrocytes play a dual role both as regulators of neuroinflammation and in scar formation. Identifying the subpopulations of reactive astrocytes that exert beneficial or harmful effects will aid in deciphering the pathological mechanisms underlying CNS injuries and ultimately provide a theoretical basis for the development of effective strategies for the treatment of associated conditions. Following CNS injury, as the disease progresses, astrocyte phenotypes undergo continuous changes. Although current research methods do not allow a comprehensive and accurate classification of astrocyte subpopulations in complex pathological contexts, they can nonetheless aid in understanding the roles of astrocytes in disease. In this review, after a brief introduction to the pathology of CNS injury, we summarize current knowledge regarding astrocyte activation following CNS injury, including: (a) the regulatory factors involved in this process; (b) the functions of different astrocyte subgroups based on the existing classification of astrocytes; and (c) attempts at astrocyte-targeted therapy.

The role of electrical stimulation for rehabilitation and regeneration after spinal cord injury

Electrical stimulation is used to elicit muscle contraction and can be utilized for neurorehabilitation following spinal cord injury when paired with voluntary motor training. This technology is now an important therapeutic intervention that results in improvement in motor function in patients with spinal cord injuries. The purpose of this review is to summarize the various forms of electrical stimulation technology that exist and their applications. Furthermore, this paper addresses the potential future of the technology.

Neuroinduction and neuroprotection co-enhanced spinal cord injury repair based on IL-4@ZIF-8-loaded hyaluronan-collagen hydrogels with nano-aligned and viscoelastic cues

Spontaneous recovery after spinal cord injury (SCI) is extremely limited since the severe inflammatory responses lead to secondary damage, and the diseased extracellular matrix (ECM) fails to provide inductive cues...

Loss-of-function manipulations to identify roles of diverse glia and stromal cells during CNS scar formation

Scar formation is the replacement of parenchymal cells by stromal cells and fibrotic extracellular matrix. Until as recently as 25 years ago, little was known about the major functional contributions of different neural and non-neural cell types in the formation of scar tissue and tissue fibrosis in the CNS. Concepts about CNS scar formation are evolving rapidly with the availability of different types of loss-of-function technologies that allow mechanistic probing of cellular and molecular functions in models of CNS disorders in vivo. Such loss-of-function studies are beginning to reveal that scar formation and tissue fibrosis in the CNS involves complex interactions amongst multiple types of CNS glia and non-neural stromal cells. For example, attenuating functions of the CNS resident glial cells, astrocytes or microglia, can disrupt the formation of limitans borders that form around stromal cell scars, which leads to increased spread of inflammation, increased loss of neural tissue, and increased fibrosis. Insights are being gained into specific neuropathological mechanisms whereby specific dysfunctions of different types of CNS glia could cause or contribute to disorder-related tissue pathology and dysfunction. CNS glia, as well as fibrosis-producing stromal cells, are emerging as potential major contributors to diverse CNS disorders either through loss- or gain-of-functions, and are thereby emerging as important potential targets for interventions. In this article, we will review and discuss the effects on CNS scar formation and tissue repair of loss-of-function studies targeted at different specific cell types in various disorder models in vivo.

Downregulation of EphB2 by RNA interference attenuates glial/fibrotic scar formation and promotes axon growth

The rapid formation of a glial/fibrotic scar is one of the main factors hampering axon growth after spinal cord injury. The bidirectional EphB2/ephrin-B2 signaling of the fibroblast-astrocyte contact-dependent interaction is a trigger for glial/fibrotic scar formation. In the present study, a new in vitro model was produced by coculture of fibroblasts and astrocytes wounded by scratching to mimic glial/fibrotic scar-like structures using an improved slide system. After treatment with RNAi to downregulate EphB2, changes in glial/fibrotic scar formation and the growth of VSC4.1 motoneuron axons were examined. Following RNAi treatment, fibroblasts and astrocytes dispersed without forming a glial/fibrotic scar-like structure. Furthermore, the expression levels of neurocan, NG2 and collagen I in the coculture were reduced, and the growth of VSC4.1 motoneuron axons was enhanced. These findings suggest that suppression of EphB2 expression by RNAi attenuates the formation of a glial/fibrotic scar and promotes axon growth. This study was approved by the Laboratory Animal Ethics Committee of Jiangsu Province, China (approval No. 2019-0506-002) on May 6, 2019.

Emerging Therapies in Friedreich's Ataxia: A Review

Friedreich's ataxia (FRDA) is an inherited, neurodegenerative disease that typically presents in childhood and results in progressive gait and limb ataxia, with the extraneural features of hypertrophic cardiomyopathy, diabetes and scoliosis. The genetic defect results in a deficiency of frataxin protein, which is important for mitochondrial function, especially in the brain and heart. Drug development has approached FRDA through pathways addressing oxidative stress, mitochondrial dysfunction, frataxin protein deficiency and DNA transcriptional deficiency, paving the way for the first disease-modifying drugs for FRDA.

A comparative study of different stem cells transplantation for spinal cord injury: a systematic review and network meta-analysis

OBJECTIVE

This study aimed to evaluate the efficacy and safety of different stem cell types for spinal cord injury (SCI) therapy and find out the superior treatment for SCI.

METHODS

A systematic literature search was performed using PubMed, Embase, the Cochrane Library, Web of Science, VIP, CNKI, and Wan Fang from database initiation to January 30, 2021. A Bayesian network meta-analysis was performed using ADDIS software. The PROSPERO registration number was CRD42020129635.

RESULTS

Twelve studies with 642 patients were enrolled in this study. Network meta-analysis revealed that bone mesenchymal stem cells combined with rehabilitation training (BMSCs + R) were significantly more effective than rehabilitation training alone (R) in improving American Spinal Injury Association (ASIA) impairment scale (AIS)-grading improvement rate (OR=94.25, 95% CI: 6.71 to 9321.95), ASIA motor score (WMD=6.67, 95% CI: 0.83 to 12.73), ASIA Sensory Functional score (WMD=12.41, 95%CI: 3.42 to 21.72), and Barthel Index (BI) score (WMD=7.24, 95% CI: 0.21 to 14.30). However, no statistically significant differences were observed between marrow mononuclear cells combined with rehabilitation training (MNCs + R), umbilical cord-derived mesenchymal stem cells combined with rehabilitation training (UCMSCs + R), or UCMSCs alone and R on all indicators. In terms of safety, there were no serious and permanent adverse effects after transplantation of BMSCs, MNCs, or UCMSCs.

CONCLUSION

BMSCs + R may be superior to the other stem cell treatments for SCI in improving AIS grading, ASIA motor score, ASIA Sensory Functional score, and BI score. The therapeutic effects of UCMSCs and MNCs remain to be confirmed.

Peptide ligands targeting FGF receptors promote recovery from dorsal root crush injury via AKT/mTOR signaling

Background: Fibroblast growth factor receptors (FGFRs) are key targets for nerve regeneration and repair. The therapeutic effect of exogenous recombinant FGFs in vivo is limited due to their high molecular weight. Small peptides with low molecular weight, easy diffusion, low immunogenicity, and nontoxic metabolite formation are potential candidates. The present study aimed to develop a novel low-molecular-weight peptide agonist of FGFR to promote nerve injury repair.

Methods: Phage display technology was employed to screen peptide ligands targeting FGFR2. The peptide ligand affinity for FGFRs was detected by isothermal titration calorimetry. Structural biology-based computer virtual analysis was used to characterize the interaction between the peptide ligand and FGFR2. The peptide ligand effect on axon growth, regeneration, and behavioral recovery of sensory neurons was determined in the primary culture of sensory neurons and dorsal root ganglia (DRG) explants in vitro and a rat spinal dorsal root injury (DRI) model in vivo. The peptide ligand binding to other membrane receptors was characterized by surface plasmon resonance (SPR) and liquid chromatography-mass spectrometry (LC-MS)/MS. Intracellular signaling pathways primarily affected by the peptide ligand were characterized by phosphoproteomics, and related pathways were verified using specific inhibitors.

Results: We identified a novel FGFR-targeting small peptide, CH02, with seven amino acid residues. CH02 activated FGFR signaling through high-affinity binding with the extracellular segment of FGFRs and also had an affinity for several receptor tyrosine kinase (RTK) family members, including VEGFR2. In sensory neurons cultured in vitro, CH02 maintained the survival of neurons and promoted axon growth. Simultaneously, CH02 robustly enhanced nerve regeneration and sensory-motor behavioral recovery after DRI in rats. CH02-induced activation of FGFR signaling promoted nerve regeneration primarily via AKT and ERK signaling downstream of FGFRs. Activation of mTOR downstream of AKT signaling augmented axon growth potential in response to CH02.

Conclusion: Our study revealed the significant therapeutic effect of CH02 on strengthening nerve regeneration and suggested a strategy for treating peripheral and central nervous system injuries.

Identification of key genes involved in recovery from spinal cord injury in adult zebrafish

Zebrafish are an effective vertebrate model to study the mechanisms underlying recovery after spinal cord injury. The subacute phase after spinal cord injury is critical to the recovery of neurological function, which involves tissue bridging and axon regeneration. In this study, we found that zebrafish spontaneously recovered 44% of their swimming ability within the subacute phase (2 weeks) after spinal cord injury. During this period, we identified 7762 differentially expressed genes in spinal cord tissue: 2950 were up-regulated and 4812 were down-regulated. These differentially expressed genes were primarily concentrated in the biological processes of the respiratory chain, axon regeneration, and cell-component morphogenesis. The genes were also mostly involved in the regulation of metabolic pathways, the cell cycle, and gene-regulation pathways. We verified the gene expression of two differentially expressed genes, clasp2 up-regulation and h1m down-regulation, in zebrafish spinal cord tissue in vitro. Pathway enrichment analysis revealed that up-regulated clasp2 functions similarly to microtubule-associated protein, which is responsible for axon extension regulated by microtubules. Down-regulated h1m controls endogenous stem cell differentiation after spinal cord injury. This study provides new candidate genes, clasp2 and h1m, as potential therapeutic intervention targets for spinal cord injury repair by neuroregeneration. All experimental procedures and protocols were approved by the Animal Ethics Committee of Tianjin Institute of Medical & Pharmaceutical Sciences (approval No. IMPS-EAEP-Q-2019-02) on September 24, 2019.

Antioxidative and Conductive Nanoparticles-Embedded Cell Niche for Neural Differentiation and Spinal Cord Injury Repair

Following spinal cord injury (SCI), the transmission of electrical signals is interrupted, and an oxidative microenvironment is generated, hindering nerve regeneration and functional recovery. The strategies of regulating oxidative pathological microenvironment while restoring endogenous electrical signal transmission hold promise for SCI treatment. However, challenges are still faced in simply fabricating bioactive scaffolds with both antioxidation and conductivity. Herein, aiming to construct an antioxidative and conductive microenvironment for nerve regeneration, the difunctional polypyrrole (PPy) nanoparticles were developed and incorporated into bioactive collagen/hyaluronan hydrogel. Owing to the embedded PPy in hydrogel, the encapsulated bone marrow mesenchymal stem cells (BMSCs) can be protected from oxidative damage, and their neuronal differentiation was promoted by the synergy between conductivity and electrical stimulation, which is proved to be related to PI3K/Akt and the mitogen-activated protein kinase (MAPK) pathway. In SCI rats, the BMSC-laden difunctional hydrogel restored the transmission of bioelectric signals and inhibited secondary damage, thereby facilitating neurogenesis, resulting in prominent nerve regeneration and functional recovery. Overall, taking advantage of a difunctional nanomaterial to meet two essential requirements in SCI repair, this work provides intriguing insights into the design of biomaterials for nerve regeneration and tissue engineering.

Engineering spinal cord repair

Neurological damage caused by spinal cord injury in humans has been observed for over three thousand years and impacts the lives of several hundred thousand people worldwide. Despite this prevalence and its associated consequences, there is no treatment to repair the injured spinal cord. Evidence gathered over the last several decades has provided mechanistic information on the complex cascade of events following traumatic spinal cord injury and this is paving the way towards mechanism based repair strategies. In this review, we summarize state-of-the-art biological and engineering repair strategies and posit that complete repair will be dependent on cataloguing the molecular signatures and growth requirements of the different neuron subpopulations in the brain and spinal cord.

Stem cell-derived neuronal relay strategies and functional electrical stimulation for treatment of spinal cord injury

The inability of adult mammals to recover function lost after severe spinal cord injury (SCI) has been known for millennia and is mainly attributed to a failure of brain-derived nerve fiber regeneration across the lesion. Potential approaches to re-establishing locomotor function rely on neuronal relays to reconnect the segregated neural networks of the spinal cord. Intense research over the past 30 years has focused on endogenous and exogenous neuronal relays, but progress has been slow and the results often controversial. Treatments with stem cell-derived neuronal relays alone or together with functional electrical stimulation offer the possibility of improved repair of neuronal networks. In this review, we focus on approaches to recovery of motor function in paralyzed patients after severe SCI based on novel therapies such as implantation of stem cell-derived neuronal relays and functional electrical stimulation. Recent research progress offers hope that SCI patients will one day be able to recover motor function and sensory perception.

Mechanisms of Stem Cell Therapy in Spinal Cord Injuries

Every year, 0.93 million people worldwide suffer from spinal cord injury (SCI) with irretrievable sequelae. Rehabilitation, currently the only available treatment, does not restore damaged tissues; therefore, the functional recovery of patients remains limited. The pathophysiology of spinal cord injuries is heterogeneous, implying that potential therapeutic targets differ depending on the time of injury onset, the degree of injury, or the spinal level of injury. In recent years, despite a significant number of clinical trials based on various types of stem cells, these aspects of injury have not been effectively considered, resulting in difficult outcomes of trials. In a specialty such as cancerology, precision medicine based on a patient’s characteristics has brought indisputable therapeutic advances. The objective of the present review is to promote the development of precision medicine in the field of SCI. Here, we first describe the multifaceted pathophysiology of SCI, with the temporal changes after injury, the characteristics of the chronic phase, and the subtypes of complete injury. We then detail the appropriate targets and related mechanisms of the different types of stem cell therapy for each pathological condition. Finally, we highlight the great potential of stem cell therapy in cervical SCI.

Hybrid SMART spheroids to enhance stem cell therapy for CNS injuries

Although stem cell therapy holds enormous potential for treating debilitating injuries and diseases in the central nervous system, low survival and inefficient differentiation have restricted its clinical applications. Recently, 3D cell culture methods, such as stem cell–based spheroids and organoids, have demonstrated advantages by incorporating tissue-mimetic 3D cell-cell interactions. However, a lack of drug and nutrient diffusion, insufficient cell-matrix interactions, and tedious fabrication procedures have compromised their therapeutic effects in vivo. To address these issues, we developed a biodegradable nanomaterial-templated 3D cell assembly method that enables the formation of hybrid stem cell spheroids with deep drug delivery capabilities and homogeneous incorporation of 3D cell-matrix interactions. Hence, high survival rates, controlled differentiation, and functional recovery were demonstrated in a spinal cord injury animal model. Overall, our hybrid stem cell spheroids represent a substantial development of material-facilitated 3D cell culture systems and can pave the way for stem cell–based treatment of CNS injuries.

Fibrotic Scar After Spinal Cord Injury: Crosstalk With Other Cells, Cellular Origin, Function, and Mechanism

The failure of axonal regeneration after spinal cord injury (SCI) results in permanent loss of sensorimotor function. The persistent presence of scar tissue, mainly fibrotic scar and astrocytic scar, is a critical cause of axonal regeneration failure and is widely accepted as a treatment target for SCI. Astrocytic scar has been widely investigated, while fibrotic scar has received less attention. Here, we review recent advances in fibrotic scar formation and its crosstalk with other main cellular components in the injured core after SCI, as well as its cellular origin, function, and mechanism. This study is expected to provide an important basis and novel insights into fibrotic scar as a treatment target for SCI.

Increasing toll-like receptor 2 on astrocytes induced by Schwann cell-derived exosomes promotes recovery by inhibiting CSPGs deposition after spinal cord injury

Background

Traumatic spinal cord injury (SCI) is a severely disabling disease that leads to loss of sensation, motor, and autonomic function. As exosomes have great potential in diagnosis, prognosis, and treatment of SCI because of their ability to easily cross the blood–brain barrier, the function of Schwann cell-derived exosomes (SCDEs) is still largely unknown.

Methods

A T10 spinal cord contusion was established in adult female mice. SCDEs were injected into the tail veins of mice three times a week for 4 weeks after the induction of SCI, and the control group was injected with PBS. High-resolution transmission electron microscope and western blot were used to characterize the SCDEs. Toll-like receptor 2 (TLR2) expression on astrocytes, chondroitin sulfate proteoglycans (CSPGs) deposition and neurological function recovery were measured in the spinal cord tissues of each group by immunofluorescence staining of TLR2, GFAP, CS56, 5-HT, and β-III-tublin, respectively. TLR2^f/f mice were crossed to the GFAP-Cre strain to generate astrocyte specific TLR2 knockout mice (TLR2^−/−). Finally, western blot analysis was used to determine the expression of signaling proteins and IKKβ inhibitor SC-514 was used to validate the involved signaling pathway.

Results

Here, we found that TLR2 increased significantly on astrocytes post-SCI. SCDEs treatment can promote functional recovery and induce the expression of TLR2 on astrocytes accompanied with decreased CSPGs deposition. The specific knockout of TLR2 on astrocytes abolished the decreasing CSPGs deposition and neurological functional recovery post-SCI. In addition, the signaling pathway of NF-κB/PI3K involved in the TLR2 activation was validated by western blot. Furthermore, IKKβ inhibitor SC-514 was also used to validate this signaling pathway.

Conclusion

Thus, our results uncovered that SCDEs can promote functional recovery of mice post-SCI by decreasing the CSPGs deposition via increasing the TLR2 expression on astrocytes through NF-κB/PI3K signaling pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02215-x.

Intraspinal Administration of Netrin-1 Promotes Locomotor Recovery after Complete Spinal Cord Transection

Complete spinal cord lesions interrupt the connection of all axonal projections with their neuronal targets below and above the lesion site. In particular, the interruption of connections with the neurons at lumbar segments after thoracic injuries impairs voluntary body control below the injury. The failure of spontaneous regrowth of transected axons across the lesion prevents the reconnection and reinnervation of the neuronal targets. At present, the only treatment in humans that has proven to promote some degree of locomotor recovery is physical therapy. The success of these strategies, however, depends greatly on the type of lesion and the level of preservation of neural tissue in the spinal cord after injury. That is the reason it is key to design strategies to promote axonal regrowth and neuronal reconnection. Here, we test the use of a developmental axon guidance molecule as a biological agent to promote axonal regrowth, axonal reconnection, and recovery of locomotor activity after spinal cord injury (SCI). This molecule, netrin-1, guides the growth of the corticospinal tract (CST) during the development of the central nervous system. To assess the potential of this molecule, we used a model of complete spinal cord transection in rats, at thoracic level 10-11. We show that in situ delivery of netrin-1 at the epicenter of the lesion: (1) promotes regrowth of CST through the lesion and prevents CST dieback, (2) promotes synaptic reconnection of regenerated motor and sensory axons, and (3) preserves the polymerization of the neurofilaments in the sciatic nerve axons. These anatomical findings correlate with a significant recovery of locomotor function. Our work identifies netrin-1 as a biological agent with the capacity to promote the functional repair and recovery of locomotor function after SCI. These findings support the use of netrin-1 as a therapeutic intervention to be tested in humans.

Longitudinal fMRI measures of cortical reactivation and hand use with and without training after sensory loss in primates

In a series of previous studies, we demonstrated that damage to the dorsal column in the cervical spinal cord deactivates the contralateral somatosensory hand cortex and impairs hand use in a reach-to-grasp task in squirrel monkeys. Nevertheless, considerable cortical reactivation and behavioral recovery occurs over the following weeks to months after lesion. This timeframe may also be a window for targeted therapies to promote cortical reactivation and functional reorganization, aiding in the recovery process. Here we asked if and how task specific training of an impaired hand would improve behavioral recovery and cortical reorganization in predictable ways, and if recovery related cortical changes would be detectable using noninvasive functional magnetic resonance imaging (fMRI). We further asked if invasive neurophysiological mapping reflected fMRI results. A reach-to-grasp task was used to test impairment and recovery of hand use before and after dorsal column lesions (DC-lesion). The activation and organization of the affected primary somatosensory cortex (area 3b) was evaluated with two types of fMRI - either blood oxygenation level dependent (BOLD) or cerebral blood volume (CBV) with a contrast agent of monocrystalline iron oxide nanocolloid (MION) - before and after DC-lesion. At the end of the behavioral and fMRI studies, microelectrode recordings in the somatosensory areas 3a, 3b and 1 were used to characterize neuronal responses and verify the somatotopy of cortical reactivations. Our results indicate that even after nearly complete DC lesions, monkeys had both considerable post-lesion behavioral recovery, as well as cortical reactivation assessed with fMRI followed by extracellular recordings. Generalized linear regression analyses indicate that lesion extent is correlated with the behavioral outcome, as well as with the difference in the percent signal change from pre-lesion peak activation in fMRI. Monkeys showed behavioral recovery and nearly complete cortical reactivation by 9-12 weeks post-lesion (particularly when the DC-lesion was incomplete). Importantly, the specific training group revealed trends for earlier behavioral recovery and had higher magnitude of fMRI responses to digit stimulation by 5-8 weeks post-lesion. Specific kinematic measures of hand movements in the selected retrieval task predicted recovery time and related to lesion characteristics better than overall task performance success. For measures of cortical reactivation, we found that CBV scans provided stronger signals to vibrotactile digit stimulation as compared to BOLD scans, and thereby may be the preferred non-invasive way to study the cortical reactivation process after sensory deprivations from digits. When the reactivation of cortex for each of the digits was considered, the reactivation by digit 2 stimulation as measured with microelectrode maps and fMRI maps was best correlated with overall behavioral recovery.

Ameliorative effects of miR-423-5p against polarization of microglial cells of the M1 phenotype by targeting a NLRP3 inflammasome signaling pathway

Spinal cord injury (SCI) causes sensation and motion dysfunction. Activation of microglial cells (MCs) in the central nervous system (CNS) is heterogeneous. Heterogeneous types of MCs can produce cytotoxic or neuroprotective effects, secrete proinflammatory or anti-inflammatory factors. The cytotoxic effect of MCs is one of the reasons for secondary damage after SCI. The NLR family pyrin domain containing 3 (NLRP3) inflammasome is a protein that can recognize pathogen-related molecular patterns or host-derived danger signal molecules, responses to microbial infection, and sterile stressors. SCI triggers activation of the NLRP3 inflammasome in the CNS. We investigated the interaction between miR-423-5p and NLRP3 in MCs polarization after SCI. A rat model of SCI was established by a modified version of Allen's method. Spinal samples were adopted for preparation and sequencing of RNA. We screenedapromising microRNA (miR-423-5p) according to the results. Then, we found that NLRP3 was one of the prediction targets of miR-423-5p. By intervening in expression of miR-423-5p and NLRP3, we observed the different polarization of MCs. We employeda dual-luciferase reporter study, proteomics, and transcriptomicsto ascertain the direct targeting relationship between miR-423-5p and NLRP3. MiR-423-5p expression was decreased significantly after SCI in vivo and in vitro. Upregulation of miR-423-5p expression could prevent MCs from lipopolysaccharide-induced M1 polarization. Knockdown of NLRP3 expression could prevent MCs from lipopolysaccharide-induced M1 polarization. MiR-423-5p inhibited MCs polarization to the M1 phenotype by targeting NLRP3.

L-leucine promotes axonal outgrowth and regeneration via mTOR activation

Discovering safe and effective drugs that promote neuron regeneration is an essential strategy for the recovery of central nervous system injuries. In this study, we found that L-leucine, an essential amino acid obtained from both supplements and food sources, could dramatically boost axonal outgrowth and regeneration. First, the effects of L-leucine on neurons were evaluated by cell apoptosis, survival, and death assays, and the results showed no changes in these processes after treatment. By live cell imaging, L-leucine was found to remarkably increase axonal length and growth velocity after axotomy. We also verified that L-leucine enhanced p-mTOR/p-S6K activation in neurons by testing with an mTOR inhibitor, rapamycin. Thereafter, we investigated the effects of L-leucine on the spinal cord injury in vivo. A mouse model of spinal cord hemi-section was established, and L-leucine was administered by tail intravenous injection. Basso mouse scale values revealed that L-leucine could improve functional recovery after injury. It was also notable that L-leucine treatment promoted axon growth across chondroitin sulfate proteoglycan (CSPG) areas. Furthermore, we used CSPGs as inhibitory environmental cues and clarified that L-leucine significantly enhanced axonal outgrowth and regeneration by promoting p-mTOR and p-S6K activation. Therefore, our study is the first to report that L-leucine promotes axonal regeneration in vitro and in vivo and could be candidate drug for axonal re-growth and nervous functional recovery.

Transplantable human motor networks as a neuron-directed strategy for spinal cord injury

To repair neural circuitry following spinal cord injury (SCI), neural stem cell (NSC) transplantation has held a primary focus; however, stochastic outcomes generate challenges driven in part by NSC differentiation and tumor formation. The recent ability to generate regionally specific neurons and their support cells now allows consideration of directed therapeutic approaches with pre-differentiated and networked spinal neural cells. Here, we form encapsulated, transplantable neuronal networks of regionally matched cervical spinal motor neurons, interneurons, and oligodendrocyte progenitor cells derived through trunk-biased neuromesodermal progenitors. We direct neurite formation in alginate-based neural ribbons to generate electrically active, synaptically connected networks, characterized by electrophysiology and calcium imaging before transplantation into rodent models of contused SCI for evaluation at 10-day and 6-week timepoints. The in vivo analyses demonstrate viability and retention of interconnected synaptic networks that readily integrate with the host parenchyma to advance goals of transplantable neural circuitry for SCI treatment.

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Neuromesodermal progenitor derivation of human spinal neurons as therapeutic cells

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Neural ribbons bridge in vitro network formation and in vivo host transplantation

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In vivo visualization of encapsulated graft placement with magnetic resonance imaging

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Six-week viability of human neuronal networks with OPCs in rat contusion SCI

miR-21a-5p Promotes Inflammation following Traumatic Spinal Cord Injury through Upregulation of Neurotoxic Reactive Astrocyte (A1) Polarization by Inhibiting the CNTF/STAT3/Nkrf Pathway

Reactive astrocytes are implicated in traumatic spinal cord injury (TSCI). Interestingly, naïve astrocytes can easily transform into neurotoxic reactive astrocytes (A1s) with inflammatory stimulation. Previous studies demonstrated that microRNA(miR)-21a-5p was up-regulated in spinal cord tissue after TSCI; however, it is not clear whether this affected reactive astrocyte polarization. Here, we aim to detect the effects of miR-21a-5p on the induction of A1 formation and the underlying mechanisms. Our study found that the expression of miR-21a-5p was significantly increased while that of Cntfr α was decreased, since naïve astrocytes transformed into A1s 3 days post-TSCI; the binding site between miR-21a-5p and Cntfr α was further confirmed in astrocytes. After treatment with CNTF, the levels of A1 markers decreased while that of A2 increased. The expression of A1 markers significantly decreased with the downregulation of miR-21a-5p, while Cntfr α siRNA treatment caused the opposite both in vitro and in vivo. To summarize, miR-21a-5p/Cntfr α promotes A1 induction and might enhance the inflammatory process of TSCI; furthermore, we identified, for the first time, the effect and potential mechanism by which CNTF inhibits naïve astrocytes transformation into A1s. Collectively, our findings demonstrate that targeting miR-21a-5p represents a prospective therapy for promoting the recovery of TSCI.

The Protein Kinase Inhibitor Midostaurin Improves Functional Neurological Recovery and Attenuates Inflammatory Changes Following Traumatic Cervical Spinal Cord Injury

Traumatic spinal cord injury (SCI) impairs neuronal function and introduces a complex cascade of secondary pathologies that limit recovery. Despite decades of preclinical and clinical research, there is a shortage of efficacious treatment options to modulate the secondary response to injury. Protein kinases are crucial signaling molecules that mediate the secondary SCI-induced cellular response and present promising therapeutic targets. The objective of this study was to examine the safety and efficacy of midostaurin—a clinically-approved multi-target protein kinase inhibitor—on cervical SCI pathogenesis. High-throughput analyses demonstrated that intraperitoneal midostaurin injection (25 mg/kg) in C6/7 injured Wistar rats altered the local inflammasome and downregulated adhesive and migratory genes at 24 h post-injury. Treated animals also exhibited enhanced recovery and restored coordination between forelimbs and hindlimbs after injury, indicating the synergistic impact of midostaurin and its dimethyl sulfoxide vehicle to improve functional recovery. Furthermore, histological analyses suggested improved tissue preservation and functionality in the treated animals during the chronic phase of injury. This study serves as a proof-of-concept experiment and demonstrates that systemic midostaurin administration is an effective strategy for mitigating cervical secondary SCI damage.

Rationally Designed, Self-Assembling, Multifunctional Hydrogel Depot Repairs Severe Spinal Cord Injury

Following severe spinal cord injury (SCI), dysregulated neuroinflammation causes neuronal and glial apoptosis, resulting in scar and cystic cavity formation during wound healing and ultimately the formation of an atrophic microenvironment that inhibits nerve regrowth. Because of this complex and dynamic pathophysiology, a systemic solution for scar- and cavity-free wound healing with microenvironment remodeling to promote nerve regrowth has rarely been explored. A one-step solution is proposed through a self-assembling, multifunctional hydrogel depot that punctually releases the anti-inflammatory drug methylprednisolone sodium succinate (MPSS) and growth factors (GFs) locally according to pathophysiology to repair severe SCI. Synergistically releasing the anti-inflammatory drug MPSS and GFs in the hydrogel depot throughout SCI pathophysiology protects spared tissues/axons from secondary injury, promotes scar boundary- and cavity-free wound healing, and results in permissive bridges for remarkable axonal regrowth. Behavioral and electrophysiological studies indicate that remnants of spared axons, not regenerating axons, mediate functional recovery, strongly suggesting that additional interventions are still required to render the rebuilt neuronal circuits functional. These findings pave the way for the development of a systemic solution to treat acute SCI.

Importance of brain alterations in spinal cord injury

Spinal cord injury (SCI) destroys the sensorimotor pathway and blocks the information flow between the peripheral nerve and the brain, resulting in autonomic function loss. Numerous studies have explored the effects of obstructed information flow on brain structure and function and proved the extensive plasticity of the brain after SCI. Great progress has also been achieved in therapeutic strategies for SCI to restore the "re-innervation" of the cerebral cortex to the limbs to some extent. Although no thorough research has been conducted, the changes of brain structure and function caused by "re-domination" have been reported. This article is a review of the recent research progress on local structure, functional changes, and circuit reorganization of the cerebral cortex after SCI. Alterations of structure and electrical activity characteristics of brain neurons, features of brain functional reorganization, and regulation of brain functions by reconfigured information flow were also explored. The integration of brain function is the basis for the human body to exercise complex/fine movements and is intricately and widely regulated by information flow. Hence, its changes after SCI and treatments should be considered.

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.

Hypoxia Response Element-Directed Expression of aFGF in Neural Stem Cells Promotes the Recovery of Spinal Cord Injury and Attenuates SCI-Induced Apoptosis

Reducing neuronal death after spinal cord injury (SCI) is considered to be an important strategy for the renovation of SCI. Studies have shown that, as an important regulator of the development and maintenance of neural structure, acidic fibroblast growth factor (aFGF) has the role of tissue protection and is considered to be an effective drug for the treatment of SCI. Neural stem cells (NSCs) are rendered with the remarkable characteristics to self-replace and differentiate into a variety of cells, so it is promising to be used in cell transplantation therapy. Based on the facts above, our main aim of this research is to explore the role of NSCs expressing aFGF meditated by five hypoxia-responsive elements (5HRE) in the treatment of SCI by constructing AAV–5HRE–aFGF–NSCs and transplanting it into the area of SCI. Our research results showed that AAV–5HRE–aFGF–NSCs can effectively restore the motor function of rats with SCI. This was accomplished by inhibiting the expression of caspase 12/caspase 3 pathway, EIF2α–CHOP pathway, and GRP78 protein to inhibit apoptosis.

Spinal cord regeneration: A brief overview of the present scenario and a sneak peek into the future

The central nervous system (CNS) portrays appreciable complexity in developing from a neural tube to controlling major functions of the body and orchestrated co-ordination in maintaining its homeostasis. Any insult or pathology to such an organized tissue leads to a plethora of events ranging from local hypoxia, ischemia, oxidative stress to reactive gliosis and scarring. Despite unravelling the pathophysiology of spinal cord injury (SCI) and linked cellular and molecular mechanism, the over exhaustive inflammatory response at the site of injury, limited intrinsic regeneration capability of CNS, and the dual role of glial scar halts the expected accomplishment. The review discusses major current treatment approaches for traumatic SCI, addressing their limitation and scope for further development in the field under three main categories- neuroprotection, neuro-regeneration, and neuroplasticity. We further propose that a multi-disciplinary combinatorial treatment approach exploring any two or all three heads simultaneously might alleviate the inhibitory milieu and ameliorate functional recovery.

Human-Induced Neural and Mesenchymal Stem Cell Therapy Combined with a Curcumin Nanoconjugate as a Spinal Cord Injury Treatment

We currently lack effective treatments for the devastating loss of neural function associated with spinal cord injury (SCI). In this study, we evaluated a combination therapy comprising human neural stem cells derived from induced pluripotent stem cells (iPSC-NSC), human mesenchymal stem cells (MSC), and a pH-responsive polyacetal-curcumin nanoconjugate (PA-C) that allows the sustained release of curcumin. In vitro analysis demonstrated that PA-C treatment protected iPSC-NSC from oxidative damage in vitro, while MSC co-culture prevented lipopolysaccharide-induced activation of nuclear factor-κB (NF-κB) in iPSC-NSC. Then, we evaluated the combination of PA-C delivery into the intrathecal space in a rat model of contusive SCI with stem cell transplantation. While we failed to observe significant improvements in locomotor function (BBB scale) in treated animals, histological analysis revealed that PA-C-treated or PA-C and iPSC-NSC + MSC-treated animals displayed significantly smaller scars, while PA-C and iPSC-NSC + MSC treatment induced the preservation of β-III Tubulin-positive axons. iPSC-NSC + MSC transplantation fostered the preservation of motoneurons and myelinated tracts, while PA-C treatment polarized microglia into an anti-inflammatory phenotype. Overall, the combination of stem cell transplantation and PA-C treatment confers higher neuroprotective effects compared to individual treatments.

Static-Dynamic Profited Viscoelastic Hydrogels for Motor-Clutch-Regulated Neurogenesis

Viscoelasticity, a time-scale mechanical feature of the native extracellular matrix (ECM), is reported to play crucial roles in plentiful cellular behaviors, whereas its effects on neuronal behavior and the underlying molecular mechanism still remain obscure. Challenges are faced in the biocompatible synthesis of neural ECM-mimicked scaffolds solely controlled with viscoelasticity and due to the lack of suitable models for neurons-viscoelastic matrix interaction. Herein, we report difunctional hyaluronan-collagen hydrogels prepared by a static-dynamic strategy. The hydrogels show aldehyde concentration-dependent viscoelasticity and similar initial elastic modulus, fibrillar morphology, swelling as well as degradability. Utilizing the resulting hydrogels, for the first time, we demonstrate matrix viscoelasticity-dependent neuronal responses, including neurite elongation and expression of neurogenic proteins. Then, a motor-clutch model modified with a tension dissipation component is developed to account for the molecular mechanism for viscoelasticity-sensitive neuronal responses. Moreover, we prove enhanced recovery of rat spinal cord injury by implanting cell-free viscoelastic grafts. As a pioneer finding on neurons-viscoelastic matrix interaction both in vitro and in vivo, this work provides intriguing insights not only into nerve repair but also into neuroscience and tissue engineering.

Circular RNA Plek promotes fibrogenic activation by regulating the miR-135b-5p/TGF-βR1 axis after spinal cord injury

Objectives: The spinal cord rarely repairs itself when damaged; however, methods for encouraging nerves to regrow are on the horizon. Although circular RNAs (circRNAs) contribute to various biological processes, including neuronal processes, their functions in the subacute phase of spinal cord injury (SCI) have not been elucidated. In this study, we identified a novel circRNA, named CircPlek, with increased expression in spinal tissues after SCI.

Materials and Methods: We predicted a regulatory relationship between CircPlek and miR-135b-5p, which showed the most obvious decrease in post-SCI expression. We established the CircPlek/miR-135b-5p/transforming growth factor-beta receptor type I (TGF-βR1) axis using a bioinformatics approach and further evaluated the potential function of the interaction network in vitro.

Results: We confirmed that in TGF-β1-induced fibroblasts, the overexpression of miR-135b-5p or/and inhibition of CircPlek inhibited fibrosis activation via the Smad pathway. Inhibitors of miR-135b-5p had antagonistic effects on CircPlek.

Conclusions: the CircPlek/miR-135b-5p/TGF-βR1 axis may exert important functions in SCI and is a potential therapeutic target.

Targeting Central Nervous System Regeneration with Cell Type Specificity

There have been tremendous advances in identifying cellular and molecular mechanisms constraining axon growth and strategies have been developed to overcome regenerative failure. However, reproducible and meaningful functional recovery remains elusive. An emerging reason is that neurons possess subtype-specific activation requirements. Much of this evidence comes from studying retinal ganglion cells following optic nerve injury. This review summarizes key neuropathologic events following spinal cord injury, and draws on findings from the optic nerve to suggest how a similar framework may be used to dissect and manipulate the heterogeneous and subtype-specific responses of neurons useful to target for spinal cord injury.

The Role of Lipids, Lipid Metabolism and Ectopic Lipid Accumulation in Axon Growth, Regeneration and Repair after CNS Injury and Disease

Axons in the adult mammalian nervous system can extend over formidable distances, up to one meter or more in humans. During development, axonal and dendritic growth requires continuous addition of new membrane. Of the three major kinds of membrane lipids, phospholipids are the most abundant in all cell membranes, including neurons. Not only immature axons, but also severed axons in the adult require large amounts of lipids for axon regeneration to occur. Lipids also serve as energy storage, signaling molecules and they contribute to tissue physiology, as demonstrated by a variety of metabolic disorders in which harmful amounts of lipids accumulate in various tissues through the body. Detrimental changes in lipid metabolism and excess accumulation of lipids contribute to a lack of axon regeneration, poor neurological outcome and complications after a variety of central nervous system (CNS) trauma including brain and spinal cord injury. Recent evidence indicates that rewiring lipid metabolism can be manipulated for therapeutic gain, as it favors conditions for axon regeneration and CNS repair. Here, we review the role of lipids, lipid metabolism and ectopic lipid accumulation in axon growth, regeneration and CNS repair. In addition, we outline molecular and pharmacological strategies to fine-tune lipid composition and energy metabolism in neurons and non-neuronal cells that can be exploited to improve neurological recovery after CNS trauma and disease.

Meeting Proceedings for SCI 2020: Launching a Decade of Disruption in Spinal Cord Injury Research

The spinal cord injury (SCI) research community has experienced great advances in discovery research, technology development, and promising clinical interventions in the past decade. To build upon these advances and maximize the benefit to persons with SCI, the National Institutes of Health (NIH) hosted a conference February 12-13, 2019 titled "SCI 2020: Launching a Decade of Disruption in Spinal Cord Injury Research." The purpose of the conference was to bring together a broad range of stakeholders, including researchers, clinicians and healthcare professionals, persons with SCI, industry partners, regulators, and funding agency representatives to break down existing communication silos. Invited speakers were asked to summarize the state of the science, assess areas of technological and community readiness, and build collaborations that could change the trajectory of research and clinical options for people with SCI. In this report, we summarize the state of the science in each of five key domains and identify the gaps in the scientific literature that need to be addressed to move the field forward.

Gsx1 promotes locomotor functional recovery after spinal cord injury

Promoting residential cells, particularly endogenous neural stem and progenitor cells (NSPCs), for tissue regeneration represents a potential strategy for the treatment of spinal cord injury (SCI). However, adult NSPCs differentiate mainly into glial cells and contribute to glial scar formation at the site of injury. Gsx1 is known to regulate the generation of excitatory and inhibitory interneurons during embryonic development of the spinal cord. In this study, we show that lentivirus-mediated expression of Gsx1 increases the number of NSPCs in a mouse model of lateral hemisection SCI during the acute stage. Subsequently, Gsx1 expression increases the generation of glutamatergic and cholinergic interneurons and decreases the generation of GABAergic interneurons in the chronic stage of SCI. Importantly, Gsx1 reduces reactive astrogliosis and glial scar formation, promotes serotonin (5-HT) neuronal activity, and improves the locomotor function of the injured mice. Moreover, RNA sequencing (RNA-seq) analysis reveals that Gsx1-induced transcriptome regulation correlates with NSPC signaling, NSPC activation, neuronal differentiation, and inhibition of astrogliosis and scar formation. Collectively, our study provides molecular insights for Gsx1-mediated functional recovery and identifies the potential of Gsx1 gene therapy for injuries in the spinal cord and possibly other parts of the central nervous system.

Restoring neuro-immune circuitry after brain and spinal cord injuries

Neuro-immune interactions are essential for our body's defense and homeostasis. Anatomical and physiological analyses have shown that the nervous system comprises multiple pathways that regulate the dynamics and functions of immune cells, which are mainly mediated by the autonomic nervous system and adrenal signals. These are disturbed when the neurons and circuits are damaged by diseases of the central nervous system (CNS). Injuries caused by stroke or trauma often cause immune dysfunction by abrogation of the immune-regulating neural pathways, which leads to an increased risk of infections. Here, I review the structures and functions of the neural pathways connecting the brain and the immune system, and the neurogenic mechanisms of immune dysfunction that emerge after CNS injuries. Recent technological advances in manipulating specific neural circuits have added mechanistic aspects of neuro-immune interactions and their dysfunctions. Understanding the neural bases of immune control and their pathological processes will deepen our knowledge of homeostasis and lead to the development of strategies to cure immune deficiencies observed in various CNS disorders.

Does There Exist a Hope to Provide an Effective Treatment for Complete Spinal Cord Injury?

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An NT-3-releasing bioscaffold supports the formation of TrkC-modified neural stem cell-derived neural network tissue with efficacy in repairing spinal cord injury

The mechanism underlying neurogenesis during embryonic spinal cord development involves a specific ligand/receptor interaction, which may be help guide neuroengineering to boost stem cell-based neural regeneration for the structural and functional repair of spinal cord injury. Herein, we hypothesized that supplying spinal cord defects with an exogenous neural network in the NT-3/fibroin-coated gelatin sponge (NF-GS) scaffold might improve tissue repair efficacy. To test this, we engineered tropomyosin receptor kinase C (TrkC)-modified neural stem cell (NSC)-derived neural network tissue with robust viability within an NF-GS scaffold. When NSCs were genetically modified to overexpress TrkC, the NT-3 receptor, a functional neuronal population dominated the neural network tissue. The pro-regenerative niche allowed the long-term survival and phenotypic maintenance of the donor neural network tissue for up to 8 weeks in the injured spinal cord. Additionally, host nerve fibers regenerated into the graft, making synaptic connections with the donor neurons. Accordingly, motor function recovery was significantly improved in rats with spinal cord injury (SCI) that received TrkC-modified NSC-derived neural network tissue transplantation. Together, the results suggested that transplantation of the neural network tissue formed in the 3D bioactive scaffold may represent a valuable approach to study and develop therapies for SCI.

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A NT-3 sustained-release scaffold confers a microenvironment partially simulating the developmental spinal cord.

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The NT-3 microenvironment boosts neuronal differentiation of TrkC-modified NSCs by interactions between ligand and receptor.

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TrkC-NSCs is self-organized into a neural network tissue with typical neural excitability in 3D bioactive scaffold in vitro.

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The grafted neural network tissue can survive and maintain neural property, and improve motor function of paralyzed rats.