Long-distance growth and connectivity of neural stem cells after severe spinal cord injury

A facilitatory role of astrocytes in axonal regeneration after acute and chronic spinal cord injury

Neuroscience dogma avers that astrocytic "scars" inhibit axonal regeneration after spinal cord injury (SCI). A recent report suggested however that astrocytes form "borders" around lesions that are permissive rather than inhibitory to axonal growth. We now provide further evidence supporting a facilitatory role of astrocytes in axonal regeneration after SCI. First, even 6months after SCI, injured axons are retained within regions of densely reactive astrocytes, in direct contact with astrocyte processes without being repelled. Second, 6 month-delayed implants of neural stem cells extend axons into reactive astrocyte borders surrounding lesions, densely contacting astrocyte surfaces. Third, bioengineered hydrogels implanted into sites of SCI re-orient reactive astrocytic processes to align along the rostral-to-caudal spinal cord axis resulting in successful regeneration into the lesion/scaffold in close association with astrocytic processes. Fourth, corticospinal axons regenerate into neural progenitor cells implanted six months after injury in close association with host astrocytic processes. Thus, astrocytes do not appear to inhibit axonal regeneration, and the close association of newly growing axons with astrocytic processes suggests a facilitatory role in axonal regeneration.

Neuronal maturation and axon regeneration: unfixing circuitry to enable repair

Mammalian neurons lose the ability to regenerate their central nervous system axons as they mature during embryonic or early postnatal development. Neuronal maturation requires a transformation from a situation in which neuronal components grow and assemble to one in which these components are fixed and involved in the machinery for effective information transmission and computation. To regenerate after injury, neurons need to overcome this fixed state to reactivate their growth programme. A variety of intracellular processes involved in initiating or sustaining neuronal maturation, including the regulation of gene expression, cytoskeletal restructuring and shifts in intracellular trafficking, have been shown to prevent axon regeneration. Understanding these processes will contribute to the identification of targets to promote repair after injury or disease.

Transplantation of Predegenerated Peripheral Nerves after Complete Spinal Cord Transection in Rats: Effect of Neural Precursor Cells and Pharmacological Treatment with the Sulfoglycolipid Tol-51

Following spinal cord injury (SCI), the regenerative capacity of the central nervous system (CNS) is severely limited by the failure of axonal regeneration. The regeneration of CNS axons has been shown to occur by grafting predegenerated peripheral nerves (PPNs) and to be promoted by the transplantation of neural precursor cells (NPCs). The introduction of a combinatorial treatment of PPNs and NPCs after SCI has to address the additional problem of glial scar formation, which prevents regenerating axons from leaving the implant and making functional connections. Previously, we discovered that the synthetic sulfoglycolipid Tol-51 inhibits astrogliosis. The objective was to evaluate axonal regeneration and locomotor function improvement after SCI in rats treated with a combination of PPN, NPC, and Tol-51. One month after SCI, the scar tissue was removed and replaced with segments of PPN or PPN+Tol-51; PPN+NPC+Tol-51. The transplantation of a PPN segment favors regenerative axonal growth; in combination with Tol-51 and NPC, 30% of the labeled descending corticospinal axons were able to grow through the PPN and penetrate the caudal spinal cord. The animals treated with PPN showed significantly better motor function. Our data demonstrate that PPN implants plus NPC and Tol-51 allow successful axonal regeneration in the CNS.

Integrating hydrogels manipulate ECM deposition after spinal cord injury for specific neural reconnections via neuronal relays

A bioinspired hydrogel composed of hyaluronic acid-graft-dopamine (HADA) and a designer peptide HGF-(RADA)4-DGDRGDS (HRR) was presented to enhance tissue integration following spinal cord injury (SCI). The HADA/HRR hydrogel manipulated the infiltration of PDGFRβ+ cells in a parallel pattern, transforming dense scars into an aligned fibrous substrate that guided axonal regrowth. Further incorporation of NT3 and curcumin promoted axonal regrowth and survival of interneurons at lesion borders, which served as relays for establishing heterogeneous axon connections in a target-specific manner. Notable improvements in motor, sensory, and bladder functions resulted in rats with complete spinal cord transection. The HADA/HRR + NT3/Cur hydrogel promoted V2a neuron accumulation in ventral spinal cord, facilitating the recovery of locomotor function. Meanwhile, the establishment of heterogeneous neural connections across the hemisected lesion of canines was documented in a target-specific manner via neuronal relays, significantly improving motor functions. Therefore, biomaterials can inspire beneficial biological activities for SCI repair.

Biomimetic electrospun PVDF/self-assembling peptide piezoelectric scaffolds for neural stem cell transplantation in neural tissue engineering

Piezoelectric materials can provide in situ electrical stimulation without external chemical or physical support, opening new frontiers for future bioelectric therapies. Polyvinylidene fluoride (PVDF) possesses piezoelectricity and biocompatibility, making it an electroactive biomaterial capable of enhancing bioactivity through instantaneous electrical stimulation, which indicates significant potential in tissue engineering. In this study, we developed electroactive and biomimetic scaffolds made of electrospun PVDF and self-assembling peptides (SAPs) to enhance stem cell transplantation for spinal cord injury regeneration. We investigated the morphology and crystalline polymorphs of the electrospun scaffolds. Morphological studies demonstrated the benefit of using mixed sodium dodecyl sulfate (SDS) and SAPs as additives to form thinner, uniform, and defect-free fibers. Regarding electroactive phases, β and γ phases-evidence of electroactivity-were predominant in aligned scaffolds and scaffolds modified with SDS and SAPs. In vitro studies showed that neural stem cells (NSCs) seeded on electrospun PVDF with additives exhibited desirable proliferation and differentiation compared to the gold standard. Furthermore, the orientation of the fibers influenced scaffold topography, resulting in a higher degree of cell orientation in fiber-aligned scaffolds compared to randomly oriented ones.

The top 100 most cited articles on axon regeneration from 2003 to 2023: a bibliometric analysis

Objective

In this study, we used a bibliometric and visual analysis to evaluate the characteristics of the 100 most cited articles on axon regeneration.

Methods

The 100 most cited papers on axon regeneration published between 2003 and 2023 were identified by searching the Web of Science Core Collection database. The extracted data included the title, author, keywords, journal, publication year, country, and institution. A bibliometric analysis was subsequently undertaken.

Results

The examined set of 100 papers collectively accumulated a total of 39,548 citations. The number of citations for each of the top 100 articles ranged from 215 to 1,604, with a median value of 326. The author with the most contributions to this collection was He, Zhigang, having authored eight papers. Most articles originated in the United States (n = 72), while Harvard University was the institution with the most cited manuscripts (n = 19). Keyword analysis unveiled several research hotspots, such as chondroitin sulfate proteoglycan, alternative activation, exosome, Schwann cells, axonal protein synthesis, electrical stimulation, therapeutic factors, and remyelination. Examination of keywords in the articles indicated that the most recent prominent keyword was "local delivery."

Conclusion

This study offers bibliometric insights into axon regeneration, underscoring that the United States is a prominent leader in this field. Our analysis highlights the growing relevance of local delivery systems in axon regeneration. Although these systems have shown promise in preclinical models, challenges associated with long-term optimization, agent selection, and clinical translation remain. Nevertheless, the continued development of local delivery technologies represents a promising pathway for achieving axon regeneration; however, additional research is essential to fully realize their potential and thereby enhance patient outcomes.

Disruption of Core Stress Granule Protein Aggregates Promotes CNS Axon Regeneration

Depletion or inhibition of core stress granule proteins, G3BP1 in mammals and TIAR-2 in C. elegans , increases axon regeneration in injured neurons that show spontaneous regeneration. Inhibition of G3BP1 by expression of its acidic or 'B-domain' accelerates axon regeneration after nerve injury bringing a potential therapeutic intervention to promote neural repair in the peripheral nervous system. Here, we asked if G3BP1 inhibition is a viable strategy to promote regeneration in the injured mammalian central nervous system where axons do not regenerate spontaneously. G3BP1 B-domain expression was found to promote axon regeneration in both the mammalian spinal cord and optic nerve. Moreover, a cell permeable peptide to a subregion of G3BP1's B-domain (rodent G3BP1 amino acids 190-208) accelerated axon regeneration after peripheral nerve injury and promoted the regrowth of reticulospinal axons into the distal transected spinal cord through a bridging peripheral nerve graft. The rodent and human G3BP1 peptides promoted axon growth from rodent and human neurons cultured on permissive substrates, and this function required alternating Glu/Asp-Pro repeats that impart a unique predicted tertiary structure. These studies point to G3BP1 granules as a critical impediment to CNS axon regeneration and indicate that G3BP1 granule disassembly represents a novel therapeutic strategy for promoting neural repair after CNS injury.

The basal forebrain cholinergic system as target for cell replacement therapy in Parkinson's disease

In recent years there has been a renewed interest in the basal forebrain cholinergic system as a target for the treatment of cognitive impairments in patients with Parkinson's disease, due in part to the need to explore novel approaches to treat the cognitive symptoms of the disease and in part to the development of more refined imaging tools that have made it possible to monitor the progressive changes in the structure and function of the basal forebrain system as they evolve over time. In parallel, emerging technologies allowing the derivation of authentic basal forebrain cholinergic neurons from human pluripotent stem cells are providing new powerful tools for the exploration of cholinergic neuron replacement in animal models of Parkinson's disease-like cognitive decline. In this review, we discuss the rationale for cholinergic cell replacement as a potential therapeutic strategy in Parkinson's disease and how this approach can be explored in rodent models of Parkinson's disease-like cognitive decline, building on insights gained from the extensive animal experimental work that was performed in rodent and primate models in the 1980s and 90s. Although therapies targeting the cholinergic system have so far been focused mainly on patients with Alzheimer's disease, Parkinson's disease with dementia may be a more relevant condition. In Parkinson's disease with dementia, the basal forebrain system undergoes progressive degeneration and the magnitude of cholinergic cell loss has been shown to correlate with the level of cognitive impairment. Thus, cell therapy aimed to replace the lost basal forebrain cholinergic neurons represents an interesting strategy to combat some of the major cognitive impairments in patients with Parkinson's disease dementia.

An improved method for generating human spinal cord neural stem cells

Neural stem cells have exhibited efficacy in pre-clinical models of spinal cord injury (SCI) and are on a translational path to human testing. We recently reported that neural stem cells must be driven to a spinal cord fate to optimize host axonal regeneration into sites of implantation in the injured spinal cord, where they subsequently form neural relays across the lesion that support significant functional improvement. We also reported methods of deriving and culturing human spinal cord neural stem cells derived from embryonic stem cells that can be sustained over serial high passage numbers in vitro, providing a potentially optimized cell source for human clinical trials. We now report further optimization of methods for deriving and sustaining cultures of human spinal cord neural stem cell lines that result in improved karyotypic stability while retaining anatomical efficacy in vivo. This development improves prospects for safe human translation.

Advancements in neuroregenerative and neuroprotective therapies for traumatic spinal cord injury

Traumatic spinal cord injuries (SCIs) continue to be a major healthcare concern, with a rising prevalence worldwide. In response to this growing medical challenge, considerable scientific attention has been devoted to developing neuroprotective and neuroregenerative strategies aimed at improving the prognosis and quality of life for individuals with SCIs. This comprehensive review aims to provide an up-to-date and thorough overview of the latest neuroregenerative and neuroprotective therapies currently under investigation. These strategies encompass a multifaceted approach that include neuropharmacological interventions, cell-based therapies, and other promising strategies such as biomaterial scaffolds and neuro-modulation therapies. In addition, the review discusses the importance of acute clinical management, including the role of hemodynamic management as well as timing and technical aspects of surgery as key factors mitigating the secondary injury following SCI. In conclusion, this review underscores the ongoing scientific efforts to enhance patient outcomes and quality of life, focusing on upcoming strategies for the management of traumatic SCI. Each section provides a working knowledge of the fundamental preclinical and patient trials relevant to clinicians while underscoring the pathophysiologic rationale for the therapies.

Salidroside promotes the repair of spinal cord injury by inhibiting astrocyte polarization, promoting neural stem cell proliferation and neuronal differentiation

Spinal cord injury (SCI) remains a formidable challenge, lacking effective treatments. Following SCI, neural stem cells (NSCs) migrate to SCI sites, offering a potential avenue for nerve regeneration, but the effectiveness of this intrinsic repair mechanism remains suboptimal. Salidroside has demonstrated pro-repair attributes in various pathological conditions, including arthritis and cerebral ischemia, and the ability to curtail early-stage inflammation following SCI. However, the specific role of salidroside in the late-stage repair processes of SCI remains less defined. In this investigation, we observed that continuous salidroside treatment in SCI mice improved motor function recovery. Immunofluorescence-staining corroborated salidroside's capacity to stimulate nerve regeneration and remyelination, suppress glial scar hyperplasia, reduce the activation of neurotoxic A1 astrocytes, and facilitate NSCs migration towards the injured region. Mechanistically, in vitro experiments elucidated salidroside's significant role in restraining astrocyte proliferation and A1 polarization. It was further established that A1 astrocytes hinder NSCs proliferation while inducing their differentiation into astrocytes. Salidroside effectively ameliorated this inhibition of NSCs proliferation through diminishing c-Jun N-terminal kinase (JNK) pathway phosphorylation and restored their differentiation into neurons by suppressing the signal transducer and activator of transcription 3 (STAT3) pathway. In summary, our findings suggest that salidroside holds promise as a therapeutic agent for traumatic SCI treatment.

Exploring the properties and potential of the neural extracellular matrix for next-generation regenerative therapies

The extracellular matrix (ECM) is a dynamic and complex network of proteins and molecules that surrounds cells and tissues in the nervous system and orchestrates a myriad of biological functions. This review carefully examines the diverse interactions between cells and the ECM, as well as the transformative chemical and physical changes that the ECM undergoes during neural development, aging, and disease. These transformations play a pivotal role in shaping tissue morphogenesis and neural activity, thereby influencing the functionality of the central nervous system (CNS). In our comprehensive review, we describe the diverse behaviors of the CNS ECM in different physiological and pathological scenarios and explore the unique properties that make ECM-based strategies attractive for CNS repair and regeneration. Addressing the challenges of scalability, variability, and integration with host tissues, we review how advanced natural, synthetic, and combinatorial matrix approaches enhance biocompatibility, mechanical properties, and functional recovery. Overall, this review highlights the potential of decellularized ECM as a powerful tool for CNS modeling and regenerative purposes and sets the stage for future research in this exciting field. This article is categorized under: Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Implantable Materials and Surgical Technologies > Nanomaterials and Implants.

Extracellular vesicles released by transforming growth factor-beta 1-preconditional mesenchymal stem cells promote recovery in mice with spinal cord injury

Spinal cord injury (SCI) causes neuroinflammation, neuronal death, and severe axonal connections. Alleviating neuroinflammation, protecting residual cells and promoting neuronal regeneration via endogenous neural stem cells (eNSCs) represent potential strategies for SCI treatment. Extracellular vesicles (EVs) released by mesenchymal stem cells have emerged as pathological mediators and alternatives to cell-based therapies following SCI. In the present study, EVs isolated from untreated (control, C-EVs) and TGF-β1-treated (T-EVs) mesenchymal stem cells were injected into SCI mice to compare the therapeutic effects and explore the underlying mechanisms. Our study demonstrated for the first time that the application of T-EVs markedly enhanced the proliferation and antiapoptotic ability of NSCs in vitro. The infusion of T-EVs into SCI mice increased the shift from the M1 to M2 polarization of reactive microglia, alleviated neuroinflammation, and enhanced the neuroprotection of residual cells during the acute phase. Moreover, T-EVs increased the number of eNSCs around the epicenter. Consequently, T-EVs further promoted neurite outgrowth, increased axonal regrowth and remyelination, and facilitated locomotor recovery in the chronic stage. Furthermore, the use of T-EVs in Rictor-/- SCI mice (conditional knockout of Rictor in NSCs) showed that T-EVs failed to increase the activation of eNSCs and improve neurogenesis sufficiently, which suggested that T-EVs might induce the activation of eNSCs by targeting the mTORC2/Rictor pathway. Taken together, our findings indicate the prominent role of T-EVs in the treatment of SCI, and the therapeutic efficacy of T-EVs for SCI treatment might be optimized by enhancing the activation of eNSCs via the mTORC2/Rictor signaling pathway.

Ischemic and hemorrhagic stroke lesion environments differentially alter the glia repair potential of neural progenitor cell and immature astrocyte grafts

Using cell grafting to direct glia-based repair mechanisms in adult CNS injuries represents a potential therapeutic strategy for supporting functional neural parenchymal repair. However, glia repair directed by neural progenitor cell (NPC) grafts is dramatically altered by increasing lesion size, severity, and mode of injury. To address this, we studied the interplay between astrocyte differentiation and cell proliferation of NPC in vitro to generate proliferating immature astrocytes (ImA) using hysteretic conditioning. ImA maintain proliferation rates at comparable levels to NPC but showed robust immature astrocyte marker expression including Gfap and Vimentin. ImA demonstrated enhanced resistance to myofibroblast-like phenotypic transformations upon exposure to serum enriched environments in vitro compared to NPC and were more effective at scratch wound closure in vitro compared to quiescent astrocytes. Glia repair directed by ImA at acute ischemic striatal stroke lesions was equivalent to NPC but better than quiescent astrocyte grafts. While ischemic injury environments supported enhanced survival of grafts compared to healthy striatum, hemorrhagic lesions were hostile towards both NPC and ImA grafts leading to poor survival and ineffective modulation of natural wound repair processes. Our findings demonstrate that lesion environments, rather than transcriptional pre-graft states, determine the survival, cell-fate, and glia repair competency of cell grafts applied to acute CNS injuries.

Injectable, self-healing hyaluronic acid-based hydrogels for spinal cord injury repair

The cystic cavity that develops following spinal cord injury is a major obstacle for repairing spinal cord injury (SCI). The injectable self-healing biomaterials treatment is a promising strategy to enhance tissue repair after traumatic spinal cord injury. Herein, a natural extracellular matrix (ECM) biopolymer hyaluronic acid-based hydrogel was developed based on multiple dynamic covalent bonds. The hydrogels exhibited excellent injectable and self-healing properties, could be effectively injected into the injury site, and filled the lesion cavity to accelerate the tissue repair of traumatic SCI. Moreover, the hydrogels were compatible with cells and various tissues and possessed proper stiffness matched with nervous tissue. Additionally, when implanted into the injured spinal cord site, the hyaluronic acid-based hydrogel promoted axonal regeneration and functional recovery by accelerating remyelination, axon regeneration, and angiogenesis. Overall, the injectable self-healing hyaluronic acid-based hydrogels are ideal biomaterials for treating traumatic SCI.

Tuneable hydrogel patterns in pillarless microfluidic devices

Organ-on-chip (OOC) technology has recently emerged as a powerful tool to mimic physiological or pathophysiological conditions through cell culture in microfluidic devices. One of its main goals is bypassing animal testing and encouraging more personalized medicine. The recent incorporation of hydrogels as 3D scaffolds into microfluidic devices has changed biomedical research since they provide a biomimetic extracellular matrix to recreate tissue architectures. However, this technology presents some drawbacks such as the necessity for physical structures as pillars to confine these hydrogels, as well as the difficulty in reaching different shapes and patterns to create convoluted gradients or more realistic biological structures. In addition, pillars can also interfere with the fluid flow, altering the local shear forces and, therefore, modifying the mechanical environment in the OOC model. In this work, we present a methodology based on a plasma surface treatment that allows building cell culture chambers with abutment-free patterns capable of producing precise shear stress distributions. Therefore, pillarless devices with arbitrary geometries are needed to obtain more versatile, reliable, and biomimetic experimental models. Through computational simulation studies, these shear stress changes are demonstrated in different designed and fabricated geometries. To prove the versatility of this new technique, a blood-brain barrier model has been recreated, achieving an uninterrupted endothelial barrier that emulates part of the neurovascular network of the brain. Finally, we developed a new technology that could avoid the limitations mentioned above, allowing the development of biomimetic OOC models with complex and adaptable geometries, with cell-to-cell contact if required, and where fluid flow and shear stress conditions could be controlled.

Clickable Granular Hydrogel Scaffolds for Delivery of Neural Progenitor Cells to Sites of Spinal Cord Injury

Spinal cord injury (SCI) is a serious condition with limited treatment options. Neural progenitor cell (NPC) transplantation is a promising treatment option, and the identification of novel biomaterial scaffolds that support NPC engraftment and therapeutic activity is a top research priority. The objective of this study is to evaluate in situ assembled poly (ethylene glycol) (PEG)-based granular hydrogels for NPC delivery in a murine model of SCI. Microgel precursors are synthesized by using thiol-norbornene click chemistry to react four-armed PEG-amide-norbornene with enzymatically degradable and cell adhesive peptides. Unreacted norbornene groups are utilized for in situ assembly into scaffolds using a PEG-di-tetrazine linker. The granular hydrogel scaffolds exhibit good biocompatibility and do not adversely affect the inflammatory response after SCI. Moreover, when used to deliver NPCs, the granular hydrogel scaffolds supported NPC engraftment, do not adversely affect the immune response to the NPC grafts, and successfully support graft differentiation toward neuronal or astrocytic lineages as well as axonal extension into the host tissue. Collectively, these data establish PEG-based granular hydrogel scaffolds as a suitable biomaterial platform for NPC delivery and justify further testing, particularly in the context of more severe SCI.

Combinatorial strategies for cell transplantation in traumatic spinal cord injury

Spinal cord injury (SCI) substantially reduces the quality of life of affected individuals. Recovery of function is therefore a primary concern of the patient population and a primary goal for therapeutic interventions. Currently, even with growing numbers of clinical trials, there are still no effective treatments that can improve neurological outcomes after SCI. A large body of work has demonstrated that transplantation of neural stem/progenitor cells (NSPCs) can promote regeneration of the injured spinal cord by providing new neurons that can integrate into injured host neural circuitry. Despite these promising findings, the degree of functional recovery observed after NSPC transplantation remains modest. It is evident that treatment of such a complex injury cannot be addressed with a single therapeutic approach. In this mini-review, we discuss combinatorial strategies that can be used along with NSPC transplantation to promote spinal cord regeneration. We begin by introducing bioengineering and neuromodulatory approaches, and highlight promising work using these strategies in integration with NSPCs transplantation. The future of NSPC transplantation will likely include a multi-factorial approach, combining stem cells with biomaterials and/or neuromodulation as a promising treatment for SCI.

Neural stem cell therapies for spinal cord injury repair: an update on recent preclinical and clinical advances

Traumatic spinal cord injury (SCI) is a leading cause of lifelong disabilities. Permanent sensory, motor and autonomic impairments after SCI are substantially attributed to degeneration of spinal cord neurons and axons, and disintegration of neural network. To date, minimal regenerative treatments are available for SCI with an unmet need for new therapies to reconstruct the damaged spinal cord neuron-glia network and restore connectivity with the supraspinal pathways. Multipotent neural precursor cells (NPCs) have a unique capacity to generate neurons, oligodendrocytes and astrocytes. Due to this capacity, NPCs have been an attractive cell source for cellular therapies for SCI. Transplantation of NPCs has been extensively tested in preclinical models of SCI in the past two decades. These studies have identified opportunities and challenges associated with NPC therapies. While NPCs have the potential to promote neuroregeneration through various mechanisms, their low long-term survival and integration within the host injured spinal cord limit the functional benefits of NPC-based therapies for SCI. To address this challenge, combinatorial strategies have been developed to optimize the outcomes of NPC therapies by enriching SCI microenvironment through biomaterials, genetic and pharmacological therapies. In this review, we will provide an in-depth discussion on recent advances in preclinical NPC-based therapies for SCI. We will discuss modes of actions and mechanism by which engrafted NPCs contribute to the repair process and functional recovery. We will also provide an update on current clinical trials and new technologies that have facilitated preparation of medical-grade human NPCs suitable for transplantation in clinical studies.

Epigenetic regulation and factors that influence the effect of iPSCs-derived neural stem/progenitor cells (NS/PCs) in the treatment of spinal cord injury

Spinal cord injury (SCI) is a severe neurological disorder that causes neurological impairment and disability. Neural stem/progenitor cells (NS/PCs) derived from induced pluripotent stem cells (iPSCs) represent a promising cell therapy strategy for spinal cord regeneration and repair. However, iPSC-derived NS/PCs face many challenges and issues in SCI therapy; one of the most significant challenges is epigenetic regulation and that factors that influence this mechanism. Epigenetics refers to the regulation of gene expression and function by DNA methylation, histone modification, and chromatin structure without changing the DNA sequence. Previous research has shown that epigenetics plays a crucial role in the generation, differentiation, and transplantation of iPSCs, and can influence the quality, safety, and outcome of transplanted cells. In this study, we review the effects of epigenetic regulation and various influencing factors on the role of iPSC-derived NS/PCs in SCI therapy at multiple levels, including epigenetic reprogramming, regulation, and the adaptation of iPSCs during generation, differentiation, and transplantation, as well as the impact of other therapeutic tools (e.g., drugs, electrical stimulation, and scaffolds) on the epigenetic status of transplanted cells. We summarize our main findings and insights in this field and identify future challenges and directions that need to be addressed and explored.

Brain Plasticity in Patients with Spinal Cord Injuries: A Systematic Review

A spinal cord injury (SCI) causes changes in brain structure and brain function due to the direct effects of nerve damage, secondary mechanisms, and long-term effects of the injury, such as paralysis and neuropathic pain (NP). Recovery takes place over weeks to months, which is a time frame well beyond the duration of spinal shock and is the phase in which the spinal cord remains unstimulated below the level of injury and is associated with adaptations occurring throughout the nervous system, often referred to as neuronal plasticity. Such changes occur at different anatomical sites and also at different physiological and molecular biological levels. This review aims to investigate brain plasticity in patients with SCIs and its influence on the rehabilitation process. Studies were identified from an online search of the PubMed, Web of Science, and Scopus databases. Studies published between 2013 and 2023 were selected. This review has been registered on OSF under (n) 9QP45. We found that neuroplasticity can affect the sensory-motor network, and different protocols or rehabilitation interventions can activate this process in different ways. Exercise rehabilitation training in humans with SCIs can elicit white matter plasticity in the form of increased myelin water content. This review has demonstrated that SCI patients may experience plastic changes either spontaneously or as a result of specific neurorehabilitation training, which may lead to positive outcomes in functional recovery. Clinical and experimental evidence convincingly displays that plasticity occurs in the adult CNS through a variety of events following traumatic or non-traumatic SCI. Furthermore, efficacy-based, pharmacological, and genetic approaches, alone or in combination, are increasingly effective in promoting plasticity.

Transplantation of fibrin-thrombin encapsulated human induced neural stem cells promotes functional recovery of spinal cord injury rats through modulation of the microenvironment

Recent studies have mostly focused on engraftment of cells at the lesioned spinal cord, with the expectation that differentiated neurons facilitate recovery. Only a few studies have attempted to use transplanted cells and/or biomaterials as major modulators of the spinal cord injury microenvironment. Here, we aimed to investigate the role of microenvironment modulation by cell graft on functional recovery after spinal cord injury. Induced neural stem cells reprogrammed from human peripheral blood mononuclear cells, and/or thrombin plus fibrinogen, were transplanted into the lesion site of an immunosuppressed rat spinal cord injury model. Basso, Beattie and Bresnahan score, electrophysiological function, and immunofluorescence/histological analyses showed that transplantation facilitates motor and electrophysiological function, reduces lesion volume, and promotes axonal neurofilament expression at the lesion core. Examination of the graft and niche components revealed that although the graft only survived for a relatively short period (up to 15 days), it still had a crucial impact on the microenvironment. Altogether, induced neural stem cells and human fibrin reduced the number of infiltrated immune cells, biased microglia towards a regenerative M2 phenotype, and changed the cytokine expression profile at the lesion site. Graft-induced changes of the microenvironment during the acute and subacute stages might have disrupted the inflammatory cascade chain reactions, which may have exerted a long-term impact on the functional recovery of spinal cord injury rats.

Chronic Spinal Cord Injury Regeneration with Combined Therapy Comprising Neural Stem/Progenitor Cell Transplantation, Rehabilitation, and Semaphorin 3A Inhibitor

Spinal cord injury (SCI) often results in various long-term sequelae, and chronically injured spinal cords exhibit a refractory feature, showing a limited response to cell transplantation therapies. To our knowledge, no preclinical studies have reported a treatment approach with results surpassing those of treatment comprising rehabilitation alone. In this study of rats with SCI, we propose a novel combined therapy involving a semaphorin 3A inhibitor (Sema3Ai), which enhances axonal regeneration, as the third treatment element in combination with neural stem/progenitor cell transplantation and rehabilitation. This comprehensive therapeutic strategy achieved significant improvements in host-derived neuronal and oligodendrocyte differentiation at the SCI epicenter and promoted axonal regeneration even in the chronically injured spinal cord. The elongated axons established functional electrical connections, contributing to significant enhancements in locomotor mobility when compared with animals treated with transplantation and rehabilitation. As a result, our combined transplantation, Sema3Ai, and rehabilitation treatment have the potential to serve as a critical step forward for chronic SCI patients, improving their ability to regain motor function.

Improved Efficacy of Delayed Treatment with Human Bone Marrow-Derived Stromal Cells Evaluated in Rats with Spinal Cord Injury

The treatment of spinal cord injury (SCI) with uncultivated human bone marrow-derived stromal cells (bmSCs) prepared by negative selection has been proposed to be therapeutically superior to treatment with stem cells that were expanded in vitro. To explore their use in clinical trials, we studied the functional effects of delayed application at 7 days after SCI by testing different doses of bmSCs. Spinal cord contusion injury was induced in adult male Wistar rats at the thoracic level T9. Human bmSCs were prepared by negative selection without expansion in vitro (NeuroCellsTM). Treatment consisted of one 150 µL injection into the cisterna magna containing 0.5 or 2.5 million fresh bmSCs or 2.5 million bmSCs. The recovery of motor functions was evaluated during a surveillance period of six weeks (6 W), during which spinal cords were assessed histologically. Treatment resulted in a significant, dose-dependent therapeutic effect on the recovery of motor performance. The histological analysis revealed a lower degree of axonal degeneration and better survival of neurons and oligodendrocytes in bmSCs treated rats. Our results support delayed intrathecal application of bmSCs prepared by negative selection without expansion in vitro as a treatment of SCI.

Mesenchymal Stem Cell-Induced Neuroprotection in Pediatric Neurological Diseases: Recent Update of Underlying Mechanisms and Clinical Utility

Pediatric neurological diseases refer to a group of disorders that affect the nervous system in children. These conditions can have a significant impact on a child's development, cognitive function, motor skills, and overall quality of life. Stem cell therapy is a new and innovative approach to treat various neurological conditions by repairing damaged neurons and replacing those that have been lost. Mesenchymal stem cells (MSCs) have gained significant recognition in this regard due to their ability to differentiate into different cell types. MSCs are multipotent self-replicating stem cells known to render promising results in the treatment of stroke and spinal cord injury in adults. When delivered to the foci of damage in the central nervous system, stem cells begin to differentiate into neural cells under the stimulation of paracrine factors and secrete various neurotrophic factors (NTFs) like nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) that expedite the repair process in injured neurons. In the present review, we will focus on the therapeutic benefits of the MSC-based therapies in salient pediatric neurological disorders including cerebral palsy, stroke, and autism.

Neuromodulation to guide circuit reorganization with regenerative therapies in upper extremity rehabilitation following cervical spinal cord injury

Spinal cord injury (SCI) is a profoundly debilitating condition with no effective treatment to date. The complex response of the central nervous system (CNS) to injury and its limited regeneration capacity pose bold challenges for restoring function. Cervical SCIs are the most prevalent and regaining hand function is a top priority for individuals living with cervical SCI. A promising avenue for addressing this challenge arises from the emerging field of regenerative rehabilitation, which combines regenerative biology with physical medicine approaches. The hypothesis for optimizing gains in upper extremity function centers on the integration of targeted neurorehabilitation with novel cell- and stem cell-based therapies. However, the precise roles and synergistic effects of these components remain poorly understood, given the intricate nature of SCI and the diversity of regenerative approaches. This perspective article sheds light on the current state of regenerative rehabilitation for cervical SCI. Notably, preclinical research has yet to fully incorporate rehabilitation protocols that mimic current clinical practices, which often rely on neuromodulation strategies to activate spared circuits below the injury level. Therefore, it becomes imperative to comprehensively investigate the combined effects of neuromodulation and regenerative medicine strategies in animal models before translating these therapies to individuals with SCI. In cases of severe upper extremity paralysis, the advent of neuromodulation strategies, such as corticospinal tract (CST) and spinal cord stimulation, holds promise as the next frontier in enhancing the effectiveness of cell- and stem cell-based therapies. Future preclinical studies should explore this convergence of neuromodulation and regenerative approaches to unlock new possibilities for upper extremity treatment after SCI.

Transplantation of Heat-Shock Preconditioned Neural Stem/Progenitor Cells Combined with RGD-Functionalised Hydrogel Promotes Spinal Cord Functional Recovery in a Rat Hemi-Transection Model

BACKGROUND

Neural stem/progenitor cell (NSPC) transplantation in spinal cord injury (SCI) is a potential treatment that supports regeneration by promoting neuroprotection, remyelination, and neurite outgrowth. However, glial scarring hinders neuroregeneration and reduces the efficiency of cell transplantation. The present study aimed to enhance this neuroregeneration by surgically removing the glial scar and transplanting heat-shock (HS) preconditioned NSPCs in combination with Arg-Gly-Asp (RGD)-functionalised hydrogel in a rat spinal cord hemi-transection model.

METHODS

Twelve Sprague-Dawley rats underwent spinal cord hemi-transection and were randomly divided into three treatment groups: hydrogel implantation (control group), NSPC-encapsulated hydrogel implantation, and HS-NSPC-encapsulated hydrogel implantation. HS preconditioning was applied to the NSPCs to reinforce cell retention and an RGD-functionalised hydrogel was used as a biomatrix.

RESULTS

In vitro culture showed that preconditioned NSPCs highly differentiated into neurons and oligodendrocytes and exhibited higher proliferation and neurite outgrowth in hydrogels. Rats in the HS-NSPC-encapsulated hydrogel implantation group showed significantly improved functional recovery, neuronal and oligodendrocyte differentiation of transplanted cells, remyelination, and low fibrotic scar formation.

CONCLUSIONS

The surgical removal of the glial scar in combination with HS-preconditioning and RGD-functionalised hydrogels should be considered as a new paradigm in NSPC transplantation for spinal cord regeneration treatment.

The combination treatment of methylprednisolone and growth factor-rich serum ameliorates the structural and functional changes after spinal cord injury in rat

STUDY DESIGN

Preclinical pharmacology.

OBJECTIVES

Our study aims to evaluate the combined effect of Methylprednisolone (MP) and growth factor-rich serum (GFRS) on structural and functional recovery in rats following spinal cord injury (SCI).

SETTING

Shiraz University of Medical Sciences, Shiraz, Iran METHODS: Male Sprague-Dawley rats were randomly assigned to five groups: sham group (laminectomy); SCI group (the spinal cord clip compression model); SCI-MP group (30 mg/kg MP was administrated intraperitoneally (IP) immediately after SCI); SCI-GFRS group (GFRS (200 µl, IP) was administrated for six consecutive days); and SCI-MP + GFRS group (the rats received MP (30 mg/kg, IP) immediately after SCI, and GFRS (200 µl, IP) for six consecutive days). Motor function was assessed weekly using the Basso, Beattie, and Bresnahan (BBB) scale. After 4 weeks, we conducted the rotarod test, then removed and prepared the spinal cords (including the epicenter of injury) for stereological and histological estimation, and biochemical assays.

RESULTS

The results showed that MP and GFRS combining treatment enhanced functional recovery, which was associated with a decrement in lesion volume, increased spared white and gray matter volume, reduced neuronal loss, as well as decreased necrosis and hemorrhage after SCI. Moreover, administration of MP and GFRS inhibited lipid peroxidation (malondialdehyde (MDA) content), and increased antioxidant enzymes including glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT) after rat SCI.

CONCLUSIONS

We suggests that the combination treatment of MP and GFRS may ameliorate the structure and functional changes following SCI by reducing oxidative stress, and increasing the level of antioxidants enzymes.

Cell Transplantation for Repair of the Spinal Cord and Prospects for Generating Region-Specific Exogenic Neuronal Cells

Spinal cord injury (SCI) is associated with currently irreversible consequences in several functional components of the central nervous system. Despite the severity of injury, there remains no approved treatment to restore function. However, with a growing number of preclinical studies and clinical trials, cell transplantation has gained significant potential as a treatment for SCI. Researchers have identified several cell types as potential candidates for transplantation. To optimize successful functional outcomes after transplantation, one key factor concerns generating neuronal cells with regional and subtype specificity, thus calling on the developmental transcriptome patterning of spinal cord cells. A potential source of spinal cord cells for transplantation is the generation of exogenic neuronal progenitor cells via the emerging technologies of gene editing and blastocyst complementation. This review highlights the use of cell transplantation to treat SCI in the context of relevant developmental gene expression patterns useful for producing regionally specific exogenic spinal cells via in vitro differentiation and blastocyst complementation.

Functional Hydrogel Co-Remolding Migration and Differentiation Microenvironment for Severe Spinal Cord Injury Repair

Spinal cord injury (SCI) activates nestin+ neural stem cells (NSCs), which can be regarded as potential seed cells for neuronal regeneration. However, the lesion microenvironment seriously hinders the migration of the nestin+ cells to the lesion epicenter and their differentiation into neurons to rebuild neural circuits. In this study, a photosensitive hydrogel scaffold is prepared as drug delivery carrier. Genetically engineered SDF1α and NT3 are designed and the scaffold is binary modified to reshape the lesion microenvironment. The binary modified scaffold can effectively induce the migration and neuronal differentiation of nestin+ NSCs in vitro. When implanted into a rat complete SCI model, many of the SCI-activated nestin+ cells migrate into the lesion site and give rise to neurons in short-term. Meanwhile, long-term repair results also show that implantation of the binary modified scaffold can effectively promote the maturation, functionalization and synaptic network reconstruction of neurons in the lesion site. In addition, animals treated with binary scaffold also showed better improvement in motor functions. The therapeutic strategy based on remolding the migration and neuronal differentiation lesion microenvironment provides a new insight into SCI repair by targeting activated nestin+ cells, which exhibits excellent clinical transformation prospects.

Research hotspots and trend analysis of cell transplantation in traumatic spinal cord injury: a bibliometric and visualized analysis

Background: A traumatic spinal cord injury (TSCI) can lead to severe nerve damage and disability. Cell transplantation therapy has shown great potential in the reconstruction of damaged spinal cords and promoting functional recovery. However, there is a lack of frontiers and futures analysis in the study of cell transplantation in TSCI. Methods: We used CiteSpace, VOSviewer and biblilometrix R package to perform bibliometric analysis on cell transplantation in TSCI from 2013 to 2023. Bibliometric records were extracted from English articles and reviews from the Web of Science core collection. Results: The bibliometric analysis included 284 papers published in 154 journals by 1,780 authors from 487 institutions in 41 countries and regions. The number of articles published in the past decade has fluctuated slightly, while the number of article citations has steadily increased. Mainland China and the United States are the leading countries and regions in this field, with the National Natural Science Foundation of China being the most funded foundation, and the United States being the country with the most funded articles. The University of Toronto in Canada is a prolific institution. Michael G. Fehlings has published the most articles, and D Michele Basso is the most cited author. Cell transplantation is the most published journal, and the Journal of Neurotrauma is the most cited journal. Cell and tissue engineering and clinical neurology are the basic disciplines in this field, and cutting-edge disciplines include developmental biology, biochemistry and molecular biology, and materials science and multidisciplinary. This study also helps scholars understand the current hotspots and future trends in this field. Marrow stromal cells, glial progenitor, and cell therapy are current research hotspots in this field, while nerve regeneration, cell therapy, and the safety of transplantation of transplantation may be potential research directions in the future. Conclusion: Cell transplantation after TSCI is receiving increasing attention. Cell therapy is both the frontier and a possible future trend in TSCI research. In addition, glial progenitor and marrow stromal cells are also current research hotspots. Meanwhile, nerve regeneration and safety of transplantation may be potential research directions. These findings will help further deepen research on cell transplantation for TSCI in scientific work.

Vimentin takes a hike - Emerging roles of extracellular vimentin in cancer and wound healing

Vimentin is a cytoskeletal protein important for many cellular processes, including proliferation, migration, invasion, stress resistance, signaling, and many more. The vimentin-deficient mouse has revealed many of these functions as it has numerous severe phenotypes, many of which are found only following a suitable challenge or stress. While these functions are usually related to vimentin as a major intracellular protein, vimentin is also emerging as an extracellular protein, exposed at the cell surface in an oligomeric form or secreted to the extracellular environment in soluble and vesicle-bound forms. Thus, this review explores the roles of the extracellular pool of vimentin (eVIM), identified in both normal and pathological states. It focuses specifically on the recent advances regarding the role of eVIM in wound healing and cancer. Finally, it discusses new technologies and future perspectives for the clinical application of eVIM.

Comparison of the Anti-Inflammatory Effects of Mouse Adipose- and Bone-Marrow-Derived Multilineage-Differentiating Stress-Enduring Cells in Acute-Phase Spinal Cord Injury

Abstract Spinal cord injury (SCI) is a serious neurological disorder, with the consequent disabilities conferred by this disorder typically persisting for life. Multilineage-differentiating stress-enduring (Muse) cells are endogenous stem cells that can be collected from various tissues as well as from mesenchymal stem cells (MSCs); additionally, these Muse cells are currently being used in clinical trials. The anti-inflammatory effect of stem cell transplantation prevents secondary injuries of SCI; however, its effect on Muse cells remains unclear. In this study, we aimed to compare the anti-inflammatory effects of adipose (AD)- and bone marrow (BM)-Muse cells that were isolated from mice (6-week-old C57BL/6J) following intralesional administration during the acute phase of SCI. Flow cytometry was used to isolate Muse cells from AD and BM MSCs. The percentage of Muse cells was 3.9 and 2.7% for AD and BM MSCs, respectively. To examine cell viability, Muse cells were incubated under H2O2-induced oxidative stress conditions. Overall, AD-Muse cells exhibited higher viability than BM-Muse cells (p = 0.032). In enzyme-linked immunosorbent assay analysis, AD-Muse cells displayed greater secretion of brain-derived neurotrophic factor (BDNF; p = 0.008), vascular endothelial growth factor (p = 0.032), and hepatocyte growth factor (p = 0.016). DNA microarray analysis revealed higher expression of Bdnf, neurotrophin-3 (Ntf3), nerve growth factor (Ngf), pleiotrophin (Ptn), and midkine (Mdk) in AD-Muse cells than in BM-Muse cells. To assess their anti-inflammatory effects in vitro, Muse cells and macrophages were co-cultured, and the levels of cytokines (tumor necrosis factor [TNF] α and interleukin [IL] 10) were measured in the medium. Consequently, we found that TNFα levels were lower in AD-Muse cells than in BM-Muse cells (p = 0.009), and IL10 levels were higher in AD-Muse cells than in BM-Muse cells (p = 0.008). Further, we induced moderate injuries via contusion of the spinal cord at the T10 level; Muse cells were transplanted intralesionally 7 days post-SCI. The number of surviving cells, alongside the number of CD86+ (M1 inflammatory effect), and CD206+ (M2 anti-inflammatory effect) macrophages in the spinal cord were measured 7 days post-transplantation. The number of surviving AD-Muse cells was higher than the number of surviving BM-Muse cells (ratio of AD-Muse/BM-Muse = 2.5, p > 0.05). The M1/M2 ratio in the AD-Muse cell-group (0.37) was lower than that in the control (phosphate-buffered saline) group (3.60, p = 0.008). The lesion area in the AD-Muse cell group was smaller than that in the BM-non-Muse (p = 0.049) and control groups (p = 0.012). As AD-Muse cells conferred a higher cell survival and neurotrophic factor secretion ability in vitro, AD-Muse cells demonstrated reduced inflammation after SCI. Overall, intralesional AD-Muse cell therapy is a potential therapeutic candidate that is expected to exhibit anti-inflammatory effects following acute SCI.

Artificially reprogrammed stem cells deliver transcytosable nanocomplexes for improved spinal cord repair

Stem cell transplantation holds great promise for restoring function after spinal cord injury (SCI), but its therapeutic efficacy heavily depends on the innate capabilities of the cells and the microenvironment at the lesion site. Herein, a potent cell therapeutic (NCs@SCs) is engineered by artificially reprogramming bone marrow mesenchymal stem cells (BMSCs) with oxidation-responsive transcytosable gene-delivery nanocomplexes (NCs), which endows cells with robust oxidative stress resistance and improved cytokine secretion. NCs@SCs can accumulate in the injured spinal cord after intravenous administration via chemotaxis and boost successive transcytosis to deliver NCs to neurons, augmenting ciliary neurotrophic factor (CNTF) production in both BMSCs and neurons in response to elevated ROS levels. Furthermore, NCs@SCs can actively sense and eliminate ROS and re-educate recruited M1-like macrophages into the anti-inflammatory M2 phenotype via a paracrine pathway, ultimately reshaping the inflammatory microenvironment. Synergistically, NCs@SCs exhibit durable survival and provide neuroprotection against secondary damage, enabling significant locomotor function recovery in SCI rats. Transcriptome analysis reveals that regulation of the ROS/MAPK signaling pathway is involved in SCI therapy by NCs@SCs. This study presents a nanomaterial-mediated cell-reprogramming approach for developing live cell therapeutics, showing significant potential in the treatment of SCI and other neuro-injury disorders.

Differences in Anatomical Outcomes Between Early Chronic and Far Chronic Time-Points After Transplantation of Spinal Cord Neural Progenitor Cells in Mice

Spinal cord injury (SCI) affects millions of people worldwide. Neural progenitor cell (NPC) transplantation is a promising treatment for regenerating lost spinal cord tissue and restoring neurological function after SCI. We conducted a literature search and found that less than a quarter of experimental rodent cell and tissue transplantation studies have investigated anatomical outcomes at longer than 4 months post-transplantation. This is a critical topic to investigate, given that stem and progenitor cell therapies would need to remain in place throughout the lifetime of an individual. We sought to determine how commonly assessed anatomical outcomes evolve between early and far chronic time-points post-NPC transplantation. At either 8 weeks or 26 weeks following transplantation of NPCs into sites of cervical SCI, we evaluated graft neuronal density, astroglial cell density, graft axon outgrowth, and regeneration of host axon populations into grafts in male and female mice. We found that graft neuronal density does not change over time, but the numbers of graft-associated astrocytes and glial fibrillary acidic protein intensity is significantly increased in the far chronic phase compared with the early chronic time-point. In addition, graft axon outgrowth was significantly decreased at 26 weeks post-transplantation compared with 8 weeks post-transplantation. In contrast, corticospinal axon regeneration into grafts was not diminished over time, but rather increased significantly from early to far chronic periods. Interestingly, we found that graft neuronal density is significantly influenced by sex of the host animal, suggesting that sex-dependent processes may shape graft composition over time. Collectively, these results demonstrate that NPC transplants are dynamic and that commonly assessed outcome measures associated with graft efficacy evolve over the weeks to months post-transplantation into the spinal cord.

Potential injectable hydrogels as biomaterials for central nervous system injury: A narrative review

Numerous modalities exist through which the central nervous system (CNS) may sustain injury or impairment, encompassing traumatic incidents, stroke occurrences, and neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. Presently available pharmacological and therapeutic interventions are incapable of restoring or regenerating damaged CNS tissue, leading to substantial unmet clinical needs among patients with CNS ailments or injuries. To address and facilitate the recovery of the impaired CNS, cell-based repair strategies encompass multiple mechanisms, such as neuronal replacement, therapeutic factor secretion, and the promotion of host brain plasticity. Despite the progression of cell-based CNS reparation as a therapeutic strategy throughout the years, substantial barriers have impeded its widespread implementation in clinical settings. The integration of cell technologies with advancements in regenerative medicine utilizing biomaterials and tissue engineering has recently facilitated the surmounting of several of these impediments. This comprehensive review presents an overview of distinct CNS conditions necessitating cell reparation, in addition to exploring potential biomaterial methodologies that enhance the efficacy of treating brain injuries.

Osteopontin enhances the effect of treadmill training and promotes functional recovery after spinal cord injury

In this study, we examined the combined impact of osteopontin (OPN) and treadmill training on mice with spinal cord injury (SCI). OPN was overexpressed by injecting AAV9-SPP1-GFP into the sensorimotor cortex, followed by a left incomplete C5 crush injury two weeks later. Mice (Ex or Ex + OPN group) were trained at 50% maximum running speed for 8 weeks. To analyze the effects, we used biotinylated dextran amine (BDA) for tracing the corticospinal tract (CST) and performed Western blotting and immunohistochemical methods to assess the activation of the mammalian target of rapamycin (mTOR). We also examined axonal regeneration and conducted behavioral tests to measure functional recovery. The results demonstrated that treadmill training promoted the expression of neurotrophic factors such as brain-derived neurotrophic factor (BNDF) and insulin-like growth factor I (IGF-1) and activated mTOR signaling. OPN amplified the effect of treadmill training on activating mTOR signaling indicated by upregulated phosphorylation of ribosomal protein S6 kinase (S6). The combination of OPN and exercise further promoted functional recovery and facilitated limited CST axonal regeneration which did not occur with treadmill training and OPN treatment alone. These findings indicate that OPN enhances the effects of treadmill training in the treatment of SCI and offer new therapeutic insights for spinal cord injury.

Enabling Survival of Transplanted Neural Precursor Cells in the Ischemic Brain

There is no effective therapy for ischemic stroke following the acute stage. Neural transplantation offers a potential option for repairing the ischemic lesion. However, this strategy is hindered by the poor survival of the neural precursor cells (NPCs) that are transplanted into the inflammatory ischemic core. Here, a chemical cocktail consisting of fibrinogen and maraviroc is developed to promote the survival of the transplanted NPCs in the ischemic core of the mouse cerebral cortex. The grafted NPCs survive in the presence of the cocktail but not fibrinogen or maraviroc alone at day 7. The surviving NPCs divide and differentiate to mature neurons by day 30, reconstituting the infarct cortex with vascularization. Molecular analysis in vivo and in vitro shows that blocking the activation of CCR5 on the NPCs protects the NPCs from apoptosis induced by pro-inflammatory factors, revealing the underlying protective effect of the cocktail for NPCs. The findings open an avenue to enable survival of the transplanted NPCs under the inflammatory neurological conditions like stroke.

Function of GSK‑3 signaling in spinal cord injury (Review)

Spinal cord injury (SCI) is a major social problem with a heavy burden on patient physiology and psychology. Glial scar formation and irreversible neuron loss are the two key points during SCI progression. During the acute phase of spinal cord injury, glial scars form, limiting the progression of inflammation. However, in the subacute or chronic phase, glial scarring inhibits axon regeneration. Following spinal cord injury, irreversible loss of neurons leads to further aggravation of spinal cord injury. Several therapies have been developed to improve either glial scar or neuron loss; however, few therapies reach the stage of clinical trials and there are no mainstream therapies for SCI. Exploring the key mechanism of SCI is crucial for finding further treatments. Glycogen synthase kinase-3 (GSK-3) is a widely expressed kinase with important physiological and pathophysiological functions in vivo. Dysfunction of the GSK-3 signaling pathway during SCI has been widely discussed for controlling neurite growth in vitro and in vivo, improving the proliferation and neuronal differentiation of endogenous neural stem cells and functional recovery from spinal cord injury. SCI can decrease the phosphorylated (p)/total (t)-GSK-3β ratio, which leads to an increase in apoptosis, whereas treatment with GSK-3 inhibitors can promote neurogenesis. In addition, several therapies for the treatment of SCI involve signaling pathways associated with GSK-3. Furthermore, signaling pathways associated with GSK-3 also participate in the pathological process of neuropathic pain that remains following SCI. The present review summarized the roles of GSK-3 signaling in SCI to aid in the understanding of GSK-3 signaling during the pathological processes of SCI and to provide evidence for the development of comprehensive treatments.

Hepatocyte growth factor pretreatment boosts functional recovery after spinal cord injury through human iPSC-derived neural stem/progenitor cell transplantation

BACKGROUND

Human induced pluripotent stem cell-derived neural stem/progenitor cell (hiPSC-NS/PC)-based cell transplantation has emerged as a groundbreaking method for replacing damaged neural cells and stimulating functional recovery, but its efficacy is strongly influenced by the state of the injured spinal microenvironment. This study evaluates the impact of a dual therapeutic intervention utilizing hepatocyte growth factor (HGF) and hiPSC-NS/PC transplantation on motor function restoration following spinal cord injury (SCI).

METHODS

Severe contusive SCI was induced in immunocompromised rats, followed by continuous administration of recombinant human HGF protein into the subarachnoid space immediately after SCI for two weeks. Acute-phase histological and RNA sequencing analyses were conducted. Nine days after the injury, hiPSC-NS/PCs were transplanted into the lesion epicenter of the injured spinal cord, and the functional and histological outcomes were determined.

RESULTS

The acute-phase HGF-treated group exhibited vascularization, diverse anti-inflammatory effects, and activation of endogenous neural stem cells after SCI, which collectively contributed to tissue preservation. Following cell transplantation into a favorable environment, the transplanted NS/PCs survived well, facilitating remyelination and neuronal regeneration in host tissues. These comprehensive effects led to substantial enhancements in motor function in the dual-therapy group compared to the single-treatment groups.

CONCLUSIONS

We demonstrate that the combined therapeutic approach of HGF preconditioning and hiPSC-NS/PC transplantation enhances locomotor functional recovery post-SCI, highlighting a highly promising therapeutic strategy for acute to subacute SCI.

Axon guidance gene-targeted siRNA delivery system improves neural stem cell transplantation therapy after spinal cord injury

BACKGROUND

Neural stem cells (NSCs) derived from the embryonic spinal cord are excellent candidates for the cellular regeneration of lost neural cells after spinal cord injury (SCI). Semaphorin 3 A (Sema3A) is well known as being implicated in the major axon guidance of the growth cone as a repulsive function during the development of the central nervous system, yet its function in NSC transplantation therapy for SCI has not been investigated. Here, we report for the first time that embryonic spinal cord-derived NSCs significantly express Sema3A in the SCI environment, potentially facilitating inhibition of cell proliferation after transplantation.

METHODS

siRNA-Sema3A was conjugated with poly-l-lysin-coated gold nanoparticles (AuNPs) through a charge interaction process. NSCs were isolated from embryonic spinal cords of rats. Then, the cells were embedded into a dual-degradable hydrogel with the siRNA- Sema3A loaded-AuNPs and transplanted after complete SCI in rats.

RESULTS

The knockdown of Sema3A by delivering siRNA nanoparticles via dual-degradable hydrogels led to a significant increase in cell survival and neuronal differentiation of the transplanted NSCs after SCI. Of note, the knockdown of Sema3A increased the synaptic connectivity of transplanted NSC in the injured spinal cord. Moreover, extracellular matrix molecule and functional recovery were significantly improved in Sema3A-inhibited rats compared to those in rats with only NSCs transplanted.

CONCLUSIONS

These findings demonstrate the important role of Sema3A in NSC transplantation therapy, which may be considered as a future cell transplantation therapy for SCI cases.

A Bioinspired Injectable, Adhesive, and Self-Healing Hydrogel with Dual Hybrid Network for Neural Regeneration after Spinal Cord Injury

Hydrogel-based regenerated scaffolds show promise as a platform for neural regeneration following spinal cord injury (SCI). Nevertheless, the persistent problem of poor mechanical strength and limited integration with the host tissue still exists. In this study, a bioinspired hydrogel with highly sophisticated features for neural regeneration after SCI is developed. The hydrogel is composed of dihydroxyphenylalanine (DOPA)-grafted chitosan and a designer peptide, offering a unique set of qualities such as being injectable, having self-healing abilities, and adhering to tissues. Compared to conventional hydrogels, this hydrogel ensures a significant promotion of immune response modulation and axon regrowth while featuring synapse formation of various neurotransmitters and myelin regeneration. Subsequently, functional recoveries are enhanced, including motor function, sensory function, and particularly bladder defect repair. These positive findings demonstrate that the hydrogel has great potential as a strategy for repairing SCI. Moreover, the versatility of this strategy goes beyond neural regeneration and holds promise for tissue regeneration in other contexts. Overall, this proposed hydrogel represents an innovative and multifaceted tool for engineering structures in the biomedical field.

Recovery of walking after paralysis by regenerating characterized neurons to their natural target region

Axon regeneration can be induced across anatomically complete spinal cord injury (SCI), but robust functional restoration has been elusive. Whether restoring neurological functions requires directed regeneration of axons from specific neuronal subpopulations to their natural target regions remains unclear. To address this question, we applied projection-specific and comparative single-nucleus RNA sequencing to identify neuronal subpopulations that restore walking after incomplete SCI. We show that chemoattracting and guiding the transected axons of these neurons to their natural target region led to substantial recovery of walking after complete SCI in mice, whereas regeneration of axons simply across the lesion had no effect. Thus, reestablishing the natural projections of characterized neurons forms an essential part of axon regeneration strategies aimed at restoring lost neurological functions.

Recent progress and challenges in the treatment of spinal cord injury

Spinal cord injury (SCI) disrupts the structural and functional connectivity between the higher center and the spinal cord, resulting in severe motor, sensory, and autonomic dysfunction with a variety of complications. The pathophysiology of SCI is complicated and multifaceted, and thus individual treatments acting on a specific aspect or process are inadequate to elicit neuronal regeneration and functional recovery after SCI. Combinatory strategies targeting multiple aspects of SCI pathology have achieved greater beneficial effects than individual therapy alone. Although many problems and challenges remain, the encouraging outcomes that have been achieved in preclinical models offer a promising foothold for the development of novel clinical strategies to treat SCI. In this review, we characterize the mechanisms underlying axon regeneration of adult neurons and summarize recent advances in facilitating functional recovery following SCI at both the acute and chronic stages. In addition, we analyze the current status, remaining problems, and realistic challenges towards clinical translation. Finally, we consider the future of SCI treatment and provide insights into how to narrow the translational gap that currently exists between preclinical studies and clinical practice. Going forward, clinical trials should emphasize multidisciplinary conversation and cooperation to identify optimal combinatorial approaches to maximize therapeutic benefit in humans with SCI.

The Promising Role of a Zebrafish Model Employed in Neural Regeneration Following a Spinal Cord Injury

Spinal cord injury (SCI) is a devastating event that results in a wide range of physical impairments and disabilities. Despite the advances in our understanding of the biological response to injured tissue, no effective treatments are available for SCIs at present. Some studies have addressed this issue by exploring the potential of cell transplantation therapy. However, because of the abnormal microenvironment in injured tissue, the survival rate of transplanted cells is often low, thus limiting the efficacy of such treatments. Many studies have attempted to overcome these obstacles using a variety of cell types and animal models. Recent studies have shown the utility of zebrafish as a model of neural regeneration following SCIs, including the proliferation and migration of various cell types and the involvement of various progenitor cells. In this review, we discuss some of the current challenges in SCI research, including the accurate identification of cell types involved in neural regeneration, the adverse microenvironment created by SCIs, attenuated immune responses that inhibit nerve regeneration, and glial scar formation that prevents axonal regeneration. More in-depth studies are needed to fully understand the neural regeneration mechanisms, proteins, and signaling pathways involved in the complex interactions between the SCI microenvironment and transplanted cells in non-mammals, particularly in the zebrafish model, which could, in turn, lead to new therapeutic approaches to treat SCIs in humans and other mammals.

Engineered human spinal cord-like tissues with dorsal and ventral neuronal progenitors for spinal cord injury repair in rats and monkeys

Transplanting human neural progenitor cells is a promising method of replenishing the lost neurons after spinal cord injury (SCI), but differentiating neural progenitor cells into the diverse types of mature functional spinal cord neurons in vivo is challenging. In this study, engineered human embryonic spinal cord-like tissues with dorsal and ventral neuronal characters (DV-SC) were generated by inducing human neural progenitor cells (hscNPCs) to differentiate into various types of dorsal and ventral neuronal cells on collagen scaffold in vitro. Transplantation of DV-SC into complete SCI models in rats and monkeys showed better therapeutic effects than undifferentiated hscNPCs, including pronounced cell survival and maturation. DV-SC formed a targeted connection with the host's ascending and descending axons, partially restored interrupted neural circuits, and improved motor evoked potentials and the hindlimb function of animals with SCI. This suggests that the transplantation of pre-differentiated hscNPCs with spinal cord dorsal and ventral neuronal characteristics could be a promising strategy for SCI repair.

Biomimetic Electrospun Self-Assembling Peptide Scaffolds for Neural Stem Cell Transplantation in Neural Tissue Engineering

Spinal cord regeneration using stem cell transplantation is a promising strategy for regenerative therapy. Stem cells transplanted onto scaffolds that can mimic natural extracellular matrix (ECM) have the potential to significantly improve outcomes. In this study, we strived to develop a cell carrier by culturing neural stem cells (NSCs) onto electrospun 2D and 3D constructs made up of specific crosslinked functionalized self-assembling peptides (SAPs) featuring enhanced biomimetic and biomechanical properties. Morphology, architecture, and secondary structures of electrospun scaffolds in the solid-state and electrospinning solution were studied step by step. Morphological studies showed the benefit of mixed peptides and surfactants as additives to form thinner, uniform, and defect-free fibers. It has been observed that β-sheet conformation as evidence of self-assembling has been predominant throughout the process except for the electrospinning solution. In vitro NSCs seeded on electrospun SAP scaffolds in 2D and 3D conditions displayed desirable proliferation, viability, and differentiation in comparison to the gold standard. In vivo biocompatibility assay confirmed the permissibility of implanted fibrous channels by foreign body reaction. The results of this study demonstrated that fibrous 2D/3D electrospun SAP scaffolds, when shaped as micro-channels, can be suitable to support NSC transplantation for regeneration following spinal cord injury.

Stem Cell Therapy in Spinal Cord Injury-Induced Neurogenic Lower Urinary Tract Dysfunction

Spinal cord injury (SCI) is a devastating condition that enormously affects an individual's health and quality of life. Neurogenic lower urinary tract dysfunction (NLUTD) is one of the most important sequelae induced by SCI, causing complications including urinary tract infection, renal function deterioration, urinary incontinence, and voiding dysfunction. Current therapeutic methods for SCI-induced NLUTD mainly target on the urinary bladder, but the outcomes are still far from satisfactory. Stem cell therapy has gained increasing attention for years for its ability to rescue the injured spinal cord directly. Stem cell differentiation and their paracrine effects, including exosomes, are the proposed mechanisms to enhance the recovery from SCI. Several animal studies have demonstrated improvement in bladder function using mesenchymal stem cells (MSCs) and neural stem cells (NSCs). Human clinical trials also provide promising results in urodynamic parameters after MSC therapy. However, there is still uncertainty about the ideal treatment window and application protocol for stem cell therapy. Besides, data on the therapeutic effects regarding NSCs and stem cell-derived exosomes in SCI-related NLUTD are scarce. Therefore, there is a pressing need for further well-designed human clinical trials to translate the stem cell therapy into a formal therapeutic option for SCI-induced NLUTD.