Regulating Endogenous Neural Stem Cell Activation to Promote Spinal Cord Injury Repair

Treatment of Syringomyelia Characterized by Focal Dilatation of the Central Canal Using Mesenchymal Stem Cells and Neural Stem Cells

BACKGROUND

Syringomyelia is a progressive chronic disease that leads to nerve pain, sensory dissociation, and dyskinesia. Symptoms often do not improve after surgery. Stem cells have been widely explored for the treatment of nervous system diseases due to their immunoregulatory and neural replacement abilities.

METHODS

In this study, we used a rat model of syringomyelia characterized by focal dilatation of the central canal to explore an effective transplantation scheme and evaluate the effect of mesenchymal stem cells and induced neural stem cells for the treatment of syringomyelia.

RESULTS

The results showed that cell transplantation could not only promote syrinx shrinkage but also stimulate the proliferation of ependymal cells, and the effect of this result was related to the transplantation location. These reactions appeared only when the cells were transplanted into the cavity. Additionally, we discovered that cell transplantation transformed activated microglia into the M2 phenotype. IGF1-expressing M2 microglia may play a significant role in the repair of nerve pain.

CONCLUSION

Cell transplantation can promote cavity shrinkage and regulate the local inflammatory environment. Moreover, the proliferation of ependymal cells may indicate the activation of endogenous stem cells, which is important for the regeneration and repair of spinal cord injury.

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.

Neural regeneration in the human central nervous system-from understanding the underlying mechanisms to developing treatments. Where do we stand today?

Mature neurons in the human central nervous system (CNS) fail to regenerate after injuries. This is a common denominator across different aetiologies, including multiple sclerosis, spinal cord injury and ischemic stroke. The lack of regeneration leads to permanent functional deficits with a substantial impact on patient quality of life, representing a significant socioeconomic burden worldwide. Great efforts have been made to decipher the responsible mechanisms and we now know that potent intra- and extracellular barriers prevent axonal repair. This knowledge has resulted in numerous clinical trials, aiming to promote neuroregeneration through different approaches. Here, we summarize the current understanding of the causes to the poor regeneration within the human CNS. We also review the results of the treatment attempts that have been translated into clinical trials so far.

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.

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.

Extracellular vesicles from UTX-knockout endothelial cells boost neural stem cell differentiation in spinal cord injury

BACKGROUND

Vascular endothelial cells are pivotal in the pathophysiological progression following spinal cord injury (SCI). The UTX (Ubiquitously Transcribed Tetratripeptide Repeat on Chromosome X) serves as a significant regulator of endothelial cell phenotype. The manipulation of endogenous neural stem cells (NSCs) offers a compelling strategy for the amelioration of SCI.

METHODS

Two mouse models were used to investigate SCI: NSCs lineage-traced mice and mice with conditional UTX knockout (UTX KO) in endothelial cells. To study the effects of UTX KO on neural differentiation, we harvested extracellular vesicles (EVs) from both UTX KO spinal cord microvascular endothelial cells (SCMECs) and negative control SCMECs. These EVs were then employed to modulate the differentiation trajectory of endogenous NSCs in the SCI model.

RESULTS

In our NSCs lineage-traced mice model of SCI, a marked decrease in neurogenesis was observed post-injury. Notably, NSCs in UTX KO SCMECs mice showed enhanced neuronal differentiation compared to controls. RNA sequencing and western blot analyses revealed an upregulation of L1 cell adhesion molecule (L1CAM), a gene associated with neurogenesis, in UTX KO SCMECs and their secreted EVs. This aligns with the observed promotion of neurogenesis in UTX KO conditions. In vivo administration of L1CAM-rich EVs from UTX KO SCMECs (KO EVs) to the mice significantly enhanced neural differentiation. Similarly, in vitro exposure of NSCs to KO EVs resulted in increased activation of the Akt signaling pathway, further promoting neural differentiation. Conversely, inhibiting Akt phosphorylation or knocking down L1CAM negated the beneficial effects of KO EVs on NSC neuronal differentiation.

CONCLUSIONS

In conclusion, our findings substantiate that EVs derived from UTX KO SCMECs can act as facilitators of neural differentiation following SCI. This study not only elucidates a novel mechanism but also opens new horizons for therapeutic interventions in the treatment of SCI. Video Abstract.

Stem cells in central nervous system diseases: Promising therapeutic strategies

Central nervous system (CNS) diseases are a leading cause of death and disability. Due to CNS neurons have no self-renewal and regenerative ability as they mature, their loss after injury or disease is irreversible and often leads to functional impairments. Unfortunately, therapeutic options for CNS diseases are still limited, and effective treatments for these notorious diseases are warranted to be explored. At present, stem cell therapy has emerged as a potential therapeutic strategy for improving the prognosis of CNS diseases. Accumulating preclinical and clinical evidences have demonstrated that multiple molecular mechanisms, such as cell replacement, immunoregulation and neurotrophic effect, underlie the use of stem cell therapy for CNS diseases. However, several issues have yet to be addressed to support its clinical application. Thus, this review article aims to summarize the role and underlying mechanisms of stem cell therapy in treating CNS diseases. And it is worthy of further evaluation for the potential therapeutic applications of stem cell treatment in CNS disease.

Electroacupuncture at ST36 acupoint regulates stem cells during experimental autoimmune encephalomyelitis

BACKGROUND

Electroacupuncture (EA) is given to assist in the treatment of MS, which is an effective therapeutic method. However, the therapy mechanism of EA related to stem cells in the treatment of MS is not yet known. In this study, we used a classic animal model of multiple sclerosis: experimental autoimmune encephalomyelitis (EAE) to evaluate the therapeutic effect of EA at Zusanli (ST36) acupoint in EAE and shed light on its potential roles in the effects of stem cells in vivo.

METHODS

The EAE animal models were established. From the first day after immunization, EAE model mice received EA at ST36 acupoint, named the EA group. The weight and clinical score of the three groups were recorded for 28 days. The demyelination, inflammatory cell infiltration, and markers of neural stem cells (NSCs), hematopoietic stem cells (HSCs), and mesenchymal stem cells (MSCs) were compared.

RESULTS

We showed that EAE mice treated with EA at ST36 acupoint, were suppressed in demyelination and inflammatory cell infiltration, and thus decreased clinical score and weight loss and mitigated the development of EAE when compared with the EAE group. Moreover, our data revealed that the proportions of NSCs, HSCs, and MSCs increased in the EA group compared with the EAE group.

CONCLUSIONS

Our study suggested that EA at ST36 acupoint was an effective nonpharmacological therapeutic protocol that not only reduced the CNS demyelination and inflammatory cell infiltration in EAE disease but also increased the proportions of various stem cells. Further study is necessary to better understand how EA at the ST36 acupoint affects EAE.

Formononetin ameliorates the LPS-induced inflammatory response and apoptosis of neuronal cells via NF-κB/NLRP3 signaling pathway

The objective of this study was to investigate the impact of formononetin on cellular apoptosis and inflammatory responses following spinal cord injury (SCI), as well as the underlying mechanisms involved. In this study, PC12 cells were treated with lipopolysaccharide (LPS) and different concentrations of Formononetin (FT) (50 μM, 100 μM, 200 μM). To confirm the effect of nuclear factor-κB (NF-κB)/NLR family pyrin domain containing 3 (NLRP3) signaling pathways, the cells in the phorbol-12-myristate-13-acetate (PMA) group were treated with 0.1 μmol/L PMA (NF-κB/NLRP3 signaling pathway activators). The lactate dehydrogenase (LDH) concentration and cell viability, proliferating cell nuclear antigen (PCNA) fluorescence intensity, and cell apoptosis were determined using an LDH kit, Cell Counting Kit-8 (CCK-8), immunofluorescence, and flow cytometry assays, respectively. Tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-16 (IL-6) expression levels were detected by quantitative ELISA assay. The expression of proteins related to the NF-κB/NLRP3 signaling pathway was detected by western blotting. Our results showed that LPS increased LDH levels in PC12 cells, suggesting that inflammation caused PC12 cell damage. However, the PC12 cell damage was decreased by methylprednisolone. Formononetin promotes cell survival and proliferation, and prevents apoptosis in a concentration-dependent manner. Formononetin reduced the TNF-α, IL-1β, and IL-6 levels in the LPS-treated model. Moreover, formononetin decreased the levels of p-p65 NF-κB and NLRP3 in PC12 cells. We conclude that formononetin ameliorated the inflammatory response and apoptosis in LPS-induced inflammatory injury in neuronal cells via the NF-κB/NLRP3 signaling pathway.

Decellularised spinal cord matrix manipulates glial niche into repairing phase via serglycin-mediated signalling pathway

Astrocytes are the most abundant and widespread glial cells in the central nervous system. The heterogeneity of astrocytes plays an essential role in spinal cord injury (SCI) repair. Decellularised spinal cord matrix (DSCM) is advantageous for repairing SCI, but little is known regarding the exact mechanisms and niche alterations. Here, we investigated the DSCM regulatory mechanism of glial niche in the neuro-glial-vascular unit using single-cell RNA sequencing. Our single cell sequencing, molecular and biochemical experiments validated that DSCM facilitated the differentiation of neural progenitor cells through increasing the number of immature astrocytes. Upregulation of mesenchyme-related genes, which maintained astrocyte immaturity, causing insensitivity to inflammatory stimuli. Subsequently, we identified serglycin (SRGN) as a functional component of DSCM, which involves inducing CD44-AKT signalling to trigger human spinal cord-derived primary astrocytes (hspASCs) proliferation and upregulation of genes related to epithelial-mesenchymal transition, thus impeding astrocyte maturation. Finally, we verified that SRGN-COLI and DSCM had similar functions in the human primary cell co-culture system to mimic the glia niche. In conclusion, our work revealed that DSCM reverted astrocyte maturation and altered the glia niche into the repairing phase through the SRGN-mediated signalling pathway.

UCHL1 facilitates protein aggregates clearance to enhance neural stem cell activation in spinal cord injury

Activation of endogenous neural stem cells (NSCs) is greatly significant for the adult neurogenesis; however, it is extremely limited in the spinal cord after injury. Recent evidence suggests that accumulation of protein aggregates impairs the ability of quiescent NSCs to activate. Ubiquitin c-terminal hydrolase l-1 (UCHL1), an important deubiquitinating enzyme, plays critical roles in protein aggregations clearance, but its effects on NSC activation remains unknown. Here, we show that UCHL1 promotes NSC activation by clearing protein aggregates through ubiquitin-proteasome approach. Upregulation of UCHL1 facilitated the proliferation of spinal cord NSCs after spinal cord injury (SCI). Based on protein microarray analysis of SCI cerebrospinal fluid, it is further revealed that C3⁺ neurotoxic reactive astrocytes negatively regulated UCHL1 and proteasome activity via C3/C3aR signaling, led to increased abundances of protein aggregations and decreased NSC proliferation. Furthermore, blockade of reactive astrocytes or C3/C3aR pathway enhanced NSC activation post-SCI by reserving UCHL1 and proteasome functions. Together, this study elucidated a mechanism regulating NSC activation in the adult spinal cord involving the UCHL1-proteasome approach, which may provide potential molecular targets and new insights for NSC fate regulation.

Bibliometric analysis of stem cells for spinal cord injury: current status and emerging frontiers

Background: This study aimed to conduct a bibliometric analysis of the literature on stem cell therapy for spinal cord injury to visualize the research status, identify hotspots, and explore the development trends in this field. Methods: We searched the Web of Science Core Collection database using relevant keywords ("stem cells" and "spinal cord injury") and retrieved the published literature between 2000 and 2022. Data such as journal title, author information, institutional affiliation, country, and keywords were extracted. Afterwards, we performed bibliometric analysis of the retrieved data using Bibliometrix, VOSviewer, and CiteSpace. Results: A total of 5375 articles related to stem cell therapy for spinal cord injury were retrieved, and both the annual publication volume and the cumulative publication volume showed an upward trend. neural regeneration research was the journal with the most publications and the fastest cumulative publication growth (162 articles), Okano Hideyuki was the author with the highest number of publications and citations (114 articles), Sun Yat-sen University was the institution with the highest number of publications (420 articles), and China was the country with the highest number of publications (5357 articles). However, different authors, institutions, and countries need to enhance their cooperation in order to promote the generation of significant academic achievements. Current research in this field has focused on stem cell transplantation, neural regeneration, motor function recovery, exosomes, and tissue engineering. Meanwhile, future research directions are primarily concerned with the molecular mechanisms, safety, clinical trials, exosomes, scaffolds, hydrogels, and inflammatory responses of stem cell therapy for spinal cord injuries. Conclusion: In summary, this study provided a comprehensive analysis of the current research status and frontiers of stem cell therapy for spinal cord injury. The findings provide a foundation for future research and clinical translation efforts of stem cell therapy in this field.

Neural Progenitor Cells and the Hypothalamus

Neural progenitor cells (NPCs) are multipotent neural stem cells (NSCs) capable of self-renewing and differentiating into neurons, astrocytes and oligodendrocytes. In the postnatal/adult brain, NPCs are primarily located in the subventricular zone (SVZ) of the lateral ventricles (LVs) and subgranular zone (SGZ) of the hippocampal dentate gyrus (DG). There is evidence that NPCs are also present in the postnatal/adult hypothalamus, a highly conserved brain region involved in the regulation of core homeostatic processes, such as feeding, metabolism, reproduction, neuroendocrine integration and autonomic output. In the rodent postnatal/adult hypothalamus, NPCs mainly comprise different subtypes of tanycytes lining the wall of the 3^rd ventricle. In the postnatal/adult human hypothalamus, the neurogenic niche is constituted by tanycytes at the floor of the 3^rd ventricle, ependymal cells and ribbon cells (showing a gap-and-ribbon organization similar to that in the SVZ), as well as suprachiasmatic cells. We speculate that in the postnatal/adult human hypothalamus, neurogenesis occurs in a highly complex, exquisitely sophisticated neurogenic niche consisting of at least four subniches; this structure has a key role in the regulation of extrahypothalamic neurogenesis, and hypothalamic and extrahypothalamic neural circuits, partly through the release of neurotransmitters, neuropeptides, extracellular vesicles (EVs) and non-coding RNAs (ncRNAs).

Recent advances in endogenous neural stem/progenitor cell manipulation for spinal cord injury repair

Traumatic spinal cord injury (SCI) can cause severe neurological impairments. Clinically available treatments are quite limited, with unsatisfactory remediation effects. Residing endogenous neural stem/progenitor cells (eNSPCs) tend to differentiate towards astrocytes, leaving only a small fraction towards oligodendrocytes and even fewer towards neurons; this has been suggested as one of the reasons for the failure of autonomous neuronal regeneration. Thus, finding ways to recruit and facilitate the differentiation of eNSPCs towards neurons has been considered a promising strategy for the noninvasive and immune-compatible treatment of SCI. The present manuscript first introduces the responses of eNSPCs after exogenous interventions to boost endogenous neurogenesis in various SCI models. Then, we focus on state-of-art manipulation approaches that enhance the intrinsic neurogenesis capacity and reconstruct the hostile microenvironment, mainly consisting of pharmacological treatments, stem cell-derived exosome administration, gene therapy, functional scaffold implantation, inflammation regulation, and inhibitory element delineation. Facing the extremely complex situation of SCI, combined treatments are also highlighted to provide more clues for future relevant investigations.

Spinal cord injury: molecular mechanisms and therapeutic interventions

Spinal cord injury (SCI) remains a severe condition with an extremely high disability rate. The challenges of SCI repair include its complex pathological mechanisms and the difficulties of neural regeneration in the central nervous system. In the past few decades, researchers have attempted to completely elucidate the pathological mechanism of SCI and identify effective strategies to promote axon regeneration and neural circuit remodeling, but the results have not been ideal. Recently, new pathological mechanisms of SCI, especially the interactions between immune and neural cell responses, have been revealed by single-cell sequencing and spatial transcriptome analysis. With the development of bioactive materials and stem cells, more attention has been focused on forming intermediate neural networks to promote neural regeneration and neural circuit reconstruction than on promoting axonal regeneration in the corticospinal tract. Furthermore, technologies to control physical parameters such as electricity, magnetism and ultrasound have been constantly innovated and applied in neural cell fate regulation. Among these advanced novel strategies and technologies, stem cell therapy, biomaterial transplantation, and electromagnetic stimulation have entered into the stage of clinical trials, and some of them have already been applied in clinical treatment. In this review, we outline the overall epidemiology and pathophysiology of SCI, expound on the latest research progress related to neural regeneration and circuit reconstruction in detail, and propose future directions for SCI repair and clinical applications.

Persistence of FoxJ1+ Pax6+ Sox2+ ependymal cells throughout life in the human spinal cord

Ependymal cells lining the central canal of the spinal cord play a crucial role in providing a physical barrier and in the circulation of cerebrospinal fluid. These cells express the FOXJ1 and SOX2 transcription factors in mice and are derived from various neural tube populations, including embryonic roof and floor plate cells. They exhibit a dorsal-ventral expression pattern of spinal cord developmental transcription factors (such as MSX1, PAX6, ARX, and FOXA2), resembling an embryonic-like organization. Although this ependymal region is present in young humans, it appears to be lost with age. To re-examine this issue, we collected 17 fresh spinal cords from organ donors aged 37-83 years and performed immunohistochemistry on lightly fixed tissues. We observed cells expressing FOXJ1 in the central region in all cases, which co-expressed SOX2 and PAX6 as well as RFX2 and ARL13B, two proteins involved in ciliogenesis and cilia-mediated sonic hedgehog signaling, respectively. Half of the cases exhibited a lumen and some presented portions of the spinal cord with closed and open central canals. Co-staining of FOXJ1 with other neurodevelopmental transcription factors (ARX, FOXA2, MSX1) and NESTIN revealed heterogeneity of the ependymal cells. Interestingly, three donors aged > 75 years exhibited a fetal-like regionalization of neurodevelopmental transcription factors, with dorsal and ventral ependymal cells expressing MSX1, ARX, and FOXA2. These results provide new evidence for the persistence of ependymal cells expressing neurodevelopmental genes throughout human life and highlight the importance of further investigation of these cells.

Metformin Improves Functional Outcomes, Activates Neural Precursor Cells, and Modulates Microglia in a Sex-Dependent Manner After Spinal Cord Injury

Spinal cord injury (SCI) results in devastating patient outcomes with few treatment options. A promising approach to improve outcomes following SCI involves the activation of endogenous precursor populations including neural stem and progenitor cells (NSPCs) which are located in the periventricular zone (PVZ), and oligodendrocyte precursor cells (OPCs) found throughout the parenchyma. In the adult spinal cord, resident NSPCs are primarily mitotically quiescent and aneurogenic, while OPCs contribute to ongoing oligodendrogenesis into adulthood. Each of these populations is responsive to SCI, increasing their proliferation and migration to the site of injury; however, their activation is not sufficient to support functional recovery. Previous work has shown that administration of the FDA-approved drug metformin is effective at promoting endogenous brain repair following injury, and this is correlated with enhanced NSPC activation. Here, we ask whether metformin can promote functional recovery and neural repair following SCI in both males and females. Our results reveal that acute, but not delayed metformin administration improves functional outcomes following SCI in both sexes. The functional improvement is concomitant with OPC activation and oligodendrogenesis. Our data also reveal sex-dependent effects of metformin following SCI with increased activation of NSPCs in females and reduced microglia activation in males. Taken together, these findings support metformin as a viable therapeutic strategy following SCI and highlight its pleiotropic effects in the spinal cord.

Mechanism of spinal cord injury regeneration and the effect of human neural stem cells-secretome treatment in rat model

BACKGROUND

Globally, complete neurological recovery of spinal cord injury (SCI) is still less than 1%, and 90% experience permanent disability. The key issue is that a pharmacological neuroprotective-neuroregenerative agent and SCI regeneration mechanism have not been found. The secretomes of stem cell are an emerging neurotrophic agent, but the effect of human neural stem cells (HNSCs) secretome on SCI is still unclear.

AIM

To investigate the regeneration mechanism of SCI and neuroprotective-neuroregenerative effects of HNSCs-secretome on subacute SCI post-laminectomy in rats.

METHODS

An experimental study was conducted with 45 Rattus norvegicus, divided into 15 normal, 15 control (10 mL physiologic saline), and 15 treatment (30 μL HNSCs-secretome, intrathecal T10, three days post-traumatic). Locomotor function was evaluated weekly by blinded evaluators. Fifty-six days post-injury, specimens were collected, and spinal cord lesion, free radical oxidative stress (F2-Isoprostanes), nuclear factor-kappa B (NF-κB), matrix metallopeptidase 9 (MMP9), tumor necrosis factor-alpha (TNF-α), interleukin-10 (IL-10), transforming growth factor-beta (TGF-β), vascular endothelial growth factor (VEGF), B cell lymphoma-2 (Bcl-2), nestin, brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF) were analyzed. The SCI regeneration mechanism was analyzed using partial least squares structural equation modeling (PLS SEM).

RESULTS

HNSCs-secretome significantly improved locomotor recovery according to Basso, Beattie, Bresnahan (BBB) scores and increased neurogenesis (nestin, BDNF, and GDNF), neuroangiogenesis (VEGF), anti-apoptotic (Bcl-2), anti-inflammatory (IL-10 and TGF-β), but decreased pro-inflammatory (NF-κB, MMP9, TNF-α), F2-Isoprostanes, and spinal cord lesion size. The SCI regeneration mechanism is valid by analyzed outer model, inner model, and hypothesis testing in PLS SEM, started with pro-inflammation followed by anti-inflammation, anti-apoptotic, neuroangiogenesis, neurogenesis, and locomotor function.

CONCLUSION

HNSCs-secretome as a potential neuroprotective-neuroregenerative agent for the treatment of SCI and uncover the SCI regeneration mechanism.

IFN-γ-STAT1-mediated CD8+ T-cell-neural stem cell cross talk controls astrogliogenesis after spinal cord injury

BACKGROUND

Spinal cord injury (SCI) causes nearly all patients to suffer from protracted disabilities. An emerging therapeutic strategy involving the recruitment of endogenous neural stem cells (NSCs) has been developed. However, endogenous NSCs in the adult spinal cord differentiate into mostly astrocytes after traumatic injury, forming glial scars, which is a major cause of regeneration failure in SCI. Thus, understanding which factors drive the activation and differentiation of endogenous NSCs after SCI is critical for developing therapeutic drugs.

METHODS

The infiltration, state, and location of CD8⁺ T cells in spinal cord after traumatic injury were analyzed by flow cytometry and immunofluorescence (IF) staining. The Basso Mouse Scale (BMS) scores and rotarod testing were used for motor behavioral analysis. NSCs were co-cultured with CD8⁺ T cells. EdU assay was used to detect proliferative cells. Western blotting was used to analyze the expression levels of STAT1, p-STAT1, and p27. ChIP-seq and ChIP-qRT-PCR analyses were used to detect the downstream of STAT1. Nestin-CreERT2::Ai9 transgenic mice were used to genetic lineage tracing of Nestin⁺ NSCs after SCI in vivo.

RESULTS

A prolonged increase of activated CD8⁺ T cells occurs in the injured spinal cords. The behavioral analysis demonstrated that the administration of an anti-CD8 antibody promotes the recovery of locomotor function. Then, we discovered that CD8⁺ T cells suppressed the proliferation of NSCs and promoted the differentiation of NSCs into astrocytes by the IFN-γ-STAT1 pathway in vitro. ChIP-seq and ChIP-qRT-PCR analysis revealed that STAT1 could directly bind to the promoters of astrocyte marker genes GFAP and Aldh1l1. Genetic lineage tracing of Nestin⁺ NSCs demonstrated that most NSCs differentiated into astrocytes following SCI. Depleting CD8⁺ T cells reduced the differentiation of NSCs into astrocytes and instead promoted the differentiation of NSCs into oligodendrocytes.

CONCLUSION

In conclusion, CD8⁺ T cells suppressed the proliferation of NSCs and promoted the differentiation of NSCs into astrocytes by the IFN-γ-STAT1-GFAP/Aldhl1l axis. Our study identifies INF-γ as a critical mediator of CD8⁺ T-cell-NSC cross talk and a potential node for therapeutic intervention in SCI.

Proper wiring of newborn neurons to control bladder function after complete spinal cord injury

Activation of endogenous neurogenesis by bioactive materials enables restoration of sensory/motor function after complete spinal cord injury (SCI) via formation of new relay neural circuits. The underlying wiring logic of newborn neurons in adult central nervous system (CNS) is unknown. Here, we report neurotrophin3-loaded chitosan biomaterial substantially recovered bladder function after SCI. Multiple neuro-circuitry tracing technologies using pseudorabies virus (PRV), rabies virus (RV), and anterograde adeno-associated virus (AAV), demonstrated that newborn neurons were integrated into the micturition neural circuits and reconnected higher brain centers and lower spinal cord centers to control voiding, and participated in the restoration of the lower urinary tract function, even in the absence of long-distance axonal regeneration. Opto- and chemo-genetic studies further supported the notion that the supraspinal control of the lower urinary tract function was partially recovered. Our data demonstrated that regenerated relay neurons could be properly integrated into disrupted long-range neural circuits to restore function of adult CNS.

Neural Stem Cells Overexpressing Arginine Decarboxylase Improve Functional Recovery from Spinal Cord Injury in a Mouse Model

Current therapeutic strategies for spinal cord injury (SCI) cannot fully facilitate neural regeneration or improve function. Arginine decarboxylase (ADC) synthesizes agmatine, an endogenous primary amine with neuroprotective effects. Transfection of human ADC (hADC) gene exerts protective effects after injury in murine brain-derived neural precursor cells (mNPCs). Following from these findings, we investigated the effects of hADC-mNPC transplantation in SCI model mice. Mice with experimentally damaged spinal cords were divided into three groups, separately transplanted with fluorescently labeled (1) control mNPCs, (2) retroviral vector (pLXSN)-infected mNPCs (pLXSN-mNPCs), and (3) hADC-mNPCs. Behavioral comparisons between groups were conducted weekly up to 6 weeks after SCI, and urine volume was measured up to 2 weeks after SCI. A subset of animals was euthanized each week after cell transplantation for molecular and histological analyses. The transplantation groups experienced significantly improved behavioral function, with the best recovery occurring in hADC-mNPC mice. Transplanting hADC-mNPCs improved neurological outcomes, induced oligodendrocyte differentiation and remyelination, increased neural lineage differentiation, and decreased glial scar formation. Moreover, locomotor and bladder function were both rehabilitated. These beneficial effects are likely related to differential BMP-2/4/7 expression in neuronal cells, providing an empirical basis for gene therapy as a curative SCI treatment option.

Application and prospects of somatic cell reprogramming technology for spinal cord injury treatment

Spinal cord injury (SCI) is a serious neurological trauma that is challenging to treat. After SCI, many neurons in the injured area die due to necrosis or apoptosis, and astrocytes, oligodendrocytes, microglia and other non-neuronal cells become dysfunctional, hindering the repair of the injured spinal cord. Corrective surgery and biological, physical and pharmacological therapies are commonly used treatment modalities for SCI; however, no current therapeutic strategies can achieve complete recovery. Somatic cell reprogramming is a promising technology that has gradually become a feasible therapeutic approach for repairing the injured spinal cord. This revolutionary technology can reprogram fibroblasts, astrocytes, NG2 cells and neural progenitor cells into neurons or oligodendrocytes for spinal cord repair. In this review, we provide an overview of the transcription factors, genes, microRNAs (miRNAs), small molecules and combinations of these factors that can mediate somatic cell reprogramming to repair the injured spinal cord. Although many challenges and questions related to this technique remain, we believe that the beneficial effect of somatic cell reprogramming provides new ideas for achieving functional recovery after SCI and a direction for the development of treatments for SCI.

Serial Gene Expression Profiling of Neural Stem Cells Shows Transcriptome Switch by Long-Term Physioxia from Metabolic Adaption to Cell Signaling Profile

Oxygen is an essential factor in the cellular microenvironment with pivotal effects on neural development with a particular sensitivity of midbrain neural stem cells (NSCs) to high atmospheric oxygen tension. However, most experiments are still performed at atmospheric O₂ levels (21%, normoxia), whereas mammalian brain tissue is physiologically exposed to substantially lower O₂ tensions around 3% (physioxia). We here performed serial Affymetrix gene array analyses to detect expression changes in mouse fetal NSCs from both midbrain and cortical tissues when kept at physioxia compared to normoxia. We identified more than 400 O₂-regulated genes involved in cellular metabolism, cell proliferation/differentiation, and various signaling pathways. NSCs from both regions showed a low number but high conformity of regulated genes (9 genes in midbrain vs. 34 in cortical NSCs; 8 concordant expression changes) after short-term physioxia (2 days) with metabolic processes and cellular processes being the most prominent GO categories pointing to cellular adaption to lower oxygen levels. Gene expression profiles changed dramatically after long-term physioxia (13 days) with a higher number of regulated genes and more diverse expression patterns when comparing the two NSC types (338 genes in midbrain vs. 121 in cortical NSCs; 75 concordant changes). Most prominently, we observed a reduction of hits in metabolic processes but an increase in biological regulation and signaling pointing to a switch towards signaling processes and stem cell maintenance. Our data may serve as a basis for identifying potential signaling pathways that maintain stem cell characteristics in cortical versus midbrain physioxic stem cell niches.