Neurogenesis as a Tool for Spinal Cord Injury

Unravelling the Road to Recovery: Mechanisms of Wnt Signalling in Spinal Cord Injury

Spinal cord injury (SCI) is a complex neurodegenerative pathology that consistently harbours a poor prognostic outcome. At present, there are few therapeutic strategies that can halt neuronal cell death and facilitate functional motor recovery. However, recent studies have highlighted the Wnt pathway as a key promoter of axon regeneration following central nervous system (CNS) injuries. Emerging evidence also suggests that the temporal dysregulation of Wnt may drive cell death post-SCI. A major challenge in SCI treatment resides in developing therapeutics that can effectively target inflammation and facilitate glial scar repair. Before Wnt signalling is exploited for SCI therapy, further research is needed to clarify the implications of Wnt on neuroinflammation during chronic stages of injury. In this review, an attempt is made to dissect the impact of canonical and non-canonical Wnt pathways in relation to individual aspects of glial and fibrotic scar formation. Furthermore, it is also highlighted how modulating Wnt activity at chronic time points may aid in limiting lesion expansion and promoting axonal repair.

Regeneration and Plasticity Induced by Epidural Stimulation in a Rodent Model of Spinal Cord Injury

Traumatic spinal cord injury is a major cause of disability for which there are currently no fully effective treatments. Recent studies using epidural electrical stimulation have shown significant advances in motor rehabilitation, even when applied during chronic phases of the disease. The present study aimed to investigate the effectiveness of epidural electric stimulation in the motor recovery of rats with spinal cord injury. Furthermore, we aimed to elucidate the neurophysiological mechanisms underlying motor recovery. First, we improved upon the impact spinal cord injury model to cause severe and permanent motor deficits lasting up to 2 months. Next, we developed and tested an implantable epidural spinal cord stimulator device for rats containing an electrode and an implantable generator. Finally, we evaluated the efficacy of epidural electrical stimulation on motor recovery after spinal cord injury in Wistar rats. A total of 60 animals were divided into the following groups: (i) severe injury with epidural electrical stimulation (injury + stim, n = 15), (ii) severe injury without stimulation (group injury, n = 15), (iii) sham implantation without battery (sham, n = 15), and (iv) a control group, without surgical intervention (control, n = 15). All animals underwent weekly evaluations using the Basso, Beattie, Bresnahan (BBB) locomotor rating scale index, inclined plane, and OpenField test starting one week before the lesion and continuing for eight weeks. After this period, the animals were sacrificed and their spinal cords were explanted and prepared for histological analysis (hematoxylin-eosin) and immunohistochemistry for NeuN, β-III-tubulin, synaptophysin, and Caspase 3. Finally, NeuN-positive neuronal nuclei were quantified through stereology; fluorescence signal intensities for β-tubulin, synaptophyin, and Caspase 3 were quantified using an epifluorescence microscope. The injury + stim group showed significant improvement on the BBB scale compared with the injured group after the 5th week (p < 0.05). Stereological analysis showed a significantly higher average count of neural cells in the injury + stim group in relation to the injury group (1783 ± 2 vs. 897 ± 3, p < 0.001). Additionally, fluorescence signal intensity for synaptophysin was significantly higher in the injury + stim group in relation to the injury group (1294 ± 46 vs. 1198 ± 23, p < 0.01); no statistically significant difference was found in β-III-tubulin signal intensity. Finally, Caspase 3 signal intensity was significantly lower in the stim group (727 ± 123) compared with the injury group (1225 ± 87 p < 0.05), approaching levels observed in the sham and control groups. Our data suggest a regenerative and protective effect of epidural electrical stimulation in rats subjected to impact-induced traumatic spinal cord injury.

Metformin enhances endogenous neural stem cells proliferation, neuronal differentiation, and inhibits ferroptosis through activating AMPK pathway after spinal cord injury

BACKGROUND

Inadequate nerve regeneration and an inhibitory local microenvironment are major obstacles to the repair of spinal cord injury (SCI). The activation and differentiation fate regulation of endogenous neural stem cells (NSCs) represent one of the most promising repair approaches. Metformin has been extensively studied for its antioxidative, anti-inflammatory, anti-aging, and autophagy-regulating properties in central nervous system diseases. However, the effects of metformin on endogenous NSCs remains to be elucidated.

METHODS

The proliferation and differentiation abilities of NSCs were evaluated using CCK-8 assay, EdU/Ki67 staining and immunofluorescence staining. Changes in the expression of key proteins related to ferroptosis in NSCs were detected using Western Blot and immunofluorescence staining. The levels of reactive oxygen species, glutathione and tissue iron were measured using corresponding assay kits. Changes in mitochondrial morphology and membrane potential were observed using transmission electron microscopy and JC-1 fluorescence probe. Locomotor function recovery after SCI in rats was assessed through BBB score, LSS score, CatWalk gait analysis, and electrophysiological testing. The expression of the AMPK pathway was examined using Western Blot.

RESULTS

Metformin promoted the proliferation and neuronal differentiation of NSCs both in vitro and in vivo. Furthermore, a ferroptosis model of NSCs using erastin treatment was established in vitro, and metformin treatment could reverse the changes in the expression of key ferroptosis-related proteins, increase glutathione synthesis, reduce reactive oxygen species production and improve mitochondrial membrane potential and morphology. Moreover, metformin administration improved locomotor function recovery and histological outcomes following SCI in rats. Notably, all the above beneficial effects of metformin were completely abolished upon addition of compound C, a specific inhibitor of AMP-activated protein kinase (AMPK).

CONCLUSION

Metformin, driven by canonical AMPK-dependent regulation, promotes proliferation and neuronal differentiation of endogenous NSCs while inhibiting ferroptosis, thereby facilitating recovery of locomotor function following SCI. Our study further elucidates the protective mechanism of metformin in SCI, providing new mechanistic insights for its candidacy as a therapeutic agent for SCI.

Efficacy of growth factor gene-modified stem cells for motor function after spinal cord injury in rodents: a systematic review and meta‑analysis

The efficacy of growth factor gene-modified stem cells in treating spinal cord injury (SCI) remains unclear. This study aims to evaluate the effectiveness of growth factor gene-modified stem cells in restoring motor function after SCI. Two reviewers searched four databases, including PubMed, Embase, Web of Science, and Scopus, to identify relevant records. Studies on rodents assessing the efficacy of transplanting growth factor gene-modified stem cells in restoring motor function after SCI were included. The results were reported using the standardized mean difference (SMD) with a 95% confidence interval (95% CI). Analyses showed that growth factor gene-modified stem cell transplantation improved motor function recovery in rodents with SCI compared to the untreated (SMD = 3.98, 95% CI 3.26-4.70, I2 = 86.8%, P < 0.0001) and stem cell (SMD = 2.53, 95% CI 1.93-3.13, I2 = 86.9%, P < 0.0001) groups. Using growth factor gene-modified neural stem/histone cells enhanced treatment efficacy. In addition, the effectiveness increased when viral vectors were employed for gene modification and high transplantation doses were administered during the subacute phase. Stem cells derived from the human umbilical cord exhibited an advantage in motor function recovery. However, the transplantation of growth factor gene-modified stem cells did not significantly improve motor function in male rodents (P = 0.136). Transplantation of growth factor gene-modified stem cells improved motor function in rodents after SCI, but claims of enhanced efficacy should be approached with caution. The safety of gene modification remains a significant concern, requiring additional efforts to enhance its clinical translatability.

LncRNA TSIX aggravates spinal cord injury by regulating the PI3K/AKT pathway via the miR-532-3p/DDOST axis

Long noncoding RNA (lncRNA)-X-inactive-specific transcript (TSIX) expression is upregulated in spinal cord tissues following spinal cord injury (SCI). However, the role of lncRNA-TSIX in SCI remains elusive. SCI animal model was established using C57BL/6 mice. LncRNA TSIX and miR-532-3p expression were determined using quantitative reverse transcription polymerase chain reaction (qRT-PCR). Apoptosis, cell proliferation, and migration were evaluated by transferase dUTP nick end labeling staining, CCK-8, and Transwell assays, respectively. The interaction of miR-532-3p with lncRNA TSIX and DDOST was explored via a dual-luciferase reporter system. Hematoxylin-eosin staining and the Basso, Beattie, and Bresnahan locomotor rating (BBB) scale were performed to investigate SCI progression. The expression of the lncRNA TSIX was found to be significantly upregulated in the serum of SCI patients and spinal cord tissues of SCI mice. The overexpression of lncRNA TSIX enhanced spinal cord neural stem cell (SC-NSC) proliferation and migration in vitro while inhibiting apoptosis and inflammatory cell infiltration in vivo. Moreover, lncRNA TSIX acted as a molecular sponge for miR-532-3p, and the knockdown of miR-532-3p promoted proliferation and migration and inhibited apoptosis of SC-NSCs. Moreover, DDOST was found to be the downstream target of miR-532-3p, and DDOST overexpression showed a similar effect as miR-532-3p silencing on the proliferation, migration, and apoptosis of SC-NSCs. Furthermore, we found that lncRNA TSIX overexpression promoted the activation of the PI3K/AKT signaling pathway. LncRNA TSIX aggravates SCI by regulating the PI3K/AKT pathway via the miR-532-3p/DDOST axis, indicating potential applications for targeted therapy of SCI regeneration.

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.

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.

Reprogramming stem cells in regenerative medicine

Induced pluripotent stem cells (iPSCs) that are generated from adult somatic cells are induced to express genes that make them pluripotent through reprogramming techniques. With their unlimited proliferative capacity and multifaceted differentiation potential and circumventing the ethical problems encountered in the application of embryonic stem cells (ESC), iPSCs have a broad application in the fields of cell therapy, drug screening, and disease models and may open up new possibilities for regenerative medicine to treat diseases in the future. In this review, we begin with different reprogramming cell technologies to obtain iPSCs, including biotechnological, chemical, and physical modulation techniques, and present their respective strengths, and limitations, as well as the recent progress of research. Secondly, we review recent research advances in iPSC reprogramming-based regenerative therapies. iPSCs are now widely used to study various clinical diseases of hair follicle defects, myocardial infarction, neurological disorders, liver diseases, and spinal cord injuries. This review focuses on the translational clinical research around iPSCs as well as their potential for growth in the medical field. Finally, we summarize the overall review and look at the potential future of iPSCs in the field of cell therapy as well as tissue regeneration engineering and possible problems. We believe that the advancing iPSC research will help drive long-awaited breakthroughs in cellular therapy.

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.

The roles and applications of neural stem cells in spinal cord injury repair

Spinal cord injury (SCI), which has no current cure, places a severe burden on patients. Stem cell-based therapies are considered promising in attempts to repair injured spinal cords; such options include neural stem cells (NSCs). NSCs are multipotent stem cells that differentiate into neuronal and neuroglial lineages. This feature makes NSCs suitable candidates for regenerating injured spinal cords. Many studies have revealed the therapeutic potential of NSCs. In this review, we discuss from an integrated view how NSCs can help SCI repair. We will discuss the sources and therapeutic potential of NSCs, as well as representative pre-clinical studies and clinical trials of NSC-based therapies for SCI repair.