Chronic spinal cord injury repair by NT3-chitosan only occurs after clearance of the lesion scar

A core scientific problem in the treatment of central nervous system diseases: newborn neurons

It has long been asserted that failure to recover from central nervous system diseases is due to the system's intricate structure and the regenerative incapacity of adult neurons. Yet over recent decades, numerous studies have established that endogenous neurogenesis occurs in the adult central nervous system, including humans'. This has challenged the long-held scientific consensus that the number of adult neurons remains constant, and that new central nervous system neurons cannot be created or renewed. Herein, we present a comprehensive overview of the alterations and regulatory mechanisms of endogenous neurogenesis following central nervous system injury, and describe novel treatment strategies that target endogenous neurogenesis and newborn neurons in the treatment of central nervous system injury. Central nervous system injury frequently results in alterations of endogenous neurogenesis, encompassing the activation, proliferation, ectopic migration, differentiation, and functional integration of endogenous neural stem cells. Because of the unfavorable local microenvironment, most activated neural stem cells differentiate into glial cells rather than neurons. Consequently, the injury-induced endogenous neurogenesis response is inadequate for repairing impaired neural function. Scientists have attempted to enhance endogenous neurogenesis using various strategies, including using neurotrophic factors, bioactive materials, and cell reprogramming techniques. Used alone or in combination, these therapeutic strategies can promote targeted migration of neural stem cells to an injured area, ensure their survival and differentiation into mature functional neurons, and facilitate their integration into the neural circuit. Thus can integration replenish lost neurons after central nervous system injury, by improving the local microenvironment. By regulating each phase of endogenous neurogenesis, endogenous neural stem cells can be harnessed to promote effective regeneration of newborn neurons. This offers a novel approach for treating central nervous system injury.

Runx2 Suppresses Astrocyte Activation and Astroglial Scar Formation After Spinal Cord Injury in Mice

After spinal cord injury, astrocytes undergo a reactive process and form an astroglial scar, which impedes the regeneration of axons. The role of Runx2 in promoting the transformation of astrocytes in the central nervous system is well-established. However, it remains unclear whether Runx2 also plays a role in the development of astroglial scar, and the precise underlying mechanism has yet to be identified. Recently, our study using cell culture and animal models has demonstrated that Runx2 actually suppresses astrocyte activation and the formation of astroglial scar following injury. The initial results demonstrated an increase in the expression of Runx2 in astrocytes following in vivo injury. Subsequently, the overexpression of Runx2 resulted in the inhibition of astrocyte activation, reduction in the total area of astroglial scar, and restoration of neural function after 14 days of injury. However, these effects were reversed by CADD522. These findings indicate that Runx2 could potentially serve as a therapeutic intervention for spinal cord injury (SCI). Furthermore, our findings suggest that the Nuclear-matrix-targeting signal (NMTS) of Runx2 is associated with its effect. In summary, the study's results propose that targeting Runx2 may be a promising treatment approach for reactive astrocytes and astroglial scar in the recovery of SCI.

microRNA-2184 orchestrates Mauthner-cell axon regeneration in zebrafish via syt3 modulation

MicroRNAs (miRNAs) play a significant role in axon regeneration following spinal cord injury. However, the functions of numerous miRNAs in axon regeneration within the central nervous system (CNS) remain largely unexplored. Here, we elucidate the positive role of miR-2184 in axon regeneration within zebrafish Mauthner cells (M-cells). The upregulation of miR-2184 in the single M-cells facilitates axon regeneration, while the specific sponge-induced silencing of miR-2184 leads to impeded axon regeneration. We show that syt3, a downstream target of miR-2184, negatively regulates axon regeneration, and the regeneration suppression by syt3 depends on its binding to Ca2+. Furthermore, pharmacological stimulation of the cAMP/PKA pathway suggests that changes in the readily releasable pool may affect axon regeneration. Our data indicate that miR-2184 promotes axon regeneration of M-cells within the CNS by modulating the downstream target syt3, providing valuable insights into potential therapeutic strategies.

Neurophysiological, histological, and behavioral characterization of animal models of distraction spinal cord injury: a systematic review

Distraction spinal cord injury is caused by some degree of distraction or longitudinal tension on the spinal cord and commonly occurs in patients who undergo corrective operation for severe spinal deformity. With the increased degree and duration of distraction, spinal cord injuries become more serious in terms of their neurophysiology, histology, and behavior. Very few studies have been published on the specific characteristics of distraction spinal cord injury. In this study, we systematically review 22 related studies involving animal models of distraction spinal cord injury, focusing particularly on the neurophysiological, histological, and behavioral characteristics of this disease. In addition, we summarize the mechanisms underlying primary and secondary injuries caused by distraction spinal cord injury and clarify the effects of different degrees and durations of distraction on the primary injuries associated with spinal cord injury. We provide new concepts for the establishment of a model of distraction spinal cord injury and related basic research, and provide reference guidelines for the clinical diagnosis and treatment of this disease.

Polysaccharides as a promising platform for the treatment of spinal cord injury: A review

Spinal cord injury is incurable and often results in irreversible damage to motor function and autonomic sensory abilities. To enhance the effectiveness of therapeutic substances such as cells, growth factors, drugs, and nucleic acids for treating spinal cord injuries, as well as to reduce the toxic side effects of chemical reagents, polysaccharides have been gained attention due to their immunomodulatory properties and the biocompatibility and biodegradability of polysaccharide scaffolds. Polysaccharides hold potential as drug delivery systems in treating spinal cord injuries. This article aims to present an extensive evaluation of the potential applications of polysaccharide materials in scaffold construction, drug delivery, and immunomodulation over the past five years so that offering new directions and opportunities for the treatment of spinal cord injuries.

The TGFβ1/SMADs/Snail1 signaling axis mediates pericyte-derived fibrous scar formation after spinal cord injury

AIMS

The deposition of fibrous scars after spinal cord injury (SCI) affects axon regeneration and the recovery of sensorimotor function. It has been reported that microvascular pericytes in the neurovascular unit are the main source of myofibroblasts after SCI, but the specific molecular targets that regulate pericyte participation in the formation of fibrous scars remain to be clarified.

METHODS

In this study, a rat model of spinal cord dorsal hemisection injury was used. After SCI, epigallocatechin gallate (EGCG) was intraperitoneally injected to block the TGFβ1 signaling pathway or LV-Snail1-shRNA was immediately injected near the core of the injury using a microsyringe to silence Snail1 expression. Western blotting and RT-qPCR were used to analyze protein expression and transcription levels in tissues. Nissl staining and immunofluorescence analysis were used to analyze neuronal cell viability, scar tissue, and axon regeneration after SCI. Finally, the recovery of hind limb function after SCI was evaluated.

RESULTS

The results showed that targeted inhibition of Snail1 could block TGFβ1-induced pericyte-myofibroblast differentiation in vitro. In vivo experiments showed that timely blockade of Snail1 could reduce fibrous scar deposition after SCI, promote axon regeneration, improve neuronal survival, and facilitate the recovery of lower limb motor function.

CONCLUSION

In summary, Snail1 promotes the deposition of fibrous scars and inhibits axonal regeneration after SCI by inducing the differentiation of pericytes into myofibroblasts. Snail1 may be a promising therapeutic target for SCI.

Hydrogel and Nanomedicine-Based Multimodal Therapeutic Strategies for Spinal Cord Injury

Spinal cord injury (SCI) is a severe neurodegenerative disease caused by mechanical and biological factors, manifesting as a loss of motor and sensory functions. Inhibition of injury expansion and even reversal of injury in the acute damage stage of SCI are important strategies for treating this disease. Hydrogels and nanoparticle (NP)-based drugs are the most effective, widely studied, and clinically valuable therapeutic strategies in the field of repair and regeneration. Hydrogels are 3D flow structures that fill the pathological gaps in SCI and provide a microenvironment similar to that of the spinal cord extracellular matrix for nerve cell regeneration. NP-based drugs can easily penetrate the blood-spinal cord barrier, target SCI lesions, and are noninvasive. Hydrogels and NPs as drug carriers can be loaded with various drugs and biological therapeutic factors for slow release in SCI lesions. They help drugs function more efficiently by exerting anti-inflammatory, antioxidant, and nerve regeneration effects to promote the recovery of neurological function. In this review, the use of hydrogels and NPs as drug carriers and the role of both in the repair of SCI are discussed to provide a multimodal strategic reference for nerve repair and regeneration after SCI.

Inhibition of spastin impairs motor function recovery after spinal cord injury

Promoting axonal regeneration is an effective strategy for recovery from traumatic spinal cord injury (SCI). Spastin, a microtubule-severing protein, modulates axonal outgrowth and branch formation by regulating microtubule dynamics. However, the exact role of spastin during recovery from SCI remains unknown. Therefore, we utilized a hemisection injury model of the mouse spinal cord and explored the effect of spastin using a spastin inhibitor, spastazoline. Results showed that spastazoline significantly suppressed the microtubule-severing activity of spastin in COS-7 cells and inhibited the promoting effect of spastin on neurite outgrowth in primarily cultured hippocampal neurons. The protein expression level of spastin was significantly upregulated in the injured spinal cord. Injured mice showed impaired motor functions, which included increased toe-off angle and foot fault steps and decreased stride length and Basso mouse scale score. Notably, these motor function impairments were aggravated by the application of spastazoline. Inhibition of spastin exacerbated neurogenesis impairment, as demonstrated by neuronal nuclei antigen staining, the inflammatory response, as shown by Iba-1 and GFAP staining, and axonal regeneration impairment, as shown by 5-hydroxytryptamine staining. Furthermore, mass spectrometry analysis revealed that the inhibition of spastin resulted in numerous dysregulated differentially expressed proteins that were closely associated with vesicle organization and transport. Taken together, our data suggest that spastin is critical for recovery from SCI and may be a potential target for the treatment of SCI.

Application of Injectable Hydrogels as Delivery Systems in Spinal Cord Injury

Spinal cord injury (SCI) is a severe neurological injury caused by traffic accidents, trauma, or falls, which leads to significant loss of sensory, motor, and autonomous functions and seriously affects the patient's life quality. Although considerable progress has been made in mitigating secondary injury and promoting the regeneration/repair of SCI, the therapeutic effects need to be improved due to drug availability. Given their good biocompatibility, biodegradability, and low immunogenicity, injectable hydrogels can be used as delivery systems to achieve controlled release of drugs and other substances (cells and proteins, etc.), offering new hope for SCI repair. In this article, we summarized the types of injectable hydrogels, analyzed their application as delivery systems in SCI, and further discussed the mechanisms of hydrogels in the treatment of SCI, such as anti-inflammatory, antioxidant, anti-apoptosis, and pro-neurogenesis. Moreover, we highlighted the potential benefits of hydrogels in the treatment of SCI in combination with therapies, including the recent advances and achievements of these promising tools. Our review may offer new strategies for the development of SCI treatments based on injectable hydrogels as delivery systems.

Epidural combined optical and electrical stimulation induces high-specificity activation of target muscles in spinal cord injured rats

Introduction

Epidural electrical stimulation (EES) has been shown to improve motor dysfunction after spinal cord injury (SCI) by activating residual locomotor neural networks. However, the stimulation current often spreads excessively, leading to activation of non-target muscles and reducing the accuracy of stimulation regulation.

Objectives

Near-infrared nerve stimulation (nINS) was combined with EES to explore its regulatory effect on lower limb muscle activity in spinal-cord-transected rats.

Methods

In this study, stimulation electrodes were implanted into the rats' L3-L6 spinal cord segment with T8 cord transected. Firstly, a series of EES parameters (0.2-0.6 mA and 20-60 Hz) were tested to determine those that specifically regulate the tibialis anterior (TA) and medial gastrocnemius (MG). Subsequently, to determine the effect of combined optical and electrical stimulation, near-infrared laser with a wavelength of 808 nm was used to irradiate the L3-L6 spinal cord segment while EES was performed. The amplitude of electromyography (EMG), the specific activation intensity of the target muscle, and the minimum stimulus current intensity to induce joint movement (motor threshold) under a series of optical stimulation parameters (power: 0.0-2.0 W; pulse width: 0-10 ms) were investigated and analyzed.

Results

EES stimulation with 40 Hz at the L3 and L6 spinal cord segments specifically activated TA and MG, respectively. High stimulation intensity (>2 × motor threshold) activated non-target muscles, while low stimulation frequency (<20 Hz) produced intermittent contraction. Compared to electrical stimulation alone (0.577 ± 0.081 mV), the combined stimulation strategy could induce stronger EMG amplitude of MG (1.426 ± 0.365 mV) after spinal cord injury (p < 0.01). The combined application of nINS effectively decreased the EES-induced motor threshold of MG (from 0.237 ± 0.001 mA to 0.166 ± 0.028 mA, p < 0.001). Additionally, the pulse width (PW) of nINS had a slight impact on the regulation of muscle activity. The EMG amplitude of MG only increased by ~70% (from 3.978 ± 0.240 mV to 6.753 ± 0.263 mV) when the PW increased by 10-fold (from 1 to 10 ms).

Conclusion

The study demonstrates the feasibility of epidural combined electrical and optical stimulation for highly specific regulation of muscle activity after SCI, and provides a new strategy for improving motor dysfunction caused by SCI.

Cellular Membrane-Engineered Nanovesicles as a Three-Stage Booster to Target the Lesion Core

The lesion core is the area with the most serious injury and vigorous repair. Existing nanocarriers are difficult to break through the targeted delivery to the lesion core for precise treatment in the intracellular and extracellular microenvironment. Herein, a cellular membrane-engineered nanovesicle (CMEV) with a hierarchical structure is constructed using the double emulsion-extrusion method by integrating a neutrophil membrane, functional antibody, and gelled drug-loaded core as a three-stage booster to target the lesion core and deliver catestatin (CST), a small therapeutic peptide, for ischemic cardiomyopathy therapy. By coating the neutrophil membrane outside the shell, CMEV is endowed with the function of neutrophil-like migration to achieve the first stage of tissue targeting. Based on the specific anchoring to injured myocardium, a myosin light chain 3 (MLC3) antibody is embedded to fulfill the second stage of CMEV accumulation in the lesion core. The gelled core containing CST-sodium alginate (NaAlg) with a pH-responsive shell is prepared by ionic cross-linking to accomplish the third stage of precise CST administration. Triggered by the microenvironment, NaAlg electrostatically adheres to the lesion core for sustained release, enhancing the efficacy of CST in improving cardiomyocyte apoptosis, excessive fibrosis, macrophage polarization, and angiogenesis. Thus, the "three-stage booster" nanovesicle significantly ameliorates cardiac function and adverse remodeling to treat ischemic cardiomyopathy.

Development and validation of a differentiation-related signature based on single-cell RNA sequencing data of immune cells in spinal cord injury

Background

After spinal cord injury (SCI), the native immune surveillance function of the central nervous system is activated, resulting in a substantial infiltration of immune cells into the affected tissue. While numerous studies have explored the transcriptome data following SCI and revealed certain diagnostic biomarkers, there remains a paucity of research pertaining the identification of immune subtypes and molecular markers related to the immune system post-spinal cord injury using single-cell sequencing data of immune cells.

Methods

The researchers conducted an analysis of spinal cord samples obtained at three time points (3,10, and 21 days) following SCI using the GSE159638 dataset. The SCI subsets were delineated through pseudo-time analysis, and differentiation related genes were identified after principal component analysis (PCA), cell clustering, and annotation techniques. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were employed to assess the differentiation-related genes (DRGs) across different subsets. The molecular subtypes of SCI were determined using consensus clustering analysis. To further explore and validate the correlation between the molecular subtypes and the immune microenvironment, the CIBERSORT algorithm was employed. High-value diagnostic gene markers were identified using LASSO regression, and their diagnostic sensitivity was assessed using receiver operating characteristic curves (ROC) and quantitative real-time polymerase chain reaction (qRT-PCR).

Results

Three SCI subsets were obtained, and differentiation-related genes were characterized. Within these subsets, two distinct molecular subtypes, namely C1 and C2, were identified. These subtypes demonstrated significant variations in terms of immune cell infiltration levels and the expression of immune checkpoint genes. Through further analysis, three candidate biomarkers (C1qa, Lgals3 and Cd63) were identified and subsequently validated.

Conclusions

Our study revealed a diverse immune microenvironment in SCI samples, highlighting the potential significance of C1qa, Lgals3 and Cd63 as immune biomarkers for diagnosing SCI. Moreover, the identification of immune checkpoints corresponding to the two molecular subtypes suggests their potential as targets for immunotherapy to enhance SCI repair in future interventions.

Multimodal therapy strategy based on a bioactive hydrogel for repair of spinal cord injury

Traumatic spinal cord injury results in permanent and serious neurological impairment, but there is no effective treatment yet. Tissue engineering approaches offer great potential for the treatment of SCI, but spinal cord complexity poses great challenges. In this study, the composite scaffold consists of a hyaluronic acid-based hydrogel, decellularized brain matrix (DBM), and bioactive compounds such as polydeoxyribonucleotide (PDRN), tumor necrosis factor-α/interferon-γ primed mesenchymal stem cell-derived extracellular vesicles (TI-EVs), and human embryonic stem cell-derived neural progenitor cells (NPC). The composite scaffold showed significant effects on regenerative prosses including angiogenesis, anti-inflammation, anti-apoptosis, and neural differentiation. In addition, the composite scaffold (DBM/PDRN/TI-EV/NPC@Gel) induced an effective spinal cord regeneration in a rat spinal cord transection model. Therefore, this multimodal approach using an integrated bioactive scaffold coupled with biochemical cues from PDRN and TI-EVs could be used as an advanced tissue engineering platform for spinal cord regeneration.

Transcription Pattern of Neurotrophic Factors and Their Receptors in Adult Zebrafish Spinal Cord

In vertebrates, neurotrophins and their receptors play a fundamental role in the central and peripheral nervous systems. Several studies reported that each neurotrophin/receptor signalling pathway can perform various functions during axon development, neuronal growth, and plasticity. Previous investigations in some fish species have identified neurotrophins and their receptors in the spinal cord under physiological conditions and after injuries, highlighting their potential role during regeneration. In our study, for the first time, we used an excellent animal model, the zebrafish (Danio rerio), to compare the mRNA localization patterns of neurotrophins and receptors in the spinal cord. We quantified the levels of mRNA using qPCR, and identified the transcription pattern of each neurotrophin/receptor pathway via in situ hybridization. Our data show that ngf/trka are the most transcribed members in the adult zebrafish spinal cord.

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.

Nano-integrated cascade antioxidases opsonized by albumin bypass the blood-brain barrier for treatment of ischemia-reperfusion injury

Potent antioxidative drugs are urgently needed to treat ischemia-reperfusion (I/R) induced reactive oxygen species (ROS)-mediated cerebrovascular and neural injury during ischemia strokes. However, current antioxidative agents have limited application in such disease due to low blood-brain barrier (BBB) penetration. We herein designed a "neutrophil piggybacking" strategy based on albumin opsonized nanoparticles co-encapsulated with antioxidases catalase (CAT) and superoxide dismutase 1 (SOD1). The system utilized the natural potential of neutrophils to target inflamed tissues to deliver antioxidases to injured sites in the brain. In addition, the system was integrated with a selenium (Se)-containing crosslinker to inhibit ferroptosis. We showed that the nanoparticles opsonized in the hybrid form rather than with an albumin-shell structure exhibited enhanced neutrophil targeting and efficient BBB penetration in vitro and in vivo. We further showed that the neutrophil-mediated delivery of antioxidases effectively reduced oxidative damage and apoptosis of neurons in brain tissue in a transient middle cerebral artery occlusion (tMCAO) mouse model. Moreover, the successful delivery of Se with the nanoparticles increased the expression of glutathione peroxidase 4 (GPX4) and effectively inhibited neuronal ferroptosis, achieving a satisfactory neuroprotective effect in I/R injury mice. Our study demonstrated that the rationally designed nanomedicines using the "neutrophil piggybacking" strategy can efficiently penetrate the BBB, greatly expanding the application of nanomedicines in the treatment of central nervous system (CNS) diseases.