Required growth facilitators propel axon regeneration across complete spinal cord injury

Autophagy-targeting modulation to promote peripheral nerve regeneration

Nerve regeneration following traumatic peripheral nerve injuries and neuropathies is a complex process modulated by diverse factors and intricate molecular mechanisms. Past studies have focused on factors that stimulate axonal outgrowth and myelin regeneration. However, recent studies have highlighted the pivotal role of autophagy in peripheral nerve regeneration, particularly in the context of traumatic injuries. Consequently, autophagy-targeting modulation has emerged as a promising therapeutic approach to enhancing peripheral nerve regeneration. Our current understanding suggests that activating autophagy facilitates the rapid clearance of damaged axons and myelin sheaths, thereby enhancing neuronal survival and mitigating injury-induced oxidative stress and inflammation. These actions collectively contribute to creating a favorable microenvironment for structural and functional nerve regeneration. A range of autophagy-inducing drugs and interventions have demonstrated beneficial effects in alleviating peripheral neuropathy and promoting nerve regeneration in preclinical models of traumatic peripheral nerve injuries. This review delves into the regulation of autophagy in cell types involved in peripheral nerve regeneration, summarizing the potential drugs and interventions that can be harnessed to promote this process. We hope that our review will offer novel insights and perspectives on the exploitation of autophagy pathways in the treatment of peripheral nerve injuries and neuropathies.

Astrocytes, reactive astrogliosis, and glial scar formation in traumatic brain injury

Traumatic brain injury is a global health crisis, causing significant death and disability worldwide. Neuroinflammation that follows traumatic brain injury has serious consequences for neuronal survival and cognitive impairments, with astrocytes involved in this response. Following traumatic brain injury, astrocytes rapidly become reactive, and astrogliosis propagates from the injury core to distant brain regions. Homeostatic astroglial proteins are downregulated near the traumatic brain injury core, while pro-inflammatory astroglial genes are overexpressed. This altered gene expression is considered a pathological remodeling of astrocytes that produces serious consequences for neuronal survival and cognitive recovery. In addition, glial scar formed by reactive astrocytes is initially necessary to limit immune cell infiltration, but in the long term impedes axonal reconnection and functional recovery. Current therapeutic strategies for traumatic brain injury are focused on preventing acute complications. Statins, cannabinoids, progesterone, beta-blockers, and cerebrolysin demonstrate neuroprotective benefits but most of them have not been studied in the context of astrocytes. In this review, we discuss the cell signaling pathways activated in reactive astrocytes following traumatic brain injury and we discuss some of the potential new strategies aimed to modulate astroglial responses in traumatic brain injury, especially using cell-targeted strategies with miRNAs or lncRNA, viral vectors, and repurposed drugs.

From single to combinatorial therapies in spinal cord injuries for structural and functional restoration

Spinal cord injury results in paralysis, sensory disturbances, sphincter dysfunction, and multiple systemic secondary conditions, most arising from autonomic dysregulation. All this produces profound negative psychosocial implications for affected people, their families, and their communities; the financial costs can be challenging for their families and health institutions. Treatments aimed at restoring the spinal cord after spinal cord injury, which have been tested in animal models or clinical trials, generally seek to counteract one or more of the secondary mechanisms of injury to limit the extent of the initial damage. Most published works on structural/functional restoration in acute and chronic spinal cord injury stages use a single type of treatment: a drug or trophic factor, transplant of a cell type, and implantation of a biomaterial. Despite the significant benefits reported in animal models, when translating these successful therapeutic strategies to humans, the result in clinical trials has been considered of little relevance because the improvement, when present, is usually insufficient. Until now, most studies designed to promote neuroprotection or regeneration at different stages after spinal cord injury have used single treatments. Considering the occurrence of various secondary mechanisms of injury in the acute and sub-acute phases of spinal cord injury, it is reasonable to speculate that more than one therapeutic agent could be required to promote structural and functional restoration of the damaged spinal cord. Treatments that combine several therapeutic agents, targeting different mechanisms of injury, which, when used as a single therapy, have shown some benefits, allow us to assume that they will have synergistic beneficial effects. Thus, this narrative review article aims to summarize current trends in the use of strategies that combine therapeutic agents administered simultaneously or sequentially, seeking structural and functional restoration of the injured spinal cord.

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.

Bioactive Peptide Hydrogel Scaffold with High Fluidity, Thermosensitivity, and Neurotropism in 3D Spatial Structure for Promoted Repair of Spinal Cord Injury

Spinal cord injury (SCI) has been considered a clinically challenging disease that is characterized by local disturbance of the microenvironment, which inhibits post-injury neural regeneration. The simulation of a microenvironment conducive to the regeneration of spinal cord is beneficial for SCI repair. In this study, bioactive composite hydrogels are developed that mimic the regenerative microenvironment of spinal cord for enhanced SCI repair. The fabricated composite hydrogels (CRP) based on chitosan (CS), RADA16 nanofibers, and nerve-promoted peptide (PPFLMLLKGSTR) exhibit excellent injectability, superior biodegradability and biocompatibility. In addition, the CRP hydrogels can form quickly (a few minutes) by mixing three components at human body temperature, showing high potential as a biomimetic matrix for in situ repair of SCI. The in vitro studies demonstrate that the CRP hydrogels can not only promote the proliferation and migration of bone marrow mesenchymal stem cells but also induce the proliferation and differentiation of neural stem cells (NSCs) into neurons. Meanwhile, the hydrogels reveal the efficiency of protecting neurons and promoting axonal growth. Furthermore, the in vivo tests prove that the CRP hydrogels can reduce post-SCI inflammatory responses, inhibit reactive astrocyte over-proliferation, and promote the migration, proliferation, and differentiation of endogenous NSCs, which agree well with the in vitro results. The pre-clinical test demonstrates that the CRP hydrogels restore the motor function in completely transected spinal cord rats, and the SCI repair mechanism may involve the activation of the PI3K/AKT/mTOR pathway. It is believed that the strategies shown in this work will be valuable for the design and synthesis of novel hydrogels for biomedical and tissue engineering applications.

Cell surface receptor-mediated signaling in CNS regeneration

Degenerative diseases and injuries of central nervous system (CNS) often cause nerve cell apoptosis and neural dysfunction. Protection of surviving cells or inducing the differentiation of stem cells into functional cells is considered to be an important way of neurorepair. In addition, transdifferentiation technology emerged recently is expected to provide new solutions for nerve regeneration. Cell surface receptors are transmembrane proteins embedded in cytoplasmic membrane, and play crucial roles in maintaining communication between extracellular signals and intracellular signaling processes. The extracellular microenvironment changed dramatically upon neural lesion, exploring the biological function of signals mediated by cell surface receptors will help to develop molecular strategies for nerve regeneration. An increasing number of studies have reported that cell surface receptor-mediated signaling affects the survival, differentiation, and functioning of neural cells, and even regulate their trans-lineage reprogramming. Here, we provide a review on the roles of cell surface receptors in CNS regeneration, thus providing new cues for better treatment of neurodegenerative diseases or nerve injury.

Clickable immune-microenvironment modulated hydrogels for spinal cord injury repair

Spinal cord injury (SCI) is a devastating condition without effective therapy currently available. The inflammatory cascade following SCI leads to neuronal apoptosis and glial cell activation. The utilization of local injectable hydrogels with immunotherapy drugs directly into injured nerve tissues represents a promising therapeutic strategy. Herein, injectable hydrogels grafted with clickable methylprednisolone (MP) and cellular adhesion peptide were developed using free radical polymerization for promoting nerve regeneration following SCI. MP conjugated hydrogels could modulate the immunoinflammatory microenvironment of SCI and sustain neuron survival. The multi-stiffness hydrogels were fabricated by adjusting concentration ratios to evaluate appropriate mechanical stimuli. In a model of dorsal root ganglion, MP grafted hydrogels with mechanical signals similar to those of adult rat spinal cords demonstrated superior efficacy in promoting dorsal root ganglion growth. MP grafted hydrogels could regulate the immune-inflammatory microenvironment, promote recovery of both motor function and sensory functions. The positive findings suggested that the interplay between immunomodulation and mechanical signals plays a crucial role in promoting nerve regeneration, indicating significant potential for hydrogels as a therapeutic approach for repairing SCI.

Regenerative medicine approaches for the treatment of spinal cord injuries: Progress and challenges

Spinal cord injury (SCI) is a profound medical condition that significantly hampers motor function, imposing substantial limitations on daily activities and exerting a considerable financial burden on patients and their families. The constrained regenerative capacity of endogenous spinal cord tissue, exacerbated by the inflammatory response following the initial trauma, poses a formidable obstacle to effective therapy. Recent advancements in the field, stem cells, biomaterials, and molecular therapy, show promising outcomes. This review provides a comprehensive analysis of tissue engineering and regenerative medicine approaches for SCI treatment, including cell transplantation, tissue-engineered construct implantation, and other potential therapeutic strategies. Additionally, it sheds light on preclinical animal studies and recent clinical trials incorporating these modalities, providing a glimpse into the evolving landscape of SCI management. STATEMENT OF SIGNIFICANCE: The investigation into spinal cord injury (SCI) treatments focuses on reducing long-term impacts by targeting scar inhibition and enhancing regeneration through stem cells, with or without growth factors. Induced pluripotent stem cells (iPSCs) show promise for autologous use, with clinical trials confirming their safety. Challenges include low cell viability and difficulty in targeted differentiation. Biomaterial scaffolds hold potential for improving cell viability and integration, and extracellular vesicles (EVs) are emerging as a novel therapy. While EV research is in its early stages, stem cell trials demonstrate safety and potential recovery. Advancing tissue engineering approaches with biomaterial scaffolds is crucial for human trials.

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.

Growth hormone promotes the reconstruction of injured axons in the hypothalamo-neurohypophyseal system

JOURNAL/nrgr/04.03/01300535-202410000-00026/figure1/v/2024-02-06T055622Z/r/image-tiff Previous studies have shown that growth hormone can regulate hypothalamic energy metabolism, stress, and hormone release. Therefore, growth hormone has great potential for treating hypothalamic injury. In this study, we established a specific hypothalamic axon injury model by inducing hypothalamic pituitary stalk electric lesions in male mice. We then treated mice by intraperitoneal administration of growth hormone. Our results showed that growth hormone increased the expression of insulin-like growth factor 1 and its receptors, and promoted the survival of hypothalamic neurons, axonal regeneration, and vascular reconstruction from the median eminence through the posterior pituitary. Altogether, this alleviated hypothalamic injury-caused central diabetes insipidus and anxiety. These results suggest that growth hormone can promote axonal reconstruction after hypothalamic injury by regulating the growth hormone-insulin-like growth factor 1 axis.

Building-Block Size Mediates Microporous Annealed Particle Hydrogel Tube Microenvironment Following Spinal Cord Injury

Spinal cord injury (SCI) is a life-altering event, which often results in loss of sensory and motor function below the level of trauma. Biomaterial therapies have been widely investigated in SCI to promote directional regeneration but are often limited by their pre-constructed size and shape. Herein, the design parameters of microporous annealed particles (MAPs) are investigated with tubular geometries that conform to the injury and direct axons across the defect to support functional recovery. MAP tubes prepared from 20-, 40-, and 60-micron polyethylene glycol (PEG) beads are generated and implanted in a T9-10 murine hemisection model of SCI. Tubes attenuate glial and fibrotic scarring, increase innate immune cell density, and reduce inflammatory phenotypes in a bead size-dependent manner. Tubes composed of 60-micron beads increase the cell density of the chronic macrophage response, while neutrophil infiltration and phenotypes do not deviate from those seen in controls. At 8 weeks postinjury, implantation of tubes composed of 60-micron beads results in enhanced locomotor function, robust axonal ingrowth, and remyelination through both lumens and the inter-tube space. Collectively, these studies demonstrate the importance of bead size in MAP construction and highlight PEG tubes as a biomaterial therapy to promote regeneration and functional recovery in SCI.

Acrylic Acid Modified Poly-ethylene Glycol Microparticles for Affinity-Based release of Insulin-Like Growth Factor-1 in Neural Applications

Sustained release of bioactive molecules via affinity-based interactions presents a promising approach for controlled delivery of growth factors. Insulin-like growth factor-1 (IGF-1) has gained increased attention due to its ability to promote axonal growth in the central nervous system. In this work, we aimed to evaluate the effect of IGF-1 delivery from polyethylene-glycol diacrylate (PEG-DA) microparticles using affinity-based sustained release on neurons. We developed PEG-DA-based microparticles with varying levels of acrylic acid (AA) as a comonomer to tune their overall charge. The particles were synthesized via precipitation polymerization under UV light, yielding microparticles (MPs) with a relatively low polydispersity index. IGF-1 was incubated with the PEG-DA particles overnight, and formulations with a higher AA content resulted in higher loading efficiency and slower release rates over 4 weeks, suggesting the presence of binding interactions between the positively charged IGF-1 and negatively charged particles containing AA. The released IGF-1 was tested in dorsal root ganglion (DRG) neurite outgrowth assay and found to retain its biological activity for up to two weeks after encapsulation. Furthermore, the trophic effect of IGF-1 was tested with stem cell-derived V2a interneurons and found to have a synergistic effect when combined with neurotrophin-3 (NT3). To assess the potential of a combinatorial approach, IGF-1-releasing MPs were encapsulated within a hyaluronic acid (HA) hydrogel and showed promise as a dual delivery system. Overall, the PEG-DA MPs developed herein deliver bioactive IGF-1 for a period of weeks and hold potential to enable axonal growth of injured neurons via sustained release.

MCT1-mediated endothelial cell lactate shuttle as a target for promoting axon regeneration after spinal cord injury

Rationale: Spinal cord injury (SCI)-induced vascular damage causes ischemia and hypoxia at the injury site, which, in turn, leads to profound metabolic disruptions. The effects of these metabolic alterations on neural tissue remodeling and functional recovery have yet to be elucidated. The current study aimed to investigate the consequences of the SCI-induced hypoxic environment at the epicenter of the injury. Methods: This study employed metabolomics to assess changes in energy metabolism after SCI. The use of a lactate sensor identified lactate shuttle between endothelial cells (ECs) and neurons. Reanalysis of single-cell RNA sequencing data demonstrated reduced MCT1 expression in ECs after SCI. Additionally, an adeno-associated virus (AAV) overexpressing MCT1 was utilized to elucidate its role in endothelial-neuronal interactions, tissue repair, and functional recovery. Results: The findings revealed markedly decreased monocarboxylate transporter 1 (MCT1) expression that facilitates lactate delivery to neurons to support their energy metabolism in ECs post-SCI. This decreased expression of MCT1 disrupts lactate transport to neurons, resulting in a metabolic imbalance that impedes axonal regeneration. Strikingly, our results suggested that administering adeno-associated virus specifically to ECs to restore MCT1 expression enhances axonal regeneration and improves functional recovery in SCI mice. These findings indicate a novel link between lactate shuttling from endothelial cells to neurons following SCI and subsequent neural functional recovery. Conclusion: In summary, the current study highlights a novel metabolic pathway for therapeutic interventions in the treatment of SCI. Additionally, our findings indicate the potential benefits of targeting lactate transport mechanisms in recovery from SCI.

Low-Dose LPS Modulates Microglia/Macrophages Phenotypic Transformation to Amplify Rehabilitation Effects in Chronic Spinal Cord Injured (CSCI) Mice

Spinal cord injury (SCI) results in stalled motor function recovery under the chronic phase. One of the reasons due to the presence of ongoing inflammation. Therefore, regulating the status of immune cells may help reopen the window for neural repair, which represents a potential therapeutic target. In this study, we aimed to investigate whether this could be achieved in mice with cervical 5 crush CSCI (4 W) by utilizing a concentration of 0.5 mg/kg of lipopolysaccharide (LPS) to stimulate microglia/macrophages. Additionally, the mice underwent rehabilitation training for another 6 weeks. Our results showed that systemic injection of LPS enhanced the effects of forelimb rehabilitation training, as evaluated through single pellet grasping (SPG). Electrophysiological studies revealed the restoration of cortical drive to the injured side's forelimb muscles in the training combined with LPS group. Tract tracing studies demonstrated the reconstruction of cortical innervation to the cervical spinal cord. Furthermore, the levels of pro-inflammatory phenotype markers, such as inducible nitric oxide synthase (INOS) and CD68, decreased, while the expression of anti-inflammatory phenotype markers, including arginase 1 (ARG-1) and CD206, increased. Importantly, this phenotypic switch in microglia/macrophages was accompanied by an increase in phagocytic activity markers as indicated by BODIPY + IBA1 + staining. Collectively, our data suggests that low-dose LPS improves the effects of rehabilitation training by regulating the phenotypic transformation of microglia/macrophages in CSCI. This study provides a fresh perspective and intervention direction for the clinical treatment of chronic spinal cord injuries.

Functional biomaterials for modulating the dysfunctional pathological microenvironment of spinal cord injury

Spinal cord injury (SCI) often results in irreversible loss of sensory and motor functions, and most SCIs are incurable with current medical practice. One of the hardest challenges in treating SCI is the development of a dysfunctional pathological microenvironment, which mainly comprises excessive inflammation, deposition of inhibitory molecules, neurotrophic factor deprivation, glial scar formation, and imbalance of vascular function. To overcome this challenge, implantation of functional biomaterials at the injury site has been regarded as a potential treatment for modulating the dysfunctional microenvironment to support axon regeneration, remyelination at injury site, and functional recovery after SCI. This review summarizes characteristics of dysfunctional pathological microenvironment and recent advances in biomaterials as well as the technologies used to modulate inflammatory microenvironment, regulate inhibitory microenvironment, and reshape revascularization microenvironment. Moreover, technological limitations, challenges, and future prospects of functional biomaterials to promote efficient repair of SCI are also discussed. This review will aid further understanding and development of functional biomaterials to regulate pathological SCI microenvironment.

Trehalose-based coacervates for local bioactive protein delivery to the central nervous system

Therapeutic outcomes of local biomolecule delivery to the central nervous system (CNS) using bulk biomaterials are limited by inadequate drug loading, neuropil disruption, and severe foreign body responses. Effective CNS delivery requires addressing these issues and developing well-tolerated, highly-loaded carriers that are dispersible within local neural parenchyma. Here, we synthesized biodegradable trehalose-based polyelectrolyte oligomers using facile A2:B3:AR thiol-ene Michael addition reactions that form complex coacervates upon mixing of oppositely charged oligomers. Coacervates permit high concentration loading and controlled release of bioactive growth factors, enzymes, and antibodies, with modular formulation parameters that confer tunable release kinetics. Coacervates are cytocompatible with cultured neural cells in vitro and can be formulated to either direct intracellular protein delivery or sequester media containing proteins and remain extracellular. Coacervates serve as effective vehicles for precisely delivering biomolecules, including bioactive neurotrophins, to the mouse striatum following intraparenchymal injection. These results support the use of trehalose-based coacervates as part of therapeutic protein delivery strategies for CNS disorders.

Challenges in advancing Schwann cell transplantation for spinal cord injury repair

BACKGROUND AIMS

In this article we aimed to provide an expert synthesis of the current status of Schwann cell (SC)therapeutics and potential steps to increase their clinical utility.

METHODS

We provide an expert synthesis based on preclinical, clinical and manufacturing experience.

RESULTS

Schwann cells (SCs) are essential for peripheral nerve regeneration and are of interest in supporting axonal repair after spinal cord injury (SCI). SCs can be isolated and cultivated in tissue culture from adult nerve biopsies or generated from precursors and neural progenitors using specific differentiation protocols leading to expanded quantities. In culture, they undergo dedifferentiation to a state similar to "repair" SCs. The known repertoire of SC functions is increasing beyond axon maintenance, myelination, and axonal regeneration to include immunologic regulation and the release of potentially therapeutic extracellular vesicles. Recently, autologous human SC cultures purified under cGMP conditions have been tested in both nerve repair and subacute and chronic SCI clinical trials. Although the effects of SCs to support nerve regeneration are indisputable, their efficacy for clinical SCI has been limited according to the outcomes examined.

CONCLUSIONS

This review discusses the current limitations of transplanted SCs within the damaged spinal cord environment. Limitations include limited post-transplant cell survival, the inability of SCs to migrate within astrocytic parenchyma, and restricted axonal regeneration out of SC-rich graft regions. We describe steps to amplify the survival and integration of transplanted SCs and to expand the repertoire of uses of SCs, including SC-derived extracellular vesicles. The relative merits of transplanting autologous versus allogeneic SCs and the role that endogenous SCs play in spinal cord repair are described. Finally, we briefly describe the issues requiring solutions to scale up SC manufacturing for commercial use.

Interfacing Neuron-Motor Pathways with Stretchable and Biocompatible Electrode Arrays

ConspectusIn the field of neuroscience, understanding the complex interactions within the intricate neuron-motor system depends crucially on the use of high-density, physiological multiple electrode arrays (MEAs). In the neuron-motor system, the transmission of biological signals primarily occurs through electrical and chemical signaling. Taking neurons for instance, when a neuron receives external stimuli, it generates an electrical signal known as the action potential. This action potential propagates along the neuron's axon and is transmitted to other neurons via synapses. At the synapse, chemical signals (neurotransmitters) are released, allowing the electrical signal to traverse the synaptic gap and influence the next neuron. MEAs can provide unparalleled insights into neural signal patterns when interfacing with the nerve systems through their excellent spatiotemporal resolution. However, the inherent differences in mechanical and chemical properties between these artificial devices and biological tissues can lead to serious complications after chronic implantation, such as body rejection, infection, tissue damage, or device malfunction. A promising strategy to enhance MEAs' biocompatibility involves minimizing their thickness, which aligns their bending stiffness with that of surrounding tissues, thereby minimizing damage over time. However, this solution has its limits; the resulting ultrathin devices, typically based on plastic films, lack the necessary stretchability, restricting their use to organs that neither stretch nor grow.For practical deployments, devices must exhibit certain levels of stretchability (ranging from 20 to 70%), tailored to the specific requirements of the target organs. In this Account, we outline recent advancements in developing stretchable MEAs that balance stretchability with sufficient electrical conductivity for effective use in physiological research, acting as sensors and stimulators. By concentrating on the neuron-motor pathways, we summarize how the stretchable MEAs meet various application needs and examine their effectiveness. We distinguish between on-skin and implantable uses, given their vastly different requirements. Within each application scope, we highlight cutting-edge technologies, evaluating their strengths and shortcomings. Recognizing that most current devices rely on elastic films with a Young's modulus value between ∼0.5 and 5 MPa, we delve into the potential for softer MEAs, particularly those using multifunctional hydrogels for an optimizing tissue-device interface and address the challenges in adapting such hydrogel-based MEAs for chronic implants. Additionally, transitioning soft MEAs from lab to fab involves connecting them to a rigid adapter and external machinery, highlighting a critical challenge at the soft-rigid interface due to strain concentration, especially in chronic studies subject to unforeseen mechanical strains. We discuss innovative solutions to this integration challenge, being optimistic that the development of durable, biocompatible, stretchable MEAs will significantly advance neuroscience and related fields.

Single-cell analysis of innate spinal cord regeneration identifies intersecting modes of neuronal repair

Adult zebrafish have an innate ability to recover from severe spinal cord injury. Here, we report a comprehensive single nuclear RNA sequencing atlas that spans 6 weeks of regeneration. We identify cooperative roles for adult neurogenesis and neuronal plasticity during spinal cord repair. Neurogenesis of glutamatergic and GABAergic neurons restores the excitatory/inhibitory balance after injury. In addition, a transient population of injury-responsive neurons (iNeurons) show elevated plasticity 1 week post-injury. We found iNeurons are injury-surviving neurons that acquire a neuroblast-like gene expression signature after injury. CRISPR/Cas9 mutagenesis showed iNeurons are required for functional recovery and employ vesicular trafficking as an essential mechanism that underlies neuronal plasticity. This study provides a comprehensive resource of the cells and mechanisms that direct spinal cord regeneration and establishes zebrafish as a model of plasticity-driven neural repair.

Affinity-based drug delivery systems for the central nervous system: exploiting molecular interactions for local, precise targeting

Objective: The effective treatment of central nervous system (CNS) disorders remains a significant challenge, primarily due to its molecular and structural complexity. Clinical translation of promising therapeutic agents is limited by the lack of optimal drug delivery systems capable of targeted, localized release of drugs to the brain and spinal cord.Approach: This review provides an overview of the potential of affinity-based drug delivery systems, which leverage molecular interactions to enhance the delivery and efficacy of therapeutic agents within the CNS.Main results: Various approaches, including hydrogels, micro- and nanoparticles, and functionalized biomaterials, are examined for their ability to provide local, sustained release of proteins, growth factors and other drugs.Significance: Furthermore, we present a detailed analysis of design considerations for developing effective affinity-based systems, incorporating insights from both existing literature and our group's research. These considerations include the biochemical modification of delivery vehicles and the optimization of physical and chemical properties to improve therapeutic outcomes.

Transplantation of olfactory mucosa mesenchymal stromal cells repairs spinal cord injury by inducing microglial polarization

STUDY DESIGN

Animal studies OBJECTIVES: To evaluate the therapeutic effect of olfactory mucosa mesenchymal stem cell (OM-MSCs) transplantation in mice with spinal cord injury (SCI) and to explore the mechanism by which OM-MSCs inhibit neuroinflammation and improve SCI.

SETTING

Xiangya Hospital, Central South University; Affiliated Hospital of Guangdong Medical University.

METHODS

Mice (C57BL/6, female, 6-week-old) were randomly divided into sham, SCI, and SCI + OM-MSC groups. The SCI mouse model was generated using Allen's method. OM-MSCs were immediately delivered to the lateral ventricle after SCI using stereotaxic brain injections. One day prior to injury and on days 1, 5, 7, 14, 21, and 28 post-injury, the Basso Mouse Scale and Rivlin inclined plate tests were performed. Inflammation and microglial polarization were evaluated using histological staining, immunofluorescence, and qRT-PCR.

RESULTS

OM-MSCs originating from the neuroectoderm have great potential in the management of SCI owing to their immunomodulatory effects. OM-MSCs administration improved motor function, alleviated inflammation, promoted the transformation of the M1 phenotype of microglia into the M2 phenotype, facilitated axonal regeneration, and relieved spinal cord injury in SCI mice.

CONCLUSIONS

OM-MSCs reduced the level of inflammation in the spinal cord tissue, protected neurons, and repaired spinal cord injury by regulating the M1/M2 polarization of microglia.

Low frequency of repetitive trans-spinal magnetic stimulation promotes functional recovery after spinal cord injury in mice through inhibiting TGF-β1/Smad2/3 signaling pathway

Spinal cord injury (SCI) remains a worldwide challenge due to limited treatment strategies. Repetitive trans-spinal magnetic stimulation (rTSMS) is among the most cutting-edge treatments for SCI. However, the mechanism underlying rTSMS on functional recovery is still unclear. In this study, 8-week-old C57BL/6J female mice were used to design SCI models followed by treatment with monotherapy (1 Hz rTSMS or LY364947) or combination therapy (rTSMS + LY364947). Our results showed obvious functional recovery after monotherapies compared to untreated mice. Immunofluorescence results demonstrated that rTSMS and LY364947 modulate the lesion scar by decreasing fibrosis and GFAP and possess the effect on neural protection. In addition, rTSMS suppressed inflammation and the activation of TGFβ1/Smad2/3 signaling pathway, as evidenced by markedly reduced TGF-βRⅠ, Smad2/3, and p-Smad2/3 compared with untreated mice. Overall, it was confirmed that 1 Hz rTSMS promotes SCI recovery by suppressing the TGFβ1/Smad2/3 signaling, revealing a novel pathological mechanism of 1 Hz rTSMS intervention, and may provide potential targets for clinical treatment.

Unleashing metabolic power for axonal regeneration

Axon regeneration requires the mobilization of intracellular resources, including proteins, lipids, and nucleotides. After injury, neurons need to adapt their metabolism to meet the biosynthetic demands needed to achieve axonal regeneration. However, the exact contribution of cellular metabolism to this process remains elusive. Insights into the metabolic characteristics of proliferative cells may illuminate similar mechanisms operating in axon regeneration; therefore, unraveling previously unappreciated roles of metabolic adaptation is critical to achieving neuron regrowth, which is connected to the therapeutic strategies for neurological conditions necessitating nerve repairs, such as spinal cord injury and stroke. Here, we outline the metabolic role in axon regeneration and discuss factors enhancing nerve regrowth, highlighting potential novel metabolic treatments for restoring nerve function.

Characteristic Profiling of Soluble Factors in the Cerebrospinal Fluid of Patients With Neurosyphilis

BACKGROUND

Soluble inflammatory factors in the cerebrospinal fluid (CSF) of patients with neurosyphilis have been investigated with low-throughput technology. This study aimed to illustrate the characteristics of soluble factor profiles in CSF of patients with neurosyphilis.

METHODS

We measured the concentrations of 45 cytokines, chemokines, and growth factors in CSF from 112 untreated syphilis cases, including latent syphilis (LS), asymptomatic neurosyphilis (ANS), meningeal neurosyphilis (MNS), meningovascular neurosyphilis (MVNS), paralytic dementia (PD), and ocular syphilis (OS).

RESULTS

Thirty-three differentially expressed soluble factors (DeSFs) were categorized into 3 clusters. DeSF scores of clusters 1 and 2 (DeSFS1 and DeSFS2) were positively correlated with elevated neopterin and neurofilament light subunit (NF-L) concentration, respectively. DeSF scores of cluster 3 were positively correlated with white blood cells, protein, NF-L, and neopterin. Patients with LS, ANS, and OS exhibited an overall lower abundance of DeSFs. Patients with PD exhibited significantly increased levels of clusters 1 and 3, and the highest total DeSF score, whereas patients with MNS and MVNS showed enhanced levels of cluster 2. Receiver operating characteristic analysis revealed that DeSFS1 effectively discriminated PD, and DeSFS2 discriminated MNS/MVNS with high accuracy.

CONCLUSIONS

Patients with neurosyphilis at different stages have distinctive patterns of soluble factors in CSF, which are correlated with immune status and neuronal damage.

Regeneration of Propriospinal Axons in Rat Transected Spinal Cord Injury through a Growth-Promoting Pathway Constructed by Schwann Cells Overexpressing GDNF

Unsuccessful axonal regeneration in transected spinal cord injury (SCI) is mainly attributed to shortage of growth factors, inhibitory glial scar, and low intrinsic regenerating capacity of severely injured neurons. Previously, we constructed an axonal growth permissive pathway in a thoracic hemisected injury by transplantation of Schwann cells overexpressing glial-cell-derived neurotrophic factor (SCs-GDNF) into the lesion gap as well as the caudal cord and proved that this novel permissive bridge promoted the regeneration of descending propriospinal tract (dPST) axons across and beyond the lesion. In the current study, we subjected rats to complete thoracic (T11) spinal cord transections and examined whether these combinatorial treatments can support dPST axons' regeneration beyond the transected injury. The results indicated that GDNF significantly improved graft-host interface by promoting integration between SCs and astrocytes, especially the migration of reactive astrocyte into SCs-GDNF territory. The glial response in the caudal graft area has been significantly attenuated. The astrocytes inside the grafted area were morphologically characterized by elongated and slim process and bipolar orientation accompanied by dramatically reduced expression of glial fibrillary acidic protein. Tremendous dPST axons have been found to regenerate across the lesion and back to the caudal spinal cord which were otherwise difficult to see in control groups. The caudal synaptic connections were formed, and regenerated axons were remyelinated. The hindlimb locomotor function has been improved.

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.

Repetitive transcranial magnetic stimulation promotes motor function recovery in mice after spinal cord injury via regulation of the Cx43-autophagy loop

Spinal cord injury (SCI) is a severe condition with an extremely high disability rate. It is mainly manifested as the loss of motor, sensory and autonomic nerve functions below the injury site. High-frequency transcranial magnetic stimulation, a recently developed neuromodulation method, can increase motor function in mice with spinal cord injury. This study aimed to explore the possible mechanism by which transcranial magnetic stimulation (TMS) restores motor function after SCI. A complete T8 transection model of the spinal cord was established in mice, and the mice were treated daily with 15 Hz high-frequency transcranial magnetic stimulation. The BMS was used to evaluate the motor function of the mice after SCI. Western blotting and immunofluorescence were used to detect the expression of Connexin43 (CX43) and autophagy-related proteins in vivo and in vitro, and correlation analysis was performed to study the relationships among autophagy, CX43 and motor function recovery after SCI in mice. Western blotting was used to observe the effect of magnetic stimulation on the expression of mTOR pathway members. In the control group, the expression of CX43 was significantly decreased, and the expression of microtubule-associated protein 1 A/1b light chain 3 (LC3II) and P62 was significantly increased after 4 weeks of spinal cord transection. After high-frequency magnetic stimulation, the level of CX43 decreased, and the levels of LC3II and P62 increased in primary astrocytes. The BMS of the magnetic stimulation group was greater than that of the control group. High-frequency magnetic stimulation can inhibit the expression of CX43, which negatively regulates autophagic flux. HF-rTMS increased the expression levels of mTOR, p-mTOR and p-S6. Our experiments showed that rTMS can restore hindlimb motor function in mice after spinal cord injury via regulation of the Cx43-autophagy loop and activation of the mTOR signalling pathway.

The LRRK2-G2019S mutation attenuates repair of brain injury partially by reducing the release of osteopontin-containing monocytic exosome-like vesicles

BACKGROUND

Brain injury has been suggested as a risk factor for neurodegenerative diseases. Accordingly, defects in the brain's intrinsic capacity to repair injury may result in the accumulation of damage and a progressive loss of brain function. The G2019S (GS) mutation in LRRK2 (leucine rich repeat kinase 2) is the most prevalent genetic alteration in Parkinson's disease (PD). Here, we sought to investigate how this LRRK2-GS mutation affects repair of the injured brain.

METHODS

Brain injury was induced by stereotaxic injection of ATP, a damage-associated molecular pattern (DAMP) component, into the striatum of wild-type (WT) and LRRK2-GS mice. Effects of the LRRK2-GS mutation on brain injury and the recovery from injury were examined by analyzing the molecular and cellular behavior of neurons, astrocytes, and monocytes.

RESULTS

Damaged neurons express osteopontin (OPN), a factor associated with brain repair. Following ATP-induced damage, monocytes entered injured brains, phagocytosing damaged neurons and producing exosome-like vesicles (EVs) containing OPN through activation of the inflammasome and subsequent pyroptosis. Following EV production, neurons and astrocytes processes elongated towards injured cores. In LRRK2-GS mice, OPN expression and monocytic pyroptosis were decreased compared with that in WT mice, resulting in diminished release of OPN-containing EVs and attenuated elongation of neuron and astrocyte processes. In addition, exosomes prepared from injured LRRK2-GS brains induced neurite outgrowth less efficiently than those from injured WT brains.

CONCLUSIONS

The LRRK2-GS mutation delays repair of injured brains through reduced expression of OPN and diminished release of OPN-containing EVs from monocytes. These findings suggest that the LRRK2-GS mutation may promote the development of PD by delaying the repair of brain injury.

Reactive Astrocytes and Emerging Roles in Central Nervous System (CNS) Disorders

In addition to their many functions in the healthy central nervous system (CNS), astrocytes respond to CNS damage and disease through a process called "reactivity." Recent evidence reveals that astrocyte reactivity is a heterogeneous spectrum of potential changes that occur in a context-specific manner. These changes are determined by diverse signaling events and vary not only with the nature and severity of different CNS insults but also with location in the CNS, genetic predispositions, age, and potentially also with "molecular memory" of previous reactivity events. Astrocyte reactivity can be associated with both essential beneficial functions as well as with harmful effects. The available information is rapidly expanding and much has been learned about molecular diversity of astrocyte reactivity. Emerging functional associations point toward central roles for astrocyte reactivity in determining the outcome in CNS disorders.

Single-cell and spatial atlases of spinal cord injury in the Tabulae Paralytica

Here, we introduce the Tabulae Paralytica-a compilation of four atlases of spinal cord injury (SCI) comprising a single-nucleus transcriptome atlas of half a million cells, a multiome atlas pairing transcriptomic and epigenomic measurements within the same nuclei, and two spatial transcriptomic atlases of the injured spinal cord spanning four spatial and temporal dimensions. We integrated these atlases into a common framework to dissect the molecular logic that governs the responses to injury within the spinal cord1. The Tabulae Paralytica uncovered new biological principles that dictate the consequences of SCI, including conserved and divergent neuronal responses to injury; the priming of specific neuronal subpopulations to upregulate circuit-reorganizing programs after injury; an inverse relationship between neuronal stress responses and the activation of circuit reorganization programs; the necessity of re-establishing a tripartite neuroprotective barrier between immune-privileged and extra-neural environments after SCI and a failure to form this barrier in old mice. We leveraged the Tabulae Paralytica to develop a rejuvenative gene therapy that re-established this tripartite barrier, and restored the natural recovery of walking after paralysis in old mice. The Tabulae Paralytica provides a window into the pathobiology of SCI, while establishing a framework for integrating multimodal, genome-scale measurements in four dimensions to study biology and medicine.

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.

Blood-based inflammatory protein biomarker panel for the prediction of relapse and severity in patients with neuromyelitis optica spectrum disorder: A prospective cohort study

BACKGROUND

To date, most existing models for predicting neuromyelitis optica spectrum disorder (NMOSD) are based primarily on clinical characteristics. Blood-based NMOSD severity and prognostic predictive immune- and inflammation-related biomarkers are needed. We aimed to investigate the associations between plasma inflammatory biomarkers and relapse and attack severity in NMOSD.

METHODS

This two-step, single-center prospective cohort study included discovery and validation cohorts. We quantified 92 plasma inflammatory proteins by using Olink's proximity extension assay and identified differentially expressed proteins in the relapse group (relapse within 1 year of follow-up) and severe attack group. To define a new molecular prognostic model, we calculated the risk score of each patient based on the key protein signatures and validated the results in the validation cohort.

RESULTS

The relapse prediction model, including FGF-23, DNER, GDNF, and SLAMF1, predicted the 1-year relapse risk. The severe attack prediction model, including PD-L1 and MCP-2, predicted the severe clinical attack risk. Both the relapse and severe attack prediction models demonstrated good discriminative ability and high accuracy in the validation cohort.

CONCLUSIONS

Our discovered biomarker signature and prediction models may complement current clinical risk stratification approaches. These inflammatory biomarkers could contribute to the discovery of therapeutic interventions and prevent NMOSD progression.

Translational Relevance of Secondary Intracellular Signaling Cascades Following Traumatic Spinal Cord Injury

Traumatic spinal cord injury (SCI) is a life-threatening and life-altering condition that results in debilitating sensorimotor and autonomic impairments. Despite significant advances in the clinical management of traumatic SCI, many patients continue to suffer due to a lack of effective therapies. The initial mechanical injury to the spinal cord results in a series of secondary molecular processes and intracellular signaling cascades in immune, vascular, glial, and neuronal cell populations, which further damage the injured spinal cord. These intracellular cascades present promising translationally relevant targets for therapeutic intervention due to their high ubiquity and conservation across eukaryotic evolution. To date, many therapeutics have shown either direct or indirect involvement of these pathways in improving recovery after SCI. However, the complex, multifaceted, and heterogeneous nature of traumatic SCI requires better elucidation of the underlying secondary intracellular signaling cascades to minimize off-target effects and maximize effectiveness. Recent advances in transcriptional and molecular neuroscience provide a closer characterization of these pathways in the injured spinal cord. This narrative review article aims to survey the MAPK, PI3K-AKT-mTOR, Rho-ROCK, NF-κB, and JAK-STAT signaling cascades, in addition to providing a comprehensive overview of the involvement and therapeutic potential of these secondary intracellular pathways following traumatic SCI.

Biomaterial strategies for regulating the neuroinflammatory response

Injury and disease in the central nervous system (CNS) can result in a dysregulated inflammatory environment that inhibits the repair of functional tissue. Biomaterials present a promising approach to tackle this complex inhibitory environment and modulate the mechanisms involved in neuroinflammation to halt the progression of secondary injury and promote the repair of functional tissue. In this review, we will cover recent advances in biomaterial strategies, including nanoparticles, hydrogels, implantable scaffolds, and neural probe coatings, that have been used to modulate the innate immune response to injury and disease within the CNS. The stages of inflammation following CNS injury and the main inflammatory contributors involved in common neurodegenerative diseases will be discussed, as understanding the inflammatory response to injury and disease is critical for identifying therapeutic targets and designing effective biomaterial-based treatment strategies. Biomaterials and novel composites will then be discussed with an emphasis on strategies that deliver immunomodulatory agents or utilize cell-material interactions to modulate inflammation and promote functional tissue repair. We will explore the application of these biomaterial-based strategies in the context of nanoparticle- and hydrogel-mediated delivery of small molecule drugs and therapeutic proteins to inflamed nervous tissue, implantation of hydrogels and scaffolds to modulate immune cell behavior and guide axon elongation, and neural probe coatings to mitigate glial scarring and enhance signaling at the tissue-device interface. Finally, we will present a future outlook on the growing role of biomaterial-based strategies for immunomodulation in regenerative medicine and neuroengineering applications in the CNS.

Osteopontin Promotes Angiogenesis in the Spinal Cord and Exerts a Protective Role Against Motor Function Impairment and Neuropathic Pain After Spinal Cord Injury

STUDY DESIGN

Basic science study using a hemisection spinal cord injury (SCI) model.

OBJECTIVE

We sought to assess the effect of blocking osteopontin (OPN) upregulation on motor function recovery and pain behavior after SCI and to further investigate the possible downstream target of OPN in the injured spinal cord.

SUMMARY OF BACKGROUND DATA

OPN is a noncollagenous extracellular matrix protein widely expressed across different tissues. Its expression substantially increases following SCI. A previous study suggested that this protein might contribute to locomotor function recovery after SCI. However, its neuroprotective potential was not fully explored, nor were the underlying mechanisms.

MATERIALS AND METHODS

We constructed a SCI mouse model and analyzed the expression of OPN at different time points and the particular cell distribution in the injured spinal cord. Then, we blocked OPN upregulation with lentivirus-delivering siRNA targeting OPN specifically and examined its effect on motor function impairment and neuropathic pain after SCI. The underlying mechanisms were explored in the OPN-knockdown mice model and cultured vascular endothelial cells.

RESULTS

The proteome study revealed that OPN was the most dramatically increased protein following SCI. OPN in the spinal cord was significantly increased three weeks after SCI. Suppressing OPN upregulation through siRNA exacerbated motor function impairment and neuropathic pain. In addition, SCI resulted in an increase in vascular endothelial growth factor (VEGF), AKT phosphorylation, and angiogenesis within the spinal cord, all of which were curbed by OPN reduction. Similarly, OPN knockdown suppressed VEGF expression, AKT phosphorylation, cell migration, invasion, and angiogenesis in cultured vascular endothelial cells.

CONCLUSION

OPN demonstrates a protective influence against motor function impairment and neuropathic pain following SCI. This phenomenon may result from the proangiogenetic effect of OPN, possibly due to activation of the VEGF and/or AKT pathways.

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.

Collagen I is a critical organizer of scarring and CNS regeneration failure

Although axotomized neurons retain the ability to initiate the formation of growth cones and attempt to regenerate after spinal cord injury, the scar area formed as a result of the lesion in most adult mammals contains a variety of reactive cells that elaborate multiple extracellular matrix and enzyme components that are not suitable for regrowth 1,2 . Newly migrating axons in the vicinity of the scar utilize upregulated LAR family receptor protein tyrosine phosphatases, such as PTPσ, to associate with extracellular chondroitin sulphate proteoglycans (CSPGs), which have been discovered to tightly entrap the regrowing axon tip and transform it into a dystrophic non-growing endball. The scar is comprised of two compartments, one in the lesion penumbra, the glial scar, composed of reactive microglia, astrocytes and OPCs; and the other in the lesion epicenter, the fibrotic scar, which is made up of fibroblasts, pericytes, endothelial cells and inflammatory cells. While the fibrotic scar is known to be strongly inhibitory, even more so than the glial scar, the molecular determinants that curtail axon elongation through the injury core are largely uncharacterized. Here, we show that one sole member of the entire family of collagens, collagen I, creates an especially potent inducer of endball formation and regeneration failure. The inhibitory signaling is mediated by mechanosensitive ion channels and RhoA activation. Staggered systemic administration of two blood-brain barrier permeable-FDA approved drugs, aspirin and pirfenidone, reduced fibroblast incursion into the complete lesion and dramatically decreased collagen I, as well as CSPG deposition which were accompanied by axonal growth and considerable functional recovery. The anatomical substrate for robust axonal regeneration was provided by laminin producing GFAP + and NG2 + bridging cells that spanned the wound. Our results reveal a collagen I-mechanotransduction axis that regulates axonal regrowth in spinal cord injury and raise a promising strategy for rapid clinical application.

Insulin-like growth factor binding protein-2 in at-risk adults and autopsy-confirmed Alzheimer brains

Insulin, insulin-like growth factors (IGF) and their receptors are highly expressed in the adult hippocampus. Thus, disturbances in the insulin-IGF signalling pathway may account for the selective vulnerability of the hippocampus to nascent Alzheimer's disease (AD) pathology. In the present study, we examined the predominant IGF-binding protein in the CSF, IGFBP2. CSF was collected from 109 asymptomatic members of the parental history-positive PREVENT-AD cohort. CSF levels of IGFBP2, core AD and synaptic biomarkers were measured using proximity extension assay, ELISA and mass spectrometry. Cortical amyloid-beta (Aβ) and tau deposition were examined using 18F-NAV4694 and flortaucipir. Cognitive assessments were performed during up to 8 years of follow-up, using the Repeatable Battery for the Assessment of Neuropsychological Status. T1-weighted structural MRI scans were acquired, and neuroimaging analyses were performed on pre-specified temporal and parietal brain regions. Next, in an independent cohort, we allocated 241 dementia-free ADNI-1 participants into four stages of AD progression based on the biomarkers CSF Aβ42 and total-tau (t-tau). In this analysis, differences in CSF and plasma IGFBP2 levels were examined across the pathological stages. Finally, IGFBP2 mRNA and protein levels were examined in the frontal cortex of 55 autopsy-confirmed AD and 31 control brains from the Quebec Founder Population (QFP) cohort, a unique population isolated from Eastern Canada. CSF IGFBP2 progressively increased over 5 years in asymptomatic PREVENT-AD participants. Baseline CSF IGFBP2 was positively correlated with CSF AD biomarkers and synaptic biomarkers, and negatively correlated with longitudinal changes in delayed memory (P = 0.024) and visuospatial abilities (P = 0.019). CSF IGFBP2 was negatively correlated at a trend-level with entorhinal cortex volume (P = 0.082) and cortical thickness in the piriform (P = 0.039), inferior temporal (P = 0.008), middle temporal (P = 0.014) and precuneus (P = 0.033) regions. In ADNI-1, CSF (P = 0.009) and plasma (P = 0.001) IGFBP2 were significantly elevated in Stage 2 [CSF Aβ(+)/t-tau(+)]. In survival analyses in ADNI-1, elevated plasma IGFBP2 was associated with a greater rate of AD conversion (hazard ratio = 1.62, P = 0.021). In the QFP cohort, IGFBP2 mRNA was reduced (P = 0.049); however, IGFBP2 protein levels did not differ in the frontal cortex of autopsy-confirmed AD brains (P = 0.462). Nascent AD pathology may induce an upregulation in IGFBP2 in asymptomatic individuals. CSF and plasma IGFBP2 may be valuable markers for identifying CSF Aβ(+)/t-tau(+) individuals and those with a greater risk of AD conversion.

Construction of a Searchable Database for Gene Expression Changes in Spinal Cord Injury Experiments

Spinal cord injury (SCI) is a debilitating condition with an estimated 18,000 new cases annually in the United States. The field has accepted and adopted standardized databases such as the Open Data Commons for Spinal Cord Injury (ODC-SCI) to aid in broader analyses, but these currently lack high-throughput data despite the availability of nearly 6000 samples from over 90 studies available in the Sequence Read Archive. This limits the potential for large datasets to enhance our understanding of SCI-related mechanisms at the molecular and cellular level. Therefore, we have developed a protocol for processing RNA-Seq samples from high-throughput sequencing experiments related to SCI resulting in both raw and normalized data that can be efficiently mined for comparisons across studies, as well as homologous discovery across species. We have processed 1196 publicly available RNA-Seq samples from 50 bulk RNA-Seq studies across nine different species, resulting in an SQLite database that can be used by the SCI research community for further discovery. We provide both the database as well as a web-based front-end that can be used to query the database for genes of interest, differential gene expression, genes with high variance, and gene set enrichments.

Decellularized extracellular matrix enriched with GDNF enhances neurogenesis and remyelination for improved motor recovery after spinal cord injury

Motor functional improvement represents a paramount treatment objective in the post-spinal cord injury (SCI) recovery process. However, neuronal cell death and axonal degeneration following SCI disrupt neural signaling, impeding the motor functional recovery. In this study, we developed a multifunctional decellularized spinal cord-derived extracellular matrix (dSECM), crosslinked with glial cell-derived neurotrophic factor (GDNF), to promote differentiation of stem cells into neural-like cells and facilitate axonogenesis and remyelination. After decellularization, the immunogenic cellular components were effectively removed in dSECM, while the crucial protein components were retained which supports stem cells proliferation and differentiation. Furthermore, sustained release of GDNF from the dSECM facilitated axonogenesis and remyelination by activating the PI3K/Akt and MEK/Erk pathways. Our findings demonstrate that the dSECM-GDNF platform promotes neurogenesis, axonogenesis, and remyelination to enhance neural signaling, thereby yielding promising therapeutic effects for motor functional improvement after SCI. STATEMENT OF SIGNIFICANCE: The dSECM promotes the proliferation and differentiation of MSCs or NSCs by retaining proteins associated with positive regulation of neurogenesis and neuronal differentiation, while eliminating proteins related to negative regulation of neurogenesis. After crosslinking, GDNF can be gradually released from the platform, thereby promoting neural differentiation, axonogenesis, and remyelination to enhance neural signaling through activation of the PI3K/Akt and MEK/Erk pathways. In vivo experiments demonstrated that dSECM-GDNF/MSC@GelMA hydrogel exhibited the ability to facilitate neuronal regeneration at 4 weeks post-surgery, while promoting axonogenesis and remyelination at 8 weeks post-surgery, ultimately leading to enhanced motor functional recovery. This study elucidates the ability of neural regeneration strategy to promote motor functional recovery and provides a promising approach for designing multifunctional tissue for SCI treatment.

Transplantation of Neural Stem Cells Loaded in an IGF-1 Bioactive Supramolecular Nanofiber Hydrogel for the Effective Treatment of Spinal Cord Injury

Spinal cord injury (SCI) leads to massive cell death, disruption, and demyelination of axons, resulting in permanent motor and sensory dysfunctions. Stem cell transplantation is a promising therapy for SCI. However, owing to the poor microenvironment that develops following SCI, the bioactivities of these grafted stem cells are limited. Cell implantation combined with biomaterial therapies is widely studied for the development of tissue engineering technology. Herein, an insulin-like growth factor-1 (IGF-1)-bioactive supramolecular nanofiber hydrogel (IGF-1 gel) is synthesized that can activate IGF-1 downstream signaling, prevent the apoptosis of neural stem cells (NSCs), improve their proliferation, and induce their differentiation into neurons and oligodendrocytes. Moreover, implantation of NSCs carried out with IGF-1 gels promotes neurite outgrowth and myelin sheath regeneration at lesion sites following SCI. In addition, IGF-1 gels can enrich extracellular vesicles (EVs) derived from NSCs or from nerve cells differentiated from these NSCs via miRNAs related to axonal regeneration and remyelination, even in an inflammatory environment. These EVs are taken up by autologous endogenous NSCs and regulate their differentiation. This study provides adequate evidence that combined treatment with NSCs and IGF-1 gels is a potential therapeutic strategy for treating SCI.

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.

Multifunctional Conductive and Electrogenic Hydrogel Repaired Spinal Cord Injury via Immunoregulation and Enhancement of Neuronal Differentiation

Spinal cord injury (SCI) is a refractory neurological disorder. Due to the complex pathological processes, especially the secondary inflammatory cascade and the lack of intrinsic regenerative capacity, it is difficult to recover neurological function after SCI. Meanwhile, simulating the conductive microenvironment of the spinal cord reconstructs electrical neural signal transmission interrupted by SCI and facilitates neural repair. Therefore, a double-crosslinked conductive hydrogel (BP@Hydrogel) containing black phosphorus nanoplates (BP) is synthesized. When placed in a rotating magnetic field (RMF), the BP@Hydrogel can generate stable electrical signals and exhibit electrogenic characteristic. In vitro, the BP@Hydrogel shows satisfactory biocompatibility and can alleviate the activation of microglia. When placed in the RMF, it enhances the anti-inflammatory effects. Meanwhile, wireless electrical stimulation promotes the differentiation of neural stem cells (NSCs) into neurons, which is associated with the activation of the PI3K/AKT pathway. In vivo, the BP@Hydrogel is injectable and can elicit behavioral and electrophysiological recovery in complete transected SCI mice by alleviating the inflammation and facilitating endogenous NSCs to form functional neurons and synapses under the RMF. The present research develops a multifunctional conductive and electrogenic hydrogel for SCI repair by targeting multiple mechanisms including immunoregulation and enhancement of neuronal differentiation.

Mesenchymal stem cell-derived exosomes as a new drug carrier for the treatment of spinal cord injury: A review

Spinal cord injury (SCI) is a devastating traumatic disease seriously impairing the quality of life in patients. Expectations to allow the hopeless central nervous system to repair itself after injury are unfeasible. Developing new approaches to regenerate the central nervous system is still the priority. Exosomes derived from mesenchymal stem cells (MSC-Exo) have been proven to robustly quench the inflammatory response or oxidative stress and curb neuronal apoptosis and autophagy following SCI, which are the key processes to rescue damaged spinal cord neurons and restore their functions. Nonetheless, MSC-Exo in SCI received scant attention. In this review, we reviewed our previous work and other studies to summarize the roles of MSC-Exo in SCI and its underlying mechanisms. Furthermore, we also focus on the application of exosomes as drug carrier in SCI. In particular, it combs the advantages of exosomes as a drug carrier for SCI, imaging advantages, drug types, loading methods, etc., which provides the latest progress for exosomes in the treatment of SCI, especially drug carrier.

Inhibition of UHRF1 Improves Motor Function in Mice with Spinal Cord Injury

Spinal-cord injury (SCI) is a severe condition that can lead to limb paralysis and motor dysfunction, and its pathogenesis is not fully understood. The objective of this study was to characterize the differential gene expression and molecular mechanisms in the spinal cord of mice three days after spinal cord injury. By analyzing RNA sequencing data, we identified differentially expressed genes and discovered that the immune system and various metabolic processes play crucial roles in SCI. Additionally, we identified UHRF1 as a key gene that plays a significant role in SCI and found that SCI can be improved by suppressing UHRF1. These findings provide important insights into the molecular mechanisms of SCI and identify potential therapeutic targets that could greatly contribute to the development of new treatment strategies for SCI.

Strongly Adhesive, Self-Healing, Hemostatic Hydrogel for the Repair of Traumatic Brain Injury

With wide clinical demands, therapies for traumatic brain injury (TBI) are a major problem in surgical procedures and after major trauma. Due to the difficulty in regeneration of neurons or axons after injury, as well as the inhibition of blood vessel growth by the formation of neural scars, existing treatment measures have limited effectiveness in repairing brain tissue. Herein, the biomultifunctional hydrogels are developed for TBI treatment based on the Schiff base reaction of calcium ion (Ca2+)-cross-linked oxidized sodium alginate (OSA) and carboxymethyl chitosan (CMCS). The obtained COCS hydrogel exhibits excellent adhesion to wet tissues, self-repair capability, and antimicrobial properties. What's particularly interesting is that the addition of Ca2+ increases the hydrogel's extensibility, enhancing its hemostatic capabilities. Biological assessments indicate that the COCS hydrogel demonstrates excellent biocompatibility, hemostatic properties, and the ability to promote arterial vessel repair. Importantly, the COCS hydrogel promotes the growth of cerebral microvessels by upregulating CD31, accelerates the proliferation of astrocytes, enhances the expression of GFAP, and stimulates the expression of neuron-specific markers such as NEUN and β-tubulin. All of these findings highlight that the strongly adhesive, self-healing, hemostatic hydrogel shows great potential for the repair of traumatic brain injury and other tissue repair therapy.

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.

Inflammatory Factor IL1α Induces Aberrant Astrocyte Proliferation in Spinal Cord Injury Through the Grin2c/Ca2+/CaMK2b Pathway

Spinal cord injury (SCI) is one of the most devastating traumas, and the aberrant proliferation of astrocytes usually causes neurological deficits. However, the mechanism underlying astrocyte over-proliferation after SCI is unclear. Grin2c (glutamate ionotropic receptor type 2c) plays an essential role in cell proliferation. Our bioinformatic analysis indicated that Grin2c and Ca2+ transport functions were inhibited in astrocytes after SCI. Suppression of Grin2c stimulated astrocyte proliferation by inhibiting the Ca2+/calmodulin-dependent protein kinase 2b (CaMK2b) pathway in vitro. By screening different inflammatory factors, interleukin 1α (IL1α) was further found to inhibit Grin2c/Ca2+/CaMK2b and enhance astrocyte proliferation in an oxidative damage model. Blockade of IL1α using neutralizing antibody resulted in increased Grin2c expression and the inhibition of astrocyte proliferation post-SCI. Overall, this study suggests that IL1α promotes astrocyte proliferation by suppressing the Grin2c/Ca2+/CaMK2b pathway after SCI, revealing a novel pathological mechanism of astrocyte proliferation, and may provide potential targets for SCI repair.

Regenerative medicine strategies for chronic complete spinal cord injury

Spinal cord injury is a condition in which the parenchyma of the spinal cord is damaged by trauma or various diseases. While rapid progress has been made in regenerative medicine for spinal cord injury that was previously untreatable, most research in this field has focused on the early phase of incomplete injury. However, the majority of patients have chronic severe injuries; therefore, treatments for these situations are of fundamental importance. The reason why the treatment of complete spinal cord injury has not been studied is that, unlike in the early stage of incomplete spinal cord injury, there are various inhibitors of neural regeneration. Thus, we assumed that it is difficult to address all conditions with a single treatment in chronic complete spinal cord injury and that a combination of several treatments is essential to target severe pathologies. First, we established a combination therapy of cell transplantation and drug-releasing scaffolds, which contributes to functional recovery after chronic complete transection spinal cord injury, but we found that functional recovery was limited and still needs further investigation. Here, for the further development of the treatment of chronic complete spinal cord injury, we review the necessary approaches to the different pathologies based on our findings and the many studies that have been accumulated to date and discuss, with reference to the literature, which combination of treatments is most effective in achieving functional recovery.