Effect of active Notch signaling system on the early repair of rat sciatic nerve injury

Molecular and cellular mechanisms underlying peripheral nerve injury-induced cellular ecological shifts: Implications for neuroregeneration

The peripheral nervous system is a complex ecological network, and its injury triggers a series of fine-grained intercellular regulations that play a crucial role in the repair process. The peripheral nervous system is a sophisticated ecological network, and its injury initiates a cascade of intricate intercellular regulatory processes that are instrumental in the repair process. Despite the advent of sophisticated microsurgical techniques, the repair of peripheral nerve injuries frequently proves inadequate, resulting in adverse effects on patients' quality of life. Accordingly, the continued pursuit of more efficacious treatments is of paramount importance. In this paper, a review of the relevant literature from recent years was conducted to identify the key cell types involved after peripheral nerve injury. These included Schwann cells, macrophages, neutrophils, endothelial cells, and fibroblasts. The review was conducted in depth. This paper analyses the phenotypic changes of these cells after injury, the relevant factors affecting these changes, and how they coordinate with neurons and other cell types. In addition, it explores the potential mechanisms that mediate the behaviour of these cells. Understanding the interactions between these cells and their mutual regulation with neurons is of great significance for the discovery of new neuroregenerative treatments and the identification of potential therapeutic targets.

The role and mechanism of Schwann cells in the repair of peripheral nerve injury

Limb injuries such as severe strains, deep cuts, gunshot wounds, and ischemia can cause peripheral nerve damage. This can result in a range of clinical symptoms including sensory deficits, limb paralysis and atrophy, neuralgia, and sweating abnormalities in the innervated areas affected by the damaged nerves. These symptoms can have a significant impact on patients' daily lives and work. Despite existing clinical treatments, some patients cannot achieve satisfactory therapeutic effects and continue to experience persistent paralysis and pain. Schwann cells are responsible for repairing and regenerating damaged nerves in the peripheral nervous system. They play a crucial role in the healing of nerve injuries and are essential for the restoration of proper nerve function. An increasing number of studies have focused on the various regulatory mechanisms that specifically affect the repair of damage by Schwann cells. This article aims to provide information on the different types of peripheral nerve injuries and their available treatments. We also discuss the various molecular mechanisms that regulate Schwann cell function during peripheral nerve repair and how they can be used to promote nerve repair and regeneration. Furthermore, we explore the potential therapeutic applications of precision regulation of Schwann cells for the treatment of peripheral nerve injuries.

Unraveling the immune system's role in peripheral nerve regeneration: a pathway to enhanced healing

Peripheral nerve injury (PNI) represents a common challenge in clinical practice. In contrast to the central nervous system (CNS), the peripheral nervous system (PNS) in mature mammals possesses a limited regenerative capacity. Upon the occurrence of PNI, peripheral nerve regeneration (PNR) is initiated, facilitated by the activation of the immune microenvironment and the intrinsic growth potential of neurons. This regenerative process encompasses several key stages, including distal axon degeneration, myelin breakdown, clearance of myelin debris, inflammatory responses from non-neuronal cells, and subsequent axonal regeneration. The immune response, recognized for its role in clearing myelin debris and modulating the local inflammatory milieu, is crucial for initiating axonal regeneration at the proximal stump of nerves. Nevertheless, the precise mechanisms by which the immune response influences PNI and the strategies to harness this process to augment regeneration remain elusive. This article provides a comprehensive overview of the diverse roles and mechanisms of the immune system in PNR and presents insights into potential therapeutic strategies. Furthermore, the article examines immune-associated signaling pathways and their impact on PNR, underscoring the significance of immune modulation in enhancing patient outcomes with PNI. Ultimately, it encapsulates and forecasts the theoretical and practical directions of this field.

Schwann cell autotransplantation for the treatment of peripheral nerve injury

Peripheral nerve injury occurs in a relatively large proportion of trauma patients, in whom it generally results in severe functional impairment and permanent disability. At present, however, there are no effective treatments available. Studies have shown that Schwann cells play an indispensable role in removing myelin debris and guiding axonal regeneration, and transplantation using autologous Schwann cells has shown good efficacy for patients with peripheral nerve injury. In recent years, Schwann cell autologous transplantation therapy has become an area of intensive research and is anticipated to provide a new strategy for the clinical treatment of peripheral nerve injury. In this article, we review the rationale for selecting Schwann cell autotransplantation therapy and the latest progress in key aspects of cell transplantation and clinical efficacy, and also summarize the future directions of research on this therapy. All of the above provide a strong basis for the further improvement and clinical promotion of this therapy.

Role and Interplay of Different Signaling Pathways Involved in Sciatic Nerve Regeneration

Regeneration of the sciatic nerve is a sophisticated process that involves the interplay of several signaling pathways that orchestrate the cellular responses critical to regeneration. Among the key pathways are the mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/AKT, cyclic adenosine monophosphate (cAMP), and Janus kinase/signal transducers and transcription activators (JAK/STAT) pathways. In particular, the cAMP pathway modulates neuronal survival and axonal regrowth. It influences various cellular behaviors and gene expression that are essential for nerve regeneration. MAPK is indispensable for Schwann cell differentiation and myelination, whereas PI3K/AKT is integral to the transcription, translation, and cell survival processes that are vital for nerve regeneration. Furthermore, GTP-binding proteins, including those of the Ras homolog gene family (Rho), regulate neural cell adhesion, migration, and survival. Notch signaling also appears to be effective in the early stages of nerve regeneration and in preventing skeletal muscle fibrosis after injury. Understanding the intricate mechanisms and interactions of these pathways is vital for the development of effective therapeutic strategies for sciatic nerve injuries. This review underscores the need for further research to fill existing knowledge gaps and improve therapeutic outcomes.

Nuclear Magnetic Resonance Treatment Induces ßNGF Release from Schwann Cells and Enhances the Neurite Growth of Dorsal Root Ganglion Neurons In Vitro

Peripheral nerve regeneration depends on close interaction between neurons and Schwann cells (SCs). After nerve injury, SCs produce growth factors and cytokines that are crucial for axon re-growth. Previous studies revealed the supernatant of SCs exposed to nuclear magnetic resonance therapy (NMRT) treatment to increase survival and neurite formation of rat dorsal root ganglion (DRG) neurons in vitro. The aim of this study was to identify factors involved in transferring the observed NMRT-induced effects to SCs and consequently to DRG neurons. Conditioned media of NMRT-treated (CM NMRT) and untreated SCs (CM CTRL) were tested by beta-nerve growth factor (ßNGF) ELISA and multiplex cytokine panels to profile secreted factors. The expression of nociceptive transient receptor potential vanilloid 1 (TRPV1) channels was assessed and the intracellular calcium response in DRG neurons to high-potassium solution, capsaicin or adenosine triphosphate was measured mimicking noxious stimuli. NMRT induced the secretion of ßNGF and pro-regenerative-signaling factors. Blocking antibody experiments confirmed ßNGF as the main factor responsible for neurotrophic/neuritogenic effects of CM NMRT. The TRPV1 expression or sensitivity to specific stimuli was not altered, whereas the viability of cultured DRG neurons was increased. Positive effects of CM NMRT supernatant on DRG neurons are primarily mediated by increased ßNGF levels.

Advances of Schwann cells in peripheral nerve regeneration: From mechanism to cell therapy

Peripheral nerve injuries (PNIs) frequently occur due to various factors, including mechanical trauma such as accidents or tool-related incidents, as well as complications arising from diseases like tumor resection. These injuries frequently result in persistent numbness, impaired motor and sensory functions, neuropathic pain, or even paralysis, which can impose a significant financial burden on patients due to outcomes that often fall short of expectations. The most frequently employed clinical treatment for PNIs involves either direct sutures of the severed ends or bridging the proximal and distal stumps using autologous nerve grafts. However, autologous nerve transplantation may result in sensory and motor functional loss at the donor site, as well as neuroma formation and scarring. Transplantation of Schwann cells/Schwann cell-like cells has emerged as a promising cellular therapy to reconstruct the microenvironment and facilitate peripheral nerve regeneration. In this review, we summarize the role of Schwann cells and recent advances in Schwann cell therapy in peripheral nerve regeneration. We summarize current techniques used in cell therapy, including cell injection, 3D-printed scaffolds for cell delivery, cell encapsulation techniques, as well as the cell types employed in experiments, experimental models, and research findings. At the end of the paper, we summarize the challenges and advantages of various cells (including ESCs, iPSCs, and BMSCs) in clinical cell therapy. Our goal is to provide the theoretical and experimental basis for future treatments targeting peripheral nerves, highlighting the potential of cell therapy and tissue engineering as invaluable resources for promoting nerve regeneration.

Review: Myelin clearance is critical for regeneration after peripheral nerve injury

Traumatic peripheral nerve injury occurs frequently and is a major clinical and public health problem that can lead to functional impairment and permanent disability. Despite the availability of modern diagnostic procedures and advanced microsurgical techniques, active recovery after peripheral nerve repair is often unsatisfactory. Peripheral nerve regeneration involves several critical events, including the recreation of the microenvironment and remyelination. Results from previous studies suggest that the peripheral nervous system (PNS) has a greater capacity for repair than the central nervous system. Thus, it will be important to understand myelin and myelination specifically in the PNS. This review provides an update on myelin biology and myelination in the PNS and discusses the mechanisms that promote myelin clearance after injury. The roles of Schwann cells and macrophages are considered at length, together with the possibility of exogenous intervention.

Advancing Our Understanding of the Chronically Denervated Schwann Cell: A Potential Therapeutic Target?

Outcomes for patients following major peripheral nerve injury are extremely poor. Despite advanced microsurgical techniques, the recovery of function is limited by an inherently slow rate of axonal regeneration. In particular, a time-dependent deterioration in the ability of the distal stump to support axonal growth is a major determinant to the failure of reinnervation. Schwann cells (SC) are crucial in the orchestration of nerve regeneration; their plasticity permits the adoption of a repair phenotype following nerve injury. The repair SC modulates the initial immune response, directs myelin clearance, provides neurotrophic support and remodels the distal nerve. These functions are critical for regeneration; yet the repair phenotype is unstable in the setting of chronic denervation. This phenotypic instability accounts for the deteriorating regenerative support offered by the distal nerve stump. Over the past 10 years, our understanding of the cellular machinery behind this repair phenotype, in particular the role of c-Jun, has increased exponentially, creating opportunities for therapeutic intervention. This review will cover the activation of the repair phenotype in SC, the effects of chronic denervation on SC and current strategies to 'hack' these cellular pathways toward supporting more prolonged periods of neural regeneration.

Dietary Soy Prevents Alcohol-Mediated Neurocognitive Dysfunction and Associated Impairments in Brain Insulin Pathway Signaling in an Adolescent Rat Model

BACKGROUND

Alcohol-related brain degeneration is linked to cognitive-motor deficits and impaired signaling through insulin/insulin-like growth factor type 1 (IGF-1)-Akt pathways that regulate cell survival, plasticity, metabolism, and homeostasis. In addition, ethanol inhibits Aspartyl-asparaginyl-β-hydroxylase (ASPH), a downstream target of insulin/IGF-1-Akt signaling and an activator of Notch networks. Previous studies have suggested that early treatment with insulin sensitizers or dietary soy could reduce or prevent the long-term adverse effects of chronic ethanol feeding.

OBJECTIVE

The goal of this study was to assess the effects of substituting soy isolate for casein to prevent or reduce ethanol's adverse effects on brain structure and function.

METHODS

Young adolescent male and female Long Evans were used in a 4-way model as follows: Control + Casein; Ethanol + Casein; Control + Soy; Ethanol + Soy; Control = 0% ethanol; Ethanol = 26% ethanol (caloric). Rats were fed isocaloric diets from 4 to 11 weeks of age. During the final experimental week, the Morris Water maze test was used to assess spatial learning (4 consecutive days), after which the brains were harvested to measure the temporal lobe expression of the total phospho-Akt pathway and downstream target proteins using multiplex bead-based enzyme-linked immunosorbent assays (ELISAs) and duplex ELISAs.

RESULTS

Ethanol inhibited spatial learning and reduced brain weight, insulin signaling through Akt, and the expression of ASPH when standard casein was provided as the protein source. The substitution of soy isolate for casein largely abrogated the adverse effects of chronic ethanol feeding. In contrast, Notch signaling protein expression was minimally altered by ethanol or soy isolate.

CONCLUSIONS

These novel findings suggest that the insulin sensitizer properties of soy isolate may prevent some of the adverse effects that chronic ethanol exposure has on neurobehavioral function and insulin-regulated metabolic pathways in adolescent brains.

The Notch signalling pathway and miRNA regulation play important roles in the differentiation of Schwann cells from adipose-derived stem cells

An exploration of the underlying mechanisms is necessary to improve nerve myelin-forming cell Schwann cell (SC) differentiation from adipose-derived stem cells (ADSCs). Primary rat ADSCs were isolated and characterised for cell surface markers using flow cytometry analysis. After treatment with a mixture of glial growth factors, ADSCs were induced to differentiate and subsequently identified by immunofluorescence staining and western blotting. A miRNA microarray analysis was performed to explore the genes and signalling pathways regulating ADSC differentiation into SCs. ELISAs were conducted to measure the expression of neurotrophic factors and changes in the level of nerve cell adhesion factor. Dual luciferase reporter assays and RIP assays were performed to explore the potential mechanism of miR-21-5p in ADSC differentiation. The isolated ADSCs were positive for CD29 and CD44 but negative for CD49. After induction with specific cytokines, the differentiated ADSCs presented a spindle-like morphology similar to SCs and expressed S100. RNA-sequencing analyses revealed that 9821 mRNAs of protein-coding genes and 175 miRNAs were differentially expressed in differentiated SC-like cells compared to primary cultures of ADSCs. KEGG and Gene Ontology analyses revealed that the involvement of the Notch signalling pathway and miRNA negative regulation may be associated with the differentiation of ADSCs into SCs. Treatment with a Notch inhibitor promoted the differentiation of ADSCs. Furthermore, mechanistic studies showed that Jag1 bound to miR-21-5p and upregulated its target gene Jag1, thus affecting ADSC differentiation. These results revealed the mechanism underlying the important roles of miRNAs and the Notch signalling pathway in the differentiation of SCs from ADSCs, enabling potential therapeutic applications of ADSCs in peripheral nerve regeneration in the future.

Mechanisms of Schwann cell plasticity involved in peripheral nerve repair after injury

The great plasticity of Schwann cells (SCs), the myelinating glia of the peripheral nervous system (PNS), is a critical feature in the context of peripheral nerve regeneration following traumatic injuries and peripheral neuropathies. After a nerve damage, SCs are rapidly activated by injury-induced signals and respond by entering the repair program. During the repair program, SCs undergo dynamic cell reprogramming and morphogenic changes aimed at promoting nerve regeneration and functional recovery. SCs convert into a repair phenotype, activate negative regulators of myelination and demyelinate the damaged nerve. Moreover, they express many genes typical of their immature state as well as numerous de-novo genes. These genes modulate and drive the regeneration process by promoting neuronal survival, damaged axon disintegration, myelin clearance, axonal regrowth and guidance to their former target, and by finally remyelinating the regenerated axon. Many signaling pathways, transcriptional regulators and epigenetic mechanisms regulate these events. In this review, we discuss the main steps of the repair program with a particular focus on the molecular mechanisms that regulate SC plasticity following peripheral nerve injury.

Ethanol-Induced White Matter Atrophy Is Associated with Impaired Expression of Aspartyl-Asparaginyl-β-Hydroxylase (ASPH) and Notch Signaling in an Experimental Rat Model

Alcohol-induced white matter (WM) degeneration is linked to cognitive-motor deficits and impairs insulin/insulin-like growth factor (IGF) and Notch networks regulating oligodendrocyte function. Ethanol downregulates Aspartyl-Asparaginyl-β-Hydroxylase (ASPH) which drives Notch. These experiments determined if alcohol-related WM degeneration was linked to inhibition of ASPH and Notch. Adult Long Evans rats were fed for 3, 6 or 8 weeks with liquid diets containing 26% ethanol (caloric) and in the last two weeks prior to each endpoint they were binged with 2 g/kg ethanol, 3×/week. Controls were studied in parallel. Histological sections of the frontal lobe and cerebellar vermis were used for image analysis. Frontal WM proteins were used for Western blotting and duplex ELISAs. The ethanol exposures caused progressive reductions in frontal and cerebellar WM. Ethanol-mediated frontal WM atrophy was associated with reduced expression of ASPH, Jagged 1, HES-1, and HIF-1α. These findings link ethanol-induced WM atrophy to inhibition of ASPH expression and signaling through Notch networks, including HIF-1α.

Molecular Mechanisms Involved in Schwann Cell Plasticity

Schwann cell incredible plasticity is a hallmark of the utmost importance following nerve damage or in demyelinating neuropathies. After injury, Schwann cells undergo dedifferentiation before redifferentiating to promote nerve regeneration and complete functional recovery. This review updates and discusses the molecular mechanisms involved in the negative regulation of myelination as well as in the reprogramming of Schwann cells taking place early following nerve lesion to support repair. Significant advance has been made on signaling pathways and molecular components that regulate SC regenerative properties. These include for instance transcriptional regulators such as c-Jun or Notch, the MAPK and the Nrg1/ErbB2/3 pathways. This comprehensive overview ends with some therapeutical applications targeting factors that control Schwann cell plasticity and highlights the need to carefully modulate and balance this capacity to drive nerve repair.

Temporal Analysis of Gene Expression in the Murine Schwann Cell Lineage and the Acutely Injured Postnatal Nerve

Schwann cells (SCs) arise from neural crest cells (NCCs) that first give rise to SC precursors (SCPs), followed by immature SCs, pro-myelinating SCs, and finally, non-myelinating or myelinating SCs. After nerve injury, mature SCs ‘de-differentiate’, downregulating their myelination program while transiently re-activating early glial lineage genes. To better understand molecular parallels between developing and de-differentiated SCs, we characterized the expression profiles of a panel of 12 transcription factors from the onset of NCC migration through postnatal stages, as well as after acute nerve injury. Using Sox10 as a pan-glial marker in co-expression studies, the earliest transcription factors expressed in E9.0 Sox10⁺ NCCs were Sox9, Pax3, AP2α and Nfatc4. E10.5 Sox10⁺ NCCs coalescing in the dorsal root ganglia differed slightly, expressing Sox9, Pax3, AP2α and Etv5. E12.5 SCPs continued to express Sox10, Sox9, AP2α and Pax3, as well as initiating Sox2 and Egr1 expression. E14.5 immature SCs were similar to SCPs, except that they lost Pax3 expression. By E18.5, AP2α, Sox2 and Egr1 expression was turned off in the nerve, while Jun, Oct6 and Yy1 expression was initiated in pro-myelinating Sox9⁺/Sox10⁺ SCs. Early postnatal and adult SCs continued to express Sox9, Jun, Oct6 and Yy1 and initiated Nfatc4 and Egr2 expression. Notably, at all stages, expression of each marker was observed only in a subset of Sox10⁺ SCs, highlighting the heterogeneity of the SC pool. Following acute nerve injury, Egr1, Jun, Oct6, and Sox2 expression was upregulated, Egr2 expression was downregulated, while Sox9, Yy1, and Nfatc4 expression was maintained at similar frequencies. Notably, de-differentiated SCs in the injured nerve did not display a transcription factor profile corresponding to a specific stage in the SC lineage. Taken together, we demonstrate that uninjured and injured SCs are heterogeneous and distinct from one another, and de-differentiation recapitulates transcriptional aspects of several different embryonic stages.