Transcriptional Control of Peripheral Nerve Regeneration

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.

Versatile conductive hydrogel orchestrating neuro-immune microenvironment for rapid diabetic wound healing through peripheral nerve regeneration

Diabetic wound (DW), notorious for prolonged healing processes due to the unregulated immune response, neuropathy, and persistent infection, poses a significant challenge to clinical management. Current strategies for treating DW primarily focus on alleviating the inflammatory milieu or promoting angiogenesis, while limited attention has been given to modulating the neuro-immune microenvironment. Thus, we present an electrically conductive hydrogel dressing and identify its neurogenesis influence in a nerve injury animal model initially by encouraging the proliferation and migration of Schwann cells. Further, endowed with the synergizing effect of near-infrared responsive release of curcumin and nature-inspired artificial heterogeneous melanin nanoparticles, it can harmonize the immune microenvironment by restoring the macrophage phenotype and scavenging excessive reactive oxygen species. This in-situ formed hydrogel also exhibits mild photothermal therapy antibacterial efficacy. In the infected DW model, this hydrogel effectively supports nerve regeneration and mitigates the immune microenvironment, thereby expediting the healing progress. The versatile hydrogel exhibits significant therapeutic potential for application in DW healing through fine-tuning the neuro-immune microenvironment.

The Intrinsic Neuronal Activation of the CXCR4 Signaling Axis Is Associated with a Pro-Regenerative State in Cervical Primary Sensory Neurons Conditioned by a Sciatic Nerve Lesion

CXCL12 and CXCR4 proteins and mRNAs were monitored in the dorsal root ganglia (DRGs) of lumbar (L4-L5) and cervical (C7-C8) spinal segments of naïve rats, rats subjected to sham operation, and those undergoing unilateral complete sciatic nerve transection (CSNT) on post-operation day 7 (POD7). Immunohistochemical, Western blot, and RT-PCR analyses revealed bilaterally increased levels of CXCR4 protein and mRNA in both lumbar and cervical DRG neurons after CSNT. Similarly, CXCL12 protein levels increased, and CXCL12 mRNA was upregulated primarily in lumbar DRGs ipsilateral to the nerve lesion. Intrathecal application of the CXCR4 inhibitor AMD3100 following CSNT reduced CXCL12 and CXCR4 protein levels in cervical DRG neurons, as well as the length of afferent axons regenerated distal to the ulnar nerve crush. Furthermore, treatment with the CXCR4 inhibitor decreased levels of activated Signal Transducer and Activator of Transcription 3 (STAT3), a critical transforming factor in the neuronal regeneration program. Administration of IL-6 increased CXCR4 levels, whereas the JAK2-dependent STAT3 phosphorylation inhibitor (AG490) conversely decreased CXCR4 levels. This indicates a link between the CXCL12/CXCR4 signaling axis and IL-6-induced activation of STAT3 in the sciatic nerve injury-induced pro-regenerative state of cervical DRG neurons. The role of CXCR4 signaling in the axon-promoting state of DRG neurons was confirmed through in vitro cultivation of primary sensory neurons in a medium supplemented with CXCL12, with or without AMD3100. The potential involvement of conditioned cervical DRG neurons in the induction of neuropathic pain is discussed.

Peripheral, central, and chemotherapy-induced neuropathic changes in pancreatic cancer

In pancreatic cancer, significant alterations occur in the local nervous system, including axonogenesis, neural remodeling, perineural invasion, and perineural neuritis. Pancreatic cancer can impact the central nervous system (CNS) through cancer cell-intrinsic factors or systemic factors, particularly in the context of cancer cachexia. These peripheral and central neuropathic changes exert substantial influence on cancer initiation and progression. Moreover, chemotherapy-induced neuropathy is common in pancreatic cancer, causing peripheral nerve damage and cognitive dysfunction. Targeting the crosstalk between pancreatic cancer and the nervous system, either peripherally or centrally, holds promise in cancer treatment, pain relief, and improved quality of life. Here, we summarize recent findings on the molecular mechanisms behind these neuropathic changes in pancreatic cancer and discuss potential intervention strategies.

Nerve injury converts Schwann cells in a long-term repair-like state in human neuroma tissue

Peripheral nerve injury (PNI) induces neuroma formation at the severed nerve stump resulting in impaired nerve regeneration and functional recovery in patients. So far, molecular mechanisms and cell types present in the neuroma impeding on regeneration have only sparsely been analyzed. Herein we compare resected human neuroma tissue with intact donor nerves from the same patient. Neuroma from several post-injury timepoints (1-13 months) were included, thereby allowing for temporal correlation with molecular and cellular processes. We observed reduced axonal area and percentage of myelin producing Schwann cells (SCs) compared to intact nerves. However, total SOX10 positive SC numbers were comparable. Notably, markers for SCs in a repair mode including c-JUN, the low-affinity neurotrophin receptor (NTR) p75, SHH (sonic hedgehog) and SC proliferation (phospho-histone H3) were upregulated in neuroma, suggesting presence of SCs in repair status. In agreement, in neuroma, pro-regenerative markers such as phosphorylated i.e. activated CREB (pCREB), ATF3, GAP43 and SCG10 were upregulated. In addition, neuroma tissue was infiltrated by several types of macrophages. Finally, when taken in culture, neuroma SCs were indistinguishable from controls SCs with regard to proliferation and morphology. However, cultured neuroma SCs retained a different molecular signature from control SCs including increased inflammation and reduced gene expression for differentiation markers such as myelin genes. In summary, human neuroma tissue consists of SCs with a repair status and is infiltrated strongly by several types of macrophages.

The Physiologic Basis of Molecular Therapeutics for Peripheral Nerve Injury: A Primer

Peripheral nerve injuries affect a significant number of patients who experience trauma affecting the hand and upper extremity. Improving unsatisfactory outcomes from repair of these injuries remains a clinical challenge despite advancements in microsurgical repair. Imperfections of the nerve regeneration process, including imprecise reinnervation, distal axon degradation, and muscular atrophy, complicate the repair process. However, the capacity for peripheral nerves to regenerate offers an avenue for therapeutic advancement. Regeneration is a temporally and spatially dynamic process coordinated by Schwann cells and neurons among other cell types. Neurotrophic factors are a primary means of controlling cell growth and differentiation in the repair setting. Sustained axon survival and regrowth and consequently functional outcomes of nerve repair in animal models are improved by the administration of neurotrophic factors, including glial cell-derived neurotrophic factor, nerve growth factor, sterile alpha and TIR motif containing 1, and erythropoietin. Targeted and sustained delivery of neurotrophic factors through gelatin-based nerve conduits, multiluminal conduits, and hydrogels have been shown to enhance the innate roles of these factors to promote expedient and accurate peripheral nerve regeneration in animal models. These delivery methods may help address the practical limitations to clinical use of neurotrophic factors, including systemic side effects and the need for carefully timed, precisely localized release schedules. In addition, tacrolimus has also improved peripheral nerve regrowth in animal models and has recently shown promise in addressing human disease. Ultimately, this realm of adjunct pharmacotherapies provides ample promise to improve patient outcomes and advance the field of peripheral nerve repair.

RNA sequencing of exosomes secreted by fibroblast and Schwann cells elucidates mechanisms underlying peripheral nerve regeneration

JOURNAL/nrgr/04.03/01300535-202408000-00035/figure1/v/2023-12-16T180322Z/r/image-tiff Exosomes exhibit complex biological functions and mediate a variety of biological processes, such as promoting axonal regeneration and functional recovery after injury. Long non-coding RNAs (lncRNAs) have been reported to play a crucial role in axonal regeneration. However, the role of the lncRNA-microRNA-messenger RNA (mRNA)-competitive endogenous RNA (ceRNA) network in exosome-mediated axonal regeneration remains unclear. In this study, we performed RNA transcriptome sequencing analysis to assess mRNA expression patterns in exosomes produced by cultured fibroblasts (FC-EXOs) and Schwann cells (SC-EXOs). Differential gene expression analysis, Gene Ontology analysis, Kyoto Encyclopedia of Genes and Genomes analysis, and protein-protein interaction network analysis were used to explore the functions and related pathways of RNAs isolated from FC-EXOs and SC-EXOs. We found that the ribosome-related central gene Rps5 was enriched in FC-EXOs and SC-EXOs, which suggests that it may promote axonal regeneration. In addition, using the miRWalk and Starbase prediction databases, we constructed a regulatory network of ceRNAs targeting Rps5, including 27 microRNAs and five lncRNAs. The ceRNA regulatory network, which included Ftx and Miat, revealed that exsosome-derived Rps5 inhibits scar formation and promotes axonal regeneration and functional recovery after nerve injury. Our findings suggest that exosomes derived from fibroblast and Schwann cells could be used to treat injuries of peripheral nervous system.

GRT-X Stimulates Dorsal Root Ganglia Axonal Growth in Culture via TSPO and Kv7.2/3 Potassium Channel Activation

GRT-X, which targets both the mitochondrial translocator protein (TSPO) and the Kv7.2/3 (KCNQ2/3) potassium channels, has been shown to efficiently promote recovery from cervical spine injury. In the present work, we investigate the role of GRT-X and its two targets in the axonal growth of dorsal root ganglion (DRG) neurons. Neurite outgrowth was quantified in DRG explant cultures prepared from wild-type C57BL6/J and TSPO-KO mice. TSPO was pharmacologically targeted with the agonist XBD173 and the Kv7 channels with the activator ICA-27243 and the inhibitor XE991. GRT-X efficiently stimulated DRG axonal growth at 4 and 8 days after its single administration. XBD173 also promoted axonal elongation, but only after 8 days and its repeated administration. In contrast, both ICA27243 and XE991 tended to decrease axonal elongation. In dissociated DRG neuron/Schwann cell co-cultures, GRT-X upregulated the expression of genes associated with axonal growth and myelination. In the TSPO-KO DRG cultures, the stimulatory effect of GRT-X on axonal growth was completely lost. However, GRT-X and XBD173 activated neuronal and Schwann cell gene expression after TSPO knockout, indicating the presence of additional targets warranting further investigation. These findings uncover a key role of the dual mode of action of GRT-X in the axonal elongation of DRG neurons.

Injury distance limits the transcriptional response to spinal injury

The ability of neurons to sense and respond to damage is fundamental to homeostasis and nervous system repair. For some cell types, notably dorsal root ganglia (DRG) and retinal ganglion cells (RGCs), extensive profiling has revealed a large transcriptional response to axon injury that determines survival and regenerative outcomes. In contrast, the injury response of most supraspinal cell types, whose limited regeneration constrains recovery from spinal injury, is mostly unknown. Here we employed single-nuclei sequencing in mice to profile the transcriptional responses of diverse supraspinal cell types to spinal injury. Surprisingly, thoracic spinal injury triggered only modest changes in gene expression across all populations, including corticospinal tract (CST) neurons. Moreover, CST neurons also responded minimally to cervical injury but much more strongly to intracortical axotomy, including upregulation of numerous regeneration and apoptosis-related transcripts shared with injured DRG and RGC neurons. Thus, the muted response of CST neuron to spinal injury is linked to the injury's distal location, rather than intrinsic cellular characteristics. More broadly, these findings indicate that a central challenge for enhancing regeneration after a spinal injury is the limited sensing of distant injuries and the subsequent modest baseline neuronal response.

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.

Deficiency of smooth muscle cell ILF3 alleviates intimal hyperplasia via HMGB1 mRNA degradation-mediated regulation of the STAT3/DUSP16 axis

Intimal hyperplasia is a complicated pathophysiological phenomenon attributable to in-stent restenosis, and the underlying mechanism remains unclear. Interleukin enhancer-binding factor 3 (ILF3), a double-stranded RNA-binding protein involved in regulating mRNA stability, has been recently demonstrated to assume a crucial role in cardiovascular disease; nevertheless, its impact on intimal hyperplasia remains unknown. In current study, we used samples of human restenotic arteries and rodent models of intimal hyperplasia, we found that vascular smooth muscle cell (VSMC) ILF3 expression was markedly elevated in human restenotic arteries and murine ligated carotid arteries. SMC-specific ILF3 knockout mice significantly suppressed injury induced neointimal formation. In vitro, platelet-derived growth factor type BB (PDGF-BB) treatment elevated the level of VSMC ILF3 in a dose- and time-dependent manner. ILF3 silencing markedly inhibited PDGF-BB-induced phenotype switching, proliferation, and migration in VSMCs. Transcriptome sequencing and RNA immunoprecipitation sequencing depicted that ILF3 maintained its stability upon binding to the mRNA of the high-mobility group box 1 protein (HMGB1), thereby exerting an inhibitory effect on the transcription of dual specificity phosphatase 16 (DUSP16) through enhanced phosphorylation of signal transducer and activator of transcription 3 (STAT3). Therefore, the results both in vitro and in vivo indicated that the loss of ILF3 in VSMC ameliorated neointimal hyperplasia by regulating the STAT3/DUSP16 axis through the degradation of HMGB1 mRNA. Our findings revealed that vascular injury activates VSMC ILF3, which in turn promotes intima formation. Consequently, targeting specific VSMC ILF3 may present a potential therapeutic strategy for ameliorating cardiovascular restenosis.

The role of kinases in peripheral nerve regeneration: mechanisms and implications

Peripheral nerve injury disease is a prevalent traumatic condition in current medical practice. Despite the present treatment approaches, encompassing surgical sutures, autologous nerve or allograft nerve transplantation, tissue engineering techniques, and others, an effective clinical treatment method still needs to be discovered. Exploring novel treatment methods to improve peripheral nerve regeneration requires more effort in investigating the cellular and molecular mechanisms involved. Many factors are associated with the regeneration of injured peripheral nerves, including the cross-sectional area of the injured nerve, the length of the nerve gap defect, and various cellular and molecular factors such as Schwann cells, inflammation factors, kinases, and growth factors. As crucial mediators of cellular communication, kinases exert regulatory control over numerous signaling cascades, thereby participating in various vital biological processes, including peripheral nerve regeneration after nerve injury. In this review, we examined diverse kinase classifications, distinct nerve injury types, and the intricate mechanisms involved in peripheral nerve regeneration. Then we stressed the significance of kinases in regulating autophagy, inflammatory response, apoptosis, cell cycle, oxidative processes, and other aspects in establishing conductive microenvironments for nerve tissue regeneration. Finally, we briefly discussed the functional roles of kinases in different types of cells involved in peripheral nerve regeneration.

HPV+ head and neck cancer-derived small extracellular vesicles communicate with TRPV1+ neurons to mediate cancer pain

ABSTRACT

Severe pain is often experienced by patients with head and neck cancer and is associated with a poor prognosis. Despite its frequency and severity, current treatments fail to adequately control cancer-associated pain because of our lack of mechanistic understanding. Although recent works have shed some light of the biology underlying pain in HPV-negative oral cancers, the mechanisms mediating pain in HPV+ cancers remain unknown. Cancer-derived small extracellular vesicles (cancer-sEVs) are well positioned to function as mediators of communication between cancer cells and neurons. Inhibition of cancer-sEV release attenuated pain in tumor-bearing mice. Injection of purified cancer-sEVs is sufficient to induce pain hypersensitivity in naive mice that is prevented by QX-314 treatment and in Trpv1-/- mice. Cancer-sEVs triggered calcium influx in nociceptors, and inhibition or ablation of nociceptors protects against cancer pain. Interrogation of published sequencing data of human sensory neurons exposed to human cancer-sEVs suggested a stimulation of protein translation in neurons. Induction of translation by cancer-sEVs was validated in our mouse model, and its inhibition alleviated cancer pain in mice. In summary, our work reveals that HPV+ head and neck squamous cell carcinoma-derived sEVs alter TRPV1+ neurons by promoting nascent translation to mediate cancer pain and identified several promising therapeutic targets to interfere with this pathway.

Neuropathic pain development following nerve injury is mediated by SOX11-ARID1A-SOCS3 transcriptional regulation in the spinal cord

BACKGROUND

Neuropathic pain, a complex condition originating from nervous system damage, remains a significant clinical challenge due to limited understanding of its underlying mechanisms. Recent research highlights the SOX11 transcription factor, known for its role in nervous system development, as a crucial player in neuropathic pain development and maintenance. This study investigates the role of the SOX11-ARID1A-SOCS3 pathway in neuropathic pain modulation within the spinal cord.

METHODS AND RESULTS

Using a spinal nerve ligation (SNL) model in mice, we observed a significant upregulation of Sox11 in the spinal cord dorsal horn post-injury. Intrathecal administration of Sox11 shRNA mitigated SNL-induced neuropathic pain behaviors, including mechanical allodynia and heat hyperalgesia. Further, we demonstrated that Sox11 regulates neuropathic pain via transcriptional control of ARID1A, with subsequent modulation of SOCS3 expression. Knockdown of ARID1A and SOCS3 via shRNA resulted in alleviation of Sox11-induced pain sensitization. Additionally, Sox11 overexpression led to an increase in ARID1A binding to the SOCS3 promoter, enhancing chromatin accessibility and indicating a direct regulatory relationship. These findings were further supported by in vitro luciferase reporter assays and chromatin accessibility analysis.

CONCLUSIONS

The SOX11-ARID1A-SOCS3 pathway plays a pivotal role in the development and maintenance of neuropathic pain. Sox11 acts as a master regulator, modulating ARID1A, which in turn influences SOCS3 expression, thereby contributing to the modulation of neuropathic pain. These findings provide a deeper understanding of the molecular mechanisms underlying neuropathic pain and highlight potential therapeutic targets for its treatment. The differential regulation of this pathway in the spinal cord and dorsal root ganglia (DRG) underscores its complexity and the need for targeted therapeutic strategies.

Acer truncatum Bunge seed oil ameliorated oxaliplatin-induced demyelination by improving mitochondrial dysfunction via the Pink1/Parkin mitophagy pathway

Dietary nutritional support for special populations is an effective and feasible method to improve the quality of life of patients and reduce medical pressure. Acer truncatum Bunge seed oil (ATSO) is widely recognized for its ability to promote nerve myelin regeneration. To evaluate the ameliorative effects of ATSO on chemotherapy-induced demyelination, a zebrafish model of chemotherapy-induced demyelination was established. The results showed that 100 μg mL-1 of ATSO reversed tail morphology damage, axon degeneration, touch response delay, ROS level upregulation and the expression of myelin basic protein decrease in chemotherapy-induced zebrafish. In addition, the expression of myelin markers (including sox10, krox20, and pmp22) in oxaliplatin-induced cells was markedly reversed by ATSO and its active components (gondoic acid, erucic acid, and nervonic acid). ATSO and its active components could reverse demyelination by ameliorating mitochondrial dysfunction. Conversely, linoleic acid and linolenic acid promoted demyelination by exacerbating mitochondrial dysfunction. Moreover, the Pink1/Parkin pathway was recognized as the main reason for ATSO and its active components improving mitochondrial function by activating mitophagy and restoring autophagic flow. Taken together, this study demonstrated that ATSO and its active components could be further developed as novel functional food ingredients to antagonize demyelination.

Calcium-Associated Proteins in Neuroregeneration

The dysregulation of intracellular calcium levels is a critical factor in neurodegeneration, leading to the aberrant activation of calcium-dependent processes and, ultimately, cell death. Ca2+ signals vary in magnitude, duration, and the type of neuron affected. A moderate Ca2+ concentration can initiate certain cellular repair pathways and promote neuroregeneration. While the peripheral nervous system exhibits an intrinsic regenerative capability, the central nervous system has limited self-repair potential. There is evidence that significant variations exist in evoked calcium responses and axonal regeneration among neurons, and individual differences in regenerative capacity are apparent even within the same type of neurons. Furthermore, some studies have shown that neuronal activity could serve as a potent regulator of this process. The spatio-temporal patterns of calcium dynamics are intricately controlled by a variety of proteins, including channels, ion pumps, enzymes, and various calcium-binding proteins, each of which can exert either positive or negative effects on neural repair, depending on the cellular context. In this concise review, we focus on several calcium-associated proteins such as CaM kinase II, GAP-43, oncomodulin, caldendrin, calneuron, and NCS-1 in order to elaborate on their roles in the intrinsic mechanisms governing neuronal regeneration following traumatic damage processes.

The Transcription Factor Ets1 Influences Axonal Growth via Regulation of Lcn2

Transcription factors are essential for the development and regeneration of the nervous system. The current study investigated key regulatory transcription factors in rat spinal cord development via RNA sequencing. The hub gene Ets1 was highly expressed in the spinal cord during the embryonic period, and then its expression decreased during spinal cord development. Knockdown of Ets1 significantly increased the axonal growth of cultured spinal cord neurons. Luciferase reporter assays and chromatin immunoprecipitation assays indicated that Ets1 could directly bind to the Lcn2 promoter and positively regulate Lcn2 transcription. In conclusion, these findings provide the first direct evidence that Ets1 regulates axon growth by controlling Lcn2 expression, and Ets1 may be a novel therapeutic target for axon regeneration in the central nervous system.

Brief Electrical Stimulation Promotes Recovery after Surgical Repair of Injured Peripheral Nerves

Injured peripheral nerves regenerate their axons in contrast to those in the central nervous system. Yet, functional recovery after surgical repair is often disappointing. The basis for poor recovery is progressive deterioration with time and distance of the growth capacity of the neurons that lose their contact with targets (chronic axotomy) and the growth support of the chronically denervated Schwann cells (SC) in the distal nerve stumps. Nonetheless, chronically denervated atrophic muscle retains the capacity for reinnervation. Declining electrical activity of motoneurons accompanies the progressive fall in axotomized neuronal and denervated SC expression of regeneration-associated-genes and declining regenerative success. Reduced motoneuronal activity is due to the withdrawal of synaptic contacts from the soma. Exogenous neurotrophic factors that promote nerve regeneration can replace the endogenous factors whose expression declines with time. But the profuse axonal outgrowth they provoke and the difficulties in their delivery hinder their efficacy. Brief (1 h) low-frequency (20 Hz) electrical stimulation (ES) proximal to the injury site promotes the expression of endogenous growth factors and, in turn, dramatically accelerates axon outgrowth and target reinnervation. The latter ES effect has been demonstrated in both rats and humans. A conditioning ES of intact nerve days prior to nerve injury increases axonal outgrowth and regeneration rate. Thereby, this form of ES is amenable for nerve transfer surgeries and end-to-side neurorrhaphies. However, additional surgery for applying the required electrodes may be a hurdle. ES is applicable in all surgeries with excellent outcomes.

ACY1215 Exerts Anti-inflammatory Effects by Inhibition of NF-κB and STAT3 Signaling Pathway to Repair Spinal Cord Injury

Spinal cord injury (SCI), a public health problem caused by mechanical injury, leads to secondary excessive inflammatory reactions and long-term damage to neurological function. ACY1215 is a highly selective histone deacetylase 6 (HDAC6) inhibitor and reportedly has anti-inflammatory effects; however, its regulatory role in SCI has not been studied. The purpose of this study was to explore the role of ACY1215 in preventing inflammation, inhibiting astrogliosis, enhancing remyelination and preserving axons after spinal cord injury and further exploring the possible cellular signaling pathways involved. First, lipopolysaccharide (LPS) was utilized to stimulate rat astrocytes in vitro. Quantitative RT (qRT)-PCR and Western blotting showed that ACY1215 inhibited the expression of glial fibrillary acidic protein (GFAP), interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNFα) in LPS-activated astrocytes. In addition, Western blotting results showed that ACY1215 could inhibit the signal transduction pathway of nuclear factor-κB (NF-κB) and signal transducer and activator of transcription 3 (STAT3). In vivo, ACY1215 could exert anti-inflammatory effects by inhibiting the expression of inflammatory cytokines, including IL-1β, IL-6, and TNF-α. Moreover, ACY1215 repaired spinal cord injury by reducing the formation of glial scars and promoting remyelination and nerve recovery. In summary, ACY1215 can inhibit the NF-κB and STAT3 signaling pathways in astrocytes, reduce inflammation and ameliorate SCI. Our results provide a novel strategy for the treatment of SCI.

Chemokine platelet factor 4 accelerates peripheral nerve regeneration by regulating Schwann cell activation and axon elongation

Schwann cells in peripheral nerves react to traumatic nerve injury by attempting to grow and regenerate. However, it is unclear what factors play a role in this process. In this study, we searched a GEO database and found that expression of platelet factor 4 was markedly up-regulated after sciatic nerve injury. Platelet factor is an important molecule in cell apoptosis, differentiation, survival, and proliferation. Further, polymerase chain reaction and immunohistochemical staining confirmed the change in platelet factor 4 in the sciatic nerve at different time points after injury. Enzyme-linked immunosorbent assay confirmed that platelet factor 4 was secreted by Schwann cells. We also found that silencing platelet factor 4 decreased the proliferation and migration of primary cultured Schwann cells, while exogenously applied platelet factor 4 stimulated Schwann cell proliferation and migration and neuronal axon growth. Furthermore, knocking out platelet factor 4 inhibited the proliferation of Schwann cells in injured rat sciatic nerve. These findings suggest that Schwann cell-secreted platelet factor 4 may facilitate peripheral nerve repair and regeneration by regulating Schwann cell activation and axon growth. Thus, platelet factor 4 may be a potential therapeutic target for traumatic peripheral nerve injury.

Unleashing Axonal Regeneration Capacities: Neuronal and Non-neuronal Changes After Injuries to Dorsal Root Ganglion Neuron Central and Peripheral Axonal Branches

Peripheral nerves obtain remarkable regenerative capacity while central nerves can hardly regenerate following nerve injury. Sensory neurons in the dorsal root ganglion (DRG) are widely used to decipher the dissimilarity between central and peripheral axonal regeneration as axons of DRG neurons bifurcate into the regeneration-incompetent central projections and the regeneration-competent peripheral projections. A conditioning peripheral branch injury facilitates central axonal regeneration and enables the growth and elongation of central axons. Peripheral axonal injury stimulates neuronal calcium influx, alters the start-point chromatin states, increases chromatin accessibility, upregulates the expressions of regeneration-promoting genes and the synthesis of proteins, and supports axonal regeneration. Following central axonal injury, the responses of DRG neurons are modest, resulting in poor intrinsic growth ability. Some non-neuronal cells in DRGs, for instance satellite glial cells, also exhibit diminished injury responses to central axon injury as compared with peripheral axon injury. Moreover, DRG central and peripheral axonal branches are respectively surrounded by inhibitory glial scars generated by central glial cells and a permissive microenvironment generated by Schwann cells and macrophages. The aim of this review is to look at changes of DRG neurons and non-neuronal cells after peripheral and central axon injuries and summarize the contributing roles of both neuronal intrinsic regenerative capacities and surrounding microenvironments in axonal regeneration.

The Dynamics of Nerve Degeneration and Regeneration in a Healthy Milieu and in Diabetes

Appropriate animal models, mimicking conditions of both health and disease, are needed to understand not only the biology and the physiology of neurons and other cells under normal conditions but also under stress conditions, like nerve injuries and neuropathy. In such conditions, understanding how genes and different factors are activated through the well-orchestrated programs in neurons and other related cells is crucial. Knowledge about key players associated with nerve regeneration intended for axonal outgrowth, migration of Schwann cells with respect to suitable substrates, invasion of macrophages, appropriate conditioning of extracellular matrix, activation of fibroblasts, formation of endothelial cells and blood vessels, and activation of other players in healthy and diabetic conditions is relevant. Appropriate physical and chemical attractions and repulsions are needed for an optimal and directed regeneration and are investigated in various nerve injury and repair/reconstruction models using healthy and diabetic rat models with relevant blood glucose levels. Understanding dynamic processes constantly occurring in neuropathies, like diabetic neuropathy, with concomitant degeneration and regeneration, requires advanced technology and bioinformatics for an integrated view of the behavior of different cell types based on genomics, transcriptomics, proteomics, and imaging at different visualization levels. Single-cell-transcriptional profile analysis of different cells may reveal any heterogeneity among key players in peripheral nerves in health and disease.

Nicotine Decreases Nerve Regeneration and Pain Behaviors via PTEN and Downstream Inflammation-Related Pathway in Two Rat Nerve Injury Models

Neuropathic pain is stubborn and associated with the peripheral nerve regeneration process. Nicotine has been found to reduce pain, but whether it is involved in the regulation of nerve regeneration and the underlying mechanism are unknown. In this study, we examined the mechanical allodynia thermal hyperalgesia together with the peripheral nerve regeneration after nicotine exposure in two rat neuropathic pain models. In the spinal nerve ligation model, in which anatomic nerve regeneration can be easily observed, nicotine reduced anatomic measures of regeneration as well as expression of regeneration marker growth-associated protein 43 (GAP43). In the tibial nerve crush model, nicotine treatment significantly suppressed GAP43 expression and functional reinnervation as measured by myelinated action potential and electromyography of gastrocnemius. In both models, nicotine treatment reduced macrophage density in the sensory ganglia and peripheral nerve. These effects of nicotine were reversed by the selective α7 nicotinic acetylcholine receptor (nAChR) blocker methyllycaconitine. In addition, nicotine significantly elevated expression of PTEN (the phosphatase and tensin homolog deleted on chromosome 10), a key player in both regeneration and pain. Pharmacological interference of PTEN could regulate GAP43 expression, pain-related behaviors, and macrophage infiltration in a nicotine-treated nerve crush model. Our results reveal that nicotine and its α7-nAChR regulate both peripheral nerve regeneration process and pain though PTEN and the downstream inflammation-related pathway.

Transcription Factor BCL11A Regulates Schwann Cell Behavior During Peripheral Nerve Regeneration

Nerve injury-induced Schwann cell dedifferentiation helps to construct a favorable microenvironment for axon growth. Transcription factors regulate cell reprogramming and thus may be critical for Schwann cell phenotype switch during peripheral nerve regeneration. Here, we show that transcription factor B-cell lymphoma/leukemia 11A (BCL11A) is up-regulated in Schwann cells of injured peripheral nerves. Bcl11a silencing suppresses Schwann cell viability, decreases Schwann cell proliferation and migration rates, and impairs the debris clearance ability of Schwann cells. Reduced Bcl11a in injured peripheral nerves results in restricted axon elongation and myelin wrapping, leading to recovery failure. Mechanistically, we demonstrate that BCL11A may mediate Schwann cell activity through binding to the promoter of nuclear receptor subfamily 2 group F member 2 (Nr2f2) and regulating Nr2f2 expression. Collectively, we conclude that BCL11A is essential for Schwann cell activation and peripheral nerve regeneration, providing a potential therapeutic target for the treatment of peripheral nerve injury.