Cooperative roles of BDNF expression in neurons and Schwann cells are modulated by exercise to facilitate nerve regeneration

Muscle-resident mesenchymal progenitors sense and repair peripheral nerve injury via the GDNF-BDNF axis

Fibro-adipogenic progenitors (FAPs) are muscle-resident mesenchymal progenitors that can contribute to muscle tissue homeostasis and regeneration, as well as postnatal maturation and lifelong maintenance of the neuromuscular system. Recently, traumatic injury to the peripheral nerve was shown to activate FAPs, suggesting that FAPs can respond to nerve injury. However, questions of how FAPs can sense the anatomically distant peripheral nerve injury and whether FAPs can directly contribute to nerve regeneration remained unanswered. Here, utilizing single-cell transcriptomics and mouse models, we discovered that a subset of FAPs expressing GDNF receptors Ret and Gfra1 can respond to peripheral nerve injury by sensing GDNF secreted by Schwann cells. Upon GDNF sensing, this subset becomes activated and expresses Bdnf. FAP-specific inactivation of Bdnf (Prrx1Cre; Bdnffl/fl) resulted in delayed nerve regeneration owing to defective remyelination, indicating that GDNF-sensing FAPs play an important role in the remyelination process during peripheral nerve regeneration. In aged mice, significantly reduced Bdnf expression in FAPs was observed upon nerve injury, suggesting the clinical relevance of FAP-derived BDNF in the age-related delays in nerve regeneration. Collectively, our study revealed the previously unidentified role of FAPs in peripheral nerve regeneration, and the molecular mechanism behind FAPs' response to peripheral nerve injury.

The protective effect of erythropoietin and its novel derived peptides in peripheral nerve injury

Peripheral nerve injury seriously endangers human life and health, but there is no clinical drug for the treatment of peripheral nerve injury, so it is imperative to develop drugs to promote the repair of peripheral nerve injury. Erythropoietin (EPO) not only has the traditional role of promoting erythropoiesis, but also has a tissue-protective effect. Over the past few decades, researchers have confirmed that EPO has neuroprotective effects. However, side effects caused by long-term use of EPO limited its clinical application. Therefore, EPO derivatives with low side effects have been explored. Among them, ARA290 has shown significant protective effects on the nervous system, but the biggest disadvantage of ARA290, its short half-life, limits its application. To address the short half-life issue, the researchers modified ARA290 with thioether cyclization to generate a thioether cyclized helical B peptide (CHBP). ARA290 and CHBP have promising applications as peptide drugs. The neuroprotective effects they exhibit have attracted continuous exploration of their mechanisms of action. This article will review the research on the role of EPO, ARA290 and CHBP in the nervous system around this developmental process, and provide a certain reference for the subsequent research.

Adipose-derived stem cells modified by TWIST1 silencing accelerates rat sciatic nerve repair and functional recovery

The regeneration of peripheral nerves after injury is often slow and impaired, which may be associated with weakened and denervated muscles subsequently leading to atrophy. Adipose-derived stem cells (ADSCs) are often regarded as cell-based therapeutic candidate due to their regenerative potential. The study aims to assess the therapeutic efficacy of gene-modified ADSCs on sciatic nerve injury. We lentivirally transduced ADSCs with shRNA-TWIST1 and transplanted modified cells to rats undergoing sciatic nerve transection and repair. Results showed that TWIST1 knockdown accelerated functional recovery of rats with sciatic nerve injury as faster nerve conduction velocity and higher wire hang scores obtained by rats transplanted with TWIST1-silenced ADSCs than scramble ADSCs. Although the rats experienced degenerated axons and decreased myelin sheath thickness after sciatic nerve injury 8 weeks after operation, those transplanted with TWIST1-silenced ADSCs exhibited more signs of regenerated nerve fibers surrounded by newly formed myelin sheaths than those with scramble ADSCs. The rats transplanted with TWIST1-silenced ADSCs presented increased expressions of neurotrophic factors including neurotrophin-3 (NT-3), brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), and glial cell line-derived neurotrophic factor (GDNF) in the sciatic nerves than those with scramble ADSCs. These results suggest that genetically modifying TWIST1 in ADSCs could facilitate peripheral nerve repair after injury in a more efficient way than that with ADSCs alone.

BDNF-loaded chitosan-based mimetic mussel polymer conduits for repair of peripheral nerve injury

Care for patients with peripheral nerve injury is multifaceted, as traditional methods are not devoid of limitations. Although the utilization of neural conduits shows promise as a therapeutic modality for peripheral nerve injury, its efficacy as a standalone intervention is limited. Hence, there is a pressing need to investigate a composite multifunctional neural conduit as an alternative treatment for peripheral nerve injury. In this study, a BDNF-loaded chitosan-based mimetic mussel polymer conduit was prepared. Its unique adhesion characteristics allow it to be suture-free, improve the microenvironment of the injury site, and have good antibacterial properties. Researchers utilized a rat sciatic nerve injury model to evaluate the progression of nerve regeneration at the 12-week postoperative stage. The findings of this study indicate that the chitosan-based mimetic mussel polymer conduit loaded with BDNF had a substantial positive effect on myelination and axon outgrowth. The observed impact demonstrated a favorable outcome in terms of sciatic nerve regeneration and subsequent functional restoration in rats with a 15-mm gap. Hence, this approach is promising for nerve tissue regeneration during peripheral nerve injury.

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.

Potential role of Schwann cells in neuropathic pain

Neuropathic pain (NPP) is a common syndrome associated with most forms of disease, which poses a serious threat to human health. NPP may persist even after the nociceptive stimulation is eliminated, and treatment is extremely challenging in such cases. Schwann cells (SCs) form the myelin sheaths around neuronal axons and play a crucial role in neural information transmission. SCs can secrete trophic factors to nourish and protect axons, and can further secrete pain-related factors to induce pain. SCs may be activated by peripheral nerve injury, triggering the transformation of myelinated and non-myelinated SCs into cell phenotypes that specifically promote repair. These differentiated SCs provide necessary signals and spatial clues for survival, axonal regeneration, and nerve regeneration of damaged neurons. They can further change the microenvironment around the regions of nerve injury, and relieve the pain by repairing the injured nerve. Herein, we provide a comprehensive overview of the biological characteristics of SCs, discuss the relationship between SCs and nerve injury, and explore the potential mechanism of SCs and the occurrence of NPP. Moreover, we summarize the feasible strategies of SCs in the treatment of NPP, and attempt to elucidate the deficiencies and defects of SCs in the treatment of NPP.

Advances of exosomes-based applications in diagnostic biomarkers for dental disease and dental regeneration

Exosomes are produced by all the cells and exist in all body fluids. They have been regarded as potentially promising to diagnostic biomarkers and therapeutic bioactive mediators since they transport DNA, RNA and protein information from cell to cell. Herein, we summarized the recent research about exosomes from gingival crevicular fluid, saliva and serum used as diagnostic markers in periodontitis and dental caries. Moreover, we highlighted the mechanisms of exosomes in dental pulp regeneration and periodontal regeneration, as well as the technological innovation of exosome delivery methods in oral disease. In the end, this review discussed the advantages and future challenges of exosomes in real clinical applications.

Treatments with the specific δ-secretase inhibitor, compound 11, promote the regeneration of motor and sensory axons after peripheral nerve injury

Limited axon regeneration following peripheral nerve injury may be related to activation of the lysosomal protease, asparaginyl endopeptidase (AEP, δ-secretase) and its degradation of the microtubule associated protein, Tau. Activity of AEP was increased at the site of sciatic nerve transection and repair but blocked in mice treated systemically with a specific AEP inhibitor, compound 11 (CP11). Treatments with CP11 enhanced axon regeneration in vivo. Amplitudes of compound muscle action potentials recorded 4 weeks after nerve transection and repair and 2 weeks after daily treatments with CP11 were double those of vehicle-treated mice. At that time after injury, axons of significantly more motor and sensory neurons had regenerated successfully and reinnervated the tibialis anterior and gastrocnemius muscles in CP11-treated mice than vehicle-treated controls. In cultured adult dorsal root ganglion neurons derived from wild type mice that were treated in vitro for 24 h with CP11, neurites were nearly 50% longer than in vehicle-treated controls and similar to neurite lengths in cultures treated with the TrkB agonist, 7,8-dihydroxyflavone (7,8-DHF). Combined treatment with CP11 and 7,8-DHF did not enhance outgrowth more than treatments with either one alone. Enhanced neurite outgrowth produced by CP11 was found also in the presence of the TrkB inhibitor, ANA-12, indicating that the enhancement was independent of TrkB signalling. Longer neurites were found after CP11 treatment in both TrkB+ and TrkB- neurons. Delta secretase inhibition by CP11 is a treatment for peripheral nerve injury with great potential.

MiRNA-206 Affects the Recovery of Sciatic Function by Stimulating BDNF Activity through the Down-regulation of Notch3 Expression

OBJECTIVE

To investigate the effects and mechanisms of microRNA 206 (miRNA-206) on neurological recovery through Notch receptor 3 (Notch3).

METHODS

The sciatic functional index (SFI), nerve conduction velocity (NCV), tricipital muscle wet weight (TWW) and cross-sectional area of the muscular fiber, and grip strength of posterior limbs were detected by establishing a model of the sciatic nerve to evaluate the effect of sciatic nerve injury model. miRNA-206 expression in the model was detected by real-time quantitative polymerase chain reaction (qRT-PCR), to regulate the effects of miRNA-206 on the proliferation of gastrocnemius myocytes by Cell Counting Kit-8 (CCK-8).

RESULTS

SFI of the model established by immediate epineurium suture after sciatic nerve resection was in the range of -150% to -100% and TWW, the average area of gastrocnemius myocytes, the NCV, and the grasping power of the hind limbs in the model were all lower than those in the normal group. And in the model, TWW, the average area of gastrocnemius myocytes, NCV, and grip strength of posterior limbs were lower in the normal group, which verified the successful establishment of the model.

CONCLUSION

Over-expression of miRNA-206 can down-regulate Notch3 expression, and then stimulate brain-derived neurotrophic factor (BDNF) activity to promote the repair and functional recovery of sciatic nerve injury.

Oral Administration of TrkB Agonist, 7, 8-Dihydroxyflavone Regenerates Hair Cells and Restores Function after Gentamicin-Induced Vestibular Injury in Guinea Pig

The causes of vestibular dysfunction include the loss of hair cells (HCs), synapses beneath the HCs, and nerve fibers. 7, 8-dihydroxyflavone (DHF) mimics the physiological functions of brain-derived neurotrophic factor. We investigated the effects of the orally-administered DHF in the guinea pig crista ampullaris after gentamicin (GM)-induced injury. Twenty animals treated with GM received daily administration of DHF or saline for 14 or 28 days (DHF (+) or DHF (-) group; N = 5, each). At 14 days after GM treatment, almost all of the HCs had disappeared in both groups. At 28 days, the HCs number in DHF (+) and DHF (-) groups was 74% and 49%, respectively, compared to GM-untreated control. In the ampullary nerves, neurofilament 200 positive rate in the DHF (+) group was 91% at 28 days, which was significantly higher than 42% in DHF (-). On day 28, the synaptic connections observed between C-terminal-binding protein 2-positive and postsynaptic density protein-95-positive puncta were restored, and caloric response was significantly improved in DHF (+) group (canal paresis: 57.4% in DHF (+) and 100% in DHF (-)). Taken together, the oral administration of DHF may be a novel therapeutic approach for treating vestibular dysfunction in humans.

Usefulness of Detecting Brain-Derived Neurotrophic Factor in Intervertebral Disc Degeneration of the Lumbosacral Spine

BACKGROUND In determining the etiology of pain of discogenic origin, attention is paid to the role of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF). Considering the potential role of BDNF in the etiology of pain during intervertebral disc degeneration (IVDD), this study aimed to assess changes in the number of BDNF-positive nerve fibers and levels of BDNF in IVDD of the lumbosacral spine in comparison to intervertebral discs (IVDs) of the control group (cadavers). MATERIAL AND METHODS The study group comprised 113 patients with IVDD of the lumbosacral spine. The control group consisted of 81 people (cadavers). We performed hematoxylin-eosin staining to assess IVD structures (degeneration), immunohistochemistry to determine the number of BDNF-positive nerve fibers, and an enzyme-linked immunosorbent assay and western blot to quantify BDNF levels in IVDs. RESULTS Levels of BDNF in the study group were significantly higher than in the control group (17.91±19.58 pg/mg; P<0.05). Furthermore, BDNF levels were significantly higher in the annulus fibrosus compared to the nucleus pulposus of the intervertebral disc (5.50±6.40 pg/mg; P<0.05). Neither the number of BDNF-positive nerves (P=0.359) nor BDNF concentration (P=0.706) were significantly correlated with the degree of perceived pain. The number of BDNF-positive fibers per 1 mm2 was not found to differ significantly according to the radiological degree of degeneration of the lumbosacral spine based on the Pfirrmann scale (P=0.735). CONCLUSIONS The level of BDNF expression may be indicative of IVD degeneration, although it does not predict the degree of this degeneration.

Exercise facilitates regeneration after severe nerve transection and further modulates neural plasticity

Patients with severe traumatic peripheral nerve injury (PNI) always suffer from incomplete recovery and poor functional outcome. Physical exercise-based rehabilitation, as a non-invasive interventional strategy, has been widely acknowledged to improve PNI recovery by promoting nerve regeneration and relieving pain. However, effects of exercise on chronic plastic changes following severe traumatic PNIs have been limitedly discussed. In this study, we created a long-gap sciatic nerve transection followed by autograft bridging in rats and tested the therapeutic functions of treadmill running with low intensity and late initiation. We demonstrated that treadmill running effectively facilitated nerve regeneration and prevented muscle atrophy and thus improved sensorimotor functions and walking performance. Furthermore, exercise could reduce inflammation at the injured nerve as well as prevent the overexpression of TRPV1, a pain sensor, in primary afferent sensory neurons. In the central nervous system, we found that PNI induced transcriptive changes at the ipsilateral lumber spinal dorsal horn, and exercise could reverse the differential expression for genes involved in the Notch signaling pathway. In addition, through neural imaging techniques, we found volumetric, microstructural, metabolite, and neuronal activity changes in supraspinal regions of interest (i.e., somatosensory cortex, motor cortex, hippocampus, etc.) after the PNI, some of which could be reversed through treadmill running. In summary, treadmill running with late initiation could promote recovery from long-gap nerve transection, and while it could reverse maladaptive plasticity after the PNI, exercise may also ameliorate comorbidities, such as chronic pain, mental depression, and anxiety in the long term.

Oral Treatments With the TrkB Ligand Prodrug, R13, Promote Enhanced Axon Regeneration Following Peripheral Nerve Injury

Axon regeneration after peripheral nerve injury is slow and inefficient, leading to generally poor functional recovery. Activity-dependent experimental therapies that increase expression of brain-derived neurotrophic factor (BDNF) and its TrkB receptors enhance regeneration, suggesting that treatments with BDNF might also be effective. However, recombinant human BDNF (rhBDNF), as well as 7,8-dihydroxyflavone (7,8-DHF), a small molecular BDNF mimetic, may have limited treatment applications because of their modest oral bioavailability and pharmacokinetic profile. R13 is a 7,8-DHF prodrug. Upon oral administration, it is converted in the liver to 7,8-DHF. In immunoblots from tissues at the site of nerve injury, a single oral treatment with R13 to mice following sciatic nerve transection and repair produced a rapid and prolonged increase in immunoreactivity to phosphorylated TrkB, prolonged phosphorylation of mitogen activated protein kinase (MAPK/Erk1/2), and a rapid but transient increase in phosphorylated AKT (protein kinase B). Intramuscular injections of fluorescent retrograde tracers into the gastrocnemius and tibialis anterior muscles 4 weeks after nerve injury resulted in significantly greater numbers of labeled motoneurons and dorsal root ganglion neurons in R13-treated mice than in vehicle-treated controls. Direct electromyographic (EMG) responses (M waves) were significantly larger in R13-treated mice 4 weeks after injury than vehicle-treated controls or mice treated with oral 7,8-DHF. Oral treatments with the prodrug, R13, are a potent therapy for stimulating axon regeneration and functional recovery after peripheral nerve injury.

Multifunctional Double-Layer Composite Hydrogel Conduit Based on Chitosan for Peripheral Nerve Repairing

Peripheral nerve regeneration and functional recovery is a major challenge in clinical practice. Nerve conduit is an effective treatment for peripheral nerve repair, but the traditional hollow nerve conduit is not satisfactory in peripheral nerve repair due to the limitation of cell migration and nutrient transport. Herein, the double cross-linked hydrogels with injectable, self-healing, and conductive properties are synthesized by the Schiff base reaction between polyaniline-modified carboxymethyl chitosan and aldehyde-modified Pluronic F-127 (F127-CHO), and the hydrophobic interaction of F127-CHO. The conductive hydrogel is injected into the cavity of chitosan conduit prepared by electrodeposition. The inner conductive hydrogel and the outer chitosan conduit are formed into a whole through the Schiff base reaction to obtain a double-layer composite hydrogel nerve conduit. The double-layer composite hydrogel neural conduit loaded with 7,8-dihydroxyflavone (DHF) has excellent degradability, biocompatibility, antioxidant activity, and Schwann cell proliferation activity. In the rat sciatic nerve defect model, the double-layer composite hydrogel nerve conduit significantly promotes sciatic nerve regeneration compared with the chitosan hollow conduit. Surprisingly, the repair ability of double-layered hydrogel nerve conduit loaded with DHF is comparable to that of autologous transplantation. Therefore, this multifunctional double-layer composite hydrogel conduit has great potential for peripheral nerve repairing.

Ageing and exercise-induced motor unit remodelling

A motor unit (MU) comprises the neuron cell body, its corresponding axon and each of the muscle fibres it innervates. Many studies highlight age-related reductions in the number of MUs, yet the ability of a MU to undergo remodelling and to expand to rescue denervated muscle fibres is also a defining feature of MU plasticity. Remodelling of MUs involves two coordinated processes: (i) axonal sprouting and new branching growth from adjacent surviving neurons, and (ii) the formation of key structures around the neuromuscular junction to resume muscle-nerve communication. These processes rely on neurotrophins and coordinated signalling in muscle-nerve interactions. To date, several neurotrophins have attracted focus in animal models, including brain-derived neurotrophic factor and insulin-like growth factors I and II. Exercise in older age has demonstrated benefits in multiple physiological systems including skeletal muscle, yet evidence suggests this may also extend to peripheral MU remodelling. There is, however, a lack of research in humans due to methodological limitations which are easily surmountable in animal models. To improve mechanistic insight of the effects of exercise on MU remodelling with advancing age, future research should focus on combining methodological approaches to explore the in vivo physiological function of the MU alongside alterations of the localised molecular environment.

Mechanisms, Mediators, and Moderators of the Effects of Exercise on Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is an adverse effect of neurotoxic antineoplastic agents commonly used to treat cancer. Patients with CIPN experience debilitating signs and symptoms, such as combinations of tingling, numbness, pain, and cramping in the hands and feet that inhibit their daily function. Among the limited prevention and treatment options for CIPN, exercise has emerged as a promising new intervention that has been investigated in approximately two dozen clinical trials to date. As additional studies test and suggest the efficacy of exercise in treating CIPN, it is becoming more critical to develop mechanistic understanding of the effects of exercise in order to tailor it to best treat CIPN symptoms and identify who will benefit most. To address the current lack of clarity around the effect of exercise on CIPN, we reviewed the key potential mechanisms (e.g., neurophysiological and psychosocial factors), mediators (e.g., anti-inflammatory cytokines, self-efficacy, and social support), and moderators (e.g., age, sex, body mass index, physical fitness, exercise dose, exercise adherence, and timing of exercise) that may illuminate the relationship between exercise and CIPN improvement. Our review is based on the studies that tested the use of exercise for patients with CIPN, patients with other types of neuropathies, and healthy adults. The discussion presented herein may be used to (1) guide oncologists in predicting which symptoms are best targeted by specific exercise programs, (2) enable clinicians to tailor exercise prescriptions to patients based on specific characteristics, and (3) inform future research and biomarkers on the relationship between exercise and CIPN.

Gastrodin promotes the regeneration of peripheral nerves by regulating miR-497/BDNF axis

Background

Gastrodin (GAS), is a kind of phenolic compound extracted from the traditional Chinese herbal medicine Gastrodia elata Blume (GEB). This study was aimed at probing into the protective effect of GAS on peripheral nerve injury (PNI) and the underlying mechanism.

Methods

A rat model with PNI was established, followed by intraperitoneal injection of GAS (20 mg/kg/day). Sciatic nerve function index (SFI) was used to analyze the function of sciatic nerve. The amplitude and latency of compound muscle action potential (CMAP) were examined by electrophysiology. Schwann cells (SCs) were isolated from fetal rats and treated with GAS 200 μg/mL, and H₂O₂-induced model of oxidative stress injury was established. EdU and Transwell assays were adopted to detect the viability and migration of SCs. Dual-luciferase reporter gene assays were applied to verify the binding site between miR-497 and brain-derived neurotrophic factor (BDNF) 3’UTR. MiR-497 expression was probed by quantitative real-time polymerase chain reaction (qRT-PCR). BDNF, neurofilament-200 (NF-200) and myelin basic protein (MBP) expression levels were detected by Western blotting. Malondialdehyde (MDA) content, superoxide dismutase (SOD) activity, glutathione content (GSH) and catalase (CAT) activity in SCs were also measured.

Results

GAS treatment could significantly increase the SFI and amplitude of CMAP, shorten the refractory period, and ameliorate muscle atrophy of the rats with PNI. GAS treatment could markedly restrain miR-497 expression and increase the expression levels of BDNF, NF-200 and MBP in SCs. BDNF was confirmed as the target of miR-497 and BDNF overexpression could reverse the impacts of miR-497 overexpression on the proliferation, migration, and oxidative stress response of SCs.

Conclusions

GAS promotes the recovery of PNI via modulating miR-497 / BDNF axis and inhibiting oxidative stress.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03483-z.

Peripheral nerve fibroblasts secrete neurotrophic factors to promote axon growth of motoneurons

Peripheral nerve fibroblasts play a critical role in nerve development and regeneration. Our previous study found that peripheral nerve fibroblasts have different sensory and motor phenotypes. Fibroblasts of different phenotypes can guide the migration of Schwann cells to the same sensory or motor phenotype. In this study, we analyzed the different effects of peripheral nerve-derived fibroblasts and cardiac fibroblasts on motoneurons. Compared with cardiac fibroblasts, peripheral nerve fibroblasts greatly promoted motoneuron neurite outgrowth. Transcriptome analysis results identified 491 genes that were differentially expressed in peripheral nerve fibroblasts and cardiac fibroblasts. Among these, 130 were significantly upregulated in peripheral nerve fibroblasts compared with cardiac fibroblasts. These genes may be involved in axon guidance and neuron projection. Three days after sciatic nerve transection in rats, peripheral nerve fibroblasts accumulated in the proximal and distal nerve stumps, and most expressed brain-derived neurotrophic factor. In vitro, brain-derived neurotrophic factor secreted from peripheral nerve fibroblasts increased the expression of β-actin and F-actin through the extracellular regulated protein kinase and serine/threonine kinase pathways, and enhanced motoneuron neurite outgrowth. These findings suggest that peripheral nerve fibroblasts and cardiac fibroblasts exhibit different patterns of gene expression. Peripheral nerve fibroblasts can promote motoneuron neurite outgrowth.

Effects of Varied Stimulation Parameters on Adipose-Derived Stem Cell Response to Low-Level Electrical Fields

Exogenous electrical fields have been explored in regenerative medicine to increase cellular expression of pro-regenerative growth factors. Adipose-derived stem cells (ASCs) are attractive for regenerative applications, specifically for neural repair. Little is known about the relationship between low-level electrical stimulation (ES) and ASC regenerative potentiation. In this work, patterns of ASC expression and secretion of growth factors (i.e., secretome) were explored across a range of ES parameters. ASCs were stimulated with low-level stimulation (20 mV/mm) at varied pulse frequencies, durations, and with alternating versus direct current. Frequency and duration had the most significant effects on growth factor expression. While a range of stimulation frequencies (1, 20, 1000 Hz) applied intermittently (1 h × 3 days) induced upregulation of general wound healing factors, neural-specific factors were only increased at 1 Hz. Moreover, the most optimal expression of neural growth factors was achieved when ASCs were exposed to 1 Hz pulses continuously for 24 h. In evaluation of secretome, apparent inconsistencies were observed across biological replications. Nonetheless, ASC secretome (from 1 Hz, 24 h ES) caused significant increase in neurite extension compared to non-stimulated control. Overall, ASCs are sensitive to ES parameters at low field strengths, notably pulse frequency and stimulation duration.

The role of exercise on peripheral nerve regeneration: from animal model to clinical application

Peripheral nerve injury is a complex condition with a variety of signs and symptoms depending on the severity and nerves involved. Peripheral nerve damage may lead to sensory and motor functions deficits and even lifelong disability, causing important socioeconomic costs worldwide. Despite the increase in knowledge of the mechanisms of injury and regeneration, a full functional recovery is still unsatisfying in the majority of patients. It is well known that exercise promotes physical and psychological well-being, by ameliorating general health. In the last years, there has been a growing interest in evaluating the effects of exercise on the peripheral nervous system. Experimental works with rodent models showed the potential utility of exercise following peripheral nerve injuries, as evinced by increasing axon regeneration, muscle reinnervation, better recovery of strength, muscle mass and higher expression of neurotrophic factors. Moreover, clinical evidence showed positive trends in favour of physical therapy following peripheral nerve damage based on the improvement of range of motion (ROM), muscle power grade and pain. After a brief overview of peripheral nerve anatomy and the different types of nerve injury, the present review aims to summarize the impact of exercise on peripheral nerve regeneration. Some clinical evidence regarding the effect of exercise after peripheral nerve injury will also be discussed.

Therapeutic Potential of Complementary and Alternative Medicines in Peripheral Nerve Regeneration: A Systematic Review

Despite the progressive advances, current standards of treatments for peripheral nerve injury do not guarantee complete recovery. Thus, alternative therapeutic interventions should be considered. Complementary and alternative medicines (CAMs) are widely explored for their therapeutic value, but their potential use in peripheral nerve regeneration is underappreciated. The present systematic review, designed according to guidelines of Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols, aims to present and discuss the current literature on the neuroregenerative potential of CAMs, focusing on plants or herbs, mushrooms, decoctions, and their respective natural products. The available literature on CAMs associated with peripheral nerve regeneration published up to 2020 were retrieved from PubMed, Scopus, and Web of Science. According to current literature, the neuroregenerative potential of Achyranthes&nbsp;bidentata, Astragalus&nbsp;membranaceus, Curcuma&nbsp;longa, Panax&nbsp;ginseng, and Hericium&nbsp;erinaceus are the most widely studied. Various CAMs enhanced proliferation and migration of Schwann cells in vitro, primarily through activation of MAPK pathway and FGF-2 signaling, respectively. Animal studies demonstrated the ability of CAMs to promote peripheral nerve regeneration and functional recovery, which are partially associated with modulations of neurotrophic factors, pro-inflammatory cytokines, and anti-apoptotic signaling. This systematic review provides evidence for the potential use of CAMs in the management of peripheral nerve injury.

Bioluminescent Optogenetics: A Novel Experimental Therapy to Promote Axon Regeneration after Peripheral Nerve Injury

Functional recovery after peripheral nerve injury (PNI) is poor, mainly due to the slow and incomplete regeneration of injured axons. Experimental therapies that increase the excitability of the injured axons have proven remarkably successful in promoting regeneration, but their clinical applicability has been limited. Bioluminescent optogenetics (BL-OG) uses luminopsins, fusion proteins of light-generating luciferase and light-sensing ion channels that could be used to increase neuronal excitability if exposed to a suitable substrate. Excitatory luminopsins were expressed in motoneurons of transgenic mice and in wildtype mice transduced with adeno-associated viral vectors. Intraperitoneal administration of coelenterazine (CTZ), a known luciferase substrate, generated intense bioluminescence in peripheral axons. This bioluminescence increased motoneuron excitability. A single administration of CTZ immediately after sciatic nerve transection and repair markedly enhanced motor axon regeneration. Compound muscle action potentials were 3–4 times larger than controls by 4 weeks after injury. The results observed with transgenic mice were comparable to those of mice in which the luminopsin was expressed using viral vectors. Significantly more motoneurons had successfully reinnervated muscle targets four weeks after nerve injury in BL-OG treated mice than in controls. Bioluminescent optogenetics is a promising therapeutic approach to enhancing axon regeneration after PNI.

Rapamycin Accelerates Axon Regeneration Through Schwann Cell-mediated Autophagy Following Inferior Alveolar Nerve Transection in Rats

Sensory disturbance in the orofacial region owing to trigeminal nerve injury is caused by dental treatment or accident. Commercially available therapeutics are ineffective for the treatment of sensory disturbance. Additionally, the therapeutic effects of rapamycin, an allosteric inhibitor of mammalian target of rapamycin (mTOR), which negatively regulates autophagy, on the sensory disturbance are not fully investigated. Thus, we investigated the therapeutic effects of rapamycin on the sensory disturbance in the mandibular region caused by inferior alveolar nerve (IAN) transection (IANX) in rats. The expression levels of the phosphorylated p70S6K, a downstream molecule of mTOR, in the proximal and distal stumps of the transected IAN were significantly reduced by rapamycin administration to the injured site. Conversely, the increments of both Beclin 1 and microtubule-associated protein-1 light chain 3-II protein levels in the proximal and distal stumps of the transected IAN was induced by rapamycin administration. Immunohistochemical analyses revealed that Beclin 1 was located in Schwann cells in the proximal stump of the IAN. Accumulation of myelin protein zero and myelin basic protein in the proximal and distal stumps of the IAN was significantly reduced by rapamycin administration. Rapamycin administration facilitated axon regeneration after IANX and increased the number of brain-derived neurotrophic factor positive neurons in the trigeminal ganglion. Thus, recovery from sensory disturbance in the lower lip caused by IANX was markedly facilitated by rapamycin. These findings suggest that rapamycin administration is a promising treatment for the sensory disturbance caused by IANX.

Brain derived neurotrophic factor mediates accelerated recovery of regenerative electrical stimulation in an animal model of stress urinary incontinence

OBJECTIVE

Stress urinary incontinence (SUI) is prevalent among older women and can result from insufficient regeneration of the pudendal nerve (PN). Electrical stimulation (ES) of the PN upregulates brain derived neurotrophic factor (BDNF) and accelerates regeneration. Using tyrosine kinase B (TrkB) to reduce the availability of free BDNF, the aim of this study was to determine if BDNF is necessary for accelerated recovery via ES in a model of SUI.

METHODS

Our SUI model consists of Female Sprague-Dawley rats, whose PNs were crushed bilaterally twice for 30 s, followed by insertion of a modified Foley catheter into the vagina with balloon inflation for 4 h. These rats were divided into 4 groups: 1) Sham PN crush and sham vaginal distension without electrode implantation and with saline treatment (sham injury); 2) SUI with sham stimulation and saline treatment (SUI); 3) SUI and ES with saline treatment (SUI&ES); and 4) SUI and ES with TrkB treatment (SUI&ES&TrkB). Animals underwent ES or sham stimulation four times a week for two weeks. Four weeks after injury, animals underwent functional testing consisting of leak point pressure (LPP) with simultaneous external urethral sphincter (EUS) electromyography (EMG) and pudendal nerve recordings. Data was analyzed using ANOVA with Holm-Sidak posthoc test (p < 0.05). EUS and PN specimen were sectioned and stained to semi-quantitatively evaluate morphology, regeneration, and reinnervation.

RESULTS

LPP and EUS EMG firing rate were significantly increased in the sham injury and SUI&ES groups compared to the SUI and SUI&ES&TrkB groups. EUS of SUI rats showed few innervated neuromuscular junctions compared to sham injured rats, while both treatment groups showed an increase in reinnervated neuromuscular junctions.

CONCLUSION

ES accelerates functional recovery via a BDNF-mediated pathway in a model of SUI. These findings suggest ES could be used as a potential regenerative therapy for women with SUI.

Neuronal androgen receptor is required for activity dependent enhancement of peripheral nerve regeneration

Neuronal activity after nerve injury can enhance axon regeneration and the restoration of function. The mechanism for this enhancement relies in part on hormone receptors, and we previously demonstrated that systemic androgen receptor antagonism blocked the effect of exercise or electrical stimulation on enhancing axon regeneration after nerve injury in both sexes. Here, we tested the hypothesis that the site of this androgen receptor signaling is both neuronal and involves the classical, genomic signaling pathway. In vivo, dorsal root ganglion neurons successfully regenerate in response to activity-dependent neuronal activation, and conditional deletion of the DNA-binding domain of the androgen receptor in adults blocks this effect in males and females. Motoneurons in males and females also respond in this manner, but we also observed a sex difference. In vitro, cultured sensory dorsal root ganglion neurons respond to androgens via traditional androgen receptor signaling mechanisms leading to enhanced neurite growth and did not respond to a testosterone conjugate that is unable to cross the cell membrane. Given our previous observation of a requirement for activity-dependent androgen receptor signaling to promote regeneration in both sexes, we interpret our results to indicate that genomic neuronal androgen receptor signaling is required for activity-dependent axon regeneration in both sexes.

LncRNA BC083743 Promotes the Proliferation of Schwann Cells and Axon Regeneration Through miR-103-3p/BDNF After Sciatic Nerve Crush

To investigate the underlying mechanism of lncRNA BC083743 in regulating the proliferation of Schwann cells (SCs) and axon regeneration after sciatic nerve crush (SNC), we used a rat model. Sciatic function index and the atrophy ratio of gastrocnemius muscle were evaluated. The relationship among BC083743, miR-103-3p, and brain-derived neurotrophic factor (BDNF) and their regulation mechanism in the repair of SNC were investigated using in vivo and in vitro experiments. The expression changes of BC083743 were positively associated with that of BDNF following SNC, but the expression changes of miR-103-3p were inversely associated with that of BDNF. The SC proliferation and BDNF expression could be promoted by overexpression of BC083743, while they were inhibited by a miR-103-3p mimic. In addition, BC083743 interacted with and regulated miR-103-3p, thereby promoting BDNF expression and SC proliferation. BC083743 overexpression also promoted axon regeneration through miR-103-3p. In vivo experiments also indicated that BC083743 overexpression promoted the repair of SNC. In conclusion, LncRNA BC083743 promotes SC proliferation and the axon regeneration through miR-103-3p/BDNF after SNC.

Asparagine Endopeptidase (δ Secretase), an Enzyme Implicated in Alzheimer's Disease Pathology, Is an Inhibitor of Axon Regeneration in Peripheral Nerves

Asparagine endopeptidase (AEP) is a lysosomal protease implicated in the pathology of Alzheimer’s disease (AD). It is known to cleave the axonal microtubule associated protein, Tau, and amyloid precursor protein (APP), both of which might impede axon regeneration following peripheral nerve injury (PNI). Active AEP, AEP-cleaved fragments of Tau (Tau N368), and APP (APP N585) were found in injured peripheral nerves. In AEP null mice, elongation of regenerating axons after sciatic nerve transection and repair was increased relative to wild-type (WT) controls. Compound muscle action potentials (M responses) were restored in reinnervated muscles twice as fast after injury in AEP knock-out (KO) mice as WT controls. Neurite elongation in cultures of adult dorsal root ganglion (DRG) neurons derived from AEP KO mice was increased significantly relative to cultures from WT controls. In AEP KO mice exposed to 1 h of 20-Hz electrical stimulation (ES) at the time of nerve injury, no further enhancement of axon regeneration was observed. These findings support inhibition of AEP as a therapeutic target to enhance axon regeneration after PNI.

Exercise is neuroprotective on the morphology of somatic motoneurons following the death of neighboring motoneurons via androgen action at the target muscle

Motoneuron loss is a severe medical problem that can result in loss of motor control and eventually death. We have previously demonstrated that partial motoneuron loss can result in dendritic atrophy and functional deficits in nearby surviving motoneurons, and that an androgen-dependent effect of exercise following injury can be neuroprotective against this dendritic atrophy. In this study, we explored where the necessary site of androgen action is for exercise-driven neuroprotective effects on induced dendritic atrophy. Motoneurons innervating the vastus medialis muscles of adult male rats were selectively killed by intramuscular injection of cholera toxin-conjugated saporin. Simultaneously, some saporin-injected animals were given implants of the androgen receptor antagonist hydroxyflutamide, either directly at the adjacent vastus lateralis musculature ipsilateral to the saporin-injected vastus medialis or interscapularly as a systemic control. Following saporin injections, some animals were allowed free access to a running wheel attached to their home cages. Four weeks later, motoneurons innervating the same vastus lateralis muscle were labeled with cholera toxin-conjugated horseradish peroxidase, and dendritic arbors were reconstructed in three dimensions. Dendritic arbor lengths of saporin-injected animals allowed to exercise were significantly longer than those not allowed to exercise. Androgen receptor blockade locally at the vastus lateralis muscle prevented the protective effect of exercise. These findings indicate that exercise following neural injury exerts a protective effect on motoneuron dendrites, which acts via androgen receptor action at the target muscle.

The Relation of the Brain-Derived Neurotrophic Factor with MicroRNAs in Neurodegenerative Diseases and Ischemic Stroke

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family of growth factors that plays a crucial role in the development of the nervous system while supporting the survival of existing neurons and instigating neurogenesis. Altered levels of BDNF, both in the circulation and in the central nervous system (CNS), have been reported to be involved in the pathogenesis of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), multiple sclerosis (MS), and ischemic stroke. MicroRNAs (miRNAs) are a class of non-coding RNAs found in body fluids such as peripheral blood and cerebrospinal fluid. Several different miRNAs, and their target genes, are recognized to be involved in the pathophysiology of neurodegenerative and neurovascular diseases. Thus, they present as promising biomarkers and a novel treatment approach for CNS disorders. Currently, limited studies provide viable evidence of miRNA-mediated post-transcriptional regulation of BDNF. The aim of this review is to provide a comprehensive assessment of the current knowledge regarding the potential diagnostic and prognostic values of miRNAs affecting BDNF expression and its role as a CNS disorders and neurovascular disease biomarker. Moreover, a novel therapeutic approach in neurodegenerative diseases and ischemic stroke targeting miRNAs associated with BDNF will be discussed.

Combinatory transplantation of mesenchymal stem cells with flavonoid small molecule in acellular nerve graft promotes sciatic nerve regeneration

Previous animal studies have demonstrated that the flavonoid small-molecule TrkB agonist, 7, 8-dihydroxyflavone (DHF), promotes axon regeneration in transected peripheral nerves. In the present study, we investigated the combined effects of 7, 8-DHF treatment and bone marrow-derived stem/stromal cells (BMSCs) engraftment into acellular nerve allografts (ANAs) and explore relevant mechanisms that may be involved. Our results show that TrkB and downstream ERK1/2 phosphorylation are increased upon 7, 8-DHF treatment compared to the negative control group. Also, 7, 8-DHF promotes proliferation, survival, and Schwann-like cell differentiation of BMSCs in vitro. While selective ERK1/2 inhibitor U0126 suppressed the effect of upregulation of ERK1/2 phosphorylation and decreased cell proliferation, survival, and Schwann-like cell differentiation partially induced by 7, 8-DHF. In vivo, 7, 8-DHF promotes survival of transplanted BMSCs and upregulates axonal growth and myelination in regenerating ANAs. 7, 8-DHF+BMSCs also improved motor endplate density of target musculature. These benefits were associated with increased motor functional recovery. 7, 8-DHF+BMSCs significantly upregulated TrkB and ERK1/2 phosphorylation expression in regenerating ANA, and increased TrkB expression in the lumbar spinal cord. The mechanism of 7, 8-DHF action may be related to its ability to upregulate TrkB signaling, and downstream activation of survival signaling molecules ERK1/2 in the regenerating ANAs and spinal cord and improved survival of transplanted BMSCs. This study provides novel foundational data connecting the benefits of 7, 8-DHF treatment in neural injury and repair to BMSCs biology and function and demonstrates a potential combination approach for the treatment of injured peripheral nerve via nerve graft transplant.

Chronic neuronal activation increases dynamic microtubules to enhance functional axon regeneration after dorsal root crush injury

After a dorsal root crush injury, centrally-projecting sensory axons fail to regenerate across the dorsal root entry zone (DREZ) to extend into the spinal cord. We find that chemogenetic activation of adult dorsal root ganglion (DRG) neurons improves axon growth on an in vitro model of the inhibitory environment after injury. Moreover, repeated bouts of daily chemogenetic activation of adult DRG neurons for 12 weeks post-crush in vivo enhances axon regeneration across a chondroitinase-digested DREZ into spinal gray matter, where the regenerating axons form functional synapses and mediate behavioral recovery in a sensorimotor task. Neuronal activation-mediated axon extension is dependent upon changes in the status of tubulin post-translational modifications indicative of highly dynamic microtubules (as opposed to stable microtubules) within the distal axon, illuminating a novel mechanism underlying stimulation-mediated axon growth. We have identified an effective combinatory strategy to promote functionally-relevant axon regeneration of adult neurons into the CNS after injury.

Augmented Buyang Huanwu Decoction facilitates axonal regeneration after peripheral nerve transection through the regulation of inflammatory cytokine production

ETHNOPHARMACOLOGICAL RELEVANCE

Herbal formulation Buyang Huanwu Decoction (BYHWD) has been used to treat cardiovascular disorders including cerebral ischemia. Recent studies showed its effects on promoting axonal regeneration after nerve injury. However, compositional reformulation supplemented with herbal components that regulates inflammation may increase its efficacy for nerve repair.

AIM OF THE STUDY

We prepared a new herbal decoction by adding selected herbal components to BYHWD (augmented BYHWD; ABHD) and investigated the effect of ABHD on the production of inflammatory cytokines and axonal regeneration using an animal model of nerve transection and coaptation (NTC).

MATERIALS AND METHODS

A rat model of NTC was performed on the sciatic nerve. The sciatic nerve and dorsal root ganglion (DRG) were isolated and used for immunofluorescence staining and western blot analysis. DRG tissue was also used to prepare primary neuron culture and the length of neurites was analyzed. Sensorimotor nerve activities were assessed by rotarod and von Frey tests.

RESULTS

Three herbal components that facilitated neurite outgrowth were chosen to formulate ABHD. ABHD administration into the sciatic nerve 1 week or 3 months after NTC facilitated axonal regeneration. Cell division cycle 2 (Cdc2) and brain-derived neurotrophic factor (BDNF) proteins were induced from the reconnected distal portion of the sciatic nerve and the levels were further elevated by in vivo administration of ABHD. Phospho-Erk1/2 level was increased by ABHD treatment as well, implying its role in mediating retrograde transport of BDNF signals into the neuronal cell body. Production of inflammatory cytokines IL-1β and TNF-α was induced in the reconnected nerve but attenuated by ABHD treatment. Behavioral tests revealed that ABHD treatment improved functional recovery of sensorimotor activities.

CONCLUSIONS

A newly formulated ABHD is effective at regulating the production of inflammatory cytokines and promoting axonal regeneration after nerve transection and may be considered to develop therapeutic strategies for peripheral nerve injury disorders.

Schwann Cell Autocrine and Paracrine Regulatory Mechanisms, Mediated by Allopregnanolone and BDNF, Modulate PKCε in Peripheral Sensory Neurons

Protein kinase type C-ε (PKCε) plays important roles in the sensitization of primary afferent nociceptors, such as ion channel phosphorylation, that in turn promotes mechanical hyperalgesia and pain chronification. In these neurons, PKCε is modulated through the local release of mediators by the surrounding Schwann cells (SCs). The progesterone metabolite allopregnanolone (ALLO) is endogenously synthesized by SCs, whereas it has proven to be a crucial mediator of neuron-glia interaction in peripheral nerve fibers. Biomolecular and pharmacological studies on rat primary SCs and dorsal root ganglia (DRG) neuronal cultures were aimed at investigating the hypothesis that ALLO modulates neuronal PKCε, playing a role in peripheral nociception. We found that SCs tonically release ALLO, which, in turn, autocrinally upregulated the synthesis of the growth factor brain-derived neurotrophic factor (BDNF). Subsequently, glial BDNF paracrinally activates PKCε via trkB in DRG sensory neurons. Herein, we report a novel mechanism of SCs-neuron cross-talk in the peripheral nervous system, highlighting a key role of ALLO and BDNF in nociceptor sensitization. These findings emphasize promising targets for inhibiting the development and chronification of neuropathic pain.

Migrating Schwann cells direct axon regeneration within the peripheral nerve bridge

Schwann cells within the peripheral nervous system possess a remarkable regenerative potential. Current research shows that peripheral nerve-associated Schwann cells possess the capacity to promote repair of multiple tissues including peripheral nerve gap bridging, skin wound healing, digit tip repair as well as tooth regeneration. One of the key features of the specialized repair Schwann cells is that they become highly motile. They not only migrate into the area of damaged tissue and become a key component of regenerating tissue but also secrete signaling molecules to attract macrophages, support neuronal survival, promote axonal regrowth, activate local mesenchymal stem cells, and interact with other cell types. Currently, the importance of migratory Schwann cells in tissue regeneration is most evident in the case of a peripheral nerve transection injury. Following nerve transection, Schwann cells from both proximal and distal nerve stumps migrate into the nerve bridge and form Schwann cell cords to guide axon regeneration. The formation of Schwann cell cords in the nerve bridge is key to successful peripheral nerve repair following transection injury. In this review, we first examine nerve bridge formation and the behavior of Schwann cell migration in the nerve bridge, and then discuss how migrating Schwann cells direct regenerating axons into the distal nerve. We also review the current understanding of signals that could activate Schwann cell migration and signals that Schwann cells utilize to direct axon regeneration. Understanding the molecular mechanism of Schwann cell migration could potentially offer new therapeutic strategies for peripheral nerve repair.

Daily acute intermittent hypoxia to improve walking function in persons with subacute spinal cord injury: a randomized clinical trial study protocol

BACKGROUND

Restoring community walking remains a highly valued goal for persons recovering from traumatic incomplete spinal cord injury (SCI). Recently, studies report that brief episodes of low-oxygen breathing (acute intermittent hypoxia, AIH) may serve as an effective plasticity-inducing primer that enhances the effects of walking therapy in persons with chronic (> 1 year) SCI. More persistent walking recovery may occur following repetitive (weeks) AIH treatment involving persons with more acute SCI, but this possibility remains unknown. Here we present our clinical trial protocol, designed to examine the distinct influences of repetitive AIH, with and without walking practice, on walking recovery in persons with sub-acute SCI (< 12 months) SCI. Our overarching hypothesis is that daily exposure (10 sessions, 2 weeks) to AIH will enhance walking recovery in ambulatory and non-ambulatory persons with subacute (< 12 months) SCI, presumably by harnessing endogenous mechanisms of plasticity that occur soon after injury.

METHODS

To test our hypothesis, we are conducting a randomized, placebo-controlled clinical trial on 85 study participants who we stratify into two groups according to walking ability; those unable to walk (non-ambulatory group) and those able to walk (ambulatory group). The non-ambulatory group receives either daily AIH (15, 90s episodes at 10.0% O2 with 60s intervals at 20.9% O2) or daily SHAM (15, 90s episodes at 20.9% O2 with 60s intervals at 20.9% O2) intervention. The ambulatory group receives either 60-min walking practice (WALK), daily AIH + WALK, or daily SHAM+WALK intervention. Our primary outcome measures assess overground walking speed (10-Meter Walk Test), endurance (6-Minute Walk Test), and balance (Timed Up & Go Test). For safety, we also measure levels of pain, spasticity, systemic hypertension, and autonomic dysreflexia. We record outcome measures at baseline, days 5 and 10, and follow-ups at 1 week, 1 month, 6 months, and 12 months post-treatment.

DISCUSSION

The goal of this clinical trial is to reveal the extent to which daily AIH, alone or in combination with task-specific walking practice, safely promotes persistent recovery of walking in persons with traumatic, subacute SCI. Outcomes from this study may provide new insight into ways to enhance walking recovery in persons with SCI.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02632422 . Registered 16 December 2015.

Possible function of GDNF and Schwann cells in wound healing of periodontal tissue

OBJECTIVE

The purpose of this study was to evaluate the function of Schwann cells in wound healing of periodontal tissue.

BACKGROUND

In our previous study, glial cell line-derived neurotrophic factor (GDNF) promoted the migration of human periodontal ligament (PDL) cells and that GDNF expression increased in wounded periodontal tissue. GDNF reportedly induces the migration of Schwann cell precursors. Schwann cells play a crucial role in the regeneration of peripheral tissues, including bone tissue. However, the role of Schwann cells on periodontal tissue regeneration remains unclear.

METHODS

A transwell assay and a WST-1 (water-soluble tetrazolium compound-1) proliferation assay were used to determine whether GDNF promotes the migration and proliferation of Schwann cells, respectively. Quantitative RT-PCR and Alizarin Red S staining were performed to examine the effect of these cells on the differentiation of human preosteoblast (Saos2 cells) using conditioned medium from YST-1 (YST-1-CM). Western blotting analysis was performed to determine whether YST-1-CM activates ERK signaling pathway in Saos2 cells. The expression of Schwann cell markers, S100 calcium-binding protein B (S100-B) and growth associated protein 43 (GAP-43), was determined in normal and wounded periodontal tissue by immunofluorescent staining.

RESULTS

Glial cell line-derived neurotrophic factor promoted the migration of YST-1 cells but did not affect the proliferation of YST-1 cells. Saos2 cells cultured with YST-1-CM increased the expression of osteoblastic markers and mineralization. YST-1-CM also induced phosphorylation of ERK1/2 in Saos2 cells. The number of S100-B-immunoreactive cells which also expressed GAP-43 was increased in rat wounded periodontal tissue during healing process.

CONCLUSION

The accumulation of Schwann cells in wounded periodontal tissue suggests that they play a significant role in wound healing of this tissue, especially alveolar bone tissue.

The Hua-Shan rehabilitation program after contralateral seventh cervical nerve transfer for spastic arm paralysis

Purpose: To propose the novel Hua-Shan rehabilitation program for patients undergoing the contralateral seventh cervical nerve transfer, and explore the influence of different rehabilitation on the postoperative recovery.Materials and methods: The Hua-Shan program was established in consideration of the three elements: the nerve regeneration, brain plasticity and group therapy. Its effect was evaluated by comparing the postoperative recovery of the hemorrhagic stroke survivors among the following three groups: Group A-standard Hua-Shan program after surgery; Group B-standard traditional program after surgery; Group C-no standard rehabilitation after surgery.Results: Significantly better functions after surgery were detected in all the groups, while the absence of standard rehabilitation massively offset the benefits of the surgery. Furthermore, the Hua-Shan program showed advantage over the traditional rehabilitation, which may largely be attributed to its improvements for the fine action of wrist&finger.Conclusions: The Hua-Shan program provided the opportunity to maximize the benefits of contralateral seventh cervical nerve transfer.IMPLICATIONS FOR REHABILITATIONStandard rehabilitation plays key roles in the recovery process for patients undergoing contralateral seventh cervical nerve transfer.The Hua-Shan program targeting nerve regeneration, brain plasticity and group therapy further improved the benefits of patients undergoing contralateral seventh cervical nerve transfer.

Treadmill exercise activates ATF3 and ERK1/2 downstream molecules to facilitate axonal regrowth after sciatic nerve injury

The purpose of this study was to investigate the effect of treadmill exer-cise on activating transcription factors such as activating transcription factor 3 (ATF3) and extracellular signal-regulated kinase (ERK1/2) sig-naling pathway to facilitate axonal regrowth after sciatic nerve injury (SNI). The experimental rats divided into the normal control (n=10), sedentary groups for 7 (n=10) and 14 days (n=10) post crush, exercise group for 7 (n=10) and 14 days (n=10) post crush (dpc). The rats in ex-ercise groups run on treadmill device at a speed of 8 m/min for 20 min once a day according to exercise duration. In order to evaluate specific regeneration markers and axonal elongation in injured sciatic nerve, we applied immunofluorescence staining and western blot techniques. Treadmill exercise further increased growth-associated protein (GAP-43) expression and axonal regrowth at 7 and 14 dpc than those in sed-entary group. Among mitogen-activated protein kinase downstream molecules, phospho-ERK1/2 (p-ERK1/2) was enhanced by treadmill ex-ercise at only 7 dpc and decreased to basal level 14 days later. But c-Jun N-terminal kinase, c-Jun, and phospho-cyclic adenosine mono-phosphate response element-binding protein showed a tendency to in-crease continuously until 14 dpc by exercise. ATF3 expression in exer-cise group was upregulated at both 7 and 14 dpc compared to the sed-entary group. These results indicate that treadmill exercise had benefi-cial effect on expression of regeneration-related proteins after SNI, suggesting that exercise might be one of various therapeutic strategies for sciatic nerve regeneration.

CSF levels of a set of neurotrophic factors (brain-derived neurotrophic factor, nerve growth factor) and neuropeptides (neuropeptide Y, galanin) in epileptic children

This paper aims to investigate the possible roles of a set of neurotrophic factors (brain-derived neurotrophic factor-BDNF, nerve growth factor-NGF) and neuropeptides (neuropeptide Y-NPY, and galanin) in children with active epileptogenesis. The cerebrospinal fluid (CSF) levels of BDNF, NPY, NGF and galanin were measured with enzyme-linked immunosorbent assays in epileptic children (n = 73) and controls (n = 64). There were no significant alterations in the CSF levels of BDNF, NPY and NGF in epileptic children with active clinical seizures compared with the levels of controls. However profoundly depressed galanin levels were found in infants with epileptic encephalopathy (mean ± SD:0.63 ± 0.19 pg/ml) and significantly increased galanin levels were measured in children with drug resistant epilepsy during the period of status epilepticus (mean ± SD: 6.92 ± 1.19, pg/ml pg/ml) compared with the levels of controls. Depressed levels of galanin might reflect a defective anti-epileptogenic effect of galanin in infants with epileptic encephalopathy. On the contrary, increased CSF levels of galanin might be a result of anti-epileptogenic effects of this peptide in epileptic children with status epilepticus.

Lithium treatment mitigates white matter injury after intracerebral hemorrhage through brain-derived neurotrophic factor signaling in mice

Intracerebral hemorrhage (ICH), a subtype of stroke with high morbidity and mortality, occurs mainly in the basal ganglia and causes white matter injury (WMI), resulting in severe motor dysfunction and poor prognosis in patients. The preservation of the white matter around the hematoma is crucial for motor function recovery, but there is currently no effective treatment for WMI following ICH. Lithium has been widely used for the treatment of bipolar disorder for decades. Although the protective effects of lithium on neurodegenerative diseases and cerebral trauma have been studied in recent years, whether it can be used to alleviate WMI after ICH remains to be researched. The results of this study revealed that ICH caused significant functional and pathological abnormalities in mice. After LiCl was administered to mice with ICH, behavioural performance and electrophysiological functions were improved and ICH-induced white matter pathological injury, including myelin sheath and axonal degeneration, was ameliorated. Furthermore, LiCl treatment decreased the death of mature oligodendrocytes (OLGs) in ICH mice, which may have been attributed to the enhanced expression of brain-derived neurotrophic factor (BDNF) regulated by the LiCl-induced inhibition of glycogen synthase kinase-3β (GSK-3β). The decreased death of OLGs was closely associated with decreased destruction of the myelin sheath and alleviated degradation of the axons. In summary, this study suggests that the protective effect of lithium on WMI after ICH might be related to an increased level of BDNF and that LiCl treatment may be a potential therapeutic method to palliate WMI after ICH.

Functional polymeric nerve guidance conduits and drug delivery strategies for peripheral nerve repair and regeneration

Peripheral nerve injuries can be extremely debilitating, resulting in sensory and motor loss-of-function. Endogenous repair is limited to non-severe injuries in which transection of nerves necessitates surgical intervention. Traditional treatment approaches include the use of biological grafts and alternative engineering approaches have made progress. The current article serves as a comprehensive, in-depth perspective on peripheral nerve regeneration, particularly nerve guidance conduits and drug delivery strategies. A detailed background of peripheral nerve injury and repair pathology, and an in-depth look into augmented nerve regeneration, nerve guidance conduits, and drug delivery strategies provide a state-of-the-art perspective on the field.

Removal of the Potassium Chloride Co-Transporter from the Somatodendritic Membrane of Axotomized Motoneurons Is Independent of BDNF/TrkB Signaling But Is Controlled by Neuromuscular Innervation

The potassium-chloride cotransporter (KCC2) maintains the low intracellular chloride found in mature central neurons and controls the strength and direction of GABA/glycine synapses. We found that following axotomy as a consequence of peripheral nerve injuries (PNIs), KCC2 protein is lost throughout the somatodendritic membrane of axotomized spinal cord motoneurons after downregulation of kcc2 mRNA expression. This large loss likely depolarizes the reversal potential of GABA/glycine synapses, resulting in GABAergic-driven spontaneous activity in spinal motoneurons similar to previous reports in brainstem motoneurons. We hypothesized that the mechanism inducing KCC2 downregulation in spinal motoneurons following peripheral axotomy might be mediated by microglia or motoneuron release of BDNF and TrkB activation as has been reported on spinal cord dorsal horn neurons after nerve injury, motoneurons after spinal cord injury (SCI), and in many other central neurons throughout development or a variety of pathologies. To test this hypothesis, we used genetic approaches to interfere with microglia activation or delete bdnf from specifically microglia or motoneurons, as well as pharmacology (ANA-12) and pharmacogenetics (F616A mice) to block TrkB activation. We show that KCC2 dysregulation in axotomized motoneurons is independent of microglia, BDNF, and TrkB. KCC2 is instead dependent on neuromuscular innervation; KCC2 levels are restored only when motoneurons reinnervate muscle. Thus, downregulation of KCC2 occurs specifically while injured motoneurons are regenerating and might be controlled by target-derived signals. GABAergic and glycinergic synapses might therefore depolarize motoneurons disconnected from their targets and contribute to augment motoneuron activity known to promote motor axon regeneration.

Corneal Nerve Migration Rate in a Healthy Control Population

PURPOSE

The purpose of this study was to establish an age-dependent normative range and factors affecting the migration rate of the corneal subbasal nerve plexus in a healthy control population.

METHODS

Corneal nerve migration rate was measured in 60 healthy participants grouped by age: A, aged 20 to 39 years (n = 20); B, 40 to 59 years (n = 20); and C, 60 to 79 years (n = 20). Laser-scanning corneal confocal microscopy was performed on the right eye of all participants at baseline and again after 3 weeks. Fully automated software was used to montage the frames. Distinctive nerve landmarks were manually reidentified between the two montages, and a software program was developed to measure the migration of these landmark points to determine corneal nerve migration rate in micrometers per week (μm/wk).

RESULTS

The mean ± SD age of all participants in the study was 47.5 ± 15.5 years; 62% of participants were male. The average corneal nerve migration rates of groups A, B, and C were 42.0 ± 14.0, 42.3 ± 15.5, and 42.0 ± 10.8 μm/wk, respectively (P = .99). There was no difference in corneal nerve migration rate between male (41.1 ± 13.5 μm/wk) and female (43.7 ± 13.2 μm/wk) participants (P = .47). There was no significant correlation between age (P = .97), smoking (P = .46), alcohol use (P = .61), and body mass index (P = .49, respectively) with corneal nerve migration rate. However, exercise frequency correlated significantly (P = .04) with corneal nerve migration rate.

CONCLUSIONS

Corneal nerve migration rate varies in healthy individuals and is not affected by age, sex, or body mass index but is related to physical activity.

Sciatic Nerve Cut and Repair Using Fibrin Glue in Adult Mice

Peripheral nerve injury (PNI) is an excellent model for studying neural responses to injury and elucidating the mechanisms that can facilitate axon regeneration. As such, several animal models have been employed to study regenerative mechanisms after PNI, including Aplysia, zebrafish, rabbits, cats and rodents. This protocol describes how to perform a sciatic nerve injury and repair in mice, one of the most frequently used models to study mechanisms that facilitate recovery after PNI, and that takes advantage of the availability of many genetic models. In this protocol, we describe a method for using fibrin glue to secure the proximal and distal stumps of an injured nerve in close alignment. This method facilitates the alignment of nerve stumps, which aids in regeneration of both sensory and motor axons and allows successful reconnection with peripheral targets.

Muscle-Derived Extracellular Vesicles Influence Motor Neuron Regeneration Accuracy

Extracellular vesicles are lipid bilayer-enclosed extracellular structures. Although the term extracellular vesicles is quite inclusive, it generally refers to exosomes (<200 nm), and microvesicles (~100-1000 nm). Such vesicles are resistant to degradation and can contain proteins, lipids, and nucleic acids. Although it was previously thought that the primary purpose of such vesicles was to rid cells of unwanted components, it is now becoming increasingly clear that they can function as intercellular messengers, sometimes operating over long distances. As such, there is now intense interest in extracellular vesicles in fields as diverse as immunology, cell biology, cancer, and more recently, neuroscience. The influence that such extracellular vesicles might exert on peripheral nerve regeneration is just beginning to be investigated. In the current studies we show that muscle-derived extracellular vesicles significantly influence the anatomical accuracy of motor neuron regeneration in the rat femoral nerve. These findings suggest a basic cellular mechanism by which target end-organs could guide their own reinnervation following nerve injury.

A Milled Microdevice to Advance Glia-Mediated Therapies in the Adult Nervous System

Neurodegenerative disorders affect millions of adults worldwide. Neuroglia have become recent therapeutic targets due to their reparative abilities in the recycling of exogenous neurotoxins and production of endogenous growth factors for proper functioning of the adult nervous system (NS). Since neuroglia respond effectively to stimuli within in vivo environments on the micron scale, adult glial physiology has remarkable synergy with microscale systems. While clinical studies have begun to explore the reparative action of Müller glia (MG) of the visual system and Schwann Cells (ShC) of the peripheral NS after neural injury, few platforms enable the study of intrinsic neuroglia responses to changes in the local microenvironment. This project developed a low-cost, benchtop-friendly microfluidic system called the glia line system, or gLL, to advance the cellular study needed for emerging glial-based therapies. The gLL was fabricated using elastomeric kits coupled with a metal mold milled via conventional computer numerical controlled (CNC) machines. Experiments used the gLL to measure the viability, adhesion, proliferation, and migration of MG and ShC within scales similar to their respective in vivo microenvironments. Results illustrate differences in neuroglia adhesion patterns and chemotactic behavior significant to advances in regenerative medicine using implants and biomaterials, as well as cell transplantation techniques. Data showed highest survival and proliferation of MG and ShC upon laminin and illustrated a four-fold and two-fold increase of MG migration to dosage-dependent signaling from vascular endothelial growth factor (VEGF) and epidermal growth factor (EGF), respectively, as well as a 20-fold increase of ShC migration toward exogenous brain-derived neurotrophic factor (BDNF), compared to media control. The ability to quantify these biological parameters within the gLL offers an effective and reliable alternative to photolithography study neuroglia in a local environment ranging from the tens to hundreds of microns, using a low-cost and easily fabricated system.