Schwann Cells Provide Iron to Axonal Mitochondria and Its Role in Nerve Regeneration.

Iron is an essential cofactor for several metabolic processes, including the generation of ATP in mitochondria, which is required for axonal function and regeneration. However, it is not known how mitochondria in long axons, such as those in sciatic nerves, acquire iron in vivo Because of their close proximity to axons, Schwann cells are a likely source of iron for axonal mitochondria in the PNS. Here we demonstrate the critical role of iron in promoting neurite growth in vitro using iron chelation. We also show that Schwann cells express the molecular machinery to release iron, namely, the iron exporter, ferroportin (Fpn) and the ferroxidase ceruloplasmin (Cp). In Cp KO mice, Schwann cells accumulate iron because Fpn requires to partner with Cp to export iron. Axons and Schwann cells also express the iron importer transferrin receptor 1 (TfR1), indicating their ability for iron uptake. In teased nerve fibers, Fpn and TfR1 are predominantly localized at the nodes of Ranvier and Schmidt-Lanterman incisures, axonal sites that are in close contact with Schwann cell cytoplasm. We also show that lack of iron export from Schwann cells in Cp KO mice reduces mitochondrial iron in axons as detected by reduction in mitochondrial ferritin, affects localization of axonal mitochondria at the nodes of Ranvier and Schmidt-Lanterman incisures, and impairs axonal regeneration following sciatic nerve injury. These finding suggest that Schwann cells contribute to the delivery of iron to axonal mitochondria, required for proper nerve repair.SIGNIFICANCE STATEMENT This work addresses how and where mitochondria in long axons in peripheral nerves acquire iron. We show that Schwann cells are a likely source as they express the molecular machinery to import iron (transferrin receptor 1), and to export iron (ferroportin and ceruloplasmin [Cp]) to the axonal compartment at the nodes of Ranvier and Schmidt-Lanterman incisures. Cp KO mice, which cannot export iron from Schwann cells, show reduced iron content in axonal mitochondria, along with increased localization of axonal mitochondria at Schmidt-Lanterman incisures and nodes of Ranvier, and impaired sciatic nerve regeneration. Iron chelation in vitro also drastically reduces neurite growth. These data suggest that Schwann cells are likely to contribute iron to axonal mitochondria needed for axon growth and regeneration.

Dynamic Change of Endocannabinoid Signaling in the Medial Prefrontal Cortex Controls the Development of Depression After Neuropathic Pain.

Many patients with chronic pain conditions suffer from depression. The mechanisms underlying pain-induced depression are still unclear. There are critical links of medial prefrontal cortex (mPFC) synaptic function to depression, with signaling through the endocannabinoid (eCB) system as an important contributor. We hypothesized that afferent noxious inputs after injury compromise activity-dependent eCB signaling in the mPFC, resulting in depression. Depression-like behaviors were tested in male and female rats with traumatic neuropathy [spared nerve injury (SNI)], and neuronal activity in the mPFC was monitored using the immediate early gene c-fos and in vivo electrophysiological recordings. mPFC eCB Concentrations were determined using mass spectrometry, and behavioral and electrophysiological experiments were used to evaluate the role of alterations in eCB signaling in depression after pain. SNI-induced pain induced the development of depression phenotypes in both male and female rats. Pyramidal neurons in mPFC showed increased excitability followed by reduced excitability in the onset and prolonged phases of pain, respectively. Concentrations of the eCBs, 2-arachidonoylglycerol (2-AG) in the mPFC, were elevated initially after SNI, and our results indicate that this resulted in a loss of CB1R function on GABAergic interneurons in the mPFC. These data suggest that excessive release of 2-AG as a result of noxious stimuli triggers use-dependent loss of function of eCB signaling leading to excessive GABA release in the mPFC, with the final result being behavioral depression.SIGNIFICANCE STATEMENT Pain has both somatosensory and affective components, so the complexity of mechanisms underlying chronic pain is best represented by a biopsychosocial model that includes widespread CNS dysfunction. Many patients with chronic pain conditions develop depression. The mechanism by which pain causes depression is unclear. Although manipulation of the eCB signaling system as an avenue for providing analgesia per se has not shown much promise in previous studies. An important limitation of past research has been inadequate consideration of the dynamic nature of the connection between pain and depression as they develop. Here, we show that activity-dependent synthesis of eCBs during the initial onset of persistent pain is the critical link leading to depression when pain is persistent.

The evolution of dystonia-like movements in TOR1A rats after transient nerve injury is accompanied by dopaminergic dysregulation and abnormal oscillatory activity of a central motor network.

TOR1A is the most common inherited form of dystonia with still unclear pathophysiology and reduced penetrance of 30-40%. ∆ETorA rats mimic the TOR1A disease by expression of the human TOR1A mutation without presenting a dystonic phenotype. We aimed to induce dystonia-like symptoms in male ∆ETorA rats by peripheral nerve injury and to identify central mechanism of dystonia development. Dystonia-like movements (DLM) were assessed using the tail suspension test and implementing a pipeline of deep learning applications. Neuron numbers of striatal parvalbumin+, nNOS+, calretinin+, ChAT+ interneurons and Nissl+ cells were estimated by unbiased stereology. Striatal dopaminergic metabolism was analyzed via in vivo microdialysis, qPCR and western blot. Local field potentials (LFP) were recorded from the central motor network. Deep brain stimulation (DBS) of the entopeduncular nucleus (EP) was performed. Nerve-injured ∆ETorA rats developed long-lasting DLM over 12 weeks. No changes in striatal structure were observed. Dystonic-like ∆ETorA rats presented a higher striatal dopaminergic turnover and stimulus-induced elevation of dopamine efflux compared to the control groups. Higher LFP theta power in the EP of dystonic-like ∆ETorA compared to wt rats was recorded. Chronic EP-DBS over 3 weeks led to improvement of DLM. Our data emphasizes the role of environmental factors in TOR1A symptomatogenesis. LFP analyses indicate that the pathologically enhanced theta power is a physiomarker of DLM. This TOR1A model replicates key features of the human TOR1A pathology on multiple biological levels and is therefore suited for further analysis of dystonia pathomechanism.

Differential effects of rat ADSCs encapsulation in fibrin matrix and combination delivery of BDNF and Gold nanoparticles on peripheral nerve regeneration.

BACKGROUND: Fibrin as an extracellular matrix feature like biocompatibility, creates a favorable environment for proliferation and migration of cells and it can act as a reservoir for storage and release of growth factors in tissue engineering. METHODS: In this study, the inner surface of electrospun poly (lactic-co-glycolic acid) (PLGA) nanofibrous conduit was biofunctionalized with laminin containing brain derived neurotrophic factor (BDNF) and gold nanoparticles in chitosan nanoparticle. The rats were randomly divided into five groups, including autograft group as the positive control, PLGA conduit coated by laminin and filled with DMEM/F12, PLGA conduit coated by laminin and filled with rat-adipose derived stem cells (r-ADSCs), PLGA conduit coated by laminin containing gold-chitosan nanoparticles (AuNPs-CNPs), BDNF-chitosan nanoparticles (BDNF-CNPs) and filled with r-ADSCs or filled with r-ADSCs suspended in fibrin matrix, and they were implanted into a 10 mm rat sciatic nerve gap. Eventually, axonal regeneration and functional recovery were assessed after 12 weeks. RESULTS: After 3 months post-surgery period, the results showed that in the PLGA conduit filled with r-ADSCs without fibrin matrix group, positive effects were obtained as compared to other implanted groups by increasing the sciatic functional index significantly (p < 0.05). In addition, the diameter nerve fibers had a significant difference mean in the PLGA conduit coated by laminin and conduit filled with r-ADSCs in fibrin matrix groups relative to the autograft group (p < 0.001). However, G-ratio and amplitude (AMP) results showed that fibrin matrix might have beneficial effects on nerve regeneration but, immunohistochemistry and real-time RT-PCR outcomes indicated that the implanted conduit which filled with r-ADSCs, with or without BDNF-CNPs and AuNPs-CNPs had significantly higher expression of S100 and MBP markers than other conduit implanted groups (p < 0.05). CONCLUSIONS: It seems, in this study differential effects of fibrin matrix, could be interfered it with other factors thereby and further studies are required to determine the distinctive effects of fibrin matrix combination with other exogenous factors in peripheral nerve regeneration.

MiR-122-5p suppresses neuropathic pain development by targeting PDK4.

The complex pathogenesis and limited efficacy of available treatment make neuropathic pain difficult for long periods of time. Several findings suggested the regulatory role of microRNA in the development of neuropathic pain. This study aims to investigate the functional role of miR-122-5p in the development of neuropathic pain. Down-regulation of miR-122-5p was observed in spinal cords of rats with neuropathic pain. We also found that overexpressing miR-122-5p by intrathecal injection of miR-122-5p lentivirus in a mouse model of chronic sciatic nerve injury (CCI) prevented neuropathic pain behavior. In HEK-293 T cells, luciferase activity was significantly decreased in the transfection group with mimic-miR-122-5p in wild-type PDK4 reporter, compared with mutant PDK4 reporter. Increased PDK4 expression was also observed during the progression of neuropathic pain. Intrathecal injection of both mimic-miR-122-5p and shPDK4 in CCI mice downregulated PDK4 expression to a lower level when compared with injected with shPDK4. In CCI mice, transfection of shPDK4 suppressed mechanical allodynia and thermal hyperalgesia, while co-transfection of shPDK4 and LV-miR-122-5p resulted in stronger levels of mechanical allodynia and thermal hyperalgesia inhibition. Taken together, the data suggest that miR-122-5p inhibits PDK4 expression, attenuating neuropathic pain. This result suggests the potential role of miR-122-5p acting as a target for the treatment of neuropathic pain.

Whole-body vibration therapy does not improve the peripheral nerve regeneration in experimental model.

OBJECTIVES: Whole-body vibration (WBV) is commonly used to improve motor function, balance and functional performance, but its effects on the body are not fully understood. The main objective was to evaluate the morphometric and functional effects of WBV in an experimental nerve regeneration model. METHODS: Wistar rats were submitted to unilateral sciatic nerve crush and treated with WBV (4-5 weeks), started at 3 or 10 days after injury. Functional performances were weekly assessed by sciatic functional index, horizontal ladder rung walking and narrow beam tests. Nerve histomorphometry analysis was assessed at the end of the protocol. RESULTS: Injured groups, sedentary and WBV started at 3 days, had similar functional deficits. WBV, regardless of the start time, did not alter the histomorphometry parameters in the regeneration process. CONCLUSIONS: The earlier therapy did not change the expected and natural recovery after the nerve lesion, but when the WBV starts later it seems to impair function parameter of recovery.

Injury-Induced HSP27 Expression in Peripheral Nervous Tissue Is Not Associated with Any Alteration in Axonal Outgrowth after Immediate or Delayed Nerve Repair.

We investigated injury-induced heat shock protein 27 (HSP27) expression and its association to axonal outgrowth after injury and different nerve repair models in healthy Wistar and diabetic Goto-Kakizaki rats. By immunohistochemistry, expression of HSP27 in sciatic nerves and DRG and axonal outgrowth (neurofilaments) in sciatic nerves were analyzed after no, immediate, and delayed (7-day delay) nerve repairs (7- or 14-day follow-up). An increased HSP27 expression in nerves and in DRG at the uninjured side was associated with diabetes. HSP27 expression in nerves and in DRG increased substantially after the nerve injuries, being higher at the site where axons and Schwann cells interacted. Regression analysis indicated a positive influence of immediate nerve repair compared to an unrepaired injury, but a shortly delayed nerve repair had no impact on axonal outgrowth. Diabetes was associated with a decreased axonal outgrowth. The increased expression of HSP27 in sciatic nerve and DRG did not influence axonal outgrowth. Injured sciatic nerves should appropriately be repaired in healthy and diabetic rats, but a short delay does not influence axonal outgrowth. HSP27 expression in sciatic nerve or DRG, despite an increase after nerve injury with or without a repair, is not associated with any alteration in axonal outgrowth.

Inhibition of PTEN activity promotes IB4-positive sensory neuronal axon growth.

Traumatic nerve injuries have become a common clinical problem, and axon regeneration is a critical process in the successful functional recovery of the injured nervous system. In this study, we found that peripheral axotomy reduces PTEN expression in adult sensory neurons; however, it did not alter the expression level of PTEN in IB4-positive sensory neurons. Additionally, our results indicate that the artificial inhibition of PTEN markedly promotes adult sensory axon regeneration, including IB4-positive neuronal axon growth. Thus, our results provide strong evidence that PTEN is a prominent repressor of adult sensory axon regeneration, especially in IB4-positive neurons.

LncRNA BC088259 promotes Schwann cell migration through Vimentin following peripheral nerve injury.

Schwann cell, the major glial cell in the peripheral nervous system, plays an essential role in peripheral nerve regeneration. However, the regulation of Schwann cell behavior following nerve injury is insufficiently explored. According to the development of high-throughput techniques, long noncoding RNAs (lncRNAs) have been recognized. Accumulating evidence shows that lncRNAs take part in diverse biological processes and diseases. Here, by microarray analysis, we identified an upregulated lncRNA profile following sciatic nerve injury and focused on BC088259 for further investigation. Silencing or overexpression of BC088259 could affect Schwann cell migration. Mechanistically, BC088259 might exert this regulatory role by directly binding with Vimentin. Collectively, our study not only revealed a set of upregulated lncRNAs following nerve injury but also identified a new functional lncRNA, BC088259, which was important for Schwann cell migration, providing a therapeutic avenue toward peripheral nerve injury.

The role of C-afferents in mediating neurogenic vasodilatation in plantar skin after acute sciatic nerve injury in rats.

BACKGROUND: Vasomotor regulation of dermal blood vessels, which are critical in the function of the skin in thermoregulatory control, involves both neural and non-neural mechanisms. Whereas the role of sympathetic nerves in regulating vasomotor activities is comprehensively studied and well recognized, that of sensory nerves is underappreciated. Studies in rodents have shown that severance of the sciatic nerve leads to vasodilatation in the foot, but whether sympathetic or sensory nerve fibers or both are responsible for the neurogenic vasodilatation remains unknown. RESULTS: In adult Sprague-Dawley rats, vasodilatation after transection of the sciatic nerve gradually diminished to normal within 3-4 days. The neurotmesis-induced neurogenic vasodilatation was not detectable when the sciatic nerve was chronically deafferentated by selective resection of the dorsal root ganglia (DRGs) that supply the nerve. Specific activation of C-afferents by intra-neural injection of capsaicin resulted in neurogenic vasodilatation to a magnitude comparable to that by neurotmesis, and transection of the sciatic nerve pre-injected with capsaicin did not induce further vasodilatation. CONCLUSIONS: Our results collectively indicate that vasodilatation after traumatic nerve injury in rats is predominantly mediated by C-fiber afferents.

Differentiated adipose-derived stem cells promote peripheral nerve regeneration.

INTRODUCTION: Many reports have indicated that adipose-derived stem cells (ADSCs) are effective for nerve regeneration. We investigated nerve regeneration by combining a polyglycolic acid collagen (PGA-c) tube, which is approved for clinical use, and Schwann cell-like differentiated ADSCs (dADSCs). METHODS: Fifteen-millimeter-long gaps in the sciatic nerve of rats were bridged in each group using tubes (group I), with tubes injected with dADSCs (group II), or by resected nerve (group III). RESULTS: Axonal outgrowth was greater in group II than in group I. Tibialis anterior muscle weight revealed recovery only in group III. Latency in nerve conduction studies was equivalent in group II and III, but action potential was lower in group II. Transplanted dADSCs maintained Schwann cell marker expression. ATF3 expression level in the dorsal root ganglia was equivalent in groups II and III. DISCUSSION: dADSCs maintained their differentiated state in the tubes and are believed to have contributed to nerve regeneration.

Low-Level Laser Therapy in Different Wavelengths on the Tibialis Anterior Muscle of Wistar Rats After Nerve Compression Injury.

OBJECTIVE: Traumatic injuries are common and may promote disruption of neuromuscular communication, triggering phenomena that lead to nerve degeneration and affect muscle function. A laser accelerates tissue recovery; however, the parameters used are varied, making it difficult to compare studies. The purpose of this study was to evaluate the effect of low-level laser therapy, at 660- and 830-nm wavelengths, on the tibialis anterior muscle of Wistar rats after sciatic nerve compression. METHODS: Twenty animals were separated into 4 groups: control, sciatic nerve injury, lesion + 660-nm laser, and lesion + 830-nm laser. In the lesion groups, the right sciatic nerve was surgically exposed and compressed with hemostatic forceps for 30 seconds. After the third postoperative day, the groups with laser therapy were submitted to treatment for 2 weeks totaling 10 applications, performed directly on the surgical scar of the nerve injury. Grip strength was analyzed before and after the nerve injury and during the treatment period. The tibialis anterior muscle was processed for light microscopy, area measurement, smaller diameter, number of fibers, nuclei, and connective tissue. RESULTS: The animals submitted to the injury experienced muscular atrophy and morphological changes in the number of muscle fibers and nuclei. In the connective tissue morphometry, there was a decrease in the treated groups compared with the untreated groups. CONCLUSION: The laser treatment at different wavelengths showed no improvement in the tibialis anterior muscle of Wistar rats within the morphological and functional aspects evaluated.

Pediatric sciatic neuropathy: Clinical presentation and long term follow up. / Neuropatía ciática en pediatría: Presentación clínica y seguimiento a largo plazo.

INTRODUCTION: Sciatic neuropathy is rare and difficult to diagnose in pediatrics, and its long-term course has not been completely understood. OBJECTIVE: To analyze the clinical presentation and evolution of a group of pediatric patients with sciatic neuropathy. PATIENTS AND METHOD: Retrospective anal ysis of the clinical characteristics of pediatric patients with sciatic neuropathy treated in two hospitals of Santiago between 2014 and 2018. Locomotor examination, muscle trophism, deep tendon reflexes, gait, sensation, and pain were assessed. Sciatic nerve conduction study and electromyography (EMG) were performed, and magnetic resonance imaging (MRI) in three patients. RESULTS: Six patients were included with an average age of 11.8 years. The etiologies were traumatic (N = 2), by compression (N = 2), vascular (N = 1), and tumor (N = 1). All of the 6 patients presented foot drop and Achilles tendon hyporeflexia/areflexia, and 5 patients presented severe neuropathic pain. The EMG showed involvement of the sciatic nerve rami and dependent muscles. In two patients, a pelvic girdle and lower limbs MRI was performed, showing selective muscle involvement in sciatic territory. One patient underwent a lumbosacral plexus MRI, and subsequently histological study showing a benign neural tumor. Out of the three patients who were followed-up longer than one year presented motor sequelae and gait disorder. CONCLUSION: Sciatic neuropathy in the study group was secondary to different causes, predominantly traumatic and compressive etiologies. The three patients that were ina long-term follow-up presented significant motor sequelae. In most of the cases, neural injury wasassoci- ated with preventable causes, such as accidents and positioning in unconscious children, which is crucial in the prevention of a pathology with a high sequelae degree.

Altered Excitability and Local Connectivity of mPFC-PAG Neurons in a Mouse Model of Neuropathic Pain.

The medial prefrontal cortex (mPFC) plays a major role in both sensory and affective aspects of pain. There is extensive evidence that chronic pain produces functional changes within the mPFC. However, our understanding of local circuit changes to defined subpopulations of mPFC neurons in chronic pain models remains unclear. A major subpopulation of mPFC neurons project to the periaqueductal gray (PAG), which is a key midbrain structure involved in endogenous pain suppression and facilitation. Here, we used laser scanning photostimulation of caged glutamate to map cortical circuits of retrogradely labeled cortico-PAG (CP) neurons in layer 5 (L5) of mPFC in brain slices prepared from male mice having undergone chronic constriction injury (CCI) of the sciatic nerve. Whole-cell recordings revealed a significant reduction in excitability for L5 CP neurons contralateral to CCI in the prelimbic (PL), but not infralimbic (IL), region of mPFC. Circuit mapping showed that excitatory inputs to L5 CP neurons in both PL and IL arose primarily from layer 2/3 (L2/3) and were significantly reduced in CCI mice. Glutamate stimulation of L2/3 and L5 elicited inhibitory inputs to CP neurons in both PL and IL, but only L2/3 input was significantly reduced in CP neurons of CCI mice. We also observed significant reduction in excitability and L2/3 inhibitory input to CP neurons ipsilateral to CCI. These results demonstrating region and laminar specific changes to mPFC-PAG neurons suggest that a unilateral CCI bilaterally alters cortical circuits upstream of the endogenous analgesic network, which may contribute to persistence of chronic pain.SIGNIFICANCE STATEMENT Chronic pain is a significant unresolved medical problem that is refractory to traditional analgesics and can negatively affect emotional health. The role of central circuits in mediating the persistent nature of chronic pain remains unclear. Local circuits within the medial prefrontal cortex (mPFC) process ascending pain inputs and can modulate endogenous analgesia via direct projections to the periaqueductal gray (PAG). However, the mechanisms by which chronic pain alters intracortical circuitry of mPFC-PAG neurons are unknown. Here, we report specific changes to local circuits of mPFC-PAG neurons in mice displaying chronic pain behavior after nerve injury. These findings provide evidence for a neural mechanism by which chronic pain disrupts the descending analgesic system via functional changes to cortical circuits.

Effects of miR-150 on neuropathic pain process via targeting AKT3.

MicroRNAs (miRNA) are reported to be a vital regulator of neuropathic pain. Even so, the molecular mechanisms of miRNA function on neuropathic pain development are known little. Our research was designed to investigate the role of miRNA in neuropathic pain development in rat modle set up by chronic sciatic nerve injury (CCI). Increasing miR-150 expression could significantly alleviate neuropathic pain in CCI rats. For farther researching the regulation mechanism of miR-150 on neuropathic pain, we screened AKT3 as a possible target of miR-150 by bioinformatic mechods and predicted a possible target of miR-150 in 3'-untranslated region (UTR) of AKT3 who serves as an oncogene. In rat model, the expression both of AKT3 mRNA and protein were significantly upregulated. The overexpressed miR-150 importantly repressed the level of AKT3 and simultaneously alleviate mechanical and thermal hyperalgesia in rat model. These suppressant impacts of miR-150 on neuropathic pain process can be reversed by the overexpression of AKT3. Considering all above results, our research declared that miR-150 can restrain neuropathic pain process though targeting AKT3 in vivo, suggesting that miR-150 could be the therapeutic target for neuropathic pain therapy by regulating AKT3.

Experimental Characterization of the Chronic Constriction Injury-Induced Neuropathic Pain Model in Mice.

Number of ligations made in the chronic constriction injury (CCI) neuropathic pain model has raised serious concerns. We compared behavioural responses, nerve morphology and expression of pain marker, c-fos among CCI models developed with one, two, three and four ligations. The numbers of ligation(s) on sciatic nerve shows no significant difference in displaying mechanical and cold allodynia, and mechanical and thermal hyperalgesia throughout 84 days. All groups underwent similar levels of nerve degeneration post-surgery. Similar c-fos level in brain cingulate cortex, parafascicular nuclei and amygdala were observed in all CCI models compared to sham-operated group. Therefore, number of ligations does not impact intensity of pain symptoms, pathogenesis and neuronal activation. A single ligation is sufficient to develop neuropathic pain, in contrast to the established model of four ligations. This study dissects and characterises the CCI model, ascertaining a more uniform animal model to surrogate actual neuropathic pain condition.

Clinical spectrum of neuropathy after primary total knee arthroplasty: A series of 54 cases.

INTRODUCTION: Neuropathy after total knee arthroplasty (TKA) can cause significant morbidity but is inconsistently reported. METHODS: We reviewed the clinical, electrodiagnostic and perioperative features of all patients who underwent primary TKA at our institution and developed a new neuropathy within 8 weeks postoperatively. RESULTS: Fifty-four cases were identified (incidence 0.37% [95% confidence interval, 0.28-0.49]) affecting the following nerve(s): peroneal (37), sciatic (11), ulnar (2), tibial (2), sural (1), and lumbosacral plexus (1). In all cases with follow-up data, motor recovery typically occurred within 1 year and was complete or near-complete. CONCLUSIONS: Post-TKA neuropathy is uncommon, typically does not require intervention and usually resolves within 1 year. Post-TKA neuropathy most often affects the nerves surgically at risk. Anesthesia type does not correlate with post-TKA neuropathy. An inflammatory etiology for post-TKA neuropathy is rare but should be considered in specific cases. Muscle Nerve 59:679-682, 2019.

Colistin induced peripheral neurotoxicity involves mitochondrial dysfunction and oxidative stress in mice.

Polymyxin is a critical antibiotic against the infection caused by multidrug-resistant gram-negative bacteria. Neurotoxicity is one of main dose-limiting factors. The present study aimed to investigate the underlying molecular mechanism on colistin induced peripheral neurotoxicity using a mouse model. Forty mice were divided into control, colistin 1-, 3- and 7-day groups, the mice were intravenously injected with saline or colistin (sulfate) at the dose of 15 mg/kg/day for 1, 3 and 7 days, respectively. The results showed that, colistin treatment for 7 days markedly resulted in the demyelination, axonal degeneration and mitochondria swelling in the mice's sciatic tissues. Colistin treatment induces oxidative stress as well as the increases of mitochondrial permeability transition, decreases of membrane potential (ΔΨm) and activities of mitochondrial respiratory chain in the mice's sciatic nerve tissues. Furthermore, in the colistin-7 day group, adenosine-triphosphate (ATP) level Na+/K+-ATPase activity decreased to 75.2% (p < 0.01) and 80.1% (p < 0.01), respectively. Meanwhile, colistin treatment down-regulates the expression of protein kinase B (Akt) and mammalian target of rapamycin (mTOR) mRNAs and up-regulates the expression of Bax and caspase-3 mRNAs. Our results reveal that colistin induced sciatic nerves damage involves oxidative stress, mitochondrial dysfunction and the inhibition of Akt/mTOR pathway.

Polycomb repression regulates Schwann cell proliferation and axon regeneration after nerve injury.

The transition of differentiated Schwann cells to support of nerve repair after injury is accompanied by remodeling of the Schwann cell epigenome. The EED-containing polycomb repressive complex 2 (PRC2) catalyzes histone H3K27 methylation and represses key nerve repair genes such as Shh, Gdnf, and Bdnf, and their activation is accompanied by loss of H3K27 methylation. Analysis of nerve injury in mice with a Schwann cell-specific loss of EED showed the reversal of polycomb repression is required and a rate limiting step in the increased transcription of Neuregulin 1 (type I), which is required for efficient remyelination. However, mouse nerves with EED-deficient Schwann cells display slow axonal regeneration with significantly low expression of axon guidance genes, including Sema4f and Cntf. Finally, EED loss causes impaired Schwann cell proliferation after injury with significant induction of the Cdkn2a cell cycle inhibitor gene. Interestingly, PRC2 subunits and CDKN2A are commonly co-mutated in the transition from benign neurofibromas to malignant peripheral nerve sheath tumors (MPNST's). RNA-seq analysis of EED-deficient mice identified PRC2-regulated molecular pathways that may contribute to the transition to malignancy in neurofibromatosis.

Crush injury to motor nerves in the G93A transgenic mouse model of amyotrophic lateral sclerosis promotes muscle reinnervation and survival of functionally intact nerve-muscle contacts.

Selective survival of small motor nerve fibers and their neuromuscular contacts in the SOD1G93A transgenic mouse model of amyotrophic lateral sclerosis (ALS) suggests that smaller regenerated nerve fibers are more able to sustain reformed nerve-muscle connections as functionally intact motor units (MUs). The sciatic nerve was crushed unilaterally in SOD1G93A transgenic mice at 40 days of age and contractile forces of reinnervated muscles and their MUs were recorded at 90 days in order to determine the capacities of the nerves to regenerate and to form and retain functional neuromuscular connections. Reduced MU numbers in fast-twitch tibialis anterior, extensor digitorum longus and medial gastrocnemius muscles and the lesser reductions in slow-twitch soleus muscle of SOD1G93A transgenic mice were reversed in reinnervated muscles: there were more reinnervated MUs and their contractile forces and the muscle forces and weights increased. In line with the contrasting ability of only small not large nerve fibers to sprout to form enlarged MUs in the SOD1G93A transgenic mouse, the smaller regenerating nerve fibers formed enlarged MUs that were better able to survive. Because nerve fibers with and without muscle contacts were severed by the sciatic nerve crush injury, the conditioning lesion is untenable as the explanation for improved maintenance of reinnervated neuromuscular junctions. Elevated neurotrophic factor expression in axotomized motoneurons and/or denervated Schwann cells and the synapse withdrawal from axotomized motoneurons are other factors that, in addition to reduced size of nerve fibers reinnervating muscles, may account for increased survival and size of reinnervated MUs in ALS.