Sciatic Nerve Crush Model Research Articles

Enhancement of Heme-Oxygenase 1 in the Injured Peripheral Nerve Following Sulforaphane Administration Fosters Regeneration via Proliferation and Maintenance of Repair Schwann Cells.

Nuclear erythroid 2-related factor 2 (Nrf2) and its downstream effector heme oxygenase 1 (HO-1) are commonly activated in response to cellular stresses. The elevated expression of HO-1 has been associated with markedly accelerated peripheral nerve regeneration. This study aimed to evaluate the impact of a naturally occurring dietary Nrf2/HO-1 activator-sulforaphane (SFN)-on regeneration in a murine sciatic nerve crush model. The beneficial safety profile of SFN has been thoroughly investigated and confirmed several times. Here, SFN was administered daily, starting immediately after C57BL/6 mice were subjected to sciatic nerve crush injury. Injured sciatic nerves were excised at various time points post injury for molecular, immunohistochemical and morphometric analyses. Moreover, functional assessment was performed by grip strength analysis and electrophysiology. Following SFN treatment, the early response to injury includes a modulation of autophagic pathways and marked upregulation of Nrf2/HO-1 expression. This enhancement of HO-1 expression was maintained throughout the regeneration phase and accompanied by a significant increase in repair Schwann cells. In these cells, elevated proliferation rates were observed. Significant improvements in grip strength test performance, nerve conduction velocity and remyelination were also noted following SFN treatment. Collectively, SFN modulates cytoprotective and autophagic pathways in the injured nerve, increasing the number of repair Schwann cells and contributing to effective nerve regeneration. Given the availability of SFN as a nutritional supplement, this compound might constitute a novel regenerative approach with broad patient accessibility and further studies on this topic are warranted.

MicroRNA-301a knockout attenuates peripheral nerve regeneration by delaying Wallerian degeneration.

Our recent study demonstrated that knockout of microRNA-301a attenuates migration and phagocytosis in macrophages. Considering that macrophages and Schwann cells synergistically clear the debris of degraded axons and myelin during Wallerian degeneration, which is a prerequisite for nerve regeneration, we hypothesized that microRNA-301a regulates Wallerian degeneration and nerve regeneration via impacts on Schwann cell migration and phagocytosis. Herein, we found low expression of microRNA-301a in intact sciatic nerves, with no impact of the microRNA-301a knockout on nerve structure and function. By contrast, we found significant upregulation of microRNA- 301a in injured sciatic nerves. We established a sciatic nerve crush model in microRNA-301a knockout mice, which exhibited attenuated morphological and functional regeneration following sciatic nerve crush injury. The microRNA-301a knockout also led to significantly inhibited Wallerian degeneration in an in vivo sciatic nerve-transection model and in an in vitro nerve explant block model. Schwann cells with the microRNA-301a knockout showed inhibition of phagocytosis and migration, which was reversible under transfection with microRNA-301a mimics. Rescue experiments involving transfection of microRNA-301a-knockout Schwann cells with microRNA-301a mimics or treatment with the C-X-C motif receptor 4 inhibitor WZ811 indicated the mechanistic involvement of the Yin Yang 1/C-X-C motif receptor 4 pathway in the role of microRNA-301a. Combined with our previous findings in macrophages, we conclude that microRNA-301a plays a key role in peripheral nerve injury and repair by regulating the migratory and phagocytic capabilities of Schwann cells and macrophages via the Yin Yang 1/C-X-C motif receptor 4 pathway.

Remodeling of the Intra-Conduit Inflammatory Microenvironment to Improve Peripheral Nerve Regeneration with a Neuromechanical Matching Protein-Based Conduit.

Peripheral nerve injury (PNI) remains a challenging area in regenerative medicine. Nerve guide conduit (NGC) transplantation is a common treatment for PNI, but the prognosis of NGC treatment is unsatisfactory due to 1) neuromechanical unmatching and 2) the intra-conduit inflammatory microenvironment (IME) resulting from Schwann cell pyroptosis and inflammatory-polarized macrophages. A neuromechanically matched NGC composed of regenerated silk fibroin (RSF) loaded with poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (P:P) and dimethyl fumarate (DMF) are designed, which exhibits a matched elastic modulus (25.1±3.5MPa) for the peripheral nerve and the highest 80% elongation at break, better than most protein-based conduits. Moreover, the NGC can gradually regulate the intra-conduit IME by releasing DMF and monitoring sciatic nerve movements via piezoresistive sensing. The combination of NGC and electrical stimulation modulates the IME to support PNI regeneration by synergistically inhibiting Schwann cell pyroptosis and reducing inflammatory factor release, shifting macrophage polarization from the inflammatory M1 phenotype to the tissue regenerative M2 phenotype and resulting in functional recovery of neurons. In a rat sciatic nerve crush model, NGC promoted remyelination and functional and structural regeneration. Generally, the DMF/RSF/P:P conduit provides a new potential therapeutic approach to promote nerve repair in future clinical treatments.

IL-33 promotes sciatic nerve regeneration in mice by modulating macrophage polarization

Despite the innate regenerative capacity of peripheral nerves, regeneration after a severe injury is insufficient, and sensorimotor recovery is incomplete. As a result, finding alternative methods for improving regeneration and sensorimotor recovery is essential. In this regard, we investigated the effect of IL-33 treatment as a chemokine with neuroprotective properties. IL-33 can facilitate tissue healing by potentiating the type 2 immune response and polarizing macrophages toward the pro-healing M2 phenotype. However, its effects on nerve regeneration remain unclear. Therefore, this research aimed to evaluate the neuroprotective effects of IL-33 on sciatic nerve injury in male C57BL/6 mice. After crushing the left sciatic nerve, the animals were given 10, 25, or 50 µg/kg IL-33 intraperitoneally for seven days. The sensorimotor recovery was then assessed eight weeks after surgery. In addition, immunohistochemistry, ELISA, and real-time PCR were used to assess macrophage polarization, cytokine secretion, and neurotrophic factor expression in the injured nerves. IL-33 at 50 and 25 µg/kg doses could significantly accelerate nerve regeneration and improve sensorimotor recovery when compared to 10 µg/kg IL-33 and control groups. Furthermore, at 50 and 25 µg/kg doses, IL-33 polarized macrophages toward an M2 phenotype and reduced proinflammatory cytokines at the injury site. It also increased the mRNA expression of NGF, VEGF, and BDNF. These findings suggest that a seven-day IL-33 treatment had neuroprotective effects in a mouse sciatic nerve crush model, most likely by inducing macrophage polarization toward M2 and regulating inflammatory microenvironments.

Effect of growth differentiation factor 11 expression after peripheral nerve injury in Sprague-Dawley rats

ABSTRACT Objectives We attempt to investigate the expression pattern of GDF11 in the sciatic nerves after injury. Methods Thirty-six healthy male Sprague Dawley (SD) rats were divided into three groups at random and were labelled as: day 1, day 4, and day 7 post-surgery. The sciatic nerve crush model was established on the left-hind limb, while the right limb was untreated, and served as the control. Nerve samples were collected at post-injury day 1, day 4 and day 7. Nerve samples collected from the proximal and distal stump of the injury site underwent immunofluorescence staining with GDF11, NF200 and CD31. GDF11 mRNA expression was analyzed by qRT-PCR. CCK-8 assay, after si-GDF11 transfection in Schwann cells (RSC96) was applied to verify its effect in cell proliferation rate. Results GDF11 was abundantly expressed in axons stained with NF200 and Schwann cells stained with S100. However, no GDF11 expression was observed in vascular endothelial tissues stained with CD31. From day 4 onwards, the level of GDF11 showed an increasing trend, up to a twofold level at day 7 after injury. Proliferation rate of RSC96 cells showed a significant decrease after the down-regulation of GDF11 by siRNAs compared to the control group. Conclusions GDF11 may play a role in the proliferation of Schwann cell during nerve regeneration process.

Astrocytic expression of CD137 in the lumbar spinal cord following sciatic nerve crush model of neuropathic pain in mice

Abstract Previously we have shown that CD137–CD137 ligand (CD137L) mediates pro-nociceptive behaviors in the sciatic nerve crush (SNC) model of neuropathic pain. Global CD137L knockout (KO) mice and wildtype (WT) mice intrathecally treated with neutralizing antibody against either CD137L or CD137 displayed significantly reduced neuropathic pain-like behaviors and faster functional recovery compared to WT mice following SNC. To identify the cellular sources of CD137 and CD137L in the spinal cord, a series of immunohistochemistry analyses was performed. While we could not detect significant expression of CD137L (in part due to both technical and biological issues), we observed CD137 expression exclusively co-localized with astrocytic marker glial fibrillary acidic filament (GFAP). We then conducted a time course study of CD137 expression in the lumbar spinal cord dorsal horn region, the region relevant to nociceptive behaviors, in B6-CD137L KO and B6 WT mice. Significant increases in CD137 expression (represented by integrated density) were observed in WT mice from days 7 to 28 following either SNC or sham surgery. The expression of CD137 in KO mice was slightly (however not statistically significantly) higher than that in WT mice at baseline, and did not change overtime post-either surgery. When RNA expression of CD137 was evaluated, although SNC induced significant upregulation of GFAP RNA expression in WT mice, no changes in CD137 RNA expression were detected in any treatment groups or any genotype of mice. Altogether, we report a novel expression of CD137 on murine spinal cord astrocytes. The underlying mechanism through which astrocytic CD137 mediates SNC-induced nociceptive behavior requires further investigation. NIH/NINDS R01NS098426 (Cao) and Peter Caradonna from the COBRE Histology and Imaging Core funded by NIH/NIGMS P20GM103643 (Meng).

LncRNA HAGLR promotes the proliferation, migration, and neurotrophic factor production of Schwann cells via miR-204/CDK5R1 after sciatic nerve injury.

Peripheral nerve injury induces motor and sensory defects and has serious impacts on patients' quality of life. Schwann cells (SCs) are the major glial cells in the peripheral nervous system and play important roles in the repair and regeneration of peripheral nerves. Long noncoding RNA HAGLR has been reported to be highly expressed in neurons and to promote neuronal differentiation but its expression decreases after nerve injury, suggesting that HAGLR may be involved in the process of nerve injury repair. This study aimed to investigate the role and mechanism of HAGLR in neural repair functions of SCs. We found that HAGLR promoted SC proliferation and migration and facilitated the secretion of neurotrophic factors. Furthermore, HAGLR functions as a competing endogenous RNA to regulate CDK5R1 expression via sponging miR-204. Overexpression of miR-204 or silencing of CDK5R1 partially abolished the promoting effect of HAGLR on SCs. Moreover, overexpression of HAGLR promoted the functional recovery of sciatic nerve crush (SNC) model rats. In summary, HAGLR promoted SC proliferation, migration, neurotrophic factor production, and facilitated functional recovery of SNC rats via miR-204/CDK5R1. Therefore, it may provide a potential therapeutic target for peripheral nerve repair and regeneration.

Polydopamine-Decorated PLCL Conduit to Induce Synergetic Effect of Electrical Stimulation and Topological Morphology for Peripheral Nerve Regeneration.

Due to the limited self-repairing capacity after peripheral nerve injuries (PNI), artificial nerve conduits are widely applied to facilitate neural regeneration. Exogenous electrical stimulation (ES) that is carried out by the conductive conduit regulates the biological behavior of Schwann cells (SCs). Meanwhile, a longitudinal surface structure counts to guide axonal growth to accelerate the end-to-end connection. Currently, there are no conduits equipped with both electrical conduction and axon-guiding surface structure. Herein, a biodegradable, conductive poly(l-lactide-co-caprolactone)/graphene (PLCL/GN) composite conduit is designed. The conduit with 20.96 ± 1.26MPa tensile strength has a micropatterned surface of 20µm groove fabricated by microimprint technology and self-assembled polydopamine (PDA). In vitro evaluation shows that the conduits with ES effectively stimulate the directional cell migration, adhesion, and elongation, and enhance neuronal expression of SCs. The rat sciatic nerve crush model demonstrates that the conductive micropatterned conduit with ES promotes the growth of myelin sheath, faster nerve regeneration, and 20-fold functional recovery in vivo. These discoveries prove that the PLCL(G)/PDA/GN composite conduit is a promising tool for PNI treatment by providing the functional integration of physical guidance, biomimetic biological regulation, and bioelectrical stimulation, which inspires a novel therapeutic approach for nerve regeneration in the future.

The effect of dietary sesame oil and ginger oil as antioxidants in the adult rat dorsal root ganglia after peripheral nerve crush injury

Aim The purpose of this study was to investigate the effect of dietary sesame oil and ginger oil supplements on the dorsal root ganglia following a sciatic nerve crush model in male Wistar albino rats. Materials and methods Crush injury models have been done by means of graded forceps (50 Newton). The animals were given a daily sesame oil (4 ml/kg/day) and ginger oil (400 mg/kg/day) via oral gavage for a period of 28 days. Dorsal root ganglia from the L5 levels were harvested. Processing of tissues was done for electron microscopy and light microscopy. Immunohistochemical staining with active caspase-3 antibody and qualitative ultrastructural analyses of tissues were made by a light and a transmission electron microscope, respectively. Results The results showed that crush injury leads to remarkable ultrastructural changes in sensory neurons, such as swollen mitochondria, disruption of cristae structure, glial cell proliferation and, consequently, phagocytosis of the damaged neuron. These ultrastructural changes were less evident in the treated groups, and both natural compounds reduced the expression of activated caspase-3, which may also affect ultrastructural changes. Conclusion The application of the natural products sesame oil and ginger oil may represent a supportive approach to the protection of sensory neurons against the destructive effects of peripheral nerve crush injury.

Enhancement of nerve regeneration with nimodipine treatment after sciatic nerve injury.

Peripheral nerve injuries (PNI/s) are common orthopedic conditions, characterized by motor and sensory deficits in the damaged region. There is growing evidence that the L-type calcium channel antagonist nimodipine has neuroprotective and neuroregenerative effects in animal models of neurological disorders. The efficacy of nimodipine on improving motor function and sensation following a sciatic nerve crush model was investigated in male Wistar rats as a model of PNI. At different time periods following damage, we evaluated motor function, sensory recovery, electrophysiology, histomorphometry, and gene expression. Moreover, we used histological and mass ratio analysis of the gastrocnemius muscle to assess atrophy. Our findings suggest that the nimodipine improves motor and sensory function more quickly in the damaged region 2, 4, and 6weeks after 1 week of treatment. Nimodipine treatment also increased the number of myelinated fibers while decreasing their thickness, as shown by histomorphometry. Additionally, nimodipine treatment increases the mRNA levels of neurotrophic factors (BDNF and NGF), which are known to contribute to the regeneration of injured neurons. The impact of nimodipine in PNI recovery may be due to its stimulation of the CREB signaling pathway and suppression of pro-inflammatory factor production.

Creatine promotes the repair of peripheral nerve injury by affecting macrophage polarization

The present study aimed to explore whether creatine promotes the repair of peripheral nerve injury and its possible mechanism. In vitro: RAW264.7 cells were used to investigate the role of proteins related to the JAK2/STAT1 pathway in the polarization of macrophages treated with creatine. In vivo: A sciatic nerve crush model was used. After the injury, IL-4 or creatine was injected. The recovery of motor function was assessed by the rotarod test and sciatic function index at 2, 6, 10, and 16 days after injury. At 16 days after injury, the ultrastructure of the nerve tissue was observed under a transmission electron microscope. Immunostaining were performed at 4 and 16 days to investigate the expression levels of macrophage-related markers as well as the distribution of macrophages after injury. Compared with the IFN-γ group, the group pretreated with creatine showed a significant decrease in p-JAK2 and p-STAT1 in vitro. The motor function of mice in the creatine group (CR1) and creatine 4 days group (CR2) was significantly improved compared to the control group (CON). The improvement in the CR2 group was more significant. Immunostaining showed that infiltrating macrophages mainly comprised M1 macrophages in the CON group and M2 macrophages in the CR group. Our study shows that creatine promotes the repair of peripheral nerve injury by affecting macrophage polarization, possibly through decreasing M1 polarization by inhibiting the JAK2/STAT1 pathway.

Robust temporal changes of cellular senescence and proliferation after sciatic nerve injury.

Cellular senescence and proliferation are essential for wound healing and tissue remodeling. However, senescence-proliferation cell fate after peripheral nerve injury has not been clearly revealed. Here, post-injury gene expression patterns in rat sciatic nerve stumps (SRP113121) and L4-5 dorsal root ganglia (SRP200823) obtained from the National Center for Biotechnology Information were analyzed to decipher cellular senescence and proliferation-associated genetic changes. We first constructed a rat sciatic nerve crush model. Then, β-galactosidase activities were determined to indicate the existence of cellular senescence in the injured sciatic nerve. Ki67 and EdU immunostaining was performed to indicate cellular proliferation in the injured sciatic nerve. Both cellular senescence and proliferation were less vigorous in the dorsal root ganglia than in sciatic nerve stumps. These results reveal the dynamic changes of injury-induced cellular senescence and proliferation from both genetic and morphological aspects, and thus extend our understanding of the biological processes following peripheral nerve injury. The study was approved by the Animal Ethics Committee of Nantong University, China (approval No. 20190226-001) on February 26, 2019.

Injectable, antioxidative, and neurotrophic factor-deliverable hydrogel for peripheral nerve regeneration and neuropathic pain relief

Although peripheral nerve system has intrinsic regeneration potential, recovery from peripheral nerve injury (PNI) is often far from optimal, leading to partial or complete loss of sensorimotor function and neuropathic pain. The failure for PNI repair can be due to multiple reasons. Excessively elevated oxidative stress in injured tissue is one of primary causes for poor nerve regeneration and pain by damaging neurons and myelin structure. In addition, deprivation in various neurotrophic factors (NTFs) in chronic nerve denervation will lose support for nerve regrowth. Here, we developed a multifunctional hyaluronic acid-phenylboronic acid-poly (vinyl alcohol) -heparin (HA-PVA-Hep) hydrogel by mixing cysteamine and phenylboronic acid modified hyaluronic acid, commercially available poly (vinyl alcohol) and maleimide functionalized heparin. This hydrogel is biocompatible, stable, injectable, antioxidative, anti-inflammatory, and capable of sustainably releasing NTFs (i.e. glial cell derived neurotrophic factor-GDNF in this study). The therapeutic effect of HA-PVA-Hep hydrogel to repair acute PNI was tested by using a mouse sciatic nerve crush model. We found the hydrogel effectively improved sensorimotor function during the recovery period and significantly prevented muscular atrophy, protected neurons from injury and promoted nerve regeneration as well as remyelination at 28 days post injury. In addition, the hydrogel could also alleviate PNI-induced pain as hydrogel treatment reversed pain-related changes induced by PNI, including increased expression of a proinflammatory modulator, TNF-α, at injured nerve, activation of microglia and upregulation of pain-sensor receptor, TRPA1 at ipsilateral spinal dorsal horn. Nevertheless, supplementing the hydrogel with GDNF interrupted the PNI recovery process and probably counteracted the pain alleviation effect of the hydrogel. Thus, therapeutic effect of GDNF through local administration on PNI treatment needs to be further determined. In summary, our work provides a hydrogel delivery system with inherent therapeutic effect for PNI therapy.

Polydatin protects Schwann cells from methylglyoxal induced cytotoxicity and promotes crushed sciatic nerves regeneration of diabetic rats.

Oxidative stress plays the main role in the pathogenesis of diabetes mellitus and peripheral neuropathy. Polydatin (PD) has been shown to exhibit strong antioxidative and antiinflammatory effects. At present, no research has focused on the possible effects of PD on Schwann cells and impaired peripheral nerves in diabetic models. Here, we used an in vitro Schwann cell damage model induced by methylglyoxal and an in vivo diabetic sciatic nerve crush model to study problems in such an area. In our experiment, we demonstrated that PD potently alleviated the decrease of cellular viability, prevented reactive oxygen species generation, and suppressed mitochondrial depolarization as well as cellular apoptosis in damaged Schwann cells. Moreover, we found that PD could upregulate Nrf2 and Glyoxalase 1 (GLO1) expression and inhibit Keap1 and receptor of AGEs (RAGE) expression of damaged Schwann cells. Finally, our in vivo experiment showed that PD could promote sciatic nerves repair of diabetic rats. Our results revealed that PD exhibited prominent neuroprotective effects on Schwann cells and sciatic nerves in diabetic models. The molecular mechanisms were associated with activating Nfr2 and GLO1 and inhibiting Keap1 and RAGE.

Photobiomodulation promotes neural regeneration when compared to simvastatin treatment in a sciatic nerve crush model.

To determine whether the effects of photobiomodulation (PBM) were associated with the use of Simvastatin in the functional recovery from sciatic nerve in mice submitted to crush injury. Fifty Swiss mice (approximately 3months old; average weight 40g) were randomly divided into six groups: naive, sham, control, PBM (660nm, 10J/cm2; 30mW; 0.6J per day for 28days; 0.06cm2; 16.8J total and 20s), Simvastatin (20mg/kg), and PBM/Simv (association of the two protocols). The sciatic functional index (SFI), thermal heat hyperalgesia, mechanical hyperalgesia, and thermographic evaluation were used as analyses. The evaluations were performed preoperatively and 7, 14, 21, and 28days after the initial injury analyzed by two-way analysis of variance (ANOVA) for mixed models followed by the Bonferroni post-test. All groups except sham and naive presented an SFI compatible with severe peripheral nerve injury on the 7th day of evaluation. The PBM group presented better results in the SFI analysis (p < 0.001) on the 21st postoperative day compared to the control group. This benefit was maintained when compared to the Simvastatin (p < 0.001) and PBM/Simv groups (p < 0.01). The results of the thermal and mechanical hyperalgesia and thermography analyses were not significant (p > 0.05). The obtained results showed that PBM alone was more effective compared to Simvastatin alone or PBM combined with Simvastatin for sciatic nerve injury in mice.

Nanochannel-Based Poration Drives Benign and Effective Nonviral Gene Delivery to Peripheral Nerve Tissue.

While gene and cell therapies have emerged as promising treatment strategies for various neurological conditions, heavy reliance on viral vectors can hamper widespread clinical implementation. Here, the use of tissue nanotransfection as a platform nanotechnology to drive nonviral gene delivery to nerve tissue via nanochannels, in an effective, controlled, and benign manner is explored. TNT facilitates plasmid DNA delivery to the sciatic nerve of mice in a voltage-dependent manner. Compared to standard bulk electroporation (BEP), impairment in toe-spread and pinprick response is not caused by TNT, and has limited to no impact on electrophysiological parameters. BEP, however, induces significant nerve damage and increases macrophage immunoreactivity. TNT is subsequently used to deliver vasculogenic cell therapies to crushed nerves via delivery of reprogramming factor genes Etv2, Foxc2, and Fli1 (EFF). The results indicate the TNT-based delivery of EFF in a sciatic nerve crush model leads to increased vascularity, reduced macrophage infiltration, and improved recovery in electrophysiological parameters compared to crushed nerves that are TNT-treated with sham/empty plasmids. Altogether, the results indicate that TNT can be a powerful platform nanotechnology for localized nonviral gene delivery to nerve tissue, in vivo, and the deployment of reprogramming-based cell therapies for nerve repair/regeneration.

Reduced inflammatory response and accelerated functional recovery following sciatic nerve crush lesion in CXCR3-deficient mice.

Despite the regenerative capacity of the peripheral nerve system (PNS), functional recovery after mechanical nerve trauma is often incomplete, resulting in motor, sensory, and autonomic deficits. The elucidation of key molecules involved in trauma-induced Wallerian degeneration and the ensuing regeneration processes is a prerequisite for the development of disease modifying drugs. The chemokine (C-X-C motif) receptor 3 (CXCR3) has been implicated in the recruitment of macrophages, the major immune cell population during the process of Wallerian degeneration. In this study, we examined whether deletion of CXCR3 affects macrophage recruitment, the expression of the proinflammatory cytokine tumor necrosis factor (TNF)- α and the CXCR3 agonist interferon gamma-induced protein 10 (CXCL10), and functional recovery in the sciatic nerve crush model. CXCR3 mice displayed significantly reduced macrophage counts preceded by diminished expression of CXCL10 and TNF- α. Furthermore, functional recovery of sciatic nerve motor function was significantly accelerated. In summary, these data indicate that the deletion of CXCR3 leads to a diminished inflammatory response and an accelerated functional recovery following sciatic nerve crush injury. Therefore, CXCR3 may be an interesting target for therapeutic interventions after traumatic nerve lesions.

Role of CD137L in lumbar spinal cord microglial responses following sciatic nerve crush

Abstract Neuropathic pain is one of the most devastating kinds of chronic pain, which is still largely treated sub-optimally in part due to incomplete understanding. Using murine sciatic nerve crush (SNC) model, we have shown that spinal cord CD137 ligand (CD137L; AKA 4-1BBL) contributes to the development of SNC-induced pain-like behaviors and functional recovery following SNC. Here, we further investigated the potential involvement of lumbar spinal cord microglial responses in CD137L-mediated behavioral changes following SNC. Mononuclear cells were isolated from lumbar spinal cords of both wild type (WT) B6 and B6_CD137L knockout (KO) mice via Percoll gradient followed by flow cytometric analysis at days 0 (naïve), 3, 7, 14, 28 and 56 following SNC or sham surgery. Microglia were identified as CD45lowCD11b+ populations. In WT mice, the total number of microglia peaked at day 14 and then gradually reduced following SNC. The increase of microglial numbers was minimal in all other groups compared to the WT SNC mice. Similar pattern of changes were also observed with the numbers of CD86+ microglia (pro-inflammatory phenotype) and CD206+ microglia (anti-inflammatory phenotype), however the numbers of CD206+ microglia were much less. Our results support the notion that reduced lumbar spinal cord microglial responses contributes to the reduction of pain-like behaviors and improved functional recovery in CD137L deficient mice. CD137L-mediated microglial responses will be further investigated to elucidate the role of spinal cord CD137L in the development of neuropathic pain. (Supported by NIH/NINDS R01NS098426 (Cao))

Naringenin complexed with hydroxypropyl-β-cyclodextrin improves the sciatic nerve regeneration through inhibition of p75NTR and JNK pathway

Peripheral nerve injuries are common conditions that often lead to dysfunctions. Although much knowledge exists on the several factors that mediate the complex biological process involved in peripheral nerve regeneration, there is a lack of effective treatments that ensure full functional recovery. Naringenin (NA) is the most abundant flavanone found in citrus fruits and it has promising neuroprotective, anti-inflammatory and antioxidant effects. This study aimed to enhance peripheral nerve regeneration using an inclusion complex containing NA and hydroxypropyl-β-cyclodextrin (HPβCD), named NA/HPβCD. A mouse sciatic nerve crush model was used to evaluate the effects of NA/HPβCD on nerve regeneration. Sensory and motor parameters, hyperalgesic behavior and the sciatic functional index (SFI), respectively, improved with NA treatment. Western blot analysis revealed that the levels of p75NTR ICD and p75NTR full length as well phospho-JNK/total JNK ratios were preserved by NA treatment. In addition, NA treatment was able to decrease levels of caspase 3. The concentrations of TNF-α and IL-1β were decreased in the lumbar spine, on the other hand there was an increase in IL-10. NA/HPβCD presented a better overall morphological profile but it was not able to increase the number of myelinated fibers. Thus, NA was able to enhance nerve regeneration, and NA/HPβCD decreased effective drug doses while maintaining the effect of the pure drug, demonstrating the advantage of using the complex over the pure compound.

A Schwann cell-enriched circular RNA circ-Ankib1 regulates Schwann cell proliferation following peripheral nerve injury.

Schwann cells (SCs) play an essential role in nerve injury repair. A striking feature of the cellular response to peripheral nerve injury is the proliferation of SCs. Circular (circ)RNAs are enriched in the nervous system and are involved in physiologic and pathologic processes. However, the potential role of circRNAs in SC proliferation post nerve injury remains largely unknown. Using a sciatic nerve crush model, we obtained an expression profiling of circRNAs in injured sciatic nerves in rats by RNA sequencing and bioinformatics analysis, and we further identified a circRNA [circ-ankyrin repeat and in-between Ring finger (IBR) domain containing 1 (Ankib1)] involved in SC proliferation by the transfection of specific small interfering RNAs. Overexpression of circ-Ankib1, which was specifically and highly enriched in SCs, impaired SC proliferation and axon regeneration following sciatic nerve injury. Mechanistically, increased expression of DEx/H-box helicase 9 (DHX9) postinjury might contribute to the down-regulation of circ-Ankib1, which further suppressed cytochrome P450, family 26, subfamily B, polypeptide 1 expression by sponging miR-423-5p, miR-485-5p, and miR-666-3p, leading to the induction of SC proliferation and nerve regeneration. Taken together, our results reveal a crucial role for circRNAs in regulating proliferation of SCs involved in sciatic nerve regeneration; as such, circRNAs may serve as a potential therapeutic avenue for nerve injury repair.-Mao, S., Zhang, S., Zhou, S., Huang, T., Feng, W., Gu, X., Yu, B. A Schwann cell-enriched circular RNA circ-Ankib1 regulates Schwann cell proliferation following peripheral nerve injury.