Functional Recovery Of Injured Nerves Research Articles

Dysregulated miR-29a-3p/PMP22 Modulates Schwann Cell Proliferation and Migration During Peripheral Nerve Regeneration.

Schwann cells switch to a repair phenotype following peripheral nerve injury and create a favorable microenvironment to drive nerve repair. Many microRNAs (miRNAs) are differentially expressed in the injured peripheral nerves and play essential roles in regulating Schwann cell behaviors. Here, we examine the temporal expression patterns of miR-29a-3p after peripheral nerve injury and demonstrate significant up-regulation of miR-29a-3p in injured sciatic nerves. Elevated miR-29a-3p inhibits Schwann cell proliferation and migration, while suppressed miR-29a-3p executes reverse effects. In vivo injection of miR-29a-3p agomir to rat sciatic nerves hinders the proliferation and migration of Schwann cells, delays the elongation and myelination of axons, and retards the functional recovery of injured nerves. Mechanistically, miR-29a-3p modulates Schwann cell activities via negatively regulating peripheral myelin protein 22 (PMP22), and PMP22 extensively affects Schwann cell metabolism. Our results disclose the vital role of miR-29a-3p/PMP22 in regulating Schwann cell phenotype following sciatic nerve injury and shed light on the mechanistic basis of peripheral nerve regeneration.

Abstract 119: Novel Application Of Common Pharmacological Agents Nimodipine And Botulinum Toxin A On Traumatic Nerve Regeneration Following Microsurgical Repair: A Pilot Study

Purpose: Peripheral nerve damage is a frequent problem in civilian and military populations; an estimated 2.8-5% of trauma admissions contain a peripheral nerve injury. Currently, end-to-end, tension-free microsurgical nerve repair (neurorrhaphy) is the gold standard treatment. However, neurorrhaphy is not neuroprotective and does not address the complex molecular environment of a regenerating nerve required for complete functional restoration. Anecdotal clinical evidence indicates that widely used pharmacological agents botulinum toxin A (BTX, a neurotoxic protein) and nimodipine (NDP, a L-type calcium channel blocker) may improve functional recovery of injured nerves, but the mechanisms remain unknown. This research investigates BTX and NDP, independently and in combination, for their novel capacity to improve neural regeneration and functional recovery following neurorrhaphy. Methods: 32 Lewis rats underwent surgical tibial nerve transection and neurorrhaphy. Post-op pharmaceutical treatment groups included: 1) Sham surgery (n=4); 2) Sham surgery+BTX (n=4); 3) NDP+saline injection (control for BTX, N=6); 4) BTX+NDP (n=6); 5) Saline+placebo pill (control for NDP, n=6); 6) BTX+placebo pill (n=6). Outcomes were assessed using behavioral (rotarod, horizontal ladder walk), electrophysiological (nerve conduction velocity [NCV], compound nerve action potential [CNAP], duration of response), and stereological means (myelinated axon count estimation, epineurial cross sectional area). Statistical significance was determined by one-way ANOVA. Results: The NDP+saline group outperformed other treatment groups in the ladder walk, resulting in the fewest deep slips (15.07% vs 30.77% in BTX+NDP, p=0.117), fewest misses (3.54% vs 4.21% in BTX+NDP, p=0.809), and most correct steps (70.53% vs 55.58% in BTX+NDP, p=0.143). Rotarod testing resulted in no clear differences between treatment groups with all groups performing worse than sham controls. There was an observed sex bias between groups in which females tended to outperform males within groups in both behavioral modalities. Electrophysiological testing portrayed similar outcomes to ladder walk testing in which NDP+saline resulted in the fastest NCV (0.81m/s vs 0.59m/s in BTX+NDP, p=0.126), and shortest duration of response (22.68µs vs 65.96µs in BTX+NDP, p=0.171) among the treatment groups. Our unbiased stereological analyses resulted in the BTX+NDP group having the highest myelinated axon count (9,249.54 vs 7,334.94 in NDP+saline, p=0.036), but when epineurial area is controlled for, this difference diminishes (0.005/um2 vs 0.0043/um2 in NDP+saline, p=0.201). When separated by sex, males tended to have higher axon counts than females (8,615.03 vs 6,052.84 in NDP+saline, p=0.036). Conclusions: This pilot study represents the first approach to test NDP with BTX in a multimodal assessment of nerve recovery and regeneration following transection and neurorrhaphy. While an additive or synergistic effect between BTX and NDP was expected, NDP alone tended to outperform the combined treatment group in behavioral and electrophysiological assessments. However, and in accordance with past studies by our group and others, histologic axon count was inversely related to nerve function recovery, portraying a disadvantageous compensatory effect. Our findings of a sex bias parallel observations present in the current literature. Future work will expand on these studies focusing on nimodipine in males and females in an effort to improve nerve recovery in trauma patients.

Effect of mammalian target of rapamycin signaling pathway on nerve regeneration

Nerve injury is a serious clinical common problem not only caused by violence usually in traffic accident but also non-violence related disease like amyotrophic lateral sclerosis and other motor neuron diseases. All these diseases always come with severe consequences including loss of function and even to paralysis which are associated with significant high mortality. Although many useful treatments have been developed, completely recovery of damaged nerve function is usually hardly obtained. Because successful functional recovery of injured nerve lie in not only axon regeneration, neuronal survival but also reconstructing transmission of myelin-based electric nerve stimulation as well as re-innervation of denervated targets. Recent research has suggested that low intrinsic capacity of neuron may be genuinely responsible for regeneration failure. PI3K/Akt/mammalian target of rapamycin (mTOR) signaling pathway has been found playing crucial roles in the growth of central nervous system axons, and confirmed as a major intracellular signaling axis that control axon regeneration. In nerve dissection animal models, the mTOR activity was suppressed and protein synthesis was impaired, while reactivating this pathway successfully led to axon regeneration. Emerging evidence show that mTOR is required during multiple intricate physiological process in nerve regeneration. This review focuses on recent study which are mTOR related, introducing basic knowledge of mTOR including protein structure and its function in either physiological or pathological process, discussing the therapeutic potential of mTOR-based treatment.

Effect of calcitonin on cultured schwann cells.

After nerve injury, calcium concentrations in intranerve fibers quickly increase. We have shown that functional recovery of injured nerves correlates with calcium absorption. A slight increase in calcium reduces the number of Schwann cells present. Calcitonin therapy greatly improves regeneration by accelerating calcium absorption. We examined the effect of adding calcitonin to higher concentration calcium media on cultured Schwann cells. The cells, isolated from intact sciatic nerves, were cultured with normal or higher concentration calcium media with or without calcitonin. Schwann cells were incubated with anti-S-100, goat-anti-mouse, and propidium iodide and then viewed through fluorescent light and phase-contrast microscopy for observation and analysis. The cells in each calcitonin-containing medium showed many Schwann cells, however, the cells in the higher concentration calcium media showed fewer and more defective Schwann cells. These results show that calcitonin protects against the harmful effects of excessive calcium encountered in peripheral nerve injury. Muscle Nerve 56: 768-772, 2017.

Proliferative effects of melatonin on Schwann cells: implication for nerve regeneration following peripheral nerve injury

Activation of proliferation of Schwann cells is crucial for axonal guidance and successful nerve regeneration following peripheral nerve injury (PNI). Considering melatonin plays an important role in proliferative regulation of central glial cells, the present study determined whether melatonin can effectively promote Schwann cell proliferation and improve nerve regeneration after PNI. The spontaneous immortalized rat Schwann cell line (RSC 96 cells) was first analyzed by quantitative polymerase chain reaction (QPCR) to detect the potential existence of melatonin receptors. The melatonin receptor-mediated signaling responsible for proliferation was examined by measuring the phosphorylation of extracellular signal-regulated kinases (ERK1/2) pathway. The in vivo model of PNI was performed by the end-to-side neurorrhaphy. The quantity of Schwann cells as well as the number of re-innervated motor end plates (MEP) on target muscles was examined to represent the functional recovery of injured nerves. QPCR results indicated that MT1 is the dominant receptor in Schwann cells. Immunoblotting and proliferation assay revealed an enhanced phosphorylation of ERK1/2 and increased number of RSC 96 cells following melatonin administration. Nonselective melatonin receptor antagonist (luzindole) treatment significantly suppressed all the above findings, suggesting that the proliferative effects of melatonin were mediated by a receptor-dependent pathway. In vivo results corresponded well with in vitro findings in which melatonin effectively increased the amount of proliferated Schwann cells and re-innervated MEP on target muscles following PNI. As melatonin successfully improves nerve regeneration by promoting Schwann cell proliferation, therapeutic use of melatonin may thus serve as a promising strategy to counteract the PNI-induced neuronal disability.

Long-term observation of auto-cell transplantation in non-human primate reveals safety and efficiency of bone marrow stromal cell-derived Schwann cells in peripheral nerve regeneration

Based on their differentiation ability, bone marrow stromal cells (MSCs) are a good source for cell therapy. Using a cynomolgus monkey peripheral nervous system injury model, we examined the safety and efficacy of Schwann cells induced from MSCs as a source for auto-cell transplantation therapy in nerve injury. Serial treatment of monkey MSCs with reducing agents and cytokines induced their differentiation into cells with Schwann cell properties at a very high ratio. Expression of Schwann cell markers was confirmed by both immunocytochemistry and reverse transcription-polymerase chain reaction. Induced Schwann cells were used for auto-cell transplantation into the median nerve and followed-up for 1 year. No abnormalities were observed in general conditions. Ki67-immunostaining revealed no sign of massive proliferation inside the grafted tube. Furthermore, 18F-fluorodeoxygluocose-positron emission tomography scanning demonstrated no abnormal accumulation of radioactivity except in regions with expected physiologic accumulation. Restoration of the transplanted nerve was corroborated by behavior analysis, electrophysiology and histological evaluation. Our results suggest that auto-cell transplantation therapy using MSC-derived Schwann cells is safe and effective for accelerating the regeneration of transected axons and for functional recovery of injured nerves. The practical advantages of MSCs are expected to make this system applicable for spinal cord injury and other neurotrauma or myelin disorders where the acceleration of regeneration is expected to enhance functional recovery.

Abstract 3656: Estradiol Improves Neural Functional Recovery After Nerve Injury by Reducing Inhibition of the Hedgehog-signaling Pathway

Background: Prior data indicate that estradiol (E2) favorably affects neovascularization in injured tissue, and that Sonic Hedgehog (Shh)-induced neovascularization is critical for nerve regeneration; however, little is known about the relationship between E2 and Shh signaling. We tested the hypothesis that E2 potentiates nerve regeneration via Shh-activated neoangiogen-esis. Methods and Results: Ovariectomized mice were subjected to unilateral sciatic nerve crush injury and treated with either E2 (via locally administered biodegradable polymer) or placebo (polymer alone). E2 treatment resulted in greater functional recovery of the nerve as evaluated by both exercise duration (P<0.05) and motor nerve conduction velocity (P<0.05), and intraneural vascularity was significantly higher in E2-treated animals than in the placebo-treatment group (P<0.05). Analyses of mRNA expression in the injured nerves of placebo-treated mice showed that the Shh pathway was activated immediately after injury, but Shh expression declined substantially within 7 days. Shh activation persisted in the E2-treatment group; Shh expression on day 7 was greater in E2-treated animals than in the placebo-treatment group (P<0.05). The expression of Hedgehog-interacting protein (HIP), an endogenous Shh inactivator, was significantly downregulated 24 hours after E2 treatment, and HIP downregulation was attenuated by the E2-receptor blocker ICI, suggesting that E2 augments Shh signaling both my enhancing Shh expression and by inhibiting HIP. Inhibition of HIP expression by E2 was also observed in vitro in Schwann cells and endothelial cells. The expression of Ptc1 (Shh receptor) and Gli1 (a downstream target of Shh) was evaluated in Ptc1-LacZ and Gli1-LacZ mice after nerve-crush injury. X-gal staining demonstrated that E2 treatment upregulated both Ptc1 and Gli1 expression within 3 days of surgery. Conclusions: E2 accelerates the functional recovery of injured nerves by enhancing angiogenesis. We propose that these effects occur in part through the inhibition of the Shh inactivator HIP, thereby preserving Shh activity after nerve injury. These findings may have identified a novel regulatory mechanism for nerve repair via E2-enhaced, Shh-mediated angiogenesis.

Schwann cell proliferation during Wallerian degeneration is not necessary for regeneration and remyelination of the peripheral nerves: Axon-dependent removal of newly generated Schwann cells by apoptosis

Peripheral nerve injury is followed by a wave of Schwann cell proliferation in the distal nerve stumps. To resolve the role of Schwann cell proliferation during functional recovery of the injured nerves, we used a mouse model in which injury-induced Schwann cell mitotic response is ablated via targeted disruption of cyclin D1. In the absence of distal Schwann cell proliferation, axonal regeneration and myelination occur normally in the mutant mice and functional recovery of injured nerves is achieved. This is enabled by pre-existing Schwann cells in the distal stump that persist but do not divide. On the other hand, in the wild type littermates, newly generated Schwann cells of injured nerves are culled by apoptosis. As a result, distal Schwann cell numbers in wild type and cyclin D1 null mice converge to equivalence in regenerated nerves. Therefore, distal Schwann cell proliferation is not required for functional recovery of injured nerves.

The Tinel sign: a historical perspective.

The Tinel sign is one of the most well-known and widely used clinical diagnostic tools in medicine. Aside from Jules Tinel, after whom the sign is named, several authors have described the famous "tingling" sign seen in regenerating injured nerves. In fact, Tinel was not the first to present the sign to the scientific community. The clinical value and utility of the Tinel sign have remained in question since its introduction; many may misinterpret the sign as a prelude to complete functional recovery of injured nerves, when in fact it only signals the progress of nerve regeneration. Today the Tinel sign is widely associated with the diagnosis of carpal tunnel syndrome and in the evaluation of regenerating peripherally injured nerves. Knowledge of the history and misconceptions surrounding the sign provides clinicians today with a greater appreciation of current debates on the use of the Tinel sign.

PCL-b-PEO Micelles as a Delivery Vehicle for FK506: Assessment of a Functional Recovery of Crushed Peripheral Nerve

The aim of this work was to test in vivo a new block copolymerbased delivery system containing lipophilic drug FK506, known as Tacrolimus. Tacrolimus is currently used in clinics as an immunosupressant agent, and more recently it has been shown that it can exert neurotrophic effects. We prepared, characterized, and assessed polycaprolactone-b-polyethylenoxyde (PCL-b-PEO) micelles containing FK506 in vitro and in vivo. By using well-established animal model of peripheral nerve injury (crushed sciatic nerve), we show that the rate of functional recovery of injured nerve is significantly enhanced in rats treated with micellar FK506. These findings support the notion that PCL-b-PEO is a suitable polymer material for FK506 and suggest its wider applicability as a delivery vehicle for other biologically active, poorly soluble therapeutic agents.