The effect of calcium modulating agents on peripheral nerve recovery after crush

Calcium homeostasis in parvalbumin DRG neurons is altered after sciatic nerve crush and sciatic nerve transection injuries

Reflex abnormalities mediated by proprioceptive sensory neurons after peripheral nerve injury (PNI) can limit functional improvement, leaving patients with disability that affects their quality of life. We examined postinjury calcium transients in a subpopulation of dorsal root ganglion (DRG) neurons consisting primarily of proprioceptors to determine whether alterations in calcium homeostasis are present in proprioceptors, as has been documented in other DRG neurons after PNI. Using transgenic mice, we restricted expression of the calcium indicator GCaMP6s to DRG neurons containing parvalbumin (PV). Mice of both sexes were randomly assigned to sham, sciatic nerve crush, or sciatic nerve transection and resuture conditions. Calcium transients were recorded from ex vivo preparations of animals at one of three postsurgery time points: 1-3 days, 7-11 days, and after 60 days of recovery. Results demonstrated that the post-PNI calcium transients of PV DRG neurons are significantly different than sham. Abnormalities were not present during the acute response to injury (1-3 days), but transients were significantly different than sham at the recovery stage where axon regeneration is thought to be underway (7-11 days). During late-stage recovery (60 days postinjury), disturbances in the decay time course of calcium transients in transection animals persisted, whereas parameters of transients from crush animals returned to normal. These findings identify a deficit in calcium homeostasis in proprioceptive neurons, which may contribute to the failure to fully recover proprioceptive reflexes after PNI. Significant differences in the calcium transients of crush versus transection animals after reinnervation illustrate calcium homeostasis alterations are distinctive to injury type.NEW & NOTEWORTHY This study examines calcium homeostasis after peripheral nerve injury in dorsal root ganglion (DRG) neurons expressing parvalbumin, a group of large-diameter afferents primarily consisting of proprioceptors, using two-photon calcium imaging in the intact DRG. Our findings identify aberrant calcium homeostasis as an additional source of sensory neuron dysfunction following peripheral nerve injury, uncover differences between two injury models, and track how these changes develop and resolve over the course of recovery.

Gelatin hydrogel membrane containing carbonate hydroxyapatite for nerve regeneration scaffold

A scaffold that mimics physicochemical structure of nerve and supplies calcium ions in axonal environment is an attractive alternative for nerve regeneration, especially when applied in critical nerve defect. Various scaffold material, design, including their combination with several growth-induced substances and cells application have been being investigated and used in the area of nerve tissue engineering. However, the development remains challenges today because they are still far from ideal concerning their stability, reproducibility, including complicated handling related to the poor mechanical strength. In view of the current basis, in this study, the introduction of carbonated hydroxyapatite (CHA) as promising candidate to increase mechanical properties of nerve scaffold is reported. The incorporation of CHA was not only expected to provide better mechanical properties of the scaffold. Under physiological condition, CHA is known to be the most stable phases of calcium phosphate compound. Therefore, CHA was expected to provide controlled release calcium for better axonal environment and promote fasten nerve regeneration. This study shows that CHA incorporated gelatin membrane has ideal microstructure to prevent fibrous tissue ingrowth into the injury site, while retaining its capability to survive nerve tissue by allowing adequate glucose and specific proteins diffusion. The provided Ca²⁺ release to the environment promoted neuronal growth, without suppressing acetylcholine esterase release activity. Neurite elongation was dramatically higher in the gelatin membrane incorporated with CHA. Introduction of CHA into gelatin membrane represents a new generation medical device for nerve reconstruction, with CHA was considered as a promising factor.

Transcutaneous carbon dioxide application with hydrogel prevents muscle atrophy in a rat sciatic nerve crush model

The acceleration of nerve regeneration remains a clinical challenge. We previously demonstrated that transcutaneous CO₂ application using a novel hydrogel increases the oxygen concentration in local tissue via an "artificial Bohr effect" with the potential to prevent muscle atrophy. In this study, we investigated the effect of transcutaneous CO₂ administration on limb function after peripheral nerve injury in a rat sciatic nerve injury model. In total, 73 Sprague-Dawley rats were divided into a sham group, a control group (crush injury to sciatic nerve and no treatment) or a CO₂ group (crush injury with transcutaneous CO₂ application). CO₂ was administered percutaneously for 20 min five times per week. Scores for the sciatic function index and pinprick test were significantly higher in the CO₂ group than control group. The muscle wet weight ratios of the tibialis anterior and soleus muscles were higher in the CO₂ group than control group. Electrophysiological examination showed that the CO₂ group had higher compound motor action potential amplitudes and shorter distal motor latency than the control group. Histological examination of the soleus muscle sections at postoperative week 2 showed shorter fiber diameter in the control group than in the CO₂ group. The mRNA expression of Atrogin-1 and MuRF-1 was lower, mRNA expression of VEGF and myogenin and MyoD was higher in CO₂ group at postoperative week 2 compared to the control group.

CLINICAL SIGNIFICANCE

Transcutaneous CO₂ application has the therapeutic potential to accelerate the recovery of muscle atrophy in peripheral nerve injury. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1653-1658, 2018.

A small molecule screen identifies in vivo modulators of peripheral nerve regeneration in zebrafish

Adult vertebrates have retained the ability to regenerate peripheral nerves after injury, although regeneration is frequently incomplete, often leading to functional impairments. Small molecule screens using whole organisms have high potential to identify biologically relevant targets, yet currently available assays for in vivo peripheral nerve regeneration are either very laborious and/or require complex technology. Here we take advantage of the optical transparency of larval zebrafish to develop a simple and fast pectoral fin removal assay that measures peripheral nerve regeneration in vivo. Twenty-four hours after fin amputation we observe robust and stereotyped nerve regrowth at the fin base. Similar to laser mediated nerve transection, nerve regrowth after fin amputation requires Schwann cells and FGF signaling, confirming that the fin amputation assay identifies pathways relevant for peripheral nerve regeneration. From a library of small molecules with known targets, we identified 21 compounds that impair peripheral nerve regeneration. Several of these compounds target known regulators of nerve regeneration, further validating the fin removal assay. Twelve of the identified compounds affect targets not previously known to control peripheral nerve regeneration. Using a laser-mediated nerve transection assay we tested ten of those compounds and confirmed six of these compounds to impair peripheral nerve regeneration: an EGFR inhibitor, a glucocorticoid, prostaglandin D2, a retinoic acid agonist, an inhibitor of calcium channels and a topoisomerase I inhibitor. Thus, we established a technically simple assay to rapidly identify valuable entry points into pathways critical for vertebrate peripheral nerve regeneration.

Calcitonin pump improves nerve regeneration after transection injury and repair

INTRODUCTION

After nerve injury, excessive calcium impedes nerve regeneration. We previously showed that calcitonin improved nerve regeneration in crush injury. We aimed to validate the direct effect of calcitonin on transected and repaired nerve.

METHODS

Two rat groups (n = 8) underwent sciatic nerve transection followed by direct repair. In the calcitonin group, a calcitonin-filled mini-osmotic pump was implanted subcutaneously, with a catheter parallel to the repaired nerve. The control group underwent repair only, without a pump. Evaluation and comparison between the groups included: (1) compound muscle action potential recording of the extensor digitorum longus (EDL) muscle; (2) tetanic muscle force test of EDL; (3) nerve calcium concentration; and (4) nerve fiber count and calcified spot count.

RESULTS

The calcitonin pump group showed superior recovery.

CONCLUSIONS

Calcitonin affects injured and repaired peripheral nerve directly. The calcitonin-filled mini-osmotic pump improved nerve functional recovery by accelerating calcium absorption from the repaired nerve. This finding has potential clinical applications.