Delayed nerve stimulation promotes axon-protective neurofilament phosphorylation, accelerates immune cell clearance and enhances remyelination in vivo in focally demyelinated nerves.

Nikki A Mclean,Bogdan F Popescu,Valerie M K Verge,Douglas W Zochodne,Tessa Gordon,Catherine Faivre-Sarrailh

doi:10.1371/journal.pone.0110174

Abstract

Rapid and efficient axon remyelination aids in restoring strong electrochemical communication with end organs and in preventing axonal degeneration often observed in demyelinating neuropathies. The signals from axons that can trigger more effective remyelination in vivo are still being elucidated. Here we report the remarkable effect of delayed brief electrical nerve stimulation (ES; 1 hour @ 20 Hz 5 days post-demyelination) on ensuing reparative events in a focally demyelinated adult rat peripheral nerve. ES impacted many parameters underlying successful remyelination. It effected increased neurofilament expression and phosphorylation, both implicated in axon protection. ES increased expression of myelin basic protein (MBP) and promoted node of Ranvier re-organization, both of which coincided with the early reappearance of remyelinated axons, effects not observed at the same time points in non-stimulated demyelinated nerves. The improved ES-associated remyelination was accompanied by enhanced clearance of ED-1 positive macrophages and attenuation of glial fibrillary acidic protein expression in accompanying Schwann cells, suggesting a more rapid clearance of myelin debris and return of Schwann cells to a nonreactive myelinating state. These benefits of ES correlated with increased levels of brain derived neurotrophic factor (BDNF) in the acute demyelination zone, a key molecule in the initiation of the myelination program. In conclusion, the tremendous impact of delayed brief nerve stimulation on enhancement of the innate capacity of a focally demyelinated nerve to successfully remyelinate identifies manipulation of this axis as a novel therapeutic target for demyelinating pathologies.

Highlights

Myelination is crucial for proper neurological function, with damage to the myelin sheath having potentially devastating consequences
The 5 day post-lysophosphatidyl choline (LPC) demyelination site was readily identified by the joint presence of FG (Figure 1B), diminished myelin basic protein (MBP; a component of myelin Figure 1C) immunofluorescence (IF) and IF for beta III tubulin (b-III) tubulin, an axonal marker (Figure 1D)
The loss of MBP signal did not extend beyond the FG-positive regions of interest (ROIs), with consistent demyelination observed in the FG-defined ROI at 5 days (d) post-LPC (Figure 1A)

Summary

Introduction

Myelination is crucial for proper neurological function, with damage to the myelin sheath having potentially devastating consequences. Despite an increased capacity for peripheral nerve remyelination in patients with Guillain-Barresyndrome [2,4], many are plagued by residual impairment [4,5] as effective remyelination and repair of focally demyelinated nervous tissue is fraught with challenges. One of these challenges is the increased loss of axons observed in demyelinating disorders, believed to be due to the vulnerability of the demyelinated axon to degenerative processes (reviewed in [6,7]). Neurofilament phosphorylation is controlled by the myelination process [18] and upon demyelination, these filaments become dephosphorylated, both in experimental models of dysmyelination [19] and in human demyelinating disease states [20]

Methods

Results

Discussion

Conclusion