Analysis of Schwann Cell Migration and Axon Regeneration Following Nerve Injury in the Sciatic Nerve Bridge.

Bing Chen,David B Parkinson,Xin-Peng Dun,Quan Chen

doi:10.3389/fnmol.2019.00308

Abstract

While it is proposed that interaction between Schwann cells and axons is key for successful nerve regeneration, the behavior of Schwann cells migrating into a nerve gap following a transection injury and how migrating Schwann cells interact with regenerating axons within the nerve bridge has not been studied in detail. In this study, we combine the use of our whole-mount sciatic nerve staining with the use of a proteolipid protein-green fluorescent protein (PLP-GFP) mouse model to mark Schwann cells and have examined the behavior of migrating Schwann cells and regenerating axons in the sciatic nerve gap following a nerve transection injury. We show here that Schwann cell migration from both nerve stumps starts later than the regrowth of axons from the proximal nerve stump. The first migrating Schwann cells are only observed 4 days following mouse sciatic nerve transection injury. Schwann cells migrating from the proximal nerve stump overtake regenerating axons on day 5 and form Schwann cell cords within the nerve bridge by 7 days post-transection injury. Regenerating axons begin to attach to migrating Schwann cells on day 6 and then follow their trajectory navigating across the nerve gap. We also observe that Schwann cell cords in the nerve bridge are not wide enough to guide all the regenerating axons across the nerve bridge, resulting in regenerating axons growing along the outside of both proximal and distal nerve stumps. From this analysis, we demonstrate that Schwann cells play a crucial role in controlling the directionality and speed of axon regeneration across the nerve gap. We also demonstrate that the use of the PLP-GFP mouse model labeling Schwann cells together with the whole sciatic nerve axon staining technique is a useful research model to study the process of peripheral nerve regeneration.

Highlights

Peripheral nerve injuries are common in both civil and military environments and are primarily transection injuries (Deumens et al, 2010; Ray and Mackinnon, 2010; Daly et al, 2012)
Previous studies have confirmed that Schwann cells of the peripheral nerves express high levels of GFP in the proteolipid proteingreen fluorescent protein (PLP-GFP) mouse model, which allows us to accurately visualize Schwann cell behavior and migration following sciatic nerve transection (Mallon et al, 2002; Cattin et al, 2015; Carr et al, 2017; Stierli et al, 2018; Dun et al, 2019)
In agreement with previous findings using the S100 marker to identify migrating Schwann cells (Parrinello et al, 2010; Cattin et al, 2015), we observed that GFP positive Schwann cells start to migrate into the nerve bridge from both proximal and distal nerve ends at 4 days post-transection in our whole-mount PLP-GFP sciatic nerve preparations (Figure 1A)

Summary

Introduction

Peripheral nerve injuries are common in both civil and military environments and are primarily transection injuries (Deumens et al, 2010; Ray and Mackinnon, 2010; Daly et al, 2012). In elegant experiments using a vascular endothelial growth factor (VEGF) bound bead to misdirect both blood vessel regeneration and Schwann cell migration in the rat sciatic nerve gap, regenerating axons followed the path of ectopic migrating Schwann cells and left the nerve bridge (Cattin et al, 2015). These findings showed that Schwann cells play a pivotal role in controlling the directionality of regenerating axons in the peripheral nerve gap. How migrating Schwann cells interact with regenerating axons in the peripheral nerve bridge during regeneration has not been fully studied, largely due to the inability to visualize Schwann cell-axon interaction in vivo, and this is the purpose of this current study

Methods

Results

Conclusion