Spatiotemporal Microrna Profile in Nerve Regeneration and Their Potential Role in Schwann Cell Migration

Purpose: While the peripheral nervous system has regenerative ability, restoration of sufficient function remains a challenge and a further understanding of the underlying biology of the regenerative process is essential.  The aims of this study were to profile the spatial and temporal expression levels of miRNAs, a class of small non-coding RNA that negatively regulates gene expression, in regenerating rat sciatic nerve after transection and explore the potential role of these miRNAs in Schwann-cell migration. 

Methods: An established rat sciatic nerve transection model combined with a nerve guide was used to investigate miRNA expression profiles at 4, 8, and 12 weeks following transection. RNA was isolated and pooled from the proximal and distal nerve ends, guide contents, and control nerve.  MiRNA expression was determined using microarray analysis and validated with qRT-PCR.  Pre-miRNA constructs were transfected into cell lines and migration potential was assessed. 

Results: Of 387 rat miRNAs analyzed, 185 (48%) were expressed in all samples. Using a standard 2-fold change as a cut-off, 62 miRNAs were differentially expressed in one or more samples compared to the control: 12 were increased and 50 decreased.  Fifty nine miRNAs were dynamically expressed in the distal nerve segment, a significantly higher proportion than observed in the guide or proximal end.  Several of the miRNAs down-regulated in the distal samples have predicted targets involved in cell migration, and were grouped together on two-way hierarchical clustering analysis.  Forced expression of select miRNAs into Schwann cells significantly reduced migration (p<0.05).  Specifically, miRNA-338, implicated in cell migration and reported to be highly expressed in Schwann cells, showed a steady increase in the regenerating proximal nerve over the course of the experiment. In the distal segment, expression levels of miRNA-338 were significantly reduced at 4 and 8 weeks (p<0.05) whereas at 12 weeks, expression was slightly higher than in the intact nerve.  An initial decrease was recorded in the guide contents; a sharp increased then occurred between 4 and 8 weeks followed by a plateau between 8 and 12 weeks. 

Conclusions: This study further elucidates the spatiotemporal profile of miRNAs in nerve regeneration and highlights the potential role of specific miRNAs in Schwann-cell migration.  These results have implication for further research avenues into the regenerative process, and may ultimately lead to enhanced therapies.