Profiling muscle-specific microRNA expression after peripheral denervation and reinnervation in a rat model

MicroRNAs (miRNAs) are a class of highly conserved, non-coding RNAs involved in post-transcriptional gene regulation. The muscle-specific miRNAs, miR-1, miR-133a, and miR-206, are expressed in skeletal muscles and have been shown to contribute to muscle development. To profile their expression after sciatic nerve denervation and reinnervation, the soleus muscles of the rats were analyzed with quantitative real-time PCR at 1 week, 1 month, 2 months, and 4 months after the experiments. In addition, a combined approach using computational prediction by the miRanda website and the Agilent Whole Rat Genome 4 x 44 k oligo microarray experiment was performed to investigate the potential target genes of these three miRNAs in the denervated and reinnervated muscles. The results revealed that with the first downregulation of miR-1 and miR-133a within 1 month in the denervated muscle, the expression of miR-1 and miR-133 increased by approximately 2-fold at 4 months after denervation and reinnervation; on the other hand, the expression of miR-206 was significantly increased to approximately 3-fold 1 month later only following reinnervation but not following denervation, and lasted at least for 4 months. The expression pattern of miR-206 was different from that of miR-1 and miR-133a. Notably, two genes (Hnrpu and Npy) and one gene (Ptprd) were potentially regulated both in the denervated and reinnervated muscle by miR-1 and miR-133a, respectively. There were six potential target genes (Hnrpu, Lsamp, MGC108776, Mef2, Npy, and Ppfibp2) of the upregulated miR-206 in the reinnervated muscle. Among these, three (Hnrpu, Npy, and MGC108776) were potentially regulated by both miR-1 and miR-206. Because the Mef2 transcription factor was reported to promote the transformation of type II fast glycolytic fibers into type I slow oxidative fibers, the upregulation of miR-206 with decreased expression of the Mef2 transcript in the 4 month reinnervated muscle, which presented type II fiber predominance 4 months after nerve microanastomosis, might indicate the role of miR-206 in determining the fiber type after peripheral nerve regeneration.