Biomechanical effects on microRNA expression in skeletal muscle differentiation

We examined whether mechanical stretch affected expression of muscle-specific microRNAs (miRNAs) that regulate proliferation (miR-133a) or differentiation (miR-1, -206). Real-time quantitative RT-PCR was used to assess miRNA regulation in the murine myoblast cell line C2C12 exposed to stretch regimens that promote either proliferation (high stretch: 17%, 1 Hz) or differentiation (moderate stretch: 10%, 0.5 Hz) after adding media that promotes differentiation. Controls consisted of myoblasts cultured under static conditions. While miRNA expression was not affected by high stretch, a significant effect of stretch (P < 0.05) was seen after 4 days with the moderate stretch regimen. All three microRNAs were upregulated by stretch, with the most significant increase for miR-1. Myoblast maturation was enhanced with a moderate stretch regimen, as assessed by a higher percentage of nuclei in straited fibers and an increase in Mef2c gene expression. Correspondingly, HDAC4 protein expression, a direct target of miR-1 and repressor of Mef2, was decreased with the moderate stretch regimen. Over-expression of miR-1 abrogated the effect of stretch on miR-1, miR-133a and miR-206 levels compared to its negative control but did not alter miR-133a or miR-206 levels. Treatment with an antisense mRNA to miR-1 similarly diminished the stretch-mediated response. Results indicate that the differential response of skeletal myoblasts to moderate and high stretch cyclic stretch regimens is due, in part, to muscle specific miRNA expression.