Regulation of alternative splicing of skeletal muscle Troponin T in C2C212 myotubes in response to cyclic strain and manipulation of mTORC1 signaling

Abstract

Experimental manipulation of body weight in rats causes precise adjustments to the pattern of fast skeletal muscle troponin T (TNNT3) alternative splicing, so that it matches that of animals with actual body weight equivalent to that of the weight-manipulated rats. In this study, we examined muscle cell-autonomous TNNT3 alternative splicing responses to increased strain, and the potential role of the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway in mediating these responses. To this end, C2C12 myotubes were exposed to intermittent cyclic strain (0.5Hz, 15%) for 24–48 hours, in the presence or absence of rapamycin. After treatment, we measured the relative abundance of individual TNNT3 splice forms in the total TNNT3 mRNA mixture, and quantified phosphorylation of S6K1, a downstream effector of mTORC1. Experimentally imposed strain caused significant alterations to the relative abundance of TNNT3 splice forms that correlated with observed changes in mTORC1 signaling. Rapamycin treatment caused effects that either were independent of, or attenuated specific TNNT3 splice form responses to imposed strain regimes. To our knowledge, these findings are the first to demonstrate effects of cyclic strain on TNNT3 alternative splicing in muscle cell culture, and suggest a modulatory role of mTORC1 signaling in the regulation of TNNT3 alternative splicing in vivo. (Supported by NIH grant DK-15658)