Biomechanical forces upregulate myogenic gene induction in the presence or absence of inflammation - a possible role of IGFR1-PI3K-AKT pathaway
Over the past decade, several studies have unraveled the important steps in skeletal muscle differentiation processes during which the members of bHLH transcription factors act synergistically with MEF2 family of co-factors to induce synthesis of muscle restricted target genes. In this study, we first induced C2C12 myoblasts to differentiate and characterized the phenotype of C2C12 cells by examining the expression patterns of crucial myogenic factors and its targets genes. Later, by means of an in vitro model system, cyclic equibiaxial stretching, and a proinflammatory cytokine, TNF-"?". We emulated the effects of tensile forces imposed on C2C12 cells during the process of differentiation. The results demonstrate that C2C12 myoblast-like cells respond to biomechanical signals in a magnitude-dependent manner, inhibiting rhTNF-"?"-induced Nos2a expression to various degrees in a magnitude/frequency dependent manner. Additionally, our findings suggest that CTS markedly upregulates the transcriptional activation of Myod1, Myog, Myh1, Myh2 and Myh4, and the final synthesis of MYHC and TPM1. The effects of TNF-"?" alone or in addition to CTS on IGFR1-PI3K-AKT pathway and the early events leading to AKT activation were examined next. We found that GSK3"?", a downstream target of AKT was phosphorylated by CTS as opposed to the unstretched groups. Further, our results show that after blocking the PI3K activity using LY294002 the CTS mediated phosphorylation of AKT is blocked at the Ser473. Finally by using different inhibitors such as AG1024 that blocks the actions of IGFR1 and IR kinases, pertussis toxin that blocks the effects of G-protein coupled receptor, we found that mechanotransduction occurs at the receptor level by activating multiple substrates including the growth factor, insulin and G-coupled receptors.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:biomechanical forces myogenesis inflammation
Date of Publication:01/01/2007