The mechanism of myoblast deformation in response to cyclic strain - A cytomechanical study

Mechanical strain is one of the important epigenetic factors that cause deformation and differentiation of skeletal muscles. This research was designed to investigate how myoblast deformation occurs after cyclic strain loading. Myoblasts were passaged three times and harvested; various cyclic strains (2.5kPa, 5kPa and 10kPa) were then loaded using a pulsatile mechanical system. The adaptive response of the myoblasts was observed at different time points (0.5h, 1h, 6h and 12h) post-loading. At the early stage of cyclic strain loading (<1h), almost no visible morphological changes were observed in the myoblasts. The actin cytoskeleton showed a disordered arrangement and a weak fluorescence expression; there was little expression of talin. At 6h and 12h post-loading, the myoblasts changed their orientation to parallel (in the 2.5kPa and 5kPa groups) or perpendicular (in the 10kPa group) to the direction of strain. Fluorescence expression of both the actin cytoskeleton and talin was significantly increased. The results suggest that cyclic strain has at least two ways to regulate adaptation of myoblasts: (1) by directly affecting actin cytoskeleton at an early stage post-loading to cause depolymerization; and (2) by later chemical signals transmitted from the extracellular side to intracellular side to initiate repolymerization.