D.P.25 Mutation in lamin A/C gene causes mechanotransduction defects in human myoblasts

Abstract The mechanisms underlying myoblast response to mechanical forces are critical for muscle development and functionality. To initiate adequate mechanotransduction events, myoblasts must be able to sense strains in their extracellular cellular matrix (ECM) substrate, transmit forces to the cell interior and activate intracellular signaling. The presence of lamin A/C is critical for intact nucleoskeleton and mechanical transmission between the nucleus and the ECM. Whether mutation in the LMNA gene (encoding for lamin A/C) causes mechanotransduction defects in human myoblasts has never been directly tested. Myoblasts with LMNA p.Lys32del mutation (D32) were obtained from a 12 year-old boy suffering from LMNA-related congenital muscular dystrophy (L-CMD). Normal sex- and age-matched human myoblasts (WT) were used as controls. Myoblasts were immortalized, cultured in a 3D fibrin matrix. 3D constructs were subjected to axial cyclic stretch (10% amplitude, 0.5 Hz, 4 h). Confocal microscopy imaging and expression of mechanosensitive genes (Iex-1 and Ccnd-1) were analyzed. Unstrained D32 myoblasts had larger and more abundant actin bundles and longer and thinner nuclei ( p < 0.01) compared with WT. Repetitive strains induced a thickening of actin stress fibers, and an alignment of cells along the longitudinal axis of the 3D matrix in WT absent in D32 cells, while a significant nuclear elongation was observed in D32 but not in WT. Addition of blebbistatin, a myosin inhibitor or Y-27632, a Rho kinase inhibitor, abolished the strain-induced WT cytoskeleton reorganization and myoblasts alignment without changing WT nuclear shape. Milder effects on actin bundles were observed in D32. Strain-induced changes in the expression of Iex-1 and Ccnd-1 were higher in WT than in D32 ( p < 0.001). We provide first evidence that lamin A/C mutation causes mechanotransduction and cytoskeleton organization defects in human myoblasts and may contribute to mechanical damage in striated muscles from L-CMD.