Biomechanical characterization of striated muscle cells from R155C VCP knock-in and W2710X filamin C knock-in mice: a novel approach to understand the pathogenesis of myofibrillar myopathies

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Myofibrillar myopathies (MFMs) are a group of sporadic and hereditary skeletal and cardiac muscle diseases that lead to severe physical disability and premature death. MFMs are caused by mutations in genes encoding desmin, filamin C, plectin, VCP, FHL1, ZASP, myotilin, alpha-B-crystallin, and BAG3. First results from our biomechanical studies on primary human myoblasts carrying desmin -and plectin mutations showed an increased stiffness and reduced mechanical stress tolerance in the form of higher mechanical vulnerability compared to control cells. We hypothesize that the higher stiffness of mutant cells leads to higher intracellular stress at physiologic stretch and shear deformations, which in turn triggers muscle fiber degeneration. In the present project, we will test this hypothesis using immortalized myoblast cells obtained from two MFM mouse models. Through the DFG research consortium FOR1228, we have access to two knock-in mouse models (R155C VCP, and W2710X filamin C), which harbor the most frequent human pathogenic VCP and filamin C mutations. Using traction force microscopy, magnetic tweezer microrheology, and a cell stretcher together with high resolution (temporal and spatial) confocal microscopy, we will address two key questions: (i) what is the influence of these mutations on the biomechanical function of cultured myoblasts and myotubes derived from skeletal muscle tissue, and (ii) what are the molecular processes that lead to altered mechanical stress tolerance in these cells. This project will provide the first insight into the biomechanical aspects of the pathogenesis of VCP- and filamin C-related myopathies.