Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.11.10.375493v1?rss=1 Authors: Vander Roest, A. S., Liu, C., Morck, M. M., Kooiker, K. B., Jung, G., Song, D., Dawood, A., Jhingran, A., Pardon, G., Ranjbarvaziri, S., Fajardo, G., Zhao, M., Campbell, K. S., Pruitt, B., Spudich, J. A., Ruppel, K. M., Bernstein, D. Abstract: Hypertrophic cardiomyopathy (HCM) is the most common inherited form of heart disease, associated with over 1000 mutations, many in {beta}-cardiac myosin (MYH7). Molecular studies of myosin with different HCM mutations have revealed a diversity of effects on ATPase and load-sensitive rate of detachment from actin. It has been difficult to predict how such diverse molecular effects combine to influence forces at the cellular level and further influence cellular phenotypes. This study focused on the P710R mutation that dramatically decreases in vitro motility and actin-activated ATPase, in contrast to other MYH7 mutations. Optical trap measurements of single myosin molecules revealed that this mutation reduced the step size of the myosin motor and the load-sensitivity of the actin detachment rate. Conversely, this mutation destabilized the super-relaxed state in larger, two-headed myosin constructs, freeing more heads to generate force. Micropatterned hiPSC-cardiomyocytes CRISPR-edited with the P710R mutation produced significantly increased force (measured by traction force microscopy) compared with isogenic control cells. The P710R mutation also caused cardiomyocyte hypertrophy and cytoskeletal remodeling, as measured by immunostaining and electron microscopy. Cellular hypertrophy was prevented in the P710R cells by inhibition of ERK or Akt. Finally, we used a computational model that integrates measured molecular changes to demonstrate that predicted force traces match the forces measured in cells. These results confirm a key role for regulation of the super-relaxed state in driving hypercontractility in HCM and demonstrate the value of a multiscale approach in revealing key mechanisms of disease. Copy rights belong to original authors. Visit the link for more info