Hypertrophic cardiomyopathy (HCM) is the most common inherited form of heart disease, associated with over 1,000 mutations, many in β-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 decreased in vitro motility velocity 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 longer, two-headed myosin constructs, freeing more heads to generate force. Micropatterned human induced pluripotent derived stem cell (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 integrated the measured molecular changes to predict the measured traction forces. These results confirm a key role for regulation of the super relaxed state in driving hypercontractility in HCM with the P710R mutation and demonstrate the value of a multiscale approach in revealing key mechanisms of disease.

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Published in PNAS, v. 118, issue 24, e2025030118.

Copyright © 2021 the Author(s). Published by PNAS.

This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).

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This work was funded by NIH Grants RM1GM131981 to J.A.S., D.B., and B.L.P.; 1R21HL13099301 to D.B. and B.L.P.; HL117138 and GM033289 to J.A.S.; HL123655 to D.B.; and HL133359 and HL149164 to K.S.C. The microscope was funded by NIH Grant S10RR026775 to J.A.S. This work was funded by the Stanford Translational and Clinical Innovation Award (to D.B. and J.A.S.). A.S.V.R. and K.B.K. were supported by NIH Grant T32 HL094274. The study was also funded by American Heart Association Grant 17CSA33590101 to B.L.P. and D.B. and a American Heart Association Postdoctoral Fellowship (20POST35211011) to A.S.V.R. M.M.M. was supported by Stanford Cellular and Molecular Biology Training Grant T32GM007276. G.P. was supported by the Swiss National Science Foundation, the Early Postdoc Mobility Fellowship (P2SKP2_164954), the Postdoc Mobility Fellowship (P400PM_180825), and the American Heart Association Postdoc Fellowship (American Heart Association Award 18POST34080160). The hiPSC line(s) were obtained from Joseph C. Wu, MD, PhD, at the Stanford Cardiovascular Institute funded by NIH Grant 75N92020D00019.

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All study data are included in the article and/or supporting information. Previously published data were used for this work [A. S. Adhikari et al., β-cardiac myosin hypertrophic cardiomyopathy mutations release sequestered heads and increase enzymatic activity. Nat. Commun. 10, 2685 (2019).]

pnas.2025030118.sapp.pdf (1662 kB)

pnas.2025030118.sm01.avi (4895 kB)
Movie 1: Actin motility of WT β-cardiac myosin sS1-AC. Playback speed 3.5x.

pnas.2025030118.sm02.avi (5847 kB)
Movie 2: Actin motility of P710R β-cardiac myosin sS1-AC. Playback speed 3.5x.