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Updated: Jun 3, 2025

Probing Myosin Ensemble Mechanics in Actin Filament Bundles Using Optical Tweezers
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A gradient of force generation at rest differentiates cardiomyopathy outcomes with variants of actin located at the

Michael R Jones1,2, Chau Tran1,2, Jaskerat Singh1,2

  • 1Department of Molecular & Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.

Journal of Molecular and Cellular Cardiology Plus
|January 13, 2025
PubMed

Insights

Cardiac actin variants R312H and R312C cause different cardiomyopathies, challenging the calcium sensitivity hypothesis. Residual myosin activity, not calcium sensitivity, may drive distinct disease development in hypertrophic and dilated cardiomyopathy.

Area of Science:

  • Cardiovascular Biology
  • Molecular Cardiology
  • Genetic Basis of Heart Disease

Background:

  • The calcium sensitivity hypothesis links sarcomere calcium sensitivity to hypertrophic (HCM) and dilated (DCM) cardiomyopathies.
  • Cardiac actin variants are implicated in HCM and DCM, generally supporting this hypothesis.
  • Two specific mutations (R312H and R312C) in cardiac actin (ACTC) present opposing disease phenotypes.

Purpose of the Study:

  • To investigate the molecular mechanisms differentiating HCM and DCM caused by ACTC R312H and R312C mutations.
  • To determine if altered calcium sensitivity or other factors explain the divergent disease outcomes.

Main Methods:

  • Characterization of recombinant R312H- and R312C-ACTC variant proteins.
  • Assessment of calcium sensitivity and residual myosin activity under varying conditions.

Main Results:

  • Both R312H and R312C ACTC variants showed identical changes in calcium sensitivity.
  • A gradient of increased residual myosin activity was observed with both variants under relaxing conditions.
  • These findings suggest calcium sensitivity alone does not explain the differing disease phenotypes.

Conclusions:

  • Factors beyond sarcomere calcium sensitivity likely contribute to the development of HCM and DCM.
  • Residual myosin activity may play a critical role in differentiating cardiomyopathy subtypes.
  • These insights are crucial for developing targeted therapies for cardiomyopathies.

Keywords:
ActinCardiovascular diseaseDilated cardiomyopathyHypertrophic cardiomyopathyMutationSarcomereTropomyosinTroponin

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