Decision letter: Prolonged cross-bridge binding triggers muscle dysfunction in a Drosophila model of myosin-based hypertrophic cardiomyopathy

K146N is a dominant mutation in human β-cardiac myosin heavy chain, which causes hypertrophic cardiomyopathy. We examined how Drosophila muscle responds to this mutation and integratively analyzed the biochemical, physiological and mechanical foundations of the disease. ATPase assays, actin motility, and indirect flight muscle mechanics suggest at least two rate constants of the cross-bridge cycle are altered by the mutation: increased myosin attachment to actin and decreased detachment, yielding prolonged binding. This increases isometric force generation, but also resistive force and work absorption during cyclical contractions, resulting in decreased work, power output, flight ability and degeneration of flight muscle sarcomere morphology. Consistent with prolonged cross-bridge binding serving as the mechanistic basis of the disease and with human phenotypes, 146N/+ hearts are hypercontractile with increased tension generation periods, decreased diastolic/systolic diameters and myofibrillar disarray. This suggests that screening mutated Drosophila hearts could rapidly identify hypertrophic cardiomyopathy alleles and treatments.

Download Full-text

Author response: Prolonged cross-bridge binding triggers muscle dysfunction in a Drosophila model of myosin-based hypertrophic cardiomyopathy

10.7554/elife.38064.025 ◽

2018 ◽

Cited By ~ 1

Author(s):

William A Kronert ◽

Kaylyn M Bell ◽

Meera C Viswanathan ◽

Girish C Melkani ◽

Adriana S Trujillo ◽

...

Keyword(s):

Hypertrophic Cardiomyopathy ◽

Author Response ◽

Muscle Dysfunction ◽

Cross Bridge ◽

Drosophila Model

Download Full-text

Faster cross-bridge detachment and increased tension cost in human hypertrophic cardiomyopathy with the R403QMYH7mutation

The Journal of Physiology ◽

10.1113/jphysiol.2014.274571 ◽

2014 ◽

Vol 592 (15) ◽

pp. 3257-3272 ◽

Cited By ~ 42

Author(s):

E. Rosalie Witjas-Paalberends ◽

Claudia Ferrara ◽

Beatrice Scellini ◽

Nicoletta Piroddi ◽

Judith Montag ◽

...

Keyword(s):

Hypertrophic Cardiomyopathy ◽

Cross Bridge ◽

Tension Cost

Download Full-text

Osmotic Compression Influences Cross-Bridge Detachment Rate in Transgenic Hypertrophic Cardiomyopathy Variant Hctnt-I79N and Non-Transgenic Mouse Cardiac Muscle

Biophysical Journal ◽

10.1016/j.bpj.2019.11.3223 ◽

2020 ◽

Vol 118 (3) ◽

pp. 596a

Author(s):

Maicon Landim Vieira ◽

Bjorn C. Knollmann ◽

Hyun S. Hwang ◽

Coen A. Ottenheijm ◽

J. Renato D. Pinto ◽

...

Keyword(s):

Hypertrophic Cardiomyopathy ◽

Cardiac Muscle ◽

Transgenic Mouse ◽

Cross Bridge ◽

Detachment Rate ◽

Osmotic Compression

Download Full-text

Hypertrophic cardiomyopathy mutation in cardiac troponin T (R95H) attenuates length-dependent activation in guinea pig cardiac muscle fibers

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00369.2017 ◽

2017 ◽

Vol 313 (6) ◽

pp. H1180-H1189 ◽

Cited By ~ 6

Author(s):

Alexis V. Mickelson ◽

Murali Chandra

Keyword(s):

Hypertrophic Cardiomyopathy ◽

Guinea Pig ◽

Central Region ◽

Cardiac Troponin ◽

Sarcomere Length ◽

Troponin T ◽

Cardiac Troponin T ◽

Cross Bridge ◽

Cardiac Muscle Fibers ◽

Length Dependent Activation

The central region of cardiac troponin T (TnT) is important for modulating the dynamics of muscle length-mediated cross-bridge recruitment. Therefore, hypertrophic cardiomyopathy mutations in the central region may affect cross-bridge recruitment dynamics to alter myofilament Ca2+ sensitivity and length-dependent activation of cardiac myofilaments. Given the importance of the central region of TnT for cardiac contractile dynamics, we studied if hypertrophic cardiomyopathy-linked mutation (TnTR94H)-induced effects on contractile function would be differently modulated by sarcomere length (SL). Recombinant wild-type TnT (TnTWT) and the guinea pig analog of the human R94H mutation (TnTR95H) were reconstituted into detergent-skinned cardiac muscle fibers from guinea pigs. Steady-state and dynamic contractile measurements were made at short and long SLs (1.9 and 2.3 µm, respectively). Our results demonstrated that TnTR95H increased pCa50 (−log of free Ca2+ concentration) to a greater extent at short SL; TnTR95H increased pCa50 by 0.11 pCa units at short SL and 0.07 pCa units at long SL. The increase in pCa50 associated with an increase in SL from 1.9 to 2.3 µm (ΔpCa50) was attenuated nearly twofold in TnTR95H fibers; ΔpCa50 was 0.09 pCa units for TnTWT fibers but only 0.05 pCa units for TnTR95H fibers. The SL dependency of rate constants of cross-bridge distortion dynamics and tension redevelopment was also blunted by TnTR95H. Collectively, our observations on the SL dependency of pCa50 and rate constants of cross-bridge distortion dynamics and tension redevelopment suggest that mechanisms underlying the length-dependent activation cardiac myofilaments are attenuated by TnTR95H. NEW & NOTEWORTHY Mutant cardiac troponin T (TnTR95H) differently affects myofilament Ca2+ sensitivity at short and long sarcomere length, indicating that mechanisms underlying length-dependent activation are altered by TnTR95H. TnTR95H enhances myofilament Ca2+ sensitivity to a greater extent at short sarcomere length, thus attenuating the length-dependent increase in myofilament Ca2+ sensitivity.

Download Full-text

Mavacamten Decreases Maximal Force and Ca2+-sensitivity in the N47K-Myosin Regulatory Light Chain Mouse Model of Hypertrophic Cardiomyopathy

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00345.2020 ◽

2020 ◽

Author(s):

Peter O Awinda ◽

Marissa Watanabe ◽

Yemeserach M. Bishaw ◽

Anna M Huckabee ◽

Keinan B Agonias ◽

...

Keyword(s):

Heart Disease ◽

Hypertrophic Cardiomyopathy ◽

Light Chain ◽

Isometric Force ◽

Regulatory Light Chain ◽

Isometric Tension ◽

Myosin Regulatory Light Chain ◽

Cardiac Myosin ◽

Cross Bridge ◽

Obstructive Hypertrophic Cardiomyopathy

Morbidity and mortality associated with heart disease is a growing threat to the global population and novel therapies are needed. Mavacamten (formerly called MYK-461) is a small molecule that binds to cardiac myosin and inhibits myosin ATPase. Mavacamten is currently in clinical trials for the treatment of obstructive hypertrophic cardiomyopathy (HCM), and it may provide benefits for treating other forms of heart disease. We investigated the effect of mavacamten on cardiac muscle contraction in two transgenic mouse lines expressing the human isoform of cardiac myosin regulatory light chain (RLC) in their hearts. Control mice expressed wild-type RLC (WT-RLC), and HCM mice expressed the N47K RLC mutation. In the absence of mavacamten, skinned papillary muscle strips from WT-RLC mice produced greater isometric force than strips from N47K mice. Adding 0.3 µM mavacamten decreased maximal isometric force and reduced Ca2+-sensitivity of contraction for both genotypes, but this reduction in pCa50 was nearly twice as large for WT-RLC vs. N47K. We also used stochastic length-perturbation analysis to characterize cross-bridge kinetics. The cross-bridge detachment rate was measured as a function of [MgATP] to determine the effect of mavacamten on myosin nucleotide handling rates. Mavacamten increased the MgADP release and MgATP binding rates for both genotypes, thereby contributing to faster cross-bridge detachment, which could speed myocardial relaxation during diastole. Our data suggest that mavacamten reduces isometric tension and Ca2+-sensitivity of contraction via decreased strong cross-bridge binding. Mavacamten may become a useful therapy for patients with heart disease, including some forms of HCM.

Download Full-text

Muscle dysfunction in hypertrophic cardiomyopathy: What is needed to move to translation?

Journal of Muscle Research and Cell Motility ◽

10.1007/s10974-014-9374-0 ◽

2014 ◽

Vol 35 (1) ◽

pp. 37-45 ◽

Cited By ~ 14

Author(s):

Corrado Poggesi ◽

Carolyn Y. Ho

Keyword(s):

Hypertrophic Cardiomyopathy ◽

Muscle Dysfunction

Download Full-text

Impact of familial hypertrophic cardiomyopathy-linked mutations in the NH2 terminus of the RLC on β-myosin cross-bridge mechanics

Journal of Applied Physiology ◽

10.1152/japplphysiol.00798.2014 ◽

2014 ◽

Vol 117 (12) ◽

pp. 1471-1477 ◽

Cited By ~ 6

Author(s):

Gerrie P. Farman ◽

Priya Muthu ◽

Katarzyna Kazmierczak ◽

Danuta Szczesna-Cordary ◽

Jeffrey R. Moore

Keyword(s):

Hypertrophic Cardiomyopathy ◽

Familial Hypertrophic Cardiomyopathy ◽

Sarcomeric Proteins ◽

Motion Generation ◽

In Vitro Motility Assay ◽

In Vitro Motility ◽

Cross Bridge ◽

Significant Difference ◽

The Impact

Familial hypertrophic cardiomyopathy (HCM) is associated with mutations in sarcomeric proteins, including the myosin regulatory light chain (RLC). Here we studied the impact of three HCM mutations located in the NH2 terminus of the RLC on the molecular mechanism of β-myosin heavy chain (MHC) cross-bridge mechanics using the in vitro motility assay. To generate mutant β-myosin, native RLC was depleted from porcine cardiac MHC and reconstituted with mutant (A13T, F18L, and E22K) or wild-type (WT) human cardiac RLC. We characterized the mutant myosin force and motion generation capability in the presence of a frictional load. Compared with WT, all three mutants exhibited reductions in maximal actin filament velocity when tested under low or no frictional load. The actin-activated ATPase showed no significant difference between WT and HCM-mutant-reconstituted myosins. The decrease in velocity has been attributed to a significantly increased duty cycle, as was measured by the dependence of actin sliding velocity on myosin surface density, for all three mutant myosins. These results demonstrate a mutation-induced alteration in acto-myosin interactions that may contribute to the pathogenesis of HCM.

Download Full-text