A Laing distal myopathy–associated proline substitution in the β-myosin rod perturbs myosin cross-bridging activity
Massimo Buvoli, Genevieve C.K. Wilson, Ada Buvoli, Jack F. Gugel, Abbi Hau, Carsten G. Bönnemann, Carmen Paradas, David M. Ryba, Kathleen C. Woulfe, Lori A. Walker, Tommaso Buvoli, Julien Ochala, Leslie A. Leinwand
Massimo Buvoli, Genevieve C.K. Wilson, Ada Buvoli, Jack F. Gugel, Abbi Hau, Carsten G. Bönnemann, Carmen Paradas, David M. Ryba, Kathleen C. Woulfe, Lori A. Walker, Tommaso Buvoli, Julien Ochala, Leslie A. Leinwand
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Research Article Muscle biology

A Laing distal myopathy–associated proline substitution in the β-myosin rod perturbs myosin cross-bridging activity

Abstract

Proline substitutions within the coiled-coil rod region of the β-myosin gene (MYH7) are the predominant mutations causing Laing distal myopathy (MPD1), an autosomal dominant disorder characterized by progressive weakness of distal/proximal muscles. We report that the MDP1 mutation R1500P, studied in what we believe to be the first mouse model for the disease, adversely affected myosin motor activity despite being in the structural rod domain that directs thick filament assembly. Contractility experiments carried out on isolated mutant muscles, myofibrils, and myofibers identified muscle fatigue and weakness phenotypes, an increased rate of actin-myosin detachment, and a conformational shift of the myosin heads toward the more reactive disordered relaxed (DRX) state, causing hypercontractility and greater ATP consumption. Similarly, molecular analysis of muscle biopsies from patients with MPD1 revealed a significant increase in sarcomeric DRX content, as observed in a subset of myosin motor domain mutations causing hypertrophic cardiomyopathy. Finally, oral administration of MYK-581, a small molecule that decreases the population of heads in the DRX configuration, significantly improved the limited running capacity of the R1500P-transgenic mice and corrected the increased DRX state of the myofibrils from patients. These studies provide evidence of the molecular pathogenesis of proline rod mutations and lay the groundwork for the therapeutic advancement of myosin modulators.

Authors

Massimo Buvoli, Genevieve C.K. Wilson, Ada Buvoli, Jack F. Gugel, Abbi Hau, Carsten G. Bönnemann, Carmen Paradas, David M. Ryba, Kathleen C. Woulfe, Lori A. Walker, Tommaso Buvoli, Julien Ochala, Leslie A. Leinwand

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Figure 7

Markov model of mouse activity shows hidden running patterns.

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Markov model of mouse activity shows hidden running patterns. (A) Runnin...
(A) Running wheel activity of 2 representative 4-month-old βWT and R1500P male mice recorded during the circadian α phase. (B) Diagram of the discrete-time Markov chain used for modeling mouse running bouts and rests. The model transitions between 1 running and 3 resting states. The condition pss < pmm < pll guarantees that leaving the short, medium, and long rest states is increasingly difficult. (C) PMFs associated with the Markov model, giving the probability of the duration of every single run and rest. PMFs are shown with a linear (Lin) and a logarithmic (log) y axis. (D) PMFs associated with the Markov model describing the duration of a single resting bout. PMFs are shown with a linear and a logarithmic y axis. The last panel on the right reports the first 1,500 seconds of the log plot. Time windows of interest are labeled i–iii. (E) Probability density plot reporting the velocity distributions of the groups as determined experimentally. βWT mice, n = 7; βWT dosed mice, R1500P mice, and R1500P dosed mice, n = 10/group.