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Sci Transl Med. 2019 Jan 23;11(476). pii: eaat1199. doi: 10.1126/scitranslmed.aat1199.

Hypertrophic cardiomyopathy mutations in MYBPC3 dysregulate myosin.

Author information

1
Department of Genetics, Harvard Medical School, Boston, MA 02115, USA. christopher_toepfer@hms.harvard.edu cseidman@genetics.med.harvard.edu.
2
Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, OX3 9DU, UK.
3
Wellcome Centre for Human Genetics, University of Oxford, OX3 7BN, UK.
4
Department of Genetics, Harvard Medical School, Boston, MA 02115, USA.
5
Department of Cardiology, Children's Hospital Boston, Boston, MA 02115, USA.
6
Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA.
7
Department of Biochemistry and Cardiovascular Research Institute (CVRI), Yong Loo Lin School of Medicine, National University of Singapore, Singapore 119228, Singapore.
8
Institute for Experimental Medical Research, Oslo University Hospital and University of Oslo, 0318 Oslo, Norway.
9
Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA.
10
Department of Molecular Pharmacology and Therapeutics, Health Sciences Division, Loyola University Chicago, Maywood, IL 60153, USA.
11
Heart, Lung and Vascular Institute, University of Cincinnati, Cincinnati, OH 45219, USA.
12
Division of Cardiovascular Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA.

Abstract

The mechanisms by which truncating mutations in MYBPC3 (encoding cardiac myosin-binding protein C; cMyBPC) or myosin missense mutations cause hypercontractility and poor relaxation in hypertrophic cardiomyopathy (HCM) are incompletely understood. Using genetic and biochemical approaches, we explored how depletion of cMyBPC altered sarcomere function. We demonstrated that stepwise loss of cMyBPC resulted in reciprocal augmentation of myosin contractility. Direct attenuation of myosin function, via a damaging missense variant (F764L) that causes dilated cardiomyopathy (DCM), normalized the increased contractility from cMyBPC depletion. Depletion of cMyBPC also altered dynamic myosin conformations during relaxation, enhancing the myosin state that enables ATP hydrolysis and thin filament interactions while reducing the super relaxed conformation associated with energy conservation. MYK-461, a pharmacologic inhibitor of myosin ATPase, rescued relaxation deficits and restored normal contractility in mouse and human cardiomyocytes with MYBPC3 mutations. These data define dosage-dependent effects of cMyBPC on myosin that occur across the cardiac cycle as the pathophysiologic mechanisms by which MYBPC3 truncations cause HCM. Therapeutic strategies to attenuate cMyBPC activity may rescue depressed cardiac contractility in patients with DCM, whereas inhibiting myosin by MYK-461 should benefit the substantial proportion of patients with HCM with MYBPC3 mutations.

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