Ablation of cardiac myosin-binding protein-C accelerates contractile kinetics in engineered cardiac tissue

Abstract

Hypertrophic cardiomyopathy (HCM) caused by mutations in cardiac myosin-binding protein-C (cMyBP-C) is a heterogenous disease in which the phenotypic presentation is influenced by genetic, environmental, and developmental factors. Though mouse models have been used extensively to study the contractile effects of cMyBP-C ablation, early postnatal hypertrophic and dilatory remodeling may overshadow primary contractile defects. The use ofa murine engineered cardiac tissue (mECT) model of cMyBP-C ablation in the present study permits delineation ofthe primary contractile kinetic abnormalitiesin an intact tissue model under mechanical loading conditions in the absence of confounding remodeling events. We generated mechanically integrated mECT using isolated post-natal day 1 mouse cardiac cells from both wild-type (WT) and cMyBP-C-null hearts. After culturing for 1 wk to establish coordinated spontaneous contraction, we measured twitch force and Ca2+transients at 37°C during pacing at 6 and 9 Hz, with and without dobutamine. Compared with WT, the cMyBP-C-null mECT demonstrated faster latecontraction kinetics and significantly faster early relaxation kinetics with no difference in Ca2+ transientkinetics. Strikingly, the ability of cMyBP-C-null mECT to increase contractile kinetics in response to adrenergicstimulation and increased pacing frequency were severely impaired. We conclude that cMyBP-C ablation resultsin constitutively accelerated contractilekinetics with preserved peak force with minimal contractile kinetic reserve. These functional abnormalities precede the development of the hypertrophic phenotype and do not result from alterations in Ca2+ transient kinetics, suggesting that alterations in contractile velocity may serveasthe primaryfunctional trigger for the development of hypertrophy in this model of HCM. Our findings stronglysupport a mechanism in which cMyBP-C functions as a physiological brake on contraction by positioning myosin headsaway from the thin filament, aconstraint which is removed upon adrenergic stimulation or cMyBP-C ablation. © 2013 de Lange et al.