The long-range goal of this proposal is to define the mechanisms by which mutations in cardiac myosin binding protein C (MyBPC) cause hypertrophic cardiomyopathy (HCM), a disease that affects up to 1 in 200 individuals, and is the leading cause of sudden death in young adults. Nearly 60% of HCM cases are due to familial inheritance (FHC) of an autosomal dominant disorder caused by mutations in sarcomeric proteins. Mutations in MyBPC are among the most common causes of FHC accounting for half of all known cases. Because MyBPC is a critical modulator of actomyosin interactions, the initial functional deficit caused by mutations in MyBPC is expected to manifest as a defect in the regulation of cardiac muscle contraction at the myofilament level. Whereas 60% of MyBPC truncation mutations are expected to cause haploinsufficiency, the remaining 40% of MyBPC mutations are missense mutations, which are expected to produce full-length MyBPC. A large number of these missense mutations are located in the central domains of MyBPC (i.e., C3-C7), which have no specific known function, and thus it is unclear how FHC mutations located in this region of MyBPC cause disease. Our limited understanding of these critical mechanisms severely limits options for therapeutic intervention for FHC patients. Our preliminary data provide novel evidence that addresses our gap in knowledge and have identified two important regulatory regions within the C4 and C5 domains of MyBPC that modulate cardiac muscle contractile function. Based on these novel observations we have devised an experimental plan that is designed to elucidate molecular mechanisms by which these key regions contribute to regulation of contractile function and how FHC mutations alter this regulation. We have devised a multidisciplinary approach that spans from computational modeling of atomic interactions to whole animal physiology which will accomplished in three principal aims designed to: 1) Establish the functional effects of central domain MyBPC FHC mutations on the magnitude and rate of force in cardiac fibers isolated from mouse hearts expressing HCM causing mutations, and utilize molecular dynamic simulations to elucidate the molecular mechanisms of altered function. 2) Define how MyBPC mutations alter actin and myosin binding properties and rotational dynamics using TPA and FRET based sensors, and 3) Determine the in vivo functional consequences of MyBPC FHC mutations in MyBPC by assessing ventricular contractile and hemodynamic function, and test the efficacy of a MyBPC-specific AAV9 gene-transfer rescue that normalizes contractile function. Parallel studies will utilize FHC patient-specific induced pluripotent stem cell cardiomyocytes (iPSC-CM) to determine how these mutations cause disease in humans. It is expected that results from these integrative studies will provide novel insights of the underlying mechanisms by which mutations in MyBPC cause disease and will aid in the development of novel therapeutic strategies for treatment MyBPC related HCM.

Public Health Relevance

Familial hypertrophic cardiomyopathy (FHC) is highly prevalent inherited cardiac disease and is the most common cause of sudden death in adolescents and young adults. Mutations in cardiac myosin binding protein C (MyBPC) are a leading cause of FHC in humans, however, the mechanisms by which these mutations cause disease are not understood. This proposal will address this important deficiency in our understanding of the mechanisms of MyBPC related FHC, specifically, how they affect cardiac muscle function. Results from these studies will contribute to the development of novel therapies to improve cardiac function in MyBPC related FHC.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Cardiac Contractility, Hypertrophy, and Failure Study Section (CCHF)
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Adhikari, Bishow B
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Case Western Reserve University
Schools of Medicine
United States
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Li, Jiayang; Gresham, Kenneth S; Mamidi, Ranganath et al. (2018) Sarcomere-based genetic enhancement of systolic cardiac function in a murine model of dilated cardiomyopathy. Int J Cardiol 273:168-176
Mamidi, Ranganath; Li, Jiayang; Doh, Chang Yoon et al. (2018) Impact of the Myosin Modulator Mavacamten on Force Generation and Cross-Bridge Behavior in a Murine Model of Hypercontractility. J Am Heart Assoc 7:e009627
Mamidi, Ranganath; Gresham, Kenneth S; Li, Jiayang et al. (2017) Cardiac myosin binding protein-C Ser302 phosphorylation regulates cardiac ?-adrenergic reserve. Sci Adv 3:e1602445
Mamidi, Ranganath; Li, Jiayang; Gresham, Kenneth S et al. (2017) Dose-Dependent Effects of the Myosin Activator Omecamtiv Mecarbil on Cross-Bridge Behavior and Force Generation in Failing Human Myocardium. Circ Heart Fail 10:
Mamidi, Ranganath; Gresham, Kenneth S; Verma, Sujeet et al. (2016) Cardiac Myosin Binding Protein-C Phosphorylation Modulates Myofilament Length-Dependent Activation. Front Physiol 7:38
Gresham, Kenneth S; Stelzer, Julian E (2016) The contributions of cardiac myosin binding protein C and troponin I phosphorylation to ?-adrenergic enhancement of in vivo cardiac function. J Physiol 594:669-86
Mamidi, Ranganath; Gresham, Kenneth S; Li, Amy et al. (2015) Molecular effects of the myosin activator omecamtiv mecarbil on contractile properties of skinned myocardium lacking cardiac myosin binding protein-C. J Mol Cell Cardiol 85:262-72
Mamidi, Ranganath; Li, Jiayang; Gresham, Kenneth S et al. (2014) Cardiac myosin binding protein-C: a novel sarcomeric target for gene therapy. Pflugers Arch 466:225-30
Mamidi, Ranganath; Gresham, Kenneth S; Stelzer, Julian E (2014) Length-dependent changes in contractile dynamics are blunted due to cardiac myosin binding protein-C ablation. Front Physiol 5:461
Gresham, Kenneth S; Mamidi, Ranganath; Stelzer, Julian E (2014) The contribution of cardiac myosin binding protein-c Ser282 phosphorylation to the rate of force generation and in vivo cardiac contractility. J Physiol 592:3747-65

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