cMyBPC and Regulation of Myocardial Contraction

描述(申请人提供)：拟议实验的长期目标是了解肌球蛋白结合蛋白-C在心脏收缩调节中的功能。心肌肌球蛋白结合蛋白-C(CMyBPC)的突变占遗传性肥厚型心肌病的近一半，cMyBP-C在变力刺激下被磷酸化，但cMyBP-C突变致病的机制和cMyBP-C在介导心脏收缩反应中的作用都不是很清楚。到目前为止，解决MyBP-C功能的主要困难是无法系统性地改变cMyBP-C的含量或选择性地影响cMyBP-C的磷酸化状态而不同时影响其他肌丝蛋白。然而，在拟议的实验中，通过使用心脏中缺乏cMyBP-C的cMyBP-C基因敲除小鼠，这两个技术限制将被克服。因此，cMyBP-C基因敲除小鼠提供了一个测试cMyBP-C在健康和疾病中作用的特定机制假说的“零”背景。基于我们对cMyBP-C基因敲除小鼠的初步研究，指导这些实验的工作假设是cMyBP-C通常会限制跨桥动力学和功率输出，而cMyBP-C的磷酸化可以解除这种抑制。我们进一步认为，cMyBP-C的收缩效应是通过在两个不同的位点与肌球蛋白结合而介导的，并且cMyBP-C结合的效应因一个或两个位点的占据而不同。作为这一想法的推论，我们认为cMyBP-C N末端与肌球蛋白S2的无调控结合，就像在一些家族性肥厚型心肌病中可能发生的那样，足以导致心肌病。这些假说将在四个特定目标下进行验证，以确定1)cMyBP-C单独或联合与不同肌球蛋白结合部位结合的收缩效应；2)cMyBP-C与肌球蛋白S2结合影响的跨桥周期中的步骤；3)cMyBP-C磷酸化在介导对肾上腺素能刺激的收缩反应中的作用；以及4)cMyBP-C N端调控序列的表达是否足以以显性负性方式诱导心肌肥大。拟议的实验结果将提供有关MyBP-C的功能、肌球蛋白调节机制以及cMyBP-C突变导致人类疾病的机制的新的和相关的信息。

DESCRIPTION (provided by applicant): The long range goal of the proposed experiments is to understand the function of myosin binding protein-C in the regulation of cardiac contraction. Mutations in cardiac myosin binding protein-C (cMyBPC) account for nearly half of all instances of inherited hypertrophic cardiomyopathy and cMyBP-C is phosphorylated in response to inotropic stimuli, but neither the mechanisms by which mutations in cMyBP-C cause disease nor the role of cMyBP-C in mediating cardiac contractile responses are well understood. Until now the central difficulty in addressing the function of MyBP-C has been the inability to systematically alter cMyBP-C content or to selectively affect cMyBP-C phosphorylation state without simultaneously affecting other myofilament proteins. However, both these technical limitations will be overcome in the proposed experiments by using cMyBP-C knockout mice that lack cMyBP-C in heart. The cMyBP-C knockout mice therefore provide a "null" background on which to test specific mechanistic hypotheses of cMyBP-C function in health and disease. Based on our initial studies characterizing the cMyBP-C knockout mice, the working hypothesis guiding these experiments is that cMyBP-C normally acts to limit cross-bridge kinetics and power output and that phosphorylation of cMyBP-C relieves this inhibition. We further propose that the contractile effects of cMyBP-C are mediated by binding to myosin at two distinct sites and effects elicited by cMyBP-C binding differ depending on whether one or both sites are occupied. As a corollary to this idea, we propose that unregulated binding of the cMyBP-C N-terminus to myosin S2, as might occur in some familial hypertrophic cardiomyopathies, is sufficient to cause cardiomyopathy. These hypotheses will be tested in four Specific Aims designed to determine 1) contractile effects of cMyBP-C binding to distinct myosin binding sites, alone and in combination; 2) steps in the cross-bridge cycle affected by cMyBP-C binding to myosin S2; 3) the role of cMyBP-C phosphorylation in mediating contractile responses to padrenergic stimuli; and 4) whether expression of cMyBP-C N-terminal regulatory sequences is sufficient to induce cardiac hypertrophy in a dominant negative fashion. Results from the proposed experiments will provide new and relevant information regarding the function of MyBP-C, mechanisms of myosin regulation, and mechanisms by which mutations in the cMyBP-C cause human disease.