Myosin Isoforms in Relation to Function in Human Heart

描述(申请人提供)：在左心室表达的肌球蛋白重链(MHC)亚型是哺乳动物心脏做功能力的主要决定因素。直到最近，流行的观点是成人的脑室表达几乎100%的βMHC(一种慢的异构体)，但当代的研究表明，正常人的脑室在以βMHC为主的背景下表达少量的αMHC(一种快速的异构体)，而衰竭的人的脑室表达100%的βMHC，几乎不表达αMHC。这些结果引发的问题是，阿尔法MHC的表达是否有助于正常人体心室的压力上升速度，以及阿尔法MHC的缺失是否有助于人类衰竭心脏的收缩性能下降。这个项目将基于一个工作假设来解决这些可能性，即少量αMHC的表达显著加快正常心肌力发展的动力学，相反，αMHC表达的减少有助于心力衰竭时力(压力)发展的抑制动力学。拟议的实验将评估由于改变α和βMHC的比例而对收缩特性的影响：(I)通过控制动物的甲状腺状态而改变MHC表达的啮齿动物心肌，以及(Ii)正常人类心脏(不用于移植的供者心脏)和衰竭心脏(移植受者的移植心脏)的心肌。力的发展和松弛的速率常数将通过笼状钙离子螯合剂光解后的力的变化来评估。结果将被用来模拟肌球蛋白亚型表达改变对大鼠和人类心肌的抽动动力学和幅度的影响。其他力学实验将研究α-MHC和β-MHC在决定心肌的功率和牵张激活反应中的作用。使用肌肉样本的MHC异构体特异性抗体和SDS-PAGE的免疫组织化学方法将量化左心室区域的MHC异构体表达模式，以测试MHC表达与收缩期壁压力相关的想法。这些研究的结果应该会为人类心力衰竭中心脏功能下降的机制提供新的见解，并应该为这种疾病的治疗提供新的治疗靶点。

DESCRIPTION (provided by applicant): The myosin heavy chain (MHC) isoforms expressed in the left ventricle are primary determinants of the work capacity of mammalian hearts. Until recently, the prevailing view was that adult human ventricles expressed virtually 100% beta MHC (a slow isoform), but contemporary studies have shown that normal human ventricles express small amounts of alpha MHC (a fast isoform) on a predominantly beta MHC background and that failing human ventricles express 100% beta MHC and virtually no alpha MHC. Questions that arise from these results are whether expression of alpha MHC contributes to the rate of rise of pressure in normal human ventricles and whether loss of alpha MHC contributes to the depressed contractile performance of human failing hearts. This project will address these possibilities based on the working hypothesis that expression of small amounts of alpha MHC significantly speeds the kinetics of force development in normal myocardium, and conversely, reduced expression of alpha MHC contributes to depressed kinetics of force (pressure) development in heart failure. The proposed experiments will assess the effects on contractile properties due to altered ratios of alpha and betaa MHC expression in (i) rodent myocardium in which MHC expression is varied by manipulating thyroid status of the animals and (ii) myocardium from normal human hearts (donor hearts not used for transplant) and failing hearts (explanted hearts from transplant recipients). Rate constants of force development and relaxation will be assessed from changes in force following photolysis of caged Ca 2+ chelators. Results will then be used to model the effects of altered myosin isoform expression on twitch kinetics and amplitude in both rat and human myocardium. Additional mechanical experiments will investigate the roles of alpha MHC and beta MHC in determining the power and stretch activation responses of myocardium. Immunohistochemistry using MHC-isoform specific antibodies and SDS-PAGE of muscle samples will quantify MHC isoform expression patterns in regions of the left ventricle to test the idea that MHC expression varies in relation to systolic wall stress. Results from these studies should provide new insights into mechanisms of depressed myocardial function in human heart failure and should also suggest new therapeutic targets for treatment of this disease.