Myosin Isoforms in Relation to Function in Human Heart

描述（由申请人提供）：在左心室表达的肌球蛋白重链（MHC）亚型是哺乳动物心脏工作能力的主要决定因素。直到最近，流行的观点是成年人的心室几乎100%表达β - MHC（一种慢亚型），但当代研究表明，正常人的心室在主要是β - MHC的背景下表达少量α - MHC（一种快亚型），而衰竭的人的心室表达100% β - MHC，几乎没有α - MHC。从这些结果中产生的问题是，α - MHC的表达是否导致了正常人类心室压力的上升速度，α - MHC的缺失是否导致了人类衰竭心脏收缩性能的下降。该项目将根据工作假设解决这些可能性，即少量α MHC的表达显着加速了正常心肌的力发展动力学，相反，α MHC表达的减少有助于心力衰竭中力（压力）发展动力学的抑制。拟议的实验将评估由于α和β - MHC表达比例的改变对收缩特性的影响，在(i)啮齿动物心肌中，MHC表达通过操纵动物的甲状腺状态而改变；（ii）来自正常人类心脏（未用于移植的供体心脏）和衰竭心脏（来自移植受体的移植心脏）的心肌中。力发展和弛豫的速率常数将通过笼状ca2 +螯合剂光解后力的变化来评估。结果将用于模拟肌球蛋白异构体表达改变对大鼠和人心肌抽搐动力学和振幅的影响。进一步的力学实验将探讨α - MHC和β - MHC在决定心肌力量和拉伸激活反应中的作用。利用MHC异构体特异性抗体和肌肉样本SDS-PAGE的免疫组织化学将量化左心室区域MHC异构体的表达模式，以检验MHC表达与收缩壁压力相关的观点。这些研究结果将为人类心力衰竭心肌功能下降的机制提供新的见解，并为治疗这种疾病提供新的治疗靶点。

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.