Miller T, Szczesna D, Housmans P R, Zhao J, de Freitas F, Gomes A V, Culbreath L, McCue J, Wang Y, Xu Y, Kerrick W G, Potter J D
University of Miami School of Medicine, Departments of Molecular and Cellular Pharmacology and Physiology and Biophysics, Miami, Florida 33136 and the Department of Anesthesiology, Mayo Foundation, Rochester, Minnesota 55905.
J Biol Chem. 2001 Feb 9;276(6):3743-55. doi: 10.1074/jbc.M006746200. Epub 2000 Nov 1.
This study characterizes a transgenic animal model for the troponin T (TnT) mutation (I79N) associated with familial hypertrophic cardiomyopathy. To study the functional consequences of this mutation, we examined a wild type and two I79N-transgenic mouse lines of human cardiac TnT driven by a murine alpha-myosin heavy chain promoter. Extensive characterization of the transgenic I79N lines compared with wild type and/or nontransgenic mice demonstrated: 1) normal survival and no cardiac hypertrophy even with chronic exercise; 2) large increases in Ca(2+) sensitivity of ATPase activity and force in skinned fibers; 3) a substantial increase in the rate of force activation and an increase in the rate of force relaxation; 4) lower maximal force/cross-sectional area and ATPase activity; 5) loss of sensitivity to pH-induced shifts in the Ca(2+) dependence of force; and 6) computer simulations that reproduced experimental observations and suggested that the I79N mutation decreases the apparent off rate of Ca(2+) from troponin C and increases cross-bridge detachment rate g. Simulations for intact living fibers predict a higher basal contractility, a faster rate of force development, slower relaxation, and increased resting tension in transgenic I79N myocardium compared with transgenic wild type. These mechanisms may contribute to mortality in humans, especially in stimulated contractile states.
本研究对与家族性肥厚型心肌病相关的肌钙蛋白T（TnT）突变（I79N）的转基因动物模型进行了表征。为了研究该突变的功能后果，我们检测了由小鼠α-肌球蛋白重链启动子驱动的人心脏TnT的野生型和两个I79N转基因小鼠品系。与野生型和/或非转基因小鼠相比，对转基因I79N品系进行的广泛表征表明：1）即使长期运动，存活率正常且无心脏肥大；2）在脱纤维中，ATP酶活性和力的Ca(2+)敏感性大幅增加；3）力激活速率大幅增加，力松弛速率增加；4）最大力/横截面积和ATP酶活性降低；5）对pH诱导的力的Ca(2+)依赖性变化的敏感性丧失；6）计算机模拟重现了实验观察结果，并表明I79N突变降低了Ca(2+)从肌钙蛋白C的表观解离速率，并增加了横桥解离速率g。对完整活纤维的模拟预测，与转基因野生型相比，转基因I79N心肌的基础收缩性更高、力发展速率更快、松弛更慢且静息张力增加。这些机制可能导致人类死亡，尤其是在收缩状态受刺激时。
