Functional consequences of the human cardiac troponin I hypertrophic cardiomyopathy mutation R145G in transgenic mice
Functional consequences of the human cardiac troponin I hypertrophic cardiomyopathy mutation R145G in transgenic mice
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DOI：
10.1074/jbc.m801661200
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发表时间：
2008-07-18
影响因子：
4.8
通讯作者：
Kerrick, W. Glenn L.
中科院分区：
文献类型：
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作者：
Wen, Yuhui;Pinto, Jose Renato;Kerrick, W. Glenn L.
在这项研究中，我们研究了转基因小鼠心肌肌钙蛋白I （hcTnI）肥厚性心肌病R145G突变的功能后果。同时测量hcTnI R145G转基因小鼠（Tg-R145G）与hcTnI野生型转基因小鼠（Tg-WT）皮肤乳头状纤维中atp酶活性和力的结果显示，最大Ca2+激活力显著降低，但最大atp酶活性没有变化，而atp酶和力发展的Ca2+敏感性都有所增加。在相同水平的桥连接（激活状态）下，没有观察到桥周转率的差异，表明Ca2+敏感性的变化不是由于桥动力学的变化。能源成本计算表明，与Tg-WT光纤相比，Tg-R145G光纤的能耗更高。在pCa 9.0添加3mM 2,3-丁二酮单肟后，Tg-R145G纤维中有2-4%的力生成桥连接，而Tg-WT纤维中只有不到1.0%的力生成桥连接，这表明该突变削弱了心肌肌钙蛋白复合物在放松条件下完全抑制桥连接的能力。与Tg-WT相比，Tg-R145G观察到电刺激完整乳头肌的长时间力和细胞内[Ca2+]瞬态。这些结果表明，肥厚性心肌病的表型很可能是由心血管系统的代偿机制引起的，这些代偿机制是由以下因素激活的：1)每桥平均力的显著降低导致心脏能量消耗增加；2)延长[Ca2+]和力瞬变导致舒张减慢（舒张功能障碍）；3)Tg-R145G小鼠在缺乏Ca2+的情况下，心脏TnI无法完全抑制激活。
In this study, we addressed the functional consequences of the human cardiac troponin I (hcTnI) hypertrophic cardiomyopathy R145G mutation in transgenic mice. Simultaneous measurements of ATPase activity and force in skinned papillary fibers from hcTnI R145G transgenic mice (Tg-R145G) versus hcTnI wild type transgenic mice (Tg-WT) showed a significant decrease in the maximal Ca2+-activated force without changes in the maximal ATPase activity and an increase in the Ca2+ sensitivity of both ATPase and force development. No difference in the cross-bridge turnover rate was observed at the same level of cross-bridge attachment (activation state), showing that changes in Ca2+ sensitivity were not due to changes in cross-bridge kinetics. Energy cost calculations demonstrated higher energy consumption in Tg-R145G fibers compared with Tg-WT fibers. The addition of 3mM 2,3-butanedione monoxime at pCa 9.0 showed that there was similar to 2-4% of force generating cross-bridges attached in Tg-R145G fibers compared with less than 1.0% in Tg-WT fibers, suggesting that the mutation impairs the ability of the cardiac troponin complex to fully inhibit cross-bridge attachment under relaxing conditions. Prolonged force and intracellular [Ca2+] transients in electrically stimulated intact papillary muscles were observed in Tg-R145G compared with Tg-WT. These results suggest that the phenotype of hypertrophic cardiomyopathy is most likely caused by the compensatory mechanisms in the cardiovascular system that are activated by 1) higher energy cost in the heart resulting from a significant decrease in average force per cross-bridge, 2) slowed relaxation (diastolic dysfunction) caused by prolonged [Ca2+] and force transients, and 3) an inability of the cardiac TnI to completely inhibit activation in the absence of Ca2+ in Tg-R145G mice.