Exploration of the pathogenic mechanisms of inherited cardiomyopathies caused by cardiac troponin T mutations

在家族性扩张型心肌病(DCM)患者中发现的心肌肌钙蛋白T(CTnT)中编码K210的三个碱基对的缺失被引入到内源性基因中。与野生型小鼠相比，突变小鼠的细胞膜通透性心肌纤维对力产生的敏感性显著降低。突变小鼠心肌细胞钙瞬变峰值增加，完整心肌纤维产生的最大等长力与野生型小鼠无显著差异，提示突变小鼠心肌细胞钙瞬变增强是为了补偿肌丝敏感性下降。然而，突变小鼠出现了明显的心脏增大、心力衰竭和频繁的猝死，这概括了DCM患者的表型，表明由于肌丝钙敏感性降低而导致的心脏整体功能缺陷不能仅通过增加细胞内钙瞬变来完全补偿。我们发现，正性肌力药匹莫本丹能直接增加肌丝对钙离子的敏感性，对预防心脏增大、心力衰竭和猝死有深远的作用。这些结果证实了这样的假设，即心肌肌丝的Ca^&lt；2+&gt；脱敏是与该突变相关的DCM发病的绝对原因，并强烈表明，Ca^&lt；2+&gt；增敏剂对治疗受肌节调节蛋白突变影响的DCM患者是有益的。

We created knock-in mice in which a deletion of three base-pairs coding for K210 in cardiac troponin T (cTnT) found in familial dilated cardiomyopathy (DCM) patients was introduced into endogenous genes. Membrane-permeabilized cardiac muscle fibers from mutant mice showed significantly lower Ca^<2+> sensitivity in force generation than those from wild-type mice. Peak amplitude of Ca^<2+> transient in cardiomyocytes was increased in mutant mice, and maximum isometric force produced by intact cardiac muscle fibers of mutant mice was not significantly different from that of wild-type mice, suggesting that Ca^<2+> transient was augmented to compensate for decreased myofilament Ca^<2+> sensitivity. Nevertheless, mutant mice developed marked cardiac enlargement, heart failure and frequent sudden death recapitulating the phenotypes of DCM patients, indicating that global functional defect of the heart due to decreased myofilament Ca^<2+> sensitivity could not be fully compensated by just increasing the intracellular Ca^<2+> transient. We found that a positive inotropic agent, pimobendan, which directly increases myofilament Ca^<2+> sensitivity, had profound effects of preventing cardiac enlargement, heart failure and sudden death. These results verify the hypothesis that Ca^<2+> desensitization of cardiac myofilament is the absolute cause of the pathogenesis of DCM associated with this mutation and strongly suggest that Ca^<2+> sensitizers are beneficial for the treatment of DCM patients affected by sarcomeric regulatory protein mutations.