Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
Illinois Institute of Technology, Chicago, IL 60616, USA.
Cardiovasc Res. 2017 Aug 1;113(10):1124-1136. doi: 10.1093/cvr/cvx060.
The E143K (Glu → Lys) mutation in the myosin essential light chain has been associated with restrictive cardiomyopathy (RCM) in humans, but the mechanisms that underlie the development of defective cardiac function are unknown. Using transgenic E143K-RCM mice, we sought to determine the molecular and cellular triggers of E143K-induced heart remodelling.
The E143K-induced abnormalities in cardiac function and morphology observed by echocardiography and invasive haemodynamics were paralleled by augmented active and passive tension measured in skinned papillary muscle fibres compared with wild-type (WT)-generated force. In vitro, E143K-myosin had increased duty ratio and binding affinity to actin compared with WT-myosin, increased actin-activated ATPase activity and slower rates of ATP-dependent dissociation of the acto-myosin complex, indicating an E143K-induced myosin hypercontractility. E143K was also observed to reduce the level of myosin regulatory light chain phosphorylation while that of troponin-I remained unchanged. Small-angle X-ray diffraction data showed a decrease in the filament lattice spacing (d1,0) with no changes in the equatorial reflections intensity ratios (I1,1/I1,0) in E143K vs. WT skinned papillary muscles. The hearts of mutant-mice demonstrated ultrastructural defects and fibrosis that progressively worsened in senescent animals and these changes were hypothesized to contribute to diastolic disturbance and to mild systolic dysfunction. Gene expression profiles of E143K-hearts supported the histopathology results and showed an upregulation of stress-response and collagen genes. Finally, proteomic analysis evidenced RCM-dependent metabolic adaptations and higher energy demands in E143K vs. WT hearts.
As a result of the E143K-induced myosin hypercontractility, the hearts of RCM mice model exhibited cardiac dysfunction, stiff ventricles and physiological, morphologic, and metabolic remodelling consistent with the development of RCM. Future efforts should be directed toward normalization of myosin motor function and the use of myosin-specific therapeutics to avert the hypercontractile state of E143K-myosin and prevent pathological cardiac remodelling.
肌球蛋白必需轻链中的 E143K（Glu→Lys）突变与人类限制性心肌病（RCM）有关，但导致心脏功能缺陷的发展的机制尚不清楚。本研究使用 E143K-RCM 转基因小鼠，旨在确定 E143K 诱导心脏重塑的分子和细胞触发因素。
超声心动图和侵入性血液动力学观察到的 E143K 引起的心脏功能和形态异常与比野生型（WT）产生的力更大的去皮乳头肌纤维中测量的主动和被动张力增强相平行。在体外，与 WT-肌球蛋白相比，E143K-肌球蛋白具有更高的占空比和与肌动蛋白的结合亲和力，增加了肌球蛋白的肌动球蛋白激活的 ATP 酶活性和肌球蛋白与肌动蛋白复合物的 ATP 依赖性解离的更慢速率，表明 E143K 诱导的肌球蛋白过度收缩。还观察到 E143K 降低了肌球蛋白调节轻链的磷酸化水平，而肌钙蛋白-I 的水平保持不变。小角 X 射线衍射数据显示，E143K 与 WT 去皮乳头肌相比，细丝晶格间距（d1,0）减小，而赤道反射强度比（I1,1/I1,0）不变。突变型小鼠的心脏表现出超微结构缺陷和纤维化，随着衰老动物的进展而逐渐恶化，这些变化被假设为导致舒张功能障碍和轻度收缩功能障碍的原因。E143K 心脏的基因表达谱支持组织病理学结果，并显示应激反应和胶原蛋白基因的上调。最后，蛋白质组学分析证明了 RCM 依赖的代谢适应和 E143K 与 WT 心脏的更高能量需求。
由于 E143K 诱导的肌球蛋白过度收缩，RCM 小鼠模型的心脏表现出心脏功能障碍、心室僵硬以及与 RCM 发展一致的生理、形态和代谢重塑。未来的努力应该致力于肌球蛋白运动功能的正常化和肌球蛋白特异性治疗的使用，以避免 E143K 肌球蛋白的过度收缩状态并防止病理性心脏重塑。
