Wang Li, Kazmierczak Katarzyna, Yuan Chen-Ching, Yadav Sunil, Kawai Masataka, Szczesna-Cordary Danuta
Departments of Anatomy and Cell Biology and Internal Medicine, University of Iowa, IA, USA.
Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine, FL, USA.
FEBS J. 2017 Jun;284(12):1897-1913. doi: 10.1111/febs.14096. Epub 2017 May 25.
We have investigated the physiology and mechanical profiles of skinned papillary muscle fibers from transgenic mice expressing the N47K mutation in the myosin regulatory light chain (RLC), shown to cause hypertrophic cardiomyopathy in humans. The results were compared with wild-type (WT) mice, both expressing the human ventricular RLC. Rate constants of a cross-bridge (XB) cycle were deduced from tension transients induced by sinusoidal length changes during maximal Ca activation, and were studied as a function of MgATP, MgADP, and Pi concentrations. N47K mutant showed slower XB cycles but higher actin-activated ATPase activity compared with WT. Consequently, N47K exhibited larger tension than WT. K (ADP association constant) and K (equilibrium constant of force generation) were larger in N47K, and K (ATP association constant) was slightly larger in N47K vs. WT, demonstrating stronger nucleotide binding and force generation abilities of the mutant, but no changes in rigor acto-myosin binding were observed. Tension per XB was similar among groups, but N47K exhibited more XB distribution in the attached state. Larger values of tension and higher ATPase in N47K suggested that more cross-bridges participated in tension production in the mutant myocardium compared with WT. In vivo analysis of heart function, performed in ~ 12.5-month-old mice by echocardiography and invasive hemodynamics, demonstrated a significant decrease in dP/dt -end-diastolic volume relationship, indicating a depression of ventricular contractility in N47K mice. Our findings suggest that the N47K mutation exerts its action through direct alterations of myosin motor function that ultimately result in pathological hypertrophic remodeling in N47K hearts.
我们研究了在肌球蛋白调节轻链（RLC）中表达N47K突变的转基因小鼠的皮肤乳头肌纤维的生理学和力学特征，该突变在人类中可导致肥厚性心肌病。将结果与同样表达人类心室RLC的野生型（WT）小鼠进行比较。通过在最大钙激活期间由正弦长度变化诱导的张力瞬变推导横桥（XB）循环的速率常数，并研究其作为MgATP、MgADP和Pi浓度的函数。与WT相比，N47K突变体显示出较慢的XB循环，但肌动蛋白激活的ATP酶活性较高。因此，N47K表现出比WT更大的张力。N47K中的K（ADP结合常数）和K（力产生平衡常数）更大，而N47K中的K（ATP结合常数）与WT相比略大，表明突变体具有更强的核苷酸结合和力产生能力，但未观察到强直肌动球蛋白结合的变化。各组之间每个XB的张力相似，但N47K在附着状态下表现出更多的XB分布。N47K中较大的张力值和较高的ATP酶表明，与WT相比，突变体心肌中有更多的横桥参与张力产生。通过超声心动图和侵入性血流动力学对约12.5月龄小鼠进行的心脏功能体内分析表明，舒张末期容积与dP/dt的关系显著降低，表明N47K小鼠的心室收缩力降低。我们的研究结果表明，N47K突变通过直接改变肌球蛋白运动功能发挥作用，最终导致N47K心脏发生病理性肥厚重塑。
