Mickelson Alexis V, Gollapudi Sampath K, Chandra Murali
Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington.
Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, Washington
Am J Physiol Heart Circ Physiol. 2017 Jan 1;312(1):H141-H149. doi: 10.1152/ajpheart.00487.2016. Epub 2016 Oct 21.
The present study investigated the functional consequences of the human hypertrophic cardiomyopathy (HCM) mutation A28V in cardiac troponin T (TnT). The A28V mutation is located within the NH terminus of TnT, a region known to be important for full activation of cardiac thin filaments. The functional consequences of the A28V mutation in TnT remain unknown. Given how α- and β-myosin heavy chain (MHC) isoforms differently alter the functional effect of the NH terminus of TnT, we hypothesized that the A28V-induced effects would be differently modulated by α- and β-MHC isoforms. Recombinant wild-type mouse TnT (TnT) and the mouse equivalent of the human A28V mutation (TnT) were reconstituted into detergent-skinned cardiac muscle fibers extracted from normal (α-MHC) and transgenic (β-MHC) mice. Dynamic and steady-state contractile parameters were measured in reconstituted muscle fibers. Step-like length perturbation experiments demonstrated that TnT decreased the magnitude of the muscle length-mediated recruitment of new force-bearing cross bridges (E) by 30% in α-MHC fibers. In sharp contrast, TnT increased E by 55% in β-MHC fibers. Inferences drawn from other dynamic contractile parameters suggest that directional changes in E in TnT + α-MHC and TnT + β-MHC fibers result from a divergent impact on cross bridge-regulatory unit (troponin-tropomyosin complex) cooperativity. TnT-mediated effects on Ca-activated maximal tension and instantaneous muscle fiber stiffness (E) were also divergently affected by α- and β-MHC. Our study demonstrates that TnT + α-MHC and TnT + β-MHC fibers show contrasting contractile phenotypes; however, only the observations from β-MHC fibers are consistent with the clinical data for A28V in humans.
NEW & NOTEWORTHY: The differential impact of α- and β-myosin heavy chain (MHC) on contractile dynamics causes a mutant cardiac troponin T (TnT) to differently modulate cardiac contractile function. TnT attenuated Ca-activated maximal tension and length-mediated cross-bridge recruitment against α-MHC but augmented these parameters against β-MHC, suggesting divergent contractile phenotypes.
本研究调查了心肌肌钙蛋白T（TnT）中人类肥厚型心肌病（HCM）突变A28V的功能后果。A28V突变位于TnT的N端，该区域已知对心脏细肌丝的完全激活很重要。TnT中A28V突变的功能后果尚不清楚。鉴于α和β肌球蛋白重链（MHC）同工型对TnT N端功能效应的影响不同，我们假设A28V诱导的效应会受到α和β-MHC同工型的不同调节。将重组野生型小鼠TnT（TnT）和人类A28V突变的小鼠等效物（TnT）重组到从正常（α-MHC）和转基因（β-MHC）小鼠中提取的去垢剂处理的心肌纤维中。在重组肌纤维中测量动态和稳态收缩参数。阶梯状长度微扰实验表明，TnT使α-MHC纤维中肌肉长度介导的新的承载力量的横桥募集（E）幅度降低了30%。形成鲜明对比的是，TnT使β-MHC纤维中的E增加了55%。从其他动态收缩参数得出的推论表明，TnT + α-MHC和TnT + β-MHC纤维中E的方向变化是由于对横桥调节单位（肌钙蛋白-原肌球蛋白复合物）协同性的不同影响。TnT对Ca激活的最大张力和瞬时肌纤维刚度（E）的介导作用也受到α和β-MHC的不同影响。我们的研究表明，TnT + α-MHC和TnT + β-MHC纤维表现出相反的收缩表型；然而，只有β-MHC纤维的观察结果与人类A28V的临床数据一致。
α和β肌球蛋白重链（MHC）对收缩动力学的不同影响导致突变型心肌肌钙蛋白T（TnT）对心脏收缩功能的调节不同。TnT减弱了α-MHC的Ca激活的最大张力和长度介导的横桥募集，但增强了β-MHC的这些参数，表明收缩表型不同。
