Molecular and Cell Physiology, Hannover Medical School, D-30625 Hannover, Germany.
J Mol Cell Cardiol. 2013 Apr;57:13-22. doi: 10.1016/j.yjmcc.2013.01.001. Epub 2013 Jan 11.
Familial Hypertrophic Cardiomyopathy (FHC) is frequently caused by mutations in the β-cardiac myosin heavy chain (β-MyHC). To identify changes in sarcomeric function triggered by such mutations, distinguishing mutation effects from other functional alterations of the myocardium is essential. We previously identified a direct effect of mutation R723G (MyHC723) on myosin function in slow Musculus soleus fibers. Here we investigate contractile features of left ventricular cardiomyocytes of FHC-patients with the same MyHC723-mutation and compare these to the soleus data. In mechanically isolated, triton-permeabilized MyHC723-cardiomyocytes, maximum force was significantly lower but calcium-sensitivity was unchanged compared to donor. Conversely, MyHC723-soleus fibers showed significantly higher maximum force and reduced calcium-sensitivity compared to controls. Protein phosphorylation, a potential myocardium specific modifying mechanism, might account for differences compared to soleus fibers. Analysis revealed reduced phosphorylation of troponin I and T, myosin-binding-protein C, and myosin-light-chain 2 in MyHC723-myocardium compared to donor. Saturation of protein-kinaseA phospho-sites led to comparable, i.e., reduced MyHC723-calcium-sensitivity in cardiomyocytes as in M. soleus fibers, while maximum force remained reduced. Myofibrillar disarray and lower density of myofibrils, however, largely account for reduced maximum force in MyHC723-cardiomyocytes. The changes seen when phosphorylation of sarcomeric proteins in myocardium of affected patients is matched to control tissue suggest that the R723G mutation causes reduced Ca(++)-sensitivity in both cardiomyocytes and M. soleus fibers. In MyHC723-myocardium, however, hypophosphorylation can compensate for the reduced calcium-sensitivity, while maximum force generation, lowered by myofibrillar deficiency and disarray, remains impaired, and may only be compensated by hypertrophy.
家族性肥厚型心肌病（FHC）常由β-心肌球蛋白重链（β-MyHC）突变引起。为了确定此类突变引发的肌节功能变化，区分突变的影响与心肌的其他功能改变至关重要。我们之前发现突变 R723G（MyHC723）对慢肌 Musculus soleus 纤维中肌球蛋白功能的直接影响。在这里，我们研究了具有相同 MyHC723 突变的 FHC 患者的左心室心肌细胞的收缩特征，并将这些特征与 soleus 数据进行了比较。在机械分离的、Triton 通透的 MyHC723 心肌细胞中，与供体相比，最大力显著降低，但钙敏感性不变。相反，与对照组相比，MyHC723-soleus 纤维表现出显著更高的最大力和降低的钙敏感性。蛋白磷酸化是一种潜在的心肌特异性修饰机制，可能是导致与 soleus 纤维差异的原因。分析显示，与供体相比，MyHC723 心肌中的肌钙蛋白 I 和 T、肌球蛋白结合蛋白 C 和肌球蛋白轻链 2 的磷酸化程度降低。蛋白激酶 A 磷酸化位点的饱和导致 MyHC723 心肌细胞中的钙敏感性与 M. soleus 纤维相似，即降低，而最大力仍然降低。然而，肌节紊乱和肌原纤维密度降低在很大程度上导致了 MyHC723 心肌细胞中最大力的降低。当匹配受影响患者心肌中肌节蛋白的磷酸化与对照组织时，所观察到的变化表明 R723G 突变导致心肌细胞和 M. soleus 纤维的 Ca（++）敏感性降低。然而，在 MyHC723 心肌中，低磷酸化可以补偿钙敏感性的降低，而由肌原纤维缺陷和紊乱引起的最大力产生仍然受损，并且可能仅通过肥大来补偿。
