Calcium Cycling Protein Mutations in Human Heart Failure

心力衰竭动物模型和人类心力衰竭中钙循环的抑制被认为至少部分地反映了肌浆网（SR）钙吸收的受损。SR的钙固存是由Ca2+转运atp酶（SERCA2）介导的，其活性受磷蛋白（PLN）磷酸化状态的可逆调节。去磷酸化的PLN是SERCA2的ca亲和力和心脏收缩力的抑制剂，而磷酸化的PLN则减轻了抑制作用。PLN水平已被证明是基础收缩力和心脏对13激动剂反应的主要决定因素。在人类心力衰竭中，PLN相对于SERCA2的水平升高，导致ca泵的ca亲和力抑制增加和舒张时间延长。此外，PLN的磷酸化状态降低，导致PLN抑制功能增强，进一步抑制SR ca循环。PLN磷酸化的降低反映了PLN磷酸酶1活性的增加，部分原因是抑制剂1 （I-1）功能的去磷酸化和衰减。因此，这两种主要的钙调节蛋白成为我们在心力衰竭中关注的焦点，确定PLN和I-1人类基因中是否可能发生遗传变异（如点突变）是很重要的，这可能会改变它们的活性并改变疾病的临床病程。事实上，我们最近已经确定了两个人类PLN突变，导致扩张型心肌病和心力衰竭在年轻的时候。我们建议在此继续我们的研究，以鉴定PLN以及1-1基因的其他突变，并确定其功能意义和病理生理相关性。

The depressed calcium cycling in animal models of heart failure and human failing hearts has been suggested to reflect, at least in part, the impaired calcium sequestration by the sarcoplasmic reticulum (SR). Calcium sequestration by the SR is mediated by a Ca2+-transport ATPase (SERCA2), whose activity is reversibly regulated by the phosphorylation status of phospholamban (PLN). Dephosphorylated PLN is an inhibitor of the Ca-affinity of SERCA2 and cardiac contractility, while phosphorylation of PLN relieves the inhibitory effects. The levels of PLN have been shown to be a major determinant of basal contractility and the heart's responses to 13-agonists. In human heart failure, the levels of PLN relative to SERCA2 are increased, resulting in increased inhibition of the Ca-pump's Ca-affinity and prolonged relaxation. In addition, the phosphorylation status of PLN is decreased, resulting in increased inhibitory function by PLN and further depression of SR Ca-cycling. The decreased PLN phosphorylation reflects increases in the PLN phosphatase 1 activity, partially due to dephosphorylation and attenuation of the inhibitor 1 (I-1) function. Thus, these two major Ca-regulatory proteins become our focus of attention in heart failure and it is important to determine whether genetic variations, such as point mutations, may occur in the PLN and I-1 human genes, which may alter their activities and modify the clinical course of the disease. Indeed, we have recently identified two human PLN mutations that led to dilated cardiomyopathy and heart failure at a young age. We propose here to continue our studies on identification of additional mutations in the PLN as well as the 1-1 genes and determine their functional significance and pathophysiological relevance, utilizing expression systems and genetically altered mice. In parallel, the subjects with the identified mutation will be closely followed to assess their cardiac function, exercise tolerance and force-interval relations (mechanical and relaxation restitution). Our findings will determine whether correlations may be established between a specific mutation in PLN or 1-1 and a specific clinical parameter or the time course of heart failure. Furthermore, these studies will provide valuable insights into the mechanisms by which specific genetic variants alter SR Ca-handling and function in heart failure.