Haghighi Kobra, Pritchard Tracy J, Liu Guan-Sheng, Singh Vivek P, Bidwell Philip, Lam Chi Keung, Vafiadaki Elizabeth, Das Parthib, Ma Jianyong, Kunduri Swati, Sanoudou Despina, Florea Stela, Vanderbilt Erica, Wang Hong-Shang, Rubinstein Jack, Hajjar Roger J, Kranias Evangelia G
Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, Cincinnati, OH 45267, United States.
Molecular Biology Division, Biomedical Research Foundation, Academy of Athens, Greece.
J Mol Cell Cardiol. 2015 Dec;89(Pt B):349-59. doi: 10.1016/j.yjmcc.2015.10.004. Epub 2015 Oct 9.
A hallmark of human and experimental heart failure is deficient sarcoplasmic reticulum (SR) Ca-uptake reflecting impaired contractile function. This is at least partially attributed to dephosphorylation of phospholamban by increased protein phosphatase 1 (PP1) activity. Indeed inhibition of PP1 by transgenic overexpression or gene-transfer of constitutively active inhibitor-1 improved Ca-cycling, preserved function and decreased fibrosis in small and large animal models of heart failure, suggesting that inhibitor-1 may represent a potential therapeutic target. We recently identified a novel human polymorphism (G109E) in the inhibitor-1 gene with a frequency of 7% in either normal or heart failure patients. Transgenic mice, harboring cardiac-specific expression of G109E inhibitor-1, exhibited decreases in contractility, Ca-kinetics and SR Ca-load. These depressive effects were relieved by isoproterenol stimulation. Furthermore, stress conditions (2Hz +/- Iso) induced increases in Ca-sparks, Ca-waves (60% of G109E versus 20% in wild types) and after-contractions (76% of G109E versus 23% of wild types) in mutant cardiomyocytes. Similar findings were obtained by acute expression of the G109E variant in adult cardiomyocytes in the absence or presence of endogenous inhibitor-1. The underlying mechanisms included reduced binding of mutant inhibitor-1 to PP1, increased PP1 activity, and dephosphorylation of phospholamban at Ser16 and Thr17. However, phosphorylation of the ryanodine receptor at Ser2808 was not altered while phosphorylation at Ser2814 was increased, consistent with increased activation of Ca/calmodulin-dependent protein kinase II (CaMKII), promoting aberrant SR Ca-release. Parallel in vivo studies revealed that mutant mice developed ventricular ectopy and complex ventricular arrhythmias (including bigeminy, trigeminy and ventricular tachycardia), when challenged with isoproterenol. Inhibition of CaMKII activity by KN-93 prevented the increased propensity to arrhythmias. These findings suggest that the human G109E inhibitor-1 variant impairs SR Ca-cycling and promotes arrhythmogenesis under stress conditions, which may present an additional insult in the compromised function of heart failure carriers.
人类和实验性心力衰竭的一个标志是肌浆网（SR）钙摄取不足，这反映了收缩功能受损。这至少部分归因于蛋白磷酸酶1（PP1）活性增加导致受磷蛋白去磷酸化。事实上，在心力衰竭的大小动物模型中，通过转基因过表达或组成型活性抑制剂-1的基因转移来抑制PP1，可改善钙循环、保留功能并减少纤维化，这表明抑制剂-1可能是一个潜在的治疗靶点。我们最近在抑制剂-1基因中发现了一种新的人类多态性（G109E），在正常或心力衰竭患者中的频率均为7%。携带心脏特异性表达G109E抑制剂-1的转基因小鼠表现出收缩力、钙动力学和SR钙负荷下降。异丙肾上腺素刺激可缓解这些抑制作用。此外，应激条件（2Hz +/- 异丙肾上腺素）在突变心肌细胞中诱导钙火花、钙波增加（G109E为60%，野生型为20%）以及后收缩增加（G109E为76%，野生型为23%）。在有无内源性抑制剂-1的情况下，通过在成年心肌细胞中急性表达G109E变体也获得了类似的结果。潜在机制包括突变抑制剂-1与PP1的结合减少、PP1活性增加以及受磷蛋白在Ser16和Thr17处去磷酸化。然而，兰尼碱受体在Ser2808处的磷酸化未改变，而在Ser2814处的磷酸化增加，这与钙/钙调蛋白依赖性蛋白激酶II（CaMKII）的激活增加一致，促进了异常的SR钙释放。平行的体内研究表明，突变小鼠在接受异丙肾上腺素刺激时会出现室性早搏和复杂的室性心律失常（包括二联律、三联律和室性心动过速）。KN-93抑制CaMKII活性可防止心律失常倾向增加。这些发现表明，人类G109E抑制剂-1变体在应激条件下损害SR钙循环并促进心律失常的发生，这可能会给心力衰竭携带者受损的心脏功能带来额外的损害。
