From the Department of Pharmacology, University of Oxford, Oxford, United Kingdom (Y.W., D.A.T., M.L.); Institute of Cardiovascular Sciences, Faculty of Medicine and Human Sciences (Y.W., H.T., Y.L., L.D., E.J.C., L.V., M.L.), Faculty of Life Science (X.W.), School of Physics and Astronomy (H.Z.), University of Manchester, Manchester, United Kingdom; Department of Biochemistry and Molecular Genetics, University of Illinois, Chicago (Y.K., R.J.S.); Department of Cardiovascular Diseases, Union Hospital, Huazhong University of Science and Technology, Wuhan, People's Republic of China (Y.S., M.L.); Physiological Laboratory, Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom (C.L.-H.H.).
Circ Arrhythm Electrophysiol. 2014 Oct;7(5):938-48. doi: 10.1161/CIRCEP.113.001198. Epub 2014 Sep 12.
Impaired sarcoplasmic reticular Ca(2+) uptake resulting from decreased sarcoplasmic reticulum Ca(2+)-ATPase type 2a (SERCA2a) expression or activity is a characteristic of heart failure with its associated ventricular arrhythmias. Recent attempts at gene therapy of these conditions explored strategies enhancing SERCA2a expression and the activity as novel approaches to heart failure management. We here explore the role of Pak1 in maintaining ventricular Ca(2+) homeostasis and electrophysiological stability under both normal physiological and acute and chronic β-adrenergic stress conditions.
Mice with a cardiomyocyte-specific Pak1 deletion (Pak1(cko)), but not controls (Pak1(f/f)), showed high incidences of ventricular arrhythmias and electrophysiological instability during either acute β-adrenergic or chronic β-adrenergic stress leading to hypertrophy, induced by isoproterenol. Isolated Pak1(cko) ventricular myocytes correspondingly showed aberrant cellular Ca(2+) homeostasis. Pak1(cko) hearts showed an associated impairment of SERCA2a function and downregulation of SERCA2a mRNA and protein expression. Further explorations of the mechanisms underlying the altered transcriptional regulation demonstrated that exposure to control Ad-shC2 virus infection increased SERCA2a protein and mRNA levels after phenylephrine stress in cultured neonatal rat cardiomyocytes. This was abolished by the Pak1-knockdown in Ad-shPak1-infected neonatal rat cardiomyocytes and increased by constitutive overexpression of active Pak1 (Ad-CAPak1). We then implicated activation of serum response factor, a transcriptional factor well known for its vital role in the regulation of cardiogenesis genes in the Pak1-dependent regulation of SERCA2a.
These findings indicate that Pak1 is required to maintain ventricular Ca(2+) homeostasis and electrophysiological stability and implicate Pak1 as a novel regulator of cardiac SERCA2a through a transcriptional mechanism.
由于肌浆网 Ca(2+) -ATP 酶 2a（SERCA2a）表达或活性降低导致的肌浆网 Ca(2+)摄取受损，是心力衰竭及其相关室性心律失常的特征。最近针对这些情况的基因治疗尝试探索了增强 SERCA2a 表达和活性的策略，作为心力衰竭管理的新方法。我们在这里探讨了 Pak1 在维持心室 Ca(2+) 稳态和电生理稳定性方面的作用，包括在正常生理和急性及慢性β-肾上腺素能应激条件下。
与对照（Pak1(f/f))相比，心肌细胞特异性 Pak1 缺失（Pak1(cko)）的小鼠在急性或慢性β-肾上腺素能应激期间（异丙肾上腺素诱导的肥大）更容易出现室性心律失常和电生理不稳定。相应地，分离的 Pak1(cko)心室肌细胞表现出异常的细胞内 Ca(2+)稳态。Pak1(cko)心脏表现出 SERCA2a 功能受损和 SERCA2a mRNA 和蛋白表达下调。对改变的转录调节机制的进一步探索表明，在培养的新生大鼠心肌细胞中，暴露于对照 Ad-shC2 病毒感染会增加苯肾上腺素应激后的 SERCA2a 蛋白和 mRNA 水平。在 Ad-shPak1 感染的新生大鼠心肌细胞中敲低 Pak1 后，这种情况被消除，而组成型过表达活性 Pak1（Ad-CAPak1）则增加了这种情况。然后我们发现血清反应因子的激活，该转录因子在调节心脏发生基因方面起着至关重要的作用，在 Pak1 依赖性调节 SERCA2a 中起作用。
这些发现表明，Pak1 对于维持心室 Ca(2+) 稳态和电生理稳定性是必需的，并暗示 Pak1 通过转录机制成为心脏 SERCA2a 的新型调节剂。
