心梗后室性心律失常发生凶险、机理不明、缺乏有效的治疗手段。预实验显示小鼠梗死边缘区ALK4、CaMKⅡN1、PCP4、Smads表达明显下调。CaMKⅡN1和PCP4是CaMKⅡ内源性抑制因子，CaMKⅡ在心梗后室性心律失常中起关键作用。我们在CaMKⅡN1-/-小鼠观察到频发室性心律失常及CaMKⅡ活性增强。预实验提示CaMKⅡN1表达是ALK4-Smads信号通路调节的，而PCP4下调可能与其降解增加和转录减少有关。故提出假设：CaMKⅡN1和PCP4表达下调使CaMKⅡ持续激活而导致心梗后室性心律失常。本项目拟研究：CaMKⅡN1和PCP4在心脏电生理特性和室性心律失常中的作用及机制；ALK4-Smads信号通路对CaMKⅡN1表达的调控作用；PCP4表达下调的机制；CaMKⅡN1和PCP4高表达对心梗后室性心律失常的抑制作用。通过以上研究为心梗后室性心律失常的防治提供新的治疗靶点。

Ventricular arrhythmias are the most important causes for the continuously-rising mortality in patients with myocardial infarction (MI), but currently not only is the underlying mechanism still unclear but also is there short of effective treatment approach. Our cDNA microarray results showed that the expression of ALK4, CaMKⅡN1, PCP4, Smad2, Smad3, and Smad4 were decreased in the border zone of the myocardial infarction in mice and the results were confirmed by Western blotting. It is well-known that CaMKⅡ is deeply involved in the pathogenesis of ventricular arrhythmias post-MI and that CaMKⅡN1 and PCP4 are endogenous CaMKⅡ inhibitors. Therefore, we generated ALK4 and CaMKⅡN1-knockout mice. The ECG recording successfully captured spontaneous ventricular arrhythmias and Western blotting demonstrated an increase in the CaMKⅡ activity in the myocardial tissue of these mice. Most importantly, ALK4-Smad2/3/4 constitutes a famous signal pathway regulating gene transcription/expression. The expression of CaMKⅡN1 in neonatal mice myocardial cells was up-regulated by treatment of activin, a specific ligand to activate ALK4. However, the expression of PCP4 was unchanged. Next in this study, we plan ① to analyze the cardiac electrophysiological characteristics and the pattern of ventricular arrhythmias in mice knocked-out of the three genes by mimicking the post-MI down-regulation of CaMKⅡN1, ALK4, and PCP4; ② to determine the role of ALK4-Smad2/3/4 pathway in the mechanism responsible for the post-MI down-regulated CaMKⅡN1; ③ to explore the mechanisms responsible for the down-regulation of PCP4 by two methods. One is to test whether it is caused by a potentiated degradation resulted from an increased activity of calpain, a Ca2+-dependent proteinase. The activity of calpain is usually upregulated under hypoxia/ischemia. Another is to test whether PCP4’s expression is suppressed by a series of traditional promoter/transcriptional factor binding interactions; ④ at last, for eagerly looking for potential treatment approaches, to test whether over-expression of CaMKⅡN1 and/or PCP4 in mice could attenuate the occurrence of the ventricular arrhythmias. Our study will expand the understanding of the pathological mechanisms of the ventricular arrhythmias after MI and provide potential therapeutic targets.