心力衰竭的病理生理机制研究一直是医学研究热点。心肌细胞是终末分化细胞，近年发现心衰时心肌细胞出现细胞周期再进入现象（cell cycle re-entry）但不完成分裂，该现象的意义还不明确。本课题组发现，抑制细胞周期再进入减轻心肌肥厚模型病变程度，而激活蛋白激酶G（PKG）减少心肌的细胞周期再进入并抑制关键分子细胞周期素依赖性蛋白激酶4（CDK4）入核。生物信息学提示CDK4是PKG潜在磷酸化底物。综上，归纳假说：PKG磷酸化CDK4并抑制其入核，从而维持心肌细胞周期停滞。病理状态下PKG活性降低，上述机制被抑制而触发心肌的细胞周期再进入，并促进心肌肥厚/心衰发展。本项目拟从心衰临床样本、动物模型、细胞模型等层面，使用腺相关病毒介导CDK4磷酸化位点特异性干预，通过形态学、分子生物学检测来论证假说。最终，有望对细胞周期再进入在心衰中的意义形成深入认识，为探索细胞周期为靶点的干预提供思路。

The explorations of pathophysiological mechanisms involved in heart failure are always hot spots in fields of Medical researches. Though cardiomyocytes are terminal differentiated, they were found to have the potential of re-entry into cell cycle but without cell devision in heart failure samples. The function of this cell cycle re-entry is unclear. Recently, we found that inhibition of cell cycle re-entry could reduce hypertrophy in a cardiomyocyte cell model, and activation of protein kinase G (PKG) could inhibit both re-entry in cell cycle of cardiomyocytes and nuclear translocation of cyclin-dependent kinase 4 (CDK4), which is a key mediator of cell cycle. Then, bioinformatical prediction showed that CDK4 is a potential substrate of PKG. Taken together, we make this hypothesis: PKG phosphorylates CDK4 and inhibits its nuclear translocation, resulting in cell cycle exit of cardiomyocytes. Under pathological conditions, the inactivation of PKG in cardiomyocytes causes dephosphorylation of CDK4, which in turn leads to cell cycle re-entry, and finally participates in the development of hypertrophy and heart failure. We will use clinical samples, animal model and primary cardiomyocyte model of hypertrophy and heart failure as objects, then employ adeno-associated virus-mediated gene delivery to make specific interference of CDK4 phosphorylation site, and the hypothesis will be verified by techniques of morphology and molecular biology. By studying this program, we will make better understanding of the functions of cardiac cell cycle re-entry in hypertrophy and heart failure. This research will also provide valuable targets of cell cycle regulation for the treatment of heart failure.