Cardiomyocyte proliferation and protection against post-myocardial infarction heart failure by cyclin D1 and Skp2 ubiquitin ligase

Cyclins and other cell-cycle regulators have been used in several studies to regenerate cardiomyocytes in ischaemic heart failure. However, proliferation of cardiomyocytes induced by nuclear-targeted cyclin D1 (D1NLS) stops after one or two rounds of cell cycles due in part to accumulation of p27Kip1, an inhibitor of cyclin-dependent kinase (CDK). Thus, expression of S-phase kinase-associated protein 2 (Skp2), a negative regulator of p27Kip1, significantly enhances the effect of D1NLS and CDK4 on cardiomyocyte proliferation in vitro. Here, we examined whether Skp2 can also improve cardiomyocyte regeneration and post-ischaemic cardiac performance in vivo.Wistar rats underwent ischaemia/reperfusion injury by ligation of the coronary artery followed by injection of adenovirus vectors for D1NLS and CDK4 with or without Skp2. Enhanced proliferation of cardiomyocytes in the presence of Skp2 was demonstrated by increased expression of Ki67, a marker of proliferating cells (1.95% vs. 4.00%), and mitotic phosphorylated histone H3 (0.24% vs. 0.58%). Compared with rats that received only D1NLS and CDK4, expression of Skp2 improved left ventricular function as measured by the maximum and minimum rates of change in left ventricular pressure, the left ventricle end-diastolic pressure, left ventricle end-diastolic volume index, and the lung/body weight ratio.Expression of Skp2 enhanced the effect of D1NLS and CDK4 on the proliferation of cardiomyocytes and further contributed to improved post-ischaemic cardiac function. Skp2 might be a versatile tool to improve the effect of cyclins on post-ischaemic regeneration of cardiomyocytes in vivo.