Effects of estradiol on cell cycle and cyclin proteins of vascular smooth muscle cells in rats

To study the effects of 17β-estradiol(E2) on the growth of cultured rat vascular smooth muscle cells (VSMC).Methods The cell cycle and the expressions of Cyclin D1 and CDK4 proteins were examined by flow cytometry in VSMC cultured in different concentrations (0～100 nmol/L) of 17β-estradiol with or without serum.Results Under serum-stimulating conditions,17β-estradiol(1,10,100 nmol/L) promoted VSMC proliferation by accelerating their cell cycle progression from G1 to S phases,and the cell rates at S were (31.89±9.14)%(35.90±4.59)% and (30.77±1.20)% respectively,significantly higher than the corresponding values of control cells (21.63±1.80)%.This was accompanied by the significantly increased expression of Cyclin D1 and CDK4 proteins.In the cultures without serum,however,high concentrations (10,100 nmol/L) of E2 induced a cell cycle arrest at G1 phase,which was characterizsed by decreased cell rates at S phase [(9.93±1.43)% and (8.76±1.80)% respectively,P<0.05] as compared with the corresponding control values and a down-regulation of expressions of Cyclin D1 and CDK4 proteins.Conclusion E2 can either promote or inhibit VSMC proliferation depending upon the presence or absence of serum mitogens.The underlying mechanism may be associated with the hormone’s action on the expression of Cyclin D1 and CDK4 which act as the G1 phase regulators.4 refs.