17β-estradiol inhibits H2O2-induced senescence in HUVEC cells through upregulating SIRT3 expression and promoting autophagy

17β-estradiol (17β-E2) has been implicated in inhibiting the senescence of vascular endothelial cells (VEC) and slowing down the process of atherosclerosis. However, the underlying molecular mechanisms are still unknown. In this study, we examined the roles of SIRT3 in 17β-E2-induced autophagy and 17β-E2-mediated inhibition of hydrogen peroxide (H2O2)-induced senescence in Human umbilical vein endothelial cells (HUVEC). Cellular senescence was measured by immunoblot analysis with antibodies against phosphorylated Rb and senescence-associated β-galactosidase staining. Immunoblot analysis with antibodies against LC3 and p62 was performed to determine autophagy flux. Our findings show that 17β-E2 activates SIRT3 promoter and upregulates SIRT3 gene expression in HUVEC cells. siRNA-mediated silencing of SIRT3 gene expression inhibits 17β-E2-induced processing of LC3-I to LC3-II and degradation of p62, two widely-used makers of autophagy. SIRT3 knockdown also blocks 17β-E2-induced inhibition of cellular senescence triggered by H2O2. Our data further reveal that SIRT3 knockdown impairs 17β-E2-induced co-localization of LC3 and VDAC1, a marker protein on mitochondria, when HUVEC cells were co-treated with H2O2. Together, our findings suggest that 17β-E2 upregulates SIRT3 gene expression by activating SIRT3 promoter and then promotes autophagy, which in turn serves to remove dysfunctional mitochondria caused by H2O2 and consequently inhibit H2O2-induced senescence in HUVEC cells.