Estrogen decreases TNF-alpha and oxidized LDL induced apoptosis in endothelial cells

Apoptosis induced by oxidized low-density lipoproteins (oxLDL) and tumor necrosis factor-alpha (TNF-alpha) is believed to contribute to atherosclerosis and vascular dysfunction. Estrogen treatment reduces apoptosis due to TNF-alpha and we hypothesized that it would also reduce apoptosis due to oxLDL. We also explored the anti-apoptotic mechanisms. We used early passage human umbilical vein endothelial cells (HUVEC) grown in steroid-depleted, red phenol-free medium. Cells were synchronized by starvation for 6h and then treated with oxLDL (75microg/ml) or TNF-alpha (20ng/ml) in the presence of 17-beta-estradiol (E2) (20nM). Apoptosis was analyzed by flow cytometry and caspase-3 cleavage. We also assessed expression of Bcl-2 and Bcl-xL and phosphorylation of BAD. At 6h TNF-alpha induced apoptosis but oxLDL did not; E2 did not affect this TNF-alpha induced apoptosis and there was no change in Bcl-2 or Bcl-xL expression. At 24h both TNF-alpha and oxLDL increased apoptosis and E2 reduced the increase. E2 also increased expression of the anti-apoptotic Bcl-2 and Bcl-xL and increased phosphorylation of proapoptotic BAD which reduces its proapoptotic activity at 1h. However at 24h there was also an increase in total BAD so that the proportion of phosphorylation of BAD decreased. oxLDL induced apoptosis occurs later than that of TNF-alpha. E2 decreased this late phase apoptosis and this likely requires the production of anti-apoptotic proteins.