Estrogen-receptor-mediated inhibition of human endothelial cell apoptosis. Estradiol as a survival factor.

Abstract

A series of studies was performed to examine the ability of estradiol (E2) to protect endothelial cells from apoptosis. Light and transmission electron microscopy demonstrated typical features of apoptosis in human umbilical vein endothelial cells (HUVEC) exposed to tumor necrosis factor-alpha (TNF-alpha). Northern and Western blot analyses revealed induction of message and protein for the interleukin-1 beta converting enzyme (ICE), which has been shown to mediate apoptosis induced by TNF-alpha. Immunofluorescent staining of HUVEC colocalized ICE expression to apoptotic HUVEC. Direct cell counting demonstrated a significant decrease in total endothelial cell number after 24 hours of TNF-alpha exposure and a dose-dependent reversal of the effect of TNF-alpha with E2 treatment. This protective effect was abrogated by an estrogen-receptor antagonist. Fluorescence-activated cell sorting analysis revealed 39.3% apoptosis after 24 hours of TNF-alpha exposure. Treatment with E2 resulted in a 50% decrease in apoptosis. Similarly, viability assays revealed 35 +/- 4% cell death after TNF-alpha exposure. Simultaneous treatment with E2 resulted in a dose-dependent reduction of cell death to a minimum of 18 +/- 2%. The protective effect of E2 was nullified by a specific estrogen-receptor antagonist. E2 treatment resulted in a dose-dependent, receptor-mediated inhibition of TNF-alpha-induced endothelial cell apoptosis. These studies indicate that E2 may also serve a maintenance function in preventing endothelial cell death after noxious stimuli and suggest that the ICE pathway may mediate cytokine-induced apoptosis in endothelial cells. Preservation of endothelial integrity represents another mechanism that may account for the atheroprotective effect of estrogen.