Akt plays a central role in the anti-apoptotic effect of estrogen in endothelial cells

Estrogen has been reported to inhibit apoptosis in vascular endothelial cells. However, its precise mechanism still remains to be elucidated. Here we determined the role of Akt in the anti-apoptotic effect of estrogen. 17Beta-estradiol prevented the apoptosis induced by TNF-alpha in bovine aortic endothelial cells, as evaluated by double staining with fluorescein isothiocyanate-conjugated annexin V and propidium iodide. Introducing a dominant negative mutant of Akt by using a cell-penetrating peptide of Tat protein inhibited the anti-apoptotic effect of estrogen in a concentration-dependent manner, and resulted in the complete inhibition of the anti-apoptotic effect of 17beta-estradiol at 1nM and higher concentrations. The dominant negative mutant without the cell-penetrating peptide and Tat peptide-conjugated protein A had no effect. The intracellular protein transduction was confirmed by immunoblot analysis. Our observations thus provide first direct evidence that Akt plays a central role in the anti-apoptotic effect of estrogen in vascular endothelial cells.