Estrogen reduces angiotensin II-induced acceleration of senescence in endothelial progenitor cells.

The interaction among estrogen, angiotensin II (Ang II), and oxidative stress in endothelial progenitor cells (EPCs) remains unknown. We therefore investigated the potential effect of estrogen on Ang II-induced EPC oxidative stress and senescence in EPCs. EPCs were isolated from peripheral blood and characterized. Both reverse transcription (RT)-polymerase chain reaction (PCR) and Western blotting were used to assess gp91phox and angiotensin type 1 receptor (AT1R) expression. Immunofluorescence of nitrotyrosine provided evidence of peroxynitrite formation. Our data indicate that Ang II increased the expression of gp91phox mRNA and protein, and these effects were attenuated by 17beta-estradiol (E2). The exposure of cultured EPCs to Ang II (100 nmol/l) significantly accelerated the rate of senescence compared to that in control cells during 14 days in culture as determined by acidic beta-galactosidase staining, and this effect was significantly inhibited by E2 (p < 0.01). Because cellular senescence is critically influenced by telomerase, which elongates telomeres, we measured telomerase activity by using a PCR-ELISA-based assay. Ang II significantly diminished telomerase activity, although the effect was significantly reduced by pre-treatment with E2 (p < 0.01). Because we previously demonstrated that both the up-regulation of gp91phox and the acceleration of cellular senescence in Ang II-stimulated EPCs could be abolished by pre-treatment with the AT1R- specific antagonist, valsartan, we also explored the effect of estrogen on AT1R expression. Ang II increased AT1R mRNA and protein expression, and these increases were prevented by E2, suggesting that AT1R may at least partially mediate the inhibitory effect of E2 on Ang II-induced acceleration of senescence in EPCs. In conclusion, estrogen reduces Ang II-induced acceleration of senescence in EPCs partially through down-regulation of AT1R expression.