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Whereas hormonal therapy (HT) may increase the risk of coronary heart disease (CHD) and stroke in menopausal women, epidemiological studies (protection in premenopausal women) suggest and experimental studies (prevention of fatty streak development in animals) demonstrate a major atheroprotective action of estradiol (E2). The understanding of the deleterious and beneficial effects of estrogens is thus required at both a cellular and molecular level. Both the endothelium and the immuno-inflammatory system play a key role in the development of fatty streak deposit as well as in the rupture of the atherosclerotic plaque. Whereas E2 favors an anti-inflammatory effect in vitro (cultured cells), it rather elicits a pro-inflammatory response in vivo at the level of several subpopulations of the immuno-inflammatory system, which could contribute to plaque destabilization. E2 promotes beneficial actions on the endothelium such as nitric oxide and prostacyclin production. E2 actions are essentially mediated by two molecular targets: estrogen receptor α (ER-α) and β (ER-β, but the former appears to mediate most of the actions of E2 on the endothelium and on the immune system. ER-α modulates target gene transcription through two activation functions (AF), AF-I and AF-2, even though signalling via ER-α located at the plasma membrane (responsible for membrane-initiated steroid signalling [MISS]/ [extra-genomic]) can also lead to an indirect effect on gene transcription. Recently, we demonstrated that ER-α AF-I is not required for the vasculoprotective actions of E2, whereas it is necessary for the effects of E2 on its reproductive targets. These results suggest that selective estrogen receptor modulators stimulating ER-α with minimal activation of ER-α AF-I could retain beneficial vascular actions, while minimizing the sexual effects. [ABSTRACT FROM AUTHOR]