Estrogen receptor -dependent Notch1 activation protects vascular endothelium against tumor necrosis factor (TNF)-induced apoptosis

Unlike age-matched men, premenopausal women benefit from cardiovascular protection. Estrogens protect against apoptosis of endothelial cells (ECs), one of the hallmarks of endothelial dysfunction leading to cardiovascular disorders, but the underlying molecular mechanisms remain poorly understood. The inflammatory cytokine TNF causes EC apoptosis while dysregulating the Notch pathway, a major contributor to EC survival. We have previously reported that 17-estradiol (E2) treatment activates Notch signaling in ECs. Here, we sought to assess whether in TNF-induced inflammation Notch is involved in E2-mediated protection of the endothelium. We treated human umbilical vein endothelial cells (HUVECs) with E2, TNF, or both and found that E2 counteracts TNF-induced apoptosis. When Notch1 was inhibited, this E2-mediated protection was not observed, whereas ectopic overexpression of Notch1 diminished TNF-induced apoptosis. Moreover, TNF reduced the levels of active Notch1 protein, which were partially restored by E2 treatment. Moreover, siRNA-mediated knockdown of estrogen receptor (ER), but not ER, abolished the effect of E2 on apoptosis. Additionally, the E2-mediated regulation of the levels of active Notch1 was abrogated after silencing ER. In summary, our results indicate that E2 requires active Notch1 through a mechanism involving ER to protect the endothelium in TNF-induced inflammation. These findings could be relevant for assessing the efficacy and applicability of menopausal hormone treatment, because they may indicate that in women with impaired Notch signaling, hormone therapy might not effectively protect the endothelium.