17β-Estradiol induces protein S-nitrosylation in the endothelium

Estrogen induces nitric oxide (NO) in the endothelium and appears to protect against inflammation and atherosclerosis. NO can induce post-translational protein modifications such as cysteine S-nitrosylation in the cellular proteins which may exert anti-inflammatory effects. However, whether estrogen can induce protein S-nitrosylation in the endothelium is not known. Given this background, we investigated the role of 17 beta-estradiol (E2 beta), the major form of estrogen in the body, on endothelial protein S-nitrosylation. Experiments were performed in human umbilical vein endothelial cells (HUVECs). S-nitrosylation was detected by immunostaining for nitrosocysteine and further confirmed by biotin switch method. Ovariectomized 12-month-old Sprague-Dawley rats with/without estradiol supplementation were used for in vivo validation of findings. We found that physiologically relevant doses of E2 beta increased protein S-nitrosylation in HUVECs through estrogen receptor-alpha (ER alpha) and endothelial nitric oxide synthase (eNOS). Interestingly, specific agonists for both ER alpha and ER beta increased eNOS protein expression, while only the former could activate eNOS through phosphorylation. S-nitrosylation by E2 beta prevented angiotensin II-induced upregulation of intercellular cell adhesion molecule-1, suggesting a potential anti-inflammatory mechanism. Finally, we showed that exogenous E2 beta could increase endothelial S-nitrosylation in vivo in a rat model. Our results demonstrate for the first time that E2 beta increases protein S-nitrosylation in the vascular endothelium, which might be a novel pathway to mediate the protective effects on the vasculature.