Endothelial Estrogen Receptor Alpha Inhibits Plaque Inflammation in Both Sexes

BACKGROUND: Atherosclerotic plaque inflammation correlates with risk of rupture, causing myocardial infarction. Lower myocardial infarction risk in young women compared with men abates post-menopause, implicating ERs (estrogen receptors). The ERa (ER alpha) is necessary for estrogen effects on atherosclerosis in mouse models, yet the mechanistic role of ERa in plaque inflammation in both sexes remains unclear. METHODS AND RESULTS: The role of ERa in driving endothelial cell (EC) adhesion molecule expression and inflammation was studied. LDLR (low-density lipoprotein receptor)-knockout mice with EC-specific ERa knockout were compared with ERa-intact littermates after 12 weeks of high-fat diet. In both sexes, EC-specific ERa knockout increased plaque inflammation and expression of adhesion molecules, including ICAM1 (intracellular adhesion molecule 1). In vitro, primary human ECs from young women expressed more ERa and less ICAM1 versus age-matched cells from men. ERa knockdown in human coronary ECs from both sexes increased adhesion molecules. Because the MR (mineralocorticoid receptor) has been implicated in ICAM1 expression and plaque inflammation in males, the impact of ERa on MR-induced ICAM1 expression was explored. In human ECs, estrogen prevented aldosterone induction of ICAM1 and MR enrichment on the ICAM1 promoter. In vivo, EC-specific MR-knockout and EC-ERa/MR-double-knockout/LDLR-knockout mice were studied as above. In females, EC-specific MR knockout did not impact ICAM1 or plaque inflammation, consistent with ERa inhibiting MR function. In the double-knockout model, the lack of MR prevented the increased inflammation and ICAM1 expression observed with loss of EC-ERa. In males, EC-specific MR knockout alone decreased inflammation and ICAM1. In the double-knockout model, the proinflammatory effects of MR and the anti-inflammatory impact of ERa offset each other. CONCLUSIONS: These findings reveal a role for ERa in regulating plaque inflammation in both sexes. In females, estrogen acts via EC-ERa to inhibit MR transcriptional upregulation of ICAM1, attenuating plaque inflammation. In males, ICAM1 expression is driven by the MR and inhibited by ERa.