Activation of estrogen receptor ? inhibits TLR4 signaling in macrophages and alleviates the instability of atherosclerotic plaques in the postmenopausal stage

Acute cardiovascular events increase significantly in postmenopausal women. The relationship between estrogen receptor (ER) and plaque stability in the postmenopausal stage remains to be elucidated. We aimed to explore whether ER alpha activation improves plaque instability in the postmenopausal stage. Here, we report that post-menopausal women showed increased macrophage activation and plaque instability with increased MCP-1, MMP9, TLR4, MYD88 and NF-kappa B p65 and decreased ER alpha and TIMP1 expression in the vascular endothelium. Moreover, ovariectomy in LDLR-/-mice resulted in a significant increase in plaque area and necrotic core area, as well as a significant decrease in collagen content and an increase in macrophage accumulation in the artery. Ovariectomy also reduced serum estrogen levels and ER alpha expression and upregulated TLR4 and MMP9 expression in arteries in LDLR-/-mice. Estrogen or phytoestrogen therapy upregulated the expression level of ER alpha in ovariectomized mice and increased plaque stability by inhibiting macrophage accumulation and TLR4 signaling. In vitro, LPS incubation of RAW264.7 cells resulted in a significant decrease in ER alpha and TIMP1 expression and an increase in TLR4 activation, and estrogen or phytoestrogen treatment increased ER alpha and TIMP1 expression and inhibited TLR4 activation and MMP9 expression in LPS-treated RAW264.7 cells. Compared to control siRNA transfected RAW264.7 cells, TLR4 siRNA promoted TIMP1 expression in RAW264.7 cells with LPS incubation, but did not affect ER alpha expression in RAW264.7 cells with or without LPS treatment. The ER alpha inhibitor MPP abolished the regulatory effect of estrogen or phytoestrogen on LPS-induced RAW264.7 cells. In conclusion, the present study demonstrates that decreased ER alpha expression promotes macrophage infil-tration and plaque instability in the postmenopausal stage, and activation of ER alpha in the postmenopausal stage alleviates atherosclerotic plaque instability by inhibiting TLR4 signaling and macrophage-related inflammation.