SUN-016 27-Hydroxycholesterol a Selective Estrogen Receptor Modulator: Profiling 27-Hydroxycholesterol Effects on Estrogen Receptor Activity in Mice

27-Hydroxycholesterol (27-HC) is the most prevalent metabolite of cholesterol in circulation, and also the first identified endogenous selective estrogen receptor (ER) modulator (SERM) (1). Previously, we found that 27-HC acts as an agonist of ER in breast cancer cells, while it acts as an antagonist of ER in endothelial cells in the cardiovasculature. Yet, potential agonistic or antagonistic effects of 27-HC on ER activity in other tissues and cell types remain largely unknown. Here, we examined the effects of 27-HC on ER activity using an ER responsive element (ERE)-luciferase transgenic mice, which have the expression plasmid that contain ERE, linked to a luciferase gene. This mouse model expresses luciferase proteins upon activation of ER, which could be further quantified and visualized by luciferase assay, and imaging respectively. To remove any artifacts from estrogens in the diet and endogenous production at the ovary, the mice were fed an estrogen depleted diet, and female mice were ovariectomized at 8 weeks of age. Both male and female mice were injected subcutaneously with either physiological dose of 27-HC (20 mg/kg body weight), 5ug/kg of 17b-estradiol (E(2)), E(2) plus 27-HC, or vehicle control, at 9am of the day of sacrifice, imaged by in vivo imaging system after treating with luciferin (150mg/kg body weight) intraperitoneally at 3pm, and sacrificed at the same day, at age of 10 weeks. Tissues were collected, homogenized, and measured for luciferase activity through luciferase assay (Promega). The tissue extraction method was also determined to make sure that the luciferase activities are comparable among tissues. The level of ER activity in the presence of E(2) was used as a positive control, and upon E(2 )treatment, ER activity was significantly increased in all analyzed tissues compared to vehicle treatment, with highest levels of ER activity in liver, testis, ovaries, and brain. Interestingly, the 27-HC treatment decreased the ER activity significantly in many tissues both in male and females, suggesting the existence of basal ER activity and an important antagonistic role of 27-HC. Yet, 27-HC showed agonistic effect and the levels of ER activity was even higher than E2 treatments in some tissues, showing a potential important role of 27-HC in these tissues. This study shed light upon potential effects of 27-HC on ER activity in various tissues, that can open the doors for further studies on 27-HC SERM characteristics. Reference:(1) Umetani, Michihisa, et al. Nature medicine 13.10 (2007): 1185.