Abstract
To distinguish the lithogenic effect of the classical estrogen receptor α (ERα) from that of the G protein-coupled receptor 30 (GPR30), a new estrogen receptor, on estrogen-induced gallstones, we investigated the entire spectrum of cholesterol crystallization pathways and sequences during the early stage of gallstone formation in gallbladder bile of ovariectomized female wild-type, GPR30((-/-)), ERα((-/-)), and GPR30((-/-))/ERα((-/-)) mice treated with 17β-estradiol (E2) at 6 µg/day and fed a lithogenic diet for 12 days. E2 disrupted biliary cholesterol and bile salt metabolism through ERα and GPR30, leading to supersaturated bile and predisposing to the precipitation of cholesterol monohydrate crystals. In GPR30((-/-)) mice, arc-like and tubular crystals formed first, followed by classical parallelogram-shaped cholesterol monohydrate crystals. In ERα((-/-)) mice, precipitation of lamellar liquid crystals, typified by birefringent multilamellar vesicles, appeared earlier than cholesterol monohydrate crystals. Both crystallization pathways were accelerated in wild-type mice with the activation of GPR30 and ERα by E2. However, cholesterol crystallization was drastically retarded in GPR30((-/-))/ERα((-/-)) mice. We concluded that E2 activates GPR30 and ERα to produce liquid crystalline versus anhydrous crystalline metastable intermediates evolving to cholesterol monohydrate crystals from supersaturated bile. GPR30 produces a synergistic lithogenic action with ERα to enhance E2-induced gallstone formation.
Highlights
To distinguish the lithogenic effect of the classical estrogen receptor ␣ (ER␣) from that of the G proteincoupled receptor 30 (GPR30), a new estrogen receptor, on estrogen-induced gallstones, we investigated the entire spectrum of cholesterol crystallization pathways and sequences during the early stage of gallstone formation in gallbladder bile of ovariectomized female wild-type, GPR30(؊/؊), ER␣(؊/؊), and GPR30(؊/؊)/ER␣(؊/؊) mice treated with 17-estradiol (E2) at 6 μg/day and fed a lithogenic diet for 12 days
These results indicated that the activation of GPR30 by E2 promoted the precipitation of solid cholesterol monohydrate crystals from liquid crystals independently of ER␣ because the latter induced cholesterol crystallization from the anhydrous crystalline pathway
Recent progress in understanding the molecular biological basis of GPR30, ER␣, and ER has provided many novel insights into the complex pathophysiological mechanisms underlying the lithogenic effect of E2 on cholesterol crystallization and gallstone formation [11]
Summary
To distinguish the lithogenic effect of the classical estrogen receptor ␣ (ER␣) from that of the G proteincoupled receptor 30 (GPR30), a new estrogen receptor, on estrogen-induced gallstones, we investigated the entire spectrum of cholesterol crystallization pathways and sequences during the early stage of gallstone formation in gallbladder bile of ovariectomized female wild-type, GPR30(؊/؊), ER␣(؊/؊), and GPR30(؊/؊)/ER␣(؊/؊) mice treated with 17-estradiol (E2) at 6 μg/day and fed a lithogenic diet for 12 days. We have found that the classical estrogen receptor ␣ (ER␣), but not ER, in the liver plays a critical role in the pathogenesis of 17-estradiol (E2)-induced gallstones in female mice [10]. Despite these observations, the metabolic abnormalities underlying the lithogenic effect of E2 on gallstone formation is not fully understood because the targeted deletion of the Er␣ gene cannot completely protect against gallstone formation in ovariectomized (OVX) female mice treated with high doses of E2 [11].
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