Estrogen Regulates Hepcidin Expression via GPR30-BMP6-Dependent Signaling in Hepatocytes

Abstract

Hepcidin, a liver-derived iron regulatory protein, plays a crucial role in iron metabolism. It is known that gender differences exist with respect to iron storage in the body; however, the effects of sex steroid hormones on iron metabolism are not completely understood. We focused on the effects of the female sex hormone estrogen on hepcidin expression. First, ovariectomized (OVX) and sham-operated mice were employed to investigate the effects of estrogen on hepcidin expression in an in vivo study. Hepcidin expression was decreased in the livers of OVX mice compared to the sham-operated mice. In OVX mice, bone morphologic protein-6 (BMP6), a regulator of hepcidin, was also found to be downregulated in the liver, whereas ferroportin (FPN), an iron export protein, was upregulated in the duodenum. Both serum and liver iron concentrations were elevated in OVX mice relative to their concentrations in sham-operated mice. In in vitro studies, 17β-estradiol (E2) increased the mRNA expression of hepcidin in HepG2 cells in a concentration-dependent manner. E2-induced hepatic hepcidin upregulation was not inhibited by ICI 182720, an inhibitor of the estrogen receptor; instead, hepcidin expression was increased by ICI 182720. E2 and ICI 182720 exhibit agonist actions with G-protein coupled receptor 30 (GPR30), the 7-transmembrane estrogen receptor. G1, a GPR30 agonist, upregulated hepcidin expression, and GPR30 siRNA treatment abolished E2-induced hepcidin expression. BMP6 expression induced by E2 was abolished by GPR30 silencing. Finally, both E2 and G1 supplementation restored reduced hepatic hepcidin and BMP6 expression and reversed the augmentation of duodenal FPN expression in the OVX mice. In contrast, serum hepcidin was elevated in OVX mice, which was reversed in these mice with E2 and G1. Thus, estrogen is involved in hepcidin expression via a GPR30-BMP6-dependent mechanism, providing new insight into the role of estrogen in iron metabolism.

Estrogen contributes to regulating iron metabolism through governing ferroportin signaling via an estrogen response element

“…Namely, a functional ERE within the promoter of FPN was responsible for the suppressive effect induced by E2. Our results offered an additional explanation for enhanced body iron storage in postmenopausal women [22]. In support of this statement, our results revealed that the expression of hepatic FPN was elevated in OVX mice, compared to SHAM mice.…”

“…The current findings would be beneficial to explain increased body iron mass in post-menopausal women. Our research group and another group have identified the regulation of hepcidin expression by estrogen [22,23]. Our previous data characterized an inhibitory effect of estrogen on hepcidin expression via a functional ERE within its promoter [23].…”

“…Hepatocytes have relatively high level of FPN on the plasma membrane [39]. Representative cell models of hepatocytes, such as HepG2 and SMMC-7721 cells, were conventionally used in estrogen-related studies [22,23]. Thus, we looked into the alteration of FPN expression upon E2 in HepG2 and SMMC-7721 cells.…”

“…For example, reduction of monthly blood loss would certainly help to retain body iron [17]. Recent studies from our research group and another group have uncovered the regulation of hepcidin by estrogen, linking estrogen to iron homeostasis [22,23]. Nonetheless, the impact of estrogen on iron metabolism is still elusive, and specifically, no insight has been gained for the potential regulation of estrogen on FPN.…”

Estrogen regulates iron homeostasis through governing hepatic hepcidin expression via an estrogen response element

“…This location differs from the one between −2474 and −2462 reported by the previous study (Yang et al, 2012). However, Ikeda and colleagues recently described different findings that the OVX mice revealed decreased hepcidin expression in livers, which was attributed to another mechanism of estrogen signaling in regulating hepcidin expression through G-coupled protein 30 (GPR30)-bone morphologic protein 6 (BMP6)-dependent pathway (Ikeda et al, 2012). The classical ERs and GPR30 are co-expressed in many types of cells and tissues, and the combined effect of estrogen on ERs and GPR30 is distinct, depending on a manner of synergism or antagonism (Prossnitz and Maggiolini, 2009).…”