Silencing steroid receptor coactivator-1 in the nucleus of the solitary tract reduces estrogenic effects on feeding and apolipoprotein A-IV expression

Ling Shen,Yin Liu,Patrick Tso,David Q.-H Wang,W Sean Davidson,Stephen C Woods,Min Liu

doi:10.1074/jbc.ra117.000237

Abstract

We previously found that 17β-estradiol (E2) stimulates apolipoprotein A-IV (apoA-IV) gene expression in the nucleus of the solitary tract (NTS) of lean ovariectomized (OVX) rodents. Here we report that in the NTS of high-fat diet-induced obese (DIO) rats, the apoA-IV mRNA level is significantly reduced and that the estrogenic effects on apoA-IV gene expression and food intake are impaired. E2 regulates apoA-IV gene expression through its nuclear receptor α (ERα), which requires co-activators, such as steroid receptor coactivator-1 (SRC-1), to facilitate the transcription of targeted genes. Interestingly, SRC-1 gene expression is significantly reduced in DIO OVX rats. SRC-1 is colocalized with apoA-IV in the cells of the NTS and E2 treatment enhances the recruitment of ERα and SRC-1 to the estrogen response element at the apoA-V promoter, implying the participation of SRC-1 in E2's stimulatory effect on apoA-IV gene expression. Using small hairpin RNA (shRNA), which was validated in cultured neuronal cells, we found that SRC-1 gene knockdown specifically in the NTS significantly diminished E2's anorectic action, leading to increased food intake and body weight. More importantly, the stimulatory effect of E2 on apoA-IV gene expression in the NTS was significantly attenuated in SRC-1 knockdown rats. These results collectively demonstrate the critical roles of NTS SRC-1 in mediating E2's actions on food intake and apoA-IV gene expression and suggest that reduced levels of endogenous SRC-1 and apoA-IV expression are responsible for the impaired E2's anorectic action in obese females.

Highlights

We previously found that 17␤-estradiol (E2) stimulates apolipoprotein A-IV gene expression in the nucleus of the solitary tract (NTS) of lean ovariectomized (OVX) rodents
Using small hairpin RNA, which was validated in cultured neuronal cells, we found that steroid receptor coactivator-1 (SRC-1) gene knockdown in the NTS significantly diminished E2’s anorectic action, leading to increased food intake and body weight
Because high-fat diet (HFD) and low-fat diet (LFD) rats consumed different amounts of energy each day, a 3rd group of rats, called pair HFD-fed (PHF) rats, received the HFD each day, but in an amount limited to the average daily caloric consumption of the rats fed the LFD ad libitum, as we reported previously [10]

Summary

The abbreviations used are

E2, 17␤-estradiol; SRC-1, steroid receptor coactivator-1; apoA-IV, apolipoprotein A-IV; OVX, ovariectomy; NTS, nucleus of the solitary tract; shRNA, small hairpin RNA; HFD, high-fat diet; LFD, low-fat diet; ER␣, estrogen receptor ␣; KO, knock-out; PHD, pair HFD-fed; DIO, dietinduced obese; qPCR, quantitative PCR; ERE, estrogen response element; shCTL, control shRNA; GFP, green fluorescent protein. E2 enhances the satiating potency of apoA-IV [2], and more importantly, compared with OVX wildtype controls, OVX apoA-IV knock-out (KO) mice have a blunted reduction of feeding in response to E2, thereby eating significantly more food and gaining more body weight during the period of cyclic E2 replacement [2] These data collectively suggest that increased endogenous apoA-IV signaling may partially mediate E2-induced inhibition of feeding in lean females. We performed in vitro and in vivo studies to determine whether SRC-1 signaling is necessary to mediate E2 effects on apoA-IV gene expression and food intake using lentiviral-mediated small hairpin RNA (shRNA), which was delivered into the NTS

Results

Discussion

Experimental procedures