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.