Mouse patatin-like phospholipase domain-containing 3 influences systemic lipid and glucose homeostasis.

UNLABELLED: Human patatin-like phospholipase domain-containing 3 (PNPLA3) is associated with increased liver fat content and liver injury. Here, we show that nutritional status regulates PNPLA3 gene expression in the mouse liver. Sterol response element binding protein-1 (SREBP-1) activated PNPLA3 gene transcription via sterol regulatory elements (SREs) mapped to the promoter region. Chromatin immunoprecipitation and electrophoretic mobility shift assays confirmed that SREBP-1 proteins bound to the identified SREs. Furthermore, SREBP-1c mediated the insulin and liver X receptor agonist TO901317-dependent induction of PNPLA3 gene expression in hepatocytes. Adenovirus-mediated overexpression of mouse PNPLA3 increased intracellular triglyceride content in primary hepatocytes, and knockdown of PNPLA3 suppressed the ability of SREBP-1c to stimulate lipid accumulation in hepatocytes. Finally, the overexpression of PNPLA3 in mouse liver increased the serum triglyceride level and impaired glucose tolerance; in contrast, the knockdown of PNPLA3 in db/db mouse liver improved glucose tolerance. CONCLUSION: Our data suggest that mouse PNPLA3, which is a lipogenic gene directly targeted by SREBP-1, promotes lipogenesis in primary hepatocytes and influences systemic lipid and glucose metabolism.

PPARγ co-activator-1α co-activates steroidogenic factor 1 to stimulate the synthesis of luteinizing hormone and aldosterone.

The orphan nuclear receptor SF-1 (steroidogenic factor 1) is highly expressed in the pituitary, gonad and adrenal glands and plays key roles at all levels of the hypothalamic-pituitary-steroidogenic tissue axis. In the present study, we show that PGC-1α [PPARγ (peroxisome-proliferator-activated receptor γ) co-activator 1α] interacts with and co-activates SF-1 to induce LHß (luteinizing hormone ß) and αGSU (α-glycoprotein subunit) gene expression, subsequently leading to the increased secretion of LH in pituitary gonadotrope-derived αT3-1 cells. PGC-1α co-activation of LHß expression requires an SF-1-binding element [GSE (gonadotrope-specific element)] mapped to the promoter region of LHß. Mammalian two-hybrid and co-immunoprecipitation assays, as well as GST (glutathione transferase) pull-down experiments demonstrated that PGC-1α interacts with SF-1 in vivo and in vitro. Additionally, PGC-1α stimulates the expression of Cyp11b2 (aldosterone synthase gene), Cyp11b1 (steroid 11ß-hydroxylase gene) and P450scc (cholesterol side-chain cleavage enzyme), and the synthesis of aldosterone in adrenal-cortex-derived Y-1 cells. Chromatin immunoprecipitation assays confirmed that endogenous PGC-1α co-localizes with SF-1 in the LHß and Cyp11b2 promoter region. Knockdown of endogenous SF-1 by siRNA (small interfering RNA) abolished the PGC-1α induction of LHß and Cyp11b2 gene expression in αT3-1 and Y-1 cells respectively. Finally, we demonstrated that PGC-1α induces SF-1 gene expression in both αT3-1 and Y-1 cells. Taken together, our findings reveal the potential role of PGC-1α and suggest that it may play important roles in steroidogenesis, gonad development and sex differentiation through SF-1.

FoxO1 represses LXRα-mediated transcriptional activity of SREBP-1c promoter in HepG2 cells.

Recent studies have demonstrated that FoxO1 modulates the expression of SREBP-1c, but the exact mechanism remains unknown. Our results demonstrate that FoxO1 suppresses the SREBP-1c promoter transcriptional activity in HepG2 cells. This repression was independent of FoxO1 binding to the SREBP-1c promoter, but LXR responsive elements (LXREs) were crucial to this phenomenon. Moreover, FoxO1 also strongly inhibited the LXRα-mediated elevated transcription by SREBP-1c promoter. Electrophoretic mobility shift assay and chromatin immuno-precipitation further suggested the ability of FoxO1 to inhibit LXRα binding with the LXRE in the SREBP-1c promoter. FoxO1-mediated suppression of SREBP-1c promoter activity could be partially alleviated by insulin.