Disruption of Gpr45 causes reduced hypothalamic POMC expression and obesity
Jing Cui, … , Tian Xu, Xiaohui Wu
Jing Cui, … , Tian Xu, Xiaohui Wu
Published August 8, 2016
Citation Information: J Clin Invest. 2016;126(9):3192-3206. https://doi.org/10.1172/JCI85676.
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Research Article Endocrinology

Disruption of Gpr45 causes reduced hypothalamic POMC expression and obesity

Abstract

A rise in the occurrence of obesity has driven exploration of its underlying genetic basis and potential targets for intervention. GWAS studies have identified obesity susceptibility pathways involving several neuropeptides that control energy homeostasis, suggesting that variations in the genes that regulate food intake and energy expenditure may contribute to obesity. In this study, we identified 5 additional obesity loci, including a neuronal orphan GPCR called Gpr45, in a forward genetic screen of mutant mice generated by piggyBac insertional mutagenesis. Disruption of Gpr45 led to increased adiposity at the time of weaning and increases in body mass, fat content, glucose intolerance, and hepatic steatosis with advancing age. Mice with disruptions in Gpr45 also displayed a reduction in expression of the metabolic regulator POMC and less energy expenditure prior to the onset of obesity. Mechanistically, we determined that GPR45 regulates POMC expression via the JAK/STAT pathway in a cell-autonomous manner. Consistent with this finding, intraventricular administration of melanotan-2, an analog of the POMC derivative α-MSH, suppressed adult obesity in Gpr45 mutants. These results reveal that GPR45 is a regulator of POMC signaling and energy expenditure, which suggests that it may be a potential intervention target to combat obesity.

Authors

Jing Cui, Yi Ding, Shu Chen, Xiaoqiang Zhu, Yichen Wu, Mingliang Zhang, Yaxin Zhao, Tong-Ruei R. Li, Ling V. Sun, Shimin Zhao, Yuan Zhuang, Weiping Jia, Lei Xue, Min Han, Tian Xu, Xiaohui Wu

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Figure 7

GPR45 regulates POMC for its role in energy expenditure.

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GPR45 regulates POMC for its role in energy expenditure. (A and B) Weste...
(A and B) Western blots shows decreased phosphorylation of JAK2 and STAT3 in primary mutant hypothalamic cells (A) and hypothalami of P14 mutants (B). Quantitative comparisons are shown on the right, with total JAK2 or STAT3 protein as the internal control. n = 3 for each genotype. (C and D) Physical interaction between JAK2 and GPR45. Immunoprecipitation (C) by anti-JAK2 antibody showing that GPR45 interacts with JAK2 in the brain of adult HA-GPR45 transgenic mice. Anti-HA antibody was used to recognize HA-tagged GPR45. In vitro binding assay (D) shows that JAK2 interacts with the carboxyl terminus (GPR45-C tail), but not the third intracellular loop of GPR45 (GPR45-i3). Anti-GST antibody was used to recognize GST-tagged GPR45 fragments. (E) Chromatin immunoprecipitation by anti-STAT3 antibody revealed reduced STAT3 recruitment to the Pomc promoter in hypothalami of P14 mutants (n = 4). (F and H) Intra-third-ventrical administration of MTII reduced both bodyweight (F) and fat mass (H) in adult male mutants. gWAT, perigonadal fat; rWAT, retroperitoneal fat; BAT, interscapular brown fat. (G) MTII treatment reduced food intake in Gpr45 mutants and their wild-type littermates. Five mice were used for each group. Data from saline-treated wild-type mice serve as the baseline for statistics. All data are shown as the mean ± SEM. *P < 0.05, **P < 0.01, and ***P < 0.001 by Student’s t test; #P < 0.05, ##P < 0.01, and ###P < 0.001, MTII-treated PB1/PB1 vs. saline-treated +/+; §P < 0.05 and §§P < 0.01, MTII-treated +/+ vs. saline-treated +/+ in F and G.