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Endocrinology. 2013 Oct;154(10):3539-51. doi: 10.1210/en.2012-2127. Epub 2013 Jul 16.

A novel experimental strategy to assess the metabolic effects of selective activation of a G(q)-coupled receptor in hepatocytes in vivo.

Author information

1
PhD, Chief, Molecular Signaling Section, Laboratory of Bioorganic Chemistry, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Building 8A, Room B1A-05, 8 Center Drive MSC 0810, Bethesda, Maryland 20892-0810. jurgenw@helix.nih.gov; or Jianhua Li, PhD, Center for Molecular Medicine, National Institutes of Health, National Heart, Lung, and Blood Institute, Building 10-CRC, Room 5-3216, 10 Center Drive MSC 1454, Bethesda, Maryland 20892-1454. E-mail: jianhuali@mail.nih.gov.

Abstract

Increased hepatic glucose production is a key pathophysiological feature of type 2 diabetes. Like all other cell types, hepatocytes express many G protein-coupled receptors (GPCRs) that are linked to different functional classes of heterotrimeric G proteins. The important physiological functions mediated by G(s)-coupled hepatic glucagon receptors are well-documented. In contrast, little is known about the in vivo physiological roles of hepatocyte GPCRs that are linked to G proteins of the G(q) family. To address this issue, we established a transgenic mouse line (Hep-Rq mice) that expressed a G(q)-linked designer receptor (Rq) in a hepatocyte-selective fashion. Importantly, Rq could no longer bind endogenous ligands but could be selectively activated by a synthetic drug, clozapine-N-oxide. Clozapine-N-oxide treatment of Hep-Rq mice enabled us to determine the metabolic consequences caused by selective activation of a G(q)-coupled GPCR in hepatocytes in vivo. We found that acute Rq activation in vivo led to pronounced increases in blood glucose levels, resulting from increased rates of glycogen breakdown and gluconeogenesis. We also demonstrated that the expression of the V(1b) vasopressin receptor, a G(q)-coupled receptor expressed by hepatocytes, was drastically increased in livers of ob/ob mice, a mouse model of diabetes. Strikingly, treatment of ob/ob mice with a selective V(1b) receptor antagonist led to reduced glucose excursions in a pyruvate challenge test. Taken together, these findings underscore the importance of G(q)-coupled receptors in regulating hepatic glucose fluxes and suggest novel receptor targets for the treatment of type 2 diabetes.

PMID:
23861369
PMCID:
PMC3776870
DOI:
10.1210/en.2012-2127
[Indexed for MEDLINE]
Free PMC Article

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