Hepatic Gi signaling regulates whole-body glucose homeostasis
Mario Rossi, … , Owen P. McGuinness, Jürgen Wess
Mario Rossi, … , Owen P. McGuinness, Jürgen Wess
Published January 16, 2018
Citation Information: J Clin Invest. 2018;128(2):746-759. https://doi.org/10.1172/JCI94505.
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Research Article Endocrinology

Hepatic Gi signaling regulates whole-body glucose homeostasis

Abstract

An increase in hepatic glucose production (HGP) is a key feature of type 2 diabetes. Excessive signaling through hepatic Gs–linked glucagon receptors critically contributes to pathologically elevated HGP. Here, we tested the hypothesis that this metabolic impairment can be counteracted by enhancing hepatic Gi signaling. Specifically, we used a chemogenetic approach to selectively activate Gi-type G proteins in mouse hepatocytes in vivo. Unexpectedly, activation of hepatic Gi signaling triggered a pronounced increase in HGP and severely impaired glucose homeostasis. Moreover, increased Gi signaling stimulated glucose release in human hepatocytes. A lack of functional Gi-type G proteins in hepatocytes reduced blood glucose levels and protected mice against the metabolic deficits caused by the consumption of a high-fat diet. Additionally, we delineated a signaling cascade that links hepatic Gi signaling to ROS production, JNK activation, and a subsequent increase in HGP. Taken together, our data support the concept that drugs able to block hepatic Gi–coupled GPCRs may prove beneficial as antidiabetic drugs.

Authors

Mario Rossi, Lu Zhu, Sara M. McMillin, Sai Prasad Pydi, Shanu Jain, Lei Wang, Yinghong Cui, Regina J. Lee, Amanda H. Cohen, Hideaki Kaneto, Morris J. Birnbaum, Yanling Ma, Yaron Rotman, Jie Liu, Travis J. Cyphert, Toren Finkel, Owen P. McGuinness, Jürgen Wess

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Figure 5

In vivo and in vitro studies with CB1 cannabinoid receptor agonists.

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In vivo and in vitro studies with CB1 cannabinoid receptor agonists. (A ...
(A and B) IGTTs in control and Hep-Gi–KO mice. Note that AEA caused impaired glucose tolerance in control mice (A) but not in Hep-Gi–KO mice (B). Mice were fasted overnight for approximately 12 hours. Ten minutes before glucose injections (2 g/kg i.p.), mice were injected with either AEA (10 mg/kg i.p.) or vehicle (Veh). Studies were performed with female mice (at least 16 weeks of age). Data represent the mean ± SEM (n = 4 or 5 mice/group). *P < 0.05, compared with the vehicle-treated group. Statistical significance was determined by Student’s t test. (C–F) Stimulation of WT mouse primary hepatocytes with CB1 receptor agonists. Hepatocytes were prepared from male WT mice (~14 weeks of age) maintained on a HFD to boost CB1 receptor expression levels (13). (C and D) Treatment of WT mouse hepatocytes with M-AEA (150 nM), a metabolically stable CB1 receptor agonist. The agonist-induced increase in glucose output was completely absent in the presence of the ROS scavenger NAC (5 mM) or the selective JNK inhibitor BI87G3 (10 μM). (E and F) Incubation of WT mouse hepatocytes with HU210, a CB1 receptor agonist. Hepatocytes were pretreated with NAC (5 mM) for 2 hours and then stimulated with HU210 (1 μM) for the indicated durations. Subsequently, p-JNK and total JNK expression levels were determined by Western blotting. (E) Representative Western blot. (F) Quantification of Western blot data. Immunoreactive bands were quantified using ImageJ. p-JNK expression levels were normalized to total JNK expression. Data represent the mean ± SEM from 3 independent experiments. *P < 0.05, **P < 0.01, and ***P < 0.001, compared with the corresponding control value. Statistical significance was determined by (A and B) 2-tailed Student’s t test and (C, D, and F) 2-way ANOVA followed by Bonferroni’s post-hoc test). See complete unedited blots in the supplemental material.