Gα12 ablation exacerbates liver steatosis and obesity by suppressing USP22/SIRT1-regulated mitochondrial respiration
Tae Hyun Kim, … , Cheol Soo Choi, Sang Geon Kim
Tae Hyun Kim, … , Cheol Soo Choi, Sang Geon Kim
Published October 9, 2018
Citation Information: J Clin Invest. 2018;128(12):5587-5602. https://doi.org/10.1172/JCI97831.
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Research Article Hepatology Metabolism

Gα12 ablation exacerbates liver steatosis and obesity by suppressing USP22/SIRT1-regulated mitochondrial respiration

Abstract

Nonalcoholic fatty liver disease (NAFLD) arises from mitochondrial dysfunction under sustained imbalance between energy intake and expenditure, but the underlying mechanisms controlling mitochondrial respiration have not been entirely understood. Heterotrimeric G proteins converge with activated GPCRs to modulate cell-signaling pathways to maintain metabolic homeostasis. Here, we investigated the regulatory role of G protein α12 (Gα12) on hepatic lipid metabolism and whole-body energy expenditure in mice. Fasting increased Gα12 levels in mouse liver. Gα12 ablation markedly augmented fasting-induced hepatic fat accumulation. cDNA microarray analysis from Gna12-KO liver revealed that the Gα12-signaling pathway regulated sirtuin 1 (SIRT1) and PPARα, which are responsible for mitochondrial respiration. Defective induction of SIRT1 upon fasting was observed in the liver of Gna12-KO mice, which was reversed by lentivirus-mediated Gα12 overexpression in hepatocytes. Mechanistically, Gα12 stabilized SIRT1 protein through transcriptional induction of ubiquitin-specific peptidase 22 (USP22) via HIF-1α increase. Gα12 levels were markedly diminished in liver biopsies from NAFLD patients. Consistently, Gna12-KO mice fed a high-fat diet displayed greater susceptibility to diet-induced liver steatosis and obesity due to decrease in energy expenditure. Our results demonstrate that Gα12 regulates SIRT1-dependent mitochondrial respiration through HIF-1α–dependent USP22 induction, identifying Gα12 as an upstream molecule that contributes to the regulation of mitochondrial energy expenditure.

Authors

Tae Hyun Kim, Yoon Mee Yang, Chang Yeob Han, Ja Hyun Koo, Hyunhee Oh, Su Sung Kim, Byoung Hoon You, Young Hee Choi, Tae-Sik Park, Chang Ho Lee, Hitoshi Kurose, Mazen Noureddin, Ekihiro Seki, Yu-Jui Yvonne Wan, Cheol Soo Choi, Sang Geon Kim

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Figure 6

Rescue of metabolic phenotype of Gna12 KO by overexpression of USP22 or SIRT1.

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Rescue of metabolic phenotype of Gna12 KO by overexpression of USP22 or ...
(A) Effect of hepatic USP22 overexpression on SIRT1 induction by fasting. Immunoblotting for SIRT1 and USP22 (center) in the liver homogenates and SIRT1 quantification (far right). WT and Gna12-KO mice at 12 weeks of age were hydrodynamically injected with the plasmid expressing USP22 or control vector (Mock) (n = 3–5/group) (left). Third panel shows densitometric analysis for USP22 in the liver (n = 3–5/group). (B) Representative oil red O staining (left) and hepatic TG contents (right) (n = 3–5/group). Scale bars: 100 μm. (C) Effect of hepatic SIRT1 overexpression on CPT1 induction by fasting. Immunoblotting for SIRT1 and CPT1 (center) in the liver homogenates and their respective quantifications (right) (n = 3–4/group). WT and Gna12-KO mice at 15 weeks of age were injected with the adenovirus carrying mouse SIRT1 (Ad-SIRT1, 2.8 × 109 PFU/mouse) or GFP control (Ad-Con)via the tail vein (left). (D) Representative oil red O staining (left) and TG contents (right) in liver tissues (n = 3–4/group). Original magnification, ×20. (E) Effect of SIRT1 overexpression on OCR in AML12 cells. OCR was measured in AML12-sh-Gα12 (or AML12-sh-Luci) cells infected with Ad-SIRT1 (or Ad-Con) in the presence of oligomycin (1 μM), carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) (1 μM), or rotenone plus antimycin A (0.5 μM each). Results represent 4 independent experiments (n = 6–8 replicates/group for each experiment). Values represent mean ± SEM. Data were analyzed by 2-tailed Student’s t test (A, USP22) or ANOVA followed by LSD (A [SIRT1], C, and E) or Bonferroni’s (B and D) post hoc tests. For A–D, only fasted groups were analyzed for ease of data presentation. For A and C, blots in each panel were run in parallel using the same samples and β-actin was used as a normalization control for densitometric analysis.