Lipogenic transcription factor ChREBP mediates fructose-induced metabolic adaptations to prevent hepatotoxicity
Deqiang Zhang, … , M. Bishr Omary, Lei Yin
Deqiang Zhang, … , M. Bishr Omary, Lei Yin
Published June 19, 2017
Citation Information: J Clin Invest. 2017;127(7):2855-2867. https://doi.org/10.1172/JCI89934.
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Research Article Hepatology Metabolism

Lipogenic transcription factor ChREBP mediates fructose-induced metabolic adaptations to prevent hepatotoxicity

Abstract

Epidemiologic and animal studies implicate overconsumption of fructose in the development of nonalcoholic fatty liver disease, but the molecular mechanisms underlying fructose-induced chronic liver diseases remain largely unknown. Here, we have presented evidence supporting the essential function of the lipogenic transcription factor carbohydrate response element–binding protein (ChREBP) in mediating adaptive responses to fructose and protecting against fructose-induced hepatotoxicity. In WT mice, a high-fructose diet (HFrD) activated hepatic lipogenesis in a ChREBP-dependent manner; however, in Chrebp-KO mice, a HFrD induced steatohepatitis. In Chrebp-KO mouse livers, a HFrD reduced levels of molecular chaperones and activated the C/EBP homologous protein–dependent (CHOP-dependent) unfolded protein response, whereas administration of a chemical chaperone or Chop shRNA rescued liver injury. Elevated expression levels of cholesterol biosynthesis genes in HFrD-fed Chrebp-KO livers were paralleled by an increased nuclear abundance of sterol regulatory element–binding protein 2 (SREBP2). Atorvastatin-mediated inhibition of hepatic cholesterol biosynthesis or depletion of hepatic Srebp2 reversed fructose-induced liver injury in Chrebp-KO mice. Mechanistically, we determined that ChREBP binds to nuclear SREBP2 to promote its ubiquitination and destabilization in cultured cells. Therefore, our findings demonstrate that ChREBP provides hepatoprotection against a HFrD by preventing overactivation of cholesterol biosynthesis and the subsequent CHOP-mediated, proapoptotic unfolded protein response. Our findings also identified a role for ChREBP in regulating SREBP2-dependent cholesterol metabolism.

Authors

Deqiang Zhang, Xin Tong, Kyle VanDommelen, Neil Gupta, Kenneth Stamper, Graham F. Brady, Zhuoxian Meng, Jiandie Lin, Liangyou Rui, M. Bishr Omary, Lei Yin

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Figure 6

ChREBP blocks HFrD-induced liver injury in part by degrading SREBP2-N to suppress cholesterol biosynthesis.

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ChREBP blocks HFrD-induced liver injury in part by degrading SREBP2-N to...
(A) HFrD feeding induced both SREBP2-FL and SREBP2-N protein expression in the livers of 70% HFrD–fed Chrebp–/– mice. (B) Restoring ChREBP expression lowered SREBP2-N in the nuclear extract from the livers of HFrD-fed Chrebp–/– mice. (C–G) Depletion of Srebp2 by shRNA ameliorated HFrD-induced liver injury in Chrebp–/– mice. Chrebp–/– mice (8 weeks of age) were injected with either Srebp2-knockdown adenovirus (Ad-shSrebp2, n = 3) or control adenovirus (Ad-shLacZ, n = 3) and then fed a HFrD for 2 weeks. (C) Srebp2-knockdown efficiency was confirmed by Western blotting, and (D) its targets expression and filipin staining detected free cholesterol. Liver injury was assessed by (C) Western blotting with antibodies against apoptotic markers, (E) a serum ALT assay, (F) liver H&E staining, and (G) TUNEL staining (arrowheads indicate apoptotic cells). (H) ChREBP promoted SREBP2 protein degradation. U2OS cells were transfected with Flag-Srebp2-N and cotransduced with Ad-GFP or Ad-Flag-Chrebp and then treated with 10 μM MG132 for 3 or 6 hours. ChREBP and SREBP2-N expression levels were assessed by Western blotting with anti-Flag antibody. (I) ChREBP promoted SREBP2 protein ubiquitination. 293A cells were transfected with Myc-Srebp2-N and cotransduced with Ad-GFP or Ad-Flag-Chrebp. Polyubiquitinated SREBP2-N was pulled down by denaturing immunoprecipitation with anti-Myc antibody and detected by Western blotting with antiubiquitin. (J) ChREBP interacted with SREBP2. 293A cells were transfected with Flag-Srebp2-N and cotransfected with pNTAP-CBP-SBP-Chrebp or pNTAP empty vector. The lysate was subjected to immunoprecipitation with streptavidin beads and to Western blotting with CBP or Flag antibodies. (K) Working model: high-fructose–induced ChREBP suppresses free cholesterol loading and protects mice from liver injury via the promotion of SREBP2 degradation. Data shown in H, I, and J are representative results of 3 independent experiments. *P < 0.05, by 2-tailed Student’s t test. Data represent the mean ± SEM. Scale bars: 100 μm. IB, immunoblot; IP, immunoprecipitation.