Nonalcoholic fatty liver disease in CLOCK mutant mice
Xiaoyue Pan, … , Joyce Queiroz, M. Mahmood Hussain
Xiaoyue Pan, … , Joyce Queiroz, M. Mahmood Hussain
Published May 12, 2020
Citation Information: J Clin Invest. 2020;130(8):4282-4300. https://doi.org/10.1172/JCI132765.
View: Text | PDF
Research Article Hepatology Metabolism Article has an altmetric score of 9

Nonalcoholic fatty liver disease in CLOCK mutant mice

Abstract

Nonalcoholic fatty liver disease (NAFLD) is becoming a major health issue as obesity increases around the world. We studied the effect of a circadian locomotor output cycles kaput (CLOCK) mutant (ClkΔ19/Δ19) protein on hepatic lipid metabolism in C57BL/6 Clkwt/wt and apolipoprotein E–deficient (Apoe−/−) mice. Both ClkΔ19/Δ19 and ClkΔ19/Δ19 Apoe−/− mice developed a full spectrum of liver diseases (steatosis, steatohepatitis, cirrhosis, and hepatocellular carcinoma) recognized in human NAFLD when challenged with a Western diet, lipopolysaccharide, or CoCl2. We identified induction of CD36 and hypoxia-inducible factor 1α (HIF1α) proteins as contributing factors for NAFLD. Mechanistic studies showed that WT CLOCK protein interacted with the E-box enhancer elements in the promoters of the proline hydroxylase domain (PHD) proteins to increase expression. In ClkΔ19/Δ19 mice, PHD levels were low, and HIF1α protein levels were increased. When its levels were high, HIF1α interacted with the Cd36 promoter to augment expression and enhance fatty acid uptake. Thus, these studies establish a regulatory link among circadian rhythms, hypoxia response, fatty acid uptake, and NAFLD. The mouse models described here may be useful for further mechanistic studies in the progression of liver diseases and in the discovery of drugs for the treatment of these disorders.

Authors

Xiaoyue Pan, Joyce Queiroz, M. Mahmood Hussain

×

Figure 6

Age-dependent changes in hepatic lipid metabolism in ClkΔ19/Δ19 Apoe−/− mice.

Options: View larger image (or click on image) Download as PowerPoint
Age-dependent changes in hepatic lipid metabolism in ClkΔ19/Δ19 Apoe−/− ...
Male ClkΔ19/Δ19 Apoe−/− and Apoe−/− (Clkwt/wt Apoe−/−) mice were fed a chow diet, and livers and plasma were collected at 3 months (2–3 months, n = 8 per group), 6 months (5–6 months, n = 6 per group), or 12 months (10–12 months, n = 12 per group). Mean ± SD; *P < 0.05, **P < 0.01, ***P < 0.001, multiple t tests. (A) Hepatic triglyceride, free fatty acid, and TBARS levels measured using kits. (B) Plasma ALT levels were high in older ClkΔ19/Δ19 Apoe−/− mice. In contrast, plasma β-HB concentrations were low in older ClkΔ19/Δ19 Apoe−/− mice. (C) [3H]OA was injected i.p. into mice. Hepatic radioactivity was measured after 2 hours. (D and E) Liver sections were stained with Oil Red O (D) and H&E (E) staining. Data are representative of 2 independent experiments. (F) Electron microscopy (scale bar: 100 μm) showed more lipid droplets in older ClkΔ19/Δ19 Apoe−/− mice. Data are representative of 2 experiments. (G) Macrophage infiltration was determined by staining for CD68 in 12-month-old mice. Data are representative of 2 experiments. (H) Liver apoptotic cells were detected by TUNEL staining and were quantified. (I) Livers from mice (12 months old, chow diet) were used to study the binding of different proteins to the HIF1α binding site in the Cd36 promoter. Data are representative of 2 experiments. (J) Representative photograph of livers in 12-month-old mice.