Hyperhomocysteinemia activates the aryl hydrocarbon receptor/CD36 pathway to promote hepatic steatosis in mice

Abstract

Hyperhomocysteinemia (HHcy) is associated with liver diseases such as fatty liver and hepatic fibrosis; however, the underlying mechanism is still largely unknown. The current study aimed to explore the signaling pathway involved in HHcyinduced hepatic steatosis (HS). C57BL/6 mice were fed a high-methionine diet (HMD) for 4 and 8 weeks to establish the HHcy mouse model. Compared to a chow diet, the HMD induced hepatic steatosis and elevated hepatic expression of CD36, a fatty acid transport protein. The increased CD36 expression was associated with activation of the aryl hydrocarbon receptor (AHR). In primary cultured hepatocytes, high levels of homocysteine (Hcy) treatment up-regulated CD36 and increased subsequent lipid uptake; both were significantly attenuated by small interfering RNA (siRNA) knockdown of CD36 and AHR. Chromatin immunoprecipitation assay revealed that Hcy promoted binding of AHR to the CD36 promoter, and transient transfection assay demonstrated markedly increased activity of the AHR response element by Hcy, which was ligand dependent. Mass spectrometry revealed significantly increased hepatic content of lipoxin A 4 (LXA 4 ), a metabolite of arachidonic acid, in HMD-fed mice. Furthermore, overexpression of 15-oxoprostaglandin 13-reductase 1, a LXA 4 inactivation enzyme, inhibited Hcy-induced AHR activation, lipid uptake, and lipid accumulation. Moreover, LXA 4 -induced up-regulation of CD36 and lipid uptake was inhibited by AHR siRNA in vitro in hepatocytes. Finally, treatment with an AHR antagonist reversed HHcy-induced lipid accumulation by inhibiting the AHR-CD36 pathway in mice. Conclusion: HHcy activates the AHR-CD36 pathway by increasing hepatic LXA 4 content, which results in hepatic steatosis. (HEPATOLOGY 2016;64:92-105) N onalcoholic fatty liver disease (NAFLD) is an increasingly recognized disease status that involves a spectrum of liver damage, ranging from simple steatosis to steatohepatitis, advanced fibrosis, and cirrhosis. Obesity, type 2 diabetes mellitus, and hyperlipidemia are important risk factors of NAFLD, but the pathogenesis of NAFLD is poorly understood. (1) Homocysteine (Hcy) is a toxic Abbreviations: 15d-PGJ2, 15-deoxy-D12,14-prostaglandin J2; 15-oxo-ETE, 15-oxo-eicosatetraenoic acid; 3-MC, 3

Orphan nuclear receptor NR4A1 suppresses hyperhomocysteinemia‐induced hepatic steatosis in vitro and in vivo

“…HepG2 cells were treated with 100 μ m Hcy for various times (0–48 h). Consistent with previous studies , oil red O staining revealed that Hcy induced lipid droplet accumulation in HepG2 cells (Fig. A).…”

Lipidomic Evaluation of Aryl Hydrocarbon Receptor-Mediated Hepatic Steatosis in Male and Female Mice Elicited by 2,3,7,8-Tetrachlorodibenzo-p-dioxin

“…The response to TCDD and related compounds is well conserved, 7,10,20 characterized by increased lipid uptake, 10,14,16 and the repression of β -oxidation 10 and de novo FA synthesis. 10,17,20 To further evaluate TCDD-elicited steatosis and progression to steatohepatitis with fibrosis, untargeted lipidomic data were integrated with complementary RNA-Seq and ChIP-Seq data sets.…”

“…11,12 For example, ceramides promote oxidative stress and inflammation which contribute to T2D and MetS development. 13 TCDD induces hepatic lipid accumulation, mediated at least in part by the induction of the lipid transporter CD36, 10,14 and characterized by increased dietary mono- and polyunsaturated fatty acid levels. 15,16 Although previous studies suggest hepatic lipid composition is altered by TCDD, 15−18 few have examined changes across lipid classes including effects on cholesterol esters and phospholipids.…”

Association between homocysteine and non-alcoholic fatty liver disease in Chinese adults: a cross-sectional study

“…On the other hand, elevated homocysteine may conversely promote the progression of liver damage. Indeed, Yao et al [23] recently found that hyperhomocysteinemia could promote hepatic steatosis in mice through activation of the aryl hydrocarbon receptor/CD36 pathway. According to several experimental studies, hepatic lipid accumulation was induced in different models of hyperhomocysteinemia [24–26].…”