High-fat diet-induced TRAF6 Upregulation Promotes Liver Cholesterol Accumulation and Fatty Liver Development Through EZH2-mediated miR-429/PPARα axis

Abstract Despite the increasing prevalence of fatty liver diseases worldwide, the molecular mechanism underlying its pathogenesis remains poorly defined. This study examines the expression and significance of TNF receptor associated factor 6 (TRAF6) in the high-fat diet (HFD)-induced mouse obesity model and the oleic acid/palmitic acid (OA/PA)-induced cell model. After developing these models, we measured the expressions of TRAF6, enhancer of the zeste homolog 2 (EZH2) and peroxisome proliferator activated receptor alpha (PPARα). The expression of TRAF6, EZH2 and PPARα was manipulated to investigate their roles in cholesterol accumulation through evaluating the plasma levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C). Co-IP assay was used to determine the interaction between TRAF6 and EZH2 and ChIP assay to detect the enrichment of EZH2 and H3K27me3 in miR-429 promoter. We found that HFD resulted in elevated TRAF6 and miR-429 in fatty liver, and reduced EZH2 and PPARα. TRAF6 mediated the ubiquitination of EZH2 and increased miR-429 expression, and miR-429 targeted PPARα. TRAF6 increased cholesterol accumulation in liver cells in vitro via the EZH2/miR-429/PPARα axis. Collectively, HFD up-regulates TRAF6 and ubiquitinates EZH2 to promote the miR-429-dependent inhibition of PPARα, leading to cholesterol accumulation in liver and the occurrence of fatty liver.