Improvement Lipophagy by Restoring Rab7 Cycle: Protective Effects of Quercetin on Ethanol-Induced Liver Steatosis

Background: Chronic alcohol consumption induces lipophagy retard which contributes the pathogenesis of liver steatosis. Lipophagy-related Rab7 responsible for the fusion between autophagosomes and lysosomes has been presumed as a crucial regulator on the progression of alcohol liver disease (ALD) despite elusive mechanisms. More importantly, whether hepatoprotective quercetin targets Rab7-associated lipophagy disorder or not, still remains uncertain. Results: ALD mice were induced by chronic-plus-single-binge ethanol feeding that manifested by hampering autophagosomes formation with lipid droplets (LDs) and fuse with lysosomes compared with the normal control, which was normalized partially by quercetin. GST-RILP pulldown assay of Rab7 indicated an improved GTP-Rab7 as quercetin treatment for ethanol-feeding mice. Lipophagy was blocked when HepG2 cells were transfected with siRNA-Rab7, which was reversed through co-transfection of Rab7Wt plasmid. Rab7-specific inhibitor CID1067700 aggravated ethanol-induced steatosis and autophagic flux disruption visualized by immunofluorescence co-localization analysis and mCherry-GFP-LC3 transfection. HepG2 cells overexpressing Rab7Wt show a stronger alleviation on alcohol-induced lipophagy dysfunction than Rab7Q67L. Furthermore, TBC1D5 responsible for Rab7 inactivation was downregulated after alcohol administration, but regained by quercetin. Rab7 circulation retarded by ethanol and corrected by quercetin was further revealed by fluorescence recovery after photobleaching (FRAP). Conclusions: Chronic alcoholic not only inactivates Rab7 but also retards TBC1D5-mediated Rab7 turnover, synergistically obstructing lipophagy flux and promoting ethanol-induced steatosis. Quercetin attenuates adipohepatic degeneration by normalizing ethanol-imposed Rab7 disorders and subsequent lipophagy disturbance, highlighting a novel mechanism and promising prospect of quercetin-like phytochemicals against the crucial first hit from the alcohol.