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Rubicon deficiency exacerbates fasting-induced hepatic steatosis

Abstract Objective: Rubicon is an inhibitory interacting protein of the autophagy-related protein Uvrag. We previously showed that Rubicon deficiency promotes autophagic flux in vivo and that autophagy can degrade lipid droplets. This study aimed to investigate the effects of Rubicon deficiency on fasting-induced hepatic steatosis. Methods: Two-month-old wild-type (WT) and Rubicon-deficient mice were subjected to feeding or fasting for 24 hours to induce hepatic steatosis. The distribution of liver lipid droplets was revealed by oil red O staining. Hepatic and plasma triglyceride, nonesterified fatty acid (NEFA), and cholesterol levels were detected using commercially available kits. Real-time reverse transcriptasepolymerase chain reaction was performed to analyze the mRNA expression of genes related to lipid metabolism in the liver. Western blot was conducted to assess autophagy-related protein levels in the liver. The animal experiments were approved by the Institutional Animal Care and Use Committee at Shanghai Jiao Tong University, China. Results: We showed that under fasting conditions, Rubicon-deficient mice had more lipid droplets in the liver than WT controls. Consistent with these results, the hepatic triglyceride, NEFA, and cholesterol levels in fasted Rubicon-deficient mice were significantly higher than those of fasted WT controls. The levels of SREBP-1, a key regulator of lipid synthesis, were significantly lower in livers from fasted WT mice than those of fed WT mice. However, the decrease in SREBP-1 in fasted mice was attenuated by Rubicon deficiency. Western blot analysis demonstrated that the fasting-induced increase in autophagic flux was amplified by Rubicon deficiency. Finally, we showed that Rubicon deficiency in mice led to elevated plasma triglyceride and NEFA acid levels under fasting conditions. Conclusion: Rubicon deficiency exacerbates fasting-induced hepatic steatosis in mice.