Interleukin-6 is associated with liver lipid homeostasis but not with cell death in experimental hepatic steatosis

Abstract

Hepatic steatosis is a risk factor for the progression of non-alcoholic fatty liver disease. The role of pro-inflammatory interleukin (IL)-6 in hepatic steatosis etiology is controversial. We investigated in vivo and in primary hepatocyte cultures whether IL-6 has a modulator role in liver and mitochondria lipid composition and cell death in a choline-deficient (CD) diet rat model of hepatic steatosis. Dietary choline deficiency increased triglycerides and cholesterol, and reduced phosphatidylcholine (PC), phosphatidylethanolamine (PE) and the membrane integrity marker PC:PE ratio in liver. Choline-deficient diet enhanced systemic IL-6, and IL-6 receptor expression and cell death vulnerability in hepatocytes. Derangement of the mitochondrial electron transport chain and of its phospholipid environment was found in CD rat liver mitochondria, which exhibited elevated concentrations of triglycerides, cardiolipin and PC and elevated PC:PE ratio. The cell treatment with IL-6, but not PC, eliminated much of the CD-promoted lipid imbalance in mitochondria but not tumor-necrosis factor (TNF)-alpha-induced cell death. However, PC supplementation prevented the TNF-alpha-induced DNA fragmentation, cytochrome-c release and caspase-3 activity in control and CD hepatocytes. In conclusion, IL-6 ameliorated the mitochondria lipid disturbance in hepatocytes isolated from steatotic animals. Furthermore, PC is identified as a new survival agent that reverses several TNFalpha-inducible responses that are likely to promote steatosis and necrosis.