Inflammatory Stress Contributes To Lipid Disorder Mediated Liver Injuries Via The Activation Of CXCL16/CXCR6 Pathway

Background Liver is a central organ for lipid metabolism. Lipid disorder plays crucial roles in liver injuries. Non-alcoholic fatty liver disease (NAFLD), characterized with early lipid accumulation and subsequent inflammation in liver, is considered as the main performance of metabolic syndrome (MS) in the liver. This study aimed to investigate the role of CXC chemokine ligand 16 (CXCL16) and its receptor CXC chemokine receptor 6 (CXCR6) in the progression of NAFLD under inflammation.Methods Eight-week male apolipoprotein E knockout mice were randomly divided into control group, high-fat diet group (HF group) and high fat diet+10% casein injection group (HF+casein group). After egiht weeks, mices were humanely killed. Plasma and livers were collected and used for experiments. In in vitro study, we used IL-1β, cholesterol loading or CXCL16 siRNA as stimulators to observe the effect of inflammation on hepatic cells using human hepatoblastoma cell line (HepG2). The plasma lipid profile analysis and inflammatory cytokines was measured by biochemical analysis and ELISA respectively. The lipid accumulation was examined by Hematoxylin eosin staining (HE), Oil Red O staining, Filipin staining, and a quantitative intracellular cholesterol assay. The gene and protein expression of molecules involved in CXCL16/CXCR6 pathway, inflammatory cytokines and extracellular matrix (ECM) were examined by real-time polymerase chain reaction (PCR), and Western blot. The fluorescent intensity of reactive oxygen species (ROS) was checked by Flow Cytometry.Results Compared with the HF group, significantly elevated levels of serum amyloid protein A (SAA), increased expression of tumor necrosis factor alpha (TNF-α) and monocytes chemotactic protein 1 (MCP-1) in livers of casein-injected mice confirmed successful induction of inflamed NAFLD model. Lipid profile assay showed that there was significant hypolipidemia in HF+casein group compared with the HF group except elevated serum HDL. Inflammation significantly increased lipid accumulation in livers of HF+casein group compared with the HF group and the controls. Furthermore, inflammation increased the expression of CXCL16, CXCR6 and a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) in livers, accompanied with increased ECM expression and ROS production. These effects were further confirmed by in vitro studies. Interestingly, CXCL16 gene knowdown in HepG2 cells induced by CXCL16 siRNA resulted in decreased lipid accumulation, ECM excretion, and ROS production.Conclusion These findings suggest that activation of CXCL16/CXCR6 mediated by inflammation induces intracellular lipid deposition, increases ECM secretion, and ROS production, thus finally accelarating the progression of NAFLD.