Macrophage-derived thrombospondin1 promotes obesity-associated non-alcoholic fatty liver disease

Thrombospondin 1 (TSP1) is a multifunctional matricellular protein. Previously we have shown that TSP1 plays an important role in obesity-associated metabolic complications including inflammation, insulin resistance, cardiovascular and renal disease. However, its contribution to obesity-associated non-alcoholic fatty liver disease (NAFLD) or non-alcoholic steatohepatitis (NASH) remains largely unknown and is determined in this study. High fat diet or AMLN diet-induced obese and insulin resistant NAFLD/NASH mouse models were utilized. In addition, tissue specific TSP1 knockout mice were utilized to determine the contribution of different cellular sources of obesity-induced TSP1 to NAFLD/NASH development. The data demonstrated that liver TSP1 levels were increased in experimental obese and insulin resistant NAFLD/NASH mouse models as well as in human obese NASH patients. Moreover, TSP1 deletion in hepatocyte or adipocytes did not protect mice from diet-induced NAFLD/NASH. However, myeloid/macrophage-specific TSP1 deletion protected mice against obesity-associated liver injury, accompanied by reduced liver inflammation and fibrosis. Importantly, this protection is independent of the levels of obesity and hepatic steatosis. Mechanistically, through an autocrine effect, macrophage-derived TSP1 suppressed SMPDL3B expression in liver, which amplified liver pro-inflammatory signaling (TLR4 signal pathway) and promoted NAFLD progression. Together, out data suggest that macrophage-derived TSP1 is a significant contributor to obesity-associated NAFLD/NASH development and progression and may serve as a therapeutic target for this disease. TSP1 floxed mice and macrophage specific TSP1 knockout mice were fed with LF or HF diet for 8 months. Then mie were sacrficed and livers were harvested for further analysis.