Macrophage-derived thrombospondin 1 promotes obesity-associated non-alcoholic fatty liver disease

Thrombospondin 1 (TSP1) is a multifunctional matricellular protein. We previously showed that TSP1 has 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/non-alcoholic steatohepatitis (NAFLD or NASH) remains largely unknown; thus, we aimed to determine its role.

High-fat diet or AMLN (amylin liver NASH) diet-induced obese and insulin-resistant NAFLD/NASH mouse models were utilised, in addition to tissue-specific Tsp1-knockout mice, to determine the contribution of different cellular sources of obesity-induced TSP1 to NAFLD/NASH development.

Liver TSP1 levels were increased in experimental obese and insulin-resistant NAFLD/NASH mouse models as well as in obese patients with NASH. Moreover, TSP1 deletion in 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 was 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 proinflammatory signalling (Toll-like receptor 4 signal pathway) and promoted NAFLD progression.

Macrophage-derived TSP1 is a significant contributor to obesity-associated NAFLD/NASH development and progression and could serve as a therapeutic target for this disease.

Obesity-associated non-alcoholic fatty liver disease is a most common chronic liver disease in the Western world and can progress to liver cirrhosis and cancer. No treatment is currently available for this disease. The present study reveals an important factor (macrophage-derived TSP1) that drives macrophage activation and non-alcoholic fatty liver disease development and progression and that could serve as a therapeutic target for non-alcoholic fatty liver disease/steatohepatitis.