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 mice were sacrificed and livers were harvested for further analysis.血小板反应蛋白1（Thrombospondin 1, TSP1）是一种多功能基质细胞蛋白。本团队既往研究证实，TSP1在肥胖相关代谢并发症中发挥关键作用，涉及炎症、胰岛素抵抗、心血管及肾脏病变。然而，其在肥胖相关非酒精性脂肪性肝病（non-alcoholic fatty liver disease, NAFLD）或非酒精性脂肪性肝炎（non-alcoholic steatohepatitis, NASH）中的作用仍未完全明确，本研究就此开展系统性探究。 本研究采用高脂饮食（high fat diet, HF）或AMLN饮食诱导的肥胖、胰岛素抵抗型NAFLD/NASH小鼠模型。此外，通过组织特异性TSP1敲除小鼠，明确肥胖诱导的不同细胞来源TSP1对NAFLD/NASH发生发展的贡献。 实验数据表明，在肥胖、胰岛素抵抗型NAFLD/NASH小鼠模型及人类肥胖型NASH患者体内，肝脏TSP1水平均显著升高。进一步实验发现，肝细胞或脂肪细胞中TSP1缺失无法缓解小鼠饮食诱导的NAFLD/NASH。但髓系/巨噬细胞特异性TSP1敲除可保护小鼠免受肥胖相关肝损伤，伴随肝脏炎症与纤维化程度显著降低。尤为重要的是，此种保护作用与肥胖程度及肝脏脂肪变水平无关。 机制层面，巨噬细胞来源的TSP1通过自分泌效应抑制肝脏内SMPDL3B的表达，进而放大肝脏促炎信号通路（Toll样受体4信号通路, TLR4信号通路），加速NAFLD的疾病进展。 综上，本研究数据显示，巨噬细胞来源的TSP1是肥胖相关NAFLD/NASH发生发展的重要促发因子，有望成为该疾病的潜在治疗靶点。 本研究将TSP1 floxed小鼠及巨噬细胞特异性TSP1敲除小鼠分别给予低脂饮食（low fat diet, LF）或高脂饮食（high fat diet, HF），持续喂养8个月。随后处死小鼠并采集肝脏组织，用于后续实验分析。