Platelet-derived thrombospondin 1 promotes immune cell liver infiltration and exacerbates diet-induced steatohepatitis.
Background and Aims: Recent studies have implicated platelets, particularly a-granules, in the development of steatohepatitis (NASH). However, the specific mechanisms involved have yet to be determined. Notably, thrombospondin 1 (TSP1) is a major component of the platelet a-granules released during platelet activation. The role of platelet-derived TSP1 in NASH remains unknown and was investigated in this study. Approach and Results: Platelet-specific TSP1 knockout mice (TSP1?pf4) and their wild type littermates (TSP1F/F) were used. NASH was induced by feeding the mice a diet enriched in fat, sucrose, fructose, and cholesterol (AMLN diet). A human liver NASH organoid model was also employed. Although TSP1 deletion in platelets did not affect diet-induced steatosis, TSP1?pf4 mice exhibited attenuated NASH and liver fibrosis, accompanied by improvements in plasma glucose and lipid homeostasis. Moreover, intrahepatic platelet accumulation, activation and chemokine production were reduced in TSP1?pf4 mice, which was correlated with decreased immune cell infiltration into the liver. Consequently, this leads to diminished pro-inflammatory signaling in the liver and mitigated the progression of NAFLD.  Moreover, in vitro data revealed that co-culturing TSP1-deficient platelets in a human liver NASH organoid model attenuated hepatic stellate cell activation and NASH progression. Additionally, TSP1 deficient platelets play a role in regulating brown fat endocrine function, specifically affecting Nrg4 production. Crosstalk between brown fat and the liver may also influence NAFLD progression. Conclusions: These data suggest that platelet a-granule-derived TSP1 is a significant contributor to diet-induced NASH and fibrosis, and may serve as a new therapeutic target for this severe liver disease. Overall design: Platelet-specific TSP1 knockout mice (TSP1/pf4: KO) and their wild type littermates (TSP1F/F: WT) were fed with LF diet or AMLN diet for 32 weeks. The effect of TSP1 depleted platelets on liver phenotype and gene expression profile were determined. Livers were collected from four groups of mice (n=4 mice)/per group) for RNA-seq analysis.