Obesity is an independent risk factor for development of non-alcoholic fatty liver disease (NAFLD). With the epidemic burden of obesity and metabolic diseases, NAFLD occurrence is steadily rising, along with the need for therapeutic options of this disease. Preliminary data from rodent and human studies provide strong evidence to support the hypothesis that monocyte/macrophage-derived TSP1 in obesity downregulates liver macrophage SMPDL3B and this downregulation feeds back to increase TSP1 binding to its receptor-CD36. This positive feedback loop together with SMPDL3B’s action on TLR pathways further amplifies liver macrophage pro-inflammatory signaling and leads to NAFLD progression. In this proposal, how SMPDL3B regulates CD36 function and then TSP1-CD36 dependent pro-inflammatory signaling in macrophages will be determined in Aim 1. The in vivo importance of macrophage SMPDL3B in NAFLD development and progression in both animal models and human liver organoids will be determined in Aim 2. Whether specific blockade of TSP1/CD36 interaction upregulates liver macrophage SMPDL3B and attenuates liver pro- inflammatory signaling and NAFLD development and progression will be determined in Aim 3. Completing these studies will provide novel information on the mechanisms by which suppressed macrophage SMPDL3B enhances liver macrophage pro-inflammatory signaling and its critical role in the progression of obesity- associated NAFLD to NASH. Further, testing a novel therapeutic application of a peptide nanoparticle conjugate to block TSP1/CD36 interaction in obesity-associated NASH in vivo will have translational significance.