Myeloid cells in liver and bone marrow acquire a functionally distinct inflammatory phenotype during obesity-related steatohepatitis

Objective: Bone marrow-derived myeloid cells accumulate in the liver as monocytes and macrophages during the progression of obesity-related non-alcoholic fatty liver disease (NAFLD) to steatohepatitis (NASH). Myeloid cells comprise heterogeneous subsets, and dietary overnutrition may affect macrophages in liver and bone marrow. We therefore aimed at characterizing in-depth the functional adaptations of myeloid cells in fatty liver. Design: We employed single-cell RNA-sequencing to comprehensively assess the heterogeneity of myeloid cells in liver and bone marrow during NAFLD, by analyzing C57BL/6 mice fed with a high-fat, high-sugar, high-cholesterol "Western diet" for 16 weeks. We also characterized NAFLD-driven functional adaptations of macrophages in vitro and their functional relevance during steatohepatitis in vivo. Liver myeloid leukocytes and their bone marrow precursors adapt a common and functionally relevant inflammatory signature during NAFLD progression. Bone marrow derived macrophages were cultivated for 7 days followed by 100 ng/ml LPS stimulation. Macrophages were preincubated for the first 4 days with and without 10 mM fatty acid (palmitic and oleic acid 1:3). ND=standard chow diet and WD=Western diet.