Dynamic Interplay between Resident and Recruited Macrophage Subsets in NASH

Macrophage-mediated inflammation is critical in the pathogenesis of non-alcoholic steatohepatitis (NASH). Here, we describe that with high fat, high sucrose diet feeding, mature Tim4pos Kupffer cells (KCs) decrease in number, while monocyte-derived Tim4neg macrophages accumulate. Through the use of single cell RNA sequencing and reporter mice we establish that monocyte-derived infiltrating macrophages comprise two subsets that can be distinguished by their expression or lack of expression of Cx3cr1. The Cx3cr1-expressing macrophages were localized to macrophage aggregates/hepatic crown like structures (hCLS) in the steatotic liver and are therefore referred to as CLuster Associated Monocyte-derived Macrophages (CLAMMs). In C- motif chemokine receptor 2 (Ccr2)-deficient mice, CLAMMs fail to appear in the liver and this is associated with a loss of macrophage aggregation despite similar degrees of liver steatosis and total macrophage content. Our data reveal the dynamic changes and functional diversity of macrophage subsets in the liver during the pathogenesis of NASH.