Dynamic Shifts in the Composition of Resident and Recruited Macrophages Influence Tissue Remodeling 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. In concert, monocyte-derived infiltrating macrophages enter the liver and consist of a transitional subset that expresses Cx3cr1/Ccr2 and a second subset characterized by expression of Trem2, Cd63, Cd9, and Gpmnb; markers ascribed to lipid-associated macrophages (LAMs). The Cx3cr1/Ccr2-expressing macrophages, referred to as C-LAMs, localize to macrophage aggregates and hepatic crown-like structures (hCLSs) in the steatotic liver. In C-motif chemokine receptor 2 (Ccr2)-deficient mice, C-LAMs fail to appear in the liver, and this prevents hCLS formation, reduces LAM numbers, and increases liver fibrosis. Taken together, our data reveal dynamic changes in liver macrophage subsets during the pathogenesis of NASH and link these shifts to pathologic tissue remodeling. [Display omitted] •Resident Kupffer cells are lost during NASH development•Recruited macrophages termed LAMs and C-LAMs infiltrate the NASH liver•LAMs and C-LAMs are essential for hepatic crown-like structure (hCLS) formation•Loss of LAMs and C-LAMs prevents hCLS formation and increases liver fibrosis Hepatic macrophages are thought to be essential in the pathogenesis of NASH; however, the underlying mechanisms remain unclear. Daemen et al. demonstrate infiltration of distinct populations of recruited monocyte-derived macrophages in the NASH liver, which form hepatic crown-like structures and influence tissue fibrosis.