<b>Notch signaling regulates macrophage-mediated inflammation in non-alcoholic steatohepatitis</b>

The liver macrophage population comprises resident Kupffer cells (KCs) and recruited monocyte-derived macrophages. Monocytes are mostly recruited during liver inflammation and can differentiate into several types of macrophages with distinct pro- or anti-inflammatory properties that affect the severity and course of liver diseases. The mechanisms that underlie macrophage differentiation and function in nonalcoholic steatohepatitis (NASH) remain mostly unknown. Here, using single-cell RNA sequencing, fate mapping, intra-vital imaging, and conditional knock-out mouse models of hepatic macrophage subpopulations, we unraveled the temporal and spatial dynamics of distinct monocyte and monocyte-derived macrophage (MDM) subsets in NASH. We uncovered a crucial role for the Notch-RBPJ signaling pathway in controlling the differentiation, localization, and functions of liver macrophages in NASH. Notch-RBPJ signaling controls the monocyte-to-macrophage transition <i>in vivo</i>, with <i>Rbpj</i> deficiency blunting inflammatory macrophage differentiation and conversely promoting the emergence of <i>Nr4a1</i>-dependent protective Ly6C^lo monocytes. Mechanistically, the absence of <i>Rbpj</i> promoted stronger lipid uptake driven by elevated CD36 expression in KCs and Ly6C^lo monocytes and enhanced their protective interactions with endothelial cells. Our findings uncovered the crucial role of Notch-RBPJ signaling in liver monocyte-to-macrophage transition, identified new cellular targets and will aid the design of novel therapeutic strategies for the treatment of NASH.