Single-cell profiling reveals hepatic monocyte-derived macrophages heterogeneity during steatotic liver disease

BACKGROUND: Monocyte-derived macrophages (MoMFs) play key roles in liver inflammation and fibrogenesis, with their heterogeneity affecting metabolic dysfunction-associated steatotic liver disease (MASLD) progression. However, current therapeutic strategies targeting macrophage-mediated inflammation have shown limited clinical efficacy in MASLD. METHODS: We conducted single-cell RNA sequencing (scRNA-seq) of liver-infiltrating 7AAD-CD45+Ly6G-CD11bhiF4/80int MoMFs from NCD-fed and MCD-fed mice. Monocle 2 and CellChat analyses explored developmental trajectories and intercellular interactions, respectively. RESULTS: Seven distinct clusters (c0-c6) with unique molecular signatures were identified. Beyond the classical CD206+ M2-polarized MoMFs, we identified 2 distinct subsets: CCR3+ (c3) MoMFs with enhanced pro-inflammatory and oxidative stress activities, and CCR7+ (c4) MoMFs with specialized antigen-presenting capacity in MASLD mouse livers. Although CCR2+ MoMFs are classically considered pro-inflammatory, our study revealed that the predominant CD14+CCR2+ (c0) MoMFs exhibit additional functional roles in fibrosis, lipid accumulation, and antigen presentation. Our pseudotime and in vitro data demonstrate that resident basal c1 MoMFs are phenotypically plastic, capable of acquiring CD14+/CCR7+ markers and transitioning toward c0-like and c4-like states, implying a potential intrahepatic origin for these subsets in diet-induced steatohepatitis. Notably, these MoMFs subsets and their dynamic changes during disease progression were conserved between the mouse models and human MASLD samples. CONCLUSIONS: Our study systematically characterized the heterogeneity and dynamic changes in intrahepatic MoMFs during MASLD progression. Resident c1 MoMFs are plastic and could be a local source for CD14+/CCR7+ subsets in MASLD without relying solely on bone marrow recruitment. These findings provide new insights into the therapeutic strategies that target macrophage-mediated inflammation in MASLD.