APOE-associated lipid-handling macrophages in hepatocellular carcinoma: ligand-receptor communication and host Apoe-linked myeloid remodeling.

BACKGROUND: Hepatocellular carcinoma (HCC) arises in the liver, an organ with active lipid metabolism, and is accompanied by marked myeloid-cell remodeling. Whether lipid-handling macrophage states are enriched in HCC and how they relate to candidate ligand-receptor communication and tumor microenvironmental remodeling remain unclear. METHODS: We analyzed paired tumor and adjacent liver single-cell transcriptomic data from 10 HCC patients. Tumor-associated lipid-handling candidates were screened using immune-cell composition, metabolic pathway activity, and tumor-upregulated lipid-related gene programs, with APOE prioritized for downstream analysis. Myeloid reclustering, module scoring, and CellChat analysis were used to characterize APOE-positive macrophages and infer APOE-positive macrophage-centered candidate communication. Hepa1-6 subcutaneous tumor models, an Nras-Myc-driven liver tumor model, mouse single-cell transcriptomics, and bone marrow-derived macrophage lipid-loading experiments were used to assess host Apoe deficiency, tumor-cell Apoe perturbation, and macrophage neutral lipid accumulation. RESULTS: HCC tumors showed altered immune-cell composition and immune-metabolic pathway activity compared with adjacent liver tissues. Among tumor-upregulated lipid-related candidates, APOE was prioritized because of its tumor-associated expression, consistent ranking across lipid-related screening strategies, and functional relevance to lipoprotein and cholesterol handling. APOE-positive macrophages were enriched in tumors and displayed lipid-routing, cholesterol-handling, endolysosomal, and redox-adaptive programs. CellChat analysis identified candidate ligand-receptor interactions involving APOE-positive macrophages, including an APOE-TREM2-related incoming interaction and SPP1-integrin/CD44 outgoing interactions. In the immunocompetent Hepa1-6 model, host Apoe deficiency attenuated tumor growth and was accompanied by reduced vascularization and increased CD8-positive cell infiltration, whereas tumor-cell Apoe knockdown did not significantly affect tumor volume or tumor weight in immunodeficient mice. In the Nras-Myc liver tumor model, Apoe deficiency reduced tumor burden and proliferative activity and was accompanied by a shift in tumor macrophage and monocyte programs away from lipid-processing and phagolysosomal activity toward inflammatory chemokine-associated activity. In lipid-loaded bone marrow-derived macrophages, Apoe deficiency increased neutral lipid accumulation. CONCLUSION: This study links APOE-associated macrophage lipid handling to inferred ligand-receptor communication and host Apoe-linked microenvironmental remodeling in HCC. These findings highlight an APOE-linked myeloid lipid-handling program as a potential component of immune microenvironmental remodeling during HCC development.