Hepatic stellate cell derived lipid droplets drive protumoral M2 macrophage polarization in hepatocellular carcinoma.

[BACKGROUND] During chronic liver injury, hepatic stellate cells (HSCs) lose their vitamin-A-rich lipid droplets (LDs), yet whether these organelles are merely degraded or released via vesicles and functionally relevant remains unclear. We investigated the fate of HSCs LDs and their impact on hepatic macrophage phenotype and hepatocellular carcinoma (HCC) development.

[METHODS] Chronic liver injury was induced in C57BL/6 mice using carbon tetrachloride (CCl) for up to 12 weeks. HSCs activation and lipid droplet dynamics were assessed by immunofluorescence, transmission electron microscopy, and flow cytometry. Single-cell RNA sequencing data from normal and inflamed livers were analyzed to characterize cell populations and interactions. HSC-derived LDs were isolated by gradient centrifugation and their effects on macrophage polarization were evaluated in vitro and in vivo. An orthotopic HCC model was used to assess the impact of lipid droplet-educated macrophages on tumor growth. Clinical relevance was validated using The Cancer Genome Atlas-liver hepatocellular carcinoma (TCGA-LIHC) cohort data.

[RESULTS] Activated HSCs in fibrotic livers showed progressive fragmentation and release of LDs, which were subsequently internalized by hepatic macrophages. Single-cell transcriptomic analysis revealed enhanced HSC-macrophage interactions and upregulation of lipid metabolism pathways in both cell types during liver inflammation. HSC-derived LDs acted as a direct metabolic cue to induced M2 polarization of macrophages, characterized by elevated secretion of transforming growth factor-beta (TGF-β1), interleukin-10 (IL-10), and C-C Motif Chemokine Ligand 17 (CCL17). In orthotopic HCC models, co-injection of tumor cells with lipid droplet-educated macrophages significantly enhanced tumor growth compared to control macrophages. TCGA analysis showed that high CD163 expression correlated with poor overall survival in HCC patients.

[CONCLUSION] Our findings identifies a distinct mechanism whereby activated HSCs transfer LDs to hepatic macrophages, inducing M2 polarization and creating a pro-tumorigenic microenvironment. This HSC-macrophage crosstalk represents a potential metabolic therapeutic target for preventing HCC development in patients with chronic liver disease.