Single-cell and bulk transcriptome analysis unveils a ligand-receptor-based signature for prognostication and reveals that TREM1 controls the malignant behaviors of hepatocellular carcinoma.

The transcriptional heterogeneity and cellular ecosystem diversity of HCC await further exploration. Single-cell and bulk RNA sequencing data from HCC cells are analyzed to generate a LASSO model for HCC prognostication. CCK-8, scratch assay, flow cytometry, and ROS assays are used to validate how TREM1 may affect HCC cell biological behaviors in vitro. qPCR, western blot analysis, immunohistochemistry, and flow cytometry are applied in a xenograft model to test the effects of TREM1 knockdown on carcinogenesis and the tumor microenvironment. A single-cell atlas of the multicellular ecosystem comprising 13 cell types in HCC is constructed. On the basis of ligand-receptor marker genes specifically extracted from the cell populations, a prognostic model is defined and subsequently validated in additional clinical cohorts. For the first time, a heterogeneous immune microenvironment is observed between low- and high-risk patients, primarily involving macrophages, CD4+ T cells, M1 macrophages, and regulatory T (Treg) cells. Sufficient evidence validates the positive effects of TREM1 on HCC cell proliferation, migration, and apoptosis. Additionally, TREM1 positively modulates the levels of the proinflammatory cytokines IL-1β, TNF-α, and MCP-1. TREM1 downregulation alters the proportions of M1 macrophages and Tregs in the tumor tissue from our HCC xenograft model. Eventually, the Nrf2/Keap1 signaling pathway, which is related to oxidative stress, is shown to be a key pathway downstream of TREM1 downregulation. In summary, we construct a novel prognostic model for HCC on the basis of ligand-receptor marker genes and investigate the role of TREM1 in HCC progression and its impact on the TME.