Abstract
BACKGROUND: Tumor-associated macrophages (TAMs) are known to facilitate cancer progression. However, the diversity of TAM subsets and their distinct roles in GC remain poorly understood. This study aimed to evaluate the impact of legumain (LGMN)(+) macrophages on GC progression and clarify the underlying mechanisms of their roles. METHODS: We used single-cell RNA sequencing (scRNA-seq) and bulk RNA sequencing (bulk RNA-seq) analyses from public databases (GEO and TCGA) to systematically evaluate the clinical prognostic significance of LGMN and to characterize the remodeling of its associated signaling pathways. To investigate the role of LGMN in mouse GC (TAMs), we generated macrophage-specific LGMN conditional knockout mice, LGMN(flox/flox); Lyz2-Cre. Utilizing a combination of subcutaneous xenograft tumor models, primary cell isolation and culture, immunofluorescence staining, and tube formation assays, we systematically elucidated the regulatory function and underlying molecular mechanisms of LGMN(+) macrophages in GC progression. RESULTS: We found that LGMN(+) macrophages are significantly enriched in GC tissues, and their high infiltration was significantly associated with poor outcomes. Additionally, scRNA-seq revealed that hypoxia and immune suppression pathways are enriched in LGMN(+) macrophages. LGMN(+) macrophages infiltration levels showed a significant positive correlation with the infiltration of regulatory T (Treg) cells and endothelial cells. Mechanistically, conditional knockout of LGMN in macrophages inhibits tumor growth by reprogramming TAMs toward an anti-tumor phenotype, reducing Treg cell infiltration, and enhancing the infiltration level of CD8(+) T cells. Furthermore, LGMN knockout can inhibit tumor angiogenesis by downregulating VEGF-A expression. CONCLUSIONS: LGMN(+) macrophages drive GC progression by promoting tumor angiogenesis and establishing an immunosuppressive microenvironment. Therefore, targeting this TAM subset may represent a novel therapeutic strategy for GC.