LysoPS-GPR34 axis enhances tumor-associated macrophages efferocytosis to promote immune escape in gastric cancer peritoneal metastasis

BACKGROUND: Metabolites sculpt the immunosuppressive tumor microenvironment (TME) that facilitates immune evasion. As a crucial signaling lysophospholipid, lysophosphatidylserine (LysoPS) correlates with advanced disease stages in multiple tumor types. However, the mechanisms by which LysoPS drives gastric cancer peritoneal metastasis remain undefined. METHODS: Single-cell transcriptomic profiling of primary tumors, normal peritoneum, and metastatic lesions delineated mechanisms underlying LysoPS-mediated tumor-associated macrophages (TAMs) reprogramming. Immunohistochemistry and multiplex immunofluorescence validated GPR34-high TAMs infiltration in peritoneal metastases. Functional validation was performed using molecular assays and in vivo models. RESULTS: LysoPS accumulated in ascites from patients with gastric cancer peritoneal metastasis, establishing an immunosuppressive TME that drove malignant progression. Using single-cell transcriptome sequencing, we identified a distinct subset of TAMs highly expressing GPR34 enriched in gastric cancer peritoneal metastases, which correlates with tumor progression and immune evasion. Mechanistically, LysoPS engagement of GPR34 activated ERK/c-Jun signaling, transcriptionally upregulating AXL and CD36 to enhance efferocytosis. This effect drove TAMs toward an immunosuppressive phenotype, characterized by enhanced interleukin-10 and transforming growth factor-β secretion. GPR34 inhibitor attenuated M2-like TAMs infiltration while bolstering cytotoxic T cells recruitment and curtailing programmed cell death protein 1 (PD-1)+T cells accumulation. Furthermore, combination with anti-PD-1 therapy synergistically suppressed tumor growth beyond monotherapy efficacy. CONCLUSIONS: LysoPS-GPR34 axis synergized with efferocytosis to amplify TAMs immunosuppressive properties, fostering an immune-evasive microenvironment; GPR34 inhibitor thus represents a promising strategy to potentiate PD-1 blockade efficacy in gastric cancer peritoneal metastasis.