SGMS2+ macrophages enhance NR4A3hi NK cell infiltration to improve prognosis and PD-1 treatment efficacy in hepatocellular carcinoma.

BACKGROUNDS: Hepatocellular carcinoma (HCC) is characterized by an immunosuppressive tumor microenvironment (TME) that critically propels malignant evolution. Sphingomyelin synthase 2 (SGMS2), the pivotal sphingolipid metabolizing enzyme, catalyzes the conversion of ceramide to sphingomyelin. Emerging evidence highlights sphingolipid metabolism as a key regulator of tumor immunity, particularly in shaping macrophage phenotypes within the TME. However, the macrophage-specific contributions of SGMS2 to HCC progression remain unexplored. This study elucidates the critical role of SGMS2 in shaping TME and influencing patient prognosis. METHODS: Bulk RNA-seq analysis was performed using TCGA-LIHC datasets (n = 371). Single-cell RNA sequencing and spatial transcriptomics were used to identify SGMS2-expressing cell types and evaluate spatial immune interactions. Clinical validation was performed on a cohort of 188 HCC patients (2017-2022) using multiplex immunofluorescence to quantify SGMS2+ macrophages and NR4A3hi NK cells. THP-1 monocytes were transfected with lentiviral SGMS2 overexpression vectors and differentiated into macrophages via PMA induction. Co-culture assays with liver tumor cells were performed in transwell plates for 48 h, followed by tumor cell apoptosis assessment using Annexin V-FITC/PI staining and flow cytometry. RESULTS: High SGMS2 expression in HCC tissues was associated with improved patient prognosis. SGMS2 was mainly expressed in macrophages within the HCC immune microenvironment, promoting their polarization toward the M1-like phenotype. High infiltration of SGMS2+ macrophages significantly prolonged overall survival (OS), recurrence-free survival (RFS), and early RFS. Notably, patients with high infiltration of SGMS2+ macrophages accompanied by low infiltration of SGMS2- macrophages had the most favorable prognosis. Mechanistically, SGMS2+ macrophages secreted CXCL2, recruiting CD56dimCD16highNR4A3high cytotoxic NK cells, enhancing tumor cell apoptosis and improving prognosis. In patients receiving PD-1 therapy, those with high infiltration of SGMS2+ macrophages and CD56dimCD16highNR4A3high NK cells demonstrated superior treatment responsiveness and prolonged survival. CONCLUSIONS: SGMS2 could polarize macrophages toward the M1 phenotype. SGMS2+ macrophages secrete CXCL2 to recruit CD56dimCD16highNR4A3high NK cells, thereby enhancing tumor apoptosis. High infiltration of SGMS2+ macrophages and CD56dimCD16highNR4A3high NK cells correlates with superior PD-1 therapy responsiveness and extended survival.