DPP7 promotes fatty acid β-oxidation in tumor-associated macrophages and determines immunosuppressive microenvironment in colorectal cancer

Background: Tumor-associated macrophages (TAMs) are pivotal mediators of the immunosuppressive tumor immune microenvironment (TIME) in colorectal cancer (CRC). However, genes of TAMs that potentiate immunotherapy remain to be explored. Methods: Single-cell RNA sequencing (scRNA-seq) data were analyzed to identify TAM molecular signatures, which were validated in patient cohorts from Huadong Hospital and TCGA to explore their clinical significance. Multidimensional characterization of CRC TIME and Dipeptidyl peptidase VII (DPP7)-positive TAMs functional state was achieved through cytometry by time-of-flight, multiplex immunofluorescence, in vitro and in vivo experiments. Mechanistic investigations integrating RNA-seq, Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)-based proteomics, and targeted lipid metabolomics have revealed the reprogramming of key metabolic pathways. Finally, the therapeutic potential of DPP7, which targets the enhancement of anti-PD-1 immunotherapy efficacy, was demonstrated. Results: DPP7 was identified as the key gene in TAMs, and DPP7⁺TAMs correlated with metastasis and worse overall survival in multiple clinical cohorts. Functional characterization demonstrated that DPP7⁺TAMs drove the immunosuppressive TIME and promoted the exhaustion of CD8⁺T cells, thus exhibiting M2-polarized features. Mechanistically, DPP7 reduced ubiquitination-induced degradation of Carnitine Palmitoyltransferase 1A (CPT1A) by binding to CPT1A in a mutually exclusive manner with TRIM25, thus enhancing fatty acid oxidation (FAO) in TAMs. This metabolic reprogramming consumes lipids (including triglycerides and free fatty acids), elevates adenosine triphosphate (ATP) generation, and induces an immunosuppressive phenotype. In vivo, DPP7 knockdown in bone marrow-derived macrophages (BMDMs) synergized with anti-PD-1 therapy, achieving significant suppression of subcutaneous xenograft tumor growth and liver metastatic burden by reversing the immunosuppressive TIME. Conclusions: DPP7 is mainly expressed in TAMs and DPP7⁺TAMs are strongly associated with adverse prognosis in CRC. Mechanistically, DPP7 enhances FAO to promote the M2-polarized phenotype in TAMs, leading to an immunosuppressive TIME. Targeting DPP7⁺TAMs may potentiate the efficacy of immunotherapy for CRC.