TAMs-derived exosomal PD-L1 drives mitochondrial dysfunction and aberrant fatty acid oxidation via PGC-1α/PPARα axis to promote peritoneal metastasis in epithelial ovarian cancer

Abstract

Tumor-associated macrophages (TAMs) are the most abundant immune cells in the ovarian cancer peritoneal microenvironment; however, how their exosomes metabolically reprogram CD8⁺ T cells to induce dysfunction and promote peritoneal metastasis remains unclear. M2-type TAMs were induced from RAW264.7 cells using IL-4/IL-13, and exosomes (TAMs-Exo) were isolated using a commercial exosome isolation kit. TAMs-Exo were co-cultured with mouse splenic CD8⁺ T cells to assess T-cell cytotoxicity, proliferative capacity, and secretion of effector molecules; the activation status of the PGC-1α/PPARα/CPT1A axis and mitochondrial function were systematically evaluated using Western blot, JC-1, ATP assays, ROS/lipid peroxidation assays, and FAO rate measurements. Causal validation was performed by stimulating cells with recombinant PD-L1 protein and using shRNA to knockdown PD-L1 in exosomes. An ID8 intraperitoneal metastasis mouse model was established to observe tumor burden and the metabolic remodeling characteristics of peritoneal CD8⁺ T cells. TAMs-Exo highly express PD-L1 and are effectively taken up by CD8⁺ T cells, significantly inhibiting T-cell cytotoxicity, proliferation, and the secretion of effector molecules (IFN-γ, granzyme B). Mechanistically, TAMs-Exo activates the PGC-1α/PPARα/CPT1A axis via PD-L1, compensatorily increasing the rate of fatty acid oxidation (FAO), but simultaneously leading to a decrease in mitochondrial membrane potential, ATP depletion, and the accumulation of ROS and lipid peroxides—characteristic of mitochondrial dysfunction. Recombinant PD-L1 protein can mimic these effects, whereas knockdown of PD-L1 in exosomes or treatment with the FAO inhibitor (Etomoxir) significantly reverses T-cell dysfunction. In vivo experiments further confirmed that TAMs-Exo promotes ascites formation and an increase in peritoneal metastatic nodules, accompanied by abnormal activation of the PGC-1α/PPARα axis and mitochondrial dysfunction in intraperitoneal CD8⁺ T cells. TAM-derived exosomes, through the PD-L1 they carry, pathologically overactivate the PGC-1α/PPARα axis in CD8⁺ T cells, inducing mitochondrial dysfunction and abnormal metabolic reprogramming of fatty acid oxidation, thereby driving CD8⁺ T-cell dysfunction and promoting peritoneal metastasis of ovarian cancer. Targeting this metabolic checkpoint—by blocking exosomal PD-L1 or inhibiting excessive FAO flux—may offer a new combination intervention strategy to overcome resistance to immunotherapy in ovarian cancer.