Hypoxic Tumor-derived Exosomal MiR-4488 Induces Macrophage M2 Polarization to Promote Liver Metastasis of Pancreatic Neuroendocrine Neoplasm Through RTN3/FABP5 Mediated Fatty Acid Oxidation

Tumor-associated macrophages (TAMs) represent a predominant cellular component within the tumor microenvironment (TME) of pancreatic neuroendocrine neoplasms (pNENs). There is a growing body of evidence highlighting the critical role of exosomes in facilitating communication between tumor cells and TAMs, thereby contributing to the establishment of the premetastatic niche. Nonetheless, the specific mechanisms through which exosomes derived from tumor cells influence macrophage polarization under hypoxic conditions in pNENs, and the manner in which these interactions support cancer metastasis, remain largely unexplored. Recognizing the capacity of exosomes to transfer miRNAs that can modify cellular behaviors, our research identified a significant overexpression of miR-4488 in exosomes derived from hypoxic pNEN cells. Furthermore, we observed that macrophages that absorbed circulating exosomal miR-4488 underwent M2-like polarization. Our investigations revealed that miR-4488 promotes M2-like polarization by directly targeting and suppressing RTN3 in macrophages. This suppression of RTN3 enhances fatty acid oxidation and activates the PI3K/AKT/mTOR signaling pathway through the interaction and downregulation of FABP5. Additionally, M2 polarized macrophages contribute to the formation of the premetastatic niche and advance pNENs metastasis by releasing MMP2, thereby establishing a positive feedback loop involving miR-4488, RTN3, FABP5, and MMP2 in pNEN cells. Together, these findings shed light on the role of exosomal miRNAs from hypoxic pNEN cells in mediating interactions between pNEN cells and intrahepatic macrophages, suggesting that miR-4488 holds potential as a valuable biomarker and therapeutic target for pNENs.