Brown Adipocyte Promotes HR+ Breast Cancer Invasiveness Through IRX3-Mediated Mitochondrial Dysfunction

Background: Adipocytes play a critical role in the breast cancer tumorigenic microenvironment. However, their effects and underlying mechanisms remain unclear. This study aims to investigate the role of adipocytes in luminal A breast cancer invasiveness at the cellular and molecular levels. Methods: Various adipocyte types were co-cultured with MCF7 breast cancer cells in direct and indirect manners. Invasiveness was assessed via proliferation, migration, and invasion, with alterations examined at morphological, cellular, and molecular levels. The role of adipocytes on MCF7 was further explored using an orthotopic breast cancer xenograft mouse model. Results: MCF7 co-cultured with adipocytes, especially brown adipocytes (BAC), showed increased invasiveness and tumorigenic potential. Morphologically, co-cultivation with BAC increased the proliferation, EMT, and stemness of MCF7. Mechanistically, co-culture of MCF7 with BAC exhibited disturbed expression of genes related to adipogenesis and mitochondrial dynamics; notably, IRX3 was the most prominently elevated one. Knockdown of IRX3 restored balanced mitochondrial function and reduced both the invasiveness of breast cancer cells in vitro and tumor growth in vivo. Conclusions: Brown adipocytes promote breast cancer invasiveness by upregulating adipogenesis-related IRX3, which acts via the mitochondrial functional regulation.