Obesity and Breast Cancer: Unraveling the Role of Adipocyte‐Derived Exosomes

Abstract

Excessive adiposity strongly influences risk, prognosis and progression of breast cancer. The revised concept of adipose tissue from an inert depot for body energy to an endocrine and immunologically active organ placed growing interest on the potential role of adipocyte secreted soluble factors and vesicles, particularly exosomes, as important players in cancer biology. In the last decades, several reports demonstrated that exosomes, small membrane‐derived vesicles, are able to modify target cell phenotype, by transferring bioactive molecules such as proteins, mRNAs, microRNAs, DNAs, lipids and transcriptional factors. However, whether adipose tissue‐derived exosomes, acting as a mode of cell‐to‐cell communication, might have a role in mediating the adverse effects of obesity on breast cancer is still not completely understood.Here, we evaluated the effects of exosomes derived from differentiated 3T3‐L1 adipocytes (3T3‐L1 A), a well recognized ‘in vitro’ model of white adipocytes, on breast cancer phenotype, using as experimental models both estrogen receptor α (ERα)‐positive MCF‐7 and triple negative MDA‐MB‐231 breast cancer cells.Exosomes from 3T3‐L1 A were isolated by sequential ultracentrifugation method, and characterized by Nanoparticle Tracking Analysis, Transmission Electron Microscopy and Immunoblotting analyses. 3T3‐L1 A‐ derived exosome uptake in both breast cancer cell lines was tested by monitoring internalization of exosomes labeled with PKH‐26. Treatment of MCF‐7 and MDA‐MB‐231 breast cancer cells with adipocyte‐derived exosomes did not modify anchorage‐dependent cell growth, while it significantly increased the ability of cells to form colonies in anchorage‐independent soft agar growth assays. In addition, we found that both breast cancer cells treated with adipocyte‐derived exosomes displayed increased migration and invasion capabilities as evidenced by wound healing, and Boyden Chamber migration and invasion assays. Accordingly, adipocyte‐derived exosomes significantly induce the expression of genes involved in Epithelial to Mesenchymal Transition (EMT) in both cell lines. Since migratory potential and EMT represent important features for breast cancer stem cells (BCSCs), we also explored the effect of 3T3L‐1 A‐derived exosomes on MCF‐7 and MDA‐MB‐231 BCSC activity. Interestingly, we found that adipocyte‐derived exosomes were able to increase Mammosphere Forming Efficiency and Self Renewal in breast cancer cells. In conclusion, our data highlight how adipocyte‐derived exosomes may contribute to a more aggressive breast cancer phenotype, providing novel insight in the link between obesity and breast cancer. This may open a new molecular window for preventive and therapeutic strategies to fight breast cancer in obese patients.Support or Funding InformationThis research was funded by Fondazione AIRC: IG #11595 to SA and IG #21414 to SC, and PRIN2017 #2017EKMFTN to SC; PRIN2017 #2017WNKSLR to IB