Adipocyte‐derived Exosomes: Novel Insight in the Link between Obesity and Breast Cancer

Abstract

Introduction Obesity has an intricate connection to both risk and clinical behaviour of breast cancer. Adipose tissue dysfunction in obesity results in a release of many adipokines that it is well known to promote breast tumor biology. In addition to soluble factors, exosomes (exo), small membrane-derived vesicles secreted by both normal and malignant cells, have been recently suggested to act as additional mediators of cell-to-cell communication. However, a clear understanding in the role of adipocyte-derived exo in mediating the adverse effects of obesity on BC is still lacking. Herein, we evaluated the involvement of adipocyte-derived exo in sustaining BC development and progression. Methods Exo were isolated and fully characterized from conditioned media (CM) of differentiated 3T3-L1 adipocytes (3T3-L1 A), a well-recognized ‘in vitro’ model of white adipocytes. We tested the effects of 3T3-L1 A exo in modulating the proliferation (MTT/soft agar assays), motility/invasion (wound healing/Boyden Chamber migration/invasion assays), and stemness (mammosphere forming efficiency/Limiting Dilution assays) of estrogen receptor α (ERα)-positive MCF-7 and triple-negative MDA-MB-231 BC cells. We also assessed co-culture experiments between BC cells and CM derived from adipocytes isolated from human mammary adipose tissues (MAT) of adult normal weight and obese women. Results The treatment with 3T3-L1 A exo significantly increased the number of colonies of MCF-7 and MDA-MB-231 cells in anchorage-independent soft agar growth assay. Also, we found that 3T3-L1 A exo induced a more aggressive phenotype in both BC cells in terms of migration, invasion and stemness. In accordance with these data, we found that 3T3-L1 A exo significantly induced the expression of the mRNA levels of genes encoding several proteins involved in Epithelial to Mesenchymal Transition (EMT) and associated with stem cell phenotype. To gain insight into the molecular mechanism we focused our attention on the expression and activity of HIF-1α, a well-known regulator of hypoxic response, involved in invasion, migration, EMT and metastasis in BC. Interestingly, 3T3-L1 A exo increased the expression of HIF-1α and its target genes, and the use of a HIF-1α translation inhibitor reduced migration and invasion capabilities induced by exo. Finally, we found that CM derived from MAT increased the migratory abilities of both employed cells in a significantly higher extent with MAT obese-CM and these effects were completely reversed in the presence of a specific exo uptake inhibitor. Conclusions Our data suggest that adipocyte exo contribute to a more aggressive BC phenotype. This may open new avenues for identifying novel specific biomarkers and innovative therapeutic strategies (i.e. HIF-1α inhibitors) in BC treatment, especially in obese patients.