Adipose Tissue-Derived Extracellular Vesicles and the Tumor Microenvironment: Revisiting the Hallmarks of Cancer.

Extracellular vesicles (EVs) are crucial elements that sustain the communication between tumor cells and their microenvironment, and have emerged as a widespread mechanism of tumor formation and metastasis. In obesity, the adipose tissue becomes hypertrophic and hyperplastic, triggering increased production of pro-inflammatory adipokines, such as tumor necrosis factor α, interleukin 6, interleukin 1, and leptin. Furthermore, obese adipose tissue undergoes dysregulation in the cargo content of the released EVs, resulting in an increased content of pro-inflammatory proteins, fatty acids, and oncogenic microRNAs. These alterations drive obesity-associated inflammatory responses both locally and systemically. After being ignored for a long time, adipose tissues have recently received considerable attention as a major player in tumor microenvironment-linked obesity and cancer. The role of adipose tissue in the establishment and progression of cancer is reinforced by its high plasticity and inflammatory content. Such a relationship may be established by direct contact between adipocytes and cancer cells within the microenvironment or systemically, via EV-mediated cell-to-cell communication. Here, we highlight cues evidencing the influence of adipose tissue-derived EVs on the hallmarks of cancer, which are critical for tumor malignancy.

Obese adipose tissue extracellular vesicles raise breast cancer cell malignancy.

Obesity is a chronic low-grade inflammatory condition that strongly impacts breast cancer. Aside from inflammatory mediators, obese adipose tissue (AT) secretes high amounts of extracellular vesicles (EVs), which are capable of transferring molecules to target cells and promoting cell-to-cell communication. Here, we investigated how soluble mediators and EVs secreted by human obese AT influence MCF-7 and MDA-MB-231 mammary adenocarcinoma cell lines by modulating cell proliferation, migration, invasion, and signaling pathways. Both cell lineages were stimulated with conditioned media (CM) or EVs obtained from cultures of AT explants collected from lean or obese individuals who underwent plastic or bariatric surgeries, respectively. EVs derived from obese AT increased the proliferative potential of both cell lines and further potentiated the migratory and invasive properties of MDA-MB-231 cells. The proliferative effects of CM and EVs on MCF-7 cells were dependent on ERK/MAPK pathway activation, while the migration and invasiveness of MDA-MB-231 cells were dependent on PI3K/AKT pathway activation. Furthermore, CM derived from obese AT potentiated the pro-angiogenic effect of MDA-MB-231 on endothelial cells. We also detected that EVs derived from obese AT were enriched in leptin and bioactive matrix metallopeptidase 9 (MMP9), and stimulation of MDA-MD-231 cells with those EVs or CM derived from obese AT potentiated the release of MMP9 by those cells. Our data indicate that obese AT secretes molecules and EVs with pro-tumoral activities capable of increasing breast cancer cell malignancy and provide strong evidence of the key role of AT-derived EV signaling in the tumor microenvironment.