Extracellular vesicles from obese human breast adipose tissue promote breast cancer cell proliferation by increasing mitochondrial mass and stimulating mitochondrial respiration

Abstract Background: Obesity is associated with increased breast cancer incidence and progression. Breast adipose tissue produces a number of factors hypothesized to contribute to this observation, including estrogens, adipokines, inflammatory mediators, and free fatty acids. Adipose tissue also releases extracellular vesicles (EVs) that can act locally or circulate to distant sites. EVs are nano-sized particles that are characterized by their lipid bilayer and contain nucleic acids, proteins, lipids and other molecules that can affect target cells. Recently, EVs derived from adipose tissue have received increasing attention and numerous studies have been conducted to explore the relationship between adipose tissue-derived EVs and different types of cancers, including breast cancer. Here, we provide novel insights into the sustained effects of EVs, collected from fresh breast adipose tissue, via effects on mitochondrial mass and respiration in estrogen receptor (ER)-positive breast cancer cells. Methods: EVs were collected from fresh breast adipose tissue from reduction mammoplasties. Long-term education was performed by treating MCF7 and T47D breast cancer cell lines with 3 doses of EVs over the course of 7 days. xCelligence was used to quantify cell proliferation. RNA Seq was performed on one of the educated MCF7 pairs. Mitochondrial respiration was evaluated using the Seahorse XF instrument. MitoTracker Green fluorescent staining and transmission electron microscopy (TEM) were used to assess mitochondrial density and morphology. Western blotting was used to identify pathways that may be involved in the effects of adipose tissue derived EVs on breast cancer cells. Results: EVs derived from adipose tissue of overweight/obese individuals (O-EVs) stimulate proliferation of MCF7 breast cancer cells compared with that from lean individuals (L-EVs). Compared with controls, O-EVs also induce proliferation of T47D breast cancer cells. RNA-Seq data reveal that genes involved in oxidative phosphorylation (OXPHOS) are significantly upregulated in O-EV-treated MCF7 cells compared to control. Compared with control cells, basal mitochondrial respiration of O-EV-treated MCF7 cells is significantly higher than control. Metformin, which inhibits mitochondrial complex I and ATP synthase, inhibits the O-EV-stimulated proliferation of MCF7 cells, while having no effect on the proliferation of control cells. Both MitoTracker Green fluorescent staining and TEM demonstrate increased mitochondrial mass/number. Western blotting reveals that O-EVs significantly increase phosphorylation of Akt, which is the major upstream regulator of mTOR signaling, and phosphorylation of P70 S6 kinase and 4EBP1, which are two main downstream effectors of mTOR signaling, affecting both protein synthesis and mitochondrial respiration. Conclusions: Breast adipose tissue EVs from overweight and obese women stimulate the proliferation of ER+ breast cancer cells by increasing mitochondrial mass and stimulating mitochondrial respiration, providing a novel mechanistic link between obesity and breast cancer. Our studies also suggest that metformin or mTOR-targeting drugs, may prove useful to break obesity-breast cancer link. Support: NIH R01CA215797, Anne Moore Breast Cancer Research Fund Citation Format: Shuchen Liu, Alberto Benito-Martin, Phoebe Piloco, Catherine Liu, Paul Paik, Jason A Spector, Fanny A Pelissier Vatter, David Lyden, David M Otterburn, Leslie Cohen, Olivier Elemento, Rohan Bareja, Leona Cohen-Gould, Samuel Calto, Kristy A Brown. Extracellular vesicles from obese human breast adipose tissue promote breast cancer cell proliferation by increasing mitochondrial mass and stimulating mitochondrial respiration [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-05-02.