Molecular characterization of human adipose-tissue derived stem cells (ASCs) from the breast in the presence and absence of exogenous estrogen

Purpose: Adipose-derived stem cells (ASCs) are multipotent cells of mesodermal origin with self-renewal and differentiation capabilities, isolated from adipose tissue. ASCs are located in adipose tissue depots throughout the body and maintained for life. Our group has extensively studied abdominal ASCs (aASCs) harvested from lean and obese individuals and how their contribution to the tumor microenvironment (TME) results in amplified breast cancer proliferation, tumorigenesis, and metastasis; in a series of processes that have been linked to leptin signaling cascades and estrogen-mediated pathways. Furthermore, these properties are exacerbated in aASCs from obese donors, which express increased levels of leptin and pro-inflammatory cytokines compared to those harvested from lean individuals. Of particular interest are ASCs located in breast adipose tissue (bASCs). These bASCs have unique immunomodulatory, anti-inflammatory, and antioxidative properties. They serve essential endocrine functions in healthy breast tissue, but they also play a role in the development and pathophysiology of breast cancer, being a critical component of the breast cancer TME. While bASCs influence their microenvironment, they are also altered by physiological changes associated with obesity, the circulating levels of the sex hormones such as estrogen and progesterone, and the adipokine leptin. The fluctuations in estrogen levels before and after menopause are also accompanied by a shift in the accumulation site of subcutaneous adipose tissue. This study aims to characterize bASCs from human donors and compare their gene expression, proliferation, differentiation properties, and response to exogenous hormonal variations, to those of aASCs. Methods: bASCs were characterized and compared to aASCs after being cultured in the presence or absence of exogenous estrogen. Adipogenic and osteogenic differentiation was induced and assessed with Oil Red O and Alizarin Red S staining, respectively. Alterations to colony-forming unit capabilities were assessed with crystal violet staining. Cell surface markers were evaluated using flow cytometry. The expression of hormonal receptors, adipogenic genes, and osteogenic genes was evaluated by real-time PCR and Simple Western. Results: bASCs display similar morphological characteristics, surface markers, colony-forming capabilities, proliferation potential, and differentiation potential to that of aASCs. However, bASCs express higher levels of hormone receptors and are more susceptible to changes in exogenous estrogen than aASCs. Conclusion: Given that hormone receptor positive breast cancers are more prevalent in obese women after menopause, while triple negative breast cancers (TNBC) are more common in obese pre-menopausal women, hormonal levels may play a role in the development of both hormone receptor-positive breast tumors and TNBC tumors by affecting the surrounding bASCs