Alteration in Aromatase and Estrogen Receptor Target Gene Expression in Human Benign Mammary Tissue After Bariatric Surgery

Abstract Background: Over 30% of US adults are obese (body mass index (BMI) of ≥ 30 kg/m2). Obesity is considered a significant and modifiable risk factor for ER+ postmenopausal breast cancer (BC). However, the effect on pre-menopausal breast cancer risk is less clear. Bariatric surgery is performed on obese patients who have a BMI of >35. It has been associated with reduced risk of BC, but the mechanisms behind this are unknown. Studies in obese patients have revealed multiple changes in the physiology of the microenvironment that contribute to BC development. The molecular changes in the stroma and epithelium from metabolic syndrome, excess inflammation, and ectopic hormone synthesis likely play key role in obesity related BC. Therefore, understanding how we can alter the risk posed will have an impact on decreasing the incidence of BC. We hypothesize that bariatric surgery will reduce the incidence of postmenopausal ER+ BC by reducing estradiol availability and ER activity. Methods: We recruited 30 women undergoing bariatric surgery, who underwent core needle biopsy at the time of surgery and after they had lost 25% of their excess body weight. Changes in hormone concentration by LCMS/MS in serum and breast tissue, protein expression in breast tissue by IHC and the altered gene expression in breast epithelium and stroma by RNA seq were measured. Results: When segregated by menopausal status, Androstenedione (p=0.02), Testosterone (p < 0.0001) and 27-hydroxycholesterol (p=0.017) showed significant reduction in the plasma post-surgery in premenopausal women. There were no significant differences in the hormone levels in the breast tissue and in postmenopausal women post-surgery. We observed that African Americans (AA) were half as likely to show a reduction in tissue concentration compared to Caucasian women. IHC was performed to examine protein expression of Ki67, leptin R, aromatase, CYP27A1, Stat3, adiponectin, CYP27B1 and ER in the breast core biopsy. Aromatase expression (p < 0.0001) was significantly reduced in both the epithelial and stromal compartments. In addition, Stat3 levels (p=0.044) were significantly reduced in the stroma. RNA -seq analysis revealed distinct differentially expressed genes pre and post-surgery. Specifically, genes associated with metabolic process, epithelial development, extracellular space, immune and inflammatory response pathways. Furthermore, known ER target genes TFF1, AGR2 expression were significantly decreased in Caucasian women, but not in AA women, post- surgery. Conclusions: Taken together, these data show that bariatric surgery decreased aromatase expression, some hormones in pre-menopausal women and reduced estrogen availability and ER activity. Further analysis of differentially regulated genes due to bariatric surgery can allow us to explore previously unknown pathways related to breast cancer risk reduction.