SAT-339 Cross-Talk with Breast Adipose Tissue Contributes to Obesity-induced DNA Damage in BRCA Mutant Breast Epithelial Cells

Background: Obese women who carry a mutation in the DNA repair enzymes BRCA1 and/or BRCA2 are at a greater risk of developing breast cancer compared with lean BRCA1/2 mutation carriers. Causative factors that drive the increased penetrance of breast cancer in obese women are poorly characterized. Previously, we showed that BMI was positively correlated with DNA damage in breast epithelium of BRCA mutation carriers. We hypothesized that obesity-associated dysfunctional adipose tissue may cause DNA damage in neighboring breast epithelial cells. If true, this would provide evidence for the initial insults associated with increased risk of tumor formation in obese women. Methods: To test the effect of locally secreted factors on DNA damage induction, conditioned media was collected over 24 hours from primary breast adipose explants obtained from lean and obese women. Conditioned media was used to treat normal breast epithelial cells (MCF10A) harboring a heterozygous BRCA1 mutation or wildtype for BRCA. Immunofluorescence (IF) staining of the DNA damage marker ƴH2AX was carried out after treatment. Cell line findings were validated in primary breast epithelial organoids isolated by collagenase digestion of breast tissue obtained from the clinic. Additionally, RNA-seq was conducted on primary breast epithelial organoids isolated from lean and obese women to identify potential drivers of gene expression differences associated with obesity and DNA damage. Results: Conditioned media from obese breast adipose tissue stimulated DNA damage in BRCA mutant breast epithelial cells while lean conditioned media did not have this effect. Similar findings were made in primary breast epithelial organoids, suggesting a role for locally secreted factors in mediating DNA damage. Ingenuity Pathway Analysis of RNA-seq data from lean and obese primary breast organoids identified several upstream regulators of gene expression differences, including signaling by estradiol and pro-inflammatory cytokines, both of which are elevated in obese breast tissue and are known inducers of DNA damage. Conclusions: These data show for the first time that local factors produced by obese breast adipose tissue induce breast epithelial cell DNA damage. Our results suggest that therapies targeting weight or dysfunctional breast adipose tissue may reduce the increased DNA damage observed in obese BRCA mutation carriers and thereby decrease tumor formation in this high-risk population of women.