Epigenetic Changes of the ESR1 Gene in Breast Tissue of Healthy Women: A Missing Link with Breast Cancer Risk Factors?

Background: Reproductive history and obesity are among the well-recognized risk factors in the development of breast cancer, which are partially mediated by the increased exposure of breast tissues to estrogens. However, only a few studies have investigated the link between these risk factors and the pattern of methylation signatures in the breast tissue of healthy women. The role of the estrogen receptor 1 (ESR1) gene hypermethylation is reportedly important in the development of breast cancer. Thus, it is speculated that such ESR1 epigenetic changes may be influenced or shaped by obesity and reproductive history-related factors before and during breast carcinogenesis. Materials and Methods: Breast samples were collected from 120 cancer-free women who had undergone cosmetic mammoplasty. DNA was extracted from the breast tissues and, then, the methylation levels at the promoter and exon 1 regions of the ESR1 gene CpG island were determined by using the methylated DNA immunoprecipitation-quantitative PCR assay. Results: The methylation level of the ESR1 promoter observed in women with a body mass index (BMI) 30kg/m(2) (p0.001) was higher than in the subgroups of women of BMI <25kg/m(2) (p<0.001) and BMI 25-29kg/m(2) (p<0.001) and was also higher in postmenopausal women compared with that in premenopausal women (p=0.046). Pearson correlation coefficient analyses also showed that the high methylation of the ESR1 promoter was correlated with increasing age (r=-0.246, p=0.007) and BMI (r=-0.331, p0.001). Finally, linear multivariate regression revealed a significant association between high methylation rates in the ESR1 gene promoter and increased BMI (=-0.285, 95% CI=-0.457 to -0.113, p=0.001). Furthermore, a higher methylation level at the ESR1 gene exon 1 was found in the BMI30 kg/m(2) subgroup compared to the BMI 25-29 kg/m(2) subgroup (p=0.023). Conclusion: These findings provide new hints about the relationship between epigenetic changes within the ESR1 gene CpG island and postmenopausal obesity and aging in cancer-free women. In terms of lifestyle intervention opportunities, this study also highlights the significance and feasibility of such interventions for BMI as a modifiable risk factor.