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) ≥30 kg/m2 (p ≤ 0.001) was higher than in the subgroups of women of BMI <25 kg/m2 (p < 0.001) and BMI 25-29 kg/m2 (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, p ≤ 0.001). Finally, linear multivariate regression revealed a significant association between high methylation rates in the ESR1 gene promoter and increased BMI (β = -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 BMI ≥ 30 kg/m2 subgroup compared to the BMI 25-29 kg/m2 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.
Keywords: CpG island methylation; ESR1 gene; MeDIP assay; breast cancer risk factors; normal breast tissue.