Leptin levels associated with obesity induce global DNA hypomethylation increasing EMT-associated genes expression in breast epithelial mammary cells

Risk factors associated with the development of breast cancer are well known, yet more than two million cases are still diagnosed worldwide each year. Therefore, there is an urgent need to characterize the molecular pathways associated with breast cancer risk in order to derive molecular biomarkers and strategies for interventional and preventive medicine. This study focuses on leptin as a mediator of breast cancer risk conferred by obesity. We found that plasma leptin correlates with levels of methylation, hydroxymethylation, and oxidation of cell-free circulating DNA in cancer-free women. We made the same observations with nuclear DNA from breast epithelial cells exposed to leptin. At the molecular level, global hypomethylation, hyperhydroxymethylation and hyperoxidation of DNA is mediated by the loss of DNMT1 and DNMT3B expression and the gain of TET1/OGG1 interaction in cells exposed to elevated leptin levels. In this model, changes in DNA methylation affects genes regulating the epithelial mesenchymal transition (EMT), in particular TBX3, LRP6, occludin and claudin-7 (CLDN7). Elevated leptin per se was however not sufficient to induce tumor formation. Finally, we show that epinutrients such as folic acid and caffeic acid limit global DNA hypomethylation caused by leptin. In conclusion, we identify global DNA hypomethylation as a leptin-induced pro-oncogenic event. This effect Is not tumorogenic by itself due to its moderate intensity but may acta as priming event. We propose DNA hypomethlyation in cell-free circulating DNA as a new biomarker to stratify women at risk of developing breast cancer and to evaluate preventive medical interventions to limit global DNA hypomethylation, such as folic acid and caffeic acid supplementation.