Correlation between dioxin and endometriosis: an epigenetic route to unravel the pathogenesis of the disease

INTRODUCTION: Environmental toxicants can act as endocrine disrupters on the female reproductive system. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is resistant to degradation and due to its lipophilic nature, accumulates in the fat tissue and in the food chain. Human and animal exposure to TCDD affects levels of the steroid receptors and steroid-responsive gene expression and has an impact on metabolism and serum transport of steroids. Gene expression is commonly altered in endometriosis and in the eutopic endometrium of women with the disease. Aberrantly expressed genes include those associated with the regulation of transcription, proliferation, sex steroid metabolism, apoptosis, cell cycle, the immune response and cell adhesion. METHODS: In this paper, we review the evidence about TCDD's effect on eutopic and ectopic endometrium, in order to unravel the machinery behind the dysregulation of immune and hormonal homeostasis caused by this environmental toxicant. CONCLUSION: The evidence collected in this review suggests that TCDD could modulate transcription at multiple levels, including the epigenetic level, and via microRNAs, thus disturbing the physiologic processes mediated through the aryl hydrocarbon receptor pathways. Exposure to TCDD also modulates the immune response by influencing the production and action of endometrial cytokines and chemokines, destroying mucosal immunity of the reproductive tract and re-directing the tissue distribution and behavior of leukocytes. Despite this large body of evidence, current human-based epidemiological studies on the association between TCDD and endometriosis remain controversial.