Long-term dietary exposure to a mixture of phthalates enhances estrogen and beta-catenin signaling pathways, leading to endometrial hyperplasia in mice.

Phthalates, synthetic chemicals widely utilized as plasticizers and stabilizers in various consumer products, present a significant concern due to their persistent presence in daily human life. While past research predominantly focused on individual phthalates, real-life human exposure typically encompasses complex mixtures of these compounds. The cumulative effects of prolonged exposure to phthalate mixtures on uterine health remain poorly understood. To address this knowledge gap, we conducted studies utilizing adult female mice exposed to a phthalate mixture for 6 and 12 months through ad libitum chow consumption. We previously reported that continuous exposure to this phthalate mixture for 6 months led to uterine fibrosis. In this study, we show that the exposure, when continued beyond 6 months to 1 year, caused fibrotic uteri to display hyperplasia with a significant increase in gland to stroma ratio. Endometrial hyperplasia is commonly caused by unopposed estrogen action, which promotes increased expression of pro-inflammatory cytokines and chemokines and proliferation of the endometrial epithelial cells. Indeed, RNA sequencing analysis revealed a marked upregulation of several estrogen-regulated genes, Wnt ligands that are involved in oncogenic pathways, as well as chemokines, in phthalate-exposed uterine tissues. Consequently, the exposed uteri exhibited increased proliferation of endometrial epithelial cells, and a heightened inflammatory response indicated by extensive homing of macrophages. Further studies revealed a marked enhancement of the Wnt/β-Catenin signaling pathway, potentially contributing to the development of endometrial hyperplasia. Collectively, this study underscores the significance of understanding the exposure to environmental factors in the pathogenesis of endometrial disorders.