Di-(2-ethylhexyl) phthalate and bisphenol A exposure impairs mouse primordial follicle assembly in vitro

Bisphenol-A (BPA) and diethylhexyl phthalate (DEHP) are estrogenic compounds widely used in commercial plastic products. Previous studies have shown that exposure to such compounds have adverse effects on various aspects of mammalian reproduction including folliculogenesis. The objective of this study was to examine the effects of BPA and DEHP exposure on primordial follicle formation. We found that germ cell nest breakdown and primordial follicle assembly were significantly reduced when newborn mouse ovaries were exposed to 10 or 100 μM BPA and DEHP in vitro. Moreover, BPA and DEHP exposure increased the number of TUNEL positive oocytes and the mRNA level of the pro-apoptotic gene Bax in oocytes. These effects were associated with decreased expression of oocyte specific genes such as LIM homeobox 8 (Lhx8), factor in the germline alpha (Figla), spermatogenesis and oogenesis helix-loop-helix (Sohlh2), and newborn ovary homeobox (Nobox). Interestingly, BPA and DEHP exposure also prevented DNA demethylation of CpG sites of the Lhx8 gene in oocytes, a process normally associated with folliculogenesis. Finally, folliculogenesis was severely impaired in BPA and DEHP exposed ovaries after transplantation into the kidney capsules of immunodeficient mice. In conclusion, BPA and DEHP exposures impair mouse primordial follicle assembly in vitro.