Accelerated Ovarian Failure Induced by 4-Vinyl Cyclohexene Diepoxide in Nrf2 Null Mice

Abstract

Genetic and biochemical analyses have uncovered an essential role for nuclear factor erythroid 2-related factor 2 (Nrf2) in regulating phase II xenobiotic metabolism and antioxidant response. Here we show that Nrf2 protects against the ovarian toxicity of 4-vinylcyclohexene diepoxide (VCD) in mice. Nrf2^−/− female mice exposed to VCD exhibit an age-dependent decline in reproduction leading to secondary infertility accompanied by hypergonadotropic hypogonadism after 30 weeks of age. VCD is shown to selectively destroy small ovarian follicles, resulting in early depletion of functional follicles. Treatment with VCD induces apoptotic death in cultured cells and in ovarian follicles, suggesting apoptosis as a mechanism of follicle loss. Loss of Nrf2 function blocks the basal and inducible expression of microsomal epoxide hydrolase, a key enzyme in the detoxification of VCD, and increases the oxidative stress in cells that is further exacerbated by VCD. Foxo3a, a repressor in the early stages of follicle activation, displays reduced expression in Nrf2^−/− ovaries, causing accelerated growth of follicles in the absence of exposure to exogenous chemicals. Furthermore, Foxo3a is degraded through the 26S proteasome pathway in untreated cells and is induced by VCD via both Nrf2-dependent transcription and protein stabilization. This study demonstrates that Nrf2 serves as an essential sensor and regulator of chemical homeostasis in ovarian cells, protecting the cells from toxic chemicals by controlling metabolic detoxification, reactive oxygen species defense, and Foxo3a expression. In addition, these findings raise the possibility that exposure to environmental or occupational ovotoxicants plays a role in the premature ovarian failure commonly associated with infertility and premature aging in women.

We thank P. Nicolaysen for valuable suggestions on mouse breeding assay, S. Young for assistance in FACS analysis, J. Antonini and J. Yao for NIOSH internal review, I. D. Clair for comments, and P. A. Willard for histopathological sample preparation.

The findings and conclusions in this report are ours and do not necessarily represent the views of NIOSH.