Platform Session 8. Effects of the Environment and Nutrition on Development and Female Reproduction
Monday, July 25, 2005
2:00 PM–4:00 PM
Location: CCQ 202
(63) ESTRADIOL REPLACEMENT RESTORES FOLLICULAR GROWTH IN ARYL HYDROCARBON RECEPTOR (AhR) DEFICIENT MICE.
Barnett, Kimberly 1, Flaws, Jodi 1, 1 University of Maryland School of Medicine, Baltimore, MD
ABSTRACT- The AhR is a ligand-activated transcription factor that mediates the toxicity of various environmental contaminants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In addition to its role in mediating toxicity, the AhR has been shown to regulate ovarian follicle growth. Previous studies in our lab have shown that follicles from AhR deficient (AhRKO) mice have slower growth from the preantral to the antral stage compared to follicles from wild-type (WT) mice. The mechanism by which the AhR regulates follicular growth is unknown. Since estradiol (E2) is a key regulator of follicular growth, the objective of this study was to determine whether E2 levels differ in AhRKO and WT mice and whether any differences in E2 levels contribute to slow follicular growth in AhRKO ovaries versus WT ovaries. To test whether E2 levels differ in AhRKO and WT mice, serum was collected from AhRKO and WT mice and subjected to measurements of E2 by enzyme-linked immunoassay (ELISA). In addition, antral follicles were isolated from AhRKO and WT ovaries on postnatal days (PD) 31-35 and cultured for 168 hours. After culture, media was collected and subjected to measurements of E2 by ELISA. To test whether E2 replacement restored growth of AhRKO follicles to WT levels, antral follicles from AhRKO and WT mice were isolated on PD 31-35 and cultured in media containing DMSO (vehicle), 1nM E2, or 10nM E2. During culture, follicle growth was assessed by measurement of follicular diameters every 24 hours for 168 hours. The results indicate that AhRKO mice had significantly lower levels of E2 compared to WT mice (WT=42±3 pg/ml, AhRKO=23±4 pg/ml, p≤0.014). In addition, AhRKO follicles secreted lower levels of E2 compared to WT follicles in vitro (WT=2463±508 pg/ml, AhRKO=971±316 pg/ml, p≤0.007). The results also indicate that treatment of AhRKO follicles with 10nM E2, but not 1nM E2, restored growth to WT levels by 168 hours of culture (WT=626.5±15.8 m, AhRKO 10nM E2=622.5≤21.9 m, p=0.88). These data indicate that AhRKO mice produce less E2 than WT mice and that administering E2 to AhRKO follicles restores AhRKO follicle growth to WT levels. Collectively, these data suggest that the AhR regulates follicular growth via mechanisms involving the E2 pathway. Supported by NIH grants GM072195-01, HD38955, and R25-GM55036.
KEY WORDS: AhR, follicular growth, estradiol