Estrogen Receptor alpha Overexpression Alters Expression of Other Receptors in the Mouse Ovary.

The role of the estrogen receptor in the regulation of reproductive functions as well as its localization in reproductive tissues is well established. The estrogen receptor subtypes namely estrogen receptor alpha (ESR1) and estrogen receptor beta (ESR2) are the mediators of the physiological responses that are brought about by estrogens. Various mouse models such as the ESR1, ESR2 and ESR1/2 knock-outs have been developed to determine the function of these receptors. Although the reproductive abnormalities of these mouse models have been well characterized, there is limited literature about transgenic mice that were specifically generated to serve as models of endocrine disruption in the ovary. Recently, we generated a transgenic mouse model in which ESR1 is overexpressed in several tissues (ESR1 OE), including the ovaries. The goal is to use these mice as models for endocrine disruption in the ovary. Previous studies using quantitative real-time PCR determined that the mRNA levels of ESR1 were significantly higher in the ESR1 OE mice compared to controls. The unique feature of this model is that it was designed using the doxycycline responsive system, thus giving us the ability to regulate the overexpression of ESR1 by administering doxycycline via food to the mice. In our previous experiment, doxycycline (200 mg/kg) was administered to the mice via food for 5 days. The results showed that there were no differences in the mRNA levels between ESR1 OE and controls, hence confirming that doxycycline treatment did indeed shut-off overexpression of ESR1. Although our ultimate goal is to determine whether overexpression of ESR1 during development results in aberrant responses to endogenous hormones or exogenous chemicals later as adults, it is necessary to first characterize this mouse model to build a foundation to design future experiments. Since ESR1 can regulate transcription of several genes, we hypothesized that ESR1 OE in the ovary alters expression of ESR2, aryl hydrocarbon receptor (AhR), androgen receptor (AR), progesterone receptor (PR), luteinizing hormone receptor (LHR) as well as follicle-stimulating hormone receptor (FSHR). The ovaries of the ESR1 OE and controls were isolated and subjected to quantitative real-time PCR using primers for the receptors. The results indicate that the mRNA levels of ESR2 were significantly lower in the ESR1 OE ovaries compared to the controls (control = 1.14 ± 0.02 genomic equivalents (ge); ESR1 OE = 0.47 ± 0.01 ge; n = 3; p ≤ 0.05). The mRNA levels of AhR as well as AR were significantly higher in ESR1 OE compared to controls (AhR mRNA levels in control = 0.23 ± 0.02 ge; ESR1 OE = 0.49 ± 0.09 ge; n = 4; p ≤ 0.05; AR mRNA levels in control = 0.78 ± 0.08 ge; ESR1 OE = 1.13 ± 0.23 ge; n = 4; p ≤ 0.05). However, the mRNA levels of PR, LHR and FSHR in ESR1 OE were not significantly different from controls (PR mRNA levels in control = 0.92 ± 0.54 ge; ESR1 OE = 0.92 ± 0.82 ge; n = 4; p = 0.1; LHR mRNA levels in control = 0.42 ± 0.36 ge; ESR1 OE = 0.42 ± 0.15 ge; n = 4; p = 0.65; FSHR mRNA levels in control = 1.18 ± 0.18 ge; ESR1 OE = 1.37 ± 0.26 ge; n = 4; p = 0.27). These data suggest possible cross-talk between ESR1 and AhR as well as AR in gene regulation. Support: NIH R21ES13061