The gonadotropin-induced expression of aromatase in granulosa cells is dependent on the signaling pathways that are activated, which is dictated by the density of each gonadotropin receptor. We hypothesize that low gonadotropin receptor densities support aromatase expression because only cAMP and Akt pathways are activated, while higher gonadotropin receptor densities do not support aromatase expression because they also stimulate the accumulation of inositol phosphates and diacylglycerol leading to the release of epiregulin and phosphorylation of EGFR and ERK1/2. Involvement of LHR to stimulate the inositol phosphate cascade as an inhibitor of aromatase expression has been reported only using gonadotropin receptor mutants expressed in primary cultures of granulosa cells. Therefore, we propose to use genetically modified mouse models to determine if activation of the ovarian inositol phosphate cascade by LHR is necessary for down regulation of aromatase expression that occurs after ovulation.
Aim 1 will generate a mouse model with a granulosa cell- specific deletion of the Gq/11-sensitive inositol phosphate cascade and characterize the expression of Gaq and Ga11 of these mice.
Aim 2 will determine the reproductive phenotype of mice produced from Aim 1. Ovarian aromatase expression will be quantified in immature female mice injected with PMSG followed by hCG to confirm our hypothesis. We will also measure serum LH, FSH, E2 and P4 of immature and 3 to 6 month old KO and wt mice. Ovarian histology and E2 and P4 serum concentrations of immature females injected with PMSG alone or PMSG and hCG will also be analyzed. If we find that aromatase expression remains high after hCG (as predicted) in the KOmice, we will then use granulosa cells from these mice to measure the different components of the proposed signaling pathway involved in the aromatase response. Regardless of the results of the proposed experiments having mice with a granulosa cell-specific deletion of the inositol phosphate cascade will allow us to test for other potential roles of the inositol phosphate cascade on ovarian physiology.
Understanding common and divergent effects of the FSH/FSHR and LH/LHR pairs on ovarian physiology will aid in the use of FSH and LH/hCG as infertility drugs and how they regulate the major hormones (estradiol and progesterone) that control reproduction.
