Normal gonadal function requires regulated secretion of LH. Hypersecretion correlates with impaired fertility in women that includes disruptions in both ovarian function and maintenance of pregnancy. Understanding the causes and effects of LH hypersecretion, however, has been hampered by the complexity of the hypothalamic-pituitary-gonadal axis and the lack of genetically defined animal models. Recently, we used the alpha subunit promoter to target expression of an LHbeta chimeric gene containing the carboxyl terminal peptide (CTP) of hCGbeta specifically to gonadotropes in transgenic mice. Female transgenics (alphaLHbetaCTP) hypersecrete chimeric LH, are infertile, and have elevated serum levels of sex steroids accompanied by a range of gonadal abnormalities including polycystic ovaries and granulosa cell tumors. Elevated LH occurring in the presence of elevated sex steroids in females suggests that expression of the alphaLHbetaCTP transgene has escaped at least some component of negative steroidal feedback. In contrast, transgenic males are fertile with normal levels of LH, suggesting that sex steroids exerted appropriate control over the chimeric alphaLHbetaCTP transgene. This new proposal builds on these findings by identifying three interrelated Specific Aims that model events associated with LH hypersecretion.
The first aim considers effects of LH hypersecretion and postulates that its developmental pattern contributes to the extent and reversibility of gonadal abnormalities.
This aim i nvolves manipulation of our existing transgenic models and includes ovarian transplantation between non-transgenic and transgenic animals. We also propose development of a new inducible transgenic model for controlling temporal onset of LH hypersecretion.
The second aim addresses potential causes of LH hypersecretion by proposing that steroid receptors in gonadotropes are critical for preventing elevated secretion of LH. Testing this hypothesis involves construction of new transgenic animals with selective overexpression or ablation of androgen receptor (AR) or estrogen receptor (ER) specifically in gonadotropes. These transgenic models will utilize either AR- or ER-transgenes as well as gonadotrope-specific ribozymes. Our last aim focuses on transcriptional mechanisms required for appropriate regulation of LH secretion. The initial experimental paradigm will focus on AR regulation of a subunit promoter activity. Testing this aim involves transfection assays with truncated and site-specific AR mutants, AR and ER exchange chimeras, and use of a yeast two-hybrid assay for identifying transcription factors that interact specifically with AR. Ultimately, this strategy will be extended to ER. Collectively, our work will generate several new mouse models that should be useful for: 1) examining the effects of LH hypersecretion on ovarian dysfunction; 2) providing potential applications for further understanding clinical syndromes such as polycystic ovary syndrome (PCOS) and congenital adrenal hyperplasia (CAH); and 3) elucidating specific transcriptional mechanisms required for preventing hypersecretion of LH.
