Abstract
Androgen and its receptor (AR) play a critical role in reproductive function, under both normal physiological and clinically pathophysiological conditions. Many women with hyperandrogenemia suffer irregular menses, oligo-anovulation and infertility. Whether high androgen levels directly or secondarily affect reproduction is unknown. Further, most animal models of hyperandrogenemia induced infertility are associated with obesity which adds a confounding variable to analysis. Therefore, we created a lean elevated androgen model by implantation of a low dose dihydrotestosterone (DHT) that separates the effects of obesity from elevated androgen. Reproduction is tightly controlled by the hypothalamus-pituitary-gonadal axis, androgen could theoretically alter neuroendocrine function at the level of brain and/or pituitary. The goal of this study is to understand how high androgen signaling via the androgen receptor (AR) in pituitary gonadotropes affects reproductive function. Mice with disruption of the Ar gene specifically in pituitary gonadotropes (PitARKO) were produced to explore the role of elevated androgen on the development of reproductive dysfunction in female mice. PitARKO-DHT mice showed significantly improved estrous cyclicity and fertility compared to DHT treated control littermates with intact pituitary Ar (Con-DHT). During 90 days of mating, PitARKO-DHT mice had a significantly increased number of litters (2.3±0.6 vs 0.5±0.3) and number of pups (5.3±2.8 vs 17.0±4.5) compared to Con-DHT mice. The improved reproductive function in PitARKO-DHT mice is partially due to improved pituitary responsiveness to GnRH stimulation. Ex vivo pituitary primary culture confirmed that DHT significantly reduced both basal and GnRH stimulated LH secretion. In vivo, LH secretion is preserved in PitARKO-DHT mice after GnRH stimulation compared to CON-DHT mice. GnRH induces the release of gonadotropins via an increase in cytosolic Ca(2+) concentration, and reduced cytoplasmic Ca(2+) concentrations may interfere with exocytosis of granules of LH. GEM, a calcium binding protein, inhibits voltage-gated Ca(2+) channel activity and reduces Ca(2+) influx in gonadotropes, which can affect gonadotropin secretion. We observed that Gem mRNA levels were significantly increased in Con-DHT treated mice (6 fold higher) compared to PitARKO-DHT mice. Further, the intracellular calcium influx signals were dramatically attenuated in Con-DHT mice compared to Con-no DHT mice, and were preserved in PitARKO-DHT mice after GnRH stimulation. These findings highlight gonadotrope AR as an extra ovarian regulator playing an important role in reproductive physiology and that high androgens may impact function through AR regulated Gem expression.