Endocrine Abstracts

JOINT3817

Mammalian reproduction and fertility rely on gonadal steroid hormone feedback within the hypothalamic-pituitary-gonadal (HPG) axis. In polycystic ovary syndrome (PCOS), diminished sensitivity to progesterone negative feedback contributes to impaired reproductive function, leading to increased pulsatile release of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH). Although the precise mechanisms underlying progesterone negative feedback in the HPG axis remain unclear, both clinical and preclinical evidence suggest that progesterone signalling through progesterone receptors (PR) in the arcuate nucleus of the hypothalamus (ARC), and potentially GABAergic neurons, plays a key role. To pinpoint the critical site of progesterone negative feedback, we investigated whether selectively disrupting progesterone sensitivity in the ARC of adult females or in all GABA neurons from birth is sufficient to induce HPG axis hyperactivity. To disrupt PR in the ARC, bilateral injections of AAV-Cre or AAV-control were stereotaxically injected into the ARC of adult transgenic PR^fl/fl mouse. To knock out (KO) PR in GABAergic neurons, PR^fl/fl mice were crossed with vesicular GABA transporter (VGAT)-Cre mice to generate GABA-specific PRKOs. Immunohistochemistry was used to assess viral targeting and site/ cell-specific loss of PR. Vaginal cytology was monitored for 14 days before and 4 weeks after Cre-mediated PR knockdown and for 3 weeks in adult GABA-specific PRKOs. Lutienizing hormone (LH) pulsatility was assessed in serial blood samples by ELISA and analysed with Pulsar software. PR expression in the ARC of AAV-Cre injected animals was significantly reduced in comparison to controls (P>0.001) and PR expression was completely absent from VGAT+ neurons in GABA-specific PRKOs. PR knockdown specific to the ARC was found to significantly decrease estrous cycle frequency (P>0.001), increase cycle length (P>0.01), and reduce time spent in proestrus (P>0.01). ARC-specific PR knockdown also increased LH pulse frequency in comparison to controls (P <0.05). In contrast, although GABA-specific PRKOs demonstrated delayed first estrous (P<0.05) and decreased estrous cycle frequency (P>0.001), there were no significant differences in LH pulse parameters from controls. Using these different transgenic approaches, we have demonstrated that although GABA-specific PRKO does not impact LH pulse frequency, knockdown of PR exclusively in the ARC in adulthood is sufficient to drive LH hypersecretion and mimic other reproductive impairments common to PCOS. Together, this work supports neurons in the ARC as the critical site for progesterone negative feedback regulation of the reproductive axis.