Arcuate nucleus-specific progesterone receptor knockdown in female mice is sufficient to induce PCOS-like hyperactivity in the reproductive axis.

Mammalian reproductive function is dependent upon gonadal steroid hormone feedback within the hypothalamic-pituitary-gonadal (HPG) axis. In polycystic ovary syndrome (PCOS), impaired progesterone (P4) negative feedback leads to hyperactive pulsatile secretion of luteinising hormone (LH) and impaired reproductive function. Although the precise upstream neuronal network modulating P4 negative feedback remains undefined, gamma-aminobutyric acid (GABA)ergic neurons in the arcuate nucleus (ARC) have been implicated. To identify the critical location of P4 negative feedback, we knocked out progesterone receptors (PR) specifically from GABA neurons by genetic cross (VGAT-Cre; PRfl/fl) or specifically from the arcuate nucleus by stereotaxic AAV-Cre delivery to PRfl/fl mice and assessed HPG axis function. Females with GABA-specific PR knockout (GABAPRKO) exhibited delayed vaginal opening and fewer estrous cycles compared to controls, but LH pulse frequency and P4 negative feedback were unaffected. In contrast, females with AAV-Cre-mediated knockdown of PR specifically in the ARC exhibited increased LH pulse frequency in comparison to control and AAV-Cre off-target animals. ARC-specific PR knockdown also resulted in significantly decreased estrous cycle frequency, increased cycle length, reduced time spent in proestrus, and impaired P4 negative feedback, but no change in testosterone levels. These data show that reduced PR signalling in the ARC of adult female mice is sufficient to drive hyperactivity within the HPG axis and mimic some but not all reproductive features of PCOS. The subtle reproductive deficits in GABAPRKO may reflect compensatory mechanisms or the involvement of multiple neuronal phenotypes in P4 negative feedback. Together, this work supports the ARC as a critical site for P4 negative feedback regulation of the reproductive axis.