Abstract
Polycystic ovary syndrome (PCOS), the most common form of anovulatory infertility, is associated with a breakdown in signaling within the hormone sensitive neural network that regulates gonadotropin-releasing hormone (GnRH) neurons, ultimately increasing GnRH neural output. Circuitry between GABAergic neurons in the arcuate nucleus (ARN) and GnRH neurons is remodeled in mice that recapitulate PCOS, implicating their role in this disorder(1). One-third of ARN GABA neurons co-express neuropeptide Y (NPY)(2), which itself has a known, yet complex role in regulating GnRH neurons and reproductive function. This project aimed to examine whether this subpopulation of NPY expressing ARN GABA neurons are also altered in a PCOS-like state. To determine whether innervation to GnRH neurons by ARN NPY neurons is altered, prenatally androgenized, PCOS-like mice were generated in mice expressing green fluorescent protein (GFP) in agouti-related peptide neurons (AgRP-Cre;τGFP mice) by administration of dihydrotestosterone (PNA) or a vehicle (VEH) control, on days 16-18 of gestataion(3). Immunohistochemistry (IHC) against GnRH and GFP was carried out, and confocal microscopy was used to assess the density of contacts to GnRH neurons made by ARN NPY fibres. This revealed that innervation from ARN NPY neurons to GnRH neurons was not different between VEH (n=5) and PNA (n=8) mice. Sensitivity to steroid hormones was also assessed by IHC detection of progesterone receptor (PR), estrogen receptor alpha (ERα) and androgen receptor (AR) within GFP-expressing ARN NPY neurons. PR and ERα expression was almost completely absent from ARN NPY neurons in both VEH and PNA mice (n=5/group). However, the proportion of ARN NPY neurons expressing AR was significantly greater in PNA mice (33.2 ± 5.34%) compared with VEH controls (18.9 ± 1.83%, n=4/group, p<0.05), suggesting heightened androgen sensitivity in an already hyper-androgenic environment. In addition, gene transcription changes in the hypothalamus were investigated using a sensitive Nanostring(TM) assay in tissue microdissected from the rostral preoptic area (rPOA), rostral periventricular area of the third ventricle (RP3V), and ARN in VEH and PNA animals (n=12/group). While transcription of Npy was unchanged in the ARN, Npy1r expression was significantly decreased in the RP3V (0.82 ± 0.07 expression of mRNA relative to VEH, p < 0.05). This may indicate reduced NPY signalling to kisspeptin neurons via the Y1 receptor in the RP3V, and therefore an indirect reduction in inhibitory NPYergic signalling to GnRH neurons in a PCOS-like state. (1)Moore et al., PNAS, 2015; 112(2): 596-601. (2)Marshall et al., Neuroendocrinology, 2017; 105(2): 157-169. (3)Sullivan & Moenter, PNAS, 2004; 101: 7129-7134.