Prenatal Androgen Exposure Alters KNDy Neurons and Their Afferent Network in a Model of Polycystic Ovarian Syndrome

Abstract

Polycystic ovarian syndrome (PCOS), the most common endocrinopathy affecting women worldwide, is characterized by elevated luteinizing hormone (LH) pulse frequency due to the impaired suppression of gonadotrophin-releasing hormone (GnRH) release by steroid hormone negative feedback. Although neurons that co-express kisspeptin, neurokinin B and dynorphin (KNDy cells) were recently defined as the GnRH/LH pulse generator, little is understood about their role in the pathogenesis of PCOS. We used a prenatal androgen-treated (PNA) mouse model of PCOS to determine whether changes in KNDy neurons or their afferent network underlie altered negative feedback. First, we identified elevated androgen receptor gene expression in KNDy cells of PNA mice, whereas progesterone receptor and dynorphin gene expression was significantly reduced, suggesting elevated androgens in PCOS disrupt progesterone negative feedback via direct actions upon KNDy cells. Second, we discovered GABAergic and glutamatergic synaptic input to KNDy neurons was reduced in PNA mice. Retrograde monosynaptic tract-tracing revealed a dramatic reduction in input originates from sexually dimorphic afferents in the preoptic area, anteroventral periventricular nucleus, anterior hypothalamic area and lateral hypothalamus. These results reveal two sites of neuronal alterations potentially responsible for defects in negative feedback in PCOS: changes in gene expression within KNDy neurons, and changes in synaptic inputs from steroid hormone-responsive hypothalamic regions. How each of these changes contribute to the neuroendocrine phenotype seen in in PCOS, and the role of specific sets of upstream KNDy afferents in the process, remains to be determined.

Chronic androgen excess in female mice does not impact luteinizing hormone pulse frequency or putative GABAergic inputs to GnRH neurons

“…Here, the number of AR immunoreactive cells in the brain was increased by 4–6‐fold in females chronically exposed to DHT. Although the phenotypes of those neurons with upregulated AR remain to be determined, increased AR expression in the PNA model has been identified in agouti‐related protein neurons, 54 as well as in ARN kisspeptin neurons 55 . This robust upregulation of AR supports direct androgen excess actions in the brain; however, the specific circuits and mechanisms involved remain to be determined.…”

“…The relative level of androgen receptor (AR) or oestrogen receptor α (ERα) immunoreactive cells across brain regions neurons. 55 This robust upregulation of AR supports direct androgen excess actions in the brain; however, the specific circuits and mechanisms involved remain to be determined. A limitation of the present study is the absence of data for PR expression in similar brain areas.…”

In vivo imaging of the GnRH pulse generator reveals a temporal order of neuronal activation and synchronization during each pulse

“…In both of these disorders, changes in LH pulse frequency disrupt follicular maturation and appropriate steroid hormone secretion, leading to infertility ( 46 ). Impairments to kisspeptin and KNDy cells have been investigated as an underlying cause for altered LH pulse secretion in preclinical models ( 47 , 48 ), and KNDy peptide antagonists have already been intensely studied as therapeutic tools in the treatment of these disorders ( 49 – 51 ). Further characterization of leader versus follower cells, and the signaling pathways controlling their synchronization, may provide a basis for development of new therapeutics to either trigger or inhibit KNDy pulses and novel approaches to the control of reproduction in fertility disorders such as PCOS.…”

The role of gonadotropin‐releasing hormone neurons in polycystic ovary syndrome

“…Such resistance to progesterone negative feedback in these animal models likely reflects reduced progesterone receptor expression in the arcuate nucleus. [100][101][102][103] Interestingly, conditional neuron-specific knockout of the androgen receptor in mice reduces the ability of postnatal DHT administration to induce PCOS-like features such as ovulatory dysfunction, polycystic ovaries and obesity. 104 These data implicate the importance of neuroendocrine androgen action in the development of PCOS-like features in this model.…”

“…PNA rodents exhibit increased arcuate nucleus Kiss1 expression and/or increased arcuate nucleus kisspeptin neuron numbers in some, but not all, studies. 103,[137][138][139] PNA rats may also exhibit increased hypothalamic Tac2 (neurokinin B) mRNA expression and increased numbers of arcuate nucleus neurons expressing neurokinin B. 137,139 In PNA ewes, arcuate nucleus kisspeptin cell body size was increased, but there was no change detected in the numbers of arcuate nucleus kisspeptin-expressing cells, and fewer arcuate nucleus neurokinin B-and dynorphin-expressing cells were reported.…”