Investigating hypothalamic gene expression in a mouse model of Polycystic ovarian syndrome (PCOS)
Polycystic ovarian syndrome (PCOS) is the leading cause of infertility in premenopausal women, characterised with a failure to ovulate, leading to multiple ovarian cysts, and an over-secretion of male sex hormone. Gonadotrophin-releasing hormone (GnRH) neurons, a subset of neurons in the hypothalamus, receive signals from steroid hormone feedback systems to regulate the release of hormones from the pituitary gland and subsequently control ovarian function. Although the aetiology of PCOS is unknown, there is compelling evidence that PCOS is a state of impaired steroid hormone feedback. Given that GnRH neurons do not express the appropriate steroid hormone receptors to respond to this hormone feedback, steroid hormones are thought to communicate through an afferent neuronal network, referred to as the ‘GnRH neuronal network’ to provide critical steroid hormone information to the GnRH neurons. Here, we employed a well-established PCOS-like mouse model of prenatal androgen (PNA) exposure and quantitative polymerase chain reaction (qPCR) technique to examine the estrous cyclicity and possible alterations in steroid hormone receptors and specific hypothalamic signalling systems that are afferent to GnRH in PNA-treated female mice. We also aimed to determine whether androgen receptor blockade using flutamide treatment in adulthood can restore normal estrous cyclicity and rescue possible changes in mRNA expression induced by PNA treatment. The hypothalamus of vehicle-treated female, PNA-treated female, male, PNA-treated female with vehicle administered and PNA-treated female with flutamide administered were harvested and divided into the anterior and posterior hypothalamus. The mRNA expression of steroid hormone receptors, including progesterone receptor (PR), estrogen receptor α (ERα) and androgen receptor (AR), and signalling systems, including kisspeptin (Kiss1), dynorphin (DYN), k-opioid receptor 1 (KOR1), neurokinin B (NKB), NKB receptor 3 (NK3), neuropeptide Y (NPY) and proopiomelanocortin (POMC), were measured in the hypothalamus using qPCR. Analysis of estrous cyclicity in PNA-treated female mice showed that PNA exposure completely disrupted the normal pattern of cycles. We observed sexual dimorphic expression in ERα, Kiss1, NKB and NPY mRNA levels between vehicle-treated female and male mice, suggesting their potential roles in mediating sex-distinctive functions. PR mRNA expression in PNA-treated female mice was significantly lower than males in anterior hypothalamus but no difference was observed between PNA-treated vs vehicle-treated female mice or vehicle-treated female mice vs male mice. No difference in mRNA expression was found in other steroid hormone receptors. Lastly, 21 days of flutamide administration in PNA-treated female mice in adulthood demonstrated neither restoration of normal estrous cyclicity nor changes in mRNA expression of the steroid hormone receptors and signalling systems in both the anterior and the posterior hypothalamus, suggesting the androgen receptor blockade in adulthood is not sufficient to rescue the changes of mRNA expression induced by PNA exposure. Further studies using in situ hybridisation and immunohistochemistry for the steroid hormone receptors and signalling systems in the hypothalamus will help clarify the changes in mRNA expression in a region-specific manner in the mouse model of PCOS. In addition, identifying the phenotype of cells containing PR mRNA in the anterior hypothalamus will lead to a better understanding of the cell mechanisms underlying progesterone-mediated negative feedback. In conclusion, the current study provides a valuable indication of changes of gene expression of the GnRH neuronal network in the hypothalamus in a mouse model of PCOS.
Advisor: Campbell, Rebecca
Degree Name: Master of Science
Degree Discipline: Department of Physiology
Publisher: University of Otago
Keywords: Polycystic ovarian syndrome; PCOS; Hypothalamic gene expression; subfertility; Prenatal exposure
Research Type: Thesis