Hypothalamic kiss1 mRNA and kisspeptin immunoreactivity are reduced in a rat model of polycystic ovary syndrome (PCOS)

Abstract

An intact hypothalamic kiss1/kisspeptin/kiss1r complex is a prerequisite for reproductive competence, and kisspeptin treatment could be a practical therapeutic approach to some problems of infertility. One such disorder is polycystic ovarian syndrome (PCOS), a common cause of infertility affecting more than 100million women. A rodent model of PCOS is the prepubertal female rat treated for a prolonged period with dihydrotestosterone (DHT), which induces many of the metabolic characteristics of the syndrome. We hypothesized that hypothalamic kiss1 mRNA levels, and kisspeptin immunoreactivity (ir), would be abnormal in these rats. Prepubertal female rats were exposed to DHT for 60days. Rats were killed in two groups: at 26 and 60days of DHT exposure. Kiss1 mRNA was quantified in hypothalamus, pituitary, ovary and visceral adipose tissue. Separate groups of rats provided brain tissue for immunohistochemical analysis of kisspeptin-ir. At 26days of DHT exposure, hypothalamic kiss1 mRNA was severely depleted. In contrast DHT had no effect on pituitary kiss1 expression but it significantly increased levels of kiss1 mRNA in fat (+9-fold; p<0.01) and in ovary (+3-fold; p<0.05). At 60days, kiss1 expression had reverted to normal in hypothalamus and ovary but remained elevated in fat (+4-fold; p<0.05). Immunohistochemical analysis revealed that after 26days of exposure to DHT, kisspeptin-ir was almost completely absent in the arcuate nucleus and a large depletion in kisspeptin +ve fibers was also seen in the paraventricular nucleus, supraoptic nucleus and in the anteroventral periventricular area. At 60days, despite restored normal levels of kiss1 mRNA, hypothalamic kisspeptin-ir remained depleted in the treated rats. In summary Kiss1 gene expression is differentially affected in various tissues by chronic exposure to dihydrotestosterone in a rat model of polycystic ovary syndrome. In hypothalamus, specifically, kiss1 mRNA, and levels of kisspeptin immunoreactivity, are significantly reduced. Since these rats exhibit many of the characteristics of polycystic ovary syndrome, we suggest that atypical kiss1 expression may contribute to the multiple tissue abnormalities observed in women with this disorder. However, and of some importance, our data do not appear to be consistent with the elevated levels of LH seen in women with PCOS; i.e. reduced levels of hypothalamic kiss1 mRNA and kisspeptin immunoreactivity observed in DHT-treated rats are unlikely to produce elevated LH secretion.