Hypothalamic Kisspeptin Expression in Hyperandrogenic Female Rats and Aging Rats

The role of Kisspeptin signaling in Oocyte maturation

Kisspeptins (KPs) secreted from the hypothalamic KP neurons act on KP receptors (KPRs) in gonadotropin (GPN) releasing hormone (GnRH) neurons to produce GnRH. GnRH acts on pituitary gonadotrophs to induce secretion of GPNs, namely follicle stimulating hormone (FSH) and luteinizing hormone (LH), which are essential for ovarian follicle development, oocyte maturation and ovulation. Thus, hypothalamic KPs regulate oocyte maturation indirectly through GPNs. KPs and KPRs are also expressed in the ovarian follicles across species. Recent studies demonstrated that intraovarian KPs also act directly on the KPRs expressed in oocytes to promote oocyte maturation and ovulation. In this review article, we have summarized published reports on the role of hypothalamic and ovarian KP-signaling in oocyte maturation. Gonadal steroid hormones regulate KP secretion from hypothalamic KP neurons, which in turn induces GPN secretion from the hypothalamic-pituitary (HP) axis. On the other hand, GPNs secreted from the HP axis act on the granulosa cells (GCs) and upregulate the expression of ovarian KPs. While KPs are expressed predominantly in the GCs, the KPRs are in the oocytes. Expression of KPs in the ovaries increases with the progression of the estrous cycle and peaks during the preovulatory GPN surge. Intrafollicular KP levels in the ovaries rise with the advancement of developmental stages. Moreover, loss of KPRs in oocytes in mice leads to failure of oocyte maturation and ovulation similar to that of premature ovarian insufficiency (POI). These findings suggest that GC-derived KPs may act on the KPRs in oocytes during their preovulatory maturation. In addition to the intraovarian role of KP-signaling in oocyte maturation, in vivo, a direct role of KP has been identified during in vitro maturation of sheep, porcine, and rat oocytes. KP-stimulation of rat oocytes, in vitro, resulted in Ca2+ release and activation of the mitogen-activated protein kinase, extracellular signal-regulated kinase 1 and 2. In vitro treatment of rat or porcine oocytes with KPs upregulated messenger RNA levels of the factors that favor oocyte maturation. In clinical trials, human KP-54 has also been administered successfully to patients undergoing assisted reproductive technologies (ARTs) for increasing oocyte maturation. Exogenous KPs can induce GPN secretion from hypothalamus; however, the possibility of direct KP action on the oocytes cannot be excluded. Understanding the direct in vivo and in vitro roles of KP-signaling in oocyte maturation will help in developing novel KP-based ARTs.

Effects of kisspeptin-10 on the reproductive performance of sows in a fixed-time artificial insemination programme

Kisspeptin (KP) is a major positive regulator of the hypothalamo-pituitary-gonadal axis and affects female reproductive cyclicity in mammals. It offers an attractive alternative strategy to control reproduction in fixed-time artificial insemination (FTAI) protocols. We aimed to evaluate the effects of different doses of kisspeptin-10 (KP-10) on sow reproductive performance in FTAI protocols. One hundred ninety-eight weaned sows were divided into three groups at random. A FTAI-GnRH group of sows (n = 98) received 100 µg (2 mL) gonadotropin-releasing hormone (GnRH; gonadorelin) by intramuscular injection at 96 h after weaning (t = 0 h); FTAI-KPL (KPL: low-dose KP-10, n = 50), and FTAI-KPH groups of sows (KPH: high-dose KP-10, n = 50) received 0.5 or 1 mg KP-10 (2 mL) respectively at 96 h after weaning. Sows were checked twice daily for oestrus. Ultrasonographic evaluations were performed to determine the follicular diameter and time of ovulation; blood samples were collected immediately before injection (t₀ = 0 min) and at 15, 30, 45, 60, 75, 90 min, 24 and 48 h postinjection. Sows were inseminated at 112 and 132 h after weaning. The oestrus rates (96 vs 92%; 96 vs 88%) and weaning-to-oestrus intervals (98.9 vs 98.6 h; 98.9 vs 97.1 h) were not affected by treatment, but oestrus in the FTAI-KPL group was significantly longer than in the FTAI-GnRH group (38.7 vs 30.0 h; P < 0.05). The peak LH concentrations were 1.29 times greater than at t₀ = 0 in the FTAI-GnRH group, and 1.45 and 1.44 times greater than at t₀ = 0 in the FTAI-KPL and FTAI-KPH groups, respectively. Follicular diameters and pregnancy rates (86 vs 88%, 86 vs 80%, respectively) did not differ between the treatments. Moreover, the total numbers of piglets born and those born alive did not differ among the three groups. These findings suggested that 0.5 mg KP-10 given at 96 h after weaning could be used in FTAI programmes to manage batch farrowing in sows.

Reproductive Deficits Induced by Prenatal Antimüllerian Hormone Exposure Require Androgen Receptor in Kisspeptin Cells

Polycystic ovary syndrome (PCOS) is a common reproductive disorder characterized by elevated androgens and antimüllerian hormone (AMH). These hormones remain elevated throughout pregnancy, and potential effects of hormone exposure on offspring from women with PCOS remain largely unexplored. Expanding on recent reports of prenatal AMH exposure in mice, we have fully characterized the reproductive consequences of prenatal AMH (pAMH) exposure throughout the lifespan of first- and second-generation offspring of both sexes. We also sought to elucidate mechanisms underlying pAMH-induced reproductive effects. There is a known reciprocal relationship between AMH and androgens, and in PCOS and PCOS-like animal models, androgen feedback is dysregulated at the level of the hypothalamus. Kisspeptin neurons express androgen receptors and play a critical role in sexual development and function. We therefore hypothesized that pAMH-induced reproductive phenotypes would be mediated by androgen signaling at the level of kisspeptin cells. We tested the pAMH model in kisspeptin-specific androgen receptor knockout (KARKO) mice and found that virtually all pAMH-induced phenotypes assayed are eliminated in KARKO offspring compared to littermate controls. By demonstrating the necessity of androgen receptor in kisspeptin cells to induce pAMH phenotypes, we have advanced understanding of the interactions between AMH and androgens in the context of prenatal exposure, which could have significant implications for children of women with PCOS.