Kisspeptin-GPR54 Signaling in Mouse NO-Synthesizing Neurons Participates in the Hypothalamic Control of Ovulation

Abstract

Reproduction is controlled in the brain by a neural network that drives the secretion of gonadotropin-releasing hormone (GnRH).Various permissive homeostatic signals must be integrated to achieve ovulation in mammals. However, the neural events controlling the timely activation of GnRH neurons are not completely understood. Here we show that kisspeptin, a potent activator of GnRH neuronal activity, directly communicates with neurons that synthesize the gaseous transmitter nitric oxide (NO) in the preoptic region to coordinate the progression of the ovarian cycle. Using a transgenic Gpr54-null IRES-LacZ knock-in mouse model, we demonstrate that neurons containing neuronal NO synthase (nNOS), which are morphologically associated with kisspeptin fibers, express the kisspeptin receptor GPR54 in the preoptic region, but not in the tuberal region of the hypothalamus. The activation of kisspeptin signaling in preoptic neurons promotes the activation of nNOS through its phosphorylation on serine 1412 via the AKT pathway and mimics the positive feedback effects of estrogens. Finally, we show that while NO release restrains the reproductive axis at stages of the ovarian cycle during which estrogens exert their inhibitory feedback, it is required for the kisspeptin-dependent preovulatory activation of GnRH neurons. Thus, interactions between kisspeptin and nNOS neurons may play a central role in regulating the hypothalamic-pituitary-gonadal axis in vivo.

Leptin-dependent neuronal NO signaling in the preoptic hypothalamus facilitates reproduction

“…Pubertal activation was never detected in Nos1 -/-Lep ob/ob mice, while the first estrous cycle occurred 13 days from the start of the leptin regimen in Nos1 +/+ Lep ob/ob littermates and remained variable thereafter, typically lasting 4 to 5 days (Figure 4, B and E). The Nos1 -/-single-mutant (Nos1 -/-Lep +/+ ) mice demonstrated an ovulatory pattern, as reported in other studies (15,30), suggesting that the lack of nNOS alone is not responsible for the continued infertility of Nos1 -/-Lep ob/ob mice.…”

“…The preoptic region of the hypothalamus is one of the major sites for the expression of nNOS within the basal forebrain (36,37), in which the release of NO has been linked to the secretion of GnRH and stimulation of the preovulatory surge of GnRH/LH (15, 38-40). The importance for nNOS activity in reproductive functioning is highlighted by the detrimental effects on fertility in nNOS-deficient female mice, ranging from sporadic ovulation and blunted preovulatory LH secretion to complete hypothalamic hypogonadism (15,30,41). Intriguingly, nNOS neurons within the preoptic region have been shown to be key integrators of neural signals involved in reproduction (15,39,42,43), in which the local activation of nNOS and subsequent production of NO exert a tonic inhibitory tone on surrounding GnRH neurons (14,15).…”

“…The importance for nNOS activity in reproductive functioning is highlighted by the detrimental effects on fertility in nNOS-deficient female mice, ranging from sporadic ovulation and blunted preovulatory LH secretion to complete hypothalamic hypogonadism (15,30,41). Intriguingly, nNOS neurons within the preoptic region have been shown to be key integrators of neural signals involved in reproduction (15,39,42,43), in which the local activation of nNOS and subsequent production of NO exert a tonic inhibitory tone on surrounding GnRH neurons (14,15). Recently, the peripheral metabolic hormone leptin has also been found to directly activate nNOS neurons (16); in this study, it has been found to induce the phosphorylation of nNOS within the preoptic region.…”

“…Hypothalamic neurons that release the neuropeptide kisspeptin, a fundamental player in the reproductive axis (22)(23)(24), functionally interact with nNOS neurons (which express the kisspeptin receptor GPR54) within the preoptic region to regulate GnRH/LH release (15). Kisspeptin neurons in the arcuate nucleus (ARH) puta- tively contain the LepR, suggesting that leptin-induced LH release involves kisspeptin/GPR54 signaling (3).…”

Actions of sex steroids on kisspeptin expression and other reproduction-related genes in the brain of the teleost fish european sea bass

“…In this context, an increasing body of evidence supports the idea that GnRH neurons in mammals are regulated by distinct neuronal networks and interactions via specific cell-cell signalling molecules, which may be affected by the modulatory influence of gonadal steroids (Bellefontaine et al, 2011;Prevot, 2002;Radovick et al, 2012). In mice, nitric oxide (NO) is probably involved in mediating the estrogenic positive feedback of Kiss1 onto GnRH neurons (Hanchate et al, 2012). Recent data in sea bass have shown that kissr2 (also referred to as gpr54-2b or kissr3) is expressed in NO-positive cells (Escobar et al, 2013b), although its potential interaction with kisspeptins and the mediation of steroid feedback is still unknown.…”