Activation of the gonadotropic axis critically depends on sufficient body energy stores, and conditions of negative energy balance result in lack of puberty onset and reproductive failure. Recently, KiSS-1 gene-derived kisspeptin, signaling through the G protein-coupled receptor 54 (GPR54), has been proven as a pivotal regulator in the control of gonadotropin secretion and puberty. However, the impact of body energy status upon hypothalamic expression and function of this system remains unexplored. In this work, we evaluated the expression of KiSS-1 and GPR54 genes at the hypothalamus as well as the ability of kisspeptin-10 to elicit GnRH and LH secretion in prepubertal rats under short-term fasting. In addition, we monitored the actions of kisspeptin on food intake and the effects of its chronic administration upon puberty onset in undernutrition. Food deprivation induced a concomitant decrease in hypothalamic KiSS-1 and increase in GPR54 mRNA levels in prepubertal rats. In addition, LH responses to kisspeptin in vivo were enhanced, and its GnRH secretagogue action in vitro was sensitized, under fasting conditions. Central kisspeptin administration failed to change food intake patterns in animals fed ad libitum or after a 12-h fast. However, chronic treatment with kisspeptin was able to restore vaginal opening (in approximately 60%) and to elicit gonadotropin and estrogen responses in a model of undernutrition. In summary, our data are the first to show an interaction between energy status and the hypothalamic KiSS-1 system, which may constitute a target for disruption (and eventual therapeutic intervention) of pubertal development in conditions of negative energy balance.

Kisspeptins, the products of KiSS-1 gene, and their receptor, GPR54, have recently emerged as essential gatekeepers of reproduction, mainly through regulation of GnRH secretion at the hypothalamus. However, the profound hypogonadotropism linked to GPR54 inactivation is likely to mask additional functions of this system at other levels of the gonadal axis, in which expression of KiSS-1 and GPR54 has been preliminarily reported. We describe herein the expression of KiSS-1 gene and kisspeptin immunoreactivity (IR) in rat ovary and evaluate its developmental and hormonal regulation. KiSS-1 and GPR54 mRNAs were persistently detected in adult ovary along estrous cycle. Yet, contrary to GPR54, ovarian KiSS-1 levels fluctuated in a cyclic-dependent manner, with a robust increase in the afternoon of proestrus, i.e. preceding ovulation. In addition, kisspeptin-IR was observed in rat ovary, with strong signals in theca layers of growing follicles, corpora lutea, and interstitial gland, compartments in which modest GPR54-IR was also detected. Interestingly, the rise in ovarian KiSS-1 mRNA at proestrus was prevented by blockade of preovulatory gonadotropin surge and restored by replacement with human chorionic gonadotropin as superagonist of LH. In addition, immature ovaries showed low to negligible levels of KiSS-1 mRNA, which were significantly enhanced by gonadotropin priming. In summary, we present novel evidence for the developmental and hormonally regulated expression of the KiSS-1 gene, and the presence of kisspeptin-IR, in rat ovary. The ability of the LH surge to timely induce ovarian expression of KiSS-1 at the preovulatory period strongly suggests a previously unsuspected role of locally produced kisspeptin in the control of ovulation.

Hypogonadotropism is a common feature of uncontrolled diabetes, for which the ultimate mechanism remains to be elucidated. Kisspeptins, ligands of G protein-coupled receptor 54 (GPR54) encoded by the KiSS-1 gene, have recently emerged as major gatekeepers of the gonadotropic axis. Alteration in the hypothalamic KiSS-1 system has been reported in adverse metabolic conditions linked to suppressed gonadotropins, such as undernutrition. However, its potential contribution to defective gonadotropin secretion in diabetes has not been evaluated. We report herein analyses of luteinizing hormone (LH) responses to kisspeptin and hypothalamic expression of the KiSS-1 gene in streptozotocin (STZ)-induced diabetic male rats. In addition, functional studies involving kisspeptin replacement or continuous administration of leptin and insulin to diabetic male rats are presented. Kisspeptin administration evoked robust LH and testosterone bursts and enhanced postgonadectomy LH concentrations, despite prevailing attenuation of gonadotropic axis in diabetic animals. In addition, hypothalamic KiSS-1 mRNA levels were unambiguously decreased in diabetic male rats, and the postorchidectomy rise in KiSS-1 mRNA was severely blunted. Repeated administration of kisspeptin to diabetic rats evoked persistent LH and testosterone responses and partially rescued prostate and testis weights. In addition, central infusion of leptin, but not insulin, was sufficient to normalize hypothalamic KiSS-1 mRNA levels, as well as LH and testosterone concentrations. In summary, we provide evidence for altered expression of the hypothalamic KiSS-1 system in a model of uncontrolled diabetes. This observation, together with the ability of exogenous kisspeptin to rescue defective LH responses in diabetic rats, unravel the physiopathological implication, and potential therapeutic intervention, of the KiSS-1 system in altered gonadotropin secretion of type 1 diabetes. Diabetes

Diabetes alters microvascular function in the vascular beds of organs, including the lungs. Cardiovascular complications of pulmonary vascular affectation may be a consequence of the overactivation of the vasoconstrictive and proliferative components of the renin-angiotensin system. We previously reported that pulmonary physiology and surfactant production is improved by the glucagon-like peptide 1 receptor (GLP-1R) agonist liraglutide (LIR) in a rat model of lung hypoplasia. Because we hypothesized that streptozotocin-induced diabetes rats would show deficiencies in lung function, including surfactant proteins, and develop an imbalance of the renin-angiotensin system in the lungs. This effect would in turn be prevented by long-acting agonists of the GLP-1R, such as LIR. The induction of diabetes reduced the surfactant protein A and B in the lungs and caused the vasoconstrictor component of the renin-angiotensin system to predominate, which in turn increased angiotensin II levels, and ultimately being associated with right ventricle hypertrophy. LIR restored surfactant protein levels and reversed the imbalance in the renin-angiotensin system in this type 1 diabetes mellitus rat model. Moreover, LIR provoked a strong increase in angiotensin-converting enzyme 2 expression in the lungs of both diabetic and control rats, and in the circulating angiotensin(1-7) in diabetic animals. These effects prompted complete reversion of right ventricle hypertrophy. The consequences of LIR administration were independent of glycemic control and of glucocorticoids, and they involved NK2 homeobox 1 signaling. This study demonstrates by first time that GLP-1R agonists, such as LIR, might improve the cardiopulmonary complications associated with diabetes.

Kisspeptins, products of the KiSS-1 gene with ability to bind G protein-coupled receptor 54 (GPR54), have been recently identified as major gatekeepers of reproductive function with ability to potently activate the GnRH/LH axis. Yet, despite the diversity of functional states of the female gonadotropic axis, pharmacological characterization of this effect has been mostly conducted in pubertal animals or adult male rodents, whereas similar studies have not been thoroughly conducted in the adult female. In this work, we evaluated maximal LH and FSH secretory responses to kisspeptin-10, as well as changes in sensitivity and hypothalamic expression of KiSS-1 and GPR54 genes, in different physiological and experimental models in the adult female rat. Kisspeptin-10 (1 nmol, intracerebroventricular) was able to elicit robust LH bursts at all phases of the estrous cycle, with maximal responses at estrus; yet, in diestrus LH, responses to kisspeptin were detected at doses as low as 0.1 pmol. In contrast, high doses of kisspeptin only stimulated FSH secretion at diestrus. Removal of ovarian sex steroids did not blunt the ability of kisspeptin to further elicit stimulated LH and FSH secretion, but restoration of maximal responses required replacement with estradiol and progesterone. Finally, despite suppressed basal levels, LH and FSH secretory responses to kisspeptin were preserved in pregnant and lactating females, although the magnitude of LH bursts and the sensitivity to kisspeptin were much higher in pregnant dams. Interestingly, hypothalamic KiSS-1 gene expression significantly increased during pregnancy, whereas GPR54 mRNA levels remained unaltered. In summary, our current data document for the first time the changes in hypothalamic expression of KiSS-1 system and the gonadotropic effects (maximal responses and sensitivity) of kisspeptin in different functional states of the female reproductive axis. The present data may pose interesting implications in light of the potential therapeutic use of kisspeptin analogs in the pharmacological manipulation of the gonadotropic axis in the female.