Kisspeptin: a novel regulator of reproductive function

Regulatory Effects of the Kiss1 Gene in the Testis on Puberty and Reproduction in Hezuo and Landrance Boars

Kisspeptin, a neuropeptide encoded by the Kiss1 gene, combines with its receptor Kiss1R to regulate the onset of puberty and male fertility by the hypothalamic-pituitary-gonadal axis. However, little is known regarding the expression signatures and molecular functions of Kiss1 in the testis. H&E staining revealed that well-arranged spermatogonia, spermatocytes, round and elongated spermatids, and spermatozoa, were observed in 4-, 6-, and 8-month-old testes compared to 1- and 3-month-old testes of Hezuo pigs; however, these were not observed in Landrance until 6 months. The diameter, perimeter, and cross-sectional area of seminiferous tubules and the perimeter and area of the tubular lumen increased gradually with age in both pigs. Still, Hezuo pigs grew faster than Landrance. The cloning results suggested that the Hezuo pigs' Kiss1 CDS region is 417 bp in length, encodes 138 amino acids, and is highly conserved in the kisspeptin-10 region. qRT-PCR and Western blot indicated that the expression trends of Kiss1 mRNA and protein were essentially identical, with higher expression levels at post-pubertal stages. Immunohistochemistry demonstrated that the Kiss1 protein was mainly located in Leydig cells and post-pubertal spermatogenic cells, ranging from round spermatids to spermatozoa. These studies suggest that Kiss1 is an essential regulator in the onset of puberty and spermatogenesis of boars.

Role of Kisspeptin in Regulation of Reproductive and Immune Reactions

The work is focused on physiological role of the hormone kisspeptin produced by neurons of the hypothalamus anterior zone, which is a key regulator of reproduction processes. Role of the hormone in transmission of information on metabolic activity and induction of the secretion of gonadotropin-releasing hormone (GnRH) by the hypothalamus that determines gestation processes involving fertilization, placentation, fetal development, and child birth is considered. The literature data on molecular mechanisms and effects of kisspeptin on reproductive system including puberty initiation are summarized and analyzed. In addition, attention is paid to hormone-mediated changes in the cardiovascular system in pregnant women. For the first time, the review examines the effect of kisspeptin on functional activity of immune system cells presenting molecular mechanisms of the hormone signal transduction on the level of lymphoid cells that lead to the immune tolerance induction. In conclusion, a conceptual model is presented that determines the role of kisspeptin as an integrator of reproductive and immune functions during pregnancy.

Kisspeptin and Testicular Function-Is it Necessary?

The role of kisspeptin in stimulating hypothalamic GnRH is undisputed. However, the role of kisspeptin signaling in testicular function is less clear. The testes are essential for male reproduction through their functions of spermatogenesis and steroidogenesis. Our review focused on the current literature investigating the distribution, regulation and effects of kisspeptin and its receptor (KISS1/KISS1R) within the testes of species studied to date. There is substantial evidence of localised KISS1/KISS1R expression and peptide distribution in the testes. However, variability is observed in the testicular cell types expressing KISS1/KISS1R. Evidence is presented for modulation of steroidogenesis and sperm function by kisspeptin signaling. However, the physiological importance of such effects, and whether these are paracrine or endocrine manifestations, remain unclear.

Absence of GPR54 and TACR3 mutations in sporadic cases of idiopathic central precocious puberty

BACKGROUND/AIMS

Kisspeptin (KISS1)/GPR54 (KISSR) signaling complex and neurokinin B (NKB)/NKB receptor (TACR3) signaling have been proposed as an integral part of the network coordinating GnRH release. GPR54 (KISS1R) and TACR3 gene mutations have been described in cases of idiopathic hypogonadotrophic hypogonadism, while limited data exist on gain-of-function mutation in GPR54 (KISS1R) gene causing idiopathic central precocious puberty (ICPP). No data on TACR3 mutations in ICPP have been described so far. The aim of this study was to elucidate the possible impact of GPR54 (KISS1R) and TACR3 mutations in ICPP.

METHODS

PCR-amplified genomic DNA of 38 girls with ICPP was analyzed for GPR54 and TACR3 gene mutations.

RESULTS

No GPR54 or TACR3 mutations were found. The A/G coding sequence single nucleotide polymorphism (SNP) on the GPR54 gene (dbSNP ID: rs10407968) was found in 2 patients with ICPP.

CONCLUSION

Our data indicate that GPR54 and TACR3 gene mutations are not a frequent cause of ICPP. The identified A/G synonymous SNP (dbSNP ID: rs10407968) located in exon 1 of the gene is not likely to have a pathogenic role in exon splicing and therefore in the premature initiation of puberty.

The actions of neuropeptide SF on the hypothalamic-pituitary-adrenal axis and behavior in rats

Present experiments focused on measuring the effect of neuropeptide SF (NPSF) on the hypothalamus-pituitary-adrenal (HPA) axis and behavior. The peptide was administered in different doses (0.25, 0.5, 1, 2 μg) intracerebroventricularly to rats, and the behavior of which was then observed by telemetry and open-field test. Effect of NPSF on core temperature was also measured via telemetry. Plasma ACTH and corticosterone concentrations were measured to assess the influence of NPSF on the HPA activation. In addition, the changes in corticotrophin-releasing hormone (CRH) level in the hypothalamic paraventricular nucleus were continuously monitored by means of intracerebral microdialysis. Our results showed that NPSF augmented paraventricular CRH release and increased ACTH and corticosterone levels in the plasma. The release of corticosterone was successfully blocked by the pre-treatment of the CRH antagonist α-helical CRH9-41. Spontaneous and exploratory locomotor activity was also stimulated according to the telemetric and open-field studies. However, NPSF only tended to alter stereotyped behavior in the open-field experiments. These results demonstrate that NPSF may play a physiologic role in the regulation of such circadian functions as the activity of motor centers and the HPA axis, through the release of CRH.

Christmas: an event driven by our hormones?

No other event in the Christian calendar has such a deep impact on our behaviour as the annual event called Christmas. Christmas is not just 'Christmas Day'; indeed, it is a long developmental rhythm with a period of almost exactly 365 days. Here, I describe the neuronal and hormonal changes and their effects on our behaviour during the preparation and the execution of the event(1) .

New genetic factors implicated in human GnRH-dependent precocious puberty: the role of kisspeptin system

Human puberty is triggered by the reemergence of GnRH pulsatile secretion with progressive activation of the gonadal function. A number of genes have been identified in the complex regulatory neuroendocrine network that controls puberty initiation. KISS1 and KISS1R genes, which encode kisspeptin and its cognate receptor, respectively, are considered crucial factors for acquisition of normal reproductive function. Recently, rare missense mutations and single nucleotide polymorphisms (SNPs) of the kisspeptin system were associated with puberty onset. Two gain-of-function mutations of the KISS1 and KISS1R genes were implicated in the pathogenesis of GnRH-dependent precocious puberty, previously considered idiopathic. These discoveries have yielded significant insights into the physiology and pathophysiology of this important life transition time. Here, we review the current molecular defects that are implicated in human GnRH-dependent precocious puberty.

Co-expression of leptin and oestrogen receptors in the preoptic-hypothalamic area

The interaction between the reproductive axis and energy balance suggests that leptin acts as a possible mediator. This hormone acts in the regulation of metabolism, feeding behaviour and reproduction. Animals homozygous for the gene 'ob' (ob/ob) are obese and infertile, and these effects are reversed after systemic administration of leptin. Thus, the present study aimed to determine: (i) whether cells that express leptin also express oestrogen receptors of type-alpha (ER-alpha) or -beta (ER-beta) in the medial preoptic area (MPOA) and in the arcuate (ARC), dorsomedial (DMH) and ventromedial hypothalamic nucleus and (ii) whether there is change in the gene and protein expression of leptin in these brain areas in ovariectomised (OVX) animals when oestrogen-primed. Wistar female rats with normal oestrous cycles or ovariectomised oestrogen-primed or vehicle (oil)-primed were utilised. To determine whether there was a co-expression, immunofluorescence was utilised for double staining. Confocal microscopy was used to confirm the co-expression. The technique of real-time polymerase chain reaction and western blotting were employed to analyse gene and protein expression, respectively. The results obtained showed co-expression of leptin and ER-alpha in the MPOA and in the DMH, as well as leptin and ER-beta in the MPOA, DMH and ARC. However, we did not detect leptin in the MPOA, ARC and DMH using western blotting and there was no statistical difference in leptin gene expression in the MPOA, DMH, ARC, pituitary or adipose tissue between OVX rats treated with oestrogen or vehicle. In conclusion, the results obtained in the present study confirm that the brain is also a source of leptin and reveal co-expression of oestrogen receptors and leptin in the same cells from areas related to reproductive function and feeding behaviour. Although these data corroborate the previous evidence obtained concerning the interaction between the action of brain leptin and reproductive function, the physiological relevance of this interaction remains uncertain and additional studies are necessary to elucidate the exact role of central leptin.

Kisspeptin directly excites anorexigenic proopiomelanocortin neurons but inhibits orexigenic neuropeptide Y cells by an indirect synaptic mechanism

The neuropeptide kisspeptin is necessary for reproduction, fertility, and puberty. Here, we show strong kisspeptin innervation of hypothalamic anorexigenic proopiomelanocortin (POMC) cells, coupled with a robust direct excitatory response by POMC neurons (n > 200) to kisspeptin, mediated by mechanisms based on activation of a sodium/calcium exchanger and possibly opening of nonselective cation channels. The excitatory actions of kisspeptin on POMC cells were corroborated with quantitative PCR data showing kisspeptin receptor GPR54 expression in the arcuate nucleus, and the attenuation of excitation by the selective kisspeptin receptor antagonist, peptide 234. In contrast, kisspeptin inhibits orexigenic neuropeptide Y (NPY) neurons through an indirect mechanism based on enhancing GABA-mediated inhibitory synaptic tone. In striking contrast, gonadotropin-inhibiting hormone (GnIH and RFRP-3) and NPY, also found in axons abutting POMC cells, inhibit POMC cells and attenuate the kisspeptin excitation by a mechanism based on opening potassium channels. Together, these data suggest that the two central peptides that regulate reproduction, kisspeptin and GnIH, exert a strong direct action on POMC neurons. POMC cells may hypothetically serve as a conditional relay station downstream of kisspeptin and GnIH to signal the availability of energy resources relevant to reproduction.

The effects of neurokinin B upon gonadotrophin release in male rodents

Growing evidence suggests the tachykinin neurokinin B (NKB) may modulate gonadotrophin secretion and play a role in sex-steroid feedback within the reproductive axis. NKB signalling has recently been identified as being necessary for normal human reproductive function, although the precise mechanisms underpinning this role remain to be established. We have used rodents to explore further the role of NKB within the reproductive axis. In particular, we have studied its interactions with kisspeptin, a neuropeptide essential for reproductive function in rodent and human with close anatomical links to NKB within the hypothalamus. Intraperitoneal administration of NKB (50 nmol) to male mice had no effect on circulating luteinsing hormone (LH) levels and, although i.p. kisspeptin (15 nmol) increased LH five-fold, co-administration of NKB and kisspeptin was indistinguishable from kisspeptin alone. Intracerebroventricular administration of NKB (10 nmol) to male mice also had no effect on LH levels, with 1 nmol kisspeptin i.c.v. significantly increasing LH compared to control (0.37 +/- 0.18 versus 5.11 +/- 0.28 ng/ml, respectively). Interestingly, i.c.v. co-administration of NKB and kisspeptin caused a significant increase in LH concentrations compared to kisspeptin alone (8.96 +/- 1.82 versus 5.11 +/- 0.28 ng/ml respectively). We used hypothalamic explants from rats to assess the effect of NKB on gonadotrpohin-releasing hormone (GnRH) secretion ex vivo. Doses of NKB up to 1000 nm failed to stimulate GnRH secretion, whereas 100 nm kisspeptin robustly increased GnRH secretion. Of note, co-administration of NKB with kisspeptin abrogated the effect of kisspeptin, producing no GnRH release above basal state. Finally, we analysed the expression of Tac2/Tacr3 (genes encoding NKB and NK3R, respectively) within the arcuate nucleus in different nutritional states. After a 48-h fast, the expression of both Tac2 and Tacr3 showed a significant increase, in contrast to levels of Kiss1 and Kiss1r mRNA, which remained unchanged. In male rodent models, NKB and kisspeptin have different effects upon gonadotrophin release and appear to interact in a complex manner.

Kisspeptin/Gpr54-independent gonadotrophin-releasing hormone activity in Kiss1 and Gpr54 mutant mice

The kisspeptin/Gpr54 signalling pathway plays a critical role in reproduction by stimulating the secretion of gonadotrophin-releasing hormone (GnRH), yet mice carrying mutations in Kiss1 (which encodes kisspeptin) or Gpr54 exhibit partial sexual maturation. For example, a proportion of female Kiss1(-/-) and Gpr54(-/-) mice exhibit vaginal oestrus, and some male Kiss1(-/-) and Gpr54(-/-) mice exhibit spermatogenesis. To characterise this partial sexual maturation, we examined the vaginal cytology of female Kiss1(-/-) and Gpr54(-/-) mice over time. Almost all mutant mice eventually enter oestrus, and then spontaneously transition from oestrus to dioestrus and back to oestrus again. These transitions are not associated with ovulation, and the frequency of these transitions increases with age. The oestrus exhibited by female Kiss1(-/-) and Gpr54(-/-) mice was disrupted by the administration of the competitive GnRH antagonist acyline, which also resulted in lower uterine weights and, in Kiss1(-/-) mice, lower serum follicle-stimulating hormone (FSH) and luteinising hormone (LH) concentrations. Similarly, male Kiss1(-/-) and Gpr54(-/-) mice treated with acyline had smaller testicular sizes and an absence of mature sperm. In addition to examining intact Kiss1(-/-) and Gpr54(-/-) mice, we also assessed the effects of acyline on gonadotrophin concentrations in gonadectomised mice. Gonadectomy resulted in a significant increase in serum FSH concentrations in male Gpr54(-/-) and Kiss1(-/-) mice. Acyline administration to gonadectomised Kiss1(-/-) and Gpr54(-/-) male mice lowered serum FSH and LH concentrations significantly. By contrast to males, gonadectomy did not result in significant gonadotrophin changes in female Kiss1(-/-) and Gpr54(-/-) mice, but acyline administration was followed by a decrease in LH concentrations. These results demonstrate that, although kisspeptin signalling is critical for the high levels of GnRH activity required for normal sexual maturation and for ovulation, Kiss1(-/-) and Gpr54(-/-) mice retain some degree of GnRH activity. This GnRH activity is sufficient to produce significant effects on vaginal cytology and uterine weights in female mice and on spermatogenesis and testicular weights in male mice.