Neurokinin B signaling in puberty: human and animal studies

Green tea catechin EGCG could prevent obesity-related precocious puberty through NKB/NK3R signaling pathway

This study aimed to explore the potential regulatory pathways of (-)-epigallocatechin-3-gallate (EGCG) in preventing obesity-related precocious puberty. A retrospective analysis on the impact of EGCG on puberty onset in obese girls was conducted on plasma samples collected from a human randomized controlled trial. In the trial, participants consumed EGCG capsules for 12 weeks. In the animal experiment, rats were divided into four groups: normal diet control (NC) group, high-fat diet (HFD) group, NC+EGCG group, and HFD+EGCG group. Blood samples were collected on postnatal days 27, 33, and 36 to detect sexual development indicators. The hypothalamic expressions of kisspeptin/Kiss1R and neurokinin B (NKB)/NK3R signaling were measured by RT-qPCR and Western blot assay. The ovary NKB protein expression was assessed by immunohistochemical assays. Serum NKB level in the EGCG group was lower than the placebo group by 0.599 ng/mL [β=-0.599, 95% CI: (-1.005, -0.193)], at the end of intervention and after adjusting for confounders (clinical study). In the animal experiment, EGCG intervention could significantly delay the vaginal opening (VO) time of rats fed with HFD. On day 33, EGCG intervention could significantly reduce serum NKB, luteinizing hormone (LH) levels, ovarian NKB protein expression, and endometrial thickness of HFD-fed rats, while EGCG intervention could remarkably increase mRNA and protein expression of NKB/NK3R. EGCG could prevent obesity-related precocious puberty through NKB/NK3R signaling pathway, which may provide a novel insight into the role of EGCG in preventing precocious puberty in obese girls.

Different pituitary action of NK3Ra and NK3Rb in grass carp

In mammals, NK3R is the specific receptor for NKB, which played an important role in reproduction. Recently, two NK3R isoforms, namely NK3Ra and NK3Rb, have been identified in fish. However, little is known about the pituitary actions of the two NK3R isoforms in fish. In this study, both NK3Ra and NK3Rb were isolated from grass carp pituitary. Although their sequence similarity was only 61.6%, the two NK3R isoforms displayed similar ligand selectivity and binding affinity to TAC3 gene products (NKBa, NKBRPa and NKBRPb). In addition, both NK3Ra and NK3Rb displayed similar signaling pathways, including PKA, PKC, MAPK and Ca²⁺ cascades. Tissue distribution indicated that both NK3Ra and NK3Rb were highly detected in grass carp pituitary. Further study found that NK3Ra was mainly located in pituitary LHβ cells, while NK3Rb was only detected in pituitary SLα cells. Furthermore, NK3Ra and NK3Rb activation could induce LHβ and SLα promoter activity, respectively. These results suggested that the two NK3R isoforms displayed different pituitary actions in fish. Using grass carp pituitary cells as model, we found that PACAP could significantly reduce NK3Ra, but induce NK3Rb mRNA expression coupled with cAMP/PKA and PLC/PKC pathways. Interestingly, PACAP could also significantly inhibit LHβ, but stimulate SLα mRNA expression in grass carp pituitary cells. Furthermore, NK3R antagonist could not only inhibit LHβ mRNA expression, but also block PACAP-induced SLα mRNA expression in grass carp pituitary cells. These results suggested that NK3Ra and NK3Rb could mediate PACAP-reduced LHβ and -induced SLα mRNA expression in grass carp pituitary, respectively.

The usefulness of circulating levels of leptin, kisspeptin, and neurokinin B in obese girls with precocious puberty

This study investigated the relationships of circulating leptin, kisspeptin, and neurokinin B (NKB) levels with precocious puberty (PP) in overweight/obese girls and evaluated the usefulness of these markers in the initiation of puberty. One hundred and twenty-eight girls aged 7.0-8.9 years with PP (group A, normal-weight; group B, overweight/obese) and 30 age-matched normal controls (NC) were enrolled. Serum levels of leptin, kisspeptin, and NKB were measured by commercial kits. Serum leptin levels were higher in group A (4.21 ng/mL) and B (5.64 ng/mL) compared to the NC (2.35 ng/mL, p < .001). Serum kisspeptin levels were lower in group A (0.59 ng/mL) than in group B (0.66 ng/mL, p = .018). Serum NKB levels were not different among the three groups. The predictive value of leptin (AUC =0.791) was lower than that of IGF-1 (AUC =0.917, p = .009), although both were significant markers for PP in the regression analysis. BMI z-score (AUC =0.806) was a predictive factor of PP. In conclusion, a higher level of leptin, IGF-1, and fatness in overweight/obese girls with PP compared to the NC confirms their roles in the regulation of puberty. Further research is needed if the effects of kisspeptin and NKB on puberty are limited at the levels of neurons or target tissue.

Basal Serum Neurokinin B Levels in Differentiating Idiopathic Central Precocious Puberty from Premature Thelarche

OBJECTIVE

To find out the diagnostic role of kisspeptin and neurokinin B in idiopathic central precocious puberty (ICPP) and premature thelarche (PT).

METHODS

The girls who presented with early breast development before the age of 8 years were evaluated. Patients with intracranial pathologies were excluded. Basal and stimulated follicle-stimulating hormone/luteinizing hormone (LH) levels and basal neurokinin B/kisspeptin levels were measured. Patients who had peak value of LH >5 mIU/mL and a bone age (BA)/chronological age (CA) ratio >1.1 were diagnosed as central precocious puberty (CPP), while cases who did not meet these criteria were diagnosed as PT. Healthy age-matched prepubertal girls were included as the control group.

RESULTS

The study group contained 25 girls with ICPP (7±0.8 years), 35 girls with PT (6.8±0.7 years), and 30 controls (6.7±0.7 years). Basal serum kisspeptin and neurokinin B levels were 2.36±0.47 ng/mL and 2.61±0.32 ng/mL, respectively in the ICPP group, 2.23±0.43 ng/mL and 2.24±0.23 ng/mL, respectively in the PT group, and 1.92±0.33 ng/mL and 2.03±0.24 ng/mL, respectively in the controls. Both kisspeptin and neurokinin B levels were higher in the ICPP and PT groups compared to controls (p<0.05). Moreover, basal neurokinin B level was different between ICPP and PT groups (p<0.01). A serum neurokinin B level of 2.42 ng/mL provided the most appropriate level to differentiate ICPP from PT, with a sensitivity of 84% and specificity of 77.1%.

CONCLUSION

Differentiation of CPP from PT is sometime difficult, and there is a need for a simple method for the differential diagnosis. Our results suggest that basal serum neurokinin B level can be used as an adjunctive parameter to differentiate ICCP from PT.

Novel Functional Role of NK3R Expression in the Potentiating Effects on Somatolactin α Autoregulation in grass carp pituitary cells

In our previous study, NKB/NK3R system has been shown to act at the pituitary level to up-regulate SLα synthesis and secretion in grass carp. However, whether NK3R expression can serve as a regulatory target at the pituitary level and contribute to NKB interactions with other SLα regulators is still unclear. In current study, using grass carp pituitary cells as a model, we have a novel finding that co-treatment of SLα/SLβ with carp TAC3 gene products, could induce a noticeable enhancement in SLα mRNA expression and these potentiating effects occurred with a parallel rise in NK3R transcript level after SLα/SLβ treatment. Interestingly, the stimulatory effects of SLα/SLβ on NK3R gene expression could be further potentiated by co-treatment with IGF-I/-II and simultaneous exposure of carp pituitary cells to SLα/SLβ and IGF-I/-II in the presence of TAC3 gene products was found to markedly elevated SLα mRNA expression (20 fold increase) and this synergistic stimulation was mediated by cAMP/PKA-, PLC/PKC- and Ca²⁺ -dependent cascades functionally coupled with NK3R activation. These findings suggest that local release of SLα via functional interactions with IGF-I/-II and TAC3/NK3R system may constitute a potent stimulatory signal for SLα gene expression in the carp pituitary via up-regulation of NK3R expression.

Delayed pubertal onset and prepubertal Kiss1 expression in female mice lacking central oestrogen receptor beta

Ovarian oestradiol is essential for pubertal maturation and adult physiology of the female reproductive axis. It acts at central and peripheral sites through two main oestrogen receptors (ER) α and β. Here we investigate the role of ERβ on central effects of oestradiol, by generating a mouse line specifically lacking the ERβ gene in neuronal and glial cells. Central ERβ deletion delays the age at vaginal opening and first oestrous and reduces uterine weight without affecting body growth. Analysis of factors necessary for pubertal progression shows reduced levels of Kiss1 transcripts at postnatal (P) day 25 in the preoptic area, but not in the mediobasal hypothalamus (MBH) of mutant females. In agreement with these data, the number of kisspeptin-immunoreactive neurons was decreased by 57-72% in the three subdivisions of the rostral periventricular area of the third ventricle (RP3V), whereas the density of kisspeptin-immunoreactive fibres was unchanged in the arcuate nucleus of mutant mice. These alterations do not involve changes in ERα mRNAs in the preoptic area and protein levels in the RP3V. The number and distribution of GnRH-immunoreactive cells were unaffected, but gonadotropin-releasing hormone (GnRH) transcript levels were higher in the P25 preoptic area of mutants. At adulthood, mutant females have normal oestrous cyclicity, kisspeptin system and exhibit unaltered sexual behaviour. They display, however, reduced ovary weight and increased anxiety-related behaviour during the follicular phase. This argues for the specific involvement of central ERβ in the regulation of pubertal onset in female reproduction, possibly through prepubertal induction of kisspeptin expression in the RP3V.

Evidence for Changes in Numbers of Synaptic Inputs onto KNDy and GnRH Neurones during the Preovulatory LH Surge in the Ewe

Kisspeptin neurones located in the arcuate nucleus (ARC) and preoptic area (POA) are critical mediators of gonadal steroid feedback onto gonadotrophin-releasing hormone (GnRH) neurones. ARC kisspeptin cells that co-localise neurokinin B (NKB) and dynorphin (Dyn), are collectively referred to as KNDy (Kisspeptin/NKB/Dyn) neurones, and have been shown in mice to also co-express the vesicular glutamate transporter, vGlut2, an established glutamatergic marker. The ARC in rodents has long been known as a site of hormone-induced neuroplasticity, and changes in synaptic inputs to ARC neurones in rodents occur over the oestrous cycle. Based on this evidence, the the present study aimed to examine possible changes across the ovine oestrous cycle in synaptic inputs onto kisspeptin cells in the ARC (KNDy) and POA, and inputs onto GnRH neurones. Gonadal-intact breeding season ewes were perfused using 4% paraformaldehyde during either the luteal or follicular phase of the oestrous cycle, with the latter group killed at the time of the luteinising hormone (LH) surge. Hypothalamic sections were processed for triple-label immunodetection of kisspeptin/vGlut2/synaptophysin or kisspeptin/vGlut2/GnRH. The total numbers of synaptophysin- and vGlut2-positive inputs to ARC KNDy neurones were significantly increased at the time of the LH surge compared to the luteal phase; because these did not contain kisspeptin, they do not arise from KNDy neurones. By contrast to the ARC, the total number of synaptophysin-positive inputs onto POA kisspeptin neurones did not differ between luteal phase and surge animals. The total number of kisspeptin and vGlut2 inputs onto GnRH neurones in the mediobasal hypothalamus (MBH) was also increased during the LH surge, and could be attributed to an increase in the number of KNDy (double-labelled kisspeptin + vGlut2) inputs. Taken together, these results provide novel evidence of synaptic plasticity at the level of inputs onto KNDy and GnRH neurones during the ovine oestrous cycle. Such changes may contribute to the generation of the preovulatory GnRH/LH surge.

Neurokinin B and reproductive functions: "KNDy neuron" model in mammals and the emerging story in fish

In mammals, neurokinin B (NKB), the gene product of the tachykinin family member TAC3, is known to be a key regulator for episodic release of luteinizing hormone (LH). Its regulatory actions are mediated by a subpopulation of kisspeptin neurons within the arcuate nucleus with co-expression of NKB and dynorphin A (commonly called the "KNDy neurons"). By forming an "autosynaptic feedback loop" within the hypothalamus, the KNDy neurons can modulate gonadotropin-releasing hormone (GnRH) pulsatility and subsequent LH release in the pituitary. NKB regulation of LH secretion has been recently demonstrated in zebrafish, suggesting that the reproductive functions of NKB may be conserved from fish to mammals. Interestingly, the TAC3 genes in fish not only encode the mature peptide of NKB but also a novel tachykinin-like peptide, namely NKB-related peptide (or neurokinin F). Recent studies in zebrafish also reveal that the neuroanatomy of TAC3/kisspeptin system within the fish brain is quite different from that of mammals. In this article, the current ideas of "KNDy neuron" model for GnRH regulation and steroid feedback, other reproductive functions of NKB including its local actions in the gonad and placenta, the revised model of tachykinin evolution from invertebrates to vertebrates, as well as the emerging story of the two TAC3 gene products in fish, NKB and NKB-related peptide, will be reviewed with stress on the areas with interesting questions for future investigations.

Novel pituitary actions of TAC3 gene products in fish model: receptor specificity and signal transduction for prolactin and somatolactin α regulation by neurokinin B (NKB) and NKB-related peptide in carp pituitary cells

TAC3 is a member of tachykinins, and its gene product neurokinin B (NKB) has recently emerged as a key regulator for LH through modulation of kisspeptin/GnRH system within the hypothalamus. In fish models, TAC3 not only encodes NKB but also a novel tachykinin-like peptide called NKB-related peptide (NKBRP), and the pituitary actions of these TAC3 gene products are still unknown. Using grass carp as a model, the direct effects and postreceptor signaling for the 2 TAC3 products were examined at the pituitary level. Grass carp TAC3 was cloned and confirmed to encode NKB and NKBRP similar to that of other fish species. In carp pituitary cells, NKB and NKBRP treatment did not affect LH release and gene expression but up-regulated prolactin (PRL) and somatolactin (SL)α secretion, protein production, and transcript expression. The stimulation by these 2 TAC3 gene products on PRL and SLα release and mRNA levels were mediated by pituitary NK2 and NK3 receptors, respectively. Apparently, NKB- and NKBRP-induced SLα secretion and transcript expression were caused by adenylate cyclase/cAMP/protein kinase A, phospholipase C/inositol 1,4,5-triphosphate/protein kinase C and Ca(2+)/calmodulin/Ca(2+)/calmodulin-dependent protein kinase II activation. The signal transduction for the corresponding responses on PRL release and mRNA expression were also similar, except that the protein kinase C component was not involved. These findings suggest that the 2 TAC3 gene products do not play a role in LH regulation at the pituitary level in carp species but may serve as novel stimulators for PRL and SLα synthesis and secretion via overlapping postreceptor signaling mechanisms coupled to NK2 and NK3 receptors, respectively.

Effect of Nourishing "Yin"-Removing "Fire" Chinese Herbal Mixture on Hypothalamic NKB/NK3R Expression in Female Precocious Rats

Aim. The present study aims to investigate the effects of nourishing "Yin"-removing "Fire" Chinese herb mixture on the hypothalamic NKB/NK3R expression in female precocious model rats. Materials and Methods. Female Sprague-Dawley rats were randomly divided into four groups: normal (N), central precocious puberty (CPP) model (M), CPP fed with Chinese herbal mixture (CHM), and CPP fed with normal saline (MS). Rats on postnatal day 5 were given a single subcutaneous injection of 300 μg to establish CPP model rats. Rats of CHM and MS groups were continuously administered with nourishing "Yin"-removing "Fire" Chinese herb mixture or saline since postnatal day 15. The expressions of hypothalamic NKB/NK3R were detected by means of real-time PCR, western blot, and immunofluorescence histochemistry. Results. The day of vaginal opening and establishment of two regular estrous cycles were delayed in the CHM group compared with M and MS groups. The expression of hypothalamic NKB/NK3R mRNA and protein in the arcuate nucleus (ARC) and medial preoptic (MPO) area were decreased significantly in the CHM group compared with the M and MS groups on the day of onset-puberty. Conclusions. These results indicate that the NKB/NK3R signaling pathway might be involved in the effect of herbal mixture treatment on CPP.

Neuroanatomy of the human hypothalamic kisspeptin system

Hypothalamic kisspeptin (KP) neurons are key players in the neuronal network that regulates the onset of puberty and the pulsatile secretion of gonadotropin-releasing hormone (GnRH). In various mammalian species, the majority of KP-synthesizing neurons are concentrated in two distinct cell populations in the preoptic region and the arcuate nucleus (ARC). While studies of female rodents have provided evidence that preoptic KP neurons play a critical sex-specific role in positive estrogen feedback, KP neurons of the ARC have been implicated in negative sex steroid feedback and they have also been hypothesized to contribute to the pulse generator network which regulates episodic GnRH secretion in both females and males. Except for relatively few morphological studies available in monkeys and humans, our neuroanatomical knowledge of the hypothalamic KP systems is predominantly based on observations of laboratory species which are phylogenetically distant from the human. This review article discusses the currently available literature on the topographic distribution, network connectivity, neurochemistry, sexual dimorphism, and aging-dependent morphological plasticity of the human hypothalamic KP neuronal system.

Agouti-related peptide plays a critical role in leptin's effects on female puberty and reproduction

Deficient leptin signaling causes infertility via reduced activity of GnRH neurons, causing a hypogonadal state in both rodents and humans. Because GnRH neurons do not express leptin receptors, leptin's effect on GnRH neurons must be indirect. Neurons within the hypothalamic arcuate nucleus that coexpress AGRP and NPY are considered to be important intermediate neurons involved in leptin regulation of GnRH neurons. Previously, we reported that the absence of AGRP and haploinsufficiency of MC4R in leptin receptor mutant (Lepr(db/db)) females result in restoration of fertility and lactation despite the persistence of obesity and insulin resistance. The overarching hypothesis in the present study is that the absence or reduction of leptin's inhibition of AGRP/NPY neurons leads to suppression of GnRH release in cases of leptin signaling deficiency. Since TAC2 (NKB)-TAC3R signaling plays a role in puberty maturation and is modulated by metabolic status, the other aim of this study is to test whether TAC2/NKB neurons in ARC regulated by melanocortinergic signals herein affect leptin's action on puberty and reproduction. Our data showed that AGRP deficiency in Lepr(db/db) females restores normal timing of vaginal opening and estrous cycling, although uterine weight gain and mammary gland development are morphologically delayed. Nonetheless, Agrp(-/-) Lepr(db/db) females are fertile and sustain adequate nutrition of pups with lactation to weaning age. AGRP deficiency results in advanced vaginal opening in wild-type female mice. The postpubertal increase in hypothalamic TAC2 mRNA was not observed in Lepr(db/db) females, whereas AGRP deficiency restored it in Lepr(db/db) females. Additionally, MC4R activation with MTII induced FOS expression in TAC2 neurons, supporting the concept of melanocortinergic regulation of TAC2 neurons. These studies suggest that AGRP imposes an inhibitory effect on puberty and that TAC2 neurons may transmit melanocortinergic inhibition of GnRH neurons.

Localization and enzymatic activity profiles of the proteases responsible for tachykinin-directed oocyte growth in the protochordate, Ciona intestinalis

We previously substantiated that Ci-TK, a tachykinin of the protochordate, Ciona intestinalis (Ci), triggered oocyte growth from the vitellogenic stage (stage II) to the post-vitellogenic stage (stage III) via up-regulation of the gene expression and enzymatic activity of the proteases: cathepsin D, carboxypeptidase B1, and chymotrypsin. In the present study, we have elucidated the localization, gene expression and activation profile of these proteases. In situ hybridization showed that the Ci-cathepsin D mRNA was present exclusively in test cells of the stage II oocytes, whereas the Ci-carboxypeptidase B1 and Ci-chymotrypsin mRNAs were detected in follicular cells of the stage II and stage III oocytes. Double-immunostaining demonstrated that the immunoreactivity of Ci-cathepsin D was largely colocalized with that of the receptor of Ci-TK, Ci-TK-R, in test cells of the stage II oocytes. Ci-cathepsin D gene expression was detected at 2h after treatment with Ci-TK, and elevated for up to 5h, and then slightly decreased. Gene expression of Ci-carboxypeptidase B1 and Ci-chymotrypsin was observed at 5h after treatment with Ci-TK, and then decreased. The enzymatic activities of Ci-cathepsin D, Ci-carboxypeptidase B1, and Ci-chymotrypsin showed similar alterations with 1-h lags. These gene expression and protease activity profiles verified that Ci-cathepsin D is initially activated, which is followed by the activation of Ci-carboxypeptidase B1 and Ci-chymotrypsin. Collectively, the present data suggest that Ci-TK directly induces Ci-cahtepsin D in test cells expressing Ci-TK receptor, leading to the secondary activation of Ci-chymotrypsin and Ci-carboxypeptidase B1 in the follicle in the tachykininergic oocyte growth pathway.