Maternal oral exposure to low-dose BPA accelerates the onset of puberty by promoting prepubertal Kiss1 expression in the AVPV nucleus of female offspring

As the incidence of precocious puberty has risen in recent years and the age at puberty onset is younger, children may be at increased risk for health consequences associated with the early onset of puberty. Bisphenol A (BPA) is recognized as an endocrine disruptor chemical that is reported to induce precocious puberty. The effect of BPA exposure modes, times, and doses (especially low dose) were controversial. In the present study, we evaluated the potential effects of maternal exposure to low-dose BPA on the hypothalamus, particularly on the arcuate (ARC) nucleus and anteroventral periventricular (AVPV) nucleus during peri-puberty in offspring of BPA-treated rats. Pregnant rats were exposed to corn oil vehicle, 0.05 mg·kg-1·day-1 BPA, or 5 mg·kg-1·day-1 from gestation day 1 (GD1) to postnatal day 21 (PND21) by daily gavage. Body weight (BW), vaginal opening (VO), ovarian follicular luteinization, and relevant hormone concentrations were measured; hypothalamic Kiss1 and GnRH1 levels by western immunoblot analysis were also assessed as indices of puberty onset. During or after exposure, low-dose BPA restricted BW after birth (at PND1 and PND5), and subsequently accelerated puberty onset by promoting the expression of prepubertal Kiss1 and GnRH1 in the AVPV nucleus on PND30, leading to advanced VO, an elevation in LH and FSH concentrations (on PND30). We also noted increased BW on PND30 and PND35. Maternal oral exposure to low-dose BPA altered the BW curve during the neonatal and peripubertal periods, and subsequently accelerated puberty onset by promoting prepubertal Kiss1 expression in the AVPV nucleus.

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.

Airway-associated adipose tissue accumulation is increased in a kisspeptin receptor knockout mouse model

Airway-associated adipose tissue increases with body mass index and is a local source of pro-inflammatory adipokines that may contribute to airway pathology in asthma co-existing with obesity. Genetic susceptibility to airway adiposity was considered in the present study through kisspeptin/kisspeptin receptor signalling, known to modulate systemic adiposity and potentially drive airway remodelling. Therefore, the aim of the study was to determine the effects of kisspeptin/kisspeptin receptor signalling in the lung, focusing on airway-associated adipose tissue deposition and impact on airway structure-function. Wild-type, heterozygous and kisspeptin receptor knockout mice were studied at 6 or 8 weeks of age. Lung mechanics were assessed before and after methacholine challenge and were subsequently fixed for airway morphometry. A separate group of mice underwent glucose tolerance testing and bronchoalveolar lavage. At 6 weeks of age, kisspeptin/kisspeptin receptor signalling did not affect body adiposity, airway inflammation, wall structure or function. Despite no differences in body adiposity, there was a greater accumulation of airway-associated adipose tissue in knockout mice. By 8 weeks of age, female knockout mice displayed a non-diabetic phenotype with increased body adiposity but not males. Airway-associated adipose tissue area was also increased in both knockout females and males at 8 weeks of age, but again no other respiratory abnormality was apparent. In summary, airway-associated adipose tissue is decoupled from body adiposity in prepubescent mice which supports a genetic susceptibility to fatty deposits localised to the airway wall. There was no evidence that airway-associated adipose tissue drives pathology or respiratory impairment in the absence of other environmental exposures.

Differential regulation of Kiss1 gene expression by oestradiol in the hypothalamus of the female Damaraland mole-rat, an induced ovulator

Kisspeptin, a product of the Kiss1 gene is considered a potent stimulator of gonadotropin release, by interacting with its receptor, the G protein-coupled receptor 54. Kiss1 neurons are known to mediate the positive and negative feedback effects of oestradiol on GnRH neurons that control the pulsatile and surge secretion of GnRH. While in spontaneously ovulating mammals the GnRH/LH surge is initiated by a rise in ovarian oestradiol secreted from maturing follicles, in induced ovulators, the primary trigger is the mating stimulus. Damaraland mole rats (Fukomys damarensis) are cooperatively breeding, subterranean rodents that exhibit induced ovulation. We have previously described in this species the distribution and differential expression pattern of Kiss1-expressing neurons in the hypothalamus of males and females. Here we examine whether oestradiol (E2) regulates the hypothalamic Kiss1 expression in a similar way as described for spontaneously ovulating rodent species. By means of in situ hybridisation, we measured Kiss1 mRNA among groups of ovary-intact, ovariectomized (OVX) and OVX females treated with E2 (OVX + E2). In the arcuate nucleus (ARC), Kiss1 expression increased after ovariectomy and decreased with E2 treatment. In the preoptic region, Kiss1 expression after gonadectomy was similar to the level of wild-caught gonad-intact controls, but was dramatically upregulated with E2 treatment. The data suggest that, similar to other species, Kiss1 neurons in the ARC, which are inhibited by E2, play a role in the negative feedback control on GnRH release. The exact role of the Kiss1 neuron population in the preoptic region, which is stimulated by E2, remains to be determined.

Central and peripheral mechanisms involved in the control of GnRH neuronal function by metabolic factors

Gonadotropin-releasing hormone (GnRH) neurons are the final output pathway for the brain control of reproduction. The activity of this neuronal population, mainly located at the preoptic area of the hypothalamus, is controlled by a plethora of metabolic signals. However, it has been documented that most of these signal impact on GnRH neurons through indirect neuronal circuits, Kiss1, proopiomelanocortin, and neuropeptide Y/agouti-related peptide neurons being some of the most prominent mediators. In this context, compelling evidence has been gathered in recent years on the role of a large range of neuropeptides and energy sensors in the regulation of GnRH neuronal activity through both direct and indirect mechanisms. The present review summarizes some of the most prominent recent advances in our understanding of the peripheral factors and central mechanisms involved in the metabolic control of GnRH neurons.

Dissecting the KNDy hypothesis: KNDy neuron-derived kisspeptins are dispensable for puberty but essential for preserved female fertility and gonadotropin pulsatility

BACKGROUND

Kiss1 neurons in the hypothalamic arcuate-nucleus (ARC) play key roles in the control of GnRH pulsatility and fertility. A fraction of ARC Kiss1 neurons, termed KNDy, co-express neurokinin B (NKB; encoded by Tac2). Yet, NKB- and Kiss1-only neurons are also found in the ARC, while a second major Kiss1-neuronal population is present in the rostral hypothalamus. The specific contribution of different Kiss1 neuron sub-sets and kisspeptins originating from them to the control of reproduction and eventually other bodily functions remains to be fully determined.

METHODS

To tease apart the physiological roles of KNDy-born kisspeptins, conditional ablation of Kiss1 in Tac2-expressing cells was implemented in vivo. To this end, mice with Tac2 cell-specific Kiss1 KO (TaKKO) were generated and subjected to extensive reproductive and metabolic characterization.

RESULTS

TaKKO mice displayed reduced ARC kisspeptin content and Kiss1 expression, with greater suppression in females, which was detectable at infantile-pubertal age. In contrast, Tac2/NKB levels were fully preserved. Despite the drop of ARC Kiss1/kisspeptin, pubertal timing was normal in TaKKO mice of both sexes. However, young-adult TaKKO females displayed disturbed LH pulsatility and sex steroid levels, with suppressed basal LH and pre-ovulatory LH surges, early-onset subfertility and premature ovarian insufficiency. Conversely, testicular histology and fertility were grossly conserved in TaKKO males. Ablation of Kiss1 in Tac2-cells led also to sex-dependent alterations in body composition, glucose homeostasis, especially in males, and locomotor activity, specifically in females.

CONCLUSIONS

Our data document that KNDy-born kisspeptins are dispensable/compensable for puberty in both sexes, but required for maintenance of female gonadotropin pulsatility and fertility, as well as for adult metabolic homeostasis.

SIGNIFICANCE STATEMENT

Neurons in the hypothalamic arcuate nucleus (ARC) co-expressing kisspeptins and NKB, named KNDy, have been recently suggested to play a key role in pulsatile secretion of gonadotropins, and hence reproduction. However, the relative contribution of this Kiss1 neuronal-subset, vs. ARC Kiss1-only and NKB-only neurons, as well as other Kiss1 neuronal populations, has not been assessed in physiological settings. We report here findings in a novel mouse-model with elimination of KNDy-born kisspeptins, without altering other kisspeptin compartments. Our data highlights the heterogeneity of ARC Kiss1 populations and document that, while dispensable/compensable for puberty, KNDy-born kisspeptins are required for proper gonadotropin pulsatility and fertility, specifically in females, and adult metabolic homeostasis. Characterization of this functional diversity is especially relevant, considering the potential of kisspeptin-based therapies for management of human reproductive disorders.

Short-term depletion of plasma estrogen affects hypothalamic kisspeptin-neurokinin B-dynorphin A neurons, gonadotrophs, and pulsatile luteinizing hormone secretion in female rats

Kisspeptin-neurokinin B-dynorphin A (KNDy) neurons in the arcuate nucleus (ARC) regulate pulsatile luteinizing hormone (LH) secretion. These neurons express estrogen receptors and are negatively regulated by estrogen. This study aimed to determine whether estrogen supplementation after short-term ovariectomy-induced estrogen depletion has different effects on KNDy neurons depending on the timing of the supplementation. To decrease endogenous estradiol (E2) for a short time, adult female rats received a tube filled with E2 one week after ovariectomy and utilized it one week later (O1w + E). From the results of immunohistochemistry, the response to E2 was attenuated in KNDy neurons of O1w + E rats. Enlarged LH-secreting cells in the anterior pituitary were found in O1w + E rats; however, such enlarged LH cells were not found in ones without previous short-term E2 depletion. From the analysis of LH pulses, plasma LH levels were increased in O1w + E rats relative to ones without previous short-term E2 depletion. These results suggested that once endogenous sex steroids were depleted, the response to E2 in hypothalamic KNDy neurons did not fully recover in one week. Thus, short-term sex steroid depletion due to gonadectomy could alter the response to the sex steroids in KNDy neurons even though the period without sex steroids is only one week, and the alteration is likely to affect plasma hormone levels.

Serum kisspeptin levels mainly depend on ovarian expression of Kiss1 mRNA in female rats

The hypothalamic kisspeptin/KISS1 receptor system is essential for puberty onset and reproductive development. Although serum kisspeptin might be associated with puberty, its levels, according to developmental stage, and its origin still remain unclear. This study evaluated the changes in serum kisspeptin levels during puberty and the corresponding Kiss1 mRNA and protein expression in various organs of female rats to identify the source of serum kisspeptin. Tissues from several organs, including the ovaries and anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC) in the hypothalamus, were obtained for assessing Kiss1 mRNA and protein expressions. Serum kisspeptin levels progressively increased with developmental stages until the peripubertal stage. The ovaries showed the highest Kiss1 expression among the organs examined. Next, we explored the changes in serum kisspeptin levels and hypothalamic Kiss1 expression in ovariectomized and estradiol-treated ovariectomized rats. Serum kisspeptin levels decreased regardless of estradiol treatment; Kiss1 expression was enhanced by ovariectomy and estradiol treatment in the ARC, while it was decreased by ovariectomy and enhanced by estradiol in the AVPV, suggesting that serum kisspeptin may be associated with pubertal development and mainly depended on ovarian Kiss1 expression. Thus, serum kisspeptin levels are associated with puberty and may serve as a downstream marker of ovarian reproductive function.

Conditional Deletion of KOR (Oprk1) in Kisspeptin Cells Does Not Alter LH Pulses, Puberty, or Fertility in Mice

Classic pharmacological studies suggested that endogenous dynorphin-KOR signaling is important for reproductive neuroendocrine regulation. With the seminal discovery of an interconnected network of hypothalamic arcuate neurons co-expressing kisspeptin, neurokinin B, and dynorphin (KNDy neurons), the KNDy hypothesis was developed to explain how gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) pulses are generated. Key to this hypothesis is dynorphin released from KNDy neurons acting in a paracrine manner on other KNDy neurons via kappa opioid receptor (KOR) signaling to terminate neural "pulse" events. While in vitro evidence supports this aspect of the KNDy hypothesis, a direct in vivo test of the necessity of KOR signaling in kisspeptin neurons for proper LH secretion has been lacking. We therefore conditionally knocked out KOR selectively from kisspeptin neurons of male and female mice and tested numerous reproductive measures, including in vivo LH pulse secretion. Surprisingly, despite validating successful knockout of KOR in kisspeptin neurons, we found no significant effect of kisspeptin cell-specific deletion of KOR on any measure of puberty, LH pulse parameters, LH surges, follicle-stimulating hormone (FSH) levels, estrous cycles, or fertility. These outcomes suggest that the KNDy hypothesis, while sufficient normally, may not be the only neural mechanism for sculpting GnRH and LH pulses, supported by recent findings in humans and mice. Thus, besides normally acting via KOR in KNDy neurons, endogenous dynorphin and other opioids may, under some conditions, regulate LH and FSH secretion via KOR in non-kisspeptin cells or perhaps via non-KOR pathways. The current models for GnRH and LH pulse generation should be expanded to consider such alternate mechanisms.

Neuroendocrine mechanisms underlying estrogen positive feedback and the LH surge

A fundamental principle in reproductive neuroendocrinology is sex steroid feedback: steroid hormones secreted by the gonads circulate back to the brain to regulate the neural circuits governing the reproductive neuroendocrine axis. These regulatory feedback loops ultimately act to modulate gonadotropin-releasing hormone (GnRH) secretion, thereby affecting gonadotropin secretion from the anterior pituitary. In females, rising estradiol (E₂) during the middle of the menstrual (or estrous) cycle paradoxically "switch" from being inhibitory on GnRH secretion ("negative feedback") to stimulating GnRH release ("positive feedback"), resulting in a surge in GnRH secretion and a downstream LH surge that triggers ovulation. While upstream neural afferents of GnRH neurons, including kisspeptin neurons in the rostral hypothalamus, are proposed as critical loci of E₂ feedback action, the underlying mechanisms governing the shift between E₂ negative and positive feedback are still poorly understood. Indeed, the precise cell targets, neural signaling factors and receptors, hormonal pathways, and molecular mechanisms by which ovarian-derived E₂ indirectly stimulates GnRH surge secretion remain incompletely known. In many species, there is also a circadian component to the LH surge, restricting its occurrence to specific times of day, but how the circadian clock interacts with endocrine signals to ultimately time LH surge generation also remains a major gap in knowledge. Here, we focus on classic and recent data from rodent models and discuss the consensus knowledge of the neural players, including kisspeptin, the suprachiasmatic nucleus, and glia, as well as endocrine players, including estradiol and progesterone, in the complex regulation and generation of E₂-induced LH surges in females.

Developmental sex differences in the peri-pubertal pattern of hypothalamic reproductive gene expression, including Kiss1 and Tac2, may contribute to sex differences in puberty onset

The mechanisms regulating puberty still remain elusive, as do the underlying causes for sex differences in puberty onset (girls before boys) and pubertal disorders. Neuroendocrine puberty onset is signified by increased pulsatile GnRH secretion, yet how and when various upstream reproductive neural circuits change developmentally to govern this process is poorly understood. We previously reported day-by-day peri-pubertal increases (Kiss1, Tac2) or decreases (Rfrp) in hypothalamic gene expression of female mice, with several brain mRNA changes preceding external pubertal markers. However, similar pubertal measures in males were not previously reported. Here, to identify possible neural sex differences underlying sex differences in puberty onset, we analyzed peri-pubertal males and directly compared them with female littermates. Kiss1 expression in male mice increased over the peri-pubertal period in both the AVPV and ARC nuclei but with lower levels than in females at several ages. Likewise, Tac2 expression in the male ARC increased between juvenile and older peri-pubertal stages but with levels lower than females at most ages. By contrast, both DMN Rfrp expressionand Rfrp neuronal activation strongly decreased in males between juvenile and peri-pubertal stages, but with similar levels as females. Neither ARC KNDy neuronal activation nor Kiss1r expression in GnRH neurons differed between males and females or changed with age. These findings delineate several peri-pubertal changes in neural populations in developing males, with notable sex differences in kisspeptin and NKB neuron developmental patterns. Whether these peri-pubertal hypothalamic sex differences underlie sex differences in puberty onset deserves future investigation.

Kisspeptins and the neuroendocrine control of reproduction: Recent progress and new frontiers in kisspeptin research

In late 2003, a major breakthrough in our understanding of the mechanisms that govern reproduction occurred with the identification of the reproductive roles of kisspeptins, encoded by the Kiss1 gene, and their receptor, Gpr54 (aka, Kiss1R). The discovery of this unsuspected reproductive facet attracted an extraordinary interest and boosted an intense research activity, in human and model species, that, in a relatively short period, established a series of basic concepts on the physiological roles of kisspeptins. Such fundamental knowledge, gathered in these early years of kisspeptin research, set the scene for the more recent in-depth dissection of the intimacies of the neuronal networks involving Kiss1 neurons, their precise mechanisms of regulation and the molecular underpinnings of the function of kisspeptins as pivotal regulators of all key aspects of reproductive function, from puberty onset to pulsatile gonadotropin secretion and the metabolic control of fertility. While no clear temporal boundaries between these two periods can be defined, in this review we will summarize the most prominent advances in kisspeptin research occurred in the last ten years, as a means to provide an up-dated view of the state of the art and potential paths of future progress in this dynamic, and ever growing domain of Neuroendocrinology.

Hypothalamic KNDy neuron expression in streptozotocin-induced diabetic female rats

Kisspeptin neurons, i.e. KNDy neurons, in the arcuate nucleus (ARC) coexpress neurokinin B and dynorphin and regulate gonadotropin-releasing hormone/luteinizing hormone (LH) pulses. Because it remains unclear whether these neurons are associated with reproductive dysfunction in diabetic females, we examined the expression of KNDy neurons detected by histochemistry in streptozotocin (STZ)-induced diabetic female rats 8 weeks after STZ injection. We also evaluated relevant metabolic parameters - glucose, 3-hydroxybutyrate, and non-esterified fatty acids - as indicators of diabetes progression. Severe diabetes with hyperglycemia and severe ketosis suppressed the mRNA expression of KNDy neurons, resulting in low plasma LH levels and persistent diestrus. In moderate diabetes with hyperglycemia and moderate ketosis, kisspeptin-immunoreactive cells and plasma LH levels were decreased, while the mRNA expression of KNDy neurons remained unchanged. Mild diabetes with hyperglycemia and slight ketosis did not affect KNDy neurons and plasma LH levels. The number of KNDy cells was strongly and negatively correlated with plasma 3-hydroxybutyrate levels. The vaginal smear analysis showed unclear proestrus in diabetic rats 3-5 days after STZ injection, and the mRNA expression of kisspeptin in the ARC was decreased 2 weeks after STZ injection in severely diabetic rats. Kisspeptin neurons in the anteroventral periventricular nucleus (AVPV), which induce an LH surge, were unaffected at 2 and 8 weeks after STZ injection regardless of the diabetes severity. These results suggest that diabetes mellitus progression in females may negatively affect ARC kisspeptin neurons but not AVPV kisspeptin neurons, implicating a potential role of ARC kisspeptin neurons in menstrual disorder and infertility.

Vasoactive intestinal peptide exerts an excitatory effect on hypothalamic kisspeptin neurons during estrogen negative feedback

Hypothalamic kisspeptin neurons are the primary modulators of gonadotropin-releasing hormone (GnRH) neurons. It has been shown that circadian rhythms driven by the suprachiasmatic nucleus (SCN) contribute to GnRH secretion. Kisspeptin neurons are potential targets of SCN neurons due to reciprocal connections with the anteroventral periventricular and rostral periventricular nuclei (AVPV/PeN) and the arcuate nucleus of the hypothalamus (ARH). Vasoactive intestinal peptide (VIP), a notable SCN neurotransmitter, modulates GnRH secretion depending on serum estradiol levels, aging or time of the day. Considering that kisspeptin neurons may act as interneurons and mediate VIP's effects on the reproductive axis, we investigated the effects of VIP on hypothalamic kisspeptin neurons in female mice during estrogen negative feedback. Our findings indicate that VIP induces a TTX-independent depolarization of approximately 30% of AVPV/PeN kisspeptin neurons in gonad-intact (diestrus) and ovariectomized (OVX) mice. In the ARH, the percentage of kisspeptin neurons that were depolarized by VIP was even higher (approximately 90%). An intracerebroventricular infusion of VIP leds to an increased percentage of kisspeptin neurons expressing the phospho^Ser133 cAMP-response-element-binding protein (pCREB) in the AVPV/PeN. On the other hand, pCREB expression in ARH kisspeptin neurons was similar between saline- and VIP-injected mice. Thus, VIP can recruit different signaling pathways to modulate AVPV/PeN or ARH kisspeptin neurons, resulting in distinct cellular responses. The expression of VIP receptors (VPACR) was upregulated in the AVPV/PeN, but not in the ARH, of OVX mice compared to mice on diestrus and estradiol-primed OVX mice. Our findings indicate that VIP directly influences distinct cellular aspects of the AVPV/PeN and ARH kisspeptin neurons during estrogen negative feedback, possibly to influence pulsatile LH secretion.

Kisspeptin impacts on circadian and ultradian rhythms of core body temperature: Evidence in kisspeptin receptor knockout and kisspeptin knockdown mice

Kisspeptin is vital for the regulation of both fertility and metabolism. Kisspeptin receptor (Kiss1r) knockout (KO) mice exhibit increased adiposity and reduced energy expenditure in adulthood. Kiss1r mRNA is expressed in brown adipose tissue (BAT) and Kiss1r KO mice exhibit reduced Ucp1 mRNA in BAT and impaired thermogenesis. We hypothesised that mice with diminished kisspeptin signalling would exhibit reduced core body temperature (Tc) and altered dynamics of circadian and ultradian rhythms of Tc. Tc was recorded every 15-min over 14-days in gonadectomised wild-type (WT), Kiss1r KO, and also Kiss1-Cre (95% reduction in Kiss1 transcription) mice. Female Kiss1r KOs had higher adiposity and lower Ucp1 mRNA in BAT than WTs. No change was detected in Kiss1-Cre mice. Mean Tc during the dark phase was lower in female Kiss1r KOs versus WTs, but not Kiss1-Cre mice. Female Kiss1r KOs had a lower mesor and amplitude of the circadian rhythm of Tc than did WTs. In WT mice, there were more episodic ultradian events (EUEs) of Tc during the dark phase than the light phase, but this measure was similar between dark and light phases in Kiss1r KO and Kiss1-Cre mice. The amplitude of EUEs was higher in the dark phase in female Kiss1r KO and male Kiss1-Cre mice. Given the lack of clear metabolic phenotype in Kiss1-Cre mice, 5% of Kiss1 transcription may be sufficient for proper metabolic control, as was shown for fertility. Moreover, the observed alterations in Tc suggest that kisspeptin has a role in circadian and ultradian rhythm-driven pathways.

Evaluation of candidate point mutation of Kisspeptin 1 gene associated with litter size in Indian Goat breeds and its effect on transcription factor binding sites

Kisspeptin gene (Kiss1) has a significant role in reproductive processes in mammals. However, only little information is available about the association of Kiss1 gene with litter size in Indian goat breeds. Thus, blood samples from 285 randomly selected animals were collected for DNA isolation and SNP profiling. The PCR product of 242 bp size harboring g.2540C>T mutation of Kiss1 gene was digested with the restriction enzyme Sac1. Least squares analysis revealed that Barbari goats showed significantly higher average litter size (2.86±0.08) compared to Beetal, Sirohi and Sojat breeds (P < 0.01). SNP locus g.2540C>T of Kiss1 gene also showed significant effect on litter size (P < 0.01). Goats with Genotype CT (2.66 ± 0.07) and TT (2.67 ± 0.26) had significantly higher (P < 0.01) litter size than CC (1.50 ± 0.05). From the transcription factor binding site analysis, it was predicted that due to g.2540C>T SNP, both native and mutant variant forms coded for putative binding sites for different transcription Factor. Allele T had putative binding sites for the androgen receptor which plays a significant role in the signaling pathway involved in increase in ovulation rate; which consequently can have a tremendous effect on average litter size.

GABAB Receptor Antagonism from Birth to Weaning Permanently Modifies Kiss1 Expression in the Hypothalamus and Gonads in Mice

INTRODUCTION

The kisspeptin gene Kiss1 is expressed in two hypothalamic areas: anteroventral periventricular nucleus/periventricular nucleus (AVPV/PeN) and arcuate nucleus (ARC), and also in gonads. Several pieces of evidence suggests that gamma-amino butyric acid B receptors (GABAB) signaling can regulate Kiss1 expression. Here, we inhibited GABAB signaling from PND2 to PND21 and evaluated the hypothalamic-pituitary-gonadal (HPG) axis.

METHODS

BALB/c mice were treated on postnatal days 2-21 (PND2-PND21) with CGP55845 (GABAB antagonist) and evaluated in PND21 and adulthood: gene expression (qPCR) in the hypothalamus and gonads, hormones by radioimmunoassay, gonad histochemistry (H&amp;E), puberty onset, and estrous cycles.

RESULTS

At PND21, CGP inhibited Kiss1 and Tac2 and increased Pdyn and Gabbr1 in the ARC of both sexes and decreased Th only in female AVPV/PeN. Serum follicle-stimulating hormone (FSH) and testis weight were decreased in CGP-males, and puberty onset was delayed. In adults, Kiss1, Tac2, Pdyn, Pgr, Cyp19a1, and Gad1 were downregulated, while Gabbr1 was upregulated in the ARC of both sexes. In the AVPV/PeN, Kiss1, Th, Cyp19a1, and Pgr were decreased while Gad1 was increased in CGP-females, whereas Cyp19a1 was increased in CGP-males. Serum FSH was increased in CGP-males while prolactin was increased in CGP-females. Testosterone and progesterone were increased in ovaries from CGP-females, in which Kiss1, Cyp19a1, and Esr1 were downregulated while Hsd3b2 was upregulated, together with increased atretic and decreased ovulatory follicles. Testes from CGP-males showed decreased progesterone, increased Gabbr1, Kiss1, Kiss1r, and Esr2 and decreased Cyp19a1, and clear signs of seminiferous tubules atrophy.

CONCLUSION

These results demonstrate that appropriate GABAB signaling during this critical prepubertal period is necessary for the normal development of the HPG axis.

Progesterone Receptors in AVPV Kisspeptin Neurons Are Sufficient for Positive Feedback Induction of the LH Surge

Kisspeptin, encoded by Kiss1, stimulates gonadotropin-releasing hormone neurons to govern reproduction. In female rodents, estrogen-sensitive kisspeptin neurons in the rostral anteroventral periventricular (AVPV) hypothalamus are thought to mediate estradiol (E2)-induced positive feedback induction of the preovulatory luteinizing hormone (LH) surge. AVPV kisspeptin neurons coexpress estrogen and progesterone receptors (PGRs) and are activated during the LH surge. While E2 effects on kisspeptin neurons have been well studied, progesterone's regulation of kisspeptin neurons is less understood. Using transgenic mice lacking PGR exclusively in kisspeptin cells (termed KissPRKOs), we previously demonstrated that progesterone action specifically in kisspeptin cells is essential for ovulation and normal fertility. Unlike control females, KissPRKO females did not generate proper LH surges, indicating that PGR signaling in kisspeptin cells is required for positive feedback. However, because PGR was knocked out from all kisspeptin neurons in the brain, that study was unable to determine the specific kisspeptin population mediating PGR action on the LH surge. Here, we used targeted Cre-mediated adeno-associated virus (AAV) technology to reintroduce PGR selectively into AVPV kisspeptin neurons of adult KissPRKO females, and tested whether this rescues occurrence of the LH surge. We found that targeted upregulation of PGR in kisspeptin neurons exclusively in the AVPV is sufficient to restore proper E2-induced LH surges in KissPRKO females, suggesting that this specific kisspeptin population is a key target of the necessary progesterone action for the surge. These findings further highlight the critical importance of progesterone signaling, along with E2 signaling, in the positive feedback induction of LH surges and ovulation.

Emerging Roles of Epigenetics in the Control of Reproductive Function: Focus on Central Neuroendocrine Mechanisms

Reproduction is an essential function for perpetuation of the species. As such, it is controlled by sophisticated regulatory mechanisms that allow a perfect match between environmental conditions and internal cues to ensure adequate pubertal maturation and achievement of reproductive capacity. Besides classical genetic regulatory events, mounting evidence has documented that different epigenetic mechanisms operate at different levels of the reproductive axis to finely tune the development and function of this complex neuroendocrine system along the lifespan. In this mini-review, we summarize recent evidence on the role of epigenetics in the control of reproduction, with special focus on the modulation of the central components of this axis. Particular attention will be paid to the epigenetic control of puberty and Kiss1 neurons because major developments have taken place in this domain recently. In addition, the putative role of central epigenetic mechanisms in mediating the influence of nutritional and environmental cues on reproductive function will be discussed.

Gene expression pattern of Kisspeptin and RFamide-related peptide (Rfrp) in the male Damaraland mole-rat hypothalamus

Damaraland mole-rats (Fukomys damarensis) are cooperatively breeding, subterranean mammals, which exhibit high reproductive skew. Reproduction is monopolized by the dominant female of the group, while subordinates are anovulatory. Similarly, male subordinates within the colony show no sexual behaviour although they have functional gonads and do not differ from reproductive males in circulating levels of pituitary hormones and testosterone. However, reproductive status affects the neuroendocrine phenotype of males with breeders possessing increased mRNA expression of androgen and progesterone receptors compared to non-breeders in several forebrain regions implicated in the regulation of reproductive behaviour. The RFamide peptides kisspeptin and RFRP-3, encoded by the Kiss1 and Rfrp gene, are considered potent regulators of gonadotropin release. In females, reproductive inhibition is associated with reduced Kiss1 expression within the arcuate nucleus (ARC) and increased Rfrp expression in the anterior hypothalamus. To assess whether differential gene expression of Kiss1 and Rfrp underlies the difference in reproductive behaviour of males, we studied the expression of both genes by means of in situ hybridisation in wild-caught male Damaraland mole-rats with different reproductive status. The distribution of Kiss1 and Rfrp within the hypothalamus was found to be similar to females. Quantification of the Kiss1 hybridisation signal revealed no significant differences in relation to reproductive status. However, there was a significant positive correlation between testis mass and the number of Kiss1-expressing cells in the ARC and the mRNA content per cell, respectively. Analysis of the Rfrp hybridisation signal along the rostro-caudal extent of the hypothalamus revealed that non-reproductive males possessed an increased number of Rfrp-expressing cells at the level of the dorsomedial hypothalamic nucleus (DMH) than reproductive males. These data suggest the Kiss1 expression within the ARC is not associated with reproductive quiescence in subordinate males but instead, inhibitory effects may be mediated by Rfrp-expressing cells in the DMH.

Kisspeptin Receptor on the Sperm Surface Reflects Epididymal Maturation in the Dog

Alongside the well-known central modulatory role, the Kisspeptin system, comprising Kiss1, its cleavage products (Kisspeptins), and Kisspeptin receptor (Kiss1R), was found to regulate gonadal functions in vertebrates; however, its functional role in the male gamete and its localization during maturation have been poorly understood. The present study analyzed Kisspeptin system in dog testis and spermatozoa recovered from different segments of the epididymis, with focus on Kiss1R on sperm surface alongside the maturation during epididymal transit, demonstrated by modification in sperm kinetic, morphology, and protamination. The proteins Kiss1 and Kiss1R were detected in dog testis. The receptor Kiss1R only was detected in total protein extracts from epididymis spermatozoa, whereas dot blot revealed Kiss1 immunoreactivity in the epidydimal fluid. An increase of the Kiss1R protein on sperm surface along the length of the epididymis, with spermatozoa in the tail showing plasma membrane integrity and Kiss1R protein (p < 0.05 vs. epididymis head and body) was observed by flow cytometry and further confirmed by epifluorescence microscopy and Western blot carried on sperm membrane preparations. In parallel, during the transit in the epididymis spermatozoa significantly modified their ability to move and the pattern of motility; a progressive increase in protaminization also occurred. In conclusion, Kisspeptin system was detected in dog testis and spermatozoa. Kiss1R trafficking toward plasma membrane along the length of the epididymis and Kiss1 in epididymal fluid suggested a new functional role of the Kisspeptin system in sperm maturation and storage.

Kisspeptin Neurons and Estrogen-Estrogen Receptor α Signaling: Unraveling the Mystery of Steroid Feedback System Regulating Mammalian Reproduction

Estrogen produced by ovarian follicles plays a key role in the central mechanisms controlling reproduction via regulation of gonadotropin-releasing hormone (GnRH) release by its negative and positive feedback actions in female mammals. It has been well accepted that estrogen receptor α (ERα) mediates both estrogen feedback actions, but precise targets had remained as a mystery for decades. Ever since the discovery of kisspeptin neurons as afferent ERα-expressing neurons to govern GnRH neurons, the mechanisms mediating estrogen feedback are gradually being unraveled. The present article overviews the role of kisspeptin neurons in the arcuate nucleus (ARC), which are considered to drive pulsatile GnRH/gonadotropin release and folliculogenesis, in mediating the estrogen negative feedback action, and the role of kisspeptin neurons located in the anteroventral periventricular nucleus-periventricular nucleus (AVPV-PeN), which are thought to drive GnRH/luteinizing hormone (LH) surge and consequent ovulation, in mediating the estrogen positive feedback action. This implication has been confirmed by the studies showing that estrogen-bound ERα down- and up-regulates kisspeptin gene (Kiss1) expression in the ARC and AVPV-PeN kisspeptin neurons, respectively. The article also provides the molecular and epigenetic mechanisms regulating Kiss1 expression in kisspeptin neurons by estrogen. Further, afferent ERα-expressing neurons that may regulate kisspeptin release are discussed.

Kiss1 is differentially regulated in male and female mice by the homeodomain transcription factor VAX1

Regulation of Kiss1 transcription is crucial to the development and function of the reproductive axis. The homeodomain transcription factor, ventral anterior homeobox 1 (VAX1), has been implicated as a potential regulator of Kiss1 transcription. However, it is unknown whether VAX1 directly mediates transcription within kisspeptin neurons or works indirectly by acting upstream of kisspeptin neuron populations. This study tested the hypothesis that VAX1 within kisspeptin neurons regulates Kiss1 gene expression. We found that VAX1 acts as a repressor of Kiss1 in vitro and within the male arcuate nucleus in vivo. In female mice, we found that the loss of VAX1 caused a reduction in Kiss1 expression and Kiss1-containing neurons in the anteroventral periventricular nucleus at the time of the preovulatory luteinizing hormone surge, but was compensated by an increase in Kiss1-cFos colocalization. Despite changes in Kiss1 transcription, gonadotropin levels were unaffected and there were no impairments to fertility.

CUBIC-Cloud provides an integrative computational framework toward community-driven whole-mouse-brain mapping

Recent advancements in tissue clearing technologies have offered unparalleled opportunities for researchers to explore the whole mouse brain at cellular resolution. With the expansion of this experimental technique, however, a scalable and easy-to-use computational tool is in demand to effectively analyze and integrate whole-brain mapping datasets. To that end, here we present CUBIC-Cloud, a cloud-based framework to quantify, visualize, and integrate mouse brain data. CUBIC-Cloud is a fully automated system where users can upload their whole-brain data, run analyses, and publish the results. We demonstrate the generality of CUBIC-Cloud by a variety of applications. First, we investigated the brain-wide distribution of five cell types. Second, we quantified Aβ plaque deposition in Alzheimer's disease model mouse brains. Third, we reconstructed a neuronal activity profile under LPS-induced inflammation by c-Fos immunostaining. Last, we show brain-wide connectivity mapping by pseudotyped rabies virus. Together, CUBIC-Cloud provides an integrative platform to advance scalable and collaborative whole-brain mapping.

Fetal Programming Effects of a Mild Food Restriction During Pregnancy in Mice: How Does It Compare to Intragestational Ghrelin Administration?

To explore in mice if a 15% food restriction protocol during pregnancy programs the offspring postnatal development, with emphasis on reproductive function, and to assess if ghrelin (Ghrl) administration to mouse dams exerts effects that mimic those obtained under mild caloric restriction. Mice were 15% food-restricted, injected with 4 nmol/animal/day of Ghrl, or injected with the vehicle (control) thorough pregnancy. After birth, the pups did not receive further treatment. Pups born from food-restricted dams (FR pups) were lighter than Ghrl pups at birth, but reached normal weight at adulthood. Ghrl pups were heavier at birth and gained more weight than control pups (C pups). This effect was not associated with plasma IGF-1. FR pups showed a delay in pinna detachment and eye opening, while an advance was observed in Ghrl pups. FR pups showed also impairment in the surface-righting reflex. In both female FR and Ghrl pups, there was an advance in vaginal opening and, in adulthood, FR pups showed a significant decrease in their own litter size and plasma progesterone, and an increase in embryo loss. A delay in testicular descent was evident in male Ghrl pups. Changes in puberty onset were not associated with differences in the expression of Kiss1 in hypothalamic nuclei. Finally, in adulthood, FR pups showed a significant decrease in sperm quality. In conclusion, a mild food restriction thorough gestation exerted programming effects on the offspring, affecting also their reproductive function in adulthood. These effects were not similar to those of intragestational Ghrl administration.

Downregulation of TTF1 in the rat hypothalamic ARC or AVPV nucleus inhibits Kiss1 and GnRH expression, leading to puberty delay

BACKGROUND

TTF1 is a transcription factor that is expressed in the hypothalamus after birth and plays crucial roles in pubertal development. TTF1 may regulate the expression of the Kiss1 gene, which may drive puberty onset in the hypothalamic arcuate (ARC) and anterior ventral paraventricular (AVPV) nuclei.

METHODS

A dual-luciferase reporter assay was used to detect binding between TTF1 and the Kiss1 gene promoter. To investigate the effects of TTF1, we modified TTF1 expression in cell lines and in the ARC or AVPV nucleus of 21-day-old female rats via lentivirus infection. TTF1 and other puberty onset-related genes were detected by qRT-PCR and western blot analyses.

RESULTS

The in vitro data indicated that TTF1 knockdown (KD) significantly reduced Kiss1 and GnRH expression. Overexpression (OE) of TTF1 promoted Kiss1 expression. In vivo, the expression of Kiss1 and GnRH decreased significantly in the rats with hypothalamic ARC- or AVPV-specific TTF1 KD. The TTF1-KD rats showed vaginal opening delay. H&E staining revealed that the corpus luteum was obviously reduced at the early puberty and adult stages in the rats with ARC- or AVPV-specific TTF1 KD.

CONCLUSION

TTF1 bound to the promoter of the Kiss1 gene and enhanced its expression. For 21-day-old female rats, decreased TTF1 in the hypothalamic ARC or AVPV nucleus resulted in delayed vaginal opening and ovarian abnormalities. These observations suggested that TTF1 regulates puberty onset by promoting the expression of Kiss1 and plays an important role in gonad development.

AMP-activated protein kinase (AMPK) signaling in GnRH neurons links energy status and reproduction

BACKGROUND

Reproduction is tightly coupled to body energy and metabolic status. GnRH neurons, master elements and final output pathway for the brain control of reproduction, directly or indirectly receive and integrate multiple metabolic cues to regulate reproductive function. Yet, the molecular underpinnings of such phenomenon remain largely unfolded. AMP-activated protein kinase (AMPK), the fundamental cellular sensor that becomes activated in conditions of energy deficit, has been recently shown to participate in the control of Kiss1 neurons, essential gatekeepers of the reproductive axis, by driving an inhibitory valence in situations of energy scarcity at puberty. However, the contribution of AMPK signaling specifically in GnRH neurons to the metabolic control of reproduction remains unknown.

METHODS

Double immunohistochemistry (IHC) was applied to evaluate expression of active (phosphorylated) AMPK in GnRH neurons and a novel mouse line, named GAMKO, with conditional ablation of the AMPK α1 subunit in GnRH neurons, was generated. GAMKO mice of both sexes were subjected to reproductive characterization, with attention to puberty and gonadotropic responses to kisspeptin and metabolic stress.

RESULTS

A vast majority (>95%) of GnRH neurons co-expressed pAMPK. Female (but not male) GAMKO mice displayed earlier puberty onset and exaggerated LH (as surrogate marker of GnRH) responses to kisspeptin-10 at the prepubertal age. In adulthood, GAMKO females retained increased LH responsiveness to kisspeptin and showed partial resilience to the inhibitory effects of conditions of negative energy balance on the gonadotropic axis. The modulatory role of AMPK in GnRH neurons required preserved ovarian function, since the differences in LH pulsatility detected between GAMKO and control mice subjected to fasting were abolished in ovariectomized animals.

CONCLUSIONS

Altogether, our data document a sex-biased, physiological role of AMPK signaling in GnRH neurons, as molecular conduit of the inhibitory actions of conditions of energy deficit on the female reproductive axis.

Sexually dimorphic effects of prolactin treatment on the onset of puberty and olfactory function in mice

The onset of puberty is associated with the psychophysiological maturation of the adolescent to an adult capable of reproduction when olfactory signals play an important role. This period begins with the secretion of the gonadotropin-releasing hormone (GnRH) from GnRH neurons within the hypothalamus. This is regulated by kisspeptin neurons that express high levels of transmembrane prolactin receptors (PRLR) that bind to and are activated by prolactin (PRL). The elevated levels of serum PRL found during lactation, or caused by chronic PRL infusion, decreases the secretion of gonadotropins and kisspeptin and compromised the estrous cyclicity and the ovulation. In the present work, we aimed to evaluate the effects of either increased or decreased PRL circulating levels within the peripubertal murine brain by administration of PRL or treatment with cabergoline (Cab) respectively. We showed that either treatment delayed the onset of puberty in females, but not in males. This was associated with the augmentation of the PRL receptor (Prlr) mRNA expression in the arcuate nucleus and decreased Kiss1 expression in the anteroventral periventricular zone. Then, during adulthood, we assessed the activation of the mitral and granular cells of the main (MOB) and accessory olfactory bulb (AOB) by cFos immunoreactivity (ir) after the exposure to soiled bedding of the opposite sex. In the MOB, the PRL treatment promoted an increased cFos-ir of the mitral cells of males and females. In the granular cells of male of either treatment an augmented activation was observed. In the AOB, an impaired cFos-ir was observed in PRL and Cab treated females after exposure to male soiled bedding. However, in males, only Cab impaired its activation. No effects were observed in the AOB-mitral cells. In conclusion, our results demonstrate that PRL contributes to pubertal development and maturation of the MOB-AOB during the murine juvenile period in a sex-dependent way.

Role of KNDy Neurons Expressing Kisspeptin, Neurokinin B, and Dynorphin A as a GnRH Pulse Generator Controlling Mammalian Reproduction

Increasing evidence accumulated during the past two decades has demonstrated that the then-novel kisspeptin, which was discovered in 2001, the known neuropeptides neurokinin B and dynorphin A, which were discovered in 1983 and 1979, respectively, and their G-protein-coupled receptors, serve as key molecules that control reproduction in mammals. The present review provides a brief historical background and a summary of our recent understanding of the roles of hypothalamic neurons expressing kisspeptin, neurokinin B, and dynorphin A, referred to as KNDy neurons, in the central mechanism underlying gonadotropin-releasing hormone (GnRH) pulse generation and subsequent tonic gonadotropin release that controls mammalian reproduction.

ERα Signaling in GHRH/Kiss1 Dual-Phenotype Neurons Plays Sex-Specific Roles in Growth and Puberty

Gonadal steroids modulate growth hormone (GH) secretion and the pubertal growth spurt via undefined central pathways. GH-releasing hormone (GHRH) neurons express estrogen receptor α (ERα) and androgen receptor (AR), suggesting changing levels of gonadal steroids during puberty directly modulate the somatotropic axis. We generated mice with deletion of ERα in GHRH cells (GHRHΔERα), which displayed reduced body length in both sexes. Timing of puberty onset was similar in both groups, but puberty completion was delayed in GHRHΔERα females. Lack of AR in GHRH cells (GHRHΔAR mice) induced no changes in body length, but puberty completion was also delayed in females. Using a mouse model with two reporter genes, we observed that, while GHRHtdTom neurons minimally colocalize with Kiss1hrGFP in prepubertal mice, ∼30% of GHRH neurons coexpressed both reporter genes in adult females, but not in males. Developmental analysis of Ghrh and Kiss1 expression suggested that a subpopulation of ERα neurons in the arcuate nucleus of female mice undergoes a shift in phenotype, from GHRH to Kiss1, during pubertal transition. Our findings demonstrate that direct actions of gonadal steroids in GHRH neurons modulate growth and puberty and indicate that GHRH/Kiss1 dual-phenotype neurons play a sex-specific role in the crosstalk between the somatotropic and gonadotropic axes during pubertal transition.SIGNIFICANCE STATEMENT Late maturing adolescents usually show delayed growth and bone age. At puberty, gonadal steroids have stimulatory effects on the activation of growth and reproductive axes, but the existence of gonadal steroid-sensitive neuronal crosstalk remains undefined. Moreover, the neural basis for the sex differences observed in the clinical arena is unknown. Lack of ERα in GHRH neurons disrupts growth in both sexes and causes pubertal delay in females. Deletion of androgen receptor in GHRH neurons only delayed female puberty. In adult females, not males, a subset of GHRH neurons shift phenotype to start producing Kiss1. Thus, direct estrogen action in GHRH/Kiss1 dual-phenotype neurons modulates growth and puberty and may orchestrate the sex differences in endocrine function observed during pubertal transition.

Androgen Suppresses In Vivo and In Vitro LH Pulse Secretion and Neural Kiss1 and Tac2 Gene Expression in Female Mice

Androgens can affect the reproductive axis of both sexes. In healthy women, as in men, elevated exogenous androgens decrease gonad function and lower gonadotropin levels; such circumstances occur with anabolic steroid abuse or in transgender men (genetic XX individuals) taking androgen supplements. The neuroendocrine mechanisms by which endogenous or exogenous androgens regulate gonadotropin release, including aspects of pulsatile luteinizing hormone (LH) secretion, remain unknown. Because animal models are valuable for interrogating neural and pituitary mechanisms, we studied effects of androgens in the normal male physiological range on in vivo LH secretion parameters in female mice and in vitro LH secretion patterns from isolated female pituitaries. We also assessed androgen effects on hypothalamic and gonadotrope gene expression in female mice, which may contribute to altered LH secretion profiles. We used a nonaromatizable androgen, dihydrotestosterone (DHT), to isolate effects occurring specifically via androgen receptor (AR) signaling. Compared with control females, DHT-treated females exhibited markedly reduced in vivo LH pulsatility, with decreases in pulse frequency, amplitude, peak, and basal LH levels. Correlating with reduced LH pulsatility, DHT-treated females also exhibited suppressed arcuate nucleus Kiss1 and Tac2 expression. Separate from these neural effects, we determined in vitro that the female pituitary is directly inhibited by AR signaling, resulting in lower basal LH levels and reduced LH secretory responses to gonadotropin-releasing hormone pulses, along with lower gonadotropin gene expression. Thus, in normal adult females, male levels of androgen acting via AR can strongly inhibit the reproductive axis at both the neural and pituitary levels.

MiR-199-3p modulates the onset of puberty in rodents probably by regulating the expression of Kiss1 via the p38 MAPK pathway

The Kiss1 gene plays an indispensable role in modulating the onset of puberty and fertility in mammals. Although an increasing number of genetic and environmental factors that influence reproduction through Kiss1 have been identified, the function of microRNAs, a class of posttranscriptional regulators, in regulating Kiss1 expression remains poorly understood. This study aimed at investigating the mechanism by which Kiss1 expression is regulated by microRNAs. A simplified miRNome screen by a dual-fluorescence reporter system based on Kiss1 was performed to identify microRNAs that affect the expression of Kiss1. The expression patterns of the identified microRNAs during the period of murine sexual development were investigated, and only miR-199-3p was studied further. Aided by bioinformatics algorithms, miR-199-3p was demonstrated to be a repressor of Kiss1 expression, as it blocked the expression of Kiss1 through the p38 MAPK pathway by simultaneously inhibiting several targets in both GT1-7 cells and primary hypothalamic neurons. Both the inhibition of the p38 MAPK pathway by the intracerebroventricular administration of chemical agents in rats and the ectopic expression of miR-199-3p by lentivirus injection in the hypothalamus in mice delayed puberty onset and gonad development. Our results presented a novel regulatory mechanism of puberty onset which the sustained downregulation of miR-199-3p might gradually release the inhibition of the p38 MAPK/Fos/CREB/Kiss1 pathway during puberty development.

No evidence that Spexin impacts LH release and seasonal breeding in the ewe

Spexin (SPX) is a recently identified peptide hormone of 14 amino acids. Interestingly, Spx and Kiss1 genes share a common ancestor gene. Considering that KISS1 peptides are key controllers of breeding in mammals and circumstantial evidence that SPX regulates gonadotropins in some fish species, we hypothesized that SPX may play a KISS1-related role in sheep. Here, we cloned the ovine Spx cDNA, performed in vivo injection and infusion of SPX (i.c.v. route, with or without concomittant KISS1 presence) and assessed a potential regulation of Spx expression by season, thyroid hormone and estradiol in the medio-basal hypothalamus of the ewe. Our data do not provide support for a role of SPX in the control of the gonadotropic axis in the ewe.

Circuit-level analysis identifies target genes of sex steroids in ewe seasonal breeding

Thyroid hormone (TH) and estradiol (E2) direct seasonal switches in ovine reproductive physiology. In sheep, as in other mammals and birds, control of thyrotropin (TSH) production by the pars tuberalis (PT) links photoperiod responsiveness to seasonal breeding. PT-derived TSH governs opposite seasonal patterns of the TH deiodinases Dio2/Dio3 expression in tanycytes of the neighboring medio-basal hypothalamus (MBH), which explain the key role of TH. We recently used RNA-Seq to identify seasonal markers in the MBH and define the impact of TH. This impact was found to be quite limited, in terms of number of target genes, and very restricted with regards to neuroanatomical location, as TH specifically impacts genes expressed in tanycytes and hypothalamus, not in the PT. Here we address the impact of E2 on these seasonal markers, which are specifically expressed in either PT, tanycytes or hypothalamus. We also investigate if progesterone (P4) may be involved in timing the seasonal transition to anestrus. Our analysis provides circuit-level insights into the impact of sex steroids on the ewe seasonal breeding cycle. First, seasonal gene expression in the PT is independent of the sex steroid status. The fact that seasonal gene expression in the PT is also TH-independent strengthens the view that the PT is a circannual timer. Second, select tanycytic markers display some level of responsiveness to E2 and P4, which indicates another potential level of feedback control by sex steroids. Third, Kiss1 neurons of the arcuate nucleus are responsive to both TH and E2, which places them at the crossroads of photoperiodic transduction pathway and sex steroid feedback. This provides strong support to the concept that these Kiss1 neurons are pivotal to the long-recognized "seasonal switch in the ability of E2 to exert negative feedback", which drives seasonal breeding.

GABAergic input through GABAB receptors is necessary during a perinatal window to shape gene expression of factors critical to reproduction such as Kiss1

Lack of GABAB receptors in GABAB1 knockout mice decreases neonatal ARC kisspeptin 1 (Kiss1) expression in the arcuate nucleus of the hypothalamus (ARC) in females, which show impaired reproduction as adults. Our aim was to selectively impair GABAB signaling during a short postnatal period to evaluate its impact on the reproductive system. Neonatal male and female mice were injected with the GABAB antagonist CGP 55845 (CGP, 1 mg/kg body wt sc) or saline from postnatal day 2 (PND2) to PND6, three times per day (8 AM, 1 PM, and 6 PM). One group was killed on PND6 for collection of blood samples (hormones by radioimmunoassay), brains for gene expression in the anteroventral periventricular nucleus-periventricular nucleus continuum (AVPV/PeN), and ARC micropunches [quantitative PCR (qPCR)] and gonads for qPCR, hormone contents, and histology. A second group of mice was injected with CGP (1 mg/kg body wt sc) or saline from PND2 to PND6, three times per day (8 AM, 1 PM, and 6 PM), and left to grow to adulthood. We measured body weight during development and parameters of sexual differentiation, puberty onset, and estrous cycles. Adult mice were killed, and trunk blood (hormones), brains for qPCR, and gonads for qPCR and hormone contents were obtained. Our most important findings on PND6 include the CGP-induced decrease in ARC Kiss1 and increase in neurokinin B (Tac2) in both sexes; the decrease in AVPV/PeN tyrosine hydroxylase (Th) only in females; the increase in gonad estradiol content in both sexes; and the increase in primordial follicles and decrease in primary and secondary follicles. Neonatally CGP-treated adults showed decreased ARC Kiss1 and ARC gonadotropin-releasing hormone (Gnrh1) and increased ARC glutamic acid decarboxylase 67 (Gad1) only in males; increased ARC GABAB receptor subunit 1 (Gabbr1) in both sexes; and decreased AVPV/PeN Th only in females. We demonstrate that ARC Kiss1 expression is chronically downregulated in males and that the normal sex difference in AVPV/PeN Th expression is abolished. In conclusion, neonatal GABAergic input through GABAB receptors shapes gene expression of factors critical to reproduction.

Inducible Kiss1 knockdown in the hypothalamic arcuate nucleus suppressed pulsatile secretion of luteinizing hormone in male mice

Accumulating evidence suggests that kisspeptin-GPR54 signaling is indispensable for gonadotropin-releasing hormone (GnRH)/gonadotropin secretion and consequent reproductive functions in mammals. Conventional Kiss1 knockout (KO) mice and rats are reported to be infertile. To date, however, no study has investigated the effect of inducible central Kiss1 KO/knockdown on pulsatile gonadotropin release in male mammals. Here we report an in vivo analysis of inducible conditional Kiss1 knockdown male mice. The mice were generated by a bilateral injections of either adeno-associated virus (AAV) vectors driving Cre recombinase (AAV-Cre) or AAV vectors driving GFP (AAV-GFP, control) into the hypothalamic arcuate nucleus (ARC) of Kiss1-floxed male mice, in which exon 3 of the Kiss1 gene were floxed with loxP sites. Four weeks after the AAV-Cre injection, the mice showed a profound decrease in the both number of ARC Kiss1-expressing cells and the luteinizing hormone (LH) pulse frequency. Interestingly, pulsatile LH secretion was apparent 8 weeks after the AAV-Cre injection despite the suppression of ARC Kiss1 expression. The control Kiss1-floxed mice infected with AAV-GFP showed apparent LH pulses and Kiss1 expression in the ARC at both 4 and 8 weeks after the AAV-GFP injection. These results with an inducible conditional Kiss1 knockdown in the ARC of male mice suggest that ARC kisspeptin neurons are responsible for pulsatile LH secretion in male mice, and indicate the possibility of a compensatory mechanism that restores GnRH/LH pulse generation.

Thermoneutral conditions correct the obese phenotype in female, but not male, Kiss1r knockout mice

Kisspeptin, a neuropeptide that activates gonadotropin-releasing hormone (GnRH) neurons, has also been implicated as a regulator of energy balance. Kisspeptin receptor (Kiss1r) knockout (KO) mice display an obese phenotype in adulthood compared to wild-type (WT) controls due to reduced energy expenditure. Additionally, experimental evidence shows that the temperature of typical rodent housing conditions (22 °C) increases the metabolism of mice above basal levels. Female Kiss1r KO mice show reduced core temperature and impaired temperature adaptation to an acute cold challenge, suggesting their temperature homeostasis processes are altered. The present study examined the phenotype of gonadectomised Kiss1r KO mice at both sub-thermoneutral and thermoneutral temperature (22 °C and 30 °C). Our results confirmed the obese phenotype in Kiss1r KO mice at 22 °C, and revealed a sexually dimorphic effect of thermal neutrality on the phenotype. In female KO mice, the obesity observed at 22 °C was attenuated at 30 °C. Plasma leptin levels were higher in KO than WT female mice at 22 °C (P < 0.001) but not at 30 °C. Importantly, the expression of Ucp1 mRNA in brown adipose tissue was lower in KO mice compared to WT mice at 22 °C (P < 0.05), but not different from WT at 30 °C. In male KO mice, a metabolic phenotype was observed at 22 °C and 30 °C. These results provide further evidence for kisspeptin-mediated regulation of adiposity via altered energy expenditure. Moreover, thermoneutral housing alleviated the obese phenotype in female Kiss1r KO mice, compared to WT, indicating the impairment in these mice may relate to an inability to adapt to the chronic cold stress that is experienced at 22 °C.

Hyperactive LH Pulses and Elevated Kisspeptin and NKB Gene Expression in the Arcuate Nucleus of a PCOS Mouse Model

Polycystic ovary syndrome (PCOS), a common reproductive disorder in women, is characterized by hyperandrogenemia, chronic anovulation, cystic ovarian follicles, and luteinizing hormone (LH) hyper-pulsatility, but the pathophysiology isn't completely understood. We recently reported a novel mouse model of PCOS using chronic letrozole (LET; aromatase inhibitor). Letrozole-treated females demonstrate multiple PCOS-like phenotypes, including polycystic ovaries, anovulation, and elevated circulating testosterone and LH, assayed in "one-off" measures. However, due to technical limitations, in vivo LH pulsatile secretion, which is elevated in PCOS women, was not previously studied, nor were the possible changes in reproductive neurons. Here, we used recent technical advances to examine in vivo LH pulse dynamics of freely moving LET female mice versus control and ovariectomized (OVX) mice. We also determined whether neural gene expression of important reproductive regulators such as kisspeptin, neurokinin B (NKB), and dynorphin, is altered in LET females. Compared to controls, LET females exhibited very rapid, elevated in vivo LH pulsatility, with increased pulse frequency, amplitude, and basal levels, similar to PCOS women. Letrozole-treated mice also had markedly elevated Kiss1, Tac2, and Pdyn expression and increased Kiss1 neuronal activation in the hypothalamic arcuate nucleus. Notably, the hyperactive LH pulses and increased kisspeptin neuron measures of LET mice were not as elevated as OVX females. Our findings indicate that LET mice, like PCOS women, have markedly elevated LH pulsatility, which likely drives increased androgen secretion. Increased hypothalamic kisspeptin and NKB levels may be fundamental contributors to the hyperactive LH pulse secretion in the LET PCOS-like condition and, perhaps, in PCOS women.

Neuro-toxic and Reproductive Effects of BPA

Background:

Bisphenol A (BPA) is one of the highest volume chemicals produced worldwide. It has recognized activity as an endocrine-disrupting chemical and has suspected roles as a neurological and reproductive toxicant. It interferes in steroid signaling, induces oxidative stress, and affects gene expression epigenetically. Gestational, perinatal and neonatal exposures to BPA affect developmental processes, including brain development and gametogenesis, with consequences on brain functions, behavior, and fertility.

Methods:

This review critically analyzes recent findings on the neuro-toxic and reproductive effects of BPA (and its ana-logues), with focus on neuronal differentiation, synaptic plasticity, glia and microglia activity, cognitive functions, and the central and local control of reproduction.

Results:

BPA has potential human health hazard associated with gestational, peri- and neonatal exposure. Beginning with BPA’s disposition, this review summarizes recent findings on the neurotoxicity of BPA and its analogues, on neuronal dif-ferentiation, synaptic plasticity, neuro-inflammation, neuro-degeneration, and impairment of cognitive abilities. Furthermore, it reports the recent findings on the activity of BPA along the HPG axis, effects on the hypothalamic Gonadotropin Releas-ing Hormone (GnRH), and the associated effects on reproduction in both sexes and successful pregnancy.

Conclusion:

BPA and its analogues impair neuronal activity, HPG axis function, reproduction, and fertility. Contrasting re-sults have emerged in animal models and human. Thus, further studies are needed to better define their safety levels. This re-view offers new insights on these issues with the aim to find the “fil rouge”, if any, that characterize BPA’s mechanism of action with outcomes on neuronal function and reproduction.

Retinoblastoma binding protein 7 is involved in Kiss1 mRNA upregulation in rodents

Kisspeptin, encoded by Kiss1, is essential for reproduction in mammals. Kiss1 expression is regulated by estrogen via histone acetylation in the Kiss1 promotor region. Thus, elucidation of histone modification factor(s) involved in the regulation of Kiss1 expression is required to gain further understanding of the mechanisms of its control. The RNA-seq analysis of isolated kisspeptin neurons, obtained from the arcuate nucleus (ARC) of female rats, revealed that Rbbp7, encoding retinoblastoma binding protein 7 (RBBP7), a member of histone modification and chromatin remodeling complexes, is highly expressed in the ARC kisspeptin neurons. Thus, the present study aimed to investigate whether RBBP7 is involved in Kiss1 expression. Histological analysis using in situ hybridization (ISH) revealed that Rbbp7 expression was located in several hypothalamic nuclei, including the ARC and the anteroventral periventricular nucleus (AVPV), where kisspeptin neurons are located. Double ISH for Rbbp7 and Kiss1 showed that a majority of kisspeptin neurons (more than 85%) expressed Rbbp7 mRNA in both the ARC and the AVPV of female rats. Further, Rbbp7 mRNA knockdown significantly decreased in vitro expression of Kiss1 in a mouse immortalized kisspeptin neuronal cell line (mHypoA-55). Estrogen treatment significantly decreased and increased Kiss1 mRNA levels in the ARC and AVPV of ovariectomized female rats, respectively, but failed to affect Rbbp7 mRNA levels in both the nuclei. Taken together, these findings suggest that RBBP7 is involved in the upregulation of Kiss1 expression in kisspeptin neurons of rodents in an estrogen-independent manner.

Neural and endocrine mechanisms underlying stress-induced suppression of pulsatile LH secretion

Stress is well-known to inhibit a variety of reproductive processes, including the suppression of episodic Gonadotropin releasing hormone (GnRH) secretion, typically measured via downstream luteinizing hormone (LH) secretion. Since pulsatile secretion of GnRH and LH are necessary for proper reproductive function in both males and females, and stress is common for both human and animals, understanding the fundamental mechanisms by which stress impairs LH pulses is of critical importance. Activation of the hypothalamic-pituitary-adrenal axis, and its corresponding endocrine factors, is a key feature of the stress response, so dissecting the role of stress hormones, including corticotrophin releasing hormone (CRH) and corticosterone, in the inhibition of LH secretion has been one key research focus. However, some evidence suggests that these stress hormones alone are not sufficient for the full inhibition of LH caused by stress, implicating the additional involvement of other hormonal or neural signaling pathways in this process (including inputs from the brainstem, amygdala, parabrachial nucleus, and dorsomedial nucleus). Moreover, different stress types, such as metabolic stress (hypoglycemia), immune stress, and psychosocial stress, appear to suppress LH secretion via partially unique neural and endocrine pathways. The mechanisms underlying the suppression of LH pulses in these models offer interesting comparisons and contrasts, including the specific roles of amygdaloid nuclei and CRH receptor types. This review focuses on the most recent and emerging insights into endocrine and neural mechanisms responsible for the suppression of pulsatile LH secretion in mammals, and offers insights in important gaps in knowledge.

Cre/lox generation of a novel whole-body Kiss1r KO mouse line recapitulates a hypogonadal, obese, and metabolically-impaired phenotype

Kisspeptin and its receptor, Kiss1r, act centrally to stimulate reproduction. Recent evidence indicates that kisspeptin is also important for body weight and metabolism, as whole-body Kiss1r KO mice, developed with gene trap technology, display obesity and reduced metabolism. Kiss1r is expressed in brain and multiple peripheral tissues, but it is unknown which is responsible for the metabolic phenotype. Here, we sought to confirm that 1) the metabolic phenotype of the gene trap Kiss1r KOs is due to disruption of kisspeptin signaling and not off-target effects of viral mutagenesis, and 2) the Kiss1r flox line is suitable for creating conditional KOs to study the metabolic phenotype. We used Cre/lox technology (Zp3-Cre/Kiss1r flox) to develop a new global Kiss1r KO ("Kiss1r gKO") to compare with the original gene trap KO phenotype. We confirmed that deleting exon 2 of Kiss1r from the entire body induces hypogonadism in both sexes. Moreover, global deletion of Kiss1r induced obesity in females, but not males, along with increased adiposity and impaired glucose tolerance, similar to the gene trap Kiss1r KOs. Likewise, Kiss1r gKO females had decreased VO₂ and VCO₂, likely underlying their obesity. These findings support that our previous results in gene trap Kiss1r KOs are due to disrupted kisspeptin signaling, and further highlight a role for Kiss1r signaling in energy expenditure and metabolism besides controlling reproduction. Moreover, given Kiss1r expression in multiple cell-types, our findings indicate that the Kiss1r flox line is viable for future investigations to isolate specific target cells of kisspeptin's metabolic effects.

Conditional knockout of kisspeptin signaling in brown adipose tissue increases metabolic rate and body temperature and lowers body weight

The peptide kisspeptin and its receptor, Kiss1r, act centrally to stimulate reproduction. Evidence indicates that kisspeptin signaling is also important for body weight (BW) and metabolism. We recently reported that Kiss1r KO mice develop obesity, along with reduced metabolism and energy expenditure, independent of estradiol levels. Outside the brain, Kiss1r is expressed in several metabolic tissues, including brown adipose tissue (BAT), but it is unknown which specific tissue is responsible for the metabolic phenotype in Kiss1r KOs. We first determined that global Kiss1r KO mice have significant alterations in body temperature and BAT thermogenic gene expression, perhaps contributing to their obesity. Next, to test whether kisspeptin signaling specifically in BAT influences BW, metabolism, or body temperature, we used Cre/lox technology to generate conditional Kiss1r knockout exclusively in BAT (BAT-Kiss1r KO). Unlike global Kiss1r KOs, BAT-Kiss1r KOs (lacking Kiss1r in just BAT) were not hypogonadal, as expected. Surprisingly, however, BAT-Kiss1r KOs of both sexes displayed significantly lower BW and adiposity than controls. This novel BAT-Kiss1r KO phenotype was of greater magnitude in females and was associated with improved glucose tolerance, increased metabolism, energy expenditure, and locomotor activity, along with increased body temperature and BAT gene expression, specifically Cox8b. Our findings suggest that the previously observed obesity and decreased metabolism in global Kiss1r KOs reflect impaired kisspeptin signaling in non-BAT tissues. However, the novel finding of increased metabolism and body temperature and lower BW in BAT-Kiss1r KOs reveal a previously unidentified role for endogenous kisspeptin signaling in BAT in modulating metabolic and thermogenic physiology.

Hypothalamic Kisspeptin Expression in Hyperandrogenic Female Rats and Aging Rats

Hypothalamic kisspeptin neurons stimulate gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) release. Kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) of rats induce an LH surge for ovulation, and those in the arcuate nucleus (ARC) regulate pulsatile LH secretion for follicle development and spermatogenesis. Dysfunction of kisspeptin neurons thus reduces the reproductive function. This review focuses on the effect of androgen or aging on kisspeptin expression in rats. Although androgen directly suppresses ARC kisspeptin neurons in female rats, the AVPV kisspeptin neurons are hardly affected. In rats, plasma LH concentrations decrease in both sexes with aging, and ARC kisspeptin expression also decreases in old rats compared with young rats. In addition, kisspeptin neurons may be associated with hyperprolactinemia in old female rats because they are known to release prolactin through hypothalamic tuberoinfundibular dopaminergic (TIDA) neurons. Hypothalamic kisspeptin neurons are thus the main regulator to secrete LH, and inhibition of kisspeptin expression leads to various kinds of reproductive dysfunction.

Gonadal hormone-dependent vs. -independent effects of kisspeptin signaling in the control of body weight and metabolic homeostasis

BACKGROUND

Kisspeptins, encoded by Kiss1, have emerged as essential regulators of puberty and reproduction by primarily acting on GnRH neurons, via their canonical receptor, Gpr54. Mounting, as yet fragmentary, evidence strongly suggests that kisspeptin signaling may also participate in the control of key aspects of body energy and metabolic homeostasis. However, characterization of such metabolic dimension of kisspeptins remains uncomplete, without an unambiguous discrimination between the primary metabolic actions of kisspeptins vs. those derived from their ability to stimulate the secretion of gonadal hormones, which have distinct metabolic actions on their own. In this work, we aimed to tease apart primary vs. secondary effects of kisspeptins in the control of key aspects of metabolic homeostasis using genetic models of impaired kisspeptin signaling and/or gonadal hormone status.

METHODS

Body weight (BW) gain and composition, food intake and key metabolic parameters, including glucose tolerance, were comparatively analyzed, in lean and obesogenic conditions, in mice lacking kisspeptin signaling due to global inactivation of Gpr54 (displaying profound hypogonadism; Gpr54-/-) vs. Gpr54 null mice with selective re-introduction of Gpr54 expression only in GnRH cells (Gpr54-/-Tg), where kisspeptin signaling elsewhere than in GnRH neurons is ablated but gonadal function is preserved.

RESULTS

In male mice, global elimination of kisspeptin signaling resulted in decreased BW, feeding suppression and increased adiposity, without overt changes in glucose tolerance, whereas Gpr54-/- female mice displayed enhanced BW gain at adulthood, increased adiposity and perturbed glucose tolerance, despite reduced food intake. Gpr54-/-Tg rescued mice showed altered postnatal BW gain in males and mildly perturbed glucose tolerance in females, with intermediate phenotypes between control and global KO animals. Yet, body composition and leptin levels were similar to controls in gonadal-rescued mice. Exposure to obesogenic insults, such as high fat diet (HFD), resulted in exaggerated BW gain and adiposity in global Gpr54-/- mice of both sexes, and worsening of glucose tolerance, especially in females. Yet, while rescued Gpr54-/-Tg males displayed intermediate BW gain and feeding profiles and impaired glucose tolerance, rescued Gpr54-/-Tg females behaved as controls, except for a modest deterioration of glucose tolerance after ovariectomy.

CONCLUSION

Our data support a global role of kisspeptin signaling in the control of body weight and metabolic homeostasis, with a dominant contribution of gonadal hormone-dependent actions. However, our results document also discernible primary effects of kisspeptin signaling in the regulation of body weight gain, feeding and responses to obesogenic insults, which occur in a sexually-dimorphic manner.

SUMMARY OF TRANSLATIONAL RELEVANCE

Kisspeptins, master regulators of reproduction, may also participate in the control of key aspects of body energy and metabolic homeostasis; yet, the nature of such metabolic actions remains debatable, due in part to the fact that kisspeptins modulate gonadal hormones, which have metabolic actions on their own. By comparing the metabolic profiles of two mouse models with genetic inactivation of kisspeptin signaling but different gonadal status (hypogonadal vs. preserved gonadal function), we provide herein a systematic dissection of gonadal-dependent vs. -independent metabolic actions of kisspeptins. Our data support a global role of kisspeptin signaling in the control of body weight and metabolic homeostasis, with a dominant contribution of gonadal hormone-dependent actions. However, our results document also discernible primary effects of kisspeptin signaling in the regulation of body weight gain, feeding and responses to obesogenic insults, which occur in a sexually-dimorphic manner. These data pave the way for future analyses addressing the eventual contribution of altered kisspeptin signaling in the development of metabolic alterations, especially in conditions linked to reproductive dysfunction.

The Role of the Brain in the Pathogenesis and Physiology of Polycystic Ovary Syndrome (PCOS)

Polycystic ovary syndrome (PCOS) is a common reproductive endocrine disorder, affecting at least 10% of women of reproductive age. PCOS is typically characterized by the presence of at least two of the three cardinal features of hyperandrogenemia (high circulating androgen levels), oligo- or anovulation, and cystic ovaries. Hyperandrogenemia increases the severity of the condition and is driven by increased luteinizing hormone (LH) pulse secretion from the pituitary. Indeed, PCOS women display both elevated mean LH levels, as well as an elevated frequency of LH pulsatile secretion. The abnormally high LH pulse frequency, reflective of a hyperactive gonadotropin-releasing hormone (GnRH) neural circuit, suggests a neuroendocrine basis to either the etiology or phenotype of PCOS. Several studies in preclinical animal models of PCOS have demonstrated alterations in GnRH neurons and their upstream afferent neuronal circuits. Some rodent PCOS models have demonstrated an increase in GnRH neuron activity that correlates with an increase in stimulatory GABAergic innervation and postsynaptic currents onto GnRH neurons. Additional studies have identified robust increases in hypothalamic levels of kisspeptin, another potent stimulator of GnRH neurons. This review outlines the different brain and neuroendocrine changes in the reproductive axis observed in PCOS animal models, discusses how they might contribute to either the etiology or adult phenotype of PCOS, and considers parallel findings in PCOS women.

Novel mechanisms for the metabolic control of puberty: implications for pubertal alterations in early-onset obesity and malnutrition

Puberty is driven by sophisticated neuroendocrine networks that timely activate the brain centers governing the reproductive axis. The timing of puberty is genetically determined; yet, puberty is also sensitive to numerous internal and external cues, among which metabolic/nutritional signals are especially prominent. Compelling epidemiological evidence suggests that alterations of the age of puberty are becoming more frequent; the underlying mechanisms remain largely unknown, but the escalating prevalence of obesity and other metabolic/feeding disorders is possibly a major contributing factor. This phenomenon may have clinical implications, since alterations in pubertal timing have been associated to adverse health outcomes, including higher risk of earlier all-cause mortality. This urges for a better understanding of the neurohormonal basis of normal puberty and its deviations. Compelling evidence has recently documented the master role of hypothalamic neurons producing kisspeptins, encoded by Kiss1, in the neuroendocrine pathways controlling puberty. Kiss1 neurons seemingly participate in transmitting the regulatory actions of metabolic cues on pubertal maturation. Key cellular metabolic sensors, as the mammalian target of rapamycin (mTOR), AMP-activated protein kinase (AMPK) and the fuel-sensing deacetylase, SIRT1, have been recently shown to participate also in the metabolic modulation of puberty. Recently, we have documented that AMPK and SIRT1 operate as major molecular effectors for the metabolic control of Kiss1 neurons and, thereby, puberty onset. Alterations of these molecular pathways may contribute to the perturbation of pubertal timing linked to conditions of metabolic stress in humans, such as subnutrition or obesity and might become druggable targets for better management of pubertal disorders.

Does kisspeptin participate in GABA-mediated modulation of GnRH and GnRH receptor biosynthesis in the hypothalamic-pituitary unit of follicular-phase ewes?

BACKGROUND

The inverse relationship between GnRH transcript level and GABA neurons activity has suggested that GABA at the hypothalamic level may exert a suppressive effect on subsequent steps of the GnRH biosynthesis. In the present study, we analyzed the effects of GABA type A receptor agonist (muscimol) or antagonist (bicuculline) on molecular mechanisms governing GnRH/LH secretion in follicular-phase sheep.

METHODS

ELISA technique was used to investigate the effects of muscimol and/or bicuculline on levels of post-translational products of genes encoding GnRH ligand and GnRH receptor (GnRHR) in the preoptic area (POA), anterior (AH) and ventromedial (VMH) hypothalamus, stalk/median eminence (SME), and GnRHR in the anterior pituitary (AP). Real-time PCR was chosen for determination of the effect of drugs on kisspeptin (Kiss 1) mRNA level in POA and VMH including arcuate nucleus (VMH/ARC), and on Kiss1 receptor (Kiss1r) mRNA abundance in POA-hypothalamic structures. These analyses were supplemented by RIA method for measurement of plasma LH concentration.

RESULTS

The study demonstrated that muscimol and bicuculline significantly decreased or increased GnRH biosynthesis in all analyzed structures, respectively, and led to analogous changes in plasma LH concentration. Similar muscimol- and bicuculline-related alterations were observed in levels of GnRHR. However, the expression of Kiss 1 and Kiss1r mRNAs in selected POA-hypothalamic areas of either muscimol- and bicuculline-treated animals remained unaltered.

CONCLUSIONS

Our data suggest that GABAergic neurotransmission is involved in the regulatory pathways of GnRH/GnRHR biosynthesis and then GnRH/LH release in follicular-phase sheep conceivably via indirect mechanisms that exclude involvement of Kiss 1 neurons.

The Emerging Role of Chromatin Remodeling Factors in Female Pubertal Development

To attain sexual competence, all mammalian species go through puberty, a maturational period during which body growth and development of secondary sexual characteristics occur. Puberty begins when the diurnal pulsatile gonadotropin-releasing hormone (GnRH) release from the hypothalamus increases for a prolonged period of time, driving the adenohypophysis to increase the pulsatile release of luteinizing hormone with diurnal periodicity. Increased pubertal GnRH secretion does not appear to be driven by inherent changes in GnRH neuronal activity; rather, it is induced by changes in transsynaptic and glial inputs to GnRH neurons. We now know that these changes involve a reduction in inhibitory transsynaptic inputs combined with increased transsynaptic and glial excitatory inputs to the GnRH neuronal network. Although the pubertal process is known to have a strong genetic component, during the last several years, epigenetics has been implicated as a significant regulatory mechanism through which GnRH release is first repressed before puberty and is involved later on during the increase in GnRH secretion that brings about the pubertal process. According to this concept, a central target of epigenetic regulation is the transcriptional machinery of neurons implicated in stimulating GnRH release. Here, we will briefly review the hormonal changes associated with the advent of female puberty and the role that excitatory transsynaptic inputs have in this process. In addition, we will examine the 3 major groups of epigenetic modifying enzymes expressed in the neuroendocrine hypothalamus, which was recently shown to be involved in pubertal development and progression.

Metabolic regulation of female puberty via hypothalamic AMPK-kisspeptin signaling

Conditions of metabolic distress, from malnutrition to obesity, impact, via as yet ill-defined mechanisms, the timing of puberty, whose alterations can hamper later cardiometabolic health and even life expectancy. AMP-activated protein kinase (AMPK), the master cellular energy sensor activated in conditions of energy insufficiency, has a major central role in whole-body energy homeostasis. However, whether brain AMPK metabolically modulates puberty onset remains unknown. We report here that central AMPK interplays with the puberty-activating gene, Kiss1, to control puberty onset. Pubertal subnutrition, which delayed puberty, enhanced hypothalamic pAMPK levels, while activation of brain AMPK in immature female rats substantially deferred puberty. Virogenetic overexpression of a constitutively active form of AMPK, selectively in the hypothalamic arcuate nucleus (ARC), which holds a key population of Kiss1 neurons, partially delayed puberty onset and reduced luteinizing hormone levels. ARC Kiss1 neurons were found to express pAMPK, and activation of AMPK reduced ARC Kiss1 expression. The physiological relevance of this pathway was attested by conditional ablation of the AMPKα1 subunit in Kiss1 cells, which largely prevented the delay in puberty onset caused by chronic subnutrition. Our data demonstrate that hypothalamic AMPK signaling plays a key role in the metabolic control of puberty, acting via a repressive modulation of ARC Kiss1 neurons in conditions of negative energy balance.