[Show abstract][Hide abstract] ABSTRACT: The reproductive impact of persistent energy excess in the female remains incompletely defined; yet, the escalating prevalence of obesity calls for better understanding of this phenomenon. Alike, the influence of ovarian hormones on the pathophysiology of obesity and its co-morbidities merits further investigation. We study here the metabolic and gonadotropic impact of sequential obesogenic insults, namely, postnatal over-nutrition (by rearing in small litters; SL) and high fat diet (HFD) after weaning, in gonadal-intact and ovariectomized (OVX) female rats. In young (4-mo) females, SL or HFD similarly increased body weight; yet, only HFD evoked additional metabolic perturbations, some of which were worsened by precedent SL. In addition, HFD concomitantly decreased LH and estradiol levels, and, when combined with SL, suppressed Kiss1 expression in the hypothalamic arcuate nucleus (ARC) in 4-mo females, whereas HFD up to 10-mo reduced luteinizing hormone responses to kisspeptin-10 also. OVX caused rapid deterioration of the metabolic profile, with overweight, increased energy intake and deregulation of leptin and glucose/insulin levels; effects whose magnitude was similar, if not higher than HFD. Summation of previous obesogenic insults maximally increased body weight, basal leptin, insulin and glucose levels, and glucose intolerance. Yet, OVX obliterated the inhibitory effects of overweight/HFD on gonadotropin levels and ARC Kiss1 expression. Our study documents the deleterious consequences of sequential obesogenic insults on the female gonadotropin axis, which involve central impairment of Kiss1 system. In addition, our work delineates the dramatic impact of the loss of ovarian secretions, as menopausal model, on the metabolic profile of female rats, especially when combined with preceding obesogenic challenges.
[Show abstract][Hide abstract] ABSTRACT: Puberty is a major developmental milestone set in motion by the interaction of genetic factors and environmental cues. The pubertal process is initiated by an increased pulsatile release of gonadotropin releasing hormone (GnRH) from neurosecretory neurons of the hypothalamus. Although single genes have been identified that are essential for puberty to occur, it appears clear now that many genes controlling diverse cellular functions contribute to the process. The polygenic nature of the neuroendocrine complex controlling puberty has prompted two important questions: are these genes functionally connected and, if they are, is their activity subject to a dynamic level of control independent of changes in DNA sequence? In this article we will discuss emerging evidence suggesting that the onset of puberty is controlled at the transcriptional level by interactive gene networks subjected to epigenetic regulation. At least two modes of epigenetic regulation provide coordination and transcriptional plasticity to these networks: changes in DNA methylation and differential association of histone modifications to genomic regions controlling gene activity. Architecturally, puberty-controlling networks are endowed with “activators,” which move the process along by setting in motion key developmental events, and “repressors,” which play a central role in preventing the untimely unfolding of these events.
Brain Crosstalk in Puberty and Adolescence, 01/2015: pages 97-119;
[Show abstract][Hide abstract] ABSTRACT: Kisspeptin, neurokinin B (NKB) and dynorphin A are co-expressed in a population of neurons in the arcuate nucleus (ARC), termed KNDy neurons, which were recently recognized as important elements for the generation of GnRH pulses. However, the topographic distribution of these peptides and their regulated expression by sex steroids are still not well understood. In this study, detailed examination of NKB and kisspeptin immunoreactivity in the rat ARC was carried out, including comparison between sexes, with and without sex steroid replacement. Neurons expressing kisspeptin and NKB were more prominent in the caudal ARC of females, whereas neurons expressing NKB, but not kisspeptin, were the most abundant in the male. Sex steroid manipulation revealed differential regulation of kisspeptin and NKB; while kisspeptin immunoreactive (-ir) cells increased in response to gonadectomy, NKB remained unchanged. Furthermore, the number of NKB-ir cells increased upon sex steroid replacement compared to gonadectomy, while kisspeptin did not, suggesting that sex steroids differently regulate these peptides. In addition, only in females did the density of kisspeptin- and NKB-ir fibers in the ARC increase upon sex steroid replacement in relation to sham and OVX, respectively, suggesting sex-specific regulation of release. In conclusion, our observations reveal sex differences in the number of kisspeptin- and NKB-ir cells, which are more prominent in the caudal ARC. The divergent regulation of kisspeptin and NKB peptide contents in the ARC as function of sex and steroid milieu enlarge our understanding on how these neuropeptides are post-transcriptionally regulated in KNDy neurons.
[Show abstract][Hide abstract] ABSTRACT: Context: Gordon Holmessyndrome (GHS) is characterized by cerebellar ataxia/atrophy and normosmic hypogonadotropic hypogonadism (nHH). The underlying pathophysiology of this combined neurodegeneration and nHH remains unknown. Objective: We aimed to provide insight in to the disease mechanism in GHS. Methods: We studied a cohort of six multiplex families with GHS through autozygosity mapping and whole exome sequencing. Results: We identified six patients from three independent families carrying loss-of-function mutations in PNPLA6, which encodes neuropathy target esterase (NTE), a lysophospholipase that maintains intracellular phospholipid homeostasis by converting lysophosphatidylcholine (LPC) to glycerophosphocholine. Wild-type PNPLA6, but not PNPLA6 bearing these mutations, rescued a well established Drosophila neurodegenerative phenotype caused by the absence of sws, the fly ortholog of mammalian PNPLA6. Inhibition of NTE activity in the LβT2 gonadotrope cell line diminished LH response to GnRH by reducing GnRH-stimulated LH exocytosis, without affecting GnRH receptor signaling or LHβ synthesis. Conclusion: These results suggest that NTE-dependent alteration of phosholipid homeostasis in GHS causes both neurodegeneration and impaired LH release from pituitary gonadotropes leading to nHH.
[Show abstract][Hide abstract] ABSTRACT: Premature ovarian failure (POF) affects 1% of women in reproductive age, but its etiology remains uncertain. While kisspeptins, the products of Kiss1 that act via Kiss1r (aka, Gpr54), are known to operate at the hypothalamus to control GnRH/gonadotropin secretion, additional actions at other reproductive organs, including the ovary, have been proposed. Yet, their physiological relevance is still unclear. We present here a series of studies in Kiss1r haplo-insufficient and null mice suggesting a direct role of kisspeptin signaling in the ovary, whose defect precipitates a state of primary POF. Kiss1r hypomorph mice displayed a premature decline in ovulatory rate, followed by progressive loss of antral follicles, oocyte loss and a reduction in all categories of pre-antral follicles. These alterations were accompanied by reduced fertility. Because of this precocious ovarian ageing, >48-wk mice showed atrophic ovaries, lacking growing follicles and corpora lutea. This phenomenon was associated to a drop in ovarian Kiss1r mRNA expression, but took place in the absence of a decrease in circulating gonadotropins. In fact, FSH levels increased in aged hypomorph animals, reflecting loss of follicular function. In turn, Kiss1r null mice, which do not spontaneously ovulate and have arrested follicular development, failed to show normal ovulatory responses to standard gonadotropin priming, and required GnRH pre-stimulation during 1-wk in order to display gonadotropin-induced ovulation. Yet, the magnitude of such ovulatory responses was ∼half of that seen in control immature WT animals. Altogether, our data are the first to demonstrate that Kiss1r haplo-insufficiency induces a state of POF, which is not attributable to defective gonadotropin secretion. We also show that the failure of follicular development and ovulation linked to the absence of Kiss1r cannot be fully rescued by (even extended) gonadotropin replacement. These findings suggest a direct ovarian role of kisspeptin signaling, whose perturbation may contribute to the pathogenesis of POF.
[Show abstract][Hide abstract] ABSTRACT: Neurotrophins (NTs), once believed to be neural-specific trophic factors, are now known to also provide developmental cues to non-neural cells. In the ovary, NTs contribute to both the formation and development of follicles. Here we show that oocyte-specific deletion of the Ntrk2 gene, which encodes the NTRK2 receptor (NTRK2) for neurotrophin-4/5 and brain-derived neurotrophic factor (BDNF), results in post-pubertal oocyte death, loss of follicular organization, and early adulthood infertility. Oocytes lacking NTRK2 do not respond to gonadotropins with activation of phosphatidylinositol 3-kinase (PI3K)-AKT-mediated signaling. Before puberty, oocytes only express a truncated NTRK2 form (NTRK2.T1), but at puberty full-length (NTRK2.FL) receptors are rapidly induced by the preovulatory gonadotropin surge. A cell line expressing both NTRK2.T1 and the kisspeptin receptor (KISS1R) responds to BDNF stimulation with activation of Ntrk2 expression only if kisspeptin is present. This suggests that BDNF and kisspeptin, which are produced by granulosa cells (GCs) of periovulatory follicles, act in concert to mediate the effect of gonadotropins on Ntrk2 expression in oocytes. In keeping with this finding, the oocytes of NTRK2-intact mice fail to respond to gonadotropins with increased Ntrk2 expression in the absence of KISS1R. Our results demonstrate that the preovulatory gonadotropin surge promotes oocyte survival at the onset of reproductive cyclicity by inducing oocyte expression of NTRK2.FL receptors, which set in motion an AKT-mediated survival pathway. They also suggest that gonadotropins activate NTRK2.FL expression via a dual communication pathway involving BDNF and kisspeptin produced in GCs and their respective receptors NTRK2.T1 and KISS1R expressed in oocytes.
[Show abstract][Hide abstract] ABSTRACT: Reproduction is sensitive to insufficient body energy reserves, especially in females. Metabolic regulation of male reproductive axis is less obvious, and the impact of conditions of persistent energy excess has received moderate attention. Yet, the escalating prevalence of obesity and the clinical evidence of its deleterious effects on male fertility have raised considerable concerns. We report here phenotypic and mechanistic studies of the reproductive impact of postnatal nutritional manipulations (mainly over-nutrition), coupled to high fat diet (HFD) after weaning. Metabolic and hormonal analyses in young (4-mo) and middle-aged (10-mo) animals revealed that HFD caused profound metabolic perturbations, including glucose intolerance, which were worsened by precedent postnatal overfeeding; these were detectable already in young males but aggravated in 10-mo-old rats. Impairment of reproductive parameters took place progressively, and HFD alone was sufficient to explain most of these alterations, regardless of postnatal under- or overnutrition. In young males, testosterone (T) levels and steroidogenic enzyme expression were suppressed by HFD, without compensatory increases of LH levels, which were in fact partially inhibited in heavier males. In addition, obese males displayed suppressed hypothalamic Kiss1 expression despite low T, and HFD inhibited LH responses to kisspeptin. Overweight anticipated some of the neuroendocrine effects of ageing, such as the suppression of hypothalamic Kiss1 expression and the decline in serum T and LH levels. Nonetheless, HFD per se caused a detectable worsening of key reproductive indices in middle-aged males, such as basal LH and FSH levels, as well as LH responses to kisspeptin. Our study demonstrates that nutritional stress, especially HFD, has a profound deleterious impact on metabolic and gonadotropic function, as well as on Kiss1 system, and precipitates neuroendocrine reproductive senescence in the male.
[Show abstract][Hide abstract] ABSTRACT: This article is part of a Special Issue "Puberty and Adolescence". Puberty is a major developmental milestone controlled by the interaction of genetic factors and environmental cues of mostly metabolic and circadian nature. An increased pulsatile release of the decapeptide gonadotropin releasing hormone (GnRH) from hypothalamic neurosecretory neurons is required for both the initiation and progression of the pubertal process. This increase is brought about by coordinated changes that occur in neuronal and glial networks associated with GnRH neurons. These changes ultimately result in increased neuronal and glial stimulatory inputs to the GnRH neuronal network and a reduction of transsynaptic inhibitory influences. While some of the major players controlling pubertal GnRH secretion have been identified using gene-centric approaches, much less is known about the system-wide control of the overall process. Because the pubertal activation of GnRH release involves a diversity of cellular phenotypes, and a myriad of intracellular and cell-to-cell signaling molecules, it appears that the overall process is controlled by a highly coordinated and interactive regulatory system involving hundreds, if not thousands, of gene products. In this article we will discuss emerging evidence suggesting that these genes are arranged as functionally connected networks organized, both internally and across sub-networks, in a hierarchical fashion. According to this concept, the core of these networks is composed of transcriptional regulators that, by directing expression of downstream subordinate genes, provide both stability and coordination to the cellular networks involved in initiating the pubertal process. The integrative response of these gene networks to external inputs is postulated to be coordinated by epigenetic mechanisms.
Hormones and Behavior 07/2013; 64(2):175-86. DOI:10.1016/j.yhbeh.2012.09.013 · 4.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Body energy stores and metabolic cues influence the onset of puberty. However, the pubertal impact of early nutritional challenges has been only fragmentarily addressed. We evaluate here the consequences, in terms of pubertal timing and hormonal markers, of various nutritional manipulations during pre- or postnatal maturation in rats of both sexes. Males and females were submitted to gestational (UNG) or peripubertal (SUB) subnutrition, or were raised in large (LL; underfeeding) or small (SL; overfeeding) litters. In addition, groups of UNG, LL and SL rats were fed on high fat diet (HFD) after weaning. Postnatal overfeeding resulted in higher body weights (BW) during pubertal transition in both sexes, but only SL males displayed overtly advanced external signs of puberty. Postnatal underfeeding persistently decreased BW gain during puberty; yet, the magnitude of pubertal delay was greater in LL males. In contrast, regardless of postnatal nutrition, HFD tended to advance the onset of puberty in females, but did not alter pubertal timing in males. Likewise, SUB females displayed a marked delay in BW gain and puberty onset whereas, despite similar reduction in BW, SUB males showed normal timing of puberty. These sex divergences were also detected in various hormonal and metabolic indices, so that postnatal overnutrition consistently increased LH, FSH, leptin and insulin levels only in pubertal females, while HFD decreased gonadotropin levels in SL females but increased them in SL males. Notably, UNG rats did not show signs of delayed puberty but displayed a striking sex dimorphism in serum insulin/glucose levels regardless of the diet, so that only UNG males had signs of presumable insulin resistance. Our data disclose important sex differences in the impact of various early nutritional challenges on the timing of puberty, which may help to explain the different trends of altered puberty and related co-morbidities between sexes.
[Show abstract][Hide abstract] ABSTRACT: Body energy balance and metabolic signals are important modulators of puberty and reproductive function, so that perturbations of metabolism and energy reserves (ranging from persistent energy insufficiency to morbid obesity) are frequently linked to reproductive disorders. The mechanisms for the tight association between body metabolic state and reproduction are multifaceted, and likely involve numerous peripheral hormones and central transmitters. In recent years, a prominent role of kisspeptins in the central pathways responsible for conveying metabolic information into the brain centers responsible for reproductive control, and specifically GnRH neurons, has been proposed on the basis of a wealth of expression and functional data. In this chapter, we will summarize such evidence, with special attention to the potential (direct and/or indirect) interaction of leptin and kisspeptin pathways. In addition, other potential metabolic modulators of kisspeptin signaling, as well as some of the putative molecular mechanisms for the metabolic regulation of Kiss1 will be briefly reviewed. Conflictive data, including those questioning an essential role of Kiss1 neurons in mediating leptin effects on the reproductive axis, will be also discussed. All in all, we aim to provide an integral and balanced view of the physiological relevance and potential mechanisms for the metabolic control of the kisspeptin system, as important pathway for the integral regulation of energy balance, puberty onset, and fertility.
Advances in Experimental Medicine and Biology 04/2013; 784:363-83. DOI:10.1007/978-1-4614-6199-9_17 · 1.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The timing of puberty is controlled by many genes. The elements coordinating this process have not, however, been identified. Here we show that an epigenetic mechanism of transcriptional repression times the initiation of female puberty in rats. We identify silencers of the Polycomb group (PcG) as principal contributors to this mechanism and show that PcG proteins repress Kiss1, a puberty-activating gene. Hypothalamic expression of two key PcG genes, Eed and Cbx7, decreased and methylation of their promoters increased before puberty. Inhibiting DNA methylation blocked both events and resulted in pubertal failure. The pubertal increase in Kiss1 expression was accompanied by EED loss from the Kiss1 promoter and enrichment of histone H3 modifications associated with gene activation. Preventing the eviction of EED from the Kiss1 promoter disrupted pulsatile gonadotropin-releasing hormone release, delayed puberty and compromised fecundity. Our results identify epigenetic silencing as a mechanism underlying the neuroendocrine control of female puberty.
[Show abstract][Hide abstract] ABSTRACT: Kisspeptins (Kp), products of the Kiss1 gene, have emerged as essential elements in the control of GnRH neurons and gonadotropic secretion. However, despite considerable progress in the field, limited attention has been paid to date to elucidate the potential interactions of Kp with other neurotransmitters known to centrally regulate the gonadotropic axis. We characterize herein the impact of manipulations of key aminoacidergic (glutamate and GABA), peptidergic (NKB, Dyn, and MCH) and gaseous (nitric oxide; NO) neurotransmission on gonadotropin responses to Kp-10 in male rats. Blockade of ionotropic glutamate receptors (of the NMDA and non-NMDA type) variably decreased LH responses to Kp-10, whereas activation of both ionotropic and metabotropic receptors, which enhanced LH and FSH release per se, failed to further increase gonadotropin responses to Kp-10. In fact, co-activation of metabotropic receptors attenuated LH and FSH responses to Kp-10. Selective activation of GABAA receptors decreased Kp-induced gonadotropin secretion, while their blockade elicited robust LH and FSH bursts, and protracted responses to Kp-10 when combined with GABAB receptor inhibition. Blockade of Dyn signaling (at κ-opioid receptors) enhanced LH responses to Kp-10, while activation of Dyn and NKB signaling modestly reduced Kp-induced LH and FSH release. Finally, MCH decreased basal LH secretion and modestly reduced FSH responses to Kp-10, whereas LH responses to Kp-10 were protracted after inhibition of NO synthesis. In sum, we present herein evidence for the putative roles of glutamate, GABA, Dyn, NKB, MCH and NO in modulating gonadotropic responses to Kp in male rats. Our pharmacological data will help to characterize the central interactions and putative hierarchy of key neuroendocrine pathways involved in the control of the gonadotropic axis.
[Show abstract][Hide abstract] ABSTRACT: Human genetic studies have revealed that neurokinin B (NKB) and its receptor, neurokinin-3 receptor (NK3R), are essential elements for normal reproduction; however, the precise role of NKB-NK3R signaling in the initiation of puberty remains unknown. We investigated here the regulation of Tac2 and Tacr3 mRNAs (encoding NKB and NK3R, respectively) in female rats and demonstrated that their hypothalamic expression is increased along postnatal maturation. At puberty, both genes were widely expressed throughout the brain, including the lateral hypothalamic area and the arcuate nucleus (ARC)/medial basal hypothalamus, where the expression of Tacr3 increased across pubertal transition. We showed that central administration of senktide (NK3R agonist) induced luteinizing hormone (LH) secretion in prepubertal and peripubertal females. Conversely, chronic infusion of an NK3R antagonist during puberty moderately delayed the timing of vaginal opening (VO) and tended to decrease LH levels. The expression of NKB and its receptor was sensitive to changes in metabolic status during puberty, as reflected by a reduction in Tacr3 (and, to a lesser extent, Tac2) expression in the ARC after a 48 h fast. Yet, acute LH responses to senktide in pubertal females were preserved, if not augmented, under fasting conditions, suggesting sensitization of the NKB-NK3R-gonadotropin-releasing hormone signaling pathway under metabolic distress. Moreover, repeated administration of senktide to female rats with pubertal arrest due to chronic undernutrition rescued VO (in ∼50% of animals) and potently elicited LH release. Altogether, our observations suggest that NKB-NK3R signaling plays a role in pubertal maturation and that its alterations may contribute to pubertal disorders linked to metabolic stress and negative energy balance.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 02/2012; 32(7):2388-97. DOI:10.1523/JNEUROSCI.4288-11.2012 · 6.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nesfatin-1, product of the precursor NEFA/nucleobindin2 (NUCB2), was initially identified as anorectic hypothalamic neuropeptide, acting in a leptin-independent manner. In addition to its central role in the control of energy homeostasis, evidence has mounted recently that nesfatin-1 is also produced in peripheral metabolic tissues, such as pancreas, adipose, and gut. Moreover, nesfatin-1 has been shown to participate in the control of body functions gated by whole-body energy homeostasis, including puberty onset. Yet, whether, as is the case for other metabolic neuropeptides, NUCB2/nesfatin-1 participates in the direct control of gonadal function remains unexplored. We document here for the first time the expression of NUCB2 mRNA in rat, mouse, and human testes, where NUCB2/nesfatin-1 protein was identified in interstitial mature Leydig cells. Yet in rats, NUCB2/nesfatin-1 became expressed in Sertoli cells upon Leydig cell elimination and was also detected in Leydig cell progenitors. Although NUCB2 mRNA levels did not overtly change in rat testis during pubertal maturation and after short-term fasting, NUCB2/nesfatin-1 content significantly increased along the puberty-to-adult transition and was markedly suppressed after fasting. In addition, testicular NUCB2/nesfatin-1 expression was up-regulated by pituitary LH, because hypophysectomy decreased, whereas human choriogonadotropin (super-agonist of LH receptors) replacement enhanced, NUCB2/nesfatin-1 mRNA and peptide levels. Finally, nesfatin-1 increased human choriogonadotropin-stimulated testosterone secretion by rat testicular explants ex vivo. Our data are the first to disclose the presence and functional role of NUCB2/nesfatin-1 in the testis, where its expression is regulated by developmental, metabolic, and hormonal cues as well as by Leydig cell-derived factors. Our observations expand the reproductive dimension of nesfatin-1, which may operate directly at the testicular level to link energy homeostasis, puberty onset, and gonadal function.
[Show abstract][Hide abstract] ABSTRACT: Mammalian puberty is initiated by an increased pulsatile release of gonadotropin-releasing hormone (GnRH) from specialized neurons located in the hypothalamus. GnRH secretion is controlled by neuronal and glial networks, whose activity appears to be coordinated via transcriptional regulation. One of the transcription factors involved in this process is thought to be the recently described gene Enhanced at Puberty 1 (EAP1), which encodes a protein with dual transcriptional activity. In this study we used gene reporter and chromatin immunoprecipitation (ChIP) assays to examine the hypothesis that EAP1 expression is controlled by transcriptional regulators earlier postulated to serve as central nodes of a gene network involved in the neuroendocrine control of puberty. These regulators include Thyroid Transcription Factor 1 (TTF1), Yin Yang 1 (YY1), and CUX1, in addition to EAP1 itself. While TTF1 has been shown to facilitate the advent of puberty, YY1 (a zinc finger protein component of the Polycomb silencing complex) may play a repressive role. The precise role of CUX1 in this context is not known, but like EAP1, CUX1 can either activate or repress gene transcription. We observed that DNA segments of two different lengths (998 and 2744bp) derived from the 5'-flanking region of the human EAP1 gene display similar transcriptional activity. TTF1 stimulates transcription from both DNA segments with equal potency, whereas YY1, CUX1, and EAP1 itself, behave as transcriptional repressors. All four proteins are recruited in vivo to the EAP1 5'-flanking region. These observations suggest that EAP1 gene expression is under dual transcriptional regulation imposed by a trans-activator (TTF1) and two repressors (YY1 and CUX1) previously postulated to be upstream components of a puberty-controlling gene network. In addition, EAP1 itself appears to control its own expression via a negative auto-feedback loop mechanism. Further studies are needed to determine if the occupancy of the EAP1 promoter by these regulatory factors changes at the time of puberty.
[Show abstract][Hide abstract] ABSTRACT: Kiss1 neurons have recently emerged as a putative conduit for the metabolic gating of reproduction, with leptin being a regulator of hypothalamic Kiss1 expression. Early perturbations of the nutritional status are known to predispose to different metabolic disorders later in life and to alter the timing of puberty; however, the potential underlying mechanisms remain poorly defined. Here we report how changes in the pattern of postnatal feeding affect the onset of puberty and evaluate key hormonal and neuropeptide [Kiss1/kisspeptin (Kp)] alterations linked to these early nutritional manipulations. Female rats were raised in litters of different sizes: small (four pups per dam: overfeeding), normal (12 pups per dam), and large litters (20 pups per litter: underfeeding). Postnatal overfeeding resulted in persistently increased body weight and earlier age of vaginal opening, as an external sign of puberty, together with higher levels of leptin and hypothalamic Kiss1 mRNA. Conversely, postnatal underfeeding caused a persistent reduction in body weight, lower ovarian and uterus weights, and delayed vaginal opening, changes that were paralleled by a decrease in leptin and Kiss1 mRNA levels. Kisspeptin-52 immunoreactivity (Kp-IR) in the hypothalamus displayed similar patterns, with lower numbers of Kp-IR neurons in the arcuate nucleus of postnatally underfed animals, and a trend for increased Kp-positive fibers in the periventricular area of early overfed rats. Yet, gonadotropin responses to Kp at puberty were similar in all groups, except for enhanced responsiveness to low doses of Kp-10 in postnatally underfed rats. In conclusion, our data document that the timing of puberty is sensitive to both overfeeding and subnutrition during early (postnatal) periods and suggest that alterations in hypothalamic expression of Kiss1/kisspeptin may underlie at least part of such programming phenomenon.
[Show abstract][Hide abstract] ABSTRACT: The 5'-AMP-activated protein kinase (AMPK) plays a fundamental role in regulating energy homeostasis as well as feeding and metabolism, through central and peripheral actions. AMPK is activated by conditions causing ATP depletion and by different metabolic molecules, such as adiponectin and AMPK agonist, such as 5-aminoimidazole- 4-carboxamide-1-β-D-ribofuranoside (AICAR). AMPK activation has also been shown to affect the migration of different cell types and to participate in the central control of reproductive function, although information concerning AMPK and the development of the hypothalamic reproductive compartment is lacking.
To explore whether AMPK activation by globular adiponectin (gAdipo) and AICAR may affect the migratory ability of GnRH neurons.
We used GN11 immature GnRH neurons (in vitro model system), RT-PCR and Western blot analysis, and Boyden's chamber assay.
gAdipo did not affect FBS-stimulated migration of GN11 cells and activated AMPK through the mandatory phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and Akt, which also interact one to each other. AICAR treatment inhibited FBS-stimulated GN11 cell migration, through a long-lasting activation of AMPK. A downstream activation of ERK1/2 by AICAR was also observed and inhibition of ERK1/2 amplified AICAR-induced inhibition of migration.
The direct, but not the indirect, activation of AMPK appears to negatively affect FBSinduced GN11 cell migration, suggesting that the final balance between pro-migratory and anti-migratory actions may also depend upon the specific sequence of intracellular signals activated by one agent.
[Show abstract][Hide abstract] ABSTRACT: Much attention has been drawn to the possible involvement of hypothalamic inflammation in the pathogenesis of metabolic disorders, especially in response to a high-fat diet. Microglia, the macrophages of the central nervous system, can be activated by proinflammatory signals resulting in the local production of specific interleukins and cytokines, which in turn could exacerbate the pathogenic process. Because obesity itself is considered to be a state of chronic inflammation, we evaluated whether being overweight results in microglial activation in the hypothalamus of rats on a normal diet. Accordingly, we used a model of neonatal overnutrition that entailed adjustment of litter size at birth (small litters: four pups/dam versus normal litters: 12 pups/dam) and resulted in a 15% increase in bodyweight and increased circulating leptin levels at postnatal day 60. Rats that were overnourished during neonatal life had an increased number of activated microglia in specific hypothalamic areas such as the ventromedial hypothalamus, which is an important site for metabolic control. However, this effect was not confined to the hypothalamus because significant microglial activation was also observed in the cerebellar white matter. There was no change in circulating tumour necrosis factor (TNF) α levels or TNFα mRNA levels in either the hypothalamus or cerebellum. Interleukin (IL)6 protein levels were higher in both the hypothalamus and cerebellum, with no change in IL6 mRNA levels. Because circulating IL6 levels were elevated, this rise in central IL6 could be a result of increased uptake. Thus, activation of microglia occurs in adult rats exposed to neonatal overnutrition and a moderate increase in weight gain on a normal diet, possibly representing a secondary response to systemic inflammation. Moreover, this activation could result in local changes in specific hypothalamic nuclei that in turn further deregulate metabolic homeostasis.
Journal of Neuroendocrinology 02/2011; 23(4):365-70. DOI:10.1111/j.1365-2826.2011.02113.x · 3.14 Impact Factor