7,577 research outputs found
Ghrelin Decreases Firing Activity of Gonadotropin-Releasing Hormone (GnRH) Neurons in an Estrous Cycle and Endocannabinoid Signaling Dependent Manner.
No full textThe orexigenic peptide, ghrelin is known to influence function of GnRH neurons, however, the direct effects of the hormone upon these neurons have not been explored, yet. The present study was undertaken to reveal expression of growth hormone secretagogue receptor (GHS-R) in GnRH neurons and elucidate the mechanisms of ghrelin actions upon them. Ca(2+)-imaging revealed a ghrelin-triggered increase of the Ca(2+)-content in GT1-7 neurons kept in a steroid-free medium, which was abolished by GHS-R-antagonist JMV2959 (10µM) suggesting direct action of ghrelin. Estradiol (1nM) eliminated the ghrelin-evoked rise of Ca(2+)-content, indicating the estradiol dependency of the process. Expression of GHS-R mRNA was then confirmed in GnRH-GFP neurons of transgenic mice by single cell RT-PCR. Firing rate and burst frequency of GnRH-GFP neurons were lower in metestrous than proestrous mice. Ghrelin (40nM-4μM) administration resulted in a decreased firing rate and burst frequency of GnRH neurons in metestrous, but not in proestrous mice. Ghrelin also decreased the firing rate of GnRH neurons in males. The ghrelin-evoked alterations of the firing parameters were prevented by JMV2959, supporting the receptor-specific actions of ghrelin on GnRH neurons. In metestrous mice, ghrelin decreased the frequency of GABAergic mPSCs in GnRH neurons. Effects of ghrelin were abolished by the cannabinoid receptor type-1 (CB1) antagonist AM251 (1µM) and the intracellularly applied DAG-lipase inhibitor THL (10µM), indicating the involvement of retrograde endocannabinoid signaling. These findings demonstrate that ghrelin exerts direct regulatory effects on GnRH neurons via GHS-R, and modulates the firing of GnRH neurons in an ovarian-cycle and endocannabinoid dependent manner
The GOAT-ghrelin system is not essential for hypoglycemia prevention during prolonged calorie restriction.
No full textGhrelin acylation by ghrelin O-acyltransferase (GOAT) has recently been reported to be essential for the prevention of hypoglycemia during prolonged negative energy balance. Using a unique set of four different genetic loss-of-function models for the GOAT/ghrelin/growth hormone secretagogue receptor (GHSR) system, we thoroughly tested the hypothesis that lack-of-ghrelin activation or signaling would lead to hypoglycemia during caloric deprivation.
Male and female knockout (KO) mice for GOAT, ghrelin, GHSR, or both ghrelin and GHSR (dKO) were subjected to prolonged calorie restriction (40% of ad libitum chow intake). Body weight, fat mass, and glucose levels were recorded daily and compared to wildtype (WT) controls. Forty-eight hour blood glucose profiles were generated for each individual mouse when 2% or less body fat mass was reached. Blood samples were obtained for analysis of circulating levels of acyl- and desacyl-ghrelin, IGF-1, and insulin.
Chronic calorie restriction progressively decreased body weight and body fat mass in all mice regardless of genotype. When fat mass was depleted to 2% or less of body weight for 2 consecutive days, random hypoglycemic events occurred in some mice across all genotypes. There was no increase in the incidence of hypoglycemia in any of the four loss-of-function models for ghrelin signaling including GOAT KO mice. Furthermore, no differences in insulin or IGF-1 levels were observed between genotypes.
The endogenous GOAT-ghrelin-GHSR system is not essential for the maintenance of euglycemia during prolonged calorie restriction
The orexigenic effect of ghrelin is mediated through central activation of the endogenous cannabinoid system
No full textINTRODUCTION: Ghrelin and cannabinoids stimulate appetite, this effect possibly being mediated by the activation of hypothalamic AMP-activated protein kinase (AMPK), a key enzyme in appetite and metabolism regulation. The cannabinoid receptor type 1 (CB1) antagonist rimonabant can block the orexigenic effect of ghrelin. In this study, we have elucidated the mechanism of the putative ghrelin-cannabinoid interaction. METHODS: The effects of ghrelin and CB1 antagonist rimonabant in wild-type mice, and the effect of ghrelin in CB1-knockout animals, were studied on food intake, hypothalamic AMPK activity and endogenous cannabinoid content. In patch-clamp electrophysiology experiments the effect of ghrelin was assessed on the synaptic inputs in parvocellular neurons of the hypothalamic paraventricular nucleus, with or without the pre-administration of a CB1 antagonist or of cannabinoid synthesis inhibitors. RESULTS AND CONCLUSIONS: Ghrelin did not induce an orexigenic effect in CB1-knockout mice. Correspondingly, both the genetic lack of CB1 and the pharmacological blockade of CB1 inhibited the effect of ghrelin on AMPK activity. Ghrelin increased the endocannabinoid content of the hypothalamus in wild-type mice and this effect was abolished by rimonabant pre-treatment, while no effect was observed in CB1-KO animals. Electrophysiology studies showed that ghrelin can inhibit the excitatory inputs on the parvocellular neurons of the paraventricular nucleus, and that this effect is abolished by administration of a CB1 antagonist or an inhibitor of the DAG lipase, the enzyme responsible for 2-AG synthesis. The effect is also lost in the presence of BAPTA, an intracellular calcium chelator, which inhibits endocannabinoid synthesis in the recorded parvocellular neuron and therefore blocks the retrograde signaling exerted by endocannabinoids. In summary, an intact cannabinoid signaling pathway is necessary for the stimulatory effects of ghrelin on AMPK activity and food intake, and for the inhibitory effect of ghrelin on paraventricular neurons
Relationships between cord blood leptin and ghrelin levels, milk intake and weight gain in human infants
No full textLeptin and ghrelin are hormones involved in the regulation of appetite and adiposity. Leptin suppresses appetite and induces weight loss; ghrelin stimulates appetite and promotes weight gain. The study reported in this thesis was designed to examine the relationship of cord blood leptin and ghrelin with milk intake over the first week of life, and with infant growth up to twelve weeks of age. One hundred term formula fed newborns were recruited at birth. Leptin and ghrelin were measured in cord blood by radioimmunoassay. Milk intake was measured by weighing of bottles of formula milk before and after feeding. Measurements of weight, length and head circumference were taken at birth, seven days and at twelve weeks of age. A number of control variables were also measured. Birthweight was a significant predictor of mean milk intake, which rose significantly from days 1 to 7, with no difference between males and females. Weight gain or loss in the early neonatal period was a direct and significant consequence of milk intake consumed over that period. There was no relationship between cord blood leptin or ghrelin (controlling for birthweight) on the infants' milk intake over the first 24 hours of life or on their mean milk intake over the first week of life. Weight gain was significantly correlated with birthweight, with higher birthweight associated with lower weight gain. There was no relationship between cord leptin and weight gain to three months of age after adjusting for birthweight; but lower cord ghrelin levels were significantly associated with slower weight gain
Avaliação da expressão imuno-histoquímica das células retais produtoras de grelina em ratos Wistar submetidos à dieta de cafeteria
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências da Saúde, Programa de Pós-Graduação em Ciências Médicas, Florianópolis, 2012Introdução: Na atualidade o sobrepeso e a obesidade, induzidos pela dieta e pelo sedentarismo, são doenças muito prevalentes em vários países. Considerados uma epidemia mundial pela Organização Mundial da Saúde (OMS), são importantes fatores de risco para inúmeras afecções, entre elas as neoplasias colorretais. Estudos prévios sugerem que em portadores de obesidade ou sobrepeso há aumento da incidência desse tipo de neoplasia e a piora do prognóstico. Com a descoberta da grelina, em 1999, que é um hormônio orexígeno com potente ação sobre a liberação do hormônio do crescimento (GH) e atuação em diversos sistemas orgânicos, fisiológicos e na carcinogênese, desenvolveram-se diversas pesquisas para elucidar o seu papel e sua importância em todas essas funções. Recentemente, evidenciou-se aumento da expressão de grelina em amostras teciduais de neoplasias colorretais quando comparadas à tecidos colônicos normais. Objetivos: Investigar o impacto da dieta de cafeteria na expressão imuno-histoquímica retal da grelina e avaliar o tipo morfológico das células identificadas. Desenho do Estudo: Estudo analítico experimental do tipo corte transversal com intervenção. Método: Vinte e quatro ratos Wistar machos foram distribuídos em 4 subgrupos de 6 animais cada denominados: SGR1 (ração e água) e SGC1 (dieta de cafeteria, ração e água) por um período de 30 dias; SGR2 (ração e água) e SGC2 (dieta de cafeteria, ração e água) por um período de 60 dias. O peso dos animais e do reto amputado, o número e o tipo de células imunorreativas à grelina foram registrados e comparados entre os subgrupos. Na análise estatística foram utilizados os testes ANOVA com correção de Bonferroni, qui quadrado, teste t pareado e teste t de Student. Resultados: Houve aumento significativo do peso corporal em todos os subgrupos (P 0,001). O peso no dia da cirurgia foi significativamente maior na comparação do SGC2 com os demais subgrupos: SGR1 (P=0,003), SGC1 (P= 0,010) e SGR2 (P= 0,001). Não houve diferença na comparação da média do número absoluto de células imunorreativas (P= 0,685) e na comparação entre expressão e não expressão (P=0,330) entre os subgrupos, nem entre o peso final (P=0,993) e o peso retal (P= 0,230) com a imunoexpressão. Todas as células imunorreativas identificadas foram do tipo "fechado". Conclusão: Os resultados do presente estudo não demonstraram influência da dieta de cafeteria sobre o número de células retais imunorreativas à grelina quando comparado aos controles nem aos dois períodos de ingesta e apenas células imunorreatoras do tipo "fechado" foram identificadas no reto de ratos Wistar.Abstract : Introduction: Obesity and overweight induced by diet and lifestyle are considered a global epidemic by the World Health Organization (WHO), especially in western countries. They are important risk factors for several conditions, including colorectal cancer. Obese and overweight patients have already demonstrated an increased incidence and worse prognosis associated with colorectal cancer. Since discovery of ghrelin in 1999, which is a potent orexigenic hormone and releaser of the growth hormone (GH) that has many physiologic functions, several studies began to elucidate its role and importance in several areas including carcinogenesis. Recently it was demonstrated an increase on tissue ghrelin expression in colorectal cancers samples. Objectives: To investigate the impact of cafeteria diet on ghrelin expression in rectal tissue and identify the morphologic cell type. Study Design: Analytical and experimental transversal study with intervention. Methods: Twenty-four male Wistar rats were divided into 4 subgroups of 6 animals each: RCG1 (rat chow and water) and CAFG1 (cafeteria diet, rat chow and water) for a period of 30 days; RCG2 (rat chow and water) and CAFG2 (cafeteria diet, rat chow and water) for a period of 60 days. The animal and rectal weight, the number and the type of immunoreactive ghrelin cells were recorded and compared between the subgroups. ANOVA with Bonferroni correction, chi square, t student and paired t tests were applied. Results: There was a significant increase in body weight in all subgroups (P=0,001). The weight on the operation day was significantly higher in the CAFG2 in comparison with others subgroups: RCG1 (P=0,003), CAFG1 (P=0,010) and RCG2 (P=0,001). There was no difference in the total of immunoreactive cells (P=0,685), presence or absence of ghrelin expression between the subgroups (P=0, 330), nor in the final weight (P= 0,993) and rectal weight (P=0,230) in comparison with imunoexpression. All the immunoreactive cells identified were closed-type. Conclusion: The present study showed no influence of cafeteria diet on the amount of immunoreactive rectal cells of ghrelin when compared to controls and with two periods of exposure. Only one type (closed-type) of immunoreactive cells was expressed in the rectum
Hypothalamic mTOR signaling mediates the orexigenic action of ghrelin.
No full textCurrent evidence suggests that ghrelin, a stomach derived peptide, exerts its orexigenic action through specific modulation of Sirtuin1 (SIRT1)/p53 and AMP-activated protein kinase (AMPK) pathways, which ultimately increase the expression of agouti-related protein (AgRP) and neuropeptide Y (NPY) in the arcuate nucleus of the hypothalamus (ARC). However, there is a paucity of data about the possible action of ghrelin on alternative metabolic pathways at this level. Here, we demonstrate that ghrelin elicits a marked upregulation of the hypothalamic mammalian target of rapamycin (mTOR) signaling pathway. Of note, central inhibition of mTOR signaling with rapamycin decreased ghrelin's orexigenic action and normalized the mRNA expression of AgRP and NPY, as well as their key downstream transcription factors, namely cAMP response-element binding protein (pCREB) and forkhead box O1 (FoxO1, total and phosphorylated). Taken together, these data indicate that, in addition to previous reported mechanisms, ghrelin also promotes feeding through modulation of hypothalamic mTOR pathway
Syndecans modulate ghrelin receptor signaling
No full textGhrelin is a gut hormone that enhances food intake and growth hormone secretion through its G-protein coupled receptor, the growth hormone secretagogue receptor (GHSR). Recently, we have shown that ghrelin interacts with syndecans (SDCs), a family of membrane proteins known to modulate hypothalamic appetite signaling. Here, we investigated whether SDCs impact ghrelin signaling at GHSR by assessing ghrelin-induced intracellular Ca2+ mobilization (iCa2+) and inositol phosphate 1 (IP1) production in HEK293 cells. Compared with controls, the overexpression of SDCs dose-dependently increased the maximum iCa2+ response two-to four-fold, without affecting EC50. The IP1 response was similarly amplified by SDCs, but it also indicated that they reduce constitutive (ghrelin-independent) activity of GHSR. These enhanced responses occurred despite a SDC dose-dependent reduction in plasma membrane GHSR levels. Although ghrelin-stimulated Gαq activation was unaltered by SDC1 expression, it failed to restore iCa2+ responsiveness in GNAQ/11 knockout cells, indicating dependence on Gαq/11, not another Gα subunit. This suggests that SDCs modulate either signaling downstream of Gαq/11 or quenching of b-arrestin2 recruitment to GHSR. Indeed, expression of SDCs at levels that only modestly suppress cell surface receptor reduced ghrelin-induced b-arrestin2 recruitment by ∼80%. SDC co-expression also delayed the peak b-arrestin2 response. However, peak b-arrestin2 recruitment follows the peak iCa2+ response, making it unclear whether reduced b-arrestin2 recruitment potentiated Ca2+ signaling. Altogether, SDCs enhanced iCa2+/IP1 and reduced b-arrestin2 recruitment by GHSR in response to ghrelin, likely by modulating signaling downstream of Gαq. This could be a novel mechanism through which SDCs affect metabolism and obesity.</p
The Role of Ghrelin and Ghrelin Signaling in Aging
No full textWith our aging society, more people hope for a long and healthy life. In recent years, researchers have focused on healthy longevity factors. In particular, calorie restriction delays aging, reduces mortality, and extends life. Ghrelin, which is secreted during fasting, is well known as an orexigenic peptide. Because ghrelin is increased by caloric restriction, ghrelin may play an important role in the mechanism of longevity mediated by calorie restriction. In this review, we will discuss the role of orexigenic peptides with a particular focus on ghrelin. We conclude that the ghrelin-growth hormone secretagogue-R signaling pathway may play an important role in the anti-aging mechanism
AMPK-Dependent Mechanisms but Not Hypothalamic Lipid Signaling Mediates GH-Secretory Responses to GHRH and Ghrelin
No full textGH (growth hormone) secretion/action is modulated by alterations in energy homeostasis, such as malnutrition and obesity. Recent data have uncovered the mechanism by which hypothalamic neurons sense nutrient bioavailability, with a relevant contribution of AMPK (AMP-activated protein kinase) and mTOR (mammalian Target of Rapamycin), as sensors of cellular energy status. However, whether central AMPK-mediated lipid signaling and mTOR participate in the regulation of pituitary GH secretion remains unexplored. We provide herein evidence for the involvement of hypothalamic AMPK signaling, but not hypothalamic lipid metabolism or CPT-1 (carnitine palmitoyltransferase I) activity, in the regulation of GH stimulatory responses to the two major elicitors of GH release in vivo, namely GHRH (growth hormone–releasing hormone) and ghrelin. This effect appeared to be GH-specific, as blocking of hypothalamic AMPK failed to influence GnRH (gonadotropin-releasing hormone)-induced LH (luteinizing hormone) secretion. Additionally, central mTOR inactivation did not alter GH responses to GHRH or ghrelin, nor this blockade affected LH responses to GnRH in vivo. In sum, we document here for the first time the indispensable and specific role of preserved central AMPK, but not mTOR, signaling, through a non-canonical lipid signaling pathway, for proper GH responses to GHRH and ghrelin in vivo
Energy homeostasis : crosstalk between adipose tissue and the human hypothalamus
No full textThere is a worldwide epidemic of obesity. Weight rise is a consequence of
continuous positive energy balance which leads to accumulation of body fat.
Recent insights into adipose tissue (AT) biology have led to the conclusion that
the adipocyte is not just a storage depot for triglycerides but also an endocrine
organ. AT secretes proteins, such as leptin, which control central appetite
regulation in the human hypothalamus. In contrast, several other proteins and
neurotransmitters regulate central energy balance, but can also influence AT
metabolism to elicit feedback on fat accumulation. This suggests a close link
between AT and the brain within an AT-to-brain crosstalk system including
feedback circuits. This thesis examines firstly, the potential of crosstalk between
AT and the brain by other adipokines and secondly, the brain-AT crosstalk by
expression of neurotransmitters and their receptors in AT. The study establishes
the presence of the adipokines adiponectin and resistin in human cerebrospinal
fluid and immunohistochemistry showed adiponectin receptors in energy
regulating nuclei of the hypothalamus. Furthermore, this thesis established that the
orexigenic neurotransmitters NPY and ghrelin are secreted by human adipocytes,
where they enhance lipid accumulation. Further, that NPY levels increase with
obesity and its in vitro secretion is enhanced by insulin. This may play an
important role in the pathogenesis of the metabolic syndrome and may induce an
escape of the appetite behaviour towards positive energy balance. Finally, this
thesis highlights the influence of a depot-specific innervation of AT on energy
homeostasis by establishing presence of nicotinic receptors in human adipocytes,
which may play a role in smoking induced changes in adipokine secretion and fat
mass.
In conclusion, this thesis suggests a tight interplay between AT and the brain and
highlights its potential relevance in human pathophysiology
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