Effect of a high-fat diet and leptin on STAT3 phosphorylation in hippocampal astrocytes.

OBJECTIVE: The aim of the current study was to evaluate the influence of HFD on the functionality of LepR by quantifying phosphorylated levels of 705Tyr-STAT3 in hippocampus astrocytes from mice that consumed an HFD either during the juvenile or the adult period. METHODS: Five- and eight-week-old male mice, fed during 8 weeks with either control chow or HFD, received a single dose of leptin and their brains were prepared for immunofluorescence to identify double-positive GFAP/p705Tyr-STAT3 cells. RESULTS: HFD intake led to increased pSTAT3 immunoreactivity in GFAP+ cells in the CA1/CA3 hippocampus areas. The effect was observed both in adolescent and adult mice. Leptin increased pSTAT3 immunoreactivity in control animals but was devoid of effect in HFD mice. HFD itself has no effect on the number of GFAP+ cells. CONCLUSIONS: Our data show that regular intake of HFD enhances STAT3 signaling in CA1/CA3 astrocytes, an effect that could be linked to the increase of leptin triggered by HFD. The increase of pSTAT3 might be integral to homeostatic mechanisms aimed at maintaining hippocampus function.

Saturated and unsaturated fat diets impair hippocampal glutamatergic transmission in adolescent mice.

Consumption of high-fat diets (HFD) has been associated with neuronal plasticity deficits and cognitive disorders linked to the alteration of glutamatergic disorders in the hippocampus. As young individuals are especially vulnerable to the effects of nutrients and xenobiotics on cognition, we studied the effect of chronic consumption of saturated (SOLF) and unsaturated oil-enriched foods (UOLF) on: i) spatial memory; ii) hippocampal synaptic transmission and plasticity; and iii) gene expression of glutamatergic receptors and hormone receptors in the hippocampus of adolescent and adult mice. Our results show that both SOLF and UOLF impair spatial short-term memory. Accordingly, hippocampal synaptic plasticity mechanisms underlying memory, and gene expression of NMDA receptor subunits are modulated by both diets. On the other hand, PPARγ gene expression is specifically down-regulated in adolescent SOLF individuals and up-regulated in adult UOLF mice.

A novel approach to childhood obesity: circulating chemokines and growth factors as biomarkers of insulin resistance.

BACKGROUND: Insulin resistance (IR) in children with obesity constitutes a risk factor that should be precisely diagnosed to prevent further comorbidities. OBJECTIVE: Chemokines were evaluated to identify novel predictors of IR with clinical application. METHODS: We analysed the levels of cytokines (tumour necrosis factor [TNF] α and interleukins [ILs] 1ß, 4, 6 and 10), chemokines (stromal cell derived factor 1α, monocyte chemoattract protein [MCP] 1, eotaxin and fractalkine) and growth factors (brain-derived neurotrophic factor, pro-fibrotic platelet-derived growth factor [PDGF-BB] and insulin-like growth factor 1) in serum of prepubertal children with obesity (61 girls/59 boys, 50% IR and 50% non-IR) and 32 controls. Factor analysis, correlation, binary logistic regression and receiver operating characteristic analysis of combined biomarkers were used to validate their capability for preventive interventions of IR. RESULTS: Changes in MCP1, eotaxin, IL1ß and PDGF-BB were observed in IR children with obesity. Bivariate correlation between stromal cell derived factor 1α, MCP1, eotaxin, TNFα, brain-derived neurotrophic factor and/or PDGF-BB explained the high variance (65.9%) defined by three components related to inflammation and growth that contribute towards IR. The combination of leptin, triglyceride/high-density lipoprotein, insulin-like growth factor 1, TNFα, MCP1 and PDGF-BB showed a sensitivity and specificity of 93.2% for the identification of IR. The percentage of correct predictions was 89.6. CONCLUSIONS: Combined set of cytokines, adipokines and chemokines constitutes a model that predicts IR, suggesting a potential application in clinical practice as biomarkers to identify children with obesity and hyperinsulinaemia.

Metabolomics allows the discrimination of the pathophysiological relevance of hyperinsulinism in obese prepubertal children.

BACKGROUND/OBJECTIVES: Insulin resistance (IR) is the cornerstone of the obesity-associated metabolic derangements observed in obese children. Targeted metabolomics was employed to explore the pathophysiological relevance of hyperinsulinemia in childhood obesity in order to identify biomarkers of IR with potential clinical application. SUBJECTS/METHODS: One hundred prepubertal obese children (50 girls/50 boys, 50% IR and 50% non-IR in each group), underwent an oral glucose tolerance test for usual carbohydrate and lipid metabolism determinations. Fasting serum leptin, total and high molecular weight-adiponectin and high-sensitivity C-reactive protein (CRP) levels were measured and the metabolites showing significant differences between IR and non-IR groups in a previous metabolomics study were quantified. Enrichment of metabolic pathways (quantitative enrichment analysis) and the correlations between lipid and carbohydrate metabolism parameters, adipokines and serum metabolites were investigated, with their discriminatory capacity being evaluated by receiver operating characteristic (ROC) analysis. RESULTS: Twenty-three metabolite sets were enriched in the serum metabolome of IR obese children (P<0.05, false discovery rate (FDR)<5%). The urea cycle, alanine metabolism and glucose-alanine cycle were the most significantly enriched pathways (PFDR<0.00005). The high correlation between metabolites related to fatty acid oxidation and amino acids (mainly branched chain and aromatic amino acids) pointed to the possible contribution of mitochondrial dysfunction in IR. The degree of body mass index-standard deviation score (BMI-SDS) excess did not correlate with any of the metabolomic components studied. In the ROC analysis, the combination of leptin and alanine showed a high IR discrimination value in the whole cohort (area under curve, AUCALL=0.87), as well as in boys (AUCM=0.84) and girls (AUCF=0.91) when considered separately. However, the specific metabolite/adipokine combinations with highest sensitivity were different between the sexes. CONCLUSIONS: Combined sets of metabolic, adipokine and metabolomic parameters can identify pathophysiological relevant IR in a single fasting sample, suggesting a potential application of metabolomic analysis in clinical practice to better identify children at risk without using invasive protocols.

Insulin resistance in prepubertal obese children correlates with sex-dependent early onset metabolomic alterations.

BACKGROUND: Insulin resistance (IR) is usually the first metabolic alteration diagnosed in obese children and the key risk factor for development of comorbidities. The factors determining whether or not IR develops as a result of excess body mass index (BMI) are still not completely understood. OBJECTIVES: This study aimed to elucidate the mechanisms underpinning the predisposition toward hyperinsulinemia-related complications in obese children by using a metabolomic strategy that allows a profound interpretation of metabolic profiles potentially affected by IR. METHODS: Serum from 60 prepubertal obese children (30 girls/30 boys, 50% IR and 50% non-IR in each group, but with similar BMIs) were analyzed by using liquid chromatography-mass spectrometry, gas chromatography-mass spectrometry and capillary electrophoresis-mass spectrometry following an untargeted metabolomics approach. Validation was then performed on a group of 100 additional children with the same characteristics. RESULTS: When obese children with and without IR were compared, 47 metabolites out of 818 compounds (P<0.05) obtained after data pre-processing were found to be significantly different. Bile acids exhibit the greatest changes (that is, approximately a 90% increase in IR). The majority of metabolites differing between groups were lysophospholipids (15) and amino acids (17), indicating inflammation and central carbon metabolism as the most altered processes in impaired insulin signaling. Multivariate analysis (OPLS-DA models) showed subtle differences between groups that were magnified when females were analyzed alone. CONCLUSIONS: Inflammation and central carbon metabolism, together with the contribution of the gut microbiota, are the most altered processes in obese children with impaired insulin signaling in a sex-specific fashion despite their prepubertal status.

Exposure to increased levels of estradiol during development can have long-term effects on the response to undernutrition in female rats.

OBJECTIVES: Undernutrition during development alters the expression of peptides that control energy expenditure and feeding behavior. Estrogens can also modulate these peptides. Here, we analyze whether the early postnatal administration of estradiol modulates the effects of undernutrition on neuroendocrine parameters in adult female Wistar rats. METHODS: Control rats were fed a control diet. Undernourished pups were submitted to a restricted diet with half of the undernourished rats receiving 0.4 mg/kg s.c. of estradiol benzoate (EB) from postnatal day (P) 6 until P13. Quantitative real-time polymerase chain reaction was performed to determine expression in the hypothalamus of agouti-related peptide (AgRP), proopiomelanocortin (POMC), neuropeptide Y (NPY), and cocaine- and amphetamine-regulated transcript. Plasma estradiol, testosterone, and adiponectin levels were measured by enzyme-linked immunosorbent assay. Total and acylated ghrelin levels were measured in plasma by radioimmunoassay. Insulin and leptin were measured by mulitplex immunoassays. RESULTS: Undernourishment decreased body weight, fat mass, plasma leptin and insulin levels, and hypothalamic POMC mRNA levels. An increase in orexigenic signals AgRP and NPY mRNA levels, and in plasma adiponectin levels were found in undernourished animals. Early postnatal treatment with EB to undernourished female rats reversed the effects of undernutrition on adult hypothalamic POMC mRNA levels. In addition, neonatal EB treatment to undernourished females significantly decreased adult plasma testosterone, estradiol, and acylated ghrelin levels. DISCUSSION: Our results suggest that increased estradiol during a critical period of development has the capacity to modulate the alterations that undernutrition produces on energy metabolism.

The metabolic response to postnatal leptin in rats varies with age and may be litter dependent.

Hyperleptinemia during postnatal life induces long-term effects on metabolism. However, these effects are controversial as both increased and decreased propensity towards obesity has been reported. To further analyze the effects of chronic neonatal hyperleptinemia on the subsequent metabolic profile, male Wistar rats proceeding from 18 different litters (8 pups/litter) received a daily subcutaneous injection of either saline (10 ml/kg, n=36) or leptin (3 µg/g, n=36) from postnatal day (PND) 2 to PND9. Rats were sacrificed at 10, 40, or 150 days of age. At 10 days of age, leptin treated rats had decreased body weight (p<0.001) and body fat (p<0.05). Leptin levels and glycemia were increased (p<0.01), whereas insulin, total lipids, triglycerides and glycerol levels were decreased (p<0.05). At PND40 rats receiving leptin had increased glycemia (p<0.01) and plasma HDL and LDL levels, but decreased total lipids (p<0.05). At PND150 neonatal leptin treatment induced different effects in rats raised in different litters. Rats from litter 1 had increased body weight (p<0.05), body fat (p<0.01), and plasma leptin (p<0.001), cholesterol (p<0.001), triglyceride (p<0.001), total lipid (p<0.001), LDL (p<0.05), and glycerol (p<0.001) levels. In rats from litter 2 these parameters did not differ from controls. Rats from litter 3 had decreased body weight (p<0.05), visceral fat (p<0.01) and plasma leptin (p<0.001), cholesterol (p<0.001), triglyceride (p<0.001), glycerol (p<0.001), and HDL (p<0.001) levels. In conclusion, the metabolic response to postnatal leptin varies with age, with the response in adulthood being variable and most likely influenced by other factors, including the genetic make-up.

Estrogen, astrocytes and the neuroendocrine control of metabolism.

Obesity, and its associated comorbidities such as type 2 diabetes, cardiovascular diseases, and certain cancers, represent major health challenges. Importantly, there is a sexual dimorphism with respect to the prevalence of obesity and its associated metabolic diseases, implicating a role for gonadal hormones. Specifically, estrogens have been demonstrated to regulate metabolism perhaps by acting as a leptin mimetic in the central nervous system (CNS). CNS estrogen receptors (ERs) include ER alpha (ERα) and ER beta (ERß), which are found in nuclear, cytoplasmic and membrane sites throughout the brain. Additionally, estrogens can bind to and activate a G protein-coupled estrogen receptor (GPER), which is a membrane-associated ER. ERs are expressed on neurons as well as glia, which are known to play a major role in providing nutrient supply for neurons and have recently received increasing attention for their potentially important involvement in the CNS regulation of systemic metabolism and energy balance. This brief overview summarizes data focusing on the potential role of astrocytic estrogen action as a key component of estrogenic modulation responsible for mediating the sexual dimorphism in body weight regulation and obesity.

Acute up-regulation of the rat brain somatostatin receptor-effector system by leptin is related to activation of insulin signaling and may counteract central leptin actions.

Leptin and somatostatin (SRIF) have opposite effects on food seeking and ingestive behaviors, functions partially regulated by the frontoparietal cortex and hippocampus. Although it is known that the acute suppression of food intake mediated by leptin decreases with time, the counter-regulatory mechanisms remain unclear. Our aims were to analyze the effect of acute central leptin infusion on the SRIF receptor-effector system in these areas and the implication of related intracellular signaling mechanisms in this response. We studied 20 adult male Wister rats including controls and those treated intracerebroventricularly with a single dose of 5 µg of leptin and sacrificed 1 or 6h later. Density of SRIF receptors was unchanged at 1h, whereas leptin increased the density of SRIF receptors at 6h, which was correlated with an elevated capacity of SRIF to inhibit forskolin-stimulated adenylyl cyclase activity in both areas. The functional capacity of SRIF receptors was unaltered as cell membrane levels of αi1 and αi2 subunits of G inhibitory proteins were unaffected in both brain areas. The increased density of SRIF receptors was due to enhanced SRIF receptor subtype 2 (sst2) protein levels that correlated with higher mRNA levels for this receptor. These changes in sst2 mRNA levels were concomitant with increased activation of the insulin signaling, c-Jun and cyclic AMP response element-binding protein (CREB); however, activation of signal transducer and activator of transcription 3 was reduced in the cortex and unchanged in the hippocampus and suppressor of cytokine signaling 3 remained unchanged in these areas. In addition, the leptin antagonist L39A/D40A/F41A blocked the leptin-induced changes in SRIF receptors, leptin signaling and CREB activation. In conclusion, increased activation of insulin signaling after leptin infusion is related to acute up-regulation of the SRIF receptor-effector system that may antagonize short-term leptin actions in the rat brain.

Neonatal treatment with a pegylated leptin antagonist has a sexually dimorphic effect on hypothalamic trophic factors and neuropeptide levels.

It is clear that the prenatal and early neonatal environments are important for determining the metabolic equilibrium in the adult animal, with prenatal/neonatal leptin levels being at least one of the factors involved. Leptin modulates hypothalamic development and, in particular, the neuronal circuits involved in metabolic control. We have recently reported that maternal deprivation (MD) for 24 h on postnatal day (PND) 9 modifies trophic factors and markers of cell turnover and neuronal maturation in the hypothalamus, as well as body weight and circulating leptin levels at PND13, with long- term effects on weight gain and circulating metabolic hormones in the adult. Moreover, these responses are sexually dimorphic. During MD, a dramatic decline in leptin levels is observed; thus, we aimed to determine which of the previously observed changes in markers of hypothalamic development might be attributed to the decline in this metabolic signal. Accordingly, male and female rats were treated with a pegylated leptin antagonist on PND9. In both sexes, hypothalamic signal transducer and activator of transcription 3 activation in response to acute leptin treatment was blocked by the antagonist. In females, hypothalamic mRNA levels for brain-derived neurotrophic factor, cocaine- and amphetamine-regulated transcript and the leptin receptor were increased, as were nestin and vimentin levels. There was also an increase in cell death in the hypothalamus, with a shift towards an anti-apoptotic balance in the Bcl2/BAX ratio. No hypothalamic effects were seen in males. Because antagonism of the actions of leptin at this specific neonatal stage affects hypothalamic cell turnover and maturation in a sex-specific manner, changes in this hormone, at least at this postnatal age, may differentially affect hypothalamic development in males and females, and may explain some of the reported sexually dimorphic responses to modifications in the early nutritional environment.

Activation of microglia in specific hypothalamic nuclei and the cerebellum of adult rats exposed to neonatal overnutrition.

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.

Metabolic signals in human puberty: effects of over and undernutrition.

Puberty in mammals is associated with important physical and psychological changes due to the increase in sex steroids and growth hormone (GH). Indeed, an increase in growth velocity and the attainment of sexual maturity for future reproductive function are the hallmark changes during this stage of life. Both growth and reproduction consume high levels of energy, requiring suitable energy stores to face these physiological functions. During the last two decades our knowledge concerning how peptides produced in the digestive tract (in charge of energy intake) and in adipose tissue (in charge of energy storage) provide information regarding metabolic status to the central nervous system (CNS) has increased dramatically. Moreover, these peptides have been shown to play an important role in modulating the gonadotropic axis with their absence or an imbalance in their secretion being able to disturb pubertal onset or progression. In this article we will review the current knowledge concerning the role played by leptin, the key adipokine in energy homeostasis, and ghrelin, the only orexigenic and growth-promoting peptide produced by the digestive tract, on sexual development. The normal evolutionary pattern of these peripherally produced metabolic signals throughout human puberty will be summarized. The effect of two opposite situations of chronic malnutrition, obesity and anorexia, on these signals and how they influence the course of puberty will also be discussed. Finally, we will briefly mention other peptides derived from the digestive tract (such as PYY) that may be involved in the regulatory link between energy homeostasis and sexual development.

Control neuroendocrino de la secreción de hormona de crecimiento / Neuroendocrine control of the growth hormone secretion

Los principales factores hipotalámicos para la secreción de hormona de crecimiento (GH) hipofisaria están constituidos por las neuronas de GHRH del núcleo arcuato y las neuronas de SS en el núcleo periventricular. Aunque existen otros neuropéptidos, neurotransmisores y fracturas localmente producidos que pueden modular la secreción de GH, la mayor parte de este efecto está mediado a través de las neuronas de GHRH y/o SS. Además, los factores circulantes y las hormonas que modulan la síntesis de GH pueden también modular la síntesis y secreción de GH mediante un efecto directo en la célula somatotropa, muy frecuentemente regulando la respuesta de las células somatotropas a SS o GHRRH o bien en el hipotálamo. La relevancia fisiológica de la proteína ghreline en la regulación de la secreción de GH, especialmente en el hipotálamo, debe aún clarificarse. Esta revisión proporciona una perspectiva histórica en el descubrimiento de la importancia del hipotálamo en el control de la secreción de GH, así como en el aislamiento e identificación de factores involucrados en este proceso. Además, se efectúa una breve descripción de los moduladores más relevantes, tanto centrales como periféricos, y sus posibles mecanismos de acción (AU)

It is clear that the main hypothalamic regulators of pituitary growth hormone secretion are GHRH neurons of the arcuate nucleus and SS neurons in the periventricular nucleus. Although numerous other neuropeptides, neurotransmitters and locally produced factors may modulate GH secretion, much of this effect is mediated through either GHRH and/or SS neurons. Furthermore, the circulating factors and hormones that modulate GH synthesis and secretion can do so either by a direct effect at the somatotroph, often modulating the somatotroph´s response to SS or GHRH, or at the level of the hypothalamus. The physiological role of ghrelin in the regulation of GH secretion, especially at the level of the hypothalamus, remains to be totally clarified. This review gives a bit of historical perspective in the discovery of how the hypothalamus was found to be important in the control of growth and GH secretion, as well as the isolation of the factors involved in this process. In addition, a brief description of the main modulators, both central and peripheral, and their possible mechanisms of action in given (AU)

Ghrelin treatment protects lactotrophs from apoptosis in the pituitary of diabetic rats.

Poorly controlled diabetes is associated with hormonal imbalances, including decreased prolactin production partially due to increased lactotroph apoptosis. In addition to its metabolic actions, ghrelin inhibits apoptosis in several cell types. Thus, we analyzed ghrelin's effects on diabetes-induced pituitary cell death and hormonal changes. Six weeks after onset of diabetes in male Wistar rats (streptozotocin 70 mg/kg), minipumps infusing saline or 24 nmol ghrelin/day were implanted (jugular). Rats were killed two weeks later. Ghrelin did not modify body weight or serum glucose, leptin or adiponectin, but increased total ghrelin (P<0.05), IGF-I (P<0.01) and prolactin (P<0.01) levels. Ghrelin decreased cell death, iNOS and active caspase-8 (P<0.05) and increased prolactin (P<0.05), Bcl-2 (P<0.01) and Hsp70 (P<0.05) content in the pituitary. In conclusion, ghrelin prevents diabetes-induced death of lactotrophs, decreasing caspase-8 activation and iNOS content and increasing anti-apoptotic pathways such as pituitary Bcl-2 and Hsp70 and serum IGF-I concentrations.

Death of hypothalamic astrocytes in poorly controlled diabetic rats is associated with nuclear translocation of apoptosis inducing factor.

Astrocytes in the hypothalamus of poorly controlled diabetic rats are reduced in number, due to increased apoptosis and decreased proliferation, and undergo morphological changes, including a decrease in projections. These changes are associated with modifications in synaptic proteins and most likely affect neuroendocrine signalling and function. The present study aimed to determine the intracellular mechanisms underlying this increase in hypothalamic cell death. Adult male Wistar rats were injected with streptozotocin (70 mg/kg, i.p) and controls received vehicle. Rats were killed at 1, 4, 6 and 8 weeks after diabetes onset (glycaemia > 300 mg/dl). Cell death, as detected by enzyme-linked immunosorbent assay, increased at 4 weeks of diabetes. Immunohistochemistry and terminal dUTP nick-end labelling (TUNEL) assays indicated that these cells corresponded to glial fibrillary acidic protein (GFAP) positive cells. No significant change in fragmentation of caspases 2, 3, 6, 7, 8, 9, or 12 was observed with western blot analysis. However, enzymatic assays indicated that caspase 3 activity increased significantly after 1 week of diabetes and decreased below control levels thereafter. In the hypothalamus, cell bodies lining the third ventricle, fibres radiating from the third ventricle and GFAP positive cells expressed fragmented caspase 3, with this labelling increasing at 1 week of diabetes. However, because no nuclear labelling was observed and this increase in activity did not correlate temporally with the increased cell death, this caspase may not be involved in astrocyte death. By contrast, nuclear translocation of apoptosis inducing factor (AIF) increased significantly in astrocytes in parallel with the increase in death and AIF was found in TUNEL positive cells. Thus, nuclear translocation of AIF could underlie the increased death, whereas fragmentation of caspase 3 could be associated with the morphological changes found in hypothalamic astrocytes of diabetic rats.

Neurorregulación de la obesidad / Neuroregulation of obesity

Debido al rápido aumento de la incidencia de obesidad en los países desarrollados con el consiguiente riesgo para la salud, también han aumentado los fondos dedicados a la investigación biomédica y al desarrollo de medicinas en el área de metabolismo y el apetito. Esto ha aumentado dramáticamente el conocimiento del control neuroendocrino de estos mecanismos. Los primeros estudios que aparecieron en la literatura describiendo al hipotálamo como un órgano fundamental en el control del peso corporal y el apetito son de hace 60 años. Actualmente conocemos algunas de las poblaciones neuronales y las conexiones implicadas en este proceso. La presente revisión describe brevemente las poblaciones neuronales más importantes relacionadas con el control metabólico, como son las del neuropéptido. Y las del propio melanocortina y sus interconexiones. Asimismo, se discute algunos de los factores centrales que recientemente han sido descritos como necesarios para un ajuste fino del sistema metabólico como son los endocanabinoides. Finalmente, se discute cómo los cambios en el ambiente local durante el desarrollo prenatal o neonatal podrían influir posteriormente en el sistema neuroendocrino del adulto haciéndolo más susceptible de padecer obesidad (AU)

Due to the rapidly increasing incidence of obesity in developing countries and the associated health risks, funding for biomedical research and drug development in the area of metabolism and appetite has also increased considerably. This has added dramatically to our understanding of the neuroendocrine control of these mechanisms. It has been over 60 years since the first descriptions of body weight and appetite appeared in the scientific literature. We now know some of the important neuronal populations and connections involved in this process. This review will briefly describe some of the most important neuronal populations involved in metabolic control, such as hypothalamic neuropeptide Y and proopiomelanocortin producing neurons, and their interconnections. We will also discuss briefly some of the central factors that have more recently been drawn to the forefront as being important for fine-tuning the metabolic system, such as the endogenous cannabinoids. Finally, we will briefly discuss how during prenatal or neonatal development changes in the local environment could have lasting influences on the neuroendocrien system in the adult animal, making it more susceptible to becoming overweight (AU)

Growth hormone-releasing peptide-6 increases insulin-like growth factor-I mRNA levels and activates Akt in RCA-6 cells as a model of neuropeptide Y neurones.

Chronic systemic administration of growth hormone (GH)-releasing peptide-6 (GHRP-6), an agonist for the ghrelin receptor, to normal adult rats increases insulin-like growth factor (IGF)-I mRNA and phosphorylated Akt (pAkt) levels in various brain regions, including the hypothalamus. Because neuropeptide Y (NPY) neurones of the arcuate nucleus express receptors for ghrelin, we investigated whether these neurones increase their IGF-I and p-Akt levels in response to this agonist. In control rats, immunoreactive pAkt was practically undetectable; however, GHRP-6 increased p-Akt immunoreactivity in the arcuate nucleus, with a subset of neurones also being immunoreactive for NPY. Immunoreactivity for IGF-I was detected in NPY neurones in both experimental groups. To determine if activation of this intracellular pathway is involved in modulation of NPY synthesis RCA-6 cells, an embryonic rat hypothalamic neuronal cell line that expresses NPY was used. We found that GHRP-6 stimulates NPY and IGF-I mRNA synthesis and activates Akt in this cell line. Furthermore, inhibition of Akt activation by LY294002 treatment did not inhibit GHRP-6 induction of NPY or IGF-I synthesis. These results suggest that some of the effects of GHRP-6 may involve stimulation of local IGF-I production and Akt activation in NPY neurones in the arcuate nucleus. However, GHRP-6 stimulation of NPY production does not involve this second messenger pathway.

Función de la proteína ghrelin en la regulación de la proliferación celular / Function of ghrelin proteína in the regulation of cellular proliferation

La proteína “ghrelin” es una hormona de 28 aminoácidos, sintetizada principalmente en las células oxínticas de la mucosa gástrica en el adulto y los islotes pancreáticos en la vida intrauterina, aunque su síntesis en muy ubicua. Ejerce una potente acciónorexígena e inductora de la secreción de hormona crecimiento (GH), modulando, además, distintos procesos fisiológicos y patológicos. El objetivo de esta revisión es el de analizar la función que esta proteína desempeña como moduladora de la proliferación celular, principalmente a cuatro niveles: en el desarrollo embrionario del páncreas, en la protección de este frente a agresiones, en el tejido adiposo y en distintos tipos de tumores (AU)

Ghrelin is a 28 aminoacid hormone, synthesized mainly by the oxintic cells of gastric mucosa in the adult, and by the pancreatic islets during fetal life, although its synthesis is very ubiquitous. It exerts a potent orexigenic action, induces the secretion of growth hormone (GH) and it modulates different physiological and pathological processes. The aim of this review is to analyze the role which this protein plays as modulator of cellular proliferation at four different levels: the pancreatic embrionary development, the protective effect on the injured pancreas, the adipose tissue and in different types of tumors (AU)

Oestrogen requires the insulin-like growth factor-I receptor for stimulation of prolactin synthesis via mitogen-activated protein kinase.

Sex steroids and growth factors interact at the intracellular level in a variety of tissues to control numerous physiological functions. Oestrogen is known to stimulate prolactin synthesis and secretion, but the effect of insulin-like growth factor (IGF)-I is less clear. We used GH3 cells, a somatolactotroph cell line, to study the interaction of 17beta-oestradiol (E(2)) and IGF-I on prolactin protein levels and the intracellular mechanisms involved. Cell cultures were treated with E(2) (10 nM) and/or IGF-I (10 ng/ml) for 8 h. The real-time reverse transcriptase-polymerase chain reaction, Western blot and enzyme-immunoassay were used to determine changes in prolactin mRNA and protein levels. At this time-point, there were no significant changes in cell number, prolactin mRNA expression, or the amount of secreted prolactin. However, E(2) increased intracellular prolactin concentrations. IGF-I alone had no effect, but blocked the stimulatory effect of E(2). MAPK (ERK1/2) activation, as determined by Western blot analysis, increased with both E(2) and IGF-I, but not with the combination of these factors. The MAPK inhibitor PD98059 blocked the ability of E(2) to increase intracellular prolactin concentrations. Similarly, the IGF-I receptor antagonist, JB1, blocked the effect of E(2) on prolactin synthesis and MAPK activation, as did the oestrogen receptor antagonist ICI182 780. These results suggest that, to stimulate prolactin synthesis, E(2) activates the MAPK cascade and that this requires the presence of both oestrogen and IGF-I receptors.

The number of lactotrophs is reduced in the anterior pituitary of streptozotocin-induced diabetic rats.

AIMS/HYPOTHESIS: Prolactin secretion is often reduced in insulin dependent diabetes mellitus, but little is known about the mechanism involved. Since changes in the hormonal environment modulate cell proliferation, death and cellular makeup of the anterior pituitary, we have analysed whether the number of lactotrophs is reduced in diabetic rats. METHODS: Streptozotocin induced diabetic rats were maintained hyperglycaemic for 2 months. Pituitary prolactin, growth hormone, Bcl-2, Bax and PCNA concentrations were analysed by western blot analysis. In situ hybridisation was used for quantification of prolactin and growth hormone mRNA containing cells. Cell death was detected by TUNEL labelling, alone and in combination with immunocytochemistry for prolactin or growth hormone. RESULTS: Diabetic rats had fewer lactotrophs ( p<0.01). This was coincident with a decrease in overall protein and prolactin content. An increase in pituitary cell death was found and some of the TUNEL labelling co-localised with prolactin immunostaining. No change in the concentration of Bcl-2 or Bax, proteins implicated in apoptosis, was detected. PCNA content was higher in the pituitaries of diabetic rats, suggesting increased proliferation. CONCLUSION/INTERPRETATION: Anterior pituitary cell turnover is affected in poorly controlled diabetes mellitus. A decrease in the number of lactotrophs, as a result of increased cell death, could underlie, at least in part, the reduction in prolactin secretion observed in diabetic animals.