RESUMEN
Polymorphisms in genes of leptin-melanocortin and insulin pathways have been associated with obesity and type 2 diabetes. We hypothesized that polymorphisms in IRS1, IRS2, MC3R, and MC4R influence metabolic and inflammatory markers and food intake composition in Brazilian subjects. This exploratory pilot study included 358 adult subjects. Clinical, anthropometric, and laboratory data were obtained through interview and access to medical records. The variants IRS1 rs2943634 AËC, IRS2 rs1865434 C>T, MC3R rs3746619 C>A, and MC4R rs17782313 T>C were analyzed by real-time polymerase chain reaction. Food intake composition was assessed in a group of subjects with obesity (n = 84) before and after a short-term nutritional counseling program (9 weeks). MC4R rs17782313 was associated with increased risk of obesity (P = .034). Multivariate linear regression analysis adjusted by covariates indicated associations of IRS2 rs1865434 with reduced low-density lipoprotein cholesterol and resistin, MC3R rs3746619 with high glycated hemoglobin, and IRS1 rs2943634 and MC4R rs17782313 with increased high-sensitivity C-reactive protein (P < .05). Energy intake and carbohydrate and total fat intakes were reduced after the diet-oriented program (P < .05). Multivariate linear regression analysis showed associations of IRS2 rs1865434 with high basal fiber intake, IRS1 rs2943634 with low postprogram carbohydrate intake, and MC4R rs17782313 with low postprogram total fat and saturated fatty acid intakes (P < .05). Although significant associations did not survive correction for multiple comparisons using the Benjamini-Hochberg method in this exploratory study, polymorphisms in IRS1, IRS2, MC3R, and MC4R influence metabolic and inflammatory status in Brazilian adults. IRS1 and MC4R variants may influence carbohydrate, total fat, and saturated fatty acid intakes in response to a diet-oriented program in subjects with obesity.
Asunto(s)
Diabetes Mellitus Tipo 2 , Adulto , Humanos , Proyectos Piloto , Diabetes Mellitus Tipo 2/genética , Polimorfismo de Nucleótido Simple , Brasil , Obesidad/genética , Obesidad/metabolismo , Ingestión de Alimentos , Carbohidratos , Ácidos Grasos , Receptor de Melanocortina Tipo 4/genética , Receptor de Melanocortina Tipo 4/metabolismo , Proteínas Sustrato del Receptor de Insulina/genética , Proteínas Sustrato del Receptor de Insulina/metabolismo , Receptor de Melanocortina Tipo 3/genética , Receptor de Melanocortina Tipo 3/metabolismoRESUMEN
OBJECTIVE: The melanocortin 4 receptor (MC4R) is a G protein-coupled receptor that plays major roles in the central control of energy balance. Loss-of-function mutations of MC4R constitute the most common monogenic cause of early-onset extreme obesity in humans, whereas gain-of-function mutations appear to be protective. In particular, two relatively frequent alleles carrying the non-synonymous coding mutations V103I or I251L are associated with lower risks of obesity and type-2 diabetes. Although V103I and I251L MC4Rs showed more efficient signalling in transfected cells, their specific effects in live animals remain unexplored. Here, we investigated whether the introduction of V103I and I251L mutations into the mouse MC4R leads to a lean phenotype and provides protection against an obesogenic diet. METHODS: Using CRISPR/Cas9, we generated two novel strains of mice carrying single-nucleotide mutations into the mouse Mc4r which are identical to those present in V103I and I251L MCR4 human alleles, and studied their phenotypic outcomes in mice fed with normal chow or a high-fat diet. In particular, we measured body weight progression, food intake and adiposity. In addition, we analysed glucose homeostasis through glucose and insulin tolerance tests. RESULTS: We found that homozygous V103I females displayed shorter longitudinal length and decreased abdominal white fat, whereas homozygous I251L females were also shorter and leaner due to decreased weight in all white fat pads examined. Homozygous Mc4rV103I/V103I and Mc4rI251L/I251L mice of both sexes showed improved glucose homeostasis when challenged in a glucose tolerance test, whereas Mc4rI251L/I251L females showed improved responses to insulin. Despite being leaner and metabolically more efficient, V103I and I251L mutants fed with a hypercaloric diet increased their fasting glucose levels and adiposity similar to their wild-type littermates. CONCLUSIONS: Our results demonstrate that mice carrying V103I and I251L MC4R mutations displayed gain-of-function phenotypes that were more evident in females. However, hypermorphic MC4R mutants were as susceptible as their control littermates to the obesogenic and diabetogenic effects elicited by a long-term hypercaloric diet, highlighting the importance of healthy feeding habits even under favourable genetic conditions.
Asunto(s)
Adiposidad/genética , Receptor de Melanocortina Tipo 4/metabolismo , Aumento de Peso/genética , Adiposidad/fisiología , Animales , Dieta Alta en Grasa , Metabolismo Energético , Femenino , Mutación con Ganancia de Función/genética , Glucosa/metabolismo , Homeostasis/genética , Humanos , Insulina/metabolismo , Masculino , Ratones , Ratones Transgénicos , Obesidad/genética , Receptor de Melanocortina Tipo 4/genéticaRESUMEN
Excessive alcohol intake affects hippocampal function and neuronal communication through oxidative stress and mitochondrial impairment. Previous studies have suggested that the melanocortin system (MCS) plays an essential role in alcohol consumption and addiction. The MCS is a hypothalamic region involved in regulating inflammatory processes in the brain, and its pharmacological activation through the melanocortin-4 receptor (MC4R) reduces both alcohol consumption and the neuroinflammatory responses in the brain. However, the cellular mechanisms involved in the beneficial actions of MCS against ethanol toxicity are not entirely understood. The objective of this study was to investigate the protective role of the MC4R pharmacological activator RO27-3225 on oxidative damage and mitochondrial impairment present in hippocampal neuronal cultures acutely exposed to ethanol (50, 75 mM, 24 h). Pre-treatment with RO27-3225 (250 nM, 1 h) prevented reactive oxygen species (ROS) increase, dysregulation of cytosolic calcium homeostasis, and mitochondrial potential loss induced by ethanol. Improvement of mitochondrial failure produced by RO27-3225 was accompanied by a significant increase in ATP production in ethanol-treated neurons. More importantly, RO27-3225 promoted the activation of the antioxidant pathway Nrf-2, demonstrated by an increase in the expression and nuclear translocation of Nrf-2, and upregulation of mRNA levels of NAD(P)H quinone oxidoreductase 1 (NQO1), an antioxidant enzyme which expression is activated by this pathway. These results suggest that the stimulation of MC4R prevents oxidative damage and mitochondrial stress induced by ethanol through the activation of the Nrf-2 pathway in cultured hippocampal neurons. These results are novel and demonstrate the critical function of MC4R in promoting antioxidant defense and reducing mitochondrial damage produced by ethanol in the brain.
Asunto(s)
Calcio/metabolismo , Potencial de la Membrana Mitocondrial/fisiología , Mitocondrias/metabolismo , Neuronas/metabolismo , Fármacos Neuroprotectores/farmacología , Estrés Oxidativo/fisiología , Péptidos/farmacología , Receptor de Melanocortina Tipo 4/metabolismo , Animales , Antioxidantes , Células Cultivadas , Depresores del Sistema Nervioso Central/toxicidad , Etanol/toxicidad , Hipocampo/citología , Inflamación/metabolismo , Potencial de la Membrana Mitocondrial/efectos de los fármacos , Mitocondrias/efectos de los fármacos , NAD(P)H Deshidrogenasa (Quinona)/efectos de los fármacos , NAD(P)H Deshidrogenasa (Quinona)/genética , Factor 2 Relacionado con NF-E2/efectos de los fármacos , Factor 2 Relacionado con NF-E2/metabolismo , Neuronas/efectos de los fármacos , Estrés Oxidativo/efectos de los fármacos , ARN Mensajero/efectos de los fármacos , ARN Mensajero/metabolismo , Ratas , Especies Reactivas de Oxígeno/metabolismo , Receptor de Melanocortina Tipo 4/agonistasRESUMEN
The central melanocortin system is composed of neurons that express either the proopiomelanocortin (POMC) or the agouti-related protein (AgRP). POMC is cleaved in bioactive peptides, including the α-melanocyte-stimulating hormone (α-MSH). α-MSH activates the melanocortin-4 receptor (MC4R) inducing satiety, whereas AgRP acts as an inverse agonist of MC4R. However, only limited information is available regarding possible area-specific differences in the interaction between α-MSH and AgRP terminals on MC4R-expressing cells. Therefore, the objective of the present study was to compare the distribution pattern of α-MSH and AgRP terminals on the perikarya of MC4R-expressing neurons. We performed a triple-label immunofluorescence reaction in brain series of MC4R-reporter mice to visualize MC4R-expressing neurons together with AgRP and α-MSH terminals. POMC and AgRP neurons project to areas that contain MC4R-expressing cells, although several brain nuclei exhibit AgRP and α-MSH terminals, but they do no express MC4R, while other brain areas contain MC4R-expressing cells and receive no apparent innervation of AgRP and POMC neurons. AgRP terminals make more presumptive appositions than α-MSH on the soma of MC4R-expressing neurons of the medial preoptic area and paraventricular nucleus of the hypothalamus (Pa). Additionally, a higher percentage of MC4R cells receive at least one presumptive apposition from AgRP terminals in the median preoptic nucleus and Pa, compared to α-MSH appositions. Thus, our study revealed area-specific differences in the interaction between α-MSH and AgRP terminals and the soma of MC4R-expressing neurons. These findings provide new insights about the relationship between first- and second-order neurons of the central melanocortin system.
Asunto(s)
Proteína Relacionada con Agouti/metabolismo , Receptor de Melanocortina Tipo 4/metabolismo , alfa-MSH/metabolismo , Animales , Axones/metabolismo , Encéfalo/metabolismo , Ingestión de Alimentos/fisiología , Metabolismo Energético/fisiología , Hipotálamo/metabolismo , Leptina/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Neuronas/metabolismo , Núcleo Hipotalámico Paraventricular/metabolismoRESUMEN
α-Melanocyte stimulating hormone (α-MSH) is a melanocortin which exerts potent anti-inflammatory and anti-apoptotic effects. Melanocortin 4 receptors (MC4R) are abundantly expressed in the brain and we previously demonstrated that [Nle(4), D-Phe(7)]melanocyte-stimulating hormone (NDP-MSH), an α-MSH analogue, increased expression of brain derived-neurotrophic factor (BDNF), and peroxisome proliferator-activated receptor-γ (PPAR-γ). We hypothesized that melanocortins could affect striatal cell survival through BDNF and PPAR-γ. First, we determined the expression of these factors in the striatum. Acute intraperitoneal administration (0.5â¯mg/kg) of α-MSH increased the levels of BDNF mRNA in rat striatum but not in rat cerebral cortex. Also, protein expression of PPAR-γ and MC4R was increased by acute treatment with α-MSH in striatum but not in cortex. No changes were observed by 48â¯h treatment. Next, we evaluated melanocortins effect on neuron and glial survival. 3-nitropropionic acid (3-NP), which is known to induce striatal degeneration, was used to induce cell death in the rat striatal cell line ST14A expressing mutant human huntingtin (Q120) or in ST14A cells expressing normal human huntingtin (Q15), in primary cultured astrocytes, and in BV2 cells. NDP-MSH protected Q15 cells, astrocytes and BV2 cells from death by 3-NP whereas it did not fully protect Q120 cells. Protection of Q15 cells and astrocytes was blocked by a MC4R specific inhibitor (JKC-363) and a PPAR-γ antagonist (GW9662). The BDNF receptor antagonist (ANA-12) abolished NDP-MSH protective effect in astrocytes but not in Q15 cells. We demonstrate for the first time that melanocortins, acting through PPAR-γ and BDNF, protect neurons and glial cells from 3-NP toxicity.
Asunto(s)
Astrocitos/efectos de los fármacos , Neuroglía/efectos de los fármacos , Neuronas/efectos de los fármacos , Nitrocompuestos/farmacología , Propionatos/farmacología , Receptor de Melanocortina Tipo 4/metabolismo , Animales , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Hormonas Estimuladoras de los Melanocitos/efectos de los fármacos , Ratas WistarRESUMEN
Brown adipose tissue (BAT) dysfunction is associated with obesity and its comorbidities, such as hypertension, and the improvement of BAT function seems important for obesity management. Here we investigated the effects of dietary calcium supplementation on BAT autonomic nerve activity, sympathoadrenal function and cardiovascular parameters in adult obese rats that were raised in small litters (SL group). Three days after birth, SL litters were adjusted to three pups to induce early overfeeding. The control group remained with 10 pups/litter until weaning (NL group). At PN120, the SL group was randomly divided into the following: rats fed with standard chow (SL) and rats fed with dietary calcium carbonate supplementation (SL-Ca, 10g/kg chow). Animals were killed either at PN120 or PN180. At both ages, SL rats had higher BAT autonomic nervous system activity, mass and adipocyte area, as well as increased heart rate and blood pressure (systolic and diastolic); 2 months of calcium supplementation normalized these parameters. At PN180 only, UCP1 and TRß1 in BAT were decreased in SL rats. These changes were also prevented by calcium treatment. Also at PN180, the SL group presented higher tyrosine hydroxylase and adrenal catecholamine contents, as well as lower hypothalamic POMC and MC4R contents. Calcium supplementation did not revert these alterations. Thus, we demonstrated that dietary calcium supplementation was able to improve cardiovascular parameters and BAT thermogenesis capacity in adult animals that were early overfed during lactation.
Asunto(s)
Tejido Adiposo Pardo/efectos de los fármacos , Fenómenos Fisiológicos Nutricionales de los Animales , Calcio de la Dieta/farmacología , Hiperfagia/fisiopatología , Adipocitos/efectos de los fármacos , Adipocitos/metabolismo , Tejido Adiposo Pardo/fisiopatología , Animales , Presión Sanguínea/efectos de los fármacos , Índice de Masa Corporal , Sistema Cardiovascular/efectos de los fármacos , Sistema Cardiovascular/metabolismo , Suplementos Dietéticos , Femenino , Hipotálamo/efectos de los fármacos , Hipotálamo/metabolismo , Masculino , Obesidad/tratamiento farmacológico , Proopiomelanocortina/metabolismo , Ratas , Ratas Wistar , Receptor de Melanocortina Tipo 4/metabolismo , Termogénesis/efectos de los fármacos , DesteteRESUMEN
Studies conducted in monozygotic and dizygotic twins have established a strong genetic component in eating behavior. Rare mutations and common variants of the melanocortin 4 receptor (MC4R) gene have been linked to obesity and eating behavior scores. However, few studies have assessed common variants in MC4R gene with the rewarding value of food in children. The objective of the study was to evaluate the association between the MC4R rs17782313 polymorphism with homeostatic and non-homeostatic eating behavior patterns in Chileans children. This is a cross-sectional study in 258 Chilean children (44 % female, 8-14 years old) showing a wide variation in BMI. Anthropometric measurements (weight, height, Z-score of BMI and waist circumference) were performed by standard procedures. Eating behavior was assessed using the Eating in Absence of Hunger Questionnaire (EAHQ), the Child Eating Behavior Questionnaire (CEBQ), the Three-Factor Eating Questionnaire (TFEQ), and the Food Reinforcement Value Questionnaire (FRVQ). Genotype of the rs17782313 nearby MC4R was determined by a Taqman assay. Association of the rs17782313 C allele with eating behavior was assessed using non-parametric tests. We found that children carrying the CC genotype have higher scores of food responsiveness (p value = 0.02). In obese girls, carriers of the C allele showed lower scores of satiety responsiveness (p value = 0.02) and higher scores of uncontrolled eating (p value = 0.01). Obese boys carrying the C allele showed lower rewarding value of food in relation to non-carriers. The rs17782313 C allele is associated with eating behavior traits that may predispose obese children to increased energy intake and obesity.
Asunto(s)
Regiones no Traducidas 3' , Predisposición Genética a la Enfermedad , Hiperfagia/genética , Sobrepeso/etiología , Obesidad Infantil/etiología , Polimorfismo Genético , Receptor de Melanocortina Tipo 4/genética , Adolescente , Alelos , Índice de Masa Corporal , Estudios de Casos y Controles , Niño , Chile , Estudios Transversales , Conducta Alimentaria , Femenino , Estudios de Asociación Genética , Humanos , Hiperfagia/metabolismo , Hiperfagia/fisiopatología , Masculino , Receptor de Melanocortina Tipo 4/metabolismo , Refuerzo en Psicología , Recompensa , Circunferencia de la CinturaRESUMEN
Melanocortin-4 receptor (MC4R) is associated with feed intake, growth, fatness, and carcass composition in many domestic animals. The aim of this study was to evaluate the association of single nucleotide polymorphisms (SNPs) in MC4R with milk production traits in water buffalo. Eight SNPs were identified by direct polymerase chain reaction sequencing of samples from 18 buffaloes. SNPs were then genotyped using the matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) method in 332 buffaloes. Two of eight SNPs were not in Hardy-Weinberg equilibrium. Based on the SNP data, seven haplotypes were constructed. Three SNPs H1 (AGT), H2 (GAT), and H3 (GAC) accounted for 93.0% of the total individuals. Statistical analysis indicated that the SNP g.1104C>T was significantly associated with milk yield, protein, and fat percentage (P < 0.05). In conclusion, these results provide evidence that polymorphisms in the buffalo MC4R gene are associated with milk production traits and might be potential biomarkers for water buffalo breeding.
Asunto(s)
Búfalos/fisiología , Lactancia/genética , Glándulas Mamarias Animales/fisiología , Leche , Receptor de Melanocortina Tipo 4/genética , Animales , Biomarcadores/análisis , Cruzamiento , Búfalos/genética , Búfalos/metabolismo , Femenino , Genotipo , Haplotipos , Glándulas Mamarias Animales/metabolismo , Fenotipo , Polimorfismo de Nucleótido Simple/genética , Receptor de Melanocortina Tipo 4/metabolismoRESUMEN
BACKGROUND/AIMS: To evaluate the association between allelic variants of melanocortin receptors -3 and -4 (MC3R and MC4R, respectively) and leptin receptor (LEPR) genes with body mass index (BMI) and eating behavior. METHODS: We selected 344 Chilean adults (57.8% women; age 39.1 ± 6.6 years) with a wide variation in BMI (30.3 ± 6.3 kg/m²). The Three-Factor Eating Questionnaire-R18 that measures uncontrolled eating (UE), emotional eating (EE) and cognitive restraint scores was adapted, validated and assessed for association with BMI. Genotypes were determined by polymerase chain reaction followed by restriction fragment length polymorphism techniques and Taqman assays. RESULTS: Higher EE scores were found in obese vs. non-obese in both men (p = 0.01) and women (p < 0.001). UE scores were significantly associated with BMI only in women (p = 0.002). No significant differences in eating behavior scores or BMI were found by LEPR (rs1137101, rs8179183 and rs1137100 polymorphisms) or MC3R (rs3746619 and rs3827103). Carriers of the C allele for MC4R rs17782313 showed significantly higher scores of UE compared to non-carriers (2.3 ± 0.8 vs. 2.0 ± 0.7; p = 0.02). Additionally, we also report a monogenic case of obesity carrying the pathogenic mutation 449C>T (Thr150Ile) in MC4R gene with no apparent alterations in eating behavior scores. CONCLUSIONS: UE scores were higher in C-allele carriers of MC4R-rs17782313 compared to non-carriers.
Asunto(s)
Conducta Alimentaria , Polimorfismo de Nucleótido Simple , Receptor de Melanocortina Tipo 4/genética , Adulto , Alelos , Índice de Masa Corporal , Chile , Femenino , Humanos , Masculino , Persona de Mediana Edad , Obesidad/genética , Receptor de Melanocortina Tipo 3/genética , Receptor de Melanocortina Tipo 3/metabolismo , Receptor de Melanocortina Tipo 4/metabolismo , Receptores de Leptina/genética , Receptores de Leptina/metabolismo , Reproducibilidad de los Resultados , Encuestas y CuestionariosRESUMEN
Melanocortins are neuropeptides with well recognized anti-inflammatory and anti-apoptotic effects in the brain. Of the five melanocortin receptors (MCR), MC4R is abundantly expressed in the brain and is the only MCR present in astrocytes. We have previously shown that MC4R activation by the α-melanocyte stimulating hormone (α-MSH) analog, NDP-MSH, increased brain-derived neurotrophic factor (BDNF) expression through the classic cAMP-Protein kinase A-cAMP responsive element binding protein pathway in rat astrocytes. Now, we examined the participation of the mitogen activated protein kinases pathway in MC4R signaling. Rat cultured astrocytes treated with NDP-MSH 1 µM for 1 h showed increased BDNF expression. Inhibition of extracellular signal-regulated kinase (ERK) and ribosomal p90 S6 kinase (RSK), an ERK substrate, but not of p38 or JNK, prevented the increase in BDNF expression induced by NDP-MSH. Activation of MC4R increased cFos expression, a target of both ERK and RSK. ERK activation by MC4R involves cAMP, phosphoinositide-3 kinase (PI3K) and the non receptor tyrosine kinase, Src. Both PI3K and Src inhibition abolished NDP-MSH-induced BDNF expression. Moreover, we found that intraperitoneal injection of α-MSH induces BDNF and MC4R expression and activates ERK and cFos in male rat hypothalamus. Our results show for the first time that MC4R-induced BDNF expression in astrocytes involves ERK-RSK-cFos pathway which is dependent on PI3K and Src, and that melanocortins induce BDNF expression and ERK-cFos activation in rat hypothalamus.
Asunto(s)
Astrocitos/metabolismo , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Hipotálamo/metabolismo , Proteínas Proto-Oncogénicas c-fos/metabolismo , Receptor de Melanocortina Tipo 4/metabolismo , Transducción de Señal/fisiología , Animales , Astrocitos/efectos de los fármacos , Células Cultivadas , Hipotálamo/efectos de los fármacos , Masculino , Fosforilación/efectos de los fármacos , Ratas , Ratas Wistar , Transducción de Señal/efectos de los fármacos , alfa-MSH/análogos & derivados , alfa-MSH/farmacologíaRESUMEN
The corticotropin-releasing factor (CRF)-producing neurons of the amygdala have been implicated in behavioral and physiological responses associated with fear, anxiety, stress, food intake and reward. To overcome the difficulties in identifying CRF neurons within the amygdala, a novel transgenic mouse line, in which the humanized recombinant Renilla reniformis green fluorescent protein (hrGFP) is under the control of the CRF promoter (CRF-hrGFP mice), was developed. First, the CRF-hrGFP mouse model was validated and the localization of CRF neurons within the amygdala was systematically mapped. Amygdalar hrGFP-expressing neurons were located primarily in the interstitial nucleus of the posterior limb of the anterior commissure, but also present in the central amygdala. Secondly, the marker of neuronal activation c-Fos was used to explore the response of amygdalar CRF neurons in CRF-hrGFP mice under different experimental paradigms. C-Fos induction was observed in CRF neurons of CRF-hrGFP mice exposed to an acute social defeat stress event, a fasting/refeeding paradigm or lipopolysaccharide (LPS) administration. In contrast, no c-Fos induction was detected in CRF neurons of CRF-hrGFP mice exposed to restraint stress, forced swimming test, 48-h fasting, acute high-fat diet (HFD) consumption, intermittent HFD consumption, ad libitum HFD consumption, HFD withdrawal, conditioned HFD aversion, ghrelin administration or melanocortin 4 receptor agonist administration. Thus, this study fully characterizes the distribution of amygdala CRF neurons in mice and suggests that they are involved in some, but not all, stress or food intake-related behaviors recruiting the amygdala.
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Amígdala del Cerebelo/citología , Amígdala del Cerebelo/fisiología , Hormona Liberadora de Corticotropina/metabolismo , Neuronas/citología , Neuronas/fisiología , Proteínas Anfibias/genética , Proteínas Anfibias/metabolismo , Amígdala del Cerebelo/efectos de los fármacos , Amígdala del Cerebelo/fisiopatología , Animales , Dieta Alta en Grasa , Dominación-Subordinación , Ingestión de Alimentos/fisiología , Ayuno/fisiología , Ghrelina/administración & dosificación , Proteínas Fluorescentes Verdes/genética , Proteínas Fluorescentes Verdes/metabolismo , Lipopolisacáridos , Masculino , Ratones Endogámicos C57BL , Ratones Transgénicos , Neuronas/efectos de los fármacos , Proteínas Proto-Oncogénicas c-fos/metabolismo , Receptor de Melanocortina Tipo 4/antagonistas & inhibidores , Receptor de Melanocortina Tipo 4/metabolismo , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Renilla , Restricción Física , Estrés Psicológico/fisiopatología , Natación/fisiologíaRESUMEN
UNLABELLED: Melanocortin receptors (MC3/4R) mediate most of the metabolic and cardiovascular actions of leptin. AIM: Here, we tested if MC4R also contributes to leptin's effects on respiratory function. METHODS: After control measurements, male Holtzman rats received daily microinjections of leptin, SHU9119 (MC3/4R antagonist) or SHU9119 combined with leptin infused into the brain lateral ventricle for 7 days. On the 6th day of treatment, tidal volume (VT ), respiratory frequency (fR ) and pulmonary ventilation (VE ) were measured by whole-body plethysmography during normocapnia or hypercapnia (7% CO2 ). Baseline mean arterial pressure (MAP), heart rate (HR) and metabolic rate were also measured. VE , VT and fR were also measured in mice with leptin receptor deletion in the entire central nervous system (LepR/Nestin-cre) or only in proopiomelanocortin neurones (LepR/POMC-cre) and in MC4R knockout (MC4R(-/-) ) and wild-type mice. RESULTS: Leptin (5 µg day(-1) ) reduced body weight (~17%) and increased ventilatory response to hypercapnia, whereas SHU9119 (0.6 nmol day(-1) ) increased body weight (~18%) and reduced ventilatory responses compared with control-PBS group (Lep: 2119 ± 90 mL min(-1) kg(-1) and SHU9119: 997 ± 67 mL min(-1) kg(-1) , vs. PBS: 1379 ± 91 mL min(-1) kg(-1) ). MAP increased after leptin treatment (130 ± 2 mmHg) compared to PBS (106 ± 3 mmHg) or SHU9119 alone (109 ± 3 mmHg). SHU9119 prevented the effects of leptin on body weight, MAP (102 ± 3 mmHg) and ventilatory response to hypercapnia (1391 ± 137 mL min(-1) kg(-1) ). The ventilatory response to hypercapnia was attenuated in the LepR/Nestin-cre, LepR/POMC-cre and MC4R(-/-) mice. CONCLUSION: These results suggest that central MC4R mediate the effects of leptin on respiratory response to hypercapnia.
Asunto(s)
Leptina/farmacología , Melanocortinas/metabolismo , Hormonas Estimuladoras de los Melanocitos/farmacología , Receptor de Melanocortina Tipo 3/metabolismo , Receptor de Melanocortina Tipo 4/metabolismo , Fenómenos Fisiológicos Respiratorios/efectos de los fármacos , Animales , Peso Corporal/efectos de los fármacos , Dióxido de Carbono/sangre , Regulación de la Expresión Génica , Hipercapnia/inducido químicamente , Leptina/administración & dosificación , Masculino , Hormonas Estimuladoras de los Melanocitos/administración & dosificación , Ratones , Ratones Noqueados , Ratas , Ratas Sprague-Dawley , Receptor de Melanocortina Tipo 3/genética , Receptor de Melanocortina Tipo 4/genéticaRESUMEN
The melanocortin 4 receptor (MC4R) is a G protein-coupled receptor involved in food intake and energy expenditure regulation. MC4R activation modifies neuronal activity but the molecular mechanisms by which this regulation occurs remain unclear. Here, we tested the hypothesis that MC4R activation regulates the activity of voltage-gated calcium channels and, as a consequence, synaptic activity. We also tested whether the proposed effect occurs in the amygdala, a brain area known to mediate the anorexigenic actions of MC4R signaling. Using the patch-clamp technique, we found that the activation of MC4R with its agonist melanotan II specifically inhibited 34.5 ± 1.5% of N-type calcium currents in transiently transfected HEK293 cells. This inhibition was concentration-dependent, voltage-independent and occluded by the Gαs pathway inhibitor cholera toxin. Moreover, we found that melanotan II specifically inhibited 25.9 ± 2.0% of native N-type calcium currents and 55.4 ± 14.4% of evoked inhibitory postsynaptic currents in mouse cultured amygdala neurons. In vivo, we found that the MC4R agonist RO27-3225 increased the marker of cellular activity c-Fos in several components of the amygdala, whereas the N-type channel blocker ω conotoxin GVIA increased c-Fos expression exclusively in the central subdivision of the amygdala. Thus, MC4R specifically inhibited the presynaptic N-type channel subtype, and this inhibition may be important for the effects of melanocortin in the central subdivision of the amygdala.
Asunto(s)
Amígdala del Cerebelo/fisiología , Canales de Calcio Tipo N/metabolismo , Terminales Presinápticos/fisiología , Receptor de Melanocortina Tipo 4/metabolismo , Amígdala del Cerebelo/efectos de los fármacos , Animales , Bloqueadores de los Canales de Calcio/farmacología , Células Cultivadas , Fármacos del Sistema Nervioso Central/farmacología , Toxina del Cólera/farmacología , Células HEK293 , Humanos , Potenciales Postsinápticos Inhibidores/efectos de los fármacos , Potenciales Postsinápticos Inhibidores/fisiología , Masculino , Ratones , Péptidos/farmacología , Péptidos Cíclicos/metabolismo , Terminales Presinápticos/efectos de los fármacos , Proteínas Proto-Oncogénicas c-fos/metabolismo , Receptor de Melanocortina Tipo 4/agonistas , alfa-MSH/análogos & derivados , alfa-MSH/metabolismo , omega-Conotoxina GVIA/farmacologíaRESUMEN
Astrocytes exert a wide variety of functions with paramount importance in brain physiology. After injury or infection, astrocytes become reactive and they respond by producing a variety of inflammatory mediators that help maintain brain homeostasis. Loss of astrocyte functions as well as their excessive activation can contribute to disease processes; thus, it is important to modulate reactive astrocyte response. Melanocortins are peptides with well-recognized anti-inflammatory and neuroprotective activity. Although melanocortin efficacy was shown in systemic models of inflammatory disease, mechanisms involved in their effects have not yet been fully elucidated. Central anti-inflammatory effects of melanocortins and their mechanisms are even less well known, and, in particular, the effects of melanocortins in glial cells are poorly understood. Of the five known melanocortin receptors (MCRs), only subtype 4 is present in astrocytes. MC4R has been shown to mediate melanocortin effects on energy homeostasis, reproduction, inflammation, and neuroprotection and, recently, to modulate astrocyte functions. In this review, we will describe MC4R involvement in anti-inflammatory, anorexigenic, and anti-apoptotic effects of melanocortins in the brain. We will highlight MC4R action in astrocytes and discuss their possible mechanisms of action. Melanocortin effects on astrocytes provide a new means of treating inflammation, obesity, and neurodegeneration, making them attractive targets for therapeutic interventions in the CNS.
Asunto(s)
Astrocitos/metabolismo , Receptor de Melanocortina Tipo 4/metabolismo , Animales , Metabolismo Energético , Humanos , Inflamación/metabolismo , Melanocortinas/metabolismoRESUMEN
Melanocortin 4 receptors (MC4R) are mainly expressed in the brain. We previously showed that the anti-inflammatory action of α-melanocyte-stimulating hormone (α-MSH) in rat hypothalamus and in cultured astrocytes involved MC4R activation. However, MC4R mechanisms of action remain undetermined. Since brain-derived neurotrophic factor (BDNF) may be mediating MC4R hypothalamic anorexigenic actions, we determined melanocortin effects on BDNF expression in rat cultured astrocytes and certain mechanisms involved in MC4R signaling. α-MSH and its analogue NDP-MSH, induced production of cAMP in astrocytes. This effect was completely blocked by the MC4R antagonist, HS024. We found that NDP-MSH increased BDNF mRNA and protein levels in astrocytes. The effect of NDP-MSH on BDNF expression was abolished by the adenylate cyclase inhibitor SQ22536, and decreased by the PKA inhibitor Rp-cAMP. Since melanocortins are immunomodulators, we investigated their actions with bacterial lipopolysaccharide (LPS) and interferon-γ (IFN-γ) stimulus. Although both α-MSH and LPS+IFN-γ increased cAMP responding element binding protein (CREB) activation, LPS+IFN-γ did not modify BDNF expression. On the other hand, α-MSH did not modify basal or LPS+IFN-γ-induced nuclear factor-κB activation. Our results show for the first time that MC4R activation in astrocytes induces BDNF expression through cAMP-PKA-CREB pathway without involving NF-κB.
Asunto(s)
Astrocitos/metabolismo , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , AMP Cíclico/metabolismo , Expresión Génica , Receptor de Melanocortina Tipo 4/metabolismo , Adenilil Ciclasas/metabolismo , Animales , Factor Neurotrófico Derivado del Encéfalo/genética , Células Cultivadas , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/metabolismo , Interferón gamma/farmacología , Interferón gamma/fisiología , Lipopolisacáridos/farmacología , FN-kappa B/metabolismo , Péptidos Cíclicos/farmacología , Ratas , Ratas Wistar , Receptor de Melanocortina Tipo 4/agonistas , Receptor de Melanocortina Tipo 4/antagonistas & inhibidores , Transducción de Señal , alfa-MSH/análogos & derivados , alfa-MSH/farmacología , alfa-MSH/fisiologíaRESUMEN
OBJECTIVE: Recent genome-wide association studies found common variants near the melanocortin 4 receptor gene associated with obesity. This study aimed to assess the influence of the identified single nucleotide polymorphisms rs17782313 and rs17700633 on general and visceral adiposity in European- and African-American youth. STUDY DESIGN: In 1890 youth (49.1% European-American, 45.6% male, mean age 16.7 years), we examined the associations of the rs17782313 and rs17700633 with anthropometry, percent body fat, visceral adipose tissue, and subcutaneous abdominal adipose tissue. Interaction of the single nucleotide polymorphisms with ethnicity or sex was investigated and haplotype analyses conducted. RESULTS: Rs17782313 was significantly associated with weight (P = .02) and waist circumference (P = .03) in all subjects and with body mass index (P = .002) in females. In females rs17700633 was significantly associated with percent body fat (P = .001), visceral adipose tissue (P < .001), and subcutaneous abdominal adipose tissue (P < .001). Rs17700633 was significantly associated with fasting insulin and homeostasis model assessment, but the significance attenuated after adjustment for percent body fat. These findings were confirmed by haplotype analysis. No significant interactions of the variants with ethnicity were found for any of these phenotypes. CONCLUSIONS: The relatively large effect of these common variants near melanocortin 4 receptor on general and visceral adiposity in childhood, especially in girls, could prove helpful in elucidating the molecular mechanisms underlying the development of obesity in early life.
Asunto(s)
Adiposidad/genética , Negro o Afroamericano , ADN/genética , Obesidad/etnología , Polimorfismo Genético , Receptor de Melanocortina Tipo 4/genética , Adiposidad/etnología , Adolescente , Peso Corporal , Europa (Continente)/etnología , Femenino , Predisposición Genética a la Enfermedad , Haplotipos , Humanos , Incidencia , Grasa Intraabdominal , Masculino , Obesidad/genética , Obesidad/metabolismo , Reacción en Cadena de la Polimerasa , Receptor de Melanocortina Tipo 4/metabolismo , Factores Sexuales , Estados Unidos/epidemiologíaRESUMEN
In 5-month-old male and female dopamine receptor 2 (D2R) knockout mice food intake per animal was unaltered while food per g BW was increased. We wished to evaluate the effect of D2R disruption on different components of energy balance and food intake regulation. We determined hypothalamic orexin precursor (PPO) expression, its receptor OX1, serum leptin levels, hypothalamic leptin receptor (OBR), circulating and pituitary alpha MSH levels, as well as central MC3 and MC4 receptors and NPY mRNA in wildtype and D2R knockout mice (KO). Loss of D2R caused a marked increase in serum prolactin levels, to higher levels in females compared to male KO mice. On the other hand, it produced a female-specific increase in circulating alphaMSH, and hypothalamic alphaMSH content, while neurointermediate alphaMSH content was decreased in both sexes. No differences were found in hypothalamic NPY, MC3R or MC4R concentration. Hypothalamic PPO mRNA expression was significantly decreased only in female KOs, while OX1 mRNA was not different between genotypes. Serum leptin levels were also similar in both genotypes. Our results show that in female and not in male mice disruption of the D2R produces two potentially anorexigenic events: an increase in serum and hypothalamic alphaMSH, and a decrease in hypothalamic orexin expression. Very high prolactin levels, which are orexigenic, probably counterbalance these effects, so that food intake is slightly altered. In males, on the other hand, hypothalamic PPO, and serum or hypothalamic alphaMSH are not modified, and increased prolactin levels may account for increased food intake per g BW. These results suggest a sexually dimorphic participation of the D2R in food intake regulation.
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Hipotálamo/metabolismo , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Neuropéptido Y/metabolismo , Neuropéptidos/metabolismo , Receptor de Melanocortina Tipo 3/metabolismo , Receptor de Melanocortina Tipo 4/metabolismo , Receptores de Dopamina D2 , Receptores Acoplados a Proteínas G/metabolismo , Receptores de Neuropéptido/metabolismo , alfa-MSH/metabolismo , Animales , Ingestión de Alimentos , Metabolismo Energético , Femenino , Masculino , Ratones , Ratones Noqueados , Receptores de Orexina , Orexinas , Precursores de Proteínas/metabolismo , Receptores de Dopamina D2/genética , Receptores de Dopamina D2/metabolismoRESUMEN
Inflammatory processes contribute widely to the development of neurodegenerative diseases. The expression of many inflammatory mediators was found to be increased in central nervous system (CNS) disorders suggesting that these molecules are major contributors to neuronal damage. Melanocortins are neuropeptides that have been implicated in a wide range of physiological processes. The melanocortin alpha-melanocyte stimulating hormone (alpha-MSH) has pleiotropic functions and exerts potent anti-inflammatory actions by antagonizing the effects of pro-inflammatory cytokines and by decreasing important inflammatory mediators. Five subtypes of melanocortin receptors (MC1R-MC5R) have been identified. Of these, the MC4 receptor is expressed predominantly throughout the CNS. Evidence of effectiveness of selective MC4R agonists in modulating inflammatory processes and their low toxicity suggest that these molecules may be useful in the treatment of CNS disorders with an inflammatory component. This review describes the involvement of the MC4R in central anti-inflammatory effects of melanocortins and discusses the potential value of MC4R agonists for the treatment of inflammatory-related disorders.
Asunto(s)
Encefalitis/metabolismo , Receptor de Melanocortina Tipo 4/metabolismo , alfa-MSH/metabolismo , Animales , Encéfalo/metabolismo , Humanos , Receptores de Melanocortina/metabolismoRESUMEN
Alpha-MSH exerts an immunomodulatory action in the brain and may play a neuroprotective role acting through melanocortin 4 receptors (MC4Rs). In the present study, we show that MC4Rs are constitutively expressed in astrocytes as determined by immunocytochemistry, RT-PCR, and Western blot analysis. alpha-MSH (5 microm) reduced the nitric oxide production and the expression of inducible nitric oxide synthase (iNOS) induced by bacterial lipopolysaccharide (LPS, 1 microg/ml) plus interferon-gamma (IFN-gamma, 50 ng/ml) in cultured astrocytes after 24 h. alpha-MSH also attenuated the stimulatory effect of LPS/IFN-gamma on prostaglandin E(2) release and cyclooxygenase-2 (COX-2) expression. Treatment with HS024, a selective MC4R antagonist, blocked the antiinflammatory effects of alpha-MSH, suggesting a MC4R-mediated mechanism in the action of this melanocortin. In astrocytes, LPS/IFN-gamma treatment reduced cell viability, increased the number of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive cells and activated caspase-3. alpha-MSH prevented these apoptotic events, and this cytoprotective effect was abolished by HS024. LPS/IFN-gamma decreased Bcl-2, whereas it increased Bax protein expression in astrocytes, thus increasing the Bax/Bcl-2 ratio. Alpha-MSH produced a shift in Bax/Bcl-2 ratio toward astrocyte survival because it increased Bcl-2 expression and also prevented the effect of LPS/IFN-gamma on Bax and Bcl-2 expression. In summary, these findings suggest that alpha-MSH, through MC4R activation, attenuates LPS/IFN-gamma-induced inflammation by decreasing iNOS and COX-2 expression and prevents LPS/IFN-gamma-induced apoptosis of astrocytes by modulating the expression of proteins of the Bcl-2 family.
Asunto(s)
Apoptosis/efectos de los fármacos , Astrocitos/fisiología , Inflamación/prevención & control , Interferón gamma/farmacología , Lipopolisacáridos/farmacología , Receptor de Melanocortina Tipo 4/metabolismo , Animales , Astrocitos/efectos de los fármacos , Astrocitos/metabolismo , Supervivencia Celular/efectos de los fármacos , Inhibidores de la Ciclooxigenasa 2/farmacología , Óxido Nítrico/antagonistas & inhibidores , Óxido Nítrico/biosíntesis , Óxido Nítrico Sintasa de Tipo II/antagonistas & inhibidores , Péptidos Cíclicos/farmacología , Proteínas Proto-Oncogénicas c-bcl-2/metabolismo , Ratas , Ratas Wistar , alfa-MSH/farmacología , Proteína X Asociada a bcl-2/antagonistas & inhibidoresRESUMEN
Obesity is a major public health concern and environmental factors are involved in its development. The hypothalamus is a primary site for the integration of signals for the regulation of energy homeostasis. Dysregulation of these pathways can lead to weight loss or gain. Some drugs in development can have favourable effects on body weight, acting on some of these pathways and leading to responses resulting in weight loss. Strategies for the management of weight reduction include exercise, diet, behavioural therapy, drug therapy and surgery. Investigational antiobesity medications can modulate energy homeostasis by stimulating catabolic or inhibiting anabolic pathways. Investigational drugs stimulating catabolic pathways consist of leptin, agonists of melanocortin receptor-4, 5-HT and dopamine; bupropion, growth hormone fragments, cholecystokinin subtype 1 receptor agonist, peptide YY3-36, oxyntomodulin, ciliary neurotrophic factor analogue, beta3-adrenergic receptor agonists, adiponectin derivatives and glucagon-like peptide-1. On the other hand, investigational drugs inhibiting anabolic pathways consist of the ghrelin receptor, neuropeptide Y receptor and melanin-concentrating hormone-1 antagonists; somatostatin analogues, peroxisome proliferator-activated receptor-gamma and -beta/delta antagonists, gastric emptying retardation agents, pancreatic lipase inhibitors, topiramate and cannabinoid-1 receptor antagonists. These differing approaches are reviewed and commented on in this article.