Glucagon-like peptide-1 (Glp1) suppresses food intake via activation of a central (i.e., brain) Glp1 receptor (Glp1r). Central AMP-activated protein kinase (AMPK) is a nutrient-sensitive regulator of food intake that is inhibited by anorectic signals. The anorectic effect elicited by hindbrain Glp1r activation is attenuated by the AMPK stimulator AICAR. This suggests that central Glp1r activation suppresses food intake via inhibition of central AMPK. The present studies examined the mechanism(s) by which central Glp1r activation inhibits AMPK. Supporting previous findings, AICAR attenuated the anorectic effect elicited by intracerebroventricular (ICV) administration of the Glp1r agonist Exendin-4 (Ex4). We demonstrate that Ex4 stimulates glycolysis and suppresses AMPK phosphorylation in a glucose-dependent manner in hypothalamic GT1-7 cells. This suggests that inhibition of AMPK and food intake by Ex4 requires central glucose metabolism. Supporting this, the glycolytic inhibitor 2-deoxyglucose (2-DG) attenuated the anorectic effect of Ex4. However, ICV glucose did not enhance the suppression of food intake by Ex4. AICAR had no effect on Ex4-mediated reduction in locomotor activity. We also tested whether other carbohydrates affect the anorectic response to Ex4. ICV pre-treatment with the sucrose metabolite fructose, an AMPK activator, attenuated the anorectic effect of Ex4. This potentially explains the increased food intake observed in sucrose-fed mice. In summary, we propose a model whereby activation of the central Glp1r reduces food intake via glucose metabolism-dependent inhibition of central AMPK. We also suggest that fructose stimulates food intake by impairing central Glp1r action. This has significant implications given the correlation between sugar consumption and obesity.
"Conversely, others failed to observe any effect of exendin-4 (a GLP-1R agonist) on mitochondrial ATP levels in primary rodent islets (110), despite the large oscillations in intracellular calcium, and the subsequent activation of ATP-consuming and – production processes (and, thereby, of cellular metabolism) to maintain intracellular calcium homeostasis (108). Alternatively, Burmeister et al. (106) proposed recently that GLP-1R-associated increase in glucose metabolism after a meal could initiate a feedback inhibition of food intake, mediated by a decrement in AMPK activity. As such, glucose could be considered as both a stimulus and a mechanistic component of GLP-1-mediated suppression of food intake (106). "
[Show abstract][Hide abstract] ABSTRACT: Type 2 diabetes (T2D) and Alzheimer disease (AD) are two major health issues nowadays. T2D is an ever increasing epidemic, affecting millions of elderly people worldwide, with major repercussions in the patients' daily life. This is mostly due to its chronic complications that may affect brain and constitutes a risk factor for AD. T2D principal hallmark is insulin resistance which also occurs in AD, rendering both pathologies more than mere unrelated diseases. This hypothesis has been reinforced in the recent years, with a high number of studies highlighting the existence of several common molecular links. As such, it is not surprising that AD has been considered as the "type 3 diabetes" or a "brain-specific T2D," supporting the idea that a beneficial therapeutic strategy against T2D might be also beneficial against AD. Herewith, we aim to review some of the recent developments on the common features between T2D and AD, namely on insulin signaling and its participation in the regulation of amyloid β (Aβ) plaque and neurofibrillary tangle formation (the two major neuropathological hallmarks of AD). We also critically analyze the promising field that some anti-T2D drugs may protect against dementia and AD, with a special emphasis on the novel incretin/glucagon-like peptide-1 receptor agonists.
Frontiers in Endocrinology 07/2014; 5:110. DOI:10.3389/fendo.2014.00110
[Show abstract][Hide abstract] ABSTRACT: Incretin peptides, principally GLP-1 and GIP, regulate islet hormone secretion, glucose concentrations, lipid metabolism, gut motility, appetite and body weight, and immune function, providing a scientific basis for utilizing incretin-based therapies in the treatment of type 2 diabetes. Activation of GLP-1 and GIP receptors also leads to nonglycemic effects in multiple tissues, through direct actions on tissues expressing incretin receptors and indirect mechanisms mediated through neuronal and endocrine pathways. Here we contrast the pharmacology and physiology of incretin hormones and review recent advances in mechanisms coupling incretin receptor signaling to pleiotropic metabolic actions in preclinical studies. We discuss whether mechanisms identified in preclinical studies have potential translational relevance for the treatment of human disease and highlight controversies and uncertainties in incretin biology that require resolution in future studies.
[Show abstract][Hide abstract] ABSTRACT: The fruit fly, Drosophila melanogaster is a broadly used model for gerontological research. Many studies are dedicated to understanding nutritional effects on ageing; however, the influence of dietary carbohydrate type and dosage is still poorly understood. We show that among three carbohydrates tested, fructose, glucose, and sucrose, the latter decreased life span by 13%-27%, being present in concentrations of 2%-20% in the diet. Life-span shortening by sucrose was accompanied by an increase in age-independent mortality. Sucrose also dramatically decreased the fecundity of the flies. The differences in life span and fecundity were determined to be unrelated to differential carbohydrate ingestion. The highest mitochondrial protein density was observed in flies fed sucrose-containing diet. However, this parameter was not affected by carbohydrate amount in the diet. Fly sensitivity to oxidative stress, induced by menadione, was increased in aged flies and was slightly affected by type and concentration of carbohydrate. In general, it has been demonstrated that sucrose, commonly used in recipes of Drosophila laboratory food, may shorten life span and lower egg-laying capability on the diets with very low protein content.
The Journals of Gerontology Series A Biological Sciences and Medical Sciences 05/2013; 69(1). DOI:10.1093/gerona/glt077 · 5.42 Impact Factor
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