ABSTRACT
GPR40 (Free fatty acid receptor 1) has emerged as an important therapeutic target for diabetes. Several studies have demonstrated the association of comorbid psychiatric conditions with decreased n-3 polyunsaturated fatty acids, which may act as an agonist for GPR40. In this study, we for the first time provide evidence of reduced GPR40 signaling in the hippocampus and cortex which may be a critical underlying mechanism mediating cognitive deficits in diabesity (diabetes and obesity together). Specifically, we showed decreased GPR40 and brain-derived neurotrophic factor (BDNF) expression in the brain regions of high-fat-diet-induced obese and db/db mice. Next, we demonstrated that chronic treatment with docosahexaenoic acid (DHA) or the synthetic GPR40 agonist, GW9508, significantly alleviates cognitive functions in mice, which correlates with increased BDNF expression in the hippocampus. This supports the hypothesis that DHA improves cognitive function in diabesity via GPR40 agonism. We also showed that DHA specifically activates GPR40 and modulates BDNF expression in primary cortical neurons mediated by the extracellular receptor kinase (ERK) and P38-mitogen-activated protein kinase (MAPK) pathways. Finally, the central nervous system (CNS)-specific blockade of GPR40 signaling abrogated the memory potentiating effects of DHA, and induction of BDNF expression in the hippocampus. Thus, we provided evidence that DHA stimulation of GPR40 mediate some of DHA's beneficial effects in metabolic syndrome and identify GPR40 as a viable therapeutic target for the treatment of CNS-related comorbidities associated with diabesity.
Subject(s)
Association Learning/physiology , Brain-Derived Neurotrophic Factor/biosynthesis , Docosahexaenoic Acids/therapeutic use , Memory Disorders/metabolism , Obesity/metabolism , Receptors, G-Protein-Coupled/biosynthesis , Animals , Association Learning/drug effects , Brain/drug effects , Brain/metabolism , Brain-Derived Neurotrophic Factor/agonists , Cells, Cultured , Diabetes Mellitus/drug therapy , Diabetes Mellitus/etiology , Diabetes Mellitus/metabolism , Diet, High-Fat/adverse effects , Docosahexaenoic Acids/pharmacology , Male , Memory Disorders/drug therapy , Mice , Mice, Inbred C57BL , Obesity/drug therapy , Obesity/etiology , Receptors, G-Protein-Coupled/agonistsABSTRACT
G protein-coupled receptors (GPCRs) are modulators of almost every physiological process, and therefore, are most favorite therapeutic target for wide spectrum of diseases. Ideally, high-throughput functional assays should be implemented that allow the screening of large compound libraries in cost-effective manner to identify agonist, antagonist, and allosteric modulators in the same assay. Taking advantage of the increased understanding of the GPCR structure and signaling, several commercially available functional assays based on fluorescence or chemiluminescence detection are being used in both academia and industry. In this chapter, we provide step-by-step method and guidelines to perform cAMP measurement using GloSensor assay. Finally, we have also discussed the analysis and interpretation of results obtained using this assay by providing several examples of Gs- and Gi-coupled GPCRs.
