Activation of the omega-3 fatty acid receptor GPR120 mediates anti-inflammatory actions in immortalized hypothalamic neurons

Denise D Belsham,Leigh Wellhauser

doi:10.1186/1742-2094-11-60

Abstract

BackgroundOvernutrition and the ensuing hypothalamic inflammation is a major perpetuating factor in the development of metabolic diseases, such as obesity and diabetes. Inflamed neurons of the CNS fail to properly regulate energy homeostasis leading to pathogenic changes in glucose handling, feeding, and body weight. Hypothalamic neurons are particularly sensitive to pro-inflammatory signals derived locally and peripherally, and it is these neurons that become inflamed first upon high fat feeding. Given the prevalence of metabolic disease, efforts are underway to identify therapeutic targets for this inflammatory state. At least in the periphery, omega-3 fatty acids and their receptor, G-protein coupled receptor 120 (GPR120), have emerged as putative targets. The role for GPR120 in the hypothalamus or CNS in general is poorly understood.MethodsHere we introduce a novel, immortalized cell model derived from the rat hypothalamus, rHypoE-7, to study GPR120 activation at the level of the individual neuron. Gene expression levels of pro-inflammatory cytokines were studied by quantitative reverse transcriptase-PCR (qRT-PCR) upon exposure to tumor necrosis factor α (TNFα) treatment in the presence or absence of the polyunsaturated omega-3 fatty acid docosahexaenoic acid (DHA). Signal transduction pathway involvement was also studied using phospho-specific antibodies to key proteins by western blot analysis.ResultsImportantly, rHypoE-7 cells exhibit a transcriptional and translational inflammatory response upon exposure to TNFα and express abundant levels of GPR120, which is functionally responsive to DHA. DHA pretreatment prevents the inflammatory state and this effect was inhibited by the reduction of endogenous GPR120 levels. GPR120 activates both AKT (protein kinase b) and ERK (extracellular signal-regulated kinase); however, the anti-inflammatory action of this omega-3 fatty acid (FA) receptor is AKT- and ERK-independent and likely involves the GPR120-transforming growth factor-β-activated kinase 1 binding protein (TAB1) interaction as identified in the periphery.ConclusionsTaken together, GPR120 is functionally active in the hypothalamic neuronal line, rHypoE-7, wherein it mediates the anti-inflammatory actions of DHA to reduce the inflammatory response to TNFα.

Highlights

Overnutrition and the ensuing hypothalamic inflammation is a major perpetuating factor in the development of metabolic diseases, such as obesity and diabetes
The rHypoE-7 cell line was screened for mRNA transcripts encoding the free fatty acid (FA) sensing G protein coupled receptors (GPRs; G-protein coupled receptor (GPR)-40 and GPR-120), the neuronal marker neuron-specific enolase (NSE), hypothalamic neuropeptides (AgRP, neuropeptide Y (NPY), and POMC), and inflammatory receptors and cytokines (Figure 1A)
tumor necrosis factor α (TNFα) activates the IKK-β/NF-κB in rHypoE-7 cells In order to determine if the rHypoE-7 cell line is capable of eliciting an innate immune response to inflammatory cytokines, we assessed the activation of IKK-β/NF-κB cascade upon TNFα exposure using western blotting and quantitative reverse transcriptase-PCR (qRT-PCR)

Summary

Introduction

Overnutrition and the ensuing hypothalamic inflammation is a major perpetuating factor in the development of metabolic diseases, such as obesity and diabetes. Regardless, the CNS maintains a functional innate immune system and expresses equivalent cytokines and receptors, supplying the CNS with a plethora of locally derived proinflammatory signals [4,5,6,7]. These cytokines, from the hypothalamus, are the first to be identified in the early stages of metabolic diseases, implicating these proinflammatory signals as predictors or perpetuators of impending pathology [8,9,10]. Genetic ablation of IKK-β/NF-κB signaling in neurons by impairing IKK-β activity is sufficient to reduce food intake, body weight gain, and glucose intolerance typically observed in high fat diets, highlighting this pathway as a promising therapeutic target [10,14,16]

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