Abstract
BackgroundHigh fat diet and its induced changes in glucose homeostasis, inflammation and obesity continue to be an epidemic in developed countries. The A2b adenosine receptor (A2bAR) is known to regulate inflammation. We used a diet-induced obesity murine knockout model to investigate the role of this receptor in mediating metabolic homeostasis, and correlated our findings in obese patient samples.Methodology/Principal FindingsAdministration of high fat, high cholesterol diet (HFD) for sixteen weeks vastly upregulated the expression of the A2bAR in control mice, while A2bAR knockout (KO) mice under this diet developed greater obesity and hallmarks of type 2 diabetes (T2D), assessed by delayed glucose clearance and augmented insulin levels compared to matching control mice. We identified a novel link between the expression of A2bAR, insulin receptor substrate 2 (IRS-2), and insulin signaling, determined by Western blotting for IRS-2 and tissue Akt phosphorylation. The latter is impaired in tissues of A2bAR KO mice, along with a greater inflammatory state. Additional mechanisms involved include A2bAR regulation of SREBP-1 expression, a repressor of IRS-2. Importantly, pharmacological activation of the A2bAR by injection of the A2bAR ligand BAY 60-6583 for four weeks post HFD restores IRS-2 levels, and ameliorates T2D. Finally, in obese human subjects A2bAR expression correlates strongly with IRS-2 expression.Conclusions/SignificanceOur study identified the A2bAR as a significant regulator of HFD-induced hallmarks of T2D, thereby pointing to its therapeutic potential.
Highlights
Glucose homeostasis is maintained through a delicate balance of exogenous dietary intake, endogenous hepatic release, and peripheral clearance by the adipose tissue and muscle
In a recent study we showed that cyclic AMP via A2b adenosine receptor (A2bAR) signaling on an Apolipoprotein E (ApoE) null background controls the level of liver SREBP-1 [21], which is an established transcriptional repressor of insulin receptor substrate 2 (IRS-2) expression [23,24]
Our current study identifies a novel role for the A2bAR in the context of type 2 diabetes (T2D), including insulin and glucose homeostasis, chronic inflammation and obesity under High Fat Diet (HFD)
Summary
Glucose homeostasis is maintained through a delicate balance of exogenous dietary intake, endogenous hepatic release, and peripheral clearance by the adipose tissue and muscle. Insulin resistance and obesity are two important risk factors that contribute to the pathogenesis of T2D. A purine nucleoside, is an important metabolite that is released from cells following insult or inflammation (reviewed in [8]). Adenosine, acting through the A2-type receptors, has been implicated in mediating inhibition of the release of inflammatory cytokines at baseline, post-injury and post-bacterial challenge (reviewed in [11]). In addition to the mediation of inflammation, adenosine and its receptors have been linked to the regulation of glucose clearance [12,13]. High fat diet and its induced changes in glucose homeostasis, inflammation and obesity continue to be an epidemic in developed countries. We used a dietinduced obesity murine knockout model to investigate the role of this receptor in mediating metabolic homeostasis, and correlated our findings in obese patient samples
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