Etanercept restores normal insulin signal transduction in β2-adrenergic receptor knockout mice.

Youde Jiang,Jena J Steinle,Eun-Ah Ye,Qiuhua Zhang

doi:10.1186/s12974-014-0137-z

Abstract

BackgroundInhibition of TNFα protects the retina against diabetic-like changes in rodent models. The mechanism by which TNFα induces deleterious retinal changes is not known. Previously, we have shown that TNFα can inhibit normal insulin signal transduction, leading to increased apoptosis in both retinal endothelial cells (REC) and Müller cells. Additionally, β2-adrenergic receptor knockout mice (β2KO) have increased TNFα levels and decreased insulin receptor activity. In this study, we hypothesized that inhibition of TNFα in β2KO mice would increase normal insulin signaling, leading to improved retinal function.MethodsC57BL6 or β2KO mice were left untreated or treated with etanercept (0.3 mg/kg subcutaneously, 3× a week) for 2 months. Electroretinogram analyses were done before treatment was initiated and after two months of treatment with etanercept on all mice. Western blot or ELISA analyses were done on whole retinal lysates from all four groups of mice for TNFα, suppressor of cytokine signaling 3 (SOCS3), insulin receptor, and apoptotic proteins.ResultsEtanercept significantly reduced TNFα levels in β2KO mice, leading to increased insulin receptor phosphorylation on tyrosine 1150/1151. SOCS3 levels were increased in β2KO mice, which were reduced after etanercept treatment. Pro-apoptotic proteins were reduced in etanercept-treated β2KO mice. Etanercept improved ERG amplitudes in β2KO mice.ConclusionsInhibition of TNFα by etanercept protects the retina likely through reduced TNFα-mediated insulin resistance, leading to reduced apoptosis.

Highlights

Inhibition of tumor necrosis factor alpha (TNFα) protects the retina against diabetic-like changes in rodent models
We have previously reported that TNFα and suppressor of cytokine signaling 3 (SOCS3) are both increased in response to high glucose in retinal endothelial cells, leading to increased phosphorylation of IRS-1Ser307 and IRTyr960 [8]
Etanercept treatment restores normal insulin receptor phosphorylation, while reducing IRS-1Ser307 levels To insure that treatment with etanercept was able to significantly reduce TNFα levels in β2-adrenergic receptor knockout mice (β2KO) mice, we performed an enzyme-linked immunosorbent assay (ELISA) analysis to show that β2KO mice have increased levels of TNFα, which were significantly reduced by etanercept treatment (Figure 1A)

Summary

Introduction

Inhibition of TNFα protects the retina against diabetic-like changes in rodent models. We have shown that TNFα can inhibit normal insulin signal transduction, leading to increased apoptosis in both retinal endothelial cells (REC) and Müller cells. We have shown that β-adrenergic retinal endothelial cells have increased apoptosis in response to high glucose and impaired insulin signaling, it is likely that impaired insulin signaling may be key to apoptosis in the retina [8]. In our previous work in retinal endothelial cells, we have reported that high glucose increases TNFα levels, leading to apoptosis of these cells [8]. We have previously reported that TNFα and SOCS3 are both increased in response to high glucose in retinal endothelial cells, leading to increased phosphorylation of IRS-1Ser307 and IRTyr960 [8]. The remaining question was whether this occurred in vivo and whether inhibition of TNFα could block all downstream responses to restore normal insulin signal transduction

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