Inhibition of the phosphoinositide 3-kinase pathway decreases innate resistance to lipopolysaccharide toxicity in TLR4 deficient mice

Johnson Chia-Shen Yang,Yi-Chan Wu,Chia-Jung Wu,Siou-Ling Tzeng,Yi-Chun Chen,Tsu-Hsiang Lu,Ching-Hua Hsieh,Cheng-Shyuan Rau,Shao-Chun Wu,Ming-Wei Lin

doi:10.1186/1423-0127-21-20

Abstract

BackgroundUpon lipopolysaccharide (LPS) stimulation, activation of both the Toll-like receptor 4 (TLR4) and phosphoinositide 3-kinase (PI3K) pathways serves to balance proinflammatory and anti-inflammatory responses. Although the antagonist to TLR4 represents an emerging promising target for the treatment of sepsis; however, the role of the PI3K pathway under TLR4-null conditions is not well understood. This goal of this study was to investigate the effect of inhibition of PI3K on innate resistance to LPS toxicity in a murine model.ResultsThe overall survival of the cohorts receiving intraperitoneal injections of 100, 500, or 1000 μg LPS from Escherichia coli serotype 026:B6 after 7 d was 100%, 10%, and 10%, respectively. In contrast, no mortality was noted after 500-μg LPS injection in Tlr4-/- mice. When the PI3K inhibitor LY294002 was injected (1 mg/25 g body weight) 1 h prior to the administration of LPS, the overall survival of the Tlr4-/- mice was 30%. In the Tlr4-/- mice, the LPS injection induced no NF-κB activation but an increased Akt phosphorylation in the lung and liver, when compared to that of the C57BL/6 mice. Injection of 500 μg LPS led to a significant induction in O2- detected by electron paramagnetic resonance (EPR) spin trapping spectroscopy in the lung and liver at 3 and 6 h in C57BL/6 but not Tlr4-/- mice. Addition of LY294002 only significantly increased the O2- level in the lung and liver of the Tlr4-/- mice but not in the C57BL/6 mice following 500-μg LPS injection. In addition, the serum IL-1β and IL-2 levels were more elevated in C57BL/6 mice than in Tlr4-/- mice. Notably, IL-1β and IL-2 were significantly increased in Tlr4-/- mice but not in the C57BL/6 mice when the PI3K pathway was inhibited by LY294002 prior to LPS injection.ConclusionsIn this study, we demonstrate that innate resistance to LPS toxicity in Tlr4-/- mice is impaired by inhibition of the PI3K pathway, with a corresponding increase in mortality and production of tissue O2- and inflammatory cytokines.

Highlights

Upon lipopolysaccharide (LPS) stimulation, activation of both the Toll-like receptor 4 (TLR4) and phosphoinositide 3-kinase (PI3K) pathways serves to balance proinflammatory and anti-inflammatory responses
We demonstrate that innate resistance to LPS toxicity in Tlr4−/− mice is reduced by the inhibition of the PI3K pathway, with a corresponding increase in mortality and production of tissue superoxide and inflammatory cytokines
After injection of 500 μg LPS in the Tlr4−/− mice, no mortality was noted throughout the experiment

Summary

Introduction

Upon lipopolysaccharide (LPS) stimulation, activation of both the Toll-like receptor 4 (TLR4) and phosphoinositide 3-kinase (PI3K) pathways serves to balance proinflammatory and anti-inflammatory responses. The antagonist to TLR4 represents an emerging promising target for the treatment of sepsis; the role of the PI3K pathway under TLR4-null conditions is not well understood This goal of this study was to investigate the effect of inhibition of PI3K on innate resistance to LPS toxicity in a murine model. In a murine model of cecal ligation and puncture-induced polymicrobial sepsis, inhibition of PI3K activity increased serum cytokine levels and mortality [20]. In contrast to these findings, stimulation of the PI3K pathway was correlated with improved outcome [20]. Administration of endotoxin to PI3Kγ-knockout mice resulted in decreased acute lung injury, suggesting that the PI3K pathway plays an important role in the pathophysiology of endotoxic injury [21]

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