Xanthine Oxidoreductase Promotes the Inflammatory State of Mononuclear Phagocytes through Effects on Chemokine Expression, Peroxisome Proliferator-activated Receptor-γ Sumoylation, and HIF-1α

Sophie Gibbings,Nancy D Elkins,Hillary Fitzgerald,Janice Tiao,Mari E Weyman,Gayle Shibao,Mehdi A Fini,Richard M Wright

doi:10.1074/jbc.m110.150847

Abstract

The protective effects of pharmacological inhibitors of xanthine oxidoreductase (XOR) have implicated XOR in many inflammatory diseases. Nonetheless, the role played by XOR during inflammation is poorly understood. We previously observed that inhibition of XOR within the inflammatory mononuclear phagocytes (MNP) prevented neutrophil recruitment during adoptive transfer demonstrating the role of XOR in MNP-mediated neutrophil recruitment. To further explore the role of XOR in the inflammatory state of MNP, we studied MNP isolated from inflammatory lungs combined with analyses of MNP cell lines. We demonstrated that XOR activity was increased in inflammatory MNP following insufflation of Th-1 cytokines in vivo and that activity was specifically increased by MNP differentiation. Inhibition of XOR reduced levels of CINC-1 secreted by MNP. Expression of peroxisome proliferator-activated receptor γ (PPARγ) in purified rat lung MNP and MNP cell lines reflected both the presence of PPARγ isoforms and PPARγ SUMOylation, and XOR inhibitors increased levels of SUMO-PPARγ in MNP cell lines. Both ectopic overexpression of XOR cDNA and uric acid supplementation reduced SUMO-PPARγ in MNP cells. Levels of the M2 markers CD36, CD206, and arginase-1 were modulated by uric acid and oxonic acid, whereas siRNA to SUMO-1 or PIAS-1 also reduced arginase-1 in RAW264.7 cells. We also observed that HIF-1α was increased by XOR inhibitors in inflammatory MNP and in MNP cell lines. These data demonstrate that XOR promotes the inflammatory state of MNP through effects on chemokine expression, PPARγ SUMOylation, and HIF-1α and suggest that strategies for inhibiting XOR may be valuable in modulating lung inflammatory disorders.

Highlights

Many cells of the tissue microenvironment, including vascular endothelial cells, tissue epithelial cells, leukocytes, or lymphocytes may be involved in the inflammatory response, mononuclear phagocytes (MNP) of the innate immune system play decisive roles in many inflammatory states
xanthine oxidoreductase (XOR) plays a central role in the function of innate immunity and inflammation, and it is an important mediator of many inflammatory diseases in humans [37, 58]
The development of inflammation as a product of the newly recruited inflammatory MNP. This observation is important because the MNP themselves contribute to injury of the lung epithelium, and XOR inhibitors may provide critical support of the inflamed lung [15, 21, 22]

Summary

Introduction

Many cells of the tissue microenvironment, including vascular endothelial cells, tissue epithelial cells, leukocytes, or lymphocytes may be involved in the inflammatory response, mononuclear phagocytes (MNP) of the innate immune system play decisive roles in many inflammatory states. Data shown here demonstrate that XOR promotes the inflammatory state of MNP in part through effects on chemokine expression, PPAR␥ sumoylation, and HIF-1␣. We observed that XOR activity was increased in U937 cells by treatment with PMA, D3/TGF␤, or MCP-1 but not by exposure to all-trans-retinoic acid (Fig. 2A).

Results

Conclusion