P2X7 Receptor Induces Tumor Necrosis Factor-α Converting Enzyme Activation and Release to Boost TNF-α Production.

Maria Barberà-Cremades,Pablo Pelegrín,Ana I Gómez,Alberto Baroja-Mazo,Carlos M Martínez,Carlos De Torre-Minguela,Laura Martínez-Alarcón

doi:10.3389/fimmu.2017.00862

Maria Barberà-Cremades, Pablo Pelegrín + Show 5 more

Open Access

https://doi.org/10.3389/fimmu.2017.00862

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Abstract

Tumor necrosis factor (TNF)-α is a major pro-inflammatory cytokine produced in response to toll-like receptor stimulation. TNF-α release is controlled by the activity of TNF-α converting enzyme (TACE) that cut membrane-bound TNF-α to shed its ectodomain as a soluble cytokine. The purinergic receptor P2X ligand-gated ion channel 7 (P2X7) is activated in response to elevated concentrations of extracellular ATP and induces different pro-inflammatory pathways in macrophages to establish an inflammatory response. P2X7 receptor promotes the activation of the inflammasome and the release of interleukin-1β, the production of inflammatory lipids, and the generation of reactive oxygen species. In this study, we analyzed the mechanism of P2X7 receptor responsible of TNF-α release after priming macrophages with LPS doses ≤100 ng/ml. We found that P2X7 receptor increases the extracellular activity of TACE through the release of the mature form of TACE in exosomes. This effect was blocked using P2X7 receptor inhibitors or in macrophages obtained from P2X7 receptor-deficient mice. Elevation of intracellular Ca2+ and p38 mitogen-activated protein kinase after P2X7 receptor activation were involved in the release of TACE, which was able to process TNF-α on nearby expressing cells. Finally, we observed an increase of TNF-α in the peritoneal lavage of mice treated with LPS and ATP. In conclusion, P2X7 receptor induces the release of TACE in exosomes to the extracellular compartment that could amplify the pro-inflammatory signal associated to this receptor. These results are important for the development of therapeutics targeting P2X7 receptor.

Highlights

The coordinated response of the innate immune system observed during inflammation requires the activation of a complex system of sensors to induce the release of different signaling molecules [1]
This result is in line with our recent work identifying tumor necrosis factor (TNF)-α as one of the proteins released in LPS-primed macrophages after the activation of P2X ligand-gated ion channel 7 (P2X7) receptor by extracellular ATP [12]
There are two main findings from the present study: first, we have identified TACE activation and TNF-α release associated to P2X7 receptor in macrophages, and second, P2X7 receptor signaling induces the release of mature TACE in exosomes that could shed

Summary

Introduction

The coordinated response of the innate immune system observed during inflammation requires the activation of a complex system of sensors to induce the release of different signaling molecules [1]. IL-1β is a key cytokine implicated in the development of different chronic inflammatory diseases and, P2X7 receptor is a potential target to develop antiinflammatory drugs to treat chronic inflammatory conditions as rheumatoid arthritis or Crohn’s disease [5,6,7]. TNF-α is a master cytokine for the inflammatory response, contributing to different inflammatory conditions, and therapeutics blocking TNF-α signaling are approved drugs for the treatment of rheumatoid arthritis or Crohn’s disease [13, 14]. TNF-α production is induced by toll-like receptor that increases TNFA gene transcription and the translation of TNF-α as an integral membrane protein that traffics from the endoplasmic reticulum to the plasma membrane. TACE is a plasma membrane member of the ADAM family of metalloproteases (a disintegrin and metalloprotease; ADAM-17), which activity is modulated by mitogen-activated protein kinases (MAPKs) and ROS [16]

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