Phosphocholine - an agonist of metabotropic but not of ionotropic functions of α9-containing nicotinic acetylcholine receptors.

K Richter,W Padberg,V Mathes,J M Mcintosh,M Althaus,V Grau,A Hecker,A J Hone,G Krasteva-Christ,A Zakrzewicz,M Fronius

doi:10.1038/srep28660

K Richter, W Padberg + Show 9 more

Open Access

https://doi.org/10.1038/srep28660

Copy DOI

Abstract

We demonstrated previously that phosphocholine and phosphocholine-modified macromolecules efficiently inhibit ATP-dependent release of interleukin-1β from human and murine monocytes by a mechanism involving nicotinic acetylcholine receptors (nAChR). Interleukin-1β is a potent pro-inflammatory cytokine of innate immunity that plays pivotal roles in host defence. Control of interleukin-1β release is vital as excessively high systemic levels cause life threatening inflammatory diseases. In spite of its structural similarity to acetylcholine, there are no other reports on interactions of phosphocholine with nAChR. In this study, we demonstrate that phosphocholine inhibits ion-channel function of ATP receptor P2X7 in monocytic cells via nAChR containing α9 and α10 subunits. In stark contrast to choline, phosphocholine does not evoke ion current responses in Xenopus laevis oocytes, which heterologously express functional homomeric nAChR composed of α9 subunits or heteromeric receptors containing α9 and α10 subunits. Preincubation of these oocytes with phosphocholine, however, attenuated choline-induced ion current changes, suggesting that phosphocholine may act as a silent agonist. We conclude that phophocholine activates immuno-modulatory nAChR expressed by monocytes but does not stimulate canonical ionotropic receptor functions.

Highlights

Life-threatening systemic inflammatory response syndrome (SIRS)[17]
LPS activates Toll-like receptors (TLR)-4 and induces the biosynthesis of pro-IL-1βthat remains within the cytoplasm, unless the cell becomes activated by another danger signal
That the inhibitory effects of PC and Cho are mediated via nicotinic acetylcholine receptors (nAChR) containing α9 and/or α1 0 subunits, we used an analogue of α-conotoxin RgIA (RgIA4, synonym CSP-4), a potent and selective antagonist of human α9*nAChR22,23

Summary

Introduction

Life-threatening systemic inflammatory response syndrome (SIRS)[17]. IL-1βrelease is tightly controlled and the underlying mechanisms are of significant clinical interest. Production of mature IL-1βby human monocytes and macrophages typically depends on two consecutive danger signals such as LPS and extracellular ATP18,19. We demonstrated that free PC and PC-modified macromolecules dose-dependently inhibit ATP-induced release of IL-1βby human monocytic cells[20]. In the same study we showed that a similar effect is provoked by nicotine, acetylcholine (ACh) and choline (Cho)[20]. Nicotine abolishes ATP-induced ion channel functions of P2X7 receptors in U937 cells, a human monocytic cell line, but does not provoke ion currents itself 20. The purpose of this study was to test the hypothesis that binding of PC and Cho to nAChR inhibit P2X7 receptor function similar to nicotine. We provide evidence that PC and Cho induce metabotropic effects via α9α10*-containing nAChR in monocytic cells that result in an inhibition of P2X7 receptor function. Canonical ionotropic functions of α9*nAChR, are triggered by Cho but strikingly not by PC

Objectives

Methods

Results

Conclusion