β-Nicotinamide Adenine Dinucleotide (β-NAD) Inhibits ATP-Dependent IL-1β Release from Human Monocytic Cells.

Sebastian Hiller,Anna Zakrzewicz,Veronika Grau,J Mcintosh,Jelena Damm,Sarah Heldmann,Günther Schmalzing,Sigrid Wilker,Wolfgang Kummer,Innokentij Jurastow,Ivan Manzini,Andreas Hecker,Gabriele Fuchs-Moll,Mira Küllmar,Katrin Richter,Winfried Padberg

doi:10.3390/ijms19041126

Abstract

While interleukin-1β (IL-1β) is a potent pro-inflammatory cytokine essential for host defense, high systemic levels cause life-threatening inflammatory syndromes. ATP, a stimulus of IL-1β maturation, is released from damaged cells along with β-nicotinamide adenine dinucleotide (β-NAD). Here, we tested the hypothesis that β-NAD controls ATP-signaling and, hence, IL-1β release. Lipopolysaccharide-primed monocytic U937 cells and primary human mononuclear leukocytes were stimulated with 2′(3′)-O-(4-benzoyl-benzoyl)ATP trieethylammonium salt (BzATP), a P2X7 receptor agonist, in the presence or absence of β-NAD. IL-1β was measured in cell culture supernatants. The roles of P2Y receptors, nicotinic acetylcholine receptors (nAChRs), and Ca2+-independent phospholipase A2 (iPLA2β, PLA2G6) were investigated using specific inhibitors and gene-silencing. Exogenous β-NAD signaled via P2Y receptors and dose-dependently (IC50 = 15 µM) suppressed the BzATP-induced IL-1β release. Signaling involved iPLA2β, release of a soluble mediator, and nAChR subunit α9. Patch-clamp experiments revealed that β-NAD inhibited BzATP-induced ion currents. In conclusion, we describe a novel triple membrane-passing signaling cascade triggered by extracellular β-NAD that suppresses ATP-induced release of IL-1β by monocytic cells. This cascade links activation of P2Y receptors to non-canonical metabotropic functions of nAChRs that inhibit P2X7 receptor function. The biomedical relevance of this mechanism might be the control of trauma-associated systemic inflammation.

Highlights

Interleukin-1β (IL-1β) is a potent pro-inflammatory cytokine, predominantly but not exclusively produced by innate immune cells, that plays a central role in host defense against infections
We demonstrate in this study that β-nicotinamide adenine dinucleotide (β-NAD) efficiently and dose-dependently inhibits BzATP-induced release of IL-1β by human monocytic cells
Upon application of β-NAD to LPS-primed monocytic U937 cells, the release of IL-1β to the cell culture supernatant is dose-dependently and fully inhibited. β-NAD is as effective as nicotine that functions as a strong inhibitor of ATP-dependent IL-1β release from human monocytic cells, as described previously [8]

Summary

Introduction

Interleukin-1β (IL-1β) is a potent pro-inflammatory cytokine, predominantly but not exclusively produced by innate immune cells, that plays a central role in host defense against infections. Multiple signals and pathways have been described that trigger the controlled biosynthesis and release of IL-1β. Danger- or pathogen-associated molecular patterns typically activate pattern recognition receptors that induce the biosynthesis of the inactive cytoplasmic precursor pro-IL-1β [2,3,4,5]. Extracellular ATP released by damaged cells is a well-known trigger of inflammasome activation. Binding of extracellular ATP to the ATP-sensitive P2X7 receptor causes opening of the ion channel, release of K+ ions, and assembly of the NLRP3 (NACHT, LRR and PYD domains-containing protein 3) inflammasome followed by activation of caspase-1 that cleaves the inactive pro-IL-1β and enables the release of mature IL-1β [2,4,5,6]

Methods

Results

Conclusion