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

• Main Authors: Sebastian Daniel Hiller, Sarah Heldmann, Katrin Richter, Innokentij Jurastow, Mira Küllmar, Andreas Hecker, Sigrid Wilker, Gabriele Fuchs-Moll, Ivan Manzini, Günther Schmalzing, Wolfgang Kummer, Winfried Padberg, J. Michael McIntosh, Jelena Damm, Anna Zakrzewicz, Veronika Grau
• Format: Article
• Language: English
• Published: MDPI AG 2018-04-01
• Series: International Journal of Molecular Sciences
• Subjects: β-NAD; β-nicotinamide adenine dinucleotide; CHRNA7; CHRNA9; CHRNA10; inflammasome; interleukin-1β; iPLA2β; monocyte; P2RY1; P2RY11; PLA2G6; U937 cells
• Online Access: http://www.mdpi.com/1422-0067/19/4/1126

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.