P2X 7 receptor is an adenosine triphosphate (ATP)-gated ion channel within the multiprotein inflammasome complex. Until now, little is known about regulation of P2X 7 effector functions in macrophages. In this study, we show that nucleoside triphosphate diphosphohydrolase 1 (NTPDase1)/CD39 is the dominant ectonucleotidase expressed by murine peritoneal macrophages and that it regulates P2X 7 -dependent responses in these cells. Macrophages isolated from NTPDase1-null mice (Entpd1) were devoid of all ADPase and most ATPase activities when compared with WT macrophages (Entpd1 1/1 ).
Entpd1À/À macrophages exposed to millimolar concentrations of ATP were more susceptible to cell death, released more IL-1b and IL-18 after TLR2 or TLR4 priming, and incorporated the fluorescent dye Yo-Pro-1 more efficiently (suggestive of increased pore formation) than Entpd1 1/1 cells. Consistent with these observations, NTPDase1 regulated P2X 7 -associated IL-1b release after synthesis, and this process occurred independently of, and prior to, cytokine maturation by caspase-1. NTPDase1 also inhibited IL-1b release in vivo in the air pouch inflammatory model. Exudates of LPS-injected Entpd1 À/À mice had significantly higher IL-1b levels when compared with Entpd1 1/1 mice. Altogether, our studies suggest that NTPDase1/CD39 plays a key role in the control of P2X 7 -dependent macrophage responses.Key words: ATP-induced death . CD39 . IL-1b . Macrophage . Nucleoside triphosphate diphosphohydrolase 1Supporting Information available online
IntroductionMonocytes/macrophages are myeloid inflammatory cells that play important roles in innate host defense and immune regulation [1]. For example, these cells represent the major source of IL-1 during inflammation, a cytokine playing a pivotal role in chronic inflammatory diseases such as rheumatoid arthritis and several neurodegenerative disorders [2,3]. Monocytes/macrophages express functional P2 receptors specific for extracellular nucleotides, which serve as ''danger'' signals and initiate the immune response [4]. At the mRNA level, primary monocytes express the ion-channel P2X 1,4,5,7 receptors and the G-protein-coupled P2Y 1,2,4,6,11-13 receptors, and macrophages express the same receptor subtypes except P2Y 13 [5]. P2Y 1 , P2Y 2 , [6][7][8]. P2X 7 receptor (formerly P2Z) plays a key role in inflammation [9,10]. P2X 7 receptor activation by extracellular adenosine triphosphate (ATP), released under inflammatory conditions, is a co-stimulus for a massive release of mature and bioactive cytokines of the IL-1 family, such as IL-1b and IL-18, from LPS-primed macrophages and other cell types [11]. The activation of P2X 7 in leucocytes also induces cell death, intracellular pathogen clearance and membrane trafficking [12][13][14]. While nano to low micromolar nucleotide concentrations are sufficient for the activation of other P2 receptors, P2X 7 is activated by far higher concentrations of ATP (in the order of the millimolar (mM)) and/ or by mono adenosine diphosphate (ADP) ribosylation [15].The ...
