View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Springer - Publisher Connector Purinergic Signalling (2006) 2:399–408 DOI 10.1007/s11302-006-9001-7 ORIGINAL ARTICLE E-NTPDases in human airways: Regulation and relevance for chronic lung diseases Lauranell H. Burch & Maryse Picher Received: 11 January 2005 /Accepted: 21 December 2005 / Published online: 30 May 2006 # Springer Science + Business Media B.V. 2006 Abstract Chronic obstructive lung diseases are char- are characterized by higher rates of nucleotide elimi- acterized by the inability to prevent bacterial infection nation, azide-sensitive E-NTPDase activities and ex- and a gradual loss of lung function caused by recurrent pression. This review integrates the biphasic regulation inflammatory responses. In the past decade, numerous of airway E-NTPDases with the function of purine studies have demonstrated the importance of nucleo- signaling in lung diseases. During acute insults, a tide-mediated bacterial clearance. Their interaction transient reduction in E-NTPDase activities may be with P2 receptors on airway epithelia provides a rapid beneficial to stimulate ATP-mediated bacterial clear- Fon-and-off_ signal stimulating mucus secretion, cilia ance. In chronic lung diseases, elevating E-NTPDase beating activity and surface hydration. On the other activities may represent an attempt to prevent P2 hand, abnormally high ATP levels resulting from receptor desensitization and nucleotide-mediated lung damaged epithelia and bacterial lysis may cause lung damage. edema and exacerbate inflammatory responses. Air- way ATP concentrations are regulated by ecto nucle- Keywords apyrase . bacterial clearance . CD39 . oside triphosphate diphosphohydrolases (E-NTPDases) chronic obstructive lung diseases . diphosphohydrolase . which are expressed on the mucosal surface and catalyze endotoxin . purinergic signaling . oxidative stress the sequential dephosphorylation of nucleoside tri- phosphates to nucleoside monophosphates (ATP Y Abbreviations ADP Y AMP). The common bacterial product, ADP adenosine 50-diphosphate Pseudomonas aeruginosa lipopolysaccharide (LPS), AMP adenosine 50-monophosphate induces an acute reduction in azide-sensitive E- ATP adenosine 50-triphosphate NTPDase activities, followed by a sustained increase ASL airway surface liquid in activity as well as NTPDase 1 and NTPDase 3 MCC mucociliary clearance expression. Accordingly, chronic lung diseases, includ- CCS cyclic compressive stress ing cystic fibrosis (CF) and primary ciliary dyskinesia, CF cystic fibrosis CFTR cystic fibrosis transmembrane regulator ENAC epithelial sodium channel L.H. Burch IL-1b interleukin-1beta Laboratory of Respiratory Biology, IL-8 interleukin-8 National Institute of Environmental Health Sciences, LPS lipopolysaccharide Research Triangle Park, Durham, North Carolina, USA MCC mucociliary clearance M. Picher ()) NS AP non-specific alkaline phosphatase Cystic Fibrosis/Pulmonary Research and Treatment Center, PCL periciliary liquid School of Medicine, PCR polymerase chain reaction University of North Carolina, 7010 Thurston-Bowles Building, Chapel Hill, NC 27599, USA TNFa tumor necrosis factor alpha 0 e-mail: [email protected] UTP uridine 5 -triphosphate 400 Purinergic Signalling (2006) 2:399–408 Introduction clearance (MCC), which constitutes the first line of defense against bacterial infection [16]. Mucosal epi- Airway epithelia constitute an essential protective thelial surfaces are protected by an airway surface barrier against lung infection, coordinating luminal liquid (ASL) layer containing a thin mucin sheath and interstitial responses to inhaled pathogens through kept above the cilia by a periciliary liquid (PCL) signals (growth factors, cytokines and nucleotides) layer (Fig. 1). Inhaled bacteria adhere to the mucin provided by epithelial, inflammatory and immune cells and are continuously displaced upward by coordinated [1]. It is now widely accepted that extracellular nucleo- cilia beating activity [17, 18]. Comparative analysis of tides provide an elaborated cell communication system the bioelectric properties of airway epithelia from in mammalian tissues [2, 3] including the airways [4, 5]. normal donors and CF patients revealed that PCL Each signaling event constitutes a brief Fon-and-off_ height is regulated by a delicate balance between switch mechanism allowing the target cells to perceive the activities of the epithelial sodium channel (ENAC) the subsequent signal. The major source of extracellu- and the cystic fibrosis transmembrane regulator (CFTR) lar nucleotides in normal airways is the epithelium, [19]. Cystic fibrosis is characterized by mutations in the releasing ATP under resting conditions and in re- gene encoding CFTR [16]. The lack of ion secretion sponse to mechanical or osmotic stress [6]. While basal through CFTR is associated with Na+ hyperabsorption ATP concentrations maintained under resting condi- by ENAC and water influx, resulting in the depletion tions are insufficient to activate surface receptors, the of the PCL layer essential for cilia beating activity. The levels reached near the site of stimulated release cilia become collapsed under a thick layer of mucus initiate a variety of P2 receptor-mediated responses filled with bacteria and leukocytes, leading to severe [7]. Two P2 receptor families have been identified: inflammatory responses and progressive loss of lung Fast-acting (ionotropic) P2X ligand-gated cation chan- function. nels and slow-acting (metabotropic) G protein-coupled Extracellular nucleotides and nucleosides regulate P2Y receptors [8]. Although ATP activates members CFTR and ENAC [20]. The basal activity of CFTR is of both families, P2X receptors generally respond to maintained by adenosine (A2B) receptors, which higher concentrations (EC50 = 1–10 mM) than P2Y induce G protein-coupled adenylate cyclase, followed receptors (EC50 = 0.1–1.0 mM). Each signal is promptly by cAMP-dependent activation of type II protein j terminated by surface conversion of ATP to adenosine kinase A [5]. In contrast, ATP stimulates Cl secretion j [9, 10] and dispersal into the interstitial fluid. Adeno- through Ca2+-activated Cl channels. This signaling sine also initiates cellular responses through P1 (A1, pathway involves P2Y2 receptors, leading to G pro- A2A,A2B or A3) surface receptors [11]. In the airways, tein-coupled phospholipase C activation and cyto- nucleotide- and adenosine-mediated communications solic Ca2+ mobilization. Water efflux is also stimulated + are involved in wound healing [4], bacterial clearance by P2Y2 receptor-mediated inhibition of Na absorp- [12] and inflammatory responses [1, 3, 13, 14]. tion by ENAC using Ca2+-dependent signaling path- Cell surface nucleotide concentrations are regulated ways [21]. Members of the P2X receptor family also j by three families of ectonucleotidases in mammalian support luminal Cl /water efflux in human airway tissues: Ecto-nucleotide pyrophosphatase/phospho- diesterases (E-NPPs: ATP Y AMP), alkaline phos- phatases (APs: ATP Y AMP Y AMP Y adenosine) and ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases: ATP Y AMP Y AMP) [15]. This review describes the importance of regulating extracel- lular nucleotide concentrations for airway homeostasis and the impact of chronic lung diseases on E-NTPDases. Few studies have addressed the activity or expression of airway E-NTPDases. In this review, the available information is complemented by original data. Fig. 1 Impact of chronic obstructive lung diseases on mucociliary clearance. The polarized epithelium is composed of columnar (ciliated or mucin-secreting) cells facing the lumen and basal cells facing the serosal compartment. Bacterial clearance in Nucleotide-mediated bacterial clearance healthy lungs is maintained by coordinated cilia beating activity within the PCL layer, moving upward the overlying mucus and pathogens. In chronic obstructive lung diseases, cilia are The importance of purine signaling in the airways is collapsed under a thick layer of mucus containing bacteria and well illustrated in nucleotide-mediated mucociliary leukocytes. Purinergic Signalling (2006) 2:399–408 401 epithelia, as demonstrated in primary cultures and cell ATP may reach ASL concentrations sufficiently high j j lines (Beas2B, 16HBE14o , Calu-3, (~CFTE-29o )by to trigger inflammatory responses and lung damage in Ussing chamber and patch-clamp experiments [22]. the absence of infection [43]. The bronchoalveolar The receptors identified in airway epithelia by RT– lavage fluid of rats subjected to positive-pressure PCR were P2X2,P2X4 and P2X5. These non-selective mechanical ventilation contains significantly higher cation channels allow Ca2+ influx, which then stim- protein, ATP and cytokine (IL-6, TNFa) levels than 2+ j ulates Ca -activated Cl channels. Interestingly, P2X7 control animals. Instillation of an equivalent ATP receptors are only detected in CF airway epithelia, concentration increased lung fluid volume, supporting primarily in nasal polyps [22]. Because they are known the existence of P2 and/or P1 receptor-mediated lung to induce apoptosis in response to high ATP concen- edema [43]. Analysis of bronchoalveolar lavage fluid trations [23], P2X7 receptors may contribute to dis- nucleotide content by etheno-derivatization revealed ease-associated epithelial damage. an increase in AMP + adenosine/ADP + ATP ratio The central role of ASL nucleotides for MCC was [44], suggesting that mechanical ventilation up-regu- further substantiated by the