title: Characterization of circulating microparticle-associated CD39 family ecto-nucleotidases in human plasma.
abstract: Phosphohydrolysis of extracellular ATP and ADP is an essential step in purinergic signaling that regulates key pathophysiological processes, such as those linked to inflammation. Classically, this reaction has been known to occur in the pericellular milieu catalyzed by membrane bound cellular ecto-nucleotidases, which can be released in the form of both soluble ecto-enzymes as well as being associated with exosomes. Circulating ecto-nucleoside triphosphate diphosphohydrolase 1 (NTPDase 1/CD39) and adenylate kinase 1 (AK1) activities have been shown to be present in plasma. However, other ecto-nucleotidases have not been characterized in depth. An in vitro ADPase assay was developed to probe the ecto-enzymes responsible for the ecto-nucleotidase activity in human platelet-free plasma, in combination with various specific biochemical inhibitors. Identities of ecto-nucleotidases were further characterized by chromatography, immunoblotting, and flow cytometry of circulating exosomes. We noted that microparticle-bound E-NTPDases and soluble AK1 constitute the highest levels of ecto-nucleotidase activity in human plasma. All four cell membrane expressed E-NTPDases are also found in circulating microparticles in human plasma, inclusive of: CD39, NTPDase 2 (CD39L1), NTPDase 3 (CD39L3), and NTPDase 8. CD39 family members and other ecto-nucleotidases are found on distinct microparticle populations. A significant proportion of the microparticle-associated ecto-nucleotidase activity is sensitive to POM6, inferring the presence of NTPDases, either -2 or/and -3. We have refined ADPase assays of human plasma from healthy volunteers and have found that CD39, NTPDases 2, 3, and 8 to be associated with circulating microparticles, whereas soluble AK1 is present in human plasma. These ecto-enzymes constitute the bulk circulating ADPase activity, suggesting a broader implication of CD39 family and other ecto-enzymes in the regulation of extracellular nucleotide metabolism.
authors.affiliation: Division of Gastroenterology and Hepatology, Department of Medicine, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA, 02115, USA, zgjiang@bidmc.harvard.edu.
authors.forename: Z Gordon
authors.initials: ZG
authors.lastname: Jiang
authors.forename: Yan
authors.initials: Y
authors.lastname: Wu
authors.forename: Eva
authors.initials: E
authors.lastname: Csizmadia
authors.forename: Linda
authors.initials: L
authors.lastname: Feldbrügge
authors.forename: Keiichi
authors.initials: K
authors.lastname: Enjyoji
authors.forename: John
authors.initials: J
authors.lastname: Tigges
authors.forename: Vasilis
authors.initials: V
authors.lastname: Toxavidis
authors.forename: Holger
authors.initials: H
authors.lastname: Stephan
authors.forename: Christa E
authors.initials: CE
authors.lastname: Müller
authors.forename: Christina E
authors.initials: CE
authors.lastname: Müller
authors.forename: C James
authors.initials: CJ
authors.lastname: McKnight
authors.forename: Alan
authors.initials: A
authors.lastname: Moss
authors.forename: Simon C
authors.initials: SC
authors.lastname: Robson
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D015703:Antigens, CD / Q000032:analysis / Q000378:metabolism*; D001081:Apyrase / Q000032:analysis / Q000378:metabolism*; D015153:Blotting, Western; D055252:Cell-Derived Microparticles / Q000201:enzymology*; D002850:Chromatography, Gel; D005434:Flow Cytometry; D006801:Humans
chemical_list: D015703:Antigens, CD; D000244:Adenosine Diphosphate; D001081:Apyrase; C067869:CD39 antigen