The vascular ectonucleotidases CD39 [ENTPD1 (ec-tonucleoside triphosphate diphosphohydrolase-1), EC 3.6.1.5] and CD73 [EC 3.1.3.5] generate adenosine from extracellular nucleotides. CD39 activity is critical in determining the response to ischemia-reperfusion injury (IRI), and CD39 null mice exhibit heightened sensitivity to renal IRI. Adenosine has multiple mechanisms of action in the vasculature including direct endothelial protection, antiinflammatory and antithrombotic effects and is protective in several models of IRI. Mice transgenic for human CD39 (hCD39) have increased capacity to generate adenosine. We therefore hypothesized that hCD39 transgenic mice would be protected from renal IRI. The overexpression of hCD39 conferred protection in a model of warm renal IRI, with reduced histological injury, less apoptosis and preserved serum creatinine and urea levels. Benefit was abrogated by pretreatment with an adenosine A2A receptor antagonist. Adoptive transfer experiments showed that expression of hCD39 on either the vasculature or circulating cells mitigated IRI. Furthermore, hCD39 transgenic kidneys transplanted into syngeneic recipients after prolonged cold storage performed significantly better and exhibited less histological injury than wild-type control grafts. Thus, systemic or local strategies to promote adenosine generation and signaling may have beneficial effects on warm and cold renal IRI, with implications for therapeutic application in clinical renal transplantation.

As part of its pathogenesis, Legionella pneumophila persists within human alveolar macrophages in non-acidified organelles that do not mature into phagolysosomes. Two L. pneumophila genes, lpg0971 and lpg1905, are predicted to encode ecto-nucleoside triphosphate diphosphohydrolases (ecto-NTPDases) that share sequence similarity with human CD39/NTPDase1. The predicted products possess five apyrase conserved domains that are typical of eukaryotic ecto-NTPDases. In this study, we found that an lpg1905 mutant was recovered in lower numbers from macrophages, alveolar epithelial cells and the amoeba, Hartmannella vermiformis compared with wild-type L. pneumophila and an lpg0971 mutant. Similar to human CD39, recombinant purified Lpg1905 exhibited ATPase and ADPase activity and possessed the ability to inhibit platelet aggregation. Mutation of a conserved Glu159 residue that is essential for CD39 activity inhibited ATPase and ADPase activity of Lpg1905. In addition, enzyme activity was inhibited in the presence of the specific ecto-NTPDase inhibitor, ARL67156. The entry and replication defect of the lpg1905 mutant was reversed upon transcomplementation with lpg1905 but not lpg1905E159A encoding an enzymatically inactive form of the protein. Although several protozoan parasites exhibit ecto-NTPDase activity, including Toxoplasma gondii, Trichomonas vaginalis and Trypanosoma cruzi, this is the first time a bacterial ecto-NTPDase has been implicated in virulence.

Platelet activation is believed to play an important role in the triggering of thrombosis of human blood by pig islets. We used a transgenic mouse model to investigate whether overexpression of CD39 (ecto nucleoside triphosphate diphosphohydrolase 1 [ENTPD1], EC 3.6.1.5), an ectonucleotidase that degrades the platelet agonists ATP, could interfere with this process. Islets isolated from CD39 transgenic mice showed 2.4-fold higher NTPDase activity than wild-type controls. When incubated with human blood, these islets significantly delayed clotting time compared to wild type islets (7.9 +/- 0.89 min versus 4.3 +/- 0.77 min, P = 0.007). Importantly, expression of human CD39 in the islets of transgenic mice had no deleterious effect on glucose metabolism. These results suggest that transgenic expression of human CD39 does not interfere with islet function and may be a useful strategy to inhibit thrombosis induced by intraportal administration of islet xenografts.