Journal
GLIA
Volume 58, Issue 14, Pages 1757-1765Publisher
WILEY
DOI: 10.1002/glia.21046
Keywords
adenosine; P2X7 receptor; astrocyte; NAD(+); ectonucleotidase; nucleoside transporter
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Funding
- Ministry of Education, Science and Culture of Japan [21590107]
- Ministry of Education, Culture, Sports, Science and Technology of the Japanese Government
- Grants-in-Aid for Scientific Research [21590107] Funding Source: KAKEN
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Nucleotides and nucleosides play important roles by maintaining brain homeostasis, and their extracellular concentrations are mainly regulated by ectonucleotidases and nucleoside transporters expressed by astrocytes. Extracellularly applied NAD(+) prevents astrocyte death caused by excessive activation of poly(ADP-ribose) polymerase-1, of which the molecular mechanism has not been fully elucidated. Recently, exogenous NAD(+) was reported to enter astrocytes via the P2X7 receptor (P2X7R)-associated channel/pore. In this study, we examined whether the intact form of NAD(+) is incorporated into astrocytes. A large portion of extracellularly added NAD(+) was degraded into metabolites such as AMP and adenosine in the extracellular space. The uptake of adenine ring-labeled [C-14]NAD(+), but not nicotinamide moiety-labeled [H-3]NAD(+), showed time-and temperature-dependency, and was significantly enhanced on addition of apyrase, and was reduced by 8-Br-cADPR and ARL67156, inhibitors of CD38 and ectoapyrase, respectively, and P2X7R knockdown, suggesting that the detected uptake of [C-14]NAD(+) resulted from [C-14] adenosine acting as a metabolite of [C-14]NAD(+). Pharmacological and genetic inhibition of P2X7R with brilliant blue G, KN-62, oxATP, and siRNA transfection resulted in a decrease of [H-3] adenosine uptake, and the uptake was also reduced by low concentration of carbenoxolone and pannexin1 selective peptide blocker (10)panx. Taken together, these results indicate that exogenous NAD(+) is degraded by ectonucleotidases and that adenosine, as its metabolite, is taken up into astrocytes via the P2X7R-associated channel/pore. (C) 2010 Wiley-Liss, Inc.
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