CD38 is a 45-kD ectoenzyme involved in the synthesis of potent calcium (Ca2+)-mobilizing agents, cyclic adenosine diphosphate-ribose (cADPR), and nicotinic acid adenine dinucleotide phosphate (NAADP+). In HIV-1-infected patients, increased CD38 expression on CD8+ T cells is linked to immune system activation and progression of HIV-1 infection. However, the role of CD38 upregulation in astrocyte function and HIV-1-associated dementia (HAD-now called HAND: HIV-1-associated neurocognitive disorder) neuropathogenesis is unclear. To these ends, we used interleukin (IL)-1β and HIV-1gp120 to activate primary human astrocytes and measured CD38 expression using real-time polymerase chain reaction and CD38 function by ADP-ribosyl cyclase activity. We also determined cADPR-mediated changes in single-cell intracellular Ca2+ transients in activated astrocytes in presence or absence of ethylene glycol tetraacetic acid. CD38 levels were downregulated using CD38 small-interfering RNA (siRNA) and intracellular Ca2+ concentration ([Ca2+]i) was measured. We previously reported a ∼20-fold rise in CD38 messenger RNA levels in IL-1β-activated astrocytes. We extend this observation and report that HIV-1gp120 potentiated CD38 expression in a dose-dependent manner and also increased CD38 enzyme activity in control and IL-1β-activated astrocytes. We demonstrate higher cADPR levels in IL-1β-activated astrocytes with a corresponding rise in [Ca2+]i upon cADPR application and its non-hydrolysable analog, 3-deaza-cADPR. In activated astrocytes, pre-treatment with the cADPR-specific antagonist 8-Br-cADPR and CD38 siRNA transfection returned elevated [Ca2+]i to baseline, thus confirming a CD38-cADPR specific response. These data are important for unraveling the mechanisms underlying the role of astrocyte-CD38 in HAD and have broader implications in other inflammatory diseases involving astrocyte activation and CD38 dysregulation.
Bibliographical noteFunding Information:
Acknowledgment This work was supported by RO1NS43113 and RO1NS48837 from NINDS to A. Ghorpade and NIH DA11806 to Dr. Timothy F Walseth. We thank Drs. Jialin Zheng and Chun-Hong Shao for assistance in Ca2+ imaging studies. We would also like to acknowledge Drs. Yuri Persidsky and Servio H. Ramirez for access to Amaxa equipment, and Ms Renee Hirtee for assistance with cyclase measurements. Lastly, we thank Drs. Wei Kou and Jessica Gardner for critical proofreading of the manuscript.
Copyright 2009 Elsevier B.V., All rights reserved.
- HIV-1-associated dementia