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Originally published In Press as doi:10.1074/jbc.M600236200 on March 20, 2006
J. Biol. Chem., Vol. 281, Issue 21, 14971-14980, May 26, 2006
Up-regulation of Microglial CD11b Expression by Nitric Oxide*
Avik Roy,
Yiu K. Fung,
Xiaojuan Liu, and
Kalipada Pahan1
From the
Section of Neuroscience, Department of Oral Biology, University of Nebraska Medical Center, Lincoln, Nebraska 68583
Increased expression of CD11b, the -integrin marker of microglia, represents microglial activation during neurodegenerative inflammation. However, the molecular mechanism behind increased microglial CD11b expression is poorly understood. The present study was undertaken to explore the role of nitric oxide (NO) in the expression of CD11b in microglial cells. Bacterial lipopolysaccharide (LPS) induced the production of NO and increased the expression of CD11b in mouse BV-2 microglial cells and primary microglia. Either a scavenger of NO (PTIO) or an inhibitor of inducible nitric-oxide synthase (L-NIL) blocked this increase in microglial CD11b expression. Furthermore, co-microinjection of PTIO with LPS was also able to suppress LPS-mediated expression of CD11b and loss of dopaminergic neuronal fibers and neurotransmitters in striatum in vivo. Similarly, other inducers of NO production such as interferon- , interleukin-1 , human immunodeficiency virus type-1 gp120, and double-stranded RNA (poly(IC)) also increased the expression of CD11b in microglia through NO. The role of NO in the expression of CD11b was corroborated further by the expression of microglial CD11b by GSNO, an NO donor. Because NO transduces many intracellular signals via guanylate cyclase (GC), we investigated the role of GC, cyclic GMP (cGMP), and cGMP-activated protein kinase (PKG) in microglial expression of CD11b. Inhibition of LPS- and GSNO-mediated up-regulation of CD11b either by NS2028 (a specific inhibitor of GC) or by KT5823 and Rp-8-bromo-cGMP (specific inhibitors of PKG), and increase in CD11b expression either by 8-bromo-cGMP or by MY-5445 (a specific inhibitor of cGMP phosphodiesterase) alone suggest that NO increases microglial expression of CD11b via GC-cGMP-PKG. In addition, GSNO induced the activation of cAMP response element-binding protein (CREB) via PKG that was involved in the up-regulation of CD11b. This study illustrates a novel biological role of NO in regulating the expression of CD11b in microglia through GC-cGMP-PKG-CREB pathway that may participate in the pathogenesis of devastating neurodegenerative disorders.
Received for publication, January 10, 2006
, and in revised form, March 17, 2006.
* This study was supported by Grants NS39940 and NS48923 from the National Institutes of Health, Grant RG3422A1/1 from the National Multiple Sclerosis Society, and the Michael J. Fox Foundation for Parkinson's Research. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 To whom correspondence should be addressed: Section of Neuroscience, Dept. of Oral Biology, University of Nebraska Medical Center, 40th and Holdrege, Lincoln, NE 68583-0740. Tel.: 402-472-1324; Fax: 402-472-2551; E-mail: kpahan{at}unmc.edu.

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Copyright © 2006 by the American Society for Biochemistry and Molecular Biology.
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