Redox regulation of glial inflammatory response to lipopolysaccharide and interferonγ

Abstract

Astrocytes and microglia, the two immune-regulatory cells of the central nervous system (CNS), are activated by a variety of pathogens and cytokines to elicit rapid transcriptional responses. This program of activation is initiated by a set of intracellular signaling cascades that includes mitogen-activated protein kinase (MAPK), nuclear factor (NF) kappaB, and Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathways. This study defines the critical role that NADPH oxidase(Phox)-derived reactive oxygen species (ROS) play in lipopolysaccharide (LPS)- and interferon (IFN)gamma-induced signaling cascades leading to gene expression in glial cells. Treatment of rat microglia and astrocytes with LPS and IFNgamma resulted in a rapid activation of Phox and the release of ROS followed by an induction of inducible nitric oxide synthase (iNOS) expression. iNOS induction was blocked by inhibitors of Phox, i.e., diphenylene iodonium chloride (DPI) and 4-(2-aminoethyl) benzenesulfonylfluoride (AEBSF), suggesting an involvement of ROS signaling in iNOS gene expression. Exogenous catalase but not superoxide dismutase suppressed the basal activity and completely blocked induced levels of NO/iNOS, suggesting that hydrogen peroxide is the ROS involved. Phox inhibitors and catalase also suppressed LPS/IFNgamma-induced expression of cytokines, i.e., interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF)alpha and blocked LPS activation of MAP kinases (i.e., p38 MAPK, c-Jun N-terminal kinase and extracellular signal-regulated kinase), NFkappaB, and IFNgamma-induced STAT1 phosphorylation. A microglial cell line stably transfected with a mutant form of Phox subunit, i.e., p47(phox) W(193)R, and primary astrocytes derived from Phox-deficient mice showed attenuated ROS production and induction of iNOS in response to LPS/IFNgamma, further strengthening the notion that Phox-derived ROS are crucial for proinflammatory gene expression in glial cells.

Signals for the induction of nitric oxide synthase in astrocytes

“…They have shown that stimulation of rat primary astrocytes leads to rapid activation of NADPH oxidase and release of ROS followed by expression of iNOS. Consistently, attenuated expression of iNOS is observed in primary astrocytes derived from gp91 Phox -deficient mice (Pawate et al, 2004). Furthermore, inhibition of (LPS + IFN-γ)-induced expression of iNOS and production of NO by exogenous addition of catalase but not superoxide dismutase suggests that H 2 O 2 but not O 2 − is actually required for astroglial expression of iNOS.…”

“…Pawate et al (2004) have defined a critical role of NADPH oxidase in (LPS + IFN-γ)-induced expression of iNOS in glial cells. They have shown that stimulation of rat primary astrocytes leads to rapid activation of NADPH oxidase and release of ROS followed by expression of iNOS.…”

The Ca2+-Activated K+ChannelKCNN4/KCa3.1 Contributes to Microglia Activation and Nitric Oxide-Dependent Neurodegeneration

“…Signal transduction pathways involving p38 MAPK and NF-B contribute to microglia activation and production of proinflammatory molecules (Pawate et al, 2004) that can lead to neurotoxicity in vivo (for review, see Zhang and Stanimirovic, 2002). Therefore, we examined whether activation of either pathway is affected by KCa3.1 channel blockade.…”

Pivotal Role of gp91 phox -Containing NADH Oxidase in Lipopolysaccharide-Induced Tumor Necrosis Factor-α Expression and Myocardial Depression

“…28,29 Recent studies have shown that NAD(P)H oxidase plays an important role in LPSinduced TNF-␣ expression and neurotoxicity in microglia and astrocytes. 30,31 In the heart, NAD(P)H oxidase activity and O 2 Ϫ production are increased in response to LPS stimulation. 12,13 However, a causal relationship between NAD(P)H oxidase activation and myocardial dysfunction during sepsis has not been reported.…”