Norepinephrine Increases IκBα Expression in Astrocytes

Abstract

The neurotransmitter norepinephrine (NE) can inhibit inflammatory gene expression in glial cells; however, the mechanisms involved are not clear. In primary astrocytes, NE dose-dependently increased the expression of inhibitory IB␣ protein accompanied by an increase in steady state levels of IB␣ mRNA. Maximal increases were observed at 30 -60 min for the mRNA and at 4 h for protein, and these effects were mediated by NE binding to ␤-adrenergic receptors. NE activated a 1.3-kilobase IB␣ promoter transfected into astrocytes or C6 glioma cells, and this activation was prevented by a ␤-antagonist and by protein kinase A inhibitors but not by an NFB inhibitor. NE increased IB␣ protein in both the cytosolic and the nuclear fractions, suggesting an increase in nuclear uptake of IB␣. IB␣ was detected in the frontal cortex of normal adult rats, and its levels were reduced if central NE levels were depleted by lesion of the locus ceruleus. The reduction of brain IB␣ levels was paralleled by increased inflammatory responses to lipopolysaccharide. These results demonstrate that IB␣ expression is regulated by NE at both transcriptional and post-transcriptional levels, which could contribute to the observed anti-inflammatory properties of NE in vitro and in vivo.The activation of inflammatory responses in brain is normally under tight regulation that prevents the accumulation of potentially cytotoxic mediators including cytokines and reactive oxygen species (1-3). It has therefore been suggested that intrinsic mechanisms exist that maintain the brain in a refractory state of inflammatory activation. In primary cultures of rat astrocytes, we showed that neurotransmitter norepinephrine (NE) 1 prevents induction of the inducible form of nitric oxide synthase (NOS2) (4, 5) by bacterial endotoxin lipopolysaccharide (LPS) or by a combination of proinflammatory cytokines (interleukin 1␤, tumor necrosis factor ␣, and interferon ␥). Similarly, others show that NE reduces glial expression of pro-inflammatory cytokines including interleukin 1␤ and tumor necrosis factor ␣ (6 -9) and of cell adhesion molecules (13). A similar role for NE in regulating inflammatory events in brain is supported by our recent findings that experimental depletion of brain NE levels by chemical lesion of the locus ceruleus (LC) increases the cortical inflammatory responses to injection of aggregated amyloid ␤ (14). The fact that LC neurons are lost in Alzheimer's disease (15) and that levels of ␤ 2 -adrenergic receptor (␤ARs) are reduced in astrocytes in multiple sclerosis patients (16,17) suggests that diminished NE levels or perturbations of the NE-signaling system contribute to the neuroinflammation that occurs in these diseases.The mechanism(s) by which NE reduces inflammatory gene expression is not yet well defined. In astrocytes, we found that NE induced protein binding to a 27-bp region of the rat NOS2 promoter, which is located immediately upstream of a NFB binding site located at bp position Ϫ107 to Ϫ96 (18). This 27-bp region contains several potenti...

Involvement of Phosphatidylinositol 3-Kinase-Mediated Up-Regulation of IκBα in Anti-Inflammatory Effect of Gemfibrozil in Microglia

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G protein-coupled receptors as therapeutic targets for multiple sclerosis

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Peroxisome Proliferator-activated Receptor γ Thiazolidinedione Agonists Increase Glucose Metabolism in Astrocytes

“…mRNA Analysis-Total cytoplasmic RNA was prepared from cells using TRIZOL reagent (Invitrogen), aliquots were converted to cDNA using random hexamer primers, and mRNA levels were estimated by real time, quantitative RT-PCR (50). The primers used for GLUT-1 detection were 939F (5Ј-TGA AAG AAG AGG GTC GGC AGA TAA-3Ј), corresponding to bases 939 -960, and 1301R (5Ј AGA TGG CCA CGA TGC TCA GAT AGG-3Ј), complementary to bases 1278 -1301 of the rat GLUT-1 cDNA sequence, which yield a 363-bp product.…”