iNOS In Glial Cells Research Articles

Minocycline protects neurons against glial cells-mediated bilirubin neurotoxicity

Unconjugated bilirubin, the end product of heme catabolism and antioxidant, induced brain damage in human neonates is a well-recognized clinical syndrome. However, the cellular and molecular mechanisms underlying bilirubin neurotoxicity remain unclear. To characterize the sequence of events leading to bilirubin-induced neurotoxicity, we investigated whether bilirubin-induced glial activation was involved in bilirubin neurotoxicity by exposing co-cultured rat glial cells and cerebellar granule neurons (CGN) to bilirubin. We found that bilirubin could markedly induce the expression of TNF-α and iNOS in glial cells, and even at low concentrations, the co-culture of glial cells with neurons significantly enhances neurotoxicity of bilirubin. Pretreatment of the co-cultured cells with minocycline protected CGN from glia-mediated bilirubin neurotoxicity and inhibited overexpression of TNF-α and iNOS in glia. Furthermore, we found that high doses of bilirubin were able to induce glial injury, and minocycline attenuated bilirubin-induced glial cell death. Our data suggest that glial cells play an important role in brain damage caused by bilirubin, and minocycline blocks bilirubin-induced encephalopathy possibly by directly and indirectly inhibiting neuronal death pathways.

L-DOPA-induced dyskinesia in Parkinson's disease: Are neuroinflammation and astrocytes key elements?

Inflammation in Parkinson's disease (PD) is a new concept that has gained ground due to the potential of mitigating dopaminergic neuron death by decreasing inflammation. The solution to this question is likely to be complex. We propose here that the significance of inflammation in PD may go beyond the nigral cell death. The pathological process that underlies PD requires years to reach its full extent. A growing body of evidence has been accumulated on the presence of multiple inflammatory signs in the brain of PD patients even in very late stages of the disease. Because neuron-microglia-astrocyte interactions play a major role in the plasticity of neuronal response to l-DOPA in post-synaptic neurons, we focused this review on our recent results of l-DOPA-induced dyskinesia in rodents correlating it to significant findings regarding glial cells and neuroinflammation. We showed that in the rat model of PD/l-DOPA-induced dyskinesia there was an increased expression of inflammatory markers, such as the enzymes COX2 in neurons and iNOS in glial cells, in the dopamine-denervated striatum. The gliosis commonly seem in PD was associated with modifications in astrocytes and microglia that occur after chronic treatment with l-DOPA. Either as a cause, consequence, or promoter of progression of neuronal degeneration, inflammation plays a role in PD. The key aims of current PD research ought to be to elucidate (a) the time sequence in which the inflammatory factors act in PD patient brain and (b) the mechanisms by which neuroinflammatory response contributes to the collateral effects of l-DOPA treatment.

Regulation of inducible nitric oxide synthase gene in glial cells.

Elevated levels of NO produced within the central nervous system (CNS) are associated with the pathogenesis of neuroinflammatory and neurodegenerative human diseases such as multiple sclerosis, HIV dementia, brain ischemia, trauma, Parkinson's disease, and Alzheimer's disease. Resident glial cells in the CNS (astroglia and microglia) express inducible nitric oxide synthase (iNOS) and produce high levels of NO in response to a wide variety of proinflammatory and degenerative stimuli. Although pathways resulting in the expression of iNOS may vary in two different glial cells of different species, the intracellular signaling events required for the expression of iNOS in these cells are slowly becoming clear. Various signaling cascades converge to activate several transcription factors that control the transcription of iNOS in glial cells. The present review summarizes different results and discusses current understandings about signaling mechanisms for the induction of iNOS expression in activated glial cells. A complete understanding of the regulation of iNOS expression in glial cells is expected to identify novel targets for therapeutic intervention in NO-mediated neurological disorders.

TAK1-mediated induction of nitric oxide synthase gene expression in glial cells.

Inflammatory cell signaling leading to transcriptional activation is primarily mediated by signal transduction via mitogen-activated protein kinase (MAPK) and NFkappaB pathways. A common upstream kinase that signals the activation of these pathways is TGFbeta-activated kinase 1 (TAK1), which itself becomes activated in response to cytokines and upon engagement of a class of cell surface receptors involved in innate immunity, that is Toll-like receptors (TLRs) by bacterial and viral pathogens. This study directly tests the role of TAK1 in the induction of inducible nitric oxide (NO) synthase (iNOS) in glial cells, which represent immune-regulatory cells of the CNS, by transient transfection assays. Transfection of C-6 glia, primary astrocytes and a rat microglial cell line with TAK1 (but not its inactive form) along with its activator protein, TAK1-binding protein 1 (TAB1) resulted in a marked stimulation of a co-transfected rat iNOS promoter-reporter construct (iNOS-Luc). TAK1-induced iNOS-Luc activity was substantially inhibited by pharmacological inhibitors of the known downstream kinases, p38 MAPK and JNK (SB203580 and SP620125), and was almost completely blocked by co-expression of a phosphorylation mutant of IkappaB. TAK1/TAB1 also induced the production of NO and the expression of iNOS in microglial cells in a p38 MAPK-, JNK- and NFkappaB-dependent manner. The results of these studies provide evidence for an important role for TAK1-mediated intracellular signaling, via p38 MAPK, JNK and NFkappaB, in the transcriptional activation of iNOS in glial cells.

Antisense blockade of inducible nitric oxide synthase in glial cells derived from adult SJL mice

Increasing evidence suggests a correlation between cytokine-induced nitric oxide synthase (iNOS) and demyelination in Multiple sclerosis (MS). Inhibition of iNOS may therefore be a novel therapeutic approach in MS. To test an antisense oligodeoxynucleotide (ODN) knockdown strategy for inhibiting iNOS, we used lipopolysaccharide (LPS) together with γ-interferon (IFN-γ) to induce iNOS in adult mouse mixed glial cell cultures. We administered an iNOS-derived antisense phosphorothiorate oligodeoxynucleotide (S-ODN) to block the induction. The antisense ODN treatment resulted in significant inhibition of LPS and IFN-γ induced iNOS mRNA and protein expression. It also inhibited nitric oxide (NO) and cyclic GMP (cGMP) production in a dose dependent fashion. Sense and random S-oligo had no effect in any of these studies. These data indicate the efficacy and specificity of the antisense oligodeoxynucleotide approach in inhibiting iNOS in glial cells.

Inducible nitric oxide synthase in glial cells

Nitric oxide (NO), a free radical gas, has been suggested to mediate both synaptic plasticity and neuronal death. NO is generated by constitutive and inducible types of NO synthase (cNOS and iNOS, respectively). The neuronal cNOS was recently cloned, sequenced and characterized. In contrast, properties of iNOS in the brain are not fully understood. It is noted that glial cells can form NO and that microglial and reactive astroglial cells are accumulated around neurodegenerative sites in the brain, suggesting a relationship between neuronal injury and NO originated from glial cells. We found that several stimuli such as endotoxin (lipopolysaccharide) and cytokines induced iNOS in glial cells of rat brain. This article reviews recent findings on characteristics and the induction mechanism of iNOS in the glial cells, and discusses the possible pathophysiological functions of iNOS in the brain.