Repression of proinflammatory cytokine and inducible nitric oxide synthase (NOS2) gene expression in activated microglia by N-acetyl-O-methyldopamine: Protein kinase a-dependent mechanism

Abstract

Excessive proinflammatory cytokine and NO production by activated microglia play a role in neurodegenerative disorders. To investigate whether the neuroprotectant N-acetyl-O-methyldopamine (NAMDA) downregulates genes associated with microglial activation, we measured gene expression of TNF-alpha, IL-1beta, inducible nitric oxide synthase (NOS2), and an associated cofactor synthesis gene, GTP cyclohydrolase I (GTPCH) in LPS-stimulated microglia cells in the presence or absence of NAMDA. The temporal pattern of cytokine gene expression showed that LPS (0.2 microg/ml) increased TNF-alpha and IL-1beta gene expression at 1 and 3 h, which was repressed by cotreatment of NAMDA. Similarly, LPS also induced GTPCH and NOS2 gene expression at 3 and 6 h, and cotreatment of NAMDA repressed the induction with parallel reduction of nitrite, an oxidative metabolite of nitric oxide. Since transcription factor NF-kappaB is involved in regulating expression of these genes, the effects of NAMDA on NF-kappaB nuclear translocation and DNA binding in immunostimulated microglia were investigated. We found that neither LPS-induced NF-kappaB translocation nor DNA binding activity was affected by cotreatment with NAMDA in BV-2 microglia. On the other hand, NAMDA increased intracellular cAMP levels and potentiated LPS-induced phosphorylated cAMP-responsive element binding protein (pCREB) expression. Treatment with adenosine 3'5'-cyclic monophosphothioate, a specific inhibitor of cAMP-dependent protein kinase (PKA), reversed not only NAMDA-induced pCREB upregulation but also NAMDA-induced repression of TNF-alpha and IL-1beta gene transcription. The data demonstrate that NAMDA represses LPS-induced proinflammatory cytokines gene expression via a cAMP-dependent protein kinase pathway. Thus, repressing proinflammatory cytokines and NOS2 gene expression in activated microglia by NAMDA may provide new therapeutic strategies for ischemic cerebral disease as well as other neurodegenerative diseases.