title: Dexamethasone suppresses monocyte chemoattractant protein-1 production via mitogen activated protein kinase phosphatase-1 dependent inhibition of Jun N-terminal kinase and p38 mitogen-activated protein kinase in activated rat microglia.
abstract: Microglial cells release monocyte chemoattractant protein-1 (MCP-1) which amplifies the inflammation process by promoting recruitment of macrophages and microglia to inflammatory sites in several neurological diseases. In the present study, dexamethasone (Dex), an anti-inflammatory and immunosuppressive drug has been shown to suppress the mRNA and protein expression of MCP-1 in activated microglia resulting in inhibition of microglial migration. This has been further confirmed by the chemotaxis assay which showed that Dex or MCP-1 neutralization with its antibody inhibits the microglial recruitment towards the conditioned medium of lipopolysaccharide (LPS)-treated microglial culture. This study also revealed that the down-regulation of the MCP-1 mRNA expression by Dex in activated microglial cells was mediated via mitogen-activated protein kinase (MAPK) pathways. It has been demonstrated that Dex inhibited the phosphorylation of Jun N-terminal kinase (JNK) and p38 MAP kinases as well as c-jun, the JNK substrate in microglia treated with LPS. The involvement of JNK and p38 MAPK pathways in induction of MCP-1 production in activated microglial cells was confirmed as there was an attenuation of MCP-1 protein release when microglial cells were treated with inhibitors of JNK and p38. In addition, Dex induced the expression of MAP kinase phosphatase-1 (MKP-1), the negative regulator of JNK and p38 MAP kinases in microglial cells exposed to LPS. Blockade of MKP-1 expression by triptolide enhanced the phosphorylation of JNK and p38 MAPK pathways and the mRNA expression of MCP-1 in activated microglial cells treated with Dex. In summary, Dex inhibits the MCP-1 production and subsequent microglial cells migration to the inflammatory site by regulating MKP-1 expression and the p38 and JNK MAPK pathways. This study reveals that the MKP-1 and MCP-1 as novel mediators of biological effects of Dex may help developing better therapeutic strategies for the treatment of patients with neuroinflammatory diseases.
authors.affiliation: Department of Anatomy, Molecular Neurobiology Laboratory, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhou
authors.forename: Eng-Ang
authors.initials: EA
authors.lastname: Ling
authors.forename: S Thameem
authors.initials: ST
authors.lastname: Dheen
mesh_terms: D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D001921:Brain / Q000187:drug effects / Q000276:immunology / Q000503:physiopathology; D018797:Cell Cycle Proteins / Q000187:drug effects / Q000378:metabolism; D002465:Cell Movement / Q000187:drug effects / Q000276:immunology; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D002633:Chemotaxis / Q000187:drug effects / Q000276:immunology; D018920:Coculture Techniques; D003907:Dexamethasone / Q000494:pharmacology*; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D054638:Dual Specificity Phosphatase 1; D004660:Encephalitis / Q000188:drug therapy* / Q000276:immunology / Q000503:physiopathology; D017874:Immediate-Early Proteins / Q000187:drug effects / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects* / Q000276:immunology; D017628:Microglia / Q000187:drug effects* / Q000201:enzymology* / Q000276:immunology; D010749:Phosphoprotein Phosphatases / Q000187:drug effects / Q000378:metabolism; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D016896:Treatment Outcome; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D000893:Anti-Inflammatory Agents; C491766:Ccl2 protein, rat; D018797:Cell Cycle Proteins; D018932:Chemokine CCL2; D017874:Immediate-Early Proteins; D003907:Dexamethasone; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054638:Dual Specificity Phosphatase 1; C517021:Dusp1 protein, rat; D017027:Protein Tyrosine Phosphatases