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Retinoic acid inhibits expression of TNF-alpha and iNOS in activated rat microglia
Authors:Dheen S Thameem  Jun Yan  Yan Zhou  Tay Samuel S W  Ling Eng Ang
Affiliation:Department of Anatomy, Molecular Neurobiology Laboratory, Faculty of Medicine, National University of Singapore, Singapore. antstd@nus.edu.sg
Abstract:The release of proinflammatory mediators such as tumor necrosis factor-alpha (TNF-alpha) and nitric oxide by microglia has been implicated in neurotoxicity in chronic neurodegenerative diseases such as Alzheimer's disease. As all-trans-retinoic acid (RA) has been reported to exert anti-inflammatory actions in various cell types, we have examined its effects on the expression of TNF-alpha and inducible nitric oxide synthase (iNOS) in microglia activated by beta-amyloid peptide (Abeta) and lipopolysaccharide (LPS). Exposure of primary cultures of rat microglial cells to Abeta or LPS stimulated the mRNA expression level of TNF-alpha (6-116-fold) and iNOS (8-500-fold) significantly. RA acted in a dose-dependent manner (0.1-10 microM) by attenuating both TNF-alpha (29-97%) and iNOS (61-96%) mRNA expression in microglia exposed to Abeta or LPS. RA-induced inhibition of TNF-alpha and iNOS mRNA expression in activated microglia was accompanied by the concomitant reduction in release of iNOS and TNF-alpha proteins as revealed by nitrite assay and ELISA, respectively. The anti-inflammatory effects of RA were correlated with the enhanced expression of retinoic acid receptor-beta, and transforming growth factor-beta1 as well as the inhibition of NF-kappaB translocation. These results suggest that RA may inhibit the neurotoxic effect of activated microglia by suppressing the production of inflammatory cytokines and cytotoxic molecules.
Keywords:microglia  retinoic acid  TNF‐α  TGF β  iNOS  RAR β  NF‐κB
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