Alpha-lipoic acid inhibits TNF-alpha induced NF-kappa B activation through blocking of MEKK1-MKK4-IKK signaling cascades.
The therapeutic effects of alpha-lipoic acid (alpha-LA) via NF-kappa B down regulation were demonstrated on joint inflammation and erosion in an animal model. In this study, we investigated how alpha-LA inhibits the pathway of NF-kappa B activation by TNF-alpha via the mitogen-activated protein kinase (MAPK) pathway in rheumatoid arthritis (RA) fibroblast-like synovial cells (FLS). FLS were stimulated with TNF-alpha following pre-treatment with or without alpha-LA. Electrophoretic mobility shift assays (EMSA) revealed that TNF-alpha activates NF-kappa B in FLS. This was inhibited by alpha-LA at concentrations of 1 mM. TNF-alpha induced IKK mediated phosphorylation of GST-I kappa B and pre-treatment with alpha-LA inhibited this pathway. FLS constitutively express MEKK1, MEKK2, MEKK3, and TAK1 and that their levels are unaffected by TNF-alpha or alpha-LA. Immunoprecipitation using anti-MEKK1 antibody phosphorylated GST-I kappa B and pre-treating the cells with alpha-LA could abolish the reaction. FLS were immunoprecipitated using an antibody to MEKK1, and MKK4 was coprecipitated with MEKK1. In addition, immune complexes precipitated with anti-MKK4 antibody phosphorylated GST-I kappa B, and pre-treatment with alpha-LA inhibited the phosphorylation. Immunoprecipitation assay showed that MEKK1, MKK4, IKK-alpha, IKK-beta, I kappa B, and NF-kappa B comprised immunocomplex. It can be concluded that TNF-alpha activates NF-kappa B in FLS through MEKK1-MKK4-IKK signaling complex, and alpha-LA inhibits this signaling at the level of or upstream of IKK-alpha and IKK-beta.
Lee
Chang-Keun
CK
Division of Allergy and Rheumatology, Department of Internal Medicine, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Republic of Korea.
Lee
Eun Young
EY
Kim
Yong Gil
YG
Mun
Se Hwan
SH
Moon
Hee-Bom
HB
Yoo
Bin
B
D002478:Cells, Cultured; D006801:Humans; D051550:I-kappa B Kinase / Q000037:antagonists & inhibitors*; D048670:MAP Kinase Kinase 4 / Q000037:antagonists & inhibitors*; D048728:MAP Kinase Kinase Kinase 1 / Q000037:antagonists & inhibitors*; D016328:NF-kappa B / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D008063:Thioctic Acid / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors*
D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D008063:Thioctic Acid; C496559:CHUK protein, human; D051550:I-kappa B Kinase; C496560:IKBKB protein, human; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human; D048670:MAP Kinase Kinase 4; C482559:MAP2K4 protein, human