Enhanced expression of mRNA for transforming growth factor β activated kinase 1 in CD34+ cells of the bone marrow in...

Transforming growth factor β activated kinase 1 (TAK1) has been found to mediate maladaptive tumour necrosis factor (TNF) signalling, leading to hyperactive downstream nuclear factor Kappa β (NF-κB) signalling. We explored the expression of TAK1 mRNA in bone marrow CD34+ cells in rheumatoid arthritis (RA) to delineate the mechanism for their abnormal response to TNF-α and differentiate into fibroblast-like cells.

CD34+ cells were purified from bone marrow samples obtained from 47 RA patients and 27 osteoarthritis (OA) patients during joint operations via aspiration from the iliac crest. The expression of mRNAs for TAK1 and NFκB1 was examined by quantitative RT-PCR.

TAK1 mRNA expression in bone marrow CD34+ cells was significantly higher in RA than in OA (TAK1/β-actin: [11.980 ± 2.380] x 10-3 and [5.593±1.307] x 10-3 [mean ± SEM], respectively; p=0.0238). TAk1 mRNA expression was not different depending on the type of operated joints or on the severity type of RA. Nor was it correlated with serum CRP or rheumatoid factor or with administration of methotrexate, other conventional synthetic disease-modifying anti-rheumatic drugs or oral glucocorticoid. TAK1 mRNA expression was significantly correlated with NFκB1 mRNA expression in RA bone marrow CD34+ cells.

These results indicate that TAK1 mRNA expression is enhanced in bone marrow CD34+ cells independently of the clinimetrics or treatment in RA. It is also suggested that the upregulation of TAK1 mRNA expression might lead to the enhanced expression of NFκB1 mRNA in bone marrow CD34+ cells, but possibly not vice versa, resulting in their abnormal response to TNF-α.