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Enhanced osteoclastogenesis in arthritis is paralleled with the increased expression of proinflammatory mediators CCL2, IL-17 and IL-18

Osteoclasts play a pivotal role in excessive bone destruction of arthritic joints. Many cytokines are involved in the pathogenesis of arthritis, acting as osteoclastogenic factors, but their effects are not fully revealed. Our aim was to compare the expression profile of selected proinflammatory factors and osteoclastogenic potential of peripheral-blood mononuclear cells (PBMC) between control subjects and arthritic patients (including rheumatoid arthritis (RA) and spondyloarthritis (SpA)). In addition, we assessed osteoclastogenic potential of PBMC and local synovial-fluid derived mononuclear cells (SFMC) in patients with RA and SpA. PBMC were collected from control subjects (n=12), whereas PBMC and SFMC were collected from RA patients (n=10) and SpA patients (n=15), either with ankylosing spondylitis (AS=5) or psoriatic arthritis (PsA=10), after the informed consent. Osteoclasts were stimulated with macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-kB ligand (RANKL), and detected as tartrate resistant acid phosphatase (TRAP)-positive multinucleated cells. RNA was extracted from PBMC/SFMC cells, reversely transcribed to cDNA, and amplified by quantitative PCR for the expression of osteoclast differentiation genes (RANK, cFms, TRAP) and inflammatory mediators (CCL2, VEGF, IL-17, IL-18, TNF-, and FasL). In addition, serum and synovial fluid levels of the same mediators were determined by ELISA. Serum levels of inflammatory mediators CCL2, IL-17 and IL-18 were higher in arthritic patients compared with control subjects, whereas synovial fluid levels of CCL2, VEGF, TNF- and IL- 18 were higher in RA compared with other patient groups. In addition, gene expression of inflammatory mediators CCL2, IL-17 and IL18 were higher in PBMC and SFMC of arthritic patients compared with control subjects. In vitro osteoclastogenesis showed higher osteoclastogenic potential for PBMC but similar for SFMC in RA compared with AS and PsA patients. In parallel, gene expression of osteoclast differentiation genes RANK and TRAP was higher in osteoclastogenic cultures derived from PBMC of RA patients. Our results indicate that patients with RA have greater osteoclastogenic potential compared with control subjects and SpA patients, which is paralleled with the increased expression of proinflammatory mediators. These findings may be relevant for the development of therapeutic approaches aimed to modulate proinflammatory as well as osteoclastogenic effects of those factors.

osteoclasts; bone loss; arthritis; cytokines

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