To compare the effects of TNF-α and IL-17A on osteogenic differentiation of isolated fibroblast-like synoviocytes (FLS) from healthy donors, osteoarthritis (OA) and rheumatoid arthritis (RA) patients.
FLS were cultured in osteogenic medium, with and without TNF-α and/or IL-17A. Extracellular matrix mineralization was evaluated by alizarin red staining and alkaline phosphatase activity (ALP) measurement. mRNA expression was analyzed by qRT-PCR for Wnt5a, BMP2 and Runx2, genes associated with osteogenesis, for DKK1 and RANKL, genes associated with osteogenesis inhibition and Schnurri-3, a new critical gene in the cross talk with osteoclasts. IL-6 and IL-8 production was measured by ELISA.
In osteogenic medium, matrix mineralization and increased ALP activity indicated that FLS can undergo osteogenic differentiation, which was increased with TNF-α and IL-17A. The expression of osteogenesis activators (BMP2 and Wnt5a) was increased with cytokines and that of the osteogenesis inhibitor DKK1 was decreased. There was no difference between all three cell types. In contrast, RA FLS were particularly sensitive to the synergistic increase of Shn3 with TNF-α and IL-17A. Levels of IL-6 and IL-8 were also higher for RA-FLS, compared to healthy and OA FLS.
IL-17A and/or TNF-α treatment favor an osteogenesis induction in isolated FLS, independent of their origin. RA-FLS were more sensitive to the synergistic increase of Schnurri-3 expression. Combined with the higher levels of inflammation, this may in turn activate osteoclastogenesis, leading to increased bone destruction seen in destructive arthritis.