These results demonstrate that FGF23 sustains differentiation of OA chondrocytes in a Klotho-independent manner.

ObjectivesFibroblast Growth Factor 23 (FGF23) is well documented as a crucial player in the systemic regulation of phosphate homeostasis. Moreover, loss-of-function experiments have revealed that FGF23 also has a phosphate-independent and local impact on skeletogenesis. Here, we used ATDC5 cell line to investigate the expression of FGF23 and the role it may play locally during the differentiation of these cells.MethodsATDC5 cells were differentiated in the presence of insulin, and treated with recombinant FGF23 (rFGF23), inorganic phosphate (Pi) and/or PD173074, an inhibitor of FGF receptors (FGFRs). The mRNA expressions of FGF23, FGFRs and markers of hypertophy, Col X and MMP13, were determined by qPCR analysis and FGF23 production was assessed by ELISA. FGFR activation was determined by immunoprecipitation and immunoblotting.ResultsFGF23 mRNA expression and production were increased during ATDC5 differentiation. At D28 in particular, rFGF23 stimulation increased hypertrophic markers expression, as Col X and MMP13, and mineralization. A synergic effect of Pi and rFGF23 stimulation was observed on these markers and on the mineralization process. The use of PD173074, a pan-FGFR inhibitor, decreased terminal differentiation of ATDC5 by preventing rFGF23 pro-hypertrophic effects.ConclusionsAltogether, our results provide evidence that FGF23 plays an important role during differentiation of ATDC5 cell line, by promoting both hypertrophy and mineralization.