Adipogenesis of the mesenchymal stromal cells and bone oedema in rheumatoid arthritis

Bone oedema is a pathological change in rheumatoid arthritis (RA) that is detectable by magnetic resonance imaging (MRI). Recent histological analyses revealed that a prominent feature of bone oedema is the replacement of adipose tissue with inflammatory cells. Here, we demonstrate the possible roles of mesenchymal stromal cells (MSCs) in bone oedema formation and the pathogenic potential of the cells in RA.

Adipogenesis of bone marrow-derived human MSCs was induced by a standard adipogenic induction medium in the presence or absence of cytokines. The cytokine productions from MSCs were screened by an antibody array system and confirmed by ELISA. The migration assay was performed to determine the locomotive abilities of undifferentiated MSCs or MSCs after adipogenesis. The expression of α smooth muscle actin (SMA) and F-actin was examined by immunostaining and phalloidin staining, respectively.

TNF-α, interleukin (IL)-1β, IL-6, and TGF-β clearly inhibited the adipogenesis of MSCs. Production of IL-6 was markedly reduced, and IL-8 secretion was augmented in MSCs after adipogenesis. The mobility of MSCs after adipogenesis was clearly reduced in migration assays compared to that of undifferentiated MSCs. Consistent with these findings, SMA and F-actin expressions were clearly suppressed in MSCs committed to adipogenesis.

Our data suggest that the inflammatory milieu promotes bone oedema by blocking adipogenesis of MSCs. In bone oedema, the enhanced IL-6 production and the increased mobility of MSCs may contribute to the progression of RA. Therefore, bone oedema may be an important target lesion in the treatment of RA.