Background Adipose-derived mesenchymal stem cells (ADSC) have the ability to differentiate into osteoblasts. This makes them promising in treatment of bone erosion occuring in rheumatoid arthritis (RA). ADSC residing in rheumatoid articular adipose tissue (AAT) are particularly interesting because of their location in the place where inflammatory response persists. The tumor necrosis factor (TNF) is present in excessive amounts in RA and is crucial for its pathogenesis. Thus, the influence of this cytokine on ADSC might be of great importance to bone repair and degradation in rheumatic joint.
Objectives 1) To compare the osteogenic potential of ADSC from RA and osteoarthritis (OA) patients. 2) To evaluate the effect of TNF on ADSC differentiation.
Methods AAT was obtained from RA and OA patients during total knee joint replacement surgery. ADSC were isolated and cultivated in DMEM/F12/10%FCS medium. After passage 4 ADSC were differentiated in osteogenic medium in the absence or presence of TNF-α (10ng/ml). After 2 weeks, expression of osteogenic markers (Runx2, osteopontin - OPN) mRNA was assessed by RT-PCR and calcium deposition by alizarin red staining. Supernatants from cell cultures were harvested on 14th day of differentiation and the concentration of proteins known to inhibit (Dickkopf-1 - DKK-1) or support (osteoprotegerin - OPG) osteogenesis were measured by ELISA.
Results Staining by the alizarin red shows calcium deposition in both RA and OA ADSC cultured in osteogenic medium. TNF enhanced this process. Runx2 and OPN mRNA as well as DKK-1 protein expression were increased after osteogenic-medium treatment, whereas OPG protein was decreased, especially in RA. TNF caused significant enhancement of Runx2 mRNA expression, OPG and DKK-1 protein secretion. By contrast, expression of late osteogenesis marker – OPN, was significantly decreased after TNF treatment.
Conclusions ADSC from OA and RA patients seem to have similar osteogenic potential (comparable results about chondrogenic potential of RA-ADSC were published ). However, significantly reduced OPG concentration in samples from osteogenic RA-ADSC cultures suggest that, to some extent, the osteogenesis in RA is impaired. RA and OA-ADSC responded similarly to TNF. It seems that TNF stimulates osteogenesis, which was already reported elswhere [2,3], but not entirely, as OPN was downregulated by TNF contrary to other markers. The influence of TNF remains unclear. Neverthless, we suppose that TNF may trigger osteogenesis to some degree and than contribute to its impairment.
Funding: Supported by grant no.N N402 369938 from Polish Ministry of Science and Higher Education and the Institute of Rheumatology (grant no. I/16)
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Disclosure of Interest None Declared