Characterization of synovial cell clones isolated from rheumatoid arthritis patients: Possible involvement of TNF-α in reduction of osteoprotegerin in synovium

Regulatory effects of bone morphogenetic protein-4 on tumour necrosis factor-α-suppressed Runx2 and osteoprotegerin expression in cementoblasts

OBJECTIVES

Root resorption is a common phenomenon presented in periodontitis and orthodontic treatment, both of which are accompanied by an elevated TNF-α expression level in the periodontal tissues. Previously, we proved that TNF-α showed an inhibitory effect on cementoblast differentiation, mineralization and proliferation. However, the effect of TNF-α on Runx2 and osteoprotegerin (OPG) expression remains undetermined. This study aimed to identify the influence of TNF-α on Runx2 and OPG expression in cementoblasts and to test whether BMP-2,-4,-6,-7 would affect TNF-α-regulated Runx2 and OPG.

MATERIALS AND METHODS

An immortalized murine cementoblast cell line OCCM-30 was used in this study. The expression of Runx2 and OPG were examined by qRT-PCR after stimulating cells with TNF-α. The role of signalling pathways, including MAPK, PI3K-Akt and NF-κB, were studied with the use of specific inhibitors. Cells were treated with TNF-α in combination with BMP-2,-4,-6 or -7, then the expression of Runx2 and OPG, the activity of MAPK and NF-κB pathways, and the proliferation ability were evaluated by qRT-PCR, Western blot and MTS assay respectively.

RESULTS

TNF-α inhibited Runx2 and OPG mRNAs in OCCM-30 cells, and the inhibitory effects were further aggravated by blocking p38 MAPK or NF-κB pathway. TNF-α-inhibited Runx2 and OPG were up-regulated by BMP-4. The p38 MAPK and Erk1/2 pathways were further activated by the combined treatment of BMP-4 and TNF-α compared with TNF-α alone. Finally, the TNF-α-suppressed proliferation was not obviously affected by BMP-2,-4,-6 or -7.

CONCLUSIONS

TNF-α inhibited Runx2 and OPG in cementoblasts, and the p38 MAPK and NF-κB pathways acted in a negative-feedback way to attenuate the inhibitory effects. TNF-α-inhibited Runx2 and OPG could be effectively up-regulated by BMP-4; however, further investigations are needed to fully elaborate the underlying mechanisms.

A Clinical Study Evaluating the Effects of Fluvastatin on Serum Osteoprotegerin Levels in Rheumatoid Arthritis Patients

Osteoprotegerin (OPG), a member of the tumor necrosis factor receptor family, has been identified as a critical regulator of bone resorption. Considering the possible role of OPG in rheumatoid arthritis (RA) and in the osteoclastogenesis suppression effects of statins, the present study aims to investigate the effects of fluvastatin on serum levels OPG and disease activity score (DAS) in patients with RA. Forty patients with RA were randomized in a placebo-controlled trial to receive 40 mg fluvastatin or placebo as an adjunct to existing disease-modifying antirheumatic drug (DMARD) therapy (methotrexate, leflunomide, hydroxychloroquine). Patients were followed up over 12 weeks. OPG and disease activity variables were measured at baseline and after 12 weeks of treatment. After 12 weeks, the OPG level was significantly increased in the fluvastatin group compared to the placebo group. DAS-28 was significantly decreased in the fluvastatin group compared to the placebo group. C-reactive protein (CRP), morning stiffness, swollen joint count (SJC), and tender joint count (TJC) were significantly decreased in the fluvastatin group compared to the placebo group; however, erythrocyte sedimentation rate (ESR), modified health assessment questionnaire (MHAQ), and visual analogue screen (VAS) were not changed significantly. In conclusion, fluvastatin administration could increase the OPG levels and improve disease activity variables in patients with RA. Therefore, fluvastatin may serve a potential benefit in the treatment of RA patients.

Osteoblastic potential of infrapatellar fat pad-derived mesenchymal stem cells from rheumatoid arthritis and osteoarthritis patients

AIM

To evaluate the osteoblastic potential of adipose-derived mesenchymal stem cells (ASCs) from infrapatellar fat pad (IPFP) of rheumatoid arthritis (RA) patients in comparison to osteoarthritis (OA) patients, as well as the influence of tumor necrosis factor alpha (TNFα) on osteoblastic ASC differentiation in vitro.

METHODS

ASCs were isolated from IPFP of RA and OA patients. After expansion, cells were cultured in osteogenic medium with or without TNFα. After 2 weeks, expression of BMP-2, Runx-2, osterix (Osx), collagen 1a1 (Col1a1) and osteopontin (OPN) messenger RNA (mRNA) was assessed by reverse transcription polymerase chain reaction and calcium deposition by alizarin red staining. Dickkopf-1 (DKK-1) and osteoprotegerin (OPG) protein concentrations were measured in culture supernatants using enzyme-linked immunosorbent assay.

RESULTS

Both RA- and OA-ASCs cultured in osteogenic medium showed calcium deposition. The expression of Runx2 and OPN mRNA was increased in RA-ASCs. These cells expressed significantly more Osx and OPN than OA-ASCs. TNFα potentiated calcium deposition, up-regulated Runx2 and BMP-2 but down-regulated Col1a1 and OPN expression. In osteogenic cultures DKK-1 concentration was increased but that of OPG decreased, whereas TNFα elevated secretion of both cytokines.

CONCLUSION

RA-ASCs have comparable or slightly stronger osteogenic potential than OA-ASCs. RA-ASCs seem to be more sensitive to TNFα treatment. TNFα exerts complex effects on ASC osteoblastogenesis, enhances expression of early osteogenic markers and calcium deposition, inhibits expression of mRNA coding for non-mineral bone components and alters ASC secretory activity.