Background It has been shown previousely that posttranslational protein modification through SUMOylation is enhanced in rheumatoid athritis synovial fibroblasts (RASF) compared to osteoathritis synovial fibroblasts (OASF) and that higher levels of SUMOylation result in a reduced capability of RASF to undergo FAS induced apoptosis.
Objectives Based on these findings, we here focussed on the expression of the SUMO specific proteases SENP5 and SENP7, both of which are essential for the maturation and deconjugation of SUMO2/3 from its target proteins.
Methods Synovial tissue samples were obtained from RA and OA patients and used for cell culture experiments and histological analysis. The expression of SENP5 and 7 was analysed by PCR and Western Blot. With specific antibodies, the expression of SENP5 and 7 was analyzed by immunohistochemistry in synovial tissue specimens. The subcellular localization of SENP5 and 7 was studied by immunocytochemical costaining with cellcompartment specific markers and confocal laser scanning microscopy.
Results We where able to show an imbalance in both SUMO specific protease 5 and 7. Both were strongly upregulated in RASF in comparison to OASF. SENP5 showed a clear nuclear localization whereas SENP7 was found also in the cytoplasm. In line with our findings in tissue samples we could show a expression of SENP5 and 7 in RASF compared to OASF. Furthermore we where able to confirm these findings in the hTNFtg mouse model of human RA. Here, we found a strong upregulation of SENP5 and 7 on protein level. However the mRNA level showed only a difference for SENP7. In immuncytochemistry experiments the nuclear and cytoplasmic staining for Senp7 could be proven.
Conclusions Our findings underline the role of posttranslational protein modifications in RASF. Strong unbalances in the SUMOylations in hand with a striking overexpression of SENP’s adds to the characteristic features of RASF that promote the diseases processes in RA fibroblasts.
Disclosure of Interest None Declared