THU0074 Transcription Factor SOX5 is an Essential Regulator of Rankl Expression in Synovial Fibroblast Contributing to Bone Erosion in Experimental Arthritis Model

Background SOX5 is a member of Sex determining region Y (SRY) box (SOX) family gene and function as transcription factors, playing important roles in the regulation of embryonic development, cell fate, and chondrogenesis.We previously reported a RANKL promoter SNP confers an elevated promoter activity after stimulation via binding to transcription factor SOX5 and is associated with younger age at onset of Rheumatoid arthritis (RA). To date, littke is known of SOX5 in RA. Here, we hypothesis that transcription factor Sox5 may be important transcriptional regulators of the RANKL gene in RA synovial fibroblast (SF). Objectives To examine the expression of SOX5 in RA patients and to elucidate their potential role in RA pathogenesis. Methods SOX expression levels in PBMC, plasma, and synovium were tested using RT-PCR, ELISA and immunohistochemistry. The interaction of SOX5 and RANKL in RA synovial fibroblast (RASF) was determined by double-immunofluorescence and immunoprecipitation. The effect of SOX5 on RANKL expression in RASF and joints was performed by lentiviral vector-mediated transfer of SOX5 cDNA or short hairpin RNA Results Among the tested 9 SOX family genes, expression of SOX5 were robust in 20 RA synovium samples. Compared to 20 osteoarthritis (OA) and 20 healthy controls (HC) samples, increased expression of SOX5 were observed consistently in synovium (p=0.01), synovial fluid and plasma (p=0.02 and p=0.001, respectively) from RA patients. SOX5 could be co-immunoprecipitated with Mab specific to RANKL upon TNFα and IL6 stimulation of rheumatoid fibroblast-like synoviocytes MH7A. Overexpression SOX5 resulted in a significantly increased RANKL level in MH7A. Transfection with SOX5 -shRNA markedly downregulated IL6 -mediated RANKL upregulation in MH7A. Intra-articular injection of lentivirus expressing shRNA for silencing SOX5 gene could significantly ameliorated clinical symptoms and bone erosion in in DAB/1mice of a CIA in part by suppression RANKL pathway. Conclusions These data support the hypothesis that transcription factor Sox5 in important transcriptional regulators of the RANKL gene in synovial fibroblast and may provide novel therapeutic targets for inhibiting RANKL expression. References Tan W, Wu H, Zhao J, Derber LA, Lee DM, Shadick NA et al. A functional RANKL polymorphism associated with younger age at onset of rheumatoid arthritis. Arthritis Rheum 2010; 62(10):2864-75. Disclosure of Interest None declared