THE ROLE OF EXTRACELLULAR SULFATASE-2 IN THE PATHOGENESIS OF RHEUMATOID ARTHRITIS

In the autoimmune disease rheumatoid arthritis (RA), inflammatory cytokines drive synovial hyperplasia which leads to progressive destruction of cartilage and bone. Tumor necrosis factor alpha (TNF-α) is an inflammatory cytokine that activates human RA synovial fibroblasts (RASFs) to produce chemokines that recruit inflammatory cells to the joint, and adhesion molecules that contribute to destructive synovial pannus formation. TNF-α triggers production of additional inflammatory cytokines including interleukin-6 (IL-6), which further activates RASFs through its trans-signaling mechanism. TNF inhibitors are now commonly used to treat RA and other autoimmune diseases, but prolonged systemic inhibition of TNF-α increases the risk of infection and malignancy, underscoring the need for alternate therapeutic approaches. Extracellular sulfatase-1 (Sulf-1) and sulfatase-2 (Sulf-2) are known to play key roles in growth factor and cytokine signaling, especially in musculoskeletal tissues. However, these enzymes have not been examined in the context of RA or in TNF-α signaling. Our studies demonstrate that extracellular sulfatases, especially Sulf-2, are highly upregulated in synovial tissues and serum of RA patients and the TNF-α transgenic mouse model of RA. Our in vitro experiments in human RASFs show that transient knockdown of Sulf-2 significantly modulates TNF-α inflammatory pathways, based on analysis of differentially expressed genes (DEGs). This work focuses primarily on Sulf-2 loss-of-function studies which demonstrate potentially therapeutic dampening effects on known inflammatory targets in RA pathogenesis. We show that knockdown of Sulf-2 limits TNF-α signaling through PKCδ and JNK pathways, significantly reducing nuclear translocation of inflammatory transcription factors NF-κB and AP-1. In addition, pharmacologic inhibition of Sulf-2 using the small molecule inhibitor OKN-007 abrogates TNF-α-induced adhesion molecules (ICAM-1, VCAM-1, cadherin-11) and inflammatory chemokines (CCL2, CCL5, CXCL5, CXCL10 and CXCL11). Interestingly, our studies show that stimulation of RASFs with IL-6 and its soluble receptor induces expression of Sulf-2, and that knockdown of Sulf-2 inhibits IL-6-induced JAK1 and downstream production of inflammatory mediators. These findings reveal novel molecular mechanisms by which Sulf-2 contributes to inflammatory cytokine signaling in RASFs, which may lead to new therapeutic approaches aimed at the site of joint destruction with reduced risks from systemic immunosuppression.