Differential inflammation-mediated function of prokineticin 2 in the synovial fibroblasts of patients with rheumatoid arthritis compared to osteoarthritis

Abstract

\n Prokineticin 2 (PK2) is a secreted protein involved in several pathological and physiological processes, including the regulation of inflammation, sickness behaviors, and the circadian rhythm. Recently, it was reported that PK2 is associated with the pathogenesis of collagen-induced arthritis in mice. However, whether PK2 influences the pathogenesis of rheumatoid arthritis (RA) or osteoarthritis (OA) remains unknown. In this study, we collected synovial tissue, plasma, synovial fluid, and fibroblast-like synoviocytes (FLS) from RA and OA patients to analyze the role of PK2 using immunohistochemistry, ELISAs, and tissue superfusion studies. PK2 and its receptors prokineticin receptor (PKR) 1 and 2 were expressed in RA and OA synovial tissues. PKR1 expression in RA synovial tissue was downregulated compared with OA synovial tissue. The PK2 concentration was higher in RA synovial fluid than in OA synovial fluid but similar between RA and OA plasma. PK2 suppressed the production of IL-6 from TNFα-prestimulated OA-FLS, and this effect was attenuated in TNFα-prestimulated RA-FLS. This phenomenon was accompanied by the upregulation of PKR1 in OA-FLS and the downregulation of PK2 and PKR1 in RA-FLS. This study provides a new model to explain some aspects underlying the chronicity of inflammation in RA.