Objective; Connexins, the major proteins of gap junctions, are expressed in various cell types and are important in the key process of intercellular communication. In the past reports, connexin 43 (Cx43) has been implicated in inflammation and differentiation of osteoclast through cell-cell communication. The objective of this study is to investigate whether Cx43 gene silencing regulates inflammation and osteoclastgenesis of rheumatoid arthritis (RA).
Methods; Osteoclast formation from RAW264.7 by treatment of receptor activator of NF-kappaB ligand (RANKL) was examined with treatment of small interfering RNA targeting for Cx43 (si-Cx43), and the number of giant multinuclear and tartrate resistant acid phosphatase (TRAP) positive cells was counted. The effects of si-Cx43 on pro-inflammatory cytokines were assessed by real-time RT-PCR and ELISA in rat fibroblast-like synoviocytes (FLS). The therapeutic effects of si-Cx43 in a rat RA model of collagen-induced arthritis (CIA) were examined by in vivo electroporation method.
Results; The number of giant multinuclear and TRAP positive cells induced by RANKL was significantly smaller in si-Cx43 group than in control group. The transfection of si-Cx43 suppressed the over-expression of pro-inflammatory cytokines in rat FLS. Treatment of CIA rats with si-Cx43 significantly ameliorated paw swelling, and significantly reduced histological arthritis scores and radiographic scores. In histological appearance of rat ankle joints, si-Cx43 treatment significantly decreased the number of osteoclast-like cells.
Discussion; The present study showed that Cx43 gene expression in RAW264.7 was enhanced by the stimulation with RANKL and that treatment with si-Cx43 reduced the number of TRAP positive multinucleated cells. This study also showed that treatment with si-Cx43 reduced the number of TRAP-positive cells in rat RA model, and provided protection against the development of synovitis and joint destruction in CIA rats. These results suggest that Cx43 may have important roles for expression of inflammatory cytokines and osteoclastogenesis in RA.