Cytosolic Phospholipase A2α Gene Silencing in the Myeloid Lineage Alters Development of Th1 Responses and Reduces Disease Severity in Collagen-Induced Arthritis

Objective. Several lines of evidence implicate cytosolic phospholipase A(2)alpha (cPLA(2)alpha) as a critical enzyme in inflammatory disorders, including rheumatoid arthritis. Since cells from the myeloid compartment regulate local and systemic disease pathogenesis, the present study was undertaken to examine the effect of cPLA(2)alpha inhibition in experimental arthritis, using a delivery system tailored to target monocyte functions by RNA interference (RNAi). Methods. Mice with collagen-induced arthritis (CIA) were injected intravenously with an anti-cPLA(2)alpha small interfering RNA (siRNA) sequence (siPLA2) formulated as lipoplexes with the RPR209120/DOPE cationic liposome and a carrier DNA. The clinical course of joint inflammation was assessed, and the immunologic balance was analyzed by measuring T helper cell frequencies and cytokine expression. Biodistribution studies of siRNA were also performed. Results. Weekly systemic injection of siPLA2 lipoplexes significantly reduced the incidence and severity of CIA, in both preventive and curative settings, as compared with findings in control animals. Histologic scores for inflammation and cartilage damage were reduced. The clinical effect was associated with local inhibition of tumor necrosis factor alpha secretion and lower cPLA(2)alpha expression and activity. The siPLA2 lipoplexes enabled triggering of in vivo RNAi-mediated gene silencing of cPLA(2)alpha in CD11b+ cells recovered from the spleen. While the treatment had no effect on anti-type II collagen (anti-CII) antibodies, CII-specific T helper cells producing interferon-gamma, but not interleukin-17, in draining lymph node cells were decreased. Conclusion. Our findings indicate that systemic RNAi-mediated cPLA(2)alpha gene silencing in CD11b+ cells is effective in the treatment of CIA, and Th1 suppression is one of the potential underlying mechanisms, whereas Th17 suppression is not.