Silencing the expression of Ras family GTPase homologues decreases inflammation and joint destruction in experimental arthritis

Changes in the expression and activation status of Ras proteins are thought to contribute to the pathological phenotype of stromal fibroblast-like synoviocytes (FLS) in rheumatoid arthritis, a prototypical immune-mediated inflammatory disease. Broad inhibition of Ras and related proteins has shown protective effects in animal models of arthritis, but each of the Ras family homologues (ie, H-, K-, and N-Ras) makes distinct contributions to cellular activation. We examined the expression of each Ras protein in synovial tissue and FLS obtained from patients with rheumatoid arthritis and other forms of inflammatory arthritis. Each Ras protein was expressed in synovial tissue and cultured FLS. Each homolog was also activated following FLS stimulation with tumor necrosis factor-α or interleukin (IL)-1β. Constitutively active mutants of each Ras protein enhanced IL-1β-induced FLS matrix metalloproteinase-3 production, while only active H-Ras enhanced IL-8 production. Gene silencing demonstrated that each Ras protein contributed to IL-1β-dependent IL-6 production, while H-Ras and N-Ras supported IL-1β-dependent matrix metalloproteinase-3 and IL-8 production, respectively. The overlap in contributions of Ras homologues to FLS activation suggests that broad targeting of Ras GTPases in vivo suppresses global inflammation and joint destruction in arthritis. Consistent with this, simultaneous silencing of H-Ras, K-Ras, and N-Ras expression significantly reduces inflammation and joint destruction in murine collagen-induced arthritis, while specific targeting of N-Ras alone is less effective in providing clinical benefits.