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Background:Tumor necrosis factor-α (TNF-α) is among the most prominent cytokines in rheumatoid arthritis (RA) and collagen-induced arthritis (CIA) is an often-used model for RA.Small interfering RNA (siRNA) offers promise as a novel therapeutic modality on autoimmune arthritis [1-3]Objective: The aim of this study was to construct vectors expressing TNF-α siRNA and to determine its therapeutic effect in CIA rat.Method: Oligos of 74 base pairs for TNF-α siRNA were chemically synthesized and digested by BamH Ⅰ and Hind Ⅲ.The digested double strands oligos were inserted into the downstream of U6 promoter of linearized pGFP-V-RS vector.Then siRNA constructs were confirmed by restrictive enzyme digestion and sequencing.At the same time, CIA model in SD rats was established.The TNF-α siRNA were injected intravenously into CIA rats 3 times weekly.Delivery was optimized using a carrier DNA for complexation with the cationic liposome lipofectaminTM 2000.The levels of IL-1 and IL-6 in serum were measured by ELISA on day 1, 5, 9 and 13 after injection.At the time when the mice were killed,the level of TNF-α mRNA was measured by reverse transcriptase polymerase chain reaction (RT-PCR).Results: CIA in the control group express high levels of IL-1, IL-6 and TNF-α.The degree of joint swelling was remarkably attenuated in the rats treated with TNF-α-siRNA.The level of IL-1 was lower in siRNA-injected groups on day 1, 5, 9 (P<0.05), but the level of IL-6 was lower in in siRNA-injected groups on day 5, 9, 13(P<0.05).The expression of TNF-α mRNA was lower in siRNA-injected groups than the control group and empty vector group on day 13(P<0.05), however,the expression of TNF-α mRNA, IL-1 and IL-6 were no difference in two siRNA-injected groups.Conclusion: TNF-α specific siRNA can suppress the level of TNF-α mRNA, meanwhile, it can decrease the levels of IL-1 and IL-6, so this will provide experimental data for gene therapy of RA.