Silencing TNF-α in macrophages and dendritic cells for arthritis treatment.

Scand J Rheumatol. 2013;42(4):266-9.

Ye C, Bhan AK, Deshpande V, Shankar P, Manjunath N.

Center of Excellence in Infectious Diseases, Paul L. Foster School of Medicine, Texas Tech University Health Sciences Center, El Paso, TX 79905, USA.



OBJECTIVES: Tumour necrosis factor (TNF)-α secreted by macrophages and dendritic cells (DCs) plays a predominant role in arthritis. Our previous studies suggest that a small peptide, RVG-9R (29-aa peptide derived from the rabies virus glycoprotein, fused to 9R residues), can deliver small interfering RNA (siRNA) to macrophages and DCs. We therefore tested whether knockdown of TNF-α expression in macrophages and DCs by RVG-9R/bound siRNA targeting TNF-α reduces the severity of collagen antibody-induced arthritis (CAIA) in mice.

METHOD: Arthritis was induced in mice by injecting a combination of antibodies to collagen followed by lipopolysaccharide (LPS) treatment. Mice were also injected with TNF-α siRNA complexed with RVG-9R peptide or an irrelevant peptide RVMAT-9R on days 1, 3, 5, and 7. As a positive control, dexamethasone was injected intravenously. Paw thickness was measured every 2 days and the mice were killed on day 10 for testing synovial TNF-α levels and histological analysis of joints.

RESULTS: In control mice, arthritis developed on day 4 and reached its peak between day 7 and day 9. Treatment with siTNF-α bound to RVG-9R, but not to RVMAT-9R, resulted in reducing paw thickness scores to the same level as dexamethasone treatment, associated with reduced TNF-α level in synovial fluid. Histological analysis of joints in the control RVMAT-9R/TNF-α siRNA-treated mice showed marked pannus formation and destruction of cartilage and subchondrial bone, as well as severe infiltration of inflammatory cells into the synovium. By contrast, the joint pathology was markedly reduced in RVG-9R/TNF-α siRNA-treated mice resembling the dexamethasone-treated mice.

CONCLUSIONS: Suppression of TNF-α expression in macrophages and DCs by RVG-9R-mediated siRNA delivery could potentially be a clinically viable strategy for treatment of arthritis.

PMID: 23582054



In this study, we have developed a method to deliver siRNA to macrophages and dentritic cells in vivo and show its utility in suppressing TNF-α as a potential treatment option for arthritis using a mouse model of collagen antibody induced arthritis (CAIA). Remarkably, targeted siRNA mediated silencing of TNF-α in macrophages ameliorated arthritis to the same extent as treatment with the standard drug, dexamethosone.

Rheumatoid arthritis (RA) is a chronic autoimmune disease associated with decreased quality of life and disability due to fatigue, pain and articular tissue destruction. Although the etiology and pathophysiology of RA is still unknown, pro- and anti-inflammatory cytokines seem to play an important role in the pathology of RA. Tumor necrosis factor α (TNF-α) is a therapeutic target of RA. TNF-neutralizing agents were found to be beneficial both experimentally and clinically. Nevertheless, 40% of RA patients do not respond to anti-TNF biotherapies, efficacy can be lost during treatment and the disease relapses when therapy is withdrawn. In addition, there is evidence that long-term treatment with anti-TNF antibody is associated with an increased risk of serious infections and malignancies.

siRNA provides a powerful method to silence specific gene expression, but the main limitation for its in vivo use is delivery to particular cell types. Recently, we have found that a small peptide derived from the Rabies virus glycoprotein (RVG) that targets acetylcholine receptor expressed by macrophages and dendritic cells can be used to deliver siRNA to these cell types. We enabled siRNA binding by synthesizing RVG with an additional 9 arginine residues at the C terminus (siRNA binds to positively charged 9R by electrostatic interaction). This reagent can be used to silence any genes expressed in macrophages and dendritic cells. Thus, we used this reagent to silence TNF-α. We have shown that systemic administration of RVG-9R/siTNF-α is sufficient to reduce the paw swelling, cartilage and bone erosion, and joint inflammation in the CAIA model of arthritis (Fig.1). Therefore, we describe a novel method of blocking TNF signaling as an alternative to monoclonal antibodies. Since any siRNA could be delivered by our method, this provides a general platform to silence any inflammatory mediator in macrophages and dendritic cells and thus, this reagent could be potentially used in a number of autoimmune diseases.

Chunting Ye-fig1

Fig.1: CAIA-mice were treated with TNF siRNA bound to RVG-9R or control RVMAT-9R peptide. Paw thickness on day 7 is shown.

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