Background/Purpose: Rheumatoid arthritis (RA) is an autoimmune disease that causes chronic inflammation and destruction of the joints and some extra-articular tissues. Netrin-1 is a laminin-like matrix protein that acts as a chemorepulsant and which is expressed during and required for osteoclast differentiation.  In other settings Netrin1 has been reported to play a pathogenic role during inflammation by preventing macrophage egress from inflamed sites. Therefore, we asked whether blockade of Netrin-1 or its receptors Unc5b and DCC may be useful therapeutic targets in the treatment of inflammatory arthritis.

Methods: The K/BxN serum transfer model was used. 8wk old C57Bl/6 mice were injected ip with 0.2ml K/BxN serum at day 0 and 2, and at the same time murine monoclonal antibodies against Netrin-1, Unc5b or DCC (10µg/mice) were injected ip (n=10 each). Antibodies were administered weekly for up to 4 weeks. Clinical signs like paw swelling and thickness were measured daily using a caliper. The scores of all four paws were added for a composite score. Animals were sacrificed 2 and 4 weeks after serum transfer, and legs were prepared for microCT and histology.

Results: Serum transfer induced an increase in paw inflammation that was maximal 2 weeks after injection, and weekly ip injection of anti-Netrin-1 or anti-Unc5b antibodies significantly reduced paw inflammation (clinical score of 9.8±0.8 and 10.4±0.9 respectively vs. 16±0 for control, p<0.001, n=10) whereas anti-DCC antibodies had no effect (13.5±0.5 vs. 16±0 for control, p=ns, n=10). The same results were observed for changes in paw thickness; weekly ip injection of anti-Netrin-1 or anti-Unc5b antibodies significantly reduced the change in paw thickness from baseline 2 weeks after serum transfer (0.4±0.05mm and 0.3±0.4mm respectively vs. 0.7±0.02mm for control, p<0.001, n=10) and anti-DCC antibodies had no effect (0.6±0.04 vs. 0.7±0.02 for control, p=ns, n=10). microCT analysis showed bony erosions in untreated or anti-DCC treated mice whereas there were no erosions in anti-Netrin-1 and anti-Unc5b treated animals. TRAP staining demonstrated a marked decrease in osteoclasts in anti-Netrin-1 and anti-Unc5b treated animals but not in anti-DCC treated or control mice (4±1 3±1 and 9±2 cells/hpf respectively vs.12±1 cells/hpf for control, p<0.001 and p=ns, n=5). Immunofluorescence staining revealed decrease Cathepsin K and CD68-positive cells in bones and joints of anti-Netrin-1 and anti-Unc5b treated animals but not in anti-DCC treated or control mice but Alkaline Phosphatase immunostaining for osteoblasts was not affected by any of the treatments.

Conclusion: Blockade of Netrin-1 and its receptor Unc5b by treatment, in vivo, with murine monoclonal antibodies prevents bone destruction and K/BxN serum transfer-induced arthritis. Netrin-1 may be a novel therapeutic target for inflammatory bone destruction and other forms of osteoclast-mediated bone resorption.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/netrin-1-and-its-receptor-unc5b-are-novel-targets-for-the-treatment-of-inflammatory-arthritis/