Effects of knockout of the receptor for advanced glycation end-products on bone mineral density and synovitis in mice with intra-articular fractures.

Our group employed the mouse closed intra-articular fracture (IAF) model to test the hypothesis that the innate immune system plays a role in initiating synovitis and post-traumatic osteoarthritis (PTOA) in fractured joints. A transgenic strategy featuring knockout of the receptor for advanced glycation end-products (RAGE -/- ) was pursued. The 42 and 84 mJ impacts used to create fractures were in the range previously reported to cause PTOA at 60 days post-fracture. MicroCT (μCT) was used to assess fracture patterns and epiphyseal and metaphyseal bone loss at 30 and 60 days post-fracture. Cartilage degeneration, synovitis, and matrix metalloproteinase (MMP-3, -13) expression were evaluated by histologic analyses. In wild-type mice, μCT imaging showed that 84 mJ impacts led to significant bone loss at 30 days (p < 0.05), but recovered to normal at 60 days. Bone losses did not occur in RAGE-/- mice. Synovitis was significantly elevated in 84 mJ impact wild-type mice at both endpoints (30 day, p = 0.001; 60 day, p = 0.05), whereas in RAGE-/- mice synovitis was elevated only at 30 days (p = 0.02). Mankin scores were slightly elevated in both mouse strains at 30 days, but not at 60 days. Immunohistochemistry revealed significant fracture-related increases in MMP-3 and -13 expression at 30 days (p < 0.05), with no significant difference between genotypes. These findings indicated that while RAGE -/- accelerated recovery from fracture and diminished synovitis, arthritic changes were temporary and too modest to detect an effect on the pathogenesis of PTOA.