Effects of uphill and downhill walking on post-traumatic osteoarthritis development in mice

Using destabilization of the medial meniscus (DMM) to induce models of osteoarthritis (OA), we sought to clarify how flat, uphill and downhill walking affects OA-related inflammation and articular cartilage degeneration. Thirty-two male C57BL/6J mice 7 weeks old underwent DMM surgery in their right knee and sham surgery in their left knee, and were then assigned to either the no walking after DMM group or the flat, uphill or downhill walking after DMM group (n = 8/group). After creating the knee OA model, the mice in the walking groups were subjected to treadmill walking 1 day after surgery, which included walking at 12 m/min for 30 min/day, 7 days/week, at inclines of 0, 20, or -20 degrees. Knee joints were harvested at the end of the intervention period. Non-demineralized frozen sections were prepared and samples were examined histologically. Osteoarthritis Research Society International scores were significantly decreased in both the uphill and flat-walking groups, compared with the no-walking group. Immunohistochemical staining showed increased levels of aggrecan and Sry-related high-mobility group box9; conversely, decreased levels of matrix metalloproteinase-13 and A disintegrin and metalloproteinase with thrombospondin motifs-5 in both the uphill and flat-walking groups. Micro-CT results showed a higher bone-volume fraction in the uphill and flat-walking groups than that in the no-walking group. Our findings indicate that flat and uphill walking may prevent the progression of OA. KEY POINTS: Flat and uphill treadmill walking can prevent the development of post-traumatic osteoarthritis in mice. Flat and uphill walking increases anabolic proteins and decreases catabolic proteins and inflammatory cytokines in articular cartilage, resulting in protection against cartilage degeneration. Downhill walking increases catabolic proteins and inflammatory cytokines in cartilage, which has negative effects on articular cartilage.