Evaluation of CCL21 role in post-knee injury inflammation and early cartilage degeneration

The expression of some chemokines and chemokine receptors is induced during the development of post-traumatic osteoarthritis (PTOA), but their involvement in the pathogenesis of the disease is unclear. The goal of this study was to test whether CCL21 and CXCL13 play a role in PTOA development. For this purpose, we evaluated the expression profiles of the chemokines Ccl21 and Cxcl13, matrix metalloproteinase enzymes Mmp3 and Mmp13, and inflammatory cell markers in response to partial medial meniscectomy and destabilization (MMD). We then assessed the effect of local administration of CCL21 neutralizing antibody on PTOA development and post-knee injury inflammation. The mRNA expression of both Ccl21 and Cxcl13 was induced early post-surgery, but only Ccl21 mRNA levels remained elevated 4 weeks post-surgery in rat MMD-operated knees compared to controls. This suggests that while both CXCL13 and CCL21 are involved in post-surgery inflammation, CCL21 is necessary for development of PTOA. A significant increase in the mRNA levels of Cd4, Cd8 and Cd20 was observed during the first 3 days post-surgery. Significantly, treatment with CCL21 antibody reduced post-surgical inflammation that was accompanied by a reduction in the expression of Mmp3 and Mmp13 and post-MMD cartilage degradation. Our findings are consistent with a role for CCL21 in mediating changes in early inflammation and subsequent cartilage degeneration in response to knee injury. Our results suggest that targeting CCL21 signaling pathways may yield new therapeutic approaches effective in delaying or preventing PTOA development following injury.