Methods: A partial discectomy was performed on the TM joints of heterozygous Ddr2-deficient (Ddr2 +/-) mice and their wild-type littermates at 2 months of age. At 2, 4, 8, 12 and 16 weeks post-surgery, articular cartilages of the TM joints were examined by histology, Safranine O/Fast Green staining. Morphological conditions of the articular cartilages were evaluated by a modified Mankin scoring system.
Results: At 4 weeks following the surgery, there were no significant differences in the morphological changes between Ddr2+/- mice and wild-type littermates. At 8 weeks post-surgery, the articular cartilage of the wild-type mice exhibited chondrocyte clusters with increased proteoglycan staining in the pericellular matrix. However, the Ddr2+/- mice displayed no significant articular cartilage changes at this time point. At 12 weeks following the surgery, the Ddr2+/- mice revealed chondrocyte clusters with increased proteoglycan staining in the pericellular matrix. This was similar to what we observed in articular cartilages of TM joints in wild-type mice at 8 weeks post-surgery. Furthermore, reduced proteoglycan staining and fibrillation were evident in the articular cartilages of TM joints of wild-type mice at 12 weeks post-discectomy.
Conclusion: Ddr2-deficient mice demonstrated at least a 4-week delay in the progression of articular cartilage degeneration in TM joints. This suggests that reduced expression of Ddr2 can lead to an attenuation of the degenerative process in the articular cartilage of the TM joints following a partial discectomy.
NIH Grant # R01-AR-051989