Immunohistochemical characterization of the mandibular condyle for type I and II collagen, aggrecan, MMP-9, and MMP-13 in MMP-2-deficient mice.

Mice devoid of matrix metalloproteinase (MMP)-2 due to gene targeting have been reported to show articular cartilage destruction in the knee joint; however, the phenotype of the mandibular condylar cartilage remains unknown. Thus, in the present study, we investigated the mandibular condyle in Mmp2^-/- mice. We obtained and bred Mmp2^-/- mice from the same source as the previous study, and performed genotyping using genomic DNA extracted from finger snips. The mandibular condyle of Mmp2^-/- mice and wild-type (WT) mice was immunohistochemically examined for the localization of extracellular matrix (ECM) proteins (type I and II collagen, and aggrecan), and MMP-9 and MMP-13. No cartilage destruction was observed in the mandibular condyle of Mmp2^-/- mice, and no difference was found in the localization of the ECM proteins between the Mmp2^-/- mice and WT mice. However, the bone marrow cavity in the subchondral bone of the mandibular condyle was more distinct in Mmp2^-/- mice than in WT mice at the age of 50 weeks. Of note, MMP-9 characteristically localized in multinucleated cells in the mandibular condyle in 50-week-old Mmp2^-/- mice. MMP-2 may be involved in the regulation of osteoclast differentiation and the formation of the bone marrow cavity in aged mice.