Abstract
MMP-13 appears to be one of the most important
MMPs in cartilage remodeling and mineralization,
because it exhibits a substrate preference for the
cartilage-specific type II collagen. The condylar
process is constructed by rapid accumulation of
hypertrophic chondrocytes during development,
but its mechanism is still unclear. To investigate the
role of MMP-13 in developing condylar cartilage, we
immunohistochemically examined the localization
of MMP-13 in the endochondral ossification of the
mandibular condyle and tibiae of newborn mice. In
the tibiae, the MMP-13 expression was detected
only in the deepest layer of the terminal hypertrophic
chondrocytes through every examined
stage (day 1 to day 10 after birth). On the other
hand, in the condylar cartilage at days 1 and 5,
MMP-13 was expressed throughout the proliferating
and the hypertrophic chondrocytes, and at
day 10, MMP-13 was mainly localized in the deepest
edge of the hypertrophic layer. A zymographical
study showed that the activity of MMP-13 in the
condyle was observed at day 1, earlier than in the
tibia, and increased until day 7. The time-dependent
and cell-specific expression of MMP-13 and its
enzymatic property suggest that in the mandibular
condylar cartilage, MMP-13 plays a role in making
the space for cell enlargement by degradation of
the cartilage matrix and in onset of mineralization
during the early stage of development.
