ENHANCED OSTEONECTIN EXPRESSION IN THE CHONDROID MATRIX OF THE UNLOADED MANDIBULAR CONDYLE

Osteonectin provided a spatial and temporal marker for proliferating a nd differentiating chondrocytes, and during the chondroid matrix forma tion. The goal of this investigation was to examine early cellular and molecular regulation of mandibular growth. Unloading was induced by a nterior functional mastication. The proliferative activity measured by tritiated thymidine incorporation increased 8.3-fold at 24 hours comp ared with the corresponding control group. Mandibular unloading for 24 hours increased osteonectin mRNA expression 60% in the condyle over t he corresponding control group. Microscopic inspection of the condyle demonstrated osteonectin immunostaining of proliferating, early hypert rophic chondrocytes, and the chondroid matrix across the sagittal sect ion in an anterior-posterior direction. An increasing gradient intensi ty from a medial-superior to posterior direction was produced with tre atment in direct contrast to the control group. The posterior chondroi d matrix immunostaining increased 11.7-fold (P = 0.038) after 24 hours treatment over a corresponding control group. Unloading of the mouse mandible caused an increased cellular proliferation, a coincident incr ease of osteonectin mRNA, and a subsequent increased secretion of the osteonectin protein in the chondroid matrix formation.