ATF-2 affects mandible condyle cartilage calcification

Objective: To determine the mechanism of Activating transcription factor-2 (ATF-2) regulating mice mandible condyle cartilage growth. Growth plate, primary cartilage, and mandible condyle, secondary cartilage, appears at different stage of embryo and has different histological structure. Type X collagen is specific to cartilage and only synthesized by hypertrophic chondrocytes. AP is involved in mineral formation in the calcifying cartilage and bone. Materials and Methods: We employed biochemistry assay, histology and immunohistochemistry to determine the consequences of ATF-2 deficiency on type X collagen and AP expression in growth plates and mandible condyles. Results: ATF-2 m/m mice exhibited growth plates that were approximately 30% smaller than those of their normal littermates, but the condyles from the ATF-2 m/m mice have the bigger (50%) hypertrophic area than those of wild type mice. Type X collagen protein levels are significantly reduced (~ 60%) in condyle extracellular matrix, while in growth plate type X are expressed in some late proliferating zone and are expressed at the same levels in the hypertrophic zone, compared with wild type growth plates. AP levels are reduced in the ATF-2 deficient mice condyles (~ 50%), but have not changed in the growth plate. Conclusion: These results suggest that ATF-2 functions in different ways in the endochondral ossification procedure of growth plate and mandible condyle.