Connective tissue growth factor (CTGF/CCN2), one of the most recently described growth factors, is produced by chondrocytes, vascular endothelial cells, and transforming growth factor (TGF)-beta-stimulated fibroblasts. CTGF was isolated from a chondrosarcoma-derived chondrocytic cell line, HCS-2/8, and found to be normally expressed in cartilage tissues, especially in hypertrophic chondrocytes, and also to stimulate both the proliferation and the differentiation of chondrocytes in vitro. Therefore, CTGF is thought to be one of the most important regulators of endochondral ossification in vivo. Herein we describe the expression pattern of the ctgf gene in the calcifying tissues of normal developing mouse embryos in comparison with that in core binding factor a1 (Cbfa1)-targeted mutant (cbfa1-null) mouse embryos, in which impaired development and growth were characteristically observed in the skeletal system. After 15 days of development (E15), the expression of ctgf was detected in the zone of hypertrophy and provisional calcification, in which ossification proceeds toward the epiphysis during the skeletal development of the mouse embryo. Furthermore, ctgf was expressed in developing molar and incisal tooth germs around the perinatal stage. However, no expression of the gene was found in the cbfa1-null mouse embryos. These results indicate that CTGF may have certain important roles in the development of the calcifying tissues in the mouse embryo.
Medication-related osteonecrosis of the jaw (MRONJ) is a severe pathological condition associated mainly with the long-term administration of bone resorption inhibitors, which are known to induce suppression of osteoclast activity and bone remodeling. Bone Morphogenetic Protein (BMP)-2 is known to be a strong inducer of bone remodeling, by directly regulating osteoblast differentiation and osteoclast activity. This study aimed to evaluate the effects of BMP-2 adsorbed onto beta-tricalcium phosphate (β-TCP), which is an osteoinductive bioceramic material and allows space retention, on the prevention and treatment of MRONJ in mice. Tooth extraction was performed after 3 weeks of zoledronate (ZA) and cyclophosphamide (CY) administration. For prevention studies, BMP-2/β-TCP was transplanted immediately after tooth extraction, and the mice were administered ZA and CY for an additional 4 weeks. The results showed that while the tooth extraction socket was mainly filled with a sparse tissue in the control group, bone formation was observed at the apex of the tooth extraction socket and was filled with a dense connective tissue rich in cellular components in the BMP-2/β-TCP transplanted group. For treatment studies, BMP-2/β-TCP was transplanted 2 weeks after tooth extraction, and bone formation was followed up for the subsequent 4 weeks under ZA and CY suspension. The results showed that although the tooth extraction socket was mainly filled with soft tissue in the control group, transplantation of BMP-2/β-TCP could significantly accelerate bone formation, as shown by immunohistochemical analysis for osteopontin, and reduce the bone necrosis in tooth extraction sockets. These data suggest that the combination of BMP-2/β-TCP could become a suitable therapy for the management of MRONJ.
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