Employing a transgenic animal model to obtain cementoblasts in vitro

Background: Proper formation of cementum, a mineralized tissue lining the t ooth root surface, is required for development of a functional periodontal ligament. Further, the presence of healthy cementum is considered to be an important criterion for predictable restoration of periodontal tissues lost as a consequence of disease. Despite the significance of cementum to gener al oral health, the mechanisms controlling development and regeneration of this tissue are not well understood and research has been hampered by the l ack of adequate in vitro experimental models. Methods: In an effort to establish cementoblast cell populations, without t he trappings of a heterogeneous population containing periodontal ligament (PDL) cells, cells were obtained from the root surface of first mandibular molars of OC-TAg transgenic mice. These mice contain the SV40 large T-antig en (TAg) under control of the osteocalcin (OC) promoter. Therefore, only ce lls that express OC also express TAg and are immortalized in vitro. Based o n results of prior in situ studies, OC is expressed by cementoblasts during root development, but not by cells within the PDL. Consequently, when popu lations are isolated from developing molars using collagenase/trypsin diges tion, only cementoblasts, not PDL cells, are immortalized and thus, will su rvive in culture. Results: The resulting immortalized cementoblast population (OC/CM) express ed bone sialoprotein (BSP), osteopontin (OPN), and OC, markers selective to cells lining the root surface. These cells also expressed type I and XII c ollagen and type I PTH/PTHrP receptor (PTH1R). In addition to expression of genes associated with cementoblasts, OC/CM cells promoted mineral nodule f ormation and exhibited a PTHrP mediated cAMP response. Conclusions: This approach for establishing cementoblasts in vitro provides a model to study cementogenesis as required to enhance our knowledge of th e mechanisms controlling development, maintenance, and regeneration of peri odontal tissues.