Establishment of Periodontal Ligament Cell Lines from Temperature-Sensitive Simian Virus 40 Large T-antigen Transgenic Rats

Orthodontic tooth movement is controlled by various cell types in the periodontal ligament (PDL). Mechanical stresses, such as orthodontic force, are thought to induce differentiation of the mesenchymal cells in the PDL into osteoblasts and cementoblasts. The details of the process of differentiation, however, are not known, in part because adequate in vitro systems for their study do not yet exist. The purpose of this study was to establish and characterize immortalized PDL cell lines derived from the PDL of transgenic rats harboring the temperature-sensitive simian virus 40 T-antigen gene (TG rats). The PDL was removed from the molar roots of TG rats and incubated in tissue culture. Outgrowth cells from the PDL explant were passaged and cloned, depending on the shape of the colonies formed. The cell lines thus established were analyzed by reverse transcription–polymerase chain reaction for expression of type-I collagen, osteopontin, fibronectin, alkaline phosphatase (bone type), bone sialoprotein, the receptor activator of NF-κ B ligand, and osteoprotegerin. In addition, the capacity for formation of mineralized nodules was assessed by incubating cells in calcification-promoting medium at 37 °C. A total of 15 stable cell lines were successfully established and characterized. These cell lines were classified into six groups based on their pattern of gene expression at 33°C. Moreover, three of these clones were capable of forming calcified nodules. In conclusion, differential gene expression was demonstrated in 15 established PDL cell lines. Some cells had the potential to differentiate into cell types found in mineralized tissues, such as osteoblasts and cementoblasts, as well as cells expressing molecules that regulate osteoclast differentiation.