Immortalized cementoblasts and periodontal ligament cells in culture

Cementum, a mineralized tissue lining the surface of the tooth root, is req uired for formation of a functional periodontal ligament attachment during development. Additionally during regeneration of tissues after disease, cem entum is thought to play a critical role in the reparative process. Researc h efforts aimed toward understanding mechanisms involved in periodontal dev elopment and regeneration, and in particular the formation of root cementum , have been hampered by an inability to isolate and culture cells involved in cementum production, i.e., cementoblasts, Using classical techniques for osteoblast isolation, immortalized, heterogeneous cementoblast/periodontal ligament cell (CM/PDL) populations were established from cells lining the tooth root surface of: 1) CD-1 mice, where cells were immortalized using SV 40, or 2) H-2K(b)tsA58 "immorto" mice, where cells containing an immortaliz ing transgene were removed and cultured. CM/PDL populations were derived fr om tissues adherent to developing tooth root surfaces, while tissues adhere nt to the surrounding alveolar bone were specifically excluded from the pop ulation. Immortalized CM/PDL cells were characterized to ensure their pheno type reflected that previously demonstrated in situ and in primary, nonimmo rtalized cultures, Proteins/mRNAs associated with bone/cementum and known t o be expressed by root lining cementoblasts, but not by PDL cells, in situ, e.g., bone sialoprotein, osteopontin, and osteocalcin, were expressed by c ells within the immortalized populations. Furthermore, CM/PDL cells, in vit ro, attached to bone sialoprotein in an arginine-glycine-aspartic acid (RGD )-dependent manner, promoted mineral nodule formation and exhibited a PTH/P THrP-mediated cAMP response, These immortalized heterogeneous populations, containing both CR I and PDL cells, provide a unique opportunity to study c ells involved in cementogenesis and to enhance our knowledge of the mechani sms controlling development, maintenance, and regeneration of periodontal t issues. (C) 1999 by Elsevier Science Inc. rill rights reserved.