Response of immortalized murine cemeatoblasts/periodontal ligament cells to parathyroid hormone and parathyroid hormone-related protein in vitro

Cementum is an essential component of the periodontium, but the mechanisms involved in regulating the activity of this tissue are poorly understood. A s one approach to better defining the cellular and molecular properties of cementum and the associated ligament, immortalized murine cell populations expressing gene markers associated with both cementoblasts (CM) and periodo ntal ligament cells (PDL), termed CM/PDL cells, were established. To furthe r characterize these cells, their responsiveness to parathyroid hormone (PT H) and parathyroid hormone-related protein (PTHrP) was examined. CM/PDL cel ls were tested for the presence of steady state PTH-1 receptor mRNA using N orthern blot analysis. In addition, the ability of PTH and PTHrP to stimula te cAMP production and c-fos mRNA expression in CM/PDL cells was determined , using a cAMP-binding assay and northern blot hybridization, respectively. Rat osteosarcoma cells (ROS 17/2.8) were used as a positive control and hu man periodontal ligament cells as a negative control. Northern blot analysi s demonstrated that cells within the CM/PDL cell population expressed PTH-1 receptor mRNA. Both PTH (1-34) and PTHrP (1-34) increased cAMP and c-fos m RNA in CM/PDL cells. Furthermore, PTHrP treatment for either 24 or 48 h dow nregulated expression of transcripts for bone sialoprotein, osteocalcin and PTH-1 receptor by CM/PDL cells and abolished CM/PDL cell-mediated minerali zation in vitro. These results indicate that cells within the CM/PDL popula tion are targets for PTH and PTHrP action and that PTHrP may play an import ant part in regulating the biomineralization of cementum. (C) 2000 Elsevier Science Ltd. All rights reserved.