Parathyroid hormone -related protein regulates cementogenesis.

Parathyroid hormone-related protein (PTHrP) plays an essential role in the development and homeostasis of many tissues/organs. This dissertation is aimed at exploring the role of PTHrP in regulating cementum formation. Initially, two parent cementoblast cell populations (SV-CM/PDL and OC-CM) were established. The SV-CM/PDL population contains both cementoblasts and periodontal ligament (PDL) cells obtained from the root surface of the first mandibular molars of CD-1 mice and immortalized with SV-40 T antigen (TAg). The OC-CM population contains cementoblasts exclusively and was established from OC-TAg transgenic mice whose cells harbor an osteocalcin promoter-driving TAg gene, TAg. To identify the cell targets for PTHrP action, clonal populations were established from the SV-CM/PDL and the OC-CM populations. Cementoblast subclones were defined cells expressing BSP and/or OCN transcripts, while PDL cell lines were designated cells lacking BSP and OCN mRNA. Cementoblasts were cuboidal and promoted biomineralization both in vitro and in vivo. In contrast, PDL subclones were spindle-shaped and failed to promote mineralized nodule formation both in vitro and in vivo. The effect of PTHrP on clonal populations was determined. Cementoblasts, but not PDL cells, expressed PTH-1 receptor mRNA and exhibited PTHrP-mediated elevation in cAMP levels and c-fos gene induction. PTHrP reduced BSP and OCN mRNA expression and blocked cementoblast-mediated mineralization in vitro. Collectively, these data strongly suggest that cementoblasts are targets for PTHrP in vivo and that PTHrP plays an inhibitory role in regulating cementoblast activities during cementogenesis. Having identified the cell target of PTHrP and determined the effects of PTHrP the molecular mechanisms underlying PTHrP regulation, focusing on PTHrP effect on BSP gene expression in cementoblasts, was investigated. Results demonstrated that long-term exposure of cementoblasts to PTHrP repressed gene expression and protein synthesis of BSP, in vitro. Further, PTHrP inhibition of BSP gene expression was dependent on transcription and protein synthesis. The inhibitory effect of PTHrP was mediated primarily via activation of the cAMP/PKA pathway, while the PKC pathway was ineffective in mediating the inhibitory actions of PTHrP. These data provide new insights into molecular mechanisms by which PTHrP regulates expression of genes associated with cementum formation.Ph.D.Biological SciencesCellular biologyDentistryHealth and Environmental SciencesMolecular biologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132436/2/9963861.pd