Cementum, a mineralized tissue located on tooth root surfaces, is considered critical for development and regeneration of a functional periodontal apparatus. Studies to date have been limited to examining the properties of cementum in situ. Advanced technologies now enable us to determine regulators of cementoblasts using both in vitro and in vivo models, allowing for improved strategies for re-engineering periodontal tissues. Based on studies to date using a murine tooth root model the investigators hypothesize: 1) that cells lining the root surface, cementoblasts, secrete a matrix required for biomineralization of cementum and respond to putative periodontal regenerative factors by expressing genes linked with biomineralization; 2) the bone sialoprotein (BSP), expressed by these cells, is required for formation of cementum; and 3) that cementoblasts exhibit a protein profile different from that of cells associated with bone, dentin, and/or enamel. These hypotheses will be tested under three specific aims: 1) Clonal populations of cementoblasts, obtained from immorto-mice molars, exposed to putative periodontal regenerative factors, IGF-I, PDGF and BMP-7, will be evaluated for changes in gene expression and in proliferation rate; 2) The ability of cementoblasts (plus and minus agents) to promote biomineralization and the importance of BSP in this process will be determined, in vitro by von Kossa/TEM and in vivo using a rat periodontal window defect. Sense and anti-sense technology will be used to overexpress and/or disrupt synthesis of BSP in cementoblasts. As factors/cells promoting biomineralization are identified, they will be incorporated into biodegradable polymers and tested for ability to foster regeneration, in vivo. The mechanical integrity of newly formed cementum will be determined using atomic force microscopy; and 3) The molecular profile of cementoblasts will be determined using mRNA differential display. The information obtained from these studies will fill major gaps in our knowledge of cellular and molecular mechanisms regulating root surface formation. This foundation is required for understanding various pathologies, e.g., hypophosphatasia, cementomas, and Paget's associated hypercementosis, and for designing effective clinical procedures for regeneration of periodontal tissues, as well as other mineralized tissues.
