Mechanisms of Periodontal Regeneration Induced by Human Recombinant Amelogenin

Application of the recombinant human amelogenin protein (rHAM+) (Taylor et al. 2000) alone, after induction of chronic periodontitis in dog model, induced significant periodontal regeneration (Deutsch et al. 2003, Haze-Filderman et al. 2003). Objectives: Explore possible molecular mechanisms associated with the regeneration process. Methods: Immunohistochenistry, in-situ hybridization, confocal microscopy co-localization, Western blot analysis, RT-PCR and sequencing. Results: In normal and regenerating periodontal tissues amelogenin was found, for the first time, to be expressed in osteoblasts and osteoclasts, in cells surrounding blood vessels, in distinct bone marrow cells, and in some PDL cells and cementoblasts along the root. Amelogenin expression was higher at sites of increased bone and PDL activity. Two weeks after treatment with rHAM+, STRO-1 and CD105 expression showed many more MSCs in the granulation tissue, PDL, bone and bone marrow as compared to control. The over-expression of CD105 (also a marker of neovascularization) in the regenerating tissues, together with increased vascularization of these tissues and amelogenin expression in cells surrounding blood vessels, suggest that amelogenin might also promote angiogenesis. In normal dog and rat long bones, amelogenin is expressed by all bone cells, by specific cells of articular cartilage and epiphyseal growth plate. In long bone marrow amelogenin expression was detected in a number of morphologically different cells, some of which are MSCs. Sequencing of mRNA from long bone marrow, human stromal cells and human bone revealed the expression of amelogenin. The amelogenin LRAP transcript was also identified in bone marrow. Conclusions: We suggest that amelogenin induces periodontal regeneration by recruitment of MSCs and directly or indirectly by increasing angiogenesis. Our discovery that amelogenin is expressed in cells of long bone, cartilage and bone marrow and its pattern of expression, suggest that amelogenin might also have a major role in normal remodeling and regeneration of these tissues. DFG-grant-Be1142/4-1.