PDGFs regulate tooth germ proliferation and ameloblast differentiation

Objective: The purpose of this study was to elucidate the effects of platelet-derived growth factors (PDGFs) during tooth development, as well as the mechanisms underlying the interactions cif growth factors with PDGF signalling during odontogenesis. Design: We used an ex vivo tooth germ organ culture system and two dental cell lines, SF2 cells and mDP cells, as models of odontogenesis. AG17, a tyrosine kinase inhibitor, was utilised for blocking PDGF receptor signalling. To analyse the expressions of PDGFs, reverse transcriptase (RT)-PCR and immunohistochemistry were performed. Proliferation was examined using a BrdU incorporation assay for the organ cultures and a cell counting kit for the cell lines. The expressions of Fgf2 and ameloblastin were analysed by real-time RTPCR. Results: The PDGF ligands PDGF-A and PDGF-B, and their receptors, PDGFRa and PDGFRB, were expressed throughout the initial stages of tooth development. In the tooth germ organ cultures, PDGF-AA, but not PDGF-BB, accelerated cusp formation. Conversely, AG17 suppressed both growth and cusp formation of tooth germs. Exogenous PDGF-BB promoted mDP cell proliferation. Furthermore, PDGF-AA decreased Fgf2 expression and increased that of ameloblastin, a marker of differentiated ameloblasts. Conclusion: Our results indicate that PDGFs are involved in initial tooth development and regulate tooth size and shape, as well as ameloblast differentiation. (C) 2010 Elsevier Ltd. All rights reserved.