Dissection Of The Odontoblast Differentiation Process In Vitro By A Combination Of Fgf1, Fgf2, And Tgf Beta 1

Dental papillae (DP) isolated from first lower molars of 17-day-old mouse embryos were cultured in the presence of combinations of the following growth factors: FGF1, FGF2, and TGF beta 1. After 6 days in culture, only the DP treated with FGF1+TGF beta 1 contained differentiated odontoblast-like cells at the periphery of the explants, and these cells secreted extracellular matrix similar to predentin. Surprisingly, treatments with FGF2+TGF beta 1 induced cell polarization at the surface of the explants but no matrix secretion was observed. Electron microscopy and histochemical analysis of odontoblast markers showed that differentiated cells induced by FGF1+TGF beta 1 exhibited cytological features of functional odontoblasts with matrix vesicle secretion and mineral formation, positive alkaline-phosphatase activity, and type-I collagen production. DP cultured in the presence of FGF2+TGF beta 1 showed cell polarization and long and thin cell processes containing matrix vesicles; however, type-I collagen secretion was not detected and alkaline-phosphatase activity was completely inhibited. Our results indicate that, in our culture system, exogenous combinations of FGF1, FGF2, and TGF beta 1 interact with pre-odontoblasts and induce cell polarization or differentiation, which can be studied separately in vitro. Thus, FGF1 and TGF beta 1 do have a synergic effect to promote morphological and functional features of differentiated odontoblasts whereas FGF2 seems to modulate TGF beta 1 action, causing morphological polarization of preodontoblasts but limiting the functional activity of these cells in terms of type-I collagen secretion and alkaline-phosphatase activity. (C) 2000 Wiley-Liss, Inc.