Effects of apatite, transforming growth factor beta-1, bone morphogenetic protein-2 and interleukin-7 on ameloblast differentiation in vitro

Preameloblasts overtly differentiate in vitro when recombined with cell-fre e predentin-dentin. The predentin-dentin components able to trigger amelobl ast terminal differentiation have not been identified, but some growth fact ors (members of the TGF beta superfamily) have been demonstrated to be asso ciated with this matrix, and in situ hybridization has demonstrated the pre sence of transcripts for TGF beta s and BMP-2 in odontoblasts facing differ entiating ameloblasts. Moreover, intense expression of receptors for the cy tokine interleukin-7 (IL-7) in polarizing ameloblasts has been reported. In this study, isolated E-18 and E-19 mouse molar enamel organs were cultured in vitro in presence of BMP-2, TGF beta-1, IL-7 or synthetic apatite. TGF beta-1 and BMP-2 combined with heparin induced cytodifferentiation of amelo blasts. IL-7 maintained the polarized state of ameloblasts. BMP-2-soaked ap atite induced functional differentiation of ameloblasts (secretion of amelo genin). Integrating these data with previous work, a working hypothesis con cerning the control of ameloblast terminal differentiation is presented: me mbers of the TGF beta superfamily secreted by odontoblasts might be trapped by predentin components first and then by dentin apatites, and these growt h factors might trigger the cytological-functional sequence of ameloblast t erminal differentiation.