Expression and localisation of αv integrins in human odontoblasts

Integrin alpha beta heterodimers mediate adhesion to the extracellular matrix and at cell-cell contacts and initiate intracellular signalling cascades in response to a variety of inductive factors. Apart from the expression of alpha v beta 3 that we have previously reported, little is known about the expression of integrins in odontoblasts. Here, we investigated the expression of alpha v-binding beta integrin subunits in healthy human dental pulp in vivo and in odontoblasts differentiated in vitro. Reverse transcription/polymerase chain reaction analysis revealed the expression of alpha v, beta 1, beta 5 and beta 8 integrin mRNA, but not beta 6, in whole pulp cells. Flow cytometry showed that the alpha v and beta 1 subunits were the most intensely expressed. Immunohistochemistry demonstrated that the beta 1 subunit was localised in newly differentiated odontoblasts in the root and in mature odontoblasts in the crown, including their intradentinal cell processes, The alpha v chain was predominantly expressed by mature odontoblasts and alpha v beta 5 was only observed in mature odontoblasts. In vitro differentiated odontoblasts expressed genes for alpha v, beta 1 and beta 5, but not for beta 6 and beta 8. A comparison of integrin profiles between cultured pulp cells and in vitro differentiated odontoblasts revealed that odontoblast maturation was characterised by a significant increase in the expression of alpha v and beta 1 subunits and alpha v beta 5 integrin. The beta 8 subunit was detected in nerve cells only. Histological analysis of teeth from alpha v knockout mice showed no obvious structural modification in the odontoblast layer. Thus, human mature odontoblasts express alpha v beta 3, alpha v beta 5 and perhaps alpha v beta 1 integrins, with the possible presence of alpha - beta 1 pairs. The roles that these molecules play in the exchange of information throughout the odontoblast layer remain to be determined.