Amelogenin gene splice products A+4 and A-4 implanted in soft tissue determine the reorientation of CD45-positive cells to an osteo-chondrogenic lineage.

Several molecules such as bone morphogenetic protein-7, bone sialoprotein (BSP), or amelogenin gene splice products (A+4 or A-4) have been shown to induce reparative dentin formation in a rat model. However, at the moment, the origin and the mechanism of differentiation of the pulp cells stimulated by the bioactive molecules remain poorly understood. The present investigation was undertaken to validate an ectopic oral mucosal mouse model to evaluate the effects of amelogenin gene splice product implantation in a non-mineralizing tissue. Agarose beads, alone or coated with amelogenin gene splice products, were implanted in the mucosa of the cheeks in mouse. An immunohistochemical characterization of the recruited cells was undertaken for 3 days, 8 days, and 30 days after the implantation. The results showed that the implantation of agarose beads in mucosa induced the recruitment of inflammatory CD45 positive cells. When the beads were coated with amelogenin gene splice products (A+4 or A-4), the expression of osteo-chondrogenic markers (RP59, Sox9, or BSP) was also observed. However, no mineralization nodule was observed, even after 30 days of implantation. The present investigation suggests that amelognin gene splice products have the capacity of recruiting among inflammatory cell mesenchymal progenitors that eventually differentiate into osteo-chondrogenic cells. Altogether, the results obtained in the pulp model and the present data suggest the existence of different pathways of cell recruitment and differentiation in different cellular environments.