Role of injured endothelial cells in the recruitment of human pulp cells.

In restorative dentistry, deep cavity preparation may lead to partial destruction of the odontoblastic layer. However, newly formed odontoblast-like cells can replace the necrotic odontoblasts and secrete a reparative dentine matrix. While growth factors such as transforming growth factor beta1 (TGFbeta1) and bone morphogenetic proteins (BMP-2 and BMP-4) seem to be involved in the proliferation and differentiation of pulp cells, little is known about the migration of the newly proliferating stem cells to the injury site. Our hypothesis was that endothelial cell injury may be involved in directing these cells towards the injury site. For this study, human pulp fibroblasts and L929 cells were fluorescence-labeled by transduction with the Enhanced Green Fluorescent Protein (EGFP). Similarly, human umbilical vein endothelial cells (HUVEC) were labeled with the Discosoma Red Fluorescent Protein-2 (DsRed2). Cell migration was then studied in an insert cell culture system. The HUVEC cells were cultured in the lower compartment while the human pulp fibroblasts or L929 were in the upper compartment. After artificial injury to the HUVEC cells, only human pulp fibroblasts migrated to the lower compartment. At early time periods (4 days), migrating cells were randomly localized on the HUVEC layer. However, after 14 and 20 days, they were perfectly aligned along the injury site. In the absence of injury, no migration was observed. These results suggest that, the endothelial injury is involved in the recruitment of odontoblast-like cells at the injury site.