Characterization of alpha-smooth muscle actin positive cells in mineralized human dental pulp cultures

In response to injury, pulp precursor cells can differentiate into odontobl ast-like cells that produce reparative dentine. In culture, pulp cells form mineralizing nodules, but the characteristics of the cells involved in thi s process are still not fully known. Human pulp cells for culture were obta ined from coronal pulp isolated from non-erupted molars, and were maintaine d in RPMI 1640 medium supplemented with fetal calf serum. Nodules were form ing in all human pulp primary cultures (HPPc) and human pulp subcultures ob served until their fifth passage (HPSc < 5). Mineralization of the nodules was confirmed by the presence of calcium and phosphate that were quantified by X-ray microanalysis. Specific immunolabeling revealed cc-smooth muscle actin and vimentin in both HPPc and HPSc < 5 cells. Cells positive for alph a -smooth muscle actin were either isolated or gathered together in the nod ules. Under transmission electron microscopy, some cells in primary pulp cu ltures exhibited features typical of myofibroblasts or pericytes, such as s tress fibers, fibronexus, indented nuclei and gap-junctions. These cells we re frequently in close contact with mineral deposits. This work demonstrate s for the first time the presence of pericytes or myofibroblasts in mineral ized human pulp cultures, but further investigation is required to determin e their origin, role and degree of differentiation. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.