Characterization of Dental Pulp Myofibroblasts in Rat Molars after Pulpotomy

Introduction: Myofibroblasts express alpha smooth muscle actin (alpha-SMA) and play a critical role in wound healing. Myofibroblast differentiation is controlled by the joint actions of transforming growth factor beta 1 (TGF-beta 1) and the extradomain A fibronectin splice variant (EDA-FN). Currently, the contribution of myofi-broblasts to dental pulp healing is unknown. Therefore, we analyzed expressional characteristics of alpha-SMA positive cells and investigated TGF-beta 1, EDA-FN, and alpha-SMA expression levels after pulpotomy to better understand dental pulp healing. Methods: The maxillary first molars of 8-week-old Wistar rats were pulpotomized with mineral trioxide aggregate. After 1 to 14 days, localization and colocalization of alpha-SMA, rat endothelial cell antigen-1 (as a marker of endothelial cells), neuron-glial antigen 2 (as a marker of perivascular cells), prolyl-4-hydroxylase (P4H, as an additional marker of myofibroblasts), and EDA-FN were analyzed using immunohistochemistry and double immunofluorescence. Time-course changes in the messenger RNA expression levels of TGF-beta 1, EDA-FN, and alpha-SMA were evaluated using quantitative real-time polymerase chain reaction analysis. Results: Spindle-shaped alpha-SMA positive cells transiently appeared after pulpotomy. These cells initially emerged in the pulp core on day 3 and then accumulated at the wound site by day 5. These cells were isolated from rat endothelial cell antigen-1 positive cells and did not express neuron-glial antigen 2 but did express P4H. The messenger RNA levels of TGF-beta 1, EDA-FN, and alpha-SMA were significantly up-regulated after pulpotomy. EDA-FN and a-SMA were colocalized at the wound sites on day 5. Conclusions: In association with up regulation of TGF-beta 1 and EDA-FN expression, alpha-SMA and P4H double-positive cells accumulated at the wound sites after pulpotomy. This suggests that myofibroblasts participate in dental pulp healing.