Role of alpha smooth muscle actin in odontogenic differentiation of dental pulp stem cells

Pulpotomy is an effective treatment for retaining vital pulp after pulp exposure caused by caries removal and/or trauma. The expression of alpha smooth muscle actin (alpha-SMA) is increased during the wound-healing process, and alpha-SMA-positive fibroblasts accelerate tissue repair. However, it remains largely unknown whether alpha-SMA-positive fibroblasts influence pulpal repair. In this study, we established an experimental rat pulpotomy model and found that the expression of alpha-SMA was increased in dental pulp after pulpotomy relative to that in normal dental pulp. In vitro results showed that the expression of alpha-SMA was increased during the induction of odontogenic differentiation in dental pulp stem cells (DPSCs) compared with untreated DPSCs. Moreover, alpha-SMA overexpression promoted the odontogenic differentiation of DPSCs via increasing mitochondrial function. Mechanistically, alpha-SMA overexpression activated the mammalian target of rapamycin (mTOR) signaling pathway. Inhibition of the mTOR signaling pathway by rapamycin decreased the mitochondrial function in alpha-SMA-overexpressing DPSCs and suppressed the odontogenic differentiation of DPSCs. Furthermore, we found that alpha-SMA overexpression increased the secretion of transforming growth factor beta-1 (TGF-beta 1). In sum, our present study demonstrates a novel mechanism by which alpha-SMA promotes odontogenic differentiation of DPSCs by increasing mitochondrial respiratory activity via the mTOR signaling pathway.