The Role of Thymosin Beta 4 on Odontogenic Differentiation in Human Dental Pulp Cells

We recently reported that overexpression of thymosin beta-4 (T beta 4) in transgenic mice promotes abnormal hair growth and tooth development, but the role of T beta 4 in dental pulp regeneration was not completely understood. The aim of this study was to investigate the role of T beta 4 on odontoblastic differentiation and the underlying mechanism regulating pulp regeneration in human dental pulp cells (HDPCs). Our results demonstrate that mRNA and protein expression of T beta 4 is upregulated during odontogenic differentiation in HDPCs. Transfection with T beta 4 siRNA decreases OM-induced odontoblastic differentiation by decreasing alkaline phosphatase (ALP) activity, mRNA expression of differentiation markers, and calcium nodule formation. In contrast, Tb4 activation with a T beta 4 peptide promotes these processes by enhancing the phosphorylation of p38, JNK, and ERK mitogen-activated protein kinases (MAPKs), bone morphogenetic protein (BMP) 2, BMP4, phosphorylation of Smad1/5/8 and Smad2/3, and expression of transcriptional factors such as Runx2 and Osterix, which were blocked by the BMP inhibitor noggin. The expression of integrin receptors alpha 1, alpha 2, alpha 3, and beta 1 and downstream signaling molecules including phosphorylated focal adhesion kinase (p-FAK), p-paxillin, and integrin-linked kinase (ILK) were increased by T beta 4 peptide in HDPCs. ILK siRNA blocked T beta 4-induced odontoblastic differentiation and activation of the BMP and MAPK transcription factor pathways in HDPCs. In conclusion, this study demonstrates for the first time that T beta 4 plays a key role in odontoblastic differentiation of HDPCs and activation of T beta 4 could provide a novel mechanism for regenerative endodontics.