Role of Protein Phosphatase 1 in Angiogenesis and Odontoblastic Differentiation of Human Dental Pulp Cells

Introduction: The aims of this study were to examine the immunolocalization of protein Phosphatase 1 (PP1) in developing mouse pulp tissue and to explore the role of PP1 in odontoblastic differentiation and in vitro angiogenesis in human dental pulp cells (HDPCs).

Methods: Immunolocalization of PP1 was assessed in developing mouse pulp tissue. Odontogenic differentiation was examined by Alkaline Phosphatase activity, alizarin red staining, and Reverse Transcriptase polymerase chain reaction. Angiogenesis was evaluated by endothelial cell migration and capillary tube formation. Signaling pathways were analyzed by Western blotting and confocal immunofluorescence.

Results: PP1 expression was detected in preodontoblasts, odontoblasts, dental pulp cells, and endothelial cells within pulp tissue during the crown formed, root formation, and root completion stages. PP1 messenger RNA (mRNA) and protein levels were up-regulated at the late mineralization stage during odontogenic differentiation of HDPCs. The PP1 activator C2 ceramide increased Alkaline Phosphatase activity, mineralized nodule formation, and mRNA expression of dentin Matrix Protein 1 and dentin sialophosphoprotein. In contrast, knockdown by PP1 small interfering RNA inhibited odontoblastic differentiation. Moreover, PP1 activator up-regulated mRNA expression of angiogenic genes in HDPCs and increased the migration and capillary tube formation of endothelial cells, whereas PP1 small interfering RNA showed opposite effects. C2 ceramide increased levels of Bone Morphogenetic Protein 2, phosphorylation of Smad 1/5/8, and mRNA expression of runt-related transcription factor 2 and osterix.

Conclusions: This study provides the first evidence that PP1 might be a potent regulator of developing pulp tissue in vivo and odontoblastic differentiation and angiogenesis in HDPCs in vitro and may have clinical implications for pulp/dentin regeneration or reparative dentinogenesis.