Intracellular distribution of desmoplakin in human odontoblasts

Coexpression of desmosomal proteins and vimentin has been reported in a specific mesenchymal phenotype. This study investigated the expression of vimentin-binding desmosomal proteins in human dental pulp fibroblasts (DPF) and odontoblasts. The dental pulp has no cells expressing desmocollin (DSC) 1-3, desmoglein (DSG) 1-3, junction plakoglobin (JUP), or desmoplakin (DPK) 1 and 2 except for odontoblasts expressing DPK. A confocal image by laser-scanning microscopy demonstrated the diffuse distribution of DPK in the cytoplasm throughout the odontoblast processes. In culture, the mRNA expression of JUP and DPK1, but not DSC1-3 and DSG1-3, was detected in all DPF clones tested and also in odontoblast-like cells (OB) expressing osteocalcin and dentin sialophosphoprotein mRNAs established in the differentiation medium. The DPF having the potential to differentiate into OB expressed vimentin, but not DPK before culturing in the differentiation medium, whereas OB expressed vimentin-binding DPK1. These results suggest that DPF usually expresses DPK1 mRNA, and that the DPK1 production and the bonding of vimentin to DPK1 occur in DPF with the differentiation into odontoblasts.