A cell-permeable fusion protein for the mineralization of human dental pulp stem cells

Human dental pulp stem cells (hDPSCs) are the only mesenchymal stem cells in pulp tissue that can differentiate into osteoblasts, odontoblasts, and adipose cells. The transcriptional co-activator with PDZ-binding motif (TAZ) protein has been reported to modulate osteogenic differentiation in mouse MSCs. Therefore, we examined whether the TAZ protein plays the same role in human pulp stem cells. In this study, TAZ was applied to cells directly with low-molecular-weight protamine (LMWP) as a cell-penetrating peptide (CPP). The LMWP-TAZ fusion proteins were expressed in an E. coli system with a pET-21b vector and efficiently transferred into hDPSCs without producing toxicity in the cells. The efficient uptake of TAZ was shown by Western blot with an anti-TAZ antibody, fluorescence-activated cell sorting, and confocal microscopy in live cells. The delivered TAZ protein increased osteogenic differentiation, as confirmed by alkaline phosphatase (ALP) staining, RT-PCR, and Western blotting. In addition, TAZ also inhibited adipogenic differentiation, regulating peroxisome proliferator-activated receptor-γ (PPAR-γ), lipoprotein lipase (LPL), and adipocyte fatty acid-binding protein (aP2) mRNA levels. These in vitro studies suggest that cell-permeable TAZ may be used as a specific regulator of hard-tissue differentiation.