Role of the N-terminal peptide of amelogenin on osteoblastic differentiation of human mesenchymal stem cells

Induction of periodontal ligament-like cells by co-culture of dental pulp cells, dedifferentiated cells generated from Epithelial cell Rests of Malassez, and umbilical vein endothelial cells

INTRODUCTION

Apart from the Epithelial Cell rests of Malassez (ERM), the dental pulp (DP) contains the same types of mesenchymal cells as the periodontal ligament (PDL). The ERM may affect the characteristics of mesenchymal cells in the PDL. The aim of this study was to examine whether DP cells cultured with ERM and human umbilical vein endothelial cells (HUVECs) could transform into PDL-like cells.

METHODS

Progenitor-dedifferentiated into stem-like cells (Pro-DSLCs) were produced by the induction of ERM with 5-Azacytidine and valproic acid. DP cells were cultured in mesenchymal stem cell (MSC) medium for 1 week under the following conditions: DP cells alone (controls); PDL cells alone; co-culture of DP cells and ERM (DP+ERM) or Pro-DSLCs (DP+Pro-DSLC); co-culture of DP cells, HUVECs, and ERM cells (DP+ERM+HUVEC) or Pro-DSLCs (DP+Pro-DSLC+HUVEC). qRT-PCR, qMSP, and flow cytometry were performed.

RESULTS

The expression levels of PDL-related markers, Msx1, Msx2, Ncam1, Postn, S100a4, and MSC-positive markers, Cd29, Cd90, Cd105, were significantly higher in the PDL cells and DP+Pro-DSLC+HUVEC cultures than in the controls (p < 0.05). The DNA methylation levels of Msx1 and Cd29 in the PDL cells and DP+Pro-DSLC+HUVEC culture were significantly lower than in the controls (p < 0.01). We found a significant increase in the number of cells stained with MSX1 (p < 0.05) and CD29 (p < 0.01) in the DP+Pro-DSLC+HUVEC culture than in the controls.

CONCLUSIONS

Co-culture of DP cells with Pro-DSLCs and HUVECs induced their transformation into PDL-like cells. This method may prove useful for periodontal regeneration via tissue engineering.

Interactions of amelogenin with phospholipids

Amelogenin protein has the potential to interact with other enamel matrix proteins, mineral, and cell surfaces. We investigated the interactions of recombinant amelogenin rP172 with small unilamellar vesicles as model membranes, toward the goal of understanding the mechanisms of amelogenin-cell interactions during amelogenesis. Dynamic light scattering (DLS), fluorescence spectroscopy, circular dichroism (CD), and nuclear magnetic resonance (NMR) were used. In the presence of phospholipid vesicles, a blue shift in the Trp fluorescence emission maxima of rP172 was observed (∼334 nm) and the Trp residues of rP172 were inaccessible to the aqueous quencher acrylamide. DLS studies indicated complexation of rP172 and phospholipids, although the possibility of fusion of phospholipids following amelogenin addition cannot be ruled out. NMR and CD studies revealed a disorder-order transition of rP172 in a model membrane environment. Strong fluorescence resonance energy transfer from Trp in rP172 to DNS-bound-phospholipid was observed, and fluorescence polarization studies indicated that rP172 interacted with the hydrophobic core region of model membranes. Our data suggest that amelogenin has ability to interact with phospholipids and that such interactions may play key roles in enamel biomineralization as well as reported amelogenin signaling activities.

Controlled Osteogenic Differentiation of Mouse Mesenchymal Stem Cells by Tetracycline-Controlled Transcriptional Activation of Amelogenin

Regenerative dental therapies for bone tissues rely on efficient targeting of endogenous and transplanted mesenchymal stem cells (MSCs) to guide bone formation. Amelogenin is the primary component of Emdogain, which is used to regenerate periodontal defects; however, the mechanisms underlying the therapeutic effects on alveolar bone remain unclear. The tetracycline (Tet)-dependent transcriptional regulatory system is a good candidate to investigate distinct roles of genes of interest during stem cell differentiation. Here, we investigated amelogenin-dependent regulation of osteogenesis in MSCs by establishing a Tet-controlled transcriptional activation system. Clonal mouse bone marrow-derived MSCs were lentivirally transduced with the Tet repressor (TetR) expression vector followed by drug selection to obtain MSCs constitutively expressing TetR (MSCs-TetR). Expression vectors that contained the Tet operator and amelogenin-coding (Amelx) cDNA fragments were constructed using the Gateway system and lentivirally introduced into MSCs-TetR to generate a Tet regulation system in MSCs (MSCs-TetR/Amelx). MSCs-TetR/Amelx significantly overexpressed the Amelx gene and protein in the presence of the tetracycline derivative doxycycline. Concomitant expression of osterix, bone sialoprotein (BSP), osteopontin, and osteocalcin was modulated by addition or removal of doxycycline under osteogenic guidance. During osteogenic induction, MSCs-TetR/Amelx treated with doxycycline showed significantly increased gene expression of osterix, type I collagen, BSP, and osteocalcin in addition to increased alkaline phosphatase activity and mineralized nodule formation. Enhanced extracellular matrix calcification was observed when forced Amelx expression commenced at the early stage but not at the intermediate or late stages of osteogenesis. These results suggest that a Tet-controlled Amelx gene regulation system for mouse MSCs was successfully established, in which transcriptional activation of Amelx was associated with enhanced osteogenic differentiation, especially in the early stage of biomineralization.