Tooth development and regeneration occur through reciprocal interactions between epithelial and ectodermal mesenchymal stem cells. However, the current studies on tooth development are limited, since epithelial stem cells are relatively difficult to obtain and maintain. Human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) may be alternative options for epithelial cell sources. To differentiate hESCs/hiPSCs into dental epithelial-like stem cells, this study investigated the hypothesis that direct interactions between pluripotent stem cells, such as hESCs or hiPSCs, and Hertwig’s epithelial root sheath/epithelial rests of Malassez (HERS/ERM) cell line may induce epithelial differentiation. Epithelial-like stem cells derived from hES (EPI-ES) and hiPSC (EPI-iPSC) had morphological and immunophenotypic characteristics of HERS/ERM cells, as well as similar gene expression. To overcome a rare population and insufficient expansion of primary cells, EPI-iPSC was immortalized with the SV40 large T antigen. The immortalized EPI-iPSC cell line had a normal karyotype, and a short tandem repeat (STR) analysis verified that it was derived from hiPSCs. The EPI-iPSC cell line co-cultured with dental pulp stem cells displayed increased amelogenic and odontogenic gene expression, exhibited higher dentin sialoprotein (DSPP) protein expression, and promoted mineralized nodule formation. These results indicated that the direct co-culture of hESCs/hiPSCs with HERS/ERM successfully established dental epithelial-like stem cells. Moreover, this differentiation protocol could help with understanding the functional roles of cell-to-cell communication and tissue engineering of teeth.

Hyun Nam, Ji-Hye Kim, Jae-Won Kim, Byoung-Moo Seo, Joo-Cheol Park, Jung-Wook Kim, and Gene Lee. Mol. Cells 2014;37:562-7. https://doi.org/10.14348/molcells.2014.0161

Yoon-Kyung Bae, Gee-Hye Kim, Jae Cheoun Lee, Byoung-Moo Seo, Kyeung-Min Joo, Gene Lee, and Hyun Nam. Mol. Cells 2017;40:386-92. https://doi.org/10.14348/molcells.2017.0004

Once tooth development is complete, odontoblasts and their progenitor cells in the dental pulp play a major role in protecting tooth vitality from external stresses. Hence, understanding the homeostasis of the mature pulp populations is just as crucial as understanding that of the young, developing ones for managing age‐related dentinal damage. Here, it is shown that loss of Cpne7 accelerates cellular senescence in odontoblasts due to oxidative stress and DNA damage accumulation. Thus, in Cpne7‐null dental pulp, odontoblast survival is impaired, and aberrant dentin is extensively formed. Intraperitoneal or topical application of CPNE7‐derived functional peptide, however, alleviates the DNA damage accumulation and rescues the pathologic dentin phenotype. Notably, a healthy dentin‐pulp complex lined with metabolically active odontoblasts is observed in 23‐month‐old Cpne7‐overexpressing transgenic mice. Furthermore, physiologic dentin was regenerated in artificial dentinal defects of Cpne7‐overexpressing transgenic mice. Taken together, Cpne7 is indispensable for the maintenance and homeostasis of odontoblasts, while promoting odontoblastic differentiation of the progenitor cells. This research thereby introduces its potential in oral disease‐targeted applications, especially age‐related dental diseases involving dentinal loss.

Hyun Nam, Ji-Hye Kim, Ji-Yoon Hwang, Gee-Hye Kim, Jae-Won Kim, Mi Jang, Jong-Ho Lee, Kyungpyo Park, and Gene Lee. Mol. Cells 2018;41:515-22. https://doi.org/10.14348/molcells.2018.0060

Han JH, et al. J Periodontal Implant Sci. 2015 Apr;45(2):69-75. https://doi.org/10.5051/jpis.2015.45.2.69