Inductive Ability of Human developing and differentiated Dental Mesenchyme

Objective: Development of cell-based therapeutic strategies to bioengineer tooth tissues is a promising approach to treat lost or damaged tooth tissues. The lack of a readily available cell source for human dental epithelial cells constrains the progress of enamel and tooth bioengineering. Previous studies in model organisms have demonstrated that developing dental mesenchyme can instruct non-dental epithelium to differentiate into enamel forming epithelium. In this study, we characterized the ability of developing and fully differentiated human dental mesenchyme to promote differentiation of human embryonic stem cell-derived epithelial cells (ES-ECs) to ameloblast-lineage.  Methods: ES-ECs were co-cultured either with dental mesenchyme from developing primary teeth from human fetal cadaver tissue (FDMCs) or with adult dental mesenchymal cells (ADMCs) in a three-dimensional culture system or in the renal capsules of SCID mice. After 8 weeks, the co-cultured cell/Matrigel complexes were harvested for histological and gene expression analyses. Transcription factors differentially upregulated in FDMCs as compared to ADMCs were characterized. Results: When co-cultured with human FDMCs, ES-ECs polarized and expressed amelogenin. Tooth bud-like and developing enamel-like structures could be detected in the complexes resulting from in vitro and ex vivo co-culture of ES-ECs and FDMCs. In contrast, co-cultured ES-ECs and ADMCs formed amorphous spherical structures and occasionally formed hair ex vivo. Transcription factors significantly upregulated in FDMCs as compared to ADMCs included MSX1, GLI1, LHX6, LHX8, LEF1 and TBX1. Transduction of ADMCs with LEF1alone was not sufficient to induce the co-cultured ES-ECs to express amelogenin. Conclusion: FDMCs but not ADMCs had the capacity to differentiate recombined hESC-derived epithelial cells into ameloblast-lineage. Further characterization of the functional differences between these two types of dental mesenchymal cell sources could potentially contribute to transcriptional reprogramming of ADMCs to enhance their odontogenic inductive competence.