Three-dimensional epithelial and mesenchymal cell co-cultures form early tooth epithelium invagination-like structures: expression patterns of relevant molecules.

Epithelium invagination is the key feature of early tooth development. In this study, we built a three-dimensional (3D) model to represent epithelium invagination-like structure by tissue engineering. Human normal oral epithelial cells (OECs) and dental pulp stem cells (DPSCs) were co-cultivated for 2-7 weeks on matrigel or collagen gel to form epithelial and mesenchymal tissues. The histological change and gene expression were analyzed by HE staining, immunostaining, and quantitative real-time RT-PCR (qRT-PCR). After 4 weeks of cultivation, OECs-formed epithelium invaginated into DPSCs-derived mesenchyme on both matrigel and collagen gel. OEC-DPSC co-cultures on matrigel showed typical invagination of epithelial cells and condensation of the underlying mesenchymal cells. Epithelial invagination-related molecules, CD44 and E-cadherin, and mesenchymal condensation involved molecules, N-cadherin and Msx1 expressed at a high level in the tissue model, suggesting the epithelial invagination is functional. However, when OECs and DPSCs were co-cultivated on collagen gel; the invaginated epithelium was transformed to several epithelial colonies inside the mesenchyme after long culture period. When DPSCs were co-cultivated with immortalized human OECs NDUSD-1, all of the above-mentioned features were not presented. Immunohistological staining and qRT-PCR analysis showed that p75, BMP2, Shh, Wnt10b, E-cadherin, N-cadherin, Msx1, and Pax9 are involved in initiating epithelium invagination and epithelial-mesenchymal interaction in the 3D OEC-DPSC co-cultures. Our results suggest that co-cultivated OECs and DPSCs on matrigel under certain conditions can build an epithelium invagination-like model. This model might be explored as a potential research tool for epithelial-mesenchymal interaction and tooth regeneration.