Oral Organoids: Progress and Challenges

Abstract

Oral organoids are complex 3-dimensional structures that develop from stem cells or organ-specific progenitors through a process of self-organization and re-create architectures and functionalities similar to in vivo organs and tissues in the oral and maxillofacial region. Recently, striking advancements have been made in the construction and application of oral organoids of the tooth, salivary gland, and tongue. Dental epithelial and mesenchymal cells isolated from tooth germs or derived from pluripotent stem cells could generate tooth germ–like organoids by self-organization in a specific culture system. Tooth organoids can also be constructed based on tissue engineering principles by seeding stem cells on a scaffold with the bioregulatory functions of odontogenic differentiation. Two main approaches have been used to construct salivary gland organoids: 1) incubation of salivary gland–derived stem/progenitor cells in a 3-dimensional culture system to form the structure of the gland through mimicking regenerative processes and 2) inducing of pluripotent stem cells to generate embryonic salivary glands by replicating the development process. Taste bud organoids can be generated by embedding isolated circumvallate papilla tissue in Matrigel with a mixture of growth factors, while lingual epithelial organoids have been constructed using lingual stem cells in a suitable culture system containing specific signaling molecules. These oral organoids usually maintain the main functions and characteristic structures of the corresponding organ to a certain extent. Furthermore, using cells isolated from patients, oral organoids could replicate specific diseases such as maxillofacial tumors and tooth dysplasia. Until now, oral organoids have been applied in the study of mechanisms of tooth development, pathology and regeneration of the salivary gland, and precision therapeutics for tongue cancer. These findings strongly demonstrate that the organoid technique is a novel paradigm for the study of the development, pathology, and regeneration of oral and maxillofacial tissue.

Organoids from human tooth showing epithelial stemness phenotype and differentiation potential

“…Such approach may be superior (both material- and function-wise) to the traditional, still suboptimal synthetic implants, among others suffering from lack of physiological functionality, inferior bone integration and absence of innervation. Embryonically derived, bioengineered mouse tooth germs have been shown capable of forming a functional tooth unit after transplantation in an emptied dental cavity of the mouse [ 18 , 20 ]. Our organoid and assembloid models may provide essential puzzle pieces toward developing human tooth germs.…”

“…Typically, epithelial organoid models are established without the need for prior isolation of the epithelial (stem) cells from the dissociated whole-tissue sample since the accompanying mesenchymal cells do not thrive in the specific culture conditions used and are swiftly lost at culture and passaging [ 13 , 14 , 16 , 17 ]. Although meanwhile derived from numerous organs, epithelial organoids have not been established yet from human tooth [ 18 , 19 ]. A previous study reported that ERM cells, seeded in Matrigel, grew as ‘organoids’ [ 8 ].…”

“…However, these structures were not deeply characterized and did not adhere to the current hallmarks of tissue-derived organoids [ 13 – 17 ] such as (clonal) derivation and expansion from epithelial tissue stem cells under WNT-promoting conditions, and robust and long-term expandability. Other studies described the construction of bioengineered 3D dental structures, however, only from animal origin (mouse, rat, dog, pig) at embryonic or neonatal age and non-expandable [ 18 , 20 – 22 ].…”

Hypes and Hopes of Stem Cell Therapies in Dentistry: a Review

“…Organoids have been established for the salivary gland, lingual epithelium, and taste buds and show similar characteristics to those of the corresponding organs [ 124 ]. Salivary gland organoids can be obtained with two methodologies.…”

A critical analysis of research methods and biological experimental models to study pulp regeneration

“…Organoid-based reconstruction strategies have emerged as a potential 3DA for reconstructing dental tissues. These strategies involve the replication of the spatial-temporal cell interactions via co-culture or the compartmentalization of dental epithelial and mesenchymal cells digested from tooth germs within scaffolds followed by the organoid culture within a bioreactor or in vivo transplantation (Gao et al, 2021). Vascular endothelial cells have been incorporated into the system to develop vascularized tooth germ organoids (Smith et al, 2017).…”