Thyroid Hormone Receptor Expression of Tooth Germ and Alveolar Bone in Amphibian Model

Objectives: Thyroid hormone (TH) is lipophilic ligands composed of two iodinated tyrosine residues that regulate cellular differentiation and development, cardiac function, and basal metabolism. Thyroid hormone receptor(THR) and TH are contribute to the development of the teeth and the regeneration of alveolar bone. Propylthiouracil (PTU) is a thiouracil-derived drug used to blocking the effect of TH. We hypothesize that the sequential developed tooth germ are induced by TH and THR network. Therefore, we investigate the effect of TH to the tooth germ and alveolar bone in development.
Methods: To investigate the relationship between the mRNA transcript levels of thyroid hormone receptor in tooth germ and alveolar bone, we examined the blocking effect of thyroid hormone in amphibian model. Amphibians offer many of the experimental advantages that permeability of the skin for small molecules. Japanese newts (Cynops pyrrhogaster) were maintained in aqueous solutions with or without PTU for one month. We observed the effect of PTU by the expression levels of mRNA of thyroid hormone receptor detected in-situ hybridization and real time RT-PCR.
Results: The amputated mandible sites were observed microscopically. The level of mineralized area of alveolar bone in amputation with PTU treatment was significantly smaller than that in the amputation in blocking the effect of TH. The expression levels of mRNA of THR was significantly increased in regenerated area of alveolar bone by real time RT-PCR(Student's t-test, p<0.001).
Conclusions: Our data suggests that TH may affect the tooth germ development and the regeneration of alveolar bone in newts. TH and THR are exist in vertebra, which include mammalian including human. In future our experimental system may apply the unique human teeth development.