Increased apoptosis in transgenic mouse model of tricho-dento-osseous syndrome

BACKGROUND: Thin, pitted enamel and taurodontism are major clinical characteristics of the Tricho-Dento-Osseous (TDO) syndrome due to DLX3 gene mutation. How mutant DLX3 protein contributes to these dental anomalies is unknown. OBJECTIVE: To generate a transgenic mouse model of TDO to permit in vivo investigation how mutant DLX3 affects enamel and dentin development. METHODS: We established transgenic mice (TG) for a 4 bp deletion mutation in DLX3 (MT-DLX3) to generate an in vivo model of TDO. We investigated the in vivo impact of this mutation on tooth development using radiography, immunohistochemistry, gene expression, scanning electron microscopy (SEM) and transfection studies. RESULTS: Three TG mice lines were generated. All were fertile and demonstrated altered bone and tooth phenotypes. Incisors were yellow and were markedly bent. High-resolution radiography indicated altered dentin formation in TG mice, with markedly enlarged pulp chambers in TG molars and incisors, similar to findings in human TDO patients. Immunohistochemical studies of teeth demonstrated that odontoblast polarization and dentin formation were dramatically reduced in TG mice molars and incisors. Expression levels of the dentin matrix proteins biglycan, decorin, dentin sialophosphoprotein, and type I collagen were restricted to the pre-dentine zone. SEM analysis demonstrated markedly reduced dentinal tubule formation and abnormal enamel structure in TG mice indicating defective dentin and enamel formation similar to that seen in TDO patients. Expression levels of the apoptotic markers caspase-3 and Poly ADP-Ribose Polymerase (PARP) were markedly increased in dentin papilla cells, odontoblasts, and ameloblasts. In vitro studies also demonstrated that the transfection of MT-DLX3 into odontoblastic MDCP-23 cells increased the expression levels of caspase-3 and PARP proteins. CONCLUSION: These data demonstrate that abnormalities in tooth development in MT-DLX3 TG mice are due to the increased apoptosis of odontoblast and ameloblast cells.