Conditional Knockout of Raptor/mTORC1 Results in Dentin Malformation

Area of Science:

• Cell Biology
• Developmental Biology
• Biochemistry

Background:

• Mammalian target of rapamycin complex 1 (mTORC1) is a central regulator of cell growth and metabolism, responding to diverse extracellular and intracellular signals.
• The specific role of mTORC1 signaling in the complex process of dentinogenesis, the formation of dentin, remains largely uncharacterized.

Purpose of the Study:

• To investigate the functional significance of Raptor/mTORC1 signaling in odontoblast differentiation and dentin formation during tooth development.
• To elucidate the molecular mechanisms by which mTORC1 influences dentinogenesis.

Main Methods:

• Generation of a conditional knockout mouse model (Raptor^fl/fl; Osx-Cre) to specifically delete Raptor, a key component of mTORC1, in odontoblasts and dental mesenchymal cells.
• Comparative analysis of postnatal tooth development between mutant (Rap-Osx) mice and wild-type littermates, focusing on dentin layer thickness, tooth volume, and pulp chamber size.

Main Results:

• Rap-Osx mice exhibited a phenotype resembling dentinogenesis imperfecta, characterized by smaller tooth volume, significantly thinner dentin layers, and enlarged pulp chambers.
• A marked attenuation in the proliferation and differentiation of odontoblasts and preodontoblasts was observed in Rap-Osx mice compared to controls.
• Inactivation of Raptor/mTORC1-pS6K1 signaling was confirmed in the mutant mice, while this pathway remained active in control mice during tooth development.

Conclusions:

• Raptor/mTORC1 signaling is essential for normal dentinogenesis, playing a critical role in promoting the proliferation and differentiation of odontoblasts and preodontoblasts.
• The pS6K1 signaling pathway is implicated as a key mediator through which Raptor/mTORC1 regulates tooth development and dentin formation.