Fgf/Mtorc1/Urb2 Axis Modulates Tooth Regeneration After Severe Injuries

Our group previously found that mTORC1 signaling is activated during tooth regeneration after injury, and this study will explore the regulatory mechanisms of mTORC1 and its associated molecular effectors in this process. 1) Targeted ablation of tooth germs in zebrafish Tg(dlx2b:Dendra2-NTR) using the NTR/Mtz system. mTORC1 was activated via L-Leucine or tsc2 mutants and regeneration was assayed by antibody staining; 2) Mandibular incisors of ICR mice were mechanically injured and treated with intraperitoneal rapamycin to inhibit mTORC1. Newborn incisors were analyzed by SEM, micro-CT, and histological staining; 3) Zebrafish urb2 mutants and the Tg(Hsp70L:urb2-flag) were generated. Rescue effects were evaluated using FISH, in situ hybridization, and alizarin red assays to validate the molecular axis of mTORC1/Urb2 in tooth regeneration; 4) Tg(hsp70l:dnFGFR-GFP) was used to inhibit FGF signaling, and potential molecular mechanisms linking FGF and the mTORC1/Urb2 were explored. 1) mTORC1 activation promotes zebrafish cell proliferation and tooth regeneration; 2) Rapamycin disrupted enamel column organization. Histological staining revealed that mTORC1 regulates incisal restoration via cellular function modulation in the cervical ring; 3) FISH revealed that mTORC1 inhibition decreased urb2 transcripts, while urb2 overexpression rescued rapamycin-induced tooth regeneration defects: enhanced Dendra2 fluorescence, upregulated tooth-specific gene expression, and accelerated tooth mineralization. 4) FGF signaling inhibition impaired tooth regeneration, while activation of the mTORC1/Urb2 axis alleviated the phenotypic impairments. FGF/mTORC1/Urb2 signaling cascade governs tooth regeneration after injury, providing new therapeutic targets for tooth tissue engineering.