Abstract
The purpose of this study is to investigate the molecular mechanisms and biological function of TGF-β-activated Smad1/5 in dental epithelium. Immunohistochemistry was used to detect the expressions of TGF-β signaling-related gene in mice molar germ. Primary dental epithelial cells were cultured and treated with TGF-β1 at a concentration of 0.5 or 5 ng/mL. Small molecular inhibitors, SB431542 and ML347, was used to inhibite ALK5 and ALK1/2, respectively. Small interfering RNA was used to knock down Smad1/5 or Smad2/3. The proliferation rate of cells was evaluated by EdU assay. In the basal layer of dental epithelial bud TGF-β1 and p-Smad1/5 were highly expressed, and in the interior of the epithelial bud TGF-β1 was lowly expressed, whereas p-Smad2/3 was highly expressed. In primary cultured dental epithelial cells, low concentration of TGF-β1 activated Smad2/3 but not Smad1/5, while high concentration of TGF-β1 was able to activate both Smad2/3 and Smad1/5. SB431542 but not ML347 was able to block the phosphorylation of Smad2/3 by TGF-β1. Either SB431542 or ML347 was able to block the phosphorylation of Smad1/5 by TGF-β1. EdU staining showed that high concentration of TGF-β1 promoted dental epithelial cell proliferation, which was reversed by silencing Smad1/5, whereas low concentration of TGF-β1 inhibited cell proliferation, which was reversed by silencing Smad2/3. In conclusions, TGF-β exhibits dual roles in the regulation of dental epithelial cell proliferation through two pathways. On the one hand, TGF-β activates canonical Smad2/3 signaling through ALK5, inhibiting the proliferation of internal dental epithelial cells. On the other hand, TGF-β activates noncanonical Smad1/5 signaling through ALK1/2-ALK5, promoting the proliferation of basal cells in the dental epithelial bud.
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All data generated or analyzed during this study are included in this published article. Further details were available from the corresponding author upon request.
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This study was supported by the grants from the National Natural Science Foundation of China (Grant Nos. 81570942, 81670952).
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HZ and YunZ conducted most of the experiments, collected and analyzed the data, and prepared the figures. HZ drafted the manuscript. YueZ searched the literature. GYu revised the manuscript. GYa conceived and designed the research, interpreted the experimental results, and critically revised the manuscript. All authors approved the final version of the manuscript.
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Zhang, H., Zhan, Y., Zhang, Y. et al. Dual roles of TGF-β signaling in the regulation of dental epithelial cell proliferation. J Mol Histol 52, 77–86 (2021). https://doi.org/10.1007/s10735-020-09925-1
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DOI: https://doi.org/10.1007/s10735-020-09925-1