Long non‐coding RNA LncTUG1 regulates favourable compression force‐induced cementocytes mineralization via PU.1/TLR4/SphK1 signalling

Abstract

Orthodontic tooth movement (OTM) is a highly coordinated biomechanical response to orthodontic forces with active remodelling of alveolar bone but minor root resorption. Such antiresorptive properties of root relate to cementocyte mineralization, the mechanisms of which remain largely unknown. This study used the microarray analysis to explore long non‐coding ribonucleic acids involved in stress‐induced cementocyte mineralization. Gain‐ and loss‐of‐function experiments, including Alkaline phosphatase (ALP) activity and Alizarin Red S staining, quantitative real‐time polymerase chain reaction (qRT‐PCR), Western blot, and immunofluorescence analyses of mineralization‐associated factors, were conducted to verify long non‐coding ribonucleic acids taurine‐upregulated gene 1 (LncTUG1) regulation in stress‐induced cementocyte mineralization, via targeting the Toll‐like receptor 4 (TLR4)/SphK1 axis. The luciferase reporter assays, chromatin immunoprecipitation assays, RNA pull‐down, RNA immunoprecipitation, and co‐localization assays were performed to elucidate the interactions between LncTUG1, PU.1, and TLR4. Our findings indicated that LncTUG1 overexpression attenuated stress‐induced cementocyte mineralization, while blocking the TLR4/SphK1 axis reversed the inhibitory effect of LncTUG1 on stress‐induced cementocyte mineralization. The in vivo findings also confirmed the involvement of TLR4/SphK1 signalling in cementocyte mineralization during OTM. Mechanistically, LncTUG1 bound with PU.1 subsequently enhanced TLR4 promotor activity and thus transcriptionally elevated the expression of TLR4. In conclusion, our data revealed a critical role of LncTUG1 in regulating stress‐induced cementocyte mineralization via PU.1/TLR4/SphK1 signalling, which might provide further insights for developing novel therapeutic strategies that could protect roots from resorption during OTM.

Abstract

The schematic summary of proposed mechanisms for stress‐induced cementocytes mineralization. Under desirable compression stress, the expression of LncTUG1 in cementocytes was downregulated, which subsequently inhibited the direct interaction between PU.1 and promotor region of TLR4 and thus reduced the activity of TLR4/SphK1 signalling pathway. Then, the mineralization‐associated factors were upregulated and cementocytes mineralization was promoted.