Mechanism of Mechanical Vibration in Enhancing Orthodontic Retention- Analysis of Global Gene Expression

Introduction: Low-magnitude, high-frequency (LMHF) mechanical vibration has been proposed as a possible adjunctive retention method after orthodontic treatment. In this study, we explored the mechanism of using LMHF vibration to improve bone formation during retention phase. We aimed to provide insight of global gene expression and cellular activities of PDL cells under tension, as well as identify novel biomarkers for induced osteogenesis by using LMHF mechanical vibration as adjunct tool in retention phase. Materials and Methods: Human PDL cells (hPDLCs) were seeded in 6-well FLEXCELL culture plates. The wells were assigned to four experimental groups as control, stretching (ST), vibration (V), and stretching + vibration (SV). In groups required stretching, 24 hours after seeding the cells were mechanically stretched (15%) for 1 hour to mimic hPDLCs under orthodontic tension. Immediately after one hour of stretching (15%), vibration (0.3g, 120Hz) or stretching+vibration, the cells were lysed for RNA collections using the RNeasy Mini kit (Qiagen). RNA sequencing was performed (NextSeq500) to observe the global gene expressions of the hPDLCs. Statistical and bioinformatic analysis were performed with R studio. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genome (KEGG) pathway enrichment analysis were performed for differential expression analysis of the genes. P-values \u3c 0.05 were considered as significantly enriched. Results: Novel biomarkers for bone remodeling including BICC1, MARCKS, and ANO6 were significantly upregulated in ST group. GO and KEGG analysis of the differentially expressed genes indicated significant upregulation of HSF-1 mediated heat shock protein (HSP) response and downregulation of osteoclast differentiation in SV group comparing to ST group. (P \u3c 0.05) Osteogenesis related genes including SOST were significantly downregulated in ST group. (P \u3c 0.05) Conclusion: Novel biomarkers and genes were identified for PDLCs under tension with or without mechanical vibration. Upregulation of HSP70/HSP40 heat shock protein response and downregulation of osteoclastogenesis were discovered as the two main biological mechanisms explaining the anabolic effect of LMHF mechanical vibration on PDLCs under tension during retention phase