Effects of Er:YAG laser irradiation on proliferation and alteration of gene expression in the MLO-Y4 osteocyte-like cells

Objective: The aim of this study was to investigate the effects of Er:YAG laser irradiation on MLO-Y4 osteocyte-like cells. Materials and Methods: MLO-Y4 cells were seeded before 72h laser-irrdiation and irradiated by Er:YAG laser at energy fluences of 3.1, 6.0 and 8.9 J/cm2. To evaluate thermal effects, cell surface temperature and gene expression of Hspa1a were measured. For evaluation of cell proliferation and cytotoxicity, CCK-8 assay, and Lactate dehydrogenase (LDH) assay of the laser-irradiated cells were performed. RNA-sequencing analysis was performed at 6h after 6.0 J/cm2 laser-irradiation and non-irradiated cells. Result: According to surface temperature and Hspa1a expression, no thermal effects were observed at 6.0 J/cm2 irradiation. CCK-8 assay revealed a significant increase in proliferative activity was observed, although LDH levels showed a slight but significant increase at 6.0 J/cm2 laser-irradiation. RNA-seq analysis identified 337 differently expressed genes. Epha, Itga5, and Tcf7, associated with mechanical stimulation, were highly upregulated in the laser-irradiated cells. KEGG pathway analysis showed upregulation of PI3K-Akt signaling pathway in the laser-irradiated cells. Upregulated DEGs belong to GO term of cellular components “euchromatin” in the laser-irradiated cells. Gene set enrichment analysis showed enrichment of TGF-beta signaling gene set and downregulation of mTORC1 signaling gene set in the laser-irradiated cells. Conclusion: Er:YAG laser irradiation promotes the proliferation of MLO-Y4 cells, osteocyte-like cells, via altering cell proliferation and mechanotransduction-related gene expression.