Purpose: Recently, low reactive level laser therapy (LLLT), which involves applying photobiomodulation (PBM) to living organisms, has been used for periodontal treatment, but there are few reports on its molecular biology, and further research is needed for clinical application. The aim of this study was to elucidate the biological effects of laser irradiation based on PBM at human gingival epithelial cells (HGKs) by analyzing gene expression and their interactions over time.
Methods: HGKs were irradiated at 0.31 J/cm2 (0.1 J, 30 pps, 10 s). DNA microarray analysis was performed at 6 hours after irradiation. We extracted differentially expressed genes (DEGs) and analyzed their biological processes (BPs). Among the included BPs, we focused on ‘cellular response to stress’ and searched for key genes that were significantly associated with multiple genes by investigating protein-protein interactions (PPIs). Chronological gene expression of the key genes was analyzed at 1, 3, 6, 12, and 24 hours after laser irradiation.
Results: We identified 10 key genes, cyclin dependent kinase inhibitor 2A (CDKN2A), fas cell surface death receptor (FAS), interleukin-6 (IL6), interferon regulatory factor 3 (IRF3), MDM2 proto-oncogene (MDM2), replication factor C subunit 3 (RFC3), replication protein A1 (RPA1), sirtuin 6 (SIRT6), sirtuin 7 (SIRT7), and X-linked inhibitor of apoptosis (XIAP), among the PPIs in the BP ‘cellular response to stress’. The results of chronological expression analysis inferred directions of interactions between the key genes.
Conclusion: LLLT increased the expression of 2,756 genes involved in cell proliferation. The influences on CDKN2A, FAS, IRF3, MDM2, RFC3, RPA1, SIRT6, SIRT7, and XIAP among the major genes of BP ‘cellular response to stress’ with LLLT were new discoveries in the dental field. The effects of LLLT on HGKs were related to inflammation, such as IL6, which was expressed immediately after irradiation, and related to cell repair, such as MDM2, which was upregulated over time. Among the key genes, MDM2 and IL6 were considered to play an important role in the associations with other genes and MDM2 had a role in the duration of the effect.
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