Irradiation with red light-emitting diode enhances proliferation and osteogenic differentiation of periodontal ligament stem cells

This study aimed to evaluate the effects of low-energy red light-emitting diode (LED) irradiation on the proliferation and osteogenic differentiation of periodontal ligament stem cells (PDLSCs). PDLSCs were derived from human periodontal ligament tissues of premolars and were irradiated with 0 (control group), 1, 3, or 5 J/cm 2 red LED in osteogenic induction medium. Cell proliferation was analyzed using the 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay. Osteogenic differentiation activity was evaluated by monitoring alkaline phosphatase (ALP) activity, alizarin red staining, and real-time polymerase chain reaction (RT-PCR) results. Osteoblast-associated proteins (Runx2, OCN, OPN, and BSP) were detected using western blotting. The results of the MTT assay indicated that PDLSCs in the irradiation groups exhibited a higher proliferation rate than those in the control group ( P < 0.05). ALP results showed that after 7 days of illumination, only 5 J/cm 2 promoted the expression of ALP of PDLSCs. However, after 14 days of illumination, the irradiation treatments did not increase ALP activity. The results of alizarin red staining showed that red LED promoted osteogenic differentiation of the PDLSCs. The real-time polymerase chain reaction (RT-PCR) results demonstrated that red LED upregulated the expression levels of osteogenic genes. Expression of the proteins BSP, OPN, OCN, and Runx2 in the irradiation groups was higher than that in the control group. Our results confirmed that low-energy red LED at 1, 3, and 5 J/cm 2 promotes proliferation and osteogenic differentiation of PDLSCs.