Purpose: Low reactive level laser therapy （LLLT） promotes wound healing. Our previous study has revealed that the LLLT with Er:YAG laser enhanced the activity of transforming growth factor beta （TGF-β） in human periodontal ligament （HPDL） cells （Kobayashi et al., 2017）. However, it is unclear how the Er:YAG irradiation facilitates the TGF-β activity in HPDL cells. The purpose of this study is to investigate factors that activate TGF-β in HPDL cells by LLLT with Er:YAG laser.
Materials and Methods: HPDL cells were irradiated with Er:YAG laser （50mJ · 10pps · 10sec） and gene expression of Matrix metalloproteinase （MMPs） was analyzed from the cell components after culture by quantitative PCR. Recombinant MMP was mixed with recombinant latent TGF-β1 to evaluate Alkaline Phosphatase （ALP） activity value in HPDL cells. MMP inhibitor was added to the culture medium for HPDL cells irradiated with Er:YAG laser and incubated, TGF-β activity was evaluated as ALP activity value, and cell proliferation ability was evaluated by MTS assay.
Result: Gene expression of MMP-2 and MMP-3 in the laser irradiation group on the day 1 of culture was prone to increase compared to that of the non-irradiation group. The group in the mixture of MMP-3 and latent TGF-β1 were significantly increased ALP activity compared to the group in recombinant latent TGF-β1 only group. In the group in which an inhibitor for MMP-2 was added in the laser-irradiated HPDL cells, both the ALP activity and the MTS assay were significantly suppressed on the day 5 of irradiation compared with the inhibitor-free group. In the group in which an inhibitor for MMP-3 was added in the laser-irradiated HPDL cells, the MTS assay on the day 5 of irradiation was significantly suppressed compared with the inhibitor-free group.
Discussion: Our results indicated that irradiation of HPDL cells with Er:YAG laser increased gene expression of MMP-2 and MMP-3. As its function, MMP-2 was involved in hard tissue induction by activating TGF-β, and MMP-2, -3 suggested to be involved in wound healing since it controls cell proliferation.