Figure 3.

In the application of PBM, photon are absorbed by chromophores which activates ROS. As a secondary messenger, ROS results in the activation and stimulation of various pathways including p38 MAPK and PRKD₂. Oxidative stress can also stimulate p38 MAPK by the presence of cytokines. The two pathways stimulate the hormone activity of melatonin, which induces osteoblast differentiation. However, p38 MAPK also increases p-ATF₂ levels, which can result in decline of chondrocytes. Created with BioRender.