Molecular mechanisms of green LED-accelerated wound healing in olive flounder (Paralichthys olivaceus)

Skin injuries of aquatic animals are common and often cause serious problems as a damaged barrier cannot maintain osmotic balance and homeostasis. A few studies have reported that particular wavelengths green light can promote wound healing in mammals and fish. However, Although Light emitting diode (LED) illumination has been applied to cure skin wound in mammals, little is known about wound healing responses in fish. The purposes of this study, therefore, were to understand healing process of skin wound of fish exposed to green LED using transcriptional data. Sixty skin-wounded olive flounder in each group were exposed to ambient, white LED (400–700 nm), blue LED (465 nm), and green LED (520 nm) light in 12-h light/ dark cycles for 28 days. Fish were observed at 28 days post injuries (dpi) to examine for wound closure. For transcriptome analysis, fish in ambient, white LED, and green LED groups were sacrificed to obtain tissue samples from the wounded area at 3 and 7 dpi. As a result, there were no significant differences between groups in survival rate for a month. However, the size of wounds of fish in the green light exposed-group was significantly reduced followed by white and blue LED groups, and ambient light group. Fish in the green LED group showed up-regulation of many genes involved in electron transfer systems and ATP/ROS production in fish. This indicates that green LED photons might be absorbed as energy in cells in the fish skin including chromophores. Those factors further activate signal pathways such as JAK/STAT, FoxO and MAPK to transmit signals to cell division and stimulating various growth factors, which are necessary for accelerating wound healing. This study demonstrates that the illumination of green LED can accelerate wound healing and will contribute to a better understanding of phototherapy and healing mechanism in fish.