Monochromatic green light-mediated melatonin promotes cecal barrier function in broilers.

Light plays a crucial role as an environmental factor, greatly affecting chick behavior, production performance and health. Melatonin, an essential marker of photoelectric signaling, plays a role in regulating various physiological functions in broilers, such as gut health. However, whether monochromatic light can mediate melatonin secretion to regulate intestinal function and its regulatory mechanism are not known. In the present study, we showed that monochromatic green light significantly enhanced the mucosal barrier function of the broiler cecum, including the up-regulation of goblet cells and their secreted MUC2 content, tight junction protein expression and enterocyte proliferative viability. However, when the pineal gland was removed, accompanied by a decrease in melatonin content, the green light advantage disappeared and the intestinal mucosal barrier function was severely impaired. Mechanistically, we found that monochromatic green light promotes melatonin secretion, which enters the intestine to bind Mel1a receptors located on macrophage membranes in cecum, inhibits its downstream TLR4/ERK/JNK/NF-κB signaling pathway, promotes M2-type macrophage polarization, reduces intestinal inflammation levels while up-regulating intestinal antioxidant levels, and ultimately strengthens the cecum mucosal barrier function. Our findings provide new theoretical support for the future use of melatonin during intestinal development, as well as theoretical guidance for the proper application of artificial lighting in the modern chicken industry to improve chicken's intestinal health.