The signal pathway of melatonin mediates the monochromatic light-induced T-lymphocyte apoptosis in chicken thymus

Our previous study revealed that under monochromatic red light (RL), the melatonin nuclear receptor reduces the proliferation activity of broiler thymic lymphocytes through the P65 signaling pathway. The main objective of this study was to investigate the signal mechanism by which RL decreases thymic lymphocyte proliferation. Initially, broilers were purchased and ran-domly assigned to be fed under white light (WL), red light (RL), green light (GL), and blue light (BL). Pinealec-tomy was performed 3 d later, and the broilers were eutha-nized after 14 d. The results showed that the expression of the antiapoptotic proteins Bcl-2/Bcl-xl decreased under RL, while the expression of the pro-apoptotic factor Bax/ caspase-3 and the pro-inflammatory factors INF-y/TNF-a/IL-6 increased. After pinealectomy, the expression of Bax/TNF-a/IL-6 increased in conjunction with the decrease in Bcl-2 expression. In vitro experiments demon-strated that exogenous melatonin decreased the expression of Bax/TNF-a/IL-6 in thymic lymphocytes of chicks reared under RL. This melatonin-induced effect was enhanced by SR1078 (RORa/RORy agonist) but attenu-ated by SR3335 (RORa antagonist) and BAY (P65 antag-onist). These findings revealed that the melatonin nuclear receptor RORa/RORy promotes the expression of the pro-apoptotic factor Bax/caspase-3 and the pro-inflamma-tory factors INF-y/TNF-a/IL-6, while inhibiting the expression of the antiapoptotic factor Bcl-2/Bcl-xl. Our research suggested the signaling pathway of monochro-matic red light impacts the apoptosis of thymus lympho-cytes in broiler.