Melatonin Nuclear Receptors Mediate Green-and-Blue-Monochromatic-Light-Combinations-Inhibited B Lymphocyte Apoptosis in the Bursa of Chickens via Reducing Oxidative Stress and Nf kappa b Expression

Previous studies found that melatonin modulates a combination of green-and-blue-light-induced B-lymphocyte proliferation via its membrane receptors Mel1a and Mel1c. However, in addition to its membrane-bound receptors, melatonin also functions through binding to nuclear receptors ROR alpha/ROR beta/ROR gamma. In this study, we raised 120 chicks under 400-700 nm white (WW), 660 nm red (RR), 560 nm green (GG) and 480 nm blue light (BB) from P0 to P26. From P27 to P42, half of the chickens in green, blue and red were switched to blue (G -> B), green (B -> G) and red (R -> B), respectively. We used immunohistochemistry, Western blotting, qRT-PCR, Elisa and MTT to investigate the influence of various monochromatic light combinations on the bursal B lymphocyte apoptosis and oxidative stress levels as well as estimate whether melatonin and its nuclear receptors were involved in this process. Consistent with the increase in the plasma melatonin concentration and antioxidant enzyme activity, we observed that G -> B significantly decreased the ROR alpha, ROR gamma mRNA level, inhibited Bax, Caspase-3 and p-i kappa b, p-p65 protein expression, increased the IL-10 level and Nrf2, HO-1 protein expression, down-regulated the MDA and pro-inflammatory IL-6, TNF-alpha and IFN-gamma levels in the bursa compared with WW, RR, GG, BB and R -> B, respectively. Our in vitro results showed exogenous melatonin supplementation inhibited B-lymphocyte apoptosis, decreased IL-6, TNF-alpha, IFN-gamma and ROS production, down-regulated ROR alpha, ROR gamma mRNA level and p-i kappa b and p-p65 protein expression, whereas it improved the IL-10 level and Nrf2 and the HO-1 protein expression in bursal B lymphocyte. Moreover, these responses were abrogated by ROR alpha agonist SR1078 but were mimicked by ROR alpha antagonist SR3335 or ROR gamma antagonist GSK2981278. In addition, p65 antagonist BAY reversed ROR alpha/ROR gamma-mediated G -> B-inhibited bursal B lymphocyte apoptosis. Overall, we concluded that melatonin nuclear ROR alpha/ROR gamma mediates G -> B-inhibited bursal B lymphocyte apoptosis via reducing oxidative stress and Nf kappa b expression.