Examination of the effects of blue light stress on monoamine oxidase-mediated immunomodulatory function in the Pacific abalone, Haliotis discus hannai

Abstract

Marine environments harbor a growing number of stressors brought about by global climate change, local human activities and the urbanization of coastal areas. The Pacific abalone, Haliotis discus hannai, is a nocturnal animal that avoids strong light and prefers darkness. Previous research showed that the abalone mortality rate under short-wavelength blue light was remarkably greater than that under darkness, natural light and orange light. In this study, the temporal variations in the dopamine content of abalone hemolymph under various light conditions were compared, and the dopamine content after exposure to blue light for 6 h was remarkably higher than that in any other group. The full-length monoamine oxidase (MAO) gene sequence for the catecholamine metabolism-related MAO enzyme was obtained by cloning. This gene encoded 545 amino acids, in which the predicted sequence contained a domain that was characteristic for monoamino oxidase. The MAO expression levels were highest in the hepatopancreas and in situ hybridization further revealed that MAO was widely localized around the hepatic nerve cord. The in vitro recombinant MAO protein could catalyze the degradation of epinephrine and dopamine. After 3 h exposure to blue light, the expression levels of MAO, Mn-superoxide dismutase (Mn-SOD), and catalase (CAT) genes were remarkably greater than those in any other group, but the lysozyme (LYZ) and sigma-glutathione-s-transferase (GSTs) expression levels began to increase at 12 h and 6 h, respectively. After the MAO expression levels were knocked-down by RNAi technology, the dopamine concentration significantly increased, but the phagocytic activity, nitric oxide concentration, and the Mn-SOD, CAT, GSTs and LYZ expression levels were remarakbly lower than in the control group and the enhanced green fluorescent protein (GFP) group, suggesting that the normal dopamine metabolism process played a vital role in maintaining the immune response. The above results show that monoamine oxidase may act as an immunomodulator in abalone when responding to adverse light conditions. These results could also be useful when drawing up conservation measures for preserving nearshore benthic biodiversity, such as optimizing urban night lighting schemes.