The Function of Apostichopus Japonicas Catalase in Sea Cucumber Intestinal Immunity

Catalase is an important oxidoreductase enzyme that catalyzes the conversion of hydrogen peroxide molecules into water and oxygen and regulates the homeostasis of ROS in animals and humans. Catalase functions in host immune defense, cellular apoptosis, aging, inflammation, and tumor formation. The intestine is not only an important site of nutrient digestion and absorption but also an important site of innate immunity against microbial infection in invertebrates. Catalase can participate in intestinal immune responses. However, the role of catalase in intestinal immunity in the sea cucumber (Aj-catalase) has not been elucidated. In this study, we showed that Aj-catalase plays a key role in intestinal immunity and microbiota homeostasis. The expression level of Aj-catalase was upregulated, and its enzymatic activity was increased in the Apostichopus japonicus intestine after challenge with Vibrio splendidus via oral infection. When Aj-catalase was knocked down by RNA interference (RNAi), the survival rate of sea cucumbers declined; microbiota homeostasis was disturbed in the intestine compared with that in the control group, and the intestinal villi protruding from the epithelial lining of the intestinal wall were damaged. Further study results demonstrated that the ROS level was increased for a long period in Aj-catalase-knockdown sea cucumbers, which is likely the main mechanism by which catalase is involved in regulating intestinal immunity. These results suggest that Aj-catalase participates in intestinal immunity and microbiota homeostasis by regulating ROS levels.