Hypoxia affects the resistance of Scylla paramamosain to Vibrio alginolyticus via changes of energy metabolism

Abstract

The dissolved oxygen (DO) level is particularly important for marine benthic crustaceans. In Scylla paramamosain, the DO level plays an important role in regulating immune and metabolic responses. The present study assessed whether the effects of hypoxia on the resistance of S. paramamosain to Vibrio alginolyticus are related to the changes in energy metabolism. In hypoxic S. paramamosain, the immune-related genes, Janus kinase, signal transducer and activator of transcription, Relish, and Astakine were significantly downregulated in hemocytes. In contrast, hypoxia inducible transcription factor-1α, lactate dehydrogenase (LDH), and prophenol oxidase mRNA levels were significantly upregulated in hypoxic S. paramamosain. The levels of pyruvic acid and lactic acid were significantly increased in hypoxic S. paramamosain, this may be closely related to the increases in pyruvate kinase and LDH activities. A significant decrease in hepatic glycogen was observed in hypoxic S. paramamosain, and the breakdown of hepatic glycogen might be the reason why no significant differences in glucose levels were found between the normoxic and hypoxic groups. In addition to the changes in metabolism-related enzyme activities, the levels of phenol oxidase (PO) activity and apoptosis increased significantly, while total hemocyte counts (THC) were significantly decreased in hypoxic S. paramamosain. After challenge with V. alginolyticus, the bacterial count was significantly lower in the hypoxic group than in the normoxic group, while the mortality rate was higher in hypoxic S. paramamosain. The decrease bacterial count might be associated with the changes in the metabolism of hypoxic S. paramamosain. These results suggested that the resistance of S. paramamosain to V. alginolyticus could be weakened when the host was under hypoxic conditions, and the weakened resistance might be related to changes in immune-related gene expression, THC, PO activity, hemocyte apoptosis, and energy metabolism.