Changes of glycolysis and gluconeogenesis key enzymes in the muscle of the shrimp Penaeus vannamei in response to hypoxia and reoxygenation

Abstract

Although the shrimp Penaeus vannamei can tolerate oxygen-limited conditions, the organisms may suffer detrimental effects in several processes, including growth, reproduction, immune responses, and others. During hypoxia, the shrimp makes metabolic adjustments in energy use and glucose homeostasis. Glucose is hydrolyzed during glycolysis and synthesized from non-glycosidic metabolites in gluconeogenesis. Although these pathways share many enzymes, the processes are not exactly the reverse of each other. We studied the first and last irreversible steps of glycolysis and gluconeogenesis catalyzed by hexokinase/glucose-6-phosphatase (HK/G6Pase) and pyruvate kinase/pyruvate carboxylase/phosphoenolpyruvate carboxykinase (PK/PC/PEPCK), respectively, in muscle under hypoxia and hypoxia followed by reoxygenation to gain insights about the coordinated metabolic responses that maintain glucose balance during oxygen stress. For the first group, HK gene expression was induced in hypoxia while G6Pase was reduced in hypoxia and reoxygenation, whereas for enzymes activity, HK was maintained and G6Pase was only detected in reoxygenation. For the second group, gene expression increased in PK in hypoxia, in PC in reoxygenation and in both cases, the enzymatic activities were maintained. Mitochondrial PEPCK expression increased during hypoxia and cytosolic PEPCK decreased, while total PEPCK activity was maintained. Intracellular lactate decreased during hypoxia while glucose levels were maintained. Altogether the results show that in limited oxygen, the expression of glycolytic enzymes-genes are induced, the gluconeogenic counterparts are active, although with more varied responses to oxygen limited conditions, and intracellular glucose levels are maintained.