Mitochondrial function and energy metabolism response of Megalobrama amblycephala under heat and hypoxia

Ongoing global climate change and anthropogenic activities are increasingly subjecting aquatic animals to heat and hypoxia stress. These environmental perturbations can profoundly impact mitochondrial function and energy metabolism. The current study aimed to delineate the adaptive mechanisms of mitochondrial dynamics and energy metabolism in the blunt snout bream (Megalobrama amblycephala) under three experimental conditions: heat stress (HT group, 35 °C of temperature), hypoxia stress (LO group, 2 mg/L of dissolved oxygen), and combined heat plus hypoxia stress (HL group, 35 °C and 2 mg/L). The results demonstrated that heat and/or hypoxia stresses damaged mitochondrial structure and disrupted fusion-fission balance. The activities of key TCA cycle enzymes (e.g. SDH, CS) were significantly decreased. Conversely, energy metabolism was regulated through an increased AMP/ATP ratio and activation of AMPKα1/AMPKα2 proteins. The expression of glycolytic enzymes (PK, PFK, HK and LDH) was up-regulated. However, heat and/or hypoxia stresses resulted in severe consumption of serum glucose and liver glycogen, with the most pronounced consumption in the HL group. Other saccharides such as mannose and lactose were also significantly reduced in HT and HL groups. The decomposition and metabolism of amino acids was an important auxiliary mechanism. Regarding lipid metabolism, the expression of lipolysis and lipogenesis related genes was down-regulated, while glycerophospholipids accumulation contributed to maintaining membrane integrity. These findings benefit the understanding of environmental adaptive characteristics in aquatic animals and provide effective strategies for aquaculture management.