Combined effects of thermal environment and gene regulation on metabolic enzyme activities of major metabolic tissues in a winter-breeding amphibian.

Variations in thermal environments can provoke diverse physiological responses in amphibians. Despite extensive studies on the thermal sensitivity of amphibian metabolic physiology, including enzyme activity at different temperatures, the rationale for selecting specific metabolic enzymes and their relationship with gene expression remains unclear. Cytochrome c oxidase (CCO), succinate dehydrogenase (SDH), and lactate dehydrogenase (LDH) are key metabolic enzymes within the primary metabolic regulatory tissues of animals. Through a comparative analysis of the effects of two different thermal conditions (12 and 18 °C) on the activities and mRNA expression levels of these enzymes within the kidney and liver tissues of a winter-breeding amphibian (Leptobrachium liui), with the field group during the breeding season as the control, we provide insights into the interplay between temperature and gene expression. The mRNA levels of CCO subunits 1 (cox1), 2 (cox2), and 3 (cox3), and LDH subunit A (ldha) were significantly higher in the kidney than in the liver of all individuals. High-temperature acclimation resulted in significantly decreased expression levels of cox1-3, ldha, and SDH complex flavoprotein subunit A (sdha) in the kidney. In the liver, the expression levels of sdha and ldha significantly reduced under high-temperature treatment, whereas cox3 expression increased. SDH and LDH activities displayed tissue-specific variations, while no significant differences in CCO activity were observed between tissues. CCO, SDH, and LDH activities in both liver and kidney tissues significantly declined after high-temperature acclimation, but simultaneously increased with up-regulated gene expression, indicating that the thermal environment and corresponding gene expression combined affect the activities of these metabolic enzymes. In conclusion, the thermal environment is a key factor affecting the physiological and biochemical responses of L. liui. Prolonged exposure to high temperatures during the breeding season could inhibit the activity of primary metabolic enzymes in the winter-breeding amphibian.