For a comprehensive understanding of fish responses to increasing thermal stress in marine environments, we investigated tissue energetics, antioxidant levels, inflammatory and cell death responses in Sparus aurata (gilthead seabream) red muscle during exposure to elevated temperatures (24 °C, 26 °C, 30 °C) compared to the control temperature of 18 °C. Energetic aspects were assessed by determining lactate, glucose and lipids levels in blood plasma, ATP, ADP and AMP levels, and AMPK phosphorylation as an indicator of regulatory changes in energy metabolism, in tissue extracts. Oxidative defence was assessed by determining superoxide dismutase, catalase and glutathione reductase maximum activities. Moreover, xanthine levels were determined as an indicator of purine conversion to xanthine and associated ROS production. In the context of inflammatory response and cell death due to oxidative stress, pro-inflammatory cytokines (IkBα phosphorylation, IL-6 and TNFα) levels, and LC3 II/I ratio and SQSTM1/p62 as indicators of autophagic-lysosomal pathway were also determined. A recovery in the efficacy of ATP production after a marked decrease during the 1st day of exposure to 24 °C is observed. This biphasic pattern is paralleled by antioxidant enzymes’ activities and inflammatory and autophagy responses, indicating a close correlation between ATP turnover and stress responses, which may benefit tissue function and survival. However, exposure beyond 24 °C caused tissue’s antioxidant capacity loss, triggering the inflammatory and cell death response, leading to increased fish mortality. The results of the present study set the thermal limits of the gilthead seabream at 22–24 °C and establish the used cellular and metabolic indicators as tools for the definition of the extreme thermal limits in marine organisms.

中文翻译：

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热应激的金鱼红肌中的能量、抗氧化、炎症和细胞死亡反应

为了全面了解鱼类对海洋环境中不断增加的热应激的反应，我们研究了暴露于高温（24°C、26°C , 30 °C) 与 18 °C 的控制温度相比。通过测定血浆中的乳酸、葡萄糖和脂质水平、ATP、ADP 和 AMP 水平以及 AMPK 磷酸化作为能量代谢调节变化的指标，在​​组织提取物中评估能量方面。通过测定超氧化物歧化酶、过氧化氢酶和谷胱甘肽还原酶的最大活性来评估氧化防御。此外，黄嘌呤水平被确定为嘌呤转化为黄嘌呤和相关 ROS 产生的指标。在氧化应激引起的炎症反应和细胞死亡的背景下，促炎细胞因子（IkBα 磷酸化、IL-6 和 TNFα）水平以及 LC3 II/I 比率和 SQSTM1/p62 作为自噬 - 溶酶体途径的指标也被确定. 观察到在暴露于 24 °C 的第一天期间 ATP 生产效率显着下降后恢复。这种双相模式与抗氧化酶的活性以及炎症和自噬反应平行，表明 ATP 转换与应激反应之间存在密切相关性，这可能有益于组织功能和存活。然而，超过 24 °C 的暴露会导致组织的抗氧化能力丧失，引发炎症和细胞死亡反应，导致鱼类死亡率增加。