Molecular clocks are known to mediate cellular responses during oxidative stress. This important interplay is less understood in fish, particularly at mucosal surfaces. Here we report the coordinated modulation of the molecular clocks and antioxidant defence following chemically induced oxidative stress in the gill mucosa of Atlantic salmon (Salmo salar). A short-term gill explant (GE) culture was used as a model in a series of experiments aiming to demonstrate how photoperiod during culture, levels of environmental reactive oxygen species (ROS), time of oxidative stress induction, and the daily light-dark cycle affect the expression of molecular clocks and antioxidant genes in the gills. Photoperiod (either 12 light:12 dark cycle, LD or 0 light:24 dark cycle, DD) during explant culture affected the transcription of two clock genes, circadian locomotor output cycles kaput (clk) and period 1 (per1), as well as one antioxidant gene, glutathione peroxidase (gpx). When the GEs were exposed to two ROS-generating oxidants (i.e., peracetic acid, PAA and hydrogen peroxide, H₂O₂), photoperiod condition was demonstrated to have a significant impact on the transcription of the core genes. PAA significantly downregulated the expression of reverb alpha (reverbα) under LD, while per1 and per2 expression were significantly upregulated under DD. Nevertheless, there was no distinct pattern in the oxidant-induced expression of clock genes. On the other hand, photoperiod was shown to influence the antioxidant defence under increased ROS level, where significant transcriptional upregulation was a hallmark response under LD. Interestingly, no changes were identified under DD. Induction of oxidative stress either at ZT2 (2 h after lights on) or at ZT14 (2 h after lights off) revealed striking differences that highlighted the temporal sensitivity of the oxidative defence repertoire. Per1 was significantly modulated following time-dependent induction of oxidative stress among the clock genes. Inducing oxidative stress at ZT2 resulted in a significant upregulation of antioxidant genes; but when the same stimuli were given at ZT14, all antioxidant genes exhibited downregulation. It was further revealed that neither of the genes demonstrated daily rhythmicity in their expression in the GE cultures. Collectively, the study revealed the coordinated expression of the core elements in the molecular clock and antioxidant systems in the gill mucosa following oxidative stress. Furthermore, the results reveal that the time of day plays a crucial influence on how defences are mobilised during oxidative stress, adding new insights into the rhythms of oxidative stress response in mucosal tissues in fish.

已知分子钟在氧化应激过程中介导细胞反应。在鱼类中，尤其是在粘膜表面，这种重要的相互作用鲜为人知。在这里，我们报道了大西洋鲑Atlantic（Salmo salar）ill黏膜化学诱导的氧化应激后分子钟和抗氧化防御的协调调节）。在一系列实验中，以短期g外植体（GE）培养为模型，旨在证明培养过程中的光周期，环境活性氧水平（ROS），氧化应激诱导时间和日暗周期影响the中分子钟和抗氧化剂基因的表达。外植体培养期间的光周期（12个光照：12个黑暗周期，LD或0个光照：24个黑暗周期，DD）影响了两个时钟基因的转录，昼夜运动输出周期kaput（clk）和周期1（per1），以及一种抗氧化剂基因，谷胱甘肽过氧化物酶（gpx）。当GEs暴露于两种产生ROS的氧化剂（即过氧乙酸，PAA和过氧化氢，H ₂ O ₂）时，证明光周期条件对核心基因的转录有重要影响。PAA显着下调了LD下混响alpha（reverbα）的表达，而per1和per2DD下表达明显上调。然而，在氧化剂诱导的时钟基因表达中没有明显的模式。另一方面，在ROS水平升高的情况下，光周期会影响抗氧化防御，其中在LD下，明显的转录上调是标志性反应。有趣的是，在DD下没有发现任何变化。ZT2（开灯后2小时）或ZT14（关灯后2小时）的氧化应激诱导显示出惊人的差异，突显了氧化防御库的时间敏感性。每1时钟基因之间的氧化应激的时间依赖性诱导后，蛋白被显着调节。在ZT2处诱导氧化应激导致抗氧化剂基因的显着上调。但是当在ZT14给予相同的刺激时，所有抗氧化剂基因均会下调。进一步揭示，这两个基因在GE培养物中的表达均未表现出日常节律性。总体而言，该研究揭示了氧化应激后g黏膜中分子钟和抗氧化剂系统中核心元素的协同​​表达。此外，研究结果还表明，一天中的时间对氧化应激过程中防御的动员方式具有至关重要的影响，这为鱼类粘膜组织中氧化应激反应的节奏增添了新见解。