Gymnocypris eckloni (G. eckloni), a cold-water economic fish, is widely cultivated in southwestern China. The increase in extreme summer weather conditions owing to global warming can significantly affect their survival and health. The fish intestine and its microbiota are closely associated with fish feeding and growth, nutritional metabolism, and immune defense. However, the mechanisms underlying the changes in the G. eckloni intestine and its microbiota under acute heat stress remain unknown. In this study, we investigated the effects of acute heat stress on the G. eckloni intestine employing histology, plasma biochemical indices, transcriptomics, and 16S rDNA sequencing. Histological analysis showed that acute heat stress induced significant morphological damage to the intestine, with microvilli detachment and mitochondrial abnormalities in the ultrastructure. Biochemical indicators associated with stress (reactive oxygen species and catalase), inflammation (interleukin-1β and tumor necrosis factor-α), and intestinal permeability (diamine oxidase and lipopolysaccharide) were significantly elevated after acute heat stress, indicating an intestinal inflammatory response and disruption of barrier function. Many DEGs were mined by transcriptomic analysis, with tfrc, pfkp, egln1 enriched in the HlF-1 signaling pathway, hsp70, hsp90aa1 and hspa4 enriched in the Antigen processing and presentation pathway, pmm1, pfkfb3 and hk1 enriched in the Fructose and mannose metabolism patyway. The HIF-1 signaling pathway is a crucial regulatory pathway during acute heat stress in the G. eckloni intestine, while significant downregulation of genes associated with adaptive immunity (mica, hla-dpa1, hla-dpb1, and hla-dqb2) suggested impaired immune function. Additionally, the composition of the intestinal microbiota was dominated by Aeromonas, Citrobacter, and Acinetobacter in the control group; but there was a significant decrease in the abundance of Citrobacter and Acinetobacter, and a significantly increased in Shewanella and Hafnia-Obesumbacterium after acute heat stress. Correlation analyses revealed that changes in the abundance of Hafnia-Obesumbacterium, Buttiauxella, and Pseudomonas were closely associated with changes in gene expression associated with stress, inflammation, and immunity. These results comprehensively demonstrate the adaptive mechanisms of the G. eckloni intestine in response to acutely high temperatures and provide a theoretical basis for the future advancement of artificial culture of cold-water fish.

中文翻译：

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综合转录组和 16S rDNA 分析表明，急性热应激会导致裸鲤肠道损伤


赤裸鲤（G. eckloni）是一种冷水性经济鱼类，在我国西南地区广泛养殖。全球变暖导致夏季极端天气条件的增加会严重影响他们的生存和健康。鱼肠道及其微生物群与鱼的摄食生长、营养代谢和免疫防御密切相关。然而，急性热应激下 G. eckloni 肠道及其微生物群变化的机制仍不清楚。在这项研究中，我们利用组织学、血浆生化指标、转录组学和 16S rDNA 测序研究了急性热应激对 G. eckloni 肠道的影响。组织学分析表明，急性热应激引起肠道显着形态学损伤，超微结构出现微绒毛脱离和线粒体异常。急性热应激后，与应激（活性氧和过氧化氢酶）、炎症（白介素-1β和肿瘤坏死因子-α）和肠道通透性（二胺氧化酶和脂多糖）相关的生化指标显着升高，表明肠道炎症反应和破坏的屏障功能。通过转录组分析挖掘出多个差异表达基因，其中tfrc、pfkp、egln1富集在HlF-1信号通路中，hsp70、hsp90aa1和hspa4富集在抗原加工和呈递通路中，pmm1、pfkfb3和hk1富集在果糖和甘露糖代谢途径中。 。 HIF-1 信号通路是 G. eckloni 肠道急性热应激期间的关键调节通路，而与适应性免疫相关的基因（云母、hla-dpa1、hla-dpb1 和 hla-dqb2）的显着下调表明免疫受损功能。 此外，对照组肠道菌群的组成以气单胞菌、柠檬酸杆菌和不动杆菌为主；但急性热应激后柠檬酸杆菌和不动杆菌的丰度显着下降，希瓦氏菌和哈夫尼亚-奥贝苏姆杆菌的丰度显着增加。相关性分析显示，哈夫尼亚-奥贝森杆菌、布蒂奥克斯菌和假单胞菌丰度的变化与应激、炎症和免疫相关的基因表达变化密切相关。这些结果全面论证了G. eckloni肠道响应急性高温的适应机制，为今后开展冷水鱼人工养殖提供理论依据。