Transcriptome analysis reveals the oxidative damage and immune-suppression of leech (Whitmania pigra Whitman) intestine induced by high-temperature stress

Temperature is a key component in regulating the survival and growth of aquatic animals. However, the mechanism of high-temperature stress in Whitmania pigra Whitman has received little attention. Therefore, the aim of this study was to investigate the possible mechanisms of high-temperature stress in W. pigra using transcriptome analysis and detection of antioxidant markers. Samples were collected at 1 d, 3 d, 5 d, and 7 d under stress in two experimental groups: the control group at 27 degrees C and the high-temperature stress group at 35 degrees C. High-temperature stress caused oxidative damage in the leech intestine, as indicated by decreased antioxidant enzyme activities (superoxide dismutase and total antioxidant capacity) and increased lipid hydroperoxide malondialdehyde. Transcriptome analysis revealed 425 DEGs in leech intestine during high-temperature stress, with 275 up-regulated and 150 down-regulated genes. According to KEGG enrichment analysis, 425 DEGs were involved in the immune system and induced abnormal expression of disease-related genes. Furthermore, when leeches were exposed to high-temperature stress, B-cell lymphoma-2, heat shock protein 70, heat shock protein 90, and nuclear factor erythroid 2-related factor 2 mRNAs were dramatically upregulated, whereas activating transcription factor, inhibitor of Nuclear factor kappa-B, sequestosome 1, and toll-like receptor 4 mRNAs were significantly downregulated. In conclusion, 35 degrees C high-temperature stress impaired leech intestinal function by decreasing antioxidant capacity, causing oxidative damage, and suppressing the activation of immune capacity. This study contributes to future research on the detailed mechanisms of high-temperature stress in leeches.