Different degrees of environmental high temperature induce varying endoplasmic reticulum stress responses in...

Heat temperature caused by changes in the global environment have significant impacts on marine organisms. Apostichopus japonicus (A. japonicus) is an economically important benthic species in China's shallow-sea aquaculture. However, its growth and survival are easily affected by rising seawater temperatures. Therefore, it is necessary to explore its response to environmental high temperature. Endoplasmic reticulum (ER)stressserves as an important regulatory strategy for organisms to respond to environmental changes. It acts as the core hub connecting stress and immunity. In this study, we analyzed the histology, ultrastructure, and transcriptome of the digestive tract of A. japonicus at three temperatures: normal (18 °C), aestivation (25 °C), and lethal (32 °C) temperatures, to explore the role of ER stress in response to high temperature. Histological and ultrastructural results indicate that high temperature caused morphological changes in the digestive tract and that the structure and morphology of the ER exhibit alterations and even varying degrees of damage. A total of 603 and 4615 differentially expressed genes (DEGs) were identified by transcriptome sequencing in the T25-vs-T18 and the T32-vs-T25 group comparisons, respectively. The GO results showed that DEGs were significantly enriched in GO terms related to protein folding, such as chaperone-mediated protein folding in both comparison groups. Additionally, KEGG enrichment analysis showed that both groups activated the pathway of protein processing in the ER and induced the ER stress response. The ER molecular chaperones, including BiP, GRP94, and HSP70, were all upregulated in expression. In addition to the aforementioned ER molecular chaperones, downstream factors in the unfolded protein response, such as S1P, TRAF2, and XBP, were also significantly upregulated in T32-vs-T25 group comparisons, indicating that UPR signaling pathways had enhanced expression. Our findings have characterized the internal molecular regulatory process of A. japonicus under high temperature from the perspective of ER stress and provides clues regarding immune response and homeostatic regulation in invertebrates under environment stress. These findings can provide a reference for the formulation of management measures to mitigate the impact of climate change on aquaculture.