Potential role of miR-8159-x in heat stress response in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) is a representative species of cold-water fish. Elevated temperatures during summer often result in significant high mortality rates. MicroRNAs (miRNAs) are class of small non-coding RNAs that play a crucial role as post-transcriptional regulators in various biological processes. Emerging evidence suggests that miRNAs are important regulators role during heat stress. Analyzing previously obtained miRNA-sequencing data, we observed substantial down regulation of miR-8159-x in the liver tissue of heat stressed rainbow trout. In this study, we conducted a dual luciferase reporter assay to validate that miR-8159-x target, a key gene involved in heat stress in rainbow trout. By examining the expression patterns of miR-8159-x and hsp90a1 in the liver tissue at 18 °C (CG) and 24 °C (HS) groups, we propose that miR-8159-x may negatively regulate hsp90a1. Furthermore, in vitro hepatocyte assay, transfection with miR-8159-x mimics significantly reduced the expression level of hsp90a1, whereas transfection with a miR-8159-x inhibitor yielded the opposite effect. Additionally, overexpression of miR-8159-x inhibited cell proliferation and induced apoptosis in normal rainbow trout hepatocytes. We further investigated the effects of miR-8159-x overexpression or inhibition on the mRNA and protein levels of the target gene hsp90a1 under heat stress conditions. In conclusion, our findings suggest that miR-8159-x participates in the biological response to heat stress by targeting hsp90a1. These results contribute to a better understanding of the molecular mechanisms underlying heat stress in rainbow trout and provide valuable insights for future research.