MiRNAs-Modulation of Nrf2 Signaling Networks in Regulation Oxidative Stress of Chinese Perch Skeletal Muscle After Fasting Treatment.

Nrf2 is an important transcription factor involved in the antioxidant response and is widely expressed in animal tissues. The function of Nrf2 is regulated by its negative regulator Keap1 by inducing its cytoplasmic degradation. Recent studies have suggested that Nrf2 is also regulated post-transcriptionally via miRNAs. However, to date, how miRNAs regulate Nrf2 in fish skeletal muscles is unknown. In this study, the full-length cDNAs with 2398 bp of the Nrf2 was firstly cloned by SMART RACE amplification tools from Chinese perch. The Nrf2 gene structure and its 3'-UTR region for possible miRNA binding sites, as well as its spatial expression profile were assayed. Then, we employed TargetScan Fish tool MiRNAnome to predict putative sites for five miRNAs including miR-181a-5p, MiR-194a, MiR-216a, miR-459-5p, and miR-724. Using qRT-PCR assay, we found that Nrf2 mRNA levels have negative correlation with all five miRNAs expression in muscle of nutritionally deprived fish, and that ectopic expression of miR-181a-5p alone reduces Nrf2 mRNA levels. Luciferase reporter assay in a heterologous cell system revealed that each of the five miRNAs reduced Nrf2 expression, suggesting a direct regulatory mechanism. Moreover, the miR-181a-5p suppression using specific antagomir led to a significant increase in Nrf2 expression in vivo. At the same time, the expression levels of the antioxidant enzymes CAT, ZnSOD, GPx, GSTA, and GSTA genes increased significantly after injecting miR-181a-5p antagomir. Taken together, these findings provide evidence that miRNAs are involved in the Nrf2 signaling networks in regulation of oxidative stress in fish, at least in Chinese perch muscle.