miR‐122‐5p as a plasma biomarker of liver injury in fish exposed to microcystin‐LR

Recent studies have shown the presence of large amounts of microRNAs (miRNAs; miRs) from damaged cells in the peripheral blood. In this study, we investigated the levels of miRNAs circulating in the blood plasma of whitefish (Coregonus lavaretus) after exposure to microcystin‐LR. We used real‐time PCR to examine the relative expression of plasma levels of 4 miRNAs (miR‐122‐5p and let‐7c‐5p, the liver‐enriched microRNAs, miR‐148a‐3p which promotes the hapatospecific phenotype in mammals, and miR‐92a‐3p, a cell proliferation and angiogenesis promoter, potentially hepatocarcinogenic) during the first 48 h after exposure to MC‐LR. We observed a rapid increase of miR‐122‐5p levels 8 h after exposure (P < 0.05), which continued to the end of the experiment. Our results demonstrated that the plasma miR‐122‐5p was indicative of MC‐LR‐induced liver injury, exhibiting areas under the curve close to 1 in ROC analysis (AUC = 0.976, P < 0.001). Although plasma levels of miR‐148a‐3p and miR‐92a‐3p were significantly elevated by the end of the experiment, their discriminative power was lower than reported for the miR‐122‐5p. Based on these results and reports on miRNA‐based diagnosis of liver injuries in mammals, plasma miR‐122‐5p could be considered as a robust, new generation diagnostic biomarker in fish, helpful for the non‐invasive diagnosis of liver damage.