The current study aims to investigate whether exosomal miRNAs are involved in lipid reduction by selenium (Se) in the liver of grass carp, through miRNA sequencing, transfection of miRNA mimic (miR-22m) or inhibitor (miR-22i), isolation of hepatocyte-derived exosomes and treatment, and detection of lipid metabolism-related genes and proteins. The miRNAs sequencing and bioinformatics revealed that miR-22 was most abundantly expressed in the differentially expressed miRNAs after selenium treatment, and was enriched in lipid metabolism-related pathways. Moreover, Se significantly up-regulated the miR-22 levels and reduced the lipid content in liver or hepatocytes of grass carp. Furthermore, the miR-22m significantly increased levels of miR-22 and reduced lipid content in grass carp hepatocytes, which were consistent with the Se-treatment. However, the miR-22i reversed these trends. Besides, the miR-22 suppressed the FGFR1-PI3K-AKT-mTOR signaling pathway and its downstream genes related to lipid synthesis. More importantly, the Se-treated hepatocyte-exosomes which were enriched in the miR-22 significantly reduced the triglycerides content in the oleic acid-treated hepatocytes. In summary, Se alleviated high fat-induced lipid accumulation in grass carp liver by up-regulating the expression of miR-22 which negatively regulates FGFR1 and its downstream regulatory genes. Moreover, exosomes participate in the lipid reduction by Se, which may be through carrying miR-22.
