Abstract
The liver is an important organ for the regulation of lipid metabolism. In genetically improved farmed tilapia (GIFT, Oreochromis niloticus), fat deposition in the liver occurs when they are fed high-lipid diets over a long term. This can affect their growth, meat quality, and disease resistance. MicroRNAs (miRNAs) are known to be crucial regulatory factors involved in lipid metabolism; however, the mechanism by which they regulate lipid deposition in GIFT remains unclear. Comparative miRNA expression profiling between GIFT fed a normal diet and those fed a high-lipid diet showed that miR-122 is closely related to lipid deposition. Using miR-122 as a candidate, we searched for a binding site for miR-122 in the 3′-untranslated region (UTR) of the stearoyl-CoA desaturase gene (SCD) using bioinformatics tools, and then confirmed its functionality using the luciferase reporter gene system. Then, the regulatory relationship between this miRNA and its target gene SCD was analyzed using real-time polymerase chain reaction (qRT-PCR) and western blotting analyses. Last, we investigated the effect of the loss of miR-122 expression on lipid metabolism in GIFT. The results showed that a sequence in the 3′-UTR region of SCD of GIFT was complementary to the miR-122 seed region, and there was a negative relationship between the expression of miRNA and SCD expression. Inhibition of miR-122 up-regulated SCD, increased the expression of fat synthesis-related genes, increased hepatic triglyceride and cholesterol contents, and promoted weight gain in fish. Our results showed that miR-122 targets SCD to mediate hepatic fat metabolism. These results provide new insights for the prevention and treatment of fatty liver disease in GIFT.
Highlights
The results of the double luciferase reporter assay showed that the miR-122 mimic significantly reduced the luciferase activity of the pGL3-stearoyl-CoA desaturase gene (SCD)-3 -untranslated region (UTR) vector (P < 0.05) (Figure 1B), while it did not affect the luciferase activity of the mutant
There was no significant difference in luciferase activity among miR-122 negative control (NC)+SCD-3 UTR wt, the miR-122 NC+SCD-3 -UTR mutant, and the miR122 mimic+SCD-3 -UTR mutant (P > 0.05), suggesting that miR-122 binds to a site in the SCD-3 -UTR sequence
To further analyze the effect of miR-122 expression on lipid regulation in GIFT, we investigated the effect of down-regulation of miR-122 on hepatic lipid metabolism-related genes and fat deposition under high-fat diet stress
Summary
Liver tissues are enriched in microRNA-122 (miR-122). This miRNA accounts for 70 and 52% of the total miRNAs in the liver of adult mice and humans, respectively (Bandiera et al, 2015). miR-122 plays important roles in promoting liver development and differentiation and in maintaining its function and balance. Liver tissues are enriched in microRNA-122 (miR-122) This miRNA accounts for 70 and 52% of the total miRNAs in the liver of adult mice and humans, respectively (Bandiera et al, 2015). MiR-122 plays important roles in promoting liver development and differentiation and in maintaining its function and balance. During liver development, the mutual restriction between miR-122 and liver-enriched transcription factors helps to maintain the balance between cell proliferation and differentiation in hepatocytes and biliary epithelial cells (Xu et al, 2010; Laudadio et al, 2012). MiR-122 plays an important role in regulating liver cholesterol and fatty acid metabolism. MiR-122 may affect cholesterol synthesis by silencing the activity of the transcriptional repressor of 3-hydroxy-3-methyl-glutaryl-CoA reductase (Krützfeldt et al, 2005; Esau et al, 2006). MiR-122-deficient mice displayed reduced plasma triglyceride and cholesterol levels and fat deposition (Esau et al, 2006)
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