The function of miR-122 in the lipid metabolism and immunity of grass carp (Ctenopharyngodon idellus)

Abstract

Abnormal lipid metabolism in the liver due to excessive fat accumulation is a widespread problem in fish. MicroRNA-122 (miR-122), a liver-specific miRNA in vertebrates, is involved in lipid metabolism. In this study, miR-122 was cloned, and its function was investigated in grass carp. MiR-122 is 99 bp in length, showing 70 % similarity to that of other species and is specifically expressed in liver tissue. After transfection with miR-122 agomir for 24 h in liver cells, we found that the overexpression of miR-122 significantly increased the TG content in cells (P < 0.05), while the expression level of transcription factors related to lipid synthesis was significantly increased (P < 0.05). After injection of miR-122 agomir in vivo, the TG content in the liver increased significantly (P < 0.05), and the mRNA expression of lipid synthesis-related genes (PPARγ, SREBP-1c, ACC, FAS and H-FABP) increased significantly (P < 0.05). The relative expression of the proinflammatory factors TNF-α, IL-6, and IL-1β also increased significantly (P < 0.05), while the relative abundance of the anti-inflammatory factors IL-10 and TGF-β1 decreased significantly (P < 0.05). In addition, we found that miR-122 regulated lipid catabolism-related genes through AMPK, and AMPK may regulate lipid synthesis-related genes through miR-122 directly or indirectly. In summary, the comparison of miRNA-122 from genomic sequences reveals strong conservation of miRNA-122 across vertebrate classes; however, its function shows species-specific actions in grass carp and mammalian models. This study provides basic data for further investigation of a miRNA related to fatty liver and other metabolic diseases.

Keywords

• Ctenopharyngodon idellus
• miR-122
• Lipid metabolism
• Immunomodulatory
• AMPK