MicroRNAs in metabolism and metabolic disorders. Nat Rev Mol Cell Biol. 2012;13:239-250. [PMID: 22436747 DOI: 10.1038/nrm3328]

Hepatic miR‑215 target Rictor and modulation of hepatic insulin signalling in rats

Increasing evidence has suggested that hepatic lipid accumulation is associated with hepatic insulin resistance; however, the underlying mechanism is yet to be determined. It was demonstrated that the levels of microRNA-215 (miR-215) expression in the liver of rats fed a high-fat diet were significantly increased compared with rats on a control diet. Additionally, it was revealed via luciferase assays and western blotting that miR-215 targets rapamycin-insensitive companion of mammalian target of rapamycin (Rictor), an important protein in the hepatic insulin signalling pathway. Following overexpression of miR-215 in the H4IIE rat hepatocarcinoma cell line, it was reported that the intracellular insulin signalling pathway was inhibited; conversely, inhibition of miR-215 expression induced this pathway. Furthermore, it was demonstrated via reverse transcription-quantitative polymerase chain reaction analysis that free fatty acids promoted the expression of miR-215. The present study provided a novel mechanistic insight into the association between nonalcoholic fatty liver and hepatic insulin resistance.

MiR-155 Enhances Insulin Sensitivity by Coordinated Regulation of Multiple Genes in Mice

miR-155 plays critical roles in numerous physiological and pathological processes, however, its function in the regulation of blood glucose homeostasis and insulin sensitivity and underlying mechanisms remain unknown. Here, we reveal that miR-155 levels are downregulated in serum from type 2 diabetes (T2D) patients, suggesting that miR-155 might be involved in blood glucose control and diabetes. Gain-of-function and loss-of-function studies in mice demonstrate that miR-155 has no effects on the pancreatic β-cell proliferation and function. Global transgenic overexpression of miR-155 in mice leads to hypoglycaemia, improved glucose tolerance and insulin sensitivity. Conversely, miR-155 deficiency in mice causes hyperglycemia, impaired glucose tolerance and insulin resistance. In addition, consistent with a positive regulatory role of miR-155 in glucose metabolism, miR-155 positively modulates glucose uptake in all cell types examined, while mice overexpressing miR-155 transgene show enhanced glycolysis, and insulin-stimulated AKT and IRS-1 phosphorylation in liver, adipose tissue or skeletal muscle. Furthermore, we reveal these aforementioned phenomena occur, at least partially, through miR-155-mediated repression of important negative regulators (i.e. C/EBPβ, HDAC4 and SOCS1) of insulin signaling. Taken together, these findings demonstrate, for the first time, that miR-155 is a positive regulator of insulin sensitivity with potential applications for diabetes treatment.

Clinical significance of miRNA changes in chronic liver diseases

MicroRNAs (miRNAs) are small molecules that regulate gene expression at the post-transcriptional level. MiRNAs could exhibit specific changes in many liver diseases, which reflects pathologic changes of hepatic tissue. To better understand the relationship between miRNAs and liver diseases, this review summarizes the roles of miRNAs in hepatitis, alcohol-induced liver injury, drug-induced liver injury and hepatocellular carcinoma. Investigation of miRNA changes in humans might not only help to elucidate the mechanism of chronic hepatitis B virus infection, but also provide new molecular markers for clinical diagnosis and evaluation of the curative effect of antiviral treatment. In addition, it might provide new ideas and methods for the diagnosis and treatment of alcoholic liver disease, drug-induced liver injury, fatty liver disease and hepatocellular carcinoma.