IRE1α prevents hepatic steatosis by processing and promoting the degradation of select microRNAs

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Science Signaling  15 May 2018:
Vol. 11, Issue 530, eaao4617
DOI: 10.1126/scisignal.aao4617

Fat, microRNAs, and liver disease

Obesity and high-fat diets are linked to fatty liver disease and repression of the cell stress protein IRE1α. By analyzing livers from mice fed a high-fat diet and from patients with hepatic steatosis, Wang et al. found that diet- or obesity-induced IRE1α functional deficiency in the liver enabled the biogenesis of select microRNAs that consequently decreased the abundance of lipid metabolism enzymes, leading to lipid accumulation in the liver. These findings reveal additional targets to explore for treating various diet-associated liver diseases.


Obesity or a high-fat diet represses the endoribonuclease activity of inositol-requiring enzyme 1α (IRE1α), a transducer of the unfolded protein response (UPR) in cells under endoplasmic reticulum (ER) stress. An impaired UPR is associated with hepatic steatosis and nonalcoholic fatty liver disease (NAFLD), which is caused by lipid accumulation in the liver. We found that IRE1α was critical to maintaining lipid homeostasis in the liver by repressing the biogenesis of microRNAs (miRNAs) that regulate lipid mobilization. In mice fed normal chow, the endoribonuclease function of IRE1α processed a subset of precursor miRNAs in the liver, including those of the miR-200 and miR-34 families, such that IRE1α promoted their degradation through the process of regulated IRE1-dependent decay (RIDD). A high-fat diet in mice or hepatic steatosis in patients was associated with the S-nitrosylation of IRE1α and inactivation of its endoribonuclease activity. This resulted in an increased abundance of these miRNA families in the liver and, consequently, a decreased abundance of their targets, which included peroxisome proliferator–activated receptor α (PPARα) and the deacetylase sirtuin 1 (SIRT1), regulators of fatty acid oxidation and triglyceride lipolysis. IRE1α deficiency exacerbated hepatic steatosis in mice. The abundance of the miR-200 and miR-34 families was also increased in cultured, lipid-overloaded hepatocytes and in the livers of patients with hepatic steatosis. Our findings reveal a mechanism by which IRE1α maintains lipid homeostasis through its regulation of miRNAs, a regulatory pathway distinct from the canonical IRE1α-UPR pathway under acute ER stress.

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