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The hepatocyte-specific HNF4?/miR-122 pathway contributes to iron overload-mediated hepatic inflammation.

ABSTRACT: Hepatic iron overload (IO) is a major complication of transfusional therapy. It was generally thought that IO triggers substantial inflammatory responses by producing reactive oxygen species in hepatic macrophages. Recently, a decrease in microRNA-122 (miR-122) expression was observed in a genetic knockout (Hfe-/-) mouse model of IO. Because hepatocyte-enriched miR-122 is a key regulator of multiple hepatic pathways, including inflammation, it is of interest whether hepatocyte directly contributes to IO-mediated hepatic inflammation. Here, we report that IO induced similar inflammatory responses in human primary hepatocytes and Thp-1-derived macrophages. In the mouse liver, IO resulted in altered expression of not only inflammatory genes but also >230 genes that are known targets of miR-122. In addition, both iron-dextran injection and a 3% carbonyl iron-containing diet led to upregulation of hepatic inflammation, which was associated with a significant reduction in HNF4? expression and its downstream target, miR-122. Interestingly, the same signaling pathway was changed in macrophage-deficient mice, suggesting that macrophages are not the only target of IO. Most importantly, hepatocyte-specific overexpression of miR-122 rescued IO-mediated hepatic inflammation. Our findings indicate the direct involvement of hepatocytes in IO-induced hepatic inflammation and are informative for developing new molecular targets and preventative therapies for patients with major hemoglobinopathy.

SUBMITTER: Li M

PROVIDER: S-EPMC5570677 | biostudies-literature | 2017 Aug

REPOSITORIES: biostudies-literature

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The hepatocyte-specific HNF4α/miR-122 pathway contributes to iron overload-mediated hepatic inflammation.

Li Min M Tang Yuxiao Y Wu Lusha L Mo Fengfeng F Wang Xin X Li Hongxia H Qi Ruirui R Zhang Hongwei H Srivastava Arun A Ling Chen C

Blood 20170627 8

Hepatic iron overload (IO) is a major complication of transfusional therapy. It was generally thought that IO triggers substantial inflammatory responses by producing reactive oxygen species in hepatic macrophages. Recently, a decrease in microRNA-122 (miR-122) expression was observed in a genetic knockout (Hfe<sup>-/-</sup>) mouse model of IO. Because hepatocyte-enriched miR-122 is a key regulator of multiple hepatic pathways, including inflammation, it is of interest whether hepatocyte directl ...[more]

PMID: 28655781

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Project description:Purpose:Mutations in hepatocyte nuclear factor 1? (HNF1?) are the cause of maturity-onset diabetes of the young type 3 (MODY3) and involved in the development of hepatocellular adenoma and abnormal lipid metabolism. Previously, we have found that the serum microRNA (miR)-122 levels in MODY3 patients were lower than those in type 2 diabetes mellitus and healthy controls. This study aimed to investigate the mechanism of decreased miR-122 levels in patients with MODY3 and whether low levels of miR-122 mediate tumorigenesis and abnormal lipid metabolism associated with HNF1? deficiency in human hepatocytes. Methods:The expression of miR-122 was examined by real-time PCR. Dual-luciferase reporter assay was performed to confirm the transcriptional regulation of miR-122 by HNF1?. HepG2 cells were transfected with siRNA or miRNA mimic to downregulate or upregulate the expression of HNF1? or miR-122, respectively. CCK-8 and colony formation assay were used to determine cell proliferation. Lipid accumulation was examined by Oil Red O staining and intracellular triglyceride and cholesterol quantification assays. Results:HNF1? regulated the expression of miR-122 by directly binding to its promoter. Knockdown of HNF1? in HepG2 cells reduced the expression of miR-122, increased proliferation and promoted intracellular cholesterol accumulation. Overexpression of miR-122 partially rescued the phenotypes associated with HNF1? deficiency in human hepatocytes. Mechanistically, HNF1? modulated cholesterol homeostasis via miR-122-dependent activation of sterol regulatory element-binding protein-2 (SREBP-2) and regulation of proprotein convertase subtilisin/kexin type 9 (PCSK9). Moreover, circulating miR-122 levels were associated with serum cholesterol levels. Conclusion:Loss of HNF1? function led to hepatocyte proliferation and abnormal cholesterol metabolism by downregulating miR-122. Our findings revealed a novel mechanism that low levels of miR-122 mediate tumorigenesis and abnormal lipid metabolism associated with MODY3. MiR-122 may be a potential therapeutic target for the treatment of MODY3.

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The hepatocyte-specific HNF4?/miR-122 pathway contributes to iron overload-mediated hepatic inflammation.

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The hepatocyte-specific HNF4α/miR-122 pathway contributes to iron overload-mediated hepatic inflammation.

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