Background & Aims

Effective treatments are needed for hepatic steatosis characterized by accumulation of triglycerides in hepatocytes, which leads to hepatocellular carcinoma. MicroRNA 122 (MIR122) is expressed only in the liver, where it regulates lipid metabolism. We investigated the mechanism by which free fatty acids (FFAs) regulate MIR122 expression and the effect of MIR122 on triglyceride synthesis.

Methods

We analyzed MIR122 promoter activity and validated its target mRNAs by transfection of Luciferase reporter plasmids into Huh7, BNL-1ME, and HEK293 cultured cell lines. We measured levels of microRNAs and mRNAs by quantitative real-time PCR analysis of RNA extracted from plasma, liver, muscle, and adipose tissues of C57BL/6 mice given the FFA-inducer CL316243. MIR122 was inhibited using an inhibitor of MIR122. Metabolic profiles of mice were determined using metabolic chambers and by histologic analyses of liver tissues. We performed RNA sequence analyses to identify metabolic pathways involving MIR122.

Results

We validated human Agpat1 and Dgat1 mRNAs, involved in triglyceride synthesis, as targets of MIR122. FFAs increased MIR122 expression in livers of mice by activating the retinoic acid-related orphan receptor alpha, and induced secretion of MIR122 from liver to blood. Circulating MIR122 entered muscle and adipose tissues of mice, reducing mRNA levels of genes involved in triglyceride synthesis. Mice injected with an inhibitor of MIR122 and then given CL316243, accumulated triglycerides in liver and muscle tissues, and had reduced rates of β-oxidation. There was a positive correlation between level of FFAs and level of MIR122 in plasma samples from 6 healthy individuals, collected before and during fasting.

Conclusions

In biochemical and histologic studies of plasma, liver, muscle, and adipose tissues from mice, we found that FFAs increase hepatic expression and secretion of MIR122, which regulates energy storage vs expenditure in liver and peripheral tissues. Strategies to reduce triglyceride levels, by increasing MIR122, might be developed for treatment of metabolic syndrome.

中文翻译：

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肝脏和肌肉组织中涉及游离脂肪酸，microRNA 122和甘油三酸酯合成的代谢循环

背景与目标

肝脂肪变性需要以肝细胞中甘油三酸酯的积累为特征的有效治疗，这会导致肝细胞癌。MicroRNA 122（MIR122）仅在肝脏中表达，在那里它调节脂质代谢。我们研究了游离脂肪酸（FFA）调节MIR122表达的机制以及MIR122对甘油三酸酯合成的影响。

方法

我们分析了MIR122启动子的活性，并通过将荧光素酶报道基因质粒转染到Huh7，BNL-1ME和HEK293培养的细胞系中来验证了其目标mRNA。我们通过定量实时PCR分析从C57BL / 6小鼠的血浆，肝，肌肉和脂肪组织中提取的RNA（通过FFA诱导剂CL316243），测量了microRNA和mRNA的水平。使用MIR122的抑制剂抑制MIR122。使用代谢室和肝组织的组织学分析确定小鼠的代谢谱。我们进行了RNA序列分析，以鉴定涉及MIR122的代谢途径。

结果

我们验证了参与甘油三酸酯合成的人类Agpat1和Dgat1 mRNA作为MIR122的靶标。FFA通过激活视黄酸相关的孤儿受体α来增加小鼠肝脏中MIR122的表达，并诱导MIR122从肝脏分泌到血液。循环的MIR122进入小鼠的肌肉和脂肪组织，从而降低了参与甘油三酸酯合成的基因的mRNA水平。小鼠注射了MIR122抑制剂，然后给予CL316243，在肝脏和肌肉组织中积累了甘油三酸酯，并且β-氧化速率降低。在禁食前和禁食期间采集的来自6名健康个体的血浆样品中FFA水平与MIR122水平呈正相关。

结论

在小鼠血浆，肝，肌肉和脂肪组织的生化和组织学研究中，我们发现FFA会增加MIR122的肝表达和分泌，从而调节能量存储与肝脏和周围组织的支出。通过增加MIR122来降低甘油三酸酯水平的策略可能已被开发出来，用于治疗代谢综合征。