MicroRNA-98 regulates hepatic cholesterol metabolism via targeting sterol regulatory element-binding protein 2

https://doi.org/10.1016/j.bbrc.2018.08.205Get rights and content

Highlights

  • The expression of miR-98 decreased while the expression of SREBP-2 increased in hypercholesterolemic patients.

  • SREBP-2 is a direct target gene of miR-98.

  • The effect of miR-98 on cholesterol metabolism is mediated by SREBP-2.

  • Overexpression of miR-98 reduced cholesterol level in vitro and in vivo.

Abstract

Hypercholesterolemia is an important risk factor for coronary heart disease. Although a lot of research has been conducted, the regulation of cholesterol metabolism is still largely unknown. Some miRNAs have been found to play critical role in the cholesterol metabolism. MiR-98 is a miRNA whose function has been reported mainly in tumorigenesis. In this study, we elucidate a novel role of miR-98 in cholesterol metabolism. We found that the expression of miR-98 was decreased significantly in hypercholesterolemic patients compared with healthy control subjects. Furthermore, we identified that SREBP-2, an important transcriptional factor in cholesterol metabolism, was a direct target of miR-98. Overexpression of miR-98 significantly repressed the 3′-UTR reporter activities of SREBP-2 in a dose-dependent manner in HepG2 cells, while the effect of miR-98 was blocked when the binding site of miR-98 within the SREBP-2 3′-UTR was mutated. And overexpression of miR-98 reduced both the mRNA and protein levels of HMGCR and LDLR significantly in vitro, which are two target genes of SREBP-2. Furthermore, MiR-98 overexpression reduced the intracellular total cholesterol levels dramatically. Moreover, we overexpressed the miR-98 by lentiviral tail vein injection in vivo. Compared with the control mice, the miR-98 overexpression mice showed lower serum cholesterol level and decreased SREBP-2, HMGCR as well as LDLR expression. Our data confirmed that reduced expression of miR-98 potentially contributes to disturbance of cholesterol metabolism. MiR-98 might be a novel therapeutic target to hypercholesterolemia.

Introduction

Cholesterol plays a vital role in the human body as a precursor of steroid hormones and bile acids, in addition to providing structure to cell membranes [1]. Whole body cholesterol metabolism is maintained by a highly coordinated balancing act between cholesterol ingestion, synthesis, absorption, and excretion [2]. The disturbance of cholesterol metabolism may result in several diseases, such as the obesity, diabetes, NAFLD and cardiovascular diseases [[3], [4], [5]]. However, although large number of researches have been conducted, regulation mechanism of cholesterol metabolism is still largely unknown.

MicroRNAs (miRNAs) are small non-coding RNAs (21–25 nt) that functions in RNA silencing and post-transcriptional regulation of target gene expression [6]. Some miRNAs have been found to play important role in the cholesterol metabolism. For example, miR-30c regulates lipid biosynthesis and lipoprotein secretion by targeting the microsomal triglyceride transfer protein (MTP) [7]. MiR-182, miR-96 and miR-183 regulate cholesterol metabolism by affecting nuclear sterol regulatory element-binding protein (SREBP) accumulation [8].

MiR-98 is an important miRNA which has been found to play an important role in the pathogenesis of several cancers, including human esophageal squamous cell carcinoma [9], restrain human ovarian cancer stem cell proliferation [10], inhibit prostate cancer growth [11], and so on. However, whether miR-98 is involved in regulating cholesterol metabolism has never been explored.

In this study, we found miR-98 was down-regulated in the serum of hypercholesterolemic patients. Overexpression of miR-98 can reduce the total cholesterol level in HepG2 cells. More importantly, we identified that miR-98 directly targets the SREBP-2 3′-UTR and regulates its expression. We also found that overexpression of miR-98 could decrease the serum cholesterol level in vivo. These results provide new insights into the cholesterol metabolism regulation and suggest miR-98 could be a novel therapeutic target to hypercholesterolemia.

Section snippets

Human subjects

The protocol of this study was approved by the ethics committee of Shandong Provincial Hospital Affiliated to Shandong University. Ten liver samples were obtained from patients who underwent surgical liver resection for liver hemangioma. Each individual underwent serum testing before surgery. Each participant completed a standardized questionnaire that included demographic characteristics, life factors, family and personal medical history, general health status and current medications. Written

Expression of miR-98 was reduced while SREBP-2 was increased in ypercholesterolemic patients and in vitro

As shown in Fig. 1A, compared with the healthy controls, the serum and hepatic levels of miR-98 were significantly reduced in the hypercholesterolemic patients (P < 0.01). However, the levels of SREBP-2 mRNA and protein were increased in the hypercholesterolemic patients compared with the healthy controls (P < 0.05; Fig. 1B). Co-treatment of oleic acid (OA) and palmitic acid (PA) in hepatocytes has been reported to can increase SREBP expression significantly [14]. In our study, we also found

Discussion

Cholesterol is an essential cell membrane component and precursor in metabolic pathways, including steroid hormone and bile acid synthesis. Control of cholesterol levels is essential to human health. Cholesterol synthesis is the main source of cholesterol in the body of human beings, in which SREBP-2 is a very important transcriptional factor, regulating the expression of HMGCR, the rate-limiting enzyme for cholesterol synthesis. In this study, we identified SREBP-2 as a new target of miR-98,

Financial interests

All authors report no conflicts of interest.

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