MicroRNA-758 regulates cholesterol efflux through posttranscriptional repression of ATP-binding cassette transporter A1

Noncoding RNAs and atherosclerosis

Noncoding RNAs (ncRNAs) represent a class of RNA molecules that typically do not code for proteins. Emerging data suggest that ncRNAs play an important role in several physiological and pathological conditions such as cancer and cardiovascular diseases, including atherosclerosis. The best-characterized ncRNAs are the microRNAs which are small, approximately 22-nucleotide sequences of RNA that regulate gene expression at the posttranscriptional level through transcript degradation or translational repression. MicroRNAs control several aspects of atherosclerosis, including endothelial cell, vascular smooth cell, and macrophage functions as well as lipoprotein metabolism. Apart from microRNAs, recently ncRNAs, especially long ncRNAs, have emerged as important potential regulators of the progression of atherosclerosis. However, the molecular mechanism of their regulation and function as well as the significance of other ncRNAs such as small nucleolar RNAs during atherogenesis is largely unknown. In this review, we summarize the recent findings in the field, highlighting the importance of ncRNAs in atherosclerosis and discuss their potential use as therapeutic targets in cardiovascular diseases.

MicroRNAs involved in the lipid metabolism and their possible implications for atherosclerosis development and treatment

Hyperlipidemia is a well-accepted risk factor in the development of atherosclerosis. MicroRNAs (miRNAs), a novel class of posttranscriptional regulators of gene expression, are involved in a variety of biological and pathological processes, including the regulation of the lipid metabolism and atherosclerosis. As our knowledge of miRNAs expands, a new class of "circulating miRNAs" has recently been described. It includes miRNAs which may be found in various bodily fluids packaged in microvesicles/exosomes, or bound to specific transporting proteins. High-density lipoprotein (HDL) particles have been identified as one such carrier. As this class of miRNAs likely plays a role in intercellular communication, it may also contribute to the atherosclerosis development and progression. This review aims to provide a comprehensive explanation of the roles of distinct miRNAs involved in the regulation of the lipid metabolism. These microRNAs seem to be promising therapeutic agents, as documented in rodents and African green monkeys. The second part of the review focuses on circulating miRNAs and their involvement in the atherosclerosis, especially as their levels have been described as altered in patients with dyslipidemia/hyperlipidemia. Special emphasis is placed on miRNAs transported in a complex with HDL particles and on those which may be considered potential atherosclerosis biomarkers.

RNA binding protein HuR regulates the expression of ABCA1

ABCA1 is a major regulator of cellular cholesterol efflux and plasma HDL biogenesis. Even though the transcriptional activation of ABCA1 is well established, the posttranscriptional regulation of ABCA1 expression is poorly understood. Here, we investigate the potential contribution of the RNA binding protein (RBP) human antigen R (HuR) on the posttranscriptional regulation of ABCA1 expression. RNA immunoprecipitation assays demonstrate a direct interaction between HuR and ABCA1 mRNA. We found that HuR binds to the 3' untranslated region of ABCA1 and increases ABCA1 translation, while HuR silencing reduces ABCA1 expression and cholesterol efflux to ApoA1 in human hepatic (Huh-7) and monocytic (THP-1) cells. Interestingly, cellular cholesterol levels regulate the expression, intracellular localization, and interaction between HuR and ABCA1 mRNA. Finally, we found that HuR expression was significantly increased in macrophages from human atherosclerotic plaques, suggesting an important role for this RBP in controlling macrophage cholesterol metabolism in vivo. In summary, we have identified HuR as a novel posttranscriptional regulator of ABCA1 expression and cellular cholesterol homeostasis, thereby opening new avenues for increasing cholesterol efflux from atherosclerotic foam macrophages and raising circulat-ing HDL cholesterol levels.

MicroRNAs in Lipid Metabolism and Atherosclerosis

BACKGROUND: MicroRNAs (miRNA) are mediators of post-transcriptional gene expression that likely regulate most biological pathways and networks. The study of miRNAs is a rapidly emerging field; recent findings have revealed a significant role for miRNAs in atherosclerosis and lipoprotein metabolism.CONTENT: Results from recent studies demonstrated a role for miRNAs in endothelial integrity, macrophage inflammatory response to oxidized low-density lipoprotein, vascular smooth muscle cell proliferation and cholesterol synthesis. These mechanisms are all vital to the initiation and proliferation of atherosclerosis and cardiovascular disease. The importance of miRNAs has recently been recognized in cardiovascular sciences and miRNAs will likely become an integral part of our fundamental comprehension of atherosclerosis and lipoprotein metabolism. The extensive impact of miRNA mediated gene regulation and the relative ease of in vivo applicable modifications highlight the enormous potential of miRNA-based therapeutics in cardiovascular diseases.SUMMARY: miRNA studies in the field of lipid metabolism and atherosclerosis are in their infancy, and thus there is tremendous opportunity for discovery in this understudied area. The ability to target miRNAs in vivo through delivery of miRNA-mimics to enhance miRNA function, or antimiRNAs which inhibit miRNAs, has opened new avenues for the development of therapeutics for dyslipidemias and atherosclerosis, offers a unique approach to treating disease by modulating entire biological pathways. These exciting findings support the development of miRNA antagonists as potential therapeutics for the treatment of dyslipidaemia, atherosclerosis and related metabolic diseases.KEYWORDS: atherosclerosis, lipoprotein, HDL, miRNA

miR-206 controls LXRα expression and promotes LXR-mediated cholesterol efflux in macrophages

Liver X receptors (LXRα and LXRβ) are key transcription factors in cholesterol metabolism that regulate cholesterol biosynthesis/efflux and bile acid metabolism/excretion in the liver and numerous organs. In macrophages, LXR signaling modulates cholesterol handling and the inflammatory response, pathways involved in atherosclerosis. Since regulatory pathways of LXR transcription control are well understood, in the present study we aimed at identifying post-transcriptional regulators of LXR activity. MicroRNAs (miRs) are such post-transcriptional regulators of genes that in the canonical pathway mediate mRNA inactivation. In silico analysis identified miR-206 as a putative regulator of LXRα but not LXRβ. Indeed, as recently shown, we found that miR-206 represses LXRα activity and expression of LXRα and its target genes in hepatic cells. Interestingly, miR-206 regulates LXRα differently in macrophages. Stably overexpressing miR-206 in THP-1 human macrophages revealed an up-regulation and miR-206 knockdown led to a down-regulation of LXRα and its target genes. In support of these results, bone marrow-derived macrophages (BMDMs) from miR-206 KO mice also exhibited lower expression of LXRα target genes. The physiological relevance of these findings was proven by gain- and loss-of-function of miR-206; overexpression of miR-206 enhanced cholesterol efflux in human macrophages and knocking out miR-206 decreased cholesterol efflux from MPMs. Moreover, we show that miR-206 expression in macrophages is repressed by LXRα activation, while oxidized LDL and inflammatory stimuli profoundly induced miR-206 expression. We therefore propose a feed-back loop between miR-206 and LXRα that might be part of an LXR auto-regulatory mechanism to fine tune LXR activity.

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Functional differences of miR-206 in the liver and macrophages

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In the liver, miR-206 suppresses LXRα expression and signaling.

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In macrophages, miR-206 increases LXRα abundance and promotes cholesterol efflux.

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In macrophages, LXRα activation represses miR-206 expression.

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In macrophages, pro-inflammatory stimuli increase miR-206 expression.

Regulation of high-density lipoprotein metabolism

There is compelling evidence from human population studies that plasma levels of high-density lipoprotein (HDL) cholesterol correlate inversely with cardiovascular risk. Identification of this relationship has stimulated research designed to understand how HDL metabolism is regulated. The ultimate goal of these studies has been to develop HDL-raising therapies that have the potential to decrease the morbidity and mortality associated with atherosclerotic cardiovascular disease. However, the situation has turned out to be much more complex than originally envisaged. This is partly because the HDL fraction consists of multiple subpopulations of particles that vary in terms of shape, size, composition, and surface charge, as well as in their potential cardioprotective properties. This heterogeneity is a consequence of the continual remodeling and interconversion of HDL subpopulations by multiple plasma factors. Evidence that the remodeling of HDLs may impact on their cardioprotective properties is beginning to emerge. This serves to highlight the importance of understanding not only how the remodeling and interconversion of HDL subpopulations is regulated but also how these processes are affected by agents that increase HDL levels. This review provides an overview of what is currently understood about HDL metabolism and how the subpopulation distribution of these lipoproteins is regulated.

MicroRNA-27a/b regulates cellular cholesterol efflux, influx and esterification/hydrolysis in THP-1 macrophages

RATIONALE

Macrophage cholesterol homeostasis maintenance is the result of a balance between influx, endogenous synthesis, esterification/hydrolysis and efflux. Excessive accumulation of cholesterol leads to foam cell formation, which is the major pathology of atherosclerosis. Previous studies have shown that miR-27 (miR-27a and miR-27b) may play a key role in the progression of atherosclerosis.

OBJECTIVE

We set out to investigate the molecular mechanisms of miR-27a/b in intracellular cholesterol homeostasis.

METHODS AND RESULTS

In the present study, our results have shown that the miR-27 family is highly conserved during evolution, present in mammals and directly targets the 3' UTR of ABCA1, LPL, and ACAT1. apoA1, ABCG1 and SR-B1 lacking miR-27 bind sites should not be influenced by miR-27 directly. miR-27a and miR-27b directly regulated the expression of endogenous ABCA1 in different cells. Treatment with miR-27a and miR-27b mimics reduced apoA1-mediated cholesterol efflux by 33.08% and 44.61% in THP-1 cells, respectively. miR-27a/b also regulated HDL-mediated cholesterol efflux in THP-1 macrophages and affected the expression of apoA1 in HepG2 cells. However, miR-27a/b had no effect on total cellular cholesterol accumulation, but regulated the levels of cellular free cholesterol and cholesterol ester. We further found that miR-27a/b regulated the expression of LPL and CD36, and then affected the ability of THP-1 macrophages to uptake Dil-oxLDL. Finally, we identified that miR-27a/b regulated cholesterol ester formation by targeting ACAT1 in THP-1 macrophages.

CONCLUSION

These findings indicate that miR-27a/b affects the efflux, influx, esterification and hydrolysis of cellular cholesterol by regulating the expression of ABCA1, apoA1, LPL, CD36 and ACAT1.

Small RNA overcomes the challenges of therapeutic targeting of microsomal triglyceride transfer protein

The plasma level of apolipoprotein B (apoB) is among the strongest risk factors for coronary artery disease. Microsomal triglyceride transfer protein (MTP) plays a key role in the lipidation of nascent apoB and the secretion of apoB-containing lipoproteins enriched with triglycerides and is thus a promising target for the treatment of hyperlipidemia. Yet, the development of MTP inhibitors to lower plasma lipid concentrations has been hindered by adverse effects on hepatic steatosis. A study recently published in Nature Medicine identifies microRNA-30c (miR-30c) as a potent repressor of MTP that controls plasma apoB-containing lipoprotein levels, in addition to decreasing hepatic lipid synthesis through direct targeting of lysophosphatidylglycerol acyltransferase 1 (LPGAT1). These findings identify miR-30c as a novel therapeutic target that coordinately reduces lipid biosynthesis and lipoprotein secretion to suppress circulating apoB lipoproteins, while sparing the liver from steatosis.

Time-dependent expression profiles of microRNAs and mRNAs in rat milk whey

Functional RNAs, such as microRNA (miRNA) and mRNA, are present in milk, but their roles are unknown. To clarify the roles of milk RNAs, further studies using experimental animals such as rats are needed. However, it is unclear whether rat milk also contains functional RNAs and what their time dependent expression profiles are. Thus, we prepared total RNA from whey isolated from rat milk collected on days 2, 9, and 16 postpartum and analyzed using microarrays and quantitative PCR. The concentration of RNA in colostrum whey (day 2) was markedly higher than that in mature milk whey (days 9 and 16). Microarray analysis detected 161 miRNAs and 10,948 mRNA transcripts. Most of the miRNAs and mRNA transcripts were common to all tested milks. Finally, we selected some immune- and development-related miRNAs and mRNAs, and analysed them by quantitative PCR (in equal sample volumes) to determine their time-dependent changes in expression in detail. Some were significantly more highly expressed in colostrum whey than in mature milk whey, but some were expressed equally. And mRNA expression levels of some cytokines and hormones did not reflect the protein levels. It is still unknown whether RNAs in milk play biological roles in neonates. However, our data will help guide future in vivo studies using experimental animals such as rats.

MicroRNA control of high-density lipoprotein metabolism and function

Recent discoveries of microRNAs (miRNAs) that control high-density lipoprotein abundance and function have expanded our knowledge of the mechanisms regulating this important lipoprotein subclass. miRNAs have been shown to regulate gene networks that control high-density lipoprotein biogenesis and uptake, as well as discrete steps in the reverse cholesterol transport pathway. Furthermore, high-density lipoprotein itself has been shown to transport miRNAs selectively in health and disease, offering new possibilities of how this lipoprotein may alter gene expression in distal target cells and tissues. Collectively, these discoveries offer new insights into the mechanisms governing high-density lipoprotein metabolism and function and open new avenues for the development of therapeutics for the treatment of cardiovascular disease.

MicroRNAs in the onset and development of cardiovascular disease

Physiological and pathological roles for small non-encoding miRNAs (microRNAs) in the cardiovascular system have recently emerged and are now widely studied. The discovery of widespread functions of miRNAs has increased the complexity of gene-regulatory processes and networks in both the cardiovascular system and cardiovascular diseases. Indeed, it has recently been shown that miRNAs are implicated in the regulation of many of the steps leading to the development of cardiovascular disease. These findings represent novel aspects in miRNA biology and, therefore, our understanding of the role of these miRNAs during the pathogenesis of cardiovascular disease is critical for the development of novel therapies and diagnostic interventions. The present review will focus on understanding how miRNAs are involved in the onset and development of cardiovascular diseases.

The effects of miR-467b on lipoprotein lipase (LPL) expression, pro-inflammatory cytokine, lipid levels and atherosclerotic lesions in apolipoprotein E knockout mice

Atherosclerosis is a lipid disorder disease characterized by chronic blood vessel wall inflammation driven by the subendothelial accumulation of macrophages. Studies have shown that lipoprotein lipase (LPL) participates in lipid metabolism, but it is not yet known whether post-transcriptional regulation of LPL gene expression by microRNAs (miRNAs) occurs in vivo. Here, we tested that miR-467b provides protection against atherosclerosis by regulating the target gene LPL which leads to reductions in LPL expression, lipid accumulation, progression of atherosclerosis and production of inflammatory cytokines in apolipoprotein E knockout (apoE(-/-)) mice. Treatment of apoE(-/-) mice with intra-peritoneal injection of miR-467b agomir led to decreased blood plasma levels of total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), IL-1β and monocyte chemotactic protein-1 (MCP-1). Using Western blots and real time PCR, we determined that LPL expression in aorta and abdominal cavity macrophages were significantly down-regulated in the miR-467b agomir group. Furthermore, systemic treatment with miR-467b antagomir accelerated the progression of atherosclerosis in the aorta of apoE(-/-) mice. The present study showed that miR-467b protects apoE(-/-) mice from atherosclerosis by reducing lipid accumulation and inflammatory cytokine secretion via downregulation of LPL expression. Therefore, targeting miR-467b may offer a promising strategy to treat atherosclerotic vascular disease.

Regulation of ABCA1 protein expression and function in hepatic and pancreatic islet cells by miR-145

OBJECTIVE

The ATP-binding cassette transporter A1 (ABCA1) protein maintains cellular cholesterol homeostasis in several different tissues. In the liver, ABCA1 is crucial for high-density lipoprotein biogenesis, and in the pancreas ABCA1 can regulate insulin secretion. In this study, our aim was to identify novel microRNAs that regulate ABCA1 expression in these tissues.

APPROACH AND RESULTS

We combined multiple microRNA prediction programs to identify 8 microRNAs that potentially regulate ABCA1. A luciferase reporter assay demonstrated that 5 of these microRNAs (miR-148, miR-27, miR-144, miR-145, and miR-33a/33b) significantly repressed ABCA1 3'-untranslated region activity with miR-145 resulting in one of the larger decreases. In hepatic HepG2 cells, miR-145 can regulate both ABCA1 protein expression levels and cholesterol efflux function. In murine islets, an increase in miR-145 expression decreased ABCA1 protein expression, increased total islet cholesterol levels, and decreased glucose-stimulated insulin secretion. Inhibiting miR-145 produced the opposite effect of increasing ABCA1 protein levels and improving glucose-stimulated insulin secretion. Finally, increased glucose levels in media significantly decreased miR-145 levels in cultured pancreatic beta cells. These findings suggest that miR-145 is involved in glucose homeostasis and is regulated by glucose concentration.

CONCLUSIONS

Our studies demonstrate that miR-145 regulates ABCA1 expression and function, and inhibiting this microRNA represents a novel strategy for increasing ABCA1 expression, promoting high-density lipoprotein biogenesis in the liver, and improving glucose-stimulated insulin secretion in islets.

MicroRNAs and Lipoprotein Metabolism

MicroRNAs(miRNAs; miRs) are small, non-protein-coding RNAs that negatively regulate the gene expression. They bind to specific mRNAs and inhibit translation or promote mRNA degradation. Recently, some miRNAs have been shown to be involved in lipid homoeostasis. In particular, miR122 and miR-33 have a significant impact on lipid homeostasis and are potential therapeutic targets for treating lipid disorders and/or atherosclerosis. In this review, we describe the current understanding of the function of miRNAs in lipid homeostasis, with a focus on lipoprotein metabolism.

MicroRNAs and atherosclerosis

MicroRNAs (miRNAs) are small, ~22 nucleotide (nt) sequences of RNA that regulate gene expression at posttranscriptional level. These endogenous gene expression inhibitors were primarily described in cancer but recent exciting findings have also demonstrated a key role in cardiovascular diseases (CVDs), including atherosclerosis. MiRNAs control endothelial cell (EC), vascular smooth muscle cell (VSMC), and macrophage functions, and thereby regulate the progression of atherosclerosis. MiRNA expression is modulated by different stimuli involved in every stage of atherosclerosis, and conversely miRNAs modulates several pathways implicated in plaque development such as cholesterol metabolism. In the present review, we focus on the importance of miRNAs in atherosclerosis, and we further discuss their potential use as biomarkers and therapeutic targets in CVDs.

MicroRNAs and metabolism crosstalk in energy homeostasis

In record time, microRNAs (miRNAs) have acquired the respected stature of important natural regulators of global gene expression. Multiple studies have demonstrated that a large number of miRNAs are under the control of various metabolic stimuli, including nutrients, hormones, and cytokines. Conversely, it is now well recognized that miRNAs control metabolism, thereby generating a bidirectional functional link, which perturbs energy homeostasis in case of disconnection in the miRNA-metabolism interplay. A challenging road lies ahead for defining the role of miRNAs in the pathogenesis of diseases such as diabetes and for establishing their usefulness as new medications and clinically reliable biomarkers.

Oxidative stress in atherosclerosis: the role of microRNAs in arterial remodeling

Atherosclerosis is the underlying condition in most cardiovascular diseases. Among the highly specific cellular and molecular responses, endothelial dysfunction plays a key role in disease initiation and progression. These events coincide with the occurrence of oxidative stress. Increased reactive oxygen species production and oxidization of low-density lipoprotein are detected throughout atherosclerosis progression. MicroRNAs (miRNAs) have emerged as important regulators of gene expression that posttranscriptionally modify cellular responses and function. Accumulating studies indicate an integrated miRNA network in the molecular mechanisms that control cellular homeostasis, vascular inflammation, and metabolism. Experimental models of atherosclerosis highlight a direct link between altered miRNA expression profiles and the pathophysiology of the disease and identify putative miRNA candidates for the development of novel therapeutic strategies. In this review, we provide an overview of the role of miRNA regulatory networks in oxidative stress in atherosclerosis and arterial remodeling and discuss their potential therapeutic implications.

MicroRNA modulation of lipid metabolism and oxidative stress in cardiometabolic diseases

The regulation of the metabolism of cholesterol has been one of the most studied biological processes since its first isolation from gallstones in 1784. High levels of plasma low-density lipoprotein (LDL) cholesterol and reduced levels of plasma high-density lipoprotein (HDL) cholesterol are widely recognized as major risk factors of cardiovascular disease. An imbalance in the production of reactive oxygen species can oxidize LDL particles, increasing the levels of the highly proatherogenic oxidized LDL. Furthermore, under pathological scenarios, numerous molecules can function as pro-oxidants, such as iron or (high levels of) glucose. In addition to the classical mechanisms regulating lipid homeostasis, recent studies have demonstrated the important role of microRNAs (miRNAs) as regulators of lipoprotein metabolism, oxidative derivatives of lipoprotein, and redox balance. Here, we summarize recent findings in the field, highlighting the contributions of some miRNAs to lipid- and oxidative-associated pathologies. We also discuss how therapeutic intervention of miRNAs may be a promising strategy to decrease LDL, increase HDL, and ameliorate lipid- and oxidative-related disorders, including atherosclerosis, nonalcoholic fatty liver disease, and metabolic syndrome.

From evolution to revolution: miRNAs as pharmacological targets for modulating cholesterol efflux and reverse cholesterol transport

There has been strong evolutionary pressure to ensure that an animal cell maintains levels of cholesterol within tight limits for normal function. Imbalances in cellular cholesterol levels are a major player in the development of different pathologies associated to dietary excess. Although epidemiological studies indicate that elevated levels of high-density lipoprotein (HDL)-cholesterol reduce the risk of cardiovascular disease, recent genetic evidence and pharmacological therapies to raise HDL levels do not support their beneficial effects. Cholesterol efflux as the first and probably the most important step in reverse cholesterol transport is an important biological process relevant to HDL function. Small non-coding RNAs (microRNAs), post-transcriptional control different aspects of cellular cholesterol homeostasis including cholesterol efflux. miRNA families miR-33, miR-758, miR-10b, miR-26 and miR-106b directly modulates cholesterol efflux by targeting the ATP-binding cassette transporter A1 (ABCA1). Pre-clinical studies with anti-miR therapies to inhibit some of these miRNAs have increased cellular cholesterol efflux, reverse cholesterol transport and reduce pathologies associated to dyslipidemia. Although miRNAs as therapy have benefits from existing antisense technology, different obstacles need to be solved before we incorporate such research into clinical care. Here we focus on the clinical potential of miRNAs as therapeutic target to increase cholesterol efflux and reverse cholesterol transport as a new alternative to ameliorate cholesterol-related pathologies.

Pro-apoptotic miRNA-128-2 modulates ABCA1, ABCG1 and RXRα expression and cholesterol homeostasis

Aberrant regulation of cholesterol homeostasis is associated with obesity as well as multiple types of cancer. However, the mechanism behind these is largely missing. Here, we show that microRNA (miRNA)-128-2 is not only a pro-apoptotic microRNA but it also alters the expression of genes involved in cellular cholesterol homeostasis. Cholesterol efflux via ATP-binding cassette transporters (ABCA1 and ABCG1) is a mechanism for cells to eliminate excess cholesterol and prevent cellular cholesterol accumulation. The regulation of these pathways is complex with transcriptional regulation by sterol-regulatory element-binding protein (SREBP) and liver X receptor/retinoid X receptor (RXR) transcription factors but poorly understood at the post-transcriptional levels. MiR-128-2 increases the expression of SREBP2 and decreases the expression of SREBP1 in HepG2, MCF7 and HEK293T cells independent of sirtuin 1 (SIRT1) status. MiR-128-2 inhibits the expression of ABCA1, ABCG1 and RXRα directly through a miR-128-2-binding site within their respective 3'untranslated regions. The administration of miR-128-2 leads to decline in the protein and mRNA levels of ABCA1, ABCG1 and RXRα. Conversely, anti-miRNA treatment leads to increased ABCA1, ABCG1 and RXRα expression. The inverse correlation between miR-128-2 and its targets viz. ABCA1 and ABCG1 was also established during high-fat diet in different mice tissues. Our data show that cholesterol efflux is attenuated by miR-128-2 overexpression and, conversely, stimulated by miR-128-2 silencing. Further, we also observed the induction of ER stress response by miR-128-2. In this study, we provide the first evidence of miR-128-2 to be a new regulator of cholesterol homeostasis. Our study shows dual role of miR-128-2, as a pro-apoptotic molecule as well as a regulator of cholesterol homeostasis.

MicroRNAs 185, 96, and 223 repress selective high-density lipoprotein cholesterol uptake through posttranscriptional inhibition

Hepatic scavenger receptor class B type I (SR-BI) plays an important role in selective high-density lipoprotein cholesterol (HDL-C) uptake, which is a pivotal step of reverse cholesterol transport. In this study, the potential involvement of microRNAs (miRNAs) in posttranscriptional regulation of hepatic SR-BI and selective HDL-C uptake was investigated. The level of SR-BI expression was repressed by miRNA 185 (miR-185), miR-96, and miR-223, while the uptake of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI)-HDL was decreased by 31.9% (P < 0.001), 23.9% (P < 0.05), and 15.4% (P < 0.05), respectively, in HepG2 cells. The inhibition of these miRNAs by their anti-miRNAs had opposite effects in these hepatic cells. The critical effect of miR-185 was further validated by the loss of regulation in constructs with mutated miR-185 target sites. In addition, these miRNAs directly targeted the 3' untranslated region (UTR) of SR-BI with a coordinated effect. Interestingly, the decrease of miR-96 and miR-185 coincided with the increase of SR-BI in the livers of ApoE KO mice on a high-fat diet. These data suggest that miR-185, miR-96, and miR-223 may repress selective HDL-C uptake through the inhibition of SR-BI in human hepatic cells, implying a novel mode of regulation of hepatic SR-BI and an important role of miRNAs in modulating cholesterol metabolism.

Strategies to deliver microRNAs as potential therapeutics in the treatment of cardiovascular pathology

CONTEXT

MicroRNAs (miRNAs) are important and powerful mediators in a variety of diseases including cardiovascular pathology. Thus, they emerged as interesting new drug targets. However, it is important to develop efficient transfer tools to successfully deliver miRNAs or antisense oligonucleotides (antagomirs) to the target tissue.

OBJECTIVE

The aim of this study was to review the scientific literature on delivery techniques currently used for transfer of miRNAs and antagomirs to animal models of cardiovascular disease and those that are likely to be used for therapeutic miRNA transport in the nearest future.

METHODS

The research was carried out by consulting the following medical websites: Medicus Medline Index, PubMed (National Library of Medicine), and a registry database of clinical trials conducted in USA ( www.clinicaltrials.gov). The selection gathers articles written in English, published from January 2012.

RESULTS

A current delivery technique includes chemical modification of antagomirs with 2-O-methyl-group or 2-O-methyoxyethyl or using locked nucleic acids to increase drug stability and affinity. Development of miRNA sponges/decoys aims to target all members of a miRNA seed family of interest. A further strategy to augment miRNA levels is to use miRNA delivery through viral-based vectors including adenoviruses, adeno-associated viruses, and lentiviruses. To date, a variety of nanocarriers is available for efficient delivery of miRNAs. Microvesicles, and apoptotic bodies that contain circulating miRNAs could be also used as therapeutic transport systems in the nearest future.

CONCLUSION

Development of new miRNA carrier systems with advanced properties and large animal data in the cardiovascular field is highly recommended.

Role of microRNAs in the regulation of drug metabolism and disposition genes in diabetes and liver disease

INTRODUCTION

The pathogenesis of diabetes mellitus and nonalcoholic fatty liver disease (NAFLD) is complex, and the underlying molecular mechanisms are only partially understood.

AREAS COVERED

This review summarizes current knowledge of the role of microRNAs (miRNAs) in the regulation of drug absorption, distribution, metabolism, and excretion genes in the pathogenesis of diabetes and NAFLD. The literature search was performed using the PubMed database (up to February 2013).

EXPERT OPINION

miRNAs play a fundamental role in diabetes and NAFLD. This review focuses on the dysregulation of miRNAs involved in the regulation of drug metabolism and disposition in the pathogenesis of these metabolic syndromes. The evidence presented indicates that better understanding of the underlying molecular mechanisms associated with dysregulation of miRNAs controlling the cellular drug metabolizing system is of great importance not only from a scientific, but also from a clinical perspective. More importantly, an association between these metabolic disorders and miRNA dysregulation suggests that correcting miRNA expression by either their up-regulation or inhibition holds a promise for treating these metabolic syndrome and alleviating disease progression.

Therapeutic gene targeting approaches for the treatment of dyslipidemias and atherosclerosis

PURPOSE OF REVIEW

Despite improved therapies, cardiovascular diseases are the leading cause of morbidity and mortality worldwide. Therefore, new therapeutic approaches are still needed. In the gene therapy field, RNA interference (RNAi) and regulation of microRNAs (miRNAs) have gained a lot of attention in addition to traditional overexpression based strategies. Here, recent findings in therapeutic gene silencing and modulation of small RNA expression related to atherogenesis and dyslipidemia are summarized.

RECENT FINDINGS

Novel gene therapy approaches for the treatment of hyperlipidemia have been addressed. Antisense oligonucleotide and RNAi-based therapies against apolipoprotein B100 and proprotein convertase subtilisin/kexin type 9 have shown already efficacy in preclinical and clinical trials. In addition, several miRNAs dysregulated in atherosclerotic lesions and regulating cholesterol homeostasis have been found, which may represent novel targets for future therapies.

SUMMARY

New therapies for lowering lipid levels are now being tested in clinical trials, and both antisense oligonucleotide and RNAi-based therapies have shown promising results in lowering cholesterol levels. However, the modulation of inflammatory component in atherosclerosis by gene therapy and targeting of the effects to plaques are still difficult challenges.

A regulatory role for microRNA 33* in controlling lipid metabolism gene expression

hsa-miR-33a and hsa-miR-33b, intronic microRNAs (miRNAs) located within the sterol regulatory element-binding protein 2 and 1 genes (Srebp-2 and -1), respectively, have recently been shown to regulate lipid homeostasis in concert with their host genes. Although the functional role of miR-33a and -b has been highly investigated, the role of their passenger strands, miR-33a* and -b*, remains unclear. Here, we demonstrate that miR-33a* and -b* accumulate to steady-state levels in human, mouse, and nonhuman primate tissues and share a similar lipid metabolism target gene network as their sister strands. Analogous to miR-33, miR-33* represses key enzymes involved in cholesterol efflux (ABCA1 and NPC1), fatty acid metabolism (CROT and CPT1a), and insulin signaling (IRS2). Moreover, miR-33* also targets key transcriptional regulators of lipid metabolism, including SRC1, SRC3, NFYC, and RIP140. Importantly, inhibition of either miR-33 or miR-33* rescues target gene expression in cells overexpressing pre-miR-33. Consistent with this, overexpression of miR-33* reduces fatty acid oxidation in human hepatic cells. Altogether, these data support a regulatory role for the miRNA* species and suggest that miR-33 regulates lipid metabolism through both arms of the miR-33/miR-33* duplex.

The plaque "micro" environment: microRNAs control the risk and the development of atherosclerosis

While the discovery of microRNAs has exponentially expanded our understanding of the regulatory mechanisms governing gene networks in many biological processes, the study of these tiny RNA powerhouses in cardiovascular disease is in its infancy. To date, there have been over 1200 human microRNAs identified, and they are estimated to affect the expression of over half of the protein-coding portion of the human genome. In this review, we will discuss miRNAs that are integral players in processes affecting risk factors for CVD, as well as miRNAs that act at the level of the vessel wall to affect atherogenesis. We will discuss how microRNAs are not only advancing the field of cardiovascular biology, but how some miRNAs are at the forefront of drug development and may be soon advancing into the clinic.

Control of cholesterol metabolism and plasma high-density lipoprotein levels by microRNA-144

RATIONALE

Foam cell formation because of excessive accumulation of cholesterol by macrophages is a pathological hallmark of atherosclerosis, the major cause of morbidity and mortality in Western societies. Liver X nuclear receptors (LXRs) regulate the expression of the adenosine triphosphate-binding cassette (ABC) transporters, including adenosine triphosphate-binding cassette transporter A1 (ABCA1) and adenosine triphosphate-binding cassette transporter G1 (ABCG1). ABCA1 and ABCG1 facilitate the efflux of cholesterol from macrophages and regulate high-density lipoprotein (HDL) biogenesis. Increasing evidence supports the role of microRNA (miRNAs) in regulating cholesterol metabolism through ABC transporters.

OBJECTIVE

We aimed to identify novel miRNAs that regulate cholesterol metabolism in macrophages stimulated with LXR agonists.

METHODS AND RESULTS

To map the miRNA expression signature of macrophages stimulated with LXR agonists, we performed an miRNA profiling microarray analysis in primary mouse peritoneal macrophages stimulated with LXR ligands. We report that LXR ligands increase miR-144 expression in macrophages and mouse livers. Overexpression of miR-144 reduces ABCA1 expression and attenuates cholesterol efflux to apolipoproteinA1 in macrophages. Delivery of miR-144 oligonucleotides to mice attenuates ABCA1 expression in the liver, reducing HDL levels. Conversely, silencing of miR-144 in mice increases the expression of ABCA1 and plasma HDL levels. Thus, miR-144 seems to regulate both macrophage cholesterol efflux and HDL biogenesis in the liver.

CONCLUSIONS

miR-144 regulates cholesterol metabolism via suppressing ABCA1 expression and modulation of miRNAs may represent a potential therapeutical intervention for treating dyslipidemia and atherosclerotic vascular disease.

A big role for small RNAs in HDL homeostasis

High-density lipoproteins play a central role in systemic cholesterol homeostasis by stimulating the efflux of excess cellular cholesterol and transporting it to the liver for biliary excretion. HDL has long been touted as the "good cholesterol" because of the strong inverse correlation of plasma HDL cholesterol levels with coronary heart disease. However, the disappointing outcomes of recent clinical trials involving therapeutic elevations of HDL cholesterol have called this moniker into question and revealed our lack of understanding of this complex lipoprotein. At the same time, the discovery of microRNAs (miRNAs) that regulate HDL biogenesis and function have led to a surge in our understanding of the posttranscriptional mechanisms regulating plasma levels of HDL. Furthermore, HDL has recently been shown to selectively transport miRNAs and thereby facilitate cellular communication by shuttling these potent gene regulators to distal tissues. Finally, that miRNA cargo carried by HDL may be altered during disease states further broadened our perspective of how this lipoprotein can have complex effects on target cells and tissues. The unraveling of how these tiny RNAs govern HDL metabolism and contribute to its actions promises to reveal new therapeutic strategies to optimize cardiovascular health.

MicroRNAs in metabolic disease

Alterations in the metabolic control of lipid and glucose homeostasis predispose an individual to develop cardiometabolic diseases, such as type 2-diabetes mellitus and atherosclerosis. Work over the last years has suggested that microRNAs (miRNAs) play an important role in regulating these physiological processes. The contribution of miRNAs in regulating metabolism is exemplified by miR-33, an intronic miRNA encoded in the Srebp genes. miR-33 controls cellular cholesterol export and fatty acid degradation, whereas its host genes stimulate cholesterol and fatty acid synthesis. Other miRNAs, such as miR-122, also play a critical role in regulating lipid homeostasis by controlling cholesterol synthesis and lipoprotein secretion in the liver. This review article summarizes the recent findings in the field, highlighting the contribution of miRNAs in regulating lipid and glucose metabolism. We will also discuss how the modulation of specific miRNAs may be a promising strategy to treat metabolic diseases.

MicroRNAs and Cardiovascular Disease

MicroRNAs (miRNAs) regulate gene expression by binding to their targets and promoting RNA degradation and/or inhibiting protein translation. In recent years, miRNAs have revolutionized our understanding of gene regulatory networks, providing new prospective tools to manage disease. Atherosclerosis and other cardiovascular diseases are a leading cause of disability and death in the US and in other western populations and pose an enormous burden on our healthcare system. Altered lipid homeostasis in liver or in the artery wall, and disruption of endothelial and smooth muscle cell function have been shown to contribute to the onset and progression of cardiovascular disease. This review focuses on recent advances in the field of vascular biology- and lipid metabolism-related miRNomics.

Gain-of-function lipoprotein lipase variant rs13702 modulates lipid traits through disruption of a microRNA-410 seed site

Genome-wide association studies (GWAS) have identified hundreds of genetic variants that are associated with lipid phenotypes. However, data supporting a functional role for these variants in the context of lipid metabolism are scarce. We investigated the association of the lipoprotein lipase (LPL) variant rs13702 with plasma lipids and explored its potential for functionality. The rs13702 minor allele had been predicted to disrupt a microRNA (miR) recognition element (MRE) seed site (MRESS) for the human microRNA-410 (miR-410). Furthermore, rs13702 is in linkage disequilibrium (LD) with several SNPs identified by GWAS. We performed a meta-analysis across ten cohorts of participants that showed a statistically significant association of rs13702 with triacylglycerols (TAG) (p = 3.18 × 10(-42)) and high-density lipoprotein cholesterol (HDL-C) (p = 1.35 × 10(-32)) with each copy of the minor allele associated with 0.060 mmol/l lower TAG and 0.041 mmol/l higher HDL-C. Our data showed that an LPL 3' UTR luciferase reporter carrying the rs13702 major T allele was reduced by 40% in response to a miR-410 mimic. We also evaluated the interaction between intake of dietary fatty acids and rs13702. Meta-analysis demonstrated a significant interaction between rs13702 and dietary polyunsaturated fatty acid (PUFA) with respect to TAG concentrations (p = 0.00153), with the magnitude of the inverse association between dietary PUFA intake and TAG concentration showing -0.007 mmol/l greater reduction. Our results suggest that rs13702 induces the allele-specific regulation of LPL by miR-410 in humans. This work provides biological and potential clinical relevance for previously reported GWAS variants associated with plasma lipid phenotypes.

MicroRNA regulation of lipid metabolism

MicroRNAs are structural components of an epigenetic mechanism of post-transcriptional regulation of messenger RNA translation. Recently, there is significant interest in the application of microRNA as a blood-based biomarker of underlying physiologic conditions, and the therapeutic administration of microRNA inhibitors and mimics. The purpose of this review is to describe the current body of knowledge on microRNA regulation of genes involved in lipid metabolism, and to introduce the role of microRNA in development and progression of atherosclerosis.

MicroRNAs and lipoproteins: a connection beyond atherosclerosis?

MicroRNAs (miRNAs) are short non-coding RNAs involved in the regulation of gene expression at the post-transcriptional level that have been involved in the pathogenesis of a number of cardiovascular diseases. Several miRNAs have been described to finely regulate lipid metabolism and the progression and regression of atherosclerosis including, miR-33, miR-122. Of note miR-33a and -33b, represent one of the most interesting and attractive targets for metabolic-related disorders and anti-miR-33 approaches are under intensive investigation. More recently miRNAs were shown to exert their activities in a paracrine manner and also systemically. The latter is possible because lipid-carriers, including lipoproteins, transport and protect miRNAs from degradation in the circulation. This review will present the complex mechanism by which miRNAs regulate lipid metabolism, illustrate how their therapeutical modulation may lead to new treatments for cardiometabolic diseases, and discuss how lipoproteins and other lipid-carriers transport miRNAs in the circulation. The emerging strong connection between miRNAs, lipoproteins and lipid metabolism indicates the existence of a reciprocal modulation that might go beyond atherosclerosis.

miRNAs, polyphenols, and chronic disease

MicroRNAs (miRNAs) are small noncoding RNAs, approximately 18-25 nucleotides in length, that modulate gene expression at the posttranscriptional level. Thousands of miRNAs have been described, and it is thought that they regulate some aspects of more than 60% of all human cell transcripts. Several polyphenols have been shown to modulate miRNAs related to metabolic homeostasis and chronic diseases. Polyphenolic modulation of miRNAs is very attractive as a strategy to target numerous cell processes and potentially reduce the risk of chronic disease. Evidence is building that polyphenols can target specific miRNAs, such as miR-122, but more studies are necessary to discover and validate additional miRNA targets.

MicroRNAs and atherosclerosis: new actors for an old movie

To date, cardiovascular diseases (CVDs) are the leading causes of morbidity and mortality worldwide. MicroRNAs (miRNAs) are endogenous, short, non-coding RNA sequences able to regulate gene expression principally at the post-transcriptional level. Initially, they were thought to be involved only in developmental timing of worms. Their involvement in human biology was recently discovered and many studies have been performed to demonstrate the role of miRNA in human cancer. Since the first observation in 2005 of their implication in cardiac biology, many studies have demonstrated their role in the genetic modulation of cardiovascular development and in cardiovascular diseases such as cardial remodeling and heart failure, cardiac arrhythmias, cardiac ischaemia, cardiac fibrosis, atherosclerosis and stroke. Thus, the aim of this review is to describe the role of miRNA in atherosclerosis development and evolution and to individuate their role as potential therapeutic target.

Genetics of cholesterol efflux

Plasma levels of high-density lipoprotein cholesterol (HDL-C) show an inverse association with coronary heart disease (CHD). As a biological trait, HDL-C is strongly genetically determined, with a heritability index ranging from 40 % to 60 %. HDL represents an appealing therapeutic target due to its beneficial pleiotropic effects in preventing CHD. This review focuses on the genetic basis of cellular cholesterol efflux, the rate-limiting step in HDL biogenesis. There are several monogenic disorders (e.g., Tangier disease, caused by mutations within ABCA1) affecting HDL biogenesis. Importantly, many disorders of cellular cholesterol homeostasis cause a reduced HDL-C. We integrate information from family studies and linkage analyses with that derived from genome-wide association studies (GWAS) and review the recent identification of micro-RNAs (miRNA) involved in cellular cholesterol metabolism. The identification of genomic pathways related to HDL may help pave the way for novel therapeutic approaches to promote cellular cholesterol efflux as a therapeutic modality to prevent atherosclerosis.

XenomiRs and miRNA homeostasis in health and disease: evidence that diet and dietary miRNAs directly and indirectly influence circulating miRNA profiles

Contributions of dietary miRNAs to circulating small RNA profiles would have profound implications for interpretation of miRNA biomarker studies: presumptive disease-specific markers might instead indicate responses to disease-associated quantitative or qualitative dietary alteration. This examination weighs the evidence for a 2-fold hypothesis: first, that ingested biological matter contributes directly to the miRNA complement of body compartments; and second, that these diet-derived exogenous miRNAs (or "xenomiRs") affect total miRNA profiles as part of a circulating miRNA homeostasis that is altered in many diseases. Homeostasis of high-density lipoprotein (HDL), a known miRNA carrier-provides a model as a proposed component of broader miRNA homeostasis. Further research into the dietary xenomiR hypothesis is needed to ensure rigor in the search for truly disease-specific miRNA biomarkers.

Epigenetic-dependent regulation of drug transport and metabolism: an update

The pharmacokinetics of a drug are subject to large interindividual variability, which can result in lack of response or adverse drug reactions. In addition to genetic polymorphisms and drug interactions, key genes involved in the metabolism and transport of drugs are demonstrated to have epigenetic influences that can potentially affect interindividual variability in drug response. Emerging studies have focused on the importance of DNA methylation for ADME gene expression and for drug action and resistance, particularly in cancer. However, the epigenetic and ncRNA-dependent regulation of these genes, as well as the pharmacological consequences, is in need of greater attention. In the current review we provide an update of epigenetic and ncRNA-dependent regulation of ADME genes.

MicroRNA Regulation of Cholesterol Metabolism

Disruption of cellular cholesterol balance results in pathologic processes including atherosclerosis, metabolic syndrome, type II diabetes and Alzheimer's disease. Maintenance of cholesterol homeostasis requires constant metabolic adjustment, achieved partly through the fine regulation of the classical transcription factors (e.g., by SREBP and LXR), but also through members of a class of noncoding RNAs termed miRNAs. Some miRNAs have now been identified to be potent post-transcriptional regulators of lipid metabolism genes, including miR-122, miR-33, miR-758, and miR-106b. Different strategies have been developed to modulate miRNA effects for therapeutic purposes. The promise demonstrated by the use of anti-miRs in human preclinical studies, in the case of miR-122, raises the possibility that miR-33, miR-758, and miR-106b may become viable therapeutic targets in future. This review summarizes the evidence for a critical role of some miRNAs in regulating cholesterol metabolism and suggests novel ways to manage dyslipidemias and cardiovascular diseases.

Gut microbiota metabolism of anthocyanin promotes reverse cholesterol transport in mice via repressing miRNA-10b

RATIONALE

We and others have demonstrated that anthocyanins have antiatherogenic capability. Because intact anthocyanins are absorbed very poorly, the low level of circulating parent anthocyanins may not fully account for their beneficial effect. We found recently that protocatechuic acid (PCA), a metabolite of cyanidin-3 to 0-β-glucoside (Cy-3-G), has a remarkable antiatherogenic effect.

OBJECTIVE

To investigate whether mouse gut microbiota metabolizes Cy-3-G into PCA and to determine whether and how PCA contributes to the antiatherogenic potency of its precursor, Cy-3-G.

METHODS AND RESULTS

PCA was determined as a gut microbiota metabolite of Cy-3-G in ApoE(-/-) mice, verified by the utilization of antibiotics to eliminate gut microbiota and further microbiota acquisition. PCA but not Cy-3-G at physiologically reachable concentrations promoted cholesterol efflux from macrophages and macrophage ABCA1 and ABCG1 expression. By conducting a miRNA microarray screening, we revealed that expression of miRNA-10b in macrophages can be reduced by PCA. Functional analyses demonstrated that miRNA-10b directly represses ABCA1 and ABCG1 and negatively regulates cholesterol efflux from murine- and human-derived macrophages. Further in vitro and ex vivo analyses verified that PCA accelerates macrophage cholesterol efflux, correlating with the regulation of miRNA-10b-ABCA1/ABCG1 cascade, whereas Cy-3-G consumption promoted macrophage RCT and regressed atherosclerotic lesion in a gut microbiotaendependent manner.

CONCLUSIONS

PCA, as the gut microbiota metabolite of Cy-3-G, exerts the antiatherogenic effect partially through this newly defined miRNA-10b-ABCA1/ABCG1-cholesterol efflux signaling cascade. Thus, gut microbiota is a potential novel target for atherosclerosis prevention and treatment.

MiR-26 controls LXR-dependent cholesterol efflux by targeting ABCA1 and ARL7

Cellular cholesterol levels are tightly regulated and represent a balance of cholesterol uptake, endogenous synthesis and efflux. Although the classic transcriptional regulations of cholesterol metabolism by liver X receptors (LXRs) have been well studied, the potential effects of LXR-responsive microRNAs (miRNAs) still need to be unveiled. Here, we describe that miR-26, an LXR-suppressed miRNA, inhibits the expression of the ATP-binding cassette transporter A1 (ABCA1) and ADP-ribosylation factor-like 7 (ARL7), two LXR target genes which play critical roles in cholesterol efflux. These findings have not only figured out an alternative mechanism for LXR regulation, but also provided a potential therapeutic target for cholesterol metabolic disorders.