MicroRNA-33 and the SREBP host genes cooperate to control cholesterol homeostasis

Profibrotic effect of miR-33a with Akt activation in hepatic stellate cells

MicroRNAs (miRNAs) attract more attention in the pathophysiology of liver fibrosis and miR-33a has been previously demonstrated as involved in the regulation of cholesterol and lipid metabolism. Transforming growth factor-beta1 (TGF-β1) is generally accepted to be the main stimulating factor in the hepatic stellate cells (HSCs) activation, which plays an important role in hepatic fibrosis. However, the involvement and underlying mechanism of miR-33a and its role in TGF-β1-induced hepatic fibrogenesis remains unknown. Here, we investigate the role of miR-33a in the activation of immortalized human HSCs, Lx-2 cells. Our findings have shown that the expression of miR-33a with its host gene sterol regulatory element-binding protein 2 (SREBP2) was more highly expressed in activation of Lx-2 cells than in quiescent cells. The expression of miR-33a on TGF-β1-induced HSCs activation may be modulated via the activation of PI3K/Akt pathway. In addition, miR-33a significantly correlated with TGF-β1-induced expression of α1 (I) collagen (Col1A1) and α-SMA in HSCs. Bioinformatics analyses predict that peroxisome proliferator activated receptor-alpha (PPAR-α) is the potential target of miR-33a. We further found that anti-miR-33a significantly increases target gene PPAR-α mRNA and protein level, suggesting that miR-33a involved in HSCs function might be modulated by targeting PPAR-α. Finally, our results indicate that the expression of miR-33a increased with the progression of liver fibrosis. These results suggested that anti-miR-33a inhibit activation and extracellular matrix production, at least in part, via the activation of PI3K/Akt pathway and PPAR-α and anti sense of miR-33a may be a novel potential therapeutic approach for treating hepatic fibrosis in the future.

Antagonism of betulinic acid on LPS-mediated inhibition of ABCA1 and cholesterol efflux through inhibiting nuclear factor-kappaB signaling pathway and miR-33 expression

ATP-binding cassette transporter A1 (ABCA1) is critical in exporting cholesterol from macrophages and plays a protective role in the development of atherosclerosis. The purpose of this study was to investigate the effects of betulinic acid (BA), a pentacyclic triterpenoid, on ABCA1 expression and cholesterol efflux, and to further determine the underlying mechanism. BA promoted ABCA1 expression and cholesterol efflux, decreased cellular cholesterol and cholesterol ester content in LPS-treated macrophages. Furthermore, we found that BA promoted ABCA1 expression via down-regulation of miR-33s. The inhibition of LPS-induced NF-κB activation further decreased miR-33s expression and enhanced ABCA1 expression and cholesterol efflux when compared with BA only treatment. In addition, BA suppressed IκB phosphorylation, p65 phosphorylation and nuclear translocation, and the transcription of NF-κB-dependent related gene. Moreover, BA reduced atherosclerotic lesion size, miR-33s levels and NF-κB activation, and promoted ABCA1 expression in apoE^−/− mice. Taken together, these results reveal a novel mechanism for the BA-mediated ABCA1 expression, which may provide new insights for developing strategies for modulating vascular inflammation and atherosclerosis.

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.

Regulation of cholesterol and bile acid homeostasis by the cholesterol 7α-hydroxylase/steroid response element-binding protein 2/microRNA-33a axis in mice

Bile acid synthesis not only produces physiological detergents required for intestinal nutrient absorption, but also plays a critical role in regulating hepatic and whole-body metabolic homeostasis. We recently reported that overexpression of cholesterol 7α-hydroxylase (CYP7A1) in the liver resulted in improved metabolic homeostasis in Cyp7a1 transgenic (Cyp7a1-tg) mice. This study further investigated the molecular links between bile acid metabolism and lipid homeostasis. Microarray gene profiling revealed that CYP7A1 overexpression led to marked activation of the steroid response element-binding protein 2 (SREBP2)-regulated cholesterol metabolic network and absence of bile acid repression of lipogenic gene expression in livers of Cyp7a1-tg mice. Interestingly, Cyp7a1-tg mice showed significantly elevated hepatic cholesterol synthesis rates, but reduced hepatic fatty acid synthesis rates, which was accompanied by increased (14) C-glucose-derived acetyl-coenzyme A incorporation into sterols for fecal excretion. Induction of SREBP2 also coinduces intronic microRNA-33a (miR-33a) in the SREBP2 gene in Cyp7a1-tg mice. Overexpression of miR-33a in the liver resulted in decreased bile acid pool, increased hepatic cholesterol content, and lowered serum cholesterol in mice.

CONCLUSION

This study suggests that a CYP7A1/SREBP2/miR-33a axis plays a critical role in regulation of hepatic cholesterol, bile acid, and fatty acid synthesis. Antagonism of miR-33a may be a potential strategy to increase bile acid synthesis to maintain lipid homeostasis and prevent nonalcoholic fatty liver disease, diabetes, and obesity.

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.

The complexity of thyroid transcription factor 1 with both pro- and anti-oncogenic activities

After the original identification of thyroid transcription factor 1 (TTF-1 or NKX2-1) biochemical activity as a transcriptional regulator of thyroglobulin in 1989, the bulk of the ensuing research has concentrated on elucidating the roles of NKX2-1 in the development of lung and thyroid tissues. Motivated by its specific expression pattern, pathologists adopted the NKX2-1 immunoreactivity to distinguish pulmonary from nonpulmonary nonthyroid adenocarcinomas. Interestingly, the concept of NKX2-1 as an active participant in lung tumorigenesis did not take hold until 2007. This minireview contrasts the recent advancements of NKX2-1-related observations primarily in the realm of pulmonary malignancies.

Adult-specific functions of animal microRNAs

MicroRNAs (miRNAs) are ~22 nt RNAs that coordinate vast regulatory networks in animals and thereby influence myriad processes. This Review examines evidence that miRNAs have continuous roles in adults in ways that are separable from developmental control. Adult-specific activities for miRNAs have been described in various stem cell populations, in the context of neural function and cardiovascular biology, in metabolism and ageing, and during cancer. In addition to reviewing recent results, we also discuss methods for studying miRNA activities specifically in adults and evaluate their relative strengths and weaknesses. A fuller understanding of continuous functions of miRNAs in adults has bearing on efforts and opportunities to manipulate miRNAs for therapeutic purposes.

Chronic administration of proanthocyanidins or docosahexaenoic acid reverses the increase of miR-33a and miR-122 in dyslipidemic obese rats

miR-33 and miR-122 are major regulators of lipid metabolism in the liver, and their deregulation has been linked to the development of metabolic diseases such as obesity and metabolic syndrome. However, the biological importance of these miRNAs has been defined using genetic models. The aim of this study was to evaluate whether the levels of miR-122 and miR-33a in rat liver correlate with lipemia in nutritional models. For this purpose, we analyzed the levels of miRNA-33a and miR-122 in the livers of dyslipidemic cafeteria diet-fed rats and of cafeteria diet-fed rats supplemented with proanthocyanidins and/or ω-3 PUFAs because these two dietary components are well-known to counteract dyslipidemia. The results showed that the dyslipidemia induced in rats that were fed a cafeteria diet resulted in the upregulation of miR-33a and miR-122 in the liver, whereas the presence of proanthocyanidins and/or ω-3 PUFAs counteracted the increase of these two miRNAs. However, srebp2, the host gene of miR-33a, was significantly repressed by ω-3 PUFAs but not by proanthocyanidins. Liver mRNA levels of the miR-122 and miR-33a target genes, fas and pparβ/δ, cpt1a and abca1, respectively, were consistent with the expression of these two miRNAs under each condition. Moreover, the miR-33a and abca1 levels were also analyzed in PBMCs. Interestingly, the miR-33a levels evaluated in PBMCs under each condition were similar to the liver levels but enhanced. This demonstrates that miR-33a is expressed in PBMCs and that these cells can be used as a non-invasive way to reflect the expression of this miRNA in the liver. These findings cast new light on the regulation of miR-33a and miR-122 in a dyslipidemic model of obese rats and the way these miRNAs are modulated by dietary components in the liver and in PBMCs.

Lipogenic gene expression profile in patients with gastric cancer

Numerous types of cancer exhibit increased lipogenesis and expression of lipogenic enzymes and transcription factors, including sterol regulatory element-binding protein-1. Lipogenic gene expression is upregulated at the mRNA level, in concert with metabolic pathways associated with changes in expression and/or activity of lipogenic transcription factors. However, this expression pattern in human gastric carcinoma has not been elucidated. In this study, lipogenic gene expression in cancer tissues was investigated using quantitative PCR. In patients with gastric cancer, carnitine O-palmitoyltransferase type I mRNA and miR-33b were significantly downregulated, suggesting that miR-33b downregulation is mediated by conditions that also affect the expression and/or activity of transcription factors involved in lipogenic gene expression. Consequently, the association between miR-33b and gastric cancer may provide a novel strategy for the genetic diagnosis of gastric cancer. However, additional studies including a larger number of samples are required to confirm these results.

Sterol regulatory element binding protein 2 activation of NLRP3 inflammasome in endothelium mediates hemodynamic-induced atherosclerosis susceptibility

BACKGROUND

The molecular basis for the focal nature of atherosclerotic lesions is poorly understood. Here, we explored whether disturbed flow patterns activate an innate immune response to form the NLRP3 inflammasome scaffold in vascular endothelial cells via sterol regulatory element binding protein 2 (SREBP2).

METHODS AND RESULTS

Oscillatory flow activates SREBP2 and induces NLRP3 inflammasome in endothelial cells. The underlying mechanisms involve SREBP2 transactivating NADPH oxidase 2 and NLRP3. Consistently, SREBP2, NADPH oxidase 2, and NLRP3 levels were elevated in atheroprone areas of mouse aortas, suggesting that the SREBP2-activated NLRP3 inflammasome causes functionally disturbed endothelium with increased inflammation. Mimicking the effect of atheroprone flow, endothelial cell-specific overexpression of the activated form of SREBP2 synergized with hyperlipidemia to increase atherosclerosis in the atheroresistant areas of mouse aortas.

CONCLUSIONS

Atheroprone flow induces NLRP3 inflammasome in endothelium through SREBP2 activation. This increased innate immunity in endothelium synergizes with hyperlipidemia to cause topographical distribution of atherosclerotic lesions.

An SREBP-responsive microRNA operon contributes to a regulatory loop for intracellular lipid homeostasis

Sterol regulatory element-binding proteins (SREBPs) have evolved as a focal point for linking lipid synthesis with other pathways that regulate cell growth and survival. Here, we have uncovered a polycistrionic microRNA (miRNA) locus that is activated directly by SREBP-2. Two of the encoded miRNAs, miR-182 and miR-96, negatively regulate the expression of Fbxw7 and Insig-2, respectively, and both are known to negatively affect nuclear SREBP accumulation. Direct manipulation of this miRNA pathway alters nuclear SREBP levels and endogenous lipid synthesis. Thus, we have uncovered a mechanism for the regulation of intracellular lipid metabolism mediated by the concerted action of a pair of miRNAs that are expressed from the same SREBP-2-regulated miRNA locus, and each targets a different protein of the multistep pathway that regulates SREBP function. These studies reveal an miRNA "operon" analogous to the classic model for genetic control in bacterial regulatory systems.

miRNAs link metabolic reprogramming to oncogenesis

The most profound biochemical phenotype of cancer cells is their ability to metabolize glucose to lactate, even under aerobic conditions. This alternative metabolic circuitry is sufficient to support the biosynthetic and energy requirements for cancer cell proliferation and metastasis. Alterations in oncogenes and tumor-suppressor genes are involved in the metabolic switch of cancer cells to aerobic glycolysis, increased glutaminolysis, and fatty acid biosynthesis. miRNAs mediate fine-tuning of genes involved directly or indirectly in cancer metabolism. In this review we discuss the regulatory role of miRNAs on enzymes, signaling pathways, and transcription factors involved in glucose and lipid metabolism. We further consider the therapeutic potential of metabolism-related miRNAs in cancer.

Quest for new biomarkers in atherosclerosis

The Cho and Baldan labs focus their efforts on novel pathways that control atherogenesis. MIF (Macrophage migration inhibitory factor) recruits macrophages to atherosclerotic lesions and activates the production of matrix proteinases, which in turn destabilize atherosclerotic plaques. On the other hand, miR-33 coordinates the expression of several sterol transporters essential for high-density lipoprotein metabolism and bile secretion. Thus, both MIF and miR-33 are promising therapeutic targets to manage patients at risk of developing atherosclerosis.

Evolution of the human-specific microRNA miR-941

MicroRNA-mediated gene regulation is important in many physiological processes. Here we explore the roles of a microRNA, miR-941, in human evolution. We find that miR-941 emerged de novo in the human lineage, between six and one million years ago, from an evolutionarily volatile tandem repeat sequence. Its copy-number remains polymorphic in humans and shows a trend for decreasing copy-number with migration out of Africa. Emergence of miR-941 was accompanied by accelerated loss of miR-941-binding sites, presumably to escape regulation. We further show that miR-941 is highly expressed in pluripotent cells, repressed upon differentiation and preferentially targets genes in hedgehog- and insulin-signalling pathways, thus suggesting roles in cellular differentiation. Human-specific effects of miR-941 regulation are detectable in the brain and affect genes involved in neurotransmitter signalling. Taken together, these results implicate miR-941 in human evolution, and provide an example of rapid regulatory evolution in the human linage.

MicroRNA-30c reduces hyperlipidemia and atherosclerosis in mice by decreasing lipid synthesis and lipoprotein secretion

Hyperlipidemia is a risk factor for various cardiovascular and metabolic disorders. Overproduction of lipoproteins, a process critically dependent on microsomal triglyceride transfer protein (MTP), can contribute to hyperlipidemia. We show that microRNA-30c (miR-30c) interacts with the 3′-untranslated region of the MTP mRNA and induces degradation leading to reductions in its activity and media apolipoprotein B. Further, miR-30c reduces hyperlipidemia and atherosclerosis in Western diet fed mice by decreasing lipid synthesis and secretion of triglyceride-rich apoB-containing lipoproteins. Therefore, miR-30c coordinately reduces lipid biosynthesis and lipoprotein secretion to control hepatic and plasma lipids and might be useful in treating hyperlipidemias and associated disorders.

Affinity analysis of differentially expressed genes in hepatocytes expressing HCV core genotype 1b or 3a

Chronic hepatitis C patients display many genotype-specific clinical features of HCV infection. The core proteins encoded by different genotypes dysregulate numerous sets of distinct host genes. In this study we tested the hypothesis that HCV core proteins 1b and 3a would actually act on a limited number of independent cellular players, as well as on several functionally linked gene products. Structural and functional tests identified a core set of host genes dysregulated by HCV core genotypes 1b and 3a. The core proteins of HCV genotypes 1b and 3a target specifically limited sets of functionally related gene products, which may be responsible for the variations in the clinical spectra associated with HCV infection.

Genome-wide and species-wide in silico screening for intragenic MicroRNAs in human, mouse and chicken

MicroRNAs (miRNAs) are non-coding RNAs (ncRNAs) involved in regulation of gene expression. Intragenic miRNAs, especially those exhibiting a high degree of evolutionary conservation, have been shown to be coordinately regulated and/or expressed with their host genes, either with synergistic or antagonistic correlation patterns. However, the degree of cross-species conservation of miRNA/host gene co-location is not known and co-expression information is incomplete and fragmented among several studies. Using the genomic resources (miRBase and Ensembl) we performed a genome-wide in silico screening (GWISS) for miRNA/host gene pairs in three well-annotated vertebrate species: human, mouse, and chicken. Approximately half of currently annotated miRNA genes resided within host genes: 53.0% (849/1,600) in human, 48.8% (418/855) in mouse, and 42.0% (210/499) in chicken, which we present in a central publicly available Catalog of intragenic miRNAs (http://www.integratomics-time.com/miR-host/catalog). The miRNA genes resided within either protein-coding or ncRNA genes, which include long intergenic ncRNAs (lincRNAs) and small nucleolar RNAs (snoRNAs). Twenty-seven miRNA genes were found to be located within the same host genes in all three species and the data integration from literature and databases showed that most (26/27) have been found to be co-expressed. Particularly interesting are miRNA genes located within genes encoding for miRNA silencing machinery (DGCR8, DICER1, and SND1 in human and Cnot3, Gdcr8, Eif4e, Tnrc6b, and Xpo5 in mouse). We furthermore discuss a potential for phenotype misattribution of miRNA host gene polymorphism or gene modification studies due to possible collateral effects on miRNAs hosted within them. In conclusion, the catalog of intragenic miRNAs and identified 27 miRNA/host gene pairs with cross-species conserved co-location, co-expression, and potential co-regulation, provide excellent candidates for further functional annotation of intragenic miRNAs in health and disease.

Characterization of novel 3'untranslated regions and related polymorphisms of the gene NPPC, encoding for the C-type natriuretic peptide

Elevated plasmatic levels of C-type natriuretic peptide (CNP) were found in patients with chronic heart failure (CHF), but its use as sensitive and specific clinical bio-marker is still controversial. In fact, high levels of CNP were also observed in patients classified in low severity New York Heart Association (NYHA) classes. CNP is encoded by a gene poorly studied (NPPC, natriuretic-precursor peptide C), where the regulatory regions are not well defined and the role of single nucleotide polymorphisms (SNPs) poorly ascertained. In the present work, we focused on the characterization of the 3'untranslated region (3'UTR) of the gene, using Rapid Amplification of cDNA 3'-End (3' RACE), and we identified two novel transcript isoforms (L-3'UTR; S-3'UTR; accession number JF420840, HQ419060 respectively). Since it could be hypothesized that genetic variations could explain the observed inter-patients differences, we searched for novel SNPs, by the use of High Resolution Melting (HRM). The results showed a complete lack of genetic variations among our series of samples. Moreover, a preliminary evaluation, using literature information and bioinformatic prediction allowed us to predicted the putative relevant microRNAs binding to the novel 3'UTRs that could modulate the post-transcriptional regulation of NPPC and affect the plasmatic levels of CNP. We obtained 750 and 1024 predicted miRNAs targeting the S- and L-3'UTRs, respectively.

MicroRNA 33 regulates glucose metabolism

Metabolic diseases are characterized by the failure of regulatory genes or proteins to effectively orchestrate specific pathways involved in the control of many biological processes. In addition to the classical regulators, recent discoveries have shown the remarkable role of small noncoding RNAs (microRNAs [miRNAs]) in the posttranscriptional regulation of gene expression. In this regard, we have recently demonstrated that miR-33a and miR33b, intronic miRNAs located within the sterol regulatory element-binding protein (SREBP) genes, regulate lipid metabolism in concert with their host genes. Here, we show that miR-33b also cooperates with SREBP1 in regulating glucose metabolism by targeting phosphoenolpyruvate carboxykinase (PCK1) and glucose-6-phosphatase (G6PC), key regulatory enzymes of hepatic gluconeogenesis. Overexpression of miR-33b in human hepatic cells inhibits PCK1 and G6PC expression, leading to a significant reduction of glucose production. Importantly, hepatic SREBP1c/miR-33b levels correlate inversely with the expression of PCK1 and G6PC upon glucose infusion in rhesus monkeys. Taken together, these results suggest that miR-33b works in concert with its host gene to ensure a fine-tuned regulation of lipid and glucose homeostasis, highlighting the clinical potential of miR-33a/b as novel therapeutic targets for a range of metabolic diseases.

Therapeutic silencing of microRNA-33 inhibits the progression of atherosclerosis in Ldlr-/- mice--brief report

OBJECTIVE

To study the efficacy of anti-miRNA-33 therapy on the progression of atherosclerosis.

APPROACH AND RESULTS

Ldlr(-/-) mice were injected subcutaneously with PBS, control, or anti-miR-33 oligonucleotides weekly and fed a Western diet for 12 weeks. At the end of treatment, the expression of miR-33 target genes was increased in the liver and aorta, demonstrating effective inhibition of miR-33 function. Interestingly, plasma high-density lipoprotein (HDL)-cholesterol was significantly increased in anti-miR-33-treated mice but only when they were fed a chow diet. However, HDL isolated from anti-miR-33-treated mice showed an increase cholesterol efflux capacity compared with HDL isolated from nontargeting oligonucleotide-treated mice. Analysis of atherosclerosis revealed a significant reduction of plaque size and macrophage content in mice receiving anti-miR-33. In contrast, no differences in collagen content and necrotic areas were observed among the 3 groups.

CONCLUSIONS

Long-term anti-miR-33 therapy significantly reduces the progression of atherosclerosis and improves HDL functionality. The antiatherogenic effect is independent of plasma HDL-cholesterol levels.

Anti-CD38 antibody therapy: windows of opportunity yielded by the functional characteristics of the target molecule

In vivo use of monoclonal antibodies (mAbs) has become a mainstay of routine clinical practice in the treatment of various human diseases. A number of molecules can serve as targets, according to the condition being treated. Now entering human clinical trials, CD38 molecule is a particularly attractive target because of its peculiar pattern of expression and its twin role as receptor and ectoenzyme. This review provides a range of analytical perspectives on the current progress in and challenges to anti-CD38 mAb therapy. We present a synopsis of the evidence available on CD38, particularly in myeloma and chronic lymphocytic leukemia (CLL). Our aim is to make the data from basic science helpful and accessible to a diverse clinical audience and, at the same time, to improve its potential for in vivo use. The topics covered include tissue distribution and signal implementation by mAb ligation and the possibility of increasing cell density on target cells by exploiting information about the molecule's regulation in combination with drugs approved for in vivo use. Also analyzed is the behavior of CD38 as an enzyme: CD38 is a component of a pathway leading to the production of adenosine in the tumor microenvironment, thus inducing local anergy. Consequently, not only might CD38 be a prime target for mAb-mediated therapy, but its functional block may contribute to general improvement in cancer immunotherapy and outcomes.

Therapeutic Potential of Modulating microRNAs in Atherosclerotic Vascular Disease

Atherosclerosis (also known as arteriosclerotic vascular disease) is a chronic inflammatory disease of the arterial wall, characterized by the formation of lipid-laden lesions. The activation of endothelial cells at atherosclerotic lesion-prone sites in the arterial tree results in the up-regulation of cell adhesion molecules and chemokines, which mediate the recruitment of circulating monocytes. Accumulation of monocytes and monocyte-derived phagocytes in the wall of large arteries leads to chronic inflammation and the development and progression of atherosclerosis. The lesion experiences the following steps: foam cell formation, fatty streak accumulation, migration and proliferation of vascular smooth muscle cells, and fibrous cap formation. Finally, the rupture of the unstable fibrous cap causes thrombosis in complications of advanced lesions that lead to unstable coronary syndromes, myocardial infarction and stroke. MicroRNAs have recently emerged as a novel class of gene regulators at the post-transcriptional level. Several functions of vascular cells, such as cell differentiation, contraction, migration, proliferation and inflammation that are involved in angiogenesis, neointimal formation and lipid metabolism underlying various vascular diseases, have been found to be regulated by microRNAs and are described in the present review as well as their potential therapeutic application.

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.

Impaired cholesterol efflux in senescent macrophages promotes age-related macular degeneration

Pathologic angiogenesis mediated by abnormally polarized macrophages plays a central role in common age-associated diseases such as atherosclerosis, cancer, and macular degeneration. Here we demonstrate that abnormal polarization in older macrophages is caused by programmatic changes that lead to reduced expression of ATP binding cassette transporter ABCA1. Downregulation of ABCA1 by microRNA-33 impairs the ability of macrophages to effectively efflux intracellular cholesterol, which in turn leads to higher levels of free cholesterol within senescent macrophages. Elevated intracellular lipid polarizes older macrophages to an abnormal, alternatively activated phenotype that promotes pathologic vascular proliferation. Mice deficient for Abca1, but not Abcg1, demonstrate an accelerated aging phenotype, whereas restoration of cholesterol efflux using LXR agonists or miR-33 inhibitors reverses it. Monocytes from older humans with age-related macular degeneration showed similar changes. These findings provide an avenue for therapeutic modulation of macrophage function in common age-related diseases.

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.

MicroRNA-144 regulates hepatic ATP binding cassette transporter A1 and plasma high-density lipoprotein after activation of the nuclear receptor farnesoid X receptor

RATIONALE

The bile acid receptor farnesoid X receptor (FXR) regulates many aspects of lipid metabolism by variouscomplex and incompletely understood molecular mechanisms. We set out to investigate the molecular mechanisms for FXR-dependent regulation of lipid and lipoprotein metabolism.

OBJECTIVE

To identify FXR-regulated microRNAs that were subsequently involved in regulating lipid metabolism.

METHODS AND RESULTS

ATP binding cassette transporter A1 (ABCA1) is a major determinant of plasma high-density lipoprotein (HDL)-cholesterol levels. Here, we show that activation of the nuclear receptor FXR in vivo increases hepatic levels of miR-144, which in turn lowers hepatic ABCA1 and plasma HDL levels. We identified 2 complementary sequences to miR-144 in the 3' untranslated region of ABCA1 mRNA that are necessary for miR-144-dependent regulation. Overexpression of miR-144 in vitro decreased both cellular ABCA1 protein and cholesterol efflux to lipid-poor apolipoprotein A-I protein, whereas overexpression in vivo reduced hepatic ABCA1 protein and plasma HDL-cholesterol. Conversely, silencing miR-144 in mice increased hepatic ABCA1 protein and HDL-cholesterol. In addition, we used tissue-specific FXR-deficient mice to show that induction of miR-144 and FXR-dependent hypolipidemia requires hepatic, but not intestinal, FXR. Finally, we identified functional FXR response elements upstream of the miR-144 locus, consistent with direct FXR regulation.

CONCLUSIONS

We have identified a novel pathway involving FXR, miR-144, and ABCA1 that together regulate plasma HDL-cholesterol.

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.

Needles in the genetic haystack of lipid disorders: single nucleotide polymorphisms in the microRNA regulome

In recent years, microRNAs (miRNA) have emerged as important posttranscriptional regulators of gene expression in a wide variety of biological pathways. Since the discovery of the liver-specific miRNA-122 (miR-122) and its critical role in hepatic function, numerous additional miRNAs have been implicated in lipid metabolism. It is now apparent that lipid homeostasis is governed in part by an intricate web of miRNA activity. miRNAs are thought to confer robustness against environmental changes, such as diet modifications. Therefore, naturally occurring genetic variation that perturbs miRNA expression and/or function is likely to contribute to interindividual variability in lipid phenotypes. Although the field is still in its infancy, this review describes the growing evidence for miRNA-related genetic variation as etiological factors in lipid disorders. Specific examples, including a variant in a miRNA transcriptional control element that leads to dyslipidemia as well as a variant in a miRNA target site that modulates the effect of diet on plasma lipid levels, are discussed. Finally, the utility of recent systems genetics approaches to uncover hidden miRNA-related genetic associations with lipid disorders are considered, thereby illuminating the needles in the genetic haystack.

Complexity of microRNA function and the role of isomiRs in lipid homeostasis

MicroRNAs (miRNAs) are key posttranscriptional regulators of biological pathways that govern lipid metabolic phenotypes. Recent advances in high-throughput small RNA sequencing technology have revealed the complex and dynamic repertoire of miRNAs. Specifically, it has been demonstrated that a single genomic locus can give rise to multiple, functionally distinct miRNA isoforms (isomiR). There are several mechanisms by which isomiRs can be generated, including processing heterogeneity and posttranscriptional modifications, such as RNA editing, exonuclease-mediated nucleotide trimming, and/or nontemplated nucleotide addition (NTA). NTAs are dominant at the 3'-end of a miRNA, are most commonly uridylation or adenlyation events, and are catalyzed by one or more of several nucleotidyl transferase enzymes. 3' NTAs can affect miRNA stability and/or activity and are physiologically regulated, whereas modifications to the 5'-ends of miRNAs likely alter miRNA targeting activity. Recent evidence also suggests that the biogenesis of specific miRNAs, or small RNAs that act as miRNAs, can occur through unconventional mechanisms that circumvent key canonical miRNA processing steps. The unveiling of miRNA diversity has significantly added to our view of the complexity of miRNA function. In this review we present the current understanding of the biological relevance of isomiRs and their potential role in regulating lipid metabolism.

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.

Upregulation of miR-15b in NAFLD models and in the serum of patients with fatty liver disease

AIM

In the present study, we examined the expression and function of miR-15b in a rat model of non-alcoholic fatty liver disease (NAFLD), and we determined whether the presence of miR-15b in serum can be used as a biomarker for this disease.

METHODS

We measured the expression of miR-15b in both the high-fat-induced non-alcoholic fatty liver disease (NAFLD) SD rat model and in the palmitate-induced NAFLD L02 cell model. Following transfection of miR-15b into QSG7701 cells, cell proliferation, glucose consumption and intracellular triglyceride levels were measured. We also measured the levels of miR-15b in the serum of fatty liver disease patients using real-time PCR.

RESULTS

We found that miR-15b was upregulated in the livers of NAFLD SD rats as well as in NAFLD L02 cells. Increased miR-15b levels could cause decreased cell proliferation and glucose consumption as well as induce the storage of intracellular triglyceride in QSG7701 cells. The expression of miR-15b was also significantly elevated in the serum of fatty liver disease patients compared with healthy subjects.

CONCLUSIONS

Increased miR-15b expression in NAFLD models may lead to decreased cell proliferation and glucose consumption while inducing the storage of intracellular triglyceride, which are all hazards of NAFLD. Therefore, increased serum miR-15b level is a potentially biomarker for the diagnosis of fatty liver disease.

MicroRNA-33a functions as a bone metastasis suppressor in lung cancer by targeting parathyroid hormone related protein

BACKGROUND

Bone is a common site of metastasis for lung cancer, and is associated with significant morbidity and a dismal prognosis. MicroRNAs (miRNAs) are increasingly implicated in regulating the progression of malignancies.

METHODS

The efficacy of miR-33a or anti-miR-33a plasmid was assessed by Real-time PCR. Luciferase assays were using One-Glo Luciferase Assay System. Measurement of secreted factors was determined by ELISA kit.

RESULTS

We have found that miR-33a, which is downregulated in lung cancer cells, directly targets PTHrP (parathyroid hormone-related protein), a potent stimulator of osteoclastic bone resorption, leading to decreased osteolytic bone metastasis. We also found that miR-33a levels are inversely correlated with PTHrP expression between human normal bronchial cell line and lung cancer cell lines. The reintroduction of miR-33a reduces the stimulatory effect of A549 on the production of osteoclastogenesis activator RANKL (receptor activator of nuclear factor kappa-B ligand) and M-CSF (macrophage colony-stimulating factor) on osteoblasts, while the expression of PTHrP is decreased in A549 cells. miR-33a overexpression also reduces the inhibitory activity of A549 on the production of OPG (osteoprotegerin), an osteoclastogenesis inhibitor. In addition, miR-33a-mediated PTHrP downregulation results in decreased IL-8 secretion in A549, which contributes to decreased lung cancer-mediated osteoclast differentiation and bone resorption.

CONCLUSIONS

These findings have led us to conclude that miR-33a may be a potent tumor suppressor, which inhibits direct and indirect osteoclastogenesis through repression of PTHrP.

GENERAL SIGNIFICANCE

miR-33a may even predict a poor prognosis for lung cancer patients.