Antagonism of microRNA-122 in mice by systemically administered LNA-antimiR leads to up-regulation of a large set of predicted target mRNAs in the liver

Potent inhibition of microRNA in vivo without degradation

Chemically modified antisense oligonucleotides (ASOs) are widely used as a tool to functionalize microRNAs (miRNAs). Reduction of miRNA level after ASO inhibition is commonly reported to show efficacy. Whether this is the most relevant endpoint for measuring miRNA inhibition has not been adequately addressed in the field although it has important implications for evaluating miRNA targeting studies. Using a novel approach to quantitate miRNA levels in the presence of excess ASO, we have discovered that the outcome of miRNA inhibition can vary depending on the chemical modification of the ASO. Although some miRNA inhibitors cause a decrease in mature miRNA levels, we have identified a novel 2′-fluoro/2′-methoxyethyl modified ASO motif with dramatically improved in vivo potency which does not. These studies show there are multiple mechanisms of miRNA inhibition by ASOs and that evaluation of secondary endpoints is crucial for interpreting miRNA inhibition studies.

miRecords: an integrated resource for microRNA-target interactions

MicroRNAs (miRNAs) are an important class of small noncoding RNAs capable of regulating other genes’ expression. Much progress has been made in computational target prediction of miRNAs in recent years. More than 10 miRNA target prediction programs have been established, yet, the prediction of animal miRNA targets remains a challenging task. We have developed miRecords, an integrated resource for animal miRNA–target interactions. The Validated Targets component of this resource hosts a large, high-quality manually curated database of experimentally validated miRNA–target interactions with systematic documentation of experimental support for each interaction. The current release of this database includes 1135 records of validated miRNA–target interactions between 301 miRNAs and 902 target genes in seven animal species. The Predicted Targets component of miRecords stores predicted miRNA targets produced by 11 established miRNA target prediction programs. miRecords is expected to serve as a useful resource not only for experimental miRNA researchers, but also for informatics scientists developing the next-generation miRNA target prediction programs. The miRecords is available at http://miRecords.umn.edu/miRecords.

Toward microRNA-based therapeutics for heart disease: the sense in antisense

MicroRNAs act as negative regulators of gene expression by inhibiting the translation or promoting the degradation of target mRNAs. Because individual microRNAs often regulate the expression of multiple target genes with related functions, modulating the expression of a single microRNA can, in principle, influence an entire gene network and thereby modify complex disease phenotypes. Recent studies have identified signature expression patterns of microRNAs associated with pathological cardiac hypertrophy, heart failure, and myocardial infarction in humans and mouse models of heart disease. Gain- and loss-of-function studies in mice have revealed profound and unexpected functions for these microRNAs in numerous facets of cardiac biology, including the control of myocyte growth, contractility, fibrosis, and angiogenesis, providing glimpses of new regulatory mechanisms and potential therapeutic targets for heart disease. Especially intriguing is the discovery of a network of muscle-specific microRNAs embedded within myosin heavy chain genes, which control myosin expression and the response of the heart to stress and thyroid hormone signaling. Disease-inducing cardiac microRNAs can be persistently silenced in vivo through systemic delivery of antimiRs, allowing for the direct therapeutic modulation of disease mechanisms. Here, we summarize current knowledge of the roles of miRNAs in heart disease and consider the advantages and potential challenges of microRNA-based approaches compared to conventional drug-based therapies.

Epigenetic modifications in rheumatoid arthritis

Over the last decades, genetic factors for rheumatoid diseases like the HLA haplotypes have been studied extensively. However, during the past years of research, it has become more and more evident that the influence of epigenetic processes on the development of rheumatic diseases is probably as strong as the genetic background of a patient. Epigenetic processes are heritable changes in gene expression without alteration of the nucleotide sequence. Such modifications include chromatin methylation and post-translational modification of histones or other chromatin-associated proteins. The latter comprise the addition of methyl, acetyl, and phosphoryl groups or even larger moieties such as binding of ubiquitin or small ubiquitin-like modifier. The combinatory nature of these processes forms a complex network of epigenetic modifications that regulate gene expression through activation or silencing of genes. This review provides insight into the role of epigenetic alterations in the pathogenesis of rheumatoid arthritis and points out how a better understanding of such mechanisms may lead to novel therapeutic strategies.

Vitamin E dependent microRNA regulation in rat liver

Dietary vitamin E (VE) is known to regulate gene expression by altering mRNA concentrations. Recently, microRNA (miRNA) have been discovered as a means of posttranscriptional gene regulation. Since the effect of VE on miRNA regulation is unknown, we fed rats for 6 months diets deficient or sufficient in VE and determined hepatic concentrations of miRNA involved in processes previously associated with VE (lipid metabolism, miRNA-122a; cancer and inflammation, miRNA-125b). VE-deficiency resulted in reduced concentrations of miRNA-122a and miRNA-125b. The findings of the present study demonstrate that differences in dietary VE may affect hepatic miRNA concentrations in vivo.

MicroRNA epigenetic alterations: predicting biomarkers and therapeutic targets in human diseases

MicroRNAs (miRNAs) consist of a class of evolutionarily conserved small non-coding RNA that regulates target messenger RNAs by mechanisms such as incomplete base pairing and post-transcriptional gene silencing. Recent studies have shown that aberrant miRNA expression is a common feature of many human disorders including aging, heart diseases, cancer, autoimmune diseases and others. It seems likely that miRNA expression levels can be used as novel diagnostic markers. MiRNAs may also provide a new strategy for therapeutic interventions. In this review, we focus on recent advances in understanding how miRNA changes contribute to disease development and their potential as novel biomarkers and therapeutic targets for human diseases.

MicroRNA: An emerging therapeutic target and intervention tool

MicroRNAs (miRNAs) are a class of short non-coding RNAs with posttranscriptional regulatory functions. To date, more than 600 human miRNAs have been experimentally identified, and estimated to regulate more than one third of cellular messenger RNAs. Accumulating evidence has linked the dysregulated expression patterns of miRNAs to a variety of diseases, such as cancer, neurodegenerative diseases, cardiovascular diseases and viral infections. MiRNAs provide its particular layer of network for gene regulation, thus possessing the great potential both as a novel class of therapeutic targets and as a powerful intervention tool. In this regard, synthetic RNAs that contain the binding sites of miRNA have been shown to work as a “decoy” or “miRNA sponge” to inhibit the function of specific miRNAs. On the other hand, miRNA expression vectors have been used to restore or overexpress specific miRNAs to achieve a long-term effect. Further, double-stranded miRNA mimetics for transient replacement have been experimentally validated. Endogenous precursor miRNAs have also been used as scaffolds for the induction of RNA interference. This article reviews the recent progress on this emerging technology as a powerful tool for gene regulation studies and particularly as a rationale strategy for design of therapeutics.

Human chromosome 21-derived miRNAs are overexpressed in down syndrome brains and hearts

Down syndrome (DS), or Trisomy 21, is the most common genetic cause of cognitive impairment and congenital heart defects in the human population. To date, the contribution of microRNAs (miRNAs) in DS has not been investigated. Bioinformatic analyses demonstrate that human chromosome 21 (Hsa21) harbors five miRNA genes; miR-99a, let-7c, miR-125b-2, miR-155, and miR-802. MiRNA expression profiling, miRNA RT-PCR, and miRNA in situ hybridization experiments demonstrate that these miRNAs are overexpressed in fetal brain and heart specimens from individuals with DS when compared with age- and sex-matched controls. We hypothesize that trisomic 21 gene dosage overexpression of Hsa21-derived miRNAs results in the decreased expression of specific target proteins and contribute, in part, to features of the neuronal and cardiac DS phenotype. Importantly, Hsa21-derived miRNAs may provide novel therapeutic targets in the treatment of individuals with DS.

LNA-mediated microRNA silencing in non-human primates

microRNAs (miRNAs) are small regulatory RNAs that are important in development and disease and therefore represent a potential new class of targets for therapeutic intervention. Despite recent progress in silencing of miRNAs in rodents, the development of effective and safe approaches for sequence-specific antagonism of miRNAs in vivo remains a significant scientific and therapeutic challenge. Moreover, there are no reports of miRNA antagonism in primates. Here we show that the simple systemic delivery of a unconjugated, PBS-formulated locked-nucleic-acid-modified oligonucleotide (LNA-antimiR) effectively antagonizes the liver-expressed miR-122 in non-human primates. Acute administration by intravenous injections of 3 or 10 mg kg(-1) LNA-antimiR to African green monkeys resulted in uptake of the LNA-antimiR in the cytoplasm of primate hepatocytes and formation of stable heteroduplexes between the LNA-antimiR and miR-122. This was accompanied by depletion of mature miR-122 and dose-dependent lowering of plasma cholesterol. Efficient silencing of miR-122 was achieved in primates by three doses of 10 mg kg(-1) LNA-antimiR, leading to a long-lasting and reversible decrease in total plasma cholesterol without any evidence for LNA-associated toxicities or histopathological changes in the study animals. Our findings demonstrate the utility of systemically administered LNA-antimiRs in exploring miRNA function in rodents and primates, and support the potential of these compounds as a new class of therapeutics for disease-associated miRNAs.

No miRNA were found in Plasmodium and the ones identified in erythrocytes could not be correlated with infection

Background

The transcriptional regulation of Plasmodium during its complex life cycle requires sequential activation and/or repression of different genetic programmes. MicroRNAs (miRNAs) are a highly conserved class of non-coding RNAs that are important in regulating diverse cellular functions by sequence-specific inhibition of gene expression. What is know about double-stranded RNA-mediated gene silencing (RNAi) and posttranscriptional gene silencing (PTGS) in Plasmodium parasites entice us to speculate whether miRNAs can also function in Plasmodium-infected RBCs.

Results

Of 132 small RNA sequences, no Plasmodium-specific miRNAs have been found. However, a human miRNA, miR-451, was highly expressed, comprising approximately one third of the total identified miRNAs. Further analysis of miR-451 expression and malaria infection showed no association between the accumulation of miR-451 in Plasmodium falciparum-iRBCs, the life cycle stage of P. falciparum in the erythrocyte, or of P. berghei in mice. Moreover, treatment with an antisense oligonucleotide to miR-451 had no significant effect on the growth of the erythrocytic-stage P. falciparum.

Methods

Short RNAs from a mixed-stage of P. falciparum-iRBC were separated in a denaturing polyacrylamide gel and cloned into T vectors to create a cDNA library. Individual clones were then sequenced and further analysed by bioinformatics prediction to discover probable miRNAs in P. falciparum-iRBC. The association between miR-451 expression and the parasite were analysed by Northern blotting and antisense oligonucleotide (ASO) of miR-451.

Conclusion

These results contribute to eliminate the probability of miRNAs in P. falciparum. The absence of miRNA in P. falciparum could be correlated with absence of argonaute/dicer genes. In addition, the miR-451 accumulation in Plasmodium-infected RBCs is independent of parasite infection. Its accumulation might be only the residual of erythroid differentiation or a component to maintain the normal function of mature RBCs.

miRNAs: effectors of environmental influences on gene expression and disease

Discovered less than a decade ago, micro-RNAs (miRNAs) have emerged as important regulators of gene expression in mammals. They consist of short nucleic acids, on average approximately 22 nucleotides in length. The miRNAs exert their effect by binding directly to target messenger RNAs (mRNAs) and inhibiting mRNA stability and translation. Each miRNA can bind to multiple targets and many miRNAs can bind to the same target mRNA, allowing for a complex pattern of regulation of gene expression. Once bound to their targets, miRNAs can suppress translation of the mRNA by either sequestration or degradation of the message. Thus, miRNAs function as powerful and sensitive posttranscriptional regulators of gene expression. This review will summarize what is known about miRNA biogenesis, expression, regulation, function, mode of action, and role in disease processes with an emphasis on miRNAs in mammals. We discuss some of the methodology employed in miRNA research and the potential of miRNAs as therapeutic targets. The role of miRNAs in signal transduction and cellular stress is reviewed. Lastly, we identify new exciting avenues of research on the role of miRNAs in toxicogenomics and the possibility of epigenetic effects on gene expression.

The utility of LNA in microRNA-based cancer diagnostics and therapeutics

MicroRNAs (miRNAs) are a novel class of small endogenous non-coding RNAs that regulate gene expression post-transcriptionally by binding to their cognate target mRNAs. Emerging evidence implies that miRNAs play important roles in cancer and thus, miRNAs have rapidly emerged as valuable markers for cancer diagnostics and promising targets for therapeutics. Locked nucleic acid (LNA) is a conformational RNA analoque that binds complementary RNA with unprecedented affinity and specificity. These properties make LNA well suited for miRNA detection and analysis for cancer diagnostics. Furthermore, recent studies on LNA-mediated silencing of miRNA function in vitro and in vivo support the potential of LNA in therapeutic intervention of cancer-associated miRNAs.

Serum CA 125 levels in early pregnancy and subsequent spontaneous abortion

Cardiovascular diseases are the most common causes of human morbidity and mortality despite significant therapeutic improvements by surgical, interventional and pharmacological approaches in the last decade. MicroRNAs (miRNAs) are important and powerful mediators in a wide range of diseases and thus emerged as interesting new drug targets. An array of animal and even human miRNA-based therapeutic studies has been performed, which validate miRNAs as being successfully targetable to treat a wide range of diseases. Here, the current knowledge about miRNAs therapeutics in cardiovascular diseases on their way to clinical use are reviewed and discussed.