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Circular RNAs (circRNAs) are a class of endogenously expressed regulatory RNAs with a single-stranded circular structure. They are generated by back splicing and their expression can be tightly regulated by RNA binding proteins. Cytoplasmic circRNAs can function as molecular sponges that inhibit microRNA-target interactions and protein function or as templates for the efficient generation of peptides via rolling circle amplification. They can also act as molecular scaffolds that enhance the reaction kinetics of enzyme-substrate interactions. In the nucleus, circRNAs might facilitate chromatin modifications and promote gene expression. CircRNAs are resistant to degradation and can be packaged in extracellular vesicles and transported in the circulation. Initial studies suggest that circRNAs have roles in kidney disease and associated cardiovascular complications. They have been implicated in hypertensive nephropathy, diabetic kidney disease, glomerular disease, acute kidney injury and kidney allograft rejection, as well as in microvascular and macrovascular complications of chronic kidney disease, including atherosclerotic vascular disease. In addition, several circRNAs have been reported to have oncogenic or tumour suppressor roles or to regulate drug resistance in kidney cancer. The available data suggest that circRNAs could be promising diagnostic and/or prognostic biomarkers and potential therapeutic targets for kidney disease, cardiovascular disease and kidney cancer., (© 2021. Springer Nature Limited.)

Background: Renal ischemia-reperfusion (I/R) injury is a major cause of AKI. Noncoding RNAs are intricately involved in the pathophysiology of this form of AKI. Transcription of hypoxia-induced, long noncoding RNA H19 , which shows high embryonic expression and is silenced in adults, is upregulated in renal I/R injury., Methods: Lentivirus-mediated overexpression, as well as antisense oligonucleotide-based silencing, modulated H19 in vitro . In vivo analyses used constitutive H19 knockout mice. In addition, renal vein injection of adeno-associated virus 2 (AAV2) carrying H19 caused overexpression in the kidney. Expression of H19 in kidney transplant patients with I/R injury was investigated., Results: H19 is upregulated in kidney biopsies of patients with AKI, in murine ischemic kidney tissue, and in cultured and ex vivo sorted hypoxic endothelial cells (ECs) and tubular epithelial cells (TECs). Transcription factors hypoxia-inducible factor 1- α , LHX8, and SPI1 activate H19 in ECs and TECs. H19 overexpression promotes angiogenesis in vitro and in vivo. In vivo , transient AAV2-mediated H19 overexpression significantly improved kidney function, reduced apoptosis, and reduced inflammation, as well as preserving capillary density and tubular epithelial integrity. Sponging of miR-30a-5p mediated the effects, which, in turn, led to target regulation of Dll4, ATG5, and Snai1., Conclusions: H19 overexpression confers protection against renal injury by stimulating proangiogenic signaling. H19 overexpression may be a promising future therapeutic option in the treatment of patients with ischemic AKI., (Copyright © 2021 by the American Society of Nephrology.)

Accurate determination of microRNA expression levels is a prerequisite in using these small non-coding RNA molecules as novel biomarkers in disease diagnosis and prognosis. Quantitative PCR is the method of choice for measuring the expression levels of microRNAs. However, a major obstacle that affects the reliability of results is the lack of validated reference controls for data normalization. Various non-coding RNAs have previously been used as reference controls, but their use may lead to variations and lack of comparability of microRNA data among the studies. Despite the growing number of studies investigating microRNA profiles to discriminate between healthy and disease stages, robust reference controls for data normalization have so far not been established. In the present article, we provide an overview of different reference controls used in various diseases, and highlight the urgent need for the identification of suitable reference controls to produce reliable data. Our analysis shows, among others, that RNU6 is not an ideal normalizer in studies using patient material from different diseases. Finally, our article tries to disclose the challenges to find a reference control which is uniformly and stably expressed across all body tissues, fluids, and diseases.

MicroRNAs (miRs) are small non-coding RNAs that regulate gene expression in physiological processes as well as in diseases. Currently miRs are already used to find novel mechanisms involved in diseases and in the future, they might serve as diagnostic markers. To identify miRs that play a role in glomerular diseases urinary miR-screenings are a frequently used tool. However, miRs that are detected in the urine might simply be filtered from the blood stream and could have been produced anywhere in the body, so they might be completely unrelated to the diseases. We performed a combined miR-screening in pooled urine samples from patients with different glomerular diseases as well as in cultured human podocytes, human mesangial cells, human glomerular endothelial cells and human tubular cells. The miR-screening in renal cells was done in untreated conditions and after stimulation with TGF-β. A merge of the detected regulated miRs led us to identify disease-specific, cell type-specific and cell stress-induced miRs. Most miRs were down-regulated following the stimulation with TGF-β in all cell types. Up-regulation of miRs after TGF-β was cell type-specific for most miRs. Furthermore, urinary miRs from patients with different glomerular diseases could be assigned to the different renal cell types. Most miRs were specifically regulated in one disease. Only miR-155 was up-regulated in all disease urines compared to control and therefore seems to be rather unspecific. In conclusion, a combined urinary and cell miR-screening can improve the interpretation of screening results. These data are useful to identify novel miRs potentially involved in glomerular diseases., (© 2019 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.)

Acute kidney injury (AKI) is a disease entity of major importance, affecting approximately 6% of all patients on the intensive care unit. The mortality rate exceeds 60%. AKI is related to several underlying conditions, including sepsis, nephrotoxicity or major surgery. Ischaemia reperfusion injury or hypoxic conditions may lead to severe injury of the kidney and is associated with a steep decline in survival rates of patients. At present, AKI is diagnosed on the basis of creatinine levels and urine output. Novel markers and knowledge of their pathophysiological role is of major importance for targeted therapeutic interventions. Noncoding RNAs (ncRNAs) have recently been introduced and are the subject of intensive research initiatives. They are arbitrarily separated into small ncRNAs (≤200 nucleotides) and long ncRNAs (lncRNAs, ≥200 nucleotides). Whereas small ncRNAs such as microRNAs have been extensively studied over the past several years, investigations into the role of linear lncRNAs and circular RNAs (circRNAs) are largely lacking. The present review article therefore aims to elucidate in detail the role of microRNAs, lncRNAs and circRNAs in animal models as well as patients with ischaemic AKI and to describe their use as biomarkers as well as their potential use as therapeutics.

The pathophysiology of many proteinuric kidney diseases is poorly understood, and microRNAs (miRs) regulation of these diseases has been largely unexplored. Here, we tested whether miR-378a-3p is a novel regulator of glomerular diseases. MiR-378a-3p has two predicted targets relevant to glomerular function, the glomerular basement membrane matrix component, nephronectin (NPNT), and vascular endothelial growth factor VEGF-A. In zebrafish (Danio rerio), miR-378a-3p mimic injection or npnt knockdown by a morpholino oligomer caused an identical phenotype consisting of edema, proteinuria, podocyte effacement, and widening of the glomerular basement membrane in the lamina rara interna. Zebrafish vegf-A protein could not rescue this phenotype. However, mouse Npnt constructs containing a mutated 3'UTR region prevented the phenotype caused by miR-378a-3p mimic injection. Overexpression of miR-378a-3p in mice confirmed glomerular dysfunction in a mammalian model. Biopsies from patients with focal segmental glomerulosclerosis and membranous nephropathy had increased miR-378a-3p expression and reduced glomerular levels of NPNT. Thus, miR-378a-3p-mediated suppression of the glomerular matrix protein NPNT is a novel mechanism for proteinuria development in active glomerular diseases., (Copyright © 2017 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Chronic renal allograft dysfunction (CAD) is a major limiting factor of long-term graft survival. It is characterized by interstitial fibrosis and tubular atrophy. The underlying pathomechanisms are incompletely understood. MicroRNAs are powerful regulators of gene expression and may have an impact on various diseases by direct mRNA decay or translational inhibition. A murine model of allogenic kidney transplantation was used resulting in CAD at 6 weeks after kidney transplantation. We identified fibrosis-associated miR-21a-5p by whole miRNAome expression analysis to be among the most highly upregulated miRNAs. In vitro in renal fibroblasts, miR-21a-5p was transcriptionally activated by interleukin 6-induced signal transducer and activator of transcription 3. Co-culture of LPS-activated macrophages with renal fibroblasts increased expression levels of miR-21a-5p and markers of fibrosis and inflammation. In addition, mature miR-21a-5p was secreted by macrophages in small vesicles, which were internalized by renal fibroblasts, thereby promoting profibrotic and proinflammatory effects. Notch2 receptor was identified as a potential target of miR-21a-5p and validated by luciferase gene reporter assays. Therapeutic silencing of miR-21a-5p in mice after allogenic kidney transplantation resulted in an amelioration of CAD, as indicated by a reduction in fibrosis development, inflammatory cell influx, tissue injury and BANFF lesion scoring. In a life-supporting model, miR-21a-5p antagonism had beneficial effects on kidney function. miR-21a-5p silencing may therefore be a viable therapeutic option in the treatment of patients following kidney transplantation to halt the development of CAD., (Copyright © 2017 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.)

Diabetic nephropathy is the main cause of end-stage renal disease. MicroRNAs are powerful regulators of the genome, and global expression profiling revealed miR-21 to be among the most highly regulated microRNAs in kidneys of mice with diabetic nephropathy. In kidney biopsies of diabetic patients, miR-21 correlated with tubulointerstitial injury. In situ PCR analysis showed a specific enrichment of miR-21 in glomerular cells. We identified cell division cycle 25a (Cdc25a) and cyclin-dependent kinase 6 (Cdk6) as novel miR-21 targets in mesangial cells. miR-21-mediated repression of Cdc25a and Cdk6 resulted in impaired cell cycle progression and subsequent mesangial cell hypertrophy. miR-21 increased podocyte motility by regulating phosphatase and tensin homolog (Pten). miR-21 antagonism in vitro and in vivo in streptozotocin-induced diabetic mice decreased mesangial expansion, interstitial fibrosis, macrophage infiltration, podocyte loss, albuminuria, and fibrotic- and inflammatory gene expression. In conclusion, miR-21 antagonism rescued various functional and structural parameters in mice with diabetic nephropathy and, thus, might be a viable option in the treatment of patients with diabetic kidney disease., (Copyright © 2017 The American Society of Gene and Cell Therapy. Published by Elsevier Inc. All rights reserved.)

Background: TGF-β is known as an important stress factor of podocytes in glomerular diseases. Apart from activation of direct pro-apoptotic pathways we wanted to analyze micro-RNA (miRs) driven regulation of components involved in the integrity of the glomerular filtration barrier induced by TGF-β. Since miR-143-3p (miR-143) is described as a TGF-β inducible miR in other cell types, we examined this specific miR and its ability to induce glomerular pathology., Methods: We analyzed miR-143 expression in cultured human podocytes after stimulation with TGF-β. We also microinjected zebrafish eggs with a miR-143 mimic or with morpholinos specific for its targets syndecan and versican and compared phenotype and proteinuria development., Results: We detected a time dependent, TGF-β inducible expression of miR-143 in human podocytes. Targets of miR-143 relevant in glomerular biology are syndecans and versican, which are known components of the glycocalyx. We found that syndecan 1 and 4 were predominantly expressed in podocytes while syndecan 3 was largely expressed in glomerular endothelial cells. Versican could be detected in both cell types. After injection of a miR-143 mimic in zebrafish larvae, syndecan 3, 4 and versican were significantly downregulated. Moreover, miR-143 overexpression or versican knockdown by morpholino caused loss of plasma proteins, edema, podocyte effacement and endothelial damage. In contrast, knockdown of syndecan 3 and syndecan 4 had no effects on glomerular filtration barrier., Conclusion: Expression of versican and syndecan isoforms is indispensable for proper barrier function. Podocyte-derived miR-143 is a mediator for paracrine and autocrine cross talk between podocytes and glomerular endothelial cells and can alter expression of glomerular glycocalyx proteins., (© 2016 The Author(s) Published by S. Karger AG, Basel.)

Background: Hypertrophic cardiomyopathy (HCM) is caused by mutations in different structural genes and induces pathological hypertrophy with sudden cardiac death as a possible consequence. HCM can be separated into hypertrophic non-obstructive and obstructive cardiomyopathy (HNCM/HOCM) with different clinical treatment approaches. We here distinguished between HNCM, HOCM, cardiac amyloidosis and aortic stenosis by using microRNA profiling and investigated potential interactions between circulating miRNA levels and the most common mutations in MYH7and MYBPC3 genes., Methods: Our study included 4 different groups: 23 patients with HNCM, 28 patients with HOCM, 47 patients with aortic stenosis and 22 healthy controls. Based on previous findings, 8 different cardiovascular known microRNAs (miR-1, miR-21, miR-29a, miR-29b, miR-29c, miR-133a, miR-155 and miR-499) were studied in serum of all patients and compared with clinically available patient data., Results: We found miR-29a levels to be increased in patients with HOCM and correlating markers of cardiac hypertrophy. This was not the case in HNCM patients. In contrast, we identified miR-29c to be upregulated in aortic stenosis but not the other patient groups. ROC curve analysis of miR-29a/c distinguished between HOCM patients and aortic stenosis patients. MiR-29a and miR-155 levels discriminated HNCM patients from patients with senile cardiac amyloidosis. MiR-29a increased mainly in HOCM patients with a mutation in MYH7, whereas miR-155 was decreased in hypertrophic cardiomyopathy patients with a mutation in MYBPC3., Conclusion: We demonstrated that miR-29a and miR-29c show a specific signature to distinguish between aortic stenosis, hypertrophic non-obstructive and obstructive cardiomyopathies and thus could be developed into clinically useful biomarkers., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Aims: Osteopontin (OPN) is a multifunctional cytokine critically involved in cardiac fibrosis. However, the underlying mechanisms are unresolved. Non-coding RNAs are powerful regulators of gene expression and thus might mediate this process., Methods and Results: OPN and miR-21 were significantly increased in cardiac biopsies of patients with myocardial fibrosis. Ang II infusion via osmotic minipumps led to specific miRNA regulations with miR-21 being strongly induced in wild-type (WT) but not OPN knockout (KO) mice. This was associated with enhanced cardiac collagen content, myofibroblast activation, ERK-MAP kinase as well as AKT signalling pathway activation and a reduced expression of Phosphatase and Tensin Homologue (PTEN) as well as SMAD7 in WT but not OPN KO mice. In contrast, cardiotropic AAV9-mediated overexpression of OPN in vivo further enhanced cardiac fibrosis. In vitro, Ang II induced expression of miR-21 in WT cardiac fibroblasts, while miR-21 levels were unchanged in OPN KO fibroblasts. As pri-miR-21 was also increased by Ang II, we studied potential involved upstream regulators; Electrophoretic Mobility Shift and Chromatin Immunoprecipitation analyses confirmed activation of the miR-21 upstream-transcription factor AP-1 by Ang II. Recombinant OPN directly activated miR-21, enhanced fibrosis, and activated the phosphoinositide 3-kinase pathway. Locked nucleic acid-mediated miR-21 silencing ameliorated cardiac fibrosis development in vivo., Conclusion: In cardiac fibrosis related to Ang II, miR-21 is transcriptionally activated and targets PTEN/SMAD7 resulting in increased fibroblast survival. OPN KO animals are protected from miR-21 increase and fibrosis development due to impaired AP-1 activation and fibroblast activation., (© The Author 2015. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Objective: MicroRNAs (miRNA/miR) are stably present in body fluids and are increasingly explored as disease biomarkers. Here, we investigated influence of impaired wound healing on the plasma miRNA signature and their functional importance in patients with type 2 diabetes mellitus., Approach and Results: miRNA array profiling identified 41 miRNAs significantly deregulated in diabetic controls when compared with patients with diabetes mellitus-associated peripheral arterial disease and chronic wounds. Quantitative real-time polymerase chain reaction validation confirmed decrease in circulating miR-191 and miR-200b levels in type 2 diabetic versus healthy controls. This was reverted in diabetic subjects with associated peripheral arterial disease and chronic wounds, who also exhibited higher circulating C-reactive protein and proinflammatory cytokine levels compared with diabetic controls. miR-191 and miR-200b were significantly correlated with C-reactive protein or cytokine levels in patients with diabetes mellitus. Indeed, proinflammatory stress increased endothelial- or platelet-derived secretion of miR-191 or miR-200b. In addition, dermal cells took up endothelial-derived miR-191 leading to downregulation of the miR-191 target zonula occludens-1. Altered miR-191 expression influenced angiogenesis and migratory capacities of diabetic dermal endothelial cells or fibroblasts, respectively, partly via its target zonula occludens-1., Conclusions: This study reports that (1) inflammation underlying nonhealing wounds in patients with type 2 diabetes mellitus influences plasma miRNA concentrations and (2) miR-191 modulates cellular migration and angiogenesis via paracrine regulation of zonula occludens-1 to delay the tissue repair process., (© 2015 American Heart Association, Inc.)

Ischaemia-reperfusion (I/R) injury of the kidney is a major cause of acute kidney injury. It may result in worsening or even loss of organ function. Transient occlusion of the renal vessel is followed by a reperfusion period, which induces further tissue damage by release of reactive oxygen and nitrogen species. Ischaemia-reperfusion injury of the kidney may be associated with surgical interventions in native kidneys and is also a common and unavoidable phenomenon in kidney transplantation. MicroRNAs are fascinating modulators of gene expression. They are capable of post-transcriptional silencing of genetic information by targeting the 3'-untranslated region of mRNAs, culminating in a suppression of protein synthesis or an increase in mRNA degradation. They might therefore be useful diagnostic and therapeutic entities during renal I/R injury; for instance, miR-21 has been shown to be enriched in kidney tissue in mice and humans with acute kidney injury. Interestingly, most recent literature suggests that modulation of vascular microRNAs might result in the amelioration of kidney function during renal I/R injury. To that end, miR-126 and miR-24, which have been demonstrated to be highly enriched in endothelial cells, were therapeutically modulated and shown to ameliorate renal I/R injury in mice. MicroRNAs in plasma, urine or enriched in microvesicles have been shown to serve as non-invasive tools for disease monitoring and to have potential impact on downstream mechanisms in recipient cells. This review highlights the latest developments regarding the role of microRNAs in renal I/R injury., (© 2015 The Authors. The Journal of Physiology © 2015 The Physiological Society.)

Rationale: Many processes in endothelial cells including angiogenic responses are regulated by microRNAs. However, there is limited information available about their complex cross-talk in regulating certain endothelial functions., Aim: The objective of this study is to identify endothelial functions of the pro-hypertrophic miR-212/132 cluster and its cross-talk with other microRNAs during development and disease., Methods and Results: We here show that anti-angiogenic stimulation by transforming growth factor-beta activates the microRNA-212/132 cluster by derepression of their transcriptional co-activator cAMP response element-binding protein (CREB)-binding protein (CBP) which is a novel target of a previously identified pro-angiogenic miRNA miR-30a-3p in endothelial cells. Surprisingly, despite having the same seed-sequence, miR-212 and miR-132 exerted differential effects on endothelial transcriptome regulation and cellular functions with stronger endothelial inhibitory effects caused by miR-212. These differences could be attributed to additional auxiliary binding of miR-212 to its targets. In vivo, deletion of the miR-212/132 cluster increased endothelial vasodilatory function, improved angiogenic responses during postnatal development and in adult mice., Conclusion: Our results identify (i) a novel miRNA-cross-talk involving miR-30a-3p and miR-212, which led to suppression of important endothelial genes such as GAB1 and SIRT1 finally culminating in impaired endothelial function; and (ii) microRNAs may have different biological roles despite having the same seed sequence., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2014. For permissions please email: journals.permissions@oup.com.)

Ischemia-reperfusion (I/R) injury of the kidney is a major cause of AKI. MicroRNAs (miRs) are powerful regulators of various diseases. We investigated the role of apoptosis-associated miR-24 in renal I/R injury. miR-24 was upregulated in the kidney after I/R injury of mice and in patients after kidney transplantation. Cell-sorting experiments revealed a specific miR-24 enrichment in renal endothelial and tubular epithelial cells after I/R induction. In vitro, anoxia/hypoxia induced an enrichment of miR-24 in endothelial and tubular epithelial cells. Transient overexpression of miR-24 alone induced apoptosis and altered functional parameters in these cells, whereas silencing of miR-24 ameliorated apoptotic responses and rescued functional parameters in hypoxic conditions. miR-24 effects were mediated through regulation of H2A histone family, member X, and heme oxygenase 1, which were experimentally validated as direct miR-24 targets through luciferase reporter assays. In vitro, adenoviral overexpression of miR-24 targets lacking miR-24 binding sites along with miR-24 precursors rescued various functional parameters in endothelial and tubular epithelial cells. In vivo, silencing of miR-24 in mice before I/R injury resulted in a significant improvement in survival and kidney function, a reduction of apoptosis, improved histologic tubular epithelial injury, and less infiltration of inflammatory cells. miR-24 also regulated heme oxygenase 1 and H2A histone family, member X, in vivo. Overall, these results indicate miR-24 promotes renal ischemic injury by stimulating apoptosis in endothelial and tubular epithelial cell. Therefore, miR-24 inhibition may be a promising future therapeutic option in the treatment of patients with ischemic AKI., (Copyright © 2014 by the American Society of Nephrology.)

Context: Circulating microRNAs (miRNAs/miRs) are used as novel biomarkers for diseases. miR-21, miR-126, and miR-210 are known to be deregulated in vivo or in vitro under diabetic conditions., Objective: The aim of this study was to investigate the circulating miR-21, miR-126, and miR-210 in plasma and urine from pediatric patients with type 1 diabetes and to link our findings to cardiovascular and diabetic nephropathy risk factors in children with type 1 diabetes., Design: miR-21, miR-126, and miR-210 concentrations were measured with quantitative RT-PCR in plasma and urine samples from 68 pediatric patients with type 1 diabetes and 79 sex- and age-matched controls., Setting: The study consisted of clinical pediatric patients with type 1 diabetes., Patients or Other Participants: Inclusion criterion for patients was diagnosed type 1 diabetes. Exclusion criteria were febrile illness during the last 3 months; chronic inflammatory or rheumatic disease; hepatitis; HIV; glucocorticoid treatment; liver, renal, or cardiac failure; or hereditary dyslipidemia. Patients were age and sex matched to controls., Main Outcome Measure(s): Main outcome parameters were changes in miR-21, miR-126, and miR-210 concentration in plasma and urine from type 1 diabetic patients compared with corresponding controls., Results: Circulating miRNA levels of miR-21 and miR-210 were significantly up-regulated in the plasma and urine of the type 1 diabetic patients. Urinary miR-126 levels in diabetic patients were significantly lower than in age- and gender-matched controls and negatively correlated between the patient's glycated hemoglobin mean and miR-126 concentration value. In contrast, circulating miR-126 levels in plasma were comparable in both cohorts. For urinary miR-21, we found by an adjusted receiver-operating characteristic-curve analysis with an area under the curve of 0.78., Conclusions: Type 1 diabetic pediatric patients revealed a significant deregulation of miR-21, miR-126, and miR-210 in plasma and urinary samples, which might indicate an early onset of diabetic-associated diseases.

Tissue damage caused by ischemia-reperfusion (I/R) injury represents a serious event, which often leads to deterioration or even loss of organ function. I/R injury is associated with transient tissue oxygen deprivation due to vessel occlusion and a subsequent reperfusion period following restoration of blood flow. Initial tissue damage inflicted by ischemia is aggravated in the reperfusion period through mechanisms such as burst of reactive oxygen and nitrogen species and inflammatory reactions. I/R injury occurs during surgical interventions, organ transplantation, diseases such as myocardial infarction, circulatory shock, and toxic insults. Recently, microRNAs have come into focus as powerful regulators of gene expression and potential diagnostic tools during I/R injury. These small noncoding ribonucleotides (~22 nucleotides in length) posttranscriptionally target mRNAs, culminating in suppression of protein synthesis or increase in mRNA degradation, thus fundamentally influencing organ function. This review highlights the latest developments regarding the role of microRNAs in cardiac and renal I/R injury., (© 2013 Elsevier Inc. All rights reserved.)

microRNAs are small, noncoding RNAs that control gene/protein expression through target messengerRNA degradation and/or inhibition of protein synthesis. An array of experimental studies has shown the importance of microRNAs for disease initiation/progression. microRNAs are generally considered to act as intracellular modulators of gene expression. However, first studies in the cancer and cardiovascular field have elucidated that microRNAs are remarkably stable in the extracellular compartment (e.g., in blood or urine). The detection and quantification of circulating microRNAs may, thus, represent a novel noninvasive tool to detect and monitor disease activity. In addition, there might be a potential biologic relevance of circulating microRNAs for cell/cell communication. The aim of the present article is to give an outline of recent work on circulating and urinary microRNAs as well as their potential paracrine activity in kidney disease.

Diabetes mellitus due to its high prevalence and associated complications is a major socioeconomic health problem. Diabetes is characterized by multiple macro- and microvascular complications (e.g. diabetic nephropathy, cardiomyopathy, neuropathy, retinopathy). Research efforts aim to elucidate pathophysiological mechanisms contributing to the disease process. MicroRNAs are endogenous small single stranded molecules regulating targets through mRNA cleavage or translational inhibition. MicroRNAs regulate many biological cellular functions and are often deregulated during diseases. The aim of the present article is to summarize the current knowledge of the impact of microRNAs on the development of diabetes and its associated complications including endothelial and vascular smooth muscle cell dysfunction, diabetic cardiomyopathy, diabetic nephropathy, regulation of pancreatic beta cell function as well as skeletal muscle and hepatic involvement.

Background: Circulating microRNAs are stably detectable in serum/plasma and other body fluids. In patients with acute kidney injury on dialysis therapy changes of miRNA patterns had been detected. It remains unclear if and how the dialysis procedure itself affects circulating microRNA level., Methods: We quantified miR-21 and miR-210 by quantitative RT-PCR in plasma of patients with acute kidney injury requiring dialysis and measured pre- and post-dialyser miRNA levels as well as their amount in the collected spent dialysate. Single treatments using the following filters were studied: F60 S (1.3 m(2), Molecular Weight Cut Off (MWCO): 30 kDa, n = 8), AV 1000 S (1.8 m(2), MWCO: 30 kDa, n = 6) and EMiC 2 (1.8 m(2), MWCO: 40 kDa, n = 6)., Results: Circulating levels of miR-21 or -210 do not differ between pre- and post-dialyzer blood samples independently of the used filter surface and pore size: miR-21: F60S: p = 0.35, AV 1000 S p = 1.0, EMiC2 p = 1.0; miR-210: F60S: p = 0.91, AV 1000 S p = 0.09, EMiC2 p = 0.31. Correspondingly, only traces of both miRNAs could be found in the collected spent dialysate and ultrafiltrate., Conclusions: In patients with acute kidney injury circulating microRNAs are not removed by dialysis. As only traces of miR-21 and -210 are detected in dialysate and ultrafiltrate, microRNAs in the circulation are likely to be transported by larger structures such as proteins and/or microvesicles. As miRNAs are not affected by dialysis they might be more robust biomarkers of acute kidney injury.

Background: In early May 2011, an outbreak of hemorrhagic colitis associated with hemolytic-uremic syndrome (HUS) first developed in Northern Germany and spread to 15 other countries in Europe. The outbreak-strain O104:H4, which combined virulence factors of typical enteroaggregative and Shiga-Toxin-producing E. coli was associated with an unusual high rate of hemolytic uremic syndrome. Also an unexpected high rate of coma and seizures leading to mechanical ventilation and ICU treatment was observed. MicroRNAs are small ribonucleotides orchestrating gene expression. We tested whether circulating microRNAs in serum of HUS patients during the 2011 epidemics are altered in this patient cohort and related to clinical manifestations., Methodology/principal Findings: We profiled microRNAs using RNA isolated from serum of patients and healthy age-matched controls. The results were validated in 38 patients at baseline, 29 patients during follow-up and 21 age-matched healthy controls by miRNA-specific quantitative RT-PCR. Circulating levels of miR-24, miR-126 were increased in HUS patients versus controls. There was no association between these microRNAs and renal function or the need for renal replacement therapy. In contrast, levels of miR-126 were associated with neurological symptoms at baseline and during follow-up. In addition, miR-126 (on admission) and miR-24 (on admission and during follow-up) were associated with platelet count., Conclusions/significance: Circulating microRNAs are strongly altered in this patient cohort and associated with neurological symptoms as well as platelet count.

Organ transplantation has evolved rapidly and there is now widespread use of donated organs for the treatment of end-stage organ failure. Although the therapeutic options achieving long-term graft survival have improved, acute and chronic rejections are still a major problem. Studies to identify noninvasive biomarkers for rejection and underlying molecular events have increased significantly in the past decade, but a major breakthrough is still missing. The recent discovery of small regulatory RNA molecules (microRNAs) resulted in a new and improved understanding of the mechanisms of gene regulation and also led to the development of the first new microRNA (miRNA)-based therapies. miRNAs are endogenous, single-stranded RNAs consisting of about 19-25 noncoding nucleotides, which have an important role in regulating gene expression. Additionally, circulating miRNAs that might be useful as novel disease biomarkers were detected. Here, we summarise current knowledge about the role of miRNAs in immunology and transplantation medicine and their role as potential biomarkers. We also focus on the molecular mechanisms and therapeutic implications of the use of miRNA-based therapeutic strategies to improve long-term allograft survival.

Circulating microRNAs may have diagnostic potential in acute coronary syndrome (ACS). Previous studies, however, were based on low patient numbers and could not assess the relation of microRNAs to clinical characteristics and their potential prognostic value. We thus assessed the diagnostic and prognostic value of cardiomyocyte-enriched microRNAs in the context of clinical variables and a sensitive myonecrosis biomarker in a larger ACS cohort. MiR-1, miR-133a, miR-133b, miR-208a, miR-208b, and miR-499 concentrations were measured by quantitative reverse transcription PCR in plasma samples obtained on admission from 444 patients with ACS. High-sensitivity troponin T (hsTnT) was measured by immunoassay. Patients were followed for 6 months regarding all-cause mortality. In a multiple linear regression analysis that included clinical variables and hsTnT, miR-1, miR-133a, miR-133b, and miR-208b were independently associated with hsTnT levels (all P<0.001). Patients with myocardial infarction presented with higher levels of miR-1, miR-133a, and miR-208b compared with patients with unstable angina. However, all six investigated microRNAs showed a large overlap between patients with unstable angina or myocardial infarction. MiR-133a and miR-208b levels were significantly associated with the risk of death in univariate and age- and gender-adjusted analyses. Both microRNAs lost their independent association with outcome upon further adjustment for hsTnT. The present study tempers speculations about the potential usefulness of cardiomyocyte-enriched microRNAs as diagnostic or prognostic markers in ACS., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Background: Myocardial infarction leads to cardiac remodeling and development of heart failure. Insufficient myocardial capillary density after myocardial infarction has been identified as a critical event in this process, although the underlying mechanisms of cardiac angiogenesis are mechanistically not well understood., Methods and Results: Here, we show that the small noncoding RNA microRNA-24 (miR-24) is enriched in cardiac endothelial cells and considerably upregulated after cardiac ischemia. MiR-24 induces endothelial cell apoptosis, abolishes endothelial capillary network formation on Matrigel, and inhibits cell sprouting from endothelial spheroids. These effects are mediated through targeting of the endothelium-enriched transcription factor GATA2 and the p21-activated kinase PAK4, which were identified by bioinformatic predictions and validated by luciferase gene reporter assays. Respective downstream signaling cascades involving phosphorylated BAD (Bcl-XL/Bcl-2-associated death promoter) and Sirtuin1 were identified by transcriptome, protein arrays, and chromatin immunoprecipitation analyses. Overexpression of miR-24 or silencing of its targets significantly impaired angiogenesis in zebrafish embryos. Blocking of endothelial miR-24 limited myocardial infarct size of mice via prevention of endothelial apoptosis and enhancement of vascularity, which led to preserved cardiac function and survival., Conclusions: Our findings indicate that miR-24 acts as a critical regulator of endothelial cell apoptosis and angiogenesis and is suitable for therapeutic intervention in the setting of ischemic heart disease.

Background and Objectives: MicroRNAs (miRNAs) are small ribonucleotides regulating gene expression. MicroRNAs are present in the blood in a remarkably stable form. We tested whether circulating miRNAs in the plasma of critically ill patients with acute kidney injury (AKI) at the inception of renal replacement therapy are deregulated and may predict survival., Design, Setting, Participants, & Measurements: We profiled miRNAs using RNA isolated from the plasma of patients with AKI and healthy controls. The results were validated in 77 patients with acute kidney injury, 30 age-matched healthy controls, and 18 critically ill patients with acute myocardial infarction by quantitative real-time PCR., Results: Circulating levels of miR-16 and miR-320 were downregulated in the plasma of kidney injury AKI patients, whereas miR-210 was upregulated compared with healthy controls (all P < 0.0001) and disease controls (miR-210 and miR-16: P < 0.0001; miR-320: P = 0.03). Cox regression (P < 0.05) and Kaplan-Meier curve analysis (P = 0.03) revealed miR-210 as an independent and powerful predictor of 28-day survival., Conclusions: Circulating miRNAs are altered in patients with kidney injury AKI. MiR-210 predicts mortality in this patient cohort and may serve as a novel biomarker AKI reflecting pathophysiological changes on a cellular level.

Chronic kidney disease (CKD) is characterized by tubulointerstitial deposition of extracellular matrix, tubular atrophy and dilatation; the replacement of organ architecture by connective tissue results in progressive loss of organ function. Micro (mi)RNAs are important mediators of tissue fibrosis under various pathological conditions and are of potential therapeutic relevance. These short, noncoding nucleotides (∼22 bases) regulate target messenger RNAs at the post-transcriptional level. Several hundred miRNAs regulate a considerable amount of the human genome and are involved in virtually all biological processes, including cellular proliferation, apoptosis and differentiation. Thus, miRNA deregulation often results in impaired cellular function and development of disease. Here, we summarize the current knowledge on the role of miRNAs in CKD, with particular emphasis on hypertensive kidney disease, diabetic nephropathy, glomerular biology, and IgA nephropathy. Identification of miRNA regulation and function in renal pathology may pinpoint miRNAs as new therapeutic targets in kidney fibrosis and related diseases. A new class of RNA therapeutics, that is, miRNA modulators (such as antagomirs) have been developed, which enable specific targeting of miRNAs and respective downstream gene networks in vivo, thus influencing the mechanisms that underlie disease initiation or progression. The therapeutic potential of miRNA-based treatment strategies in CKD are discussed.