The lncRNA MRPL20-AS1 is associated with severe OSAS and downregulated upon hypoxic injury of endothelial cells.

INTRODUCTION: Obstructive sleep apnea syndrome (OSAS) is the most common sleep disorder in humans. Although OSAS is clearly related to arterial hypertension, coronary artery disease, and heart failure, it remains unknown through which pathomechanisms OSAS influences cardiovascular health. Recent research has pinpointed long non-coding RNAs (lncRNA) as important molecular mediators of various cardiovascular pathologies. In this study, we have identified the lncRNA MRPL20-AS1 to be affected by OSAS in patients as well as by hypoxia in vitro. METHODS AND RESULTS: A transcriptomic analysis was performed on peripheral blood from four patients with severe OSAS taken after one night of polygraphic assessment. We found that three lncRNAs were significantly dysregulated, of which MRPL20-AS1 was the most significant. In a larger cohort of 22 OSAS patients, MRPL20-AS1 was inversely correlated with the apnea-hypopnea index (AHI). This indicates that OSAS patients with higher AHI levels and therefore more severe OSAS had lower levels of MRPL20-AS1 in the blood. The results were recapitulated in vitro by subjecting endothelial cells to hypoxia. In these experiments, hypoxia led to a significant downregulation of MRPL20-AS1 in endothelial cells. CONCLUSION: MRPL20-AS1 may serve as a useful tool to identify patients suffering from severe OSAS and further research should be done to evaluate the therapeutic potential of MRPL20-AS1 as a target to counteract the cardiovascular effects of OSAS.

Circulating MicroRNA-122-5p Is Associated With a Lack of Improvement in Left Ventricular Function After Transcatheter Aortic Valve Replacement and Regulates Viability of Cardiomyocytes Through Extracellular Vesicles.

BACKGROUND: Transcatheter aortic valve replacement (TAVR) is a well-established treatment option for high- and intermediate-risk patients with severe symptomatic aortic valve stenosis. A majority of patients exhibit improvements in left ventricular ejection fraction (LVEF) after TAVR in response to TAVR-associated afterload reduction. However, a specific role for circulating microRNAs (miRNAs) in the improvement of cardiac function for patients after TAVR has not yet been investigated. Here, we profiled the differential expression of miRNAs in circulating extracellular vesicles (EVs) in patients after TAVR and, in particular, the novel role of circulating miR-122-5p in cardiomyocytes. METHODS: Circulating EV-associated miRNAs were investigated by use of an unbiased Taqman-based human miRNA array. Several EV miRNAs (miR-122-5p, miR-26a, miR-192, miR-483-5p, miR-720, miR-885-5p, and miR-1274) were significantly deregulated in patients with aortic valve stenosis at day 7 after TAVR compared with the preprocedural levels in patients without LVEF improvement. The higher levels of miR-122-5p were negatively correlated with LVEF improvement at both day 7 (r=-0.264 and P=0.015) and 6 months (r=-0.328 and P=0.0018) after TAVR. RESULTS: Using of patient-derived samples and a murine aortic valve stenosis model, we observed that the expression of miR-122-5p correlates negatively with cardiac function, which is associated with LVEF. Mice with graded wire injury-induced aortic valve stenosis demonstrated a higher level of miR-122-5p, which was related to cardiomyocyte dysfunction. Murine ex vivo experiments revealed that miR-122-5p is highly enriched in endothelial cells compared with cardiomyocytes. Coculture experiments, copy-number analysis, and fluorescence microscopy with Cy3-labeled miR-122-5p demonstrated that miR-122-5p can be shuttled through large EVs from endothelial cells into cardiomyocytes. Gain- and loss-of-function experiments suggested that EV-mediated shuttling of miR-122-5p increases the level of miR-122-5p in recipient cardiomyocytes. Mechanistically, mass spectrometry, miRNA pulldown, electrophoretic mobility shift assay, and RNA immunoprecipitation experiments confirmed that miR-122-5p interacts with the RNA-binding protein hnRNPU (heterogeneous nuclear ribonucleoprotein U) in a sequence-specific manner to encapsulate miR-122-5p into large EVs. On shuttling, miR-122-5p reduces the expression of the antiapoptotic gene BCL2 by binding to its 3' untranslated region to inhibit its translation, thereby decreasing the viability of target cardiomyocytes. CONCLUSIONS: Increased levels of circulating proapoptotic EV-incorporated miR-122-5p are associated with reduced LVEF after TAVR. EV shuttling of miR-122-5p regulates the viability and apoptosis of cardiomyocytes in a BCL2-dependent manner.

Analysis of nocturnal, hypoxia-induced miRNAs in sleep apnea patients.

INTRODUCTION: Obstructive sleep apnea syndrome (OSAS) is associated with an increased cardiovascular risk. The underlying mechanisms are largely unclear. MicroRNAs (miRNAs) are RNAs circulating in the blood that can be released into the bloodstream during hypoxia. In the present study, we investigate if OSAS-induced hypoxia results in a release of miRNAs that may mediate OSAS-associated cardiovascular damage. METHODS: Blood was sampled from 23 OSAS patients before and after a polygraphically monitored night. Total circulating RNA was isolated from the plasma and quantified using real-time qPCR. Using a Taqman miRNA array, the levels of 384 different miRNAs were compared between evening and morning after polysomnography. The most highly upregulated miRNA (miRNA-505) and four additionally upregulated miRNAs (miRNA-127, miRNA-133a, miRNA-145, and miRNA-181a) were then quantified in a bigger patient cohort individually. RESULTS: Apnea/Hypopnea-Index (AHI) was evaluated and averaged at 26 per hour on nocturnal polygraphy. In an initial miRNA array, a total of 4 miRNAs were significantly regulated. A significant increase of miRNA-145 was observed in the larger patient cohort. No significant changes in concentration were detected for miRNA-127, miRNA-133a, miRNA-181a, and miRNA-505 in this larger cohort. CONCLUSION: OSAS results in the nocturnal release of miRNAs into the bloodstream. Our collected data may indicate a hypoxia-induced release of miRNAs into the bloodstream of OSAS-patients. In vitro experiments are needed to confirm the secretion of these miRNAs under hypoxia and evaluate the effect on the cardio vasculature.

Large extracellular vesicles in the left atrial appendage in patients with atrial fibrillation-the missing link?

Atrial fibrillation (AF) is the most frequent arrhythmic disease in humans, which leads to thrombus formation in the left atrial appendage and stroke through peripheral embolization. Depending on their origin, large extracellular vesicles (lEVs) can exert pro-coagulant functions. In the present study, we investigated how different types of AF influence the levels of large EV subtypes in three distinct atrial localizations. Blood samples were collected from the right and left atrium and the left atrial appendage of 58 patients. 49% of the patients had permanent AF, 34% had non-permanent AF, and 17% had no history of AF. Flow cytometric analysis of the origin of the lEVs showed that the proportion of platelet-derived lEVs in the left atrial appendage was significantly higher in permanent AF patients compared to non-permanent AF. When we grouped patients according to their current heart rhythm, we also detected significantly higher levels of platelet-derived lEVs in the left atrial appendage (LAA) in patients with atrial fibrillation. In vitro studies revealed, that platelet activation with lipopolysaccharide (LPS) leads to higher levels of miR-222-3p and miR-223-3p in platelet-derived lEVs. Treatment with lEVs from LPS- or thrombin-activated platelets reduces the migration of endothelial cells in vitro. These results suggest that permanent atrial fibrillation is associated with increased levels of platelet-derived lEVs in the LAA, which are potentially involved in LAA thrombus formation.

MicroRNA-mediated vascular intercellular communication is altered in chronic kidney disease.

AIMS: Chronic kidney disease (CKD) is an independent risk factor for the development of coronary artery disease (CAD). For both, CKD and CAD, the intercellular transfer of microRNAs (miRs) through extracellular vesicles (EVs) is an important factor of disease development. Whether the combination of CAD and CKD affects endothelial function through cellular crosstalk of EV-incorporated miRs is still unknown. METHODS AND RESULTS: Out of 172 screened CAD patients, 31 patients with CAD + CKD were identified and matched with 31 CAD patients without CKD. Additionally, 13 controls without CAD and CKD were included. Large EVs from CAD + CKD patients contained significantly lower levels of the vasculo-protective miR-130a-3p and miR-126-3p compared to CAD patients and controls. Flow cytometric analysis of plasma-derived EVs revealed significantly higher numbers of endothelial cell-derived EVs in CAD and CAD + CKD patients compared to controls. EVs from CAD + CKD patients impaired target human coronary artery endothelial cell (HCAEC) proliferation upon incubation in vitro. Consistent with the clinical data, treatment with the uraemia toxin indoxyl sulfate (IS)-reduced miR-130a-3p levels in HCAEC-derived EVs. EVs from IS-treated donor HCAECs-reduced proliferation and re-endothelialization in EV-recipient cells and induced an anti-angiogenic gene expression profile. In a mouse-experiment, intravenous treatment with EVs from IS-treated endothelial cells significantly impaired endothelial regeneration. On the molecular level, we found that IS leads to an up-regulation of the heterogenous nuclear ribonucleoprotein U (hnRNPU), which retains miR-130a-3p in the cell leading to reduced vesicular miR-130a-3p export and impaired EV-recipient cell proliferation. CONCLUSION: Our findings suggest that EV-miR-mediated vascular intercellular communication is altered in patients with CAD and CKD, promoting CKD-induced endothelial dysfunction.

Activation of neutral sphingomyelinase 2 through hyperglycemia contributes to endothelial apoptosis via vesicle-bound intercellular transfer of ceramides.

BACKGROUND: Pro-apoptotic and pro-inflammatory ceramides are crucially involved in atherosclerotic plaque development. Local cellular ceramide accumulation mediates endothelial apoptosis, especially in type 2 diabetes mellitus, which is a major cardiovascular risk factor. In recent years, large extracellular vesicles (lEVs) have been identified as an important means of intercellular communication and as regulators of cardiovascular health and disease. A potential role for lEVs as vehicles for ceramide transfer and inductors of diabetes-associated endothelial apoptosis has never been investigated. METHODS AND RESULTS: A mass-spectrometric analysis of human coronary artery endothelial cells (HCAECs) and their lEVs revealed C16 ceramide (d18:1-16:0) to be the most abundant ceramide in lEVs and to be significantly increased in lEVs after hyperglycemic injury to HCAECs. The increased packaging of ceramide into lEVs after hyperglycemic injury was shown to be dependent on neutral sphingomyelinase 2 (nSMase2), which was upregulated in glucose-treated HCAECs. lEVs from hyperglycemic HCAECs induced apoptosis in the recipient HCAECs compared to native lEVs from untreated HCAECs. Similarly, lEVs from hyperglycemic mice after streptozotocin injection induced higher rates of apoptosis in murine endothelial cells compared to lEVs from normoglycemic mice. To generate lEVs with high levels of C16 ceramide, ceramide was applied exogenously and shown to be effectively packaged into the lEVs, which then induced apoptosis in lEV-recipient HCAECs via activation of caspase 3. Intercellular transfer of ceramide through lEVs was confirmed by use of a fluorescently labeled ceramide analogue. Treatment of HCAECs with a pharmacological inhibitor of nSMases (GW4869) or siRNA-mediated downregulation of nSMase2 abrogated the glucose-mediated effect on apoptosis in lEV-recipient cells. In contrast, for small EVs (sEVs), hyperglycemic injury or GW4869 treatment had no effect on apoptosis induction in sEV-recipient cells. CONCLUSION: lEVs mediate the induction of apoptosis in endothelial cells in response to hyperglycemic injury through intercellular transfer of ceramides.

NcRNAs in Vascular and Valvular Intercellular Communication.

Non-coding RNAs have been shown to be important biomarkers and mediators of many different disease entities, including cardiovascular (CV) diseases like atherosclerosis, aneurysms, and valvulopathies. Growing evidence suggests a central role of ncRNAs as regulators of different pathological pathways involved in endothelial dysfunction, cardiovascular inflammation, cell differentiation, and calcification. This review will discuss the role of protein-bound and extracellular vesicular-bound ncRNAs as biomarkers of vascular and valvular diseases, their role as intercellular communicators, and regulators of disease pathways and also highlights possible treatment strategies.

CAD increases the long noncoding RNA PUNISHER in small extracellular vesicles and regulates endothelial cell function via vesicular shuttling.

Long noncoding RNAs (lncRNAs) have emerged as biomarkers and regulators of cardiovascular disease. However, the expression pattern of circulating extracellular vesicle (EV)-incorporated lncRNAs in patients with coronary artery disease (CAD) is still poorly investigated. A human lncRNA array revealed that certain EV-lncRNAs are significantly dysregulated in CAD patients. Circulating small EVs (sEVs) from patients with (n = 30) or without (n = 30) CAD were used to quantify PUNISHER (also known as AGAP2-antisense RNA 1 [AS1]), GAS5, MALAT1, and H19 RNA levels. PUNISHER (p = 0.002) and GAS5 (p = 0.02) were significantly increased in patients with CAD, compared to non-CAD patients. Fluorescent labeling and quantitative real-time PCR of sEVs demonstrated that functional PUNISHER was transported into the recipient cells. Mechanistically, the RNA-binding protein, heterogeneous nuclear ribonucleoprotein K (hnRNPK), interacts with PUNISHER, regulating its loading into sEVs. Knockdown of PUNISHER abrogated the EV-mediated effects on endothelial cell (EC) migration, proliferation, tube formation, and sprouting. Angiogenesis-related gene profiling showed that the expression of vascular endothelial growth factor A (VEGFA) RNA was significantly increased in EV recipient cells. Protein stability and RNA immunoprecipitation indicated that the PUNISHER-hnRNPK axis regulates the stability and binding of VEGFA mRNA to hnRNPK. Loss of PUNISHER in EVs abolished the EV-mediated promotion of VEGFA gene and protein expression. Intercellular transfer of EV-incorporated PUNISHER promotes a pro-angiogenic phenotype via a VEGFA-dependent mechanism.

Vascular pathologies in chronic kidney disease: pathophysiological mechanisms and novel therapeutic approaches.

Cardiovascular disease (CVD) is a major cause of death in patients with chronic kidney disease (CKD). Both conditions are rising in incidence as well as prevalence, creating poor outcomes for patients and high healthcare costs. Recent data suggests CKD to be an independent risk factor for CVD. Accumulation of uremic toxins, chronic inflammation, and oxidative stress have been identified to act as CKD-specific alterations that increase cardiovascular risk. The association between CKD and cardiovascular mortality is markedly influenced through vascular alterations, in particular atherosclerosis and vascular calcification (VC). While numerous risk factors promote atherosclerosis by inducing endothelial dysfunction and its progress to vascular structural damage, CKD affects the medial layer of blood vessels primarily through VC. Ongoing research has identified VC to be a multifactorial, cell-mediated process in which numerous abnormalities like mineral dysregulation and especially hyperphosphatemia induce a phenotype switch of vascular smooth muscle cells to osteoblast-like cells. A combination of pro-calcifying stimuli and an impairment of inhibiting mechanisms like fetuin A and vitamin K-dependent proteins like matrix Gla protein and Gla-rich protein leads to mineralization of the extracellular matrix. In view of recent studies, intercellular communication pathways via extracellular vesicles and microRNAs represent key mechanisms in VC and thereby a promising field to a deeper understanding of the involved pathomechanisms. In this review, we provide an overview about pathophysiological mechanisms connecting CKD and CVD. Special emphasis is laid on vascular alterations and more recently discovered molecular pathways which present possible new therapeutic targets.

The RNA-binding protein hnRNPU regulates the sorting of microRNA-30c-5p into large extracellular vesicles.

The transfer of microRNAs (miRs) via extracellular vesicles (EVs) is a functionally relevant mechanism of intercellular communication that regulates both organ homoeostasis and disease development. Little is known about the packaging of miRs into EVs. Previous studies have shown that certain miRs are exported by RNA-binding proteins into small EVs, while for other miRs and for large EVs, in general, the export mechanisms remain unclear. Therefore, a proteomic analysis of endothelial cell-derived large EVs was performed, which revealed that heterogeneous nuclear ribonucleoprotein U (hnRNPU) is abundantly present in EVs. EVs were characterized by electron microscopy, immunoblotting and nanoparticle tracking analysis. Taqman microRNA array and single qPCR experiments identified specific miR patterns to be exported into EVs in an hnRNPU-dependent way. The specific role of hnRNPU for vesicular miR-sorting was confirmed independently by gain- and loss-of-function experiments. In our study, miR-30c-5p was the miR whose export was most significantly regulated by hnRNPU. Mechanistically, in silico binding analysis showed that the export of miRs into EVs depends on the binding efficiency of the respective miRs to hnRNPU. Among the exported miRs, a significant enrichment of the sequence motif AAMRUGCU was detected as a potential sorting signal. Experimentally, binding of miR-30c-5p to hnRNPU was confirmed independently by RNA-immunoprecipitation, electrophoretic mobility shift assay and reciprocally by miR-pulldown. Nuclear binding of miR-30c-5p to hnRNPU and subsequent stabilization was associated with a lower cytoplasmatic abundance and consequently reduced availability for vesicular export. hnRNPU-dependent miR-30c-5p export reduced cellular migration as well as pro-angiogenic gene expression in EV-recipient cells. In summary, hnRNPU retains miR-30c-5p and other miRs and thereby prevents their export into large EVs. The data presented provide a novel and functionally relevant mechanism of vesicular miR export.

MicroRNAs As Master Regulators of Atherosclerosis: From Pathogenesis to Novel Therapeutic Options.

Significance: Cardiovascular disease (CVD) remains the major cause of morbidity and mortality worldwide. Accumulating evidence indicates that atherosclerosis and its sequelae, coronary artery disease, contribute to the majority of cardiovascular deaths. Atherosclerosis is a chronic inflammatory disease of the arteries in which atherosclerotic plaques form within the vessel wall. Epidemiological studies have identified various risk factors for atherosclerosis, such as diabetes, hyperlipidemia, smoking, genetic predisposition, and sedentary lifestyle. Recent Advances: Through the advancement of genetic manipulation techniques and their use in cardiovascular biology, it was shown that small RNAs, especially microRNAs (miRNAs), are dynamic regulators of disease pathogenesis. They are considered to be central during the regulation of gene expression through numerous mechanisms and provide a means to develop biomarkers and therapeutic tools for the diagnosis and therapy of atherosclerosis. Circulating miRNAs encapsulated within membrane-surrounded vesicles, which originate from diverse subcellular compartments, are now emerging as novel regulators of intercellular communication. The miRNAs, in both freely circulating and vesicle-bound forms, represent a valuable tool for diagnosing and monitoring CVD, recently termed as "liquid biopsy." Critical Issues: However, despite the recent advancements in miRNA-based diagnostics and therapeutics, understanding how miRNAs can regulate atherosclerosis is still crucial to achieving an effective intervention and reducing the disease burden. Future Directions: We provide a landscape of the current developmental progression of RNA therapeutics as a holistic approach for treating CVD in different animal models and clinical trials. Future interrogations are warranted for the development of miRNA-based therapeutics to overcome challenges for the treatment of the disease.

Aortic Valve Stenosis: From Basic Mechanisms to Novel Therapeutic Targets.

Aortic valve stenosis is the most prevalent heart valve disease worldwide. Although interventional treatment options have rapidly improved in recent years, symptomatic aortic valve stenosis is still associated with high morbidity and mortality. Calcific aortic valve stenosis is characterized by a progressive fibro-calcific remodeling and thickening of the aortic valve cusps, which subsequently leads to valve obstruction. The underlying pathophysiology is complex and involves endothelial dysfunction, immune cell infiltration, myofibroblastic and osteoblastic differentiation, and, subsequently, calcification. To date, no pharmacotherapy has been established to prevent aortic valve calcification. However, novel promising therapeutic targets have been recently identified. This review summarizes the current knowledge of pathomechanisms involved in aortic valve calcification and points out novel treatment strategies.

Investigation of RNA Editing Sites within Bound Regions of RNA-Binding Proteins.

Studies in epitranscriptomics indicate that RNA is modified by a variety of enzymes. Among these RNA modifications, adenosine to inosine (A-to-I) RNA editing occurs frequently in the mammalian transcriptome. These RNA editing sites can be detected directly from RNA sequencing (RNA-seq) data by examining nucleotide changes from adenosine (A) to guanine (G), which substitutes for inosine (I). However, a careful investigation of such nucleotide changes must be conducted to distinguish sequencing errors and genomic mutations from the genuine editing sites. Building upon our recent introduction of an easy-to-use bioinformatics tool, RNA Editor, to detect RNA editing events from RNA-seq data, we examined the extent by which RNA editing events affect the binding of RNA-binding proteins (RBP). Through employing bioinformatic techniques, we uncovered that RNA editing sites occur frequently in RBP-bound regions. Moreover, the presence of RNA editing sites are more frequent when RNA editing islands were examined, which are regions in which RNA editing sites are present in clusters. When the binding of one RBP, human antigen R [HuR; encoded by ELAV-like protein 1 (ELAV1)], was quantified experimentally, its binding was reduced upon silencing of the RNA editing enzyme adenosine deaminases acting on RNA (ADAR) compared to the control-suggesting that the presence of RNA editing islands influence HuR binding to its target regions. These data indicate RNA editing as an important mediator of RBP-RNA interactions-a mechanism which likely constitutes an additional mode of post-transcription gene regulation in biological systems.

Atherosclerotic Conditions Promote the Packaging of Functional MicroRNA-92a-3p Into Endothelial Microvesicles.

RATIONALE: Microvesicle-incorporated microRNAs (miRs) are biomarkers and effectors of cardiovascular disease. Whether microvesicle-miR expression is regulated in coronary artery disease (CAD) or not is unknown. OBJECTIVE: Here, we explore the expression of circulating microvesicle-miRs in patients with CAD and investigate the role of microvesicle-miR in endothelial cells. METHODS AND RESULTS: Circulating microvesicles were isolated from patients' plasma by using ultracentrifugation. Electron microscopy was used to determine the size of the microvesicles. A Taqman miR array revealed certain microvesicle-miRs are significantly regulated in patients with stable CAD compared with patients with ACS. To validate the miR array results, 180 patients with angiographically excluded CAD (n=41), stable CAD (n=77), and acute coronary syndrome (n=62) were prospectively studied. Nine miRs involved in regulation of vascular performance-miR-126-3p, miR-222-3p, miR-let-7d-5p, miR-21-5p, miR-26a-5p, miR-92a-3p, miR-139-5p, miR-30b-5p, and miR-199a-5p-were quantified in circulating microvesicles by real-time polymerase chain reaction (PCR). Among these, miR-92a-3p was significantly increased in patients with CAD compared with non-CAD patients. Microvesicle-sorting experiments showed endothelial cells (ECs) were the major cell source for microvesicles containing miR-92a-3p. In vitro oxLDL (oxidized low-density lipoprotein) and IL-6 (interleukin-6) stimulation increased miR-92a-3p expression in parent ECs and upregulated the expression level of endothelial microvesicle (EMV)-incorporated miR-92a-3p. Labeling of miR-92a-3p and EMVs demonstrated that functional miR-92a-3p was transported into recipient ECs, which accelerated cell migration and proliferation. Knockdown of miR-92a-3p in EMVs abrogated EMV-mediated effects on EC migration, proliferation, and blocked vascular network formation in a matrigel plug. Polymerase chain reaction-based gene profiling showed that the expression of THBS1 (thrombospondin 1) protein-a target of miR-92a-3p and an inhibitor of angiogenesis-was significantly reduced in ECs by EMVs. Knockdown of miR-92a-3p in EMVs abrogated EMV-mediated inhibition of the THBS1 gene and protein expression. CONCLUSIONS: Atherosclerotic conditions promote the packaging of endothelial miR-92a-3p into EMVs. EMV-mediated transfer of functional miR-92a-3p regulates angiogenesis in recipient ECs by a THBS1-dependent mechanism.

A novel long non-coding RNA Myolinc regulates myogenesis through TDP-43 and Filip1.

Myogenesis is a complex process required for skeletal muscle formation during embryonic development and for regeneration and growth of myofibers in adults. Accumulating evidence suggests that long non-coding RNAs (lncRNAs) play key roles in regulating cell fate decision and function in various tissues. However, the role of lncRNAs in the regulation of myogenesis remains poorly understood. In this study, we identified a novel muscle-enriched lncRNA called 'Myolinc (AK142388)', which we functionally characterized in the C2C12 myoblast cell line. Myolinc is predominately localized in the nucleus, and its levels increase upon induction of the differentiation. Knockdown of Myolinc impairs the expression of myogenic regulatory factors and formation of multi-nucleated myotubes in cultured myoblasts. Myolinc also regulates the expression of Filip1 in a cis-manner. Similar to Myolinc, knockdown of Filip1 inhibits myogenic differentiation. Furthermore, Myolinc binds to TAR DNA-binding protein 43 (TDP-43), a DNA/RNA-binding protein that regulates the expression of muscle genes (e.g. Acta1 and MyoD). Knockdown of TDP-43 inhibits myogenic differentiation. We also show that Myolinc-TDP-43 interaction is essential for the binding of TDP-43 to the promoter regions of muscle marker genes. Finally, we show that silencing of Myolinc inhibits skeletal muscle regeneration in adult mice. Altogether, our study identifies a novel lncRNA that controls key regulatory networks of myogenesis.

Airn Regulates Igf2bp2 Translation in Cardiomyocytes.

RATIONALE: Increasing evidence indicates the presence of lncRNAs in various cell types. Airn is an imprinting gene transcribed from the paternal chromosome. It is in antisense orientation to the imprinted, but maternally derived, Igf2r gene, on which Airn exerts its regulation in cis. Although Airn is highly expressed in the heart, functions aside from imprinting remain unknown. OBJECTIVE: Here, we studied the functions of Airn in the heart, especially cardiomyocytes. METHODS AND RESULTS: Silencing of Airn via siRNAs augmented cell death, vulnerability to cellular stress, and reduced cell migration. To find the cause of such phenotypes, the potential binding partners of Airn were identified via RNA pull-down followed by mass spectrometry, which indicated Igf2bp2 (insulin-like growth factor 2 mRNA-binding protein 2) and Rpa1 (replication protein A1) as potential binding partners. Further experiments showed that Airn binds to Igf2bp2 to control the translation of several genes. Moreover, silencing of Airn caused less binding of Igf2bp2 to other mRNAs and reduced translation of Igf2bp2 protein. CONCLUSIONS: Our study uncovers a new function of Airn and demonstrates that Airn is important for the physiology of cardiomyocytes.