Trbp regulates heart function through microRNA-mediated Sox6 repression

Two-motif model illuminates DICER cleavage preferences

In humans, DICER is a key regulator of gene expression through its production of miRNAs and siRNAs by processing miRNA precursors (pre-miRNAs), short-hairpin RNAs (shRNAs), and long double-stranded RNAs (dsRNAs). To advance our understanding of this process, we employed high-throughput dicing assays using various shRNA variants and both wild-type and mutant DICER. Our analysis revealed that DICER predominantly cleaves shRNAs at two positions, specifically at 21 (DC21) and 22 (DC22) nucleotides from their 5'-end. Our investigation identified two different motifs, mWCU and YCR, that determine whether DICER cleaves at DC21 or DC22, depending on their locations in shRNAs/pre-miRNAs. These motifs can work together or independently to determine the cleavage sites of DICER. Furthermore, our findings indicate that dsRNA-binding domain (dsRBD) of DICER enhances its cleavage, and mWCU strengthens the interaction between dsRBD and RNA, leading to an even greater enhancement of the cleavage. Conversely, YCR functions independently of dsRBD. Our study proposes a two-motif model that sheds light on the intricate regulatory mechanisms involved in gene expression by elucidating how DICER recognizes its substrates, providing valuable insights into this critical biological process.

Advances in the study of exosomes in cardiovascular diseases

BACKGROUND

Cardiovascular disease (CVD) has been the leading cause of death worldwide for many years. In recent years, exosomes have gained extensive attention in the cardiovascular system due to their excellent biocompatibility. Studies have extensively researched miRNAs in exosomes and found that they play critical roles in various physiological and pathological processes in the cardiovascular system. These processes include promoting or inhibiting inflammatory responses, promoting angiogenesis, participating in cell proliferation and migration, and promoting pathological progression such as fibrosis.

AIM OF REVIEW

This systematic review examines the role of exosomes in various cardiovascular diseases such as atherosclerosis, myocardial infarction, ischemia-reperfusion injury, heart failure and cardiomyopathy. It also presents the latest treatment and prevention methods utilizing exosomes. The study aims to provide new insights and approaches for preventing and treating cardiovascular diseases by exploring the relationship between exosomes and these conditions. Furthermore, the review emphasizes the potential clinical use of exosomes as biomarkers for diagnosing cardiovascular diseases.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Exosomes are nanoscale vesicles surrounded by lipid bilayers that are secreted by most cells in the body. They are heterogeneous, varying in size and composition, with a diameter typically ranging from 40 to 160 nm. Exosomes serve as a means of information communication between cells, carrying various biologically active substances, including lipids, proteins, and small RNAs such as miRNAs and lncRNAs. As a result, they participate in both physiological and pathological processes within the body.

KNOCKDOWN OF CIRC_0001379 ATTENUATES HYPOXIA/REOXYGENATION-INDUCED CARDIOMYOCYTE APOPTOSIS AND INFLAMMATORY RESPONSE BY MIR-98-5P/SOX6 AXIS

ABSTRACT

Background: Aberrant expression of circular RNAs (circRNAs) has been revealed to have crucial roles in the pathological processes of cardiovascular disease. Here, this study aimed to investigate the role and mechanism of circ_0001379 in hypoxia/reoxygenation (H/R)-induced cardiomyocyte injury to explore the potential action of circ_0001379 in acute myocardial infarction (AMI). Methods: Levels of genes and proteins were examined by quantitative real-time polymerase chain reaction and western blot. Cell counting kit-8 assay, 5-ethynyl-2'-deoxyuridine assay, and flow cytometry were used to detect cardiomyocyte proliferation and apoptosis, respectively. The activity of IL-1β, IL-6, and TNF-α was determined by ELISA analysis. The target relationship between miR-98-5p and circ_0001379 or SOX6 (SRY-Box Transcription Factor 6) was verified by dual-luciferase reporter and RNA immunoprecipitation assays. Results: Circ_0001379 was highly expressed in AMI mouse model and H/R-induced cardiomyocytes. Functionally, circ_0001379 silencing attenuated H/R-evoked cardiomyocyte apoptosis and inflammatory response. Mechanistically, circ_0001379 functioned as a sponge for miR-98-5p, which directly targeted SOX6. Moreover, circ_0001379 could regulate SOX6 expression via sponging miR-98-5p. Further rescue experiments showed that inhibition of miR-98-5p reversed the protective effects of circ_0001379 silencing on H/R-induced cardiomyocytes. Besides that, miR-98-5p overexpression abolished H/R-evoked cardiomyocyte apoptosis and inflammatory response, while this condition was abated by SOX6. Conclusion: Circ_0001379 silencing protects cardiomyocytes from H/R-induced apoptosis and inflammatory response by miR-98-5p/SOX6 axis, suggesting a novel therapeutic strategy for AMI prevention.

MicroRNA-499-5p promotes vascular smooth muscle cell proliferation and migration via inhibiting SOX6

Atherosclerosis (AS) is the primary etiology of cardiovascular disease, which is considered the leading cause of death all over the world. MicroRNA miR-499-5p was involved in the functional regulation of myocardial and skeletal muscle, whereas its role in atherosclerosis, especially in vascular smooth muscle cells (VSMCs), remains unclear. Our study aims to investigate the effects of miR-499-5p in the proliferation and migration of VSMCs and potential mechanisms. We used mouse aortic vascular smooth muscle cells (MOVAS) and ApoE^-/- mice to establish the models of AS in vitro and in vivo, respectively. RT-PCR was performed to detect the expression level of miR-499-5p. Subsequently, Cell Counting Kit-8 (CCK-8) assays, Transwell assays, and wound-healing assays were used to evaluate cell proliferation and migration. Dual-luciferase reporter assay was performed to validate the interaction between miR-499-5p and SOX6. miR-499-5p significantly increased in aorta tissues of mice in AS tissues and vascular smooth muscle cells treated with ox-LDL. miR-499-5p overexpression could promote the proliferation and migration of MOVAS. Bioinformatics analysis predicted and further experiments verified that miR-499-5p could directly bind to the 3'-untranslated region (UTR) region of SOX6. Further, miR-499-5p induced an increased expression of smooth muscle proliferation and migration-related genes, PCNA, cyclin D1, and matrix metalloproteinase (MMP2), as well as the decreased expression of proliferation inhibiting factor p21, which was significantly reversed by SOX6 overexpression. miR-499-5p boosts the proliferation and migration of smooth muscle cells by binding and inhibiting SOX6 expression. The miR-499-5p/SOX6 axis may present a promising therapeutic implication for the prevention and treatment of cardiovascular diseases.

Effect of miR-499-5p/SOX6 axis on atrial fibrosis in rats with atrial fibrillation

Atrial fibrosis is involved in the progression of atrial fibrillation (AF). miR-499-5p is the most downregulated microRNA in arrhythmogenic cardiomyopathy hearts. Sry-related high-mobility-group box 6 (SOX6) is associated with apoptosis, inflammatory responses, and fibrosis. This study investigated the mechanism of miR-499-5p in ameliorating AF rats by regulating SOX6. AF rat models were established by injecting Ach-CaCl₂ mixture, and the rats were treated with Lv-miR-499-5p/oe-SOX6/si-SOX6 before modeling. AF duration was recorded using electrocardiogram. miR-499-5p and SOX6 expression levels in the myocardium were determined by reverse transcription-quantitative polymerase chain reaction. The binding of miR-499-5p and SOX6 was validated. The atrial fibrosis degree and cardiomyocyte apoptosis were assessed using the Masson and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining methods. Levels of SOX6, atrial fibrosis markers (collage I/α-SMA/TGFβ1), cell cycle-related proteins (p21/CDC25/Cyclin B1), and cell senescence markers (SA-β-gal/γ-H2AX) were measured using Western blotting and immunohistochemistry. miR-499-5p was downregulated and SOX6 was upregulated in AF rats. miR-499-5p overexpression shortened the AF duration, alleviated atrial fibrosis, and decreased collage I/α-SMA/TGFβ1. miR-499-5p targeted SOX6 to ameliorate atrial fibrosis. AF rats exhibited increased p21/CDC25/Cyclin B1/SA-β-gal/γ-H2AX levels and raised cardiomyocyte apoptosis. SOX6 silencing downregulated p21 and alleviated cardiomyocyte cycle arrest, cell senescence, and apoptosis in AF rats. Shortly, miR-499-5p suppresses atrial fibrosis and cardiomyocyte senescence by targeting SOX6 and downregulating p21, thus mitigating AF in rats.

Counteraction of Myocardial Ferritin Heavy Chain Deficiency by Heme Oxygenase-1

Given the abundance of heme proteins (cytochromes) in the mitochondrion, it is evident that a meticulously orchestrated iron metabolism is essential for cardiac health. Here, we examined the functional significance of myocardial ferritin heavy chain (FtH) in a model of acute myocardial infarction. We report that FtH deletion did not alter either the mitochondrial regulatory and surveillance pathways (fission and fusion) or mitochondrial bioenergetics in response to injury. Furthermore, deletion of myocardial FtH did not affect cardiac function, assessed by measurement of left ventricular ejection fraction, on days 1, 7, and 21 post injury. To identify the modulated pathways providing cardiomyocyte protection coincident with FtH deletion, we performed unbiased transcriptomic analysis. We found that following injury, FtH deletion was associated with upregulation of several genes with anti-ferroptotic properties, including heme oxygenase-1 (HO-1) and the cystine/glutamate anti-porter (Slc7a11). These results suggested that HO-1 overexpression mitigates ferroptosis via upregulation of Slc7a11. Indeed, using transgenic mice with HO-1 overexpression, we demonstrate that overexpressed HO-1 is coupled with increased Slc7a11 expression. In conclusion, we demonstrate that following injury, myocardial FtH deletion leads to a compensatory upregulation in a number of anti-ferroptotic genes, including HO-1. Such HO-1 induction leads to overexpression of Slc7a11 and protects the heart against ischemia-reperfusion-mediated ferroptosis, preserves mitochondrial function, and overall function of the myocardium.

Discovery of a Novel Small-Molecule Inhibitor Disrupting TRBP-Dicer Interaction against Hepatocellular Carcinoma via the Modulation of microRNA Biogenesis

MicroRNAs (miRNAs) are key players in human hepatocellular carcinoma (HCC) tumorigenesis. Therefore, small molecules targeting components of miRNA biogenesis may provide new therapeutic means for HCC treatment. By a high-throughput screening and structural simplification, we identified a small molecule, CIB-3b, which suppresses the growth and metastasis of HCC in vitro and in vivo by modulating expression profiles of miRNAome and proteome in HCC cells. Mechanistically, CIB-3b physically binds to transactivation response (TAR) RNA-binding protein 2 (TRBP) and disrupts the TRBP-Dicer interaction, thereby altering the activity of Dicer and mature miRNA production. Structure-activity relationship study via the synthesis of 45 CIB-3b derivatives showed that some compounds exhibited a similar inhibitory effect on miRNA biogenesis to CIB-3b. These results support TRBP as a potential therapeutic target in HCC and warrant further development of CIB-3b along with its analogues as a novel therapeutic strategy for the treatment of HCC.

Cardiac CIP protein regulates dystrophic cardiomyopathy

Heart failure is a leading cause of fatality in Duchenne muscular dystrophy (DMD) patients. Previously, we discovered that cardiac and skeletal-muscle-enriched CIP proteins play important roles in cardiac function. Here, we report that CIP, a striated muscle-specific protein, participates in the regulation of dystrophic cardiomyopathy. Using a mouse model of human DMD, we found that deletion of CIP leads to dilated cardiomyopathy and heart failure in young, non-syndromic mdx mice. Conversely, transgenic overexpression of CIP reduces pathological dystrophic cardiomyopathy in old, syndromic mdx mice. Genome-wide transcriptome analyses reveal that molecular pathways involving fibrogenesis and oxidative stress are affected in CIP-mediated dystrophic cardiomyopathy. Mechanistically, we found that CIP interacts with dystrophin and calcineurin (CnA) to suppress the CnA-Nuclear Factor of Activated T cells (NFAT) pathway, which results in decreased expression of Nox4, a key component of the oxidative stress pathway. Overexpression of Nox4 accelerates the development of dystrophic cardiomyopathy in mdx mice. Our study indicates CIP is a modifier of dystrophic cardiomyopathy and a potential therapeutic target for this devastating disease.

miR-208a in Cardiac Hypertrophy and Remodeling

Various stresses, including pressure overload and myocardial stretch, can trigger cardiac remodeling and result in heart diseases. The disorders are associated with high risk of morbidity and mortality and are among the major health problems in the world. MicroRNAs, a class of ~22nt-long small non-coding RNAs, have been found to participate in regulating heart development and function. One of them, miR-208a, a cardiac-specific microRNA, plays key role(s) in modulating gene expression in the heart, and is involved in a broad array of processes in cardiac pathogenesis. Genetic deletion or pharmacological inhibition of miR-208a in rodents attenuated stress-induced cardiac hypertrophy and remodeling. Transgenic expression of miR-208a in the heart was sufficient to cause hypertrophic growth of cardiomyocytes. miR-208a is also a key regulator of cardiac conduction system, either deletion or transgenic expression of miR-208a disturbed heart electrophysiology and could induce arrhythmias. In addition, miR-208a appeared to assist in regulating the expression of fast- and slow-twitch myofiber genes in the heart. Notably, this heart-specific miRNA could also modulate the “endocrine” function of cardiac muscle and govern the systemic energy homeostasis in the whole body. Despite of the critical roles, the underlying regulatory networks involving miR-208a are still elusive. Here, we summarize the progress made in understanding the function and mechanisms of this important miRNA in the heart, and propose several topics to be resolved as well as the hypothetical answers. We speculate that miR-208a may play diverse and even opposite roles by being involved in distinct molecular networks depending on the contexts. A deeper understanding of the precise mechanisms of its action under the conditions of cardiac homeostasis and diseases is needed. The clinical implications of miR-208a are also discussed.

Modulation of MicroRNA Processing by Dicer via Its Associated dsRNA Binding Proteins

MicroRNAs (miRNAs) are small non-coding RNAs that are about 22 nucleotides in length. They regulate gene expression post-transcriptionally by guiding the effector protein Argonaute to its target mRNA in a sequence-dependent manner, causing the translational repression and destabilization of the target mRNAs. Both Drosha and Dicer, members of the RNase III family proteins, are essential components in the canonical miRNA biogenesis pathway. miRNA is transcribed into primary-miRNA (pri-miRNA) from genomic DNA. Drosha then cleaves the flanking regions of pri-miRNA into precursor-miRNA (pre-miRNA), while Dicer cleaves the loop region of the pre-miRNA to form a miRNA duplex. Although the role of Drosha and Dicer in miRNA maturation is well known, the modulation processes that are important for regulating the downstream gene network are not fully understood. In this review, we summarized and discussed current reports on miRNA biogenesis caused by Drosha and Dicer. We also discussed the modulation mechanisms regulated by double-stranded RNA binding proteins (dsRBPs) and the function and substrate specificity of dsRBPs, including the TAR RNA binding protein (TRBP) and the adenosine deaminase acting on RNA (ADAR).

LncRNA LncHrt preserves cardiac metabolic homeostasis and heart function by modulating the LKB1-AMPK signaling pathway

Metabolic modulation is a promising therapeutic approach to prevent adverse remodeling of the ischemic heart. Because little is known about the involvement of long non-coding RNAs (lncRNAs) in regulating cardiac metabolism, we used unbiased transcriptome profiling in a mouse model of myocardial infarction (MI). We identified a novel cardiomyocyte-enriched lncRNA, called LncHrt, which regulates metabolism and the pathophysiological processes that lead to heart failure. AAV-based LncHrt overexpression protects the heart from MI as demonstrated by improved contractile function, preserved metabolic homeostasis, and attenuated maladaptive remodeling responses. RNA-pull down followed by mass spectrometry and RNA immunoprecipitation (RIP) identified SIRT2 as a LncHrt-interacting protein involved in cardiac metabolic regulation. Mechanistically, we established that LncHrt interacts with SIRT2 to preserve SIRT2 deacetylase activity by interfering with the CDK5 and SIRT2 interaction. This increases downstream LKB1-AMPK kinase signaling, which ameliorates functional and metabolic deficits. Importantly, we found the expression of the human homolog of mouse LncHrt was decreased in patients with dilated cardiomyopathy. Together, these studies identify LncHrt as a cardiac metabolic regulator that plays an essential role in preserving heart function by regulating downstream metabolic signaling pathways. Consequently, LncHrt is a potentially novel RNA-based therapeutic target for ischemic heart disease.

The SRSF4-GAS5-Glucocorticoid Receptor Axis Regulates Ventricular Hypertrophy

Supplemental Digital Content is available in the text.

RBPs (RNA-binding proteins) play critical roles in human biology and disease. Aberrant RBP expression affects various steps in RNA processing, altering the function of the target RNAs. The RBP SRSF4 (serine/arginine-rich splicing factor 4) has been linked to neuropathies and cancer. However, its role in the heart is completely unknown.

Identification of a Novel TAR RNA-Binding Protein 2 Modulator with Potential Therapeutic Activity against Hepatocellular Carcinoma

Imbalance miRNAs contribute to tumor formation; therefore, the development of small-molecule compounds that regulate miRNA biogenesis is an important strategy in oncotherapy. Here, (-)-Gomisin M1 (GM) was found to modulate miRNA biogenesis to inhibit the proliferation, migration, and invasion of hepatocellular carcinoma (HCC) cells. GM modulated expression profiles of miRNA and protein in HCC cells and suppressed tumor growth in a mouse model. Mechanistically, GM affected miRNA maturation by targeting TAR RNA-binding protein 2 (TRBP), with an efficacy higher than that of enoxacin, and promoted the binding of TRBP with Dicer. Structural simplification and a preliminary structure-activity relationship study via the synthesis of 20 GM derivatives showed that compound 9 exhibited more potent inhibitory activity in HCC cell proliferation and affinity for TRBP than did GM. These results suggest that TRBP may be a novel potential therapeutic target in HCC and compound 9 may be a potential drug candidate for the treatment of HCC.

Circular RNA circMYBPC1 promotes skeletal muscle differentiation by targeting MyHC

Skeletal muscle development is a complex and highly orchestrated biological process mediated by a series of myogenesis regulatory factors. Numerous studies have demonstrated that circular RNAs (circRNAs) are involved in muscle differentiation, but the exact molecular mechanisms involved remain unclear. Here, we analyzed the expression of circRNAs at the adult and embryo development stages of cattle musculus longissimus. A stringent set of 1,318 circRNAs candidates were identified, and we found that 495 circRNAs were differentially expressed between embryonic and adult tissue libraries. We subsequently focused on one of the most downregulated circRNAs (using the adult stage expression as control), and this was named muscle differentiation-associated circular RNA (circMYBPC1). With RNA binding protein immunoprecipitation (RIP) and RNA pull-down assays, circMYBPC1 was identified to promote myoblast differentiation by directly binding miR-23a to relieve its inhibition on myosin heavy chain (MyHC). In addition, RIP assays demonstrated that circMYBPC1 could directly bind MyHC protein. In vivo observations also suggested that circMYBPC1 may stimulate skeletal muscle regeneration after muscle damage. These results revealed that the novel non-coding circRNA circMYBPC1 promotes differentiation of myoblasts and may promote skeletal muscle regeneration. Our results provided a basis for in-depth analysis of the role of circRNA in myogenesis and muscle diseases.

GPR39 promotes cardiac hypertrophy by regulating the AMPK-mTOR pathway and protein synthesis

Hypertrophic growth of the cardiomyocytes is one of the core mechanisms underlying cardiac hypertrophy. However, the mechanism underlying cardiac hypertrophy remains not fully understood. Here we provided evidence that G protein-coupled receptor 39 (GPR39) promotes cardiac hypertrophy via inhibiting AMP-activated protein kinase (AMPK) signaling. GRP39 expression is overexpressed in hypertrophic hearts of humans and transverse aortic constriction (TAC)-induced cardiac hypertrophy in mice. In neonatal cardiomyocytes, adenovirus-mediated overexpression of GPR39 promoted angiotensin II-induced cardiac hypertrophy, while GPR39 knockdown repressed hypertrophic response. Adeno-associated virus 9-mediated knockdown of GPR39 suppressed TAC-induced decline in fraction shortening and ejection fraction, increase in heart weight and cardiomyocyte size, as well as overexpression of hypertrophic fetal genes. A mechanism study demonstrated that GPR39 repressed the activation of AMPK to activate the mammalian target of rapamycin (mTOR) and ribosomal protein S6 kinase β-1 (S6K1), subsequently promoted de novo protein synthesis. Inhibition of mTOR with rapamycin blocked the effects of GPR39 overexpression on protein synthesis and repressed cardiac hypertrophy. Collectively, our findings demonstrated that GPR39 promoted cardiac hypertrophy via regulating the AMPK-mTOR-S6K1 signaling pathway, and GRP39 can be targeted for the treatment of cardiac hypertrophy.

Emerging roles of Sox6 in the renal and cardiovascular system

The function of Sex-determining Region Y (SRY)-related high-mobility-group box (Sox) family of transcription factors in cell fate decisions during embryonic development are well-established. Accumulating evidence indicates that the Sox family of transcription factors are fundamental in adult tissue homeostasis, regeneration, and physiology. The SoxD subfamily of genes are expressed in various cell types of different organs during embryogenesis and adulthood and have been involved in cell-fate determination, cellular proliferation and survival, differentiation, and terminal maturation in a number of cell lineages. The dysregulation in the function of SoxD proteins (i.e. Sox5, Sox6, Sox13, and Sox23) have been implicated in different disease conditions such as chondrodysplasia, cancer, diabetes, hypertension, autoimmune diseases, osteoarthritis among others. In this minireview, we present recent developments related to the transcription factor Sox6, which is involved in a number of diseases such as diabetic nephropathy, adipogenesis, cardiomyopathy, inflammatory bowel disease, and cancer. Sox6 has been implicated in the regulation of renin expression and JG cell recruitment in mice during sodium depletion and dehydration. We provide a current perspective of Sox6 research developments in last five years, and the implications of Sox6 functions in cardiovascular physiology and disease conditions.

Intercalated disc protein Xinβ is required for Hippo-YAP signaling in the heart

Intercalated discs (ICD), specific cell-to-cell contacts that connect adjacent cardiomyocytes, ensure mechanical and electrochemical coupling during contraction of the heart. Mutations in genes encoding ICD components are linked to cardiovascular diseases. Here, we show that loss of Xinβ, a newly-identified component of ICDs, results in cardiomyocyte proliferation defects and cardiomyopathy. We uncovered a role for Xinβ in signaling via the Hippo-YAP pathway by recruiting NF2 to the ICD to modulate cardiac function. In Xinβ mutant hearts levels of phosphorylated NF2 are substantially reduced, suggesting an impairment of Hippo-YAP signaling. Cardiac-specific overexpression of YAP rescues cardiac defects in Xinβ knock-out mice—indicating a functional and genetic interaction between Xinβ and YAP. Our study reveals a molecular mechanism by which cardiac-expressed intercalated disc protein Xinβ modulates Hippo-YAP signaling to control heart development and cardiac function in a tissue specific manner. Consequently, this pathway may represent a therapeutic target for the treatment of cardiovascular diseases.

Intercalated discs ensure mechanical and electrochemical coupling during contraction of the heart. Here, the authors show that loss of Xinβ results in cardiomyocyte proliferation defects and cardiomyopathy by influencing the Hippo-YAP signalling pathway, thus affecting cardiac development and function.

Dicer's Helicase Domain: A Meeting Place for Regulatory Proteins

The function of Dicer’s helicase domain has been enigmatic since its discovery. Why do only some Dicers require ATP, despite a high degree of sequence conservation in their helicase domains? We discuss evolutionary considerations based on differences between vertebrate and invertebrate antiviral defense, and how the helicase domain has been co-opted in extant organisms as the binding site for accessory proteins. Many accessory proteins are double-stranded RNA binding proteins, and we propose models for how they modulate Dicer function and catalysis.

Human umbilical cord mesenchymal stem cells-derived exosomes transfers microRNA-19a to protect cardiomyocytes from acute myocardial infarction by targeting SOX6

Exosomes secreted by human umbilical cord mesenchymal stem cells (hucMSCs) protect cardiomyocytes from anoxia-reoxygenation injury. But the mechanism of hucMSC-exo-microRNA (miR)-19a in acute myocardial infarction (AMI) remains unclear. For this study, cardiac function related indicators, inflammatory factors and markers of myocardial injury, cardiomyocyte injury, infarct size, and apoptosis were detected in vivo experiments. The gain-and loss-of function was performed to evaluate the effects of hucMSC-exo with down/upregulated miR-19a on AMI rats and hypoxic H9C2 cells. Western blot analysis was used to detect levels of AKT/JNK3/caspase-3 axis-related proteins. Consequently, hucMSC-exo alleviated AMI and inhibited cardiomyocyte apoptosis. miR-19a was downregulated in AMI tissues and cells, and increased after hucMSC-exo treatment. miR-19a knockdown in hucMSC-exo impaired the protective role of hucMSC-exo alone in the AMI damage. SOX6 is a target gene of miR-19a and its inhibition lightened hypoxic damage of H9C2 cells. SOX6 knockdown together with miR-19a inhibition in hucMSC-exo activated AKT and inhibited JNK3/caspase-3 axis. Taken together, hucMSC-exo protected cardiomyocytes from AMI injury by transferring miR-19a, targeting SOX6, activating AKT, and inhibiting JNK3/caspase-3 activation. This study may provide new understanding for AMI treatment.

Dicer partner protein tunes the length of miRNAs using base-mismatch in the pre-miRNA stem

Dicer partner proteins Drosophila Loquacious-PB (Loqs-PB) and human TRBP tune the length of miRNAs produced by Dicer from a subset of pre-miRNAs and thereby alter their target repertoire, by an unknown mechanism. Here, we developed a novel high-throughput method that we named Dram-seq (Dice randomized pre-miRNA pool and seq) to study length distributions of miRNAs produced from thousands of different pre-miRNA variants. Using Dram-seq, we found that a base-mismatch in the pre-miRNA stem can alter the length of miRNAs compared with a base-pair at the same position in both Drosophila and human, and is important for the miRNA length tuning by Loqs-PB. Loqs-PB directly bound base-mismatched nucleotides in the pre-miRNA stem. We speculate that Loqs-PB tunes miRNA length by changing the conformation of base-mismatched nucleotides in the pre-miRNA stem to that of base-paired ones and thereby altering the distance of the pre-miRNA stem.

Altered erythroid-related miRNA levels as a possible novel biomarker for detection of autologous blood transfusion misuse in sport

BACKGROUND

Autologous blood transfusion (ABT) is a performance-enhancing method prohibited in sport; its detection is a key issue in the field of anti-doping. Among novel markers enabling ABT detection, microRNAs (miRNAs) might be considered a promising analytical tool.

STUDY DESIGN AND METHODS

We studied the changes of erythroid-related microRNAs following ABT, to identify novel biomarkers. Fifteen healthy trained males were studied from a population of 24 subjects, enrolled and randomized into a Transfusion (T) and a Control (C) group. Seriated blood samples were obtained in the T group before and after the two ABT procedures (withdrawal, with blood refrigerated or cryopreserved, and reinfusion), and in the C group at the same time points. Traditional hematological parameters were assessed. Samples were tested by microarray analysis of a pre-identified set of erythroid-related miRNAs.

RESULTS

Hematological parameters showed moderate changes only in the T group, particularly following blood withdrawal. Among erythroid-related miRNAs tested, following ABT a pool of 7 miRNAs associated with fetal hemoglobin and regulating transcriptional repressors of gamma-globin gene was found stable in C and differently expressed in three out of six T subjects in the completed phase of ABT, independently from blood conservation. Particularly, two or more erythropoiesis-related miRNAs within the shortlist constituted of miR-126-3p, miR-144-3p, miR-191-3p, miR-197-3p, miR-486-3p, miR-486-5p, and miR-92a-3p were significantly upregulated in T subjects after reinfusion, with a person-to-person variability but with congruent changes.

CONCLUSIONS

This study describes a signature of potential interest for ABT detection in sports, based on the analysis of miRNAs associated with erythroid features.

Loss of SRSF3 in Cardiomyocytes Leads to Decapping of Contraction-Related mRNAs and Severe Systolic Dysfunction

RATIONALE

RBPs (RNA binding proteins) play critical roles in the cell by regulating mRNA transport, splicing, editing, and stability. The RBP SRSF3 (serine/arginine-rich splicing factor 3) is essential for blastocyst formation and for proper liver development and function. However, its role in the heart has not been explored.

OBJECTIVE

To investigate the role of SRSF3 in cardiac function.

METHODS AND RESULTS

Cardiac SRSF3 expression was high at mid gestation and decreased during late embryonic development. Mice lacking SRSF3 in the embryonic heart showed impaired cardiomyocyte proliferation and died in utero. In the adult heart, SRSF3 expression was reduced after myocardial infarction, suggesting a possible role in cardiac homeostasis. To determine the role of this RBP in the adult heart, we used an inducible, cardiomyocyte-specific SRSF3 knockout mouse model. After SRSF3 depletion in cardiomyocytes, mice developed severe systolic dysfunction that resulted in death within 8 days. RNA-Seq analysis revealed downregulation of mRNAs encoding sarcomeric and calcium handling proteins. Cardiomyocyte-specific SRSF3 knockout mice also showed evidence of alternative splicing of mTOR (mammalian target of rapamycin) mRNA, generating a shorter protein isoform lacking catalytic activity. This was associated with decreased phosphorylation of 4E-BP1 (eIF4E-binding protein 1), a protein that binds to eIF4E (eukaryotic translation initiation factor 4E) and prevents mRNA decapping. Consequently, we found increased decapping of mRNAs encoding proteins involved in cardiac contraction. Decapping was partially reversed by mTOR activation.

CONCLUSIONS

We show that cardiomyocyte-specific loss of SRSF3 expression results in decapping of critical mRNAs involved in cardiac contraction. The molecular mechanism underlying this effect likely involves the generation of a short mTOR isoform by alternative splicing, resulting in reduced 4E-BP1 phosphorylation. The identification of mRNA decapping as a mechanism of systolic heart failure may open the way to the development of urgently needed therapeutic tools.

Myricetin improves endurance capacity by inducing muscle fiber type conversion via miR-499

Background

Reprogramming of fast-to-slow myofiber switch can improve endurance capacity and alleviate fatigue. Accumulating evidence suggests that a muscle-specific microRNA, miR-499 plays a crucial role in myofiber type transition. In this study, we assessed the effects of natural flavonoid myricetin on exercise endurance and muscle fiber constitution, and further investigated the underlying mechanism of myricetin in vivo and in vitro.

Methods

A total of 66 six-week-old male Sprague Dawley rats were divided into non-exercise or exercise groups with/without orally administered myricetin (50 or 150 mg/kg) for 2 or 4 weeks. Time-to-exhaustion, blood biochemical parameters, muscle fiber type proportion, the expression of muscle type decision related genes were measured. Mimic/ inhibitor of miR-499 were transfected into cultured L6 myotubes, the expressions of muscle type decision related genes and mitochondrial respiration capacity were investigated.

Results

Myricetin treatment significantly improved the time-to-exhaustion in trained rats. The enhancement of endurance capacity was associated with an increase of the proportion of slow-twitch myofiber in both soleus and gastrocnemius muscles. Importantly, myricetin treatment amplified the expression of miR-499 and suppressed the expression of Sox6, the down-stream target gene of miR-499, both in vivo and in vitro. Furthermore, inhibition of miR-499 overturned the effects of myricetin on down-regulating Sox6.

Conclusions

Myricetin promoted the reprogramming of fast-to-slow muscle fiber type switch and reinforced the exercise endurance capacity. The precise mechanisms responsible for the effects of myricetin are not resolved but likely involve regulating miR-499/Sox6 axis.

Therapeutic role of miR-19a/19b in cardiac regeneration and protection from myocardial infarction

The primary cause of heart failure is the loss of cardiomyocytes in the diseased adult heart. Previously, we reported that the miR-17-92 cluster plays a key role in cardiomyocyte proliferation. Here, we report that expression of miR-19a/19b, members of the miR-17-92 cluster, is induced in heart failure patients. We show that intra-cardiac injection of miR-19a/19b mimics enhances cardiomyocyte proliferation and stimulates cardiac regeneration in response to myocardial infarction (MI) injury. miR-19a/19b protected the adult heart in two distinctive phases: an early phase immediately after MI and long-term protection. Genome-wide transcriptome analysis demonstrates that genes related to the immune response are repressed by miR-19a/19b. Using an adeno-associated virus approach, we validate that miR-19a/19b reduces MI-induced cardiac damage and protects cardiac function. Finally, we confirm the therapeutic potential of miR-19a/19b in protecting cardiac function by systemically delivering miR-19a/19b into mice post-MI. Our study establishes miR-19a/19b as potential therapeutic targets to treat heart failure.

Long Noncoding RNA CPR (Cardiomyocyte Proliferation Regulator) Regulates Cardiomyocyte Proliferation and Cardiac Repair

BACKGROUND

The adult mammalian cardiomyocytes lose their proliferative capacity, which is responsible for cardiac dysfunction and heart failure following injury. The molecular mechanisms underlying the attenuation of adult cardiomyocyte proliferation remain largely unknown. Because long noncoding RNAs (lncRNAs) have a critical role in the development of cardiovascular problems, we investigated whether lncRNAs have any role in the regulation of cardiomyocyte proliferation and cardiac repair.

METHODS

Using bioinformatics and initial analysis, we identified an lncRNA, named CPR (cardiomyocyte proliferation regulator), that has a potential regulatory role in cardiomyocyte proliferation. For in vivo experiments, we generated CPR knockout and cardiac-specific CPR-overexpressing mice. In isolated cardiomyocytes, we used adenovirus for silencing (CPR-small interfering RNA) or overexpressing CPR. To investigate the mechanisms of CPR function in cardiomyocyte proliferation, we performed various analyses including quantitative reverse transcription-polymerase chain reaction, Western blot, histology, cardiac function (by echocardiography), transcriptome analyses (microarray assay), RNA pull-down assay, and chromatin immunoprecipitation assay.

RESULTS

CPR level is comparatively higher in the adult heart than in the fetal stage. The silencing of CPR significantly increased cardiomyocyte proliferation in postnatal and adult hearts. Moreover, CPR deletion restored the heart function after myocardial injury, which was evident from increased cardiomyocyte proliferation, improvement of myocardial function, and reduced scar formation. In contrast, the neonatal cardiomyocyte proliferation and cardiac regeneration were remarkably suppressed in CPR-overexpressing mice or adeno-associated virus serotype 9-CPR-overexpressing heart. These results indicate that CPR acts as a negative regulator of cardiomyocyte proliferation and regeneration. Next, we found that CPR targets minichromosome maintenance 3, an initiator of DNA replication and cell cycle progression, to suppress cardiomyocyte proliferation. CPR silenced minichromosome maintenance 3 expression through directly interacting and recruiting DNMT3A to its promoter cysteine-phosphate-guanine sites, as evident from decreased minichromosome maintenance 3 promoter methylation and increased minichromosome maintenance 3 expression in CPR knocked-down cardiomyocytes and CPR knockout mouse heart. These results were confirmed in CPR-overexpressing cardiomyocytes and CPR-overexpressing mouse heart.

CONCLUSIONS

Together, our findings identified that CPR is a suppressor of cardiomyocyte proliferation and indicated that lncRNAs take part in the regulation of cardiomyocyte proliferation and cardiac repair. Our study provides an lncRNA-based therapeutic strategy for effective cardiac repair and regeneration.

LncRNA Riken-201 and Riken-203 modulates neural development by regulating the Sox6 through sequestering miRNAs

Objectives

Long non‐coding RNAs (LncRNAs) play important roles in epigenetic regulatory function during the development processes. In this study, we found that through alternative splicing, LncRNA C130071C03Riken variants Riken‐201 (Riken‐201) and Riken‐203 (Riken‐203) are both expressed highly in brain, and increase gradually during neural differentiation. However, the function of Rik‐201 and Rik‐203 is unknown.

Materials and methods

Embryonic stem cells (ESCs); RNA sequencing; gene expression of mRNAs, LncRNAs and miRNAs; over‐expression and RNA interference of genes; flow cytometry; real‐time quantity PCR; and Western blot were used in the studies. RNA pull‐down assay and PCR were employed to detect any miRNA that attached to Rik‐201 and Rik‐203. The binding of miRNA with mRNA of Sox6 was presented by the luciferase assay.

Results

Repression of Rik‐201 and Rik‐203 inhibited neural differentiation from mouse embryonic stem cells. Moreover, Rik‐201 and Rik‐203 functioned as the competing endogenous RNA (ceRNA) to repress the function of miR‐96 and miR‐467a‐3p, respectively, and modulate the expression of Sox6 to further regulate neural differentiation. Knockout of the Rik‐203 and Rik‐201 induced high ratio of brain developmental retardation. Further we found that C/EBPβ might potentially activated the transcription of Rik‐201 and Rik‐203.

Conclusions

These findings identify the functional role of Rik‐201 and Rik‐203 in facilitating neural differentiation and further brain development, and elucidate the underlying miRNAs‐Sox6‐associated molecular mechanisms.

MicroRNA-135a-5p promotes neuronal differentiation of pluripotent embryonal carcinoma cells by repressing Sox6/CD44 pathway

MicroRNA-135a-5p has been reported to play a potential role in the generation of new neurons. However, the underlying targets of miR-135a-5p in regulating neuronal differentiation have been poorly understood. Our study recently has uncovered that Sox6 and CD44 genes were significantly downregulated during neuronal differentiation of P19 cells, a multipotent cell type. We then found that Sox6 directly bound to the promoter of CD44. Importantly, we identified Sox6 as a direct target of miR-135a-5p. Additionally, we demonstrated that miR-135a-5p is crucial for the neuronal differentiation of P19 cells. More significantly, we found that Sox6 overexpression could overturn miR-135a-5p-mediated neuronal differentiation and dendrite development. In conclusion, these findings indicated that miR-135a-5p/Sox6/CD44 axis provides an important molecular target mechanism for neurodifferentiation.

miR-26a-5p Regulates Synovial Fibroblast Invasion in Patients with Rheumatoid Arthritis by Targeting Smad 1

BACKGROUND We studied the expression and effect of miR-26a-5p in synovial fibroblast in patients with rheumatoid arthritis (RA). MATERIAL AND METHODS The synovial tissues of 55 RA patients with total knee arthroplasty performed from January 2016 to December 2016 were collected as the RA group, and 62 patients without RA history amputation or total knee arthroplasty served as the control group. The expressions of miR-26a-5p and Smad 1 mRNA in synovial fibroblast in patients with RA were detected by qPCR; The expression of Smad 1 and TGF-β1 protein in synovial tissue or synovial fibroblasts was detected by immunoblotting. Transwell assay was used to detect the invasive ability of synovial fibroblasts. RESULTS The expression of miR-26a-5p and Smad 1 in synovial fibroblast in patients with RA were significantly higher than those in the control group (P<0.05). The expression of miR-26a-5p in synovial tissue of RA patients was positively correlated with the expression of Smad 1 mRNA (r=0.8982, P<0.001). The luciferase system showed that miR-26a-5p targeting synovial membrane FLS cells (P<0.05); the expression of MMP-1, MMP-3, MMP-13, and TGF-b1 protein and mRNA in the synovial FLS cells of RA patients was significantly decreased; and the expression of miR-26a-5p was significantly decreased in FLS cells with invasive ability. CONCLUSIONS miR-26a-5p is highly expressed in synovial tissue of patients with RA, and its high expression can improve the invasive ability of synovial fibroblasts by targeting Smad 1 gene and accelerating the progression of RA.

Non-coding RNAs and exercise: pathophysiological role and clinical application in the cardiovascular system

There is overwhelming evidence that regular exercise training is protective against cardiovascular disease (CVD), the main cause of death worldwide. Despite the benefits of exercise, the intricacies of their underlying molecular mechanisms remain largely unknown. Non-coding RNAs (ncRNAs) have been recognized as a major regulatory network governing gene expression in several physiological processes and appeared as pivotal modulators in a myriad of cardiovascular processes under physiological and pathological conditions. However, little is known about ncRNA expression and role in response to exercise. Revealing the molecular components and mechanisms of the link between exercise and health outcomes will catalyse discoveries of new biomarkers and therapeutic targets. Here we review the current understanding of the ncRNA role in exercise-induced adaptations focused on the cardiovascular system and address their potential role in clinical applications for CVD. Finally, considerations and perspectives for future studies will be proposed.

Cardiomyocytes have mosaic patterns of protein expression

Skeletal myocytes have well-established fast and slow twitch fibers with unique gene and protein specific expression patterns. By immunohistochemical staining, these show a mosaic pattern across myocytes. We hypothesized cardiac myocytes may behave similarly where some proteins are differentially expressed between mature cardiomyocytes. We utilized the tool HPASubC on over 52,000 cardiac images of the Human Protein Atlas to identify differential protein expression patterns by immunohistochemistry across the cardiomyocytes. We matched identified proteins to open chromatin and gene expression data. We identified 143 putative proteins with mosaic patterns of expression across the cardiomyocytes. We validated four of these proteins (MYL3, MYL4, PAM, and MYOM1) and demonstrated unique atrial or ventricular patterns of expression for each. Acetylation of histone H3K27 at the promoters of these four genes were consistent with the atrial/ventricular expression patterns. Despite the generally accepted homogeneity of cardiomyocytes, a small subset of proteins varies between cardiomyocytes in a mosaic pattern. This fundamental process has been previously uncharacterized. These changes may inform on different functional and disease-related activities of proteins in individual cardiomyocytes.

Mitochondria regulate cardiac contraction through ATP-dependent and independent mechanisms

The multipurpose organelle mitochondria play an essential role(s) in controlling cardiac muscle contraction. Mitochondria, not only function as the powerhouses and the energy source of myocytes but also modulate intracellular Ca²⁺ homeostasis, the production of intermediary metabolites/reactive oxygen species (ROS), and other cellular processes. Those molecular events can substantially influence myocardial contraction. Mitochondrial dysfunction is usually associated with cardiac remodelling, and is the causal factor of heart contraction defects in many cases. The manipulation of mitochondria or mitochondria-relevant pathways appears to be a promising therapeutic approach to treat the diseases.

Expression of TARBP1 protein in human non-small-cell lung cancer and its prognostic significance

The aim of the present study was to investigate the expression of transactivation response RNA-binding protein (TARBP)1 and its clinical significance in human non-small-cell lung cancer (NSCLC). TARBP1 expression at the mRNA level was detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) in 10 NSCLC tissues and paired adjacent normal tissues. TARBP1 protein expression was analyzed in 90 paraffin-embedded NSCLC tissue samples and paired adjacent normal tissues by immunohistochemistry. Statistical analyses were performed to assess the clinicopathological significance of TARBP1 expression. The expression of TARBP1 mRNA was higher in the 10 NSCLC samples than in the paired adjacent non-tumor tissues (P=0.0017). In the paraffin-embedded tissue samples, the expression level of TARBP1 was higher in the cancer tissues than in the adjacent non-cancerous tissues. TARBP1 expression was detected in 76.67% (69/90) of the NSCLC samples and in 22.22% (20/90) of the adjacent normal lung tissues (P<0.001). The expression of TARBP1 was significantly associated with histological grade (P<0.001), clinical stage (P=0.024) and pathological type (P<0.001), along with a decreased overall survival (OS) rate (P<0.001). On multivariate analysis, the expression of TARBP1 was an independent prognostic factor for hazard ratio (OS, 2.729; 95% confidence interval, 1.471-5.061; P=0.003). TARBP1 is overexpressed in NSCLC, and the expression of TARBP1 is associated with pathological grade, clinical stage and pathological type. Thus, TARBP1 may be an independent prognostic marker in patients with NSCLC.

Temporally Distinct Six2-Positive Second Heart Field Progenitors Regulate Mammalian Heart Development and Disease

The embryonic process of forming a complex structure such as the heart remains poorly understood. Here, we show that Six2 marks a dynamic subset of second heart field progenitors. Six2-positive (Six2⁺) progenitors are rapidly recruited and assigned, and their descendants are allocated successively to regions of the heart from the right ventricle (RV) to the pulmonary trunk. Global ablation of Six2⁺ progenitors resulted in RV hypoplasia and pulmonary atresia. An early stage-specific ablation of a small subset of Six2⁺ progenitors did not cause any apparent structural defect at birth but rather resulted in adult-onset cardiac hypertrophy and dysfunction. Furthermore, Six2 expression depends in part on Shh signaling, and Shh deletion resulted in severe deficiency of Six2⁺ progenitors. Collectively, these findings unveil the chronological features of cardiogenesis, in which the mammalian heart is built sequentially by temporally distinct populations of cardiac progenitors, and provide insights into late-onset congenital heart disease.

Physiology of Cardiac Development: From Genetics to Signaling to Therapeutic Strategies

The heart is one of the first organs to form and function during embryonic development. It is comprised of multiple cell lineages, each integral for proper cardiac development, and include cardiomyocytes, endothelial cells, epicardial cells and neural crest cells. The molecular mechanisms regulating cardiac development and morphogenesis are dependent on signaling crosstalk between multiple lineages through paracrine interactions, cell-ECM interactions, and cell-cell interactions, which together, help facilitate survival, growth, proliferation, differentiation and migration of cardiac tissue. Aberrant regulation of any of these processes can induce developmental disorders and pathological phenotypes. Here, we will discuss each of these processes, the genetic factors that contribute to each step of cardiac development, as well as the current and future therapeutic targets and mechanisms of heart development and disease. Understanding the complex interactions that regulate cardiac development, proliferation and differentiation is not only vital to understanding the causes of congenital heart defects, but to also finding new therapeutics that can treat both pediatric and adult cardiac disease in the near future.

Kinome and Transcriptome Profiling Reveal Broad and Distinct Activities of Erlotinib, Sunitinib, and Sorafenib in the Mouse Heart and Suggest Cardiotoxicity From Combined Signal Transducer and Activator of Transcription and Epidermal Growth Factor Receptor Inhibition

BACKGROUND

Most novel cancer therapeutics target kinases that are essential to tumor survival. Some of these kinase inhibitors are associated with cardiotoxicity, whereas others appear to be cardiosafe. The basis for this distinction is unclear, as are the molecular effects of kinase inhibitors in the heart.

METHODS AND RESULTS

We administered clinically relevant doses of sorafenib, sunitinib (cardiotoxic multitargeted kinase inhibitors), or erlotinib (a cardiosafe epidermal growth factor receptor inhibitor) to mice daily for 2 weeks. We then compared the effects of these 3 kinase inhibitors on the cardiac transcriptome using RNAseq and the cardiac kinome using multiplexed inhibitor beads coupled with mass spectrometry. We found unexpectedly broad molecular effects of all 3 kinase inhibitors, suggesting that target kinase selectivity does not define either the molecular response or the potential for cardiotoxicity. Using in vivo drug administration and primary cardiomyocyte culture, we also show that the cardiosafety of erlotinib treatment may result from upregulation of the cardioprotective signal transducer and activator of transcription 3 pathway, as co-treatment with erlotinib and a signal transducer and activator of transcription inhibitor decreases cardiac contractile function and cardiomyocyte fatty acid oxidation.

CONCLUSIONS

Collectively our findings indicate that preclinical kinome and transcriptome profiling may predict the cardiotoxicity of novel kinase inhibitors, and suggest caution for the proposed therapeutic strategy of combined signal transducer and activator of transcription/epidermal growth factor receptor inhibition for cancer treatment.

An integrated expression atlas of miRNAs and their promoters in human and mouse

MicroRNAs (miRNAs) are short non-coding RNAs with key roles in cellular regulation. As part of the fifth edition of the Functional Annotation of Mammalian Genome (FANTOM5) project, we created an integrated expression atlas of miRNAs and their promoters by deep-sequencing 492 short RNA (sRNA) libraries, with matching Cap Analysis Gene Expression (CAGE) data, from 396 human and 47 mouse RNA samples. Promoters were identified for 1,357 human and 804 mouse miRNAs and showed strong sequence conservation between species. We also found that primary and mature miRNA expression levels were correlated, allowing us to use the primary miRNA measurements as a proxy for mature miRNA levels in a total of 1,829 human and 1,029 mouse CAGE libraries. We thus provide a broad atlas of miRNA expression and promoters in primary mammalian cells, establishing a foundation for detailed analysis of miRNA expression patterns and transcriptional control regions.

Cnot3 enhances human embryonic cardiomyocyte proliferation by promoting cell cycle inhibitor mRNA degradation

Uncovering the molecular basis of mammalian cardiomyocyte proliferation may eventually lead to better approaches for heart regeneration. Compared to extensively-studied transcriptional regulation, the roles of posttranscriptional regulation in cardiac cell fate decisions remain largely unknown. Here, we identified Cnot3 as a critical regulator in cardiomyocyte proliferation at the late stage of cardiac differentiation from human ESCs. Cnot3 was highly expressed in cardiomyocytes with higher proliferation potential in both human and mouse, and its depletion resulted in significant reduction in the proliferative capacity of cells. Furthermore, Cnot3 overexpression greatly enhanced proliferation in both cultured human cardiomyocytes and infarcted murine hearts. Mechanistically, the Ccr4-Not complex preferentially interacted with anti-proliferation gene transcripts in a Cnot3-dependent manner, and promoted their degradation. Together, our study supported the model that Cnot3 enhances cardiomyocyte proliferation by promoting cell cycle inhibitor mRNA degradation. It revealed a previously unrecognized role of mRNA degradation in cardiomyocyte growth, and suggested a potential strategy to control cardiac cell fates in development and diseases.

EED orchestration of heart maturation through interaction with HDACs is H3K27me3-independent

In proliferating cells, where most Polycomb repressive complex 2 (PRC2) studies have been performed, gene repression is associated with PRC2 trimethylation of H3K27 (H3K27me3). However, it is uncertain whether PRC2 writing of H3K27me3 is mechanistically required for gene silencing. Here, we studied PRC2 function in postnatal mouse cardiomyocytes, where the paucity of cell division obviates bulk H3K27me3 rewriting after each cell cycle. EED (embryonic ectoderm development) inactivation in the postnatal heart (Eed^CKO) caused lethal dilated cardiomyopathy. Surprisingly, gene upregulation in Eed^CKO was not coupled with loss of H3K27me3. Rather, the activating histone mark H3K27ac increased. EED interacted with histone deacetylases (HDACs) and enhanced their catalytic activity. HDAC overexpression normalized Eed^CKO heart function and expression of derepressed genes. Our results uncovered a non-canonical, H3K27me3-independent EED repressive mechanism that is essential for normal heart function. Our results further illustrate that organ dysfunction due to epigenetic dysregulation can be corrected by epigenetic rewiring.

DOI:http://dx.doi.org/10.7554/eLife.24570.001

Poly(C)-binding protein 1 (Pcbp1) regulates skeletal muscle differentiation by modulating microRNA processing in myoblasts

Regulation of gene expression during muscle development and disease remains incompletely understood. microRNAs are a class of small non-coding RNAs that regulate gene expression and function post-transcriptionally. The poly(C)-binding protein1 (Pcbp1, hnRNP-E1, or αCP-1) is an RNA-binding protein that has been reported to bind the 3'-UTRs of target genes to regulate mRNA stability and protein translation. However, Pcbp1's biological function and the general mechanism of action remain largely undetermined. Here, we report that Pcbp1 is a component of the miRNA-processing pathway that regulates miRNA biogenesis. siRNA-based inhibition of Pcbp1 in mouse skeletal muscle myoblasts led to dysregulated cellular proliferation and differentiation. We also found that Pcbp1 null mutant mice exhibit early embryonic lethality, indicating that Pcbp1 is indispensable for embryonic development. Interestingly, hypomorphic Pcbp1 mutant mice displayed defects in muscle growth due to defects in the proliferation and differentiation of myoblasts and muscle satellite cells, in addition to a slow to fast myofibril switch. Moreover, Pcbp1 modulated the processing of muscle-enriched miR-1, miR-133, and miR-206 by physically interacting with argonaute 2 (AGO2) and other miRNA pathway components. Our study, therefore, uncovers the important function of Pcbp1 in skeletal muscle and the microRNA pathway, signifying its potential as a therapeutic target for muscle disease.

Preparation of rAAV9 to Overexpress or Knockdown Genes in Mouse Hearts

Controlling the expression or activity of specific genes through the myocardial delivery of genetic materials in murine models permits the investigation of gene functions. Their therapeutic potential in the heart can also be determined. There are limited approaches for in vivo molecular intervention in the mouse heart. Recombinant adeno-associated virus (rAAV)-based genome engineering has been utilized as an essential tool for in vivo cardiac gene manipulation. The specific advantages of this technology include high efficiency, high specificity, low genomic integration rate, minimal immunogenicity, and minimal pathogenicity. Here, a detailed procedure to construct, package, and purify the rAAV9 vectors is described. Subcutaneous injection of rAAV9 into neonatal pups results in robust expression or efficient knockdown of the gene(s) of interest in the mouse heart, but not in the liver and other tissues. Using the cardiac-specific TnnT2 promoter, high expression of GFP gene in the heart was obtained. Additionally, target mRNA was inhibited in the heart when a rAAV9-U6-shRNA was utilized. Working knowledge of rAAV9 technology may be useful for cardiovascular investigations.

Molecular inotropy mediated by cardiac miR-based PDE4D/PRKAR1α/phosphoprotein signaling

Molecular inotropy refers to cardiac contractility that can be modified to affect overall heart pump performance. Here we show evidence of a new molecular pathway for positive inotropy by a cardiac-restricted microRNA (miR). We report enhanced cardiac myocyte performance by acute titration of cardiac myosin-embedded miR-208a. The observed positive effect was independent of host gene myosin effects with evidence of negative regulation of cAMP-specific 3',5'-cyclic phosphodiesterase 4D (PDE4D) and the regulatory subunit of PKA (PRKAR1α) content culminating in PKA-site dependent phosphorylation of cardiac troponin I (cTnI) and phospholamban (PLN). Further, acute inhibition of miR-208a in adult myocytes in vitro increased PDE4D expression causing reduced isoproterenol-mediated phosphorylation of cTnI and PLN. Next, rAAV-mediated miR-208a gene delivery enhanced heart contractility and relaxation parameters in vivo. Finally, acute inducible increases in cardiac miR-208a in vivo reduced PDE4D and PRKAR1α, with evidence of increased content of several complementary miRs harboring the PDE4D recognition sequence. Physiologically, this resulted in significant cardiac cTnI and PLN phosphorylation and improved heart performance in vivo. As phosphorylation of cTnI and PLN is critical to myocyte function, titration of miR-208a represents a potential new mechanism to enhance myocardial performance via the PDE4D/PRKAR1α/PKA phosphoprotein signaling pathway.

How cardiomyocytes sense pathophysiological stresses for cardiac remodeling

In the past decades, the cardiovascular community has laid out the fundamental signaling cascades that become awry in the cardiomyocyte during the process of pathologic cardiac remodeling. These pathways are initiated at the cell membrane and work their way to the nucleus to mediate gene expression. Complexity is multiplied as the cardiomyocyte is subjected to cross talk with other cells as well as a barrage of extracellular stimuli and mechanical stresses. In this review, we summarize the signaling cascades that play key roles in cardiac function and then we proceed to describe emerging concepts of how the cardiomyocyte senses the mechanical and environmental stimuli to transition to the deleterious genetic program that defines pathologic cardiac remodeling. As a highlighting example of these processes, we illustrate the transition from a compensated hypertrophied myocardium to a decompensated failing myocardium, which is clinically manifested as decompensated heart failure.

Pharmacology of heart failure: From basic science to novel therapies

Chronic heart failure is one of the leading causes for hospitalization in the United States and Europe, and is accompanied by high mortality. Current pharmacological therapy of chronic heart failure with reduced ejection fraction is largely based on compounds that inhibit the detrimental action of the adrenergic and the renin-angiotensin-aldosterone systems on the heart. More than one decade after spironolactone, two novel therapeutic principles have been added to the very recently released guidelines on heart failure therapy: the HCN-channel inhibitor ivabradine and the combined angiotensin and neprilysin inhibitor valsartan/sacubitril. New compounds that are in phase II or III clinical evaluation include novel non-steroidal mineralocorticoid receptor antagonists, guanylate cyclase activators or myosine activators. A variety of novel candidate targets have been identified and the availability of gene transfer has just begun to accelerate translation from basic science to clinical application. This review provides an overview of current pharmacology and pharmacotherapy in chronic heart failure at three stages: the updated clinical guidelines of the American Heart Association and the European Society of Cardiology, new drugs which are in clinical development, and finally innovative drug targets and their mechanisms in heart failure which are emerging from preclinical studies will be discussed.

AAV9 Delivery of shRNA to the Mouse Heart

RNA interference (RNAi) is a rapid approach to dissect loss-of-function phenotype for a gene of interest. However, it is challenging to perform RNAi in specific organs and tissues in vivo. Engineered viruses can provide a useful tool for delivery of small RNAs in vivo. Recombinant adeno-associated viruses (rAAVs) are the preferred method for delivering genes or gene modulators to target cells due to their high titer, low immune response, ability to transduce many types of cell, and overall safety. In this unit, we describe protocols for use of rAAVs as a cargo to deliver miRNA backbone-based shRNA controlled by a cardiac-specific promoter into the mouse heart. © 2016 by John Wiley & Sons, Inc.

The Drosophila Dicer-1 Partner Loquacious Enhances miRNA Processing from Hairpins with Unstable Structures at the Dicing Site

In Drosophila, Dicer-1 binds Loquacious-PB (Loqs-PB) as its major co-factor. Previous analyses indicated that loqs mutants only partially impede miRNA processing, but the activity of minor isoforms or maternally deposited Loqs was not eliminated in these studies. We addressed this by generating a cell line from loqs-null embryos and found that only ∼40% of miRNAs showed clear Loqs dependence. Genome-wide comparison of the hairpin structure and Loqs dependence suggested that Loqs substrates are influenced by base-pairing status at the dicing site. Artificial alteration of base-pairing stability at this position in model miRNA hairpins resulted in predicted changes in Loqs dependence, providing evidence for this hypothesis. Finally, we found that evolutionarily young miRNA genes tended to be Loqs dependent. We propose that Loqs may have roles in assisting the de novo emergence of miRNA genes by facilitating dicing of suboptimal hairpin substrates.

Trbp Is Required for Differentiation of Myoblasts and Normal Regeneration of Skeletal Muscle

Global inactivation of Trbp, a regulator of miRNA pathways, resulted in developmental defects and postnatal lethality in mice. Recently, we showed that cardiac-specific deletion of Trbp caused heart failure. However, its functional role(s) in skeletal muscle has not been characterized. Using a conditional knockout model, we generated mice lacking Trbp in the skeletal muscle. Unexpectedly, skeletal muscle specific Trbp mutant mice appear to be phenotypically normal under normal physiological conditions. However, these mice exhibited impaired muscle regeneration and increased fibrosis in response to cardiotoxin-induced muscle injury, suggesting that Trbp is required for muscle repair. Using cultured myoblast cells we further showed that inhibition of Trbp repressed myoblast differentiation in vitro. The impaired myogenesis is associated with reduced expression of muscle-specific miRNAs, miR-1a and miR-133a. Together, our study demonstrated that Trbp participates in the regulation of muscle differentiation and regeneration.

Role of miRNAs and alternative mRNA 3'-end cleavage and polyadenylation of their mRNA targets in cardiomyocyte hypertrophy

miRNAs play critical roles in heart disease. In addition to differential miRNA expression, miRNA-mediated control is also affected by variable miRNA processing or alternative 3'-end cleavage and polyadenylation (APA) of their mRNA targets. To what extent these phenomena play a role in the heart remains unclear. We sought to explore miRNA processing and mRNA APA in cardiomyocytes, and whether these change during cardiac hypertrophy. Thoracic aortic constriction (TAC) was performed to induce hypertrophy in C57BL/6J mice. RNA extracted from cardiomyocytes of sham-treated, pre-hypertrophic (2 days post-TAC), and hypertrophic (7 days post-TAC) mice was subjected to small RNA- and poly(A)-test sequencing (PAT-Seq). Differential expression analysis matched expectations; nevertheless we identified ~400 mRNAs and hundreds of noncoding RNA loci as altered with hypertrophy for the first time. Although multiple processing variants were observed for many miRNAs, there was little change in their relative proportions during hypertrophy. PAT-Seq mapped ~48,000 mRNA 3'-ends, identifying novel 3' untranslated regions (3'UTRs) for over 7000 genes. Importantly, hypertrophy was associated with marked changes in APA with a net shift from distal to more proximal mRNA 3'-ends, which is predicted to decrease overall miRNA repression strength. We independently validated several examples of 3'UTR proportion change and showed that alternative 3'UTRs associate with differences in mRNA translation. Our work suggests that APA contributes to altered gene expression with the development of cardiomyocyte hypertrophy and provides a rich resource for a systems-level understanding of miRNA-mediated regulation in physiological and pathological states of the heart.