NET silencing by let-7i in postural tachycardia syndrome

Repressive H3K27me3 drives hyperglycemia-induced oxidative and inflammatory transcriptional programs in human endothelium

BACKGROUND

Histone modifications play a critical role in chromatin remodelling and regulate gene expression in health and disease. Histone methyltransferases EZH1, EZH2, and demethylases UTX, JMJD3, and UTY catalyse trimethylation of lysine 27 on histone H3 (H3K27me3). This study was designed to investigate whether H3K27me3 triggers hyperglycemia-induced oxidative and inflammatory transcriptional programs in the endothelium.

METHODS

We studied human aortic endothelial cells exposed to high glucose (HAEC) or isolated from individuals with diabetes (D-HAEC). RT-qPCR, immunoblotting, chromatin immunoprecipitation (ChIP-qPCR), and confocal microscopy were performed to investigate the role of H3K27me3. We determined superoxide anion (O2-) production by ESR spectroscopy, NF-κB binding activity, and monocyte adhesion. Silencing/overexpression and pharmacological inhibition of chromatin modifying enzymes were used to modulate H3K27me3 levels. Furthermore, isometric tension studies and immunohistochemistry were performed in aorta from wild-type and db/db mice.

RESULTS

Incubation of HAEC to high glucose showed that upregulation of EZH2 coupled to reduced demethylase UTX and JMJD3 was responsible for the increased H3K27me3. ChIP-qPCR revealed that repressive H3K27me3 binding to superoxide dismutase and transcription factor JunD promoters is involved in glucose-induced O2- generation. Indeed, loss of JunD transcriptional inhibition favours NOX4 expression. Furthermore, H3K27me3-driven oxidative stress increased NF-κB p65 activity and downstream inflammatory genes. Interestingly, EZH2 inhibitor GSK126 rescued these endothelial derangements by reducing H3K27me3. We also found that H3K27me3 epigenetic signature alters transcriptional programs in D-HAEC and aortas from db/db mice.

CONCLUSIONS

EZH2-mediated H3K27me3 represents a key epigenetic driver of hyperglycemia-induced endothelial dysfunction. Targeting EZH2 may attenuate oxidative stress and inflammation and, hence, prevent vascular disease in diabetes.

Postural orthostatic tachycardia syndrome: New concepts in pathophysiology and management

Postural orthostatic tachycardia syndrome (POTS) is a common and therapeutically challenging condition affecting numerous people worldwide. Recent studies have begun to shed light on the pathophysiology of this disorder. At the same time, both non-pharmacologic and pharmacologic therapies have emerged that offer additional treatment options for those afflicted with this condition. This paper reviews new concepts in both the pathophysiology and management of POTS.

Recent advances in the functional explorations of nuclear microRNAs

Approximately 22 nucleotide-long non-coding small RNAs (ncRNAs) play crucial roles in physiological and pathological activities, including microRNAs (miRNAs). Long ncRNAs often stay in the cytoplasm, modulating post-transcriptional gene expression. Briefly, miRNA binds with the target mRNA and builds a miRNA-induced silencing complex to silence the transcripts or prevent their translation. Interestingly, data from recent animal and plant studies suggested that mature miRNAs are present in the nucleus, where they regulate transcriptionally whether genes are activated or silenced. This significantly broadens the functional range of miRNAs. Here, we reviewed and summarized studies on the functions of nuclear miRNAs to better understand the modulatory networks associated with nuclear miRNAs.

Non-canonical features of microRNAs: paradigms emerging from cardiovascular disease

Research showing that microRNAs (miRNAs) are versatile regulators of gene expression has instigated tremendous interest in cardiovascular research. The overwhelming majority of studies are predicated on the dogmatic notion that miRNAs regulate the expression of specific target mRNAs by inhibiting mRNA translation or promoting mRNA decay in the RNA-induced silencing complex (RISC). These efforts mostly identified and dissected contributions of multiple regulatory networks of miRNA-target mRNAs to cardiovascular pathogenesis. However, evidence from studies in the past decade indicates that miRNAs also operate beyond this canonical paradigm, featuring non-conventional regulatory functions and cellular localizations that have a pathophysiological role in cardiovascular disease. In this Review, we highlight the functional relevance of atypical miRNA biogenesis and localization as well as RISC heterogeneity. Moreover, we delineate remarkable non-canonical examples of miRNA functionality, including direct interactions with proteins beyond the Argonaute family and their role in transcriptional regulation in the nucleus and in mitochondria. We scrutinize the relevance of non-conventional biogenesis and non-canonical functions of miRNAs in cardiovascular homeostasis and pathology, and contextualize how uncovering these non-conventional properties can expand the scope of translational research in the cardiovascular field and beyond.

Pivotal role of the sympathetic nerves of the human heart in mental stress responses and triggered cardiovascular catastrophes

Mental stress can trigger cardiac catastrophes, explicitly evident during national disasters such as earthquakes. Activation of the cardiac sympathetic outflow and inhibition of the cardiac vagus are important mediating mechanisms. This manuscript describes efforts by the Human Neurotransmitters Research Laboratory of the Baker Institute in Melbourne to develop investigative methods to study the sympathetic nerves of the human heart, and to apply these in mental stress research. With laboratory mental stress, activation of the adrenal medulla was found to occur, accompanied by a regionalized sympathetic nervous response directed to the heart, but sparing the sympathetic outflow to the skeletal muscle vasculature. Patients with panic disorder are at increased cardiovascular risk. They exhibit high-level sympathetic activation during a panic attack, sometimes accompanied by coronary artery spasm. Patients with sudden ventricular arrhythmias causing collapse in the community were found to have as the predisposing substrate high baseline cardiac sympathetic activity, from previously unrecognized mild heart failure; it was surprising at the time that we did not find critical coronary artery stenosis as the substrate. In some the arrhythmia event had a behavioural trigger. In Takotsubo cardiomyopathy ("Broken Heart Syndrome") the myocardial stunning appears to represent a catecholamine cardiomyopathy, from astronomically high plasma adrenaline concentrations, rather than be caused by activation of the cardiac sympathetic nerves. Some diseases (essential hypertension, heart failure, panic disorder) have forms of sympathetic neural enhancement which contribute to cardiovascular risk: reuptake of noradrenaline by sympathetic nerves after release is faulty and single sympathetic fibres fire in multiple salvos within a single cardiac cycle. Paradoxically, obesity-hypertension does not share in this sympathetic neural augmentation, which is present only in normal-weight hypertensive patients, providing the possible basis for an observed "Obesity Paradox" (longer survival in obesity-hypertension than in normal weight hypertension). Community-wide specific prevention of cardiovascular triggering is not currently possible, due to there being no available simple screening tests which could be applied to the community at-large for the commonest substrates, silent coronary artery disease and mild heart failure. Standard medical preventive measures for coronary atherosclerosis will of course be helpful. Targeted prevention of triggering can be done in those with a detected predisposing substrate, such as genetic Long QT Syndrome, and in survivors of a serious triggered event, who need detailed, appropriate testing.

Nuclear functions of microRNAs relevant to the cardiovascular system

A fraction of the transcriptome is translated into proteins. The rest is classified as non-protein coding RNA (Ribonucleic Acid) but has gained increased attention as functional and regulatory group of transcripts. The gene regulatory role of non-coding RNAs (ncRNAs) has now been widely accepted in diverse biological processes in both physiology and disease. MicroRNAs fall into this latter group and are widely known for their diverse post-transcriptional regulatory role. MicroRNA sequences are embedded in the long ncRNAs, known as primary microRNAs, are processed into precursor microRNAs and are typically transported out of the nucleus for maturation and loading into a protein complex forming RNA-induced silencing complex (RISC) that either drives the degradation of messenger RNA (mRNA) or blocks its translation. A new phenomenon is emerging where microRNAs have active roles within the nucleus. The presence of RISC components including microRNAs in the nucleus supports this notion. They may integrate with chromatin modifiers, microprocessing machinery and mRNA stabilizing transcripts to play a multifunctional role in the nucleus. Although a limited number of studies appreciate this novel activity of microRNAs relevant to the cardiovascular system, they provide proof-of-concept that requires consideration while targeting miRNAs with therapeutic potential.

Epigenetic evidence of an Ac/Dc axis by VPA and SAHA

BACKGROUND

Valproic acid (VPA) is one of the most commonly used anti-epileptic drugs with pharmacological actions on GABA and blocking voltage-gated ion channels. VPA also inhibits histone deacetylase (HDAC) activity. Suberoylanilide hydroxamic acid is also a member of a larger class of compounds that inhibit HDACs. At the time of this article, there are 123 active international clinical trials for VPA (also known as valproate, convulex, divalproex, and depakote) and SAHA (vorinostat, zolinza). While it is well known that VPA and SAHA influence the accumulation of acetylated lysine residues on histones, their true epigenetic complexity remains poorly understood.

RESULTS

Primary human cells were exposed to VPA and SAHA to understand the extent of histone acetylation (H3K9/14ac) using chromatin immunoprecipitation followed by sequencing (ChIP-seq). Because histone acetylation is often associated with modification of lysine methylation, we also examined H3K4me3 and H3K9me3. To assess the influence of the HDAC inhibitors on gene expression, we used RNA sequencing (RNA-seq). ChIP-seq reveals a distribution of histone modifications that is robust and more broadly regulated than previously anticipated by VPA and SAHA. Histone acetylation is a characteristic of the pharmacological inhibitors that influenced gene expression. Surprisingly, we observed histone deacetylation by VPA stimulation is a predominant signature following SAHA exposure and thus defines an acetylation/deacetylation (Ac/Dc) axis. ChIP-seq reveals regionalisation of histone acetylation by VPA and broader deacetylation by SAHA. Independent experiments confirm H3K9/14 deacetylation of NFκB target genes by SAHA.

CONCLUSIONS

The results provide an important framework for understanding the Ac/Dc axis by highlighting a broader complexity of histone modifications by the most established and efficacious anti-epileptic medication in this class, VPA and comparison with the broad spectrum HDAC inhibitor, SAHA.

Activity and Exercise Intolerance After Concussion: Identification and Management of Postural Orthostatic Tachycardia Syndrome

Supplemental Digital Content is Available in the Text.

Background and Purpose:

Postural orthostatic tachycardia syndrome (POTS) is increasingly recognized as a complication affecting recovery from concussion. Individuals with POTS demonstrate refractory dizziness, lightheadedness, cognitive dysfunction, fatigue, headache, chronic pain, nausea and gastrointestinal dysmotility, activity and exercise intolerance, syncope, and tachycardia. Subtypes of POTS may include hypovolemia, hyperadrenergic states, autonomic neuropathy, and underlying autoimmunity, which may variably impact response to rehabilitation in varying ways. The subtle presentation of POTS postconcussion is often mistaken for underlying anxiety, conversion disorder, or lack of motivation for recovery. This article will present clinical features of POTS that may arise after concussion, and propose a role for physical therapists in the diagnosis and management of POTS during concussion recovery.

Summary of Key Points:

Data recorded and entered into a database during clinic visits from a large pediatric institution indicate that 11.4% of individuals diagnosed with POTS report onset of symptoms within 3 months of sustaining a concussion. Activation of the sympathetic nervous system can result in lightheadedness, shortness of breath, chest pain, tachycardia, palpitations on standing or with exertion, and activity and exercise intolerance. Identified comorbidities in people with POTS such as joint hypermobility and autoimmune disorders can further influence recovery.

Recommendations for Clinical Practice:

Physical therapists may identify signs and symptoms of POTS in a subset of individuals who remain refractory to typical interventions and who exhibit symptom exacerbation with orthostatic activity. Incorporation of an individualized POTS exercise program into current established concussion interventions may be useful, with emphasis on initial recumbent exercises and ongoing physical therapy assessment of exercise tolerance for dosing of activity intensity and duration.

Video Abstract available for more insights from the authors (see Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A211).

Sex-Based Mhrt Methylation Chromatinizes MeCP2 in the Heart

In the heart, primary microRNA-208b (pri-miR-208b) and Myheart (Mhrt) are long non-coding RNAs (lncRNAs) encoded by the cardiac myosin heavy chain genes. Although preclinical studies have shown that lncRNAs regulate gene expression and are protective for pathological hypertrophy, the mechanism underlying sex-based differences remains poorly understood. In this study, we examined DNA- and RNA-methylation-dependent regulation of pri-miR-208b and Mhrt. Expression of pri-miR-208b is elevated in the left ventricle of the female heart. Despite indistinguishable DNA methylation between sexes, the interaction of MeCP2 on chromatin is subject to RNase digestion, highlighting that affinity of the methyl-CG reader is broader than previously thought. A specialized procedure to isolate RNA from soluble cardiac chromatin emphasizes sex-based affinity of an MeCP2 co-repressor complex with Rest and Hdac2. Sex-specific Mhrt methylation chromatinizes MeCP2 at the pri-miR-208b promoter and extends the functional relevance of default transcriptional suppression in the heart.

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Mechanisms underlying sex-based gene expression are poorly understood

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Expression of primary miR-208b is independent of DNA methylation in the heart

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Sex-specific methylation of the long non-coding RNA Mhrt distinguishes MeCP2

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Procedures assessing soluble chromatin emphasize RNA-dependent affinities

Epigenetics, cardiovascular disease, and cellular reprogramming

Under the seeming disorder of "junk" sequences the last decade has seen developments in our understanding of non-coding RNA's (ncRNAs). It's a complex revised order and nowhere is this more relevant than in the developing heart whereby old rules have been set aside to make room for new ones. The development of the mammalian heart has been studied at the genetic and cellular level for several decades because these areas were considered ideal control points. As such, detailed mechanisms governing cell lineages are well described. Emerging evidence suggests a complex new order regulated by epigenetic mechanisms mark cardiac cell lineage. Indeed, molecular cardiologists are in the process of shedding light on the roles played by ncRNAs, nucleic acid methylation and histone/chromatin modifications in specific pathologies of the heart. The aim of this article is to discuss some of the recent advances in the field of cardiovascular epigenetics that are related to direct cell reprogramming and repair. As such, we explore ncRNAs as nodes regulating signaling networks and attempt to make sense of regulatory disorder by reinforcing the importance of epigenetic components in the developmental program.

MeCP2 interacts with chromosomal microRNAs in brain

Although methyl CpG binding domain protein-2 (MeCP2) is commonly understood to function as a silencing factor at methylated DNA sequences, recent studies also show that MeCP2 can bind unmethylated sequences and coordinate gene activation. MeCP2 displays broad binding patterns throughout the genome, with high expression levels similar to histone H1 in neurons. Despite its significant presence in the brain, only subtle gene expression changes occur in the absence of MeCP2. This may reflect a more complex regulatory mechanism of MeCP2 to complement chromatin binding. Using an RNA immunoprecipitation of native chromatin technique, we identify MeCP2 interacting microRNAs in mouse primary cortical neurons. In addition, comparison with mRNA sequencing data from Mecp2-null mice suggests that differentially expressed genes may indeed be targeted by MeCP2-interacting microRNAs. These findings highlight the MeCP2 interaction with microRNAs that may modulate its binding with chromatin and regulate gene expression.

Epigenetics and precision medicine in cardiovascular patients: from basic concepts to the clinical arena

Cardiovascular diseases (CVDs) remain the leading cause of mortality worldwide and also inflict major burdens on morbidity, quality of life, and societal costs. Considering that CVD preventive medications improve vascular outcomes in less than half of patients (often relative risk reductions range from 12% to 20% compared with placebo), precision medicine offers an attractive approach to refine the targeting of CVD medications to responsive individuals in a population and thus allocate resources more wisely and effectively. New tools furnished by advances in basic science and translational medicine could help achieve this goal. This approach could reach beyond the practitioners 'eyeball' assessment or venerable markers derived from the physical examination and standard laboratory evaluation. Advances in genetics have identified novel pathways and targets that operate in numerous diseases, paving the way for 'precision medicine'. Yet the inherited genome determines only part of an individual's risk profile. Indeed, standard genomic approaches do not take into account the world of regulation of gene expression by modifications of the 'epi'genome. Epigenetic modifications defined as 'heritable changes to the genome that do not involve changes in DNA sequence' have emerged as a new layer of biological regulation in CVD and could advance individualized risk assessment as well as devising and deploying tailored therapies. This review, therefore, aims to acquaint the cardiovascular community with the rapidly advancing and evolving field of epigenetics and its implications in cardiovascular precision medicine.

Contemporary Trends Emerging in Epigenomics and Metabolism

Diabetes is the disease of our time. It is a complex disorder. It is increasingly appreciated that genetic factors cannot fully explain susceptibility to diabetes and its complications. For almost a decade, the epigenetics field has grown tremendously becoming an alternative but integral component of how we interpret gene regulation. Some consider the field an epiphenomenon with an evidence base awaiting critical testing. The advent of experimental tools combined with the development of research methods has brought with the field technological advancements that allow scientists to assess ideas that have not yet been tested critically. If there was ever a time not to give up on epigenetics, then that time would be now. Under the seeming disorder of more than 3 billion base pairs, the human genome works successfully with order. It is a complex order. Instructed by a chemical code that is largely uncharted in metabolic disease, developmental studies have clearly shown that code exclusivity is key to unlocking the genetic blueprint. Central to this chemical code are specific modifications to DNA and RNA, histones and nonhistone proteins: these tiny chemical marks that have wide-ranging functions. Robustness is key, and these marks are written to be precisely read and accurately erased.

Epigenetics and Trained Immunity

SIGNIFICANCE

A growing body of clinical and experimental evidence has challenged the traditional understanding that only the adaptive immune system can mount immunological memory. Recent findings describe the adaptive characteristics of the innate immune system, underscored by its ability to remember antecedent foreign encounters and respond in a nonspecific sensitized manner to reinfection. This has been termed trained innate immunity. Although beneficial in the context of recurrent infections, this might actually contribute to chronic immune-mediated diseases, such as atherosclerosis. Recent Advances: In line with its proposed role in sustaining cellular memories, epigenetic reprogramming has emerged as a critical determinant of trained immunity. Recent technological and computational advances that improve unbiased acquisition of epigenomic profiles have significantly enhanced our appreciation for the complexities of chromatin architecture in the contexts of diverse immunological challenges.

CRITICAL ISSUES

Key to resolving the distinct chromatin signatures of innate immune memory is a comprehensive understanding of the precise physiological targets of regulatory proteins that recognize, deposit, and remove chemical modifications from chromatin as well as other gene-regulating factors. Drawing from a rapidly expanding compendium of experimental and clinical studies, this review details a current perspective of the epigenetic pathways that support the adapted phenotypes of monocytes and macrophages.

FUTURE DIRECTIONS

We explore future strategies that are aimed at exploiting the mechanism of trained immunity to improve the prevention and treatment of infections and immune-mediated chronic disorders.

Long Noncoding RNAs in Diabetes and Diabetic Complications

SIGNIFICANCE

Diabetes is associated with markedly accelerated rates of micro- and macrovascular complications that increase morbidity and mortality. Understanding the molecular mechanisms can promote much needed therapeutics. Recent Advances: Long noncoding RNAs (lncRNAs) are important regulators of gene regulation and cellular function and are emerging as important players in diabetes and its complications. There are number of examples in which lncRNAs are responsive to hyperglycemia and clearly involved in regulation of genes and pathways associated with the development of diabetic complications.

CRITICAL ISSUES

As there are likely thousands of lncRNAs that are expressed in any given tissue, understanding how they are regulated and function in the normal healthy state as well as pathological states is a challenge.

FUTURE DIRECTIONS

Further studies in how lncRNAs are involved in the development and progression of diabetic complications as well as development of methods to target dysregulated lncRNAs or evaluate them as biomarkers of early detection of organ dysfunction will be highly beneficial to treating diabetic patients.