Epigenomic changes associated with impaired norepinephrine transporter function in postural tachycardia syndrome

Adaptive expansion of ERVK solo-LTRs is associated with Passeriformes speciation events

Endogenous retroviruses (ERVs) are ancient retroviral remnants integrated in host genomes, and commonly deleted through unequal homologous recombination, leaving solitary long terminal repeats (solo-LTRs). This study, analysing the genomes of 362 bird species and their reptilian and mammalian outgroups, reveals an unusually higher level of solo-LTRs formation in birds, indicating evolutionary forces might have purged ERVs during evolution. Strikingly in the order Passeriformes, and especially the parvorder Passerida, endogenous retrovirus K (ERVK) solo-LTRs showed bursts of formation and recurrent accumulations coinciding with speciation events over past 22 million years. Moreover, our results indicate that the ongoing expansion of ERVK solo-LTRs in these bird species, marked by high transcriptional activity of ERVK retroviral genes in reproductive organs, caused variation of solo-LTRs between individual zebra finches. We experimentally demonstrated that cis-regulatory activity of recently evolved ERVK solo-LTRs may significantly increase the expression level of ITGA2 in the brain of zebra finches compared to chickens. These findings suggest that ERVK solo-LTRs expansion may introduce novel genomic sequences acting as cis-regulatory elements and contribute to adaptive evolution. Overall, our results underscore that the residual sequences of ancient retroviruses could influence the adaptive diversification of species by regulating host gene expression.

Lipid-dependent regulation of neurotransmitter release from sympathetic nerve endings in mice atria

Neurotransmitter release from sympathetic terminals is a key avenue for heart regulation. Herein, presynaptic exocytotic activity was monitored in mice atrial tissue using a false fluorescent neurotransmitter FFN511, a substrate for monoamine transporters. FFN511 labeling had similarity with tyrosine hydroxylase immunostaining. High [K+]o depolarization caused FFN511 release, which was augmented by reserpine, an inhibitor of neurotransmitter uptake. However, reserpine lost the ability to increase depolarization-induced FFN511 unloading after depletion of ready releasable pool with hyperosmotic sucrose. Cholesterol oxidase and sphingomyelinase modified atrial membranes, changing in opposite manner fluorescence of lipid ordering-sensitive probe. Plasmalemmal cholesterol oxidation increased FFN511 release upon K+-depolarization and more markedly potentiated FFN511 unloading in the presence of reserpine. Hydrolysis of plasmalemmal sphingomyelin profoundly enhanced the rate of FFN511 loss due to K+-depolarization, but completely prevented potentiating action of reserpine on FFN511 unloading. If cholesterol oxidase or sphingomyelinase got access to membranes of recycling synaptic vesicles, then the enzyme effects were suppressed. Hence, a fast neurotransmitter reuptake dependent on exocytosis of vesicles from ready releasable pool occurs during presynaptic activity. This reuptake can be enhanced or inhibited by plasmalemmal cholesterol oxidation or sphingomyelin hydrolysis, respectively. These modifications of plasmalemmal (but not vesicular) lipids increase the evoked neurotransmitter release.

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.

Norepinephrine transporter defects lead to sympathetic hyperactivity in Familial Dysautonomia models

Familial dysautonomia (FD), a rare neurodevelopmental and neurodegenerative disorder affects the sympathetic and sensory nervous system. Although almost all patients harbor a mutation in ELP1, it remains unresolved exactly how function of sympathetic neurons (symNs) is affected; knowledge critical for understanding debilitating disease hallmarks, including cardiovascular instability or dysautonomic crises, that result from dysregulated sympathetic activity. Here, we employ the human pluripotent stem cell (hPSC) system to understand symN disease mechanisms and test candidate drugs. FD symNs are intrinsically hyperactive in vitro, in cardiomyocyte co-cultures, and in animal models. We report reduced norepinephrine transporter expression, decreased intracellular norepinephrine (NE), decreased NE re-uptake, and excessive extracellular NE in FD symNs. SymN hyperactivity is not a direct ELP1 mutation result, but may connect to NET via RAB proteins. We found that candidate drugs lowered hyperactivity independent of ELP1 modulation. Our findings may have implications for other symN disorders and may allow future drug testing and discovery.

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.

Postural Tachycardia Syndrome in Children and Adolescents: Pathophysiology and Clinical Management

Postural tachycardia syndrome (POTS), characterized by chronic (≥6 months) orthostatic intolerance symptoms with a sustained and excessive heart rate increase while standing without postural hypotension, is common in children and adolescents. Despite the unclear pathogenesis of POTS, the present opinion is that POTS is a heterogeneous and multifactorial disorder that includes altered central blood volume, abnormal autonomic reflexes, "hyperadrenergic" status, damaged skeletal muscle pump activity, abnormal local vascular tension and vasoactive factor release, mast cell activation, iron insufficiency, and autoimmune dysfunction. A number of pediatric POTS patients are affected by more than one of these pathophysiological mechanisms. Therefore, individualized treatment strategies are initiated in the management of POTS, including basal non-pharmacological approaches (e.g., health education, the avoidance of triggers, exercise, or supplementation with water and salt) and special pharmacological therapies (e.g., oral rehydration salts, midodrine hydrochloride, and metoprolol). As such, the recent progress in the pathogenesis, management strategies, and therapeutic response predictors of pediatric POTS are reviewed here.

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

Postural tachycardia syndrome: current perspectives

Postural tachycardia syndrome (POTS) is the combination of an exaggerated heart rate response to standing, in association with symptoms of lightheadedness or pre-syncope that improve when recumbent. The condition is often associated with fatigue and brain fog, resulting in significant disruptions at a critical time of diagnosis in adolescence and young adulthood. The heterogeneity of the underlying pathophysiology and the variable response to therapeutic interventions make management of this condition challenging for both patients and physicians alike. Here, we aim to review the factors and mechanisms that may contribute to the symptoms and signs of POTS and to present our perspectives on the clinical approach toward the diagnosis and management of this complex syndrome.