Circulating microRNAs predispose to takotsubo syndrome following high-dose adrenaline exposure.

AIMS: Takotsubo syndrome (TTS) is an acute heart failure, typically triggered by high adrenaline during physical or emotional stress. It is distinguished from myocardial infarction (MI) by a characteristic pattern of ventricular basal hypercontractility with hypokinesis of apical segments, and in the absence of culprit coronary occlusion. We aimed to understand whether recently discovered circulating biomarkers miR-16 and miR-26a, which differentiate TTS from MI at presentation, were mechanistically involved in the pathophysiology of TTS. METHODS AND RESULTS: miR-16 and miR-26a were co-overexpressed in rats with AAV and TTS induced with an adrenaline bolus. Untreated isolated rat cardiomyocytes were transfected with pre-/anti-miRs and functionally assessed. Ventricular basal hypercontraction and apical depression were accentuated in miR-transfected animals after induction of TTS. In vitro miR-16 and/or miR-26a overexpression in isolated apical (but not basal), cardiomyocytes produced strong depression of contraction, with loss of adrenaline sensitivity. They also enhanced the initial positive inotropic effect of adrenaline in basal cells. Decreased contractility after TTS-miRs was reproduced in non-failing human apical cardiomyocytes. Bioinformatic profiling of miR targets, followed by expression assays and functional experiments, identified reductions of CACNB1 (L-type calcium channel Cavß subunit), RGS4 (regulator of G-protein signalling 4), and G-protein subunit Gß (GNB1) as underlying these effects. CONCLUSION: miR-16 and miR-26a sensitize the heart to TTS-like changes produced by adrenaline. Since these miRs have been associated with anxiety and depression, they could provide a mechanism whereby priming of the heart by previous stress causes an increased likelihood of TTS in the future.

Bridge to recovery: what remains to be discovered?

The use of left ventricular assist devices to induce substantial myocardial recovery with explantation of the device, bridge to recovery (BTR), is an exciting but currently grossly underused application. Recently acquired knowledge relating to BTR and its mechanisms offers unprecedented opportunities to streamline its use and unravel some of the secrets of heart failure with much wider implications. This article reviews the status, challenges, and future of cardiac recovery.

Adult progenitor cell transplantation influences contractile performance and calcium handling of recipient cardiomyocytes.

Adult progenitor cell transplantation has been proposed for the treatment of heart failure, but the mechanisms effecting functional improvements remain unknown. The aim of this study was to test the hypothesis that, in failing hearts treated with cell transplantation, the mechanical properties and excitation-contraction coupling of recipient cardiomyocytes are altered. Adult rats underwent coronary artery ligation, leading to myocardial infarction and chronic heart failure. After 3 wk, they received intramyocardial injections of either 10(7) green fluorescence protein (GFP)-positive bone marrow mononuclear cells or 5 x 10(6) GFP-positive skeletal myoblasts. Four weeks after injection, both cell types increased ejection fraction and reduced cardiomyocyte size. The contractility of isolated GFP-negative cardiomyocytes was monitored by sarcomere shortening assessment, Ca(2+) handling by indo-1 and fluo-4 fluorescence, and electrophysiology by patch-clamping techniques. Injection of either bone marrow cells or skeletal myoblasts normalized the impaired contractile performance and the prolonged time to peak of the Ca(2+) transient observed in failing cardiomyocytes. The smaller and slower L-type Ca(2+) current observed in heart failure normalized after skeletal myoblast, but not bone marrow cell, transplantation. Measurement of Ca(2+) sparks suggested a normalization of sarcoplasmic reticulum Ca(2+) leak after skeletal myoblast transplantation. The increased Ca(2+) wave frequency observed in failing myocytes was reduced by either bone marrow cells or skeletal myoblasts. In conclusion, the morphology, contractile performance, and excitation-contraction coupling of individual recipient cardiomyocytes are altered in failing hearts treated with adult progenitor cell transplantation.

The effects of overexpression of the Na+/Ca2+ exchanger on calcium regulation in hypertrophied mouse cardiac myocytes.

In cardiac hypertrophy and failure it has been shown that the amount of Na/Ca exchanger protein can increase. Several studies have investigated this modification in overt heart failure. However, the role of Na/Ca exchanger overexpression during the development of hypertrophy is unknown. To address this question we investigated Ca2+ regulation in an early stage of cardiac hypertrophy before signs of heart failure occurred and evaluated the role of Na/Ca exchanger overexpression. Cardiac hypertrophy was induced by a constant infusion of angiotensin II (Ang, 1 microg/min/kg) via an osmotic pump for 14 days. Thereafter, ventricular myocytes from either wild type (NON) or transgenic mice overexpressing the Na/Ca exchanger (TR) were isolated. Myocytes were loaded with indo-1 AM or fluo-4 AM to monitor cytoplasmic [Ca2+] with all experiments performed at 37 degrees C. In myocytes exposed to Ang there was an increase in cell capacitance of more than 20% indicating cellular hypertrophy. Ca2+ transients were prolonged in hypertrophied NON myocytes but not in TR myocytes. Action potentials had a less negative plateau in TR myocytes. Sarcoplasmic reticulum (SR) Ca2+ content, measured using rapid caffeine application, was greater in TR myocytes but unaffected by hypertrophy. Ca2+ spark frequency was significantly greater in TR. Na/Ca exchanger overexpression prevented the prolongation of the Ca2+ transient observed in hypertrophy and maintained a similar SR Ca2+ leak suggesting a compensatory role in Ca2+ regulation in hypertrophied cardiac myocytes from transgenic mice. We suggest this compensatory effect is mediated by increased SR Ca2+ content and faster Ca2+ removal via the Na/Ca exchanger.

Effects of Na(+)/Ca(2+)-exchanger overexpression on excitation-contraction coupling in adult rabbit ventricular myocytes.

The Na(+)/Ca(2+)-exchanger (NCX) is the main mechanism by which Ca(2+) is transported out of the ventricular myocyte. NCX levels are raised in failing human heart, and the consequences of this for excitation-contraction coupling are still debated. We have increased NCX levels in adult rabbit myocytes by adenovirally-mediated gene transfer and examined the effects on excitation-contraction coupling after 24 and 48 h. Infected myocytes were identified through expression of green fluorescent protein (GFP), transfected under a separate promoter on the same viral construct. Control experiments were done with both non-infected myocytes and those infected with adenovirus expressing GFP only. Contraction amplitude was markedly reduced in NCX-overexpressing myocytes at either time point, and neither increasing frequency nor raising extracellular Ca(2+) could reverse this depression. Resting membrane potential and action potential duration were largely unaffected by NCX overexpression, as was peak Ca(2+) entry via the L-type Ca(2+) channel. Systolic and diastolic Ca(2+) levels were significantly reduced, with peak systolic Ca(2+) in NCX-overexpressing myocytes lower than diastolic levels in control cells at 2 m m extracellular Ca(2+). Both cell relengthening and the decay of the Ca(2+) transient were significantly slowed. Sarcoplasmic reticulum (SR) Ca(2+) stores were completely depleted in a majority of myocytes, and remained so despite increasingly vigorous loading protocols. Depressed contractility following NCX overexpression is therefore related to decreased SR Ca(2+) stores and low diastolic Ca(2+) levels rather than reduced Ca(2+) entry.