Reduced activity of the calcium-transporting ATPase SERCA2a is a hallmark of heart failure; here, microRNAs that downregulate SERCA2a function are identified, and antagonism of one, miR-25, is shown to halt heart failure in mice. Chronic heart failure occurs when the cardiac muscles steadily lose their ability to contract. The condition is associated with reduced activity of the calcium-transporting ATPase SERCA2a. Restoration of SERCA2a function has shown beneficial effects in preclinical models of heart failure, and gene therapy approaches to restore SERCA2a function are being tested in clinical trials. Mark Mercola and colleagues performed a functional screen of the human microRNAome to identify microRNAs that downregulate SERCA2a function. One potent hit, miR-25, is upregulated in human heart failure and antagonism of miR-25 halts established heart failure in mice. This finding highlights inhibition of miR-25 as a potential strategy for the treatment of heart failure. Heart failure is characterized by a debilitating decline in cardiac function1, and recent clinical trial results indicate that improving the contractility of heart muscle cells by boosting intracellular calcium handling might be an effective therapy2,3. MicroRNAs (miRNAs) are dysregulated in heart failure4,5 but whether they control contractility or constitute therapeutic targets remains speculative. Using high-throughput functional screening of the human microRNAome, here we identify miRNAs that suppress intracellular calcium handling in heart muscle by interacting with messenger RNA encoding the sarcoplasmic reticulum calcium uptake pump SERCA2a (also known as ATP2A2). Of 875 miRNAs tested, miR-25 potently delayed calcium uptake kinetics in cardiomyocytes in vitro and was upregulated in heart failure, both in mice and humans. Whereas adeno-associated virus 9 (AAV9)-mediated overexpression of miR-25 in vivo resulted in a significant loss of contractile function, injection of an antisense oligonucleotide (antagomiR) against miR-25 markedly halted established heart failure in a mouse model, improving cardiac function and survival relative to a control antagomiR oligonucleotide. These data reveal that increased expression of endogenous miR-25 contributes to declining cardiac function during heart failure and suggest that it might be targeted therapeutically to restore function.

Extracellular vesicles (EVs)—particularly exosomes and microvesicles (MVs)—are attracting considerable interest in the cardiovascular field as the wide range of their functions is recognized. These capabilities include transporting regulatory molecules including different RNA species, lipids, and proteins through the extracellular space including blood and delivering these cargos to recipient cells to modify cellular activity. EVs powerfully stimulate angiogenesis, and can protect the heart against myocardial infarction. They also appear to mediate some of the paracrine effects of cells, and have therefore been proposed as a potential alternative to cell-based regenerative therapies. Moreover, EVs of different sources may be useful biomarkers of cardiovascular disease identities. However, the methods used for the detection and isolation of EVs have several limitations and vary widely between studies, leading to uncertainties regarding the exact population of EVs studied and how to interpret the data. The number of publications in the exosome and MV field has been increasing exponentially in recent years and, therefore, in this ESC Working Group Position Paper, the overall objective is to provide a set of recommendations for the analysis and translational application of EVs focussing on the diagnosis and therapy of the ischaemic heart. This should help to ensure that the data from emerging studies are robust and repeatable, and optimize the pathway towards the diagnostic and therapeutic use of EVs in clinical studies for patient benefit.

Left ventricular (LV) remodeling leads to congestive heart failure and is a main determinant of morbidity and mortality following myocardial infarction. Therapeutic options to prevent LV remodeling are limited, which necessitates the exploration of alternative therapeutic targets. Toll-like receptors (TLRs) serve as pattern recognition receptors within the innate immune system. Activation of TLR4 results in an inflammatory response and is involved in extracellular matrix degradation, both key processes of LV remodeling following myocardial infarction. To establish the role of TLR4 in postinfarct LV remodeling, myocardial infarction was induced in wild-type BALB/c mice and TLR4-defective C3H- Tlr4 ^LPS−d mice. Without affecting infarct size, TLR4 defectiveness reduced the extent of LV remodeling (end-diastolic volume: 103.7±6.8 μL versus 128.5±5.7 μL; P <0.01) and preserved systolic function (ejection fraction: 28.2±3.1% versus 16.6±1.3%; P <0.01), as assessed by MRI. In the noninfarcted area, interstitial fibrosis, and myocardial hypertrophy were reduced in C3H- Tlr4 ^LPS−d mice. In the infarcted area, however, collagen density was increased, which was accompanied by fewer macrophages, reduced inflammation regulating cytokine expression levels (interleukin [IL]-1α, IL-2, IL-4, IL-5, IL-6, IL-10, IL-17, tumor necrosis factor-α, interferon-γ, granulocyte/macrophage colony-stimulating factor), and reduced matrix metalloproteinase-2 (4684±515 versus 7573±611; P =0.002) and matrix metalloproteinase-9 activity (76.0±14.3 versus 168.0±36.2; P =0.027). These data provide direct evidence for a causal role of TLR4 in postinfarct maladaptive LV remodeling, probably via inflammatory cytokine production and matrix degradation. TLR4 may therefore constitute a novel target in the treatment of ischemic heart failure.

Objective— To improve regeneration of the injured myocardium, it is necessary to enhance the intrinsic capacity of the heart to regenerate itself and/or replace the damaged tissue by cell transplantation. Cardiomyocyte progenitor cells (CMPCs) are a promising cell population, easily expanded and efficiently differentiated into beating cardiomyocytes. Recently, several studies have demonstrated that microRNAs (miRNAs) are important for stem cell maintenance and differentiation via translational repression. We hypothesize that miRNAs are also involved in proliferation/differentiation of the human CMPCs in vitro. Methods and Results— Human fetal CMPCs were isolated, cultured, and efficiently differentiated into beating cardiomyocytes. miRNA expression profiling demonstrated that muscle-specific miR-1 and miR-499 were highly upregulated in differentiated cells. Transient transfection of miR-1 and -499 in CMPC reduced proliferation rate by 25% and 15%, respectively, and enhanced differentiation into cardiomyocytes in human CMPCs and embryonic stem cells, likely via the repression of histone deacetylase 4 or Sox6. Histone deacetylase 4 and Sox6 protein levels were reduced, and small interference RNA (siRNA)-mediated knockdown of Sox6 strongly induced myogenic differentiation. Conclusion— miRNAs regulate the proliferation of human CMPC and their differentiation into cardiomyocytes. By modulating miR-1 and -499 expression levels, human CMPC function can be altered and differentiation directed, thereby enhancing cardiomyogenic differentiation.