Eilidh A. MacDonald

Aims: Heart failure with preserved ejection fraction (HFpEF) continues to increase in prevalence and has limited treatment options. HFpEF is a systemic condition with a broad phenotype including diastolic dysfunction, pulmonary oedema, exercise intolerance, and left ventricular hypertrophy, collectively resulting in enhanced morbidity and mortality. The transcription factor RUNX1 has recently been identified as a mediator of pathological changes in multiple cardiac diseases; however, its role in HFpEF remained unknown. Methods and results: Here, we show that inhibition of Runx1 limits adverse cardiac remodelling in a mouse model of HFpEF. Cardiomyocyte-specific tamoxifen-inducible Runx1-deficient mice with HFpEF are protected, with preservation of diastolic function, and attenuation of pulmonary oedema, exercise intolerance, and hypertrophy. Furthermore, targeting Runx1 in HFpEF by using gene transfer or small-molecule inhibitor Ro5-3335 improves diastolic function and reduces pulmonary oedema, both in female and male mice. Conclusion: Overall, this work enhances our understanding of RUNX1 in cardiac disease and presents a novel translational target for the treatment of HFpEF.

The heart is an electrically controlled, mechanical pump that provides a constant supply of blood to the body. It is not surprising, then, that the heartbeat, which occurs on average one or twice every second and over 2.5 billion times without fail in most lifetimes, is maintained by a redundant and robust pacemaking system that ensures regular, rhythmic cardiac excitation. This excitation is initiated in the sinoatrial node (the heart's natural pacemaker), which displays intrinsic spontaneous electrical activity, responsible for the heart's automaticity. As part of the special issue on Pacemaking in Multicellular Organ Systems, in this review we provide a basic overview of the mechanisms responsible for cardiac automaticity intended for a general audience – to allow for comparison with other organs in which pacemaking activity is present – and discuss often overlooked factors critical for integrated cardiac pacemaker function. Ultimately, we hope that a better understanding of pacemaking in the heart, and how it relates to that seen in other organs, will improve our overall understanding of physiological cardiac function, automaticity observed in experimental model systems, and aberrant excitation responsible for deadly cardiac arrhythmias. image

Introduction: The most clinically representative murine models of heart failure with preserved ejection fraction (HFpEF) include a ‘2-hit’ model combining nitrosative stress with metabolic perturbation and a ‘3-hit’ model that also includes ageing. Both models have important limitations with regard to substrain and sex. Methods: The 2-hit model protocol was modified to reproduce HFpEF in both C57BL/6N and 6J mice by increasing L-NAME doses (0.5 g/L to 1.75 g/L) and protocol lengths (7 weeks to 13 weeks). For the 3-hit model, in addition to deoxycorticosterone pivalate (DOCP), we added 1% NaCl drinking water to enhance and prolong the effect of DOCP (‘4-hit’). To maintain the phenotype, a second bolus of DOCP was administered after 8 weeks. Results: HFpEF was successfully induced in C57BL/6J mice when exposed to a 13-week 2-hit L-NAME protocol with gradually increasing dosage from 1.0 to 1.75 g/L. For the 4-hit mice, a clear HFpEF phenotype was observed in C57BL/6N and 6J mice in both male and females, and maintained for up to 12 weeks. Conclusion: These modifications ensure the 2-hit model is induced in J substrain of C57BL/6 mice. The 4-hit model prevents aldosterone escape and enhances reproducibility across sexes and substrains.

Heart failure with preserved ejection fraction (HFpEF) is a public health problem and an elusive illness for which there are few treatment options. HFpEF is a systemic condition with a broad phenotype including diastolic dysfunction, pulmonary oedema, exercise intolerance, and left ventricular (LV) hypertrophy, collectively resulting in enhanced morbidity and mortality. Master-regulator transcription factor RUNX1 has recently been identified as a mediator of pathological changes in many cardiac diseases, however its role in HFpEF was unknown. Here we show that inhibition of Runx 1 limits adverse cardiac remodelling in a clinically relevant mouse model of HFpEF. Cardiomyocyte-specific tamoxifen-inducible Runx 1-deficient mice with HFpEF are protected, with preservation of diastolic function, and attenuation of pulmonary oedema, exercise intolerance, and hypertrophy. Furthermore, targeting Runx 1 in HFpEF by using gene transfer or small molecule inhibitors improves diastolic function, both in female and male mice. Overall, our research enhances our understanding of RUNX1 in cardiac disease and demonstrates a novel translational target for the treatment of HFpEF. Keywords: Heart failure with preserved ejection fraction, metabolic heart failure, diastolic dysfunction, hypertrophy, pulmonary oedema, exercise intolerance CLINICAL PERSPECTIVE: Heart failure (HF) is a leading cause of death world-wide and traditionally divided into different subtypes according to cardiac ejection fraction (EF). In contrast to HF with reduced EF (HFrEF), there are limited treatment options for HF with preserved EF which is of considerable concern given that HFpEF is projected to become the dominant HF subtype in the future ¹ . RUNX1 has been demonstrated to play an important role in the development of many cardiac and non-cardiac diseases. As a result, the potential for RUNX1 inhibitors as therapeutic agents across various conditions has become increasingly evident. In this study we established the therapeutic potential of targeting RUNX1 in the context of HFpEF. Targeting RUNX1 in cardiomyocytes markedly attenuates the development of the HFpEF phenotype and therefore this novel translational therapeutic target has great potential to address one of the biggest challenges in cardiac research.

Myocardial infarction (MI) is a major cause of death worldwide. Effective treatments are required to improve recovery of cardiac function following MI, with the aim of improving patient outcomes and preventing progression to heart failure. The perfused but hypocontractile region bordering an infarct is functionally distinct from the remote surviving myocardium and is a determinant of adverse remodelling and cardiac contractility. Expression of the transcription factor RUNX1 is increased in the border zone 1-day after MI, suggesting potential for targeted therapeutic intervention. This study sought to investigate whether an increase in RUNX1 in the border zone can be therapeutically targeted to preserve contractility following MI. In this work we demonstrate that Runx1 drives reductions in cardiomyocyte contractility, calcium handling, mitochondrial density, and expression of genes important for oxidative phosphorylation. Both tamoxifen-inducible Runx1-deficient and essential co-factor common β subunit (Cbfβ)-deficient cardiomyocyte-specific mouse models demonstrated that antagonizing RUNX1 function preserves the expression of genes important for oxidative phosphorylation following MI. Antagonizing RUNX1 expression via short-hairpin RNA interference preserved contractile function following MI. Equivalent effects were obtained with a small molecule inhibitor (Ro5-3335) that reduces RUNX1 function by blocking its interaction with CBFβ. Our results confirm the translational potential of RUNX1 as a novel therapeutic target in MI, with wider opportunities for use across a range of cardiac diseases where RUNX1 drives adverse cardiac remodelling.

Approximately 7 million people are affected by acute myocardial infarction (MI) each year, and despite significant therapeutic and diagnostic advancements, MI remains a leading cause of mortality worldwide. Preclinical animal models have significantly advanced our understanding of MI and have enabled the development of therapeutic strategies to combat this debilitating disease. Notably, some drugs currently used to treat MI and heart failure (HF) in patients had initially been studied in preclinical animal models. Despite this, preclinical models are limited in their ability to fully reproduce the complexity of MI in humans. The preclinical model must be carefully selected to maximise the translational potential of experimental findings. This review describes current experimental models of MI and considers how they have been used to understand drug mechanisms of action and support translational medicine development.LINKED ARTICLES: This article is part of a themed issue on Preclinical Models for Cardiovascular disease research (BJP 75th Anniversary). To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.5/issuetoc