Heart failure with preserved ejection fraction (HFpEF) constitutes a clinical syndrome in which the diagnostic criteria of heart failure are not accompanied by gross disturbances of systolic function, as assessed by ejection fraction. In turn, under most circumstances, diastolic function is impaired. Although it now represents over 50 % of all patients with heart failure, the mechanisms of HFpEF remain understood, precluding effective therapy. Understanding the pathophysiology of HFpEF has been restricted by both limited access to human myocardial biopsies and by the lack of animal models that fully mimic human pathology. Animal models are valuable research tools to clarify subcellular and molecular mechanisms under conditions where the comorbidities and other confounding factors can be precisely controlled. Although most of the heart failure animal models currently available represent heart failure with reduced ejection fraction, several HFpEF animal models have been proposed. However, few of these fulfil all the features present in human disease. In this review we will provide an overview of the currently available models to study HFpEF from rodents to large animals as well as present advantages and disadvantages of these models.

Aim: Calcium ions play a pivotal role in matching energy supply and demand in cardiac muscle. Mitochondrial calcium concentration is lower in animal models of heart failure with reduced ejection fraction (HFrEF), but limited information is available about mitochondrial calcium handling in heart failure with preserved ejection fraction (HFpEF).Methods: We assessed mitochondrial Ca²⁺ handling in intact cardiomyocytes from Zucker/fatty Spontaneously hypertensive F1 hybrid (ZSF1)‐lean (control) and ZSF1‐obese rats, a metabolic risk‐related model of HFpEF. A mitochondrially targeted Ca²⁺ indicator (MitoCam) was expressed in cultured adult rat cardiomyocytes. Cytosolic and mitochondrial Ca²⁺ transients were measured at different stimulation frequencies. Mitochondrial respiration and swelling, and expression of key proteins were determined ex vivo.Results: At rest, mitochondrial Ca²⁺ concentration in ZSF1‐obese was larger than in ZSF1‐lean. The diastolic and systolic mitochondrial Ca²⁺ concentrations increased with stimulation frequency, but the steady‐state levels were larger in ZSF1‐obese. The half‐widths of the contractile responses, the resting cytosolic Ca²⁺ concentration and the decay half‐times of the cytosolic Ca²⁺ transients were higher in ZSF1‐obese, likely because of a lower SERCA2a/phospholamban ratio. Mitochondrial respiration was lower, particularly with nicotinamide adenine dinucleotide (NADH) (complex I) substrates, and mitochondrial swelling was larger in ZSF1‐obese.Conclusion: The free mitochondrial calcium concentration is higher in HFpEF owing to alterations in mitochondrial and cytosolic Ca²⁺ handling. This coupling between cytosolic and mitochondrial Ca²⁺ levels may compensate for myocardial ATP supply in vivo under conditions of mild mitochondrial dysfunction. However, if mitochondrial Ca²⁺ concentration is sustainedly increased, it might trigger mitochondrial permeability transition pore opening.

Angiogenesis is a biological process with a central role in retinal diseases. The choice of the ideal method to study angiogenesis, particularly in the retina, remains a problem. Angiogenesis can be assessed throughin vitroandin vivostudies. In spite of inherent limitations,in vitrostudies are faster, easier to perform and quantify, and typically less expensive and allow the study of isolated angiogenesis steps. We performed a systematic review of PubMed searching for original articles that appliedin vitroor ex vivo angiogenic retinal assays until May 2017, presenting the available assays and discussing their applicability, advantages, and disadvantages. Most of the studies evaluated migration, proliferation, and tube formation of endothelial cells in response to inhibitory or stimulatory compounds. Other aspects of angiogenesis were studied by assessing cell permeability, adhesion, or apoptosis, as well as by implementing organotypic models of the retina. Emphasis is placed on how the methods are applied and how they can contribute to retinal angiogenesis comprehension. We also discuss how to choose the best cell culture to implement these methods. When applied together,in vitroand ex vivo studies constitute a powerful tool to improve retinal angiogenesis knowledge. This review provides support for researchers to better select the most suitable protocols in this field.

The role of epicardial adipose tissue (EAT) in the pathophysiology of coronary artery disease (CAD) remains unclear. The present systematic review aimed at compiling dysregulated proteins/genes from different studies to dissect the potential role of EAT in CAD pathophysiology. Exhaustive literature research was performed using the keywords “epicardial adipose tissue and coronary artery disease”, to highlight a group of proteins that were consistently regulated among all studies. Reactome, a pathway analysis database, was used to clarify the function of the selected proteins and their intertwined association. SignalP/SecretomeP was used to clarify the endocrine function of the selected proteins. Overall, 1886 proteins/genes were identified from 44 eligible studies. The proteins were separated according to the control used in each study (EAT non-CAD or subcutaneous adipose tissue (SAT) CAD) and by their regulation (up- or downregulated). Using a Venn diagram, we selected the proteins that were upregulated and downregulated (identified as 27 and 19, respectively) in EAT CAD for both comparisons. The analysis of these proteins revealed the main pathways altered in the EAT and how they could communicate with the heart, potentially contributing to CAD development. In summary, in this study, the identified dysregulated proteins highlight the importance of inflammatory processes to modulate the local environment and the progression of CAD, by cellular and metabolic adaptations of epicardial fat that facilitate the formation and progression of atherogenesis of coronaries.

The heart is constantly challenged with acute bouts of stretching or overload. Systolic adaptations to these challenges are known but adaptations in diastolic stiffness remain unknown. We evaluated adaptations in myocardial stiffness due to acute stretching and characterized the underlying mechanisms. Left ventricles (LVs) of intact rat hearts, rabbit papillary muscles and myocardial strips from cardiac surgery patients were stretched. After stretching, there was a sustained >40% decrease in end-diastolic pressure (EDP) or passive tension (PT) for 15 min in all species and experimental preparations. Stretching by volume loading in volunteers and cardiac surgery patients resulted in E/E’ and EDP decreases, respectively, after sustained stretching. Stretched samples had increased myocardial cGMP levels, increased phosphorylated vasodilator-stimulated phosphoprotein phosphorylation, as well as, increased titin phosphorylation, which was reduced by prior protein kinase G (PKG) inhibition (PKGi). Skinned cardiomyocytes from stretched and non-stretched myocardia were studied. Skinned cardiomyocytes from stretched hearts showed decreased PT, which was abrogated by protein phosphatase incubation; whereas those from non-stretched hearts decreased PT after PKG incubation. Pharmacological studies assessed the role of nitric oxide (NO) and natriuretic peptides (NPs). PT decay after stretching was significantly reduced by combined NP antagonism, NO synthase inhibition and NO scavenging, or by PKGi. Response to stretching was remarkably reduced in a rat model of LV hypertrophy, which also failed to increase titin phosphorylation. We describe and translate to human physiology a novel adaptive mechanism, partly mediated by titin phosphorylation through cGMP–PKG signalling, whereby myocardial compliance increases in response to acute stretching. This mechanism may not function in the hypertrophic heart.