Epicardial slices: an innovative 3D organotypic model to study epicardial cell physiology and activation

Ex vivo modelling of cardiac injury identifies ferroptosis-related pathways as a potential therapeutic avenue for translational medicine

BACKGROUND

Heart failure (HF) is a burgeoning health problem worldwide. Often arising as a result of cardiac injury, HF has become a major cause of mortality with limited availability of effective treatments. Ferroptotic pathways, triggering an iron-dependent form of cell death, are known to be potential key players in heart disease. This form of cell death does not exhibit typical characteristics of programmed cell death, and is mediated by impaired iron metabolism and lipid peroxidation signalling.

OBJECTIVES

The aim of this study is to establish an ex-vivo model of myocardial injury in living myocardial slices (LMS) and to identify novel underlying mechanisms and potential therapeutic druggable target(s).

METHODS AND RESULTS

In this study, we employed LMS as an ex vivo model of cardiac injury to investigate underlying mechanisms and potential therapeutic targets. Cryoinjury was induced in adult rat LMS, resulting in 30 % tissue damage. Cryoinjured LMS demonstrated impaired contractile function, cardiomyocyte hypertrophy, inflammation, and cardiac fibrosis, closely resembling in vivo cardiac injury characteristics. Proteomic analysis revealed an enrichment of factors associated with ferroptosis in the injured LMS, suggesting a potential causative role. To test this hypothesis, we pharmacologically inhibited ferroptotic pathways using ferrostatin (Fer-1) in the cryoinjured rat LMS, resulting in attenuation of structural changes and repression of pro-fibrotic processes. Furthermore, LMS generated from failing human hearts were used as a model of chronic heart failure. In this model, Fer-1 treatment was observed to reduce the expression of ferroptotic genes, enhances contractile function and improves tissue viability. Blocking ferroptosis-associated pathways in human cardiac fibroblasts (HCFs) resulted in a downregulation of fibroblast activation genes, a decrease in fibroblast migration capacity, and a reduction in reactive oxygen species production. RNA sequencing analysis of Fer-1-treated human LMS implicated metallothioneins as a potential underlying mechanism for the inhibition of these pathways. This effect is possibly mediated through the replenishment of glutathione reserves.

CONCLUSIONS

Our findings highlight the potential of targeting ferroptosis-related pathways and metallothioneins as a promising strategy for the treatment of heart disease.

Epicardial EMT and cardiac repair: an update

Epicardial epithelial-to-mesenchymal transition (EMT) plays a pivotal role in both heart development and injury response and involves dynamic cellular changes that are essential for cardiogenesis and myocardial repair. Specifically, epicardial EMT is a crucial process in which epicardial cells lose polarity, migrate into the myocardium, and differentiate into various cardiac cell types during development and repair. Importantly, following EMT, the epicardium becomes a source of paracrine factors that support cardiac growth at the last stages of cardiogenesis and contribute to cardiac remodeling after injury. As such, EMT seems to represent a fundamental step in cardiac repair. Nevertheless, endogenous EMT alone is insufficient to stimulate adequate repair. Redirecting and amplifying epicardial EMT pathways offers promising avenues for the development of innovative therapeutic strategies and treatment approaches for heart disease. In this review, we present a synthesis of recent literature highlighting the significance of epicardial EMT reactivation in adult heart disease patients.

Preclinical Models of Cardiac Disease: A Comprehensive Overview for Clinical Scientists

For recent decades, cardiac diseases have been the leading cause of death and morbidity worldwide. Despite significant achievements in their management, profound understanding of disease progression is limited. The lack of biologically relevant and robust preclinical disease models that truly grasp the molecular underpinnings of cardiac disease and its pathophysiology attributes to this stagnation, as well as the insufficiency of platforms that effectively explore novel therapeutic avenues. The area of fundamental and translational cardiac research has therefore gained wide interest of scientists in the clinical field, while the landscape has rapidly evolved towards an elaborate array of research modalities, characterized by diverse and distinctive traits. As a consequence, current literature lacks an intelligible and complete overview aimed at clinical scientists that focuses on selecting the optimal platform for translational research questions. In this review, we present an elaborate overview of current in vitro, ex vivo, in vivo and in silico platforms that model cardiac health and disease, delineating their main benefits and drawbacks, innovative prospects, and foremost fields of application in the scope of clinical research incentives.

The role of cardiac pericytes in health and disease: therapeutic targets for myocardial infarction

Millions of cardiomyocytes die immediately after myocardial infarction, regardless of whether the culprit coronary artery undergoes prompt revascularization. Residual ischaemia in the peri-infarct border zone causes further cardiomyocyte damage, resulting in a progressive decline in contractile function. To date, no treatment has succeeded in increasing the vascularization of the infarcted heart. In the past decade, new approaches that can target the heart's highly plastic perivascular niche have been proposed. The perivascular environment is populated by mesenchymal progenitor cells, fibroblasts, myofibroblasts and pericytes, which can together mount a healing response to the ischaemic damage. In the infarcted heart, pericytes have crucial roles in angiogenesis, scar formation and stabilization, and control of the inflammatory response. Persistent ischaemia and accrual of age-related risk factors can lead to pericyte depletion and dysfunction. In this Review, we describe the phenotypic changes that characterize the response of cardiac pericytes to ischaemia and the potential of pericyte-based therapy for restoring the perivascular niche after myocardial infarction. Pericyte-related therapies that can salvage the area at risk of an ischaemic injury include exogenously administered pericytes, pericyte-derived exosomes, pericyte-engineered biomaterials, and pharmacological approaches that can stimulate the differentiation of constitutively resident pericytes towards an arteriogenic phenotype. Promising preclinical results from in vitro and in vivo studies indicate that pericytes have crucial roles in the treatment of coronary artery disease and the prevention of post-ischaemic heart failure.

Culture of vibrating microtome tissue slices as a 3D model in biomedical research

The basic idea behind the use of 3-dimensional (3D) tools in biomedical research is the assumption that the structures under study will perform at the best in vitro if cultivated in an environment that is as similar as possible to their natural in vivo embedding. Tissue slicing fulfills this premise optimally: it is an accessible, unexpensive, imaging-friendly, and technically rather simple procedure which largely preserves the extracellular matrix and includes all or at least most supportive cell types in the correct tissue architecture with little cellular damage. Vibrating microtomes (vibratomes) can further improve the quality of the generated slices because of the lateral, saw-like movement of the blade, which significantly reduces tissue pulling or tearing compared to a straight cut. In spite of its obvious advantages, vibrating microtome slices are rather underrepresented in the current discussion on 3D tools, which is dominated by methods as organoids, organ-on-chip and bioprinting. Here, we review the development of vibrating microtome tissue slices, the major technical features underlying its application, as well as its current use and potential advances, such as a combination with novel microfluidic culture chambers. Once fully integrated into the 3D toolbox, tissue slices may significantly contribute to decrease the use of laboratory animals and is likely to have a strong impact on basic and translational research as well as drug screening.

Porcine Organotypic Epicardial Slice Protocol: A Tool for the Study of Epicardium in Cardiovascular Research

The epicardium has recently gained interest in the cardiovascular field due to its capacity to support heart regeneration after ischemic injury. Models to study the epicardium of large animals in vitro are limited and mainly based on epicardial cell isolation/differentiation from stem cells, followed by 2D cells culture. In this method paper, we describe the procedure to obtain and culture 3D organotypic heart slices presenting an intact epicardium, as a novel model to study the epicardial physiology and activation. Epicardial slices are obtained from porcine hearts using a high-precision vibratome and retain a healthy epicardial layer embedded in its native extracellular environment and connected with other cardiac cells (cardiomyocytes, fibroblasts, vascular cells etc.). Epicardial slices can be cultured for 72 h, providing an ideal model for studying the epicardium physiology or perform pharmacological interventions/gene therapy approaches. We also report on methods to assesses the viability and composition of the epicardial slices, and evaluate their architecture in 3D through tissue decoloration. Finally, we present a potential application for a nanomaterial-based gene transfer method for tracking of epicardial cells within the slice. Crucially, given the similarity in morphology and physiology of porcine heart with its human counterpart, our system provides a platform for translational research while providing a clinically relevant and ethical alternative to the use of small animals in this type of research.