Inhibition of TGF-β/Smad3 Signaling Disrupts Cardiomyocyte Cell Cycle Progression and Epithelial-Mesenchymal Transition-Like Response During Ventricle Regeneration

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.

Spatiotemporal modulation of nitric oxide and Notch signaling by hemodynamic-responsive Trpv4 is essential for ventricle regeneration

Zebrafish have a remarkable ability to regenerate injured hearts. Altered hemodynamic forces after larval ventricle ablation activate the endocardial Klf2a-Notch signaling cascade to direct zebrafish cardiac regeneration. However, how the heart perceives blood flow changes and initiates signaling pathways promoting regeneration is not fully understood. The present study demonstrated that the mechanosensitive channel Trpv4 sensed the altered hemodynamic forces in injured hearts and its expression was regulated by blood flow. In addition to mediating the endocardial Klf2a-Notch signal cascade around the atrioventricular canal (AVC), we discovered that Trpv4 regulated nitric oxide (NO) signaling in the bulbus arteriosus (BA). Further experiments indicated that Notch signaling primarily acted at the early stage of regeneration, and the major role of NO signaling was at the late stage and through TGF-β pathway. Overall, our findings revealed that mechanosensitive channels perceived the changes in hemodynamics after ventricle injury, and provide novel insights into the temporal and spatial coordination of multiple signaling pathways regulating heart regeneration.

Optogenetic control of YAP can enhance the rate of wound healing

BACKGROUND

Tissues need to regenerate to restore function after injury. Yet, this regenerative capacity varies significantly between organs and between species. For example, in the heart, some species retain full regenerative capacity throughout their lifespan but human cardiac cells display a limited ability to repair the injury. After a myocardial infarction, the function of cardiomyocytes is impaired and reduces the ability of the heart to pump, causing heart failure. Therefore, there is a need to restore the function of an injured heart post myocardial infarction. We investigate in cell culture the role of the Yes-associated protein (YAP), a transcriptional co-regulator with a pivotal role in growth, in driving repair after injury.

METHODS

We express optogenetic YAP (optoYAP) in three different cell lines. We characterised the behaviour and function of optoYAP using fluorescence imaging and quantitative real-time PCR of downstream YAP target genes. Mutant constructs were generated using site-directed mutagenesis. Nuclear localised optoYAP was functionally tested using wound healing assay.

RESULTS

Utilising optoYAP, which enables precise control of pathway activation, we show that YAP induces the expression of downstream genes involved in proliferation and migration. optoYAP can increase the speed of wound healing in H9c2 cardiomyoblasts. Interestingly, this is not driven by an increase in proliferation, but by collective cell migration. We subsequently dissect specific phosphorylation sites in YAP to identify the molecular driver of accelerated healing.

CONCLUSIONS

This study shows that optogenetic YAP is functional in H9c2 cardiomyoblasts and its controlled activation can potentially enhance wound healing in a range of conditions.

Dynamic Involvement of Telocytes in Modulating Multiple Signaling Pathways in Cardiac Cytoarchitecture

Cardiac interstitium is a complex and dynamic environment, vital for normal cardiac structure and function. Telocytes are active cellular players in regulating main events that feature myocardial homeostasis and orchestrating its involvement in heart pathology. Despite the great amount of data suggesting (microscopically, proteomically, genetically, etc.) the implications of telocytes in the different physiological and reparatory/regenerative processes of the heart, understanding their involvement in realizing the heart's mature cytoarchitecture is still at its dawn. Our scrutiny of the recent literature gave clearer insights into the implications of telocytes in the WNT signaling pathway, but also TGFB and PI3K/AKT pathways that, inter alia, conduct cardiomyocytes differentiation, maturation and final integration into heart adult architecture. These data also strengthen evidence for telocytes as promising candidates for cellular therapies in various heart pathologies.

Heart regeneration: 20 years of progress and renewed optimism

Cardiovascular disease is a leading cause of death worldwide, and thus there remains great interest in regenerative approaches to treat heart failure. In the past 20 years, the field of heart regeneration has entered a renaissance period with remarkable progress in the understanding of endogenous heart regeneration, stem cell differentiation for exogenous cell therapy, and cell-delivery methods. In this review, we highlight how this new understanding can lead to viable strategies for human therapy. For the near term, drugs, electrical and mechanical devices, and heart transplantation will remain mainstays of cardiac therapies, but eventually regenerative therapies based on fundamental regenerative biology may offer more permanent solutions for patients with heart failure.

Reawakening the Intrinsic Cardiac Regenerative Potential: Molecular Strategies to Boost Dedifferentiation and Proliferation of Endogenous Cardiomyocytes

Despite considerable efforts carried out to develop stem/progenitor cell-based technologies aiming at replacing and restoring the cardiac tissue following severe damages, thus far no strategies based on adult stem cell transplantation have been demonstrated to efficiently generate new cardiac muscle cells. Intriguingly, dedifferentiation, and proliferation of pre-existing cardiomyocytes and not stem cell differentiation represent the preponderant cellular mechanism by which lower vertebrates spontaneously regenerate the injured heart. Mammals can also regenerate their heart up to the early neonatal period, even in this case by activating the proliferation of endogenous cardiomyocytes. However, the mammalian cardiac regenerative potential is dramatically reduced soon after birth, when most cardiomyocytes exit from the cell cycle, undergo further maturation, and continue to grow in size. Although a slow rate of cardiomyocyte turnover has also been documented in adult mammals, both in mice and humans, this is not enough to sustain a robust regenerative process. Nevertheless, these remarkable findings opened the door to a branch of novel regenerative approaches aiming at reactivating the endogenous cardiac regenerative potential by triggering a partial dedifferentiation process and cell cycle re-entry in endogenous cardiomyocytes. Several adaptations from intrauterine to extrauterine life starting at birth and continuing in the immediate neonatal period concur to the loss of the mammalian cardiac regenerative ability. A wide range of systemic and microenvironmental factors or cell-intrinsic molecular players proved to regulate cardiomyocyte proliferation and their manipulation has been explored as a therapeutic strategy to boost cardiac function after injuries. We here review the scientific knowledge gained thus far in this novel and flourishing field of research, elucidating the key biological and molecular mechanisms whose modulation may represent a viable approach for regenerating the human damaged myocardium.