Cardiac Fibroblasts and Myocardial Regeneration

Nanoparticles for the Delivery of Pro-regenerative Cardiac Progenitor Secretory Proteins Targeting Cellular Senescence and Vasculogenesis

Contemporary therapies following heart failure center on regenerative approaches to account for the loss of cardiomyocytes and limited regenerative capacity of the adult heart. While the delivery of cardiac progenitor cells has been shown to improve cardiac function and repair following injury, recent evidence has suggested that their paracrine effects (or secretome) provides a significant contribution towards modulating regeneration, rather than the progenitor cells intrinsically. The direct delivery of secretory biomolecules, however, remains a challenge due to their lack of stability and tissue retention, limiting their prolonged therapeutic efficacy. We hypothesized that polyurethane-based nanoparticles with heteropolar-hydrophobic-ionic chemistry (DPHI-NPs) could enable the delivery of a subset of pro-regenerative cardiac progenitor cell proteins [bone morphogenetic protein-4 (BMP-4) and angiotensin 1-7 (Ang1-7)] to promote biological pathways conducive to repair processes such as antisenescence (through the quantification of β-galactosidase and interleukin-6) and vasculogenesis (through the formation of endothelial tubes), demonstrated in vitro with human cardiac fibroblasts (hCFs) and human microvascular endothelial cells (hMECs), respectively. DPHI-NPs with a diameter of 190 ± 2 nm (polydispersity index < 0.2) and a zeta potential of -40 ± 1 mV were generated using an emulsion inversion technique and loaded with both therapeutic proteins (BMP-4 and Ang1-7) by optimizing surface charge, loading solution concentration, coating duration, and coating efficiency. Senescence-induced hCFs treated with functionalized DPHI-NPs were found to exhibit a significant reduction in expressed β-galactosidase and IL-6 (p < 0.05). Additionally, hMECs treated with NPBMP-4 were found to display enhanced vasculogenesis compared to control culture conditions alone (p < 0.05). The development of a DPHI-NP vector for the delivery of pro-regenerative secretome biomolecules may present an effective translatable strategy to improve their therapeutic efficacy with respect to cell function.

Competitive signaling and cellular communications in myocardial infarction response

Cell communication and competition pathways are malleable to Myocardial Infarction (MI). Key signals, transcriptive regulators, and metabolites associated with apoptotic responses such as Myc, mTOR, and p53 are important players in the myocardium. The individual state of cardiomyocytes, fibroblasts, and macrophages in the heart tissue are adaptable in times of stress. The overlapping communication pathways of Wnt/β-catenin, Notch, and c-Kit exhibit the involvement of important factors in cell competition in the myocardium. Depending on the effects of these pathways on genetic expression and signal amplification, the proliferative capacities of the previously stated cells that make up the myocardium, amplify or diminish. This creates a distinct classification of "fit" and "unfit" cells. Beyond straightforward traits, the intricate metabolite interactions between neighboring cells unveil a complex battle. Strategic manipulation of these pathways holds translational promise for rapid cardiac recovery post-trauma.

Extracellular PKM2 Preserves Cardiomyocytes and Reduces Cardiac Fibrosis During Myocardial Infarction

Substantial loss of cardiomyocytes during heart attacks and onset of other cardiovascular diseases is a major cause of mortality. Preservation of cardiomyocytes during cardiac injury would be the most effective strategy to manage these diseases in clinic. However, there is no effective treatment strategy that is able to prevent cardiomyocyte loss. We demonstrate here that the systemic administration of a recombinant PKM2 mutant (G415R) preserves cardiomyocytes and reduces cardiac fibrosis during myocardial infarction. G415R preserves cardiomyocytes by protecting the cardiomyocytes from dying and by promoting cardiomyocyte proliferation. Preservation of cardiomyocytes by extracellular PKM2 (EcPKM2) reduces cardiac fibrosis because of the decreased activation of cardiac fibroblasts. Our experiments show that EcPKM2 (G415R) exerts its action by interacting with integrin avb3 on cardiomyocytes. EcPKM2(G415R) activates the integrin-FAK-PI3K signaling axis, which subsequently suppresses PTEN expression and consequently regulates cardiomyocyte apoptosis resistance and proliferation under hypoxia and oxidative stress conditions. Our studies uncover an important cardiomyocyte protection mechanism. More importantly, the activity/action of EcPKM2 (G415R) in preserving cardiomyocyte suggesting a possible therapeutic strategy and target for the treatment of heart attacks and other cardiovascular diseases.

Heart regeneration from the whole-organism perspective to single-cell resolution

Cardiac regenerative potential in the animal kingdom displays striking divergence across ontogeny and phylogeny. Here we discuss several fundamental questions in heart regeneration and provide both a holistic view of heart regeneration in the organism as a whole, as well as a single-cell perspective on intercellular communication among diverse cardiac cell populations. We hope to provide valuable insights that advance our understanding of organ regeneration and future therapeutic strategies.

Myocardial Recovery versus Myocardial Regeneration: Mechanisms and Therapeutic Modulation

Myocardial recovery is characterized by a return toward normal structure and function of the heart after an injury. Mechanisms of myocardial recovery include restoration and/or adaptation of myocyte structure and function, mitochondrial activity and number, metabolic homeostasis, electrophysiological stability, extracellular matrix remodeling, and myocardial perfusion. Myocardial regeneration is an element of myocardial recovery that involves the generation of new myocardial tissue, a process which is limited in adult humans but may be therapeutically augmented. Understanding the mechanisms of myocardial recovery and myocardial regeneration will lead to novel therapies for heart failure.

The Use of Hematopoietic Stem Cells for Heart Failure: A Systematic Review

The purpose of this review is to summarize the current understanding of the therapeutic effect of stem cell-based therapies, including hematopoietic stem cells, for the treatment of ischemic heart damage. Following PRISMA guidelines, we conducted electronic searches in MEDLINE, and EMBASE. We screened 592 studies, and included RCTs, observational studies, and cohort studies that examined the effect of hematopoietic stem cell therapy in adult patients with heart failure. Studies that involved pediatric patients, mesenchymal stem cell therapy, and non-heart failure (HF) studies were excluded from our review. Out of the 592 studies, 7 studies met our inclusion criteria. Overall, administration of hematopoietic stem cells (via intracoronary or myocardial infarct) led to positive cardiac outcomes such as improvements in pathological left-ventricular remodeling, perfusion following acute myocardial infarction, and NYHA symptom class. Additionally, combined death, rehospitalization for heart failure, and infarction were significantly lower in patients treated with bone marrow-derived hematopoietic stem cells. Our review demonstrates that hematopoietic stem cell administration can lead to positive cardiac outcomes for HF patients. Future studies should aim to increase female representation and non-ischemic HF patients.

Structural, angiogenic, and immune responses influencing myocardial regeneration: a glimpse into the crucible

Complete cardiac regeneration remains an elusive therapeutic goal. Although much attention has been focused on cardiomyocyte proliferation, especially in neonatal mammals, recent investigations have unearthed mechanisms by which non-cardiomyocytes, such as endothelial cells, fibroblasts, macrophages, and other immune cells, play critical roles in modulating the regenerative capacity of the injured heart. The degree to which each of these cell types influence cardiac regeneration, however, remains incompletely understood. This review highlights the roles of these non-cardiomyocytes and their respective contributions to cardiac regeneration, with emphasis on natural heart regeneration after cardiac injury during the neonatal period.

MicroRNAs regulating signaling pathways in cardiac fibrosis: potential role of the exercise training

Cardiovascular and metabolic diseases such as hypertension, type 2 diabetes, and obesity develop long-term fibrotic processes in the heart, promoting pathological cardiac remodeling, including after myocardial infarction, reparative fibrotic processes also occur. These processes are regulated by many intracellular signaling pathways that have not yet been completely elucidated, including those associated with microRNA (miRNA) expression. miRNAs are small RNA transcripts (18-25 nucleotides in length) that act as posttranscriptionally regulators of gene expression, inhibiting or degrading one or more target messenger RNAs (mRNAs), and proven to be involved in many biological processes such as cell cycle, differentiation, proliferation, migration, and apoptosis, directly affecting the pathophysiology of several diseases, including cardiac fibrosis. Exercise training can modulate the expression of miRNAs and it is known to be beneficial in various cardiovascular diseases, attenuating cardiac fibrosis processes. However, the signaling pathways modulated by the exercise associated with miRNAs in cardiac fibrosis were not fully understood. Thus, this review aims to analyze the expression of miRNAs that modulate signaling pathways in cardiac fibrosis processes that can be regulated by exercise training.

Reticulon 3 deficiency ameliorates post-myocardial infarction heart failure by alleviating mitochondrial dysfunction and inflammation

Multiple molecular mechanisms are involved in the development of heart failure (HF) after myocardial infarction (MI). However, interventions targeting these pathological processes alone remain clinically ineffective. Therefore, it is essential to identify new therapeutic targets for alleviating cardiac dysfunction after MI. Here, gain- and loss-of-function approaches were used to investigate the role of reticulon 3 (RTN3) in HF after MI. We found that RTN3 was elevated in the myocardium of patients with HF and mice with MI. Cardiomyocyte-specific RTN3 overexpression decreased systolic function in mice under physiological conditions and exacerbated the development of HF induced by MI. Conversely, RTN3 knockout alleviated cardiac dysfunction after MI. Mechanistically, RTN3 bound and mediated heat shock protein beta-1 (HSPB1) translocation from the cytosol to the endoplasmic reticulum. The reduction of cytosolic HSPB1 was responsible for the elevation of TLR4, which impaired mitochondrial function and promoted inflammation through toll-like receptor 4 (TLR4)/peroxisome proliferator-activated receptor gamma coactivator-1 alpha(PGC-1α) and TLR4/Nuclear factor-kappa B(NFκB) pathways, respectively. Furthermore, the HSPB1 inhibitor reversed the protective effect of RTN3 knockout on MI. Additionally, elevated plasma RTN3 level is associated with decreased cardiac function in patients with acute MI. This study identified RTN3 as a critical driver of HF after MI and suggests targeting RTN3 as a promising therapeutic strategy for MI and related cardiovascular diseases.

Almost 50 Years of Monomeric Extracellular Ubiquitin (eUb)

Monomeric ubiquitin (Ub) is a 76-amino-acid highly conserved protein found in eukaryotes. The biological activity of Ub first described in the 1970s was extracellular, but it quickly gained relevance due to its intracellular role, i.e., post-translational modification of intracellular proteins (ubiquitination) that regulate numerous eukaryotic cellular processes. In the following years, the extracellular role of Ub was relegated to the background, until a correlation between higher survival rate and increased serum Ub concentrations in patients with sepsis and burns was observed. Although the mechanism of action (MoA) of extracellular ubiquitin (eUb) is not yet well understood, further studies have shown that it may ameliorate the inflammatory response in tissue injury and multiple sclerosis diseases. These observations, compounded with the high stability and low immunogenicity of eUb due to its high conservation in eukaryotes, have made this small protein a relevant candidate for biotherapeutic development. Here, we review the in vitro and in vivo effects of eUb on immunologic, cardiovascular, and nervous systems, and discuss the potential MoAs of eUb as an anti-inflammatory, antimicrobial, and cardio- and brain-protective agent.

Human myofibroblasts increase the arrhythmogenic potential of human induced pluripotent stem cell-derived cardiomyocytes

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have the potential to remuscularize infarcted hearts but their arrhythmogenicity remains an obstacle to safe transplantation. Myofibroblasts are the predominant cell-type in the infarcted myocardium but their impact on transplanted hiPSC-CMs remains poorly defined. Here, we investigate the effect of myofibroblasts on hiPSC-CMs electrophysiology and Ca2+ handling using optical mapping of advanced human cell coculture systems mimicking cell-cell interaction modalities. Human myofibroblasts altered the electrophysiology and Ca2+ handling of hiPSC-CMs and downregulated mRNAs encoding voltage channels (KV4.3, KV11.1 and Kir6.2) and SERCA2a calcium pump. Interleukin-6 was elevated in the presence of myofibroblasts and direct stimulation of hiPSC-CMs with exogenous interleukin-6 recapitulated the paracrine effects of myofibroblasts. Blocking interleukin-6 reduced the effects of myofibroblasts only in the absence of physical contact between cell-types. Myofibroblast-specific connexin43 knockdown reduced functional changes in contact cocultures only when combined with interleukin-6 blockade. This provides the first in-depth investigation into how human myofibroblasts modulate hiPSC-CMs function, identifying interleukin-6 and connexin43 as paracrine- and contact-mediators respectively, and highlighting their potential as targets for reducing arrhythmic risk in cardiac cell therapy.

Cellular mechanotransduction in health and diseases: from molecular mechanism to therapeutic targets

Cellular mechanotransduction, a critical regulator of numerous biological processes, is the conversion from mechanical signals to biochemical signals regarding cell activities and metabolism. Typical mechanical cues in organisms include hydrostatic pressure, fluid shear stress, tensile force, extracellular matrix stiffness or tissue elasticity, and extracellular fluid viscosity. Mechanotransduction has been expected to trigger multiple biological processes, such as embryonic development, tissue repair and regeneration. However, prolonged excessive mechanical stimulation can result in pathological processes, such as multi-organ fibrosis, tumorigenesis, and cancer immunotherapy resistance. Although the associations between mechanical cues and normal tissue homeostasis or diseases have been identified, the regulatory mechanisms among different mechanical cues are not yet comprehensively illustrated, and no effective therapies are currently available targeting mechanical cue-related signaling. This review systematically summarizes the characteristics and regulatory mechanisms of typical mechanical cues in normal conditions and diseases with the updated evidence. The key effectors responding to mechanical stimulations are listed, such as Piezo channels, integrins, Yes-associated protein (YAP) /transcriptional coactivator with PDZ-binding motif (TAZ), and transient receptor potential vanilloid 4 (TRPV4). We also reviewed the key signaling pathways, therapeutic targets and cutting-edge clinical applications of diseases related to mechanical cues.

RNA-Binding Proteins as Critical Post-Transcriptional Regulators of Cardiac Regeneration

Myocardial injury causes death to cardiomyocytes and leads to heart failure. The adult mammalian heart has very limited regenerative capacity. However, the heart from early postnatal mammals and from adult lower vertebrates can fully regenerate after apical resection or myocardial infarction. Thus, it is of particular interest to decipher the mechanism underlying cardiac regeneration that preserves heart structure and function. RNA-binding proteins, as key regulators of post-transcriptional gene expression to coordinate cell differentiation and maintain tissue homeostasis, display dynamic expression in fetal and adult hearts. Accumulating evidence has demonstrated their importance for the survival and proliferation of cardiomyocytes following neonatal and postnatal cardiac injury. Functional studies suggest that RNA-binding proteins relay damage-stimulated cell extrinsic or intrinsic signals to regulate heart regenerative capacity by reprogramming multiple molecular and cellular processes, such as global protein synthesis, metabolic changes, hypertrophic growth, and cellular plasticity. Since manipulating the activity of RNA-binding proteins can improve the formation of new cardiomyocytes and extend the window of the cardiac regenerative capacity in mammals, they are potential targets of therapeutic interventions for cardiovascular disease. This review discusses our evolving understanding of RNA-binding proteins in regulating cardiac repair and regeneration, with the aim to identify important open questions that merit further investigations.

Nanoengineering of gold nanoribbon-embedded isogenic stem cell-derived cardiac organoids

Cardiac tissue engineering is an emerging field providing tools to treat and study cardiovascular diseases (CVDs). In the past years, the integration of stem cell technologies with micro- and nanoengineering techniques has enabled the creation of novel engineered cardiac tissues (ECTs) with potential applications in disease modeling, drug screening, and regenerative medicine. However, a major unaddressed limitation of stem cell-derived ECTs is their immature state, resembling a neonatal phenotype and genotype. The modulation of the cellular microenvironment within the ECTs has been proposed as an efficient mechanism to promote cellular maturation and improve features such as cellular coupling and synchronization. The integration of biological and nanoscale cues in the ECTs could serve as a tool for the modification and control of the engineered tissue microenvironment. Here we present a proof-of-concept study for the integration of biofunctionalized gold nanoribbons (AuNRs) with hiPSC-derived isogenic cardiac organoids to enhance tissue function and maturation. We first present extensive characterization of the synthesized AuNRs, their PEGylation and cytotoxicity evaluation. We then evaluated the functional contractility and transcriptomic profile of cardiac organoids fabricated with hiPSC-derived cardiomyocytes (mono-culture) as well as with hiPSC-derived cardiomyocytes and cardiac fibroblasts (co-culture). We demonstrated that PEGylated AuNRs are biocompatible and do not induce cell death in hiPSC-derived cardiac cells and organoids. We also found an improved transcriptomic profile of the co-cultured organoids indicating maturation of the hiPSC-derived cardiomyocytes in the presence of cardiac fibroblasts. Overall, we present for the first time the integration of AuNRs into cardiac organoids, showing promising results for improved tissue function.

Pluripotent stem cell-derived committed cardiac progenitors remuscularize damaged ischemic hearts and improve their function in pigs

Ischemic heart disease, which is often associated with irreversibly damaged heart muscle, is a major global health burden. Here, we report the potential of stem cell-derived committed cardiac progenitors (CCPs) have in regenerative cardiology. Human pluripotent embryonic stem cells were differentiated to CCPs on a laminin 521 + 221 matrix, characterized with bulk and single-cell RNA sequencing, and transplanted into infarcted pig hearts. CCPs differentiated for eleven days expressed a set of genes showing higher expression than cells differentiated for seven days. Functional heart studies revealed significant improvement in left ventricular ejection fraction at four and twelve weeks following transplantation. We also observed significant improvements in ventricular wall thickness and a reduction in infarction size after CCP transplantation (p-value < 0.05). Immunohistology analyses revealed in vivo maturation of the CCPs into cardiomyocytes (CM). We observed temporary episodes of ventricular tachyarrhythmia (VT) in four pigs and persistent VT in one pig, but the remaining five pigs exhibited normal sinus rhythm. Importantly, all pigs survived without the formation of any tumors or VT-related abnormalities. We conclude that pluripotent stem cell-derived CCPs constitute a promising possibility for myocardial infarction treatment and that they may positively impact regenerative cardiology.

Contribution of S100A4-expressing fibroblasts to anti-SSA/Ro-associated atrioventricular nodal calcification and soluble S100A4 as a biomarker of clinical severity

Background

Fibrosis and dystrophic calcification disrupting conduction tissue architecture are histopathological lesions characterizing cardiac manifestations of neonatal lupus (cardiac-NL) associated with maternal anti-SSA/Ro antibodies.

Objectives

Increased appreciation of heterogeneity in fibroblasts encourages re-examination of existing models with the consideration of multiple fibroblast subtypes (and their unique functional differences) in mind. This study addressed fibroblast heterogeneity by examining expression of α-Smooth Muscle Actin (myofibroblasts) and of S100 Calcium-Binding Protein A4 (S100A4).

Methods

Using a previously established model of rheumatic scarring/fibrosis in vitro, supported by the evaluation of cord blood from cardiac-NL neonates and their healthy (anti-SSA/Ro-exposed) counterparts, and autopsy tissue from fetuses dying with cardiac-NL, the current study was initiated to more clearly define and distinguish the S100A4-positive fibroblast in the fetal cardiac environment.

Results

S100A4 immunostaining was observed in 4 cardiac-NL hearts with positional identity in the conduction system at regions of dystrophic calcification but not fibrotic zones, the latter containing only myofibroblasts. In vitro, fibroblasts cultured with supernatants of macrophages transfected with hY3 (noncoding ssRNA) differentiated into myofibroblasts or S100A4+ fibroblasts. Myofibroblasts expressed collagen while S100A4+ fibroblasts expressed pro-angiogenic cytokines and proteases that degrade collagen. Cord blood levels of S100A4 in anti-SSA/Ro-exposed neonates tracked disease severity and, in discordant twins, distinguished affected from unaffected.

Conclusions

These findings position the S100A4+ fibroblast alongside the canonical myofibroblast in the pathogenesis of cardiac-NL. Neonatal S100A4 levels support a novel biomarker of poor prognosis.

Single-cell genomics illustrates heterogeneous phenotypes of myocardial fibroblasts under ischemic insults

Myocardial regenerative strategies are promising where the choice of ideal cell population is crucial for successful translational applications. Herein, we explored the regenerative/repair responses of infarct zone cardiac fibroblast(s) (CF) by unveiling their phenotype heterogeneity at single-cell resolution. CF were isolated from the infarct zone of Yucatan miniswine that suffered myocardial infarction, cultured under simulated ischemic and reperfusion, and grouped into control, ischemia, and ischemia/reperfusion. The single-cell RNA sequencing analysis revealed 19 unique cell clusters suggesting distinct subpopulations. The status of gene expression (log2 fold change (log2 FC) > 2 and log2 FC < -2) was used to define the characteristics of each cluster unveiling with diverse features, including the pro-survival/cardioprotective (Clusters 1, 3, 5, 9, and 18), vasculoprotective (Clusters 2 and 5), anti-inflammatory (Clusters 4 and 17), proliferative (Clusters 4 and 5), nonproliferative (Clusters 6, 8, 11, 16, 17, and 18), proinflammatory (Cluster 6), profibrotic/pathologic (Clusters 8 and 19), antihypertrophic (Clusters 8 and 10), extracellular matrix restorative (Clusters 9 and 12), angiogenic (Cluster 16), and normal (Clusters 7 and 15) phenotypes. Further understanding of these unique phenotypes of CF will provide significant translational opportunities for myocardial regeneration and cardiac management.

Biomaterials-Based Cell Therapy for Myocardial Tissue Regeneration

Cardiovascular diseases (CVDs) have been the leading cause of death worldwide during the past several decades. Cell loss is the main problem that results in cardiac dysfunction and further mortality. Cell therapy aiming to replenish the lost cells is proposed to treat CVDs especially ischemic heart diseases which lead to a big portion of cell loss. Due to the direct injection's low cell retention and survival ratio, cell therapy using biomaterials as cell carriers has attracted more and more attention because of their promotion of cell delivery and maintenance at the aiming sites. In this review, the three main factors involved in cell therapy for myocardial tissue regeneration: cell sources (somatic cells, stem cells, and engineered cells), chemical components of cell carriers (natural materials, synthetic materials, and electroactive materials), and categories of cell delivery materials (patches, microspheres, injectable hydrogels, nanofiber and microneedles, etc.) are systematically summarized. An introduction of the methods including magnetic resonance/radionuclide/photoacoustic and fluorescence imaging for tracking the behavior of transplanted cells in vivo is also included. Current challenges of biomaterials-based cell therapy and their future directions are provided to give both beginners and professionals a clear view of the development and future trends in this area.

Healing the Broken Hearts: A Glimpse on Next Generation Therapeutics

Cardiovascular diseases are the leading cause of death worldwide, accounting for 32% of deaths globally and thus representing almost 18 million people according to WHO. Myocardial infarction, the most prevalent adult cardiovascular pathology, affects over half a million people in the USA according to the last records of the AHA. However, not only adult cardiovascular diseases are the most frequent diseases in adulthood, but congenital heart diseases also affect 0.8–1.2% of all births, accounting for mild developmental defects such as atrial septal defects to life-threatening pathologies such as tetralogy of Fallot or permanent common trunk that, if not surgically corrected in early postnatal days, they are incompatible with life. Therefore, both congenital and adult cardiovascular diseases represent an enormous social and economic burden that invariably demands continuous efforts to understand the causes of such cardiovascular defects and develop innovative strategies to correct and/or palliate them. In the next paragraphs, we aim to briefly account for our current understanding of the cellular bases of both congenital and adult cardiovascular diseases, providing a perspective of the plausible lines of action that might eventually result in increasing our understanding of cardiovascular diseases. This analysis will come out with the building blocks for designing novel and innovative therapeutic approaches to healing the broken hearts.

Recent Advances in Cardiac Patches: Materials, Preparations, and Properties

Cardiac patches are biomaterials that can be used for transplantation and repair of damaged myocardium by combining seed cells with the ability to form cardiomyocytes and suitable scaffold materials. On the one hand, they provide temporary support to the infarcted area, and on the other hand, they repair the damaged myocardium by delivering cells or bioactive factors to integrate with the host, which have gradually become a hot research topic in recent years. This paper summarizes the structural properties of natural myocardium and reviews the recent research progress of cardiac patches, including the seed cells and scaffold materials used in patch preparation, as well as the main methods of scaffold preparation and the structure properties of various scaffolds. In addition, a comprehensive analysis of the problems faced in the clinical implementation of cardiac patches is presented. Finally, we look forward to the development of cardiac patches and point out that precisely tunable anisotropic tissue engineering scaffolds close to natural myocardial tissue will become an important direction for future research.

Myocardial regeneration protocols towards the routine clinical scenario: An unseemly path from bench to bedside

Heart failure secondary to cardiomyocyte loss and/or dysfunction is the number one killer worldwide. The field of myocardial regeneration with its far-reaching primary goal of cardiac remuscularization and its hard-to-accomplish translation from bench to bedside, has been filled with ups and downs, steps forward and steps backward, controversies galore and, unfortunately, scientific scandals. Despite the present morass in which cardiac remuscularization is stuck in, the search for clinically effective regenerative approaches remains keenly active. Starting with a concise overview of the still highly debated regenerative capacity of the adult mammalian heart, we focus on the main interventions, that have reached or are close to clinical use, critically discussing key findings, successes, and failures. Finally, some promising and innovative approaches for myocardial repair/regeneration still at the pre-clinical stage are discussed to offer a holistic view on the future of myocardial repair/regeneration for the prevention/management of heart failure in the clinical scenario.

FUNDING

This research was funded by Grants from the Ministry of University and Research PRIN2015 2015ZTT5KB_004; PRIN2017NKB2N4_005; PON-AIM - 1829805-2.

Artificial Scaffolds in Cardiac Tissue Engineering

Cardiovascular diseases are a leading cause of death worldwide. Current treatments directed at heart repair have several disadvantages, such as a lack of donors for heart transplantation or non-bioactive inert materials for replacing damaged tissue. Because of the natural lack of regeneration of cardiomyocytes, new treatment strategies involve stimulating heart tissue regeneration. The basic three elements of cardiac tissue engineering (cells, growth factors, and scaffolds) are described in this review, with a highlight on the role of artificial scaffolds. Scaffolds for cardiac tissue engineering are tridimensional porous structures that imitate the extracellular heart matrix, with the ability to promote cell adhesion, migration, differentiation, and proliferation. In the heart, there is an important requirement to provide scaffold cellular attachment, but scaffolds also need to permit mechanical contractility and electrical conductivity. For researchers working in cardiac tissue engineering, there is an important need to choose an adequate artificial scaffold biofabrication technique, as well as the ideal biocompatible biodegradable biomaterial for scaffold construction. Finally, there are many suitable options for researchers to obtain scaffolds that promote cell-electrical interactions and tissue repair, reaching the goal of cardiac tissue engineering.

Piezo1 Channel as a Potential Target for Hindering Cardiac Fibrotic Remodeling

Fibrotic tissues share many common features with neoplasms where there is an increased stiffness of the extracellular matrix (ECM). In this review, we present recent discoveries related to the role of the mechanosensitive ion channel Piezo1 in several diseases, especially in regulating tumor progression, and how this can be compared with cardiac mechanobiology. Based on recent findings, Piezo1 could be upregulated in cardiac fibroblasts as a consequence of the mechanical stress and pro-inflammatory stimuli that occurs after myocardial injury, and its increased activity could be responsible for a positive feedback loop that leads to fibrosis progression. The increased Piezo1-mediated calcium flow may play an important role in cytoskeleton reorganization since it induces actin stress fibers formation, a well-known characteristic of fibroblast transdifferentiation into the activated myofibroblast. Moreover, Piezo1 activity stimulates ECM and cytokines production, which in turn promotes the phenoconversion of adjacent fibroblasts into new myofibroblasts, enhancing the invasive character. Thus, by assuming the Piezo1 involvement in the activation of intrinsic fibroblasts, recruitment of new myofibroblasts, and uncontrolled excessive ECM production, a new approach to blocking the fibrotic progression can be predicted. Therefore, targeted therapies against Piezo1 could also be beneficial for cardiac fibrosis.

miR-214-3p Protects and Restores the Myocardial Tissue of Rat Myocardial Infarction Model by Targeting PTEN

Myocardial infarction (MI), which results in myocardial cell dysfunction and irreversible loss, is one of the most serious health threats today. This study was started with rats, by which the consequence of miRNA expression dysregulation to the occurrence and progression of cardiovascular diseases was explored. We first conducted miRNA sequencing on the myocardial tissues separately from myocardial infarction treatment and sham operation treatment to clarify those differently expressed miRNAs; then, our experiment of functional verification of those key miRNAs was initiated so as to dig out the molecular mechanism behind the miRNA's regulation in myocardial infarction. And it turned out that there were 32 upregulated miRNAs and 16 downregulated miRNAs according to our comparison from the myocardial infarction model group to the sham operation group; of all those upregulated, alteration in miR-214-3p expression was the most conspicuous. Overexpression of miR-214-3p greatly alleviated myocardial infarct area and ameliorated myocardial tissue structure, even reducing myocardial fibrosis and the devastation in the tissues. On the molecular level, miR-214-3p overexpression brought down both the apoptosis rate and cleaved caspase 3 expression. Besides that, we verified that PTEN is the target gene of miR-214-3p through a dual-luciferase assay. A cotransfection of miR-214-3p and PTEN brought about an obvious elevation in the myocardial infarct area, tissue damage, and fibrosis, even in the aspect of cellular apoptosis than a mere transfection of miR-214-3p. All the results above verified miR-214-3p′s effects in protecting myocardial tissues and reducing the infarct area, and it was reasonable to assume that those functions of miR-214-3p came into effect by targeting PTEN, which was then justified by the inversion to miR-214-3p′s protection via PTEN overexpression.

Regulation of Epicardial Cell Fate during Cardiac Development and Disease: An Overview

The epicardium is the outermost cell layer in the vertebrate heart that originates during development from mesothelial precursors located in the proepicardium and septum transversum. The epicardial layer plays a key role during cardiogenesis since a subset of epicardial-derived cells (EPDCs) undergo an epithelial–mesenchymal transition (EMT); migrate into the myocardium; and differentiate into distinct cell types, such as coronary vascular smooth muscle cells, cardiac fibroblasts, endothelial cells, and presumably a subpopulation of cardiomyocytes, thus contributing to complete heart formation. Furthermore, the epicardium is a source of paracrine factors that support cardiac growth at the last stages of cardiogenesis. Although several lineage trace studies have provided some evidence about epicardial cell fate determination, the molecular mechanisms underlying epicardial cell heterogeneity remain not fully understood. Interestingly, seminal works during the last decade have pointed out that the adult epicardium is reactivated after heart damage, re-expressing some embryonic genes and contributing to cardiac remodeling. Therefore, the epicardium has been proposed as a potential target in the treatment of cardiovascular disease. In this review, we summarize the previous knowledge regarding the regulation of epicardial cell contribution during development and the control of epicardial reactivation in cardiac repair after damage.

The dynamic facets of the cardiac stroma: from classical markers to omics and translational perspectives

Cardiac stromal cells have been long underestimated in their functions in homeostasis and repair. Recent evidence has changed this perspective in that many more players and facets than just "cardiac fibroblasts" have entered the field. Single cell transcriptomic studies on cardiac interstitial cells have shed light on the phenotypic plasticity of the stroma, whose transcriptional profile is dynamically regulated in homeostatic conditions and in response to external stimuli. Different populations and/or functional states that appear in homeostasis and pathology have been described, particularly increasing the complexity of studying the cardiac response to injury. In this review, we outline current phenotypical and molecular markers, and the approaches developed for identifying and classifying cardiac stromal cells. Significant advances in our understanding of cardiac stromal populations will provide a deeper knowledge on myocardial functional cellular components, as well as a platform for future developments of novel therapeutic strategies to counteract cardiac fibrosis and adverse cardiac remodeling.

Phase I investigator-initiated study of the safety of MTC001 in patients with chronic ischemic heart failure

BACKGROUND

: Heart failure (HF) is a global pandemic most commonly caused by coronary artery disease. Despite coronary revascularization, the infarcted myocardium can develop into an irreversible scar toward chronic ischemic HF. This is due to the limited regenerative capacity of the adult human heart. Recently, the vascular cell adhesion molecule 1 positive cardiac fibroblast (VCF) has been shown to directly improve cardiac contractility in addition to promoting myocardial growth in preclinical studies. This clinical trial aims to explore the safety and, in part, the efficacy of autologous VCF therapy for chronic ischemic HF.

METHODS

: This first-in-human trial is an open-label, single-arm, phase 1 study conducted at a single center. This study will include 6 patients with chronic ischemic HF in stage C and NYHA class II or III despite receiving the standard of care, including coronary revascularization. Participants will undergo cardiac biopsy to manufacture autologous VCFs expressing CD90 and CD106. Under electro-anatomical mapping guidance, participants will receive a transendocardial injection of VCF in a modified 3 + 3 design. The first 3 patients will receive a standard dose (2 × 107 cells) of VCF with a 4-week interval for safety assessment before subsequent enrollment. In the absence of safety issues, the final 3 patients will receive the standard dose of VCF without a 4-week interval. In the presence of safety issues, the final 3 patients will receive a reduced dose (1.5 × 107 cells) of VCF with the 4-week interval.

DISCUSSION

This is the first clinical study of cardiac regeneration using VCFs for the treatment of chronic ischemic HF. The study results will contribute to the development of a minimally invasive cell therapy for patients with HF failed by the standard of care.

TRIAL REGISTRATION

This study was registered with the Japan Registry of Clinical Trials (jRCT2033210078).

Human Induced Pluripotent Stem Cell as a Disease Modeling and Drug Development Platform-A Cardiac Perspective

A comprehensive understanding of the pathophysiology and cellular responses to drugs in human heart disease is limited by species differences between humans and experimental animals. In addition, isolation of human cardiomyocytes (CMs) is complicated because cells obtained by biopsy do not proliferate to provide sufficient numbers of cells for preclinical studies in vitro. Interestingly, the discovery of human-induced pluripotent stem cell (hiPSC) has opened up the possibility of generating and studying heart disease in a culture dish. The combination of reprogramming and genome editing technologies to generate a broad spectrum of human heart diseases in vitro offers a great opportunity to elucidate gene function and mechanisms. However, to exploit the potential applications of hiPSC-derived-CMs for drug testing and studying adult-onset cardiac disease, a full functional characterization of maturation and metabolic traits is required. In this review, we focus on methods to reprogram somatic cells into hiPSC and the solutions for overcome immaturity of the hiPSC-derived-CMs to mimic the structure and physiological properties of the adult human CMs to accurately model disease and test drug safety. Finally, we discuss how to improve the culture, differentiation, and purification of CMs to obtain sufficient numbers of desired types of hiPSC-derived-CMs for disease modeling and drug development platform.

Altered Expression of ORAI and STIM Isoforms in Activated Human Cardiac Fibroblasts

Cardiac fibrotization is a well-known process characteristic of many cardiac pathological conditions. The key element is excessive activation of cardiac fibroblasts, their transdifferentiation into myofibroblasts, increased production, and accumulation of extracellular matrix proteins, resulting in cardiac stiffness. The exact cellular mechanisms and molecular components involved in the process are not fully elucidated, but the SOCE mechanism could play an important role. Its key molecules are the molecular sensor of calcium in ER/SR - STIM and the highly selective calcium channels Orai located in the plasma membrane. This study aims to evaluate selected SOCE-associated genes in the activation of HCF cell culture by several known substances (phenylephrine, isoprenaline) that represent cardiovascular overload. After cell cultivation, cell medium was collected to measure the soluble collagen content. From the harvested cells, qRT-PCR was performed to determine the mRNA levels of the corresponding genes. The activation of cells was based on changes in the relative expression of collagen genes as well as the collagen content in the medium of the cell culture. We detected an increase in the expression of the Orai2 isoform, a change in the Orai1/Orai3 ratio and also an increase in the expression of the STIM2 isoform. These results suggest an increased activation of the SOCE mechanism under stress conditions of fibroblasts, which supports the hypothesis of fibroblast activation in pathological processes by altering calcium homeostasis through the SOCE mechanism.

MiR-218-5p Mediates Myocardial Fibrosis after Myocardial Infarction by Targeting CX43

BACKGROUND

Myocardial fibrosis after myocardial infarction (MI) has been considered a core factor in the deterioration of cardiac function. Previous studies have shown that miRNA plays an important role in various pathophysiological processes of the heart. However, the role of miRNA in myocardial fibrosis regulation after MI remains unclear. In the present study, we documented that miR-218-5p was significantly decreased in myocardial fibroblasts after MI.

METHODS

The miRNA expression profiles of MI were downloaded from GEO Datasets. The expression of a fibrosis-related gene in vivo and in vitro was analyzed by RT-PCR, western blotting, and immunohistochemical staining.

RESULTS

Total 7 up- and 9 downregulated common miRNAs were found in the two profiles. Among these common genes, miR-218-5p was downregulated in the MI mice. MiR-218-5p mediated the myocardial fibrosis in vivo and in vitro. Mechanistically, we found that GJA1 (CX43) may be the target of miR218-5p, and overexpressed CX43 can partly block the function of miR-218-5p in fibrosis inhibition.

CONCLUSION

Our results suggested that miR-218-5p plays an important role in myocardial fibrosis after MI by targeting CX43. Thus, miR-218-5p promises to be a potential diagnosis and treatment of myocardial fibrosis after MI.

Advanced Technologies to Target Cardiac Cell Fate Plasticity for Heart Regeneration

The adult human heart can only adapt to heart diseases by starting a myocardial remodeling process to compensate for the loss of functional cardiomyocytes, which ultimately develop into heart failure. In recent decades, the evolution of new strategies to regenerate the injured myocardium based on cellular reprogramming represents a revolutionary new paradigm for cardiac repair by targeting some key signaling molecules governing cardiac cell fate plasticity. While the indirect reprogramming routes require an in vitro engineered 3D tissue to be transplanted in vivo, the direct cardiac reprogramming would allow the administration of reprogramming factors directly in situ, thus holding great potential as in vivo treatment for clinical applications. In this framework, cellular reprogramming in partnership with nanotechnologies and bioengineering will offer new perspectives in the field of cardiovascular research for disease modeling, drug screening, and tissue engineering applications. In this review, we will summarize the recent progress in developing innovative therapeutic strategies based on manipulating cardiac cell fate plasticity in combination with bioengineering and nanotechnology-based approaches for targeting the failing heart.