Therapeutic approaches for cardiac regeneration and repair

Single-cell transcriptomics uncover distinct innate and adaptive cell subsets during tissue homeostasis and regeneration

Recently, immune cell-mediated tissue repair and regeneration has been an emerging paradigm of regenerative medicine. Immune cells form an essential part of the wound as induction of inflammation is a necessary step to elicit tissue healing. Rapid progress in transcriptomic analyses by high-throughput next-generation sequencing has been developed to study gene regulatory network and establish molecular signatures of immune cells that could potentially predict their functional roles in tissue repair and regeneration. However, the identification of cellular heterogeneity especially on the rare cell subsets has been limited in transcriptomic analyses of bulk cell populations. Therefore, genome-wide, single-cell RNA sequencing (scRNA-Seq) has offered an unprecedented approach to unravel cellular diversity and to study novel immune cell populations involved in tissue repair and regeneration through unsupervised sampling of individual cells without the need to rely on prior knowledge about cell-specific markers. The analysis of gene expression patterns at a single-cell resolution also holds promises to uncover the mechanisms and therefore the development of therapeutic strategy promoting immunoregenerative medicine. In this review, we will discuss how scRNA-Seq facilitates the characterization of immune cells, including macrophages, innate lymphoid cells and T and B lymphocytes, discovery of immune cell heterogeneity, identification of novel subsets, and tracking of developmental trajectories of distinct immune cells during tissue homeostasis, repair, and regeneration.

Cardiac Stem Cell-Loaded Delivery Systems: A New Challenge for Myocardial Tissue Regeneration

Cardiovascular disease (CVD) remains the leading cause of death in Western countries. Post-myocardial infarction heart failure can be considered a degenerative disease where myocyte loss outweighs any regenerative potential. In this scenario, regenerative biology and tissue engineering can provide effective solutions to repair the infarcted failing heart. The main strategies involve the use of stem and progenitor cells to regenerate/repair lost and dysfunctional tissue, administrated as a suspension or encapsulated in specific delivery systems. Several studies demonstrated that effectiveness of direct injection of cardiac stem cells (CSCs) is limited in humans by the hostile cardiac microenvironment and poor cell engraftment; therefore, the use of injectable hydrogel or pre-formed patches have been strongly advocated to obtain a better integration between delivered stem cells and host myocardial tissue. Several approaches were used to refine these types of constructs, trying to obtain an optimized functional scaffold. Despite the promising features of these stem cells’ delivery systems, few have reached the clinical practice. In this review, we summarize the advantages, and the novelty but also the current limitations of engineered patches and injectable hydrogels for tissue regenerative purposes, offering a perspective of how we believe tissue engineering should evolve to obtain the optimal delivery system applicable to the everyday clinical scenario.

Strategies and Challenges to Improve Cellular Programming-Based Approaches for Heart Regeneration Therapy

Limited adult cardiac cell proliferation after cardiovascular disease, such as heart failure, hampers regeneration, resulting in a major loss of cardiomyocytes (CMs) at the site of injury. Recent studies in cellular reprogramming approaches have provided the opportunity to improve upon previous techniques used to regenerate damaged heart. Using these approaches, new CMs can be regenerated from differentiation of iPSCs (similar to embryonic stem cells), the direct reprogramming of fibroblasts [induced cardiomyocytes (iCMs)], or induced cardiac progenitors. Although these CMs have been shown to functionally repair infarcted heart, advancements in technology are still in the early stages of development in research laboratories. In this review, reprogramming-based approaches for generating CMs are briefly introduced and reviewed, and the challenges (including low efficiency, functional maturity, and safety issues) that hinder further translation of these approaches into a clinical setting are discussed. The creative and combined optimal methods to address these challenges are also summarized, with optimism that further investigation into tissue engineering, cardiac development signaling, and epigenetic mechanisms will help to establish methods that improve cell-reprogramming approaches for heart regeneration.

Single-cell protein expression of hiPSC-derived cardiomyocytes using Single-Cell Westerns

The ability to reprogram human somatic cells into human induced pluripotent stem cells (hiPSCs) has enabled researchers to generate cell types in vitro that have the potential to faithfully recapitulate patient-specific disease processes and phenotypes. hiPSC-derived cardiomyocytes (hiPSC-CMs) offer the promise of in vitro patient- and disease-specific models for drug testing and the discovery of novel therapeutic approaches for treating cardiovascular diseases. While methods to differentiate hiPSCs into cardiomyocytes have been demonstrated, the heterogeneity and immaturity of these differentiated populations have restricted their potential in reproducing human disease and the associated target cell phenotypes. These barriers may be overcome through comprehensive single-cell characterization to dissect the rich heterogeneity of hiPSC-CMs and to study the source of varying cell fates. In this study, we optimized and validated a new Single-Cell Western method to assess protein expression in hiPSC-CMs. To better understand distinct subpopulations generated from cardiomyocyte differentiations and to track populations at single-cell resolution over time, we measured and quantified the expression of cardiomyocyte subtype-specific proteins (MLC2V and MLC2A) using Single-Cell Westerns. By understanding their heterogeneity through single-cell protein expression and quantification, we may improve upon current cardiomyocyte differentiation protocols, generate hiPSC-CMs that are more representative of in vivo derived cardiomyocytes for disease modeling, and utilize hiPSC-CMs for regenerative medicine purposes. Single-Cell Westerns provide a robust platform for protein expression analysis at single-cell resolution.

SARS-CoV-2 infection of human iPSC-derived cardiac cells predicts novel cytopathic features in hearts of COVID-19 patients

Although COVID-19 causes cardiac dysfunction in up to 25% of patients, its pathogenesis remains unclear. Exposure of human iPSC-derived heart cells to SARS-CoV-2 revealed productive infection and robust transcriptomic and morphological signatures of damage, particularly in cardiomyocytes. Transcriptomic disruption of structural proteins corroborated adverse morphologic features, which included a distinct pattern of myofibrillar fragmentation and numerous iPSC-cardiomyocytes lacking nuclear DNA. Human autopsy specimens from COVID-19 patients displayed similar sarcomeric disruption, as well as cardiomyocytes without DNA staining. These striking cytopathic features provide new insights into SARS-CoV-2 induced cardiac damage, offer a platform for discovery of potential therapeutics, and raise serious concerns about the long-term consequences of COVID-19.

Biomaterials Loaded with Growth Factors/Cytokines and Stem Cells for Cardiac Tissue Regeneration

Myocardial infarction causes cardiac tissue damage and the release of damage-associated molecular patterns leads to activation of the immune system, production of inflammatory mediators, and migration of various cells to the site of infarction. This complex response further aggravates tissue damage by generating oxidative stress, but it eventually heals the infarction site with the formation of fibrotic tissue and left ventricle remodeling. However, the limited self-renewal capability of cardiomyocytes cannot support sufficient cardiac tissue regeneration after extensive myocardial injury, thus, leading to an irreversible decline in heart function. Approaches to improve cardiac tissue regeneration include transplantation of stem cells and delivery of inflammation modulatory and wound healing factors. Nevertheless, the harsh environment at the site of infarction, which consists of, but is not limited to, oxidative stress, hypoxia, and deficiency of nutrients, is detrimental to stem cell survival and the bioactivity of the delivered factors. The use of biomaterials represents a unique and innovative approach for protecting the loaded factors from degradation, decreasing side effects by reducing the used dosage, and increasing the retention and survival rate of the loaded cells. Biomaterials with loaded stem cells and immunomodulating and tissue-regenerating factors can be used to ameliorate inflammation, improve angiogenesis, reduce fibrosis, and generate functional cardiac tissue. In this review, we discuss recent findings in the utilization of biomaterials to enhance cytokine/growth factor and stem cell therapy for cardiac tissue regeneration in small animals with myocardial infarction.

Perspective on human pluripotent stem cell-derived cardiomyocytes in heart disease modeling and repair

Heart diseases (HDs) are the leading cause of morbidity and mortality worldwide. Despite remarkable clinical progress made, current therapies cannot restore the lost myocardium, and the correlation of genotype to phenotype of many HDs is poorly modeled. In the past two decades, with the rapid developments of human pluripotent stem cell (hPSC) biology and technology that allow the efficient preparation of cardiomyocytes from individual patients, tremendous efforts have been made for using hPSC‐derived cardiomyocytes in preclinical and clinical cardiac therapy as well as in dissection of HD mechanisms to develop new methods for disease prediction and treatment. However, their applications have been hampered by several obstacles. Here, we discuss recent advances, remaining challenges, and the potential solutions to advance this field.

Tanshinone IIA promotes cardiac differentiation and improves cell motility by modulating the Wnt/β‑catenin signaling pathway

Although the cardiovascular pharmacological actions of Tanshinone IIA (TanIIA) have been extensively studied, research on its roles in cardiac regeneration is still insufficient. The present study employed the cardiac myoblast cell line H9c2 to evaluate the possible roles of TanIIA in cardiac regeneration. It was found that certain concentration of TanIIA inhibited cell proliferation by suppressing the expression of proteins related to the cell cycle [cyclin dependent kinase (CDK)4, CDK6 and cyclin D1] and proliferation [c-Myc, octamer-binding transcription factor 4 (Oct4) and proliferating cell nuclear antigen (PCNA)] without inducing apoptosis. In this process, the expression of cardiac troponin in the treated cells was significantly increased and the migration of the treated cells toward the wound area was significantly enhanced. Meanwhile, TanIIA inhibited the canonical signaling pathway through increasing the expression of glycogen synthase kinase 3β (GSK-3β) and adenomatous polyposis coli (APC) and increased the expression of Wnt11 and Wnt5a in the noncanonical Wnt signaling pathway. Following β-catenin agonist WAY-262611 intervention, the effect of TanIIA on the promotion of cardiac differentiation and improved cell migration was significantly reduced. In conclusion, it was hypothesized that TanIIA could promote cardiac differentiation and improve cell motility by modulating the Wnt/β-catenin signaling pathway. These results suggest that TanIIA may play beneficial roles in myocardial regeneration following stem cell transplantation.

Agrin Promotes Coordinated Therapeutic Processes Leading to Improved Cardiac Repair in Pigs

BACKGROUND

Ischemic heart diseases are leading causes of death and reduced life quality worldwide. Although revascularization strategies significantly reduce mortality after acute myocardial infarction (MI), a large number of patients with MI develop chronic heart failure over time. We previously reported that a fragment of the extracellular matrix protein agrin promotes cardiac regeneration after MI in adult mice.

METHODS

To test the therapeutic potential of agrin in a preclinical porcine model, we performed ischemia-reperfusion injuries using balloon occlusion for 60 minutes followed by a 3-, 7-, or 28-day reperfusion period.

RESULTS

We demonstrated that local (antegrade) delivery of recombinant human agrin to the infarcted pig heart can target the affected regions in an efficient and clinically relevant manner. A single dose of recombinant human agrin improved heart function, infarct size, fibrosis, and adverse remodeling parameters 28 days after MI. Short-term MI experiments along with complementary murine studies revealed myocardial protection, improved angiogenesis, inflammatory suppression, and cell cycle reentry as agrin's mechanisms of action.

CONCLUSIONS

A single dose of agrin is capable of reducing ischemia-reperfusion injury and improving heart function, demonstrating that agrin could serve as a therapy for patients with acute MI and potentially heart failure.

MicroRNA-Mediated Direct Reprogramming of Human Adult Fibroblasts Toward Cardiac Phenotype

Modulation of microRNA expression holds the promise to achieve direct reprogramming of fibroblasts into cardiomyocyte-like cells as a new strategy for myocardial regeneration after ischemic heart disease. Previous reports have shown that murine fibroblasts can be directly reprogrammed into induced cardiomyocytes (iCMs) by transient transfection with four microRNA mimics (miR-1, 133, 208, and 499, termed "miRcombo"). Hence, study on the effect of miRcombo transfection on adult human cardiac fibroblasts (AHCFs) deserves attention in the perspective of a future clinical translation of the approach. In this brief report, we studied for the first time whether miRcombo transient transfection of AHCFs by non-viral vectors might trigger direct reprogramming of AHCFs into cardiomyocyte-like cells. Initially, efficient miRNA delivery to cells was demonstrated through the use of a commercially available transfection agent (DharmaFECT1). Transient transfection of AHCFs with miRcombo was found to upregulate early cardiac transcription factors after 7 days post-transfection and cardiomyocyte specific marker cTnT after 15 days post-transfection, and to downregulate the expression of fibroblast markers at 15 days post-transfection. The percentage of cTnT-positive cells after 15 days from miRcombo transfection was ∼11%, as evaluated by flow cytometry. Furthermore, a relevant percentage of miRcombo-transfected AHCFs (∼38%) displayed spontaneous calcium transients at 30 days post-transfection. Results evidenced the role of miRcombo transfection on triggering the trans differentiation of AHCFs into iCMs. Although further investigations are needed to achieve iCM maturation, early findings from this study pave the way toward new advanced therapies for human cardiac regeneration.

Requirements for Proper Immunosuppressive Regimens to Limit Translational Failure of Cardiac Cell Therapy in Preclinical Large Animal Models

Various cell-based therapies are currently investigated in an attempt to tackle the high morbidity and mortality associated with heart failure. The need for these therapies to move towards the clinic is pressing. Therefore, preclinical large animal studies that use non-autologous cells are needed to evaluate their potential. However, non-autologous cells are highly immunogenic and trigger immune rejection responses resulting in potential loss of efficacy. To overcome this issue, adequate immunosuppressive regimens are of imminent importance but clear guidelines are currently lacking. In this review, we assess the immunological barriers regarding non-autologous cell transplantation and immune modulation with immunosuppressive drugs. In addition, we provide recommendations with respect to immunosuppressive regimens in preclinical cardiac cell-replacement studies.

Identification of transcription factors MYC and C/EBPβ mediated regulatory networks in heart failure based on gene expression omnibus datasets

Background

Heart failure is one of leading cause of death worldwide. However, the transcriptional profiling of heart failure is unclear. Moreover, the signaling pathways and transcription factors involving the heart failure development also are largely unknown. Using published Gene Expression Omnibus (GEO) datasets, in the present study, we aim to comprehensively analyze the differentially expressed genes in failing heart tissues, and identified the critical signaling pathways and transcription factors involving heart failure development.

Methods

The transcriptional profiling of heart failure was identified from previously published gene expression datasets deposited in GSE5406, GSE16499 and GSE68316. The enriched signaling pathways and transcription factors were analyzed using Database for Annotation, Visualization and Integrated Discovery (DAVID) website and gene set enrichment analysis (GSEA) assay. The transcriptional networks were created by Cytoscape.

Results

Compared with the normal heart tissues, 90 genes were particularly differentially expressed in failing heart tissues, and those genes were associated with multiple metabolism signaling pathways and insulin signaling pathway. Metabolism and insulin signaling pathway were both inactivated in failing heart tissues. Transcription factors MYC and C/EBPβ were both negatively associated with the expression profiling of failing heart tissues in GSEA assay. Moreover, compared with normal heart tissues, MYC and C/EBPβ were down regulated in failing heart tissues. Furthermore, MYC and C/EBPβ mediated downstream target genes were also decreased in failing heart tissues. MYC and C/EBPβ were positively correlated with each other. At last, we constructed MYC and C/EBPβ mediated regulatory networks in failing heart tissues, and identified the MYC and C/EBPβ target genes which had been reported involving the heart failure developmental progress.

Conclusions

Our results suggested that metabolism pathways and insulin signaling pathway, transcription factors MYC and C/EBPβ played critical roles in heart failure developmental progress.

Gene Therapy for the Heart Lessons Learned and Future Perspectives

While clinical gene therapy celebrates its first successes, with several products already approved for clinical use and several hundreds in the final stages of the clinical approval pipeline, there is not a single gene therapy approach that has worked for the heart. Here, we review the past experience gained in the several cardiac gene therapy clinical trials that had the goal of inducing therapeutic angiogenesis in the ischemic heart and in the attempts at modulating cardiac function in heart failure. Critical assessment of the results so far achieved indicates that the efficiency of cardiac gene delivery remains a major hurdle preventing success but also that improvements need to be sought in establishing more reliable large animal models, choosing more effective therapeutic genes, better designing clinical trials, and more deeply understanding cardiac biology. We also emphasize a few areas of cardiac gene therapy development that hold great promise for the future. In particular, the transition from gene addition studies using protein-coding cDNAs to the modulation of gene expression using small RNA therapeutics and the improvement of precise gene editing now pave the way to applications such as cardiac regeneration after myocardial infarction and gene correction for inherited cardiomyopathies that were unapproachable until a decade ago.

Multiaxial Lenticular Stress-Strain Relationship of Native Myocardium is Preserved by Infarct-Induced Natural Heart Regeneration in Neonatal Mice

Neonatal mice exhibit natural heart regeneration after myocardial infarction (MI) on postnatal day 1 (P1), but this ability is lost by postnatal day 7 (P7). Cardiac biomechanics intricately affect long-term heart function, but whether regenerated cardiac muscle is biomechanically similar to native myocardium remains unknown. We hypothesized that neonatal heart regeneration preserves native left ventricular (LV) biomechanical properties after MI. C57BL/6J mice underwent sham surgery or left anterior descending coronary artery ligation at age P1 or P7. Echocardiography performed 4 weeks post-MI showed that P1 MI and sham mice (n = 22, each) had similar LV wall thickness, diameter, and ejection fraction (59.6% vs 60.7%, p = 0.6514). Compared to P7 shams (n = 20), P7 MI mice (n = 20) had significant LV wall thinning, chamber enlargement, and depressed ejection fraction (32.6% vs 61.8%, p < 0.0001). Afterward, the LV was explanted and pressurized ex vivo, and the multiaxial lenticular stress-strain relationship was tracked. While LV tissue modulus for P1 MI and sham mice were similar (341.9 kPa vs 363.4 kPa, p = 0.6140), the modulus for P7 MI mice was significantly greater than that for P7 shams (691.6 kPa vs 429.2 kPa, p = 0.0194). We conclude that, in neonatal mice, regenerated LV muscle has similar biomechanical properties as native LV myocardium.

A Roadmap for Fixing the Heart: RNA Regulatory Networks in Cardiac Disease

With the continuous development of RNA biology and massive genome-wide transcriptome analysis, more and more RNA molecules and their functions have been explored in the last decade. Increasing evidence has demonstrated that RNA-related regulatory networks play an important role in a variety of human diseases, including cardiovascular diseases. In this review, we focus on RNA regulatory networks in heart disease, most of which are devastating conditions with no known cure. We systemically summarize recent discoveries of important new components of RNA regulatory networks, including microRNAs, long non-coding RNAs, and circular RNAs, as well as multiple regulators that affect the activity of these networks in cardiac physiology and pathology. In addition, this review covers emerging micropeptides, which represent short open reading frames (sORFs) in long non-coding RNA transcripts that may modulate cardiac physiology. Based on the current knowledge of RNA regulatory networks, we think that ongoing discoveries will not only provide us a better understanding of the molecular mechanisms that underlie heart disease, but will also identify novel biomarkers and therapeutic targets for the diagnosis and treatment of cardiac disease.

Combining Nanomaterials and Developmental Pathways to Design New Treatments for Cardiac Regeneration: The Pulsing Heart of Advanced Therapies

The research for heart therapies is challenged by the limited intrinsic regenerative capacity of the adult heart. Moreover, it has been hampered by the poor results obtained by tissue engineering and regenerative medicine attempts at generating functional beating constructs able to integrate with the host tissue. For this reason, organ transplantation remains the elective treatment for end-stage heart failure, while novel strategies aiming to promote cardiac regeneration or repair lag behind. The recent discovery that adult cardiomyocytes can be ectopically induced to enter the cell cycle and proliferate by a combination of microRNAs and cardioprotective drugs, like anti-oxidant, anti-inflammatory, anti-coagulants and anti-platelets agents, fueled the quest for new strategies suited to foster cardiac repair. While proposing a revolutionary approach for heart regeneration, these studies raised serious issues regarding the efficient controlled delivery of the therapeutic cargo, as well as its timely removal or metabolic inactivation from the site of action. Especially, there is need for innovative treatment because of evidence of severe side effects caused by pleiotropic drugs. Biocompatible nanoparticles possess unique physico-chemical properties that have been extensively exploited for overcoming the limitations of standard medical therapies. Researchers have put great efforts into the optimization of the nanoparticles synthesis and functionalization, to control their interactions with the biological milieu and use as a viable alternative to traditional approaches. Nanoparticles can be used for diagnosis and deliver therapies in a personalized and targeted fashion. Regarding the treatment of cardiovascular diseases, nanoparticles-based strategies have provided very promising outcomes, in preclinical studies, during the last years. Efficient encapsulation of a large variety of cargos, specific release at the desired site and improvement of cardiac function are some of the main achievements reached so far by nanoparticle-based treatments in animal models. This work offers an overview on the recent nanomedical applications for cardiac regeneration and highlights how the versatility of nanomaterials can be combined with the newest molecular biology discoveries to advance cardiac regeneration therapies.

Epicardial transplantation of atrial appendage micrograft patch salvages myocardium after infarction

BACKGROUND

Ischemic heart disease remains the leading cause of mortality and morbidity worldwide despite improved possibilities in medical care. Alongside interventional therapies, such as coronary artery bypass grafting, adjuvant tissue-engineered and cell-based treatments can provide regenerative improvement. Unfortunately, most of these advanced approaches require multiple lengthy and costly preparation stages without delivering significant clinical benefits.

METHODS

We evaluated the effect of epicardially delivered minute pieces of atrial appendage tissue material, defined as atrial appendage micrografts (AAMs), in a mouse myocardial infarction model. An extracellular matrix patch was used to cover and fix the AAMs onto the surface of the infarcted heart.

RESULTS

The matrix-covered AAMs salvaged the heart from the infarction-induced loss of functional myocardium and attenuated scarring. Site-selective proteomics of injured ischemic and uninjured distal myocardium from AAMs-treated and -untreated tissue sections revealed increased expression of several cardiac regeneration-associated proteins (i.e., periostin, transglutaminases, and glutathione peroxidases) and activation of pathways responsible for angiogenesis and cardiogenesis in relation to AAMs therapy.

CONCLUSIONS

Epicardial delivery of AAMs encased in an extracellular matrix patch scaffold salvages functional cardiac tissue from ischemic injury and restricts fibrosis after myocardial infarction. Our results support the use of AAMs as tissue-based therapy adjuvants for salvaging the ischemic myocardium.

Deterministic paracrine repair of injured myocardium using microfluidic-based cocooning of heart explant-derived cells

While encapsulation of cells within protective nanoporous gel cocoons increases cell retention and pro-survival integrin signaling, the influence of cocoon size and intra-capsular cell-cell interactions on therapeutic repair are unknown. Here, we employ a microfluidic platform to dissect the impact of cocoon size and intracapsular cell number on the regenerative potential of transplanted heart explant-derived cells. Deterministic increases in cocoon size boosted the proportion of multicellular aggregates within cocoons, reduced vascular clearance of transplanted cells and enhanced stimulation of endogenous repair. The latter being attributable to cell-cell stimulation of cytokine and extracellular vesicle production while also broadening of the miRNA cargo within extracellular vesicles. Thus, by tuning cocoon size and cell occupancy, the paracrine signature and retention of transplanted cells can be enhanced to promote paracrine stimulation of endogenous tissue repair.

Aging Attenuates Cardiac Contractility and Affects Therapeutic Consequences for Myocardial Infarction

Cardiac function of the human heart changes with age. The age-related change of systolic function is subtle under normal conditions, but abrupt under stress or in a pathogenesis state. Aging decreases the cardiac tolerance to stress and increases susceptibility to ischemia, which caused by aging-induced Ca2+ transient impairment and metabolic dysfunction. The changes of contractility proteins and the relative molecules are in a non-linear fashion. Specifically, the expression and activation of cMLCK increase first then fall during ischemia and reperfusion (I/R). This change is responsible for the nonmonotonic contractility alteration in I/R which the underlying mechanism is still unclear. Contractility recovery in I/R is also attenuated by age. The age-related change in cardiac contractility influences the therapeutic effect and intervention timepoint. For most cardiac ischemia therapies, the therapeutic result in the elderly is not identical to the young. Anti-aging treatment has the potential to prevent the development of ischemic injury and improves cardiac function. In this review we discuss the mechanism underlying the contractility changes in the aged heart and age-induced ischemic injury. The potential mechanism underlying the increased susceptibility to ischemic injury in advanced age is highlighted. Furthermore, we discuss the effect of age and the administration time for intervention in cardiac ischemia therapies.

Insulin-like growth factor-II overexpression accelerates parthenogenetic stem cell differentiation into cardiomyocytes and improves cardiac function after acute myocardial infarction in mice

Background

Parthenogenetic stem cells (PSCs) are a promising source of regenerated cardiomyocytes; however, their application may be limited without a paternal genome. Insulin-like growth factor-II (IGF-II), a paternally expressed growth hormone, is critical in embryonic differentiation. This study investigated whether forced expression of IGF-II in PSCs can accelerate their differentiation.

Methods

Overexpression and re-knockdown of IGF-II in PSCs were performed to investigate the role of IGF-II in PSC differentiation. The derivatives of PSCs with different IGF-II manipulations were transplanted into infarcted murine hearts to investigate the role of IGF-II in cardiomyocyte differentiation in vivo.

Results

Data showed that the expression of cardiac troponin T and troponin I in IGF-II-PSC outgrowths preceded that of parental PSC outgrowths, suggesting that IGF-II can accelerate PSC differentiation into cardiac lineage. Overexpression of IGF-II accelerated PSC differentiation towards cardiomyocytes while inhibiting PSC proliferation via the IGF-II/IGF1R signaling. Similar to that observed in cardiac marker expression, on differentiation day 24, IGF-II-PSCs showed PCNA and cyclin D2 expression comparable to juvenile mouse cardiomyocytes, showing that IGF-II-PSCs at this stage possess differential and proliferative properties similar to those of juvenile cardiomyocytes. Moreover, the expression pattern of cardiac markers in IGF-II-overexpressing PSC derivatives resembled that of juvenile mouse cardiomyocytes. After transplantation into the infarcted mouse hearts, IGF-II-PSC-derived cardiomyocytes displayed significant characteristics of mature cardiomyocytes, and IGF-II-depletion by shRNA significantly reversed these effects, suggesting the critical role of IGF-II in promoting cardiomyocyte maturation in vivo. Furthermore, IGF-II-overexpressing PSC derivatives reduced collagen deposition and mitochondrial damage in the infarcted areas and improved cardiac function. The re-knockdown of IGF-II could counteract these favorable effects of IGF-II.

Conclusions

These findings suggest that the ectopic expression of IGF-II accelerates PSC differentiation into the cardiac lineage and promotes cardiomyocyte maturation. The underlying process includes the IGF-II/IGF1R signaling, which is involved in the suppressive effect of IGF-II on PSC proliferation. Moreover, transplanting IGF-II-overexpressing PSC derivatives into the infarcted heart could reduce collagen deposition and improve mitochondria biogenesis and measurements of cardiac function, highlighting the importance of IGF-II in the application of PSCs in cardiac regeneration.

Optimizing cardiac ischemic preconditioning and postconditioning via epitranscriptional regulation

Ischemic cardiac preconditioning protects the heart during myocardial infarction by activating critical cardioprotective genes such as eNOS, SOD, and HO-1. Clinical trials only show marginal effects of conventional preconditioning strategies, however, in part due to transient activation of cardioprotective genes. Recent studies have shown that N6-methyladenosine (m6A) mRNA methylation is the most abundant RNA modification in eukaryotes, and governs mRNA stability and, in turn, the level of protein expression. We hypothesize that regulation of m6A mRNA methylation levels of cardioprotective mRNAs will result in stable expression of the cardioprotective proteins, rendering ischemic cardiac preconditioning more robust and reducing infarct size. To test this hypothesis, we will test the effects of introducing m6A methylases/demethylases into ischemic preconditioned/post conditioned hearts and subjecting them to myocardial infarction. We will assess the half-life of key cardioprotective mRNAs (e.g., eNOS, SOD, and HO-1) and cardiac apoptosis to determine which m6A methylases/demethylases have a synergistic effect on cardiac preconditioning.

Coadministration of an Adhesive Conductive Hydrogel Patch and an Injectable Hydrogel to Treat Myocardial Infarction

Over the past decade, tissue-engineering strategies, mainly involving injectable hydrogels and epicardial biomaterial patches, have been pursued to treat myocardial infarction. However, only limited therapeutic efficacy is achieved with a single means. Here, a combined therapy approach is proposed, that is, the coadministration of a conductive hydrogel patch and injectable hydrogel to the infarcted myocardium. The self-adhesive conductive hydrogel patch is fabricated based on Fe³⁺-induced ionic coordination between dopamine-gelatin (GelDA) conjugates and dopamine-functionalized polypyrrole (DA-PPy), which form a homogeneous network. The injectable and cleavable hydrogel is formed in situ via a Schiff base reaction between oxidized sodium hyaluronic acid (HA-CHO) and hydrazided hyaluronic acid (HHA). Compared with a single-mode system, injecting the HA-CHO/HHA hydrogel intramyocardially followed by painting a conductive GelDA/DA-PPy hydrogel patch on the heart surface results in a more pronounced improvement of the cardiac function in terms of echocardiographical, histological, and angiogenic outcomes.

Pluripotent stem cell-derived cardiomyocytes for treatment of cardiomyopathic damage: Current concepts and future directions

Today, cell replacement therapy using pluripotent stem cell-derived cardiomyocytes (PSC-CMs) remains a research endeavor, with several hurdles that must be overcome before delivery of PSC-CMs can become a therapeutic reality. In this review, we highlight major findings to date from pre-clinical studies involving delivery of PSC-CMs and consider remaining challenges that must be addressed for successful clinical translation. Our goal is to provide an overview of the current status of cardiomyocyte replacement therapy and what challenges must be addressed before successful clinical translation of such therapies will be possible.

Direct Cardiac Reprogramming for Cardiovascular Regeneration and Differentiation

Cardiovascular disease is the leading cause of death worldwide. Cardiomyocytes have limited regenerative capacity; consequently, regenerative therapies are in high demand. There are currently several potential strategies for heart regeneration, with one approach involving in situ generation of new cardiomyocytes from endogenous cell sources. Direct cardiac reprogramming has emerged as a novel therapeutic approach to regenerating the damaged heart by directly converting endogenous cardiac fibroblasts into cardiomyocyte-like cells. Following our first report of direct cardiac reprogramming, significant advances have elucidated the molecular mechanisms associated with cardiac reprogramming. These advances have also improved cardiac-reprogramming efficiency by enabling direct in vivo cardiac reprogramming. Moreover, progress has been made in cardiac reprogramming of human fibroblasts. Although basic research has supported substantial progress in this field, numerous challenges remain in terms of clinical application. Here, we review the current state of cardiac reprogramming as a new technology for understanding and treating cardiovascular diseases.

Stem cell-derived cell sheet transplantation for heart tissue repair in myocardial infarction

Stem cell-derived sheet engineering has been developed as the next-generation treatment for myocardial infarction (MI) and offers attractive advantages in comparison with direct stem cell transplantation and scaffold tissue engineering. Furthermore, induced pluripotent stem cell-derived cell sheets have been indicated to possess higher potential for MI therapy than other stem cell-derived sheets because of their capacity to form vascularized networks for fabricating thickened human cardiac tissue and their long-term therapeutic effects after transplantation in MI. To date, stem cell sheet transplantation has exhibited a dramatic role in attenuating cardiac dysfunction and improving clinical manifestations of heart failure in MI. In this review, we retrospectively summarized the current applications and strategy of stem cell-derived cell sheet technology for heart tissue repair in MI.

Development of Injectable Amniotic Membrane Matrix for Postmyocardial Infarction Tissue Repair

Ischemic heart disease represents the leading cause of death worldwide. Heart failure following myocardial infarction (MI) is associated with severe fibrosis formation and cardiac remodeling. Recently, injectable hydrogels have emerged as a promising approach to repair the infarcted heart and improve heart function through minimally invasive administration. Here, a novel injectable human amniotic membrane (hAM) matrix is developed to enhance cardiac regeneration following MI. Human amniotic membrane is isolated from human placenta and engineered to be a thermoresponsive, injectable gel around body temperature. Ultrasound-guided injection of hAM matrix into rat MI hearts significantly improves cardiac contractility, as measured by ejection fraction (EF), and decrease fibrosis. The results of this study demonstrate the feasibility of engineering as an injectable hAM matrix and its efficacy in attenuating degenerative changes in cardiac function following MI, which may have broad applications in tissue regeneration.

Scar Formation with Decreased Cardiac Function Following Ischemia/Reperfusion Injury in 1 Month Old Swine

Studies in mice show a brief neonatal period of cardiac regeneration with minimal scar formation, but less is known about reparative mechanisms in large mammals. A transient cardiac injury approach (ischemia/reperfusion, IR) was used in weaned postnatal day (P)30 pigs to assess regenerative repair in young large mammals at a stage when cardiomyocyte (CM) mitotic activity is still detected. Female and male P30 pigs were subjected to cardiac ischemia (1 h) by occlusion of the left anterior descending artery followed by reperfusion, or to a sham operation. Following IR, myocardial damage occurred, with cardiac ejection fraction significantly decreased 2 h post-ischemia. No improvement or worsening of cardiac function to the 4 week study end-point was observed. Histology demonstrated CM cell cycling, detectable by phospho-histone H3 staining, at 2 months of age in multinucleated CMs in both sham-operated and IR pigs. Inflammation and regional scar formation in the epicardial region proximal to injury were observed 4 weeks post-IR. Thus, pigs subjected to cardiac IR at P30 show myocardial damage with a prolonged decrease in cardiac function, formation of a regional scar, and increased inflammation, but do not regenerate myocardium even in the presence of CM mitotic activity.

Glial cells influence cardiac permittivity as evidenced through in vitro and in silico models

Excitation-contraction (EC) coupling in the heart has, until recently, been solely accredited to cardiomyocytes. The inherent complexities of the heart make it difficult to examine non-muscle contributions to contraction in vivo, and conventional in vitro models fail to capture multiple features and cellular heterogeneity of the myocardium. Here, we report on the development of a 3D cardiac μTissue to investigate changes in the cellular composition of native myocardium in vitro. Cells are encapsulated within micropatterned gelatin-based hydrogels formed via visible light photocrosslinking. This system enables spatial control of the microarchitecture, perturbation of the cellular composition, and functional measures of EC coupling via video microscopy and a custom algorithm to quantify beat frequency and degree of coordination. To demonstrate the robustness of these tools and evaluate the impact of altered cell population densities on cardiac μTissues, contractility and cell morphology were assessed with the inclusion of exogenous non-myelinating Schwann cells (SCs). Results demonstrate that the addition of exogenous SCs alter cardiomyocyte EC, profoundly inhibiting the response to electrical pacing. Computational modeling of connexin-mediated coupling suggests that SCs impact cardiomyocyte resting potential and rectification following depolarization. Cardiac μTissues hold potential for examining the role of cellular heterogeneity in heart health, pathologies, and cellular therapies.

Leading progress in heart regeneration and repair

Ischemic heart disease is one of the leading causes of mortality. Myocardial infarction causes loss of cardiomyocytes in the injury area accompanied by formation of a fibrotic scar. This initiates a cascade of events including further loss of myocyte, increased fibrosis, and pathological cardiac hypertrophy, eventually leading to the heart failure. Cardiomyocytes in mammals have limited regenerative potential due to post mitotic nature of cardiomyocytes. Recently, multiple studies have provided substantial insights in to the molecular pathways governing this block in adult cardiomyocyte proliferation, and successfully employed that understanding to achieve cardiac regeneration. These strategies include directly reprograming the cardiomyocytes or manipulating the cardiac interstitium to repair the injured heart. In this review, we discuss the recent advances made in the field in the past two years.

Phenotypic Screen with the Human Secretome Identifies FGF16 as Inducing Proliferation of iPSC-Derived Cardiac Progenitor Cells

Paracrine factors can induce cardiac regeneration and repair post myocardial infarction by stimulating proliferation of cardiac cells and inducing the anti-fibrotic, antiapoptotic, and immunomodulatory effects of angiogenesis. Here, we screened a human secretome library, consisting of 923 growth factors, cytokines, and proteins with unknown function, in a phenotypic screen with human cardiac progenitor cells. The primary readout in the screen was proliferation measured by nuclear count. From this screen, we identified FGF1, FGF4, FGF9, FGF16, FGF18, and seven additional proteins that induce proliferation of cardiac progenitor cells. FGF9 and FGF16 belong to the same FGF subfamily, share high sequence identity, and are described to have similar receptor preferences. Interestingly, FGF16 was shown to be specific for proliferation of cardiac progenitor cells, whereas FGF9 also proliferated human cardiac fibroblasts. Biosensor analysis of receptor preferences and quantification of receptor abundances suggested that FGF16 and FGF9 bind to different FGF receptors on the cardiac progenitor cells and cardiac fibroblasts. FGF16 also proliferated naïve cardiac progenitor cells isolated from mouse heart and human cardiomyocytes derived from induced pluripotent cells. Taken together, the data suggest that FGF16 could be a suitable paracrine factor to induce cardiac regeneration and repair.

Function Follows Form - A Review of Cardiac Cell Therapy

The investment of nearly 2 decades of clinical investigation into cardiac cell therapy has yet to change cardiovascular practice. Recent insights into the mechanism of cardiac regeneration help explain these results and provide important context in which we can develop next-generation therapies. Non-contractile cells such as bone marrow or adult heart derivatives neither engraft long-term nor induce new muscle formation. Correspondingly, these cells offer little functional benefit to infarct patients. In contrast, preclinical data indicate that transplantation of bona fide cardiomyocytes derived from pluripotent stem cells induces direct remuscularization. This new myocardium beats synchronously with the host heart and induces substantial contractile benefits in macaque monkeys, suggesting that regeneration of contractile myocardium is required to fully recover function. Through a review of the preclinical and clinical trials of cardiac cell therapy, distinguishing the primary mechanism of benefit as either contractile or non-contractile helps appreciate the barriers to cardiac repair and establishes a rational path to optimizing therapeutic benefit.

The small molecule Chicago Sky Blue promotes heart repair following myocardial infarction in mice

The adult mammalian heart regenerates poorly after injury and, as a result, ischemic heart diseases are among the leading causes of death worldwide. The recovery of the injured heart is dependent on orchestrated repair processes including inflammation, fibrosis, cardiomyocyte survival, proliferation, and contraction properties that could be modulated in patients. In this work we designed an automated high-throughput screening system for small molecules that induce cardiomyocyte proliferation in vitro and identified the small molecule Chicago Sky Blue 6B (CSB). Following induced myocardial infarction, CSB treatment reduced scar size and improved heart function of adult mice. Mechanistically, we show that although initially identified using in vitro screening for cardiomyocyte proliferation, in the adult mouse CSB promotes heart repair through (i) inhibition of CaMKII signaling, which improves cardiomyocyte contractility; and (ii) inhibition of neutrophil and macrophage activation, which attenuates the acute inflammatory response, thereby contributing to reduced scarring. In summary, we identified CSB as a potential therapeutic agent that enhances cardiac repair and function by suppressing postinjury detrimental processes, with no evidence for cardiomyocyte renewal.

Quantitative proteomic analyses reveal that GPX4 downregulation during myocardial infarction contributes to ferroptosis in cardiomyocytes

Ischaemic heart disease (IHD) is the leading cause of death worldwide. Although myocardial cell death plays a significant role in myocardial infarction (MI), its underlying mechanism remains to be elucidated. To understand the progression of MI and identify potential therapeutic targets, we performed tandem mass tag (TMT)-based quantitative proteomic analysis using an MI mouse model. Gene ontology (GO) analysis and gene set enrichment analysis (GSEA) revealed that the glutathione metabolic pathway and reactive oxygen species (ROS) pathway were significantly downregulated during MI. In particular, glutathione peroxidase 4 (GPX4), which protects cells from ferroptosis (an iron-dependent programme of regulated necrosis), was downregulated in the early and middle stages of MI. RNA-seq and qRT-PCR analyses suggested that GPX4 downregulation occurred at the transcriptional level. Depletion or inhibition of GPX4 using specific siRNA or the chemical inhibitor RSL3, respectively, resulted in the accumulation of lipid peroxide, leading to cell death by ferroptosis in H9c2 cardiomyoblasts. Although neonatal rat ventricular myocytes (NRVMs) were less sensitive to GPX4 inhibition than H9c2 cells, NRVMs rapidly underwent ferroptosis in response to GPX4 inhibition under cysteine deprivation. Our study suggests that downregulation of GPX4 during MI contributes to ferroptotic cell death in cardiomyocytes upon metabolic stress such as cysteine deprivation.

Fatty Acid-Treated Induced Pluripotent Stem Cell-Derived Human Cardiomyocytes Exhibit Adult Cardiomyocyte-Like Energy Metabolism Phenotypes

Human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs) (iPSC-CMs) are a promising cell source for myocardial regeneration, disease modeling and drug assessment. However, iPSC-CMs exhibit immature fetal CM-like characteristics that are different from adult CMs in several aspects, including cellular structure and metabolism. As an example, glycolysis is a major energy source for immature CMs. As CMs mature, the mitochondrial oxidative capacity increases, with fatty acid β-oxidation becoming a key energy source to meet the heart’s high energy demand. The immaturity of iPSC-CMs thereby limits their applications. The aim of this study was to investigate whether the energy substrate fatty acid-treated iPSC-CMs exhibit adult CM-like metabolic properties. After 20 days of differentiation from human iPSCs, iPSC-CMs were sequentially cultured with CM purification medium (lactate+/glucose-) for 7 days and maturation medium (fatty acids+/glucose-) for 3–7 days by mimicking the adult CM’s preference of utilizing fatty acids as a major metabolic substrate. The purity and maturity of iPSC-CMs were characterized via the analysis of: (1) Expression of CM-specific markers (e.g., troponin T, and sodium and potassium channels) using RT-qPCR, Western blot or immunofluorescence staining and electron microscopy imaging; and (2) cell energy metabolic profiles using the XF96 Extracellular Flux Analyzer. iPSCs-CMs (98% purity) cultured in maturation medium exhibited enhanced elongation, increased mitochondrial numbers with more aligned Z-lines, and increased expression of matured CM-related genes, suggesting that fatty acid-contained medium promotes iPSC-CMs to undergo maturation. In addition, the oxygen consumption rate (OCR) linked to basal respiration, ATP production, and maximal respiration and spare respiratory capacity (representing mitochondrial function) was increased in matured iPSC-CMs. Mature iPSC-CMs also displayed a larger change in basal and maximum respirations due to the utilization of exogenous fatty acids (palmitate) compared with non-matured control iPSC-CMs. Etomoxir (a carnitine palmitoyltransferase 1 inhibitor) but not 2-deoxyglucose (an inhibitor of glycolysis) abolished the palmitate pretreatment-mediated OCR increases in mature iPSC-CMs. Collectively, our data demonstrate for the first time that fatty acid treatment promotes metabolic maturation of iPSC-CMs (as evidenced by enhanced mitochondrial oxidative function and strong capacity of utilizing fatty acids as energy source). These matured iPSC-CMs might be a promising human CM source for broad biomedical application.

Gene therapy for refractory angina and cell therapy for heart failure: experience of a Brazilian research group

Cell therapy has shown impressive effects in experimental cardiomyopathy models. To a lesser extent, gene therapy has also been studied. In both cases, translation to clinical therapy has been disappointing. This paper is intended to describe the experience and achievements of a multicenter working group located in Porto Alegre, southern Brazil, in experimental and translational research projects for cell-based and gene therapy methods in the treatment of dilated and ischemic cardiomyopathies. The results of preclinical and clinical studies showed that bone marrow mononuclear stem cells indeed have an effect in improving myocardial perfusion and contractile function, but the overall results are poorly translated to the clinical level. Gene therapy studies with direct myocardial injections of naked VEGF 165 plasmid showed improvement in myocardial perfusion and function in animal models. A randomized clinical trial found that this method is safe and improved myocardial perfusion, but the benefits disappeared after 1 year. An animal experiment associating VEGF 165 with angiopoietin was undertaken in mini pigs to extend the durability of that therapy. In conclusion, our efforts to better understand the mechanisms and functions of gene and cell-based therapies in cardiology resulted in significant findings and propose a future look at cell-free therapeutic approaches.

MicroRNA-302d promotes the proliferation of human pluripotent stem cell-derived cardiomyocytes by inhibiting LATS2 in the Hippo pathway

Recent evidence has shown that cardiomyocytes (CMs) can proliferate at a low level after myocardial infarction (MI), but it is insufficient to reestablish heart function. Several microRNAs (miRNAs) have been proven to sufficiently induce rodent CM proliferation. However, whether miRNAs identified in rodents can promote human CM proliferation is unknown due to the poorly conserved functions of miRNAs among species. In the present study, we demonstrate that i) expression of microRNA-302d (miR-302d) decreased significantly during CM differentiation from human pluripotent stem cells (hPSCs) from day 4 to day 18; ii) miR-302d efficiently promoted proliferation of hPSC-derived CMs; iii) miR-302d promoted CM proliferation by targeting LATS2 in the Hippo pathway; and iv) RNA-sequencing analysis revealed that overexpression of miR-302d induced changes in gene expression, which mainly converged on the cell cycle. Our study provides further evidence for the therapeutic potential of miR-302d.

Cardiac regeneration with pluripotent stem cell-derived cardiomyocytes and direct cardiac reprogramming

Cardiovascular disease is the leading cause of death globally. Cardiomyocytes (CMs) have poor regenerative capacity, and pharmacological therapies have limited efficacy in severe heart failure. Currently, there are several promising strategies for cardiac regeneration. The most promising approach to remuscularize failing hearts is cell transplantation therapy using newly generated CMs from exogenous sources, such as pluripotent stem cells. Alternatively, approaches to generate new CMs from endogenous cell sources in situ may also repair the injured heart and improve cardiac function. Direct cardiac reprogramming has emerged as a novel therapeutic approach to regenerate injured hearts by directly converting endogenous cardiac fibroblasts into CM-like cells. Through cell transplantation and direct cardiac reprogramming, new CMs can be generated and scar tissue reduced to improve cardiac function; therefore, cardiac regeneration may serve as a powerful strategy for treatment of severe heart failure. While substantial progress has been made in these two strategies for cardiac regeneration over the past several years, challenges remain for clinical translation. This review provide an overview of previous reports and current challenges in this field.

miR-199a-3p promotes cardiomyocyte proliferation by inhibiting Cd151 expression

Adult mammalian cardiomyocytes have extremely limited capacity to regenerate, and it is believed that a strong intrinsic mechanism is prohibiting the cardiomyocytes from entering the cell cycle. microRNAs that promote proliferation in cardiomyocyte can be used as probes to identify novel genes suppressing cardiomyocytes proliferation, thus dissecting the mechanism(s) preventing cardiomyocytes from duplication. In particular, miR-199a-3p has been found as a potent activator of proliferation in rodent cardiomyocyte, although its molecular targets remain elusive. Here, we identified Cd151 as a direct target of miR-199a-3p, and its expression is greatly suppressed by miR-199a-3p. Cd151 gain-of-function reduced cardiomyocyte proliferation, conversely Cd151 loss-of-function increased cardiomyocytes proliferation. Overexpression of Cd151 blocks the activating effect of miR-199a-3p on cardiomyocyte proliferation, suggesting Cd151 is a functional target of miR-199a-3p in cardiomyocytes. Mechanistically, we found that Cd151 induces p38 expression, a known negative regulator of cardiomyocyte proliferation, and pharmacological inhibition of p38 rescued the inhibitory effect of Cd151 on proliferation. Together, this work proposes Cd151 as a novel suppressor of cardiomyocyte proliferation, which may provide a new molecular target for developing therapies to promote cardiac regeneration.

Lymphocytic subsets play distinct roles in heart diseases

Heart diseases are one of the leading causes of death for humans in the world. Increasing evidence has shown that myocardial injury induced innate and adaptive immune responses upon early cellular damage but also during chronic phases post-injury. The immune cells can not only aggravate the injury but also play an essential role in the induction of wound healing responses, which means they play a complex role throughout the acute inflammatory response and reparative response after cardiac injury. This review will summarize the current experimental and clinical evidence of lymphocytes, one of the major types of immune cells, participate in heart diseases and try to explain the possible role of these immune cells following cardiac injury.

Cardiac Reprogramming Factors Synergistically Activate Genome-wide Cardiogenic Stage-Specific Enhancers

The cardiogenic transcription factors (TFs) Mef2c, Gata4, and Tbx5 can directly reprogram fibroblasts to induced cardiac-like myocytes (iCLMs), presenting a potential source of cells for cardiac repair. While activity of these TFs is enhanced by Hand2 and Akt1, their genomic targets and interactions during reprogramming are not well studied. We performed genome-wide analyses of cardiogenic TF binding and enhancer profiling during cardiac reprogramming. We found that these TFs synergistically activate enhancers highlighted by Mef2c binding sites and that Hand2 and Akt1 coordinately recruit other TFs to enhancer elements. Intriguingly, these enhancer landscapes collectively resemble patterns of enhancer activation during embryonic cardiogenesis. We further constructed a cardiac reprogramming gene regulatory network and found repression of EGFR signaling pathway genes. Consistently, chemical inhibition of EGFR signaling augmented reprogramming. Thus, by defining epigenetic landscapes these findings reveal synergistic transcriptional activation across a broad landscape of cardiac enhancers and key signaling pathways that govern iCLM reprogramming.

Three in a Box: Understanding Cardiomyocyte, Fibroblast, and Innate Immune Cell Interactions to Orchestrate Cardiac Repair Processes

Following an insult by both intrinsic and extrinsic pathways, complex cellular, and molecular interactions determine a successful recovery or inadequate repair of damaged tissue. The efficiency of this process is particularly important in the heart, an organ characterized by very limited regenerative and repair capacity in higher adult vertebrates. Cardiac insult is characteristically associated with fibrosis and heart failure, as a result of cardiomyocyte death, myocardial degeneration, and adverse remodeling. Recent evidence implies that resident non-cardiomyocytes, fibroblasts but also macrophages -pillars of the innate immunity- form part of the inflammatory response and decisively affect the repair process following a cardiac insult. Multiple studies in model organisms (mouse, zebrafish) of various developmental stages (adult and neonatal) combined with genetically engineered cell plasticity and differentiation intervention protocols -mainly targeting cardiac fibroblasts or progenitor cells-reveal particular roles of resident and recruited innate immune cells and their secretome in the coordination of cardiac repair. The interplay of innate immune cells with cardiac fibroblasts and cardiomyocytes is emerging as a crucial platform to help our understanding and, importantly, to allow the development of effective interventions sufficient to minimize cardiac damage and dysfunction after injury.

Implications of scar structure and mechanics for post-infarction cardiac repair and regeneration

Regenerating cardiac muscle lost during a heart attack is a topic of broad interest and enormous potential impact. One promising approach is to regenerate or re-engineer new myocardium in situ, at the site of damage, by injecting cells, growth factors, and other materials, or by reprogramming aspects of the normal wound healing process. A wide variety of strategies have been explored, from promoting angiogenesis to injection of a variety of different progenitor cell types, to re-engineering resident cells to produce key growth factors or even transdifferentiate into myocytes. Despite substantial progress and continued promise, clinical impact of this work has fallen short of expectations. One contributing factor may be that many efforts focus primarily on generating cardiomyocytes, with less attention to re-engineering the extracellular matrix (ECM). Yet the role of the ECM is particularly crucial to consider following myocardial infarction, which leads to rapid formation of a collagen-rich scar. This review combines a brief summary of current efforts to regenerate cardiomyocytes with what is currently known about the structure and mechanics of post-infarction scar, with the goal of identifying principles that can guide efforts to produce new myocytes embedded in an extracellular environment that facilitates their differentiation, maintenance, and function.

Cellular Therapy for Ischemic Heart Disease: An Update

Ischemic heart disease (IHD), which includes heart failure (HF) induced by heart attack (myocardial infarction, MI), is a significant cause of morbidity and mortality worldwide (Benjamin, et al. Circulation 139:e56-e66, 2019). MI occurs at an alarmingly high rate in the United States (approx. One case every 40 seconds), and the failure to repair damaged myocardium is the leading cause of recurrent heart attacks, heart failure (HF), and death within 5 years of MI (Benjamin, et al. Circulation 139:e56-e66, 2019). At present, HF represents an unmet need with no approved clinical therapies to replace the damaged myocardium. As the population ages, the number of heart failure patients is projected to increase, doubling the annual cost by 2030 (Benjamin, et al. Circulation 139:e56-e66, 2019). In the past decades, stem cell therapy has become a promising strategy for cardiac regeneration. However, stem cell-based therapy yielded modest success in human clinical trials. This chapter examines the types of cells examined in cardiac therapy in the setting of IHD, with a brief introduction to ongoing research aiming at enhancing the therapeutic potential of transplanted cells.

DMPE-PEG scaffold binding with TGF-β1 receptor enhances cardiomyogenic differentiation of adipose-derived stem cells

Background

Heart failure has become a global health problem with increasing incidences worldwide. Traditional pharmacological treatments can delay but cannot reverse the underlying disease processes. The clinical application of myocardial tissue engineering represents a promising strategy because it features cell-based replacement therapies that replace partially or fully damaged cardiac tissues with in vitro-generated tissue equivalents. However, the effectiveness of this therapy is limited by poor viability and differentiation of the grafted cells. This limitation could be overcome by rapidly increasing the numbers of functional cardiomyocytes. In this study, we aimed to obtain functional myocardial tissue engineering seed cells with high proliferation and differentiation rates by combining 1,2-dimyristoyl-sn-glycero-3-phosphoethan-olamine-polyethylene glycol (DMPE-PEG) and recombinant transforming growth factor-β1 receptor I (rTGF-β1 RI), followed by binding to human adipose-derived stromal cells (hADSCs).

Methods

To induce higher expression level of TGF-β1 RI, DMPE-PEG was inoculated with rTGF-β1 RI to modify the surface of hADSCs. The differentiation ability and morphological characteristics of the modified hADSCs were examined in vitro and in vivo.

Results

The caridiomyocartic differentiation ability of TGF-β1 RI-modified hADSCs was significantly enhanced, as indicated by elevated expression levels of the cardiac markers cardiac troponin T (cTnT) and α-smooth muscle actin (SMA) via increased phosphorylation of the Smad signaling pathway-related proteins.

Conclusion

Our findings provide new insights into stem cell transplantation therapy in myocardial tissue engineering.

Pretargeting and Bioorthogonal Click Chemistry-Mediated Endogenous Stem Cell Homing for Heart Repair

Stem cell therapy is one of the promising strategies for the treatment of ischemic heart disease. However, the clinical application of stem cells transplantation is limited by low cell engraftment in the infarcted myocardium. Taking advantage of pretargeting and bioorthogonal chemistry, we engineered a pretargeting and bioorthogonal chemistry (PTBC) system to capture endogenous circulating stem cells and target them to the injured heart for effective repair. Two bioorthogonal antibodies were i.v. administrated with a pretargeting interval (48 h). Through bioorthogonal click reaction, the two antibodies are linked in vivo, engaging endogenous stem cells with circulating platelets. As a result, the platelets redirect the stem cells to the injured heart. In vitro and in vivo studies demonstrated that bioorthogonal click reaction was able to induce the conjugation of platelets and endothelial progenitor cells (EPCs) and enhance the binding of EPCs to collagen and injured blood vessels. More importantly, in a mouse model of acute myocardial infarction, the in vivo results of cardiac function, heart morphometry, and immunohistochemistry assessment all confirmed effective heart repair by the PTBC system.

Genetic and epigenetic regulation of cardiomyocytes in development, regeneration and disease

Embryonic and postnatal life depend on the uninterrupted function of cardiac muscle cells. These cells, termed cardiomyocytes, display many fascinating behaviors, including complex morphogenic movements, interactions with other cell types of the heart, persistent contractility and quiescence after birth. Each of these behaviors depends on complex interactions between both cardiac-restricted and widely expressed transcription factors, as well as on epigenetic modifications. Here, we review recent advances in our understanding of the genetic and epigenetic control of cardiomyocyte differentiation and proliferation during heart development, regeneration and disease. We focus on those regulators that are required for both heart development and disease, and highlight the regenerative principles that might be manipulated to restore function to the injured adult heart.