Regenerating the heart

Three-dimensional scaffold-free microtissues engineered for cardiac repair

Cardiovascular diseases, including myocardial infarction (MI), persist as the leading cause of mortality and morbidity worldwide. The limited regenerative capacity of the myocardium presents significant challenges specifically for the treatment of MI and, subsequently, heart failure (HF). Traditional therapeutic approaches mainly rely on limiting the induced damage or the stress on the remaining viable myocardium through pharmacological regulation of remodeling mechanisms, rather than replacement or regeneration of the injured tissue. The emerging alternative regenerative medicine-based approaches have focused on restoring the damaged myocardial tissue with newly engineered functional and bioinspired tissue units. Cardiac regenerative medicine approaches can be broadly categorized into three groups: cell-based therapies, scaffold-based cardiac tissue engineering, and scaffold-free cardiac tissue engineering. Despite significant advancements, however, the clinical translation of these approaches has been critically hindered by two key obstacles for successful structural and functional replacement of the damaged myocardium, namely: poor engraftment of engineered tissue into the damaged cardiac muscle and weak electromechanical coupling of transplanted cells with the native tissue. To that end, the integration of micro- and nanoscale technologies along with recent advancements in stem cell technologies have opened new avenues for engineering of structurally mature and highly functional scaffold-based (SB-CMTs) and scaffold-free cardiac microtissues (SF-CMTs) with enhanced cellular organization and electromechanical coupling for the treatment of MI and HF. In this review article, we will present the state-of-the-art approaches and recent advancements in the engineering of SF-CMTs for myocardial repair.

Electroconductive Hydrogels for Tissue Engineering: Current Status and Future Perspectives

Over the past decade, electroconductive hydrogels, integrating both the biomimetic attributes of hydrogels and the electrochemical properties of conductive materials, have gained significant attention. Hydrogels, three-dimensional and swollen hydrophilic polymer networks, are an important class of tissue engineering (TE) scaffolds owing to their microstructural and mechanical properties, ability to mimic the native extracellular matrix, and promote tissue repair. However, hydrogels are intrinsically insulating and therefore unable to emulate the complex electrophysiological microenvironment of cardiac and neural tissues. To overcome this challenge, electroconductive materials, including carbon-based materials, nanoparticles, and polymers, have been incorporated within nonconductive hydrogels to replicate the electrical and biological characteristics of biological tissues. This review gives a brief introduction on the rational design of electroconductive hydrogels and their current applications in TE, especially for neural and cardiac regeneration. The recent progress and development trends of electroconductive hydrogels, their challenges, and clinical translatability, as well as their future perspectives, with a focus on advanced manufacturing technologies, are also discussed.

Protective Effects of Polyphenols against Ischemia/Reperfusion Injury

Myocardial infarction (MI) is a leading cause of morbidity and mortality across the world. It manifests as an imbalance between blood demand and blood delivery in the myocardium, which leads to cardiac ischemia and myocardial necrosis. While it is not easy to identify the first pathogenic cause of MI, the consequences are characterized by ischemia, chronic inflammation, and tissue degeneration. A poor MI prognosis is associated with extensive cardiac remodeling. A loss of viable cardiomyocytes is replaced with fibrosis, which reduces heart contractility and heart function. Recent advances have given rise to the concept of natural polyphenols. These bioactive compounds have been studied for their pharmacological properties and have proven successful in the treatment of cardiovascular diseases. Studies have focused on their various bioactivities, such as their antioxidant and anti-inflammatory effects and free radical scavenging. In this review, we summarized the effects and benefits of polyphenols on the cardiovascular injury, particularly on the treatment of myocardial infarction in animal and human studies.

CIRM tools and technologies: Breaking bottlenecks to the development of stem cell therapies

The California Institute for Regenerative Medicine (CIRM) has a mission to accelerate stem cell treatments to patients with unmet medical needs. This perspective describes successful examples of work funded by CIRM's New Cell Lines and Tools and Technologies Initiatives, which were developed to address bottlenecks to stem cell research and translation. The tools developed through these programs evolved from more discovery-oriented technologies, such as disease models, differentiation processes, and assays, to more translation focused tools, including scalable good manufacturing processes, animal models, and tools for clinical cell delivery. These tools are available to the research community and many are facilitating translation of regenerative therapeutics today.

Detachment of cell sheets from clinically ubiquitous cell culture vessels by ultrasonic vibration

Proteinases that digest the extracellular matrix are usually used to harvest cells from culture vessels in a general culture process, which lowers the initial adhesion rate in regenerative medicine. Cell sheet engineering is one of the most important technologies in this field, especially for transplantation, because fabricated cell sheets have rich extracellular matrixes providing strong initial adhesion. Current cell sheet fabrication relies on temperature-responsive polymer-coated dishes. Cells are cultured on such specialized dishes and subjected to low temperature. Thus, we developed a simple but versatile cell sheet fabrication method using ubiquitous culture dishes/flasks without any coating or temperature modulation. Confluent mouse myoblasts (C2C12 cell line) were exposed to ultrasonic vibration from underneath and detached as cell sheets from entire culture surfaces. Because of the absence of low temperature, cell metabolism was statically increased compared with the conventional method. Furthermore, viability, morphology, protein expression, and mRNA expression were normal. These analyses indicated no side effects of ultrasonic vibration exposure. Therefore, this novel method may become the standard for cell sheet fabrication. Our method can be easily conducted following a general culture procedure with a typical dish/flask, making cell sheets more accessible to medical experts.

Will cell therapies provide the solution for the shortage of transplantable organs?

PURPOSE OF REVIEW

The potential to regenerate ischemically damaged kidneys while being perfused ex-vivo offers the best near-term solution to increasing kidney allografts for transplantation.

RECENT FINDINGS

There are a number of stem-cell sources including: stromal mesenchymal cells (MSC), induced adult pluripotent stem cells, fetal stem cells from placenta, membranes, amniotic fluid and umbilical cord and hematopoietic cells. MSC are increasingly the stem cell of choice and studies are primarily focused on novel induction immunosuppression to prevent rejection. Stem-cell therapies applied in vivo may be of limited benefit because the nonintegrating cells do not remain in the kidney and are not detectable in the body after several days. MSC therapies for transplantation have demonstrated early safety and feasibility. However, efficacy has not been clearly established. A more feasible application of a stem-cell therapy in transplantation is the administration of MSC to treat damaged renal allografts directly while being perfused ex vivo. Initial feasibility has been established demonstrating MSC-treatment results in statistically significant reduction of inflammatory responses, increased ATP and growth factor synthesis and mitosis.

SUMMARY

The ability to regenerate renal tissue ex-vivo sufficiently to result in immediate function could revolutionize transplantation by solving the chronic organ shortage.

An overview of the myocardial regeneration potential of cardiac c-Kit+ progenitor cells via PI3K and MAPK signaling pathways

In recent years, several studies have investigated cell transplantation as an innovative strategy to restore cardiac function following heart failure. Previous studies have also shown cardiac progenitor cells as suitable candidates for cardiac cell therapy compared with other stem cells. Cellular kit (c-kit) plays an important role in the survival and migration of cardiac progenitor cells. Like other types of cells, in the heart, cellular responses to various stimuli are mediated via coordinated pathways. Activation of c-kit⁺ cells leads to subsequent activation of several downstream mediators such as PI3K and the MAPK pathways. This review aims to outline current research findings on the role of PI3K/AKT and the MAPK pathways in myocardial regeneration potential of c-kit⁺.

Inducing Endogenous Cardiac Regeneration: Can Biomaterials Connect the Dots?

Heart failure (HF) after myocardial infarction (MI) due to blockage of coronary arteries is a major public health issue. MI results in massive loss of cardiac muscle due to ischemia. Unfortunately, the adult mammalian myocardium presents a low regenerative potential, leading to two main responses to injury: fibrotic scar formation and hypertrophic remodeling. To date, complete heart transplantation remains the only clinical option to restore heart function. In the last two decades, tissue engineering has emerged as a promising approach to promote cardiac regeneration. Tissue engineering aims to target processes associated with MI, including cardiomyogenesis, modulation of extracellular matrix (ECM) remodeling, and fibrosis. Tissue engineering dogmas suggest the utilization and combination of two key components: bioactive molecules and biomaterials. This chapter will present current therapeutic applications of biomaterials in cardiac regeneration and the challenges still faced ahead. The following biomaterial-based approaches will be discussed: Nano-carriers for cardiac regeneration-inducing biomolecules; corresponding matrices for their controlled release; injectable hydrogels for cell delivery and cardiac patches. The concept of combining cardiac patches with controlled release matrices will be introduced, presenting a promising strategy to promote endogenous cardiac regeneration.

Targeting Purinergic Signaling and Cell Therapy in Cardiovascular and Neurodegenerative Diseases

Extracellular purines exert several functions in physiological and pathophysiological mechanisms. ATP acts through P2 receptors as a neurotransmitter and neuromodulator and modulates heart contractility, while adenosine participates in neurotransmission, blood pressure, and many other mechanisms. Because of their capability to differentiate into mature cell types, they provide a unique therapeutic strategy for regenerating damaged tissue, such as in cardiovascular and neurodegenerative diseases. Purinergic signaling is pivotal for controlling stem cell differentiation and phenotype determination. Proliferation, differentiation, and apoptosis of stem cells of various origins are regulated by purinergic receptors. In this chapter, we selected neurodegenerative and cardiovascular diseases with clinical trials using cell therapy and purinergic receptor targeting. We discuss these approaches as therapeutic alternatives to neurodegenerative and cardiovascular diseases. For instance, promising results were demonstrated in the utilization of mesenchymal stem cells and bone marrow mononuclear cells in vascular regeneration. Regarding neurodegenerative diseases, in general, P2X7 and A_2A receptors mostly worsen the degenerative state. Stem cell-based therapy, mainly through mesenchymal and hematopoietic stem cells, showed promising results in improving symptoms caused by neurodegeneration. We propose that purinergic receptor activity regulation combined with stem cells could enhance proliferative and differentiation rates as well as cell engraftment.

Arrhythmogenic risks of stem cell replacement therapy for cardiovascular diseases

Ischemic heart disease and congestive heart failure are major contributors to high morbidity and mortality. Approximately 1.5 million cases of myocardial infarction occur annually in the United States; the yearly incidence rate is approximately 600 cases per 100,000 people. Although significant progress to improve the survival rate has been made by medications and implantable medical devices, damaged cardiomyocytes are unable to be recovered by current treatment strategies. After almost two decades of research, stem cell therapy has become a very promising approach to generate new cardiomyocytes and enhance the function of the heart. Along with clinical trials with stem cells conducted in cardiac regeneration, concerns regarding safety and potential risks have emerged. One of the contentious issues is the electrical dysfunctions of cardiomyocytes and cardiac arrhythmia after stem cell therapy. In this review, we focus on the cell sources currently used for stem cell therapy and discuss related arrhythmogenic risk.

Dual-peptide functionalized acetalated dextran-based nanoparticles for sequential targeting of macrophages during myocardial infarction

The advent of nanomedicine has recently started to innovate the treatment of cardiovascular diseases, in particular myocardial infarction. Although current approaches are very promising, there is still an urgent need for advanced targeting strategies. In this work, the exploitation of macrophage recruitment is proposed as a novel and synergistic approach to improve the addressability of the infarcted myocardium achieved by current peptide-based heart targeting strategies. For this purpose, an acetalated dextran-based nanosystem is designed and successfully functionalized with two different peptides, atrial natriuretic peptide (ANP) and linTT1, which target, respectively, cardiac cells and macrophages associated with atherosclerotic plaques. The biocompatibility of the nanocarrier is screened on both macrophage cell lines and primary macrophages, showing high safety, in particular after functionalization of the nanoparticles' surface. Furthermore, the system shows higher association versus uptake ratio towards M2-like macrophages (approximately 2-fold and 6-fold increase in murine and human primary M2-like macrophages, respectively, compared to M1-like). Overall, the results demonstrate that the nanosystem has potential to exploit the "hitchhike" effect on M2-like macrophages and potentially improve, in a dual targeting strategy, the ability of the ANP peptide to target infarcted heart.

Clinical potential and current progress of mesenchymal stem cells for Parkinson's disease: a systematic review

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease characterized by severe dyskinesia due to a progressive loss of dopaminergic neurons along the nigro-striatal pathway. The current focus of treatment is to relieve symptoms through administration of levodopa, such as L-3,4-dihydroxy phenylalanine replacement therapy, dopaminergic agonist administration, functional neurosurgery, and gene therapy, rather than preventing dopaminergic neuronal damage. Hence, the application and development of neuroprotective/disease modification strategies is absolutely necessary. Currently, stem cell therapy has been considered for PD treatment. As for the stem cells, mesenchymal stem cells (MSCs) seem to be the most promising. In this review, we analyze the mechanisms of action of MSCs in Parkinson's disease, including growth factor secretion, exocytosis, and attenuation of neuroinflammation. To determine efficacy and protect patients from possible adverse effects, ongoing rigorous and controlled studies of MSC treatment will be critical.

Re-enforcing hypoxia-induced polyploid cardiomyocytes enter cytokinesis through activation of β-catenin

Cardiomyocyte (CM) loss is a characteristic of various heart diseases, including ischaemic heart disease. Cardiac regeneration has been suggested as a promising strategy to address CM loss. Although many studies of regeneration have focused mainly on mononucleated or diploid CM, the limitations associated with the cytokinesis of polyploid and multinucleated CMs remain less well known. Here, we show that β-catenin, a key regulator in heart development, can increase cytokinesis in polyploid multinucleated CMs. The activation of β-catenin increases the expression of the cytokinesis-related factor epithelial cell transforming 2 (ECT2), which regulates the actomyosin ring and thus leads to the completion of cytokinesis in polyploid CMs. In addition, hypoxia can induce polyploid and multinucleated CMs by increasing factors related to the G1-S-anaphase of the cell cycle, but not those related to cytokinesis. Our study therefore reveals that the β-catenin can promote the cytokinesis of polyploid multinucleated CMs via upregulation of ECT2. These findings suggest a potential field of polyploid CM research that may be exploitable for cardiac regeneration therapy.

Nanoscale Technologies for Prevention and Treatment of Heart Failure: Challenges and Opportunities

The adult myocardium has a limited regenerative capacity following heart injury, and the lost cells are primarily replaced by fibrotic scar tissue. Suboptimal efficiency of current clinical therapies to resurrect the infarcted heart results in injured heart enlargement and remodeling to maintain its physiological functions. These remodeling processes ultimately leads to ischemic cardiomyopathy and heart failure (HF). Recent therapeutic approaches (e.g., regenerative and nanomedicine) have shown promise to prevent HF postmyocardial infarction in animal models. However, these preclinical, clinical, and technological advancements have yet to yield substantial enhancements in the survival rate and quality of life of patients with severe ischemic injuries. This could be attributed largely to the considerable gap in knowledge between clinicians and nanobioengineers. Development of highly effective cardiac regenerative therapies requires connecting and coordinating multiple fields, including cardiology, cellular and molecular biology, biochemistry and chemistry, and mechanical and materials sciences, among others. This review is particularly intended to bridge the knowledge gap between cardiologists and regenerative nanomedicine experts. Establishing this multidisciplinary knowledge base may help pave the way for developing novel, safer, and more effective approaches that will enable the medical community to reduce morbidity and mortality in HF patients.

Magnetic Nanomaterials for Advanced Regenerative Medicine: The Promise and Challenges

The recent emergence of numerous nanotechnologies is expected to facilitate the development of regenerative medicine, which is a tissue regeneration technique based on the replacement/repair of diseased tissue or organs to restore the function of lost, damaged, and aging cells in the human body. In particular, the unique magnetic properties and specific dimensions of magnetic nanomaterials make them promising innovative components capable of significantly advancing the field of tissue regeneration. Their potential applications in tissue regeneration are the focus here, beginning with the fundamentals of magnetic nanomaterials. How nanomaterials-both those that are intrinsically magnetic and those that respond to an externally applied magnetic field-can enhance the efficiency of tissue regeneration is also described. Applications including magnetically controlled cargo delivery and release, real-time visualization and tracking of transplanted cells, magnetic regulation of cell proliferation/differentiation, and magnetic activation of targeted ion channels and signal pathways involved in regeneration are highlighted, and comments on the perspectives and challenges in magnetic nanomaterial-based tissue regeneration are given.

Cardiac Sca-1+ Cells Are Not Intrinsic Stem Cells for Myocardial Development, Renewal, and Repair

BACKGROUND

For more than a decade, Sca-1⁺ cells within the mouse heart have been widely recognized as a stem cell population with multipotency that can give rise to cardiomyocytes, endothelial cells, and smooth muscle cells in vitro and after cardiac grafting. However, the developmental origin and authentic nature of these cells remain elusive.

METHODS

Here, we used a series of high-fidelity genetic mouse models to characterize the identity and regenerative potential of cardiac resident Sca-1⁺ cells.

RESULTS

With these novel genetic tools, we found that Sca-1 does not label cardiac precursor cells during early embryonic heart formation. Postnatal cardiac resident Sca-1⁺ cells are in fact a pure endothelial cell population. They retain endothelial properties and exhibit minimal cardiomyogenic potential during development, normal aging and upon ischemic injury.

CONCLUSIONS

Our study provides definitive insights into the nature of cardiac resident Sca-1⁺ cells. The observations challenge the current dogma that cardiac resident Sca-1⁺ cells are intrinsic stem cells for myocardial development, renewal, and repair, and suggest that the mechanisms of transplanted Sca-1⁺ cells in heart repair need to be reassessed.

Compromised Anti-inflammatory Action of Neutrophil Extracellular Traps in PAD4-Deficient Mice Contributes to Aggravated Acute Inflammation After Myocardial Infarction

Innate immune responses and rapid recruitment of leukocytes, which regulate inflammation and subsequent healing, play a key role in acute myocardial infarction (MI). Peptidylarginine deiminase 4 (PAD4) is critically involved in chromatin decondensation during the release of Neutrophil Extracellular Traps (NETs) by activated neutrophils. Alternatively, activated macrophages (M2) and accurate collagen deposition determine the repair of the infarcted heart. In this study, we investigated the impact of NETs on macrophage polarization and their role for acute cardiac inflammation and subsequent cardiac healing in a mouse model of acute MI. NETs were found to promote in vitro macrophage polarization toward a reparative phenotype. NETs suppressed pro-inflammatory macrophages (M1) under hypoxia and diminished IL-6 and TNF-α expression. Further on, NETs strongly supported M2b polarization and IL-10 expression. In cardiac fibroblasts, NETs increased TGF-ß expression under hypoxic culture conditions. PAD4^-/- mice subjected to permanent ligation of the left anterior descending artery suffered from overwhelming inflammation in the acute phase of MI. Noteworthy, PAD4^-/- neutrophils were unable to release NETs upon ex vivo stimulation with ionomycin or PMA, but produced significantly higher amounts of reactive oxygen species (ROS). Increased levels of circulating cell-free DNA, mitochondrial DNA and cardiac troponin were found in PAD4^-/- mice in the acute phase of MI when compared to WT mice. Reduced cardiac expression of IL-6, IL-10, and M2 marker genes, as well as increased TNF-α expression, suggested a pro-inflammatory state. PAD4^-/- mice displayed significantly increased cardiac MMP-2 expression under baseline conditions. At day 1, post-MI, PAD4^-/- mice showed increased end-diastolic volume and increased thinning of the left ventricular wall. Interestingly, improved cardiac function, as demonstrated by significantly increased ejection fraction, was found at day 21. Altogether, our results indicate that NETs support macrophage polarization toward an M2 phenotype, thus displaying anti-inflammatory properties. PAD4 deficiency aggravates acute inflammation and increases tissue damage post-MI, partially due to the lack of NETs.

Cardiac regenerative therapy: Many paths to repair

Cardiovascular disease remains the primary cause of death in the United States and in most nations worldwide, despite ongoing intensive efforts to promote cardiac health and treat heart failure. Replacing damaged myocardium represents perhaps the most promising treatment strategy, but also the most challenging given that the adult mammalian heart is notoriously resistant to endogenous repair. Cardiac regeneration following pathologic challenge would require proliferation of surviving tissue, expansion and differentiation of resident progenitors, or transdifferentiation of exogenously applied progenitor cells into functioning myocardium. Adult cardiomyocyte proliferation has been the focus of investigation for decades, recently enjoying a renaissance of interest as a therapeutic strategy for reversing cardiomyocyte loss due in large part to ongoing controversies and frustrations with myocardial cell therapy outcomes. The promise of cardiac cell therapy originated with reports of resident adult cardiac stem cells that could be isolated, expanded and reintroduced into damaged myocardium, producing beneficial effects in preclinical animal models. Despite modest functional improvements, Phase I clinical trials using autologous cardiac derived cells have proven safe and effective, setting the stage for an ongoing multi-center Phase II trial combining autologous cardiac stem cell types to enhance beneficial effects. This overview will examine the history of these two approaches for promoting cardiac repair and attempt to provide context for current and future directions in cardiac regenerative research.

Mechanism of Enhanced MerTK-Dependent Macrophage Efferocytosis by Extracellular Vesicles

OBJECTIVE

Extracellular vesicles secreted by cardiosphere-derived cells (CDC_ev) polarize macrophages toward a distinctive phenotype with enhanced phagocytic capacity (M_CDCev). These changes underlie cardioprotection by CDC_ev and by the parent CDCs, notably attenuating the no-reflow phenomenon following myocardial infarction, but the mechanisms are unclear. Here, we tested the hypothesis that M_CDCev are especially effective at scavenging debris from dying cells (ie, efferocytosis) to attenuate irreversible damage post-myocardial infarction. Approach and Results: In vitro efferocytosis assays with bone marrow-derived macrophages, and in vivo transgenic rodent models of myocardial infarction, demonstrate enhanced apoptotic cell clearance with M_CDCev. CDC_ev exposure induces sustained MerTK expression in M_CDCev through extracellular vesicle transfer of microRNA-26a (via suppression of Adam17); the cardioprotective response is lost in animals deficient in MerTK. Single-cell RNA-sequencing revealed phagocytic pathway activation in M_CDCev, with increased expression of complement factor C1qa, a phagocytosis facilitator.

CONCLUSIONS

Together, these data demonstrate that extracellular vesicle modulation of MerTK and C1qa expression leads to enhanced macrophage efferocytosis and cardioprotection.

Therapeutic Potential of Pluripotent Stem Cells for Cardiac Repair after Myocardial Infarction

Myocardial infarction occurs as a result of acute arteriosclerotic plaque rupture in the coronary artery, triggering strong inflammatory responses. The necrotic cardiomyocytes are gradually replaced with noncontractile scar tissue that eventually manifests as heart failure. Pluripotent stem cells (PSCs) show great promise for widespread clinical applications, particularly for tissue regeneration, and are being actively studied around the world to help elucidate disease mechanisms and in the development of new drugs. Human induced PSCs also show potential for regeneration of the myocardial tissue in experiments with small animals and in in vitro studies. Although emerging evidence points to the effectiveness of these stem cell-derived cardiomyocytes in cardiac regeneration, several challenges remain before clinical application can become a reality. Here, we provide an overview of the present state of PSC-based heart regeneration and highlight the remaining hurdles, with a particular focus on graft survival, immunogenicity, posttransplant arrhythmia, maintained function, and tumor formation. Rapid progress in this field along with advances in biotechnology are expected to resolve these issues, which will require international collaboration and standardization.

Application of nanomaterials in three-dimensional stem cell culture

Petri dish cultured cells have for long provided scientists an aperture to understanding cell's behavior both in normal and disease states as well as in vitro and in vivo. But recent advances have brought to light how the architecture and composite nature of the immediate environment within which the cell is proliferated can profoundly influence its phenotypic features and functions, thus making obvious, limitations of the conventional two-dimensional cell culture despite it cost effectiveness. Fortunately, the transition to three-dimensional (3D) cell culture has occurred concurrently with expanded knowledge of nanoscience and materials, thereby lending significant impetus for innovative research. This review is focused on the application of nanoparticles in 3D stem cell breeding, recent trends and developments in medical sciences for improved drug delivery, and treatment approaches to some human diseases. We also reviewed prevailing challenges and concerns of nanotoxicity as it continues to impede and delay clinical applications as well the ongoing concerted and multidisciplinary efforts to overcome them.

Pluripotent Stem Cell-Derived Cardiomyocyte Transplantation for Heart Disease Treatment

PURPOSE OF REVIEW

Cardiovascular disease is the leading cause of mortality worldwide. Pluripotent stem cell-derived cardiomyocytes (PSC-CMs) have great potential to treat heart disease, owing to their capacity of engraftment and remuscularization in the host heart after transplantation. In the current review, we provide an overview of PSC-CMs for clinical transplantation.

RECENT FINDINGS

Studies have shown that PSC-CMs can survive, engraft, and form gap junctions after transplantation, with functional benefit. Engrafted PSC-CMs matured gradually in host hearts. Only in a large animal model, transient ventricular arrhythmias were detected, mainly because of the ectopic pacing from the grafted PSC-CMs. Although intense immunosuppression is unavoidable in xenotransplantation, immunosuppression remains necessary for MHC-matched allogenic non-human primate PSC-CMs transplantation. This review offers insights on how PSC-CMs contribute to functional benefit after transplantation to injured non-human primate hearts. We believe that PSC-CM transplantation represents a potentially novel treatment for ischemic heart diseases, provided that several technological and biological limitations can be overcome.

[Analysis of Biological Properties of Human Adult Mesenchymal Stem Cells and Their Effect on Mouse Hind Limb Ischemia]

BACKGROUND

Due to their self-renewal, proliferation, differentiation, and angiogenesis-inducing capacity, human adipose mesenchymal stem cells (AMSC) have potential clinical applications in the treatment of limb ischemia. AMSC from healthy donors have been shown to induce neovascularization in animal models. However, when cells were obtained from donors suffering from any pathology, their autologous application showed limited effectiveness. We studied whether liposuction niche and obesity could determine the regenerative properties of cells meaning that not all cell batches are suitable for clinical practice.

METHODS

AMSC obtained from 10 donors, obese and healthy, were expanded in vitro following a good manufacturing practice-like production protocol. Cell viability, proliferation kinetics, morphological analysis, phenotype characterization, and stemness potency were assessed over the course of the expansion process. AMSC selected for having the most suitable biological properties were used as an experimental treatment in a preclinical mouse model of hind limb ischemia.

RESULT

All cell batches were positively characterized as mesenchymal stem cells, but not all of them showed the same properties or were successfully expanded in vitro, depending on the characteristics of the donor and the extraction area. Notably, AMSC from the abdomen of obese donors showed undesirable biological properties. AMSC with low duplication times and multilineage differentiation potential and forming large densely packed colonies, were able, following expansion in vitro, to increase neovascularization and repair when implanted in the ischemic tissue of mice.

CONCLUSION

An extensive AMSC biological properties study could be useful to predict the potential clinical efficacy of cells before in vivo transplantation. Thus, peripheral ischemia and possibly other pathologies could benefit from stem cell treatments as shown in our preclinical model in terms of tissue damage repair and regeneration after ischemic injury.

Apela Promotes Cardiomyocyte Differentiation from Transgenic Human Embryonic Stem Cell Lines

Although embryonic stem (ES) cells (ESCs) may be a promising donor source for the repair of infarcted or ischemic heart tissues, their successful application in regenerative medicine has been hampered by difficulties in enriching, identifying, and selecting cardiomyocytes from the differentiating cells. We established transgenic human ES cell lines by transcriptional control of the α-cardiac myosin heavy chain (α-MHC) promoter driving green fluorescent protein (GFP) expression. Differentiated GFP-expressing cells display the characteristics of cardiomyocytes (CMs). Apela, a recently identified short peptide, up-regulated the expression of the cardiac-restricted transcription factors Tbx5 and GATA4 as well as differentiated the cardiomyocyte markers α-MHC and β-MHC. Flow cytometric analysis showed that apela increased the percentage of GFP-expressing cells in the beating foci of the embryoid bodies. The percentage of cardiac troponin T (TNT)-positive cells and the protein expression of TNT were increased in the ES cell-derived CMs with apela treatment. Functionally, the contractile frequency of the ES-derived CMs responded appropriately to the vasoactive drugs isoprenaline and carbachol. Our work presented a protocol for specially labelling and enriching CMs by combining transgenic human ES cell lines and exogenous growth factor treatment.

Lipopolysaccharides Improve Mesenchymal Stem Cell-Mediated Cardioprotection by MyD88 and stat3 Signaling in a Mouse Model of Cardiac Ischemia/Reperfusion Injury

Bone marrow-derived mesenchymal stem cells (MSCs) improve cardiac function after ischemia/reperfusion injury, in part, due to the release of cytoprotective paracrine factors. Toll-like receptor 4 (TLR4) is expressed in MSCs and regulates the expression of cytoprotective factors, cytokines, and chemokines. Lipopolysaccharide (LPS) stimulation of TLR4 activates two distinct signaling pathways that are either MyD88 dependent or MyD88 independent/TIR-domain-containing adapter-inducing interferon-β (TRIF) dependent. While it was reported previously that LPS treatment improved MSC-mediated cardioprotection, the mechanism underlying such improved effect remains unknown. To study the role of MyD88 signaling in MSC cardioprotective activity, wild type (WT) and MyD88^-/- MSCs were treated with LPS (200 ng/mL) for 24 h. WT and MyD88^-/- MSCs with or without LPS pretreatment were infused into the coronary circulation of isolated mouse hearts (Langendorff model) and then subjected to ischemia (25 min) and reperfusion (50 min). Saline served as a negative control. Both untreated and LPS-pretreated WT MSCs significantly improved postischemic recovery of myocardial function of isolated mouse hearts, as evidenced by improved left ventricular developed pressure and ventricular contractility assessment (ie, the rate of left ventricle pressure change over time, ± dp/dt). LPS-pretreated WT MSCs conferred better cardiac function recovery than untreated MSCs; however, such effect of LPS was abolished when using MyD88^-/- MSCs. In addition, LPS stimulated stat3 activity in WT MSCs, but not MyD88^-/- MSCs. stat3 small interfering RNA abolished the effect of LPS in improving the cardioprotection of WT MSCs. In conclusion, this study demonstrates that LPS improves MSC-mediated cardioprotection by MyD88-dependent activation of stat3.

Sirtuin 6 mediated stem cell cardiomyogenesis on protein coated nanofibrous scaffolds

The cellular niche provides combination of biomolecular and biophysical cues to control stem cell fate. Three-dimensional (3D) aligned nanofibrous scaffolds can effectively augment stem cell cardiomyogenesis. This work aims to understand the role of biomolecular signals from extracellular matrix (ECM) proteins and leverage them to further promote cardiomyogenesis on nanofibrous scaffolds. Human mesenchymal stem cells (hMSCs) were cultured on 3D aligned polycaprolactone scaffolds coated with different ECM proteins. Among multiple coatings tested, collagen coated fibers were most effective in promoting cardiomyogenesis as determined from increased expression of cardiac biomarkers and intracellular calcium flux. At molecular level, enhanced differentiation on collagen coated fibers was associated with an increased level of sirtuin 6 (SIRT6). Depletion of SIRT6 using siRNA attenuated the differentiation process through activation of Wnt signaling pathway. This study, thus, demonstrates that protein coated scaffolds can augment cardiomyogenic differentiation of stem cells through a combination of topographical and biomolecular signals.

Oxygen as a key regulator of cardiomyocyte proliferation: New results about cell culture conditions!

The goal of the new therapeutically strategies aimed to treat cardiovascular diseases (CVDs) is to enhance the natural ability of the heart to regenerate. This represents a great challenge for the coming years as all the mechanisms underlying the replacement of dying cells by functional cells of the same type are not completely elucidated. Among these, stimulating cardiomyocyte proliferation seems to be crucial for the restoration of normal cardiac function after CVDs. In this review, we summarized the recent advances about the modulation of cardiomyocyte proliferation in physiological (during ageing) and pathological conditions. We highlighted the role of oxygen and we presented new results demonstrating that performing neonatal cardiomyocyte cell cultures in "normoxic" oxygen conditions (i.e. 3% oxygen) increases their proliferation rate, when compared to "hyperoxic" conventional conditions (i.e. 20% oxygen). Thus, oxygen concentration seems to be a key factor in the control of cardiomyocyte proliferation.

DPP-4 inhibition enhanced renal tubular and myocardial GLP-1 receptor expression decreased in CKD with myocardial infarction

Background

Chronic kidney disease (CKD) is strongly associated with cardiovascular disease and is a significant risk factor for increased morbidity and mortality. In contrast, GLP-1 receptor (GLP-1R) activation has been shown to confer both renal and cardiovascular protection, though its relationship with CKD and CKD with myocardial ischemia/reperfusion (MI/R) remains poorly understood. Here, we investigated changes in renal and myocardial GLP-1R expression in the CKD rat model with MI/R.

Methods

Male Sprague Dawley rats with 5/6 nephrectomy were used as a rat model of CKD and CKD with MI/R. For myocardial ischemia, the left coronary artery was ligated and released for 30 min 1 week after 5/6 nephrectomy. Dipeptidyl-peptidase 4 (DPP-4) inhibitors were administered orally with linagliptin once daily for 8 weeks. Renal cortical and myocardial GLP-1R expression were measured via immunohistochemistry and western blot analysis.

Results

DPP-4 activity was increased in CKD. Western blot density of GLP-1R in renal cortex extracts revealed increased abundance 2 weeks after 5/6 nephrectomy, followed by a decrease at 8 weeks. In contrast, CKD and CKD with MI/R rats showed decreases in renal and cardiac expression of GLP-1R; these effects were attenuated in rats treated with linagliptin.

Conclusions

In CKD with MI/R, linagliptin attenuated renal injury and increased renal and myocardial GLP-1R expression. These data suggest that activation of renal and myocardial GLP-1R expression may provide both cardio- and renoprotective effects.

Electronic supplementary material

The online version of this article (10.1186/s12882-019-1243-z) contains supplementary material, which is available to authorized users.

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.

The Effects of Metabolic Substrate Availability on Human Adipose-Derived Stem Cell Spheroid Survival

IMPACT STATEMENT

Human adipose-derived stem cells (hADSCs) spheroids have displayed remarkable potential for treating ischemic injury. However, low nutrient (i.e., glucose and oxygen) availability in ischemic environments results in limited tissue viability posttransplantation. To develop an understanding of the effects of nutrient availability on spheroid survival, we utilized both in vitro and computational models to examine the limiting factors in metabolic supply for avascular microtissues, revealing the critical role of glucose to improve hADSC spheroid survival in ischemic conditions. These results may impact future strategies for improving hADSC transplantation efficacy through codelivery of metabolic substrates.

Chitosan/silk fibroin modified nanofibrous patches with mesenchymal stem cells prevent heart remodeling post-myocardial infarction in rats

Poor functional survival of the engrafted stem cells limits the therapeutic efficacy of stem-cell-based therapy for myocardial infarction (MI). Cardiac patch-based system for cardiac repair has emerged as a potential regenerative strategy for MI. This study aimed to design a cardiac patch to improve the retention of the engrafted stem cells and provide mechanical scaffold for preventing the ventricular remodeling post-MI. The patches were fabricated with electrospinning cellulose nanofibers modified with chitosan/silk fibroin (CS/SF) multilayers via layer-by-layer (LBL) coating technology. The patches engineered with adipose tissue-derived mesenchymal stem cells (AD-MSCs) (cell nano-patch) were adhered to the epicardium of the infarcted region in rat hearts. Bioluminescence imaging (BLI) revealed higher cell viability in the cell nano-patch group compared with the intra-myocardial injection group. Echocardiography demonstrated less ventricular remodeling in cell nano-patch group, with a decrease in the left ventricular end-diastolic volume and left ventricular end-systolic volume compared with the control group. Additionally, left ventricular ejection fraction and fractional shortening were elevated after cell nano-patch treatment compared with the control group. Histopathological staining demonstrated that cardiac fibrosis and apoptosis were attenuated, while local neovascularization was promoted in the cell nano-patch group. Western blot analysis illustrated that the expression of biomarkers for myocardial fibrosis (TGF-β1, P-smad3 and Smad3) and ventricular remodeling (BNP, β-MHC: α-MHC ratio) were decreased in cell nano patch-treated hearts. This study suggests that CS/SF-modified nanofibrous patches promote the functional survival of engrafted AD-MSCs and restrain ventricular remodeling post-MI through attenuating myocardial fibrosis. STATEMENT OF SIGNIFICANCE: First, the nanofibrous patches fabricated from the electrospun cellulose nanofibers could mimic the natural extracellular matrix (ECM) of hearts to improve the microenvironment post-MI and provide three dimensional (3D) scaffolds for the engrafted AD-MSCs. Second, CS and SF which have exhibited excellent properties in previous tissue engineering research, such as nontoxicity, biodegradability, anti-inflammatory, strong hydrophilic nature, high cohesive strength, and intrinsic antibacterial properties further optimized the biocompatibility of the nanofibrous patches via LBL modification. Finally, the study revealed that beneficial microenvironment and biomimetic ECM improve the retention and viability of the engrafted AD-MSCs and the mechanical action of the cell nano-patches for the expanding ventricular post-MI leads to suppression of HF progression by inhibition of ventricular remodeling.

What will it take before a bioengineered heart will be implanted in patients?

PURPOSE OF REVIEW

Heart transplantation is the only curative treatment option for end-stage heart failure. However, a shortage of donor organs is a major limitation of this approach. Regenerative medicine targets the goal of increasing the number of available hearts for transplantation. In this review, we highlight the state of the art of building a bioartificial heart. We summarize the components needed, the hurdles, and likely translational steps to make the dream of transplanting a totally functional bioartificial heart a possibility.

RECENT FINDINGS

The therapies being developed in regenerative medicine aim not only to repair, but also to regenerate or replace failing tissues and organs. The engineering of bioartificial hearts utilizing patient-derived cells could theoretically solve the two main complications of heart transplantations: graft rejection and lifelong immunosuppression. Although many hurdles remain, scientists have reached a point in which some of these hurdles have been overcome. Decellularized heart scaffolds have emerged over the past decade as one of the most promising biofabrications. Two possible options for organ scaffolds exist: nontransplantable human hearts and porcine hearts. The use of these scaffolds could lead to the availability of an unlimited number of transplantable organs. The current challenge remains improving processes required for recellularization - including those for cells, bioreactors, and physiologic conditioning. Researchers should focus to solve these hurdles and pave the way toward the dream of in-vivo bioengineered heart maturation.

SUMMARY

Regenerative medicine has emerged as one of the most promising fields of translational research and has the potential to both minimize the need for donor organs and increase their availability. Meeting the challenge of implanting a totally functional bioengineered heart lies in solving multiple issues simultaneously. Dwarfing the technical hurdles, cost is the largest barrier to success. The scientific hurdles mainly involve scaling up and scaling out of laboratory cell processes, building bioreactors, and delivering cells into every needed region of an organ scaffold. Maintaining sterility and quantifying readiness of the nascent organs are also critical for success.

Bioengineering functional smooth muscle with spontaneous rhythmic contraction in vitro

Oriented smooth muscle layers in the intestine contract rhythmically due to the action of interstitial cells of Cajal (ICC) that serve as pacemakers of the intestine. Disruption of ICC networks has been reported in various intestinal motility disorders, which limit the quality and expectancy of life. A significant challenge in intestinal smooth muscle engineering is the rapid loss of function in cultured ICC and smooth muscle cells (SMC). Here we demonstrate a novel approach to maintain the function of both ICC and SMC in vitro. Primary intestinal SMC mixtures cultured on feeder cells seeded electrospun poly(3-caprolactone) scaffolds exhibited rhythmic contractions with directionality for over 10 weeks in vitro. The simplicity of this system should allow for wide usage in research on intestinal motility disorders and tissue engineering, and may prove to be a versatile platform for generating other types of functional SMC in vitro.

Specific Cell (Re-)Programming: Approaches and Perspectives

Many disorders are manifested by dysfunction of key cell types or their disturbed integration in complex organs. Thereby, adult organ systems often bear restricted self-renewal potential and are incapable of achieving functional regeneration. This underlies the need for novel strategies in the field of cell (re-)programming-based regenerative medicine as well as for drug development in vitro. The regenerative field has been hampered by restricted availability of adult stem cells and the potentially hazardous features of pluripotent embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). Moreover, ethical concerns and legal restrictions regarding the generation and use of ESCs still exist. The establishment of direct reprogramming protocols for various therapeutically valuable somatic cell types has overcome some of these limitations. Meanwhile, new perspectives for safe and efficient generation of different specified somatic cell types have emerged from numerous approaches relying on exogenous expression of lineage-specific transcription factors, coding and noncoding RNAs, and chemical compounds.It should be of highest priority to develop protocols for the production of mature and physiologically functional cells with properties ideally matching those of their endogenous counterparts. Their availability can bring together basic research, drug screening, safety testing, and ultimately clinical trials. Here, we highlight the remarkable successes in cellular (re-)programming, which have greatly advanced the field of regenerative medicine in recent years. In particular, we review recent progress on the generation of cardiomyocyte subtypes, with a focus on cardiac pacemaker cells. Graphical Abstract.

Genetic Lineage Tracing of Nonmyocyte Population by Dual Recombinases

Background:

Whether the adult mammalian heart harbors cardiac stem cells for regeneration of cardiomyocytes is an important yet contentious topic in the field of cardiovascular regeneration. The putative myocyte stem cell populations recognized without specific cell markers, such as the cardiosphere-derived cells, or with markers such as Sca1 + , Bmi1 + , Isl1 + , or Abcg2 + cardiac stem cells have been reported. Moreover, it remains unclear whether putative cardiac stem cells with unknown or unidentified markers exist and give rise to de novo cardiomyocytes in the adult heart.

Methods:

To address this question without relying on a particular stem cell marker, we developed a new genetic lineage tracing system to label all nonmyocyte populations that contain putative cardiac stem cells. Using dual lineage tracing system, we assessed whether nonmyocytes generated any new myocytes during embryonic development, during adult homeostasis, and after myocardial infarction. Skeletal muscle was also examined after injury for internal control of new myocyte generation from nonmyocytes.

Results:

By this stem cell marker–free and dual recombinases–mediated cell tracking approach, our fate mapping data show that new myocytes arise from nonmyocytes in the embryonic heart, but not in the adult heart during homeostasis or after myocardial infarction. As positive control, our lineage tracing system detected new myocytes derived from nonmyocytes in the skeletal muscle after injury.

Conclusions:

This study provides in vivo genetic evidence for nonmyocyte to myocyte conversion in embryonic but not adult heart, arguing again the myogenic potential of putative stem cell populations for cardiac regeneration in the adult stage. This study also provides a new genetic strategy to identify endogenous stem cells, if any, in other organ systems for tissue repair and regeneration.

Origin of Reparative Stem Cells in Fracture Healing

PURPOSE OF REVIEW

The identity and functional roles of stem cell population(s) that contribute to fracture repair remains unclear. This review provides a brief history of mesenchymal stem cell (MSCs) and provides an updated view of the many stem/progenitor cell populations contributing to fracture repair.

RECENT FINDINGS

Functional studies show MSCs are not the multipotential stem cell population that form cartilage and bone during fracture repair. Rather, multiple studies have confirmed the periosteum is the primary source of stem/progenitor cells for fracture repair. Newer work is also identifying other stem/progenitor cells that may also contribute to healing. Although the heterogenous periosteal cells migrate to the fracture site and contribute directly to callus formation, other cell populations are involved. Pericytes and bone marrow stromal cells are now thought of as key secretory centers that mostly coordinate the repair process. Other populations of stem/progenitor cells from the muscle and transdifferentiated chondroctyes may also contribute to repair, and their functional role is an area of active research.

Cellular self-assembly into 3D microtissues enhances the angiogenic activity and functional neovascularization capacity of human cardiopoietic stem cells

While cell therapy has been proposed as next-generation therapy to treat the diseased heart, current strategies display only limited clinical efficacy. Besides the ongoing quest for the ideal cell type, in particular the very low retention rate of single-cell (SC) suspensions after delivery remains a major problem. To improve cellular retention, cellular self-assembly into 3D microtissues (MTs) prior to transplantation has emerged as an encouraging alternative. Importantly, 3D-MTs have also been reported to enhance the angiogenic activity and neovascularization potential of stem cells. Therefore, here using the chorioallantoic membrane (CAM) assay we comprehensively evaluate the impact of cell format (SCs versus 3D-MTs) on the angiogenic potential of human cardiopoietic stem cells, a promising second-generation cell type for cardiac repair. Biodegradable collagen scaffolds were seeded with human cardiopoietic stem cells, either as SCs or as 3D-MTs generated by using a modified hanging drop method. Thereafter, seeded scaffolds were placed on the CAM of living chicken embryos and analyzed for their perfusion capacity in vivo using magnetic resonance imaging assessment which was then linked to a longitudinal histomorphometric ex vivo analysis comprising blood vessel density and characteristics such as shape and size. Cellular self-assembly into 3D-MTs led to a significant increase of vessel density mainly driven by a higher number of neo-capillary formation. In contrast, SC-seeded scaffolds displayed a higher frequency of larger neo-vessels resulting in an overall 1.76-fold higher total vessel area (TVA). Importantly, despite that larger TVA in SC-seeded group, the mean perfusion capacity (MPC) was comparable between groups, therefore suggesting functional superiority together with an enhanced perfusion efficacy of the neo-vessels in 3D-MT-seeded scaffolds. This was further underlined by a 1.64-fold higher perfusion ratio when relating MPC to TVA. Our study shows that cellular self-assembly of human cardiopoietic stem cells into 3D-MTs substantially enhances their overall angiogenic potential and their functional neovascularization capacity. Hence, the concept of 3D-MTs may be considered to increase the therapeutic efficacy of future cell therapy concepts.

New Myocyte Formation in the Adult Heart: Endogenous Sources and Therapeutic Implications

Death of adult cardiac myocytes and supportive tissues resulting from cardiovascular diseases such as myocardial infarction is the proximal driver of pathological ventricular remodeling that often culminates in heart failure. Unfortunately, no currently available therapeutic barring heart transplantation can directly replenish myocytes lost from the injured heart. For decades, the field has struggled to define the intrinsic capacity and cellular sources for endogenous myocyte turnover in pursuing more innovative therapeutic strategies aimed at regenerating the injured heart. Although controversy persists to this day as to the best therapeutic regenerative strategy to use, a growing consensus has been reached that the very limited capacity for new myocyte formation in the adult mammalian heart is because of proliferation of existing cardiac myocytes but not because of the activity of an endogenous progenitor cell source of some sort. Hence, future therapeutic approaches should take into consideration the fundamental biology of myocyte renewal in designing strategies to potentially replenish these cells in the injured heart.

Electrospinning: An enabling nanotechnology platform for drug delivery and regenerative medicine

Electrospinning provides an enabling nanotechnology platform for generating a rich variety of novel structured materials in many biomedical applications including drug delivery, biosensing, tissue engineering, and regenerative medicine. In this review article, we begin with a thorough discussion on the method of producing 1D, 2D, and 3D electrospun nanofiber materials. In particular, we emphasize on how the 3D printing technology can contribute to the improvement of traditional electrospinning technology for the fabrication of 3D electrospun nanofiber materials as drug delivery devices/implants, scaffolds or living tissue constructs. We then highlight several notable examples of electrospun nanofiber materials in specific biomedical applications including cancer therapy, guiding cellular responses, engineering in vitro 3D tissue models, and tissue regeneration. Finally, we finish with conclusions and future perspectives of electrospun nanofiber materials for drug delivery and regenerative medicine.

Suppression of Pro-fibrotic Signaling Potentiates Factor-mediated Reprogramming of Mouse Embryonic Fibroblasts into Induced Cardiomyocytes

Trans-differentiation of one somatic cell type into another has enormous potential to model and treat human diseases. Previous studies have shown that mouse embryonic, dermal, and cardiac fibroblasts can be reprogrammed into functional induced-cardiomyocyte-like cells (iCMs) through overexpression of cardiogenic transcription factors including GATA4, Hand2, Mef2c, and Tbx5 both in vitro and in vivo. However, these previous studies have shown relatively low efficiency. In order to restore heart function following injury, mechanisms governing cardiac reprogramming must be elucidated to increase efficiency and maturation of iCMs. We previously demonstrated that inhibition of pro-fibrotic signaling dramatically increases reprogramming efficiency. Here, we detail methods to achieve a reprogramming efficiency of up to 60%. Furthermore, we describe several methods including flow cytometry, immunofluorescent imaging, and calcium imaging to quantify reprogramming efficiency and maturation of reprogrammed fibroblasts. Using the protocol detailed here, mechanistic studies can be undertaken to determine positive and negative regulators of cardiac reprogramming. These studies may identify signaling pathways that can be targeted to promote reprogramming efficiency and maturation, which could lead to novel cell therapies to treat human heart disease.

Thermoreversible Hyaluronic Acid-PNIPAAm Hydrogel Systems for 3D Stem Cell Culture

Human pluripotent stem cells (hPSCs) offer considerable potential for biomedical applications including drug screening and cell replacement therapies. Clinical translation of hPSCs requires large quantities of high quality cells, so scalable methods for cell culture are needed. However, current methods are limited by scalability, the use of animal-derived components, and/or low expansion rates. A thermoresponsive 3D hydrogel for scalable hPSC expansion and differentiation into several defined lineages is recently reported. This system would benefit from increased control over material properties to further tune hPSC behavior, and here a scalable 3D biomaterial with the capacity to tune both the chemical and the mechanical properties is demonstrated to promote hPSC expansion under defined conditions. This 3D biomaterial, comprised of hyaluronic acid and poly(N-isopropolyacrylamide), has thermoresponsive properties that readily enable mixing with cells at low temperatures, physical encapsulation within the hydrogel upon elevation at 37 °C, and cell recovery upon cooling and reliquefaction. After optimization, the resulting biomaterial supports hPSC expansion over long cell culture periods while maintaining cell pluripotency. The capacity to modulate the mechanical and chemical properties of the hydrogel provides a new avenue to expand hPSCs for future therapeutic application.

Auxetic Cardiac Patches with Tunable Mechanical and Conductive Properties toward Treating Myocardial Infarction

An auxetic conductive cardiac patch (AuxCP) for the treatment of myocardial infarction (MI) is introduced. The auxetic design gives the patch a negative Poisson's ratio, providing it with the ability to conform to the demanding mechanics of the heart. The conductivity allows the patch to interface with electroresponsive tissues such as the heart. Excimer laser microablation is used to micropattern a re-entrant honeycomb (bow-tie) design into a chitosan-polyaniline composite. It is shown that the bow-tie design can produce patches with a wide range in mechanical strength and anisotropy, which can be tuned to match native heart tissue. Further, the auxetic patches are conductive and cytocompatible with murine neonatal cardiomyocytes in vitro. Ex vivo studies demonstrate that the auxetic patches have no detrimental effect on the electrophysiology of both healthy and MI rat hearts and conform better to native heart movements than unpatterned patches of the same material. Finally, the AuxCP applied in a rat MI model results in no detrimental effect on cardiac function and negligible fibrotic response after two weeks in vivo. This approach represents a versatile and robust platform for cardiac biomaterial design and could therefore lead to a promising treatment for MI.

Surface-modified polymers for cardiac tissue engineering

Cardiovascular disease (CVD), leading to myocardial infarction and heart failure, is one of the major causes of death worldwide. The physiological system cannot significantly regenerate the capabilities of a damaged heart. The current treatment involves pharmacological and surgical interventions; however, less invasive and more cost-effective approaches are sought. Such new approaches are developed to induce tissue regeneration following injury. Hence, regenerative medicine plays a key role in treating CVD. Recently, the extrinsic stimulation of cardiac regeneration has involved the use of potential polymers to stimulate stem cells toward the differentiation of cardiomyocytes as a new therapeutic intervention in cardiac tissue engineering (CTE). The therapeutic potentiality of natural or synthetic polymers and cell surface interactive factors/polymer surface modifications for cardiac repair has been demonstrated in vitro and in vivo. This review will discuss the recent advances in CTE using polymers and cell surface interactive factors that interact strongly with stem cells to trigger the molecular aspects of the differentiation or formulation of cardiomyocytes for the functional repair of heart injuries or cardiac defects.

Vitamin K‑dependent proteins involved in bone and cardiovascular health (Review)

In postmenopausal women and elderly men, bone density decreases with age and vascular calcification is aggravated. This condition is closely associated with vitamin K2 deficiency. A total of 17 different vitamin K-dependent proteins have been identified to date. Vitamin K-dependent proteins are located within the bone, heart and blood vessels. For instance, carboxylated osteocalcin is beneficial for bone and aids the deposition of calcium into the bone matrix. Carboxylated matrix Gla protein effectively protects blood vessels and may prevent calcification within the vascular wall. Furthermore, carboxylated Gla-rich protein has been reported to act as an inhibitor in the calcification of the cardiovascular system, while growth arrest-specific protein-6 protects endothelial cells and vascular smooth muscle cells, resists apoptosis and inhibits the calcification of blood vessels by inhibiting the apoptosis of vascular smooth muscle cells. In addition, periostin may promote the differentiation, aggregation, adhesion and proliferation of osteoblasts. Periostin also occurs in the heart and may be associated with the reconstruction of heart function. These vitamin K-dependent proteins may exert their functions following γ-carboxylation with vitamin K, and different vitamin K-dependent proteins may exhibit synergistic effects or antagonistic effects on each other. In the cardiovascular system with vitamin K antagonist supplement or vitamin K deficiency, calcification occurs in the endothelium of blood vessels and vascular smooth muscle cells are transformed into osteoblast-like cells, a phenomenon that resembles bone growth. Both the bone and cardiovascular system are closely associated during embryonic development. Thus, the present study hypothesized that embryonic developmental position and tissue calcification may have a certain association for the bone and the cardiovascular system. This review describes and briefly discusses several important vitamin K-dependent proteins that serve an important role in bone and the cardiovascular system. The results of the review suggest that the vascular calcification and osteogenic differentiation of vascular smooth muscle cells may be associated with the location of the bone and cardiovascular system during embryonic development.

Human Pluripotent Stem Cell-Derived Atrial and Ventricular Cardiomyocytes Develop from Distinct Mesoderm Populations

The ability to direct the differentiation of human pluripotent stem cells (hPSCs) to the different cardiomyocyte subtypes is a prerequisite for modeling specific forms of cardiovascular disease in vitro and for developing novel therapies to treat them. Here we have investigated the development of the human atrial and ventricular lineages from hPSCs, and we show that retinoic acid signaling at the mesoderm stage of development is required for atrial specification. Analyses of early developmental stages revealed that ventricular and atrial cardiomyocytes derive from different mesoderm populations that can be distinguished based on CD235a and RALDH2 expression, respectively. Molecular and electrophysiological characterization of the derivative cardiomyocytes revealed that optimal specification of ventricular and atrial cells is dependent on induction of the appropriate mesoderm. Together these findings provide new insights into the development of the human atrial and ventricular lineages that enable the generation of highly enriched, functional cardiomyocyte populations for therapeutic applications.

Imaging cellular pharmacokinetics of 18F-FDG and 6-NBDG uptake by inflammatory and stem cells

OBJECTIVES

Myocardial infarction (MI) causes significant loss of cardiomyocytes, myocardial tissue damage, and impairment of myocardial function. The inability of cardiomyocytes to proliferate prevents the heart from self-regeneration. The treatment for advanced heart failure following an MI is heart transplantation despite the limited availability of the organs. Thus, stem-cell-based cardiac therapies could ultimately prevent heart failure by repairing injured myocardium that reverses cardiomyocyte loss. However, stem-cell-based therapies lack understanding of the mechanisms behind a successful therapy, including difficulty tracking stem cells to provide information on cell migration, proliferation and differentiation. In this study, we have investigated the interaction between different types of stem and inflammatory cells and cell-targeted imaging molecules, 18F-FDG and 6-NBDG, to identify uptake patterns and pharmacokinetics in vitro.

METHODS

Macrophages (both M1 and M2), human induced pluripotent stem cells (hiPSCs), and human amniotic mesenchymal stem cells (hAMSCs) were incubated with either 18F-FDG or 6-NBDG. Excess radiotracer and fluorescence were removed and a 100 μm-thin CdWO4 scintillator plate was placed on top of the cells for radioluminescence microscopy imaging of 18F-FDG uptake, while no scintillator was needed for fluorescence imaging of 6-NBDG uptake. Light produced following beta decay was imaged with a highly sensitive inverted microscope (LV200, Olympus) and an Electron Multiplying Charge-Couple Device (EM-CCD) camera. Custom-written software was developed in MATLAB for image processing.

RESULTS

The average cellular activity of 18F-FDG in a single cell of hAMSCs (0.670±0.028 fCi/μm2, P = 0.001) was 20% and 36% higher compared to uptake in hiPSCs (0.540±0.026 fCi/μm2, P = 0.003) and macrophages (0.430±0.023 fCi/μm2, P = 0.002), respectively. hAMSCs exhibited the slowest influx (0.210 min-1) but the fastest efflux (0.327 min-1) rate compared to the other tested cell lines for 18F-FDG. This cell line also has the highest phosphorylation but exhibited the lowest rate of de-phosphorylation. The uptake pattern for 6-NBDG was very different in these three cell lines. The average cellular activity of 6-NBDG in a single cell of macrophages (0.570±0.230 fM/μm2, P = 0.004) was 38% and 14% higher compared to hiPSCs (0.350±0.160 fM/μm2, P = 0.001) and hAMSCs (0.490±0.028 fM/μm2, P = 0.006), respectively. The influx (0.276 min-1), efflux (0.612 min-1), phosphorylation (0.269 min-1), and de-phosphorylation (0.049 min-1) rates were also highest for macrophages compared to the other two tested cell lines.

CONCLUSION

hAMSCs were found to be 2-3× more sensitive to 18F-FDG molecule compared to hiPSCs/macrophages. However, macrophages exhibited the most sensitivity towards 6-NBDG. Based on this result, hAMSCs targeted with 18F-FDG could be more suitable for understanding the mechanisms behind successful therapy for treating MI patients by gathering information on cell migration, proliferation and differentiation.