Life and death of cardiac stem cells: a paradigm shift in cardiac biology

Precision Treatment of Anthracycline-Induced Cardiotoxicity: An Updated Review

OPINION STATEMENT

Anthracycline (ANT)-induced cardiotoxicity (AIC) is a particularly prominent form of cancer therapy-related cardiovascular toxicity leading to the limitations of ANTs in clinical practice. Even though AIC has drawn particular attention, the best way to treat it is remaining unclear. Updates to AIC therapy have been made possible by recent developments in research on the underlying processes of AIC. We review the current molecular pathways leading to AIC: 1) oxidative stress (OS) including enzymatic-induced and other mechanisms; 2) topoisomerase; 3) inflammatory response; 4) cardiac progenitor cell damage; 5) epigenetic changes; 6) renin-angiotensin-aldosterone system (RAAS) dysregulation. And we systematically discuss current prevention and treatment strategies and novel pathogenesis-based therapies for AIC: 1) dose reduction and change; 2) altering drug delivery methods; 3) antioxidants, dexrezosen, statina, RAAS inhibitors, and hypoglycemic drugs; 4) miRNA, natural phytochemicals, mesenchymal stem cells, and cardiac progenitor cells. We also offer a fresh perspective on the management of AIC by outlining the current dilemmas and challenges associated with its prevention and treatment.

Is Human Aging a Form of Phenoptosis?

A much debated question is whether aging is the cumulative consequence of degenerative factors insufficiently opposed by natural selection, or, on the contrary, an ordered process, genetically determined and regulated, modeled by natural selection, and for which the definition of phenoptotic phenomenon would be entirely appropriate. In this review, theoretical arguments and empirical data about the two hypotheses are exposed, with more evidence in support of the thesis of aging as a form of phenoptosis. However, as the thesis of aging as an adaptive and programmed phenomenon necessarily requires the existence of specific mechanisms that determine to age, such as the subtelomere-telomere theory proposed for this purpose, the evidence supporting the mechanisms described by this theory is reported. In particular, it is highlighted that the recent interpretation of the role of TERRA sequences in the context of subtelomere-telomere theory is a fundamental point in supporting the hypothesized mechanisms. Furthermore, some characteristics of the mechanisms proposed by the theory, such as epigenetic modifications in aging, gradual cell senescence, cell senescence, limits in cell duplications, and fixed size of the telomeric heterochromatin hood, are exposed in their compatibility with both the thesis of aging as phenoptotic phenomenon and the opposite thesis. In short, aging as a form of phenoptosis appears a scientifically sound hypothesis while the opposite thesis should clarify the meaning of various phenomena that appear to invalidate it.

Cytology, function and dynamics of stem and progenitor cells in decapod crustaceans

Stem cells play key roles in development, tissue homeostasis, regeneration, ageing and diseases. Comprehensive reviews on stem cells are available for the determinately growing mammals and insects and some lower invertebrates like hydra but are rare for larger, indeterminately growing invertebrates that can live for many decades. This paper reviews the cytology, function and dynamics of stem and progenitor cells in the decapod crustaceans, a species-rich and ecologically and economically important animal group that includes mainly indeterminate growers but also some determinate growers. Further advantages of decapods for stem cell research are almost 1000-fold differences in body size and longevity, the regeneration of damaged appendages and the virtual absence of age-related diseases and tumours in the indeterminately growing species. The available data demonstrate that the Decapoda possess a remarkable variety of structurally and functionally different stem cells in embryos and larvae, and in the epidermis, musculature, haematopoietic tissue, heart, brain, hepatopancreas, olfactory sense organs and gonads of adults. Some of these seem to be rather continuously active over a lifetime but others are cyclically activated and silenced in periods of days, weeks and years, depending on the specific organ and function. Stem cell proliferation is triggered by signals related to development, moulting, feeding, reproduction, injury, infection, environmental enrichment and social status. Some regulatory pathways have already been identified, including the evolutionarily conserved GATA-binding and runt-domain transcription factors, the widespread neurotransmitter serotonin, the arthropod-specific hormone 20-hydroxyecdysone and the novel astakine growth factors. Knowledge of stem cells in decapods primarily refines our picture on the development, growth and maintenance of tissues and organs in this animal group. Cultured decapod stem cells have good potential for toxicity testing and virus research with practical relevance for aquaculture. Knowledge of stem cells in decapods also broadens our understanding of the evolution of stem cells and regeneration in the animal kingdom. The stem cells of long-lived, indeterminately growing decapods may hold the key to understanding how stem and progenitor cells function into old age without adverse side effects, possibly evoking new ideas for the development of anti-ageing and anti-cancer treatments in humans.

Intracellular Development of Resident Cardiac Stem Cells: An Overlooked Phenomenon in Myocardial Self-Renewal and Regeneration

At present, the approaches aimed at increasing myocardial regeneration after infarction are not available. The key question is the identity of cells capable of producing functional cardiac myocytes (CMs), replenishing those lost during ischemia. With identification of resident cardiac stem cells (CSCs), it has been supposed that this cell population may be crucial for myocardial self-renewal and regeneration. In the last few years, the focus has been shifted towards another concept, implying that new CMs are produced by dedifferentiation and proliferation of mature CMs. The observation that CSCs can undergo development inside immature cardiac cells by formation of “cell-in-cell structures” (CICSs) has enabled us to conclude that encapsulated CICSs are implicated in mammalian cardiomyogenesis over the entire lifespan. Earlier we demonstrated that new CMs are produced through formation of CSC-derived transitory amplifying cells (TACs) either in the CM colonies or inside encapsulated CICSs. In this study, we described the phenomenon of CSC penetration into mature CMs, resulting in the formation of vacuole-like CICSs (or non-encapsulated CICSs) containing proliferating CSCs with subsequent differentiation of CSC progeny into TACs and their release. In addition, we compared the phenotypes of TACs derived from encapsulated and non-encapsulated CICSs developing in immature and mature CMs, respectively.

The Aging Vasculature: Glucose Tolerance, Hypoglycemia and the Role of the Serum Response Factor

The fastest growing demographic in the U.S. at the present time is those aged 65 years and older. Accompanying advancing age are a myriad of physiological changes in which reserve capacity is diminished and homeostatic control attenuates. One facet of homeostatic control lost with advancing age is glucose tolerance. Nowhere is this more accentuated than in the high proportion of older Americans who are diabetic. Coupled with advancing age, diabetes predisposes affected subjects to the onset and progression of cardiovascular disease (CVD). In the treatment of type 2 diabetes, hypoglycemic episodes are a frequent clinical manifestation, which often result in more severe pathological outcomes compared to those observed in cases of insulin resistance, including premature appearance of biomarkers of senescence. Unfortunately, molecular mechanisms of hypoglycemia remain unclear and the subject of much debate. In this review, the molecular basis of the aging vasculature (endothelium) and how glycemic flux drives the appearance of cardiovascular lesions and injury are discussed. Further, we review the potential role of the serum response factor (SRF) in driving glycemic flux-related cellular signaling through its association with various proteins.

Exercise promotes heart regeneration in aged rats by increasing regenerative factors in myocardial tissue

Exercise-induced stem cell activation is implicated in cardiovascular regeneration. However, ageing limits the capacity of cellular and molecular remodelling of the heart. It has been shown that exercise improves structure regeneration and function in the process of ageing. Aged male Wistar rats (n = 24) were divided into three groups: Control (CO), High-intensity interval training (HIIT) (80-100% of the maximum speed), and continuous endurance training (CET) (60-70% of the maximum speed) groups. Training groups were trained for 6 weeks. The expression of the Nkx2.5 gene was determined by real-time (RT-PCRs) analysis. Immunohistochemical staining was performed to assess the C-kit positive cardiac progenitor and Ki67 positive cells. The mRNA level of Nkx2.5 was significantly increased in the CET and HIIT groups (P < 0.05). Also, cardiac progenitor cells positive for C-kit were increased in both the CET and HIIT groups (P < 0.05). Exercise training improved the ejection fraction and fractional shortening in both training groups (P < 0.05). This study indicated that training initiates the activation of cardiac progenitor cells, leading to the generation of new myocardial cells (R = 0.737, P = 0.001). It seems that C-kit positive cells in training groups showed an increase in the expression of some transcription factors (Nkx2.5 gene), representing an increased regenerative capacity of cardiomyocytes during the training period. These findings suggest that the endogenous regenerative capacity of the adult heart, mediated by cardiac stem cells, would be increased in response to exercise.

The Roles of mitochondrial dysfunction and Reactive Oxygen Species in Aging and Senescence

The aging process deteriorates organs' function at different levels, causing its progressive decline to resist stress, damage, and disease. In addition to alterations in metabolic control and gene expression, the rate of aging has been connected with the generation of high amounts of Reactive Oxygen Species (ROS). The essential perspective in free radical biology is that reactive oxygen species (ROS) and free radicals are toxic, mostly cause direct biological damage to targets, and are thus a major cause of oxidative stress. Different enzymatic and non-enzymatic compounds in the cells have roles in neutralizing this toxicity. Oxidative damage in aging is mostly high in particular molecular targets, such as mitochondrial DNA and aconitase, and oxidative stress in mitochondria can cause tissue aging across intrinsic apoptosis. Mitochondria's function and morphology are impaired through aging, following a decrease in the membrane potential by an increase in peroxide generation and size of the organelles. Telomeres may be the significant trigger of replicative senescence. Oxidative stress accelerates telomere loss, whereas antioxidants slow it down. Oxidative stress is a crucial modulator of telomere shortening, and that telomere-driven replicative senescence is mainly a stress response. The age-linked mitochondrial DNA mutation and protein dysfunction aggregate in some organs like the brain and skeletal muscle, thus contributing considerably to these post-mitotic tissues' aging. The aging process is mostly due to accumulated damage done by harmful species in some macromolecules such proteins, DNA, and lipids. The degradation of non-functional, oxidized proteins is a crucial part of the antioxidant defenses of cells, in which the clearance of these proteins occurs through autophagy in the cells, which is known as mitophagy for mitochondria.

Micro-endoscopy for Live Small Animal Fluorescent Imaging

Intravital microscopy has emerged as a powerful technique for the fluorescent visualization of cellular- and subcellular-level biological processes in vivo. However, the size of objective lenses used in standard microscopes currently makes it difficult to access internal organs with minimal invasiveness in small animal models, such as mice. Here we describe front- and side-view designs for small-diameter endoscopes based on gradient-index lenses, their construction, their integration into laser scanning confocal microscopy platforms, and their applications for in vivo imaging of fluorescent cells and microvasculature in various organs, including the kidney, bladder, heart, brain, and gastrointestinal tracts, with a focus on the new techniques developed for each imaging application. The combination of novel fluorescence techniques with these powerful imaging methods promises to continue providing novel insights into a variety of diseases.

Xenogeneic and Stem Cell-Based Therapy for Cardiovascular Diseases: Genetic Engineering of Porcine Cells and Their Applications in Heart Regeneration

Cardiovascular diseases represent a major health concern worldwide with few therapy options for ischemic injuries due to the limited regeneration potential of affected cardiomyocytes. Innovative cell replacement approaches could facilitate efficient regenerative therapy. However, despite extensive attempts to expand primary human cells in vitro, present technological limitations and the lack of human donors have so far prevented their broad clinical use. Cell xenotransplantation might provide an ethically acceptable unlimited source for cell replacement therapies and bridge the gap between waiting recipients and available donors. Pigs are considered the most suitable candidates as a source for xenogeneic cells and tissues due to their anatomical and physiological similarities with humans. The potential of porcine cells in the field of stem cell-based therapy and regenerative medicine is under intensive investigation. This review outlines the current progress and highlights the most promising approaches in xenogeneic cell therapy with a focus on the cardiovascular system.

Apoptotic Bodies of Cardiomyocytes and Fibroblasts - Regulators of Directed Differentiation of Heart Stem Cells

We studied the effects of apoptotic bodies of cardiomyocytes (ApBc) and fibroblasts (ApBf) on myocardial regeneration and contractility in rats and the dynamics of RNA concentrations in cardiomyocytes and fibroblasts at different stages of apoptosis. ApBc increase the contractility of rat myocardium, while ApBf reduce it. ApBc stimulate the development of clones of cardiomyocyte precursors in the myocardium, while ApBf stimulate the formation of endothelial precursor clones. In doxorubicin cardiomyopathy, ApBc, similar to the reference drug (ACE inhibitor) improve animal survival, while ApBf produce no such effect. RNA concentrations in cardiomyocytes and fibroblasts before apoptosis and at the beginning of cell death significantly differed, while in apoptotic bodies of these cells, it was practically the same. It has been hypothesized that RNA complex present in ApBc and ApBf represents an "epigenetic code" of directed differentiation of cardiac stem cells.

Dormant cardiac stem cells: A promising tool in cardiac regeneration

Stem cells represent an old niche with various new potential therapeutics. Besides drug treatment, reperfusion procedures and surgical revascularization, stem cell therapy could be a good option in ischemic cardiac diseases. A study was performed on a small group of cases who died of cardiac arrhythmia secondary to scarring myocardial infarctions. Tissue cardiac samples were taken from these cases (from the anterior and lateral wall of the left ventricle), for microscopy examination, in order to investigate the presence of cardiac stem cells (CSC). Multiple series of histological sections were also performed and examined, along with immunohistochemical analysis (IHC). The cells were identified in close contact with the residual ischemic cardiomyocytes, in the proximity of the myocardial collagenous scar, in old myocardial infarctions. They were activated by hypoxic ischemia and were influenced by the capillary microvascular density and the interstitial micro-environment conditions. In chronic intermittent ischemia they seem to turn themselves from dormant quiescent cells into activated progenitor committed cells.

A Brief Review of Cardiovascular Diseases, Associated Risk Factors and Current Treatment Regimes

Cardiovascular diseases (CVDs) are the leading cause of premature death and disability in humans and their incidence is on the rise globally. Given their substantial contribution towards the escalating costs of health care, CVDs also generate a high socio-economic burden in the general population. The underlying pathogenesis and progression associated with nearly all CVDs are predominantly of atherosclerotic origin that leads to the development of coronary artery disease, cerebrovascular disease, venous thromboembolism and, peripheral vascular disease, subsequently causing myocardial infarction, cardiac arrhythmias or stroke. The aetiological risk factors leading to the onset of CVDs are well recognized and include hyperlipidaemia, hypertension, diabetes, obesity, smoking and, lack of physical activity. They collectively represent more than 90% of the CVD risks in all epidemiological studies. Despite high fatality rate of CVDs, the identification and careful prevention of the underlying risk factors can significantly reduce the global epidemic of CVDs. Beside making favorable lifestyle modifications, primary regimes for the prevention and treatment of CVDs include lipid-lowering drugs, antihypertensives, antiplatelet and anticoagulation therapies. Despite their effectiveness, significant gaps in the treatment of CVDs remain. In this review, we discuss the epidemiology and pathology of the major CVDs that are prevalent globally. We also determine the contribution of well-recognized risk factors towards the development of CVDs and the prevention strategies. In the end, therapies for the control and treatment of CVDs are discussed.

Key Success Factors for Regenerative Medicine in Acquired Heart Diseases

Stem cell therapy offers a breakthrough opportunity for the improvement of ischemic heart diseases. Numerous clinical trials and meta-analyses appear to confirm its positive but variable effects on heart function. Whereas these trials widely differed in design, cell type, source, and doses reinjected, cell injection route and timing, and type of cardiac disease, crucial key factors that may favour the success of cell therapy emerge from the review of their data. Various types of cell have been delivered. Injection of myoblasts does not improve heart function and is often responsible for severe ventricular arrythmia occurrence. Using bone marrow mononuclear cells is a misconception, as they are not stem cells but mainly a mix of various cells of hematopoietic lineages and stromal cells, only containing very low numbers of cells that have stem cell-like features; this likely explain the neutral results or at best the modest improvement in heart function reported after their injection. The true existence of cardiac stem cells now appears to be highly discredited, at least in adults. Mesenchymal stem cells do not repair the damaged myocardial tissue but attenuate post-infarction remodelling and contribute to revascularization of the hibernated zone surrounding the scar. CD34+ stem cells - likely issued from pluripotent very small embryonic-like (VSEL) stem cells - emerge as the most convincing cell type, inducing structural and functional repair of the ischemic myocardial area, providing they can be delivered in large amounts via intra-myocardial rather than intra-coronary injection, and preferentially after myocardial infarct rather than chronic heart failure.

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⁺.

A stochastic model of adult neurogenesis coupling cell cycle progression and differentiation

Long-term tissue homeostasis requires a precise balance between stem cell self-renewal and the generation of differentiated progeny. Recently, it has been shown that in the adult murine brain, neural stem cells (NSCs) divide mostly symmetrically. This finding suggests that the required balance for tissue homeostasis is accomplished at the population level. However, it remains unclear how this balance is enabled. Furthermore, there is experimental evidence that proneural differentiation factors not only promote differentiation, but also cell cycle progression, suggesting a link between the two processes in NSCs. To study the effect of such a link on NSC dynamics, we developed a stochastic model in which stem cells have an intrinsic probability to progress through cell cycle and to differentiate. Our results show that increasing heterogeneity in differentiation probabilities leads to a decreased probability of long-term tissue homeostasis, and that this effect can be compensated when cell cycle progression and differentiation are positively coupled. Using single-cell RNA-Seq profiling of adult NSCs, we found a positive correlation in the expression levels of cell cycle and differentiation markers. Our findings suggest that a coupling between cell cycle progression and differentiation on the cellular level is part of the process that maintains tissue homeostasis in the adult brain.

Augmented O-GlcNAcylation attenuates intermittent hypoxia-induced cardiac remodeling through the suppression of NFAT and NF-κB activities in mice

Type 2 diabetes mellitus (T₂DM) has been reported to be associated with cardiac remodeling. Although O-GlcNAcylation is known to be elevated in diabetic and ischemic hearts, the effects of O-GlcNAcylation on cardiac remodeling induced by intermittent hypoxia (IH), such as sleep apnea syndrome (SAS), remain unknown. To evaluate the effects, we induced IH in wild-type (WT) and transgenic O-GlcNAc transferase (Ogt-Tg) mice. Two weeks of IH increased O-GlcNAcylation in the heart tissues of both strains of mice, whereas O-GlcNAcylation in Ogt-Tg mice was significantly higher than that in WT mice under both normoxic and IH conditions. WT mice exhibited cardiac remodeling after IH, whereas cardiac remodeling was significantly attenuated in Ogt-Tg mice. Oxidative stress and apoptosis increased after IH in both strains of mice, whereas the rate of increase in these processes in Ogt-Tg mice was significantly lower than that in WT mice. To examine the mechanism of cardiac remodeling attenuation in Ogt-Tg mice after IH, the effects of O-GlcNAcylation on the activities of the master regulators nuclear factor of activated T cells (NFAT) and NF-κB were determined. The O-GlcNAcylation of GSK-3β, a negative regulator of NFAT, was significantly increased in Ogt-Tg mice, whereas the phosphorylation of GSK-3β was reciprocally reduced. The same result was observed for NF-κB p65. An in vitro reporter assay showed that the augmentation of O-GlcNAcylation by an O-GlcNAcase inhibitor suppressed NFAT and NF-κB promoter activity. These data suggest that augmented O-GlcNAcylation mitigates IH-induced cardiac remodeling by suppressing NFAT and NF-κB activities through the O-GlcNAcylation of GSK-3β and NF-κB p65.

Thyroid hormone signaling and consequences for cardiac development

The fetal heart undergoes its own growth and maturation stages all while supplying blood and nutrients to the growing fetus and its organs. Immature contractile cardiomyocytes proliferate to rapidly increase and establish cardiomyocyte endowment in the perinatal period. Maturational changes in cellular maturation, size and biochemical capabilities occur, and require, a changing hormonal environment as the fetus prepares itself for the transition to extrauterine life. Thyroid hormone has long been known to be important for neuronal development, but also for fetal size and survival. Fetal circulating 3,5,3'-triiodothyronine (T3) levels surge near term in mammals and are responsible for maturation of several organ systems, including the heart. Growth factors like insulin-like growth factor-1 stimulate proliferation of fetal cardiomyocytes, while thyroid hormone has been shown to inhibit proliferation and drive maturation of the cells. Several cell signaling pathways appear to be involved in this complicated and coordinated process. The aim of this review was to discuss the foundational studies of thyroid hormone physiology and the mechanisms responsible for its actions as we speculate on potential fetal programming effects for cardiovascular health.

Ventricular remodeling of single-chambered myh6-/- adult zebrafish hearts occurs via a hyperplastic response and is accompanied by elastin deposition in the atrium

Zebrafish (Danio rerio) is widely used as an animal model to understand the pathophysiology of cardiovascular diseases. Here, we present the adult cardiac phenotype of weak atrium, myh6^-/-, which carry mutations in the zebrafish atrial myosin heavy chain. Homozygous mutants survive to adulthood and are fertile despite their initial weak atrial beat. In adult mutants, the atrium remains hypoplastic and shows elastin deposition while mutant ventricles exhibit increased size. In mammals, hypertrophy is the most common mechanism resulting in cardiomegaly. Using immunohistochemistry and confocal microscopy to measure cardiomyocyte cell size, density and proliferation, we show that the enlargement of the myh6^-/- ventricle is predominantly due to hyperplasia. However, we identified similar transcriptional profiles to the mammalian hypertrophy response via RT-PCR of the hyperplastic ventricles. Furthermore, we show activation of the ER-stress pathway by western blot analysis. In conclusion, we can assume, based on our model, that molecular signaling pathways associated with hypertrophy in mammals, in combination with ER-stress activation, result in hyperplasia in zebrafish. In addition, to our knowledge, this is the first time to report elastin deposition in the atrium.

Cortical Bone Derived Stem Cells for Cardiac Wound Healing

Ischemic heart disease can lead to myocardial infarction (MI), a major cause of morbidity and mortality worldwide. Adoptive transfer of multiple stem cell types into failing human hearts has demonstrated safety however the beneficial effects in patients with cardiovascular disorders have been modest. Modest improvement in patients with cardiac complications warrants identification of a novel stem cell population that possesses effective reparative properties and improves cardiac function after injury. Recently we have shown in a mouse model and a porcine pre-clinical animal model, that cortical bone derived stem cells (CBSCs) enhance cardiac function after MI and/or ischemia-reperfusion injury. These beneficial effects of allogeneic cell delivery appear to be mediated by paracrine mechanisms rather than by transdifferentiation of injected cells into vessels and/or immature myocytes. This review will discuss role of CBSCs in cardiac wound healing. After having modest beneficial improvement in most of the clinical trials, a critical need is to understand the interaction of the transplanted stem cells with the ischemic cardiac environment. Transplanted stem cells are exposed to pro-inflammatory factors and activated immune cells and fibroblasts, but their interactions remain unknown. We have shown that CBSCs modulate different processes including modulation of the immune response, angiogenesis, and restriction of infarct sizes after cardiac injury. This review will provide information on unique protective signature of CBSCs in rodent/swine animal models for heart repair that should provide basis for developing novel therapies for treating heart failure patients.

Elimination of Senescent Cells: Prospects According to the Subtelomere-Telomere Theory

Cell senescence is an artificially reversible condition activated by various factors and characterized by replicative senescence and typical general alteration of cell functions, including extra-cellular secretion. The number of senescent cells increases with age and contributes strongly to the manifestations of aging. For these reasons, research is under way to obtain "senolytic" compounds, defined as drugs that eliminate senescent cells and therefore reduce aging-associated decay, as already shown in some experiments on animal models. This objective is analyzed in the context of the programmed aging paradigm, as described by the mechanisms of the subtelomere-telomere theory. In this regard, positive effects of the elimination of senescent cells and limits of this method are discussed. For comparison, positive effects and limits of telomerase activation are also analyzed, as well of the combined action of the two methods and the possible association of opportune gene modifications. Ethical issues associated with the use of these methods are outlined.

Rat Left Ventricular Cardiomyocytes Characterization in the Process of Postinfarction Myocardial Remodeling

Ischemic lesions of the heart, including myocardial infarction, are the most common pathologies of human cardiovascular system. Despite all the research and achievements of medicine in this field, the mortality from this disease remains heavy. Therefore, studying of processes occurring in the myocardium in the early and late postinfarction periods remains important. Rat left ventricular cardiomyocyte (CMC) ploidy, hypertrophy, hyperplasia, and ultrastructure were investigated in 2, 6, and 26 weeks after experimental myocardial infarction, caused by permanent ligation of left coronary artery. Cytofluorimetric study of CMC ploidy revealed no difference between normal, sham-operated, and infarcted animals for all the tested stages. However, interference microscopy indicated significant changes in cells size. CMC dry mass of infarcted rats in 2 weeks after surgery was 1.5 times lower than in control and sham operated groups. Electron microscopy analysis of CMC revealed disruption of sarcomere structure. However, in 6 weeks after surgery CMC dry mass was 1.6 times higher than in control. In 26 weeks after myocardial infarction CMC dry mass exceeded control only in peri-infarction zone. Cell counting showed that the number of left ventricular CMC, reduced as a result of myocardial infarction, was not restored during myocardial remodeling. © 2019 International Society for Advancement of Cytometry.

Injury-induced fetal reprogramming imparts multipotency and reparative properties to pericardial adipose stem cells

Background

Injury may induce a sequential activation of intrinsic reparative activity that supports the maintenance of tissue homeostasis.

Method

In the present experiments, we investigated whether myocardial infarction (MI) was able to reinstate the expression of Wilms’ tumor factor 1 (WT1) as a key hallmark of fetal reprograming in the pericardial adipose-derived stem cells (pADSC). We characterized the immunophenotypical markers, cardiac potential, and reparative activity of WT1-expressing pADSC (WT1^pos) isolated MI Wistar rats with an intact pericardial sac in which cardiac transudate was accumulated, sampled, and analyzed.

Results

The WT1^pos cells formed colony-like aggregates in culture that subsequently generated phase-bright cells that homogenously constituted WT1 expression (> 98%). The WT1^pos cells shared identical surface markers with canonical pADSC, but enhanced transcripts for cardiogenesis (isl-1, gata-4, Sox2 and Tbx18) as well as cardiac commitment (endothelial: 28%; cardiomyogenic: 12.3%) in defined conditions. Remarkably, cardiac transplantation of WT1^pos cells promoted regional angiogenesis and myogenesis which led to significant functional amelioration of the infarcted hearts. Furthermore, we demonstrated that WT1^pos cells uniquely secreted hepatocyte growth factor (HGF) as a key antiapoptotic factor that promotes cardiac repair.

Conclusion

Injury-associated fetal reprogramming in pADSC facilitates cardiac differentiation and promotes the reparative activity by enhancing HGF production. As such, injury-“conditioned” pADSC may represent a useful autologous cell donor from infarcted patients for cell-based therapy.

Calcium-dependent potassium channels control proliferation of cardiac progenitor cells and bone marrow-derived mesenchymal stem cells

KEY POINTS

Ex vivo proliferated c-Kit⁺ endogenous cardiac progenitor cells (eCPCs) obtained from mouse and human cardiac tissues have been reported to express a wide range of functional ion channels. In contrast to previous reports in cultured c-Kit⁺ eCPCs, we found that ion currents were minimal in freshly isolated cells. However, inclusion of free Ca²⁺ intracellularly revealed a prominent inwardly rectifying current identified as the intermediate conductance Ca²⁺ -activated K⁺ current (KCa3.1) Electrical function of both c-Kit⁺ eCPCs and bone marrow-derived mesenchymal stem cells is critically governed by KCa3.1 calcium-dependent potassium channels. Ca²⁺ -induced increases in KCa3.1 conductance are necessary to optimize membrane potential during Ca²⁺ entry. Membrane hyperpolarization due to KCa3.1 activation maintains the driving force for Ca²⁺ entry that activates stem cell proliferation. Cardiac disease downregulates KCa3.1 channels in resident cardiac progenitor cells. Alterations in KCa3.1 may have pathophysiological and therapeutic significance in regenerative medicine.

ABSTRACT

Endogenous c-Kit⁺ cardiac progenitor cells (eCPCs) and bone marrow (BM)-derived mesenchymal stem cells (MSCs) are being developed for cardiac regenerative therapy, but a better understanding of their physiology is needed. Here, we addressed the unknown functional role of ion channels in freshly isolated eCPCs and expanded BM-MSCs using patch-clamp, microfluorometry and confocal microscopy. Isolated c-Kit⁺ eCPCs were purified from dog hearts by immunomagnetic selection. Ion currents were barely detectable in freshly isolated c-Kit⁺ eCPCs with buffering of intracellular calcium (Ca²⁺_i ). Under conditions allowing free intracellular Ca²⁺ , freshly isolated c-Kit⁺ eCPCs and ex vivo proliferated BM-MSCs showed prominent voltage-independent conductances that were sensitive to intermediate-conductance K⁺ -channel (KCa3.1 current, I_KCa3.1 ) blockers and corresponding gene (KCNN4)-expression knockdown. Depletion of Ca²⁺_i induced membrane-potential (V_mem ) depolarization, while store-operated Ca²⁺ entry (SOCE) hyperpolarized V_mem in both cell types. The hyperpolarizing SOCE effect was substantially reduced by I_KCa3.1 or SOCE blockade (TRAM-34, 2-APB), and I_KCa3.1 blockade (TRAM-34) or KCNN4-knockdown decreased the Ca²⁺ entry resulting from SOCE. I_KCa3.1 suppression reduced c-Kit⁺ eCPC and BM-MSC proliferation, while significantly altering the profile of cyclin expression. I_KCa3.1 was reduced in c-Kit⁺ eCPCs isolated from dogs with congestive heart failure (CHF), along with corresponding KCNN4 mRNA. Under perforated-patch conditions to maintain physiological [Ca²⁺ ]_i , c-Kit⁺ eCPCs from CHF dogs had less negative resting membrane potentials (-58 ± 7 mV) versus c-Kit⁺ eCPCs from control dogs (-73 ± 3 mV, P < 0.05), along with slower proliferation. Our study suggests that Ca²⁺ -induced increases in I_KCa3.1 are necessary to optimize membrane potential during the Ca²⁺ entry that activates progenitor cell proliferation, and that alterations in KCa3.1 may have pathophysiological and therapeutic significance in regenerative medicine.

Qualitative and Quantitative Analysis of Cardiac Progenitor Cells in Cases of Myocarditis and Cardiomyopathy

We aimed to identify and quantify CD117⁺ and CD90⁺ endogenous cardiac progenitor cells (CPC) in human healthy and diseased hearts. We hypothesize that these cells perform a locally acting, contributing function in overcoming medical conditions of the heart by endogenous means. Human myocardium biopsies were obtained from 23 patients with the following diagnoses: Dilatative cardiomyopathy (DCM), ischemic cardiomyopathy (ICM), myocarditis, and controls from healthy cardiac patients. High-resolution scanning microscopy of the whole slide enabled a computer-based immunohistochemical quantification of CD117 and CD90. Those signals were evaluated by Definiens Tissue Phenomics® Technology. Co-localization of CD117 and CD90 was determined by analyzing comparable serial sections. CD117⁺/CD90⁺ cardiac cells were detected in all biopsies. The highest expression of CD90 was revealed in the myocarditis group. CD117 was significantly higher in all patient groups, compared to healthy specimens (^*p < 0.05). The highest co-expression was found in the myocarditis group (6.75 ± 3.25 CD90⁺CD117⁺ cells/mm²) followed by ICM (4 ± 1.89 cells/mm²), DCM (1.67 ± 0.58 cells/mm²), and healthy specimens (1 ± 0.43 cells/mm²). We conclude that the human heart comprises a fraction of local CD117⁺ and CD90⁺ cells. We hypothesize that these cells are part of local endogenous progenitor cells due to the co-expression of CD90 and CD117. With novel digital image analysis technologies, a quantification of the CD117 and CD90 signals is available. Our experiments reveal an increase of CD117 and CD90 in patients with myocarditis.

Engineered Microenvironments for Maturation of Stem Cell Derived Cardiac Myocytes

Through the use of stem cell-derived cardiac myocytes, tissue-engineered human myocardial constructs are poised for modeling normal and diseased physiology of the heart, as well as discovery of novel drugs and therapeutic targets in a human relevant manner. This review highlights the recent bioengineering efforts to recapitulate microenvironmental cues to further the maturation state of newly differentiated cardiac myocytes. These techniques include long-term culture, co-culture, exposure to mechanical stimuli, 3D culture, cell-matrix interactions, and electrical stimulation. Each of these methods has produced various degrees of maturation; however, a standardized measure for cardiomyocyte maturation is not yet widely accepted by the scientific community.

Stem Cell-Derived Exosomes, Autophagy, Extracellular Matrix Turnover, and miRNAs in Cardiac Regeneration during Stem Cell Therapy

Stem cell therapy (SCT) raises the hope for cardiac regeneration in ischemic hearts. However, underlying molecular mechanisms for repair of dead myocardium by SCT in the ischemic heart is poorly understood. Growing evidences suggest that cardiac matrix stiffness and differential expressions of miRNAs play a crucial role in stem cell survival and differentiation. However, their roles on transplanted stem cells, for myocardial repair of the ischemic heart, remain unclear. Transplanted stem cells may act in an autocrine and/or paracrine manner to regenerate the dead myocardium. Paracrine mediators such as stem cell-derived exosomes are emerging as a novel therapeutic strategy to overcome some of the limitations of SCT. These exosomes carry microRNAs (miRNAs) that may regulate stem cell differentiation into a specific lineage. MicroRNAs may also contribute to stiffness of surrounding matrix by regulating extracellular matrix (ECM) turnover. The survival of transplanted stem cell depends on its autophagic process that maintains cellular homeostasis. Therefore, exosomes, miRNAs, extracellular matrix turnover, and autophagy may have an integral role in improving the efficacy of SCT. This review elaborates the specific roles of these regulatory components on cardiac regeneration in the ischemic heart during SCT.

Tilianin Post-Conditioning Attenuates Myocardial Ischemia/Reperfusion Injury via Mitochondrial Protection and Inhibition of Apoptosis

BACKGROUND The aim of this study was to investigate the role of tilianin in modulating mitochondrial functions and mitochondria-mediated apoptosis during cardio-protection. MATERIAL AND METHODS Myocardial ischemia/reperfusion (I/R) injury was induced by 30 minutes coronary occlusion followed by two hours reperfusion in Sprague-Dawley rats. To investigate the cardio-protective effects of tilianin, apoptosis was evaluated by TUNEL. Mitochondrial ultrastructure and function were assessed by transmission electron microscopy, dynamics of mitochondrial permeability transition pore (mPTP) opening and ATP production in the myocardium; Ca2+ content and reactive oxygen species (ROS) were measured to evaluated the level of damage factors in the mitochondria. The related apoptotic proteins were analyzed through immunoblot. RESULTS Pretreatment with tilianin significantly reduced apoptosis after I/R injury in rats (p<0.05). In addition, tilianin could alleviate mitochondrial damage, markedly inhibited mPTP opening and improved ATP production (p<0.05). There was also a significant reduction for content of Ca2+ and ROS in the mitochondria (p<0.01). Apoptosis protein analysis found that treatment with tilianin led to the downregulation of apoptosis-inducing factor (AIF) (p<0.01), and suppressed the leakage of cytochrome c and activation of caspase-3 (p<0.05). CONCLUSIONS This study showed that tilianin can alleviate apoptosis of cardiomyocytes and protect myocardium, possibly via the protection of mitochondria and repression of mitochondrial apoptotic pathways. Mechanistically, inhibition of Ca2+ overload, mPTP opening, and ROS production in mitochondria may explain the observed tilianin-mediated treatment effects.

Cardiac Progenitor Cells and the Interplay with Their Microenvironment

The microenvironment plays a crucial role in the behavior of stem and progenitor cells. In the heart, cardiac progenitor cells (CPCs) reside in specific niches, characterized by key components that are altered in response to a myocardial infarction. To date, there is a lack of knowledge on these niches and on the CPC interplay with the niche components. Insight into these complex interactions and into the influence of microenvironmental factors on CPCs can be used to promote the regenerative potential of these cells. In this review, we discuss cardiac resident progenitor cells and their regenerative potential and provide an overview of the interactions of CPCs with the key elements of their niche. We focus on the interaction between CPCs and supporting cells, extracellular matrix, mechanical stimuli, and soluble factors. Finally, we describe novel approaches to modulate the CPC niche that can represent the next step in recreating an optimal CPC microenvironment and thereby improve their regeneration capacity.

Chasing c-Kit through the heart: Taking a broader view

Stem cell mediated cardiac repair is an exciting and controversial area of cardiovascular research that holds the potential to produce novel, revolutionary therapies for the treatment of heart disease. Extensive investigation to define cell types contributing to cardiac formation, homeostasis and regeneration has produced several candidates, including adult cardiac c-Kit+ expressing stem and progenitor cells that have even been employed in a Phase I clinical trial demonstrating safety and feasibility of this therapeutic approach. However, the field of cardiac cell based therapy remains deeply divided due to strong disagreement among researchers and clinicians over which cell types, if any, are the best candidates for these applications. Research models that identify and define specific cardiac cells that effectively contribute to heart repair are urgently needed to resolve this debate. In this review, current c-Kit reporter models are discussed with respect to myocardial c-Kit cell biology and function, and future designs imagined to better represent endogenous myocardial c-Kit expression.

Myocardial Viability on Cardiac Magnetic Resonance

The study of myocardial viability is of great importance in the orientation and management of patients requiring myocardial revascularization or angioplasty. The technique of delayed enhancement (DE) is accurate and has transformed the study of viability into an easy test, not only for the detection of fibrosis but also as a binary test detecting what is viable or not. On DE, fibrosis equal to or greater than 50% of the segmental area is considered as non-viable, whereas that below 50% is considered viable. During the same evaluation, cardiac magnetic resonance (CMR) may also use other techniques for functional and perfusion studies to obtain a global evaluation of ischemic heart disease. This study aims to highlight the current concepts and broadly emphasize the use of CMR as a method that over the last 20 years has become a reference in the detection of infarction and assessment of myocardial viability. Resumo O estudo de viabilidade miocárdica é de grande importância para a orientação e manejo de pacientes que necessitam de cirurgia de revascularização miocárdica ou angioplastia. A técnica de realce tardio (RT) é precisa e transformou o estudo de viabilidade em um teste fácil, não só para a detecção de fibrose, mas também como um modelo binário para a detecção do que é ou não é viável. Uma fibrose identificada pelo RT é considerada como não viável quando igual ou maior do que 50% da área segmentar e como viável quando menor que 50%. A ressonância magnética cardíaca (RMC) também pode lançar mão de outras técnicas para estudo funcional e de perfusão para uma avaliação global da doença isquêmica do coração no mesmo exame. Este estudo tem como objetivo destacar os conceitos atuais e enfatizar amplamente o uso da RMC como um método que nos últimos 20 anos se tornou referência na detecção de infarto e avaliação de viabilidade miocárdica.

Transcription factor-induced activation of cardiac gene expression in human c-kit+ cardiac progenitor cells

Although transplantation of c-kit+ cardiac progenitor cells (CPCs) significantly alleviates post-myocardial infarction left ventricular dysfunction, generation of cardiomyocytes by exogenous CPCs in the recipient heart has often been limited. Inducing robust differentiation would be necessary for improving the efficacy of the regenerative cardiac cell therapy. We assessed the hypothesis that differentiation of human c-kit+ CPCs can be enhanced by priming them with cardiac transcription factors (TFs). We introduced five different TFs (Gata4, MEF2C, NKX2.5, TBX5, and BAF60C) into CPCs, either alone or in combination, and then examined the expression of marker genes associated with the major cardiac cell types using quantitative RT-PCR. When introduced individually, Gata4 and TBX5 induced a subset of myocyte markers. Moreover, Gata4 alone significantly induced smooth muscle cell and fibroblast markers. Interestingly, these gene expression changes brought by Gata4 were also accompanied by morphological changes. In contrast, MEF2C and NKX2.5 were largely ineffective in initiating cardiac gene expression in CPCs. Surprisingly, introduction of multiple TFs in different combinations mostly failed to act synergistically. Likewise, addition of BAF60C to Gata4 and/or TBX5 did not further potentiate their effects on cardiac gene expression. Based on our results, it appears that GATA4 is able to potentiate gene expression programs associated with multiple cardiovascular lineages in CPCs, suggesting that GATA4 may be effective in priming CPCs for enhanced differentiation in the setting of stem cell therapy.

Stem Cells in Regenerative Cardiology

The common prevalence of heart failure and limitations in its treatment are leading cause of attention and interest towards the induction of cardiac regeneration with novel approaches. Recent studies provide growing evidence regarding bona fide cardiac regeneration post genetic manipulations, administration of stimulatory factors and myocardial injuries in animal models and human studies. To this end, stem cells of different sources have been tested to treat heart failure for the development of cellular therapies. Endogenous and exogenous stem cells sources used in regenerative cardiology have provided a proof of concept and applicability of cellular therapies in myocardial improvement. Recent clinical studies, especially, based on the endogenous cardiac progenitor and stem cells highlighted the possibility to regenerate lost cardiomyocytes in the myocardium. This review discusses emerging concepts in cardiac stem cell therapy, their sources and route of administration, and plausibility of de novo cardiomyocyte formation.

Developmental origin and lineage plasticity of endogenous cardiac stem cells

Over the past two decades, several populations of cardiac stem cells have been described in the adult mammalian heart. For the most part, however, their lineage origins and in vivo functions remain largely unexplored. This Review summarizes what is known about different populations of embryonic and adult cardiac stem cells, including KIT(+), PDGFRα(+), ISL1(+)and SCA1(+)cells, side population cells, cardiospheres and epicardial cells. We discuss their developmental origins and defining characteristics, and consider their possible contribution to heart organogenesis and regeneration. We also summarize the origin and plasticity of cardiac fibroblasts and circulating endothelial progenitor cells, and consider what role these cells have in contributing to cardiac repair.

Exercise for the heart: signaling pathways

Physical exercise, a potent functional intervention in protecting against cardiovascular diseases, is a hot topic in recent years. Exercise has been shown to reduce cardiac risk factors, protect against myocardial damage, and increase cardiac function. This improves quality of life and decreases mortality and morbidity in a variety of cardiovascular diseases, including myocardial infarction, cardiac ischemia/reperfusion injury, diabetic cardiomyopathy, cardiac aging, and pulmonary hypertension. The cellular adaptation to exercise can be associated with both endogenous and exogenous factors: (1) exercise induces cardiac growth via hypertrophy and renewal of cardiomyocytes, and (2) exercise induces endothelial progenitor cells to proliferate, migrate and differentiate into mature endothelial cells, giving rise to endothelial regeneration and angiogenesis. The cellular adaptations associated with exercise are due to the activation of several signaling pathways, in particular, the growth factor neuregulin1 (NRG1)-ErbB4-C/EBPβ and insulin-like growth factor (IGF)-1-PI3k-Akt signaling pathways. Of interest, microRNAs (miRNAs, miRs) such as miR-222 also play a major role in the beneficial effects of exercise. Thus, exploring the mechanisms mediating exercise-induced benefits will be instrumental for devising new effective therapies against cardiovascular diseases.

Activation of Endogenous Cardiac Stem Cells by Apelin-13 in Infarcted Rat Heart

Our previous study demonstrated that the apelin-APJ pathway contributed to myocardial regeneration and functional recovery after bone marrow-derived mesenchymal stem cell (BM-MSC) transplantation during the differentiation of BM-MSCs into cardiomyogenic cells in acute myocardial infarction (AMI) rat models. However, the underlying mechanisms by which apelin promotes cardiac repair and functional recovery have not been completely clarified. In the present study, we investigated whether apelin could mobilize and activate endogenous cardiac stem cells and progenitors, thereby mediating regeneration and repair of the myocardium after AMI in rat models. Six-week-old male Sprague-Dawley rats underwent AMI and received apelin-13 (200 ng, n = 10) or an equivalent volume of saline by intramyocardial injection (n = 10); there was also a sham operation group (n = 8). Proliferation of endogenous cardiac stem cells was analyzed by immunofluorescence staining in rat infarcted myocardium, and heart function was evaluated by echocardiography at 28 days after apelin-13 injection. Treatment with apelin-13 led to a significant increase of Ki-67⁺-c-kit⁺/Sca-1⁺/Flk-1⁺ endogenous cardiac stem or progenitor cells in the border zone and infarct zone of rat hearts at 28 days after myocardial infarction (MI). Significant increases in the expression of c-kit, Sca-1, and Flk-1 on both levels of transcription and translation were confirmed by real-time polymerase chain reaction (RT-PCR) and Western blot. Treatment of apelin-13 also resulted in a significant reduction of infarct size and improvement of cardiac function post-MI. We conclude that apelin-13 is able to enhance mobilization, survival, and proliferation of endogenous myocardial stem cells in the injured heart, providing a novel mechanistic explanation for how apelin-13 might repair the heart and improve cardiac function. Thus, apelin-13 or pharmacological agonists of the APJ receptor could act as novel therapies for heart regeneration.

The potential of GMP-compliant platelet lysate to induce a permissive state for cardiovascular transdifferentiation in human mediastinal adipose tissue-derived mesenchymal stem cells

Human adipose tissue-derived mesenchymal stem cells (ADMSCs) are considered eligible candidates for cardiovascular stem cell therapy applications due to their cardiac transdifferentiation potential and immunotolerance. Over the years, the in vitro culture of ADMSCs by platelet lysate (PL), a hemoderivate containing numerous growth factors and cytokines derived from platelet pools, has allowed achieving a safe and reproducible methodology to obtain high cell yield prior to clinical administration. Nevertheless, the biological properties of PL are still to be fully elucidated. In this brief report we show the potential ability of PL to induce a permissive state of cardiac-like transdifferentiation and to cause epigenetic modifications. RTPCR results indicate an upregulation of Cx43, SMA, c-kit, and Thy-1 confirmed by immunofluorescence staining, compared to standard cultures with foetal bovine serum. Moreover, PL-cultured ADMSCs exhibit a remarkable increase of both acetylated histones 3 and 4, with a patient-dependent time trend, and methylation at lysine 9 on histone 3 preceding the acetylation. Expression levels of p300 and SIRT-1, two major regulators of histone 3, are also upregulated after treatment with PL. In conclusion, PL could unravel novel biological properties beyond its routine employment in noncardiac applications, providing new insights into the plasticity of human ADMSCs.

Reconstitute the damaged heart via the dual reparative roles of pericardial adipose-derived flk-1+ stem cells

BACKGROUND

The pericardial adipose derived stromal cells (pADSC) own a developmental origin from the "second heart field" and thus favor myogenic differentiation. The present experiments extended our previous observation by defining a subset of pADSC marked with the expression of flk-1, a type II receptor for VEGF to efficiently enhance cardiac repair.

METHODS AND RESULTS

Immunofluorescence and flow cytometry showed that flk-1 positive cells represented about 12% in the pericardial tissue and the total isolated pADSC. The purified flk-1 positive pADSC by magnetic sorting (flk-1pospADSC) show the ability of forming spherical structure in which both myogenic (cTnT+) and angiogenic (vWF+) precursors were concurrently generated in culture. After being intramyocardially transplanted into the ischemic hearts, flk-1pospADSC yielded superior structural repair to PBS control or flk-1negpADSC, characterized by the thickening of the infarcted wall in which both myogenesis and angiogenesis of microvasculature (preferentially with ϕ<50 μm) were significantly ensured (p<0.01). The structure benefits were also translated into a functional restoration 28 days after transplantation (EF=44% vs. 62%, p<0.01). Further pulse-chase labeling experiments with BrdU revealed that neomyogenesis and neoangiogenesis contribute in the structural repair. The newly formed myocardium was resulted from the proliferation of pre-existing cardiomyocytes that re-entered cell cycle (ki-67 positive).

CONCLUSION

Flk-1pospADSC are capable of concurrently giving rise to both myogenic and angiogenic precursors in vitro and, after transplantation in vivo, to reconstitute the damaged heart by the neoformation of microvasculature and of cardiomyocytes and thus represent an attracting donor cells for stem cell-based therapy.

Reactive Oxygen Species in Mesenchymal Stem Cell Aging: Implication to Lung Diseases

MSCs have become an emerging cell source with their immune modulation, high proliferation rate, and differentiation potential; indeed, they have been challenged in clinical trials. Recently, it has shown that ROS play a dual role as both deleterious and beneficial species depending on their concentration in MSCs. Various environmental stresses-induced excessive production of ROS triggers cellular senescence and abnormal differentiation on MSCs. Moreover, MSCs have been suggested to participate in the treatment of ALI/ARDS and COPD as a major cause of high morbidity and mortality. Therapeutic mechanisms of MSCs in the treatment of ARDS/COPD were focused on cell engraftment and paracrine action. However, ROS-mediated therapeutic mechanisms of MSCs still remain largely unknown. Here, we review the key factors associated with cell cycle and chromatin remodeling to accelerate or delay the MSC aging process. In addition, the enhanced ROS production and its associated pathophysiological pathways will be discussed along with the MSC senescence process. Furthermore, the present review highlights how the excessive amount of ROS-mediated oxidative stress might interfere with homeostasis of lungs and residual lung cells in the pathogenesis of ALI/ARDS and COPD.

Cardiac regeneration in children

Very young mammals have an impressive cardiac regeneration capacity. In contrast, cardiac regeneration is very limited in adult humans. The hearts of young children have a higher regenerative capacity compared with adults, as, for example, seen after surgical correction of an anomalous left coronary artery arising from the pulmonary artery or in children with univentricular hearts, who present enormous morphological changes after volume unloading. In addition, the enormous regenerative potential of growing children's hearts is reflected in the spontaneous courses of children with severely deteriorated cardiac function (e.g., patients with dilated cardiomyopathy). The extent of this regenerative capacity and its time dependency remain to be elucidated in the future and should be exploited to improve the treatment of children with severe heart insufficiency.

Noncoding RNAs as regulators of cardiomyocyte proliferation and death

Cardiovascular diseases are currently the main cause of morbidity and mortality worldwide. Ischemic heart disease, in particular, is responsible for the majority of cardiac-related deaths. Given the negligible regenerative potential of the human myocardium, there is a strong need for therapeutic strategies aiming at enhancing cardiomyocyte survival and proliferation following injury or at inhibiting their death. MicroRNAs (miRNAs) are small non-coding RNA molecules regulating gene expression at a post-transcriptional level with important functions in cardiovascular physiology and disease. It has been demonstrated that miRNAs can influence the ability of cardiomyocytes to enter the cell cycle and/or escape from death pathways. Additionally, long non coding-RNAs could be involved in such pathways. This review summarizes recent evidences on noncoding RNAs regulating proliferation and death of cardiomyocytes representing a future therapeutic for the treatment of heart diseases. This article is part of a Special Issue entitled SI: Non-coding RNAs.

The Role of MicroRNAs in Cardiac Stem Cells

Stem cells are considered as the next generation drug treatment in patients with cardiovascular disease who are resistant to conventional treatment. Among several stem cells used in the clinical setting, cardiac stem cells (CSCs) which reside in the myocardium and epicardium of the heart have been shown to be an effective option for the source of stem cells. In normal circumstances, CSCs primarily function as a cell store to replace the physiologically depleted cardiovascular cells, while under the diseased condition they have been shown to experimentally regenerate the diseased myocardium. In spite of their major functional role, molecular mechanisms regulating the CSCs proliferation and differentiation are still unknown. MicroRNAs (miRs) are small, noncoding RNA molecules that regulate gene expression at the posttranscriptional level. Recent studies have demonstrated the important role of miRs in regulating stem cell proliferation and differentiation, as well as other physiological and pathological processes related to stem cell function. This review summarises the current understanding of the role of miRs in CSCs. A deeper understanding of the mechanisms by which miRs regulate CSCs may lead to advances in the mode of stem cell therapies for the treatment of cardiovascular diseases.

Cardiac mesenchymal progenitors from postmortem cardiac tissues retained cellular characterization

BACKGROUND AND OBJECTIVE

Currently, cells for transplantation in regenerative medicine are derived from either autologous or allogeneic tissue. The former has the drawbacks that the quality of donor cells may depend on the condition of the patient, while the quantity of the cells may also be limited. To solve these problems, we investigated the potential of allogeneic cardiac mesenchymal progenitors (CMPs) derived from postmortem hearts, which may be immunologically privileged similar to bone marrow-derived mesenchymal progenitors.

MATERIALS AND METHODS

We examined whether viable CMPs could be isolated from C57/B6 murine cardiac tissues harvested at 24 hours postmortem. After 2- to 3-week propagation with a high dose of basic fibroblast growth factor, we performed cellular characteristics analyses, which included proliferation and differentiation property flow cytometry and microarray analyses.

RESULTS

Postmortem CMPs had a longer lag phase after seeding than CMPs obtained from living tissues, but otherwise had similar characteristics in all the analyses. In addition, global gene expression analysis by microarray showed that cells derived from postmortem and living tissues had similar characteristics.

CONCLUSION

These results indicate that allogeneic postmortem CMPs have potential for cell transplantation because they circumvent the issue of both the quality and quantity of donor cells.