Stem cell niches in the adult mouse heart

Establishment of a 3D organoid culture model for the investigation of adult slow-cycling putative intestinal stem cells

The study of intestinal stem cells is a prerequisite for the development of therapies aimed at regenerating the gut. To enable investigation of adult slow-cycling H2B-GFP-retaining putative small intestinal (SI) stem cells in vitro, we have developed a three-dimensional (3D) SI organoid culture model based on the Tet-Op histone 2 B (H2B)-green fluorescent protein (GFP) fusion protein (Tet-Op-H2B-GFP) transgenic mouse. SI crypts were isolated from 6- to 12-week-old Tet-Op-H2B-GFP transgenic mice and cultured with appropriate growth factors and an animal-derived matrix (Matrigel). For in vitro transgene expression, doxycycline was added to the culture medium for 24 h. By pulse-chase experiments, H2B-GFP expression and retention were assessed through direct GFP fluorescence observations, both by confocal and fluorescence microscopy and by immunohistochemistry. The percentages of H2B-GFP-retaining putative SI stem cells and H2B-GFP-retaining Paneth cells persisting in organoids were determined by scoring relevant GFP-positive cells. Our results indicate that 24 h exposure to doxycycline (pulse) induced ubiquitous expression of H2B-GFP in the SI organoids. During subsequent culture, in the absence of doxycycline (chase), there was a gradual loss (due to cell division) of H2B-GFP. At 6-day chase, slow-cycling H2B-GFP-retaining putative SI stem cells and H2B-GFP-retaining Paneth cells were detected in the SI organoids. The developed culture model allows detection of slow-cycling H2B-GFP-retaining putative SI stem cells and will enable the study of self-renewal and regeneration for further characterization of these cells.

A review on regulation of DNA methylation during post-myocardial infarction

Myocardial infarction (MI) imposes a huge medical and economic burden on society, and cardiac repair after MI involves a complex series of processes. Understanding the key mechanisms (such as apoptosis, autophagy, inflammation, and fibrosis) will facilitate further drug development and patient treatment. Presently, a substantial body of evidence suggests that the regulation of epigenetic processes contributes to cardiac repair following MI, with DNA methylation being among the notable epigenetic factors involved. This article will review the research on the mechanism of DNA methylation regulation after MI to provide some insights for future research and development of related drugs.

Cardiovascular aging: spotlight on mitochondria

Mitochondria are cellular organelles critical for ATP production and are particularly relevant to cardiovascular diseases including heart failure, atherosclerosis, ischemia-reperfusion injury, and cardiomyopathies. With advancing age, even in the absence of clinical disease, mitochondrial homeostasis becomes disrupted (e.g., redox balance, mitochondrial DNA damage, oxidative metabolism, and mitochondrial quality control). Mitochondrial dysregulation leads to the accumulation of damaged and dysfunctional mitochondria, producing excessive reactive oxygen species and perpetuating mitochondrial dysfunction. In addition, mitochondrial DNA, cardiolipin, and N-formyl peptides are potent activators of cell-intrinsic and -extrinsic inflammatory pathways. These age-related mitochondrial changes contribute to the development of cardiovascular diseases. This review covers the impact of aging on mitochondria and links these mechanisms to therapeutic implications for age-associated cardiovascular diseases.

Urokinase-Type Plasminogen Activator Receptor Regulates Prosurvival and Angiogenic Properties of Cardiac Mesenchymal Stromal Cells

One of the largest challenges to the implementation of cardiac cell therapy is identifying selective reparative targets to enhance stem/progenitor cell therapeutic efficacy. In this work, we hypothesized that such a target could be an urokinase-type plasminogen activator receptor (uPAR)-a glycosyl-phosphatidyl-inositol-anchored membrane protein, interacting with urokinase. uPAR is able to form complexes with various transmembrane proteins such as integrins, activating intracellular signaling pathway and thus regulating multiple cell functions. We focused on studying the CD117+ population of cardiac mesenchymal progenitor cells (MPCs), expressing uPAR on their surface. It was found that the number of CD117+ MPCs in the heart of the uPAR-/- mice is lower, as well as their ability to proliferate in vitro compared with cells from wild-type animals. Knockdown of uPAR in CD117+ MPCs of wild-type animals was accompanied by a decrease in survival rate and Akt signaling pathway activity and by an increase in the level of caspase activity in these cells. That suggests the role of uPAR in supporting cell survival. After intramyocardial transplantation of uPAR(-) MPCs, reduced cell retention and angiogenesis stimulation were observed in mice with myocardial infarction model compared to uPAR(+) cells transplantation. Taken together, the present results appear to prove a novel mechanism of uPAR action in maintaining the survival and angiogenic properties of CD117+ MPCs. These results emphasize the importance of the uPAR as a potential pharmacological target for the regulation of reparative properties of myocardial mesenchymal progenitor cells.

Mechanisms of Cardiac Repair in Cell Therapy

Heart failure is an important cause of morbidity and mortality. More than 20 years ago, special interest was drawn to cell therapy as a means of restoring damaged hearts to working condition. But progress has not been straightforward as many of our initial assumptions turned out to be wrong. In this review, we critically examine the last 20 years of progress in cardiac cell therapy and focus on several of the popular beliefs surrounding cell therapy to illustrate the mechanisms involved in restoring heart function after cardiac injury. Are they true or false?

Ubiquitin-specific protease 28: the decipherment of its dual roles in cancer development

As significant posttranslational modifications, ubiquitination and deubiquitination, whose balance is modulated by ubiquitin-conjugating enzymes and deubiquitinating enzymes (DUBs), can regulate many biological processes, such as controlling cell cycle progression, signal transduction and transcriptional regulation. Belonging to DUBs, ubiquitin-specific protease 28 (USP28) plays an essential role in turning over ubiquitination and then contributing to the stabilization of quantities of substrates, including several cancer-related proteins. In previous studies, USP28 has been demonstrated to participate in the progression of various cancers. Nevertheless, several reports have recently shown that in addition to promoting cancers, USP28 can also play an oncostatic role in some cancers. In this review, we summarize the correlation between USP28 and tumor behaviors. We initially give a brief introduction of the structure and related biological functions of USP28, and we then introduce some concrete substrates of USP28 and the underlying molecular mechanisms. In addition, the regulation of the actions and expression of USP28 is also discussed. Moreover, we concentrate on the impacts of USP28 on diverse hallmarks of cancer and discuss whether USP28 can accelerate or inhibit tumor progression. Furthermore, clinical relevance, including impacting clinical prognosis, influencing therapy resistance and being the therapy target in some cancers, is depicted systematically. Thus, assistance may be given to future experimental designs by the information provided here, and the potential of targeting USP28 for cancer therapy is emphasized.

The Role of Blood-Derived Factors in Protection and Regeneration of Aged Tissues

Tissue regeneration substantially relies on the functionality of tissue-resident endogenous adult stem cell populations. However, during aging, a progressive decline in organ function and regenerative capacities impedes endogenous repair processes. Especially the adult human heart is considered as an organ with generally low regenerative capacities. Interestingly, beneficial effects of systemic factors carried by young blood have been described in diverse organs including the heart, brain and skeletal muscle of the murine system. Thus, the interest in young blood or blood components as potential therapeutic agents to target age-associated malignancies led to a wide range of preclinical and clinical research. However, the translation of promising results from the murine to the human system remains difficult. Likewise, the establishment of adequate cellular models could help to study the effects of human blood plasma on the regeneration of human tissues and particularly the heart. Facing this challenge, this review describes the current knowledge of blood plasma-mediated protection and regeneration of aging tissues. The current status of preclinical and clinical research examining blood borne factors that act in stem cell-based tissue maintenance and regeneration is summarized. Further, examples of cellular model systems for a more detailed examination of selected regulatory pathways are presented.

The Effects of Mesenchymal Stem Cells on Oral Cancer and Possible Therapy Regime

Mesenchymal stem cells (MSCs) are characterized by self-renewal, rapid proliferation, multipotent differentiation, and low immunogenicity. In addition, the tropism of MSCs towards injured tissues and tumor lesions makes them attractive candidates as cell carriers for therapeutic agent delivery and genetic material transfer. The interaction between tumor cells and MSCs in the tumor microenvironment plays an important role in tumor progression. Oral cancer is one of the most common malignant diseases in the head and neck. Although considerable improvements in the treatment of oral cancer were achieved, more effective and safer novel agents and treatments are still needed, and deeper studies on the etiology, pathology, and treatment of the oral cancer are desirable. In the past decades, many studies have reported the beneficial effects of MSCs-based therapies in the treatment of various diseases, including oral cancers. Meanwhile, other studies demonstrated that MSCs may enhance the growth and metastasis of oral cancer. In this paper, we reviewed the research progress of the effects of MSCs on oral cancers, the underlying mechanisms, and their potential applications in the treatment of oral cancers.

Cardiac stem cells: Current knowledge and future prospects

Regenerative medicine is the field concerned with the repair and restoration of the integrity of damaged human tissues as well as whole organs. Since the inception of the field several decades ago, regenerative medicine therapies, namely stem cells, have received significant attention in preclinical studies and clinical trials. Apart from their known potential for differentiation into the various body cells, stem cells enhance the organ's intrinsic regenerative capacity by altering its environment, whether by exogenous injection or introducing their products that modulate endogenous stem cell function and fate for the sake of regeneration. Recently, research in cardiology has highlighted the evidence for the existence of cardiac stem and progenitor cells (CSCs/CPCs). The global burden of cardiovascular diseases’ morbidity and mortality has demanded an in-depth understanding of the biology of CSCs/CPCs aiming at improving the outcome for an innovative therapeutic strategy. This review will discuss the nature of each of the CSCs/CPCs, their environment, their interplay with other cells, and their metabolism. In addition, important issues are tackled concerning the potency of CSCs/CPCs in relation to their secretome for mediating the ability to influence other cells. Moreover, the review will throw the light on the clinical trials and the preclinical studies using CSCs/CPCs and combined therapy for cardiac regeneration. Finally, the novel role of nanotechnology in cardiac regeneration will be explored.

Cardiac stem cells: Current knowledge and future prospects

Regenerative medicine is the field concerned with the repair and restoration of the integrity of damaged human tissues as well as whole organs. Since the inception of the field several decades ago, regenerative medicine therapies, namely stem cells, have received significant attention in preclinical studies and clinical trials. Apart from their known potential for differentiation into the various body cells, stem cells enhance the organ's intrinsic regenerative capacity by altering its environment, whether by exogenous injection or introducing their products that modulate endogenous stem cell function and fate for the sake of regeneration. Recently, research in cardiology has highlighted the evidence for the existence of cardiac stem and progenitor cells (CSCs/CPCs). The global burden of cardiovascular diseases' morbidity and mortality has demanded an in-depth understanding of the biology of CSCs/CPCs aiming at improving the outcome for an innovative therapeutic strategy. This review will discuss the nature of each of the CSCs/CPCs, their environment, their interplay with other cells, and their metabolism. In addition, important issues are tackled concerning the potency of CSCs/CPCs in relation to their secretome for mediating the ability to influence other cells. Moreover, the review will throw the light on the clinical trials and the preclinical studies using CSCs/CPCs and combined therapy for cardiac regeneration. Finally, the novel role of nanotechnology in cardiac regeneration will be explored.

From Spheroids to Organoids: The Next Generation of Model Systems of Human Cardiac Regeneration in a Dish

Organoids are tiny, self-organized, three-dimensional tissue cultures that are derived from the differentiation of stem cells. The growing interest in the use of organoids arises from their ability to mimic the biology and physiology of specific tissue structures in vitro. Organoids indeed represent promising systems for the in vitro modeling of tissue morphogenesis and organogenesis, regenerative medicine and tissue engineering, drug therapy testing, toxicology screening, and disease modeling. Although 2D cell cultures have been used for more than 50 years, even for their simplicity and low-cost maintenance, recent years have witnessed a steep rise in the availability of organoid model systems. Exploiting the ability of cells to re-aggregate and reconstruct the original architecture of an organ makes it possible to overcome many limitations of 2D cell culture systems. In vitro replication of the cellular micro-environment of a specific tissue leads to reproducing the molecular, biochemical, and biomechanical mechanisms that directly influence cell behavior and fate within that specific tissue. Lineage-specific self-organizing organoids have now been generated for many organs. Currently, growing cardiac organoid (cardioids) from pluripotent stem cells and cardiac stem/progenitor cells remains an open challenge due to the complexity of the spreading, differentiation, and migration of cardiac muscle and vascular layers. Here, we summarize the evolution of biological model systems from the generation of 2D spheroids to 3D organoids by focusing on the generation of cardioids based on the currently available laboratory technologies and outline their high potential for cardiovascular research.

Regenerative Medicine for the Treatment of Ischemic Heart Disease; Status and Future Perspectives

Cardiovascular disease is now the leading cause of adult death in the world. According to new estimates from the World Health Organization, myocardial infarction (MI) is responsible for four out of every five deaths due to cardiovascular disease. Conventional treatments of MI are taking aspirin and nitroglycerin as intermediate treatments and injecting antithrombotic agents within the first 3 h after MI. Coronary artery bypass grafting and percutaneous coronary intervention are the most common long term treatments. Since none of these interventions will fully regenerate the infarcted myocardium, there is value in pursuing more innovative therapeutic approaches. Regenerative medicine is an innovative interdisciplinary method for rebuilding, replacing, or repairing the missed part of different organs in the body, as similar as possible to the primary structure. In recent years, regenerative medicine has been widely utilized as a treatment for ischemic heart disease (one of the most fatal factors around the world) to repair the lost part of the heart by using stem cells. Here, the development of mesenchymal stem cells causes a breakthrough in the treatment of different cardiovascular diseases. They are easily obtainable from different sources, and expanded and enriched easily, with no need for immunosuppressing agents before transplantation, and fewer possibilities of genetic abnormality accompany them through multiple passages. The production of new cardiomyocytes can result from the transplantation of different types of stem cells. Accordingly, due to its remarkable benefits, stem cell therapy has received attention in recent years as it provides a drug-free and surgical treatment for patients and encourages a more safe and feasible cardiac repair. Although different clinical trials have reported on the promising benefits of stem cell therapy, there is still uncertainty about its mechanism of action. It is important to conduct different preclinical and clinical studies to explore the exact mechanism of action of the cells. After reviewing the pathophysiology of MI, this study addresses the role of tissue regeneration using various materials, including different types of stem cells. It proves some appropriate data about the importance of ethical problems, which leads to future perspectives on this scientific method.

Adult stem cell niches for tissue homeostasis

Adult stem cells are fundamental to maintain tissue homeostasis, growth, and regeneration. They reside in specialized environments called niches. Following activating signals, they proliferate and differentiate into functional cells that are able to preserve tissue physiology, either to guarantee normal turnover or to counteract tissue damage caused by injury or disease. Multiple interactions occur within the niche between stem cell‐intrinsic factors, supporting cells, the extracellular matrix, and signaling pathways. Altogether, these interactions govern cell fate, preserving the stem cell pool, and regulating stem cell proliferation and differentiation. Based on their response to body needs, tissues can be largely classified into three main categories: tissues that even in normal conditions are characterized by an impressive turnover to replace rapidly exhausting cells (blood, epidermis, or intestinal epithelium); tissues that normally require only a basal cell replacement, though able to efficiently respond to increased tissue needs, injury, or disease (skeletal muscle); tissues that are equipped with less powerful stem cell niches, whose repairing ability is not able to overcome severe damage (heart or nervous tissue). The purpose of this review is to describe the main characteristics of stem cell niches in these different tissues, highlighting the various components influencing stem cell activity. Although much has been done, more work is needed to further increase our knowledge of niche interactions. This would be important not only to shed light on this fundamental chapter of human physiology but also to help the development of cell‐based strategies for clinical therapeutic applications, especially when other approaches fail.

Metabolic and Redox Regulation of Cardiovascular Stem Cell Biology and Pathology

Significance: Cardiovascular stem cells are important for regeneration and repair of damaged tissue. Recent Advances: Pluripotent stem cells have a unique metabolism, which is adopted for their energetic and biosynthetic demand as rapidly proliferating cells. Stem cell differentiation requires an exceptional metabolic flexibility allowing for metabolic remodeling between glycolysis and oxidative phosphorylation. Critical Issues: Respiration is associated with the generation of reactive oxygen species (ROS) by the mitochondrial respiratory chain. But also the membrane-bound protein nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase, NOX) contributes to ROS levels. ROS not only play a significant role in stem cell differentiation and tissue renewal but also cause senescence and contribute to tissue aging. Future Directions: For utilization of stem cells in therapeutic approaches, a deep understanding of the molecular mechanisms how metabolism and the cellular redox state regulate stem cell differentiation is required. Modulating the redox state of stem cells using antioxidative agents may be suitable to enhance activity of endothelial progenitor cells. Antioxid. Redox Signal. 35, 163-181.

Cultured cardiac fibroblasts and myofibroblasts express Sushi Containing Domain 2 and assemble a unique fibronectin rich matrix

Cardiac fibroblasts and myofibroblasts assemble and maintain extracellular matrix during normal development and following injury. Culture expansion of these cells yield a bioengineered matrix that could lead to intriguing therapeutic opportunities. For example, we reported that cultured rat cardiac fibroblasts form a matrix that can be used to delivery therapeutic stem cells. Furthermore, we reported that matrix derived from cultured human cardiac fibroblasts/myofibroblasts converted monocytes into macrophages that express interesting anti-inflammatory and pro-angiogenic properties. Expanding these matrix investigations require characterization of the source cells for quality control. In these efforts, we observed and herein report that Sushi Containing Domain 2 (SUSD2) is a novel and consistent marker for cultured human cardiac fibroblast and myofibroblasts.

Secreted Frizzled Related Proteins in Cardiovascular and Metabolic Diseases

Abnormal gene expression and secreted protein levels are accompanied by extensive pathological changes. Secreted frizzled related protein (SFRP) family members are antagonistic inhibitors of the Wnt signaling pathway, and they were recently found to be involved in the pathogenesis of a variety of metabolic diseases, which has led to extensive interest in SFRPs. Previous reports highlighted the importance of SFRPs in lipid metabolism, obesity, type 2 diabetes mellitus and cardiovascular diseases. In this review, we provide a detailed introduction of SFRPs, including their structural characteristics, receptors, inhibitors, signaling pathways and metabolic disease impacts. In addition to summarizing the pathologies and potential molecular mechanisms associated with SFRPs, this review further suggests the potential future use of SFRPs as disease biomarkers therapeutic targets.

Cardiac fibroblast derived matrix-educated macrophages express VEGF and IL-6, and recruit mesenchymal stromal cells

The polarization of monocytes into macrophages that possess anti-inflammatory and pro-angiogenic properties could provide a novel therapeutic strategy for patients who are at a high risk for developing heart failure following myocardial infarction (MI). Here in, we describe a novel method of "educating" monocytes into a distinct population of macrophages that exhibit anti-inflammatory and pro-angiogenic features through a 3-day culture on fibronectin-rich cardiac matrix (CX) manufactured using cultured human cardiac fibroblasts. Our data suggest that CX can educate monocytes into a unique macrophage population termed CX educated macrophages (CXMq) that secrete high levels of VEGF and IL-6. In vitro, CXMq also demonstrate the ability to recruit mesenchymal stromal cells (MSC) with known anti-inflammatory properties. Selective inhibition of fibronectin binding to αVβ3 surface integrins on CXMq prevented MSC recruitment. This suggests that insoluble fibronectin within CX is, at least in part, responsible for CXMq conversion.

Blood Serum Stimulates p38-Mediated Proliferation and Changes in Global Gene Expression of Adult Human Cardiac Stem Cells

During aging, senescent cells accumulate in various tissues accompanied by decreased regenerative capacities of quiescent stem cells, resulting in deteriorated organ function and overall degeneration. In this regard, the adult human heart with a generally low regenerative potential is of extreme interest as a target for rejuvenating strategies with blood borne factors that might be able to activate endogenous stem cell populations. Here, we investigated for the first time the effects of human blood plasma and serum on adult human cardiac stem cells (hCSCs) and showed significantly increased proliferation capacities and metabolism accompanied by a significant decrease of senescent cells, demonstrating a beneficial serum-mediated effect that seemed to be independent of age and sex. However, RNA-seq analysis of serum-treated hCSCs revealed profound effects on gene expression depending on the age and sex of the plasma donor. We further successfully identified key pathways that are affected by serum treatment with p38-MAPK playing a regulatory role in protection from senescence and in the promotion of proliferation in a serum-dependent manner. Inhibition of p38-MAPK resulted in a decline of these serum-mediated beneficial effects on hCSCs in terms of decreased proliferation and accelerated senescence. In summary, we provide new insights in the regulatory networks behind serum-mediated protective effects on adult human cardiac stem cells.

Unravelling the Biology of Adult Cardiac Stem Cell-Derived Exosomes to Foster Endogenous Cardiac Regeneration and Repair

Cardiac remuscularization has been the stated goal of the field of regenerative cardiology since its inception. Along with the refreshment of lost and dysfunctional cardiac muscle cells, the field of cell therapy has expanded in scope encompassing also the potential of the injected cells as cardioprotective and cardio-reparative agents for cardiovascular diseases. The latter has been the result of the findings that cell therapies so far tested in clinical trials exert their beneficial effects through paracrine mechanisms acting on the endogenous myocardial reparative/regenerative potential. The endogenous regenerative potential of the adult heart is still highly debated. While it has been widely accepted that adult cardiomyocytes (CMs) are renewed throughout life either in response to wear and tear and after injury, the rate and origin of this phenomenon are yet to be clarified. The adult heart harbors resident cardiac/stem progenitor cells (CSCs/CPCs), whose discovery and characterization were initially sufficient to explain CM renewal in response to physiological and pathological stresses, when also considering that adult CMs are terminally differentiated cells. The role of CSCs in CM formation in the adult heart has been however questioned by some recent genetic fate map studies, which have been proved to have serious limitations. Nevertheless, uncontested evidence shows that clonal CSCs are effective transplantable regenerative agents either for their direct myogenic differentiation and for their paracrine effects in the allogeneic setting. In particular, the paracrine potential of CSCs has been the focus of the recent investigation, whereby CSC-derived exosomes appear to harbor relevant regenerative and reparative signals underlying the beneficial effects of CSC transplantation. This review focuses on recent advances in our knowledge about the biological role of exosomes in heart tissue homeostasis and repair with the idea to use them as tools for new therapeutic biotechnologies for "cell-less" effective cardiac regeneration approaches.

Rats are protected from the stress of chronic pressure overload compared with mice

The goal of this investigation was to compare the effects of chronic (4 wk) transverse aortic constriction (TAC) in Sprague-Dawley rats and C57BL/6J mice. TAC, after 1 day, induced similar left ventricular (LV) pressure gradients in both rats (n = 7) and mice (n = 7) (113 ± 5.4 vs. 103 ± 11.5 mmHg), and after 4 wk, the percent increase in LV hypertrophy, as reflected by LV/tibial length (51% vs 49%), was similar in rats (n = 12) and mice (n = 12). After 4 wk of TAC, LV systolic and diastolic function were preserved in TAC rats. In contrast, in TAC mice, LV ejection fraction decreased by 31% compared with sham, along with increases in LV end-diastolic pressure (153%) and LV systolic wall stress (86%). Angiogenesis, as reflected by Ki67 staining of capillaries, increased more in rats (n = 6) than in mice (n = 6; 10 ± 2 vs. 6 ± 1 Ki67-positive cells/field). Myocardial blood flow fell by 55% and coronary reserve by 28% in mice with TAC (n = 4), but they were preserved in rats (n = 4). Myogenesis, as reflected by c-kit-positive myocytes staining positively for troponin I, is another mechanism that can confer protection after TAC. However, the c-kit-positive cells in rats with TAC were all negative for troponin I, indicating the absence of myogenesis. Thus, rats showed relative tolerance to severe pressure overload compared with mice, with mechanisms involving angiogenesis but not myogenesis.

State of the art of stem cell therapy for ischaemic cardiomyopathy. Part 2

Ischemic cardiomyopathy is becoming a leading cause of morbidity and mortality in the whole world. Stem cell-based therapy is emerging as a promising option for treatment of ischemic cardiomyopathy. Several stem cell types, including cardiac-derived stem cells, bone marrow-derived stem cells, mesenchymal stem cells, skeletal myoblasts, CD34+ and CD133+ stem cells have been used in clinical trials. Clinical effects mostly depend on transdifferentiation and paracrine factors. One important issue is that a low survival and residential rate of transferred stem cells blocks the effective advances in cardiac improvement. Many other factors associated with the efficacy of cell replacement therapy for ischemic cardiomyopathy mainly including the route of delivery, the type and number of stem cell infusion, the timing of injection, patient's physical conditions, the particular microenvironment onto which the cells are delivered, and clinical conditions remain to be addressed. Here we provide an overview of modern methods of stem cell delivery, types of stem cells and discuss the current state of their therapeutic potential.

Laminin-511 Supplementation Enhances Stem Cell Localization With Suppression in the Decline of Cardiac Function in Acute Infarct Rats

BACKGROUND

The extracellular matrix, in particular basement membrane components such as laminins (LMs), is essential for stem cell differentiation and self-renewal. LM511 and LM221 are the main extracellular matrix components of the epicardium, where stem cells were abundant. Here, we examined whether LMs affected the regeneration process by modulating stem cell activities.

METHODS

In vitro, adhesive, and proliferative activities of mesenchymal stem cells (MSCs) were evaluated on LM511 and LM221. To examine the effects of LMs in vivo, we established an acute myocardial infarction model by ligation of the proximal part of the left anterior descending artery at the height of the left atrial appendage and then placed atelocollagen sheets with or without LM511 and LM221 over the anterolateral surface of the left ventricular wall. Four or 8 weeks later, cardiac function, histology, and cytokine expressions were analyzed.

RESULTS

MSCs showed greater proliferation and adhesive properties on LM511 than on LM221. In vivo, at 4 weeks, isolectin B4-positive cells were significantly higher in the LM511-transplanted group than in the control group. Moreover, some isolectin B4-positive cells expressed both platelet-derived growth factor receptor α and CD90, suggesting that LM511 enhanced MSC recruitment and attachment at the implanted site. After 8 weeks, these cells were more abundant than at 4 weeks. Transplantation with LM511-conjugated sheets increased the expression of cardioprotective and angiogenic factors.

CONCLUSIONS

Transplantation with LM511-conjugated sheets enhanced MSC localization to the implantation site and modulated stem cells activities, leading to angiogenesis in acute myocardial infarction rat models.

A new structure from cardiac cells cultured in vitro: Cardiomyocyte-annulation of neonatal rats

To explore the formation, morphological characteristics, cell composition, and differentiation potential of cardiomyocyte annulation (cardio-annulation) during in vitro culture of cardiac cells. Cardiac cells were isolated and cultured. A live-cell imaging system was used to observe cardio-annulation. Cardiac troponin-T (cTnT) and vimentin were labeled with double immunofluorescence staining, and coexpressions of cTnT and connexin43 (Cx43), cTnT and nanog, c-kit and nanog, and c-kit and stem cell antigen (sca-1) were detected. The location of various types of cells within the cardio-annulation structure was observed. Adipogenic- and osteogenic-inducing fluids were used separately for in situ induction to detect the multidirectional differentiation potential of cells during the annulation process. After 3 to 6 days, cardiac cells migrated and formed an open or closed annulus with a diameter of 800 to 3500 μm. The annulus wall comprised the medial, middle, and lateral regions. The cells in the medial region were small, abundant, and laminated, while those in the middle region were larger with fewer layers, and those in the lateral region were less abundant, and loosely arranged in a single layer. Cardiomyocytes were distributed mainly on the surface of the medial region; nanog⁺ , c-kit⁺ , and sca-1⁺ cells were located mainly at the bottom of the annulus wall and fibroblasts were located mainly between these layers. The annulus cavity contained a large number of small, round cells, and telocytes. Cx43 was expressed in all cell types, and nanog, c-kit, and sca-1 were coexpressed in the cardio-annulation cells, which possess adipogenic and osteogenic differentiation potential. Cardio-annulation was discovered during an in vitro culture of cardiac cells. The structure contains cardiomyocytes, fibroblasts, telocytes, and abundant stem cells. These results provide insight into the relationship among cardiac cells in vitro.

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.

Adult Cardiac Stem Cell Aging: A Reversible Stochastic Phenomenon?

Aging is by far the dominant risk factor for the development of cardiovascular diseases, whose prevalence dramatically increases with increasing age reaching epidemic proportions. In the elderly, pathologic cellular and molecular changes in cardiac tissue homeostasis and response to injury result in progressive deteriorations in the structure and function of the heart. Although the phenotypes of cardiac aging have been the subject of intense study, the recent discovery that cardiac homeostasis during mammalian lifespan is maintained and regulated by regenerative events associated with endogenous cardiac stem cell (CSC) activation has produced a crucial reconsideration of the biology of the adult and aged mammalian myocardium. The classical notion of the adult heart as a static organ, in terms of cell turnover and renewal, has now been replaced by a dynamic model in which cardiac cells continuously die and are then replaced by CSC progeny differentiation. However, CSCs are not immortal. They undergo cellular senescence characterized by increased ROS production and oxidative stress and loss of telomere/telomerase integrity in response to a variety of physiological and pathological demands with aging. Nevertheless, the old myocardium preserves an endogenous functionally competent CSC cohort which appears to be resistant to the senescent phenotype occurring with aging. The latter envisions the phenomenon of CSC ageing as a result of a stochastic and therefore reversible cell autonomous process. However, CSC aging could be a programmed cell cycle-dependent process, which affects all or most of the endogenous CSC population. The latter would infer that the loss of CSC regenerative capacity with aging is an inevitable phenomenon that cannot be rescued by stimulating their growth, which would only speed their progressive exhaustion. The resolution of these two biological views will be crucial to design and develop effective CSC-based interventions to counteract cardiac aging not only improving health span of the elderly but also extending lifespan by delaying cardiovascular disease-related deaths.

Does cardiac development provide heart research with novel therapeutic approaches?

Embryonic heart progenitors arise at specific spatiotemporal periods that contribute to the formation of distinct cardiac structures. In mammals, the embryonic and fetal heart is hypoxic by comparison to the adult heart. In parallel, the cellular metabolism of the cardiac tissue, including progenitors, undergoes a glycolytic to oxidative switch that contributes to cardiac maturation. While oxidative metabolism is energy efficient, the glycolytic-hypoxic state may serve to maintain cardiac progenitor potential. Consistent with this proposal, the adult epicardium has been shown to contain a reservoir of quiescent cardiac progenitors that are activated in response to heart injury and are hypoxic by comparison to adjacent cardiac tissues. In this review, we discuss the development and potential of the adult epicardium and how this knowledge may provide future therapeutic approaches for cardiac repair.

Hypoxia induces hypomethylation of the HMGB1 promoter via the MAPK/DNMT1/HMGB1 pathway in cardiac progenitor cells

Apoptosis is involved in the death of cardiac progenitor cells (CPCs) after myocardial infarction (MI) in the heart. The loss of CPCs results in infarct scar and further deterioration of the heart function. Though stem cell-based therapy provides an effective approach for heart function recovery after MI, the retention of CPCs in the infarcted area of the heart is the main barrier that limits its promising therapy. Therefore, the underlying mechanisms of CPC apoptosis in hypoxia are important for the development of new therapeutic targets for MI patients. In this work, we found that the expression of high-mobility group box 1(HMGB1) was upregulated in CPCs under hypoxia conditions. Further study demonstrated that HMGB1 was regulated by DNA methyltransferases 1 (DNMT1) via changing the methylation state of CpGs in the promoter of HMGB1 in CPCs during hypoxia process. Additionally, mitogen-activated protein kinase (MAPK) signaling pathway was found to be involved in regulating DNMT1/HMGB1-mediated CPC apoptosis in hypoxia process. In conclusion, our findings demonstrate a novel regulatory mechanism for CPC apoptosis and proliferation under hypoxia conditions, which may provide a new therapeutic approach for MI patients.

Development of the Myocardial Interstitium

The space between cardiac myocytes is commonly referred-to as the cardiac interstitium (CI). The CI is a unique, complex and dynamic microenvironment in which multiple cell types, extracellular matrix molecules, and instructive signals interact to crucially support heart homeostasis and promote cardiac responses to normal and pathologic stimuli. Despite the biomedical and clinical relevance of the CI, its detailed cellular structure remains to be elucidated. In this review, we will dissect the organization of the cardiac interstitium by following its changing cellular and molecular composition from embryonic developmental stages to adulthood, providing a systematic analysis of the biological components of the CI. The main goal of this review is to contribute to our understanding of the CI roles in health and disease. Anat Rec, 302:58-68, 2019. © 2018 Wiley Periodicals, Inc.

Long non-coding RNA H19 contributes to hypoxia-induced CPC injury by suppressing Sirt1 through miR-200a-3p

Cardiomyocyte death is the chief obstacle that prevents the heart function recovery in myocardial infarction (MI)-induced heart failure (HF). Cardiac progenitor cells (CPCs)-based myocardial regeneration has provided a promising method for heart function recovery after MI. However, CPCs can easily lose their proliferation ability due to oxygen deficiency in infarcted myocardium. Revealing the underlying molecular mechanism for CPC proliferation is critical for effective MI therapy. In the present study, we set up a CoCl2-induced hypoxia model in CPCs. We found that the expression of long non-coding RNA H19 was significantly down-regulated in CPCs after hypoxia stimuli. In addition, H19 suppression attenuated the proliferation and migration of CPCs under hypoxia stress. Furthermore, we discovered that H19 regulated the proliferation and migration of CPCs through mediating the expression of Sirt1 which is a target of miR-200a-3p under hypoxia. In conclusion, our findings demonstrate a novel regulatory mechanism for the proliferation and migration of CPCs under hypoxia condition, which provides useful information for the development of new therapeutic targets for MI therapy.

Two mechanisms of cardiac stem cell-mediated cardiomyogenesis in the adult mammalian heart include formation of colonies and cell-in-cell structures

Aims

Because the mechanism of mature cardiomyocyte (CM) development from cardiac stem cells (CSCs) is not fully understood, we explored the involvement of CSCs into two pathways of cardiomyogenesis in adult mammalian heart: (1) via colony formation and (2) by means of intracellular development of CSCs inside CMs followed by the formation of “cell-in-cell structures” (CICSs).

Methods and Results

Using immunostaining and confocal microscopy, we studied the presence of CSC-derived colonies, CICSs and transitory amplifying cells (TACs), released from ruptured CICSs, in a suspension of ex vivo freshly isolated myocardial cells of mammals of different age and species, human including. All subsets of CSCs (c-kit+, Sca-1+ and Isl-1+) were found in mammals of different age. It was shown that c-kit+ and Sca-1+ CSCs produce both colonies and CICSs. However, Isl-1+ CSCs seem to be involved in cardiac growth during first month of age only both through colony formation and CICS generation. In turn, the studies on myocardial cell suspensions of adult C57/bl6N mice, one-year-old bull and 45-year-old woman not only confirmed the involvement of c-kit+ and Sca-1+ CSCs in both mechanisms of cardiomyogenesis, but also showed that Isl-1+ colonies are present in the myocardium of adult mice and rarely in human.

Conclusions

The presence of CSC-derived colonies, CICSs and TACs in all experimental specimens of myocardium proved our previous hypothesis about two pathways that generate new CMs in adult heart. Moreover, we suggest that TACs play a central role in self-renewal of myocardium throughout the lifetime of mammals.

Hypoxia-stressed cardiomyocytes promote early cardiac differentiation of cardiac stem cells through HIF-1α/Jagged1/Notch1 signaling

Hypoxia is beneficial for the differentiation of stem cells transplanted for myocardial injury, but mechanisms underlying this benefit remain unsolved. Here, we report the impact of hypoxia-induced Jagged1 expression in cardiomyocytes (CMs) for driving the differentiation of cardiac stem cells (CSCs). Forced hypoxia-inducible factor 1α (HIF-1α) expression and physical hypoxia (5% O₂) treatment could induce Jagged1 expression in neonatal rat CMs. Pharmacological inhibition of HIF-1α by YC-1 attenuated hypoxia-promoted Jagged1 expression in CMs. An ERK inhibitor (PD98059), but not inhibitors of JNK (SP600125), Notch (DAPT), NF-κB (PTDC), JAK (AG490), or STAT3 (Stattic) suppressed hypoxia-induced Jagged1 protein expression in CMs. c-Kit⁺ CSCs isolated from neonatal rat hearts using a magnetic-activated cell sorting method expressed GATA4, SM22α or vWF, but not Nkx2.5 and cTnI. Moreover, 87.3% of freshly isolated CSCs displayed Notch1 receptor expression. Direct co-culture of CMs with BrdU-labeled CSCs enhanced CSCs differentiation, as evidenced by an increased number of BrdU⁺/Nkx2.5⁺ cells, while intermittent hypoxia for 21 days promoted co-culture-triggered differentiation of CSCs into CM-like cells. Notably, YC-1 and DAPT attenuated hypoxia-induced differentiation. Our results suggest that hypoxia induces Jagged1 expression in CMs primarily through ERK signaling, and facilitates early cardiac lineage differentiation of CSCs in CM/CSC co-cultures via HIF-1α/Jagged1/Notch signaling.

Heterocellular molecular contacts in the mammalian stem cell niche

Adult tissue homeostasis and repair relies on prompt and appropriate intervention by tissue-specific adult stem cells (SCs). SCs have the ability to self-renew; upon appropriate stimulation, they proliferate and give rise to specialized cells. An array of environmental signals is important for maintenance of the SC pool and SC survival, behavior, and fate. Within this special microenvironment, commonly known as the stem cell niche (SCN), SC behavior and fate are regulated by soluble molecules and direct molecular contacts via adhesion molecules providing connections to local supporting cells and the extracellular matrix. Besides the extensively discussed array of soluble molecules, the expression of adhesion molecules and molecular contacts is another fundamental mechanism regulating niche occupancy and SC mobilization upon activation. Some adhesion molecules are differentially expressed and have tissue-specific consequences, likely reflecting the structural differences in niche composition and design, especially the presence or absence of a stromal counterpart. However, the distribution and identity of intercellular molecular contacts for adhesion and adhesion-mediated signaling within stromal and non-stromal SCN have not been thoroughly studied. This review highlights common details or significant differences in cell-to-cell contacts within representative stromal and non-stromal niches that could unveil new standpoints for stem cell biology and therapy.

Molecular basis of functional myogenic specification of Bona Fide multipotent adult cardiac stem cells

Ischemic Heart Disease (IHD) remains the developed world's number one killer. The improved survival from Acute Myocardial Infarction (AMI) and the progressive aging of western population brought to an increased incidence of chronic Heart Failure (HF), which assumed epidemic proportions nowadays. Except for heart transplantation, all treatments for HF should be considered palliative because none of the current therapies can reverse myocardial degeneration responsible for HF syndrome. To stop the HF epidemic will ultimately require protocols to reduce the progressive cardiomyocyte (CM) loss and to foster their regeneration. It is now generally accepted that mammalian CMs renew throughout life. However, this endogenous regenerative reservoir is insufficient to repair the extensive damage produced by AMI/IHD while the source and degree of CM turnover remains strongly disputed. Independent groups have convincingly shown that the adult myocardium harbors bona-fide tissue specific cardiac stem cells (CSCs). Unfortunately, recent reports have challenged the identity and the endogenous myogenic capacity of the c-kit expressing CSCs. This has hampered progress and unless this conflict is settled, clinical tests of repair/regenerative protocols are unlikely to provide convincing answers about their clinical potential. Here we review recent data that have eventually clarified the specific phenotypic identity of true multipotent CSCs. These cells when coaxed by embryonic cardiac morphogens undergo a precisely orchestrated myogenic commitment process robustly generating bona-fide functional cardiomyocytes. These data should set the path for the revival of further investigation untangling the regenerative biology of adult CSCs to harness their potential for HF prevention and treatment.

Cardiac Stem Cells in the Postnatal Heart: Lessons from Development

Heart development in mammals is followed by a postnatal decline in cell proliferation and cell renewal from stem cell populations. A better understanding of the developmental changes in cardiac microenvironments occurring during heart maturation will be informative regarding the loss of adult regenerative potential. We reevaluate the adult heart's mitotic potential and the reported adult cardiac stem cell populations, as these are two topics of ongoing debate. The heart's early capacity for cell proliferation driven by progenitors and reciprocal signalling is demonstrated throughout development. The mature heart architecture and environment may be more restrictive on niches that can host progenitor cells. The engraftment issues observed in cardiac stem cell therapy trials using exogenous stem cells may indicate a lack of supporting stem cell niches, while tissue injury adds to a hostile microenvironment for transplanted cells. Engraftment may be improved by preconditioning the cultured stem cells and modulating the microenvironment to host these cells. These prospective areas of further research would benefit from a better understanding of cardiac progenitor interactions with their microenvironment throughout development and may lead to enhanced cardiac niche support for stem cell therapy engraftment.

Cardiac regeneration in Xenopus tropicalis and Xenopus laevis: discrepancies and problems

Two studies have recently focused on adult heart regeneration in Xenopus. While we reported on cardiac myogenic regeneration in Xenopus tropicalis after injury, Marshall and colleagues found no regeneration in an injured heart in Xenopus laevis. Here, we would like to join the discussion initiated by Marshall et al. who debated the methods and species differences in both studies. We agree with their view that the species difference in cardiac regenerative capacity could lead to different results in both of these studies. Moreover, we suggest that the age of the animals used in these studies could lead to differences in regeneration. A 5-year old X. laevis is much more advanced in age than a 1-year old X. tropicalis. The other reason for the discrepancies could be the size of the clot. Due to different resection protocols, the clot formed after the endoscopic resection performed by Marshall et al. was much larger than that after a conventional resection, as used in our study. Furthermore, the difference in the site of injury could influence the healing and regeneration differences. The influence of the organismal age, techniques used to induce injury and site of injury on regeneration need to be examined in detail to assess the regenerative potential of the amphibian heart.

Mechanisms of Cardiac Repair and Regeneration

Cardiovascular regenerative therapies are pursued on both basic and translational levels. Although efficacy and value of cell therapy for myocardial regeneration can be debated, there is a consensus that profound deficits in mechanistic understanding limit advances, optimization, and implementation. In collaboration with the TACTICS (Transnational Alliance for Regenerative Therapies in Cardiovascular Syndromes), this review overviews several pivotal aspects of biological processes impinging on cardiac maintenance, repair, and regeneration. The goal of summarizing current mechanistic understanding is to prompt innovative directions for fundamental studies delineating cellular reparative and regenerative processes. Empowering myocardial regenerative interventions, whether dependent on endogenous processes or exogenously delivered repair agents, ultimately depends on mastering mechanisms and novel strategies that take advantage of rather than being limited by inherent myocardial biology.

Symmetry from Asymmetry or Asymmetry from Symmetry?

The processes of DNA replication and mitosis allow the genetic information of a cell to be copied and transferred reliably to its daughter cells. However, if DNA replication and cell division were always performed in a symmetric manner, the result would be a cluster of tumor cells instead of a multicellular organism. Therefore, gaining a complete understanding of any complex living organism depends on learning how cells become different while faithfully maintaining the same genetic material. It is well recognized that the distinct epigenetic information contained in each cell type defines its unique gene expression program. Nevertheless, how epigenetic information contained in the parental cell is either maintained or changed in the daughter cells remains largely unknown. During the asymmetric cell division (ACD) of Drosophila male germline stem cells, our previous work revealed that preexisting histones are selectively retained in the renewed stem cell daughter, whereas newly synthesized histones are enriched in the differentiating daughter cell. We also found that randomized inheritance of preexisting histones versus newly synthesized histones results in both stem cell loss and progenitor germ cell tumor phenotypes, suggesting that programmed histone inheritance is a key epigenetic player for cells to either remember or reset cell fates. Here, we will discuss these findings in the context of current knowledge on DNA replication, polarized mitotic machinery, and ACD for both animal development and tissue homeostasis. We will also speculate on some potential mechanisms underlying asymmetric histone inheritance, which may be used in other biological events to achieve the asymmetric cell fates.

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.

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.

Role and therapeutic potential of vascular stem/progenitor cells in pathological neovascularisation during chronic portal hypertension

OBJECTIVE

Pathological neovascularisation is intimately involved in portal hypertension (PH). Here, we determined the contribution of vascular stem/progenitor cells (VSPCs) to neovessel growth in PH and whether the RNA-binding protein cytoplasmic polyadenylation element binding protein-4 (CPEB4) was behind the mechanism controlling VSPC function.

DESIGN

To identify and monitor VSPCs in PH rats (portal vein-ligated), we used a combinatorial approach, including sphere-forming assay, assessment of self-renewal, 5-bromo-2'-desoxyuridine label retention technique, in vitro and in vivo stem/progenitor cell (SPC) differentiation and vasculogenic capability, cell sorting, as well as immunohistochemistry, immunofluorescence and confocal microscopy expression analysis. We also determined the role of CPEB4 on VSPC proliferation using genetically engineered mouse models.

RESULTS

We demonstrated the existence in the mesenteric vascular bed of VSPCs displaying capability to form cellular spheres in suspension culture, self-renewal ability, expression of molecules commonly found in SPCs, slow-cycling features, in addition to other cardinal properties exhibited by SPCs, like capacity to differentiate into endothelial cells and pericytes with remarkable vasculogenic activity. Such VSPCs showed, after PH induction, an early switch in proliferation, and differentiated in vivo into endothelial cells and pericytes, contributing, structurally and functionally, to abnormal neovessel formation. Quantification of VSPC-dependent neovessel formation in PH further illustrated the key role played by VSPCs. We also demonstrated that CPEB4 regulates the proliferation of the activated VSPC progeny upon PH induction.

CONCLUSIONS

These findings demonstrate that VSPC-derived neovessel growth (ie, vasculogenesis) and angiogenesis cooperatively stimulate mesenteric neovascularisation in PH and identify VSPC and CPEB4 as potential therapeutic targets.

Pim1 Kinase Overexpression Enhances ckit+ Cardiac Stem Cell Cardiac Repair Following Myocardial Infarction in Swine

BACKGROUND

Pim1 kinase plays an important role in cell division, survival, and commitment of precursor cells towards a myocardial lineage, and overexpression of Pim1 in ckit⁺ cardiac stem cells (CSCs) enhances their cardioreparative properties.

OBJECTIVES

The authors sought to validate the effect of Pim1-modified CSCs in a translationally relevant large animal preclinical model of myocardial infarction (MI).

METHODS

Human cardiac stem cells (hCSCs, n = 10), hckit⁺ CSCs overexpressing Pim1 (Pim1⁺; n = 9), or placebo (n = 10) were delivered by intramyocardial injection to immunosuppressed Yorkshire swine (n = 29) 2 weeks after MI. Cardiac magnetic resonance and pressure volume loops were obtained before and after cell administration.

RESULTS

Whereas both hCSCs reduced MI size compared to placebo, Pim1⁺ cells produced a ∼3-fold greater decrease in scar mass at 8 weeks post-injection compared to hCSCs (-29.2 ± 2.7% vs. -8.4 ± 0.7%; p < 0.003). Pim1⁺ hCSCs also produced a 2-fold increase of viable mass compared to hCSCs at 8 weeks (113.7 ± 7.2% vs. 65.6 ± 6.8%; p <0.003), and a greater increase in regional contractility in both infarct and border zones (both p < 0.05). Both CSC types significantly increased ejection fraction at 4 weeks but this was only sustained in the Pim1⁺ group at 8 weeks compared to placebo. Both hCSC and Pim1⁺ hCSC treatment reduced afterload (p = 0.02 and p = 0.004, respectively). Mechanoenergetic recoupling was significantly greater in the Pim1⁺ hCSC group (p = 0.005).

CONCLUSIONS

Pim1 overexpression enhanced the effect of intramyocardial delivery of CSCs to infarcted porcine hearts. These findings provide a rationale for genetic modification of stem cells and consequent translation to clinical trials.

[Role of telocytes in the heart in health and diseases]

This review summarizes the data available in the literature on the development, structure, and function of telocytes (TCs) and their role in the heart in health and diseases. At the present time, TCs have been found in many organs of mammals and humans. TC is a small oval cell that contains a nucleus surrounded by small amounts of cytoplasm, with extremely long and thin processes named telopodias. TCs have unique ultrastructural and immunohistochemical features; double positive labeling for CD34/PDGFR-β and CD34/vimentin is suitable for their identification. The role of TCs in the heart at different study stages is the subject of debate. There are currently available data on a decline in the number of cardiac TCs in patients with various heart diseases. Relying on a number of investigations showing that TCs are present in the subepicardial stem cell niches, the authors consider a hypothesis for the key role of cardiac TCs in the regeneration and reparation of the heart.

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.

Dual roles for bone marrow-derived Sca-1 cells in cardiac function

Recruitment of stem cells from the bone marrow (BM) is an important aspect of cardiac healing that becomes inefficient with age. We investigated the role of young stem cell antigen 1 (Sca-1)-positive BM cells on the aged heart by microarray analysis after BM reconstitution. Sca-1⁺ and Sca-1^- BM cells from young green fluorescent protein (GFP)-positive mice were used to reconstitute the BM of aged mice. Myocardial infarction (MI) was induced 3 mo later. GFP⁺ cells were more abundant in the BM, blood, and heart of Sca-1⁺ mice, which corresponded to preserved cardiac function after MI. At baseline, Sca-1⁺ BM reconstitution increased cardiac expression of serum response factor, vascular endothelial growth factor A, and myogenic genes, but reduced the expression of Il-1β. After MI, inflammation was identified as a key difference between Sca-1^- and Sca-1⁺ groups, as cytokine expression and cell surface markers associated with inflammatory cells were up-regulated with Sca-1⁺ reconstitution. Mac-3 and F4/80 staining showed that the postinfarction heart was composed of a mixture of GFP⁺ (donor) macrophages, GFP^- (host) macrophages, and GFP⁺ cells that did not contribute to the macrophage population. This study demonstrates that Sca-1⁺ BM cells regulate cardiac healing though an acute inflammatory response and also before injury by stimulating formation of a beneficial cardiac niche.-Tobin, S. W., Li, S.-H., Li, J., Wu, J., Yeganeh, A., Yu, P., Weisel, R. D., Li, R.-K. Dual roles for bone marrow-derived Sca-1 cells in cardiac function.

Stem Cell Spheroids and Ex Vivo Niche Modeling: Rationalization and Scaling-Up

Improved protocols/devices for in vitro culture of 3D cell spheroids may provide essential cues for proper growth and differentiation of stem/progenitor cells (S/PCs) in their niche, allowing preservation of specific features, such as multi-lineage potential and paracrine activity. Several platforms have been employed to replicate these conditions and to generate S/PC spheroids for therapeutic applications. However, they incompletely reproduce the niche environment, with partial loss of its highly regulated network, with additional hurdles in the field of cardiac biology, due to debated resident S/PCs therapeutic potential and clinical translation. In this contribution, the essential niche conditions (metabolic, geometric, mechanical) that allow S/PCs maintenance/commitment will be discussed. In particular, we will focus on both existing bioreactor-based platforms for the culture of S/PC as spheroids, and on possible criteria for the scaling-up of niche-like spheroids, which could be envisaged as promising tools for personalized cardiac regenerative medicine, as well as for high-throughput drug screening.

Interactions of human embryonic stem cell-derived cardiovascular progenitor cells with immobilized extracellular matrix proteins

Human embryonic stem cell-derived cardiovascular progenitor cells (hESC-CVPCs) hold great promise for cell-based therapies of heart diseases. However, little is known about their niche microenvironment and in particular the required extracellular matrix (ECM) components. Here we screened combinations of surface-immobilized ECM proteins to identify substrates that support the attachment and survival of hESC-CVPCs. Covalent immobilization of ECM proteins laminin (Lm), fibronectin (Fn), collagen I (CI), collagen III (CIII), and collagen IV (CIV) in multiple combinations and concentrations was achieved by reductive amination on transparent acetaldehyde plasma polymer (AAPP) interlayer coatings. We identified that CI, CIII, CIV, and Fn and their combinations were important for hESC-CVPC attachment and survival, while Lm was dispensable. Moreover, for coatings displaying single ECM proteins, CI and CIII performed better than CIV and Fn, while coatings displaying the combined ECM proteins CIII + CIV and Fn + CIII + CIV at 100 µg/mL were comparable to Matrigel in regard to supporting hESC-CVPC attachment and viability. Our results identify ECM proteins required for hESC-CVPCs and demonstrate that coatings displaying multiple immobilized ECM proteins offer a suitable microenvironment for the attachment and survival of hESC-CVPCs. This knowledge contributes to the development of approaches for maintaining hESC-CVPCs and therefore to advances in cardiovascular regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1094-1104, 2017.

Cardiac Mechanoperception: A Life-Long Story from Early Beats to Aging and Failure

The life-long story of the heart starts concomitantly with primary differentiation events occurring in multipotent progenitors located in the so-called heart tube. This initially tubular structure starts a looping process, which leads to formation of the final four-chambered heart with a primary contribution of geometric and position-associated cell sensing. While this establishes the correct patterning of the final cardiac structure, it also provides feedbacks to fundamental cellular machineries controlling proliferation and differentiation, thus ensuring a coordinated restriction of cell growth and a myocyte terminal differentiation. Novel evidences provided by embryological and cell engineering studies have clarified the relevance of mechanics-supported position sensing for the correct recognition of cell fate inside developing embryos and multicellular aggregates. One of the main components of this pathway, the Hippo-dependent signal transduction machinery, is responsible for cell mechanics intracellular transduction with important consequences for gene transcription and cell growth control. Being the Hippo pathway also directly connected to stress responses and altered metabolism, it is tempting to speculate that permanent alterations of mechanosensing may account for modifying self-renewal control in tissue homeostasis. In the present contribution, we translate these concepts to the aging process and the failing of the human heart, two pathophysiologic conditions that are strongly affected by stress responses and altered metabolism.

Β-blockers treatment of cardiac surgery patients enhances isolation and improves phenotype of cardiosphere-derived cells

Β-blockers (BB) are a primary treatment for chronic heart disease (CHD), resulting in prognostic and symptomatic benefits. Cardiac cell therapy represents a promising regenerative treatment and, for autologous cell therapy, the patients clinical history may correlate with the biology of resident progenitors and the quality of the final cell product. This study aimed at uncovering correlations between clinical records of biopsy-donor CHD patients undergoing cardiac surgery and the corresponding yield and phenotype of cardiospheres (CSs) and CS-derived cells (CDCs), which are a clinically relevant population for cell therapy, containing progenitors. We describe a statistically significant association between BB therapy and improved CSs yield and CDCs phenotype. We show that BB-CDCs have a reduced fibrotic-like CD90 + subpopulation, with reduced expression of collagen-I and increased expression of cardiac genes, compared to CDCs from non-BB donors. Moreover BB-CDCs had a distinctive microRNA expression profile, consistent with reduced fibrotic features (miR-21, miR-29a/b/c downregulation), and enhanced regenerative potential (miR-1, miR-133, miR-101 upregulation) compared to non-BB. In vitro adrenergic pharmacological treatments confirmed cytoprotective and anti-fibrotic effects of β1-blocker on CDCs. This study shows anti-fibrotic and pro-commitment effects of BB treatment on endogenous cardiac reparative cells, and suggests adjuvant roles of β-blockers in cell therapy applications.