Cardiac explant-derived cells are regulated by Notch-modulated mesenchymal transition

Isolation, growth kinetics, and immunophenotypic characterization of adult human cardiac progenitor cells

The discovery of cardiac progenitor cells (CPCs) has raised expectations for the development of cell-based therapy of the heart. Although cell therapy is emerging as a novel treatment for heart failure, several issues still exist concerning an unambiguous definition of the phenotype of CPC types. There is a need to define and validate the methods for the generation of quality CPC populations used in cell therapy applications. Considering the critical roles of cardiac cell progenitors in cellular therapy, we speculate that long term culture might modulate the immunophenotypes of CPCs. Hence, a strategy to validate the isolation and cell culture expansion of cardiac cell populations was devised. Isolation of three subpopulations of human CPCs was done from a single tissue sample using explant, enzymatic isolation, and c-kit⁺ immunomagnetic sorting methods. The study assessed the effects of ex vivo expansion on proliferation, immunophenotypes, and differentiation of CPCs. Additionally, we report that an explant culture can take over 2 months to achieve similar cell yields, and cell sorting requires a much larger starting population to match this expansion time frame. In comparison, an enzymatic method is expected to yield equivalent quantities of CPCs in 2-3 weeks, notably at a significantly lower cost, which may intensify their use in therapeutic approaches. We determined that ex vivo expansion caused changes in cellular characteristics, and hence propose validated molecular signatures should be established to evaluate the impact of ex vivo expansion for a safe cell therapy product.

Mybl2 rejuvenates heart explant-derived cells from aged donors after myocardial infarction

While cell therapy is emerging as a promising option for patients with ischemic cardiomyopathy (ICM), the influence of advanced donor age and a history of ischemic injury on the reparative performance of these cells are not well defined. As such, intrinsic changes that result from advanced donor age and ischemia are explored in hopes of identifying a molecular candidate capable of restoring the lost reparative potency of heart explant‐derived cells (EDCs) used in cell therapy. EDCs were cultured from myocardial biopsies obtained from young or old mice 4 weeks after randomization to experimental myocardial infarction or no intervention. Advanced donor age reduces cell yield while increasing cell senescence and the secretion of senescence‐associated cytokines. A history of ischemic injury magnifies these effects as cells are more senescent and have lower antioxidant reserves. Consistent with these effects, intramyocardial injection of EDCs from aged ischemic donors provided less cell‐mediated cardiac repair. A transcriptome comparison of ICM EDCs shows aging modifies many of the pathways responsible for effective cell cycle control and DNA damage/repair. Over‐expression of the barely explored antisenescent transcription factor, Mybl2, in EDCs from aged ICM donors reduces cell senescence while conferring salutary effects on antioxidant activity and paracrine production. In vivo, we observed an increase in cell retention and vasculogenesis after treatment with Mybl2‐over‐expressing EDCs which improved heart function in infarcted recipient hearts. In conclusion, Mybl2 over‐expression rejuvenates senescent EDCs sourced from aged ICM donors to confer cell‐mediated effects comparable to cells from young nonischemic donors.

[Perspectives of cell therapy for myocardial infarction and heart failure based on cardiosphere cells]

Cardiovascular diseases are the leading cause of morbidity and mortality worldwide. In recent years, researchers are attracted to the use of cell therapy based on stem cell and progenitor cells, which has been a promising strategy for cardiac repair after injury. However, conducted research using intracoronary or intramyocardial transplantation of various types of stem/progenitor cells as a cell suspension showed modest efficiency. This is due to the low degree of integration and cell survival after transplantation. To overcome these limitations, the concept of the use of multicellular spheroids modeling the natural microenvironment of cells has been proposed, which allows maintaining their viability and therapeutic properties. It is of great interest to use so-called cardial spheroids (cardiospheres) spontaneously forming three-dimensional structures under low-adhesive conditions, consisting of a heterogeneous population of myocardial progenitor cells and extracellular matrix proteins. This review presents data on methods for creating cardiospheres, directed regulation of their properties and reparative potential, as well as the results of preclinical and clinical studies on their use for the treatment of heart diseases.

Skip is essential for Notch signaling to induce Sox2 in cerebral arteriovenous malformations

Notch signaling and Sry-box (Sox) family transcriptional factors both play critical roles in endothelial cell (EC) differentiation in vascularization. Recent studies have shown that excessive Notch signaling induces Sox2 to cause cerebral arteriovenous malformations (AVMs). Here, we examine human pulmonary AVMs and find no induction of Sox2. Results of epigenetic studies also show less alteration of Sox2-DNA binding in pulmonary AVMs than in cerebral AVMs. We identify high expression of ski-interacting protein (Skip) in brain ECs, a Notch-associated chromatin-modifying protein that is lacking in lung ECs. Knockdown of Skip abolished Notch-induction of Sox2 in brain ECs, while restoration of Skip in lung ECs enabled Notch-mediated Sox2 induction. The results suggest that Skip is a key factor for induction of Sox2 in cerebral AVMs.

Crosstalk between BMP and Notch Induces Sox2 in Cerebral Endothelial Cells

Bone morphogenetic protein (BMP) and Notch signaling are critical for endothelial cell (EC) differentiation in vascular development. Recent studies have shown that excess BMP activity induces Notch signaling in cerebral ECs resulting in arteriovenous malformation (AVMs). However, it is unclear how the crosstalk between BMP and Notch signaling affects cerebral EC differentiation at the gene regulatory level. Here, we report that BMP6 activates the activin receptor-like kinase (ALK) 3, a BMP type 1 receptor, to induce Notch1 receptor and Jagged1 and Jagged2 ligands. We show that increased expression of the Notch components alters the transcriptional regulatory complex in the SRY-Box 2 (Sox2) promoter region so as to induce its expression in cerebral ECs. Together, our results identify Sox2 as a direct target of BMP and Notch signaling and provide information on how altered BMP and Notch signaling affects the endothelial transcriptional landscape.

Cardiac repair by epicardial EMT: Current targets and a potential role for the primary cilium

Despite therapeutic advances that have prolonged life, myocardial infarction (MI) remains a leading cause of death worldwide and imparts a significant economic burden. The advancement of treatments to improve cardiac repair post-MI requires the discovery of new targeted treatment strategies. Recent studies have highlighted the importance of the epicardial covering of the heart in both cardiac development and lower vertebrate cardiac regeneration. The epicardium serves as a source of cardiac cells including smooth muscle cells, endothelial cells and cardiac fibroblasts. Mammalian adult epicardial cells are typically quiescent. However, the fetal genetic program is reactivated post-MI, and epicardial epithelial-to-mesenchymal transition (EMT) occurs as an inherent mechanism to support neovascularization and cardiac healing. Unfortunately, endogenous EMT is not enough to encourage sufficient repair. Recent developments in our understanding of the mechanisms supporting the EMT process has led to a number of studies directed at augmenting epicardial EMT post-MI. With a focus on the role of the primary cilium, this review outlines the newly demonstrated mechanisms supporting EMT, the role of epicardial EMT in cardiac development, and promising advances in augmenting epicardial EMT as potential therapeutics to support cardiac repair post-MI.

Beta2-adrenergic signaling affects the phenotype of human cardiac progenitor cells through EMT modulation

Human cardiac progenitor cells (CPCs) offer great promises to cardiac cell therapy for heart failure. Many in vivo studies have shown their therapeutic benefits, paving the way for clinical translation. The 3D model of cardiospheres (CSs) represents a unique niche-like in vitro microenvironment, which includes CPCs and supporting cells. CSs have been shown to form through a process mediated by epithelial-to-mesenchymal transition (EMT). β2-Adrenergic signaling significantly affects stem/progenitor cells activation and mobilization in multiple tissues, and crosstalk between β2-adrenergic signaling and EMT processes has been reported. In the present study, we aimed at investigating the biological response of CSs to β2-adrenergic stimuli, focusing on EMT modulation in the 3D culture system of CSs. We treated human CSs and CS-derived cells (CDCs) with the β2-blocker butoxamine (BUT), using either untreated or β2 agonist (clenbuterol) treated CDCs as control. BUT-treated CS-forming cells displayed increased migration capacity and a significant increase in their CS-forming ability, consistently associated with increased expression of EMT-related genes, such as Snai1. Moreover, long-term BUT-treated CDCs contained a lower percentage of CD90+ cells, and this feature has been previously correlated with higher cardiogenic and therapeutic potential of the CDCs population. In addition, long-term BUT-treated CDCs had an increased ratio of collagen-III/collagen-I gene expression levels, and showed decreased release of inflammatory cytokines, overall supporting a less fibrosis-prone phenotype. In conclusion, β2 adrenergic receptor block positively affected the stemness vs commitment balance within CSs through the modulation of type1-EMT (so called "developmental"). These results further highlight type-1 EMT to be a key process affecting the features of resident cardiac progenitor cells, and mediating their response to the microenvironment.

Exosomal clusterin, identified in the pericardial fluid, improves myocardial performance following MI through epicardial activation, enhanced arteriogenesis and reduced apoptosis

BACKGROUND

We recently demonstrated that epicardial progenitor cells participate in the regenerative response to myocardial infarction (MI) and factors released in the pericardial fluid (PF) may play a key role in this process. Exosomes are secreted nanovesicles of endocytic origin, identified in most body fluids, which may contain molecules able to modulate a variety of cell functions. Here, we investigated whether exosomes are present in the PF and their potential role in cardiac repair.

METHODS AND RESULTS

Early gene expression studies in 3day-infarcted mouse hearts showed that PF induces epithelial-to-mesenchymal transition (EMT) in epicardial cells. Exosomes were identified in PFs from non-infarcted patients (PFC) and patients with acute MI (PFMI). A shotgun proteomics analysis identified clusterin in exosomes isolated from PFMI but not from PFC. Notably, clusterin has a protective effect on cardiomyocytes after acute MI in vivo and is an important mediator of TGFβ-induced. Clusterin addition to the pericardial sac determined an increase in epicardial cells expressing the EMT marker α-SMA and, interestingly, an increase in the number of epicardial cells ckit(+)/α-SMA(+), 7days following MI. Importantly, clusterin treatment enhanced arteriolar length density and lowered apoptotic rates in the peri-infarct area. Hemodynamic studies demonstrated an improvement in cardiac function in clusterin-treated compared to untreated infarcted hearts.

CONCLUSIONS

Exosomes are present and detectable in the PFs. Clusterin was identified in PFMI-exosomes and might account for an improvement in myocardial performance following MI through a framework including EMT-mediated epicardial activation, arteriogenesis and reduced cardiomyocyte apoptosis.

Generation of cardiac progenitor cells through epicardial to mesenchymal transition

The epithelial to mesenchymal transition (EMT) is a biological process that drives the formation of cells involved both in tissue repair and in pathological conditions, including tissue fibrosis and tumor metastasis by providing cancer cells with stem cell properties. Recent findings suggest that EMT is reactivated in the heart following ischemic injury. Specifically, epicardial EMT might be involved in the formation of cardiac progenitor cells (CPCs) that can differentiate into endothelial cells, smooth muscle cells, and, possibly, cardiomyocytes. The identification of mechanisms and signaling pathways governing EMT-derived CPC generation and differentiation may contribute to the development of a more efficient regenerative approach for adult heart repair. Here, we summarize key literature in the field.

Targeting pleiotropic signaling pathways to control adult cardiac stem cell fate and function

The identification of different pools of cardiac progenitor cells resident in the adult mammalian heart opened a new era in heart regeneration as a means to restore the loss of functional cardiac tissue and overcome the limited availability of donor organs. Indeed, resident stem cells are believed to participate to tissue homeostasis and renewal in healthy and damaged myocardium although their actual contribution to these processes remain unclear. The poor outcome in terms of cardiac regeneration following tissue damage point out at the need for a deeper understanding of the molecular mechanisms controlling CPC behavior and fate determination before new therapeutic strategies can be developed. The regulation of cardiac resident stem cell fate and function is likely to result from the interplay between pleiotropic signaling pathways as well as tissue- and cell-specific regulators. Such a modular interaction—which has already been described in the nucleus of a number of different cells where transcriptional complexes form to activate specific gene programs—would account for the unique responses of cardiac progenitors to general and tissue-specific stimuli. The study of the molecular determinants involved in cardiac stem/progenitor cell regulatory mechanisms may shed light on the processes of cardiac homeostasis in health and disease and thus provide clues on the actual feasibility of cardiac cell therapy through tissue-specific progenitors.

Retrograde coronary vein infusion of cardiac explant-derived c-Kit+ cells improves function in ischemic heart failure

BACKGROUND

Progenitor cells isolated from cardiac explant-derived cells improve cardiac function after myocardial infarction (MI). To fully realize the therapeutic potential of these cells, it is essential to develop a safe and efficient delivery method. Therefore, the objective of this study was to determine the efficacy of our newly developed approach to retrograde coronary vein (RCV) infusion of cardiac c-Kit(+) cells in a small-animal model of congestive heart failure (CHF).

METHODS

Sprague-Dawley rats underwent experimental MI. After 21 days, cardiac explant-derived c-Kit(+) cells were delivered to both sham and CHF animals using RCV delivery. Vehicle-treated (serum-free medium) sham and CHF animals were used as controls. Cardiac function and heart tissues were evaluated 21 days post-transplantation.

RESULTS

RCV-delivered cells were retained in infarcted hearts for at least 21 days after transplantation. At 21 days post-RCV infusion, the majority of transplanted c-Kit(+)/GFP(+) cells were localized in the left ventricle. Compared with vehicle-treated CHF animals, RCV-treated rats showed a significant improvement in cardiac function. Furthermore, RCV-treated rats exhibited an increase in capillary density, a decrease in total heart collagen, and a reduction in both infarct size and cardiomyocyte hypertrophy when compared with vehicle-treated CHF rats.

CONCLUSIONS

Our study showed that the RCV infusion approach is an efficient technique for targeted cell delivery to the infarcted myocardium. Cardiac c-Kit(+) cells, delivered using RCV infusion ameliorated progression of heart failure, improved cardiac function and retarded myocardial remodeling in heart failure rats.

Resident cardiac stem cells and their role in stem cell therapies for myocardial repair

Despite advances in treatment, heart failure remains one of the top killers in Canada. This recognition motivated a new research focus to harness the fundamental repair properties of the human heart. Since then, cardiac stem cells (CSCs) have emerged as a promising cell candidate to regenerate damaged hearts. The rationale of this approach is simple with ex vivo amplification of CSCs from clinical-grade biopsies, followed by delivery to areas of injury, where they engraft and regenerate the heart. In this review we will summarize recent advances and discuss future developments in CSC-mediated cardiac repair to treat the growing number of Canadians living with and dying from heart failure.

Chronic heart failure is associated with transforming growth factor beta-dependent yield and functional decline in atrial explant-derived c-Kit+ cells

BACKGROUND

Cardiac c-Kit+ cells isolated from cardiac explant-derived cells modestly improve cardiac functions after myocardial infarction; however, their full potential has not yet been realized. For instance, the majority of potential candidates for cell therapy suffer from chronic heart failure (CHF), and it is unclear how this disease affects the explant-derived progenitor cells. Therefore, the objective of this study was to determine the effect of CHF on the number and phenotype of cardiac explant c-Kit+ progenitors and elucidate mechanisms of their regulation.

METHODS AND RESULTS

Myocardial infarction was created by left anterior descending coronary artery occlusion. Sham-operated animals were used as a control group. CHF-developed infarcted animals were selected on the basis of left ventricle end-diastolic pressure ≥ 20 mm Hg and scar size ≥ 30%. Here, we found that CHF atrial explants produced less c-Kit+ cells than sham explants. CHF-derived c-Kit+ cells exhibited upregulated transforming growth factor-β (TGF-β) signaling, increased level of epithelial to mesenchymal transition markers, and diminished expression of pluripotency markers compared with shams. We show that intervention with TGF-β signaling by inhibiting TGF-β receptor type I or Smad 2/3 using small-molecule inhibitors improved c-Kit+ cell yield, attenuated epithelial to mesenchymal transition markers, stimulated the pluripotency marker Nanog, and improved efficiency of c-Kit+ cell differentiation toward cardiomyocyte-like cells in vitro.

CONCLUSIONS

Taken together, our findings suggest that TGF-β inhibition positively modulates c-Kit+ cell phenotype and function in vitro, and this strategy may be considered in optimizing cardiac progenitor function and cell expansion protocols for clinical application.

Isolation and culture of neonatal mouse cardiomyocytes

Cultured neonatal cardiomyocytes have long been used to study myofibrillogenesis and myofibrillar functions. Cultured cardiomyocytes allow for easy investigation and manipulation of biochemical pathways, and their effect on the biomechanical properties of spontaneously beating cardiomyocytes. The following 2-day protocol describes the isolation and culture of neonatal mouse cardiomyocytes. We show how to easily dissect hearts from neonates, dissociate the cardiac tissue and enrich cardiomyocytes from the cardiac cell-population. We discuss the usage of different enzyme mixes for cell-dissociation, and their effects on cell-viability. The isolated cardiomyocytes can be subsequently used for a variety of morphological, electrophysiological, biochemical, cell-biological or biomechanical assays. We optimized the protocol for robustness and reproducibility, by using only commercially available solutions and enzyme mixes that show little lot-to-lot variability. We also address common problems associated with the isolation and culture of cardiomyocytes, and offer a variety of options for the optimization of isolation and culture conditions.