Human blood and cardiac stem cells synergize to enhance cardiac repair when cotransplanted into ischemic myocardium

An infusible biologically active adhesive for chemotherapy-related heart failure in elderly rats

Chemotherapy-induced cardiotoxicity with subsequent heart failure (HF) is a major cause of morbidity and mortality in cancer survivors worldwide. Chemotherapy-induced HF is exceptionally challenging as it generally manifests in patients who are typically not eligible for left ventricular device implantation or heart transplantation. To explore alternative treatment strategies for cancer survivors suffering from chemotherapy-induced HF, we developed a minimally invasive infusible cardiac stromal cell secretomes adhesive (MISA) that could be delivered locally through an endoscope-guided intrapericardial injection. To mimic the typical clinical presentation of chemotherapy-induced HF in elder patients, we established an aged rat model in which restrictive cardiomyopathy with sequential HF was induced via consecutive doxorubicin injections. In vitro, we prove that MISA not only enhanced cardiomyocytes proliferation potency and viability, but also inhibited their apoptosis. In vivo, we prove that MISA improved the ventricular contractility indexes and led to beneficial effects on histological and structural features of restrictive cardiomyopathy via promoting cardiomyocyte proliferation, angiogenesis, and mitochondrial respiration. Additionally, we also evaluated the safety and feasibility of MISA intrapericardial delivery in a healthy porcine model with an intact immune system. In general, our data indicates that MISA has a strong potential for translation into large animal models and ultimately clinical applications for chemotherapy-induced HF prior to the final option of heart transplantation.

Atrial Fibrosis and Inflammation in Postoperative Atrial Fibrillation: Comparative Effects of Amiodarone, Colchicine, or Exosomes

BACKGROUND

Extracellular vesicles (EVs) isolated from human heart-derived cells have shown promise in suppressing inflammation and fibroblast proliferation. However, their precise benefits in atrial fibrillation (AF) prevention and the role of their antifibrotic/anti-inflammatory properties remain unclear.

OBJECTIVES

The purpose of this study was to conduct a head-to-head comparison of antiarrhythmic strategies to prevent postoperative AF using a rat model of sterile pericarditis. Specifically, we aimed to assess the efficacy of amiodarone (a classic antiarrhythmic drug), colchicine (an anti-inflammatory agent), and EVs derived from human heart-derived cells, which possess anti-inflammatory and antifibrotic properties, on AF induction, inflammation, and fibrosis progression.

METHODS

Heart-derived cells were cultured from human atrial appendages under serum-free xenogen-free conditions. Middle-aged Sprague Dawley rats were randomized into different groups, including sham operation, sterile pericarditis with amiodarone treatment, sterile pericarditis with colchicine treatment (2 dose levels), and sterile pericarditis with intra-atrial injection of EVs or vehicle. Invasive electrophysiological testing was performed 3 days after surgery before sacrifice.

RESULTS

Sterile pericarditis increased the likelihood of inducing AF. Colchicine and EVs exhibited anti-inflammatory effects, but only EV treatment significantly reduced AF probability, whereas colchicine showed a positive trend without statistical significance. EVs and high-dose colchicine reduced atrial fibrosis by 46% ± 2% and 26% ± 2%, respectively. Amiodarone prevented AF induction but had no effect on inflammation or fibrosis.

CONCLUSIONS

In this study, both amiodarone and EVs prevented AF, whereas treatment with colchicine was ineffective. The additional anti-inflammatory and antifibrotic effects of EVs suggest their potential as a comprehensive therapeutic approach for AF prevention, surpassing the effects of amiodarone or colchicine.

Combination human umbilical cord perivascular and endothelial colony forming cell therapy for ischemic cardiac injury

Cell-based therapeutics are promising interventions to repair ischemic cardiac tissue. However, no single cell type has yet been found to be both specialized and versatile enough to heal the heart. The synergistic effects of two regenerative cell types including endothelial colony forming cells (ECFC) and first-trimester human umbilical cord perivascular cells (FTM HUCPVC) with endothelial cell and pericyte properties respectively, on angiogenic and regenerative properties were tested in a rat model of myocardial infarction (MI), in vitro tube formation and Matrigel plug assay. The combination of FTM HUCPVCs and ECFCs synergistically reduced fibrosis and cardiomyocyte apoptosis, while promoting favorable cardiac remodeling and contractility. These effects were in part mediated by ANGPT2, PDGF-β, and VEGF-C. PDGF-β signaling-dependent synergistic effects on angiogenesis were also observed in vitro and in vivo. FTM HUCPVCs and ECFCs represent a cell combination therapy for promoting and sustaining vascularization following ischemic cardiac injury.

Paracrine Factors Released by Stem Cells of Mesenchymal Origin and their Effects in Cardiovascular Disease: A Systematic Review of Pre-clinical Studies

Mesenchymal stem cell (MSC) therapy has gained significant traction in the context of cardiovascular repair, and have been proposed to exert their regenerative effects via the secretion of paracrine factors. In this systematic review, we examined the literature and consolidated available evidence for the "paracrine hypothesis". Two Ovid SP databases were searched using a strategy encompassing paracrine mediated MSC therapy in the context of ischemic heart disease. This yielded 86 articles which met the selection criteria for inclusion in this study. We found that the MSCs utilized in these articles were primarily derived from bone marrow, cardiac tissue, and adipose tissue. We identified 234 individual protective factors across these studies, including VEGF, HGF, and FGF2; which are proposed to exert their effects in a paracrine manner. The data collated in this systematic review identifies secreted paracrine factors that could decrease apoptosis, and increase angiogenesis, cell proliferation, and cell viability. These included studies have also demonstrated that the administration of MSCs and indirectly, their secreted factors can reduce infarct size, and improve left ventricular ejection fraction, contractility, compliance, and vessel density. Furthering our understanding of the way these factors mediate repair could lead to the identification of therapeutic targets for cardiac regeneration.

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.

Combined meta-analysis of preclinical cell therapy studies shows overlapping effect modifiers for multiple diseases

Introduction

Cell therapy has been studied in many different research domains. Cellular replacement of damaged solid tissues is at an early stage of development, with much still to be understood. Systematic reviews and meta-analyses are widely used to aggregate data and find important patterns of results within research domains.

We set out to find common biological denominators affecting efficacy in preclinical cell therapy studies for renal, neurological and cardiac disease.

Methods

We used datasets of five previously published meta-analyses investigating cell therapy in preclinical models of chronic kidney disease, spinal cord injury, stroke and ischaemic heart disease. We transformed primary outcomes to ratios of means to permit direct comparison across disease areas. Prespecified variables of interest were species, immunosuppression, cell type, cell origin, dose, delivery and timing of the cell therapy.

Results

The five datasets from 506 publications yielded data from 13 638 animals. Animal size affects therapeutic efficacy in an inverse manner. Cell type influenced efficacy in multiple datasets differently, with no clear trend for specific cell types being superior. Immunosuppression showed a negative effect in spinal cord injury and a positive effect in cardiac ischaemic models. There was a dose–dependent relationship across the different models. Pretreatment seems to be superior compared with administration after the onset of disease.

Conclusions

Preclinical cell therapy studies are affected by multiple variables, including species, immunosuppression, dose and treatment timing. These data are important when designing preclinical studies before commencing clinical trials.

Direct comparison of different therapeutic cell types susceptibility to inflammatory cytokines associated with COVID-19 acute lung injury

Background

Although 90% of infections with the novel coronavirus 2 (COVID-19) are mild, many patients progress to acute respiratory distress syndrome (ARDS) which carries a high risk of mortality. Given that this dysregulated immune response plays a key role in the pathology of COVID-19, several clinical trials are underway to evaluate the effect of immunomodulatory cell therapy on disease progression. However, little is known about the effect of ARDS associated pro-inflammatory mediators on transplanted stem cell function and survival, and any deleterious effects could undermine therapeutic efficacy. As such, we assessed the impact of inflammatory cytokines on the viability, and paracrine profile (extracellular vesicles) of bone marrow-derived mesenchymal stromal cells, heart-derived cells, and umbilical cord-derived mesenchymal stromal cells.

Methods

All cell products were manufactured and characterized to established clinical release standards by an accredited clinical cell manufacturing facility. Cytokines and Extracellular vesicles in the cell conditioned media were profiled using proteomic array and nanoparticle tracking analysis. Using a survey of the clinical literature, 6 cytotoxic cytokines implicated in the progression of COVID-19 ARDS. Flow cytometry was employed to determine receptor expression of these 6 cytokines in three cell products. Based on clinical survey and flow cytometry data, a cytokine cocktail that mimics cytokine storm seen in COVID-19 ARDS patients was designed and the impact on cytokine cocktail on viability and paracrine secretory ability of cell products were assessed using cell viability and nanoparticle tracking analysis.

Results

Flow cytometry revealed the presence of receptors for all cytokines but IL-6, which was subsequently excluded from further experimentation. Despite this widespread expression, exposure of each cell type to individual cytokines at doses tenfold greater than observed clinically or in combination at doses associated with severe ARDS did not alter cell viability or extracellular vesicle character/production in any of the 3 cell products.

Conclusions

The paracrine production and viability of the three leading cell products under clinical evaluation for the treatment of severe COVID-19 ARDS are not altered by inflammatory mediators implicated in disease progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02699-7.

Co-transplantation of Mesenchymal Stromal Cells and Induced Pluripotent Stem Cell-Derived Cardiomyocytes Improves Cardiac Function After Myocardial Damage

Induced pluripotent stem cell-derived cardiomyocytes (iPS-CMs) represent an attractive resource for cardiac regeneration. However, survival and functional integration of transplanted iPS-CM is poor and remains a major challenge for the development of effective therapies. We hypothesized that paracrine effects of co-transplanted mesenchymal stromal cells (MSCs) augment the retention and therapeutic efficacy of iPS-CM in a mouse model of myocardial infarction (MI). To test this, either iPS-CM, MSC, or both cell types were transplanted into the cryoinfarction border zone of syngeneic mice immediately after injury. Bioluminescence imaging (BLI) of iPS-CM did not confirm enhanced retention by co-application of MSC during the 28-day follow-up period. However, histological analyses of hearts 28 days after cell transplantation showed that MSC increased the fraction of animals with detectable iPS-CM by 2-fold. Cardiac MRI analyses showed that from day 14 after transplantation on, the animals that have received cells had a significantly higher left ventricular ejection fraction (LVEF) compared to the placebo group. There was no statistically significant difference in LVEF between animals transplanted only with iPS-CM or only with MSC. However, combined iPS-CM and MSC transplantation resulted in higher LVEF compared to transplantation of single-cell populations during the whole observation period. Histological analyses revealed that MSC increased the capillarization in the myocardium when transplanted alone or with iPS-CM and decreased the infarct scar area only when transplanted in combination with iPS-CM. These results indicate that co-transplantation of iPS-CM and MSC improves cardiac regeneration after cardiac damage, demonstrating the potential of combining multiple cell types for increasing the efficacy of future cardiac cell therapies.

Bidirectional relationship between cardiac extracellular matrix and cardiac cells in ischemic heart disease

Ischemic heart diseases (IHDs), including myocardial infarction and cardiomyopathies, are a leading cause of mortality and morbidity worldwide. Cardiac-derived stem and progenitor cells have shown promise as a therapeutic for IHD but are limited by poor cell survival, limited retention, and rapid washout. One mechanism to address this is to encapsulate the cells in a matrix or three-dimensional construct, so as to provide structural support and better mimic the cells' physiological microenvironment during administration. More specifically, the extracellular matrix (ECM), the native cellular support network, has been a strong candidate for this purpose. Moreover, there is a strong consensus that the ECM and its residing cells, including cardiac stem cells, have a constant interplay in response to tissue development, aging, disease progression, and repair. When externally stimulated, the cells and ECM work together to mutually maintain the local homeostasis by initially altering the ECM composition and stiffness, which in turn alters the cellular response and behavior. Given this constant interplay, understanding the mechanism of bidirectional cell-ECM interaction is essential to develop better cell implantation matrices to enhance cell engraftment and cardiac tissue repair. This review summarizes current understanding in the field, elucidating the signaling mechanisms between cardiac ECM and residing cells in response to IHD onset. Furthermore, this review highlights recent advances in native ECM-mimicking cardiac matrices as a platform for modulating cardiac cell behavior and inducing cardiac repair.

Electrophysiological engineering of heart-derived cells with calcium-dependent potassium channels improves cell therapy efficacy for cardioprotection

We have shown that calcium-activated potassium (KCa)-channels regulate fundamental progenitor-cell functions, including proliferation, but their contribution to cell-therapy effectiveness is unknown. Here, we test the participation of KCa-channels in human heart explant-derived cell (EDC) physiology and therapeutic potential. TRAM34-sensitive KCa3.1-channels, encoded by the KCNN4 gene, are exclusively expressed in therapeutically bioactive EDC subfractions and maintain a strongly polarized resting potential; whereas therapeutically inert EDCs lack KCa3.1 channels and exhibit depolarized resting potentials. Somatic gene transfer of KCNN4 results in membrane hyperpolarization and increases intracellular [Ca²⁺], which boosts cell-proliferation and the production of pro-healing cytokines/nanoparticles. Intramyocardial injection of EDCs after KCNN4-gene overexpression markedly increases the salutary effects of EDCs on cardiac function, viable myocardium and peri-infarct neovascularization in a well-established murine model of ischemic cardiomyopathy. Thus, electrophysiological engineering provides a potentially valuable strategy to improve the therapeutic value of progenitor cells for cardioprotection and possibly other indications.

Strategies to improve the function of damaged hearts with progenitor cells have stalled. Here, the authors show that gene transfer of a calcium-dependent potassium channel enhances the functional properties and ability of explant-derived cells to improve heart function after a heart attack.

Delivery of cardiovascular progenitors with biomimetic microcarriers reduces adverse ventricular remodeling in a rat model of chronic myocardial infarction

Despite tremendous progress in cell-based therapies for heart repair, many challenges still exist. To enhance the therapeutic potential of cell therapy one approach is the combination of cells with biomaterial delivery vehicles. Here, we developed a biomimetic and biodegradable micro-platform based on polymeric microparticles (MPs) capable of maximizing the therapeutic potential of cardiac progenitor cells (CPCs) and explored its efficacy in a rat model of chronic myocardial infarction. The transplantation of CPCs adhered to MPs within the infarcted myocardial microenvironment improved the long-term engraftment of transplanted cells for up to one month. Furthermore, the enhancement of cardiac cellular retention correlated with an increase in functional recovery. In consonance, better tissue remodeling and vasculogenesis were observed in the animals treated with cells attached to MPs, which presented smaller infarct size, thicker right ventricular free wall, fewer deposition of periostin and greater density of vessels than animals treated with CPCs alone. Finally, we were able to show that part of this beneficial effect was mediated by CPC-derived extracellular vesicles (EVs). Taken together, these findings indicate that the biomimetic microcarriers support stem cell survival and increase cardiac function in chronic myocardial infarction through modulation of cardiac remodeling, vasculogenesis and CPCs-EVs mediated therapeutic effects. The biomimetic microcarriers provide a solution for biomaterial-assisted CPC delivery to the heart. STATEMENT OF SIGNIFICANCE: In this study, we evaluate the possibility of using a biomimetic and biodegradable micro-platform to improve cardiovascular progenitor therapy. The strategy reported herein serves as an injectable scaffold for adherent cells due to their excellent injectability through cardiac catheters, capacity for biomimetic three-dimensional stem cell support and controllable biodegradability. In a rat model of chronic myocardial infarction, the biomimetic microcarriers improved cardiac function, reduced chronic cardiac remodeling and increased vasculogenesis through the paracrine signaling of CPCs. We have also shown that extracellular vesicles derived from CPCs cultured on biomimetic substrates display antifibrotic effects, playing an important role in the therapeutic effects of our tissue-engineered approach. Therefore, biomimetic microcarriers represent a promising and effective strategy for biomaterial-assisted CPC delivery to the heart.

Enhancing myocardial repair with CardioClusters

Cellular therapy to treat heart failure is an ongoing focus of intense research, but progress toward structural and functional recovery remains modest. Engineered augmentation of established cellular effectors overcomes impediments to enhance reparative activity. Such 'next generation' implementation includes delivery of combinatorial cell populations exerting synergistic effects. Concurrent isolation and expansion of three distinct cardiac-derived interstitial cell types from human heart tissue, previously reported by our group, prompted design of a 3D structure that maximizes cellular interaction, allows for defined cell ratios, controls size, enables injectability, and minimizes cell loss. Herein, mesenchymal stem cells (MSCs), endothelial progenitor cells (EPCs) and c-Kit⁺ cardiac interstitial cells (cCICs) when cultured together spontaneously form scaffold-free 3D microenvironments termed CardioClusters. scRNA-Seq profiling reveals CardioCluster expression of stem cell-relevant factors, adhesion/extracellular-matrix molecules, and cytokines, while maintaining a more native transcriptome similar to endogenous cardiac cells. CardioCluster intramyocardial delivery improves cell retention and capillary density with preservation of cardiomyocyte size and long-term cardiac function in a murine infarction model followed 20 weeks. CardioCluster utilization in this preclinical setting establish fundamental insights, laying the framework for optimization in cell-based therapeutics intended to mitigate cardiomyopathic damage.

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.

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

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

Physiologic expansion of human heart-derived cells enhances therapeutic repair of injured myocardium

Background

Serum-free xenogen-free defined media and continuous controlled physiological cell culture conditions have been developed for stem cell therapeutics, but the effect of these conditions on the relative potency of the cell product is unknown. As such, we conducted a head-to-head comparison of cell culture conditions on human heart explant-derived cells using established in vitro measures of cell potency and in vivo functional repair.

Methods

Heart explant-derived cells cultured from human atrial or ventricular biopsies within a serum-free xenogen-free media and a continuous physiological culture environment were compared to cells cultured under traditional (high serum) cell culture conditions in a standard clean room facility.

Results

Transitioning from traditional high serum cell culture conditions to serum-free xenogen-free conditions had no effect on cell culture yields but provided a smaller, more homogenous, cell product with only minor antigenic changes. Culture within continuous physiologic conditions markedly boosted cell proliferation while increasing the expression of stem cell-related antigens and ability of cells to stimulate angiogenesis. Intramyocardial injection of physiologic cultured cells into immunodeficient mice 1 week after coronary ligation translated into improved cardiac function and reduced scar burden which was attributable to increased production of pro-healing cytokines, extracellular vesicles, and microRNAs.

Conclusions

Continuous physiological cell culture increased cell growth, paracrine output, and treatment outcomes to provide the greatest functional benefit after experimental myocardial infarction.

Glyoxalase 1 Prevents Chronic Hyperglycemia Induced Heart-Explant Derived Cell Dysfunction

Decades of work have shown that diabetes increases the risk of heart disease and worsens clinical outcomes after myocardial infarction. Because diabetes is an absolute contraindication to heart transplant, cell therapy is increasingly being explored as a means of improving heart function for these patients with very few other options. Given that hyperglycemia promotes the generation of toxic metabolites, the influence of the key detoxification enzyme glyoxalase 1 (Glo1) on chronic hyperglycemia induced heart explant-derived cell (EDC) dysfunction was investigated.

Methods: EDCs were cultured from wild type C57Bl/6 or Glo1 over-expressing transgenic mice 2 months after treatment with the pancreatic beta cell toxin streptozotocin or vehicle. The effects of Glo1 overexpression was evaluated using in vitro and in vivo models of myocardial ischemia.

Results: Chronic hyperglycemia reduced overall culture yields and increased the reactive dicarbonyl cell burden within EDCs. These intrinsic cell changes reduced the angiogenic potential and production of pro-healing exosomes while promoting senescence and slowing proliferation. Compared to intra-myocardial injection of normoglycemic cells, chronic hyperglycemia attenuated cell-mediated improvements in myocardial function and reduced the ability of transplanted cells to promote new blood vessel and cardiomyocyte growth. In contrast, Glo1 overexpression decreased oxidative damage while restoring both cell culture yields and EDC-mediated repair of ischemic myocardium. The latter was associated with enhanced production of pro-healing extracellular vesicles by Glo1 cells without altering the pro-healing microRNA cargo within.

Conclusions: Chronic hyperglycemia decreases the regenerative performance of EDCs. Overexpression of Glo1 reduces dicarbonyl stress and prevents chronic hyperglycemia-induced dysfunction by rejuvenating the production of pro-healing extracellular vesicles.

Mixing old and young: enhancing rejuvenation and accelerating aging

Donor age and recipient age are factors that influence transplantation outcomes. Aside from age-associated differences in intrinsic graft function and alloimmune responses, the ability of young and old cells to exert either rejuvenating or aging effects extrinsically may also apply to the transplantation of hematopoietic stem cells or solid organ transplants. While the potential for rejuvenation mediated by the transfer of youthful cells is currently being explored for therapeutic applications, aspects that relate to accelerating aging are no less clinically significant. Those effects may be particularly relevant in transplantation with an age discrepancy between donor and recipient. Here, we review recent advances in understanding the mechanisms by which young and old cells modify their environments to promote rejuvenation- or aging-associated phenotypes. We discuss their relevance to clinical transplantation and highlight potential opportunities for therapeutic intervention.

Mesenchymal stem cells facilitate cardiac differentiation in Sox2-expressing cardiac C-kit cells in coculture

Stem cell therapy offers hope to reconstitute injured myocardium and salvage heart from failing. A recent approach using combinations of derived Cardiac-derived c-kit expressing cells (CCs) and mesenchymal stem cells (MSCs) in transplantation improved infarcted hearts with a greater functional outcome, but the effects of MSCs on CCs remain to be elucidated. We used a novel two-step protocol to clonogenically amplify colony forming c-kit expressing cells from 4- to 6-week-old C57BL/6N mice. This method yielded highly proliferative and clonogenic CCs with an average population doubling time of 17.2 ± 0.2, of which 80% were at the G1 phase. We identified two distinctly different CC populations based on its Sox2 expression, which was found to inversely related to their nkx2.5 and gata4 expression. To study CCs after MSC coculture, we developed micron-sized particles of iron oxide-based magnetic reisolation method to separate CCs from MSCs for subsequent analysis. Through validation using the sex and species mismatch CC-MSC coculture method, we confirmed that the purity of the reisolated cells was greater than 85%. In coculture experiment, we found that MSCs prominently enhanced Ctni and Mef2c expressions in Sox2 ^pos CCs after the induction of cardiac differentiation, and the level was higher than that of conditioned medium Sox2 ^pos CCs. However, these effects were not found in Sox2 ^neg CCs. Immunofluorescence labeling confirmed the presence of cardiac-like cells within Sox2 ^pos CCs after differentiation, identified by its cardiac troponin I and α-sarcomeric actinin expressions. In conclusion, this study shows that MSCs enhance CC differentiation toward cardiac myocytes. This enhancement is dependent on CC stemness state, which is determined by Sox2 expression.

Concise Review: Heart-Derived Cell Therapy 2.0: Paracrine Strategies to Increase Therapeutic Repair of Injured Myocardium

Despite progress in cardiovascular medicine, the incidence of heart failure is rising and represents a growing challenge. To address this, ex vivo proliferated heart-derived cell products have emerged as a promising investigational cell-treatment option. Despite being originally proposed as a straightforward myocyte replacement strategy, emerging evidence has shown that cell-mediated gains in cardiac function are leveraged on paracrine stimulation of endogenous repair and tissue salvage. In this concise review, we focus on the paracrine repertoire of heart-derived cells and outline strategies used to boost cell potency by targeting cytokines, metabolic preconditioning and supportive biomaterials. Mechanistic insights from these studies will shape future efforts to use defined factors and/or synthetic cell approaches to help the millions of patients worldwide suffering from heart failure. Stem Cells 2018;36:1794-10.

Bradykinin-mediated Ca2+ signalling regulates cell growth and mobility in human cardiac c-Kit+ progenitor cells

Our recent study showed that bradykinin increases cell cycling progression and migration of human cardiac c‐Kit⁺ progenitor cells by activating pAkt and pERK1/2 signals. This study investigated whether bradykinin‐mediated Ca²⁺ signalling participates in regulating cellular functions in cultured human cardiac c‐Kit⁺ progenitor cells using laser scanning confocal microscopy and biochemical approaches. It was found that bradykinin increased cytosolic free Ca²⁺ (Cai2+) by triggering a transient Ca²⁺ release from ER IP3Rs followed by sustained Ca²⁺ influx through store‐operated Ca²⁺ entry (SOCE) channel. Blockade of B2 receptor with HOE140 or IP3Rs with araguspongin B or silencing IP3R3 with siRNA abolished both Ca²⁺ release and Ca²⁺ influx. It is interesting to note that the bradykinin‐induced cell cycle progression and migration were not observed in cells with siRNA‐silenced IP3R3 or the SOCE component TRPC1, Orai1 or STIM1. Also the bradykinin‐induced increase in pAkt and pERK1/2 as well as cyclin D1 was reduced in these cells. These results demonstrate for the first time that bradykinin‐mediated increase in free Cai2+ via ER‐IP3R3 Ca²⁺ release followed by Ca²⁺ influx through SOCE channel plays a crucial role in regulating cell growth and migration via activating pAkt, pERK1/2 and cyclin D1 in human cardiac c‐Kit⁺ progenitor cells.

Deterministic Encapsulation of Human Cardiac Stem Cells in Variable Composition Nanoporous Gel Cocoons To Enhance Therapeutic Repair of Injured Myocardium

Although cocooning explant-derived cardiac stem cells (EDCs) in protective nanoporous gels (NPGs) prior to intramyocardial injection boosts long-term cell retention, the number of EDCs that finally engraft is trivial and unlikely to account for salutary effects on myocardial function and scar size. As such, we investigated the effect of varying the NPG content within capsules to alter the physical properties of cocoons without influencing cocoon dimensions. Increasing NPG concentration enhanced cell migration and viability while improving cell-mediated repair of injured myocardium. Given that the latter occurred with NPG content having no detectable effect on the long-term engraftment of transplanted cells, we found that changing the physical properties of cocoons prompted explant-derived cardiac stem cells to produce greater amounts of cytokines, nanovesicles, and microRNAs that boosted the generation of new blood vessels and new cardiomyocytes. Thus, by altering the physical properties of cocoons by varying NPG content, the paracrine signature of encapsulated cells can be enhanced to promote greater endogenous repair of injured myocardium.

Interleukin-6 Mediates Post-Infarct Repair by Cardiac Explant-Derived Stem Cells

Although patient-sourced cardiac explant-derived stem cells (EDCs) provide an exogenous source of new cardiomyocytes post-myocardial infarction, poor long-term engraftment indicates that the benefits seen in clinical trials are likely paracrine-mediated. Of the numerous cytokines produced by EDCs, interleukin-6 (IL-6) is the most abundant; however, its role in cardiac repair is uncertain. In this study, a custom short-hairpin oligonucleotide lentivirus was used to knockdown IL-6 in human EDCs, revealing an unexpected pro-healing role for the cytokine.

METHODS

EDCs were cultured from atrial appendages donated by patients undergoing clinically indicated cardiac surgery. The effects of lentiviral mediated knockdown of IL-6 was evaluated using in vitro and in vivo models of myocardial ischemia.

RESULTS

Silencing IL-6 in EDCs abrogated much of the benefits conferred by cell transplantation and revealed that IL-6 prompts cardiac fibroblasts and macrophages to reduce myocardial scarring while increasing the generation of new cardiomyocytes and recruitment of blood stem cells.

CONCLUSIONS

This study suggests that IL-6 plays a pivotal role in EDC-mediated cardiac repair and may provide a means of increasing cell-mediated repair of ischemic myocardium.

Cardiac Stem Cells for Myocardial Regeneration: They Are Not Alone

Heart failure is the number one killer worldwide with ~50% of patients dying within 5 years of prognosis. The discovery of stem cells, which are capable of repairing the damaged portion of the heart, has created a field of cardiac regenerative medicine, which explores various types of stem cells, either autologous or endogenous, in the hope of finding the “holy grail” stem cell candidate to slow down and reverse the disease progression. However, there are many challenges that need to be overcome in the search of such a cell candidate. The ideal cells have to survive the harsh infarcted environment, retain their phenotype upon administration, and engraft and be activated to initiate repair and regeneration in vivo. Early bench and bedside experiments mostly focused on bone marrow-derived cells; however, heart regeneration requires multiple coordinations and interactions between various cell types and the extracellular matrix to form new cardiomyocytes and vasculature. There is an observed trend that when more than one cell is coadministered and cotransplanted into infarcted animal models the degree of regeneration is enhanced, when compared to single-cell administration. This review focuses on stem cell candidates, which have also been tested in human trials, and summarizes findings that explore the interactions between various stem cells in heart regenerative therapy.

Isolation of human explant derived cardiac stem cells from cryopreserved heart tissue

The value of preserving high quality bio specimens for fundamental research is significant as linking cellular and molecular changes to clinical and epidemiological data has fueled many recent advances in medicine. Unfortunately, storage of traditional biospecimens is limited to fixed samples or isolated genetic material. Here, we report the effect of cryopreservation of routine myocardial biopsies on explant derived cardiac stem cell (EDC) culture outcomes. We demonstrate that immediate cryopreservation or delayed cryopreservation after suspension within cardioplegia for 12 hours did not alter EDC yields, proliferative capacity, antigenic phenotype or paracrine signature. Cryopreservation had negligible effects on the ability of EDCs to adopt a cardiac lineage, stimulate new vessel growth, attract circulating angiogenic cells and repair injured myocardium. Finally, cryopreservation did not influence the ability of EDCs to undergo genetic reprogramming into inducible pluripotent stem cells. This study establishes a means of storing cardiac samples as a retrievable live cell source for cardiac repair or disease modeling.

Targeting chronic cardiac remodeling with cardiac progenitor cells in a murine model of ischemia/reperfusion injury

BACKGROUND

Translational failure for cardiovascular disease is a substantial problem involving both high research costs and an ongoing lack of novel treatment modalities. Despite the progress already made, cell therapy for chronic heart failure in the clinical setting is still hampered by poor translation. We used a murine model of chronic ischemia/reperfusion injury to examine the effect of minimally invasive application of cardiac progenitor cells (CPC) in cardiac remodeling and to improve clinical translation.

METHODS

28 days after the induction of I/R injury, mice were randomized to receive either CPC (0.5 million) or vehicle by echo-guided intra-myocardial injection. To determine retention, CPC were localized in vivo by bioluminescence imaging (BLI) two days after injection. Cardiac function was assessed by 3D echocardiography and speckle tracking analysis to quantify left ventricular geometry and regional myocardial deformation.

RESULTS

BLI demonstrated successful injection of CPC (18/23), which were mainly located along the needle track in the anterior/septal wall. Although CPC treatment did not result in overall restoration of cardiac function, a relative preservation of the left ventricular end-diastolic volume was observed at 4 weeks follow-up compared to vehicle control (+5.3 ± 2.1 μl vs. +10.8 ± 1.5 μl). This difference was reflected in an increased strain rate (+16%) in CPC treated mice.

CONCLUSIONS

CPC transplantation can be adequately studied in chronic cardiac remodeling using this study set-up and by that provide a translatable murine model facilitating advances in research for new therapeutic approaches to ultimately improve therapy for chronic heart failure.

Optimizing the host substrate environment for cardiac angiogenesis, arteriogenesis, and myogenesis

INTRODUCTION

The diseased host milieu, such as endothelial dysfunction (ED), decreased NO bioavailability, and ischemic/inflammatory post-MI environment, hamper the clinical success of existing cardiac regenerative therapies. Area covered: In this article, current strategies including pharmacological and nonpharmacological approaches for improving the diseased host milieu are reviewed. Specifically, the authors provide focus on: i) the mechanism of ED in patients with cardiovascular diseases, ii) the current results of ED improving strategies in pre-clinical and clinical studies, and iii) the use of biomaterials as a novel modulator in damaged post-MI environment. Expert opinion: Adjunct therapies which improve host endothelial function have demonstrated promising outcomes, potentially overcoming disappointing results of cell therapy in human studies. In the future, elucidation of the interactions between the host tissue and therapeutic agents, as well as downstream signaling pathways, will be the next challenges in enhancing regenerative therapy. More careful investigations are also required to establish these agents' safety and efficacy for wide usage in humans.

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.

Towards the standardization of stem cell therapy studies for ischemic heart diseases: Bridging the gap between animal models and the clinical setting

Today there is an increasing demand for heart transplantations for patients diagnosed with heart failure. Though, shortage of donors as well as the large number of ineligible patients hurdle such treatment option. This, in addition to the considerable number of transplant rejections, has driven the clinical research towards the field of regenerative medicine. Nonetheless, to date, several stem cell therapies tested in animal models fall by the wayside and when they meet the criteria to clinical trials, subjects often exhibit modest improvements. A main issue slowing down the admission of such therapies in the domain of human trials is the lack of protocol standardization between research groups, which hampers comparison between different approaches as well as the lack of thought regarding the clinical translation. In this sense, given the large amount of reports on stem cell therapy studies in animal models reported in the last 3years, we sought to evaluate their advantages and limitations towards the clinical setting and provide some suggestions for the forthcoming investigations. We expect, with this review, to start a new paradigm on regenerative medicine, by evoking the debate on how to plan novel stem cell therapy studies with animal models in order to achieve more consistent scientific production and accelerate the admission of stem cell therapies in the clinical setting.

Glyoxalase-1 Overexpression Reverses Defective Proangiogenic Function of Diabetic Adipose-Derived Stem Cells in Streptozotocin-Induced Diabetic Mice Model of Critical Limb Ischemia

Adipose‐derived stem cell (ADSC)‐based therapy is promising for critical limb ischemia (CLI) treatment, especially in patients with diabetes. However, the therapeutic effects of diabetic ADSCs (D‐ADSCs) are impaired by the diabetes, possibly through intracellular reactive oxygen species (ROS) accumulation. The objective of the present study was to detect whether overexpression of methylglyoxal‐metabolizing enzyme glyoxalase‐1 (GLO1), which reduces ROS in D‐ADSCs, can restore their proangiogenic function in a streptozotocin‐induced diabetic mice model of CLI. GLO1 overexpression in D‐ADSCs (G‐D‐ADSCs) was achieved using the lentivirus method. G‐D‐ADSCs showed a significant decrease in intracellular ROS accumulation, increase in cell viability, and resistance to apoptosis under high‐glucose conditions compared with D‐ADSCs. G‐D‐ADSCs also performed better in terms of migration, differentiation, and proangiogenic capacity than D‐ADSCs in a high‐glucose environment. Notably, these properties were restored to the same level as that of nondiabetic ADSCs under high‐glucose conditions. G‐D‐ADSC transplantation induced improved reperfusion and an increased limb salvage rate compared D‐ADSCs in a diabetic mice model of CLI. Histological analysis revealed higher microvessel densities and more G‐D‐ADSC‐incorporated microvessels in the G‐D‐ADSC group than in the D‐ADSC group, which was comparable to the nondiabetic ADSC group. Higher expression of vascular endothelial growth factor A and stromal cell‐derived factor‐1α and lower expression of hypoxia‐induced factor‐1α were also detected in the ischemic muscles from the G‐D‐ADSC group than that of the D‐ADSC group. The results of the present study have demonstrated that protection from ROS accumulation by GLO1 overexpression is effective in reversing the impaired biological function of D‐ADSCs in promoting neovascularization of diabetic CLI mice model and warrants the future clinical application of D‐ADSC‐based therapy in diabetic patients. Stem Cells Translational Medicine2017;6:261–271

Thermosensitive and Highly Flexible Hydrogels Capable of Stimulating Cardiac Differentiation of Cardiosphere-Derived Cells under Static and Dynamic Mechanical Training Conditions

Cardiac stem cell therapy has been considered as a promising strategy for heart tissue regeneration. Yet achieving cardiac differentiation after stem cell transplantation remains challenging. This compromises the efficacy of current stem cell therapy. Delivery of cells using matrices that stimulate the cardiac differentiation may improve the degree of cardiac differentiation in the heart tissue. In this report, we investigated whether elastic modulus of highly flexible poly(N-isopropylamide) (PNIPAAm)-based hydrogels can be modulated to stimulate the encapsulated cardiosphere derived cells (CDCs) to differentiate into cardiac lineage under static condition and dynamic stretching that mimics the heart beating condition. We have developed hydrogels whose moduli do not change under both dynamic stretching and static conditions for 14 days. The hydrogels had the same chemical structure but different elastic moduli (11, 21, and 40 kPa). CDCs were encapsulated into these hydrogels and cultured under either native heart-mimicking dynamic stretching environment (12% strain and 1 Hz frequency) or static culture condition. CDCs were able to grow in all three hydrogels. The greatest growth was found in the hydrogel with elastic modulus of 40 kPa. The dynamic stretching condition stimulated CDC growth. The CDCs demonstrated elastic modulus-dependent cardiac differentiation under both static and dynamic stretching conditions as evidenced by gene and protein expressions of cardiac markers such as MYH6, CACNA1c, cTnI, and Connexin 43. The highest differentiation was found in the 40 kPa hydrogel. These results suggest that delivery of CDCs with the 40 kPa hydrogel may enhance cardiac differentiation in the infarct hearts.

The impact of patient co-morbidities on the regenerative capacity of cardiac explant-derived stem cells

BACKGROUND

Although patient-sourced cardiac stem cells repair damaged myocardium, the extent to which medical co-morbidities influence cardiac-derived cell products is uncertain. Therefore, we investigated the influence of atherosclerotic risk factors on the regenerative performance of human cardiac explant-derived cells (EDCs).

METHODS

In this study, the Long Term Stratification for survivors of acute coronary syndromes model was used to quantify the burden of cardiovascular risk factors within a group of patients with established atherosclerosis. EDCs were cultured from human atrial appendages and injected into immunodeficient mice 7 days post-left coronary ligation. Cytokine arrays and enzyme linked immunoassays were used to determine the release of cytokines by EDCs in vitro, and echocardiography was used to determine regenerative capabilities in vivo.

RESULTS

EDCs sourced from patients with more cardiovascular risk factors demonstrated a negative correlation with production of pro-healing cytokines (such as stromal cell derived factor 1α) and exosomes which had negative effects on the promotion of angiogenesis and chemotaxis. Reductions in exosomes and pro-healing cytokines with accumulating medical co-morbidities were associated with increases in production of the pro-inflammatory cytokine interleukin-6 (IL-6) by EDCs. Increased patient co-morbidities were also correlated with significant attenuation in improvements of left ventricular ejection fraction.

CONCLUSIONS

The regenerative performance of the earliest precursor cell population cultured from human explant tissue declines with accumulating medical co-morbidities. This effect is associated with diminished production of pro-cardiogenic cytokines and exosomes while IL-6 is markedly increased. Predictors of cardiac events demonstrated a lower capacity to support angiogenesis and repair injured myocardium in a mouse model of myocardial infarction.

Antifibrotic therapies to control cardiac fibrosis

Cardiac fibrosis occurs naturally after myocardial infarction. While the initially formed fibrotic tissue prevents the infarcted heart tissue from rupture, the progression of cardiac fibrosis continuously expands the size of fibrotic tissue and causes cardiac function decrease. Cardiac fibrosis eventually evolves the infarcted hearts into heart failure. Inhibiting cardiac fibrosis from progressing is critical to prevent heart failure. However, there is no efficient therapeutic approach currently available. Myofibroblasts are primarily responsible for cardiac fibrosis. They are formed by cardiac fibroblast differentiation, fibrocyte differentiation, epithelial to mesenchymal transdifferentiation, and endothelial to mesenchymal transition, driven by cytokines such as transforming growth factor beta (TGF-β), angiotensin II and platelet-derived growth factor (PDGF). The approaches that inhibit myofibroblast formation have been demonstrated to prevent cardiac fibrosis, including systemic delivery of antifibrotic drugs, localized delivery of biomaterials, localized delivery of biomaterials and antifibrotic drugs, and localized delivery of cells using biomaterials. This review addresses current progresses in cardiac fibrosis therapies.

Paracrine Engineering of Human Explant-Derived Cardiac Stem Cells to Over-Express Stromal-Cell Derived Factor 1α Enhances Myocardial Repair

First generation cardiac stem cell products provide indirect cardiac repair but variably produce key cardioprotective cytokines, such as stromal-cell derived factor 1α, which opens the prospect of maximizing up-front paracrine-mediated repair. The mesenchymal subpopulation within explant derived human cardiac stem cells underwent lentiviral mediated gene transfer of stromal-cell derived factor 1α. Unlike previous unsuccessful attempts to increase efficacy by boosting the paracrine signature of cardiac stem cells, cytokine profiling revealed that stromal-cell derived factor 1α over-expression prevented lv-mediated "loss of cytokines" through autocrine stimulation of CXCR4+ cardiac stem cells. Stromal-cell derived factor 1α enhanced angiogenesis and stem cell recruitment while priming cardiac stem cells to readily adopt a cardiac identity. As compared to injection with unmodified cardiac stem cells, transplant of stromal-cell derived factor 1α enhanced cells into immunodeficient mice improved myocardial function and angiogenesis while reducing scarring. Increases in myocardial stromal-cell derived factor 1α content paralleled reductions in myocyte apoptosis but did not influence long-term engraftment or the fate of transplanted cells. Transplantation of stromal-cell derived factor 1α transduced cardiac stem cells increased the generation of new myocytes, recruitment of bone marrow cells, new myocyte/vessel formation and the salvage of reversibly damaged myocardium to enhance cardiac repair after experimental infarction. Stem Cells 2016;34:1826-1835.

Electrical effects of stem cell transplantation for ischaemic cardiomyopathy: friend or foe?

Despite advances in other realms of cardiac care, the mortality attributable to ischaemic cardiomyopathy has only marginally decreased over the last 10 years. These findings highlight the growing realization that current pharmacological and device therapies rarely reverse disease progression and rationalize a focus on novel means to reverse, repair and re-vascularize damaged hearts. As such, multiple candidate cell types have been used to regenerate damaged hearts either directly (through differentiation to form new tissue) or indirectly (via paracrine effects). Emerging literature suggests that robust engraftment of electrophysiolgically heterogeneous tissue from transplanted cells comes at the cost of a high incidence of ventricular arrhythmias. Similar electrophysiological studies of haematological stem cells raised early concerns that transplant of depolarized, inexcitable cells that also induce paracrine-mediated electrophysiological remodelling may be pro-arrhythmic. However, meta-analyses suggest that patients receiving haematological stem cells paradoxically may experience a decrease in ventricular arrhythmias, an observation potentially related to the extremely poor long-term survival of injected cells. Finally, early clinical and preclinical data from technologies capable of differentiating to a mature cardiomyocyte phenotype (such as cardiac-derived stem cells) suggests that these cells are not pro-arrhythmic although they too lack robust long-term engraftment. These results highlight the growing understanding that as next generation cell therapies are developed, emphasis should also be placed on understanding possible anti-arrhythmic contributions of transplanted cells while vigilance is needed to predict and treat the inadvertent effects of regenerative cell therapies on the electrophysiological stability of the ischaemic cardiomyopathic heart.

Improving Cell Engraftment in Cardiac Stem Cell Therapy

Myocardial infarction (MI) affects millions of people worldwide. MI causes massive cardiac cell death and heart function decrease. However, heart tissue cannot effectively regenerate by itself. While stem cell therapy has been considered an effective approach for regeneration, the efficacy of cardiac stem cell therapy remains low due to inferior cell engraftment in the infarcted region. This is mainly a result of low cell retention in the tissue and poor cell survival under ischemic, immune rejection and inflammatory conditions. Various approaches have been explored to improve cell engraftment: increase of cell retention using biomaterials as cell carriers; augmentation of cell survival under ischemic conditions by preconditioning cells, genetic modification of cells, and controlled release of growth factors and oxygen; and enhancement of cell survival by protecting cells from excessive inflammation and immune surveillance. In this paper, we review current progress, advantages, disadvantages, and potential solutions of these approaches.

Roles of store-operated Ca2+ channels in regulating cell cycling and migration of human cardiac c-kit+ progenitor cells

Cardiac c-kit(+) progenitor cells are important for maintaining cardiac homeostasis and can potentially contribute to myocardial repair. However, cellular physiology of human cardiac c-kit(+) progenitor cells is not well understood. The present study investigates the functional store-operated Ca(2+) entry (SOCE) channels and the potential role in regulating cell cycling and migration using confocal microscopy, RT-PCR, Western blot, coimmunoprecipitation, cell proliferation, and migration assays. We found that SOCE channels mediated Ca(2+) influx, and TRPC1, STIM1, and Orai1 were involved in the formation of SOCE channels in human cardiac c-kit(+) progenitor cells. Silencing TRPC1, STIM1, or Orai1 with the corresponding siRNA significantly reduced the Ca(2+) signaling through SOCE channels, decreased cell proliferation and migration, and reduced expression of cyclin D1, cyclin E, and/or p-Akt. Our results demonstrate the novel information that Ca(2+) signaling through SOCE channels regulates cell cycling and migration via activating cyclin D1, cyclin E, and/or p-Akt in human cardiac c-kit(+) cells.

Paracrine Engineering of Human Cardiac Stem Cells With Insulin-Like Growth Factor 1 Enhances Myocardial Repair

BACKGROUND

Insulin-like growth factor 1 (IGF-1) activates prosurvival pathways and improves postischemic cardiac function, but this key cytokine is not robustly expressed by cultured human cardiac stem cells. We explored the influence of an enhanced IGF-1 paracrine signature on explant-derived cardiac stem cell-mediated cardiac repair.

METHODS AND RESULTS

Receptor profiling demonstrated that IGF-1 receptor expression was increased in the infarct border zones of experimentally infarcted mice by 1 week after myocardial infarction. Human explant-derived cells underwent somatic gene transfer to overexpress human IGF-1 or the green fluorescent protein reporter alone. After culture in hypoxic reduced-serum media, overexpression of IGF-1 enhanced proliferation and expression of prosurvival transcripts and prosurvival proteins and decreased expression of apoptotic markers in both explant-derived cells and cocultured neonatal rat ventricular cardiomyocytes. Transplant of explant-derived cells genetically engineered to overexpress IGF-1 into immunodeficient mice 1 week after infarction boosted IGF-1 content within infarcted tissue and long-term engraftment of transplanted cells while reducing apoptosis and long-term myocardial scarring.

CONCLUSIONS

Paracrine engineering of explant-derived cells to overexpress IGF-1 provided a targeted means of improving cardiac stem cell-mediated repair by enhancing the long-term survival of transplanted cells and surrounding myocardium.

Contemporary perspective on endogenous myocardial regeneration

Considering the complex nature of the adult heart, it is no wonder that innate regenerative processes, while maintaining adequate cardiac function, fall short in myocardial jeopardy. In spite of these enchaining limitations, cardiac rejuvenation occurs as well as restricted regeneration. In this review, the background as well as potential mechanisms of endogenous myocardial regeneration are summarized. We present and analyze the available evidence in three subsequent steps. First, we examine the experimental research data that provide insights into the mechanisms and origins of the replicating cardiac myocytes, including cell populations referred to as cardiac progenitor cells (i.e., c-kit+ cells). Second, we describe the role of clinical settings such as acute or chronic myocardial ischemia, as initiators of pathways of endogenous myocardial regeneration. Third, the hitherto conducted clinical studies that examined different approaches of initiating endogenous myocardial regeneration in failing human hearts are analyzed. In conclusion, we present the evidence in support of the notion that regaining cardiac function beyond cellular replacement of dysfunctional myocardium via initiation of innate regenerative pathways could create a new perspective and a paradigm change in heart failure therapeutics. Reinitiating cardiac morphogenesis by reintroducing developmental pathways in the adult failing heart might provide a feasible way of tissue regeneration. Based on our hypothesis “embryonic recall”, we present first supporting evidence on regenerative impulses in the myocardium, as induced by developmental processes.

Agonists of growth hormone-releasing hormone stimulate self-renewal of cardiac stem cells and promote their survival

The beneficial effects of agonists of growth hormone-releasing hormone receptor (GHRH-R) in heart failure models are associated with an increase in the number of ckit(+) cardiac stem cells (CSCs). The goal of the present study was to determine the presence of GHRH-R in CSCs, the effect of GHRH-R agonists on their proliferation and survival, and the mechanisms involved. We investigated the expression of GHRH-R in CSCs of different species and the effect of GHRH-R agonists on their cell proliferation and survival. GHRH-R is expressed in ckit(+) CSCs isolated from mouse, rat, and pig. Treatment of porcine CSCs with the GHRH-R agonist JI-38 significantly increased the rate of cell division. Similar results were observed with other GHRH-R agonists, MR-356 and MR-409. JI-38 exerted a protective effect on survival of porcine CSCs under conditions of oxidative stress induced by exposure to hydrogen peroxide. Treatment with JI-38 before exposure to peroxide significantly reduced cell death. A similar effect was observed with MR-356. Addition of GHRH-R agonists to porcine CSCs induced activation of ERK and AKT pathways as determined by increased expression of phospho-ERK and phospho-AKT. Inhibitors of ERK and AKT pathways completely reversed the effect of GHRH-R agonists on CSC proliferation. Our findings extend the observations of the expression of GHRH-R by CSCs and demonstrate that GHRH-R agonists have a direct effect on proliferation and survival of CSCs. These results support the therapeutic use of GHRH-R agonists for stimulating endogenous mechanisms for myocardial repair or for preconditioning of stem cells before transplantation.

Hyperglycemia inhibits cardiac stem cell-mediated cardiac repair and angiogenic capacity

BACKGROUND

The impact of diabetes mellitus on the cardiac regenerative potential of cardiac stem cells (CSCs) is unknown yet critical, given that individuals with diabetes mellitus may well require CSC therapy in the future. Using human and murine CSCs from diabetic cardiac tissue, we tested the hypothesis that hyperglycemic conditions impair CSC function.

METHODS AND RESULTS

CSCs cultured from the cardiac biopsies of patients with diabetes mellitus (hemoglobin A1c, 10±2%) demonstrated reduced overall cell numbers compared with nondiabetic sourced biopsies (P=0.04). When injected into the infarct border zone of immunodeficient mice 1 week after myocardial infarction, CSCs from patients with diabetes mellitus demonstrated reduced cardiac repair compared with nondiabetic patients. Conditioned medium from CSCs of patients with diabetes mellitus displayed a reduced ability to promote in vitro blood vessel formation (P=0.02). Similarly, conditioned medium from CSCs cultured from the cardiac biopsies of streptozotocin-induced diabetic mice displayed impaired angiogenic capacity (P=0.0008). Somatic gene transfer of the methylglyoxal detoxification enzyme, glyoxalase-1, restored the angiogenic capacity of diabetic CSCs (diabetic transgenic versus nondiabetic transgenic; P=0.8). Culture of nondiabetic murine cardiac biopsies under high (25 mmol/L) glucose conditions reduced CSC yield (P=0.003), impaired angiogenic (P=0.02) and chemotactic (P=0.003) response, and reduced CSC-mediated cardiac repair (P<0.05).

CONCLUSIONS

Diabetes mellitus reduces the ability of CSCs to repair injured myocardium. Both diabetes mellitus and preconditioning CSCs in high glucose attenuated the proangiogenic capacity of CSCs. Increased expression of glyoxalase-1 restored the proangiogenic capacity of diabetic CSCs, suggesting a means of reversing diabetic CSC dysfunction by interfering with the accumulation of reactive dicarbonyls.

Quantitative assessment of barriers to the clinical development and adoption of cellular therapies: A pilot study

There has been a large increase in basic science activity in cell therapy and a growing portfolio of cell therapy trials. However, the number of industry products available for widespread clinical use does not match this magnitude of activity. We hypothesize that the paucity of engagement with the clinical community is a key contributor to the lack of commercially successful cell therapy products. To investigate this, we launched a pilot study to survey clinicians from five specialities and to determine what they believe to be the most significant barriers to cellular therapy clinical development and adoption. Our study shows that the main concerns among this group are cost-effectiveness, efficacy, reimbursement, and regulation. Addressing these concerns can best be achieved by ensuring that future clinical trials are conducted to adequately answer the questions of both regulators and the broader clinical community.

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.