Survival, integration, and differentiation of cardiomyocyte grafts: a study in normal and injured rat hearts

Bioengineering Approaches to Mature Human Pluripotent Stem Cell-Derived Cardiomyocytes

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CM) represent a potential unlimited cell supply for cardiac tissue engineering and possibly regenerative medicine applications. However, hPSC-CMs produced by current protocols are not representative of native adult human cardiomyocytes as they display immature gene expression profile, structure and function. In order to improve hPSC-CM maturity and function, various approaches have been developed, including genetic manipulations to induce gene expression, delivery of biochemical factors, such as triiodothyronine and alpha-adrenergic agonist phenylephrine, induction of cell alignment in 3D tissues, mechanical stress as a mimic of cardiac load and electrical stimulation/pacing or a combination of these. In this mini review, we discuss biomimetic strategies for the maturation for hPSC-CMs with a particular focus on electromechanical conditioning methods.

In Vivo Maturation of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes in Neonatal and Adult Rat Hearts

We hypothesized that the neonatal rat heart would bring transplanted human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to maturity as it grows to adult size. In neonatal rat heart, engrafted hiPSC derivatives developed partially matured myofibrils after 3 months, with increasing cell size and sarcomere length. There was no difference between grafts from hiPSC-CMs or hiPSC-derived cardiac progenitors (hiPSC-CPs) at 3 months, nor was maturation influenced by infarction. Interestingly, the infarcted adult heart induced greater human cardiomyocyte hypertrophy and induction of cardiac troponin I expression than the neonatal heart. Although human cardiomyocytes at all time points were significantly smaller than the host rat cardiomyocytes, transplanted neonatal rat cardiomyocytes reached adult size and structure by 3 months. Thus, the adult rat heart induces faster maturation than the neonatal heart, and human cardiomyocytes mature more slowly than rat cardiomyocytes. The slower maturation of human cardiomyocytes could be related to environmental mismatch or cell-autonomous factors.

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HiPSC-CMs and hiPSC-CPs can engraft and partially mature in neonatal rat hearts

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There is greater maturation of hiPSC-CMs in adult rat hearts than in neonates

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Engrafted rat cardiomyocytes reached adult size by 3 months in growing rat hearts

Dexmedetomidine Protects Cardiomyocytes against Hypoxia/Reoxygenation Injury by Suppressing TLR4-MyD88-NF-κB Signaling

OBJECTIVE

We previously reported that dexmedetomidine (DEX) offers cardioprotection against ischemia/reperfusion injury in rats. Here, we evaluated the role of toll-like receptors 4- (TLR4-) myeloid differentiation primary response 88- (MyD88-) nuclear factor-kappa B (NF-κB) signaling in DEX-mediated protection of cardiomyocytes using in vitro models of hypoxia/reoxygenation (H/R).

METHODS

The experiments were carried out in H9C2 cells and in primary neonatal rat cardiomyocytes. Cells pretreated with vehicle or DEX were exposed to hypoxia for 1 h followed by reoxygenation for 12 h. We analyzed cell viability and lactate dehydrogenase (LDH) activity and measured tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β mRNA levels, TLR4, MyD88, and nuclear NF-κB p65 protein expression and NF-κB p65 nuclear localization. TLR4 knock-down by TLR4 siRNA transfection and overexpression by TLR4 DNA transfection were used to further confirm our findings.

RESULTS

DEX protected against H/R-induced cell damage and inflammation, as evidenced by increased cell survival rates, decreased LDH activity, and decreased TNF-α, IL-6, and IL-1β mRNA levels, as well as TLR4 and NF-κB protein expression. TLR4 knock-down partially prevented cell damage following H/R injury, while overexpression of TLR4 abolished the DEX-mediated protective effects.

CONCLUSIONS

DEX pretreatment protects rat cardiomyocytes against H/R injury. This effect is partly mediated by TLR4 suppression via TLR4-MyD88-NF-κB signaling.

(-)-Epigallocatechin-3-gallate alleviates doxorubicin-induced cardiotoxicity in sarcoma 180 tumor-bearing mice

AIMS

(-)-Epigallocatechin-3-gallate (EGCG), a major green tea polyphenol compound, plays an important role in the prevention of cardiovascular disease and cancer. The present study aimed to investigate the effects of EGCG on doxorubicin (DOX)-induced cardiotoxicity in Sarcoma 180 (S180) tumor-bearing mice.

MAIN METHODS

S180 tumor-bearing mice were established by subcutaneous inoculation of S180 cells attached to the axillary region. The extent of myocardial injury was accessed by the amount of lactate dehydrogenase (LDH) released in serum. Heart tissue was morphologically studied with transmission electron microscopy. Apoptosis, reactive oxygen species (ROS) generation, mitochondrial membrane potential (ΔѰm) as well as calcium concentration were measured by flow cytometric analysis. Expression levels of manganese superoxide dismutase (MnSOD) were analyzed by Western blot.

KEY FINDINGS

Results showed that the combination with EGCG and DOX significantly inhibited tumor growth and enhanced induction of apoptosis compared with DOX alone. Moreover, administration of EGCG could suppress DOX-induced cardiotoxicity as evidenced by alleviating LDH release and apoptosis in cardiomyocyte. EGCG-evoked cardioprotection was in association with the increase of ΔѰm and MnSOD expression. EGCG was also found to attenuate ROS generation and myocardial calcium overload in Sarcoma 180 tumor-bearing mice subjected to DOX.

SIGNIFICANCE

EGCG alleviated DOX-induced cardiotoxicity possibly in part mediated by increasing of MnSOD and Ѱm, reducing myocardial calcium overload and subsequently attenuating the apoptosis and LDH release. Our findings suggest that co-administration of EGCG and DOX have potential as a feasible strategy to mitigate cardiotoxicity of DOX without compromising its chemotherapeutic value.

Physiological and hypoxic oxygen concentration differentially regulates human c-Kit+ cardiac stem cell proliferation and migration

Cardiac stem cells (CSCs) are being evaluated for their efficacy in the treatment of heart failure. However, numerous factors impair the exogenously delivered cells' regenerative capabilities. Hypoxia is one stress that contributes to inadequate tissue repair. Here, we tested the hypothesis that hypoxia impairs cell proliferation, survival, and migration of human CSCs relative to physiological and room air oxygen concentrations. Human endomyocardial biopsy-derived CSCs were isolated, selected for c-Kit expression, and expanded in vitro at room air (21% O2). To assess the effect on proliferation, survival, and migration, CSCs were transferred to physiological (5%) or hypoxic (0.5%) O2 concentrations. Physiological O2 levels increased proliferation (P < 0.05) but did not affect survival of CSCs. Although similar growth rates were observed in room air and hypoxia, a significant reduction of β-galactosidase activity (-4,203 fluorescent units, P < 0.05), p16 protein expression (0.58-fold, P < 0.001), and mitochondrial content (0.18-fold, P < 0.001) in hypoxia suggests that transition from high (21%) to low (0.5%) O2 reduces senescence and promotes quiescence. Furthermore, physiological O2 levels increased migration (P < 0.05) compared with room air and hypoxia, and treatment with mesenchymal stem cell-conditioned media rescued CSC migration under hypoxia to levels comparable to physiological O2 migration (2-fold, P < 0.05 relative to CSC media control). Our finding that physiological O2 concentration is optimal for in vitro parameters of CSC biology suggests that standard room air may diminish cell regenerative potential. This study provides novel insights into the modulatory effects of O2 concentration on CSC biology and has important implications for refining stem cell therapies.

Stem cell-based therapy: Improving myocardial cell delivery

Stem cell-based therapies form an exciting new class of medicine that attempt to provide the body with the building blocks required for the reconstruction of damaged organs. However, delivering cells to the correct location, while preserving their integrity and functional properties, is a complex undertaking. These challenges have led to the development of a highly dynamic interdisciplinary research field, wherein medical, biological, and chemical sciences have collaborated to develop strategies to overcome the physiological barriers imposed on the cellular therapeutics. In this respect, improving the acute retention and subsequent survival of stem cells is key to effectively increase the effect of the therapy, while proper tissue integration is imperative for stem cells to functionally replace lost cells in damaged organs. In this review, we will use the heart as an example to highlight the current knowledge of therapeutic stem cell utilization, the existing pitfalls and limitations, and the approaches that have been developed to overcome them.

Intramyocardially Transplanted Neonatal Cardiomyocytes (NCMs) Show Structural and Electrophysiological Maturation and Integration and Dose-Dependently Stabilize Function of Infarcted Rat Hearts

Cardiac cell replacement therapy is a promising therapy to improve cardiac function in heart failure. Persistence, structural and functional maturation, and integration of transplanted cardiomyocytes into recipients' hearts are crucial for a safe and efficient replacement of lost cells. We studied histology, electrophysiology, and quantity of intramyocardially transplanted rat neonatal cardiomyocytes (NCMs) and performed a detailed functional study with repeated invasive (pressure-volume catheter) and noninvasive (echocardiography) analyses of infarcted female rat hearts including pharmacological stress before and 3 weeks after intramyocardial injection of 5 × 106 (low NCM) or 25 × 106 (high NCM) syngeneic male NCMs or medium as placebo (Ctrl). Quantitative real-time polymerase chain reaction (PCR) for Y-chromosome confirmed a fivefold higher persisting male cell number in high NCM versus low NCM after 3 weeks. Sharp electrode measurements within viable slices of recipient hearts demonstrated that transplanted NCMs integrate into host myocardium and mature to an almost adult phenotype, which might be facilitated through gap junctions between host myocardium and transplanted NCMs as indicated by connexin43 in histology. Ejection fraction of recipient hearts was severely impaired after ligation of left anterior descending (LAD; pressure-volume catheter: 39.2 ± 3.6%, echocardiography: 39.9 ± 1.4%). Repeated analyses revealed a significant further decline within 3 weeks in Ctrl and a dose-dependent stabilization in cell-treated groups. Consistently, stabilized cardiac function/morphology in cell-treated groups was seen in stroke volume, cardiac output, ventricle length, and wall thickness. Our findings confirm that cardiac cell replacement is a promising therapy for ischemic heart disease since immature cardiomyocytes persist, integrate, and mature after intramyocardial transplantation, and they dose-dependently stabilize cardiac function after myocardial infarction.

Nanowires and Electrical Stimulation Synergistically Improve Functions of hiPSC Cardiac Spheroids

The advancement of human induced pluripotent stem-cell-derived cardiomyocyte (hiPSC-CM) technology has shown promising potential to provide a patient-specific, regenerative cell therapy strategy to treat cardiovascular disease. Despite the progress, the unspecific, underdeveloped phenotype of hiPSC-CMs has shown arrhythmogenic risk and limited functional improvements after transplantation. To address this, tissue engineering strategies have utilized both exogenous and endogenous stimuli to accelerate the development of hiPSC-CMs. Exogenous electrical stimulation provides a biomimetic pacemaker-like stimuli that has been shown to advance the electrical properties of tissue engineered cardiac constructs. Recently, we demonstrated that the incorporation of electrically conductive silicon nanowires to hiPSC cardiac spheroids led to advanced structural and functional development of hiPSC-CMs by improving the endogenous electrical microenvironment. Here, we reasoned that the enhanced endogenous electrical microenvironment of nanowired hiPSC cardiac spheroids would synergize with exogenous electrical stimulation to further advance the functional development of nanowired hiPSC cardiac spheroids. For the first time, we report that the combination of nanowires and electrical stimulation enhanced cell-cell junction formation, improved development of contractile machinery, and led to a significant decrease in the spontaneous beat rate of hiPSC cardiac spheroids. The advancements made here address critical challenges for the use of hiPSC-CMs in cardiac developmental and translational research and provide an advanced cell delivery vehicle for the next generation of cardiac repair.

Remodeling an infarcted heart: novel hybrid treatment with transmyocardial revascularization and stem cell therapy

Transmyocardial revascularization (TMR) has emerged as an additional therapeutic option for patients suffering from diffuse coronary artery disease (CAD), providing immediate angina relief. Recent studies indicate that the volume of surgical cases being performed with TMR have been steadily rising, utilizing TMR as an adjunctive therapy. Therefore the purpose of this review is to provide an up-to-date appreciation of the current state of TMR and its future developmental directions on CAD treatment. The current potential of this therapy focuses on the implementation of stem cells, in order to create a synergistic angiogenic effect while increasing myocardial repair and regeneration. Although TMR procedures provide increased vascularization within the myocardium, patients suffering from ischemic cardiomyopathy may not benefit from angiogenesis alone. Therefore, the goal of introducing stem cells is to restore the functional state of a failing heart by providing these cells with a favorable microenvironment that will enhance stem cell engraftment.

Rebuilding the Damaged Heart: Mesenchymal Stem Cells, Cell-Based Therapy, and Engineered Heart Tissue

Mesenchymal stem cells (MSCs) are broadly distributed cells that retain postnatal capacity for self-renewal and multilineage differentiation. MSCs evade immune detection, secrete an array of anti-inflammatory and anti-fibrotic mediators, and very importantly activate resident precursors. These properties form the basis for the strategy of clinical application of cell-based therapeutics for inflammatory and fibrotic conditions. In cardiovascular medicine, administration of autologous or allogeneic MSCs in patients with ischemic and nonischemic cardiomyopathy holds significant promise. Numerous preclinical studies of ischemic and nonischemic cardiomyopathy employing MSC-based therapy have demonstrated that the properties of reducing fibrosis, stimulating angiogenesis, and cardiomyogenesis have led to improvements in the structure and function of remodeled ventricles. Further attempts have been made to augment MSCs' effects through genetic modification and cell preconditioning. Progression of MSC therapy to early clinical trials has supported their role in improving cardiac structure and function, functional capacity, and patient quality of life. Emerging data have supported larger clinical trials that have been either completed or are currently underway. Mechanistically, MSC therapy is thought to benefit the heart by stimulating innate anti-fibrotic and regenerative responses. The mechanisms of action involve paracrine signaling, cell-cell interactions, and fusion with resident cells. Trans-differentiation of MSCs to bona fide cardiomyocytes and coronary vessels is also thought to occur, although at a nonphysiological level. Recently, MSC-based tissue engineering for cardiovascular disease has been examined with quite encouraging results. This review discusses MSCs from their basic biological characteristics to their role as a promising therapeutic strategy for clinical cardiovascular disease.

Engineered cardiac micromodules for the in vitro fabrication of 3D endogenous macro-tissues

The in vitro fabrication of an endogenous cardiac muscle would have a high impact for both in vitro studies concerning cardiac tissue physiology and pathology, as well as in vivo application to potentially repair infarcted myocardium. To reach this aim, we engineered a new class of cardiac tissue precursor (CTP), specifically conceived in order to promote the synthesis and the assembly of a cardiac extracellular matrix (ECM). The CTPs were obtained by culturing a mixed cardiac cell population, composed of myocyte and non-myocyte cells, into porous gelatin microspheres in a dynamic bioreactor. By engineering the culture conditions, the CTP developed both beating properties and an endogenous immature cardiac ECM. By following a bottom-up approach, a macrotissue was fabricated by molding and packing the engineered tissue precursor in a maturation chamber. During the macrotissue formation, the tissue precursors acted as cardiac tissue depots by promoting the formation of an endogenous and interconnected cardiac network embedding the cells and the microbeads. The myocytes cell fraction pulled on ECM network and induced its compaction against the internal posts represented by the initial porous microbeads. This reciprocal interplay induced ECM consolidation without the use of external biophysical stimuli by leading to the formation of a beating and endogenous macrotissue. We have thus engineered a new class of cardiac micromodules and show its potential for the fabrication of endogenous cardiac tissue models useful for in vitro studies that involve the cardiac tissue remodeling.

Biomimetic Polymers for Cardiac Tissue Engineering

Heart failure is a morbid disorder characterized by progressive cardiomyocyte (CM) dysfunction and death. Interest in cell-based therapies is growing, but sustainability of injected CMs remains a challenge. To mitigate this, we developed an injectable biomimetic Reverse Thermal Gel (RTG) specifically engineered to support long-term CM survival. This RTG biopolymer provided a solution-based delivery vehicle of CMs, which transitioned to a gel-based matrix shortly after reaching body temperature. In this study we tested the suitability of this biopolymer to sustain CM viability. The RTG was biomolecule-functionalized with poly-l-lysine or laminin. Neonatal rat ventricular myocytes (NRVM) and adult rat ventricular myocytes (ARVM) were cultured in plain-RTG and biomolecule-functionalized-RTG both under 3-dimensional (3D) conditions. Traditional 2D biomolecule-coated dishes were used as controls. We found that the RTG-lysine stimulated NRVM to spread and form heart-like functional syncytia. Regarding cell contraction, in both RTG and RTG-lysine, beating cells were recorded after 21 days. Additionally, more than 50% (p value < 0.05; n = 5) viable ARVMs, characterized by a well-defined cardiac phenotype represented by sarcomeric cross-striations, were found in the RTG-laminin after 8 days. These results exhibit the tremendous potential of a minimally invasive CM transplantation through our designed RTG-cell therapy platform.

Embryonic cardiomyocytes can orchestrate various cell protective mechanisms to survive mitochondrial stress

Whereas adult cardiomyocytes are highly susceptible to stress, cardiomyocytes in the prenatal heart appear to be rather resistant. To investigate how embryonic cardiomyocytes respond to metabolic stress in vivo, we utilized tissue mosaicism for mitochondrial dysfunction in 13.5dpc mouse hearts. The latter is based on inactivation of the X-linked gene encoding Holocytochrome c synthase (Hccs), which is essential for mitochondrial respiration. In heterozygous heart conditional Hccs knockout females (cHccs(+/-)) random X chromosomal inactivation results in a mosaic of healthy and HCCS deficient cells in the myocardium. Microarray RNA expression analyses identified genes involved in unfolded protein response (UPR) and programmed cell death as differentially expressed in cHccs(+/-) versus control embryonic hearts. Activation of the UPR is localized to HCCS deficient cardiomyocytes but does not involve ER stress pathways, suggesting that it is caused by defective mitochondria. Consistently, mitochondrial chaperones, such as HSP10 and HSP60, but not ER chaperones are induced in defective cells. Mitochondrial dysfunction can result in oxidative stress, but no evidence for excessive ROS (reactive oxygen species) production was observed in cHccs(+/-) hearts. Instead, the antioxidative proteins SOD2 and PRDX3 are induced, suggesting that ROS detoxification prevents oxidative damage in HCCS deficient cardiomyocytes. Mitochondrial dysfunction and unrestricted UPR can induce cell death, and we detected the initiation of upstream events of both intrinsic as well as extrinsic apoptosis in cHccs(+/-) hearts. Cell death is not executed, however, suggesting the activation of antiapoptotic mechanisms. Whereas most apoptosis inhibitors are either unchanged or downregulated in HCCS deficient cardiomyocytes, Bcl-2 and ARC (apoptosis repressor with caspase recruitment domain) are induced. Given that ARC can inhibit both apoptotic pathways as well as necrosis and attenuates UPR, we generated cHccs(+/-) embryos on an Arc knockout background (cHccs(+/-),Arc(-/-)). Surprisingly, the absence of ARC does not induce cell death in embryonic or postnatal HCCS deficient cardiomyocytes and adult cHccs(+/-),Arc(-/-) mice exhibit normal cardiac morphology and function. Taken together, our data demonstrate an impressive plasticity of embryonic cardiomyocytes to respond to metabolic stress, the loss of which might be involved in the high susceptibility of postnatal cardiomyocytes to cell death.

Tumorigenesis of nuclear transfer-derived embryonic stem cells is reduced through differentiation and enrichment following transplantation in the infarcted rat heart

The aim of the present study was to evaluate the tumorigenic potential of nuclear transfer-derived (nt) mouse embryonic stem cells (mESCs) transplanted into infarcted rat hearts. The nt‑mESCs were cultured using a bioreactor system to develop embryoid bodies, which were induced with 1% ascorbic acid to differentiate into cardiomyocytes. The nt‑mESC‑derived cardiomyocytes (nt‑mESCs‑CMs) were enriched using Percoll density gradient separation to generate nt‑mESCs‑percoll‑enriched (PE)‑CMs. Ischemia was induced by ligating the left anterior descending coronary artery in female Sprague‑Dawley rats. Immunosuppressed rats (daily intraperitoneal injections of cyclosporine A and methylprednisolone) were randomly assigned to receive an injection containing 5x106 mESCs, nt‑mESCs, nt‑mESC‑CMs or nt‑mESC‑PE‑CMs. Analysis performed 8 weeks following transplantation revealed teratoma formation in 80, 86.67 and 33.33% of the rats administered with the mESCs, nt‑mESCs and nt‑mESC‑CMs, respectively, indicating no significant difference between the mESCs and nt‑mESCs; but significance (P<0.05) between the nt‑mESC‑CMs and nt‑mESCs. The mean tumor volumes were 82.72±6.52, 83.17±3.58 and 50.40±5.98 mm3, respectively (P>0.05 mESCs, vs. nt‑mESCs; P<0.05 nt‑mESC‑CMs, vs. nt‑mESCs). By contrast, no teratoma formation was detected in the rats, which received nt‑mESC‑PE‑CMs. Octamer‑binding transcription factor‑4, a specific marker of undifferentiated mESCs, was detected using polymerase chain reaction in the rats, which received nt‑mESCs and nt‑mESC‑CMs, but not in rats administered with nt‑mESC‑PE‑CMs. In conclusion, nt‑mESCs exhibited the same pluripotency as mESCs, and teratoma formation following nt‑mESC transplantation was reduced by cell differentiation and enrichment.

Cardiomyocytes in Young Infants With Congenital Heart Disease: a Three-Month Window of Proliferation

Perinatal reduction in cardiomyocyte cell cycle activity is well established in animal models and humans. However, cardiomyocyte cell cycle activity in infants with congenital heart disease (CHD) is unknown, and may provide important information to improve treatment. Human right atrial specimens were obtained from infants during routine surgery to repair ventricular septal defects. The specimens were divided into three groups: group A (age 1–3 months); group B (age, 4–6 months); and group C (age 7–12 months). A dramatic fall in the number of Ki67 -positive CHD cardiac myocytes occurred after three months. When cultured in vitro, young CHD myocytes (≤3 months) showed more abundant Ki67-positive cardiomyocytes and greater incorporation of EdU, indicating enhanced proliferation. YAP1 and NICD—important transcript factors in cardiomyocyte development and proliferation—decreased with age and β-catenin increased with age. Compared with those of older infants, cardiomyocytes of young CHD infants (≤3 months) have a higher proliferating capacity in vivo and in vitro. From the perspective of cardiac muscle regeneration, CHD treatment at a younger age (≤3 months) may be more optimal.

Muscle-on-chip: An in vitro model for donor-host cardiomyocyte coupling

A key aspect of cardiac cell–based therapy is the proper integration of newly formed cardiomyocytes into the remnant myocardium after injury. In this issue, Aratyn-Schaus et al. (2016. J. Cell Biol.http://dx.doi.org/10.1083/jcb.201508026) describe an in vitro model for heterogeneous cardiomyocyte coupling in which force transmission between cells can be measured.

Stem cell-based therapies to promote angiogenesis in ischemic cardiovascular disease

Stem cell therapy is a promising approach for the treatment of tissue ischemia associated with myocardial infarction and peripheral arterial disease. Stem and progenitor cells derived from bone marrow or from pluripotent stem cells have shown therapeutic benefit in boosting angiogenesis as well as restoring tissue function. Notably, adult stem and progenitor cells including mononuclear cells, endothelial progenitor cells, and mesenchymal stem cells have progressed into clinical trials and have shown positive benefits. In this review, we overview the major classes of stem and progenitor cells, including pluripotent stem cells, and summarize the state of the art in applying these cell types for treating myocardial infarction and peripheral arterial disease.

Heart regeneration

Regenerating an injured heart holds great promise for millions of patients suffering from heart diseases. Since the human heart has very limited regenerative capacity, this is a challenging task. Numerous strategies aiming to improve heart function have been developed. In this review we focus on approaches intending to replace damaged heart muscle by new cardiomyocytes. Different strategies for the production of cardiomyocytes from human embryonic stem cells or human induced pluripotent stem cells, by direct reprogramming and induction of cardiomyocyte proliferation are discussed regarding their therapeutic potential and respective advantages and disadvantages. Furthermore, different methods for the transplantation of pluripotent stem cell-derived cardiomyocytes are described and their clinical perspectives are discussed. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

Proteasome Inhibition Diminishes the Formation of Neutrophil Extracellular Traps and Prevents the Death of Cardiomyocytes in Coculture with Activated Neutrophils during Anoxia-Reoxygenation

OBJECTIVE

Polymorphic mononuclear neutrophils (PMN) are very important cells participating in nonspecific defense of the organism. Among their well-known functions, the formation of neutrophil extracellular traps (NET) is interesting and potentially dangerous for the mechanisms of other cells. Ubiquitin-dependent proteasomal proteolysis is a very important regulator of all cellular activities, but the role of proteasomal proteolysis in NET formation has not been investigated.

METHODS

We performed experiments with PMN activated to form NET with phorbol 12-myristate 13-acetate (PMA) and the application of a proteasome inhibitor. We also added activated neutrophils to primary culture of isolated rat neonatal cardiomyocytes with or without anoxia-reoxygenation modeling.

RESULTS

The data obtained show that proteasomes participate in NET formation and proteasome inhibitors facilitate the blocking of the NET program. The percentage of NET after PMA application was 70.8 ± 7.2 and the proteasome inhibitor decreased this amount to 4.7 ± 0.9%. In coculture with cardiomyocytes during anoxia-reoxygenation, this effect prevented cardiac cell death induced by activated PMN. The stimulation of NET formation by PMA in coculture with isolated cardiomyocytes led to an increase in the number of necrotic cardiomyocytes of up to 33.1 ± 12.9% and a corresponding decrease in living cardiomyocytes to 66.9 ± 12.9%. The number of living cardiomyocytes in coculture after incubation with both PMA and proteasome inhibitor was 76.6 ± 13.3% (p < 0.05), and the number of necrotic cardiomyocytes was 23.4 ± 13.3% (p < 0.05).

CONCLUSION

Proteasome inhibition blocks NET formation and prevents cardiomyocyte necrosis in coculture with activated neutrophils.

C-Kit Promotes Growth and Migration of Human Cardiac Progenitor Cells via the PI3K-AKT and MEK-ERK Pathways

A recent phase I clinical trial (SCIPIO) has shown that autologous c-kit+ cardiac progenitor cells (CPCs) improve cardiac function and quality of life when transplanted into patients with ischemic heart disease. Although c-kit is widely used as a marker of resident CPCs, its role in the regulation of the cellular characteristics of CPCs remains unknown. We hypothesized that c-kit plays a role in the survival, growth, and migration of CPCs. To test this hypothesis, human CPCs were grown under stress conditions in the presence or absence of SCF, and the effects of SCF-mediated activation of c-kit on CPC survival/growth and migration were measured. SCF treatment led to a significant increase in cell survival and a reduction in cell death under serum depletion conditions. In addition, SCF significantly promoted CPC migration in vitro. Furthermore, the pro-survival and pro-migratory effects of SCF were augmented by c-kit overexpression and abrogated by c-kit inhibition with imatinib. Mechanistically, c-kit activation in CPCs led to activation of the PI3K and the MAPK pathways. With the use of specific inhibitors, we confirmed that the SCF/c-kit-dependent survival and chemotaxis of CPCs are dependent on both pathways. Taken together, our findings suggest that c-kit promotes the survival/growth and migration of human CPCs cultured ex vivo via the activation of PI3K and MAPK pathways. These results imply that the efficiency of CPC homing to the injury site as well as their survival after transplantation may be improved by modulating the activity of c-kit.

Preconditioning Human Cardiac Stem Cells with an HO-1 Inducer Exerts Beneficial Effects After Cell Transplantation in the Infarcted Murine Heart

The regenerative potential of c‐kit⁺ cardiac stem cells (CSCs) is severely limited by the poor survival of cells after transplantation in the infarcted heart. We have previously demonstrated that preconditioning human CSCs (hCSCs) with the heme oxygenase‐1 inducer, cobalt protoporphyrin (CoPP), has significant cytoprotective effects in vitro. Here, we examined whether preconditioning hCSCs with CoPP enhances CSC survival and improves cardiac function after transplantation in a model of myocardial infarction induced by a 45‐minute coronary occlusion and 35‐day reperfusion in immunodeficient mice. At 30 minutes of reperfusion, CoPP‐preconditioned hCSCs^GFP+, hCSCs^GFP+, or medium were injected into the border zone. Quantitative analysis with real‐time qPCR for the expression of the human‐specific gene HLA revealed that the number of survived hCSCs was significantly greater in the preconditioned‐hCSC group at 24 hours and 7 and 35 days compared with the hCSC group. Coimmunostaining of tissue sections for both green fluorescent protein (GFP) and human nuclear antigen further confirmed greater hCSC numbers at 35 days in the preconditioned‐hCSC group. At 35 days, compared with the hCSC group, the preconditioned‐hCSC group exhibited increased positive and negative left ventricular (LV) dP/dt, end‐systolic elastance, and anterior wall/apical strain rate (although ejection fraction was similar), reduced LV remodeling, and increased proliferation of transplanted cells and of cells apparently committed to cardiac lineage. In conclusion, CoPP‐preconditioning of hCSCs enhances their survival and/or proliferation, promotes greater proliferation of cells expressing cardiac markers, and results in greater improvement in LV remodeling and in indices of cardiac function after infarction. Stem Cells2015;33:3596–3607

Functional Effects of a Tissue-Engineered Cardiac Patch From Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes in a Rat Infarct Model

A tissue-engineered cardiac patch provides a method to deliver cardiomyoctes to the injured myocardium with high cell retention and large, controlled infarct coverage, enhancing the ability of cells to limit remodeling after infarction. The patch environment can also yield increased survival. In the present study, we sought to assess the efficacy of a cardiac patch made from human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to engraft and limit left ventricular (LV) remodeling acutely after infarction. Cardiac patches were created from hiPSC-CMs and human pericytes (PCs) entrapped in a fibrin gel and implanted acutely onto athymic rat hearts. hiPSC-CMs not only remained viable after in vivo culture, but also increased in number by as much as twofold, consistent with colocalization of human nuclear antigen, cardiac troponin T, and Ki-67 staining. CM+PC patches led to reduced infarct sizes compared with myocardial infarction-only controls at week 4, and CM+PC patch recipient hearts exhibited greater fractional shortening over all groups at both 1 and 4 weeks after transplantation. However, a decline occurred in fractional shortening for all groups over 4 weeks, and LV thinning was not mitigated. CM+PC patches became vascularized in vivo, and microvessels were more abundant in the host myocardium border zone, suggesting a paracrine mechanism for the improved cardiac function. PCs in a PC-only control patch did not survive 4 weeks in vivo. Our results indicate that cardiac patches containing hiPSC-CMs engraft onto acute infarcts, and the hiPSC-CMs survive, proliferate, and contribute to a reduction in infarct size and improvements in cardiac function.

SIGNIFICANCE

In the present study, a cardiac patch was created from human induced pluripotent stem cell-derived cardiomyocytes and human pericytes entrapped in a fibrin gel, and it was transplanted onto infarcted rat myocardium. It was found that a patch that contained both cardiomyocytes and pericytes survived transplantation and resulted in improved cardiac function and a reduced infarct size compared with controls.

Arrhythmia in stem cell transplantation

Stem cell regenerative therapies hold promise for treating diseases across the spectrum of medicine. While significant progress has been made in the preclinical stages, the clinical application of cardiac cell therapy is limited by technical challenges. Certain methods of cell delivery, such as intramyocardial injection, carry a higher rate of arrhythmias. Other potential contributors to the arrhythmogenicity of cell transplantation include reentrant pathways caused by heterogeneity in conduction velocities between graft and host as well as graft automaticity. In this article, the arrhythmogenic potential of cell delivery to the heart is discussed.

On the existence of cardiomesenchymal stem cells

The most efficient cells for cardiac regeneration are myocardium-resident cardiac stem cells. However, the limited availability of these cells restricts their utility for cardiac cellular therapy. Mesenchymal stem cells can differentiate into a wide variety of tissues, but it is not simple to accurately direct cell differentiation into a specific lineage, such as cardiac tissue; this renders a low efficiency for cardiac regeneration therapy. Given the heterogeneity of mesenchymal stem cells, it may be possible to find specific stem cell subpopulations with a definite differentiation capacity toward cardiac lineage. A parameter to assess cardiac differentiation specificity could be surface marker expression; a population with an immunophenotype similar to cardiac stem cells may have a superior therapeutic value than unsorted mesenchymal stem cells. We hypothesize the existence of a cell line that combines the expression of cardiac stem cell surface markers with those of mesenchymal stem cells, a suitable name for this population is cardiomesenchymal stem cells (CMSC); such cells would be ideal for cardiac regeneration.

Combined hypoxia and sodium nitrite pretreatment for cardiomyocyte protection in vitro

Methods that increase cardiomyocyte survival upon exposure to ischemia, hypoxia and reoxygenation injuries are required to improve the efficacy of cardiac cell therapy and enhance the viability and function of engineered tissues. We investigated the effect of combined hypoxia/NaNO2 pretreatment on rat neonatal cardiomyocyte (CM), cardiac fibroblast, and human embryonic stem cell-derived CM (hESC-CM) survival upon exposure to hypoxia/reoxygenation (H/R) injury in vitro. Cells were pretreated with and without hypoxia and/or various concentrations of NaNO2 for 20 min, then incubated for 2 h under hypoxic conditions, followed by 2 h in normoxia. The control cells were maintained under normoxia for 4 h. Pretreatment with either hypoxia or NaNO2 significantly increased CM viability but had no effect on cardiac fibroblast viability. Combined hypoxia/NaNO2 pretreatment significantly increased CM viability but significantly decreased cardiac fibroblast viability. In rat neonatal CMs, cell death, as determined by lactate dehydrogenase (LDH) activity, was significantly reduced with hypoxia/NaNO2 pretreatment; and in hESC-CMs, hypoxia/NaNO2 pretreatment increased the BCL-2/BAX gene expression ratio, suggesting that hypoxia/NaNO2 pretreatment promotes cell viability by downregulating apoptosis. Additionally, we found a correlation between the prosurvival effect of hypoxia/NaNO2 pretreatment and the myoglobin content of the cells by comparing neonatal rat ventricular and atrial CMs, which express high and low myoglobin respectively. Functionally, hypoxia/NaNO2 pretreatment significantly improved the excitation threshold upon H/R injury to the level observed for uninjured cells, whereas pretreatment did not affect the maximum capture rate. Hence, hypoxia/NaNO2 pretreatment may serve as a strategy to increase CM survival in cardiac regenerative therapy applications and tissue engineering.

The winding road to regenerating the human heart

Regenerating the human heart is a challenge that has engaged researchers and clinicians around the globe for nearly a century. From the repair of the first septal defect in 1953, followed by the first successful heart transplant in 1967, and later to the first infusion of bone marrow-derived cells to the human myocardium in 2002, significant progress has been made in heart repair. However, chronic heart failure remains a leading pathological burden worldwide. Why has regenerating the human heart been such a challenge, and how close are we to achieving clinically relevant regeneration? Exciting progress has been made to establish cell transplantation techniques in recent years, and new preclinical studies in large animal models have shed light on the promises and challenges that lie ahead. In this review, we will discuss the history of cell therapy approaches and provide an overview of clinical trials using cell transplantation for heart regeneration. Focusing on the delivery of human stem cell-derived cardiomyocytes, current experimental strategies in the field will be discussed as well as their clinical translation potential. Although the human heart has not been regenerated yet, decades of experimental progress have guided us onto a promising path.

SUMMARY

Previous work in clinical cell therapy for heart repair using bone marrow mononuclear cells, mesenchymal stem cells, and cardiac-derived cells have overall demonstrated safety and modest efficacy. Recent advancements using human stem cell-derived cardiomyocytes have established them as a next generation cell type for moving forward, however certain challenges must be overcome for this technique to be successful in the clinics.

Opportunities and challenges: stem cell-based therapy for the treatment of ischemic stroke

Stem cell-based therapy for ischemic stroke has been widely explored in animal models and provides strong evidence of benefits. In this review, we summarize the types of stem cells, various delivery routes, and tracking tools for stem cell therapy of ischemic stroke. MSCs, EPCs, and NSCs are the most explored cell types for ischemic stroke treatment. Although the mechanisms of stem cell-based therapies are not fully understood, the most possible functions of the transplanted cells are releasing growth factors and regulating microenvironment through paracrine mechanism. Clinical application of stem cell-based therapy is still in its infancy. The next decade of stem cell research in stroke field needs to focus on combining different stem cells and different imaging modalities to fully explore the potential of this therapeutic avenue: from bench to bedside and vice versa.

Neuregulin-1β induces mature ventricular cardiac differentiation from induced pluripotent stem cells contributing to cardiac tissue repair

Stem cell-derived cardiomyocytes (CMs) are often electrophysiologically immature and heterogeneous, which represents a major barrier to their in vitro and in vivo application. Therefore, the purpose of this study was to examine whether Neuregulin-1β (NRG-1β) treatment could enhance in vitro generation of mature "working-type" CMs from induced pluripotent stem (iPS) cells and assess the regenerative effects of these CMs on cardiac tissue after acute myocardial infarction (AMI). With that purpose, adult mouse fibroblast-derived iPS from α-MHC-GFP mice were derived and differentiated into CMs through NRG-1β and/or dimethyl sulfoxide (DMSO) treatment. Cardiac specification and maturation of the iPS was analyzed by gene expression array, quantitative real-time polymerase chain reaction, immunofluorescence, electron microscopy, and patch-clamp techniques. In vivo, the iPS-derived CMs or culture medium control were injected into the peri-infarct region of hearts after coronary artery ligation, and functional and histology changes were assessed from 1 to 8 weeks post-transplantation. On differentiation, the iPS displayed early and robust in vitro cardiogenesis, expressing cardiac-specific genes and proteins. More importantly, electrophysiological studies demonstrated that a more mature ventricular-like cardiac phenotype was achieved when cells were treated with NRG-1β and DMSO compared with DMSO alone. Furthermore, in vivo studies demonstrated that iPS-derived CMs were able to engraft and electromechanically couple to heart tissue, ultimately preserving cardiac function and inducing adequate heart tissue remodeling. In conclusion, we have demonstrated that combined treatment with NRG-1β and DMSO leads to efficient differentiation of iPS into ventricular-like cardiac cells with a higher degree of maturation, which are capable of preserving cardiac function and tissue viability when transplanted into a mouse model of AMI.

Derivation and high engraftment of patient-specific cardiomyocyte sheet using induced pluripotent stem cells generated from adult cardiac fibroblast

BACKGROUND

Induced pluripotent stem cells (iPSCs) can be differentiated into potentially unlimited lineages of cell types for use in autologous cell therapy. However, the efficiency of the differentiation procedure and subsequent function of the iPSC-derived cells may be influenced by epigenetic factors that the iPSCs retain from their tissues of origin; thus, iPSC-derived cells may be more effective for treatment of myocardial injury if the iPSCs were engineered from cardiac-lineage cells, rather than dermal fibroblasts.

METHODS AND RESULTS

We show that human cardiac iPSCs (hciPSCs) can be generated from cardiac fibroblasts and subsequently differentiated into exceptionally pure (>92%) sheets of cardiomyocytes (CMs). The hciPSCs passed through all the normal stages of differentiation before assuming a CM identity. When using the fibrin gel-enhanced delivery of hciPSC-CM sheets at the site of injury in infarcted mouse hearts, the engraftment rate was 31.91%±5.75% at Day 28 post transplantation. The hciPSC-CM in the sheet also appeared to develop a more mature, structurally aligned phenotype 28 days after transplantation and was associated with significant improvements in cardiac function, vascularity, and reduction in apoptosis.

CONCLUSIONS

These data strongly support the potential of hciPSC-CM sheet transplantation for the treatment of heart with acute myocardial infarction.

How to make a cardiomyocyte

During development, cardiogenesis is orchestrated by a family of heart progenitors that build distinct regions of the heart. Each region contains diverse cell types that assemble to form the complex structures of the individual cardiac compartments. Cardiomyocytes are the main cell type found in the heart and ensure contraction of the chambers and efficient blood flow throughout the body. Injury to the cardiac muscle often leads to heart failure due to the loss of a large number of cardiomyocytes and its limited intrinsic capacity to regenerate the damaged tissue, making it one of the leading causes of morbidity and mortality worldwide. In this Primer we discuss how insights into the molecular and cellular framework underlying cardiac development can be used to guide the in vitro specification of cardiomyocytes, whether by directed differentiation of pluripotent stem cells or via direct lineage conversion. Additional strategies to generate cardiomyocytes in situ, such as reactivation of endogenous cardiac progenitors and induction of cardiomyocyte proliferation, will also be discussed.

Hepatocyte growth factor modification enhances the anti-arrhythmic properties of human bone marrow-derived mesenchymal stem cells

Background/Aims

Chronic myocardial infarction (MI) results in the formation of arrhythmogenic substrates, causing lethal ventricular arrhythmia (VA). We aimed to determine whether mesenchymal stem cells (MSCs) carrying a hepatocyte growth factor (HGF) gene modification (HGF-MSCs) decrease the levels of arrhythmogenic substrates and reduce the susceptibility to developing VA compared with unmodified MSCs and PBS in a swine infarction model.

Methods

The left descending anterior artery was balloon-occluded to establish an MI model. Four weeks later, the randomly grouped pigs were administered MSCs, PBS or HGF-MSCs via thoracotomy. After an additional four weeks, dynamic electrocardiography was performed to assess heart rate variability, and programmed electrical stimulation was conducted to evaluate the risk for VA. Then, the pigs were euthanized for morphometric, immunofluorescence and western blot analyses. Results: The HGF-MSC group displayed the highest vessel density and Cx43 expression levels, and the lowest levels of apoptosis, and tyrosine hydroxylase (TH) and growth associated protein 43 (GAP43) expression. Moreover, the HGF-MSC group exhibited a decrease in the number of sympathetic nerve fibers, substantial decreases in the low frequency and the low-/high- frequency ratio and increases in the root mean square of successive differences (rMSSD) and the percentage of successive normal sinus R-R intervals longer than 50 ms (pNN50), compared with the other two groups. Finally, the HGF-MSC group displayed the lowest susceptibility to developing VA.

Conclusion

HGF-MSCs displayed potent antiarrhythmic effects, reducing the risk for VA.

Transplantation of iPSc ameliorates neural remodeling and reduces ventricular arrhythmias in a post-infarcted swine model

Neural remodeling after myocardial infarction (MI) may cause malignant ventricular arrhythmia, which is the main cause of sudden cardiac death following MI. Herein, we aimed to examine whether induced pluripotent stem cells (iPSc) transplantation can ameliorate neural remodeling and reduce ventricular arrhythmias (VA) in a post-infarcted swine model. Left anterior descending coronary arteries were balloon-occluded to generate MI. Animals were then divided into Sham, PBS control, and iPS groups. Dynamic electrocardiography programmed electric stimulation were performed to evaluate VA. The spatial distribution of vascularization, Cx43 and autonomic nerve regeneration were evaluated by immunofluorescence staining. Associated protein expression was detected by Western blotting. Likewise, we measured the enzymatic activities of superoxide dismutase and content of malondialdehyde. Six weeks later, the number of blood vessels increased significantly in the iPSc group. The expression of vascular endothelial growth factor and connexin 43 in the iPS group was significantly higher than the PBS group; however, the levels of nerve growth factor and tyrosine hydroxylase were lower. The oxidative stress was ameliorated by iPSc transplantation. Moreover, the number of sympathetic nerves in the iPSc group was reduced, while the parasympathetic nerve fibers had no obvious change. The transplantation of iPSc also significantly decreased the low-/high-frequency ratio and arrhythmia score of programmed electric stimulation-induced VA. In conclusion, iPSc intramyocardial transplantation reduces vulnerability to VAs, and the mechanism was related to the remodeling amelioration of autonomic nerves and gap junctions. Moreover, possible mechanisms of iPSc transplantation in improving neural remodeling may be related to attenuated oxidative stress and inflammatory response.

Tissue engineering: construction of a multicellular 3D scaffold for the delivery of layered cell sheets

Many tissues, such as the adult human hearts, are unable to adequately regenerate after damage.(2,3) Strategies in tissue engineering propose innovations to assist the body in recovery and repair. For example, TE approaches may be able to attenuate heart remodeling after myocardial infarction (MI) and possibly increase total heart function to a near normal pre-MI level.(4) As with any functional tissue, successful regeneration of cardiac tissue involves the proper delivery of multiple cell types with environmental cues favoring integration and survival of the implanted cell/tissue graft. Engineered tissues should address multiple parameters including: soluble signals, cell-to-cell interactions, and matrix materials evaluated as delivery vehicles, their effects on cell survival, material strength, and facilitation of cell-to-tissue organization. Studies employing the direct injection of graft cells only ignore these essential elements.(2,5,6) A tissue design combining these ingredients has yet to be developed. Here, we present an example of integrated designs using layering of patterned cell sheets with two distinct types of biological-derived materials containing the target organ cell type and endothelial cells for enhancing new vessels formation in the "tissue". Although these studies focus on the generation of heart-like tissue, this tissue design can be applied to many organs other than heart with minimal design and material changes, and is meant to be an off-the-shelf product for regenerative therapies. The protocol contains five detailed steps. A temperature sensitive Poly(N-isopropylacrylamide) (pNIPAAM) is used to coat tissue culture dishes. Then, tissue specific cells are cultured on the surface of the coated plates/micropattern surfaces to form cell sheets with strong lateral adhesions. Thirdly, a base matrix is created for the tissue by combining porous matrix with neovascular permissive hydrogels and endothelial cells. Finally, the cell sheets are lifted from the pNIPAAM coated dishes and transferred to the base element, making the complete construct.

Silencing of TERT decreases levels of miR-1, miR-21, miR-29a and miR-208a in cardiomyocytes

To test the hypothesis that telomerase reverse transcriptase (TERT) as an RNA-dependent RNA polymerase could be involved in the amplification of microRNA (miRNA), we have determined the levels of immature and mature miRNA in cultured neonatal rat cardiomyocytes, during the silencing of TERT by siRNA. The silencing of the TERT gene led to the reduction of both telomerase activity and the TERT mRNA expression when compared with scrambled RNA. TERT gene silencing resulted in the decrement of three studied mature miRNAs levels: miRNA-21, miRNA-29a and miRNA-208a when compared with scrambled RNA; but miRNA-1, it was not changed significantly. At the same time, levels of immature miRNA-1 and miRNA-208a were not changed, although the levels of immature miRNA-29a and pri-miRNA-1 were decreased. The data obtained allow us to permit that TERT is a genome-independent source of mature miRNA, and the changes in telomerase activity can significantly influence the level of miRNA in cardiomyocytes.

Cell-based delivery of dATP via gap junctions enhances cardiac contractility

The transplantation of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) is a promising strategy to treat myocardial infarction and reverse heart failure, but to date the contractile benefit in most studies remains modest. We have previously shown that the nucleotide 2-deoxyadenosine triphosphate (dATP) can substitute for ATP as the energy substrate for cardiac myosin, and increasing cellular dATP content by globally overexpressing ribonucleotide reductase (R1R2) can dramatically enhance cardiac contractility. Because dATP is a small molecule, we hypothesized that it would diffuse readily between cells via gap junctions and enhance the contractility of neighboring coupled wild type cells. To test this hypothesis, we performed studies with the goals of (1) validating gap junction-mediated dATP transfer in vitro and (2) investigating the use of R1R2-overexpressing hPSC-CMs in vivo as a novel strategy to increase cardiac function. We first performed intracellular dye transfer studies using dATP conjugated to fluorescein and demonstrated rapid gap junction-mediated transfer between cardiomyocytes. We then cocultured wild type cardiomyocytes with either cardiomyocytes or fibroblasts overexpressing R1R2 and saw more than a twofold increase in the extent and rate of contraction of wild type cardiomyocytes. Finally, we transplanted hPSC-CMs overexpressing R1R2 into healthy uninjured rat hearts and noted an increase in fractional shortening from 41±4% to 53±5% just five days after cell transplantation. These findings demonstrate that dATP is an inotropic factor that spreads between cells via gap junctions. Our data suggest that transplantation of dATP-producing hPSC-CMs could significantly increase the effectiveness of cardiac cell therapy.

Cardiac stem cell therapy for cardiac repair

The discovery of adult cardiac stem cells (CSCs) and their potential to restore functional cardiac tissue has fueled unprecedented interest in recent years. Indeed, stem-cell–based therapies have the potential to transform the treatment and prognosis of heart failure, for they have the potential to eliminate the underlying cause of the disease by reconstituting the damaged heart with functional cardiac cells. Over the last decade, several independent laboratories have demonstrated the utility of c-kit+/Lin- resident CSCs in alleviating left ventricular dysfunction and remodeling in animal models of acute and chronic myocardial infarction. Recently, the first clinical trial of autologous CSCs for treatment of heart failure resulting from ischemic heart disease (Stem Cell Infusion in Patients with Ischemic cardiOmyopathy [SCIPIO]) has been conducted, and the interim results are quite promising. In this phase I trial, no adverse effects attributable to the CSC treatment have been noted, and CSC-treated patients showed a significant improvement in ejection fraction at 1 year (+13.7 absolute units versus baseline), accompanied by a 30.2 % reduction in infarct size. Moreover, the CSC-induced enhancement in cardiac structure and function was associated with a significant improvement in the New York Heart Association (NYHA) functional class and in the quality of life, as measured by the Minnesota Living with Heart failure Questionnaire. These results are exciting and warrant larger, phase II studies. However, CSC therapy for cardiac repair is still in its infancy, and many hurdles need to be overcome to further enhance the therapeutic efficacy of CSCs.

Pluripotent stem cell derived cardiomyocytes for cardiac repair

OPINION STATEMENT

The adult mammalian heart has limited capacity for regeneration, and any major injury such as a myocardial infarction results in the permanent loss of up to 1 billion cardiomyocytes. The field of cardiac cell therapy aims to replace these lost contractile units with de novo cardiomyocytes to restore lost systolic function and prevent progression to heart failure. Arguably, the ideal cell for this application is the human cardiomyocyte itself, which can electromechanically couple with host myocardium and contribute active systolic force. Pluripotent stem cells from human embryonic or induced pluripotent lineages are attractive sources for cardiomyocytes, and preclinical investigation of these cells is in progress. Recent work has focused on the efficient generation and purification of cardiomyocytes, tissue engineering efforts, and examining the consequences of cell transplantation from mechanical, vascular, and electrical standpoints. Here we discuss historical and contemporary aspects of pluripotent stem cell-based cardiac cell therapy, with an emphasis on recent preclinical studies with translational goals.

c-kit+ Cardiac stem cells alleviate post-myocardial infarction left ventricular dysfunction despite poor engraftment and negligible retention in the recipient heart

Although transplantation of c-kit+ cardiac stem cells (CSCs) has been shown to alleviate left ventricular (LV) dysfunction induced by myocardial infarction (MI), the number of exogenous CSCs remaining in the recipient heart following transplantation and their mechanism of action remain unclear. We have previously developed a highly sensitive and accurate method to quantify the absolute number of male murine CSCs in female recipient organs after transplantation. In the present study, we used this method to monitor the number of donor CSCs in the recipient heart after intracoronary infusion. Female mice underwent a 60-min coronary occlusion followed by reperfusion; 2 days later, 100,000 c-kit+/lin- syngeneic male mouse CSCs were infused intracoronarily. Only 12.7% of the male CSCs present in the heart immediately (5 min) after infusion were still present in the heart at 24 h, and their number declined rapidly thereafter. By 35 days after infusion, only ∼1,000 male CSCs were found in the heart. Significant numbers of male CSCs were found in the lungs and kidneys, but only in the first 24 h. The number of CSCs in the lungs increased between 5 min and 24 h after infusion, indicating recirculation of CSCs initially retained in other organs. Despite the low retention and rapid disappearance of CSCs from the recipient heart, intracoronary delivery of CSCs significantly improved LV function at 35 days (Millar catheter). These results suggest that direct differentiation of CSCs alone cannot account for the beneficial effects of CSCs on LV function; therefore, paracrine effects must be the major mechanism. The demonstration that functional improvement is dissociated from survival of transplanted cells has major implications for our understanding of cell therapy. In addition, this new quantitative method of stem cell measurement will be useful in testing approaches of enhancing CSC engraftment and survival after transplantation.

Mesenchymal stem cells prevent hypertrophic scar formation via inflammatory regulation when undergoing apoptosis

The cutaneous wound-healing process can lead to hypertrophic scar formation, during which exaggerated inflammation has been demonstrated to have an important role. Therefore, an exploration of strategies designed to regulate this inflammatory process is warranted. Mesenchymal stem cells (MSCs) have recently been demonstrated to regulate inflammation in various diseases. In this regard, using a rabbit model, we locally injected human mesenchymal stem cells (hMSCs) derived from bone marrow to treat hypertrophic scar formation, and explored their underlying mechanisms. We found that hMSC therapy efficiently regulated inflammation and prevented scar formation. We attributed the therapeutic effects of hMSCs to their secretion of an anti-inflammatory protein, TNF-alpha-stimulated gene/protein 6 (TSG-6). Unexpectedly, after injection, the number of surviving hMSCs decreased markedly and the hMSCs underwent extensive apoptosis, which was demonstrated to promote their secretion of TSG-6, partially through the activation of caspase-3. Moreover, H2O2-induced apoptotic hMSCs showed higher inflammatory regulatory abilities. The inhibition of caspase-3 decreased the inflammatory regulatory abilities of hMSCs and attenuated their therapeutic effects. Our results demonstrate that hMSCs can efficiently prevent hypertrophic scar formation via inflammatory regulation. In addition, we found that apoptosis has an important role in the activation of the inflammatory regulatory abilities of hMSCs.

Engineering adolescence: maturation of human pluripotent stem cell-derived cardiomyocytes

The discovery of human pluripotent stem cells (hPSCs), including both human embryonic stem cells and human-induced pluripotent stem cells, has opened up novel paths for a wide range of scientific studies. The capability to direct the differentiation of hPSCs into functional cardiomyocytes has provided a platform for regenerative medicine, development, tissue engineering, disease modeling, and drug toxicity testing. Despite exciting progress, achieving the optimal benefits has been hampered by the immature nature of these cardiomyocytes. Cardiac maturation has long been studied in vivo using animal models; however, finding ways to mature hPSC cardiomyocytes is only in its initial stages. In this review, we discuss progress in promoting the maturation of the hPSC cardiomyocytes, in the context of our current knowledge of developmental cardiac maturation and in relation to in vitro model systems such as rodent ventricular myocytes. Promising approaches that have begun to be examined in hPSC cardiomyocytes include long-term culturing, 3-dimensional tissue engineering, mechanical loading, electric stimulation, modulation of substrate stiffness, and treatment with neurohormonal factors. Future studies will benefit from the combinatorial use of different approaches that more closely mimic nature's diverse cues, which may result in broader changes in structure, function, and therapeutic applicability.

Concise review: reprogramming strategies for cardiovascular regenerative medicine: from induced pluripotent stem cells to direct reprogramming

Myocardial cell-replacement therapies are emerging as novel therapeutic paradigms for myocardial repair but are hampered by the lack of sources of autologous human cardiomyocytes. The recent advances in stem cell biology and in transcription factor-based reprogramming strategies may provide exciting solutions to this problem. In the current review, we describe the different reprogramming strategies that can give rise to cardiomyocytes for regenerative medicine purposes. Initially, we describe induced pluripotent stem cell technology, a method by which adult somatic cells can be reprogrammed to yield pluripotent stem cells that could later be coaxed ex vivo to differentiate into cardiomyocytes. The generated induced pluripotent stem cell-derived cardiomyocytes could then be used for myocardial cell transplantation and tissue engineering strategies. We also describe the more recent direct reprogramming approaches that aim to directly convert the phenotype of one mature cell type (fibroblast) to another (cardiomyocyte) without going through a pluripotent intermediate cell type. The advantages and shortcomings of each strategy for cardiac regeneration are discussed, along with the hurdles that need to be overcome on the road to clinical translation.

Triptolide improves early survival of mesenchymal stem cells transplanted into rat myocardium

OBJECTIVE

To investigate whether triptolide can prolong the survival of rat mesenchymal stem cells (MSCs) transfected with the mouse hyperpolarization-activated cyclic nucleotide-gated channel 4 (mHCN4) gene in the myocardium.

METHODS

Grafted cell survival was determined using a sex-mismatched cell transplantation model and analysis of Y chromosome-specific Sry gene expression from hearts harvested at different time points after cell transplantation. ELISA and RT-PCR were used to measure protein and mRNA levels, respectively, of nuclear factor (NF)-κB, IL-1β, IL-6 and TNF-α.

RESULTS

Donor cell numbers decreased over time. Pretreatment with triptolide improved graft survival both 24 (29.3 ± 0.9%) and 72 h (17.5 ± 1.2%) after transplantation of MSCs and resulted in a 2.5-fold increase in the total cell number 72 h after cell transplantation. The mRNA expression and protein content of NF-κB, IL-1β, IL-6 and TNF-α were significantly reduced in the triptolide-treated group compared with the control groups. In addition, triptolide downregulated Bax but upregulated Bcl-2 in the injected region.

CONCLUSIONS

Transient treatment with triptolide may significantly improve the early survival of MSCs in vivo. The mechanism underlying this effect involves attenuating the inflammatory response via inhibition of the NF-κB signaling pathway.

Evaluation of polyelectrolyte complex-based scaffolds for mesenchymal stem cell therapy in cardiac ischemia treatment

Three-dimensional (3D) scaffolds hold great potential for stem cell-based therapies. Indeed, recent results have shown that biomimetic scaffolds may enhance cell survival and promote an increase in the concentration of therapeutic cells at the injury site. The aim of this work was to engineer an original polymeric scaffold based on the respective beneficial effects of alginate and chitosan. Formulations were made from various alginate/chitosan ratios to form opposite-charge polyelectrolyte complexes (PECs). After freeze-drying, the resultant matrices presented a highly interconnected porous microstructure and mechanical properties suitable for cell culture. In vitro evaluation demonstrated their compatibility with mesenchymal stell cell (MSC) proliferation and their ability to maintain paracrine activity. Finally, the in vivo performance of seeded 3D PEC scaffolds with a polymeric ratio of 40/60 was evaluated after an acute myocardial infarction provoked in a rat model. Evaluation of cardiac function showed a significant increase in the ejection fraction, improved neovascularization, attenuated fibrosis as well as less left ventricular dilatation as compared to an animal control group. These results provide evidence that 3D PEC scaffolds prepared from alginate and chitosan offer an efficient environment for 3D culturing of MSCs and represent an innovative solution for tissue engineering.

Intramyocardial cell delivery: observations in murine hearts

Previous studies showed that cell delivery promotes cardiac function amelioration by release of cytokines and factors that increase cardiac tissue revascularization and cell survival. In addition, further observations revealed that specific stem cells, such as cardiac stem cells, mesenchymal stem cells and cardiospheres have the ability to integrate within the surrounding myocardium by differentiating into cardiomyocytes, smooth muscle cells and endothelial cells. Here, we present the materials and methods to reliably deliver noncontractile cells into the left ventricular wall of immunodepleted mice. The salient steps of this microsurgical procedure involve anesthesia and analgesia injection, intratracheal intubation, incision to open the chest and expose the heart and delivery of cells by a sterile 30-gauge needle and a precision microliter syringe. Tissue processing consisting of heart harvesting, embedding, sectioning and histological staining showed that intramyocardial cell injection produced a small damage in the epicardial area, as well as in the ventricular wall. Noncontractile cells were retained into the myocardial wall of immunocompromised mice and were surrounded by a layer of fibrotic tissue, likely to protect from cardiac pressure and mechanical load.

Left-ventricular aneurysms: from disease to repair

Myocardial infarction may be complicated by the formation of a left-ventricular aneurysm that distorts the normal elliptical geometry of the ventricle to produce a dilated spherical ventricle with limited contractile and filling capacities. One of the consequences is congestive heart failure, which may be refractory to medical therapy and require surgical treatment. Surgical methods to restore the volume and shape of the left ventricle have evolved over the years. Nevertheless, although surgery for left-ventricular aneurysms has been performed for almost 50 years, the most appropriate approach is still controversial. This review gives an overview of the postinfarction left-ventricular aneurysm, tackling issues from the disease itself to surgical and other techniques of ventricular remodeling.

Isolation and expansion of resident cardiac progenitor cells

After myocardial infarction, loss of viable cardiomyocytes severely impairs cardiac function. Recently, stem cell transplantation has been put forward as a promising approach to repair the damaged heart. Although several clinical trials have already been performed, the dominant beneficial effects are probably due to neoangiogenesis and arteriogenesis. However, replacement of cardiomyocytes is vital to improve cardiac function in the long term. Stem cells and progenitor cells, with the capacity to differentiate into cardiomyocytes, have been described in both embryonic and adult tissues. Upon stimulation, cardiac progenitor cells proliferate and differentiate into cardiomyocytes, vascular smooth muscle cells, and endothelial cells. Currently however, high proliferation rates and differentiation of cardiac progenitor cells beyond the fetal stage have not yet been achieved. Full differentiation into adult cardiomyocytes in vitro and in vivo might be important for efficient integration with the host environment and therefore more research is needed to study factors that influence proliferation and differentiation. Here we will discuss the isolation of cardiac progenitor cells, their potential to differentiate into various cell types needed for cardiac repair, the possible mechanisms behind these events, and how these cells may be implemented in future clinical settings.

Optimization of the cardiovascular therapeutic properties of mesenchymal stromal/stem cells-taking the next step

Despite current treatment options, cardiac failure is associated with significant morbidity and mortality highlighting a compelling clinical need for novel therapeutic approaches. Based on promising pre-clinical data, stem cell therapy has been suggested as a possible therapeutic strategy. Of the candidate cell types evaluated, mesenchymal stromal/stem cells (MSCs) have been widely evaluated due to their ease of isolation and ex vivo expansion, potential allogeneic utility and capacity to promote neo-angiogenesis and endogenous cardiac repair. However, the clinical application of MSCs for mainstream cardiovascular use is currently hindered by several important limitations, including suboptimal retention and engraftment and restricted capacity for bona fide cardiomyocyte regeneration. Consequently, this has prompted intense efforts to advance the therapeutic properties of MSCs for cardiovascular disease. In this review, we consider the scope of benefit from traditional plastic adherence-isolated MSCs and the lessons learned from their conventional use in preclinical and clinical studies. Focus is then given to the evolving strategies aimed at optimizing MSC therapy, including discussion of cell-targeted techniques that encompass the preparation, pre-conditioning and manipulation of these cells ex vivo, methods to improve their delivery to the heart and innovative substrate-directed strategies to support their interaction with the host myocardium.