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

A Novel Approach Utilizing Domain Adversarial Neural Networks for the Detection and Classification of Selective Sweeps

The identification and classification of selective sweeps are of great significance for improving the understanding of biological evolution and exploring opportunities for precision medicine and genetic improvement. Here, a domain adaptation sweep detection and classification (DASDC) method is presented to balance the alignment of two domains and the classification performance through a domain-adversarial neural network and its adversarial learning modules. DASDC effectively addresses the issue of mismatch between training data and real genomic data in deep learning models, leading to a significant improvement in its generalization capability, prediction robustness, and accuracy. The DASDC method demonstrates improved identification performance compared to existing methods and excels in classification performance, particularly in scenarios where there is a mismatch between application data and training data. The successful implementation of DASDC in real data of three distinct species highlights its potential as a useful tool for identifying crucial functional genes and investigating adaptive evolutionary mechanisms, particularly with the increasing availability of genomic data.

Cardiac progenitor cell therapy: mechanisms of action

Heart failure (HF) is an end-stage of many cardiac diseases and one of the main causes of death worldwide. The current management of this disease remains suboptimal. The adult mammalian heart was considered a post-mitotic organ. However, several reports suggest that it may possess modest regenerative potential. Adult cardiac progenitor cells (CPCs), the main players in the cardiac regeneration, constitute, as it may seem, a heterogenous group of cells, which remain quiescent in physiological conditions and become activated after an injury, contributing to cardiomyocytes renewal. They can mediate their beneficial effects through direct differentiation into cardiac cells and activation of resident stem cells but majorly do so through paracrine release of factors. CPCs can secrete cytokines, chemokines, and growth factors as well as exosomes, rich in proteins, lipids and non-coding RNAs, such as miRNAs and YRNAs, which contribute to reparation of myocardium by promoting angiogenesis, cardioprotection, cardiomyogenesis, anti-fibrotic activity, and by immune modulation. Preclinical studies assessing cardiac progenitor cells and cardiac progenitor cells-derived exosomes on damaged myocardium show that administration of cardiac progenitor cells-derived exosomes can mimic effects of cell transplantation. Exosomes may become new promising therapeutic strategy for heart regeneration nevertheless there are still several limitations as to their use in the clinic. Key questions regarding their dosage, safety, specificity, pharmacokinetics, pharmacodynamics and route of administration remain outstanding. There are still gaps in the knowledge on basic biology of exosomes and filling them will bring as closer to translation into clinic.

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

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

Receptor tyrosine kinase inhibitors negatively impact on pro-reparative characteristics of human cardiac progenitor cells

Receptor tyrosine kinase inhibitors improve cancer survival but their cardiotoxicity requires investigation. We investigated these inhibitors’ effects on human cardiac progenitor cells in vitro and rat heart in vivo. We applied imatinib, sunitinib or sorafenib to human cardiac progenitor cells, assessing cell viability, proliferation, stemness, differentiation, growth factor production and second messengers. Alongside, sunitinib effects were assessed in vivo. Inhibitors decreased (p < 0.05) cell viability, at levels equivalent to ‘peak’ (24 h; imatinib: 91.5 ± 0.9%; sunitinib: 83.9 ± 1.8%; sorafenib: 75.0 ± 1.6%) and ‘trough’ (7 days; imatinib: 62.3 ± 6.2%; sunitinib: 86.2 ± 3.5%) clinical plasma levels, compared to control (100% viability). Reduced (p < 0.05) cell cycle activity was seen with imatinib (29.3 ± 4.3% cells in S/G2/M-phases; 50.3 ± 5.1% in control). Expression of PECAM-1, Nkx2.5, Wnt2, linked with cell differentiation, were decreased (p < 0.05) 2, 2 and 6-fold, respectively. Expression of HGF, p38 and Akt1 in cells was reduced (p < 0.05) by sunitinib. Second messenger (p38 and Akt1) blockade affected progenitor cell phenotype, reducing c-kit and growth factor (HGF, EGF) expression. Sunitinib for 9 days (40 mg/kg, i.p.) in adult rats reduced (p < 0.05) cardiac ejection fraction (68 ± 2% vs. baseline (83 ± 1%) and control (84 ± 4%)) and reduced progenitor cell numbers. Receptor tyrosine kinase inhibitors reduce cardiac progenitor cell survival, proliferation, differentiation and reparative growth factor expression.

Mitochondrial Membrane Potential Identifies a Subpopulation of Mesenchymal Progenitor Cells to Promote Angiogenesis and Myocardial Repair

Identifying effective donor cells is one of obstacles that limits cell therapy for heart disease. In this study, we sorted a subpopulation of human mesenchymal progenitor cells (hMPCs) from the right atrial appendage using the low mitochondrial membrane potential. Compared to the non-sorted cells, hMPCs hold the capacity for stemness and enrich mesenchymal stem cell markers. The hMPCs display better ability for survival, faster proliferation, less production of reactive oxygen species (ROS), and greater release of cytoprotective cytokines. The hMPCs exhibit decreased expression of senescence genes and increased expression of anti-apoptotic and antioxidant genes. Intramyocardial injection of hMPCs into the infarcted heart resulted in increased left ventricular ejection fraction and reduced cardiac remodeling and infarct size in the group of animals receiving hMPCs. Both in vitro and in vivo studies indicated hMPCs have the potential to differentiate into endothelial cells and smooth muscle cells. Immunohistochemistry staining showed that cell therapy with hMPCs enhances cardiac vascular regeneration and cardiac proliferation, and decreases cardiac cell apoptosis, which is associated with the increased secretion of cytoprotective and pro-angiogenic cytokines. Overall, we discovered a subpopulation of human mesenchymal progenitor cells via their low mitochondrial membrane potential, which might provide an alternative donor cell source for cellular therapy for ischemic heart disease.

Effect of intravenous cell therapy in rats with old myocardial infarction

Mounting evidence shows that cell therapy provides therapeutic benefits in experimental and clinical settings of chronic heart failure. However, direct cardiac delivery of cells via transendocardial injection is logistically complex, expensive, entails risks, and is not amenable to multiple dosing. Intravenous administration would be a more convenient and clinically applicable route for cell therapy. Thus, we determined whether intravenous infusion of three widely used cell types improves left ventricular (LV) function and structure and compared their efficacy. Rats with a 30-day-old myocardial infarction (MI) received intravenous infusion of vehicle (PBS) or 1 of 3 types of cells: bone marrow mesenchymal stromal cells (MSCs), cardiac mesenchymal cells (CMCs), and c-kit-positive cardiac cells (CPCs), at a dose of 12 × 106 cells. Rats were followed for 35 days after treatment to determine LV functional status by serial echocardiography and hemodynamic studies. Blood samples were collected for Hemavet analysis to determine inflammatory cell profile. LV ejection fraction (EF) dropped ≥ 20 points in all hearts at 30 days after MI and deteriorated further at 35-day follow-up in the vehicle-treated group. In contrast, deterioration of EF was halted in rats that received MSCs and attenuated in those that received CMCs or CPCs. None of the 3 types of cells significantly altered scar size, myocardial content of collagen or CD45-positive cells, or Hemavet profile. This study demonstrates that a single intravenous administration of 3 types of cells in rats with chronic ischemic cardiomyopathy is effective in attenuating the progressive deterioration in LV function. The extent of LV functional improvement was greatest with CPCs, intermediate with CMCs, and least with MSCs.

Intracoronary Delivery of Porcine Cardiac Progenitor Cells Overexpressing IGF-1 and HGF in a Pig Model of Sub-Acute Myocardial Infarction

Human cardiac progenitor cells (hCPC) are considered a good candidate in cell therapy for ischemic heart disease, demonstrating capacity to improve functional recovery after myocardial infarction (MI), both in small and large preclinical animal models. However, improvements are required in terms of cell engraftment and efficacy. Based on previously published reports, insulin-growth factor 1 (IGF-1) and hepatocyte growth factor (HGF) have demonstrated substantial cardioprotective, repair and regeneration activities, so they are good candidates to be evaluated in large animal model of MI. We have validated porcine cardiac progenitor cells (pCPC) and lentiviral vectors to overexpress IGF-1 (co-expressing eGFP) and HGF (co-expressing mCherry). pCPC were transduced and IGF1-eGFP^pos and HGF-mCherry^pos populations were purified by cell sorting and further expanded. Overexpression of IGF-1 has a limited impact on pCPC expression profile, whereas results indicated that pCPC-HGF-mCherry cultures could be counter selecting high expresser cells. In addition, pCPC-IGF1-eGFP showed a higher cardiogenic response, evaluated in co-cultures with decellularized extracellular matrix, compared with native pCPC or pCPC-HGF-mCherry. In vivo intracoronary co-administration of pCPC-IGF1-eGFP and pCPC-HFG-mCherry (1:1; 40 × 10⁶/animal), one week after the induction of an MI model in swine, revealed no significant improvement in cardiac function.

Human cardiac stem cells rejuvenated by modulating autophagy with MHY-1685 enhance the therapeutic potential for cardiac repair

Stem cell-based therapies with clinical applications require millions of cells. Therefore, repeated subculture is essential for cellular expansion, which is often complicated by replicative senescence. Cellular senescence contributes to reduced stem cell regenerative potential as it inhibits stem cell proliferation and differentiation as well as the activation of the senescence-associated secretory phenotype (SASP). In this study, we employed MHY-1685, a novel mammalian target of rapamycin (mTOR) inhibitor, and examined its long-term priming effect on the activities of senile human cardiac stem cells (hCSCs) and the functional benefits of primed hCSCs after transplantation. In vitro experiments showed that the MHY-1685‒primed hCSCs exhibited higher viability in response to oxidative stress and an enhanced proliferation potential compared to that of the unprimed senile hCSCs. Interestingly, priming MHY-1685 enhanced the expression of stemness-related markers in senile hCSCs and provided the differentiation potential of hCSCs into vascular lineages. In vivo experiment with echocardiography showed that transplantation of MHY-1685‒primed hCSCs improved cardiac function than that of the unprimed senile hCSCs at 4 weeks post-MI. In addition, hearts transplanted with MHY-1685-primed hCSCs exhibited significantly lower cardiac fibrosis and higher capillary density than that of the unprimed senile hCSCs. In confocal fluorescence imaging, MHY-1685‒primed hCSCs survived for longer durations than that of the unprimed senile hCSCs and had a higher potential to differentiate into endothelial cells (ECs) within the infarcted hearts. These findings suggest that MHY-1685 can rejuvenate senile hCSCs by modulating autophagy and that as a senescence inhibitor, MHY-1685 can provide opportunities to improve hCSC-based myocardial regeneration.

Transcriptional features of biological age maintained in human cultured cardiac interstitial cells

Ex vivo expansion of cells is necessary in regenerative medicine to generate large populations for therapeutic use. Adaptation to culture conditions prompt an increase in transcriptome diversity and decreased population heterogeneity in cKit+ cardiac interstitial cells (cCICs). The "transcriptional memory" influenced by cellular origin remained unexplored and is likely to differ between neonatal versus senescent input cells undergoing culture expansion. Transcriptional profiles derived from single cell RNASEQ platforms characterized human cCIC derived from neonatal and adult source tissue. Bioinformatic analysis revealed contrasting imprint of age influencing targets of 1) cell cycle, 2) senescence associated secretory phenotype (SASP), 3) RNA transport, and 4) ECM-receptor/fibrosis. A small subset of cCICs exist in a transcriptional continuum between "youthful" phenotype and the damaged microenvironment of LVAD tissue in which they were embedded. The connate transcriptional phenotypes offer fundamental biological insight and highlights cellular input as a consideration in culture expansion and adoptive transfer protocols.

Targeted delivery of therapeutic agents to the heart

For therapeutic materials to be successfully delivered to the heart, several barriers need to be overcome, including the anatomical challenges of access, the mechanical force of the blood flow, the endothelial barrier, the cellular barrier and the immune response. Various vectors and delivery methods have been proposed to improve the cardiac-specific uptake of materials to modify gene expression. Viral and non-viral vectors are widely used to deliver genetic materials, but each has its respective advantages and shortcomings. Adeno-associated viruses have emerged as one of the best tools for heart-targeted gene delivery. In addition, extracellular vesicles, including exosomes, which are secreted by most cell types, have gained popularity for drug delivery to several organs, including the heart. Accumulating evidence suggests that extracellular vesicles can carry and transfer functional proteins and genetic materials into target cells and might be an attractive option for heart-targeted delivery. Extracellular vesicles or artificial carriers of non-viral and viral vectors can be bioengineered with immune-evasive and cardiotropic properties. In this Review, we discuss the latest strategies for targeting and delivering therapeutic materials to the heart and how the knowledge of different vectors and delivery methods could successfully translate cardiac gene therapy into the clinical setting.

The Impact of Spaceflight and Microgravity on the Human Islet-1+ Cardiovascular Progenitor Cell Transcriptome

Understanding the transcriptomic impact of microgravity and the spaceflight environment is relevant for future missions in space and microgravity-based applications designed to benefit life on Earth. Here, we investigated the transcriptome of adult and neonatal cardiovascular progenitors following culture aboard the International Space Station for 30 days and compared it to the transcriptome of clonally identical cells cultured on Earth. Cardiovascular progenitors acquire a gene expression profile representative of an early-stage, dedifferentiated, stem-like state, regardless of age. Signaling pathways that support cell proliferation and survival were induced by spaceflight along with transcripts related to cell cycle re-entry, cardiovascular development, and oxidative stress. These findings contribute new insight into the multifaceted influence of reduced gravitational environments.

Stem Cells in Cardiovascular Diseases: 30,000-Foot View

Stem cell and regenerative approaches that might rejuvenate the heart have immense intuitive appeal for the public and scientific communities. Hopes were fueled by initial findings from preclinical models that suggested that easily obtained bone marrow cells might have significant reparative capabilities; however, after initial encouraging pre-clinical and early clinical findings, the realities of clinical development have placed a damper on the field. Clinical trials were often designed to detect exceptionally large treatment effects with modest patient numbers with subsequent disappointing results. First generation approaches were likely overly simplistic and relied on a relatively primitive understanding of regenerative mechanisms and capabilities. Nonetheless, the field continues to move forward and novel cell derivatives, platforms, and cell/device combinations, coupled with a better understanding of the mechanisms that lead to regenerative capabilities in more primitive models and modifications in clinical trial design suggest a brighter future.

Atrial myxoma: the cardiac chameleon

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Stem Cell Metabolism: Powering Cell-Based Therapeutics

Cell-based therapeutics for cardiac repair have been extensively used during the last decade. Preclinical studies have demonstrated the effectiveness of adoptively transferred stem cells for enhancement of cardiac function. Nevertheless, several cell-based clinical trials have provided largely underwhelming outcomes. A major limitation is the lack of survival in the harsh cardiac milieu as only less than 1% donated cells survive. Recent efforts have focused on enhancing cell-based therapeutics and understanding the biology of stem cells and their response to environmental changes. Stem cell metabolism has recently emerged as a critical determinant of cellular processes and is uniquely adapted to support proliferation, stemness, and commitment. Metabolic signaling pathways are remarkably sensitive to different environmental signals with a profound effect on cell survival after adoptive transfer. Stem cells mainly generate energy through glycolysis while maintaining low oxidative phosphorylation (OxPhos), providing metabolites for biosynthesis of macromolecules. During commitment, there is a shift in cellular metabolism, which alters cell function. Reprogramming stem cell metabolism may represent an attractive strategy to enhance stem cell therapy for cardiac repair. This review summarizes the current literature on how metabolism drives stem cell function and how this knowledge can be applied to improve cell-based therapeutics for cardiac repair.

After the storm: an objective appraisal of the efficacy of c-kit+ cardiac progenitor cells in preclinical models of heart disease

The falsification of data related to c-kit+ cardiac progenitor cells (CPCs) by a Harvard laboratory has been a veritable tragedy. Does this fraud mean that CPCs are not beneficial in models of ischemic cardiomyopathy? At least 50 studies from 26 laboratories independent of the Harvard group have reported beneficial effects of CPCs in mice, rats, pigs, and cats. The mechanism of action remains unclear. Our group has shown that CPCs do not engraft in the diseased heart, do not differentiate into new cardiac myocytes, do not regenerate dead myocardium, and thus work via paracrine mechanisms. A casualty of the misconduct at Harvard has been the SCIPIO trial, a collaboration between the Harvard group and the group in Louisville. The retraction of the SCIPIO paper was caused exclusively by issues with data generated at Harvard, not those generated in Louisville. In the retraction notice, the Lancet editors stated: "Although we do not have any reservations about the clinical work in Louisville that used the preparations from Anversa's laboratory in good faith, the lack of reliability regarding the laboratory work at Harvard means that we are now retracting this paper". We must be careful not to dismiss all work on CPCs because of one laboratory's misconduct. An unbiased review of the literature supports the therapeutic potential of CPCs for heart failure at the preclinical level.

PIM1 Promotes Survival of Cardiomyocytes by Upregulating c-Kit Protein Expression

Enhancing cardiomyocyte survival is crucial to blunt deterioration of myocardial structure and function following pathological damage. PIM1 (Proviral Insertion site in Murine leukemia virus (PIM) kinase 1) is a cardioprotective serine threonine kinase that promotes cardiomyocyte survival and antagonizes senescence through multiple concurrent molecular signaling cascades. In hematopoietic stem cells, PIM1 interacts with the receptor tyrosine kinase c-Kit upstream of the ERK (Extracellular signal-Regulated Kinase) and Akt signaling pathways involved in cell proliferation and survival. The relationship between PIM1 and c-Kit activity has not been explored in the myocardial context. This study delineates the interaction between PIM1 and c-Kit leading to enhanced protection of cardiomyocytes from stress. Elevated c-Kit expression is induced in isolated cardiomyocytes from mice with cardiac-specific overexpression of PIM1. Co-immunoprecipitation and proximity ligation assay reveal protein–protein interaction between PIM1 and c-Kit. Following treatment with Stem Cell Factor, PIM1-overexpressing cardiomyocytes display elevated ERK activity consistent with c-Kit receptor activation. Functionally, elevated c-Kit expression confers enhanced protection against oxidative stress in vitro. This study identifies the mechanistic relationship between PIM1 and c-Kit in cardiomyocytes, demonstrating another facet of cardioprotection regulated by PIM1 kinase.

The Roles of Nanoparticles in Stem Cell-Based Therapy for Cardiovascular Disease

Cardiovascular disease (CVD) is currently one of the primary causes of mortality and morbidity worldwide. Nanoparticles (NPs) are playing increasingly important roles in regulating stem cell behavior because of their special features, including shape, size, aspect ratio, surface charge, and surface area. In terms of cardiac disease, NPs can facilitate gene delivery in stem cells, track the stem cells in vivo for long-term monitoring, and enhance retention after their transplantation. The advantages of applying NPs in peripheral vascular disease treatments include facilitating stem cell therapy, mimicking the extracellular matrix environment, and utilizing a safe non-viral gene delivery tool. However, the main limitation of NPs is toxicity, which is related to their size, shape, aspect ratio, and surface charge. Currently, there have been many animal models proving NPs’ potential in treating CVD, but no extensive applications of stem-cell therapy using NPs are available in clinical practice. In conclusion, NPs might have significant potential uses in clinical trials of CVD in the future, thereby meeting the changing needs of individual patients worldwide.

[Expression and role of Pim1 in cultured cortical neurons with oxygen-glucose deprivation/reoxygen injury]

OBJECTIVE

To study the expression and effect of Pim1 in primary cortical neurons after hypoxic-ischemic injury.

METHODS

Cortical neurons were isolated from 1-day-old C57BL/6 mice and cultured in neurobasal medium. On the 8th day of neuron culture, cells were subjected to oxygen-glucose deprivation/reoxygen (OGD/R) treatment to mimic in vivo hypoxic injury of neurons. Briefly, medium were changed to DMEM medium, and cells were cultured in 1% O₂ for 3 hours and then changed back to normal medium and conditions. Cells were collected at 0 hour, 6 hours, 12 hours and 24 hours after OGD/R. Primary neurons were transfected with Pim1 overexpression plasmid or mock plasmid, and then were exposed to normal conditions or OGD/R treatment. They were named as Pim1 group, control group, OGD/R group and OGD/R+Pim1 group respectively. Real-time PCR was used to detect Pim1 mRNA expression. Western blot was used to detect the protein expression of Pim1 and apoptotic related protein cleaved caspase 3 (CC3). TUNEL staining was used to detect cell apoptosis.

RESULTS

Real-time PCR and Western blot results showed that Pim1 mRNA and protein were significantly decreased in neurons after OGD/R. They began to decrease at 0 hour after OGD/R, reached to the lowest at 12 hours after OGD/R, and remained at a lower level at 24 hours after OGD/R (P<0.01). Overexpression of Pim1 significantly upregulated the protein level of Pim1. Under OGD/R conditions, the CC3 expression and the apoptosis rate in cells of the Pim1 group were significantly lower than in un-transfected cells (P<0.01).

CONCLUSIONS

Hypoxic-ischemic injury may decrease Pim1 expression in neurons. Overexpressed Pim1 may inhibit apoptosis induced by OGD/R.

Adaptation within embryonic and neonatal heart environment reveals alternative fates for adult c-kit+ cardiac interstitial cells

Cardiac interstitial cells (CICs) perform essential roles in myocardial biology through preservation of homeostasis as well as response to injury or stress. Studies of murine CIC biology reveal remarkable plasticity in terms of transcriptional reprogramming and ploidy state with important implications for function. Despite over a decade of characterization and in vivo utilization of adult c-Kit+ CIC (cCIC), adaptability and functional responses upon delivery to adult mammalian hearts remain poorly understood. Limitations of characterizing cCIC biology following in vitro expansion and adoptive transfer into the adult heart were circumvented by delivery of the donated cells into early cardiogenic environments of embryonic, fetal, and early postnatal developing hearts. These three developmental stages were permissive for retention and persistence, enabling phenotypic evaluation of in vitro expanded cCICs after delivery as well as tissue response following introduction to the host environment. Embryonic blastocyst environment prompted cCIC integration into trophectoderm as well as persistence in amniochorionic membrane. Delivery to fetal myocardium yielded cCIC perivascular localization with fibroblast-like phenotype, similar to cCICs introduced to postnatal P3 heart with persistent cell cycle activity for up to 4 weeks. Fibroblast-like phenotype of exogenously transferred cCICs in fetal and postnatal cardiogenic environments is consistent with inability to contribute directly toward cardiogenesis and lack of functional integration with host myocardium. In contrast, cCICs incorporation into extra-embryonic membranes is consistent with fate of polyploid cells in blastocysts. These findings provide insight into cCIC biology, their inherent predisposition toward fibroblast fates in cardiogenic environments, and remarkable participation in extra-embryonic tissue formation.

Pharmacological inhibition of mTOR attenuates replicative cell senescence and improves cellular function via regulating the STAT3-PIM1 axis in human cardiac progenitor cells

The mammalian target of rapamycin (mTOR) signaling pathway efficiently regulates the energy state of cells and maintains tissue homeostasis. Dysregulation of the mTOR pathway has been implicated in several human diseases. Rapamycin is a specific inhibitor of mTOR and pharmacological inhibition of mTOR with rapamycin promote cardiac cell generation from the differentiation of mouse and human embryonic stem cells. These studies strongly implicate a role of sustained mTOR activity in the differentiating functions of embryonic stem cells; however, they do not directly address the required effect for sustained mTOR activity in human cardiac progenitor cells. In the present study, we evaluated the effect of mTOR inhibition by rapamycin on the cellular function of human cardiac progenitor cells and discovered that treatment with rapamycin markedly attenuated replicative cell senescence in human cardiac progenitor cells (hCPCs) and promoted their cellular functions. Furthermore, rapamycin not only inhibited mTOR signaling but also influenced signaling pathways, including STAT3 and PIM1, in hCPCs. Therefore, these data reveal a crucial function for rapamycin in senescent hCPCs and provide clinical strategies based on chronic mTOR activity.

Adult human cardiac stem cell supplementation effectively increases contractile function and maturation in human engineered cardiac tissues

BACKGROUND

Delivery of stem cells to the failing heart is a promising therapeutic strategy. However, the improvement in cardiac function in animal studies has not fully translated to humans. To help bridge the gap between species, we investigated the effects of adult human cardiac stem cells (hCSCs) on contractile function of human engineered cardiac tissues (hECTs) as a species-specific model of the human myocardium.

METHODS

Human induced pluripotent stem cell-derived cardiomyoctes (hCMs) were mixed with Collagen/Matrigel to fabricate control hECTs, with an experimental group of hCSC-supplemented hECT fabricated using a 9:1 ratio of hCM to hCSC. Functional testing was performed starting on culture day 6, under spontaneous conditions and also during electrical pacing from 0.25 to 1.0 Hz, measurements repeated at days 8 and 10. hECTs were then frozen and processed for gene analysis using a Nanostring assay with a cardiac targeted custom panel.

RESULTS

The hCSC-supplemented hECTs displayed a twofold higher developed force vs. hCM-only controls by day 6, with approximately threefold higher developed stress and maximum rates of contraction and relaxation during pacing at 0.75 Hz. The spontaneous beat rate characteristics were similar between groups, and hCSC supplementation did not adversely impact beat rate variability. The increased contractility persisted through days 8 and 10, albeit with some decrease in the magnitude of the difference of the force by day 10, but with developed stress still significantly higher in hCSC-supplemented hECT; these findings were confirmed with multiple hCSC and hCM cell lines. The force-frequency relationship, while negative for both, control (- 0.687 Hz^- 1; p = 0.013 vs. zero) and hCSC-supplemented (- 0.233 Hz^- 1;p = 0.067 vs. zero) hECTs, showed a significant rectification in the regression slope in hCSC-supplemented hECT (p = 0.011 vs. control). Targeted gene exploration (59 genes) identified a total of 14 differentially expressed genes, with increases in the ratios of MYH7/MHY6, MYL2/MYL7, and TNNI3/TNNI1 in hCSC-supplemented hECT versus controls.

CONCLUSIONS

For the first time, hCSC supplementation was shown to significantly improve human cardiac tissue contractility in vitro, without evidence of proarrhythmic effects, and was associated with increased expression of markers of cardiac maturation. These findings provide new insights about adult cardiac stem cells as contributors to functional improvement of human myocardium.

Cardiac regenerative therapy: Many paths to repair

Cardiovascular disease remains the primary cause of death in the United States and in most nations worldwide, despite ongoing intensive efforts to promote cardiac health and treat heart failure. Replacing damaged myocardium represents perhaps the most promising treatment strategy, but also the most challenging given that the adult mammalian heart is notoriously resistant to endogenous repair. Cardiac regeneration following pathologic challenge would require proliferation of surviving tissue, expansion and differentiation of resident progenitors, or transdifferentiation of exogenously applied progenitor cells into functioning myocardium. Adult cardiomyocyte proliferation has been the focus of investigation for decades, recently enjoying a renaissance of interest as a therapeutic strategy for reversing cardiomyocyte loss due in large part to ongoing controversies and frustrations with myocardial cell therapy outcomes. The promise of cardiac cell therapy originated with reports of resident adult cardiac stem cells that could be isolated, expanded and reintroduced into damaged myocardium, producing beneficial effects in preclinical animal models. Despite modest functional improvements, Phase I clinical trials using autologous cardiac derived cells have proven safe and effective, setting the stage for an ongoing multi-center Phase II trial combining autologous cardiac stem cell types to enhance beneficial effects. This overview will examine the history of these two approaches for promoting cardiac repair and attempt to provide context for current and future directions in cardiac regenerative research.

Animal- and human-based evidence for the protective effects of stem cell therapy against cardiovascular disorders

The increasing rate of mortality and morbidity because of cardiac diseases has called for efficient therapeutic needs. With the advancement in cell-based therapies, stem cells are abundantly studied in this area. Nearly, all sources of stem cells are experimented to treat cardiac injuries. Tissue engineering has also backed this technique by providing an advantageous platform to improve stem cell therapy. After in vitro studies, primary treatment-based research studies comprise small and large animal studies. Furthermore, these studies are implemented in human models in the form of clinical trials. Purpose of this review is to highlight the animal- and human-based studies, exploiting various stem cell sources, to treat cardiovascular disorders.

Cardiac ageing: extrinsic and intrinsic factors in cellular renewal and senescence

Cardiac ageing manifests as a decline in function leading to heart failure. At the cellular level, ageing entails decreased replicative capacity and dysregulation of cellular processes in myocardial and nonmyocyte cells. Various extrinsic parameters, such as lifestyle and environment, integrate important signalling pathways, such as those involving inflammation and oxidative stress, with intrinsic molecular mechanisms underlying resistance versus progression to cellular senescence. Mitigation of cardiac functional decline in an ageing organism requires the activation of enhanced maintenance and reparative capacity, thereby overcoming inherent endogenous limitations to retaining a youthful phenotype. Deciphering the molecular mechanisms underlying dysregulation of cellular function and renewal reveals potential interventional targets to attenuate degenerative processes at the cellular and systemic levels to improve quality of life for our ageing population. In this Review, we discuss the roles of extrinsic and intrinsic factors in cardiac ageing. Animal models of cardiac ageing are summarized, followed by an overview of the current and possible future treatments to mitigate the deleterious effects of cardiac ageing.

Preclinical Studies of Stem Cell Therapy for Heart Disease

As part of the TACTICS (Transnational Alliance for Regenerative Therapies in Cardiovascular Syndromes) series to enhance regenerative medicine, here, we discuss the role of preclinical studies designed to advance stem cell therapies for cardiovascular disease. The quality of this research has improved over the past 10 to 15 years and overall indicates that cell therapy promotes cardiac repair. However, many issues remain, including inability to provide complete cardiac recovery. Recent studies question the need for intact cells suggesting that harnessing what the cells release is the solution. Our contribution describes important breakthroughs and current directions in a cell-based approach to alleviating cardiovascular disease.

Enhanced cardiac repair by telomerase reverse transcriptase over-expression in human cardiac mesenchymal stromal cells

We have previously reported a subpopulation of mesenchymal stromal cells (MSCs) within the platelet-derived growth factor receptor-alpha (PDGFRα)/CD90 co-expressing cardiac interstitial and adventitial cell fraction. Here we further characterise PDGFRα/CD90-expressing cardiac MSCs (PDGFRα + cMSCs) and use human telomerase reverse transcriptase (hTERT) over-expression to increase cMSCs ability to repair the heart after induced myocardial infarction. hTERT over-expression in PDGFRα + cardiac MSCs (hTERT + PDGFRα + cMSCs) modulates cell differentiation, proliferation, survival and angiogenesis related genes. In vivo, transplantation of hTERT + PDGFRα + cMSCs in athymic rats significantly increased left ventricular function, reduced scar size, increased angiogenesis and proliferation of both cardiomyocyte and non-myocyte cell fractions four weeks after myocardial infarction. In contrast, transplantation of mutant hTERT + PDGFRα + cMSCs (which generate catalytically-inactive telomerase) failed to replicate this cardiac functional improvement, indicating a telomerase-dependent mechanism. There was no hTERT + PDGFRα + cMSCs engraftment 14 days after transplantation indicating functional improvement occurred by paracrine mechanisms. Mass spectrometry on hTERT + PDGFRα + cMSCs conditioned media showed increased proteins associated with matrix modulation, angiogenesis, cell proliferation/survival/adhesion and innate immunity function. Our study shows that hTERT can activate pro-regenerative signalling within PDGFRα + cMSCs and enhance cardiac repair after myocardial infarction. An increased understanding of hTERT’s role in mesenchymal stromal cells from various organs will favourably impact clinical regenerative and anti-cancer therapies.

Safety profiling of genetically engineered Pim-1 kinase overexpression for oncogenicity risk in human c-kit+ cardiac interstitial cells

Advancement of stem cell-based treatment will involve next-generation approaches to enhance therapeutic efficacy which is often modest, particularly in the context of myocardial regenerative therapy. Our group has previously demonstrated the beneficial effect of genetic modification of cardiac stem cells with Pim-1 kinase overexpression to rejuvenate aged cells as well as potentiate myocardial repair. Despite these encouraging findings, concerns were raised regarding potential for oncogenic risk associated with Pim-1 kinase overexpression. Testing of Pim-1 engineered c-kit+ cardiac interstitial cells (cCIC) derived from heart failure patient samples for indices of oncogenic risk was undertaken using multiple assessments including soft agar colony formation, micronucleation, gamma-Histone 2AX foci, and transcriptome profiling. Collectively, findings demonstrate comparable phenotypic and biological properties of cCIC following Pim-1 overexpression compared with using baseline control cells with no evidence for oncogenic phenotype. Using a highly selective and continuous sensor for quantitative assessment of PIM1 kinase activity revealed a sevenfold increase in Pim-1 engineered vs. control cells. Kinase activity profiling using a panel of sensors for other kinases demonstrates elevation of IKKs), AKT/SGK, CDK1-3, p38, and ERK1/2 in addition to Pim-1 consistent with heightened kinase activity correlating with Pim-1 overexpression that may contribute to Pim-1-mediated effects. Enhancement of cellular survival, proliferation, and other beneficial properties to augment stem cell-mediated repair without oncogenic risk is a feasible, logical, and safe approach to improve efficacy and overcome current limitations inherent to cellular adoptive transfer therapeutic interventions.

Cardiac interstitial tetraploid cells can escape replicative senescence in rodents but not large mammals

Cardiomyocyte ploidy has been described but remains obscure in cardiac interstitial cells. Ploidy of c-kit+ cardiac interstitial cells was assessed using confocal, karyotypic, and flow cytometric technique. Notable differences were found between rodent (rat, mouse) c-kit+ cardiac interstitial cells possessing mononuclear tetraploid (4n) content, compared to large mammals (human, swine) with mononuclear diploid (2n) content. In-situ analysis, confirmed with fresh isolates, revealed diploid content in human c-kit+ cardiac interstitial cells and a mixture of diploid and tetraploid content in mouse. Downregulation of the p53 signaling pathway provides evidence why rodent, but not human, c-kit+ cardiac interstitial cells escape replicative senescence. Single cell transcriptional profiling reveals distinctions between diploid versus tetraploid populations in mouse c-kit+ cardiac interstitial cells, alluding to functional divergences. Collectively, these data reveal notable species-specific biological differences in c-kit+ cardiac interstitial cells, which could account for challenges in extrapolation of myocardial from preclinical studies to clinical trials.

Dose-dependent improvement of cardiac function in a swine model of acute myocardial infarction after intracoronary administration of allogeneic heart-derived cells

BACKGROUND

Allogeneic cardiac-derived progenitor cells (CPC) without immunosuppression could provide an effective ancillary therapy to improve cardiac function in reperfused myocardial infarction. We set out to perform a comprehensive preclinical feasibility and safety evaluation of porcine CPC (pCPC) in the infarcted porcine model, analyzing biodistribution and mid-term efficacy, as well as safety in healthy non-infarcted swine.

METHODS

The expression profile of several pCPC isolates was compared with humans using both FACS and RT-qPCR. ELISA was used to compare the functional secretome. One week after infarction, female swine received an intracoronary (IC) infusion of vehicle (CON), 25 × 10⁶ pCPC (25 M), or 50 × 10⁶ pCPC (50 M). Animals were followed up for 10 weeks using serial cardiac magnetic resonance imaging to assess functional and structural remodeling (left ventricular ejection fraction (LVEF), systolic and diastolic volumes, and myocardial salvage index). Statistical comparisons were performed using Kruskal-Wallis and Mann-Whitney U tests. Biodistribution analysis of ¹⁸F-FDG-labeled pCPC was also performed 4 h after infarction in a different subset of animals.

RESULTS

Phenotypic and functional characterization of pCPC revealed a gene expression profile comparable to their human counterparts as well as preliminary functional equivalence. Left ventricular functional and structural remodeling showed significantly increased LVEF 10 weeks after IC administration of 50 M pCPC, associated to the recovery of left ventricular volumes that returned to pre-infarction values (LVEF at 10 weeks was 42.1 ± 10.0% in CON, 46.5 ± 7.4% in 25 M, and 50.2 ± 4.9% in 50 M, p < 0.05). Infarct remodeling was also improved following pCPC infusion with a significantly higher myocardial salvage index in both treated groups (0.35 ± 0.20 in CON; 0.61 ± 0.20, p = 0.04, in 25 M; and 0.63 ± 0.17, p = 0.01, in 50 M). Biodistribution studies demonstrated cardiac tropism 4 h after IC administration, with substantial myocardial retention of pCPC-associated tracer activity (18% of labeled cells in the heart), and no obstruction of coronary flow, indicating their suitability as a cell therapy product.

CONCLUSIONS

IC administration of allogeneic pCPC at 1 week after acute myocardial infarction is feasible, safe, and associated with marked structural and functional benefit. The robust cardiac tropism of pCPC and the paracrine effects on left ventricle post-infarction remodeling established the preclinical bases for the CAREMI clinical trial (NCT02439398).

BNIP3L/NIX and FUNDC1-mediated mitophagy is required for mitochondrial network remodeling during cardiac progenitor cell differentiation

Cell-based therapies represent a very promising strategy to repair and regenerate the injured heart to prevent progression to heart failure. To date, these therapies have had limited success due to a lack of survival and retention of the infused cells. Therefore, it is important to increase our understanding of the biology of these cells and utilize this information to enhance their survival and function in the injured heart. Mitochondria are critical for progenitor cell function and survival. Here, we demonstrate the importance of mitochondrial autophagy, or mitophagy, in the differentiation process in adult cardiac progenitor cells (CPCs). We found that mitophagy was rapidly induced upon initiation of differentiation in CPCs. We also found that mitophagy was mediated by mitophagy receptors, rather than the PINK1-PRKN/PARKIN pathway. Mitophagy mediated by BNIP3L/NIX and FUNDC1 was not involved in regulating progenitor cell fate determination, mitochondrial biogenesis, or reprogramming. Instead, mitophagy facilitated the CPCs to undergo proper mitochondrial network reorganization during differentiation. Abrogating BNIP3L- and FUNDC1-mediated mitophagy during differentiation led to sustained mitochondrial fission and formation of donut-shaped impaired mitochondria. It also resulted in increased susceptibility to cell death and failure to survive the infarcted heart. Finally, aging is associated with accumulation of mitochondrial DNA (mtDNA) damage in cells and we found that acquiring mtDNA mutations selectively disrupted the differentiation-activated mitophagy program in CPCs. These findings demonstrate the importance of BNIP3L- and FUNDC1-mediated mitophagy as a critical regulator of mitochondrial network formation during differentiation, as well as the consequences of accumulating mtDNA mutations. Abbreviations: Baf: bafilomycin A₁; BCL2L13: BCL2 like 13; BNIP3: BCL2 interacting protein 3; BNIP3L: BCL2 interacting protein 3 like; CPCs: cardiac progenitor cells; DM: differentiation media; DNM1L: dynamin 1 like; EPCs: endothelial progenitor cells; FCCP: carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone; FUNDC1: FUN14 domain containing 1; HSCs: hematopoietic stem cells; MAP1LC3B/LC3: microtubule-associated protein 1 light chain 3 beta; MFN1/2: mitofusin 1/2; MSCs: mesenchymal stem cells; mtDNA: mitochondrial DNA; OXPHOS: oxidative phosphorylation; PPARGC1A: PPARG coactivator 1 alpha; PHB2: prohibitin 2; POLG: DNA polymerase gamma, catalytic subunit; SQSTM1: sequestosome 1; TEM: transmission electron microscopy; TMRM: tetramethylrhodamine methyl ester.

Hypoxia Prevents Mitochondrial Dysfunction and Senescence in Human c-Kit+ Cardiac Progenitor Cells

Senescence-associated dysfunction deleteriously affects biological activities of human c-Kit⁺ cardiac progenitor cells (hCPCs), particularly under conditions of in vitro culture. In comparison, preservation of self-renewal and decreases in mitochondrial reactive oxygen species (ROS) are characteristics of murine CPCs in vivo that reside within hypoxic niches. Recapitulating hypoxic niche oxygen tension conditions of ∼1% O₂ in vitro for expansion of hCPCs rather than typical normoxic cell culture conditions (21% O₂ ) could provide significant improvement of functional and biological activities of hCPCs. hCPCs were isolated and expanded under permanent hypoxic (hCPC-1%) or normoxic (hCPC-21%) conditions from left ventricular tissue explants collected during left ventricular assist device implantation. hCPC-1% exhibit increased self-renewal and suppression of senescence characteristics relative to hCPC-21%. Oxidative stress contributed to higher susceptibility to apoptosis, as well as decreased mitochondrial function in hCPC-21%. Hypoxia prevented accumulation of dysfunctional mitochondria, supporting higher oxygen consumption rates and mitochondrial membrane potential. Mitochondrial ROS was an upstream mediator of senescence since treatment of hCPC-1% with mitochondrial inhibitor antimycin A recapitulated mitochondrial dysfunction and senescence observed in hCPC-21%. NAD⁺ /NADH ratio and autophagic flux, which are key factors for mitochondrial function, were higher in hCPC-1%, but hCPC-21% were highly dependent on BNIP3/NIX-mediated mitophagy to maintain mitochondrial function. Overall, results demonstrate that supraphysiological oxygen tension during in vitro expansion initiates a downward spiral of oxidative stress, mitochondrial dysfunction, and cellular energy imbalance culminating in early proliferation arrest of hCPCs. Senescence is inhibited by preventing ROS through hypoxic culture of hCPCs. Stem Cells 2019;37:555-567.

Age-Appropriateness of Porcine Models Used for Cell Transplantation

Pigs have traditionally been used for preclinical experiments, and body size-matching is important for cell therapy in animal models used for preclinical trials. It has been shown that the efficacy of the transplanted cells is dependent on the response of the host heart and the age of experimental pigs.

Future directions for therapeutic strategies in post-ischaemic vascularization: a position paper from European Society of Cardiology Working Group on Atherosclerosis and Vascular Biology

Modulation of vessel growth holds great promise for treatment of cardiovascular disease. Strategies to promote vascularization can potentially restore function in ischaemic tissues. On the other hand, plaque neovascularization has been shown to associate with vulnerable plaque phenotypes and adverse events. The current lack of clinical success in regulating vascularization illustrates the complexity of the vascularization process, which involves a delicate balance between pro- and anti-angiogenic regulators and effectors. This is compounded by limitations in the models used to study vascularization that do not reflect the eventual clinical target population. Nevertheless, there is a large body of evidence that validate the importance of angiogenesis as a therapeutic concept. The overall aim of this Position Paper of the ESC Working Group of Atherosclerosis and Vascular biology is to provide guidance for the next steps to be taken from pre-clinical studies on vascularization towards clinical application. To this end, the current state of knowledge in terms of therapeutic strategies for targeting vascularization in post-ischaemic disease is reviewed and discussed. A consensus statement is provided on how to optimize vascularization studies for the identification of suitable targets, the use of animal models of disease, and the analysis of novel delivery methods.

Can We Engineer a Human Cardiac Patch for Therapy?

Some of the most significant leaps in the history of modern civilization-the development of article in China, the steam engine, which led to the European industrial revolution, and the era of computers-have occurred when science converged with engineering. Recently, the convergence of human pluripotent stem cell technology with biomaterials and bioengineering have launched a new medical innovation: functional human engineered tissue, which promises to revolutionize the treatment of failing organs including most critically, the heart. This compendium covers recent, state-of-the-art developments in the fields of cardiovascular tissue engineering, as well as the needs and challenges associated with the clinical use of these technologies. We have not attempted to provide an exhaustive review in stem cell biology and cardiac cell therapy; many other important and influential reports are certainly merit but already been discussed in several recent reviews. Our scope is limited to the engineered tissues that have been fabricated to repair or replace components of the heart (eg, valves, vessels, contractile tissue) that have been functionally compromised by diseases or developmental abnormalities. In particular, we have focused on using an engineered myocardial tissue to mitigate deficiencies in contractile function.

Enhancement Strategies for Cardiac Regenerative Cell Therapy: Focus on Adult Stem Cells

The idiom heart of the matter refers to the focal point within a topic and, with regard to health and longevity, the heart is truly pivotal for quality of life. Societal trends worldwide continue toward increased percent body fat and decreased physical activity with coincident increases in chronic diseases including cardiovascular disease as the top global cause of death along with insulin resistance, accelerated aging, cancer. Although long-term survival rates for cardiovascular disease patients are grim, intense research efforts continue to improve both prevention and treatment options. Pharmacological interventions remain the predominant interventional strategy for mitigating progression and managing symptoms, but cellular therapies have the potential to cure or even mediate remission of cardiovascular disease. Adult stem cells are the most studied cellular therapy in both preclinical and clinical investigation. This review will focus on the advanced therapeutic strategies to augment products and methods of delivery, which many think heralds the future of clinical investigations. Advanced preclinical strategies using adult stem cells are examined to promote synergism between preclinical and clinical research, streamline implementation, and improve this imminent matter of the heart.

Age-Related Impaired Efficacy of Bone Marrow Cell Therapy for Myocardial Infarction Reflects a Decrease in B Lymphocytes

Treatment of myocardial infarction (MI) with bone marrow cells (BMCs) improves post-MI cardiac function in rodents. However, clinical trials of BMC therapy have been less effective. While most rodent experiments use young healthy donors, patients undergoing autologous cell therapy are older and post-MI. We previously demonstrated that BMCs from aged and post-MI donor mice are therapeutically impaired, and that donor MI induces inflammatory changes in BMC composition including reduced levels of B lymphocytes. Here, we hypothesized that B cell alterations in bone marrow account for the reduced therapeutic potential of post-MI and aged donor BMCs. Injection of BMCs from increasingly aged donor mice resulted in progressively poorer cardiac function and larger infarct size. Flow cytometry revealed fewer B cells in aged donor bone marrow. Therapeutic efficacy of young healthy donor BMCs was reduced by depletion of B cells. Implantation of intact or lysed B cells improved cardiac function, whereas intact or lysed T cells provided only minor benefit. We conclude that B cells play an important paracrine role in effective BMC therapy for MI. Reduction of bone marrow B cells because of age or MI may partially explain why clinical autologous cell therapy has not matched the success of rodent experiments.

Mesenchymal Stem Cell-Based Therapy for Cardiovascular Disease: Progress and Challenges

Administration of mesenchymal stem cells (MSCs) to diseased hearts improves cardiac function and reduces scar size. These effects occur via the stimulation of endogenous repair mechanisms, including regulation of immune responses, tissue perfusion, inhibition of fibrosis, and proliferation of resident cardiac cells, although rare events of transdifferentiation into cardiomyocytes and vascular components are also described in animal models. While these improvements demonstrate the potential of stem cell therapy, the goal of full cardiac recovery has yet to be realized in either preclinical or clinical studies. To reach this goal, novel cell-based therapeutic approaches are needed. Ongoing studies include cell combinations, incorporation of MSCs into biomaterials, or pre-conditioning or genetic manipulation of MSCs to boost their release of paracrine factors, such as exosomes, growth factors, microRNAs, etc. All of these approaches can augment therapeutic efficacy. Further study of the optimal route of administration, the correct dose, the best cell population(s), and timing for treatment are parameters that still need to be addressed in order to achieve the goal of complete cardiac regeneration. Despite significant progress, many challenges remain.

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.

Current status of stem cells in cardiac repair

One out of every two men and one out of every three women greater than the age of 40 will experience an acute myocardial infarction (AMI) at some time during their lifetime. As more patients survive their AMIs, the incidence of congestive heart failure (CHF) is increasing. 6 million people in the USA have ischemic cardiomyopathies and CHF. The search for new and innovative treatments for patients with AMI and CHF has led to investigations and use of human embryonic stem cells, cardiac stem/progenitor cells, bone marrow-derived mononuclear cells and mesenchymal stem cells for treatment of these heart conditions. This paper reviews current investigations with human embryonic, cardiac, bone marrow and mesenchymal stem cells, and also stem cell paracrine factors and exosomes.

Concise Review: Optimized Strategies for Stem Cell-Based Therapy in Myocardial Repair: Clinical Translatability and Potential Limitation

Ischemic heart diseases (IHDs) remain major public health problems with high rates of morbidity and mortality worldwide. Despite significant advances, current therapeutic approaches are unable to rescue the extensive and irreversible loss of cardiomyocytes caused by severe ischemia. Over the past 16 years, stem cell-based therapy has been recognized as an innovative strategy for cardiac repair/regeneration and functional recovery after IHDs. Although substantial preclinical animal studies using a variety of stem/progenitor cells have shown promising results, there is a tremendous degree of skepticism in the clinical community as many stem cell trials do not confer any beneficial effects. How to accelerate stem cell-based therapy toward successful clinical application attracts considerate attention. However, many important issues need to be fully addressed. In this Review, we have described and compared the effects of different types of stem cells with their dose, delivery routes, and timing that have been routinely tested in recent preclinical and clinical findings. We have also discussed the potential mechanisms of action of stem cells, and explored the role and underlying regulatory components of stem cell-derived secretomes/exosomes in myocardial repair. Furthermore, we have critically reviewed the different strategies for optimizing both donor stem cells and the target cardiac microenvironments to enhance the engraftment and efficacy of stem cells, highlighting their clinical translatability and potential limitation. Stem Cells 2018;36:482-500.

Combining cell and gene therapy to advance cardiac regeneration

INTRODUCTION

The characterization of multipotent endogenous cardiac stem cells (eCSCs) and the breakthroughs of somatic cell reprogramming to boost cardiomyocyte replacement have fostered the prospect of achieving functional heart repair/regeneration.

AREAS COVERED

Allogeneic CSC therapy through its paracrine stimulation of the endogenous resident reparative/regenerative process produces functional meaningful myocardial regeneration in pre-clinical porcine myocardial infarction models and is currently tested in the first-in-man human trial. The in vivo test of somatic reprogramming and cardioregenerative non-coding RNAs revived the interest in gene therapy for myocardial regeneration. The latter, together with the advent of genome editing, has prompted most recent efforts to produce genetically-modified allogeneic CSCs that secrete cardioregenerative factors to optimize effective myocardial repair.

EXPERT OPINION

The current war against heart failure epidemics in western countries seeks to find effective treatments to set back the failing hearts prolonging human lifespan. Off-the-shelf allogeneic-genetically-modified CSCs producing regenerative agents are a novel and evolving therapy set to be affordable, safe, effective and available at all times for myocardial regeneration to either prevent or treat heart failure.

Protein Kinase C Inhibition With Ruboxistaurin Increases Contractility and Reduces Heart Size in a Swine Model of Heart Failure With Reduced Ejection Fraction

Inotropic support is often required to stabilize the hemodynamics of patients with acute decompensated heart failure; while efficacious, it has a history of leading to lethal arrhythmias and/or exacerbating contractile and energetic insufficiencies. Novel therapeutics that can improve contractility independent of beta-adrenergic and protein kinase A-regulated signaling, should be therapeutically beneficial. This study demonstrates that acute protein kinase C-α/β inhibition, with ruboxistaurin at 3 months' post-myocardial infarction, significantly increases contractility and reduces the end-diastolic/end-systolic volumes, documenting beneficial remodeling. These data suggest that ruboxistaurin represents a potential novel therapeutic for heart failure patients, as a moderate inotrope or therapeutic, which leads to beneficial ventricular remodeling.

Empowering human cardiac progenitor cells by P2Y14 nucleotide receptor overexpression

KEY POINTS

Autologous cardiac progenitor cell (CPC) therapy is a promising approach for treatment of heart failure (HF). There is an unmet need to identify inherent deficits in aged/diseased human CPCs (hCPCs) derived from HF patients in the attempts to augment their regenerative capacity prior to use in the clinical setting. Here we report significant functional correlations between phenotypic properties of hCPCs isolated from cardiac biopsies of HF patients, clinical parameters of patients and expression of the P2Y₁₄ purinergic receptor (P2Y₁₄ R), a crucial detector for extracellular UDP-sugars released during injury/stress. P2Y₁₄ R is downregulated in hCPCs derived from HF patients with lower ejection fraction or diagnosed with diabetes. Augmenting P2Y₁₄ R expression levels in aged/diseased hCPCs antagonizes senescence and improves functional responses. This study introduces purinergic signalling modulation as a potential strategy to rejuvenate and improve phenotypic characteristics of aged/functionally compromised hCPCs prior to transplantation in HF patients.

ABSTRACT

Autologous cardiac progenitor cell therapy is a promising alternative approach to current inefficient therapies for heart failure (HF). However, ex vivo expansion and pharmacological/genetic modification of human cardiac progenitor cells (hCPCs) are necessary interventions to rejuvenate aged/diseased cells and improve their regenerative capacities. This study was designed to assess the potential of improving hCPC functional capacity by targeting the P2Y₁₄ purinergic receptor (P2Y₁₄ R), which has been previously reported to induce regenerative and anti-senescence responses in a variety of experimental models. c-Kit⁺ hCPCs were isolated from cardiac biopsies of multiple HF patients undergoing left ventricular assist device implantation surgery. Significant correlations existed between the expression of P2Y₁₄ R in hCPCs and clinical parameters of HF patients. P2Y₁₄ R was downregulated in hCPCs derived from patients with a relatively lower ejection fraction and patients diagnosed with diabetes. hCPC lines with lower P2Y₁₄ R expression did not respond to P2Y₁₄ R agonist UDP-glucose (UDP-Glu) while hCPCs with higher P2Y₁₄ R expression showed enhanced proliferation in response to UDP-Glu stimulation. Mechanistically, UDP-Glu stimulation enhanced the activation of canonical growth signalling pathways ERK1/2 and AKT. Restoring P2Y₁₄ R expression levels in functionally compromised hCPCs via lentiviral-mediated overexpression improved proliferation, migration and survival under stress stimuli. Additionally, P2Y₁₄ R overexpression reversed senescence-associated morphology and reduced levels of molecular markers of senescence p16^INK4a , p53, p21 and mitochondrial reactive oxygen species. Findings from this study unveil novel biological roles of the UDP-sugar receptor P2Y₁₄ in hCPCs and suggest purinergic signalling modulation as a promising strategy to improve phenotypic properties of functionally impaired hCPCs.

Translational cardiac stem cell therapy: advancing from first-generation to next-generation cell types

Acute myocardial infarction and chronic heart failure rank among the major causes of morbidity and mortality worldwide. Except for heart transplantation, current therapy options only treat the symptoms but do not cure the disease. Stem cell-based therapies represent a possible paradigm shift for cardiac repair. However, most of the first-generation approaches displayed heterogeneous clinical outcomes regarding efficacy. Stemming from the desire to closely match the target organ, second-generation cell types were introduced and rapidly moved from bench to bedside. Unfortunately, debates remain around the benefit of stem cell therapy, optimal trial design parameters, and the ideal cell type. Aiming at highlighting controversies, this article provides a critical overview of the translation of first-generation and second-generation cell types. It further emphasizes the importance of understanding the mechanisms of cardiac repair and the lessons learned from first-generation trials, in order to improve cell-based therapies and to potentially finally implement cell-free therapies.

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

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

Concurrent Isolation of 3 Distinct Cardiac Stem Cell Populations From a Single Human Heart Biopsy

RATIONALE

The relative actions and synergism between distinct myocardial-derived stem cell populations remain obscure. Ongoing debates on optimal cell population(s) for treatment of heart failure prompted implementation of a protocol for isolation of multiple stem cell populations from a single myocardial tissue sample to develop new insights for achieving myocardial regeneration.

OBJECTIVE

Establish a robust cardiac stem cell isolation and culture protocol to consistently generate 3 distinct stem cell populations from a single human heart biopsy.

METHODS AND RESULTS

Isolation of 3 endogenous cardiac stem cell populations was performed from human heart samples routinely discarded during implantation of a left ventricular assist device. Tissue explants were mechanically minced into 1 mm³ pieces to minimize time exposure to collagenase digestion and preserve cell viability. Centrifugation removes large cardiomyocytes and tissue debris producing a single cell suspension that is sorted using magnetic-activated cell sorting technology. Initial sorting is based on tyrosine-protein kinase Kit (c-Kit) expression that enriches for 2 c-Kit⁺ cell populations yielding a mixture of cardiac progenitor cells and endothelial progenitor cells. Flowthrough c-Kit^- mesenchymal stem cells are positively selected by surface expression of markers CD90 and CD105. After 1 week of culture, the c-Kit⁺ population is further enriched by selection for a CD133⁺ endothelial progenitor cell population. Persistence of respective cell surface markers in vitro is confirmed both by flow cytometry and immunocytochemistry.

CONCLUSIONS

Three distinct cardiac cell populations with individualized phenotypic properties consistent with cardiac progenitor cells, endothelial progenitor cells, and mesenchymal stem cells can be successfully concurrently isolated and expanded from a single tissue sample derived from human heart failure patients.

PIM1-minicircle as a therapeutic treatment for myocardial infarction

PIM1, a pro-survival gene encoding a serine/ threonine kinase, influences cell proliferation and survival. Modification of cardiac progenitor cells (CPCs) or cardiomyocytes with PIM1 using a lentivirus-based delivery method showed long-term improved cardiac function after myocardial infarction (MI). However, lentivirus based delivery methods have stringent FDA regulation with respect to clinical trials. To provide an alternative and low risk PIM1 delivery method, this study examined the use of a non-viral modified plasmid-minicircle (MC) as a vehicle to deliver PIM1 into mouse CPCs (mCPCs) in vitro and the myocardium in vivo. MC containing a turbo gfp reporter gene (gfp-MC) was used as a transfection and injection control. PIM1 was subcloned into gfp-MC (PIM1-MC) and then transfected into mCPCs at an efficiency of 29.4±3.7%. PIM1-MC engineered mCPCs (PIM1-mCPCs) exhibit significantly (P<0.05) better survival rate under oxidative treatment. PIM1-mCPCs also exhibit 1.9±0.1 and 2.2±0.2 fold higher cell proliferation at 3 and 5 days post plating, respectively, as compared to gfp-MC transfected mCPCs control. PIM1-MC was injected directly into ten-week old adult FVB female mice hearts in the border zone immediately after MI. Delivery of PIM1 into myocardium was confirmed by GFP⁺ cardiomyocytes. Mice with PIM1-MC injection showed increased protection compared to gfp-MC injection groups measured by ejection fraction at 3 and 7 days post injury (P = 0.0379 and P = 0.0262 by t-test, respectively). Success of PIM1 delivery and integration into mCPCs in vitro and cardiomyocytes in vivo by MC highlights the possibility of a non-cell based therapeutic approach for treatment of ischemic heart disease and MI.