Assessment and optimization of cell engraftment after transplantation into the heart

Insulin secretion of mixed insulinoma aggregates-gelatin hydrogel microspheres after subcutaneous transplantation

Introduction

The objective of this study is to evaluate the insulin secretion of mixed aggregates of insulinoma cells (INS-1) and gelatin hydrogel microspheres after their subcutaneous transplantation.

Methods

Gelatin hydrogel microspheres were prepared by the conventional w/o emulsion method. Cell aggregates mixed with or without the hydrogel microspheres were encapsulated into a pouched-device of polytetrafluoroethylene membrane. An agarose hydrogel or MedGel™ incorporating basic fibroblast growth factor (bFGF) was subcutaneously implanted to induce vascularization. After the vascularization induction, cell aggregates encapsulated in the pouched-device was transplanted.

Results

The vascularization had the potential to enable transplanted cell aggregates to enhance the level of insulin secretion compared with those of no vascularization induction. In addition, the insulin secretion of cell aggregates was significantly promoted by the mixing of gelatin hydrogel microspheres even in the pouched-device encapsulated state.

Conclusion

It is possible that the microspheres mixing gives cells in aggregates better survival condition, resulting in promoted insulin secretion.

•

INS-1 cell aggregates incorporating gelatin hydrogel microspheres are prepared.

•

The ratio and number of cells and gelatin hydrogel microspheres affected the formation of cell aggregates.

•

Gelatin hydrogel microspheres incorporation improves glucose-induced insulin secretion of cell aggregates in vitro.

•

Gelatin hydrogel microspheres incorporation has the tendency to improve glucose-induced insulin secretion of cell aggregates in vivo.

•

Vascularization has the potential to improve cell function.

Transplantation of Allogeneic Pericytes Improves Myocardial Vascularization and Reduces Interstitial Fibrosis in a Swine Model of Reperfused Acute Myocardial Infarction

BACKGROUND

Transplantation of adventitial pericytes (APCs) promotes cardiac repair in murine models of myocardial infarction. The aim of present study was to confirm the benefit of APC therapy in a large animal model.

METHODS AND RESULTS

We performed a blind, randomized, placebo-controlled APC therapy trial in a swine model of reperfused myocardial infarction. A first study used human APCs (hAPCs) from patients undergoing coronary artery bypass graft surgery. A second study used allogeneic swine APCs (sAPCs). Primary end points were (1) ejection fraction as assessed by cardiac magnetic resonance imaging and (2) myocardial vascularization and fibrosis as determined by immunohistochemistry. Transplantation of hAPCs reduced fibrosis but failed to improve the other efficacy end points. Incompatibility of the xenogeneic model was suggested by the occurrence of a cytotoxic response following in vitro challenge of hAPCs with swine spleen lymphocytes and the failure to retrieve hAPCs in transplanted hearts. We next considered sAPCs as an alternative. Flow cytometry, immunocytochemistry, and functional/cytotoxic assays indicate that sAPCs are a surrogate of hAPCs. Transplantation of allogeneic sAPCs benefited capillary density and fibrosis but did not improve cardiac magnetic resonance imaging indices of contractility. Transplanted cells were detected in the border zone.

CONCLUSIONS

Immunologic barriers limit the applicability of a xenogeneic swine model to assess hAPC efficacy. On the other hand, we newly show that transplantation of allogeneic sAPCs is feasible, safe, and immunologically acceptable. The approach induces proangiogenic and antifibrotic benefits, though these effects were not enough to result in functional improvements.

Human Mesenchymal Stem Cell Failure to Adapt to Glucose Shortage and Rapidly Use Intracellular Energy Reserves Through Glycolysis Explains Poor Cell Survival After Implantation

Mesenchymal stem cells (MSCs) hold considerable promise in tissue engineering (TE). However, their poor survival when exogenously administered limits their therapeutic potential. Previous studies from our group demonstrated that lack of glucose (glc) (but not of oxygen) is fatal to human MSCs because it serves as a pro-survival and pro-angiogenic molecule for human MSCs (hMSCs) upon transplantation. However, which energy-providing pathways MSCs use to metabolize glc upon transplantation? Are there alternative energetic nutrients to replace glc? And most importantly, do hMSCs possess significant intracellular glc reserves for ensuring their survival upon transplantation? These remain open questions at the forefront of TE based-therapies. In this study, we established for the first time that the in vivo environment experienced by hMSCs is best reflected by near-anoxia (0.1% O₂ ) rather than hypoxia (1%-5% O₂ ) in vitro. Under these near-anoxia conditions, hMSCs rely almost exclusively on glc through anerobic glycolysis for ATP production and are unable to use either exogenous glutamine, serine, or pyruvate as energy substrates. Most importantly, hMSCs are unable to adapt their metabolism to the lack of exogenous glc, possess a very limited internal stock of glc and virtually no ATP reserves. This lack of downregulation of energy turnover as a function of exogenous glc level results in a rapid depletion of hMSC energy reserves that explains their poor survival rate. These new insights prompt for the development of glc-releasing scaffolds to overcome this roadblock plaguing the field of TE based-therapies. Stem Cells 2018;36:363-376.

Paracrine Mechanisms of Mesenchymal Stem Cells in Tissue Repair

Tissue regeneration from transplanted mesenchymal stromal cells (MSC) either through transdifferentiation or cell fusion was originally proposed as the principal mechanism underlying their therapeutic action. However, several studies have now shown that both these mechanisms are very inefficient. The low MSC engraftment rate documented in injured areas also refutes the hypothesis that MSC repair tissue damage by replacing cell loss with newly differentiated cells. Indeed, despite evidence of preferential homing of MSC to the site of myocardial ischemia, exogenously administered MSC show poor survival and do not persist in the infarcted area. Therefore, it has been proposed that the functional benefits observed after MSC transplantation in experimental models of tissue injury might be related to the secretion of soluble factors acting in a paracrine fashion. This hypothesis is supported by pre-clinical studies demonstrating equal or even improved organ function upon infusion of MSC-derived conditioned medium (MSC-CM) compared with MSC transplantation. Identifying key MSC-secreted factors and their functional role seems a reasonable approach for a rational design of nextgeneration MSC-based therapeutics. Here, we summarize the major findings regarding both different MSC-mediated paracrine actions and the identification of paracrine mediators.

Establishing Early Functional Perfusion and Structure in Tissue Engineered Cardiac Constructs

Myocardial infarction (MI) causes massive heart muscle death and remains a leading cause of death in the world. Cardiac tissue engineering aims to replace the infarcted tissues with functional engineered heart muscles or revitalize the infarcted heart by delivering cells, bioactive factors, and/or biomaterials. One major challenge of cardiac tissue engineering and regeneration is the establishment of functional perfusion and structure to achieve timely angiogenesis and effective vascularization, which are essential to the survival of thick implants and the integration of repaired tissue with host heart. In this paper, we review four major approaches to promoting angiogenesis and vascularization in cardiac tissue engineering and regeneration: delivery of pro-angiogenic factors/molecules, direct cell implantation/cell sheet grafting, fabrication of prevascularized cardiac constructs, and the use of bioreactors to promote angiogenesis and vascularization. We further provide a detailed review and discussion on the early perfusion design in nature-derived biomaterials, synthetic biodegradable polymers, tissue-derived acellular scaffolds/whole hearts, and hydrogel derived from extracellular matrix. A better understanding of the current approaches and their advantages, limitations, and hurdles could be useful for developing better materials for future clinical applications.

Manipulation of Panx1 Activity Increases the Engraftment of Transplanted Lacrimal Gland Epithelial Progenitor Cells

Purpose

Sjögren's syndrome is a systemic chronic autoimmune inflammatory disease that primarily targets the salivary and lacrimal glands (LGs). Currently there is no cure; therefore, cell-based regenerative therapy may be a viable option. LG inflammation is facilitated by extracellular ATP and mediated by the Pannexin-1 (Panx1) membrane channel glycoprotein. We propose that suppression of inflammation through manipulation of Panx1 activity can stimulate epithelial cell progenitor (EPCP) engraftment.

Methods

The expression of pannexins in the mouse and human LG was assayed by qRT-PCR and immunostaining. Acute LG inflammation was induced by interleukin-1α (IL1α) injection. Prior to EPCP transplantation, IL1α-injured or chronically inflamed LGs of thrombospondin-1–null mice (TSP-1^−/−) were treated with the Panx1-specific blocking peptide (¹⁰panx) or the self-deliverable RNAi (sdRNAi). The efficacy of cell engraftment and the area of inflammation were analyzed by microscopy.

Results

Panx1 and Panx2 were detected in the mouse and human LGs. Panx1 and proinflammatory factors were upregulated during acute inflammation at days 1 to 3 after the IL1α injection. The analysis of EPCP engraftment demonstrated a significant and reproducible positive correlation between the ¹⁰panx peptide or Panx1 sdRNAi treatment and the number of engrafted cells. Similarly, treatment of the LG of the TSP-1^−/− mouse (mouse model of chronic LG inflammation) by either Panx1 or Caspase-4 (also known as Casp11) sdRNAi showed a significant decrease in expression of proinflammatory markers and the lymphocyte infiltration.

Conclusions

Our results suggest that blocking Panx1 and/or Casp4 activities is a beneficial strategy to enhance donor cell engraftment and LG regeneration through the reduction of inflammation.

Evaluation of Hydrogels Presenting Extracellular Matrix-Derived Adhesion Peptides and Encapsulating Cardiac Progenitor Cells for Cardiac Repair

Cell therapy is an emerging paradigm for the treatment of heart disease. In spite of the exciting and promising preclinical results, the benefits of cell therapy for cardiac repair in patients have been modest at best. Biomaterials-based approaches may overcome the barriers of poor differentiation and retention of transplanted cells. In this study, we prepared and tested hydrogels presenting extracellular matrix (ECM)-derived adhesion peptides as delivery vehicles for c-kit⁺ cardiac progenitor cells (CPCs). We assessed their effects on cell behavior in vitro as well as cardiac repair in rats undergoing ischemia reperfusion. Hydrogels presenting the collagen-derived GFOGER peptide induced cardiomyocyte differentiation of CPCs as demonstrated by increased expression of cardiomyocyte structural proteins. However, conditioned media obtained from GFOGER hydrogels showed lower levels of secreted reparative factors. Interestingly, following injection in rats undergoing ischemia-reperfusion, treatment with CPCs encapsulated in nonadhesive RDG-presenting hydrogels resulted in the preservation of cardiac contractility and attenuation of postinfarct remodeling whereas the adhesion peptide-presenting hydrogels did not induce any functional improvement. Retention of cells was significantly higher when delivered with nonadhesive hydrogels compared to ECM-derived peptide gels. These data suggest that factors including cell differentiation state, paracrine factors and interaction with biomaterials influence the effectiveness of biomaterials-based cell therapy. A holistic consideration of these multiple variables should be included in cell-biomaterial combination therapy designs.

Highly sensitive and specific Alu-based quantification of human cells among rodent cells

Alu elements are primate-specific short interspersed elements (SINEs), over 1 million copies of which are present in the human genome; thus, Alu elements are useful targets for detecting human cells. However, previous Alu-based techniques for detecting human genomic DNA do not reach the theoretical limits of sensitivity and specificity. In this study, we developed a highly sensitive and specific Alu-based real-time PCR method for discriminating human cells from rodent cells, using a primer and probe set carefully designed to avoid possible cross-reactions with rodent genomes. From 100 ng of mixed human and rodent genomes, 1 fg of human genome, equivalent to 1 human cell in 100 million rodent cells, was detectable. Furthermore, in vivo mouse subrenal capsule xenotransplantation assays revealed that 10 human cells per mouse organ were detectable. In addition, after intravenous injection of human mesenchymal stem cells into NOD/SCID mice via tail vein, the biodistribution of human cells was trackable in the mouse lungs and kidneys for at least 1 week. Our findings indicate that our primer and probe set is applicable for the quantitative detection of tiny amounts of human cells, such as xenotransplanted human cancer or stem cells, in rodents.

Adipose Extracellular Matrix/Stromal Vascular Fraction Gel Secretes Angiogenic Factors and Enhances Skin Wound Healing in a Murine Model

Mesenchymal stem cells are an attractive cell type for cytotherapy in wound healing. The authors recently developed a novel, adipose-tissue-derived, injectable extracellular matrix/stromal vascular fraction gel (ECM/SVF-gel) for stem cell therapy. This study was designed to assess the therapeutic effects of ECM/SVF-gel on wound healing and potential mechanisms. ECM/SVF-gel was prepared for use in nude mouse excisional wound healing model. An SVF cell suspension and phosphate-buffered saline injection served as the control. The expression levels of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and monocyte chemotactic protein-1 (MCP-1) in ECM/SVF-gel were analyzed at different time points. Angiogenesis (tube formation) assays of ECM/SVF-gel extracts were evaluated, and vessels density in skin was determined. The ECM/SVF-gel extract promoted tube formation in vitro and increased the expression of the angiogenic factors VEGF and bFGF compared with those in the control. The expression of the inflammatory chemoattractant MCP-1 was high in ECM/SVF-gel at the early stage and decreased sharply during the late stage of wound healing. The potent angiogenic effects exerted by ECM/SVF-gel may contribute to the improvement of wound healing, and these effects could be related to the enhanced inflammatory response in ECM/SVF-gel during the early stage of wound healing.

Platelet-Targeted Delivery of Peripheral Blood Mononuclear Cells to the Ischemic Heart Restores Cardiac Function after Ischemia-Reperfusion Injury

One of the major hurdles in intravenous regenerative cell therapy is the low homing efficiency to the area where these cells are needed. To increase cell homing toward areas of myocardial damage, we developed a bispecific tandem single-chain antibody (Tand-scFv_{Sca-1+GPIIb/IIIa}) that binds with high affinity to activated platelets via the activated glycoprotein (GP)IIb/IIIa receptor, and to a subset of peripheral blood mononuclear cells (PBMC) which express the stem cell antigen-1 (Sca-1) receptor. Methods: The Tand-scFv_{Sca-1+GPIIb/IIIa} was engineered, characterized and tested in a mouse model of ischemia-reperfusion (IR) injury applying left coronary artery occlusion for 60 min. Fluorescence cell tracking, cell infiltration studies, echocardiographic and histological analyses were performed. Results: Treatment of mice undergoing myocardial infarction with targeted-PBMCs led to successful cell delivery to the ischemic-reperfused myocardium, followed by a significant decrease in infiltration of inflammatory cells. Homing of targeted-PBMCs as shown by fluorescence cell tracking ultimately decreased fibrosis, increased capillary density, and restored cardiac function 4 weeks after ischemia-reperfusion injury. Conclusion: Tand-scFv_{Sca-1+GPIIb/IIIa} is a promising candidate to enhance therapeutic cell delivery in order to promote myocardial regeneration and thereby preventing heart failure.

The role of β-adrenergic receptors and p38MAPK signaling pathways in physiological processes of cardiosphere-derived cells

The effects of β adrenergic receptors (β-ARs) and p38 mitogen-activated protein kinases (MAPK) pathways on cardiosphere-derived cells (CDCs) are largely unknown. This study aimed to investigate the roles of β-ARs and p38MAPK pathways on the proliferation, apoptosis, and differentiation capacity of CDCs. The CDCs were treated with β1-AR blocker (Met group), β2-AR antagonist (ICI group), and p38MAPK inhibitor (SB group), non-selective β-AR blocker (PRO group), and β-AR agonist (ISO group). The viability, apoptotic rate and differentiation status of CDCs were determined by MST-1 assay, flow cytometery, and Western blot, respectively. The CDCs viability significantly reduced in ICI group (all P < 0.05), and SB group had a significant high viability after 48 h treatment (P < 0.05). Compared with control group, all treated groups had a low apoptotic rate. After treatment for 72 h, ISO treatment elevated the expression of Nkx2.5, and could partially or fully attenuate the inhibitory effects of β-AR antagonists and/or p38MAPK inhibitor. A similar overall trend of protein expression levels among all groups could be observed between protein pairs of cTnT and β1-AR as well as c-Kit and β2-AR, respectively. These results suggested that β-ARs and p38MAPK signaling pathways play crucial roles in the proliferation and differentiation of CDCs. Our findings should be helpful for better understanding the molecular mechanism underlying the physiological processes of CDCs.

Cellular mechanisms underlying cardiac engraftment of stem cells

INTRODUCTION

Over the past decade, it has become clear that long-term engraftment of any ex vivo expanded cell product transplanted into injured myocardium is modest and all therapeutic regeneration is mediated by stimulation of endogenous repair rather than differentiation of transplanted cells into working myocardium. Given that increasing the retention of transplanted cells boosts myocardial function, focus on the fundamental mechanisms limiting retention and survival of transplanted cells may enable strategies to help to restore normal cardiac function. Areas covered: This review outlines the challenges confronting cardiac engraftment of ex vivo expanded cells and explores means of enhancing cell-mediated repair of injured myocardium. Expert opinion: Stem cell therapy has already come a long way in terms of regenerating damaged hearts though the poor retention of transplanted cells limits the full potential of truly cardiotrophic cell products. Multifaceted strategies directed towards fundamental mechanisms limiting the long-term survival of transplanted cells will be needed to enhance transplanted cell retention and cell-mediated repair of damaged myocardium for cardiac cell therapy to reach its full potential.

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

BACKGROUND

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Normal versus Pathological Cardiac Fibroblast-Derived Extracellular Matrix Differentially Modulates Cardiosphere-Derived Cell Paracrine Properties and Commitment

Human resident cardiac progenitor cells (CPCs) isolated as cardiosphere-derived cells (CDCs) are under clinical evaluation as a therapeutic product for cardiac regenerative medicine. Unfortunately, limited engraftment and differentiation potential of transplanted cells significantly hamper therapeutic success. Moreover, maladaptive remodelling of the extracellular matrix (ECM) during heart failure progression provides impaired biological and mechanical signals to cardiac cells, including CPCs. In this study, we aimed at investigating the differential effect on the phenotype of human CDCs of cardiac fibroblast-derived ECM substrates from healthy or diseased hearts, named, respectively, normal or pathological cardiogel (CG-N/P). After 7 days of culture, results show increased levels of cardiogenic gene expression (NKX2.5, CX43) on both decellularized cardiogels compared to control, while the proportion and staining patterns of GATA4, OCT4, NKX2.5, ACTA1, VIM, and CD90-positive CPCs were not affected, as assessed by immunofluorescence microscopy and flow cytometry analyses. Nonetheless, CDCs cultured on CG-N secreted significantly higher levels of osteopontin, FGF6, FGF7, NT-3, IGFBP4, and TIMP-2 compared to those cultured on CG-P, suggesting overall a reduced trophic and antiremodelling paracrine profile of CDCs when in contact with ECM from pathological cardiac fibroblasts. These results provide novel insights into the bidirectional interplay between cardiac ECM and CPCs, potentially affecting CPC biology and regenerative potential.

Liquid marbles as bioreactors for the study of three-dimensional cell interactions

Liquid marble as a bioreactor platform for cell-based studies has received significant attention, especially for developing 3D cell-based assays. This platform is particularly suitable for 3D in-vitro modeling of cell-cell interactions. For the first time, we demonstrated the interaction of olfactory ensheathing cells (OECs) with nerve debris and meningeal fibroblast using liquid marbles. As the transplantation of OECs can be used for repairing nerve injury, degenerating cell debris within the transplantation site can adversely affect the survival of transplanted OECs. In this paper, we used liquid marbles to mimic the hostile 3D environment to analyze the functional behavior of the cells and to form the basis for cell-based therapy. We show that OECs interact with debris and enhanced cellular aggregation to form a larger 3D spheroidal tissue. However, these spheroids indicated limitation in biological functions such as the inability of cells within the spheroids to migrate out and adherence to neighboring tissue by fusion. The coalescence of two liquid marbles allows for analyzing the interaction between two distinct cell types and their respective environment. We created a microenvironment consisting of 3D fibroblast spheroids and nerve debris and let it interact with OECs. We found that OECs initiate adherence with nerve debris in this 3D environment. The results suggest that liquid marbles are ideal for developing bioassays that could substantially contribute to therapeutic applications. Especially, insights for improving the survival and adherence of transplanted cells.

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.

Magnetic Resonance Imaging of Myocardial Function Following Intracoronary and Intramyocardial Stem Cell Injection

Stem cell-based therapy is a new therapeutic option that can be used in patients with cardiac diseases caused by myocardial injury. Cardiac magnetic resonance imaging (MRI) is a new noninvasive imaging method with an increasingly widespread indication. The aim of this review was to evaluate the role of cardiac MRI in patients with myocardial infarction undergoing stem cell therapy. We studied the role of MRI in the assessment of myocardial viability, stem cell tracking, assessment of cell survival rate, and monitoring of the long-term effects of stem cell therapy. Based on the current knowledge in this field, this noninvasive, in vivo cardiac imaging technique has a large indication in this group of patients and plays an important role in all stages of stem cell therapy, from the indication to the long-term follow-up of patients.

Cardioprotective Effects of Wharton Jelly Derived Mesenchymal Stem Cell Transplantation in a Rodent Model of Myocardial Injury

Background

Whartons jelly-derived mesenchymal stem cells are a valuable alternative source that possess multipotent properties, easy to obtain and available in large scale compared to BMMSCs. We investigated the possibility of cardiac function improvement post isoproterenol induced cardiac injury in a rat model following human WJMSCs transplantation.

Materials and Methods

MSCs were extracted and cultured from cord WJ, characterized by morphology, Immunophenotyping and differentiation to osteoblast and adipocytes. WJMSCs were labeled with PKH2 linker dye. Wistar rats were divided into control group, ISO group (injected with 2 doses of isoproterenol) to induce myocardial injury and ISO group transplanted with labelled WJMSCs. ECG, electrocardiographic patterns, cardiac marker enzymes, tracing of labeled MSCs and immunohistochemical analysis of myocardial cryosections were studied.

Results and Conclusions

WJ derived MSCs were expanded for more than 14 passages while maintaining their undifferentiated state, were positive for MSC markers and were able to differentiate into adipocyte and osteoblast. We demonstrated that intravenously administered WJMSCs were capable of homing predominently in the ischemic myocardium. Cardiac markers were positively altered in stem cell treated group compared to ISO group. ECG and ECHO changes were improved with higher survival rate. WJMSCs could differentiate into cardiac-like cells (positive for cardiac specific proteins) in vivo. WJMSCs infusion promoted cardiac protection and reduced mortality, emphasizing a promising therapeutic role for myocardial insufficiency.

Exosomal MicroRNA Transfer Into Macrophages Mediates Cellular Postconditioning

BACKGROUND

Cardiosphere-derived cells (CDCs) confer cardioprotection in acute myocardial infarction by distinctive macrophage (Mϕ) polarization. Here we demonstrate that CDC-secreted exosomes (CDC_exo) recapitulate the cardioprotective effects of CDC therapy known as cellular postconditioning.

METHODS

Rats and pigs underwent myocardial infarction induced by ischemia/reperfusion before intracoronary infusion of CDC_exo, inert fibroblast exosomes (Fb_exo; control), or vehicle. Two days later, infarct size was quantified. Macrophages were isolated from cardiac tissue or bone marrow for downstream analyses. RNA sequencing was used to determine exosome content and alterations in gene expression profiles in Mϕ.

RESULTS

Administration of CDC_exo but not Fb_exo after reperfusion reduces infarct size in rat and pig models of myocardial infarction. Furthermore, CDC_exo reduce the number of CD68+ Mϕ within infarcted tissue and modify the polarization state of Mϕ so as to mimic that induced by CDCs. CDC_exo are enriched in several miRNAs (including miR-146a, miR-181b, and miR-126) relative to Fb_exo. Reverse pathway analysis of whole-transcriptome data from CDC_exo-primed Mϕ implicated miR-181b as a significant (P=1.3x10^-21) candidate mediator of CDC-induced Mϕ polarization, and PKCδ (protein kinase C δ) as a downstream target. Otherwise inert Fb_exo loaded selectively with miR-181b alter Mϕ phenotype and confer cardioprotective efficacy in a rat model of myocardial infarction. Adoptive transfer of PKCδ-suppressed Mϕ recapitulates cardioprotection.

CONCLUSIONS

Our data support the hypothesis that exosomal transfer of miR-181b from CDCs into Mϕ reduces PKCδ transcript levels and underlies the cardioprotective effects of CDCs administered after reperfusion.

Non-invasive in vivo imaging of cardiac stem/progenitor cell biodistribution and retention after intracoronary and intramyocardial delivery in a swine model of chronic ischemia reperfusion injury

Background

The safety and efficacy of cardiac stem/progenitor cells (CSC) have been demonstrated in previous preclinical and clinical assays for heart failure. However, their optimal delivery route to the ischemic heart has not yet been assessed. This study was designed to determine by a non-invasive imaging technique (PET/CT) the biodistribution and acute retention of allogeneic pig CSC implanted by two different delivery routes, intracoronary (IC) and intramyocardial (IM), in a swine preclinical model of chronic ischemia–reperfusion.

Methods

Ischemia–reperfusion was induced in six Goettingen hybrid minipigs by 90 min coronary artery occlusion followed by reperfusion. Thirty days later, animals were allocated to receive IC (n = 3) or NOGA^®-guided IM injection (n = 3) of 50 million of ¹⁸F-FDG/GFP-labeled allogeneic pig CSC. Acute retention was quantified by PET/CT 4 h after injection and cell engraftment assessed by immunohistochemical quantification of GFP⁺ cells three days post-injection.

Results

Biodistribution of ¹⁸F-FDG-labeled CSC was clearly visualized by PET/CT imaging and quantified. No statistical differences in acute cell retention (percentage of injected dose, %ID) were found in the heart when cells were administered by NOGA^®-guided IM (13.4 ± 3.4%ID) or IC injections (17.4 ± 4.1%ID). Interestingly, engrafted CSC were histologically detected only after IM injection.

Conclusion

PET/CT imaging of ¹⁸F-FDG-labeled CSC allows quantifying biodistribution and acute retention of implanted cells in a clinically relevant pig model of chronic myocardial infarction. Similar levels of acute retention are achieved when cells are IM or IC administered. However, acute cell retention does not correlate with cell engraftment, which is improved by IM injection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1157-0) contains supplementary material, which is available to authorized users.

Delivery of growth factor-based therapeutics in vascular diseases: Challenges and strategies

Either cardiovascular or peripheral vascular diseases have become the major cause of morbidity and mortality worldwide. Recently, growth factors therapeutics, whatever administrated in form of exogenous growth factors or their relevant genes have been discovered to be an effective strategy for the prevention and therapy of vascular diseases, because of their promoting angiogenesis. Besides, as an alternative, stem cell-based therapy has been also developed in view of their paracrine-mediated effect or ability of differentiation toward angiogenesis-related cells under assistance of growth factors. Despite of being specific and potent, no matter growth factors or stem cells-based therapy, their full clinical transformation is limited from bench to bedside. In this review, the potential choices of therapeutic modes based on types of different growth factors or stem cells were firstly summarized for vascular diseases. The confronted various challenges such as lack of non-invasive delivery method, the physiochemical challenge, the short half-life time, and poor cell survival, were carefully analyzed for these therapeutic modes. Various strategies to overcome these limitations are put forward from the perspective of drug delivery. The expertised design of a suitable delivery form will undoubtedly provide valuable insight into their clinical application in the regenerative medicine.

Cell therapy for heart disease after 15 years: Unmet expectations

Over the past two decades cardiac cell therapy (CCT) has emerged as a promising new strategy to cure heart diseases at high unmet need. Thousands of patients have entered clinical trials for acute or chronic heart conditions testing different cell types, including autologous or allogeneic bone marrow (BM)-derived mononuclear or selected cells, BM- or adipose tissue-derived mesenchymal cells, or cardiac resident progenitors based on their potential ability to regenerate scarred or dysfunctional myocardium. Nowadays, the original enthusiasm surrounding the regenerative medicine field has been cushioned by a cumulative body of evidence indicating an inefficient or modest efficacy of CCT in improving cardiac function, along with the continued lack of indisputable proof for long-term prognostic benefit. In this review, we have firstly comprehensively outlined the positive and negative results of cell therapy studies in patients with acute myocardial infarction, refractory angina and chronic heart failure. Next, we have discussed cell therapy- and patient-related variables (e.g. cell intrinsic and extrinsic characteristics as well as criteria of patient selection and proposed methodologies) that might have dampened the efficacy of past cell therapy trials. Finally, we have addressed critical factors to be considered before embarking on further clinical trials.

Cell Therapies in Cardiomyopathy: Current Status of Clinical Trials

Because the human heart has limited potential for regeneration, the loss of cardiomyocytes during cardiac myopathy and ischaemic injury can result in heart failure and death. Stem cell therapy has emerged as a promising strategy for the treatment of dead myocardium, directly or indirectly, and seems to offer functional benefits to patients. The ideal candidate donor cell for myocardial reconstitution is a stem-like cell that can be easily obtained, has a robust proliferation capacity and a low risk of tumour formation and immune rejection, differentiates into functionally normal cardiomyocytes, and is suitable for minimally invasive clinical transplantation. The ultimate goal of cardiac repair is to regenerate functionally viable myocardium after myocardial infarction (MI) to prevent or heal heart failure. This review provides a comprehensive overview of treatment with stem-like cells in preclinical and clinical studies to assess the feasibility and efficacy of this novel therapeutic strategy in ischaemic cardiomyopathy.

Fibroblasts Rendered Antifibrotic, Antiapoptotic, and Angiogenic by Priming With Cardiosphere-Derived Extracellular Membrane Vesicles

BACKGROUND

Cardiosphere-derived cells mediate therapeutic regeneration in patients after myocardial infarction and are undergoing further clinical testing for cardiomyopathy. The beneficial effects of cardiosphere-derived cells are mediated by the secretion of exosomes and possibly other extracellular membrane vesicles (EMVs).

OBJECTIVES

This study sought to investigate the effect of cardiosphere-derived EMVs (CSp-EMVs) on fibroblasts in vitro and tested whether priming with CSp-EMVs could confer salutary properties on fibroblasts in vivo.

METHODS

CSp-EMVs were isolated from serum-free media conditioned for 3 days by cardiospheres. Dermal fibroblasts were primed with CSp-EMVs for 24 h followed by exosomal micro-ribonucleic acid profiling. In vivo, we injected CSp-EMV-primed or -unprimed dermal fibroblasts (or CSp-EMVs) in a chronic rat model of myocardial infarction and defined the functional and structural consequences.

RESULTS

CSp-EMVs amplified their own biological signals: exposure of "inert" fibroblasts to CSp-EMVs rendered the fibroblasts therapeutic. Intramyocardially injected CSp-EMV-primed (but not unprimed) fibroblasts increased global pump function and vessel density while reducing scar mass. CSp-EMV priming caused fibroblasts to secrete much higher levels of stromal-cell-derived factor 1 and vascular endothelial growth factor and dramatically changed the micro-ribonucleic acid profile of fibroblast-secreted EMVs in vitro. The priming was followed by significant angiogenic and cardioprotective effects.

CONCLUSIONS

CSp-EMVs alter fibroblast phenotype and secretome in a salutary positive-feedback loop. The phenotypic conversion of inert cells to therapeutically active cells reveals a novel mechanism for amplification of exosome bioactivity.

Characterisation of Development and Electrophysiological Mechanisms Underlying Rhythmicity of the Avian Lymph Heart

Despite significant advances in tissue engineering such as the use of scaffolds, bioreactors and pluripotent stem cells, effective cardiac tissue engineering for therapeutic purposes has remained a largely intractable challenge. For this area to capitalise on such advances, a novel approach may be to unravel the physiological mechanisms underlying the development of tissues that exhibit rhythmic contraction yet do not originate from the cardiac lineage. Considerable attention has been focused on the physiology of the avian lymph heart, a discrete organ with skeletal muscle origins yet which displays pacemaker properties normally only found in the heart. A functional lymph heart is essential for avian survival and growth in ovo. The histological nature of the lymph heart is similar to skeletal muscle although molecular and bioelectrical characterisation during development to assess mechanisms that contribute towards lymph heart contractile rhythmicity have not been undertaken. A better understanding of these processes may provide exploitable insights for therapeutic rhythmically contractile tissue engineering approaches in this area of significant unmet clinical need. Here, using molecular and electrophysiological approaches, we describe the molecular development of the lymph heart to understand how this skeletal muscle becomes fully functional during discrete in ovo stages of development. Our results show that the lymph heart does not follow the normal transitional programme of myogenesis as documented in most skeletal muscle, but instead develops through a concurrent programme of precursor expansion, commitment to myogenesis and functional differentiation which offers a mechanistic explanation for its rapid development. Extracellular electrophysiological field potential recordings revealed that the peak-to-peak amplitude of electrically evoked local field potentials elicited from isolated lymph heart were significantly reduced by treatment with carbachol; an effect that could be fully reversed by atropine. Moreover, nifedipine and cyclopiazonic acid both significantly reduced peak-to-peak local field potential amplitude. Optical recordings of lymph heart showed that the organ’s rhythmicity can be blocked by the HCN channel blocker, ZD7288; an effect also associated with a significant reduction in peak-to-peak local field potential amplitude. Additionally, we also show that isoforms of HCN channels are expressed in avian lymph heart. These results demonstrate that cholinergic signalling and L-type Ca²⁺ channels are important in excitation and contraction coupling, while HCN channels contribute to maintenance of lymph heart rhythmicity.

Tissue Engineering Strategies for Myocardial Regeneration: Acellular Versus Cellular Scaffolds?

Heart disease remains one of the leading causes of death in industrialized nations with myocardial infarction (MI) contributing to at least one fifth of the reported deaths. The hypoxic environment eventually leads to cellular death and scar tissue formation. The scar tissue that forms is not mechanically functional and often leads to myocardial remodeling and eventual heart failure. Tissue engineering and regenerative medicine principles provide an alternative approach to restoring myocardial function by designing constructs that will restore the mechanical function of the heart. In this review, we will describe the cellular events that take place after an MI and describe current treatments. We will also describe how biomaterials, alone or in combination with a cellular component, have been used to engineer suitable myocardium replacement constructs and how new advanced culture systems will be required to achieve clinical success.

Combinatorial extracellular matrix microenvironments promote survival and phenotype of human induced pluripotent stem cell-derived endothelial cells in hypoxia

Recent developments in cell therapy using human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) hold great promise for treating ischemic cardiovascular tissues. However, poor post-transplantation viability largely limits the potential of stem cell therapy. Although the extracellular matrix (ECM) has become increasingly recognized as an important cell survival factor, conventional approaches primarily rely on single ECMs for in vivo co-delivery with cells, even though the endothelial basement membrane is comprised of a milieu of different ECMs. To address this limitation, we developed a combinatorial ECM microarray platform to simultaneously interrogate hundreds of micro-scale multi-component chemical compositions of ECMs on iPSC-EC response. After seeding iPSC-ECs onto ECM microarrays, we performed high-throughput analysis of the effects of combinatorial ECMs on iPSC-EC survival, endothelial phenotype, and nitric oxide production under conditions of hypoxia (1% O2) and reduced nutrients (1% fetal bovine serum), as is present in ischemic injury sites. Using automated image acquisition and analysis, we identified combinatorial ECMs such as collagen IV+gelatin+heparan sulfate+laminin and collagen IV+fibronectin+gelatin+heparan sulfate+laminin that significantly improved cell survival, nitric oxide production, and CD31 phenotypic expression, in comparison to single-component ECMs. These results were further validated in conventional cell culture platforms and within three-dimensional scaffolds. Furthermore, this approach revealed complex ECM interactions and non-intuitive cell behavior that otherwise could not be easily determined using conventional cell culture platforms. Together these data suggested that iPSC-EC delivery within optimal combinatorial ECMs may improve their survival and function under the condition of hypoxia with reduced nutrients.

STATEMENT OF SIGNIFICANCE

Human endothelial cells (ECs) derived from induced pluripotent stem cells (iPSC-ECs) are promising for treating diseases associated with reduced nutrient and oxygen supply like heart failure. However, diminished iPSC-EC survival after implantation into diseased environments limits their therapeutic potential. Since native ECs interact with numerous extracellular matrix (ECM) proteins for functional maintenance, we hypothesized that combinatorial ECMs may improve cell survival and function under conditions of reduced oxygen and nutrients. We developed a high-throughput system for simultaneous screening of iPSC-ECs cultured on multi-component ECM combinations under the condition of hypoxia and reduced serum. Using automated image acquisition and analytical algorithms, we identified combinatorial ECMs that significantly improved cell survival and function, in comparison to single ECMs. Furthermore, this approach revealed complex ECM interactions and non-intuitive cell behavior that otherwise could not be easily determined.

Magnet-Bead Based MicroRNA Delivery System to Modify CD133+ Stem Cells

Aim. CD133⁺ stem cells bear huge potential for regenerative medicine. However, low retention in the injured tissue and massive cell death reduce beneficial effects. In order to address these issues, we intended to develop a nonviral system for appropriate cell engineering. Materials and Methods. Modification of human CD133⁺ stem cells with magnetic polyplexes carrying microRNA was studied in terms of efficiency, safety, and targeting potential. Results. High microRNA uptake rates (~80-90%) were achieved without affecting CD133⁺ stem cell properties. Modified cells can be magnetically guided. Conclusion. We developed a safe and efficient protocol for CD133⁺ stem cell modification. Our work may become a basis to improve stem cell therapeutical effects as well as their monitoring with magnetic resonance imaging.

Cell Size Critically Determines Initial Retention of Bone Marrow Mononuclear Cells in the Heart after Intracoronary Injection: Evidence from a Rat Model

Intracoronary injection of bone marrow mononuclear cells (BMMNC) is an emerging treatment for heart failure. Initial donor cell retention in the heart is the key to the success of this approach, but this process remains insufficiently characterized. Although it is assumed that cell size of injected cells may influence their initial retention, no scientific evidence has been reported. We developed a unique model utilizing an ex-vivo rat heart perfusion system, enabling quantitative assessment of retention of donor cells after intracoronary injection. The initial (5 minutes after intracoronary injection) retention rate of BMMNC was as low as approximately 20% irrespective of donor cell doses injected (1×10⁶, 8×10⁶, 4×10⁷). Quantitative cell-size assessment revealed a positive relationship between the size of BMMNC and retention ratio; larger subpopulations of BMMNC were more preferentially retained compared to smaller ones. Furthermore, a larger cell type—bone marrow-derived mesenchymal stromal cells (median size = 11.5μm versus 7.0μm for BMMNC)—had a markedly increased retention rate (77.5±1.8%). A positive relationship between the cell size and retention ratio was also seen in mesenchymal stromal cells. Flow-cytometric studies showed expression of cell-surface proteins, including integrins and selectin-ligands, was unchanged between pre-injection BMMNC and those exited from the heart, suggesting that biochemical interaction between donor cells and host coronary endothelium is not critical for BMMNC retention. Histological analyses showed that retained BMMNC and mesenchymal stromal cells were entrapped in the coronary vasculature and did not extravasate by 60 minutes after transplantation. Whilst BMMNC did not change coronary flow after intracoronary injection, mesenchymal stromal cells reduced it, suggesting coronary embolism, which was supported by the histological finding of intravascular cell-clump formation. These data indicate that cell-size dependent, passive (mechanical), intravascular entrapment is responsible for the initial donor cell retention after intracoronary injection of BMMNC in the heart having normal vasculatures (at least).

Combinatorial therapy with three-dimensionally cultured adipose-derived stromal cells and self-assembling peptides to enhance angiogenesis and preserve cardiac function in infarcted hearts

Even though stem cell therapy is a promising angiogenic strategy to treat ischaemic diseases, including myocardial infarction (MI), therapeutic efficacy is limited by low survival and retention of transplanted cells in ischaemic tissues. In addition, therapeutic angiogenesis depends on stimulating host angiogenesis with paracrine factors released by transplanted cells rather than on direct blood vessel formation by transplanted cells. In the present study, to overcome these limitations and to enhance the therapeutic efficacy of MI treatment, combinatorial therapy with three-dimensional cell masses (3DCMs) and self-assembling peptides (SAPs) was tested in a rat MI model. Spheroid-type 3DCMs, which are vascular differentiation-induced cells, were prepared by culturing human adipose-derived stromal cells on a fibroblast growth factor-immobilized surface. The SAPs were used as the carrier material to increase engraftment of transplanted cells. After coronary artery ligation, 3DCMs were combined with SAPs and were transplanted into ischaemic lesions. The therapeutic potential was evaluated 4 weeks after treatment. By combining 3DCMs and SAPs, survival and retention of transplanted cells increased threefold when compared with treatment with 3DCMs alone and transplanted cells established vascular networks in infarcted hearts. In addition, the size of the infarct in the 3DCM + SAP group was reduced to 6.09 ± 2.83% by the promotion of host angiogenesis and cardiac function was preserved, as demonstrated by a 54.25 ± 4.42% increase in the ejection fraction. This study indicates that combinatorial therapy with 3DCM and SAPs could be a promising strategy for therapeutic angiogenesis to treat MI. Copyright © 2016 John Wiley & Sons, Ltd.

Dendritic Polymers for Theranostics

Dendritic polymers are highly branched polymers with controllable structures, which possess a large population of terminal functional groups, low solution or melt viscosity, and good solubility. Their size, degree of branching and functionality can be adjusted and controlled through the synthetic procedures. These tunable structures correspond to application-related properties, such as biodegradability, biocompatibility, stimuli-responsiveness and self-assembly ability, which are the key points for theranostic applications, including chemotherapeutic theranostics, biotherapeutic theranostics, phototherapeutic theranostics, radiotherapeutic theranostics and combined therapeutic theranostics. Up to now, significant progress has been made for the dendritic polymers in solving some of the fundamental and technical questions toward their theranostic applications. In this review, we briefly summarize how to control the structures of dendritic polymers, the theranostics-related properties derived from their structures and their theranostics-related applications.

Transplantation Effectiveness of Induced Pluripotent Stem Cells Is Improved by a Fibrinogen Biomatrix in an Experimental Model of Ischemic Heart Failure

OBJECTIVES

The aim of this study was to investigate whether a fibrinogen biomatrix improves the transplantation effectiveness of induced pluripotent stem cells (iPSCs) in a model of myocardial infarction.

BACKGROUND

Early retention, engraftment, and cell proliferation are important factors for successful cardiac stem cell therapy. Common transplantation techniques involve the direction injection of cells in aqueous media. However, this approach yields low retention and variable cell biodistribution, leading to reduced grafts that are unable to sufficiently regenerate damaged myocardium. Biologically compatible scaffolds that improve the retention of injected cells can improve cardiac stem cell therapy.

METHODS

Murine iPSCs were transfected for luciferase reporter gene expression. First, in vitro experiments were performed comparing cell viability in fibrinogen and medium. Second, iPSCs were transplanted intramyocardially by direct injection into ischemic myocardium of immunodeficient mice, following permanent left coronary artery ligation. Cells were delivered in medium or fibrinogen. Follow-up included graft assessment by bioluminescence imaging, the evaluation of cardiac function by magnetic resonance imaging, and histology to evaluate graft size and determine the extent of myocardial scarring.

RESULTS

In vitro experiments showed proliferation of iPSCs in fibrinogen from 6.4×10(3)±8.0×10(2) after 24 h to 2.1×10(4)±3.2×10(3) after 72 h. Early cardiac cell amount in control group animals was low (23.7%±0.7%) with massive cell accumulation in the right (46.3%±1.0%) and the left lung (30.0%±0.6%). When iPSCs were injected applying the fibrinogen biomatrix, intramyocardial cell amount was increased (66.3%±0.9%) with demonstrable graft proliferation over the experimental time course. Left ventricle-function was higher in the fibrinogen group (42.9%±2.8%), also showing a higher fraction of refilled infarcted-area (66.9%±2.7%).

CONCLUSIONS

The fibrinogen biomatrix improved cardiac iPSc retention, sustaining functional improvement and cellular refill of infarcted myocardium. Therefore, fibrinogen can be considered an ideal biological scaffold for intramyocardial stem cell transplantations.

Microtissues in Cardiovascular Medicine: Regenerative Potential Based on a 3D Microenvironment

More people die annually from cardiovascular diseases than from any other cause. In particular, patients who suffer from myocardial infarction may be affected by ongoing adverse remodeling processes of the heart that may ultimately lead to heart failure. The introduction of stem and progenitor cell-based applications has raised substantial hope for reversing these processes and inducing cardiac regeneration. However, current stem cell therapies using single-cell suspensions have failed to demonstrate long-lasting efficacy due to the overall low retention rate after cell delivery to the myocardium. To overcome this obstacle, the concept of 3D cell culture techniques has been proposed to enhance therapeutic efficacy and cell engraftment based on the simulation of an in vivo-like microenvironment. Of great interest is the use of so-called microtissues or spheroids, which have evolved from their traditional role as in vitro models to their novel role as therapeutic agents. This review will provide an overview of the therapeutic potential of microtissues by addressing primarily cardiovascular regeneration. It will accentuate their advantages compared to other regenerative approaches and summarize the methods for generating clinically applicable microtissues. In addition, this review will illustrate the unique properties of the microenvironment within microtissues that makes them a promising next-generation therapeutic approach.

Matrix metalloproteinase-13 mediated degradation of hyaluronic acid-based matrices orchestrates stem cell engraftment through vascular integration

A critical design parameter for the function of synthetic extracellular matrices is to synchronize the gradual cell-mediated degradation of the matrix with the endogenous secretion of natural extracellular matrix (ECM) (e.g., creeping substitution). In hyaluronic acid (HyA)-based hydrogel matrices, we have investigated the effects of peptide crosslinkers with different matrix metalloproteinases (MMP) sensitivities on network degradation and neovascularization in vivo. The HyA hydrogel matrices consisted of cell adhesive peptides, heparin for both the presentation of exogenous and sequestration of endogenously synthesized growth factors, and MMP cleavable peptide linkages (i.e., QPQGLAK, GPLGMHGK, and GPLGLSLGK). Sca1(+)/CD45(-)/CD34(+)/CD44(+) cardiac progenitor cells (CPCs) cultured in the matrices with the slowly degradable QPQGLAK hydrogels supported the highest production of MMP-2, MMP-9, MMP-13, VEGF165, and a range of angiogenesis related proteins. Hydrogels with QPQGLAK crosslinks supported prolonged retention of these proteins via heparin within the matrix, stimulating rapid vascular development, and anastomosis with the host vasculature when implanted in the murine hindlimb.

Long-Term Outcome of Administration of c-kit(POS) Cardiac Progenitor Cells After Acute Myocardial Infarction: Transplanted Cells Do not Become Cardiomyocytes, but Structural and Functional Improvement and Proliferation of Endogenous Cells Persist for at Least One Year

RATIONALE

Cardiac progenitor cells (CPCs) improve left ventricular remodeling and function after acute or chronic myocardial infarction. However, the long-term (>5 weeks) effects, potential tumorigenicity, and fate of transplanted CPCs are unknown.

OBJECTIVE

To assess the outcome of CPC therapy at 1 year.

METHODS AND RESULTS

Female rats underwent a 90-minute coronary occlusion; 4 hours after reperfusion, they received intracoronarily vehicle or 1 million male, syngeneic CPCs. One year later, CPC-treated rats exhibited smaller scars and more viable myocardium in the risk region, along with improved left ventricular remodeling and regional and global left ventricular function. No tumors were observed. Some transplanted (Y-chromosome(POS)) CPCs (or their progeny) persisted and continued to proliferate, but they failed to acquire a mature cardiomyocyte phenotype and were too few (4-8% of nuclei) to account for the benefits of CPC therapy. Surprisingly, CPC transplantation triggered a prolonged proliferative response of endogenous cells, resulting in increased formation of endothelial cells and Y-chromosome(NEG) CPCs for 12 months and increased formation, for at least 7 months, of small cells that expressed cardiomyocytic proteins (α-sarcomeric actin) but did not have a mature cardiomyocyte phenotype.

CONCLUSIONS

The beneficial effects of CPCs on left ventricular remodeling and dysfunction are sustained for at least 1 year and thus are likely to be permanent. Because transplanted CPCs do not differentiate into mature myocytes, their major mechanism of action must involve paracrine actions. These paracrine mechanisms could be very prolonged because some CPCs engraft, proliferate, and persist at 1 year. This is the first report that transplantation of any cell type in the heart induces a proliferative response that lasts at least 1 year. The results strongly support the safety and clinical utility of CPC therapy.

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

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

Cell Therapy in Ischemic Heart Disease: Interventions That Modulate Cardiac Regeneration

The incidence of severe ischemic heart disease caused by coronary obstruction has progressively increased. Alternative forms of treatment have been studied in an attempt to regenerate myocardial tissue, induce angiogenesis, and improve clinical conditions. In this context, cell therapy has emerged as a promising alternative using cells with regenerative potential, focusing on the release of paracrine and autocrine factors that contribute to cell survival, angiogenesis, and tissue remodeling. Evidence of the safety, feasibility, and potential effectiveness of cell therapy has emerged from several clinical trials using different lineages of adult stem cells. The clinical benefit, however, is not yet well established. In this review, we discuss the therapeutic potential of cell therapy in terms of regenerative and angiogenic capacity after myocardial ischemia. In addition, we addressed nonpharmacological interventions that may influence this therapeutic practice, such as diet and physical training. This review brings together current data on pharmacological and nonpharmacological approaches to improve cell homing and cardiac repair.

Optimisation of conductive polymer biomaterials for cardiac progenitor cells

The characterisation of biomaterials for cardiac tissue engineering applications is vital for the development of effective treatments for the repair of cardiac function.

Cardiac-Derived Extracellular Matrix Enhances Cardiogenic Properties of Human Cardiac Progenitor Cells

The use of biomaterials has been demonstrated as a viable strategy to promote cell survival and cardiac repair. However, limitations on combinational cell-biomaterial therapies exist, as cellular behavior is influenced by the microenvironment and physical characteristics of the material. Among the different scaffolds employed for cardiac tissue engineering, a myocardial matrix hydrogel has been shown to promote cardiogenesis in murine cardiac progenitor cells (mCPCs) in vitro. In this study, we investigated the influence of the hydrogel on Sca-1-like human fetal and adult CPCs (fCPCs and aCPCs) when encapsulated in three-dimensional (3D) material in vitro. fCPCs encapsulated in the myocardial matrix showed an increase in the gene expression level of cardiac markers GATA-4 and MLC2v and the vascular marker vascular endothelial growth factor receptor 2 (VEGFR2) after 4 days in culture, and a significant increase in GATA-4 up to 1 week. Increased gene expression levels of Nkx2.5, MEF2c, VEGFR2, and CD31 were also observed when aCPCs were cultured in the matrix compared to collagen. Cell survival was sustained in both hydrogels up to 1 week in culture with the myocardial matrix capable of enhancing the expression of the proliferation marker Ki-67 after 4 days in culture. When encapsulated CPCs were treated with H₂O₂, an improved survival of the cells cultured in the myocardial matrix was observed. Finally, we evaluated the use of the myocardial matrix as hydrogel for in vivo cell transplantation and demonstrated that the gelation properties of the hydrogel are not influenced by the cells. In summary, we showed that the myocardial matrix hydrogel promotes human CPC cardiogenic potential, proliferation, and survival and is a favorable hydrogel for 3D in vitro culture. Furthermore, we demonstrated the in vivo applicability of the matrix as a potential vehicle for cell transplantation.

Human Cardiac Progenitor Spheroids Exhibit Enhanced Engraftment Potential

A major obstacle to an effective myocardium stem cell therapy has always been the delivery and survival of implanted stem cells in the heart. Better engraftment can be achieved if cells are administered as cell aggregates, which maintain their extra-cellular matrix (ECM). We have generated spheroid aggregates in less than 24 h by seeding human cardiac progenitor cells (hCPCs) onto methylcellulose hydrogel-coated microwells. Cells within spheroids maintained the expression of stemness/mesenchymal and ECM markers, growth factors and their cognate receptors, cardiac commitment factors, and metalloproteases, as detected by immunofluorescence, q-RT-PCR and immunoarray, and expressed a higher, but regulated, telomerase activity. Compared to cells in monolayers, 3D spheroids secreted also bFGF and showed MMP2 activity. When spheroids were seeded on culture plates, the cells quickly migrated, displaying an increased wound healing ability with or without pharmacological modulation, and reached confluence at a higher rate than cells from conventional monolayers. When spheroids were injected in the heart wall of healthy mice, some cells migrated from the spheroids, engrafted, and remained detectable for at least 1 week after transplantation, while, when the same amount of cells was injected as suspension, no cells were detectable three days after injection. Cells from spheroids displayed the same engraftment capability when they were injected in cardiotoxin-injured myocardium. Our study shows that spherical in vivo ready-to-implant scaffold-less aggregates of hCPCs able to engraft also in the hostile environment of an injured myocardium can be produced with an economic, easy and fast protocol.

Intracellular transduction of TAT-Hsp27 fusion protein enhancing cell survival and regeneration capacity of cardiac stem cells in acute myocardial infarction

Myocardial infarction (MI) results in the substantial loss of functional cardiomyocytes, which frequently leads to intractable heart disorders. Cardiac stem cells (CSCs) that retain the capacity to replace all cardiac cells might be a promising strategy for providing a source of new functional cardiomyocytes; however, the poor survival and engraftment of transplanted CSCs in the hostile environment of MI critically mitigate their therapeutic benefits. To capitalize their therapeutic potential, an ex vivo strategy in which CSCs were introduced to the recombinant heat shock protein 27 (Hsp27) through a TAT protein transduction domain for increasing the viability and engraftment in the infarcted myocardium was designed. A recombinant TAT fused Hsp27 (TAT-Hsp27) was able to enter CSCs in a dose-dependent manner. CSCs transduced with TAT-Hsp27 expressed not only endogenous Hsp27 but externally introduced Hsp27, resulting in substantial increase of their anti-oxidative and anti-apoptotic properties via suppressing reactive oxygen species production, the MAPKs signaling pathway, and caspase activation. TAT-Hsp27 enabled CSCs to be protected from apoptotic- and hypoxic-induced cell death during in vitro cardiomyogenic differentiation. In vivo studies demonstrated that CSCs transduced TAT-Hsp27 significantly increased the survival and engraftment in the acutely infarcted myocardium, which is closely related to caspase activity suppression. Finally, CSCs transduced TAT-Hsp27 improved cardiac function and attenuated cardiac remodeling in comparison with non-transduced CSCs. Overall, our approach, which is based on the ex vivo intracellular transduction of TAT-Hsp27 into CSCs before myocardial delivery, might be effective in treating MI.

Novel xeno-free human heart matrix-derived three-dimensional scaffolds

Rationale

Myocardial infarction (MI) results in damaged heart tissue which can progress to severely reduce cardiac function, leading to death. Recent studies have injected dissociated, suspended cardiac cells into coronary arteries to restore function with limited results attributed to poor cell retention and cell death. Extracellular matrix (ECM) injected into damaged cardiac tissue sites show some promising effects. However, combined use of human cardiac ECM and cardiac cells may produce superior benefits to restore cardiac function.

Objective

This study was designed to assess use of new three-dimensional human heart ECM-derived scaffolds to serve as vehicles to deliver cardiac-derived cells directly to damaged heart tissue and improve cell retention at these sites while also providing biomechanical support and attracting host cell recruitment.

Methods and Results

ECM-derived porous protein scaffolds were fabricated from human heart tissues. These scaffolds were designed to carry, actively promote and preserve cardiac cell phenotype, viability and functional retention in tissue sites. ECM scaffolds were optimized and were seeded with human cardiomyocytes, cultured and subsequently implanted ex vivo onto infarcted murine epicardium. Seeded human cardiomyocytes readily adhered to human cardiac-derived ECM scaffolds and maintained representative phenotypes including expression of cardiomyocyte-specific markers, and remained electrically synchronous within the scaffold in vitro. Ex vivo, cardiomyocyte-seeded ECM scaffolds spontaneously adhered and incorporated into murine ventricle.

Conclusions

Decellularized human cardiac tissue-derived 3D ECM scaffolds are effective delivery vehicles for human cardiac cells to directly target ischemic heart tissue and warrant further studies to assess their therapeutic potential in restoring essential cardiac functions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0559-0) contains supplementary material, which is available to authorized users.

An Injectable, Self-Healing Hydrogel to Repair the Central Nervous System

An injectable, self-healing hydrogel (≈1.5 kPa) is developed for healing nerve-system deficits. Neurosphere-like progenitors proliferate in the hydrogel and differentiate into neuron-like cells. In the zebrafish injury model, the central nervous system function is partially rescued by injection of the hydrogel and significantly rescued by injection of the neurosphere-laden hydrogel. The self-healing hydrogel may thus potentially repair the central nervous system.

Concomitant Retrograde Coronary Venous Infusion of Basic Fibroblast Growth Factor Enhances Engraftment and Differentiation of Bone Marrow Mesenchymal Stem Cells for Cardiac Repair after Myocardial Infarction

Aim: Basic fibroblast growth factor (bFGF) increases the migration and viability of bone marrow mesenchymal stem cells (MSCs) in vitro. Retrograde coronary venous infusion can provide both increased regional bFGF concentrations and homogeneous cell dissemination. We determined whether retrograde delivery of bFGF enhances the potency of transplanted MSCs for cardiac repair in a canine infarct model.

Methods and Results: Under hypoxic conditions, cellular migration was significantly increased in MSCs co-cultured with bFGF compared to vascular endothelial growth factor or insulin-like growth factor, and bFGF promoted MSCs differentiation into a cardiomyocyte phenotype. A canine infarct model was employed by coronary ligation. One week later, animals were subjected to retrograde infusion of combination bFGF (200ng/mL) and MSCs (1×10⁸ cells) (n=5), MSCs (1×10⁸ cells, n=5), bFGF (200ng/mL, n=5), or placebo (phosphate-buffered saline, n=3). Four weeks after infusion, only the bFGF+MSCs therapy exhibited significantly increased left ventricular ejection fraction (LVEF) by echocardiography (p<0.01 vs pre-infusion), and the treatment effect (delta LVEF) was greater in the bFGF+MSCs group compared to saline (7.43±1.51% versus -10.07±2.94%; p<0.001). Morphologic analysis revealed an increased infarct wall thickness in the bFGF+MSCs group compared to all others (p<0.05), accompanied by increased vascular density and reduced apoptosis. Immunofluorescence demonstrated increased cell engraftment and enhanced vascular differentiation in the bFGF+MSCs group compared to MSCs alone (p<0.05).

Conclusions: Retrograde coronary venous bFGF infusion augments engraftment and differentiation capacity of transplanted MSCs, recovering cardiac function and preventing adverse remodeling. This novel combined treatment and delivery method is a promising strategy for cardiac repair after ischemic injury.