Improving survival and efficacy of pluripotent stem cell-derived cardiac grafts

Chemically defined production of engineered cardiac tissue microspheres from hydrogel-encapsulated pluripotent stem cells

Chemically defined, suspension culture conditions are a key requirement in realizing clinical translation of engineered cardiac tissues (ECTs). Building on our previous work producing functional ECT microspheres through differentiation of biomaterial encapsulated human induced pluripotent stem cells (hiPSCs), here we establish the ability to use chemically defined culture conditions, including stem cell media (E8) and cardiac differentiation media (chemically defined differentiation media with three components, CDM3). A custom microfluidic cell encapsulation system was used to encapsulate hiPSCs at a range of initial cell concentrations and diameters in the hybrid biomaterial, poly(ethylene glycol)-fibrinogen (PF), for the formation of highly spherical and uniform ECT microspheres for subsequent cardiac differentiation. Initial microsphere diameter could be tightly controlled, and microspheres could be produced with an initial diameter between 400 and 800 µm. Three days after encapsulation, cardiac differentiation was initiated through small molecule modulation of Wnt signaling in CDM3. Cardiac differentiation occurred resulting in in situ ECT formation; results showed that this differentiation protocol could be used to achieve cardiomyocyte (CM) contents greater than 90%, although there was relatively high variability in CM content and yield between differentiation batches. Spontaneous contraction of ECT microspheres initiated between Days 7 and 10 of differentiation and ECT microspheres responded to electrical pacing up to 1.5 Hz. Resulting CMs had well-defined sarcomeres and the gap junction protein, connexin 43, and had appropriate temporal changes in gene expression. In summary, this study demonstrated the proof-of-concept to produce functional ECT microspheres with chemically defined media in suspension culture in combination with biomaterial support of microsphere encapsulated hiPSCs.

Research Advances of Injectable Functional Hydrogel Materials in the Treatment of Myocardial Infarction

Myocardial infarction (MI) has become one of the serious diseases threatening human life and health. However, traditional treatment methods for MI have some limitations, such as irreversible myocardial necrosis and cardiac dysfunction. Fortunately, recent endeavors have shown that hydrogel materials can effectively prevent negative remodeling of the heart and improve the heart function and long-term prognosis of patients with MI due to their good biocompatibility, mechanical properties, and electrical conductivity. Therefore, this review aims to summarize the research progress of injectable hydrogel in the treatment of MI in recent years and to introduce the rational design of injectable hydrogels in myocardial repair. Finally, the potential challenges and perspectives of injectable hydrogel in this field will be discussed, in order to provide theoretical guidance for the development of new and effective treatment strategies for MI.

Enhanced cellular engraftment of adipose-derived mesenchymal stem cell spheroids by using nanosheets as scaffolds

The short survival time of transplanted adipose-derived mesenchymal stem cells (ASCs) is a problem for skin wound healing. Transplantation after the formation of cellular spheroids has been investigated as a promising method for prolonging cellular survival. However, there have been technical restrictions for transplantation of spheroids in clinical practice. Here, we show an effective method for transplantation of ASC spheroids onto skin wounds in order to efficiently cure refractory ulcers. To assist anchoring of spheroids onto skin wounds, we used a 120-nm-thick free-standing film (nanosheet) that has a highly adhesive property. Bioluminescence imaging showed that ASC spheroids carried by the nanosheet survived for 14 days, which is about two-times longer than that previously reported. Wounds treated with a nanosheet carrying ASC spheroids were 4-times smaller than untreated wounds on day 14. This method for transplantation of spheroids could be applied to cell therapy for various refractory skin wounds.

The Myocardial Microenvironment Modulates the Biology of Transplanted Mesenchymal Stem Cells

PURPOSE

The maximal efficacy of cell therapy depends on the survival of stem cells, as well as on the phenotypic and biologic changes that may occur on these cells after transplantation. It has been hypothesized that the post-ischemic myocardial microenvironment can play a critical role in these changes, potentially affecting the survival and reparative potential of mesenchymal stem cells (MSCs). Here, we use a dual reporter gene sensor for the in vivo monitoring of the phenotype of MSCs and study their therapeutic effect on cardiac function.

PROCEDURES

The mitochondrial sensor was tested in cell culture in response to different mitochondrial stressors. For in vivo testing, MSCs (3 × 10⁵) were delivered in a murine ischemia-reperfusion (IR) model. Bioluminescence imaging was used to assess the mitochondrial biology and the viability of transplanted MSCs, while high-resolution ultrasound provided a non-invasive analysis of cardiac contractility and dyssynchrony.

RESULTS

The mitochondrial sensor showed increased activity in response to mitochondrial stressors. Furthermore, when tested in the living subject, it showed a significant increase in mitochondrial dysfunction in MSCs delivered in IR, compared with those delivered under sham conditions. Importantly, MSCs delivered to ischemic hearts, despite their mitochondrial stress and poor survival, were able to induce a significant improvement in cardiac function, through decreased collagen deposition and resynchronization/contractility of left ventricular wall motion.

CONCLUSIONS

The ischemic myocardium induces changes in the phenotype of transplanted MSCs. Despite their limited survival, MSCs still elicit a certain therapeutic response, as evidenced by improvement in myocardial remodeling and cardiac function. Maximization of the survival and reparative efficacy of stem cells remains a key for the success of stem cell therapies.

Engineered cardiac tissue microsphere production through direct differentiation of hydrogel-encapsulated human pluripotent stem cells

Engineered cardiac tissues that can be directly produced from human induced pluripotent stem cells (hiPSCs) in scalable, suspension culture systems are needed to meet the demands of cardiac regenerative medicine. Here, we demonstrate successful production of functional cardiac tissue microspheres through direct differentiation of hydrogel encapsulated hiPSCs. To form the microspheres, hiPSCs were suspended within the photocrosslinkable biomaterial, PEG-fibrinogen (25 million cells/mL), and encapsulated at a rate of 420,000 cells/minute using a custom microfluidic system. Even at this high cell density and rapid production rate, high intra-batch and batch-to-batch reproducibility was achieved. Following microsphere formation, hiPSCs maintained high cell viability and continued to grow within and beyond the original PEG-fibrinogen matrix. These initially soft microspheres (<250 Pa) supported efficient cardiac differentiation; spontaneous contractions initiated by differentiation day 8, and the microspheres contained >75% cardiomyocytes (CMs). CMs responded appropriately to pharmacological stimuli and exhibited 1:1 capture up to 6.0 Hz when electrically paced. Over time, cells formed cell-cell junctions and aligned myofibril fibers; engineered cardiac microspheres were maintained in culture over 3 years. The capability to rapidly generate uniform cardiac microsphere tissues is critical for advancing downstream applications including biomanufacturing, multi-well plate drug screening, and injection-based regenerative therapies.

Transplanted microvessels improve pluripotent stem cell-derived cardiomyocyte engraftment and cardiac function after infarction in rats

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) offer an unprecedented opportunity to remuscularize infarcted human hearts. However, studies have shown that most hiPSC-CMs do not survive after transplantation into the ischemic myocardial environment, limiting their regenerative potential and clinical application. We established a method to improve hiPSC-CM survival by cotransplanting ready-made microvessels obtained from adipose tissue. Ready-made microvessels promoted a sixfold increase in hiPSC-CM survival and superior functional recovery when compared to hiPSC-CMs transplanted alone or cotransplanted with a suspension of dissociated endothelial cells in infarcted rat hearts. Microvessels showed unprecedented persistence and integration at both early (~80%, week 1) and late (~60%, week 4) time points, resulting in increased vessel density and graft perfusion, and improved hiPSC-CM maturation. These findings provide an approach to cell-based therapies for myocardial infarction, whereby incorporation of ready-made microvessels can improve functional outcomes in cell replacement therapies.

Humanized Mouse Models for Evaluation of PSC Immunogenicity

New human pluripotent stem cell (hPSC)-derived therapies are advancing to clinical trials at an increasingly rapid pace. In addition to ensuring that the therapies function properly, there is a critical need to investigate the human immune response to these cell products. A robust allogeneic (or autologous) immune response could swiftly eliminate an otherwise promising cell therapy, even in immunosuppressed patients. In coming years, researchers in the regenerative medicine field will need to utilize a number of in vitro and in vivo assays and models to evaluate and better understand hPSC immunogenicity. Humanized mouse models-mice engrafted with functional human immune cell types-are an important research tool for investigating the mechanisms of the adaptive immune response to hPSC therapies. This article provides an overview of humanized mouse models relevant to the study of hPSC immunogenicity and explores central considerations for investigators seeking to utilize these powerful models in their research. © 2020 Wiley Periodicals LLC.

Biologics and their delivery systems: Trends in myocardial infarction

Cardiovascular disease is the leading cause of death around the world, in which myocardial infarction (MI) is a precipitating event. However, current therapies do not adequately address the multiple dysregulated systems following MI. Consequently, recent studies have developed novel biologic delivery systems to more effectively address these maladies. This review utilizes a scientometric summary of the recent literature to identify trends among biologic delivery systems designed to treat MI. Emphasis is placed on sustained or targeted release of biologics (e.g. growth factors, nucleic acids, stem cells, chemokines) from common delivery systems (e.g. microparticles, nanocarriers, injectable hydrogels, implantable patches). We also evaluate biologic delivery system trends in the entire regenerative medicine field to identify emerging approaches that may translate to the treatment of MI. Future developments include immune system targeting through soluble factor or chemokine delivery, and the development of advanced delivery systems that facilitate the synergistic delivery of biologics.

Programmed cell death in stem cell-based therapy: Mechanisms and clinical applications

Stem cell-based therapy raises hopes for a better approach to promoting tissue repair and functional recovery. However, transplanted stem cells show a high death percentage, creating challenges to successful transplantation and prognosis. Thus, it is necessary to investigate the mechanisms underlying stem cell death, such as apoptotic cascade activation, excessive autophagy, inflammatory response, reactive oxygen species, excitotoxicity, and ischemia/hypoxia. Targeting the molecular pathways involved may be an efficient strategy to enhance stem cell viability and maximize transplantation success. Notably, a more complex network of cell death receives more attention than one crucial pathway in determining stem cell fate, highlighting the challenges in exploring mechanisms and therapeutic targets. In this review, we focus on programmed cell death in transplanted stem cells. We also discuss some promising strategies and challenges in promoting survival for further study.

Enhancement of Wound Healing by Conditioned Medium of Adipose-Derived Stromal Cell with Photobiomodulation in Skin Wound

Background and Objectives

The objective of this study was to investigate whether conditioned medium from photobiomodulation (PBM) irradiated adipose-derived stromal cell (ASC) spheroids prior to implanting could stimulate angiogenesis and tissue regeneration to improve functional recovery of skin tissue in an animal skin wound model.

Methods and Results

ASC were split and seeded on chitosan-coated 24 well plate at a density of 7.5×10⁴ cells/cm², and allowed to adhere at 37℃. Within 3 days of culture, ASC formed spheroids by PBM irradiation. Conditioned medium (CM) fractions were collected from the PBM-ASC to yield nor adipose-derived stromal cell spheroid (spheroid) and PBM-spheroid, respectively, centrifuged at 13,000 g at 4℃ for 10 min, and stored prior to use for ELISA, protein assay, or in vivo wound-healing assays. Phosphate-buffered saline, cultured CM from ASCs, PBM irradiation prior to implanting conditioned medium from ASC, cultured CM from ASC spheroid, and PBM–spheroid-CM (PSC) were transplanted into a wound bed in athymic mice to evaluate therapeutic effects of PSC in vivo. PSC enhanced wound closure in a skin injury model compared to PBS, CM, PBM–CM, and spheroid-CM. The density of vascular formations increased as a result of angiogenic factors released by the wound bed and enhanced tissue regeneration at the lesion site.

Conclusions

These results indicate that implant of PSC can significantly improve functional recovery compared to PBS, CM, PBM–CM, or spheroid-CM treatment. Implant of PSC may be an effective form of paracrine mediated therapy for treating a wound bed.

Hyaluronate supports hESC-cardiomyocyte cell therapy for cardiac regeneration after acute myocardial infarction

Introduction

Enormous progress has been made in cardiac regeneration using human embryonic stem cell‐derived cardiomyocyte (hESC‐CM) grafts in pre‐clinical trials. However, the rate of cell survival has remained very low due to anoikis after transplantation into the heart as single cells. Numerous solutions have been proposed to improve cell survival, and one of these strategies is to co‐transplant biocompatible materials or hydrogels with the hESC‐CMs.

Methods

In our study, we screened various combinations of biomaterials that could promote anoikis resistance and improve hESC‐CM survival upon co‐transplantation and promote cardiac functional recovery. We injected different combinations of Matrigel, alginate and hyaluronate with hESC‐CM suspensions into the myocardium of rat models with myocardial infarction (MI).

Results

Our results showed that the group treated with a combination of hyaluronate and hESC‐CMs had the lowest arrhythmia rates when stimulated with programmed electrical stimulation. While all three combinations of hydrogel‐hESC‐CM treatments improved rat cardiac function compared with the saline control group, the combination with hyaluronate most significantly reduced pathological changes from left ventricular remodelling and improved both left ventricular function and left ventricular ejection fraction by 28 days post‐infarction.

Conclusion

Hence, we concluded that hyaluronate‐hESC‐CM is a superior combination therapy for promoting cardiac regeneration after myocardial infarction.

Suppression of inflammation and fibrosis using soluble epoxide hydrolase inhibitors enhances cardiac stem cell-based therapy

Stem cell replacement offers a great potential for cardiac regenerative therapy. However, one of the critical barriers to stem cell therapy is a significant loss of transplanted stem cells from ischemia and inflammation in the host environment. Here, we tested the hypothesis that inhibition of the soluble epoxide hydrolase (sEH) enzyme using sEH inhibitors (sEHIs) to decrease inflammation and fibrosis in the host myocardium may increase the survival of the transplanted human induced pluripotent stem cell derived-cardiomyocytes (hiPSC-CMs) in a murine postmyocardial infarction model. A specific sEHI (1-trifluoromethoxyphenyl-3-(1-propionylpiperidine-4-yl)urea [TPPU]) and CRISPR/Cas9 gene editing were used to test the hypothesis. TPPU results in a significant increase in the retention of transplanted cells compared with cell treatment alone. The increase in the retention of hiPSC-CMs translates into an improvement in the fractional shortening and a decrease in adverse remodeling. Mechanistically, we demonstrate a significant decrease in oxidative stress and apoptosis not only in transplanted hiPSC-CMs but also in the host environment. CRISPR/Cas9-mediated gene silencing of the sEH enzyme reduces cleaved caspase-3 in hiPSC-CMs challenged with angiotensin II, suggesting that knockdown of the sEH enzyme protects the hiPSC-CMs from undergoing apoptosis. Our findings demonstrate that suppression of inflammation and fibrosis using an sEHI represents a promising adjuvant to cardiac stem cell-based therapy. Very little is known regarding the role of this class of compounds in stem cell-based therapy. There is consequently an enormous opportunity to uncover a potentially powerful class of compounds, which may be used effectively in the clinical setting.

Emulsion-based encapsulation of pluripotent stem cells in hydrogel microspheres for cardiac differentiation

Cardiovascular disease is the leading cause of death worldwide, and current treatments are ineffective or unavailable to majority of patients. Engineered cardiac tissue (ECT) is a promising treatment to restore function to the damaged myocardium; however, for these treatments to become a reality, tissue fabrication must be amenable to scalable production and be used in suspension culture. Here, we have developed a low-cost and scalable emulsion-based method for producing ECT microspheres from poly(ethylene glycol) (PEG)-fibrinogen encapsulated mouse embryonic stem cells (mESCs). Cell-laden microspheres were formed via water-in-oil emulsification; encapsulation occurred by suspending the cells in hydrogel precursor solution at cell densities from 5 to 60 million cells/ml, adding to mineral oil and vortexing. Microsphere diameters ranged from 30 to 570 μm; size variability was decreased by the addition of 2% poly(ethylene glycol) diacrylate. Initial cell encapsulation density impacted the ability for mESCs to grow and differentiate, with the greatest success occurring at higher cell densities. Microspheres differentiated into dense spheroidal ECTs with spontaneous contractions occurring as early as Day 10 of cardiac differentiation; furthermore, these ECT microspheres exhibited appropriate temporal changes in gene expression and response to pharmacological stimuli. These results demonstrate the ability to use an emulsion approach to encapsulate pluripotent stem cells for use in microsphere-based cardiac differentiation.

Stem cell therapy of myocardial infarction: a promising opportunity in bioengineering

Myocardial infarction (MI) is a life-threatening disease resulting from irreversible death of cardiomyocytes (CMs) and weakening of the heart blood-pumping function. Stem cell-based therapies have been studied for MI treatment over the last two decades with promising outcome. In this review, we critically summarize the past work in this field to elucidate the advantages and disadvantages of treating MI using pluripotent stem cells (PSCs) including both embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), adult stem cells, and cardiac progenitor cells. The main advantage of the latter is their cytokine production capability to modulate immune responses and control the progression of healing. However, human adult stem cells have very limited (if not 'no') capacity to differentiate into functional CMs in vitro or in vivo. In contrast, PSCs can be differentiated into functional CMs although the protocols for the cardiac differentiation of PSCs are mainly for adherent cells under 2D culture. Derivation of PSC-CMs in 3D, allowing for large-scale production of CMs via modulation of the Wnt/β-catenin signal pathway with defined chemicals and medium, may be desired for clinical translation. Furthermore, the technology of purification and maturation of the PSC-CMs may need further improvements to eliminate teratoma formation after in vivo implantation of the PSC-CMs for treating MI. In addition, in vitro derived PSC-CMs may have mechanical and electrical mismatch with the patient's cardiac tissue, which causes arrhythmia. This supports the use of PSC-derived cells committed to cardiac lineage without beating for implantation to treat MI. In this case, the PSC derived cells may utilize the mechanical, electrical, and chemical cues in the heart to further differentiate into mature/functional CMs in situ. Another major challenge facing stem cell therapy of MI is the low retention/survival of stem cells or their derivatives (e.g., PSC-CMs) in the heart for MI treatment after injection in vivo. This may be resolved by using biomaterials to engineer stem cells for reduced immunogenicity, immobilization of the cells in the heart, and increased integration with the host cardiac tissue. Biomaterials have also been applied in the derivation of CMs in vitro to increase the efficiency and maturation of differentiation. Collectively, a lot has been learned from the past failure of simply injecting intact stem cells or their derivatives in vivo for treating MI, and bioengineering stem cells with biomaterials is expected to be a valuable strategy for advancing stem cell therapy towards its widespread application for treating MI in the clinic.

Pluripotent stem cell-derived cardiomyocytes for treatment of cardiomyopathic damage: Current concepts and future directions

Today, cell replacement therapy using pluripotent stem cell-derived cardiomyocytes (PSC-CMs) remains a research endeavor, with several hurdles that must be overcome before delivery of PSC-CMs can become a therapeutic reality. In this review, we highlight major findings to date from pre-clinical studies involving delivery of PSC-CMs and consider remaining challenges that must be addressed for successful clinical translation. Our goal is to provide an overview of the current status of cardiomyocyte replacement therapy and what challenges must be addressed before successful clinical translation of such therapies will be possible.

Increasing the Efficacy of Stem Cell Therapy via Triple-Function Inorganic Nanoparticles

Stem cell therapy in heart disease is challenged by mis-injection, poor survival, and low cell retention. Here, we describe a biocompatible multifunctional silica-iron oxide nanoparticle to help solve these issues. The nanoparticles were made via an in situ growth of Fe₃O₄ nanoparticles on both the external surfaces and pore walls of mesocellular foam silica nanoparticles. In contrast to previous work, this approach builds a magnetic moiety inside the pores of a porous silica structure. These materials serve three roles: drug delivery, magnetic manipulation, and imaging. The addition of Fe₃O₄ to the silica nanoparticles increased their colloidal stability, T₂-based magnetic resonance imaging contrast, and superparamagnetism. We then used the hybrid materials as a sustained release vehicle of insulin-like growth factor-a pro-survival agent that can increase cell viability. In vivo rodent studies show that labeling stem cells with this nanoparticle increased the efficacy of stem cell therapy in a ligation/reperfusion model. The nanoparticle-labeled cells increase the mean left ventricular ejection fraction by 11 and 21% and the global longitudinal strain by 24 and 34% on days 30 and 60, respectively. In summary, this multifunctional nanomedicine improves stem cell survival via the sustained release of pro-survival agents.

A brief review of cytotoxicity of nanoparticles on mesenchymal stem cells in regenerative medicine

Multipotent mesenchymal stem cells have shown great promise for application in regenerative medicine owing to their particular therapeutic effects, such as significant self-renewability, low immunogenicity, and ability to differentiate into a variety of specialized cells. However, there remain certain complicated and unavoidable problems that limit their further development and application. One of the challenges is to noninvasively monitor the delivery and biodistribution of transplanted stem cells during treatment without relying on behavioral endpoints or tissue histology, and it is important to explore the potential mechanisms to clarify how stem cells work in vivo. To solve these problems, various nanoparticles (NPs) and their corresponding imaging methods have been developed recently and have made great progress. In this review, we mainly discuss NPs used to label stem cells and their toxic effects on the latter, the imaging techniques to detect such NPs, and the current existing challenges in this field.

Aggregation of Child Cardiac Progenitor Cells Into Spheres Activates Notch Signaling and Improves Treatment of Right Ventricular Heart Failure

RATIONALE

Congenital heart disease can lead to life-threatening right ventricular (RV) heart failure. Results from clinical trials support expanding cardiac progenitor cell (CPC) based therapies. However, our recent data show that CPCs lose function as they age, starting as early as 1 year.

OBJECTIVE

To determine whether the aggregation of child (1-5-year-old) CPCs into scaffold-free spheres can improve differentiation by enhancing Notch signaling, a known regulator of CPC fate. We hypothesized that aggregated (3-dimensional [3D]) CPCs will repair RV heart failure better than monolayer (2-dimensional [2D]) CPCs.

METHODS AND RESULTS

Spheres were produced with 1500 CPCs each using a microwell array. CPC aggregation significantly increased gene expression of Notch1 compared with 2D CPCs, accompanied by significant upregulation of cardiogenic transcription factors (GATA4, HAND1, MEF2C, NKX2.5, and TBX5) and endothelial markers (CD31, FLK1, FLT1, VWF). Blocking Notch receptor activation with the γ-secretase inhibitor DAPT (N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester) diminished these effects. To evaluate the therapeutic improvements of CPC aggregation, RV heart failure was induced in athymic rats by pulmonary artery banding, and cells were implanted into the RV free wall. Echocardiographic measurements 28 days postimplantation showed significantly improved RV function with 3D compared with 2D CPCs. Tracking implanted CPCs via DiR (1,1'-dioctadecyl-3,3,3',3'-tetramethylindotricarbocyanine iodide)-labeling showed improved retention of 3D CPCs. Transducing 3D CPCs with Notch1-shRNA (short hairpin RNA) did not reduce retention, but significantly reduced RV functional improvements. Histological analyses showed 3D treatment reduced RV fibrosis and increased angiogenesis. Although 3D CPCs formed CD31⁺ vessel-like cells in vivo, these effects are more likely because of improved 3D CPC exosome function compared with 2D CPC exosomes.

CONCLUSIONS

Spherical aggregation improves child CPC function in a Notch-dependent manner. The strong reparative ability of CPC spheres warrants further investigation as a treatment for pediatric heart failure, especially in older children where reparative ability may be reduced.

Targeting Oxidative Stress Using Nanoparticles as a Theranostic Strategy for Cardiovascular Diseases

SIGNIFICANCE

Nanomedicine is an application of nanotechnology that provides solutions to unmet medical challenges. The unique features of nanoparticles, such as their small size, modifiable components, and diverse functionality, make them attractive and suitable materials for novel diagnostic, therapeutic, or theranostic applications. Cardiovascular diseases (CVDs) are the major cause of noncommunicable illness in both developing and developed countries. Nanomedicine offers novel theranostic options for the treatment of CVDs. Recent Advances: Many innovative nanoparticles to target reactive oxygen species (ROS) have been developed. In this article, we review the characteristics of nanoparticles that are responsive to ROS, their limitations, and their potential clinical uses. Significant advances made in diagnosis of atherosclerosis and treatment of acute coronary syndrome using nanoparticles are discussed.

CRITICAL ISSUES

Although there is a tremendous potential for the nanoparticle applications in medicine, their safety should be considered while using in humans. We discuss the challenges that may be encountered with some of the innovative nanoparticles used in CVDs.

FUTURE DIRECTIONS

The unique properties of nanoparticles offer novel diagnostic tool and potential therapeutic strategies. However, nanomedicine is still in its infancy, and further in-depth studies are needed before wide clinical application is achieved.

Promoting vascularization for tissue engineering constructs: current strategies focusing on HIF-regulating scaffolds

INTRODUCTION

Vascularization remains one of the greatest yet unmet challenges in tissue engineering. When engineered tissues are scaled up to therapeutically relevant dimensions, their demand of oxygen and nutrients can no longer be met by diffusion. Thus, there is a need for perfusable vascular structures. Hypoxia-inducible factors (HIF) act as transcriptional oxygen sensors and regulate a multitude of genes involved in adaptive processes to hypoxia, including angiogenesis. Thus, targeting HIFs is a promising strategy to induce vascularization of engineered tissues.

AREAS COVERED

Here we review current vascularization strategies and summarize the present knowledge regarding activation of HIF signaling by ions, iron chelating agents, α-Ketoglutarate (αKG) analogues, and the lipid-lowering drug simvastatin to induce angiogenesis. Specifically, we focus on the incorporation of HIF-activating agents into biomaterials and scaffolds for controlled release.

EXPERT OPINION

Vascularization of tissue constructs through activation of upstream regulators of angiogenesis offers advantages but also suffers from drawbacks. HIFs can induce a complete angiogenic program; however, this program appears to be too slow to vascularize larger constructs before cell death occurs. It is therefore crucial that HIF-activation is combined with cell protective strategies and prevascularization techniques to obtain fully vascularized, vital tissues of therapeutically relevant dimensions.

Lower retention after retrograde coronary venous infusion compared with intracoronary infusion of mesenchymal stromal cells in the infarcted porcine myocardium

BACKGROUND

Commonly used strategies for cell delivery to the heart are intramyocardial injection and intracoronary (IC) infusion, both having their advantages and disadvantages. Therefore, alternative strategies, such as retrograde coronary venous infusion (RCVI), are explored. The aim of this confirmatory study was to compare cardiac cell retention between RCVI and IC infusion. As a secondary end point, the procedural safety of RCVI is assessed.

METHODS

Four weeks after myocardial infarction, 12 pigs were randomised to receive mesenchymal stromal cells, labelled with Indium-111, via RCVI (n=6) or IC infusion (n=6). Four hours after cell administration, nuclear imaging was performed to determine the number of cells retained in the heart both in vivo and ex vivo. Procedure-related safety measures were reported.

RESULTS

Cardiac cell retention is significantly lower after RCVI compared with IC infusion (in vivo: RCVI: median 2.89% vs IC: median 13.74%, p=0.002, ex vivo: RCVI: median 2.55% vs IC: median 39.40%, p=0.002). RCVI led to development of pericardial fluid and haematomas on the frontal wall of the heart in three cases. Coronary venous dissection after RCVI was seen in three pigs, of which one also developed pericardial fluid and a haematoma. IC infusion led to no flow in one pig.

CONCLUSION

RCVI is significantly less efficient in delivering cells to the heart compared with IC infusion. RCVI led to more procedure-related safety issues than IC infusion, with multiple cases of venous dissection and development of haematomas and pericardial fluid collections.

Regulation of Ca2+ signaling by acute hypoxia and acidosis in cardiomyocytes derived from human induced pluripotent stem cells

AIMS

The effects of acute (100 s) hypoxia and/or acidosis on Ca²⁺ signaling parameters of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) are explored here for the first time.

METHODS AND RESULTS

1) hiPSC-CMs express two cell populations: rapidly-inactivating I_Ca myocytes (τ_i<40 ms, in 4-5 day cultures) and slowly-inactivating I_Ca (τ_i  ≥ 40 ms, in 6-8 day cultures). 2) Hypoxia suppressed I_Ca by 10-20% in rapidly- and 40-55% in slowly-inactivating I_Ca cells. 3) Isoproterenol enhanced I_Ca in hiPSC-CMs, but either enhanced or did not alter the hypoxic suppression. 4) Hypoxia had no differential suppressive effects in the two cell-types when Ba²⁺ was the charge carrier through the calcium channels, implicating Ca²⁺-dependent inactivation in O₂ sensing. 5) Acidosis suppressed I_Ca by ∼35% and ∼25% in rapidly and slowly inactivating I_Ca cells, respectively. 6) Hypoxia and acidosis suppressive effects on Ca-transients depended on whether global or RyR2-microdomain were measured: with acidosis suppression was ∼25% in global and ∼37% in RyR2 Ca²⁺-microdomains in either cell type, whereas with hypoxia suppression was ∼20% and ∼25% respectively in global and RyR2-microdomaine in rapidly and ∼35% and ∼45% respectively in global and RyR2-microdomaine in slowly-inactivating cells.

CONCLUSIONS

Variability in I_Ca inactivation kinetics rather than cellular ancestry seems to underlie the action potential morphology differences generally attributed to mixed atrial and ventricular cell populations in hiPSC-CMs cultures. The differential hypoxic regulation of Ca²⁺-signaling in the two-cell types arises from differential Ca²⁺-dependent inactivation of the Ca²⁺-channel caused by proximity of Ca²⁺-release stores to the Ca²⁺ channels.

The Effects of Metabolic Substrate Availability on Human Adipose-Derived Stem Cell Spheroid Survival

IMPACT STATEMENT

Human adipose-derived stem cells (hADSCs) spheroids have displayed remarkable potential for treating ischemic injury. However, low nutrient (i.e., glucose and oxygen) availability in ischemic environments results in limited tissue viability posttransplantation. To develop an understanding of the effects of nutrient availability on spheroid survival, we utilized both in vitro and computational models to examine the limiting factors in metabolic supply for avascular microtissues, revealing the critical role of glucose to improve hADSC spheroid survival in ischemic conditions. These results may impact future strategies for improving hADSC transplantation efficacy through codelivery of metabolic substrates.

Therapeutic applications of adipose-derived stem cells in cardiovascular disease

Cardiovascular disease (CVD) is the number one cause of death globally, and new therapeutic techniques outside of traditional pharmaceutical and surgical interventions are currently being developed. At the forefront is stem cell-centered therapy, with adipose derived stem cells (ADSCs), an adult stem population, providing significant clinical promise. When introduced into damaged heart tissue, ADSCs promote cardiac regeneration by a variety of mechanisms including differentiation into new cardiomyocytes and secretion of paracrine factors acting on endogenous cardiac cells. We discuss the application of ADSCs, their biochemical capabilities, availability, ease of extraction, clinical trial results, and areas of concern. The multipotent capacity of ADSCs along with their ability to secrete factors promoting cell survival and regeneration, along with their immunosuppressive capacity, make them an extremely promising approach in the field of CVD therapy.

Changing Metabolism in Differentiating Cardiac Progenitor Cells-Can Stem Cells Become Metabolically Flexible Cardiomyocytes?

The heart is a metabolic omnivore and the adult heart selects the substrate best suited for each circumstance, with fatty acid oxidation preferred in order to fulfill the high energy demand of the contracting myocardium. The fetal heart exists in an hypoxic environment and obtains the bulk of its energy via glycolysis. After birth, the "fetal switch" to oxidative metabolism of glucose and fatty acids has been linked to the loss of the regenerative phenotype. Various stem cell types have been used in differentiation studies, but most are cultured in high glucose media. This does not change in the majority of cardiac differentiation protocols. Despite the fact that metabolic state affects marker expression and cellular function and activity, the substrate composition is currently being overlooked. In this review we discuss changes in cardiac metabolism during development, the various protocols used to differentiate progenitor cells to cardiomyocytes, what is known about stem cell metabolism and how consideration of metabolism can contribute toward maturation of stem cell-derived cardiomyocytes.

New Myocyte Formation in the Adult Heart: Endogenous Sources and Therapeutic Implications

Death of adult cardiac myocytes and supportive tissues resulting from cardiovascular diseases such as myocardial infarction is the proximal driver of pathological ventricular remodeling that often culminates in heart failure. Unfortunately, no currently available therapeutic barring heart transplantation can directly replenish myocytes lost from the injured heart. For decades, the field has struggled to define the intrinsic capacity and cellular sources for endogenous myocyte turnover in pursuing more innovative therapeutic strategies aimed at regenerating the injured heart. Although controversy persists to this day as to the best therapeutic regenerative strategy to use, a growing consensus has been reached that the very limited capacity for new myocyte formation in the adult mammalian heart is because of proliferation of existing cardiac myocytes but not because of the activity of an endogenous progenitor cell source of some sort. Hence, future therapeutic approaches should take into consideration the fundamental biology of myocyte renewal in designing strategies to potentially replenish these cells in the injured heart.

The harsh microenvironment in infarcted heart accelerates transplanted bone marrow mesenchymal stem cells injury: the role of injured cardiomyocytes-derived exosomes

Stem cell therapy can be used to repair and regenerate damaged hearts tissue; nevertheless, the low survival rate of transplanted cells limits their therapeutic efficacy. Recently, it has been proposed that exosomes regulate multiple cellular processes by mediating cell survival and communication among cells. The following study investigates whether injured cardiomyocytes-derived exosomes (cardiac exosomes) affect the survival of transplanted bone marrow mesenchymal stem cells (BMSCs) in infarcted heart. To mimic the harsh microenvironment in infarcted heart that the cardiomyocytes or transplanted BMSCs encounter in vivo, cardiomyocytes conditioned medium and cardiac exosomes collected from H₂O₂-treated cardiomyocytes culture medium were cultured with BMSCs under oxidative stress in vitro. Cardiomyocytes conditioned medium and cardiac exosomes significantly accelerated the injury of BMSCs induced by H₂O₂; increased cleaved caspase-3/caspase-3 and apoptotic percentage, and decreased the ratio of Bcl-2/Bax and cell viability in those cells. Next, we explored the role of cardiac exosomes in the survival of transplanted BMSCs in vivo by constructing a Rab27a knockout (KO) mice model by a transcription activator-like effector nuclease (TALEN) genome-editing technique; Rab27a is a family of GTPases, which has critical role in secretion of exosomes. Male mouse GFP-modified BMSCs were implanted into the viable myocardium bordering the infarction in Rab27a KO and wild-type female mice. The obtained results showed that the transplanted BMSCs survival in infarcted heart was increased in Rab27a KO mice by the higher level of Y-chromosome Sry DNA, GFP mRNA, and the GFP fluorescence signal intensity. To sum up, these findings revealed that the injured cardiomyocytes-derived exosomes accelerate transplanted BMSCs injury in infarcted heart, thus highlighting a new mechanism underlying the survival of transplanted cells after myocardial infarction.

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.

An Injectable Oxygen Release System to Augment Cell Survival and Promote Cardiac Repair Following Myocardial Infarction

Oxygen deficiency after myocardial infarction (MI) leads to massive cardiac cell death. Protection of cardiac cells and promotion of cardiac repair are key therapeutic goals. These goals may be achieved by re-introducing oxygen into the infarcted area. Yet current systemic oxygen delivery approaches cannot efficiently diffuse oxygen into the infarcted area that has extremely low blood flow. In this work, we developed a new oxygen delivery system that can be delivered specifically to the infarcted tissue, and continuously release oxygen to protect the cardiac cells. The system was based on a thermosensitive, injectable and fast gelation hydrogel, and oxygen releasing microspheres. The fast gelation hydrogel was used to increase microsphere retention in the heart tissue. The system was able to continuously release oxygen for 4 weeks. The released oxygen significantly increased survival of cardiac cells under the hypoxic condition (1% O₂) mimicking that of the infarcted hearts. It also reduced myofibroblast formation under hypoxic condition (1% O₂). After implanting into infarcted hearts for 4 weeks, the released oxygen significantly augmented cell survival, decreased macrophage density, reduced collagen deposition and myofibroblast density, and stimulated tissue angiogenesis, leading to a significant increase in cardiac function.

Extracellular Matrix and Regenerative Therapies from the Cardiac Perspective

Cardiovascular diseases are the leading cause of death and a major cause of financial burden. Regenerative therapies for heart diseases bring the promise of alternative treatment modalities for myocardial infarction, ischemic heart disease, and congestive heart failure. Although, clinical trials attest to the safety of stem cell injection therapies, researchers need to overcome the underlying mechanisms that are limiting the success of future regenerative options. This article aims to review the basic scientific concepts in the field of mechanobiology and the effects of extracellular functions on stem cell fate.

Noninvasive Monitoring of the Mitochondrial Function in Mesenchymal Stromal Cells

PURPOSE

Mitochondria are a gatekeeper of cell survival and mitochondrial function can be used to monitor cell stress. Here we validate a pathway-specific reporter gene to noninvasively image the mitochondrial function of stem cells.

PROCEDURES

We constructed a mitochondrial sensor with the firefly luciferase (Fluc) reporter gene driven by the NQO1 enzyme promoter. The sensor was introduced in stem cells and validated in vitro and in vivo, in a mouse model of myocardial ischemia/reperfusion (IR).

RESULTS

The sensor activity showed an inverse relationship with mitochondrial function (R (2) = -0.975, p = 0.025) and showed specificity and sensitivity for mitochondrial dysfunction. In vivo, NQO1-Fluc activity was significantly higher in IR animals vs. controls, indicative of mitochondrial dysfunction, and was corroborated by ex vivo luminometry.

CONCLUSIONS

Reporter gene imaging allows assessment of the biology of transplanted mesenchymal stromal cells (MSCs), providing important information that can be used to improve the phenotype and survival of transplanted stem cells.

Mechanism of action of the anti-inflammatory connexin43 mimetic peptide JM2

Connexin-based therapeutics have shown the potential for therapeutic efficacy in improving wound healing. Our previous work demonstrated that the connexin43 (Cx43) mimetic peptide juxtamembrane 2 (JM2) reduced the acute inflammatory response to a submuscular implant model by inhibiting purinergic signaling. Given the prospective application in improving tissue-engineered construct tolerance that these results indicated, we sought to determine the mechanism of action for JM2 in the present study. Using confocal microscopy, a gap-FRAP cell communication assay, and an ethidium bromide uptake assay of hemichannel function we found that the peptide reduced cell surface Cx43 levels, Cx43 gap junction (GJ) size, GJ communication, and hemichannel activity. JM2 is based on the sequence of the Cx43 microtubule binding domain, and microtubules have a confirmed role in intracellular trafficking of Cx43 vesicles. Therefore, we tested the effect of JM2 on Cx43-microtubule interaction and microtubule polymerization. We found that JM2 enhanced Cx43-microtubule interaction and that microtubule polymerization was significantly enhanced. Taken together, these data suggest that JM2 inhibits trafficking of Cx43 to the cell surface by promoting irrelevant microtubule polymerization and thereby reduces the number of hemichannels in the plasma membrane available to participate in proinflammatory purinergic signaling. Importantly, this work indicates that JM2 may have therapeutic value in the treatment of proliferative diseases such as cancer. We conclude that the targeted action of JM2 on Cx43 channels may improve the tolerance of implanted tissue-engineered constructs against the innate inflammatory response.

Tert-butylhydroquinone promotes angiogenesis and improves heart functions in rats after myocardial infarction

BACKGROUND

Hypertension is an increased risk of heart failure and acute myocardial infarction (MI). Tert-butylhydroquinone (tBHQ), as an antioxidant, shows multiple cardioprotective actions including the reduction in blood pressure. The aim of this study was to investigate whether and how tBHQ improves heart functions in rats.

METHODS

The MI model was established in WKY and spontaneously hypertensive rats (SHRs) by ligation of left anterior descending coronary artery. Akt phosphorylation was examined by western blot in human umbilical vein endothelial cells (HUVECs) or in rats. Angiogenesis was assessed by immunohistochemistry and immunofluorescence. Heart function was determined by echocardiography.

RESULTS

tBHQ increased Akt phosphorylation, promoted cell proliferations and migrations in HUVECs, which were abolished by Akt inhibitor wortmannin. In SHRs following MI, administration of tBHQ significantly increased Akt phosphorylation, promoted angiogenesis, reduced infarct size, and improved heart functions after 14 postoperative days. Importantly, these in vivo effects of tBHQ were ablated by wortmannin in SHRs.

CONCLUSION

tBHQ via Akt activation promotes ischemia-induced angiogenesis and improves heart functions in hypertensive rats. In perspectives, the application of tBHQ should be considered in patients with ischemic diseases such as MI and stroke.

Transplantation of HGF gene-engineered skeletal myoblasts improve infarction recovery in a rat myocardial ischemia model

BACKGROUND

Skeletal myoblast transplantation seems a promising approach for the repair of myocardial infarction (MI). However, the low engraftment efficacy and impaired angiogenic ability limit the clinical efficiency of the myoblasts. Gene engineering with angiogenic growth factors promotes angiogenesis and enhances engraftment of transplanted skeletal myoblasts, leading to improved infarction recovery in myocardial ischemia. The present study evaluated the therapeutic effects of hepatocyte growth factor (HGF) gene-engineered skeletal myoblasts on tissue regeneration and restoration of heart function in a rat MI model.

METHODS AND RESULTS

The skeletal myoblasts were isolated, expanded, and transduced with adenovirus carrying the HGF gene (Ad-HGF). Male SD rats underwent ligation of the left anterior descending coronary artery. After 2 weeks, the surviving rats were randomized into four groups and treated with skeletal myoblasts by direct injection into the myocardium. The survival and engraftment of skeletal myoblasts were determined by real-time PCR and in situ hybridization. The cardiac function with hemodynamic index and left ventricular architecture were monitored; The adenovirus-mediated-HGF gene transfection increases the HGF expression and promotes the proliferation of skeletal myoblasts in vitro. Transplantation of HGF-engineered skeletal myoblasts results in reduced infarct size and collagen deposition, increased vessel density, and improved cardiac function in a rat MI model. HGF gene modification also increases the myocardial levels of HGF, VEGF, and Bcl-2 and enhances the survival and engraftment of skeletal myoblasts.

CONCLUSIONS

HGF engineering improves the regenerative effect of skeletal myoblasts on MI by enhancing their survival and engraftment ability.

Contractile force generation by 3D hiPSC-derived cardiac tissues is enhanced by rapid establishment of cellular interconnection in matrix with muscle-mimicking stiffness

Engineering 3D human cardiac tissues is of great importance for therapeutic and pharmaceutical applications. As cardiac tissue substitutes, extracellular matrix-derived hydrogels have been widely explored. However, they exhibit premature degradation and their stiffness is often orders of magnitude lower than that of native cardiac tissue. There are no reports on establishing interconnected cardiomyocytes in 3D hydrogels at physiologically-relevant cell density and matrix stiffness. Here we bioengineer human cardiac microtissues by encapsulating human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) in chemically-crosslinked gelatin hydrogels (1.25 × 10⁸/mL) with tunable stiffness and degradation. In comparison to the cells in high stiffness (16 kPa)/slow degrading hydrogels, hiPSC-CMs in low stiffness (2 kPa)/fast degrading and intermediate stiffness (9 kPa)/intermediate degrading hydrogels exhibit increased intercellular network formation, α-actinin and connexin-43 expression, and contraction velocity. Only the 9 kPa microtissues exhibit organized sarcomeric structure and significantly increased contractile stress. This demonstrates that muscle-mimicking stiffness together with robust cellular interconnection contributes to enhancement in sarcomeric organization and contractile function of the engineered cardiac tissue. This study highlights the importance of intercellular connectivity, physiologically-relevant cell density, and matrix stiffness to best support 3D cardiac tissue engineering.

Cell number per spheroid and electrical conductivity of nanowires influence the function of silicon nanowired human cardiac spheroids

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) provide an unlimited cell source to treat cardiovascular diseases, the leading cause of death worldwide. However, current hiPSC-CMs retain an immature phenotype that leads to difficulties for integration with adult myocardium after transplantation. To address this, we recently utilized electrically conductive silicon nanowires (e-SiNWs) to facilitate self-assembly of hiPSC-CMs to form nanowired hiPSC cardiac spheroids. Our previous results showed addition of e-SiNWs effectively enhanced the functions of the cardiac spheroids and improved the cellular maturation of hiPSC-CMs. Here, we examined two important factors that can affect functions of the nanowired hiPSC cardiac spheroids: (1) cell number per spheroid (i.e., size of the spheroids), and (2) the electrical conductivity of the e-SiNWs. To examine the first factor, we prepared hiPSC cardiac spheroids with four different sizes by varying cell number per spheroid (∼0.5k, ∼1k, ∼3k, ∼7k cells/spheroid). Spheroids with ∼3k cells/spheroid was found to maximize the beneficial effects of the 3D spheroid microenvironment. This result was explained with a semi-quantitative theory that considers two competing factors: 1) the improved 3D cell-cell adhesion, and 2) the reduced oxygen supply to the center of spheroids with the increase of cell number. Also, the critical role of electrical conductivity of silicon nanowires has been confirmed in improving tissue function of hiPSC cardiac spheroids. These results lay down a solid foundation to develop suitable nanowired hiPSC cardiac spheroids as an innovative cell delivery system to treat cardiovascular diseases.

STATEMENT OF SIGNIFICANCE

Cardiovascular disease is the leading cause of death and disability worldwide. Due to the limited regenerative capacity of adult human hearts, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have received significant attention because they provide a patient specific cell source to regenerate damaged hearts. Despite the progress, current human hiPSC-CMs retain an immature phenotype that leads to difficulties for integration with adult myocardium after transplantation. To address this, we recently utilized electrically conductive silicon nanowires (e-SiNWs) to facilitate self-assembly of hiPSC-CMs to form nanowired hiPSC cardiac spheroids. Our previous results showed addition of e-SiNWs effectively enhanced the functions of the cardiac spheroids and improved the cellular maturation of hiPSC-CMs. In this manuscript, we examined the effects of two important factors on the functions of nanowired hiPSC cardiac spheroids: (1) cell number per spheroid (i.e., size of the spheroids), and (2) the electrical conductivity of the e-SiNWs. The results from these studies will allow for the development of suitable nanowired hiPSC cardiac spheroids to effectively deliver hiPSC-CMs for heart repair.

Priming mobilized peripheral blood mononuclear cells with the "activated platelet supernatant" enhances the efficacy of cell therapy for myocardial infarction of rats

AIM

Various methods are used to augment the efficacy of cell therapy in myocardial infarction (MI). In this study, we used the "activated platelet supernatant (APS)" to prime autologous "granulocyte colony-stimulating factor-mobilized peripheral blood mononuclear cells ((mob) PBMCs)" and investigated the efficacy of cell-based therapy in MI.

METHOD

Rat (mob) PBMCs were isolated after daily subcutaneous injections of G-CSF at 100 μg/kg for 3 days. APS was isolated separately after activating rat platelets with thrombin 0.5 U/mL for 2 hours. Priming was performed with APS for 6 hours. To check the paracrine effect of primed (mob) PBMCs, we used the 36-hour culture supernatant of the primed cells. A rat MI model was used for an in vivo model.

RESULT

Cytokines such as IL-1β, IL-10, and TGFβ were 3.7±0.9-fold, 3.4±1.2-fold, and 1.2±0.1-fold higher in APS, respectively, compared with naïve platelet supernatant. By APS priming, (mob) PBMCs showed M2 polarization and upregulation of angiogenic molecules (i.e., TEK, IL-10, CXCL1, and CX3CR1). APS-primed (mob) PBMCs had a 2.3-fold increased adhesion ability, induced by upregulated integrins. Rat endothelial cells cultured in the 36-hour culture supernatant of APS-primed (mob) PBMCs showed a 1.6-fold augmented proliferation and capillary network formation. In vivo transplantation of APS-primed (mob) PBMCs into rat MI models showed a significant trend of reduction in fibrosis area (P=.001) and wall thinning (P=.030), which lead to improvement in cardiac function measured by echocardiography.

CONCLUSION

Our data reveal that APS priming can enhance the wound-healing potential of (mob) PBMCs. APS priming may be a promising method for cell-based therapy of MI.

Exosome-like silica nanoparticles: a novel ultrasound contrast agent for stem cell imaging

Ultrasound is critical in many areas of medicine including obstetrics, oncology, and cardiology with emerging applications in regenerative medicine. However, one critical limitation of ultrasound is the low contrast of target tissue over background. Here, we describe a novel cup-shaped silica nanoparticle that is reminiscent of exosomes and that has significant ultrasound impedance mismatch for labelling stem cells for regenerative medicine imaging. These exosome-like silica nanoparticles (ELS) were created through emulsion templating and the silica precursors bis(triethoxysilyl)ethane (BTSE) and bis(3-trimethoxysilyl-propyl)amine (TSPA). We found that 40% TSPA resulted in the exosome like-morphology and a positive charge suitable for labelling mesenchymal stem cells. We then compared this novel structure to other silica structures used in ultrasound including Stober silica nanoparticles (SSN), MCM-41 mesoporous silica nanoparticles (MSN), and mesocellular foam silica nanoparticles (MCF) and found that the ELS offered enhanced stem cell signal due to its positive charge to facilitate cell uptake as well as inherently increased echogenicity. The in vivo detection limits were <500 cells with no detectable toxicity at the concentrations used for labelling. This novel structure may eventually find utility in applications beyond imaging requiring an exosome-like shape including drug delivery.

An in vitro investigation to assess procedure parameters for injecting therapeutic hydrogels into the myocardium

Localized delivery of stem cells is potentially a promising therapeutic strategy for regenerating damaged myocardium. Many studies focus on limiting the biologic component of cell loss, but few address the contribution of mechanical factors. This study investigates optimal parameters for retaining the largest volume of cell loaded hydrogels post intramyocardial injection, without compromising cell viability. In vitro, hydrogel was injected into porcine hearts using various needle designs. Hydrogel retention and distribution pattern was then determined. The two most promising needles were then investigated to understand the effect of needle geometry on stem cell viability. The needle to best impact cell viability was then used to investigate the effect of differing hydrogels on retention and distribution. Three-dimensional experimental modeling revealed needles with smaller diameter's to have greater poloxamer 407 hydrogel retention. No difference in retention existed among various needle designs of similar gauge, despite differences in bolus geometries. When hMSC's, embedded in fibrin hydrogel, were injected through helical and 26G bevel needles no difference in the percent of live cells was seen at 48 h. However, the helical group had almost half the metabolic activity of the 26G bevel group at both time points, and had a significant decline in the percent of live cells from 24 to 48 h. Varying gel type resulted in significantly more alginate being retained in the tissue in comparison to fibrin or poloxamer hydrogels. In conclusion, mechanical properties of injected hydrogels, and the diameter of the needle used, highly influences the volume of hydrogel retained. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2618-2629, 2017.

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.

Antifibrotic therapies to control cardiac fibrosis

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

Position Paper of the European Society of Cardiology Working Group Cellular Biology of the Heart: cell-based therapies for myocardial repair and regeneration in ischemic heart disease and heart failure

Despite improvements in modern cardiovascular therapy, the morbidity and mortality of ischaemic heart disease (IHD) and heart failure (HF) remain significant in Europe and worldwide. Patients with IHD may benefit from therapies that would accelerate natural processes of postnatal collateral vessel formation and/or muscle regeneration. Here, we discuss the use of cells in the context of heart repair, and the most relevant results and current limitations from clinical trials using cell-based therapies to treat IHD and HF. We identify and discuss promising potential new therapeutic strategies that include ex vivo cell-mediated gene therapy, the use of biomaterials and cell-free therapies aimed at increasing the success rates of therapy for IHD and HF. The overall aim of this Position Paper of the ESC Working Group Cellular Biology of the Heart is to provide recommendations on how to improve the therapeutic application of cell-based therapies for cardiac regeneration and repair.

Stem cell death and survival in heart regeneration and repair

Cardiovascular diseases are major causes of mortality and morbidity. Cardiomyocyte apoptosis disrupts cardiac function and leads to cardiac decompensation and terminal heart failure. Delineating the regulatory signaling pathways that orchestrate cell survival in the heart has significant therapeutic implications. Cardiac tissue has limited capacity to regenerate and repair. Stem cell therapy is a successful approach for repairing and regenerating ischemic cardiac tissue; however, transplanted cells display very high death percentage, a problem that affects success of tissue regeneration. Stem cells display multipotency or pluripotency and undergo self-renewal, however these events are negatively influenced by upregulation of cell death machinery that induces the significant decrease in survival and differentiation signals upon cardiovascular injury. While efforts to identify cell types and molecular pathways that promote cardiac tissue regeneration have been productive, studies that focus on blocking the extensive cell death after transplantation are limited. The control of cell death includes multiple networks rather than one crucial pathway, which underlies the challenge of identifying the interaction between various cellular and biochemical components. This review is aimed at exploiting the molecular mechanisms by which stem cells resist death signals to develop into mature and healthy cardiac cells. Specifically, we focus on a number of factors that control death and survival of stem cells upon transplantation and ultimately affect cardiac regeneration. We also discuss potential survival enhancing strategies and how they could be meaningful in the design of targeted therapies that improve cardiac function.

Biochip-based study of unidirectional mitochondrial transfer from stem cells to myocytes via tunneling nanotubes

Tunneling nanotubes (TNTs) are small membranous tubes of 50-1000 nm diameter observed to connect cells in culture. Transfer of subcellular organelles through TNTs was observed in vitro and in vivo, but the formation and significance of these structures is not well understood. A polydimethylsiloxane biochip-based coculture model was devised to constrain TNT orientation and explore both TNT-formation and TNT-mediated mitochondrial transfer. Two parallel microfluidic channels connected by an array of smaller microchannels enabled localization of stem cell and cardiomyocyte populations while allowing connections to form between them. Stem cells and cardiomyocytes were deposited in their respective microfluidic channels, and stem cell-cardiomyocyte pairs were formed via the microchannels. Formation of TNTs and transfer of stained mitochondria through TNTs was observed by 24 h real-time video recording. The data show that stem cells are 7.7 times more likely to initiate contact by initial extension of filopodia. By 24 h, 67% of nanotube connections through the microchannels are composed of cardiomyocyte membrane. Filopodial extension and retraction by stem cells draws an extension of TNTs from cardiomyocytes. MitoTracker staining shows that unidirectional transfer of mitochondria between stem cell-cardiomyocyte pairs invariably originates from stem cells. Control experiments with cardiac fibroblasts and cardiomyocytes show little nanotube formation between homotypic or mixed cell pairs and no mitochondrial transfer. These data identify a novel biological process, unidirectional mitochondrial transfer, mediated by heterotypic TNT connections. This suggests that the enhancement of cardiomyocyte function seen after stem-cell injection may be due to a bioenergetic stimulus provided by mitochondrial transfer.

A prosurvival and proangiogenic stem cell delivery system to promote ischemic limb regeneration

Stem cell therapy is one of the most promising strategies to restore blood perfusion and promote muscle regeneration in ischemic limbs. Yet its therapeutic efficacy remains low owing to the inferior cell survival under the low oxygen and nutrient environment of the injured limbs. To increase therapeutic efficacy, high rates of both short- and long-term cell survival are essential, which current approaches do not support. In this work, we hypothesized that a high rate of short-term cell survival can be achieved by introducing a prosurvival environment into the stem cell delivery system to enhance cell survival before vascularization is established; and that a high rate of long-term cell survival can be attained by building a proangiogenic environment in the system to quickly vascularize the limbs. The system was based on a biodegradable and thermosensitive poly(N-Isopropylacrylamide)-based hydrogel, a prosurvival and proangiogenic growth factor bFGF, and bone marrow-derived mesenchymal stem cells (MSCs). bFGF can be continuously released from the system for 4weeks. The released bFGF significantly improved MSC survival and paracrine effects under low nutrient and oxygen conditions (0% FBS and 1% O2) in vitro. The prosurvival effect of the bFGF on MSCs was resulted from activating cell Kruppel-like factor 4 (KLF4) pathway. When transplanted into the ischemic limbs, the system dramatically improved MSC survival. Some of the engrafted cells were differentiated into skeletal muscle and endothelial cells, respectively. The system also promoted the proliferation of host cells. After only 2weeks of implantation, tissue blood perfusion was completely recovered; and after 4weeks, the muscle fiber diameter was restored similarly to that of the normal limbs. These pronounced results demonstrate that the developed stem cell delivery system has a potential for ischemic limb regeneration.

STATEMENT OF SIGNIFICANCE

Stem cell therapy is a promising strategy to restore blood perfusion and promote muscle regeneration in ischemic limbs. Yet its therapeutic efficacy remains low owing to the inferior cell survival under the ischemic environment of the injured limbs. To increase therapeutic efficacy, high rate of cell survival is essential, which current approaches do not support. In this work, we tested the hypothesis that a stem cell delivery system that can continuously release a prosurvival and proangiogenic growth factor will promote high rates of cell survival in the ischemic limbs. The prosurvival effect could augment cell survival before vascularization is established, while the proangiogenic effect could stimulate quick angiogenesis to achieve long-term cell survival. Meanwhile, the differentiation of stem cells into endothelial and myogenic lineages, and cell paracrine effects will enhance vascularization and muscle regeneration.