Stem cell-mediated neovascularization in heart repair

Recent advances in mesenchymal stem cell therapy for myocardial infarction

Myocardial infarction refers to the ischemic necrosis of myocardium, characterized by a sharp reduction or interruption of blood flow in the coronary arteries due to the coronary artery occlusion, resulting in severe and prolonged ischemia in the corresponding myocardium and ultimately leading to ischemic necrosis of the myocardium. Given its high risk, it is considered as one of the most serious health threats today. In current clinical practice, multiple approaches have been explored to diminish myocardial oxygen consumption and alleviate symptoms, but notable success remains elusive. Accumulated clinical evidence has showed that the implantation of mesenchymal stem cell for treating myocardial infarction is both effective and safe. Nevertheless, there persists controversy and variability regarding the standardizing MSC transplantation protocols, optimizing dosage, and determining the most effective routes of administration. Addressing these remaining issues will pave the way of integration of MSCs as a feasible mainstream cardiac treatment.

Enhancement strategy for effective vascular regeneration following myocardial infarction through a dual stem cell approach

Since an impaired coronary blood supply following myocardial infarction (MI) negatively affects heart function, therapeutic neovascularization is considered one of the major therapeutic strategies for cell-based cardiac repair. Here, to more effectively achieve therapeutic neovascularization in ischemic hearts, we developed a dual stem cell approach for effective vascular regeneration by utilizing two distinct types of stem cells, CD31⁺-endothelial cells derived from human induced pluripotent stem cells (hiPSC-ECs) and engineered human mesenchymal stem cells that continuously secrete stromal derived factor-1α (SDF-eMSCs), to simultaneously promote natal vasculogenesis and angiogenesis, two core mechanisms of neovascularization. To induce more comprehensive vascular regeneration, we intramyocardially injected hiPSC-ECs to produce de novo vessels, possibly via vasculogenesis, and a 3D cardiac patch encapsulating SDF-eMSCs (SDF-eMSC-PA) to enhance angiogenesis through prolonged secretion of paracrine factors, including SDF-1α, was implanted into the epicardium of ischemic hearts. We verified that hiPSC-ECs directly contribute to de novo vessel formation in ischemic hearts, resulting in enhanced cardiac function. In addition, the concomitant implantation of SDF1α-eMSC-PAs substantially improved the survival, retention, and vasculogenic potential of hiPSC-ECs, ultimately achieving more comprehensive neovascularization in the MI hearts. Of note, the newly formed vessels through the dual stem cell approach were significantly larger and more functional than those formed by hiPSC-ECs alone. In conclusion, these results provide compelling evidence that our strategy for effective vascular regeneration can be an effective means to treat ischemic heart disease.

A treatment involving two different types of stem cells leads to repairing failed hearts by making new functional blood vessels. Researchers at the City University of Hong Kong and the Catholic University of Korea induced heart attacks in rats before injecting the hearts with endothelial cells derived from human induced pluripotent stem cells, specialized to form blood vessels. These cells successfully induced the formation of new blood vessels in the damaged hearts. The researchers combined this treatment with a cardiac patch containing engineered human adult stem cells, which improved the survival and performance of the endothelial cells. And this dual stem cell treatment resulted in enhanced cardiac function and a higher number of larger and stronger new blood vessels than those produced by the single-cell treatment suggesting an effective way to repair failed hearts.

Considerations in the Development of Small-Diameter Vascular Graft as an Alternative for Bypass and Reconstructive Surgeries: A Review

BACKGROUND

Current design strategies for small diameter vascular grafts (< 6 mm internal diameter; ID) are focused on mimicking native vascular tissue because the commercially available grafts still fail at small diameters, notably due to development of intimal hyperplasia and thrombosis. To overcome these challenges, various design approaches, material selection, and surface modification strategies have been employed to improve the patency of small-diameter grafts.

REVIEW

The purpose of this review is to outline various considerations in the development of small-diameter vascular grafts, including material choice, surface modifications to enhance biocompatibility/endothelialization, and mechanical properties of the graft, that are currently being implanted. Additionally, we have taken into account the general vascular physiology, tissue engineering approaches, and collective achievements of the authors in this area. We reviewed both commercially available synthetic grafts (e-PTFE and PET), elastic polymers such as polyurethane and biodegradable and bioresorbable materials. We included naturally occurring materials by focusing on their potential application in the development of future vascular alternatives.

CONCLUSION

Until now, there are few comprehensive reviews regarding considerations in the design of small-diameter vascular grafts in the literature. Here-in, we have discussed in-depth the various strategies employed to generate engineered vascular graft due to their high demand for vascular surgeries. While some TEVG design strategies have shown greater potential in contrast to autologous or synthetic ePTFE conduits, many are still hindered by high production cost which prevents their widespread adoption. Nonetheless, as tissue engineers continue to develop on their strategies and procedures for improved TEVGs, soon, a reliable engineered graft will be available in the market. Hence, we anticipate a viable TEVG with resorbable property, fabricated via electrospinning approach to hold a greater potential that can overcome the challenges observed in both autologous and allogenic grafts. This is because they can be mechanically tuned, incorporated/surface-functionalized with bioactive molecules and mass-manufactured in a reproducible manner. It is also found that most of the success in engineered vascular graft approaching commercialization is for large vessels rather than small-diameter grafts used as cardiovascular bypass grafts. Consequently, the field of vascular engineering is still available for future innovators that can take up the challenge to create a functional arterial substitute.

Merging 3D printing with electrospun biodegradable small-caliber vascular grafts immobilized with VEGF

The major challenge of commercially available vascular substitutes comes from their limitations in terms of hydrophobic surface, which is hostile to cell growth. To date, tissue-engineered and synthetic grafts have not translated well to clinical trials when looking at small diameters. We conceptualized a cell-free structurally reinforced biodegradable vascular graft recapitulating the anisotropic feature of a native blood vessel. The nanofibrous scaffold is designed in such a way that it will gradually degrade systematically to yield a neo-vessel, facilitated by an immobilized bioactive molecule-vascular endothelial growth factor (VEGF). The nano-topographic cue of the device is capable of direct host cell infiltration. We evaluated the burst pressure, histology, hemocompatibility, compression test, and mechanical analysis of the new graft. The graft implanted into the carotid artery of a porcine model demonstrated a good patency rate as early as two week post-implantation. This graft reinforced design approach when employed in vascular tissue engineering might strongly influencing regenerative medicine.

Therapeutic potential of menstrual blood-derived endometrial stem cells in cardiac diseases

Despite significant developments in medical and surgical strategies, cardiac diseases remain the leading causes of morbidity and mortality worldwide. Numerous studies involving preclinical and clinical trials have confirmed that stem cell transplantation can help improve cardiac function and regenerate damaged cardiac tissue, and stem cells isolated from bone marrow, heart tissue, adipose tissue and umbilical cord are the primary candidates for transplantation. During the past decade, menstrual blood-derived endometrial stem cells (MenSCs) have gradually become a promising alternative for stem cell-based therapy due to their comprehensive advantages, which include their ability to be periodically and non-invasively collected, their abundant source material, their ability to be regularly donated, their superior proliferative capacity and their ability to be used for autologous transplantation. MenSCs have shown positive therapeutic potential for the treatment of various diseases. Therefore, aside from a brief introduction of the biological characteristics of MenSCs, this review focuses on the progress being made in evaluating the functional improvement of damaged cardiac tissue after MenSC transplantation through preclinical and clinical studies. Based on published reports, we conclude that the paracrine effect, transdifferentiation and immunomodulation by MenSC promote both regeneration of damaged myocardium and improvement of cardiac function.

Engineering Stem Cells for Biomedical Applications

Stem cells are characterized by a number of useful properties, including their ability to migrate, differentiate, and secrete a variety of therapeutic molecules such as immunomodulatory factors. As such, numerous pre-clinical and clinical studies have utilized stem cell-based therapies and demonstrated their tremendous potential for the treatment of various human diseases and disorders. Recently, efforts have focused on engineering stem cells in order to further enhance their innate abilities as well as to confer them with new functionalities, which can then be used in various biomedical applications. These engineered stem cells can take on a number of forms. For instance, engineered stem cells encompass the genetic modification of stem cells as well as the use of stem cells for gene delivery, nanoparticle loading and delivery, and even small molecule drug delivery. The present Review gives an in-depth account of the current status of engineered stem cells, including potential cell sources, the most common methods used to engineer stem cells, and the utilization of engineered stem cells in various biomedical applications, with a particular focus on tissue regeneration, the treatment of immunodeficiency diseases, and cancer.

Surface modification and endothelialization of biomaterials as potential scaffolds for vascular tissue engineering applications

This review highlights the recent developments of surface modification and endothelialization of biomaterials in vascular tissue engineering applications.

Cell-based therapy for therapeutic lymphangiogenesis

Lymphedema is a medically irreversible condition for which currently conservative and surgical therapies are either ineffective or impractical. The potential use of progenitor and stem cell-based therapies has offered a paradigm that may provide alternative treatment options for lymphatic disorders. Moreover, basic research, preclinical studies, as well as clinical trials have evaluated the therapeutic potential of various cell therapies in the field of lymphatic regeneration medicine. Among the available cell approaches, mesenchymal stem cells (MSCs) seem to be the most promising candidate mainly due to their abundant sources and easy availability as well as evitable ethical and immunological issues confronted with embryonic stem cells and induced pluripotent stem cells. In this context, the purpose of this review is to summarize various cell-based therapies for lymphedema, along with strengths and weaknesses of these therapies in the clinical application for lymphedema treatment. Particularly, we will highlight the use of MSCs for lymphatic regeneration medicine. In addition, the future perspectives of MSCs in the field of lymphatic regeneration will be discussed.

Improved transfection in human mesenchymal stem cells: effective intracellular release of pDNA by magnetic polyplexes

AIM

Magnetically guided transfection has been shown as a promising approach for the genetic modification of cells. We observed that polyethylenimine (PEI)-condensed pDNA, combined with magnetic nanoparticles (MNPs) via biotin-streptavidin interactions could provide higher transfection efficiency than pDNA/PEI alone, even without the application of a magnetic force. Therefore, we intended to investigate the beneficial properties of MNP-based transfection.

MATERIALS & METHODS

We performed three-color fluorescent labeling of magnetic transfection complexes and traced them inside human mesenchymal stem cells over time using confocal microscopy in order to study pDNA release kinetics by colocalization studies.

RESULTS

We demonstrated that MNP-combined pDNA/PEI complexes provide more rapid and efficient release of pDNA than pDNA/PEI alone, which could be explained by the retention of PEI on the surface of the MNPs due to strong biotin-streptavidin interactions.

CONCLUSION

The process of pDNA liberation may significantly influence the efficiency of the transfection vector. Therefore, it should be carefully considered when creating novel gene delivery agents.

Innovative strategy for microRNA delivery in human mesenchymal stem cells via magnetic nanoparticles

Bone marrow derived human mesenchymal stem cells (hMSCs) show promising potential in regeneration of defective tissue. Recently, gene silencing strategies using microRNAs (miR) emerged with the aim to expand the therapeutic potential of hMSCs. However, researchers are still searching for effective miR delivery methods for clinical applications. Therefore, we aimed to develop a technique to efficiently deliver miR into hMSCs with the help of a magnetic non-viral vector based on cationic polymer polyethylenimine (PEI) bound to iron oxide magnetic nanoparticles (MNP). We tested different magnetic complex compositions and determined uptake efficiency and cytotoxicity by flow cytometry. Additionally, we monitored the release, processing and functionality of delivered miR-335 with confocal laser scanning microscopy, real-time PCR and live cell imaging, respectively. On this basis, we established parameters for construction of magnetic non-viral vectors with optimized uptake efficiency (~75%) and moderate cytotoxicity in hMSCs. Furthermore, we observed a better transfection performance of magnetic complexes compared to PEI complexes 72 h after transfection. We conclude that MNP-mediated transfection provides a long term effect beneficial for successful genetic modification of stem cells. Hence, our findings may become of great importance for future in vivo applications.

Adipose tissue-derived stem cells embedded with eNOS restore cardiac function in acute myocardial infarction model

This study assessed the potential therapeutic efficacy of endothelial NO syntheses (eNOS)-expressing adipose tissue-derived stem cells (ADSCs) on infarcted hearts. We isolated CD29+, CD44+, CD45- cells from adipose tissue. Multipotent property of ADSCs was characterized by induction to differentiate into myogenic, neurogenic, and endothelic lineages. We hypothesized that combination of eNOS over-expression and transplantation of ADSCs could restore NO bioavailability and improve cardiac function in infarcted hearts. Here with several lines of experimental evidences, we demonstrated that ADSCs with eNOS overexpression induced eNOS expression in host endothelial cells and vascular smooth muscle cells, both in vitro and in vivo. This effect was possibly mediated by calcium signal. Transplantation of ADSCs with eNOS embedded showed great therapeutic efficacy in reduction of infarcted size, compared with normal ADSC. Results of this study suggest that ADSCs could be an attractive vehicle for the exogenous eNOS expression into heart after infarction, which is beneficial to restoration of cardiac function. Paracrine effect by mobilizing the host endothelial cells and smooth muscle cells may be the mechanism underlying the therapeutic effect.

Ischemic preconditioning promotes intrinsic vascularization and enhances survival of implanted cells in an in vivo tissue engineering model

Ischemic preconditioning (IPC) is a potent and effective means of protecting cells against ischemic injury. The protection has been demonstrated to involve release of paracrine factors that promote cell survival and angiogenesis, factors important for successful tissue engineering. The aim of the present study was to determine whether IPC of a vascular bed in vivo is an effective strategy to prepare it for tissue engineering with implanted cells. To test this hypothesis, an in vivo vascularized tissue engineering approach was employed, whereby polyacrylic chambers were placed around the femoral vessels of adult Sprague-Dawley rats. IPC was induced by 3 cycles of 5 min femoral artery occlusion interspersed with 5-min periods of reperfusion. Rats subjected to IPC generated bigger tissue constructs at 7 and 28 days postimplantation of empty chambers (∼50% increase in weight and volume, p<0.05). Morphometric counting of Masson trichrome stained tissue sections revealed significantly greater tissue construct volumes in ischemic preconditioned vascular beds at 7 and 28 days, increasing both fibrin matrix and vascularized tissue. Furthermore, morphometry of lectin-labeled blood vessels indicated an increase in vascular volume in IPC tissue constructs (∼100% increase vs. control, p<0.05). To investigate the cytoprotective effect of IPC, we implanted DiI-labeled neonatal rat cardiomyocytes in the chambers for 3 days, and IPC significantly reduced apoptosis of implanted cells as determined by the TUNEL assay and cleaved caspase-3 immunostaining. Furthermore, IPC significantly increased the cardiac muscle volume and vascular volume at 28 days after implantation of cardiomyocytes. In conclusion, in vivo IPC promotes survival of implanted cardiomyocytes and is associated with enhanced angiogenesis. IPC may represent a new approach to optimize tissue engineering with implanted cells.

Magnetic targeting strategies in gene delivery

Gene delivery is a process of the insertion of transgenes into cells with the purpose to obtain the expression of encoded protein. The therapeutic application of this process is termed gene therapy, which is becoming a promising instrument to treat genetic and acquired diseases. Although numerous methods of gene transfer have already been developed, including biological, physical and chemical approaches, the optimal strategy has to be discovered. Importantly, it should be effective, selective and safe to be translated to the clinic. Magnetic targeting has been demonstrated as an effective strategy to decrease side effects of gene transfer, while increasing the selectivity and efficiency of the applied vector. This article will focus on the latest progress in the development of different magnetic vectors, based on both viral and nonviral gene delivery agents. It will also include a description of magnetic targeting applications in stem cells and in vivo, which has gained interest in recent years due to the rapid development of technology.

Patterning human stem cells and endothelial cells with laser printing for cardiac regeneration

Recent study showed that mesenchymal stem cells (MSC) could inhibit apoptosis of endothelial cells in hypoxic condition, increase their survival, and stimulate the angiogenesis process. In this project we applied Laser-Induced-Forward-Transfer (LIFT) cell printing technique and prepared a cardiac patch seeded with human umbilical vein endothelial cells (HUVEC) and human MSC (hMSC) in a defined pattern for cardiac regeneration. We seeded HUVEC and hMSC in a defined pattern on a Polyester urethane urea (PEUU) cardiac patch. On control patches an equal amount of cells was randomly seeded without LIFT. Patches were cultivated in vitro or transplanted in vivo to the infarcted zone of rat hearts after LAD-ligation. Cardiac performance was measured by left ventricular catheterization 8 weeks post infarction. Thereafter hearts were perfused with fluorescein tomato lectin for the assessment of functional blood vessels and stored for histology analyses. We demonstrated that LIFT-derived cell seeding pattern definitely modified growth characteristics of co-cultured HUVEC and hMSC leading to increased vessel formation and found significant functional improvement of infarcted hearts following transplantation of a LIFT-tissue engineered cardiac patch. Further, we could show enhanced capillary density and integration of human cells into the functionally connected vessels of murine vascular system. LIFT-based Tissue Engineering of cardiac patches for the treatment of myocardial infarction might improve wound healing and functional preservation.

A new strategy of promoting vascularization of skin substitutes by capturing endothelial progenitor cells automatically

How to promote vascularization of a skin substitute is the key to successful skin transplantation. Current methods are mainly through releasing angiogenesis-related factors (ARF) or seeding angiogenesis-related cells (ARC), but the efficacy of these methods is not satisfactory, because angiogenesis needs participation of multiple factors, extracellular matrix and related cells. The latest research has demonstrated that endothelial progenitor cells (EPCs) originating from bone marrow and existing in peripheral blood are the key element participating in revascularization of adult tissues. They directly participate in both stem cell vasculogenesis of ischemic tissues and local angiogenesis. We therefore hypothesize whether it is possible to construct a new skin substitute and use it to mobilize EPCs in bone marrow to peripheral circulation and capture EPCs automatically as a simple and effective method of promoting vascularization of the skin substitute for the sake of improving its post-transplant survival.

Cell origin of human mesenchymal stem cells determines a different healing performance in cardiac regeneration

The possible different therapeutic efficacy of human mesenchymal stem cells (hMSC) derived from umbilical cord blood (CB), adipose tissue (AT) or bone marrow (BM) for the treatment of myocardial infarction (MI) remains unexplored. This study was to assess the regenerative potential of hMSC from different origins and to evaluate the role of CD105 in cardiac regeneration. Male SCID mice underwent LAD-ligation and received the respective cell type (400.000/per animal) intramyocardially. Six weeks post infarction, cardiac catheterization showed significant preservation of left ventricular functions in BM and CD105(+)-CB treated groups compared to CB and nontreated MI group (MI-C). Cell survival analyzed by quantitative real time PCR for human GAPDH and capillary density measured by immunostaining showed consistent results. Furthermore, cardiac remodeling can be significantly attenuated by BM-hMSC compared to MI-C. Under hypoxic conditions in vitro, remarkably increased extracellular acidification and apoptosis has been detected from CB-hMSC compared to BM and CD105 purified CB-derived hMSC. Our findings suggests that hMSC originating from different sources showed a different healing performance in cardiac regeneration and CD105(+) hMSC exhibited a favorable survival pattern in infarcted hearts, which translates into a more robust preservation of cardiac function.

Animal models of cardiac disease and stem cell therapy

Animal models that mimic cardiovascular diseases are indispensable tools for understanding the mechanisms underlying the diseases at the cellular and molecular level. This review focuses on various methods in preclinical research to create small animal models of cardiac diseases, such as myocardial infarction, dilated cardiomyopathy, heart failure, myocarditis and cardiac hypertrophy, and the related stem cell treatment for these diseases.

Construction of ureteral grafts by seeding urothelial cells and bone marrow mesenchymal stem cells into polycaprolactone-lecithin electrospun fibers

The aim of the present study was to investigated the construction of polycaprolactone-lecithin (PCL-L) electrospun fibers as a novel scaffold material for a tissue-engineered ureter. The effect of bone marrow mesenchymal stem cells (BM-MSCs) on the neovascularization of the scaffolds and the viability of planted urothelial cells (UCs) on PCL-L were also studied. UCs were obtained from New Zealand rabbit bladders, cultured and then seeded onto the lumen of the tubular scaffolds before being subcutaneously transplanted into the space of nude mice. The cultured UCs showed vacuolar degeneration after 7 days of transplantation and they gradually degraded thereafter. To facilitate the regeneration of the tissue-engineered ureter and the survival of UCs in the implant, MSCs were seeded into the tubular grafts by rolling up the nanofibrous membrane, followed by the seeding of UCs. This facilitated the survival of the UCs, which formed several cellular layers after 30 days. The mean microvessel density was significantly increased in tissues seeded with MSCs. Cell-tracking experiments revealed that the transplanted MSCs did not integrate directly into capillaries for angiogenesis. Our results demonstrated that the PCL-L electrospun fibrous scaffold has a high potential for a tissue-engineered ureter especially when seeded with BM-MSCs, which enhanced angiogenesis.

Lin- cells mediate tissue repair by regulating MCP-1/CCL-2

Exogenous bone marrow-derived cells (BMDCs) are promising therapeutic agents for the treatment of tissue ischemia and traumatic injury. However, until we identify the molecular mechanisms that underlie their actions, there can be no rational basis for the design of therapeutic strategies using BMDCs. The pro-healing effects of BMDCs are apparent very shortly after treatment, which suggests that they may exert their effects by the modulation of acute inflammation. We investigated this hypothesis by taking advantage of the fact that BMDCs from healthy, young, but not obese, diabetic mice stimulate vascular growth. By comparing both in vitro secretion and in vivo local induction of acute phase inflammatory cytokines by these cells, we identified monocyte chemoattractant factor 1 and tumor necrosis factor α as potential mediators of BMDC-induced tissue repair. In vivo analysis of BMDC-treated ischemic limbs and cutaneous wounds revealed that the production of monocyte chemoattractant factor 1 by exogenous and endogenous BMDCs is essential for BMDC-mediated vascular growth and tissue healing, while the inability of BMDCs to produce tumor necrosis factor α appears to play a lesser but still meaningful role. Thus, measurements of the secretion of cytokines by BMDCs may allow us to identify a priori individuals who would or would not be good candidates for BMDC-based therapies.

Intracardiac injection of matrigel induces stem cell recruitment and improves cardiac functions in a rat myocardial infarction model

Matrigel promotes angiogenesis in the myocardium from ischemic injury and prevents remodelling of the left ventricle. We assessed the therapeutic efficacy of intracardiac matrigel injection and matrigel-mediated stem cell homing in a rat myocardial infarction (MI) model. Following MI, matrigel (250 μl) or phosphate-buffered solution (PBS) was delivered by intracardiac injection. Compared to the MI control group (MI-PBS), matrigel significantly improved left ventricular function (n= 11, P < 0.05) assessed by pressure–volume loops after 4 weeks. There is no significant difference in infarct size between MI-matrigel (MI-M; 21.48 ± 1.49%, n= 10) and MI-PBS hearts (20.98 ± 1.25%, n= 10). The infarct wall thickness of left ventricle is significantly higher (P < 0.01) in MI-M (0.72 ± 0.02 mm, n= 10) compared with MI-PBS (0.62 ± 0.02 mm, n= 10). MI-M hearts exhibited higher capillary density (border 130.8 ± 4.7 versus 115.4 ± 6.0, P < 0.05; vessels per high-power field [HPF; 400×], n= 6) than MI-PBS hearts. c-Kit⁺ stem cells (38.3 ± 5.3 versus 25.7 ± 1.5 c-Kit⁺ cells per HPF [630×], n= 5, P < 0.05) and CD34⁺ cells (13.0 ± 1.51 versus 5.6 ± 0.68 CD34⁺ cells per HPF [630×], n= 5, P < 0.01) were significantly more numerous in MI-M than in MI-PBS in the infarcted hearts (n= 5, P < 0.05). Intracardiac matrigel injection restores myocardial functions following MI, which may attribute to the improved recruitment of CD34⁺ and c-Kit⁺ stem cells.