Attenuation of hind-limb ischemia in mice with endothelial-like cells derived from different sources of human stem cells

Fundamental considerations for designing endothelialized in vitro models of thrombosis

Endothelialized in vitro models for cardiovascular disease have contributed greatly to our current understanding of the complex molecular mechanisms underlying thrombosis. To further elucidate these mechanisms, it is important to consider which fundamental aspects to incorporate into an in vitro model. In this review, we will focus on the design of in vitro endothelialized models of thrombosis. Expanding our understanding of the relation and interplay between the different pathways involved will rely in part on complex models that incorporate endothelial cells, blood, the extracellular matrix, and flow. Importantly, the use of tissue-specific endothelial cells will help in understanding the heterogeneity in thrombotic responses between different vascular beds. The dynamic and complex responses of endothelial cells to different shear rates underlines the importance of incorporating appropriate shear in in vitro models. Alterations in vascular extracellular matrix composition, availability of bioactive molecules, and gradients in concentration and composition of these molecules can all regulate the function of both endothelial cells and perivascular cells. Factors modulating these elements in in vitro models should therefore be considered carefully depending on the research question at hand. As the complexity of in vitro models increases, so can the variability. A bottom-up approach to designing such models will remain an important tool for researchers studying thrombosis. As new techniques are continuously being developed and new pathways are brought to light, research question-dependent considerations will have to be made regarding what aspects of thrombosis to include in in vitro models.

Verification of Therapeutic Effect through Accelerator Mass Spectrometry-Based Single Cell Level Quantification of hESC-Endothelial Cells Distributed into an Ischemic Model

As the potential of pluripotent stem cell-derived differentiated cells has been demonstrated in regenerative medicine, differentiated vascular endothelial cells (ECs) are emerging as a therapeutic agent for the cardiovascular system. To verify the therapeutic efficacy of differentiated ECs in an ischemic model, human embryonic stem cells (hESCs) are induced as EC lineage and produce high-purity ECs through fluorescence-activated cell sorting (FACS). When hESC-ECs are transplanted into a hindlimb ischemic model, it is confirmed that blood flow and muscle regeneration are further improved by creating new blood vessels together with autologous ECs than the primary cell as cord blood endothelial progenitor cells (CB-EPCs). In addition, previously reported studies show the detection of transplanted cells engrafted in blood vessels through various tracking methods, but fail to provide accurate quantitative values over time. In this study, it is demonstrated that hESC-ECs are engrafted approximately sevenfold more than CB-EPCs by using an accelerator mass spectrometry (AMS)-based cell tracking technology that can perform quantification at the single cell level. An accurate quantification index is suggested. It has never been reported in in vivo kinetics of hESC-ECs that can act as therapeutic agents.

Generation and Application of Directly Reprogrammed Endothelial Cells

Cell-based therapy has emerged as a promising option for treating advanced ischemic cardiovascular disease by inducing vascular regeneration. However, clinical trials with adult cells turned out disappointing in general. As a newer approach, direct reprogramming has emerged to efficiently generate endothelial cells (ECs), which can promote neovascularization and vascular regeneration. This review provides recent updates on the direct endothelial reprogramming. In general, directly reprogrammed ECs can be generated by two approaches: one by transitioning through a plastic intermediate state and the other in a one-step transition without any intermediate states toward pluripotency. Moreover, the methods to deliver reprogramming factors and chemicals for the fate conversion are highlighted. Next, the therapeutic effects of the directly reprogrammed ECs on animal models are reviewed in detail. Other applications using directly reprogrammed ECs, such as tissue engineering and disease modeling, are also discussed. Lastly, the remaining questions and foremost challenges are addressed.

Tissue Engineered Neurovascularization Strategies for Craniofacial Tissue Regeneration

Craniofacial tissue injuries, diseases, and defects, including those within bone, dental, and periodontal tissues and salivary glands, impact an estimated 1 billion patients globally. Craniofacial tissue dysfunction significantly reduces quality of life, and successful repair of damaged tissues remains a significant challenge. Blood vessels and nerves are colocalized within craniofacial tissues and act synergistically during tissue regeneration. Therefore, the success of craniofacial regenerative approaches is predicated on successful recruitment, regeneration, or integration of both vascularization and innervation. Tissue engineering strategies have been widely used to encourage vascularization and, more recently, to improve innervation through host tissue recruitment or prevascularization/innervation of engineered tissues. However, current scaffold designs and cell or growth factor delivery approaches often fail to synergistically coordinate both vascularization and innervation to orchestrate successful tissue regeneration. Additionally, tissue engineering approaches are typically investigated separately for vascularization and innervation. Since both tissues act in concert to improve craniofacial tissue regeneration outcomes, a revised approach for development of engineered materials is required. This review aims to provide an overview of neurovascularization in craniofacial tissues and strategies to target either process thus far. Finally, key design principles are described for engineering approaches that will support both vascularization and innervation for successful craniofacial tissue regeneration.

Human Induced Pluripotent Stem Cell-Derived Vascular Cells: Recent Progress and Future Directions

Human induced pluripotent stem cells (hiPSCs) hold great promise for cardiovascular regeneration following ischemic injury. Considerable effort has been made toward the development and optimization of methods to differentiate hiPSCs into vascular cells, such as endothelial and smooth muscle cells (ECs and SMCs). In particular, hiPSC-derived ECs have shown robust potential for promoting neovascularization in animal models of cardiovascular diseases, potentially achieving significant and sustained therapeutic benefits. However, the use of hiPSC-derived SMCs that possess high therapeutic relevance is a relatively new area of investigation, still in the earlier investigational stages. In this review, we first discuss different methodologies to derive vascular cells from hiPSCs with a particular emphasis on the role of key developmental signals. Furthermore, we propose a standardized framework for assessing and defining the EC and SMC identity that might be suitable for inducing tissue repair and regeneration. We then highlight the regenerative effects of hiPSC-derived vascular cells on animal models of myocardial infarction and hindlimb ischemia. Finally, we address several obstacles that need to be overcome to fully implement the use of hiPSC-derived vascular cells for clinical application.

Induced endothelial cells from peripheral arterial disease patients and neonatal fibroblasts have comparable angiogenic properties

Induced endothelial cells (iECs) generated from neonatal fibroblasts via transdifferentiation have been shown to have pro-angiogenic properties and are a potential therapy for peripheral arterial disease (PAD). It is unknown if iECs can be generated from fibroblasts collected from PAD patients and whether these cells are pro-angiogenic. In this study fibroblasts were collected from four PAD patients undergoing carotid endarterectomies. These cells, and neonatal fibroblasts, were transdifferentiated into iECs using modified mRNA. Endothelial phenotype and pro-angiogenic cytokine secretion were investigated. NOD-SCID mice underwent surgery to induce hindlimb ischaemia in a murine model of PAD. Mice received intramuscular injections with either control vehicle, or 1 × 106 neonatal-derived or 1 × 106 patient-derived iECs. Recovery in perfusion to the affected limb was measured using laser Doppler scanning. Perfusion recovery was enhanced in mice treated with neonatal-derived iECs and in two of the three patient-derived iEC lines investigated in vivo. Patient-derived iECs can be successfully generated from PAD patients and for specific patients display comparable pro-angiogenic properties to neonatal-derived iECs.

Strategies of Prevascularization in Tissue Engineering and Regeneration of Craniofacial Tissues

Craniofacial tissue defects caused by trauma, developmental malformation, or surgery are critical issues of high incidence, which are harmful to physical and psychological health. Transplantation of engineered tissues or biomaterials is a potential method to repair defects and regenerate the craniofacial tissues. Revascularization is essential to ensure the survival and regeneration of the grafts. Since microvessels play a critical role in blood circulation and substance exchange, the pre-establishment of the microvascular network in transplants provides a technical basis for the successful regeneration of the tissue defect. In this study, we reviewed the recent development of strategies and applications of prevascularization in tissue engineering and regeneration of craniofacial tissues. We focused on the cellular foundation of the in vitro prevascularized microvascular network, the cell source for prevascularization, and the strategies of prevascularization. Several key strategies, including coculture, microspheres, three-dimensional printing and microfluidics, and microscale technology, were summarized and the feasibility of these technologies in the clinical repair of craniofacial defects was discussed.

In vitro and in vivo study on angiogenesis of porcine induced pluripotent stem cell-derived endothelial cells

Pluripotent stem cells (PSCs) are a promising source of endothelial cells (ECs) for the treatment of cardiovascular diseases. Since clinical application of embryo stem cells (ESCs) involves issues of medical ethics and risk of immune rejection, induced pluripotent stem cells (iPSCs) will facilitate cell transplantation therapy for the cardiovascular diseases. Swine is identified as an ideal large-animal model for human, because of its similar organ size and physiological characteristics. However, there are very few studies on EC differentiation of porcine iPSCs (piPSCs). In recent study, we provided an efficient protocol to differentiate piPSCs into ECs with the purity of 19.76% CD31 positive cells within 16 days. Passaging of these cells yielded a nearly pure population, which also expressed other endothelial markers such as CD144, eNOS and vWF. Besides, these cells exhibited functions of ECs such as uptake of low-density lipoprotein and formation of tubes in vitro or blood vessels in vivo. Our study successfully obtained ECs from piPSCs via a feeder- and serum-free monolayer system and demonstrated their angiogenic function in vivo and in vitro. piPSC-ECs derivation is not only potential for the autologous cell transplantation and cardiovascular drug screening, but also for the mechanistic studies on EC differentiation and endothelial dysfunction.

Human-Induced Pluripotent Stem-Cell-Derived Smooth Muscle Cells Increase Angiogenesis to Treat Hindlimb Ischemia

Induced pluripotent stem cells (iPSC) represent an innovative, somatic cell-derived, easily obtained and renewable stem cell source without considerable ethical issues. iPSC and their derived cells may have enhanced therapeutic and translational potential compared with other stem cells. We previously showed that human iPSC-derived smooth muscle cells (hiPSC-SMC) promote angiogenesis and wound healing. Accordingly, we hypothesized that hiPSC-SMC may be a novel treatment for human patients with chronic limb-threatening ischemia who have no standard options for therapy. We determined the angiogenic potential of hiPSC-SMC in a murine hindlimb ischemia model. hiPSC-SMC were injected intramuscularly into nude mice after creation of hindlimb ischemia. Functional outcomes and perfusion were measured using standardized scores, laser Doppler imaging, microCT, histology and immunofluorescence. Functional outcomes and blood flow were improved in hiPSC-SMC-treated mice compared with controls (Tarlov score, p < 0.05; Faber score, p < 0.05; flow, p = 0.054). hiPSC-SMC-treated mice showed fewer gastrocnemius fibers (p < 0.0001), increased fiber area (p < 0.0001), and enhanced capillary density (p < 0.01); microCT showed more arterioles (<96 μm). hiPSC-SMC treatment was associated with fewer numbers of macrophages, decreased numbers of M1-type (p < 0.05) and increased numbers of M2-type macrophages (p < 0.0001). Vascular endothelial growth factor (VEGF) expression in ischemic limbs was significantly elevated with hiPSC-SMC treatment (p < 0.05), and inhibition of VEGFR-2 with SU5416 was associated with fewer capillaries in hiPSC-SMC-treated limbs (p < 0.0001). hiPSC-SMC promote VEGF-mediated angiogenesis, leading to improved hindlimb ischemia. Stem cell therapy using iPSC-derived cells may represent a novel and potentially translatable therapy for limb-threatening ischemia.

Cell Therapy for Critical Limb Ischemia: Advantages, Limitations, and New Perspectives for Treatment of Patients with Critical Diabetic Vasculopathy

PURPOSE OF REVIEW

To provide a highlight of the current state of cell therapy for the treatment of critical limb ischemia in patients with diabetes.

RECENT FINDINGS

The global incidence of diabetes is constantly growing with consequent challenges for healthcare systems worldwide. In the UK only, NHS costs attributed to diabetic complications, such as peripheral vascular disease, amputation, blindness, renal failure, and stroke, average £10 billion each year, with cost pressure being estimated to get worse. Although giant leaps forward have been registered in the scope of early diagnosis and optimal glycaemic control, an effective treatment for critical limb ischemia is still lacking. The present review aims to provide an update of the ongoing work in the field of regenerative medicine. Recent advancements but also limitations imposed by diabetes on the potential of the approach are addressed. In particular, the review focuses on the perturbation of non-coding RNA networks in progenitor cells and the possibility of using emerging knowledge on molecular mechanisms to design refined protocols for personalized therapy. The field of cell therapy showed rapid progress but has limitations. Significant advances are foreseen in the upcoming years thanks to a better understanding of molecular bottlenecks associated with the metabolic disorders.

Hypoxia as a Driving Force of Pluripotent Stem Cell Reprogramming and Differentiation to Endothelial Cells

Inadequate supply of oxygen (O₂) is a hallmark of many diseases, in particular those related to the cardiovascular system. On the other hand, tissue hypoxia is an important factor regulating (normal) embryogenesis and differentiation of stem cells at the early stages of embryonic development. In culture, hypoxic conditions may facilitate the derivation of embryonic stem cells (ESCs) and the generation of induced pluripotent stem cells (iPSCs), which may serve as a valuable tool for disease modeling. Endothelial cells (ECs), multifunctional components of vascular structures, may be obtained from iPSCs and subsequently used in various (hypoxia-related) disease models to investigate vascular dysfunctions. Although iPSC-ECs demonstrated functionality in vitro and in vivo, ongoing studies are conducted to increase the efficiency of differentiation and to establish the most productive protocols for the application of patient-derived cells in clinics. In this review, we highlight recent discoveries on the role of hypoxia in the derivation of ESCs and the generation of iPSCs. We also summarize the existing protocols of hypoxia-driven differentiation of iPSCs toward ECs and discuss their possible applications in disease modeling and treatment of hypoxia-related disorders.

Stem Cell Therapy for Thromboangiitis Obliterans (Buerger’s Disease)

Buerger’s disease or Thromboangiitis Obliterans (TAO) is a nonatherosclerotic segmental vascular disease which affects small and medium arteries and veins in the upper and lower extremities. Based on pathological findings, TAO can be considered as a distinct form of vasculitis that is most prevalent in young male smokers. There is no definitive cure for this disease as therapeutic modalities are limited in number and efficacy. Surgical bypass has limited utility and 24% of patients will ultimately require amputation. Recently, studies have shown that therapeutic angiogenesis and immunomodulatory approaches through the delivery of stem cells to target tissues are potential options for ischemic lesion treatment. In this review, we summarize the current knowledge of TAO treatment and provide an overview of stem cell-based treatment modalities.

A nitric oxide-releasing hydrogel for enhancing the therapeutic effects of mesenchymal stem cell therapy for hindlimb ischemia

Therapeutic angiogenesis with mesenchymal stem cells (MSCs) is promising for the clinical treatment of peripheral artery disease (PAD). However, the heterogeneous proangiogenic nature of MSCs is a key challenge in developing more effective treatments with MSCs for therapeutic angiogenesis purposes. Here, we propose to enhance the therapeutic function of human placenta-derived MSCs (hP-MSCs) in hindlimb ischemia therapy by using nitric oxide (NO)-releasing chitosan hydrogel (CS-NO). Our data showed that the co-transplantation of CS-NO hydrogel with hP-MSCs remarkably improved the grafting of hP-MSCs and ameliorated the functional recovery of ischemic hindlimbs. Moreover, we found that the neovascularization of damaged hindlimbs was significantly increased after co-transplanting CS-NO hydrogel and hP-MSCs, as confirmed by bioluminescence imaging (BLI). Further analysis revealed an endothelial-like status transformation of hP-MSCs in the presence of NO, which was identified as a potential mechanism contributing to the enhanced endothelium-protective and proangiogenic capacities of hP-MSCs that promote angiogenesis in mouse models of hindlimb ischemia. In conclusion, this study provides a promising approach for using NO hydrogel to improve the proangiogenic potency of MSCs in ischemic diseases, and the strategy used here facilitates the development of controlled-release scaffolds for enhancing the therapeutic efficiency of MSCs in angiogenic therapy. STATEMENT OF SIGNIFICANCE: The heterogeneous proangiogenic nature of mesenchymal stem cells (MSCs) is a key challenge in developing more effective treatments with MSCs for therapeutic angiogenesis purposes. In this study, we investigated whether nitric oxide (NO)-releasing chitosan hydrogel (CS-NO) could improve the proangiogenic potency of MSCs in ischemic diseases. Our results revealed an endothelial-like status transformation of human placenta-derived MSCs (hP-MSCs) in the presence of NO, which was identified as a potential mechanism contributing to the enhanced endothelium-protective and proangiogenic capacities of hP-MSCs that promote angiogenesis in mouse models of hindlimb ischemia. The strategy for enhancing the pro-angiogenic activity of MSCs with biomaterials provides a practical idea for overcoming the challenges associated with the clinical application of MSCs in therapeutic angiogenesis.

Electrospun Nanofibers for Improved Angiogenesis: Promises for Tissue Engineering Applications

Angiogenesis (or the development of new blood vessels) is a key event in tissue engineering and regenerative medicine; thus, a number of biomaterials have been developed and combined with stem cells and/or bioactive molecules to produce three-dimensional (3D) pro-angiogenic constructs. Among the various biomaterials, electrospun nanofibrous scaffolds offer great opportunities for pro-angiogenic approaches in tissue repair and regeneration. Nanofibers made of natural and synthetic polymers are often used to incorporate bioactive components (e.g., bioactive glasses (BGs)) and load biomolecules (e.g., vascular endothelial growth factor (VEGF)) that exert pro-angiogenic activity. Furthermore, seeding of specific types of stem cells (e.g., endothelial progenitor cells) onto nanofibrous scaffolds is considered as a valuable alternative for inducing angiogenesis. The effectiveness of these strategies has been extensively examined both in vitro and in vivo and the outcomes have shown promise in the reconstruction of hard and soft tissues (mainly bone and skin, respectively). However, the translational of electrospun scaffolds with pro-angiogenic molecules or cells is only at its beginning, requiring more research to prove their usefulness in the repair and regeneration of other highly-vascularized vital tissues and organs. This review will cover the latest progress in designing and developing pro-angiogenic electrospun nanofibers and evaluate their usefulness in a tissue engineering and regenerative medicine setting.

Targeting Purinergic Signaling and Cell Therapy in Cardiovascular and Neurodegenerative Diseases

Extracellular purines exert several functions in physiological and pathophysiological mechanisms. ATP acts through P2 receptors as a neurotransmitter and neuromodulator and modulates heart contractility, while adenosine participates in neurotransmission, blood pressure, and many other mechanisms. Because of their capability to differentiate into mature cell types, they provide a unique therapeutic strategy for regenerating damaged tissue, such as in cardiovascular and neurodegenerative diseases. Purinergic signaling is pivotal for controlling stem cell differentiation and phenotype determination. Proliferation, differentiation, and apoptosis of stem cells of various origins are regulated by purinergic receptors. In this chapter, we selected neurodegenerative and cardiovascular diseases with clinical trials using cell therapy and purinergic receptor targeting. We discuss these approaches as therapeutic alternatives to neurodegenerative and cardiovascular diseases. For instance, promising results were demonstrated in the utilization of mesenchymal stem cells and bone marrow mononuclear cells in vascular regeneration. Regarding neurodegenerative diseases, in general, P2X7 and A_2A receptors mostly worsen the degenerative state. Stem cell-based therapy, mainly through mesenchymal and hematopoietic stem cells, showed promising results in improving symptoms caused by neurodegeneration. We propose that purinergic receptor activity regulation combined with stem cells could enhance proliferative and differentiation rates as well as cell engraftment.

Shear Stress Promotes Arterial Endothelium-Oriented Differentiation of Mouse-Induced Pluripotent Stem Cells

Establishment of a functional vascular network, which is required in tissue repair and regeneration, needs large-scale production of specific arterial or venous endothelial cells (ECs) from stem cells. Previous in vitro studies by us and others revealed that shear stress induces EC differentiation of bone marrow-derived mesenchymal stem cells and embryonic stem cells. In this study, we focused on the impact of different magnitudes of shear stress on the differentiation of mouse-induced pluripotent stem cells (iPSCs) towards arterial or venous ECs. When iPSCs were exposed to shear stress (5, 10, and 15 dyne/cm²) with 50 ng/mL vascular endothelial growth factor and 10 ng/mL fibroblast growth factor, the expression levels of the general EC markers and the arterial markers increased, and the stress amplitude of 10 dyne/cm² could be regarded as a proper promoter, whereas the venous and lymphatic markers had little or no expression. Further, shear stress caused cells to align parallel to the direction of the flow, induced cells forming functional tubes, and increased the secretion of nitric oxide. In addition, Notch1 was significantly upregulated, and the Notch ligand Delta-like 4 was activated in response to shear stress, while inhibition of Notch signaling by DAPT remarkably abolished the shear stress-induced arterial epithelium differentiation. Taken together, our results indicate that exposure to appropriate shear stress facilitated the differentiation of mouse iPSCs towards arterial ECs via Notch signaling pathways, which have potential applications for both disease modeling and regenerative medicine.

Secretome of Mesenchymal Stem Cells and Its Potential Protective Effects on Brain Pathologies

Previous studies have indicated that mesenchymal stem cells (MSCs) have a fundamental role in the repair and regeneration of damaged tissues. There is strong evidence showing that much of the beneficial effects of these cells are due to the secretion of bioactive molecules-besides microRNAs, hormones, and neurotrophins-with anti-inflammatory, immunoregulatory, angiogenic, and trophic effects. These factors have been reported by many studies to possess protective effects on the nervous tissue. Although the beneficial effects of the secretory factors of MSCs have been suggested for various neurological diseases, their actions on astrocytic cells are not well understood. Hence, it is important to recognize the specific effects of MSCs derived from adipose tissue, in addition to the differences presented by the secretome, depending on the source and methods of analysis. In this paper, the different sources of MSCs and their main characteristics are described, as well as the most significant advances in regeneration and protection provided by the secretome of MSCs. Also, we discuss the possible neuroprotective mechanisms of action of the MSC-derived biomolecules, with special emphasis on the effect of MSCs derived from adipose tissue and their impact on glial cells and brain pathologies.

The potential and limitations of induced pluripotent stem cells to achieve wound healing

Wound healing is the physiologic response to a disruption in normal skin architecture and requires both spatial and temporal coordination of multiple cell types and cytokines. This complex process is prone to dysregulation secondary to local and systemic factors such as ischemia and diabetes that frequently lead to chronic wounds. Chronic wounds such as diabetic foot ulcers are epidemic with great cost to the healthcare system as they heal poorly and recur frequently, creating an urgent need for new and advanced therapies. Stem cell therapy is emerging as a potential treatment for chronic wounds, and adult-derived stem cells are currently employed in several commercially available products; however, stem cell therapy is limited by the need for invasive harvesting techniques, immunogenicity, and limited cell survival in vivo. Induced pluripotent stem cells (iPSC) are an exciting cell type with enhanced therapeutic and translational potential. iPSC are derived from adult cells by in vitro induction of pluripotency, obviating the ethical dilemmas surrounding the use of embryonic stem cells; they are harvested non-invasively and can be transplanted autologously, reducing immune rejection; and iPSC are the only cell type capable of being differentiated into all of the cell types in healthy skin. This review focuses on the use of iPSC in animal models of wound healing including limb ischemia, as well as their limitations and methods aimed at improving iPSC safety profile in an effort to hasten translation to human studies.

Stem/Progenitor Cells and Their Therapeutic Application in Cardiovascular Disease

Cardiovascular disease is the leading cause of death in the world. The stem/progenitor cell-based therapy has emerged as a promising approach for the treatment of a variety of cardiovascular diseases including myocardial infarction, stroke, peripheral arterial disease, and diabetes. An increasing number of evidence has shown that stem/progenitor cell transplantation could replenish damaged cells, improve cardiac and vascular functions, and repair injured tissues in many pre-clinical studies and clinical trials. In this review, we have outlined the major types of stem/progenitor cells, and summarized the studies in applying these cells, especially endothelial stem/progenitor cells and their derivatives, in the treatment of cardiovascular disease. Here the strategies used to improve the stem/progenitor cell-based therapies in cardiovascular disease and the challenges with these therapies in clinical applications are also reviewed.

Efficient Differentiation of Human Pluripotent Stem Cells to Endothelial Cells

Endothelial cells (ECs) line the interior surface of blood and lymphatic vessels, and play a key role in a variety of physiological or pathological processes such as thrombosis, inflammation, or vascular wall remodeling. Human-induced pluripotent stem cell (iPSCs)-derived ECs provide a new opportunity for vascular regeneration and serve as a model to study the mechanism and to screen for novel therapies. We use developmental cues in a monolayer differentiation approach to efficiently generate mesoderm cells from iPSCs via small-molecule activation of WNT signaling in chemically defined medium for 4 days, and subsequent EC specification using vascular endothelial growth factor and fibroblast growth factor for another 4 days. After 8 days of differentiation, mature ECs are further purified using magnetic-activated cell sorting for the EC surface marker CD144. These ECs exhibit molecular and cellular characteristics consistent with native ECs, such as expression of specific surface markers, formation of tube-like structures and acetylated low-density lipoprotein uptake. © 2018 by John Wiley & Sons, Inc.

Engineered Microvasculature in PDMS Networks Using Endothelial Cells Derived from Human Induced Pluripotent Stem Cells

In this study, we used a polydimethylsiloxane (PDMS)-based platform for the generation of intact, perfusion-competent microvascular networks in vitro. COMSOL Multiphysics, a finite-element analysis and simulation software package, was used to obtain simulated velocity, pressure, and shear stress profiles. Transgene-free human induced pluripotent stem cells (hiPSCs) were differentiated into partially arterialized endothelial cells (hiPSC-ECs) in 5 d under completely chemically defined conditions, using the small molecule glycogen synthase kinase 3β inhibitor CHIR99021 and were thoroughly characterized for functionality and arterial-like marker expression. These cells, along with primary human umbilical vein endothelial cells (HUVECs), were seeded in the PDMS system to generate microvascular networks that were subjected to shear stress. Engineered microvessels had patent lumens and expressed VE-cadherin along their periphery. Shear stress caused by flowing medium increased the secretion of nitric oxide and caused endothelial cells s to align and to redistribute actin filaments parallel to the direction of the laminar flow. Shear stress also caused significant increases in gene expression for arterial markers Notch1 and EphrinB2 as well as antithrombotic markers Kruppel-like factor 2 (KLF-2)/4. These changes in response to shear stress in the microvascular platform were observed in hiPSC-EC microvessels but not in microvessels that were derived from HUVECs, which indicated that hiPSC-ECs may be more plastic in modulating their phenotype under flow than are HUVECs. Taken together, we demonstrate the feasibly of generating intact, engineered microvessels in vitro, which replicate some of the key biological features of native microvessels.

Robust Revascularization in Models of Limb Ischemia Using a Clinically Translatable Human Stem Cell-Derived Endothelial Cell Product

Pluripotent stem cell-derived differentiated endothelial cells offer high potential in regenerative medicine in the cardiovascular system. With the aim of translating the use of a human stem cell-derived endothelial cell product (hESC-ECP) for treatment of critical limb ischemia (CLI) in man, we report a good manufacturing practice (GMP)-compatible protocol and detailed cell tracking and efficacy data in multiple preclinical models. The clinical-grade cell line RC11 was used to generate hESC-ECP, which was identified as mostly endothelial (60% CD31⁺/CD144⁺), with the remainder of the subset expressing various pericyte/mesenchymal stem cell markers. Cell tracking using MRI, PET, and qPCR in a murine model of limb ischemia demonstrated that hESC-ECP was detectable up to day 7 following injection. Efficacy in several murine models of limb ischemia (immunocompromised/immunocompetent mice and mice with either type I/II diabetes mellitus) demonstrated significantly increased blood perfusion and capillary density. Overall, we demonstrate a GMP-compatible hESC-ECP that improved ischemic limb perfusion and increased local angiogenesis without engraftment, paving the way for translation of this therapy.

Integration of induced pluripotent stem cell-derived endothelial cells with polycaprolactone/gelatin-based electrospun scaffolds for enhanced therapeutic angiogenesis

BACKGROUND

Induced pluripotent stem-cell derived endothelial cells (iPSC-ECs) can be generated from any somatic cell and their iPSC sources possess unlimited self-renewal. Previous demonstration of their proangiogenic activity makes them a promising cell type for treatment of ischemic injury. As with many other stem cell approaches, the low rate of in-vivo survival has been a major limitation to the efficacy of iPSC-ECs to date. In this study, we aimed to increase the in-vivo lifetime of iPSC-ECs by culturing them on electrospun polycaprolactone (PCL)/gelatin scaffolds, before quantifying the subsequent impact on their proangiogenic function.

METHODS

iPSC-ECs were isolated and stably transfected with a luciferase reporter to facilitate quantification of cell numbers and non-invasive imaging in-vivo PCL/gelatin scaffolds were engineered using electrospinning to obtain woven meshes of nanofibers. iPSC-ECs were cultured on scaffolds for 7 days. Subsequently, cell growth and function were assessed in vitro followed by implantation in a mouseback subcutaneous model for 7 days.

RESULTS

Using a matrix of conditions, we found that scaffold blends with ratios of PCL:gelatin of 70:30 (PG73) spun at high flow rates supported the greatest levels of iPSC-EC growth, retention of phenotype, and function in vitro. Implanting iPSC-ECs seeded on PG73 scaffolds in vivo improved their survival up to 3 days, compared to cells directly injected into control wounds, which were no longer observable within 1 h. Enhanced engraftment improved blood perfusion, observed through non-invasive laser Doppler imaging. Immunohistochemistry revealed a corresponding increase in host angiogenic mechanisms characterized by the enhanced recruitment of macrophages and the elevated expression of proangiogenic cytokines vascular endothelial growth factor and placental growth factor.

CONCLUSIONS

Knowledge of these mechanisms combined with a deeper understanding of the scaffold parameters influencing this function provides the groundwork for optimizing future iPSC-EC therapies utilizing engraftment platforms. The development of combined scaffold and iPSC-EC therapies could ultimately improve therapeutic angiogenesis and the treatment of ischemic injury.

Protein-engineered hydrogels enhance the survival of induced pluripotent stem cell-derived endothelial cells for treatment of peripheral arterial disease

A key feature of peripheral arterial disease (PAD) is damage to endothelial cells (ECs), resulting in lower limb pain and restricted blood flow. Recent preclinical studies demonstrate that the transplantation of ECs via direct injection into the affected limb can result in significantly improved blood circulation. Unfortunately, the clinical application of this therapy has been limited by low cell viability and poor cell function. To address these limitations we have developed an injectable, recombinant hydrogel, termed SHIELD (Shear-thinning Hydrogel for Injectable Encapsulation and Long-term Delivery) for cell transplantation. SHIELD provides mechanical protection from cell membrane damage during syringe flow. Additionally, secondary in situ crosslinking provides a reinforcing network to improve cell retention, thereby augmenting the therapeutic benefit of cell therapy. In this study, we demonstrate the improved acute viability of human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) following syringe injection delivery in SHIELD, compared to saline. Using a murine hind limb ischemia model of PAD, we demonstrate enhanced iPSC-EC retention in vivo and improved neovascularization of the ischemic limb based on arteriogenesis following transplantation of iPSC-ECs delivered in SHIELD.

Differentiation, Evaluation, and Application of Human Induced Pluripotent Stem Cell-Derived Endothelial Cells

The emergence of induced pluripotent stem cell (iPSC) technology paves the way to generate large numbers of patient-specific endothelial cells (ECs) that can be potentially delivered for regenerative medicine in patients with cardiovascular disease. In the last decade, numerous protocols that differentiate EC from iPSC have been developed by many groups. In this review, we will discuss several common strategies that have been optimized for human iPSC-EC differentiation and subsequent studies that have evaluated the potential of human iPSC-EC as a cell therapy or as a tool in disease modeling. In addition, we will emphasize the importance of using in vivo vessel-forming ability and in vitro clonogenic colony-forming potential as a gold standard with which to evaluate the quality of human iPSC-EC derived from various protocols.

High glucose-induced endothelial progenitor cell dysfunction

Vascular complications contribute significantly to morbidity and mortality of diabetes mellitus. The primary cause of vascular complications in diabetes mellitus is hyperglycaemia, associated with endothelial dysfunction and impaired neovascularization. Circulating endothelial progenitor cells was shown to play important roles in vascular repair and promoting neovascularization. In this review, we will demonstrate the individual effect of high glucose on endothelial progenitor cells. Endothelial progenitor cells isolated from healthy subjects exposed to high glucose conditions or endothelial progenitor cells isolated from diabetic patients exhibit reduced number of endothelial cell colony forming units, impaired abilities of differentiation, proliferation, adhesion and migration, tubulization, secretion, mobilization and homing, whereas enhanced senescence. Increased production of reactive oxygen species by the mitochondria seems to play a crucial role in high glucose-induced endothelial progenitor cells deficit. Later, we will review the agents that might be used to alleviate dysfunction of endothelial progenitor cells induced by high glucose. The conclusions are that the relationship between hyperglycaemia and endothelial progenitor cells dysfunction is only beginning to be recognized, and future studies should pay more attention to the haemodynamic environment of endothelial progenitor cells and ageing factors to discover novel treatment agents.

Endothelial and smooth muscle cells derived from human cardiac explants demonstrate angiogenic potential and suitable for design of cell-containing vascular grafts

Background

Endothelial and smooth muscle cells are considered promising resources for regenerative medicine and cell replacement therapy. It has been shown that both types of cells are heterogeneous depending on the type of vessels and organs in which they are located. Therefore, isolation of endothelial and smooth muscle cells from tissues relevant to the area of research is necessary for the adequate study of specific pathologies. However, sources of specialized human endothelial and smooth muscle cells are limited, and the search for new sources is still relevant. The main goal of our study is to demonstrate that functional endothelial and smooth muscle cells can be obtained from an available source—post-surgically discarded cardiac tissue from the right atrial appendage and right ventricular myocardium.

Methods

Heterogeneous primary cell cultures were enzymatically isolated from cardiac explants and then grown in specific endothelial and smooth muscle growth media on collagen IV-coated surfaces. The population of endothelial cells was further enriched by immunomagnetic sorting for CD31, and the culture thus obtained was characterized by immunocytochemistry, ultrastructural analysis and in vitro functional tests. The angiogenic potency of the cells was examined by injecting them, along with Matrigel, into immunodeficient mice. Cells were also seeded on characterized polycaprolactone/chitosan membranes with subsequent analysis of cell proliferation and function.

Results

Endothelial cells isolated from cardiac explants expressed CD31, VE-cadherin and VEGFR2 and showed typical properties, namely, cytoplasmic Weibel-Palade bodies, metabolism of acetylated low-density lipoproteins, formation of capillary-like structures in Matrigel, and production of extracellular matrix and angiogenic cytokines. Isolated smooth muscle cells expressed extracellular matrix components as well as α-actin and myosin heavy chain. Vascular cells derived from cardiac explants demonstrated the ability to stimulate angiogenesis in vivo. Endothelial cells proliferated most effectively on membranes made of polycaprolactone and chitosan blended in a 25:75 ratio, neutralized by a mixture of alkaline and ethanol. Endothelial and smooth muscle cells retained their functional properties when seeded on the blended membranes.

Conclusions

We established endothelial and smooth muscle cell cultures from human right atrial appendage and right ventricle post-operative explants. The isolated cells revealed angiogenic potential and may be a promising source of patient-specific cells for regenerative medicine.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1156-1) contains supplementary material, which is available to authorized users.

Endothelial progenitor cells as a therapeutic option in intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is the most severe cerebrovascular disease, which represents a leading cause of death and disability in developed countries. However, therapeutic options are limited, so is mandatory to investigate repairing processes after stroke in order to develop new therapeutic strategies able to promote brain repair processes. Therapeutic angiogenesis and vasculogenesis hold promise to improve outcome of ICH patients. In this regard, circulating endothelial progenitor cells (EPCs) have recently been suggested to be a marker of vascular risk and endothelial function. Moreover, EPC levels have been associated with good neurological and functional outcome as well as reduced residual hematoma volume in ICH patients. Finally, experimental and clinical studies indicate that EPC might mediate endothelial cell regeneration and neovascularization. Therefore, EPC-based therapy could be an excellent therapeutic option in ICH. In this mini-review, we discuss the present status of knowledge about the possible therapeutic role of EPCs in ICH, molecular mechanisms, and the future perspectives and strategies for their use in clinical practice.

MicroRNA let-7g possesses a therapeutic potential for peripheral artery disease

Peripheral artery disease (PAD) is a manifestation of systemic atherosclerosis and conveys a significant health burden globally. Critical limb ischaemia encompasses the most severe consequence of PAD. Our previous studies indicate that microRNA let‐7g prevents atherosclerosis and improves endothelial functions. This study aimed to investigate whether and how let‐7g therapy may improve blood flow to ischaemic limbs. The present study shows that let‐7g has multiple pro‐angiogenic effects on mouse ischaemic limb model and could be a potential therapeutic agent for PAD. Mice receiving intramuscular injection of let‐7g had more neovascularization, better local perfusion and increased recruitment of endothelial progenitor cells after hindlimb ischaemia. The therapeutic effects of let‐7g's on angiogenesis are mediated by multiple regulatory machinery. First, let‐7g increased expression of vascular endothelial growth factor‐A (VEGF‐A) and VEGF receptor‐2 (VEGFR‐2) through targeting their upstream regulators HIF‐3α and TP53. In addition, let‐7g affected the splicing factor SC35 which subsequently enhanced the alternative splicing of VEGF‐A from the anti‐angiogenic isoform VEGF‐A_165b towards the pro‐angiogenic isoform VEGF‐A_164a. The pleiotropic effects of let‐7g on angiogenesis imply that let‐7g may possess a therapeutic potential in ischaemic diseases.

The Promise and Challenge of Induced Pluripotent Stem Cells for Cardiovascular Applications

The recent discovery of human-induced pluripotent stem cells (iPSCs) has revolutionized the field of stem cells. iPSCs have demonstrated that biological development is not an irreversible process and that mature adult somatic cells can be induced to become pluripotent. This breakthrough is projected to advance our current understanding of many disease processes and revolutionize the approach to effective therapeutics. Despite the great promise of iPSCs, many translational challenges still remain. In this article, we review the basic concept of induction of pluripotency as a novel approach to understand cardiac regeneration, cardiovascular disease modeling and drug discovery. We critically reflect on the current results of preclinical and clinical studies using iPSCs for these applications with appropriate emphasis on the challenges facing clinical translation.

H2O2-responsive antioxidant polymeric nanoparticles as therapeutic agents for peripheral arterial disease

Peripheral artery disease (PAD) is a common circulatory disorder in which narrowed arteries limit blood flow to the lower extremity and affect millions of people worldwide. Therapeutic angiogenesis has emerged as a promising strategy to treat PAD patients because surgical intervention has been showing limited success. Leg muscles of PAD patients have significantly high level of ROS (reactive oxygen species) and the increased production of ROS is a key mechanism of initiation and progression of PAD. We have recently developed H2O2-responsive polymer PVAX, which is designed to rapidly scavenge H2O2 and release vanillyl alcohol with antioxidant and anti-inflammatory activity. In this study, we investigated the therapeutic efficacy of PVAX nanoparticles for PAD using a cell culture model and a mouse model of hindlimb ischemia. PVAX nanoparticles significantly enhanced the expression of angiogenic inducers such as vascular endothelial growth factor (VEGF) and platelet endothelial cell adhesion molecule (PECAM)-1 in human umbilical vein endothelial cells (HUVEC). PVAX nanoparticles promoted revascularization and restoration of blood perfusion into ischemic tissues by upregulating angiogenic VEGF and PECAM-1. This work demonstrates that H2O2-responsive PVAX nanoparticles facilitate therapeutic angiogenesis and hold tremendous translational potential as therapeutic systems for ischemic diseases such as PAD.

Angio-Vasculogenic Properties of Endothelial-Induced Mesenchymal Stem Cells Derived From Human Adipose Tissue

BACKGROUND

Although stem cells have been regarded as a promising therapeutic option, the marginal therapeutic effects of stem cells are limitations that must be overcome for the development of effective cell therapy. This study sought to identify the angio-vasculogenic properties of endothelial differentiated mesenchymal stem cells (MSCs) and to determine whether these cells are effective for vascular repair.

METHODS AND RESULTS

Adipose MSCs were cultured for 10 days under endothelial cell (EC) culture conditions. These endothelial cell differentiated adipose MSCs (EA) and undifferentiated adipose MSCs (UA) were characterized via angiogenesis and adhesion assays. These cells were transplanted into a hindlimb ischemia (HLI) model to determine therapeutic effects and their underlying mechanisms. EA displayed low adhesion and angiogenic properties in vitro compared with UA. When implanted into mouse HLI models, EA exhibited the decreased recovery of blood perfusion in limb ischemia than uncultured UA. Histology data showed that injected EA exhibited lower retention, angiogenic cytokine levels, and neovascularization in vivo than did UA. Short-term differentiated EA display less cell engraftment and angio-vasculogenic potential, and are less effective for peripheral vascular repair than UA.

CONCLUSIONS

EC differentiation of MSCs may not present an effective strategy for the promotion of therapeutic neovascularization.

Mesenchymoangioblast-derived mesenchymal stromal cells inhibit cell damage, tissue damage and improve peripheral blood flow following hindlimb ischemic injury in mice

BACKGROUND AIMS

Existing treatments have limited success in modifying the course of peripheral artery disease, which may eventually lead to limb-threatening ulcers and amputation. Cellular therapies have the potential to provide a new treatment option for this condition, but isolation of cells by conventional means has limitations with respect to reproducibility and scalability.

METHODS

Induced pluripotent stem cells (iPSCs) were differentiated into precursor cells known as mesenchymoangioblasts (MCAs) and subsequently into mesenchymal stromal cells (MSCs). Hindlimb ischemia in mice was created by ligating both the iliac and femoral arteries of one hindlimb. Immediately after surgery, each animal received intramuscular injections of 5 × 10(6) cells or media in the ischemic limb. Toe necrosis was assessed visually, and hindlimb blood flow was measured by laser Doppler using a set region of interest (ROI) and by tracing the entire foot. Myofiber heterogeneity, nuclear centralization, fatty degeneration, fibrosis and capillary angiogenesis in the gastrocnemius muscle were assessed histologically.

RESULTS

Blood flow in the MCA-derived MSC-treated animals was higher at each day (P <0.006), and these mice recovered faster than control animals (3.6 vs. 2.5 for set ROI; 7.5 vs. 4.1 foot tracing; slope; P <0.001). There was significantly less myofiber heterogeneity, nuclear centralization, fatty degeneration and fibrosis in MCA-derived MSC-treated animals, indicating less tissue damage.

DISCUSSION

MCA-derived MSCs improved limb blood flow, reduced necrosis and maintained muscle mass and gross muscle appearance. We conclude that MCA-derived MSCs have a significant and protective effect against ischemic insults.

Vascular repair strategies in type 2 diabetes: novel insights

Impaired functions of vascular cells are responsible for the majority of complications in patients with type 2 diabetes (T2D). Recently a better understanding of mechanisms contributing to development of vascular dysfunction and the role of systemic inflammatory activation and functional alterations of several secretory organs, of which adipose tissue has more recently been investigated, has been achieved. Notably, the progression of vascular disease within the context of T2D appears to be driven by a multitude of incremental signaling shifts. Hence, successful therapies need to target several mechanisms in parallel, and over a long time period. This review will summarize the latest molecular strategies and translational developments of cardiovascular therapy in patients with T2D.

MicroRNA-21 coordinates human multipotent cardiovascular progenitors therapeutic potential

Published clinical trials in patients with ischemic diseases show limited benefit of adult stem cell-based therapy, likely due to their restricted plasticity and commitment toward vascular cell lineage. We aim to uncover the potent regenerative ability of MesP1/stage-specific embryonic antigen 1 (SSEA-1)-expressing cardiovascular progenitors enriched from human embryonic stem cells (hESCs). Injection of only 10(4) hESC-derived SSEA-1(+) /MesP1(+) cells, or their progeny obtained after treatment with VEGF-A or PDGF-BB, was effective enough to enhance postischemic revascularization in immunodeficient mice with critical limb ischemia (CLI). However, the rate of incorporation of hESC-derived SSEA-1(+) /MesP1(+) cells and their derivatives in ischemic tissues was modest. Alternatively, these cells possessed a unique miR-21 signature that inhibited phosphotase and tensin homolog (PTEN) thereby activating HIF-1α and the systemic release of VEGF-A. Targeting miR-21 limited cell survival and inhibited their proangiogenic capacities both in the Matrigel model and in mice with CLI. We next assessed the impact of mR-21 in adult angiogenesis-promoting cells. We observed an impaired postischemic angiogenesis in miR-21-deficient mice. Notably, miR-21 was highly expressed in circulating and infiltrated monocytes where it targeted PTEN/HIF-1α/VEGF-A signaling and cell survival. As a result, miR-21-deficient mice displayed an impaired number of infiltrated monocytes and a defective angiogenic phenotype that could be partially restored by retransplantation of bone marrow-derived cells from wild-type littermates. hESC-derived SSEA-1(+) /MesP1(+) cells progenitor cells are powerful key integrators of therapeutic angiogenesis in ischemic milieu and miR-21 is instrumental in this process as well as in the orchestration of the biological activity of adult angiogenesis-promoting cells.

Generating induced pluripotent stem cell derived endothelial cells and induced endothelial cells for cardiovascular disease modelling and therapeutic angiogenesis

Standard therapy for atherosclerotic coronary and peripheral arterial disease is insufficient in a significant number of patients because extensive disease often precludes effective revascularization. Stem cell therapy holds promise as a supplementary treatment for these patients, as pre-clinical and clinical research has shown transplanted cells can promote angiogenesis via direct and paracrine mechanisms. Induced pluripotent stem cells (iPSCs) are a novel cell type obtained by reprogramming somatic cells using exogenous transcription factor cocktails, which have been introduced to somatic cells via viral or plasmid constructs, modified mRNA or small molecules. IPSCs are now being used in disease modelling and drug testing and are undergoing their first clinical trial, but despite recent advances, the inefficiency of the reprogramming process remains a major limitation, as does the lack of consensus regarding the optimum transcription factor combination and delivery method and the uncertainty surrounding the genetic and epigenetic stability of iPSCs. IPSCs have been successfully differentiated into vascular endothelial cells (iPSC-ECs) and, more recently, induced endothelial cells (iECs) have also been generated by direct differentiation, which bypasses the pluripotent intermediate. IPSC-ECs and iECs demonstrate endothelial functionality in vitro and have been shown to promote neovessel growth and enhance blood flow recovery in animal models of myocardial infarction and peripheral arterial disease. Challenges remain in optimising the efficiency, safety and fidelity of the reprogramming and endothelial differentiation processes and establishing protocols for large-scale production of clinical-grade, patient-derived cells.

Concise review: MicroRNAs as modulators of stem cells and angiogenesis

MicroRNAs (miRs) are highly conserved, short noncoding RNA molecules that negatively regulate messenger RNA (mRNA) stability and/or translational efficiency. Since a given miR can control the expression of many mRNAs, their importance in governing gene expression in specific cell types including vascular cells and their progenitor cells has become increasingly clear. Understanding how the expression of miRs themselves is regulated and how miRs exert their influence on post-transcriptional gene control provides novel opportunities to dissect gene regulatory networks in clinically relevant cell types. A multitude of miRs have been identified with key roles in vascular development, homeostasis, function, disease, and regeneration. In this review, we will describe the impact of miRs on angiogenesis and their capacity to modulate the behavior of stem and progenitor cells which may be utilitarian for promoting vascular growth in ischemic tissue. Moreover, we summarize these strategies available for modulating miR expression and function and future therapeutic applications.

miRNAs in post-ischaemic angiogenesis and vascular remodelling

miRNAs are highly conserved non-coding RNA molecules that negatively control gene expression by binding to target mRNAs promoting their degradation. A multitude of miRNAs have been reported to be involved in angiogenesis and vascular remodelling. In the present review, we aim to describe the effect of miRNAs in post-ischaemic repair. First, we describe the miRNAs reported in ischaemic diseases and in angiogenesis. Then we examine their capacity to modulate the behaviour of stem and progenitor cells which could be utilized for vascular repair. And finally we discuss the potential of miRNAs as new clinical biomarkers and therapeutic targets.

Pravastatin reverses obesity-induced dysfunction of induced pluripotent stem cell-derived endothelial cells via a nitric oxide-dependent mechanism

AIMS

High-fat diet-induced obesity (DIO) is a major contributor to type II diabetes and micro- and macro-vascular complications leading to peripheral vascular disease (PVD). Metabolic abnormalities of induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) from obese individuals could potentially limit their therapeutic efficacy for PVD. The aim of this study was to compare the function of iPSC-ECs from normal and DIO mice using comprehensive in vitro and in vivo assays.

METHODS AND RESULTS

Six-week-old C57Bl/6 mice were fed with a normal or high-fat diet. At 24 weeks, iPSCs were generated from tail tip fibroblasts and differentiated into iPSC-ECs using a directed monolayer approach. In vitro functional analysis revealed that iPSC-ECs from DIO mice had significantly decreased capacity to form capillary-like networks, diminished migration, and lower proliferation. Microarray and ELISA confirmed elevated apoptotic, inflammatory, and oxidative stress pathways in DIO iPSC-ECs. Following hindlimb ischaemia, mice receiving intramuscular injections of DIO iPSC-ECs had significantly decreased reperfusion compared with mice injected with control healthy iPSC-ECs. Hindlimb sections revealed increased muscle atrophy and presence of inflammatory cells in mice receiving DIO iPSC-ECs. When pravastatin was co-administered to mice receiving DIO iPSC-ECs, a significant increase in reperfusion was observed; however, this beneficial effect was blunted by co-administration of the nitric oxide synthase inhibitor, N(ω)-nitro-l-arginine methyl ester.

CONCLUSION

This is the first study to provide evidence that iPSC-ECs from DIO mice exhibit signs of endothelial dysfunction and have suboptimal efficacy following transplantation in a hindlimb ischaemia model. These findings may have important implications for future treatment of PVD using iPSC-ECs in the obese population.

Bone marrow mesenchymal stem cells overexpressing human basic fibroblast growth factor increase vasculogenesis in ischemic rats

Administration or expression of growth factors, as well as implantation of autologous bone marrow cells, promote in vivo angiogenesis. This study investigated the angiogenic potential of combining both approaches through the allogenic transplantation of bone marrow-derived mesenchymal stem cells (MSCs) expressing human basic fibroblast growth factor (hbFGF). After establishing a hind limb ischemia model in Sprague Dawley rats, the animals were randomly divided into four treatment groups: MSCs expressing green fluorescent protein (GFP-MSC), MSCs expressing hbFGF (hbFGF-MSC), MSC controls, and phosphate-buffered saline (PBS) controls. After 2 weeks, MSC survival and differentiation, hbFGF and vascular endothelial growth factor (VEGF) expression, and microvessel density of ischemic muscles were determined. Stable hbFGF expression was observed in the hbFGF-MSC group after 2 weeks. More hbFGF-MSCs than GFP-MSCs survived and differentiated into vascular endothelial cells (P<0.001); however, their differentiation rates were similar. Moreover, allogenic transplantation of hbFGF-MSCs increased VEGF expression (P=0.008) and microvessel density (P<0.001). Transplantation of hbFGF-expressing MSCs promoted angiogenesis in an in vivo hind limb ischemia model by increasing the survival of transplanted cells that subsequently differentiated into vascular endothelial cells. This study showed the therapeutic potential of combining cell-based therapy with gene therapy to treat ischemic disease.

Strategies for whole lung tissue engineering

Recent work has demonstrated the feasibility of using decellularized lung extracellular matrix scaffolds to support the engineering of functional lung tissue in vitro. Rendered acellular through the use of detergents and other reagents, the scaffolds are mounted in organ-specific bioreactors where cells in the scaffold are provided with nutrients and appropriate mechanical stimuli such as ventilation and perfusion. Though initial studies are encouraging, a great deal remains to be done to advance the field and transition from rodent lungs to whole human tissue engineered lungs. To do so, a variety of hurdles must be overcome. In particular, a reliable source of human-sized scaffolds, as well as a method of terminal sterilization of scaffolds, must be identified. Continued research in lung cell and developmental biology will hopefully help identify the number and types of cells that will be required to regenerate functional lung tissue. Finally, bioreactor designs must be improved in order to provide more precise ventilation stimuli and vascular perfusion in order to avoid injury to or death of the cells cultivated within the scaffold. Ultimately, the success of efforts to engineer a functional lung in vitro will critically depend on the ability to create a fully endothelialized vascular network that provides sufficient barrier function and alveolar-capillary surface area to exchange gas at rates compatible with healthy lung function.

Specific role of impaired glucose metabolism and diabetes mellitus in endothelial progenitor cell characteristics and function

The disease burden of diabetes mellitus (DM) and its associated cardiovascular complications represent a growing and major global health problem. Recent studies suggest that circulating exogenous endothelial progenitor cells (EPCs) play an important role in endothelial repair and neovascularization at sites of injury or ischemia. Both experimental and clinical studies have demonstrated that hyperglycemia related to DM can induce alterations to EPCs. The reduction and dysfunction of EPCs related to DM correlate with the occurrence and severity of microvascular and macrovascular complications, suggesting a close mechanistic link between EPC dysfunction and impaired vascular function/repair in DM. These alterations to EPCs, likely mediated by multiple pathophysiological mechanisms, including inflammation, oxidative stress, and alterations in Akt and the nitric oxide pathway, affect EPCs at multiple stages: differentiation and mobilization in the bone marrow, trafficking and survival in the circulation, and homing and neovascularization. Several different therapeutic approaches have consequently been proposed to reverse the reduction and dysfunction of EPCs in DM and may represent a novel therapeutic approach to prevent and treat DM-related cardiovascular complications.

The epidermal growth factor receptor and its ligands in cardiovascular disease

The epidermal growth factor receptor (EGFR) family and its ligands serve as a switchboard for the regulation of multiple cellular processes. While it is clear that EGFR activity is essential for normal cardiac development, its function in the vasculature and its role in cardiovascular disease are only beginning to be elucidated. In the blood vessel, endothelial cells and smooth muscle cells are both a source and a target of EGF-like ligands. Activation of EGFR has been implicated in blood pressure regulation, endothelial dysfunction, neointimal hyperplasia, atherogenesis, and cardiac remodeling. Furthermore, increased circulating EGF-like ligands may mediate accelerated vascular disease associated with chronic inflammation. Although EGFR inhibitors are currently being used clinically for the treatment of cancer, additional studies are necessary to determine whether abrogation of EGFR signaling is a potential strategy for the treatment of cardiovascular disease.