Cotransfection of vascular endothelial growth factor-A and platelet-derived growth factor-B via recombinant adeno-associated virus resolves chronic ischemic malperfusion role of vessel maturation

Heart immunoengineering by lentiviral vector-mediated genetic modification during normothermic ex vivo perfusion

Heart transplantation is associated with major hurdles, including the limited number of available organs for transplantation, the risk of rejection due to genetic discrepancies, and the burden of immunosuppression. In this study, we demonstrated the feasibility of permanent genetic engineering of the heart during ex vivo perfusion. Lentiviral vectors encoding for short hairpin RNAs targeting beta2-microglobulin (shβ2m) and class II transactivator (shCIITA) were delivered to the graft during two hours of normothermic EVHP. Highly efficient genetic engineering was indicated by stable reporter gene expression in endothelial cells and cardiomyocytes. Remarkably, swine leucocyte antigen (SLA) class I and SLA class II expression levels were decreased by 66% and 76%, respectively, in the vascular endothelium. Evaluation of lactate, troponin T, and LDH levels in the perfusate and histological analysis showed no additional cell injury or tissue damage caused by lentiviral vectors. Moreover, cytokine secretion profiles (IL-6, IL-8, and TNF-α) of non-transduced and lentiviral vector-transduced hearts were comparable. This study demonstrated the ex vivo generation of genetically engineered hearts without compromising tissue integrity. Downregulation of SLA expression may contribute to reduce the immunogenicity of the heart and support graft survival after allogeneic or xenogeneic transplantation.

Thymosin ß4 and MRTF-A mitigate vessel regression despite cardiovascular risk factors

Since clinical revascularization techniques of coronary or peripheral artery disease (CAD/PAD) focus on macrovessels of the heart, the microcirculatory compartment largely goes unnoticed. However, cardiovascular risk factors not only drive large vessel atherosclerosis, but also microcirculatory rarefaction, an instance unmet by current therapeutic schemes. Angiogenic gene therapy has the potential to reverse capillary rarefaction, but only if the disease-causing inflammation and vessel-destabilization are addressed. This review summarizes the current knowledge with regard to capillary rarefaction due to cardiovascular risk factors. Moreover, the potential of Thymosin ß4 (Tß4) and its downstream signal, myocardin-related transcription factor-A (MRTF-A), to counteract capillary rarefaction are discussed.

Internal Ribosome Entry Site (IRES)-Mediated Translation and Its Potential for Novel mRNA-Based Therapy Development

Many conditions can benefit from RNA-based therapies, namely, those targeting internal ribosome entry sites (IRESs) and their regulatory proteins, the IRES trans-acting factors (ITAFs). IRES-mediated translation is an alternative mechanism of translation initiation, known for maintaining protein synthesis when canonical translation is impaired. During a stress response, it contributes to cell reprogramming and adaptation to the new environment. The relationship between IRESs and ITAFs with tumorigenesis and resistance to therapy has been studied in recent years, proposing new therapeutic targets and treatments. In addition, IRES-dependent translation initiation dysregulation is also related to neurological and cardiovascular diseases, muscular atrophies, or other syndromes. The participation of these structures in the development of such pathologies has been studied, yet to a far lesser extent than in cancer. Strategies involving the disruption of IRES–ITAF interactions or the modification of ITAF expression levels may be used with great impact in the development of new therapeutics. In this review, we aim to comprehend the current data on groups of human pathologies associated with IRES and/or ITAF dysregulation and their application in the designing of new therapeutic approaches using them as targets or tools. Thus, we wish to summarise the evidence in the field hoping to open new promising lines of investigation toward personalised treatments.

Interdependence of Angiogenesis and Arteriogenesis in Development and Disease

The structure of arterial networks is optimized to allow efficient flow delivery to metabolically active tissues. Optimization of flow delivery is a continuous process involving synchronization of the structure and function of the microcirculation with the upstream arterial network. Risk factors for ischemic cardiovascular diseases, such as diabetes mellitus and hyperlipidemia, adversely affect endothelial function, induce capillary regression, and disrupt the micro- to macrocirculation cross-talk. We provide evidence showing that this loss of synchronization reduces arterial collateral network recruitment upon arterial stenosis, and the long-term clinical outcome of current revascularization strategies in these patient cohorts. We describe mechanisms and signals contributing to synchronized growth of micro- and macrocirculation in development and upon ischemic challenges in the adult organism and identify potential therapeutic targets. We conclude that a long-term successful revascularization strategy should aim at both removing obstructions in the proximal part of the arterial tree and restoring “bottom-up” vascular communication.

Endothelial Retargeting of AAV9 In Vivo

Adeno-associated viruses (AAVs) are frequently used for gene transfer and gene editing in vivo, except for endothelial cells, which are remarkably resistant to unmodified AAV-transduction. AAVs are retargeted here toward endothelial cells by coating with second-generation polyamidoamine dendrimers (G2) linked to endothelial-affine peptides (CNN). G2CNN AAV9-Cre (encoding Cre recombinase) are injected into mTmG-mice or mTmG-pigs, cell-specifically converting red to green fluorescence upon Cre-activity. Three endothelial-specific functions are assessed: in vivo quantification of adherent leukocytes after systemic injection of - G2CNN AAV9 encoding 1) an artificial adhesion molecule (S1FG) in wildtype mice (day 10) or 2) anti-inflammatory Annexin A1 (Anxa1) in ApoE-/- mice (day 28). Moreover, 3) in Cas9-transgenic mice, blood pressure is monitored till day 56 after systemic application of G2CNN AAV9-gRNAs, targeting exons 6-10 of endothelial nitric oxide synthase (eNOS), a vasodilatory enzyme. G2CNN AAV9-Cre transduces microvascular endothelial cells in mTmG-mice or mTmG-pigs. Functionally, G2CNN AAV9-S1FG mediates S1FG-leukocyte adhesion, whereas G2CNN AAV9-Anxa1-application reduces long-term leukocyte recruitment. Moreover, blood pressure increases in Cas9-expressing mice subjected to G2CNN AAV9-gRNAeNOS . Therefore, G2CNN AAV9 may enable gene transfer in vascular and atherosclerosis models.

Dual VEGF/PDGF knockdown suppresses vasculogenic mimicry formation in choroidal melanoma cells via the Wnt5a/β-catenin/AKT signaling pathway

OBJECTIVE

This study aimed to explore the effects of knocking down both vascular endothelial growth factor (VEGF) and platelet derived growth factor (PDGF) on vasculogenic mimicry (VM) formation in choroidal melanoma (CM) cells.

METHODS

Cell counting Kit (CCK)-8, monoclonal formation, wound healing, transwell and flow cytometry assays were used to observe the cell effects in CM cell line, ocular choroidal melanoma-1 cells (OCM-1) with respect to proliferation, migration, invasion and apoptosis. Three-dimensional (3D) cultures were also used to characterize VM tube structural effects in OCM-1 cells and western blotting was used to characterize protein expression changes in VM-related markers.

RESULTS

Dual VEGF/PDGF knockdown suppressed cell proliferation, migration and invasion, but promoted cell apoptosis. It also reduced VM tube structures in OCM-1 cells. VM associated markers including, VE-cadherin, EphA2 and MT1-MMP were also down-regulated in OCM-1 cells. Similarly, Wnt5a, β-catenin and phosphorylated-AKT levels were also down-regulated. Western blotting and 3D cultures further demonstrated that combined Wnt5a silencing with dual VEGF/PDGF knockdown significantly decreased VE-cadherin and EphA2 levels and reduced VM tube structures in OCM-1 cells.

CONCLUSIONS

Dual VEGF/PDGF knockdown suppressed cell growth and metastasis in OCM-1 cells, and blocked the Wnt5a/β-catenin/AKT signaling pathway thereby inhibiting VM formation.

AAV2-VEGF-B gene therapy failed to induce angiogenesis in ischemic porcine myocardium due to inflammatory responses

Therapeutic angiogenesis induced by gene therapy is a promising approach to treat patients suffering from severe coronary artery disease. In small experimental animals, adeno-associated viruses (AAVs) have shown good transduction efficacy and long-term transgene expression in heart muscle and other tissues. However, it has been difficult to achieve cardiac-specific angiogenic effects with AAV vectors. We tested the hypothesis whether AAV2 gene transfer (1 × 10¹³ vg) of vascular endothelial growth factor B (VEGF-B186) together with immunosuppressive corticosteroid treatment can induce long-term cardiac-specific therapeutic effects in the porcine ischemic heart. Gene transfers were delivered percutaneously using direct intramyocardial injections, improving targeting and avoiding direct contact with blood, thus reducing the likelihood of immediate immune reactions. After 1- and 6-month time points, the capillary area was analyzed, myocardial perfusion reserve (MPR) was measured with radiowater positron emission tomography ([¹⁵O]H₂O-PET), and fluorodeoxyglucose ([¹⁸F]FDG) uptake was used to evaluate myocardial viability. Clinical chemistry and immune responses were analyzed using standard methods. After 1- and 6-month follow-up, AAV2-VEGF-B186 gene transfer failed to induce angiogenesis and improve myocardial perfusion and viability. Here, we show that inflammatory responses attenuated the therapeutic effect of AAV2 gene transfer by significantly reducing successful transduction and long-term gene expression despite the efforts to reduce the likelihood of immune reactions and the use of targeted local gene transfer methods.

Mitochondrial-cell cycle cross-talk drives endoreplication in heart disease

[Figure: see text].

Cas9-expressing chickens and pigs as resources for genome editing in livestock

Genetically modified animals continue to provide important insights into the molecular basis of health and disease. Research has focused mostly on genetically modified mice, although other species like pigs resemble the human physiology more closely. In addition, cross-species comparisons with phylogenetically distant species such as chickens provide powerful insights into fundamental biological and biomedical processes. One of the most versatile genetic methods applicable across species is CRISPR-Cas9. Here, we report the generation of transgenic chickens and pigs that constitutively express Cas9 in all organs. These animals are healthy and fertile. Functionality of Cas9 was confirmed in both species for a number of different target genes, for a variety of cell types and in vivo by targeted gene disruption in lymphocytes and the developing brain, and by precise excision of a 12.7-kb DNA fragment in the heart. The Cas9 transgenic animals will provide a powerful resource for in vivo genome editing for both agricultural and translational biomedical research, and will facilitate reverse genetics as well as cross-species comparisons.

Strategies for re-vascularization and promotion of angiogenesis in trauma and disease

The maintenance of a healthy vascular system is essential to ensure the proper function of all organs of the human body. While macrovessels have the main role of blood transportation from the heart to all tissues, microvessels, in particular capillaries, are responsible for maintaining tissues' functionality by providing oxygen, nutrients and waste exchanges. Occlusion of blood vessels due to atherosclerotic plaque accumulation remains the leading cause of mortality across the world. Autologous vein and artery grafts bypassing are the current gold standard surgical procedures to substitute primarily obstructed vascular structures. Ischemic scenarios that condition blood supply in downstream tissues may arise from blockage phenomena, as well as from other disease or events leading to trauma. The (i) great demand for new vascular substitutes, arising from both the limited availability of healthy autologous vessels, as well as the shortcomings associated with small-diameter synthetic vascular grafts, and (ii) the challenging induction of the formation of adequate and stable microvasculature are current driving forces for the growing interest in the development of bioinspired strategies to ensure the proper function of vasculature in all its dimensional scales. Here, a critical review of well-established technologies and recent biotechnological advances to substitute or regenerate the vascular system is provided.

Large Animal Models of Cell-Free Cardiac Regeneration

The adult mammalian heart lacks the ability to sufficiently regenerate itself, leading to the progressive deterioration of function and heart failure after ischemic injuries such as myocardial infarction. Thus far, cell-based therapies have delivered unsatisfactory results, prompting the search for cell-free alternatives that can induce the heart to repair itself through cardiomyocyte proliferation, angiogenesis, and advantageous remodeling. Large animal models are an invaluable step toward translating basic research into clinical applications. In this review, we give an overview of the state-of-the-art in cell-free cardiac regeneration therapies that have been tested in large animal models, mainly pigs. Cell-free cardiac regeneration therapies involve stem cell secretome- and extracellular vesicles (including exosomes)-induced cardiac repair, RNA-based therapies, mainly regarding microRNAs, but also modified mRNA (modRNA) as well as other molecules including growth factors and extracellular matrix components. Various methods for the delivery of regenerative substances are used, including adenoviral vectors (AAVs), microencapsulation, and microparticles. Physical stimulation methods and direct cardiac reprogramming approaches are also discussed.

Somatic gene editing ameliorates skeletal and cardiac muscle failure in pig and human models of Duchenne muscular dystrophy

Frameshift mutations in the DMD gene, encoding dystrophin, cause Duchenne muscular dystrophy (DMD), leading to terminal muscle and heart failure in patients. Somatic gene editing by sequence-specific nucleases offers new options for restoring the DMD reading frame, resulting in expression of a shortened but largely functional dystrophin protein. Here, we validated this approach in a pig model of DMD lacking exon 52 of DMD (DMDΔ52), as well as in a corresponding patient-derived induced pluripotent stem cell model. In DMDΔ52 pigs1, intramuscular injection of adeno-associated viral vectors of serotype 9 carrying an intein-split Cas9 (ref. 2) and a pair of guide RNAs targeting sequences flanking exon 51 (AAV9-Cas9-gE51) induced expression of a shortened dystrophin (DMDΔ51-52) and improved skeletal muscle function. Moreover, systemic application of AAV9-Cas9-gE51 led to widespread dystrophin expression in muscle, including diaphragm and heart, prolonging survival and reducing arrhythmogenic vulnerability. Similarly, in induced pluripotent stem cell-derived myoblasts and cardiomyocytes of a patient lacking DMDΔ52, AAV6-Cas9-g51-mediated excision of exon 51 restored dystrophin expression and amelioreate skeletal myotube formation as well as abnormal cardiomyocyte Ca2+ handling and arrhythmogenic susceptibility. The ability of Cas9-mediated exon excision to improve DMD pathology in these translational models paves the way for new treatment approaches in patients with this devastating disease.

Therapeutic vascularization in regenerative medicine

Therapeutic angiogenesis, that is, the generation of new vessels by delivery of specific factors, is required both for rapid vascularization of tissue‐engineered constructs and to treat ischemic conditions. Vascular endothelial growth factor (VEGF) is the master regulator of angiogenesis. However, uncontrolled expression can lead to aberrant vascular growth and vascular tumors (angiomas). Major challenges to fully exploit VEGF potency for therapy include the need to precisely control in vivo distribution of growth factor dose and duration of expression. In fact, the therapeutic window of VEGF delivery depends on its amount in the microenvironment around each producing cell rather than on the total dose, since VEGF remains tightly bound to extracellular matrix (ECM). On the other hand, short‐term expression of less than about 4 weeks leads to unstable vessels, which promptly regress following cessation of the angiogenic stimulus. Here, we will briefly overview some key aspects of the biology of VEGF and angiogenesis and discuss their therapeutic implications with a particular focus on approaches using gene therapy, genetically modified progenitors, and ECM engineering with recombinant factors. Lastly, we will present recent insights into the mechanisms that regulate vessel stabilization and the switch between normal and aberrant vascular growth after VEGF delivery, to identify novel molecular targets that may improve both safety and efficacy of therapeutic angiogenesis.

Human Cardiac Gene Therapy

In the past 10 years, there has been tremendous progress made in the field of gene therapy. Effective treatments of Leber congenital amaurosis, hemophilia, and spinal muscular atrophy have been largely based on the efficiency and safety of adeno-associated vectors. Myocardial gene therapy has been tested in patients with heart failure using adeno-associated vectors with no safety concerns but lacking clinical improvements. Cardiac gene therapy is adapting to the new developments in vectors, delivery systems, targets, and clinical end points and is poised for success in the near future.

Tβ4 Increases Neovascularization and Cardiac Function in Chronic Myocardial Ischemia of Normo- and Hypercholesterolemic Pigs

Translations of new therapeutic options for cardiovascular disease from animal studies into a clinical setting have been hampered, in part by an improper reflection of a relevant patient population in animal models. In this study, we investigated the impact of thymosin β4 (Tβ4), which promotes collateralization and capillarization, during hypercholesterolemia, a known risk factor of coronary artery disease. Initial in vitro results highlighted an improved endothelial cell function upon Tβ4 treatment under control conditions and during hypercholesterolemic stress (scratch area [pixels]: oxidized low-density lipoprotein [oxLDL], 191,924 ± 7,717; and oxLDL + Tβ4, 105,621 ± 11,245). To mimic the common risk factor of hypercholesterolemia in vivo, pigs on regular (NC) or high-fat (HC) diet underwent chronic myocardial ischemia followed by recombinant adeno-associated virus (rAAV)-mediated transduction of Tβ4 or LacZ as a control. We show that Tβ4 overexpression improves capillarization and collateralization (collaterals: NC + rAAV.LacZ, 2.1 ± 0.5; NC + rAAV.Tβ4, 6.7 ± 0.5; HC + rAAV.LacZ, 3.0 ± 0.3; and HC + rAAV.Tβ4, 6.0 ± 0.4), ultimately leading to an improved myocardial function in both diet groups (ejection fraction [EF] at day 56 [%]: NC + rAAV.LacZ, 26 ± 1.1; NC + rAAV.Tβ4, 45 ± 1.5; HC + rAAV.LacZ, 26 ± 2.5; and HC + rAAV.Tβ4, 41 ± 2.6). These results demonstrate the potency of Tβ4 in a patient-relevant large animal model of chronic myocardial ischemia.

Adeno-Associated Virus Gene Therapy: Translational Progress and Future Prospects in the Treatment of Heart Failure

Despite advances in treatment over the past decade, heart failure remains a significant public health burden and a leading cause of death in the developed world. Gene therapy provides a promising approach for preventing and reversing cardiac abnormalities, however, clinical application has shown limited success to date. A substantial effort is being invested into the development of recombinant adeno-associated viruses (AAVs) for cardiac gene therapy as AAV gene therapy offers a high safety profile and provides sustained and efficient transgene expression following a once-off administration. Due to the physiological, anatomical and genetic similarities between large animals and humans, preclinical studies using large animal models for AAV gene therapy are crucial stepping stones between the laboratory and the clinic. Many molecular targets selected to treat heart failure using AAV gene therapy have been chosen because of their potential to regulate and restore cardiac contractility. Other genes targeted with AAV are involved with regulating angiogenesis, beta-adrenergic sensitivity, inflammation, physiological signalling and metabolism. While significant progress continues to be made in the field of AAV cardiac gene therapy, challenges remain in overcoming host neutralising antibodies, improving AAV vector cardiac-transduction efficiency and selectivity, and optimising the dose, route and method of delivery.

Vascular endothelial growth factor-B: Impact on physiology and pathology

Angiogenesis plays an important role in controlling tissue development and maintaining normal tissue function. Dysregulated angiogenesis is implicated in the pathogenesis of a variety of diseases, particularly diabetes, cancers, and neurodegenerative disorders. As the major regulator of angiogenesis, the vascular endothelial growth factor (VEGF) family is composed of a group of crucial members including VEGF-B. While the physiological roles of VEGF-B remain debatable, increasing evidence suggests that this protein is able to protect certain type of cells from apoptosis under pathological conditions. More importantly, recent studies reveal that VEGF-B is involved in lipid transport and energy metabolism, implicating this protein in obesity, diabetes and related metabolic complications. This article summarizes the current knowledge and understanding of VEGF-B in physiology and pathology, and shed light on the therapeutic potential of this crucial protein.

Steerable Induction of the Thymosin β4/MRTF-A Pathway via AAV-Based Overexpression Induces Therapeutic Neovascularization

Viral vectors have been frequently used in a variety of preclinical animal models to deliver genetic constructs into tissues. Among the vectors used, adeno-associated viral vectors (AAVs) may be targeted to specific tissues, depending on the serotype used. Moreover, they show robust expression for prolonged periods of time and have a low immunogenic potential. Furthermore, AAVs, unlike other vector systems, only display a low rate of genomic integration. However, to ensure efficient transgene production, expression is typically driven by constitutively active promoters, such as the cytomegalovirus (CMV) promoter. Tetracyclin responsive promoters represent a promising alternative to unregulated promoters. The present study compares AAVs encoding either constitutively active CMV or tet-off promoter regions in the preclinical models of hindlimb and chronic myocardial ischemia. Therapeutically, mediators regulating vessel maturation, specifically thymosin beta 4 (Tβ4) and the downstream signaling molecule myocardin-related transcription factor A (MRTF-A) as well as the endothelial activator angiopoietin-2 (Ang2) were overexpressed via AAVs using both promotors. In the model of rabbit hindlimb ischemia, temporary (tet-off) expression of Tβ4 improved capillary density, collateralization, and perfusion in the ischemic hindlimb, with no detectable difference to constitutive Tβ4 overexpression. Similarly, constitutive overexpression of MRTF-A alone was able to improve capillarization, collateralization and perfusion. Temporary expression of Ang2 for 7 days further increased capillary density and pericyte coverage compared with MRTF-A alone, without further improving collateralization or perfusion. In the pig model of chronic myocardial ischemia constitutive expression of Tβ4 for 4 weeks induced capillary and collateral growth similarly to a pulsed expression (2 day expression per week for 3 weeks). Taken together these findings demonstrate for two models of preclinical interventions that temporary gene expression may lead to similar results as constitutive expression, highlighting the potential of controlled temporary gene expression for induction of vascular growth as a therapeutic approach.

Diabetes Mellitus-Induced Microvascular Destabilization in the Myocardium

BACKGROUND

Diabetes mellitus causes microcirculatory rarefaction and may impair the responsiveness of ischemic myocardium to proangiogenic factors.

OBJECTIVES

This study sought to determine whether microvascular destabilization affects organ function and therapeutic neovascularization in diabetes mellitus.

METHODS

The authors obtained myocardial samples from patients with end-stage heart failure at time of transplant, with or without diabetes mellitus. Diabetic (db) and wild-type (wt) pigs were used to analyze myocardial vascularization and function. Chronic ischemia was induced percutaneously (day 0) in the circumflex artery. At day 28, recombinant adeno-associated virus (rAAV) (5 × 10¹² viral particles encoding vascular endothelial growth factor-A [VEGF-A] or thymosin beta 4 [Tβ4]) was applied regionally. CD31+ capillaries per high power field (c/hpf) and NG2+ pericyte coverage were analyzed. Global myocardial function (ejection fraction [EF] and left ventricular end-diastolic pressure) was assessed at days 28 and 56.

RESULTS

Diabetic human myocardial explants revealed capillary rarefaction and pericyte loss compared to nondiabetic explants. Hyperglycemia in db pigs, even without ischemia, induced capillary rarefaction in the myocardium (163 ± 14 c/hpf in db vs. 234 ± 8 c/hpf in wt hearts; p < 0.005), concomitant with a distinct loss of EF (44.9% vs. 53.4% in nondiabetic controls; p < 0.05). Capillary density further decreased in chronic ischemic hearts, as did EF (both p < 0.05). Treatment with rAAV.Tβ4 enhanced capillary density and maturation in db hearts less efficiently than in wt hearts, similar to collateral growth. rAAV.VEGF-A, though stimulating angiogenesis, induced neither pericyte recruitment nor collateral growth. As a result, rAAV.Tβ4 but not rAAV.VEGF-A improved EF in db hearts (34.5 ± 1.4%), but less so than in wt hearts (44.8 ± 1.5%).

CONCLUSIONS

Diabetes mellitus destabilized microvascular vessels of the heart, affecting the amplitude of therapeutic neovascularization via rAAV.Tβ4 in a translational large animal model of hibernating myocardium.

Cardiac gene therapy with adeno-associated virus-based vectors

PURPOSE OF REVIEW

Cardiac gene therapy with adeno-associated virus (AAV)-based vectors is emerging as an entirely new platform to treat, or even cure, so far intractable cardiac disorders. This review describes our current knowledge of cardiac AAV gene therapy with a particular focus on the biggest obstacle for the successful translation of cardiac AAV gene therapy into the clinic, namely the efficient delivery of the therapeutic gene to the myocardium.

RECENT FINDINGS

We summarize the significant recent progress that has been made in treating heart failure in preclinically relevant animal models with AAV gene therapy and the recent results of clinical trials with cardiac AAV gene therapy for the treatment of heart failure. We also discuss the benefits and shortcomings of the currently available delivery methods of AAV to the heart. Finally, we describe the current state of identifying novel AAV variants that have enhanced tropism for human cardiomyocytes and that show increased resistance to preexisting neutralizing antibodies.

SUMMARY

Here, we describe the successes and challenges in cardiac AAV gene therapy, a treatment modality that has the potential to transform current treatment approaches for cardiac diseases.

Optimizing the host substrate environment for cardiac angiogenesis, arteriogenesis, and myogenesis

INTRODUCTION

The diseased host milieu, such as endothelial dysfunction (ED), decreased NO bioavailability, and ischemic/inflammatory post-MI environment, hamper the clinical success of existing cardiac regenerative therapies. Area covered: In this article, current strategies including pharmacological and nonpharmacological approaches for improving the diseased host milieu are reviewed. Specifically, the authors provide focus on: i) the mechanism of ED in patients with cardiovascular diseases, ii) the current results of ED improving strategies in pre-clinical and clinical studies, and iii) the use of biomaterials as a novel modulator in damaged post-MI environment. Expert opinion: Adjunct therapies which improve host endothelial function have demonstrated promising outcomes, potentially overcoming disappointing results of cell therapy in human studies. In the future, elucidation of the interactions between the host tissue and therapeutic agents, as well as downstream signaling pathways, will be the next challenges in enhancing regenerative therapy. More careful investigations are also required to establish these agents' safety and efficacy for wide usage in humans.

Differential regulation of blood flow-induced neovascularization and mural cell recruitment by vascular endothelial growth factor and angiopoietin signalling

KEY POINTS

Combining nitric oxide (NO)-mediated increased blood flow with angiopoietin-1-Tie2 receptor signalling induces arteriolargenesis - the formation of arterioles from capillaries - in a model of physiological angiogenesis. This NO-Tie-mediated arteriolargenesis requires endogenous vascular endothelial growth factor (VEGF) signalling. Inhibition of VEGF signalling increases pericyte coverage in microvessels. Together these findings indicate that generation of functional neovasculature requires close titration of NO-Tie2 signalling and localized VEGF induction, suggesting that the use of exogenous VEGF expression as a therapeutic for neovascularization may not be successful.

ABSTRACT

Signalling through vascular endothelial growth factor (VEGF) receptors and the tyrosine kinase with IgG and EGF domains-2 (Tie2) receptor by angiopoietins is required in combination with blood flow for the formation of a functional vascular network. We tested the hypothesis that VEGF and angiopoietin-1 (Ang1) contribute differentially to neovascularization induced by nitric oxide (NO)-mediated vasodilatation, by comparing the phenotype of new microvessels in the mesentery during induction of vascular remodelling by over-expression of endothelial nitric oxide synthase in the fat pad of the adult rat mesentery during inhibition of angiopoietin signalling with soluble Tie2 (sTie2) and VEGF signalling with soluble Fms-like tyrosine kinase receptor-1 (sFlt1). We found that NO-mediated angiogenesis was blocked by inhibition of VEGF with sFlt1 (from 881 ± 98% increase in functional vessel area to 279 ± 72%) and by inhibition of angiopoietin with sTie2 (to 337 ± 67%). Exogenous angiopoietin-1 was required to induce arteriolargenesis (8.6 ± 1.3% of vessels with recruitment of vascular smooth muscle cells; VSMCs) in the presence of enhanced flow. sTie2 and sFlt1 both inhibited VSMC recruitment (both 0%), and VEGF inhibition increased pericyte recruitment to newly formed vessels (from 27 ± 2 to 54 ± 3% pericyte ensheathment). We demonstrate that a fine balance of VEGF and angiopoietin signalling is required for the formation of a functional vascular network. Endogenous VEGF signalling prevents excess neovessel pericyte coverage, and is required for VSMC recruitment during increased nitric oxide-mediated vasodilatation and angiopoietin signalling (NO-Tie-mediated arteriogenesis). Therapeutic vascular remodelling paradigms may therefore require treatments that modulate blood flow to utilize endogenous VEGF, in combination with exogenous Ang1, for effective neovascularization.

Selective Pressure-Regulated Retroinfusion for Gene Therapy Application in Ischemic Heart Disease

Coronary heart disease is still the leading cause of death in industrialized nations. Even though revascularization strategies such as coronary artery bypass graft surgery, percutaneous coronary intervention and enhanced drug therapy significantly improved the outcome, about 30 % of patients develop chronic heart failure. Ischemic heart disease and heart failure are characterized by an adverse remodeling of the heart, featuring cardiomyocyte hypertrophy, increased fibrosis and capillary rarefaction. Therefore, gene therapeutic approaches for the treatment of heart failure, such as the modulating contractile function or therapeutic neovascularization, seem to be promising. To achieve an efficient transduction of the gene therapeutic agent, the time point and the application route seem to be important for the therapeutic success. In contrast to the classical systemic application regional intra-coronary application offers the possibility of higher transduction efficacy in the target area accompanied by a reduced off-target contamination. Antegrade delivery however, may be impaired by coronary heart disease, such as stenosis or occlusion of a coronary artery. Coronary veins appear not to be affected and might therefore be the preferable application route for gene therapy. For an effective and safe retrograde application in gene therapy, selective catheterization of the coronary vein draining the target area is necessary. In addition, to avoid coronary vein injury, a pressure regulated infusion enhances safety. Therefore, a selective pressure regulation of retroinfusion (SSR) seems to be a favorable approach for gene therapy transduction in combination with reduced systemic contamination.

Limb ischemia and vessel regeneration: Is there a role for VEGF?

Vascular endothelial growth factor (VEGF), as an endothelial cell-specific mitogen, is crucial for new blood vessels formation. Atherosclerosis affecting the cardiovascular system causes ischemia and functio laesa in tissues supplied by the occluded vessels. When such a situation occurs in the lower extremities, it causes critical limb ischemia (CLI) often requiring leg amputation. Low oxygen tension leads to upregulation of hypoxia-regulated genes (i.e. VEGF), that should help to restore the impaired blood flow. In CLI these rescue mechanisms are, however, often inefficient. Moreover, there are many contradictory reports showing either induction, no changes or even down-regulation of VEGF in specimens taken from patients with CLI, as well as in samples collected from animals subjected to hindlimb ischemia. Additionally, taking into account numerous experimental and clinical data demonstrating rather insufficient therapeutic potential of VEGF, we called into question the role of this protein in limb ischemia and vessel regeneration. In this review we are also summarizing several aspects which can influence VEGF expression and its measurement in the ischemic tissues.

Suppression of oxidative stress in endothelial progenitor cells promotes angiogenesis and improves cardiac function following myocardial infarction in diabetic mice

Myocardial infarction is a major contributor to morbidity and mortality in diabetes, which is characterized by inadequate angiogenesis and consequent poor blood reperfusion in the diabetic ischemic heart. The aim of the present study was to investigate the effect that oxidative stress in endothelial progenitor cells (EPCs) has on cardiac angiogenesis in diabetic mice. EPCs derived from diabetic mice revealed reductions in superoxide dismutase (SOD) expression levels and activity compared with those from normal mice. An endothelial tube formation assay showed that angiogenesis was markedly delayed for diabetic EPCs, compared with normal controls. EPCs subjected to various pretreatments were tested as a cell therapy in a diabetic mouse model of myocardial infarction. Induction of oxidative stress in normal EPCs by H₂O₂ or small interfering RNA-mediated knockdown of SOD reduced their angiogenic activity in the ischemic myocardium of the diabetic mice. Conversely, cell therapy using EPCs from diabetic mice following SOD gene overexpression or treatment with the antioxidant Tempol normalized their ability to promote angiogenesis. These results indicate that decreased expression levels of SOD in EPCs contribute to impaired angiogenesis. In addition, normalization of diabetic EPCs by ex vivo SOD gene therapy accelerates the ability of the EPCs to promote angiogenesis and improve cardiac function when used as a cell therapy following myocardial infarction in diabetic mice.

Long-term safety and stability of angiogenesis induced by balanced single-vector co-expression of PDGF-BB and VEGF164 in skeletal muscle

Therapeutic angiogenesis by growth factor delivery is an attractive treatment strategy for ischemic diseases, yet clinical efficacy has been elusive. The angiogenic master regulator VEGF-A can induce aberrant angiogenesis if expressed above a threshold level. Since VEGF remains localized in the matrix around expressing cells, homogeneous dose distribution in target tissues is required, which is challenging. We found that co-expression of the pericyte-recruiting factor PDGF-BB at a fixed ratio with VEGF from a single bicistronic vector ensured normal angiogenesis despite heterogeneous high VEGF levels. Taking advantage of a highly controlled gene delivery platform, based on monoclonal populations of transduced myoblasts, in which every cell stably produces the same amount of each factor, here we rigorously investigated a) the dose-dependent effects, and b) the long-term safety and stability of VEGF and PDGF-BB co-expression in skeletal muscle. PDGF-BB co-expression did not affect the normal angiogenesis by low and medium VEGF doses, but specifically prevented vascular tumors by high VEGF, yielding instead normal and mature capillary networks, accompanied by robust arteriole formation. Induced angiogenesis persisted unchanged up to 4 months, while no tumors appeared. Therefore, PDGF-BB co-expression is an attractive strategy to improve safety and efficacy of therapeutic angiogenesis by VEGF gene delivery.

Negative pressure wound therapy promotes vessel destabilization and maturation at various stages of wound healing and thus influences wound prognosis

Negative pressure wound therapy (NPWT) has been observed to accelerate the wound healing process in humans through promoting angiogenesis. However, the potential biological effect and relevant molecular mechanisms, including microvessel destabilization, regression and endothelial cell proliferation in the early stage (1–3 days), and the neovascular stabilization and maturation in the later stage (7–15 days), have yet to be fully elucidated. The current study aimed to research the potential effect of NPWT on angiogenesis and vessel maturation, and investigate relevant association between mature microvessels and wound prognosis, as well as the regulatory mechanisms in human wound healing. Patients in the present study (n=48) were treated with NPWT or a petrolatum gauze, and relevant growth factors and vessel changes were detected using various experimental methods. NPWT increased the expression levels of angiogenin-2 (Ang-2), and decreased the expression levels of Ang-1 and ratios of Ang-1/Ang-2 in the initial stages of wound healing. However, in the latter stages of wound healing, NPWT increased the expression levels of Ang-1 and ratios of Ang-1/Ang-2, as well as the phosphorylation level of tyrosine kinase receptor-2. Consequently, microvessel pericyte coverage was gradually elevated, and the basement membrane was gradually supplied with new blood at the later stage of wound healing. In conclusion, NPWT may preferentially stimulate microvessel destabilization and regression in the early stage of wound healing, and as a consequence, increase angiogenesis. Subsequently, in the later stage of wound healing, NPWT may preferentially promote microvessel stabilization, thereby promoting microvessel maturation in human wounds through the angiogenin/tyrosine kinase receptor-2 signaling pathway. The results of the present study results demonstrated that NPWT was able to accelerate wound healing speed, and thus influence wound prognosis, as a result of an abundance of mature microvessels in human wounds.

Cardiac shockwave therapy improves myocardial function in patients with refractory coronary artery disease by promoting VEGF and IL-8 secretion to mediate the proliferation of endothelial progenitor cells

Cardiac shockwave therapy (CSWT) is a potential and effective remedy to promote revascularization in the ischemic myocardium of patients with refractory coronary heart disease (CHD). The technique is both safe and non-invasive; however, the underlying molecular mechanism remains unclear. The aim of this study was to evaluate the efficacy of CSWT in treating CHD patients and investigate a potential mechanism. A total of 26 patients with CHD were enrolled in the study, and CSWT was performed over a 3-month period. The efficacy of CSWT was assessed using several clinical parameters. Peripheral blood (PB) was collected prior to and following treatment. The number of circulating endothelial progenitor cells (EPCs) in the PB was counted using a flow cytometer, and the levels of vascular endothelial growth factor (VEGF), interleukin-8 (IL-8), stromal cell-derived factor 1 and matrix metalloproteinase 9 in the PB were analyzed. Mononuclear cells were isolated from the PB and cultured in vitro. The EPCs and EPC-colony forming units (EPC-CFUs) in the PB mononuclear cell culture were counted using an inverted phase contrast microscope. Following CSWT, the tested clinical parameters were significantly improved. The levels of circulating EPCs, VEGF and IL-8 in the PB were significantly increased, as were the EPCs and EPC-CFUs from the PB mononuclear cell culture. We suggest that EPC proliferation, mediated by VEGF and IL-8 secretion, may be among the potential mechanisms associated with CSWT.

Heme Oxygenase-1 Gene Therapy Provides Cardioprotection Via Control of Post-Ischemic Inflammation: An Experimental Study in a Pre-Clinical Pig Model

BACKGROUND

Heme oxygenase-1 (HO-1) is an inducible stress-responsive enzyme converting heme to bilirubin, carbon monoxide, and free iron, which exerts anti-inflammatory and antiapoptotic effects. Although efficient cardioprotection after HO-1 overexpression has been reported in rodents, its role in attenuating post-ischemic inflammation is unclear.

OBJECTIVES

This study assessed the efficacy of recombinant adenoassociated virus (rAAV)-encoding human heme oxygenase-1 (hHO-1) in attenuating post-ischemic inflammation in a murine and a porcine ischemia/reperfusion model.

METHODS

Murine ischemia was induced by 45 min of left anterior descending occlusion, followed by 24 h of reperfusion and functional as well as fluorescent-activated cell sorting analysis. Porcine hearts were subjected to 60 min of ischemia and 24h of reperfusion before hemodynamic and histologic analyses were performed.

RESULTS

Human microvascular endothelial cells transfected with hHO-1 displayed an attenuated interleukin-6 and intercellular adhesion molecule 1 expression, resulting in reduced monocytic THP-1 cell recruitment in vitro. In murine left anterior descending occlusion and reperfusion, the post-ischemic influx of CD45(+) leukocytes, Ly-6G(+) neutrophils, and Ly-6C(high) monocytes was further exacerbated in HO-1-deficient hearts and reversed by rAAV.hHO-1 treatment. Conversely, in our porcine model of ischemia, the post-ischemic influx of myeloperoxidase-positive neutrophils and CD14(+) monocytes was reduced by 49% and 87% after rAAV.hHO-1 transduction, similar to hHO-1 transgenic pigs. Functionally, rAAV.hHO-1 and hHO-1 transgenic left ventricles displayed a smaller loss of ejection fraction than control animals.

CONCLUSIONS

Whereas HO-1 deficiency exacerbates post-ischemic cardiac inflammation in mice, hHO-1 gene therapy attenuates inflammation after ischemia and reperfusion in murine and porcine hearts. Regional hHO-1 gene therapy provides cardioprotection in a pre-clinical porcine ischemia/reperfusion model.

Galectin-2 induces a proinflammatory, anti-arteriogenic phenotype in monocytes and macrophages

Galectin-2 is a monocyte-expressed carbohydrate-binding lectin, for which increased expression is genetically determined and associated with decreased collateral arteriogenesis in obstructive coronary artery disease patients. The inhibiting effect of galectin-2 on arteriogenesis was confirmed in vivo, but the mechanism is largely unknown. In this study we aimed to explore the effects of galectin-2 on monocyte/macrophage phenotype in vitro and vivo, and to identify the receptor by which galectin-2 exerts these effects. We now show that the binding of galectin-2 to different circulating human monocyte subsets is dependent on monocyte surface expression levels of CD14. The high affinity binding is blocked by an anti-CD14 antibody but not by carbohydrates, indicating a specific protein-protein interaction. Galectin-2 binding to human monocytes modulated their transcriptome by inducing proinflammatory cytokines and inhibiting pro-arteriogenic factors, while attenuating monocyte migration. Using specific knock-out mice, we show that galectin-2 acts through the CD14/toll-like receptor (TLR)-4 pathway. Furthermore, galectin-2 skews human macrophages to a M1-like proinflammatory phenotype, characterized by a reduced motility and expression of an anti-arteriogenic cytokine/growth factor repertoire. This is accompanied by a switch in surface protein expression to CD40-high and CD206-low (M1). In a murine model we show that galectin-2 administration, known to attenuate arteriogenesis, leads to increased numbers of CD40-positive (M1) and reduced numbers of CD206-positive (M2) macrophages surrounding actively remodeling collateral arteries. In conclusion galectin-2 is the first endogenous CD14/TLR4 ligand that induces a proinflammatory, non-arteriogenic phenotype in monocytes/macrophages. Interference with CD14-Galectin-2 interaction may provide a new intervention strategy to stimulate growth of collateral arteries in genetically compromised cardiovascular patients.

Internal ribosome entry site-based vectors for combined gene therapy

Gene therapy appears as a promising strategy to treat incurable diseases. In particular, combined gene therapy has shown improved therapeutic efficiency. Internal ribosome entry sites (IRESs), RNA elements naturally present in the 5’ untranslated regions of a few mRNAs, constitute a powerful tool to co-express several genes of interest. IRESs are translational enhancers allowing the translational machinery to start protein synthesis by internal initiation. This feature allowed the design of multi-cistronic vectors expressing several genes from a single mRNA. IRESs exhibit tissue specificity, and drive translation in stress conditions when the global cell translation is blocked, which renders them useful for gene transfer in hypoxic conditions occurring in ischemic diseases and cancer. IRES-based viral and non viral vectors have been used successfully in preclinical and clinical assays of combined gene therapy and resulted in therapeutic benefits for various pathologies including cancers, cardiovascular diseases and degenerative diseases.

Thymosin-β4-mediated therapeutic neovascularization: role of the PI3K/AKT pathway

OBJECTIVES

Thymosin β4 (Tβ4) is known to have pro-angogenic abilities in vitro and in vivo, and its cardioprotective effect is PI3/AKT-dependent. Tβ4-induced vessel formation requires transcriptional activation via the MRTF/SRF pathway. However, the relevance of PI3/AKT signaling for Tβ4-induced angiogenesis remains unclear. Here, we analyzed the PI3K/AKT cascade after Tβ4 transduction in models of chronic hindlimb ischemia.

METHODS

Tube formation assays of endothelial cells transfected with Tβ4 ± AKT-dn or PI3Kα/Rho inhibition were performed. In mice, rAAV.Tβ4 was injected (intramuscular [i.m.]) 14 days before femoral artery ligation. In addition, either rAAV.AKT-dn was co-applied or Rho/PI3K/AKT pathways were inhibited. Capillary density and hindlimb perfusion were obtained. In rabbits, chronic ischemia was induced by femoral artery excision and subsequent i.m. injection of rAAV.Tβ4 ± rAAV.AKT-dn. Analyses of capillary density, collateral formation and perfusion were performed.

RESULTS

Tβ4-induced ring formation was blunted by inhibiting the Rho-kinase (ROCK) or the PI3K/AKT pathway. In vivo, Tβ4 transduction induced angiogenesis and perfusion, an effect abrogated by inhibition of Rho-signaling, or PI3Kα/AKT. In the rabbit model, inhibition of AKT in the lower limb not only abolished angiogenesis but also collateral formation.

CONCLUSION

Tβ4 requires PI3Kα/AKT pathway signaling for induction of therapeutic neovascularization in ischemic limb disease.

Adeno-associated virus vectors as therapeutic and investigational tools in the cardiovascular system

The use of vectors based on the small parvovirus adeno-associated virus has gained significant momentum during the past decade. Their high efficiency of transduction of postmitotic tissues in vivo, such as heart, brain, and retina, renders these vectors extremely attractive for several gene therapy applications affecting these organs. Besides functional correction of different monogenic diseases, the possibility to drive efficient and persistent transgene expression in the heart offers the possibility to develop innovative therapies for prevalent conditions, such as ischemic cardiomyopathy and heart failure. Therapeutic genes are not only restricted to protein-coding complementary DNAs but also include short hairpin RNAs and microRNA genes, thus broadening the spectrum of possible applications. In addition, several spontaneous or engineered variants in the virus capsid have recently improved vector efficiency and expanded their tropism. Apart from their therapeutic potential, adeno-associated virus vectors also represent outstanding investigational tools to explore the function of individual genes or gene combinations in vivo, thus providing information that is conceptually similar to that obtained from genetically modified animals. Finally, their single-stranded DNA genome can drive homology-directed gene repair at high efficiency. Here, we review the main molecular characteristics of adeno-associated virus vectors, with a particular view to their applications in the cardiovascular field.

SDF-1 fused to a fractalkine stalk and a GPI anchor enables functional neovascularization

The facilitated recruitment of vascular progenitor cells (VPCs) to ischemic areas might be a therapeutic target for neovascularization and repair. However, efficient and directed attraction of VPCs remains a major challenge in clinical application. To enhance VPC homing, we developed a fusion protein (S1FG), based on the biology of stroma-derived factor-1/CXCL12 and the mucin backbone taken from fractalkine/CXCL12. A GPI-anchor was included to link the fusion-protein to the cell surface. HUVECs transfected with S1FG were capable of increasing firm adhesion of CXCR4+-mononuclear cells (THP-1) under shear stress conditions in vitro. In an in vivo rabbit model of chronic hind limb ischemia, local S1FG application enhanced the recruitment of adoptively transferred embryonic EPCs (eEPCs) to the ischemic muscles 2.5-fold. S1FG combined with eEPC(low) (2 × 10(6)) yielded similar capillary growth as eEPC(high) (5 × 10(6)) alone. Compared to controls, collateral formation was increased in the S1FG eEPC(low) group, but not the eEPC(high) group without S1FG, whereas perfusion was found enhanced in both groups. In addition, S1FG also increased collateral formation and flow when combined with AMD3100 treatment, to increase circulating levels of endogenous VPC. These data demonstrate that the fusion protein S1FG is capable of enhancing the recruitment of exogenously applied or endogenously mobilized progenitor cells to sites of injury. Recombinant versions of S1FG applied via catheters in combination with progenitor cell mobilization may be useful in the treatment of chronic ischemic syndromes requiring improved perfusion.

VEGF-B: a more balanced approach toward cardiac neovascularization?

There is an urgent need for new pharmacologic approaches to combat the clinical consequences of ischemic cardiomyopathy. In this issue of EMBO Molecular Medicine, Kivelä et al show that transgenic expression of VEGF-B in the rat heart leads to expansion of the coronary arterial tree and an increase in functional coronary reserve, accompanied by a shift in myocardial metabolism from fatty acid to glucose utilization. See also: R Kivelä et al (March 2014)

The bottleneck stent model for chronic myocardial ischemia and heart failure in pigs

A large animal model of chronic myocardial ischemia and heart failure is crucial for the development of novel therapeutic approaches. In this study we developed a novel percutaneous one- and two-vessel model for chronic myocardial ischemia using a stent coated with a polytetrafluoroethylene tube formed in a bottleneck shape. The bottleneck stent was implanted in the proximal left anterior descending (LAD) or proximal circumflex artery (LCX), or in both proximal LCX and mid LAD 1 wk later (2-vessel model), and pigs were followed for 4–5 wk. Ejection fraction (EF), infarct size, collateral growth, and myocardial perfusion were assessed. Pigs were given antiarrhythmic medication to prevent sudden death. The occlusion time of the bottleneck stent and the timing of myocardial infarction could be modulated by the duration of antiplatelet medication. Fractional flow reserve measurements and positron emission tomography imaging showed severe ischemia after bottleneck stenting covering over 50% of the left ventricle in the proximal LAD model. Complete coronary occlusion was necessary for significant collateral growth, which mostly had occurred already during the first wk after the stent occlusion. Dynamic and competitive collateral growth patterns were observed. EF declined from 64 to 41% in the LCX model and to 44% in the LAD model 4 wk after stenting with 12 and 21% infarcted left ventricle in the LCX and LAD models, respectively. The mortality was 32 and 37% in the LCX and LAD models but very (71%) high in the two-vessel disease model. The implantation of a novel bottleneck stent in the proximal LAD or LCX is a novel porcine model of reversible myocardial ischemia (open stent) and ischemic heart failure (occluded stent) and is feasible for the development of new therapeutic approaches.

Repetitive myocardial ischemia promotes coronary growth in the adult mammalian heart

BACKGROUND

Coronary artery disease and ischemic cardiomyopathy represent the leading cause of heart failure and continue to grow at exponential rates. Despite widespread availability of coronary bypass surgery and percutaneous coronary intervention, subsequent ischemic events and progression to heart failure continue to be common occurrences. Previous studies have shown that a subgroup of patients develop collateral blood vessels that serve to connect patent and occluded arteries and restore perfusion to ischemic territories. The presence of coronary collaterals has been correlated with improved clinical outcomes; however, the molecular mechanisms governing this process remain largely unknown.

METHODS AND RESULTS

To date, no mouse models of coronary arterial growth have been described. Using a closed-chest model of myocardial ischemia, we have demonstrated that brief episodes of repetitive ischemia are sufficient to promote the growth of both large coronary arteries and the microvasculature. Induction of large coronary artery and microvascular growth resulted in improvements in myocardial perfusion after prolonged ischemia and protected from subsequent myocardial infarction. We further show that repetitive ischemia did not lead to increased expression of classic proangiogenic factors but instead resulted in activation of the innate immune system and recruitment of macrophages to growing blood vessels.

CONCLUSIONS

These studies describe a novel model of coronary angiogenesis and implicate the cardiac macrophage as a potential mediator of ischemia-driven coronary growth.

Tongxinluo Improves Cardiac Function and Ameliorates Ventricular Remodeling in Mice Model of Myocardial Infarction through Enhancing Angiogenesis

Background. Myocardial infarction (MI) is a major cause of morbidity and mortality in the world. Tongxinluo (TXL) is a traditional Chinese compound prescription which has cardioprotective functions. The present study was aimed to determine the effect of TXL on postischemic cardiac dysfunction and cardiac remodeling and to elucidate the underlying mechanisms. Methods and Results. MI was performed by ligation of left anterior descending coronary artery (LAD) in male adult mice. Mice were randomly divided into four groups: (1) sham group (Sham); (2) MI-control group (Control); (3) MI-low dose TXL group (TXL-L); and (4) MI-high dose TXL (TXL-H) group. Compared with the control group, TXL treatment restored cardiac function, increased revascularization, attenuated cardiomyocyte apoptosis, and reduced interstitial fibrosis. TXL treatment increased the phosphorylation of Akt, extracellular signal regulated kinase (ERK), and endothelial nitric oxide synthase (eNOS); the expression of phosphatidylinositol3-kinase (PI3K), hypoxia-inducible factors 1α (HIF-1α), and vascular endothelial growth factor (VEGF); and the DNA binding activity of HIF-1α after MI. Conclusion. TXL may improve cardiac function and ameliorate cardiac remodeling by increasing neovascularization through enhancing the phosphorylation of Akt and ERK, the expression and activity of HIF-1α, and the protein level of VEGF and p-eNOS.

Arteriogenic therapy based on simultaneous delivery of VEGF-A and FGF4 genes improves the recovery from acute limb ischemia

Background

Gene therapy stimulating the growth of blood vessels is considered for the treatment of peripheral and myocardial ischemia. Here we aimed to achieve angiogenic synergism between vascular endothelial growth factor-A (VEGF-A, VEGF) and fibroblast growth factor 4 (FGF4) in murine normoperfused and ischemic limb muscles.

Methods

Adeno-associated viral vectors (AAVs) carrying β-galactosidase gene (AAV-LacZ), VEGF-A (AAV-VEGF-A) or two angiogenic genes (AAV-FGF4-IRES-VEGF-A) were injected into the normo-perfused adductor muscles of C57Bl/6 mice. Moreover, in a different experiment, mice were subjected to unilateral hindlimb ischemia by femoral artery ligation followed by intramuscular injections of AAV-LacZ, AAV-VEGF-A or AAV-FGF4-IRES-VEGF-A below the site of ligation. Post-ischemic blood flow recovery was assessed sequentially by color laser Doppler. Mice were monitored for 28 days.

Results

VEGF-A delivered alone (AAV-VEGF-A) or in combination with FGF4 (AAV-FGF4-IRES-VEGF-A) increased the number of capillaries in normo-perfused hindlimbs when compared to AAV-LacZ. Simultaneous overexpression of both agents (VEGF-A and FGF4) stimulated the capillary wall remodeling in the non-ischemic model. Moreover, AAV-FGF4-IRES-VEGF-A faster restored the post-ischemic foot blood flow and decreased the incidence of toe necrosis in comparison to AAV-LacZ.

Conclusions

Synergy between VEGF-A and FGF4 to produce stable and functional blood vessels may be considered a promising option in cardiovascular gene therapy.

Pleiotrophin gene therapy for peripheral ischemia: evaluation of full-length and truncated gene variants

Pleiotrophin (PTN) is a growth factor with both pro-angiogenic and limited pro-tumorigenic activity. We evaluated the potential for PTN to be used for safe angiogenic gene therapy using the full length gene and a truncated gene variant lacking the domain implicated in tumorigenesis. Mouse myoblasts were transduced to express full length or truncated PTN (PTN or T-PTN), along with a LacZ reporter gene, and injected into mouse limb muscle and myocardium. In cultured myoblasts, PTN was expressed and secreted via the Golgi apparatus, but T-PTN was not properly secreted. Nonetheless, no evidence of uncontrolled growth was observed in cells expressing either form of PTN. PTN gene delivery to myocardium, and non-ischemic skeletal muscle, did not result in a detectable change in vascularity or function. In ischemic hindlimb at 14 days post-implantation, intramuscular injection with PTN-expressing myoblasts led to a significant increase in skin perfusion and muscle arteriole density. We conclude that (1) delivery of the full length PTN gene to muscle can be accomplished without tumorigenesis, (2) the truncated PTN gene may be difficult to use in a gene therapy context due to inefficient secretion, (3) PTN gene delivery leads to functional benefit in the mouse acute ischemic hindlimb model.

Early vessel destabilization mediated by Angiopoietin-2 and subsequent vessel maturation via Angiopoietin-1 induce functional neovasculature after ischemia

Background

We assessed whether Angiopoietin-2 (Ang2), a Tie2 ligand and partial antagonist of Angiopoietin-1 (Ang1), is required for early vessel destabilization during postischemic angiogenesis, when combined with vascular growth factors.

Methods

In vitro, matrigel co-cultures assessed endothelial-cell tube formation and pericyte recruitment after stimulation of VEGF-A, Apelin (APLN), Ang1 with or without Ang2. In a murine hindlimb ischemia model, adeno-associated virus (rAAV, 3×10¹² virusparticles) transduction of VEGF-A, APLN and Ang1 with or without Ang2 (continuous or early expression d0-3) was performed intramuscularly (d-14). Femoral artery ligation was performed at d0, followed by laser doppler perfusion meassurements (LDI) 7 and 14. At d7 (early timepoint) and d14 (late timepoint), histological analysis of capillary/muscle fiber ratio (CMF-R, PECAM-1) and pericyte/capillary ratio (PC-R, NG2) was performed.

Results

In vitro, VEGF-A, APLN and Ang1 induced ring formation, but only APLN and Ang1 recruited pericytes. Ang2 did not affect tube formation by APLN, but reduced pericyte recruitment after APLN or Ang1 overexpression. In vivo, rAAV.VEGF-A did not alter LDI-perfusion at d14, consistent with an impaired PC-R despite a rise in CMF-R. rAAV.APLN improved perfusion at d14, with or without continuous Ang2, increasing CMF-R and PC-R. rAAV.Ang1 improved perfusion at d14, when combined with rAAV.Ang2 (d0-3), accompanied by an increased CMF-R and PC-R.

Conclusion

The combination of early vessel destabilization (Ang2 d0-3) and continuous Ang1 overexpression improves hindlimb perfusion, pointing to the importance of early vessel destabilization and subsequent vessel maturation for enhanced therapeutic neovascularization.

Advances in growth factor delivery for therapeutic angiogenesis

Therapeutic angiogenesis is a new revascularization strategy involving the administration of growth factors to induce new vessel formation. The biology and delivery of angiogenic growth factors involved in vessel formation have been extensively studied but success in translating the angiogenic capacity of growth factors into benefits for vascular disease patients is still limited. This could be attributed to issues related to patient selection, growth factor delivery methods or lack of vessel maturation. Comprehensive understanding of the cellular and molecular cross-talk during the different stages of vascular development is needed for the design of efficient therapeutic strategies. The presentation of angiogenic factors either in series or in parallel using a strategy that mimics physiological events, such as concentration and spatio-temporal profiles, is an immediate requirement for functional blood vessel formation. This review provides an overview of the recent delivery strategies of angiogenic factors and discusses targeting neovascular maturation as a promising approach to induce stable and functional vessels for therapeutic angiogenesis.

Cell and gene therapy approaches for cardiac vascularization

Despite encouraging preclinical results for therapeutic angiogenesis in ischemia, a suitable approach providing sustained, safe and efficacious vascular growth in the heart is still lacking. Vascular Endothelial Growth Factor (VEGF) is the master regulator of angiogenesis, but it also can easily induce aberrant and dysfunctional vascular growth if its expression is not tightly controlled. Control of the released level in the microenvironment around each cell in vivo and its distribution in tissue are critical to induce stable and functional vessels for therapeutic angiogenesis. The present review discusses the limitations and perspectives of VEGF gene therapy and of different cell-based approaches for the implementation of therapeutic angiogenesis in the treatment of cardiac ischemia.