Vascular gene delivery of anticoagulants by transplantation of retrovirally-transduced endothelial progenitor cells

Cyclic Stretch Induces Vascular Smooth Muscle Cells to Secrete Connective Tissue Growth Factor and Promote Endothelial Progenitor Cell Differentiation and Angiogenesis

Endothelial progenitor cells (EPCs) play a vital role in endothelial repair following vascular injury by maintaining the integrity of endothelium. As EPCs home to endothelial injury sites, they may communicate with exposed vascular smooth muscle cells (VSMCs), which are subjected to cyclic stretch generated by blood flow. In this study, the synergistic effect of cyclic stretch and communication with neighboring VSMCs on EPC function during vascular repair was investigated. In vivo study revealed that EPCs adhered to the injury site and were contacted to VSMCs in the Sprague-Dawley (SD) rat carotid artery injury model. In vitro, EPCs were cocultured with VSMCs, which were exposed to cyclic stretch at a magnitude of 5% (which mimics physiological stretch) and a constant frequency of 1.25 Hz for 12 h. The results indicated that stretched VSMCs modulated EPC differentiation into mature endothelial cells (ECs) and promoted angiogenesis. Meanwhile, cyclic stretch upregulated the mRNA expression and secretion level of connective tissue growth factor (CTGF) in VSMCs. Recombinant CTGF (r-CTGF) treatment promoted endothelial differentiation of EPCs and angiogenesis, and increased their protein levels of FZD8 and β-catenin. CTGF knockdown in VSMCs inhibited cyclic stretch-induced EPC differentiation into ECs and attenuated EPC tube formation via modulation of the FZD8/β-catenin signaling pathway. FZD8 knockdown repressed endothelial differentiation of EPCs and their angiogenic activity. Wnt signaling inhibitor decreased the endothelial differentiation and angiogenetic ability of EPCs cocultured with stretched VSMCs. Consistently, an in vivo Matrigel plug assay demonstrated that r-CTGF-treated EPCs exhibited enhanced angiogenesis; similarly, stretched VSMCs also induced cocultured EPC differentiation toward ECs. In a rat vascular injury model, r-CTGF improved EPC reendothelialization capacity. The present results indicate that cyclic stretch induces VSMC-derived CTGF secretion, which, in turn, activates FZD8 and β-catenin to promote both differentiation of cocultured EPCs into the EC lineage and angiogenesis, suggesting that CTGF acts as a key intercellular mediator and a potential therapeutic target for vascular repair.

Platelet-derived microvesicles promote endothelial progenitor cell proliferation in intimal injury by delivering TGF-β1

Intimal injury is an early stage of several cardiovascular diseases. Endothelial progenitor cells (EPCs) play a significant role in endothelial repair following vascular injury. Once the intima is damaged, EPCs are mobilized from the bone marrow to the injury site. Meanwhile, the injury to the intimal surface triggers platelet degranulation, aggregation, and adhesion to the damaged endothelium, and exposed collagen stimulates platelet to secrete platelet-derived microvesicles (PMVs). However, the role of PMVs in EPC function during this process remains unknown. In an in vivo study, EPCs and platelets were found to adhere to the injury site in Sprague-Dawley (SD) rat vascular injury model. In vitro, collagen stimulation induced the release of PMVs, and collagen-activated PMVs (ac.PMVs) significantly promoted EPC proliferation. Transforming growth factor-β1 (TGF-β1) content was increased in ac.PMVs. Activated PMVs significantly upregulated Smad3 phosphorylation in EPCs and increased Smad3 nuclear translocation from the cytoplasm. TGF-β1 knockdown ac.PMVs downregulated EPC proliferation. Recombinant TGF-β1 enhanced EPC proliferation. The TGF-β1 inhibitor SB431542 significantly repressed the intracellular signal triggered by ac.PMVs. Furthermore, the Smad3-specific phosphorylation inhibitor SIS3 effectively reversed the cell proliferation induced by ac.PMVs. Smad3 translocated to the nucleus and enhanced EPC proliferation via its downstream genes tenascin C (TNC), CDKN1A, and CDKN2A. r-TGF-β1 promoted reendothelialization and EPC proliferation in vivo. Our data demonstrate that activated PMVs deliver TGF-β1 from collagen-activated platelets to EPCs, which in turn activates Smad3 phosphorylation and regulates TNC, CDKN1A, and CDKN2A expression to promote EPC proliferation, suggesting that PMVs act as a key transporter and a potential therapeutic target for vascular injury.

Activating α7nAChRs enhances endothelial progenitor cell function partially through the JAK2/STAT3 signaling pathway

Microvascular injury is a common pathological process in ischemia-reperfusion injury. Endothelial progenitor cells (EPCs) are vital cells for angiogenesis and endothelial repair. These cells can home to injury sites and secrete angiogenic growth factors. α7nAChRs are pivotal in cholinergic angiogenesis, which is associated with endothelial cells and EPCs. Our study was designed to determine whether activating α7nAChRs enhances the function of EPCs and to explore the underlying mechanism. EPCs were derived from the bone marrow of male Sprague-Dawley rats and treated with an α7nAChR agonist (PNU282987), an α7nAChR antagonist (MLA) and a JAK2 antagonist (AG490). We then assayed the angiogenic abilities of the EPCs, including proliferation ability, adhesion ability, migration ability and in vitro tube formation ability. The levels of total JAK2 (t-JAK2), phosphorylated JAK2 (p-JAK2), total STAT3 (t-STAT3) and phosphorylated STAT3 (p-STAT3) were estimated by western blot analysis. PNU282987 treatment facilitated the angiogenic abilities of EPCs compared with the control regimen. The western blot data suggested that PNU282987 increased the levels of p-JAK2 and p-STAT3. However, the differences in t-JAK2 levels and t-STAT3 levels between the agonist-treated group and the control group were not significant. Moreover, treating EPCs with AG490 reduced STAT3 phosphorylation and attenuated the PNU282987-induced enhancement of EPCs. We demonstrated that activating α7nAChRs can enhance EPC functions partially through the JAK2/STAT3 signaling pathway. This study reveals that α7nAChRs are potential therapeutic targets for angiogenesis and that the JAK2/STAT3 pathway plays a vital role in the associated therapeutic mechanism.

Endothelial Progenitor Cells for Ischemic Stroke: Update on Basic Research and Application

Ischemic stroke is one of the leading causes of human death and disability worldwide. So far, ultra-early thrombolytic therapy is the most effective treatment. However, most patients still live with varying degrees of neurological dysfunction due to its narrow therapeutic time window. It has been confirmed in many studies that endothelial progenitor cells (EPCs), as a kind of adult stem cells, can protect the neurovascular unit by repairing the vascular endothelium and its secretory function, which contribute to the recovery of neurological function after an ischemic stroke. This paper reviews the basic researches and clinical trials of EPCs especially in the field of ischemic stroke and addresses the combination of EPC application with new technologies, including neurovascular intervention, synthetic particles, cytokines, and EPC modification, with the aim of shedding some light on the application of EPCs in treating ischemic stroke in the future.

Effects of amniotic epithelial cell transplantation in endothelial injury

Purpose

Human amniotic epithelial cells (hAECs) are promising tools for endothelial repair in vascular regenerative medicine. We hypothesized that these epithelial cells are capable of repairing the damaged endothelial layer following balloon injury of the carotid artery in adult male rats.

Results

Two days after injury, the transplanted hAECs were observed at the luminal side of the arterial wall. Then, 4 weeks after the injury, significant intimal thickening was observed in both untreated and cell implanted vessels. Constriction was decreased in both implanted and control animals. Immunohistochemical analysis showed a few surviving cells in the intact arterial wall, but no cells were observed at the site of injury. Interestingly, acetylcholine-induced dilation was preserved in the intact side and the sham-transplanted injured arteries, but it was a trend toward decreased vasodilation in the hAECs’ transplanted vessels.

Conclusion

We conclude that hAECs were able to incorporate into the arterial wall without immunosuppression, but failed to improve vascular function, highlighting that morphological implantation does not necessarily result in functional benefits and underscoring the need to understand other mechanisms of endothelial regeneration.

Local Endovascular Delivery, Gene Therapy, and Cell Transplantation for Peripheral Arterial Disease

Advances in catheter technology, gene identification, and cell biology may provide novel treatment options for patients with peripheral arterial disease (PAD) who are not candidates for standard revascularization procedures. Animal studies and recent results in human beings suggest that transfer of growth factors or regulatory genes and transplantation of progenitor cells may provide novel therapy options by inducing therapeutic angiogenesis or by inhibiting restenosis. This review will discuss the development of a variety of catheters for localized endovascular delivery, as well as the various cellular and genetic strategies that exist to restore blood flow to ischemic tissue and to reduce neointimal hyperplasia.

Combined hypoxia inducible factor-1α and homogeneous endothelial progenitor cell therapy attenuates shunt flow-induced pulmonary arterial hypertension in rabbits

BACKGROUND

Hyperkinetic pulmonary arterial hypertension (PAH) is a common complication in congenital heart disease, and affects operations, indications, and prognoses for patients. Gene-based stem cell transplantation is an alternative treatment that can attenuate PAH.

METHODS

Hyperkinetic PAH rabbit models were successfully established, using common carotid artery and jugular vein anastomosis. Endothelial progenitor cells (EPCs) were isolated from the bone marrow, cultured, and transfected with human hypoxia inducible factor-1 alpha (hHIF-1α), using lentiviruses. Two weeks after the transfected EPCs were transplanted into the rabbits, catheterization was applied to collect hemodynamic data. The hypertrophy of the right ventricle and pulmonary vascular remodeling were evaluated by measuring the right ventricle hypertrophy index, the medial wall thickness, and the medial wall area. Western blot and immunohistochemistry analyses were used to detect the expression of hHIF-1α in the pulmonary small arteries.

RESULTS

Two weeks after transplantation, systolic pulmonary arterial pressure and mean pulmonary arterial pressure were both attenuated. The hypertrophy of the right ventricle, and pulmonary vascular remodeling were reversed. Expression of hHIF-1α in the hHIF-1α-transfected EPCs that had been transplanted was high, and the number of pulmonary small arteries had increased. In addition, combined HIF-1α and homogeneous EPC therapy was more effective at attenuating PAH and increasing the density of pulmonary small arteries, compared with EPC transplantation alone.

CONCLUSIONS

Both the therapy with HIF-1α-transfected EPCs, and EPC transplantation, attenuated shunt flow-induced PAH, by means of an angiogenic effect. The former therapeutic method was more effective.

A systematic approach to the establishment and characterization of endothelial progenitor cells for gene therapy

It has been recently demonstrated that endothelial progenitor cells (EPCs) have increasing potential for gene therapy or regenerative cell therapy for cardiovascular diseases and cancer. However, current therapies involving EPCs are inefficient because of the very low level of EPCs in the available sources, for example, in blood. One solution is to derive in vitro an expanded population of EPCs from circulation. In addition, EPCs like other progenitor cells have an intrinsic predisposition of differentiating into mature cell types, for example, mature endothelial cells; therefore, establishing a sufficient amount of EPCs alongside maintaining the EPC characteristic phenotype during genetic modification and long-term culture presents a significant challenge to the field of gene and cell therapies. In this study, we have systematically investigated EPCs from different sources and used multiple parameters, including cell surface markers and a tubule formation assay to identify factors that influence the establishment, characteristics, and vector transduction capability of EPCs. Our results show the considerable promise, as well as certain limitations in the establishment and manipulation of genetically modified EPCs for gene therapy. While obtaining high transduction efficiency and robust in vitro tubule formation of EPCs using lentiviral vectors, we also observed that lentiviral vector transduction significantly altered EPC phenotype as demonstrated by an increased percentage of CD34(+) progenitor cells and increased expression of adhesion molecule CD144 (VE-cadherin). Taking account of the increased expression of CD144 reported in cancer patients, the altered expression of EPC-related markers, for example, VE-cadherin and the enrichment of CD34(+) cells, after vector transduction indicates the importance of extensive characterization and vigorous safety control of genetically modified EPCs before they are accepted for clinical use.

Actin stabilization by jasplakinolide affects the function of bone marrow-derived late endothelial progenitor cells

Background

Bone marrow-derived endothelial progenitor cells (EPCs), especially late EPCs, play a critical role in endothelial maintenance and repair, and postnatal vasculogenesis. Although the actin cytoskeleton has been considered as a modulator that controls the function and modulation of stem cells, its role in the function of EPCs, and in particular late EPCs, remains poorly understood.

Methodology/Principal Finding

Bone marrow-derived late EPCs were treated with jasplakinolide, a compound that stabilizes actin filaments. Cell apoptosis, proliferation, adhesion, migration, tube formation, nitric oxide (NO) production and endothelial NO synthase (eNOS) phosphorylation were subsequently assayed in vitro. Moreover, EPCs were locally infused into freshly balloon-injured carotid arteries, and the reendothelialization capacity was evaluated after 14 days. Jasplakinolide affected the actin distribution of late EPCs in a concentration and time dependent manner, and a moderate concentration of (100 nmol/l) jasplakinolide directly stabilized the actin filament of late EPCs. Actin stabilization by jasplakinolide enhanced the late EPC apoptosis induced by VEGF deprivation, and significantly impaired late EPC proliferation, adhesion, migration and tube formation. Furthermore, jasplakinolide attenuated the reendothelialization capacity of transplanted EPCs in the injured arterial segment in vivo. However, eNOS phosphorylation and NO production were increased in late EPCs treated with jasplakinolide. NO donor sodium nitroprusside (SNP) rescued the functional activities of jasplakinolide-stressed late EPCs while the endothelial NO synthase inhibitor L-NAME led to a further dysfunction induced by jasplakinolide in late EPCs.

Conclusions/Significance

A moderate concentration of jasplakinolide results in an accumulation of actin filaments, enhancing the apoptosis induced by cytokine deprivation, and impairing the proliferation and function of late EPCs both in vitro and in vivo. NO donor reverses these impairments, suggesting the role of NO-related mechanisms in jasplakinolide-induced EPC downregulation. Actin cytoskeleton may thus play a pivotal role in regulating late EPC function.

Treatment of murine fulminant hepatitis with genetically engineered endothelial progenitor cells

BACKGROUND & AIMS

Cell therapy has been used to attenuate liver injury. Here we evaluated whether genetic engineering of either bone marrow-derived mononuclear cells (MNC) or endothelial progenitor cells (EPC) many enhance their hepatoprotective properties.

METHODS

Mice with ConA-induced hepatitis or with lethal fulminant hepatitis resulting from administration of an adenovirus encoding CD40L (AdCD40L) received an intra-splenic injection of saline or 2 × 10(6) unmodified MNC or EPC or the same cells transduced ex vivo with an adenovirus expressing luciferase (MNCLUC and EPCLUC) or encoding the hepatoprotective cytokine cardiotrophin-1 (CT-1) (MNCCT-1 and EPCCT-1). We analyzed the extent of liver damage, the intensity of inflammatory reaction, and animal survival.

RESULTS

Luciferase immunohistochemistry showed that after injection into the spleen, the engineered cells migrated efficiently to the damaged liver. In mice with ConA hepatitis EPCCT-1, but not other forms of cell therapy, significantly decreased serum transaminases and induced more intense histological improvement than other treatments. This superior therapeutic effect was associated with upregulation of cytoprotective molecules including IGF-I and EGF, lower expression of proinflammatory cytokines, IL-1b and TNFα, and decreased granzyme B levels. In AdCD40L-induced lethal fulminant hepatitis, EPCCT-1 also exceeded other cell therapies in attenuating the expression of proinflammatory mediators and hepatic injury enabling 35.7% survival while mortality was 100% in the other treatment groups.

CONCLUSIONS

Genetic engineering of EPC to overexpress CT-1 enhances the hepatoprotective properties of EPC and constitutes a therapy that deserves consideration for acute liver failure.

Endothelial progenitor cells: a novel tool for the therapy of ischemic diseases

Circulating endothelial progenitor cells (EPCs) are believed to home to sites of neovascularization, contributing to vascular regeneration either directly via incorporation into newly forming vascular structures or indirectly via the secretion of pro-angiogenic growth factors, thereby enhancing the overall vascular and hemodynamic recovery of ischemic tissues. The therapeutic application of EPCs has been shown to be effective in animal models of ischemia, and we as well as other groups involved in clinical trials have demonstrated that the use of EPCs was safe and feasible for the treatment of critical limb ischemia and cardiovascular diseases. However, many issues in the field of EPC biology, especially in regard to the proper and unambiguous molecular characterization of these cells, still remain unresolved, hampering not only basic research but also the effective therapeutic use and widespread application of these cells. Further, recent evidence suggests that several diseases and pathological conditions are correlated with a reduction in the number and biological activity of EPCs, making the development of novel strategies to overcome the current limitations and shortcomings of this promising but still limited therapeutic tool by refinement and improvement of EPC purification, expansion, and administration techniques, a rather pressing issue.

Endothelial progenitor cells as therapeutic agents in the microcirculation: an update

This review evaluates novel beneficial effects of circulating endothelial progenitor cells (EPCs) as shown by several preclinical studies and clinical trials carried out to test the safety and feasibility of using EPCs. There are 31 registered clinical trials (and many others still ongoing) and 19 published studies. EPCs originate in the bone marrow and migrate into the bloodstream where they undergo a differentiation program leading to major changes in their antigenic characteristics. EPCs lose typical progenitor markers and acquire endothelial markers, and two important receptors, (VEGFR and CXCR-4), which recruit circulating EPCs to damaged or ischemic microcirculatory (homing to damaged tissues) beds. Overall, therapeutic angiogenesis will likely change the face of regenerative medicine in the next decade with many patients worldwide predicted to benefit from these treatments.

Endothelial lineage cell as a vehicle for systemic delivery of cancer gene therapy

A major limitation of cancer gene therapy is the difficulty of delivering a therapeutic gene to distant sites of metastatic disease. A promising strategy to address this difficulty is to use expanded ex vivo cells to produce a therapeutic protein. As with other approaches to gene therapy, this strategy is attractive when the therapeutic protein is unstable ex vivo or has a short circulating half life in vivo. The initial step to develop a cancer gene therapy using autologous cell delivery is the identification of a cell type that migrates to the tumor site, is readily available for harvesting, and is manipulated easily ex vivo. Recent evidence suggests that endothelial progenitor, precursor, and blood outgrowth endothelial cells are attracted to the tumor vasculature by its angiogenic drive. Here, we review recent advances in the study of circulating endothelial cell-mediated tumor vasculogenesis and discuss the advantages and challenges of bringing endothelial lineage-based cancer gene therapy closer to clinical application.

Transdifferentiation of bone marrow-derived endothelial progenitor cells into the smooth muscle cell lineage mediated by tansforming growth factor-beta1

OBJECTIVE

The aim of this study was to investigate the transdifferentiation of bone marrow (BM)-derived endothelial progenitor cells (EPCs) into the smooth muscle cell (SMC) lineage in vitro and in vivo.

METHODS AND RESULTS

EPCs were obtained from BM of rats and cultured on fibronectin-coated dishes for 15 days. Treatment of EPCs with transforming growth factor (TGF)-beta1 for 7 days changed morphology of EPCs, reduced the expression of endothelial markers in EPCs, induced the expression of SMC markers, and enhanced their proliferation. EPCs expressed TGF-beta receptor type II (TGF-beta RII) and TGF-beta1 induced the phosphorylation of Smad 2 in EPCs. TGF-beta1-induced transdifferentiation was specifically inhibited by neutralizing antibody against TGF-beta and gene silencing of TGF-beta RII. Local transplantation of autologous EPCs enhanced intimal hyperplasia of the balloon-injured artery on day 28. Transplanted EPCs were localized near the endothelial layer on day 14 but widely distributed within the hypertrophic neointima on day 28 differentiating toward SMC lineage. Neither expression of growth factors such as TGF-beta1 nor early inflammatory reactions within the denuded arteries were promoted by transplantation of EPCs.

CONCLUSIONS

TGF-beta1 induced the transdifferentiation of BM-derived EPCs toward SMC lineage mediated by TGF-beta RII. The augmentation of intimal hyperplasia by transplantation of EPCs was probably due to the transdifferentiation and proliferation of EPCs induced by TGF-beta1.

Transfection of HGF gene enhances endothelial progenitor cell (EPC) function and improves EPC transplant efficiency for balloon-induced arterial injury in hypercholesterolemic rats

Risk factors for coronary heart disease can reduce the number of endothelial progenitor cells (EPCs) and impair EPC function, thus hindering their utility in the treatment of cardiovascular diseases. In the present study, we began exploring the feasibility of genetic modification of EPCs with hepatocyte growth factor (HGF) to counter the effects of these risk factors and enhance the biological functions of EPCs. The effects of HGF transfection on proliferation, migration and angiogenesis of EPCs were investigated. Additionally, the role of ERK1/2 in this process was evaluated through the observation of ERK1/2 and ERK1/2 phosphorylation as well as by pharmacological analysis. Finally, we evaluated the effect of HGF-transfected EPCs (HGF-EPCs) on neointima formation after balloon-induced arterial injury in hypercholesterolemic rats. Our data showed that EPCs transfected with the HGF gene released high levels of soluble HGF protein, which were maintained for at least nine days. Transfection with HGF also enhanced the proliferative, migratory and angiogenic capabilities of EPCs, and promoted the activation of ERK1/2 without affecting its expression. ERK1/2 blockade by the chemical inhibitor PD98059 partially inhibited these effects. In hypercholesterolemic rats, HGF-EPCs homed to the site of vascular injury at a significantly higher rate than did EPCs without the exogenous HGF gene. Furthermore, systemically applied HGF-EPCs were more effective in decreasing neointima formation and increasing re-endothelialization. These data suggest that gene delivery combined with EPC transplant may be a practical and promising therapy for the prevention of neointimal formation after vascular injury.

The relative potency and safety of endothelial progenitor cells and unselected mononuclear cells for recovery from myocardial infarction and ischemia

Endothelial progenitor cells (EPCs) are a subset of the total mononuclear cell population (tMNCs) that possess an enhanced potential for differentiation within the endothelial-cell lineage. Typically, EPCs are selected from tMNCs via the expression of both hematopoietic stem-cell markers and endothelial-cell markers, such as CD34, or by culturing tMNCs in media selective for endothelial cells. Both EPCs and tMNCs participate in vascular growth and regeneration, and their potential use for treatment of myocardial injury or disease has been evaluated in early-phase clinical studies. Direct comparisons between EPCs and tMNCs are rare, but the available evidence appears to favor EPCs, particularly CD34+ cells, and the potency of EPCs may be increased as much as 30-fold through genetic modification. However, these observations must be interpreted with caution because clinical investigations of EPC therapy are ongoing. We anticipate that with continued development, EPC therapy will become a safe and effective treatment option for patients with acute myocardial infarction or chronic ischemic disease.

Endothelial progenitor cells in neovascularization of infarcted myocardium

Historically, revascularization of ischemic tissue was believed to occur through the migration and proliferation of endothelial cells in nearby tissues; however, evidence accumulated in recent years indicates that a subpopulation of adult, peripheral-blood cells, collectively referred to as endothelial progenitor cells (EPCs), can differentiate into mature endothelial cells. After ischemic insult, EPCs are believed to home to sites of neovascularization, where they contribute to vascular regeneration by forming a structural component of capillaries and by secreting angiogenic factors; new evidence indicates that EPCs can also differentiate into cardiomyocytes and smooth-muscle cells. These insights into the molecular and cellular processes of tissue formation suggest that cardiac function may be preserved after myocardial infarction by transplanting EPCs into ischemic heart tissue, thereby enhancing vascular and myocardial recovery. This therapeutic strategy has been effective in animal models of ischemic disorders, and results from randomized clinical trials suggest that cell-based strategies may be safe and feasible for treatment of myocardial infarction in humans and have provided early evidence of efficacy. However, the scarcity of EPCs in the peripheral blood and evidence that several disease states reduce EPC number and/or function have prompted the development of several strategies to overcome these limitations, such as the administration of genetically modified EPCs that overexpress angiogenic growth factors. To optimize therapeutic outcomes, researchers must continue to refine methods of EPC purification, expansion, and administration, and to develop techniques that overcome the intrinsic scarcity and phenotypic deficiencies of EPCs.

Cellular MRI and its role in stem cell therapy

Hematopoietic, stromal and organ-specific stem cells are under evaluation for therapeutic efficacy in cell-based therapies of cardiac, neurological and other disorders. It is critically important to track the location of directly transplanted or infused cells that can serve as gene carrier/delivery vehicles for the treatment of disease processes and be able to noninvasively monitor the temporal and spatial homing of these cells to target tissues. Moreover, it is also necessary to determine their engraftment efficiency and functional capability following transplantation. There are various in vivo imaging modalities used to track the movement and incorporation of administered cells. Tagging stem cells with different contrast agents can make these cells probes for different imaging modalities. Recent reports have shown that stem cells labeled with iron oxides can be used as cellular MRI probes demonstrating the cell trafficking to target tissues. In this review, we will discuss the status and future prospect of stem cell tracking by cellular MRI for cell-based therapy.

Gene and stem cell therapy in peripheral arterial occlusive disease

Abstract

Peripheral arterial occlusive disease (PAOD) is a manifestation of systemic atherosclerosis strongly associated with a high risk of cardiovascular morbidity and mortality. In a considerable proportion of patients with PAOD, revascularization either by endovascular means or by open surgery combined with best possible risk factor modification does not achieve limb salvage or relief of ischaemic rest pain. As a consequence, novel therapeutic strategies have been developed over the last two decades aiming to promote neovascularization and remodelling of collaterals. Gene and stem cell therapy are the main directions for clinical investigation concepts. For both, preclinical studies have shown promising results using a wide variety of genes encoding for growth factors and populations of adult stem cells, respectively. As a consequence, clinical trials have been performed applying gene and stem cell-based concepts. However, it has become apparent that a straightforward translation into humans is not possible. While several trials reported relief of symptoms and functional improvement, other trials did not confirm this early promise of efficacy. Ongoing clinical trials with an improved study design are needed to confirm the potential that gene and cell therapy may have and to prevent the gaps in our scientific knowledge that will jeopardize the establishment of angiogenic therapy as an additional medical treatment of PAOD. This review summarizes the experimental background and presents the current status of clinical applications and future perspectives of the therapeutic use of gene and cell therapy strategies for PAOD.

Blood-derived smooth muscle cells as a target for gene delivery

OBJECTIVE

To examine the feasibility of using blood-derived smooth muscle cells (BD-SMCs) as a target for to deliver therapeutic proteins.

MATERIALS AND METHODS

Mononuclear cells (MNC) were isolated from peripheral blood. The outgrowth colonies from MNC culture were differentiated into BD-SMCs in media containing platelet-derived growth factor BB. Phenotypic characterization of BD-SMCs was assessed by immunocytochemistry. Cell proliferation, gene transfer efficiency with a retroviral vector, apoptosis, and the biological activity of the transduced gene product from the BD-SMCs were evaluated in vitro and in vivo in comparison with vascular derived SMC (VSMCs).

RESULTS

BD-SMCs stained positive for SMC markers. No significant difference was observed between BD-SMCs and VSMCs in cell proliferation, migration, adhesiveness, and gene transfer efficiency. After BD-SMCs were transduced with a retroviral vector carrying the secreted alkaline phosphatase gene (SEAP), 174 +/- 50 mug biologically active SEAP was produced per 10(6) cells over 24 hours. After injecting 5 x 10(6) cells expressing SEAP intravenously into rabbits, SEAP concentration increased significantly in the circulation from 0.14 +/- 0.04 mug/ml to 2.34 +/- 0.16 mug/ml 3 days after cell injection (P < .01, n = 3). Circulating levels of SEAP decreased to 1.76 mug /ml 1 week later and remained at this level up to 8 weeks, then declined to pre-cell injection level at 12 weeks. VSMC in vivo gene expression data were equivalent.

CONCLUSION

BD-SMCs have similar characteristics to mature VSMCs and can be used as a novel target for gene transfer to deliver a therapeutic protein.

Genetic modification of cells for transplantation

Progress in gene therapy has produced promising results that translate experimental research into clinical treatment. Gene modification has been extensively employed in cell transplantation. The main barrier is an effective gene delivery system. Several viral vectors were utilized in end-stage differentiated cells. Recently, successful applications were described with adenovirus-associated vectors. As an alternative, embryonic stem cell- and stem cell-like systems were established for generation of tissue-specified gene-modified cells. Owing to the feasibility for genetic manipulations and the self-renewing potency of these cells they can be used in a way enabling large-scale in vitro production. This approach offers the establishment of in vitro cell culture systems that will deliver sufficient amounts of highly purified, immunoautologous cells suitable for application in regenerative medicine. In this review, the current technology of gene delivery systems to cells is recapitulated and the latest developments for cell transplantation are discussed.

Evidence for a Possible Inhibitory Interaction between the HO-1/CO- and Akt/NO-Pathways in Human Endothelial Cells

OBJECTIVE

The protective properties of heme oxygenase 1 (HO-1) give reason to study this mechanism as a potential therapeutic target for inflammatory and cardiovascular diseases. Recent evidence suggests a possible interaction between the HO-1/CO- and the protein kinase Akt/NO-pathway. This study was designed to examine the effects of continuous HO-1 overexpression in endothelial cells.

METHODS

Oncoretroviral vectors were constructed to achieve constitutive overexpression of HO-1, Akt, and green fluorescence protein in human umbilical vein endothelial cells. [(3)H]thymidine-incorporation and lipid-peroxidation were measured following exposure to heme and H(2)O(2). Expression of HO-1, Akt and its downstream-target endothelial NO-synthase were quantified by Western blot analysis. NO-synthase-activity was measured using the citrulline-conversion-assay.

RESULTS

HO-1-overexpression reduced proliferative rates and DNA-synthesis of HUVEC, but provided potent protection from oxidative stress induced by heme and H(2)O(2). Phosphorylated-Akt and eNOS was downregulated in HO-1-HUVEC. eNOS-activity was reduced in HO-1-HUVEC. Co-infection with the Akt-retrovirus restored proliferative rates and eNOS-expression and -activity.

CONCLUSION

Continuously elevated HO-1-activity protects EC from oxidative stress but inhibits Akt-mediated proliferation and eNOS-expression. This inhibitory feedback mechanism could be a limitation of HO-1 as a target for the treatment of vascular disease.

Microenvironmental regulation of biomacromolecular therapies

There is currently great interest in molecular therapies to treat various diseases, and this has prompted extensive efforts to achieve target-specific and controlled delivery of bioactive macromolecules (for example, proteins, antibodies, DNA and small interfering RNA) through the design of smart drug carriers. By contrast, the influence of the microenvironment in which the target cell resides and the effect it might have on the success of biomacromolecular therapies has been under-appreciated. The extracellular matrix (ECM) component of the cellular niche may be particularly important, as many diseases and injury disrupt the normal ECM architecture, the cell adhesion to ECM, and the subsequent cellular activities. This Review will discuss the importance of the ECM and the ECM-cell interactions on the cell response to bioactive macromolecules, and suggest how this information could lead to new criteria for the design of novel drug delivery systems.

Autologous endothelial progenitor cells transplantation promoting endothelial recovery in mice

Transplantation of endothelial progenitor cells (EPCs) restores endothelial function. The present study was designed to determine the effect of autologous EPCs transplantation on the regeneration of endothelium in mice. Mice splenectomy was performed 14 days before carotid artery injury, and mononuclear cells were isolated and cultured in endothelial growth media for 7 days. EPCs were confirmed by immunostaining (CD31, endothelial nitric oxide synthase (eNOS) and double positive for 1,1'dioctadecyl-3,3,3',3-tetramethylindocarbocyanine (DiI)-low-density lipoprotein and ulex europaeus agglutinin (UEA)). Cell counts and fluorescence-activated cell sorting for stem cell marker were performed. 1 x 10(6) 4-,6-Diamidino-2-phenylindole- labeled EPCs or saline were injected through tail vein after wire injury. Two weeks after transplantation, cell tracking and immunohistochemical staining showed homing and incorporation of labeled EPCs in injury artery. Administration of EPCs enhanced reendothelialization (P < 0.05) after 1 week and inhibition of neointima formation at 3 weeks compared with that of saline (P < 0.05, n = 6). These data demonstrate that delivery of autologous EPCs is associated with accelerated reendothelialization and reduced neointimal formation. Thus, delivery of autologous EPCs represents an important vasculoprotective approach to attenuate the response to acute vascular injury.

Endothelial progenitor cells as therapeutic vectors in cardiovascular disorders: from experimental models to human trials

Cell-based therapy approaches for the restoration of blood flow in ischemic organs has recently received growing interest. A considerable number of reports have documented the presence of circulating, bone marrow-derived endothelial progenitor cells (EPC) in adult peripheral blood. These putative cells are thought to participate in postnatal growth of new blood vessels. Mounting evidence from animal studies point to potential therapeutic applications of EPCs in the treatment of a wide range of cardiovascular (CV) disorders, while preliminary results from the pilot clinical trials still remain equivocal. Here, we review the experimental data that has accumulated so far from animal and clinical studies regarding the potential importance of EPCs. In addition, we discuss the potential hurdles as well as future options of EPC-based therapy.

Transduction of the anti-apoptotic PTD-FNK protein improves the efficiency of transplantation of bone marrow mononuclear cells

Since most transplanted cells rapidly die in an ischemic environment by hypoxia and hyponutrition, it is crucial to know how to protect transplanted cells for improving transplantation efficiency. We examined whether the transduction of an artificial anti-cell death protein (PTD-FNK) into bone marrow mononuclear cells (BM-MNCs) prevents cell death and improves the transplantation efficiency of BM-MNCs in ischemic regions. Rat bone marrow cells were prepared from the femur and tibia and cultured on dishes precoated with human fibronectin in the absence of serum. BM-MNCs transduced with PTD-FNK survived better than those without the protein (P<0.008) and retained the potential to differentiate into endothelial progenitor cells (EPCs), as judged by the uptake of an acetylated low-density lipoprotein and the ability to bind lectin. Next, we used a co-culture system comprising human umbilical vein endothelial cells (HUVECs) and fibroblasts to examine angiogenic potential. HUVECs pretreated with PTD-FNK survived and formed a blood-vessel-like structure better than untreated cells (P<0.001). When BM-MNCs expressing EGFP were transplanted into ischemic areas of a male rat ischemic hindlimb model, the cells pretreated with PTD-FNK were incorporated into blood vessel with a higher efficiency than the untreated BM-MNCs (P=0.03). BM-MNCs protected through transduction of PTD-FNK maintained their angiogenic potential. Thus, PTD-FNK improves the transplantation efficiency of BM-MNCs into ischemic regions.

Magnetically targeted endothelial cell localization in stented vessels

OBJECTIVES

A novel method to magnetically localize endothelial cells at the site of a stented vessel wall was developed. The application of this strategy in a large animal model is described.

BACKGROUND

Local delivery of blood-derived endothelial cells has been shown to facilitate vascular healing in animal models. Therapeutic utilization has been limited by an inability to retain cells in the presence of blood flow. We hypothesized that a magnetized stent would facilitate local retention of superparamagnetically labeled cells.

METHODS

Cultured porcine endothelial cells were labeled with endocytosed superparamagnetic iron oxide microspheres. A 500:1 microsphere-to-cell ratio was selected for in vivo experiments based on bromo-deoxyuridine incorporation and terminal deoxynucleotidyl transferase mediated dUTP nick end labeling assays. Stents were magnetized and implanted in porcine coronary and femoral arteries using standard interventional equipment. Labeled endothelial cells were delivered locally during transient occlusion of blood flow.

RESULTS

The delivered cells were found attached to the stent struts and were also distributed within the adjacent denuded vessel wall at 24 h.

CONCLUSIONS

Magnetic forces can be used to rapidly place endothelial cells at the site of a magnetized intravascular stent. The delivered cells are retained in the presence of blood flow and also spread to the adjacent injured vessel wall. Potential applications include delivering a cell-based therapeutic effect to the local vessel wall as well as downstream tissue.

Aldosterone Impairs Bone Marrow–Derived Progenitor Cell Formation

Aldosterone has been suggested recently to cause vascular injury by directly acting on the vasculature, in addition to causing injury by raising the blood pressure. Bone marrow–derived endothelial progenitor cells (EPCs) have been shown to exert an important role in the repair of the endothelium. In addition, cell-based therapy using EPCs is emerging as a novel therapeutic strategy for myocardial and peripheral vascular diseases. However, impaired formation and function of EPCs has been observed in patients with risk factors for cardiovascular diseases. We evaluated the possible effects of aldosterone on EPCs by examining the progenitor cell formation from bone marrow mononuclear cells ex vivo. Aldosterone (10 to 1000 nmol/L) reduced the formation of progenitor cells in a concentration-dependent manner. This effect of aldosterone was attenuated by cotreatment with spironolactone. Aldosterone reduced the mRNA levels of vascular endothelial growth factor (VEGF) receptor (VEGFR) 2 without having any effect on the production of VEGF or mRNA levels of VEGF and hepatocyte growth factor in the progenitor cells. However, the expression of stromal-derived growth factor 1 mRNA was paradoxically increased. Consistent with the downregulation of VEGFR-2, VEGF-induced phosphorylation of Akt was abolished in the progenitor cells after aldosterone treatment. N-acetylcysteine, an antioxidant, attenuated the inhibitory effects of aldosterone. These data indicate that aldosterone inhibits the formation of bone marrow–derived progenitor cells, at least partly, by attenuating VEGFR-2 expression and the subsequent Akt signaling. Reduction of aldosterone levels, blockade of mineralocorticoid receptor, and/or cotreatment with antioxidants may, therefore, enhance vascular regeneration by EPCs.

Endothelial progenitor cells: from bench to bedside

Strong evidence suggests that bone marrow-derived cells play a role in physiological and pathological blood vessel growth in the adult, both by augmenting angiogenesis through the secretion of angiogenic growth factors and by providing a rich source of progenitor cells that can differentiate into mature vascular endothelial cells. This is a true paradigm shift, since adult neovascularization processes were thought to be limited to angiogenesis. The cells that are critical to postnatal blood vessel growth – endothelial progenitor cells – may be analogous to the embryonic angioblast, in that they can circulate, proliferate and participate in the development of vascular networks by differentiating in situ, probably via the formation of cell clusters into mature endothelial cells. Therefore, initial reports have seen analogs to the process of vasculogenesis in the embryo, where the de novo synthesis of vessels occurs through the formation of blood island-like clusters, which subsequently connect and eventually form systemic vasculature. Recent work implicates precursors of endothelial cells in such processes as myocardial ischemia and infarction, limb ischemia, wound healing, atherosclerosis, endogenous endothelial repair and tumor vascularization. These new insights into the vascular biology of endothelial regeneration and repair led to the development of new cell therapeutic strategies to enhance adult neovascularization and re-endothelialization in ischemic cardiovascular diseases.

Review: application of stem cells for vascular tissue engineering

As the prevalence of vascular disease has continued to expand, the need for a suitable arterial replacement has prompted researchers to look beyond synthetic and autologous grafts toward the field of tissue engineering. Advances in vascular tissue engineering have utilized both mesenchymal and hematopoietic stem cells as a cell source in an attempt to create a fully engineered small-diameter graft. Stem cells offer enormous potential as a cell source because of their proliferative and growth potential, and the application of stem cell technology has far-reaching implications for future applications. The innovative use of stem cells for vascular tissue engineering has opened new possibilities for a fully engineered blood vessel. The purpose of this review is to summarize the current perspective on the use of stem cells for vascular tissue engineering. It focuses principally on the classes of stem cells used, techniques for differentiation scaffolding technology, and the successes and failures of models.

Local gene transduction of cyclooxygenase-1 increases blood flow in injured atherosclerotic rabbit arteries

BACKGROUND

Cyclooxygenase-1 (COX-1) is the rate-limiting component in the synthesis of prostacyclin (PGI2), an important vasodilator and antithrombotic molecule. In balloon-injured, atherosclerosis-free porcine arteries, COX-1 gene transduction increases PGI2 production, induces durable vasodilation, and reduces thrombus formation. We tested the effectiveness of COX-1 local gene transduction for the prevention of postangioplasty restenosis in atherosclerotic arteries in a hypercholesterolemic rabbit model.

METHODS AND RESULTS

We injured 1 carotid artery in 43 Watanabe heritable hyperlipidemic rabbits and performed local gene transduction using a viral vector containing the COX-1 gene (AdCOX-1, n=22) or no genes (Adnull, n=21). Three days later, AdCOX-1-treated arteries stimulated with arachidonic acid produced 100% more PGI2 (P<0.01), 400% more prostaglandin E2 (PGE2) (P<0.01), 400% more prostaglandin E1 (PGE1) (P<0.01), and 250% more cAMP (P<0.05) than Adnull-treated arteries. Twenty-eight days after treatment, Doppler sonography showed that blood flow velocity was preserved in AdCOX-1-treated arteries (ratio 0.92, injured compared with contralateral uninjured carotid artery) but reduced in Adnull-treated arteries (ratio 0.39), suggesting that AdCOX-1 prevented restenosis after injury. COX-1-transduced arteries also showed 80% greater lumen area 28 days after injury (P<0.01).

CONCLUSIONS

The effectiveness of COX-1 in preventing restenosis and preserving normal blood flow 28 days after injury results from increased lumen area caused by durable vasodilation. COX-1 efficacy correlates with an early increase in the production of PGI2, PGE2, PGE1 (known to cause vasodilation), and cAMP. These results demonstrate for the first time that COX-1 gene transduction is an effective treatment for the prevention of postangioplasty restenosis of atherosclerotic arteries under clinically relevant conditions.

Effect of tissue plasminogen activator on vascular smooth muscle cells

OBJECTIVE

Engineered overexpression of tissue plasminogen activator (tPA) in vascular cells has been proposed as a means to decrease intravascular thrombosis; however, tPA gene transfer has augmented intimal hyperplasia in vivo in some studies. The purpose of this study was to define in vitro the effect of tPA gene transfer on smooth muscle cells (SMCs).

METHODS

Human SMCs were retrovirally transduced with the tPA gene (SMCs/tPA).

RESULTS

In the absence of plasminogen, no statistical differences in proliferation, migration, and morphology were observed between SMCs/tPA and SMCs. In the presence of plasminogen, many differences became apparent. Matrix metalloproteinase-2 (MMP-2) activation was 10-fold higher in SMCs/tPA than in SMCs. This activation was inhibited by aprotinin, a plasmin inhibitor. Collagen degradation increased sevenfold in SMCs/tPA. SMCs/tPA contracted dramatically in the presence of plasminogen. This cell contraction, indicative of extracellular matrix degradation, was blocked by aprotinin and partially inhibited by MMP inhibitors. SMC/tPA-conditioned medium induced significantly more SMC proliferation. The migration of SMCs/tPA through a porous membrane significantly exceeded untransduced SMCs.

CONCLUSIONS

Over-expression of tPA in SMCs results in increased extracellular matrix degradation and can promote cell proliferation and migration. This effect is mediated via plasmin, which further activates MMP-2.

CLINICAL RELEVANCE

TPA has been clinically used as a thrombolytic agent in the treatment of acute thrombotic disorders. Transferring the tPA gene into vascular cells as a strategy of gene therapy has been proposed to enhance fibrinolytic capability and therefore inhibit thrombosis and restenosis after vascular interventions. The mechanism(s) by which tPA affects SMC proliferation and vascular remodeling has not been thoroughly characterized. This study unveils the relationship between thrombolytic activity and intimal hyperplasia by showing how the elevated expression of tPA affects the vascular remodeling. This study underscores that the overexpression of an enzyme thought beneficial to blood flow can potentially compromise blood flow by altering the biology of the cell engineered to express it. The results are important to the rational engineering of bioactive grafts with better patency. A new strategy to enhance the thrombolytic ability of a vascular surface without inducing excessive neointimal hyperplasia is proposed.

Efficient transduction of vascular endothelial cells with recombinant adeno-associated virus serotype 1 and 5 vectors

Recombinant adeno-associated virus (rAAV) has become an attractive tool for gene therapy because of its ability to transduce both dividing and nondividing cells, elicit a limited immune response, and the capacity for imparting long-term transgene expression. Previous studies have utilized rAAV serotype 2 predominantly and found that transduction of vascular cells is relatively inefficient. The purpose of the present study was to evaluate the transduction efficiency of rAAV serotypes 1 through 5 in human and rat aortic endothelial cells (HAEC and RAEC). rAAV vectors with AAV2 inverted terminal repeats containing the human alpha1-antitrypsin (hAAT) gene were transcapsidated using helper plasmids to provide viral capsids for the AAV1 through 5 serotypes. True type rAAV2 and 5 vectors encoding beta-galactosidase or green fluorescence protein were also studied. Infection with rAAV1 resulted in the most efficient transduction in both HAEC and RAEC compared to other serotypes (p < 0.001) at 7 days posttransduction. Interestingly, expression was increased in cells transduced with rAAV5 to levels surpassing rAAV1 by day 14 and 21. Transduction with rAAV1 was completely inhibited by removal of sialic acid with sialidase, while heparin had no effect. These studies are the first demonstration that sialic acid residues are required for rAAV1 transduction in endothelial cells. Transduction of rat aortic segments ex vivo and in vivo demonstrated significant transgene expression in endothelial and smooth muscle cells with rAAV1 and 5 serotype vectors, in comparison to rAAV2. These results suggest the unique potential of rAAV1 and rAAV5-based vectors for vascular-targeted gene-based therapeutic strategies.

Therapeutic uses of autologous endothelial cells for vascular disease

Endothelial cells play important structural and functional roles in vascular homoeostasis. Perturbations in endothelial cell number and function are directly involved with the initiation and progression of multiple cardiovascular diseases, including atherosclerosis, hypertension and congestive heart failure. Attempts to modify these disorders have included pharmacological strategies to improve vascular and thus endothelial function. A goal of biological approaches to these disorders is the delivery of endothelial cells that might act to provide beneficial endothelial-derived factors. However, this approach has generally been limited by the lack of readily available autologous endothelial cells for delivery. The isolation of circulation-derived endothelial progenitor cells allows for direct access to autologous endothelial cells for preclinical and clinical studies. Preclinical studies using autologous endothelial cells have demonstrated beneficial effects when delivered in animal models of vascular injury and grafting. These effects are related to the endothelial nature of the cells and may be paracrine in nature. Ongoing studies are aimed at defining the nature of these effects and optimizing delivery strategies cognizant of these mechanisms.

Therapeutic potential of endothelial progenitor cells in cardiovascular diseases

Endothelial dysfunction and cell loss are prominent features in cardiovascular disease. Endothelial progenitor cells (EPCs) originating from the bone marrow play a significant role in neovascularization of ischemic tissues and in re-endothelialization of injured blood vessels. Several studies have shown the therapeutic potential of EPC transplantation in rescue of tissue ischemia and in repair of blood vessels and bioengineering of prosthetic grafts. Recent small-scale trials have provided preliminary evidence of feasibility, safety, and efficacy in patients with myocardial and critical limb ischemia. However, several studies have shown that age and cardiovascular disease risk factors reduce the availability of circulating EPCs (CEPCs) and impair their function to varying degrees. In addition, the relative scarcity of CEPCs limits the ability to expand these cells in sufficient numbers for some therapeutic applications. Priority must be given to the development of strategies to enhance the number and improve the function of CEPCs. Furthermore, alternative sources of EPC such as chord blood need to be explored. Strategies for improvement of cell adhesion, survival, and prevention of cell senescence are also essential to ensure therapeutic viability. Genetic engineering of EPCs may be a useful approach to developing these cells into efficient therapeutic tools. In the clinical arena there is pressing need to standardize the protocols for isolation, culture, and therapeutic application of EPC. Large-scale multi-center randomized trials are required to evaluate the long-term safety and efficacy of EPC therapy. Despite these hurdles, the outlook for EPC-based therapy for cardiovascular disease is promising.

Local endovascular delivery, gene therapy, and cell transplantation for peripheral arterial disease

Advances in catheter technology, gene identification, and cell biology may provide novel treatment options for patients with peripheral arterial disease (PAD) who are not candidates for standard revascularization procedures. Animal studies and recent results in human beings suggest that transfer of growth factors or regulatory genes and transplantation of progenitor cells may provide novel therapy options by inducing therapeutic angiogenesis or by inhibiting restenosis. This review will discuss the development of a variety of catheters for localized endovascular delivery, as well as the various cellular and genetic strategies that exist to restore blood flow to ischemic tissue and to reduce neointimal hyperplasia.

Intrarenal Injection of Bone Marrow-Derived Angiogenic Cells Reduces Endothelial Injury and Mesangial Cell Activation in Experimental Glomerulonephritis

Loss of glomerular endothelial cells has been suggested to contribute to the progression of glomerular injury. Although therapeutic angiogenesis induced by administration of bone marrow-derived endothelial progenitor cells has been observed in disease models of endothelial injury, the effects on renal disease have not been clarified. Whether administration of culture-modified bone marrow mononuclear cells would mitigate the glomerular endothelial injury in anti-Thy1.1 nephritis was investigated. After cultivation under conditions that promote endothelial progenitor cell growth, bone marrow mononuclear cells were labeled with CM-DiI, a fluorescence marker, and injected into the left renal artery of Lewis rats with anti-Thy1.1 glomerulonephritis. The decrease in glomerular endothelial cells was significantly attenuated in the left kidney, as compared with the right, in nephritic rats that received the cell infusion. Glomerular injury score, the area positive for mesangial alpha-smooth muscle actin, and infiltration of macrophages were significantly decreased in the left kidney. CM-DiI-positive cells were distributed in glomeruli of the left kidney but not in those of the right kidney. Among CM-DiI-labeled cells incorporated into glomeruli, 16.5 +/- 1.2% of cells were stained with an endothelial marker, rat endothelial cell antigen-1. Culture-modified mononuclear cells secreted 281.2 +/- 85.0 pg of vascular endothelial growth factor per 10(5) cells per day. In conclusion, intra-arterial administration of culture-modified bone marrow mononuclear cells reduced endothelial injury and mesangial activation in anti-Thy1.1 glomerulonephritis. Incorporation into the glomerular endothelial lining and production of angiogenic factor(s) are likely to contribute to the protective effects of culture-modified mononuclear cells against glomerular injury.

Neointimal hyperplasia on a cell-seeded polytetrafluoroethylene graft is promoted by transfer of tissue plasminogen activator gene and inhibited by transfer of nitric oxide synthase gene

OBJECTIVE

The objective of this study was to examine the effect of tissue plasminogen activator (tPA) and endothelial nitric oxide synthase (eNOS) on thrombosis and neointimal hyperplasia on a polytetrafluoroethylene (PTFE) graft seeded with smooth muscle cells (SMCs).

METHODS

SMCs retrovirally transduced with tPA and eNOS genes were seeded on PTFE grafts and then implanted into the infrarenal rabbit aorta. Thrombosis and neointimal hyperplasia on the grafts were examined after 30 and 100 days of implantation.

RESULTS

At 30 days of implantation, thrombus was observed on the luminal surface of both unseeded and SMC seeded control grafts, whereas grafts seeded with SMCs secreting tPA were nearly free of thrombus. At 100 days, the neointima on grafts seeded with tPA transduced SMCs was significantly thicker (925 +/- 150 microm, n = 5) than neointima on the other grafts (range, 132 to 374 microm; P < .001). Neointima thickness on grafts seeded with eNOS transduced SMCs (154 +/- 27 microm) was similar to that of unseeded grafts (132 +/- 16 microm, P > .05); both were thinner than those on grafts seeded with SMCs transduced with only lacZ gene (287 +/- 35 microm). The ratio of seeded cells in the neointima was significantly higher on SMC/tPA grafts (46% +/- 8%) than SMC/NOS grafts (21% +/- 6%, P < .05), indicating tPA transduced cells proliferated more than eNOS transduced cells.

CONCLUSIONS

Engineered tPA expression in seeded SMCs causes significantly more neointimal hyperplasia, despite the favorable inhibition of luminal thrombus. eNOS expression in the seeded cells inhibits neointimal hyperplasia.

The hemangioblast: Cradle to clinic

In the embryo, the mesodermal precursor cell, the hemangioblast, gives rise to blood and blood vessels. During adult life, the hematopoietic stem cell (HSC) also exhibits this bipotential hemangioblast activity, serving as a rich source for circulating endothelial progenitor cells (EPCs). As a result of this finding, many questions have arisen as to whether the adult HSC is involved in the day-to-day maintenance of tissues, what mechanisms influence this adult hemangioblast activity, and whether blood vessels harbor hematopoietic capability. In answering these questions, the power of adult hemangioblast activity could be harnessed to evaluate and treat diseases such as myocardial infarction, stroke, cancer, and blindness. Enumeration of activated EPCs aims to alert the patient as to the severity of their disease, predict response to therapy, and gauge for relapse potential. Identification of hemangioblast stimulatory or inhibitory cues would allow physicians to regulate neovascularization in their patient, augmenting vessel production in situations of hypo-proliferation such as wound healing and inhibiting vessel production in situations of hyper-proliferation such as cancer. Finally, given that EPCs home to sites of new blood vessel growth, genetic engineering of harvested HSC or EPC offers the potential to deliver vasoregulatory factors directly to sites of neovascularization.

Genetically Engineered Stem Cell Therapy for Tissue Regeneration

Therapeutic angiogenesis/vasculogenesis represents a new approach to treat patients with ischemic disease not curable with conventional treatment. This review focuses on the rationale and preliminary results of combining stem cell and gene therapy for regenerative medicine. Under disease conditions, impaired neovascularization results from diminished vascular growth factor production and primary dysfunction of endothelial cells and their progenitors. Advances in our ability to genetically manipulate cells ex vivo has provided the technological platform to implement stem cell biology and circumvent the potential hazard of direct gene transfer. Ex vivo engineered endothelial progenitor cells have been used for the treatment of peripheral limb ischemia. The approach eliminates the drawback of immune response against viral vectors and makes feasible repeating the therapeutic procedure in case of injury recurrence. The strategy of using stem cells as vectors for curative agents proved to be of value for the treatment of pulmonary hypertension and thrombosis. Transplantation of neural stem cells genetically modified to secrete nerve growth factor was able to ameliorate the death of striatal projection neurons caused by transient focal ischemia in the adult rat. By a similar approach, engineered neural stem cells might be used for treating neurodegenerative disorders. Therefore, genetic manipulation of stem cells opens new avenues for regenerative medicine.