VEGF increases engraftment of bone marrow-derived endothelial progenitor cells (EPCs) into vasculature of newborn murine recipients

Endometrial and placental stem cells in successful and pathological pregnancies

The endometrium is a dynamic tissue that undergoes extensive remodeling during the menstrual cycle and further gets modified during pregnancy. Different kinds of stem cells are reported in the endometrium. These include epithelial stem cells, endometrial mesenchymal stem cells, side population stem cells, and very small embryonic-like stem cells. Stem cells are also reported in the placenta which includes trophoblast stem cells, side population trophoblast stem cells, and placental mesenchymal stem cells. The endometrial and placental stem cells play a pivotal role in endometrial remodeling and placental vasculogenesis during pregnancy. The dysregulation of stem cell function is reported in various pregnancy complications like preeclampsia, fetal growth restriction, and preterm birth. However, the mechanisms by which it does so are yet elusive. Herein, we review the current knowledge of the different type of stem cells involved in pregnancy initiation and also highlight how their improper functionality leads to pathological pregnancy.

Shaping the brain vasculature in development and disease in the single-cell era

The CNS critically relies on the formation and proper function of its vasculature during development, adult homeostasis and disease. Angiogenesis - the formation of new blood vessels - is highly active during brain development, enters almost complete quiescence in the healthy adult brain and is reactivated in vascular-dependent brain pathologies such as brain vascular malformations and brain tumours. Despite major advances in the understanding of the cellular and molecular mechanisms driving angiogenesis in peripheral tissues, developmental signalling pathways orchestrating angiogenic processes in the healthy and the diseased CNS remain incompletely understood. Molecular signalling pathways of the 'neurovascular link' defining common mechanisms of nerve and vessel wiring have emerged as crucial regulators of peripheral vascular growth, but their relevance for angiogenesis in brain development and disease remains largely unexplored. Here we review the current knowledge of general and CNS-specific mechanisms of angiogenesis during brain development and in brain vascular malformations and brain tumours, including how key molecular signalling pathways are reactivated in vascular-dependent diseases. We also discuss how these topics can be studied in the single-cell multi-omics era.

Regulation of Endothelial Progenitor Cell Functions in Ischemic Heart Disease: New Therapeutic Targets for Cardiac Remodeling and Repair

Ischemic heart disease (IHD) is the leading cause of morbidity and mortality worldwide. Ischemia and hypoxia following myocardial infarction (MI) cause subsequent cardiomyocyte (CM) loss, cardiac remodeling, and heart failure. Endothelial progenitor cells (EPCs) are involved in vasculogenesis, angiogenesis and paracrine effects and thus have important clinical value in alternative processes for repairing damaged hearts. In fact, this study showed that the endogenous repair of EPCs may not be limited to a single cell type. EPC interactions with cardiac cell populations and mesenchymal stem cells (MSCs) in ischemic heart disease can attenuate cardiac inflammation and oxidative stress in a microenvironment, regulate cell survival and apoptosis, nourish CMs, enhance mature neovascularization, alleviate adverse ventricular remodeling after infarction and enhance ventricular function. In this review, we introduce the definition and discuss the origin and biological characteristics of EPCs and summarize the mechanisms of EPC recruitment in ischemic heart disease. We focus on the crosstalk between EPCs and endothelial cells (ECs), smooth muscle cells (SMCs), CMs, cardiac fibroblasts (CFs), cardiac progenitor cells (CPCs), and MSCs during cardiac remodeling and repair. Finally, we discuss the translation of EPC therapy to the clinic and treatment strategies.

Endothelial Colony-Forming Cells Dysfunctions Are Associated with Arterial Hypertension in a Rat Model of Intrauterine Growth Restriction

Infants born after intrauterine growth restriction (IUGR) are at risk of developing arterial hypertension at adulthood. The endothelium plays a major role in the pathogenesis of hypertension. Endothelial colony-forming cells (ECFCs), critical circulating components of the endothelium, are involved in vasculo-and angiogenesis and in endothelium repair. We previously described impaired functionality of ECFCs in cord blood of low-birth-weight newborns. However, whether early ECFC alterations persist thereafter and could be associated with hypertension in individuals born after IUGR remains unknown. A rat model of IUGR was induced by a maternal low-protein diet during gestation versus a control (CTRL) diet. In six-month-old offspring, only IUGR males have increased systolic blood pressure (tail-cuff plethysmography) and microvascular rarefaction (immunofluorescence). ECFCs isolated from bone marrow of IUGR versus CTRL males displayed a decreased proportion of CD31+ versus CD146+ staining on CD45- cells, CD34 expression (flow cytometry, immunofluorescence), reduced proliferation (BrdU incorporation), and an impaired capacity to form capillary-like structures (Matrigel test), associated with an impaired angiogenic profile (immunofluorescence). These dysfunctions were associated with oxidative stress (increased superoxide anion levels (fluorescent dye), decreased superoxide dismutase protein expression, increased DNA damage (immunofluorescence), and stress-induced premature senescence (SIPS; increased beta-galactosidase activity, increased p16INK4a, and decreased sirtuin-1 protein expression). This study demonstrated an impaired functionality of ECFCs at adulthood associated with arterial hypertension in individuals born after IUGR.

Endothelial Progenitor Cells Dysfunctions and Cardiometabolic Disorders: From Mechanisms to Therapeutic Approaches

Metabolic syndrome (MetS) is a cluster of several disorders, such as hypertension, central obesity, dyslipidemia, hyperglycemia, insulin resistance and non-alcoholic fatty liver disease. Despite health policies based on the promotion of physical exercise, the reduction of calorie intake and the consumption of healthy food, there is still a global rise in the incidence and prevalence of MetS in the world. This phenomenon can partly be explained by the fact that adverse events in the perinatal period can increase the susceptibility to develop cardiometabolic diseases in adulthood. Individuals born after intrauterine growth restriction (IUGR) are particularly at risk of developing cardiovascular diseases (CVD) and metabolic disorders later in life. It has been shown that alterations in the structural and functional integrity of the endothelium can lead to the development of cardiometabolic diseases. The endothelial progenitor cells (EPCs) are circulating components of the endothelium playing a major role in vascular homeostasis. An association has been found between the maintenance of endothelial structure and function by EPCs and their ability to differentiate and repair damaged endothelial tissue. In this narrative review, we explore the alterations of EPCs observed in individuals with cardiometabolic disorders, describe some mechanisms related to such dysfunction and propose some therapeutical approaches to reverse the EPCs dysfunction.

Factors Affecting the Re-Endothelialization of Endothelial Progenitor Cell

The vascular endothelium, which plays an essential role in maintaining the normal shape and function of blood vessels, is a natural barrier between the circulating blood and the vascular wall tissue. The endothelial damage can cause vascular lesions, such as atherosclerosis and restenosis. After the vascular intima injury, the body starts the endothelial repair (re-endothelialization) to inhibit the neointimal hyperplasia. Endothelial progenitor cell is the precursor of endothelial cells and plays an important role in the vascular re-endothelialization. However, re-endothelialization is inevitably affected in vivo and in vitro by factors, which can be divided into two types, namely, promotion and inhibition, and act on different links of the vascular re-endothelialization. This article reviews these factors and related mechanisms.

Sustained oxidative stress instigates differentiation of cancer stem cells into tumor endothelial cells: Pentose phosphate pathway, reactive oxygen species and autophagy crosstalk

Tumor angiogenesis plays a vital role in tumor growth and metastasis. It is proven that in tumor vasculature, endothelial cells (ECs) originate from a small population of cancer cells introduced as cancer stem cells (CSCs). Autophagy has a vital role in ECs differentiation from CSCs and tumor angiogenesis. High levels of reactive oxygen species (ROS) increased autophagy by inhibition of glucose-6-phosphate dehydrogenase (G6PD) and inactivation of the pentose phosphate pathway (PPP). Previously, we suggested that cancer cells initially increase the glycolysis rate when encountering ROS, then the metabolic balance is changed from glycolysis to PPP, following the continuation of oxidative stress. In this study, we investigate the possible role of persistent oxidative stress in the differentiation of CSCs into tumor ECs by relying on the relationship between the ROS, PPP and autophagy. Because tumor angiogenesis plays an important role in the growth and development of cancer, understanding the mechanisms involved in differentiating ECs from CSCs can help find promising treatments for cancer.

Ischemia-induced Netrin-4 promotes neovascularization through endothelial progenitor cell activation via Unc-5 Netrin receptor B

Endothelial progenitor cells (EPCs) promote neovascularization and tissue repair by migrating to vascular injury sites; therefore, factors that enhance EPC homing to damaged tissues are of interest. Here, we provide evidence of the prominent role of the Netrin-4 (NTN4)-Unc-5 Netrin receptor B (UNC5B) axis in EPC-specific promotion of ischemic neovascularization. Our results showed that NTN4 promoted the proliferation, chemotactic migration, and paracrine effects of small EPCs (SEPCs) and significantly increased the incorporation of large EPCs (LEPCs) into tubule networks. Additionally, NTN4 prominently augmented neovascularization in mice with hindlimb ischemia by increasing the homing of exogenously transplanted EPCs to the ischemic limb and incorporating EPCs into vessels. Moreover, silencing of UNC5B, an NTN4 receptor, abrogated the NTN4-induced cellular activities of SEPCs in vitro and blood-flow recovery and neovascularization in vivo in ischemic muscle by reducing EPC homing and incorporation. These findings suggest NTN4 as an EPC-based therapy for treating angiogenesis-dependent diseases.

Identification of a pro-angiogenic functional role for FSP1-positive fibroblast subtype in wound healing

Fibrosis accompanying wound healing can drive the failure of many different organs. Activated fibroblasts are the principal determinants of post-injury pathological fibrosis along with physiological repair, making them a difficult therapeutic target. Although activated fibroblasts are phenotypically heterogeneous, they are not recognized as distinct functional entities. Using mice that express GFP under the FSP1 or αSMA promoter, we characterized two non-overlapping fibroblast subtypes from mouse hearts after myocardial infarction. Here, we report the identification of FSP1-GFP⁺ cells as a non-pericyte, non-hematopoietic fibroblast subpopulation with a predominant pro-angiogenic role, characterized by in vitro phenotypic/cellular/ultrastructural studies and in vivo granulation tissue formation assays combined with transcriptomics and proteomics. This work identifies a fibroblast subtype that is functionally distinct from the pro-fibrotic αSMA-expressing myofibroblast subtype. Our study has the potential to shift our focus towards viewing fibroblasts as molecularly and functionally heterogeneous and provides a paradigm to approach treatment for organ fibrosis.

Activated fibroblasts are key contributors to tissue repair after cardiac injury. Here, Saraswati et al. identify and characterize a subpopulation of FSP1-positive cardiac fibroblasts with proangiogenic properties in infarcted hearts.

Putative endothelial progenitor cells do not promote vascular repair but attenuate pericyte-myofibroblast transition in UUO-induced renal fibrosis

Background

Putative endothelial progenitor cells (pEPCs) have been confirmed to participate in alleviation of renal fibrosis in several ischaemic diseases. However, their mechanistic effect on renal fibrosis, which is characterized by vascular regression and further rarefaction-related pathology, remains unknown.

Methods

To explore the effect and molecular mechanisms by which pEPCs act on unilateral ureteral obstruction (UUO)-induced renal fibrosis, we isolated pEPCs from murine bone marrow. In vivo, pEPCs (2 × 10⁵ cells/day) and pEPC-MVs (microvesicles) were injected into UUO mice via the tail vein. In vitro, pEPCs were co-cultured with renal-derived pericytes. Pericyte-myofibroblast transition was evaluated using the myofibroblast marker α-smooth muscle actin (α-SMA) and pericyte marker platelet-derived growth factor receptor β (PDGFR-β).

Results

Exogenous supply of bone marrow-derived pEPCs attenuated renal fibrosis by decreasing pericyte-myofibroblast transition without significant vascular repair in the UUO model. Our results indicated that pEPCs regulated pericytes and their transition into myofibroblasts via pEPC-MVs. Co-culture of pericytes with pEPCs in vitro suggested that pEPCs inhibit transforming growth factor-β (TGF-β)-induced pericyte–myofibroblast transition via a paracrine pathway.

Conclusion

pEPCs effectively attenuated UUO-induced renal fibrosis by inhibiting pericyte–myofibroblast transition via a paracrine pathway, without promoting vascular repair.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1201-5) contains supplementary material, which is available to authorized users.

Lymphatic Tissue Engineering and Regeneration

The lymphatic system is a major circulatory system within the body, responsible for the transport of interstitial fluid, waste products, immune cells, and proteins. Compared to other physiological systems, the molecular mechanisms and underlying disease pathology largely remain to be understood which has hindered advancements in therapeutic options for lymphatic disorders. Dysfunction of the lymphatic system is associated with a wide range of disease phenotypes and has also been speculated as a route to rescue healthy phenotypes in areas including cardiovascular disease, metabolic syndrome, and neurological conditions. This review will discuss lymphatic system functions and structure, cell sources for regenerating lymphatic vessels, current approaches for engineering lymphatic vessels, and specific therapeutic areas that would benefit from advances in lymphatic tissue engineering and regeneration.

Bone marrow derived endothelial progenitor cells retain their phenotype and functions after a limited number of culture passages and cryopreservation

A critical limitation for tissue engineering and autologous therapeutic applications of bone marrow derived EPCs is their low frequency, which is even lower in number and activity level in patients with cardiovascular risk factors and other diseases. New strategies for obtaining and reserving sufficient ready-to-use EPCs for clinical use have hit major obstacles, because effects of serial passage and cryopreservation on EPC phenotype and functions are still needed to be explored. The present study aims at investigating effects of a limited number of culture passages as well as cryopreservation on EPC phenotype and functions. We isolated EPCs from rat bone marrow and cultured them up to passage 12 (totaling achievements of 40 population doublings). The phenotype and functions of fresh cultured and post-cryopreserved EPCs at passages 7 and 12, respectively, were evaluated. EPCs at passage 12 maintained the morphological characteristics, marker phenotype, Dil-ac-LDL uptake and FITC-UEA-1 binding functions, enhanced EPCs proliferation, tube formation and migration, but decreased CD133 expression compared with EPCs at passage 7. Cryopreservation caused limited impairment in EPC phenotype and functions. In brief, our results demonstrated that a limited number of culture passages and cryopreservation did not change EPC phenotype and functions, and can be used for the development of robust strategies and quality control criterion for obtaining sufficient and high-quality ready-to-use EPCs for tissue engineering and therapeutic applications.

The effect of estrogen on diabetic wound healing is mediated through increasing the function of various bone marrow-derived progenitor cells

OBJECTIVE

Endothelial progenitor cells (EPCs) are the key cells of postnatal neovascularization, and mesenchymal stem cells (MSCs) possess pluripotent differentiation capacity and contribute to tissue regeneration and wound healing. Both EPCs and MSCs are critical to the wound repair process, which is hindered in diabetes mellitus. Diabetes has been shown to decrease the function of these progenitor cells, whereas estrogen has beneficial wound healing effects. However, the role of estrogen in modulating EPC and MSC biology in diabetes is unknown. We investigated the effect of estrogen on improving bone marrow (BM)-derived EPC and MSC function using a murine diabetic wound healing model.

METHODS

Female diabetic db⁺/db⁺ and nondiabetic control mice were wounded cutaneously and treated with topical estrogen or placebo cream. On day 5 after wounding, BM cells were harvested to quantify EPC number and colony-forming units of EPCs and MSCs. Wound healing rate was concurrently studied. Vessel density and scar density were then quantified using whole body perfusion and laser confocal microscopy. EPC recruitment was documented by immunohistochemistry to identify CD34- and vascular endothelial growth factor receptor 2-positive cells in the vessel wall. Data were analyzed by analysis of variance.

RESULTS

Topical estrogen significantly increased colony-forming units of both EPCs and MSCs compared with placebo treatment, indicating improved viability and proliferative ability of these cells. Consistently, increased recruitment of EPCs to diabetic wounds and higher vessel density were observed in estrogen-treated compared with placebo-treated mice. Consequently, topical estrogen significantly accelerated wound healing as early as day 6 after wounding. In addition, scar density resulting from collagen deposition was increased in the estrogen-treated group, reflecting increased MSC activity and differentiation.

CONCLUSIONS

Estrogen treatment increases wound healing and wound neovascularization in diabetic mice. Our data implicate that these beneficial effects may be mediated through improving the function of BM-derived EPCs and MSCs.

VEGF promotes endothelial progenitor cell differentiation and vascular repair through connexin 43

Background

Endothelial progenitor cell (EPC) differentiation is considered crucial for vascular repair. Vascular endothelial growth factor (VEGF) induces EPC differentiation, but the underlying mechanism of this phenomenon remains unclear. Connexin 43 (Cx43) is reported to be involved in the regulation of stem cell differentiation. Therefore, we sought to determine whether Cx43 is involved in VEGF-induced EPC differentiation and vascular repair.

Methods

Rat spleen-derived EPCs were cultured and treated with various concentrations of VEGF (0, 10, or 50 ng/mL), and the relationship between EPC differentiation and Cx43 expression was evaluated. Thereafter, fluorescence redistribution after photobleaching was performed to assess the relationship between adjacent EPC differentiation and Cx43-induced gap junction intercellular communication (GJIC). After carotid artery injury, EPCs pretreated with VEGF were injected into the tail veins, and the effects of Cx43 on vascular repair were evaluated.

Results

EPCs cultured with VEGF exhibited accelerated differentiation and increased expression of Cx43. However, inhibition of Cx43 expression using short interfering RNA (siRNA) attenuated EPC GJIC and consequent EPC differentiation. VEGF-pretreated EPC transplantation promoted EPC homing and reendothelialization, and inhibited neointimal formation. These effects were attenuated by siRNA inhibition of Cx43.

Conclusions

Our results from in vivo and in vitro experiments indicated that VEGF promotes EPC differentiation and vascular repair through Cx43.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0684-1) contains supplementary material, which is available to authorized users.

Fresh Noncultured Endothelial Progenitor Cells Improve Neonatal Lung Hyperoxia-Induced Alveolar Injury

Treatment of preterm human infants with high oxygen can result in disrupted lung alveolar and vascular development. Local or systemic administration of endothelial progenitor cells (EPCs) is reported to remedy such disruption in animal models. In this study, the effects of both fresh (enriched for KDR) and cultured bone marrow (BM)-derived cell populations with EPC characteristics were examined following hyperoxia in neonatal mouse lungs. Intraperitoneal injection of fresh EPCs into five-day-old mice treated with 90% oxygen resulted in full recovery of hyperoxia-induced alveolar disruption by 56 days of age. Partial recovery in septal number following hyperoxia was observed following injection of short-term cultured EPCs, yet aberrant tissue growths appeared following injection of long-term cultured cells. Fresh and long-term cultured cells had no impact on blood vessel development. Short-term cultured cells increased blood vessel number in normoxic and hyperoxic mice by 28 days but had no impact on day 56. Injection of fresh EPCs into normoxic mice significantly reduced alveolarization compared with phosphate buffered saline-injected normoxic controls. These results indicate that fresh BM EPCs have a higher and safer corrective profile in a hyperoxia-induced lung injury model compared with cultured BM EPCs but may be detrimental to the normoxic lung. The appearance of aberrant tissue growths and other side effects following injection of cultured EPCs warrants further investigation. Stem Cells Translational Medicine 2017;6:2094-2105.

Characterization of a Fetal Liver Cell Population Endowed with Long-Term Multiorgan Endothelial Reconstitution Potential

Stable reconstitution of vascular endothelial beds upon transplantation of progenitor cells represents an important challenge due to the paucity and generally limited integration/expansion potential of most identified vascular related cell subsets. We previously showed that mouse fetal liver (FL) hemato/vascular cells from day 12 of gestation (E12), expressing the Stem Cell Leukaemia (SCL) gene enhancer transgene (SCL‐PLAP⁺ cells), had robust endothelial engraftment potential when transferred to the blood stream of newborns or adult conditioned recipients, compared to the scarce vascular contribution of adult bone marrow cells. However, the specific SCL‐PLAP⁺ hematopoietic or endothelial cell subset responsible for the long‐term reconstituting endothelial cell (LTR‐EC) activity and its confinement to FL developmental stages remained unknown. Using a busulfan‐treated newborn transplantation model, we show that LTR‐EC activity is restricted to the SCL‐PLAP⁺VE‐cadherin⁺CD45⁻ cell population, devoid of hematopoietic reconstitution activity and largely composed by Lyve1⁺ endothelial‐committed cells. SCL‐PLAP⁺ Ve‐cadherin⁺CD45⁻ cells contributed to the liver sinusoidal endothelium and also to the heart, kidney and lung microvasculature. LTR‐EC activity was detected at different stages of FL development, yet marginal activity was identified in the adult liver, revealing unknown functional differences between fetal and adult liver endothelial/endothelial progenitors. Importantly, the observations that expanding donor‐derived vascular grafts colocalize with proliferating hepatocyte‐like cells and participate in the systemic circulation, support their functional integration into young livers. These findings offer new insights into the engraftment, phonotypical, and developmental characterization of a novel endothelial/endothelial progenitor cell subtype with multiorgan LTR‐EC activity, potentially instrumental for the treatment/genetic correction of vascular diseases. Stem Cells2017;35:507–521

BMP9 Induces Cord Blood-Derived Endothelial Progenitor Cell Differentiation and Ischemic Neovascularization via ALK1

OBJECTIVE

Modulating endothelial progenitor cells (EPCs) is essential for therapeutic angiogenesis, and thus various clinical trials involving EPCs are ongoing. However, the identification of environmental conditions and development of optimal methods are required to accelerate EPC-driven vasculogenesis.

APPROACH AND RESULTS

We evaluated gene expression profiles of cord blood-derived EPCs and endothelial cells to identify the key factors in EPC→endothelial cell differentiation and to show that transforming growth factor-β family members contribute to EPC differentiation. The expression levels of activin receptor-like kinase 1 (ALK1) and its high-affinity ligand, bone morphogenetic protein 9 (BMP9) were markedly changed in EPC→endothelial cell differentiation. Interestingly, BMP9 induced EPC→endothelial cell differentiation and EPC incorporation into vessel-like structures by acting on ALK1 expressed on EPCs in vitro. BMP9 also induced neovascularization in mice with hindlimb ischemia by increasing vessel formation and the incorporation of EPCs into vessels. Conversely, neovascularization was impaired when ALK1 signaling was blocked. Furthermore, EPCs exposed to either short- or long-term BMP9 stimulation demonstrated these functions in EPC-mediated neovascularization.

CONCLUSIONS

Collectively, our results indicated that BMP9/ALK1 augmented vasculogenesis and angiogenesis, and thereby enhanced neovascularization. Thus, we suggest that BMP9/ALK1 may improve the efficacy of EPC-based therapies for treating ischemic diseases.

Role of angiogenesis in bone repair

Bone vasculature plays a vital role in bone development, remodeling and homeostasis. New blood vessel formation is crucial during both primary bone development as well as fracture repair in adults. Both bone repair and bone remodeling involve the activation and complex interaction between angiogenic and osteogenic pathways. Interestingly studies have demonstrated that angiogenesis precedes the onset of osteogenesis. Indeed reduced or inadequate blood flow has been linked to impaired fracture healing and old age related low bone mass disorders such as osteoporosis. Similarly the slow penetration of host blood vessels in large engineered bone tissue grafts has been cited as one of the major hurdle still impeding current bone construction engineering strategies. This article reviews the current knowledge elaborating the importance of vascularization during bone healing and remodeling, and the current therapeutic strategies being adapted to promote and improve angiogenesis.

Differential characteristics and in vitro angiogenesis of bone marrow- and peripheral blood-derived endothelial progenitor cells: evidence from avian species

OBJECTIVES

This study was conducted to compare phenotypes and in vitro angiogenic capacity of putative endothelial progenitor cells (EPCs) derived from bone marrow (BM) and peripheral blood (PB), from an avian species.

MATERIALS AND METHODS

Mononuclear cells were isolated from chicken BM and PB (BMMNCs and PBMNCs) and cultured in EGM-2 medium. Cells at days 7-14 were used for the experiments. Expression of progenitor and endothelial markers, number of Dil-ac-LDL/lectin dual-positive cells and adipogenic and osteogenic differentiation were determined. Migration and in vitro angiogenic ability between BMMNC- and PBMNC-derived cells were compared.

RESULTS

PBMNCs developed typical EPC appearance, with initial spindle shape followed by a cobblestone form, whereas BMMNC-derived cells retained their constitutive spindle-like morphology throughout the study. Cells derived from both sources expressed CD133, CD31 and VEGFR-2, although PBMNCs-derived cells had lower CD133 expression. Nevertheless, number of Dil-ac-LDL/lectin dual-positive cells did not differ between groups. Adipogenic and osteogenic lineages were verified in BMMNC- but not in PBMNC-derived cells. PBMNC-derived cells formed tubular networks on Matrigel. However, BMMNC-derived cells formed few tube-like structures, which were not morphologically comparable to those developed by their counterparts.

CONCLUSION

Our results suggest that so called EPCs derived from BMMNCs are not 'true' EPCs, supporting previous findings on mammals that BM may not serve as an optimal isolation source of EPCs.

Kallikrein gene-modified EPCs induce angiogenesis in rats with ischemic hindlimb and correlate with integrin αvβ3 expression

Background

Human tissue kallikrein (hTK) plays an essential role in the physiological and pathological mechanisms of blood vessels. This study aimed to determine whether angiogenesis induced by endothelial progenitor cells (EPCs) transduced with the adenovirus-mediated hTK gene could improve blood flow in rat hindlimb ischemia in vivo and to establish a promising mechanism in vitro.

Methods

EPCs transduced with adenovirus encoding hTK-162 (i.e., Ad/hTK-transduced EPCs or Ad/GFP-transduced EPCs) were administered to Wister rats with hindlimb ischemia through therapeutic neovascularization. Muscular capillary density (MCD), blood flow (BF), and the number of myofibers were measured at days 7, 14, and 21 after treatment. Expressions of integrin αvβ3 and endothelial nitric oxide synthase (eNOS) were detected on the surface of EPCs.

Results

MCD, BF, and the number of myofibers in rats with Ad/hTK-transduced EPCs remarkably increased at day 21 after treatment compared with rats with Ad/GFP-transduced EPCs or the control group (P<0.01). Expressions of integrin αvβ3 and eNOS protein on the surface of EPCs also increased in rats with Ad/hTK-transduced EPCs. The levels of integrin αvβ3 expression were reduced by PI3K and eNOS blockade, and the inhibitor of integrin αvβ3 abrogated the migration and adhesion of hTK-transduced EPCs (P<0.05).

Conclusion

hTK gene delivery in vivo improves the natural angiogenic response to ischemia. The ability of hTK gene-transduced EPCs can be enhanced in vitro, in which integrin αvβ3 plays a role in the process.

BMP2 genetically engineered MSCs and EPCs promote vascularized bone regeneration in rat critical-sized calvarial bone defects

Current clinical therapies for critical-sized bone defects (CSBDs) remain far from ideal. Previous studies have demonstrated that engineering bone tissue using mesenchymal stem cells (MSCs) is feasible. However, this approach is not effective for CSBDs due to inadequate vascularization. In our previous study, we have developed an injectable and porous nano calcium sulfate/alginate (nCS/A) scaffold and demonstrated that nCS/A composition is biocompatible and has proper biodegradability for bone regeneration. Here, we hypothesized that the combination of an injectable and porous nCS/A with bone morphogenetic protein 2 (BMP2) gene-modified MSCs and endothelial progenitor cells (EPCs) could significantly enhance vascularized bone regeneration. Our results demonstrated that delivery of MSCs and EPCs with the injectable nCS/A scaffold did not affect cell viability. Moreover, co-culture of BMP2 gene-modified MSCs and EPCs dramatically increased osteoblast differentiation of MSCs and endothelial differentiation of EPCs in vitro. We further tested the multifunctional bone reconstruction system consisting of an injectable and porous nCS/A scaffold (mimicking the nano-calcium matrix of bone) and BMP2 genetically-engineered MSCs and EPCs in a rat critical-sized (8 mm) caviarial bone defect model. Our in vivo results showed that, compared to the groups of nCS/A, nCS/A+MSCs, nCS/A+MSCs+EPCs and nCS/A+BMP2 gene-modified MSCs, the combination of BMP2 gene -modified MSCs and EPCs in nCS/A dramatically increased the new bone and vascular formation. These results demonstrated that EPCs increase new vascular growth, and that BMP2 gene modification for MSCs and EPCs dramatically promotes bone regeneration. This system could ultimately enable clinicians to better reconstruct the craniofacial bone and avoid donor site morbidity for CSBDs.

Hypoxia Biomarkers, Oxidative Stress, and Circulating Microparticles in Pediatric Patients With Thalassemia in Upper Egypt

This study aimed to investigate the oxidative stress, hypoxia biomarkers, and circulating microparticles (MPs) in β thalassemia major. The study included 56 children with thalassemia and 46 healthy controls. Hypoxia biomarkers, oxidative stress biomarkers, and total plasma fragmented DNA (fDNA) were detected by the standard methods. The MPs were assessed by flow cytometry. Hypoxia and oxidative stress biomarkers, fDNA, and MPs were higher and total antioxidant capacity (TAC) was lower in patients with thalassemia than the controls. In splenectomized patients and those who had complications, vascular endothelial growth factor (VEGF), malondialdehyde, fDNA, endothelial, platelet, and activated platelet MP levels were higher while, TAC was lower than the nonsplenectomized patients. In conclusion, the increased tissue hypoxia, oxidative stress in β thalassemia, and its relationship with DNA damage and MPs release could explain many complications of thalassemia and may have therapeutic implications. The VEGF could serve as an important indicator for adequacy of blood transfusion in thalassemia.

Hypoxia and oxidative stress markers in pediatric patients undergoing hemodialysis: cross section study

Background

Tissue injury due to hypoxia and/or free radicals is common in a variety of disease processes. This cross-sectional study aimed to investigate effect of chronic kidney diseases (CKD) and hemodialysis (HD) on hypoxia and oxidative stress biomarkers.

Methods

Forty pediatric patients with CKD on HD and 20 healthy children were recruited. Plasma hypoxia induced factor-1α (HIF-1α), vascular endothelial growth factor (VEGF) were measured by specific ELISA kits while, total antioxidant capacity (TAC), total peroxide (TPX), pyruvate and lactate by enzymatic/chemical colorimetric methods. Oxidative stress index (OSI) and lactate/pyruvate (L/P) ratio were calculated.

Results

TAC was significantly lower while TPX, OSI and VEGF were higher in patients at before- and after-dialysis session than controls. Lactate and HIF-1α levels were significantly higher at before-dialysis session than controls. Before dialysis, TAC and L/P ratio were lower than after-dialysis. In before-dialysis session, VEGF correlated positively with pyruvate, HIF-1α and OSI correlated positively with TPX, but, negatively with TAC. In after-dialysis session, HIF-1α correlated negatively with TPX and OSI; while, OSI correlated positively with TPX.

Conclusions

CKD patients succumb considerable tissue hypoxia with oxidative stress. Hemodialysis ameliorated hypoxia but lowered antioxidants as evidenced by decreased levels of HIF-1α and TAC at before- compared to after-dialysis levels.

Endothelial progenitor cells and integrins: adhesive needs

In the last decade there have been multiple studies concerning the contribution of endothelial progenitor cells (EPCs) to new vessel formation in different physiological and pathological settings. The process by which EPCs contribute to new vessel formation in adults is termed postnatal vasculogenesis and occurs via four inter-related steps. They must respond to chemoattractant signals and mobilize from the bone marrow to the peripheral blood; home in on sites of new vessel formation; invade and migrate at the same sites; and differentiate into mature endothelial cells (ECs) and/or regulate pre-existing ECs via paracrine or juxtacrine signals. During these four steps, EPCs interact with different physiological compartments, namely bone marrow, peripheral blood, blood vessels and homing tissues. The success of each step depends on the ability of EPCs to interact, adapt and respond to multiple molecular cues. The present review summarizes the interactions between integrins expressed by EPCs and their ligands: extracellular matrix components and cell surface proteins present at sites of postnatal vasculogenesis. The data summarized here indicate that integrins represent a major molecular determinant of EPC function, with different integrin subunits regulating different steps of EPC biology. Specifically, integrin α4β1 is a key regulator of EPC retention and/or mobilization from the bone marrow, while integrins α5β1, α6β1, αvβ3 and αvβ5 are major determinants of EPC homing, invasion, differentiation and paracrine factor production. β2 integrins are the major regulators of EPC transendothelial migration. The relevance of integrins in EPC biology is also demonstrated by many studies that use extracellular matrix-based scaffolds as a clinical tool to improve the vasculogenic functions of EPCs. We propose that targeted and tissue-specific manipulation of EPC integrin-mediated interactions may be crucial to further improve the usage of this cell population as a relevant clinical agent.

Studying vascular progenitor cells in a neonatal mouse model

While many murine models have been developed to study adult disease, animal research focused on neonatal and pediatric medicine has been limited by the small size of the mouse pups. Several transplantation, injection, and implantation systems have been used to study the function and role of vascular progenitor populations in adult mice; however, such techniques have been difficult to translate into newborn animals. Herein, we describe a model of neonatal murine intravascular injections that opens opportunity to study many diseases unique to the newborn that might benefit from vascular repair strategies and regenerative medicine.

Increased endothelial progenitor cells and vasculogenic factors in higher-staged arteriovenous malformations

ACKGROUND:: Arteriovenous malformations cause significant morbidity, primarily because they expand over time and recur after treatment. The authors hypothesized that neovascularization might contribute to arteriovenous malformation progression.

METHODS

Arteriovenous malformation tissue was collected prospectively from 12 patients after resection. Schobinger stage was determined by clinical history. Neovascularization in stage II lesions (n=7) was compared with stage III arteriovenous malformations (n=5) that had progressed. Specimens were analyzed using immunohistochemistry for CD31, Ki67, and CD34/CD133. Quantitative real-time reverse-transcriptase polymerase chain reaction was used to determine mRNA expression of factors that recruit endothelial progenitor cells: vascular endothelial growth factor (VEGF), stromal cell-derived factor-1α (SDF-1α), and hypoxia-inducible factor-1α (HIF-1α). VEGF receptors (VEGFR1, VEGFR2, neuropilin 1, and neuropilin 2) also were quantified using quantitative real-time reverse-transcriptase polymerase chain reaction.

RESULTS

Stage III arteriovenous malformations showed greater microvessel density (5.8 percent) than stage II lesions (1.3 percent) (p=0.004); no difference in proliferating endothelial cells was noted (p=0.67). CD133CD34 endothelial progenitor cells were elevated in stage III (0.53 percent) compared with stage II arteriovenous malformations (0.25 percent) (p=0.03). HIF-1α and SDF-1α were increased 7.6- and 7.9-fold in stage III compared with stage II lesions (1.7-fold and 3.3-fold), respectively (p=0.02). Neuropilin 1 and neuropilin 2 expression was greater in stage III (5.8-fold and 4.6-fold) than stage II arteriovenous malformations (3.0-fold and 2.4-fold) (p=0.03).

CONCLUSIONS

Higher-staged arteriovenous malformations exhibit increased expression of endothelial progenitor cells and factors that stimulate their recruitment. Neovascularization by vasculogenesis may be involved in progression of arteriovenous malformation.

Halting angiogenesis by non-viral somatic gene therapy alleviates psoriasis and murine psoriasiform skin lesions

Dysregulated angiogenesis is a hallmark of chronic inflammatory diseases, including psoriasis, a common skin disorder that affects approximately 2% of the population. Studying both human psoriasis in 2 complementary xenotransplantation models and psoriasis-like skin lesions in transgenic mice with epidermal expression of human TGF-β1, we have demonstrated that antiangiogenic non-viral somatic gene therapy reduces the cutaneous microvasculature and alleviates chronic inflammatory skin disorders. Transient muscular expression of the recombinant disintegrin domain (RDD) of metargidin (also known as ADAM-15) by in vivo electroporation reduced cutaneous angiogenesis and vascularization in all 3 models. As demonstrated using red fluorescent protein-coupled RDD, the treatment resulted in muscular expression of the gene product and its deposition within the cutaneous hyperangiogenic connective tissue. High-resolution ultrasound revealed reduced cutaneous blood flow in vivo after electroporation with RDD but not with control plasmids. In addition, angiogenesis- and inflammation-related molecular markers, keratinocyte proliferation, epidermal thickness, and clinical disease scores were downregulated in all models. Thus, non-viral antiangiogenic gene therapy can alleviate psoriasis and may do so in other angiogenesis-related inflammatory skin disorders.

Pyrvinium, a potent small molecule Wnt inhibitor, promotes wound repair and post-MI cardiac remodeling

Wnt signaling plays an important role in developmental and stem cell biology. To test the hypothesis that temporary inhibition of Wnt signaling will enhance granulation tissue and promote angiogenesis in tissue repair, we employed a recently characterized small molecule Wnt inhibitor. Pyrvinium is an FDA-approved drug that we identified as a Wnt inhibitor in a chemical screen for small molecules that stabilize β-catenin and inhibit Axin degradation. Our subsequent characterization of pyrvinium has revealed that its critical cellular target in the Wnt pathway is Casein Kinase 1α. Daily administration of pyrvinium directly into polyvinyl alcohol (PVA) sponges implanted subcutaneously in mice generated better organized and vascularized granulation tissue; this compound also increased the proliferative index of the tissue within the sponges. To evaluate its effect in myocardial repair, we induced a myocardial infarction (MI) by coronary artery ligation and administered a single intramyocardial dose of pyrvinium. Mice were evaluated by echocardiography at 7 and 30 days post-MI and treatment; post mortem hearts were evaluated by histology at 30 days. Pyrvinium reduced adverse cardiac remodeling demonstrated by decreased left ventricular internal diameter in diastole (LVIDD) as compared to a control compound. Increased Ki-67+ cells were observed in peri-infarct and distal myocardium of pyrvinium-treated animals. These results need to be further followed-up to determine if therapeutic inhibition of canonical Wnt may avert adverse remodeling after ischemic injury and its impact on myocardial repair and regeneration.

Identification of E-selectin as a novel target for the regulation of postnatal neovascularization: implications for diabetic wound healing

OBJECTIVES

We previously reported that stromal cell-derived factor-1α (SDF-1α, a homing signal for recruiting endothelial progenitor cells (EPC) to areas of neovascularization), is down-regulated in diabetic wounds (Gallagher et al, J Clin Invest. 2007;117:1249-1259). We now investigate signals whereby mature endothelial cells (EC) and circulating EPC achieve SDF-1α-mediated EPC homing.

METHODS

SDF-1α in diabetic wounds were therapeutically increased by injection of SDF-1α-engineered bone marrow-derived fibroblasts versus control cells (N = 48 [20, non-obese diabetic (NOD)], [28, streptozotocin-C57]). Polymerase chain reaction-array gene expression differences were validated by Western blotting and immunohistochemistry. The role of adhesion molecule(s) in mediating SDF-1α-induced EPC homing, and wound healing was furthered studied using antagonists in vitro and in vivo.

RESULTS

Increasing wound SDF-1α via cell-based therapy promotes healing in diabetic mice (∼20% increase in healing rates by day 3, P = 0.006). SDF-1α increased EC-EPC adhesion and specifically upregulated E-selectin expression in human microvascular EC (2.3-fold increase, P < 0.01). This effect was also significant in blood vessels of the experimental mice and resulted in increased wound neovascularization. The regulatory effects of SDF-1α on EC-EPC adhesion and EPC homing were specifically mediated by E-selectin, as the application of E-selectin antagonists significantly inhibited SDF-1α-induced EC-EPC adhesion, EPC homing, wound neovascularization, and wound healing.

CONCLUSIONS

SDF-1α-engineered cell-based therapy promotes diabetic wound healing in mice by specifically upregulating E-selectin expression in mature EC leading to increase EC-EPC adhesion, EPC homing, and increased wound neovascularization. These findings provide novel insight into the signals underlying the biological effect of SDF-1α on EPC homing and point to E-selectin as a new potential target for therapeutic manipulation of EPC trafficking in diabetic wound healing.

Effects of atorvastatin on the regeneration of pancreatic {beta}-cells after streptozotocin treatment in the neonatal rodent

To investigate the role of statins in beta-cell regeneration a model of streptozotocin (STZ)-induced beta-cell injury was used in the neonatal rat. We hypothesized that beta-cell growth and regeneration would increase following treatment with atorvastatin and that this would be associated with intraislet vasculogenesis. Pregnant Wistar rats were gavaged with 20 or 40 mg/kg atorvastatin for 21 days commencing on gestation day 15. Atorvastatin was detected in the circulation of the offspring. On postnatal day 4, the pups were given either a control or STZ (70 mg/kg ip) injection. beta-Cell mass had partially recovered by postnatal day 44 following STZ treatment, and atorvastatin (20 mg/kg) significantly increased beta-cell mass in both STZ-treated and control animals. An increase in the numbers of small islets at postnatal day 44 was seen in STZ-treated animals following atorvastatin, suggestive of neogenesis, and glucose tolerance was improved. Treatment with atorvastatin caused an increase in the numbers of intraislet endothelial cells at postnatal day 14 and the percentage of endothelial cells undergoing DNA synthesis, suggesting that angiogenesis had preceded the increase in beta-cell mass. The results indicate that functional beta-cell mass was expanded with atorvastatin in both control and STZ-treated neonatal rats and suggests a novel effect of a statin in promoting islet plasticity.

Adult stem cel diferentiation and trafficking and their implications in disease

Stem cells are unspecialized precursor cells that mainly reside in the bone marrow and have important roles in the establishment of embryonic tissue. They also have critical functions during adulthood, where they replenish short-lived mature effector cells and regeneration of injured tissue. They have three main characteristics: self-renewal, differentiation and homeostatic control. In order to maintain a pool of stem cells that support the production of blood cells, stromal elements and connective tissue, stem cells must be able to constantly replenish their own number. They must also possess the ability to differentiate and give rise to a heterogeneous group of functional cells. Finally, stem cells must possess the ability to modulate and balance differentiation and self-renewal according to environmental stimuli and whole-organ needs to prevent the production of excessive number of effector cells.(1) In addition to formation of these cells, regulated movement of stem cells is critical for organogenesis, homeostasis and repair in adulthood. Stem cells require specific inputs from particular environments in order to perform their various functions. Some similar trafficking mechanisms are shared by leukocytes, adult and fetal stem cells, as well as cancer stem cells.(1,2) Achieving proper trafficking of stem cells will allow increased efficiency of targeted cell therapy and drug delivery.(2) In addition, understanding similarities and differences in homing and migration of malignant cancer stem cells will also clarify molecular events of tumor progression and metastasis.(2) This chapter focuses on the differentiation, trafficking and homing of the major types of adult bone marrow stem cells: hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) and the term"stem cell" will refer to "adult stem cells" unless otherwise specified.

Diabetic foot ulcers: effects of hyperoxia and SDF-1α on endothelial progenitor cells

Diabetes mellitus is a common disease afflicting many people. In addition to coronary artery disease, diabetic retinopathy and renal failure, diabetic patients face abnormal wound healing and have increased lower extremity ulcers and amputations. In diabetes, wound healing is altered due to both macrovascular and microvascular processes. While the former can be addressed with surgical intervention, the latter is more difficult to correct. Neovascularization within the granulation tissue via angiogenesis and vasculogenesis is critical for wound healing. Endothelial progenitor cells (EPCs) have been implicated in vasculogenesis. Mobilization of EPCs from the bone marrow is impaired in diabetes and homing of EPCs to the wound is also abnormal. Recent studies show that hyperoxia and administration of exogenous stromal-derived factor-1α increases circulatory and wound levels of EPCs and improves wound healing in diabetic mice. These findings have great potential for translation into human counterparts as the treatment for this prevalent disease matures.

B-type natriuretic peptide enhances vasculogenesis by promoting number and functional properties of early endothelial progenitor cells

OBJECTIVE

To test the hypothesis that B-type natriuretic peptide (BNP) acts as a potent vasculogenic agent by enhancing the number, proliferation, adhesion, and migration of endothelial progenitor cells (EPCs).

BACKGROUND

BNP is a neurohormonal peptide that predicts outcome and used for treatment in chronic heart failure patients. It has been shown to promote angiogenesis in experimental animals. EPCs have been demonstrated to contribute to postnatal angiogenesis and vasculogenesis.

METHODS

The number of EPC colony forming units (CFU) and levels of N-terminal ProBNP were assayed in patients with severe, yet controlled, New York Heart Association (NYHA) II-IV heart failure. The in vitro effects of BNP on early EPC-CFU numbers, proliferation, migration, adhesive, and vascular tube formation capacities were studied using human and murine systems. The effects of in vivo BNP administration on Sca-1/Flk-1 progenitors and on vasculogenesis in the hindlimb ischemia model were then assayed in wild-type mice.

RESULTS

A significant correlation was found between circulating N-terminal ProBNP levels and EPC-CFU numbers. We observed a dose-dependent effect of BNP on the numbers of CFU and proliferation capacity of human EPCs as well as on their adhesive, migratory, and tube formation properties, in vitro. Systemic BNP administration to mice led to a significant increase in bone marrow Sca-1/Flk-1 EPCs and improvement in blood flow and capillary density in the ischemic limbs of mice.

CONCLUSIONS

BNP promotes vessel growth by increasing the number of endothelial progenitors and enhancing their functional properties. These provasculogenic properties of BNP could account for some of its beneficial effects in chronic heart failure patients and may be harnessed for the purpose of improving collateral formation in ischemic subjects.

Endothelial progenitor cells do not contribute to tumor endothelium in primary and metastatic tumors

Despite extensive research, the contribution of bone-marrow-derived endothelial progenitor cells (BM-EPC) to tumor angiogenesis remains controversial. In previous publications, the extent of incorporation of BM-EPCs into the endothelial cell (EC) layer in different tumor models has been reported as significant in some studies but undetectable in others. Here, we studied the differentiation of BM-EPCs and its contribution to tumor vessels in experimental and spontaneous lung metastasis (B16 melanoma and prostate carcinoma), in an autochthonous transgenic model of prostate tumorigenesis, in orthotopically implanted lung tumors [Lewis lung carcinoma (LLC)], in heterotopic subcutaneous models (LLC and C1 prostate carcinoma) growing in green fluorescent protein (GFP)-expressing bone marrow (BM) chimeras. Immunofluorescence was performed with a set of endothelial and hematopoietic markers and confocal microscopy was used to generate 3D reconstruction images. By performing rigorously conducted morphological studies, we found no evidence of BM-EPCs differentiation into tumor endothelium independently of tumor type, grade and organ site in primary and metastatic tumors. The vast majority of GFP(+) cells were trafficking leucocytes or periendothelial myeloid cells. To explore the possibility that local overexpression of vascular endothelial growth factor (VEGF) might increase the numbers of incorporated BM-EPCs, we analyzed tumors genetically manipulated to overexpress VEGF(164). Local VEGF production induces a massive infiltration of bone-marrow-derived cells, but did not lead to vessel wall integration of these cells. Collectively, these findings suggest that during tumor progression vascularization occurs primarily via classical tumor angiogenesis (e.g., sprouting of pre-existing ECs), whereas BM-EPCs do not incorporate into the vessel wall to any significant extent.

Low invasive angiogenic therapy for myocardial infarction by retrograde transplantation of mononuclear cells expressing the VEGF gene

BACKGROUND

Although transplantation of mononuclear cells (MNCs) induces angiogenesis in myocardial infarction, transplantation requires a large amount of bone marrow or peripheral blood cells. We examined the effects of transplantation of peripheral MNCs expressing an exogenous vascular endothelial growth factor (VEGF) gene in a pig model of acute myocardial infarction (AMI).

METHODS

MNCs were isolated from 20 ml peripheral blood from pigs and transfected with 10 microg of human VEGF165 plasmid (phVEGF). Myocardial infarction was induced by occlusion of the mid portion of the left anterior descending coronary artery (LAD) in anesthetized pigs. At 4 h after total occlusion, 5 x 10(6) VEGF-transfected MNCs were retrogradely transplanted into the pig via the coronary vein. Cardiac function, neovascularization and histology of the ischemic tissue were evaluated 4 weeks after transplantation.

RESULTS

MNCs expressing hVEGF and infused via the coronary vein were efficiently delivered the heart in pigs with myocardial infarction. Transplantation of MNCs expressing hVEGF significantly increased left ventricular (LV) function, collateral vessels, and capillary density in heart from AMI model pigs. Transplantation of MNCs expressing hVEGF increased the wall thickness of the scar in the heart after AMI.

CONCLUSIONS

Retrograde transplantation of peripheral blood MNCs expressing hVEGF efficiently induced angiogenesis and improved the impaired LV function in hearts of pigs with AMI. These findings indicate that angiogenic cells and gene therapy may be useful to treat ischemic heart disease.

GM-CSF accelerates proliferation of endothelial progenitor cells from murine bone marrow mononuclear cells in vitro

OBJECTIVE

To test whether the GM-CSF accelerates the proliferation of bone marrow endothelial progenitor cells (BM EPCs).

METHODS

BM EPCs were induced by endothelial cell conditioned medium (EC-CM). The effect of different concentrations of GM-CSF on the proliferation of BM EPCs was evaluated by the formation of EC-cols, MTT assay, and cell cycle assay. The single progenitor cell growth curves were quantified.

RESULTS

The data indicated that GM-CSF accelerated the proliferation of BM EPCs both in colony numbers and colony size. MTT confirmed the effect of GM-CSF on accelerating the proliferation of BM EPCs. The single colony experiments showed that EC-cols expressed different proliferation capacity, suggesting that the EC-cols with different proliferation potentials might have been derived from different levels of immature progenitors. The cell cycle assay showed that the rate of cells entering into S phase was 9.3% in the group treated with GM-CSF and 2.1% in the controls. Furthermore, these cells displayed the specific endothelial cell markers and formed capillary-like structures.

CONCLUSIONS

GM-CSF accelerates proliferation of BM EPCs. The potential beneficial of GM-CSF in the application of treating vascular ischemic patients is promising.

The angiogenic and prognostic implications of VEGF, Ang-1, Ang-2, and MMP-9 for hepatocellular carcinoma with background of hepatitis B virus

The objective of this study was to investigate the expressions of angiogenic factors and elucidate their angiogenic and prognostic roles in hepatocellular carcinoma (HCC) with background of hepatitis B virus (HBV). We evaluated microvessel density (MVD) of HCC, and investigated immunohistochemical expression of vascular endothelial growth factor (VEGF), angiopoietins (Ang-1 and Ang-2), and matrix metalloproteinases-9 (MMP-9) in 67 specimens of surgically resected HCC, which were all positive for hepatitis B surface antigen. We investigated the relationship between their expressions and clinicopathological factors or prognosis. The microvessel density (MVD) of tumor tissue and surrounding normal liver tissue was 93.1 +/- 43.8/mm2 and 30.4 +/- 14.8/mm2, respectively. The MVD of well-differentiated HCC was significantly less than that of poorly differentiated HCC. MVD was positively correlated with VEGF and Ang-2 expression (P = 0.0023 and 0.0265, respectively). There was less tumor recurrence in low Ang-2 and low MMP-9 group than high Ang-2 and/or high MMP-9 group (P = 0.002). In Cox regression model, portal vein thrombus and intrahepatic metastasis was the risk factors of tumor recurrence (P = 0.003 and 0.001, respectively). Our study showed that the expression of VEGF and Ang-2 were positively correlated with MVD. Ang-2 expression and/or MMP-9 expression might be a significant predictive factor for recurrence after resection in HCC patients with the background of HBV.

Hyperoxia, endothelial progenitor cell mobilization, and diabetic wound healing

Diabetic foot disease is a major health problem, which affects 15% of the 200 million patients with diabetes worldwide. Diminished peripheral blood flow and decreased local neovascularization are critical factors that contribute to the delayed or nonhealing wounds in these patients. The correction of impaired local angiogenesis may be a key component in developing therapeutic protocols for treating chronic wounds of the lower extremity and diabetic foot ulcers. Endothelial progenitor cells (EPCs) are the key cellular effectors of postnatal neovascularization and play a central role in wound healing, but their circulating and wound-level numbers are decreased in diabetes, implicating an abnormality in EPC mobilization and homing mechanisms. The deficiency in EPC mobilization is presumably due to impairment of eNOS-NO cascade in bone marrow (BM). Hyperoxia, induced by a clinically relevant hyperbaric oxygen therapy (HBO) protocol, can significantly enhance the mobilization of EPCs from the BM into peripheral blood. However, increased circulating EPCs failed to reach to wound tissues. This is partly a result of downregulated production of SDF-1alpha in local wound lesions with diabetes. Administration of exogenous SDF-1alpha into wounds reversed the EPC homing impairment and, with hyperoxia, synergistically enhanced EPC mobilization, homing, neovascularization, and wound healing.

Endothelial stem cells and precursors for tissue engineering: cell source, differentiation, selection, and application

Endothelial cells are of great interest because of their potential in cell therapy for vascular diseases and ischemic tissue, tissue engineering for vascular grafts and vascularized tissue beds, and modeling for pharmaceutical transport across endothelial barriers. However, limited availability and proliferation capability of mature endothelial cells hampers development of these applications. Recent advances in stem cell technology have enabled researchers to derive endothelial or endothelial-like cells from stem cells or other precursor populations. The current state of these cell sources and their in vitro differentiation, selection, and applications are discussed in this review.

Widespread nonhematopoietic tissue distribution by transplanted human progenitor cells with high aldehyde dehydrogenase activity

Transplanted adult progenitor cells distribute to peripheral organs and can promote endogenous cellular repair in damaged tissues. However, development of cell-based regenerative therapies has been hindered by the lack of preclinical models to efficiently assess multiple organ distribution and difficulty defining human cells with regenerative function. After transplantation into beta-glucuronidase (GUSB)-deficient NOD/SCID/mucopolysaccharidosis type VII mice, we characterized the distribution of lineage-depleted human umbilical cord blood-derived cells purified by selection using high aldehyde dehydrogenase (ALDH) activity with CD133 coexpression. ALDH(hi) or ALDH(hi)CD133+ cells produced robust hematopoietic reconstitution and variable levels of tissue distribution in multiple organs. GUSB+ donor cells that coexpressed human leukocyte antigen (HLA-A,B,C) and hematopoietic (CD45+) cell surface markers were the primary cell phenotype found adjacent to the vascular beds of several tissues, including islet and ductal regions of mouse pancreata. In contrast, variable phenotypes were detected in the chimeric liver, with HLA+/CD45+ cells demonstrating robust GUSB expression adjacent to blood vessels and CD45-/HLA- cells with diluted GUSB expression predominant in the liver parenchyma. However, true nonhematopoietic human (HLA+/CD45-) cells were rarely detected in other peripheral tissues, suggesting that these GUSB+/HLA-/CD45- cells in the liver were a result of downregulated human surface marker expression in vivo, not widespread seeding of nonhematopoietic cells. However, relying solely on continued expression of cell surface markers, as used in traditional xenotransplantation models, may underestimate true tissue distribution. ALDH-expressing progenitor cells demonstrated widespread and tissue-specific distribution of variable cellular phenotypes, indicating that these adult progenitor cells should be explored in transplantation models of tissue damage.

Ex vivo priming of endothelial progenitor cells with SDF-1 before transplantation could increase their proangiogenic potential

OBJECTIVE

As SDF-1 and its cognate receptor CXCR4 play a key role in the survival and mobilization of immature cells, we examined whether preconditioning of endothelial progenitor cells (EPCs) with SDF-1 could further promote their capacity to enhance angiogenesis.

METHODS AND RESULTS

EPC exposure to 100 ng/mL SDF-1 for 30 min induced a proangiogenic phenotype, with cell migration and differentiation into vascular cords in Matrigel and increased their therapeutic potential in a nude mouse model of hindlimb ischemia. This pretreatment enhanced EPC adhesion to activated endothelium in physiological conditions of blood flow by stimulating integrin-mediated EPCs binding to endothelial cells. Pretreated EPCs showed significantly upregulated surface alpha4 and alphaM integrin subunit expression involved in the homing of immature cells to a neovasculature and enhanced FGF-2 and promatrix metalloproteinase (MMP)-2 secretion. All these effects were significantly attenuated by EPC incubation with AMD-3100, a CXCR4 antagonist, by prior HSPGs disruption and by HUVEC incubation with anti-intercellular adhesion molecule1 (ICAM-1) and anti-vascular cell adhesion molecule (VCAM) blocking antibodies. Pretreated EPCs adhered very rapidly (within minutes) and were resistant to shear stresses of up to 2500 s(-1).

CONCLUSIONS

SDF-1 pretreatment during EPC expansion stimulates EPC adhesion to endothelial cells and thus augments the efficiency of cell therapy for ischemic vascular diseases.

Transplantation of adult neural progenitor cells transfected with vascular endothelial growth factor rescues grafted cells in the rat brain

Growth factors are currently evaluated as therapeutics in stroke and neurodegeneration. Besides direct neurotrophic effects, they promote proliferation, survival, and differentiation of both transplanted and endogenous neural precursor cells (NPCs). In the current study, we investigated whether NPCs expressing Vascular Endothelial Growth Factor VEGF-A165 are a useful vehicle for growth factor delivery after transplantation into the caudate putamen of the rat brain. We found an increased survival of adenovirally transfected NPCs after 11 days, but not after 24 hours or 4 days. Additional brain immunohistochemistry revealed increased expression of the endothelial cell marker PECAM-1 (CD31) after 24 hours, 4 day, and 11 days after transplantation. In conclusion, we show that the graft itself is a useful vehicle for growth factor delivery, promoting the survival of NPCs. Moreover, transplantation of VEGF-expressing NPCs supports angiogenesis in the brain, which may contribute to potential brain repair.

Endothelial progenitor cells, cardiovascular risk factors, cytokine levels and atherosclerosis--results from a large population-based study

Background

EPC number and functionality are assumed to reflect the endogenous vascular repair capacity with the EPC pool declining in higher ages and being exhausted by unfavorable life-style and risk factors. This intriguing and clinically highly relevant concept, however, has so far been derived from small case-control studies and patient series.

Methodology and Principle Findings

In the population-based Bruneck Study EPC number and EPC-colony forming units (EPC-CFU) were assessed as part of the fourth follow-up evaluation (2005) in 571 and 542 subjects, respectively. EPC number declined with age (p = 0.013), was significantly lower in women (p = 0.006) and higher in subjects on statin, hormone replacement or ACE inhibitor/angiotensin-receptor blockers, and correlated positively with moderate alcohol consumption. Unexpectedly, a positive relation between EPC number and several vascular risk factors emerged. In a step forward multivariate linear regression analysis EPC number was independently related with SDF1α, MMP-9, triglycerides, alcohol consumption, and Hba1c. EPC-CFU in turn was related to SDF1α and diastolic blood pressure. Moreover, EPC number showed a significant positive association with the Framingham risk score (P = 0.001). Finally, there was an inverse association between EPC number and common carotid artery intima-media thickness (p = 0.02) and the carotid artery atherosclerosis score (p = 0.059).

Conclusions

Our population-based data confirm the decline of EPC number with advancing age and lend first epidemiological support to a role of SDF-1α and MMP9 in EPC differentiation, mobilization and homing, but are conflict with the view that EPC number is unfavorably affected by cardiovascular risk factors. EPC number increases with the cardiovascular risk estimated by the Framingham risk score (FRS), which in the absence of similar changes for EPC-CFU. Finally, we demonstrate a significant inverse association between EPC number and extent of carotid atherosclerosis even though this association was only of moderate strength and not entirely consistent in other vascular territories.