Hematopoietic stem cells and endothelial cell precursors express Tie-2, CD31 and CD45

Early theories of tumor angiogenesis suggested that preexisting vessels surrounding the tumor were the principal source of the tumor vasculature but recent evidence suggests that endothelial progenitor cells (EPC) migrate from the marrow play an important role in developing the tumor blood supply. In a mouse model, in which the vascularization of a transplantable tumor was studied after bone marrow (BM) transplantation, we show that cells that express Tie-2, Sca-1, CD31 and CD45 function as both BM EPC and primitive hematopoietic stem cells. BM cells from transgenic mice expressing green fluorescent protein (GFP) under the control of the endothelial lineage-specific Tie-2 promoter (Tie-2 /GFP) were used to reconstitute irradiated (12 Gy) wild-type mice. Five donor BM cell populations were studied: (1) whole BM; (2) Sca-1-enriched BMC; (3) GFP/Tie-2+, Sca-1+ BMC; (4) GFP/Tie-2-, Sca-1+ BMC and (5) Sca-1-depleted BMC. After 4 weeks, the mice were injected with Tg.AC tumor cells. Three weeks later, sections from the tumors were stained for CD31 and examined for Tie-2-driven GFP expression. BM-derived endothelial cells were found only in mice transplanted with bone marrow containing populations of Tie-2+, Sca-1+ cells. As few as 3500 of these cells were sufficient to radioprotect lethally irradiated mice. Thus, we conclude that a rare subset of BMC (approximately 4 x 10(-3)%) with the putative properties of hemangioblasts have an active Tie-2 promoter. Selection of Tie-2+Sca-1+ BMC enriches for marrow-derived EPCs that participate in tumor angiogenesis and cells that can provide hematopoietic reconstitution of marrow-ablated mice.     

Bone marrow-derived circulating endothelial precursors do not contribute to vascular endothelium and are not needed for tumor growth

The mechanisms by which bone marrow (BM)-derived stem cells might contribute to angiogenesis and the origin of neovascular endothelial cells (ECs) are controversial. Neovascular ECs have been proposed to originate from VEGF receptor 2-expressing (VEGFR-2+) stem cells mobilized from the BM by VEGF or tumors, and it is thought that angiogenesis and tumor growth may depend on such endothelial precursors or progenitors. We studied the mobilization of BM cells to circulation by inoculating mice with VEGF polypeptides, adenoviral vectors expressing VEGF, or tumors. We induced angiogenesis by syngeneic melanomas, APCmin adenomas, adenoviral VEGF delivery, or matrigel plugs in four different genetically tagged universal or endothelial cell-specific chimeric mouse models, and subsequently analyzed the contribution of BM-derived cells to endothelium in a wide range of time points. To study the existence of circulating ECs in a nonmyeloablative setting, pairs of genetically marked parabiotic mice with a shared anastomosed circulatory system were created. We did not observe specific mobilization of VEGFR-2+ cells to circulation by VEGF or tumors. During angiogenesis, abundant BM-derived perivascular cells were recruited close to blood vessel wall ECs but did not form part of the endothelium. No circulation-derived vascular ECs were observed in the parabiosis experiments. Our results show that no BM-derived VEGFR-2+ or other EC precursors contribute to vascular endothelium and that cancer growth does not require BM-derived endothelial progenitors. Endothelial differentiation is not a typical in vivo function of normal BM-derived stem cells in adults, and it has to be an extremely rare event if it occurs at all.     

Chemokines direct endothelial progenitors into tumor neovessels

Tumor neovasculature substantially derives from sprouting of existing vessels, whereas the functional contribution of bone marrow-derived progenitors to neovessels remains controversial. We used transgenic mouse models of multistep carcinogenesis to monitor incorporation of bone marrow-derived cells into the neovasculature and to elucidate mechanisms of endothelial precursor cell (EPC) recruitment into the tumor microenvironment. We unequivocally demonstrate integration of bone marrow cells into the tumor vasculature as a late event in carcinogenesis that temporally correlates with VEGF release by the tumor and mobilization of circulating EPC in the periphery. Moreover, we demonstrate a chemokine-dependent mechanism of EPC homing into tumor, whereby neovessels of late-stage tumors release a battery of CC chemokines, which direct CCR2(+) and CCR5(+) progenitors into the vasculature. Thus, we show that tumor vessels promote their own growth and development in a self-amplifying fashion.     

Stimulation of immune-suppressive bone marrow cells by colony-stimulating factors

In previous studies, we demonstrated that immune-suppressive bone marrow cells appeared during a period of myelopoietic stimulation in mice bearing Lewis lung carcinoma (LLC) tumors and could be induced from normal bone marrow cells during 3 days of culture with supernatants of LLC variant cells. We have now shown that the capacity of LLC variants to induce immune suppressor cells was associated with the capacity to produce colony-stimulating factor (CSF) activities. The LLC variants that secreted more CSF activities also produced more bone marrow immune suppressor cell-inducing activity. The induction of immune-suppressive bone marrow cells was dependent on bone marrow cell proliferation because irradiation of bone marrow cells prior to culture with the CSF-containing supernatants blocked induction of suppressor cells. Culture supernatants of WEHI-3 cells and of pokeweed mitogen-stimulated spleen cells, rich sources of interleukin 3 (IL-3) and granulocyte-monocyte-CSF (GM-CSF), as well as recombinant mouse GM-CSF and recombinant mouse IL-3, also stimulated bone marrow suppressor cell activity. The combination of GM-CSF with IL-3 resulted in a synergistic rather than simply an additive induction of bone marrow suppressor cells. Conditioned medium of CSF-1-producing L cells did not induce bone marrow immune suppressor cells. These results suggest that during heightened periods of myelopoiesis, induction of bone marrow-derived immune suppressor cells may be stimulated by CSFs, such as by the singular or combined effects of GM-CSF and IL-3.     

Bone marrow cells participate in tumor vessel formation that supports the growth of Ewing’s sarcoma in the lung

An MHC-mismatch bone marrow (BM) transplant Ewing’s sarcoma mouse model was used to investigate whether BM cells participate in the vessel formation that support Ewing’s sarcoma lung metastasis. BM cells from H-2K^b/d donor mice were transplanted into sublethally irradiated H-2K^d recipient mice. Donor BM cells were identified using the H-2K^b marker. Engraftment was confirmed by identifying the H-2K^b IL-1β-type specific polymorphism. After engraftment highly lung metastatic TC71-PM4 cells were injected intravenously. Mice were sacrificed 10 weeks after tumor cell injection. Hematoxylin-and-eosin staining was performed to identify lung metastatic foci. These tumors were then evaluated using immunohistochemical analysis. H-2K^b-positive cells were found in lung metastases but not in normal lung, liver or spleen tissues. Injection of CM-Dil-labeled BM cells into tumor bearing and control mice showed that nonspecific organ migration occurred at 24 h, but that these cells were absent 1 week later in control mice. These data suggest that the migration of the H-2K^b BM cells to lung nodules was specific because these cells were observed 14 weeks after transplantation. Co-localization of H-2K^b and CD31 or VE-Cadherin demonstrated that some endothelial cells were BM-derived. Co-localization of H-2K^b and Desmin, smooth muscle actin (α-SMA) or PDGFR-β indicated that a fraction of pericytes was also BM-derived. These results suggest that BM cells participate in the vascular formation that supports the growth of Ewing’s sarcoma lung metastases. BM cells migrated to the metastatic tumor and differentiated into endothelial cells and pericytes. These data indicated that targeting this process may have therapeutic potential.     

Impaired development and dysfunction of endothelial progenitor cells in type 2 diabetic mice

AimDysfunction of circulating endothelial progenitor cells (EPCs) has been shown to affect the development of microvascular diseases in diabetes patients. The aim of this study was to elucidate the development and mechanical dysfunction of EPCs in type 2 diabetes (T2D).MethodsThe colony-forming capacity of EPCs and differentiation potential of bone marrow (BM) c-Kit(+)/Sca-I(+) lineage-negative mononuclear cells (KSL) were examined in T2D mice, db/db mice and KKA^y mice, using EPC colony-forming assay (EPC-CFA).ResultsT2D mice had fewer BM stem/progenitor cells, and proliferation of KSL was lowest in the BM of db/db mice. In T2D mice, the frequency of large colony-forming units (CFUs) derived from BM-KSL was highly reduced, indicating dysfunction of differentiation into mature EPCs. Only a small number of BM-derived progenitors [CD34(+) KSL cells], which contribute to the supply of EPCs for postnatal neovascularization, was also found. Furthermore, in terms of their plasticity to transdifferentiate into various cell types, BM-KSL exhibited a greater potential to differentiate into granulocyte macrophages (GMs) than into other cell types.ConclusionT2D affected EPC colony formation and differentiation of stem cells to mature EPCs or haematopoietic cells. These data suggest opposing regulatory mechanisms for differentiation into mature EPCs and GMs in T2D mice.     

Erythropoietin is a potent physiologic stimulus for endothelial progenitor cell mobilization

Increasing evidence suggests that postnatal neovascularization involves the recruitment of circulating endothelial progenitor cells (EPCs). Hematopoietic and endothelial cell lineages share common progenitors. Cytokines formerly thought to be specific for the hematopoietic system have only recently been shown to affect several functions in endothelial cells. Accordingly, we investigated the stimulatory potential of erythropoietin (Epo) on EPC mobilization and neovascularization. The bone marrow of Epo-treated mice showed a significant increase in number and proliferation of stem and progenitor cells as well as in colony-forming units. The number of isolated EPCs and CD34+/flk-1+ precursor cells was significantly increased in spleen and peripheral blood of Epo-treated mice compared with phosphate-buffered saline-treated mice. In in vivo models of postnatal neovascularization, Epo significantly increased inflammation- and ischemia-induced neovascularization. The physiologic relevance of these findings was investigated in patients with coronary heart disease. In a multivariate regression model, serum levels of Epo and vascular endothelial growth factor were significantly associated with the number of stem and progenitor cells in the bone marrow as well as with the number and function of circulating EPCs. In conclusion, the present study suggests that Epo stimulates postnatal neovascularization at least in part by enhancing EPC mobilization from the bone marrow. Epo appears to physiologically regulate EPC mobilization in patients with ischemic heart disease. Thus, Epo serum levels may help in identifying patients with impaired EPC recruitment capacity.     

Insulin modulates ischemia-induced endothelial progenitor cell mobilization and neovascularization in diabetic mice

Decreased levels of circulating endothelial progenitor cells (EPCs) predict increased risk of cardiovascular events in diabetic patients. Insulin treatment exerts important cardiovascular protection. Whether and how insulin participates in the EPC regulation of postnatal neovascularization are currently unclear. We employed a mouse hindlimb ischemia model to study EPC mobilization in non-diabetic and streptozotocin-induced diabetic mice. Insulin was administered to diabetic animals postoperatively. To determine the role of EPCs contributing to postnatal vasculogenesis, we used bone marrow-transplanted mice whose bone marrow cells selectively expressed enhanced green fluorescent protein (EGFP). Insulin treatment improved EPC mobilization into peripheral blood, accelerated transcutaneous oxygen pressure restoration and increased capillary density in the ischemic limb associated with partial incorporation of EGFP-positive cells into the capillaries. Insulin treatment restored ischemia-induced release of stromal-derived growth factor 1α and vascular endothelial growth factor (VEGF), and consequently enhanced the activity of Akt and endothelial nitric oxide synthase (eNOS) as well as matrix metalloproteinase-9 in bone marrow. Insulin also augmented tissue-level activation of VEGF/Akt/eNOS pathway. However, all such effects of insulin were completely blocked by combined treatment with a NOS inhibitor. Our data suggested that insulin treatment improved ischemia-induced EPC mobilization and contributed to compensatory neovascularization in diabetic mice through a VEGF/eNOS-related pathway.     

Erythropoietin improves cardiac function through endothelial progenitor cell and vascular endothelial growth factor mediated neovascularization.

AIMS: Erythropoietin (EPO) improves cardiac function and induces neovascularization in chronic heart failure (CHF), although the exact mechanism has not been elucidated. We studied the effects of EPO on homing and incorporation of endothelial progenitor cells (EPC) into the myocardial microvasculature and myocardial expression of angiogenic factors. METHODS AND RESULTS: CHF was induced in rats by coronary artery ligation resulting in myocardial infarction (MI) after bone marrow had been replaced by human placental alkaline phosphatase (hPAP) transgenic cells. We studied the effects of darbepoetin alfa treatment (EPO, 40 microg/kg, every 3 weeks, starting 3 weeks after MI) on longitudinal changes in left ventricular (LV) function, circulating EPC, myocardial histology, and expression of vascular endothelial growth factor (VEGF) determined 9 weeks after MI. EPO prevented LV-dilatation and improved cardiac function (all P < 0.05), which was associated with 42% increased capillary growth (P < 0.01). EPO-induced mobilization of EPC from the bone marrow (P < 0.01), which resulted in a three-fold increased homing of EPC into the cardiac microvasculature. The percentage of the endothelium that consisted of bone marrow derived cells was significantly increased (3.9 +/- 0.5 vs. 11.4 +/- 1%, P < 0.001) comprising 30% of the newly formed capillaries. In addition, EPO treatment resulted in a 4.5-fold increased myocardial expression of VEGF, which correlated strongly with neovascularization (r = 0.67; P < 0.001). VEGF was equally expressed by endothelial cells of myocardial and bone marrow origin. CONCLUSION: EPO-induced neovascularization in post-MI heart failure is mediated through a combination of EPC recruitment from the bone marrow and increased myocardial expression of VEGF.     

Estrogen-mediated endothelial progenitor cell biology and kinetics for physiological postnatal vasculogenesis

Estrogen has been demonstrated to promote therapeutic reendothelialization after vascular injury by bone marrow (BM)-derived endothelial progenitor cell (EPC) mobilization and phenotypic modulation. We investigated the primary hypothesis that estrogen regulates physiological postnatal vasculogenesis by modulating bioactivity of BM-derived EPCs through the estrogen receptor (ER), in cyclic hormonally regulated endometrial neovascularization. Cultured human EPCs from peripheral blood mononuclear cells (PB-MNCs) disclosed consistent gene expression of ER alpha as well as downregulated gene expressions of ER beta. Under the physiological concentrations of estrogen (17beta-estradiol, E2), proliferation and migration were stimulated, whereas apoptosis was inhibited on day 7 cultured EPCs. These estrogen-induced activities were blocked by the receptor antagonist, ICI182,780 (ICI). In BM transplanted (BMT) mice with ovariectomy (OVX) from transgenic mice overexpressing beta-galactosidase (lacZ) regulated by an endothelial specific Tie-2 promoter (Tie-2/lacZ/BM), the uterus demonstrated a significant increase in BM-derived EPCs (lacZ expressing cells) incorporated into neovasculatures detected by CD31 immunohistochemistry after E2 administration. The BM-derived EPCs that were incorporated into the uterus dominantly expressed ER alpha, rather than ER beta in BMT mice from BM of transgenic mice overexpressing EGFP regulated by Tie-2 promoter with OVX (Tie-2/EGFP/BMT/OVX) by ERs fluorescence immunohistochemistry. An in vitro assay for colony forming activity as well as flow cytometry for CD133, CD34, KDR, and VE-cadherin, using human PB-MNCs at 5 stages of the female menstrual-cycle (early-proliferative, pre-ovulatory, post-ovulatory, mid-luteal, late-luteal), revealed cycle-specific regulation of EPC kinetics. These findings demonstrate that physiological postnatal vasculogenesis involves cyclic, E2-regulated bioactivity of BM-derived EPCs, predominantly through the ER alpha.     

Caveolin plays a central role in endothelial progenitor cell mobilization and homing in SDF-1-driven postischemic vasculogenesis

When neovascularization is triggered in ischemic tissues, angiogenesis but also (postnatal) vasculogenesis is induced, the latter requiring the mobilization of endothelial progenitor cells (EPC) from the bone marrow. Caveolin, the structural protein of caveolae, was recently reported to directly influence the angiogenic process through the regulation of the vascular endothelial growth factor (VEGF)/nitric oxide pathway. In this study, using caveolin-1 null mice (Cav(-/-)), we examined whether caveolin was also involved in the EPC recruitment in a model of ischemic hindlimb. Intravenous infusion of Sca-1(+) Lin(-) progenitor cells, but not bone marrow transplantation, rescued the defective neovascularization in Cav(-/-) mice, suggesting a defect in progenitor mobilization. The adhesion of Cav(-/-) EPC to bone marrow stromal cells indeed appeared to be resistant to the otherwise mobilizing SDF-1 (Stromal cell-Derived Factor-1) exposure because of a defect in the internalization of the SDF-1 cognate receptor CXCR4. Symmetrically, the attachment of Cav(-/-) EPC to SDF-1-presenting endothelial cells was significantly increased. Finally, EPC transduction with caveolin small interfering RNA reproduced this advantage in vitro and, importantly, led to a more extensive rescue of the ischemic hindlimb after intravenous infusion (versus sham-transfected EPC). These results underline the critical role of caveolin in ensuring the caveolae-mediated endocytosis of CXCR4, regulating both the SDF-1-mediated mobilization and peripheral homing of progenitor cells in response to ischemia. In particular, a transient reduction in caveolin expression was shown to therapeutically increase the engraftment of progenitor cells.     

Bone marrow-derived cells are not involved in reendothelialized endothelium as endothelial cells after simple endothelial denudation in mice

It has been shown that bone marrow (BM)-derived cells are involved in repaired endothelium induced by a model such as neointima-produced wire injury in mice. This has not been shown in a less invasive model that results in simple reendothelialization. A new wire-induced simple endothelial denudation model of the common carotid artery (CCA) of mice, which did not form neointima at 14 days after the operation, was established. At 7 days after operation, the CCAs were reendothelialized from the aortic arch and the carotid bifurcation but not completely, shown by whole-mount CD31 immunohistochemical staining. Scanning electron microscopy revealed that unendothelialized area was covered with platelets. To determine the involvement of BM-derived cells in the repaired endothelium, the wild-type (WT) C57BL/6 mice, in which BM cells derived from strain-matched green fluorescent protein (GFP)-transgenic mice were transplanted, were operated upon. As a result, there was no GFP-positive endothelial cell (EC) in reendothelialized endothelium, otherwise GFP-positive ‘dendritic’-like cells were recruited under the repaired endothelial layer. Administration of recombinant human erythropoietin [1,000 IU/(kg day) at 0–3 days after operation subcutaneously], which has been shown to increase endothelial progenitor cells in peripheral blood, also could not recruit BM-derived cells as ECs in BM-transplanted mice despite accelerating reendothelialization in WT mice [%reendothelialized area of the administrated group 78.0 ± 9.4% (mean ± SD) vs. the control group 63.0 ± 4.4%, P < 0.05]. These results suggest that BM-derived cells may not be involved in reendothelialization as ECs after simple endothelial denudation in mice.     

Human gastric cancer organizes neighboring lymphatic vessels via recruitment of bone marrow-derived lymphatic endothelial progenitor cells

Background

Lymphatic metastasis is a critical determinant of prognosis in human gastrointestinal cancers. Studies suggest that lymphatic metastasis has been linked to lymphangiogenesis, the growth of lymphatic vessels, while the mechanisms of tumor lymphangiogenesis remain poorly characterized.

Methods

Human gastric cancer cells, MKN45, were implanted under the gastric submucosa of nude mice receiving green fluorescent protein-positive bone marrow (BM) transplants. In addition, MKN45 cells were subcutaneously injected into the back of each mouse as a model of human tumor xenografts. The tumor tissue was analyzed 3?weeks after implantation.

Results

The mice with MKN45 cells represent recruitment and incorporation of BM-derived lymphatic endothelial progenitor cells (LEPC) into gastric lymphatics. Moreover, in a xenograft model, MKN45 cells induced lymphangiogenesis as well as recruitment of BM-derived LEPC in tumor lymphatics in a xenograft model.

Conclusions

These findings of this study suggest that human gastric adenocarcinoma induces tumor lymphangiogenesis via recruitment of LEPC from BM.     

Presence of bone marrow-derived circulating progenitor endothelial cells in the newly formed lymphatic vessels

Bone marrow (BM)-derived circulating endothelial precursor cells (CEPCs) have been reported to incorporate into newly formed blood vessels under physiologic and pathologic conditions. However, it is unknown if CEPCs contribute to lymphangiogenesis. Here we show that in a corneal lymphangiogenesis model of irradiated mice reconstituted with enhanced green fluorescent protein (EGFP)-positive donor bone marrow cells, CEPCs are present in the newly formed lymphatic vessels. Depletion of bone marrow cells by irradiation remarkably suppressed lymphangiogenesis in corneas implanted with fibroblast growth factor-2 (FGF-2). Further, transplantation of isolated EGFP-positive/vascular endothelial growth factor receptor-3-positive (EGFP+/VEGFR-3+) or EGFP+/VEGFR-2+ cell populations resulted in incorporation of EGFP+ cells into the newly formed lymphatic vessels. EGFP+/CEPCs were also present in peritumoral lymphatic vessels of a fibrosarcoma. These data suggest that BM-derived CEPCs may play a role in "lymphvasculogenesis."     

Critical role of scavenger receptor-BI-expressing bone marrow-derived endothelial progenitor cells in the attenuation of allograft vasculopathy after human apo A-I transfer

Allograft vasculopathy is the leading cause of death in patients with heart transplantation. Accelerated endothelial regeneration mediated by enhanced endothelial progenitor cell (EPC) incorporation may attenuate the development of allograft vasculopathy. We investigated the hypothesis that modulation of EPC biology and attenuation of allograft vasculopathy by increased high-density lipoprotein cholesterol after human apo A-I (AdA-I) transfer requires scavenger receptor (SR)-BI expression in bone marrow-derived EPCs. After AdA-I transfer, the number of circulating EPCs increased 2.0-fold (P < .001) at different time points in C57BL/6 mice transplanted with SR-BI(+/+) bone marrow but remained unaltered in mice with SR-BI(-/-) bone marrow. The effect of high-density lipoprotein on EPC migration in vitro requires signaling via SR-BI and extracellular signal-regulated kinases and is dependent on increased nitric oxide (NO) production in EPCs. Human apo A-I transfer 2 weeks before paratopic artery transplantation reduced intimal area at day 21 3.7-fold (P < .001) in mice with SR-BI(+/+) bone marrow but had no effect in mice with SR-BI(-/-) bone marrow. AdA-I transfer potently stimulated EPC incorporation and accelerated endothelial regeneration in chimeric SR-BI(+/+) mice but not in chimeric SR-BI(-/-) mice. In conclusion, human apo A-I transfer accelerates endothelial regeneration mediated via SR-BI expressing bone marrow-derived EPCs, thereby preventing allograft vasculopathy.     

Pressure-induced cardiac overload induces upregulation of endothelial and myocardial progenitor cells

AIM: The regulation of angiogenesis in the hypertrophied overloaded heart is incompletely understood. Bone-marrow-derived progenitor cells have been shown to contribute to endothelial homeostasis, repair, and new blood vessel formation. We therefore studied the effects of pressure overload on angiogenesis and progenitor cells. METHODS AND RESULTS: Pressure overload induced by transaortic constriction (TAC, C57/Bl6 mice, 360 microm for 35 days) increased left ventricular (LV) systolic pressure, the ratio of heart weight to tibia length, cardiomyocyte diameters, and cardiac apoptosis and fibrosis compared to sham-operated mice. In the TAC group, the number of cycling Ki67 pos cells increased from none to 0.1 +/- 0.02% in cardiomyocytes and from 0.17 +/- 0.02% to 0.65 +/- 0.1% in non-cardiomyocytes, P < 0.001. stem cell antigen 1(pos)/vascular endothelial growth factor receptor 2 pos endothelial progenitor cells (EPC) increased to 210 +/- 25% in the blood and to 196 +/- 21% in the bone marrow (P < 0.01). TAC upregulated cultured spleen-derived DiLDL pos/lectin pos EPC to 221 +/- 37%, P < 0.001. Cardiac hypertrophy and upregulation of EPC secondary to cardiac pressure overload were associated with increased extra-cardiac neoangiogenesis (54 +/- 12% increase, P < 0.05). In endothelial nitric oxide synthase double knockout mice, the upregulation of EPC by TAC was abolished. Maladaptive myocardial remodelling in TAC mice was characterized by a reduction of CD31 pos cells. In mice transplanted with green fluorescent protein pos bone marrow, TAC markedly increased myocardial bone marrow-derived CD31 pos cells from 2.37 +/- 0.4% to 7.76 +/- 1.5% and MEF2 pos cells from 1.8 +/- 0.4/mm2 to 20.5 +/- 5.3/mm2, P < 0.05. CONCLUSION: Pressure-induced myocardial hypertrophy leads to upregulation of systemic EPCs, increased extra-cardiac angiogenesis, and upregulation of intra-myocardial bone marrow-derived endothelial and myocyte precursor cells. The data show that afterload-dependent regulation of bone marrow-derived progenitor cells contributes to angiogenesis in myocardial hypertrophy.     

SDF-1 involvement in endothelial phenotype and ischemia-induced recruitment of bone marrow progenitor cells

Chemokine stromal derived factor 1 (SDF-1) is involved in trafficking of hematopoietic stem cells (HSCs) from the bone marrow (BM) to peripheral blood (PB) and has been found to enhance postischemia angiogenesis. This study was aimed at investigating whether SDF-1 plays a role in differentiation of BM-derived c-kit(+) stem cells into endothelial progenitor cells (EPCs) and in ischemia-induced trafficking of stem cells from PB to ischemic tissues. We found that SDF-1 enhanced EPC number by promoting alpha(2), alpha(4), and alpha(5) integrin-mediated adhesion to fibronectin and collagen I. EPC differentiation was reduced in mitogen-stimulated c-kit(+) cells, while cytokine withdrawal or the overexpression of the cyclin-dependent kinase (CDK) inhibitor p16(INK4) restored such differentiation, suggesting a link between control of cell cycle and EPC differentiation. We also analyzed the time course of SDF-1 expression in a mouse model of hind-limb ischemia. Shortly after femoral artery dissection, plasma SDF-1 levels were up-regulated, while SDF-1 expression in the bone marrow was down-regulated in a timely fashion with the increase in the percentage of PB progenitor cells. An increase in ischemic tissue expression of SDF-1 at RNA and protein level was also observed. Finally, using an in vivo assay such as injection of matrigel plugs, we found that SDF-1 improves formation of tubulelike structures by coinjected c-kit(+) cells. Our findings unravel a function for SDF-1 in increase of EPC number and formation of vascular structures by bone marrow progenitor cells.     

Sympathetic nervous system regulates bone marrow-derived cell egress through endothelial nitric oxide synthase activation: role in postischemic tissue remodeling

OBJECTIVE: Catecholamines have been shown to control bone marrow (BM)-derived cell egress, yet the cellular and molecular mechanisms involved in this effect and their subsequent participation to postischemic vessel growth are poorly understood. METHODS AND RESULTS: Tyrosine hydroxylase mRNA levels, as well as dopamine (DA) and norepinephrine (NE) contents, were increased in the ischemic BM of mice with right femoral artery ligation. Angiographic score, capillary density, and arteriole number were markedly increased by treatments with DA (IP, 50 mg/kg, 5 days) or NE (IP, 2.5 mg/kg, 5 days). Using chimeric mice lethally irradiated and transplanted with BM-derived cells from green fluorescent protein mice, we showed that DA and NE enhanced by 70% (P<0.01) and 62% (P<0.001), respectively, the number of green fluorescent protein-positive BM-derived cells in ischemic tissue and promoted their ability to differentiate into cells with endothelial and inflammatory phenotypes. Similarly, both DA and NE increased the in vitro differentiation of cultured BM-derived cells into cells with endothelial phenotype. This increase was blunted by the nitric oxide synthase inhibitor Nω-nitro-L-arginine methyl ester. DA and NE also upregulated the number of CD45-positive cells in blood 3 days after ischemia and that of macrophages in ischemic tissue 21 days after ischemia. Of interest, DA and NE increased BM endothelial nitric oxide synthase (eNOS) mRNA levels and were unable to promote BM-derived cell mobilization in chimeric eNOS-deficient mice lethally irradiated and transplanted with BM-derived cells from wild-type animals. Furthermore, administration of a β2 adrenergic agonist (clenbuterol, IP, 2 mg/kg, 5 days) and that of a dopaminergic D1/D5 receptor agonist (SKF-38393, IP, 2.5 mg/kg, 5 days) also enhanced BM-derived cell mobilization and subsequently postischemic vessel growth. CONCLUSION These results unravel, for the first time, a major role for the sympathetic nervous system in BM-derived cell egress through stromal eNOS activation.     

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

OBJECTIVE: Recent studies have documented the presence of bone marrow-derived endothelial progenitor cells (EPC) in the circulation of several species. This study was designed to evaluate the use of engineered EPC for vascular gene delivery into angioplasty-induced arterial lesions. METHODS AND RESULTS: EPC could easily be isolated from whole bone marrow and peripheral blood of adult rats. Differentiation was induced by culture on fibronectin in the presence of endothelial specific growth factors. Rat EPC shared several phenotypic and functional properties with mature endothelial cells. Recombinant retroviruses were generated encoding for the anticoagulants tissue-type plasminogen activator (tPA) and hirudin. Efficient (>90%) ex vivo gene transfer could be achieved resulting in high levels of transgene production. Engineered EPC were locally infused into freshly balloon-injured carotid arteries. Analysis of day 7 vessels showed 73+/-10% luminal coverage of the lesioned arterial bed with transduced EPC. Sustained secretion of both anticoagulants could be detected in organ cultures of explanted arteries. EPC seeding inhibited dilation of the injured arterial segment and prevented reduction of media thickness. However, rapid repopulation with EPC failed to attenuate neointima formation in this model. CONCLUSIONS: Peripheral blood and bone marrow can be used as source for endothelial lineage cells. Cultured EPC can be genetically engineered by retroviral gene transfer and serve as cellular vehicles for vascular gene and drug delivery of anticoagulants. Local transplantation of EPC attenuates reendothelialization of angioplasty-injured arteries but fails to inhibit neointima proliferation.     

Diverse contribution of bone marrow-derived late-outgrowth endothelial progenitor cells to vascular repair under pulmonary arterial hypertension and arterial neointimal formation

AimsIt is still controversial whether bone marrow (BM)-derived endothelial progenitor cells (EPCs) can contribute to vascular repair and prevent the progression of vascular diseases. We aimed to characterize BM-derived EPC subpopulations and to evaluate their therapeutic efficacies to repair injured vascular endothelium of systemic and pulmonary arteries.Methods and resultsBM mononuclear cells of Fisher-344 rats were cultured under endothelial cell-conditions. Early EPCs appeared on days 3–6. Late-outgrowth and very late-outgrowth EPCs (LOCs and VLOCs) were defined as cells forming cobblestone colonies on days 9–14 and 17–21, respectively. Among EPC subpopulations, LOCs showed the highest angiogenic capability with enhanced proliferation potential and secretion of proangiogenic proteins. To investigate the therapeutic effects of these EPCs, Fisher-344 rats underwent wire-mediated endovascular injury in femoral artery (FA) and were concurrently injected intraperitoneally with 60 mg/kg monocrotaline (MCT). Injured rats were then treated with six injections of one of three EPCs (1 × 10⁶ per time). After 4 weeks, transplanted LOCs, but not early EPCs or VLOCs, significantly attenuated neointimal lesion formation in injured FAs. Some of CD31⁺ LOCs directly replaced the injured FA endothelium (replacement ratio: 11.7 ± 7.0%). In contrast, any EPC treatment could neither replace MCT-injured endothelium of pulmonary arterioles nor prevent the progression of pulmonary arterial hypertension (PAH). LOCs modified protectively the expression profile of angiogenic and inflammatory genes in injured FAs, but not in MCT-injured lungs.ConclusionBM-derived LOCs can contribute to vascular repair of injured systemic artery; however, even they cannot rescue injured pulmonary vasculature under MCT-induced PAH.