Role of Bone Marrow–Derived Progenitor Cells in Cuff-Induced Vascular Injury in Mice

Arterial Adventitial Vasa Vasorum Hyperplasia involved in Atherosclerotic Plaque Formation in a Rabbit Model

OBJECTIVE

It was previously believed that atherosclerotic (AS) plaque starts to develop from the intima and that intraplaque vasa vasorum (VV) hyperplasia promotes adventitial VV (AVV) hyperplasia. However, recent studies have shown that arterial AVV hyperplasia precedes early intimal thickening, suggesting its possible role as an initiating factor of AS. To provide further insight into this process, in this study, we examine the evolution of AAV and VV development in a preclinical model of early AS with longitudinal ultrasound imaging.

METHODS

Models of early AS were established. Duplex ultrasound scanning and contrast-enhanced ultrasound were performed for diagnosis. Pearson correlation tests were used to analyze the relationships between AVV hyperplasia and VV hyperplasia, or between AVV hyperplasia and intima-media thickness (IMT).

RESULTS

During 0-12 wk of high-fat feeding, AVV gradually increased and intima-media thickened gradually in the observation area; in the 2nd wk of high-fat feeding, the observation area showed obvious AVV proliferation; at the 4th wk, the intima-media membrane became thicker; at the 12th wk, early plaque formation and intraplaque VV proliferation were observed. There was a strong positive correlation between AVV proliferation and IMT thickening and a strong negative correlation between AVV proliferation and the change rate of vessel diameter.

CONCLUSION

This study demonstrated that AVV proliferation in the arteries occurred earlier than IMT thickening and was positively correlated with IMT. At present, the indicators of ultrasonic diagnosis of AS, such as IMT, Intraplaque VV, Echo property, all appear in the advanced stage of AS. The AVV may be an innovative diagnostic target for the early stage of AS plaque.

Carbon Monoxide Suppresses Neointima Formation in Transplant Arteriosclerosis by Inhibiting Vascular Progenitor Cell Differentiation

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VEGF treatment promotes bone marrow-derived CXCR4+ mesenchymal stromal stem cell differentiation into vessel endothelial cells

Stem/progenitor cells serve an important role in the process of blood vessel repair. However, the mechanism of vascular repair mediated by C-X-C chemokine receptor type 4-positive (CXCR4⁺) bone marrow-derived mesenchymal stem cells (BMSCs) following myocardial infarction remains unclear. The aim of the present study was to investigate the effects of vascular endothelial growth factor (VEGF) on vessel endothelial differentiation from BMSCs. CXCR4⁺ BMSCs were isolated from the femoral bone marrow of 2-month-old mice and the cells were treated with VEGF. Expression of endothelial cell markers and the functional properties were assessed by reverse transcription-quantitative polymerase chain reaction, flow cytometry and vascular formation analyses. The results indicated that the CXCR4⁺ BMSCs from femoral bone marrow cells expressed putative cell surface markers of mesenchymal stem cells. Treatment with VEGF induced platelet/endothelial cell adhesion molecule-1 (PECAM-1) and von Willebrand factor (vWF) expression at the transcriptional and translational levels, compared with untreated controls. Moreover, VEGF treatment induced CXCR4⁺ BMSCs to form hollow tube-like structures on Matrigel, suggesting that the differentiated endothelial cells had the functional properties of blood vessels. The results demonstrate that the CXCR4⁺ BMSCs were able to differentiate into vessel endothelial cells following VEGF treatment. For cell transplantation in vascular disease, it may be concluded that CXCR4⁺ BMSCs are a novel source of endothelial progenitor cells with high potential for application in vascular repair.

Cuff-Induced Neointimal Formation in Mouse Models

Ischemic heart failure caused by atherosclerosis is a major cause of death worldwide. Although remarkable technological advances have been made in the treatment of coronary heart disease, there is as yet no treatment that can sufficiently suppress the progression of atherosclerosis, including neointimal thickening. Therefore, a precise understanding of the mechanism of neointimal hyperplasia will provide the development of new technologies. Both ApoE-KO and LDLR-KO mice have been employed to generate other relevant mouse models of cardiovascular disease through breeding strategies. Although these mice are effective tools for the investigation of atherosclerosis, development of a progressive atherosclerotic lesion takes a long time, resulting in increase of both the costs and the space needed for the research. Thus, it is necessary to develop simpler tools that would allow easy evaluation of atherosclerosis in mouse models. In this review, we discuss our experience in generating mouse models of cuff-induced injury of the femoral artery and attempt to provide a better understanding of cuff-induced neointimal formation.

Vascular wall progenitor cells in health and disease

The vasculature plays an indispensible role in organ development and maintenance of tissue homeostasis, such that disturbances to it impact greatly on developmental and postnatal health. Although cell turnover in healthy blood vessels is low, it increases considerably under pathological conditions. The principle sources for this phenomenon have long been considered to be the recruitment of cells from the peripheral circulation and the re-entry of mature cells in the vessel wall back into cell cycle. However, recent discoveries have also uncovered the presence of a range of multipotent and lineage-restricted progenitor cells in the mural layers of postnatal blood vessels, possessing high proliferative capacity and potential to generate endothelial, smooth muscle, hematopoietic or mesenchymal cell progeny. In particular, the tunica adventitia has emerged as a progenitor-rich compartment with niche-like characteristics that support and regulate vascular wall progenitor cells. Preliminary data indicate the involvement of some of these vascular wall progenitor cells in vascular disease states, adding weight to the notion that the adventitia is integral to vascular wall pathogenesis, and raising potential implications for clinical therapies. This review discusses the current body of evidence for the existence of vascular wall progenitor cell subpopulations from development to adulthood and addresses the gains made and significant challenges that lie ahead in trying to accurately delineate their identities, origins, regulatory pathways, and relevance to normal vascular structure and function, as well as disease.

The interferon stimulated gene 12 inactivates vasculoprotective functions of NR4A nuclear receptors

RATIONALE

Innate and adaptive immune responses alter numerous homeostatic processes that are controlled by nuclear hormone receptors. NR4A1 is a nuclear receptor that is induced in vascular pathologies, where it mediates protection.

OBJECTIVE

The underlying mechanisms that regulate the activity of NR4A1 during vascular injury are not clear. We therefore searched for modulators of NR4A1 function that are present during vascular inflammation.

METHODS AND RESULTS

We report that the protein encoded by interferon stimulated gene 12 (ISG12), is a novel interaction partner of NR4A1 that inhibits the transcriptional activities of NR4A1 by mediating its Crm1-dependent nuclear export. Using 2 models of vascular injury, we show that ISG12-deficient mice are protected from neointima formation. This effect is dependent on the presence of NR4A1, as mice deficient for both ISG12 and NR4A1 exhibit neointima formation similar to wild-type mice.

CONCLUSIONS

These findings identify a previously unrecognized feedback loop activated by interferons that inhibits the vasculoprotective functions of NR4A nuclear receptors, providing a potential new therapeutic target for interferon-driven pathologies.

It is all in the blood: the multifaceted contribution of circulating progenitor cells in diabetic complications

Diabetes mellitus (DM) is a worldwide growing disease and represents a huge social and healthcare problem owing to the burden of its complications. Micro- and macrovascular diabetic complications arise from excess damage through well-known biochemical pathways. Interestingly, microangiopathy hits the bone marrow (BM) microenvironment with features similar to retinopathy, nephropathy and neuropathy. The BM represents a reservoir of progenitor cells for multiple lineages, not limited to the hematopoietic system and including endothelial cells, smooth muscle cells, cardiomyocytes, and osteogenic cells. All these multiple progenitor cell lineages are profoundly altered in the setting of diabetes in humans and animal models. Reduction of endothelial progenitor cells (EPCs) along with excess smooth muscle progenitor (SMP) and osteoprogenitor cells creates an imbalance that promote the development of micro- and macroangiopathy. Finally, an excess generation of BM-derived fusogenic cells has been found to contribute to diabetic complications in animal models. Taken together, a growing amount of literature attributes to circulating progenitor cells a multi-faceted role in the pathophysiology of DM, setting a novel scenario that puts BM and the blood at the centre of the stage.

Magnetic resonance imaging of bone marrow cell-mediated interleukin-10 gene therapy of atherosclerosis

Background

A characteristic feature of atherosclerosis is its diffuse involvement of arteries across the entire human body. Bone marrow cells (BMC) can be simultaneously transferred with therapeutic genes and magnetic resonance (MR) contrast agents prior to their transplantation. Via systemic transplantation, these dual-transferred BMCs can circulate through the entire body and thus function as vehicles to carry genes/contrast agents to multiple atherosclerosis. This study was to evaluate the feasibility of using in vivo MR imaging (MRI) to monitor BMC-mediated interleukin-10 (IL-10) gene therapy of atherosclerosis.

Methodology

For in vitro confirmation, donor mouse BMCs were transduced by IL-10/lentivirus, and then labeled with a T2-MR contrast agent (Feridex). For in vivo validation, atherosclerotic apoE^−/− mice were intravenously transplanted with IL-10/Feridex-BMCs (Group I, n = 5) and Feridex-BMCs (Group II, n = 5), compared to controls without BMC transplantation (Group III, n = 5). The cell migration to aortic atherosclerotic lesions was monitored in vivo using 3.0T MRI with subsequent histology correlation. To evaluate the therapeutic effect of BMC-mediated IL-10 gene therapy, we statistically compared the normalized wall indexes (NWI) of ascending aortas amongst different mouse groups with various treatments.

Principal Findings

Of in vitro experiments, simultaneous IL-10 transduction and Feridex labeling of BMCs were successfully achieved, with high cell viability and cell labeling efficiency, as well as IL-10 expression efficiency (≥90%). Of in vivo experiments, MRI of animal groups I and II showed signal voids within the aortic walls due to Feridex-created artifacts from the migrated BMCs in the atherosclerotic plaques, which were confirmed by histology. Histological quantification showed that the mean NWI of group I was significantly lower than those of group II and group III (P<0.05).

Conclusion

This study has confirmed the possibility of using MRI to track, in vivo, IL-10/Feridex-BMCs recruited to atherosclerotic lesions, where IL-10 genes function to prevent the progression of atherosclerosis.

CXCR4+ progenitors derived from bone mesenchymal stem cells differentiate into endothelial cells capable of vascular repair after arterial injury

Recent findings indicate that bone marrow mesenchymal stem cells (BMSCs) participate in the process of neovascularization in response to repair to injury and are involved in postinfarction myocardial repair. It is unclear what special characteristics the vascular progenitors of bone marrow origin has. CXCR4(+) stem/progenitor cells mobilized to the infarct area and improved the myocardial repair. In present study, we aimed to determine whether CXCR4(+)BMSCs contribute to the angiogenic capacity in vitro and in vivo. CXCR4(+)BMSCs were separated by using paramagnetic microbeads and cultured. RT-PCR and FACS analysis confirmed the gene expression phenotype. The uptake of acetylated low density lipoprotein (acLDL) and the tube formation evaluated the function of CXCR4(+)BMSCs. The effect of CXCR4(+)BMSCs transplantation on neovascularization was investigated in a murine model hindlimb ischemia. After induced by VEGF, CXCR4(+)BMSCs expressed the endothelial cells (ECs) phenotype. The expression of EC markers, PECAM-1, and von Willebrand factor (vWF) increased significantly at both the mRNA and protein levels. In addition, CXCR4(+)BMSCs enhanced the uptakes of Dil-acLDL and form capillary-like tubes in vitro. In vivo the local transfer of CXCR4(+)BMSCs increased neovascularization in ischemic hindlimb. These results demonstrate that CXCR4(+)BMSCs differentiate into ECs and contribute to neovascularization in the vascular lesion,, which indicate the important therapeutic implications for cardiovascular diseases and a new cell source for cell-based vascular engineering and repair in the future.

Dual transfer of GFP gene and MGd into stem-progenitor cells: toward in vivo MRI of stem cell-mediated gene therapy of atherosclerosis

RATIONALE AND OBJECTIVES

The aim of this study was to develop a new technique, the use of magnetic resonance (MR) imaging (MRI) to monitor gene/MR-cotransferred stem-progenitor cells (SPCs) recruited to atherosclerosis.

MATERIALS AND METHODS

First, a green fluorescent protein (GFP) gene and a T1 MR contrast agent (motexafin gadolinium [MGd]) were cotransferred into neural or bone marrow (BM)-derived SPCs. GFP expression and MGd signal were confirmed by fluorescent microscopy and quantified by flow cytometry. Cell viability and proliferation were then evaluated by trypan blue exclusion and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay, and GFP/MGd-transferred cells were imaged using 1.5-T and 9.4-T MR scanners. For in vivo validation, GFP/MGd-cotransferred beta-galactosidase-BM SPCs were transplanted to apolipoprotein E-knockout mice, and cell migration to atherosclerotic aortas was monitored using 9.4-T micro-MRI with subsequent histologic correlations.

RESULTS

Fluorescent microscopy demonstrated simultaneous GFP expression and MGd signals in cotransferred-cells. Quantitative flow cytometry showed GFP-positive cells at 47 +/- 25% and 56 +/- 12% and MGd-positive cells at 96 +/- 6% and 57 +/- 11% for neural stem cells and BM cells, respectively. Cell viability and metabolic rates of cotransferred cells were 86 +/- 4% and 84 +/- 12%, respectively. In vivo MRI revealed high MR signals of the aortic walls in GFP/MGd-transferred mice, which were confirmed by histologic correlations.

CONCLUSION

This study has initially proven the new concept of MRI for plaque-specific, cell-mediated gene expression of atherosclerosis.

Hemodynamic influences on abdominal aortic aneurysm disease: Application of biomechanics to aneurysm pathophysiology

"Atherosclerotic" abdominal aortic aneurysms (AAAs) occur with the greatest frequency in the distal aorta. The unique hemodynamic environment of this area predisposes it to site-specific degenerative changes. In this review, we summarize the differential hemodynamic influences present along the length of the abdominal aorta, and demonstrate how alterations in aortic flow and wall shear stress modify AAA progression in experimental models. Improved understanding of aortic hemodynamic risk profiles provides an opportunity to modify patient activity patterns to minimize the risk of aneurysmal degeneration.

Effects of exogenous peripheral-blood-derived endothelial progenitor cells or unfractionated bone-marrow-derived cells on neointimal formation and inflammation in cholesterol-fed, balloon-denuded, and radiated iliac arteries of inbred rabbits

BACKGROUND

Injection of bone marrow cells (BMC) and endothelial progenitor cells (EPC) or application of stem-cell-mobilizing factors has been associated both with reduction or exacerbation of atherosclerosis and with unstable plaque phenotype. The discrepancies may reflect the cell type, dosing, duration, and route of administration of cells in these studies. The aim of this study was to determine the effects of peripheral-blood-derived endothelial progenitor cells (PBEPC) or unfractionated BMC obtained from inbred siblings on neointimal formation and inflammation in cholesterol-fed, balloon-denuded, and radiated rabbit iliac arteries.

METHODS

Rabbits were fed a 1.0% cholesterol diet for 14 days, followed by endothelial denudation in both iliac arteries, and continued on a 0.15% cholesterol diet. On day 42, denuded areas were radiated, and animals were randomized. The first group received PBEPC (n=5), the second group received BMC (n=4), and the third group received heparinized (20 IU) saline (Control; n=3). PBEPC were characterized by flow cytometry. Cells (5x10(6)) or saline was administered twice through the ear vein: the first time at 1 h after radiation and the second time at 2 weeks after radiation. Four weeks after radiation, the animals were sacrificed, and arterial segments were processed for morphometry.

RESULTS

Administration of BMC or PBEPC from inbred siblings had no adverse effect. Lumen area (0.93+/-0.53 mm(2)), neointimal area (0.65+/-0.29 mm(2)), percent stenosis (44+/-21), and macrophage score (0.6+/-0.3) in controls were similar to those in cell-treated groups.

CONCLUSION

This study demonstrates that, in the current animal model, either PBEPC or BMC failed to affect neointimal formation or inflammation.

Recipient-derived neoangiogenesis of arterioles and lymphatics in quilty lesions of cardiac allografts

BACKGROUND

The contribution of extracardiac cells to tissue turnover in heart allografts has recently been demonstrated. Complex subendocardial infiltrates, known as Quilty lesions, are frequently observed in cardiac allografts. The origin of the different cellular components of Quilty lesions is not known.

METHODS

Different constituents of these lymphonodular infiltrates were analyzed with regard to donor or recipient derivation. Laser-assisted microdissection with subsequent short tandem repeat polymerase chain reaction (PCR)-based "genetic fingerprinting" was employed. Combined immunofluorescence and fluorescence in situ hybridization for sex chromosomes was performed for confirmation in cases of gender-mismatched transplantation. Expression of angiogenic factors (FGF-2, PDGF-alpha, PDGF-alpha-receptor, and VEGF-alpha) was analyzed by quantitative real-time reverse-transcription PCR and immunohistochemistry.

RESULTS

The inflammatory, nonvascular component of Quilty lesions was completely recipient-derived. Blood vessels were of mixed origin. Different compartments of blood vessels displayed different rates of recipient derivation (endothelium up to 50%, smooth muscle cells up to 15%). Lymphatic vessels were mainly recipient-derived. Of the angiogenic molecules, VEGF-alpha expression was significantly increased in the adjacent myocardium, compared to controls and the Quilty lesions themselves.

CONCLUSIONS

The inflammatory compartment of Quilty lesions is of recipient origin and shows chimeric neoangiogenesis of blood and lymphatic vessels. VEGF-alpha produced in the adjacent myocardium appears to stimulate the chimeric neoangiogenesis.

Endothelium-targeted transgenic GTP-cyclohydrolase I overexpression inhibits neointima formation in mouse carotid artery

1. Tetrahydrobiopterin (BH(4)) is an essential cofactor that maintains the normal function of endothelial nitric oxide (NO) synthase. Restenosis is a key complication after transluminal angioplasty. Guanosine 5'-triphosphate-cyclohydrolase I (GTPCH) is the first rate-limiting enzyme for de novo BH(4) synthesis. However, the role of GTPCH in restenosis is not fully understood. The present study tested the hypothesis that endothelial-targeted GTPCH overexpression retards neointimal formation, a hallmark of restenosis, in mouse carotid artery. 2. Transluminal wire injury was induced in the left carotid arteries of adult male wild-type C57BL/6 (WT) and endothelial GTPCH transgenic (Tg-GCH) mice. Re-endothelialization was confirmed with in vivo Evans blue staining. Endothelium-dependent and -independent relaxations were measured using isometric tension recording. Morphological analysis was performed 2 and 4 weeks after carotid injury to assess neointimal formation. Fluorescence-based high-performance liquid chromatography (HPLC) was used to determine GTPCH activity and BH(4) levels. Basal NO release following carotid injury was assessed by N(G)-nitro-L-arginine methyl ester-induced vascular contraction. 3. The endothelium was completely removed upon transluminal wire injury and full re-endothelialization was achieved at Day 10. Endothelium-dependent relaxation was impaired 10 days and 4 weeks after carotid injury, whereas endothelium-independent relaxation remained unaffected. Morphological analysis revealed that the endothelial-specific overexpression of GTPCH reduced neointimal formation and medial hypertrophy 2 and 4 weeks after carotid injury. Both arterial GTPCH enzyme activity and BH(4) levels were significantly elevated in Tg-GCH mice compared with WT mice and basal NO release of the injured carotid artery tended to increase in Tg-GCH mice. 4. These findings suggest that the endothelial overexpression of GTPCH increased endothelial BH(4) synthesis and played a preventive role in neointimal formation induced by endothelium denudation.

MRI of intravenously injected bone marrow cells homing to the site of injured arteries

The aim of this study was to test the feasibility of using MRI to detect magnetically labeled, intravenously injected bone marrow (BM) cells homing to injured arteries. In the first phase, BM cells from LacZ-transgenic or green fluorescent protein (GFP)-transgenic mice were transplanted into eight recipient mice. The left femoral arteries of recipient mice were injured using a cuff-constriction or endothelium-damage approach, and the right femoral arteries were uninjured to serve as controls. The location and distribution of migrated LacZ-BM or GFP-BM cells were confirmed with histology. In the second phase, BM-derived cells from LacZ-transgenic mice were labeled with superparamagnetic iron oxide (Feridex) and then transplanted into eight recipient mice with cuff-induced injuries in the left femoral arteries. Migrated Feridex/LacZ-BM cells were monitored in vivo using a 4.7 T MR scanner. Subsequently, high-resolution ex vivo MRI was performed on 9.4 T and 11.7 T. LacZ-positive or GFP-positive cells in the thickened adventitia of the injured arteries were evident on histology. Both in vivo and ex vivo MRI showed larger regions of hypointensity with Feridex-labeled cells at the sites of the injured arteries compared with control arteries (P < 0.01). This study provides initial evidence that may support the potential use of MRI to detect homing of intravenously injected BM cells to injured arteries.

Hypercholesterolemia contributes to the development of atherosclerosis and vascular remodeling by recruiting bone marrow-derived cells in cuff-induced vascular injury

Recently, the role of bone marrow (BM)-derived endothelial cells and smooth muscle cells (SMCs) has been extensively studied in the pathogenesis of atherosclerosis. In this study we examined the effect of hypercholesterolemia on cuff-induced intimal thickening in LDL-receptor knockout (LDLR-/-) mice fed with a high-fat diet. We transplanted BM of green fluorescence protein (GFP)-transgenic mice to LDLR-/- mice to identify the cell lineage in the lesion. After BM transplantation mice were fed with a high-fat diet for 4 weeks and were then planted a polyethylene cuff on the right femoral artery. Two weeks after cuff placement, atherosclerotic lesions developed in the intima predominantly consisting of a massive accumulation of foam cells with a number of alpha smooth muscle actin (alphaSMA)- and GFP-positive cells. Adventitial small vessels were positive both for CD31 and GFP. Our data indicate that BM-derived cells can contribute to the development of atherosclerosis in the presence of hypercholesterolemia.

In vivo MR imaging of bone marrow cells trafficking to atherosclerotic plaques

PURPOSE

To develop a magnetic resonance imaging (MRI)-based method to monitor in vivo trafficking of bone marrow (BM) cells to atherosclerotic lesions.

MATERIALS AND METHODS

BM cells from LacZ-transgenic mice were labeled with a superparamagnetic iron oxide (Feridex) and then transplanted into ApoE(-/-) recipient mice that were fed an atherogenic diet. Twenty-four ApoE(-/-) mice were divided into three study groups: 1) group I with Feridex-labeled BM transplantation (BMT) cells (N = 9), 2) group II with unlabeled BMT cells (N = 10), and 3) group III with no BMT cells (N = 5). Migrated Feridex/LacZ-BM cells to atherosclerotic aortic walls were monitored in vivo using a 4.7T MR scanner and correlated with histopathological findings.

RESULTS

In group I with Feridex-BMT cells, histology examination displayed plaques in five of nine animals. In four of these five animals, in vivo MRI showed large MR signal voids of the aorta walls (due to the "blooming" effect of migrated Feridex-BM cells in plaques), which were correlated with Feridex- and/or LacZ-positive cells detected in the atherosclerotic lesions. No signal voids could be visualized in the two control animal groups (groups II and III).

CONCLUSION

This study demonstrates the potential use of in vivo MRI to monitor the trafficking of magnetically labeled BM cells to atherosclerotic lesions.

Bone marrow cells contribute to neointimal formation after stent implantation in swine

BACKGROUND

Recent studies suggest that neointimal cells in atherosclerotic lesions are partly derived from bone marrow (BM) cells. However, studies with large animal models have not yet clarified how BM cells contribute to neointimal formation in restenotic lesions. We examined the expression of CD34, a hematopoietic stem cell marker, in the neointima after coronary stent implantation in porcine.

METHODS

Pigs underwent balloon injury in the coronary arteries followed by stent implantation. The arteries were harvested at 3, 7, and 28 days after the stenting. The samples were used for immunohistochemistry for CD34, smooth muscle embryo (SMemb), alpha-smooth muscle cell actin (alpha-SMA), macrophage, c-kit, and AC133 antibodies. In morphometric analysis, each layer of vascular wall was calculated in the sections.

RESULTS

At 3 days, the expressions of CD34 and SMemb were minimal, and many macrophages were seen around the stent struts. At 7 days, co-expression of CD34 and SMemb was observed around the struts, and 11.5% of the neointimal cells were stained by CD34. In addition, c-kit positive cells and AC133 positive cells are detected in neointimal area. At 28 days, the neointima had thickened and expressed alpha-SMA rather than SMemb, and a few CD34-positive cells were detected. In morphometric analysis, luminal area/total vascular area was significantly smaller and intimal area/total vascular area was significantly bigger in 7 and 28 days than in the day of implantation.

CONCLUSION

BM cells of possibly hematopoietic origin partially contributed to neointimal formation after coronary stent implantation in a large animal model.

The role of vascular stem cells in atherogenesis and post-angioplasty restenosis

It is well known that atherosclerosis prevails in elderly populations as ageing acts as a recognized risk factor for this disease. Although the pathogenic factors leading to atherosclerosis are highly heterogeneous, traditionally speaking, the causative risk factors include hyperlipidemia, hypertension, diabetes mellitus and smoking, which can damage to endothelial function, and subsequently promote lipid penetration and inflammatory cell infiltration. Damaged endothelial cells (ECs) may be replaced by neighboring cell division, while damaged smooth muscle cells (SMCs) may be replaced by medial SMCs emigrating into the intima during atherogenesis. However, this standpoint is challenged by recent findings that vascular progenitor/stem cells (VPCs) may contribute to atherogenesis and post-angioplasty restenosis. VPCs are a group of primitive cells that have the potential to produce mature, functional cells in the vascular wall. VPCs residing in bone marrow, vascular wall or circulating in the peripheral blood may be stimulated by a variety of pathogenic factors. These stem cells then participate in regeneration, repair and remodeling of the injured arterial wall. This new concept may bring about a great breakthrough in understanding the pathogenesis of atherosclerosis and develop novel therapeutic strategies for coronary heart disease. This article will mainly review the role of VPCs in atherogenesis, thus providing a novel understanding about the pathophysiology of atherosclerosis.

From the laboratory bench to the patient's bedside: an update on clinical trials with mesenchymal stem cells

Mesenchymal Stem Cells (MSCs) are non-hematopoietic multi-potent stem-like cells that are capable of differentiating into both mesenchymal and non-mesenchymal lineages. In fact, in addition to bone, cartilage, fat, and myoblasts, it has been demonstrated that MSCs are capable of differentiating into neurons and astrocytes in vitro and in vivo. MSCs are of interest because they are isolated from a small aspirate of bone marrow and can be easily expanded in vitro. As such, these cells are currently being tested for their potential use in cell and gene therapy for a number of human diseases. Nevertheless, there are still some open questions about origin, multipotentiality, and anatomical localization of MSCs. In this review, we discuss clinical trials based on the use of MSCs in cardiovascular diseases, such as treatment of acute myocardial infarction, endstage ischemic heart disease, or prevention of vascular restenosis through stem cell-mediated injury repair. We analyze data from clinical trials for treatment of osteogenesis imperfecta (OI), which is a genetic disease characterized by production of defective type I collagen. We describe progress for neurological disease treatment with MSC transplants. We discuss data on amyotrophic lateral sclerosis (ALS) and on lysosomal storage diseases (Hurler syndrome and metachromatic leukodystrophy). A section of review is dedicated to ongoing clinical trials, involving MSCs in treatment of steroid refractory Graft Versus Host Disease (GVHD); periodontitis, which is a chronic disease affecting periodontium and causing destruction of attachment apparatus, heart failure, and bone fractures. Finally, we will provide information about biotech companies developing MSC therapy.

Residual late radiation damage in mouse stromal tissue assessed by the tumor bed effect

Irradiation of murine subcutaneous stroma before implantation of tumor cells leads to retarded tumor growth. This effect is called Tumor Bed Effect (TBE) and can be used to assess the sensitivity of stromal tissue to radiation. We tested the ability of stromal tissue to recover from X-ray-induced damage as a function of the time interval between X-irradiation and implantation of tumor cells over a period of 195 days. We also assessed the effects of a second test treatment of X-irradiation before implantation to assess residual damage by the first radiation treatment. The tumor bed effect in C57Bl10xDBA2 mice observed after X-ray treatment and implantation of M8013 cells (from a transplantable mouse mammary carcinoma) declines with the time that elapses between X-rays and implantation. Implantation of tumor cells 195 days after initial irradiation of 10 or 20 Gy resulted in a considerably smaller TBE. The half-time of the decay is estimated as about 50 days. The extent of the recovery was then tested in two-fraction experiments, with radiation fractions separated by intervals of 30 or 180 days. In the experiment with re-irradiation at an interval of 30 days after the first radiation dose of 20 Gy hardly any recovery was observed, whereas at an interval of 180 days a considerable recovery was observed. We presume that the recovery in TBE that was observed a long time after the irradiation results from a proliferative stimulus to endothelial cells which takes place during the post-irradiation period. The proliferative response leads to cell death of the X-ray damaged endothelial cells and thereafter these are replaced by healthy cells.

Urokinase-type plasminogen activator deficiency (uPA-KO) prevented carotid artery ligation-induced vascular remodeling in mice

It has been demonstrated that urokinase-type plasminogen activator (uPA) plays an important role in vascular remodeling. This study was designed to determine whether uPA deficiency (KO) affects carotid artery ligation-induced vessel remodeling and the interaction with angiotensin II (Ang II). Ligation of the left common carotid artery in 6-month-old wild-type (C57 black/6J) mice for 4 weeks induced a concentric remodeling with vessel wall thickening, characterized by cell proliferation in neointima, media, and adventitia, and with lumen narrowing without a significant enlargement of overall vessel dimension. Intima lesions were characterized by alpha-actin positive smooth muscle cell (SMC) proliferation in a matrix background. No detectable presence of MAC-3 positive macrophages existed in the vascular wall. The ligation-induced vascular neointimal formation and adventitial proliferation, but not lumen narrowing and media expansion, were completely prevented in age-matched uPA-KO mice. Chronic infusion of Ang II (1.44 mg/kg per day) via a subcutaneously implanted osmotic minipump did not significantly affect the gross morphology of the nonligated carotid artery from both wild-type and uPA-KO mice, but it enhanced ligation-induced vascular remodeling. However, in the presence of Ang II, uPA deficiency had no effects on ligation-induced mophermetric change, but it partially and significantly reduced cell proliferation. These data indicate that uPA may play a critical role in ligation-induced vessel remodeling. Ang II may activate other mechanisms independent of uPA to exacerbate ligation-induced vascular remodeling.

Protection of atherogenesis in thromboxane A2 receptor-deficient mice is not associated with thromboxane A2 receptor in bone marrow-derived cells

In the previous study, we generated mice lacking thromboxane A2 receptor (TP) and apolipoprotein E, apoE(-/-)TP(-/-) mice, and reported that the double knockout mice developed markedly smaller atherosclerotic lesions than those in apoE(-/-) mice. To investigate the mechanism responsible for reduced atherosclerosis in apoE(-/-)TP(-/-) mice, we examined the role of TP in bone marrow (BM)-derived cells in the development of the atherosclerotic lesions. When we compared the function of macrophages in apoE(-/-) and in apoE(-/-)TP(-/-) mouse in vitro, there was no difference in the expression levels of cytokines and chemokines after stimulation with lipopolysaccharide. We then transplanted the BM from either apoE(-/-) or apoE(-/-)TP(-/-) mice to either apoE(-/-) or apoE(-/-)TP(-/-) mice after sublethal irradiation. After 12 weeks with high fat diet, we analyzed the atherosclerotic lesion of aortic sinus. When the BM from apoE(-/-) or apoE(-/-)TP(-/-) mice was transplanted to apoE(-/-) mice, the lesion size was almost the same as that of apoE(-/-) mice without BM transplantation. In contrast, when the BM from apoE(-/-) or apoE(-/-)TP(-/-) mice was transplanted to apoE(-/-)TP(-/-) mice, the lesion size was markedly reduced. These results indicate that the protection of atherogenesis in TP(-/-) mice is not associated with TP in BM-derived cells.

M-CSF accelerates neointimal formation in the early phase after vascular injury in mice: the critical role of the SDF-1-CXCR4 system

OBJECTIVE

Since the macrophage colony-stimulating factor (M-CSF) has been shown to stimulate differentiation and proliferation of monocyte/macrophage lineage and to be involved in the process of neointimal formation after vascular injury, we tested the effects of M-CSF on the recruitment of bone marrow-derived progenitor cells in neointimal formation after vascular injury in mice.

METHODS AND RESULTS

Wire-mediated vascular injury was produced in the femoral artery of C57BL/6 mice. Recombinant human M-CSF [500 microg/(kg x day)] or saline (control) was administered for 10 consecutive days, starting 4 days before the injury. Treatment with M-CSF accelerated neointimal formation in the early phase after injury, and this neointimal lesion mainly consisted of bone marrow-derived cells. M-CSF treatment had no effect on the mobilization of endothelial progenitor cells (EPCs: CD34+/Flk-1+) and reendothelialization after injury. The stromal cell-derived factor-1 (SDF-1) was markedly expressed in the neointima and media after injury, whereas CXCR4+ cells were observed in the neointima. Further, a novel CXCR4 antagonist, AMD3100, significantly attenuated the M-CSF-induced neointimal formation.

CONCLUSIONS

These findings suggest that M-CSF accelerated neointimal formation after vascular injury via the SDF-1-CXCR4 system, and the inhibition of this system has therapeutic potential for the treatment of cardiovascular diseases.

In vivo recellularization of plain decellularized xenografts with specific cell characterization in the systemic circulation: histological and immunohistochemical study

Decellularized biological scaffolds have been used for the tissue engineering of heart valves with good results in the pulmonary circulation. However, little information is available on the recellularization of plain decellularized biological scaffolds in the systemic circulation. The aim of this study was to determine whether plain decellularized xenografts (PDXs) can recellularize with specific cell characterization in the systemic circulation. The xenogenic aortic valved conduit grafts of rabbits were implanted in the abdominal aorta of dogs after decellularization. The grafts were explanted at 4, 12, or 24 weeks after implantation for histological, immunohistochemical examination, scanning electron microscope, and Western blot analysis. Although the valvular structures were completely lost after implantation, supravalvular conduits showed normal shapes and endothelialization. The PDXs were repopulated with basic vascular cell components in approximate natural proportions without immunological responses. The PDXs had been recellularized with specific cell characterization in the systemic circulation.

Sca-1+ progenitors derived from embryonic stem cells differentiate into endothelial cells capable of vascular repair after arterial injury

BACKGROUND

Embryonic stem cells possess the ability to differentiate into endothelium. The ability to produce large volumes of endothelium from embryonic stem cells could provide a potential therapeutic modality for vascular injury. We describe an approach that selects endothelial cells using magnetic beads that may be used therapeutically to treat arterial injury.

METHODS AND RESULTS

Large numbers of endothelial cells (ECs) with high purity were produced using Sca-1+ cells isolated with magnetic beads from predifferentiated embryonic stem cells (ESCs) cultured in alpha-MEM containing 10 ng/mL VEGF165 for a minimum of 21 days (esEC). The transcription regulator histone deacetylase (HDAC3) was essential for VEGF-induced EC differentiation. Immunofluorescence or fluorescence-activated cell sorter (FACS) analysis revealed that esECs expressed a full range of EC lineage-specific markers including CD31, CD106, CD144, Flk-1, Flt-1, and von Willebrand factor (vWF). FACS analysis confirmed that 99% of esECs were CD31-positive and 75% vWF-positive. Furthermore, almost all cells were positive for DiI-acLDL uptake. When matrigel containing esECs was subcutaneously implanted into mice, various vessel-like structures were observed indicating their endothelial cell like phenotype. In keeping with this, when esECs infected with adenovirus-LacZ were injected into denuded femoral arteries of mice, they were found to form a neo-endothelium that covered the injured areas (86%+/-13.6%), which resulted in a 73% decrease in neointimal area 2 weeks after injury.

CONCLUSIONS

We conclude that Sca-1+ cells can differentiate into functional ECs via activation of HDAC3, accelerating re-endothelialization of injured arteries and reducing neointima formation.

Plasminogen Activator Inhibitor-1 From Bone Marrow–Derived Cells Suppresses Neointimal Formation After Vascular Injury in Mice

Objective— To investigate the ability of bone marrow (BM)–derived cells to modulate neointimal growth after injury by expressing plasminogen activator inhibitor-1 (PAI-1).

Methods and Results— We performed BM transplantation (BMT) in lethally irradiated wild-type (WT) and PAI-1−/− mice. Three weeks after carotid injury with ferric chloride, analysis of Y-chromosome DNA expression in the vessel wall of female hosts revealed that 20.8±6.0% of the cells in the neointima and 37.6±5.7% of those in the media were of BM origin. Lack of PAI-1 in either the host or the donor cells did not affect recruitment of BM-derived cells into sites of vascular injury. The neointima consisted predominantly of smooth muscle cells, and a proportion of these cells expressed PAI-1. Overall, lack of PAI-1 was associated with enhanced neointimal formation. However, importantly, BMT WT→PAI-1−/− mice exhibited reduced neointimal area ( P =0.05) and luminal stenosis ( P =0.04) compared with BMT PAI-1−/−→PAI-1−/− mice. Although PAI-1–expressing cells were shown to be present in BMT WT→PAI-1−/− lesions, these mice did not exhibit detectable levels of the inhibitor in the circulation, suggesting that local production of PAI-1 by cells in the neointima and media was sufficient to reduce luminal stenosis.

Conclusions— PAI-1 from BM-derived cells appears capable of suppressing neointimal growth after vascular injury.

The impact of progenitor cells in atherosclerosis

During the pathogenesis of arteriosclerosis, endothelial cells on the arterial wall damaged by various means were initially thought to be replaced by replication of neighboring cells. Smooth-muscle cells (SMCs) were also thought to migrate from the media into the intima, where they constituted arteriosclerotic lesions. This concept has been challenged, however, by the discovery that progenitor cells in the circulation and adventitia contribute to endothelial repair and SMC accumulation. Studies have demonstrated that atherosclerosis is a pathophysiologic process initiated by endothelial death in specific areas, such as bifurcation regions, and with subsequent replacement by endothelial progenitor cells. Differentiation of the neoendothelial cells into mature endothelium takes several days or weeks, during which LDL deposits in the intima. Blood mononuclear cells also adhere to neoendothelial cells and migrate into the subendothelial space. Meanwhile, progenitor cells from blood and the adventitia migrate into the intima, where they proliferate and differentiate into neo-SMCs. All risk factors for atherosclerosis can exert their effects on the vessel wall partly via increase in endothelial turnover, inhibition of progenitor-cell differentiation, and promotion of smooth-muscle and macrophage accumulation in lesions. Thus, progenitor cells comprise the main cell source responsible for the formation of atherosclerotic lesions, which appear in the context of inflammatory disease. Here I provide an update on research and discuss the role of progenitor cells in the pathogenesis of atherosclerosis.

Adventitial progenitor cells contribute to arteriosclerosis

Accumulating evidence indicates the involvement of vascular progenitor cells in the development of arteriosclerosis, including transplant arteriosclerosis, angioplasty-induced restenosis, vein graft atherosclerosis, and spontaneous atherosclerosis. Recently, it was found that the adventitia of the arterial wall contains a large number of progenitor cells, which can differentiate into smooth muscle cells in vitro and in vivo. These progenitor cells were able to migrate from the adventitia into the intima, where they accumulate to contribute to atherosclerotic lesions of vein grafts in apoE-deficient mice. Thus, these cells may be a source of smooth muscle cells and might have implications for cellular, genetic, and tissue engineering approaches to vascular disease.

Endothelial NO Synthase Deficiency Promotes Smooth Muscle Progenitor Cells in Association With Upregulation of Stromal Cell-Derived Factor-1α in a Mouse Model of Carotid Artery Ligation

Background— Endothelial NO deficiency (endothelial NO synthase [eNOS]–knockout [KO]) enhanced smooth muscle cell (SMC)–rich neointimal lesion formation in a mouse model of carotid artery ligation (CAL). Recent evidence indicated that stromal cell-derived factor-1α (SDF-1α)–mediated recruitment of circulating SMC progenitor cells substantially contributed to the SMC-rich neointimal hyperplasia induced by vascular injury. The goal of this study was to investigate the effects of eNOS deficiency on the expression of SDF-1α and mobilization of circulating SMC progenitor cells in CAL model.

Methods and Results— Two- to 3-month-old C57BL/6J wild-type (WT) and eNOS-KO mice were evaluated 1, 2, or 4 weeks after CAL. CAL-induced expression of SDF-1α, as detected by immunohistochemical staining and further quantified by ELISA in the ligated carotid arteries, was moderate and transient with a peak at 1 week in WT mice. SDF-1α expression was significantly higher at 1 week and persisted through 2 weeks in eNOS-KO mice. CAL was associated with increased circulating stem cell antigen-1+ (Sca-1 + )/c-Kit − /Lin − cells (interpreted as SMC progenitor cells), which peaked at 1 week in WT mice. This effect was also significantly greater and longer-lasting in eNOS-KO than WT mice. The number of circulating Sca-1 + /c-Kit − /Lin − cells was positively correlated with the expression of SDF-1α but not vascular endothelial growth factor in the ligated carotid arteries. Furthermore, immunostaining showed abundant Sca-1–positive cells in the adventitia of the 1-week ligated carotid arteries from eNOS-KO mice but not in WT mice. We also determined that eNOS deficiency enhanced CAL-induced intimal cell proliferation in the ligated arteries as detected by proliferating cell nuclear antigen staining but did not induce cell apoptosis as detected by staining for active caspase-3.

Conclusion— Our results indicate that eNOS deficiency exacerbates CAL-induced expression of SDF-1α and its receptor CXCR4. This is correlated with an increase in Sca-1 + cells in peripheral blood and adventitia, which may contribute to vascular remodeling and SMC-rich neointimal lesion formation. This suggests that constitutive eNOS inhibits SDF-1α expression and provides an important vasculoprotective mechanism for intact endothelium to limit SMC proliferation and recruitment in response to vascular injury.

Role of histamine produced by bone marrow-derived vascular cells in pathogenesis of atherosclerosis

To clarify the role of histamine-producing cells and its origin in atherosclerosis, we investigated histidine decarboxylase (HDC; histamine-producing enzyme) expression in murine arteries with vascular injuries after the animal had received transplanted bone marrow (BM) from green fluorescent protein (GFP)-transgenic mice. The neointima in the ligated carotid arteries contained BM-derived HDC+ cells that expressed macrophage (Mac-3) or smooth muscle cell antigen (alpha-SMA). In contrast, the HDC+ BM-derived cells, which were positive for Mac-3, were mainly located in the adventitia in the cuff replacement model. In apolipoprotein E-knockout mice on a high cholesterol diet, BM-derived cells expressing Mac-3 in the atheromatous plaques were also positive for HDC. In comparison with wild-type mice, HDC-/- mice showed reduced neointimal thickening and a decreased intima-to-media ratio after ligation and cuff replacement. These results indicate that histamine produced from BM-derived progenitor cells, which could transdifferentiate into SMC- or macrophage-like cells, are important for the formation of neointima and atheromatous plaques.

Increase of smooth muscle cell migration and of intimal hyperplasia in mice lacking the alpha/beta hydrolase domain containing 2 gene

Multiple steps, including the migration of vascular smooth muscle cells (SMCs), are involved in the pathogenesis of atherosclerosis. To discover genes which are involved in these steps, we screened mutant mouse lines established by the exchangeable gene trap method utilizing X-gal staining during their embryonic development. One of these lines showed strong reporter gene expression in the vitelline vessels of yolk sacs at embryonic day (E) 12.5. The trap vector was inserted into the fifth intron of alpha/beta hydrolase domain containing 2 (Abhd2) gene which was shown to be expressed in vascular and non-vascular SMCs of adult mice. Although homozygous mutant mice were apparently normal, enhanced SMC migration in the explants SMCs culture and marked intimal hyperplasia after cuff placement were observed in homozygous mice in comparison with wild-type mice. Our results show that Abhd2 is involved in SMC migration and neointimal thickening on vascular SMCs.

Renin-Angiotensin System Intervention to Prevent In-Stent Restenosis

The occurrence of in-stent restenosis is a major drawback of percutaneous transluminal coronary angioplasty with stent placement. Target vessel revascularization is necessary in 15% of patients who receive a stent. Recent advances in the development of drug-eluting stents have reduced these numbers tremendously. However refinement of antirestenotic therapies remains obligatory. The emerging interest in more physiological antirestenotic therapies might unchain an interest in the well-known inhibitors of the rennin-angiotensin system (RAS), the angiotensin-converting enzyme inhibitors, and the angiotensin II type I receptor blockers. Contradictory results overshadow the discussion of whether intervention in the RAS could prevent in-stent restenosis. This review discusses the pathophysiology of in-stent restenosis, the role of the RAS in in-stent restenosis, and the possible role of RAS intervention in the prevention of in-stent restenosis.