Vascular Precursors Research Articles

Human BCAS3 Expression in Embryonic Stem Cells and Vascular Precursors Suggests a Role in Human Embryogenesis and Tumor Angiogenesis

Cancer is often associated with multiple and progressive genetic alterations in genes that are important for normal development. BCAS3 (Breast Cancer Amplified Sequence 3) is a gene of unknown function on human chromosome 17q23, a region associated with breakpoints of several neoplasms. The normal expression pattern of BCAS3 has not been studied, though it is implicated in breast cancer progression. Rudhira, a murine WD40 domain protein that is 98% identical to BCAS3 is expressed in embryonic stem (ES) cells, erythropoiesis and angiogenesis. This suggests that BCAS3 expression also may not be restricted to mammary tissue and may have important roles in other normal as well as malignant tissues. We show that BCAS3 is also expressed in human ES cells and during their differentiation into blood vascular precursors. We find that BCAS3 is aberrantly expressed in malignant human brain lesions. In glioblastoma, hemangiopericytoma and brain abscess we note high levels of BCAS3 expression in tumor cells and some blood vessels. BCAS3 may be associated with multiple cancerous and rapidly proliferating cells and hence the expression, function and regulation of this gene merits further investigation. We suggest that BCAS3 is mis-expressed in brain tumors and could serve as a human ES cell and tumor marker.

Myeloid lineage of high proliferative potential human smooth muscle outgrowth cells circulating in blood and vasculogenic smooth muscle-like cells in vivo

Emerging experimental data supports a circulating precursor origin for some smooth muscle cells that participate in vasculogenesis but uncertainty exists on the precise phenotype and lineage of these vascular precursors. We determined the lineage of human smooth muscle outgrowth cells (SOC) derived from circulating blood mononuclear cells and smooth muscle-like cells present in regions of vasculogenesis in diseased arteries. Immunophenotypic characterization of SOC was performed using FACS and immunofluorescence (IF). An SOC hierarchy was determined based on in vitro clonogenic and proliferative potential. Lineage of smooth muscle-like cells in vasculogenic regions in vivo was also determined by dual IF for myeloid and smooth muscle specific markers combined with FISH for the X and Y chromosome in diseased vessel of human subjects who had undergone gender mismatched cardiac transplantation. We show here that primary high proliferative potential smooth muscle outgrowth cells (HPP-SOC) expanded in culture from human peripheral blood mononuclear cells (PBMC) and recipient-derived chimeric smooth muscle cells participating in vasculogenesis in vivo share a myeloid phenotype (CD68 and CD14 positivity). Moreover, HPP-SOC in vitro are distinct in being negative for several myeloid markers such as CD11b, CD13 and CD33, and CD45 surface antigens and chimeric SMC in vivo show no evidence of cell fusion propensity. This study provides evidence of a possible myeloid subpopulation origin for smooth muscle outgrowth cells in blood and vasculogenic smooth muscle-like cells in the intima and adventitial microvasculature of diseased arteries. These data have significant implications for understanding the role myeloid cells play in smooth muscle cell biology and vascular remodelling.

Identification of Myocardial and Vascular Precursor Cells in Human and Mouse Epicardium

During cardiac development, the epicardium is the source of multipotent mesenchymal cells, which give rise to endothelial and smooth muscle cells in coronary vessels and also, possibly, to cardiomyocytes. The aim of the present study was to determine whether stem cells are retained in the adult human and murine epicardium and to investigate the regenerative potential of these cells following acute myocardial infarction. We show that c-kit(+) and CD34(+) cells can indeed be detected in human fetal and adult epicardium and that they represent 2 distinct populations. Both subsets of cells were negative for CD45, a cell surface marker that identifies the hematopoietic cell lineage. Immunofluorescence revealed that freshly isolated c-kit(+) and CD34(+) cells expressed early and late cardiac transcription factors and could acquire an endothelial phenotype in vitro. In the murine model of myocardial infarction, there was an increase in the absolute number and proliferation of epicardial c-kit(+) cells 3 days after coronary ligation; at this time point, epicardial c-kit(+) cells were identified in the subepicardial space and expressed GATA4. Furthermore, 1 week after myocardial infarction, cells coexpressing c-kit(+), together with endothelial or smooth muscle cell markers, were identified in the wall of subepicardial blood vessels. In summary, the postnatal epicardium contains a cell population with stem cell characteristics that retains the ability to give rise to myocardial precursors and vascular cells. These cells may play a role in the regenerative response to cardiac damage.

Time‐lapse imaging of Arabidopsis leaf development shows dynamic patterns of procambium formation

The principles underlying the formation of leaf veins have long intrigued developmental biologists. In leaves, networks of vascular precursor procambial cells emerge from seemingly homogeneous subepidermal tissue through the selection of anatomically inconspicuous preprocambial cells. Understanding dynamics of procambium formation has been hampered by the difficulty of observing the process in vivo. Here we present a live-imaging technique that allows visual access to complex events occurring in developing leaves. We combined this method with stage-specific fluorescent markers in Arabidopsis (Arabidopsis thaliana) to visualize preprocambial strand formation and procambium differentiation during the undisturbed course of development and upon defined perturbations of vein ontogeny. Under all experimental conditions, we observed extension, termination and fusion of preprocambial strands and simultaneous initiation of procambium differentiation along entire individual veins. Our findings strongly suggest that progressiveness of preprocambial strand formation and simultaneity of procambium differentiation represent inherent properties of the mechanism underlying vein formation.

Cellular control of tissue architectures using a three-dimensional tissue fabrication technique

Tissue engineering seeks to provide regenerated tissue architectures in vitro but has not yet successfully created thick, highly vascularized, multi-functional tissues replicating native structure. We describe a novel method to fabricate pre-vascularized tissue equivalents using multi-layered cultures combining micro-patterned endothelial cells as vascular pre-cursors with fibroblast monolayer sheets as tissue matrix. Stratified tissue equivalents are constructed by alternately layering fibroblast monolayer sheets with patterned endothelial cell sheets harvested from newly developed thermo-responsive micro-patterned surfaces alternating 20 μm-wide cell-adhesive lanes with 60 μm non-adhesive zones. Cell culture substrates covalently grafted with different thermo-responsive polymers permit spatial switching of cell adhesion and detachment using applied small temperature changes. Endothelial cell patterning fidelity was maintained within the multi-layer tissue constructs after assembly, leading to self-organization into microvascular-like networks after 5-day tissue culture. This novel technique holds promise for the study of cell-cell communications and angiogenesis in reconstructed, three-dimensional environments as well as for the fabrication of tissues with complex, multicellular architecture.

PRDM6 is enriched in vascular precursors during development and inhibits endothelial cell proliferation, survival, and differentiation

The mechanisms that regulate the differentiation program of multipotential stem cells remain poorly understood. In order to define the cues that delineate endothelial commitment from precursors, we screened for candidate regulatory genes in differentiating mouse embryoid bodies. We found that the PR/SET domain protein, PRDM6, is enriched in flk1(+) hematovascular precursor cells using a microarray-based approach. As determined by 5′ RACE, full-length PRDM6 protein contains a PR domain and four Krüppel-like zinc fingers. In situ hybridization in mouse embryos demonstrates staining of the primitive streak, allantois, heart, outflow tract, paraaortic splanchnopleura (P-Sp)/aorto–gonadal–mesonephric (AGM) region and yolk sac, all sites known to be enriched in vascular precursor cells. PRDM6 is also detected in embryonic and adult-derived endothelial cell lines. PRDM6 is co-localized with histone H4 and methylates H4–K20 (but not H3) in vitro and in vivo, which is consistent with the known participation of PR domains in histone methyltransferase activity. Overexpression of PRDM6 in mouse embryonic endothelial cells induces apoptosis by activating caspase-3 and inducing G1 arrest. PRDM6 inhibits cell proliferation as determined by BrdU incorporation in endothelial cells, but not in rat aortic smooth muscle cells. Overexpression of PRDM6 also results in reduced tube formation in cultured endothelial cells grown in Matrigel. Taken together, our data indicate that PRDM6 is expressed by vascular precursors, has differential effects in endothelial cells and smooth muscle cells, and may play a role in vascular precursor differentiation and survival by modulating local chromatin-remodeling activity within hematovascular subpopulations during development.

Decap to Form Veins

The balance between synthesis and decay controls protein abundance at multiple levels. Goeres et al . found that a specific 5′→3′ mRNA degradation pathway involving an mRNA decapping complex was crucial for seedling development in Arabidopsis thaliana . The phenotypes of mutants in the VCS and TDT genes were similar, with defective leaf formation with vein defects, short roots with swollen root hairs, and short swollen hypocotyls. Confocal microscopy revealed that the shoot apical meristem cells were disorganized in the vcs-7 and tdt-1 plants and that leaf primordia were absent in seedlings that were 3 days old, which is when the leaf primordia appear in wild-type plants. Reporter gene analysis for vascular tissue and precursors suggested that the tdt-1 mutant vascular phenotype arose as a consequence of defective formation of the provascular cell specification, which is controlled by auxin signaling, in the hypocotyl to cotyledon transition zone. Cloning revealed that TDT encoded a protein homologous to yeast and mammalian DCP2, a NUDIX and muT-domain containing mRNA decapping enzyme. VCS, which interacted with TDT in a yeast two-hybrid assay, appeared to be important for localizing TDT to cytoplasmic P-bodies, which are the sites of mRNA decapping and degradation. In vcs-7 mutants, localization of a green fluorescent protein (GFP) TDT fusion protein to cytoplasmic foci with characteristics of P-bodies was lost. Analysis of specific mRNAs, as well as microarray analysis, indicated that TDT and VCS were involved in controlling mRNA abundance. However, not all mRNAs exhibited decreased decay rates, suggesting that this particular mRNA decay pathway was specific to a subset of transcripts. The transcripts that did accumulate in the mutants exhibited the presence of the 5′ cap, consistent with VCS and TDT as constituents of the decapping pathway. D. C. Goeres, J. M. Van Norman, W. Zhang, N. A. Fauver, M. L. Spencer, L. E. Sieburth, Components of the Arabidopsis mRNA decappng complex are required for early seedling development. Plant Cell 19 , 1549-1564 (2007). [Abstract] [Full Text]

BMPER is a conserved regulator of hematopoietic and vascular development in zebrafish

For the proper development of vertebrate embryos as well as for survival of the adult organism, it is essential to form a functional vascular system. Molecules involved in this process are members of highly conserved families of proteins that exert conserved functions across species. Bone morphogenetic proteins (BMP) are extracellular factors that are regulated by extracellular modulators and bind to BMP receptors, which in turn activate intracellular signaling cascades. BMPs are necessary not only for induction of endothelial and hematopoietic lineages but also for further endothelial and hematopoietic cell differentiation. Previously, we identified BMPER (BMP endothelial cell precursor derived regulator) and demonstrated its spatiotemporal expression at sites of vasculogenesis and direct modulation of BMP activity. To directly investigate the role of BMPER in vascular development, we cloned the BMPER ortholog in zebrafish ( zbmper). It is expressed at sites of high BMP activity, including vascular precursor cells located in the aortic arches and the intermediate cell mass during zebrafish embryonic development. Knockdown of zbmper results in a dorsalized phenotype, a reduced number of gata1 expressing hematopoietic precursor cells and of circulating blood cells as well as in a vascular phenotype. The generation of the caudal vein is compromised and the pattern guiding of the intersomitic vessels is disturbed, indicating that zbmper is required for early steps in vascular pattern formation and hematopoiesis in zebrafish.

Pathophysiology of stem cells in restenosis.

Recent evidence has shown that vascular function depends not only on cells within the vessels, but is also significantly modulated by circulating cells derived from the bone marrow. A number of studies indicate that an early reendothelialization by circulating endothelial precursors after vascular injury prevents excessive cell proliferation and restenosis. Conversely, other studies concluded that the homing of other cell fractions, consisting mainly of smooth muscle precursors, cause pathological remodelling. Different cell types have been identified and characterized so far as circulating precursors able to participate in vascular repair by homing and differentiating towards endothelial cells or smooth muscle cells. Among these, endothelial precursor cells, smooth muscle progenitor cells, mesenchymal stem cells and others have been described. The origins, the hierarchy, the role and the markers of these different cell populations are still controversial. Nevertheless, different strategies have been developed so far in animal models to induce the mobilization and the recruitment of stem cells to the injury site, based on physical training, hormone injection and application of stem cell-capturing coated stents. It should also be mentioned that the limited data currently available derived from clinical trials provide contrasting results about the effective role of vascular cell precursors in restenosis prevention, thus indicating that conclusions derived from studies in animal models cannot always be directly applied to humans and that caution should be used in the manipulation of circulating progenitor cells for therapeutic strategies.

Hyperoxia inhibits several critical aspects of vascular development

Normal human retinal vascular development uses angiogenesis and vasculogenesis, both of which are interrupted in the vaso-obliteration phase of retinopathy of prematurity (ROP). Canine oxygen-induced retinopathy (OIR) closely resembles human ROP. Canine retinal endothelial cells (ECs) and angioblasts were used to model OIR and characterize the effects of hyperoxia on angiogenesis and vasculogenesis. Cell cycle analysis showed that hyperoxia reduced the number of G1 phase cells and showed increased arrest in S phase for both cell types. Migration of ECs was significantly inhibited in hyperoxia (P < 0.01). Hyperoxia disrupted the cytoskeleton of angioblasts but not ECs after 2 days. Differentiation of angioblasts into ECs (determined by acetylated low-density lipoprotein uptake) was evaluated after basic fibroblast growth factor treatment. Differentiation of angioblasts into pericytes was determined by smooth muscle actin expression after treatment with platelet-derived growth factor. Differentiation into ECs was significantly inhibited by hyperoxia (P < 0.0001). The percentage of CXCR4(+) cells (a marker for retinal vascular precursors) increased in both treatment groups after hyperoxia. These data show novel mechanisms of hyperoxia-induced disruption of vascular development.

356: Reduced number and function of circulating endothelial progenitor cells in patients with pulmonary arterial hypertension

Purpose: Pulmonary arterial hypertension (PAH) is associated with endothelial dysfunction. Circulating vascular precursor cells, endothelial progenitor cells (EPCs), may play a role in the pathogenesis. However, the characteristics of EPCs in patients with PAH are not well understood. We sought to test the hypothesis that EPC number and function are altered in PAH.

Obliterative vasculopathy in systemic sclerosis: endothelial precursor cells as novel targets for therapy

Evaluation of: Kuwana M, Kaburaki J, Okazaki Y et al. Increase in circulating endothelial precursors by atorvastatin in patients with systemic sclerosis. Arthritis Rheum. 54(6), 1946–1951 (2006).Systemic sclerosis (SSc) is associated with a progressive obliterative vasculopathy that accounts for serious clinical manifestations of the disease, and has, to date, no effective treatment. Vascular obliteration is accompanied by defective vasculogenesis due to impaired production, mobilization or function of bone marrow-derived vascular precursor cells. Statins enhance vascular precursor cell production in chronic cardiovascular diseases and may also have a therapeutic role in SSc. This paper evaluates the results from a recent open-label clinical trial of atorvastatin that support this notion. Larger controlled trials are now needed to critically evaluate the efficacy of statins for repairing vascular damage, enhancing vasculogenesis, and attenuating the burden of chronic vasculopathy in SSc.

Protophloem Differentiation in Early Arabidopsis thaliana Development

During Arabidopsis embryogenesis, procambial cells undergo coordinated, asymmetric cell divisions, giving rise to vascular precursor cells (protophloem and protoxylem precursors). After germination, these cells terminally differentiate into specialized conducting cells, referred to as protophloem and protoxylem cells. Few readily identifiable markers of the onset of specification and differentiation are available, hampering the molecular genetic analysis of protophloem development. Confocal microscopy was used to investigate the patterning and differentiation of phloem cells during early plant development. Longitudinal divisions of phloem initials allowed the identification of protophloem precursor cells and adjacent metaphloem initials along the length of the plant. During germination, protophloem differentiation was observed at two independent locations, in the cotyledons and the hypocotyl. In both locations, differentiation was concomitant with cell elongation. We identified five gene-trap lines (PD1-PD5) with marker gene expression in immature protophloem elements. The spatio-temporal marker expression pattern of the lines divides them into two groups. The early specification markers PD4 and PD5 were expressed in developing organs before procambium formation and then became restricted to phloem initial cells. The protophloem precursor markers PD1-PD3 were expressed in differentiating protophloem cells at different stages of their development. All markers were expressed transiently and iteratively during the differentiation of protophloem in newly formed organs. Flanking genes were identified for four out of five gene-trap insertion lines. The possible function of these genes with respect to phloem differentiation is discussed.

Regulation of endothelial progenitor cell homing after arterial injury

Adult bone marrow and peripheral blood contain sub-populations of vascular precursor cells, which can differentiate into mature endothelial cells and have therefore been commonly termed endothelial progenitor cells (EPCs). Although EPCs encompass rather heterogeneous cell sub-populations of multiple origins and localization, these cells were basically characterized by expression of progenitor markers and by the development of colony-forming units and late endothelial outgrowth with terminal differentiation into mature endothelial cells. Notably, functional studies in vivo have implied the contribution of EPCs to therapeutic reendothelialization and inhibition of neointimal growth following endothelial injury. In the context of this regenerative arterial remodeling, an adequate homing of EPCs plays a central role. This multi-step process of EPC mobilization, recruitment and firm adhesion is regulated by key angiogenic chemokines (CCL2, CXCL1, CXCL7, CXCL12) and their respective receptors (CCR2, CXCR2, CXCR4). Furthermore, the recruitment of circulating EPCs to sites of arterial injury is synchronized by activated platelets and adhesion molecules of the selectin and integrin family. Thus, translating this molecular knowledge to interventional cardiovascular medicine, such a detailed understanding in the complex regulation of EPC homing may be helpful for more effectively preventing "in-stent" stenosis by facilitating stent endothelialization.

Retinopathy of Prematurity: Two Distinct Mechanisms That Underlie Zone 1 and Zone 2 Disease

In its most severe form, retinopathy of prematurity (ROP) is located in posterior retina and affects the smallest, most premature infants. We hypothesize that, depending on whether vasculogenesis (de novo formation of new vessels by transformation of vascular precursor cells (VPCs)) or angiogenesis (budding from existing vessels) is perturbed, it results in significant differences in clinical presentation and therapeutic outcome observed in zone 1 vs zone 2 ROP. The study is a retrospective analysis of the difference in outcome between zones 1 and 2 ROP after cryotherapy and laser therapy. A review of the clinical presentation of zones 1 and 2 ROP that correlate this with the topography of formation of human retinal vasculature through vasculogenesis and angiogenesis. Population data on susceptible infants, and outcome statistics of clinical trials are given. Digital images show a correlation between ROP in zone 1 with the region of the retina vascularized through vasculogenesis. Zone 1 ROP is correlated with vessel development by vasculogenesis, relative insensitivity to laser/cryotherapy and poorer anatomic and visual outcomes. This suggests that, if the vasculogenic process is perturbed, it results in a distinct clinical presentation, poorer response to therapy, and poorer visual outcome. When the current international classification was developed, knowledge of the processes of human retinal vascular development was incomplete. The work presented here provides a framework for the development of a modification to incorporate these ideas without sacrifice of the essential elements of the international classification of ROP.

Sustained Bmp signaling is essential for cloaca development in zebrafish

Bone morphogenetic protein (Bmp) signaling has long been known to be important for the early development of the ventral mesoderm, including blood, vasculature and kidney cells. Although Bmp genes are continually expressed in the ventral cells throughout gastrulation and somitogenesis, previous studies in zebrafish have not addressed how the role of Bmp signaling changes over time to regulate ventral mesoderm development. Here, we describe the use of a transgenic inducible dominant-negative Bmp receptor line to examine the temporal roles of Bmp signaling in ventral mesoderm patterning. Surprisingly, we find that Bmp signaling from the mid-gastrula stage through early somitogenesis is important for excluding blood and vascular precursors from the extreme ventral mesoderm, and we show that this domain is normally required for development of the cloaca (the common gut and urogenital opening). Using a novel assay for cloacal function, we find that larvae with reduced mid-gastrula Bmp signaling cannot properly excrete waste. We show that the cloacal defects result from alterations in the morphogenesis of the cloaca and from changes in the expression of genes marking the excretory system. Finally, we show that HrT, a T-box transcription factor, is a Bmp-regulated gene that has an essential function in cloacal development. We conclude that sustained Bmp signaling plays an important role in specification of the zebrafish cloaca by maintaining the fate of extreme ventral cells during the course of gastrulation and early somitogenesis. Furthermore, our data suggest that alterations in Bmp signaling are one possible cause of anorectal malformations during human embryogenesis.

Canine retinal angioblasts are multipotent

The purpose of this study was to culture and characterize endothelial cells and angioblasts, vascular precursors, from adult and neonatal dog retina and determine if angioblasts are committed to endothelial cell lineage or have the potential to be multipotent, i.e. express phenotypic characteristics of other vascular cell types. Endothelial cells were established from adult dog retina (ADREC) by the technique of Gitlin and D'Amore. For angioblasts, pieces of neonatal day 2 (P2) avascular peripheral retina were placed under coverslips until sufficient cells had explanted. All cells were maintained initially on hyaluronic acid (HA)/fibronectin (FN) substratum. Neonatal canine retinal angioblasts (NCRA) were maintained initially on retinal-derived growth factor with alpha-amino adipic acid to inhibit growth of Muller cells. Cell lines were characterized by enzyme histochemistry [menadione-dependent alpha glycerophosphate dehydrogenase (αGPDH), marker for angioblasts] and immunocytochemistry. Once characterized, cells were grown on FN, or collagens I or IV substrata and fed platelet-derived growth factor-BB (PDGF-BB) or fibroblast growth factor-2 (FGF-2). The phenotypic expression of a marker for endothelial cells [acetylated LDL (acLDL) uptake] or a marker for pericytes and smooth muscle cells, production of alpha smooth muscle actin (αSMA), was evaluated under those conditions. The canine retinal cell lines that were established had the following characteristics when maintained on serum and a retinal extract. Angioblasts had low expression of vWf and VEGF-R2 (two markers for canine endothelial cells), and very low uptake of acLDL but high expression of αGPDH and adenosine A2a receptors (A2aR) (two markers for canine angioblasts in vivo). ADREC had high expression of endothelial cell markers (vWf, VEGF-R2, and acLDL uptake) but minimal expression of αGPDH and A2aR. Both angioblasts and endothelial cells expressed CXCR4, a marker for hemangioblasts. Angioblasts grown on any of the substrata in the presence of FGF-2 had high uptake of acLDL and low expression of αSMA, while those grown in the presence of PDGF-BB had high expression of αSMA and low uptake of acLDL. In conclusion, angioblasts cultured from peripheral vascular retina have low expression of endothelial cell markers and high αGPDH and A2aR, markers for canine angioblasts in vivo. Angioblasts will internalize acLDL when maintained on FGF-2 and express αSMA when maintained on PDGF-BB, suggesting that they have the potential to become endothelial cells or pericytes, i.e. are multipotent.

In Vitro Generation of Cardiovascular Tissues

Cardiovascular diseases are leading causes of mortality and morbidity. New cell-based therapies offer new strategies in treating these disorders. We have focused on using a collagen tube cell scaffold on which cardiovascular tissues can be grown and manipulated. This scaffold has been used to investigate cardiac myocytes (CMs), cardiac valves, and coronary vessel development. Spontaneously contracting CMs have been cultured for months on the tubular scaffold without dedifferentiation or fibroblast overgrowth. This attribute was used to study valve formation. These studies found that valve leaflet formation was dependent on the presence of CMs. We are investigating if the role that CMs play in the valve forming process is that of a source of juxacrine signals or as generators of critical fluid flow or both. The role CMs play in the formation of coronary vasculature has also been tested in this system. Our data indicate that CMs significantly enhanced endothelial and smooth muscle cell proliferation. Vessel formation was also increased in co-cultures of CMs and proepicardial cells (coronary vascular precursors). Mechanistic investigations of this process are underway. Again, the properties of the tube scaffold are used to investigate both chemical and mechanical components. The generation these cardiovascular tissues in vitro allows for the investigation of the developmental mechanisms that drive morphogenesis. Understanding these mechanisms enables the rational use of cell-based therapies.

Even Flow

The appreciation that biomechanical forces induce signaling responses that regulate vascular tone and inflammatory responses has had a paradigm-shifting effect on our understanding of vascular biology. Endothelial cells are constantly exposed to rheologically imposed forces that vary due to vascular anatomic features and hemodynamic parameters, and of course shear fluctuates cyclically during the cardiac cycle. Simple laminar flow and high shear forces elicit a cellular response characterized by quiescence and alignment of endothelial cells in the direction of fluid flow, whereas disturbed flow and low shear forces induce an inflammatory procoagulant phenotype. These cellular effects are mediated through well-defined signaling pathways and gene expression responses. The cellular sensors or receptors for shear forces are incompletely characterized, but detection of stress seems to depend on the transmission of forces to points of cell–matrix and cell–cell attachment and requires specific conformational activation of integrins.1 From a pathophysiological perspective, disturbed laminar flow has been linked to inflammatory responses that initiate atheroma formation and elicit plaque instability. It is also generally accepted that flow is required for some aspects of vascular remodeling during vascular development and in adult angiogenic responses; however, specific roles for flow in vascular developmental programs have been incompletely characterized. See page 1817 Two recent reports, including one published in this issue of Arteriosclerosis, Thrombosis, and …

Local delivery of AIF-1 to rat carotid arteries increases restenosis, local G-CSF expression, and contributes to recruitment of bone marrow-derived cells

Recent studies suggest that host bone-marrow derived vascular precursors are a source of donor intimal cells in transplant arteriopathy. Recruitment of these cells to the site of vascular injury may contribute to development of coronary artery transplant vasculopathy (CAV). Allograft Inflammatory Factor-1 (AIF-1) is highly expressed in coronary arteries of transplanted human hearts. AIF-1 stimulates growth and migration of vascular smooth muscle cells (VSMC) by induction of Granulocyte-Colony Stimulating Factor (G-CSF) expression.