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Graphical demonstration of a cross section through middle sized artery. The EPCs are localized within a distinct zone of the vascular wall called " vasculogenic zone " which is localized mainly within the adventitial layer but in close proximity to the smooth muscle cell layer of the vascular wall
Source publication
Tumor growth and metastasis need new vessel formation by angiogenesis provided by mature endothelial cells and postnatal vasculogenesis provided by endothelial progenitor cells (EPCs). Emerging data suggest a coordinated interaction between EPCs and hematopoietic progenitor cells (HPCs) in these processes. The complexity of the mechanisms governing...
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Blood vessel formation (neovascularization) in tumors can occur through two mechanisms: angiogenesis and vasculogenesis. Angiogenesis results from proliferation and sprouting of existing blood vessels close to the tumor, while vasculogenesis is believed to arise from recruitment of circulating cells, largely derived from the bone marrow, and de nov...
Solid tumors carry out the formation of new vessels providing blood supply for growth, tumor maintenance, and metastasis. Several processes take place during tumor vascularization. In angiogenesis, new vessels are derived from endothelial cells of pre-existing vessels; while in vasculogenesis, new vessels are formed de novo from endothelial progeni...
Introduction
The proof‐of‐concept in vivo : the cell, the read‐out and the animal model
EPCs defined in vitro : the achilles heel in EPC biology
Summary
Abstract
In the past decade, researchers have gained important insights on the role of bone marrow (BM)‐derived cells in adult neovascularization. A subset of BM‐derived cells, called endothelial...
It was generally considered that blood vessel formation during postnatal life is restricted to angiogenesis only, and for decades tumor vascularization was thought to be the exclusive result of the sprouting of new vessels from the preexisting ones. However, recent studies demonstrated the existence of additional angiogenic and vasculogenic mechani...
Recent experimental evidence suggests that vasculogenesis may play an important role in tumour vascularisation. While angiogenesis involves the proliferation and migration of endothelial cells (ECs) in pre-existing vessels, vasculogenesis involves the mobilisation of bone-marrow-derived endothelial progenitor cells (EPCs) into the bloodstream. Once...
Citations
... The tumors enhance the mobilization of circulating progenitor cells form the bone marrow thus affecting tumor new vascularization. [26,27] In the present study, the level of CECs after high dose radiotherapy was highly increased reflecting the impact of high dose radiation on the integrity of vascular endothelium. Moreover, it reflects the direct toxicity of radiation to the endothelium. ...
... Vascular wall-resident stem and progenitor cells (VW-SCs) were shown to deliver vascular progenitors, but also non-vascular cells like cardiomyocytes and macrophages [29][30][31][32]. VW-SCs can be activated and mobilized from their adventitial niche due to coculture with tumor cells further underscoring their potential to facilitate tumor angiogenesis [33][34][35][36]. However, the impact of bone marrow-independent VW-SC-derived macrophages on vascular progenitor cell activation and angiogenesis remains unclear [37][38][39]. ...
... Eight-week-old male C57BL/6 J (Jackson Laboratory, Bar Harbor, ME, USA), FlkSwitch mice [33,34], and NCX1 −/− mice [35,36] were housed in specific pathogen-free conditions on a 12:12-h dark-light cycle and fed a standard chow ad libitum. All experiments were performed according to German and American animal protection law. ...
Pathological angiogenesis promotes tumor growth, metastasis, and atherosclerotic plaque rupture. Macrophages are key players in these processes. However, whether these macrophages differentiate from bone marrow-derived monocytes or from local vascular wall-resident stem and progenitor cells (VW-SCs) is an unresolved issue of angiogenesis. To answer this question, we analyzed vascular sprouting and alterations in aortic cell populations in mouse aortic ring assays (ARA). ARA culture leads to the generation of large numbers of macrophages, especially within the aortic adventitia. Using immunohistochemical fate-mapping and genetic in vivo-labeling approaches we show that 60% of these macrophages differentiate from bone marrow-independent Ly6c+/Sca-1+ adventitial progenitor cells. Analysis of the NCX−/− mouse model that genetically lacks embryonic circulation and yolk sac perfusion indicates that at least some of those progenitor cells arise yolk sac-independent. Macrophages represent the main source of VEGF in ARA that vice versa promotes the generation of additional macrophages thereby creating a pro-angiogenetic feedforward loop. Additionally, macrophage-derived VEGF activates CD34+ progenitor cells within the adventitial vasculogenic zone to differentiate into CD31+ endothelial cells. Consequently, depletion of macrophages and VEGFR2 antagonism drastically reduce vascular sprouting activity in ARA. In summary, we show that angiogenic activation induces differentiation of macrophages from bone marrow-derived as well as from bone marrow-independent VW-SCs. The latter ones are at least partially yolk sac-independent, too. Those VW-SC-derived macrophages critically contribute to angiogenesis, making them an attractive target to interfere with pathological angiogenesis in cancer and atherosclerosis as well as with regenerative angiogenesis in ischemic cardiovascular disorders.
... Capillaries also contain an intima that is lined by ECs and enwrapped by a discontinuous layer of pericytes from the outside. While both vascular intima and media are constructed by mature cells, the outermost vascular adventitia has been identified as a niche for vascular stem and progenitor cells (VW-SCs) that can deliver all vascular cells and even some types of blood cells upon activation, e.g. by angiogenic stimuli [19,[21][22][23]. Considering this complexity of the in situ vascular systems, it will probably not suffice when mature endothelial tubes alone or in combination with mature SMCs are printed. ...
... Next, we wanted to characterize the cells forming the vascular-like channels at the immunophenotypic level using immunostaining on paraffin sections for markers that are specific for ECs such CD31, for peri-ECs such as NG2 and αSMA, and for vascular progenitor cells such as CD34 [21,22,45,46], The presented results demonstrate that indeed all vascular cell types are present in the wall of the vascular-like channels developed after extrusion of hiMPCs into the alginate + collagen type I hydrogel ( figure 4(C)). Moreover, the spatial organization of these cell types within the wall of vessel-like channels was very similar to that in vivo as CD31 + ECs lined the luminal surface of the vascular channels, the NG2 + or αSMA + cells were found to cover the endothelial layer from outside and more surprisingly a part of CD34 + cells was found in the outermost layer of the vessel wall, again similar to the adventitial layer of blood vessels in situ ( figure 4(C3)). ...
Post-fabrication formation of a proper vasculature remains an unresolved challenge in bioprinting. Established strategies focus on the supply of the fabricated structure with nutrients and oxygen and either rely on the mere formation of a channel system using fugitive inks or additionally use mature endothelial cells and/or peri-endothelial cells such as smooth muscle cells for the formation of blood vessels in vitro. Functional vessels, however, exhibit a hierarchical organization and multilayered wall structure that is important for their function. Human induced pluripotent stem cell-derived mesodermal progenitor cells (hiMPCs) have been shown to possess the capacity to form blood vessels in vitro, but have so far not been assessed for their applicability in bioprinting processes. Here, we demonstrate that hiMPCs, after formulation into an alginate/collagen type I bioink and subsequent extrusion, retain their ability to give rise to the formation of complex vessels that display a hierarchical network in a process that mimics the embryonic steps of vessel formation during vasculogenesis. Histological evaluations at different time points of extrusion revealed the initial formation of spheres, followed by lumen formation and further structural maturation as evidenced by building a multilayered vessel wall and a vascular network. These findings are supported by immunostainings for endothelial and peri-endothelial cell markers as well as electron microscopic analyses at the ultrastructural level. Moreover, endothelial cells in capillary-like vessel structures deposited a basement membrane-like matrix at the basal side between the vessel wall and the alginate-collagen matrix. After transplantation of the printed constructs into the chicken chorioallantoic membrane (CAM) the printed vessels connected to the CAM blood vessels and get perfused in vivo. These results evidence the applicability and great potential of hiMPCs for the bioprinting of vascular structures mimicking the basic morphogenetic steps of de novo vessel formation during embryogenesis.
... Vasculogenesis (Figure 1) is the de novo formation of vessels from precursor cells mobilized from the bone marrow, that enter the circulation and migrate to the site of vessel formation [14][15][16]. It typically occurs in the embryo, and post-natal vasculogenesis is considered a sporadic event, restricted to sites of physiological revascularization, injury repair, and vessel formation in pathological conditions. ...
... Tumors can recruit vascular precursor cells, including endothelial progenitor cells (EPC), from bone marrow and also from adjacent tissues or circulating cells [16]. Stimulated by cytokines and growth factors produced by the tumor cells, mobilized precursor cells enter the circulation and are recruited to the tumor site, where they can be found associated to the vasculature. ...
Simple Summary
Tumors rely on blood vessels to grow and metastasize. Malignant tumors can employ different strategies to create a functional vascular network. Tumor cells can use normal processes of vessel formation but can also employ cancer-specific mechanisms, by co-opting normal vessels present in tissues or by turning themselves into vascular cells. These different types of tumor vessels have specific molecular and functional characteristics that profoundly affect tumor behavior and response to therapies, including drugs targeting the tumor vasculature (antiangiogenic therapies). In this review, we discuss how vessels formed by different mechanisms affect the intrinsic sensitivity of tumors to therapy and, on the other hand, how therapies can affect tumor vessel formation, leading to resistance to drugs, cancer recurrence, and treatment failure. Potential strategies to avoid vessel-mediated resistance to antineoplastic therapies will be discussed.
Abstract
Blood vessels in tumors are formed through a variety of different mechanisms, each generating vessels with peculiar structural, molecular, and functional properties. This heterogeneity has a major impact on tumor response or resistance to antineoplastic therapies and is now emerging as a promising target for strategies to prevent drug resistance and improve the distribution and efficacy of antineoplastic treatments. This review presents evidence of how different mechanisms of tumor vessel formation (vasculogenesis, glomeruloid proliferation, intussusceptive angiogenesis, vasculogenic mimicry, and vessel co-option) affect tumor responses to antiangiogenic and antineoplastic therapies, but also how therapies can promote alternative mechanisms of vessel formation, contributing to tumor recurrence, malignant progression, and acquired drug resistance. We discuss the possibility of tailoring treatment strategies to overcome vasculature-mediated drug resistance or to improve drug distribution and efficacy.
... Interessanterweise stellten knochenmarkstämmiger Vorläuferzellen erfolgt. Vielmehr scheinen sich schon vor Ort befindliche residente endotheliale Vorläuferzellen in einer Art Ruhezustand zu befinden und nach Aktivierung an der Gefäßneubildung im Rahmen der Vaskulogenese zu beteiligen[261][262][263] . Ob die Aktivierung residenter EPC einen Beitrag zur Gefäßneubildung leistet und diese im Kontext einer chronischen Niereninsuffizienz im Gegensatz zum gesunden adulten Organismus allerdings vermindert oder gänzlich inhibiert ist, bedarf weiterer detaillierter Untersuchungen.7.5 Angiogenese -Stimulation der GefäßneubildungDie zweite mögliche Ursache einer verminderten Kapillarisierung bei CKD wäre eine bei Niereninsuffizienz inadäquate Angiogenese. ...
Die chronische Nierenerkrankung (chronic kidney disease, CKD) stellt eine Erkrankung dar, von der weltweit über 10% der Bevölkerung betroffen sind. Hierbei ist trotz des medizinischen Fortschritts die Sterblichkeitsrate unverhältnismäßig hoch und primär durch kardiovaskuläre Komplikationen begründet. Aktuelle Daten lassen vermuten, dass eine verminderte und/oder fehlerhafte Angiogenese diese kardiovaskulären Komplikationen begünstigt. Hierbei handelt es sich um die Neubildung von Blutgefäßen, welche durch Sprossung aus bereits bestehenden Gefäßen heraus erfolgt. Eine weitere Variante der Angiogenese stellt die Vaskulogenese dar, welche durch die Rekrutierung knochenmarkstämmiger endothelialer Vorläuferzellen (endothelial progenitor cells, EPC) ermöglicht wird. Um den Einfluss einer CKD auf die Gefäßneubildung zu betrachten, wurde das etablierte Tiermodell der subtotalen Nephrektomie (SnX) gewählt. Hier erfolgt durch operative Entfernung von 5/6 der Nierenmasse eine stabile Reduktion der Nierenfunktion, welche sowohl durch klinische Parameter als auch histologische Darstellungen bestätigt wird. Zusätzlich wird zur Charakterisierung der Funktionalität endothelialer Vorläuferzellen bei CKD eine Knochenmarktransplantation mit Knochenmark von hPAP-transgenen Tieren durchgeführt. Dadurch wird es ermöglicht knochenmarkstämmige Zellen eindeutig zu identifizieren. Durch den in dieser Arbeit verwendeten experimentellen Aufbau konnte ein etwa 50%iger Austausch des endogenen Knochenmarks erreicht werden. Dabei konnte bei SnX-Tieren im Vergleich zu nierengesunden Kontrolltieren keine vermehrte Rekrutierung knochenmark-stämmiger Zellen in Niere und Herz beobachtet werden. Überaschenderweise konnten in beiden Organen keine knochenmarkstämmigen Endothelzellen gefunden werden, sodass zu vermuten ist, dass diese keine Rolle bei der Gefäßneubildung spielen. Vielmehr handelt es sich bei den eingewanderten Zellen mehrheitlich um Entzündungszellen. Ein besonderes Augenmerk lag hier auf den Monozyten und Makrophagen, welche nach SnX vermehrt vorhanden sind. Diese tragen einerseits durch profibrotische-Eigenschaften (M2-Makrophagen), durch Differenzierung zu Myofibroblasten (profibrotisch) und andererseits durch Sekretion anti-angiogener Zytokine zu einer verminderten Kapillarisierung bei. Die starke Fibrosierung im Herzen von SnX-Tieren entsteht primär durch Myofibroblasten und trägt vermutlich durch Differenzierung aus Pericyten ebenfalls zum Kapillarverlust bei. Eine experimentelle Gentherapie zur Verbesserung der Kapillarisierung bei CKD mit dem vaskulären endothelialen Wachstumsfaktor (vascular endothelial growth factor, VEGF) wurde durchgeführt. Hierbei war der Wachstumsfaktor in der Niere nach SnX auf RNA-Ebene vermindert. Die VEGF-Gentherapie konnte keinen der dargestellten Einschränkungen der Herz- und Nierenfunktion in SnX-Modell entgegenwirken und auch keine Verbesserung der Kapillarisierung erzielen.
... The tumors enhance the mobilization of circulating progenitor cells form the bone marrow thus affecting tumor new vascularization. [26,27] In the present study, the level of CECs after high dose radiotherapy was highly increased reflecting the impact of high dose radiation on the integrity of vascular endothelium. Moreover, it reflects the direct toxicity of radiation to the endothelium. ...
Background
Vascular injuries caused by irradiation include acute vasculitis with neutrophil invasion, endothelial cell (EC) swelling, capillary loss, and activation of coagulator mechanisms, along with local ischemia and fibrosis. The circulating endothelial cells (CECs), increase dramatically in diseases with vascular damage.
Aim
The aim of this study is to provide data on the endothelial dysfunction due to occupational exposure to low dose ionizing radiation versus high dose exposure during radiotherapy (RT).
Patients and Methods
This study included 100 subjects divided into three main groups: Group I: High dose exposure group: 50 breast cancer patients treated with post-operative radiotherapy. Group II: Low dose exposure group: 25 hospital radiation workers. Group III: 25 healthy volunteers' age and sex matched as control group who had never worked in radiation-related jobs. TM levels measured by enzyme linked immunosorbent assay (ELISA). Circulating endothelial cells (CEC) enumerated in peripheral blood by flow cytometric analysis of their signature receptor CD146.
Results
% CD146+ cells and plasma TM were significantly increased in radiation workers and after exposure to radiotherapy treatment in breast cancer patients. When comparing patients group with radiation workers group, we found significant elevation in plasma TM in radiation workers while insignificant difference was found in % CD146+ cells.
Conclusion
CECs and plasma TM both are increased in radiation workers and patients treated with radiotherapy. They may constitute valuable markers of endothelial injury. Workers exposed to low doses of ionizing radiation may develop significant endothelial dysfunction predisposes them to cardiovascular complications namely thrombosis, mostly due to oxidative stress among other causes.
... In vielen Publikationen werden mittlerweile zwei Zonen in der Gefäßwand beschrieben, in denen Stamm-und Progenitorzellen vorkommen, in der subendothelialen Zone der Tunica intima und in der Tunica Adventitia. Letztere wird auch als vaskulogene Zone bezeichnet [9,10,[134][135][136][137][138][139]. ...
In dieser Dissertation wurden murine Aorta-Explantate im experimentellen Ansatz des "Aortic Ring Assay" über elf Tage kultiviert, erstmalig die Differenzierung zu F4/80(+)-Makrophagen gezeigt und eine nahezu vollständige Depletion dieser Zellen durch Clodronat-Liposomen bewirkt. Diese Adventitia-generierten Makrophagen wurden als die Hauptquelle des lokal gebildeten VEGF nachgewiesen. Die daraus resultierende Depletion des parakrin wirkenden VEGF resultierte in einer teilweisen Konservierung der CD34(+) „Vaskulogenen Zone“ der aortalen Adventitia. Zu der Bestätigung dieser Ergebnisse wurde experimentell über den VEGF-Rezeptor-Blocker E7080 in das VEGF-VEGFR-2 System eingegriffen. Die Versuchsansätze mit diesem Rezeptorblocker resultierten in einem ähnlichen Ergebnis wie die Versuche unter Makrophagen-Depletion.
... There may be three types of progenitor stem cells, such as endothelial progenitor cells (EPCs), hematopoietic progenitor cells (HPCs), as well as local EPCs residing within the vascular wall. The literature suggests that the vascular wall harboring the EPCs and HPCs in the perivascular space provides a microenvironment where cells can exist as well as mobilize on the basis of the needs of the tissue (Erguen et al., 2008;Zengin et al., 2006). Thus EPCs and HPCs can aid the processes of angiogenesis and vasculogenesis. ...
Cancer in its various forms is considered as one of the world's most devastating diseases. The triumph over cancer depends on the ability of therapeutics to reach the particular intracellular and intercellular targets, while lessening their accumulation at nonspecific sites. The advancement in nanotechnology and biotechnology has contributed immensely to the development of biocompatible nanocarriers adapted to specific needs and they have the ability to deliver therapeutic payloads specifically to the target tissue(s). The microenvironment of tumors possesses several unique features, thus the knowledge and understandings of tumor microenvironment are crucial for the development of nanocarriers targeted towards several specific types of tumors. Nanocarriers also possess the potential of delivering multiple drugs directed against different molecular targets, resulting in suppression of multidrug-resistant phenotypes as well as a decrease in multidrug-resistant based drug efflux. Surface amendment with various polymers, such as polyethylene glycol, improves circulation time by minimizing nonspecific uptake while inclusion of active targeting ligands allow for more precise tumor targeting. This chapter focuses on the modalities for overcoming different physiological barriers to tumor targeting using different types of multifunctional target-specific nanocarriers to facilitate more specific entry of drugs into the tumor for better therapeutic outcome, along with future directives to improve the frequency of translation of nanomedicine from laboratories to clinic.
... While it is unclear what exact cell population is required to treat CLI, EPCs and hematopoietic stem cells are critical for angiogenesis and vasculogenesis. [22][23][24][25] In addition, MSCs and hematopoietic stem cells have been shown to cross talk and create a stem cell niche that is beneficial for both stem cell types. 26,27 Soluble factors released from one progenitor cell type to another have been shown to be required for cell survival and proliferation of colonies. ...
Critical limb ischemia (CLI) is a terminal disease with high morbidity and healthcare costs due to limb loss. There are no effective medical therapies for patients with CLI to prevent amputation. Cell-based therapies are currently being investigated to address this unmet clinical need and have shown promising preliminary results. The purpose of this study was to characterize the output of a point-of-care cell separator (MarrowStim P.A.D. Kit), currently under investigation for the treatment of CLI, and compare its output with Ficoll-based separation. The outputs of the MarrowStim P.A.D. Kit and Ficoll separation were characterized using an automated hematology analyzer, colony-forming unit (CFU) assays, and tubulogenesis assays. Hematology analysis indicated that the MarrowStim P.A.D. Kit concentrated the total nucleated cells, mononuclear cells, and granulocytes compared with baseline bone marrow aspirate. Cells collected were positive for VEGFR-2, CD3, CD14, CD34, CD45, CD56, CD105, CD117, CD133, and Stro-1 antigen. CFU assays demonstrated that the MarrowStim P.A.D. Kit output a significantly greater number of mesenchymal stem cells and hematopoietic stem cells compared with cells output by Ficoll separation. There was no significant difference in the number of endothelial progenitor cells output by the two separation techniques. Isolated cells from both techniques formed interconnected nodes and microtubules in a three-dimensional cell culture assay. This information, along with data currently being collected in large-scale clinical trials, will help instruct how different cellular fractions may affect the outcomes for CLI patients.
... Similarly, the endothelial precursors recruited and responding to the hypoxic milieu of the CSCs niche are sub-mitted to the identical miR regulation. Tumour endothelial cells were found to share the same abnormalities as found in cancer cells [42], which could be due to a common cancer/endothelial cell progenitor [43], to cancer-to-endothelial cell transdifferentiation [44], to fusion between cancer and ECs [45], or to cancer stem-like cells undergoing vascular mimicry. In contrast, tumour endothelial cells have unique properties [46] suggesting that oncogene-bearing circulating endothelial cell precursors might be one of the possible identities of cancer stem cells. ...
The tumour microenvironment, long considered as determining cancer development, still offers research fields to define hallmarks of cancer. An early key-step, the "angiogenic switch", allows tumour growth. Pathologic angiogenesis is a cancer hallmark as it features results of tumour-specific properties that can be summarised as a response to hypoxia. The hypoxic state occurs when the tumour mass reaches a volume sufficient not to permit oxygen diffusion inside the tumour centre. Thus tumour cells turn on adaptation mechanisms to the low pO2 level, inducing biochemical responses in terms of cytokines/chemokines/receptors and consequently recruitment of specific cell types, as well as cell-selection inside the tumour. Moreover, these changes are orchestrated by the microRNA balance strongly reflecting the hypoxic milieu and mediating the cross-talk between endothelial and tumour cells. MicroRNAs control of the endothelial precursor-vascular settings shapes the niche for selection of cancer stem cells.
