Angiogenesis and Vasculogenesis in Health and Disease

Developmental Biology, 2004

Erythropoietin (EPO) is an essential growth factor that regulates erythrocyte production in mammals. In this study, we demonstrate a novel role of EPO in regulating angiogenesis in vivo. Epo and Epo receptor (EpoR) are expressed in the vasculature during embryogenesis. Deletion of Epo or EpoR leads to angiogenic defects starting at E10.5, 2 days before ventricular hypoplasia and 3 days before the onset of the embryonic lethal phenotype. Overall, angiogenesis was severely affected in the mutant embryos: vascular anomalies included decreased complexity of the vessel networks. However, de novo vasculogenesis remained intact, consistent with the differential expression of Epo and EpoR during the early stages of embryonic development. The aforementioned angiogenesis defect can be partially rescued by expressing human EPO during embryogenesis. Moreover, Ang-1 expression is regulated by EPO/EPOR under normoxic conditions. Taken together, our results suggest important roles of EPO and EPOR in angiogenesis.

Cell, 2011

Blood vessels form extensive networks that nurture all tissues in the body. Abnormal vessel growth and function are hallmarks of cancer and ischemic and inflammatory diseases, and they contribute to disease progression. Therapeutic approaches to block vascular supply have reached the clinic, but limited efficacy and resistance pose unresolved challenges. Recent insights establish how endothelial cells communicate with each other and with their environment to form a branched vascular network. The emerging principles of vascular growth provide exciting new perspectives, the translation of which might overcome the current limitations of pro-and antiangiogenic medicine.

Leukemia, 2003

The role of erythropoietin (Epo) in angiogenesis has not been completely clarified. Epo induces endothelial cell proliferation and migration and stimulates angiogenesis on rat aortic rings in vitro and in vivo in the chick embryo chorioallantoic membrane (CAM) assay. The aim of the present study was to evaluate the ultrastructural aspects of angiogenesis in the CAM vasculature after recombinant human Epo (rHuEpo) exposure. The results demonstrated that after rHuEpo stimulation, the generation of new blood vessels occurred more frequently following an intussusceptive microvascular growth (IMG) mechanism. We have performed our experiments between days 8 and 12 of incubation, that is, when in the normal condition the capillary network expands mainly by IMG, and because it is generally accepted that implants made from days 8 to 10 are strongly angiogenic. This response is peculiar of rHuEpo, because it is abolished when an Epo-blocking antibody was coadministered with Epo.

Blood, 1999

Hematopoietic and endothelial cell lineages share common progenitors. Accordingly, cytokines formerly thought to be specific for the hematopoietic system have been shown to affect several functions in endothelial cells, including angiogenesis. In this study, we investigated the angiogenic potential of erythropoietin (Epo), the main hormone regulating proliferation, differentiation, and survival of erythroid cells. Epo receptors (EpoRs) have been identified in the human EA.hy926 endothelial cell line by Western blot analysis. Also, recombinant human Epo (rHuEpo) stimulates Janus Kinase-2 (JAK-2) phosphorylation, cell proliferation, and matrix metalloproteinase-2 (MMP-2) production in EA.hy926 cells and significantly enhances their differentiation into vascular structures when seeded on Matrigel. In vivo, rHuEpo induces a potent angiogenic response in the chick embryo chorioallantoic membrane (CAM). Accordingly, endothelial cells of the CAM vasculature express EpoRs, as shown by immun...

Journal of Investigative Dermatology, 2006

Trends in Pharmacological Sciences, 2002

Annals of the New York Academy of Sciences, 1995

A fundamental property of vascular endothelial cells is the ability to proliferate and form a network of capillaries.'.2 This process is known as "angiogenesis" and requires at least three steps: i) degradation of the extracellular matrix of a local venule, ii) chemotaxis of endothelial cells toward an angiogenic stimulus, and iii) proliferation of endothelial cells. Angiogenesis is prominent during embryonic development and somatic growth but in a normal adult it only takes place following injury or, in a cyclical fashion, in the endometrium and in the ovary.'%2 Angiogenesis plays a significant role in the pathogenesis of a variety of disorders including cancer, proliferative retinopathies, rheumatoid arthritis or psoriasis. Therefore, inhibition of angiogenesis may constitute an attractive strategy for the treatment of such disorders. Conversely, disorders characterized by inadequate tissue perfusion such as obstructive atherosclerosis and diabetes are expected to benefit from agents able to promote endothelial cell growth and angiogenesis. A variety of factors have been identified as potential positive regulators of angiogenesis: aFGF, bFGF, EGF, TGF-a, TGF-P, PGE2, monobutyrin, TNF-a, PD-ECGF, angiogenin and interleukin-8.'~~ This article will review a recently identified family of directly-acting endothelial cell mitogens and angiogenic factors known as vascular endothelial growth factor (VEGF) or vascular permeability factor (VPF).3,4 These factors are products of the same gene and, by alternative exon splicing, may exist in four different iso-form^.^-^ Recent studies point to VEGF as a major regulator of physiological and pathological angiogenesis. Furthermore, the angiogenic activity of VEGF appears to be sufficient to achieve therapeutic benefit in animal models of coronary or limb ischemia. Biological Properties of VEGF A unique aspect of VEGF is its target all specificity.' VEGF is a potent mitogen (ED5o 2-10 pM) for vascular endothelial cells, but it is apparently devoid of mitogenic activity for other cell types.'-" VEGF is also able to induce a marked angiogenic response in the chick chorioallantoic membrane.'O-I2 VEGF also proa Corresponding author.

Experimental Hematology, 2007

Objective. The ability of erythropoietin (EPO) to elicit a pro-angiogenic effect on human mesenchymal stem cells (hMSC) was tested. hMSC are currently under study as therapeutic delivery agents that target tumor vessels. Hypoxia favors the differentiation of hMSC towards a pro-angiogenic program. However, the classical angiogenic factors, vascular endothelial growth factor and basic fibroblast growth factor, are not fully capable of restoring this effect. The hypoxia-regulated factor, EPO, induces angiogenesis in endothelial cells. Here, EPO's pro-angiogenic effect on hMSC was analyzed. Methods. hMSC were tested for EPO receptor expression by western blot, immunofluorescence, and flow cytometry assays. Downstream receptor signaling components JAK and STAT were measured by standard assays. Pro-angiogenesis effects mediated by EPO treatment of hMSC were measured by proliferation, cytokine, or pro-angiogenesis factor secretion, metalloprotease activation, migration, invasion, wound healing, and tubule formation assays. Results. hMSC express the cognate EPO receptor and are capable of promoting angiogenesis following EPO treatment in all the angiogenesis assays tested. EPO-treated hMSC proliferate and secrete pro-angiogenesis factors more readily than untreated hMSC. EPO leads to increased hMSC chemotaxis, migration, and activation of matrix metalloprotease-2. This treatment causes greater recruitment of vessels as measured in an in vivo angiogenesis assay. Conclusion. EPO is capable of eliciting a pro-angiogenesis program in hMSC that instigates secretion of angiogenic factors and the subsequent recruitment of endothelium. This study defines a novel mechanism for tumor cell recruitment of blood vessels that is important to consider in the design of stem cell-based therapies. Ó

Journal of dental education, 2002

Angiogenesis, the process that leads to the formation of new blood vessels or neovascularization, continues to be a topic of major scientific and public interest. As knowledge of the molecular mechanisms that regulate neovascularization continues to emerge, there is increasing hope that new discoveries will lead to newer therapies that target angiogenesis as a reliable option for disease therapy. For example, it may be possible to develop strategies that, on the one hand, are designed to limit angiogenesis for the treatment of chronic diseases such as cancer or rheumatoid arthritis and, on the other, to promote angiogenesis in the ischemic heart or diabetic limb. With the emergence of tissue engineering as a discipline, it has become increasingly clear that long-term success in organ and tissue reconstruction will depend on the ability to develop a stable, renewable supply of blood vessels. In this review, I will provide a brief overview of this remarkably versatile biological respo...

Cell Cycle, 2008

A balance between angiogenesis inducers and inhibitors in the microenvironment controls the rate of new blood vessel formation. We hypothesized that fibroblasts, an important cellular constituent of the tissue stroma, secrete molecules that contribute to this balance. We further hypothesized that fibroblasts secrete molecules that promote angiogenesis when they are in a proliferative state and molecules that inhibit angiogenesis when they are not actively cycling (quiescent). Microarray analysis revealed that angiogenesis inducers and inhibitors are regulated as fibroblasts transition into a quiescent state and re-enter the cell cycle in response to changes in serum. To assess whether changes in transcript levels result in changes in the levels of secreted proteins, we collected conditioned medium from proliferating and quiescent fibroblasts and performed immunoblotting for selected proteins. Secreted protein levels of the angiogenesis inhibitor PEDF were higher in quiescent than proliferating fibroblasts. Conversely, proliferating fibroblasts secreted increased levels of the angiogenesis inducer VEGF-C. For the angiogenesis inhibitor thrombospondin-2, quiescent cells secreted a prominent 160 kDa form in addition to the 200 kDa form secreted by proliferating and restimulated fibroblasts. Using immunohistochemistry we discovered that fibroblasts surround blood vessels and that the angiogenesis inhibitor PEDF is expressed by quiescent fibroblasts in uterine tissue, supporting a role for PEDF in maintaining quiescence of the vasculature. This work takes a new approach to the study of angiogenesis by examining the expression of multiple angiogenesis genes secreted from a key stromal cell, the fibroblast.