Several lines of evidence indicate that Flt-1, a fms-like tyrosine kinase receptor, which

Background-Monocytes are cellular components of wound repair, arteriogenesis, and atherogenesis. Vascular endothelial growth factor (VEGF)-A and placental growth factor recruit monocytes to sites of arteriogenesis via stimulation of VEGF receptor-1 (VEGFR-1). The chemotactic response of monocytes to VEGF-A is attenuated in individuals with diabetes mellitus (DM). This VEGF resistance correlates with impaired collateral growth. The aim of this study is to elucidate the molecular basis of VEGF resistance and impaired monocyte response in DM. Methods and Results-Phosphorylation of Akt, p38, and extracellular signal-regulated kinase 1/2 (ERK1/2) could be stimulated with either placental growth factor-1 or VEGF-A in monocytes from non-DM but not DM individuals. In contrast, formyl-methionyl-leucyl-phenylalanine caused a comparable activation of these molecules in both DM and non-DM monocytes. Baseline phosphorylation of Akt, p38, and ERK1/2 was significantly elevated in monocytes from DM compared with non-DM subjects. Of note, H 2 O 2 activated Akt, p38, and ERK1/2 in non-DM monocytes ex vivo. Protein tyrosine phosphatases had stronger oxidative modifications in monocytes from DM than from non-DM individuals, which reflects functional protein tyrosine phosphatase inhibition, similar to that seen after H 2 O 2 challenge. Overall, protein tyrosine phosphatase and protein tyrosine phosphatase-1B activity were reduced in DM monocytes. DM monocytes revealed higher expression of the receptor for advanced glycation end products. Stimulation with advanced glycation end products ligands resulted in activation of non-DM monocytes and inhibition of VEGFR-1-mediated chemotaxis. The elevated baseline phosphorylation/activation of Akt, p38, and ERK1/2 in DM monocytes likely causes the resistance to further stimulation with specific stimuli such as VEGF-A, revealing a molecular explanation of the DM-related signal transduction defect. Conclusions-We propose that elevated advanced glycation end products expression and increased oxidative stress in diabetic monocytes lead to activation of VEGFR-1-related signaling pathways and to desensitization of VEGFR-1 responses. These data establish VEGF resistance as a novel molecular concept for DM-related cellular dysfunction. Key Words: diabetes mellitus Ⅲ monocytes Ⅲ signal transduction Ⅲ vascular endothelial growth factor receptor-1 G rowth factors are potent and crucial mediators of vascular growth processes, including angiogenesis and arteriogenesis. 1,2 Both processes can enhance regional blood flow and restore impaired tissue function. Monocytes contribute to arteriogenesis by recruitment to the growing vessel wall. [3][4][5] Moreover, angiogenesis is monocyte dependent in the context of wound healing. 6 Editorial see p 104 Clinical Perspective on p 159The family of vascular endothelial growth factor (VEGF) and its receptors (VEGFR) are mediators of angiogenesis and arteriogenesis in both embryonic development and adult life. 1,4,7 VEGFR-2 mediates crucial functions of endothelial cel...

Objective-To elucidate the downstream mechanisms of vascular endothelial growth factor receptor 2 (VEGFR2), a key receptor in angiogenesis, which has been associated with atherosclerotic plaque growth and instability. Methods and Results-By using a yeast-2-hybrid assay, we identified A Disintegrin And Metalloprotease 10 (ADAM10) as a novel binding partner of VEGFR2. ADAM10 is a metalloprotease with sheddase activity involved in cell migration; however, its exact function in endothelial cells (ECs), angiogenesis, and atherosclerosis is largely unknown. For the first time to our knowledge, we show ADAM10 expression in human atherosclerotic lesions, associated with plaque progression and neovascularization. We demonstrate ADAM10 expression and activity in ECs to be induced by VEGF; also, ADAM10 mediates the ectodomain shedding of VEGFR2. Furthermore, VEGF induces ADAM10-mediated cleavage of vascular endothelium (VE)-cadherin, which could increase vascular permeability and facilitate EC migration. Indeed, VEGF increases vascular permeability in an ADAM10-and ADAM17-dependent way; inhibition of ADAM10 reduces EC migration and chemotaxis. Conclusion-These data provide the first evidence of ADAM10 expression in atherosclerosis and neovascularization. Key Words: angiogenesis Ⅲ atherosclerosis Ⅲ endothelial function Ⅲ growth factors Ⅲ metalloproteinases A ngiogenesis is associated with tumor growth, metastasis, and growth and instability of atherosclerotic plaques. The latter contribute to plaque rupture and its clinical complications. 1 Expression of the major angiogenic factor, vascular endothelial growth factor (VEGF) A, increases during atherogenesis. In endothelial cells (ECs), VEGF exerts its stimulatory effect mostly via VEGF receptor (VEGFR) 2 (kinase insert domain receptor [KDR]/fetal liver kinase-1 ) and is a potent angiogenic mediator of EC migration, proliferation, and survival. 2 VEGF binding induces VEGFR2 dimerization, followed by (auto)phosphorylation on tyrosine residues. Activation of VEGFR2 induces signaling via phospholipase C (PLC)␥, activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) 1/2 pathway, and EC proliferation. Furthermore, activation of p38 -mitogen-activated protein kinase or phosphatidylinositol 3-kinase (PI3K) leads to EC migration, survival, and increased permeability. 2,3 See accompanying article on page 2087In addition to angiogenesis, VEGF and its receptors are associated with development of atherosclerosis, plaque angiogenesis, and plaque instability. Recently, it was suggested that VEGF may induce a more vulnerable plaque phenotype by promoting leukocyte recruitment. 4 6 The neutralizing VEGF antibody bevacizumab (Avastin) is an effective anticancer therapy that inhibits tumor angiogenesis; however, it is associated with an increase in cardiovascular adverse effects based on thrombosis and plaque instability. 7 Unraveling downstream VEGFR signaling mechanisms involved in angiogenesis and atherosclerosis will identify novel therapeutic...

Objective-Arteriogenesis, the growth of preexisting arterioles into functional arteries, is dependent on the proper function of monocytes. Likewise, wound healing is monocyte-dependent. The activation of vascular endothelial growth factor receptor-1 (VEGFR-1) in monocytes induces a chemotactic response, triggers the expression of tissue factor, and gene expression of cytokines and chemokines. Little is known about intracellular signaling pathways mediating the biological functions triggered by VEGFR-1 in primary monocytes. Methods and Results-Monocytes were isolated from peripheral venous blood of young healthy individuals using indirect magnetic labeling. Stimulation of monocytes with either vascular endothelial growth factor-A (VEGF-A) or placenta growth factor (PlGF-1) triggered VEGFR-1 autophosphorylation and phosphorylation of distinct downstream proteins: phosphatidylinositol-3 kinase (PI-3K), Akt, p38, and extracellular signal-regulated kinase-1/2 (ERK1/2). PI-3K appears to be a central regulator in VEGFR-1 signaling in monocytes as the activation of Akt, p38, and ERK1/2 are PI-3-K-dependent. In addition, Akt activation functions downstream of p38 kinase. VEGFR-1-mediated chemotaxis of monocytes is dependent on the activation of PI-3K, p38 kinase, Akt, and ERK1/2, when assessed in a modified Boyden chamber. Conclusions-Both

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