Interleukin-8 (IL-8/CXCL8) is a chemokine that increases endothelial permeability during early stages of angiogenesis. However, the mechanisms involved in IL-8/CXCL8-induced permeability are poorly understood. Here, we show that permeability induced by this chemokine requires the activation of vascular endothelial growth factor receptor-2 (VEGFR2/fetal liver kinase 1/KDR). IL-8/CXCL8 stimulates VEGFR2 phosphorylation in a VEGF-independent manner, suggesting VEGFR2 transactivation. We investigated the possible contribution of physical interactions between VEGFR2 and the IL-8/CXCL8 receptors leading to VEGFR2 transactivation. Both IL-8 receptors interact with VEGFR2 after IL-8/CXCL8 treatment, and the time course of complex formation is comparable with that of VEGFR2 phosphorylation. Src kinases are involved upstream of receptor complex formation and VEGFR2 transactivation during IL-8/CXCL8-induced permeability. An inhibitor of Src kinases blocked IL-8/CXCL8-induced VEGFR2 phosphorylation, receptor complex formation, and endothelial permeability. Furthermore, inhibition of the VEGFR abolishes RhoA activation by IL-8/CXCL8, and gap formation, suggesting a mechanism whereby VEGFR2 transactivation mediates IL-8/CXCL8-induced permeability. This study points to VEGFR2 transactivation as an important signaling pathway used by chemokines such as IL-8/CXCL8, and it may lead to the development of new therapies that can be used in conditions involving increases in endothelial permeability or angiogenesis, particularly in pathological situations associated with both IL-8/CXCL8 and VEGF. INTRODUCTIONAngiogenesis is a multistep process in which quiescent blood vessels give rise to new blood vessels. After endothelial cells are exposed to an angiogenic factor, the endothelium is destabilized, leading to a decrease in endothelial cell adhesion and an increase in vascular permeability. Simultaneously, matrix metalloproteinases are produced and activated, which degrade the basal lamina in discrete regions of the blood vessel. The endothelial cells are then able to proliferate and migrate into surrounding connective tissue, forming a "sprout," or cord of endothelial cells, which subsequently develops a lumen; sprouts from adjacent arterioles and venules fuse to form a network of blood vessels.The nascent vessels then recruit periendothelial cells, smooth muscle-like cells that stabilize the endothelium by promoting basal lamina deposition and intercellular adhesions (Daniel and Abrahamson, 2000;Conway et al., 2001).During inflammation and angiogenesis, multiple factors, including tumor necrosis factor-␣ (Nwariaku et al., 2002), histamine (Leach et al., 1995;van Nieuw Amerongen et al., 1998;Andriopoulou et al., 1999), thrombin (van Nieuw Amerongen et al., 1998;Moldobaeva and Wagner, 2002), and vascular endothelial growth factor (VEGF) (Esser et al., 1998;Kevil et al., 1998;Eliceiri et al., 1999;Chang et al., 2000), increase vascular permeability by altering cell-cell adhesion, gap formation between endothelial cells, or both. Anothe...

Background: Regenerative wound repair is a goal of modern medicine. This is important not only for the local repair but also for its beneficial effect to systemic physiological processes. When wounds become chronic, individuals are susceptible to generalized inflammatory cascades that can affect many organs and even lead to death. Skin is the most commonly injured tissue, and its proper repair is important for reestablishment of its barrier function.

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Angiogenesis, the development of new blood vessel from pre-existing vessels, is a key process in the formation of the granulation tissue during wound healing. The appropriate development of new blood vessels, along with their subsequent maturation and differentiation, establishes the foundation for functional wound neovasculature. We performed studies in vivo and used a variety of cellular and molecular approaches in vitro to show that insulin stimulates angiogenesis and to elucidate the signalling mechanisms by which this protein stimulates microvessel development. Mice skin injected with insulin shows longer vessels with more branches, along with increased numbers of associated α-smooth muscle actin-expressing cells, suggesting the appropriate differentiation and maturation of the new vessels. We also found that insulin stimulates human microvascular endothelial cell migration and tube formation, and that these effects occur independently of VEGF/VEGFR signalling, but are dependent upon the insulin receptor itself. Downstream signalling pathways involve PI3K, Akt, sterol regulatory element-binding protein 1 (SREBP-1) and Rac1; inhibition of these pathways results in elimination of endothelial cell migration and tube formation and significantly decreases the development of microvessels. Our findings strongly suggest that insulin is a good candidate for the treatment of ischaemic wounds and other conditions in which blood vessel development is impaired.

Proper healing of cutaneous wounds progresses through a series of overlapping phases. Non-healing wounds are defective in one or more of these processes and represent a major clinical problem. A critical issue in developing treatments for chronic wounds is the paucity of animal models to study the mechanisms underlying the defects in healing. Here we show that deletion of Tumor Necrosis Factor Superfamily Member 14 (TNFSF14/LIGHT) leads to impaired wounds in mice that have the characteristics of non-chronic and chronic ulcers. These wounds show: (1) Excessive production of cytokines, in particular three chemokines (KC/CXCL8, MCP-1/CCL2, IP-10/CXCL10), that may be key to the abnormal initiation and resolution of inflammation; (2) defective basement membranes, explaining blood vessel leakage and disruption of dermal/epidermal interactions; (3) granulation tissue that contains high levels of Coll III whereas Coll I is virtually absent and does not form fibrils. We also see major differences between non-chronic and chronic wounds, with the latter populated by bacterial films and producing eotaxin, a chemokine that attracts leukocytes that combat multicellular organisms (which biofilms can be considered to be). This new mouse model captures many defects observed in impaired and chronic human wounds, and provides a vehicle to address their underlying cell and molecular mechanisms.

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Resolution of inflammation is critical for normal wound healing. Inflammation is prolonged and fails to resolve properly in chronic wounds. We used in vivo and in vitro approaches to show that vascular endothelial growth factor (VEGF) induces macrophage apoptosis and to delineate mechanisms involved in this process. VEGF inhibition during wound healing leads to an increased number of macrophages remaining in wounds, suggesting the involvement of VEGF in removal of these cells from the wound. If this effect has physiological relevance, it likely occurs via apoptosis. We show that VEGF increases apoptosis of macrophages in vitro using Annexin V-FITC staining and caspase activation. Microarray analysis, reverse transcription-polymerase chain reaction, and immunoblotting showed that VEGF increases the expression of tumor necrosis factor superfamily member 14 (TNFSF14/LIGHT) in macrophages. We also show that in macrophages LIGHT promotes apoptosis through the lymphotoxin beta receptor. Moreover, inhibition of LIGHT prevents VEGF-induced death, suggesting that LIGHT mediates VEGF-induced macrophage apoptosis. Taken together, our results identify a novel role for VEGF and for LIGHT in macrophage apoptosis during wound healing, an event critical in the resolution of inflammation. This finding may lead to the development of new strategies to improve resolution of inflammation in problematic wounds.

Angiogenesis is essential in many physiological and pathological processes and can be stimulated by many different factors. To better understand and to manipulate this process more effectively, it would be beneficial to identify molecules common to the signaling pathways stimulated by different classes of angiogenic factors. Sterol regulatory element-binding proteins (SREBPs) are involved in the metabolism of cholesterol and fatty acids, molecules that are critical in membrane biology, and hence, many of the processes involved in angiogenesis. Here, we show that angiogenic factors of different families, such as basic fibroblast growth factor, thrombin, and interleukin (IL)-8, stimulate SREBP activation, whereas nonangiogenic factors, such as transforming growth factor-beta1, do not. We focused our detailed studies on IL-8 in vitro and in vivo, as this chemokine is also involved in inflammation and hence, has the potential to be critical in inflammation-induced angiogenesis, a process common to many diseases. Using human microvascular endothelial cells, a rabbit skin wound-healing model, and the chorioallantoic membrane assay, we show that IL-8 stimulates the activation of SREBP-1 and -2, and this activation is specific and receptor-mediated. SREBP activation leads to activation of RhoA through 3-hydroxy-3-methylglutaryl CoA reductase. RhoA is a small guanosinetriphosphatase, important in cytoskeletal functions, which in turn, are critical in many of the cellular processes needed for angiogenesis. Given that diverse, angiogenic factors use different cell-surface receptors, identification of this common step in the signal-transduction pathway provides the opportunity for novel approaches for prevention and treatment of diseases involving abnormal angiogenesis.