A Role for a CXCR2/Phosphatidylinositol 3-Kinase γ Signaling Axis in Acute and Chronic Vascular Permeability

Abstract

Most proangiogenic polypeptide growth factors and chemokines enhance vascular permeability, including vascular endothelial growth factor (VEGF), the main target for anti-angiogenic-based therapies, and interleukin-8 (IL-8), a potent proinflammatory mediator. Here, we show that in endothelial cells IL-8 initiates a signaling route that converges with that deployed by VEGF at the level of the small GTPase Rac1 and that both act through the p21-activated kinase to promote the phosphorylation and internalization of VE-cadherin. However, whereas VEGF activates Rac1 through Src-related kinases, IL-8 specifically signals to Rac1 through its cognate G protein-linked receptor, CXCR2, and the stimulation of the phosphatidylinositol 3-kinase ␥ (PI3K␥) catalytic isoform, thereby providing a specific molecular targeted intervention in vascular permeability. These results prompted us to investigate the potential role of IL-8 signaling in a mouse model for retinal vascular hyperpermeability. Importantly, we observed that IL-8 is upregulated upon laser-induced retinal damage, which recapitulates enhanced vascularization, leakage, and inflammatory responses. Moreover, blockade of CXCR2 and PI3K␥ was able to limit neovascularization and choroidal edema, as well as macrophage infiltration, therefore contributing to reduce retinal damage. These findings indicate that the CXCR2 and PI3K␥ signaling pathway may represent a suitable target for the development of novel therapeutic strategies for human diseases characterized by vascular leakage.During embryonic development, blood vessels arise from endothelial precursors which share their origin with hematopoietic precursors (8). These progenitors assemble into a primitive vascular network of small capillaries, through a process called vasculogenesis, and this vascular plexus progressively expands and remodels into a highly organized pattern by the growth of blood vessels from preexisting ones, a process referred to as angiogenesis (8). During adulthood, endothelial cells that form the vascular wall retain their plasticity and can be engaged in neovascularization in response to physiological stimuli, such as hypoxia, wound healing, and tissue repair. In addition, numerous human diseases and pathological conditions are characterized by an excessive, uncontrolled, and aberrant angiogenesis (35). This physiological process is often co-opted by tumor cells to build a new vascular network dedicated to supply oxygen and nutrients to the cancerous cells, thereby enabling them to proliferate and metastasize (16).Aberrant angiogenesis occurs in numerous pathological conditions, such as in acute and chronic inflammation, thrombotic reactions, edema, tumor-induced angiogenesis, and metastasis (35). For example, this process is central to the progression of many ocular diseases, where blood vessels show a disorganized and anarchic pattern and are frequently leaky (17). Indeed, the breakdown of the endothelial barrier, characterized by an uncontrolled increase in vascular permeability, contributes to...

Remodeling of VE-cadherin junctions by the human herpes virus 8 G-protein coupled receptor

“…In addition, our results suggest that blocking the PI(3)Kg by AS 605402 can effectively interfere with loss of endothelial barrier function provoked by vGPCR, therefore placing PI(3)Kg activity as a multi-functional molecular target for the treatment of patients with KS. Of note, suppression of PI (3)Kg action has been successfully tested in animal models for several pro-angiogenic and pro-inflammatory diseases, such as retinal hyper-permeability, glomerulonephritis, joint inflammation and rheumatoid arthritis (Barber et al, 2005;Camps et al, 2005;Gavard et al, 2009).…”

“…HHV8 vGPCR elicits increased endothelial cell monolayer permeability through Rac As vGPCR induces Rac activation on one hand, and CXCR2, the closest homologue of vGPCR, requires Rac activity to increase permeability on the other hand (Montaner et al, 2004;Gavard et al, 2009), we asked whether Rac could be involved in vGPCR-driven endothelial leakiness. First, stable expression of vGPCR in mouse SVECs activates Rac and its downstream effector the serine/threonine p21 activated kinase (PAK) (Figure 2a).…”

“…We recently showed that VEGF induces Rac activation through a Src/Vav2 signaling axis, whereas CXCR2 involves the PI(3)Kg pathway in the increase of endothelial permeability (Gavard and Gutkind, 2006;Gavard et al, 2009). In addition, Akt, a well known downstream target of PI(3)K signaling, has a prominent role in vGPCR sarcomagenesis (Sodhi et al, 2004b).…”

“…Of interest, we have recently shown that CXCR2 stimulation by its natural ligand IL-8, induces vascular leakage, inflammation and neo-vascularization (Gavard et al, 2009). We therefore investigated the molecular mechanisms by which vGPCR expression could affect vascular integrity and explored whether this process is co-opted in human KS.…”

G Protein-Coupled Receptor Dependent NF-κB Signaling in Atherogenesis

“…IL-8 is upregulated within developing atherosclerotic lesions, in part due to the stimulatory effect of Ox-LDL (Braunersreuther et al, 2007). Among its many effects, IL-8 induces expression of vascular endothelial growth factor (VEGF), which is synthesized and released by endothelial cells and can act in an autocrine/paracrine fashion to induce angiogenesis within the lipid core and to increase vascular permeability (Gavard et al, 2009). As with Ang II and thrombin, many of the pro-inflammatory effects of IL-8 can be attributed to the activation of NF-B.…”