Active Rac1 improves pathologic VEGF neovessel architecture and reduces vascular leak: mechanistic similarities with angiopoietin-1

Abstract

Architecturally defective, leaky blood vessels typify pathologic angiogenesis induced by vascular endothelial growth factor-A (VEGF-A). Such neovascular defects aggravate disease pathology and seriously compromise the therapeutic utility of VEGF. Endothelial cell (EC) transduction with active L61Rac1 strongly improved VEGF-driven angiogenesis in vivo as measured by increased neovascular density, enhanced lumen formation, and reduced vessel leakiness. Conversely, transduction with dominant-negative N17Rac1 strongly inhibited neovascularization. In vitro, active L61Rac1 promoted organization of cortical actin filaments and vascular cords and improved EC-EC junctions, indicating that improved cytoskeletal dynamics are important to the mechanism by which active L61Rac1 rectifies VEGF-driven angiogenesis. SEW2871, a sphingosine 1-phosphate receptor-1 agonist that activates Rac1 in ECs, improved cord formation and EC-EC junctions in vitro similarly to active L61Rac. Moreover, SEW2871 administration in vivo markedly improved VEGF neovessel architecture and reduced neovascular leak. Angiopoietin-1, a cytokine that “normalizes” VEGF neovessels in vivo, activated Rac1 and improved cord formation and EC-EC junctions in vitro comparably to active L61Rac1, and a specific Rac1 inhibitor blocked these effects. These studies distinguish augmentation of Rac1 activity as a means to rectify the pathologic angioarchitecture and dysfunctionality of VEGF neovessels, and they identify a rational pharmacologic strategy for improving VEGF angiogenesis.

Junctional Protein Regulation by Sphingosine Kinase 2 Contributes to Blood–Brain Barrier Protection in Hypoxic Preconditioning-Induced Cerebral Ischemic Tolerance

“…Indeed, there is evidence from studies in the peripheral vasculature that S1P activates endothelial nitric oxide synthase via PI3K/ Akt, counteracts the deleterious effects of reactive oxygen species on vascular endothelium via ERK1/2 and endothelial nitric oxide synthase (Igarashi and Michel, 2008), and regulates pericyte recruitment via N-cadherin signaling (Paik et al, 2004). Sphingosine-1-phosphate R1 receptor activation also induces intracellular calcium release from the endoplasmic reticulum and Rac-1 activation, promoting adherens junction formation at the endothelial cell periphery that can block vascular endothelial growth factorinduced vascular permeability (Hoang et al, 2011;Mehta et al, 2005). Finally, vascular barrier enhancement by S1P may require lipid rafts where activated tyrosine kinases phosphorylate signaling molecules that lead to reduced vascular permeability (Zhao et al, 2009).…”

Effective Treatment of Edema and Endothelial Barrier Dysfunction With Imatinib

“…2,21 Rac1 activity may enforce endothelial cell-cell junctions via mediators like angiopoietin-1. 29 Of note, Rac1 was also described to mediate peripheral accumulation of FAs, thereby enhancing endothelial barrier function. 21 A direct interrelation between Arg, Rac1, and integrin-mediated adhesion was recently suggested in a fibroblast study that demonstrated that Arg inhibits Rac1 activity and integrin function.…”

The tumor vessel targeting agent NGR-TNF controls the different stages of the tumorigenic process in transgenic mice by distinct mechanisms

“…29 The other three genes that are modulated in NGRmTNF-treated tumors encode proinflammatory cytokines: IL-6, IL-1b, and IFNg. IL-6 and IL-1b, which are secreted by many tumor stroma cells, 30 including M1-like macrophages, [31][32][33] contribute to the activation of the protective adaptive immunity.…”