Purchase this article with an account.
J. Ambati, M. Nozaki, E. Sakurai, B.J. Raisler, J.Z. Baffi, R.A. Brekken, E.H. Sage, M. Shibuya, B.K. Ambati; Pro– and Anti–Angiogenic Actions of VEGF–A are Differentially Routed via VEGFR–1 and VEGFR–2 Through SPARC Switching . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4755.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine interactions among vascular endothelial growth factor (VEGF)–A, VEGFR–1 and VEGFR–2, secreted protein, acidic and rich in cysteine (SPARC), monocyte chemoattractant protein–1 (Ccl–2), and its receptor Ccr–2 in injury models of ocular neovascularization. Methods: Choroidal (CNV) or corneal (KNV) neovascularization was induced by laser injury or combined chemical/mechanical injury, respectively, in mice. CNV volume was measured by lectin staining of choroid flatmounts. KNV area was measured by CD31 staining of cornea flatmounts. Injections into the vitreous or cornea were performed 1 day before or 1 day after injury. ELISA, immunoblotting, and flow cytometry were used to quantify molecular and cellular markers. Results: VEGF–A, exogenously introduced or endogenously upregulated 1 day before injury, increased CNV and KNV by 50–60%; however, if done so 1 day after injury, they decreased CNV and KNV by 50–60%. Experiments with receptor–specific ligands PlGF–1 and VEGF–E, receptor–preferential antagonists SU5416 and SU1498, and Vegfr–1 tyrosine kinase–/– mice, confirmed that the pre–injury pro–angiogenic action of VEGF–A was mediated via VEGFR–2, whereas the post–injury anti–angiogenic action of VEGF–A was mediated via VEGFR–1. Injury decreased SPARC levels in the RPE/choroid and the cornea, releasing its silencing of VEGFR–1 signaling, as confirmed by experiments with recombinant SPARC, neutralizing SPARC antibody, and SPARC–/– mice. VEGFR–1 signaling blocked VEGFR–2 activation via SHP–1 as confirmed by experiments with SHP–1 antagonists and Shp–1–/– mice. Pre–injury VEGF–A elevation increased Ccl–2 and macrophage infiltration, promoting CNV and KNV, while post–injury VEGF–A elevation decreased them, suppressing CNV and KNV, as confirmed by experiments with neutralizing Ccl–2 antibody, Ccl2–/– and Ccr2–/– mice. Conclusions: Increased VEGF–A meets divergent fates because constitutive VEGFR–1 activation is silenced by SPARC, which declines transiently after injury creating a temporal window where VEGF–A signaling is routed through VEGFR–1. These data suggest that anti–VEGF–A clinical trials can be optimized by tailoring them to the status of SPARC–VEGFR–1 interactions and VEGF–A levels.
This PDF is available to Subscribers Only