Lack of netrin-4 modulates pathologic neovascularization in the eye

Netrins are a family of matrix-binding proteins that function as guidance signals. Netrin-4 displays pathologic roles in tumorigenesis and neovascularization. To answer the question whether netrin-4 acts either pro- or anti-angiogenic, angiogenesis in the retina was assessed in Ntn-4 ^-/- mice with oxygen-induced retinopathy (OIR) and laser-induced choroidal neovascularization (CNV), mimicking hypoxia-mediated neovascularization and inflammatory mediated angiogenesis. The basement membrane protein netrin-4 was found to be localised to mature retinal blood vessels. Netrin-4, but not netrin-1 mRNA expression, increased in response to relative hypoxia and recovered to normal levels at the end of blood vessel formation. No changes in the retina were found in normoxic Ntn-4^-/- mice. In OIR, Ntn-4^-/- mice initially displayed larger avascular areas which recovered faster to revascularization. Ganzfeld electroretinography showed faster recovery of retinal function in Ntn-4^-/- mice. Expression of netrin receptors, Unc5H2 (Unc-5 homolog B, C. elegans) and DCC (deleted in colorectal carcinoma), was found in Müller cells and astrocytes. Laser-induced neovascularization in Nnt-4^-/- mice did not differ to that in the controls. Our results indicate a role for netrin-4 as an angiogenesis modulating factor in O₂-dependent vascular homeostasis while being less important during normal retinal developmental angiogenesis or during inflammatory neovascularization.