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A. Ohlmann, R. Seitz, D. Seitz, B. M. Braunger, M. R. Bösl, E. R. Tamm; Norrin Is an Angiogenic Factor That Protects Against Vascular Degeneration and Induces Retinal Recapillarization in Oxygen Induced Retinopathy. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6171.
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© ARVO (1962-2015); The Authors (2016-present)
To analyze, if norrin, the secreted protein product of the Norrie disease gene (Ndp), has direct angiogenic and vasoprotective properties in vitro and in vivo in mice with oxygen induced retinopathy (OIR). Ndp(y/-) mutant mice that are deficient in norrin lack the deep capillary layers of the retina, a phenotype that is completely rescued in mixed (beta)B1-norrin/Ndp(y/-) mice with transgenic overexpression of norrin (Ohlmann et al., J. Neurosci. 2005).
Human recombinant norrin was isolated and purified from conditioned cell culture media of 293-EBNA cells by chromatography. Human retinal vascular endothelial cells (HRMEC) were treated with recombinant norrin to analyze its effects on proliferation, viability, migration and tube formation. In addition, OIR was induced in (beta)B1-norrin mice with transgenic ocular overexpression of norrin and in their wild-type littermates by exposure to 75% O2 at postnatal day 7 (P7) for either 18 hours or 5 days. Following O2 exposure, flat mounts of FITC-dextran-perfused retinae were isolated and areas with obliterated vessels were quantified by morphometry. For controls, Dickkopf (DKK)-1 was added to block WNT/(beta)-catenin signaling, as norrin activates the classical WNT pathway by acting primarily via the frizzeled-4 receptor.
Recombinant norrin significantly increased proliferation, viability, migration and tube formation in HRMEC. The effects could be blocked significantly by adding DKK-1. Following exposure to 75% O2 for either 18 hours or 5 days, vasoobliterated areas were significantly smaller in (beta)B1-norrin mice as compared to wild-type littermates. Moreover, after O2 exposure for 5 days, recapillarization of vasoobliterated areas was markedly increased in (beta)B1-norrin mice as compared to wild-type controls. Again, the effect on recapillarization was decreased significantly by adding DKK-1.
Norrin is an angiogenic factor for retinal microvascular endothelial cells with an important role for development, recapillarization and maintenance of retinal capillaries.
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