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Stanley A. Vinores, Hu Huang, Sara Van de Veire, Mansi Dalal, Richard Semba, Peter Carmeliet; Retinal And Choroidal Neovascularization, Blood-retinal Barrier Breakdown, And Apoptosis Are Inhibited In The Absence Of Prolyl Hydroxylase-1. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1792.
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Oxidative stress is implicated in a number of ocular disorders, including AMD and ROP. In hypoxia, the prolyl hydroxylases (PHDs) act as oxygen sensors and stabilize the HIFs to promote the expression of proinflammatory, vasopermeability, and proapoptotic factors. Blocking PHD1 may be beneficial to ischemic retinopathies.
Oxygen-induced ischemic retinopathy (OIR) was generated as a model for ROP by placing P7 mice in 75% oxygen for 5d and returning them to the relative hypoxia of room air for 5d. CNV was induced by laser. NV was assessed by image analysis. BRB breakdown was assessed using 3H-mannitol as a tracer. Apoptosis was detected with TUNEL staining. Oxidative stress markers, HIF1α, and VEGF were detected by immunohistochemistry and HIF1α, and VEGF were quantified using Western blot and ELISA.
Retinal NV tufts and avascular areas were significantly reduced by 59 and 63% at P17, as was the associated retinal vascular leakage in OIR in the absence of PHD1. This could be accounted for by a 74% reduction in hyperoxia-associated vascular obliteration at P12 and reduced expression of HIF1α and VEGF. Apoptosis in the retina was also reduced at P9, after 2d in hyperoxia. Laser-induced CNV was reduced by 92% at 2wks and by 56% at 5wks. This was associated with a decrease in oxidative stress markers, acrolein and nitrotyrosine.
Inhibition of the hypoxia→HIF1α→VEGF pathway due to PHD1 deficiency leads to inhibition of both ischemia-induced retinal NV and laser-induced CNV. However, the regulatory mechanism by PHD1 in the two models appears to be different. In OIR, the lack of PHD1 prevents the degradation of HIF1α in hyperoxia, which induces VEGF expression, thus preventing hyperoxia-related vessel loss. Without a vessel deficiency, there would not be relative hypoxia when the mice are returned to room air and there would be no need for signaling to initiate angiogenesis. In CNV, there is protection from oxidative stress in PHD1 deficient mice, leading to blocking the hypoxia→HIF1α→VEGF pathway that promotes NV. Oxidative stress is involved in inflammation and neuroprotection, as well as angiogenesis and vascular permeability. In addition to AMD and ROP, it has been implicated with diabetic retinopathy, atherosclerosis, Alzheimer’s and Parkinson’s Disease, epilepsy, amyotrophic lateral sclerosis, and other inflammatory and neurodegenerative disorders, suggesting that regulation of the PHDs could have beneficial effects in these disorders.
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