Role of Nrf2 in retinal vascular development and the vaso-obliterative phase of oxygen-induced retinopathy

Abstract

In the initial stage of retinopathy of prematurity (ROP), hyperoxia causes retinal blood vessel obliteration. This is thought to occur in part through oxidative stress-induced apoptosis of endothelial cells. This study was designed to determine what role NF-E2-related factor 2 (Nrf2) plays in this process. Nrf2 is a transcription factor of the anti-oxidant response element that, if induced, may protect the retina from hyperoxia-induced oxidative stress. Nrf2 knockout mice (Nrf2−/−), Nrf2 wild type control mice (Nrf2 +/+), and C57BL/6 mice were exposed to hyperoxia (75% O2) or normoxia from P7 through P12. Mice were sacrificed on P9 and P12 and the retinas were stained with GSA lectin-Cy3 to visualize retinal blood vessels. Hyperoxia exposed retinas were flat mounted and photographed, then the size of the avascular areas was determined. Additionally, retinas were cryopreserved after lectin staining and area analysis and then sectioned. Secondary or deep capillaries were then hand-counted in sections. In hyperoxia-treated mice, the avascular areas in Nrf2−/− P9 mice were significantly larger than those in Nrf2+/+ P9 mice (P = 0.01). However, there was no significant difference between Nrf2−/− and Nrf2+/+ mice at P12. Avascular areas at P12 were significantly smaller than that at P9 in Nrf2−/−, Nrf2+/+, and C57BL/6 mice (P = 0.0011, P = 0.009, and P = 0.001 respectively). The numbers of deep or secondary capillaries in air-reared Nrf2−/− mice were significantly decreased, when compared to Nrf2+/+ mice at P9 (P = 0.0082). On the other hand, there was no significant difference in deep capillary formation between air-reared Nrf2−/− and Nrf2+/+ mice at P12. Akt signaling activates Nrf2 and Akt was localized to retinal blood vessels in all animals and was increased in Nrf2+/+ and Nrf2−/− mice exposed to hyperoxia as compared to normoxia mice. Interestingly, during normal development this protection by Nrf2 occurs in a specific window of time that is also shared by angiogenesis. Hyperoxia treatment revealed a similar window of time where Nrf2 regulated anti-oxidant production was beneficial and contributed to the endothelial survival.

Nrf2 Regulates Angiogenesis: Effect on Endothelial Cells, Bone Marrow-Derived Proangiogenic Cells and Hind Limb Ischemia

“…-/ -mice under non-inflammatory conditions (48), whereas in response to ischemia the Nrf2 deficiency increased blood flow restoration following left pulmonary artery ligation (42) or femoral artery ligation (FAL) (23). Thus, to examine proangiogenic function of Nrf2 we investigated its role in angiogenic signal transduction in endothelial cells and in regulation of angiogenic potential of both endothelial cells and BM-derived PACs.…”

Expression of NF‑E2‑related factor 2 in a rat dural arteriovenous fistula model

“…Nrf2 then activates its downstream target genes, including HO-1 and NQO1, which are involved in regulating redox reactions in the cells (40,41). However, the function of Nrf2 action may be much broader since it also regulates angiogenesis; for example, it may promote the formation of blood vessels to protect the retina from oxidative injury that occurs following hyperoxic stimulation (42). Furthermore, it has been demonstrated that downregulation of Nrf2 inhibits cancer cell vasculogenesis and migration in vivo and in vitro (21)(22)(23).…”

Retinal Vein Occlusion Induced by a MEK Inhibitor - Impact of Oxidative Stress on the Blood-Retinal Barrier

“…To re-establish retinal perfusion, the retina mounts an exaggerated intravitreal preretinal neovascularization, which may ultimately result in retinal detachment and vision loss. Many features of ROP are recapitulated in oxygen induced retinopathy (OIR) (Brafman et al, 2004;Gu et al, 2002;Uno et al, 2010), in which neonatal animals are exposed to hyperoxia, leading to the generation of ROS, which have been postulated to be causal for vaso-obliteration, death of endothelial cells, and consequently, impairment of the BRB.…”

“…Retinopathy of prematurity (ROP) is a vasoproliferative disease that often develops when premature infants are given supplemental oxygen, and is a leading cause of blindness in children (Hardy et al, 2005;Uno et al, 2010). The developing eye is at an increased risk for oxidative injury from hyperoxia, as the retinal vasculature in premature infants lacks fullydeveloped mechanisms to auto-regulate oxygen tension (Hardy et al, 2005).…”