Inhibition of polyamine oxidase reduces hyperoxia‐mediated neurovascular injury in retina

Abstract

Retinopathy of prematurity (ROP) is a potentially blinding eye disease that affects premature infants and often leads to lifelong vision impairment. Hyperoxia treatment is shown to induce neurovascular damage in the developing retina. Using an oxygen‐induced retinopathy (OIR) mouse model for ROP, we have demonstrated that deletion of the arginase 2 reduced hyperoxia–induced retinal neurodegeneration through the regulation of polyamine metabolism. The present study was undertaken to study the impact of polyamine oxidase (PAO) inhibitor, MDL 72527, on hyperoxia‐induced retinal neurovascular injury in the OIR retina. Newborn wild‐type (WT) mice pups were exposed to 70% oxygen from postnatal day (P) 7 to P12. Pups were treated daily starting at P6 with either vehicle or MDL 72527 (39 mg/kg of body weight, in saline, i.p.) and sacrificed at different stages of hyperoxia treatment. Retinal cryostat sections were used for neurodegeneration studies using immunolabeling of retinal neurons. Analysis of vaso‐obliteration (N=10–12), vessel sprouting (N=7–9) and microglial activation (N=6) were performed on retinal flat mounts. Mixed rat retinal neuronal cultures (7 DIV) were subjected to normoxia (21%) or hyperoxia (50%) with or without MDL 72527 at different time points (N=6–8). These were processed for cellular signaling analysis using Western blotting. Immunolabeling studies using synaptophysin antibody showed the presence of improved synaptic contacts in MDL 72527‐treated OIR retina (P12) compared to vehicle treated groups. Analysis of retinal flat mounts showed significantly reduced a vascular area at P9 and P12( p<0.05) and increased vascular sprouting at P9 (p<0.01) in MDL 72527‐treated compared to vehicle‐treated OIR retinas after 2 or 5 days of hyperoxia. These results demonstrate reduced vascular injury in OIR retina in response to PAO inhibition. Immunolabeling studies using Iba‐1 antibody showed that activation of microglia was significantly reduced and number of resting microglia were increased in the OIR retina with MDL treatment (p<0.05). Analysis of signaling pathways in retinal neurons in response to hyperoxia showed activation of neuro‐inflammatory signaling studied by increased p‐NFkB, p‐ERK1/2 and cytochrome‐C levels, which were significantly reduced by MDL treatment. Our data suggest that PAO inhibition offers a new therapeutic target towards hyperoxia‐induced retinal neurovascular injury.Support or Funding InformationThese studies are supported by AHA 11SDG7440088, Culver VDI Pilot Grant Award and NEI‐R01‐EY011766.