Retinal Oxidative Stress in a Mouse Model of Bronchopulmonary Dysplasia

Abstract

 

Purpose

 

Bronchopulmonary dysplasia (BPD), a complication of preterm birth affecting lung development, is treated with postnatal oxygen. Postnatal oxygen can also cause retinopathy of prematurity (ROP), and approximately 60-70% of infants with ROP also have BPD. Using a mouse model of BPD, we hypothesized that reactive oxygen species (ROS) would be generated in the retina upon removal from hyperoxia.

 

Methods

 

Mice pups (C57BL/6) were exposed to 75% oxygen from P0 to P14. Exposure to hyperoxia was continuous with brief interruptions for animal care. Dams were rotated from hyperoxia to room air every 48 hours. Following the hyperoxia exposure, mice were either euthanized immediately (P14) or left in room air for either 1 day (P15), or 7 days (P21). Age-matched control room air mice were euthanized at similar time points. One group of eyes (N=4 per group) at each time-point was flash frozen for cryo-sectioning. For the remaining eyes, retinas were freshly dissected and homogenized for protein extraction. The sectioned eyes were stained with dihydroethidium (DHE), a marker that stains DNA in the presence of superoxide, and dichlorofluorescein (DCF), a marker for reactive oxygen species (ROS). NADPH oxidase-1 (NOX1) and NOX4 protein expression were quantified using western blots of retinal lysates.

 

Results

 

Hyperoxic mice had increased DHE and DCF staining in the inner and outer segments compared to room air mice. NOX1 and NOX4 protein levels did not differ significantly at P14 between high oxygen and room air mice. NOX4 protein levels were increased at P21 hyperoxic mice compared to room air mice. Analysis of NOX1 and NOX4 protein levels in retinal lysates for remaining time-points are currently underway.

 

Conclusions

 

In a mouse model of BPD, relative hypoxia following removal from hyperoxia exposure leads to oxidative stress in the photoreceptors. Further analysis is underway to improve our understanding of the mechanism of ROS generation in the BPD model, which may ultimately reveal new therapeutic strategies for treating BPD and ROP.  

 

Immunohistochemistry dichlorofluorescein (DCF, green) staining in P15 mice in room air (A) or high oxygen P1-P14 (B). Confocal microscopy of flash frozen tissue (10 μm sections; magnification x63), showing brightfield overlaid onto the IHC image. Control serial sections incubated without DCF showed no specific staining. PR= photoreceptor layers, ONL= outer nuclear layer, INL= inner nuclear layer.