NADPH oxidase, NOX1, is a key source of oxidative stress in retinopathy and neovascularization

Abstract

Purpose: Neovascularization is a hallmark feature of retinal vasculopathies such as retinopathy of prematurity (ROP) and diabetic retinopathy and plays a critical role in vision impairment. Its pathomechanism is, however, not fully understood and no specific therapeutic intervention is available. Reactive oxygen species (ROS) have been suggested to play a role in physiological and pathological vascularization. Several potential enzymatic sources of ROS are known but NADPH oxidases (NOX) stand out as they are the only enzyme family whose only known function is to produce ROS. Here we evaluated the cellular source of NOX isoforms involved in retinal neovascularization and whether a deficiency in these isoforms influenced ROP.

Methods: Primary cultures of retinal microglia, glia, ganglion cells, endothelial cells and pericytes were evaluated for the expression of NOX1, NOX2 and NOX4. Microglial cultures were exposed to normoxia, hypoxia and blockers of the renin-angiotensin system, a known stimulator of ROP and NOX. ROP was induced in NOX1, NOX2 and NOX4 knockout mice and their wildtype controls. Comparisons were made to room air controls.

Results: Microglia were found to express NOX1, NOX2, and NOX4. However, only mice with a deletion of the NOX1, but not the NOX2 or NOX4 genes, showed reduced levels of ROS and microglial density as well as of pro-angiogenic and pro-inflammatory factors and vascular leakage. This coincided with less leukostasis and vaso-obliteration with a striking protection against ROP. In retinal microglial cultures, angiotensin II and aldosterone induced microglial NOX expression, ROS generation and vascular endothelial growth factor and cytokine production in a manner that was pharmacologically reversible by angiotensin II and aldosterone blockade.

Conclusions: NOX1 is a key mediator of retinal neovascularization, opening up the possibility for mechanism-based therapy for this otherwise vision-impairing condition.

Keywords: 706 retinopathy of prematurity • 634 oxidation/oxidative or free radical damage • 609 neovascularization