Effect of aldose reductase in an animal model of oxygen-induced retinopathy

Abstract



Retinopathy of prematurity (ROP) commonly occurs in premature babies, with the first phase of vessel cessation followed by a second phase of vessel proliferation. In addition to vascular changes, neuronal abnormalities have also been observed. However, evidence for morphological changes of retinal neurons at the cellular level is lacking.

Oxidative stress has been highly indicated in the pathogenesis of ROP. Increased oxidative stress level was demonstrated in preterm babies expecially in those with ROP. The activity of aldose reductase (AR), the first enzyme in the polyol pathway, has been found to contribute to oxidative stress. Therefore, the role of AR in ROP was examined using a mouse model of oxygen-induced retinopathy (OIR), which was a well-established model to mimic human ROP.

Studies in examining the effects of AR on retinal vasculature showed that genetic deletion or pharmacological inhibition of AR reduced vaso-obliteration and neovascularization, possibly through regulating VEGF-induced pathway. In addition, morphological changes of various retinal neurons at different time points in the mouse model of OIR were also demonstrated. The degree of effects from hyperoxic and hypoxic exposure appeared to depend on the different stages of maturation of various retinal neurons. AR deficiency showed protective effects on retinal neurons including horizontal cells, rod bipolar cells and amacrine cells, possibly through attenuating the damage on blood vessels as well as facilitating blood vessel re-growth in the avascular area which provide more nutrients and supply to the retinal neurons.

To elucidate the protective role of AR deficiency in ROP, the changes in oxidative stress and oxygen-dependent gene expression including HIF-1α and iNOS were investigated. AR deficiency attenuated oxidative stress induction to protect the neonatal retina. In addition, AR deficiency also showed attenuated HIF-1α expression and enhanced iNOS expression. This served to strictly control the HIF-1α level which in turn can tightly regulate VEGF induction in the mouse retinae after OIR.

In order to further elucidate the role of AR in the pathogenesis of ROP, effects of AR deficiency on glial cells and microglia were investigated. AR deficiency reduced retinal astrocytic activation in hyperoxia and induced early M?ller cell gliosis in hypoxia. In addition, AR deficiency enhanced the specific function of microglia in different areas with facilitation of revascularization in avascular area and promotion of tufts regression in neovascular area. Moreover, AR deficiency also reduced the activation of a key inflammatory mediator NF-κB, which was considered to contribute to neovascularization. Therefore, AR deficiency demonstrated regulatory roles in reponses of glial cells, microglia and inflammation, contributing to the protective effects on neonatal retina in the mouse model of OIR.

Taken together, AR deficiency reduced the vascular and neuronal changes possibly through attenuating oxidative stress and glial responses as well as modulating inflammatory responses, indicating a beneficial role of AR inhibition in OIR. These findings highly suggest the therapeutic potential of AR inhibition in the treatment of ROP.