Role of oxidative stress in photoreceptor degeneration

Reactive oxygen species (ROS) are constitutively produced by mitochondria and represent the major cellular source of oxidative stress. ROS are capable of attacking molecules such as DNA, proteins and lipids, and of compromising either the structural and functional integrity or the survival of cells. Mitochondria also play a key role in apoptosis, the major mechanism of cell death in retinitis pigmentosa (RP), which is a diverse group of inherited human retinal dystrophies associated with progressive degeneration of photoreceptor cells. Mutations in numerous genes have been implicated in RP, which have distinct pathophysiological mechanisms and lead to retinal degeneration at different rates. The aim of this thesis was to investigate the role of oxidative stress in disease progression using mouse models of human RP. The mouse mutants retinal degeneration 1 (rdl/rdl), atypical retinal degeneration 1 (atrdl/atrdl), rhodopsin knockout (R/?c/ ~) and peripherin/retinal degeneration slow (rds/rds) were firstly investigated for evidence of oxidative damage by analysis of oxidative stress markers. Secondly, the mutants were crossed to a superoxide dismutase 2 heterozygous mouse (Sod2+/~), with decreased mitochondrial antioxidant activity, to examine the effect on disease progression. Thirdly, mutants were treated with a mitochondrially targeted ubiquinone derivative (MitoQ), which is a powerful antioxidant, to try and slow the rate of retinal degeneration. MitoQ was administered orally during pregnancy and for an extended postnatal period and uptake, toxicity, breeding behaviour and survival were assessed. Rates of photoreceptor degeneration were estimated by morphometric and apoptosis assays, while the cellular redox status was assessed by glutathione assays and by measuring the activities of the mitochondrial enzymes NADH:ubiquinone oxidoreductase (complex I), which is oxidative stress-sensitive, compared with citrate synthase, which is oxidative stressinsensitive. All retinal degeneration mutants were found to show significantly reduced complex I activities, while citrate synthase was unchanged, indicating mitochondrial oxidative stress. Rates of photoreceptor degeneration were unchanged either by crossing to a Sod2+' genetic background or by MitoQ administration. Only the rds/rds mutant, with the slowest rate of degeneration, showed a significant increase in complex I activity after MitoQ administration. Although mitochondrial oxidative stress is shown to be present in all of the retinal degeneration mutants, altering the oxidative status of the retina had no effect on photoreceptor survival.

Grantor dc:publisher

The University of Edinburgh

Year dc:date.issued

2007

Author dc:creator

• Vlachantoni, Dafni

Handle dc:identifier.uri

http://hdl.handle.net/1842/29410

OAI identifier oai:identifier

oai:era.ed.ac.uk:1842/29410