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