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Photoreceptor dystrophy in the RCS rat: roles of oxygen, debris, and bFGF
1NSW Retinal Dystrophy Research Centre, Department of Anatomy and Histology, University of Sydney, Australia.
Insights
Hypoxia accelerates photoreceptor death in Royal College of Surgeons (RCS) rats during a critical developmental window, despite increased basic fibroblast growth factor (bFGF). This damage, linked to subretinal debris, is oxygen-dependent before postnatal day 27.
Area of Science:
- Ophthalmology
- Retinal Degeneration
- Developmental Biology
Background:
- Photoreceptor dystrophies, like that in Royal College of Surgeons (RCS) rats, involve progressive photoreceptor cell death.
- The subretinal space environment, including oxygen availability and growth factors, is crucial for photoreceptor survival.
- Retinal pigment epithelium (RPE) phagocytotic failure in RCS rats leads to photoreceptor debris accumulation.
Purpose of the Study:
- To investigate the influence of oxygen levels (hypoxia and hyperoxia) and basic fibroblast growth factor (bFGF) on photoreceptor degeneration in RCS rats.
- To determine the role of photoreceptor debris in the pathogenesis of RCS rat retinal dystrophy.
Main Methods:
- RCS rat pups were exposed to varying oxygen concentrations (hypoxia and hyperoxia) during a critical developmental period (postnatal days 16-24).
- Photoreceptor death rates, subretinal debris accumulation, and bFGF protein and mRNA expression were quantified.
- Comparisons were made between retinal regions and across different postnatal ages.
Main Results:
- Hypoxia accelerated photoreceptor death and increased bFGF levels during the critical period, while hyperoxia had a dose-related protective effect and decreased bFGF.
- Oxygen's effect on photoreceptor death was not directly correlated with subretinal debris levels.
- The influence of oxygen on photoreceptor death diminished significantly after postnatal day 27.
Conclusions:
- Hypoxia, potentially exacerbated by subretinal debris from RPE phagocytotic failure, is a key factor in early photoreceptor death (postnatal days 16-27) in RCS rats.
- The retina attempts to counteract hypoxia by upregulating bFGF, but this protective mechanism is insufficient to prevent damage.
- Later stages of RCS rat dystrophy may involve different pathogenic mechanisms than early hypoxia-induced death.
Purpose:
To examine the roles of oxygen, basic fibroblast growth factor (bFGF), and photoreceptor debris in the photoreceptor dystrophy of the Royal College of Surgeons (RCS) rat.
Methods:
Pups were exposed during the critical period of their development (postnatal day [P] 16-24) and for some days thereafter to hypoxia and hyperoxia. The effects of these exposures on photoreceptor death, debris accumulation in the subretinal space, and the expression of bFGF protein and mRNA by surviving cells were studied.
Results:
During the critical period hyperoxia slowed photoreceptor death in a dose-related fashion and decreased bFGF protein levels, whereas hypoxia accelerated death and increased bFGF levels. At the edges of the retina, where photoreceptors survive longest in normoxia, hypoxia had little effect on either photoreceptor death or bFGF protein levels. Oxygen-induced modulation of rates of death could not be related to the accumulation of debris in the subretinal space. After P27, the relationship between oxygen and photoreceptor death changed markedly, hyperoxia no longer delaying and hypoxia no longer accelerating death.
Conclusions:
The death of RCS rat photoreceptors in the period P16 to P27 is precipitated by hypoxia that may result from the accumulation of photoreceptor debris in the subretinal space. This debris, the result of the phagocytotic failure of the retinal pigment epithelium in this strain, lies in the normal pathway of oxygen diffusing to the photoreceptors from the choriocapillaris. During this period the retina responds to hypoxia by increasing expression of a potentially protective protein (bFGF), but hypoxia-induced damage overwhelms any protection provided by this or other mechanisms. Later stages of the dystrophy may not be hypoxia-induced.
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