Abstract
Purpose: :
Both intravitreal injection of LIF and preconditioning by exposure to moderately bright light have been shown to protect photoreceptors from subsequent light damage in mice. When mice are preconditioned, LIF is upregulated, suggesting that it is involved in preconditioning-induced protection. Oxidative injury is known to be a pathological component of light damage. Our purpose was to determine whether or not LIF protected photoreceptors from light damage by preventing or reducing protein oxidation.
Methods: :
Balb/CJ mice were injected with LIF in one eye and PBS in the other. The levels of retinal protein carbonyls and nitrotyrosines were measured following light damage (4,000 LUX for 5 h). Controls with no injection with and without light damage were also performed. Mice were kept in the dark for 4 h prior to collecting retinas for Western blot and dot blot analyses. In other experiments, Balb/CJ mice were subjected to a preconditioning model (600 lux; 12 h on: 12 h off) for 6 days. At the end of 6th light cycle, some animals were exposed to light damage. Unexposed mice served as controls. Their eyes were collected at different time points, and TUNEL staining was performed on paraffin sections and analyzed by epifluorescence microscopy.
Results: :
Injection of LIF or preconditioning with moderately bright light induces protection of photoreceptors from light damage. Carbonyl-modified proteins were increased by light damage and by injection alone. LIF did not reduce the formation of these products after light damage. Consistently, injection with LIF or PBS caused a 2-fold increase in protein nitrotyrosine content compared to uninjected controls, and LIF did not reduce nitrotyrosine induced by light damage. Light damage dramatically increased the number of TUNEL-positive photoreceptors. In retinas from preconditioned mice a significant number of photoreceptors were still TUNEL positive following light damage.
Conclusions: :
Our data suggest that light damage induces oxidative injury including DNA damage resulting in TUNEL positive staining. The protective effect of LIF or preconditioning occurs without reducing the levels of oxidized proteins or reducing the number of TUNEL positive photoreceptors immediately following light damage. The fact that preconditioning and LIF can prevent photoreceptor death despite positive TUNEL staining suggests that preconditioning or LIF prevent cell death by enhancing DNA repair rather than preventing protein or DNA oxidative damage.
Keywords: oxidation/oxidative or free radical damage • photoreceptors • neuroprotection