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A. K. Klettner, V. Waetzig, H. Hasselbach, J. Roider; Activation and Cell Death Involvement of MAPK in RPE Cells Induced by Hypoxia and Oxidative Stress: A Comparison. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5068.
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Age-related macular degeneration is the leading cause of legal blindness among the elderly in the western world. The loss or dysfunction of the retinal pigment epithelia (RPE) is a probable cause for the loss of photoreceptor cells, leading to vision impairment. Two mechanisms which contribute to this disease are hypoxia and oxidative stress. Comparing the activation of the mitogen-activated protein kinases (MAPK) JNK, p38 and ERK1/2 by oxidative stress, induced by hydrogen peroxide (H2O2), to the activation by hypoxia, chemically induced by desferrioxamine (DFM), and their influence on RPE cell death.
Primary RPE cell cultures and RPE perfusion tissue cultures were established from pigs eyes obtained from a local slaughterhouse. Cells and perfusion tissue cultures were stimulated with hydrogen peroxide or desferrioxamine. SP600125 was used to inhibit JNK activity. Cell death was assessed by trypan blue exclusion assay. MAPK activity was determined using phospho-specific antibodies in Western Blot.
Both agents induced significant cell death, hydrogen peroxide (200 µM) being more potent than DFM (260 µM) (32,2% and 21%, respectively). Both activate ERK1/2 rapidly, while p38 is activated by DFM. Hydrogen peroxide induced a rapid activation of JNK, in contrast, no early activation could be found in chemically induced hypoxia. Moreover, inhibition of JNK by SP600125 (20 µM) attenuated hydrogen peroxide induced cell death, while it showed not protective effect in hypoxia.
These results suggest that oxidative stress and hypoxia act via different pathways to exert their cell damaging effects in the retinal pigment epithelia. As both factors contribute to RPE deterioration, future strategies to prevent RPE dysfunction should appreciate the complexity of the underlying mechanisms.
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