PURPOSE. To investigate the hypothesis that there are topographic and age-related changes in the expression of heme oxygenase (HO)-1 and catalase in the RPE. METHODS. Cryosections of the macula and periphery of human eyes (n = 18; aged 27-87 years) were subjected to a high-sensitivity digoxigenin (DIG)-labeled cRNA in situ hybridization protocol to determine the expression of HO-1 and catalase. The immunoreactivity of HO-1 and catalase were also investigated in the same sample set. Specimens were examined by light microscopy, and images were captured with a digital camera. The total number of RPE cells and HO-1- and catalase-labeled RPE cells was counted in each section, and the ratio of labeled RPE cells to total RPE cells was calculated in both the macular and the peripheral regions of each donor eye. RESULTS. There was a mosaic pattern of mRNA and protein expression of HO-1 and catalase in macular and peripheral RPE. Topographical differences in the expression of HO-1 at the mRNA level and catalase at both the mRNA and protein levels was also observed. The topographical differences between the expression of HO-1 in the macula and periphery protein were not statistically significant but showed similar trends. For HO-1, the only significant age-related decline in expression was observed in the macula and periphery. Expression of HO-1 at the protein level and that of catalase at both the mRNA and protein levels showed no significant decline with age. CONCLUSIONS. There is a possible age-related decline in HO-1 expression, whereas catalase expression remains unchanged with aging. Both exhibit mosaic patterns in the RPE monolayer.
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