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J. C. O'Connor, D. M. Wallace, C. J. O' Brien, T. G. Cotter; A Novel Antioxidant Role of the Tumour Suppressor p53 in the Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):237.
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Recent evidence has suggested that the tumour suppressor p53 may have a role as an antioxidant. We sought to investigate whether p53 has such a role within the retina, with special reference to the retinal ganglion cell, which by extension may have implications for survival of the retinal ganglion cell in glaucoma.
We first evaluated the expression levels of p53 and the antioxidants GPX1, Sestrin 2, SOD1 and SOD2 in the developing retina by performing Western blotting analysis of whole retinal lysates at different timepoints in the developing C57 mouse. The expression levels of p53 and these antioxidants in the RGC-5 cell line were analysed by immunoblotting. siRNA specific to p53 was used to knock down the expression levels of p53 which were then assessed by immunoblotting as were antioxidant levels.
We found that p53 was differentially expressed during development, decreasing to low levels in adulthood in the C57 retina as analysed by immunoblotting. The expression levels of the aforementioned antioxidant proteins were also examined and were found to mirror p53 levels. To further elucidate the putative role of p53 in regulation of antioxidants in the retina we utilised the retinal ganglion cell line RGC-5. In RGC-5 cells in culture we found that p53 was expressed highly in the unstressed cell. Antioxidant proteins were also expressed at significant levels. On treatment with siRNA specific to p53, a knockdown was observed between 48 and 96 hours, with a peak knockdown of 60% at 72 hours. All antioxidants examined showed a concomitant decrease in expression corresponding to the p53 level.
We have demonstrated that p53 has a definite upstream influence on a number of antioxidants in the RGC-5 cell line. GPX1, Sestrin 2 and SOD 1 and 2 all appear to be under the regulation of p53. Our findings point to a possible antioxidant role of p53 in an in vitro model of the retinal ganglion cell, discovery of which may have implications for the survival of this cell type in the healthy or glaucomatous eye.
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