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Vivek S. Yellore, Sylvia Rayner, Anthony J. Aldave; Differential Expression Of ZEB1 And COL4A3 In The Corneal Endothelium In PPCD3 And Controls. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1088.
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© ARVO (1962-2015); The Authors (2016-present)
Posterior polymorphous corneal dystrophy 3 (PPCD3) is a corneal endothelial dystrophy that is caused by nonsense mutations in the transcription factor ZEB1. These mutations are purported to lead to haploinsufficiency of ZEB1, resulting in loss of inhibition of COL4A3 expression, and ectopic expression of COL4A3 in the corneal endothelium. To test this hypothesis, we studied the expression of ZEB1 and COL4A3 in the corneal endothelium from affected and unaffected eyes.
Descemet’s membrane and endothelium removed from 3 healthy adult human corneas that were obtained from eye banks and from an individual with PPCD3 secondary to a nonsense ZEB1 mutation at the time of DSEK surgery. Semi-quantitative PCR (qPCR) was performed to determine the levels of expression of COL4A3 mRNA and ZEB1 mRNA in normal and PPCD3 corneas, using GAPDH mRNA levels as the reference. Immunohistochemical detection of COL4A3 and ZEB1 expression in frozen sections of healthy corneas was performed using commercially available antibodies to COL4A3 and ZEB1.
Both COL4A3 and ZEB1 mRNA were detected in the healthy adult human corneal endothelium and in the corneal endothelium of an individual with PPCD3 by qPCR. ZEB1 expression in PPCD3 endothelium was reduced by 30-40% when compared to the mean expression in healthy endothelium, while COL4A3 expression was increased by 400-500% when compared to the mean expression in healthy endothelium. COL4A3 and ZEB1 expression in healthy adult human corneal endothelium was confirmed with immunohistochemical detection of ZEB1 in corneal endothelial nuclei, and COL4A3 in corneal endothelial cytoplasm.
ZEB1 and COL4A3 are expressed in healthy adult human corneal endothelial cells, and thus the pathogenesis of PPCD3 cannot be attributed simply to ectopic expression of COL4A3 in the corneal endothelium. While it remains possible that nonsense mutations in ZEB1 result in PPCD3 via decreased inhibition of COL4A3 expression in the corneal endothelium, the simple expression of COL4A3 in the corneal endothelium does not appear to be sufficient to explain the pathogenesis of PPCD3.
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