The PPCD1 Mouse: Characterization of a Mouse Model for Posterior Polymorphous Corneal Dystrophy and Identification of a Candidate Gene

Anna L Shen,Christopher J Murphy,Richard R Dubielzig,Charles B Kasper,Christopher A Bradfield,Kathleen A O’leary ,Norman R Drinkwater

doi:10.1371/journal.pone.0012213

Abstract

The PPCD1 mouse, a spontaneous mutant that arose in our mouse colony, is characterized by an enlarged anterior chamber resulting from metaplasia of the corneal endothelium and blockage of the iridocorneal angle by epithelialized corneal endothelial cells. The presence of stratified multilayered corneal endothelial cells with abnormal patterns of cytokeratin expression are remarkably similar to those observed in human posterior polymorphous corneal dystrophy (PPCD) and the sporadic condition, iridocorneal endothelial syndrome. Affected eyes exhibit epithelialized corneal endothelial cells, with inappropriate cytokeratin expression and proliferation over the iridocorneal angle and posterior cornea. We have termed this the “mouse PPCD1” phenotype and mapped the mouse locus for this phenotype, designated “Ppcd1”, to a 6.1 Mbp interval on Chromosome 2, which is syntenic to the human Chromosome 20 PPCD1 interval. Inheritance of the mouse PPCD1 phenotype is autosomal dominant, with complete penetrance on the sensitive DBA/2J background and decreased penetrance on the C57BL/6J background. Comparative genome hybridization has identified a hemizygous 78 Kbp duplication in the mapped interval. The endpoints of the duplication are located in positions that disrupt the genes Csrp2bp and 6330439K17Rik and lead to duplication of the pseudogene LOC100043552. Quantitative reverse transcriptase-PCR indicates that expression levels of Csrp2bp and 6330439K17Rik are decreased in eyes of PPCD1 mice. Based on the observations of decreased gene expression levels, association with ZEB1-related pathways, and the report of corneal opacities in Csrp2bptm1a(KOMP)Wtsi heterozygotes and embryonic lethality in nulls, we postulate that duplication of the 78 Kbp segment leading to haploinsufficiency of Csrp2bp is responsible for the mouse PPCD1 phenotype. Similarly, CSRP2BP haploinsufficiency may lead to human PPCD.

Highlights

The inherited human corneal endothelial dystrophies, posterior polymorphous corneal dystrophy (PPCD), congenital hereditary endothelial dystrophy (CHED), and Fuchs endothelial dystrophy (FECD), are characterized by abnormal development, dysfunction and/or proliferation of the corneal endothelium [1,2,3]
Origin of the PPCD1 mouse Four founder males, all derived from the embryonal stem (ES) cell clone designated G1, gave rise to progeny exhibiting the phenotype of an enlarged anterior chamber that we designate as mouse PPCD1 (Fig. 1A)
The mouse PPCD1 phenotype is characterized by abnormal growth of epithelialized corneal endothelial cells over the iridocorneal angle, posterior cornea, and iris and presents with early onset of an enlarged anterior chamber

Summary

Introduction

The inherited human corneal endothelial dystrophies, posterior polymorphous corneal dystrophy (PPCD), congenital hereditary endothelial dystrophy (CHED), and Fuchs endothelial dystrophy (FECD), are characterized by abnormal development, dysfunction and/or proliferation of the corneal endothelium [1,2,3]. These corneal dystrophies and the sporadic disorder, iridocorneal endothelial syndrome (ICE), exhibit overlapping clinical and pathological features, including ultrastructural changes and abnormal patterns of cytokeratin expression consistent with epithelialization[4,5,6]. Mutations in the COL8A2 gene, located on chromosome 1 and encoding the alpha chain of type VIII collagen, have been associated with both PPCD (PPCD2, MIM #609140) and FECD [24,25]

Methods

Results

Conclusion