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Xiaojie Ji, Ye Liu, Ron Hurd, Jieping Wang, Bernard FitzMaurice, Jürgen Naggert, Patsy M Nishina, Bo Chang; A protein kinase C theta mutation causes early-onset exudative retinal detachment. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5380.
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© ARVO (1962-2015); The Authors (2016-present)
The mechanisms underlying retinal detachment (RD) remain largely unknown. To study RD, we screened for novel murine models of early-onset exudative RD. Here we identified a model, rpea1, with a mutation in the Prkcq gene, which encodes protein kinase C, theta (PKCθ).
The chromosomal location of the causal mutation was mapped by recombinant analysis, and the mutation identified through comparison of whole exome sequences of the mutant and WT controls. A complementation of the Prkcqrpea1 allele and the targeted null allele confirmed the causative mutation. The impact of Prkcq deficiency was determined by clinical evaluation, electroretinography (ERG), light microscopy, marker and western blot analyses.
We found that PKCθ is predominantly expressed in the lateral plasma membrane of the retinal pigment epithelium (RPE), co-localizing with both tight and adherens junction proteins. The strong PKCθ localization in RPE cells suggests that RD is likely to be caused by pathology or dysfunction in RPE cells. In line with this hypothesis, aberrant F-actin perijunctional rings were observed in RPE flat mounts with PKCθ deficiency. Although PKCθ was previously reported to be the kinase responsible for the phosphorylation of ezrin/radixin/moesin (ERM) proteins, which links actin filaments to membrane-associated proteins, the level of phosphorylated ERM proteins was increased in PKCθ deficient RPE/choroid cells. This indicates that PKCθ is unlikely to phosphorylate ERM proteins directly in RPE cells in vivo, but may negatively and indirectly regulate their phosphorylation and activation.
Previous studies have shown that PKCθ and the actin cytoskeleton, especially the perijunctional actin ring, may play an important role in maintaining barrier function. Our results demonstrate that PKCθ deficiency-induced aberrant F-actin perijunctional rings in RPE cells may be in part due to the change of ERM protein phosphorylation, and the consequent weakening of the barrier function and defective fluid homeostasis in the posterior retina. Aberrant RPE barrier function that leads to suboptimal regulation of subretinal fluid homeostasis may be a common theme for RD.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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