Transgenic Expression of AQP1 in AQP0 Mutant CatTohm and AQP0 Knockout Mouse Lenses

Abstract

Purpose: : AQP1 in lens epithelial cells and AQP0 in fiber cells are the main sources of lens water transport. Mutations or knockout of AQP0 resulted in cataract. The severity of cataract development in AQP0 mutant models and the AQP0 knockout (AQP0^–/–) is significantly different. The purpose of this investigation is to determine the effect of gain of function or loss of function of AQP0 in the mammalian lens.

Methods: : Transgenic mice that express AQP1 in lens fiber cells were generated using αA–crystallin promoter with EGFP tag. Homozygous transgenic (Tg–AQP1^+/+) mice were crossed with Cat^Tohm/Tohm mice or AQP0^–/– mice to generate double heterozygous mouse models (Tg–AQP1^+/–/AQP0^+/Tohm and Tg–AQP1^+/–/AQP0^+/–) .

Results: : Heterozygous Cat^Tohm and AQP0^+/– mouse lenses had compromised homeostasis as demonstrated by loss of transparency and development of cataract. Tg–AQP1^+/–/AQP0^+/Tohm and Tg–AQP1^+/–/ AQP0^+/– mouse lenses showed significant increase in water permeability and considerable improvement in transparency. However, the improvement in lens transparency was greater in Tg–AQP1^+/– / AQP0^+/– compared to that in Tg–AQP1^+/– /AQP0^+/Tohm mouse.

Conclusions: : Expression of AQP1 in the lens fiber cells of AQP0 mutant Cat^–Tohm mouse partly rescued the lens transparency and reduced the severity of cataract. However, lens transparency and reduction in cataract are comparatively less in Tg–AQP1^+/–/AQP0^+/Tohm than in Tg–AQP1^+/– / AQP0^+/– mouse lenses indicating that the severe cataract phenotype in Cat^Tohm mouse lenses may be due to hetero–oligomerization of wildtype AQP0 and mutant AQP0. The cataract phenotype in the heterozygous Cat^Tohm may be due to deleterious gain of function(s) by the mutant AQP0.

Keywords: cataract • transgenics/knock-outs • protein structure/function