Purpose: To investigate the involvement of aquaporin (AQP)-1 in lens epithelial cell water permeability and maintenance of lens transparency in experimental models of cataract formation.
Methods: Comparative studies were performed on wild-type versus AQP1-null mice. Osmotic water permeability was measured in calcein-stained epithelial cells in intact lenses from fluorescence changes in response to osmotic gradients. Lens water content was measured by gravimetry using kerosene-bromobenzene density gradients, and from wet/dry weight measurements. Lens transparency was measured by contrast analysis of transmitted grid images. Cataract formation was induced in vitro by incubation in high-glucose solutions and in vivo by acetaminophen toxicity.
Results: Immunofluorescence showed AQP1 expression in wild-type mice in epithelial cells covering the anterior surface of the lens. AQP1 deletion did not alter baseline lens morphology or transparency, though basal water content was approximately 3% greater (P < 0.001). AQP1 deficiency reduced plasma membrane water permeability in lens epithelium by 2.8 +/- 0.3-fold (P < 0.0001). Loss of lens transparency was accelerated by more than 50-fold in AQP1-null lenses bathed in a 55-mM glucose solution for 18 hours. At 4 hours after acetaminophen administration in 3-methylcholantrene-treated mice, lens opacification was seen in none of the six wild-type mice and in six of six AQP1-null mice.
Conclusions: Lens AQP1 facilitates the maintenance of transparency and opposes cataract formation.