Deletion of Seventeen Amino Acids at the C-Terminal End of Aquaporin 0 Causes Distortion Aberration and Cataract in the Lenses of AQP0(ΔC/ΔC) Mice

PURPOSE: Investigate the effects of the absence of 17 amino acids at the C-terminal end of Aquaporin 0 (AQP0) on lens transparency, focusing property, and homeostasis. METHODS: A knockin (KI) mouse model (AQP0(ΔC/ΔC)) was developed to express AQP0 only as the end-cleaved form in the lens. For this, AQP0 was genetically engineered as C-terminally end-cleaved with amino acids 1 to 246, instead of the full length 1 to 263 of the wild type (WT). After verifying the KI integration into the genome and its expression, the mouse model was bred for several generations. AQP0 KI homozygous (AQP0(ΔC/ΔC)) and heterozygous (AQP0(+/ΔC)) lenses were imaged and analyzed at different developmental stages for transparency. Correspondingly, aberrations in the lens were characterized using the standard metal grid focusing method. Data were compared with age-matched WT, AQP0 knockout (AQP0(−/−)), and AQP0 heterozygous (AQP0(+/−)) lenses. RESULTS: AQP0(ΔC/ΔC) lenses were transparent throughout the embryonic development and until postnatal day 15 (P15) in contrast to age-matched AQP0(−/−) lenses, which developed cataract at embryonic stage itself. However, there was distortion aberration in AQP0(ΔC/ΔC) lens at P5; after P15, cataract began to develop and progressed faster surpassing that of age-matched AQP0(−/−) lenses. AQP0(+/ΔC) lenses were transparent even at the age of 1 year in contrast to AQP0(+/−) lenses; however, there was distortion aberration starting at P15. CONCLUSIONS: A specific distribution profile of intact and end-cleaved AQP0 from the outer cortex to the inner nucleus is required in the lens for establishing refractive index gradient to enable proper focusing without aberrations and for maintaining transparency.