C-Terminal End of Aquaporin 0 Regulates Lens Gap Junction Channel Function

Purpose: We reported previously that aquaporin 0 (AQP0) modulates lens fiber cell gap junction (GJ) channel function. The present study was conducted to find out whether the C-terminal end of AQP0 is involved in this regulation. Methods: A mouse model, AQP0ΔC/ΔC, was genetically engineered to express AQP0 with 1-246 amino acids, without the normal intact AQP0 (1-263 amino acids) in the lens. Transparency and focusing of the lens were assessed. Intracellular impedance was measured to determine GJ coupling resistance. Intracellular hydrostatic pressure (HP) was also determined. Western blotting was performed to determine connexin (Cx46 and Cx50) expression levels. Results: At postnatal day 10, AQP0ΔC/ΔC mouse lenses relative to age-matched wild-type lenses showed loss of transparency and abnormal optical distortion; GJ coupling resistance increased in the differentiating (1.6-fold) and mature (8-fold) fiber cells; lens HP increased approximately 1.5-fold at the junction between the differentiating and mature fiber cells and approximately 2.0-fold in the center; there was no significant change (P > 0.05) in expression levels of Cx46 or Cx50. Conclusions: The increase in GJ coupling resistance was not associated with reduced connexin expression, suggesting either a reduction in the open probability or some physical change in plaque location. The increase in resistance was significantly greater than the increase in HP, suggesting less pressure-driven water flow through each open GJ channel. These changes may lead to a loss of transparency and abnormal optical distortion. Overall, our data demonstrate the C-terminal end of AQP0 is involved in modulating GJ coupling to maintain lens transparency and homeostasis.