The Major Intrinsic Protein of the Lens (Aquaporin–0) Is Expressed in the Murine Retina

Abstract

Purpose: : Previous studies have demonstrated that several lens proteins, such as crystallins, are expressed in the retina. Likewise, Aquaporin–0 (AQP–0) has, heretofore, been only described in the lens, hence its alternate name Major Intrinsic Protein of the lens (MIP26). The goal of this study is to determine the expression and role of AQP–0 in other ocular tissues.

Methods: : Quantitative RT–PCR and Western blot analysis were utilized to determine expression levels of AQP–0 in adult wild–type (WT) murine ocular tissues. Immunohistochemistry was performed to show its localization in WT retinas. Electroretinography (ERG) was utilized on WT mice and the cataract Fraser (Cat^Fr) mouse model which only expresses a mutated form of AQP–0 to determine the effect of this mutation on retinal function. Retinal histology was performed on WT and Cat^Fr mice to evaluate any structural abnormalities associated with this mutation.

Results: : We demonstrated that the mRNA and protein for AQP–0 is present in the WT murine retina and lens but absent in the cornea or RPE/choroid/sclera. Immunohistochemistry revealed localization of AQP–0 in cells of the inner nuclear layer. ERG analyses demonstrated that the Cat^Fr mouse has a decreased scotopic ERG and a nearly absent photopic b–wave amplitude as compared to WT. No structural abnormalities were detected in retinal histology from Cat^Fr animals.

Conclusions: : These data demonstrate that AQP–0 is expressed in the mouse retina, albeit at levels several–fold lower than its level in the lens. The exact physiological role of AQP–0 in the retina is still unclear. Further examination is needed to elucidate the role AQP–0 might play in phototransduction.

Keywords: gene/expression • retina • proteins encoded by disease genes