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Woo-Kuen Lo, Sondip K Biswas, Lawrence Brako, Alan Shiels, Sumin Gu, Jean X Jiang; Aquaporin-0 Targets Interlocking Protrusions to Control Integrity and Transparency of the Mouse Lens. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1684.
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Lens fiber cell membranes contain aquaporin-0 (AQP0) which constitutes approximately 50% of total integral fiber-cell membrane proteins and plays a dual function as a water channel protein and an adhesion molecule. Fiber cell membranes also develop an elaborate interlocking system that is required for maintaining the structural order, stability and lens transparency. Here we use an AQP0-deficient mouse model to investigate an unconventional adhesion role of AQP0 in maintaining a normal structure of interlocking protrusions in the lens.
The loss of AQP0 in lens fibers of AQP0-/- mice was verified by a purified AQP0 polyclonal antibody using Western blotting and immunofluorescence analyses. Changes in membrane surface structures of lens fibers of wild-type and AQP0-/- mice at 3 to 12 weeks old were examined with scanning electron microscopy. Preferential distribution of AQP0 in fiber cell membranes in wild-type controls was analyzed with confocal immunofluorescence and immunogold labeling using freeze-fracture TEM.
Interlocking protrusions in young differentiating fiber cells developed normally but showed minor abnormalities at approximately 50 μm deep from the surface in the absence of AQP0 in all ages studied. Strikingly, interlocking protrusions in maturing fiber cells specifically underwent uncontrolled elongation, deformation and fragmentation while the cells still possessed fairly normal configurations in the early process. These changes eventually resulted in fiber-cell separation, breakdown and cataract formation in the lens core. Immunolabeling at the light and electron microscopic levels demonstrated that AQP0 was particularly enriched in interlocking protrusions in wild-type lenses.
This study suggests that AQP0 exerts its primary adhesion or suppression role specifically to maintain the normal structure of interlocking protrusions that is critical to the integrity and transparency of the lens.
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