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Kulandaiappan Varadaraj, Subramaniam Eswaramoorthy, Richard T. Mathias, S S. Kumari; Novel Cell-to-Cell Adhesion Role of AQP0 for Lens Fiber Cell Architecture. Invest. Ophthalmol. Vis. Sci. 2011;52(14):404.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate whether AQP0 has a unique role in the ocular lens to maintain transparency and homeostasis.
We studied the ultrastructure of lens in wild type (WT), AQP0 knockout (AQP0-/-) and transgene AQP1 expressing AQP0 knockout mouse (TgAQP1+/+/AQP0-/-) using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Tensile strength of lens cortex fibers was assayed in the different mice genotypes. Cell-to-cell adhesion and aggregation properties of AQP0 were tested along with negative (AQP1, AQP4-M1) and positive (AQP4-M23, E-cadherin) controls expressed in L-cells using a newly devised method involving a microplate reader and a traditional assay using a rotary gyratory shaker.
Wild type lenses were transparent with typical ‘Y’ sutures. SEM images showed fibers of uniform hexagonal shape arranged as concentric growth shells in the cortex. Fibers contained normal opposite end curvature and lateral interdigitations such as ball-and-socket in the outer, and tongue-and-groove in the inner cortex. AQP0-/- lenses were cataractous and lacked Y sutures, ordered packing and well-defined lateral interdigitations. TgAQP1+/+/AQP0-/- mice lenses showed improvement in the outer cortex with fibers having ball-and-socket lateral interdigitations. However, the inner cortex fibers were mostly disintegrated. SEM and TEM images exhibited tight packing of fiber cells in the WT whereas AQP0-/- and TgAQP1+/+/AQP0-/- lenses contained wide extracellular spaces between adjacent fibers. Fiber-to-fiber holding strength assay revealed easy separation of fibers in AQP0-/- and TgAQP1+/+/AQP0-/- mice compared to the WT. Cell-to-cell aggregation and adhesion assays showed that AQP0 expressing L-cells promoted both at a higher degree compared to AQP4-M23 and at a lesser degree compared to L-cells expressing E-cadherin (positive control). AQP1 or AQP4-M1 expressing cells did not show significant level of cell-to-cell adhesion or aggregation.
Data suggest that compensation of water permeability alone is inadequate to restore complete lens transparency in the AQP0-/- mouse. The disorganization of the fiber cells in the TgAQP1+/+/AQP0-/- lens and in vitro cell-to-cell adhesion capability of AQP0 indicate that the unique function of AQP0 could be cell-to-cell adhesion to provide structural integrity through tightly ordered packing of the fiber cells to maintain lenticular architecture and to minimize light scattering.
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