Unique and analogous functions of Aquaporin 0 for fiber cell architecture and ocular lens transparency

S. Sindhu Kumari (1) , Subramaniam Eswaramoorthy (2) , Richard T. Mathias (1) , Kulandaiappan Varadaraj (1)

1 Department of Physiology and Biophysics
2 Biology Department

Aquaporin (AQP) 1 and AQP0 water channels are expressed in lens epithelial and fiber cells, respectively, facilitating fluid circulation for nourishing the avascular lens to maintain transparency. Even though AQP0 water permeability is 40-fold less than AQP1, AQP0 is selectively expressed in the fibers. Delimited AQP0 fiber expression is attributed to a unique structural role as an adhesion protein. To validate this notion, we determined if wild type (WT) lens ultrastructure and fiber cell adhesion are different in AQP0, and TgAQP1/AQP0 mice that transgenically express AQP1 (TgAQP1) in fiber cells without AQP0 (AQP0). In WT, lenses were transparent with 'Y' sutures. Fibers contained opposite end curvature, lateral interdigitations and hexagonal shape, and were arranged as concentric growth shells. AQP0 lenses were cataractous, lacked 'Y' sutures, ordered packing and well-defined lateral interdigitations. TgAQP1/AQP0 lenses showed improvement in transparency and lateral interdigitations in the outer cortex while inner cortex and nuclear fibers were severely disintegrated. Transmission electron micrographs exhibited tightly packed fiber cells in WT whereas AQP0 and TgAQP1/AQP0 lenses had wide extracellular spaces. Fibers were easily separable by teasing in AQP0 and TgAQP1/AQP0 lenses compared to WT. Our data suggest that the increased water permeability through AQP1 does not compensate for loss of AQP0 expression in TgAQP1/AQP0 mice. Fiber cell AQP0 expression is required to maintain their organization, which is a requisite for lens transparency. AQP0 appears necessary for cell-to-cell adhesion and thereby to minimize light scattering since in the AQP0 and TgAQP1/AQP0 lenses, fiber cell disorganization was evident.

Mots clés: AQP1; TgAQP1; TgAQP1+/+/AQP0-/-; AQP0; lens cataract; cell-to-cell adhesion; analogous function; unique function; lenticular architecture and transparency

Domaines: Biochimie, Biologie Moléculaire

S. Sindhu Kumari, Subramaniam Eswaramoorthy, Richard T. Mathias, Kulandaiappan Varadaraj. Unique and analogous functions of Aquaporin 0 for fiber cell architecture and ocular lens transparency. Biochimica et Biophysica Acta - Molecular Basis of Disease, 2011, 1812 (9), pp.1089. ⟨10.1016/j.bbadis.2011.04.001⟩. ⟨hal-00719829⟩