Verification and spatial localization of aquaporin-5 in the ocular lens

• Published in: Experimental eye research 2013-03, Vol.108, p.94-102
• Main Authors: Grey, Angus C., Walker, Kerry L., Petrova, Rosica S., Han, Jun, Wilmarth, Phillip A., David, Larry L., Donaldson, Paul J., Schey, Kevin L.
• Format: Article
• Language: English
• Subjects: Aged; Amino Acid Sequence; Animals; Aquaporin 5 - analysis; aquaporins; Blotting, Western; Cattle; Cell Differentiation; Humans; Immunohistochemistry; lens; Lens, Crystalline - chemistry; Lens, Crystalline - cytology; Mice; Mice, Inbred C57BL; Microscopy, Confocal; Middle Aged; Molecular Sequence Data; Protein Transport; proteomics; Proteomics - methods; Rats; Rats, Wistar; Tandem Mass Spectrometry; water permeability
• ISSN: 0014-4835; 1096-0007
• DOI: 10.1016/j.exer.2012.12.004

Until recently, the lens was thought to express only two aquaporin (AQP) water channels, AQP1 and AQP0. In this study we confirm lenticular AQP5 protein expression by Western blotting and mass spectrometry in lenses from a variety of species. In addition, confocal microscopy was used to map cellular distributions of AQP5 in mouse, rat and human lenses. Tandem mass spectrometry of a human lens membrane preparation revealed extensive sequence coverage (56.2%) of AQP5. Western blotting performed on total fiber cell membranes from mouse, rat, bovine and human lenses confirmed AQP5 protein expression is conserved amongst species. Western blotting of dissected lens fractions suggests that AQP5 is processed in the lens core by C-terminal truncation. Immunohistochemistry showed that AQP5 signal was most abundant in the lens outer cortex and decreased in intensity in the lens core. Furthermore, AQP5 undergoes differentiation-dependent changes in subcellular location from an intracellular localization in differentiating fiber cells to the plasma membrane of mature fiber cells upon the loss of fiber cell nuclei. Our results show that AQP5 is a significant component of lens fiber cell membranes, representing the second most abundant water channel in these cells. Together, the changes to AQP5 distribution and structure are likely to modulate the functional role of AQP5 in different regions of the lens. ► AQP5 is present in rat, mouse, cow and human lens fiber cells. ► AQP5 abundance decreases from cortical to core fiber cells in all species. ► Human AQP5 appears as a doublet by Western blot suggesting modification. ► AQP5 shifts from intracellular to membranous location with fiber cell age.