Abstract
Purpose :
The lens epithelium plays a major role in continued formation and growth of the underlying fiber cells. The lens water transport is conducted by AQP1 for the epithelium and AQP0 for fiber cells. Here, we report that the epithelial AQP1 responds directly to the deficiency of AQP0 in underlying fiber cells.
Methods :
Lenses from AQP0-KO mice of heterozygotes and homozygotes (2 wks-4 mos old) and WT were used for immunolabeling of AQP1 mAb, AQP0 pAb and Cx43 mAb on frozen sections and lens epithelial whole mounts. The structural condition of lens epithelium in all genotypes was examined with DAPI, phalloidin and electron microscopy.
Results :
Surprisingly, strongly labeled AQP1 was only observed in the equatorial epithelial cells (~250 µm along the epithelial layer) on frozen sections and confirmed with wholemount samples in all WT (2 wks-11 mos old) examined. Trace or absence of AQP1 labeling was seen in the major parts of the anterior epithelium. In sharp contrast, strong AQP1 labeling was seen consistently in the equatorial and anterior epithelial cells in the AQP0-KO-/- lenses at various ages (2 wks-4 mos old). The labeling intensity of AQP1 in the anterior epithelium was increased with age. Furthermore, AQP1 was also upregulated in the AQP0-KO+/- lenses. Slightly less intense AQP1 labeling was consistently observed in the entire anterior epithelium at various ages, suggesting that upregulation of AQP1 in the anterior epithelium can be induced by a partial deficiency of AQP0 in lens fibers. By comparison, labeling of Cx43 was present evenly in the equatorial and anterior lens epithelia in both WT and AQP0-KO-/- mice. Morphological analyses revealed that the anterior lens epithelium in the AQP0-KO-/- lenses maintained a regular structural feature and contained many normal organelles and cytoskeletal filaments despite some noticeable cellular damage occurring in underlying superficial fiber cells.
Conclusions :
This study uncovers that AQP1 is expressed strongly only in the equatorial lens epithelial cells in WT mice. This suggests that the lens equatorial region is the major active route for inflow and outflow of water between the epithelium and fiber cells. When AQP0 deficiency occurred in the fiber cells, AQP1 was significantly upregulated in the entire anterior epithelial cells. The large increase in water influx from anterior epithelium into underlying superficial fibers may cause further damage to fiber cells.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.