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zhengping Hu, Sumin Gu, Sondip K Biswas, Alan Shiels, Thomas William White, Woo-Kuen Lo, Jean X Jiang; Connexin 50 Functions as an Adhesive Molecule and Promotes the Cell-Cell Adhesion Function of Aquaporin 0 in the Lens. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2644.
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Aquaporin 0 (AQP0) is known to act as a cell-cell adhesion molecule in addition to its role in water transport in the lens. We have shown earlier that the interaction between connexin (Cx) 50 and AQP0 enhances gap junction channel activity. However, the impact of this interaction on cell adhesion of lens fibers remains elusive.
High titter recombinant retroviruses containing vehicle, chick Cx50, Cx46, Cx43 and AQP0 were prepared and were used to infect chick embryonic fibroblast (CEF) cells. Cell-cell adhesion assay was conducted using a “parachuting” adhesion method with fluorescence-labeled donor or receipt cells expressing various combinations of lens connexins, AQP0 or vehicle controls. Cell morphology was examined using rhodamine-labeled wheat germ agglutinin (WGA) in lens tissue samples from Cx50/AQP0 double knockout in comparison with Cx50 or AQP0 single knockout mouse models. The structure of lens gap junctional plaques of these transgenic mouse models were characterized by freeze-fracture electron microscopy.
Cell-cell adhesion studies showed that co-expression with Cx50 enhanced the adhesive capability of AQP0 in CEF cells. Interestingly, expression of Cx50 alone also increased cell adhesion at a level comparable to AQP0. The enhancement of the cell-cell adhesion was not observed in cells expressing Cx43 or Cx46 alone, or in combination with AQP0. Plasma membrane labeling by WGA showed that the integrity and structural organization of fiber cells were disrupted in lenses deficient of AQP0 and were further exacerbated in Cx50/AQP0 double knockout lenses. This observation is partially consistent with data obtained from freeze-fracture electron microscopy analysis. As compared to wild-type lenses with mixed sizes of large and small gap junctional plaques, Cx50/AQP0 double knockout lenses possessed almost all small sized junctional plaques, while either AQP0 or Cx50-deficient lenses contained many small sized, along with some medium or large sized gap junctional plaques.
These results reveal a new role for Cx50. Besides forming channels, Cx50 also mediates a cell-cell adhesion function in the lens and co-expression with AQP0 further augments this capacity. Furthermore, a deficiency of both Cx50 and AQP0 not only disrupts the organization of lens fibers but also greatly reduces the size of gap junctional plaques. <br />
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