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X. Gong, C. Cheng, C.-H. Xia, Q. Huang, L. Ding, J. Horwitz; Studies of AlphaA-crystallin R54C, R54H and Y118D Mutations in vivo and in vitro. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4507. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the mechanisms of how aA-crystallin R54C, R54H and Y118D mutations lead to recessive or dominant cataracts, to determine specific molecular and/or cellular events affected by R54C, R54H and Y118D mutations during lens development, to exam the functional alterations of these mutated aA-crystallins in cultured cells and to measure the chaperone-like activities of mutant proteins in vitro.
Lens morphological and cellular alterations were assessed by histology, immunohistochemistry and electron microscopic analysis. Mutated aA-crystallin genes were expressed transiently or stably in cultured cells to evaluate their functional properties. Native and recombinant proteins were prepared for chaperone-like activity assays in vitro.
R54C recessive whole cataracts was associated with a lack of normal elongated fiber cells while R54H recessive nuclear cataracts was associated with normal elongated fiber cells, but inner fiber cells abnormally containing nuclei. Cultured cells stably expressing the R54C mutant protein, but not the R54H mutant protein, became hypersensitive to oxidative stress. R54C mutant proteins had a reduced chaperone-like activity while R54H mutant proteins showed reduced chaperone like activity only to select target substrates. The Y118D mutation caused dominant nuclear cataracts. The growth rate of Y118D lenses was obviously reduced at three weeks after birth. Unexpectedly, Y118D mutant proteins displayed an increased chaperone-like activity in suppressing the aggregation of insulin or lactalbumin when compared to wild-type aA-crystallins and an overexpression of Y118D mutant proteins was toxic to transfected cells.
This work suggests that distinct recessive cataracts are associated with decreased chaperone-like activities of the R54C and R54H mutant proteins while the dominant cataract is associated with an increased chaperone-like activity of the Y118D mutant protein. R54C, R54H and Y118D mutations cause suppressed cell elongation, delayed cell denucleation, and reduced lens growth, respectively. Thus, mutated aA-crystallins display unique lens phenotypes when compared to aA(-/-) knockout. Further investigation will probably lead to additional new mechanistic information about the roles of aA-crystallin during lens development or cataract formation.
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