The Common Modification in αA-Crystallin in the Lens, N101D, Is Associated with Increased Opacity in a Mouse Model

To elucidate the morphological and cellular changes due to introduction of a charge during development and the possible mechanism that underlies cataract development in humans as a consequence of an additional charge, we generated a transgenic mouse model mimicking deamidation of Asn at position 101. The mouse model expresses a human alpha A-crystallin gene in which Asn-101 was replaced with Asp, which is referred to as alpha AN101D-transgene and is considered to be deamidated in this study. Mice expressing alpha AN101D-transgene are referred to here CRYAA(N101D) mice. All of the lines showed the expression of alpha AN101D-transgene. Compared with the lenses of mice expressing wild-type (WT) alpha A-transgene (referred to as CRYAA(WT) mice), the lenses of CRYAA(N101D) mice showed (a) altered alpha A-crystallin membrane protein (aquaporin-0 (AQP0), a specific lens membrane protein) interaction, (b) extracellular spaces between outer cortical fiber cells, (c) attenuated denucleation during confocal microscopic examination, (d) disrupted normal fiber cell organization and structure during scanning electron microscopic examination, (e) distorted posterior suture lines by bright field microscopy, and (f) development of a mild anterior lens opacity in the superior cortical region during the optical coherence tomography scan analysis. Relative to lenses with WT alpha A-crystallin, the lenses containing the deamidated alpha A-crystallin also showed an aggregation of alpha A-crystallin and a higher level of water-insoluble proteins, suggesting that the morphological and cellular changes in these lenses are due to the N101D mutation. This study provides evidence for the first time that expression of deamidated alpha A-crystallin caused disruption of fiber cell structural integrity, protein aggregation, insolubilization, and mild cortical lens opacity.