αA-crystallin R49Cneo mutation influences the architecture of lens fiber cell membranes and causes posterior and nuclear cataracts in mice

Background: alpha A-crystallin (CRYAA/HSPB4), a major component of all vertebrate eye lenses, is a small heat shock protein responsible for maintaining lens transparency. The R49C mutation in the alpha A-crystallin protein is linked with non-syndromic, hereditary human cataracts in a four-generation Caucasian family. Methods: This study describes a mouse cataract model generated by insertion of a neomycin-resistant (neo(r)) gene into an intron of the gene encoding mutant R49C alpha A-crystallin. Mice carrying the neo(r) gene and wild-type Cryaa were also generated as controls. Heterozygous knock-in mice containing one wild type gene and one mutated gene for alpha A-crystallin (WT/R49C(neo)) and homozygous knock-in mice containing two mutated genes (R49C(neo)/R49C(neo)) were compared. Results: By 3 weeks, WT/R49C(neo) mice exhibited large vacuoles in the cortical region 100 mu m from the lens surface, and by 3 months posterior and nuclear cataracts had developed. WT/R49C(neo) mice demonstrated severe posterior cataracts at 9 months of age, with considerable posterior nuclear migration evident in histological sections. R49C(neo)/R49C(neo) mice demonstrated nearly complete lens opacities by 5 months of age. In contrast, R49C mice in which the neo(r) gene was deleted by breeding with CreEIIa mice developed lens abnormalities at birth, suggesting that the neo(r) gene may suppress expression of mutant R49C alpha A-crystallin protein. Conclusion: It is apparent that modification of membrane and cell-cell interactions occurs in the presence of the alpha A-crystallin mutation and rapidly leads to lens cell pathology in vivo.