Comparative Proteomic Analysis Identifies Age-Dependent Increases in the Abundance of Specific Proteins after Deletion of the Small Heat Shock Proteins αA- and αB-Crystallin

Mice
with deletion of genes for small heat shock proteins αA-
and αB-crystallin (αA/αB–/–) develop cataracts. We used proteomic analysis to identify lens
proteins that change in abundance after deletion of these α-crystallin
genes. Wild-type (WT) and αA/αB–/– knockout (DKO) mice were compared using two-dimensional difference
gel electrophoresis and mass spectrometric analysis, and protein identifications
were validated by Mascot proteomic software. The abundance of histones
H2A, H4, and H2B fragment, and a low molecular weight β1-catenin
increased 2–3-fold in postnatal day 2 lenses of DKO lenses
compared with WT lenses. Additional major increases were observed
in abundance of βB2-crystallin and vimentin in 30-day-old lenses
of DKO animals compared with WT animals. Lenses of DKO mice were comprised
of nine protein spots containing βB2-crystallin at 10–40-fold
higher abundance and three protein spots containing vimentin at ≥2-fold
higher abundance than in WT lenses. Gel permeation chromatography
identified a unique 328 kDa protein in DKO lenses, containing β-crystallin,
demonstrating aggregation of β-crystallin in the absence of
α-crystallins. Together, these changes provide biochemical evidence
for possible functions of specific cell adhesion proteins, cytoskeletal
proteins, and crystallins in lens opacities caused by the absence
of the major chaperones, αA- and αB-crystallins.