The role of
proteolytic enzymes in Shumiya
cataract rats in alterations to
lens proteins during
cataract formation was studied immunohistochemically using
antibodies against
exopeptidases, such as lysosomal
dipeptidyl peptidase II (DPP II), cytosolic
dipeptidyl peptidase III, and soluble and membrane-bound alanyl
aminopeptidases, and against cytosolic
endopeptidases such as mu- and m-calpains, and
20S proteasome. AlphaB-
crystallin was detected as a proteolytic marker in the
lenses. A constant immunoreactivity against all the
antibodies employed was observed in the lens epithelium independent of the strain and age of the rats. A weak immunoreactivity against exo- and
endopeptidases and an intense reactivity against alphaB-
crystallin were observed in the lens fibres of control rats at all ages. The immunoreactivity of these
peptidases in lens fibres increased with age in
cataract rats, but that of alphaB-
crystallin decreased. No reactivity against exo- and
endopeptidases was seen in the perinuclear region of
lenses of control rats at all ages or in Shumiya
cataract rats at 8 and 10 weeks of age, but an intense reactivity against these
peptidases was observed in the lens perinuclear region of
lenses in
cataract rats at 12 and 14 weeks of age. AlphaB-
crystallin immunoreactivity was observed with ordered striations in the lens perinuclear region of all control rats whereas the striations in this area of
cataract rat lens were disorganized. Membrane-bound
alanyl aminopeptidase was detected feebly in the lens epithelium and fibres of both types of rat at all weeks of age. These findings indicate that exo- and
endopeptidases, except for membrane-bound
alanyl aminopeptidase, are expressed intensively and are age-dependent. Conversely, the amount of alphaB-
crystallin decreased with age in lens fibres of
cataract rats. Calpains (mu- and m-),
20S proteasome,
dipeptidyl peptidases II and III and soluble
alanyl aminopeptidase are thought to induce lens opacification kinetically during
cataract formation in Shumiya
cataract rats through the intracellular turnover of
lens proteins.