Calpains in the Lens and Cataractogenesis
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Many types of cataracts in the lens of the eye show elevated concentrations of calcium, which could activate calpains, and
thus this chapter presents the techniques specialized for measuring calpain activity in lens. Ubiquitous calpain has been
assayed in lenses from man, cow, pig, rat, sheep, mouse, guinea pig, and rabbit (1
). Further, a lens-specific calpain, termed Lp82, was recently discovered in young rat lens (2
). Cloning and sequencing of the cDNA for Lp82 calpain showed that Lp82 is actually a splice variant of muscle-type calpain
p94 missing several exons and containing a new exon 1. Examples of calpain-induced proteolysis are found in rodent cataracts
induced by selenite, buthionine sulfoximine, calcium ionophore A23187, hydrogen peroxide, diamide, xylose, galactose, and
streptozotocin; and in several animal models, Nakano mice, UPL hereditary rat cataract, Shumiya cataract rat (SCR), and transgenic
mice expressing human immunodeficiency virus (HIV) protease (1
). Calpain-induced proteolysis of lens crystallins is also a common feature of maturing rodent lenses (3
).
