Shumiya Cataract Rat Research Articles

Calpains in the lens and cataractogenesis.

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 (). Further, a lens-specific calpain, termed Lp82, was recently discovered in young rat lens (). 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 (). Calpain-induced proteolysis of lens crystallins is also a common feature of maturing rodent lenses ().

Evidence for the involvement of calpain in cataractogenesis in Shumiya cataract rat (SCR)

The Shumiya cataract rat (SCR) is a hereditary cataract model in which lens opacity appears spontaneously in the nuclear and perinuclear portions at 11–12 weeks of age. It was found that the proteolysis of some crystallins and cytoskeletal proteins is significantly enhanced in cataractous SCR lenses. The calcium concentrations in cataractous lenses rise markedly with age as compared with control lenses and the autolytic product of calpain is also detected in cataractous lenses. In order to provide direct evidence for the involvement of calpain in the proteolytic modification of lens proteins, we developed antibodies exclusively specific to the proteolytic products of some lens proteins produced by the action of calpain and analyzed their degradation during cataractogenesis in SCR by Western blotting and immunohistochemical staining. The results demonstrate that calpain participates in the proteolytic modification of lens proteins, at least α-crystallin (A and B chain), βB1-crystallin, and α-fodrin. The proteolytic products formed by the action of calpain on these proteins are detected in cataractous lenses of SCR as young as 8 weeks of age and accumulate with age. It was also found that βB1-crystallin, originally a soluble protein, is converted to an insoluble form by limited calpain proteolysis. The chaperon-like activity of α-crystallin from control lens is markedly reduced by calpain proteolysis in vitro, and α-crystallin in opaque lens that has already undergone proteolysis by calpain shows significantly reduced chaperon-like activity. Immunohistochemical studies reveal that the area where the calpain-mediated α-crystallin proteolysis is in progress coincides well with the area developing and destined to develop the opacification. These results strongly suggest that calpain may contribute to lens opacification during cataract formation in SCR.

Histopathological Study of Hereditary Cataractous Lenses in SCR Strain Rat

A new cataractous rat strain, Shumiya Cataract Rat (SCR), which was derived from the cross-breeder formed between the spontaneous hypertensive rat and the Zucker fatty rat, was studied by light and electron microscopy. The earliest change was the occurrence of some displaced nuclei in the posterior cortical fibres at birth. By 2 weeks of age, mild dysplasia of the anterior suture, aggregated epithelial cells overlying the sutural area, and poorly differentiated epithelial cells at the bow area were observable. At 3 weeks, unusually dense lens fibres near dense epithelial cells were found at the equator, and some epithelial cells showed acellularity after 4 weeks. Swelling and liquefaction of the lens fibres appeared in the anterior cortex by this stage. By 6 weeks, these changes extended toward the equatorial region. At 7 weeks, a sutural gap occurred at the anterior polar area, and this gap reached a maximum at 8 weeks. At this time, swelling of the posterior extremities of the lens fibres appeared, showing a small placoid opacity of the posterior subcapsular region under a dissecting microscope. At 10 weeks, small amounts of liquefaction were observed in this region. Between 10·5 and 11 weeks, as the posterior suture separated, opacification appeared around the separated sutural area and rapidly developed into a mature cataract. The mechanism of cataract formation in the SCR rat lens may be associated with the continuous occurrence of a small proportion of poorly-differentiated epithelial cells at the bow area and sutural dysplasia of the anterior lens fibres.