Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0086543 (cataract)
 29,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study reports the first demonstration of a marked reduction in alpha-crystallin chaperone activity in an experimental model of cataract, and the study implicates activation of the cysteine protease calpain II (EC 3.4.22.17) as the in vivo protease responsible for decreased chaperone activity. Chaperone activity of normal alpha-crystallin from lenses of young rats was assayed by measuring attenuation of heat-induced aggregation and scattering of beta L-crystallin. alpha-Crystallin from the nucleus of lenses with selenite cataract showed specific selective proteolysis, and chaperone activity was diminished. Proteolysis of alpha-crystallin from selenite cataract lenses was mimicked by incubating normal alpha-crystallin with calpain II, and this also resulted in loss of chaperone activity. Two-dimensional gel electrophoresis and peptide mapping were used to identify four partially degraded alpha A- and alpha B-crystallin polypeptides following incubation of normal alpha-crystallin with calpain. Similar partially degraded alpha A and alpha B polypeptides were found in selenite cataract. Previous experiments indicated that alpha-crystallin chaperone activity decreases because of removal of the COOH terminus. Our experiments support this observation and suggest that calpain proteolysis of alpha-crystallin at the COOH terminus may result in a loss of chaperone activity in selenite cataract.
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PMID:alpha-Crystallin chaperone activity is reduced by calpain II in vitro and in selenite cataract. 839 20

Incubation of soluble proteins from rat lens with the protease calpain II caused the precipitation of beta-crystallin polypeptides. Two-dimensional electrophoresis and sequence analysis identified beta-crystallin polypeptides both before and after their precipitation by calpain II. beta-crystallin polypeptides precipitated by calpain were cleaved at their NH2-terminal extensions. These cleavage sites were similar to cleavage sites occurring in beta-crystallin polypeptides precipitated during formation of experimental cataract induced by an overdose of selenite. These data suggested that calpain II caused beta-crystallin insolubilization during cataract formation, and indicated that the process can be mimicked in vitro.
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PMID:Beta-crystallins insolubilized by calpain II in vitro contain cleavage sites similar to beta-crystallins insolubilized during cataract. 840 63

Abnormal activation of the protease calpain in the lens may be a cause of cataracts. Cataracts were induced in 10-day-old rats by a single overdose of sodium selenite. The water-insoluble protein from the opaque lens nucleus was separated by two-dimensional electrophoresis, electroblotted onto membranes, and the NH2-terminal sequence of partially degraded beta-crystallin polypeptides determined. Selenite cataractous lenses contained four major structural proteins, beta B1, beta B3, beta A3/A1, and beta A4 crystallins, missing from 5 to 49 amino acids from their NH2 termini. Incubation of intact beta-crystallins with calpain II in vitro produced identical cleavage sites. This provided further evidence for the role of calpain in the production of light scattering insoluble protein in cataractous lenses and also suggested that a similar process may lead to lens protein insolubilization during aging.
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PMID:Sequence analysis of lens beta-crystallins suggests involvement of calpain in cataract formation. 842 Sep 67

Light scattering intensities of rat lenses obtained in the I,, and I+ modes were analysed using the random density and orientation fluctuation theory. Rat lenses incubated in calcium rich media had the same density fluctuation parameters as rat lenses incubated in control (low-calcium) media. However, the correlation length of the orientation fluctuations decreased during cataract formation by 100 to 200 nm while the amplitude of the fluctuations increased. The correlation length, or the size of the optically anisotropic domains, is related to the size of the cytoskeleton, especially vimentin. Vimentin has been shown to degrade when calcium activates calpain. This has been observed in SDS-gel electrophoretic experiments in rat lenses in calcium rich media. The amplitude factor of orientation fluctuations, that is, the mean squared deviation from the average refractive index, increased between two- and seven-fold during cataractogenesis. These results indicate that calcium cataract formation at the beginning (first 72 hr incubation) has little to do with aggregation or syneresis but it is largely the result of changes in the intrinsic birefringence of the lens due to vimentin degradation.
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PMID:Light scattering parameters of rat lenses with calcium-induced cataracts. 869 36

Overactivation of calcium-activated neutral protease (calpain) has been implicated in the pathophysiology of several degenerative conditions, including stroke, myocardial ischemia, neuromuscular degeneration, and cataract formation. Alpha-mercaptoacrylate derivatives (exemplified by PD150606), with potent and selective inhibitory actions against calpain, have been identified. PD150606 exhibits the following characteristics: (i) Ki values for mu- and m-calpains of 0.21 microM and 0.37 microM, respectively, (ii) high specificity for calpains relative to other proteases, (iii) uncompetitive inhibition with respect to substrate, and (iv) it does not shield calpain against inactivation by the active-site inhibitor trans-(epoxysuccinyl)-L-leucyl-amido-3-methylbutane, suggesting a nonactive site action for PD150606. The recombinant calcium-binding domain from each of the large or small subunits of mu-calpain was found to interact with PD150606. In low micromolar range, PD15O6O6 inhibited calpain activity in two intact cell systems. The neuroprotective effects of this class of compound were also demonstrated by the ability of PD150606 to attenuate hypoxic/hypoglycemic injury to cerebrocortical neurons in culture and excitotoxic injury to Purkinje cells in cerebellar slices.
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PMID:An alpha-mercaptoacrylic acid derivative is a selective nonpeptide cell-permeable calpain inhibitor and is neuroprotective. 869 79

Calpains are Ca-activated neutral proteases present in all cells together with an endogenous inhibitor, calpastatin. Proposed substrates are; cytoskeletal proteins like microtubules and actin, protein kinases such as PKC and membrane-bound enzymes like Ca-ATPase and the Ca-channel. In lenses from different species calpains have been detected in decreasing amounts from the epithelium to the cortex to the nucleus. Several substrates for calpain in the lens have been demonstrated: crystallins, vimentin, actin, beaded filaments and MP26 among others. Both studies on animal models and capsulorhexis indicate that calpains are mainly involved in cortical cataract.
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PMID:Calpains in the human lens: relations to membranes and possible role in cataract formation. 872 65

The overall goal of this study was to provide data on the function and physiologic significance of lens calpain I, a cysteine protease requiring low amounts of calcium for activation. Reverse-transcriptase polymerase chain reaction was used to detect mRNAs for calpains I and II in young rat lenses. An in vitro model of crystallin precipitation was used to assess the ability of calpain I to induce hydrolysis and precipitation of crystallins. We found that incubation of crystallins with purified calpain I was indeed a powerful inducer of crystallin precipitation. However, mRNA levels for calpain I in whole lens appeared to be lower compared to calpain-II mRNA. Participation of calpain I in crystallin precipitation during normal maturation of rodent lenses or cataract formation is thus theoretically possible, but unlikely, because of the low level of expression of calpain I.
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PMID:In vitro precipitation of rat lens crystallins by calpain I--a calpain requiring low amounts of calcium for activation. 888 97

The purpose of these experiments was to describe the expression of mRNA for calpain II proteolytic enzyme (EC 3.4.22.17) during normal maturation of rat lens and in cataract formation. Quantitative RT-PCR indicated that the concentration of mRNA for calpain II in whole lens was 3-24 times higher than in age-matched rat liver, kidney, lung and brain, and it was at least five times higher than in young human lens. mRNA levels for calpain II were highest in the outer regions of young rat lens at 5 x 10(6) copies microgram-1 total RNA. Early-stage experimental cataract caused increased calpain II mRNA, while mature nuclear cataract showed a 64% loss. In contrast, mRNA levels for GAPDH, beta-actin, and lens-specific structural protein beta A4 remained constant during experimental cataract formation. Unlike the lower and constant levels in rat liver, kidney and lung; calpain II mRNA levels in whole rat lens decreased with age. These data help explain the high enzymatic activity of calpain II in young rat lens, susceptibility of young rat lens to a variety of cataracts showing increased calcium and calpain-induced proteolysis, and low calpain enzyme activity in human lens. Since the up-regulation of calpain II mRNA was more dynamic than either the amounts of calpain II enzyme or proteolysis of crystallins in cortex, resulting proteolytic activity against the bulk of lens proteins seems to be regulated by post-translational factors, such as increased calcium. The precise role of the up-regulation of calpain II mRNA is unknown, but we hypothesize that it may be associated with the initial cataractogenic response in the epithelial cells or peripheral cortical fibers.
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PMID:Changes in calpain II mRNA in young rat lens during maturation and cataract formation. 919 96

The UPL (Upjohn Pharmaceutical Limited) rat is a dominant hereditary cataract model that develops early-onset cataracts (E-type) in rats homozygous for the trait, and late-onset cataracts (L-type) in heterozygous rats. Using antibodies specific to the calpain-proteolyzed forms of alpha-crystallin, we determined their immunohistochemical localization of the L- and E-rat lenses. Immunoreactivity indicating the proteolyzed forms was detected and found restricted to degenerated lens fibers of the mature stage of the L-rat cataract. Lenses from E-rats, which have abnormally elongated lens fibers during the fetal period, had proteolyzed alpha-crystallin forms at 1 week of age. The results of this present study indicate that calpain-mediated proteolysis of alpha-crystallin occurred in the UPL rat lenses during cataract formation and that calpain may be an important factor in the development of complete lens opacification.
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PMID:Immunohistochemical study of calpain-mediated alpha-crystallin proteolysis in the UPL rat hereditary cataract. 924 7

The purposes of this experiment were to: (1), characterize the peptide aldehyde SJA6017, N-(4-fluorophenylsulfonyl)-L-valyl-L-leucinal, a newly synthesized inhibitor of calpain, and (2) test the effect of SJA6017 in preventing calcium ionophore-induced cataract in cultured rat lenses. In vitro, SJA6017 strongly inhibited purified m-calpain from porcine kidney. Casein zymography confirmed that SJA6017 reversibly bound to the active site of m-calpain. SJA6017 was also confirmed to be a cell-permeable inhibitor in Molt-4 cells. In cultured lenses, SJA6017 reduced nuclear opacity and proteolysis of crystallins and alpha-spectrin caused by calcium ionophore A23187. These results suggested that SJA6017 is a reversible and cell-permeable calpain inhibitor which may possess great efficacy against calcium-induced models of cataract.
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PMID:SJA6017, a newly synthesized peptide aldehyde inhibitor of calpain: amelioration of cataract in cultured rat lenses. 937 5


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