Molecular chaperones: small heat shock proteins in the limelight.
(1/2726)
Small heat shock proteins have been the Cinderellas of the molecular chaperone world, but now the crystal structure of a small heat shock protein has been solved and mutation of two human homologues implicated in genetic disease. Intermediate filaments appear to be one of the key targets of their chaperone activity. (+info)
Modifications to rat lens major intrinsic protein in selenite-induced cataract.
(2/2726)
PURPOSE: To identify modifications to rat lens major intrinsic protein (MIP) isolated from selenite-induced cataract and to determine whether m-calpain (EC 3.4.22.17) is responsible for cleavage of MIP during cataractogenesis. METHODS: Cataracts were induced in rats by a single injection of sodium selenite. Control and cataract lenses were harvested on day 16 and dissected into cortical and nuclear regions. Membranes were washed with urea buffer followed by NaOH. The protein was reduced/alkylated, delipidated, and cleaved with cyanogen bromide (CNBr). Cleavage products were fractionated by high-performance liquid chromatography (HPLC), and peptides were characterized by mass spectrometry and tandem mass spectrometry. MIP cleavage by m-calpain was carried out by incubation with purified enzyme, and peptides released from the membrane were analyzed by Edman sequencing. RESULTS: The intact C terminus, observed in the control nuclear and cataractous cortical membranes, was not observed in the cataractous nuclear membranes. Mass spectrometric analysis revealed heterogeneous cleavage of the C terminus of MIP in control and cataract nuclear regions. The major site of cleavage was between residues 238 and 239, corresponding to the major site of in vitro cleavage by m-calpain. However, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and mass spectrometric analysis indicated that in vivo proteolysis during cataract formation also included sites closer to the C terminus not produced by m-calpain in vitro. Evidence for heterogeneous N-terminal cleavage was also observed at low levels with no differences between control and cataractous lenses. The major site of phosphorylation was determined to be at serine 235. CONCLUSIONS: Specific sites of MIP N- and C-terminal cleavage in selenite-induced cataractous lenses were identified. The heterogeneous cleavage pattern observed suggests that m-calpain is not the sole enzyme involved in MIP C-terminal processing in rat lens nuclei. (+info)
Anterior polar cataracts in CS rats: a predictor of mature cataract formation.
(3/2726)
PURPOSE: The objective of this study was to characterize the morphology of the anterior opacities formed during recovery from posterior subcapsular cataract (PSC) in Royal College of Surgeons (RCS) rats. METHODS: Lenses from RCS rats at 8 and 12 weeks postnatal (n = 14 and 12, respectively) were examined under a dissecting microscope for the presence of anterior opacities. Lenses with anterior opacities were fixed, embedded in epoxy resin, and sectioned along the optic axis for light microscopy (LM) and transmission electron microscopy (TEM). RESULTS: At eight weeks postnatal, 21.5% of animals (3/14) had anterior cataracts. Light microscopy of 1- to 2-microm-thick sections revealed an anomalous layer of material located at the epithelium-fiber interface, which was identified as a zone of liquefaction by TEM. Epithelial cells had minor structural defects but were not necrotic. Anterior portions of elongating and cortical fibers under the zone of liquefaction were undisrupted, whereas their posterior portions had numerous vacuoles. The anterior opacities were classified as anterior polar cataracts (APCs) based on the location and type of morphologic damage in the affected lenses. At twelve weeks postnatal, 25% of animals (3/12) had APCs that involved prominent vesiculation of the anterior cortex. Ultrastructural examination showed that large vesicles were located between and inside anterior fibers and that most extracellular spaces were abnormally widened. Posteriorly, internalization of the PSC by new fiber growth was disordered and displayed vesiculation and density variations. In the bow region, LM revealed minor structural irregularities that were identified as groups of apparently degenerating fibers by TEM. CONCLUSIONS: APCs in RCS rats are caused by degeneration of elongating fibers in the bow region and subsequent damage in the superficial anterior cortex. The percentage of animals with APCs (25%) was consistent with the percentage of animals in which mature cataracts eventually develop. The morphologic changes, time of onset, and percentage of animals affected suggest that APC is the initial manifestation of mature cataract formation in RCS rats. (+info)
Effect of dietary taurine supplementation on GSH and NAD(P)-redox status, lipid peroxidation, and energy metabolism in diabetic precataractous lens.
(4/2726)
PURPOSE: To evaluate changes in glutathione and NAD(P)-redox status, taurine and malondialdehyde (MDA) levels, glucose utilization, and energy metabolism in diabetic precataractous lenses and to assess whether these changes can be prevented with dietary taurine supplementation. METHODS: The experimental groups included control and streptozotocin-diabetic rats with a 3-week duration of diabetes fed unsupplemented or taurine (1% or 5%)-supplemented diets. The levels of glucose, sorbitol, fructose, myo-inositol, oxidized glutathione (GSSG), glycolytic intermediates, malate, alpha-glycerophosphate, and adenine nucleotides were assayed in individual lenses spectrofluorometrically by enzymatic methods, reduced glutathione (GSH) spectrofluorometrically with O-phthaldialdehyde, MDA colorimetrically with N-methyl-2-phenylindole, and taurine by high-performance liquid chromatography. Free cytosolic NAD+/NADH and NADP+/NADPH ratios were calculated from the lactate dehydrogenase and malic enzyme systems. RESULTS: Sorbitol pathway metabolites and MDA were increased, and GSH and taurine levels were reduced in diabetic rats versus controls. The profile of glycolytic intermediates (an increase in glucose 6-phosphate, no change in fructose 6-phosphate and fructose 1,6-diphosphate, an increase in dihydroxyacetone phosphate, a decrease in 3-phosphoglycerate, phosphoenolpyruvate, and pyruvate, and no change in lactate), and a 9.2-fold increase in alpha-glycerophosphate suggest diabetes-induced inhibition of glycolysis. Free cytosolic NAD+/NADH ratios, ATP levels, ATP/ADP, and adenylate charge were reduced, whereas free cytosolic NADP+/NADPH ratios were elevated. Lens taurine levels in diabetic rats were not affected by supplementation with 1% taurine. With 5% taurine supplementation, they were increased approximately 2.2-fold higher than those in untreated diabetics but remained 3.4-fold lower than in controls. Lens GSH levels were similar in diabetic rats fed unsupplemented and 5% taurine-supplemented diets, whereas GSSG and MDA levels and GSSG/GSH ratios were reduced by 5% taurine supplementation. The decrease in free cytosolic NAD+/NADH, ATP/ADP, and adenylate energy charge were ameliorated by 5% taurine supplementation, whereas accumulation of sorbitol pathway intermediates, depletion of myoinositol, inhibition of glycolysis, a decrease in ATP and total adenine nucleotide, and an increase in free cytosolic NADP+/NADPH were not prevented. CONCLUSIONS: Dietary taurine supplementation ameliorates MDA levels, GSSG/GSH, and NAD+/NADH and fails to prevent the osmotically mediated depletion of GSH and taurine and the decrease in glucose utilization and ATP levels in diabetic precataractous lens. Dietary taurine supplementation cannot be regarded as an alternative to aldose reductase inhibition in eliminating antioxidant and metabolic deficits contributing to diabetes-associated cataractogenesis. (+info)
Cardiac involvement in proximal myotonic myopathy.
(5/2726)
Proximal myotonic myopathy (PROMM) is a recently described autosomal dominantly inherited disorder resulting in proximal muscles weakness, myotonia, and cataracts. A few patients with cardiac involvement (sinus bradycardia, supraventricular bigeminy, conduction abnormalities) have been reported. The cases of three relatives with PROMM (weakness of neck flexors and proximal extremity muscles, calf hypertrophy, myotonia, cataracts) are reported: a 54 year old man, his 73 year old mother, and 66 year old aunt. All three presented with conduction abnormalities and one had repeated, life threatening, sustained monomorphic ventricular tachycardia. This illustrates that severe cardiac involvement may occur in PROMM. (+info)
Changing trends in barriers to cataract surgery in India.
(6/2726)
Cataract is a major cause of blindness in Asia. Efforts in India to provide cataract surgical services have had limited success in reaching the cataract-blind population. Earlier studies identified the major barriers to cataract surgery as poverty, lack of transportation or felt need, or sex related; and the critical barriers in rural areas as lack of awareness, difficult access, and cost. Compared with these earlier data, the results of the present study in Karnataka State indicate a shift in the character of the barriers. They now appear to be more related to case selection and service provision. These shifts are analysed and alternative strategies to increase the uptake to cataract surgery are recommended. (+info)
Deamidation of alpha-A crystallin from nuclei of cataractous and normal human lenses.
(7/2726)
PURPOSE: To quantitate the extent of deamidation of asparagine-101, glutamine-50, and glutamine-6 of alpha-A crystallin in the nucleus from human cataractous and normal lenses. METHODS: Reverse phase chromatography was used to prepare alpha-A crystallin from total proteins of the nucleus from cataractous and age-matched normal human lenses. Synthetic peptides were made corresponding to the expected amidated and deamidated tryptic fragments containing asparagine-101, glutamine-50, and glutamine-6. The peptides were used to identify and quantitate amidated and deamidated forms of tryptic fragments from alpha-A crystallin eluting from a reverse phase column. RESULTS: Significant amounts of deamidation of asparagine-101 and glutamine-50, but not glutamine-6, were present in alpha-A crystallin from nuclear sections of both cataractous and age-matched normal lenses. Quantitative analysis of tryptic peptides containing these residues indicated no statistical difference in deamidation in cataractous versus normal lenses. CONCLUSIONS: There was no significant difference in the extent of deamidation of asparagine-101, glutamine-50, and glutamine-6 for alpha-A crystallin, purified from the nucleus of cataractous versus age-matched normal lenses. These results strongly suggest that deamidation of these residues does not play a role in the biogenesis of human nuclear cataract. (+info)
Management of phacolytic glaucoma: experience of 135 cases.
(8/2726)
We retrospectively analyzed 135 eyes with phacolytic glaucoma. A trabeculectomy was added to standard cataract surgery if symptoms endured for more than seven days, or if preoperative control of intraocular pressure (IOP) with maximal medical treatment was inadequate. In the early postoperative period, IOP was significantly lower in the combined surgery group (89 eyes) compared to the cataract surgery group (46 eyes) (p < 0.001). At 6 months there was no difference in IOP or visual acuity between the two groups. There were no serious complications related to trabeculectomy. It is reasonable to conclude that in eyes with a long duration of phacolytic glaucoma, addition of a trabeculectomy to cataract surgery is safe, prevents postoperative rise in intraocular pressure and decreases the need for systemic hypotensive medications. A randomized trial is on to further address this question. (+info)