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Alpha-crystallin B chain (Alpha(B)-crystallin) (Heat shock protein beta-5) (HspB5) (Renal carcinoma antigen NY-REN-27) (Rosenthal fiber component) [CRYA2] [HSPB5]


Binding of a glaucoma-associated myocilin variant to the αB-crystallin chaperone impedes protein clearance in trabecular meshwork cells.

Myocilin ([i]MYOC[/i]) was discovered more than 20 years ago and is the gene whose mutations are most commonly observed in individuals with glaucoma. Despite extensive research efforts, the function of WT MYOC has remained elusive, and how mutant MYOC is linked to glaucoma is unclear. Mutant MYOC is believed to be misfolded within the endoplasmic reticulum, and under normal physiological conditions misfolded MYOC should be retro-translocated to the cytoplasm for degradation. To better understand mutant MYOC pathology, we CRISPR-engineered a rat to have a MYOC Y435H substitution that is the equivalent of the pathological human MYOC Y437H mutation. Using this engineered animal model, we discovered that the chaperone αB-crystallin (CRYAB) is a MYOC-binding partner and that co-expression of these two proteins increases protein aggregates. Our results suggest that the misfolded mutant MYOC aggregates with cytoplasmic CRYAB and thereby compromises protein clearance mechanisms in trabecular meshwork cells, and this process represents the primary mode of mutant MYOC pathology. We propose a model by which mutant MYOC causes glaucoma, and we propose that therapeutic treatment of patients having a [i]MYOC[/i] mutation may focus on disrupting the MYOC-CRYAB complexes.

MeSH Terms

  • Amino Acid Substitution
  • Animals
  • Crystallins
  • Cytoskeletal Proteins
  • Disease Models, Animal
  • Eye Proteins
  • Female
  • Glaucoma
  • Glycoproteins
  • Humans
  • Male
  • Mice, Mutant Strains
  • Microtubule-Associated Proteins
  • Mutation, Missense
  • Protein Binding
  • Rats, Sprague-Dawley
  • Trabecular Meshwork
  • alpha-Crystallin B Chain


  • CRISPR/Cas
  • aggregation
  • aging
  • animal model
  • cell biology
  • crystallin
  • genetic disease
  • glaucoma
  • myocilin
  • secretion

Quantitative proteomics analysis by iTRAQ in human nuclear cataracts of different ages and normal lens nuclei.

The goal of this study was to quantitatively identify the differentially expressed proteins in nuclear cataracts of different ages and normal lens nuclei in humans. Forty-eight human lens nucleus samples with hardness grades III, IV were obtained during cataract surgery by extracapsular cataract extraction. Seven normal transparent human lens nuclei were obtained from fresh normal cadaver eyes during corneal transplantation surgery. Lens nuclei were divided into seven groups according to age and optic axis: Group A (average age 80.8 ± 1.2 years), Group B (average age 57.0 ± 4.0 years), Group C average age 80.3 ± 4.5 years), Group D (average age 56.9 ± 4.2 years), Group E (average age 78.1 ± 2.5 years), Group F (average age 57.6 ± 3.3 years) and Group G (seven normal transparent human lenses from normal cadaver eyes, average age 34.7 ± 4.2 years). Water-soluble, water-insoluble, and water-insoluble-urea-soluble protein fractions were extracted from samples. The three-part protein fractions from the individual lenses were combined to form the total proteins of each sample. The proteomic profiles of each group were further analyzed using 8-plex iTRAQ labeling combined with 2D-LC-MS/MS. The data were analyzed with the ProteinPilot software for peptide matching, protein identification, and quantification. Differentially expressed proteins were validated by Western blotting. We employed biological and technical replicates and selected the intersection of the two results, which included 80 proteins. Nine proteins were differentially expressed among the 80 proteins identified using proteomic techniques. In age-related nuclear cataracts (ARNC), the expression levels of fatty acid-binding protein and pterin-4-alpha-carbinolamine dehydratase were upregulated, whereas the levels of alpha-crystallin B chain (CRYAB), GSH synthetase, phakinin, gamma-crystallin C, phosphoglycerate kinase 1, betaine-homocysteine S-methyltransferase 1 (BHMT1), and spectrin beta chain were downregulated. These proteins may be associated with abnormal protein aggregation and oxidative stress. GSH synthetase and CRYAB expression levels in the nuclear cataract decreased with age. The mass spectrometric analysis results were consistent with the Western blot validation. The results indicate that CRYAB and GSH synthetase may be involved in ARNC pathogenesis. iTRAQ combined with 2D-LC-MS/MS provides new methods for future studies of pathological mechanisms and protective drug development for ARNC.

MeSH Terms

  • Aged
  • Aged, 80 and over
  • Aging
  • Amino Acid Sequence
  • Blotting, Western
  • Cataract
  • Eye Proteins
  • Female
  • Glutathione Synthase
  • Humans
  • Isotope Labeling
  • Lens Nucleus, Crystalline
  • Male
  • Mass Spectrometry
  • Middle Aged
  • Molecular Sequence Data
  • Peptides
  • Proteomics
  • alpha-Crystallin B Chain


  • Alpha-crystallin B chain
  • GSH synthetase
  • Human
  • iTRAQ Nuclear cataract

CRYAB and HSPB2 deficiency alters cardiac metabolism and paradoxically confers protection against myocardial ischemia in aging mice.

The abundantly expressed small molecular weight proteins, CRYAB and HSPB2, have been implicated in cardioprotection ex vivo. However, the biological roles of CRYAB/HSPB2 coexpression for either ischemic preconditioning and/or protection in situ remain poorly defined. Wild-type (WT) and age-matched ( approximately 5-9 mo) CRYAB/HSPB2 double knockout (DKO) mice were subjected either to 30 min of coronary occlusion and 24 h of reperfusion in situ or preconditioned with a 4-min coronary occlusion/4-min reperfusion x 6, before similar ischemic challenge (ischemic preconditioning). Additionally, WT and DKO mice were subjected to 30 min of global ischemia in isolated hearts ex vivo. All experimental groups were assessed for area at risk and infarct size. Mitochondrial respiration was analyzed in isolated permeabilized cardiac skinned fibers. As a result, DKO mice modestly altered heat shock protein expression. Surprisingly, infarct size in situ was reduced by 35% in hearts of DKO compared with WT mice (38.8 /- 17.9 vs. 59.8 /- 10.6% area at risk, P < 0.05). In DKO mice, ischemic preconditioning was additive to its infarct-sparing phenotype. Similarly, infarct size after ischemia and reperfusion ex vivo was decreased and the production of superoxide and creatine kinase release was decreased in DKO compared with WT mice (P < 0.05). In permeabilized fibers, ADP-stimulated respiration rates were modestly reduced and calcium-dependent ATP synthesis was abrogated in DKO compared with WT mice. In conclusion, contrary to expectation, our findings demonstrate that CRYAB and HSPB2 deficiency induces profound adaptations that are related to 1) a reduction in calcium-dependent metabolism/respiration, including ATP production, and 2) decreased superoxide production during reperfusion. We discuss the implications of these disparate results in the context of phenotypic responses reported for CRYAB/HSPB2-deficient mice to different ischemic challenges.

MeSH Terms

  • Aging
  • Animals
  • Female
  • HSP27 Heat-Shock Proteins
  • Heat-Shock Proteins
  • Male
  • Mice
  • Mice, Knockout
  • Myocardial Ischemia
  • Myocardium
  • alpha-Crystallin B Chain