Alpha-crystallin mutations alter lens metabolites in mouse models of human cataracts

Abstract

Cataracts are a major cause of blindness worldwide and commonly occur in individuals over 70 years old. Cataracts can also appear earlier in life due to genetic mutations. The lens proteins, αA-and αB-crystallins, are chaperone proteins that have important roles maintaining protein solubility to prevent cataract formation. Mutations in the CRYAA and CRYAB crystallin genes are associated with autosomal dominant early onset human cataracts. Although studies about the proteomic and genomic changes that occur in cataracts have been reported, metabolomics studies are very limited. Here, we directly investigated cataract metabolism using gas-chromatography-mass spectrometry (GC-MS) to analyze the metabolites in adult Cryaa-R49C and Cryab-R120G knock-in mouse lenses. The most abundant metabolites were myo-inositol, L-(+)-lactic acid, cholesterol, phosphate, glycerol phosphate, palmitic and 9-octadecenoic acids, α-D-mannopyranose, and β-D-glucopyranose. Cryaa-R49C knock-in mouse lenses had a significant decrease in the number of sugars and minor sterols, which occurred in concert with an increase in lactic acid. Cholesterol composition was unchanged. In contrast, Cryab-R120G knock-in lenses exhibited increased total amino acid content including valine, alanine, serine, leucine, isoleucine, glycine, and aspartic acid. Minor sterols, including cholest-7-en-3-ol and glycerol phosphate were decreased. These studies indicate that lenses from Cryaa-R49C and Cryab-R120G knock-in mice, which are models for human cataracts, have unique amino acid and metabolite profiles.

Oxysterol Compounds in Mouse Mutant αA- and αB-Crystallin Lenses Can Improve the Optical Properties of the Lens

“…Using knock-in mice that express Cryab -R120G or Cryaa -R49C mutations associated with human cataracts, we previously analyzed the in vivo substrates of these molecular chaperones in the lens by proteomics, examined the transcriptome changes in lenses associated with cataract development, and developed strategies to reduce lens opacification using small molecules in vivo. 6 , 37 , 45 , 46 However, before the current study, the effects of α-crystallin mutations on refractive index gradients in lenses have not been compared with those in WT lenses. Our previous work showed that VP1-001 treatment of mouse eyes in vivo reduces lens opacity grade and increases the proportion of soluble protein in the mouse lenses.…”

Cataract-causing allele in CRYAA (Y118D) proceeds through endoplasmic reticulum stress in mouse model

“…Increases in water-insoluble proteins in the lens can cause a cloudy appearance and the occurrence of dominant nuclear cataracts ( Andley et al, 2016 ; Cheng et al, 2010 ). Previous studies have reported that αA-crystallin mutations can lead to the appearance of the cataract phenotype and an increase in the expression of certain factors in the ERS-UPR signaling pathway ( Frankfater et al, 2020 ). However, systematic study on ER homeostasis is lacking.…”

A native chemical chaperone in the human eye lens

“…Lens inositol depletion in a mouse knock-in of a human cataract-associated αB-crystallin variant was recently reported. 42 A typical human diet is estimated to contain 1-2 g of myo-inositol per day, and ~4 g/day is produced endogenously from glucose in the liver and kidney. 43 Of all human tissues in which myo-inositol levels have been studied, the lens appears to have the highest, while the second-highest levels are found in the cytoplasm of nerve cells in the brain.…”