?A and ?B peptides from human cataractous lenses show antichaperone activity and enhance aggregation of lens proteins

Purpose: To identify and characterize properties of ??A- and ??B-crystallins??? low molecular weight peptides (molecular weight [Mr] < 5 kDa) that were present in a 62-year-old human nuclear cataract, but not in normal 62-year-old human lenses. Methods: Low molecular weight peptides (< 5 kDa) were isolated with a trichloroacetic acid (TCA) solubilization method from water-soluble (WS) and water-insoluble (WI) proteins of nuclear cataractous lenses of a 62-year-old donor and normal human lenses from an age-matched donor. Five commercially synthesized peptides (found only in cataractous lenses and not in normal lenses) were used to determine their chaperone and antichaperone activity and aggregation properties. Results: Mass spectrometric analysis showed 28 peptides of ??A-crystallin and 38 peptides of ??B-crystallin were present in the cataractous lenses but not in the normal lenses. Two ??A peptides (named ??AP1 and ??AP2; both derived from the ??A N-terminal domain (NTD) region) and three ??B peptides (named ??BP3, ??BP4, and ??BP5, derived from the ??B NTD-, core domain (CD), and C-terminal extension (CTE) regions, respectively) were commercially synthesized. ??AP1 inhibited the chaperone activity of ??A- and ??B-crystallins, but the other four peptides (??AP2, ??BP3, ??BP4, and ??BP5) exhibited mixed effects on chaperone activity. Upon incubation with human WS proteins and peptides in vitro, the ??BP4 peptide showed higher aggregation properties relative to the ??AP1 peptide. During in vivo experiments, the cell-penetrating polyarginine-labeled ??AP1 and ??BP4 peptides showed 57% and 85% aggregates, respectively, around the nuclei of cultured human lens epithelial cells compared to only 35% by a scrambled peptide. Conclusions: The antichaperone activity of the ??AP1 peptide and the aggregation property of the ??BP4 peptide with lens proteins could play a potential role during the development of lens opacity.