Alpha-crystallin-mediated protection of lens cells against heat and oxidative stress-induced cell death

In addition to their key role as structural lens proteins, alpha-crystallins also appear to confer protection against many eye diseases, including cataract, retinitis pigmentosa, and macular degeneration. Exogenous recombinant alpha-crystallin proteins were examined for their ability to prevent cell death induced by heat or oxidative stress in a human lens epithelial cell line (HLE-B3). Wild type alpha A- or alpha B-crystallin (WT-alpha A and WT-alpha B) and alpha A- or alpha B-crystallins, modified by the addition of a cell penetration peptide (CPP) designed to enhance the uptake of proteins into cells (gC-alpha B, TAT-alpha B, gC-alpha A), were produced by recombinant methods. In vitro chaperone-like assays were used to assay the ability of alpha-crystallins to protect client proteins from chemical or heat induced aggregation. In vivo viability assays were performed in HLE-B3 to determine whether pre-treatment with alpha-crystallins reduced death after exposure to oxidative or heat stress. Most of the five recombinant alpha-crystallin proteins tested conferred some in vitro protection from protein aggregation, with the greatest effect seen with WT-alpha B and gC-alpha B. All alpha-crystallins displayed significant protection to oxidative stress induced cell death, while only the alpha B-crystallins reduced cell death induced by thermal stress. Our findings indicate that the addition of the gC tag enhanced the protective effect of alpha B-crystallin against oxidative but not thermally-induced cell death. In conclusion, modifications that increase the uptake of alpha-crystallin proteins into cells, without destroying their chaperone-like activity and anti-apoptotic functions, create the potential to use these proteins therapeutically. (C) 2013 Elsevier B.V. All rights reserved.