Chaperone Peptides of α-Crystallin Inhibit Epithelial Cell Apoptosis, Protein Insolubilization, and Opacification in Experimental Cataracts

Rooban B Nahomi,Benlian Wang,Cibin T Raghavan,Oliver Voss,Andrea I Doseff,Puttur Santhoshkumar,Ram H Nagaraj

doi:10.1074/jbc.m112.440214

Abstract

α-Crystallin is a member of the small heat-shock protein (sHSP) family and consists of two subunits, αA and αB. Both αA- and αB-crystallin act as chaperones and anti-apoptotic proteins. Previous studies have identified the peptide (70)KFVIFLDVKHFSPEDLTVK(88) in αA-crystallin and the peptide (73)DRFSVNLDVKHFSPEELKVK(92) in αB-crystallin as mini-chaperones. In the human lens, lysine 70 (Lys(70)) of αA and Lys(92) of αB (in the mini-chaperone sequences) are acetylated. In this study, we investigated the cellular effects of the unmodified and acetyl mini-chaperones. The αA- and αB-crystallin peptides inhibited stress-induced aggregation of four client proteins, and the αA-acetyl peptide was more effective than the native peptide against three of the client proteins. Both the acetyl and native crystallin peptides inhibited stress-induced apoptosis in two mammalian cell types, and this property was directly related to the inhibition of cytochrome c release from mitochondria and the activity of caspase-3 and -9. In organ-cultured rat lenses, the peptides inhibited calcimycin-induced epithelial cell apoptosis. Intraperitoneal injection of the peptides inhibited cataract development in selenite-treated rats, which was accompanied by inhibition of oxidative stress, protein insolubilization, and caspase activity in the lens. These inhibitory effects were more pronounced for acetyl peptides than native peptides. A scrambled αA-crystallin peptide produced no such effects. The results suggest that the α-crystallin chaperone peptides could be used as therapeutic agents to treat cataracts and diseases in which protein aggregation and apoptosis are contributing factors.

Highlights

Peptides derived from the core domain of human ␣-crystallin act as molecular chaperones
The primary objective of this study was to determine whether chaperone ␣-crystallin peptides could inhibit apoptosis in cells and experimental cataracts in animals
The second objective was to determine whether the acetyl peptides inhibited apoptosis and cataracts more efficiently than the native peptides

Summary

Background

Peptides derived from the core domain of human ␣-crystallin act as molecular chaperones. Results: Chaperone peptides of ␣-crystallin inhibit stress-induced apoptosis in cultured cells and prevent experimental cataracts in rats. Intraperitoneal injection of the peptides inhibited cataract development in selenite-treated rats, which was accompanied by inhibition of oxidative stress, protein insolubilization, and caspase activity in the lens These inhibitory effects were more pronounced for acetyl peptides than native peptides. ␣A-Crystallin is present mainly in the lens, whereas ␣B-crystallin, in addition to the lens, is present in several other tissues, including the retina, heart, and kidney [4, 5] These peptides act as molecular chaperones and prevent the aggregation of structurally perturbed proteins. We show that the ␣-crystallin mini-chaperones and acetyl derivatives can inhibit apoptosis in mammalian cells by blocking cytochrome c release from mitochondria and preventing procaspase-3 activation. We present evidence that these peptides can inhibit protein aggregation and epithelial cell apoptosis in cataracts

EXPERIMENTAL PROCEDURES

RESULTS

Findings

DISCUSSION