α crystallin from human cataractous lens has chaperone activity to protect other soluble proteins against heat-induced aggregation

Purpose: Several laboratories have demonstrated that the ability of lens α-crystallin to protect against thermal aggregation is age-dependent. It was hypothesized that the opacification and scattering in the cataractous lens is related with reduced chaperonc activity of α-crystallin. The purpose of this study was to evaluate the anti-aggregation ability of α-crystallin from human cataractous lenses. Methods: The soluble homogenates from cortical, nuclear, or whole portion of 1 traumatic, 2 congenital, and 10 senile cataractous lenses were analyzed respectively by gel-filtration HPLC and electrophoresis, and were heated to monitor the degree of turbidity. Results: When the soluble homogenates were heated at 60°C for 1 hour, there was no formation of insoluble protein in all samples; however, marked increase in turbidity was noted at 70°C for 1 hour in samples from nuclear portion of senile cataractous lenses, which showed relatively low α crystallin fraction in HPLC elution profile. When α-crystallins were selectively removed from the soluble homogenates, all samples became turbid upon heating. Conclusion: With the development of more severe senile cataract the fewer amounts of water soluble protein can be extracted. α-Crystallin from cataractous lenses can still protect other soluble proteins against thermal aggregation; the reduced anti-aggregation ability in some nuclear samples is mainly due to the decreased amounts of α-crystallin.