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Ferritin H- and L-Chains in Fiber Cell Canine and Human Lenses of Different Ages

From the Department of Molecular Biomedical Sciences, North Carolina State University, Raleigh, North Carolina.

PURPOSE. This study was designed to elucidate potential age-related changes in the concentration, structure, and assembly pattern of ferritin chains in lens fiber cells.

METHODS. Canine and human lens fiber cell homogenate proteins were separated by one-dimensional and two-dimensional SDS-PAGE. Ferritin chains were immunodetected and quantitated with ferritin chain-specific antibodies. Total ferritin concentration was measured by ELISA. Binding of iron was determined in vitro with ⁵⁹Fe.

RESULTS. Ferritin H- and L-chains in canine and human fiber cells of healthy lenses were extensively modified. The H-chain in both species was truncated, and its concentration increased with age. Canine L-chain was approximately 11 kDa larger than standard canine L-chain, whereas human L-chain was of the proper size. Two-dimensional separation revealed age-related polymorphism of human and canine lens fiber cell L-chains and human H-chains. Normal size ferritin chains were not identified in canine fiber cells, but a small amount of fully assembled ferritin was detected, and its concentration decreased with age.

CONCLUSIONS. Such significantly altered ferritin chains are not likely to form functional ferritin capable of storing iron. Therefore, lens fiber cells, particularly from older lenses, may have limited ability to protect themselves against iron-catalyzed oxidative damage.