Distribution of ferritin chains in noncataractous and cataractous canine lenses

Abstract

Ferritin consists of 24 subunits of light (19 kDa) and heavy (21 kDa) chains each with roles in storing iron and protecting cells from iron induced oxidative damage. Changes in subunits can alter iron storage in ferritin. Nuclear cataractogenesis is associated with age and oxidative damage. We compared ferritin chains from fiber cells of normal and cataractous canine lenses separated into six layers. The ferritin chains from each layer were analyzed by Western. The iron binding of assembled ferritin was determined by 59Fe labeling. The chains in lens fiber cells differed from the standard canine ferritin H (21 kDa) and L‐chain (19 kDa). The L‐chain was larger (30 kDa) and there were two modified ferritin H‐chains (12 and 29 kDa). The 30 kDa L‐chain was present in the cortex of all lenses. The 12 kDa H‐chain was found in cortex and outer nuclei of both lens types. The 29 kDa H‐chain was present only in nuclei of cataractous lenses. 59Fe labeling showed that assembled ferritin from cataractous lenses bound more iron than ferritin from normal lenses. All altered ferritin chains in lens fibers were unevenly distributed throughout the lens. The characteristics and distribution of H‐chain in cataractous lenses were different from those in normal lenses. The higher content of differentially modified H‐chain in the nucleus and higher affinity for iron of ferritin in cataractous lenses may be a part of cell defense against oxidative damage.