IRON UPTAKE BY CULTURED LENS EPITHELIAL-CELLS

Background: Transferrin and Fe concentrations increase in the intraocu lar fluids in pathological conditions and the lens accumulates Fe duri ng ocular inflammation. Tissues take up Fe from transferrin by two mec hanisms, receptor-medicated endocytosis of diferric transferrin and a process occurring at the cell membrane which may be mediated by an oxi do-reductase. However, Fe metabolism, transport and storage have not b een previously investigated in the lens. This study was designed to ch aracterize the uptake of Fe from transferrin by lens epithelial cells in culture. Methods: Primary, secondary and tertiary cultures of canin e lens epithelial cells and cultures obtained from cataractous lenses were studied. Uptake of Fe-59 from transferrin by these cultured cells was measured. Transferrin receptor populations were determined in rec eptor-binding assays. Results: There was a distinct relationship betwe en the amount of Fe-transferrin added and the amount of Fe taken up, w hich was linear for the primary cultures but significantly reduced for the secondary, tertiary and cataract cultures (252 +/- 21, 169 +/- 14 153 +/- 14 and 96 +/- 2 ng Fe/mg protein, respectively). Transferring receptor expression in lens cell cultures was reduced 10-fold within 2 days of addition of serum to cells grown in low-Fe, serum-free mediu m for 1 week. Conclusions: The reduction of Fe uptake by the subcultur ed and cataract cell lines probably reflects a decrease in transferrin receptor expression and in the activity of an alternative pathway for Fe transferrin uptake occurring over time. This reduced Fe uptake may result from long-term exposure to relatively high Fe concentration in the media. A reduction in the expression of the transferrin receptor after incubation with high concentrations of Fe supports this conclusi on.