Mc. Mcgahan et al., IRON UPTAKE BY CULTURED LENS EPITHELIAL-CELLS, Graefe's archive for clinical and experimental ophthalmology, 233(6), 1995, pp. 354-359
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.