Iron and manganese uptake in glial cell cultures from hypotransferrinemic (Hp) mice

Hp mice have a splicing defect in the transferrin (Tf) gene which results in the expression of <1% of the normal plasma circulating levels of Tf. Thus, this animal offers the opportunity to examine the role of Tf in iron and Manganese (Mn) distribution to cells. In this study, we use mixed glial cultures from Hp mice and unaffected wild type controls. The mice expressing the Hp mutation are pale compared to unaffected littennates and can be identified at birth. The brains of Hp and unaffected animals were removed within 2-3 days of birth and mixed glial cultures were prepared according to standard procedures. The cultures were established in 10% fetal calf serum for 7 days and subsequently changed to a defined, serum-free, Tf containing or Tf-free medium for 1 day. Subsequently, 5FeCl₃ or ⁵⁴Mn was added to the medium for 3,6 or 24 hrs. In the absence of Tf, iron uptake was elevated in both normal and Hp mice at 3 and 6 hrs but not at 24 hrs. The amount of iron uptake in the Hp mouse mixed glial cultures was 2-10X higher than in the normal mice over a 3 hr incubation period. The efflux of iron from the cells in the culture was influenced by Tf in the medium. More iron remained in cells from both Hp and normal mice if Tf was removed from the medium. There was no effect on Mn uptake or efflux in any of the conditions examined. These results demonstrate that Tf is not required for iron or Mn uptake into mixed glial cell cultures, indeed its absence resulted in an increase in iron uptake. These results indicate the presence of a non-Tf dependent iron and Mn delivery system in mixed glial cells and also suggest that the role for Tf in these cells may be to regulate the intracellular concentration of iron.