Manganese transport via the transferrin mechanism

Excessive manganese (Mn) uptake by brain cells, particularly in regions like the basal ganglia, can lead to toxicity. Mn²⁺ is transported into cells via a number of mechanisms, while Mn³⁺ is believed to be transported similarly to iron (Fe) via the transferrin (Tf) mechanism. Cellular Mn uptake is therefore determined by the activity of the mechanisms transporting Mn into each type of cell and by the amounts of Mn²⁺, Mn³⁺ and their complexes to which these cells are exposed; this complicates understanding the contributions of each transporter to Mn toxicity. While uptake of Fe³⁺ via the Tf mechanism is well understood, uptake of Mn³⁺ via this mechanism has not been systematically studied. The stability of the Mn³⁺Tf complex allowed us to form and purify this complex and label it with a fluorescent (Alexa green) tag. Using purified and labeled Mn³⁺Tf and biophysical tools, we have developed a novel approach to study Mn³⁺Tf transport independently of other Mn transport mechanisms. This approach was used to compare the uptake of Mn³⁺Tf into neuronal cell lines with published descriptions of Fe³⁺ uptake via the Tf mechanism, and to obtain quantitative information on Mn uptake via the Tf mechanism. Results confirm that in these cell lines significant Mn³⁺ is transported by the Tf mechanism similarly to Fe³⁺Tf transport; although Mn³⁺Tf transport is markedly slower than other Mn transport mechanisms. This novel approach may prove useful for studying Mn toxicity in other systems and cell types.