Expression of divalent metal transporter 1 in primary hippocampal neurons: Reconsidering its role in non-transferrin-bound iron influx

The divalent metal transporter 1 (DMT1) is the best characterized Fe 2+ transporter involved in cellular iron uptake in mammals. Four possible isoforms have been identified as a result of alternative promoter (DMT1-1A and DMT1-1B) and alternative splicing involving the C-terminus and producing transcripts with or without an iron responsive element [DMT1-IRE(+) and DMT1-IRE(-), respectively]. Despite the general importance of DMT1 in controlling iron homeostasis, the distribution and the role of the transporter in the CNS is still controversial. In this study, we characterize the expression of DMT1 in hippocampal neurons and astrocytes. We found that the main isoform endogenously expressed is DMT1-1B/IRE(+), which shows cytoplasmic distribution, colocalization with late endosome/lysosome markers and iron regulation, as expected from the presence of an iron responsive element. Our results also show that DMT1-1B/IRE(+) isoform does not sustain iron entry, even after its neuronal over-expression. Overall, our results argue against a physiological role of the endogenous DMT1 in neuronal iron uptake but do not exclude that, under pathological conditions, the expression of other DMT1 isoforms might contribute to iron overload. Neurons and iron uptake: which role for DMT1?This study investigates the role of DMT1, the best-known iron transporter in mammals, on the mechanisms sustaining non-transferrin-bound iron (NTBI) uptake in neurons. The expression analysis of DMT1 isoforms, as well as functional studies of iron uptake, indicate that this transporter does not play a relevant role in neuronal NTBI import. These findings draw the attention to mechanisms other than DMT1-mediated iron transport in the neuronal iron accumulation observed during aging and in several neurodegenerative disorders. The confocal analysis of the fluorescent DMT1-1B/IRE(+) overexpressed in hippocampal neurons, reveals a cytoplasmatic punctate staining, similarly to the endogenous protein. The overexpressed DMT1 was recognized by an anti-DMT1 antibody and showed a colocalization with lysosomal marker. © 2011 The Authors.