The ZIP3 Zinc Transporter Is Localized to Mossy Fiber Terminals and Is Required for Kainate-Induced Degeneration of...

Tight regulation of neuronal Zn²⁺ is critical for physiological function. Multiple Zn²⁺ transporters are expressed in the brain, yet their spatial distribution and distinct roles are largely unknown. Here, we show developmental regulation of the expression of Zn²⁺ transporters ZIP1 and ZIP3 in mouse hippocampal neurons, corresponding to previously described increase in neuronal vesicular Zn²⁺ during the first postnatal month. Rates of Zn²⁺ uptake in cultured mouse hippocampal neurons, monitored using FluoZin-3 fluorescence, were higher in mature neurons, which express higher levels of ZIP1 and ZIP3. Zn²⁺ uptake was attenuated by ∼50% following silencing of either ZIP1 or ZIP3. Expression of both ZIP1 and ZIP3 was ubiquitous on somas and most neuronal processes in the cultured neurons. In contrast, we observed distinct localization of the transporters in adult mouse hippocampal brain, with ZIP1 predominantly expressed in the CA3 stratum pyramidale, and ZIP3 primarily localized to the stratum lucidum. Consistent with their localization, silencing of ZIP1 expression in vivo reduced Zn²⁺ uptake in CA3 neurons while ZIP3 silencing reduced Zn²⁺ influx into dentate gyrus (DG) granule cells in acute hippocampal slices. Strikingly, in vivo silencing of ZIP3, but not ZIP1, protected CA3 neurons from neurodegeneration following kainate-induced seizures. Our results indicate that distinct Zn²⁺ transporters control Zn²⁺ accumulation and toxicity in different neuronal populations in the hippocampus and suggest that selective regulation of Zn²⁺ transporters can prevent seizure induced brain damage.SIGNIFICANCE STATEMENT Zinc plays a major role in neuronal function and its dysregulation is associated with neurodegeneration. Multiple zinc transporters are expressed in neurons, yet little is known on their distinct roles. Here, we show that the plasma membrane ZIP1 and ZIP3 zinc transporters are expressed on distinct neuronal populations in the CA3 region of the hippocampus. We show that ZIP1 mediates zinc influx into postsynaptic cells, while ZIP3 is responsible for zinc re-uptake from this synapse into dentate granule cells. We further show that silencing of ZIP3, but not ZIP1, can rescue the postsynaptic cells from kainate-induced neurodegeneration. This suggests that neuronal zinc toxicity and degeneration can be modulated by regulation of specific zinc transporters function.