The Ins and Outs of Manganese: ZIP14 facilitates the efflux of excess manganese from the brain.

Manganese (Mn) is essential for many enzymatic processes in the brain; however, Mn overload can lead to neurotoxicity and behavioral deficits. The blood-brain barrier (BBB), comprised of polarized endothelial cells, tightly regulates metals in and out of the brain. ZIP14 (SLC39A14) is a metal transporter more recently found to transport Mn, with mutations in human SLC39A14 resulting in brain Mn accumulation and neurological deficits. However, ZIP14s precise localization and role in BBB endothelial cells remain unclear. Here, we show in vivo ZIP14 expression in BBB endothelial cells, which upregulates following Mn supplementation. Using expansion microscopy, we observed a shift in ZIP14 localization from an equal apical-basolateral distribution to predominantly basolateral after Mn exposure. Endothelial-specific Zip14 KO (EKO) mice exhibited impaired Mn efflux from the brain and increased brain Mn accumulation after nasal delivery and dietary Mn supplementation. In vitro studies using primary endothelial cells from EKO mice and ZIP14-overexpressing hCMEC/D3 cells confirmed that ZIP14 primarily mediates basolateral-to-apical Mn transport. Collectively, our results demonstrate that ZIP14 is critical for brain Mn clearance, highlighting its potential as a therapeutic target to mitigate Mn-induced neurotoxicity. Significance StatementOur study reveals that the endothelial metal transporter ZIP14 plays a critical role in removing excess Mn from the brain. Using expansion microscopy, genetic manipulation, metallomics, and transport studies employing radiolabeled Mn, we demonstrate that ZIP14 undergoes strategic relocalization in response to Mn exposure and primarily functions in basolateral-to-apical transport. Deletion of endothelial ZIP14 leads to brain Mn accumulation, establishing its fundamental role in protecting against Mn-induced neurotoxicity. This finding provides mechanistic insight into how the brain protects itself against Mn overload and why ZIP14 mutations in humans result in brain Mn accumulation.