Localization of ZIP14 and ZIP8 in HIBCPP Cells

Abstract

The blood–cerebrospinal fluid barrier (BCB) is important in maintaining brain manganese (Mn) homeostasis. This barrier consists of a single layer of epithelial cells, connected by tight junctions, that restrict the passage of nutrients to only allow molecules to be carried through the membrane by a transporter. These epithelial cells are polarized with asymmetrical blood-facing and cerebrospinal fluid-facing sides. Here, we have established a polarized model of a human choroid plexus papilloma cell line, HIBCPP. For the first time, Mn importers ZIP14 and ZIP8 were identified in HIBCPP cells and were found to be enriched at the basolateral and apical sides of the cell monolayer, respectively. The localization of each ZIP protein adds to the understanding of Mn transport across the HIBCPP BCB model to help understand the mechanism of Mn homeostasis within the brain.

Calcium and the Ca-ATPase SPCA1 modulate plasma membrane abundance of ZIP8 and ZIP14 to regulate Mn(II) uptake in brain microvascular endothelial cells

“…We also demonstrated that whereas ZIP8 was equally abundant in the apical (blood) and basolateral (abluminal) membranes of hBMVECs grown in transwells, 90% of plasma membrane–associated ZIP14 was found on the ‘brain’ side of this model BBB. A comparable asymmetric localization has been reported for these two transporters in the HIBCPP choroid plexus cell line ( 41 ). That these two transporters might contribute differentially to cellular manganese homeostasis was indicated also by differences in the regulation of their plasma membrane localization.…”

“…A similar pattern of ZIP8 re-localization from primarily intracellular to cell surface presentation was observed in HEK293 cells treated with iron (38). Note, however, that in hBMVECs, only a small fraction of total ZIP8 is in the plasma membrane compared to total cellular protein, a finding reported also in the A549 lung epithelial and HIBCPP choroid plexus papilloma cell lines (41,42), and human proximal tubular epithelial cells (43). In addition, the pattern of ZIP8 and ZIP14 cell localization observed in these latter cells is equivalent to the results shown herein.…”

“…The former observation suggests that the residence lifetime of ZIP14 in the plasma membrane is regulated by dynamin-dependent retrieval. The literature also shows that the steady-state plasma membrane abundance of either transporter represents only a small fraction of the cell total of either protein ( 24 , 38 , 41 ). Taken together, the data are consistent with the premise that the efficacy of these two manganese and iron transporters can be regulated by modulation of their anterograde and retrograde trafficking to and from the plasma membrane.…”

Manganese Accumulation in the Brain via Various Transporters and Its Neurotoxicity Mechanisms

“…ZIP8 in the brain microvascular capillary endothelial cells also plays a critical role in Mn uptake into the brain [ 53 ]. ZIP8 expression is enriched at the apical side of human choroid plexus papilloma cells, which are related to the blood-cerebrospinal fluid (CSF) barrier, contributing to Mn accumulation in these cells [ 54 ]. These findings suggest that ZIP8 transporter is important in Mn transport into the brain.…”

“…A zebrafish model lacking ZIP14 accumulated higher Mn levels in the brain compared to those in wild-type (WT), leading to altered locomotor activity [ 58 ]. ZIP14 is enriched on the basolateral side of choroid plexus cells, contributing to Mn transport through these cells and the subsequent excretion [ 54 ]. ZIP14 mutation caused Mn accumulation in early-onset parkinsonism dystonia patients, suggesting the important role of ZIP14 in the regulation of Mn levels in the brain to prevent Mn neurotoxicity in humans [ 58 ].…”