Manganese (Mn) is an essential element necessary for proper development and brain function. Circulating Mn levels are regulated by hepatobiliary clearance to limit toxic levels and prevent tissue deposition. To characterize mechanisms involved in hepatocyte Mn uptake, polarized human HepaRG cells were used for this study. Western blot analysis and immunofluorescence microscopy showed the Mn transporter ZIP14 was expressed and localized to the basolateral surface of polarized HepaRG cells. HepaRG cells took up 54Mn in a time- and temperature-dependent manner but uptake was reduced after exposure to Mn. This loss in transport activity was associated with decreased ZIP14 protein levels in response to Mn exposure. Mn-induced degradation of ZIP14 was blocked by bafilomycin A1, which increased localization of the transporter in Lamp1-positive vesicles. Mn exposure also down-regulated the Golgi proteins TMEM165 and GPP130 while the ER stress marker BiP was induced. These results indicate that Mn exposure decreases ZIP14 protein levels to limit subsequent uptake of Mn as a cytoprotective response. Thus, high levels of Mn may compromise first-pass-hepatic clearance mechanisms.

中文翻译：

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ZIP14 会因接触锰而降解。


锰 (Mn) 是正常发育和大脑功能所必需的重要元素。循环中的锰水平由肝胆清除率调节，以限制毒性水平并防止组织沉积。为了表征肝细胞 Mn 摄取的机制，本研究使用了极化的人 HepaRG 细胞。蛋白质印迹分析和免疫荧光显微镜显示，Mn 转运蛋白 ZIP14 表达并定位于极化 HepaRG 细胞的基底外侧表面。 HepaRG 细胞以时间和温度依赖性方式吸收 54Mn，但接触 Mn 后吸收量减少。这种转运活性的丧失与锰暴露导致的 ZIP14 蛋白水平降低有关。 Mn 诱导的 ZIP14 降解被巴弗洛霉素 A1 阻断，从而增加了 Lamp1 阳性囊泡中转运蛋白的定位。锰暴露还下调高尔基体蛋白 TMEM165 和 GPP130，同时诱导 ER 应激标记 BiP。这些结果表明，接触 Mn 会降低 ZIP14 蛋白水平，从而限制随后作为细胞保护反应的 Mn 摄取。因此，高水平的锰可能会损害首过肝脏清除机制。