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Published on: May 4, 2020
ZIP14 is degraded in response to manganese exposure
Khristy J Thompson1, Marianne Wessling-Resnick2
1Department of Genetics and Complex Diseases, Harvard T.H. Chan School of Public Health, 665 Huntington Avenue, Boston, MA, 02115, USA. kthompso@hsph.harvard.edu.
Abstract:
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.
Insights
Manganese (Mn) uptake by liver cells decreases with Mn exposure due to reduced ZIP14 transporter levels. This response protects cells but may impair manganese clearance.
Area of Science:
- Hepatology
- Cell Biology
- Trace Element Metabolism
Background:
- Manganese (Mn) is essential for development and brain function.
- Hepatobiliary clearance regulates circulating Mn levels, preventing toxicity.
- Understanding Mn uptake mechanisms in hepatocytes is crucial for managing Mn homeostasis.
Purpose of the Study:
- To investigate the mechanisms of Mn uptake in polarized human HepaRG cells.
- To characterize the role of the Mn transporter ZIP14 in hepatocyte Mn uptake.
- To determine the cellular response to Mn exposure regarding ZIP14 expression and function.
Main Methods:
- Utilized polarized human HepaRG cells.
- Employed Western blot analysis and immunofluorescence microscopy.
- Performed 54Mn uptake assays and treated cells with Mn and bafilomycin A1.
Main Results:
- ZIP14 transporter was identified on the basolateral surface of HepaRG cells.
- Mn uptake was time- and temperature-dependent but reduced by Mn exposure.
- Mn exposure decreased ZIP14 protein levels, blocked by bafilomycin A1, indicating lysosomal degradation.
- Downregulation of Golgi proteins (TMEM165, GPP130) and induction of ER stress marker BiP were observed.
Conclusions:
- Mn exposure reduces ZIP14 protein levels, limiting Mn uptake as a cytoprotective mechanism.
- This adaptive response suggests that high Mn levels could impair first-pass hepatic clearance.
- Further research is needed to understand the implications for Mn toxicity and homeostasis.
