Copper metabolism and copper-mediated alterations in the metabolism of cultured astrocytes

Copper is an essential element that is required for a variety of important cellular functions. Since not only copper deficiency, but also excess of copper can seriously affect cellular functions, cellular copper metabolism is tightly regulated. Disturbances of copper homeostasis are the underlying defect of the inherited diseases Menkes and Wilson s disease and have also been linked to several neurodegenerative diseases including Alzheimer s disease and Parkinson s disease. Known astrocytes features strongly suggest a pivotal role of theses cells in the metal metabolism of the brain. Using astrocyte-rich primary cultures as model system, this thesis investigated the copper metabolism as well as copper-mediated alterations in the metabolism of astrocytes. Cultured astrocytes efficiently accumulated copper with saturable kinetics. The characteristics of the observed copper accumulation suggest that both copper transporter receptor 1 (Ctr1) and a Ctr1-independent mechanism are involved in astrocytic copper accumulation. Cultured astrocytes were also found to release copper in a time-, concentration- and temperature-dependent manner. Copper export from these cells most likely involves the copper-ATPase ATP7A. Thus, with being capable of both taking up and exporting copper, astrocytes possess the cellular machinery required to transport copper from the blood-brain barrier to the brain parenchyma. Cultured astrocytes were remarkable resistance against copper-induced toxicity. Nevertheless, prolonged copper treatment led to profound alterations in their metabolism. For example, copper accumulation by cultured astrocytes was accompanied by a stimulation of glycolytic flux, an increase in the cellular glutathione content and an acceleration of glutathione export. Such copper-mediated alterations in the metabolism of astrocytes may also occur in vivo, for example in copper overload conditions such in Wilson s disease and could either contribute to disease progression or serve as compensatory response to protect the brain against the toxic effects of an excess of copper

Copper metabolism of astrocytes

This short review will summarize the current knowledge on the uptake, storage and export of copper ions by astrocytes and will address the potential roles of astrocytes in copper homeostasis in the normal and diseased brain. Astrocytes in culture efficiently accumulate copper by processes that include both the copper transporter Ctr1 and Ctr1-independent mechanisms. Exposure of astrocytes to copper induces an increase in cellular glutathione (GSH) content as well as synthesis of metallothioneins, suggesting that excess of copper is stored as complex with GSH and in metallothioneins. Furthermore, exposure of astrocytes to copper accelerates the release of GSH and of glycolytically generated lactate. Astrocytes are able to export copper and express the Menkes protein ATP7A. This protein undergoes reversible, copper-dependent trafficking between the trans-Golgi network and vesicular structures. The ability of astrocytes to efficiently take up, store and export copper suggests that astrocytes play a key role in the supply of neurons with copper and that astrocytes should be considered as target for therapeutic inventions that aim to correct disturbances in brain copper homeostasis

The intestinal metal transporter ZIP14 maintains systemic manganese homeostasis

ZIP14 (encoded by the solute carrier 39 family member 14 (SLC39A14) gene) is a manganese transporter that is abundantly expressed in the liver and small intestine. Loss-of-function mutations in SLC39A14 cause severe hypermanganesemia. Because the liver is regarded as the main regulatory organ involved in manganese homeostasis, impaired hepatic manganese uptake for subsequent biliary excretion has been proposed as the underlying disease mechanism. However, liver-specific Zip14 KO mice exhibit decreased manganese only in the liver and do not develop manganese accumulation in other tissues under normal conditions. This suggests that impaired hepatobiliary excretion is not the primary cause for manganese overload observed in individuals lacking functional ZIP14. We therefore hypothesized that increased intestinal manganese absorption could induce manganese hyperaccumulation when ZIP14 is inactivated. To elucidate the role of ZIP14 in manganese absorption, here we used CaCo-2 Transwell cultures as a model system for intestinal epithelia. The generation of a ZIP14-deficient CaCo-2 cell line enabled the identification of ZIP14 as the major transporter mediating basolateral manganese uptake in enterocytes. Lack of ZIP14 severely impaired basolateral-to-apical (secretory) manganese transport and strongly enhanced manganese transport in the apical-to-basolateral (absorptive) direction. Mechanistic studies provided evidence that ZIP14 restricts manganese transport in the absorptive direction via direct basolateral reuptake of freshly absorbed manganese. In support of such function of intestinal ZIP14 in vivo, manganese levels in the livers and brains of intestine-specific Zip14 KO mice were significantly elevated. Our findings highlight the importance of intestinal ZIP14 in regulating systemic manganese homeostasis.National Institutes of Health [R00DK104066]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Kupfer-Stoffwechsel von Astrozyten und durch Kupfer bewirkte Veränderungen im Stoffwechsel von Astrozyten

Copper is an essential element that is required for a variety of important cellular functions. Since not only copper deficiency, but also excess of copper can seriously affect cellular functions, cellular copper metabolism is tightly regulated. Disturbances of copper homeostasis are the underlying defect of the inherited diseases Menkes and Wilson s disease and have also been linked to several neurodegenerative diseases including Alzheimer s disease and Parkinson s disease. Known astrocytes features strongly suggest a pivotal role of theses cells in the metal metabolism of the brain. Using astrocyte-rich primary cultures as model system, this thesis investigated the copper metabolism as well as copper-mediated alterations in the metabolism of astrocytes. Cultured astrocytes efficiently accumulated copper with saturable kinetics. The characteristics of the observed copper accumulation suggest that both copper transporter receptor 1 (Ctr1) and a Ctr1-independent mechanism are involved in astrocytic copper accumulation. Cultured astrocytes were also found to release copper in a time-, concentration- and temperature-dependent manner. Copper export from these cells most likely involves the copper-ATPase ATP7A. Thus, with being capable of both taking up and exporting copper, astrocytes possess the cellular machinery required to transport copper from the blood-brain barrier to the brain parenchyma. Cultured astrocytes were remarkable resistance against copper-induced toxicity. Nevertheless, prolonged copper treatment led to profound alterations in their metabolism. For example, copper accumulation by cultured astrocytes was accompanied by a stimulation of glycolytic flux, an increase in the cellular glutathione content and an acceleration of glutathione export. Such copper-mediated alterations in the metabolism of astrocytes may also occur in vivo, for example in copper overload conditions such in Wilson s disease and could either contribute to disease progression or serve as compensatory response to protect the brain against the toxic effects of an excess of copper

Manganese Uptake by A549 Cells is Mediated by Both ZIP8 and ZIP14

The alveolar epithelia of the lungs require manganese (Mn) as an essential nutrient, but also provide an entry route for airborne Mn that can cause neurotoxicity. Transporters involved in Mn uptake by alveolar epithelial cells are unknown. Recently, two members of the Zrt- and Irt-like protein (ZIP) family of metal transporters, ZIP8 and ZIP14, have been identified as crucial Mn importers in vivo. ZIP8 is by far most abundantly expressed in the lungs, whereas ZIP14 expression in the lungs is low compared to other tissues. We hypothesized that Mn uptake by alveolar epithelial cells is primarily mediated by ZIP8. To test our hypothesis, we used A549 cells, a type II alveolar cell line. Mirroring the in vivo situation, A549 cells expressed higher levels of ZIP8 than cell models for the liver, intestines, and kidney. Quantification of ZIP8 and ZIP14 revealed a strong enrichment of ZIP8 over ZIP14 in A549 cells. Using siRNA technology, we identified ZIP8 and ZIP14 as the major transporters mediating Mn uptake by A549 cells. To our surprise, knockdown of either ZIP8 or ZIP14 impaired Mn accumulation to a similar extent, which we traced back to similar amounts of ZIP8 and ZIP14 at the plasma membrane. Our study highlights the importance of both ZIP8 and ZIP14 in Mn metabolism of alveolar epithelial cells.National Institutes of Health [R00DK104066]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Copper : effects of deficiency and overload

Copper is an essential trace metal that is required for the catalysis of several important cellular enzymes. However, since an excess of copper can also harm cells due to its potential to catalyze the generation of toxic reactive oxygen species, transport of copper and the cellular copper content are tightly regulated. This chapter summarizes the current knowledge on the importance of copper for cellular processes and on the mechanisms involved in cellular copper uptake, storage and export. In addition, we will give an overview on disturbances of copper homeostasis that are characterized by copper overload or copper deficiency or have been connected with neurodegenerative disorders. © Springer Science+Business Media Dordrecht 2013