ZnT‐1 expression in astroglial cells protects against zinc toxicity and slows the accumulation of intracellular zinc

Abstract

Zinc ions are emerging as an important factor in the etiology of neurodegenerative disorders and in brain damage resulting from ischemia or seizure activity. High intracellular levels of zinc are toxic not only to neurons but also to astrocytes, the major population of glial cells in the brain. In the present study, the role of ZnT-1 in reducing zinc-dependent cell damage in astrocytes was assessed. Zinc-dependent cell damage was apparent within 2 h of exposure to zinc, and occurred within a narrow range of approximately 200 microM. Pretreatment with sublethal concentrations of zinc rendered astrocytes less sensitive to toxic zinc levels, indicating that preconditioning protects astrocytes from zinc toxicity. Fluorescence cell imaging revealed a steep reduction in intracellular zinc accumulation for the zinc-pretreated cells mediated by L-type calcium channels. Heterologous expression of ZnT-1 had similar effects; intracellular zinc accumulation was slowed down and the sensitivity of astrocytes to toxic zinc levels was reduced, indicating that this is specifically mediated by ZnT-1 expression. Immunohistochemical analysis demonstrated endogenous ZnT-1 expression in cultured astroglia, microglia, and oligodendrocytes. Pretreatment with zinc induced a 4-fold increase in the expression of the putative zinc transporter ZnT-1 in astroglia as shown by immunoblot analysis. The elevated ZnT-1 expression following zinc priming or after heterologous expression of ZnT-1 may explain the reduced zinc accumulation and the subsequent reduction in sensitivity toward toxic zinc levels. Induction of ZnT-1 may play a protective role when mild episodes of stroke or seizures are followed by a massive brain insult.

Heterodimerization, Altered Subcellular Localization, and Function of Multiple Zinc Transporters in Viable Cells Using Bimolecular Fluorescence Complementation

“…ZnTs are known to localize at distinct subcellular compartments, depending on their function as well as their tissue-specific expression pattern (6,33). ZnT1 is predominantly localized at the PM, and it displays a major role as a zinc exporter that protects cells from zinc toxicity (6,34). ZnT3 was shown to localize at synaptic vesicles (20), whereas ZnT2 and ZnT4 have been shown to reside in the membrane of intracellular vesicles/granules, including lysosomes and endosomes (6,26,35), and in a small fraction of cells in the PM (36).…”

Molecular Basis for Zinc Transporter 1 Action as an Endogenous Inhibitor of L-type Calcium Channels

“…Recent studies have shown that ZnT-1 is an endogenous negative regulator of the LTCC (30,31), particularly in the heart, where it appears to participate in cardiac electrical remodeling following atrial fibrillation (31), and in the brain, where it may affect synaptic release (37,40). Nevertheless, the mechanism underlying ZnT-1-induced inhibition of the LTCC has yet to be elucidated.…”

“…This transmembrane protein has been investigated mainly in the context of zinc metabolism and has been shown to confer resistance to zinc toxicity (32)(33)(34)(35)(36). ZnT-1 is expressed in most tissues, with high levels of expression observed primarily in the brain, the pancreas, the testes, and the heart (37)(38)(39). ZnT-1 inhibition of LTCC activity has recently been confirmed in several cell types (30,31,40).…”

Redox Regulation of Intracellular Zinc: Molecular Signaling in the Life and Death of Neurons

“…Unlike MT, changes in ZnT1 mRNA and protein expression in preconditioned neurons have not been extensively investigated. However, a conceptually similar investigation has been performed in astrocytes (85). In these cells, sublethal exogenous Zn 2þ exposure induced ZnT1 protein expression and conferred resistance to subsequent lethal Zn 2þ toxicity (85).…”

“…However, a conceptually similar investigation has been performed in astrocytes (85). In these cells, sublethal exogenous Zn 2þ exposure induced ZnT1 protein expression and conferred resistance to subsequent lethal Zn 2þ toxicity (85). Further, in nonpreconditioned astrocytes, heterologous expression of ZnT1 reduced toxic intracellular Zn 2þ accumulations and induced Zn 2þ -tolerance (85).…”