Intracellular labile zinc is a determinant of vulnerability of cultured astrocytes to oxidative stress

Abstract

Recently, we found that treatment of cultured mouse astrocytes of ddY-strain mice (ddY-astrocytes) with 400 μM H2O2 for 24 h increased the intracellular labile zinc level without cell toxicity. In contrast, 170 μM H2O2 for 12 h is reported to kill mouse astrocytes obtained from C57BL/6-strain mice (C57BL/6-astrocytes) with an increase in intracellular labile zinc. To clarify this discrepancy, we compared the intracellular zinc levels and cell toxicity in H2O2-treated ddY- and C57BL/6-astrocytes. Exposure of C57BL/6-astrocytes to 170 or 400 μM H2O2 for 12 h dose-dependently decreased the cell viability and administration of plasma membrane-permeable zinc chelator TPEN prevented the 170 μM H2O2-induced astrocyte death, while neither concentration of H2O2 killed ddY-astrocytes. The intracellular zinc level in H2O2-treated C57BL/6-astrocytes was higher than that in H2O2-treated ddY-astrocytes, and this increase was suppressed by TPEN. There was no apparent difference in the expression levels of zinc transporters ZIPs and ZnTs between the two types of astrocytes, while expression of zinc releasable channel TRPM7 was found on the plasma membrane in ddY-astrocytes, but not in C57BL/6-astrocytes, although the total cellular expression levels were almost the same. In addition, a TRPM7 blocker, 2-aminoethoxydiphenyl borate, increased the intracellular zinc level in H2O2-treated ddY-, but not C57BL/6-astrocytes. Collectively, it is suggested that vulnerability of astrocytes to oxidative stress depends on an increased level of intracellular labile zinc, and TRPM7 localized on the plasma membrane contributes, at least in part, to ameliorate the cell injury by decreasing the zinc level.