Metallothionein‐3 regulates lysosomal function in cultured astrocytes under both normal and oxidative conditions

Abstract

Cellular zinc plays a key role in lysosomal change and cell death in neurons and astrocytes under oxidative stress. Here, using astrocytes lacking metallothionein-3 (MT3), a potential source of labile zinc in the brain, we studied the role of MT3 in oxidative stress responses. H(2)O(2) induced a large increase in labile zinc in wild-type (WT) astrocytes, but stimulated only a modest rise in MT3-null astrocytes. In addition, H(2)O(2)-induced lysosomal membrane permeabilization (LMP) and cell death were comparably attenuated in MT3-null astrocytes. Expression and glycosylation of Lamp1 (lysosome-associated membrane protein 1) and Lamp2 were increased in MT3-null astrocytes, and the activities of several lysosomal enzymes were significantly reduced, indicating an effect of MT3 on lysosomal components. Consistent with lysosomal dysfunction in MT3-null cells, the level of LC3-II (microtubule-associated protein 1 light chain 3), a marker of early autophagy, was increased by oxidative stress in WT astrocytes, but not in MT3-null cells. Similar changes in Lamp1, LC3, and cathepsin-D were induced by the lysosomal inhibitors bafilomycin A1, chloroquine, and monensin, indicating that lysosomal dysfunction may lie upstream of changes observed in MT3-null astrocytes. Consistent with this idea, lysosomal accumulation of cholesterol and lipofuscin were augmented in MT3-null astrocytes. Similar to the results seen in MT3-null cells, MT3 knockdown by siRNA inhibited oxidative stress-induced increases in zinc and LMP. These results indicate that MT3 may play a key role in normal lysosomal function in cultured astrocytes.

The role of intracellular zinc release in aging, oxidative stress, and Alzheimer’s disease

“…Further, MT III can act as both an acceptor and a donor of zinc, and thus changes in MT III expression could have different effects depending on the cellular environment and redox state within neurons. Knockdown of MT III in astrocytes has also been shown to lead to a decrease in the degradative capacity of lysosomes (Lee et al, 2010), consistent with the reduced autophagy observed during AD. However, the lack of MT III also corresponds with decreased oxidant-induced zinc release, revealing the need for further studies to fully understand the role of MT III and its association with zinc in autophagic dysfunction.…”

Astrocyte-Specific Overexpression of Nrf2 Delays Motor Pathology and Synuclein Aggregation throughout the CNS in the Alpha-Synuclein Mutant (A53T) Mouse Model

“…7C). The smeared bands for Lamp1 are indicative of increased Lamp1 glycosylation (Lee et al, 2010). All changes were absent in the double transgenic mice [AN(+/+)].…”

Zinc in innate and adaptive tumor immunity

“…Although there are examples of zinc's effect on autophagy in bacteria and yeast [168], it is not as clear how these can be translated to mammals. Zn mediates tamoxifen-induced autophagy in breast cancer cells [169], hippocampal neurons [170], retinal cells [167], and in astrocytes via increases in oxidative stress and induction of lysosomal membrane permeabilization [171]. The newer studies have used animals deficient in metallothionein to study the changes and importance of zinc.…”