Changes in Intracellular Calcium and Glutathione in Astrocytes as the Primary Mechanism of Amyloid Neurotoxicity

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Abstract
Although the accumulation of the neurotoxic peptide β amyloid (βA) in the CNS is a hallmark of Alzheimer9s disease, the mechanism of βA neurotoxicity remains controversial. In cultures of mixed neurons and astrocytes, we found that both the full-length peptide βA (1–42) and the neurotoxic fragment (25–35) caused sporadic cytoplasmic calcium [intracellular calcium ([Ca2+]c)] signals in astrocytes that continued for hours, whereas adjacent neurons were completely unaffected. Nevertheless, after 24 hr, although astrocyte cell death was marginally increased, ∼50% of the neurons had died. The [Ca2+]c signal was entirely dependent on Ca2+ influx and was blocked by zinc and by clioquinol, a heavy-metal chelator that is neuroprotective in models of Alzheimer9s disease. Neuronal death was associated with Ca2+-dependent glutathione depletion in both astrocytes and neurons. Thus, astrocytes appear to be the primary target of βA, whereas the neurotoxicity reflects the neuronal dependence on astrocytes for antioxidant support.