Beta-amyloid peptides induce mitochondrial dysfunction and oxidative stress in astrocytes and death of neurons through activation of NADPH oxidase - PubMed (original) (raw)

β-Amyloid causes depolarization of mitochondria in astrocytes but not in neurons. Changes in Δψm were measured using Rh123 in dequench mode; the loss of potential is seen as an increase in fluorescence. A, Changes in Δψm from a neuron (black line) and an astrocyte (gray symbols) in a mixed culture from rat hippocampus (15 DIV) after exposure to 50 μ

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βA 25-35. In the example shown, βA 25-35 caused a slow progressive collapse of Δψm in the astrocyte, whereas no change at all was seen in a nearby neuron. Application of 300 μ

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glutamate caused a rapid collapse of Δψm in the neuron but promoted recovery of Δψm in the astrocyte. On subsequent removal of external Ca2+, neuronal Δψm recovered, showing that mitochondrial injury was still reversible. In this and all subsequent records, the protonophore FCCP was added at the end of the experiment to determine the extent of the Rh123 signal in response to complete mitochondrial depolarization. The Rh123 fluorescence signal in these traces is normalized between 0, representing the resting Rh123 fluorescence, and 100, representing the maximal increase in Rh123 fluorescence in response to complete mitochondrial depolarization by 1 μ

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FCCP. In traces in which the Rh123 signal was lost in some cells during exposure to βA, this normalization was not possible, and so the data are shown normalized only to a baseline set at 100%. Thus, the trace shown in A is actually very similar to some of the traces in B, in which FCCP responses were maintained. In B is shown an example of an experiment using astrocytes in culture in response to the full peptide βA 1-42 (5 μ

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). The cells responded with a slow loss of mitochondrial potential on which were superimposed abrupt depolarizing transitions. Some of these were reversible, but the larger depolarizations were followed by loss of the dye, suggesting cell death. Some examples of these traces are extracted from another data set to illustrate these three types of response in C. The series of images shown in D illustrate examples from an extended time sequence showing the transient increases in signal and the gradual increase in basal signal in response to βA 25-35. The image after FCCP saturates the display at this range because it is much brighter than the rest of the sequence and so is not shown. The time of each extracted image is indicated in minutes. In Eii and Eii are shown records from two astrocytes co-loaded with fura-2 and Rh123 to measure [Ca2+]c (black triangles) and Δψm (gray lines and filled circles) simultaneously during exposure to 50 μ

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βA 25-35. As we have shown previously, βA caused fluctuations in [Ca2+]c in the astrocytes. Although the abrupt mitochondrial depolarizations were clearly associated with [Ca2+]c signals, they did not show a tight or fixed correlation in time or amplitude. Thus, large changes in Δψm followed large changes in [Ca2+]c, and some small transient depolarizations of Δψm could be seen associated with [Ca2+]c transients (asterisks in Eii).