Further evidence on mitochondrial targeting of ß-amyloid and specificity of ß-amyloid-induced mitotoxicity in neurons.

ABSTRACT

BACKGROUND/AIMS: Impaired mitochondrial function has been described in Alzheimer's disease. We previously reported that, in neuronal cells, ß-amyloid 1-42 (Aß(1-42)) is targeted to mitochondria. We have also reported that, when incubated with isolated rat brain mitochondria, Aß(1-42) inhibits complex IV, uncouples the mitochondrial respiratory chain, and promotes opening of the membrane permeability transition pore. Here, we further analyzed the targeting and mitotoxicity of Aß(1-42). METHODS AND RESULTS: Immunoelectron microscopy revealed that the mitochondrial targeting of Aß(1-42) was concentration- and time-dependent. Incubation of human neuroblastoma cells with Aß(1-42) increased the release of adenylate kinase, a mitochondrial enzyme released after membrane permeability transition pore opening. However, it failed to trigger DNA fragmentation and apoptosis, suggesting that the ability of this peptide to uncouple the respiratory chain underlies its mitotoxicity and cytotoxicity. Aß(1-42) targeting to mitochondria was blocked by caprospinol, a steroid derivative shown to protect neuronal cells against Aß(1-42)-induced neurotoxicity. Further experiments revealed that the mitotoxic effect of Aß(1-42) is specific to its primary amino acid sequence and suggested that it may be also related to its tertiary structure. Importantly, the mitotoxic effect of Aß(1-42) was not restricted to brain cells, indicating that it is not cell- or tissue-specific. CONCLUSION: Taken together, these results suggest that extracellular Aß(1-42) targets neuronal mitochondria to exert its toxic effects.