amyloid-beta-peptides and Mitochondrial-Diseases

Mitochondrial dysfunction is observed in Alzheimer's disease (AD) brain and peripheral tissues. Amyloid-β (Aβ) peptides are known to interact with several proteins inside the mitochondria, leading to mitochondrial dysfunction. Recent studies have provided substantial evidence that mitochondria serve as direct targets for Aβ-mediated neuronal toxicity. The observations that Aβ progressively accumulates in cortical mitochondria from AD patients and transgenic AD type mouse models suggest the role of mitochondrial Aβ in the pathogenesis or development of AD. Herein, we studied the downstream signaling pathways induced by Aβ-mediated mitochondrial metabolism alterations and its consequences on cellular fate. We found that Aβ peptides induced an increase in NAD+levels and a decrease in ATP levels, which was related with decreases in acetylated tubulin levels and tau hyperphosphorylation. As a result of microtubule disruption, alterations in macroautophagy, like a decrease in autophagossome degradation and altered cellular distribution of LC3B, were found. Taxol, a microtubule stabilizer drug, was able to restore microtubule network and to prevent cell death induced by Aβ peptides. Our data shows for the first time that mitochondrial and cytosolic Aβ oligomers were significantly reduced upon microtubule dynamics re-establishment. These observations point out that an intervention at a microtubule level may be effective as a disease modifying therapy.

Topics: Adenine Nucleotides; Amyloid beta-Peptides; Antineoplastic Agents, Phytogenic; Autophagy; Blotting, Western; Caspases; Cell Line, Tumor; Cell Proliferation; Coloring Agents; Electron Transport Complex IV; Enzyme Activation; Humans; Lysosomes; Microscopy, Confocal; Microtubules; Mitochondrial Diseases; Mitochondrial Membranes; NAD; Paclitaxel; Peptide Fragments; Signal Transduction; Tetrazolium Salts; Thiazoles; Tubulin

Increasing evidence is implicating mitochondrial dysfunction as a central factor in the etiology of Alzheimer's disease (AD). The most significant risk factor in AD is advanced age and an important neuropathological correlate of AD is the deposition of amyloid-beta peptide (Abeta40 and Abeta42) in the brain. An AD-like dementia is also common in older individuals with Down syndrome (DS), though with a much earlier onset. We have shown that somatic mitochondrial DNA (mtDNA) control region (CR) mutations accumulate with age in post-mitotic tissues including the brain and that the level of mtDNA mutations is markedly elevated in the brains of AD patients. The elevated mtDNA CR mutations in AD brains are associated with a reduction in the mtDNA copy number and in the mtDNA L-strand transcript levels. We now show that mtDNA CR mutations increase with age in control brains; that they are markedly elevated in the brains of AD and DS and dementia (DSAD) patients; and that the increased mtDNA CR mutation rate in DSAD brains is associated with reduced mtDNA copy number and L-strand transcripts. The increased mtDNA CR mutation rate is also seen in peripheral blood DNA and in lymphoblastoid cell DNAs of AD and DSAD patients, and distinctive somatic mtDNA mutations, often at high heteroplasmy levels, are seen in AD and DSAD brain and blood cells DNA. In aging, DS, and DSAD, the mtDNA mutation level is positively correlated with beta-secretase activity and mtDNA copy number is inversely correlated with insoluble Abeta40 and Abeta42 levels. Therefore, mtDNA alterations may be responsible for both age-related dementia and the associated neuropathological changes observed in AD and DSAD.

Topics: Adolescent; Adult; Aged; Aged, 80 and over; Alzheimer Disease; Amyloid beta-Peptides; Child; Child, Preschool; Dementia; DNA, Mitochondrial; Down Syndrome; Female; Humans; Infant; Infant, Newborn; Male; Middle Aged; Mitochondrial Diseases; Peptide Fragments; Young Adult