Alzheimer's disease (AD) is characterized by amyloid-beta (A␤)-containing plaques, neurofibrillary tangles, and neuron and synapse loss. Tangle formation has been reproduced in P301L tau transgenic pR5 mice, whereas APP sw PS2 N141I double-transgenic APP152 mice develop A␤ plaques. Cross-breeding generates triple transgenic ( triple AD) mice that combine both pathologies in one model. To determine functional consequences of the combined A␤ and tau pathologies, we performed a proteomic analysis followed by functional validation. Specifically, we obtained vesicular preparations from triple AD mice, the parental strains, and nontransgenic mice, followed by the quantitative mass-tag labeling proteomic technique iTRAQ and mass spectrometry. Within 1,275 quantified proteins, we found a massive deregulation of 24 proteins, of which one-third were mitochondrial proteins mainly related to complexes I and IV of the oxidative phosphorylation system (OXPHOS). Notably, deregulation of complex I was tau dependent, whereas deregulation of complex IV was A␤ dependent, both at the protein and activity levels. Synergistic effects of A␤ and tau were evident in 8-month-old triple AD mice as only they showed a reduction of the mitochondrial membrane potential at this early age. At the age of 12 months, the strongest defects on OXPHOS, synthesis of ATP, and reactive oxygen species were exhibited in the triple AD mice, again emphasizing synergistic, age-associated effects of A␤ and tau in perishing mitochondria. Our study establishes a molecular link between A␤ and tau protein in AD pathology in vivo, illustrating the potential of quantitative proteomics.amyloid-beta peptide ͉ electron transport chain ͉ energy metabolism ͉ mitochondrial complexes ͉ tau protein A lzheimer's disease (AD) is a devastating neurodegenerative disorder affecting Ͼ15 million people worldwide (1). The key histopathological features are amyloid-beta (A␤)-containing plaques and microtubule-associated protein tau-containing neurofibrillary tangles (NFTs), along with neuronal and synapse loss in selected brain areas (2, 3). In determining the role of distinct proteins in these processes, traditionally, candidate-driven approaches have been pursued, linking neuronal dysfunction to the distribution of known proteins in healthy compared with degenerating neurons, or in transgenic compared with control brain. In comparison, proteomics offers a powerful nonbiased approach as shown by us previously (4, 5).APP152 (APP/PS2) double-transgenic mice model the A␤ plaque pathology of AD (6); they coexpress the N141I mutant form of PS2 together with the APP sw mutant found in familial cases of AD. The mice display age-related cognitive deficits associated with discrete brain A␤ deposition and inflammation (6). pR5 mice model the tangle pathology of AD (7-9). They express P301L mutant tau found in familial cases of frontotemporal dementia (FTD), a dementia related to AD. The pR5 mice show a hippocampus-and amygdala-dependent behavioral impairment related to AD (10). Crossing of ...

Evidence suggests that amyloid-beta (Ab) protein is a key factor in the pathogenesis of Alzheimer's disease (AD) and it has been recently proposed that mitochondria are involved in the biochemical pathway by which Ab can lead to neuronal dysfunction. Here we investigated the specific effects of Ab on mitochondrial function under physiological conditions. Mitochondrial respiratory functions and energy metabolism were analyzed in control and in human wild-type amyloid precursor protein (APP) stably transfected human neuroblastoma cells (SH-SY5Y). Mitochondrial respiratory capacity of mitochondrial electron transport chain (ETC) in vital cells was measured with a high-resolution respirometry system (Oxygraph-2k). In addition, we determined the individual activities of mitochondrial complexes I-IV that compose ETC and ATP cellular levels. While the activities of complexes I and II did not change between cell types, complex IV activity was significantly reduced in APP cells. In contrast, activity of complex III was significantly enhanced in APP cells, as compensatory response in order to balance the defect of complex IV. However, this compensatory mechanism could not prevent the strong impairment of total respiration in vital APP cells. As a result, the respiratory control ratio (state3/state4) together with ATP production decreased in the APP cells in comparison with the control cells. Chronic exposure to soluble Ab protein may result in an impairment of energy homeostasis due to a decreased respiratory capacity of mitochondrial electron transport chain which, in turn, may accelerate neurons demise.

Background: Arginine 85 of NDUFS2, a subunit of mitochondrial complex I, is symmetrically dimethylated.Results: NDUFAF7, a protein methylase in the matrix of mitochondria, modifies arginine 85 of NDUFS2 during assembly of complex I.Conclusion: Methylation of arginine 85 of NDUFS2 is required for assembly of complex I.Significance: The arginine protein methylase, NDUFAF7, is an assembly factor for human complex I.

We recently provided evidence for a mitochondrial dysfunction in P301L tau transgenic mice, a strain modeling the tau pathology of Alzheimer's disease (AD) and frontotemporal dementia (FTD). In addition to tau aggregates, the AD brain is further characterized by Aβ peptide-containing plaques. When we addressed the role of Aβ, this indicated a synergistic action of tau and Aβ pathology on the mitochondria. In the present study, we compared the toxicity of different Aβ42 conformations in light of recent studies suggesting that oligomeric rather than fibrillar Aβ might be the actual toxic species. Interestingly, both oligomeric and fibrillar, but not disaggregated (mainly monomeric) Aβ42 caused a decreased mitochondrial membrane potential in cortical brain cells obtained from FTD P301L tau transgenic mice. This was not observed with cerebellar preparations indicating selective vulnerability of cortical neurons. Furthermore, we found reductions in state 3 respiration, the respiratory control ratio, and uncoupled respiration when incubating P301L tau mitochondria either with oligomeric or fibrillar preparations of Aβ42. Finally, we found that aging specifically increased the sensitivity of mitochondria to oligomeric Aβ42 damage indicating that oligomeric and fibrillar Aβ42 are both toxic, but exert different degrees of toxicity.

Tauopathies like the "frontotemporal dementia with Parkinsonism linked to chromosome 17" (FTDP-17) are characterized by an aberrant accumulation of intracellular neurofibrillary tangles composed of hyperphosphorylated tau. For FTDP-17, a pathogenic tau mutation P301L was identified. Impaired mitochondrial function including disturbed dynamics such as fission and fusion are most likely major pathomechanisms of most neurodegenerative diseases. However, very little is known if tau itself affects mitochondrial function and dynamics. We addressed this question using SY5Y cells stably overexpressing wild-type (wt) and P301L mutant tau. P301L overexpression resulted in a substantial complex I deficit accompanied by decreased ATP levels and increased susceptibility to oxidative stress. This was paralleled by pronounced changes in mitochondrial morphology, decreased fusion and fission rates accompanied by reduced expression of several fission and fusion factors like OPA-1 or DRP-1. In contrast, overexpression of wt tau exhibits protective effects on mitochondrial function and dynamics including enhanced complex I activity. Our findings clearly link tau bidirectional to mitochondrial function and dynamics, identifying a novel aspect of the physiological role of tau and the pathomechanism of tauopathies.

The histopathological characteristics of Alzheimer’s disease (AD) are amyloid-β (Aβ) containing plaques and neurofibrillary tangles (NFTs) as well as neuronal and synaptic loss. Until today, the underlying mechanisms of the interplay of plaques and tangles remained unresolved. There is increasing evidence that mitochondrial dysfunction might be a possible link, as revealed by studies in several APP and tau transgenic mouse models. Recently, we examined mitochondrial function in a novel triple transgenic mouse model (pR5/APP/PS2)—tripleAD mice—that combines both pathologic features of the disease in brain. Using comparative, quantitative proteomics (iTRAQ) and mass spectroscopy, we found a massive deregulation of 24 proteins, of which one third were mitochondrial proteins mainly related to complexes I and IV of the oxidative phosphorylation system (OXPHOS). Remarkably, deregulation of complex I was related to tau, whereas deregulation of complex IV was Aβ dependent, both at the protein and activity levels. The tripleAD mice showed synergistic effects of Aβ and tau already at the age of 8 months, resulting in a depolarized mitochondrial membrane potential. At 12 months, the strongest defects on OXPHOS, synthesis of ATP and reactive oxygen species, were exhibited in the tripleAD mice, again emphasizing synergistic, age-associated effects of Aβ and tau in impairing mitochondria. This review highlights the convergence of Aβ and tau on mitochondria and establishes a molecular link in AD pathology in vivo.

Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM) are leading causes of morbidity and mortality in the elderly. Both diseases are characterized by amyloid deposition in target tissues: aggregation of amylin in T2DM is associated with loss of insulin-secreting beta-cells, while amyloid beta (A beta) aggregation in AD brain is associated with neuronal loss. Here, we used quantitative iTRAQ proteomics as a discovery tool to show that both A beta and human amylin (HA) deregulate identical proteins, a quarter of which are mitochondrial, supporting the notion that mitochondrial dysfunction is a common target in these two amyloidoses. A functional validation revealed that mitochondrial complex IV activity was significantly reduced after treatment with either HA or A beta, as was mitochondrial respiration. In comparison, complex I activity was reduced only after treatment with HA. A beta and HA, but not the non-amyloidogenic rat amylin, induced significant increases in the generation of ROS. Co-incubation of HA and A beta did not produce an augmented effect in ROS production, again suggesting common toxicity mechanisms. In conclusion, our data suggest that A beta and HA both exert toxicity, at least in part, via mitochondrial dysfunction, thus restoring their function may be beneficial for both AD and T2DM.

Background: Mitochondrial dysfunction has been identified in neurodegenerative disorders including Alzheimer’s disease, where accumulation of β-amyloid (Aβ) and oxidative stress seem to play central roles in the pathogenesis, by probably directly leading to mitochondrial dysfunction. Objective: In order to study the in vivo effect of Aβ load during aging, we evaluated the mitochondrial function of brain cells from transgenic mice bearing either mutant amyloid precursor protein (tgAPP) or mutant amyloid precursor protein and mutant PS1 (tgAPP/PS1) as well as from nontransgenic wild-type littermates. tgAPP mice exhibit onset of Aβ plaques at an age of 6 months, but the intracellular soluble Aβ load is already increased at 3 months of age. In contrast, onset of Aβ plaques starts at an age of 3 months in tgAPP/PS1 mice. In addition, we investigated the effects of different Aβ preparations on mitochondrial function of brain cells from tau transgenic mice. Results: Of note, mitochondrial damage such as reduced mitochondrial membrane potential and ATP levels can already be detected in the brains from these mice before the onset of plaques. In agreement with our findings in tgAPP mice, soluble Aβ induced mitochondrial dysfunction in brain cells from tau transgenic mice. Conclusion: Our results indicate that mitochondrial dysfunction is exacerbated by the presence of soluble Aβ species as a very early event during pathogenesis.