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.

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.

BackgroundEnergy deficiency and mitochondrial failure have been recognized as a prominent, early event in Alzheimer's disease (AD). Recently, we demonstrated that chronic exposure to amyloid-beta (Aβ) in human neuroblastoma cells over-expressing human wild-type amyloid precursor protein (APP) resulted in (i) activity changes of complexes III and IV of the oxidative phosphorylation system (OXPHOS) and in (ii) a drop of ATP levels which may finally instigate loss of synapses and neuronal cell death in AD. Therefore, the aim of the present study was to investigate whether standardized Ginkgo biloba extract LI 1370 (GBE) is able to rescue Aβ-induced defects in energy metabolism.Methodology/Principal FindingsWe used a high-resolution respiratory protocol to evaluate OXPHOS respiratory capacity under physiological condition in control (stably transfected with the empty vector) and APP cells after treatment with GBE. In addition, oxygen consumption of isolated mitochondria, activities of mitochondrial respiratory enzymes, ATP and reactive oxygen species (ROS) levels as well as mitochondrial membrane mass and mitochondrial DNA content were determined. We observed a general antioxidant effect of GBE leading to an increase of the coupling state of mitochondria as well as energy homeostasis and a reduction of ROS levels in control cells and in APP cells. GBE effect on OXPHOS was even preserved in mitochondria after isolation from treated cells. Moreover, these functional data were paralleled by an up-regulation of mitochondrial DNA. Improvement of the OXPHOS efficiency was stronger in APP cells than in control cells. In APP cells, the GBE-induced amelioration of oxygen consumption most likely arose from the modulation and respective normalization of the Aβ-induced disturbance in the activity of mitochondrial complexes III and IV restoring impaired ATP levels possibly through decreasing Aβ and oxidative stress level.Conclusions/SignificanceAlthough the underlying molecular mechanisms of the mode of action of GBE remain to be determined, our study clearly highlights the beneficial effect of GBE on the cellular OXPHOS performance and restoration of Aβ-induced mitochondrial dysfunction.

Heavy metals are increasingly being implicated as causative agents in neurodegenerative diseases such as Alzheimer's disease (AD). Cobalt, a positively charged transition metal, has previously been shown to be in elevated levels in the brain of AD patients compared with age-matched controls. In this study, we investigate the effects of cobalt as an inducer of oxidative stress/cell cytotoxicity and the resultant metabolic implications for neural cells. We show that cobalt is able to induce cell cytotoxicity (reduced MTT metabolism) and oxidative stress (reduced cellular glutathione). The pre-treatment of cells with the pineal indoleamine melatonin, prevented cell cytotoxicity and the induction of oxidative stress. Cobalt treatment of SHSY5Y cells increased the release of beta-amyloid (Abeta) compared with untreated controls (ratio Abeta 40/42). Melatonin pre-treatment reversed the deleterious effects of cobalt. These findings are significant as cobalt is an essential nutritional requirement, usually bound to cobalamin (vitamin B12), for all animals which in the unbound form could lead to neurotoxicity.