Amyloid-beta Leads to Impaired Cellular Respiration, Energy Production and Mitochondrial Electron Chain Complex Activities in Human Neuroblastoma Cells

Abstract

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.

Constitutive cAMP response element binding protein (CREB) activation by Alzheimer's disease presenilin-driven inositol trisphosphate receptor (InsP 3 R) Ca 2+ signaling

“…Neuronal exposure to Aβ oligomers may have detrimental consequences, including synapse disruption, oxidative stress, altered [Ca 2+ ] i signaling, and cell death (41,42,(61)(62)(63)(64). Here we have confirmed that FAD PS enhances susceptibility to Aβ toxicity and have demonstrated a molecular mechanism through which altered [Ca 2+ ] i homeostasis plays a role in this phenotype.…”

Amyloid-β and tau synergistically impair the oxidative phosphorylation system in triple transgenic Alzheimer's disease mice

“…Energy deficiency and mitochondrial dysfunction have been recognized as a prominent, early event in AD, but the mechanisms leading to mitochondrial failure are not well understood (15,(17)(18)(19)(20)(21)(22)(23)(24). Recently, we had shown in vivo that P301L mutant tau was capable of inducing mitochondrial dysfunction and increasing levels of ROS in pR5 mice (4).…”

“…Mitochondria were isolated from mouse forebrains to investigate mitochondrial OXPHOS and respiratory capacity. Mitochondrial oxygen consumption was measured at 37°C using an Oroboros Oxygraph-2k system (4,21). Several mitochondrial enzyme activities (complex I, complex IV, and citrate synthase) were examined (13, 21) (see SI Methods for details).…”

The Mitochondrial Secret(ase) of Alzheimer's Disease

“…1). Supporters of the amyloid cascade hypothesis have used it to explain AD-related mitochondrial pathology because: 1) AβPP and Aβ accumulates in mitochondria from brains of transgenic mice and AD subjects [144][145][146][147]; 2) binding of Aβ to the mitochondrial proteins Aβ-binding alcohol dehydrogenase and cyclophilin D is associated with increased oxidative stress, cytochrome c release, reduced mitochondrial membrane potential, and neuronal cell death [146,148]; 3) features of reduced Krebs cycle and ETC enzymatic activity, impaired state 3 and state 4 respiration, and in vivo elevation of oxidative stress demonstrated in AD and transgenic mouse brains were associated with Aβ [126,[149][150][151][152][153][154][155]; and 4) the direct reduction of cytochrome oxidase expression and activity by Aβ 42 and Aβ 25−35 (a toxic Aβ fragment) supported this hypothesis [48,156,157]. Though evidence for Aβ-induced pathology is plentiful, PET-scan measured reductions in brain glucose metabolism in MCI and AD individuals [158][159][160][161] warrant a further look at the role mitochondrial bioenergetics play.…”