amyloid-beta-peptides and 3-nitropropionic-acid

beta-site APP cleaving enzyme-1 (BACE1), the rate-limiting enzyme for beta-amyloid (Abeta) production, is elevated in Alzheimer's disease (AD). Here, we show that energy deprivation induces phosphorylation of the translation initiation factor eIF2alpha (eIF2alpha-P), which increases the translation of BACE1. Salubrinal, an inhibitor of eIF2alpha-P phosphatase PP1c, directly increases BACE1 and elevates Abeta production in primary neurons. Preventing eIF2alpha phosphorylation by transfection with constitutively active PP1c regulatory subunit, dominant-negative eIF2alpha kinase PERK, or PERK inhibitor P58(IPK) blocks the energy-deprivation-induced BACE1 increase. Furthermore, chronic treatment of aged Tg2576 mice with energy inhibitors increases levels of eIF2alpha-P, BACE1, Abeta, and amyloid plaques. Importantly, eIF2alpha-P and BACE1 are elevated in aggressive plaque-forming 5XFAD transgenic mice, and BACE1, eIF2alpha-P, and amyloid load are correlated in humans with AD. These results strongly suggest that eIF2alpha phosphorylation increases BACE1 levels and causes Abeta overproduction, which could be an early, initiating molecular mechanism in sporadic AD.

Topics: Age Factors; Aged, 80 and over; Alzheimer Disease; Amyloid beta-Peptides; Amyloid beta-Protein Precursor; Amyloid Precursor Protein Secretases; Animals; Antimetabolites; Aspartic Acid Endopeptidases; Cells, Cultured; Cerebral Cortex; Convulsants; Dactinomycin; Deoxyglucose; Disease Models, Animal; eIF-2 Kinase; Embryo, Mammalian; Enzyme Activation; Gene Expression Regulation; Glucose; Humans; Mice; Mice, Inbred C57BL; Mice, Transgenic; Neurons; Nitro Compounds; Peptide Fragments; Phosphorylation; Plaque, Amyloid; Propionates; Protein Synthesis Inhibitors; Time Factors; Transcription Factors; Transfection

Alzheimer's disease amyloid beta protein (Abeta) inhibits cellular reduction of the dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Kaneko et al. have previously hypothesized that Abeta works by suppressing mitochondrial succinate dehydrogenase (SDH), but Liu and Schubert have recently demonstrated that Abeta decreases cellular MTT reduction by accelerating the exocytosis of MTT formazan in neuronal cells. To ask which is the case in astrocytes, we compared the effects of Abeta and 3-nitropropionic acid (3-NP), a specific SDH inhibitor, on MTT reduction in cultured rat cortical astrocytes. Treatment with 3-NP (10 mM) decreased cellular activity of MTT reduction, regardless of the time of incubation with MTT. On the other hand. Abeta-induced inhibition of cellular MTT reduction was dependent on the time of incubation with MTT. The cells treated with Abeta (0.1-1000 nM) exhibited normal capacity for MTT reduction at an early stage of incubation ( < 30 min), but ceased to reduce MTT at the late stage (> 1 h). Microscopic examination revealed that Abeta treatment accelerated the appearance of needle-like MTT formazan crystals at the cell surface. These observations support that Abeta accelerates the exocytosis of MTT formazan in astrocytes. In addition to inhibition of MTT reduction, Abeta is known to induce morphological changes in astrocytes. Following addition of Abeta (20 microM), polygonal astrocytes changed into process-bearing stellate cells. To explore a possible linkage between these two effects of Abeta, we tested if astrocyte stellation is induced by agents that mimic the effect of Abeta on MTT reduction. Cholesterol (5 5000 nM) and lysophosphatidic acid (0.2-20 microg/ml) were found to accelerate the exocytosis of MTT formazan in a similar manner to Abeta, but failed to induce astrocyte stellation. Therefore, Abeta-induced inhibition of MTT reduction is unlikely to be directly linked to its effect on astrocyte morphology.

Topics: Amyloid beta-Peptides; Animals; Animals, Newborn; Antihypertensive Agents; Astrocytes; Biological Transport; Cells, Cultured; Cerebral Cortex; Cholesterol; Coloring Agents; Exocytosis; Formazans; Hippocampus; Lysophospholipids; Mitochondria; Neurons; Nitro Compounds; Oxidation-Reduction; Peptide Fragments; Propionates; Rats; Rats, Wistar; Succinate Dehydrogenase; Tetrazolium Salts; Time Factors