title: Inhibition of choline acetyltransferase as a mechanism for cholinergic dysfunction induced by amyloid-β peptide oligomers.
abstract: Dysregulated cholinergic signaling is an early hallmark of Alzheimer disease (AD), usually ascribed to degeneration of cholinergic neurons induced by the amyloid-β peptide (Aβ). It is now generally accepted that neuronal dysfunction and memory deficits in the early stages of AD are caused by the neuronal impact of soluble Aβ oligomers (AβOs). AβOs build up in AD brain and specifically attach to excitatory synapses, leading to synapse dysfunction. Here, we have investigated the possibility that AβOs could impact cholinergic signaling. The activity of choline acetyltransferase (ChAT, the enzyme that carries out ACh production) was inhibited by ~50% in cultured cholinergic neurons exposed to low nanomolar concentrations of AβOs. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction, lactate dehydrogenase release, and [(3)H]choline uptake assays showed no evidence of neuronal damage or loss of viability that could account for reduced ChAT activity under these conditions. Glutamate receptor antagonists fully blocked ChAT inhibition and oxidative stress induced by AβOs. Antioxidant polyunsaturated fatty acids had similar effects, indicating that oxidative damage may be involved in ChAT inhibition. Treatment with insulin, previously shown to down-regulate neuronal AβO binding sites, fully prevented AβO-induced inhibition of ChAT. Interestingly, we found that AβOs selectively bind to ~50% of cultured cholinergic neurons, suggesting that ChAT is fully inhibited in AβO-targeted neurons. Reduction in ChAT activity instigated by AβOs may thus be a relevant event in early stage AD pathology, preceding the loss of cholinergic neurons commonly observed in AD brains.
authors.affiliation: Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21944-590, Brazil.
authors.forename: Nilson
authors.initials: N
authors.lastname: Nunes-Tavares
authors.forename: Luís Eduardo
authors.initials: LE
authors.lastname: Santos
authors.forename: Bernardo
authors.initials: B
authors.lastname: Stutz
authors.forename: Jordano
authors.initials: J
authors.lastname: Brito-Moreira
authors.forename: William L
authors.initials: WL
authors.lastname: Klein
authors.forename: Sérgio T
authors.initials: ST
authors.lastname: Ferreira
authors.forename: Fernando G
authors.initials: FG
authors.lastname: de Mello
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism* / Q000473:pathology; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D030161:Avian Proteins / Q000235:genetics / Q000378:metabolism*; D018929:Cell Culture Techniques; D002478:Cells, Cultured; D002645:Chickens; D002795:Choline O-Acetyltransferase / Q000378:metabolism*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism* / Q000473:pathology; D018384:Oxidative Stress
chemical_list: D016229:Amyloid beta-Peptides; D000975:Antioxidants; D030161:Avian Proteins; D018691:Excitatory Amino Acid Antagonists; D002795:Choline O-Acetyltransferase