It is suggested that intracellular tau protein (τ), when released extracellularly upon neuron degeneration, could evoke direct toxic effects on the cholinergic neurotransmitter system through muscarinic receptors and thus contribute to the pathogenesis of Alzheimer's disease. In this study, we evaluated the in vitro effects of six naturally occurring monomeric τ isoforms on rat hippocampal synaptosomal choline transporters CHT1 (large transmembrane proteins associated with high-affinity choline transport and vulnerable to actions of amyloid β peptides (Aβ) applied in vitro or in vivo). Some τ isoforms at nM concentrations inhibited choline transport in a dose- and time-dependent saturable manner (352 = 441 > 410 = 383 > 381 = 412) and effects were associated with changes in the Michaelis constant rather than in maximal velocity. Moreover, the actions of τ 352/441 were not influenced by previous depolarisation of synaptosomes or by previous depletion of membrane cholesterol. Specific binding of [3H]hemicholinium-3 was not significantly altered by τ 352/441 at higher nM concentrations. Results of in vitro tests on CHT1 transporters from cholesterol-depleted synaptosomes supported interactions between Aβ 1-40 and τ 352. In addition, we developed surface plasmon resonance biosensors to monitor complexes of Aβ 1-42 and τ 352 using a sandwich detection format. It seems, therefore, that protein τ, similar to Aβ peptides, can contribute to the pathogenesis of Alzheimer's disease through its actions on CHT1 transporters. However, the interaction mechanisms are quite different (τ probably exerts its effects through direct interactions of microtubule binding repeats with extracellular portions of the CHT1 protein without influencing the choline recognition site, Aβ rather through lipid rafts in the surrounding membranes). An N-terminal insert of τ is not necessary but the N-terminal projection domain plays a role. The developed biosensor will be used to detect Aβ-τ complexes in cerebrospinal fluid in order to evaluate them as prospective biomarkers of Alzheimer's disease.

• MeSH
• Amyloid beta-Peptides metabolism   MeSH
• Hippocampus metabolism   MeSH
• Rats MeSH
• Rats, Wistar MeSH
• Surface Plasmon Resonance MeSH
• Cation Transport Proteins metabolism   MeSH
• tau Proteins metabolism   MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Amyloid beta-Peptides MeSH
• CHT1 protein, rat MeSH Browser
• Cation Transport Proteins MeSH
• tau Proteins MeSH

Amyloid β peptides appear to play a role in physiological processes; however, they are also involved in the pathogenesis of Alzheimer disease. Their actions under normal conditions are probably mediated by soluble monomeric L-isoforms at low concentrations, perhaps via highly specific interactions. On the contrary, toxic effects of aggregated natural L-isoforms/synthetic D-isoforms on membranes are very similar, but synthetic reverse/random L: -isoforms without pronounced aggregation properties are not toxic. Our previous work reported interactions of non-aggregated/aggregated L-isoforms of amyloid β peptides 1-40/1-42 with racemic 24-hydroxycholesterol. In this study, stereospecificity in the interactions of natural 24(S)hydroxycholesterol (cerebrosterol) or synthetic 24(R)hydroxycholesterol with soluble fragment 1-40 was evaluated by means of an in vitro test based on increased vulnerability of the hemicholinium-3 sensitive high-affinity choline uptake system in rat hippocampal cholesterol-depleted synaptosomes to the actions of amyloid β; computational simulations were also performed. Our results suggest that: (1) 24(S)hydroxycholesterol interacts with L-peptide 1-40 but not with the reverse L-peptide 40-1, (2) 24(R)hydroxycholesterol does not interact with L-peptide 1-40 or reverse 40-1, and (3) both enantiomers can probably interact with D-peptide 1-40. Therefore, the binding of 24(S)hydroxycholesterol is not fully stereospecific and the interaction could not reflect a physiological mechanism. Data from the computational simulation indicate that the hydrophobic core of the amyloid β molecule interacts with the hydrophobic part of 24(S)hydroxycholesterol, but no hydrogen bonds with high stability were found. Using this procedure, globular amyloid β could retain 24(S)hydroxycholesterol and thus contribute to its pathological accumulation in the brains of patients with Alzheimer disease.

• MeSH
• Amyloid beta-Peptides metabolism   MeSH
• Hippocampus metabolism   MeSH
• Hydroxycholesterols metabolism   MeSH
• Rats MeSH
• Peptide Fragments metabolism   MeSH
• Rats, Wistar MeSH
• Protein Binding MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• 24-hydroxycholesterol MeSH Browser
• amyloid beta-protein (1-40) MeSH Browser
• Amyloid beta-Peptides MeSH
• Hydroxycholesterols MeSH
• Peptide Fragments MeSH