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Background: Despite the clear physical association between activated astrocytes and amyloid-β (Aβ) plaques, the importance of astrocytes and their therapeutic potential in Alzheimer's disease remain elusive. Soluble Aβ aggregates, such as protofibrils, have been suggested to be responsible for the widespread neuronal cell death in Alzheimer's disease, but the mechanisms behind this remain unclear. Moreover, ineffective degradation is of great interest when it comes to the development and progression of neurodegeneration. Based on our previous results that astrocytes are extremely slow in degrading phagocytosed material, we hypothesized that astrocytes may be an important player in these processes. Hence, the aim of this study was to clarify the role of astrocytes in clearance, spreading and neuronal toxicity of Aβ. Results: To examine the role of astrocytes in Aβ pathology, we added Aβ protofibrils to a co-culture system of primary neurons and glia. Our data demonstrates that astrocytes rapidly engulf large amounts of Aβ protofibrils, but then store, rather than degrade the ingested material. The incomplete digestion results in a high intracellular load of toxic, partly N-terminally truncated Aβ and severe lysosomal dysfunction. Moreover, secretion of microvesicles containing N-terminally truncated Aβ, induce apoptosis of cortical neurons. Conclusions: Taken together, our results suggest that astrocytes play a central role in the progression of Alzheimer's disease, by accumulating and spreading toxic Aβ species. [ABSTRACT FROM AUTHOR]

The Alzheimer' disease (AD)-related peptide amyloid-β (Aβ) has a propensity to aggregate into various assemblies including toxic soluble Aβ protofibrils. Several studies have reported the existence of anti-Aβ antibodies in humans. However, it is still debated whether levels of anti-Aβ antibodies are altered in AD patients compared to healthy individuals. Formation of immune complexes with plasmaAβ makes it difficult to reliably measure the concentration of circulating anti-Aβ antibodies with certain immunoassays, potentially leading to an underestimation. Here we have investigated anti-Aβ antibody production on a cellular level by measuring the amount of anti-Aβ antibody producing cells instead of the plasma level of anti-Aβ antibodies. To our knowledge, this is the first time the anti-Aβ antibody response in plasma has been compared in AD patients and age-matched healthy individuals using the enzyme-linked immunospot (ELISpot) technique. Both AD patients and healthy individuals had low levels of B cells producing antibodies binding Aβ40 monomers, whereas the number of cells producing antibodies toward Aβ42 protofibrils was higher overall and significantly higher in AD compared to healthy controls. This study shows, by an alternative and reliable method, that there is a specific immune response to the toxic Aβ protofibrils, which is significantly increased in AD patients. [ABSTRACT FROM AUTHOR]

Amyloid-β (Aβ) oligomers of different sizes and forms have recently been the focus for many Alzheimer's disease (AD) researchers. Various immunoassays have been used to detect low concentrations of these elusive Aβ species in different forms of human samples using little or no sample dilutions. However, the possibility that positive results may be caused by interference from heterophilic antibodies (HA) is often overlooked. HA, which recognize immunoglobulins from other species, are present in human plasma and cerebrospinal fluid (CSF) and may cause interference in sandwich immunoassays like enzyme-linked immunosorbent assays (ELISAs) by cross-binding the capture and detection antibodies of the assay. They thus may generate a false positive signal. Here we show that when assessing the Aβ oligomer content in plasma samples from 44 individuals with a sandwich ELISA, none of the 21 positive signals remained when the assay was repeated in the presence of factors blocking HA. Similarly, in CSF samples from 104 individuals, the signals from the 22 positive samples were strongly reduced when analyzed after anti-HA treatment. Taken together, HA interference is a problem that needs to be addressed when measuring low levels of an antigen in human plasma and CSF samples. [ABSTRACT FROM AUTHOR]

Soluble oligomeric aggregates of the amyloid-β peptide (Aβ) have been implicated in the pathogenesis of Alzheimer's disease (AD). Although the conformation adopted by Aβ within these aggregates is not known, a β-hairpin conformation is known to be accessible to monomeric Aβ. Here we show that this β-hairpin is a building block of toxic Aβ oligomers by engineering a double-cysteine mutant (called Aβcc) in which the β-hairpin is stabilized by an intramolecular disulfide bond. Aβ40cc and Aβ42cc both spontaneously form stable oligomeric species with distinct molecular weights and secondary-structure content, but both are unable to convert into amyloid fibrils. Biochemical and biophysical experiments and assays with conformation-specific antibodies used to detect Aβ aggregates in vivo indicate that the wild-type oligomer structure is preserved and stabilized in Aβcc oligomers. Stable oligomers are expected to become highly toxic and, accordingly, we find that β-sheet-containing Aβ42cc oligomers or protofibrillar species formed by these oligomers are 50 times more potent inducers of neuronal apoptosis than amyloid fibrils or samples of monomeric wild-type Aβ42, in which toxic aggregates are only transiently formed. The possibility of obtaining completely stable and physiologically relevant neurotoxic Aβ oligomer preparations will facilitate studies of their structure and role in the pathogenesis of AD. For example, here we show how kinetic partitioning into different aggregation pathways can explain why Aβ42 is more toxic than the shorter Aβ40, and why certain inherited mutations are linked to protofibril formation and early-onset AD. [ABSTRACT FROM AUTHOR]