| 1. |
- Englund, Hillevi, 1980-
(författare)
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Soluble amyloid-β aggregates in Alzheimer’s disease
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Soluble oligomeric aggregates of the amyloid-β (Aβ) peptide are suggested to initiate Alzheimer's disease (AD), leading to impaired synapse signalling, widespread neuronal death and loss of cognitive functions. These aggregates seem tightly linked to disease progression, and have therefore gained much attention as potential novel disease markers. In this thesis soluble oligomeric Aβ aggregates in general, and the Aβ protofibril species in particular, have been investigated with the aim to quantify and determine their role in AD pathogenesis. Sandwich-ELISAs specifically measuring Aβ42 peptides are widely used both in AD research and as complements for clinical diagnosis. Here it was demonstrated that presence of soluble Aβ aggregates disturbs such analyses, making it difficult to interpret the results. This discovery was made through analyses of samples from cell- and mouse models carrying the AD causing 'Arctic' APP mutation. When analyzed by ELISA, Aβ42 levels were reduced in Arctic samples, in contrast to levels measured by denaturing SDS-PAGE Western blot. The same divergence in Aβ42-levels between analyses was observed in CSF samples from Down syndrome infants. The discrepancy between methods was hypothesized to be due to presence of soluble Aβ aggregates leading to impaired ELISA detection caused by epitope masking. This was confirmed by developing a protofibril specific ELISA, by which samples from Arctic cell- and mouse models were demonstrated to have enhanced Aβ protofibril levels. AD patients have reduced ELISA-measured Aβ42-levels in CSF compared to healthy controls. To test if this reduction was due to oligomeric Aβ species present in AD CSF, Aβ42-levels were analyzed under both denaturing and non-denaturing conditions. These two measures were combined and an Aβ42 oligomer ratio established. Higher ratios were found in AD patients than healthy controls, implying that Aβ oligomers are present in CSF during Alzheimer pathogenesis. The observations from AD patients and young Down syndrome individuals suggest that Aβ42 oligomer formation is an early mechanism of AD pathogenesis, which potentially could be used as a biomarker to monitor disease development.
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| 2. |
- Lord, Anna, 1979-
(författare)
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Targeting Early Stages of Alzheimer’s Disease in a Transgenic Model
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Arctic mutation causes early-onset Alzheimer’s disease (AD), and makes amyloid-β (Aβ) peptides more prone to form Aβ protofibrils. The aims of this thesis were to investigate the mechanisms of the Arctic mutation in vivo, and to use transgenic models to determine the role of early intermediates of Aβ aggregation, like protofibrils, in the pathogenesis. In addition, we aimed to evaluate protofibrils as a therapeutic target.Transgenic models with Arctic and Swedish mutations (tg-ArcSwe), and with the Swedish mutation alone (tg-Swe) were created. The Arctic mutation favored amyloidogenic processing of amyloid-β precursor protein (APP) in transgenic mice and cultured cells. The observed shift in the subcellular location and processing of APP led to increased production of intracellular Aβ in vitro, and also partly explained the early accumulation of intraneuronal Aβ in tg-ArcSwe mice. The intraneuronal Aβ in combination with enhanced levels of protofibrils appeared long before extracellular plaques emerged. Elevated protofibril levels were associated with intraneuronal Aβ and linked to spatial learning deficits in young mice, suggesting that protofibrils cause AD-related cognitive deficits. The Arctic mutation also enhanced senile plaque pathology in aged tg-ArcSwe mice, and the accelerated plaque deposition was accompanied by decreased intraneuronal Aβ. This suggests a dynamic equilibrium between the early accumulation of intraneuronal Aβ and the later senile plaque pathology.Aβ protofibrils were evaluated as a therapeutic target in tg-ArcSwe mice with passive immunization using a protofibril-selective antibody. This treatment cleared protofibrils without removing senile plaques. However, plaque formation was prevented if treatment began early, indicating that protofibrils are intermediate species of Aβ fibrillization in vivo. Targeting senile plaques with immunotherapy requires early diagnosis and intervention, whereas protofibrils can be specifically cleared from brain despite substantial AD-like deposition of insoluble Aβ. The early and persistent presence of protofibrils throughout Aβ amyloidosis makes them a promising target for future diagnostic and therapeutic strategies in AD.
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| 3. |
- Sehlin, Dag
(författare)
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Aβ Conformation Dependent Antibodies and Alzheimer's Disease
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Soluble intermediates of the amyloid-β (Aβ) aggregation process are suggested to play a central role in the pathogenesis of Alzheimer’s disease (AD) by causing synaptic dysfunction and neuronal loss. In this thesis, soluble Aβ aggregates have been studied with a particular focus on the Aβ protofibril, which has served as the antigen for developing conformation dependent monoclonal antibodies. Antibodies generated from mice immunized with Aβ protofibrils were characterized regarding Aβ binding properties and the amino acid sequences of their antigen binding sites. A conformation dependent IgG antibody, mAb158, was further characterized and found to bind to Aβ protofibrils with a 200-fold higher affinity than to monomeric Aβ without affinity for soluble amyloid-β precursor protein (AβPP) or other amyloidogenic proteins. A sandwich enzyme-linked immunosorbent assay (ELISA) based on mAb158 was used to measure soluble Aβ protofibrils in brain extracts from AβPP-transgenic mice. Low levels of protofibrils could also be detected in human AD brain. However, positive signals generated from measurements in AD and control CSF samples were attributed to interference from heterophilic antibodies (HA), generating false positive signals by cross-binding the assay antibodies; consequently, a study on HA interference in Aβ oligomer ELISAs was initiated. A large set of plasma and CSF samples from AD and non-AD subjects were analyzed with and without measures taken to block HA interference, revealing that virtually all signals above the assay limit of detection were false and generated by HA interference. Many types of soluble Aβ aggregates have been described and suggested to impair neuron and synapse function. To investigate the soluble Aβ pool, synthetic Aβ and brain extracts from AβPP-transgenic mice and AD patients were ultracentrifuged on a density gradient to separate Aβ by size under native conditions. Four distinct gradient fractions were defined based on the appearance of synthetic Aβ in atomic force microscopy (AFM) and immunoreactivity in our protofibril specific sandwich ELISA. Interestingly, most Aβ from AD patients and AβPP-transgenic mice separated in the same fraction as toxic synthetic protofibrils.
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