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Cerebral vascular amyloid seeds drive amyloid β -protein fibril assembly with a distinct anti-parallel structure

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ABSTRACT

Cerebrovascular accumulation of amyloid β-protein (Aβ), a condition known as cerebral amyloid angiopathy (CAA), is a common pathological feature of patients with Alzheimer's disease. Familial Aβ mutations, such as Dutch-E22Q and Iowa-D23N, can cause severe cerebrovascular accumulation of amyloid that serves as a potent driver of vascular cognitive impairment and dementia. The distinctive features of vascular amyloid that underlie its unique pathological properties remain unknown. Here, we use transgenic mouse models producing CAA mutants (Tg-SwDI) or overproducing human wild-type Aβ (Tg2576) to demonstrate that CAA-mutant vascular amyloid influences wild-type Aβ deposition in brain. We also show isolated microvascular amyloid seeds from Tg-SwDI mice drive assembly of human wild-type Aβ into distinct anti-parallel β-sheet fibrils. These findings indicate that cerebrovascular amyloid can serve as an effective scaffold to promote rapid assembly and strong deposition of Aβ into a unique structure that likely contributes to its distinctive pathology.

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Quantitative immunohistochemical analysis of cerebral human wild-type Aβ deposition in the different transgenic mice.Brain sections obtained from the different transgenic mouse lines at eighteen months of age were double immunolabelled for human Aβ using a polyclonal anti-Aβ (pAb-Aβ) antibody which recognizes both wild-type and CAA mutant Aβ, (green) (a–d) and mAb4G8, which recognizes wild-type Aβ, but not CAA mutant Aβ, (red) (e–h) and images were merged (i–l). Scale bars, 50 μm. (m) The levels of pAb-Aβ-positive total Aβ (green) and mAb4G8-positive wild-type Aβ (red) in parenchymal plaque and capillary deposits were determined in the different transgenic lines. The data presented are the mean±s.d. of 15 deposits per each line of mice.
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f6: Quantitative immunohistochemical analysis of cerebral human wild-type Aβ deposition in the different transgenic mice.Brain sections obtained from the different transgenic mouse lines at eighteen months of age were double immunolabelled for human Aβ using a polyclonal anti-Aβ (pAb-Aβ) antibody which recognizes both wild-type and CAA mutant Aβ, (green) (a–d) and mAb4G8, which recognizes wild-type Aβ, but not CAA mutant Aβ, (red) (e–h) and images were merged (i–l). Scale bars, 50 μm. (m) The levels of pAb-Aβ-positive total Aβ (green) and mAb4G8-positive wild-type Aβ (red) in parenchymal plaque and capillary deposits were determined in the different transgenic lines. The data presented are the mean±s.d. of 15 deposits per each line of mice.

Mentions: Subsequently, we determined whether CAA mutant or wild-type Aβ accumulation was responsible for the large increase in capillary amyloid volume observed in the bigenic Tg-SwDI/Tg2576 mice. To differentiate between human wild-type Aβ and human Dutch/Iowa CAA mutant Aβ peptides, we performed immunolabelling using the mAb4G8 antibody, which recognizes a mid-region epitope on human wild-type Aβ peptides33. The presence of the E22Q Dutch and D23N Iowa mutations abolishes the 4G8 epitope in human Aβ as confirmed by dot blot analysis (Supplementary Fig. 7). On the other hand, the rabbit polyclonal antibody directed towards an N-terminal epitope on Aβ (pAb-Aβ)34 equally recognizes wild-type and CAA mutant human Aβ peptides (Supplementary Fig. 7). Although pAb-Aβ recognized the characteristic small punctate capillary amyloid deposits in Tg-SwDI mice (Fig. 6d) these Aβ deposits were not appreciably labelled with mAb4G8 due to the presence of the Dutch and Iowa CAA mutations in the Aβ peptides (Fig. 6h). In contrast, both pAb-Aβ and mAb4G8 equally labelled plaque deposits in Tg2576 mice since they are composed of human wild-type Aβ (Fig. 6a,e, respectively). However, in the bigenic Tg-SwDI/Tg2576 mice both the large volume capillary amyloid deposits, as well as the parenchymal plaques, were strongly immunolabelled with both pAb-Aβ and mAb4G8 indicating that they are primarily composed of human wild-type Aβ derived from the Tg2576 background.


Cerebral vascular amyloid seeds drive amyloid β -protein fibril assembly with a distinct anti-parallel structure
Quantitative immunohistochemical analysis of cerebral human wild-type Aβ deposition in the different transgenic mice.Brain sections obtained from the different transgenic mouse lines at eighteen months of age were double immunolabelled for human Aβ using a polyclonal anti-Aβ (pAb-Aβ) antibody which recognizes both wild-type and CAA mutant Aβ, (green) (a–d) and mAb4G8, which recognizes wild-type Aβ, but not CAA mutant Aβ, (red) (e–h) and images were merged (i–l). Scale bars, 50 μm. (m) The levels of pAb-Aβ-positive total Aβ (green) and mAb4G8-positive wild-type Aβ (red) in parenchymal plaque and capillary deposits were determined in the different transgenic lines. The data presented are the mean±s.d. of 15 deposits per each line of mice.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121328&req=5

f6: Quantitative immunohistochemical analysis of cerebral human wild-type Aβ deposition in the different transgenic mice.Brain sections obtained from the different transgenic mouse lines at eighteen months of age were double immunolabelled for human Aβ using a polyclonal anti-Aβ (pAb-Aβ) antibody which recognizes both wild-type and CAA mutant Aβ, (green) (a–d) and mAb4G8, which recognizes wild-type Aβ, but not CAA mutant Aβ, (red) (e–h) and images were merged (i–l). Scale bars, 50 μm. (m) The levels of pAb-Aβ-positive total Aβ (green) and mAb4G8-positive wild-type Aβ (red) in parenchymal plaque and capillary deposits were determined in the different transgenic lines. The data presented are the mean±s.d. of 15 deposits per each line of mice.
Mentions: Subsequently, we determined whether CAA mutant or wild-type Aβ accumulation was responsible for the large increase in capillary amyloid volume observed in the bigenic Tg-SwDI/Tg2576 mice. To differentiate between human wild-type Aβ and human Dutch/Iowa CAA mutant Aβ peptides, we performed immunolabelling using the mAb4G8 antibody, which recognizes a mid-region epitope on human wild-type Aβ peptides33. The presence of the E22Q Dutch and D23N Iowa mutations abolishes the 4G8 epitope in human Aβ as confirmed by dot blot analysis (Supplementary Fig. 7). On the other hand, the rabbit polyclonal antibody directed towards an N-terminal epitope on Aβ (pAb-Aβ)34 equally recognizes wild-type and CAA mutant human Aβ peptides (Supplementary Fig. 7). Although pAb-Aβ recognized the characteristic small punctate capillary amyloid deposits in Tg-SwDI mice (Fig. 6d) these Aβ deposits were not appreciably labelled with mAb4G8 due to the presence of the Dutch and Iowa CAA mutations in the Aβ peptides (Fig. 6h). In contrast, both pAb-Aβ and mAb4G8 equally labelled plaque deposits in Tg2576 mice since they are composed of human wild-type Aβ (Fig. 6a,e, respectively). However, in the bigenic Tg-SwDI/Tg2576 mice both the large volume capillary amyloid deposits, as well as the parenchymal plaques, were strongly immunolabelled with both pAb-Aβ and mAb4G8 indicating that they are primarily composed of human wild-type Aβ derived from the Tg2576 background.

View Article: PubMed Central - PubMed

ABSTRACT

Cerebrovascular accumulation of amyloid β-protein (Aβ), a condition known as cerebral amyloid angiopathy (CAA), is a common pathological feature of patients with Alzheimer's disease. Familial Aβ mutations, such as Dutch-E22Q and Iowa-D23N, can cause severe cerebrovascular accumulation of amyloid that serves as a potent driver of vascular cognitive impairment and dementia. The distinctive features of vascular amyloid that underlie its unique pathological properties remain unknown. Here, we use transgenic mouse models producing CAA mutants (Tg-SwDI) or overproducing human wild-type Aβ (Tg2576) to demonstrate that CAA-mutant vascular amyloid influences wild-type Aβ deposition in brain. We also show isolated microvascular amyloid seeds from Tg-SwDI mice drive assembly of human wild-type Aβ into distinct anti-parallel β-sheet fibrils. These findings indicate that cerebrovascular amyloid can serve as an effective scaffold to promote rapid assembly and strong deposition of Aβ into a unique structure that likely contributes to its distinctive pathology.

No MeSH data available.


Related in: MedlinePlus