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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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Aβ40-DI CAA mutant amyloid fibril seeds promote the rapid assembly of wild-type Aβ40 and Aβ42 fibrils.(a) FTIR spectra of Aβ40-DI having anti-parallel (green) and parallel (black) β-sheet secondary structure. The anti-parallel fibrils were formed at 4-6 °C using the protocol of Tycko2223 (Supplementary Fig. 2) and are stable to at least 22 °C (Supplementary Fig. 3). (b) TEM of anti-parallel Aβ40-DI obtained at 22 °C. Scale bar, 150 nm. Freshly prepared solutions of wild-type Aβ40 (c,d) or wild-type Aβ42 (e,f) were incubated in the absence (blue) or presence (red) of parallel (c,e) or anti-parallel (d,f) Aβ40-DI fibrillar seeds. The rate and extent of fibril formation was assessed by thioflavin T fluorescence measurements at 37 °C. TEM, transmission electron microscopy.
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f1: Aβ40-DI CAA mutant amyloid fibril seeds promote the rapid assembly of wild-type Aβ40 and Aβ42 fibrils.(a) FTIR spectra of Aβ40-DI having anti-parallel (green) and parallel (black) β-sheet secondary structure. The anti-parallel fibrils were formed at 4-6 °C using the protocol of Tycko2223 (Supplementary Fig. 2) and are stable to at least 22 °C (Supplementary Fig. 3). (b) TEM of anti-parallel Aβ40-DI obtained at 22 °C. Scale bar, 150 nm. Freshly prepared solutions of wild-type Aβ40 (c,d) or wild-type Aβ42 (e,f) were incubated in the absence (blue) or presence (red) of parallel (c,e) or anti-parallel (d,f) Aβ40-DI fibrillar seeds. The rate and extent of fibril formation was assessed by thioflavin T fluorescence measurements at 37 °C. TEM, transmission electron microscopy.

Mentions: In our studies, parallel and anti-parallel β-sheet structures are distinguished by Fourier transform infrared (FTIR) spectroscopy on the basis of isotope-induced shifts and intensity changes observed in the amide I vibration upon specific 13C labelling (Supplementary Fig. 1)3031. The amide I region of the FTIR spectrum is shown in Fig. 1a for Aβ40-DI fibrils having anti-parallel (green) and parallel (black) β-sheet structure. The different fibril forms were obtained using the protocols developed by Tycko2728 and colleagues (Supplementary Fig. 2). The ∼1,630 cm−1 band observed in these spectra is characteristic of β-sheet secondary structure. In addition, the Aβ peptide used in these experiments contains a specific 13C=O label at Gly33, a residue within the hydrophobic C-terminus that typically forms β-sheet in Aβ fibrils. The 13C substitution lowers the frequency of the C=O stretching coordinate and results in isotope-shifted resonances at 1,610 and 1,600 cm−1, which differ in intensity depending on whether the β-strands hydrogen-bond in a parallel or anti-parallel orientation. The increase of intensity at 1,610 cm−1 relative to 1,600 cm−1 is a signature of anti-parallel β-sheet30.


Cerebral vascular amyloid seeds drive amyloid β -protein fibril assembly with a distinct anti-parallel structure
Aβ40-DI CAA mutant amyloid fibril seeds promote the rapid assembly of wild-type Aβ40 and Aβ42 fibrils.(a) FTIR spectra of Aβ40-DI having anti-parallel (green) and parallel (black) β-sheet secondary structure. The anti-parallel fibrils were formed at 4-6 °C using the protocol of Tycko2223 (Supplementary Fig. 2) and are stable to at least 22 °C (Supplementary Fig. 3). (b) TEM of anti-parallel Aβ40-DI obtained at 22 °C. Scale bar, 150 nm. Freshly prepared solutions of wild-type Aβ40 (c,d) or wild-type Aβ42 (e,f) were incubated in the absence (blue) or presence (red) of parallel (c,e) or anti-parallel (d,f) Aβ40-DI fibrillar seeds. The rate and extent of fibril formation was assessed by thioflavin T fluorescence measurements at 37 °C. TEM, transmission electron microscopy.
© Copyright Policy - open-access
Related In: Results  -  Collection

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f1: Aβ40-DI CAA mutant amyloid fibril seeds promote the rapid assembly of wild-type Aβ40 and Aβ42 fibrils.(a) FTIR spectra of Aβ40-DI having anti-parallel (green) and parallel (black) β-sheet secondary structure. The anti-parallel fibrils were formed at 4-6 °C using the protocol of Tycko2223 (Supplementary Fig. 2) and are stable to at least 22 °C (Supplementary Fig. 3). (b) TEM of anti-parallel Aβ40-DI obtained at 22 °C. Scale bar, 150 nm. Freshly prepared solutions of wild-type Aβ40 (c,d) or wild-type Aβ42 (e,f) were incubated in the absence (blue) or presence (red) of parallel (c,e) or anti-parallel (d,f) Aβ40-DI fibrillar seeds. The rate and extent of fibril formation was assessed by thioflavin T fluorescence measurements at 37 °C. TEM, transmission electron microscopy.
Mentions: In our studies, parallel and anti-parallel β-sheet structures are distinguished by Fourier transform infrared (FTIR) spectroscopy on the basis of isotope-induced shifts and intensity changes observed in the amide I vibration upon specific 13C labelling (Supplementary Fig. 1)3031. The amide I region of the FTIR spectrum is shown in Fig. 1a for Aβ40-DI fibrils having anti-parallel (green) and parallel (black) β-sheet structure. The different fibril forms were obtained using the protocols developed by Tycko2728 and colleagues (Supplementary Fig. 2). The ∼1,630 cm−1 band observed in these spectra is characteristic of β-sheet secondary structure. In addition, the Aβ peptide used in these experiments contains a specific 13C=O label at Gly33, a residue within the hydrophobic C-terminus that typically forms β-sheet in Aβ fibrils. The 13C substitution lowers the frequency of the C=O stretching coordinate and results in isotope-shifted resonances at 1,610 and 1,600 cm−1, which differ in intensity depending on whether the β-strands hydrogen-bond in a parallel or anti-parallel orientation. The increase of intensity at 1,610 cm−1 relative to 1,600 cm−1 is a signature of anti-parallel β-sheet30.

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