Aβ40 Protects Non-toxic Aβ42 Monomer from Aggregation

Rempel

Proc. Natl. Acad. Sci. U.S.A.

et al. 2013

113

179

Probing the conformational changes of amyloid beta (Aβ) peptide aggregation is challenging owing to the vast heterogeneity of the resulting soluble aggregates. To investigate the formation of these aggregates in solution, we designed an MS-based biophysical approach and applied it to the formation of soluble aggregates of the Aβ 42 peptide, the proposed causative agent in Alzheimer's disease. The approach incorporates pulsed hydrogen-deuterium exchange coupled with MS analysis. The combined approach provides evidence for a self-catalyzed aggregation with a lag phase, as observed previously by fluorescence methods. Unlike those approaches, pulsed hydrogen-deuterium exchange does not require modified Aβ 42 (e.g., labeling with a fluorophore). Furthermore, the approach reveals that the center region of Aβ 42 is first to aggregate, followed by the C and N termini. We also found that the lag phase in the aggregation of soluble species is affected by temperature and Cu 2+ ions. This MS approach has sufficient structural resolution to allow interrogation of Aβ aggregation in physiologically relevant environments. This platform should be generally useful for investigating the aggregation of other amyloid-forming proteins and neurotoxic soluble peptide aggregates.soluble Aβ oligomers | amyloid beta peptide | copper | electrospray ionization | Finke-Watsky mode P rotein aggregation is one of the immediate causes of Alzheimer's, Parkinson, and Huntington diseases, motivating biophysical studies of the responsible proteins. More than 20 small proteins undergo amyloidosis in humans. In Alzheimer's disease (AD), the aggregation of the 40-or 42-aa-long amyloid beta (Aβ) peptide, generally called Aβ 40 or Aβ 42 , respectively, is proposed to be involved in the onset of the disease (1, 2). Aβ 42 is more amyloidogenic and more neurotoxic than Aβ 40 . Although the amyloid-cascade hypothesis suggests that the Aβ-containing amyloid plaques are responsible for neurodegeneration (3-7), other studies suggest that soluble aggregates of Aβ 42 are more neurotoxic than the amyloid plaques (8-13).The amyloid plaques in AD-affected brains contain high levels of copper, zinc, and iron (14-20). Among these, Cu has drawn the most attention because the Aβ precursor protein is likely a Cuchaperone protein (21). Several studies of Cu 2+ -Aβ 40 interactions show that Cu 2+ can promote Aβ 40 aggregation (14,18,19).The structure of Aβ 42 and its aggregates, although studied extensively, remains of high interest. Studies of amyloid fibrils invoke X-ray crystallography (22-24), EM (19,25,26), and thioflavin T fluorescence (19, 27), revealing the polypeptide's global behavior, whereas NMR studies provide residue-level information for the fibrils (28-30). Nevertheless, we know little about soluble Aβ aggregates owing to their intrinsically high heterogeneity.MS should offer an opportunity for investigating soluble aggregates of Aβ 42 . Thus far, there are no MS-based, timedependent studies of the formation of soluble aggregates. Moreover, there are no ot...

Section: Resultssupporting

confidence: 91%

Pulsed hydrogen–deuterium exchange mass spectrometry probes conformational changes in amyloid beta (Aβ) peptide aggregation

Rempel

Proc. Natl. Acad. Sci. U.S.A.

et al. 2013

113

179

Journal of Biological Chemistry

“…A␤ 40 potentially delays A␤ 42 aggregation through "non-productive" interactions. Although these conclusions are in agreement with previous reports (25,27,46), our cross-seeding data suggest that A␤ 40 monomers specifically require A␤ 40 oligomers to induce growth of mature fibrils, whereas A␤ 42 monomers are less selective and are stimulated by all types of seeds.…”

Section: Discussionsupporting

confidence: 93%

“…We therefore expect that the populations of the two peptides in the aggregates will be mixed. This explains and expands previous data (23,25,27) that indicate that A␤ 40 and A␤ 42 influence their respective aggregation properties.…”

Section: Discussionsupporting

confidence: 90%

“…The structural fingerprints of pure A␤ 42 and A␤ 40 peptides by the 15 N-1 H N HSQC spectra are in excellent agreement with data shown in the literature (Fig. 2) (27,34). The spectra of 15 Nlabeled A␤ 42 at different molar ratios do not present chemical shift variations, not even for the resonances of the C terminus, which should be the most sensitive to even a small change of environment (Fig.…”

Section: Direct Interactions Between A␤supporting

confidence: 89%

“…Different architectures of in vitro-generated amyloid fibrils from pure A␤ 40 and A␤ 42 peptides have been revealed by nuclear magnetic resonance (NMR) (18), electron microscopy (EM) (19), and x-ray fiber diffraction methods (20 -22). A limited number of studies have demonstrated that A␤ 40 and A␤ 42 each affect the aggregation rates of the other, and it is generally reported that A␤ 40 inhibits the aggregation of A␤ 42 (12,14,(23)(24)(25)(26)(27).…”

mentioning

confidence: 99%

See 2 more Smart Citations

Structural Basis for Increased Toxicity of Pathological Aβ42:Aβ40 Ratios in Alzheimer Disease

Pauwels

Williams

Morris

et al. 2012

220

223

Background: Amyloid ␤ peptide plays a role in Alzheimer disease. Results: Interaction of amyloid ␤ peptides with 40 and 42 amino acids has consequences for oligomer formation. Conclusion: Increased production of amyloid ␤ peptide with 42 amino acids affects the behavior of the entire amyloid ␤ peptide pool. Significance: This might explain the synaptotoxic effect observed with a shift in amyloid ␤ peptide production.

Cross‐seeding between Aβ40 and Aβ42 in Alzheimer's disease

et al. 2016

Aβ42 is the major component of parenchymal plaques in the brain of Alzheimer’s patients, while Aβ40 is the major component of cerebrovascular plaques. Since Aβ40 and Aβ42 co-exist in the brain, understanding the interaction between Aβ40 and Aβ42 during their aggregation is important to delineate the molecular mechanism underlying Alzheimer’s disease. Here, we present a rigorous and systematic study of the cross-seeding effects between Aβ40 and Aβ42. We show that Aβ40 fibril seeds can promote Aβ42 aggregation in a concentration-dependent manner, and vice versa. Our results also suggest that seeded aggregation and spontaneous aggregation may be two separate pathways. These findings may partly resolve conflicting observations in the literature regarding the cross-seeding effects between Aβ40 and Aβ42.