Aβ40 and Aβ42 Amyloid Fibrils Exhibit Distinct Molecular Recycling Properties

Rempel

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

et al. 2013

112

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: Application Of Finke-watzky Modeling and Statistical Evaluatsupporting

confidence: 92%

mentioning

confidence: 99%

See 1 more Smart Citation

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

112

179

“…In the AD amyloid hypothesis, the extracellular accumulation of soluble Aβ peptide leads to CNS formation of soluble oligomers, fibrils and amyloid plaques, and the distribution between brain and blood compartments, reflects the imbalance between Aβ production and clearance [2]. The Aβ fibril formation is currently considered a dynamic and reversible process, as Aβ fibrils are continuously dissolving and reforming [3]. Because AD stage severity correlates more with soluble Aβ brain levels than with Aβ plaque abundance [2,4,5], the amyloid monomers and oligomers are considered to be more toxic [1,6].…”

Section: Introductionmentioning

confidence: 99%

Rapid Improvement of Canine Cognitive Dysfunction with Immunotherapy designed for Alzheimer's Disease

Bosch¹,

Bayon²,

Rodrı́guez³

et al. 2013

CAR

ABSTRACT:Immunotherapy against amyloid-beta (Aβ) may improve rodent cognitive function by reducing amyloid neuropathology and is being validated in clinical trials with positive preliminary results. However, for a complete understanding of the direct and long-term immunization responses in the aged patient, and also to avoid significant side effects, several key aspects remain to be clarified. Thus, to investigate brain Aβ clearance and Th2 responses in the elderly, and the reverse inflammatory events not found in the immunized rodent, better Alzheimer's disease (AD) models are required. In the aged familiar canine with a cognitive dysfunction syndrome (CDS) we describe the rapid effectiveness and the full safety profile of a new active vaccine candidate for human AD prevention and treatment. In these aged animals, besides a weak immune system, the antibody response activated a coordinated central and peripheral Aβ clearance, that rapidly improved their cognitive function in absence of any side effects. Our results also confirm the interest to use familiar dogs to develop innovative and reliable therapies for AD.

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

“…These two forms of Aβ are known to display significantly different aggregation propensities at the same pH values and concentrations (9)(10)(11), but the underlying origin of these differences has not yet been firmly established.…”

mentioning

confidence: 99%

Differences in nucleation behavior underlie the contrasting aggregation kinetics of the Aβ40 and Aβ42 peptides

Meisl

Yang

Hellstrand

et al. 2014

433

647

The two major forms of the amyloid-beta (Aβ) peptide found in plaques in patients suffering from Alzheimer's disease, Aβ40 and Aβ42, only differ by two amino acids in the C-terminal region, yet they display markedly different aggregation behavior. The origins of these differences have remained challenging to connect to specific molecular-level processes underlying the aggregation reaction. In this paper we use a general strategy to apply the conventional workflow of chemical kinetics to the aggregation of the Aβ40 peptide to identify the differences between Aβ40 and Aβ42 in terms of the microscopic determinants of the aggregation reaction. Our results reveal that the major source of aggregates in the case of Aβ40 is a fibril-catalyzed nucleation process, the multistep nature of which is evident through its saturation behavior. Moreover, our results show that the significant differences in the observed behavior of the two proteins originate not simply from a uniform increase in all microscopic rates for Aβ42 compared with Aβ40, but rather are due to a shift of more than one order of magnitude in the relative importance of primary nucleation versus fibril-catalyzed secondary nucleation processes. This analysis sheds light on the microscopic determinants of the aggregation behavior of the principal forms of Aβ and outlines a general approach toward achieving an understanding at the molecular level of the aberrant deposition of insoluble peptides in neurodegenerative disorders.protein aggregation | rate law | neurodegeneration | aggregation mechanism