Functionalized Mesoporous Silicas Direct Structural Polymorphism of Amyloid-β Fibrils

Abstract

The aggregation of Amyloid-b (Ab) is associated with the onset of Alzheimer's Disease (AD) and involves a complex kinetic pathway as monomers self-assemble into fibrils. A central feature of amyloid fibrils is the existence of multiple structural polymorphs, which complicates the development of disease-relevant structure-function relationships. Developing these relationships requires new methods to control fibril structure. In this work, we demonstrate that mesoporous silicas (SBA-15) functionalized with hydrophobic (SBA-PFDTS) and hydrophilic groups (SBA-PEG) direct the aggregation kinetics and resulting structure of Ab1-40 fibrils. The hydrophilic SBA-PEG had little effect on amyloid kinetics while as-synthesized and hydrophobic SBA-PFDTS accelerated aggregation kinetics. Subsequently, we quantified the relative population of fibril structures formed in the presence of each material using electron microscopy. Fibrils formed from Ab1-40 exposed to SBA-PEG were structurally similar to control fibrils. In contrast, Ab1-40 incubated with SBA-15 or SBA-PFDTS formed fibrils with shorter cross-over distances that were more structurally representative of fibrils found in AD patient-derived samples. Overall, these results suggest that mesoporous silicas and other exogenous materials are promising scaffolds for the de novo production of specific fibril polymorphs of Ab1-40 and other amyloidogenic proteins. Significance StatementA major challenge in understanding the progression of Alzheimer's Disease lies in the various fibril structures, or polymorphs, adopted by Amyloid-b (Ab). Heterogenous fibril populations may be responsible for different disease phenotypes and growing evidence suggests that Ab fibrils formed in vitro are structurally distinct from patient-derived fibrils. To help bridge 3 this gap, we used surface-functionalized mesoporous silicas to influence the formation of Ab1-40 fibrils and evaluated the distribution of resulting fibril polymorphs using electron microscopy (EM). We found that silicas modified with hydrophobic surfaces resulted in fibril populations with shorter cross-over distances that are more representative of Ab fibrils observed ex vivo. Overall, our results indicate that mesoporous silicas may be leveraged for the production of specific Ab polymorphs.

Cross-Seeding Controls Aβ Fibril Populations and Resulting Functions

“…As reported previously 22 and as seen in Figure 2b (generation 0), WT Aβ 1−40 primarily formed fibrils with crossover distances of 120 nm (73 ± 14%), 60 nm (7 ± 7%), and no crossovers (20 ± 9%). 26 In order to evaluate if any fibril polymorphs were able to pass on their structure, we seeded 30 μM of fresh WT Aβ 1−40 monomer with 5 μM of pre-formed fibril "seeds." We repeated this process twice to produce three generations of fibrils.…”

“…23,24 While simulations measuring the nucleation barrier and the initial dimerization process in aggregate formation suggest kinetic control on fibril polymorphism, 25 our previous study using sodium dodecyl sulfate (SDS) to artificially accelerate amyloid aggregation to a rate similar to those of mesoporous silica materials demonstrated a nuance in kinetic control; similar kinetic lag times could still result in different fibril polymorph distributions depending on the nucleation condition. 26 As recent studies have shown that structural variants can display differing phenotypes and disease subtypes, 27−31 the large number of possible fibril conformations produced from different peptide sequences and nucleation in vitro and in vitro conditions complicates the development of effective therapeutics and hinders our understanding of the role of fibrils in disease progression.…”