skip to main content

Title: Big versus small: The impact of aggregate size in disease

Protein aggregation results in an array of different size soluble oligomers and larger insoluble fibrils. Insoluble fibrils were originally thought to cause neuronal cell deaths in neurodegenerative diseases due to their prevalence in tissue samples and disease models. Despite recent studies demonstrating the toxicity associated with soluble oligomers, many therapeutic strategies still focus on fibrils or consider all types of aggregates as one group. Oligomers and fibrils require different modeling and therapeutic strategies, targeting the toxic species is crucial for successful study and therapeutic development. Here, we review the role of different‐size aggregates in disease, and how factors contributing to aggregation (mutations, metals, post‐translational modifications, and lipid interactions) may promote oligomers opposed to fibrils. We review two different computational modeling strategies (molecular dynamics and kinetic modeling) and how they are used to model both oligomers and fibrils. Finally, we outline the current therapeutic strategies targeting aggregating proteins and their strengths and weaknesses for targeting oligomers versus fibrils. Altogether, we aim to highlight the importance of distinguishing the difference between oligomers and fibrils and determining which species is toxic when modeling and creating therapeutics for protein aggregation in disease.

more » « less
Award ID(s):
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Protein Science
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Amyloid fibril formation is central to the etiology of a wide range of serious human diseases, such as Alzheimer’s disease and prion diseases. Despite an ever growing collection of amyloid fibril structures found in the Protein Data Bank (PDB) and numerous clinical trials, therapeutic strategies remain elusive. One contributing factor to the lack of progress on this challenging problem is incomplete understanding of the mechanisms by which these locally ordered protein aggregates self-assemble in solution. Many current models of amyloid deposition diseases posit that the most toxic species are oligomers that form either along the pathway to forming fibrils or in competition with their formation, making it even more critical to understand the kinetics of fibrillization. A recently introduced topological model for aggregation based on network Hamiltonians is capable of recapitulating the entire process of amyloid fibril formation, beginning with thousands of free monomers and ending with kinetically accessible and thermodynamically stable amyloid fibril structures. The model can be parameterized to match the five topological classes encompassing all amyloid fibril structures so far discovered in the PDB. This paper introduces a set of network statistical and topological metrics for quantitative analysis and characterization of the fibrillization mechanisms predicted by the network Hamiltonian model. The results not only provide insight into different mechanisms leading to similar fibril structures, but also offer targets for future experimental exploration into the mechanisms by which fibrils form.

    more » « less
  2. Abstract

    Aggregation and accumulation of amyloid‐β peptide (Aβ) are a critical trigger for the onset of Alzheimer's disease (AD). While the plaques are the most outstanding Aβ pathological feature, much of the recent research emphasis has been on soluble Aβ species because of their diffusible, proinflammatory, and toxic properties. The focus on soluble aggregated Aβ species has also increased the interest in antibodies that are selective for different Aβ conformations. In the current study, we developed and characterized a new class of monoclonal antibodies (referred to as mAbSL) that are selective for Aβ protofibrils. Cloning and sequencing of the heavy and light chain variable regions for multiple antibodies identified sequence characteristics that may impart the conformational selectivity by the antibodies. Transfection of FreeStyle 293F cells with the plasmids permitted in‐house expression and purification of mAbSL antibodies along with non‐conformation‐selective Aβ monoclonal antibodies (Aβ mAbs). Several of the purified mAbSL antibodies demonstrated significant affinity and selectivity for Aβ42 protofibrils compared with Aβ42 monomers and Aβ42 fibrils. Competition ELISA assays assessing the best overall antibody, mAbSL 113, yielded affinity constants of 7 nM for the antibody‐Aβ42 protofibril interaction, while the affinity for either Aβ42 monomers or Aβ42 fibrils was roughly 80 times higher. mAbSL 113 significantly inhibited Aβ42 monomer aggregation by a unique mechanism compared with the inhibition displayed by Aβ mAb 513. Aβ42 protofibril dynamics were also markedly altered in the presence of mAbSL 113, whereby insoluble complex formation and protofibril deposition were stimulated by the antibody at low substoichiometric molar ratios. As the field contemplates the therapeutic effectiveness of Aβ conformation‐selective antibodies, the findings presented here demonstrate new information on a monoclonal antibody that selectively targets Aβ protofibrils and impacts Aβ dynamics.image

    more » « less
  3. Abstract

    Amyloid protein aggregation is associated with many neurodegenerative diseases, including amyloid‐β (Aβ)in Alzheimer disease, human islet amyloid polypeptide (hIAPP) in type II diabetes, and human calcitonin (hCT) in medullary thyroid carcinoma. Significant efforts have been made to develop different diagnostic and prevention strategies for the early detection and intervention of these disease‐causative protein aggregates. However, conventional design wisdoms are mostly limited to the molecules with either single function (amyloid imaging or amyloid prevention) or single targeting protein (Aβ, hIAPP, or hCT). Here, a rational design strategy of an amyloid‐aggregation‐induced emission (AIE)‐active molecule is demonstrated by conjugating an amyloid fragment of GNNQQNY (G7) with an AIE fluorescent molecule of triphenylvinyl benzoic acid (namely, G7‐TBA), making G7‐TBA as multiple‐target, dual‐function, amyloid probes and amyloid modulators for detecting, monitoring, and altering amyloid aggregation of three different amyloid proteins (Aβ, hIAPP, and hCT). G7‐TBA probe shows conformationally specific binding affinities to amyloid aggregates, switching from an “off” state (low fluorescence) for amyloid monomers to an “on” state (high fluorescence) for β‐structure‐rich amyloid oligomers and fibrils in aqueous solution. Further surface immobilization of TBA probes on surface plasmon resonance surfaces allows to amplify detection sensitivity and binding affinity to amyloid aggregates formed at different aggregation stages. G7‐TBA as amyloid modulator enables acceleration of amyloid fibrillization and selectively protects cells from hIAPP‐induced toxicity. The distinct amyloid detection and modulation of G7‐TBA are essentially derived from the cross‐seeding between G7 and amyloid aggregation via β‐structure interaction, which by far exceed the binding affinity between commercial ThT and amyloid aggregates. Such design concepts of amyloid‐AIE conjugates can be further explored as multiple‐function and target probes and/or modulators for biomedical applications.

    more » « less
  4. Abstract

    Oligomers populated during the early amyloid aggregation process are more toxic than mature fibrils, but pinpointing the exact toxic species among highly dynamic and heterogeneous aggregation intermediates remains a major challenge. β-barrel oligomers, structurally-determined recently for a slow-aggregating peptide derived from αB crystallin, are attractive candidates for exerting amyloid toxicity due to their well-defined structures as therapeutic targets and compatibility to the “amyloid-pore” hypothesis of toxicity. To assess whether β-barrel oligomers are common intermediates to amyloid peptides - a necessary step toward associating β-barrel oligomers with general amyloid cytotoxicity, we computationally studied the oligomerization and fibrillization dynamics of seven well-studied fragments of amyloidogenic proteins with different experimentally-determined aggregation morphologies and cytotoxicity. In our molecular dynamics simulations, β-barrel oligomers were only observed in five peptides self-assembling into the characteristic cross-β aggregates, but not the other two that formed polymorphic β-rich aggregates as reported experimentally. Interestingly, the latter two peptides were previously found nontoxic. Hence, the observed correlation between β-barrel oligomers formation and cytotoxicity supports the hypothesis of β-barrel oligomers as the common toxic intermediates of amyloid aggregation.

    more » « less
  5. Misfolding and aggregation of amyloid peptides are critical pathological events in numerous protein misfolding diseases (PMDs), such as Alzheimer's disease (AD), type II diabetes (T2D), and medullary thyroid carcinoma (MTC). While developing effective amyloid detectors and inhibitors to probe and prevent amyloid aggregation is a crucial diagnostic and therapeutic strategy for treating debilitating diseases, it is important to recognize that amyloid detection and amyloid prevention are two distinct strategies for developing pharmaceutical drugs. Here, we reported novel fluorescent BO21 as a versatile “dual-function, multi-target” amyloid probe and inhibitor for detecting and preventing amyloid aggregates of different sequences (Aβ, hIAPP, or hCT) and sizes (monomers, oligomers, or fibrils). As an amyloid probe, BO21 demonstrated a higher sensitivity and binding affinity to oligomeric and fibrillar amyloids compared to ThT, resulting in up to 18–39 fold fluorescence enhancements. As an amyloid inhibitor, BO21 also demonstrated its strong amyloid inhibition property by effectively preventing amyloid aggregation, disaggregating preformed amyloid fibrils, and reducing amyloid-induced cytotoxicity. The findings of this study offer a new perspective for the discovery of dual-functional amyloid probes and inhibitors, which have the potential to greatly expand the diagnostic and therapeutic treatments available for PMDs. 
    more » « less