BACTERIAL AMYLOID CURLI INFLUENCES AGGREGATION OF AMYLOID BETA PEPTIDES ASSOCIATED WITH ALZHEIMER ́S DISEASE
Date
2023-10-02
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0009-0003-6321-4751
Type
Thesis
Degree Level
Masters
Abstract
Amyloid proteins are associated with various disorders such as Alzheimer's, Parkinson's,
prion diseases, and type 2 diabetes. Each of these illnesses involves a specific amyloid protein or
peptide that misfolds and forms fibrils. Apart from pathological amyloids, there are amyloids that
are considered functional amyloids. Functional amyloids are produced by different organisms, and
in contrast to pathological amyloids, they serve various biological functions. For my MSc. project
I focus on the pathological amyloid-β (Aβ) associated with Alzheimer's disease and the functional
amyloid curli. Curli is produced by the foodborne pathogen Salmonella and the commensal
bacteria Escherichia coli. Curli is classified as a functional amyloid because it provides a structural
role in the biofilm extracellular matrix. CsgA and CsgB are the curli structural components. When
CsgA and CsgB reach the cell surface, they change from an unstructured state as secreted proteins
to -rich structures that assemble into amyloid fibrils at the cell surface. Despite being encoded by
distinct protein sequences, curli fibrils share a common 3D structure with Aβ. The mechanism of
how Aβ peptides convert from soluble functional proteins into insoluble amyloid fibrils is not fully
understood. Given that both proteins are naturally amyloidogenic and share a similar structural
fold, the subject of my M.Sc. research is to investigate if Salmonella curli can cross-react with A
peptides. The effects of curli on aggregation and aggregate cytotoxicity of Aβ(1-42) and A(1-40)
peptides were investigated by a combination of biophysical (Western blot analysis and kinetic
studies with thioflavin T fluorescence) and cellular assays (cell viability in male and female human
fibroblasts). I demonstrate that curli can physically interact with both A peptides in vitro. The
biophysical data shows that curli promotes Aβ(1-42) fibrillization and accelerate the overall
aggregation of Aβ(1-40) (i.e., oligomers + fibrils). The data with cultured cells shows that Aβ(1-
42)/curli aggregates are less cytotoxic that Aβ(1-42) aggregates. Our results support mounting
evidence that oligomers—as opposed to mature fibrils— are probably the more toxic species of
the peptides. Although we cannot correlate our results to the complex pathology of AD yet, our
findings contribute to evidence that exogenous (sometimes bacterial) amyloids may influence and
cross-react with host amyloids. Moreover, the interactions shown in my work may provide new
insights into the molecular mechanisms of interactions between bacterial amyloids and human
amyloids.
Description
Keywords
Amyloids, curli, Salmonella, Alzheimer's Disease
Citation
Degree
Master of Science (M.Sc.)
Department
Biochemistry
Program
Microbiology and Immunology