Filice, Carina Teresa2025-06-102025-06-102025-06-102025-05-20https://hdl.handle.net/10012/21847Alzheimer’s disease (AD) is a prominent health concern among the aging population. This disease impairs neuronal cells, in part, through the accumulation of amyloid-β(1-42) peptide (Aβ1-42) and its various toxic mechanisms. With the advent of controversial anti-amyloid drugs, the efficacy of newly developed treatments is still not high. Investigations into novel treatment strategies highlight the potential protective abilities of natural products; one of which is melatonin, a hormone produced by the pineal gland. Due to its inherent lipophilicity and interaction with membranes, melatonin is investigated in this work as a novel membrane-protection strategy. The difficulty in discovering effective anti-amyloid drug targets may be related to Aβ1-42’s physiological role as an antimicrobial peptide. Several hypotheses suggest microbial infections as a causative risk factor of AD through the stimulation of Aβ1-42 and neuroinflammation. This work specifically focuses on the contributions of bacterial functional amyloids, known as ‘curli fibers’, to Aβ1-42 processes. The basis for this investigation into curli fiber-amyloid interactions lies in multiple established instances of cross-seeding with other amyloidogenic peptides. Recently published studies demonstrate this interaction but many questions still remain as to the nature and effect that this interaction will have on other AD processes. In this work, we intend 1) to elucidate the molecular mechanism of melatonin membrane protection against amyloid toxicity and 2) to investigate the interaction of infection-establishing bacterial curli fibers with Aβ1-42 and the effect of these complexes on AD-associated mechanisms. To explore these mechanisms, we used multiple methods in biophysics, molecular biology, and computational chemistry to provide an interdisciplinary perspective. Previously published lipid models mimicking various AD-afflicted neuronal membranes were pre-treated with melatonin prior to Aβ1-42 and resulting damage was assessed via atomic force microscopy (AFM) imaging and black lipid membrane electrophysiology. In this work we demonstrated melatonin’s ability to inhibit peptide binding and promote membrane repair after Aβ1-42 exposure is dependent on its fluidic nature working in combination with lipid composition of target membranes. Similarly, high speed-AFM, AFM, and BLM studies evaluated the differences in antimicrobial and toxic mechanisms of Aβ1-42 in comparison to a known antimicrobial peptide. These evaluations revealed that anionic bacterial membranes repel Aβ1-42 indicating antimicrobial activity is not likely related to the same non-specific membrane binding as is its toxicity. Next, curli-amyloid interactions and the identification of participating aggregation states were evaluated through molecular dynamics simulations, transmission electron microscopy and AFM, as well as a novel biomolecular condensate assay. We confirmed that not only do curli fibers and Aβ1-42 interact and form peptide complexes, but also identified that this interaction is solely carried out by early aggregation species such as monomers and oligomers. Additionally, the effects of curli fibers on Aβ1-42 toxicity were first modelled by MD simulations and experimentally confirmed through measurements of damage on simple eukaryotic-based models by AFM and BLM, cell viability assays of murine microglial cell cultures, and immunogenicity evaluations using enzyme-linked immunosorbent assays. We also established that these curli-amyloid complexes reduce toxicity directly related to membrane perforation mechanisms but still negatively affect cell viability, presumably due to a heightened immunogenicity of the peptide complexes. Our findings lead us to propose a novel membrane-centric neuroprotection strategy against Aβ1-42 toxicity. This proposed mechanism intends to expand our knowledge of melatonin’s effect on membranes in AD and could inform therapeutic development. Furthermore, our investigations into curli-amyloid interactions and their effect on AD processes highlights the important role of Aβ1-42 in physiology and how this can relate to AD onset. These findings can reinforce the current research paradigm shift to microbial infections, the gut-brain axis, and the role of microbial products as potent initiators of AD onset pathways. Therefore, this entire body of work aims to develop knowledge of important AD mechanisms to guide new research, diagnostics, and treatment avenues.enAlzheimer's diseaseinfectionneuroprotectionantimicrobial peptidesmelatoninamyloid betacurli fibersDoctoral Thesis