Manipulation of Protein Aggregation and Aggregates Structures Using Nanoparticles on Brain-Mimicking Lipid Bilayers

Abstract

Cells in our body have several tens of microns in size and they respond to their microenvironment. Abnormal symptoms or extraordinary signs in the body are usually obtained by misleading cell-cell communication and signal transductions. More specifically, cell-cell communication and cell-extracellular matrix (ECM) interactions are generated at the cell membrane which makes physical barrier to shield intracellular components from the outside. Cell membranes provide a basic platform to investigate many biological processes including material transport, trafficking, and pathogenic pathways. In this regard, it is needed to develop bio-mimicking platforms and materials to understand the mechanism and progress of diseases perfectly. Microscale features could affect the whole-cell guidance and their responses, but nanoscale stimuli also have emerged as fascinating features for several decades. Subcellular structures such as lysosomes, lipids, transmembrane proteins, ion channels are of nanometer scales, so that nanomaterial could be one of attractive candidates to manipulate intra-and extracellular signals. Therefore, supported lipid bilayers (SLBs) have been used as the cell membrane model and hybridized with various membrane-associated molecules to mimic living cells and envision molecular reactions on the membrane surface. For more precise investigation of complex biological processes, nanomaterials would be hybridized with the bio-mimicking system and have boosted the development of new platforms and methodologies. Therefore, Chapter 1 will explain manipulation of protein assemblies and aggregation process with a variety of nanomaterials and detection of biomolecular interactions on the cell membrane using SLB and nanomaterials. In chapter 2, we studied the formation of various Aβ aggregate structures with gold nanoparticles (AuNPs) and brain total lipid extract-based supported lipid bilayer (brain SLB). Understanding and manipulating amyloid-β (Aβ) aggregation provide key knowledge and means for the diagnosis and cure of Alzheimers disease (AD) and the applications of Aβ-based aggregation systems. The roles of AuNPs and brain SLB in forming Aβ aggregates were studied in real time, and the structural details of Aβ aggregates were monitored and analyzed with the dark-field imaging of plasmonic AuNPs that allows for long-term in situ imaging of Aβ aggregates with great structural details without further labeling. It was shown that the fluid brain SLB platform provides the binding sites for Aβ and drives the fast and efficient formation of Aβ aggregate structures and, importantly, large Aβ plaque structures (>15 μm in diameter), a hallmark for AD, were formed without going through fibril structures when Aβ peptides were co-incubated with AuNPs on the brain SLB. The dark-field scattering and circular dichroism-correlation data suggest that AuNPs were heavily involved with Aβ aggregation on the brain SLB and less α-helix, less β-sheet and more random coil structures were found in large plaque-like Aβ aggregates. In chapter 3, we studied the effect of the size, shape, and surface charge of Au nanoparticles (AuNPs) on amyloid beta (Aβ) aggregation on a total brain lipid-based supported lipid bilayer (brain SLB), a fluid platform that facilitates Aβ-AuNP aggregation process. We found that larger AuNPs induce large and amorphous aggregates on the brain SLB, whereas smaller AuNPs induce protofibrillar Aβ structures. Positively charged AuNPs were more strongly attracted to Aβ than negatively charged AuNPs, and the stronger interactions between AuNPs and Aβ resulted in fewer β-sheets and more random coil structures. We also compared spherical AuNPs, gold nanorods (AuNRs), and gold nanocubes (AuNCs) to study the effect of nanoparticle shape on Aβ aggregation on the brain SLB. Aβ was preferentially bound to the long axis of AuNRs and fewer fibrils were formed whereas all the facets of AuNCs interacted with Aβ to produce the fibril networks. Finally, it was revealed that different nanostructures induce different cytotoxicity on neuroblastoma cells, and, overall, smaller Aβ aggregates induce higher cytotoxicity. The results offer insight into the roles of NPs and brain SLB in Aβ aggregation on the cell membrane and can facilitate the understanding of Aβ-nanostructure co-aggregation mechanism and tuning Aβ aggregate structures.