Structural variations of amyloid-like peptides and their interaction with neural cells

Abstract

The nervous system, including the peripheral nervous system (PNS) and the central nervous system (CNS), is composed of multiple neurons that are classified based on diverse molecular, morphological, connectional, and functional properties. Although there are a wide variety of neurons, they have one thing in common, that is, neurons are sensitive to subtle physical changes and biochemical cues arising from the environment. Therefore, this thesis focuses on structural variations of amyloid-like self-assembling peptides – a promising material for artificial neural scaffolds – and their interaction with neural cells. Amyloid-like peptides, associated with neurodegenerative diseases, such as Parkinson’s, Alzheimer’s, and Huntington’s, are misfolded peptide molecules that are highly resistant to degradation. The misfolding or self-assembly occurs under physiological conditions and is affected by various factors, such as the peptide sequence, concentration, and solvent effect. Taking advantage of their non-degradable characteristic and diverse assembly morphologies, amyloid-like peptides have been used as hierarchical nano-templates for neuroscience, neural drug development, and neural tissue engineering. The goal of this thesis is to investigate the correlation between the structure of self-assembling peptides and the bioactivity of neural cells. The most straightforward strategy is employed first: a library of nine amyloid-like peptides is designed by systematically varying the hydrophobic core of the peptide backbone. The physicochemical properties of the peptides are extensively analyzed from the atomistic, molecular, and microscopic level. Furthermore, molecular dynamics simulations are used to provide theoretical insights to explain the differences in peptide assembly. With deeper structural insights, these peptides are examined for their neural activity using a human neuroblastoma cell line to understand the relationship between peptide structure and neural activity. The results of this project demonstrated that the computational simulations could help the rational design of peptide sequences for neural repair. The following chapter, an important but often overlooked factor, the solvent effect, is investigated to understand how the solvation effect influences the assembly behavior of amyloid-like peptide and their neural activity. The same peptide sequence that is produced by different manufacturers, dissolved in different solvents, or tested at various time points, demonstrates different self-assembly behavior. The difference derived from the self-assembly behavior is reflected in the activation of the formyl peptide receptor 1 in both mouse and human neural cells, highlighting that the processing history and solvent effect influenced the structure-property relationship of amyloid-like peptide and neural activity. Neural differentiation requires a long period of incubation, so it is of importance to build a stable amyloid-like SAP substrate that can resist frequent washing. Amyloid-like peptides functionalized with vinyl groups are synthesized and immobilized on thiolated substrates prepared by chemical vapor deposition via a photo-triggered thiol-ene reaction. This peptide immobilization strategy offers a facile route to fabricate a large and customized two-dimensional amyloid-like peptide layer to manipulate neural cell adhesion. In summary, this thesis aims to investigate different factors that influence the self-assembled structure of amyloid-like peptides and correlate the structural differences with neural behavior to provide insights into the structure-property relationship between amyloid-like peptides and neural cells.