Patricia Cho

Protein aggregation is implicated in a variety of neurodegenerative diseases including Alzheimer’s disease, Huntington’s disease and Parkinson’s disease. Theses diseases are characterized by the deposition of protein aggregates, termed amyloid. Alzheimer’s disease (AD), which is the most common form of dementia occurring in the elderly, is associated with the aggregation of β-amyloid (Aβ) peptide. Aβ spontaneously self-assemble into soluble oligomers and insoluble fibrils, and substantial evidences have suggested that this process is causally linked to AD pathogenesis. However, the exact relationship of Aβ aggregation and AD pathogenesis is still elusive and much remains an area of controversy.

Interestingly, it was discovered from studies on transgenic mice model of AD that transthyretin (TTR), which is another amyloidogenic protein, might play a protective role against AD pathogenesis. In addition, TTR has been shown to bind directly to Aβ and affect Aβ aggregation and toxicity in vitro. Based on these, it was hypothesized that TTR naturally plays a protective role against AD through direct interaction with Aβ that alters Aβ aggregation which in turn affects Aβ toxicity. However, the exact relationship between Aβ­-TTR binding, effect of TTR on Aβ aggregation and cellular toxicity is not yet estAβlished. Therefore, we propose to characterize the interaction of Aβ and TTR and relate it to the effect of TTR on Aβ aggregation and on Aβ toxicity in order to elucidate how TTR acts against AD pathogenesis. Increased understanding of the mechanism may lead to the development of novel rational strategies for AD therapy. Specific aims for the proposed research are as follows. 

Specific Aim 1: Characterize how the quaternary structure/stability of TTR and the aggregation state of Aβ affect binding of Aβ and TTR.
It was observed from previous studies in our lab that TTR quaternary structure/stability modulates binding to Aβ and influences its effect on Aβ aggregation and on Aβ toxicity. In addition, aggregation state of Aβ was shown to affect Aβ-TTR binding. We will characterize in detail how the quaternary structure/stability of TTR and the aggregation state of Aβ affect Aβ-TTR binding by testing how Aβ at different aggregation state binds to TTR mutants with different quaternary structure/stability.

Specific Aim 2: Relate binding of Aβ and TTR to the effect of TTR on Aβ aggregation and on Aβ toxicity.
Light scattering and electron microscopy will monitor aggregation kinetics of Aβ in the presence of TTR mutants generated in specific aim 1. The effect of the mutants on Aβ-mediated cellular toxicity will be also studied. Specific aim 1 and 2 will allow us to relate Aβ-TTR binding and the effect of TTR on Aβ aggregation and on Aβ toxicity.

Specific Aim 3:  Identify the Aβ binding domains on TTR by scanning alanine mutagenesis.
Scanning alanine mutagenesis will be conducted on the limited region of TTR to identify the binding domain of Aβ. Specifically, residues in hydrophobic channel and EF-helix/loop region of TTR will be targeted.