UCLA

Abnormal intracellular protein inclusions are consistently observable in the motor neurons affected by amyotrophic lateral sclerosis (ALS), also commonly referred as Lou Gehrig's disease. This disease was named after the famous Hall of Fame baseball player, Lou Gehrig, who suddenly experienced loss of physical strength and was diagnosed with ALS. The most prevalent hypothesis regarding the mechanism of ALS points to a toxic gain of function resulting from protein misfolding and aggregation. In the SOD1-ALS transgenic mouse model, protein aggregates composed of primarily full length apo SOD1 are consistently found in the spinal cords of mice exhibiting ALS symptoms. Moreover, these aggregates possess a filamentous structure, suggesting the involvement of SOD1 amyloid fibril in ALS pathology.

Research on understanding the formation mechanism of SOD1 fibrils spurred over the past few years. Scientists are now convinced that the demetallated form of SOD1 is the most susceptible to aggregation. In this dissertation, we sought to understand the molecular mechanism by which apo SOD1 rearranges to adopt the fibrillar structure, seek SOD1 amyloid inhibitors as potential therapeutic leads, and use small molecules to modulate and stabilize SOD1 oligomeric intermediates from the amyloid pathway that have never been characterized before. We found that the SOD1 amyloid core is composed of the N-terminal sequence 1-63. The N-terminal tryptic fragment 1-69 is consistently the most trypsin resistant in all the fibrils examined, including WT and six SOD1 mutants. WT fibril displays regular twist pattern along the lateral axis with an average helical pitch distance of 62 nm. While some mutants (L38V, G93A, and G93S) have similar twist pattern as WT, a single point mutation resides within the fibril core can alter the overall amyloid morphology. This is most evident in mutants such as G37R and G41D.

We successfully discovered several SOD1 amyloid inhibitors. Studies from a selection of SOD1 amyloid inhibitors (non-SOD1 synthetic peptides and small molecules) suggest that although peptides exhibiting a beta-strand conformation, such as DpV16 and DpV19, effectively inhibit SOD1 amyloid formation, peptides lacking beta-strand secondary structure, such as AzV31 and colivelin-tat are also effective. Out of all the inhibitors tested, only small molecules such as EGCG (a green tea derived flavonoid) and CLR01 (a molecular tweezer) formed stable oligomers with SOD1. SOD1 oligomers were never observed with peptide inhibitors. DpV16 was able to inhibit the initiation of fibrillation by reduced apo SOD1 but had no effect on the elongation phase, suggesting that it might prevent the formation of amyloid-competent nuclei. For the first time, we characterized SOD1 oligomers isolated from the in-vitro fibrillation assay. These CLR01-stabilized oligomers have an estimated molecular mass of 87,000 and exhibit a significant amount of beta-sheet content.