Eternal sunshine of a spotless worm mind: in vivo effects of peptide inhibitors of amyloid beta aggregation.

Deposition of amyloid beta peptide (Aβ) in the brain is one of the major hallmarks in Alzheimer´s disease (AD) pathogenesis. The amino acid sequence of the Aβ peptide is essential for its self-assemble properties, a complex process that involves the production of soluble intermediates that lead to amyloid plaque deposition. Currently, soluble Aβ oligomers formed in early aggregation are being considered as primary neurotoxic agents and prevention of Aβ aggregation has emerged as a therapeutical target for AD. An approach in the development of peptide inhibitors of aggregation is the use of Aβ as a starting point. Previously, we generated three Aβ peptides variants by introducing the point mutations M35C, A30W or K28A in each one of two Aβ peptides of different length, 40 and 42 amino acids, respectively. All these substitutions lie in key regions that participate during the aggregation process. Cell culture assays showed a decrease in reactive oxygen species production correlated with a reduction in cytotoxicity but not with the aggregation properties of the variants. Furthermore, the 1-40 mutants were able to disorganize pre-formed WT aggregates while 1-42 mutants disorganized and prevented de novo aggregation of the WT peptide.
Caenorhabditis elegans is an in vivo model that allows for the screening of Aβ aggregation inhibitors and the evaluation of their associated effects on behavior. In this work, samples of around 30 age-synchronized worms were treated with each peptide. Lifespan and chemotaxis assays were performed in a wildtype strain to evaluate toxicity and associative memory. For chemotaxis assays, C. elegans was conditioned with benzaldehyde beginning at the egg stage. The conditioned worms associated the odor cue with the presence of food and were capable to remember the association, allowing the testing of memory recall in the worms. Additionally, the progression of an Aβ-dependent paralysis phenotype was assessed in transgenic worm strains expressing Aβ (CL4176 and CL2006). Only A30W mutant 1-40 variant showed a slightly reduced toxicity at 40µM with 20% of worms surviving up to 19 days, while the remaining peptides had little to non-effect in toxicity in comparison to wildtype Aβ. However, treatment with A30W and K28A peptides 1-42 variant was able to prevent loss of associative memory, while M35C and K28A mutants caused a delay of up to 48 hours of the paralysis phenotype onset. Although further studies need to be conducted to analyze the effectiveness of the peptides, these results suggest that some of the mutants could improve Aβ related phenotypes in C. elegans and, therefore, have a putative potential for the design of future drugs against Alzheimer’s Disease.