Levels of Amyloid Beta (Aβ) Expression in the Caenorhabditis elegans Neurons Influence the Onset and Severity of Neuronally Mediated Phenotypes

A characteristic feature of Alzheimer’s disease (AD) is the formation of neuronal extracellular senile plaques composed of aggregates of fibrillar amyloid β (Aβ) peptides, with the Aβ1-42 peptide being the most abundant species. These Aβ peptides have been proposed to contribute to the pathophysiology of the disease; however, there are few tools available to test this hypothesis directly. In particular, there are no data that establish a dose–response relationship between Aβ peptide expression level and disease. We have generated a panel of transgenic Caenorhabditis elegans strains expressing the human Aβ1-42 peptide under the control of promoter regions of two pan-neuronal expressed genes, snb-1 and rgef-1. Phenotypic data show strong age-related defects in motility, subtle changes in chemotaxis, reduced median and maximum lifespan, changes in health span indicators, and impaired learning. The Aβ1-42 expression level of these strains differed as a function of promoter identity and transgene copy number, and the timing and severity of phenotypes mediated by Aβ1-42 were strongly positively correlated with expression level. The pan-neuronal expression of varying levels of human Aβ1-42 in a nematode model provides a new tool to investigate the in vivo toxicity of neuronal Aβ expression and the molecular and cellular mechanisms underlying AD progression in the absence of endogenous Aβ peptides. More importantly, it allows direct quantitative testing of the dose–response relationship between neuronal Aβ peptide expression and disease for the first time. These strains may also be used to develop screens for novel therapeutics to treat Alzheimer’s disease.