Amyloid beta 1-40 and 1-42 fibril ratios and maturation level cause conformational differences with minimal impact on autophagy and cytotoxicity

The amyloid beta (A beta) peptide has a central role in Alzheimer's disease (AD) pathology. The peptide length can vary between 37 and 49 amino acids, with A beta 1-42 being considered the most disease-related length. However, A beta 1-40 is also found in A beta plaques and has shown to form intertwined fibrils with A beta 1-42. The peptides have previously also shown to form different fibril conformations, proposed to be related to disease phenotype. To conduct more representative in vitro experiments, it is vital to uncover the impact of different fibril conformations on neurons. Hence, we fibrillized different A beta 1-40:42 ratios in concentrations of 100:0, 90:10, 75:25, 50:50, 25:75, 10:90 and 0:100 for either 24 h (early fibrils) or 7 days (aged fibrils). These were then characterized based on fibril width, LCO-staining and antibody-staining. We further challenged differentiated neuronal-like SH-SY5Y human cells with the different fibrils and measured A beta content, cytotoxicity and autophagy function at three different time-points: 3, 24, and 72 h. Our results revealed that both A beta 1-40:42 ratio and fibril maturation affect conformation of fibrils. We further show the impact of these conformation changes on the affinity to commonly used A beta antibodies, primarily affecting A beta 1-40 rich aggregates. In addition, we demonstrate uptake of the aggregates by neuronally differentiated human cells, where aggregates with higher A beta 1-42 ratios generally caused higher cellular levels of A beta. These differences in A beta abundance did not cause changes in cytotoxicity nor in autophagy activation. Our results show the importance to consider conformational differences of A beta fibrils, as this can have fundamental impact on A beta antibody detection. Overall, these insights underline the need for further exploration of the impact of conformationally different fibrils and the need to reliably produce disease relevant A beta aggregates.image