Amyloid aggregation in the presence of mechanical stress and hydrophobic interfaces

Amyloid fibrils are self-assembled protein nanostructures associated with several pathological conditions. The destabilization of the protein native structure is the key event which triggers amyloid fibril formation and much research effort is devoted to identifying the physico-chemical factors favouring the aggregation process. Several pieces of evidence suggest that the presence of hydrophobic interfaces and mechanical stress favour protein destabilization and therefore can enhance protein aggregation. This work explores the effect of shear forces and hydrophobic interfaces in the aggregation process. The attention has been focused on the process which takes place in cardiac tissue, that is a typical deposition site of amyloid fibrils associated with cardiac amyloidosis. To this purpose, a prototype of a device has been set up to mimic the cardiac environment in its chemical composition and mechanical behavior. Exposure of hydrophobic interfaces is achieved by exploiting contraction/expansion cycles of a flexible polymeric cell. Cell walls are functionalized with elastin, a typical component of the physiological environment of cardiac tissue which exposes hydrophobic regions when subject to stress. To set up the experimental conditions, k-casein was chosen as a protein model. Amyloid aggregation was studied both in the absence and in the presence of shear stress. Protein aggregates were characterized by atomic force microscopy (AFM) and fluorescence spectroscopy measurements. The experimental results obtained in the present work will yield insight into the mechanisms of protein aggregation under pathological conditions.