Activation of the 20S proteasome as a possible strategy to counteract amylin oligomerization in type 2 diabetes

Human amylin, called also islet amyloid polypeptide (hIAPP), is the principal constituent of amyloid deposits in the pancreatic islets. Together with hyperglycemia, hIAPP-derived oligomers and aggregates are important culprits in type 2 diabetes mellitus (T2DM). Preventing aggregation, and in particular inhibiting the formation and/or stimulating degradation of toxic amylin oligomers formed early in the process, may reduce the negative effects of T2DM. Such therapeutic intervention may be enabled by activation of the 20S proteasome, a proteolytic system responsible for digesting proteins that are damaged or natively exhibit aggregation tendencies. In this work, we showed that in the lag phase of the aggregation process, soluble oligomers of small size (dimer to heptamer) were present alongside the amylin monomer. These oligomers inhibited the activity of the human 20S proteasome (h20S). To counteract this inhibition, we designed two activators that proved to be effective in restoring the peptidase efficiency of h20S to basal levels and even stimulating the enzyme to degrade the fluorogenic substrate more efficiently. They showed this effect both against isolated h20S and in cell lysate.