Novel Amylin Analogues Reduce Amyloid-β Cross-Seeding Aggregation and Neurotoxicity

Background: Type 2 diabetes related human islet amyloid polypeptide (hIAPP) plays a dual role in Alzheimer's disease (AD). hIAPP has neuroprotective effects in AD mouse models whereas, high hIAPP concentrations can promote co-aggregation with amyloid-beta (A beta) to promote neurodegeneration. In fact, both low and high plasma hIAPP concentration has been associated with AD. Therefore, non-aggregating hIAPP analogues have garnered interest as a treatment for AD. The aromatic amino acids F23 and 126 in hIAPP have been identified as the key residues involved in self-aggregation and A beta cross-seeding. Objective: Three novel IAPP analogues with single and double alanine mutations (A1 = F23, A2 =126, and A3 = F23 +126) were assessed for their ability to aggregate, modulate A beta oligomer formation, and alter neurotoxicity. Methods: A range of biophysical methods including Thioflavin-T, gel electrophoresis, photo-crosslinking, circular dichroism combined with cell viability assays were utilized to assess protein aggregation and toxicity. Results: All IAPP analogues showed significantly less self-aggregation than hIAPP. Co-aggregated A beta(42)-A2 and A3 also showed reduced aggregation compared to A beta(42)-hIAPP mixtures. Self- and co-oligomerized A1, A2, and A3 exhibited random coil conformations with reduced beta sheet content compared to hIAPP and A beta(42)-hIAPP aggregates. A1 was toxic at high concentrations compared to A2 and A3. However, co-aggregated A beta(42)-A1, A2, or A3 showed reduced neurotoxicity compared to A beta(42), hIAPP, and A beta(42)-hIAPP aggregates. Conclusion: These findings confirm that hIAPP analogues with non-aromatic residues at positions 23 and 26 have reduced self-aggregation and the ability to neutralize A beta(42) toxicity. This warrants further characterization of their protective effects in pre-clinical AD models.