Novel Amylin Analogues Reduce Amyloid-ß 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-ß (Aß) 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 I26 in hIAPP have been identified as the key residues involved in self-aggregation and Aß cross-seeding. OBJECTIVE: Three novel IAPP analogues with single and double alanine mutations (A1 = F23, A2 = I26, and A3 = F23 + I26) were assessed for their ability to aggregate, modulate Aß 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 Aß42-A2 and A3 also showed reduced aggregation compared to Aß42-hIAPP mixtures. Self- and co-oligomerized A1, A2, and A3 exhibited random coil conformations with reduced beta sheet content compared to hIAPP and Aß42-hIAPP aggregates. A1 was toxic at high concentrations compared to A2 and A3. However, co-aggregated Aß42-A1, A2, or A3 showed reduced neurotoxicity compared to Aß42, hIAPP, and Aß42-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 Aß42 toxicity. This warrants further characterization of their protective effects in pre-clinical AD models.