Affiliations: [a] Curtin Medical School, Curtin Health Innovation Research Institute, Curtin University, Perth, WA, Australia
| [b] Centre of Excellence for Alzheimer’s Disease Research and Care, School of Medical and Health Sciences, Edith Cowan University, Perth, WA, Australia
| [c] School of Biomedical Science, Macquarie University, Sydney, NSW, Australia
Correspondence:
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Correspondence to: Dr. Prashant Bharadwaj, Centre of Excellence for Alzheimer’s Disease Research and Care, School of Medical and Health Sciences, Edith Cowan University, Perth WA 6027, Australia. Tel.: +61433579575; E-mail: p.bharadwaj@ecu.edu.au.
Note: [1] These authors contributed equally to this work.
Abstract: 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-β (Aβ) 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 Aβ 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 Aβ 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 Aβ42-A2 and A3 also showed reduced aggregation compared to Aβ42-hIAPP mixtures. Self- and co-oligomerized A1, A2, and A3 exhibited random coil conformations with reduced beta sheet content compared to hIAPP and Aβ42-hIAPP aggregates. A1 was toxic at high concentrations compared to A2 and A3. However, co-aggregated Aβ42-A1, A2, or A3 showed reduced neurotoxicity compared to Aβ42, hIAPP, and Aβ42-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 Aβ42 toxicity. This warrants further characterization of their protective effects in pre-clinical AD models.
