Cross-domain binding of anti-fibrillation peptide TNGQ to islet amyloid polypeptide provides cytoprotective effects in giant unilamellar vesicles and pancreatic β-cells.

Islet amyloid polypeptide (IAPP) fibrillation induces β-cell dysfunction and toxicity in patients with type 2 diabetes. Cytotoxicity is caused by the ability of IAPP fibrils and fibrillar intermediates to permeate the cellular membrane of pancreatic β-cells, trigger endoplasmic reticular stress, induce reactive oxygen species production, and upregulate apoptosis-related genes. Thus, inhibition of IAPP fibrillation is of great interest for preventing associated cytotoxicity. In this study, the cellular protective effects of three anti-fibrillation tetrapeptides, YMSV, MANT, and TNGQ, against IAPP fibrillation-induced membrane leakage in giant unilamellar vesicles (GUVs) and toxicity in RIN-m cells were evaluated. The anti-fibrillation activity of TNGQ translated to cytoprotective effects as it resulted in a 69.0 ± 7.9% decrease in calcein release in GUVs and a significant increase in cell viability from 6.4 ± 6.4% with IAPP to 47.5 ± 3.8% with the addition of TNGQ. MANT slightly inhibited IAPP-induced GUV leakage and increased cell viability. In contrast, the protective effect of YMSV against IAPP fibrillation-induced membrane damage in GUVs was completely diminished in β-cells. Molecular docking of pentameric IAPP showed that Asn21 and Asn22 of IAPP are important for inhibitor binding, which, coupled with the cross-domain binding interactions of TNGQ, explains its stronger anti-fibrillation and cytoprotective effects than MANT and YMSV. These findings provide insights into the functional significance of peptide-IAPP binding interactions in mitigating fibrillation and IAPP fibrillation-induced cytotoxicity.