New insights into the roles of cell surface glycosaminoglycans in plasma membrane perturbation associated with amyloidoses

Noé Quittot, Mathilde Fortier, Margaryta Babych, Phuong Trang Nguyen, Mathew Sebastiao and Steve Bourgault

Department of Chemistry, Université du Québec à Montréal, C.P. 8888, Succursale Centre-Ville, Montréal, H3C 3P8, Canada
Center of Excellence in Research on Orphan Diseases - Courtois Foundation, CERMO-FC
Quebec Network for Research on Protein Function, Engineering and Applications, PROTEO

Glycosaminoglycans (GAGs) are long and unbranched anionic heteropolysaccharides that have been associated with virtually all amyloid deposits. Soluble sulfated GAGs are known for their propensity to promote the self-assembly of numerous amyloidogenic proteins and to modulate their cytotoxicity. Nonetheless, although GAGs are prevalent on the outer leaflet of eukaryotic cell plasma membrane as part of proteoglycans, their contributions in the perturbation of lipid bilayer induced by amyloid polypeptides remain unknown. Herein, we investigate the roles of GAGs in the cytotoxicity and plasma membrane perturbation induced by the islet amyloid polypeptide (IAPP), whose deposition in the pancreatic islets is associated with type II diabetes. Cellular assays using GAG-deficient cells reveal that GAGs exacerbate IAPP-induced cytotoxicity and permeabilization of the plasma membrane. Confocal microscopy and flow cytometry analyses show that IAPP binding and sequestration at the cell surface are dependent of GAGs and of the aggregation propensity of the peptide. Using giant plasma membrane vesicles (GPMVs) prepared from GAG-deficient cells, we validate the contributions of membrane-embedded proteoglycans in IAPP-induced membrane disassembly. In sharp contrast to soluble sulfated GAGs, kinetics of amyloid self-assembly expose that the presence of GAGs on GPMVs does not significantly modulate amyloid formation. Overall, this study indicates that cell surface GAGs increase the local concentration of IAPP in the vicinity of the plasma membrane, promoting lipid bilayer perturbation and cell death.