Overall Sulfation of Heparan Sulfate from Pancreatic Islet β-TC3 Cells Increases Maximal Fibril Formation but Does Not Determine Binding to the Amyloidogenic Peptide Islet Amyloid Polypeptide

Islet amyloid, a pathologic feature of type 2 diabetes, contains the islet beta-cell peptide islet amyloid polypeptide (IAPP) as its unique amyloidogenic component. Islet amyloid also contains heparan sulfate proteoglycans (HSPGs) that may contribute to amyloid formation by binding IAPP via their heparan sulfate (HS) chains. We hypothesized that beta-cells produce HS that bind IAPP via regions of highly sulfated disaccharides. Unexpectedly, HS from the beta-cell line beta-TC3 contained fewer regions of highly sulfated disaccharides compared with control normal murine mammary gland (NMuMG) cells. The proportion of HS that bound IAPP was similar in both cell lines ( 65%). The sulfation pattern of IAPP-bound versus non-bound HS from beta-TC3 cells was similar. In contrast, IAPP-bound HS from NMuMG cells contained frequent highly sulfated regions, whereas the nonbound material demonstrated fewer sulfated regions. Fibril formation from IAPP was stimulated equally by IAPP-bound beta-TC3 HS, non-bound beta-TC3 HS, and non-bound NMuMG HS but was stimulated to a greater extent by the highly sulfated IAPP-bound NMuMG HS. Desulfation of HS decreased the ability of both beta-TC3 and NMuMG HS to stimulate IAPP maximal fibril formation, but desulfated HS from both cell types still accelerated fibril formation relative to IAPP alone. In summary, neither binding to nor acceleration of fibril formation from the amyloidogenic peptide IAPP is dependent on overall sulfation in HS synthesized by beta-TC3 cells. This information will be important in determining approaches to reduce HS-IAPP interactions and ultimately prevent islet amyloid formation and its toxic effects in type 2 diabetes.