Highly sulfated domains of heparan sulfate (HS), alias HS S-domains, consist of consecutive clusters of a trisulfated disaccharide unit [iduronic acid (2S)-glucosamine (NS, 6S)]. 1 These HS S-domains are a major determinant of specific interactions between HS and its protein ligands, including growth factors, chemokines, and morphogens, and thus they regulate HS functions in diverse biological processes. 2,3 In addition to being involved in biological processes, HS is associated with various amyloid deposits, including those in transthyretin amyloidosis (ATTR amyloidosis), 4 Alzheimer disease (AD), 5e7 light-chain amyloidosis, 8 and amyloid A (AA) amyloidosis, 9 which suggests that HS may affect amyloid deposition and amyloidosis pathology. Indeed, HS and heparin, whose major components are HS S-domains, reportedly promoted fibrillogenesis of various amyloidogenic proteins, such as transthyretin (TTR) in ATTR amyloidosis, 4,10 amyloid b (Ab) in AD, 11e13 cellular prion, Ig light chain in light-chain amyloidosis, 14 and serum AA in AA amyloidosis. 15e17 Also, HS at the cell surface mediated interactions of cells with and cytotoxicity of amyloid fibrils or protein aggregates, including those of t protein and a-synuclein, 18 Ab, 19 Supported in part by the Japan Society for the Promotion of Science grants-in-aid for young scientists B-15K19488 (K.N.