On the association between amyloid fibrils and glycosaminoglycans; possible interactive role of Ca2+ and amyloid P-component

Abstract

SUMMARYWe have previously reported the specific association of glycosaminoglycans (GAG) and proteoglycans (PG) with amyloid fibrils and characterized the polysaccharides directly extracted from amyloid-laden tissues. In the present study we further elucidate the association between purified amyloid fibrils and GAG/PG with special reference to those GAG/PG associated with amyloid Pcomponent (AP) and the interactive role of Ca2+ ions. Amyloid fibrils were isolated from human hepatic AA amyloid employing water extraction with and without preceding removal of AP, an extrafibrillar protein component of all amyloids, using sodium citrate. GAG/PG co-isolated with the amyloid extracts, with and without AP, were isolated and characterized. Agarose-affinity chromatography of extracts containing AP was performed, and the GAG associated with this extrafibrillary protein were characterized as well. Several different GAG/PG populations were demonstrated in the various extracts. The abolition of calcium-dependent binding markedly influenced the amount of GAG/PG recovered in the fibril extracts, as well as the total amount of amyloid material obtained. Thus, it seems that calcium plays an important role in the association between the fibrils and the sugar moieties, and that a significant fraction of the GAG found in amyloid exhibits a Ca2+-dependent fibril-GAG interaction. No significant difference in the proportion between galactosaminoglycans and glucosamines was, however, disclosed when the two extraction protocols were compared, suggesting that no particular GAG species has a higher affinity for the fibrils themselves. Both dermatan/chondroitin sulphate and heparan sulphate identified in the present study exhibited a Ca2+-dependent interaction with AP, supporting previous findings. However, the amyloid-associated galactosaminoglycans found, especially the large PG appearing in small amounts, seemed to have a higher affinity for the extrafibrillar AP than the other GAG.

Characterization of Proteoglycans and Glycosaminoglycans in Splenic AA Amyloid Induced in Mink

“…Again, similar findings in mice suggest these phenomena to be of importance for amyloidosis in general [20, 21]. Previous observations made by our group [49] strongly indicate that GAGs bind directly to the AA fibrils via a calcium‐dependent mechanism. In addition, computer analyses [50] have predicted a putative GAG‐binding site in mink SAA, and recently a binding site for heparin/HS in mouse SAA was identified [51].…”

Protease resistance of ex vivo amyloid fibrils implies the proteolytic selection of disease-associated fibril morphologies

“…Up to 12% (w/w) of the anhydrous mass of ex vivo fibrils were reported to be originate from lipids, with sphingolipids, cholesterol and cholesterol esters being in particular abundant [42]. Up to 2% (w/w) of the mass can be glycosaminoglycans [44], in particular heparan sulphate and dermatan sulphate [45]. We cannot rule out that SAP in conjunction with other non-fibril components of amyloid deposits that were not tested in our study contribute to defining the proteolytic stability of ex vivo amyloid fibrils.…”

Preferential association of serum amyloid P component with fibrillar deposits in familial British and Danish dementias: Similarities with Alzheimer's disease

“…SAP is associated in vivo with all types of amyloid deposits in which its presence has been investigated. Although originally thought that the binding to amyloid molecules involved glycosaminoglycans commonly associated with the in vivo formed fibrils [7,8], SAP has been demonstrated to bind avidly in vitro to fibrils formed exclusively from pure proteins or peptides [1]. It is now believed that the tissue accumulation of SAP in different types of amyloids originates from its particular affinity for the various amyloid molecules.…”