title: Collagenous Alzheimer amyloid plaque component assembles amyloid fibrils into protease resistant aggregates.
abstract: Recently, a novel plaque-associated protein, collagenous Alzheimer amyloid plaque component (CLAC), was identified in brains from patients with Alzheimer's disease. CLAC is derived from a type II transmembrane collagen precursor protein, termed CLAC-P (collagen XXV). The biological function and the contribution of CLAC to the pathogenesis of Alzheimer's disease and plaque formation are unknown. In vitro studies indicate that CLAC binds to fibrillar, but not to monomeric, amyloid beta-peptide (Abeta). Here, we examined the effects of CLAC on Abeta fibrils using assays based on turbidity, thioflavin T binding, sedimentation analysis, and electron microscopy. The incubation of CLAC with preformed Abeta fibrils led to increased turbidity, indicating that larger aggregates were formed. In support of this contention, more Abeta was sedimented in the presence of CLAC, as determined by gel electrophoresis. Moreover, electron microscopy revealed an increased amount of Abeta fibril bundles in samples incubated with CLAC. Importantly, the frequently used thioflavin T-binding assay failed to reveal these effects of CLAC. Digestion with proteinase K or trypsin showed that Abeta fibrils, incubated together with CLAC, were more resistant to proteolytic degradation. Therefore, CLAC assembles Abeta fibrils into fibril bundles that have an increased resistance to proteases. We suggest that CLAC may act in a similar way in vivo.
authors.affiliation: Karolinska Institutet and Sumitomo Pharmaceuticals Alzheimer Center (KASPAC), Neurotec, Novum, Huddinge, Sweden.
authors.forename: Linda
authors.initials: L
authors.lastname: Söderberg
authors.forename: Camilla
authors.initials: C
authors.lastname: Dahlqvist
authors.forename: Hiroyoshi
authors.initials: H
authors.lastname: Kakuyama
authors.forename: Johan
authors.initials: J
authors.lastname: Thyberg
authors.forename: Akira
authors.initials: A
authors.lastname: Ito
authors.forename: Bengt
authors.initials: B
authors.lastname: Winblad
authors.forename: Jan
authors.initials: J
authors.lastname: Näslund
authors.forename: Lars O
authors.initials: LO
authors.lastname: Tjernberg
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism* / Q000473:pathology; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D052160:Benzothiazoles; D005456:Fluorescent Dyes / Q000378:metabolism; D006801:Humans; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D024041:Non-Fibrillar Collagens / Q000737:chemistry / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D013844:Thiazoles / Q000378:metabolism
chemical_list: D016229:Amyloid beta-Peptides; D052160:Benzothiazoles; C456021:COL25A1 protein, human; D005456:Fluorescent Dyes; D009419:Nerve Tissue Proteins; D024041:Non-Fibrillar Collagens; D010446:Peptide Fragments; D013844:Thiazoles; C078592:amyloid beta-protein (1-40); C009462:thioflavin T