Mostly Separate Distributions of CLAC- versus Aβ40- or Thioflavin S-Reactivities in Senile Plaques Reveal Two Distinct Subpopulations of β-Amyloid Deposits

Abstract

Collagenous Alzheimer amyloid plaque component (CLAC) is a unique non-Abeta amyloid component of senile plaques (SP) derived from a transmembrane collagen termed CLAC-precursor. Here we characterize the chronological and spatial relationship of CLAC with other features of SP amyloid in the brains of patients with Alzheimer's disease (AD), Down syndrome (DS), and of PSAPP transgenic mice. In AD and DS cerebral cortex, CLAC invariably colocalized with Abeta42 but often lacked Abeta40- or thioflavin S (thioS)-reactivities. Immunoelectron microscopy of CLAC-positive SP showed labeling of fibrils that are more loosely dispersed compared to typical amyloid fibrils in CLAC-negative SP. In DS cerebral cortex, diffuse plaques in young patients were negative for CLAC, whereas a subset of SP became CLAC-positive in patients aged 35 to 50 years, before the appearance of Abeta40. In DS cases over 50 years of age, Abeta40-positive SP dramatically increased, whereas CLAC burden remained at a constant level. In PSAPP transgenic mice, CLAC was positive in the diffuse Abeta deposits surrounding huge-cored plaques. Thus, CLAC and Abeta40 or thioS exhibit mostly separate distribution patterns in SP, suggesting that CLAC is a relatively early component of SP in human brains that may have inhibitory effects against the maturation of SP into beta-sheet-rich amyloid deposits.

CLAC Binds to Amyloid β Peptides through the Positively Charged Amino Acid Cluster within the Collagenous Domain 1 and Inhibits Formation of Amyloid Fibrils

“…DAEFRHDS-GYE) that may interact with positive charges on CLAC. Our recent immunohistochemical analysis of postmortem brains from patients with AD or Down's syndrome showed that CLAC is a relatively early component of senile plaque amyloid coexisting with A␤42, whereas deposition of A␤40 occurs chiefly in CLAC-negative senile plaques at a later stage (17). This apparently suggested that CLAC may have different affinities to A␤42 and A␤40.…”

“…We also showed that the ectodomain of CLAC-P is shed by furin convertase and secreted as a soluble form of CLAC (sCLAC) (15). Immunohistochemical analysis of postmortem human brains revealed a unique pattern of CLAC deposition in AD and Down's syndrome brains (17); CLAC was negative in A␤42-positive, A␤40-negative pure diffuse plaques that are considered to be the earliest form of A␤ deposition, whereas a fraction of primitive-type senile plaques became CLAC-positive at a relatively early stage of plaque maturation as the fibrillization of A␤ progresses. Notably, mature plaques that appear at later stages were A␤40/thioflavin S-positive but remained CLAC-negative (17).…”

“…Immunohistochemical analysis of postmortem human brains revealed a unique pattern of CLAC deposition in AD and Down's syndrome brains (17); CLAC was negative in A␤42-positive, A␤40-negative pure diffuse plaques that are considered to be the earliest form of A␤ deposition, whereas a fraction of primitive-type senile plaques became CLAC-positive at a relatively early stage of plaque maturation as the fibrillization of A␤ progresses. Notably, mature plaques that appear at later stages were A␤40/thioflavin S-positive but remained CLAC-negative (17). These findings suggested the possibility that CLAC may play an inhibitory role in the deposition of senile plaque amyloid by binding to early A␤ deposits and preventing further incorporation of A␤ peptides to develop ␤-sheet-rich, mature senile plaques.…”

Binding mode of Thioflavin T and other molecular probes in the context of amyloid fibrils—current status

“…Thioflavin S (ThS) has been applied to some extent, but mainly for diagnosis of amyloid fibril deposits in tissue sections using fluorescence microscopy [61,62]. ThS is less suitable for kinetics analysis than ThT since free ThS fluorescence interferes significantly with the determination of the fibrilbound species [40,46].…”

“…Radioactively labelled [55,56] PTAA Fluorescence [57] Resveratrol Fluorescence [58] SH-516 Fluorescence [59][60][61] T-284 Fluorescence [59,61] Thiazin red Fluorescence [62] Thioflavin S* Fluorescence [63,64] Thioflavin T Fluorescence [65,66] X-34 Fluorescence [67] *Mixture of planar asymmetric dyes with charged group at the end of the molecule.…”