Copper accumulation and the effect of chelation treatment on cerebral amyloid angiopathy compared to parenchymal amyloid plaques

Abstract

Accumulation of fibrillar amyloid β-protein (Aβ) in parenchymal plaques and in blood vessels of the brain, the latter condition known as cerebral amyloid angiopathy (CAA), are hallmark pathologies of Alzheimer's disease (AD) and related disorders. Cerebral amyloid deposits have been reported to accumulate various metals, most notably copper and zinc. Here we show that, in human AD, copper is preferentially accumulated in amyloid-containing brain blood vessels compared to parenchymal amyloid plaques. In light of this observation, we evaluated the effects of reducing copper levels in Tg2576 mice, a transgenic model of AD amyloid pathologies. The copper chelator, tetrathiomolybdate (TTM), was administered to twelve month old Tg2576 mice for a period of five months. Copper chelation treatment significantly reduced both CAA and parenchymal plaque load in Tg2576 mice. Further, copper chelation reduced parenchymal plaque copper content but had no effect on CAA copper levels in this model. These findings indicate that copper is associated with both CAA deposits and parenchymal amyloid plaques in humans, but less in Tg2576 mice. TTM only reduces copper levels in plaques in Tg2576 mice. Reducing copper levels in the brain may beneficially lower amyloid pathologies associated with AD.

Fig. 1.

Higher copper content in cerebral vascular amyloid deposits compared to parenchymal plaque amyloid deposits in the same AD brain tissue. Epifluorescence images of the thioflavin S staining and corresponding copper XFM images of parenchymal (A,C) and cerebral vascular (B,D) amyloid deposits from the same AD brain tissue. Scale bars = 5 μm. (E) Relative copper levels in the vascular amyloid deposits were ~3-fold higher than in parenchymal amyloid plaques. Data shown are mean ± S.D. of n = 5 for each type of amyloid deposit from the same tissues.

Fig. 2.

ELISA analysis of cerebral Aβ40 and Aβ42 peptides in control and TTM-treated Tg2576 mice. The total levels of Aβ40 peptides (black bars) and Aβ42 peptides (gray bars) in the forebrains of control and TTM-treated Tg2576 mice were measured by ELISA as described under “Materials and Methods.” The data presented are the means ± S.D. of triplicate measurements of n = 5–6 mice per group.

Fig. 3.

TTM treatment reduces CAA load in Tg2576 mice. Brain sections from control (A) and TTM-treated (B) Tg2576 mice were stained for fibrillar amyloid using thioflavin-S (green) and immunolabeled for collagen type IV to identify cerebral blood vessels (red). Scale bars = 50 μM. (C) Quantitation of cortical vascular thioflavin-S positive amyloid load in control and TTM-treated Tg2576 mice. Data shown are mean ± S.D. of n = 5 Tg2576 mice per group.

Fig. 4.

TTM treatment reduces cortical amyloid plaque load in Tg2576 mice. Brain sections from control (A) and TTM-treated (B) Tg2576 mice were stained for fibrillar amyloid using thioflavin-S (green) and immunolabeled for collagen type IV to identify cerebral blood vessels (red). Scale bars = 50 μM. (C) Quantitation of cortical thioflavin-S positive amyloid plaque load in control and TTM-treated Tg2576 mice. Data shown are mean ± S.D. of n = 5 Tg2576 mice per group.

Fig. 5.

TTM treatment reduces cortical amyloid plaque copper levels in Tg2576 mice. Brain sections from control and TTM-treated Tg2576 mice were stained with thioflavin S to identify fibrillar amyloid deposits in cerebral vessels (V) and parenchymal amyloid plaques (P). The relative copper levels in these deposits were determined using XFM and tissue density was normalized using FTIR microspectroscopy. All Cu images are shown on the same intensity scale. Histograms shown are mean ± S.D. of n = 5 Tg2576 mice per group.