Senile plaques in Alzheimer's disease arise from Aβ‐ and Cathepsin D‐enriched mixtures leaking out during intravascular haemolysis and microaneurysm rupture

Abstract

Senile plaques are a pathological hallmark of Alzheimer's disease (AD), yet the mechanism underlying their generation remains unknown. Beta‐amyloid peptide (Aβ) is a major component of senile plaques. We analysed AD brain tissues with histochemistry, immunohistochemistry and fluorescence imaging to examine the neural, vascular or blood Aβ contribution to senile plaque development. We found little neural marker co‐expression with plaque Aβ, while co‐expression of blood markers, such as Haemin and ApoE, was abundant. The plaque cores were structured with vascular and glial proteins outside and blood metabolites inside, co‐localizing with a characteristic of Hoechst staining‐independent blue autofluorescence. Erythrocyte‐interacting Aβ is linked to coagulation, elevated calcium and blue autofluorescence, and it is associated with intravascular haemolysis, atherosclerosis, cerebral amyloid angiopathy, microaneurysm, and often with Cathepsin D co‐expression. We identified microaneurysms as major sites of amyloid formation. Our data suggest that senile plaques arise from Aβ‐ and Cathepsin D‐enriched mixtures leaking out during intravascular haemolysis and microaneurysm rupture.

Re-evaluating the nuclear staining on pathological sections in Alzheimer’s disease

“…The chance of dense-core senile plaques being derived from individual neurons is low. Secondly, the centers of dense-core senile plaques contained blood vessels as previously reported 2,7,8 . Thirdly，the plaque cores contained Aβ and a large amount of blood-derived materials such as HBA , Hemin and ApoE 2 .…”

“…We did observe that some nucleated neural cells have diffusive spotted Aβ signals representing neuronal cell Aβ expression. However, neural cell Aβ staining was quite different from the aggregated amyloid plaque Aβ staining and was significantly weaker, as we analyzed in the published study 2 . We also did Cathepsin D immunostaining experiments with no nuclear counter stains.…”

“…Several previous studies had found that there is characteristic blue auto fluorescence in the senile plaques and also in CAA 2–6 . All of the cores of dense-core senile plaques have strong blue auto fluorescence with no exception according to our observations.…”

“…PI labeling of 59 dense-core plaques were recorded. None of them showed PI labeling in the plaque cores, which means that, most of the time the cores of dense-core plaques have no nuclei staining 2 . In our experiments, nuclear staining and plaque core fibrillar Aβ or MetaBlue auto fluorescence staining is mutually exclusive.…”

“…However, we noticed that all of the nuclei staining in this paper was based on fluorescent images in the blue fluorescence channel. We did extensive studies on the senile plaque blue autofluorescence material, which was assigned a temporary name of MetaBlue in our pervious study 2 , and found that senile plaque MetaBlue autofluorescence could be easily mistaken as blue nuclei staining. Thus, the blue “nuclei” staining in this paper is probably inaccurate since it was not verified in other fluorescent channels and their “nuclei”-related data might be mis-interpreted.…”