The amyloid plaque proteome in early onset Alzheimer’s disease and Down syndrome

Abstract

Amyloid plaques contain many proteins in addition to beta amyloid (Aβ). Previous studies examining plaque-associated proteins have shown these additional proteins are important; they provide insight into the factors that drive amyloid plaque development and are potential biomarkers or therapeutic targets for Alzheimer’s disease (AD). The aim of this study was to comprehensively identify proteins that are enriched in amyloid plaques using unbiased proteomics in two subtypes of early onset AD: sporadic early onset AD (EOAD) and Down Syndrome (DS) with AD. We focused our study on early onset AD as the drivers of the more aggressive pathology development in these cases is unknown and it is unclear whether amyloid-plaque enriched proteins differ between subtypes of early onset AD. Amyloid plaques and neighbouring non-plaque tissue were microdissected from human brain sections using laser capture microdissection and label-free LC–MS was used to quantify the proteins present. 48 proteins were consistently enriched in amyloid plaques in EOAD and DS. Many of these proteins were more significantly enriched in amyloid plaques than Aβ. The most enriched proteins in amyloid plaques in both EOAD and DS were: COL25A1, SMOC1, MDK, NTN1, OLFML3 and HTRA1. Endosomal/lysosomal proteins were particularly highly enriched in amyloid plaques. Fluorescent immunohistochemistry was used to validate the enrichment of four proteins in amyloid plaques (moesin, ezrin, ARL8B and SMOC1) and to compare the amount of total Aβ, Aβ40, Aβ42, phosphorylated Aβ, pyroglutamate Aβ species and oligomeric species in EOAD and DS. These studies showed that phosphorylated Aβ, pyroglutamate Aβ species and SMOC1 were significantly higher in DS plaques, while oligomers were significantly higher in EOAD. Overall, we observed that amyloid plaques in EOAD and DS largely contained the same proteins, however the amount of enrichment of some proteins was different in EOAD and DS. Our study highlights the significant enrichment of many proteins in amyloid plaques, many of which may be potential therapeutic targets and/or biomarkers for AD.

GTP energy dependence of endocytosis and autophagy in the aging brain and Alzheimer’s disease

“…However, overexpression of Arl8b also caused a striking alkalinization of lysosomes and movement toward the cell periphery versus a more uniform distribution of lysosomes throughout the cytoplasm [ 105 ]. A proteomic study in human tissue reported enrichment of Arl8b in amyloid plaques [ 106 ]. These data suggest that changes in the expression or functioning of Arl8 affects the fusion of the lysosome with the autophagosome or late endosome, which could have implications in autophagosome accumulation observed in AD.…”

Brain Amyloid in Sporadic Young Onset Alzheimer’s Disease

“…Others support a spectrum of YOAD and that emphasis of genetic variants such as the prion protein gene (PRNP) and the microtubular associated protein tau (MAPT) in AD plus studies of biofluids, multimodal imaging, and other methodologies may help to gain insight into YOAD [26,27]. Furthermore, the investigation of the amyloid plaque proteome in YOAD and Down syndrome using laser capture microdissection suggest that lysosomal proteins, like secreted modular calcium-binding protein 1, phosphorylated A␤, and pyroglutamate A␤ may be important divergents to neuritic plaques from old onset patients, suggesting therapeutic possibilities [28].…”

Why are amyloid-β plaques detected by X-ray phase-contrast imaging? Role of metals revealed through combined synchrotron infrared and X-ray fluorescence microscopies

“…Aβ fibrils, which match the fluorescence area and exceed the core area, cannot explain this difference as similar levels of fibrils were measured with µFTIR. Other factors, such as structural [49] or proteomic [56] differences between strains, might play a role.…”