Proteins that mediate protein aggregation and cytotoxicity distinguish Alzheimer's hippocampus from normal controls

Abstract

SummaryNeurodegenerative diseases are distinguished by characteristic protein aggregates initiated by disease‐specific ‘seed’ proteins; however, roles of other co‐aggregated proteins remain largely unexplored. Compact hippocampal aggregates were purified from Alzheimer's and control‐subject pools using magnetic‐bead immunoaffinity pulldowns. Their components were fractionated by electrophoretic mobility and analyzed by high‐resolution proteomics. Although total detergent‐insoluble aggregates from Alzheimer's and controls had similar protein content, within the fractions isolated by tau or Aβ1–42 pulldown, the protein constituents of Alzheimer‐derived aggregates were more abundant, diverse, and post‐translationally modified than those from controls. Tau‐ and Aβ‐containing aggregates were distinguished by multiple components, and yet shared >90% of their protein constituents, implying similar accretion mechanisms. Alzheimer‐specific protein enrichment in tau‐containing aggregates was corroborated for individuals by three analyses. Five proteins inferred to co‐aggregate with tau were confirmed by precise in situ methods, including proximity ligation amplification that requires co‐localization within 40 nm. Nematode orthologs of 21 proteins, which showed Alzheimer‐specific enrichment in tau‐containing aggregates, were assessed for aggregation‐promoting roles in C. elegans by RNA‐interference ‘knockdown’. Fifteen knockdowns (71%) rescued paralysis of worms expressing muscle Aβ, and 12 (57%) rescued chemotaxis disrupted by neuronal Aβ expression. Proteins identified in compact human aggregates, bound by antibody to total tau, were thus shown to play causal roles in aggregation based on nematode models triggered by Aβ1–42. These observations imply shared mechanisms driving both types of aggregation, and/or aggregate‐mediated cross‐talk between tau and Aβ. Knowledge of protein components that promote protein accrual in diverse aggregate types implicates common mechanisms and identifies novel targets for drug intervention.

Aging dependent effect of nuclear tau

“…These alterations are related to changes in chromatin organization, which directly affects proper gene expression, suggesting that nuclear alteration could contribute to aging (Feser and Tyler, 2011;Cruickshanks and Adams, 2011). Tau is a relevant protein involved in the axonal formation and cytoplasmic aggregates NFT specifically observed in the age-related Alzheimer's disease (Ayyadevara et al, 2016), but has also been biochemically demonstrated in the cell nuclei and by immunofluorescence in the nucleolus (Sjöberg et al, 2006;Bukar Maina et al, 2016). Here, we studied by immunohistochemistry and immunofluorescence the AT100 epitope of nuclear tau and its relation to cell aging and to aging pathologies.…”

The Molecular Chaperone CCT/TRiC: An Essential Component of Proteostasis and a Potential Modulator of Protein Aggregation

“…As changes in CCT subunit expression occur in aging and in several neurodegenerative diseases (Brehme et al, 2014) CCT activity will be altered and the consequences potentially difficult to predict. Furthermore, increased levels of post-translational modifications to aggregating proteins, such as phosphorylation of tau, are observed during neurodegenerative aggregation (Ayyadevara et al, 2016). If these modified forms of proteins are recognized to a lesser degree than the unmodified forms then this would compound the effects of reduced chaperones during aging and neurodegenerative diseases.…”

Using Proteomics to Understand Alzheimer’s Disease Pathogenesis

“…However, one advantage of using varied lysis methods is that combined analysis of proteomic studies that use various lysis methods provides a richer view of molecular changes in the AD brain. For example, some studies have specifically examined differences in the insoluble proteome in AD (21,25,30,37), which enriches for proteins that are associated with the insoluble plaques or NFTs in AD, as well as other proteins that are independently prone to insolubility in the AD brain. Of these studies, Hales et al provide the most comprehensive analysis of insoluble protein changes in AD (30).…”

“…However, despite this limitation, there have been two recent studies that have developed alternative ways to examine the Aβ interactome. The first study isolated aggregated Aβ complexes from human brain samples using a non-specific Aβ antibody (that also recognizes APP), but limited their downstream proteomic analysis to only those proteins present in the insoluble fraction, with the assumption that the resulting interacting proteins were limited to those present in insoluble Aβ-containing aggregates rather than APP (37). The second study used a more traditional approach of binding recombinant monomeric Aβ42 or oligomeric Aβ42 to beads that were then used to pull down interacting proteins from human brain samples (74).…”

“…To date, all studies examining the tau interactome have used total tau antibodies that identify proteins that interact with all tau species. Two studies have examined using human brain tissue (37,75), while others have examined tau interactors in mouse brains (76)(77)(78)(79) and in cells expressing human tau (80). These studies found that different isoforms or domains of tau regulate different protein interactions, identified the major protein families that tau preferentially binds to, and identified new potential drug targets for preventing tau toxicity.…”