Cerebral β-amyloidosis can be exogenously induced by the intracerebral injection of brain extracts containing aggregated β-amyloid (Aβ) into young, pre-depositing Aβ precursor protein- (APP) transgenic mice. Previous work has shown that the induction involves a prion-like seeding mechanism in which the seeding agent is aggregated Aβ itself. Here we report that the β-amyloid-inducing activity of Alzheimer’s disease (AD) brain tissue or aged APP-transgenic mouse brain tissue is preserved, albeit with reduced efficacy, after formaldehyde fixation. Moreover, spectral analysis with amyloid conformation-sensitive luminescent conjugated oligothiophene dyes reveals that the strain-like properties of aggregated Aβ are maintained in fixed tissues. The resistance of Aβ seeds to inactivation and structural modification by formaldehyde underscores their remarkable durability, which in turn may contribute to their persistence and spread within the body. The present findings can be exploited to establish the relationship between the molecular structure of Aβ aggregates and the variable clinical features and disease progression of AD even in archived, formalin-fixed autopsy material.

Aging is the most important risk factor for neurodegenerative diseases associated with pathological protein aggregation such as Alzheimer’s disease. Although aging is an important player, it remains unknown which molecular changes are relevant for disease initiation. Recently, it has become apparent that widespread protein aggregation is a common feature of aging. Indeed, several studies demonstrate that 100s of proteins become highly insoluble with age, in the absence of obvious disease processes. Yet it remains unclear how these misfolded proteins aggregating with age affect neurodegenerative diseases. Importantly, several of these aggregation-prone proteins are found as minor components in disease-associated hallmark aggregates such as amyloid-β plaques or neurofibrillary tangles. This co-localization raises the possibility that age-dependent protein aggregation directly contributes to pathological aggregation. Here, we show for the first time that highly insoluble proteins from aged Caenorhabditis elegans or aged mouse brains, but not from young individuals, can initiate amyloid-β aggregation in vitro. We tested the seeding potential at four different ages across the adult lifespan of C. elegans. Significantly, protein aggregates formed during the early stages of aging did not act as seeds for amyloid-β aggregation. Instead, we found that changes in protein aggregation occurring during middle-age initiated amyloid-β aggregation. Mass spectrometry analysis revealed several late-aggregating proteins that were previously identified as minor components of amyloid-β plaques and neurofibrillary tangles such as 14-3-3, Ubiquitin-like modifier-activating enzyme 1 and Lamin A/C, highlighting these as strong candidates for cross-seeding. Overall, we demonstrate that widespread protein misfolding and aggregation with age could be critical for the initiation of pathogenesis, and thus should be targeted by therapeutic strategies to alleviate neurodegenerative diseases.

Pathological, genetic, and biochemical hallmarks of Alzheimer's disease (AD) are linked to amyloid-␤ (A␤) peptide aggregation. Especially misfolded A␤ 42 peptide is sufficient to promote amyloid plaque formation. However, the cellular compartment facilitating the conversion of monomeric A␤ to aggregated toxic A␤ species remains unknown. In vitro models suggest lipid membranes to be the driving force of A␤ conversion. To this end, we generated two novel mouse models, expressing either membrane-anchored or nonanchored versions of the human A␤ 42 peptide. Strikingly, membrane-anchored A␤ 42 robustly accelerated A␤ deposition and exacerbated amyloidassociated toxicity upon crossing with A␤ precursor protein transgenic mice. These in vivo findings support the hypothesis that A␤-membrane interactions play a pivotal role in early-onset AD as well as neuronal damage and provide evidence to study A␤-membrane interactions as therapeutic targets.

An early event in Alzheimer’s disease (AD) pathogenesis is the formation of extracellular aggregates of amyloid-β peptide (Aβ), thought to be initiated by a prion-like seeding mechanism. However, the molecular nature and location of the Aβ seeds remain rather elusive. Active Aβ seeds are found in crude homogenates of amyloid-laden brains and in the soluble fraction thereof. To analyze the seeding activity of the pellet fraction, we have either separated or directly immunoisolated membranes from such homogenates. Here, we found considerable Aβ seeding activity associated with membranes in the absence of detectable amyloid fibrils. We also found that Aβ seeds on mitochondrial or associated membranes efficiently induced Aβ aggregation in vitro and seed β-amyloidosis in vivo. Aβ seeds at intracellular membranes may contribute to the spreading of Aβ aggregation along neuronal pathways and to the induction of intracellular pathologies downstream of Aβ.

Schizophrenia is a psychiatric disorder that is still not readily treatable. Pharmaceutical advances in the treatment of schizophrenia have mainly focused on the protein coding part of the human genome. However, the vast majority of the human transcriptome consists of non-coding RNAs. MicroRNAs are small non-coding RNAs that control the transcriptome at the systems level. In the present study we analyzed the microRNAome in blood and postmortem brains of controls and schizophrenia patients and found that miR 99b-5p was downregulated in both the prefrontal cortex and blood of patients. At the mechanistic level we show that inhibition of miR-99b-5p leads to schizophrenia-like phenotypes in mice and induced inflammatory processes in microglia linked to synaptic pruning. The miR-99b-5p mediated inflammatory response in microglia depended on Z DNA binding protein 1 (Zbp1) which we identified as a novel miR-99b-5p target. Antisense oligos (ASOs) against Zbp1 ameliorated the pathological phenotypes caused by miR-99b-5p inhibition. In conclusion, we report a novel miR-99b-5p-Zbp1 pathway in microglia that contributes to the pathogenesis of schizophrenia. Our data suggest that strategies to increase the levels of miR-99b-5p or inhibit Zbp1 could become a novel therapeutic strategy.