Nine families with autosomal dominant Alzheimer's disease (AD), all of whom had the Ala431Glu substitution in the PSEN1 gene and came from Jalisco State in Mexico, have been previously reported. As they shared highly polymorphic flanking dinucleotide marker alleles, this strongly suggests that this mutation arose from a common founder. In the current letter, we expand this observation by describing an additional 15 independent families with the Ala431Glu substitution in the PSEN1 gene and conclude that this mutation is not an uncommon cause of early-onset autosomal dominant AD in persons of Mexican origin.

To address the need for more meaningful biomarkers of tauopathies, we have developed an ultrasensitive tau seed amplification assay (4R RT-QuIC) for the 4-repeat (4R) tau aggregates of progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and other diseases with 4R tauopathy. The assay detected seeds in 10⁶-10⁹-fold dilutions of 4R tauopathy brain tissue but was orders of magnitude less responsive to brain with other types of tauopathy, such as from Alzheimer's disease cases. The analytical sensitivity for synthetic 4R tau fibrils was ~ 50 fM or 2 fg/sample. A novel dimension of this tau RT-QuIC testing was the identification of three disease-associated classes of 4R tau seeds; these classes were revealed by conformational variations in the in vitro amplified tau fibrils as detected by thioflavin T fluorescence amplitudes and FTIR spectroscopy. Tau seeds were detected in postmortem cerebrospinal fluid (CSF) from all neuropathologically confirmed PSP and CBD cases but not in controls. CSF from living subjects had weaker seeding activities; however, mean assay responses for cases clinically diagnosed as PSP and CBD/corticobasal syndrome were significantly higher than those from control cases. Altogether, 4R RT-QuIC provides a practical cell-free method of detecting and subtyping pathologic 4R tau aggregates as biomarkers.

In Alzheimer's disease (AD) and tauopathies, tau aggregation accompanies progressive neurodegeneration. Aggregated tau appears to spread between adjacent neurons and adjacent brain regions by prion-like seeding. Hence, inhibitors of this seeding offer a possible route to managing tauopathies. Here, we report the 1.0 Å resolution micro-electron diffraction structure of an aggregation-prone segment of tau with the sequence SVQIVY, present in the cores of patient-derived fibrils from AD and tauopathies. This structure illuminates how distinct interfaces of the parent segment, containing the sequence VQIVYK, foster the formation of distinct structures. Peptide-based fibril-capping inhibitors designed to target the two VQIVYK interfaces blocked proteopathic seeding by patient-derived fibrils. These VQIVYK inhibitors add to a panel of tau-capping inhibitors that targets specific polymorphs of recombinant and patient-derived tau fibrils. Inhibition of seeding initiated by brain tissue extracts differed among donors with different tauopathies, suggesting that particular fibril polymorphs of tau are associated with certain tauopathies. Donors with progressive supranuclear palsy exhibited more variation in inhibitor sensitivity, suggesting that fibrils from these donors were more polymorphic and potentially vary within individual donor brains. Our results suggest that a subset of inhibitors from our panel could be specific for particular disease-associated polymorphs, whereas inhibitors that blocked seeding by extracts from all of the tauopathies tested could be used to broadly inhibit seeding by multiple disease-specific tau polymorphs. Moreover, we show that tau-capping inhibitors can be transiently expressed in HEK293 tau biosensor cells, indicating that nucleic acid-based vectors can be used for inhibitor delivery.

The original version of this article unfortunately contained a mistake. The Panel A in the published figure 5 is incorrect. The corrected Figure 5 is placed in the following page.

Background

Spanish-language screening tests that are sensitive to the early cognitive changes of Alzheimer's disease (AD) are needed. Persons known to be at 50% risk for young-onset AD due to presenilin-1 (PSEN1) mutations provide the opportunity to assess which measures on the Mini-mental State Examination (MMSE) are most sensitive to these early changes.

Methods

We performed genetic and Spanish-language cognitive testing on 50 Mexican persons without dementia at risk for inheriting PSEN1 mutations. We then compared the performance on sub-items of the MMSE between PSEN1 mutation carriers (MCs) and non-carriers (NCs) using t-tests and Fisher's exact tests. Exploratory multiple logistic regression analyses were also performed.

Results

Twenty-nine persons were MCs and 21 NCs. NCs tended to achieve higher levels of education (p = 0.039) than did MCs. MCs tended to perform more poorly when spelling "MUNDO" backwards and on Orientation, particularly regarding the date. In multiple regression analyses the ability of backwards spelling to predict PSEN1 mutation status was reduced when education was included as an independent variable.

Conclusion

Subjects in the earliest stage of PSEN1-related AD showed deficits on orientation to date and in divided attention when spelling backwards. It is unclear if educational level should be considered an associated feature or a con-founding variable in this population although it should be taken into account when considering performance on the MMSE task of divided attention. The relative lack of deficits on delayed recall of three words probably represents the insensitivity of this measure in early AD. This study supports the utility of autosomal dominant AD as a model of the more common sporadic form of the disorder.

Soluble oligomers of aggregated tau accompany the accumulation of insoluble amyloid fibrils, a histological hallmark of Alzheimer disease (AD) and two dozen related neurodegenerative diseases. Both oligomers and fibrils seed the spread of Tau pathology, and by virtue of their low molecular weight and relative solubility, oligomers may be particularly pernicious seeds. Here, we report the formation of in vitro tau oligomers formed by an ionic liquid (IL15). Using IL15-induced recombinant tau oligomers and a dot blot assay, we discovered a mAb (M204) that binds oligomeric tau, but not tau monomers or fibrils. M204 and an engineered single-chain variable fragment (scFv) inhibited seeding by IL15-induced tau oligomers and pathological extracts from donors with AD and chronic traumatic encephalopathy. This finding suggests that M204-scFv targets pathological structures that are formed by tau in neurodegenerative diseases. We found that M204-scFv itself partitions into oligomeric forms that inhibit seeding differently, and crystal structures of the M204-scFv monomer, dimer, and trimer revealed conformational differences that explain differences among these forms in binding and inhibition. The efficiency of M204-scFv antibodies to inhibit the seeding by brain tissue extracts from different donors with tauopathies varied among individuals, indicating the possible existence of distinct amyloid polymorphs. We propose that by binding to oligomers, which are hypothesized to be the earliest seeding-competent species, M204-scFv may have potential as an early-stage diagnostic for AD and tauopathies, and also could guide the development of promising therapeutic antibodies.

One of the potential benefits of using data-independent acquisition (DIA) proteomics protocols is that information not originally targeted by the study may be present and discovered by subsequent analysis. Herein, we reanalyzed DIA data originally recorded for global proteomic analysis to look for isomerized peptides, which occur as a result of spontaneous chemical modifications to long-lived proteins. Examination of a large set of human brain samples revealed a striking relationship between Alzheimer's disease (AD) status and isomerization of aspartic acid in a peptide from tau. Relative to controls, a surprising increase in isomer abundance was found in both autosomal dominant and sporadic AD samples. To explore potential mechanisms that might account for these observations, quantitative analysis of proteins related to isomerization repair and autophagy was performed. Differences consistent with reduced autophagic flux in AD-related samples relative to controls were found for numerous proteins, including most notably p62, a recognized indicator of autophagic inhibition. These results suggest, but do not conclusively demonstrate, that lower autophagic flux may be strongly associated with loss of function in AD brains. This study illustrates that DIA data may contain unforeseen results of interest and may be particularly useful for pilot studies investigating new research directions. In this case, a promising target for future investigations into the therapy and prevention of AD has been identified.

Microsatellite repeat expansion disease loci can exhibit pleiotropic clinical and biological effects depending on repeat length. Large expansions in C9orf72 (100s-1000s of units) are the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal degeneration (FTD). However, whether intermediate expansions also contribute to neurodegenerative disease is not well understood. Several studies have identified intermediate repeats in Parkinson's disease patients, but the association was not found in autopsy-confirmed cases. We hypothesized that intermediate C9orf72 repeats are a genetic risk factor for corticobasal degeneration (CBD), a neurodegenerative disease that can be clinically similar to Parkinson's but has distinct tau protein pathology. Indeed, intermediate C9orf72 repeats were significantly enriched in autopsy-proven CBD (n = 354 cases, odds ratio = 3.59, p = 0.00024). While large C9orf72 repeat expansions are known to decrease C9orf72 expression, intermediate C9orf72 repeats result in increased C9orf72 expression in human brain tissue and CRISPR/cas9 knockin iPSC-derived neural progenitor cells. In contrast to cases of FTD/ALS with large C9orf72 expansions, CBD with intermediate C9orf72 repeats was not associated with pathologic RNA foci or dipeptide repeat protein aggregates. Knock-in cells with intermediate repeats exhibit numerous changes in gene expression pathways relating to vesicle trafficking and autophagy. Additionally, overexpression of C9orf72 without the repeat expansion leads to defects in autophagy under nutrient starvation conditions. These results raise the possibility that therapeutic strategies to reduce C9orf72 expression may be beneficial for the treatment of CBD.

Neurofilament light chain (NfL) is a promising fluid biomarker of disease progression for various cerebral proteopathies. Here we leverage the unique characteristics of the Dominantly Inherited Alzheimer Network and ultrasensitive immunoassay technology to demonstrate that NfL levels in the cerebrospinal fluid (n = 187) and serum (n = 405) are correlated with one another and are elevated at the presymptomatic stages of familial Alzheimer's disease. Longitudinal, within-person analysis of serum NfL dynamics (n = 196) confirmed this elevation and further revealed that the rate of change of serum NfL could discriminate mutation carriers from non-mutation carriers almost a decade earlier than cross-sectional absolute NfL levels (that is, 16.2 versus 6.8 years before the estimated symptom onset). Serum NfL rate of change peaked in participants converting from the presymptomatic to the symptomatic stage and was associated with cortical thinning assessed by magnetic resonance imaging, but less so with amyloid-β deposition or glucose metabolism (assessed by positron emission tomography). Serum NfL was predictive for both the rate of cortical thinning and cognitive changes assessed by the Mini-Mental State Examination and Logical Memory test. Thus, NfL dynamics in serum predict disease progression and brain neurodegeneration at the early presymptomatic stages of familial Alzheimer's disease, which supports its potential utility as a clinically useful biomarker.