Tau PTM Profiles Identify Patient Heterogeneity and Stages of Alzheimer's Disease.

To elucidate the role of Tau isoforms and post-translational modification (PTM) stoichiometry in Alzheimer's disease (AD), we generated a high-resolution quantitative proteomics map of 95 PTMs on multiple isoforms of Tau isolated from postmortem human tissue from 49 AD and 42 control subjects. Although Tau PTM maps reveal heterogeneity across subjects, a subset of PTMs display high occupancy and frequency for AD, suggesting importance in disease. Unsupervised analyses indicate that PTMs occur in an ordered manner, leading to Tau aggregation. The processive addition and minimal set of PTMs associated with seeding activity was further defined by analysis of size-fractionated Tau. To summarize, features in the Tau protein critical for disease intervention at different stages of disease are identified, including enrichment of 0N and 4R isoforms, underrepresentation of the C terminus, an increase in negative charge in the proline-rich region (PRR), and a decrease in positive charge in the microtubule binding domain (MBD).

Somatic genomic changes in single Alzheimer's disease neurons.

Dementia in Alzheimer's disease progresses alongside neurodegeneration1-4, but the specific events that cause neuronal dysfunction and death remain poorly understood. During normal ageing, neurons progressively accumulate somatic mutations5 at rates similar to those of dividing cells6,7 which suggests that genetic factors, environmental exposures or disease states might influence this accumulation5. Here we analysed single-cell whole-genome sequencing data from 319 neurons from the prefrontal cortex and hippocampus of individuals with Alzheimer's disease and neurotypical control individuals. We found that somatic DNA alterations increase in individuals with Alzheimer's disease, with distinct molecular patterns. Normal neurons accumulate mutations primarily in an age-related pattern (signature A), which closely resembles 'clock-like' mutational signatures that have been previously described in healthy and cancerous cells6-10. In neurons affected by Alzheimer's disease, additional DNA alterations are driven by distinct processes (signature C) that highlight C>A and other specific nucleotide changes. These changes potentially implicate nucleotide oxidation4,11, which we show is increased in Alzheimer's-disease-affected neurons in situ. Expressed genes exhibit signature-specific damage, and mutations show a transcriptional strand bias, which suggests that transcription-coupled nucleotide excision repair has a role in the generation of mutations. The alterations in Alzheimer's disease affect coding exons and are predicted to create dysfunctional genetic knockout cells and proteostatic stress. Our results suggest that known pathogenic mechanisms in Alzheimer's disease may lead to genomic damage to neurons that can progressively impair function. The aberrant accumulation of DNA alterations in neurodegeneration provides insight into the cascade of molecular and cellular events that occurs in the development of Alzheimer's disease.

LRP1 is a master regulator of tau uptake and spread.

The spread of protein aggregates during disease progression is a common theme underlying many neurodegenerative diseases. The microtubule-associated protein tau has a central role in the pathogenesis of several forms of dementia known as tauopathies-including Alzheimer's disease, frontotemporal dementia and chronic traumatic encephalopathy1. Progression of these diseases is characterized by the sequential spread and deposition of protein aggregates in a predictable pattern that correlates with clinical severity2. This observation and complementary experimental studies3,4 have suggested that tau can spread in a prion-like manner, by passing to naive cells in which it templates misfolding and aggregation. However, although the propagation of tau has been extensively studied, the underlying cellular mechanisms remain poorly understood. Here we show that the low-density lipoprotein receptor-related protein 1 (LRP1) controls the endocytosis of tau and its subsequent spread. Knockdown of LRP1 significantly reduced tau uptake in H4 neuroglioma cells and in induced pluripotent stem cell-derived neurons. The interaction between tau and LRP1 is mediated by lysine residues in the microtubule-binding repeat region of tau. Furthermore, downregulation of LRP1 in an in vivo mouse model of tau spread was found to effectively reduce the propagation of tau between neurons. Our results identify LRP1 as a key regulator of tau spread in the brain, and therefore a potential target for the treatment of diseases that involve tau spread and aggregation.

SORL1 is a receptor for tau that promotes tau seeding.

Sortilin-related receptor 1 (SORL1) is an intracellular sorting receptor genetically implicated in Alzheimer's disease (AD) that impacts amyloid precursor protein trafficking. The objective of these studies was to test the hypothesis that SORL1 binds tau, modulates its cellular trafficking and impacts the aggregation of cytoplasmic tau induced by pathological forms of tau. Using surface plasmon resonance measurements, we observed high-affinity binding of tau to SORL1 and the vacuolar protein sorting 10 domain of SORL1. Interestingly, unlike LDL receptor-related protein 1, SORL1 binds tau at both pH 7.4 and pH 5.5, revealing its ability to bind tau at endosomal pH. Immunofluorescence studies confirmed that exogenously added tau colocalized with SORL1 in H4 neuroglioma cells, while overexpression of SORL1 in LDL receptor-related protein 1-deficient Chinese hamster ovary (CHO) cells resulted in a marked increase in the internalization of tau, indicating that SORL1 can bind and mediate the internalization of monomeric forms of tau. We further demonstrated that SORL1 mediates tau seeding when tau RD P301S FRET biosensor cells expressing SORL1 were incubated with high molecular weight forms of tau isolated from the brains of patients with AD. Seeding in H4 neuroglioma cells is significantly reduced when SORL1 is knocked down with siRNA. Finally, we demonstrate that the N1358S mutant of SORL1 significantly increases tau seeding when compared to WT SORL1, identifying for the first time a potential mechanism that connects this specific SORL1 mutation to Alzheimer's disease. Together, these studies identify SORL1 as a receptor that contributes to trafficking and seeding of pathogenic tau.

All the Tau We Cannot See.

Alzheimer's disease (AD) was described in 1906 as a dementing disease marked by the presence of two types of fibrillar aggregates in the brain: neurofibrillary tangles and senile plaques. The process of aggregation and formation of the aggregates has been a major focus of investigation ever since the discoveries that the tau protein is the predominant protein in tangles and amyloid ß is the predominant protein in plaques. The idea that smaller, oligomeric species of amyloid may also be bioactive has now been clearly established. This review examines the possibility that soluble, nonfibrillar, bioactive forms of tau-the "tau we cannot see"-comprise a dominant driver of neurodegeneration in AD.

Report of the APOE4 National Institute on Aging/Alzheimer Disease Sequencing Project Consortium Working Group: Reducing APOE4 in Carriers is a Therapeutic Goal for Alzheimer's Disease.

Alzheimer's disease (AD) is the most common neurodegenerative disorder and one of the leading causes of disability worldwide. The apolipoprotein E4 gene (APOE4) is the strongest genetic risk factor for AD. In 2023, the APOE4 National Institute on Aging/Alzheimer's Disease Sequencing Project working group came together to gather data and discuss the question of whether to reduce or increase APOE4 as a therapeutic intervention for AD. It was the unanimous consensus that cumulative data from multiple studies in humans and animal models support that lowering APOE4 should be a target for therapeutic approaches for APOE4 carriers. ANN NEUROL 2024;95:625-634.

Alzheimer proteopathic tau seeds are biochemically a forme fruste of mature paired helical filaments.

Aggregation prone molecules, such as tau, form both historically well characterized fibrillar deposits (neurofibrillary tangles) and recently identified phosphate-buffered saline (PBS) extract species called proteopathic seeds. Both can cause normal endogenous tau to undergo templated misfolding. The relationship of these seeds to the fibrils that define tau-related diseases is unknown. We characterized the aqueous extractable and sarkosyl insoluble fibrillar tau species derived from human Alzheimer brain using mass spectrometry and in vitro bioassays. Post-translational modifications (PTMs) including phosphorylation, acetylation and ubiquitination are identified in both preparations. PBS extract seed competent tau can be distinguished from sarkosyl insoluble tau by the presence of overlapping, but less abundant, PTMs and an absence of some PTMs unique to the latter. The presence of ubiquitin and other PTMs on the PBS-extracted tau species correlates with the amount of tau in the seed competent size exclusion fractions, with the bioactivity and with the aggressiveness of clinical disease. These results demonstrate that the PTMs present on bioactive, seed competent PBS extract tau species are closely related to, but distinct from, the PTMs of mature paired helical filaments, consistent with the idea that they are a forme fruste of tau species that ultimately form fibrils.

Utility of cortical tissue analysis in normal pressure hydrocephalus.

Clinical improvement following neurosurgical cerebrospinal fluid shunting for presumed idiopathic normal pressure hydrocephalus is variable. Idiopathic normal pressure hydrocephalus patients may have undetected Alzheimer's disease-related cortical pathology that confounds diagnosis and clinical outcomes. In this study, we sought to determine the utility of cortical tissue immuno-analysis in predicting shunting outcomes in idiopathic normal pressure hydrocephalus patients. We performed a pooled analysis using a systematic review as well as analysis of a new, original patient cohort. Of the 2707 screened studies, 3 studies with a total of 229 idiopathic normal pressure hydrocephalus patients were selected for inclusion in this meta-analysis alongside our original cohort. Pooled statistics of shunting outcomes for the 229 idiopathic normal pressure hydrocephalus patients and our new cohort of 36 idiopathic normal pressure hydrocephalus patients revealed that patients with Aß + pathology were significantly more likely to exhibit shunt nonresponsiveness than patients with negative pathology. Idiopathic normal pressure hydrocephalus patients with Alzheimer's disease -related cortical pathology may be at a higher risk of treatment facing unfavorable outcomes following cerebrospinal fluid shunting. Thus, cortical tissue analysis from living patients may be a useful diagnostic and prognostic adjunct for patients with presumed idiopathic normal pressure hydrocephalus and potentially other neurodegenerative conditions affecting the cerebral cortex.

APOE2 gene therapy reduces amyloid deposition and improves markers of neuroinflammation and neurodegeneration in a mouse model of Alzheimer disease.

Epidemiological studies show that individuals who carry the relatively uncommon APOE ε2 allele rarely develop Alzheimer disease, and if they do, they have a later age of onset, milder clinical course, and less severe neuropathological findings than people without this allele. The contrast is especially stark when compared with the major genetic risk factor for Alzheimer disease, APOE ε4, which has an age of onset several decades earlier, a more aggressive clinical course and more severe neuropathological findings, especially in terms of the amount of amyloid deposition. Here, we demonstrate that brain exposure to APOE ε2 via a gene therapy approach, which bathes the entire cortical mantle in the gene product after transduction of the ependyma, reduces Aß plaque deposition, neurodegenerative synaptic loss, and, remarkably, reduces microglial activation in an APP/PS1 mouse model despite continued expression of human APOE ε4. This result suggests a promising protective effect of exogenous APOE ε2 and reveals a cell nonautonomous effect of the protein on microglial activation, which we show is similar to plaque-associated microglia in the brain of Alzheimer disease patients who inherit APOE ε2. These data increase the potential that an APOE ε2 therapeutic could be effective in Alzheimer disease, even in individuals born with the risky ε4 allele.

Endothelial Cells Are Heterogeneous in Different Brain Regions and Are Dramatically Altered in Alzheimer's Disease.

Vascular endothelial cells play an important role in maintaining brain health, but their contribution to Alzheimer's disease (AD) is obscured by limited understanding of the cellular heterogeneity in normal aged brain and in disease. To address this, we performed single nucleus RNAseq on tissue from 32 human AD and non-AD donors (19 female, 13 male) each with five cortical regions: entorhinal cortex, inferior temporal gyrus, prefrontal cortex, visual association cortex, and primary visual cortex. Analysis of 51,586 endothelial cells revealed unique gene expression patterns across the five regions in non-AD donors. Alzheimer's brain endothelial cells were characterized by upregulated protein folding genes and distinct transcriptomic differences in response to amyloid ß plaques and cerebral amyloid angiopathy. This dataset demonstrates previously unrecognized regional heterogeneity in the endothelial cell transcriptome in both aged non-AD and AD brain.SIGNIFICANCE STATEMENT In this work, we show that vascular endothelial cells collected from five different brain regions display surprising variability in gene expression. In the presence of Alzheimer's disease pathology, endothelial cell gene expression is dramatically altered with clear differences in regional and temporal changes. These findings help explain why certain brain regions appear to differ in susceptibility to disease-related vascular remodeling events that may impact blood flow.