Disease-specific tau polymorphs are associated with unique protein networks across proteinopathies.

Proteomic and Phosphoproteomic Characterization of Disease-Associated Alterations in Nerve Terminals and Protein Inclusions of Alzheimer's Disease Patients.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by synaptic dysfunction, protein aggregation, and widespread molecular alterations in the brain. In this study, we applied quantitative mass spectrometry-based proteomics and phosphoproteomics to characterize synaptosomes and sarkosyl-insoluble protein inclusions from the post-mortem frontal lobes of AD and control cases. We identified >3700 proteins across both fractions, revealing AD-associated changes in synaptic composition and phosphorylation patterns. Proteomic analyses indicated mitochondrial deficits and disruptions in vesicle trafficking within synapses, whereas insoluble protein inclusions showed an accumulation of spliceosomal components and glial activation markers as well as an enrichment of N-terminally truncated amyloid beta peptides in AD cases, suggesting involvement of postfibrillar processing events mediated by specific proteases in amyloid plaque pathology. Phosphoproteomic analysis revealed extensive alterations in pathways regulating vesicle trafficking, Golgi homeostasis, and synaptic function. We observed increased tau phosphorylation at AD-associated sites in insoluble inclusions and distinct phosphorylation changes in synaptic tau, particularly at S285 and S305, suggesting altered tau function and aggregation properties. These findings provide new molecular insights into AD-related nerve terminal composition and protein aggregation, advancing our understanding of disease-associated changes at the subcellular level.

Tau isoform imbalance and aggregation are pathological hallmarks of X-linked dystonia-parkinsonism

Tauopathies encompass diverse neurodegenerative diseases unified by aberrant patterns of tau deposition in brain. Although most appear sporadic, some are linked to genetic etiologies that offer unique mechanistic insights. Here we report that X-linked Dystonia-Parkinsonism (XDP), caused by a non-coding retrotransposon-associated repeat insertion in TAF1, involves a significant imbalance of tau isoforms and the accumulation of hyperphosphorylated, four-repeat tau in the brain. In striatal tissue, both misfolded tau accumulation, predominantly in astrocytes, and MAPT exon 10 inclusion correlated with repeat length within the causal insertion. Transcriptomic profiling across brain regions revealed dysregulation of known tau-related pathways. Levels of phosphorylated tau181, glial fibrillary acidic protein, and neurofilament light chain were elevated in patient plasma and discriminated XDP from controls. These findings implicate defective tau proteostasis as a key pathogenic mechanism and position XDP as a genetic model for uncovering cellular drivers that may disrupt tau in other more common neurodegenerative diseases.

Alzheimers disease blood biomarkers reveal proteomic modules of disease progression

Tau-Targeted PROTACs Degrade Pathology-Associated Tau and Improve Memory in Alzheimer's Disease Models.

Tau aggregation and hyperphosphorylation are key pathological features of Alzheimer's disease (AD). Because Tau is intrinsically disordered, conventional small-molecule inhibitors have achieved limited success. Proteolysis-targeting chimeras (PROTACs) enable the targeted proteasomal degradation of previously considered undruggable proteins. We designed Tau-targeted PROTAC candidates using methylene blue (MB) as a recognition moiety for aggregation-prone motifs within the microtubule-binding region and varied the linker lengths and E3 ligase recruitment ligands to optimize degradation efficiency. Cell-based screening revealed that MB-2-VHL1 and MB-2-VHL2 are active degraders. In vivo studies confirmed a reduction in total Tau levels and degradation of phosphorylated Tau (p-Tau). In 3xTg-AD mice, subcutaneous administration of MB-2-VHL2 was associated with reduced hippocampal Tau and p-Tau levels and improved recognition memory and spatial learning. MB-2-VHL2 was also detectable in both serum and brain tissue by LC-MS/MS after subcutaneous administration and did not cause detectable histological or biochemical toxicity. These results indicate that MB-2-VHL2 can reduce both total Tau and p-Tau levels in vivo. Although the reduction in p-Tau appeared more pronounced under our experimental conditions, whether MB-2-VHL2 preferentially targets pathological Tau remains to be determined. Overall, these findings support further optimization and preclinical evaluation of Tau-targeted PROTACs as a potential therapeutic strategy for AD.

Quantitation of Spatial Proteoforms in Alzheimer’s Disease

Alzheimer’s disease (AD) pathogenesis involves complex, multifactorial changes to the brain proteome that conventional unfractionated analyses may obscure. Proteins frequently occupy multiple subcellular compartments as spatial proteoforms, yet the contribution of aberrant protein localization to AD pathogenesis remains poorly understood. To address this, we fractionated post-mortem human hippocampi from 13 AD and 14 non-AD individuals into four subcellular fractions and quantified 6,123 proteins by TMT-LC-MS. Although 75% of proteins were detected in more than one fraction, 78% of significant AD-associated alterations were restricted to a single fraction, demonstrating that subcellular localization is a primary determinant of disease vulnerability. Discordant abundance patterns between fractions revealed retromer complex mislocalization, nuclear transport dysfunction, and insoluble protein accumulation, with the endosomal-lysosomal and protein folding pathways most consistently perturbed. To examine how these perturbations evolve with disease progression, we applied the QUAD strategy to measure protein degradation in two fractions of APPswePS1delta9 mouse cortex at 2, 5, and 12 months. Degradation rates diverged between fractions and genotypes in an age-dependent manner, and cross-dataset comparison identified six proteins altered at the earliest pre-pathological timepoint, implicating vesicle transport and proteostasis disruption as initiating features of AD. These findings establish spatial proteoforms as essential units of pathogenic analysis and reveal disease-relevant signals invisible to bulk tissue approaches.

Kinase-specific phosphorylation of tau outside the amyloid core encodes fibril fold selection

Tauopathies are defined by the accumulation of filamentous tau assemblies that adopt disease-specific molecular conformations, or tau strains. Although tau is extensively hyperphosphorylated in Alzheimer’s disease, how phosphorylation patterns influence tau folding and strain selection remains unclear. Here, we show that site-specific phosphorylation of 0N3R tau by extracellular signal-regulated kinase 2 (ERK2), occurring predominantly within the proline-rich region and largely excluding the microtubule-binding domain, is sufficient to direct tau assembly into a structurally homogeneous fibril conformation. Residue-resolved NMR spectroscopy identifies a defined and quantifiable ERK2 phosphorylation pattern in the proline-rich region of tau. Cryo-electron microscopy at 3.0 Å resolution reveals that ERK2-phosphorylated 3R tau assembles into filaments with an ordered cross-β fold adopting an Alzheimer’s disease PHF fold, despite the absence of phospho-sites within the fibril core. These filaments exhibit robust seeding activity in tau biosensor cells. Together, these results demonstrate that kinase-specific phosphorylation outside the amyloid core can be sufficient to bias tau toward a defined fibril structure, establishing a direct mechanistic link between kinase specificity, post-translational modification, and tau strain formation.