The study, published in Nature Communications, enrolled eighteen patients with suspected normal pressure hydrocephalus, a neurological condition that already requires neurosurgery. These patients were undergoing ventriculoperitoneal shunt placement, a procedure in which a tube is implanted to drain excess cerebrospinal fluid. Because the surgery already involves passing through the parieto-occipital cortex, the surgeons were able to take a tiny rice-grain-sized core of brain tissue at the same time, with the patients’ informed consent. Before the operation, each participant received an intravenous infusion of isotopically labelled leucine, an amino acid that crosses the blood-brain barrier and becomes incorporated into newly synthesized proteins. By measuring how much of this label appeared in tau and amyloid-beta proteins extracted from the biopsy, the researchers could determine when those molecules were made.

This technique, known as stable isotope labelling kinetics, has been used before to measure protein turnover in cerebrospinal fluid, but never before has it been combined with direct sampling of living human brain tissue in this way. The result is a kind of molecular timestamp. Proteins carrying the heavy carbon signature of the labelled leucine were manufactured during the hours or days before surgery; proteins without it are older. The approach gives researchers something that post-mortem studies fundamentally cannot: a snapshot of disease biology in real time, at the very earliest stages of the Alzheimer continuum, before symptoms have fully declared themselves.

What the team found in those tiny biopsies was striking. Half of the samples contained amyloid-beta pathology, visible as cored plaques, diffuse deposits and, in one case, cerebral amyloid angiopathy, where amyloid accumulates in blood vessel walls. Tau pathology, the second hallmark, was present but limited, appearing mostly as neuritic threads and tau associated with plaques rather than the mature neurofibrillary tangles seen in end-stage disease. Crucially, the researchers showed that phosphorylated tau, specifically the pTau217 form that has become one of the most accurate blood-based biomarkers for Alzheimer disease, was physically concentrated within and around the amyloid plaques themselves. The signal decreased progressively with distance from the plaque centre, providing direct visual evidence in living human tissue that tau phosphorylation and amyloid deposition are spatially coupled.

This co-localization matters because it speaks to one of the central unanswered questions in Alzheimer research: how amyloid and tau interact to drive neurodegeneration. Dystrophic neurites, the swollen and damaged neuronal processes that surround plaques, contain phosphorylated tau and are associated with synaptic dysfunction. The new findings suggest that this periplaque tau pool, rather than the aggregated tau inside mature tangles, may be the source of the pTau217 that appears in cerebrospinal fluid and blood. That would explain why fluid levels of this biomarker track so closely with plaque burden, and it offers a mechanistic explanation for why amyloid-targeting antibodies such as donanemab, which specifically clears pyroglutamate-modified amyloid-beta, also slow the accumulation of tau pathology even though they have no direct effect on tau metabolism.

The isotope labelling also yielded a remarkable measurement of tau biology. Labelled leucine was detectable in newly synthesized tau protein within just over three hours of the infusion starting, demonstrating that tau is translated rapidly in the human brain. By modelling the decay of the isotopic signal across the cohort, the researchers estimated that the half-life of tau in brain tissue is approximately thirty-four days, broadly consistent with the roughly twenty-three-day turnover previously measured in lumbar cerebrospinal fluid. When the researchers stratified their samples by plaque status, they found that tau labelling was significantly higher in biopsy samples that contained amyloid plaques compared to those that did not, providing ex vivo support for the idea that amyloid pathology drives increased tau production.

In sharp contrast to tau, the amyloid-beta peptides in the insoluble plaque fraction showed no detectable isotope labelling at all, despite the researchers using assays sensitive enough to detect enrichment as low as 1.87 percent and validating their findings across two independent mass spectrometry laboratories. This absence is not a technical failure but a biological finding in its own right. It suggests that amyloid plaques are remarkably stable structures, built up over years or decades, that do not dynamically incorporate significant amounts of new amyloid-beta within the few-hour window of the labelling period. The plaques in these early-stage samples were chemically immature, containing less than forty percent isomerised amyloid-beta species, compared with roughly ninety percent isomerisation in post-mortem Alzheimer tissue, where plaques have had years to accumulate molecular damage.

That isomerisation clock is one of the most conceptually powerful tools to emerge from this work. Aspartate residues in amyloid-beta spontaneously convert from their native L-form to non-native isomeric forms over time, at a rate that can be used to estimate the age of a plaque. Previous work has suggested that around fifty percent isomerisation corresponds to a mean plaque age of roughly eight months, while eighty-five percent indicates an age of about four years. By quantifying these isomers in living tissue, the researchers could distinguish freshly formed, immature plaques from older, more established deposits. This kind of molecular dating has never before been possible in living human brain, and it opens the door to staging the disease biochemically rather than relying on crude measures of plaque quantity, which notoriously correlate poorly with cognitive symptoms.

The team also used matrix-assisted laser desorption ionization mass spectrometry imaging to map the chemical architecture of individual plaques at ten-micrometre resolution. This revealed a striking degree of spatial organization within single deposits. Amyloid-beta 1-40 and pyroglutamate-modified amyloid-beta species were concentrated in the dense plaque core, while amyloid-beta 1-42 and related C-terminal species were distributed more homogeneously across both the core and the diffuse periphery. This peptide-specific spatial segregation, previously observed only in mouse models and post-mortem tissue, confirms that pyroglutamate-modified amyloid sits at the growing edge of plaques and may be a key driver of plaque expansion, making it a particularly relevant target for immunotherapies like donanemab that are designed to clear exactly this modified species.

One further finding carries practical implications for how Alzheimer biomarkers are interpreted. The researchers compared tau profiles in ventricular cerebrospinal fluid, collected during shunt surgery directly from the brain’s fluid spaces, with those in lumbar cerebrospinal fluid collected from the lower spine. Ventricular fluid closely mirrored the tau peptide profile seen in brain tissue itself, while lumbar fluid showed a distinctly different pattern with reduced C-terminal abundance. The team attributes this partly to iatrogenic contamination, as the shunt insertion procedure inevitably releases intracellular brain proteins into the ventricular fluid. Even so, the observation that ventricular cerebrospinal fluid can serve as a surrogate for brain tissue chemistry is significant, particularly for normal pressure hydrocephalus patients, in whom amyloid pathology is common and brain biopsy during shunt surgery is already practised as a diagnostic adjunct by many specialists.

The study is a proof of principle, and the authors are careful to acknowledge its limitations. The cohort is small, the participants were recruited for a hydrocephalus indication rather than Alzheimer disease itself, and the biopsies came from a single brain region that may not represent disease burden elsewhere. The tau half-life estimate rests on a statistical model with sparse timepoints around the peak of the labelling curve. Even so, the conceptual advance is hard to overstate. For the first time, researchers have captured the molecular birth of Alzheimer pathology in living human brains, dated plaques by their chemistry, watched tau being synthesized in real time, and visualized the physical interface between the disease’s two hallmark proteins. The methods developed here should be applicable to other neurodegenerative conditions, and they promise to reshape how clinical trials of the future are designed, allowing therapies to be matched to the specific molecular stage of disease rather than to symptoms alone.

Subject of Research: Molecular characterization of amyloid and tau pathology in living human brain tissue using stable isotope labelling and mass spectrometry imaging

Article Title: Spatiotemporal characterization of Alzheimer disease pathology in living human brain tissue

Article References: Aslanyan, A., Mukherjee, S., Moncur, E. M., Szadziewska, A., He, Y., Kac, P. R., Coyle, R., Camporesi, E., Sato, C., Ghoshal, N., Barthélemy, N. R., Wood, J., Ge, J., Dulewicz, M., Koutarapu, S., Schwetye, K., Roberts, K. F., Murphy, E. C., Carletti, F., … Paterson, R. W. (2026). Spatiotemporal characterization of Alzheimer disease pathology in living human brain tissue. Nature Communications, 17(1), Article 9878. https://doi.org/10.1038/s41467-026-76494-4

Image Credits: AI Generated

DOI: 10.1038/s41467-026-76494-4

Keywords: Alzheimer disease, amyloid-beta, tau, stable isotope labelling, mass spectrometry imaging, normal pressure hydrocephalus, pTau217, pyroglutamate, protein turnover, biomarkers, brain biopsy, neurodegeneration