The concept of prion-like transmission has shadowed tau research for years. Prions, the proteinaceous infectious agents behind Creutzfeldt-Jakob disease and bovine spongiform encephalopathy, propagate by coaxing normally folded prion proteins into the abnormal, misfolded state. Distinct folding patterns of the abnormal protein behave as different prion strains, each carrying its own incubation period and clinical profile. Tau, a microtubule-binding protein implicated in more than twenty neurodegenerative diseases, forms amyloid-like filaments in patient brains and has long been suspected of spreading through a similar templating mechanism. Cryo-electron microscopy studies have already shown that each tauopathy is defined by a unique tau filament fold, and that the same fold recurs across different brain regions within a single patient, implying that specific structures amplify and propagate as disease advances.

What remained unproven was whether tau filaments of different structures genuinely cause distinct disease pathologies through prion-like mechanisms, and whether those structural signatures survive the journey from cell to cell. The new study, titled Prion-like transmission of human tau strains in the mouse brain and published on September 30, 2026, answers both questions with unusual clarity. The work was a collaboration involving Dr. Aki Shimozawa and Dr. Airi Tarutani in Tokyo alongside Dr. Sofia Lövestam, Dr. Michel Goedert, and Dr. Sjors H.W. Scheres in Cambridge, with Lövestam, Shimozawa, and Tarutani serving as co-first authors.

The experimental design was elegantly simple. Tau filaments were extracted from the brains of Alzheimer’s disease and corticobasal degeneration patients and injected into the striatum of wild-type mice aged six to eighteen weeks. No genetic engineering was involved; the animals carried only their own normal mouse tau. Within six to nine months after injection, the mice developed tau pathologies that closely resembled those seen in the patient brains from which the seeds had come. Immunohistochemical staining revealed that the pathology had spread well beyond the injection site, reaching the cerebral cortex, the corpus callosum, and other distant brain regions, mirroring the progressive spread of tau lesions in human disease.

A critical series of controls established that the accumulating pathology was not simply the injected material persisting in the brain. Time-course analysis showed that the human tau filaments degraded and disappeared within approximately one week of injection. Endogenous tau accumulation began to re-emerge one to three months later, and by six to nine months the disease-characteristic lesions had fully appeared. Immunoblotting of the sarkosyl-insoluble fractions, a biochemical preparation that isolates aggregated tau, showed that the insoluble tau in the mouse brains reacted with an antibody specific to mouse tau, called mTau, but not with HT7, an antibody specific to human tau. The pathology, in other words, was built entirely from the mice’s own protein, assembled under the direction of the transient human seeds.

The most consequential finding came from cryo-electron microscopy, a technique that freezes biological molecules in place and resolves their three-dimensional structures at atomic scale. Filaments harvested from the mouse brains adopted the exact same folded structures as the injected human tau filaments. In mice seeded with Alzheimer’s-derived tau, the majority of amplified filaments were helical structures composed of two twisted protofilaments, resolved at 3.6 angstroms and shown to be identical to the paired helical filaments characteristic of Alzheimer’s patient brains. In mice seeded with corticobasal degeneration-derived tau, two filament types emerged: roughly seventy percent were single protofilaments and thirty percent were doublets of two twisted protofilaments, with the single protofilaments resolved at 3.4 angstroms and proven identical to Type 1 filaments found in corticobasal degeneration patients.

Equally revealing was how the two seed types produced visibly different diseases in the same kind of host. Mice injected with Alzheimer’s-derived tau developed pathology concentrated in the cell bodies and processes of neurons. Mice injected with corticobasal degeneration-derived tau showed tau accumulation not only in neurons but also in glial cells, forming structures that resembled astrocytic plaques and coiled bodies, the hallmark lesions used to diagnose corticobasal degeneration in human neuropathology. Astrocytic plaques are tau deposits in the distal processes of astrocytes, while coiled bodies are fibrous, comma-shaped inclusions in oligodendrocytes. The structural identity of the seed therefore determined not just the shape of the filaments but which cell types would be affected and how the pathology would be distributed across the brain.

Immunoelectron microscopy of the insoluble fractions confirmed the picture, revealing abundant filament structures decorated by both mTau and AT8 antibodies, markers of mouse tau and pathological phosphorylation respectively. Further biochemical profiling with antibodies recognizing the C-terminal region of tau showed that the aggregates formed by Alzheimer’s-derived and corticobasal degeneration-derived seeds carried distinct biochemical signatures, reinforcing the conclusion that the injected structures had imposed their identities on the newly formed mouse tau. At the ultrastructural level, the Alzheimer’s-seeded mice produced filaments with the tight twisted configuration typical of that disease, while the corticobasal degeneration-seeded mice produced filaments with a longer twist.

The implications reach well beyond the laboratory. These findings provide concrete evidence that tau propagates through the brain the way prion strains do, using filament seeds as structural templates that convert normal protein into copies of themselves while preserving their characteristic folds through successive rounds of amplification and cell-to-cell transmission. Because the mouse model recapitulates disease-specific pathology without any genetic manipulation, it offers researchers a powerful and physiologically faithful platform for dissecting how different tau filament structures produce different diseases, and for testing interventions designed to block seeding, spread, or specific filament conformations.

For the millions of people affected by Alzheimer’s disease and related tauopathies, the study points toward a new class of therapeutic logic. If disease progression depends on tau strains templating their own propagation, then drugs that stabilize normal tau, block filament uptake, or disrupt the templating surface could halt the spread of pathology even after it has begun. The research was supported by the Tokyo Metropolitan Government, the Japan Agency for Medical Research and Development, the Japan Science and Technology Agency, and the Japan Society for the Promotion of Science KAKENHI program, and all animal experiments were approved by the Animal Care and Use Committee of the Tokyo Metropolitan Institute of Medical Science. Patient brain tissue was provided by collaborating institutions across Japan and the University of Manchester, a reminder that this advance in molecular neuroscience rests on the generosity of patients and families who donated tissue for research.

Subject of Research: Prion-like transmission of disease-specific tau filament structures in the mouse brain

Article Title: Demonstration of prion-like transmission of tau in the mouse brain—elucidating the mechanisms behind disease-specific pathogenesis—

Article References: Demonstration of prion-like transmission of tau in the mouse brain—elucidating the mechanisms behind disease-specific pathogenesis—. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: tau, prion-like transmission, Alzheimer's disease, corticobasal degeneration, cryo-electron microscopy, neurodegeneration, tauopathies, protein aggregation, mouse model, amyloid filaments, seeding, Nature

The study, published in the Journal of Neurology by researchers at the University of Catania led by Giulia Donzuso and Mario Zappia, tackles one of the most stubborn problems in movement disorders: telling idiopathic Parkinson’s disease apart from the atypical parkinsonian syndromes, namely progressive supranuclear palsy, multiple system atrophy, and corticobasal degeneration. In the early stages, these conditions can look almost identical in the clinic. All produce slowness of movement, rigidity, and gait disturbance. Yet their underlying pathology, prognosis, and response to therapy diverge dramatically, and misdiagnosis carries real consequences, from inappropriate dopaminergic treatment to exclusion from disease-targeted clinical trials.

The diagnostic stakes are high. Even in specialist centers, clinical accuracy for Parkinson’s disease is estimated at roughly eighty percent, with the highest misdiagnosis rates occurring within the first two years of symptom onset. That is precisely the window in which disease-modifying therapies, should they emerge, would matter most. The Catania team reasoned that a simple, zero-cost bedside test already embedded in routine cognitive screening could be squeezed for far more diagnostic information than the traditional binary scoring allows.

Their instrument of choice was the Qualitative Scoring Pentagon Test, or QSPT, a method first developed by Caffarra and colleagues to distinguish dementia with Lewy bodies from Alzheimer’s disease. Instead of judging the interlocking pentagons as simply correct or incorrect, the QSPT breaks the drawing into five graded components. The number of correctly reproduced internal angles, out of ten, is scored from zero to four. The accuracy of the intersection where the two shapes overlap is scored from zero to four. The degree to which the figure’s contours are closed contributes zero to two points, as does angular rotation away from the model. Finally, the presence of the so-called closing-in phenomenon, in which the drawing crowds against or overlaps the printed model, subtracts a point. The maximum score is thirteen, and in the study every drawing was rated by two trained raters blinded to the patients’ diagnoses.

The cohort comprised one hundred and forty patients, including ninety-one with Parkinson’s disease, twenty-three with progressive supranuclear palsy, seventeen with multiple system atrophy, and nine with corticobasal degeneration, alongside ninety-two healthy controls matched to the Parkinson’s group for age and overall MMSE performance. The results were strikingly graded. Healthy controls performed near the ceiling, averaging 12.7 out of 13, confirming that pentagon copying is essentially intact in healthy aging when global cognition is preserved. Patients with Parkinson’s disease averaged 11.5, those with multiple system atrophy fell in between, patients with progressive supranuclear palsy scored lower still, and those with corticobasal degeneration achieved the lowest mean of all, at 7.7. The differences between Parkinson’s disease and each atypical syndrome were statistically significant, and the effect size between controls and corticobasal degeneration was among the largest reported, at nearly one full standard deviation.

Which features of the drawing carried the diagnostic signal? The sub-item analysis pointed to rotation errors and the accuracy of the ten internal angles as the most discriminating parameters. In progressive supranuclear palsy, prominent rotation errors may reflect the oculomotor dysfunction and impaired spatial reference frame processing that are hallmarks of the condition, particularly its classic Richardson’s syndrome phenotype. In corticobasal degeneration, the profound visuoconstructive failure is consistent with the parieto-frontal cortical degeneration and ideomotor apraxia that define the disease. The closing-in phenomenon, meanwhile, distinguished Parkinson’s disease from the atypical group as a whole, especially corticobasal degeneration, and is thought to arise from a loss of spatial inhibition tied to posterior parietal cortical degeneration.

The quantitative scores did not float free of the rest of the clinical picture. QSPT performance correlated significantly with the MMSE, the Frontal Assessment Battery, and the time taken on the Trail Making Test Part A, a measure of processing speed and visual scanning that depends on fronto-striatal and parietal networks. This convergence suggests that the pentagon task taps a shared substrate of cortical-subcortical network integrity that is preferentially damaged in atypical parkinsonism. Notably, QSPT scores showed no relationship with disease duration or with levodopa equivalent daily dose, indicating that the signal reflects disease biology rather than treatment burden or time since diagnosis.

Perhaps the most intriguing finding emerged from the brain imaging data. In the one hundred and six patients who had undergone MRI, the researchers computed the Magnetic Resonance Parkinsonism Index, a morphometric ratio combining pons and midbrain areas with the widths of the middle and superior cerebellar peduncles. This index is typically elevated in progressive supranuclear palsy, and indeed PSP patients in this cohort showed markedly high values while multiple system atrophy patients showed the lowest. Across the whole patient sample, QSPT scores correlated negatively with the MRPI, meaning that worse pentagon drawing tracked with progressive brainstem neurodegeneration. The finding gives the cognitive-neuroimaging relationship a plausible structural anchor: prior work on isolated brainstem lesions and functional imaging of visually guided motor control both implicate the pons and midbrain in visuospatial integration, positioning the brainstem as an activating hub within broader cognitive networks.

The statistical performance of the test was then distilled into diagnostic cutoffs. In multivariate logistic regression adjusted for motor severity, medication dose, and disease duration, lower QSPT scores were independently associated with atypical parkinsonian syndromes, with an odds ratio of 0.620 per point. Receiver operating characteristic analysis showed that a score of twelve or below separated all parkinsonian patients from healthy controls with an area under the curve of 0.759, while a score of eight or below separated Parkinson’s disease from the atypical syndromes with an area under the curve of 0.764 and a specificity of 92.3 percent. Most impressively, a cutoff of eleven or below distinguished synucleinopathies, meaning Parkinson’s disease and multiple system atrophy, from tauopathies, meaning progressive supranuclear palsy and corticobasal degeneration, with an area under the curve of 0.804. That such a neuropathology-level division, alpha-synuclein aggregation versus tau aggregation, can be glimpsed in a pencil sketch is the study’s most provocative implication.

The authors are careful to frame the tool as supportive rather than definitive. Sensitivity at the chosen cutoffs was modest, at 49 percent for the Parkinson’s-versus-atypical comparison and 65 percent for the patient-versus-control comparison, and the score distributions overlap at the individual level, so a high QSPT score cannot rule out atypical disease and must be paired with other clinical markers. The study was also retrospective, the atypical subgroups were small, diagnoses were clinical rather than neuropathologically confirmed, and the MRI analysis was limited to brainstem morphometry without assessment of the parietal and frontal cortex most directly implicated in visuoconstruction. Healthy controls were not formally matched for education, a known influence on drawing tasks. Still, the core message stands: a task that costs nothing, takes under a minute, and already sits inside the most widely used cognitive screen in the world can, when scored quantitatively, offer a graded, biologically meaningful window into which kind of parkinsonism a patient has. The team calls for prospective validation in early-stage cohorts and longitudinal follow-up, but the vision is clear: the next revolution in neurological diagnosis may arrive not from an expensive scanner or a spinal fluid assay, but from watching, carefully and systematically, how a patient draws two simple shapes.

Subject of Research: Quantitative pentagon-copying assessment of visuospatial deficits for differentiating parkinsonian syndromes

Article Title: Interlocking pentagons task and visuospatial deficit in parkinsonian syndrome: a quantitative approach

Article References: Donzuso, G., Cilio, F., Ferrante, E., D’Agate, C., Fazzina, G., Cicero, C. E., Mostile, G., Nicoletti, A., & Zappia, M. (2026). Interlocking pentagons task and visuospatial deficit in parkinsonian syndrome: a quantitative approach. Journal of Neurology, 273(10), Article 628. https://doi.org/10.1007/s00415-026-14163-8

Image Credits: AI Generated

DOI: 10.1007/s00415-026-14163-8

Keywords: Parkinson's disease, atypical parkinsonism, progressive supranuclear palsy, multiple system atrophy, corticobasal degeneration, MMSE pentagon copying, Qualitative Scoring Pentagon Test, visuospatial function, differential diagnosis, MRI morphometry, tauopathies, synucleinopathies

Tau has long been associated with Alzheimer’s disease because abnormal forms of the protein can be detected in cerebrospinal fluid and blood before symptoms become apparent. In affected brain tissue, tau accumulates inside neurons in structures known as neurofibrillary tangles. Under normal conditions, tau binds to and helps stabilize microtubules, the intracellular tracks that support the transport of materials through nerve cells. In disease, however, tau can become excessively phosphorylated, meaning that phosphate groups are attached to numerous sites along the protein. This modification alters tau’s behavior, location and ability to interact with other cellular components.

The Stanford-led study, published online in Neuron on Aug. 6, suggests that hyperphosphorylated tau can cause damage even without forming tangles. Researchers found that particular phosphorylation patterns allow tau to move into mitochondria, the organelles responsible for producing most of a cell’s adenosine triphosphate, or ATP. ATP supplies the energy required for neuronal communication, transport and maintenance. Because neurons have exceptionally high energy demands, mitochondrial dysfunction can rapidly compromise their structure and function.

Inside mitochondria, the modified tau molecules interact with NDUFS3, a component of complex I, the first major enzyme assembly in the mitochondrial electron-transport chain. Under normal conditions, electrons pass through a series of protein complexes embedded in the inner mitochondrial membrane. The energy released during this process pumps protons across the membrane, creating an electrochemical gradient that powers ATP synthase. Tau’s binding to NDUFS3 appears to distort the complex and interfere with the normal direction of electron flow.

The result is a process called reverse electron transport. Instead of moving forward through the respiratory chain, electrons flow backward under conditions that favor the reaction, producing unusually large quantities of reactive oxygen species. These chemically reactive molecules can damage proteins, lipids and nucleic acids, while also activating inflammatory signaling pathways. The researchers found evidence of reverse electron transport in fruit flies and mice with tau-related disease, as well as in human brain tissue affected by tauopathy. Healthy neurons showed little or no evidence of the process.

The findings emerged from experiments involving multiple disease models, including animals carrying tau mutations associated with human tauopathies and laboratory-generated human neurons derived from patient cells. The team also studied neurons with a gene duplication linked to an increased risk of early Alzheimer’s disease. Across these systems, mitochondrial stress was closely associated with phosphorylated tau. Removing or reducing tau genetically prevented the abnormal electron flow, while an experimental compound called CPT blocked the interaction between hyperphosphorylated tau and NDUFS3 without stopping normal electron transport.

Animal experiments provided additional evidence that this interaction contributes directly to neurological decline. Fruit flies lacking tau were protected from the severe nervous-system damage and shortened lifespan normally caused by prolonged heat stress. CPT treatment produced similar protection in tau-producing flies and extended their survival. In mice, tau reduction or CPT treatment helped preserve cognition under stressful conditions. In mice with severe tauopathy and cognitive impairment, longer-term CPT administration reduced reverse electron transport in brain mitochondria and improved performance across several behavioral tests.

The treatment also appeared to reduce biological signs of neurodegeneration. CPT-treated animals showed less nerve-cell inflammation and were protected against changes including reduced cortical thickness and loss of total brain volume. In human neurons generated from induced pluripotent stem cells carrying disease-associated tau mutations, CPT prevented several stress-related cellular abnormalities. The convergence of results from animal models, patient-derived neurons and human brain tissue suggests that the mechanism may operate in the human nervous system, although it does not yet establish that CPT is safe or effective as a treatment for patients.

The researchers describe the process as a self-reinforcing loop. Reverse electron transport generates reactive oxygen species, which can promote still more tau phosphorylation. Newly modified tau molecules may then enter mitochondria, bind additional NDUFS3 and further impair respiration. This cycle could help explain how an initially limited mitochondrial disturbance develops into widespread neuronal dysfunction. It also raises the possibility that blocking the tau–NDUFS3 interaction or preventing reverse electron transport could interrupt disease progression without eliminating tau’s normal functions.

The work broadens the range of tau-related mechanisms under investigation in Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, frontotemporal dementia and progressive supranuclear palsy. It may also have relevance to other conditions involving phosphorylated tau and mitochondrial stress, including stroke, traumatic brain injury and some brain tumors. CPT remains an experimental compound, and substantial research will be required before clinical trials can be considered. Bingwei Lu, the study’s senior author, is a co-founder and advisory-board member of Cerapeut Inc., which is developing CPT for neurodegenerative diseases. The study also involved researchers from the University of California, San Francisco, and was supported by grants from the U.S. National Institutes of Health.

Subject of Research: The role of hyperphosphorylated tau in mitochondrial dysfunction and tauopathies.

Article Title: Hyperphosphorylated Tau Disrupts Mitochondrial Energy Production Through Reverse Electron Transport

News Publication Date: Aug. 6

Web References: Stanford Medicine; Stanford School of Medicine; med.stanford.edu

References: Study published online in Neuron; National Institutes of Health grants R21AG083863, R01NS084412, R01AG089752, R37NS083417 and R01NS120219.

Keywords: Alzheimer’s disease, tau, tauopathies, mitochondria, reverse electron transport, NDUFS3, oxidative stress, neurodegeneration, CPT, mitochondrial dysfunction