The research team, led by Sungwoo Kang and Byoung Seok Ye of Yonsei University Severance Hospital in Seoul, analyzed 387 patients with amyloid-confirmed Alzheimer’s disease spanning the full clinical spectrum from mild cognitive impairment to dementia. All participants underwent detailed neuropsychological testing, 3.0-Tesla structural MRI, amyloid PET with florbetaben, and dual-phase FP-CIT PET imaging. The cohort was divided into 205 APOE4 carriers and 182 non-carriers, and the researchers carefully excluded 58 patients who showed two or more core clinical features of Lewy body disease, such as parkinsonism, cognitive fluctuation, REM sleep behavior disorder, or recurrent visual hallucinations, to ensure the cohort remained as Alzheimer’s-consistent as possible.

Two imaging biomarkers anchored the analysis. The first was basal forebrain volume, measured from the Ch4 region corresponding to the nucleus basalis of Meynert, the principal source of acetylcholine to the cortex and a structure long known to degenerate in Alzheimer’s disease. The second was striatal dopamine transporter uptake, quantified from late-phase FP-CIT PET scans, with the posterior caudate selected as the representative dopaminergic marker because it showed the strongest relationship with basal forebrain volume. Regional brain perfusion was derived from early-phase FP-CIT PET using a data-driven normalization method called the subject residual profile, which captures each patient’s region-relative perfusion deviations without relying on a potentially disease-affected reference region such as the pons or cerebellum.

The first striking result was a clean genetic dissociation of the two neurotransmitter systems. APOE4 carriers showed significantly lower basal forebrain volume than non-carriers, consistent with decades of autopsy work linking the ε4 allele to reduced cholinergic activity in the nucleus basalis and greater loss of presynaptic cholinergic markers in the neocortex. Non-carriers, by contrast, showed lower posterior caudate dopamine transporter uptake, indicating more pronounced nigrostriatal dopaminergic degeneration. Both patient groups had reduced basal forebrain volume and striatal transporter uptake compared with 53 healthy controls, but the relative burden of damage flipped according to genotype, a pattern confirmed by statistically significant interaction terms between APOE4 status and each biomarker.

The perfusion maps told a parallel story. In APOE4 carriers, lower basal forebrain volume was associated with hypoperfusion across the temporoparietal association cortices and the posterior cingulate cortex, the classic Alzheimer’s signature, in addition to medial temporal changes seen in both groups. In non-carriers, lower dopamine transporter uptake was linked to a broader set of perfusion alterations, including frontal hypoperfusion and relative hyperperfusion in the amygdala, hippocampus, and ventral occipitotemporal regions, patterns that echo the metabolic signatures of Lewy body pathology. The researchers suggest that in carriers, Lewy-type alpha-synuclein involvement may be expressed more through cholinergic and cortical-limbic pathways, whereas in non-carriers, brainstem-predominant Lewy pathology may drive the dopaminergic signal, consistent with autopsy studies showing genotype-dependent differences in the anatomical distribution of Lewy-related pathology.

When the team connected these biomarkers to symptoms, the divergence sharpened. In APOE4 carriers, lower basal forebrain volume was associated with poorer memory performance and with more severe neuropsychiatric symptoms including hallucinations, delusions, anxiety, apathy, aberrant motor behavior, and appetite changes. Mediation analyses showed that the link between cholinergic degeneration and memory dysfunction was statistically mediated by posterior cingulate hypoperfusion, meaning the structural damage appeared to act on cognition through its effect on cortical function. After accounting for regional perfusion, direct associations remained for hallucinations, delusions, and apathy, suggesting that cholinergic loss contributes to these behavioral disturbances through mechanisms beyond cortical hypoperfusion alone.

In non-carriers, the picture was almost inverted. Lower posterior caudate dopamine transporter uptake was associated with poorer performance across all cognitive domains measured, including attention, language, visuospatial ability, memory, and executive function, and with more severe hallucinations, delusions, and anxiety. Remarkably, these associations largely persisted even after adjustment for regional perfusion, indicating that dopaminergic degeneration in this group exerts direct effects on cognition and behavior rather than acting purely through cortical metabolic decline. Mediation analyses identified significant indirect pathways through angular gyrus hypoperfusion for memory and executive function, but the direct associations remained significant alongside them. The researchers also observed a synergistic interaction in non-carriers, where the association between dopaminergic loss and delusion severity was strongest in patients who also had the smallest basal forebrain volumes.

The memory findings deserve particular attention because they challenge the assumption that memory impairment in Alzheimer’s always reflects the same circuit damage. In APOE4 carriers, memory dysfunction tracked hypoperfusion in the posterior cingulate cortex and medial temporal lobe, regions densely connected to the cholinergic basal forebrain and heavily burdened by tau in carriers. In non-carriers, memory problems correlated most strongly with parietal hypoperfusion, particularly in the angular gyrus, a region more often implicated in atypical, non-amnestic presentations. This topographic split aligns with prior imaging work showing greater medial temporal atrophy and tau accumulation in carriers versus greater frontoparietal cortical thinning and tau burden in non-carriers, and it helps explain why non-carriers more frequently present with atypical clinical syndromes.

The study’s authors are careful about its limits. The cross-sectional design cannot establish causality, and the possibility that chronic clinical dysfunction drives secondary hypoperfusion and subcortical atrophy cannot be excluded, although prior longitudinal work shows that basal forebrain degeneration precedes and predicts the cortical spread of Alzheimer’s pathology. Basal forebrain volume is also an indirect structural surrogate rather than a direct measure of cholinergic synaptic activity, though multimodal studies have validated it against vesicular acetylcholine transporter and acetylcholinesterase PET. The cohort was enriched for patients referred for FP-CIT PET, potentially inflating dopaminergic abnormalities, and tau and alpha-synuclein pathology were not directly assessed. Effect sizes were modest, and the authors emphasize the need for validation in independent cohorts with molecular biomarkers of tau, synuclein, and TDP-43 pathology.

Even with those caveats, the implications are substantial. If APOE4 genotype defines two neurochemical subtypes of amyloid-confirmed Alzheimer’s disease, then cholinergic and dopaminergic imaging markers could become powerful tools for patient stratification in anti-amyloid trials, where treatment responses have been notoriously heterogeneous. The findings also raise the prospect of genotype-guided symptomatic therapy: cholinesterase inhibitors may matter most for the basal-forebrain-dominant carrier subtype, while dopaminergic pathways may deserve greater attention in non-carriers. As the authors conclude, combining APOE4 status with neurotransmitter imaging may move the field closer to a precision medicine framework in which the neurochemical fingerprint of each patient’s disease, not just its amyloid burden, determines the therapeutic strategy.

Subject of Research: APOE4-dependent cholinergic and dopaminergic degeneration and their relationships to cognitive and neuropsychiatric symptoms across the Alzheimer's disease spectrum

Article Title: APOE4-dependent cholinergic/dopaminergic contributions to clinical symptoms across Alzheimer’s disease spectrum: A retrospective observational study

Article References: Kang, S., Jeon, S., Lee, D., Lee, H., Jeon, S.-H., Choi, M., Lee, Y.-G., Shin, N.-Y., Yun, M., & Ye, B. S. (2026). APOE4-dependent cholinergic/dopaminergic contributions to clinical symptoms across Alzheimer’s disease spectrum: A retrospective observational study. European Journal of Nuclear Medicine and Molecular Imaging. https://doi.org/10.1007/s00259-026-08165-x

Image Credits: AI Generated

DOI: 10.1007/s00259-026-08165-x

Keywords: Alzheimer's disease, APOE4, cholinergic system, dopaminergic system, basal forebrain, dopamine transporter, FP-CIT PET, brain perfusion, neuropsychiatric symptoms, memory dysfunction, Lewy body pathology, biomarkers

The study focuses on glucocerebrosidase, commonly abbreviated as GCase, an enzyme encoded by the GBA gene. GCase is located primarily inside lysosomes, the cell’s recycling compartments, where it helps break down specific fatty molecules known as glucosylceramides. Variants in GBA can reduce the enzyme’s efficiency and are among the most common genetic risk factors for Parkinson’s disease. Some variants cause Gaucher disease, a lysosomal storage disorder, while others produce subtler biochemical changes that increase Parkinson’s susceptibility without necessarily causing Gaucher disease.

Parkinson’s disease is also characterized by the accumulation of α-synuclein, a neuronal protein that can assemble into abnormal structures and contribute to Lewy bodies and Lewy neurites. However, α-synuclein is not a single, chemically uniform molecule. It exists in multiple “proteoforms,” meaning molecular variants created by differences in processing, chemical modification, truncation, aggregation state or interactions with other cellular components. These forms may behave differently in neurons, and distinguishing them could help explain why some types of α-synuclein are more toxic or more strongly associated with disease progression.

Morella and colleagues investigated these mechanisms in human brains collected after death from people with Parkinson’s disease linked to GBA alterations, people with idiopathic Parkinson’s disease, and comparison groups. The use of post-mortem tissue is crucial because it allows researchers to examine the molecular environment in the affected organ itself rather than relying only on blood, cerebrospinal fluid, cultured cells or experimental animals. At the same time, brain tissue collected after death presents analytical challenges, including differences in disease duration, medication history, tissue preservation, brain region and the extent of neuronal loss.

The central feature of the research is quantitative biochemical profiling. Rather than simply determining whether GCase or α-synuclein is present, this approach aims to measure how much enzymatic activity remains and which molecular forms of α-synuclein are present. Measuring GCase activity is particularly important because enzyme abundance alone does not necessarily indicate function. A neuron may contain detectable GCase protein while the enzyme is improperly folded, trapped in the wrong cellular compartment, chemically modified or otherwise less active.

The investigators’ examination of α-synuclein proteoforms adds another layer to the analysis. Standard laboratory tests can detect total α-synuclein, but total protein measurements may conceal biologically meaningful differences. For example, soluble α-synuclein, phosphorylated species, truncated fragments and aggregated forms may have distinct effects on synaptic function, cellular transport and lysosomal degradation. A detailed profile can therefore reveal whether GCase impairment is associated with a particular molecular signature rather than with a simple increase in the overall amount of α-synuclein.

The connection between GCase and α-synuclein is thought to operate in both directions. Reduced lysosomal GCase activity may interfere with the clearance of α-synuclein, allowing damaging species to accumulate. Conversely, α-synuclein aggregates may disrupt lysosomal trafficking or prevent GCase from reaching the compartment where it normally functions. This creates a potentially self-reinforcing cycle in which impaired cellular recycling promotes protein accumulation, while protein pathology further weakens the recycling system.

Comparing GBA-related Parkinson’s disease with idiopathic Parkinson’s disease is especially valuable because it can separate mechanisms that are specific to genetic risk from those shared across the broader Parkinson’s spectrum. If the two groups show similar biochemical patterns, that would support the idea that lysosomal dysfunction is a common pathway in Parkinson’s disease, even when no GBA mutation is identified. If they show distinct patterns, those differences could help explain variations in age of onset, clinical progression or treatment response and could guide the development of more targeted therapies.

The findings also have potential implications for drug development. Several experimental strategies are designed to increase GCase activity, improve its delivery to lysosomes, stabilize the enzyme or correct its trafficking. Other approaches aim to reduce harmful α-synuclein species or enhance their clearance. Quantitative measurements from human brain tissue can help determine whether these treatments are affecting the intended molecular targets. They may also help researchers identify biomarkers that reflect treatment response in living patients, although translating post-mortem biochemical signatures into clinical tests will require further validation.

By placing enzyme function and α-synuclein diversity in the same analytical framework, the study underscores a broader shift in Parkinson’s research. The disease is increasingly understood not as a single disorder with one uniform molecular cause, but as a collection of overlapping biological pathways that can converge on neuronal degeneration. Human-brain profiling cannot by itself establish causation, and post-mortem studies cannot fully capture the sequence of events that occurred during life. Yet by mapping the biochemical terrain with greater precision, this work may help reveal which molecular changes are drivers, which are consequences and which could serve as practical targets for the next generation of Parkinson’s therapies.

Subject of Research: Quantitative biochemical profiling of GCase activity and α-synuclein proteoforms in post-mortem human brains from GBA-related and idiopathic Parkinson’s disease.

Article Title: Quantitative biochemical profiling of GCase activity and α-synuclein proteoforms in post-mortem human brains from GBA-related and idiopathic Parkinson’s disease.

Article References: Morella, M.L., Teneketzi, M., Ferraro, F. et al. “Quantitative biochemical profiling of GCase activity and α-synuclein proteoforms in post-mortem human brains from GBA-related and idiopathic Parkinson’s disease.” npj Parkinson’s Disease (2026). https://doi.org/10.1038/s41531-026-01488-4

Image Credits: AI Generated

DOI: 10.1038/s41531-026-01488-4

Keywords: Parkinson’s disease, GBA, glucocerebrosidase, GCase, α-synuclein, proteoforms, lysosomes, neurodegeneration, post-mortem human brain, biochemical profiling

Parkinson’s disease, a condition marked by progressive motor dysfunction resulting from the loss of dopaminergic neurons in the substantia nigra, has long been linked to the accumulation of misfolded alpha-synuclein proteins. These proteins aggregate into fibrillar structures known as Lewy bodies, which disrupt neuronal function and ultimately lead to cell death. Traditional therapeutic approaches have largely focused on symptom management or slowing disease progression through indirect means. However, the study from Sevenich and colleagues takes a radical step forward by directly targeting the fibrillar aggregates themselves, aiming to reverse the fundamental pathogenic process.

The team’s novel solution hinges on the use of an all-D-peptide—a synthetic peptide wholly composed of D-amino acids, which confer remarkable stability and resistance against proteolytic degradation. This structural uniqueness not only enhances the peptide’s bioavailability and longevity within biological systems but also equips it with the capacity to bind to alpha-synuclein fibrils and induce their direct disassembly. The researchers meticulously validated the peptide’s efficacy, meticulously documenting its ability to break down the fibrillar alpha-synuclein into monomeric units, which are far less toxic and pathogenic.

What is striking about this approach is its mechanistic clarity. Prior strategies often struggled with indirect targeting or required complex cellular machinery to reverse aggregation, but this all-D-peptide acts as a molecular disruptor, engaging directly with the beta-sheet rich fibrillar structure to unravel it. The peptide’s binding initiates a cascade of destabilization events, effectively ‘unzipping’ the fibril and liberating soluble monomers. This mechanistic insight advances the field by offering a tangible means to directly interfere with protein aggregation, a pathological hallmark shared not only by Parkinson’s but also other synucleinopathies.

Sevenich et al. leveraged a battery of advanced biophysical and biochemical techniques to characterize the interaction between the all-D-peptide and alpha-synuclein fibrils. Methods such as transmission electron microscopy (TEM), circular dichroism (CD) spectroscopy, and Thioflavin T assays provided robust evidence for the peptide-mediated fibril disassembly. These complementary data illustrated a gradual dissolution of mature fibrils, accompanied by a reduction in beta-sheet content—a signature conformational element of pathological aggregates. Importantly, the collection of evidence aligns to affirm the targeted and efficient nature of fibril disruption.

Beyond the biochemical milieu, the study explored the peptide’s functional implications in cellular models of Parkinson’s. Here, the peptide not only prevented further aggregation but actively reversed existing fibrillar deposits within neuronal cultures. These results underscore the therapeutic potential of the all-D-peptide by demonstrating a capacity not merely for prophylaxis but for remediation of already established pathological protein aggregates. The implications for disease-modifying treatment are profound, signaling a shift from symptomatic management to targeted molecular repair.

One of the remarkable features of the all-D-peptide strategy is its translational potential. All-D-peptides are inherently less immunogenic and more pharmacokinetically stable than their L-peptide counterparts, aspects that bode well for future in vivo applications. The researchers discuss the peptide’s ability to permeate cellular membranes, a critical prerequisite for effectively targeting intracellular aggregates. This cellular uptake, combined with the resistance to protease degradation, charts a promising pathway toward clinical development, potentially allowing systemic administration or blood-brain barrier penetration.

The therapeutic window afforded by direct fibril disassembly could also circumvent challenges that have impeded other therapies, such as antibody-based immunotherapies that rely on immune activation. By leveraging a purely biochemical mechanism, the all-D-peptide circumvents potential inflammatory side effects while directly addressing the misfolded protein burden. Such precision medicine elevates the possibility of reducing off-target effects and enhancing patient safety profiles, two pivotal concerns in neurodegenerative disease therapeutics.

Moreover, the study situates this breakthrough within the broader context of protein aggregation diseases. The method’s conceptual framework may be adaptable to other pathological amyloids beyond alpha-synuclein. Diseases such as Alzheimer’s, characterized by amyloid-beta and tau aggregation, could potentially benefit from similar peptide-mediated disassembly approaches, offering a versatile platform technology for neurodegenerative disorders grounded in aggregation pathology.

In the intricate battle against Parkinson’s disease, one of the largest hurdles has been addressing the stubborn, insoluble aggregates resistant to conventional treatments. Sevenich and colleagues’ demonstration of direct fibril disassembly represents a transformative leap. The clarity of their mechanistic insights, coupled with convincing experimental validation, establishes a robust foundation for further preclinical studies. The next frontier will entail validating these findings in animal models and investigating toxicity, pharmacodynamics, and ultimately clinical efficacy.

The scientific community has greeted this development with enthusiasm, recognizing the potential for a new class of therapeutics that could fundamentally change disease progression trajectories. While additional hurdles remain before translation to patients, the study provides a much-needed light at the end of the tunnel, one based on molecular precision rather than symptomatic relief alone. The discovery fuels optimism that Parkinson’s disease, historically considered intractable, may be confronted with effective disease-modifying therapies on the horizon.

Furthermore, the ability of the all-D-peptide to disassemble preformed fibrils implies potential use not only for early intervention but also for patients with established pathology. This feature is critical because Parkinson’s diagnosis often lags behind early pathogenic events. Having a treatment that can reverse existing pathological aggregates opens therapeutic windows previously deemed too late to intervene, offering hope to millions affected worldwide.

In addition to efficacy, the peptide’s design introduces a versatile scaffold for further chemical optimization. Structure-activity relationship experiments could yield derivatives with enhanced binding affinity or cellular uptake, allowing tailored therapies for different stages or subtypes of synucleinopathies. This modularity enables a personalized medicine approach, fostering therapies aligned with patient-specific molecular profiles—an exciting frontier in neurodegenerative disease management.

From a broader perspective, this work underscores the profound utility of D-peptides in biomedical science. Their exceptional stability, low immunogenicity, and unique interactions with protein aggregates position them as potent tools for drug design. This paradigm may extend beyond neurodegeneration, impacting fields such as oncology, infectious disease, and immunology, wherever pathological protein-protein interactions play critical roles.

In conclusion, the study by Sevenich et al. constitutes a landmark achievement in neurodegenerative research. By harnessing an all-D-peptide to directly disassemble alpha-synuclein fibrils into benign monomers, they have unlocked a new therapeutic avenue with far-reaching implications. This research not only advances our understanding of Parkinson’s disease pathology but also pioneers a generalizable strategy against protein misfolding disorders, propelling the field toward more effective and lasting treatments.

Subject of Research: Parkinson’s disease; disassembly of alpha-synuclein fibrils using all-D-peptides.

Article Title: Direct disassembly of α-syn preformed fibrils into α-syn monomers by an all-D-peptide.

Article References:
Sevenich, M., Gering, I., Kass, B. et al. Direct disassembly of α-syn preformed fibrils into α-syn monomers by an all-D-peptide. npj Parkinsons Dis. 11, 271 (2025). https://doi.org/10.1038/s41531-025-01132-7

Image Credits: AI Generated