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 team’s extensive research indicates that a deficiency of HDL cholesterol, often referred to as “good cholesterol,” within the brain has a profound impact on increasing Alzheimer’s disease risk. Under normal circumstances, ABCA1 functions to produce HDL cholesterol, but the study illustrates a troubling paradox in Alzheimer-affected brains. While ABCA1 levels are elevated, its functionality diminishes, resulting in a concerning lack of HDL. This contradiction has long been a topic of intrigue within the scientific community, prompting researchers to delve deeper into the cellular dynamics that underlie these phenomena.

Hussein Yassine, a leading figure in this study and professor of medicine and neurology, emphasizes the complexity of this conundrum. He explains that the increased presence of ABCA1 in Alzheimer’s-affected brains does not correlate with its expected activity levels, raising critical questions about the functionality of this protein in the pathological context of Alzheimer’s disease. By employing advanced research techniques, including proteomics and lipidomics, the team successfully identified key changes in cholesterol and lipid dynamics within brain cells, uncovering a pivotal connection between ABCA1, its location within the cell, and the presence of oxidative stress.

The research team uncovered that in cases involving both Alzheimer’s-afflicted brains and genetically predisposed individuals, ABCA1 becomes sequestered within cellular structures known as lysosomes, which are responsible for waste clearance. This entrapment is not merely a logistical issue; it signifies a cellular dysfunction that contributes significantly to neurodegeneration. This observation aligns with the rise of oxysterols, a modified form of cholesterol that accumulates within the cells, leading to the adverse outcomes associated with Alzheimer’s disease, including inflammation and cellular senescence, a process where cells lose their ability to divide and function effectively.

Through their experiments in animal models and human biochemical samples, the researchers made an intriguing and promising discovery: lowering oxysterol levels resulted in freeing ABCA1 from its cellular captivity. This restoration of ABCA1 function allowed for the proper production of HDL cholesterol, breaking the cycle of inflammation and cellular aging that often underlies Alzheimer’s pathogenesis. The implications of this research are profound, as it not only elucidates a key molecular pathway involved in Alzheimer’s disease but also offers potential therapeutic avenues for intervention during the disease’s early stages.

In an environment where clinical trials focusing on increasing HDL cholesterol have often yielded disappointing results, this study redefines the approach toward Alzheimer’s prevention and treatment. Understanding the dynamics of ABCA1’s retention within lysosomes offers novel insights into why previous strategies failed and emphasizes the importance of targeting underlying cellular mechanisms rather than solely addressing symptomatic manifestations through amyloid and tau accumulation reduction.

The current findings could herald a transformative shift in Alzheimer’s treatment paradigms, steering research efforts towards addressing these early alterations within the brain’s cellular microenvironment. By targeting the oxysterol-mediated entrapment of ABCA1, researchers can explore the development of new pharmacological agents that may effectively alter the course of the disease before it progresses to its later, more debilitating stages.

Furthermore, the study opens up discussions surrounding additional therapeutic targets, such as cytosolic phospholipase A2 (CPLA2), an enzyme that, similar to ABCA1, plays a role in oxidative processes leading to inflammation within the brain. By inhibiting CPLA2, the potential exists to further curb the neuroinflammatory processes linked to Alzheimer’s disease. Thus, researchers underscore the urgency of exploring diverse mechanisms of action within the complex landscape of neurodegeneration.

Beyond immediate treatment implications, this research contributes significantly to our understanding of the broader implications of cholesterol metabolism in neurodegenerative diseases. It positions the cholesterol modification pathways as critical players in the intricate web of Alzheimer’s disease, suggesting that future therapeutic interventions may benefit from a multifaceted approach targeting various aspects of cellular metabolism.

As research progresses, further investigations into the relationship between cellular cholesterol levels, ABCA1 functionality, and neuroinflammation are anticipated. This work not only stands as a definitive achievement in the realm of neurodegenerative research but also poses critical questions about the nature of cellular dysregulation in Alzheimer’s disease, underlining the necessity for ongoing inquiry into the early stages of disease progression.

With research funding support from various esteemed institutions, including the National Institutes of Health and the Alzheimer’s Drug Discovery Foundation, this study embodies the spirit of collaborative scientific effort. It underscores the importance of interdisciplinary relationships in the pursuit of significant advancements in medical research, particularly in complex fields such as neurodegeneration.

As the implications of this research unfold, the scientific community eagerly awaits novel therapeutic strategies that may emerge from understanding the interactions between cholesterol metabolism, inflammation, and Alzheimer’s disease. With the lingering effects of Alzheimer’s disease affecting millions globally, the urgency for innovative treatments firmly places this research at the forefront of neurodegenerative disease studies, heralding hope for both patients and caregivers alike.

In summary, this burgeoning exploration of brain cellular mechanisms promises to reshape not only the understanding of Alzheimer’s disease but also the broader field of neurodegeneration. The focus on ABCA1 and its interactions within the cell offers tantalizing prospects for new treatment avenues, demonstrating how targeted research can illuminate pathways previously shrouded in mystery and setting the stage for future breakthroughs in managing this devastating condition.

Subject of Research: Alzheimer’s Disease Pathophysiology
Article Title: Cellular Senescence Induced by Cholesterol Accumulation is Mediated by Lysosomal ABCA1 in APOE4 and AD
News Publication Date: [Not Provided]
Web References: [Not Provided]
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Keywords

– Alzheimer’s disease
– Cellular senescence
– ABCA1
– HDL cholesterol
– Oxysterols
– Neuroinflammation
– Cholesterol metabolism
– Neurodegenerative diseases
– CPLA2
– Therapeutic targets
– Cellular mechanisms
– Proteomics and lipidomics