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 blood–brain barrier is not a simple wall but a dynamic interface built from specialized endothelial cells, pericytes, astrocyte endfeet, and a dense basement membrane. Together these components tightly regulate which molecules and cells can enter the brain, maintaining the precise ionic and metabolic environment that neurons require. In Alzheimer’s disease, imaging and post-mortem studies have repeatedly shown that this barrier becomes leaky decades before overt dementia, allowing blood-borne proteins, fibrin, thrombin, and immune cells to infiltrate brain tissue. This vascular leakage is thought to amplify neuroinflammation, impair amyloid clearance, and accelerate neuronal injury. Yet the molecular switches that flip the barrier from protective to permissive in Alzheimer’s have remained poorly defined, particularly with respect to how genetic risk translates into physical barrier breakdown.

The new work focuses on apolipoprotein E, or APOE, a lipid-transport protein produced abundantly in the brain by astrocytes and microglia. The ε4 variant of APOE is carried by roughly one in four people and multiplies Alzheimer’s risk several-fold compared with the common ε3 variant. Carriers of ε4 show earlier and more pronounced blood–brain barrier leakage, pericyte loss, and cerebral amyloid angiopathy, but the intermediate steps connecting APOE4 expression to vascular failure have been elusive. Bhattarai, Yilmaz and their colleagues reasoned that APOE4 might reprogram astrocytes, the star-shaped glial cells that normally cradle blood vessels and help maintain barrier integrity, into a state that actively undermines the very interface they are supposed to support.

Using a combination of human brain tissue analysis, Alzheimer’s disease mouse models carrying humanized APOE variants, and single-cell molecular profiling, the team discovered that astrocytes in APOE4-bearing brains dramatically upregulate the production of fibronectin, encoded by the FN1 gene. Fibronectin is an extracellular matrix glycoprotein that is normally present at very low levels in the adult brain’s vascular basement membrane. In developing tissue and in peripheral wounds, fibronectin provides a scaffold for repair, but its accumulation in the mature brain vasculature appears to be anything but helpful. The researchers found that fibronectin deposits accumulate around brain capillaries and arterioles in Alzheimer’s disease, and that this accumulation is markedly greater in individuals and animals carrying the ε4 allele.

The mechanistic story that emerges from the study is one of a vicious cycle. Amyloid-beta peptides, which accumulate in Alzheimer’s disease and deposit in cerebral blood vessels as cerebral amyloid angiopathy, stimulate astrocytes to secrete fibronectin, and APOE4 amplifies this response. The excess fibronectin then remodels the vascular basement membrane, disrupting the molecular interactions that keep endothelial tight junctions sealed and pericytes anchored to their vessels. The result is a barrier that becomes progressively more permeable, allowing plasma proteins to leak into the brain parenchyma. Some of these leaked proteins, including fibrinogen, are themselves pro-inflammatory and can further activate astrocytes and microglia, perpetuating the cycle of vascular damage and neuroinflammation that characterizes the Alzheimer’s brain.

Crucially, the researchers did not stop at correlation. In experimental models, reducing fibronectin production or interfering with its deposition produced striking protective effects. Animals with diminished fibronectin signaling maintained better barrier integrity despite the presence of APOE4 and amyloid pathology, showing less vascular leakage, reduced inflammatory activation, and improved structural preservation of the neurovascular unit. These findings position FN1 not merely as a biomarker of vascular damage but as an active, druggable participant in the disease process. The authors highlight FN1 as a potential therapeutic target, a designation that carries real weight because fibronectin biology is already well understood pharmacologically, with existing tools and compounds capable of modulating fibronectin assembly and its interactions with integrin receptors.

The implications for Alzheimer’s drug development are significant. Most therapeutic efforts to date have targeted amyloid-beta and tau, the canonical protein pathologies of the disease, with recent anti-amyloid antibodies demonstrating the ability to slow cognitive decline, albeit modestly. Vascular-targeted approaches have attracted growing interest precisely because blood–brain barrier breakdown appears so early in the disease course and correlates strongly with cognitive impairment independent of plaque burden. If fibronectin sits at the junction of genetic risk, amyloid pathology, and vascular failure, then therapies aimed at curbing fibronectin deposition could protect the barrier in ε4 carriers, a population that represents a large fraction of Alzheimer’s patients and that responds differently to some existing treatments.

The study also reframes the role of astrocytes in neurodegeneration. Long viewed primarily as support cells, astrocytes are increasingly recognized as active regulators of brain health whose dysfunction can drive disease. The finding that APOE4 pushes astrocytes toward a fibronectin-secreting, matrix-remodeling state adds to a growing body of evidence that reactive astrocyte phenotypes are not uniform and that specific astrocyte outputs, in this case a single extracellular matrix protein, can have outsized consequences for the entire neurovascular unit. It also helps explain a long-standing clinical observation: ε4 carriers tend to show more hemorrhagic and vascular contributions to their dementia, and therapies that address only amyloid may leave this vascular component untreated.

As with any study, important questions remain. The precise molecular pathway by which APOE4 sensitizes astrocytes to amyloid-driven fibronectin expression will need to be mapped in detail, and the safety of chronically inhibiting a protein that also participates in normal tissue repair must be carefully evaluated. Translating findings from mouse models and human tissue into a therapy that can be tested in patients will take years. Nevertheless, the identification of astrocyte-derived fibronectin as a mediator of APOE4-driven blood–brain barrier dysfunction provides the field with a concrete, mechanistically grounded target that connects the strongest genetic risk factor for Alzheimer’s disease to one of its earliest and most consequential pathological events. For the millions of people carrying the ε4 allele, that connection may prove to be one of the most important discoveries in the vascular dimension of Alzheimer’s research.

Subject of Research: Astrocyte-derived fibronectin mediates APOE4-driven blood–brain barrier dysfunction in Alzheimer's disease

Article Title: Fibronectin mediates APOE4-driven blood–brain barrier dysfunction in Alzheimer’s disease

Article References: Fibronectin mediates APOE4-driven blood–brain barrier dysfunction in Alzheimer’s disease. (n.d.). https://doi.org/10.1038/s43587-026-01204-0

Image Credits: AI Generated

DOI: 10.1038/s43587-026-01204-0

Keywords: Alzheimer's disease, APOE4, blood–brain barrier, fibronectin, astrocytes, FN1, amyloid-beta, cerebral amyloid angiopathy, neurovascular unit, Nature Aging, therapeutic target, neuroinflammation