Abstract Body

The human brain vasculature is of vast medical importance: its dysfunction causes disability and death, and the specialized structure it forms—the blood-brain barrier—impedes treatment of nearly all brain disorders. Yet, no molecular atlas of the human brain vasculature exists. Here, we develop Vessel Isolation and Nuclei Extraction for Sequencing (VINE-seq) to profile the major human brain vascular and perivascular cell types through 143,793 single-nucleus transcriptomes from 25 hippocampus and cortex samples of 17 cognitively normal and Alzheimer’s disease (AD) patients. We identify brain region-enriched pathways and genes divergent between humans and mice, including those involved in disease. We describe the principles of human arteriovenous organization, recapitulating a gradual endothelial and punctuated mural cell continuum; but discover that many zonation and cell-type markers differ between species. We discover two subtypes of human pericytes, marked by solute transport and extracellular matrix (ECM) organization; and define perivascular versus meningeal fibroblast specialization. In AD, we observe a selective vulnerability of ECM-maintaining pericytes and gene expression patterns implicating dysregulated blood flow. With an expanded survey of brain cell types, we find that 30 of the top 45 AD GWAS genes are expressed in the human brain vasculature, confirmed in situ. Vascular GWAS genes map to endothelial protein transport, adaptive immune, and ECM pathways. Many are microglia-specific in mice, suggesting an evolutionary transfer of AD risk to human vascular cells. Our work unravels the molecular basis of the human brain vasculature, informing our understanding of overall brain health, disease, and therapy.

Aims

Dementia with Lewy bodies (DLB) and Parkinson’s disease dementia (PDD), collectively known as Lewy body diseases (LBDs) are neuropathologically characterised by the presence of alpha-synuclein. However, it is common for DLB and PDD to also exhibit pathology more commonly associated with Alzheimer’s disease (AD) (i.e. hyperphosphorylated tau and amyloid β (Aβ). Aβ can be deposited in the walls of blood vessels in the brains of individuals with AD, termed cerebral amyloid angiopathy (CAA). The aim of this study was to investigate the type and distribution of CAA in DLB and PDD, and if this differs from AD.

Methods

CAA type, severity, and topographical distribution was assessed in human post-mortem tissue from 103 AD cases, 34 DLB cases, and 13 PDD cases. The cortical brain regions assessed included frontal, temporal, parietal, and occipital cortices.

Results

Type 1 CAA was observed in AD and DLB cases (32% and 14% respectively), whilst it was absent in PDD. The occipital lobe was the region most affected by CAA in all cases assessed, however this was closely followed by the frontal cortex (AD 87% of cases, DLB 63%, whilst only 22% of PDD cases were affected by CAA).

Conclusions

Topographical patterns of CAA in DLB more closely resembled AD rather than PDD, and as type 1 CAA is associated with clinical dementia in AD, further investigations are warranted into whether the presence of type 1 CAA in DLB and absence in PDD are related to the onset of cognitive symptoms and is a distinguishing factor between LBDs.

Aims

ABCA7 is a major risk gene for Alzheimer’s disease (AD). Rare premature termination codon (PTC) and missense mutations are enriched in AD patients, but clinicopathological phenotype of the carriers is not yet clear.

Methods

Genetic screening of ABCA7 in Belgian AD patients (n=1365) and cerebral amyloid angiopathy (CAA) patients (n=83), with genotype-phenotype comparison of the ABCA7 carriers using demographic and clinicopathology data.

Results

In a large Belgian AD cohort, we identified 69 PTC (5.0%) and 87 (6.5%) missense mutations carriers. Mean onset age of the PTC carriers is 69.6±9.9 years (range 48-90), comparable to the missense carriers, 68.0±10.3 years (range 48-92). Probable AD is diagnosed in 73.1% of PTC and 78.0% of missense carriers. Important vascular involvement is present in 12 PTC (16.4%) and 6 missense (6.9%) mutation carriers. Imaging features compatible with CAA were described in six PTC (7.5%) and 2 missense (2.3%) carriers. Postmortem examination is available for 10 PTC and 7 missense carriers, showing AD neuropathology with moderate-to-severe levels of CAA in all 17 patients. Widespread levels of CAA are present in both the meningeal and capillary blood vessels and moderate to high levels of CAA in the parenchymal blood vessels (figure 1, table 1).

Genetic screening of 83 CAA patients identified 14 ABCA7 (16.9%), carriers, 5 PTC, 8 missense and 1 deletion mutations.

Conclusions

Carriers of rare ABCA7 mutations present with a classical AD phenotype. But apart the AD pathology prominent levels of CAA were present. Our study might have important implications for research and clinical practice.

Aims

Cerebral microbleeds (CMBs) are common in persons with Alzheimer’s disease (AD) and are associated with hemorrhage and cognitive decline. The aim of this study was to examine the association between CMBs and amyloid pathology in individuals with normal cognition (NC), mild cognitive impairment (MCI) and dementia.

Methods

We included 781 participants with NC, 355 participants with MCI and 230 participants with dementia from 8 cohorts included in the Amyloid Biomarker Study. Amyloid-beta positivity was determined with amyloid-PET (center-specific cutoffs) or aß42 level in CSF (data-driven cutoffs). Participants were classified as having any CMBs (≥1) yes/no. Associations of amyloid positivity, APOE-e4 carriership, cognitive status, sex and age with CMBs were assessed using generalized-estimating-equations.

Results

Forty-seven percent of participants were amyloid-beta positive, 38% were APOE-e4 carrier, 48% were female and 19% had CMBs. The mean age was 68.5 years (SD11.2). CMB prevalence increased with age (p<0.001) and was associated with amyloid-beta status, depending on age (p<0.001). In those under 75 years of age, CMBs were more common in amyloid positive than amyloid negative participants. This association was reversed at older ages, where amyloid negative participants had CMBs more often. Cognitive status, APOE-e4 carriership and sex were not associated with CMB occurrence in this sample, most of whom were memory clinic patients.

Conclusions

CMB prevalence is associated with amyloid positivity in an age-dependent manner. This sheds light on the underlying pathophysiology. Future research on the background incidence rate of CMBs considering AD biomarker status would be helpful for clinical trial design and safety evaluations of AD therapies.

Aims

Associations of AD and cerebrovascular pathologies with neurodegeneration in aging and dementia is not fully understood. We investigated biomarkers of amyloid-beta, tau neurofibrillary tangle (NFT), and cerebrovascular pathology in relation to regional GM volume in patients with dementia with Lewy bodies (DLB), in comparison to Alzheimer’s disease (AD) and cognitively unimpaired (CU) elderly.

Methods

We included 30 DLB and 48 AD dementia patients from the Mayo Clinic ADRC, who underwent 11C-PiB PET, 18F-Flortaucipir PET, and MRI. An age and sex matched CU group was also included (n=100). We conducted univariate and multivariable analyses to investigate unique and combined associations of PiB standard uptake value ratio (SUVr), Flortaucipir SUVr and WMH volume with regional GM volume as a marker of neurodegeneration.

Results

In DLB, higher Flortaucipir SUVr was associated with GM atrophy in the fusiform cortex and WMH volume predicted neurodegeneration in inferior-medial frontal lobe and insula in the multivariable model. In contrast, in AD dementia, Flortaucipir SUVr was associated with GM atrophy involving most of the cortex. In CU, elevation in all three biomarkers (PiB and Flortaucipir SUVrs, and WMH volume) were associated with neurodegeneration in the medial temporal lobe and WMH was associated with atrophy in the insula and orbitofrontal regions.

Conclusions

Although amyloid-beta, tau NFT, and cerebrovascular pathologies often coexist in DLB, AD dementia, and CU, their associations with neurodegeneration seem to be different, which may in part determine pathogenesis and clinical expression.

Aims

ARIA are the most common serious side effects of Alzheimer’s disease immunotherapy with monoclonal antibodies targeting brain-deposited amyloid-beta protein (Aβ). Similar ARIA manifestations occur spontaneously in cerebral amyloid angiopathy-related inflammation (CAA-ri), a rare autoimmune encephalopathy characterized by increased CSF levels of anti-Aβ autoantibodies.

The neuroinflammatory nature and the association between ARIA and microglial activation in the context of high anti-Aβ antibodies has never been demonstrated in-vivo.

Methods

A consecutive series of patients with CAA-ri, diagnosed by clinicoradiological evidence of white matter hyperintensities (WMHs) due to vasogenic edema (spontaneous ARIA-E) and hemosiderin deposition/hemorrhage (spontaneous ARIA-H), according to current diagnostic criteria. A multimodal imaging and CSF protocol for the longitudinal evaluation of the spatial distribution and temporal variation of microglial activation associated with ARIA, including ¹¹C-PK11195-PET for activated microglia, AT(N) biomarkers and anti-Aβ autoantibody CSF profile.

Results

At presentation, we found focal peaks of microglial activation co-localized with ARIA-E, which markedly reduced following resolution of ARIA-E. Conversely, no variations were observed when ARIA-E did not solve at follow-up. All patients had high CSF anti-Aβ autoantibody levels at presentation, which significantly decreased at follow-up only when ARIA-E and microglial activation reduced. We also observed some scattered clusters of microglial activation associated with ARIA-H. However, these clusters were diffused and remained unchanged at follow-up. No microglial activation were observed within the periventricular and deep WMHs of sporadic non-amyloid microangiopathy.

Conclusions

We provide the first in-vivo evidence for a spatial and temporal association between microglial activation and ARIA-E manifestations in CAA-ri patients presenting with high anti-Aβ autoantibodies.

Abstract Body

Apolipoprotein E4 (APOE4), the main susceptibility gene for Alzheimer’s disease (AD), exerts cerebrovascular toxicity and accelerates vascular dysfunction, amyloid-b and tau pathology, neurodegenerative disorder and dementia in AD. How these different pathologies relate to each other to confer APOE4-associated cognitive impairment remains still unclear and challenging to dissect. Here, I will briefly review 1) our recent findings in human APOE4 carriers and non-carriers (APOE3 homozygotes) suggesting the role of blood-brain barrier (BBB) breakdown in development of early human cognitive dysfunction and APOE4-associated cognitive decline both in individuals with positive and negative AD amyloid-b and tau biomarkers abnormalities; and 2) our recent cellular and molecular studies in humanized APOE knock-in mice including comprehensive large-scale analysis of cell-specific BBB mechanisms by single-nucleus RNA-sequencing, phosphoproteome and proteome analysis suggesting that changes in APOE4 disrupts multiple BBB signaling mechanisms that precedes loss of neurites, post-synaptic PSD95 interactome dysregulation, and behavioral deficits. Finally, I will briefly discuss potential therapeutic opportunities to control neurodegenerative and cognitive disorders by targeting BBB signaling mechanisms that regulate cerebrovascular integrity.