Introduction
Vascular contributions to cognitive impairment are increasingly recognized
1–5
as shown by neuropathological
6,7
, neuroimaging
4,8–11
, and cerebrospinal fluid (CSF) biomarker
4,12
studies. Moreover, small vessel disease of the brain has been estimated to contribute
to approximately 50% of all dementias worldwide, including those caused by Alzheimer’s
disease (AD)
3,4,13
. Vascular changes in AD have been typically attributed to vasoactive and/or vasculotoxic
effects of amyloid-β (Aβ)
3,11,14
, and more recently tau
15
. Animal studies suggest that Aβ and tau lead to blood vessel abnormalities and blood-brain
barrier (BBB) breakdown
14–16
. Although neurovascular dysfunction
3,11
and BBB breakdown develop early in AD
1,4,5,8–10,12,13
, how they relate to changes in AD classical biomarkers Aβ and tau, which also develop
prior to dementia
17
, remains unknown. To address this question, here we studied brain capillary damage
using a novel CSF biomarker of BBB-associated capillary mural cell pericyte, a soluble
platelet-derived growth factor receptor-β (sPDGFRβ)
8,18
, and regional BBB permeability using dynamic contrast-enhanced (DCE)-magnetic resonance
imaging (MRI)
8–10
. Our data show that individuals with early cognitive dysfunction develop brain capillary
damage and BBB breakdown in the hippocampus irrespective of Alzheimer’s Aβ and/or
tau biomarker changes, suggesting that BBB breakdown is an early biomarker of human
cognitive dysfunction independent of Aβ and tau.
We studied individuals who were cognitively normal as well as those with early cognitive
dysfunction who were stratified upon CSF analysis as either Aβ-positive (Aβ1–42+,
<190 pg/mL) or Aβ-negative (Aβ1–42-, >190 pg/mL), or pTau-positive (pTau+, >78 pg/mL)
or pTau-negative (pTau-, <78 pg/mL), using accepted cutoff values
19–21
. Supplementary Tables 1 and 2 show demographics, clinical data and prevalence of
vascular risk factors (VRFs) by level of Clinical Dementia Rating (CDR) score and
number of cognitive domains impaired, respectively. Individuals diagnosed with vascular
dementia and vascular cognitive impairment, and other disorders that might account
for cognitive impairment were excluded (see Methods).
PDGFRβ is primarily expressed in brain by vascular mural cells – capillary pericytes
and vascular smooth muscle cells (SMCs), but not by neurons, astrocytes, endothelial
cells, oligodendrocytes and/or microglia
22–25
. PDGFRβ expression in pericytes is noticeably higher than in SMCs
18,25,26
. Human brain pericytes, but not SMCs, shed sPDGFRβ in the culture media, which is
increased by hypoxia or injurious stimuli
8,18
. Additionally, loss of pericytes in mice elevates CSF sPDGFRβ
8
. In individuals with mild cognitive impairment, increased CSF sPDGFRβ correlates
with increased DCE-MRI measures of BBB dysfunction
8
. Consistent with findings that ADAM10 (disintegrin and metalloproteinase domain-containing
protein 10) sheds sPDGFRβ in fibroblasts
27
, we found that ADAM10 mediates sPDGFRβ shedding in human pericytes but not SMCs (Extended
Data Fig. 1), supporting that sPDGFRβ is primarily a biomarker of brain capillary
pericytes
8,18
.
We found increased CSF sPDGFRβ with more advanced CDR impairment (CDR 1 > 0.5 > 0)
(Figure 1a), suggesting progressive damage of pericytes
8,18
with cognitive dysfunction. There were no significant differences in CSF Aβ1–42 or
pTau levels between CDR 0.5 and CDR 0 individuals, although we saw reduced CSF Aβ1–42
in CDR 1 relative to CDR 0.5 participants (Figure 1b-c; for site-specific analysis
see Extended Data Figure 2a-b). sPDGFRβ was increased in participants with CDR 0.5
relative to CDR 0 regardless of CSF Aβ1–42 (Figure 1d) or pTau (Figure 1e) status,
i.e., irrespective of Aβ+ or Aβ-, or pTau+ or pTau-, as confirmed by site-specific
analyses (Extended Data Figure 2c-d). Higher CSF sPDGFRβ remained a significant predictor
of cognitive impairment after statistically controlling for CSF Aβ1–42 and pTau, as
shown by estimated marginal means from ANCOVA models (Figure 1f) indicating medium-to-large
incremental effect sizes with η2
partial range = .10–.12, which has been confirmed by logistic regression models (Supplementary
Table 3a-c). There was a significant positive correlation between CSF sPDGFRβ with
classical biomarkers of BBB breakdown including CSF/plasma albumin ratio and CSF fibrinogen
(Extended Data Fig. 2e-f). Among the subset of 35 participants who underwent Pittsburgh
compound B (PiB)-positron emission tomography (PET), those with CDR 0.5 exhibited
increased CSF sPDGFRβ relative to those with CDR 0, after statistically controlling
for amyloid levels (Extended Data Figure 2g), consistent with CSF Aβ findings (Figure
1d). Additionally, we found no differences in CSF Aβ and tau oligomers levels between
CDR 0 and CDR 0.5 groups (Extended Data Figure 2h-i). CSF sPDGFRβ remained significantly
elevated in CDR analysis after statistically controlling for CSF tau oligomers in
ANCOVA models (Extended Data Figure 2j), suggesting that sPDGFRβ increase is not dependent
on oligomer levels.
Increased CSF sPDGFRβ in impaired individuals was independent of vascular factors,
as indicated by VRF burden analysis for the entire sample and confirmed by site-specific
analysis (Extended Data Figure 3a-c). Of note, there were no differences in CSF biomarkers
of glial and inflammatory response, or neuronal degeneration
28,29
between impaired and unimpaired individuals on CDR exams, as illustrated with a few
representative biomarkers out of 20 studied (see online Methods) (Extended Data Figure
4a); also confirmed by site-specific analysis (Extended Data Figure 4b-c). Collectively,
our findings indicate that damage to brain capillary pericytes, which critically maintain
the BBB integrity
22,30,31
, develops early in older adults with cognitive dysfunction, which is independent
of Aβ and tau biomarker changes, is not influenced by VRFs, and is not associated
with glial and/or inflammatory response, or detectable neuronal degeneration.
The DCE-MRI analysis of regional BBB permeability in a subset of 73 participants with
CDR 0.5 compared to those with CDR 0, indicated increased BBB permeability to gadolinium-based
contrast agent in the hippocampus (HC) and its CA1, CA3 and dentate gyrus subfields,
and parahippocampal gyrus (PHC), but not in other studied brain regions including
frontal and temporal cortex, subcortical white matter, corpus callosum, and internal
capsule, and deep gray matter regions including thalamus, and striatum (Extended Data
Figure 5a-b). These findings are consistent with a recent report demonstrating that
BBB breakdown during normal aging and MCI starts in the HC
8
. Surprisingly, we also found that individuals with CDR 0.5 compared to those who
were cognitively normal (CDR 0) exhibited BBB breakdown in the HC, PHC and HC subfields
regardless of CSF Aβ1–42 (Figure 1g-h), and pTau (Figure 1i-j) status. Increased regional
BBB permeability in HC, PHC and HC subfields remained a significant predictor of cognitive
impairment after statistically controlling for CSF Aβ1–42 and pTau, as shown by estimated
marginal means from ANCOVA models (Figure 1k) indicating medium-to-large incremental
effect sizes (η2
partial range = .09–.28), also confirmed by logistic regression models (Supplementary
Table 3d-h).
The regional BBB analysis indicated that Aβ and tau status does not affect BBB integrity
in other studied brain regions (Extended Data Figure 5c-d). Similar to sPDGFRβ findings,
the VRF burden did not influence BBB permeability changes in the HC and PHC in individuals
with CDR 0.5 compared to CDR 0, and also had no effect on BBB integrity in other studied
brain regions (Extended Data Figure 5e-f). Consistent with previous findings
8
, in the present cohort we also observed a significant positive correlation between
increases in CSF sPDGFRβ and DCE-MRI measures of BBB permeability in the HC and PHC
in all studied participants (Extended Data Figure 5g-h), which was not the case for
other studied brain regions, as illustrated here for the white matter regions (Extended
Data Figure 5i-j).
As the present study sample excluded participants with vascular dementia and vascular
cognitive impairment and substantial cerebrovascular pathology, it is probably not
surprising that BBB dysfunction in the present analysis was independent of traditional
systemic VRFs. The possibility of interactive or synergistic effects of traditional
VRFs and BBB dysfunction in populations with more severe vascular lesions, vascular
dementia and vascular cognitive impairment is not ruled out, however, by the present
findings. Nevertheless, the fact that brain capillary mural cell damage and BBB breakdown
is independent of traditional VRFs, as we show, is critical information that underscores
the heterogeneity of vascular pathologies in the aging brain.
In order to address whether changes in CSF sPDGFRβ and DCE-MRI BBB permeability measures
depend on HC volume, we conducted ANCOVA analyses and hierarchical logistic regression
correcting for FreeSurfer-derived HC and/or PHC volumes (Figure 2a). In participants
with CDR 0.5 vs. CDR 0, we found no significant changes in HC volume, but a significant
decrease in PHC volume (Figure 2b). HC or PHC volumes did not statistically differ
between participants that were CSF Aβ+ vs. Aβ- (Figure 2c) or pTau+ vs. pTau- (Figure
2d) in either CDR 0 or CDR 0.5 groups. Importantly, CSF sPDGFRβ increases remained
significant after controlling for HC and PHC volumes (estimated as marginal means
from ANCOVA models) (Figure 2e), and remained increased when stratifying by CSF Aβ1–42
and pTau status (Figure 2f-g). Similarly, HC and PHC BBB permeability increases remained
significant after controlling for HC and PHC volumes, respectively (Figure 2h), and
when stratifying by Aβ1–42 and pTau status (Figure 2i-j). All findings exhibited medium-to-large
incremental effect sizes after controlling for HC and PHC volume (η2
partial range = .09–.31) and were corroborated by logistic regression models (Supplementary
Table 4a-c). Collectively, these data suggest that BBB-impairment that is represented
by CSF sPDGFRβ and DCE-MRI measures is not only independent of CSF AD biomarkers,
but is also not correlated to HC volume.
To determine whether our findings hold when cognitive dysfunction was evaluated by
neuropsychological performance, we analyzed CSF biomarkers and BBB integrity using
normalized scores from 10 neuropsychological tests used to evaluate impairment in
memory, attention/executive function and language, and global cognition, as described
in online Methods. This analysis indicated elevated CSF sPDGFRβ in participants with
one cognitive domain impaired relative to those with no domains impaired (Figure 3a;
see Extended Data Figure 6a-b for site-specific analyses). There was no difference,
however, in CSF Aβ1–42 between participants with one domain impaired and those with
no domains impaired (Figure 3b). Participants with one domain impaired showed, however,
increased CSF pTau relative to those with no domains impaired (Figure 3c).
Stratification of participants into those with and without classic AD biomarker abnormalities
revealed increased CSF sPDGFRβ in participants with one or more domain impaired regardless
of CSF Aβ1–42 (Figure 3d) or pTau (Figure 3e) status (see Extended Data Figure 6c-d
for site-specific analyses), or VRFs burden, as shown in the entire sample and confirmed
by site-specific analysis (Extended Data Figure 6e-g). Higher CSF sPDGFRβ levels remained
a significant predictor of cognitive impairment after statistically controlling for
CSF Aβ1–42 and pTau, as shown by estimated marginal means from ANCOVA models (Figure
3f) indicating medium-to-large incremental effect sizes (η2
partial range = .07–.14), which has been confirmed by logistic regression models at
both sites (Supplementary Table 5a-c).
Similar as for CDR analysis, in the subset of participants who underwent PiB-PET scans,
participants with domain impairment exhibited increased CSF sPDGFRβ relative to those
without impairment, after statistically controlling for amyloid levels (Extended Data
Figure 7a) corroborating CSF Aβ data (Figure 3d). There was no difference in CSF Aβ
and tau oligomers between participants with impairment in 1 or more cognitive domains
and those without cognitive impairment (Extended Data Figure 7b-c). CSF sPDGFRβ remained
significantly increased in domain analysis after statistically controlling for CSF
tau oligomers in ANCOVA models (Extended Data Figure 7d).
There were no differences in CSF markers of glial and/or inflammatory response, or
neuronal degeneration
28,29
between impaired and unimpaired participants on neuropsychological exams, as illustrated
with a few examples (Extended Data Figure 8a; also confirmed by site-specific analysis
in Extended Data Figure 8b-c).
Among participants undergoing DCE-MRI scans, those with domain impairment relative
to those without impairment exhibited BBB breakdown in the HC, PHC and HC subfields,
but not in other studied brain regions (Extended Data Figure 9a-b) regardless of CSF
Aβ1–42 (Figure 3g-h; Extended Data Figure 9c) or pTau (Figure 3i-j; Extended Data
Figure 9d) status, or VRF status (Extended Data Figure 9e-f). Increased regional BBB
permeability in HC, PHC and HC subfields remained a significant predictor of cognitive
impairment after statistically controlling for CSF Aβ1–42 and pTau, as shown by estimated
marginal means from ANCOVA models (Figure 1k) indicating medium-to-large incremental
effect sizes (η2
partial range = .07–.18), also confirmed by logistic regression analysis (Supplementary
Table 5d-h).
An increase in DCE-MRI BBB permeability in several medial temporal lobe structures
that sub serve episodic memory (e.g., HC, PHC, and CA1, CA3 and dentate gyrus HC subfields)
was associated with worse CDR scores (CDR 0 vs. 0.5) and with impairment in multiple
cognitive domains (impairment in 0 vs. one or more domains) (Figure 1g-k; Figure 3g-k).
Although this provides a perfect anatomical substrate for episodic memory impairment,
it is less clear whether BBB pathology in HC and medial temporal lobe can contribute
to changes seen in other domains in participants with CDR 0.5 or with impairment in
multiple domains, which involves areas of the brain outside the medial temporal lobe
that we found were not affected by BBB breakdown in the present cohort (Extended Data
Figure 5a-b and 9a-b). Numerous studies, however, have linked HC structure and function
to each of the cognitive domains and subdomains investigated in the present study.
For example, experimental studies in animals and observational human studies have
found that attention, working memory and executive function can become dysfunctional
as a result of HC-prefrontal pathway disruption
32–35
. HC functional activation has been found to underpin normal performance on semantic
fluency tasks
36
, and neuroimaging-based markers of HC structure and function correlate with performance
on semantic fluency and confrontation naming tasks in both normal and pathological
human aging
37
. Thus, BBB breakdown within the HC and medial temporal regions may disrupt the ability
of these structures and their connecting pathways to support an array of cognitive
functions. Additionally, we noted increased BBB permeability in the caudate nucleus
(Extended Data Figure 5a-b and 9a-b), a structure known to support frontal-subcortical
processes involved in attention/executive functions and verbal fluency
38,39
. Although less salient than the HC and PHC findings, it is possible that BBB breakdown
within the caudate may contribute to the observed deficits in domains beyond memory.
As with CDR analysis, there were no significant changes in HC volume, but a significant
decrease in PHC volume, in participants with 1+ cognitive domains impaired compared
to 0 domains impaired, which did not statistically differ between participants that
were CSF Aβ+ vs. Aβ- or pTau+ vs. pTau- (Figure 4a-c). CSF sPDGFRβ increases remained
significant after controlling for HC and PHC volumes (Figure 4d), and also remained
increased when stratifying by CSF Aβ1–42 and pTau status (Figure 4e-f). HC and PHC
BBB permeability increases remained significant after controlling for HC and PHC volumes
(Figure 4g), respectively, and when stratifying by Aβ1–42 and pTau status (Figure
4h-i). These findings exhibited medium-to-large incremental effect sizes after controlling
for HC and PHC volume (η2
partial range = .19–.25) and were corroborated by logistic regression models (Supplementary
Table 6a-c).
Finally, we asked did CSF sPDGFRβ and DCE-MRI BBB increases correlate with age? Neither
CSF sPDGFRβ (Extended Data Figure 10a-b) nor regional BBB permeability HC and PHC
values (Extended Data Figure 10c-f) were correlated with age in either the CDR 0 or
CDR 0.5 groups. Since all CDR and domain impairment group differences in CSF sPDGFRβ
and in HC and PHC BBB permeability values were significant after age-corrections (Figure
1; Figure 3), these data indicate that CSF sPDGFRβ and HC and PHC BBB measures reflect
cognitive impairment independent of normal aging, and therefore may be good biomarkers
of early cognitive dysfunction.
In summary, we show that older adults with early cognitive dysfunction develop brain
capillary damage associated with mural cell pericyte injury and BBB breakdown in the
HC irrespective of Aβ and/or tau changes, suggesting that BBB breakdown is an independent,
early biomarker of cognitive impairment unrelated to Aβ and tau. The independence
of the BBB breakdown pathway from Aβ/tau pathway in predicting cognitive impairment
is further supported by logistic regression models indicating that BBB breakdown is
not mediating the relationship between AD biomarkers and cognitive impairment (Supplementary
Tables 7–10). Biomarker-based diagnostic approaches, including the recent research
recommendations for AD
17
, mention vascular biomarkers, but suggest that CSF Aβ1–42 and pTau and amyloid PET
and tau PET are the key biomarkers defining AD pathology, although they may not be
causal to the disease process
5,17,40
. Our present findings support that neurovascular dysfunction may represent a previously
underappreciated factor contributing to cognitive and functional decline, independent
of the classic pathophysiological hallmarks of AD. Moreover, our findings point to
the brain vasculature as an important new biomarker of cognitive dysfunction in both
individuals without and with Aβ or pTau positivity, the latter indicating individuals
in the Alzheimer’s continuum
17
.
Online Methods
Study Participants
Participants were recruited from two sites, including the University of Southern California
(USC), Los Angeles, CA, and Washington University, St. Louis, MO. At the USC site,
participants were recruited through the USC Alzheimer’s Disease Research Center (ADRC):
combined USC and the Huntington Medical Research Institutes (HMRI), Pasadena, CA.
At the Washington University site, participants were recruited through the Washington
University Knight ADRC. The study and procedures were approved by the Institutional
Review Board of USC ADRC and Washington University Knight ADRC indicating compliance
with all ethical regulations, and informed consent was obtained from all participants
prior to study enrollment. Participants from both sites were included in cerebrospinal
fluid (CSF) biomarker studies. All participants underwent neurological and neuropsychological
evaluations performed using the Uniform Data Set (UDS), and additional neuropsychological
tests, as described below. Participants from the USC ADRC were included in dynamic
contrast-enhanced (DCE)-MRI studies for assessment of blood-brain barrier (BBB) permeability
if they had no contraindications for contrast injection or MRI.
We included 161 participants for CSF biomarker studies (74 from USC/HMRI and 87 from
Washington University). A group of 35 participants from the Washington University
Knight ADRC underwent Pittsburgh compound B (PiB)-positron emission tomography (PET)
imaging for amyloid. A group of 73 participants recruited from the USC ADRC underwent
DCE-MRI. All biomarker assays and quantitative MRI scans were conducted by investigators
blinded to the clinical status of the participant.
Inclusion/Exclusion Criteria
Included participants (≥45 years of age) with neuropsychologically-confirmed no cognitive
dysfunction and/or early cognitive dysfunction had no current or prior history of
any neurological or psychiatric conditions that might better account for any observed
cognitive impairment, including organ failure, brain tumors, epilepsy, hydrocephalus,
schizophrenia, major depression. Participants were stratified based on CSF analysis
as either Aβ1–42-positive (Aβ1–42+, <190 pg/mL) or Aβ1–42-negative (Aβ-, >190 pg/mL),
or pTau181-positive (pTau+, >78 pg/mL) or pTau181-negative (pTau-, <78 pg/mL), using
the accepted cutoff values
19–21
. Participants were excluded if they were diagnosed with vascular cognitive impairment
or vascular dementia. These clinical diagnoses were conducted by neurologists and
the criteria whether the patient 1) had a known vascular brain injury and 2) the clinician
judged that the vascular brain injury played a role in their cognitive impairment,
and/or pattern and course of symptoms. In addition to clinical diagnosis, presence
of vascular lesions was confirmed by moderate-to-severe white matter changes and lacunar
infarcts by fluid-attenuated inversion recovery (FLAIR) MRI and/or subcortical microbleeds
by T2*-weighted MRI
13
. Participants were also excluded if they were diagnosed with Parkinson’s disease,
Lewy body dementia or frontotemporal dementia. History of a single stroke or transient
ischemic attack was not an exclusion unless it was related to symptomatic onset of
cognitive impairment. Participants also did not have current contraindications to
MRI and were not currently using medications that might better account for any observed
cognitive impairment.
Clinical Dementia Rating (CDR)
Clinical Dementia Rating (CDR) assessments followed the standardized UDS procedures.
Participants underwent clinical interview, including health history, and a physical
exam. Knowledgeable informants were also interviewed. Given the lack of scientific
consensus regarding the categorization of older adults along the aging-to-MCI-to-AD
dementia spectrum and the time course and sequence of biomarker abnormalities, we
did not use clinical diagnosis in our biomarker comparisons but rather stratified
participants along objective neuropsychological metrics of cognitive impairment and
biological metrics of AD biomarker status using established cutoffs
19,20
. Participant CDR score was obtained through standardized interview and assessment
with the participant and a knowledgeable informant.
Neuropsychological Evaluation and Domains of Impairment
Neuropsychological performance was used to identify domain impairment. All participants
underwent neuropsychological testing using the UDS battery (v2.0 or 3.0) plus supplemental
neuropsychological tests at each site. Test impairment for UDS tests was determined
using age-, sex- and education-corrected scores from the National Alzheimer’s Coordinating
Center (NACC) (www.alz.washington.edu). Normalized scores from a total of 10 neuropsychological
tests were used in determining domain impairment, including three tests per cognitive
domain (memory, attention/executive function and language) and one test of global
cognition. Domain impairment was determined using previously described neuropsychological
criteria
21
, and was defined as a score >1 standard deviation (SD) below norm-referenced values
on two or more tests within a domain
41
. Multiple domain impairment (2+) was assigned when more than one domain fit the impairment
criteria, or three or more tests were impaired across domains
21,41
. Prior studies have established improved sensitivity and specificity of these criteria
relative to those employing a single test score, as well as adaptability of this diagnostic
approach to various neuropsychological batteries
21,41,42
. Cognition was presumed normal unless multiple impaired tests were identified as
specified by the criteria. Individuals with low Mini Mental State Exam (MMSE) or Montreal
Cognitive Assessment (MOCA) scores (<25) who had multiple missing neuropsychological
test scores due to difficulty completing testing were considered to have domain impairment.
Test battery specifics for each UDS version and recruitment site are listed below.
Global cognition
Mini Mental State Exam (MMSE) for UDS v2 and Montreal Cognitive Assessment (MOCA)
for UDS v3.
Memory
The Logical Memory Story A Immediate and Delayed free recall tests [modified from
the original Wechsler Memory Scales – Third Edition (WMS-III)] for UDS v2 and the
Craft Stories Immediate and Delayed free recall for UDS v3. For supplemental tests
the USC participants underwent the California Verbal Learning Test – Second Edition
(CVLT-II) and the Selective Reminding Test (SRT) sum of free recall trials. Norm-referenced
scores for these supplemental test scores were derived from a nationally representative
sample published with the test manual (CVLT-II)
43
and in studies of normally aging adults (SRT).
Attention / Executive Function
The Trails A, Trails B and Wechsler Adult Intelligence Scale - Revised (WAIS-R) Digit
Span Backwards tests for UDS v2 and the Trails A, Trails B and Number Span Backwards
for UDS v3.
Language
The Animal Fluency, Vegetable Fluency and Boston Naming Tests for UDS v2 and the Animal
Fluency, Vegetable Fluency and Multilingual Naming Test (MINT) for UDS v3.
Vascular Risk Factors
Participant vascular risk factor (VRF) burden was evaluated through physical exam,
clinical blood tests and interviews with the participant and informant, and included
history of cardiovascular disease (heart failure, angina, stent placement, coronary
artery bypass graft, intermittent claudication), hypertension, hyperlipidemia, type
2 diabetes, atrial fibrillation, and transient ischemic attack (TIA) or minor stroke,
and total VRF burden was defined by the sum of these risk factors. We have previously
shown that older adults with AD exhibiting two or more VRFs are more likely to exhibit
occult cerebrovascular disease at autopsy, whereas a single VRF is common and not
necessarily associated with increased cerebrovascular disease in this population
44,45
. Thus, elevated VRFs burden was defined as having two or more VRFs.
Lumbar Puncture and Venipuncture
Participants underwent lumbar puncture in the morning after an overnight fast. The
CSF was collected in polypropylene tubes, processed (centrifuged at 2000 rcf, 10 minutes,
4°C), aliquoted into polypropylene tubes and stored at −80°C until assay. Participants
underwent venipuncture in the morning after an overnight fast. Blood was collected
into EDTA tubes and processed (centrifuged at 2000 rcf, 10 minutes, 4°C). Plasma and
buffy coat were aliquoted in polypropylene tubes and stored at −80°C; buffy coat was
used for DNA extraction and APOE genotyping.
APOE Genotyping
DNA was extracted from buffy coat using the Quick-gDNA Blood MiniPrep (Cat. No. D3024,
Zymo Research, Irvine, CA). APOE genotyping was performed using polymerase chain reaction
restriction fragment length polymorphism approach (PCR-RFLP). The PCR was amplified
in a 50 μL reaction with Qiagen reagents (Qiagen Cat. #201203 and 201900). Two primers
were used to amplify a 318 base pair fragment: upstream sequence (5’ ACTGACCCCGGTGGCGGAGGAGACGCGTGC)
and downstream sequence (5’ TGTTCCACC AGGGGCCCCAGGCGCTCGCGG). The upstream primer
introduces an AflIII site in the amplified product, yielding a unique RFLP pattern
for each APOE allele following enzymatic digestion. The PCR reaction mixture was incubated
at 94°C for 3 min, then 40 cycles of amplification (94°C, 10 sec; 65°C, 30 sec; 72°C,
30 sec), and finally elongation at 72°C for 7 min. Restriction digests containing
10 μl amplicons and either 2.5 U AflIII or 1.5 U HaeII were incubated at 37°C overnight.
The digested products were analyzed on a 4% agarose gel. APOE genotype was determined
from the unique digestion pattern: APOE2/2 [A: 231; H: 267], APOE2/3 [A: 231; H: 231
and 267], APOE2/4 [A: 231 and 295; H: 231 and 267], APOE3/3 [A: 231; H: 231], APOE3/4
[A: 231 and 295; H: 231], and APOE4/4 [A: 295; H: 231]; the brackets denote base pairs
of amplicons following the AflIII (A) and HaeII (H) digestions.
Molecular Biomarkers in the Cerebrospinal Fluid (CSF) Assays
Quantitative Western Blotting of sPDGFRβ
The quantitative Western blot analysis was used to detect sPDGFRβ in human CSF (ng/mL),
as we previously reported
8
. Standard curves were generated using recombinant human PDGFRβ (Cat. No. 385-PR-100/CF,
R&D Systems, Minneapolis, MN).
Astrocyte marker
CSF levels of the astrocytic cytokine, S100B, were determined using ELISA (Cat. No.
EZHS100B-33K, EMD Millipore, Billerica, MA).
Inflammatory markers
Meso Scale Discovery (MSD) multiplex assay was used to determine CSF levels of interleukin-2
(IL-2), IL-4, IL-6, IL-8, IL-10, IL-12p70, IL-13, IL-1β, tumor necrosis factor α (TNF-α),
and interferon γ (IFN-γ) (Cat. No. K15049G, MSD, Rockville, MD).
Amyloid-β peptide
MSD multiplex assay (Cat. No. K15200E, MSD, Rockville, MD) was used to determine CSF
levels of Aβ38, Aβ40 and Aβ42. The CSF Aβ42 cutoff level of 190 pg/mL was applied
as previously reported for the MSD Aβ peptide assay
19
.
Amyloid-β oligomers
CSF Aβ oligomers were measured by ELISA (protocol modified from IBL Cat. No. 27725
and Holtta et al
46
). Aβ1–16 peptide dimer was used as the standard protein prepared at 0, 1, 2.5, 5,
7.5, 10, 15, 20 pM, and 100 μL of prepared standards and neat CSF were added to each
well on an uncoated 96-well plate along with 20 μL/well of HRP-conjugated anti-human
Aβ (N) (82E1) mouse IgG monoclonal antibody; the plates were incubated overnight at
4°C on an orbital plate shaker at 600 rpm. 100 μL/well was transferred to a 96-well
plate precoated with anti-human Aβ (N) (82E1) mouse IgG monoclonal antibody and incubated
for 1 hour at 4°C with shaking. Plates were washed (Tris buffered saline with 0.1%
Tween-20, TBST) and ELAST ELISA amplification was performed (Perkin Elmer). Briefly,
100 μL/well of biotinyl-tyramide (1:100 dilution) was incubated for 15 minutes at
room temperature with shaking. Plates were washed and 100 μL/well of streptavidin-HRP
(1:500 dilution) was incubated for 30 minutes at room temperature with shaking. Plates
were washed and 100 μL/well of tetramethylbenzidine (TMB) substrate (Kirkegaard &
Perry Laboratories Cat. No. 53–00-01) was incubated in the dark for 60 minutes, then
100 μL/well of 2N HCl was added, and the plates were read at 450 nm.
Tau
MSD assay was used to determine CSF levels of total tau (Cat. No. K15121G, MSD, Rockville,
MD). Phosphorylated tau (pT181) was determined by ELISA (Cat. No. 81581, Innotest,
Belgium). The CSF pTau181 cutoff level of 78 pg/mL was applied as previously reported
20
.
Tau oligomers
CSF tau oligomers were measured by direct ELISA using tau oligomer-specific antibody
(T22)
47
. Briefly, 12 μL CSF was diluted in a total volume of 50 μL 0.05 M carbonate-bicarbonate
buffer, added to a 96-well MaxiSorp plate (Nunc) and incubated overnight at 4°C on
an orbital plate shaker at 600 rpm. Plates were washed (TBST) and blocked with 300
μL of 10% nonfat dry milk (BioRad) for 2 hours room temperature with shaking. Plates
were washed and incubated with 100 μL/well of T22 antibody (1:250 diluted in 5% nonfat
milk) and incubated for 1 hour at room temperature with shaking. Plates were washed
and incubated with HRP-conjugated anti-rabbit IgG antibody (1:3000 diluted in 5% nonfat
dry milk) and incubated for 1 hour at room temperature with shaking. Plates were washed
and incubated in the dark with 100 μL/well TMB substrate for 14 minutes, then 100
μL/well 2N HCl was added, and the plates were read at 450 nm.
Neuronal marker
CSF levels of neuron specific enolase (NSE) were determined using ELISA (Cat. No.
E-80NEN, Immunology Consultant Laboratories, Portland, OR).
In vitro analysis of sPDGFRβ shedding
Primary human brain mural cell isolation and culture
Primary human brain vascular smooth muscle cells (SMCs) were isolated from leptomeningeal
arteries (>100 μm diameter) as described and characterized as reported
18
. SMCs were >98% positive for α-smooth muscle actin (SMA), myosin heavy chain, calponin
and SM22 and negative for von Willebrand factor (endothelial cells), GFAP (astrocytes)
and CD11b (microglia). Cells were cultured in smooth muscle cell medium (Cat. No.
1101, ScienCell) in 5% CO2 at 37°C. Early passage (P5-P6) cultures were used in the
present study.
Primary human brain microvascular pericytes were isolated from cortical brain tissue
after removal of leptomeninges as previously described
18,48
. Pericytes were derived from intraparenchymal microvessels that were completely free
from leptomeningeal vessel contamination. Purified microvessels were largely brain
capillaries (>97%) with diameter <6 μm. Cells were cultured in human pericyte medium
(Cat. No. 1201, ScienCell) in 5% CO2 at 37°C and were then characterized. Pericytes
were positive for the pericyte markers PDGFRβ, NG2 and CD13 and negative for von Willebrand
factor (endothelial cells), GFAP (astrocytes) and CD11b (microglia). Early passage
(P5-P6) cultures were used in the present study.
Treatment conditions
Primary human brain SMCs and pericytes were plated in equal cell number for all conditions.
For ADAM10 knockdown, accell ADAM10 siRNA (Cat. No. E-004503–00-0010, Dharmacon) at
a final concentration of 1 μM in Acell Delivery Media (Cat. No. B-005000–500, Dharmacon)
was added into 90% confluent cultured pericytes in twelve-well tissue culture plates
and after 96 hours as recommended by the manufacturer, cells underwent treatment conditions.
Specifically, cells were subjected to treatment with ionomycin (2.5 μM) and/or marimastat
(4 μM) prepared in reduced serum OptiMEM (Gibco) or media only (control condition)
for 40 minutes at 37°C, as previously described
27
. After the 40-minute treatment, the media and cell lysates were collected for additional
analysis described below.
Immunoprecipitation of sPDGFRβ
Immunoprecipitation was performed on the pericyte and SMCs media as described by the
manufacturer with optimizations (all wash steps performed as described). For antibody-bead
coupling, 50 μL protein G Dynabeads (Cat. No. 10004D, Invitrogen) and 2 μg of PDGFRβ
antibody (goat anti-human, Cat. No. AF385, R&D Systems) were incubated with rotating
for 10 minutes at room temperature. Conditioned media and equal volume lysis buffer
were added to the Dynabeads-coupled PDGFRβ antibody and incubated with rotating for
30 minutes at room temperature. Target antigen was eluted in denaturing conditions
and quantitative Western immunoblot was performed as described below.
Western immunoblot analysis
Quantitative Western immunoblot on immunoprecipitated media was performed using carrier-free
human recombinant PDGFRβ as a protein standard (Cat. No. 385-PR/CF, R&D Systems).
Gel transfer was performed using iBlot2 (R&D Systems) at 20 V for 9 minutes. The nitrocellulose
membrane was incubated with SuperBlock-TBST (Thermo Fisher Scientific) for 1 hour
at room temperature and primary antibody (Cat. No. AF385, R&D Systems, 1 μg/mL) prepared
in SuperBlock was incubated overnight at room temperature with shaking. Secondary
anti-goat antibody (1:5000) prepared in 5% nonfat dry milk was incubated for 1 hour
at room temperature with shaking. SuperSignal West Pico PLUS (Thermo Fisher Scientific)
and film was used to develop the membrane, and sample protein concentration (ng/ml)
was calculated.
Western immunoblot analysis of primary human brain pericyte cell lysates was performed
with primary antibodies ADAM10 (Cat. No. ab124695, Abcam) and GAPDH (Cat. No. 2118L,
Cell Signaling).
Magnetic Resonance Imaging
The MR data set was obtained at Keck Medical Center of USC. The study was approved
by the USC Institutional Review Board. All participants underwent a blood draw to
ensure appropriate kidney function for contrast agent (CA) administration prior to
imaging. The imaging protocol performed was developed to detect subtle BBB changes
in patients with cognitive impairment and is detailed in Montagne et al. 2015
8
. Briefly, all images were obtained on a GE 3 T HDXT MR scanner with a standard eight-channel
array head coil. Anatomical coronal spin echo T2-weighted scans were first obtained
through the hippocampi (TR/TE 1550/97.15 ms, NEX = 1, slice thickness 5 mm with no
gap, FOV = 188 × 180 mm, matrix size = 384 × 384). Baseline coronal T1-weighted maps
were then acquired using a T1-weighted 3D spoiled gradient echo (SPGR) pulse sequence
and variable flip angle method using flip angles of 2°, 5° and 10°. Coronal dynamic
contrast-enhanced (DCE)-MRI covering the hippocampi and temporal lobes were acquired
using a T1-weighted 3D SPGR pulse sequence (FA = 15°, TR/TE = 8.29/3.09 ms, NEX =
1, slice thickness 5 mm with no gap, FOV 188 × 180 mm, matrix size 160 × 160, voxel
size was 0.625 × 0.625 × 5 mm3). This sequence was repeated for a total of 16 min
with an approximate time resolution of 15.4 s. Gadolinium-based CA, Gadobenate dimeglumine
(MultiHance®, Bracco, Princeton, New Jersey) or Gadoterate meglumine (Dotarem®, Guerbet,
France) (0.05 mmol/kg) was administered intravenously into the antecubital vein using
a power injector, at a rate of 3 mL/s followed by a 25 mL saline flush, 30 s into
the DCE scan.
Quantification of the Subtle Blood-Brain Barrier Permeability
Post-processing analysis was performed using Rocketship
49
running with Matlab. The arterial input function (AIF), which was extracted from a
region-of-interest (ROI) positioned at the internal carotid artery, was fitted with
a bi-exponential function prior to fitting with Patlak model
50
. The Patlak linearized regression mathematical analysis was used to generate the
BBB permeability K
trans
maps
8,49,50
with high spatial and temporal resolutions allowing not only simultaneous measurements
of the regional BBB permeability in different white (WM) and gray matter (GM) regions,
but also accurate calculations of the K
trans
values in anatomical regions as small as the subdivisions of the hippocampus. We determined
in each individual AIF from the internal carotid artery. In a few cases when the common
carotid artery was not clearly visible a nearby large vessel was used. Individual
AIF measurements are important particularly if the studied population diverges by
age as changes in blood volume and flow may affect AIF and the K
trans
measurements.
The present analysis requires that the tracer’s diffusion across the BBB remains unidirectional
during the acquisition time. The total tracer concentration in the tissue, C
tissue
(t), can be described as a function of the blood concentration, C
AIF
(t), the intravascular blood volume, v
p
, and a blood-to-brain transfer constant, K
trans
, that represents the flow from the intravascular to the extravascular extracellular
space using equation below:
C
t
i
s
s
u
e
(
t
)
=
K
t
r
a
n
s
∫
0
t
C
A
I
F
(
u
)
d
u
+
v
p
A
I
F
(
t
)
A statistically significant intersubject variability in the measurement of v
p
was not observed.
ROI-averaged analysis of DCE-MRI output maps was performed by an experienced neuroradiologist
who manually drew ROIs for each participant based on their own anatomy since a substantial
variability between individuals is seen at a macroscopic level (e.g., enlarged ventricles,
cortical atrophy, hippocampal shrinkage, etc.). Thus, the regional BBB K
trans
permeability were measured in 13 different GM ROIs including the hippocampi [HC] and
their subfields (i.e., CA1, CA3, and dentate gyrus [DG]), parahippocampus [PHC], caudate
nucleus [Caud], superior frontal cortical gyri [SFG Cx], inferior temporal cortical
gyri [ITG Cx], thalamus [Thal], and striatum [Str] and WM ROIs including subcortical
white matter fibers [SubP WM fibers], corpus callosum (CC), and internal capsule (IC).
Quantification of Regional Brain Volumes
HC and PHC morphometry were performed using the FreeSurfer (v5.3.0) software package
51
, which is documented and freely available online (http://surfer.nmr.mgh.harvard.edu/).
In brief, HC and PHC gyri were segmented using the included FreeSurfer Desikan-Killiany
and subcortical atlases
52,53
. Then, regional volumes (mm3) were derived accordingly. The technical details of
this procedure are described in previous publications
54,55
. Data processing was performed using the Laboratory of Neuro Imaging (LONI) pipeline
system (http://pipeline.loni.usc.edu)
56,57
.
Positron Emission Tomography
Pittsburgh compound B (PiB)-positron emission tomography (PET) imaging was conducted
at Washington University Knight ADRC using procedures and analysis as previously described
58,59
.
Statistical Analyses
All continuous variables were screened for outliers (+/− 3 SDs from mean) and evaluated
for departures from normality through quantitative examination of skewness and kurtosis,
as well as visual inspection of frequency distributions. Where departures of normality
were identified, log10-transformations were applied, and distribution normalization
was confirmed prior to parametric analyses. Participant demographics and clinical
characteristics were initially compared across both CDR and domain impairment stratifications
using chi-square tests and one-way ANOVAs, with post-hoc Tukey tests.
All CSF biomarkers were compared in parallel analyses applied across the entire sample
stratified by the global CDR score and the number of impaired cognitive domains using
ANCOVA, with post-hoc Bonferroni corrected comparisons. For CDR analyses, model covariates
included age, sex, education and APOE-ε4 carrier status. For domain impairment analyses,
age, sex and education-corrected values were used to identify impairment groups and
APOE-ε4 carrier status was used as a covariate. Site-specific analyses and interaction
effect analyses did not include APOE-ε4 carrier status as a covariate to conserve
statistical power. For analysis of interactions by Aβ1–42, pTau and VRF burden, statistical
interactions and main effects were examined in similar ANCOVA models.
The same approach described above was used in all analyses of other CSF glial, inflammatory
and neuronal markers, and for DCE-MRI data. With regard to missing data, all participants
had complete data for primary outcomes (CSF sPDGFRβ and DCE-MRI), and the extent of
missing data was capped at < 10% for all other CSF biomarkers and clinical measures
(i.e., >90% of participants had complete data).
Given the large number of analyses, false discovery rate (FDR)-correction was applied
to all ANCOVA omnibus p-values using the Benjamini-Hochberg method
60
.
Where significant CSF sPDGFRβ and BBB Ktrans findings were identified (CDR 0.5 vs.
0 and domain impairment 1+ vs. 0), separate post-hoc analyses of CSF sPDGFRβ and BBB
Ktrans differences controlling for CSF Aβ1–42 and pTau, PiB-PET amyloid deposition,
pTau oligomers, and HC and PHC volumes also utilized ANCOVA models. In addition, separate
hierarchical logistic regression analyses evaluated whether CSF sPDGFRβ and BBB Ktrans
predicted cognitive impairment (CDR 0.5 vs. 0 and domain impairment 1+ vs. 0) after
controlling for CSF Aβ1–42 and pTau, PiB-PET amyloid deposition, pTau oligomers, and
HC and PHC volumes. For both ANCOVA and logistic regression analyses, covariates were
entered into the model in the first block and in the second block either CSF sPDGFRβ
or specific regional BBB Ktrans values were entered. Additional demographics and APOE4
carrier status were included in overall models correcting for CSF Aβ1–42 and pTau,
and models correcting for HC and PHC volumes.
Extended Data
Extended Data Figure 1.
ADAM10 mediates soluble PDGFRβ (sPDGFRβ) shedding in human brain pericytes in vitro.
(a) Primary human brain vascular smooth muscle cells (SMCs) and pericytes were subjected
to treatment with ionomycin (IM) (2.5 μM), a calcium ionophore that activates ADAM10,
or control treatment (media only), and media was immunoprecipitated (IP) to measure
sPDGFRβ by quantitative Western immunoblot. Compared to pericytes, SMCs shed extremely
low levels of sPDGFRβ, which was not significantly increased by IM. Pericytes shed
high basal levels of sPDGFRβ that was significantly increased by > 5-fold by treatment
with IM, which activated ADAM10. To further determine ADAM10’s involvement, IM treatment
was conducted in the presence of ADAM10 pharmacological inhibition with marimastat
(MM, 4 μM) that inhibits ADAM10 by binding to active site zinc, and genetic siRNA
knockdown of ADAM10. Both pharmacologic (MM) and genetic (siRNA) inhibition of ADAM10
significantly reduced sPDGFRβ shedding activated by IM by > 90% and 75%, respectively.
(b) The siRNA ADAM10 knockdown efficiency in this study was 85% as shown by Western
analysis. Data generated from n=3–6 independent culture experiments and plotted as
means ± SEM. Statistical analyses: Panel a: SMC data by two-tailed Student’s t-test;
pericyte data by ANOVA with Tukey post-hoc test. Panel b: Two-tailed Student’s t-test.
Significance at α=0.05 for all analyses.
Extended Data Figure 2.
CSF sPDGFRβ increases with CDR impairment, independent of Aβ and tau, and reflects
blood-brain barrier (BBB) breakdown.
(a-b) Site-specific analysis of CSF sPDGFRβ and standard AD biomarkers, Aβ42 and pTau,
indicates an early increase in sPDGFRβ with increasing CDR in both independent clinical
sites, USC (a) and Washington University (b). There were no changes in Aβ42 and pTau
at USC site (a), whereas Aβ42, but not pTau, was altered at Washington University
site; supports Figure 1 a-c. (c-d) Site-specific analysis of CSF sPDGFRβ increases
with CDR, independent of CSF Aβ42 and pTau status in two independent sites, USC (c)
and Washington University (d); supports Figure 1 d-f. (e-f) CSF sPDGFRβ is associated
with blood-brain barrier (BBB) breakdown. CSF sPDGFRβ positively correlates with conventional
biochemical biomarkers of BBB breakdown including CSF:plasma albumin ratio (Qalb)
(e) and CSF fibrinogen (f); supports Figures 1 and 3. (g) CSF sPDGFRβ is increased
with CDR, independent of amyloid positivity by (11)C-Pittsburgh compound B positron
emission tomography (PiB-PET); supports Figure 1 d and f. (h-i) No differences were
observed in CSF Aβ oligomer levels (h) and tau oligomer levels (i) in individuals
with CDR 0 vs. CDR 0.5; supports Figure 1 d-f. (j-k) Increases in CSF sPDGFRβ (j)
and regional BBB K
trans
in the hippocampus (HC) and parahippocampal gyrus (PHC) (k) of individuals with CDR
0.5 vs. CDR 0 remain significant after statistically controlling for the impact of
CSF tau oligomers; supports Figure 1 d-f. Panels a-d, g-i: Box-and-whisker plot lines
indicate median values, boxes indicate interquartile range and whiskers indicate minimum
and maximum values. Panels a-d, g: significance tests from ANCOVAs. Panels e-f: Statistical
significance determined by Pearson correlation; r = Pearson correlation coefficient.
Panels h-i: Significance by two-tailed Student’s t-test at α=0.05. Panels j-k: ANCOVA
models representing estimated marginal means ± SEM. Brackets denote sample size (n)
in each analysis.
Extended Data Figure 3.
sPDGFRβ increases with CDR independent of vascular risk factors (VRFs), and no change
in other neurovascular unit biomarkers.
(a-c) CSF sPDGFRβ is increased with CDR, independent of VRFs burden in the combined
site analysis (a) and in two independent clinical sites from USC (b) and Washington
University (c). VRFs 0–1: no or 1 vascular risk factor. VRFs 2+: 2 or more vascular
risk factors. See Supplementary Table 1 for the list of VRFs; supports Figure 1 a-f.
Box-and-whisker plot lines indicate median values, boxes indicate interquartile range
and whiskers indicate minimum and maximum values. Significance tests from ANCOVAs.
Brackets denote sample size (n) in each analysis.
Extended Data Figure 4.
Other CSF biomarkers of the neurovascular unit are not altered with CDR cognitive
impairment.
(a-c) CSF markers of glial, inflammatory, or neuronal injury exhibited no significant
differences between unimpaired and impaired individuals on CDR, including S100 calcium-binding
protein B (S100B), interleukin-6 (IL-6), tumor necrosis factor-α (TNFα), or neuron-specific
enolase (NSE) in the combined site analysis (a) and similarly in site-specific analysis
of individuals from USC (b) and from Washington University (c); supports Figure 1
a-c. Box-and-whisker plot lines indicate median values, boxes indicate interquartile
range and whiskers indicate minimum and maximum values. Significance tests from ANCOVAs.
Brackets denote sample size (n) in each analysis.
Extended Data Figure 5.
Regional blood-brain barrier (BBB) breakdown Ktrans increases with CDR independent
of CSF Aβ and tau and vascular risk factors (VRFs), and relates to sPDGFRβ only in
hippocampal gray matter regions.
(a-b) An increase in Ktrans values in the hippocampus (HC), parahippocampal gyrus
(PHC) and CA1, CA3 and dentate gyrus (DG) hippocampus subfields, with increasing CDR
(a), but not in other brain regions including superior frontal cortical gyrus (Sup
Front) and inferior temporal cortical gyrus (Inf Temp), white matter regions including
subcortical white matter fibers (white matter, WM), corpus callosum (CC), and internal
capsule (IC), and deep gray matter regions including thalamus (Thal), caudate nucleus
(Caud) and striatum (b). (c-d) Additional brain regions showed no significant differences
in Ktrans BBB permeability values in individuals with CDR 0 and CDR 0.5, regardless
of CSF Aβ42 (c) or pTau (d) status. (e-f) VRFs burden does not influence an increase
in the Ktrans BBB permeability values with increasing CDR in the HC, PHC, and hippocampus
subfields (i.e., CA1, CA3, DG) (e), and no change in the Ktrans BBB permeability values
in other brain regions (f). See Supplementary Table 1 for the list of VRFs. Panels
a-f support Figure 1 g-k. (g-j) CSF sPDGFRβ is associated with BBB breakdown measured
by neuroimaging in hippocampal gray matter regions (g-h), but not in WM regions (i-j);
supports Figures 1 and 3. Panels a-f: Box-and-whisker plot lines indicate median values,
boxes indicate interquartile range and whiskers indicate minimum and maximum values.
Significance tests after FDR correction from ANCOVAs. Panels g-j: Statistical significance
determined by Pearson correlation; r = Pearson correlation coefficient. Brackets denote
sample size (n) in each analysis; applies to all regions within each panel.
Extended Data Figure 6.
CSF sPDGFRβ increases with CDR impairment, independent of Aβ, tau, and vascular risk
factors (VRFs).
(a-b) Site-specific analysis of CSF sPDGFRβ and standard AD biomarkers, Aβ42 and pTau,
indicates an early increase in sPDGFRβ with increasing domains impaired in both independent
clinical sites, USC (a) and Washington University (b); supports Figure 3 a-c. (c-d)
Site-specific analysis of CSF sPDGFRβ indicates increases with the number of cognitive
domains impaired, independent of CSF Aβ42 and pTau status in two independent sites,
USC (c) and Washington University (d); supports Figure 3 d-f. (e-g) CSF sPDGFRβ is
increased with increasing number of cognitive domains impaired, independent of VRFs
burden in the combined site analysis (e) and in two independent clinical sites, USC
(f) and Washington University (g). VRFs 0–1: no or 1 vascular risk factor. VRFs 2+:
2 or more vascular risk factors. See Supplementary Table 2 for the list of VRFs. Supports
Figure 3 a-f. Panels a-g: Box-and-whisker plot lines indicate median values, boxes
indicate interquartile range and whiskers indicate minimum and maximum values. Significance
tests from ANCOVAs. Brackets denote sample size (n) in each analysis.
Extended Data Figure 7.
BBB breakdown is independent of amyloid and tau oligomers.
(a) CSF sPDGFRβ is increased with cognitive domains impaired, independent of amyloid
positivity by (11)C-Pittsburgh compound B positron emission tomography (PiB-PET);
supports Figure 3 d and f. (b-c) No differences were observed in CSF Aβ oligomer levels
(b) and tau oligomer levels (c) in individuals with 0 or 1+ cognitive domains impaired.
(d-e) Increases in CSF sPDGFRβ (d) and regional blood-brain barrier (BBB) K
trans
in the hippocampus (HC) and parahippocampal gyrus (PHC) (e) of individuals with 1+
versus 0 cognitive domain impairment remain significant after statistically controlling
for the impact of CSF tau oligomers; supports Figure 3 d-f. Panels a-c: Box-and-whisker
plot lines indicate median values, boxes indicate interquartile range and whiskers
indicate minimum and maximum values. Panel a: significance tests from ANCOVAs. Panels
b-c: Significance by two-tailed Student’s t-test at α=0.05. Panels d-e: ANCOVA models
representing estimated marginal means ± SEM. Brackets denote sample size (n) in each
analysis.
Extended Data Figure 8.
Other CSF biomarkers of the neurovascular unit are not altered with cognitive domain
impairment.
(a-c) CSF markers of glial, inflammatory, or neuronal injury exhibited no significant
differences between unimpaired and impaired individuals on neuropsychological exams,
including S100 calcium-binding protein B (S100B), interleukin-6* (IL-6), tumor necrosis
factor-α† (TNFα), or neuron-specific enolase† (NSE) in the combined site analysis
(a) or in the site-specific analysis of individuals from USC (b) or from Washington
University (c). Panels a-c: Box-and-whisker plot lines indicate median values, boxes
indicate interquartile range and whiskers indicate minimum and maximum values. Significance
tests after FDR correction from ANCOVAs with post-hoc Bonferroni comparisons. Brackets
denote sample size (n) in each analysis. *Analysis did not survive significance after
FDR correction. †Individual group comparison p values reported because omnibus test
was p < 0.05 but post-hoc group comparisons were null. Supports Figure 3 a-c.
Extended Data Figure 9.
Regional blood-brain barrier (BBB) breakdown Ktrans increases with cognitive domain
impairment, independent of CSF Aβ and tau and vascular risk factors (VRFs).
(a-b) An increase in K
trans
values in the hippocampus (HC), parahippocampal gyrus (PHC), and CA1, CA3 and dentate
gyrus (DG) hippocampal subfields with increasing cognitive impairment measured by
the number of cognitive domains impaired (a), but not in other brain regions including
superior frontal cortical gyrus (Sup Front) and inferior temporal cortical gyrus (Inf
Temp), white matter regions including subcortical white matter fibers (white matter),
corpus callosum (CC), and internal capsule (IC), and deep gray matter regions including
thalamus (Thal), caudate nucleus (Caud) and striatum (b). (c-d) Additional brain regions
showed no significance difference in K
trans
BBB permeability in individuals with 0 and 1+ cognitive domains impaired, regardless
of CSF Aβ42 (c) and pTau (d) status. (e-f) K
trans
BBB permeability is increased with increasing cognitive domain impairment in the HC,
PHC, and hippocampal subfields (i.e., CA1, CA3, DG), independent of VRFs burden (e),
but not in other brain regions (f). VRFs 0–1: no or 1 vascular risk factor; VRFs 2+:
2 or more vascular risk factors. See Supplementary Table 2 for the list of VRFs. Panels
a-f: Box-and-whisker plot lines indicate median values, boxes indicate interquartile
range and whiskers indicate minimum and maximum values. Significance tests after FDR
correction from ANCOVAs. Brackets denote sample size (n) in each analysis; applies
to all regions within each panel. Supports Figure 3 g-k.
Extended Data Figure 10.
CSF sPDGFRβ and medial temporal BBB permeability Ktrans values are not correlated
with age, indicating that changes in CSF sPDGFRβ and Ktrans capture processes relating
to cognitive impairment independent of normal aging. In CDR 0 individuals, age does
not correlate with CSF sPDGFRβ.
(a) or regional Ktrans in the hippocampus (HC) (c) and parahippocampal gyrus (PHC)
(e). Similarly, in CDR 0.5 individuals, age does not correlate with CSF sPDGFRβ (a)
or regional Ktrans in the hippocampus (HC) (c) and parahippocampal gyrus (PHC) (e).
Statistical significance determined by Pearson correlation; r = Pearson correlation
coefficient. Brackets denote sample size (n) in each analysis. Supports Figures 1
and 3.
Supplementary Material
1
Statistics Tables