Evidence of Pericyte Damage in a Cognitively Normal Cohort: Association With CSF and PET Biomarkers of Alzheimer Disease.

BACKGROUND: Blood-brain barrier (BBB) dysfunction is emerging as an important pathophysiologic factor in Alzheimer disease (AD). Cerebrospinal fluid (CSF) platelet-derived growth factor receptor-ß (PDGFRß) is a biomarker of BBB pericyte injury and has been implicated in cognitive impairment and AD. METHODS: We aimed to study CSF PDGFRß protein levels, along with CSF biomarkers of brain amyloidosis and tau pathology in a well-characterized population of cognitively unimpaired individuals and correlated CSF findings with amyloid-PET positivity. We performed an institutional review board (IRB)-approved cross-sectional analysis of a prospectively enrolled cohort of 36 cognitively normal volunteers with available CSF, Pittsburgh compound B PET/CT, Mini-Mental State Exam score, Global Deterioration Scale, and known apolipoprotein E ( APOE ) ε4 status. RESULTS: Thirty-six subjects were included. Mean age was 63.3 years; 31 of 36 were female, 6 of 36 were amyloid-PET-positive and 12 of 36 were APOE ε4 carriers. We found a moderate positive correlation between CSF PDGFRß and both total Tau (r=0.45, P =0.006) and phosphorylated Tau 181 (r=0.51, P =0.002). CSF PDGFRß levels were not associated with either the CSF Aß42 or the amyloid-PET. CONCLUSIONS: We demonstrated a moderate positive correlation between PDGFRß and both total Tau and phosphorylated Tau 181 in cognitively normal individuals. Our data support the hypothesis that BBB dysfunction represents an important early pathophysiologic step in AD, warranting larger prospective studies. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT00094939.

Effects of repeated sleep deprivation on brain pericytes in mice.

The damaging effects of sleep deprivation (SD) on brain parenchyma have been extensively studied. However, the specific influence of SD on brain pericytes, a primary component of the blood-brain barrier (BBB) and the neurovascular unit (NVU), is still unclear. The present study examined how acute or repeated SD impairs brain pericytes by measuring the cerebrospinal fluid (CSF) levels of soluble platelet-derived growth factor receptor beta (sPDGFRß) and quantifying pericyte density in the cortex, hippocampus, and subcortical area of the PDGFRß-P2A-CreERT2/tdTomato mice, which predominantly express the reporter tdTomato in vascular pericytes. Our results showed that a one-time 4 h SD did not significantly change the CSF sPDGFRß level. In contrast, repeated SD (4 h/day for 10 consecutive days) significantly elevated the CSF sPDGFRß level, implying explicit pericyte damages due to repeated SD. Furthermore, repeated SD significantly decreased the pericyte densities in the cortex and hippocampus, though the pericyte apoptosis status remained unchanged as measured with Annexin V-affinity assay and active Caspase-3 staining. These results suggest that repeated SD causes brain pericyte damage and loss via non-apoptosis pathways. These changes to pericytes may contribute to SD-induced BBB and NVU dysfunctions. The reversibility of this process implies that sleep improvement may have a protective effect on brain pericytes.

Infection of Brain Pericytes Underlying Neuropathology of COVID-19 Patients.

A wide range of neurological manifestations have been associated with the development of COVID-19 following SARS-CoV-2 infection. However, the etiology of the neurological symptomatology is still largely unexplored. Here, we used state-of-the-art multiplexed immunostaining of human brains (n = 6 COVID-19, median age = 69.5 years; n = 7 control, median age = 68 years) and demonstrated that expression of the SARS-CoV-2 receptor ACE2 is restricted to a subset of neurovascular pericytes. Strikingly, neurological symptoms were exclusive to, and ubiquitous in, patients that exhibited moderate to high ACE2 expression in perivascular cells. Viral dsRNA was identified in the vascular wall and paralleled by perivascular inflammation, as signified by T cell and macrophage infiltration. Furthermore, fibrinogen leakage indicated compromised integrity of the blood-brain barrier. Notably, cerebrospinal fluid from additional 16 individuals (n = 8 COVID-19, median age = 67 years; n = 8 control, median age = 69.5 years) exhibited significantly lower levels of the pericyte marker PDGFRß in SARS-CoV-2-infected cases, indicative of disrupted pericyte homeostasis. We conclude that pericyte infection by SARS-CoV-2 underlies virus entry into the privileged central nervous system space, as well as neurological symptomatology due to perivascular inflammation and a locally compromised blood-brain barrier.

Associations between Vascular Function and Tau PET Are Associated with Global Cognition and Amyloid.

Tau pathology and vascular dysfunction are important contributors to Alzheimer's disease (AD), but vascular-tau associations and their effects on cognition are poorly understood. We investigated these associations in male and female humans by conducting voxelwise comparisons between cerebral blood flow (CBF) and tau positron emission tomography (PET) images in independent discovery [cognitively normal (CN), 19; mild cognitive impairment (MCI) risk, 43; MCI, 6] and replication (CN,73; MCI, 45; AD, 20) cohorts. In a subgroup, we assessed relationships between tau and soluble platelet-derived growth factor ß (sPDGFRß), a CSF marker of pericyte injury. We tested whether CBF/sPDGFRß-tau relationships differed based on Montreal Cognitive Assessment (MoCA) global cognition performance, or based on amyloid burden. Mediation analyses assessed relationships among CBF/sPDGFRß, tau, and cognition. Negative CBF-tau correlations were observed predominantly in temporal-parietal regions. In the replication cohort, early negative CBF-tau correlations increased in spatial extent and in strength of correlation with increased disease severity. Stronger CBF-tau and sPDGFRß-tau correlations were observed in participants with greater amyloid burden and lower MoCA scores. Importantly, when stratifying by amyloid status, stronger CBF-tau relationships in individuals with lower MoCA scores were driven by amyloid+ participants. Tau PET was a significant mediator CBF/sPDGFRß-MoCA relationships in numerous regions. Our results demonstrate vascular-tau associations across the AD spectrum and suggest that early vascular-tau associations are exacerbated in the presence of amyloid, consistent with a two-hit model of AD on cognition. Combination treatments targeting vascular health, as well as amyloid-ß and tau levels, may preserve cognitive function more effectively than single-target therapies.SIGNIFICANCE STATEMENT Emerging evidence demonstrates a role for vascular dysfunction as a significant contributor to Alzheimer's pathophysiology. However, associations between vascular dysfunction and tau pathology, and their effects on cognition remain poorly understood. Multimodal neuroimaging data from two independent cohorts were analyzed to provide novel in vivo evidence of associations between cerebral blood flow (CBF), an MRI measure of vascular health, and tau pathology using PET. CBF-tau associations were related to cognition and driven in part by amyloid burden. Soluble platelet-derived growth factor ß, an independent CSF vascular biomarker, confirmed vascular-tau associations in a subgroup analysis. These results suggest that combination treatments targeting vascular health, amyloid-ß, and tau levels may more effectively preserve cognitive function than single-target therapies.

APOE4 leads to blood-brain barrier dysfunction predicting cognitive decline.

Vascular contributions to dementia and Alzheimer's disease are increasingly recognized1-6. Recent studies have suggested that breakdown of the blood-brain barrier (BBB) is an early biomarker of human cognitive dysfunction7, including the early clinical stages of Alzheimer's disease5,8-10. The E4 variant of apolipoprotein E (APOE4), the main susceptibility gene for Alzheimer's disease11-14, leads to accelerated breakdown of the BBB and degeneration of brain capillary pericytes15-19, which maintain BBB integrity20-22. It is unclear, however, whether the cerebrovascular effects of APOE4 contribute to cognitive impairment. Here we show that individuals bearing APOE4 (with the ε3/ε4 or ε4/ε4 alleles) are distinguished from those without APOE4 (ε3/ε3) by breakdown of the BBB in the hippocampus and medial temporal lobe. This finding is apparent in cognitively unimpaired APOE4 carriers and more severe in those with cognitive impairment, but is not related to amyloid-ß or tau pathology measured in cerebrospinal fluid or by positron emission tomography23. High baseline levels of the BBB pericyte injury biomarker soluble PDGFRß7,8 in the cerebrospinal fluid predicted future cognitive decline in APOE4 carriers but not in non-carriers, even after controlling for amyloid-ß and tau status, and were correlated with increased activity of the BBB-degrading cyclophilin A-matrix metalloproteinase-9 pathway19 in cerebrospinal fluid. Our findings suggest that breakdown of the BBB contributes to APOE4-associated cognitive decline independently of Alzheimer's disease pathology, and might be a therapeutic target in APOE4 carriers.

A novel sensitive assay for detection of a biomarker of pericyte injury in cerebrospinal fluid.

INTRODUCTION: Blood-brain barrier (BBB) breakdown and loss of brain capillary pericytes contributes to cognitive impairment. Pericytes express platelet-derived growth factor receptor-ß (PDGFRß) that regulates brain angiogenesis and blood vessel stability. Elevated soluble PDGFRß (sPDGFRß) levels in cerebrospinal fluid (CSF) indicate pericyte injury and BBB breakdown, which is an early biomarker of human cognitive dysfunction. METHODS: A combination of reagents and conditions were tested, optimized, and validated on the Meso Scale Discovery electrochemiluminescence platform to develop a new sPDGFRß immunoassay that was used to measure sPDGFRß in human CSF from 147 individuals. RESULTS: We developed standard operating procedures for a highly sensitive and reproducible sPDGFRß immunoassay with a dynamic range from 100 to 26,000 pg/mL, and confirmed elevated CSF sPDGFRß levels in individuals with cognitive dysfunction. DISCUSSION: This assay could be applied at different laboratories to study brain pericytes and microvascular damage in relation to cognition in disorders associated with neurovascular and cognitive dysfunction.

Cerebrospinal Fluid Changes in the Renin-Angiotensin System in Alzheimer's Disease.

Observations in autopsied brain tissue indicate that overactivation of the classical renin-angiotensin system (cRAS) and underactivity within regulatory RAS pathways (rRAS) are associated with pathology in Alzheimer's disease (AD). The primary aim of this study was to investigate whether cerebrospinal fluid (CSF) markers of RAS are altered in AD in relation to established CSF markers of disease pathology (lower Aß42 and elevated tau) and CSF markers of capillary dysfunction. We studied 40 controls and 40 AD cases grouped according to a biomarker profile (i.e., AD cases t-tau>400 pg/mL, pTau >60 pg/mL, and Aß42 <550 pg/mL). Angiotensin-II converting enyme-1 (ACE1) and ACE2 enzyme activity was measured using fluorogenic peptide substrates; sPDGFRß and albumin level by sandwich ELISA; and angiotensin-I (Ang-I), Ang-II, and Ang-(1-7) by direct ELISA. CSF Aß42, total, and phosphorylated tau levels were previously measured by INNOTEST sandwich ELISA. CSF ACE1 activity was significantly elevated in AD (p = 0.008) and positively correlated with ACE2 in AD (r = 0.420, p = 0.007). CSF ACE1 weakly correlated with t-tau (r = 0.294, p = 0.066) and p-tau (r = 0.329, p = 0.038) but not with Aß42 in the controls but not in AD. ACE1 correlated positively with sPDGFRß (r = 0.426, p = 0.007), a marker of pericyte injury, and ACE2 correlated positively with albumin (r = 0.422, p = 0.008), a marker of blood-brain barrier integrity. CSF Ang-I, Ang-II, and Ang-(1-7) levels were unchanged in AD. This cross-sectional CSF study indicates RAS dysfunction in relation to capillary damage in AD.

CSF evidence of pericyte damage in Alzheimer's disease is associated with markers of blood-brain barrier dysfunction and disease pathology.

BACKGROUND: We aimed to assess the relationship between levels of a cerebrospinal fluid (CSF) marker of pericyte damage, soluble platelet-derived growth factor receptor ß (sPDGFRß) and CSF markers of blood-brain barrier (BBB) integrity (CSF albumin and CSF/serum albumin ratio) and disease pathology (reduced CSF Aß42 and elevated CSF total and phosphorylated tau) in Alzheimer's disease (AD). METHODS: sPDGFRß and albumin were measured by sandwich ELISA in ante-mortem CSF from 39 AD and 39 age-matched controls that were grouped according to their biomarker profile (i.e. AD cases t-tau > 400 pg/mL, p-tau > 60 pg/mL and Aß42 < 550 pg/mL). sPDGFRß was also measured in matched serum and CSF samples (n = 23) in a separate neurologically normal group for which the CSF/serum albumin ratio had been determined. RESULTS: CSF sPDGFRß level was significantly increased in AD (p = 0.0038) and correlated positively with albumin (r = 0.45, p = 0.007), total tau (r = 0.50, p = 0.0017) and phosphorylated tau (r = 0.41, p = 0.013) in AD but not in controls. CSF sPDGFRß did not correlate with Aß42. Serum and CSF sPDGFRß were positively correlated (r = 0.547, p = 0.0085) in the independent neurologically normal CSF/serum matched samples. CONCLUSIONS: We provide further evidence of an association between pericyte injury and BBB breakdown in AD and novel evidence that a CSF marker of pericyte injury is related to the severity of AD pathology.

Crosstalk between soluble PDGF-BB and PDGFRß promotes astrocytic activation and synaptic recovery in the hippocampus after subarachnoid hemorrhage.

Platelet-derived growth factor receptor ß (PDGFRß) dynamically changes after brain injury, possibly mediating the neuroprotective role of soluble homodimers of the platelet-derived growth factor ß subunit (PDGF-BB) that is secreted by microcirculation cells. The aim of this study was to determine whether binding of PDGF-BB to astrocytic PDGFRß enhanced crosstalk among the various components of the neurovascular unit, leading to synaptic recovery after subarachnoid hemorrhage (SAH). The soluble PDGF-BB from the cerebrospinal fluid (CSF) of patients with SAH was measured. The relationship between PDGF-BB treatment and astrocytic PDGFRß signaling was further explored in vivo and in vitro in experimental SAH models. Compared with the levels in the control samples, the PDGF-BB protein levels in the CSF of patients with SAH were significantly increased. After the generation of experimental SAH, astrocyte activation markers were markedly induced by the binding of PDGF-BB to astrocytic PDGFRß, accompanied by improved levels of synaptic recovery and cognitive function. Soluble PDGF-BB and astrocytic PDGFRß signaling are essential for the neuroprotective effect in the hippocampus and the coculture system in vitro after SAH that otherwise leads to cognitive dysfunction and neuronal damage.-Zhou, X., Wu, Q., Lu, Y., Zhang, X., Lv, S., Shao, J., Zhou, Y., Chen, J., Hou, L., Huang, C., Zhang, X. Crosstalk between soluble PDGF-BB and PDGFRß promotes astrocytic activation and synaptic recovery in the hippocampus after subarachnoid hemorrhage.

Blood-brain barrier breakdown is an early biomarker of human cognitive dysfunction.

Vascular contributions to cognitive impairment are increasingly recognized1-5 as shown by neuropathological6,7, neuroimaging4,8-11, and cerebrospinal fluid biomarker4,12 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 the vasoactive and/or vasculotoxic effects of amyloid-ß (Aß)3,11,14, and more recently tau15. Animal studies suggest that Aß and tau lead to blood vessel abnormalities and blood-brain barrier (BBB) breakdown14-16. Although neurovascular dysfunction3,11 and BBB breakdown develop early in AD1,4,5,8-10,12,13, how they relate to changes in the AD classical biomarkers Aß and tau, which also develop before dementia17, remains unknown. To address this question, we studied brain capillary damage using a novel cerebrospinal fluid biomarker of BBB-associated capillary mural cell pericyte, soluble platelet-derived growth factor receptor-ß8,18, and regional BBB permeability using dynamic contrast-enhanced magnetic resonance imaging8-10. Our data show that individuals with early cognitive dysfunction develop brain capillary damage and BBB breakdown in the hippocampus irrespective of Alzheimer's Aß and/or tau biomarker changes, suggesting that BBB breakdown is an early biomarker of human cognitive dysfunction independent of Aß and tau.

The rise of soluble platelet-derived growth factor receptor ß in CSF early after subarachnoid hemorrhage correlates with cerebral vasospasm.

Platelet-derived growth factor ß (PDGFß) has been proposed to contribute to the development of cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH), and soluble PDGFRß (sPDGFRß) is considered to be an inhibitor of PDGF signaling. We aimed at determining the sPDGFRß concentrations in the cerebrospinal fluid (CSF) of patients with aneurysmal SAH (aSAH) and analyzing the relationship between sPDGFRß level and CVS. CSF was sampled from 32 patients who suffered aSAH and five normal controls. Enzyme-linked immunosorbent assay was performed to determine the sPDGFRß concentrations in the CSF. Functional outcome was assessed using modified Rankin scale (mRS) at 6 months after aSAH. CVS was identified using transcranial Doppler or angio-CT or DSA. The cutoff of sPDGFRß for CVS was defined on the ROC curve. The concentrations of sPDGFRß following aSAH were both higher than those of normal controls on days 1-3 and 4-6, and peaked on days 7-9 post-SAH. The cutoff value of sPDGFRß level on days 1-3 for CVS was defined as 975.38 pg/ml according to the ROC curve (AUC = 0.680, p = 0.082). In addition, CSF sPDGFRß concentrations correlated with CVS (r = 0.416, p = 0.018), and multivariate analysis indicated that sPDGFRß level higher than 975.38 pg/ml on days 1-3 was an independent predictor of CVS (p = 0.001, OR = 19.22, 95% CI: 3.27-113.03), but not for unfavorable outcome after aSAH in the current study. CSF sPDGFRß level increases after aSAH and is higher in patients who developed CVS, and sPDGFRß level higher than 975.38 pg/ml on days 1-3 is a potential predictor for CVS after SAH.