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Prevalence of dementia continues to increase because of the aging population and limited treatment options. Cerebral small vessel disease and Alzheimer disease are the two most common causes of dementia with vascular dysfunction being a large component of both their pathophysiologies. The neurogliovascular unit, in particular the blood-brain barrier (BBB), is required for maintaining brain homeostasis. A complex interaction exists among the endothelial cells, which line the blood vessels and pericytes, which surround them in the neurogliovascular unit. Disruption of the BBB in dementia precipitates cognitive decline. This review highlights how dysfunction of the endothelial-pericyte crosstalk contributes to dementia, and focuses on cerebral small vessel disease and Alzheimer disease. It also examines loss of pericyte coverage and subsequent downstream changes. Furthermore, it examines how disruption of the intimate crosstalk between endothelial cells and pericytes leads to alterations in cerebral blood flow, transcription, neuroinflammation, and transcytosis, contributing to breakdown of the BBB. Finally, this review illustrates how cumulation of loss of endothelial-pericyte crosstalk is a major driving force in dementia pathology.

Apolipoprotein E4 (APOE4), the main susceptibility gene for Alzheimer’s disease (AD), leads to vascular dysfunction, amyloid-β pathology, neurodegeneration and dementia. How these different pathologies contribute to advanced-stage AD remains unclear. Using aged APOE knock-in mice crossed with 5xFAD mice, we show that, compared to APOE3, APOE4 accelerates blood–brain barrier (BBB) breakdown, loss of cerebral blood flow, neuronal loss and behavioral deficits independently of amyloid-β. BBB breakdown was associated with activation of the cyclophilin A-matrix metalloproteinase-9 BBB-degrading pathway in pericytes. Suppression of this pathway improved BBB integrity and prevented further neuronal loss and behavioral deficits in APOE4;5FAD mice while having no effect on amyloid-β pathology. Thus, APOE4 accelerates advanced-stage BBB breakdown and neurodegeneration in Alzheimer’s mice via the cyclophilin A pathway in pericytes independently of amyloid-β, which has implication for the pathogenesis and treatment of vascular and neurodegenerative disorder in AD. This study shows that APOE4, one of the largest genetic risk factors for Alzheimer’s disease, promotes advanced-stage vascular dysfunction and neurodegeneration in old mice via activation of the cyclophilin A pathway in pericytes and independently of the presence of amyloid-β.

Gestational maternal immune activation (MIA) in mice induces persistent brain microglial activation and a range of neuropathologies in the adult offspring. Although long-term phenotypes are well documented, how MIA in utero leads to persistent brain inflammation is not well understood. Here, we found that offspring of mothers treated with polyriboinosinic–polyribocytidylic acid [poly(I:C)] to induce MIA at gestational day 13 exhibit blood–brain barrier (BBB) dysfunction throughout life. Live MRI in utero revealed fetal BBB hyperpermeability 2 d after MIA. Decreased pericyte–endothelium coupling in cerebral blood vessels and increased microglial activation were found in fetal and 1- and 6-mo-old offspring brains. The long-lasting disruptions result from abnormal prenatal BBB formation, driven by increased proliferation of cyclooxygenase-2 (COX2; Ptgs2)-expressing microglia in fetal brain parenchyma and perivascular spaces. Targeted deletion of the Ptgs2 gene in fetal myeloid cells or treatment with the inhibitor celecoxib 24 h after immune activation prevented microglial proliferation and disruption of BBB formation and function, showing that prenatal COX2 activation is a causal pathway of MIA effects. Thus, gestational MIA disrupts fetal BBB formation, inducing persistent BBB dysfunction, which promotes microglial overactivation and behavioral alterations across the offspring life span. Taken together, the data suggest that gestational MIA disruption of BBB formation could be an etiological contributor to neuropsychiatric disorders.

Introduction Blood-brain barrier (BBB) breakdown and loss of brain capillary pericytes contributes to cognitive impairment. Pericytes express platelet-derived growth factor receptor-β (PDGFRβ) that regulates brain angiogenesis and blood vessel stability. Elevated soluble PDGFRβ (sPDGFRβ) 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 sPDGFRβ immunoassay that was used to measure sPDGFRβ in human CSF from 147 individuals. Results We developed standard operating procedures for a highly sensitive and reproducible sPDGFRβ immunoassay with a dynamic range from 100 to 26,000 pg/mL, and confirmed elevated CSF sPDGFRβ 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.

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-β or tau pathology measured in cerebrospinal fluid or by positron emission tomography23. High baseline levels of the BBB pericyte injury biomarker soluble PDGFRβ7,8 in the cerebrospinal fluid predicted future cognitive decline in APOE4 carriers but not in non-carriers, even after controlling for amyloid-β 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.

Alzheimer's disease (AD) and cerebral small vessel disease (cSVD) are the two main causes of dementia with blood-brain barrier (BBB) breakdown being a common contributor. Recent advances in neuroimaging techniques offer new possibilities to understand how the brain functions in health and disease. This includes methods such as dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) which allows the detection of subtle regional changes in the BBB integrity. The purpose of this work is to provide a review on the recent DCE-MRI findings of subtle BBB leakage focusing on cSVD and AD, including both clinical and pre-clinical studies. Despite being widely used and well-established, we also highlight some of the DCE-MRI challenges and pitfalls faced in the context of dementia inherent to the subtle nature of BBB impairment.

Exposure to ambient air pollution particulate matter (PM) is associated with increased risk of dementia and accelerated cognitive loss. Vascular contributions to cognitive impairment are well recognized. Chronic cerebral hypoperfusion (CCH) promotes neuroinflammation and blood-brain barrier weakening, which may augment neurotoxic effects of PM.This study examined interactions of nanoscale particulate matter (nPM; fine particulate matter with aerodynamic diameternPM was collected using a particle sampler near a Los Angeles, California, freeway. Mice were exposed to 10 wk of reaerosolized nPM or filtered air (FA) for 150 h. CCH was induced by BCAS surgery. Mice (C57BL/6J males) were randomized to four exposure paradigms:The jointOur data suggest that nPM and CCH contribute to white matter injury in a synergistic manner in a mouse model. Adverse neurological effects may be aggravated in a susceptible population exposed to air pollution. https://doi.org/10.1289/EHP8792.

Pericytes are positioned between brain capillary endothelial cells, astrocytes and neurons. They degenerate in multiple neurological disorders. However, their role in the pathogenesis of these disorders remains debatable. Here we generate an inducible pericyte-specific Cre line and cross pericyte-specific Cre mice with iDTR mice carrying Cre-dependent human diphtheria toxin receptor. After pericyte ablation with diphtheria toxin, mice showed acute blood-brain barrier breakdown, severe loss of blood flow, and a rapid neuron loss that was associated with loss of pericyte-derived pleiotrophin (PTN), a neurotrophic growth factor. Intracerebroventricular PTN infusions prevented neuron loss in pericyte-ablated mice despite persistent circulatory changes. Silencing of pericyte-derived Ptn rendered neurons vulnerable to ischemic and excitotoxic injury. Our data demonstrate a rapid neurodegeneration cascade that links pericyte loss to acute circulatory collapse and loss of PTN neurotrophic support. These findings may have implications for the pathogenesis and treatment of neurological disorders that are associated with pericyte loss and/or neurovascular dysfunction.

Subcortical white matter (WM) stroke accounts for 25% of all strokes and is the second leading cause of dementia. Despite such clinical importance, we still do not have an effective treatment for ischemic WM stroke, and the mechanisms of WM postischemic neuroprotection remain elusive. 3K3A-activated protein C (APC) is a signaling-selective analogue of endogenous blood protease APC that is currently in development as a neuroprotectant for ischemic stroke patients. Here, we show that 3K3A-APC protects WM tracts and oligodendrocytes from ischemic injury in the corpus callosum in middle-aged mice by activating protease-activated receptor 1 (PAR1) and PAR3. We show that PAR1 and PAR3 were also required for 3K3A-APC’s suppression of post–WM stroke microglia and astrocyte responses and overall improvement in neuropathologic and functional outcomes. Our data provide new insights into the neuroprotective APC pathway in the WM and illustrate 3K3A-APC’s potential for treating WM stroke in humans, possibly including multiple WM strokes that result in vascular dementia.

Both men and women can have Alzheimer’s disease (AD), and there might be sex differences. AD is a neurodegenerative disease, and its frequency is often reported to be higher for women than men: almost two-thirds of patients with AD are women. One prevailing view is that women live longer than men on average of 4.5 years, plus there are more women aged 85 years or older than men in most global subpopulations; and older age is the greatest risk factor for AD. However, the differences in the actual risk of developing AD for men and women of the same age is difficult to assess, and the findings have been mixed. An increasing body of evidence from preclinical and clinical studies as well as the complications in estimating incidence support the sex-specific biological mechanisms in diverging AD risk as an important adjunct explanation to the epidemiologic perspective. While some of the sex differences in AD prevalence are due to differences in longevity, other distinct biological mechanisms increase the risk and progression of AD in women. These risk factors include 1) deviations in brain structure and biomarkers, 2) psychosocial stress responses, 3) pregnancy, menopause, and sex hormones, 4) genetic background (i.e., APOE), 5) inflammation, gliosis, and immune module (i.e., TREM2), and 6) vascular disorders. More studies focusing on the underlying biological mechanisms for this phenomenon are needed to better understand AD. This review presents the most recent data in sex differences in AD – the gateway to precision medicine, therefore, shaping expert perspectives, inspiring researchers to go in new directions, and driving development of future diagnostic tools and treatments for AD in a more customized way.

A recombinant variant of activated protein C, 3K3A-APC, was recently tested in a successful phase II clinical trial for ischemic stroke (RHAPSODY), which demonstrated that the treatment may reduce hemorrhages and is safe in patients that were treated with tPA and/or thrombectomy. Animal models of large ischemic stroke (middle cerebral artery occlusion) and neurodegeneration have shown that the effects of 3K3A-APC are mediated by preserved APC cell signaling activities (anti-apoptotic neuronal protection, protection of blood-brain barrier (BBB) integrity and anti-inflammatory activities). Because recent studies have suggested a role of protease activated receptor 1 (PAR1) in oligodendrocyte recovery after white matter damage, we wanted to test whether biased PAR1 signaling mediated by 3K3A-APC would protect oligodendrocytes in in vivo and ex vivo models of ischemic white matter stroke. First, we used a mouse model of white matter stroke induced by injecting a vasoconstrictor N 5 -(1-Iminoethyl)-L-ornithine (L-NIO) into the corpus callosum. Our results show that treatment with recombinant murine 3K3A-APC (0.2 mg/kg, starting 4h after stroke) protected oligodendrocytes (OLS, Olig2+CNPase+) and oligodendrocyte precursor cells (OPCs, Olig2+PDGFRα+) from cell death at 1 and 7 days after stroke. In vitro , 3K3A-APC protected primary mouse oligodendrocytes from apoptosis when exposed to OGD conditions at nanomolar concentrations (EC50 concentration was 5.2 nM). Improved oligodendrocyte viability in vivo was associated by about ~67% reduction in overall cell death (cresyl violet staining, T2w and diffusion tensor MRI) and reduced BBB leakage (fibrin staining and DCE-MRI) as well as improved functional recovery (adhesive removal and grid walking tests). Protective effects of 3K3A-APC were abolished by silencing of PAR1 with small interfering RNA (siRNA) in vivo and in vitro . In conclusion, PAR1 mediated signaling initiated by 3K3A-APC protects oligodendrocyte pools in models of ischemic white matter damage with preservation of neurovascular unit integrity.

Endothelial low-density lipoprotein receptor–related protein 1 (LRP1) protects against neurodegeneration by inhibiting the proinflammatory cyclophilin A–matrix metalloproteinase-9 pathway at the blood–brain barrier. These findings have implications for the pathophysiology and treatment of neurodegenerative disorders linked to vascular dysfunction., The low-density lipoprotein receptor–related protein 1 (LRP1) is an endocytic and cell signaling transmembrane protein. Endothelial LRP1 clears proteinaceous toxins at the blood–brain barrier (BBB), regulates angiogenesis, and is increasingly reduced in Alzheimer’s disease associated with BBB breakdown and neurodegeneration. Whether loss of endothelial LRP1 plays a direct causative role in BBB breakdown and neurodegenerative changes remains elusive. Here, we show that LRP1 inactivation from the mouse endothelium results in progressive BBB breakdown, followed by neuron loss and cognitive deficits, which is reversible by endothelial-specific LRP1 gene therapy. LRP1 endothelial knockout led to a self-autonomous activation of the cyclophilin A–matrix metalloproteinase-9 pathway in the endothelium, causing loss of tight junctions underlying structural BBB impairment. Cyclophilin A inhibition in mice with endothelial-specific LRP1 knockout restored BBB integrity and reversed and prevented neuronal loss and behavioral deficits. Thus, endothelial LRP1 protects against neurodegeneration by inhibiting cyclophilin A, which has implications for the pathophysiology and treatment of neurodegeneration linked to vascular dysfunction.

Objective: Our objective is to explore whether blood–cerebrospinal fluid (CSF) barrier biomarkers differ in episodic migraine (EM) or chronic migraine (CM) from controls. Background: Reports of blood–brain barrier and blood–cerebrospinal fluid barrier (BCSFB) disruption in migraine vary. Our hypothesis is that investigation of biomarkers associated with blood, CSF, brain, cell adhesion, and inflammation will help elucidate migraine pathophysiology. Methods: We recruited 14 control volunteers without headache disorders and 42 individuals with EM or CM as classified using the International Classification of Headache Disorders, 3rd edition, criteria in a cross-sectional study located at our Pasadena and Stanford headache research centers in California. Blood and lumbar CSF samples were collected once from those diagnosed with CM or those with EM during two states: during a typical migraine, before rescue therapy, with at least 6/10 level of pain (ictal); and when migraine free for at least 48 h (interictal). The average number of headaches per month over the previous year was estimated by those with EM; this enabled comparison of biomarker changes between controls and three headache frequency groups: alb: mean ± standard deviation (SD): 5.6 ± 2.3 vs. 4.1 ± 1.9) and fibrinogen (Qfib mean ± SD: 1615 ± 99.0 vs. 86.1 ± 55.0). Mean CSF but not plasma soluble vascular cell adhesion molecule-1 (sVCAM-1) levels were significantly higher in those with more frequent migraine: (4.5 ng/mL ± 1.1 in those with fib ratio was inversely related to headache frequency. We did not find any difference in individuals with EM or CM from controls for CSF cell count, total protein, matrix metalloproteinase-9, soluble platelet-derived growth factor receptor β, tumor necrosis factor-alpha, interferon-gamma, interleukin (IL)-6, IL-8, IL-10, or C-reactive protein. Conclusions: The higher Qalb and Qfib ratios may indicate that the transport of these blood-derived proteins is disturbed at the BCSFB in persons with migraine. These changes most likely occur at the choroid plexus epithelium, as there are no signs of typical endothelial barrier disruption. The most striking finding in this hypothesis-generating study of migraine pathophysiology is that sVCAM-1 levels in CSF may be a biomarker of higher frequency of migraine and CM. An effect from migraine medications cannot be excluded, but there is no known mechanism to suggest they have a role in altering the CSF biomarkers.

Cerebral small vessel disease (SVD) is a major health burden, yet the pathophysiology remains poorly understood with no effective treatment. Since much of SVD develops silently and insidiously, non-invasive neuroimaging such as MRI is fundamental to detecting and understanding SVD in humans. Several relevant SVD rodent models are established for which MRI can monitor in vivo changes over time prior to histological examination. Here, we critically review the MRI methods pertaining to salient rodent models and evaluate synergies with human SVD MRI methods. We found few relevant publications, but argue there is considerable scope for greater use of MRI in rodent models, and opportunities for harmonisation of the rodent-human methods to increase the translational potential of models to understand SVD in humans. We summarise current MR techniques used in SVD research, provide recommendations and examples and highlight practicalities for use of MRI SVD imaging protocols in pre-selected, relevant rodent models. Electronic supplementary material The online version of this article (10.1007/s12975-020-00843-8) contains supplementary material, which is available to authorised users.

3K3A-APC is a recombinant variant of activated protein C (APC) with > 90% reduced anticoagulant activity but preserved cell signaling activity. Benefical effects are mediated by its antiapoptotic direct neuronal protective and vasculoprotective effects including protection of blood-brain barrier (BBB) integrity as well as anti-inflammatiory activity as shown in multiple animal models of large ischemic stroke (middle cerebral artery occlusion) and neurodegeneration. These preclinical studies led to a successfully completed phase II clinical trial of 3K3A-APC for ischemic stroke (RHAPSODY). RHAPSODY trial showed that 3K3A-APC is safe and may reduce hemorrhage in patients that were treated with tPA and/or thrombectomy standard of care therapy for stroke. Even though the protective effects of 3K3A-APC are well known to be mediated by biased signaling via protease activated receptor 1 (PAR1) activation, the role of PAR1 has not been studied in ischemic white matter stroke. In the present study, we used a mouse model of white matter stroke induced by injecting a vasoconstrictor N 5 -(1-Iminoethyl)-L-ornithine (L-NIO) into the corpus callosum. Our results suggest that 4 hrs post-treatment with 3K3A-APC (0.2 mg/kg) reduced lesion volumes by about ~67% (cresyl violet staining and T2w MRI), which was associated with reduced BBB leakage (fibrinogen staining and DCE-MRI), and improved function of oligodendrocytes (OLS, Olig2+CNPase+) and oligodendrocyte precursor cell (OPCs, Olig2+PDGFRα+) at 1 and 7 days after stroke. Beneficial effects of 3K3A-APC were associated with reduced axonal damage on diffusion tensor MRI, and improved behavioral performance on adhesive removal and grid walking tests. We next showed that PAR1 is expressed in all major cell types in the white matter (e.g., OLS, OPCs, microglia and astrocytes) and that silencing PAR1 with small interfering RNA (siRNA) abolishes the protective effect of 3K3A-APC in this model. Taken together, our data suggest that 3K3A-APC is protective in ischemic white matter disease via PAR1 mediated signaling, which improves oligovascular integrity and neuronal survival.

Pericytes play a key role in maintaining the blood-brain barrier (BBB) integrity. BBB disruption occurs during early stages after ischemic stroke. However, the role of pericytes in the pathogenesis of ischemic stroke remains still understudied. 3K3A-APC, a recombinant variant of activated protein C, has shown benefits in preclinical models of ischemic stroke and has favorable safety profile and reduces hemorrhage in Phase 2 study in ischemic stroke patients (RHAPSODY). In the present study, we used PDGFRβ heterozygous knockout (PDGFRβ+/-) mice to investigate the effects of pericyte deficiency on ischemic brain injury using transient proximal middle cerebral artery occlusion (tMCAO). Additionally, we investigated the effects of 3K3A-APC therapy (0.2mg/kg i.v. 4h after stroke) in this model. Compared to controls, pericyte deficiency in PDGFRβ+/- mice resulted in ~35% increase in the infarct and edema volumes, reduction in pericyte coverage from 58% to 25%, and increased IgG and fibrin deposition suggesting accelerated BBB breakdown 24h after stroke. Additionally, PDGFRβ+/- mice showed by 36% more degenerating Fluoro-Jade+ neurons and exhibited accelerated neurobehavioral abnormalities. 3K3A-APC improved neuropathological changes and functional deficits. Our results suggest that pericyte deficiency worsens brain damage and functional outcome after ischemic stroke in mice suggesting that pericytes may play an important role in protecting brain from post-ischemic. We also suggests that 3K3A-APC protects pericyte function in stroked mice which could contribute to its overall neuroprotective effects.

Perivascular spaces include a variety of passageways around arterioles, capillaries and venules in the brain, along which a range of substances can move. Although perivascular spaces were first identified over 150 years ago, they have come to prominence recently owing to advances in knowledge of their roles in clearance of interstitial fluid and waste from the brain, particularly during sleep, and in the pathogenesis of small vessel disease, Alzheimer disease and other neurodegenerative and inflammatory disorders. Experimental advances have facilitated in vivo studies of perivascular space function in intact rodent models during wakefulness and sleep, and MRI in humans has enabled perivascular space morphology to be related to cognitive function, vascular risk factors, vascular and neurodegenerative brain lesions, sleep patterns and cerebral haemodynamics. Many questions about perivascular spaces remain, but what is now clear is that normal perivascular space function is important for maintaining brain health. Here, we review perivascular space anatomy, physiology and pathology, particularly as seen with MRI in humans, and consider translation from models to humans to highlight knowns, unknowns, controversies and clinical relevance.

Montagne et al. examine the role of blood–brain barrier (BBB) dysfunction in Alzheimer’s neurodegeneration and how targeting the BBB can influence the course of neurological disorder in transgenic models with human APP, PSEN1 and TAU mutations, APOE4 (major genetic risk), and pericyte degeneration causing loss of BBB integrity., The blood–brain barrier (BBB) keeps neurotoxic plasma-derived components, cells, and pathogens out of the brain. An early BBB breakdown and/or dysfunction have been shown in Alzheimer’s disease (AD) before dementia, neurodegeneration and/or brain atrophy occur. However, the role of BBB breakdown in neurodegenerative disorders is still not fully understood. Here, we examine BBB breakdown in animal models frequently used to study the pathophysiology of AD, including transgenic mice expressing human amyloid-β precursor protein, presenilin 1, and tau mutations, and apolipoprotein E, the strongest genetic risk factor for AD. We discuss the role of BBB breakdown and dysfunction in neurodegenerative process, pitfalls in BBB measurements, and how targeting the BBB can influence the course of neurological disorder. Finally, we comment on future approaches and models to better define, at the cellular and molecular level, the underlying mechanisms between BBB breakdown and neurodegeneration as a basis for developing new therapies for BBB repair to control neurodegeneration.

Background and Purpose- APOE-ε4 genotype is a risk factor for sporadic Alzheimer disease and reduced recovery from brain injury. Since data on APOE genotype and dementia associated with transient ischemic attack/stroke are sparse, we determined the associations in a longitudinal population-based cohort. Methods- All patients with transient ischemic attack or stroke (2002-2012) in a defined population of 92 728 OxVASC (Oxford Vascular Study) had follow-up to 5-years. Pre-event and incident postevent dementia were ascertained through direct patient assessment and follow-up, supplemented by review of hospital/primary care records. Associations between pre- and post-event dementia and APOE genotype (ε4/ε4-homozygous and ε4/ε3-heterozygous versus ε3/ε3) were examined using logistic regression and Cox regression models, respectively, adjusted for age, sex, education, cerebrovascular burden (stroke severity, prior stroke, white matter disease), diabetes mellitus, and dysphasia. Results- Among 1767 genotyped patients (mean/SD age, 73.0/13.0 years, 901 [51%] male, 602 [34%] transient ischemic attack), 1058 (59.9%) were APOE-ε3/ε3, 403 (22.8%) were ε4/ε3 and 30 (1.7%) were ε4-homozygous. Homozygosity was associated with both pre-event (adjusted odds ratio, 5.81 [95% CI, 1.93-17.48]

Introduction Blood-brain barrier (BBB) breakdown is an early independent biomarker of human cognitive dysfunction, as found using gadolinium (Gd) as a contrast agent. Whether Gd accumulates in brains of individuals with an age-dependent BBB breakdown and/or mild cognitive impairment remains unclear. Methods We analyzed T1-weighted magnetic resonance imaging (MRI) scans from 52 older participants with BBB breakdown in the hippocampus 19-28 months after either cyclic or linear Gd agent. Results There was no change in T1-weighted signal intensity between the baseline contrast MRI and unenhanced MRI on re-examination in any of the studied 10 brain regions with either Gd agent suggesting undetectable Gd brain retention. Discussion Gd does not accumulate in brains of older individuals with a BBB breakdown in the hippocampus. Thus, Gd agents can be used without risk of brain retention within a ∼2-year follow-up to study BBB in the aging human brain in relation to cognition and/or other pathologies.

Introduction: Subcortical white matter stroke (WMS) accounts for 25% of all incidences of stroke and results in severe motor and cognitive disability. WMS stands as the second leading cause of dementia and is notably prevalent in older adults. Activated protein C (APC), a plasma serine protease with potent antithrombotic and cell-signaling activities, was engineered to reduce bleeding risk while retaining normal cell-signaling activities (anti-inflammatory, anti-apoptotic, and neuroregenerative, etc. activities). The engineered variant, 3K3A-APC, is neuroprotective in preclinical models of ischemic stroke with large infarcts involving common large arteries and gray matter. A multicenter Phase 2 randomized clinical trial enrolled 110 patients to assess the safety, pharmacokinetics, and efficacy of human recombinant 3K3A-APC in acute ischemic stroke patients following endovascular treatments (NCT02222714). Methods: In this new study, a murine WMS was induced by the vasoconstrictor N5-(1-iminoethyl)-L-ornithine, dihydrochloride (L-Nio) by injection into the subcortical white matter ventral to the mouse forelimb motor cortex using the Neurostar motorized ultra-precise small animal stereotaxic instrument. Mice received intravenously 0.2 mg/kg recombinant murine 3K3A-APC or saline at 4, 24, 48 and 72 h after L-Nio. Then MRI scans were performed using a 7T PET/MRI scanner (MR Solutions) and a standard quadrature coil at 1 and 7 days after the stroke. Results: Both MRI and histological results showed that 3K3A-APC significantly reduced the lesion volume, increased the viability of oligodendrocytes and neurons, and protected against blood brain barrier damage at 1 and 7 days after stroke. Behavioral tests showed that 3K3A-APC improved functional recovery. Conclusions: These results demonstrated that 3K3A-APC might be an effective treatment for white matter stroke.

Increasing evidence recognizes Alzheimer's disease (AD) as a multifactorial and heterogeneous disease with multiple contributors to its pathophysiology, including vascular dysfunction. The recently updated AD Research Framework put forth by the National Institute on Aging-Alzheimer's Association describes a biomarker-based pathologic definition of AD focused on amyloid, tau, and neuronal injury. In response to this article, here we first discussed evidence that vascular dysfunction is an important early event in AD pathophysiology. Next, we examined various imaging sequences that could be easily implemented to evaluate different types of vascular dysfunction associated with, and/or contributing to, AD pathophysiology, including changes in blood-brain barrier integrity and cerebral blood flow. Vascular imaging biomarkers of small vessel disease of the brain, which is responsible for >50% of dementia worldwide, including AD, are already established, well characterized, and easy to recognize. We suggest that these vascular biomarkers should be incorporated into the AD Research Framework to gain a better understanding of AD pathophysiology and aid in treatment efforts. (C) 2018 the Alzheimer's Association. Published by Elsevier Inc. All rights reserved.

Craniosynostosis results from premature fusion of the cranial suture(s), which contain mesenchymal stem cells (MSCs) that are crucial for calvarial expansion in coordination with brain growth. Infants with craniosynostosis have skull dysmorphology, increased intracranial pressure, and complications such as neurocognitive impairment that compromise quality of life. Animal models recapitulating these phenotypes are lacking, hampering the development of urgently needed innovative therapies. Here we show that Twist1(+/−) mice with craniosynostosis have increased intracranial pressure and neurocognitive behavioral abnormalities, recapitulating features of human Saethre-Chotzen syndrome. Using a biodegradable material combined with MSCs, we have successfully regenerated a functional cranial suture that corrects skull deformity, normalizes intracranial pressure and rescues neurocognitive behavior deficits. The regenerated suture creates a niche into which endogenous MSCs migrated, sustaining calvarial bone homeostasis and repair. MSC-based cranial suture regeneration offers a paradigm shift in treatment to reverse skull and neurocognitive abnormalities in this devastating disease.

Neurovascular dysfunction, including blood-brain barrier (BBB) breakdown and cerebral blood flow (CBF) dysregulation and reduction, are increasingly recognized to contribute to Alzheimer's disease (AD). The spatial and temporal relationships between different pathophysiological events during preclinical stages of AD, including cerebrovascular dysfunction and pathology, amyloid and tau pathology, and brain structural and functional changes remain, however, still unclear. Recent advances in neuroimaging techniques, i.e., magnetic resonance imaging (MRI) and positron emission tomography (PET), offer new possibilities to understand how the human brain works in health and disease. This includes methods to detect subtle regional changes in the cerebrovascular system integrity. Here, we focus on the neurovascular imaging techniques to evaluate regional BBB permeability (dynamic contrast-enhanced MRI), regional CBF changes (arterial spin labeling- and functional-MRI), vascular pathology (structural MRI), and cerebral metabolism (PET) in the living human brain, and examine how they can inform about neurovascular dysfunction and vascular pathophysiology in dementia and AD. Altogether, these neuroimaging approaches will continue to elucidate the spatio-temporal progression of vascular and neurodegenerative processes in dementia and AD and how they relate to each other.

The blood-brain barrier (BBB) prevents neurotoxic plasma components, blood cells, and pathogens from entering the brain. At the same time, the BBB regulates transport of molecules into and out of the central nervous system (CNS), which maintains tightly controlled chemical composition of the neuronal milieu that is required for proper neuronal functioning. In this review, we first examine molecular and cellular mechanisms underlying the establishment of the BBB. Then, we focus on BBB transport physiology, endothelial and pericyte transporters, and perivascular and paravascular transport. Next, we discuss rare human monogenic neurological disorders with the primary genetic defect in BBB-associated cells demonstrating the link between BBB breakdown and neurodegeneration. Then, we review the effects of genes underlying inheritance and/or increased susceptibility for Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease, and amyotrophic lateral sclerosis (ALS) on BBB in relation to other pathologies and neurological deficits. We next examine how BBB dysfunction relates to neurological deficits and other pathologies in the majority of sporadic AD, PD, and ALS cases, multiple sclerosis, other neurodegenerative disorders, and acute CNS disorders such as stroke, traumatic brain injury, spinal cord injury, and epilepsy. Lastly, we discuss BBB-based therapeutic opportunities. We conclude with lessons learned and future directions, with emphasis on technological advances to investigate the BBB functions in the living human brain, and at the molecular and cellular level, and address key unanswered questions.

Blood–brain barrier (BBB) dysfunction has been implicated in ischemic risk following aneurysmal subarachnoid hemorrhage (aSAH), but never directly imaged. We prospectively examined whether post-bleed day 4 dynamic contrast-enhanced magnetic resonance (DCE-MR) BBB permeability imaging could predict development of delayed cerebral ischemia (DCI). Global MR-derived BBB permeability ( Ktrans) was significantly higher in aSAH patients who subsequently developed DCI (five patients; 2.28 ± 0.09 × 10−3 min−1) compared to those who experienced radiographic vasospasm only (three patients; 1.85 ± 0.12 × 10−3 min−1; p −3 min−1; p trans > 2 × 10−3 min−1 predicted development of DCI (AUC = 0.98, 95% CI: 0.93–1). Global BBB dysfunction following aSAH is detectable with DCE-MR and predictive of ischemic risk.

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-β (Aβ)3,11,14, and more recently tau15. Animal studies suggest that Aβ 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 Aβ 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-β8,18, 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 Aβ and/or tau biomarker changes, suggesting that BBB breakdown is an early biomarker of human cognitive dysfunction independent of Aβ and tau.

Diffuse white-matter disease associated with small-vessel disease and dementia is prevalent in the elderly. The biological mechanisms, however, remain elusive. Using pericyte-deficient mice, magnetic resonance imaging, viral-based tract-tracing, and behavior and tissue analysis, we found that pericyte degeneration disrupted white-matter microcirculation, resulting in an accumulation of toxic blood-derived fibrin(ogen) deposits and blood-flow reductions, which triggered a loss of myelin, axons and oligodendrocytes. This disrupted brain circuits, leading to white-matter functional deficits before neuronal loss occurs. Fibrinogen and fibrin fibrils initiated autophagy-dependent cell death in oligodendrocyte and pericyte cultures, whereas pharmacological and genetic manipulations of systemic fibrinogen levels in pericyte-deficient, but not control mice, influenced the degree of white-matter fibrin(ogen) deposition, pericyte degeneration, vascular pathology and white-matter changes. Thus, our data indicate that pericytes control white-matter structure and function, which has implications for the pathogenesis and treatment of human white-matter disease associated with small-vessel disease.

Subcortical white matter stroke constitutes up to 30% of all stroke subtypes, occurs initially as silent infarcts in the white matter (WM), and contributes significantly to the development of vascular dementia. Activated protein C (APC) is a plasma serine protease that is capable of antithrombotic, anti-inflammatory, anti-apoptotic, and cell-signaling activities. 3K3A-APC, a recombinant variant of APC with reduced (>90%) anticoagulant activity, engineered to reduce APC-associated bleeding risk while retaining normal cell-signaling activity, has shown benefits in preclinical models of ischemic stroke with big infarcts involving large brain arteries and gray matter. A multicenter Phase 2 randomized clinical trial has enrolled 110 patients to assess the safety, pharmacokinetics, and efficacy of human recombinant 3K3A-APC in acute ischemic stroke patients following endovascular thrombolysis (NCT02222714). In this study, subcortical WM stroke model was induced by vasoconstrictor N5-(1-iminoethyl)-L-ornithine, dihydrochloride (L-Nio). L-Nio (Calbiochem) was injected into subcortical WM of the anterior cingulum (AC) of the corticolimbic circuit or the subcortical white matter ventral to the mouse forelimb motor cortex using the Neurostar motorized ultra-precise small animal stereotaxic instrument (Model 963SD). Mice received 0.2 mg/kg intravenously of recombinant murine 3K3A-APC or saline at 4, 24, 48 and 72 h after stroke. The results indicate that 3K3A-APC significantly reduces the lesion volume and protected blood brain barrier damage 3 days after stroke, and improves remote memory function 4 weeks after stroke, compared to vehicle. These results demonstrate that 3K3A-APC might be an effective treatment for white matter stroke.

International audience; Although the extracellular serine protease tissue plasminogen activator (tPA) is involved in pathophysiological processes such as learning and memory, anxiety, epilepsy, stroke, and Alzheimer's disease, information about its regional, cellular, and subcellular distribution in vivo is lacking. In the present study, we observed, in healthy mice and rats, the presence of tPA in endothelial cells, oligodendrocytes, mastocytes, and ependymocytes, but not in pericytes, microglial cells, and astrocytes. Moreover, blockage of the axo-dendritic transport unmasked tPA expression in neurons of cortical and hippocampal areas. Interestingly, combined electrophysiological recordings, single-cell reverse transcription polymerase chain reaction (RT-PCR), and immunohistological analyses revealed that the presence of tPA is restricted to subsets of excitatory pyramidal glutamatergic neurons. We further evidenced that tPA is stored in synaptobrevin-2-positive glutamatergic synaptic vesicles. Based on all these data, we propose the existence of tPA-ergic neurons in the mature brain.

Purpose: To determine optimal parameters for acquisition and processing of dynamic contrast-enhanced MRI (DCE-MRI) to detect small changes in near normal low blood–brain barrier (BBB) permeability. Methods: Using a contrast-to-noise ratio metric (K-CNR) for K_(trans) precision and accuracy, the effects of kinetic model selection, scan duration, temporal resolution, signal drift, and length of baseline on the estimation of low permeability values was evaluated with simulations. Results: The Patlak model was shown to give the highest K-CNR at low K_(trans). The K_(trans) transition point, above which other models yielded superior results, was highly dependent on scan duration and tissue extravascular extracellular volume fraction (v_e). The highest K-CNR for low K_(trans) was obtained when Patlak model analysis was combined with long scan times (10–30 min), modest temporal resolution (

Cerebral blood flow (CBF) regulation is essential for normal brain function. The mammalian brain has evolved a unique mechanism for CBF control known as neurovascular coupling. This mechanism ensures a rapid increase in the rate of CBF and oxygen delivery to activated brain structures. The neurovascular unit is composed of astrocytes, mural vascular smooth muscle cells and pericytes, and endothelia, and regulates neurovascular coupling. This Review article examines the cellular and molecular mechanisms within the neurovascular unit that contribute to CBF control, and neurovascular dysfunction in neurodegenerative disorders such as Alzheimer disease.

International audience; Interactions between platelet glycoprotein (Gp) IIb/IIIa and plasma proteins mediate platelet cross-linking in arterial thrombi. However, GpIIb/IIIa inhibitors fail to disperse platelet aggregates after myocardial infarction or ischemic stroke. These results suggest that stability of occlusive thrombi involves additional and as-yet-unidentified mechanisms. In the present study, we investigated the mechanisms driving platelet cross-linking during occlusive thrombus formation. Using computational fluid dynamic simulations and in vivo thrombosis models, we demonstrated that the inner structure of occlusive thrombi is heterogeneous and primarily determined by the rheological conditions that prevailed during thrombus growth. Unlike the first steps of thrombus formation, which are GpIIb/IIIa-dependent, our findings reveal that closure of the arterial lumen is mediated by GpIbα-von Willebrand Factor (VWF) interactions. Accordingly, disruption of platelet cross-linking using GpIbα-VWF inhibitors restored vessel patency and improved outcome in a mouse model of ischemic stroke, although the thrombi were resistant to fibrinolysis or traditional antithrombotic agents. Overall, our study demonstrates that disruption of GpIbα-VWF interactions restores vessel patency after occlusive thrombosis by specifically disaggregating the external layer of occlusive thrombi, which is constituted of platelet aggregates formed under very high shear rates.