Cerebral Vessel Density Research Articles

Aquaporin 4 is differentially increased and dislocated in association with tau and amyloid-beta

AimsNeurovascular-glymphatic dysfunction plays an important role in Alzheimer's disease and has been analysed mainly in relation to amyloid-beta (Aβ) pathology. Here, we aim to investigate the neurovascular alterations and mapping of aquaporin 4 (AQP4) distribution and dislocation associated with tau and Aβ. Materials and methodsPerfusion, susceptibility weighted imaging and structural magnetic resonance imaging (MRI) were performed in the pR5 mouse model of 4-repeat tau and the arcAβ mouse model of amyloidosis. Immunofluorescence staining was performed using antibodies against AQP4, vessel, astroglia, microglia, phospho-tau and Aβ in brain tissue slices from pR5, arcAβ and non-transgenic mice. Key findingspR5 mice showed regional atrophy, preserved cerebral blood flow, and reduced cerebral vessel density compared to non-transgenic mice, while arcAβ mice showed cerebral microbleeds and reduced cerebral vessel density. AQP4 dislocation and peri-tau enrichment in the hippocampus and increased AQP4 levels in the cortex and hippocampus were detected in pR5 mice compared to non-transgenic mice. In comparison, cortical AQP4 dislocation and cortical/hippocampal peri-plaque increases were observed in arcAβ mice. Increased expression of reactive astrocytes were detected around the tau inclusions in pR5 mice and Aβ plaques in arcAβ mice. SignificanceWe demonstrated the neurovascular alterations, microgliosis, astrogliosis and increased AQP4 regional expression in pR5 tau and arcAβ mice. We observed a divergent region-specific AQP4 dislocation and association with phospho-tau and Aβ pathologies.

Plasminogen deficiency causes reduced angiogenesis and behavioral recovery after stroke in mice

Plasminogen is involved in the process of angiogenesis; however, the underlying mechanism is unclear. Here, we investigated the potential contribution of plasmin/plasminogen in mediating angiogenesis and thereby contributing to functional recovery post-stroke. Wild-type plasminogen naive (Plg+/+) mice and plasminogen knockout (Plg−/−) mice were subjected to unilateral permanent middle cerebral artery occlusion (MCAo). Blood vessels were labeled with FITC-dextran. Functional outcomes, and cerebral vessel density were compared between Plg+/+ and Plg−/− mice at different time points after stroke. We found that Plg−/− mice exhibited significantly reduced functional recovery, associated with significantly decreased vessel density in the peri-infarct area in the ipsilesional cortex compared with Plg+/+ mice. In vitro, cerebral endothelial cells harvested from Plg−/− mice exhibited significantly reduced angiogenesis assessed using tube formation assay, and migration, as evaluated using Scratch assays, compared to endothelial cells harvested from Plg+/+ mice. In addition, using Western blots, expression of thrombospondin (TSP)-1 and TSP-2 were increased after MCAo in the Plg−/− group compared to Plg+/+ mice, especially in the ipsilesional side of brain. Taken together, our data suggest that plasmin/plasminogen down-regulates the expression level of TSP-1 and TSP-2, and thereby promotes angiogenesis in the peri-ischemic brain tissue, which contributes to functional recovery after ischemic stroke.

CT assessment of the increased density of cerebral vessels in plateau region

In this study, the relationship between the brain parenchymal density, the cerebral vessel density, the mean corpuscular hemoglobin (MCH) content, the mean corpuscular hemoglobin concentration (MCHC), and the morbidity associated with lacunar infarction of residents living in either the plains or the plateau regions were analyzed and compared for their potential clinical implications. Clinical data from the brain CT scans of individuals living in either the plain or plateau regions (129 each) were collected. Specifically, the CT values for basal ganglia, the middle cerebral artery, and the superior sagittal sinus, along with the number of patients with lacunar infarction, were collected. In addition, the MCH and MCHC values were measured in blood samples collected within 48 h following the CT scans. For statistical analysis, an independent sample t-test, Pearson's correlation test (permutation test), and Chi-squared test were employed. The inhabitants of the plateau had a significantly higher CT value of basal ganglia, the middle cerebral artery, and superior sagittal sinus and also higher levels of MCH and MCHC in the blood (ps < 0.001) than the inhabitants of the plains region. Further, there was a significant positive correlation between the three aforementioned CT values and the MCH and MCHC findings. However, no significant differences were found in the morbidity of lacunar infarction between these two regions (p > 0.05). The inhabitants in the plateau have a significantly higher brain parenchymal density, higher CT value for cerebral vessels density, and higher blood MCH and MCHC levels in comparison with individuals occupying the plains. Concurrently, the parenchymal density and the CT values are shown to be positively correlated with the MCH and MCHC content in the blood.

Microglia exacerbate white matter injury via complement C3/C3aR pathway after hypoperfusion.

Microglial activation participates in white matter injury after cerebral hypoperfusion. However, the underlying mechanism is unclear. Here, we explore whether activated microglia aggravate white matter injury via complement C3-C3aR pathway after chronic cerebral hypoperfusion.Methods: Adult male Sprague-Dawley rats (n = 80) underwent bilateral common carotid artery occlusion for 7, 14, and 28 days. Cerebral vessel density and blood flow were examined by synchrotron radiation angiography and three-dimensional arterial spin labeling. Neurobehavioral assessments, CLARITY imaging, and immunohistochemistry were performed to evaluate activation of microglia and C3-C3aR pathway. Furthermore, C3aR knockout mice were used to establish the causal relationship of C3-C3aR signaling on microglia activation and white matter injury after hypoperfusion.Results: Cerebral vessel density and blood flow were reduced after hypoperfusion (p<0.05). Spatial learning and memory deficits and white matter injury were shown (p<0.05). These impairments were correlated with aberrant microglia activation and an increase in the number of reactive microglia adhering to and phagocytosed myelin in the hypoperfusion group (p<0.05), which were accompanied by the up-regulation of complement C3 and its receptors C3aR (p<0.05). Genetic deletion of C3ar1 significantly inhibited aberrant microglial activation and reversed white matter injury after hypoperfusion (p<0.05). Furthermore, the C3aR antagonist SB290157 decreased the number of microglia adhering to myelin (p<0.05), attenuated white matter injury and cognitive deficits in chronic hypoperfusion rats (p<0.05).Conclusions: Our results demonstrated that aberrant activated microglia aggravate white matter injury via C3-C3aR pathway during chronic hypoperfusion. These findings indicate C3aR plays a critical role in mediating neuroinflammation and white matter injury through aberrant microglia activation, which provides a novel therapeutic target for the small vessel disease and vascular dementia.

Association of Cardiovascular Risk Factors With MRI Indices of Cerebrovascular Structure and Function and White Matter Hyperintensities in Young Adults

Risk of stroke and brain atrophy in later life relate to levels of cardiovascular risk in early adulthood. However, it is unknown whether cerebrovascular changes are present in young adults. To examine relationships between modifiable cardiovascular risk factors and cerebrovascular structure, function, and white matter integrity in young adults. A cross-sectional observational study of 125 young adults (aged 18-40 years) without clinical evidence of cerebrovascular disease. Data collection was completed between August 2014 and May 2016 at the University of Oxford, United Kingdom. Final data collection was completed on May 31, 2016. The number of modifiable cardiovascular risk factors at recommended levels, based on the following criteria: body mass index (BMI) <25; highest tertile of cardiovascular fitness and/or physical activity; alcohol consumption <8 drinks/week; nonsmoker for >6 months; blood pressure on awake ambulatory monitoring <130/80 mm Hg; a nonhypertensive diastolic response to exercise (peak diastolic blood pressure <90 mm Hg); total cholesterol <200 mg/dL; and fasting glucose <100mg/dL. Each risk factor at the recommended level was assigned a value of 1, and participants were categorized from 0-8, according to the number of risk factors at recommended levels, with higher numbers indicating healthier risk categories. Cerebral vessel density, caliber and tortuosity, brain white matter hyperintensity lesion count. In a subgroup (n = 52), brain blood arrival time and cerebral blood flow assessed by brain magnetic resonance imaging (MRI). A total of 125 participants, mean (SD) age 25 (5) years, 49% women, with a mean (SD) score of 6.0 (1.4) modifiable cardiovascular risk factors at recommended levels, completed the cardiovascular risk assessment and brain MRI protocol. Cardiovascular risk factors were correlated with cerebrovascular morphology and white matter hyperintensity count in multivariable models. For each additional modifiable risk factor categorized as healthy, vessel density was greater by 0.3 vessels/cm3 (95% CI, 0.1-0.5; P = .003), vessel caliber was greater by 8 μm (95% CI, 3-13; P = .01), and white matter hyperintensity lesions were fewer by 1.6 lesions (95% CI, -3.0 to -0.5; P = .006). Among the 52 participants with available data, cerebral blood flow varied with vessel density and was 2.5 mL/100 g/min higher for each healthier category of a modifiable risk factor (95% CI, 0.16-4.89; P = .03). In this preliminary study involving young adults without clinical evidence of cerebrovascular disease, a greater number of modifiable cardiovascular risk factors at recommended levels was associated with higher cerebral vessel density and caliber, higher cerebral blood flow, and fewer white matter hyperintensities. Further research is needed to verify these findings and determine their clinical importance.

Thrombospondin-1 Gene Deficiency Worsens the Neurological Outcomes of Traumatic Brain Injury in Mice.

Background: Thrombospondin-1 (TSP-1) is an extracellular matrix protein that plays multiple physiological and pathophysiological roles in the brain. Experimental reports suggest that TSP-1 may have an adverse role in neuronal function recovery under certain injury conditions. However, the roles of TSP-1 in traumatic brain injury (TBI) have not been elucidated. In this study we for the first time investigated the roles of TSP-1 in a controlled cortical impact (CCI) model of TBI in TSP-1 knockout (TSP-1 KO) and wild type (WT) mice.Methods: We examined blood brain-barrier (BBB) damage using at 1 day post-TBI by measuring Evans Blue leakage, and neurological functional recovery at 3 weeks post-TBI by measuring neurological severity score (NSS), wire gripping, corner test and Morris Water Maze (MWM). Mechanistically, we quantified pro-angiogenic biomarkers including cerebral vessel density, vascular endothelial growth factors (VEGF) and angiopoietin-1 (Ang-1) protein expression, synaptic biomarker synaptophysin, and synaptogenesis marker brain-derived neurotrophic factor (BDNF) protein expression in contralateral and ipsilateral (peri-lesion) cortex at 21 days after TBI using immunohistochemistry and Western Blot.Results: TSP-1 is upregulated at early phase of TBI in WT mice. Compared to WT mice, TSP-1 KO (1) significantly worsened TBI-induced BBB leakage at 1 day after TBI; (2) had similar lesion size as WT mice at 3 weeks after TBI; (3) exhibited a significantly worse neurological deficits in motor and cognitive functions; (4) had no significant difference in cerebral vessel density, but significant increase of VEGF and Ang-1 protein expressions in peri-lesion cortex; (5) significantly increased BDNF but not synaptophysin protein level in peri-lesion cortex compared to sham, but both synaptophysin and BDNF expressions were significantly decreased in contralateral cortex compared to WT.Conclusion: Our results suggest that TSP-1 may be beneficial for maintaining BBB integrity in the early phase and functional recovery in late phase after TBI. The molecular mechanisms of TSP-1 in early BBB pathophysiology, and long-term neurological function recovery after TBI need to be further investigated.

Chronic central nervous system expression of HIV-1 Tat leads to accelerated rarefaction of neocortical capillaries and loss of red blood cell velocity heterogeneity.

HIV-1 infection of the CNS is associated with impairment of CBF and neurocognitive function, and accelerated signs of aging. As normal aging is associated with rarefaction of the cerebral vasculature, we set out to examine chronic viral effects on the cerebral vasculature. DOX-inducible HIV-1 Tat-tg and WT control mice were used. Animals were treated with DOX for three weeks or five to seven months. Cerebral vessel density and capillary segment length were determined from quantitative image analyses of sectioned cortical tissue. In addition, movement of red blood cells in individual capillaries was imaged in vivo using multiphoton microscopy, to determine RBCV and flux. Mean RBCV was not different between Tat-tg mice and age-matched WT controls. However, cortical capillaries from Tat-tg mice showed a significant loss of RBCV heterogeneity and increased RBCF that was attributed to a marked decrease in total cortical capillary length (35-40%) compared to WT mice. Cerebrovascular rarefaction is accelerated in HIV-1 Tat-transgenic mice, and this is associated with alterations in red cell blood velocity. These changes may have relevance to the pathogenesis of HIV-associated neurocognitive disorders in an aging HIV-positive population.

Adult responses to an ischemic stroke in a rat model of neonatal stress and morphine treatment

Critically ill newborn infants experience stressors that may alter brain development. Using a rodent model, we previously showed that neonatal stress, morphine, and stress plus morphine treatments each influence early gene expression and may impair neurodevelopment and learning behavior. We hypothesized that the combination of neonatal stress with morphine may alter neonatal angiogenesis and/or adult cerebral blood vessel density and thus increase injury after cerebral ischemia in adulthood. To test this, neonatal Lewis rats underwent 8h/d maternal separation, plus morning/afternoon hypoxia exposure and either saline or morphine treatment (2mg/kg s.c.) from postnatal day 3–7. A subset received bromodeoxyuridine to track angiogenesis. Adult brains were stained with collagen IV to quantify cerebral blood vessel density. To examine vulnerability to brain injury, postnatal day 80 adult rats underwent right middle cerebral artery occlusion (MCAO) to produce unilateral ischemic lesions. Brains were removed and processed for histology 48h after injury. Brain injury was assessed by histological evaluation of hematoxylin and eosin, and silver staining. In contrast to our hypothesis, neither neonatal morphine, stress, nor the combination affected cerebral vessel density or MCAO-induced brain injury. Neonatal angiogenesis was not detected in adult rats possibly due to turnover of endothelial cells. Although unrelated to angiogenesis, hippocampal granule cell neurogenesis was detected and there was a trend (P=0.073) toward increased bromodeoxyuridine incorporation in rats that underwent neonatal stress. These findings are discussed in contrast to other data concerning the effects of morphine on cerebrovascular function, and acute effects of morphine on hippocampal neurogenesis.

An angiogenic role for the α5β1 integrin in promoting endothelial cell proliferation during cerebral hypoxia

Fibronectin is a critical regulator of vascular modelling, both in development and in the adult. In the hypoxic adult central nervous system (CNS), fibronectin is induced on angiogenic vessels, and endothelial cells show strong induction of the two fibronectin receptors α5β1 and αvβ3 integrins. In a previous study, we found that the αvβ3 integrin is dispensable for hypoxic-induced cerebral angiogenesis, but a role for the endothelial α5β1 integrin was suggested. To directly investigate the role of endothelial α5 integrin in cerebral angiogenesis, wild-type mice and mice lacking α5 integrin expression in endothelial cells (α5-EC-KO) were subject to hypoxia (8% O2) for 0, 2, 4, 7 or 14days. Quantification of cerebral vessel density and endothelial-specific proteins claudin-5 and Glut-1 revealed that α5-EC-KO mice displayed an attenuated angiogenic response, which correlated with delayed endothelial proliferation. α5-EC-KO mice showed no defect in the ability to organize a cerebrovascular fibronectin matrix, and no compensatory increase in vascular αvβ3 integrin expression. Consistent with these findings, primary α5KO brain endothelial cells (BEC) in culture exhibited delayed growth and proliferation. Taken together, these studies demonstrate an important angiogenic role for the α5β1 integrin in promoting BEC proliferation in response to cerebral hypoxia.

Abstract 2716: Patients with Leukoaraiosis Have Poor Recruitment of Collaterals After Middle Cerebral Artery Occlusion

Background: Previous studies have shown reduced penumbral salvage in ischemic stroke patients with higher leukoaraisosis (LA) volume. Although unproven, decreased cerebral vessel density and diminished capacity of cerebral vessels to dilate in response to reduced blood flow in severe LA, are considered among the factors that might explain the association between LA burden and infarct growth in ischemic stroke. Both of these factors, in theory, might negatively affect the extent of collateral blood flow, an important predictor of tissue and clinical outcome in patients with acute ischemic stroke. In this study, we therefore analyzed whether extent of LA adversely affected the degree of collateral circulation in a cohort of patients presenting with middle cerebral artery occlusion. Methods: We retrospectively analyzed a consecutive series of patients admitted with a diagnosis of middle cerebral artery occlusion. Computed tomography angiography source images (CTA-SI) were used to assess the degree of collateral circulation, based on a previously validated scoring system which grades collateral vessels in the sylvian fissure and leptomeningeal convexity separately on a scale from 1 to 5, with 1 being the worst and 5 the best. The extent of LA was determined on FLAIR images by using the Fazekas scale. Multivariate analysis was used to explore the relationship between extent of LA and degree of collateral circulation, adjusted for other covariates like age, gender, vascular risk factors and time from symptom onset to CTA imaging. Results: A total of 51 patients (31 female, 20 male) were included into the study. LA severity was significantly and negatively correlated with the degree of collateral supply (r=-0.31, p=0.03). LA severity (OR 5.9, 95%CI 1.5-24.0) and history of prior stroke (OR 7.8, 95%CI 1.0-59.3) were the only significant variables associated with insufficient collaterals (defined as a combined sylvian and lepotmeningeal collateral score of 5 or less) in the multivariate logistic regression analysis. Conclusion: Patients with higher LA burden have a poor recruitment of collateral vessels after middle cerebral artery occlusion. This association might contribute to reduced penumbral salvage and increased susceptibility to infarct growth observed in patients with severe LA.