Cerebral hypoperfusion exacerbates vascular dysfunction after traumatic brain injury.

Traumatic brain injuries are extremely common, and although most patients recover from their injuries many TBI patients suffer prolonged symptoms and remain at a higher risk for developing cardiovascular disease and neurodegeneration. Moreover, it remains challenging to identify predictors of poor long-term outcomes. Here, we tested the hypothesis that preexisting cerebrovascular impairment exacerbates metabolic and vascular dysfunction and leads to worse outcomes after TBI. Male mice underwent a mild surgical reduction in cerebral blood flow using a model of bilateral carotid artery stenosis (BCAS) wherein steel microcoils were implanted around the carotid arteries. Then, 30 days post coil implantation, mice underwent TBI or sham surgery. Gene expression profiles, cerebral blood flow, metabolic function, oxidative damage, vascular health and angiogenesis were assessed. Single nuclei RNA sequencing of endothelial cells isolated from mice after TBI showed differential gene expression profiles after TBI and BCAS, that were further altered when mice underwent both challenges. TBI but not BCAS increased mitochondrial oxidative metabolism. Both BCAS and TBI decreased cerebrovascular responses to repeated whisker stimulation. BCAS induced oxidative damage and inflammation in the vasculature as well as loss of vascular density, and reduced the numbers of angiogenic tip cells. Finally, intravascular protein accumulation was increased among mice that experienced both BCAS and TBI. Overall, our findings reveal that a prior vascular impairment significantly alters the profile of vascular health and function of the cerebrovasculature, and when combined with TBI may result in worsened outcomes.

Reproductive hormones in relation to white matter hyperintensity volumes among midlife women.

INTRODUCTION: Although reproductive hormones are implicated in cerebral small vessel disease in women, few studies consider measured hormones in relation to white matter hyperintensity volume (WMHV), a key indicator of cerebral small vessel disease. Even fewer studies consider estrone (E1), the primary postmenopausal estrogen, or follicle-stimulating hormone (FSH), an indicator of ovarian age. We tested associations of estradiol (E2), E1, and FSH to WMHV among women. METHODS: Two hundred twenty-two women (mean age = 59) underwent hormone assays (E1, E2, FSH) and 3T brain magnetic resonance imaging. Associations of hormones to WMHV were tested with linear regression. RESULTS: Higher E2 (B[standard error (SE)] = -0.17[0.06], P = 0.008) and E1 (B[SE] = -0.26[0.10], P = 0.007) were associated with lower whole-brain WMHV, and higher FSH (B[SE] = 0.26[0.07], P = 0.0005) with greater WMHV (covariates age, race, education). When additionally controlling for cardiovascular disease risk factors, associations of E1 and FSH to WMHV remained. DISCUSSION: Reproductive hormones, particularly E1 and FSH, are important to women's cerebrovascular health. HIGHLIGHTS: Despite widespread belief that sex hormones are important to women's brain health, little work has considered how these hormones in women relate to white matter hyperintensities (WMH), a major indicator of cerebral small vessel disease. We considered relations of estradiol (E2), estrone (E1), and follicle-stimulating hormone (FSH) to WMH in midlife women. Higher E2 and E1 were associated with lower whole-brain WMH volume (WMHV), and higher FSH with higher whole-brain WMHV. Associations of E1 and FSH, but not E2, to WMHV persisted with adjustment for cardiovascular disease risk factors. Findings underscore the importance of E2 and FSH to women's cerebrovascular health.

Cerebral hypoperfusion exacerbates traumatic brain injury in male but not female mice.

Mild-moderate traumatic brain injuries (TBIs) are prevalent, and while many individuals recover, there is evidence that a significant number experience long-term health impacts, including increased vulnerability to neurodegenerative diseases. These effects are influenced by other risk factors, such as cardiovascular disease. Our study tested the hypothesis that a pre-injury reduction in cerebral blood flow (CBF), mimicking cardiovascular disease, worsens TBI recovery. We induced bilateral carotid artery stenosis (BCAS) and a mild-moderate closed-head TBI in male and female mice, either alone or in combination, and analyzed CBF, spatial learning, memory, axonal damage, and gene expression. Findings showed that BCAS and TBI independently caused a ~10% decrease in CBF. Mice subjected to both BCAS and TBI experienced more significant CBF reductions, notably affecting spatial learning and memory, particularly in males. Additionally, male mice showed increased axonal damage with both BCAS and TBI compared to either condition alone. Females exhibited spatial memory deficits due to BCAS, but these were not worsened by subsequent TBI. Gene expression analysis in male mice highlighted that TBI and BCAS individually altered neuronal and glial profiles. However, the combination of BCAS and TBI resulted in markedly different transcriptional patterns. Our results suggest that mild cerebrovascular impairments, serving as a stand-in for preexisting cardiovascular conditions, can significantly worsen TBI outcomes in males. This highlights the potential for mild comorbidities to modify TBI outcomes and increase the risk of secondary diseases.

On presentation of cerebral arteries via cortical openings.

The presentation of cortical arteries is challenging, as most of their course is hidden in the depth of the sulci. Despite that, demonstrating the arteries on the cortical surface is a standard way of their presentation. To keep advantages of surface presentation while lessening its limitation, we propose a novel context-related method of cerebrovasculature presentation by cortical openings consisting in the removal of a selected region from the cortical mantle and exposing underlying structures. We also introduce a reverse than standard vessel-to-context mapping from a gyrus/lobule to vessels supplying it.The method has the following steps: define a cortical opening, develop a tool to perform them, create cortical openings for gyri and lobules with underlying white matter and intracranial arteries, generate labeled and parcellated images for the created openings, and integrate the cortical opening images with the NOWinBRAIN public repository of 8600 3D neuroimages.The cortical openings are created for 64 gyri and six lobules for the left and right cerebral hemispheres resulting in 210 images arranged in triples as spatially corresponding non-parcellated and unlabeled, parcellated by color and unlabeled, and parcellated and labeled images.The cortical opening approach, generally, increases vessel exposure in a higher number of depicted branches, revealing arteries otherwise hidden deep in sulci, a more complete vessel course, and a lower number of required views.The gyrus/lobule-to-arteries mapping facilitates exploration of a studied region, encapsulates all local arteries, and reduces vascular complexity by decomposing the entire vascular system into smaller sets involved in the studied region.

Proteomic changes in the human cerebrovasculature in Alzheimer's disease and related tauopathies linked to peripheral biomarkers in plasma and cerebrospinal fluid.

INTRODUCTION: Cerebrovascular dysfunction is a pathological hallmark of Alzheimer's disease (AD). Nevertheless, detecting cerebrovascular changes within bulk tissues has limited our ability to characterize proteomic alterations from less abundant cell types. METHODS: We conducted quantitative proteomics on bulk brain tissues and isolated cerebrovasculature from the same individuals, encompassing control (N = 28), progressive supranuclear palsy (PSP) (N = 18), and AD (N = 21) cases. RESULTS: Protein co-expression network analysis identified unique cerebrovascular modules significantly correlated with amyloid plaques, cerebrovascular amyloid angiopathy (CAA), and/or tau pathology. The protein products within AD genetic risk loci were concentrated within cerebrovascular modules. The overlap between differentially abundant proteins in AD cerebrospinal fluid (CSF) and plasma with cerebrovascular network highlighted a significant increase of matrisome proteins, SMOC1 and SMOC2, in CSF, plasma, and brain. DISCUSSION: These findings enhance our understanding of cerebrovascular deficits in AD, shedding light on potential biomarkers associated with CAA and vascular dysfunction in neurodegenerative diseases.

Vascular Heparan Sulfate and Amyloid-ß in Alzheimer's Disease Patients.

Alzheimer's disease (AD) is a debilitating neurodegenerative disease characterized by the accumulation of extracellular amyloid-ß peptides (Aß) within the cerebral parenchyma and vasculature, which is known as cerebral amyloid angiopathy (CAA). This study utilized confocal imaging to investigate heparan sulfate (HS) expression within the cerebrovasculature and its associations with Aß, gender, and ApoE4 genotype in AD. Our investigation revealed elevated levels of HS in the cerebrovasculature of AD patients with severe CAA. Additionally, these patients exhibited higher HS colocalization with Aß in the cerebrovasculature, including both endothelial and vascular smooth muscle cell compartments. Intriguingly, a reversal in the polarized expression of HS within the cerebrovasculature was detected in AD patients with severe CAA. Furthermore, male patients exhibited lower levels of both parenchymal and cerebrovascular HS. Additionally, ApoE4 carriers displayed heightened cerebrovascular Aß expression and a tendency of elevated cerebrovascular HS levels in AD patients with severe CAA. Overall, these findings reveal potential intricate interplay between HS, Aß, ApoE, and vascular pathology in AD, thereby underscoring the potential roles of cerebrovascular HS in CAA development and AD pathology. Further study of the underlying mechanisms may present novel therapeutic avenues for AD treatment.

Lower GLUT1 and unchanged MCT1 in Alzheimer's disease cerebrovasculature.

The brain is a highly demanding organ, utilizing mainly glucose but also ketone bodies as sources of energy. Glucose transporter-1 (GLUT1) and monocarboxylates transporter-1 (MCT1) respectively transport glucose and ketone bodies across the blood-brain barrier. While reduced glucose uptake by the brain is one of the earliest signs of Alzheimer's disease (AD), no change in the uptake of ketone bodies has been evidenced yet. To probe for changes in GLUT1 and MCT1, we performed Western immunoblotting in microvessel extracts from the parietal cortex of 60 participants of the Religious Orders Study. Participants clinically diagnosed with AD had lower cerebrovascular levels of GLUT1, whereas MCT1 remained unchanged. GLUT1 reduction was associated with lower cognitive scores. No such association was found for MCT1. GLUT1 was inversely correlated with neuritic plaques and cerebrovascular ß-secretase-derived fragment levels. No other significant associations were found between both transporters, markers of Aß and tau pathologies, sex, age at death or apolipoprotein-ε4 genotype. These results suggest that, while a deficit of GLUT1 may underlie the reduced transport of glucose to the brain in AD, no such impairment occurs for MCT1. This study thus supports the exploration of ketone bodies as an alternative energy source for the aging brain.

Circulating small extracellular vesicles mediate vascular hyperpermeability in diabetes.

AIMS/HYPOTHESIS: A hallmark chronic complication of type 2 diabetes mellitus is vascular hyperpermeability, which encompasses dysfunction of the cerebrovascular endothelium and the subsequent development of associated cognitive impairment. The present study tested the hypothesis that during type 2 diabetes circulating small extracellular vesicles (sEVs) exhibit phenotypic changes that facilitate pathogenic disruption of the vascular barrier. METHODS: sEVs isolated from the plasma of a mouse model of type 2 diabetes and from diabetic human individuals were characterised for their ability to disrupt the endothelial cell (EC) barrier. The contents of sEVs and their effect on recipient ECs were assessed by proteomics and identified pathways were functionally interrogated with small molecule inhibitors. RESULTS: Using intravital imaging, we found that diabetic mice (Leprdb/db) displayed hyperpermeability of the cerebrovasculature. Enhanced vascular leakiness was recapitulated following i.v. injection of sEVs from diabetic mice into non-diabetic recipient mice. Characterisation of circulating sEV populations from the plasma of diabetic mice and humans demonstrated increased quantity and size of sEVs compared with those isolated from non-diabetic counterparts. Functional experiments revealed that sEVs from diabetic mice or humans induced the rapid and sustained disruption of the EC barrier through enhanced paracellular and transcellular leak but did not induce inflammation. Subsequent sEV proteome and recipient EC phospho-proteome analysis suggested that extracellular vesicles (sEVs) from diabetic mice and humans modulate the MAPK/MAPK kinase (MEK) and Rho-associated protein kinase (ROCK) pathways, cell-cell junctions and actin dynamics. This was confirmed experimentally. Treatment of sEVs with proteinase K or pre-treatment of recipient cells with MEK or ROCK inhibitors reduced the hyperpermeability-inducing effects of circulating sEVs in the diabetic state. CONCLUSIONS/INTERPRETATION: Diabetes is associated with marked increases in the concentration and size of circulating sEVs. The modulation of sEV-associated proteins under diabetic conditions can induce vascular leak through activation of the MEK/ROCK pathway. These data identify a new paradigm by which diabetes can induce hyperpermeability and dysfunction of the cerebrovasculature and may implicate sEVs in the pathogenesis of cognitive decline during type 2 diabetes.

Proteomic Changes in the Human Cerebrovasculature in Alzheimer's Disease and Related Tauopathies Linked to Peripheral Biomarkers in Plasma and Cerebrospinal Fluid.

Dysfunction of the neurovascular unit stands as a significant pathological hallmark of Alzheimer's disease (AD) and age-related neurodegenerative diseases. Nevertheless, detecting vascular changes in the brain within bulk tissues has proven challenging, limiting our ability to characterize proteomic alterations from less abundant cell types. To address this challenge, we conducted quantitative proteomic analyses on both bulk brain tissues and cerebrovascular-enriched fractions from the same individuals, encompassing cognitively unimpaired control, progressive supranuclear palsy (PSP), and AD cases. Protein co-expression network analysis identified modules unique to the cerebrovascular fractions, specifically enriched with pericytes, endothelial cells, and smooth muscle cells. Many of these modules also exhibited significant correlations with amyloid plaques, cerebral amyloid angiopathy (CAA), and/or tau pathology in the brain. Notably, the protein products within AD genetic risk loci were found concentrated within modules unique to the vascular fractions, consistent with a role of cerebrovascular deficits in the etiology of AD. To prioritize peripheral AD biomarkers associated with vascular dysfunction, we assessed the overlap between differentially abundant proteins in AD cerebrospinal fluid (CSF) and plasma with a vascular-enriched network modules in the brain. This analysis highlighted matrisome proteins, SMOC1 and SMOC2, as being increased in CSF, plasma, and brain. Immunohistochemical analysis revealed SMOC1 deposition in both parenchymal plaques and CAA in the AD brain, whereas SMOC2 was predominantly localized to CAA. Collectively, these findings significantly enhance our understanding of the involvement of cerebrovascular abnormalities in AD, shedding light on potential biomarkers and molecular pathways associated with CAA and vascular dysfunction in neurodegenerative diseases.

Mild traumatic brain injury induces pericyte detachment independent of stroke vulnerability.

Mild traumatic brain injury (mTBI) is an independent risk factor for ischemic stroke and can result in poorer outcomes- an effect presumed to involve the cerebral vasculature. Here we tested the hypothesis that mTBI-induced pericyte detachment from the cerebrovascular endothelium is responsible for worsened stroke outcomes. We performed a mild closed-head injury and/or treated C57/bl6 mice with imatinib mesylate, a tyrosine kinase inhibitor that induces pericyte detachment. The time course of pericyte detachment was assessed 7, 14, and 28 days post injury (DPI). To test the role of pericytes in TBI-induced exacerbation of ischemic stroke outcomes, we induced mTBI and/or treated mice with imatinib for one week prior to transient middle cerebral artery occlusion. We found that injury promoted pericyte detachment from the vasculature commensurate with the levels of detachment seen in imatinib-only treated animals, and that the detachment persisted for at least 14DPI, but recovered to sham levels by 28DPI. Further, mTBI, but not imatinib-induced pericyte detachment, increased infarct volume. Thus, we conclude that the transient detachment of pericytes caused by mTBI may not be sufficient to exacerbate subsequent ischemic stroke damage. These data have important implications for understanding cerebrovascular dysfunction following mTBI and potential mechanisms of increased risk for future ischemic strokes.

SARS-CoV-2 Spike Protein Intensifies Cerebrovascular Complications in Diabetic hACE2 Mice through RAAS and TLR Signaling Activation.

Diabetics are more vulnerable to SARS-CoV-2 neurological manifestations. The molecular mechanisms of SARS-CoV-2-induced cerebrovascular dysfunction in diabetes are unclear. We hypothesize that SARS-CoV-2 exacerbates diabetes-induced cerebrovascular oxidative stress and inflammation via activation of the destructive arm of the renin-angiotensin-aldosterone system (RAAS) and Toll-like receptor (TLR) signaling. SARS-CoV-2 spike protein was injected in humanized ACE2 transgenic knock-in mice. Cognitive functions, cerebral blood flow, cerebrovascular architecture, RAAS, and TLR signaling were used to determine the effect of SARS-CoV-2 spike protein in diabetes. Studies were mirrored in vitro using human brain microvascular endothelial cells treated with high glucose-conditioned media to mimic diabetic conditions. Spike protein exacerbated diabetes-induced cerebrovascular oxidative stress, inflammation, and endothelial cell death resulting in an increase in vascular rarefaction and diminished cerebral blood flow. SARS-CoV-2 spike protein worsened cognitive dysfunction in diabetes compared to control mice. Spike protein enhanced the destructive RAAS arm at the expense of the RAAS protective arm. In parallel, spike protein significantly exacerbated TLR signaling in diabetes, aggravating inflammation and cellular apoptosis vicious circle. Our study illustrated that SAR-CoV-2 spike protein intensified RAAS and TLR signaling in diabetes, increasing cerebrovascular damage and cognitive dysfunction.

Time-efficient, high-resistance inspiratory muscle strength training increases cerebrovascular reactivity in midlife and older adults.

Aging is associated with increased risk for cognitive decline and dementia due in part to increases in systolic blood pressure (SBP) and cerebrovascular dysfunction. High-resistance inspiratory muscle strength training (IMST) is a time-efficient, intensive respiratory training protocol (30 resisted inspirations/day) that lowers SBP and improves peripheral vascular function in midlife/older adults with above-normal SBP. However, whether, and by what mechanisms, IMST can improve cerebrovascular function is unknown. We hypothesized that IMST would increase cerebrovascular reactivity to hypercapnia (CVR to CO2), which would coincide with changes to the plasma milieu that improve brain endothelial cell function and enhance cognitive performance (NIH Toolbox). We conducted a 6-wk double-blind, randomized, controlled clinical trial investigating high-resistance IMST [75% maximal inspiratory pressure (PImax); 6×/wk; 4 females, 5 males] vs. low-resistance sham training (15% PImax; 6×/wk; 2 females, 5 males) in midlife/older adults (age 50-79 yr) with initial above-normal SBP. Human brain endothelial cells (HBECs) were exposed to participant plasma and assessed for acetylcholine-stimulated nitric oxide (NO) production. CVR to CO2 increased after high-resistance IMST (pre: 1.38 ± 0.66 cm/s/mmHg; post: 2.31 ± 1.02 cm/s/mmHg, P = 0.020). Acetylcholine-stimulated NO production increased in HBECs exposed to plasma from after vs. before the IMST intervention [pre: 1.49 ± 0.33; post: 1.73 ± 0.35 arbitrary units (AU); P < 0.001]. Episodic memory increased modestly after the IMST intervention (pre: 95 ± 13; post: 103 ± 17 AU; P = 0.045). Cerebrovascular and cognitive function were unchanged in the sham control group. High-resistance IMST may be a promising strategy to improve cerebrovascular and cognitive function in midlife/older adults with above-normal SBP, a population at risk for future cognitive decline and dementia.NEW & NOTEWORTHY Midlife/older adults with above-normal blood pressure are at increased risk of developing cognitive decline and dementia. Our findings suggest that high-resistance inspiratory muscle strength training (IMST), a novel, time-efficient (5-10 min/day) form of physical training, may increase cerebrovascular reactivity to CO2 and episodic memory in midlife/older adults with initial above-normal blood pressure.

Pericyte dysfunction is a key mediator of the risk of cerebral ischemia.

Pericytes are critical yet understudied cells that are a central component of the neurovascular unit. They are connected to the cerebrovascular endothelium and help control vascular contractility and maintain the blood-brain barrier. Pericyte dysfunction has the potential to mediate many of the deleterious vascular consequences of ischemic stroke. Current therapeutics are designed to be administered after stroke onset and limit damage, but there are few options to target vascular risk factors pre-ischemia which likely contribute to stroke outcomes. Here, we focus on the role of pericytes in health and disease, and discuss how pericyte dysfunction can increase the risk of ischemic injury. Additionally, we note that despite the importance of pericytes in cerebrovascular disease, there are relatively few current therapeutic options that target pericyte function.

Differential effect of gold nanoparticles on cerebrovascular function and biomechanical properties.

Human stroke serum (HSS) has been shown to impair cerebrovascular function, likely by factors released into the circulation after ischemia. 20 nm gold nanoparticles (GNPs) have demonstrated anti-inflammatory properties, with evidence that they decrease pathologic markers of ischemic severity. Whether GNPs affect cerebrovascular function, and potentially protect against the damaging effects of HSS on the cerebral circulation remains unclear. HSS obtained 24 h poststroke was perfused through the lumen of isolated and pressurized third-order posterior cerebral arteries (PCAs) from male Wistar rats with and without GNPs (~2 × 109 GNP/ml), or GNPs in vehicle, in an arteriograph chamber (n = 8/group). All vessels were myogenically reactive ≥60 mmHg intravascular pressure; however, vessels containing GNPs had significantly less myogenic tone. GNPs increased vasoreactivity to small and intermediate conductance calcium activated potassium channel activation via NS309; however, reduced vasoconstriction to nitric oxide synthase inhibition. Hydraulic conductivity and transvascular filtration, were decreased by GNPs, suggesting a protective effect on the blood-brain barrier. The stress-strain curves of PCAs exposed to GNPs were shifted leftward, indicating increased vessel stiffness. This study provides the first evidence that GNPs affect the structure and function of the cerebrovasculature, which may be important for their development and use in biomedical applications.

Cortical cerebrovascular and metabolic perturbations in the 5xFAD mouse model of Alzheimer's disease.

Introduction: The 5xFAD mouse is a popular model of familial Alzheimer's disease (AD) that is characterized by early beta-amyloid (Aß) deposition and cognitive decrements. Despite numerous studies, the 5xFAD mouse has not been comprehensively phenotyped for vascular and metabolic perturbations over its lifespan. Methods: Male and female 5xFAD and wild type (WT) littermates underwent in vivo 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging at 4, 6, and 12 months of age to assess regional glucose metabolism. A separate cohort of mice (4, 8, 12 months) underwent "vessel painting" which labels all cerebral vessels and were analyzed for vascular characteristics such as vessel density, junction density, vessel length, network complexity, number of collaterals, and vessel diameter. Results: With increasing age, vessels on the cortical surface in both 5xFAD and WT mice showed increased vessel length, vessel and junction densities. The number of collateral vessels between the middle cerebral artery (MCA) and the anterior and posterior cerebral arteries decreased with age but collateral diameters were significantly increased only in 5xFAD mice. MCA total vessel length and junction density were decreased in 5xFAD mice compared to WT at 4 months. Analysis of 18F-FDG cortical uptake revealed significant differences between WT and 5xFAD mice spanning 4-12 months. Broadly, 5xFAD males had significantly increased 18F-FDG uptake at 12 months compared to WT mice. In most cortical regions, female 5xFAD mice had reduced 18F-FDG uptake compared to WT across their lifespan. Discussion: While the 5xFAD mouse exhibits AD-like cognitive deficits as early as 4 months of age that are associated with increasing Aß deposition, we only found significant differences in cortical vascular features in males, not in females. Interestingly, 5xFAD male and female mice exhibited opposite effects in 18F-FDG uptake. The MCA supplies blood to large portions of the somatosensory cortex and portions of motor and visual cortex and increased vessel length alongside decreased collaterals which coincided with higher metabolic rates in 5xFAD mice. Thus, a potential mismatch between metabolic demand and vascular delivery of nutrients in the face of increasing Aß deposition could contribute to the progressive cognitive deficits seen in the 5xFAD mouse model.

Chronic social defeat alters brain vascular-associated cell gene expression patterns leading to vascular dysfunction and immune system activation.

Brain vascular integrity is critical for brain health, and its disruption is implicated in many brain pathologies, including psychiatric disorders. Brain-vascular barriers are a complex cellular landscape composed of endothelial, glial, mural, and immune cells. Yet currently, little is known about these brain vascular-associated cells (BVACs) in health and disease. Previously, we demonstrated that 14 days of chronic social defeat (CSD), a mouse paradigm that produces anxiety and depressive-like behaviors, causes cerebrovascular damage in the form of scattered microbleeds. Here, we developed a technique to isolate barrier-related cells from the mouse brain and subjected the isolated cells to single-cell RNA sequencing. Using this isolation technique, we found an enrichment in BVAC populations, including distinct subsets of endothelial and microglial cells. In CSD compared to non-stress, home-cage control, differential gene expression patterns disclosed biological pathways involving vascular dysfunction, vascular healing, and immune system activation. Overall, our work demonstrates a unique technique to study BVAC populations from fresh brain tissue and suggests that neurovascular dysfunction is a key driver of psychosocial stress-induced brain pathology.

Aging drives cerebrovascular network remodeling and functional changes in the mouse brain.

Aging is the largest risk factor for neurodegenerative disorders, and commonly associated with compromised cerebrovasculature and pericytes. However, we do not know how normal aging differentially impacts the vascular structure and function in different brain areas. Here we utilize mesoscale microscopy methods (serial two-photon tomography and light sheet microscopy) and in vivo imaging (wide field optical spectroscopy and two-photon imaging) to determine detailed changes in aged cerebrovascular networks. Whole-brain vascular tracing showed an overall ~10% decrease in vascular length and branching density, and light sheet imaging with 3D immunolabeling revealed increased arteriole tortuosity in aged brains. Vasculature and pericyte densities showed significant reductions in the deep cortical layers, hippocampal network, and basal forebrain areas. Moreover, in vivo imaging in awake mice identified delays in neurovascular coupling and disrupted blood oxygenation. Collectively, we uncover regional vulnerabilities of cerebrovascular network and physiological changes that can mediate cognitive decline in normal aging.

Cerebrovascular super-resolution 4D Flow MRI - Sequential combination of resolution enhancement by deep learning and physics-informed image processing to non-invasively quantify intracranial velocity, flow, and relative pressure.

The development of cerebrovascular disease is tightly coupled to regional changes in intracranial flow and relative pressure. Image-based assessment using phase contrast magnetic resonance imaging has particular promise for non-invasive full-field mapping of cerebrovascular hemodynamics. However, estimations are complicated by the narrow and tortuous intracranial vasculature, with accurate image-based quantification directly dependent on sufficient spatial resolution. Further, extended scan times are required for high-resolution acquisitions, and most clinical acquisitions are performed at comparably low resolution (>1 mm) where biases have been observed with regard to the quantification of both flow and relative pressure. The aim of our study was to develop an approach for quantitative intracranial super-resolution 4D Flow MRI, with effective resolution enhancement achieved by a dedicated deep residual network, and with accurate quantification of functional relative pressures achieved by subsequent physics-informed image processing. To achieve this, our two-step approach was trained and validated in a patient-specific in-silico cohort, showing good accuracy in estimating velocity (relative error: 15.0 ± 0.1%, mean absolute error (MAE): 0.07 ± 0.06 m/s, and cosine similarity: 0.99 ± 0.06 at peak velocity) and flow (relative error: 6.6 ± 4.7%, root mean square error (RMSE): 0.56 mL/s at peak flow), and with the coupled physics-informed image analysis allowing for maintained recovery of functional relative pressure throughout the circle of Willis (relative error: 11.0 ± 7.3%, RMSE: 0.3 ± 0.2 mmHg). Furthermore, the quantitative super-resolution approach is applied to an in-vivo volunteer cohort, effectively generating intracranial flow images at <0.5 mm resolution and showing reduced low-resolution bias in relative pressure estimation. Our work thus presents a promising two-step approach to non-invasively quantify cerebrovascular hemodynamics, being applicable to dedicated clinical cohorts in the future.

Therapeutic effect of human ApoA-I-Milano variant in aged transgenic mouse model of Alzheimer's disease.

BACKGROUND AND PURPOSE: Therapies based on apolipoprotein A-I (ApoA-I), classically tested for cardiovascular diseases, were recently proposed for Alzheimer's disease (AD). Based on a drug reprofiling approach, our objective was to explore the use of a natural variant of ApoA-I form, ApoA-I-Milano (M), as a treatment for AD. ApoA-I-M contains the R173C mutation, and confers protection against atherosclerosis development, although ApoA-I-M carriers exhibit low HDL levels. EXPERIMENTAL APPROACH: Middle-aged (12-month-old) and aged (21-month-old) APP23 mice were intraperitoneally treated for 10 weeks with human recombinant ApoA-I-M (hrApoA-I-M) protein or saline. Pathology progression through behavioural parameters and biochemical determinations was evaluated. KEY RESULTS: In middle-aged group, hrApoA-I-M treatment reduced the anxiety behaviour associated with this AD model. In aged mice, hrApoA-I-M reversed T-Maze performance alterations, a cognitive improvement accompanied by neuronal loss recovery in the dentate gyrus. Aged mice treated with hrApoA-I-M showed lower brain Aß40 soluble levels and elevated Aß40 levels in cerebrospinal fluid, without modifying insoluble brain Aß burden. Interestingly, hrApoA-I-M sub-chronic treatment induced a molecular effect on the cerebrovasculature, increasing occludin expression and ICAM-1 presence, as well as promoting an elevation of plasma soluble RAGE in all hrApoA-I-M-treated mice, drastically decreasing the AGEs/sRAGE ratio, a marker of endothelial damage. CONCLUSION AND IMPLICATIONS: Peripheral hrApoA-I-M treatment shows a beneficial impact on working memory, involving mechanisms related with brain Aß mobilization and modulation of the levels of cerebrovascular markers. Our study shows the potential therapeutic applicability of a safe and non-invasive treatment based on peripheral administration of hrApoA-I-M in AD.