Brain Barrier Function Research Articles

Abstract TP312: Pharmacologically Reducing Acetylated Tau Prevents Traumatic Brain Injury-Induced Acceleration of Alzheimer’s Disease

Traumatic brain injury (TBI) afflicts 70 million people worldwide annually and is the 3rd overall risk factor for developing Alzheimer's disease (AD), behind genetics and aging. In patients with AD, a history of TBI is associated with a 3-4 year earlier onset of cognitive impairment. TBI and AD share many pathologies, including blood brain barrier dysfunction, neuroinflammation, and protein aggregation. Yet, the underlying mechanism of this relationship is not understood, and there are no treatments that protect patients from accelerated AD after TBI. We recently reported that tau, a microtubule binding protein essential for neuronal health, is acetylated after TBI. Acetylation impairs tau binding to microtubules, leading to its mis-localization into the cell soma and pathological aggregation. Acetylated tau is also elevated early in AD, and acetylated tau was significantly more elevated in the brains of human AD subjects with a history of TBI, compared to AD alone and healthy controls. Therefore, we hypothesize that TBI-induced tau acetylation drives the acceleration of AD. To study this phenomenon, we developed a mouse model of TBI that accelerates AD-like pathology and cognitive impairment in 5xFAD mice, and amyloid-driven AD model. Our unique model of multimodal TBI produces a complex and reproducible brain injury with neurodegeneration and neurobehavioral impairment, beginning with acute axonal degeneration and persisting chronically with blood-brain barrier degradation and nerve cell death. This model of TBI also produces the same systemic metabolic alterations that are reported in TBI patients. TBI causes learning deficits in young 5xFAD mice that are not seen in either sham-injured 5xFAD mice or in wild type littermates subjected to TBI. TBI also accelerates amyloid deposition in 5xFAD mice. We hypothesize that TBI will also worsen blood brain barrier function in 5xFAD mice. Importantly, 5xFAD mice show greater elevation of acetylated tau after TBI, compared to WT mice. Preliminary data suggests that treatment with the FDA-approved non-steroidal inflammatory drug diflunisal, which inhibits the enzyme that acetylates tau, reduces acetylated tau and rescues behavior deficits after TBI in 5xFAD mice.

Fecal microbiota transplantation alleviates cognitive impairment by improving gut microbiome composition and barrier function in male rats of traumatic brain injury following gas explosion.

Dysbiosis of gut microbiota (GM) is intricately linked with cognitive impairment and the incidence of traumatic brain injury (TBI) in both animal models and human subjects. However, there is limited understanding of the impact and mechanisms of fecal microbiota transplantation (FMT) on brain and gut barrier function in the treatment of TBI induced by gas explosion (GE). We have employed FMT technology to establish models of gut microbiota dysbiosis in male rats, and subsequently conducted non-targeted metabolomics and microbiota diversity analysis to explore the bacteria with potential functional roles. Hematoxylin-eosin and transmission electron microscopy revealed that GE induced significant pathological damage and inflammation responses, as well as varying degrees of mitochondrial impairment in neuronal cells in the brains of rats, which was associated with cognitive decline. Furthermore, GE markedly elevated the levels of regulatory T cell (Tregs)-related factors interleukin-10, programmed death 1, and fork head box protein P3 in the brains of rats. Similar changes in these indicators were also observed in the colon; however, these alterations were reversed upon transfer of normal flora into the GE-exposed rats. Combined microbiome and metabolome analysis indicated up-regulation of Clostridium_T and Allobaculum, along with activation of fatty acid biosynthesis after FMT. Correlation network analysis indirectly suggested a causal relationship between FMT and alleviation of GE-induced TBI. FMT improved intestinal structure and up-regulated expression of tight junction proteins Claudin-1, Occludin, and ZO-1, potentially contributing to its protective effects on both brain and gut. Transplantation of gut microbiota from healthy rats significantly enhanced cognitive function in male rats with traumatic brain injury caused by a gas explosion, through the modulation of gut microbiome composition and the improvement of both gut and brain barrier integrity via the gut-brain axis. These findings may offer a scientific foundation for potential clinical interventions targeting gas explosion-induced TBI using FMT.

Aging Deteriorates Blood Brain Barrier Function and Polarizes Adaptive T Cell Expansion Contributing to Neurocognitive Damage in Experimental Cirrhosis.

Cirrhosis incidence is significantly increased with age and frequently complicated with neurocognitive dysfunction. We have evaluated the contribution of aging to neuroinflammation in the liver-brain axis in advanced chronic liver disease. Young (6-week-old) and old (9-month-old) mice were included in a 12-week protocol of CCl4-induced cirrhosis. Liver damage, neuromotor and cognitive capacities, blood brain barrier integrity and function, liver and brain T cell subpopulations and ammonia levels were evaluated. Timp1 and Acta2 gene expression was upregulated in old cirrhotic mice. Increased liver damage was confirmed histologically by Sirius red staining, expression of alpha-SMA, collagen 1-alpha1 and vimentin in aged CCl4-treated mice. Aging further compromised the neuromotor and cognition capabilities in cirrhotic animals. Stress axis components Crh and its receptor Nr3c1 gene expression levels were upregulated in the paraventricular nucleus and hippocampus of old cirrhotic mice. CCl4-damage significantly increased ammonia levels in the liver, brain and serum of cirrhotic mice. Circulating ammonia was significantly higher in old cirrhotic mice. Significant correlations were established between brain ammonia, neuromotor capabilities and results on the object recognition tests. A decreased integrity of blood brain barrier was accompanied by astrocyte activation and increased apoptosis-linked cleaved Caspase 3 in old cirrhotic mice. Liver resident CD4+ T-cell subpopulations were contracted in cirrhosis, although they showed a pro-inflammatory Th17 profile. Liver and brain resident CD8+ T-cell subpopulations were expanded in old cirrhotic animals, along with reduced tissue cytolytic activity. CD8+ T cell expansion and reduced perforin levels in the brain correlated with neuromotor and cognitive dysfunction. In conclusion, aging aggravates liver fibrosis, worsens neuromotor and cognitive functions and shifts liver and brain adaptive T cell profiles compromising the BBB integrity in experimental advanced chronic liver disease. Results strengthen the impact of aging in the liver-brain axis and neuroinflammation in cirrhosis.

P155: Circadian Rhythms and Alzheimer's Disease

Introduction:Major neurocognitive disorder (or simply Dementia) is one of the main causes of disability and burden disease to caregivers and the health system, and a frequent cause of mortality worldwide. Alzheimer`s disease (AD) is the most common type (60-70%).AD is a progressive neurodegenerative disorder characterized by amyloid-β (Aβ) deposition, causing neuronal and synaptic loss with subsequent cognitive disfunction.There is cumulating evidence that sleep disturbances are associated with several pathological conditions, and AD is one of these. The prevalence and severity of sleep disorders is significant in AD patients, with sleep disturbances often precede its clinical diagnosis in many years. Some studies focus on possible mechanisms by which (abnormal) sleep participate in AD pathogenesis, and concluded individuals with sleep disturbances are at higher risk of developing dementia.Objectives:To highlight the current evidence on whether sleep disorders could precipitate or accelerate the clinical course of AD.Methods:Non-systematic review about sleep abnormalities and AD pathogenesis.Results:Several authors described a two-way relationship between sleep and amyloid pathology - sleep deprivation would lead to increased production and decreased clearance of Aβ; once Aβ is accumulated it results in more disrupted sleep, with an increase of Aβ production during wakefulness and a decrease of its clearance during sleep.Recent data showed that sleep continuity and architecture (decreased total sleep time, slow-wave sleep, and REM sleep) are disturbed in AD patients.Otherwise, sleep deprivation may be associated with decreased glymphatic system clearance, leading to accumulation of neurotoxic proteins, particularly Aβ (and tau). It`s also associated with proinflammatory states due to accumulation of reactive oxygen species, nucleotides and proteins during wakefulness, which leads to immune response that causes neuronal dysfunction and cellular death. Insomnia and sleep deprivation were also associated with activation of complement pathway and immunoglobulins secretion. Many studies suggest chronic sleep disruption changes blood–brain barrier structure and function leading to Aβ accumulation.Conclusions:There is emerging evidence that points sleep disturbances as both a potential marker for AD pathology and risk predictor of developing the disease. Future investigations should evaluate the relationship between specific sleep disorders and AD physiopathology.

Neural responses to peripheral infection in Alzheimer’s disease model mice

AbstractBackgroundClinical and animal studies have suggested that peripheral inflammation affects the central nervous system (CNS) and may be a major factor in the pathophysiology of neurodegenerative diseases like AD. Furthermore, a variety of signaling factors originating in the periphery, such as inflammatory mediators, have been associated with the regulation of brain barrier functions. Here, we hypothesized that the presence of peripheral inflammation dysregulates brain barriers’ integrity and induces neuroinflammation with consequences on amyloid pathology.MethodIn this study, we employed an AD mouse model nasally infected with Staphylococcus aureus to assess the impact of chronic or acute peripheral inflammation on brain transcriptome and amyloid pathology. We utilized both single cell and Spatial Transcriptomics to better determine transcriptional response to peripheral inflammation.ResultThe chronic exposure increased the diffuse and compact amyloid plaques and blood cytokine levels. Following a short‐term exposure, single‐cell and spatial transcriptomics uncovered cell type‐ and spatial‐specific transcriptional changes indicating a dysregulation of the brain barriers, including the blood‐brain and the blood‐cerebrospinal fluid barriers. Brain macrophages exhibited increased Apoe expression and macrophage‐specific genes were upregulated at ventricular areas of infected mice. In addition, we report an increase of disease associated microglia genes around the Ab plaques, together with disbalances in neuronal expression in response to peripheral inflammation.ConclusionWe observed that low‐grade peripheral infection triggers transcriptional responses linked to brain barriers and brain infiltrated/resident macrophages indicate a fundamental importance of them in the mechanisms linking peripheral inflammation and AD pathogenesis. Finally, we showed that bacterial infection caused molecular changes restricted to specific cell types and/or brain spatial microenvironments, which highlights the relevance of studying brain molecular responses with high resolution in order to have new insights on AD etiology.

Increase in Matrix Metaloproteinase‐10 is associated with tau, neurodegeneration and reduced brain perfusion in the right temporal lobe

AbstractBackgroundBlood brain barrier dysfunction amplifies neuroinflammation, which may drive Alzheimer’s Dementia (AD) pathology. Regional cerebral blood flow (RCBF), measured by HMPAO SPECT, is an established biomarker for AD diagnosis. Matrix Metalloproteinase‐10 (MMP‐10), an enzyme involved in blood brain barrier function through regulating the breakdown of extracellular matrix, was recently proposed as a biomarker of progression to AD. In this study, we examine the relationship between RCBF and levels of MMP‐10 in the cerebrospinal fluid (CSF).Materials and MethodsDatasets of 91 participants from a heterogenous clinical cohort, investigated for dementia due to cognitive complaints were analysed. CSF levels of MMP‐10 were measured using the OLINK proximity extension array platform. HMPAO SPECT scans were analysed using Statistical Parametric Mapping (SPM). A univariate linear regression model was used in SPM to quantify the impact of MMP‐10 changes on brain perfusion.ResultsSPM results showed that higher levels of MMP‐10 in CSF are associated with significant reduction in RCBF (family‐wise error corrected p<0.05). The neuroimaging signature of changes in RCBF with increasing MMP‐10 is outlined in Figure 1. The main cluster of reduction in perfusion is on the right temporal lobe with an additional cluster on the right medial frontal lobe.ConclusionIncreased levels of MMP‐10 in CSF have been associated with blood brain barrier vulnerability and faster cognitive decline in AD. Here we identified a right sided neuroimaging signature in RCBF with increasing levels MMP‐10. This may indicate that by the time of symptoms onset the right side is the fastest progressing as it is catching up with the left side. Right sided changes have been previously associated with delusions, disinhibition and irritability in AD and linked with increased carer burden. The significant reduction in RCBF of the right temporal lobe identified in our study, further reinforces a role for MMP‐10 as a marker of progression to AD.Acknowledgement: Dr Sofia Michopoulou, is funded through an Integrated Clinical Academic Lectureship by Health Education England (HEE) / NIHR for this research project (NIHR301287). The views expressed in this publication are those of the authors.

Closing the sex/gender gap in dementia: homing in on the vasculature (in vitro/iPSCs)

AbstractInduced pluripotent stem cell (iPSC) models are increasingly being used to model the blood brain barrier (BBB) and to examine the contributions of genetic risk factors to neurovascular disease. While clinical and rodent studies clearly demonstrate the importance of sex in vascular‐related neurodegeneration, only a handful of published studies have thus far begun to employ iPSC modeling to examine the biology that underlies these sex‐related differences. Early reports suggested that female iPSC‐derived brain microvascular endothelial cells (BMECs) exhibit increased transendothelial electrical resistance (TEER) and thus decreased permeability than male BMEC counterparts. Conversely, male pluripotent cells were found to differentiate more readily into BMECs. However, these initial studies were often underpowered and failed to account for the considerable variability inherent between iPSC lines. More recently, consortiums have begun to generate and examine BMECs and glia from a large number of subjects with various neurodegenerative diseases. While much of this work is currently unpublished, these large‐scale datasets further support the concept that sex alters the transcriptome and function of BMECs and vascular‐associated glia. The development and use of ‘isogenic’ male and female iPSC lines derived from Klinefelter syndrome subjects is providing another powerful new approach to study sex‐dependent effects on cellular function. Both the complexity and utility of in vitro iPSC‐modeling of brain vasculature continues to improve and now includes both bioengineered vascular networks and vascularized organoids. In addition, recent progress with xenotransplantation models is providing further avenues to study the interactions between human glial, blood brain barrier function, and cerebral amyloid angiopathy. Nevertheless, there remains a pressing need to further examine and understand both the intrinsic and extrinsic effects of sex on BBB function and vascular‐related neurodegenerative disease, a topic that will be extensively discussed during this AAIC perspectives panel.

Brain Endothelial Cells as Potential Therapeutic Targets in Neurological Diseases

Brain homeostasis highly depends on Blood Brain Barrier (BBB) function and integrity. BBB displays some changes as individuals age, and brain endothelium damage has a key role in the pathology of neurological diseases such as ischemic stroke and neurodegenerative disorders

Pericytes are protective in experimental pneumococcal meningitis through regulating leukocyte infiltration and blood–brain barrier function

BackgroundBrain pericytes participate in the regulation of cerebral blood flow and the maintenance of blood–brain barrier integrity. Because of their perivascular localization, their receptor repertoire, and their potential ability to respond to inflammatory and infectious stimuli by producing various cytokines and chemokines, these cells are also thought to play an active role in the immune response to brain infections. This assumption is mainly supported by in vitro studies, investigations in in vivo disease models are largely missing. Here, we analysed the role of brain pericytes in pneumococcal meningitis, in vitro and in vivo in two animal models of pneumococcal meningitis.MethodsPrimary murine and human pericytes were stimulated with increasing concentrations of different serotypes of Streptococcus pneumoniae in the presence or absence of Toll-like receptor inhibitors and their cell viability and cytokine production were monitored. To gain insight into the role of pericytes in brain infection in vivo, we performed studies in a zebrafish embryo model of pneumococcal meningitis in which pericytes were pharmacologically depleted. Furthermore, we analyzed the impact of genetically induced pericyte ablation on disease progression, intracranial complications, and brain inflammation in an adult mouse model of this disease.ResultsBoth murine and human pericytes reacted to pneumococcal exposure with the release of selected cytokines. This cytokine release is pneumolysin-dependent, TLR-dependent in murine (but not human) pericytes and can be significantly increased by macrophage-derived IL-1b. Pharmacological depletion of pericytes in zebrafish embryos resulted in increased cerebral edema and mortality due to pneumococcal meningitis. Correspondingly, in an adult mouse meningitis model, a more pronounced blood–brain barrier disruption and leukocyte infiltration, resulting in an unfavorable disease course, was observed following genetic pericyte ablation. The degree of leukocyte infiltration positively correlated with an upregulation of chemokine expression in the brains of pericyte-depleted mice.ConclusionsOur findings show that pericytes play a protective role in pneumococcal meningitis by impeding leukocyte migration and preventing blood–brain barrier breaching. Thus, preserving the integrity of the pericyte population has the potential as a new therapeutic strategy in pneumococcal meningitis.

Pericyte loss impairs the blood–brain barrier and cognitive function in aged mice after anesthesia/surgery

AimsThis study was designed to investigate the role of pericytes in the pathogenesis of perioperative neurocognitive disorder (PND). MethodsIn this study, we established a PND model via sevoflurane anesthesia and tibial fracture surgery in 2-month-old and 16-month-old male C57BL/6 mice. On the third postoperative day, the mice were subjected to behavioral testing or sacrificed to collect brain tissue. The progression of hippocampal blood–brain barrier (BBB) disruption and neuroinflammation was detected using transmission electron microscope and immunofluorescence. We also used western blotting to measure the levels of plasma-derived protein immunoglobulin G (IgG) and albumin in the hippocampus to assess the leakage of the BBB. ResultsAged mice did not experience age-related cognitive decline and BBB disruption compared with younger mice but only increased glial cell activity. Anesthesia/Surgery damaged cognitive function, reduced pericyte coverage, decreased the length of capillaries and levels of occludin and claudin-5, destroyed the structure of the BBB, exacerbated IgG and albumin accumulation in the hippocampus, and enhanced the activation of microglia and astrocytes in the hippocampus of aged mice. However, these negative effects did not occur in young mice. ConclusionOur study showed that the loss of pericytes led to increased BBB permeability and neuroinflammation after anesthesia/surgery in aged mice, ultimately resulting in cognitive dysfunction.

Characterizing the blood-brain barrier and gut barrier with super-resolution imaging: opportunities and challenges.

Brain and gut barriers have been receiving increasing attention in health and diseases including in psychiatry. Recent studies have highlighted changes in the blood-brain barrier and gut barrier structural properties, notably a loss of tight junctions, leading to hyperpermeability, passage of inflammatory mediators, stress vulnerability, and the development of depressive behaviors. To decipher the cellular processes actively contributing to brain and gut barrier function in health and disease, scientists can take advantage of neurophotonic tools and recent advances in super-resolution microscopy techniques to complement traditional imaging approaches like confocal and electron microscopy. Here, we summarize the challenges, pros, and cons of these innovative approaches, hoping that a growing number of scientists will integrate them in their study design exploring barrier-related properties and mechanisms.

D-2-hydroxyglutarate regulates human brain vascular endothelial cell proliferation and barrier function.

Gain-of-function mutations in isocitrate dehydrogenase (IDH) genes result in excessive production of (D)-2-hydroxyglutarate (D-2HG) which intrinsically modifies tumor cell epigenetics and impacts surrounding noncancerous cells through nonepigenetic pathways. However, whether D-2HG has a paracrine effect on endothelial cells in the tumor microenvironment needs further clarification. We quantified microvessel density by immunohistochemistry using tissue sections from 60 high-grade astrocytic gliomas with or without IDH mutation. Microvessel density was found to be reduced in tumors carrying an IDH mutation. Ex vivo experiments showed that D-2HG inhibited endothelial cell migration, wound healing, and tube formation by suppressing cell proliferation but not viability, possibly through reduced activation of the mTOR/STAT3 pathway. Further, D-2HG reduced fluorescent dextran permeability and decreased paracellular T-cell transendothelial migration by augmenting expression of junctional proteins thereby collectively increasing endothelial barrier function. These results indicate that D-2HG may influence the tumor vascular microenvironment by reducing the intratumoral vasculature density and by inhibiting the transport of metabolites and extravasation of circulating cells into the astrocytoma microenvironment. These observations provide a rationale for combining IDH inhibition with antitumor immunological/angiogenic approaches and suggest a molecular basis for resistance to antiangiogenic drugs in patients whose tumors express a mutant IDH allele.

Dynamic contrast-enhanced MRI shows altered blood–brain barrier function of deep gray matter structures in neuroborreliosis: a case–control study

BackgroundMain aim was assessment of regional blood–brain barrier (BBB) function by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in patients with neuroborreliosis. Secondary aim was to study the correlation of BBB function with biochemical, clinical, and cognitive parameters.MethodsRegional ethical committee approved this prospective single-center case–control study. Within 1 month after diagnosis of neuroborreliosis, 55 patients underwent DCE-MRI. The patient group consisted of 25 males and 30 females with mean age 58 years, and the controls were 8 males and 7 females with mean age 57 years. Pharmacokinetic compartment modelling with Patlak fit was applied, providing estimates for capillary leakage rate and blood volume fraction. Nine anatomical brain regions were sampled with auto-generated binary masks. Fatigue, severity of clinical symptoms and findings, and cognitive function were assessed in the acute phase and 6 months after treatment.ResultsLeakage rates and blood volume fractions were lower in patients compared to controls in the thalamus (p = 0.027 and p = 0.018, respectively), caudate nucleus (p = 0.009 for both), and hippocampus (p = 0.054 and p = 0.009). No correlation of leakage rates with fatigue, clinical disease severity or cognitive function was found.ConclusionsIn neuroborreliosis, leakage rate and blood volume fraction in the thalamus, caudate nucleus, and hippocampus were lower in patients compared to controls. DCE-MRI provided new insight to pathophysiology of neuroborreliosis, and can serve as biomarker of BBB function and regulatory mechanisms of the neurovascular unit in infection and inflammation.Relevance statementDCE-MRI provided new insight to pathophysiology of neuroborreliosis, and can serve as biomarker of blood–brain barrier function and regulatory mechanisms of the neurovascular unit in infection and inflammation.Key points• Neuroborreliosis is an infection with disturbed BBB function.• Microvessel leakage can be studied with DCE-MRI.• Prospective case–control study showed altered microvessel properties in thalamus, caudate, and hippocampus.Graphical

Claudin-10 in the Blood Brain Barrier Function of Cerebral Endothelial Cells and Transendothelial Invasion of Breast Cancer Cells.

Claudin-10 (CLDN10) is a membrane integral protein. It is one of the widely expressed tight junctional claudins with functions not well defined. In the present study, the expression profile and its role in cerebral endothelial cells and in the interaction between breast cancer and endothelial cells were investigated. CLDN10 expression was examined in a wide range of cell types. Brain endothelial cell models with or without CLDN10 expression were generated using the hCMEC/D3 cell line and used to test the barrier and permeability functions. Transendothelial drug delivery and invasion were also evaluated. hCMEC/D3 cells express high levels of CLDN10, compared with peripheral endothelial cells, mesothelial cells, fibroblasts, and breast cancer cells, which were either negative or expressed low levels of CLDN10. Knockdown of CLDN10 in hCMEC/D3 cells resulted in impaired tight junctions as seen by reduced transendothelial electric resistance and paracellular permeability. It also accelerated invasion of breast cancer cells through the endothelial cell layer. CLDN10 knockdown in hCMEC/D3 cells led to an increase in transendothelial chemodrug delivery. Furthermore, the SRC kinase inhibitor (AZM475271) was able to decrease the impedance and increase the paracellular permeability in cerebral endothelial cells. Cerebral endothelial cells express high levels of CLDN10, a protein regulating barrier function and thereby drug permeability and cancer invasiveness in brain endothelial cells, suggesting that it is a novel therapeutic target for the treatment of brain metastasis-related diseases.

Differential effects of SARS-CoV-2 variants on central nervous system cells and blood–brain barrier functions

BackgroundAlthough mainly causing a respiratory syndrome, numerous neurological symptoms have been identified following of SARS-CoV-2 infection. However, how the virus affects the brain and how the mutations carried by the different variants modulate those neurological symptoms remain unclear.MethodsWe used primary human pericytes, foetal astrocytes, endothelial cells and a microglial cell line to investigate the effect of several SARS-CoV-2 variants of concern or interest on their functional activities. Cells and a 3D blood–brain barrier model were infected with the wild-type form of SARS-CoV-2, Alpha, Beta, Delta, Eta, or Omicron (BA.1) variants at various MOI. Cells and supernatant were used to evaluate cell susceptibility to the virus using a microscopic assay as well as effects of infection on (i) cell metabolic activity using a colorimetric MTS assay; (ii) viral cytopathogenicity using the xCELLigence system; (iii) extracellular glutamate concentration by fluorometric assay; and (iv) modulation of blood–brain barrier permeability.ResultsWe demonstrate that productive infection of brain cells is SARS-CoV-2 variant dependent and that all the variants induce stress to CNS cells. The wild-type virus was cytopathic to all cell types except astrocytes, whilst Alpha and Beta variants were only cytopathic for pericytes, and the Omicron variant cytopathic for endothelial cells and pericytes. Lastly wild-type virus increases blood–brain barrier permeability and all variants, except Beta, modulate extracellular glutamate concentration, which can lead to excitotoxicity or altered neurotransmission.ConclusionsThese results suggest that SARS-CoV-2 is neurotropic, with deleterious consequences for the blood–brain barrier integrity and central nervous system cells, which could underlie neurological disorders following SARS-CoV-2 infection.

Multi-transcriptomics reveals brain cellular responses to peripheral infection in Alzheimer’s disease model mice

Peripheral inflammation has been linked to various neurodegenerative disorders, including Alzheimer's disease (AD). Here we perform bulk, single-cell, and spatial transcriptomics in APP/PS1 mice intranasally exposed to Staphylococcus aureus to determine how low-grade peripheral infection affects brain transcriptomics and AD-like pathology. Chronic exposure led to increased amyloid plaque burden and plaque-associated microglia, significantly affecting the transcription of brain barrier-associated cells, which resulted in barrier leakage. We reveal cell-type- and spatial-specific transcriptional changes related to brain barrier function and neuroinflammation during the acute infection. Both acute and chronic exposure led to brain macrophage-associated responses and detrimental effects in neuronal transcriptomics. Finally, we identify unique transcriptional responses at the amyloid plaque niches following acute infection characterized by higher disease-associated microglia gene expression and a larger effect on astrocytic or macrophage-associated genes, which could facilitate amyloid and related pathologies. Our findings provide important insights into the mechanisms linking peripheral inflammation to AD pathology.

Induced pluripotent stem cell model revealed impaired neurovascular interaction in genetic small vessel disease Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy.

Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) is the most common genetic small vessel disease caused by variants in the NOTCH3 gene. Patients with CADASIL experience recurrent strokes, developing into cognitive defect and vascular dementia. CADASIL is a late-onset vascular condition, but migraine and brain MRI lesions appear in CADASIL patients as early as their teens and twenties, suggesting an abnormal neurovascular interaction at the neurovascular unit (NVU) where microvessels meet the brain parenchyma. To understand the molecular mechanisms of CADASIL, we established induced pluripotent stem cell (iPSC) models from CADASIL patients and differentiated the iPSCs into the major NVU cell types including brain microvascular endothelial-like cells (BMECs), vascular mural cells (MCs), astrocytes and cortical projection neurons. We then built an in vitro NVU model by co-culturing different neurovascular cell types in Transwells and evaluated the blood brain barrier (BBB) function by measuring transendothelial electrical resistance (TEER). Results showed that, while the wild-type MCs, astrocytes and neurons could all independently and significantly enhance TEER of the iPSC-BMECs, such capability of MCs from iPSCs of CADASIL patients was significantly impaired. Additionally, the barrier function of the BMECs from CADASIL iPSCs was significantly decreased, accompanied with disorganized tight junctions in iPSC-BMECs, which could not be rescued by the wild-type MCs or sufficiently rescued by the wild-type astrocytes and neurons. Our findings provide new insight into early disease pathologies on the neurovascular interaction and BBB function at the molecular and cellular levels for CADASIL, which helps inform future therapeutic development.

INFLUENCE OF CHRONIC AT1 RECEPTOR BLOCKADE ON GASTRIC BARRIER FUNCTION IN MICE

Objective: The AT1 receptor blocker Telmisartan (TEL) is beneficial for the treatment of individuals suffering the Metabolic Syndrome as TEL reveals not only antihypertensive effects but also improves the glucose and lipid control and lowers body weight. As we have recently shown that TEL has impact on gut microbiota and brain barrier function we here investigated whether TEL influences gut barrier function which may participate in decrease of energy intake. Design and method: BL6 mice were fed with chow or high fat diet (45% fat) and were additionally treated with vehicle (CONchow or CONHFD) or TEL (8 mg/kg/d, 12 w, TELchow or TELHFD). Visceral and subcutaneous fat mass was quantified by MRI. Segments of large intestine were Canoy fixed to determine thickness of mucus by immunohistochemistry. PAS staining was performed for depicting goblet cells. The signalling pathway being involved in necroptosis was investigated by Western blots and qPCR. Results: Compared to chow feeding, gain in body weight increased by HFD (3.4±0.5 vs. 14.4g±1.2 g) and was reduced by TEL (1.7±0.5 vs. 2.8±0.5g). Visceral fat and liver mass was higher in CONHFD than CONchow but remained normal by TEL treatment. The mucus thickness was lower in CONHFD than CONchow. Independent on feeding, TEL additionally reduced mucus thickness. Numbers of goblet cells were not affected by HFD feeding and TEL treatment. RIP3 was particularly increased in TELHFD mice, while muc2 and ki67 almost remained unaffected by TEL. Conclusions: In contrast to our expectation, the antiobese effect of TEL was associated with a decrease in mucus thickness. Increase in RIP3 indicates that necroptosis may be enhanced by TEL. Further studies have to be performed to elucidate whether this detrimental TEL effect is true and be relevant for gastrointestinal function.

Brain Calcifications: Genetic, Molecular, and Clinical Aspects.

Many conditions can present with accumulation of calcium in the brain and manifest with a variety of neurological symptoms. Brain calcifications can be primary (idiopathic or genetic) or secondary to various pathological conditions (e.g., calcium-phosphate metabolism derangement, autoimmune disorders and infections, among others). A set of causative genes associated with primary familial brain calcification (PFBC) has now been identified, and include genes such as SLC20A2, PDGFB, PDGFRB, XPR1, MYORG, and JAM2. However, many more genes are known to be linked with complex syndromes characterized by brain calcifications and additional neurologic and systemic manifestations. Of note, many of these genes encode for proteins involved in cerebrovascular and blood-brain barrier functions, which both represent key anatomical structures related to these pathological phenomena. As a growing number of genes associated with brain calcifications is identified, pathways involved in these conditions are beginning to be understood. Our comprehensive review of the genetic, molecular, and clinical aspects of brain calcifications offers a framework for clinicians and researchers in the field.

Monomeric C-reactive protein: A novel biomarker predicting neurodegenerative disease and vascular dysfunction.

Circulating C-reactive protein (pCRP) concentrations rise dramatically during both acute (e.g., following stroke) or chronic infection and disease (e.g., autoimmune conditions such as lupus), providing complement fixation through C1q protein binding. It is now known, that on exposure to the membranes of activated immune cells (and microvesicles and platelets), or damaged/dysfunctional tissue, it undergoes lysophosphocholine (LPC)-phospholipase-C-dependent dissociation to the monomeric form (mCRP), concomitantly becoming biologically active. We review histological, immunohistochemical, and morphological/topological studies of post-mortem brain tissue from individuals with neuroinflammatory disease, showing that mCRP becomes stably distributed within the parenchyma, and resident in the arterial intima and lumen, being "released" from damaged, hemorrhagic vessels into the extracellular matrix. The possible de novo synthesis via neurons, endothelial cells, and glia is also considered. In vitro, in vivo, and human tissue co-localization analyses have linked mCRP to neurovascular dysfunction, vascular activation resulting in increased permeability, and leakage, compromise of blood brain barrier function, buildup of toxic proteins including tau and beta amyloid (Aβ), association with and capacity to "manufacture" Aβ-mCRP-hybrid plaques, and, greater susceptibility to neurodegeneration and dementia. Recently, several studies linked chronic CRP/mCRP systemic expression in autoimmune disease with increased risk of dementia and the mechanisms through which this occurs are investigated here. The neurovascular unit mediates correct intramural periarterial drainage, evidence is provided here that suggests a critical impact of mCRP on neurovascular elements that could suggest its participation in the earliest stages of dysfunction and conclude that further investigation is warranted. We discuss future therapeutic options aimed at inhibiting the pCRP-LPC mediated dissociation associated with brain pathology, for example, compound 1,6-bis-PC, injected intravenously, prevented mCRP deposition and associated damage, after temporary left anterior descending artery ligation and myocardial infarction in a rat model.