FACS isolation of endothelial cells and pericytes from mouse brain microregions

Glioblastoma Neurovascular Progenitor Orchestrates Tumor Cell Type Diversity

Glioblastoma (GBM) is the deadliest form of primary brain tumor with limited treatment options. Recent studies have profiled GBM tumor heterogeneity, revealing numerous axes of variation that explain the molecular and spatial features of the tumor. Here, we seek to bridge descriptive characterization of GBM cell type heterogeneity with the functional role of individual populations within the tumor. Our lens leverages a gene program-centric meta-atlas of published transcriptomic studies to identify commonalities between diverse tumors and cell types in order to decipher the mechanisms that drive them. This approach led to the discovery of a tumor-derived stem cell population with mixed vascular and neural stem cell features, termed a neurovascular progenitor (NVP). Following in situ validation and molecular characterization of NVP cells in GBM patient samples, we characterized their function in vivo. Genetic depletion of NVP cells resulted in altered tumor cell composition, fewer cycling cells, and extended survival, underscoring their critical functional role. Clonal analysis of primary patient tumors in a human organoid tumor transplantation system demonstrated that the NVP has dual potency, generating both neuronal and vascular tumor cells. Although NVP cells comprise a small fraction of the tumor, these clonal analyses demonstrated that they strongly contribute to the total number of cycling cells in the tumor and generate a defined subset of the whole tumor. This study represents a paradigm by which cell type-specific interrogation of tumor populations can be used to study functional heterogeneity and therapeutically targetable vulnerabilities of GBM.

Single-cell analysis of mesenchymal cells in permeable neural vasculature reveals novel diverse subpopulations of fibroblasts

BACKGROUND

In the choroid plexus and pituitary gland, vasculature is known to have a permeable, fenestrated phenotype which allows for the free passage of molecules in contrast to the blood brain barrier observed in the rest of the CNS. The endothelium of these compartments, along with secretory, neural-lineage cells (choroid epithelium and pituitary endocrine cells) have been studied in detail, but less attention has been given to the perivascular mesenchymal cells of these compartments.

METHODS

The Hic1CreERT2 Rosa26LSL-TdTomato mouse model was used in conjunction with a PdgfraH2B-EGFP mouse model to examine mesenchymal cells, which can be subdivided into Pdgfra+ fibroblasts and Pdgfra- pericytes within the choroid plexus (CP) and pituitary gland (PG), by histological, immunofluorescence staining and single-cell RNA-sequencing analyses.

RESULTS

We found that both CP and PG possess substantial populations of distinct Hic1+ mesenchymal cells, including an abundance of Pdgfra+ fibroblasts. Within the pituitary, we identified distinct subpopulations of Hic1+ fibroblasts in the glandular anterior pituitary and the neurosecretory posterior pituitary. We also identified multiple distinct markers of CP, PG, and the meningeal mesenchymal compartment, including alkaline phosphatase, indole-n-methyltransferase and CD34.

CONCLUSIONS

Novel, distinct subpopulations of mesenchymal cells can be found in permeable vascular interfaces, including the CP, PG, and meninges, and make distinct contributions to both organs through the production of structural proteins, enzymes, transporters, and trophic molecules.

Engagement of N6-methyladenisine methylation of Gng4 mRNA in astrocyte dysfunction regulated by CircHECW2

The N6-methyladenosine (m6A) modification is the most prevalent modification of eukaryotic mRNAs and plays a crucial role in various physiological processes by regulating the stability or function of target mRNAs. Accumulating evidence has suggested that m6A methylation may be involved in the pathological process of major depressive disorder (MDD), a common neuropsychiatric disorder with an unclear aetiology. Here, we found that the levels of the circular RNA HECW2 (circHECW2) were significantly increased in the plasma of both MDD patients and the chronic unpredictable stress (CUS) mouse model. Notably, the downregulation of circHECW2 attenuated astrocyte dysfunction and depression-like behaviors induced by CUS. Furthermore, we demonstrated that the downregulation of circHECW2 increased the expression of the methylase WTAP, leading to an increase in Gng4 expression via m6A modifications. Our findings provide functional insight into the correlation between circHECW2 and m6A methylation, suggesting that circHECW2 may represent a potential target for MDD treatment.

RGD-coated polymeric microbubbles promote ultrasound-mediated drug delivery in an inflamed endothelium-pericyte co-culture model of the blood-brain barrier

Drug delivery to central nervous pathologies is compromised by the blood-brain barrier (BBB). A clinically explored strategy to promote drug delivery across the BBB is sonopermeation, which relies on the combined use of ultrasound (US) and microbubbles (MB) to induce temporally and spatially controlled opening of the BBB. We developed an advanced in vitro BBB model to study the impact of sonopermeation on the delivery of the prototypic polymeric drug carrier pHPMA as a larger molecule and the small molecule antiviral drug ribavirin. This was done under standard and under inflammatory conditions, employing both untargeted and RGD peptide-coated MB. The BBB model is based on human cerebral capillary endothelial cells and human placental pericytes, which are co-cultivated in transwell inserts and which present with proper transendothelial electrical resistance (TEER). Sonopermeation induced a significant decrease in TEER values and facilitated the trans-BBB delivery of fluorescently labeled pHPMA (Atto488-pHPMA). To study drug delivery under inflamed endothelial conditions, which are typical for e.g. tumors, neurodegenerative diseases and CNS infections, tumor necrosis factor (TNF) was employed to induce inflammation in the BBB model. RGD-coated MB bound to and permeabilized the inflamed endothelium-pericyte co-culture model, and potently improved Atto488-pHPMA and ribavirin delivery. Taken together, our work combines in vitro BBB bioengineering with MB-mediated drug delivery enhancement, thereby providing a framework for future studies on optimization of US-mediated drug delivery to the brain.

Interrogation of endothelial and mural cells in brain metastasis reveals key immune-regulatory mechanisms

Brain metastasis (BrM) is a common malignancy, predominantly originating from lung, melanoma, and breast cancers. The vasculature is a key component of the BrM tumor microenvironment with critical roles in regulating metastatic seeding and progression. However, the heterogeneity of the major BrM vascular components, namely endothelial and mural cells, is still poorly understood. We perform single-cell and bulk RNA-sequencing of sorted vascular cell types and detect multiple subtypes enriched specifically in BrM compared to non-tumor brain, including previously unrecognized immune regulatory subtypes. We integrate the human data with mouse models, creating a platform to interrogate vascular targets for the treatment of BrM. We find that the CD276 immune checkpoint molecule is significantly upregulated in the BrM vasculature, and anti-CD276 blocking antibodies prolonged survival in preclinical trials. This study provides important insights into the complex interactions between the vasculature, immune cells, and cancer cells, with translational relevance for designing therapeutic interventions.

Continued dysfunction of capillary pericytes promotes no-reflow after experimental stroke in vivo

Incomplete reperfusion of the microvasculature ('no-reflow') after ischaemic stroke damages salvageable brain tissue. Previous ex vivo studies suggest pericytes are vulnerable to ischaemia and may exacerbate no-reflow, but the viability of pericytes and their association with no-reflow remains under-explored in vivo. Using longitudinal in vivo two-photon single-cell imaging over 7 days, we showed that 87% of pericytes constrict during cerebral ischaemia and remain constricted post reperfusion, and 50% of the pericyte population are acutely damaged. Moreover, we revealed ischaemic pericytes to be fundamentally implicated in capillary no-reflow by limiting and arresting blood flow within the first 24 h post stroke. Despite sustaining acute membrane damage, we observed that over half of all cortical pericytes survived ischaemia and responded to vasoactive stimuli, upregulated unique transcriptomic profiles and replicated. Finally, we demonstrated the delayed recovery of capillary diameter by ischaemic pericytes after reperfusion predicted vessel reconstriction in the subacute phase of stroke. Cumulatively, these findings demonstrate that surviving cortical pericytes remain both viable and promising therapeutic targets to counteract no-reflow after ischaemic stroke.

Profiling human brain vascular cells using single-cell transcriptomics and organoids

Angiogenesis and neurogenesis are functionally interconnected during brain development. However, the study of the vasculature has trailed other brain cell types because they are delicate and of low abundance. Here we describe a protocol extension to purify prenatal human brain endothelial and mural cells with FACS and utilize them in downstream applications, including transcriptomics, culture and organoid transplantation. This approach is simple, efficient and generates high yields from small amounts of tissue. When the experiment is completed within a 24 h postmortem interval, these healthy cells produce high-quality data in single-cell transcriptomics experiments. These vascular cells can be cultured, passaged and expanded for many in vitro assays, including Matrigel vascular tube formation, microfluidic chambers and metabolic measurements. Under these culture conditions, primary vascular cells maintain expression of cell-type markers for at least 3 weeks. Finally, we describe how to use primary vascular cells for transplantation into cortical organoids, which captures key features of neurovascular interactions in prenatal human brain development. In terms of timing, tissue processing and staining requires ~3 h, followed by an additional 3 h of FACS. The transplant procedure of primary, FACS-purified vascular cells into cortical organoids requires an additional 2 h. The time required for different transcriptomic and epigenomic protocols can vary based on the specific application, and we offer strategies to mitigate batch effects and optimize data quality. In sum, this vasculo-centric approach offers an integrated platform to interrogate neurovascular interactions and human brain vascular development.

Bicarbonate signalling via G protein-coupled receptor regulates ischaemia-reperfusion injury

Homoeostatic regulation of the acid-base balance is essential for cellular functional integrity. However, little is known about the molecular mechanism through which the acid-base balance regulates cellular responses. Here, we report that bicarbonate ions activate a G protein-coupled receptor (GPCR), i.e., GPR30, which leads to Gq-coupled calcium responses. Gpr30-Venus knock-in mice reveal predominant expression of GPR30 in brain mural cells. Primary culture and fresh isolation of brain mural cells demonstrate bicarbonate-induced, GPR30-dependent calcium responses. GPR30-deficient male mice are protected against ischemia-reperfusion injury by a rapid blood flow recovery. Collectively, we identify a bicarbonate-sensing GPCR in brain mural cells that regulates blood flow and ischemia-reperfusion injury. Our results provide a perspective on the modulation of GPR30 signalling in the development of innovative therapies for ischaemic stroke. Moreover, our findings provide perspectives on acid/base sensing GPCRs, concomitantly modulating cellular responses depending on fluctuating ion concentrations under the acid-base homoeostasis.

Endothelial TDP-43 controls sprouting angiogenesis and vascular barrier integrity, and its deletion triggers neuroinflammation

TAR DNA-binding protein 43 (TDP-43) is a DNA/RNA-binding protein that regulates gene expression, and its malfunction in neurons has been causally associated with multiple neurodegenerative disorders. Although progress has been made in understanding the functions of TDP-43 in neurons, little is known about its roles in endothelial cells (ECs), angiogenesis, and vascular function. Using inducible EC-specific TDP-43-KO mice, we showed that TDP-43 is required for sprouting angiogenesis, vascular barrier integrity, and blood vessel stability. Postnatal EC-specific deletion of TDP-43 led to retinal hypovascularization due to defects in vessel sprouting associated with reduced EC proliferation and migration. In mature blood vessels, loss of TDP-43 disrupted the blood-brain barrier and triggered vascular degeneration. These vascular defects were associated with an inflammatory response in the CNS with activation of microglia and astrocytes. Mechanistically, deletion of TDP-43 disrupted the fibronectin matrix around sprouting vessels and reduced β-catenin signaling in ECs. Together, our results indicate that TDP-43 is essential for the formation of a stable and mature vasculature.

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.

The Therapeutic Potential of Pericytes in Bone Tissue Regeneration

Pericytes, as perivascular cells, are present in all vascularized organs and tissues, and they actively interact with endothelial cells in capillaries and microvessels. Their involvement includes functions like blood pressure regulation, tissue regeneration, and scarring. Studies have confirmed that pericytes play a crucial role in bone tissue regeneration through direct osteodifferentiation processes, paracrine actions, and vascularization. Recent preclinical and clinical experiments have shown that combining perivascular cells with osteogenic factors and tissue-engineered scaffolds can be therapeutically effective in restoring bone defects. This approach holds promise for addressing bone-related medical conditions. In this review, we have emphasized the characteristics of pericytes and their involvement in angiogenesis and osteogenesis. Furthermore, we have explored recent advancements in the use of pericytes in preclinical and clinical investigations, indicating their potential as a therapeutic resource in clinical applications.

Loss of Endothelial TDP-43 Leads to Blood Brain Barrier Defects in Mouse Models of Amyotrophic Lateral Sclerosis and Frontotemporal Dementia

Loss of nuclear TDP-43 occurs in a wide range of neurodegenerative diseases, and specific mutations in the TARDBP gene that encodes the protein are linked to familial Frontal Temporal Lobar Dementia (FTD), and Amyotrophic Lateral Sclerosis (ALS). Although the focus has been on neuronal cell dysfunction caused by TDP-43 variants, TARDBP mRNA transcripts are expressed at similar levels in brain endothelial cells (ECs). Since increased permeability across the blood brain barrier (BBB) precedes cognitive decline, we postulated that altered functions of TDP-43 in ECs contributes to BBB dysfunction in neurodegenerative disease. To test this hypothesis, we examined EC function and BBB properties in mice with either knock-in mutations found in ALS/FTLD patients (TARDBPG348C and GRNR493X) or EC-specific deletion of TDP-43 throughout the endothelium (Cdh5(PAC)CreERT2; Tardbpff) or restricted to brain endothelium (Slco1c1(BAC)CreERT2; Tardbpff). We found that TARDBPG348C mice exhibited increased permeability to 3kDa Texas Red dextran and NHS-biotin, relative to their littermate controls, which could be recapitulated in cultured brain ECs from these mice. Nuclear levels of TDP-43 were reduced in vitro and in vivo in ECs from TARDBPG348C mice. This coincided with a reduction in junctional proteins VE-cadherin, claudin-5 and ZO-1 in isolated ECs, supporting a cell autonomous effect on barrier function through a loss of nuclear TDP-43. We further examined two models of Tardbp deletion in ECs, and found that the loss of TDP-43 throughout the endothelium led to systemic endothelial activation and permeability. Deletion specifically within the brain endothelium acutely increased BBB permeability, and eventually led to hallmarks of FTD, including fibrin deposition, microglial and astrocyte activation, and behavioral defects. Together, these data show that TDP-43 dysfunction specifically within brain ECs would contribute to the BBB defects observed early in the progression of ALS/FTLD.

Neuronal activity drives IGF2 expression from pericytes to form long-term memory

Investigations of memory mechanisms have been, thus far, neuron centric, despite the brain comprising diverse cell types. Using rats and mice, we assessed the cell-type-specific contribution of hippocampal insulin-like growth factor 2 (IGF2), a polypeptide regulated by learning and required for long-term memory formation. The highest level of hippocampal IGF2 was detected in pericytes, the multi-functional mural cells of the microvessels that regulate blood flow, vessel formation, the blood-brain barrier, and immune cell entry into the central nervous system. Learning significantly increased pericytic Igf2 expression in the hippocampus, particularly in the highly vascularized stratum lacunosum moleculare and stratum moleculare layers of the dentate gyrus. Igf2 increases required neuronal activity. Regulated hippocampal Igf2 knockout in pericytes, but not in fibroblasts or neurons, impaired long-term memories and blunted the learning-dependent increase of neuronal immediate early genes (IEGs). Thus, neuronal activity-driven signaling from pericytes to neurons via IGF2 is essential for long-term memory.

Universal method for the isolation of microvessels from frozen brain tissue: A proof-of-concept multiomic investigation of the neurovasculature

The neurovascular unit, comprised of vascular cell types that collectively regulate cerebral blood flow to meet the needs of coupled neurons, is paramount for the proper function of the central nervous system. The neurovascular unit gatekeeps blood-brain barrier properties, which experiences impairment in several central nervous system diseases associated with neuroinflammation and contributes to pathogenesis. To better understand function and dysfunction at the neurovascular unit and how it may confer inflammatory processes within the brain, isolation and characterization of the neurovascular unit is needed. Here, we describe a singular, standardized protocol to enrich and isolate microvessels from archived snap-frozen human and frozen mouse cerebral cortex using mechanical homogenization and centrifugation-separation that preserves the structural integrity and multicellular composition of microvessel fragments. For the first time, microvessels are isolated from postmortem ventromedial prefrontal cortex tissue and are comprehensively investigated as a structural unit using both RNA sequencing and Liquid Chromatography with tandem mass spectrometry (LC-MS/MS). Both the transcriptome and proteome are obtained and compared, demonstrating that the isolated brain microvessel is a robust model for the NVU and can be used to generate highly informative datasets in both physiological and disease contexts.

CD13 facilitates immune cell migration and aggravates acute injury but promotes chronic post-stroke recovery

INTRODUCTION

Acute stroke leads to the activation of myeloid cells. These cells express adhesion molecules and transmigrate to the brain, thereby aggravating injury. Chronically after stroke, repair processes, including angiogenesis, are activated and enhance post-stroke recovery. Activated myeloid cells express CD13, which facilitates their migration into the site of injury. However, angiogenic blood vessels which play a role in recovery also express CD13. Overall, the specific contribution of CD13 to acute and chronic stroke outcomes is unknown.

METHODS

CD13 expression was estimated in both mice and humans after the ischemic stroke. Young (8-12 weeks) male wild-type and global CD13 knockout (KO) mice were used for this study. Mice underwent 60 min of middle cerebral artery occlusion (MCAO) followed by reperfusion. For acute studies, the mice were euthanized at either 24- or 72 h post-stroke. For chronic studies, the Y-maze, Barnes maze, and the open field were performed on day 7 and day 28 post-stroke. Mice were euthanized at day 30 post-stroke and the brains were collected for assessment of inflammation, white matter injury, tissue loss, and angiogenesis. Flow cytometry was performed on days 3 and 7 post-stroke to quantify infiltrated monocytes and neutrophils and CXCL12/CXCR4 signaling.

RESULTS

Brain CD13 expression and infiltrated CD13+ monocytes and neutrophils increased acutely after the stroke. The brain CD13+lectin+ blood vessels increased on day 15 after the stroke. Similarly, an increase in the percentage area CD13 was observed in human stroke patients at the subacute time after stroke. Deletion of CD13 resulted in reduced infarct volume and improved neurological recovery after acute stroke. However, CD13KO mice had significantly worse memory deficits, amplified gliosis, and white matter damage compared to wild-type animals at chronic time points. CD13-deficient mice had an increased percentage of CXCL12+cells but a reduced percentage of CXCR4+cells and decreased angiogenesis at day 30 post-stroke.

CONCLUSIONS

CD13 is involved in the trans-migration of monocytes and neutrophils after stroke, and acutely, led to decreased infarct size and improved behavioral outcomes. However, loss of CD13 led to reductions in post-stroke angiogenesis by reducing CXCL12/CXCR4 signaling.

Altered serum levels of platelet-derived growth factor receptor β and cluster of differentiation 13 suggest a role for pericytes in West syndrome

BACKGROUND

Pericytes play a role in the maintenance of the blood-brain barrier and neuroinflammation, attracting attention as to whether they are also involved in the pathogenesis of epilepsy.This study aimed to explore the relationship between West syndrome and pericytes.

METHODS

Eighteen Japanese pediatric West syndrome patients and nine controls aged 2 years or younger were retrospectively enrolled in this study. We assessed theserumlevels of pericyte markers, serum PDGFRβ (platelet-derived growth factor receptorβ),CD13 (aminopeptidase N), and 27 cytokines in 17 pediatric patients with West syndrome and the control group.

RESULTS

Patients with West syndrome exhibited significantly increased CD13 and decreased PDGFRβ levels, compared with controls but not serum cytokine levels. These values did not differ significantly between symptomatic and idiopathic West syndrome.

CONCLUSION

Pericytes might be implicated in the pathogenesis of West syndrome.

VEGF-A in serum protects against memory impairment in APP/PS1 transgenic mice by blocking neutrophil infiltration

Activation of innate immunity in the brain is a prominent feature of Alzheimer's disease (AD). The present study investigated the regulation of innate immunity by wild-type serum injection in a transgenic AD mouse model. We found that treatment with wild-type mouse serum significantly reduced the number of neutrophils and microglial reactivity in the brains of APP/PS1 mice. Mimicking this effect, neutrophil depletion via Ly6G neutralizing antibodies resulted in improvements in AD brain functions. Serum proteomic analysis identified vascular endothelial growth factor-A (VEGF-A) and chemokine (C-X-C motif) ligand 1 (CXCL1) as factors enriched in serum samples, which are crucial for neutrophil migration and chemotaxis, leukocyte migration, and cell chemotaxis. Exogenous VEGF-A reversed amyloid β (Aβ)-induced decreases in cyclin-dependent kinase 5 (Cdk5) and increases in CXCL1 in vitro and blocked neutrophil infiltration into the AD brain. Endothelial Cdk5 overexpression conferred an inhibitory effect on CXCL1 and neutrophil infiltration, thereby restoring memory abilities in APP/PS1 mice. Our findings uncover a previously unknown link between blood-derived VEGF signaling and neutrophil infiltration and support targeting endothelial Cdk5 signaling as a potential therapeutic strategy for AD.

Effects of repeated sleep deprivation on brain pericytes in mice

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

Disentangling brain vasculature in neurogenesis and neurodegeneration using single-cell transcriptomics

The vasculature is increasingly recognized to impact brain function in health and disease across the life span. During embryonic brain development, angiogenesis and neurogenesis are tightly coupled, coordinating the proliferation, differentiation, and migration of neural and glial progenitors. In the adult brain, neurovascular interactions continue to play essential roles in maintaining brain function and homeostasis. This review focuses on recent advances that leverage single-cell transcriptomics of vascular cells to uncover their subtypes, their organization and zonation in the embryonic and adult brain, and how dysfunction in neurovascular and gliovascular interactions contributes to the pathogenesis of neurodegenerative diseases. Finally, we highlight key challenges for future research in neurovascular biology.

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.

Hierarchical deconvolution for extensive cell type resolution in the human brain using DNA methylation

Introduction

The human brain comprises heterogeneous cell types whose composition can be altered with physiological and pathological conditions. New approaches to discern the diversity and distribution of brain cells associated with neurological conditions would significantly advance the study of brain-related pathophysiology and neuroscience. Unlike single-nuclei approaches, DNA methylation-based deconvolution does not require special sample handling or processing, is cost-effective, and easily scales to large study designs. Existing DNA methylation-based methods for brain cell deconvolution are limited in the number of cell types deconvolved.

Methods

Using DNA methylation profiles of the top cell-type-specific differentially methylated CpGs, we employed a hierarchical modeling approach to deconvolve GABAergic neurons, glutamatergic neurons, astrocytes, microglial cells, oligodendrocytes, endothelial cells, and stromal cells.

Results

We demonstrate the utility of our method by applying it to data on normal tissues from various brain regions and in aging and diseased tissues, including Alzheimer's disease, autism, Huntington's disease, epilepsy, and schizophrenia.

Discussion

We expect that the ability to determine the cellular composition in the brain using only DNA from bulk samples will accelerate understanding brain cell type composition and cell-type-specific epigenetic states in normal and diseased brain tissues.

Time-resolved single-cell transcriptomics reveals the landscape and dynamics of hepatic cells in sepsis-induced acute liver dysfunction

Background & Aims

Sepsis-induced acute liver dysfunction often occurs early in sepsis and can exacerbate the pathology by triggering multiple organ dysfunction and increasing lethality. Nevertheless, our understanding of the cellular heterogeneity and dynamic regulation of major nonparenchymal cell lineages remains unclear.

Methods

Here, single-cell RNA sequencing was used to profile multiple nonparenchymal cell subsets and dissect their crosstalk during sepsis-induced acute liver dysfunction in a clinically relevant polymicrobial sepsis model. The transcriptomes of major liver nonparenchymal cells from control and sepsis mice were analysed. The alterations in the endothelial cell and neutrophil subsets that were closely associated with acute liver dysfunction were validated using multiplex immunofluorescence staining. In addition, the therapeutic efficacy of inhibiting activating transcription factor 4 (ATF4) in sepsis and sepsis-induced acute liver dysfunction was explored.

Results

Our results present the dynamic transcriptomic landscape of major nonparenchymal cells at single-cell resolution. We observed significant alterations and heterogeneity in major hepatic nonparenchymal cell subsets during sepsis. Importantly, we identified endothelial cell (CD31⁺Sele⁺Glut1⁺) and neutrophil (Ly6G⁺Lta4h⁺Sort1⁺) subsets that were closely associated with acute liver dysfunction during sepsis progression. Furthermore, we found that ATF4 inhibition alleviated sepsis-induced acute liver dysfunction, prolonging the survival of septic mice.

Conclusions

These results elucidate the potential mechanisms and subsequent therapeutic targets for the prevention and treatment of sepsis-induced acute liver dysfunction and other liver-related diseases.

Impact and Implications

Sepsis-induced acute liver dysfunction often occurs early in sepsis and can lead to the death of the patient. Nevertheless, the pathogenesis of sepsis-induced acute liver dysfunction is not yet clear. We identified the major cell types associated with acute liver dysfunction and explored their interactions during sepsis. In addition, we also found that ATF-4 inhibition could be invoked as a potential therapeutic for sepsis-induced acute liver dysfunction.

Modeling angiogenesis in the human brain in a tissue-engineered post-capillary venule

Angiogenesis plays an essential role in embryonic development, organ remodeling, wound healing, and is also associated with many human diseases. The process of angiogenesis in the brain during development is well characterized in animal models, but little is known about the process in the mature brain. Here, we use a tissue-engineered post-capillary venule (PCV) model incorporating stem cell derived induced brain microvascular endothelial-like cells (iBMECs) and pericyte-like cells (iPCs) to visualize the dynamics of angiogenesis. We compare angiogenesis under two conditions: in response to perfusion of growth factors and in the presence of an external concentration gradient. We show that both iBMECs and iPCs can serve as tip cells leading angiogenic sprouts. More importantly, the growth rate for iPC-led sprouts is about twofold higher than for iBMEC-led sprouts. Under a concentration gradient, angiogenic sprouts show a small directional bias toward the high growth factor concentration. Overall, pericytes exhibited a broad range of behavior, including maintaining quiescence, co-migrating with endothelial cells in sprouts, or leading sprout growth as tip cells.

Connexin 43-mediated neurovascular interactions regulate neurogenesis in the adult brain subventricular zone

The subventricular zone (SVZ) is the largest neural stem cell (NSC) niche in the adult brain; herein, the blood-brain barrier is leaky, allowing direct interactions between NSCs and endothelial cells (ECs). Mechanisms by which direct NSC-EC interactions in the adult SVZ control NSC behavior are unclear. We found that Cx43 is highly expressed by SVZ NSCs and ECs, and its deletion in either leads to increased NSC proliferation and neuroblast generation, suggesting that Cx43-mediated NSC-EC interactions maintain NSC quiescence. This is further supported by single-cell RNA sequencing and in vitro studies showing that ECs control NSC proliferation by regulating expression of genes associated with NSC quiescence and/or activation in a Cx43-dependent manner. Cx43 mediates these effects in a channel-independent manner involving its cytoplasmic tail and ERK activation. Such insights inform adult NSC regulation and maintenance aimed at stem cell therapies for neurodegenerative disorders.

Neural cell isolation from adult macaques for high-throughput analyses and neurosphere cultures

The low number of neural progenitor cells (NPCs) present in the adult and aged primate brains represents a challenge for generating high-yield and viable in vitro cultures of primary brain cells. Here we report a step-by-step approach for the fast and reproducible isolation of high-yield and viable primary brain cells, including mature neurons, immature cells and NPCs, from adult and aged macaques. We describe the anesthesia, transcardial perfusion and brain tissue preparation; the subsequent microdissection of the regions of interest and their enzymatic dissociation, leading to the separation of single cells. The cell isolation steps of our protocol can also be used for routine cell culturing, in particular for NPC expansion and differentiation, suitable for studies of hippocampal neurogenesis in the adult macaque brain. The purified primary brain cells are largely free from myelin debris and erythrocytes, paving the way for multiple downstream applications in vitro and in vivo. When combined with single-cell profiling techniques, this approach allows an unbiased and comprehensive mapping of cell states in the adult and aged macaque brain, which is needed to advance our understanding of human cognitive and neurological diseases. The neural cell isolation protocol requires 4 h and a team of four to six users with expertize in primary brain cell isolation to avoid tissue hypoxia during the time-sensitive steps of the procedure.

SIRT1 attenuates blood-spinal cord barrier disruption after spinal cord injury by deacetylating p66Shc

Disruption of the blood-spinal cord barrier (BSCB) leads to inflammatory cell infiltration and neural cell death, thus, contributing to poor functional recovery after spinal cord injury (SCI). Previous studies have suggested that Sirtuin 1 (SIRT1), an NAD⁺-dependent class III histone deacetylase, is abundantly expressed in endothelial cells and promotes endothelial homeostasis. However, the role of SIRT1 in BSCB function after SCI remains poorly defined. Here, we report that SIRT1 is highly expressed in spinal cord endothelial cells, and its expression significantly decreases after SCI. Using endothelial cell-specific SIRT1 knockout mice, we observed that endothelial cell-specific knockout of SIRT1 aggravated BSCB disruption, thus, resulting in widespread inflammation, neural cell death and poor functional recovery after SCI. In contrast, activation of SIRT1 by the agonist SRT1720 had beneficial effects. In vitro, knockdown of SIRT1 exacerbated IL-1β-induced endothelial barrier disruption in bEnd.3 cells, whereas overexpression of SIRT1 was protective. Using RNA-seq and IP/MS analysis, we identified p66Shc, a redox protein, as the potential target of SIRT1. Further studies demonstrated that SIRT1 interacts with and deacetylates p66Shc, thereby attenuating oxidative stress and protecting endothelial barrier function. Overall, our results indicate that SIRT1 decreases endothelial ROS production and attenuates BSCB disruption by deacetylating p66Shc after SCI, and suggest that SIRT1 activation has potential as a therapeutic approach to promote functional recovery against BSCB disruption following SCI.

Biotinylated Fluorescent Polymeric Nanoparticles for Enhanced Immunostaining

The performance of fluorescence immunostaining is physically limited by the brightness of organic dyes, whereas fluorescence labeling with multiple dyes per antibody can lead to dye self-quenching. The present work reports a methodology of antibody labeling by biotinylated zwitterionic dye-loaded polymeric nanoparticles (NPs). A rationally designed hydrophobic polymer, poly(ethyl methacrylate) bearing charged, zwitterionic and biotin groups (PEMA-ZI-biotin), enables preparation of small (14 nm) and bright fluorescent biotinylated NPs loaded with large quantities of cationic rhodamine dye with bulky hydrophobic counterion (fluorinated tetraphenylborate). The biotin exposure at the particle surface is confirmed by Förster resonance energy transfer with dye-streptavidin conjugate. Single-particle microscopy validates specific binding to biotinylated surfaces, with particle brightness 21-fold higher than quantum dot-585 (QD-585) at 550 nm excitation. The nanoimmunostaining method, which couples biotinylated antibody (cetuximab) with bright biotinylated zwitterionic NPs through streptavidin, significantly improves fluorescence imaging of target epidermal growth factor receptors (EGFR) on the cell surface compared to a dye-based labeling. Importantly, cetuximab labeled with PEMA-ZI-biotin NPs can differentiate cells with distinct expression levels of EGFR cancer marker. The developed nanoprobes can greatly amplify the signal from labeled antibodies, and thus become a useful tool in the high-sensitivity detection of disease biomarkers.

A flow cytometry-based protocol for syngenic isolation of neurovascular unit cells from mouse and human tissues

The neurovascular unit (NVU), composed of endothelial cells, pericytes, juxtaposed astrocytes and microglia together with neurons, is essential for proper central nervous system functioning. The NVU critically regulates blood-brain barrier (BBB) function, which is impaired in several neurological diseases and is therefore a key therapeutic target. To understand the extent and cellular source of BBB dysfunction, simultaneous isolation and analysis of NVU cells is needed. Here, we describe a protocol for the EPAM-ia method, which is based on flow cytometry for simultaneous isolation and analysis of endothelial cells, pericytes, astrocytes and microglia. This method is based on differential processing of NVU cell types using enzymes, mechanical homogenization and filtration specific for each cell type followed by combining them for immunostaining and fluorescence-activated cell sorting. The gating strategy encompasses cell-type-specific and exclusion markers for contaminating cells to isolate the major NVU cell types. This protocol takes ~6 h for two sets of one or two animals. The isolation part requires experience in animal handling, fresh tissue processing and immunolabeling for flow cytometry. Sorted NVU cells can be used for downstream applications including transcriptomics, proteomics and cell culture. Multiple cell-type analyses using UpSet can then be applied to obtain robust targets from single or multiple NVU cell types in neurological diseases associated with BBB dysfunction. The EPAM-ia method is also amenable to isolation of several other cell types, including cancer cells and immune cells. This protocol is applicable to healthy and pathological tissue from mouse and human sources and to several cell types compared with similar protocols.

Protective effects of omega-3 fatty acids in a blood-brain barrier-on-chip model and on postoperative delirium-like behaviour in mice

BACKGROUND

Peripheral surgical trauma can trigger neuroinflammation and ensuing neurological complications, such as delirium. The mechanisms whereby surgery contributes to postoperative neuroinflammation remain unclear and without effective therapies. Here, we developed a microfluidic-assisted blood-brain barrier (BBB) device and tested the effects of omega-3 fatty acids on neuroimmune interactions after orthopaedic surgery.

METHODS

A microfluidic-assisted BBB device was established using primary human cells. Tight junction proteins, vascular cell adhesion molecule 1 (VCAM-1), BBB permeability, and astrocytic networks were assessed after stimulation with interleukin (IL)-1β and in the presence or absence of a clinically available omega-3 fatty acid emulsion (Omegaven®; Fresenius Kabi, Bad Homburg, Germany). Mice were treated 1 h before orthopaedic surgery with 10 μl g-1 body weight of omega-3 fatty acid emulsion i.v. or equal volumes of saline. Changes in pericytes, perivascular macrophages, BBB opening, microglial activation, and inattention were evaluated.

RESULTS

Omega-3 fatty acids protected barrier permeability, endothelial tight junctions, and VCAM-1 after exposure to IL-1β in the BBB model. In vivo studies confirmed that omega-3 fatty acid treatment inhibited surgery-induced BBB impairment, microglial activation, and delirium-like behaviour. We identified a novel role for pericyte loss and perivascular macrophage activation in mice after surgery, which were rescued by prophylaxis with i.v. omega-3 fatty acids.

CONCLUSIONS

We present a new approach to study neuroimmune interactions relevant to perioperative recovery using a microphysiological BBB platform. Changes in barrier function, including dysregulation of pericytes and perivascular macrophages, provide new targets to reduce postoperative delirium.

Approaches for the isolation and long-term expansion of pericytes from human and animal tissues

Pericytes surround capillaries in every organ of the human body. They are also present around the vasa vasorum, the small blood vessels that supply the walls of larger arteries and veins. The clinical interest in pericytes is rapidly growing, with the recognition of their crucial roles in controlling vascular function and possible therapeutic applications in regenerative medicine. Nonetheless, discrepancies in methods used to define, isolate, and expand pericytes are common and may affect reproducibility. Separating pure pericyte preparations from the continuum of perivascular mesenchymal cells is challenging. Moreover, variations in functional behavior and antigenic phenotype in response to environmental stimuli make it difficult to formulate an unequivocal definition of bona fide pericytes. Very few attempts were made to develop pericytes as a clinical-grade product. Therefore, this review is devoted to appraising current methodologies' pros and cons and proposing standardization and harmonization improvements. We highlight the importance of developing upgraded protocols to create therapeutic pericyte products according to the regulatory guidelines for clinical manufacturing. Finally, we describe how integrating RNA-seq techniques with single-cell spatial analysis, and functional assays may help realize the full potential of pericytes in health, disease, and tissue repair.

Expression patterns of NKCC1 in neurons and non-neuronal cells during cortico-hippocampal development

The Na-K-2Cl cotransporter NKCC1 is widely expressed in cells within and outside the brain. However, our understanding of its roles in brain functions throughout development, as well as in neuropsychiatric and neurological disorders, has been severely hindered by the lack of reliable data on its developmental and (sub)cellular expression patterns. We provide here the first properly controlled analysis of NKCC1 protein expression in various cell types of the mouse brain using custom-made antibodies and an NKCC1 knock-out validated immunohistochemical procedure, with parallel data based on advanced mRNA approaches. NKCC1 protein and mRNA are expressed at remarkably high levels in oligodendrocytes. In immature neurons, NKCC1 protein was located in the somata, whereas in adult neurons, only NKCC1 mRNA could be clearly detected. NKCC1 immunoreactivity is also seen in microglia, astrocytes, developing pericytes, and in progenitor cells of the dentate gyrus. Finally, a differential expression of NKCC1 splice variants was observed, with NKCC1a predominating in non-neuronal cells and NKCC1b in neurons. Taken together, our data provide a cellular basis for understanding NKCC1 functions in the brain and enable the identification of major limitations and promises in the development of neuron-targeting NKCC1-blockers.

The Multiple Roles of Pericytes in Vascular Formation and Microglial Functions in the Brain

In the capillary walls, vascular endothelial cells are covered with mural cells, such as smooth muscle cells and pericytes. Although pericytes had been thought to play simply a structural role, emerging evidence has highlighted their multiple functions in the embryonic, postnatal, and adult brain. As the central nervous system (CNS) develops, the brain's vascular structure gradually matures into a hierarchical network, which is crucial for the proper development of neural lineage cells by providing oxygen and nutrients. Pericytes play an essential role in vascular formation and regulate blood‒brain barrier (BBB) integrity as a component of the neurovascular unit (NVU), in collaboration with other cells, such as vascular endothelial cells, astrocytes, neurons, and microglia. Microglia, the resident immune cells of the CNS, colonize the brain at embryonic day (E) 9.5 in mice. These cells not only support the development and maturation of neural lineage cells but also help in vascular formation through their extensive migration. Recent studies have demonstrated that pericytes directly contact microglia in the CNS, and their interactions have a profound effect on physiological and pathological aspects. This review summarizes the function of pericytes, focusing on the interplay between pericytes and microglia.

CRISPR-mediated MECOM depletion retards tumor growth by reducing cancer stem cell properties in lung squamous cell carcinoma

Targeted therapy for lung squamous cell carcinoma (LUSC) remains a challenge due to the lack of robust targets. Here, we identified MECOM as a candidate of therapeutic target for LUSC by screening 38 genes that were commonly amplified in three pairs of primary tumors and patient-derived xenografts (PDXs) using a clustered regularly interspaced short palindromic repeats (CRISPR)-mediated approach. High MECOM expression levels were associated with poor prognosis. Forced expression of MECOM in LUSC cell lines promoted cancer stem cell (CSC) properties, and its knockout inhibited CSC phenotypes. Furthermore, systemic delivery of CRISPR-mediated MECOM depletion cassette using adenovirus with an adaptor, which is composed of a single-chain fragment variable (scFv) against epithelial cell adhesion molecules (EpCAM) fused to the ectodomain of coxsackievirus and adenovirus receptor, and a protector, which consists of the scFv connected to the hexon symmetry of the adenovirus, could specifically target subcutaneous and orthotopic LUSC and retard tumor growth. This study could provide a novel therapeutic strategy for LUSC with high efficacy and specificity.

Maternal immune activation leads to defective brain-blood vessels and intracerebral hemorrhages in male offspring

Intracerebral hemorrhages are recognized risk factors for neurodevelopmental disorders and represent early biomarkers for cognitive dysfunction and mental disability, but the pathways leading to their occurrence are not well defined. We report that a single intrauterine exposure of the immunostimulant Poly I:C to pregnant mice at gestational day 9, which models a prenatal viral infection and the consequent maternal immune activation, induces the defective formation of brain vessels and causes intracerebral hemorrhagic events, specifically in male offspring. We demonstrate that maternal immune activation promotes the production of the TGF-β1 active form and the consequent enhancement of pSMAD1-5 in males' brain endothelial cells. TGF-β1, in combination with IL-1β, reduces the endothelial expression of CD146 and claudin-5, alters the endothelium-pericyte interplay resulting in low pericyte coverage, and increases hemorrhagic events in the adult offspring. By showing that exposure to Poly I:C at the beginning of fetal cerebral angiogenesis results in sex-specific alterations of brain vessels, we provide a mechanistic framework for the association between intragravidic infections and anomalies of the neural vasculature, which may contribute to neuropsychiatric disorders.

Soluble ANPEP Released From Human Astrocytes as a Positive Regulator of Microglial Activation and Neuroinflammation: Brain Renin-Angiotensin System in Astrocyte-Microglia Crosstalk

Astrocytes are major supportive glia and immune modulators in the brain; they are highly secretory in nature and interact with other cell types via their secreted proteomes. To understand how astrocytes communicate during neuroinflammation, we profiled the secretome of human astrocytes following stimulation with proinflammatory factors. A total of 149 proteins were significantly upregulated in stimulated astrocytes, and a bioinformatics analysis of the astrocyte secretome revealed that the brain renin-angiotensin system (RAS) is an important mechanism of astrocyte communication. We observed that the levels of soluble form of aminopeptidase N (sANPEP), an RAS component that converts angiotensin (Ang) III to Ang IV in a neuroinflammatory milieu, significantly increased in the astrocyte secretome. To elucidate the role of sANPEP and Ang IV in neuroinflammation, we first evaluated the expression of Ang IV receptors in human glial cells because Ang IV mediates biological effects through its receptors. The expression of angiotensin type 1 receptor was considerably upregulated in activated human microglial cells but not in human astrocytes. Moreover, interleukin-1β release from human microglial cells was synergistically increased by cotreatment with sANPEP and its substrate, Ang III, suggesting the proinflammatory action of Ang IV generated by sANPEP. In a mouse neuroinflammation model, brain microglial activation and proinflammatory cytokine expression levels were increased by intracerebroventricular injection of sANPEP and attenuated by an enzymatic inhibitor and neutralizing antibody against sANPEP. Collectively, our results indicate that astrocytic sANPEP-induced increase in Ang IV exacerbates neuroinflammation by interacting with microglial proinflammatory receptor angiotensin type 1 receptor, highlighting an important role of indirect crosstalk between astrocytes and microglia through the brain RAS in neuroinflammation.

Histones of Neutrophil Extracellular Traps Induce CD11b Expression in Brain Pericytes Via Dectin-1 after Traumatic Brain Injury

The brain pericyte is a unique and indispensable part of the blood-brain barrier (BBB), and contributes to several pathological processes in traumatic brain injury (TBI). However, the cellular and molecular mechanisms by which pericytes are regulated in the damaged brain are largely unknown. Here, we show that the formation of neutrophil extracellular traps (NETs) induces the appearance of CD11b+ pericytes after TBI. These CD11b+ pericyte subsets are characterized by increased permeability and pro-inflammatory profiles compared to CD11b- pericytes. Moreover, histones from NETs by Dectin-1 facilitate CD11b induction in brain pericytes in PKC-c-Jun dependent manner, resulting in neuroinflammation and BBB dysfunction after TBI. These data indicate that neutrophil-NET-pericyte and histone-Dectin-1-CD11b are possible mechanisms for the activation and dysfunction of pericytes. Targeting NETs formation and Dectin-1 are promising means of treating TBI.

Ensembles of endothelial and mural cells promote angiogenesis in prenatal human brain

Interactions between angiogenesis and neurogenesis regulate embryonic brain development. However, a comprehensive understanding of the stages of vascular cell maturation is lacking, especially in the prenatal human brain. Using fluorescence-activated cell sorting, single-cell transcriptomics, and histological and ultrastructural analyses, we show that an ensemble of endothelial and mural cell subtypes tile the brain vasculature during the second trimester. These vascular cells follow distinct developmental trajectories and utilize diverse signaling mechanisms, including collagen, laminin, and midkine, to facilitate cell-cell communication and maturation. Interestingly, our results reveal that tip cells, a subtype of endothelial cells, are highly enriched near the ventricular zone, the site of active neurogenesis. Consistent with these observations, prenatal vascular cells transplanted into cortical organoids exhibit restricted lineage potential that favors tip cells, promotes neurogenesis, and reduces cellular stress. Together, our results uncover important mechanisms into vascular maturation during this critical period of human brain development.

Pathological pericyte expansion and impaired endothelial cell-pericyte communication in endothelial Rbpj deficient brain arteriovenous malformation

Pericytes, like vascular smooth muscle cells, are perivascular cells closely associated with blood vessels throughout the body. Pericytes are necessary for vascular development and homeostasis, with particularly critical roles in the brain, where they are involved in regulating cerebral blood flow and establishing the blood-brain barrier. A role for pericytes during neurovascular disease pathogenesis is less clear—while some studies associate decreased pericyte coverage with select neurovascular diseases, others suggest increased pericyte infiltration in response to hypoxia or traumatic brain injury. Here, we used an endothelial loss-of-function Recombination signal binding protein for immunoglobulin kappa J region (Rbpj)/Notch mediated mouse model of brain arteriovenous malformation (AVM) to investigate effects on pericytes during neurovascular disease pathogenesis. We tested the hypothesis that pericyte expansion, via morphological changes, and Platelet-derived growth factor B/Platelet-derived growth factor receptor β (Pdgf-B/Pdgfrβ)-dependent endothelial cell-pericyte communication are affected, during the pathogenesis of Rbpj mediated brain AVM in mice. Our data show that pericyte coverage of vascular endothelium expanded pathologically, to maintain coverage of vascular abnormalities in brain and retina, following endothelial deletion of Rbpj. In Rbpj-mutant brain, pericyte expansion was likely attributed to cytoplasmic process extension and not to increased pericyte proliferation. Despite expanding overall area of vessel coverage, pericytes from Rbpj-mutant brains showed decreased expression of Pdgfrβ, Neural (N)-cadherin, and cluster of differentiation (CD)146, as compared to controls, which likely affected Pdgf-B/Pdgfrβ-dependent communication and appositional associations between endothelial cells and pericytes in Rbpj-mutant brain microvessels. By contrast, and perhaps by compensatory mechanism, endothelial cells showed increased expression of N-cadherin. Our data identify cellular and molecular effects on brain pericytes, following endothelial deletion of Rbpj, and suggest pericytes as potential therapeutic targets for Rbpj/Notch related brain AVM.

Proteomic profiling of concurrently isolated primary microvascular endothelial cells, pericytes, and vascular smooth muscle cells from adult mouse heart

The microcirculation serves crucial functions in adult heart, distinct from those carried out by epicardial vessels. Microvessels are governed by unique regulatory mechanisms, impairment of which leads to microvessel-specific pathology. There are few treatment options for patients with microvascular heart disease, primarily due to limited understanding of underlying pathology. High throughput mRNA sequencing and protein expression profiling in specific cells can improve our understanding of microvessel biology and disease at the molecular level. Understanding responses of individual microvascular cells to the same physiological or pathophysiological stimuli requires the ability to isolate the specific cell types that comprise the functional units of the microcirculation in the heart, preferably from the same heart, to ensure that different cells have been exposed to the same in-vivo conditions. We developed an integrated process for simultaneous isolation and culture of the main cell types comprising the microcirculation in adult mouse heart: endothelial cells, pericytes, and vascular smooth muscle cells. These cell types were characterized with isobaric labeling quantitative proteomics and mRNA sequencing. We defined microvascular cell proteomes, identified novel protein markers, and confirmed established cell-specific markers. Our results allow identification of unique markers and regulatory proteins that govern microvascular physiology and pathology.

Brain Microvascular Pericytes—More than Bystanders in Breast Cancer Brain Metastasis

Brain tissue contains the highest number of perivascular pericytes compared to other organs. Pericytes are known to regulate brain perfusion and to play an important role within the neurovascular unit (NVU). The high phenotypic and functional plasticity of pericytes make this cell type a prime candidate to aid physiological adaptations but also propose pericytes as important modulators in diverse pathologies in the brain. This review highlights known phenotypes of pericytes in the brain, discusses the diverse markers for brain pericytes, and reviews current in vitro and in vivo experimental models to study pericyte function. Our current knowledge of pericyte phenotypes as it relates to metastatic growth patterns in breast cancer brain metastasis is presented as an example for the crosstalk between pericytes, endothelial cells, and metastatic cells. Future challenges lie in establishing methods for real-time monitoring of pericyte crosstalk to understand causal events in the brain metastatic process.

Protrudin regulates FAK activation, endothelial cell migration and angiogenesis

During angiogenesis, endothelial cells form protrusive sprouts and migrate towards the angiogenic stimulus. In this study, we investigate the role of the endoplasmic reticulum (ER)-anchored protein, Protrudin, in endothelial cell protrusion, migration and angiogenesis. Our results demonstrate that Protrudin regulates angiogenic tube formation in primary endothelial cells, Human umbilical vein endothelial cells (HUVECs). Analysis of RNA sequencing data and its experimental validation revealed cell migration as a prominent cellular function affected in HUVECs subjected to Protrudin knockdown. Further, our results demonstrate that knockdown of Protrudin inhibits focal adhesion kinase (FAK) activation in HUVECs and human aortic endothelial cells (HAECs). This is associated with a loss of polarized phospho-FAK distribution upon Protrudin knockdown as compared to Protrudin expressing HUVECs. Reduction of Protrudin also results in a perinuclear accumulation of mTOR and a decrease in VEGF-mediated S6K activation. However, further experiments suggest that the observed inhibition of angiogenesis in Protrudin knockdown cells is not affected by mTOR disturbance. Therefore, our findings suggest that defects in FAK activation and its abnormal subcellular distribution upon Protrudin knockdown are associated with a detrimental effect on endothelial cell migration and angiogenesis. Furthermore, mice with global Protrudin deletion demonstrate reduced retinal vascular progression. To conclude, our results provide evidence for a novel key role of Protrudin in endothelial cell migration and angiogenesis.

Isolation of the side population from neurogenic niches enriches for endothelial cells

In stem cell research, DNA-binding dyes offer the ability to purify live stem cells using flow cytometry as they form a low-fluorescence side population due to the activity of ABC transporters. Adult neural stem cells exist within the lateral ventricle and dentate gyrus of the adult brain yet the ability of DNA-binding dyes to identify these adult stem cells as side populations remains untested. The following experiments utilize the efflux of a DNA-binding dye, Vyrbant DyeCycle Violet (DCV), to isolate bona fide side populations in the mouse dentate gyrus and subventricular zone (SVZ), and test their sensitivity to ABC transporter inhibitors. A distinct side population was found in both the adult lateral ventricle and dentate gyrus using DCV fluorescence and forward scatter instead of the conventional dual fluorescence approach. These side populations responded strongly to inhibition with the ABC transporter antagonists, verapamil and fumitremorgin C. The majority of the cells residing in the side populations of dentate gyrus and SVZ were characterized by their expression of CD31. Additionally, at least 90% of all CD31+ cells found in the dentate gyrus and SVZ were negative for the hematopoietic marker CD45, leading to the hypothesis that the CD31+ cells in the side population were endothelial cells. These findings, therefore, suggest that the side population analysis provides an efficient method to purify CD31-expressing endothelial cells, but not adult neural stem cells.

Direct FACS Isolation of Neural Stem/Progenitor Lineages from the Adult Brain

Adult neural stem and progenitor cells reside in the neurogenic niche of the adult brain and have tremendous potential in regenerative medicine. Compelling evidence suggests that adult neurogenesis plays an important role in hippocampal memory formation, plasticity, and mood regulation. Understanding the mechanisms that regulate the function of neural stem/progenitor cells within the brain is a critical step for the development of regenerative strategies to maintain or enhance neurological function. A major challenge in studying these cells is the limited cell number of adult neural stem cells, and the significant changes in their properties induced by in vitro culture and expansion. To best understand the regulation of these cells, they must be studied within their niche context. In this chapter, we provide a simplified protocol for the harvest and isolation of neural stem cell lineages directly from the murine brain, to provide input material for single-cell RNA-seq. This approach will elucidate the true transcriptional signatures and activated pathways in neural stem cell lineages, within the context of their niche environment.

Profiling the neurovascular unit unveils detrimental effects of osteopontin on the blood-brain barrier in acute ischemic stroke

Blood-brain barrier (BBB) dysfunction, characterized by degradation of BBB junctional proteins and increased permeability, is a crucial pathophysiological feature of acute ischemic stroke. Dysregulation of multiple neurovascular unit (NVU) cell types is involved in BBB breakdown in ischemic stroke that may be further aggravated by reperfusion therapy. Therefore, therapeutic co-targeting of dysregulated NVU cell types in acute ischemic stroke constitutes a promising strategy to preserve BBB function and improve clinical outcome. However, methods for simultaneous isolation of multiple NVU cell types from the same diseased central nervous system (CNS) tissue, crucial for the identification of therapeutic targets in dysregulated NVU cells, are lacking. Here, we present the EPAM-ia method, that facilitates simultaneous isolation and analysis of the major NVU cell types (endothelial cells, pericytes, astrocytes and microglia) for the identification of therapeutic targets in dysregulated NVU cells to improve the BBB function. Applying this method, we obtained a high yield of pure NVU cells from murine ischemic brain tissue, and generated a valuable NVU transcriptome database ( https://bioinformatics.mpi-bn.mpg.de/SGD_Stroke ). Dissection of the NVU transcriptome revealed Spp1, encoding for osteopontin, to be highly upregulated in all NVU cells 24 h after ischemic stroke. Upregulation of osteopontin was confirmed in stroke patients by immunostaining, which was comparable with that in mice. Therapeutic targeting by subcutaneous injection of an anti-osteopontin antibody post-ischemic stroke in mice resulted in neutralization of osteopontin expression in the NVU cell types investigated. Apart from attenuated glial activation, osteopontin neutralization was associated with BBB preservation along with decreased brain edema and reduced risk for hemorrhagic transformation, resulting in improved neurological outcome and survival. This was supported by BBB-impairing effects of osteopontin in vitro. The clinical significance of these findings is that anti-osteopontin antibody therapy might augment current approved reperfusion therapies in acute ischemic stroke by minimizing deleterious effects of ischemia-induced BBB disruption.

[Impaired production of platelet-endothelial cell adhesion molecules as an early diagnostic marker of heart transplant rejection]

OBJECTIVE

Reveal the involvement of platelet-endothelial cell adhesion molecules PECAM-1 in the transplanted heart rejection pathogenesis and determine the CD31 marker significance for biopsy diagnostics of the process form and degree.

MATERIAL AND METHODS

Sections from endomyocardial biopsies of 56 heart transplant recipients were stained with hematoxylin and eosin. The streptavidin-biotin method was used to determine the expression of T-lymphocytes (CD3), B-lymphocytes (CD20), macrophages (CD68) and the C4d component of complement to determine the form and degree of graft rejection. Additionally, the expression of platelet-endothelial cell adhesion molecules PECAM-1 (CD31) was detected. Using computer morphometry in digital images, the area of pathological changes and the area of CD31 expression was measured with the calculation of the staining area coefficient.

RESULTS

The highest levels of PECAM-1 expression were found in the absence of a heart transplant rejection. The degree of rejection of 1R is characterized by a decrease in expression by 1.3 times, when there are no significant signs of necrosis in the myocardium, the area of which increases sharply at degree 2R by 163.7 times, and at 3R by 570.7 times compared with 1R. The process proceeds in parallel with a further decrease in the level of CD31 expression and is accompanied by the development of hemorrhagic manifestations. The intensity of hemorrhages in the myocardium increases by 7.3 times with grade 3R compared with 1R.

CONCLUSION

Expression of PECAM-1 reflects the state of the vascular bed of the heart transplant. Its decrease can be considered as an early pathomorphological marker of transplanted heart rejection. The expression of CD31 continues to decrease with increasing severity of rejection and is accompanied by the progressive development of necrosis and hemorrhages in the graft heart muscle.

An Optimized Protocol for the Mapping of Cell Type-Specific Ribosome-Associated Transcript Isoforms from Small Mouse Brain Regions

Over the past years, technological advances in transcriptomics provided deep insights into gene expression programs and their role in tissue organization and cellular functions. The isolation of ribosome-associated transcripts is a powerful approach for deep profiling of cell type-specific transcripts, and particularly well-suited for quantitative analysis of transcript isoforms. This method employs conditional ribosome epitope-tagging in genetically defined cell types, followed by affinity-isolation of ribosome-associated mRNAs. Advantages of this approach are twofold: first, the method enables rapid retrieval of mRNAs without tissue dissociation and cell sorting steps. Second, capturing of ribosome-associated mRNAs, enriches for transcripts recruited for active translation, therefore providing an approximation to the cellular translatome. Here, we describe one application of this method for the identification of the transcriptome of excitatory neuronal cells (mitral and tufted cells) of the mouse olfactory bulb, through RiboTag isolation from the vGlut2-IRES-cre mouse line as genetic driver of endogenously tagged ribosome expression.

Individual human cortical progenitors can produce excitatory and inhibitory neurons

The cerebral cortex is a cellularly complex structure comprising a rich diversity of neuronal and glial cell types. Cortical neurons can be broadly categorized into two classes-excitatory neurons that use the neurotransmitter glutamate, and inhibitory interneurons that use γ-aminobutyric acid (GABA). Previous developmental studies in rodents have led to a prevailing model in which excitatory neurons are born from progenitors located in the cortex, whereas cortical interneurons are born from a separate population of progenitors located outside the developing cortex in the ganglionic eminences^1-5. However, the developmental potential of human cortical progenitors has not been thoroughly explored. Here we show that, in addition to excitatory neurons and glia, human cortical progenitors are also capable of producing GABAergic neurons with the transcriptional characteristics and morphologies of cortical interneurons. By developing a cellular barcoding tool called 'single-cell-RNA-sequencing-compatible tracer for identifying clonal relationships' (STICR), we were able to carry out clonal lineage tracing of 1,912 primary human cortical progenitors from six specimens, and to capture both the transcriptional identities and the clonal relationships of their progeny. A subpopulation of cortically born GABAergic neurons was transcriptionally similar to cortical interneurons born from the caudal ganglionic eminence, and these cells were frequently related to excitatory neurons and glia. Our results show that individual human cortical progenitors can generate both excitatory neurons and cortical interneurons, providing a new framework for understanding the origins of neuronal diversity in the human cortex.

Application of vascular endothelial cells in stem cell medicine

Stem cell medicine is gaining momentum in the development of therapy for various end-stage diseases. The search for new seed cells and exploration of their application prospects are topics of interest in stem cell medicine. In recent years, vascular endothelial cells (VECs) have attracted wide attention from scholars. VECs, which form the inner lining of blood vessels, are critically involved in many physiological functions, including permeability, angiogenesis, blood pressure regulation, immunity, and pathological development, such as atherosclerosis and malignant tumors. VECs have significant therapeutic effects and broad application prospects in stem cell medicine for the treatment of various refractory diseases, including atherosclerosis, myocardial infarction, diabetic complications, hypertension, coronavirus disease 2019, and malignant tumors. On the one hand, VECs and their extracellular vesicles can be directly used for the treatment of these diseases. On the other hand, VECs can be used as therapeutic targets for some diseases. However, there are still some obstacles to the use of VECs in stem cell medicine. In this review, advances in the applications and challenges that come with the use of these cells are discussed.

Hexokinase 2-driven glycolysis in pericytes activates their contractility leading to tumor blood vessel abnormalities

Defective pericyte-endothelial cell interaction in tumors leads to a chaotic, poorly organized and dysfunctional vasculature. However, the underlying mechanism behind this is poorly studied. Herein, we develop a method that combines magnetic beads and flow cytometry cell sorting to isolate pericytes from tumors and normal adjacent tissues from patients with non-small cell lung cancer (NSCLC) and hepatocellular carcinoma (HCC). Pericytes from tumors show defective blood vessel supporting functions when comparing to those obtained from normal tissues. Mechanistically, combined proteomics and metabolic flux analysis reveals elevated hexokinase 2(HK2)-driven glycolysis in tumor pericytes, which up-regulates their ROCK2-MLC2 mediated contractility leading to impaired blood vessel supporting function. Clinically, high percentage of HK2 positive pericytes in blood vessels correlates with poor patient overall survival in NSCLC and HCC. Administration of a HK2 inhibitor induces pericyte-MLC2 driven tumor vasculature remodeling leading to enhanced drug delivery and efficacy against tumor growth. Overall, these data suggest that glycolysis in tumor pericytes regulates their blood vessel supporting role.

Pericyte-endothelial cells interaction defines tumor vasculature and has implications in tumorigenesis development and therapy efficacy. Here, the authors show that hexokinase 2- driven glycolysis activates ROCK1-MLC2 mediated contractility in pericytes leading to tumor blood vessel abnormality.

An autofluorescence-based isolation of Leydig cells for testosterone deficiency treatment

Effective procedures for the purification of Leydig cells (LCs) can facilitate functional studies and transplantation therapies. However, current methods to purify LCs from testes are still far from satisfactory. Here, we found that testicular autofluorescence existed in the interstitium along with the gradual maturation of LCs from birth to adulthood. These autofluorescent cells were further isolated by fluorescence-activated cell sorting (FACS) and determined to be composed of LCs and macrophages. To further purify LCs, we combined two fluorescence channels of FACS and successfully separated LCs and macrophages. Of note, we confirmed that the obtained LCs not only possessed high purity, viability and quantity but also had intact steroidogenic activity and excellent responsiveness to luteinizing hormone. Moreover, subcutaneous transplantation of isolated LCs could alleviate the symptoms of testosterone deficiency in castrated mice. In summary, we established an effective autofluorescence-based method for isolating LCs. This method will aid in the future success of using LCs for basic and translational applications.