Circulating small extracellular vesicles mediate vascular hyperpermeability in diabetes

AIMS/HYPOTHESIS

A hallmark chronic complication of type 2 diabetes mellitus is vascular hyperpermeability, which encompasses dysfunction of the cerebrovascular endothelium and the subsequent development of associated cognitive impairment. The present study tested the hypothesis that during type 2 diabetes circulating small extracellular vesicles (sEVs) exhibit phenotypic changes that facilitate pathogenic disruption of the vascular barrier.

METHODS

sEVs isolated from the plasma of a mouse model of type 2 diabetes and from diabetic human individuals were characterised for their ability to disrupt the endothelial cell (EC) barrier. The contents of sEVs and their effect on recipient ECs were assessed by proteomics and identified pathways were functionally interrogated with small molecule inhibitors.

RESULTS

Using intravital imaging, we found that diabetic mice (Leprdb/db) displayed hyperpermeability of the cerebrovasculature. Enhanced vascular leakiness was recapitulated following i.v. injection of sEVs from diabetic mice into non-diabetic recipient mice. Characterisation of circulating sEV populations from the plasma of diabetic mice and humans demonstrated increased quantity and size of sEVs compared with those isolated from non-diabetic counterparts. Functional experiments revealed that sEVs from diabetic mice or humans induced the rapid and sustained disruption of the EC barrier through enhanced paracellular and transcellular leak but did not induce inflammation. Subsequent sEV proteome and recipient EC phospho-proteome analysis suggested that extracellular vesicles (sEVs) from diabetic mice and humans modulate the MAPK/MAPK kinase (MEK) and Rho-associated protein kinase (ROCK) pathways, cell-cell junctions and actin dynamics. This was confirmed experimentally. Treatment of sEVs with proteinase K or pre-treatment of recipient cells with MEK or ROCK inhibitors reduced the hyperpermeability-inducing effects of circulating sEVs in the diabetic state.

CONCLUSIONS/INTERPRETATION

Diabetes is associated with marked increases in the concentration and size of circulating sEVs. The modulation of sEV-associated proteins under diabetic conditions can induce vascular leak through activation of the MEK/ROCK pathway. These data identify a new paradigm by which diabetes can induce hyperpermeability and dysfunction of the cerebrovasculature and may implicate sEVs in the pathogenesis of cognitive decline during type 2 diabetes.

Exercise-Dependent Modulation of Immunological Response Pathways in Endurance Athletes With and Without Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) is a common arrhythmia characterized by uncoordinated atrial electrical activity. Lone AF occurs in the absence of traditional risk factors and is frequently observed in male endurance athletes, who face a 2- to 5-fold higher risk of AF compared with healthy, moderately active males. Our understanding of how endurance exercise contributes to the pathophysiology of lone AF remains limited. This study aimed to characterize the circulating protein fluctuations during high-intensity exercise as well as explore potential biomarkers of exercise-associated AF.

METHODS AND RESULTS

A prospective cohort of 12 male endurance cyclists between the ages of 40 and 65 years, 6 of whom had a history of exercise-associated AF, were recruited to participate using a convenience sampling method. The circulating proteome was subsequently analyzed using multiplex immunoassays and aptamer-based proteomics before, during, and after an acute high-intensity endurance exercise bout to assess temporality and identify potential markers of AF. The endurance exercise bout resulted in significant alterations to proteins involved in immune modulation (eg, growth/differentiation factor 15), skeletal muscle metabolism (eg, α-actinin-2), cell death (eg, histones), and inflammation (eg, interleukin-6). Subjects with AF differed from those without, displaying modulation of proteins previously known to have associations with incident AF (eg, C-reactive protein, insulin-like growth factor-1, and angiopoietin-2), and also with proteins having no previous association (eg, tapasin-related protein and α2-Heremans-Schmid glycoprotein).

CONCLUSIONS

These findings provide insights into the proteomic response to acute intense exercise, provide mechanistic insights into the pathophysiology behind AF in athletes, and identify targets for future study and validation.

The liver and muscle secreted HFE2-protein maintains central nervous system blood vessel integrity

Liver failure causes breakdown of the Blood CNS Barrier (BCB) leading to damages of the Central-Nervous-System (CNS), however the mechanisms whereby the liver influences BCB-integrity remain elusive. One possibility is that the liver secretes an as-yet to be identified molecule(s) that circulate in the serum to directly promote BCB-integrity. To study BCB-integrity, we developed light-sheet imaging for three-dimensional analysis. We show that liver- or muscle-specific knockout of Hfe2/Rgmc induces BCB-breakdown, leading to accumulation of toxic-blood-derived fibrinogen in the brain, lower cortical neuron numbers, and behavioral deficits in mice. Soluble HFE2 competes with its homologue RGMa for binding to Neogenin, thereby blocking RGMa-induced downregulation of PDGF-B and Claudin-5 in endothelial cells, triggering BCB-disruption. HFE2 administration in female mice with experimental autoimmune encephalomyelitis, a model for multiple sclerosis, prevented paralysis and immune cell infiltration by inhibiting RGMa-mediated BCB alteration. This study has implications for the pathogenesis and potential treatment of diseases associated with BCB-dysfunction.

Directional Endothelial Communication by Polarized Extracellular Vesicle Release

BACKGROUND

Extracellular vesicles (EVs) contain bioactive cargo including miRNAs and proteins that are released by cells during cell-cell communication. Endothelial cells (ECs) form the innermost lining of all blood vessels, interfacing with cells in the circulation and vascular wall. It is unknown whether ECs release EVs capable of governing recipient cells within these 2 separate compartments. Given their boundary location, we propose ECs use bidirectional release of distinct EV cargo in quiescent (healthy) and activated (atheroprone) states to communicate with cells within the circulation and blood vessel wall.

METHODS

EVs were isolated from primary human aortic ECs (plate and transwell grown; ±IL [interleukin]-1β activation), quantified, visualized, and analyzed by miRNA transcriptomics and proteomics. Apical and basolateral EC-EV release was determined by miRNA transfer, total internal reflection fluorescence and electron microscopy. Vascular reprogramming (RNA sequencing) and functional assays were performed on primary human monocytes or smooth muscle cells±EC-EVs.

RESULTS

Activated ECs increased EV release, with miRNA and protein cargo related to atherosclerosis. EV-treated monocytes and smooth muscle cells revealed activated EC-EV altered pathways that were proinflammatory and atherogenic. ECs released more EVs apically, which increased with activation. Apical and basolateral EV cargo contained distinct transcriptomes and proteomes that were altered by EC activation. Notably, activated basolateral EC-EVs displayed greater changes in the EV secretome, with pathways specific to atherosclerosis. In silico analysis determined compartment-specific cargo released by the apical and basolateral surfaces of ECs can reprogram monocytes and smooth muscle cells, respectively, with functional assays and in vivo imaging supporting this concept.

CONCLUSIONS

Demonstrating that ECs are capable of polarized EV cargo loading and directional EV secretion reveals a novel paradigm for endothelial communication, which may ultimately enhance the design of endothelial-based therapeutics for cardiovascular diseases such as atherosclerosis where ECs are persistently activated.

High sensitivity c-reactive protein and circulating biomarkers of endothelial dysfunction in patients with chronic myeloid leukemia receiving tyrosine kinase inhibitors

Tyrosine kinase inhibitors (TKIs) have revolutionized the management of patients with chronic myelogenous leukemia (CML); however, they may cause cardiovascular (CV) toxicities. In this cross-sectional study, we explored whether high-sensitivity C-reactive protein (hsCRP) and novel markers of vascular dysfunction were associated with exposure to specific TKIs, in 262 CML patients. Hs-CRP level was not associated with CML disease activity or treatment with a specific TKI. Body mass index (OR: 1.15, 95% CI: 1.108-1.246; p < 0.001) and CML duration (OR: 1.004, 95% CI: 1.001-1.008; p = 0.024) were independently associated with higher hs-CRP. In exploratory analyses, novel endothelial-centric markers (e.g. ET-1 and VCAM-1) were differential across the various TKIs, particularly amongst nilotinib- and ponatinib-treated patients. While Levels of hs-CRP do not appear to be correlated with specific TKIs, circulating markers of vascular dysfunction were altered in patients treated with specific TKIs and should be explored as potential markers of TKI-associated CV risk.

The Role and Therapeutic Implications of Inflammation in the Pathogenesis of Brain Arteriovenous Malformations

Brain arteriovenous malformations (bAVMs) are focal vascular lesions composed of abnormal vascular channels without an intervening capillary network. As a result, high-pressure arterial blood shunts directly into the venous outflow system. These high-flow, low-resistance shunts are composed of dilated, tortuous, and fragile vessels, which are prone to rupture. BAVMs are a leading cause of hemorrhagic stroke in children and young adults. Current treatments for bAVMs are limited to surgery, embolization, and radiosurgery, although even these options are not viable for ~20% of AVM patients due to excessive risk. Critically, inflammation has been suggested to contribute to lesion progression. Here we summarize the current literature discussing the role of the immune system in bAVM pathogenesis and lesion progression, as well as the potential for targeting inflammation to prevent bAVM rupture and intracranial hemorrhage. We conclude by proposing that a dysfunctional endothelium, which harbors the somatic mutations that have been shown to give rise to sporadic bAVMs, may drive disease development and progression by altering the immune status of the brain.

Multimodality Cardiac Imaging, Cardiac Symptoms, and Clinical Outcomes in Patients Who Recovered from Mild COVID-19

Background Many patients have persistent cardiac symptoms after mild COVID-19. However, studies assessing the relationship between symptoms and cardiac imaging are limited. Purpose To assess the relationship between multi-modality cardiac imaging parameters, symptoms, and clinical outcomes in patients recovered from mild COVID-19 compared to COVID-19 negative controls. Materials and Methods Patients who underwent PCR testing for SARS-CoV-2 between August 2020 and January 2022 were invited to participate in this prospective, single-center study. Participants underwent cardiac MRI, echocardiography, and assessment of cardiac symptoms at 3-6 months after SARS-CoV-2 testing. Cardiac symptoms and outcomes were also evaluated at 12-18 months. Statistical analysis included Fisher's exact test and logistic regression. Results This study included 122 participants who recovered from COVID-19 ([COVID+] mean age, 42 years ± 13 [SD]; 73 females) and 22 COVID-19 negative controls (mean age, 46 years ± 16 [SD]; 13 females). At 3-6 months, 20% (24/122) and 44% (54/122) of COVID+ participants had at least one abnormality on echocardiography and cardiac MRI, respectively, which did not differ compared to controls (23% [5/22]; P = .77 and 41% [9/22]; P = .82, respectively). However, COVID+ participants more frequently reported cardiac symptoms at 3-6 months compared to controls (48% [58/122] vs. 23% [4/22]; P = .04). An increase in native T1 (10 ms) was associated with increased odds of cardiac symptoms at 3-6 months (OR, 1.09 [95% CI: 1.00, 1.19]; P = .046) and 12-18 months (OR, 1.14 [95% CI: 1.01, 1.28]; P = .028). No major adverse cardiac events occurred during follow-up. Conclusion Patients recovered from mild COVID-19 reported increased cardiac symptoms 3-6 months after diagnosis compared to controls, but the prevalence of abnormalities on echocardiography and cardiac MRI did not differ between groups. Elevated native T1 was associated with cardiac symptoms 3-6 months and 12-18 months after mild COVID-19.

Endothelial cells secrete small extracellular vesicles bidirectionally containing distinct cargo to uniquely reprogram vascular cells in the circulation and vessel wall

Rationale

Extracellular vesicles (EVs) contain bioactive cargo including microRNAs (miRNAs) and proteins that are released by cells as a form of cell-cell communication. Endothelial cells (ECs) form the innermost lining of all blood vessels and thereby interface with cells in the circulation as well as cells residing in the vascular wall. It is unknown whether ECs have the capacity to release EVs capable of governing recipient cells within two separate compartments, and how this is affected by endothelial activation commonly seen in atheroprone regions.

Objective

Given their boundary location, we propose that ECs utilize bidirectional release of distinct EV cargo in quiescent and activated states to communicate with cells within the circulation and blood vessel wall.

Methods and Results

EVs were isolated from primary human aortic endothelial cells (ECs) (+/-IL-1β activation), quantified, and analysed by miRNA transcriptomics and proteomics. Compared to quiescent ECs, activated ECs increased EV release, with miRNA and protein cargo that were related to atherosclerosis. RNA sequencing of EV-treated monocytes and smooth muscle cells (SMCs) revealed that EVs from activated ECs altered pathways that were pro-inflammatory and atherogenic. Apical and basolateral EV release was assessed using ECs on transwells. ECs released more EVs apically, which increased with activation. Apical and basolateral EV cargo contained distinct transcriptomes and proteomes that were altered by EC activation. Notably, basolateral EC-EVs displayed greater changes in the EV secretome, with pathways specific to atherosclerosis. In silico analysis determined that compartment-specific cargo released by the apical and basolateral surfaces of ECs can reprogram monocytes and SMCs, respectively.

Conclusions

The demonstration that ECs are capable of polarized EV cargo loading and directional EV secretion reveals a novel paradigm for endothelial communication, which may ultimately enhance our ability to design endothelial-based therapeutics for cardiovascular diseases such as atherosclerosis where ECs are persistently activated.

Myocardial Inflammation on FDG PET/MRI and Clinical Outcomes in Symptomatic and Asymptomatic Participants after COVID-19 Vaccination

Purpose

To evaluate potential cardiac sequelae of COVID-19 vaccination at 2-month follow-up and relate cardiac symptoms to myocardial tissue changes on fluorodeoxyglucose (FDG) PET/MRI, blood biomarkers, health-related quality of life, and adverse outcomes.

Materials and Methods

In this prospective study (ClinicalTrials.gov: NCT04967807), a convenience sample of individuals aged ≥17 years were enrolled after COVID-19 vaccination and were categorized as symptomatic myocarditis (new cardiac symptoms within 14 days of vaccination and met diagnostic criteria for acute myocarditis), symptomatic no myocarditis (new cardiac symptoms but did not meet criteria for myocarditis), and asymptomatic (no new cardiac symptoms). Standardized evaluation was performed 2 months after vaccination, including cardiac fluorine 18 FDG PET/MRI, blood biomarkers, and health-related quality of life. Statistical analysis included Kruskal-Wallis and Fisher exact tests.

Results

Fifty-four participants were evaluated a median of 72 days (IQR: 42, 91) after COVID-19 vaccination, 17 symptomatic with myocarditis (36±[SD]15 years, 13 males), 17 symptomatic without myocarditis (42±12 years, 7 males), and 20 asymptomatic (45±14 years, 9 males). No participants in the symptomatic without myocarditis or asymptomatic groups had focal FDG-uptake, myocardial edema or impaired ventricular function. Two participants with symptomatic myocarditis had focal FDG-uptake, and three had high T2 on MRI. Health-related quality of life was lower in the symptomatic myocarditis group than the asymptomatic group. There were no adverse cardiac events beyond myocarditis in any participant.

Conclusions

At two-month follow-up, FDG PET/MRI showed evidence of myocardial inflammation in 2/17 participants diagnosed with acute myocarditis early after COVID-19 vaccination, but not in symptomatic and asymptomatic participants without acute myocarditis.Keywords: Myocarditis, Vaccination, COVID-19, PET/MRI, Cardiac MRI, FDG-PET.

Angiopoietin-1 derived peptide hydrogel promotes molecular hallmarks of regeneration and wound healing in dermal fibroblasts

By providing an ideal environment for healing, biomaterials can be designed to facilitate and encourage wound regeneration. As the wound healing process is complex, there needs to be consideration for the cell types playing major roles, such as fibroblasts. As a major cell type in the dermis, fibroblasts have a large impact on the processes and outcomes of wound healing. Prevopisly, conjugating the angiopoietin-1 derived Q-peptide (QHREDGS) to a collagen-chitosan hydrogel created a biomaterial with in vivo success in accelerating wound healing. This study utilized solvent cast Q-peptide conjugated collagen-chitosan seeded with fibroblast monolayers to investigate the direct impact of the material on this major cell type. After 24 h, fibroblasts had a significant change in release of anti-inflammatory, pro-healing, and ECM deposition cytokines, with demonstrated immunomodulatory effects on macrophages and upregulated expression of critical wound healing genes.

Endothelial ACKR1 is induced by neutrophil contact and down-regulated by secretion in extracellular vesicles

Atypical chemokine receptor-1 (ACKR1), previously known as the Duffy antigen receptor for chemokines, is a widely conserved cell surface protein that is expressed on erythrocytes and the endothelium of post-capillary venules. In addition to being the receptor for the parasite causing malaria, ACKR1 has been postulated to regulate innate immunity by displaying and trafficking chemokines. Intriguingly, a common mutation in its promoter leads to loss of the erythrocyte protein but leaves endothelial expression unaffected. Study of endothelial ACKR1 has been limited by the rapid down-regulation of both transcript and protein when endothelial cells are extracted and cultured from tissue. Thus, to date the study of endothelial ACKR1 has been limited to heterologous over-expression models or the use of transgenic mice. Here we report that exposure to whole blood induces ACKR1 mRNA and protein expression in cultured primary human lung microvascular endothelial cells. We found that contact with neutrophils is required for this effect. We show that NF-κB regulates ACKR1 expression and that upon removal of blood, the protein is rapidly secreted by extracellular vesicles. Finally, we confirm that endogenous ACKR1 does not signal upon stimulation with IL-8 or CXCL1. Our observations define a simple method for inducing endogenous endothelial ACKR1 protein that will facilitate further functional studies.

Abstract 284: Transcriptional Profiling Of Human Abdominal Aortic Aneurysm Tissue Reveals Distinct Extracellular Vesicle-Derived MicroRNA Cargo

Aim: Abdominal aortic aneurysm (AAA) contributes to significant post-rupture mortality in aging populations. AAA management with watchful waiting and surgical repair is based on our limited understanding of disease processes, and current research foci including extracellular vesicles (EVs; nano-sized packages of proteins, RNAs, and lipids that facilitate intercellular communication) may aid in developing novel AAA therapies. To characterize this regulatory cargo, we isolated EVs from human AAA tissue or control aortic punch biopsies and profiled EV content with microRNA (miRNA) sequencing to identify dysregulated pathways.

Methods: The study was approved by the University Health Network Research Ethics Board. EVs were isolated from human AAA or aortic punch tissue and enriched using size exclusion chromatography (SEC; qEVoriginal columns 70 nm, Izon Science Ltd.) (n=3). EV size and concentration were determined using nanoparticle tracking analysis (NTA; NanoSight NS300, Malvern Panalytical Ltd.). EV-miRNA sequencing was performed with Illumina NextSeq (HTG Molecular Diagnostics Inc.) and analyzed using Partek Genomics Suite (v.10) and MIENTURNET (19-11-25).

Results: Patients were selected for infrarenal AAA requiring surgical repair (AAA) or coronary artery disease requiring bypass graft surgery (control). EV size and concentration were confirmed with NTA. Principal components and gene set analyses revealed distinct clustering of tissue types with 901 and 687 miRNAs enriched in AAA and control samples, respectively. Pathway prediction using established AAA miRNAs (e.g., miR-122, miR-146a, and miR-503) identified significant interactions with proaneurysmal signaling pathways (e.g., PI3K-AKT, JAK-STAT, and HIF-1) as well as cell senescence and adhesion processes (FDR < 0.05).

Conclusion: EV-derived miRNAs from patients with AAA prominently associate with cell signaling, senescence, and adhesion pathways in aneurysm pathogenesis. To our knowledge, this is the first study to profile the EV-miRNA landscape in human AAA tissue. Further investigation will explore EV-miRNAs as mediators of communication between distinct vascular cell populations that contribute to AAA development.

Abstract 347: Using Deep Convolutional Neural Networks To Automate Classification Of Carotid Plaques From Ultrasound Imaging

Background: Stroke is a devastating consequence of plaque rupture from the carotid arteries. Current management of carotid plaques involves waiting for symptoms (e.g., stroke or mini-stroke), as intervention itself has risk of stroke and not all plaques are vulnerable to rupture. There is a need to better risk-stratify plaque that causes stroke. Carotid ultrasound (US) is a non-invasive and inexpensive visualization of plaques but is limited by human interpretation. We hypothesize that convolutional neural networks (CNNs) will identify unique features of carotid plaques for automated risk stratification.

Methods: Our workflow is illustrated in Fig. a. A total of 141 B-mode US images of carotid arteries were included; 64 high-risk with symptomatic carotid plaques and 75 low-risk with no significant plaque. Data was cropped and divided into training (70%) and holdout test (30%) subsets. During model training, an ensemble of ResNet-18 CNNs learned classification of low-risk and high-risk cases using five-fold stratified cross validation and was used to predict on the holdout test set. The model was evaluated using ROC-AUC and sensitivity. Saliency maps were used for model interpretability to highlight relevant pixels for model decisions.

Results: The cross-validation AUC was 0.995 ± 0.010. The testing AUC was 0.909 and class-wise sensitivities were 0.88 (low-risk) and 0.79 (high-risk). The density plot (Fig. b) shows that the classifier correctly identifies both classes with confidence. Model interpretability using saliency maps (Fig. c) shows pixels corresponding to carotid artery vessel edges and in high-risk cases, carotid plaques.

Conclusions: Using this proof-of-concept model, carotid US long axis images are sufficient to identify high-risk plaques in symptomatic patients - we now need to determine whether we can identify high-risk plaques before symptoms to prevent devastating stroke caused by carotid disease.

The Endothelium as a Hub for Cellular Communication in Atherogenesis: Is There Directionality to the Message?

Endothelial cells line every blood vessel and thereby serve as an interface between the blood and the vessel wall. They have critical functions for maintaining homeostasis and orchestrating vascular pathogenesis. Atherosclerosis is a chronic disease where cholesterol and inflammatory cells accumulate in the artery wall below the endothelial layer and ultimately form plaques that can either progress to occlude the lumen or rupture with thromboembolic consequences – common outcomes being myocardial infarction and stroke. Cellular communication lies at the core of this process. In this review, we discuss traditional (e.g., cytokines, chemokines, nitric oxide) and novel (e.g., extracellular vesicles) modes of endothelial communication with other endothelial cells as well as circulating and vessel wall cells, including monocytes, macrophages, neutrophils, vascular smooth muscle cells and other immune cells, in the context of atherosclerosis. More recently, the growing appreciation of endothelial cell plasticity during atherogenesis suggests that communication strategies are not static. Here, emerging data on transcriptomics in cells during the development of atherosclerosis are considered in the context of how this might inform altered cell-cell communication. Given the unique position of the endothelium as a boundary layer that is activated in regions overlying vascular inflammation and atherosclerotic plaque, there is a potential to exploit the unique features of this group of cells to deliver therapeutics that target the cellular crosstalk at the core of atherosclerotic disease. Data are discussed supporting this concept, as well as inherent pitfalls. Finally, we briefly review the literature for other regions of the body (e.g., gut epithelium) where cells similarly exist as a boundary layer but provide discrete messages to each compartment to govern homeostasis and disease. In this light, the potential for endothelial cells to communicate in a directional manner is explored, along with the implications of this concept – from fundamental experimental design to biomarker potential and therapeutic targets.

Cardiovascular signatures of COVID-19 predict mortality and identify barrier stabilizing therapies

Background

Endothelial cell (EC) activation, endotheliitis, vascular permeability, and thrombosis have been observed in patients with severe coronavirus disease 2019 (COVID-19), indicating that the vasculature is affected during the acute stages of SARS-CoV-2 infection. It remains unknown whether circulating vascular markers are sufficient to predict clinical outcomes, are unique to COVID-19, and if vascular permeability can be therapeutically targeted.

Methods

Prospectively evaluating the prevalence of circulating inflammatory, cardiac, and EC activation markers as well as developing a microRNA atlas in 241 unvaccinated patients with suspected SARS-CoV-2 infection allowed for prognostic value assessment using a Random Forest model machine learning approach. Subsequent ex vivo experiments assessed EC permeability responses to patient plasma and were used to uncover modulated gene regulatory networks from which rational therapeutic design was inferred.

Findings

Multiple inflammatory and EC activation biomarkers were associated with mortality in COVID-19 patients and in severity-matched SARS-CoV-2-negative patients, while dysregulation of specific microRNAs at presentation was specific for poor COVID-19-related outcomes and revealed disease-relevant pathways. Integrating the datasets using a machine learning approach further enhanced clinical risk prediction for in-hospital mortality. Exposure of ECs to COVID-19 patient plasma resulted in severity-specific gene expression responses and EC barrier dysfunction, which was ameliorated using angiopoietin-1 mimetic or recombinant Slit2-N.

Interpretation

Integration of multi-omics data identified microRNA and vascular biomarkers prognostic of in-hospital mortality in COVID-19 patients and revealed that vascular stabilizing therapies should be explored as a treatment for endothelial dysfunction in COVID-19, and other severe diseases where endothelial dysfunction has a central role in pathogenesis.

Funding Information

This work was directly supported by grant funding from the Ted Rogers Center for Heart Research, Toronto, Ontario, Canada and the Peter Munk Cardiac Center, Toronto, Ontario, Canada.

Vasculature-on-a-chip platform with innate immunity enables identification of angiopoietin-1 derived peptide as a therapeutic for SARS-CoV-2 induced inflammation

Coronavirus disease 2019 (COVID-19) was primarily identified as a novel disease causing acute respiratory syndrome. However, as the pandemic progressed various cases of secondary organ infection and damage by severe respiratory syndrome coronavirus 2 (SARS-CoV-2) have been reported, including a breakdown of the vascular barrier. As SARS-CoV-2 gains access to blood circulation through the lungs, the virus is first encountered by the layer of endothelial cells and immune cells that participate in host defense. Here, we developed an approach to study SARS-CoV-2 infection using vasculature-on-a-chip. We first modeled the interaction of virus alone with the endothelialized vasculature-on-a-chip, followed by the studies of the interaction of the virus exposed-endothelial cells with peripheral blood mononuclear cells (PBMCs). In an endothelial model grown on a permeable microfluidic bioscaffold under flow conditions, both human coronavirus (HCoV)-NL63 and SARS-CoV-2 presence diminished endothelial barrier function by disrupting VE-cadherin junctions and elevating the level of pro-inflammatory cytokines such as interleukin (IL)-6, IL-8, and angiopoietin-2. Inflammatory cytokine markers were markedly more elevated upon SARS-CoV-2 infection compared to HCoV-NL63 infection. Introduction of PBMCs with monocytes into the vasculature-on-a-chip upon SARS-CoV-2 infection further exacerbated cytokine-induced endothelial dysfunction, demonstrating the compounding effects of inter-cellular crosstalk between endothelial cells and monocytes in facilitating the hyperinflammatory state. Considering the harmful effects of SARS-CoV-2 on endothelial cells, even without active virus proliferation inside the cells, a potential therapeutic approach is critical. We identified angiopoietin-1 derived peptide, QHREDGS, as a potential therapeutic capable of profoundly attenuating the inflammatory state of the cells consistent with the levels in non-infected controls, thereby improving the barrier function and endothelial cell survival against SARS-CoV-2 infection in the presence of PBMC.

Combined Cardiac Fluorodeoxyglucose-Positron Emission Tomography/Magnetic Resonance Imaging Assessment of Myocardial Injury in Patients Who Recently Recovered From COVID-19

IMPORTANCE

Although myocardial injury can occur with acute COVID-19, there is limited understanding of changes with myocardial metabolism in recovered patients.

OBJECTIVE

To examine myocardial metabolic changes early after recovery from COVID-19 using fluorodeoxyglucose-positron emission tomography (PET) and associate these changes to abnormalities in cardiac magnetic resonance imaging (MRI)-based function and tissue characterization measures and inflammatory blood markers.

DESIGN, SETTING, AND PARTICIPANTS

This prospective cohort study took place at a single-center tertiary referral hospital system. A volunteer sample of adult patients within 3 months of a diagnosis of COVID-19 who responded to a mail invitation were recruited for cardiac PET/MRI and blood biomarker evaluation between November 2020 and June 2021.

EXPOSURES

Myocardial inflammation as determined by focal fluorodeoxyglucose (FDG) uptake on PET.

MAIN OUTCOMES AND MEASURES

Demographic characteristics, cardiac and inflammatory blood markers, and fasting combined cardiac 18F-FDG PET/MRI imaging were obtained. All patients with focal FDG uptake at baseline returned for repeated PET/MRI and blood marker assessment 2 months later.

RESULTS

Of 47 included patients, 24 (51%) were female, and the mean (SD) age was 43 (13) years. The mean (SD) interval between COVID-19 diagnosis and PET/MRI was 67 (16) days. Most patients recovered at home during the acute infection (40 [85%]). Eight patients (17%) had focal FDG uptake on PET consistent with myocardial inflammation. Compared with those without FDG uptake, patients with focal FDG uptake had higher regional T2, T1, and extracellular volume (colocalizing with focal FDG uptake), higher prevalence of late gadolinium enhancement (6 of 8 [75%] vs 9 of 39 [23%], P = .009), lower left ventricular ejection fraction (mean [SD], 55% [4%] vs 62% [5%], P < .001), worse global longitudinal and circumferential strain (mean [SD], -16% [2%] vs -17% [2%], P = .02 and -18% [2%] vs -20% [2%], P = .047, respectively), and higher systemic inflammatory blood markers including interleukin 6, interleukin 8, and high-sensitivity C-reactive protein. Among patients with focal FDG uptake, PET/MRI, and inflammatory blood markers resolved or improved at follow-up performed a mean (SD) of 52 (17) days after baseline PET/MRI.

CONCLUSIONS AND RELEVANCE

In this study of patients recently recovered from COVID-19, myocardial inflammation was identified on PET in a small proportion of patients, was associated with cardiac MRI abnormalities and elevated inflammatory blood markers at baseline, and improved at follow-up.

MiR-30 promotes fatty acid beta-oxidation and endothelial cell dysfunction and is a circulating biomarker of coronary microvascular dysfunction in pre-clinical models of diabetes

Background

Type 2 diabetes (T2D) is associated with coronary microvascular dysfunction, which is thought to contribute to compromised diastolic function, ultimately culminating in heart failure with preserved ejection fraction (HFpEF). The molecular mechanisms remain incompletely understood, and no early diagnostics are available. We sought to gain insight into biomarkers and potential mechanisms of microvascular dysfunction in obese mouse (db/db) and lean rat (Goto-Kakizaki) pre-clinical models of T2D-associated diastolic dysfunction.

Methods

The microRNA (miRNA) content of circulating extracellular vesicles (EVs) was assessed in T2D models to identify biomarkers of coronary microvascular dysfunction/rarefaction. The potential source of circulating EV-encapsulated miRNAs was determined, and the mechanisms of induction and the function of candidate miRNAs were assessed in endothelial cells (ECs).

Results

We found an increase in miR-30d-5p and miR-30e-5p in circulating EVs that coincided with indices of coronary microvascular EC dysfunction (i.e., markers of oxidative stress, DNA damage/senescence) and rarefaction, and preceded echocardiographic evidence of diastolic dysfunction. These miRNAs may serve as biomarkers of coronary microvascular dysfunction as they are upregulated in ECs of the left ventricle of the heart, but not other organs, in db/db mice. Furthermore, the miR-30 family is secreted in EVs from senescent ECs in culture, and ECs with senescent-like characteristics are present in the db/db heart. Assessment of miR-30 target pathways revealed a network of genes involved in fatty acid biosynthesis and metabolism. Over-expression of miR-30e in cultured ECs increased fatty acid β-oxidation and the production of reactive oxygen species and lipid peroxidation, while inhibiting the miR-30 family decreased fatty acid β-oxidation. Additionally, miR-30e over-expression synergized with fatty acid exposure to down-regulate the expression of eNOS, a key regulator of microvascular and cardiomyocyte function. Finally, knock-down of the miR-30 family in db/db mice decreased markers of oxidative stress and DNA damage/senescence in the microvascular endothelium.

Conclusions

MiR-30d/e represent early biomarkers and potential therapeutic targets that are indicative of the development of diastolic dysfunction and may reflect altered EC fatty acid metabolism and microvascular dysfunction in the diabetic heart.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12933-022-01458-z.

MiR-30 promotes fatty acid beta-oxidation and endothelial cell dysfunction and is a circulating biomarker of coronary microvascular dysfunction in pre-clinical models of diabetes

BACKGROUND

Type 2 diabetes (T2D) is associated with coronary microvascular dysfunction, which is thought to contribute to compromised diastolic function, ultimately culminating in heart failure with preserved ejection fraction (HFpEF). The molecular mechanisms remain incompletely understood, and no early diagnostics are available. We sought to gain insight into biomarkers and potential mechanisms of microvascular dysfunction in obese mouse (db/db) and lean rat (Goto-Kakizaki) pre-clinical models of T2D-associated diastolic dysfunction.

METHODS

The microRNA (miRNA) content of circulating extracellular vesicles (EVs) was assessed in T2D models to identify biomarkers of coronary microvascular dysfunction/rarefaction. The potential source of circulating EV-encapsulated miRNAs was determined, and the mechanisms of induction and the function of candidate miRNAs were assessed in endothelial cells (ECs).

RESULTS

We found an increase in miR-30d-5p and miR-30e-5p in circulating EVs that coincided with indices of coronary microvascular EC dysfunction (i.e., markers of oxidative stress, DNA damage/senescence) and rarefaction, and preceded echocardiographic evidence of diastolic dysfunction. These miRNAs may serve as biomarkers of coronary microvascular dysfunction as they are upregulated in ECs of the left ventricle of the heart, but not other organs, in db/db mice. Furthermore, the miR-30 family is secreted in EVs from senescent ECs in culture, and ECs with senescent-like characteristics are present in the db/db heart. Assessment of miR-30 target pathways revealed a network of genes involved in fatty acid biosynthesis and metabolism. Over-expression of miR-30e in cultured ECs increased fatty acid β-oxidation and the production of reactive oxygen species and lipid peroxidation, while inhibiting the miR-30 family decreased fatty acid β-oxidation. Additionally, miR-30e over-expression synergized with fatty acid exposure to down-regulate the expression of eNOS, a key regulator of microvascular and cardiomyocyte function. Finally, knock-down of the miR-30 family in db/db mice decreased markers of oxidative stress and DNA damage/senescence in the microvascular endothelium.

CONCLUSIONS

MiR-30d/e represent early biomarkers and potential therapeutic targets that are indicative of the development of diastolic dysfunction and may reflect altered EC fatty acid metabolism and microvascular dysfunction in the diabetic heart.

Dysfunctional Vascular Endothelium as a Driver of Atherosclerosis: Emerging Insights Into Pathogenesis and Treatment

Atherosclerosis, the chronic accumulation of cholesterol-rich plaque within arteries, is associated with a broad spectrum of cardiovascular diseases including myocardial infarction, aortic aneurysm, peripheral vascular disease, and stroke. Atherosclerotic cardiovascular disease remains a leading cause of mortality in high-income countries and recent years have witnessed a notable increase in prevalence within low- and middle-income regions of the world. Considering this prominent and evolving global burden, there is a need to identify the cellular mechanisms that underlie the pathogenesis of atherosclerosis to discover novel therapeutic targets for preventing or mitigating its clinical sequelae. Despite decades of research, we still do not fully understand the complex cell-cell interactions that drive atherosclerosis, but new investigative approaches are rapidly shedding light on these essential mechanisms. The vascular endothelium resides at the interface of systemic circulation and the underlying vessel wall and plays an essential role in governing pathophysiological processes during atherogenesis. In this review, we present emerging evidence that implicates the activated endothelium as a driver of atherosclerosis by directing site-specificity of plaque formation and by promoting plaque development through intracellular processes, which regulate endothelial cell proliferation and turnover, metabolism, permeability, and plasticity. Moreover, we highlight novel mechanisms of intercellular communication by which endothelial cells modulate the activity of key vascular cell populations involved in atherogenesis, and discuss how endothelial cells contribute to resolution biology - a process that is dysregulated in advanced plaques. Finally, we describe important future directions for preclinical atherosclerosis research, including epigenetic and targeted therapies, to limit the progression of atherosclerosis in at-risk or affected patients.

Abstract P104: The Transcription Factor Erg Governs Chromatin Accessibility And Gene Expression Programs Underlying Vascular Dysfunction In Aortic Endothelial Cells

Aims: The transcription factor ERG has emerged as an important regulator of vascular function through its ability to repress inflammation in endothelial cells (ECs) and ERG dysregulation is associated with chronic inflammation in atherosclerosis and aortic aneurysms. To characterize the cellular mechanisms that underlie this regulation, we deleted ERG in human aortic ECs and assessed genome-wide chromatin accessibility and gene expression to identify dysregulated pathways. Furthermore, we have begun to investigate ERG expression in mouse atherosclerotic plaque.

Methods: CRISPR/Cas9 was used to delete ERG exon 6 in immortalized human aortic ECs. Wildtype or Δ ERG ECs were profiled with ATAC-seq and RNA-seq (n=2-4). GREAT and clusterProfiler were used to identify enriched pathways (log 2 FC>|1|; FDR<0.05). Regulatory regions were defined as 5kb upstream and 1kb downstream of transcription start sites with ≤1Mb nearest gene extension. To determine if ERG expression is altered during atherosclerosis, 8-week-old Ldlr −/− mice were fed a 12-week high-cholesterol diet (1.25%) before sacrifice. Ascending aortic sections were stained with anti-CD68 and anti-ERG (n=2). Images were obtained using a Leica SP8 confocal microscope.

Results: Pathway analysis of >21,000 differentially accessible chromatin regions identified 67 enriched processes in Δ ERG ECs. Of these, the top 20% included disrupted wound healing, abnormal aorta morphology, and aneurysm, which were driven by association with proatherogenic and proaneurysmal genes including PDGFRB and TGFBR1 . Gene expression analysis revealed that loss of ERG contributes to endothelial to mesenchymal transition (increased KLF4 and SNAI2 ), inflammation (increased IL18 ), and dysregulated extracellular matrix and cell adhesion (increased FBLN2 and VCAN ). In the mouse aorta, preliminary data suggest that ERG expression may be elevated in EC nuclei overlying plaque compared to non-atherosclerotic regions.

Conclusions: The loss of ERG has a broad impact on chromatin accessibility and gene expression in aortic ECs, with enrichment of vascular dysfunction pathways. Further investigation will establish how altered ERG expression contributes to in vivo models of atherosclerosis and aortic aneurysms.

Conserved regulatory logic at accessible and inaccessible chromatin during the acute inflammatory response in mammals

The regulatory elements controlling gene expression during acute inflammation are not fully elucidated. Here we report the identification of a set of NF-κB-bound elements and common chromatin landscapes underlying the acute inflammatory response across cell-types and mammalian species. Using primary vascular endothelial cells (human/mouse/bovine) treated with the pro-inflammatory cytokine, Tumor Necrosis Factor-α, we identify extensive (~30%) conserved orthologous binding of NF-κB to accessible, as well as nucleosome-occluded chromatin. Regions with the highest NF-κB occupancy pre-stimulation show dramatic increases in NF-κB binding and chromatin accessibility post-stimulation. These 'pre-bound' regions are typically conserved (~56%), contain multiple NF-κB motifs, are utilized by diverse cell types, and overlap rare non-coding mutations and common genetic variation associated with both inflammatory and cardiovascular phenotypes. Genetic ablation of conserved, 'pre-bound' NF-κB regions within the super-enhancer associated with the chemokine-encoding CCL2 gene and elsewhere supports the functional relevance of these elements.

RIPK1 Expression Associates With Inflammation in Early Atherosclerosis in Humans and Can Be Therapeutically Silenced to Reduce NF-κB Activation and Atherogenesis in Mice

BACKGROUND

Chronic activation of the innate immune system drives inflammation and contributes directly to atherosclerosis. We previously showed that macrophages in the atherogenic plaque undergo RIPK3 (receptor-interacting serine/threonine-protein kinase 3)-MLKL (mixed lineage kinase domain-like protein)-dependent programmed necroptosis in response to sterile ligands such as oxidized low-density lipoprotein and damage-associated molecular patterns and that necroptosis is active in advanced atherosclerotic plaques. Upstream of the RIPK3-MLKL necroptotic machinery lies RIPK1 (receptor-interacting serine/threonine-protein kinase 1), which acts as a master switch that controls whether the cell undergoes NF-κB (nuclear factor κ-light-chain-enhancer of activated B cells)-dependent inflammation, caspase-dependent apoptosis, or necroptosis in response to extracellular stimuli. We therefore set out to investigate the role of RIPK1 in the development of atherosclerosis, which is driven largely by NF-κB-dependent inflammation at early stages. We hypothesize that, unlike RIPK3 and MLKL, RIPK1 primarily drives NF-κB-dependent inflammation in early atherogenic lesions, and knocking down RIPK1 will reduce inflammatory cell activation and protect against the progression of atherosclerosis.

METHODS

We examined expression of RIPK1 protein and mRNA in both human and mouse atherosclerotic lesions, and used loss-of-function approaches in vitro in macrophages and endothelial cells to measure inflammatory responses. We administered weekly injections of RIPK1 antisense oligonucleotides to Apoe^-/- mice fed a cholesterol-rich (Western) diet for 8 weeks.

RESULTS

We find that RIPK1 expression is abundant in early-stage atherosclerotic lesions in both humans and mice. Treatment with RIPK1 antisense oligonucleotides led to a reduction in aortic sinus and en face lesion areas (47.2% or 58.8% decrease relative to control, P<0.01) and plasma inflammatory cytokines (IL-1α [interleukin 1α], IL-17A [interleukin 17A], P<0.05) in comparison with controls. RIPK1 knockdown in macrophages decreased inflammatory genes (NF-κB, TNFα [tumor necrosis factor α], IL-1α) and in vivo lipopolysaccharide- and atherogenic diet-induced NF-κB activation. In endothelial cells, knockdown of RIPK1 prevented NF-κB translocation to the nucleus in response to TNFα, where accordingly there was a reduction in gene expression of IL1B, E-selectin, and monocyte attachment.

CONCLUSIONS

We identify RIPK1 as a central driver of inflammation in atherosclerosis by its ability to activate the NF-κB pathway and promote inflammatory cytokine release. Given the high levels of RIPK1 expression in human atherosclerotic lesions, our study suggests RIPK1 as a future therapeutic target to reduce residual inflammation in patients at high risk of coronary artery disease.

Overcoming Barriers: The Endothelium As a Linchpin of Coronavirus Disease 2019 Pathogenesis?

OBJECTIVE

Coronavirus disease 2019 (COVID-19) is a global pandemic involving >5 500 000 cases worldwide as of May 26, 2020. The culprit is the severe acute respiratory syndrome coronavirus-2, which invades cells by binding to ACE2 (angiotensin-converting enzyme 2). While the majority of patients mount an appropriate antiviral response and recover at home, others progress to respiratory distress requiring hospital admission for supplemental oxygen. In severe cases, deterioration to acute respiratory distress syndrome necessitating mechanical ventilation, development of severe thrombotic events, or cardiac injury and dysfunction occurs. In this review, we highlight what is known to date about COVID-19 and cardiovascular risk, focusing in on the putative role of the endothelium in disease susceptibility and pathogenesis. Approach and Results: Cytokine-driven vascular leak in the lung alveolar-endothelial interface facilitates acute lung injury in the setting of viral infection. Given that the virus affects multiple organs, including the heart, it likely gains access into systemic circulation by infecting or passing from the respiratory epithelium to the endothelium for viral dissemination. Indeed, cardiovascular complications of COVID-19 are highly prevalent and include acute cardiac injury, myocarditis, and a hypercoagulable state, all of which may be influenced by altered endothelial function. Notably, the disease course is worse in individuals with preexisting comorbidities that involve endothelial dysfunction and may be linked to elevated ACE2 expression, such as diabetes mellitus, hypertension, and cardiovascular disease.

CONCLUSIONS

Rapidly emerging data on COVID-19, together with results from studies on severe acute respiratory syndrome coronavirus-1, are providing insight into how endothelial dysfunction may contribute to the pandemic that is paralyzing the globe. This may, in turn, inform the design of biomarkers predictive of disease course, as well as therapeutics targeting pathogenic endothelial responses.

c-Myb Exacerbates Atherosclerosis through Regulation of Protective IgM-Producing Antibody-Secreting Cells

Mechanisms that govern transcriptional regulation of inflammation in atherosclerosis remain largely unknown. Here, we identify the nuclear transcription factor c-Myb as an important mediator of atherosclerotic disease in mice. Atherosclerosis-prone animals fed a diet high in cholesterol exhibit increased levels of c-Myb in the bone marrow. Use of mice that either harbor a c-Myb hypomorphic allele or where c-Myb has been preferentially deleted in B cell lineages revealed that c-Myb potentiates atherosclerosis directly through its effects on B lymphocytes. Reduced c-Myb activity prevents the expansion of atherogenic B2 cells yet associates with increased numbers of IgM-producing antibody-secreting cells (IgM-ASCs) and elevated levels of atheroprotective oxidized low-density lipoprotein (OxLDL)-specific IgM antibodies. Transcriptional profiling revealed that c-Myb has a limited effect on B cell function but is integral in maintaining B cell progenitor populations in the bone marrow. Thus, targeted disruption of c-Myb beneficially modulates the complex biology of B cells in cardiovascular disease.

Somatic Gain of KRAS Function in the Endothelium Is Sufficient to Cause Vascular Malformations That Require MEK but Not PI3K Signaling

Supplemental Digital Content is available in the text.

Rationale:

We previously identified somatic activating mutations in the KRAS (Kirsten rat sarcoma viral oncogene homologue) gene in the endothelium of the majority of human sporadic brain arteriovenous malformations; a disorder characterized by direct connections between arteries and veins. However, whether this genetic abnormality alone is sufficient for lesion formation, as well as how active KRAS signaling contributes to arteriovenous malformations, remains unknown.

Objective:

To establish the first in vivo models of somatic KRAS gain of function in the endothelium in both mice and zebrafish to directly observe the phenotypic consequences of constitutive KRAS activity at a cellular level in vivo, and to test potential therapeutic interventions for arteriovenous malformations.

Methods and Results:

Using both postnatal and adult mice, as well as embryonic zebrafish, we demonstrate that endothelial-specific gain of function mutations in Kras (G12D or G12V) are sufficient to induce brain arteriovenous malformations. Active KRAS signaling leads to altered endothelial cell morphogenesis and increased cell size, ectopic sprouting, expanded vessel lumen diameter, and direct connections between arteries and veins. Furthermore, we show that these lesions are not associated with altered endothelial growth dynamics or a lack of proper arteriovenous identity but instead seem to feature exuberant angiogenic signaling. Finally, we demonstrate that KRAS-dependent arteriovenous malformations in zebrafish are refractory to inhibition of the downstream effector PI3K but instead require active MEK (mitogen-activated protein kinase kinase 1) signaling.

Conclusions:

We demonstrate that active KRAS expression in the endothelium is sufficient for brain arteriovenous malformations, even in the setting of uninjured adult vasculature. Furthermore, the finding that KRAS-dependent lesions are reversible in zebrafish suggests that MEK inhibition may represent a promising therapeutic treatment for arteriovenous malformation patients.

Cellular senescence contributes to age-dependent changes in circulating extracellular vesicle cargo and function

Extracellular vesicles (EVs) have emerged as important regulators of inter‐cellular and inter‐organ communication, in part via the transfer of their cargo to recipient cells. Although circulating EVs have been previously studied as biomarkers of aging, how circulating EVs change with age and the underlying mechanisms that contribute to these changes are poorly understood. Here, we demonstrate that aging has a profound effect on the circulating EV pool, as evidenced by changes in concentration, size, and cargo. Aging also alters particle function; treatment of cells with EV fractions isolated from old plasma reduces macrophage responses to lipopolysaccharide, increases phagocytosis, and reduces endothelial cell responses to vascular endothelial growth factor compared to cells treated with young EV fractions. Depletion studies indicate that CD63⁺ particles mediate these effects. Treatment of macrophages with EV‐like particles revealed that old particles increased the expression of EV miRNAs in recipient cells. Transfection of cells with microRNA mimics recapitulated some of the effects seen with old EV‐like particles. Investigation into the underlying mechanisms using bone marrow transplant studies revealed circulating cell age does not substantially affect the expression of aging‐associated circulating EV miRNAs in old mice. Instead, we show that cellular senescence contributes to changes in particle cargo and function. Notably, senolytic treatment of old mice shifted plasma particle cargo and function toward that of a younger phenotype. Collectively, these results demonstrate that senescent cells contribute to changes in plasma EVs with age and suggest a new mechanism by which senescent cells can affect cellular functions throughout the body.

Human cardiac fibrosis-on-a-chip model recapitulates disease hallmarks and can serve as a platform for drug testing

While interstitial fibrosis plays a significant role in heart failure, our understanding of disease progression in humans is limited. To address this limitation, we have engineered a cardiac-fibrosis-on-a-chip model consisting of a microfabricated device with live force measurement capabilities using co-cultured human cardiac fibroblasts and pluripotent stem cell-derived cardiomyocytes. Transforming growth factor-β was used as a trigger for fibrosis. Here, we have reproduced the classic hallmarks of fibrosis-induced heart failure including high collagen deposition, increased tissue stiffness, BNP secretion, and passive tension. Force of contraction was significantly decreased in fibrotic tissues that displayed a transcriptomic signature consistent with human cardiac fibrosis/heart failure. Treatment with an anti-fibrotic drug decreased tissue stiffness and BNP secretion, with corresponding changes in the transcriptomic signature. This model represents an accessible approach to study human heart failure in vitro, and allows for testing anti-fibrotic drugs while facilitating the real-time assessment of cardiomyocyte function.

Minimal information for studies of extracellular vesicles 2018 (MISEV2018): a position statement of the International Society for Extracellular Vesicles and update of the MISEV2014 guidelines

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles ("MISEV") guidelines for the field in 2014. We now update these "MISEV2014" guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points.

Single cell RNA sequencing of human liver reveals distinct intrahepatic macrophage populations

The liver is the largest solid organ in the body and is critical for metabolic and immune functions. However, little is known about the cells that make up the human liver and its immune microenvironment. Here we report a map of the cellular landscape of the human liver using single-cell RNA sequencing. We provide the transcriptional profiles of 8444 parenchymal and non-parenchymal cells obtained from the fractionation of fresh hepatic tissue from five human livers. Using gene expression patterns, flow cytometry, and immunohistochemical examinations, we identify 20 discrete cell populations of hepatocytes, endothelial cells, cholangiocytes, hepatic stellate cells, B cells, conventional and non-conventional T cells, NK-like cells, and distinct intrahepatic monocyte/macrophage populations. Together, our study presents a comprehensive view of the human liver at single-cell resolution that outlines the characteristics of resident cells in the liver, and in particular provides a map of the human hepatic immune microenvironment.

The development of single cell RNA sequencing technologies has been instrumental in advancing our understanding of tissue biology. Here, MacParland et al. performed single cell RNA sequencing of human liver samples, and identify distinct populations of intrahepatic macrophages that may play specific roles in liver disease.

The transcriptional regulator CCCTC-binding factor limits oxidative stress in endothelial cells

The CCCTC-binding factor (CTCF) is a versatile transcriptional regulator required for embryogenesis, but its function in vascular development or in diseases with a vascular component is poorly understood. Here, we found that endothelial Ctcf is essential for mouse vascular development and limits accumulation of reactive oxygen species (ROS). Conditional knockout of Ctcf in endothelial progenitors and their descendants affected embryonic growth, and caused lethality at embryonic day 10.5 because of defective yolk sac and placental vascular development. Analysis of global gene expression revealed Frataxin (Fxn), the gene mutated in Friedreich's ataxia (FRDA), as the most strongly down-regulated gene in Ctcf-deficient placental endothelial cells. Moreover, in vitro reporter assays showed that Ctcf activates the Fxn promoter in endothelial cells. ROS are known to accumulate in the endothelium of FRDA patients. Importantly, Ctcf deficiency induced ROS-mediated DNA damage in endothelial cells in vitro, and in placental endothelium in vivo Taken together, our findings indicate that Ctcf promotes vascular development and limits oxidative stress in endothelial cells. These results reveal a function for Ctcf in vascular development, and suggest a potential mechanism for endothelial dysfunction in FRDA.

Abstract 661: Regulation of CCL2 Expression in Vascular Endothelial Cells by a Long Noncoding RNA

Vascular inflammation is a critical driver of chronic diseases such as atherosclerosis. A network of NF-κB-dependent leukocyte adhesion molecules and chemokines are induced in endothelial cells (ECs) in response to inflammatory mediators. This includes chemokine (C-C motif) ligand 2 ( CCL2 ), which contributes to atherosclerosis by recruiting monocytes to the endothelium. Recently, long noncoding RNAs (lncRNAs) have been implicated in regulating gene expression through epigenetic mechanisms, but lncRNAs remain poorly studied in the context of vascular inflammation and NF-kB pathway regulation. LncRNAs are frequently retained in the nucleus where they interact with chromatin remodelling complexes to modulate the expression of neighboring protein-coding genes. Hence, identifying NF-kB-regulated neighboring mRNA-lncRNA pairs in vascular endothelial cells may uncover functional lncRNAs that play a role in fine-tuning the expression of their neighboring inflammatory genes.

The Arraystar human lncRNA microarray V3 was employed to identify differentially expressed lncRNAs and mRNAs in ECs stimulated with the pro-inflammatory cytokine, IL-1β. Neighboring IL-1β-regulated mRNA-lncRNA pairs demonstrated a larger magnitude of mRNA induction than mRNAs lacking a neighboring lncRNA. This phenomenon was associated with shared regulatory elements and localization within the same topologically associated domain. Follow-up analysis was performed on the nuclear-enriched, lncRNA-CCL2 , which is transcribed through a super-enhancer near CCL2 . Both lncRNA-CCL2 and CCL2 responded to the same inflammatory stimuli. Similar to CCL2 , lncRNA-CCL2 transcript was elevated in unstable human atherosclerotic plaques. Knockdown of lncRNA-CCL2 decreased CCL2 mRNA levels in multiple EC cell lines, but had no effect on other inflammatory genes or distal CCL genes. Hence, our approach has uncovered neighboring IL-1β-regulated mRNA-lncRNA pairs and identified a novel functional lncRNA, lncRNA-CCL2 .

Abstract 673: Discovering and Dissecting the Function of Conserved NF-κB Binding Events in the Human Genome

The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) transcription factor plays a prominent role in inflammation and contributes to the development of atherosclerosis. Genome-wide DNA binding assays of the human NF-κB subunit RELA (p65) have revealed tens of thousands of NF-κB binding sites and hundreds of target genes. However, the function of individual RELA binding sites and the extent to which NF-κB occupancy and function is conserved across mammals are not well understood. To better understand the function of NF-κB we characterized the genome-wide binding of RELA in primary vascular endothelial cells (ECs) isolated from the aortas of human, mouse and cow. ECs were stimulated acutely with the pro-inflammatory cytokine tumor necrosis factor alpha (TNFA) and we profiled RELA occupancy, open chromatin, select histone modifications, and RNA expression. We found ~5000 RELA binding events conserved across all three species and these highly conserved human binding events were enriched for genes controlling vascular development, apoptosis, and pro-inflammatory responses. Approximately 2000 of these highly conserved RELA binding events were also shared across multiple human cell types, revealing a conserved core of robustly bound NF-κB sites. These NF-κB binding sites were also prominent components of ~40 inflammation-induced super-enhancers (SE) common to several tissues. To gain insight into the function of individual conserved NF-κB binding sites we focused on the inflammation-induced SE proximal to the monocyte recruiting chemokine CCL2 , which we detected as a SE in all three species and across multiple cell types. We tested the functional significance of six conserved RELA binding sites comprising this SE using CRISPR/Cas9 genome editing. We found that only deletion of the most proximal upstream RELA binding site could abolish the induction of CCL2 upon TNFA treatment. This site also contains a disease associated variant that can modulate CCL2 induction. Overall, our comparative genomics assessment of NF-κB binding gives new insight into NF-κB biology and the function of conserved transcription factor binding events within mammalian super-enhancers.

Somatic Activating KRAS Mutations in Arteriovenous Malformations of the Brain

BACKGROUND

Sporadic arteriovenous malformations of the brain, which are morphologically abnormal connections between arteries and veins in the brain vasculature, are a leading cause of hemorrhagic stroke in young adults and children. The genetic cause of this rare focal disorder is unknown.

METHODS

We analyzed tissue and blood samples from patients with arteriovenous malformations of the brain to detect somatic mutations. We performed exome DNA sequencing of tissue samples of arteriovenous malformations of the brain from 26 patients in the main study group and of paired blood samples from 17 of those patients. To confirm our findings, we performed droplet digital polymerase-chain-reaction (PCR) analysis of tissue samples from 39 patients in the main study group (21 with matching blood samples) and from 33 patients in an independent validation group. We interrogated the downstream signaling pathways, changes in gene expression, and cellular phenotype that were induced by activating KRAS mutations, which we had discovered in tissue samples.

RESULTS

We detected somatic activating KRAS mutations in tissue samples from 45 of the 72 patients and in none of the 21 paired blood samples. In endothelial cell-enriched cultures derived from arteriovenous malformations of the brain, we detected KRAS mutations and observed that expression of mutant KRAS (KRAS^G12V) in endothelial cells in vitro induced increased ERK (extracellular signal-regulated kinase) activity, increased expression of genes related to angiogenesis and Notch signaling, and enhanced migratory behavior. These processes were reversed by inhibition of MAPK (mitogen-activated protein kinase)-ERK signaling.

CONCLUSIONS

We identified activating KRAS mutations in the majority of tissue samples of arteriovenous malformations of the brain that we analyzed. We propose that these malformations develop as a result of KRAS-induced activation of the MAPK-ERK signaling pathway in brain endothelial cells. (Funded by the Swiss Cancer League and others.).

Extracellular Vesicles as Protagonists of Diabetic Cardiovascular Pathology

Extracellular vesicles (EVs) represent an emerging mechanism of cell–cell communication in the cardiovascular system. Recent data suggest that EVs are produced and taken up by multiple cardiovascular cell types, influencing target cells through signaling or transfer of cargo (including proteins, lipids, messenger RNA, and non-coding RNA). The concentration and contents of circulating EVs are altered in several diseases and represent explicit signatures of cellular activation, making them of particular interest as circulating biomarkers. EVs also actively contribute to the progression of various cardiovascular diseases, including diabetes-related vascular disease. Understanding the relationships between circulating EVs, diabetes, and cardiovascular disease is of importance as diabetic patients are at elevated risk for developing several debilitating cardiovascular pathologies, including diabetic cardiomyopathy (DCM), a disease that remains an enigma at the molecular level. Enhancing and exploiting our understanding of EV biology could facilitate the development of effective non-invasive diagnostics, prognostics, and therapeutics. This review will focus on EV biology in diabetic cardiovascular diseases, including atherosclerosis and DCM. We will review EV biogenesis and functional properties, as well as provide insight into their emerging role in cell–cell communication. Finally, we will address the utility of EVs as clinical biomarkers and outline their impact as a biomedical tool in the development of therapeutics.

Extracellular Vesicles Secreted by Atherogenic Macrophages Transfer MicroRNA to Inhibit Cell Migration

OBJECTIVE

During inflammation, macrophages secrete vesicles carrying RNA, protein, and lipids as a form of extracellular communication. In the vessel wall, extracellular vesicles (EVs) have been shown to be transferred between vascular cells during atherosclerosis; however, the role of macrophage-derived EVs in atherogenesis is not known. Here, we hypothesize that atherogenic macrophages secrete microRNAs (miRNAs) in EVs to mediate cell-cell communication and promote proinflammatory and proatherogenic phenotypes in recipient cells.

APPROACH AND RESULTS

We isolated EVs from mouse and human macrophages treated with an atherogenic stimulus (oxidized low-density lipoprotein) and characterized the EV miRNA expression profile. We confirmed the enrichment of miR-146a, miR-128, miR-185, miR-365, and miR-503 in atherogenic EVs compared with controls and demonstrate that these EVs are taken up and transfer exogenous miRNA to naive recipient macrophages. Bioinformatic pathway analysis suggests that atherogenic EV miRNAs are predicted to target genes involved in cell migration and adhesion pathways, and indeed delivery of EVs to naive macrophages reduced macrophage migration both in vitro and in vivo. Inhibition of miR-146a, the most enriched miRNA in atherogenic EVs, reduced the inhibitory effect of EVs on macrophage migratory capacity. EV-mediated delivery of miR-146a repressed the expression of target genes IGF2BP1 (insulin-like growth factor 2 mRNA-binding protein 1) and HuR (human antigen R or ELAV-like RNA-binding protein 1) in recipient cells, and knockdown of IGF2BP1 and HuR using short interfering RNA greatly reduced macrophage migration, highlighting the importance of these EV-miRNA targets in regulating macrophage motility.

CONCLUSIONS

EV-derived miRNAs from atherogenic macrophages, in particular miR-146a, may accelerate the development of atherosclerosis by decreasing cell migration and promoting macrophage entrapment in the vessel wall.

Paradoxical Suppression of Atherosclerosis in the Absence of microRNA-146a

RATIONALE

Inflammation is a key contributor to atherosclerosis. MicroRNA-146a (miR-146a) has been identified as a critical brake on proinflammatory nuclear factor κ light chain enhancer of activated B cells signaling in several cell types, including endothelial cells and bone marrow (BM)-derived cells. Importantly, miR-146a expression is elevated in human atherosclerotic plaques, and polymorphisms in the miR-146a precursor have been associated with risk of coronary artery disease.

OBJECTIVE

To define the role of endogenous miR-146a during atherogenesis.

METHODS AND RESULTS

Paradoxically, Ldlr^-/- (low-density lipoprotein receptor null) mice deficient in miR-146a develop less atherosclerosis, despite having highly elevated levels of circulating proinflammatory cytokines. In contrast, cytokine levels are normalized in Ldlr^-/-;miR-146a^-/- mice receiving wild-type BM transplantation, and these mice have enhanced endothelial cell activation and elevated atherosclerotic plaque burden compared with Ldlr^-/- mice receiving wild-type BM, demonstrating the atheroprotective role of miR-146a in the endothelium. We find that deficiency of miR-146a in BM-derived cells precipitates defects in hematopoietic stem cell function, contributing to extramedullary hematopoiesis, splenomegaly, BM failure, and decreased levels of circulating proatherogenic cells in mice fed an atherogenic diet. These hematopoietic phenotypes seem to be driven by unrestrained inflammatory signaling that leads to the expansion and eventual exhaustion of hematopoietic cells, and this occurs in the face of lower levels of circulating low-density lipoprotein cholesterol in mice lacking miR-146a in BM-derived cells. Furthermore, we identify sortilin-1(Sort1), a known regulator of circulating low-density lipoprotein levels in humans, as a novel target of miR-146a.

CONCLUSIONS

Our study reveals that miR-146a regulates cholesterol metabolism and tempers chronic inflammatory responses to atherogenic diet by restraining proinflammatory signaling in endothelial cells and BM-derived cells.

Dynamic regulation of VEGF-inducible genes by an ERK/ERG/p300 transcriptional network

The transcriptional pathways activated downstream of vascular endothelial growth factor (VEGF) signaling during angiogenesis remain incompletely characterized. By assessing the signals responsible for induction of the Notch ligand delta-like 4 (DLL4) in endothelial cells, we find that activation of the MAPK/ERK pathway mirrors the rapid and dynamic induction of DLL4 transcription and that this pathway is required for DLL4 expression. Furthermore, VEGF/ERK signaling induces phosphorylation and activation of the ETS transcription factor ERG, a prerequisite for DLL4 induction. Transcription of DLL4 coincides with dynamic ERG-dependent recruitment of the transcriptional co-activator p300. Genome-wide gene expression profiling identified a network of VEGF-responsive and ERG-dependent genes, and ERG chromatin immunoprecipitation (ChIP)-seq revealed the presence of conserved ERG-bound putative enhancer elements near these target genes. Functional experiments performed in vitro and in vivo confirm that this network of genes requires ERK, ERG and p300 activity. Finally, genome-editing and transgenic approaches demonstrate that a highly conserved ERG-bound enhancer located upstream of HLX (which encodes a transcription factor implicated in sprouting angiogenesis) is required for its VEGF-mediated induction. Collectively, these findings elucidate a novel transcriptional pathway contributing to VEGF-dependent angiogenesis.

Fingerprint of long non-coding RNA regulated by cyclic mechanical stretch in human aortic smooth muscle cells: implications for hypertension

Emerging evidence suggests that long non-coding RNAs (lncRNAs) represent a cellular hub coordinating various cellular processes that are critical in health and disease. Mechanical stress triggers changes in vascular smooth muscle cells (VSMCs) that in turn contribute to pathophysiological changes within the vasculature. We sought to evaluate the role that lncRNAs play in mechanical stretch-induced alterations of human aortic smooth muscle cells (HASMCs). RNA (lncRNA and mRNA) samples isolated from HASMCs that had been subjected to 10 or 20% elongation (1 Hz) for 24 h were profiled with the Arraystar Human LncRNA Microarray V3.0. LncRNA expression was quantified in parallel via qRT-PCR. Of the 30,586 human lncRNAs screened, 580 were differentially expressed (DE, P < 0.05) in stretched HASMCs. Amongst the 26,109 protein-coding transcripts evaluated, 25 of those DE were associated with 25 of the aforementioned DE lncRNAs (P < 0.05). Subsequent Kyoto Encyclopedia of Genes and Genomes analysis revealed that the DE mRNAs were largely associated with the tumor necrosis factor signaling pathway and inflammation. Gene Ontology analysis indicated that the DE mRNAs were associated with cell differentiation, stress response, and response to external stimuli. We describe the first transcriptome profile of stretch-induced changes in HASMCs and provide novel insights into the regulatory switches that may be fundamental in governing aberrant VSMC remodeling.

Abstract 599: Extracellular Vesicles Secreted by Atherogenic Macrophages Transfer Microrna to Inhibit Cell Migration

During inflammation, macrophages secrete vesicles carrying RNA, protein and lipids as a form of extracellular communication. In the vessel wall, extracellular vesicles (EVs) have been shown to be transferred between vascular cells during atherosclerosis, however, the role of macrophage-derived EVs in promoting atherogenesis is not known. Here, we hypothesize that atherogenic macrophages secrete microRNAs (miRNA) in EVs to mediate cell-cell communication and promote pro-inflammatory and pro-atherogenic phenotypes in recipient cells.

Results: We isolated EVs from mouse and human macrophages treated with an atherogenic stimulus (oxidized LDL) and characterized the EV-derived miRNA expression profile. Using microarrays and Q-PCR, we confirmed the enrichment of miR-146a, miR-128, miR-185, miR-365 and miR-503 in atherogenic EVs compared to controls. Live-cell imaging demonstrated that macrophage-derived EVs are taken up and transfer exogenous miRNA ( C. elegans) to naive recipient macrophages. Bioinformatic analysis suggests that atherogenic EV-derived miRNAs are predicted to target genes involved in cell migration and adhesion pathways. Indeed, treatment of naïve macrophages with EVs from atherogenic but not control macrophages inhibited the migration of naïve cells towards a chemokine stimulus (80% decrease in migration, p≤0.01). In vivo , delivery of EVs also abolished LPS-induced emigration of mouse peritoneal macrophages . Moreover, inhibition of miR-146a (using anti-miR oligonucleotides or miR-146a -/- macrophages), the most enriched miRNA in atherogenic EVs, reduced the inhibitory effect of EVs on macrophage migratory capacity. EV-mediated delivery of miR-146a repressed the expression of target genes IGF2BP1 and HuR in recipient cells, and knockdown of IGF2BP1 and HuR using siRNA reduced macrophage migration, highlighting the importance of these EV-miRNA targets in regulating macrophage motility. Notably, expression of miR-146a was elevated in mouse and human atherosclerotic lesions compared to controls. Thus, EV-derived miRNAs from atherogenic macrophages, in particular miR-146a, may accelerate the development of atherosclerosis by decreasing cell migration and promoting macrophage entrapment in the vessel wall.