Angiopoietin 2 mediates microvascular and hemodynamic alterations in sepsis

Cathepsin K cleavage of angiopoietin-2 creates detrimental Tie2 antagonist fragments in sepsis

Elevated angiopoietin-2 is associated with diverse inflammatory conditions, including sepsis, a leading global cause of mortality. During inflammation, angiopoietin-2 antagonizes the endothelium-enriched receptor Tie2 to destabilize the vasculature. In other contexts, angiopoietin-2 stimulates Tie2. The basis for context-dependent antagonism remains incompletely understood. Here, we show that inflammation-induced proteolytic cleavage of angiopoietin-2 converts this ligand from Tie2 agonist to antagonist. Conditioned media from stimulated macrophages induced endothelial angiopoietin-2 secretion. Unexpectedly, this was associated with reduction of the 75 kDa full-length protein and appearance of new 25 and 50 kDa C-terminal fragments. Peptide sequencing proposed cathepsin K as a candidate protease. Cathepsin K was necessary and sufficient to cleave angiopoietin-2. Recombinant 25 and 50 kDa angiopoietin-2 fragments (cANGPT225 and cANGPT250) bound and antagonized Tie2. Cathepsin K inhibition with the phase 3 small-molecule inhibitor odanacatib improved survival in distinct murine sepsis models. Full-length angiopoietin-2 enhanced survival in endotoxemic mice administered odanacatib and, conversely, increased mortality in the drug's absence. Odanacatib's benefit was reversed by heterologous cANGPT225. Septic humans accumulated circulating angiopoietin-2 fragments, which were associated with adverse outcomes. These results identify cathepsin K as a candidate marker of sepsis and a proteolytic mechanism for the conversion of angiopoietin-2 from Tie2 agonist to antagonist, with therapeutic implications for inflammatory conditions associated with angiopoietin-2 induction.

Sepsis-associated endothelial glycocalyx damage: a review of animal models, clinical evidence, and molecular mechanisms

In the mammalian cardiovascular system, endothelial glycocalyx is a gel-like layer that covers the luminal surface of endothelial cells (ECs) and plays crucial roles in vascular homeostasis, permeability and leukocyte adhesion. Degradation of this structure occurs early in sepsis and becomes accordingly dysfunctional. In severe cases, it is not self-regulated by the organism. However, the relationship between the glycocalyx and the occurrence and development of sepsis remains poorly understood. One possibility is that thinned glycocalyx promotes leukocyte recognition and adhesion, thereby facilitating the elimination of pathogens from infected areas. This may represent a protective mechanism developed by the organism during through evolutionary processes. However, if the damage persists and disrupts the dynamic balance of the microcirculation, interstitial edema or organ failure can occur. Thus, we asked the questions, what is the precise composition and structure of the glycocalyx? How is it degraded? What animal models are available to study the relationship between the glycocalyx and sepsis? What glycocalyx biomarkers are found in the blood of patients with sepsis? To determine whether sepsis can be treated by interfering with the glycocalyx, this study provides a systematic summary and discussion of the latest progress in addressing these questions.

Biological subphenotypes in patients hospitalized with suspected infection in Thailand: a secondary analysis of a prospective observational study

Background

Subphenotypes of infected patients have been reported in Europe and North America, but few studies have investigated populations in Southeast Asia. We sought to identify and differentiate subphenotypes of patients hospitalized with suspected infection in rural Thailand using biological markers implicated in the dysregulated host response.

Methods

In a cohort of prospectively enrolled patients hospitalized with suspected infection in northeastern Thailand, we measured 15 circulating biomarkers from a random selection of 585 subjects and developed latent profile models to identify subphenotypes. Patient characteristics were compared after subphenotype assignment, and a parsimonious model was developed to identify patient subphenotypes.

Findings

We identified and assigned 585 patients to three subphenotypes termed latent biological profile (LBP)-1 (52%), LBP-2 (39%) and LBP-3 (9%). Patients assigned to LBP-3 had a higher risk of 28-day mortality compared to those in LBP-1 and LBP-2 (adjusted relative risk 1.8, 95% confidence interval [CI] 1.1-2.9, P = 0.02). Patient clinical characteristics and biomarker concentrations also differed by subphenotype assignment. A parsimonious three-biomarker model identified subphenotypes in an internal validation cohort (LBP-1: area under the receiver operating curve [AUC] 0.96, 95% CI: 0.94-0.98; LBP-2: AUC 0.77, 95% CI 0.71-0.83; LBP-3: AUC 0.99, 95% CI 0.98-1.00).

Interpretation

We identified three biological subphenotypes of patients with suspected infection in rural Thailand, where the burden of infection is high but understudied. Patient subphenotype assignment was characterized by distinct clinical outcomes and biological profiles which could inform contextualized future study design.

Funding

The US National Institutes of Health, the Wellcome Trust, and the Firland Foundation.

Astragaloside IV alleviates septic myocardial injury through DUSP1-Prohibitin 2 mediated mitochondrial quality control and ER-autophagy

INTRODUCTION

Septic cardiomyopathy (SCM) is a complication of myocardial injury in patients with severe sepsis.

OBJECTIVES

This study highlights the potential of Astragaloside IV(AS) in the treatment of septic cardiomyopathy and provides a reference for developing cardioprotective drugs targeting DUSP1-PHB2-related mitochondria-ER interaction.

METHODS

Dual specificity phosphatase-1 (DUSP1)/Prohibitin 2 cardiomyocyte-specific knockout mice (DUSP1/PHB2CKO) /DUSP1 transgenic mice (DUSP1/PHB2TG) were used to generate LPS-induced sepsis models. The pathological mechanism by which AS-IV improves heart injury was detected using cardiac ultrasound, fluorescence staining, transmission electron microscopy, and western blotting. After siRNA treatment of cardiomyocytes with DUSP-1/PHB2, changes in mitochondrial function and morphology were determined using qPCR, western blotting, ELISA, and laser confocal microscopy, and the targeted therapeutic effects of AS-IV were further examined.

RESULTS

SCM treatment leads to severe mitochondrial dysfunction. However, Astragaloside IV (AS) treatment normalizes mitochondrial homeostasis and ER function. Notably, the protective effect was blocked in DUSP1/Prohibitin 2 cardiomyocyte-specific knockout mice (DUSP1/PHB2CKO) but remained unaffected in DUSP1 transgenic mice (DUSP1/PHB2TG).

CONCLUSION

This study highlights the potential of AS in the treatment of septic cardiomyopathy and provides a reference for developing cardioprotective drugs targeting DUSP1-PHB2 related mitochondria-ER interaction.

Angiopoietin-2 as a prognostic biomarker in septic adult patients: a systemic review and meta-analysis

BACKGROUND

The impairment of endothelial function represents a key pathophysiological mechanism in the development of sepsis. This research aimed to evaluate the prognostic significance of angiopoietin-2 (Ang-2), an endothelial biomarker, in predicting mortality in sepsis patients.

METHODS

Chinese and English studies were systematically retrieved in PubMed, Cochrane Library, Embase, WanFang, CNKI, CQVIP, and CBM databases up to July 16, 2023. We conducted a study selection established upon predefined inclusion and exclusion criteria and used the Newcastle-Ottawa scale (NOS) to assess its quality. We extracted available data from the included studies for data analysis.

RESULTS

The final inclusion comprised 33 studies with 4703 participants. According to the NOS, one study was of medium quality, while the rest were of high quality. In comparison to survivors, the levels of Ang-2 in non-survivors were markedly elevated [standardized mean difference (SMD) = 1.08, 95% confidence intervals (CI) 0.68-1.49, P < 0.001], and the same results were also observed in the subgroup that met sepsis 3.0 diagnosis criteria (SMD = 0.63, 95% CI 0.11-1.14, P = 0.017). The results comparing Ang-2 levels between non-survivors and survivors were independent of duration of follow-up, sample sources, type of study, and region. Ang-2 was a risk factor for mortality [odds ratios (OR) = 1.16, 95% CI 1.09-1.23, P < 0.001]. Ang-2 was demonstrated to be able to predict mortality in septic adult patients [area under the curve (AUC) = 0.76, 95% CI 0.70-0.82, P < 0.001].

CONCLUSIONS

Ang-2 level was positively correlated with risk of death in sepsis patients. Ang-2 might be a useful and valuable biomarker for predicting mortality in septic adult patients.

Angiopoietin II in Critically Ill Septic Patients: A Post Hoc Analysis of the DRAK Study

INTRODUCTION

Angiopoietin II (Ang-II) plays a pivotal role in the development of microcirculatory dysfunction as it provokes endothelial barrier disruption in patients with sepsis or septic shock. In particular, those with acute kidney injury show high Ang-II concentrations. So far, it is unclear which covariates influence Ang-II concentration in the early phase of sepsis, especially if extracorporeal therapies also do.

METHODS

Ang-II concentrations were measured in 171 patients with sepsis after the first day of antibiotic treatment between 03/2013 and 01/2015. Ang-II was correlated with potential influencing factors (Spearman correlation). A multivariate model was established including the significant correlating parameters. The Mann-Whitney U test and the Kruskal-Wallis test were used to detect significant differences in Ang-II concentration.

RESULTS

The median Ang-II concentration was 8015 pg/mL (interquartile range (IQR): 5024-14,185). A total of forty patients were treated with kidney replacement therapy (KRT) and 20 were supported by venovenous extracorporeal membrane oxygenation (vv-ECMO). Sequential organ failure assessment (SOFA) score (r = 0.541), creatinine clearance (r = -0.467), urinary output (r = -0.289), interleukin (IL)-6 (r = 0.529), C-reactive protein (CRP) (r = 0.241), platelet count (r = -0.419), bilirubin (r = 0.565), lactate (r = 0.322), KRT (r = 0.451), and fluid balance (r = 0.373) significantly correlated with Ang-II concentration and were included in the multivariate model. There, creatinine clearance (p < 0.01, b = -26.3, 95% confidence interval (CI) -41.8--10.8), fluid balance (p = 0.002, b = 0.92, 95% CI 0.33-1.51), and CRP (p = 0.004, b = 127.6, 95% CI 41.6-213.7) were associated with Ang-II concentration. Furthermore, patients with KRT (median: 15,219 pg/mL, IQR: 10,548-20,270) had significantly (p < 0.01) higher Ang-II concentrations than those with vv-ECMO support (median: 6412 pg/mL, IQR: 5246-10,257) or those without extracorporeal therapy (median: 7156 pg/mL, IQR: 4409-12,741).

CONCLUSION

Increased CRP, positive fluid balance, and impaired kidney function were associated with higher Ang-II concentrations in critically ill patients in the early stage of sepsis in this post hoc analysis. In particular, patients with KRT had very high Ang-II concentrations, whereas the use of vv-ECMO was not related to higher Ang-II concentrations. The significance for clinical practice should be clarified by a prospective study with standardized measurements.

Pulsatile flow increases METTL14-induced m 6 A modification and attenuates septic cardiomyopathy: an experimental study

INTRODUCTION

Septic cardiomyopathy is a sepsis-mediated cardiovascular complication with severe microcirculatory malperfusion. Emerging evidence has highlighted the protective effects of pulsatile flow in case of microcirculatory disturbance, yet the underlying mechanisms are still elusive. The objective of this study was to investigate the mechanisms of N 6 -methyladenosine (m 6 A) modification in the alleviation of septic cardiomyopathy associated with extracorporeal membrane oxygenation (ECMO)-generated pulsatile flow.

METHODS

Rat model with septic cardiomyopathy was established and was supported under ECMO either with pulsatile or non-pulsatile flow. Peripheral perfusion index (PPI) and cardiac function parameters were measured using ultrasonography. Dot blot assay was applied to examine the m 6 A level, while qRT-PCR, Western blot, immunofluorescence, and immunohistochemistry were used to measure the expressions of related genes. RNA immunoprecipitation assay was performed to validate the interaction between molecules.

RESULTS

The ECMO-generated pulsatile flow significantly elevates microcirculatory PPI, improves myocardial function, protects the endothelium, and prolongs survival in rat models with septic cardiomyopathy. The pulsatile flow mediates the METTL14-mediated m 6 A modification to zonula occludens-1 (ZO-1) mRNA (messenger RNA), which stabilizes the ZO-1 mRNA depending on the presence of YTHDF2. The pulsatile flow suppresses the PI3K-Akt signaling pathway, of which the downstream molecule Foxo1, a negative transcription factor of METTL14, binds to the METTL14 promoter and inhibits the METTL14-induced m 6 A modification.

CONCLUSION

The ECMO-generated pulsatile flow increases METTL14-induced m 6 A modification in ZO-1 and attenuates the progression of septic cardiomyopathy, suggesting that pulsatility might be a new therapeutic strategy in septic cardiomyopathy by alleviating microcirculatory disturbance.

Bispecific VEGF-A and Angiopoietin-2 Antagonist RO-101 Preclinical Efficacy in Model of Neovascular Eye Disease

Objective

To investigate preclinical data regarding the efficacy and biocompatibility of a bispecific protein, RO-101, with effects on VEGF-A and angiopoietin-2 (Ang-2) for use in retinal diseases.

Design

Experimental study.

Subjects

Brown Norway rats and New Zealand White Cross rabbits.

Methods

Preclinical study data of RO-101 in terms of target-specific enzyme-linked immunosorbent assay binding affinity to VEGF-A and Ang-2, vitreous half-life, inhibition of target-receptor interaction, laser choroidal neovascular membrane animal model, human umbilical vein endothelial cell migration, and biocompatibility was obtained. Where applicable, study data were compared with other anti-VEGF agents.

Main Outcome Measures

Binding affinity, half-life, biocompatibility, and efficacy of RO-101. Neovascularization prevention by RO-101.

Results

RO-101 demonstrated a strong binding affinity for VEGF-A and Ang-2 and in vitro was able to inhibit binding to the receptor with higher affinity than faricimab. The half-life of RO-101 is comparable to or longer than current VEGF inhibitors used in retinal disease. RO-101 was found to be biocompatible with retinal tissue in Brown Norway rats. RO-101 was as effective or more effective than current anti-VEGF therapeutics in causing regression of neovascular growth in vivo.

Conclusions

RO-101 is a promising candidate for use in retinal diseases. In preclinical models, RO-101 demonstrated similar or higher regression of neovascular growth to current anti-VEGF therapeutics with comparable or longer half-life. It also demonstrates a strong binding affinity for VEGF-A and Ang-2. It also was shown to be biocompatible with retinal tissue in animal studies, indicating potential compatibility for use in humans.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

A Razor's Edge: Vascular Responses to Acute Inflammatory Lung Injury/Acute Respiratory Distress Syndrome

Historically considered a metabolically inert cellular layer separating the blood from the underlying tissue, the endothelium is now recognized as a highly dynamic, metabolically active tissue that is critical to organ homeostasis. Under homeostatic conditions, lung endothelial cells (ECs) in healthy subjects are quiescent, promoting vasodilation, platelet disaggregation, and anti-inflammatory mechanisms. In contrast, lung ECs are essential contributors to the pathobiology of acute respiratory distress syndrome (ARDS), as the quiescent endothelium is rapidly and radically altered upon exposure to environmental stressors, infectious pathogens, or endogenous danger signals into an effective and formidable regulator of innate and adaptive immunity. These dramatic perturbations, produced in a tsunami of inflammatory cascade activation, result in paracellular gap formation between lung ECs, sustained lung edema, and multi-organ dysfunction that drives ARDS mortality. The astonishing plasticity of the lung endothelium in negotiating this inflammatory environment and efforts to therapeutically target the aberrant ARDS endothelium are examined in further detail in this review.

Exploring adjunctive therapies for cerebral malaria

Cerebral malaria (CM) is one of the most severe complications of malaria infection characterized by coma and neurological effects. Despite standardized treatment of malaria infection with artemisinin-based combination therapies (ACT), the mortality rate is still high, and it primarily affects pediatric patients. ACT reduces parasitemia but fails to adequately target the pathogenic mechanisms underlying CM, including blood-brain-barrier (BBB) disruption, endothelial activation/dysfunction, and hyperinflammation. The need for adjunctive therapies to specifically treat this form of severe malaria is critical as hundreds of thousands of people continue to die each year from this disease. Here we present a summary of some potential promising therapeutic targets and treatments for CM, as well as some that have been tested and deemed ineffective or, in some cases, even deleterious. Further exploration into these therapeutic agents is warranted to assess the effectiveness of these potential treatments for CM patients.

Intravenous administration of umbilical cord lining stem cells in left ventricular assist device recipients: Results of the uSTOP LVAD BLEED pilot study

Background

Left ventricular assist device (LVAD) implantation improves survival in advanced heart failure. Despite this, angiodysplastic bleeding complications remain a significant driver of costs as well as morbidity. Mechanisms implicated in post-LVAD implant bleeding include the dysregulation of angiogenic factors seen in this population. The present pilot study evaluates the safety of umbilical cord lining stem cells (ULSCs) in LVAD recipients while exploring any early evidence of efficacy to improve bleeding.

Methods

In a 3 + 3 design, 9 patients received an intravenous (IV) infusion of ULSCs at escalating doses. The primary endpoint was safety and tolerability, secondary exploratory outcomes included antibodies against hemoglobin to quantify the amount of blood in stool without the need for dietary restriction.

Results

The primary safety and tolerability outcomes were met as no infusion-related adverse events or toxic responses were observed. There was no sensitization after administration of ULSCs as assessed by panel reactive antibody. An increase in angiopoietin-1 levels and a decrease in angiopoietin-2 levels from baseline to 30 days were observed in 4 patients. Quantitative Faecal Immunochemical Test suggested a decrease in the mean blood content of stool from baseline to 30 days.

Conclusions

In this first-ever IV administration of ULSCs in LVAD patients, infusion was noted to be safe and tolerable and did not cause immune sensitization. Half of the patients were noted to have angiogenic stabilization, and there was a trend toward decreasing amounts of blood noted in the stool, suggesting an early signal of efficacy.

Global trends in research on endothelial cells and sepsis between 2002 and 2022: A systematic bibliometric analysis

Sepsis is a systemic syndrome involving physiological, pathological, and biochemical abnormalities precipitated by infection and is a major global public health problem. Endothelial cells (ECs) dysfunction is a major contributor to sepsis-induced multiple organ failure. This bibliometric analysis aimed to identify and characterize the status, evolution of the field, and new research trends of ECs and sepsis over the past 20 years. For this analysis, the Web of Science Core Collection database was searched to identify relevant publications on ECs in sepsis published between January 1, 2002, and December 31, 2022. Microsoft Excel 2021, VOSviewer software, CiteSpace software, and the online analysis platform of literature metrology (http://bibliometric.com) were used to visualize the trends of publications' countries/regions, institutions, authors, journals, and keywords. In total, 4200 articles were identified and screened, primarily originating from 86 countries/regions and 3489 institutions. The USA was the leading contributor to this research field, providing 1501 articles (35.74 %). Harvard University's scientists were the most prolific, with 129 articles. Overall, 21,944 authors were identified, among whom Bae Jong Sup was the most prolific, contributing 129 publications. Additionally, Levi Marcel was the most frequently co-cited author, appearing 538 times. The journals that published the most articles were SHOCK, CRITICAL CARE MEDICINE, and PLOS ONE, accounting for 10.79 % of the total. The current emerging hotspots are concentrated on "endothelial glycocalyx," "NLRP3 inflammasome," "extracellular vesicle," "biomarkers," and "COVID-19," among others. In conclusion, this study provides a comprehensive overview of the scientific productivity and emerging research trends in the field of ECs in sepsis. The evidence supporting the significant role of ECs in both physiological and pathological responses to sepsis is continuously growing. More in-depth studies of the molecular mechanisms underlying sepsis-induced endothelial dysfunction and EC-targeted therapies are warranted in the future.

Mechanisms of kidney fibrosis and routes towards therapy

Kidney fibrosis is the final common pathway of virtually all chronic kidney diseases (CKDs) and is therefore considered to be a promising therapeutic target for these conditions. However, despite great progress in recent years, no targeted antifibrotic therapies for the kidney have been approved, likely because the complex mechanisms that initiate and drive fibrosis are not yet completely understood. Recent single-cell genomic approaches have allowed novel insights into kidney fibrosis mechanisms in mouse and human, particularly the heterogeneity and differentiation processes of myofibroblasts, the role of injured epithelial cells and immune cells, and their crosstalk mechanisms. In this review we summarize the key mechanisms that drive kidney fibrosis, including recent advances in understanding the mechanisms, as well as potential routes for developing novel targeted antifibrotic therapeutics.

Capillary leak and endothelial permeability in critically ill patients: a current overview

Capillary leak syndrome (CLS) represents a phenotype of increased fluid extravasation, resulting in intravascular hypovolemia, extravascular edema formation and ultimately hypoperfusion. While endothelial permeability is an evolutionary preserved physiological process needed to sustain life, excessive fluid leak-often caused by systemic inflammation-can have detrimental effects on patients' outcomes. This article delves into the current understanding of CLS pathophysiology, diagnosis and potential treatments. Systemic inflammation leading to a compromise of endothelial cell interactions through various signaling cues (e.g., the angiopoietin-Tie2 pathway), and shedding of the glycocalyx collectively contribute to the manifestation of CLS. Capillary permeability subsequently leads to the seepage of protein-rich fluid into the interstitial space. Recent insights into the importance of the sub-glycocalyx space and preserving lymphatic flow are highlighted for an in-depth understanding. While no established diagnostic criteria exist and CLS is frequently diagnosed by clinical characteristics only, we highlight more objective serological and (non)-invasive measurements that hint towards a CLS phenotype. While currently available treatment options are limited, we further review understanding of fluid resuscitation and experimental approaches to target endothelial permeability. Despite the improved understanding of CLS pathophysiology, efforts are needed to develop uniform diagnostic criteria, associate clinical consequences to these criteria, and delineate treatment options.

Pathogenetic mechanisms and treatment targets in cerebral malaria

Malaria, the most prevalent mosquito-borne infectious disease worldwide, has accompanied humanity for millennia and remains an important public health issue despite advances in its prevention and treatment. Most infections are asymptomatic, but a small percentage of individuals with a heavy parasite burden develop severe malaria, a group of clinical syndromes attributable to organ dysfunction. Cerebral malaria is an infrequent but life-threatening complication of severe malaria that presents as an acute cerebrovascular encephalopathy characterized by unarousable coma. Despite effective antiparasite drug treatment, 20% of patients with cerebral malaria die from this disease, and many survivors of cerebral malaria have neurocognitive impairment. Thus, an important unmet clinical need is to rapidly identify people with malaria who are at risk of developing cerebral malaria and to develop preventive, adjunctive and neuroprotective treatments for cerebral malaria. This Review describes important advances in the understanding of cerebral malaria over the past two decades and discusses how these mechanistic insights could be translated into new therapies.

Precision fluid and vasoactive drug therapy for critically ill patients

There are several clinical practice guidelines concerning the use of fluid and vasoactive drug therapies in critically ill adult patients, but the recommendations in these guidelines are often based on low-quality evidence. Further, some were compiled prior to the publication of landmark clinical trials, particularly in the comparison of balanced crystalloid and normal saline. An important consideration in the treatment of critically ill patients is the application of precision medicine to provide the most effective care to groups of patients most likely to benefit from the therapy. Although not currently widely integrated into these practice guidelines, the utility of precision medicine in critical illness is a recognized research priority for fluid and vasoactive therapy management. The purpose of this narrative review was to illustrate the evaluation and challenges of providing precision fluid and vasoactive therapies to adult critically ill patients. The review includes a discussion of important investigations published after the release of currently available clinical practice guidelines to provide insight into how recommendations and research priorities may change future guidelines and bedside care for critically ill patients.

ANG2 Blockade Diminishes Proangiogenic Cerebrovascular Defects Associated With Models of Hereditary Hemorrhagic Telangiectasia

BACKGROUND

Hereditary hemorrhagic telangiectasia (HHT) is a vascular disorder characterized by arteriovenous malformations and blood vessel enlargements. However, there are no effective drug therapies to combat arteriovenous malformation formation in patients with HHT. Here, we aimed to address whether elevated levels of ANG2 (angiopoietin-2) in the endothelium is a conserved feature in mouse models of the 3 major forms of HHT that could be neutralized to treat brain arteriovenous malformations and associated vascular defects. In addition, we sought to identify the angiogenic molecular signature linked to HHT.

METHODS

Cerebrovascular defects, including arteriovenous malformations and increased vessel calibers, were characterized in mouse models of the 3 common forms of HHT using transcriptomic and dye injection labeling methods.

RESULTS

Comparative RNA sequencing analyses of isolated brain endothelial cells revealed a common, but unique proangiogenic transcriptional program associated with HHT. This included a consistent upregulation in cerebrovascular expression of ANG2 and downregulation of its receptor Tyr kinase with Ig and EGF homology domains (TIE2/TEK) in HHT mice compared with controls. Furthermore, in vitro experiments revealed TEK signaling activity was hampered in an HHT setting. Pharmacological blockade of ANG2 improved brain vascular pathologies in all HHT models, albeit to varying degrees. Transcriptomic profiling further indicated that ANG2 inhibition normalized the brain vasculature by impacting a subset of genes involved in angiogenesis and cell migration processes.

CONCLUSIONS

Elevation of ANG2 in the brain vasculature is a shared trait among the mouse models of the common forms of HHT. Inhibition of ANG2 activity can significantly limit or prevent brain arteriovenous malformation formation and blood vessel enlargement in HHT mice. Thus, ANG2-targeted therapies may represent a compelling approach to treat arteriovenous malformations and vascular pathologies related to all forms of HHT.

Ocular Vascular Diseases: From Retinal Immune Privilege to Inflammation

The eye is an immune privileged tissue that insulates the visual system from local and systemic immune provocation to preserve homeostatic functions of highly specialized retinal neural cells. If immune privilege is breached, immune stimuli will invade the eye and subsequently trigger acute inflammatory responses. Local resident microglia become active and release numerous immunological factors to protect the integrity of retinal neural cells. Although acute inflammatory responses are necessary to control and eradicate insults to the eye, chronic inflammation can cause retinal tissue damage and cell dysfunction, leading to ocular disease and vision loss. In this review, we summarized features of immune privilege in the retina and the key inflammatory responses, factors, and intracellular pathways activated when retinal immune privilege fails, as well as a highlight of the recent clinical and research advances in ocular immunity and ocular vascular diseases including retinopathy of prematurity, age-related macular degeneration, and diabetic retinopathy.

Pericyte Loss in Diseases

Pericytes are specialized cells located in close proximity to endothelial cells within the microvasculature. They play a crucial role in regulating blood flow, stabilizing vessel walls, and maintaining the integrity of the blood-brain barrier. The loss of pericytes has been associated with the development and progression of various diseases, such as diabetes, Alzheimer's disease, sepsis, stroke, and traumatic brain injury. This review examines the detection of pericyte loss in different diseases, explores the methods employed to assess pericyte coverage, and elucidates the potential mechanisms contributing to pericyte loss in these pathological conditions. Additionally, current therapeutic strategies targeting pericytes are discussed, along with potential future interventions aimed at preserving pericyte function and promoting disease mitigation.

Endothelial progenitor cells in the host defense response

Extensive injury of endothelial cells in blood vasculature, especially in the microcirculatory system, frequently occurs in hosts suffering from sepsis and the accompanied systemic inflammation. Pathological factors, including toxic components derived from invading microbes, oxidative stress associated with tissue ischemia/reperfusion, and vessel active mediators generated during the inflammatory response, are known to play important roles in mediating endothelial injury. Collapse of microcirculation and tissue edema developed from the failure of endothelial barrier function in vital organ systems, including the lung, brain, and kidney, are detrimental, which often predict fatal outcomes. The host body possesses a substantial capacity for maintaining vascular homeostasis and repairing endothelial damage. Bone marrow and vascular wall niches house endothelial progenitor cells (EPCs). In response to septic challenges, EPCs in their niche environment are rapidly activated for proliferation and angiogenic differentiation. In the meantime, release of EPCs from their niches into the blood stream and homing of these vascular precursors to tissue sites of injury are markedly increased. The recruited EPCs actively participate in host defense against endothelial injury and repair of damage in blood vasculature via direct differentiation into endothelial cells for re-endothelialization as well as production of vessel active mediators to exert paracrine and autocrine effects on angiogenesis/vasculogenesis. In recent years, investigations on significance of EPCs in host defense and molecular signaling mechanisms underlying regulation of the EPC response have achieved substantial progress, which promotes exploration of vascular precursor cell-based approaches for effective prevention and treatment of sepsis-induced vascular injury as well as vital organ system failure.

Angiopoietin 2 Is Associated with Vascular Necroptosis Induction in Coronavirus Disease 2019 Acute Respiratory Distress Syndrome

Vascular injury is a well-established, disease-modifying factor in acute respiratory distress syndrome (ARDS) pathogenesis. Recently, coronavirus disease 2019 (COVID-19)-induced injury to the vascular compartment has been linked to complement activation, microvascular thrombosis, and dysregulated immune responses. This study sought to assess whether aberrant vascular activation in this prothrombotic context was associated with the induction of necroptotic vascular cell death. To achieve this, proteomic analysis was performed on blood samples from COVID-19 subjects at distinct time points during ARDS pathogenesis (hospitalized at risk, N = 59; ARDS, N = 31; and recovery, N = 12). Assessment of circulating vascular markers in the at-risk cohort revealed a signature of low vascular protein abundance that tracked with low platelet levels and increased mortality. This signature was replicated in the ARDS cohort and correlated with increased plasma angiopoietin 2 levels. COVID-19 ARDS lung autopsy immunostaining confirmed a link between vascular injury (angiopoietin 2) and platelet-rich microthrombi (CD61) and induction of necrotic cell death [phosphorylated mixed lineage kinase domain-like (pMLKL)]. Among recovery subjects, the vascular signature identified patients with poor functional outcomes. Taken together, this vascular injury signature was associated with low platelet levels and increased mortality and can be used to identify ARDS patients most likely to benefit from vascular targeted therapies.

Glycocalyx heparan sulfate cleavage promotes endothelial cell angiopoietin-2 expression by impairing shear stress-related AMPK/FoxO1 signaling

Angiopoietin-2 (Ang-2) is a key mediator of vascular disease during sepsis, and elevated plasma levels of Ang-2 are associated with organ injury scores and poor clinical outcomes. We have previously observed that biomarkers of endothelial glycocalyx (EG) damage correlate with plasma Ang-2 levels, suggesting a potential mechanistic linkage between EG injury and Ang-2 expression during states of systemic inflammation. However, the cell signaling mechanisms regulating Ang-2 expression following EG damage are unknown. In the current study, we determined the temporal associations between plasma heparan sulfate (HS) levels as a marker of EG erosion and plasma Ang-2 levels in children with sepsis and in mouse models of sepsis. Secondly, we evaluated the role of shear stress-mediated 5'-adenosine monophosphate-activated protein kinase (AMPK) signaling in Ang-2 expression following enzymatic HS cleavage from the surface of human primary lung microvascular endothelial cells (HLMVEC). We found that plasma HS levels peak prior to plasma Ang-2 levels in children and mice with sepsis. Further, we discovered that impaired AMPK signaling contributes to increased Ang-2 expression following HS cleavage from flow conditioned HLMVECs, establishing a novel paradigm by which Ang-2 may be upregulated during sepsis.

Role of Angiopoietin-Tie axis in vascular and lymphatic systems and therapeutic interventions

The Angiopoietin (Ang)-Tyrosine kinase with immunoglobulin-like and EGF-like domains (Tie) axis is an endothelial cell-specific ligand-receptor signaling pathway necessary for vascular and lymphatic development. The Ang-Tie axis is involved in regulating angiogenesis, vascular remodeling, vascular permeability, and inflammation to maintain vascular quiescence. Disruptions in the Ang-Tie axis are involved in many vascular and lymphatic system diseases and play an important role in physiological and pathological vascular conditions. Given recent advances in the Ang-Tie axis in the vascular and lymphatic systems, this review focuses on the multiple functions of the Ang-Tie axis in inflammation-induced vascular permeability, vascular remodeling, atherosclerosis, ocular angiogenesis, tumor angiogenesis, and metastasis. A summary of relevant therapeutic approaches to the Ang-Tie axis, including therapeutic antibodies, recombinant proteins and small molecule drugs are also discussed. The purpose of this review is to provide new hypotheses and identify potential therapeutic strategies based on the Ang-Tie signaling axis for the treatment of vascular and lymphatic-related diseases.

Regulation and Dysregulation of Endothelial Permeability during Systemic Inflammation

Systemic inflammation can be triggered by infection, surgery, trauma or burns. During systemic inflammation, an overshooting immune response induces tissue damage resulting in organ dysfunction and mortality. Endothelial cells make up the inner lining of all blood vessels and are critically involved in maintaining organ integrity by regulating tissue perfusion. Permeability of the endothelial monolayer is strictly controlled and highly organ-specific, forming continuous, fenestrated and discontinuous capillaries that orchestrate the extravasation of fluids, proteins and solutes to maintain organ homeostasis. In the physiological state, the endothelial barrier is maintained by the glycocalyx, extracellular matrix and intercellular junctions including adherens and tight junctions. As endothelial cells are constantly sensing and responding to the extracellular environment, their activation by inflammatory stimuli promotes a loss of endothelial barrier function, which has been identified as a hallmark of systemic inflammation, leading to tissue edema formation and hypotension and thus, is a key contributor to lethal outcomes. In this review, we provide a comprehensive summary of the major players, such as the angiopoietin-Tie2 signaling axis, adrenomedullin and vascular endothelial (VE-) cadherin, that substantially contribute to the regulation and dysregulation of endothelial permeability during systemic inflammation and elucidate treatment strategies targeting the preservation of vascular integrity.

Angiopoietin-2 Inhibition of Thrombomodulin-Mediated Anticoagulation-A Novel Mechanism That May Contribute to Hypercoagulation in Critically Ill COVID-19 Patients

Hypercoagulation and endothelial dysfunction play central roles in severe forms of COVID-19 infections, but the molecular mechanisms involved are unclear. Increased plasma levels of the inflammatory cytokine and TIE2 receptor antagonist Angiopoietin-2 were reported in severely ill COVID-19 patients. In vitro experiments suggest that Angiopoietin-2 bind and inhibits thrombomodulin. Thrombomodulin is expressed on the luminal surface of endothelial cells where it is an important member of the intrinsic anticoagulant pathway through activation of protein C. Using clinical data, mouse models, and in vitro assays, we tested if Angiopoietin-2 plays a causal role in COVID-19-associated hypercoagulation through direct inhibition of thrombin/thrombomodulin-mediated physiological anticoagulation. Angiopoietin-2 was measured in 61 patients at admission, and after 10 days in the 40 patients remaining in the ICU. We found that Angiopoietin-2 levels were increased in COVID-19 patients in correlation with disease severity, hypercoagulation, and mortality. In support of a direct effect of Angiopoietin-2 on coagulation, we found that injected Angiopoietin-2 in mice associated to thrombomodulin and resulted in a shortened tail bleeding time, decreased circulating levels of activated protein C, and increased plasma thrombin/antithrombin complexes. Conversely, bleeding time was increased in endothelial-specific Angiopoietin-2 knockout mice, while knockout of Tie2 had no effect on tail bleeding. Using in vitro assays, we found that Angiopoietin-2 inhibited thrombomodulin-mediated anticoagulation and protein C activation in human donor plasma. Our data suggest a novel in vivo mechanism for Angiopoietin-2 in COVID-19-associated hypercoagulation, implicating that Angiopoietin-2 inhibitors may be effective in the treatment of hypercoagulation in severe COVID-19 infection.

Increased Capillary Permeability in Heart Induces Diastolic Dysfunction Independently of Inflammation, Fibrosis, or Cardiomyocyte Dysfunction

BACKGROUND

While endothelial dysfunction is suggested to contribute to heart failure with preserved ejection fraction pathophysiology, understanding the importance of the endothelium alone, in the pathogenesis of diastolic abnormalities has not yet been fully elucidated. Here, we investigated the consequences of specific endothelial dysfunction on cardiac function, independently of any comorbidity or risk factor (diabetes or obesity) and their potential effect on cardiomyocyte.

METHODS

The ubiquitine ligase Pdzrn3, expressed in endothelial cells (ECs), was shown to destabilize tight junction. A genetic mouse model in which Pdzrn3 is overexpressed in EC (iEC-Pdzrn3) in adults was developed.

RESULTS

EC-specific Pdzrn3 expression increased cardiac leakage of IgG and fibrinogen blood-born molecules. The induced edema demonstrated features of diastolic dysfunction, with increased end-diastolic pressure, alteration of dP/dt min, increased natriuretic peptides, in addition to limited exercise capacity, without major signs of cardiac fibrosis and inflammation. Electron microscopic images showed edema with disrupted EC-cardiomyocyte interactions. RNA sequencing analysis of gene expression in cardiac EC demonstrated a decrease in genes coding for endothelial extracellular matrix proteins, which could be related to the fragile blood vessel phenotype. Irregularly shaped capillaries with hemorrhages were found in heart sections of iEC-Pdzrn3 mice. We also found that a high-fat diet was not sufficient to provoke diastolic dysfunction; high-fat diet aggravated cardiac inflammation, associated with an altered cardiac metabolic signature in EC-Pdzrn3 mice, reminiscent of heart failure with preserved ejection fraction features.

CONCLUSIONS

An increase of endothelial permeability is responsible for mediating diastolic dysfunction pathophysiology and for aggravating detrimental effects of a high-fat diet on cardiac inflammation and metabolism.

Identification of Clinical Phenotypes in Septic Patients Presenting With Hypotension or Elevated Lactate

Introduction

Targeted therapies for sepsis have failed to show benefit due to high variability among subjects. We sought to demonstrate different phenotypes of septic shock based solely on clinical features and show that these relate to outcome.

Methods

A retrospective analysis was performed of a 1,023-subject cohort with early septic shock from the ProCESS trial. Twenty-three clinical variables at baseline were analyzed using hierarchical clustering, with consensus clustering used to identify and validate the ideal number of clusters in a derivation cohort of 642 subjects from 20 hospitals. Clusters were visualized using heatmaps over 0, 6, 24, and 72 h. Clinical outcomes were 14-day all-cause mortality and organ failure pattern. Cluster robustness was confirmed in a validation cohort of 381 subjects from 11 hospitals.

Results

Five phenotypes were identified, each with unique organ failure patterns that persisted in time. By enrollment criteria, all patients had shock. The two high-risk phenotypes were characterized by distinct multi-organ failure patterns and cytokine signatures, with the highest mortality group characterized most notably by liver dysfunction and coagulopathy while the other group exhibited primarily respiratory failure, neurologic dysfunction, and renal dysfunction. The moderate risk phenotype was that of respiratory failure, while low-risk phenotypes did not have a high degree of additional organ failure.

Conclusions

Sepsis phenotypes with distinct biochemical abnormalities may be identified by clinical characteristics alone and likely provide an opportunity for early clinical actionability and prognosis.

Intravenous administration of umbilical cord lining stem cells in left ventricular assist device recipient: Rationale and design of the uSTOP LVAD BLEED pilot study

Background

Left ventricular assist device (LVAD) implantation provides a robust survival advantage, however despite improvements in mortality, the adverse event burden of durable mechanical circulatory support remains high. Bleeding complications are one such significant complication. The uSTOP LVAD BLEED (Utilization of umbilical cord lining Stem cells TO Prevent LVAD associated angiodysplastic BLEEDing) pilot study is designed to evaluate the safety and tolerability of escalating doses of umbilical cord lining stem cells (ULSCs) in LVAD recipients to ameliorate the dysregulation of angiogenic factors seen in this population.

Design

This Phase Ia single-ascending dose pilot study will evaluate the IV administration of ULSCs in stable out-patients supported with an LVAD. In a 3 + 3 design, a maximum of 18 patients will receive an IV infusion of ULSCs.

Main outcome measures

The primary endpoints are safety and tolerability, secondary exploratory endpoints will include biomarker evaluation of angiogenic dysregulation.

Summary

This represents a novel cell type and route of administration in this population, while collecting initial data regarding the magnitude and duration of effects of cell therapy, and assessing the possibility of decreasing bleeding by a strategy of vascular stabilization.

Clinical trial registration

ClinicalTrials.gov Identifier: NCT04811261. https://clinicaltrials.gov/ct2/show/NCT04811261.

Myocardial oedema: pathophysiological basis and implications for the failing heart

Myocardial fluid homeostasis relies on a complex interplay between microvascular filtration, interstitial hydration, cardiomyocyte water uptake and lymphatic removal. Dysregulation of one or more of these mechanisms may result in myocardial oedema. Interstitial and intracellular fluid accumulation disrupts myocardial architecture, intercellular communication, and metabolic pathways, decreasing contractility and increasing myocardial stiffness. The widespread use of cardiac magnetic resonance enabled the identification of myocardial oedema as a clinically relevant imaging finding with prognostic implications in several types of heart failure. Furthermore, growing experimental evidence has contributed to a better understanding of the physical and molecular interactions in the microvascular barrier, myocardial interstitium and lymphatics and how they might be disrupted in heart failure. In this review, we summarize current knowledge on the factors controlling myocardial water balance in the healthy and failing heart and pinpoint the new potential therapeutic avenues.

Interdependence of Angiogenesis and Arteriogenesis in Development and Disease

The structure of arterial networks is optimized to allow efficient flow delivery to metabolically active tissues. Optimization of flow delivery is a continuous process involving synchronization of the structure and function of the microcirculation with the upstream arterial network. Risk factors for ischemic cardiovascular diseases, such as diabetes mellitus and hyperlipidemia, adversely affect endothelial function, induce capillary regression, and disrupt the micro- to macrocirculation cross-talk. We provide evidence showing that this loss of synchronization reduces arterial collateral network recruitment upon arterial stenosis, and the long-term clinical outcome of current revascularization strategies in these patient cohorts. We describe mechanisms and signals contributing to synchronized growth of micro- and macrocirculation in development and upon ischemic challenges in the adult organism and identify potential therapeutic targets. We conclude that a long-term successful revascularization strategy should aim at both removing obstructions in the proximal part of the arterial tree and restoring “bottom-up” vascular communication.

Angiopoietins as Prognostic Markers for Future Kidney Disease and Heart Failure Events after Acute Kidney Injury

BACKGROUND

The mechanisms underlying long-term sequelae after AKI remain unclear. Vessel instability, an early response to endothelial injury, may reflect a shared mechanism and early trigger for CKD and heart failure.

METHODS

To investigate whether plasma angiopoietins, markers of vessel homeostasis, are associated with CKD progression and heart failure admissions after hospitalization in patients with and without AKI, we conducted a prospective cohort study to analyze the balance between angiopoietin-1 (Angpt-1), which maintains vessel stability, and angiopoietin-2 (Angpt-2), which increases vessel destabilization. Three months after discharge, we evaluated the associations between angiopoietins and development of the primary outcomes of CKD progression and heart failure and the secondary outcome of all-cause mortality 3 months after discharge or later.

RESULTS

Median age for the 1503 participants was 65.8 years; 746 (50%) had AKI. Compared with the lowest quartile, the highest quartile of the Angpt-1:Angpt-2 ratio was associated with 72% lower risk of CKD progression (adjusted hazard ratio [aHR], 0.28; 95% confidence interval [CI], 0.15 to 0.51), 94% lower risk of heart failure (aHR, 0.06; 95% CI, 0.02 to 0.15), and 82% lower risk of mortality (aHR, 0.18; 95% CI, 0.09 to 0.35) for those with AKI. Among those without AKI, the highest quartile of Angpt-1:Angpt-2 ratio was associated with 71% lower risk of heart failure (aHR, 0.29; 95% CI, 0.12 to 0.69) and 68% less mortality (aHR, 0.32; 95% CI, 0.15 to 0.68). There were no associations with CKD progression.

CONCLUSIONS

A higher Angpt-1:Angpt-2 ratio was strongly associated with less CKD progression, heart failure, and mortality in the setting of AKI.

Endothelial Dysfunction after Hematopoietic Stem Cell Transplantation: A Review Based on Physiopathology

Endothelial dysfunction (ED) is frequently encountered in transplant medicine. ED is an argument of high complexity, and its understanding requires a wide spectrum of knowledge based on many fields of basic sciences such as molecular biology, immunology, and pathology. After hematopoietic stem cell transplantation (HSCT), ED participates in the pathogenesis of various complications such as sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD), graft-versus-host disease (GVHD), transplant-associated thrombotic microangiopathy (TA-TMA), idiopathic pneumonia syndrome (IPS), capillary leak syndrome (CLS), and engraftment syndrome (ES). In the first part of the present manuscript, we briefly review some biological aspects of factors involved in ED: adhesion molecules, cytokines, Toll-like receptors, complement, angiopoietin-1, angiopoietin-2, thrombomodulin, high-mobility group B-1 protein, nitric oxide, glycocalyx, coagulation cascade. In the second part, we review the abnormalities of these factors found in the ED complications associated with HSCT. In the third part, a review of agents used in the treatment of ED after HSCT is presented.

Modulation of the Permeability-Inducing Factor Angiopoietin-2 Through Bifonazole in Systemic Inflammation

BACKGROUND

Vascular barrier breakdown in sepsis represents a key component of the maladaptive host response to infection and the release of endothelial Angiopoietin-2 (Angpt-2) is a mechanistic driver of endothelial hyperpermeability. Angpt-2 is associated with morbidity and mortality but a targeted therapeutic approach is not available. We screened for U.S. Food and Drug Administration (FDA) approved drugs that might have off-target effects decreasing Angpt-2 and therefore, ameliorating capillary leakage.

METHODS

Endothelial cells were isolated from human umbilical veins (HUVECs) and used for in vitro studies at baseline and after stimulation (FDA-library screening, RT-PCR, ELISA, immunocytochemistry, MTT assay). On the functional level, we assessed real-time transendothelial electrical resistance (TER) using an electric cell-substrate impedance sensing device.

RESULTS

We found that the anti-fungal Bifonazole (BIFO) reduces spontaneous Angpt-2 release in a time- and dose-dependent manner after 8, 12, and 24 h (24 h: veh: 15.6 ± 0.7 vs. BIFO: 8.6 ± 0.8 ng/mL, P < 0.0001). Furthermore, we observed a reduction in its intra-cellular content by 33% (P < 0.001). Stimulation with tumor necrosis factor α induced a strong release of Angpt-2 that could analogously be blocked by additional treatment with BIFO (veh: 1.58 ± 0.2 vs. BIFO: 1.02 ± 0.1, P < 0.0001). Quantification of endothelial permeability by TER revealed that BIFO was sufficient to reduce Thrombin-induced barrier breakdown (veh: 0.82 ± 0.1 vs. BIFO: 1.01 ± 0.02, P < 0.05).

CONCLUSION

The antifungal BIFO reduces both release and biosynthesis of the endothelial-destabilizing factor Angpt-2 in vitro thereby improving vascular barrier function. Additional studies are needed to further investigate the underlying mechanism and to translate these findings to in vivo models.

Endothelial dysfunction: a therapeutic target in bacterial sepsis?

INTRODUCTION

Endothelial cells maintain vascular integrity, tone, and patency and have important roles in hemostasis and inflammatory responses. Although some degree of endothelial dysfunction with increased vascular permeability may be necessary to control local infection, excessive dysfunction plays a central role in the pathogenesis of sepsis-related organ dysfunction and failure as it results in dysregulated inflammation, vascular leakage, and abnormal coagulation. The vascular endothelium has thus been proposed as a potential target for therapeutic intervention in patients with sepsis.

AREAS COVERED

Different mechanisms underlying sepsis-related dysfunction of the vascular endothelium are discussed, including glycocalyx shedding, nitrosative stress, and coagulation factors. Potential therapeutic implications of each mechanism are mentioned.

EXPERT OPINION

Multiple targets to protect or restore endothelial function have been suggested, but endothelium-driven treatments remain a future potential at present. As some endothelial dysfunction and permeability may be necessary to remove infection and repair damaged tissue, targeting the endothelium may be a particular challenge. Ideally, therapies should be guided by biomarkers related to that specific pathway to ensure they are given only to patients most likely to respond. This enrichment based on biological plausibility and theragnostics will increase the likelihood of a beneficial response in individual patients and enable more personalized treatment.

Serum VEGF and Ang-2 Levels in Infants Before and After Laser Treatment for Retinopathy of Prematurity

To investigate VEGF and Ang-2 level changes in the systemic circulation after laser photocoagulation in premature infants with ROP. Methods: Eleven infants (4 girls and 7 boys) had serum levels determined for VEGF and Ang-2, collected 1 day prior to and 7 days after ROP laser therapy. Serum levels of VEGF and Ang-2 were quantified by enzyme-linked immunosorbent assay (ELISA). Results: Serum VEGF levels were significantly lower at 7 days after laser therapy compared to that at 1 day prior to laser therapy (p = 0.045). Serum Ang-2 levels increased significantly at 7 days after laser therapy compared with that at 1 day prior to laser therapy (p = 0.046). Conclusions: Serum VEGF levels in patients with ROP were suppressed and Ang-2 levels elevated significantly after laser therapy. The results suggest that changes in VEGF and Ang-2 serum levels may reflect regression and treatment of ROP.

The role of mural cells in hemorrhage of brain arteriovenous malformation

Brain arteriovenous malformation (bAVM) is the most common cause of intracranial hemorrhage (ICH), particularly in young patients. However, the exact cause of bAVM bleeding and rupture is not yet fully understood. In bAVMs, blood bypasses the entire capillary bed and directly flows from arteries to veins. The vessel walls in bAVMs have structural defects, which impair vascular integrity. Mural cells are essential structural and functional components of blood vessels and play a critical role in maintaining vascular integrity. Changes in mural cell number and coverage have been implicated in bAVMs. In this review, we discussed the roles of mural cells in bAVM pathogenesis. We focused on 1) the recent advances in human and animal studies of bAVMs; 2) the importance of mural cells in vascular integrity; 3) the regulatory signaling pathways that regulate mural cell function. More specifically, the platelet-derived growth factor-B (PDGF-B)/PDGF receptor-β (PDGFR-β), EphrinB2/EphB4, and angiopoietins/tie2 signaling pathways that regulate mural cell-recruitment during vascular remodeling were discussed in detail.

Apoptosis signal-regulating kinase 1 (ASK1) inhibition reduces endothelial cytokine production without improving permeability after toll-like receptor 4 (TLR4) challenge

Sepsis represents a life-threatening event often mediated by the host's response to pathogens such as gram-negative organisms, which release the proinflammatory lipopolysaccharide (LPS). Within the endothelium, the mitogen-activated protein kinase (MAPK) pathway is an important driver of endothelial injury during sepsis, of which oxidant-sensitive apoptosis signal-regulating kinase 1 (ASK1) is postulated to be a critical upstream regulator. We hypothesized that ASK1 would play a key role in endothelial inflammation during bacterial challenge. Utilizing RNA sequencing data from patients and cultured human microvascular endothelial cells (HMVECs), ASK1 expression was increased in sepsis and after LPS challenge. Two ASK1 inhibitors, GS444217 and MSC2023964A, reduced cytokine production in HMVECs following LPS stimulation, but had no effect on permeability as measured by transendothelial electrical resistance and intercellular space. MAPKs are known to interact with endothelial nitric oxide synthase (eNOS) and ASK1 expression levels correlated with eNOS expression in patients with septic shock. In addition, eNOS physically interacted with ASK1, though this interaction was not altered by ASK1 inhibition, nor did inhibition alter MAPK p38 activity. Instead, among MAPKs, ASK1 inhibition only impaired LPS-induced JNK phosphorylation. The reduction in JNK activation caused by ASK1 inhibition impaired JNK-mediated cytokine production without affecting permeability. Thus, LPS triggers JNK-dependent cytokine production that requires ASK1 activation, but both its effects on permeability and activation of p38 are ASK1-independent. These data demonstrate how distinct MAPK signaling pathways regulate endothelial inflammatory outputs during acute infectious challenge.

New mechanism-based approaches to treating and evaluating the vasculopathy of scleroderma

PURPOSE OF REVIEW

Utilizing recent insight into the vasculopathy of scleroderma (SSc), the review will highlight new opportunities for evaluating and treating the disease by promoting stabilization and protection of the microvasculature.

RECENT FINDINGS

Endothelial junctional signaling initiated by vascular endothelial-cadherin (VE-cadherin) and Tie2 receptors, which are fundamental to promoting vascular health and stability, are disrupted in SSc. This would be expected to not only diminish their protective activity, but also increase pathological processes that are normally restrained by these signaling mediators, resulting in pathological changes in vascular function and structure. Indeed, key features of SSc vasculopathy, from the earliest signs of edema and puffy fingers to pathological disruption of hemodynamics, nutritional blood flow, capillary structure and angiogenesis are all consistent with this altered endothelial signaling. It also likely contributes to further progression of the disease including tissue fibrosis, and organ and tissue injury.

SUMMARY

Restoring protective endothelial junctional signaling should combat the vasculopathy of SSc and prevent further deterioration in vascular and organ function. Indeed, this type of targeted approach has achieved remarkable results in preclinical models for other diseases. Furthermore, tracking this endothelial junctional signaling, for example by assessing vascular permeability, should facilitate insight into disease progression and its response to therapy.

Lung Pericytes in Pulmonary Vascular Physiology and Pathophysiology

Pericytes are mesenchymal-derived mural cells localized within the basement membrane of pulmonary and systemic capillaries. Besides structural support, pericytes control vascular tone, produce extracellular matrix components, and cytokines responsible for promoting vascular homeostasis and angiogenesis. However, pericytes can also contribute to vascular pathology through the production of pro-inflammatory and pro-fibrotic cytokines, differentiation into myofibroblast-like cells, destruction of the extracellular matrix, and dissociation from the vessel wall. In the lung, pericytes are responsible for maintaining the integrity of the alveolar-capillary membrane and coordinating vascular repair in response to injury. Loss of pericyte communication with alveolar capillaries and a switch to a pro-inflammatory/pro-fibrotic phenotype are common features of lung disorders associated with vascular remodeling, inflammation, and fibrosis. In this article, we will address how to differentiate pericytes from other cells, discuss the molecular mechanisms that regulate the interactions of pericytes and endothelial cells in the pulmonary circulation, and the experimental tools currently used to study pericyte biology both in vivo and in vitro. We will also discuss evidence that links pericytes to the pathogenesis of clinically relevant lung disorders such as pulmonary hypertension, idiopathic lung fibrosis, sepsis, and SARS-COVID. Future studies dissecting the complex interactions of pericytes with other pulmonary cell populations will likely reveal critical insights into the origin of pulmonary diseases and offer opportunities to develop novel therapeutics to treat patients afflicted with these devastating disorders. © 2021 American Physiological Society. Compr Physiol 11:2227-2247, 2021.

Intrinsic differences in the mechanisms of Tie2 binding to angiopoietins exploited by directed evolution to create an Ang2-selective ligand trap

Angiopoietins Ang1 and Ang2 are secreted ligands for the endothelial receptor tyrosine kinase Tie2 essential for vascular development and maintenance. Ang1 acts as an agonist to maintain normal vessel function, whereas Ang2 acts as a Tie2 antagonist. Ang2 is increased in macular edema, sepsis, and other conditions, in which it blocks Ang1-mediated signaling, causing vascular dysfunction and contributing to disease pathology. Therefore, Ang2 is an attractive therapeutic target. Previously, we reported a Tie2 ectodomain variant that selectively binds Ang2 and acts as soluble ligand trap to sequester Ang2; however, the mechanism of Ang2-binding selectivity is unknown. In the present study, we used directed protein evolution to enhance Ang2-binding affinity of this Tie2 ectodomain trap. We examined contributions of individual residues in the ligand-binding interface of Tie2 to Ang1 and Ang2 binding. Surprisingly, different combinations of Tie2 residues were found to bind each ligand, with hydrophobic residues binding both ligands and polar residues contributing selectively to either Ang1 or Ang2 binding. Our analysis also identified a single Tie2 residue, His168, with a pivotal role in both Ang1 and Ang2 binding, enabling competition between binding ligands. In summary, this study reports an enhanced-affinity Ang2-selective ligand trap with potential for therapeutic development and reveals the mechanism behind its selectivity. It also provides the first analysis of contributions of individual Tie2 residues to Ang1 and Ang2 binding and identifies selectivity-determining residues that could be targeted in the future design of small molecule and other inhibitors of Ang2 for the treatment of vascular dysfunction.

AntimiR-132 Attenuates Myocardial Hypertrophy in an Animal Model of Percutaneous Aortic Constriction

BACKGROUND

Pathological cardiac hypertrophy is a result of afterload-increasing pathologies including untreated hypertension and aortic stenosis. It features progressive adverse cardiac remodeling, myocardial dysfunction, capillary rarefaction, and interstitial fibrosis often leading to heart failure.

OBJECTIVES

This study aimed to establish a novel porcine model of pressure-overload-induced heart failure and to determine the effect of inhibition of microribonucleic acid 132 (miR-132) on heart failure development in this model.

METHODS

This study developed a novel porcine model of percutaneous aortic constriction by implantation of a percutaneous reduction stent in the thoracic aorta, inducing progressive remodeling at day 56 (d56) after pressure-overload induction. In this study, an antisense oligonucleotide specifically inhibiting miR-132 (antimiR-132), was regionally applied via intracoronary injection at d0 (percutaneous transverse aortic constriction induction) and d28.

RESULTS

At d56, antimiR-132 treatment diminished cardiomyocyte cross-sectional area (188.9 ± 2.8 vs. 258.4 ± 9.0 μm² in untreated hypertrophic hearts) and improved global cardiac function (ejection fraction 48.9 ± 1.0% vs. 36.1 ± 1.7% in control hearts). Moreover, at d56 antimiR-132-treated hearts displayed less increase of interstitial fibrosis compared with sham-operated hearts (Δsham 1.8 ± 0.5%) than control hearts (Δsham 10.8 ± 0.6%). Of note, cardiac platelet and endothelial cell adhesion molecule 1⁺ capillary density was higher in the antimiR-132-treated hearts (647 ± 20 cells/mm²) compared with in the control group (485 ± 23 cells/mm²).

CONCLUSIONS

The inhibition of miR-132 is a valid strategy in prevention of heart failure progression in hypertrophic heart disease and may be developed as a treatment for heart failure of nonischemic origin.

Generation of a new immortalized human lung pericyte cell line: a promising tool for human lung pericyte studies

Pericytes apposed to the capillary endothelium are known to stabilize and promote endothelial integrity. Recent studies indicate that lung pericytes play a prominent role in lung physiology, and they are involved in the development of various lung diseases including lung injury in sepsis, pulmonary fibrosis, asthma, and pulmonary hypertension. Accordingly, human lung pericyte studies are important for understanding the mechanistic basis of lung physiology and pathophysiology; however, human lung pericytes can only be cultured for a few passages and no immortalized human lung pericyte cell line has been established so far. Thus, our study aims to establish an immortalized human lung pericyte cell line. Developed using SV40 large T antigen lentivirus, immortalized pericytes exhibit stable SV40T expression, sustained proliferation, and have significantly higher telomerase activity compared to normal human lung pericytes. In addition, these cells retained pericyte characteristics, marked by similar morphology, and expression of pericyte cell surface markers such as PDGFRβ, NG2, CD44, CD146, CD90, and CD73. Furthermore, similar to that of primary pericytes, immortalized pericytes promoted endothelial cell tube formation and responded to different stimuli. Our previous data showed that friend leukemia virus integration 1 (Fli-1), a member of the ETS transcription factor family, is a key regulator that modulates inflammatory responses in mouse lung pericytes. We further demonstrated that Fli-1 regulates inflammatory responses in immortalized human lung pericytes. To summarize, we successfully established an immortalized human lung pericyte cell line, which serves as a promising tool for in vitro pericyte studies to understand human lung pericyte physiology and pathophysiology.

Analysis of Inflammatory Mediator Profiles in Sepsis Patients Reveals That Extracellular Histones Are Strongly Elevated in Nonsurvivors

The timely recognition of sepsis and the prediction of its clinical course are challenging due to the complex molecular mechanisms leading to organ failure and to the heterogeneity of sepsis patients. Treatment strategies relying on a “one-fits-all” approach have failed to reduce mortality, suggesting that therapeutic targets differ between patient subgroups and highlighting the need for accurate analysis of the molecular cascades to assess the highly variable host response. Here, we characterized a panel of 44 inflammatory mediators, including cytokines, chemokines, damage-associated molecular patterns, and coagulation-related factors, as well as markers of endothelial activation in 30 patients suffering from renal failure in the course of sepsis. All patients received continuous veno-venous hemodialysis with either high cut-off filters or with standard filters, and mediators were quantified for all patients at the initiation of dialysis and after 24 h and 48 h. Mediator concentrations in individual patients ranged widely, demonstrating the heterogeneity of sepsis patients. None of the mediators correlated with SAPS III or TISS scores. The overall in-hospital mortality of the study population was 56.7% (57.1% vs. 56.3% for high cut-off vs. standard filter). The two filter groups differed regarding most of the mediator levels at baseline, prohibiting conclusions regarding the effect of standard filters versus high cut-off filters on mediator depletion. The elevation and correlation of damage-associated molecular patterns and markers of endothelial activation gave evidence of severe tissue damage. In particular, extracellular histones were strongly increased and were almost 30-fold higher in nonsurvivors as compared to survivors, indicating their diagnostic and prognostic potential.

A study of the effects of hydroxyapatite bioceramic extract on Ang/Tie2 system of umbilical vein endothelial cells

OBJECTIVE:

We aimed to investigate the effects of hydroxyapatite bioceramic extract on Ang/Tie2 system and cell proliferation of umbilical vein endothelial cells.

METHODS:

Human umbilical vein endothelial cells (HUVECs) were used in this research. There are two induvial groups, control group and hydroxyapatite bioceramics extract treatment group. Cell Counting Kit-8 (CCK-8) was used to evaluate cell proliferation. Western blot and real time quantitative PCR (Q-PCR) were used to evaluate the protein and mRNA expression levels of Ang1, Ang2 and Tie2 in Ang/Tie2 system, respectively. All the results were statistically analyzed by Spss19.0. All data were presented as mean ± standard error of mean (SEM). Student’s t-test was performed to determine the differences among grouped data.

RESULTS:

Hydroxyapatite bioceramics extract showed no effect on the cell morphology and cell proliferation of HUVECs. Interestingly, we found that both Ang2 and Tie2 protein and mRNA level were markedly increased by hydroxyapatite bioceramics extract.

CONCLUSIONS:

Hydroxyapatite bioceramic extract showed no cytotoxicity to HUVECs, and might regulate vascular remodeling by mediating Ang/Tie2 system.

Emerging Role of Pericytes and Their Secretome in the Heart

Pericytes, as mural cells covering microvascular capillaries, play an essential role in vascular remodeling and maintaining vascular functions and blood flow. Pericytes are crucial participants in the physiological and pathological processes of cardiovascular disease. They actively interact with endothelial cells, vascular smooth muscle cells (VSMCs), fibroblasts, and other cells via the mechanisms involved in the secretome. The secretome of pericytes, along with diverse molecules including proinflammatory cytokines, angiogenic growth factors, and the extracellular matrix (ECM), has great impacts on the formation, stabilization, and remodeling of vasculature, as well as on regenerative processes. Emerging evidence also indicates that pericytes work as mesenchymal cells or progenitor cells in cardiovascular regeneration. Their capacity for differentiation also contributes to vascular remodeling in different ways. Previous studies primarily focused on the roles of pericytes in organs such as the brain, retina, lung, and kidney; very few studies have focused on pericytes in the heart. In this review, following a brief introduction of the origin and fundamental characteristics of pericytes, we focus on pericyte functions and mechanisms with respect to heart disease, ending with the promising use of cardiac pericytes in the treatment of ischemic heart failure.

Sphingosine-1-Phosphate Attenuates Lipopolysaccharide-Induced Pericyte Loss via Activation of Rho-A and MRTF-A

The high mortality seen in sepsis is caused by a systemic hypotension in part owing to a drastic increase in vascular permeability accompanied by a loss of pericytes. As has been shown previously, pericyte retention in the perivascular niche during sepsis can enhance the integrity of the vasculature and promote survival via recruitment of adhesion proteins such as VE-cadherin and N-cadherin. Sphingosine-1-phosphate (S1P) represents a lipid mediator regulating the deposition of the crucial adhesion molecule VE-cadherin at sites of interendothelial adherens junctions and of N-cadherin at endothelial-pericyte adherens junctions. Furthermore, in septic patients, S1P plasma levels are decreased and correlate with mortality in an indirectly proportional way. In the present study, we investigated the potential of S1P to ameliorate a lipopolysaccharide-induced septic hypercirculation in mice. Here we establish S1P as an antagonist of pericyte loss, vascular hyperpermeability, and systemic hypotension, resulting in an increased survival in mice. During sepsis S1P preserved VE-cadherin and N-cadherin deposition, mediated by a reduction of Src and cadherin phosphorylation. At least in part, this effect is mediated by a reduction of globular actin and a subsequent increase in nuclear translocation of MRTF-A (myocardin-related transcription factor A). These findings indicate that S1P may counteract pericyte loss and microvessel disassembly during sepsis and additionally emphasize the importance of pericyte-endothelial interactions to stabilize the vasculature.

Single-Cell Analysis of Blood-Brain Barrier Response to Pericyte Loss

RATIONALE

Pericytes are capillary mural cells playing a role in stabilizing newly formed blood vessels during development and tissue repair. Loss of pericytes has been described in several brain disorders, and genetically induced pericyte deficiency in the brain leads to increased macromolecular leakage across the blood-brain barrier (BBB). However, the molecular details of the endothelial response to pericyte deficiency remain elusive.

OBJECTIVE

To map the transcriptional changes in brain endothelial cells resulting from lack of pericyte contact at single-cell level and to correlate them with regional heterogeneities in BBB function and vascular phenotype.

METHODS AND RESULTS

We reveal transcriptional, morphological, and functional consequences of pericyte absence for brain endothelial cells using a combination of methodologies, including single-cell RNA sequencing, tracer analyses, and immunofluorescent detection of protein expression in pericyte-deficient adult Pdgfbret/ret mice. We find that endothelial cells without pericyte contact retain a general BBB-specific gene expression profile, however, they acquire a venous-shifted molecular pattern and become transformed regarding the expression of numerous growth factors and regulatory proteins. Adult Pdgfbret/ret brains display ongoing angiogenic sprouting without concomitant cell proliferation providing unique insights into the endothelial tip cell transcriptome. We also reveal heterogeneous modes of pericyte-deficient BBB impairment, where hotspot leakage sites display arteriolar-shifted identity and pinpoint putative BBB regulators. By testing the causal involvement of some of these using reverse genetics, we uncover a reinforcing role for angiopoietin 2 at the BBB.

CONCLUSIONS

By elucidating the complexity of endothelial response to pericyte deficiency at cellular resolution, our study provides insight into the importance of brain pericytes for endothelial arterio-venous zonation, angiogenic quiescence, and a limited set of BBB functions. The BBB-reinforcing role of ANGPT2 (angiopoietin 2) is paradoxical given its wider role as TIE2 (TEK receptor tyrosine kinase) receptor antagonist and may suggest a unique and context-dependent function of ANGPT2 in the brain.

Angiopoietin-2 outperforms other endothelial biomarkers associated with severe acute kidney injury in patients with severe sepsis and respiratory failure

BACKGROUND

Endothelial dysfunction and injury is a major pathophysiologic feature of sepsis. Sepsis is also the most frequent cause of acute kidney injury (AKI) in critically ill patients. Though most studies of AKI in sepsis have focused on tubular epithelial injury, the role of endothelial dysfunction and injury is less well studied. The goal of this study was first to investigate whether endothelial dysfunction and injury biomarkers were associated with severe AKI in sepsis patients. The second goal was to determine the best performing biomarker for severe AKI and whether this biomarker was associated with severe AKI across different etiologies of sepsis and clinical outcomes.

METHODS

We studied adults with severe sepsis and acute respiratory failure (ARF) enrolled in the prospective observational Validating Acute Lung Injury markers for Diagnosis (VALID) study. Plasma endothelial dysfunction and injury biomarkers, including angiopoietin-2, soluble vascular endothelial cadherin (sVE-cadherin), endocan and syndecan-1, were measured at study enrollment. Primary analysis focused on the association between endothelial biomarker levels with severe AKI (defined as Kidney Disease: Improving Global Outcomes [KDIGO] AKI stage 2 or 3), other organ dysfunctions (defined by Brussels organ failure scores), and comparison of pulmonary versus non-pulmonary sepsis.

RESULTS

Among 228 sepsis patients enrolled, 141 developed severe AKI. Plasma levels of angiopoietin-2, endocan, sVE-cadherin, and syndecan-1 were significantly higher in sepsis patients with severe AKI compared to those without severe AKI. Among four endothelial biomarkers, only angiopoietin-2 was independently associated with severe AKI (odds ratio 6.07 per log increase, 95% CI 2.34-15.78, p < 0.001). Plasma angiopoietin-2 levels by quartile were significantly higher in sepsis patients with hepatic, coagulation, and circulatory failure. Plasma angiopoietin-2 levels were also significantly higher in patients with non-pulmonary sepsis compared to subjects with pulmonary sepsis.

CONCLUSION

Among four biomarkers of endothelial dysfunction and injury, angiopoietin-2 had the most robust independent association with development of severe AKI in patients with severe sepsis and ARF. Plasma angiopoietin-2 levels were also associated with other organ dysfunctions, non-pulmonary sepsis, and death. These findings highlight the importance of early endothelial dysfunction and injury in the pathogenesis of sepsis-induced AKI.