Endothelial Barrier Integrity Is Disrupted In Vitro by Heme and by Serum From Sickle Cell Disease Patients

Effects of Amyloid Beta (Aβ) Oligomers on Blood-Brain Barrier Using a 3D Microfluidic Vasculature-on-a-Chip Model

The disruption of the blood-brain barrier (BBB) in Alzheimer's Disease (AD) is largely influenced by amyloid beta (Aβ). In this study, we developed a high-throughput microfluidic BBB model devoid of a physical membrane, featuring endothelial cells interacting with an extracellular matrix (ECM). This paper focuses on the impact of varying concentrations of Aβ1-42 oligomers on BBB dysfunction by treating them in the luminal. Our findings reveal a pronounced accumulation of Aβ1-42 oligomers at the BBB, resulting in the disruption of tight junctions and subsequent leakage evidenced by a barrier integrity assay. Additionally, cytotoxicity assessments indicate a concentration-dependent increase in cell death in response to Aβ1-42 oligomers (LC50 ~ 1 μM). This study underscores the utility of our membrane-free vascular chip in elucidating the dysfunction induced by Aβ with respect to the BBB.

Whole blood coagulation in an ex vivo thrombus is sufficient to induce clot neutrophils to adopt a myeloid-derived suppressor cell signature and shed soluble Lox-1

BACKGROUND

Blood clots are living tissues that release inflammatory mediators including IL-8/CXCL8 and MCP-1/CCL2. A deeper understanding of blood clots is needed to develop new therapies for prothrombotic disease states and regenerative medicine.

OBJECTIVES

To identify a common transcriptional shift in cultured blood clot leukocytes.

METHODS

Differential gene expression of whole blood and cultured clots (4 hours at 37 °C) was assessed by RNA sequencing (RNAseq), reverse transcriptase-polymerase chain reaction, proteomics, and histology (23 diverse healthy human donors). Cultured clot serum bioactivity was tested in endothelial barrier functional assays.

RESULTS

All cultured clots developed a polymorphonuclear myeloid-derived suppressor cell (PMN-MDSC) signature, including up-regulation of OLR1 (mRNA encoding lectin-like oxidized low-density lipoprotein receptor 1 [Lox-1]), IL-8/CXCL8, CXCL2, CCL2, IL10, IL1A, SPP1, TREM1, and DUSP4/MKP. Lipopolysaccharide enhanced PMN-MDSC gene expression and specifically induced a type II interferon response with IL-6 production. Lox-1 was specifically expressed by cultured clot CD15+ neutrophils. Cultured clot neutrophils, but not activated platelets, shed copious amounts of soluble Lox-1 (sLox-1) with a donor-dependent amplitude. sLox-1 shedding was enhanced by phorbol ester and suppressed by heparin and by beta-glycerol phosphate, a phosphatase inhibitor. Cultured clot serum significantly enhanced endothelial cell monolayer barrier function, consistent with a proresolving bioactivity.

CONCLUSION

This study suggests that PMN-MDSC activation is part of the innate immune response to coagulation which may have a protective role in inflammation. The cultured blood clot is an innovative thrombus model that can be used to study both sterile and nonsterile inflammatory states and could be used as a personalized medicine tool for drug screening.

Heme-Inducing Endothelial Pyroptosis Plays a Key Role in Radiofrequency Ablation of Hepatic Hemangioma Leading to Systemic Inflammatory Response Syndrome

Purpose

Systemic inflammatory response syndrome (SIRS) is a common complication of radiofrequency ablation (RFA) for hepatic hemangiomas. RFA can cause hemolytic reactions during hepatic hemangioma ablation. However, the mechanisms underlying RFA-induced SIRS remain unclear.

Methods

We established an orthotopic liver hemangioma model and performed radiofrequency ablation. The levels of interleukin (IL)-1β and IL-18 and the production of ROS were measured. The wet-to-dry lung ratio, inflammation score, and in vivo endothelial cell permeability were examined. GSDMD-/- mice were used to investigate the effect of heme-inducing SIRS. RNA sequencing (RNA-seq) was performed to identify the main pathways underlying heme-induced SIRS. Western blotting and immunoprecipitation were used to determine the changes and interactions of associated proteins.

Results

The levels of heme, IL-1β, and IL-18 were significantly increased after RFA. The wet-to-dry lung ratio increased in hepatic hemangiomas after RFA, indicating that SIRS occurred. Heme induced increased levels of IL-1β and IL-18, cell death, wet-to-dry lung radio, and inflammation score in vitro and in vivo, indicating that heme induced SIRS and pyroptosis. Furthermore, GSDMD participates in heme-induced SIRS in mice, and GSDMD deletion in mice reverses the effect of heme. Heme regulates NLRP3 activation through the NOX4/ROS/TXNIP-TRX pathway, and an N-acetyl-L-cysteine (NAC) or NOX4 inhibitor (GLX351322) reverses heme-induced SIRS.

Conclusion

Our findings suggest that heme induces endothelial cell pyroptosis and SIRS in mice and decreasing heme levels and ROS scavengers may prevent SIRS in hepatic hemangioma after RFA.

The inflammatory profiles of pulmonary alveolar macrophages and alveolar type 2 cells in SCD

The lung microenvironment plays a crucial role in maintaining lung homeostasis as well as the initiation and resolution of both acute and chronic lung injury. Acute chest syndrome (ACS) is a complication of sickle cell disease (SCD) like acute lung injury. Both the endothelial cells and peripheral blood mononuclear cells are known to secrete proinflammatory cytokines elevated during ACS episodes. However, in SCD, the lung microenvironment that may favor excessive production of proinflammatory cytokines and the contribution of other lung resident cells, such as alveolar macrophages and alveolar type 2 epithelial (AT-2) cells, to ACS pathogenesis is not completely understood. Here, we sought to understand the pulmonary microenvironment and the proinflammatory profile of lung alveolar macrophages (LAMs) and AT-2 cells at steady state in Townes sickle cell (SS) mice compared to control mice (AA). In addition, we examined lung function and micromechanics molecules essential for pulmonary epithelial barrier function in these mice. Our results showed that bronchoalveolar lavage (BAL) fluid in SS mice had elevated protein levels of pro-inflammatory cytokines interleukin (IL)-1β and IL-12 (p ⩽ 0.05) compared to AA controls. We showed for the first time, significantly increased protein levels of inflammatory mediators (Human antigen R (HuR), Toll-like receptor 4 (TLR4), MyD88, and PU.1) in AT-2 cells (1.4 to 2.2-fold) and LAM (17-21%) isolated from SS mice compared to AA control mice at steady state. There were also low levels of anti-inflammatory transcription factors (Nrf2 and PPARy) in SS mice compared to AA controls (p ⩽ 0.05). Finally, we found impaired lung function and a dysregulated composition of surfactant proteins (B and C). Our results demonstrate that SS mice at steady state had a compromised lung microenvironment with elevated expression of proinflammatory cytokines by AT-2 cells and LAM, as well as dysregulated expression of surfactant proteins necessary for maintaining the alveolar barrier integrity and lung function.

Endothelial superoxide dismutase 2 is decreased in sickle cell disease and regulates fibronectin processing

Sickle cell disease (SCD) is a genetic red blood cell disorder characterized by increased reactive oxygen species (ROS) and a concordant reduction in antioxidant capacity in the endothelium. Superoxide dismutase 2 (SOD2) is a mitochondrial-localized enzyme that catalyzes the dismutation of superoxide to hydrogen peroxide. Decreased peripheral blood expression of SOD2 is correlated with increased hemolysis and cardiomyopathy in SCD. Here, we report for the first time that endothelial cells exhibit reduced SOD2 protein expression in the pulmonary endothelium of SCD patients. To investigate the impact of decreased SOD2 expression in the endothelium, SOD2 was knocked down in human pulmonary microvascular endothelial cells (hPMVECs). We found that SOD2 deficiency in hPMVECs results in endothelial cell dysfunction, including reduced cellular adhesion, diminished migration, integrin protein dysregulation, and disruption of permeability. Furthermore, we uncover that SOD2 mediates changes in endothelial cell function via processing of fibronectin through its inability to facilitate dimerization. These results demonstrate that endothelial cells are deficient in SOD2 expression in SCD patients and suggest a novel pathway for SOD2 in regulating fibronectin processing.

Circulating Small Extracellular Vesicles May Contribute to Vaso-Occlusive Crises in Sickle Cell Disease

We previously found that the plasma of patients with sickle cell disease (SCD) contains large numbers of small extracellular vesicles (EVs) and that the EVs disrupt the integrity of endothelial cell monolayers (especially if obtained during episodes of acute chest syndrome, ACS). The present study was designed to test the generality of this finding to other complications of SCD, specifically to evaluate the possibility that circulating EVs isolated during a vaso-occlusive crises (VOC) also cause damage to the intercellular connections between endothelial cells. Plasma was obtained from nine pediatric subjects at baseline and during VOC episodes. EVs isolated from these samples were added to cultures of microvascular endothelial cells. Immunofluorescence microscopy was employed to assess monolayer integrity and to localize two intercellular junction proteins (VE-cadherin and connexin43). The EVs isolated during VOC caused significantly greater monolayer disruption than those isolated at baseline. The extent of disruption varied between different episodes of VOC or ACS in the same patient. The VOC EVs disrupted the integrity of both junction proteins at appositional membranes. These results suggest that circulating EVs may be involved in modulating endothelial integrity contributing to the pathogenesis of different complications of SCD.

Total parasite biomass but not peripheral parasitaemia is associated with endothelial and haematological perturbations in Plasmodium vivax patients

Plasmodium vivax is the major cause of human malaria in the Americas. How P. vivax infection can lead to poor clinical outcomes, despite low peripheral parasitaemia, remains a matter of intense debate. Estimation of total P. vivax biomass based on circulating markers indicates existence of a predominant parasite population outside of circulation. In this study, we investigate associations between both peripheral and total parasite biomass and host response in vivax malaria. We analysed parasite and host signatures in a cohort of uncomplicated vivax malaria patients from Manaus, Brazil, combining clinical and parasite parameters, multiplexed analysis of host responses, and ex vivo assays. Patterns of clinical features, parasite burden, and host signatures measured in plasma across the patient cohort were highly heterogenous. Further data deconvolution revealed two patient clusters, here termed Vivax^low and Vivax^high. These patient subgroups were defined based on differences in total parasite biomass but not peripheral parasitaemia. Overall Vivax^low patients clustered with healthy donors and Vivax^high patients showed more profound alterations in haematological parameters, endothelial cell (EC) activation, and glycocalyx breakdown and levels of cytokines regulating different haematopoiesis pathways compared to Vivax^low. Vivax^high patients presented more severe thrombocytopenia and lymphopenia, along with enrichment of neutrophils in the peripheral blood and increased neutrophil-to-lymphocyte ratio (NLCR). When patients' signatures were combined, high association of total parasite biomass with a subset of markers of EC activation, thrombocytopenia, and lymphopenia severity was observed. Finally, machine learning models defined a combination of host parameters measured in the circulation that could predict the extent of parasite infection outside of circulation. Altogether, our data show that total parasite biomass is a better predictor of perturbations in host homeostasis in P. vivax patients than peripheral parasitaemia. This supports the emerging paradigm of a P. vivax tissue reservoir, particularly in the haematopoietic niche of bone marrow and spleen.

Critical Role of Hemopexin Mediated Cytoprotection in the Pathophysiology of Sickle Cell Disease

Circulating hemopexin is the primary protein responsible for the clearance of heme; therefore, it is a systemic combatant against deleterious inflammation and oxidative stress induced by the presence of free heme. This role of hemopexin is critical in hemolytic pathophysiology. In this review, we outline the current research regarding how the dynamic activity of hemopexin is implicated in sickle cell disease, which is characterized by a pathological aggregation of red blood cells and excessive hemolysis. This pathophysiology leads to symptoms such as acute kidney injury, vaso-occlusion, ischemic stroke, pain crises, and pulmonary hypertension exacerbated by the presence of free heme and hemoglobin. This review includes in vivo studies in mouse, rat, and guinea pig models of sickle cell disease, as well as studies in human samples. In summary, the current research indicates that hemopexin is likely protective against these symptoms and that rectifying depleted hemopexin in patients with sickle cell disease could improve or prevent the symptoms. The data compiled in this review suggest that further preclinical and clinical research should be conducted to uncover pathways of hemopexin in pathological states to evaluate its potential clinical function as both a biomarker and therapy for sickle cell disease and related hemoglobinopathies.

Significance of Heme and Heme Degradation in the Pathogenesis of Acute Lung and Inflammatory Disorders

The heme molecule serves as an essential prosthetic group for oxygen transport and storage proteins, as well for cellular metabolic enzyme activities, including those involved in mitochondrial respiration, xenobiotic metabolism, and antioxidant responses. Dysfunction in both heme synthesis and degradation pathways can promote human disease. Heme is a pro-oxidant via iron catalysis that can induce cytotoxicity and injury to the vascular endothelium. Additionally, heme can modulate inflammatory and immune system functions. Thus, the synthesis, utilization and turnover of heme are by necessity tightly regulated. The microsomal heme oxygenase (HO) system degrades heme to carbon monoxide (CO), iron, and biliverdin-IXα, that latter which is converted to bilirubin-IXα by biliverdin reductase. Heme degradation by heme oxygenase-1 (HO-1) is linked to cytoprotection via heme removal, as well as by activity-dependent end-product generation (i.e., bile pigments and CO), and other potential mechanisms. Therapeutic strategies targeting the heme/HO-1 pathway, including therapeutic modulation of heme levels, elevation (or inhibition) of HO-1 protein and activity, and application of CO donor compounds or gas show potential in inflammatory conditions including sepsis and pulmonary diseases.