Differential Mechanisms of Septic Human Pulmonary Microvascular Endothelial Cell Barrier Dysfunction Depending on the Presence of Neutrophils

HMGB1 released from pyroptotic vascular endothelial cells promotes immune disorders in exertional heatstroke

BACKGROUND AND OBJECTIVE

Exertional heatstroke (EHS) mainly occurs in healthy young people with rapid onset and high mortality. EHS immune disorders can cause systemic inflammatory responses and multiple organ failure; however, the underlying mechanisms remain unclear. As high mobility group box 1 (HMGB1) is a prototypical alarmin that activates inflammatory and immune responses, this study aimed to investigate the effect and mechanism of HMGB1 in the pathogenesis of EHS.

METHODS

Peripheral blood mononuclear cell (PBMC) transcriptome sequencing of healthy volunteers, classical heatstroke patients, and EHS patients was performed. A mouse model of EHS was established and murine tissue damage was evaluated by H&E staining. HMGB1 localization and release were visualized using immunofluorescence staining. Human umbilical vein endothelial cells (HUVECs) and THP-1 cells were co-cultured to study the effects of HMGB1 on macrophages. A neutralizing anti-HMGB1 antibody was used to evaluate the efficacy of EHS treatment in mice.

RESULTS

Plasma and serum HMGB1 levels were significantly increased in EHS patients or mice. EHS-induced endothelial cell pyroptosis promoted HMGB1 release in mice. HMGB1 derived from endothelial cell pyroptosis enhanced macrophage pyroptosis, resulting in immune disorders under EHS conditions. Administration of anti-HMGB1 markedly alleviated tissue injury and systemic inflammatory responses after EHS.

CONCLUSIONS

The release of HMGB1 from pyroptotic endothelial cells after EHS promotes pyroptosis of macrophages and systemic inflammatory response, and HMGB1-neutralizing antibody therapy has good application prospects for EHS.

HYDROGEN PREVENTS LIPOPOLYSACCHARIDE-INDUCED PULMONARY MICROVASCULAR ENDOTHELIAL CELL INJURY BY INHIBITING STORE-OPERATED Ca 2+ ENTRY REGULATED BY STIM1/ORAI1

ABSTRACT

Background: Sepsis is a type of life-threatening organ dysfunction that is caused by a dysregulated host response to infection. The lung is the most vulnerable target organ under septic conditions. Pulmonary microvascular endothelial cells (PMVECs) play a critical role in acute lung injury (ALI) caused by severe sepsis. The impairment of PMVECs during sepsis is a complex regulatory process involving multiple mechanisms, in which the imbalance of calcium (Ca 2+ ) homeostasis of endothelial cells is a key factor in its functional impairment. Our preliminary results indicated that hydrogen gas (H 2 ) treatment significantly alleviates lung injury in sepsis, protects PMVECs from hyperpermeability, and decreases the expression of plasma membrane stromal interaction molecule 1 (STIM1), but the underlying mechanism by which H 2 maintains Ca 2+ homeostasis in endothelial cells in septic models remains unclear. Thus, the purpose of the present study was to investigate the molecular mechanism of STIM1 and Ca 2+ release-activated Ca 2+ channel protein1 (Orai1) regulation by H 2 treatment and explore the effect of H 2 treatment on Ca 2+ homeostasis in lipopolysaccharide (LPS)-induced PMVECs and LPS-challenged mice. Methods: We observed the role of H 2 on LPS-induced ALI of mice in vivo . The lung wet/dry weight ratio, total protein in the bronchoalveolar lavage fluid, and Evans blue dye assay were used to evaluate the pulmonary endothelial barrier damage of LPS-challenged mice. The expression of STIM1 and Orai1 was also detected using epifluorescence microscopy. Moreover, we also investigated the role of H 2 -rich medium in regulating PMVECs under LPS treatment, which induced injury similar to sepsis in vitro . The expression of STIM1 and Orai1 as well as the Ca 2+ concentration in PMVECs was examined. Results:In vivo , we found that H 2 alleviated ALI of mice through decreasing lung wet/dry weight ratio, total protein in the bronchoalveolar lavage fluid and permeability of lung. In addition, H 2 also decreased the expression of STIM1 and Orai1 in pulmonary microvascular endothelium. In vitro , LPS treatment increased the expression levels of STIM1 and Orai1 in PMVECs, while H 2 reversed these changes. Furthermore, H 2 ameliorated Ca 2+ influx under sepsis-mimicking conditions. Treatment with the sarco/endoplasmic reticulum Ca 2+ adenosine triphosphatase inhibitor, thapsigargin, resulted in a significant reduction in cell viability as well as a reduction in the expression of junctional proteins, including vascular endothelial-cadherin and occludin. Treatment with the store-operated Ca 2+ entry inhibitor, YM-58483 (BTP2), increased the cell viability and expression of junctional proteins. Conclusions: The present study suggested that H 2 treatment alleviates LPS-induced PMVEC dysfunction by inhibiting store-operated Ca 2+ entry mediated by STIM1 and Orai1 in vitro and in vivo .

Nrf2 activation: a key mechanism in stem cell exosomes-mediated therapies

Exosomes are nano-sized membrane extracellular vesicles which can be released from various types of cells. Exosomes originating from inflammatory or injured cells can have detrimental effects on recipient cells, while exosomes derived from stem cells not only facilitate the repair and regeneration of damaged tissues but also inhibit inflammation and provide protective effects against various diseases, suggesting they may serve as an alternative strategy of stem cells transplantation. Exosomes have a fundamental role in communication between cells, through the transfer of proteins, bioactive lipids and nucleic acids (like miRNAs and mRNAs) between cells. This transfer significantly impacts both the physiological and pathological functions of recipient cells. Nuclear factor erythroid 2-related factor 2 (Nrf2), a transcription factor, is able to mitigate damage caused by oxidative stress and inflammation through various signaling pathways. The positive effects resulting from the activation of the Nrf2 signaling pathway in different disorders have been documented in various types of literature. Studies have confirmed that exosomes derived from stem cells could act as Nrf2 effective agonists. However, limited studies have explored the Nrf2 role in the therapeutic effects of stem cell-derived exosomes. This review provides a comprehensive overview of the existing knowledge concerning the role of Nrf2 signaling pathways in the impact exerted by stem cell exosomes in some common diseases.

Lipocalin 10 is essential for protection against inflammation-triggered vascular leakage by activating LDL receptor-related protein 2-slingshot homologue 1 signalling pathway

AIMS

Systemic inflammation occurs commonly during many human disease settings and increases vascular permeability, leading to organ failure, and lethal outcomes. Lipocalin 10 (Lcn10), a poorly characterized member of the lipocalin family, is remarkably altered in the cardiovascular system of human patients with inflammatory conditions. Nonetheless, whether Lcn10 regulates inflammation-induced endothelial permeability remains unknown.

METHODS AND RESULTS

Systemic inflammation models were induced using mice by injection of endotoxin lipopolysaccharide (LPS) or caecal ligation and puncture (CLP) surgery. We observed that the expression of Lcn10 was dynamically altered only in endothelial cells (ECs), but not in either fibroblasts or cardiomyocytes isolated from mouse hearts following the LPS challenge or CLP surgery. Using in vitro gain- and loss-of-function approaches and an in vivo global knockout mouse model, we discovered that Lcn10 negatively regulated endothelial permeability upon inflammatory stimuli. Loss of Lcn10 augmented vascular leakage, leading to severe organ damage and higher mortality following LPS challenge, compared to wild-type controls. By contrast, overexpression of Lcn10 in ECs displayed opposite effects. A mechanistic analysis revealed that both endogenous and exogenous elevation of Lcn10 in ECs could activate slingshot homologue 1 (Ssh1)-Cofilin signalling cascade, a key axis known to control actin filament dynamics. Accordingly, a reduced formation of stress fibre and increased generation of cortical actin band were exhibited in Lcn10-ECs, when compared to controls upon endotoxin insults. Furthermore, we identified that Lcn10 interacted with LDL receptor-related protein 2 (LRP2) in ECs, which acted as an upstream factor of the Ssh1-Confilin signalling. Finally, injection of recombinant Lcn10 protein into endotoxic mice showed therapeutic effects against inflammation-induced vascular leakage.

CONCLUSION

This study identifies Lcn10 as a novel regulator of EC function and illustrates a new link in the Lcn10-LRP2-Ssh1 axis to controlling endothelial barrier integrity. Our findings may provide novel strategies for the treatment of inflammation-related diseases.

LncRNA HCG18 loaded by polymorphonuclear neutrophil-secreted exosomes aggravates sepsis acute lung injury by regulating macrophage polarization

Polymorphonuclear neutrophils (PMNs) exert significant roles in septic acute lung injury (ALI). Accumulating evidence suggests that PMN-derived exosomes (PMN-exo) are a novel subcellular entity that is the fundamental link between PMN-driven inflammation and tissue damage. However, the role of PMN-exo in septic ALI and the underlying mechanisms remain unclear. Tumor necrosis factor-α (TNF-α), a key regulator of innate immunity in septic ALI, was used to induce PMN activation in vitro. Using an in vitro co-culture system, the rat alveolar macrophage cell line NR8383 was co-cultured with TNF-α-stimulated PMN-released exosomes (TNF-α-exo) to further confirm the results of the in vitro studies and explore the underlying mechanisms involved. A septic lung injury model was established by cecal ligation and puncture surgery, and PMN-exo were injected into septic mice through the tail vein, and then lung injury, inflammatory release, macrophage polarization, and apoptosis were examined. The results reported that TNF-α-exo promoted the activation of M1 macrophages after i.p. injection in vivo or co-culture in vitro. Furthermore, TNF-α-exo affected alveolar macrophage polarization by delivering HCG18. Mechanistic studies indicated that HCG18 mediated the function of TNF-α-exo by targeting IL-32 in macrophages. In addition, tail vein injection of si-HCG18 in septic mice significantly reduced TNF-α-exo-induced M1 macrophage activation and lung macrophage death, as well as histological lesions. In conclusion, TNF-α-exo-loaded HCG18 contributes to septic ALI by regulating macrophage polarization. These findings may provide new insights into novel mechanisms of PMN-macrophage polarization interactions in septic ALI and may provide new therapeutic strategies for patients with sepsis.

Hyaluronic acid restored protein permeability across injured human lung microvascular endothelial cells

Lung endothelial permeability is a key pathological feature of acute respiratory distress syndrome. Hyaluronic acid (HA), a major component of the glycocalyx layer on the endothelium, is generated by HA synthase (HAS) during inflammation and injury and is critical for repair. We hypothesized that administration of exogenous high molecular weight (HMW) HA would restore protein permeability across human lung microvascular endothelial cells (HLMVEC) injured by an inflammatory insult via upregulation of HAS by binding to CD44. A transwell coculture system was used to study the effects of HA on protein permeability across HLMVEC injured by cytomix, a mixture of IL-1β, TNFα, and IFNγ, with or without HMW or low molecular weight (LMW) HA. Coincubation with HMW HA, but not LMW HA, improved protein permeability following injury at 24 h. Fluorescence microscopy demonstrated that exogenous HMW HA partially prevented the increase in "actin stress fiber" formation. HMW HA also increased the synthesis of HAS2 mRNA expression and intracellular HMW HA levels in HLMVEC following injury. Pretreatment with an anti-CD44 antibody or 4-methylumbelliferone, a HAS inhibitor, blocked the therapeutic effects. In conclusion, exogenous HMW HA restored protein permeability across HLMVEC injured by an inflammatory insult in part through upregulation of HAS2.

Cardiovascular Responses During Sepsis

Sepsis is the life-threatening organ dysfunction arising from a dysregulated host response to infection. Although the specific mechanisms leading to organ dysfunction are still debated, impaired tissue oxygenation appears to play a major role, and concomitant hemodynamic alterations are invariably present. The hemodynamic phenotype of affected individuals is highly variable for reasons that have been partially elucidated. Indeed, each patient's circulatory condition is shaped by the complex interplay between the medical history, the volemic status, the interval from disease onset, the pathogen, the site of infection, and the attempted resuscitation. Moreover, the same hemodynamic pattern can be generated by different combinations of various pathophysiological processes, so the presence of a given hemodynamic pattern cannot be directly related to a unique cluster of alterations. Research based on endotoxin administration to healthy volunteers and animal models compensate, to an extent, for the scarcity of clinical studies on the evolution of sepsis hemodynamics. Their results, however, cannot be directly extrapolated to the clinical setting, due to fundamental differences between the septic patient, the healthy volunteer, and the experimental model. Numerous microcirculatory derangements might exist in the septic host, even in the presence of a preserved macrocirculation. This dissociation between the macro- and the microcirculation might account for the limited success of therapeutic interventions targeting typical hemodynamic parameters, such as arterial and cardiac filling pressures, and cardiac output. Finally, physiological studies point to an early contribution of cardiac dysfunction to the septic phenotype, however, our defective diagnostic tools preclude its clinical recognition. © 2021 American Physiological Society. Compr Physiol 11:1605-1652, 2021.

Tumor necrosis factor-α requires Ezrin to regulate the cytoskeleton and cause pulmonary microvascular endothelial barrier damage

Acute respiratory distress syndrome (ARDS) is a rapidly progressive disease with unknown pathogenesis. Damage of pulmonary microvascular endothelial cells (PMVECs) caused by inflammatory storm caused by cytokines such as TNF-α is the potential pathogenesis of ARDS. In this study, we examined the role of ezrin and Rac1 in TNF-α-related pathways, which regulates the permeability of PMVECs. Primary rat pulmonary microvascular endothelial cells (RPMVECs) were isolated and cultured. RPMVECs were treated with rat TNF-α (0, 1, 10, 100 ng/ml), and the cell activity of each group was measured using a CCK8 kit. The integrity of endothelial barrier was measured by transendothelial resistance (TEER) and FITC-BSA flux across RPMVECs membranes. Pulldown assay and Western blot was used to detect the activity of RAS-associated C3 botulinum toxin substrate 1 (Rac1) and Ezrin phosphorylation. Short hairpin RNA (shRNA) targeting ezrin and Rac1 was utilized to evaluate the effect of RPMVECs permeability and related pathway. The effects of ezrin and Rac1 on cytoskeleton were confirmed by immunofluorescence. Our results revealed that active Rac1 was essential for protecting the RPMVEC barrier stimulated by TNF-α, while active ezrin could partially destroy the PMVEC barrier by reducing Rac1 activity and regulating the subcellular structure of the cytoskeleton. These findings may be used to create new therapeutic strategies for targeting Rac1 in the treatment of ARDS.

Endothelial Injury and Glycocalyx Degradation in Critically Ill Coronavirus Disease 2019 Patients: Implications for Microvascular Platelet Aggregation

Objectives

Coronavirus disease 2019 is caused by the novel severe acute respiratory syndrome coronavirus 2 virus. Patients admitted to the ICU suffer from microvascular thrombosis, which may contribute to mortality. Our aim was to profile plasma thrombotic factors and endothelial injury markers in critically ill coronavirus disease 2019 ICU patients to help understand their thrombotic mechanisms.

Design

Daily blood coagulation and thrombotic factor profiling with immunoassays and in vitro experiments on human pulmonary microvascular endothelial cells.

Setting

Tertiary care ICU and academic laboratory.

Subjects

All patients admitted to the ICU suspected of being infected with severe acute respiratory syndrome coronavirus 2, using standardized hospital screening methodologies, had daily blood samples collected until testing was confirmed coronavirus disease 2019 negative on either ICU day 3 or ICU day 7 if the patient was coronavirus disease 2019 positive.

Interventions

None.

Measurement and Main Results

Age- and sex-matched healthy control subjects and ICU patients that were either coronavirus disease 2019 positive or coronavirus disease 2019 negative were enrolled. Cohorts were well balanced with the exception that coronavirus disease 2019 positive patients were more likely than coronavirus disease 2019 negative patients to suffer bilateral pneumonia. Mortality rate for coronavirus disease 2019 positive ICU patients was 40%. Compared with healthy control subjects, coronavirus disease 2019 positive patients had higher plasma von Willebrand factor (p < 0.001) and glycocalyx-degradation products (chondroitin sulfate and syndecan-1; p < 0.01). When compared with coronavirus disease 2019 negative patients, coronavirus disease 2019 positive patients had persistently higher soluble P-selectin, hyaluronic acid, and syndecan-1 (p < 0.05), particularly on ICU day 3 and thereafter. Thrombosis profiling on ICU days 1-3 predicted coronavirus disease 2019 status with 85% accuracy and patient mortality with 86% accuracy. Surface hyaluronic acid removal from human pulmonary microvascular endothelial cells with hyaluronidase treatment resulted in depressed nitric oxide, an instigating mechanism for platelet adhesion to the microvascular endothelium.

Conclusions

Thrombosis profiling identified endothelial activation and glycocalyx degradation in coronavirus disease 2019 positive patients. Our data suggest that medications to protect and/or restore the endothelial glycocalyx, as well as platelet inhibitors, should be considered for further study.

Quantification of adherens junction disruption and contiguous paracellular protein leak in human lung endothelial cells under septic conditions

OBJECTIVE

Sepsis is associated with dysfunction of MVEC resulting in organ edema and inflammation. VE-cadherin, a component of MVEC adherens junctions, may be disrupted in sepsis. However, the direct connection between individual MVEC VE-cadherin disruption and increased paracellular permeability is uncertain.

METHODS

Human pulmonary MVEC were cultured on a biotin matrix and treated with cytomix, as a model of sepsis, vs PBS. MVEC permeability was assessed by trans-MVEC monolayer leak of Oregon green 488-conjugated avidin, which bound subcellular biotin to localize sites of paracellular leak. Leak was correlated with individual cell-specific MVEC surface VE-cadherin continuity by fluorescence microscopy.

RESULTS

Cytomix treatment reduced total MVEC VE-cadherin density, disrupted surface VE-cadherin continuity, was associated with intercellular gap formation, and enhanced paracellular avidin leak. Cytomix-induced MVEC paracellular avidin leak was strongly correlated temporally and was highly contiguous with focal MVEC surface VE-cadherin disruption. Total cellular VE-cadherin density was less strongly correlated with MVEC paracellular avidin leak and individual cell-specific focal surface VE-cadherin discontinuity.

CONCLUSIONS

These data support a mechanistic link between septic human lung MVEC VE-cadherin disruption and contiguous paracellular protein leak, and will permit more detailed assessment of individual cell-specific mechanisms of septic MVEC barrier dysfunction.