Lung Endothelial Cells Research Articles

Peroxiredoxin 6 suppresses erastin‐induced ferroptosis in lung endothelial cells

Ferroptosis is a newly described form of regulated cell death driven by an iron‐dependent accumulation of phospholipid hydroperoxides. Glutathione peroxidase 4 (GPx4) suppresses ferroptosis through its ability to reduce phospholipid hydroperoxides. Peroxiredoxin 6 (Prdx6) expresses phospholipid hydroperoxide glutathione peroxidase activity, but its role in the regulation of ferroptosis remains unexplored. We compared Prdx6 and GPx4 mRNA levels in murine lungs. Prdx6 expression was five times higher than GPx4 expression. We then visualized the spatial localization of lung Prdx6. Prdx6 was expressed in both pulmonary epithelial (epCAM+) and endothelial (Ve‐cadherin+) cells. We studied the role of Prdx6 on lung ferroptosis induced by erastin, an inhibitor of the cystine‐glutamate antiporter, which is critical to glutathione production. Erastin (1‐5μM, 24h) increased lipid peroxidation and cell death in mouse pulmonary microvascular endothelial cells (MPMVECs) in primary culture; this effect was higher in Prdx6‐KO MPMVECs than in WT‐MPMVECs. Co‐treatment with the ferroptosis suppressor ferrostatin‐1 prevented erastin‐induced lipid peroxidation and cell death in both WT and Prdx6‐KO MPMVECs. Similarly, knockdown (KD) of Prdx6 in human pulmonary microvascular endothelial cells (HPMVECs) increased erastin‐induced cell death, suggesting that Prdx6 limits ferroptosis in the pulmonary endothelium. We then conducted extracellular flux assays and RNA‐seq analyses in Prdx6‐deficient cells to further explore how the loss of Prdx6 sensitizes cells to ferroptosis. Cellular respiration and mitochondrial function were blunted in Prdx6‐deficient cells compared to corresponding controls. Top differentially expressed genes in Prdx6‐KD HPMVECs include known regulators of iron metabolism and ferroptosis such as hmox1, cybrd1, and sfxn1. Upregulated Reactome pathways enriched in Prdx6‐KD HPMVECs include mitochondrial and amino acid metabolism and p53‐mediated DNA damage response, while downregulated pathways include biological oxidations, transport of bile salts and organic acids, metal ions and amine compounds, cytochrome P450, and phase 1 metabolism. These results show that loss of Prdx6 sensitizes lung endothelial cells to ferroptosis by promoting lipid peroxidation and altering transcriptional signatures associated with cell cycle progression and mitochondrial metabolism.

Abstract 122: Rabeprazole Enhances Vascular Repair And Resolution Of Sepsis-induced Lung Injury Through HIF1/FoxM1 Signaling

Objective: There are currently no effective treatments for sepsis-induced inflammatory lung injury, including acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). The repositioning of existing drugs is one possible strategy for the treatment of ALI/ARDS. We previously showed that vascular repair and resolution of ALI is dependent upon hypoxia-inducible factor 1 alpha (HIF1a) and forkhead box M1 (FoxM1) in endothelial cells. The aim of this study was to identify a candidate agonist of HIF1a/FoxM1 signaling to treat ALI/ARDS. Approach and Results: First, we adopted a high throughput screening approach of a library of 1200 FDA-approved drugs by using hypoxia response element (HRE)-driven luciferase reporter assays, cell toxicity assays, and molecular analyses of human lung endothelial cells, to identify candidate HIF1 agonists in vitro . One of the top candidate drugs, Rabeprazole (also known as Aciphex), gave rise to dose-dependent increases in HRE luciferase activity without concurrent increases in cell death. Next, we performed dose-response studies of Rabeprazole in a mouse model of sepsis-induced ALI. By treating wild type mice orally with Rabeprazole on 2 consecutive days after endotoxic sepsis challenge, we were able to identify a dose of Rabeprazole that is well tolerated and enhanced vascular repair and resolution of ALI. In timeline studies of murine inflammatory lung injury, we found that Rabeprazole treatment resulted in reductions in lung vascular leakage, edema, and inflammatory cytokine expression during the repair phrase following sepsis-induced ALI. Finally, we used conditional knockout mice to show that Rabeprazole increases vascular repair and resolution of ALI via HIF1a/FoxM1 signaling. Conclusions: Rabeprazole is a HIF1a agonist that improves vascular repair and resolution of sepsis-induced inflammatory lung injury. Rabeprazole represents a promising candidate for repurposing to treat ALI/ARDS.

Pulmonary Endothelial Activation with COVID‐19: Possible Role of Reactive Oxygen Species

IntroductionRecent research suggests that endothelial activation plays a role in COVID‐19 pathogenesis by promoting a pro‐coagulative and pro‐inflammatory state. However, the mechanism by which the endothelium is activated in COVID‐19 is unclear.ObjectiveTo investigate the mechanism by which COVID‐19 activates the pulmonary endothelium.HypothesisThe pulmonary endothelium generates reactive oxygen species (ROS) upon exposure to the “inflammatory load” of the systemic circulation.MethodsCOVID‐19 was recreated in vitro and ex vivo, by exposing human lung endothelial cells (EC) or donor human lung slices (human precision‐cut lung slices or huPCLS) to medium supplemented with serum from COVID‐19 affected subjects. Sera were acquired from patients with COVID‐19 infection admitted to the Intensive Care Unit of the Hospital at the University of Pennsylvania. ROS (fluorescent dye, CellROX) and intercellular adhesion molecule (ICAM‐1) levels were assessed by fluorescence labeling and imaging.ResultsBoth EC activation (as monitored by ROS production) and pro‐inflammatory phenotype (as assessed by ICAM‐1), were significantly higher with COVID‐19 as compared to normal subjects.ConclusionsThe endothelium is activated with COVID‐19 via ROS production; thus, the ROS produced drive a pro‐inflammatory phenotype by inducing the expression of ICAM‐1, a pivotal marker of endothelium inflammation. As ROS mediates EC activation and inflammation during COVID‐19, ROS blockade could be a therapeutic target in maintaining vascular health.

Single‐Cell Sequencing in the Genetic Model of Mitochondrial Dysfunction Reveals Heterogeneity of Lung Endothelial Cells and Novel Targets in Pulmonary Hypertension

IntroductionPulmonary hypertension (PH) is a complex, lethal vascular disease and currently has very limited treatment options with no cure. Severe pulmonary vascular remodeling and right ventricular (RV) hypertrophy in PH ultimately lead to RV failure. Endothelial dysfunction (ED) is demonstrated to play a key role in the initiation of PH. However, the pathogenic mechanisms leading up to ED remain unclear.HypothesisWe hypothesized that mitochondrial dysfunction (MD) in endothelial cells (EC) would produce a specific gene expression pattern in each EC subpopulation, revealing pathogenic pathways that trigger ED.MethodsRats with the NFU1G206C mutation spontaneously develop PH, recapitulating the human disease in patients with multiple mitochondrial dysfunctions syndrome and PH. Transcriptomics was performed with the 10X Genomics kit on isolated single cell EC’s from WT and NFU1G206C rats. EC clustering was done with the Seurat V4 R package. The Database for Annotation, Visualization and Integrated Discovery (DAVID) identified enriched biological pathways. RV function was determined by echocardiography imaging (Vevo 3100 system).ResultsEcho results confirmed that NFU1G206C rats showed a spontaneous PH phenotype. Thirteen distinctive subpopulations of EC’s were identified in WT and NFU1G206C rats with UMAP and tSNE analysis, based on specific marker expressions such as alveolar capillary ECs (expressing ca4), small capillary ECs (fabp4), lymphatic ECs (prox1) and ECs regulating arteriogenesis (gja5) to ECs undergoing endothelial mesenchymal transition (EndMT) (acta2, encoding for α‐SMA). DAVID analysis of genes expressed in individual EC clusters showed heterogenous functions such as cell adhesion, inflammatory response, migration, and angiogenesis, highlighting the physiological relevance of EC’s. Cells were then classified as either senescent, quiescent, or proliferative, based on genes enriched in the respective pathways. We found that EC clusters of NFU1G206C rats significantly deviated from conventional gene expression profiles of WT clusters. The cluster1 of NFU1G206C rats showed an increase in senescence marker, lamb1 and decreased mki67. On the other hand, genes associated with proliferation were significantly increased in cluster2. We also identified EC’s with increased association of EndMT genes in cluster7. Most remarkably, in clusters 3, 5 and 9 of the NFU1G206C rats, we discovered a significant decrease in genes controlling cell adhesion and junction proteins, which could potentiate EC barrier dysfunction, an important contributor to PH pathobiology. These global aberrations from conventional EC functions could initiate pathobiological transformation.ConclusionWe demonstrate that EC functions are diverse and crucial for normal vascular function and maintenance. We also highlight that MD can shift the EC’s from their native to pathological states. Therefore, treatment approaches that attenuate MD or targets the specific changes leading up to ED would effectively control PH.

GPR68 Inhibition with a Novel Group of Ogremorphin Inhibitors Upregulate Endothelial Barrier Function and Protect Against Bacterial Pathogens or Acidosis‐induced Inflammation in Lung Endothelium

BackgroundEndothelial dysfunction characterized by an increase in endothelial permeability and inflammatory responses are two major pathological hallmarks of various lung disorders including the current global pandemic COVID‐19. Thus, drugs targeting the preservation and restoration of endothelial function represent an attractive therapeutic target to treat endothelial dysfunction‐derived cardiopulmonary diseases. G protein‐coupled receptors (GPCRs), especially a sub‐family of proton‐sensing GPCRs including GPR4 and GPR68, have been recently suggested to play a role in the modulation of endothelial function. In this study, we investigated the barrier protective and anti‐inflammatory effects of two recently developed novel class of GPR68 inhibitors: ogremorphins OGM8345 and OGM‐1 in cultured human lung endothelial cells as well as in mice.MethodsEndothelial permeability was measured by monitoring transendothelial electrical resistance (TER) across human pulmonary arterial endothelial cells (HPAECs). Protein and mRNA expression levels of endothelial inflammation markers were analyzed by western blot and quantitative real time PCR, respectively. Acidosis was induced by switching cells to acidic pH (6.5) medium and luciferase‐based Tango assay was performed to evaluate GPR68 activation. C57BL/6 mice were exposed to lipopolysaccharide (LPS from Escherichia coli) or heat‐killed Staphylococcus aureus (HKSA), and vascular leak/inflammation was assessed by determining the extravasation of intravenously injected Evans blue tracer into lungs and total cells/protein count in bronchoalveolar lavage samples.ResultsBoth OGM8345 (1‐5 µM) and OGM‐1 (0.3‐1.5 µM) induced a robust dose‐dependent increase in basal EC barrier function that was evident by an 150‐200% increase in TER values. Both inhibitors also markedly attenuated LPS‐ and HKSA‐induced endothelial hyperpermeability. LPS or HKSA‐induced upregulation of inflammatory cytokines/chemokines genes TNF‐α, ICAM‐1, VCAM‐1, IL‐6, IL‐8, IL‐1β, and CXCL5 was significantly attenuated by OGMs as demonstrated by RT‐PCR analysis. Consistently, both OGMs suppressed LPS‐ and HKSA‐induced protein expression of phospho‐NFkB, VCAM‐1 and ICAM‐1. In contrast, pharmacologic inhibition of GPR4 by NE 52‐QQ57 failed to alleviate LPS or HKSA‐induced EC barrier dysfunction and inflammation. Importantly, LPS, HKSA or acidosis stimulation resulted in increased GPR68 mRNA expression as well as GPR68 activity that was inhibited by OGMs. Both OGMs attenuated vascular leak and lung inflammation caused by intratracheal injection of LPS or HKSA in C57BL/6 mice as illustrated by reduced Evans blue accumulation in the lungs and significant inhibition of inflammatory cells and protein content in bronchoalveolar lavage samples.ConclusionAltogether, these results establish an essential role of GPR68 in endothelial dysfunction and strongly suggest a therapeutic potential of GPR68‐selective inhibitors in improving endothelial dysfunction‐derived lung injuries.

Pulmonary Endothelial Tau Aggregation After Infection

Patients who recover from nosocomial pneumonia oftentimes exhibit long‐lasting cognitive impairment comparable to what is observed in Alzheimer’s Disease patients. We previously hypothesized that the lung endothelium contributes to infection‐related neurocognitive dysfunction, since bacteria‐exposed endothelial cells release a form(s) of cytotoxic tau that is sufficient to impair long‐term potentiation in the hippocampus. However, lung endothelial tau isoform(s) have yet to be resolved and it remains unclear whether the infection‐induced endothelial cytotoxic tau can trigger neuronal tau aggregation which is the major hallmark of several neuropathologies. Here, we demonstrate that lung endothelial cells express a big tau isoform and three additional tau isoforms that are similar to neuronal tau, each containing four microtubule‐binding repeat domains, and that tau is expressed in lung capillaries in vivo. To test whether infection elicits endothelial tau capable of causing transmissible tau aggregation, cells were infected with P. aeruginosa. The infection‐induced tau released from endothelium into the medium induced neuronal tau aggregation in reporter cells, including reporter cells that express either the four microtubule‐binding repeat domains or the full‐length tau. Infection‐induced release of pathological tau variant(s) from endothelium, and the ability of the endothelial‐derived tau to cause neuronal tau aggregation, was abolished using tau knockout cells. After bacterial lung infection, brain homogenates from wild‐type mice, but not from tau knockout mice, initiated tau aggregation. Notably, plasma samples obtained from pneumonia‐positive patients showed significantly higher tau aggregation activity when compared to pneumonia‐negative plasma samples. Thus, bacterial pneumonia initiates the release of lung endothelial‐derived cytotoxic tau into the circulation, which is capable of propagating a neuronal tauopathy.

Hydrostatic Pressure Controls Angiogenesis through Endothelial YAP1 during Lung Regeneration

Pulmonary artery (PA) pressure increases during lung growth after unilateral pneumonectomy (PNX). The objective of this study is to understand the mechanism by which increases in PA pressure control angiogenesis during lung regeneration. Mechanosensitive transcriptional co‐activator, yes‐associated protein (YAP1), in endothelial cells (ECs) is necessary for angiogenesis during post‐PNX lung growth. We investigate whether increases in PA pressure following PNX controls angiogenesis through YAP1. When hydrostatic pressure is applied to human pulmonary arterial ECs (HPAECs), the expression of YAP1, transcription factor TEAD1, and angiogenic factor receptor Tie2 increases, while these effects are inhibited when HPAECs are treated with YAP1 siRNA or YAP1S94A mutant that fails to bind to TEAD1. Hydrostatic pressure also stimulates DNA synthesis and cell migration in HPAECs, while YAP1 knockdown or YAP1S94A mutant inhibits the effects. Gene enrichment analysis reveals that the levels of extracellular matrix or cell adhesion molecules are altered in post‐PNX mouse lung ECs, which interact with YAP1. These results suggest that increases in PA pressure stimulate angiogenesis through YAP1 during regenerative lung growth.

Abstract 388: Role Of The Antiapoptotic C-iap2 On The Generation Of An Endothelial Memory In Schistosomiasis-associated Pulmonary Arterial Hypertension

Introduction: Schistosomiasis-associated Pulmonary Arterial Hypertension (Sch-PAH) is a life-threatening complication of chronic S. mansoni infection, which can evolve to heart failure and death. During PAH, hyperproliferation of apoptosis-resistant endothelial cells (ECs) has been extensively reported, but therapeutic approaches to reverse this pathological phenotype remain clinically challenging. Hypothesis: Thus, our hypothesis is that antigenic molecules from S. mansoni eggs amplify the secretion of inhibitor of apoptosis protein 2 (c-IAP2), leading to generation of an abnormal EC memory of survival and the development of PAH. Methods/Results: Previously, we showed that depletion of the anti-apoptotic protein Caveolin-1 (Cav-1) via shedding of extracellular vesicles (EVs) leads to the survival of an abnormal EC phenotype through an unclear mechanism. Analysis of survival-associated genes in isolated murine lung ECs from Flk1 +/GFP ;Cav1 -/- mice, revealed high expression of the anti-apoptotic genes BIRC3 and BIRC5 (which encodes cIAP2 and survivin, respectively) when compared to control ECs. Interesting, exposure to 1 μg/mL of the major S. mansoni egg antigen Sm-p40 induced time-dependent phosphorylation of Cav-1 at residue Tyr14 in human lung microvascular EC (HMVEC-L: 228.2 +/- 38.28% of control; p<0.05; n=4), culminating in c-IAP2 expression with no difference on the constitutive expression of c-IAP1. Furthermore, Sm-p40 treatment of HMVEC-L in the presence of pro-inflammatory mediators IL-6, TNF-α, and ATP induced a significant release of EVs containing c-IAP2. Finally, in vivo analysis of lungs from S. mansoni -infected mice confirmed a significant decrease in Cav-1 expression unique to the egg-dependent granuloma area, indicating that local inflammatory response due to egg-derived antigenic molecules is essential for reprogramming and survival of an abnormal EC phenotype during Sch-PAH. Conclusions: Our data suggest that S. mansoni -induced Cav-1 depletion promotes the secretion of the anti-apoptotic c-IAP2 protein, which may be critical for prolonged survival of a pathogenic EC phenotype during the development of Sch-PAH.

Mitochondrial TOM70 in Hyperoxia‐induced Acute Lung Injury

Study objectiveHyperoxia‐induced acute lung injury (HALI) leads to respiratory failure and mitochondrial dysfunction is a critical mediator of HALI. We previously reported Toll‐Like Receptor (TLR)4 prevents oxidant‐induced ALI by maintaining mitochondrial bioenergetics in mammalian lung endothelium (Ec). Translocase of Outer Mitochondrial Membrane (TOM) have recently been identified to play important roles in mitochondrial quality control, primarily in yeast [1]. TOM70 is an essential subunit of TOM and mediates uptake of newly synthesized proteins to mitochondria as well has putative anti‐oxidant and anti‐apoptotic properties. TOM70 appeared to parallel many of the cytoprotective signaling properties of TLR4 [2‐4]. Therefore, our hypothesis is TLR4 regulates TOM70 expression and TOM70 has mitochondrial and lung protective functions in HALI.MethodsC57BL/6J mice (6‐8 wks, both sex) were purchased from Jackson Laboratory, and Tlr4‐/‐ mice were bred at Duke Animal facilities (IACUC A160‐19‐07) [5]. For hyperoxia exposure, mice were placed in a Plexiglas chamber with 5L/min of 100% oxygen continuous flow with food and water ad libitum. We previously reported 72 h of continuous hyperoxia as a time of maximal lung injury [6], which we used as a representative time point. Bodyweight and survival were monitored daily. Bronchoalveolar lavage (BAL) were collected and BAL protein were determined by a BCA assay. Protein and RNA were extracted from lung tissues and expression was determined by western blot and qPCR, respectively. Mouse lung Ec (MLEC) were isolated from lung tissues and treated with control or Tom70siRNA for 48 h. Statistical differences were analyzed by a Student‐t test.ResultsTlr4‐/‐ MLEC decreased TOM70 and increased Parkin, PINK1, and MFN2 protein expression compared to WT. Tom70 siRNA effectively silenced Tom70 with >75% efficiency at 48 h after transfection. Tom70 siRNA‐treated MLEC showed increased Mfn1, Mff, and Fis1mRNA expression, which are markers of mitochondrial fusion‐fission. Hyperoxia‐exposed mice showed marked weight loss and higher levels of BAL proteins compared to control, indicating increased permeability of the alveolar‐capillary membrane. Moreover, TOM70 protein expression was significantly decreased by hyperoxia in both male and female mice.ConclusionTLR4 deficiency decreased TOM70 expression and induced mitophagy and mitochondrial fusion, indicating that TOM70 is regulated by TLR4. Silencing TOM70 resulted in increased mitochondrial fusion and fission in MLEC, suggesting that TOM70 impacts mitochondrial quality control in mammalian, primary cells (MLEC) that are critical for lung airspace barrier function. Hyperoxia decreased TOM70 protein expression in mouse lungs, which may be a potential mechanism whereby hyperoxia leads to respiratory failure. Given that TOM70 maintains mitochondrial health, our data suggest that TOM70 may play a key role in the pathological mechanisms of HALI.1. Liu et al. (2021) bioRxiv, 2. Zhang et al. (2019) Antioxid Redox Signal, 3. Zhang et al. (2016) Antioxid Redox Signal, 4. Takyar et al. (2015) FASEB J. 5. Kim et al. (2019) Aging Cell. 6. Zhang et al. (2021) AJP Lung Cell Mol Physiol.

Differences in Extracellular NAD+ and NMN Metabolism on the Surface of Vascular Endothelial Cells.

Simple SummaryNicotinamide adenine dinucleotide (NAD+) is a multifunctional metabolite involved in many key cellular processes. Outside the cell, NAD+ or its metabolites are important signaling molecules, related especially to calcium homeostasis, which controls the functioning of the heart. The cleavage of NAD+ or its precursor, nicotinamide mononucleotide (NMN), produces derivatives entering the cell to rebuild the intracellular NAD+ pool, which is important for cells with high energy turnover. Abnormalities in NAD+ and NMN metabolism can lead to cell aging and the development of cardiovascular diseases. In this study, we demonstrated that the extracellular metabolism of NAD+ and NMN is vastly different in the vascular endothelium obtained from different species and locations. This may have implications for strategies to modulate the NAD+ system and may cause difficulties for comparing the results of different reports.The disruption of the metabolism of extracellular NAD+ and NMN may affect related signaling cascades and pathologies, such as cardiovascular or respiratory system diseases. We aimed to study NAD+ and NMN hydrolysis on surface endothelial cells of diverse origins and with genetically modified nucleotide catabolism pathways. We tested lung endothelial cells isolated from C57BL/6 J wild-type (WT) and C57BL/6 J CD73 knockout (CD73 KO) mice, the transfected porcine iliac artery endothelial cell line (PIEC) with the human E5NT gene for CD73 (PIEC CD73), and a mock-transfected control (PIEC MOCK), as well as HMEC-1 and H5V cells. Substrate conversion into the product was followed by high-performance liquid chromatography (HPLC). We showed profound differences in extracellular NAD+ and NMN metabolism related to the vessel origin, species diversity, and type of culture. We also confirmed the involvement of CD38 and CD73 in NAD+ and NMN cleavage.

NORAD modulates miR-30c-5p-LDHA to protect lung endothelial cells damage.

Acute lung injury (ALI) is a devastating human malignancy characterized by excessively uncontrolled inflammation and lung endothelial dysfunction. Non-coding RNAs play essential roles in endothelial protections during the pathological processes of ALI. The precise functions and molecular mechanisms of the lncRNA-NORAD-mediated endothelial protection remain obscure. This study reports NORAD was significantly induced in human pulmonary microvascular endothelial cells (HPMECs) under lipopolysaccharide (LPS) treatment. Silencing NORAD effectively protected HPMECs against the LPS-induced cell dysfunction. In addition, RNA pull-down and luciferase assay validated that NORAD sponged miR-30c-5p, which showed reverse functions of NORAD in the LPS-induced cell injury of HPMECs. Furthermore, the glucose metabolism of HPMECs was significantly elevated under LPS stimulation which promoted the glucose consumption and extracellular acidification rate (ECAR) of HPMECs. Inhibiting NORAD or overexpressing miR-30c-5p suppressed glucose metabolism in HPMECs, leading to protective effects on HPMECs under LPS stimulation. The glycolysis key enzyme, lactate dehydrogenase-A (LDHA), was subsequently identified as a direct target of miR-30c-5p. Finally, recovery of miR-30c-5p in NORAD-overexpressing HPMECs effectively overrode the NORAD-promoted glycolysis and impaired endothelial dysfunction under LPS stimulation by targeting LDHA. Summarily, we demonstrated a NORAD-miR-30c-5p-LDHA-glycolysis axis in the LPS-induced HPMECs dysfunction in vitro and in vivo, contributing to the development of anti-ALI therapeutic approaches.

Inhibition of the C3a receptor attenuates sepsis-induced acute lung injury by suppressing pyroptosis of the pulmonary vascular endothelial cells

Acute lung injury (ALI) is the leading cause of bacterial sepsis-related death because of disrupted pulmonary endothelial barrier, resulting in protein-rich pulmonary oedema, an influx of pro-inflammatory cells and refractory hypoxaemia. Several studies have reported that C3a levels are significantly higher in organs with sepsis and their peripheral organs and are closely associated with organ dysfunction and poor prognosis in sepsis. However, the role of the C3a complement in sepsis ALI remains unclear. Therefore, this study aimed to investigate the important role and mechanism of C3a in preventing the occurrence of pyroptosis (a pro-inflammatory form of cell death) to protect the lung endothelial cells (ECs) in sepsis-induced ALI. A septic mouse model was established with cecal ligation and puncture (CLP), which demonstrated that C3a mediated EC pyroptosis through its C3aR receptor. Furthermore, inhibition of the C3a–C3aR axis could block both NLRP3/caspase-1 and caspase-11 pathways, thus preventing pulmonary EC from pyroptosis. These results indicate that inhibition of the C3A–C3AR complement axis can inhibit pulmonary vascular EC pyroptosis, a potential target for the treatment of ALI.

Angiopathic activity of LRG1 is induced by the IL-6/STAT3 pathway

Leucine-rich α-2-glycoprotein 1 (LRG1) is a secreted glycoprotein that under physiological conditions is produced predominantly by the liver. In disease, its local induction promotes pathogenic neovascularisation while its inhibition leads to reduced dysfunctional angiogenesis. Here we examine the role of interleukin-6 (IL-6) in defective angiogenesis mediated by LRG1. IL-6 treatment induced LRG1 expression in endothelial cells and ex vivo angiogenesis cultures and promoted vascular growth with reduced mural cell coverage. In Lrg1−/− explants, however, IL-6 failed to stimulate angiogenesis and vessels exhibited improved mural cell coverage. IL-6 activated LRG1 transcription through the phosphorylation and binding of STAT3 to a conserved consensus site in the LRG1 promoter, the deletion of which abolished activation. Blocking IL-6 signalling in human lung endothelial cells, using the anti-IL6 receptor antibody Tocilizumab, significantly reduced LRG1 expression. Our data demonstrate that IL-6, through STAT3 phosphorylation, activates LRG1 transcription resulting in vascular destabilisation. This observation is especially timely in light of the potential role of IL-6 in COVID-19 patients with severe pulmonary microvascular complications, where targeting IL-6 has been beneficial. However, our data suggest that a therapy directed towards blocking the downstream angiopathic effector molecule LRG1 may be of greater utility.

DRG2 Depletion Promotes Endothelial Cell Senescence and Vascular Endothelial Dysfunction.

Endothelial cell senescence is involved in endothelial dysfunction and vascular diseases. However, the detailed mechanisms of endothelial senescence are not fully understood. Here, we demonstrated that deficiency of developmentally regulated GTP-binding protein 2 (DRG2) induces senescence and dysfunction of endothelial cells. DRG2 knockout (KO) mice displayed reduced cerebral blood flow in the brain and lung blood vessel density. We also determined, by Matrigel plug assay, aorta ring assay, and in vitro tubule formation of primary lung endothelial cells, that deficiency in DRG2 reduced the angiogenic capability of endothelial cells. Endothelial cells from DRG2 KO mice showed a senescence phenotype with decreased cell growth and enhanced levels of p21 and phosphorylated p53, γH2AX, senescence-associated β-galactosidase (SA-β-gal) activity, and senescence-associated secretory phenotype (SASP) cytokines. DRG2 deficiency in endothelial cells upregulated arginase 2 (Arg2) and generation of reactive oxygen species. Induction of SA-β-gal activity was prevented by the antioxidant N-acetyl cysteine in endothelial cells from DRG2 KO mice. In conclusion, our results suggest that DRG2 is a key regulator of endothelial senescence, and its downregulation is probably involved in vascular dysfunction and diseases.

MG53 attenuates nitrogen mustard-induced acute lung injury.

Nitrogen mustard (NM) is an alkylating vesicant that causes severe pulmonary injury. Currently, there are no effective means to counteract vesicant‐induced lung injury. MG53 is a vital component of cell membrane repair and lung protection. Here, we show that mice with ablation of MG53 are more susceptible to NM‐induced lung injury than the wild‐type mice. Treatment of wild‐type mice with exogenous recombinant human MG53 (rhMG53) protein ameliorates NM‐induced lung injury by restoring arterial blood oxygen level, by improving dynamic lung compliance and by reducing airway resistance. Exposure of lung epithelial and endothelial cells to NM leads to intracellular oxidative stress that compromises the intrinsic cell membrane repair function of MG53. Exogenous rhMG53 protein applied to the culture medium protects lung epithelial and endothelial cells from NM‐induced membrane injury and oxidative stress, and enhances survival of the cells. Additionally, we show that loss of MG53 leads to increased vulnerability of macrophages to vesicant‐induced cell death. Overall, these findings support the therapeutic potential of rhMG53 to counteract vesicant‐induced lung injury.

Hydrostatic Pressure Controls Angiogenesis Through Endothelial YAP1 During Lung Regeneration.

Pulmonary artery (PA) pressure increases during lung growth after unilateral pneumonectomy (PNX). Mechanosensitive transcriptional co-activator, yes-associated protein (YAP1), in endothelial cells (ECs) is necessary for angiogenesis during post-PNX lung growth. We investigate whether increases in PA pressure following PNX control-angiogenesis through YAP1. When hydrostatic pressure is applied to human pulmonary arterial ECs (HPAECs), the expression of YAP1, transcription factor TEAD1, and angiogenic factor receptor Tie2 increases, while these effects are inhibited when HPAECs are treated with YAP1 siRNA or YAP1S94A mutant that fails to bind to TEAD1. Hydrostatic pressure also stimulates DNA synthesis, cell migration, and EC sprouting in HPAECs, while YAP1 knockdown or YAP1S94A mutant inhibits the effects. Gene enrichment analysis reveals that the levels of genes involved in extracellular matrix (ECM), cell adhesion, regeneration, or angiogenesis are altered in post-PNX mouse lung ECs, which interact with YAP1. Exosomes are known to promote tissue regeneration. Proteomics analysis reveals that exosomes isolated from conditioned media of post-PNX mouse lung ECs contain the higher levels of ECM and cell-adhesion proteins compared to those from sham-operated mouse lung ECs. Recruitment of host lung ECs and blood vessel formation are stimulated in the fibrin gel containing exosomes isolated from post-PNX mouse lung ECs or pressurized ECs, while YAP1 knockdown inhibits the effects. These results suggest that increases in PA pressure stimulate angiogenesis through YAP1 during regenerative lung growth.

Integrin Beta 4E Promotes Endothelial Phenotypic Changes and Attenuates Lung Endothelial Cell Inflammatory Responses.

We previously reported integrin beta 4 (ITGB4) is an important mediator of lung vascular protection by simvastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A-reductase inhibitor. In this study, we report increased endothelial cell (EC) expression specifically of ITGB4E, an ITGB4 mRNA splice variant, by simvastatin with effects on EC protein expression and inflammatory responses. In initial experiments, human pulmonary artery ECs were treated using simvastatin (5 μM, 24 h) prior to immunoprecipitation of integrin alpha 6 (ITGA6), which associates with ITGB4, and Western blotting for full-length ITGB4 and ITGB4E, uniquely characterized by a truncated 114 amino acid cytoplasmic domain. These experiments confirmed a significant increase in both full-length ITGB4 and ITGB4E. To investigate the effects of increased ITGB4E expression alone, ECs were transfected with ITGB4E or control vector, and cells were seeded in wells containing Matrigel to assess effects on angiogenesis or used for scratch assay to assess migration. Decreased angiogenesis and migration were observed in ITGB4E transfected ECs compared with controls. In separate experiments, PCR and Western blots from transfected cells demonstrated significant changes in EC protein expression associated with increased ITGB4E, including marked decreases in platelet endothelial cell adhesion molecule-1 (PECAM-1) and vascular endothelial-cadherin (VE-cadherin) as well as increased expression of E-cadherin and N-cadherin along with increased expression of the Slug and Snail transcription factors that promote endothelial-to-mesenchymal transition (EndMT). We, then, investigated the functional effects of ITGB4E overexpression on EC inflammatory responses and observed a significant attenuation of lipopolysaccharide (LPS)-induced mitogen-activated protein kinase (MAPK) activation, including decreased phosphorylation of both extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), as well as reduced inflammatory cytokines (IL-6 and IL-8), expressed in the media of EC after either LPS or excessive cyclic stretch (CS). Finally, EC expression-increased ITGB4E demonstrated decreased barrier disruption induced by thrombin as measured by transendothelial electrical resistance. Our data support distinct EC phenotypic changes induced by ITGB4E that are also associated with an attenuation of cellular inflammatory responses. These findings implicate ITGB4E upregulation as an important mediator of lung EC protection by statins and may lead to novel therapeutic strategies for patients with or at risk for acute lung injury (ALI).

A cortactin CTTN coding SNP contributes to lung vascular permeability and inflammatory disease severity in African descent subjects

The cortactin gene (CTTN), encoding an actin-binding protein critically involved in cytoskeletal dynamics and endothelial cell (EC) barrier integrity, contains single nucleotide polymorphisms (SNPs) associated with severe asthma in Black patients. As loss of lung EC integrity is a major driver of mortality in the Acute Respiratory Distress Syndrome (ARDS), sepsis, and the acute chest syndrome (ACS), we speculated CTTN SNPs that alter EC barrier function will associate with clinical outcomes from these types of conditions in Black patients. In case-control studies, evaluation of a nonsynonymous CTTN coding SNP Ser484Asn (rs56162978, G/A) in a severe sepsis cohort (725 Black subjects) revealed significant association with increased risk of sepsis mortality. In a separate cohort of sickle cell disease (SCD) subjects with and without ACS (177 SCD Black subjects), significantly increased risk of ACS and increased ACS severity (need for mechanical ventilation) was observed in carriers of the A allele. Human lung EC expressing the cortactin S484N transgene exhibited: (i) delayed EC barrier recovery following thrombin-induced permeability; (ii) reduced levels of critical Tyr486 cortactin phosphorylation; (iii) inhibited binding to the cytoskeletal regulator, nmMLCK; and (iv) attenuated EC barrier-promoting lamellipodia dynamics and biophysical responses. ARDS-challenged Cttn+/- heterozygous mice exhibited increased lung vascular permeability (compared to wild-type mice) which was significantly attenuated by IV delivery of liposomes encargoed with CTTN WT transgene but not by CTTN S484N transgene. In summary, these studies suggest that the CTTN S484N coding SNP contributes to severity of inflammatory injury in Black patients, potentially via delayed vascular barrier restoration.

Sex differences and altered mitophagy in experimental pulmonary hypertension.

Pulmonary hypertension (PH) is a debilitating condition characterized by increased pulmonary arterial pressures and remodeling of pulmonary arteries, leading to right heart failure. Women have a higher prevalence of PH, whereas men have more severe disease and poorer outcomes. Animal models also show female-predominant disease. Despite the known sex differences in PH, little is known about how pathogenesis differs between the sexes. There is growing evidence of mitochondrial dysfunction, as well as altered mitophagy in PH. We hypothesized that sexual dimorphism contributes to mitochondrial dysfunction and altered mitophagy in PH. Using mouse lung endothelial cells, we exposed both wild-type and Parkin-/- cells to hypoxia and measured the effects on mitochondrial function and mitophagy-associated proteins. Our results show that females have more Parkin expression at baseline as well as increased mitochondrial respiratory capacity when exposed to oxidative stress. Inhibition of Parkin increased metabolic activity but reduced cell proliferation but to different degrees depending on sex, with results differing by sex. Our findings demonstrate sexual dimorphism in mitophagy-associated proteins and in mitochondrial respiration, which may help shed light on how the pathogenesis of PH may differ between the sexes.

Interferon-γ Preferentially Promotes Necroptosis of Lung Epithelial Cells by Upregulating MLKL.

Necroptosis, a form of programmed lytic cell death, has emerged as a driving factor in the pathogenesis of acute lung injury (ALI). As ALI is often associated with a cytokine storm, we determined whether pro-inflammatory cytokines modulate the susceptibility of lung cells to necroptosis and which mediators dominate to control necroptosis. In this study, we pretreated/primed mouse primary lung epithelial and endothelial cells with various inflammatory mediators and assessed cell type-dependent responses to different necroptosis inducers and their underlying mechanisms. We found that interferon-γ (IFNγ) as low as 1 ng/mL preferentially promoted necroptosis and accelerated the release of damage-associated molecular patterns from primary alveolar and airway epithelial cells but not lung microvascular endothelial cells. Type-I IFNα was about fifty-fold less effective than IFNγ. Conversely, TNFα or agonists of Toll-like receptor-3 (TLR3), TLR4, TLR7 and TLR9 had a minor effect. The enhanced necroptosis in IFNγ-activated lung epithelial cells was dependent on IFNγ signaling and receptor-interacting protein kinase-3. We further showed that necroptosis effector mixed lineage kinase domain-like protein (MLKL) was predominantly induced by IFNγ, contributing to the enhanced necroptosis in lung epithelial cells. Collectively, our findings indicate that IFNγ is a potent enhancer of lung epithelial cell susceptibility to necroptosis.