GM-CSF expression by human lung microvascular endothelial cells: in vitro and in vivo findings

Deciphering the role of endothelial granulocyte macrophage-CSF in chronic inflammation associated with HIV

People with HIV (PWH) experience endothelial dysfunction (ED) that is aggravated by chronic inflammation and microbial translocation across a damaged gut barrier. Although this paradigm is well-described, downstream pathways that terminate in endothelial dysfunction are only partially understood. This study found increased expression of granulocyte macrophage colony stimulating factor (GM-CSF), toll-like receptor-4 (TLR4), and myeloperoxidase in the aortic endothelium of PWH compared to those without HIV. Bacteria-derived lipopolysaccharide (LPS) heightened glucose uptake and induced GM-CSF expression in primary human endothelial cells. Exposure to sodium-glucose cotransporter-2 (SGLT2) inhibitors reduced glucose uptake, GM-CSF release, and ED in LPS-activated endothelial cells ex vivo, and PWH treated with SGLT2 inhibitors for diabetes had significantly lower plasma GM-CSF levels than non-diabetic PWH not on this medication. The findings suggest that microbial products trigger glucose uptake and GM-CSF expression in the endothelium, contributing to localized inflammation in PWH. Modifying this altered state could offer therapeutic benefits.

Role of GM-CSF in lung balance and disease

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hematopoietic growth factor originally identified as a stimulus that induces the differentiation of bone marrow progenitor cells into granulocytes and macrophages. GM-CSF is now considered to be a multi-origin and pleiotropic cytokine. GM-CSF receptor signals activate JAK2 and induce nuclear signals through the JAK-STAT, MAPK, PI3K, and other pathways. In addition to promoting the metabolism of pulmonary surfactant and the maturation and differentiation of alveolar macrophages, GM-CSF plays a key role in interstitial lung disease, allergic lung disease, alcoholic lung disease, and pulmonary bacterial, fungal, and viral infections. This article reviews the latest knowledge on the relationship between GM-CSF and lung balance and lung disease, and indicates that there is much more to GM-CSF than its name suggests.

Single-cell immune profiling reveals a developmentally distinct CD4+ GM-CSF+ T-cell lineage that induces GI tract GVHD

Gastrointestinal (GI) tract involvement is a major determinant for subsequent morbidity and mortality arising during graft-versus-host disease (GVHD). CD4+ T cells that produce granulocyte-macrophage colony stimulating factor (GM-CSF) have emerged as central mediators of inflammation in this tissue site as GM-CSF serves as a critical cytokine link between the adaptive and innate arms of the immune system. However, cellular heterogeneity within the CD4+ GM-CSF+ T-cell population due to the concurrent production of other inflammatory cytokines has raised questions as to whether these cells have a common ontology or if a unique CD4+ GM-CSF+ subset exists that differs from other defined T helper subtypes. Using single-cell RNA sequencing analysis (scRNAseq), we identified two CD4+ GM-CSF+ T-cell populations that arose during GVHD and were distinguishable according to the presence or absence of interferon-γ (IFN-γ) coexpression. CD4+ GM-CSF+ IFN-γ- T cells, which emerged preferentially in the colon, had a distinct transcriptional profile, used unique gene regulatory networks, and possessed a nonoverlapping T-cell receptor repertoire compared with CD4+ GM-CSF+ IFN-γ+ T cells as well as all other transcriptionally defined CD4+ T-cell populations in the colon. Functionally, this CD4+ GM-CSF+ T-cell population contributed to pathologic damage in the GI tract that was critically dependent on signaling through the interleukin-17 (IL-7) receptor but was independent of type 1 interferon signaling. Thus, these studies help to unravel heterogeneity within CD4+ GM-CSF+ T cells that arise during GVHD and define a developmentally distinct colitogenic T helper subtype GM-CSF+ subset that mediates immunopathology.

GM-CSF: Orchestrating the Pulmonary Response to Infection

This review summarizes the structure and function of the alveolar unit, comprised of alveolar macrophage and epithelial cell types that work in tandem to respond to infection. Granulocyte-macrophage colony-stimulating factor (GM-CSF) helps to maintain the alveolar epithelium and pulmonary immune system under physiological conditions and plays a critical role in restoring homeostasis under pathologic conditions, including infection. Given the emergence of novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and global spread of coronavirus disease 2019 (COVID-19), with subsequent acute respiratory distress syndrome, understanding basic lung physiology in infectious diseases is especially warranted. This review summarizes clinical and preclinical data for GM-CSF in respiratory infections, and the rationale for sargramostim (yeast-derived recombinant human [rhu] GM-CSF) as adjunctive treatment for COVID-19 and other pulmonary infectious diseases.

Distinct macrophage phenotypes skewed by local granulocyte macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF) are associated with tissue destruction and intimal hyperplasia in giant cell arteritis

Objective

To determine the presence and spatial distribution of different macrophage phenotypes, governed by granulocyte macrophage colony‐stimulating factor (GM‐CSF) and macrophage colony‐stimulating factor (M‐CSF) skewing signals, in giant cell arteritis (GCA) lesions.

Methods

Temporal artery biopsies (TABs, n = 11) from treatment‐naive GCA patients, aorta samples from GCA‐related aneurysms (n = 10) and atherosclerosis (n = 10) were stained by immunohistochemistry targeting selected macrophage phenotypic markers, cytokines, matrix metalloproteinases (MMPs) and growth factors. In vitro macrophage differentiation (n = 10) followed by flow cytometry, Luminex assay and ELISA were performed to assess whether GM‐CSF and M‐CSF are drivers of macrophage phenotypic heterogeneity.

Results

A distinct spatial distribution pattern of macrophage phenotypes in TABs was identified. CD206⁺/MMP‐9⁺ macrophages were located at the site of tissue destruction, whereas FRβ⁺ macrophages were located in the inner intima of arteries with high degrees of intimal hyperplasia. Notably, this pattern was also observed in macrophage‐rich areas in GCA aortas but not in atherosclerotic aortas. Flow cytometry showed that GM‐CSF treatment highly upregulated CD206 expression, while FRβ was expressed by M‐CSF‐skewed macrophages, only. Furthermore, localised expression of GM‐CSF and M‐CSF was detected, likely contributing to macrophage heterogeneity in the vascular wall.

Conclusions

Our data document a distinct spatial distribution pattern of CD206⁺/MMP‐9⁺ macrophages and FRβ⁺ macrophages in GCA linked to tissue destruction and intimal proliferation, respectively. We suggest that these distinct macrophage phenotypes are skewed by sequential GM‐CSF and M‐CSF signals. Our study adds to a better understanding of the development and functional role of macrophage phenotypes in the pathogenesis of GCA and opens opportunities for the design of macrophage‐targeted therapies.

The anti-viral facet of anti-rheumatic drugs: Lessons from COVID-19

The outbreak of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has posed the world at a pandemic risk. Coronavirus-19 disease (COVID-19) is an infectious disease caused by SARS-CoV-2, which causes pneumonia, requires intensive care unit hospitalization in about 10% of cases and can lead to a fatal outcome. Several efforts are currently made to find a treatment for COVID-19 patients. So far, several anti-viral and immunosuppressive or immunomodulating drugs have demonstrated some efficacy on COVID-19 both in vitro and in animal models as well as in cases series. In COVID-19 patients a pro-inflammatory status with high levels of interleukin (IL)-1B, IL-1 receptor (R)A and tumor necrosis factor (TNF)-α has been demonstrated. Moreover, high levels of IL-6 and TNF-α have been observed in patients requiring intensive-care-unit hospitalization. This provided rationale for the use of anti-rheumatic drugs as potential treatments for this severe viral infection. Other agents, such as hydroxychloroquine and chloroquine might have a direct anti-viral effect. The anti-viral aspect of immunosuppressants towards a variety of viruses has been known since long time and it is herein discussed in the view of searching for a potential treatment for SARS-CoV-2 infection.

Inter-α-inhibitor Ameliorates Endothelial Inflammation in Sepsis

PURPOSE

Vascular endothelial cells demonstrate severe injury in sepsis, and a reduction in endothelial inflammation would be beneficial. Inter-α-Inhibitor (IαI) is a family of abundant plasma proteins with anti-inflammatory properties and has been investigated in human and animal sepsis with encouraging results. We hypothesized that IαI may protect endothelia from sepsis-related inflammation.

METHODS

IαI-deficient or sufficient mice were treated with endotoxin or underwent complement-induced lung injury. VCAM-1 and ICAM-1 expression was measured in blood and lung as marker of endothelial activation. Human endothelia were exposed to activated complement C5a with or without IαI. Blood from human sepsis patients was examined for VCAM-1 and ICAM-1 and levels were correlated with blood levels of IαI.

RESULTS

IαI-deficient mice showed increased endothelial activation in endotoxin/sepsis- and complement-induced lung injury models. In vitro, levels of endothelial pro-inflammatory cytokines and cell growth factors induced by activated complement C5a were significantly decreased in the presence of IαI. This effect was associated with decreased ERK and NFκB activation. IαI levels were inversely associated with VCAM-1 and ICAM-1 levels in a human sepsis cohort.

CONCLUSIONS

IαI ameliorates endothelial inflammation and may be beneficial as a treatment of sepsis.

Hypercapnic acidosis induces mitochondrial dysfunction and impairs the ability of mesenchymal stem cells to promote distal lung epithelial repair

Acute respiratory distress syndrome (ARDS) is a devastating disorder characterized by diffuse inflammation and edema formation. The main management strategy, low tidal volume ventilation, can be associated with the development of hypercapnic acidosis (HCA). Mesenchymal stem cells (MSCs) are a promising therapeutic candidate currently in early-phase clinical trials. The effects of HCA on the alveolar epithelium and capillary endothelium are not well established. The therapeutic efficacy of MSCs has never been reported in HCA. In the present study, we evaluated the effects of HCA on inflammatory response and reparative potential of the primary human small airway epithelial and lung microvasculature endothelial cells as well as on the capacity of bone marrow-derived MSCs to promote wound healing in vitro. We demonstrate that HCA attenuates the inflammatory response and reparative potential of primary human small airway epithelium and capillary endothelium and induces mitochondrial dysfunction. It was found that MSCs promote lung epithelial wound repair via the transfer of functional mitochondria; however, this proreparative effect of MSCs was lost in the setting of HCA. Therefore, HCA may adversely impact recovery from ARDS at the cellular level, whereas MSCs may not be therapeutically beneficial in patients with ARDS who develop HCA.-Fergie, N., Todd, N., McClements, L., McAuley, D., O'Kane, C., Krasnodembskaya, A. Hypercapnic acidosis induces mitochondrial dysfunction and impairs the ability of mesenchymal stem cells to promote distal lung epithelial repair.

Antibodies to major histocompatibility complex class II antigens directly prime neutrophils and cause acute lung injury in a two-event in vivo rat model

BACKGROUND

Transfusion-related acute lung injury (TRALI) is a significant cause of mortality, especially after transfusions containing antibodies to major histocompatibility complex (MHC) class II antigens. We hypothesize that a first event induces both 1) polymorphonuclear neutrophils (PMNs) to express MHC class II antigens, and 2) activation of the pulmonary endothelium, leading to PMN sequestration, so that the infusion of specific MHC class II antibodies to these antigens causes PMN-mediated acute lung injury (ALI).

STUDY DESIGN AND METHODS

Rats were treated with saline (NS), endotoxin (lipopolysaccharide [LPS]), or cytokines (interferon-γ [IFNγ], macrophage colony-stimulating factor [MCSF], tumor necrosis factor-α [TNFα]); the PMNs were isolated; and the surface expression of the MHC class II antigen OX6 and priming by OX6 antibodies were measured by flow cytometry or priming assays.

RESULTS

A two-event model of ALI was completed with NS, LPS, or IFNγ/MCSF/TNFα (first events) and the infusion of OX6 (second event). Compared with NS incubation, rats treated with either LPS or IFNγ/MCSF/TNFα exhibited OX6 PMN surface expression, OX6 antibodies primed the formyl-methionyl-leucyl phenylalanine (fMLF)-activated respiratory burst, and PMN sequestration was increased. OX6 antibody infusion into LPS-incubated or IFNγ/MCSF/TNFα-incubated rats elicited ALI, the OX6 antibody was present on the PMNs, and PMN depletion abrogated ALI.

CONCLUSION

Proinflammatory first events induce PMN MHC class II surface expression, activation of the pulmonary endothelium, and PMN sequestration such that the infusion of cognate antibodies precipitates TRALI.

Influenza-Induced Priming and Leak of Human Lung Microvascular Endothelium upon Exposure to Staphylococcus aureus

A major cause of death after influenza virus infection is lung injury due to a bacterial superinfection, yet the mechanism is unknown. Death has been attributed to virus-induced immunosuppression and bacterial overgrowth, but this hypothesis is based on data from the preantibiotic era and animal models that omit antimicrobial therapy. Because of diagnostic uncertainty, most patients with influenza receive antibiotics, making bacterial overgrowth unlikely. Respiratory failure after superinfection presents as acute respiratory distress syndrome, a disorder characterized by lung microvascular leak and edema. The objective of this study was to determine whether the influenza virus sensitizes the lung endothelium to leak upon exposure to circulating bacterial-derived molecular patterns from Staphylococcus aureus. In vitro as well as in vivo models of influenza followed by S. aureus superinfection were used. Molecular mechanisms were explored using molecular biology, knockout mice, and human autopsy specimens. Influenza virus infection sensitized human lung endothelium to leak when challenged with S. aureus, even at low doses of influenza and even when the pathogens were given days apart. Influenza virus increased endothelial expression of TNFR1 both in vitro and in intact lungs, a finding corroborated by human autopsy specimens of patients with influenza. Leak was recapitulated with protein A, a TNFR1 ligand, and sequential infection caused protein A-dependent loss of IκB, cleavage of caspases 8 and 3, and lung endothelial apoptosis. Mice infected sequentially with influenza virus and S. aureus developed significantly increased lung edema that was protein A and TNFR1 dependent. Influenza virus primes the lung endothelium to leak, predisposing patients to acute respiratory distress syndrome upon exposure to S. aureus.

Activation of silenced cytokine gene promoters by the synergistic effect of TBP-TALE and VP64-TALE activators

Recent work has shown that the combinatorial use of multiple TALE activators can selectively activate certain cellular genes in inaccessible chromatin regions. In this study, we aimed to interrogate the activation potential of TALEs upon transcriptionally silenced immune genes in the context of non-immune cells. We designed a unique strategy, in which a single TALE fused to the TATA-box binding protein (TBP-TALE) is coupled with multiple VP64-TALE activators. We found that our strategy is significantly more potent than multiple TALE activators alone in activating expression of IL-2 and GM-CSF in diverse cell origins in which both genes are otherwise completely silenced. Chromatin analysis revealed that the gene activation was due in part to displacement of a distinctly positioned nucleosome. These studies provide a novel epigenetic mechanism for artificial gene induction and have important implications for targeted cancer immunotherapy, DNA vaccine development, as well as rational design of TALE activators.

HDL-transferred microRNA-223 regulates ICAM-1 expression in endothelial cells

High-density lipoproteins (HDL) have many biological functions, including reducing endothelial activation and adhesion molecule expression. We recently reported that HDL transport and deliver functional microRNAs (miRNA). Here we show that HDL suppresses expression of intercellular adhesion molecule 1 (ICAM-1) through the transfer of miR-223 to endothelial cells. After incubation of endothelial cells with HDL, mature miR-223 levels are significantly increased in endothelial cells and decreased on HDL. However, miR-223 is not transcribed in endothelial cells and is not increased in cells treated with HDL from miR-223(-/-) mice. HDL inhibit ICAM-1 protein levels, but not in cells pretreated with miR-223 inhibitors. ICAM-1 is a direct target of HDL-transferred miR-223 and this is the first example of an extracellular miRNA regulating gene expression in cells where it is not transcribed. Collectively, we demonstrate that HDL's anti-inflammatory properties are conferred, in part, through HDL-miR-223 delivery and translational repression of ICAM-1 in endothelial cells.

Lipopolysaccharide-induced lung injury involves the nitration-mediated activation of RhoA

Acute lung injury (ALI) is characterized by increased endothelial hyperpermeability. Protein nitration is involved in the endothelial barrier dysfunction in LPS-exposed mice. However, the nitrated proteins involved in this process have not been identified. The activation of the small GTPase RhoA is a critical event in the barrier disruption associated with LPS. Thus, in this study we evaluated the possible role of RhoA nitration in this process. Mass spectroscopy identified a single nitration site, located at Tyr(34) in RhoA. Tyr(34) is located within the switch I region adjacent to the nucleotide-binding site. Utilizing this structure, we developed a peptide designated NipR1 (nitration inhibitory peptide for RhoA 1) to shield Tyr(34) against nitration. TAT-fused NipR1 attenuated RhoA nitration and barrier disruption in LPS-challenged human lung microvascular endothelial cells. Further, treatment of mice with NipR1 attenuated vessel leakage and inflammatory cell infiltration and preserved lung function in a mouse model of ALI. Molecular dynamics simulations suggested that the mechanism by which Tyr(34) nitration stimulates RhoA activity was through a decrease in GDP binding to the protein caused by a conformational change within a region of Switch I, mimicking the conformational shift observed when RhoA is bound to a guanine nucleotide exchange factor. Stopped flow kinetic analysis was used to confirm this prediction. Thus, we have identified a new mechanism of nitration-mediated RhoA activation involved in LPS-mediated endothelial barrier dysfunction and show the potential utility of "shielding" peptides to prevent RhoA nitration in the management of ALI.

Effects of tobacco on cytokine expression from human endothelial cells

OBJECTIVE

To investigate the effects of nicotine and cigarette smoke condensate (CSC) exposure on cytokine expression from human endothelial cells in order to identify one possible mechanism that smoking plays in the pathogenesis of both periodontal disease (PDD) and cardiovascular disease (CVD).

METHODS

Human endothelial cells (HUVECs) were exposed to different concentrations of nicotine and CSC to examine the effects that they have on cell proliferation and cytotoxicity. Non-toxic levels were then used to examine cytokine expression using cytokine protein arrays.

RESULTS

Exposure to nicotine caused significant down-regulation in the expression of IL-10 (P = 0.046), growth-regulated oncogene (GRO)α (P = 0.036), MCP-1 (P = 0.046), and GMCSF (P = 0.004) compared with the control untreated HUVECs. Exposure to CSC caused significant down-regulation in the expression of GRO (P = 0.04), GROα (P = 0.01), IL-6 (P = 0.03), and MCP-1 (P = 0.04) compared with the control untreated HUVECs.

CONCLUSIONS

Exposure of HUVECs to nicotine or CSC affects the levels of cytokine expression including reduction in anti-inflammatory and chemoattractant cytokines. This may subsequently affect the host defensive mechanisms of the tissues. The action of toxic chemicals in tobacco smoke on endothelial cells is a potential pathogenic mechanism that may in part explain the association between tobacco, PDD, and CVD.

Effect of nanoparticles and environmental particles on a cocultures model of the air-blood barrier

Exposure to engineered nanoparticles (NPs) and to ambient particles (PM) has increased significantly. During the last decades the application of nano-objects to daily-life goods and the emissions produced in highly urbanized cities have considerably augmented. As a consequence, the understanding of the possible effects of NPs and PM on human respiratory system and particularly on the air-blood barrier (ABB) has become of primary interest. The crosstalk between lung epithelial cells and underlying endothelial cells is indeed essential in determining the effects of inhaled particles. Here we report the effects of metal oxides NPs (CuO and TiO₂) and of PM on an in vitro model of the ABB constituted by the type II epithelial cell line (NCI-H441) and the endothelial one (HPMEC-ST1.6R). The results demonstrate that apical exposure of alveolar cells induces significant modulation of proinflammatory proteins also in endothelial cells.

Hematopoietic stem and progenitor cells as effectors in innate immunity

Recent research has shed light on novel functions of hematopoietic stem and progenitor cells (HSPC). While they are critical for maintenance and replenishment of blood cells in the bone marrow, these cells are not limited to the bone marrow compartment and function beyond their role in hematopoiesis. HSPC can leave bone marrow and circulate in peripheral blood and lymph, a process often manipulated therapeutically for the purpose of transplantation. Additionally, these cells preferentially home to extramedullary sites of inflammation where they can differentiate to more mature effector cells. HSPC are susceptible to various pathogens, though they may participate in the innate immune response without being directly infected. They express pattern recognition receptors for detection of endogenous and exogenous danger-associated molecular patterns and respond not only by the formation of daughter cells but can themselves secrete powerful cytokines. This paper summarizes the functional and phenotypic characterization of HSPC, their niche within and outside of the bone marrow, and what is known regarding their role in the innate immune response.

Co-culture systems for vascularization--learning from nature

The endothelial cell (EC) is practically ubiquitous in the human body and forms the inner cellular lining of the entire cardiovascular system. Following tissue injury, the microcirculation becomes the stage for both the inflammatory response and the subsequent healing reaction to restore physiological function to the damaged tissue. The advent of the multidisciplinary field of Regenerative Medicine (RegMed), of which Tissue Engineering (TE) and drug delivery using modern stimuli-responsive or interactive biomaterials are important components, has opened up new approaches to the acceleration of the healing response. A central and rate-limiting role in the latter is played by the process of vascularization or neovascularization, so that it is not surprising that in RegMed concepts have been developed for the drug- and gene-delivery of potent stimuli such as vascular-endothelial growth factor (VEGF) to promote neovessel development. However, not all of these novel materials can be tested in vivo, and in vitro co-culture model systems using human primary cells are being developed to pre-evaluate and determine which of the RegMed concepts exhibit the most promising potential for success after implantation. This review describes some of the growing number of in vitro co-cultures model systems that are being used to study cell-cell and cell-material interactions at the cellular and molecular levels to determine which materials are best suited to integrate into the host, promote a rapid vascularization and fit into the regenerative process without disturbing or slowing the normal healing steps.

Harvesting, identification and barrier function of human lung microvascular endothelial cells

Endothelial barrier dysfunction is an important contributor to the pathogenesis of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Even though approaches that target the prevention and repair of endothelial barrier dysfunction are clearly needed, our understanding of the molecular regulation of pulmonary microvascular endothelial permeability remains incomplete. Cultured pulmonary microvascular endothelial cells represent an attractive paradigm for the study of barrier function. Here, we describe a method for the harvest, identification and culture of human lung microvascular endothelial cells (HLMVEC). HLMVEC thus obtained, grow as a monolayer, exhibit contact inhibition and have the typical cobblestone appearance. They express endothelial proteins, such as von Willebrand factor and endothelial nitric oxide synthase and take up an acetylated LDL. Furthermore, HLMVEC respond predictably and with superior sensitivity to the barrier disruptive effects of Gram positive and Gram negative bacterial products, thrombin, vascular endothelial growth factor and microtubule disrupting agents. These HLMVEC present an in-house-derived alternative to commercially available human cells for the study of mechanisms contributing to ALI and ARDS.

Effect of PPARgamma inhibition on pulmonary endothelial cell gene expression: gene profiling in pulmonary hypertension

Peroxisome proliferator-activated receptor type gamma (PPARgamma) is a subgroup of the PPAR transcription factor family. Recent studies indicate that loss of PPARgamma is associated with the development of pulmonary hypertension (PH). We hypothesized that the endothelial dysfunction associated with PPARgamma inhibition may play an important role in the disease process by altering cellular gene expression and signaling cascades. We utilized microarray analysis to determine if PPARgamma inhibition induced changes in gene expression in pulmonary arterial endothelial cells (PAEC). We identified 100 genes and expressed sequence tags (ESTs) that were upregulated by >1.5-fold and 21 genes and ESTs that were downregulated by >1.3-fold (P < 0.05) by PPARgamma inhibition. The upregulated genes can be broadly classified into four functional groups: cell cycle, angiogenesis, ubiquitin system, and zinc finger proteins. The genes with the highest fold change in expression: hyaluronan-mediated motility receptor (HMMR), VEGF receptor 2 (Flk-1), endothelial PAS domain protein 1 (EPAS1), basic fibroblast growth factor (FGF-2), and caveolin-1 in PAEC were validated by real time RT-PCR. We further validated the upregulation of HMMR, Flk-1, FGF2, and caveolin-1 by Western blot analysis. In keeping with the microarray results, PPARgamma inhibition led to re-entry of cell cycle at G(1)/S phase and cyclin C upregulation. PPARgamma inhibition also exacerbated VEGF-induced endothelial barrier disruption. Finally we confirmed the downregulation of PPARgamma and the upregulation of HMMR, Flk-1, FGF2, and Cav-1 proteins in the peripheral lung tissues of an ovine model of PH. In conclusion, we have identified an array of endothelial genes modulated by attenuated PPARgamma signaling that may play important roles in the development of PH.

Mechanisms of nitric oxide synthase uncoupling in endotoxin-induced acute lung injury: role of asymmetric dimethylarginine

Acute lung injury (ALI) is associated with severe alterations in lung structure and function and is characterized by hypoxemia, pulmonary edema, low lung compliance and widespread capillary leakage. Asymmetric dimethylarginine (ADMA), a known cardiovascular risk factor, has been linked to endothelial dysfunction and the pathogenesis of a number of cardiovascular diseases. However, the role of ADMA in the pathogenesis of ALI is less clear. ADMA is metabolized via hydrolytic degradation to l-citrulline and dimethylamine by the enzyme, dimethylarginine dimethylaminohydrolase (DDAH). Recent studies suggest that lipopolysaccharide (LPS) markedly increases the level of ADMA and decreases DDAH activity in endothelial cells. Thus, the purpose of this study was to determine if alterations in the ADMA/DDAH pathway contribute to the development of ALI initiated by LPS-exposure in mice. Our data demonstrate that LPS exposure significantly increases ADMA levels and this correlates with a decrease in DDAH activity but not protein levels of either DDAH I or DDAH II isoforms. Further, we found that the increase in ADMA levels cause an early decrease in nitric oxide (NO(x)) and a significant increase in both NO synthase (NOS)-derived superoxide and total nitrated lung proteins. Finally, we found that decreasing peroxynitrite levels with either uric acid or Manganese (III) tetrakis (1-methyl-4-pyridyl) porphyrin (MnTymPyp) significantly attenuated the lung leak associated with LPS-exposure in mice suggesting a key role for protein nitration in the progression of ALI. In conclusion, this is the first study that suggests a role of the ADMA/DDAH pathway during the development of ALI in mice and that ADMA may be a novel therapeutic biomarker to ascertain the risk for development of ALI.

Phagocytosis of apoptotic cells by neutrophil granulocytes: diminished proinflammatory neutrophil functions in the presence of apoptotic cells

Neutrophil granulocytes are rapidly recruited from the bloodstream to the site of acute inflammation where they die in large numbers. Because release of toxic substances from dead neutrophils can propagate the inflammatory response leading to tissue destruction, clearance of dying inflammatory neutrophils has a critical function in the resolution of the inflammatory response. Apoptotic neutrophils are phagocytosed primarily by macrophages, provided these cells are present in adequate numbers. However, macrophages are rare at sites of acute inflammation, whereas the number of neutrophils can be extremely high. In the current study, in vitro experiments with human neutrophils were carried out to investigate whether neutrophils can ingest apoptotic neutrophils. We show that naïve granulocytes isolated from venous blood have a limited capacity to phagocytose apoptotic cells. However, exposure to activating stimuli such as LPS, GM-CSF and/or IFN-gamma results in enhanced phagocytosis of apoptotic cells. The efficient uptake of apoptotic cells by neutrophils was found to depend on the presence of heat labile serum factors. Importantly, the contact to or uptake of apoptotic cells inhibited neutrophil functions such as respiratory burst and the release of the proinflammatory cytokines TNF-alpha and interferon-inducible protein-10. Contact to apoptotic cells, however, induced the secretion of IL-8 and growth-related oncogene-alpha, which was independent of NF-kappaB and p38 MAPK but involved C5a and the ERK1/2 pathway. The data suggest that activated neutrophils participate in the clearance of apoptotic cells. In addition, because apoptotic cells inhibit proinflammatory functions of neutrophils, uptake of apoptotic cells by neutrophils contributes to the resolution of inflammation.

Effect of PPARgamma inhibition on pulmonary endothelial cell gene expression: gene profiling in pulmonary hypertension

Peroxisome proliferator-activated receptor type gamma (PPARgamma) is a subgroup of the PPAR transcription factor family. Recent studies indicate that loss of PPARgamma is associated with the development of pulmonary hypertension (PH). We hypothesized that the endothelial dysfunction associated with PPARgamma inhibition may play an important role in the disease process by altering cellular gene expression and signaling cascades. We utilized microarray analysis to determine if PPARgamma inhibition induced changes in gene expression in pulmonary arterial endothelial cells (PAEC). We identified 100 genes and expressed sequence tags (ESTs) that were upregulated by >1.5-fold and 21 genes and ESTs that were downregulated by >1.3-fold (P < 0.05) by PPARgamma inhibition. The upregulated genes can be broadly classified into four functional groups: cell cycle, angiogenesis, ubiquitin system, and zinc finger proteins. The genes with the highest fold change in expression: hyaluronan-mediated motility receptor (HMMR), VEGF receptor 2 (Flk-1), endothelial PAS domain protein 1 (EPAS1), basic fibroblast growth factor (FGF-2), and caveolin-1 in PAEC were validated by real time RT-PCR. We further validated the upregulation of HMMR, Flk-1, FGF2, and caveolin-1 by Western blot analysis. In keeping with the microarray results, PPARgamma inhibition led to re-entry of cell cycle at G(1)/S phase and cyclin C upregulation. PPARgamma inhibition also exacerbated VEGF-induced endothelial barrier disruption. Finally we confirmed the downregulation of PPARgamma and the upregulation of HMMR, Flk-1, FGF2, and Cav-1 proteins in the peripheral lung tissues of an ovine model of PH. In conclusion, we have identified an array of endothelial genes modulated by attenuated PPARgamma signaling that may play important roles in the development of PH.

The antioxidant, taurine reduced lipopolysaccharide (LPS)-induced generation of ROS, and activation of MAPKs and Bax in cultured pneumocytes

Lipopolysaccharide (LPS) can cause damage to the epithelia of the respiratory tract. However, taurine can protect the lung tissue from such oxidant-induced inflammation. This study examined the effects of a LPS treatment on the intracellular calcium levels ([Ca(2+)]i) as well as the specific mechanisms of LPS-induced cell death in pneumocytes. In addition, the effects of taurine on the LPS-induced increase in the accumulation of reactive oxygen species (ROS) in pneumocytes were investigated. The [Ca(2+)]i in cultured pneumocytes was determined using microfluorescence techniques. The level of activation of the mitogen-activated protein kinases (MAPKs) and Bax protein were measured by Western blotting. LPS at 10 and 100 ng/ml induced cell death and decreased the viability of MRC-5 cells. Moreover, the intracellular Ca(2+) and ROS levels were increased by LPS. The LPS treatment led to the phosphorylation of ERK1/2, JNK and the activation of Bax. A pretreatment with 20 mM taurine reduced the LPS-induced production of ROS and MARK activity. These results show that a LPS treatment induces cell death in MRC-5 cells by increasing the intracellular ROS and Ca(2+) levels. The increase in the intracellular level of ROS promotes MAPKs activation and Bax translocation. Overall, LPS induces lung cell death by activating MAPKs. Furthermore, taurine decreased the LPS-induced generation of ROS and activation of MAPK and Bax.

Primary human coculture model of alveolo-capillary unit to study mechanisms of injury to peripheral lung

In order to delineate individual pathomechanisms in acute lung injury and pulmonary toxicology, we developed a primary coculture system to simulate the human alveolo-capillary barrier. Human pulmonary microvascular endothelial cells (HPMEC) were cocultivated with primary isolated human type II alveolar epithelial cells (HATII) on opposite sides of a permeable filter support, thereby constituting a bilayer. Within 7-11 days of coculture, the HATII cells partly transdifferentiated to type-I-like (HATI-like) cells, as demonstrated by morphological changes from a cuboidal to a flattened morphology, the loss of HATII-cell-specific organelles and the increase of HATI-cell-related markers (caveolin-1, aquaporin-5, receptor for advanced glycation end-products). Immunofluorescent analysis detected type-II-like and type-I-like alveolar epithelial cells mimicking the heterocellular composition of alveolar epithelium in vivo. The heterocellular epithelial monolayer showed a circumferential staining of tight-junctional (ZO-1, occludin) and adherens-junctional (E-cadherin, beta-catenin) proteins. HPMEC on the opposite side also developed tight and adherens junctions (VE-cadherin, beta-catenin). Under integral barrier properties, exposure to the proinflammatory cytokine tumour necrosis factor-alpha from either the endothelial (basolateral) or the epithelial (apical) side caused a largely compartmentalized release of the chemokines interleukin-8 and monocyte chemoattractant protein-1. Thus, the established coculture provides a suitable in vitro model to examine barrier function at the distal lung, including the interaction of microvascular endothelial cells with ATII-like and ATI-like epithelial cells. The compartmentalization of the barrier-forming bilayer also allows mechanisms of lung injury to be studied in both the epithelial (intra-alveolar) and the endothelial (intravascular) compartments.

Endothelial permeability is increased by the supernatant of peripheral blood mononuclear cells stimulated with HLA Class II antibody

BACKGROUND

The generation of inflammatory mediators from monocytes activated by HLA Class II antibodies is thought to play important roles in the etiology of nonhemolytic transfusion reactions. Increased permeability of endothelial cells contributes to the pathogenesis of rash, urticaria, angioedema, and pulmonary edema, which are symptoms of transfusion reactions.

STUDY DESIGN AND METHODS

We investigated whether inflammatory mediators released from monocytes upon stimulation by HLA Class II antibodies could increase endothelial permeability. Human endothelial cell monolayers were incubated with cell-free supernatants of peripheral blood mononuclear cells (PBMNCs) stimulated with HLA Class II antibody-containing plasma (anti-HLA-DR plasma), which has been implicated in severe nonhemolytic transfusion reactions. The permeability of endothelial cells to dextran was measured.

RESULTS

The supernatants of PBMNCs stimulated with the anti-HLA-DR plasma in corresponding antigen-antibody combinations were able to increase endothelial permeability. At least 3 hours of exposure of PBMNCs to anti-HLA-DR plasma was required to produce a supernatant that could induce a significant increase in permeability. Simultaneous addition of tumor necrosis factor alpha (TNF-alpha) and interleukin 1 beta (IL-1 beta) neutralizing antibodies to the activated PBMNC supernatant significantly reduced the increase in permeability. Treatment of the endothelial cells with an inhibitor of nuclear factor kappaB (NF-kappaB), but not inhibitors of apoptosis, significantly prevented the increase in permeability.

CONCLUSION

Both TNF-alpha and IL-1 beta, generated from PBMNCs by anti-HLA-DR plasma in a corresponding antigen-antibody-dependent manner, led to an increase in endothelial permeability. The activation of monocytes by the HLA-DR antibodies and the resultant inflammatory mediators could contribute to the pathogenesis of rash, urticaria, angioedema, and pulmonary edema after transfusion.

Airway eosinophils: allergic inflammation recruited professional antigen-presenting cells

The capacity of airway eosinophils, potentially pertinent to allergic diseases of the upper and lower airways, to function as professional APCs, those specifically able to elicit responses from unprimed, Ag-naive CD4(+) T cells has been uncertain. We investigated whether airway eosinophils are capable of initiating naive T cell responses in vivo. Eosinophils, isolated free of other APCs from the spleens of IL-5 transgenic mice, following culture with GM-CSF expressed MHC class II and the costimulatory proteins, CD40, CD80, and CD86. Eosinophils, incubated with OVA Ag in vitro, were instilled intratracheally into wild-type recipient mice that adoptively received i.v. infusions of OVA Ag-specific CD4(+) T cells from OVA TCR transgenic mice. OVA-exposed eosinophils elicited activation (CD69 expression), proliferation (BrdU incorporation), and IL-4, but not IFN-gamma, cytokine production by OVA-specific CD4(+) T cells in paratracheal lymph nodes (LN). Exposure of eosinophils to lysosomotropic NH(4)Cl, which inhibits Ag processing, blocked each of these eosinophil-mediated activation responses of CD4(+) T cells. By three-color fluorescence microscopy, OVA Ag-loaded eosinophil APCs were physically interacting with naive OVA-specific CD4(+) T cells in paratracheal LN after eosinophil airway instillation. Thus, recruited luminal airway eosinophils are distinct allergic "inflammatory" professional APCs able to activate primary CD4(+) T cell responses in regional LNs.

Albumin leak across human pulmonary microvascular vs. umbilical vein endothelial cells under septic conditions

Human pulmonary microvascular endothelial cell (HPMVEC) injury is central to the pathophysiology of human lung injury. However, septic HPMVEC barrier dysfunction and the contribution of neutrophils have not been directly addressed in vitro. Instead, human EC responses are often extrapolated from studies of human umbilical vein EC (HUVEC). We hypothesized that HUVEC was not a good model for investigating HPMVEC barrier function under septic conditions. HPMVEC was isolated from lung tissue resected from lung cancer patients using magnetic bead-bound anti-PECAM-1 antibody. In confluent monolayers in 3-mum cell-culture inserts, we assessed trans-EC Evans-Blue (EB)-conjugated albumin leak under basal, unstimulated conditions and following stimulation with either lipopolysaccharide or a mixture of equal concentrations of TNF-alpha, IL-1beta and IFN-gamma (cytomix). Basal EB-albumin leak was significantly lower across HPMVEC than HUVEC (0.64 +/- 0.06% vs. 1.13 +/- 0.10%, respectively, P < 0.001). Lipopolysaccharide and cytomix increased leak across both HPMVEC and HUVEC in a dose-dependent manner, with a similar increase relative to basal leak in both cell types. The presence of neutrophils markedly and dose-dependently enhanced cytomix-induced EB-albumin leak across HPMVEC (P < 0.01), but had no effect on EB-albumin leak across HUVEC. Both cytomix and lipopolysaccharide-induced albumin leak was not associated with a loss of cell viability. In conclusion, HPMVEC barrier dysfunction under septic conditions is dramatically enhanced by neutrophil presence, and HUVEC is not a suitable model for studying HPMVEC septic barrier responses. The direct study of HPMVEC septic responses will lead to a better understanding of human lung injury.

Activation of vascular endothelial growth factor receptor-2 in bone marrow leads to accumulation of myeloid cells: role of granulocyte-macrophage colony-stimulating factor

Vascular endothelial growth factor (VEGF) is a secreted cytokine that plays a major role in the formation and maintenance of the hemopoietic and vascular compartments. VEGF and its receptors, VEGFR-1 and VEGFR-2, have been found to be expressed on subsets of normal and malignant hemopoietic cells, but the role of the individual receptors in hemopoiesis requires further study. Using a VEGFR-2 fusion protein that can be dimerized with a synthetic drug, we were able to specifically examine the effects of VEGFR-2 signaling in hemopoietic cells in vivo. Mice transplanted with bone marrow transduced with this inducible VEGFR-2 fusion protein demonstrated expansion of myeloid cells (Gr-1+, CD11b+). Levels of myeloid progenitors were also increased following VEGFR-2 activation, through autocrine and paracrine mechanisms, as measured by clonogenic progenitor assays. VEGFR-2 activation induced expression of GM-CSF and increased serum levels in vivo. Abrogation of GM-CSF activity, either with neutralizing Abs or by using GM-CSF-null hemopoietic cells, inhibited VEGFR-2-mediated myeloid progenitor activity. Our findings indicate that VEGF signaling through VEGFR-2 promotes myelopoiesis through GM-CSF-dependent and -independent mechanisms.

IL-17 and IL-17F modulate GM-CSF production by lung microvascular endothelial cells stimulated with IL-1beta and/or TNF-alpha

In this study, we investigated the roles of CD4 T cell cytokines IL-17 and IL-17F in GM-CSF production from lung microvascular endothelial cells (LMVECs). While a wide range of doses of IL-17 or IL-17F alone did not induce GM-CSF release from LMVECs, IL-17 had an enhancing effect on macrophage-derived IL-1beta- and TNF-alpha-induced GM-CSF mRNA expression and production, whereas IL-17F had an enhancing effect on IL-1beta-induced GM-CSF production, but a marked inhibitory effect on TNF-alpha-induced secretion. GM-CSF production was further enhanced with the combination of three cytokines IL-1beta, TNF-alpha and IL-17 or IL-17F. Additionally, when Th1 or Th2 cytokine was combined with IL-1beta or TNF-alpha, both Th1 and Th2 cytokines had a modest stimulatory effect on TNF-alpha-induced GM-CSF production, whereas IL-4 and IFN-gamma profoundly attenuated IL-1beta-induced secretion. Moreover, the regulation by IL-17 plus Th1 or Th2 cytokine of GM-CSF production from LMVECs treated with IL-1beta or TNF-alpha was dependent on the concentration of IL-17. Our findings indicate that IL-17 and IL-17F play a differential regulatory role in GM-CSF production by LMVECs stimulated with IL-1beta and/or TNF-alpha, which is sensitive to Th1 and Th2 cytokine modulation.

15-Deoxy-Δ12,14-prostaglandin J2 inhibits the expression of granulocyte-macrophage colony-stimulating factor in endothelial cells stimulated with lipopolysaccharide

Granulocyte-macrophage colony-stimulating factor (GM-CSF), one of major hematopoietic growth factors, activates mature leukocytes. GM-CSF is produced by endothelial cells stimulated with lipopolysaccharide (LPS), and the LPS-induced GM-CSF production may play an important role in the activation of neutrophils on the endothelial surface. 15-Deoxy-delta 12,14-prostaglandin J2 (15d-PGJ2) is a ligand for peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and modulates inflammatory reactions by regulating the expression of various genes. We studied the effect of 15d-PGJ2 on the LPS-induced GM-CSF expression in endothelial cells. Human umbilical vein endothelial cells (HUVEC) were cultured and the expressions of GM-CSF mRNA and protein were analyzed by reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. 15d-PGJ2 inhibited the LPS-induced GM-CSF expression in a concentration-dependent manner; but ciglitazone, another agonist for PPAR-gamma, had no effect. This suggests that 15d-PGJ2 inhibits GM-CSF expression through a mechanism unrelated to PPAR-gamma. 15d-PGJ2 induced, by itself, the expression of interleukin-8, a potent proinflammatory chemokine, in HUVEC. 15d-PGJ2 may regulate inflammatory reactions by controlling the balance of various cytokines.

Endothelial cell heterogeneity

OBJECTIVE

To review recent advances in the field of endothelial cell heterogeneity, and to apply this knowledge to an understanding of site-specific vasculopathy, including acute lung injury.

DATA SOURCES AND STUDY SELECTION

Published research and review articles in the English language related to endothelial cell biology and endothelial cell heterogeneity.

DATA EXTRACTION AND SYNTHESIS

The results of published studies have been used to provide a perspective of endothelial cell phenotypes in health and disease.

CONCLUSIONS

The structure and function of endothelial cells are differentially regulated in space and time. Far from being a giant monopoly of homogeneous cells, the endothelium represents a consortium of smaller enterprises of cells located within blood vessels of different tissues. Although united in certain functions, each enterprise is uniquely adapted to meet the demands of the underlying tissue. The endothelium may also vary in its response to pathophysiologic stimuli and therefore contribute to the focal nature of vasculopathic disease states. In acute lung injury, the unique properties of the endothelium may conspire with systemic imbalances to localize pathology to the pulmonary vasculature.

Protease-activated receptor (PAR)-1 and PAR-2 participate in the cell growth of alveolar capillary endothelium in primary lung adenocarcinomas

BACKGROUND

Cell growth can be induced via elicitation of protease-activated receptors (PAR) with serine proteases such as thrombin and trypsin.

METHODS

To understand whether PAR are involved in tumor vessel formation in the neoplastic cell-bearing alveolar walls, immunohistochemical and reverse transcriptase-polymerase chain reaction analyses were performed using the lung tissues from 16 patients with primary lung adenocarcinomas.

RESULTS

In microdissected tumor alveolar walls, the expressions of PAR-1 and PAR-2 mRNA were increased by 10-fold (P < 0.05) and 16-fold (P < 0.01), respectively, as compared with normal alveolar walls. Confocal microscopy revealed that tumor capillary endothelial cells in alveolar walls lost thrombomodulin expression. Instead, the expression of PAR-2 often became obvious at the normal border. Both PAR-1 and PAR-2 were expressed in the microvessel endothelial cells in tumors. Trypsin mRNA was expressed in 7 of the 16 cancer cell-bearing tissue specimens in contrast to 1 of the 14 normal alveolar walls. Immunohistochemically, trypsin was positive in the neoplastic cells from 10 patients and in lung adenocarcinoma cell lines (A549, HLC-1, LC-2, and PC-14). An in vitro assay showed a significant increase in idoxuridine (IdU) or bromodeoxyuridine uptake in human pulmonary artery endothelial cells and human umbilical cord vein endothelial cells after treatments with alpha-thrombin or activating peptides; SFLLRN for PAR-1 and SLIGKV for PAR-2, respectively.

CONCLUSIONS

Thus, proliferation of alveolar capillary endothelial cells is initialized in part by PAR activation with serum thrombin and neoplastic cell-released trypsin. These results suggest a synergistic effect of PAR with vascular endothelial growth factor in alveolar angiogenesis.