ANP attenuates inflammatory signaling and Rho pathway of lung endothelial permeability induced by LPS and TNFalpha

Reversal of the detrimental effects of social isolation on ischemic cerebral injury and stroke-associated pneumonia by inhibiting small intestinal T-cell migration into the brain and lung

Social isolation (ISO) is associated with an increased risk and poor outcomes of ischemic stroke. However, the roles and mechanisms of ISO in stroke-associated pneumonia (SAP) remain unclear. Adult male mice were single- or pair-housed with an ovariectomized female mouse and then subjected to transient middle cerebral artery occlusion. Isolated mice were treated with the natriuretic peptide receptor A antagonist A71915 or anti-gamma-delta (γδ) TCR monoclonal antibody, whereas pair-housed mice were treated with recombinant human atrial natriuretic peptide (rhANP). Subdiaphragmatic vagotomy (SDV) was performed 14 days before single- or pair-housed conditions. We found that ISO significantly worsened brain and lung injuries relative to pair housing, which was partially mediated by elevated interleukin (IL)-17A levels and the migration of small intestine-derived inflammatory γδ T-cells into the brain and lung. However, rhANP treatment or SDV could ameliorate ISO-exacerbated post-stroke brain and lung damage by reducing IL-17A levels and inhibiting the migration of inflammatory γδ T-cells into the brain and lung. Our results suggest that rhANP mitigated ISO-induced exacerbation of SAP and ischemic cerebral injury by inhibiting small intestine-derived γδ T-cell migration into the lung and brain, which could be mediated by the subdiaphragmatic vagus nerve.

Pleiotropic Roles of Atrial Natriuretic Peptide in Anti-Inflammation and Anti-Cancer Activity

Simple Summary

The relationship between inflammation and carcinogenesis, as well as the response to anti-tumor therapy, is intimate. Atrial natriuretic peptides (ANPs) play a pivotal role in the homeostatic control of blood pressure, electrolytes, and water balance. In addition, ANPs exert immune-modulatory effects in the tissue microenvironment, thus exhibiting a fascinating ability to prevent inflammation-related tumorigenesis and cancer recurrence. In cancers, ANPs show anti-proliferative effects through several molecular pathways. Furthermore, ANPs attenuate the side effects of cancer therapy. Therefore, ANPs have potential therapeutic value in tumors. Here, we summarized the roles of ANPs in diverse aspects of the immune system and the molecular mechanisms underlying the anti-cancer effects of ANPs, contributing to the development of ANP-based anti-cancer agents.

Abstract

The atrial natriuretic peptide (ANP), a cardiovascular hormone, plays a pivotal role in the homeostatic control of blood pressure, electrolytes, and water balance and is approved to treat congestive heart failure. In addition, there is a growing realization that ANPs might be related to immune response and tumor growth. The anti-inflammatory and immune-modulatory effects of ANPs in the tissue microenvironment are mediated through autocrine or paracrine mechanisms, which further suppress tumorigenesis. In cancers, ANPs show anti-proliferative effects through several molecular pathways. Furthermore, ANPs attenuate the side effects of cancer therapy. Therefore, ANPs act on several hallmarks of cancer, such as inflammation, angiogenesis, sustained tumor growth, and metastasis. In this review, we summarized the contributions of ANPs in diverse aspects of the immune system and the molecular mechanisms underlying the anti-cancer effects of ANPs.

RhANP attenuates endotoxin-derived cognitive dysfunction through subdiaphragmatic vagus nerve-mediated gut microbiota-brain axis

BACKGROUND

Atrial natriuretic peptide (ANP) secreted from atrial myocytes is shown to possess anti-inflammatory, anti-oxidant and immunomodulatory effects. The aim of this study is to assess the effect of ANP on bacterial lipopolysaccharide (LPS)-induced endotoxemia-derived neuroinflammation and cognitive impairment.

METHODS

LPS (5 mg/kg) was given intraperitoneally to mice. Recombinant human ANP (rhANP) (1.0 mg/kg) was injected intravenously 24 h before and/or 10 min after LPS injection. Subdiaphragmatic vagotomy (SDV) was performed 14 days before LPS injection or 28 days before fecal microbiota transplantation (FMT). ANA-12 (0.5 mg/kg) was administrated intraperitoneally 30 min prior to rhANP treatment.

RESULTS

LPS (5.0 mg/kg) induced remarkable splenomegaly and an increase in the plasma cytokines at 24 h after LPS injection. There were positive correlations between spleen weight and plasma cytokines levels. LPS also led to increased protein levels of ionized calcium-binding adaptor molecule (iba)-1, cytokines and inducible nitric oxide synthase (iNOS) in the hippocampus. LPS impaired the natural and learned behavior, as demonstrated by an increase in the latency to eat the food in the buried food test and a decrease in the number of entries and duration in the novel arm in the Y maze test. Combined prophylactic and therapeutic treatment with rhANP reversed LPS-induced splenomegaly, hippocampal and peripheral inflammation as well as cognitive impairment. However, rhANP could not further enhance the protective effects of SDV on hippocampal and peripheral inflammation. We further found that PGF mice transplanted with fecal bacteria from rhANP-treated endotoxemia mice alleviated the decreased protein levels of hippocampal polyclonal phosphorylated tyrosine kinase receptor B (p-TrkB), brain-derived neurotrophic factor (BDNF) and cognitive impairment, which was abolished by SDV. Moreover, TrkB/BDNF signaling inhibitor ANA-12 abolished the improving effects of rhANP on LPS-induced cognitive impairment.

CONCLUSIONS

Our results suggest that rhANP could mitigate LPS-induced hippocampal inflammation and cognitive dysfunction through subdiaphragmatic vagus nerve-mediated gut microbiota-brain axis.

Very-Short-Term Sleep Deprivation Slows Early Recovery of Lymphocytes in Septic Patients

Sleep plays an important role in immune function. However, the effects of very-short-term sleep deprivation on the early recovery of immune function after sepsis remain unclear. This study was conducted in the intensive care unit to investigate the effects of 2 consecutive days of sleep deprivation (SD) on lymphocyte recovery over the following few days in septic patients who were recovering from a critical illness. The patients' self-reports of sleep quality was assessed using the Richards–Campbell Sleep Questionnaire at 0 and 24 h after inclusion. The demographic, clinical, laboratory, treatment, and outcome data were collected and compared between the good sleep group and poor sleep group. We found that 2 consecutive days of SD decreased the absolute lymphocyte count (ALC) and ALC recovery at 3 days after SD. Furthermore, post-septic poor sleep decreased the plasma levels of atrial natriuretic peptide (ANP) immediately after 2 consecutive days of SD. The ANP levels at 24 h after inclusion were positively correlated with ALC recovery, the number of CD3⁺ T cells, or the number of CD3⁺ CD4⁺ cells in the peripheral blood on day 5 after inclusion. Our data suggested that very-short-term poor sleep quality could slow down lymphocyte recovery over the following few days in septic patients who were recovering from a critical illness. Our results underscore the significance of very-short-term SD on serious negative effects on the immune function. Therefore, it is suggested that continuous SD or several short-term SD with short intervals should be avoided in septic patients.

Molecular Dambusters: What Is Behind Hyperpermeability in Bradykinin-Mediated Angioedema?

In the last few decades, a substantial body of evidence underlined the pivotal role of bradykinin in certain types of angioedema. The formation and breakdown of bradykinin has been studied thoroughly; however, numerous questions remained open regarding the triggering, course, and termination of angioedema attacks. Recently, it became clear that vascular endothelial cells have an integrative role in the regulation of vessel permeability. Apart from bradykinin, a great number of factors of different origin, structure, and mechanism of action are capable of modifying the integrity of vascular endothelium, and thus, may participate in the regulation of angioedema formation. Our aim in this review is to describe the most important permeability factors and the molecular mechanisms how they act on endothelial cells. Based on endothelial cell function, we also attempt to explain some of the challenging findings regarding bradykinin-mediated angioedema, where the function of bradykinin itself cannot account for the pathophysiology. By deciphering the complex scenario of vascular permeability regulation and edema formation, we may gain better scientific tools to be able to predict and treat not only bradykinin-mediated but other types of angioedema as well.

The Rationale for Angiotensin Receptor Neprilysin Inhibitors in a Multi-Targeted Therapeutic Approach to COVID-19

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) disease (COVID-19) determines the angiotensin converting enzyme 2 (ACE2) down-regulation and related decrease in angiotensin II degradation. Both these events trigger “cytokine storm” leading to acute lung and cardiovascular injury. A selective therapy for COVID-19 has not yet been identified. Clinical trials with remdesivir gave discordant results. Thus, healthcare systems have focused on “multi-targeted” therapeutic strategies aiming at relieving systemic inflammation and thrombotic complications. No randomized clinical trial has demonstrated the efficacy of renin angiotensin system antagonists in reducing inflammation related to COVID-19. Dexamethasone and tocilizumab showed encouraging data, but their use needs to be further validated. The still-controversial efficacy of these treatments highlighted the importance of organ injury prevention in COVID-19. Neprilysin (NEP) might be an interesting target for this purpose. NEP expression is increased by cytokines on lung fibroblasts surface. NEP activity is elevated in acute respiratory distress syndrome and it is conceivable that it is also high in COVID-19. NEP is implicated in the degradation of natriuretic peptides, bradykinin, substance P, adrenomedullin, and apelin that account for prevention of organ injury. Thus, NEP/angiotensin receptor type 1 (AT1R) inhibitor sacubitril/valsartan (SAC/VAL) may increase levels of these molecules and block AT1Rs required for ACE2 endocytosis in SARS-CoV-2 infection. Moreover, SAC/VAL has a positive impact on acute heart failure that is very frequently observed in deceased COVID-19 patients. The current review aims to summarize actual therapeutic strategies for COVID-19 and to examine the data supporting the potential benefits of SAC/VAL in COVID-19 treatment.

An impaired natriuretic peptide hormone system may play a role in COVID-19 severity in vulnerable populations

Advanced age, underlying cardiovascular disease (including hypertension), and obesity are associated with a higher risk of progression to severe hypoxemia, acute respiratory distress syndrome (ARDS), and death in COVID-19-infected patients. African Americans have a higher degree of COVID-19 mortality. The incidence of salt-sensitive hypertension is higher in older individuals and African Americans. Lower circulating levels of natriuretic peptides, key regulators of vascular tone and kidney function, have been associated with salt-sensitive hypertension and obesity. Evidence has accumulated that ANP administered to pulmonary endothelial cells, isolated lungs, and patients suffering from ARDS reduces endothelial damage and preserves the endothelial barrier, thereby reducing pulmonary edema and inflammation. Epidemiologic and pharmacologic data suggest that deficiencies in the natriuretic peptide hormone system may contribute to the development of severe lung pathology in COVID-19 patients, and treatments that augment natriuretic peptide signaling may have potential to limit progression to ARDS.

Possible contribution of the neprilysin/ACE pathway to sepsis in mice

AIM

Omapatrilat is an antagonist of angiotensin-converting (ACE) and neprilysin-neuropeptidase (NEP) enzymes. The aim of our study is to show that omapatrilat may have beneficial effects as a treatment for polymicrobial sepsis.

MAIN METHODS

A cecal ligation and puncture (CLP) sepsis model was used to evaluate 10 and 20 mg/kg doses of omapatrilat in mice (n = 30) fasted for 12 h. The lungs were removed 12 h after CLP, and lung levels of cytokines (tumor necrosis factor-alpha [TNF-α], interleukin-6 [IL-6], NF-κB), iNOS and eNOS mRNA expression, GSH and MDA levels, and ACE and NEP activities were determined. Histopathological examinations were also performed.

KEY FINDINGS

Omapatrilat treatment provided a dose-dependent reduction in oxidative stress and inflammatory parameters in lung tissues. Omapatrilat administration decreased lung iNOS and eNOS mRNA levels at 20 mg/kg dose. Histopathological analysis revealed a decline in the thickening and edema areas in the alveolar septa in the Sepsis+OMA20 group.

SIGNIFICANCE

Omapatrilat, a dual ACE and NEP inhibitor, protected lung tissue from sepsis damage by reducing ACE and NEP activities, by decreasing the mRNA expression levels of pro-inflammatory cytokines (TNF-α, IL-6, and NF-κB), by suppressing leukocyte infiltration and edema, by restoring iNOS and eNOS levels, and by restoring SOD activity and GSH and MDA levels, thereby reducing oxidative stress.

Inflammation and Circulating Natriuretic Peptide Levels

BACKGROUND

NPs (natriuretic peptides) are cardiac-derived hormones that promote natriuresis, diuresis, and vasodilation. Preclinical evidence suggests that nonhemodynamic triggers for NP release exist, with a few studies implicating inflammatory stimuli. We examined the association between inflammation and NP levels in humans.

METHODS

The associations between inflammation and NP levels were examined in 3 independent studies. First, in 5481 MESA (Multi-Ethnic Study of Atherosclerosis) participants, the cross-sectional (exam 1) and longitudinal (exams 1 to 3) associations between circulating IL6 (interleukin-6) and NT-proBNP (N terminal pro B-type natriuretic peptide) levels were examined in multivariable-adjusted models. Second, in a prospective study of 115 healthy individuals, changes in NP levels were quantified following exposure to lipopolysaccharide as an inflammatory stimulus. Third, in 13 435 hospitalized patients, the association between acute inflammatory conditions and circulating NP levels was assessed using multivariable-adjusted models.

RESULTS

At the baseline MESA exam, each 1-unit higher natural log IL6 was associated with 16% higher NT-proBNP level ([95% CI, 10%-22%]; P=0.002). Each 1-unit higher baseline natural log IL6 level also associated with 6% higher NT-proBNP level ([95% CI, 1%-11%]; P=0.02) at 4-year follow-up. In the lipopolysaccharide study, median NT-proBNP levels rose from 21 pg/mL pre-lipopolysaccharide to 54 pg/mL post-lipopolysaccharide, P<0.001. In the hospitalized patient study, acute inflammatory conditions were associated with 36% higher NP levels ([95% CI, 17%-60%]; P<0.001).

CONCLUSIONS

Inflammation appears to be associated with NP release. Interpretation of NP levels should therefore take into account inflammatory conditions.

Extracellular adenosine enhances pulmonary artery vasa vasorum endothelial cell barrier function via Gi/ELMO1/Rac1/PKA-dependent signaling mechanisms

The vasa vasorum (VV), the microvascular network around large vessels, has been recognized as an important contributor to the pathological vascular remodeling in cardiovascular diseases. In bovine and rat models of hypoxic pulmonary hypertension (PH), we have previously shown that chronic hypoxia profoundly increased pulmonary artery (PA) VV permeability, associated with infiltration of inflammatory and progenitor cells in the arterial wall, perivascular inflammation, and structural vascular remodeling. Extracellular adenosine was shown to exhibit a barrier-protective effect on VV endothelial cells (VVEC) via cAMP-independent mechanisms, which involved adenosine A1 receptor-mediated activation of Gi-phosphoinositide 3-kinase-Akt pathway and actin cytoskeleton remodeling. Using VVEC isolated from the adventitia of calf PA, in this study we investigated in more detail the mechanisms linking Gi activation to downstream barrier protection pathways. Using a small-interference RNA (siRNA) technique and transendothelial electrical resistance assay, we found that the adaptor protein, engulfment and cell motility 1 (ELMO1), the tyrosine phosphatase Src homology region 2 domain-containing phosphatase-2, and atypical Gi- and Rac1-mediated protein kinase A activation are implicated in VVEC barrier enhancement. In contrast, the actin-interacting GTP-binding protein, girdin, and the p21-activated kinase 1 downstream target, LIM kinase, are not involved in this response. In addition, adenosine-dependent cytoskeletal rearrangement involves activation of cofilin and inactivation of ezrin-radixin-moesin regulatory cytoskeletal proteins, consistent with a barrier-protective mechanism. Collectively, our data indicate that targeting adenosine receptors and downstream barrier-protective pathways in VVEC may have a potential translational significance in developing pharmacological approach for the VV barrier protection in PH.

The endothelial barrier and cancer metastasis: Does the protective facet of platelet function matter?

Overwhelming evidence suggests that platelets have a detrimental role in promoting cancer spread via platelet-cancer cell interactions linked to thrombotic mechanisms. On the other hand, a beneficial role of platelets in the preservation of the endothelial barrier in inflammatory conditions has been recently described, a phenomenon that could also operate in cancer-related inflammation. It is tempting to speculate that some antiplatelet strategies to combat cancer metastasis may impair the endogenous platelet-dependent mechanisms preserving endothelial barrier function. If the protective function of platelets is impaired, it may lead to increased endothelial permeability and more efficient cancer cell intravasation in the primary tumor and cancer cell extravasation at metastatic sites. In this commentary, we discuss current evidence that could support this hypothesis.

TRIM21 Mitigates Human Lung Microvascular Endothelial Cells' Inflammatory Responses to LPS

Endothelial cell (EC) inflammation is regarded as an important pathogenic feature of many inflammatory diseases, including acute lung injury and sepsis. An increase in EC inflammation results in neutrophil infiltration from the blood to the site of inflammation, further promoting EC permeability. The ubiquitin E3 ligase TRIM21 has been implicated in human disorders; however, the roles of TRIM21 in endothelial dysfunction and acute lung injury have not been reported. Here, we reveal an antiinflammatory property of TRIM21 in a mouse model of acute lung injury and human lung microvascular ECs. Overexpression of TRIM21 by lentiviral vector infection effectively dampened LPS-induced neutrophil infiltration, cytokine release, and edema in mice. TRIM21 inhibited human lung microvascular endothelial cell inflammatory responses as evidenced by attenuation of the NF-κB pathway, release of IL-8, expression of intercellular adhesion molecules, and adhesion of monocytes to ECs. Furthermore, we demonstrated that TRIM21 was predominantly degraded by an increase in its monoubiquitination and lysosomal degradation after inflammatory stimuli. Thus, inhibition of vascular endothelial inflammation by TRIM21 provides a novel therapeutic target to lessen pulmonary inflammation.

Attenuation of lipopolysaccharide-induced lung inflammation by ascorbic acid in rats: Histopathological and ultrastructural study

Introduction:

Lipopolysaccharide is a bacterial endotoxin that induces acute lung injury in experimental animals, which is similar to acute respiratory distress syndrome in humans. The induced tissue trauma ends in fibrosis. Understanding the pathogenesis is important in the prevention and treatment of the complications. This study was assigned to investigate the long-term lipopolysaccharide-induced lung injury and the postulated protective effect of ascorbic acid on these changes.

Materials and methods:

Twenty-four adult male albino rats were divided into three groups. Group I was the controls, group II received lipopolysaccharide and group III received lipopolysaccharide and ascorbic acid. After 30 days of starting treatment, lung tissue samples were obtained.

Results:

Group II lung tissues showed marked thickening of the alveolar septa with collapsed alveolar sacs, detached bronchial epithelium, inflammatory cell infiltration and excessive deposition of collagen. Group III showed mild thickening of the alveolar walls, scanty inflammatory cell infiltration, mild parabronchial fibrosis and less marked collagen deposition. α-Smooth muscle actin staining of group II showed marked expression of the actin-positive cells. Less potential expression of the dye was found in group III. Ultrastructural examination of group II showed evident structural changes in pneumocytes with capillary basement membrane irregularity and interruption compared to uniform basement membrane in group III with less prominent intracellular changes in pneumocytes.

Conclusion:

Ascorbic acid attenuated the inflammatory response and fibrosis in the lungs of rats treated with lipopolysaccharide as evidenced by the histological, immunohistochemical and ultrastructural studies.

Substrate stiffness-dependent exacerbation of endothelial permeability and inflammation: mechanisms and potential implications in ALI and PH (2017 Grover Conference Series)

The maintenance of endothelial barrier integrity is absolutely essential to prevent the vascular leak associated with pneumonia, pulmonary edema resulting from inhalation of toxins, acute elevation to high altitude, traumatic and septic lung injury, acute lung injury (ALI), and its life-threatening complication, acute respiratory distress syndrome (ARDS). In addition to the long-known edemagenic and inflammatory agonists, emerging evidences suggest that factors of endothelial cell (EC) mechanical microenvironment such as blood flow, mechanical strain of the vessel, or extracellular matrix stiffness also play an essential role in the control of endothelial permeability and inflammation. Recent studies from our group and others have demonstrated that substrate stiffening causes endothelial barrier disruption and renders EC more susceptible to agonist-induced cytoskeletal rearrangement and inflammation. Further in vivo studies have provided direct evidence that proinflammatory stimuli increase lung microvascular stiffness which in turn exacerbates endothelial permeability and inflammation and perpetuates a vicious circle of lung inflammation. Accumulating evidence suggests a key role for RhoA GTPases signaling in stiffness-dependent mechanotransduction mechanisms defining EC permeability and inflammatory responses. Vascular stiffening is also known to be a key contributor to other cardiovascular diseases such as arterial pulmonary hypertension (PH), although the precise role of stiffness in the development and progression of PH remains to be elucidated. This review summarizes the current understanding of stiffness-dependent regulation of pulmonary EC permeability and inflammation, and discusses potential implication of pulmonary vascular stiffness alterations at macro- and microscale in development and modulation of ALI and PH.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Dai-Huang-Fu-Zi-Tang alleviates pulmonary and intestinal injury with severe acute pancreatitis via regulating aquaporins in rats

BACKGROUND

Dai-Huang-Fu-Zi-Tang (DHFZT) is a famous traditional Chinese prescription with intestinal obstruction, acute pancreatitis and cholecystalgia for thousands of years. Our previous work found that DHFZT could act against pulmonary and intestinal pathological injury in rats with severe acute pancreatitis (SAP). But the underlying mechanism has not been fully elucidated. The aim of present study was to investigate whether DHFZT could relieve pulmonary and intestinal injury by regulating aquaporins after SAP induced by sodium taurocholate in rats.

METHODS

Forty of SD rats were used for dose dependant experiments of DHFZT.Accurate-mass Time-of-flight liquid chromatography-mass spectrometry was used for qualitative screening of chemical compositions of DHFZT. Twenty-four rats were randomly divided into 3 groups: sham group (n = 8), model group (SAP, n = 8), DHFZT group (SAP with DHFZT treatment, n = 8). SAP models were established by retrograde injections of 5% sodium taurocholate solutions into rat pancreaticobiliary ducts. Blood samples were taken at 0, 12, 24, 48 h post-operation for detecting serum amylase, lipase, endotoxin, TNF-α, IL-6 and IL-10. Protein expression and location of aquaporin (AQP)1, 5, 8 and 9 were assessed by immunohistochemistry, western blot and immunofluorescence respectively.

RESULTS

The study showed that 27 kinds of chemical composition were identified, including 10 kinds in positive ion mode and 17 kinds in negative ion mode. The results showed that AQP1, AQP5 of lung, and AQP1, AQP5, AQP8 of intestine in model group were significantly lower than that of sham group (P < 0.05), and which were obviously reversed by treatment with DHFZT. In addition, protein levels of pro-inflammatory cytokines such as TNF-α, IL-6 and endotoxin in peripheral blood were significantly suppressed by DHFZT, and that anti-inflammatory cytokine like IL-10 was just opposite. Finally, we also noted that DHFZT reduced serum levels of amylase, lipase and endotoxin, and also improved edema and pathological scores of lung and intestine after SAP.

CONCLUSIONS

DHFZT ameliorated the pulmonary and intestinal edema and injury induced by SAP via the upregulation of different AQPs in lung and intestine, and suppressed TNF-α, IL-6 expression and enhanced IL-10 expression.

Anti-Inflammatory Effects of OxPAPC Involve Endothelial Cell-Mediated Generation of LXA4

RATIONALE

Oxidation of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OxPAPC) generates a group of bioactive oxidized phospholipid products with a broad range of biological activities. Barrier-enhancing and anti-inflammatory effects of OxPAPC on pulmonary endothelial cells are critical for prevention of acute lung injury caused by bacterial pathogens or excessive mechanical ventilation. Anti-inflammatory properties of OxPAPC are associated with its antagonistic effects on Toll-like receptors and suppression of RhoA GTPase signaling.

OBJECTIVE

Because OxPAPC exhibits long-lasting anti-inflammatory and lung-protective effects even after single administration in vivo, we tested the hypothesis that these effects may be mediated by additional mechanisms, such as OxPAPC-dependent production of anti-inflammatory and proresolving lipid mediator, lipoxin A4 (LXA4).

METHODS AND RESULTS

Mass spectrometry and ELISA assays detected significant accumulation of LXA4 in the lungs of OxPAPC-treated mice and in conditioned medium of OxPAPC-exposed pulmonary endothelial cells. Administration of LXA4 reproduced anti-inflammatory effect of OxPAPC against tumor necrosis factor-α in vitro and in the animal model of lipopolysaccharide-induced lung injury. The potent barrier-protective and anti-inflammatory effects of OxPAPC against tumor necrosis factor-α and lipopolysaccharide challenge were suppressed in human pulmonary endothelial cells with small interfering RNA-induced knockdown of LXA4 formyl peptide receptor-2 (FPR2/ALX) and in mFPR2^-/- (mouse formyl peptide receptor 2) mice lacking the mouse homolog of human FPR2/ALX.

CONCLUSIONS

This is the first demonstration that inflammation- and injury-associated phospholipid oxidation triggers production of anti-inflammatory and proresolution molecules, such as LXA4. This lipid mediator switch represents a novel mechanism of OxPAPC-assisted recovery of inflamed lung endothelium.

RAGE Plays a Role in LPS-Induced NF-κB Activation and Endothelial Hyperpermeability

Endothelial functional dysregulation and barrier disruption contribute to the initiation and development of sepsis. The receptor for advanced glycation end products (RAGE) has been demonstrated to be involved in the pathogenesis of sepsis. The present study aimed to investigate the role of RAGE in lipopolysaccharide (LPS)-induced nuclear factor-κB (NF-κB) activation in endothelial cells and the consequent endothelial hyperpermeability. LPS-induced upregulation of RAGE protein expression in human umbilical vein endothelial cells (HUVECs) was detected by western blotting. Activation of NF-κB was revealed using western blotting and immunofluorescent staining. LPS-elicited endothelial hyperpermeability was explored by transendothelial electrical resistance (TER) assay and endothelial monolayer permeability assay. The blocking antibody specific to RAGE was used to confirm the role of RAGE in LPS-mediated NF-κB activation and endothelial barrier disruption. We found that LPS upregulated the protein expression of RAGE in a dose- and time-dependent manner in HUVECs. Moreover, LPS triggered a significant phosphorylation and degradation of IκBα, as well as NF-κB p65 nuclear translocation. Moreover, we observed a significant increase in endothelial permeability after LPS treatment. However, the RAGE blocking antibody attenuated LPS-evoked NF-κB activation and endothelial hyperpermeability. Our results suggest that RAGE plays an important role in LPS-induced NF-κB activation and endothelial barrier dysfunction.

Atrial natriuretic peptide down-regulates LPS/ATP-mediated IL-1β release by inhibiting NF-kB, NLRP3 inflammasome and caspase-1 activation in THP-1 cells

Atrial natriuretic peptide (ANP) is an hormone/paracrine/autocrine factor regulating cardiovascular homeostasis by guanylyl cyclase natriuretic peptide receptor (NPR-1). ANP plays an important role also in regulating inflammatory and immune systems by altering macrophages functions and cytokines secretion. Interleukin-1β (IL-1β) is a potent pro-inflammatory cytokine involved in a wide range of biological responses, including the immunological one. Unlike other cytokines, IL-1β production is rigorously controlled. Primarily, NF-kB activation is required to produce pro-IL-1β; subsequently, NALP3 inflammasome/caspase-1 activation is required to cleave pro-IL-1β into the active secreted protein. NALP3 is a molecular platform capable of sensing a large variety of signals and a major player in innate immune defense. Due to their pleiotropism, IL-1β and NALP3 dysregulation is a common feature of a wide range of diseases. Therefore, identifying molecules regulating IL-1β/NALP3/caspase-1 expression is an important step in the development of new potential therapeutic agents. The aim of our study was to evaluate the effect of ANP on IL-1β/NALP3/caspase-1 expression in LPS/ATP-stimulated human THP1 monocytes. We provided new evidence of the direct involvement of ANP/NPR-1/cGMP axis on NF-kB/NALP3/caspase-1-mediated IL-1β release and NF-kB-mediated pro-IL-1β production. In particular, ANP inhibited both NF-kB and NALP3/caspase-1 activation leading to pro- and mature IL-1β down-regulation. Our data, pointing out a modulatory role of this endogenous peptide on IL-1β release and on NF-kB/NALP3/caspase-1 activation, indicate an important anti-inflammatory and immunomodulatory effect of ANP via these mechanisms. We suggest a possible employment of ANP for the treatment of inflammatory/immune-related diseases and IL-1β/NALP3-associated disorders, affecting millions of people worldwide.

The role of atrial natriuretic peptide to attenuate inflammation in a mouse skin wound and individually perfused rat mesenteric microvessels

We tested the hypothesis that the anti‐inflammatory actions of atrial natriuretic peptide (ANP) result from the modulation of leukocyte adhesion to inflamed endothelium and not solely ANP ligation of endothelial receptors to stabilize endothelial barrier function. We measured vascular permeability to albumin and accumulation of fluorescent neutrophils in a full‐thickness skin wound on the flank of LysM‐EGFP mice 24 h after formation. Vascular permeability in individually perfused rat mesenteric microvessels was also measured after leukocytes were washed out of the vessel lumen. Thrombin increased albumin permeability and increased the accumulation of neutrophils. The thrombin‐induced inflammatory responses were attenuated by pretreating the wound with ANP (30 min). During pretreatment ANP did not lower permeability, but transiently increased baseline albumin permeability concomitant with the reduction in neutrophil accumulation. ANP did not attenuate acute increases in permeability to histamine and bradykinin in individually perfused rat microvessels. The hypothesis that anti‐inflammatory actions of ANP depend solely on endothelial responses that stabilize the endothelial barrier is not supported by our results in either individually perfused microvessels in the absence of circulating leukocytes or the more chronic skin wound model. Our results conform to the alternate hypothesis that ANP modulates the interaction of leukocytes with the inflamed microvascular wall of the 24 h wound. Taken together with our previous observations that ANP reduces deformability of neutrophils and their strength of attachment, rolling, and transvascular migration, these observations provide the basis for additional investigations of ANP as an anti‐inflammatory agent to modulate leukocyte–endothelial cell interactions.

Endothelium-Derived 5-Methoxytryptophan Protects Endothelial Barrier Function by Blocking p38 MAPK Activation

The endothelial junction is tightly controlled to restrict the passage of blood cells and solutes. Disruption of endothelial barrier function by bacterial endotoxins, cytokines or growth factors results in inflammation and vascular damage leading to vascular diseases. We have identified 5-methoxytryptophan (5-MTP) as an anti-inflammatory factor by metabolomic analysis of conditioned medium of human fibroblasts. Here we postulated that endothelial cells release 5-MTP to protect the barrier function. Conditioned medium of human umbilical vein endothelial cells (HUVECs) prevented endothelial hyperpermeability and VE-cadherin downregulation induced by VEGF, LPS and cytokines. We analyzed the metabolomic profile of HUVEC conditioned medium and detected 5-MTP but not melatonin, serotonin or their catabolites, which was confirmed by enzyme-linked immunosorbent assay. Addition of synthetic pure 5-MTP preserved VE-cadherin and maintained barrier function despite challenge with pro-inflammatory mediators. Tryptophan hydroxylase-1, an enzyme required for 5-MTP biosynthesis, was downregulated in HUVECs by pro-inflammatory mediators and it was accompanied by reduction of 5-MTP. 5-MTP protected VE-cadherin and prevented endothelial hyperpermeability by blocking p38 MAPK activation. A chemical inhibitor of p38 MAPK, SB202190, exhibited a similar protective effect as 5-MTP. To determine whether 5-MTP prevents vascular hyperpermeability in vivo, we evaluated the effect of 5-MTP administration on LPS-induced murine microvascular permeability with Evans blue. 5-MTP significantly prevented Evans blue dye leakage. Our findings indicate that 5-MTP is a new class of endothelium-derived molecules which protects endothelial barrier function by blocking p38 MAPK.

Chronic high-magnitude cyclic stretch stimulates EC inflammatory response via VEGF receptor 2-dependent mechanism

Ventilator-induced lung injury (VILI) is associated with activated inflammatory signaling, such as cytokine production by endothelial and epithelial cells and macrophages, although the precise mechanisms of inflammatory activation induced by VILI-relevant cyclic stretch (CS) amplitude remain poorly understood. We show that exposure of human pulmonary endothelial cells (EC) to chronic CS at 18% linear distension (18% CS), but not at physiologically relevant 5% CS, induces "EC-activated phenotype," which is characterized by time-dependent increase in ICAM1 and VCAM1 expression. A preconditioning of 18% CS also increased in a time-dependent fashion the release of soluble ICAM1 (sICAM1) and IL-8. Investigation of potential signaling mechanisms of CS-induced EC inflammatory activation showed that 18% CS, but not 5% CS, induced time-dependent upregulation of VEGF receptor 2 (VEGFR2), as monitored by increased protein expression and VEGFR2 tyrosine phosphorylation. Both CS-induced VEGFR2 expression and tyrosine phosphorylation were abrogated by cotreatment with reactive oxygen species inhibitor, N-acetyl cysteine. Molecular inhibition of VEGFR2 expression by gene-specific siRNA or treatment with VEGFR2 pharmacological inhibitor SU-1498 attenuated CS-induced activation of ICAM1 and VCAM1 expression and sICAM1 release. Chronic EC preconditioning at 18% CS augmented EC inflammation and barrier-disruptive response induced by proinflammatory cytokine TNF-α. This effect of chronic 18% CS preconditioning was attenuated by siRNA-induced VEGFR2 knockdown. This study demonstrates for the first time a VEGFR2-dependent mechanism of EC inflammatory activation induced by pathological CS. We conclude that, despite the recognized role of VEGF as a prosurvival and angiogenic factor, excessive activation of VEGFR2 signaling by high-tidal-volume lung mechanical ventilation may contribute to ventilator-induced (biotrauma) lung inflammation and barrier dysfunction by augmenting cell response to VILI-associated inflammatory mediators.

Recombinant human brain natriuretic peptide attenuates trauma-/haemorrhagic shock-induced acute lung injury through inhibiting oxidative stress and the NF-κB-dependent inflammatory/MMP-9 pathway

Acute lung injury (ALI) is one of the most serious complications in traumatic patients and is an important part of multiple organ dysfunction syndrome (MODS). Recombinant human brain natriuretic peptide (rhBNP) is a peptide with a wide range of biological activity. In this study, we investigated local changes in oxidative stress and the NF-κB-dependent matrix metalloproteinase-9 (MMP-9) pathway in rats with trauma/haemorrhagic shock (TH/S)-induced ALI and evaluated the effects of pretreatment with rhBNP. Forty-eight rats were randomly divided into four groups: sham operation group, model group, low-dosage rhBNP group and high-dosage rhBNP group (n = 12 for each group). Oxidative stress and MPO activity were measured by ELISA kits. MMP-9 activity was detected by zymography analysis. NF-κB activity was determined using Western blot assay. With rhBNP pretreatment, TH/S-induced protein leakage, increased MPO activity, lipid peroxidation and metalloproteinase (MMP)-9 activity were inhibited. Activation of antioxidative enzymes was reversed. The phosphorylation of NF-κB and the degradation of its inhibitor IκB were suppressed. The results suggested that the protection mechanism of rhBNP is possibly mediated through upregulation of anti-oxidative enzymes and inhibition of NF-κB activation. More studies are needed to further evaluate whether rhBNP is a suitable candidate as an effective inhaling drug to reduce the incidence of TH/S-induced ALI.

Dexmedetomidine alleviates pulmonary edema by upregulating AQP1 and AQP5 expression in rats with acute lung injury induced by lipopolysaccharide

This study aims to elucidate the mechanisms by which dexmedetomidine alleviates pulmonary edema in rats with acute lung injury induced by lipopolysaccharide (LPS). Male Wistar rats were randomly divided into five groups: normal saline control (NS) group, receiving intravenous 0.9% normal saline (5 mL/kg); LPS group, receiving intravenous LPS (10 mg/kg); small-dose dexmedetomidine (S) group, treated with a small dose of dexmedetomidine (0.5 μg · kg(-1) · h(-1)); medium-dose dexmedetomidine (M) group, treated with a medium dose of dexmedetomidine (2.5 μg · kg(-1) · h(-1)); high-dose dexmedetomidine (H) group, treated with a high dose of dexmedetomidine (5 μg · kg(-1) · h(-1)). The rats were sacrificed 6 h after intravenous injection of LPS or NS, and the lungs were removed for evaluating histological characteristics and determining the lung wet/dry weight ratio (W/D). The levels of tumor necrosis factor-alpha (TNF-α) and interleukin-1β (IL-1β) in the lung tissues were assessed by enzyme- linked immunosorbent assay (ELISA). The mRNA and protein expression levels of aquaporin-1 (AQP1) and aquaporin-5 (AQP5) were detected by RT-PCR, immunohistochemistry, and Western blotting. The lung tissues from the LPS groups were significantly damaged, which were less pronounced in the H group but not in the small-dose dexmedetomidine group or medium-dose dexmedetomidine group. The W/D and the concentrations of TNF-α and IL-1β in the pulmonary tissues were increased in the LPS group as compared with those in NS group, which were reduced in the H group but not in S group or M group (P<0.01). The expression of AQP1 and AQP5 was lower in the LPS group than in the NS group, and significantly increased in the H group but not in the S group or M group (P<0.01). Our findings suggest that dexmedetomidine may alleviate pulmonary edema by increasing the expression of AQP-1 and AQP-5.

Lysosome and Cytoskeleton Pathways Are Robustly Enriched in the Blood of Septic Patients: A Meta-Analysis of Transcriptomic Data

Background. Sepsis is a leading cause of mortality in intensive care units worldwide. A better understanding of the blood systems response to sepsis should expedite the identification of biomarkers for early diagnosis and therapeutic interventions. Methods. We analyzed microarray studies whose data is available from the GEO repository and which were performed on the whole blood of septic patients and normal controls. Results. We identified 6 cohorts consisting of 450 individuals (sepsis = 323, control = 127) providing genome-wide messenger RNA (mRNA) expression data. Through meta-analysis we found the “Lysosome” and “Cytoskeleton” pathways were upregulated in human sepsis patients relative to controls, in addition to previously known signaling pathways (including MAPK, TLR). The key regulatory genes in the “Lysosome” pathway include lysosomal acid hydrolases (e.g., protease cathepsin A, D) as well as the major (LAMP1, 2) and minor (SORT1, LAPTM4B) membrane proteins. In contrast, pathways related to “Ribosome”, “Spliceosome” and “Cell adhesion molecules” were found to be downregulated, along with known pathways for immune dysfunction. Overall, our study revealed distinct mRNA activation profiles and protein-protein interaction networks in blood of human sepsis. Conclusions. Our findings suggest that aberrant mRNA expression in the lysosome and cytoskeleton pathways may play a pivotal role in the molecular pathobiology of human sepsis.

Attenuation of lipopolysaccharide-induced lung vascular stiffening by lipoxin reduces lung inflammation

Reversible changes in lung microstructure accompany lung inflammation, although alterations in tissue micromechanics and their impact on inflammation remain unknown. This study investigated changes in extracellular matrix (ECM) remodeling and tissue stiffness in a model of LPS-induced inflammation and examined the role of lipoxin analog 15-epi-lipoxin A4 (eLXA4) in the reduction of stiffness-dependent exacerbation of the inflammatory process. Atomic force microscopy measurements of live lung slices were used to directly measure local tissue stiffness changes induced by intratracheal injection of LPS. Effects of LPS on ECM properties and inflammatory response were evaluated in an animal model of LPS-induced lung injury, live lung tissue slices, and pulmonary endothelial cell (EC) culture. In vivo, LPS increased perivascular stiffness in lung slices monitored by atomic force microscopy and stimulated expression of ECM proteins fibronectin, collagen I, and ECM crosslinker enzyme, lysyl oxidase. Increased stiffness and ECM remodeling escalated LPS-induced VCAM1 and ICAM1 expression and IL-8 production by lung ECs. Stiffness-dependent exacerbation of inflammatory signaling was confirmed in pulmonary ECs grown on substrates with high and low stiffness. eLXA4 inhibited LPS-increased stiffness in lung cross sections, attenuated stiffness-dependent enhancement of EC inflammatory activation, and restored lung compliance in vivo. This study shows that increased local vascular stiffness exacerbates lung inflammation. Attenuation of local stiffening of lung vasculature represents a novel mechanism of lipoxin antiinflammatory action.

Angiotensin type 1 receptor mediates chronic ethanol consumption-induced hypertension and vascular oxidative stress

OBJECTIVES

We hypothesized that chronic ethanol intake enhances vascular oxidative stress and induces hypertension through renin-angiotensin system (RAS) activation.

METHODS AND RESULTS

Male Wistar rats were treated with ethanol (20% v/v). The increase in blood pressure induced by ethanol was prevented by losartan (10mg/kg/day; p.o. gavage), a selective AT1 receptor antagonist. Chronic ethanol intake increased plasma renin activity (PRA), angiotensin converting enzyme (ACE) activity, plasma angiotensin I (ANG I) and angiotensin II (ANG II) levels and serum aldosterone levels. No differences on plasma osmolality and sodium or potassium levels were detected after treatment with ethanol. Ethanol consumption did not alter ACE activity, as well as the levels of ANG I and ANG II in the rat aorta or mesenteric arterial bed (MAB). Ethanol induced systemic and vascular oxidative stress (aorta and MAB) and these effects were prevented by losartan. The decrease on plasma and vascular nitrate/nitrite (NOx) levels induced by ethanol was prevented by losartan. Ethanol intake did not alter protein expression of ACE, AT1 or AT2 receptors in both aorta and MAB. Aortas from ethanol-treated rats displayed decreased ERK1/2 phosphorylation and increased protein expression of SAPK/JNK. These responses were prevented by losartan. MAB from ethanol-treated rats displayed reduced phosphorylation of p38MAPK and ERK1/2 and losartan did not prevent these responses.

CONCLUSIONS

Our study provides novel evidence that chronic ethanol intake increases blood pressure, induces vascular oxidative stress and decreases nitric oxide (NO) bioavailability through AT1-dependent mechanisms.

Atrial natriuretic peptide prevents cancer metastasis through vascular endothelial cells

Most patients suffering from cancer die of metastatic disease. Surgical removal of solid tumors is performed as an initial attempt to cure patients; however, surgery is often accompanied with trauma, which can promote early recurrence by provoking detachment of tumor cells into the blood stream or inducing systemic inflammation or both. We have previously reported that administration of atrial natriuretic peptide (ANP) during the perioperative period reduces inflammatory response and has a prophylactic effect on postoperative cardiopulmonary complications in lung cancer surgery. Here we demonstrate that cancer recurrence after curative surgery was significantly lower in ANP-treated patients than in control patients (surgery alone). ANP is known to bind specifically to NPR1 [also called guanylyl cyclase-A (GC-A) receptor]. In mouse models, we found that metastasis of GC-A-nonexpressing tumor cells (i.e., B16 mouse melanoma cells) to the lung was increased in vascular endothelium-specific GC-A knockout mice and decreased in vascular endothelium-specific GC-A transgenic mice compared with control mice. We examined the effect of ANP on tumor metastasis in mice treated with lipopolysaccharide, which mimics systemic inflammation induced by surgical stress. ANP inhibited the adhesion of cancer cells to pulmonary arterial and micro-vascular endothelial cells by suppressing the E-selectin expression that is promoted by inflammation. These results suggest that ANP prevents cancer metastasis by inhibiting the adhesion of tumor cells to inflamed endothelial cells.

Prostacyclin post-treatment improves LPS-induced acute lung injury and endothelial barrier recovery via Rap1

Protective effects of prostacyclin (PC) or its stable analog beraprost against agonist-induced lung vascular inflammation have been associated with elevation of intracellular cAMP and Rac GTPase signaling which inhibited the RhoA GTPase-dependent pathway of endothelial barrier dysfunction. This study investigated a distinct mechanism of PC-stimulated lung vascular endothelial (EC) barrier recovery and resolution of LPS-induced inflammation mediated by small GTPase Rap1. Efficient barrier recovery was observed in LPS-challenged pulmonary EC after prostacyclin administration even after 15 h of initial inflammatory insult and was accompanied by the significant attenuation of p38 MAP kinase and NFκB signaling and decreased production of IL-8 and soluble ICAM1. These effects were reproduced in cells post-treated with 8CPT, a small molecule activator of Rap1-specific nucleotide exchange factor Epac. By contrast, pharmacologic Epac inhibitor, Rap1 knockdown, or knockdown of cell junction-associated Rap1 effector afadin attenuated EC recovery caused by PC or 8CPT post-treatment. The key role of Rap1 in lung barrier restoration was further confirmed in the murine model of LPS-induced acute lung injury. Lung injury was monitored by measurements of bronchoalveolar lavage protein content, cell count, and Evans blue extravasation and live imaging of vascular leak over 6 days using a fluorescent tracer. The data showed significant acceleration of lung recovery by PC and 8CPT post-treatment, which was abrogated in Rap1a(-/-) mice. These results suggest that post-treatment with PC triggers the Epac/Rap1/afadin-dependent mechanism of endothelial barrier restoration and downregulation of p38MAPK and NFκB inflammatory cascades, altogether leading to accelerated lung recovery.

Asef mediates HGF protective effects against LPS-induced lung injury and endothelial barrier dysfunction

Increased vascular endothelial permeability and inflammation are major pathological mechanisms of pulmonary edema and its life-threatening complication, the acute respiratory distress syndrome (ARDS). We have previously described potent protective effects of hepatocyte growth factor (HGF) against thrombin-induced hyperpermeability and identified the Rac pathway as a key mechanism of HGF-mediated endothelial barrier protection. However, anti-inflammatory effects of HGF are less understood. This study examined effects of HGF on the pulmonary endothelial cell (EC) inflammatory activation and barrier dysfunction caused by the gram-negative bacterial pathogen lipopolysaccharide (LPS). We tested involvement of the novel Rac-specific guanine nucleotide exchange factor Asef in the HGF anti-inflammatory effects. HGF protected the pulmonary EC monolayer against LPS-induced hyperpermeability, disruption of monolayer integrity, activation of NF-kB signaling, expression of adhesion molecules intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, and production of IL-8. These effects were critically dependent on Asef. Small-interfering RNA-induced downregulation of Asef attenuated HGF protective effects against LPS-induced EC barrier failure. Protective effects of HGF against LPS-induced lung inflammation and vascular leak were also diminished in Asef knockout mice. Taken together, these results demonstrate potent anti-inflammatory effects by HGF and delineate a key role of Asef in the mediation of the HGF barrier protective and anti-inflammatory effects. Modulation of Asef activity may have important implications in therapeutic strategies aimed at the treatment of sepsis and acute lung injury/ARDS-induced gram-negative bacterial pathogens.

Nonstructural protein 1 (NS1)-mediated inhibition of c-Abl results in acute lung injury and priming for bacterial co-infections: insights into 1918 H1N1 pandemic?

BACKGROUND

Nonstructural protein 1 (NS1) proteins from avian influenza viruses like the 1918 pandemic NS1 are capable of inhibiting the key signaling integrator c-Abl (Abl1), resulting in massive cytopathic cell alterations.

METHODS

In the current study, we addressed the consequences of NS1-mediated alteration of c-Abl on acute lung injury and pathogenicity in an in vivo mouse model.

RESULTS

Comparing isogenic strains that differ only in their ability to inhibit c-Abl, we observed elevated pathogenicity for the c-Abl-inhibiting virus. NS1-mediated blockade of c-Abl resulted in severe lung pathology and massive edema formation and facilitated secondary bacterial pneumonia. This phenotype was independent of differences in replication and immune responses, defining it as an NS1 virulence mechanism distinct from its canonical functions. Microarray analysis revealed extensive downregulation of genes involved in cell integrity and vascular endothelial regulation.

CONCLUSIONS

NS1 protein-mediated blockade of c-Abl signaling drives acute lung injury and primes for bacterial coinfections revealing potential insights into the pathogenicity of the 1918 pandemic virus.

Role of microtubules in attenuation of PepG-induced vascular endothelial dysfunction by atrial natriuretic peptide

Apart from control of circulating fluid, atrial natriuretic peptide (ANP) exhibits anti-inflammatory effects in the lung. However, molecular mechanisms of ANP anti-inflammatory effects are not well-understood. Peripheral microtubule (MT) dynamics is essential for agonist-induced regulation of vascular endothelial permeability. Here we studied the role of MT-dependent signaling in ANP protective effects against endothelial cell (EC) barrier dysfunction and acute lung injury induced by Staphylococcus aureus-derived peptidoglican-G (PepG). PepG-induced vascular endothelial dysfunction was accompanied by MT destabilization and disruption of MT network. ANP attenuated PepG-induced MT disassembly, NFκB signaling and activity of MT-associated Rho activator GEF-H1 leading to attenuation of EC inflammatory activation reflected by expression of adhesion molecules ICAM1 and VCAM1. ANP-induced EC barrier preservation and MT stabilization were linked to phosphorylation and inactivation of MT-depolymerizing protein stathmin. Expression of stathmin phosphorylation-deficient mutant abolished ANP protective effects against PepG-induced inflammation and EC permeability. In contrast, siRNA-mediated stathmin knockdown prevented PepG-induced peripheral MT disassembly and endothelial barrier dysfunction. ANP protective effects in a murine model of PepG-induced lung injury were associated with increased phosphorylation of stathmin, while exacerbated lung injury in the ANP knockout mice was accompanied by decreased pool of stable MT. Stathmin knockdown in vivo reversed exacerbation of lung injury in the ANP knockout mice. These results show a novel MT-mediated mechanism of endothelial barrier protection by ANP in pulmonary EC and animal model of PepG-induced lung injury via stathmin-dependent control of MT assembly.

Atrial natriuretic peptide: an old hormone or a new cytokine?

Atrial natriuretic peptide (ANP) a cardiovascular hormone mainly secreted by heart atria in response to stretching forces induces potent diuretic, natriuretic and vasorelaxant effects and plays a major role in the homeostasis of blood pressure as well as of water and salt balance. The hormone can also act as autocrine/paracrine factor and modulate several immune functions as well as cytoprotective effects. ANP contributes to innate immunity being able to: (i) stimulate the host defense against extracellular microbes by phagocytosis and Reactive Oxygen Species (ROS) release; (ii) inhibit the synthesis and release of proinflammatory markers such as TNF-α, IL-1, MCP-1, nitric oxide (NO), cyclooxygenase-2 (COX-2); (iii) inhibit the expression of adhesion molecules such as ICAM-1 and E-selectin. ANP can also affect the adaptive immunity being able to: (i) reduce the number of CD4(+) CD8(+) lymphocytes as well as to increase the CD4(-) CD8(-) cells; (ii) stimulate the differentiation of naïve CD4(+) cells toward the Th2 and/or Th17 phenotype. The hormone shows protective effects during: (i) ventricular hypertrophy and myocardial injury; (ii) atherosclerosis and hypertension by the induction of antiproliferative effects; (iii) oxidative stress counteracting the dangerous effects of ROS; (iv) growth of tumors cells by the induction of apoptosis or necrosis. Since not much is known about of the role of ANP locally produced and released by non-cardiac cells, this review outlines the contribution of ANP in different aspect of innate as well as adaptive immunity also with respect to the excessive cell growth in physiological and/or pathological conditions.

Stiffness-activated GEF-H1 expression exacerbates LPS-induced lung inflammation

Acute lung injury (ALI) is accompanied by decreased lung compliance. However, a role of tissue mechanics in modulation of inflammation remains unclear. We hypothesized that bacterial lipopolysacharide (LPS) stimulates extracellular matrix (ECM) production and vascular stiffening leading to stiffness-dependent exacerbation of endothelial cell (EC) inflammatory activation and lung barrier dysfunction. Expression of GEF-H1, ICAM-1, VCAM-1, ECM proteins fibronectin and collagen, lysyl oxidase (LOX) activity, interleukin-8 and activation of Rho signaling were analyzed in lung samples and pulmonary EC grown on soft (1.5 or 2.8 kPa) and stiff (40 kPa) substrates. LPS induced EC inflammatory activation accompanied by expression of ECM proteins, increase in LOX activity, and activation of Rho signaling. These effects were augmented in EC grown on stiff substrate. Stiffness-dependent enhancement of inflammation was associated with increased expression of Rho activator, GEF-H1. Inhibition of ECM crosslinking and stiffening by LOX suppression reduced EC inflammatory activation and GEF-H1 expression in response to LPS. In vivo, LOX inhibition attenuated LPS-induced expression of GEF-H1 and lung dysfunction. These findings present a novel mechanism of stiffness-dependent exacerbation of vascular inflammation and escalation of ALI via stimulation of GEF-H1-Rho pathway. This pathway represents a fundamental mechanism of positive feedback regulation of inflammation.

Atrial natriuretic peptide inhibits lipopolysaccharide-induced acute lung injury

OBJECTIVES

We recently reported that administration of atrial natriuretic peptide during the perioperative period has prophylactic effects with respect to not only cardiovascular but also respiratory complications following pulmonary resection. However, its mechanisms are not well understood. The objective of the present study was to investigate the mechanism of the prophylactic effects of atrial natriuretic peptide in an acute lung injury model.

METHODS

For the evaluation of the early phase of pulmonary inflammation, in vitro and in vivo studies using lipopolysaccharide were used. In the in vitro study, the effects of atrial natriuretic peptide on the induction of E-selectin by lipopolysaccharide in human pulmonary artery endothelial cells were evaluated. In the in vivo study, the effects of atrial natriuretic peptide on lipopolysaccharide-induced inflammatory cell infiltration and cytokine levels including tumor necrosis factor-alpha and interleukin-6 in the bronchoalveolar lavage fluid in the lungs of C57/B6 mice were examined. The number of myeloperoxidase-positive staining cells in the tissue sections of the lung of lipopolysaccharide-administered C57/B6 mice was also evaluated.

RESULTS

Atrial natriuretic peptide significantly attenuated the up-regulation of E-selectin expression induced by lipopolysaccharide in human pulmonary artery endothelial cells. There were significantly lower cell counts and levels of tumor necrosis factor-alpha and interleukin-6 in the bronchoalveolar lavage fluid of atrial natriuretic peptide-treated mice compared to control mice after lipopolysaccharide injection. In addition, there were significantly fewer myeloperoxidase-positive cells in atrial natriuretic peptide-treated mice than in control mice after lipopolysaccharide injection.

CONCLUSIONS

Atrial natriuretic peptide had a protective effect in the lipopolysaccharide-induced acute lung injury model. Atrial natriuretic peptide may be of value in therapeutic strategies aimed at the treatment of acute lung injury such as pneumonia or acute respiratory distress syndrome.

Control of vascular permeability by atrial natriuretic peptide via a GEF-H1-dependent mechanism

Microtubule (MT) dynamics is involved in a variety of cell functions, including control of the endothelial cell (EC) barrier. Release of Rho-specific nucleotide exchange factor GEF-H1 from microtubules activates the Rho pathway of EC permeability. In turn, pathologic vascular leak can be prevented by treatment with atrial natriuretic peptide (ANP). This study investigated a novel mechanism of vascular barrier protection by ANP via modulation of GEF-H1 function. In pulmonary ECs, ANP suppressed thrombin-induced disassembly of peripheral MT and attenuated Rho signaling and cell retraction. ANP effects were mediated by the Rac1 GTPase effector PAK1. Activation of Rac1-PAK1 promoted PAK1 interaction with the Rho activator GEF-H1, inducing phosphorylation of total and MT-bound GEF-H1 and leading to attenuation of Rho-dependent actin remodeling. In vivo, ANP attenuated lung injury caused by excessive mechanical ventilation and TRAP peptide (TRAP/HTV), which was further exacerbated in ANP(-/-) mice. The protective effects of ANP against TRAP/HTV-induced lung injury were linked to the increased pool of stabilized MT and inactivation of Rho signaling via ANP-induced, PAK1-dependent inhibitory phosphorylation of GEF-H1. This study demonstrates a novel protective mechanism of ANP against pathologic hyperpermeability and suggests a novel pharmacological intervention for the prevention of increased vascular leak via PAK1-dependent modulation of GEF-H1 activity.

Emerging therapeutic strategies to prevent infection-related microvascular endothelial activation and dysfunction

Recent evidence suggests that loss of endothelial barrier function and resulting microvascular leak play important mechanistic roles in the pathogenesis of infection-related end-organ dysfunction and failure. Several distinct therapeutic strategies, designed to prevent or limit infection-related microvascular endothelial activation and permeability, thereby mitigating end-organ injury/dysfunction, have recently been investigated in pre-clinical models. In this review, these potential therapeutic strategies, namely, VEGFR2/Src antagonists, sphingosine-1-phosphate agonists, fibrinopeptide Bβ_15–42, slit2N, secinH3, angiopoietin-1/tie-2 agonists, angiopoietin-2 antagonists, statins, atrial natriuretic peptide, and mesenchymal stromal (stem) cells, are discussed in terms of their translational potential for the management of clinical infectious diseases.

Guanine nucleotide exchange factor-H1 signaling is involved in lipopolysaccharide-induced endothelial barrier dysfunction

BACKGROUND

Gram-negative bacterial lipopolysaccharide (LPS) leads to the pathologic increase of vascular leakage under septic conditions. However, the mechanisms behind LPS-induced vascular hyperpermeability remain incompletely understood. In this study, we tested hypothesis that guanine nucleotide exchange factor-H1 (GEF-H1) signaling might be a key pathway involved in endothelial cells (ECs) barrier dysfunction.

METHODS

The roles of GEF-H1 signaling pathway in LPS-induced ECs barrier dysfunction were accessed by Evans blue dye-labeled albumin (EB-albumin) leak across the human umbilical vein EC (HUVEC) monolayers and Western blot assays. Furthermore, the effect of GEF-H1 signaling on LPS-induced alteration of cytoskeletal proteins and disruption of cell-cell junctions were analyzed by immunofluorescent analysis and Western blot assays, respectively.

RESULTS

We found that LPS could rapidly activated GEF-H1/RhoA/Rho-associated protein kinase (ROCK) signaling pathway in ECs. The LPS-mediated increase in EB-albumin flux across human HUVECs monolayers could be prevented by GEF-H1 depletion or ROCK inactivation. ECs permeability is controlled by actin filaments and cell-cell contact protein complexes. Actin stress fiber formation and/or cell-cell contact proteins loss cause vascular barrier disruption. Here, GEF-H1 knockdown or ROCK inactivation both not only significantly inhibited LPS-induced actin stress fiber formation, phosphorylation of myosin light chain, and myosin-associated phosphatase type 1, but also suppressed LPS-induced loss of occludin, claudin-1, and vascular endothelial (VE)-cadherin in ECs, which suggested that LPS-induced stress fiber formation and cell-cell junctions disruption were closely associated with GEF-H1/RhoA/ROCK signaling activation.

CONCLUSION

Our findings indicate that GEF-H1/RhoA/ROCK pathway in ECs plays an important role in LPS-mediated alteration of cell morphology and disruption of cell-cell junctions, consequently regulate LPS-induced vascular permeability dysfunction.

Cell-type-specific crosstalk between p38 MAPK and Rho signaling in lung micro- and macrovascular barrier dysfunction induced by Staphylococcus aureus-derived pathogens

Lung inflammation and alterations in endothelial cell (EC) micro- and macrovascular permeability are key events to development of acute lung injury. Using ECs derived from human pulmonary artery and lung microvasculature, we investigated the interplay between p38 stress mitogen-activated protein kinase (MAPK) and Rho guanosine triphosphatase signaling in inflammatory and hyperpermeability responses. Both cell types were treated with Staphylococcus aureus-derived peptidoglycan (PepG) and lipoteichoic acid (LTA) with or without pretreatment with p38 MAPK or Rho kinase inhibitors. LTA and PepG increased permeability markedly in both pulmonary macrovascular and microvascular ECs. Agonist-induced hyperpermeability was accompanied by cytoskeletal remodeling, disruption of cell-cell contacts, formation of paracellular gaps, and activation of p38 MAPK, nuclear factor kappa-B (NFκB), and Rho/Rho kinase signaling. In macrovascular ECs, pharmacologic inhibition of Rho kinase with Y27632 suppressed p38 MAP kinase cascade activation significantly, whereas inhibition of p38 MAPK with SB203580 had no effect on Rho activation. In contrast, inhibition of p38 MAPK in microvascular ECs suppressed LTA/PepG-induced activation of Rho, whereas the Rho inhibitor suppressed activation of p38 MAPK. Inhibition of either p38 MAPK or Rho kinase attenuated activation of NFκB signaling substantially. These results demonstrate cell-type-specific differences in signaling induced by Staphylococcus aureus-derived pathogens in pulmonary endothelium. Thus, although Gram-positive bacterial compounds caused barrier dysfunction in both EC types, it was induced by a different pattern of crosstalk between Rho, p38 MAPK, and NFκB signaling. These observations may have important implications in defining microvasculature-specific therapeutic strategies aimed at the treatment of sepsis and acute lung injury induced by Gram-positive bacterial pathogens.

Chlamydia trachomatis inclusion membrane protein CT228 recruits elements of the myosin phosphatase pathway to regulate release mechanisms

Chlamydia trachomatis replicates within a membrane-bound compartment termed an inclusion. The inclusion membrane is modified by the insertion of multiple proteins known as Incs. In a yeast two-hybrid screen, an interaction was found between the inclusion membrane protein CT228 and MYPT1, a subunit of myosin phosphatase. MYPT1 was recruited peripherally around the inclusion, whereas the phosphorylated, inactive form was localized to active Src-family kinase-rich microdomains. Phosphorylated myosin light chain 2 (MLC2), myosin light chain kinase (MLCK), myosin IIA, and myosin IIB also colocalized with inactive MYPT1. The role of these proteins was examined in the context of host-cell exit mechanisms (i.e., cell lysis and extrusion of intact inclusions). Inhibition of myosin II or small interfering RNA depletion of myosin IIA, myosin IIB, MLC2, or MLCK reduced chlamydial extrusion, thus favoring lytic events as the primary means of release. These studies provide insights into the regulation of egress mechanisms by C. trachomatis.

Vascular endothelial cadherin expression in lung specimens of patients with sepsis-induced acute respiratory distress syndrome and endothelial cell cultures

AIMS

Vascular endothelial (VE) cadherin is a cell adhesion molecule localized at endothelial cell (EC) junctions. As a major component of endothelial adherens junctions, its main function is the maintenance and regulation of EC integrity. In the acute respiratory distress syndrome (ARDS), increased vascular permeability is a major mechanism in pulmonary edema and lung dysfunction. In this study, VE-cadherin expression was investigated in ARDS lungs and control tissue as well as in an ARDS cell culture model.

METHODS

Lung specimens of patients with ARDS due to Gram-negative sepsis (n = 20; control lung tissue: n = 41) and cell cultures of human pulmonary microvascular ECs and human umbilical vein ECs stimulated with LPS, TNF-α and IFN-γ were stained with a VE-cadherin antibody. Staining intensity was semiquantitatively evaluated by conventional light and immunofluorescence microscopy.

RESULTS

VE-cadherin expression was statistically significantly reduced in the endothelium of all vessel types in ARDS lungs compared to control tissue. Cell cultures showing disrupted cellular borders confirmed these results.

CONCLUSION

Reduced expression of VE-cadherin has to be considered as a major mechanism of increased vessel permeability in ARDS. The previously described vessel-type-specific expression pattern of VE-cadherin in the human lung is not influenced by ARDS.

Adenosine A1 receptors promote vasa vasorum endothelial cell barrier integrity via Gi and Akt-dependent actin cytoskeleton remodeling

BACKGROUND

In a neonatal model of hypoxic pulmonary hypertension, a dramatic pulmonary artery adventitial thickening, accumulation of inflammatory cells in the adventitial compartment, and angiogenic expansion of the vasa vasorum microcirculatory network are observed. These pathophysiological responses suggest that rapidly proliferating vasa vasorum endothelial cells (VVEC) may exhibit increased permeability for circulating blood cells and macromolecules. However, the molecular mechanisms underlying these observations remain unexplored. Some reports implicated extracellular adenosine in the regulation of vascular permeability under hypoxic and inflammatory conditions. Thus, we aimed to determine the role of adenosine in barrier regulation of VVEC isolated from the pulmonary arteries of normoxic (VVEC-Co) or chronically hypoxic (VVEC-Hyp) neonatal calves.

PRINCIPAL FINDINGS

We demonstrate via a transendothelial electrical resistance measurement that exogenous adenosine significantly enhanced the barrier function in VVEC-Co and, to a lesser extent, in VVEC-Hyp. Our data from a quantitative reverse transcription polymerase chain reaction show that both VVEC-Co and VVEC-Hyp express all four adenosine receptors (A1, A2A, A2B, and A3), with the highest expression level of A1 receptors (A1Rs). However, A1R expression was significantly lower in VVEC-Hyp compared to VVEC-Co. By using an A1R-specific agonist/antagonist and siRNA, we demonstrate that A1Rs are mostly responsible for adenosine-induced enhancement in barrier function. Adenosine-induced barrier integrity enhancement was attenuated by pretreatment of VVEC with pertussis toxin and GSK690693 or LY294002, suggesting the involvement of Gi proteins and the PI3K-Akt pathway. Moreover, we reveal a critical role of actin cytoskeleton in VVEC barrier regulation by using specific inhibitors of actin and microtubule polymerization. Further, we show that adenosine pretreatment blocked the tumor necrosis factor alpha (TNF-α)-induced permeability in VVEC-Co, validating its anti-inflammatory effects.

CONCLUSIONS

We demonstrate for the first time that stimulation of A1Rs enhances the barrier function in VVEC by activation of the Gi/PI3K/Akt pathway and remodeling of actin microfilament.

Histamine H2 receptor activation exacerbates myocardial ischemia/reperfusion injury by disturbing mitochondrial and endothelial function

There is evidence that H2R blockade improves ischemia/reperfusion (I/R) injury, but the underlying cellular mechanisms remain unclear. Histamine is known to increase vascular permeability and induce apoptosis, and these effects are closely associated with endothelial and mitochondrial dysfunction, respectively. Here, we investigated whether activation of the histamine H2 receptor (H2R) exacerbates myocardial I/R injury by increasing mitochondrial and endothelial permeability. Serum histamine levels were measured in patients with coronary heart disease, while the influence of H2R activation was assessed on mitochondrial and endothelial function in cultured cardiomyocytes or vascular endothelial cells, and myocardial I/R injury in mice. The serum histamine level was more than twofold higher in patients with acute myocardial infarction than in patients with angina or healthy controls. In neonatal rat cardiomyocytes, histamine dose-dependently reduced viability and induced apoptosis. Mitochondrial permeability and the levels of p-ERK1/2, Bax, p-DAPK2, and caspase 3 were increased by H2R agonists. In cultured human umbilical vein endothelial cells (HUVECs), H2R activation increased p-ERK1/2 and p-moesin levels and also enhanced permeability of HUVEC monolayer. All of these effects were abolished by the H2R blocker famotidine or the ERK inhibitor U0126. After I/R injury or permanent ischemia, the infarct size was reduced by famotidine and increased by an H2R agonist in wild-type mice. In H2R KO mice, the infarct size was smaller; myocardial p-ERK1/2, p-DAPK2, and mitochondrial Bax were downregulated. These findings indicate that H2R activation exaggerates myocardial I/R injury by promoting myocardial mitochondrial dysfunction and by increasing cardiac vascular endothelial permeability.

Exchange protein directly activated by cAMP (epac): a multidomain cAMP mediator in the regulation of diverse biological functions

Since the discovery nearly 60 years ago, cAMP is envisioned as one of the most universal and versatile second messengers. The tremendous feature of cAMP to tightly control highly diverse physiologic processes, including calcium homeostasis, metabolism, secretion, muscle contraction, cell fate, and gene transcription, is reflected by the award of five Nobel prizes. The discovery of Epac (exchange protein directly activated by cAMP) has ignited a new surge of cAMP-related research and has depicted novel cAMP properties independent of protein kinase A and cyclic nucleotide-gated channels. The multidomain architecture of Epac determines its activity state and allows cell-type specific protein-protein and protein-lipid interactions that control fine-tuning of pivotal biologic responses through the "old" second messenger cAMP. Compartmentalization of cAMP in space and time, maintained by A-kinase anchoring proteins, phosphodiesterases, and β-arrestins, contributes to the Epac signalosome of small GTPases, phospholipases, mitogen- and lipid-activated kinases, and transcription factors. These novel cAMP sensors seem to implement certain unexpected signaling properties of cAMP and thereby to permit delicate adaptations of biologic responses. Agonists and antagonists selective for Epac are developed and will support further studies on the biologic net outcome of the activation of Epac. This will increase our current knowledge on the pathophysiology of devastating diseases, such as diabetes, cognitive impairment, renal and heart failure, (pulmonary) hypertension, asthma, and chronic obstructive pulmonary disease. Further insights into the cAMP dynamics executed by the Epac signalosome will help to optimize the pharmacological treatment of these diseases.

Multiple facets of cAMP signalling and physiological impact: cAMP compartmentalization in the lung

Therapies involving elevation of the endogenous suppressor cyclic AMP (cAMP) are currently used in the treatment of several chronic inflammatory disorders, including chronic obstructive pulmonary disease (COPD). Characteristics of COPD are airway obstruction, airway inflammation and airway remodelling, processes encompassed by increased airway smooth muscle mass, epithelial changes, goblet cell and submucosal gland hyperplasia. In addition to inflammatory cells, airway smooth muscle cells and (myo)fibroblasts, epithelial cells underpin a variety of key responses in the airways such as inflammatory cytokine release, airway remodelling, mucus hypersecretion and airway barrier function. Cigarette smoke, being next to environmental pollution the main cause of COPD, is believed to cause epithelial hyperpermeability by disrupting the barrier function. Here we will focus on the most recent progress on compartmentalized signalling by cAMP. In addition to G protein-coupled receptors, adenylyl cyclases, cAMP-specific phospho-diesterases (PDEs) maintain compartmentalized cAMP signalling. Intriguingly, spatially discrete cAMP-sensing signalling complexes seem also to involve distinct members of the A-kinase anchoring (AKAP) superfamily and IQ motif containing GTPase activating protein (IQGAPs). In this review, we will highlight the interaction between cAMP and the epithelial barrier to retain proper lung function and to alleviate COPD symptoms and focus on the possible molecular mechanisms involved in this process. Future studies should include the development of cAMP-sensing multiprotein complex specific disruptors and/or stabilizers to orchestrate cellular functions. Compartmentalized cAMP signalling regulates important cellular processes in the lung and may serve as a therapeutic target.

Atrial natriuretic peptide attenuates agonist-induced pulmonary edema in mice with targeted disruption of the gene for natriuretic peptide receptor-A

Atrial natriuretic peptide (ANP) inhibits agonist-induced pulmonary edema formation, but the signaling pathway responsible is not well defined. To investigate the role of the particulate guanylate cyclase-linked receptor, natriuretic peptide receptor-A (NPR-A), we measured acute lung injury responses in intact mice and pulmonary microvascular endothelial cells (PMVEC) with normal and disrupted expression of NPR-A. NPR-A wild-type (NPR-A+/+), heterozygous (NPR-A+/-), and knockout (NPR-A-/-) mice were anesthetized and treated with thrombin receptor agonist peptide (TRAP) or lipopolysaccharide (LPS). Lung injury was assessed by lung wet-to-dry (W/D) weight and by protein and cell concentration of bronchoalveolar lavage (BAL) fluid. No difference in pulmonary edema formation was seen between NPR-A genotypes under baseline conditions. TRAP and LPS increased lung W/D weight and BAL fluid cell counts more in NPR-A-/- mice than in NPR-A+/- or NPR-A+/+ mice, but no genotype-related differences were seen in TRAP-induced increases in bloodless lung W/D weight or LPS-induced increases in BAL protein concentration. Pretreatment with ANP infusion completely blocked TRAP-induced increases in lung W/D weight and blunted LPS-induced increases in BAL cell counts and protein concentration in both NPR-A-/- and NPR-A+/+ mice. Thrombin decreased transmembrane electrical resistance in monolayers of PMVECs in vitro, and this effect was attenuated by ANP in PMVECs isolated from both genotypes. Administration of the NPR-C-specific ligand, cANF, also blocked TRAP-induced increases in lung W/D weight and LPS-induced increases in BAL cell count and protein concentration in NPR-A+/+ and NPR-A-/- mice. We conclude that ANP is capable of attenuating agonist-induced lung edema in the absence of NPR-A. The protective effect of ANP on agonist-induced lung injury and pulmonary barrier function may be mediated by NPR-C.