Stimulation of Rho signaling by pathologic mechanical stretch is a "second hit" to Rho-independent lung injury induced by IL-6

Cell response to mechanical microenvironment cues via Rho signaling: From mechanobiology to mechanomedicine

Mechanical cues in the cell microenvironment such as those from extracellular matrix properties, stretching, compression and shear stress, play a critical role in maintaining homeostasis. Upon sensing mechanical stimuli, cells can translate these external forces into intracellular biochemical signals to regulate their cellular behaviors, but the specific mechanisms of mechanotransduction at the molecular level remain elusive. As a subfamily of the Ras superfamily, Rho GTPases have been recognized as key intracellular mechanotransduction mediators that can regulate multiple cell activities such as proliferation, migration and differentiation as well as biological processes such as cytoskeletal dynamics, metabolism, and organ development. However, the upstream mechanosensors for Rho proteins and downstream effectors that respond to Rho signal activation have not been well illustrated. Moreover, Rho-mediated mechanical signals in previous studies are highly context-dependent. In this review, we systematically summarize the types of mechanical cues in the cell microenvironment and provide recent advances on the roles of the Rho-based mechanotransduction in various cell activities, physiological processes and diseases. Comprehensive insights into the mechanical roles of Rho GTPase partners would open a new paradigm of mechanomedicine for a variety of diseases. STATEMENT OF SIGNIFICANCE: In this review, we highlight the critical role of Rho GTPases as signal mediators to respond to physical cues in microenvironment. This article will add a distinct contribution to this set of knowledge by intensively addressing the relationship between Rho signaling and mechanobiology/mechanotransduction/mechanomedcine. This topic has not been discussed by the journal, nor has it yet been developed by the field. The comprehensive picture that will develop, from molecular mechanisms and engineering methods to disease treatment strategies, represents an important and distinct contribution to the field. We hope that this review would help researchers in various fields, especially clinicians, oncologists and bioengineers, who study Rho signal pathway and mechanobiology/mechanotransduction, understand the critical role of Rho GTPase in mechanotransduction.

Rho-Proteins and Downstream Pathways as Potential Targets in Sepsis and Septic Shock: What Have We Learned from Basic Research

Sepsis and septic shock are associated with acute and sustained impairment in the function of the cardiovascular system, kidneys, lungs, liver, and brain, among others. Despite the significant advances in prevention and treatment, sepsis and septic shock sepsis remain global health problems with elevated mortality rates. Rho proteins can interact with a considerable number of targets, directly affecting cellular contractility, actin filament assembly and growing, cell motility and migration, cytoskeleton rearrangement, and actin polymerization, physiological functions that are intensively impaired during inflammatory conditions, such as the one that occurs in sepsis. In the last few decades, Rho proteins and their downstream pathways have been investigated in sepsis-associated experimental models. The most frequently used experimental design included the exposure to bacterial lipopolysaccharide (LPS), in both in vitro and in vivo approaches, but experiments using the cecal ligation and puncture (CLP) model of sepsis have also been performed. The findings described in this review indicate that Rho proteins, mainly RhoA and Rac1, are associated with the development of crucial sepsis-associated dysfunction in different systems and cells, including the endothelium, vessels, and heart. Notably, the data found in the literature suggest that either the inhibition or activation of Rho proteins and associated pathways might be desirable in sepsis and septic shock, accordingly with the cellular system evaluated. This review included the main findings, relevance, and limitations of the current knowledge connecting Rho proteins and sepsis-associated experimental models.

ROCK inhibitor attenuates carbon blacks-induced pulmonary fibrosis in mice via Rho/ROCK/NF-kappa B pathway

Exposure to carbon blacks (CBs) has been associated with the progression of pulmonary fibrosis, whereas the mechanism is still not clear. We therefore aimed to investigate the effect of RhoA/ROCK pathway on pulmonary fibrosis caused by CBs exposure. Western blot analysis indicated that CBs could promote the activation of RhoA/ROCK pathway and phosphorylation of p65 and IκBα in mice lung. However, ROCK inhibitor Y-27632 could attenuate phosphorylation levels of p65 and IκBα and restore histopathological changes of the lung tissue. Then, we evaluated the effect of RhoA/ROCK pathway on pulmonary fibrosis by detecting the expression levels of α-SMA, vimentin, and Collagen type-I (Col-I), which could be partly inhibited by Y-27632. It was assumed that inhibition of ROCK could be a promising therapeutic candidate for CBs-induced pulmonary fibrosis, which possibly through the blockage of RhoA/ROCK/NF-κB pathway.

COVID-19 and Oxidative Stress

Pathogenesis of the novel coronavirus infection COVID-19 is the subject of active research around the world. COVID-19 caused by the SARS-CoV-2 is a complex disease in which interaction of the virus with target cells, action of the immune system and the body’s systemic response to these events are closely intertwined. Many respiratory viral infections, including COVID-19, cause death of the infected cells, activation of innate immune response, and secretion of inflammatory cytokines. All these processes are associated with the development of oxidative stress, which makes an important contribution to pathogenesis of the viral infections. This review analyzes information on the oxidative stress associated with the infections caused by SARS-CoV-2 and other respiratory viruses. The review also focuses on involvement of the vascular endothelium in the COVID-19 pathogenesis.

Inhibiting the ROCK Pathway Ameliorates Acute Lung Injury in Mice following Myocardial Ischemia/reperfusion

To clarify the role of Y-27632, a selective inhibitor of Rho-associated coiled-coil forming protein kinase (ROCK), in acute lung injury (ALI) induced by myocardial ischemia/reperfusion (I/R). Mice were randomized into Sham, I/R, and Y-27632 (10, 20 or 30 mg/kg) + I/R groups, and hemodynamics, infarcted area, the protein concentration, neutrophils in bronchoalveolar lavage fluid (BALF), malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) levels were assessed. Pathological changes were evaluated by hematoxylin-eosin (HE) staining; protein and gene expression were measured by Western blotting, enzyme-linked immunosorbent assay (ELISA), immunohistochemistry and quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR); and apoptosis was assessed by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) staining. ROCK1 and ROCK2 expression was up-regulated in lung tissues of I/R mice compared to sham mice. Y-27632 decreased the protein concentration and the neutrophils in BALF in I/R mice, improved hemodynamics and reduced infarct size (IS)/area at risk (AAR) ratio. In addition, pathological changes in lung tissues of Y-27632-treated mice were mitigated, and these alterations were accompanied by decreases in MDA levels in lung tissues and increases in SOD and GSH-Px levels. Moreover, in I/R group, the number of apoptotic cells in lung tissue was higher than that in sham group, and p53, Caspase-3 and Bax expression was up-regulated; however, following treatment with Y-27632 (10, 20 and 30 mg/kg), these changes were reversed. Inhibition of ROCK pathway by Y-27632 ameliorated ALI in myocardial I/R mice by mitigating oxidative stress, inflammation and cell apoptosis.

Transient receptor potential canonical 1 channel mediates the mechanical stress‑induced epithelial‑mesenchymal transition of human bronchial epithelial (16HBE) cells

Airway remodeling is a central event in the pathology of chronic obstructive pulmonary disease (COPD) that leads to airway narrowing and subsequently, to increased mechanical pressure. High mechanical pressure can exacerbate airway remodeling. Thus, a treatment regimen aimed at disrupting this high-pressure airway remodeling vicious cycle may improve the prognosis of patients with COPD. Recent studies have demonstrated that mechanical stress induces lung epithelial-mesenchymal transition (EMT), which is commonly present in airway epithelial cells of patients with COPD. As TRPC1 functions as a mechanosensitive channel that mediates non-selective cation entry in response to increased membrane stretch, the present study investigated the role of TRPC1 in the occurrence of EMT induced by mechanical stress. In the present study, the expression of TRPC1 in the bronchial epithelium was examined in vivo by immunohistochemistry. In vitro, human bronchial epithelial (16HBE) cells were subjected to mechanical stretching for up to 48 h, and TRPC1 expression was then examined by RT-qPCR and western blot analysis. In addition, TRPC1 receptor function was assessed by Ca²⁺ imaging and siRNA transfection. EMT was identified using immunofluorescence, western blot analysis and RT-qPCR. It was found that TRPC1 expression was upregulated in patients with COPD and in 16HBE cells subjected to mechanical stretch. The mechanical stress-induced activation of TRPC1 in 16HBE cells increased the intracellular calcium concentration and subsequently decreased the expression of cytokeratin 8 and E-cadherin, and increased the expression of α-smooth muscle actin, indicating the occurrence of EMT. On the whole, the findings of the present study demonstrate that TRPC1 plays a key role in the occurrence of EMT in human lung epithelial cells in response to mechanical stretch; thus, this protein may serve as a novel therapeutic target for progressive airway remodeling in COPD.

The RNFT2/IL-3Rα axis regulates IL-3 signaling and innate immunity

Interleukin-3 (IL-3) receptor α (IL-3Rα) is the α subunit of the ligand-specific IL-3R and initiates intracellular signaling in response to IL-3. IL-3 amplifies proinflammatory signaling and cytokine storm in murine sepsis models. Here we found that RNFT2 (RING finger transmembrane-domain containing protein 2, also TMEM118), a previously uncharacterized RING finger ubiquitin E3 ligase, negatively regulated IL-3-dependent cellular responses through IL-3Rα ubiquitination and degradation in the proteasome. In vitro, IL-3 stimulation promoted IL-3Rα proteasomal degradation dependent on RNFT2, and we identified IL-3Rα lysine 357 as a ubiquitin acceptor site. We determined that LPS priming reduces RNFT2 abundance, extends IL-3Rα half-life, and sensitizes cells to the effects of IL-3, acting synergistically to increase proinflammatory signaling. In vivo, IL-3 synergized with LPS to exacerbate lung inflammation in LPS and Pseudomonas aeruginosa-challenged mice; conversely, IL-3 neutralization reduced LPS-induced lung injury. Further, RNFT2 overexpression reduced lung inflammation and injury, whereas Rnft2 knockdown exacerbated inflammatory responses in LPS-induced murine lung injury. Last, we examined RNFT2 and IL-3Rα in human lung explants from patients with cystic fibrosis and also showed that IL-3 is elevated in mechanically ventilated critically ill humans at risk for acute respiratory distress syndrome. These results identify RNFT2 as a negative regulator of IL-3Rα and show a potential role for the RNFT2/IL-3Rα/IL-3 axis in regulating innate immune responses in the lung.

Biomechanical Forces and Oxidative Stress: Implications for Pulmonary Vascular Disease

Significance: Oxidative stress in the cell is characterized by excessive generation of reactive oxygen species (ROS). Superoxide (O₂^-) and hydrogen peroxide (H₂O₂) are the main ROS involved in the regulation of cellular metabolism. As our fundamental understanding of the underlying causes of lung disease has increased it has become evident that oxidative stress plays a critical role. Recent Advances: A number of cells in the lung both produce, and respond to, ROS. These include vascular endothelial and smooth muscle cells, fibroblasts, and epithelial cells as well as the cells involved in the inflammatory response, including macrophages, neutrophils, eosinophils. The redox system is involved in multiple aspects of cell metabolism and cell homeostasis. Critical Issues: Dysregulation of the cellular redox system has consequential effects on cell signaling pathways that are intimately involved in disease progression. The lung is exposed to biomechanical forces (fluid shear stress, cyclic stretch, and pressure) due to the passage of blood through the pulmonary vessels and the distension of the lungs during the breathing cycle. Cells within the lung respond to these forces by activating signal transduction pathways that alter their redox state with both physiologic and pathologic consequences. Future Directions: Here, we will discuss the intimate relationship between biomechanical forces and redox signaling and its role in the development of pulmonary disease. An understanding of the molecular mechanisms induced by biomechanical forces in the pulmonary vasculature is necessary for the development of new therapeutic strategies.

Mechanical Ventilation Induces Desensitization of Lung Axl Tyrosine Kinase Receptors

BACKGROUND

Lower tidal volumes are increasingly used in acute respiratory distress syndrome, but mortality has changed little in the last 20 yr. Therefore, in addition to ventilator settings, it is important to target molecular mediators of injury. Sepsis and other inflammatory states increase circulating concentrations of Gas6, a ligand for the antiinflammatory receptor Axl, and of a soluble decoy form of Axl. We investigated the effects of lung stretch on Axl signaling.

METHODS

We used a mouse model of early injury from high tidal volume and assessed the effects of inhibiting Axl on in vivo lung injury (using an antagonist R428, n = 4/group). We further determined the effects of stretch on Axl activation using in vitro lung endothelial cells.

RESULTS

High tidal volume caused mild injury (compliance decreased 6%) as intended, and shedding of the Axl receptor (soluble Axl in bronchoalveolar fluid increased 77%). The Axl antagonist R428 blocked the principal downstream Axl target (suppressor of cytokine signaling 3 [SOCS3]) but did not worsen lung physiology or inflammation. Cyclic stretch in vitro caused Axl to become insensitive to activation by its agonist, Gas6. Finally, in vitro Axl responses were rescued by blocking stretch-activated calcium channels (using guanidinium chloride [GdCl3]), and the calcium ionophore ionomycin replicated the effect of stretch.

CONCLUSIONS

These data suggest that lung endothelial cell overdistention activates ion channels, and the resultant influx of Ca inactivates Axl. Downstream inactivation of Axl by stretch was not anticipated; preventing this would be required to exploit Axl receptors in reducing lung injury.

Molecular Mechanisms of Ventilator-Induced Lung Injury

OBJECTIVE

Mechanical ventilation (MV) has long been used as a life-sustaining approach for several decades. However, researchers realized that MV not only brings benefits to patients but also cause lung injury if used improperly, which is termed as ventilator-induced lung injury (VILI). This review aimed to discuss the pathogenesis of VILI and the underlying molecular mechanisms.

DATA SOURCES

This review was based on articles in the PubMed database up to December 2017 using the following keywords: "ventilator-induced lung injury", "pathogenesis", "mechanism", and "biotrauma".

STUDY SELECTION

Original articles and reviews pertaining to mechanisms of VILI were included and reviewed.

RESULTS

The pathogenesis of VILI was defined gradually, from traditional pathological mechanisms (barotrauma, volutrauma, and atelectrauma) to biotrauma. High airway pressure and transpulmonary pressure or cyclic opening and collapse of alveoli were thought to be the mechanisms of barotraumas, volutrauma, and atelectrauma. In the past two decades, accumulating evidence have addressed the importance of biotrauma during VILI, the molecular mechanism underlying biotrauma included but not limited to proinflammatory cytokines release, reactive oxygen species production, complement activation as well as mechanotransduction.

CONCLUSIONS

Barotrauma, volutrauma, atelectrauma, and biotrauma contribute to VILI, and the molecular mechanisms are being clarified gradually. More studies are warranted to figure out how to minimize lung injury induced by MV.

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.

Microtubules-associated Rac regulation of endothelial barrier: a role of Asef in acute lung injury

The endothelial barrier function regulated by the cytoskeletal reorganizations has been implicated in the pathogenesis of multiple lung diseases including asthma, sepsis, edema, and acute respiratory distress syndrome. The extensive studies have established that activation of small GTPase Rac is a key mechanism in endothelial barrier protection but the role of microtubules-associated Rac in the endothelial functions remains poorly understood. With the emerging evidences that microtubules disassembly also plays a critical role in actin cytoskeleton remodeling leading to endothelial permeability, the knowledge on microtubules-mediated regulation of endothelial barrier is imperative to better understand the etiology of lung injuries as well as to develop novel therapeutics against these disorders. In this regard, our recent studies have revealed some novel aspects of microtubules-mediated regulation of endothelial barrier functions and unraveled a putative role of Rac-specific guanine nucleotide exchange factor Asef in mediating the barrier protective effects of hepatocyte growth factor. In this review, we will discuss the role of this novel Rac activator Asef in endothelial barrier protection and its regulation by microtubules.

Dephosphorylation of Y685-VE-Cadherin Involved in Pulmonary Microvascular Endothelial Barrier Injury Induced by Angiotensin II

Angiotensin II (AngII) caused pulmonary microvascular endothelial barrier injury, which induced acute aortic dissection (AAD) combined with acute lung injury (ALI). However, the exact mechanism is unclear. We investigated the role of dephosphorylation of Y685-VE-cadherin in the AngII induced pulmonary microvascular endothelial barrier injury. Mice or pulmonary microvascular endothelial cells (PMVECs) were divided into control group, AngII group, AngII+PP2 (Src kinase inhibitor) group, and PP2 group. PP2 was used to inhibit the phosphorylation of Y685-VE-cadherin. Pathological changes, infiltration of macrophages and neutrophils, and pulmonary microvascular permeability were used to determine the pulmonary microvascular endothelial barrier function. Flow cytometry was used to determine the apoptosis of PMVECs, and immunofluorescence was used to determine the skeletal arrangement. Transendothelial resistance was used to detect the permeability of endothelial barrier. Phosphorylation of Y685-VE-cadherin was significantly reduced after AngII stimulation (P < 0.05), together with skeletal rearrangement, and elevation of endothelial permeability which finally induced endothelial barrier injury. After PP2 interference, the phosphorylation of Y685-VE-cadherin was further reduced and the endothelial permeability was further elevated. These data indicated that AngII could induce pulmonary injury by triggering endothelial barrier injury, and such process may be related to the dephosphorylation of Y685-VE-cadherin and the endothelial skeletal rearrangement.

VE-cadherin involved in the pulmonary microvascular endothelial cell barrier injury induced by angiotensin II through modulating the cellular apoptosis and skeletal rearrangement

OBJECTIVE

Angiotensin II (AngII) involved in the pathogenesis of pulmonary injury through impairing the integrity of pulmonary microvascular endothelial barrier, but the mechanism is still not clear. We aim to determine the roles of VE-cadherin, playing crucial roles in the adhesion of the vascular endothelial barrier and the barrier function, in the pulmonary microvascular endothelial cell (PMVEC) barrier injury mediated by AngII.

METHODS

Mice acute lung injury (ALI) model was induced through pumping of AngII. The infiltration of macrophages and neutrophils as well as the PMVEC permeability were determined in order to determine the barrier injury in vivo and in vitro. Knockdown of VE-cadherin was established using siRNA technique, and its roles in the apoptosis and skeletal rearrangement in the PMVECs were evaluated.

RESULTS

After AngII interference, the expression of VE-cadherin in the PMVECs and pulmonary tissues in mice was down-regulated. Upon VE-cadherin knockdown through siRNA technique, AngII induced susceptibility of PMVECs to apoptosis. Knockdown of VE-cadherin contributed to the skeletal rearrangement in the endothelial cells, together with increase of permeability.

CONCLUSIONS

VE-cadherin expression is closely related to the apoptosis and skeletal rearrangement of PMVECs induced by AngII.

Selective Role of Vinculin in Contractile Mechanisms of Endothelial Permeability

Increased vascular endothelial cell (EC) permeability is a result of intercellular gap formation that may be induced by contraction-dependent and contraction-independent mechanisms. This study investigated a role of the adaptor protein vinculin in EC permeability induced by contractile (thrombin) and noncontractile (IL-6) agonists. Although thrombin and IL-6 caused a similar permeability increase in human pulmonary ECs and disrupted the association between vinculin and vascular endothelial-cadherin, they induced different patterns of focal adhesion (FA) arrangement. Thrombin, but not IL-6, caused formation of large, vinculin-positive FAs, phosphorylation of FA proteins, FA kinase and Crk-associated substrate, and increased vinculin-talin association. Thrombin-induced formation of talin-positive FA and intercellular gaps were suppressed in ECs with small interfering RNA-induced vinculin knockdown. Vinculin knockdown and inhibitors of Rho kinase and myosin-II motor activity also attenuated thrombin-induced EC permeability. Importantly, ectopic expression of the vinculin mutant lacking the F-actin-binding domain decreased thrombin-induced Rho pathway activation and EC permeability. In contrast, IL-6-induced EC permeability did not involve RhoA- or myosin-dependent mechanisms but engaged Janus kinase/signal transducer and activator of transcription-mediated phosphorylation and internalization of vascular endothelial-cadherin. This process was vinculin independent but Janus kinase/tyrosine kinase Src-dependent. These data suggest that vinculin participates in a contractile-dependent mechanism of permeability by integrating FA with stress fibers, leading to maximal RhoA activation and EC permeability response. Vinculin inhibition does not affect contractile-independent mechanisms of EC barrier failure. This study provides, for the first time, a comparative analysis of two alternative mechanisms of vascular endothelial barrier dysfunction and defines a specific role for vinculin in the contractile type of permeability response.

Using cultured endothelial cells to study endothelial barrier dysfunction: Challenges and opportunities

Despite considerable progress in the understanding of endothelial barrier regulation and the identification of approaches that have the potential to improve endothelial barrier function, no drug- or stem cell-based therapy is presently available to reverse the widespread vascular leak that is observed in acute respiratory distress syndrome (ARDS) and sepsis. The translational gap suggests a need to develop experimental approaches and tools that better mimic the complex environment of the microcirculation in which the vascular leak develops. Recent studies have identified several elements of this microenvironment. Among these are composition and stiffness of the extracellular matrix, fluid shear stress, interaction of endothelial cells (ECs) with pericytes, oxygen tension, and the combination of toxic and mechanic injurious stimuli. Development of novel cell culture techniques that integrate these elements would allow in-depth analysis of EC biology that closely approaches the (patho)physiological conditions in situ. In parallel, techniques to isolate organ-specific ECs, to define EC heterogeneity in its full complexity, and to culture patient-derived ECs from inducible pluripotent stem cells or endothelial progenitor cells are likely to advance the understanding of ARDS and lead to development of therapeutics. This review 1) summarizes the advantages and pitfalls of EC cultures to study vascular leak in ARDS, 2) provides an overview of elements of the microvascular environment that can directly affect endothelial barrier function, and 3) discusses alternative methods to bridge the gap between basic research and clinical application with the intent of improving the translational value of present EC culture approaches.

Modulation of Endothelial Inflammation by Low and High Magnitude Cyclic Stretch

Excessive mechanical ventilation exerts pathologic mechanical strain on lung vascular endothelium and promotes endothelial cell (EC) inflammatory activation; however, the specific mechanisms underlying EC inflammatory response caused by mechanical ventilation related cyclic stretch (CS) remain unclear. This study investigated the effects of chronic exposure to CS at physiologic (5%) and pathologic (18%) magnitude on pulmonary EC inflammatory status in control conditions and bacterial lipopolysacharide (LPS)-stimulated conditions. EC exposure to high or low CS magnitudes for 28–72 hrs had distinct effects on EC inflammatory activation. 18% CS increased surface expression of endothelial adhesion molecule ICAM1 and release of its soluble form (sICAM1) and inflammatory cytokine IL-8 by CS-stimulated pulmonary endothelial cells (EC). EC inflammatory activation was not observed in EC exposed to 5% CS. Chronic exposure to 18% CS, but not to 5% CS, augmented ICAM1 and IL-8 production and EC monolayer barrier disruption induced by LPS. 18% CS, but not 5% CS, stimulated expression of RhoA GTPase-specific guanine nucleotide exchange factor GEF-H1. GEF-H1 knockdown using gene-specific siRNA abolished 18% CS-induced ICAM1 expression and sICAM1 and IL-8 release by EC. GEF-H1 knockdown also prevented disruption of EC monolayer integrity and attenuated sICAM1 and IL-8 release in the two-hit model of EC barrier dysfunction caused by combined stimulation with 18% CS and LPS. These data demonstrate that exacerbation of inflammatory response by pulmonary endothelium exposed to excessive mechanical stretch is mediated by CS-induced induction of Rho activating protein GEF-H1.

Activation of Vascular Endothelial Growth Factor (VEGF) Receptor 2 Mediates Endothelial Permeability Caused by Cyclic Stretch

High tidal volume mechanical ventilation and the resultant excessive mechanical forces experienced by lung vascular endothelium are known to lead to increased vascular endothelial leak, but the underlying molecular mechanisms remain incompletely understood. One reported mechanotransduction pathway of increased endothelial cell (EC) permeability caused by high magnitude cyclic stretch (18% CS) involves CS-induced activation of the focal adhesion associated signalosome, which triggers Rho GTPase signaling. This study identified an alternative pathway of CS-induced EC permeability. We show here that high magnitude cyclic stretch (18% CS) rapidly activates VEGF receptor 2 (VEGFR2) signaling by dissociating VEGFR2 from VE-cadherin at the cell junctions. This results in VEGFR2 activation, Src-dependent VE-cadherin tyrosine phosphorylation, and internalization leading to increased endothelial permeability. This process is also accompanied by CS-induced phosphorylation and internalization of PECAM1. Importantly, CS-induced endothelial barrier disruption was attenuated by VEGFR2 inhibition. 18% CS-induced EC permeability was linked to dissociation of cell junction scaffold afadin from the adherens junctions. Forced expression of recombinant afadin in pulmonary endothelium attenuated CS-induced VEGFR2 and VE-cadherin phosphorylation, preserved adherens junction integrity and VEGFR2·VE-cadherin complex, and suppressed CS-induced EC permeability. This study shows for the first time a mechanism whereby VEGFR2 activation mediates EC permeability induced by pathologically relevant cyclic stretch. In this mechanism, CS induces dissociation of the VE-cadherin·VEGFR2 complex localized at the adherens juctions, causing activation of VEGFR2, VEGFR2-mediated Src-dependent phosphorylation of VE-cadherin, disassembly of adherens junctions, and EC barrier failure.

Anti-inflammatory and anti-apoptotic effects of oxysophoridine on lipopolysaccharide-induced acute lung injury in mice

Oxysophoridine (OSR) is an alkaloid with multiple pharmacological activities. This study aimed to investigate the protective effects and underlying mechanisms of OSR on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice. Here, we found that OSR treatment markedly mitigated LPS-induced body weight loss and significant lung injury characterized by the deterioration of histopathology, histologic scores, wet-to-dry ratio, exduate volume, and protein leakage. OSR dramatically attenuated LPS-induced lung inflammation, as evidenced by the reduced levels of total cells, neutrophils, lymphocytes, and macrophages and pro-inflammatory cytokines (i.e., tumor necrosis factor-α, interleukin (IL)-1β, IL-6, and monocyte chemoattractant protein-1) in bronchoalveolar lavage fluid and of their mRNA expression in lung tissues. OSR also inhibited LPS-induced expression and activation of nuclear factor-κB p65 in pulmonary tissue. Additionally, OSR administration markedly prevented LPS-induced pulmonary cell apoptosis in mice, as reflected by the decrease in expression of procaspase-8, procaspase-3, cleaved caspase-8, and cleaved caspase-3, and Bcl-2-associated X/B-cell lymphoma 2 ratio. These results indicate that OSR is a potential therapeutic drug for treating LPS-induced ALI.

Mechanisms of ventilator-induced lung injury in healthy lungs

Mechanical ventilation is an essential method of patient support, but it may induce lung damage, leading to ventilator-induced lung injury (VILI). VILI is the result of a complex interplay among various mechanical forces that act on lung structures, such as type I and II epithelial cells, endothelial cells, macrophages, peripheral airways, and the extracellular matrix (ECM), during mechanical ventilation. This article discusses ongoing research focusing on mechanisms of VILI in previously healthy lungs, such as in the perioperative period, and the development of new ventilator strategies for surgical patients. Several experimental and clinical studies have been conducted to evaluate the mechanisms of mechanotransduction in each cell type and in the ECM, as well as the role of different ventilator parameters in inducing or preventing VILI. VILI may be attenuated by reducing the tidal volume; however, the use of higher or lower levels of positive end-expiratory pressure (PEEP) and recruitment maneuvers during the perioperative period is a matter of debate. Many questions concerning the mechanisms of VILI in surgical patients remain unanswered. The optimal threshold value of each ventilator parameter to reduce VILI is also unclear. Further experimental and clinical studies are necessary to better evaluate ventilator settings during the perioperative period in different types of surgery.

Coming to terms with tissue engineering and regenerative medicine in the lung

Lung diseases such as emphysema, interstitial fibrosis, and pulmonary vascular diseases cause significant morbidity and mortality, but despite substantial mechanistic understanding, clinical management options for them are limited, with lung transplantation being implemented at end stages. However, limited donor lung availability, graft rejection, and long-term problems after transplantation are major hurdles to lung transplantation being a panacea. Bioengineering the lung is an exciting and emerging solution that has the ultimate aim of generating lung tissues and organs for transplantation. In this article we capture and review the current state of the art in lung bioengineering, from the multimodal approaches, to creating anatomically appropriate lung scaffolds that can be recellularized to eventually yield functioning, transplant-ready lungs. Strategies for decellularizing mammalian lungs to create scaffolds with native extracellular matrix components vs. de novo generation of scaffolds using biocompatible materials are discussed. Strengths vs. limitations of recellularization using different cell types of various pluripotency such as embryonic, mesenchymal, and induced pluripotent stem cells are highlighted. Current hurdles to guide future research toward achieving the clinical goal of transplantation of a bioengineered lung are discussed.

Activation of EP4 receptors prevents endotoxin-induced neutrophil infiltration into the airways and enhances microvascular barrier function

BACKGROUND AND PURPOSE

Pulmonary vascular dysfunction is a key event in acute lung injury. We recently demonstrated that PGE₂ , via activation of E-prostanoid (EP)₄ receptors, strongly enhances microvascular barrier function in vitro. The aim of this study was to investigate the beneficial effects of concomitant EP₄ receptor activation in murine models of acute pulmonary inflammation.

EXPERIMENTAL APPROACH

Pulmonary inflammation in male BALB/c mice was induced by LPS (20 μg per mouse intranasally) or oleic acid (0.15 μL·g^-1 , i.v^. ). In-vitro, endothelial barrier function was determined by measuring electrical impedance.

KEY RESULTS

PGE₂ activation of EP₄ receptors reduced neutrophil infiltration, pulmonary vascular leakage and TNF-α concentration in bronchoalveolar lavage fluid from LPS-induced pulmonary inflammation. Similarly, pulmonary vascular hyperpermeability induced by oleic acid was counteracted by EP₄ receptor activation. In lung function assays, the EP₄ agonist ONO AE1-329 restored the increased resistance and reduced compliance upon methacholine challenge in mice treated with LPS or oleic acid. In agreement with these findings, EP₄ receptor activation increased the in vitro vascular barrier function of human and mouse pulmonary microvascular endothelial cells and diminished the barrier disruption induced by LPS. The EP₂ agonist ONO AE1-259 likewise reversed LPS-induced lung dysfunction without enhancing vascular barrier function.

CONCLUSION AND IMPLICATIONS

Our results show that activation of the EP₄ receptor strengthens the microvascular barrier function and thereby ameliorates the pathology of acute lung inflammation, including neutrophil infiltration, vascular oedema formation and airway dysfunction. This suggests a potential benefit for EP₄ agonists in acute pulmonary inflammation.

The intracerebroventricular injection of rimonabant inhibits systemic lipopolysaccharide-induced lung inflammation

We investigated the role of intracerebroventricular (ICV) injection of rimonabant (500ng), a CB1 antagonist, on lipopolysaccharide ((LPS) 5mg/kg)-induced pulmonary inflammation in rats in an isolated perfused lung model. There were decreases in pulmonary capillary pressure (Ppc) and increases in the ((Wet-Dry)/Dry lung weight)/(Ppc) ratio in the ICV-vehicle/LPS group at 4h. There were decreases in TLR4 pathway markers, such as interleukin receptor-associated kinase-1, IκBα, Raf1 and phospho-SFK (Tyr416) at 30min and at 4h increases in IL-6, vascular cell adhesion molecule-1 and myeloperoxidase in lung homogenate. Intracerebroventricular rimonabant attenuated these LPS-induced responses, indicating that ICV rimonabant modulates LPS-initiated pulmonary inflammation.

Mechanical Ventilation Induces an Inflammatory Response in Preinjured Lungs in Late Phase of Sepsis

Mechanical ventilation (MV) may amplify the lung-specific inflammatory response in preinjured lungs by elevating cytokine release and augmenting damage to the alveolar integrity. In this study, we test the hypothesis that MV exerts different negative impacts on inflammatory response at different time points of postlung injury. Basic lung injury was induced by cecal ligation and puncture (CLP) surgery in rats. Physiological indexes including blood gases were monitored during MV and samples were assessed following each experiment. Low V_T (tidal volume) MV caused a slight increase in cytokine release and tissue damage at day 1 and day 4 after sepsis induced lung injury, while cytokine release from the lungs in the two moderately ventilated V_T groups was amplified. Interestingly, in the two groups where rats received low V_T MV, we found that infiltration of inflammatory cells was only profound at day 4 after CLP. Marked elevation of protein leakage indicated a compromise in alveolar integrity in rats that received moderate V_T MV at day 4 following CLP, correlating with architectural damage to the alveoli. Our study indicates that preinjured lungs are more sensitive to mechanical MV at later phases of sepsis, and this situation may be a result of differing immune status.

Alterations of lung microbiota in a mouse model of LPS-induced lung injury

Acute lung injury (ALI) and the more severe acute respiratory distress syndrome are common responses to a variety of infectious and noninfectious insults. We used a mouse model of ALI induced by intratracheal administration of sterile bacterial wall lipopolysaccharide (LPS) to investigate the changes in innate lung microbiota and study microbial community reaction to lung inflammation and barrier dysfunction induced by endotoxin insult. One group of C57BL/6J mice received LPS via intratracheal injection (n = 6), and another received sterile water (n = 7). Bronchoalveolar lavage (BAL) was performed at 72 h after treatment. Bacterial DNA was extracted and used for qPCR and 16S rRNA gene-tag (V3-V4) sequencing (Illumina). The bacterial load in BAL from ALI mice was increased fivefold (P = 0.03). The community complexity remained unchanged (Simpson index, P = 0.7); the Shannon diversity index indicated the increase of community evenness in response to ALI (P = 0.07). Principal coordinate analysis and analysis of similarity (ANOSIM) test (P = 0.005) revealed a significant difference between microbiota of control and ALI groups. Bacteria from families Xanthomonadaceae and Brucellaceae increased their abundance in the ALI group as determined by Metastats test (P < 0.02). In concordance with the 16s-tag data, Stenotrohomonas maltophilia (Xanthomonadaceae) and Ochrobactrum anthropi (Brucellaceae) were isolated from lungs of mice from both groups. Metabolic profiling of BAL detected the presence of bacterial substrates suitable for both isolates. Additionally, microbiota from LPS-treated mice intensified IL-6-induced lung inflammation in naive mice. We conclude that the morbid transformation of ALI microbiota was attributed to the set of inborn opportunistic pathogens thriving in the environment of inflamed lung, rather than the external infectious agents.

A Standardized Traditional Chinese Medicine Preparation Named Yejuhua Capsule Ameliorates Lipopolysaccharide-Induced Acute Lung Injury in Mice via Downregulating Toll-Like Receptor 4/Nuclear Factor-κB

A standardized traditional Chinese medicine preparation named Yejuhua capsule (YJH) has been clinically used in treatments of various acute respiratory system diseases with high efficacy and low toxicity. In this study, we were aiming to evaluate potential effects and to elucidate underlying mechanisms of YJH against lipopolysaccharide- (LPS-) induced acute lung injury (ALI) in mice. Moreover, the chemical analysis and chromatographic fingerprint study were performed for quality evaluation and control of this drug. ALI was induced by intratracheal instillation of LPS (5 mg/kg) into the lung in mice and dexamethasone (5 mg/kg, p.o.) was used as a positive control drug. Results demonstrated that pretreatments with YJH (85, 170, and 340 mg/kg, p.o.) effectively abated LPS-induced histopathologic changes, attenuated the vascular permeability enhancement and edema, inhibited inflammatory cells migrations and protein leakages, suppressed the ability of myeloperoxidase, declined proinflammatory cytokines productions, and downregulated activations of nuclear factor-κB (NF-κB) and expressions of toll-like receptor 4 (TLR4). This study demonstrated that YJH exerted potential protective effects against LPS-induced ALI in mice and supported that YJH was a potential therapeutic drug for ALI in clinic. And its mechanisms were at least partially associated with downregulations of TLR4/NF-κB pathways.

Novel regulators of endothelial barrier function

Endothelial barrier function is an essential and tightly regulated process that ensures proper compartmentalization of the vascular and interstitial space, while allowing for the diffusive exchange of small molecules and the controlled trafficking of macromolecules and immune cells. Failure to control endothelial barrier integrity results in excessive leakage of fluid and proteins from the vasculature that can rapidly become fatal in scenarios such as sepsis or the acute respiratory distress syndrome. Here, we highlight recent advances in our understanding on the regulation of endothelial permeability, with a specific focus on the endothelial glycocalyx and endothelial scaffolds, regulatory intracellular signaling cascades, as well as triggers and mediators that either disrupt or enhance endothelial barrier integrity, and provide our perspective as to areas of seeming controversy and knowledge gaps, respectively.

Differential and opposing effects of imatinib on LPS- and ventilator-induced lung injury

Endothelial dysfunction underlies the pathophysiology of vascular disorders such as acute lung injury (ALI) syndromes. Recent work has identified the Abl family kinases (c-Abl and Arg) as important regulators of endothelial cell (EC) barrier function and suggests that their inhibition by currently available pharmaceutical agents such as imatinib may be EC protective. Here we describe novel and differential effects of imatinib in regulating lung pathophysiology in two clinically relevant experimental models of ALI. Imatinib attenuates endotoxin (LPS)-induced vascular leak and lung inflammation in mice but exacerbates these features in a mouse model of ventilator-induced lung injury (VILI). We next explored these discrepant observations in vitro through investigation of the roles for Abl kinases in cultured lung EC. Imatinib attenuates LPS-induced lung EC permeability, restores VE-cadherin junctions, and reduces inflammation by suppressing VCAM-1 expression and inflammatory cytokine (IL-8 and IL-6) secretion. Conversely, in EC exposed to pathological 18% cyclic stretch (CS) (in vitro model of VILI), imatinib decreases VE-cadherin expression, disrupts cell-cell junctions, and increases IL-8 levels. Downregulation of c-Abl expression with siRNA attenuates LPS-induced VCAM-1 expression, whereas specific reduction of Arg reduces VE-cadherin expression in 18% CS-challenged ECs to mimic the imatinib effects. In summary, imatinib exhibits pulmonary barrier-protective and anti-inflammatory effects in LPS-injured mice and lung EC; however, imatinib exacerbates VILI as well as dysfunction in 18% CS-EC. These findings identify the Abl family kinases as important modulators of EC function and potential therapeutic targets in lung injury syndromes.

Epithelial and endothelial damage induced by mechanical ventilation modes

PURPOSE OF REVIEW

The adult respiratory distress syndrome (ARDS) is a common cause of respiratory failure with substantial impact on public health. Patients with ARDS generally require mechanical ventilation, which risks further lung damage. Recent improvements in ARDS outcomes have been attributed to reductions in deforming stress associated with lung protective mechanical ventilation modes and settings. The following review details the mechanics of the lung parenchyma at different spatial scales and the response of its resident cells to deforming stress in order to provide the biologic underpinnings of lung protective care.

RECENT FINDINGS

Although lung injury is typically viewed through the lens of altered barrier properties and mechanical ventilation-associated immune responses, in this review, we call attention to the importance of heterogeneity and the physical failure of the load bearing cell and tissue elements in the pathogenesis of ARDS. Specifically, we introduce a simple elastic network model to better understand the deformations of lung regions, intra-acinar alveoli and cells within a single alveolus, and consider the role of regional distension and interfacial stress-related injury for various ventilation modes.

SUMMARY

Heterogeneity of stiffness and intercellular and intracellular stress failure are fundamental components of ARDS and their development also depends on the ventilation mode.

The protective effects of the supercritical-carbon dioxide fluid extract of Chrysanthemum indicum against lipopolysaccharide-induced acute lung injury in mice via modulating Toll-like receptor 4 signaling pathway

The supercritical-carbon dioxide fluid extract of Chrysanthemum indicum Linné. (CFE) has been demonstrated to be effective in suppressing inflammation. The aim of this study is to investigate the preventive action and underlying mechanisms of CFE on acute lung injury (ALI) induced by lipopolysaccharide (LPS) in mice. ALI was induced by intratracheal instillation of LPS into lung, and dexamethasone was used as a positive control. Results revealed that pretreatment with CFE abated LPS-induced lung histopathologic changes, reduced the wet/dry ratio and proinflammatory cytokines productions (TNF-α, IL-1β, and IL-6), inhibited inflammatory cells migrations and protein leakages, suppressed the levels of MPO and MDA, and upregulated the abilities of antioxidative enzymes (SOD, CAT, and GPx). Furthermore, the pretreatment with CFE downregulated the activations of NF-κB and the expressions of TLR4/MyD88. These results suggested that CFE exerted potential protective effects against LPS-induced ALI in mice and was a potential therapeutic drug for ALI. Its mechanisms were at least partially associated with the modulations of TLR4 signaling pathways.

Gap junction protein connexin43 exacerbates lung vascular permeability

Increased vascular permeability causes pulmonary edema that impairs arterial oxygenation and thus contributes to morbidity and mortality associated with Acute Respiratory Distress Syndrome and sepsis. Although components of intercellular adhesive and tight junctions are critical for maintaining the endothelial barrier, there has been limited study of the roles of gap junctions and their component proteins (connexins). Since connexins can modulate inflammatory signaling in other systems, we hypothesized that connexins may also regulate pulmonary endothelial permeability. The relationships between connexins and the permeability response to inflammatory stimuli were studied in cultured human pulmonary endothelial cells. Prolonged treatment with thrombin, lipopolysaccharide, or pathological cyclic stretch increased levels of mRNA and protein for the major connexin, connexin43 (Cx43). Thrombin and lipopolysaccharide both increased intercellular communication assayed by transfer of microinjected Lucifer yellow. Although thrombin decreased transendothelial resistance in these cells, the response was attenuated by pretreatment with the connexin inhibitor carbenoxolone. Additionally, the decreases of transendothelial resistance produced by either thrombin or lipopolysaccharide were attenuated by reducing Cx43 expression by siRNA knockdown. Both carbenoxolone and Cx43 knockdown also abrogated thrombin-induced phosphorylation of myosin light chain. Taken together, these data suggest that increased lung vascular permeability induced by inflammatory conditions may be amplified via increased expression of Cx43 and intercellular communication among pulmonary endothelial cells.

GRP78 is a novel receptor initiating a vascular barrier protective response to oxidized phospholipids

Vascular integrity and the maintenance of blood vessel continuity are fundamental features of the circulatory system maintained through endothelial cell-cell junctions. Defects in the endothelial barrier become an initiating factor in several pathologies, including ischemia/reperfusion, tumor angiogenesis, pulmonary edema, sepsis, and acute lung injury. Better understanding of mechanisms stimulating endothelial barrier enhancement may provide novel therapeutic strategies. We previously reported that oxidized phospholipids (oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine [OxPAPC]) promote endothelial cell (EC) barrier enhancement both in vitro and in vivo. This study examines the initiating mechanistic events triggered by OxPAPC to increase vascular integrity. Our data demonstrate that OxPAPC directly binds the cell membrane-localized chaperone protein, GRP78, associated with its cofactor, HTJ-1. OxPAPC binding to plasma membrane-localized GRP78 leads to GRP78 trafficking to caveolin-enriched microdomains (CEMs) on the cell surface and consequent activation of sphingosine 1-phosphate receptor 1, Src and Fyn tyrosine kinases, and Rac1 GTPase, processes essential for cytoskeletal reorganization and EC barrier enhancement. Using animal models of acute lung injury with vascular hyperpermeability, we observed that HTJ-1 knockdown blocked OxPAPC protection from interleukin-6 and ventilator-induced lung injury. Our data indicate for the first time an essential role of GRP78 and HTJ-1 in OxPAPC-mediated CEM dynamics and enhancement of vascular integrity.

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.

Rho GTPases in the regulation of pulmonary vascular barrier function

Pulmonary endothelial permeability is an important determinant of vascular adaptation to changes in oxygen tension, blood pressure, levels of growth factors or inflammatory cytokines. The Ras homologous (Rho) family of guanosine triphosphate phosphatases (Rho GTPases), key regulators of the actin cytoskeleton, regulate endothelial barrier function in response to a variety of environmental factors and signalling agents via the reorganization of the actin cytoskeleton, changes in receptor trafficking or the phosphorylation of junctional proteins. This review provides a brief summary of recent knowledge on Rho-GTPase-mediated effects on pulmonary endothelial barrier function and focuses in particular on their role in pulmonary vascular disorders, including pulmonary hypertension, chronic obstructive pulmonary disease, acute lung injury and acute respiratory distress syndrome.

Targeting the mevalonate cascade as a new therapeutic approach in heart disease, cancer and pulmonary disease

The cholesterol biosynthesis pathway, also known as the mevalonate (MVA) pathway, is an essential cellular pathway that is involved in diverse cell functions. The enzyme 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (HMGCR) is the rate-limiting step in cholesterol biosynthesis and catalyzes the conversion of HMG-CoA to MVA. Given its role in cholesterol and isoprenoid biosynthesis, the regulation of HMGCR has been intensely investigated. Because all cells require a steady supply of MVA, both the sterol (i.e. cholesterol) and non-sterol (i.e. isoprenoid) products of MVA metabolism exert coordinated feedback regulation on HMGCR through different mechanisms. The proper functioning of HMGCR as the proximal enzyme in the MVA pathway is essential under both normal physiologic conditions and in many diseases given its role in cell cycle pathways and cell proliferation, cholesterol biosynthesis and metabolism, cell cytoskeletal dynamics and stability, cell membrane structure and fluidity, mitochondrial function, proliferation, and cell fate. The blockbuster statin drugs ('statins') directly bind to and inhibit HMGCR, and their use for the past thirty years has revolutionized the treatment of hypercholesterolemia and cardiovascular diseases, in particular coronary heart disease. Initially thought to exert their effects through cholesterol reduction, recent evidence indicates that statins also have pleiotropic immunomodulatory properties independent of cholesterol lowering. In this review we will focus on the therapeutic applications and mechanisms involved in the MVA cascade including Rho GTPase and Rho kinase (ROCK) signaling, statin inhibition of HMGCR, geranylgeranyltransferase (GGTase) inhibition, and farnesyltransferase (FTase) inhibition in cardiovascular disease, pulmonary diseases (e.g. asthma and chronic obstructive pulmonary disease (COPD)), and cancer.

Topical application of phosphatidyl-inositol-3,5-bisphosphate for acute lung injury in neonatal swine

Hypoxemic respiratory failure of the neonatal organism involves increased acid sphingomyelinase (aSMase) activity and production of ceramide, a second messenger of a pro-inflammatory pathway that promotes increased vascular permeability, surfactant alterations and alveolar epithelial apoptosis. We comparatively assessed the benefits of topical aSMase inhibition by either imipramine (Imi) or phosphatidylinositol-3,5-bisphosphate (PIP2) when administered into the airways together with surfactant (S) for fortification. In this translational study, a triple-hit acute lung injury model was used that entails repeated airway lavage, injurious ventilation and tracheal lipopolysaccharide instillation in newborn piglets subject to mechanical ventilation for 72 hrs. After randomization, we administered an air bolus (control), S, S+Imi, or S+PIP2. Only in the latter two groups we observed significantly improved oxygenation and ventilation, dynamic compliance and pulmonary oedema. S+Imi caused systemic aSMase suppression and ceramide reduction, whereas the S+PIP2 effect remained compartmentalized in the airways because of the molecule's bulky structure. The surfactant surface tensions improved by S+Imi and S+PIP2 interventions, but only to a minor extent by S alone. S+PIP2 inhibited the migration of monocyte-derived macrophages and granulocytes into airways by the reduction of CD14/CD18 expression on cell membranes and the expression of epidermal growth factors (amphiregulin and TGF-β1) and interleukin-6 as pro-fibrotic factors. Finally we observed reduced alveolar epithelial apoptosis, which was most apparent in S+PIP2 lungs. Exogenous surfactant “fortified” by PIP2, a naturally occurring surfactant component, improves lung function by topical suppression of aSMase, providing a potential treatment concept for neonates with hypoxemic respiratory failure.

Hyperoxia increases the elastic modulus of alveolar epithelial cells through Rho kinase

Patients with acute lung injury are administered high concentrations of oxygen during mechanical ventilation, and while both hyperoxia and mechanical ventilation are necessary, each can independently cause additional injury. However, the precise mechanisms that lead to injury are not well understood. We hypothesized that alveolar epithelial cells may be more susceptible to injury caused by mechanical ventilation because hyperoxia causes cells to be stiffer due to increased filamentous actin (f-actin) formation via the GTPase RhoA and its effecter Rho kinase (ROCK). We examined cytoskeletal structures in cultured murine lung alveolar epithelial cells (MLE-12) under normoxic and hyperoxic (48 h) conditions. We also measured cell elasticity (E) using an atomic force microscope in the indenter mode. Hyperoxia caused increased f-actin stress fibers and bundle formation, an increase in g- and f-actin, an increase in nuclear area and a decrease in nuclear height, and cells became stiffer (higher E). Treatment with an inhibitor (Y-27632) of ROCK significantly decreased E and prevented the cytoskeletal changes, while it did not influence the nuclear height and area. Pre-exposure of cells to hyperoxia promoted detachment when cells were subsequently stretched cyclically, but the ROCK inhibitor prevented this effect. Hyperoxia caused thickening of vinculin focal adhesion plaques, and inhibition of ROCK reduced the formation of distinct focal adhesion plaques. Phosphorylation of focal adhesion kinase was significantly reduced by both hyperoxia and treatment with Y-27632. Hyperoxia caused increased cell stiffness and promoted cell detachment during stretch. These effects were ameliorated by inhibition of ROCK.

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.

In the absence of effector proteins, the Pseudomonas aeruginosa type three secretion system needle tip complex contributes to lung injury and systemic inflammatory responses

Herein we describe a pathogenic role for the Pseudomonas aeruginosa type three secretion system (T3SS) needle tip complex protein, PcrV, in causing lung endothelial injury. We first established a model in which P. aeruginosa wild type strain PA103 caused pneumonia-induced sepsis and distal organ dysfunction. Interestingly, a PA103 derivative strain lacking its two known secreted effectors, ExoU and ExoT [denoted PA103 (ΔU/ΔT)], also caused sepsis and modest distal organ injury whereas an isogenic PA103 strain lacking the T3SS needle tip complex assembly protein [denoted PA103 (ΔPcrV)] did not. PA103 (ΔU/ΔT) infection caused neutrophil influx into the lung parenchyma, lung endothelial injury, and distal organ injury (reminiscent of sepsis). In contrast, PA103 (ΔPcrV) infection caused nominal neutrophil infiltration and lung endothelial injury, but no distal organ injury. We further examined pathogenic mechanisms of the T3SS needle tip complex using cultured rat pulmonary microvascular endothelial cells (PMVECs) and revealed a two-phase, temporal nature of infection. At 5-hours post-inoculation (early phase infection), PA103 (ΔU/ΔT) elicited PMVEC barrier disruption via perturbation of the actin cytoskeleton and did so in a cell death-independent manner. Conversely, PA103 (ΔPcrV) infection did not elicit early phase PMVEC barrier disruption. At 24-hours post-inoculation (late phase infection), PA103 (ΔU/ΔT) induced PMVEC damage and death that displayed an apoptotic component. Although PA103 (ΔPcrV) infection induced late phase PMVEC damage and death, it did so to an attenuated extent. The PA103 (ΔU/ΔT) and PA103 (ΔPcrV) mutants grew at similar rates and were able to adhere equally to PMVECs post-inoculation indicating that the observed differences in damage and barrier disruption are likely attributable to T3SS needle tip complex-mediated pathogenic differences post host cell attachment. Together, these infection data suggest that the T3SS needle tip complex and/or another undefined secreted effector(s) are important determinants of P. aeruginosa pneumonia-induced lung endothelial barrier disruption.

Novel concepts of acute lung injury and alveolar-capillary barrier dysfunction

In this review we summarize recent major advances in our understanding on the molecular mechanisms, mediators, and biomarkers of acute lung injury (ALI) and alveolar-capillary barrier dysfunction, highlighting the role of immune cells, inflammatory and noninflammatory signaling events, mechanical noxae, and the affected cellular and molecular entities and functions. Furthermore, we address novel aspects of resolution and repair of ALI, as well as putative candidates for treatment of ALI, including pharmacological and cellular therapeutic means.

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.

IL-6 trans-signaling promotes pancreatitis-associated lung injury and lethality

Acute lung injury (ALI) is an inflammatory disease with a high mortality rate. Although typically seen in individuals with sepsis, ALI is also a major complication in severe acute pancreatitis (SAP). The pathophysiology of SAP-associated ALI is poorly understood, but elevated serum levels of IL-6 is a reliable marker for disease severity. Here, we used a mouse model of acute pancreatitis-associated (AP-associated) ALI to determine the role of IL-6 in ALI lethality. Il6-deficient mice had a lower death rate compared with wild-type mice with AP, while mice injected with IL-6 were more likely to develop lethal ALI. We found that inflammation-associated NF-κB induced myeloid cell secretion of IL-6, and the effects of secreted IL-6 were mediated by complexation with soluble IL-6 receptor, a process known as trans-signaling. IL-6 trans-signaling stimulated phosphorylation of STAT3 and production of the neutrophil attractant CXCL1 in pancreatic acinar cells. Examination of human samples revealed expression of IL-6 in combination with soluble IL-6 receptor was a reliable predictor of ALI in SAP. These results demonstrate that IL-6 trans-signaling is an essential mediator of ALI in SAP across species and suggest that therapeutic inhibition of IL-6 may prevent SAP-associated ALI.

Endothelial barrier disruption and recovery is controlled by substrate stiffness

Circulating barrier disruptive agonists bind specific cell membrane receptors and trigger signal transduction pathways leading to the activation of cell contractility and endothelial cell (EC) permeability. Although all cells in tissues including vascular EC are surrounded by compliant extracellular matrix, the impact of matrix stiffness on agonist-induced signaling, cytoskeletal remodeling and EC barrier regulation is not well understood. This study examined agonist-induced cytoskeletal and signaling changes associated with EC barrier disruption and recovery using pulmonary EC grown on compliant substrates of physiologically relevant (8.6 kPa) stiffness, very low (0.55 kPa) and very high (42 kPa) stiffness. Human pulmonary microvascular and macrovascular EC grown on 0.55 kPa substrate contained a few actin stress fibers, while stress fiber amount increased with increasing matrix stiffness. Thrombin-induced stress fiber formation was maximal in EC grown on 42 kPa substrate, diminished on 8.6 kPa substrate, and was minimal on 0.55 kPa substrate. These effects were linked to a stiffness-dependent increase in thrombin-induced phosphorylation of the Rho kinase target, myosin light chain phosphatase (MYPT1), and regulatory myosin light chains (MLC). Surprisingly, EC barrier recovery and activation of Rac GTPase-dependent barrier protective signaling reached maximal levels in EC grown on 8.6 kPa, but not on 0.55 kPa substrate. In conclusion, these data show a critical role of extracellular matrix stiffness in the regulation of the Rac/Rho signaling balance during onset and resolution of agonist-induced EC permeability. The optimal conditions for the Rho/Rac signaling switch, which provides an effective and reversible EC cytoskeletal and permeability response to agonist, are reached in cells grown on the matrix of physiologically relevant stiffness.

Diosgenin down-regulates NF-κB p65/p50 and p38MAPK pathways and attenuates acute lung injury induced by lipopolysaccharide in mice

Diosgenin (Dio), a major active component of steroidal sapogenin of the traditional Chinese herb Dioscorea zingiberensis C.H.Wright, shows various activities including anti-inflammatory, anti-thrombotic activities, anti-cancer properties etc. In the present study, we found that diosgenin significantly suppressed the phosphorylation of lung NF-κB p50/p65 and MAPK/p38 in lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice, when given orally at doses of 0.1, 1.0 and 10mg/kg 1h prior to LPS challenge (30 mg/kg, intravenous injection). Moreover, diosgenin attenuated the lung histopathological changes such as pulmonary edema, coagulation and infiltration of inflammatory cells. In addition, diosgenin significantly decreased the lung wet to dry weight (W/D) ratio and nitrite/nitrate content at three doses, and also markedly inhibited LPS-induced body temperature decrease and nitrite/nitrate elevation in plasma. Besides, diosgenin could significantly suppress activation of NF-κB p65/p50, p38 and expression of inducible nitric oxide synthase (iNOS) in LPS-induced THP-1 cells. Our findings indicate the potential application of diosgenin for ALI treatment.