Acute lung injury (ALI) results from infectious challenges and from pathologic lung distention produced by excessive tidal volume delivered during mechanical ventilation (ventilator-induced lung injury [VILI]) and is characterized by extensive alveolar and vascular dysfunction. Identification of novel ALI therapies is hampered by the lack of effective ALI/VILI biomarkers. We explored endothelial cell (EC)-derived microparticles (EMPs) (0.1–1 μm) as potentially important markers and potential mediators of lung vascular injury in preclinical models of ALI and VILI. We characterized EMPs (annexin V and CD31 immunoreactivity) produced from human lung ECs exposed to physiologic or pathologic mechanical stress (5 or 18% cyclic stretch [CS]) or to endotoxin (LPS). EC exposure to 18% CS or to LPS resulted in increased EMP shedding compared with static cells (∼ 4-fold and ∼ 2.5-fold increases, respectively). Proteomic analysis revealed unique 18% CS–derived (n = 10) and LPS-derived EMP proteins (n = 43). VILI-challenged mice (40 ml/kg, 4 h) exhibited increased plasma and bronchoalveolar lavage CD62E (E-selectin)-positive MPs compared with control mice. Finally, mice receiving intratracheal instillation of 18% CS–derived EMPs displayed significant lung inflammation and injury. These findings indicate that ALI/VILI-producing stimuli induce significant shedding of distinct EMP populations that may serve as potential ALI biomarkers and contribute to the severity of lung injury.
microparticles; ventilator-induced lung injury; cyclic stretch; LPS; proteomics
Increased nicotinamide phosphoribosyltransferase (NAMPT) transcription is mechanistically linked to ventilator-induced inflammatory lung injury (VILI), with VILI severity attenuated by reduced NAMPT bioavailability. The molecular mechanisms of NAMPT promoter regulation in response to excessive mechanical stress remain poorly understood. The objective of this study was to define the contribution of specific transcription factors, acute respiratory distress syndrome (ARDS)-associated single nucleotide polymorphisms (SNPs), and promoter demethylation to NAMPT transcriptional regulation in response to mechanical stress. In vivo NAMPT protein expression levels were examined in mice exposed to high tidal volume mechanical ventilation. In vitro NAMPT expression levels were examined in human pulmonary artery endothelial cells exposed to 5 or 18% cyclic stretch (CS), with NAMPT promoter activity assessed using NAMPT promoter luciferase reporter constructs with a series of nested deletions. In vitro NAMPT transcriptional regulation was further characterized by measuring luciferase activity, DNA demethylation, and chromatin immunoprecipitation. VILI-challenged mice exhibited significantly increased NAMPT expression in bronchoalveolar lavage leukocytes and in lung endothelium. A mechanical stress–inducible region (MSIR) was identified in the NAMPT promoter from −2,428 to −2,128 bp. This MSIR regulates NAMPT promoter activity, mRNA expression, and signal transducer and activator of transcription 5 (STAT5) binding, which is significantly increased by 18% CS. In addition, NAMPT promoter activity was increased by pharmacologic promoter demethylation and inhibited by STAT5 silencing. ARDS-associated NAMPT promoter SNPs rs59744560 (−948G/T) and rs7789066 (−2,422A/G) each significantly elevated NAMPT promoter activity in response to 18% CS in a STAT5-dependent manner. Our results show that NAMPT is a key novel ARDS therapeutic target and candidate gene with genetic/epigenetic transcriptional regulation in response to excessive mechanical stress.
acute respiratory distress syndrome; cyclic stretch; nicotinamide phosphoribosyltransferase; B cell colony-enhancing factor; signal transducer and activator of transcription 5
Rationale: Sphingosine kinases (SphKs) 1 and 2 regulate the synthesis of
the bioactive sphingolipid sphingosine-1-phosphate (S1P), an important lipid mediator
that promotes cell proliferation, migration, and angiogenesis.
Objectives: We aimed to examine whether SphKs and their product, S1P,
play a role in the development of pulmonary arterial hypertension (PAH).
SphK2−/−, and S1P lyase
mice, a pharmacologic SphK inhibitor (SKI2), and a S1P receptor 2 (S1PR2) antagonist
(JTE013) were used in rodent models of hypoxia-mediated pulmonary hypertension (HPH).
S1P levels in lung tissues from patients with PAH and pulmonary arteries (PAs) from
rodent models of HPH were measured.
Measurements and Main Results: mRNA and protein levels of
SphK1, but not SphK2, were significantly
increased in the lungs and isolated PA smooth muscle cells (PASMCs) from patients
with PAH, and in lungs of experimental rodent models of HPH. S1P levels were
increased in lungs of patients with PAH and PAs from rodent models of HPH. Unlike
SphK1−/− mice were
protected against HPH, whereas
Sgpl1+/− mice were
more susceptible to HPH. Pharmacologic SphK1 and S1PR2 inhibition prevented the
development of HPH in rodent models of HPH. Overexpression of SphK1 and stimulation
with S1P potentially via ligation of S1PR2 promoted PASMC proliferation in
vitro, whereas SphK1 deficiency inhibited PASMC proliferation.
Conclusions: The SphK1/S1P axis is a novel pathway in PAH that promotes
PASMC proliferation, a major contributor to pulmonary vascular remodeling. Our
results suggest that this pathway is a potential therapeutic target in PAH.
S1P; sphingosine kinase 1; S1P receptor 2; pulmonary arterial hypertension; pulmonary vascular remodeling
Ventilator-induced inflammatory lung injury (VILI) is mechanistically linked to increased NAMPT transcription and circulating levels of nicotinamide phosphoribosyl-transferase (NAMPT/PBEF). Although VILI severity is attenuated by reduced NAMPT/PBEF bioavailability, the precise contribution of NAMPT/PBEF and excessive mechanical stress to VILI pathobiology is unknown. We now report that NAMPT/PBEF induces lung NFκB transcriptional activities and inflammatory injury via direct ligation of Toll–like receptor 4 (TLR4). Computational analysis demonstrated that NAMPT/PBEF and MD-2, a TLR4-binding protein essential for LPS-induced TLR4 activation, share ~30% sequence identity and exhibit striking structural similarity in loop regions critical for MD-2-TLR4 binding. Unlike MD-2, whose TLR4 binding alone is insufficient to initiate TLR4 signaling, NAMPT/PBEF alone produces robust TLR4 activation, likely via a protruding region of NAMPT/PBEF (S402-N412) with structural similarity to LPS. The identification of this unique mode of TLR4 activation by NAMPT/PBEF advances the understanding of innate immunity responses as well as the untoward events associated with mechanical stress-induced lung inflammation.
We previously identified the intracellular nicotinamide phosphoribosyltransferase (iNAMPT, aka pre–B-cell colony enhancing factor) as a candidate gene promoting acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury (VILI) with circulating nicotinamide phosphoribosyltransferase potently inducing NF-κB signaling in lung endothelium. iNAMPT also synthesizes intracellular nicotinamide adenine dinucleotide (iNAD) in response to extracellular oxidative stress, contributing to the inhibition of apoptosis via ill-defined mechanisms. We now further define the role of iNAMPT activity in the pathogenesis of ARDS/VILI using the selective iNAMPT inhibitor FK-866. C57/B6 mice were exposed to VILI (40 ml/kg, 4 h) or LPS (1.5 mg/kg, 18 h) after osmotic pump delivery of FK-866 (100 mg/kg/d, intraperitoneally). Assessment of total bronchoalveolar lavage (BAL) protein, polymorphonuclear neutrophil (PMN) levels, cytokine levels (TNF-α, IL-6, IL-1α), lung iNAD levels, and injury scores revealed that FK-866–mediated iNAMPT inhibition successfully reduced lung tissue iNAD levels, BAL injury indices, inflammatory cell infiltration, and lung injury scores in LPS- and VILI-exposed mice. FK-866 further increased lung PMN apoptosis, as reflected by caspase-3 activation in BAL PMNs. These findings support iNAMPT inhibition via FK-866 as a novel therapeutic agent for ARDS via enhanced apoptosis in inflammatory PMNs.
apoptosis; FK-866; nicotinamide phosphoribosyltransferase; polymorphonuclear neutrophil; vascular endothelium
Myosin light chain kinase (MLCK; gene code, MYLK) is a multifunctional enzyme involved in isoform-specific nonmuscle (nm) and smooth muscle contraction, inflammation, and vascular permeability, processes directly relevant to asthma pathobiology. In this report, we highlight the contribution of the nm isoform (nmMLCK) to asthma susceptibility and severity, supported by studies in two lines of transgenic mice with knocking out nmMLCK or selectively overexpressing nmMLCK in endothelium. These mice were sensitized to exhibit ovalbumin-mediated allergic inflammation. Genetically engineered mice with targeted nmMLCK deletion (nmMLCK−/−) exhibited significant reductions in lung inflammation and airway hyperresponsiveness. Conversely, mice with overexpressed nmMLCK in endothelium (nmMLCKec/ec) exhibited elevated susceptibility and severity in asthmatic inflammation. In addition, reduction of nmMLCK expression in pulmonary endothelium by small interfering RNA results in reduced asthmatic inflammation in wild-type mice. These pathophysiological assessments demonstrate the positive contribution of nmMLCK to asthmatic inflammation, and a clear correlation of the level of nmMLCK with the degree of experimental allergic inflammation. This study confirms MYLK as an asthma candidate gene, and verifies nmMLCK as a novel molecular target in asthmatic pathobiology.
asthma; endothelial permeability; nonmuscle myosin light chain kinase; transgenic mice
Effective therapies are needed to reverse the increased vascular permeability that characterizes acute inflammatory diseases such as acute lung injury (ALI). FTY720 is a pharmaceutical analog of the potent barrier-enhancing phospholipid, sphingosine 1-phosphate (S1P). Because both FTY720 and S1P have properties that may limit their usefulness in patients with ALI, alternative compounds are needed for therapeutic use. The objective of this study is to characterize the effects of FTY720 (S)-phosphonate (Tys), a novel analog of FTY720-phosphate, on parameters of pulmonary vascular permeability in vitro and alveolar-capillary permeability in vivo.
University-affiliated research institute.
Cultured human pulmonary endothelial cells (EC); C57BL/6 mice.
EC were stimulated with S1P receptor 1 (S1PR1) agonists to determine effects on S1PR1 expression. ALI was induced in C57BL/6 mice with bleomycin to assess effects of S1PR1 agonists.
Measurements and Main Results
Tys potently increases human pulmonary EC barrier function in vitro as measured by transendothelial electrical resistance (TER). Reduction of S1P receptor 1 (S1PR1) with siRNA significantly attenuates this TER elevation. Tys maintains endothelial S1PR1 protein expression in contrast to >50% reduction after incubation with S1P, FTY720, or other S1PR1 agonists. Tys does not induce β-arrestin recruitment, S1PR1 ubiquitination, and proteosomal degradation that occur after other agonists. Intraperitoneal administration of Tys every other day for 1 week in normal or bleomycin-injured mice maintains significantly higher lung S1PR1 expression compared with FTY720. FTY720 fails to protect against bleomycin-induced ALI in mice, while Tys significantly decreases lung leak and inflammation.
FTY720 (S)-phosphonate is a promising barrier-promoting agent that effectively maintains S1PR1 levels and improves outcomes in the bleomycin model of ALI.
vascular permeability; endothelium; ubiquitination; ARDS; GPCR; bleomycin
The possibility that mu opioid agonists can influence cancer recurrence is a subject of recent interest. Epidemiologic studies suggested that there were differences in cancer recurrence in breast and prostate cancer contingent on anesthetic regimens. In this study, we identify a possible mechanism for these epidemiologic findings based on mu opioid receptor (MOR) regulation of Lewis lung carcinoma (LLC) tumorigenicity in cell and animal models.
We utilized human lung tissue and human non-small cell lung cancer (NSCLC) cell lines and evaluated MOR expression using immunoblot and immunohistochemical analysis. LLC cells were treated with the peripheral opioid antagonist methylnalnaltrexone (MNTX) or MOR shRNA and evaluated for proliferation, invasion and soft agar colony formation in vitro and primary tumor growth and lung metastasis in C57BL/6 and MOR knockout mice using Visen FMT imaging and immunohistochemical analysis.
We provide several lines of evidence that the MOR may be a potential target for lung cancer, a disease with high mortality and few treatment options. We first observed that there is ~5 to 10 fold increase in MOR expression in lung samples from patients with NSCLC and in several human NSCLC cell lines. The MOR agonists morphine and DAMGO increased in vitro LLC cell growth. Treatment with MNTX or silencing MOR expression inhibited LLC invasion and anchorage-independent growth by 50–80%. Injection of MOR silenced LLC lead to a ~65% reduction in mouse lung metastasis. In addition, MOR knockout mice do not develop significant tumors when injected with LLC as compared to wildtype controls. Finally, continuous infusion of the peripheral opioid antagonist methylnaltrexone attenuates primary LLC tumor growth and reduces lung metastasis.
Taken together, our data suggests a possible direct effect of opiates on lung cancer progression, and provides a plausible explanation for the epidemiologic findings. Our observations further suggest a possible therapeutic role for opioid antagonists.
Patients with acute respiratory distress syndrome (ARDS) exhibit elevated levels of interleukin-6 (IL-6), which correlate with increased morbidity and mortality. The exact role of IL-6 in ARDS has proven difficult to study because it exhibits either pro- or anti-inflammatory actions in mouse models of lung injury, depending on the model utilized. In order to improve understanding of the role of this complex cytokine in ARDS, we evaluated IL-6 using the clinically relevant combination of lipopolysaccharide (LPS) and ventilator-induced lung injury (VILI) in IL-6−/− mice. Bronchoalveolar lavage fluid (BAL), whole-lung tissue, and histology were evaluated for inflammatory markers of injury. Transendothelial electrical resistance was used to evaluate the action of IL-6 on endothelial cells in vitro. In wild-type mice, the combination model showed a significant increase in lung injury compared to either LPS or VILI alone. IL-6−/− mice exhibited a statistically significant decrease in BAL cellular inflammation as well as lower histologic scores for lung injury, changes observed only in the combination model. A paradoxical increase in BAL total protein was observed in IL-6−/− mice exposed to LPS, suggesting that IL-6 provides protection from vascular leakage. However, in vitro data showed that IL-6, when combined with its soluble receptor, actually caused a significant increase in endothelial cell permeability, suggesting that the protection seen in vivo was likely due to complex interactions of IL-6 and other inflammatory mediators rather than to direct effects of IL-6. These studies suggest that a dual-injury model exhibits utility in evaluating the pleiotropic effects of IL-6 in ARDS on inflammatory cells and lung endothelium.
acute respiratory distress syndrome (ARDS); interleukin-6 (IL-6); lipopolysaccharide (LPS); ventilator-induced lung injury (VILI)
The inflamed lung exhibits oxidative and nitrative modifications of multiple target proteins, potentially reflecting disease severity and progression. We identified sphingosine-1–phosphate receptor–3 (S1PR3), a critical signaling molecule mediating cell proliferation and vascular permeability, as a nitrated plasma protein in mice with acute lung injury (ALI). We explored S1PR3 as a potential biomarker in murine and human ALI. In vivo nitrated and total S1PR3 concentrations were determined by immunoprecipitation and microarray studies in mice, and by ELISA in human plasma. In vitro nitrated S1PR3 concentrations were evaluated in human lung vascular endothelial cells (ECs) or within microparticles shed from ECs after exposure to barrier-disrupting agonists (LPS, low-molecular-weight hyaluronan, and thrombin). The effects of S1PR3-containing microparticles on EC barrier function were assessed by transendothelial electrical resistance (TER). Nitrated S1PR3 was identified in the plasma of murine ALI and in humans with severe sepsis-induced ALI. Elevated total S1PR3 plasma concentrations (> 251 pg/ml) were linked to sepsis and ALI mortality. In vitro EC exposure to barrier-disrupting agents induced S1PR3 nitration and the shedding of S1PR3-containing microparticles, which significantly reduced TER, consistent with increased permeability. These changes were attenuated by reduced S1PR3 expression (small interfering RNAs). These results suggest that microparticles containing nitrated S1PR3 shed into the circulation during inflammatory lung states, and represent a novel ALI biomarker linked to disease severity and outcome.
acute lung injury; sphingosine-1–phosphate receptor–3; microparticles; nitration; biomarker
Exposure to particulate air pollution is associated with increased cardiopulmonary morbidity and mortality, although the pathogenic mechanisms are poorly understood. We previously demonstrated that particulate matter (PM) exposure triggers massive oxidative stress in vascular endothelial cells (ECs), resulting in the loss of EC integrity and lung vascular hyperpermeability. We investigated the protective role of hydrogen sulfide (H2S), an endogenous gaseous molecule present in the circulation, on PM-induced human lung EC barrier disruption and pulmonary inflammation. Alterations in EC monolayer permeability, as reflected by transendothelial electrical resistance (TER), the generation of reactive oxygen species (ROS), and murine pulmonary inflammatory responses, were studied after exposures to PM and NaSH, an H2S donor. Similar to N-acetyl cysteine (5 mM), NaSH (10 μM) significantly scavenged PM-induced EC ROS and inhibited the oxidative activation of p38 mitogen-activated protein kinase. Concurrent with these events, NaSH (10 μM) activated Akt, which helps maintain endothelial integrity. Both of these pathways contribute to the protective effect of H2S against PM-induced endothelial barrier dysfunction. Furthermore, NaSH (20 mg/kg) reduced vascular protein leakage, leukocyte infiltration, and proinflammatory cytokine release in bronchoalveolar lavage fluids in a murine model of PM-induced lung inflammation. These data suggest a potentially protective role for H2S in PM-induced inflammatory lung injury and vascular hyperpermeability.
particulate matter; hydrogen sulfide; endothelial permeability; Akt
Multiple events are involved in the development of acute inflammation and injury in the lungs. A progressive rise of oxidative stress due to altered reduction-oxidation (redox) homeostasis appears to be one of the hallmarks of lung pathologies such as injury, inflammation and ischemia/reperfusion. However, despite the growing evidence that alteration of the redox balance in the lungs, antioxidant therapy may attenuate acute lung injury and inflammation. We studied the effect of thiol antioxidant compound, amifostine, on acute lung dysfunction and pulmonary endothelial barrier compromise induced by gram-negative bacterial wall lypopolysacharide (LPS). In vitro, LPS as well as other producers of reactive oxygen spices (ROS), interleukin-6 (IL-6) and hydrogen peroxide (H2O2), induced significant reorganization of actin cytoskeleton accompanied by formation of stress fibers and paracellular gaps and associated with decreased transendothelial electrical resistance, a hallmark of endothelial barrier dysfunction. These disruptive effects were inhibited by pretreatment of endothelial monolayer with amifostine. Moreover, amifostine inhibited LPS-mediated ROS production and significantly suppressed LPS-, IL-6-, and H2O2-induced activation of redox sensitive signaling mechanisms including p38 and Erk1/2 MAP kinases, and NFκB pathway. In the murine model of LPS-induced acute lung injury, intraperitoneal administration of amifostine reduced LPS-induced oxidative stress and neutrophil recruitment to the lungs. These studies demonstrate for the first time that amifostine dramatically reduces endothelial cell barrier dysfunction and acute lung injury caused by bacterial products via inhibition of oxidative stress and redox-sensitive inflammatory pathways, and may therefore be considered for therapeutic treatment of lung inflammation.
permeability; endothelium; lung; LPS; ROS; MAPK
Pulmonary hypertension (PH) and cancer pathology share growth factor- and MAPK stress-mediated signaling pathways resulting in endothelial and smooth muscle cell dysfunction and angioproliferative vasculopathy. In this study, we assessed sorafenib, an antineoplastic agent and inhibitor of multiple kinases important in angiogenesis [VEGF receptor (VEGFR)-1–3, PDGF receptor (PDGFR)-β, Raf-1 kinase] as a potential PH therapy. Two PH rat models were used: a conventional hypoxia-induced PH model and an augmented PH model combining dual VEGFR-1 and -2 inhibition (SU-5416, single 20 mg/kg injection) with hypoxia. In addition to normoxia-exposed control animals, four groups were maintained at 10% inspired O2 fraction for 3.5 wk (hypoxia/vehicle, hypoxia/SU-5416, hypoxia/sorafenib, and hypoxia/SU-5416/sorafenib). Compared with normoxic control animals, rats exposed to hypoxia/SU-5416 developed hemodynamic and histological evidence of severe PH while rats exposed to hypoxia alone displayed only mild elevations in hemodynamic values (pulmonary vascular and right ventricular pressures). Sorafenib treatment (daily gavage, 2.5 mg/kg) prevented hemodynamic changes and demonstrated dramatic attenuation of PH-associated vascular remodeling. Compared with normoxic control rats, expression profiling (Affymetrix platform) of lung RNA obtained from hypoxia [false discovery rate (FDR) 6.5%]- and hypoxia/SU-5416 (FDR 1.6%)-challenged rats yielded 1,019 and 465 differentially regulated genes (fold change >1.4), respectively. A novel molecular signature consisting of 38 differentially expressed genes between hypoxia/SU-5416 and hypoxia/SU-5416/sorafenib (FDR 6.7%) was validated by either real-time RT-PCR or immunoblotting. Finally, immunoblotting studies confirmed the upregulation of the MAPK cascade in both PH models, which was abolished by sorafenib. In summary, sorafenib represents a novel potential treatment for severe PH with the MAPK cascade a potential canonical target.
microarrays; SU-5416; bioinformatics
The role of thyroid hormone metabolism in clinical outcomes of the critically ill remains unclear. Using preclinical models of acute lung injury (ALI), we assessed the gene and protein expression of type 2 deiodinase (DIO2), a key driver for synthesis of biologically active triiodothyronine, and addressed potential association of DIO2 genetic variants with ALI in a multiethnic cohort. DIO2 gene and protein expression levels in murine lung were validated by microarrays and immunoblotting. Lung injury was assessed by levels of bronchoalveolar lavage protein and leukocytes. Single-nucleotide polymorphisms were genotyped and ALI susceptibility association assessed. Significant increases in both DIO2 gene and D2 protein expression were observed in lung tissues from murine ALI models (LPS- and ventilator-induced lung injury), with expression directly increasing with the extent of lung injury. Mice with reduced levels of DIO2 expression (by silencing RNA) demonstrated reduced thyroxine levels in plasma and increased lung injury (increased bronchoalveolar lavage protein and leukocytes), suggesting a protective role for DIO2 in ALI. The G (Ala) allele of the Thr92Ala coding single-nucleotide polymorphism (rs225014) was protective in severe sepsis and severe sepsis–associated ALI after adjustments for age, sex, and genetic ancestry in a logistic regression model in European Americans. Our studies indicate that DIO2 is a novel ALI candidate gene, the nonsynonymous Thr92Ala coding variant of which confers ALI protection. Increased DIO2 expression may dampen the ALI inflammatory response, thereby strengthening the premise that thyroid hormone metabolism is intimately linked to the integrated response to inflammatory injury in critically ill patients.
acute respiratory distress syndrome; hypothyroidism; mechanical ventilation; sepsis
Lung transplantation remains the only viable therapy for patients with end-stage lung disease. However, the full utilization of this strategy is severely compromised by a lack of donor lung availability. The vast majority of donor lungs available for transplantation are from individuals after brain death (BD). Unfortunately, the early autonomic storm that accompanies BD often results in neurogenic pulmonary edema (NPE), producing varying degrees of lung injury or leading to primary graft dysfunction after transplantation. We demonstrated that sphingosine 1–phosphate (S1P)/analogues, which are major barrier-enhancing agents, reduce vascular permeability via the S1P1 receptor, S1PR1. Because primary lung graft dysfunction is induced by lung vascular endothelial cell barrier dysfunction, we hypothesized that the S1PR1 agonist, SEW-2871, may attenuate NPE when administered to the donor shortly after BD. Significant lung injury was observed after BD, with increases of approximately 60% in bronchoalveolar lavage (BAL) total protein, cell counts, and lung tissue wet/dry (W/D) weight ratios. In contrast, rats receiving SEW-2871 (0.1 mg/kg) 15 minutes after BD and assessed after 4 hours exhibited significant lung protection (∼ 50% reduction, P = 0.01), as reflected by reduced BAL protein/albumin, cytokines, cellularity, and lung tissue wet/dry weight ratio. Microarray analysis at 4 hours revealed a global impact of both BD and SEW on lung gene expression, with a differential gene expression of enriched immune-response/inflammation pathways across all groups. Overall, SEW served to attenuate the BD-mediated up-regulation of gene expression. Two potential biomarkers, TNF and chemokine CC motif receptor-like 2, exhibited gene array dysregulation. We conclude that SEW-2871 significantly attenuates BD-induced lung injury, and may serve as a potential candidate to improve human donor availability.
neurogenic pulmonary edema; lung injury; sphingosine 1–phosphate; sphingolipids; lung transplant donors
Rationale: The stress-induced growth arrest and DNA damage–inducible α (GADD45a) gene is up-regulated by mechanical stress with GADD45a knockout (GADD45a−/−) mice demonstrating both increased susceptibility to ventilator-induced lung injury (VILI) and reduced levels of the cell survival and vascular permeability signaling effector (Akt). However, the functional role of GADD45a in the pathogenesis of VILI is unknown.
Objectives: We sought to define the role of GADD45a in the regulation of Akt activation induced by mechanical stress.
Methods: VILI-challenged GADD45a−/− mice were administered a constitutively active Akt1 vector and injury was assessed by bronchoalveolar lavage cell counts and protein levels. Human pulmonary artery endothelial cells (EC) were exposed to 18% cyclic stretch (CS) under conditions of GADD45a silencing and used for immunoprecipitation, Western blotting or immunofluoresence. EC were also transfected with mutant ubiquitin vectors to characterize site-specific Akt ubiquitination. DNA methylation was measured using methyl-specific polymerase chain reaction assay.
Measurements and Main Results: Studies exploring the linkage of GADD45a with mechanical stress and Akt regulation revealed VILI-challenged GADD45a−/− mice to have significantly reduced lung injury on overexpression of Akt1 transgene. Increased mechanical stress with 18% CS in EC induced Akt phosphorylation via E3 ligase tumor necrosis factor receptor–associated factor 6 (TRAF6)–mediated Akt K63 ubiquitination resulting in Akt trafficking and activation at the membrane. GADD45a is essential to this process because GADD45a-silenced endothelial cells and GADD45a−/− mice exhibited increased Akt K48 ubiquitination leading to proteasomal degradation. These events involve loss of ubiquitin carboxyl terminal hydrolase 1 (UCHL1), a deubiquitinating enzyme that normally removes K48 polyubiquitin chains bound to Akt thus promoting Akt K63 ubiquitination. Loss of GADD45a significantly reduces UCHL1 expression via UCHL1 promoter methylation resulting in increased Akt K48 ubiquitination and reduced Akt levels.
Conclusions: These studies highlight a novel role for GADD45a in the regulation of site-specific Akt ubiquitination and activation and implicate a significant functional role for GADD45a in the clinical predisposition to VILI.
GADD45a; AKT; UCHL1; ubiquitin; mechanical stress
Novel therapies are desperately needed for radiation-induced lung injury (RILI), which, despite aggressive corticosteroid therapy, remains a potentially fatal and dose-limiting complication of thoracic radiotherapy. We assessed the utility of simvastatin, an anti-inflammatory and lung barrier–protective agent, in a dose- and time-dependent murine model of RILI (18–(25 Gy). Simvastatin reduced multiple RILI indices, including vascular leak, leukocyte infiltration, and histological evidence of oxidative stress, while reversing RILI-associated dysregulated gene expression, including p53, nuclear factor–erythroid-2–related factor, and sphingolipid metabolic pathway genes. To identify key regulators of simvastatin-mediated RILI protection, we integrated whole-lung gene expression data obtained from radiated and simvastatin-treated mice with protein–protein interaction network analysis (single-network analysis of proteins). Topological analysis of the gene product interaction network identified eight top-prioritized genes (Ccna2a, Cdc2, fcer1 g, Syk, Vav3, Mmp9, Itgam, Cd44) as regulatory nodes within an activated RILI network. These studies identify the involvement of specific genes and gene networks in RILI pathobiology, and confirm that statins represent a novel strategy to limit RILI.
radiation pneumonitis; lung vascular permeability; simvastatin; gene dysregulation; protein–protein interaction
Acute lung injury (ALI) and mechanical ventilator-induced lung injury (VILI), major causes of acute respiratory failure with elevated morbidity and mortality, are characterized by significant pulmonary inflammation and alveolar/vascular barrier dysfunction. Previous studies highlighted the role of the non–muscle myosin light chain kinase isoform (nmMLCK) as an essential element of the inflammatory response, with variants in the MYLK gene that contribute to ALI susceptibility. To define nmMLCK involvement further in acute inflammatory syndromes, we used two murine models of inflammatory lung injury, induced by either an intratracheal administration of lipopolysaccharide (LPS model) or mechanical ventilation with increased tidal volumes (the VILI model). Intravenous delivery of the membrane-permeant MLC kinase peptide inhibitor, PIK, produced a dose-dependent attenuation of both LPS-induced lung inflammation and VILI (∼50% reductions in alveolar/vascular permeability and leukocyte influx). Intravenous injections of nmMLCK silencing RNA, either directly or as cargo within angiotensin-converting enzyme (ACE) antibody–conjugated liposomes (to target the pulmonary vasculature selectively), decreased nmMLCK lung expression (∼70% reduction) and significantly attenuated LPS-induced and VILI-induced lung inflammation (∼40% reduction in bronchoalveolar lavage protein). Compared with wild-type mice, nmMLCK knockout mice were significantly protected from VILI, with significant reductions in VILI-induced gene expression in biological pathways such as nrf2-mediated oxidative stress, coagulation, p53-signaling, leukocyte extravasation, and IL-6–signaling. These studies validate nmMLCK as an attractive target for ameliorating the adverse effects of dysregulated lung inflammation.
endotoxin/lipopolysaccharide; nmMLCK; mice; lung injury; endothelial barrier
The therapeutic options for ameliorating the profound vascular permeability, alveolar flooding, and organ dysfunction that accompanies acute inflammatory lung injury (ALI) remain limited. Extending our previous finding that the intravenous administration of the sphingolipid angiogenic factor, sphingosine 1–phosphate (S1P), attenuates inflammatory lung injury and vascular permeability via ligation of S1PR1, we determine that a direct intratracheal or intravenous administration of S1P, or a selective S1P receptor (S1PR1) agonist (SEW-2871), produces highly concentration-dependent barrier-regulatory responses in the murine lung. The intratracheal or intravenous administration of S1P or SEW-2871 at < 0.3 mg/kg was protective against LPS-induced murine lung inflammation and permeability. However, intratracheal delivery of S1P at 0.5 mg/kg (for 2 h) resulted in significant alveolar–capillary barrier disruption (with a 42% increase in bronchoalveolar lavage protein), and produced rapid lethality when delivered at 2 mg/kg. Despite the greater selectivity for S1PR1, intratracheally delivered SEW-2871 at 0.5 mg/kg also resulted in significant alveolar–capillary barrier disruption, but was not lethal at 2 mg/kg. Consistent with the S1PR1 regulation of alveolar/vascular barrier function, wild-type mice pretreated with the S1PR1 inverse agonist, SB-649146, or S1PR1+/− mice exhibited reduced S1P/SEW-2871–mediated barrier protection after challenge with LPS. In contrast, S1PR2−/− knockout mice as well as mice with reduced S1PR3 expression (via silencing S1PR3-containing nanocarriers) were protected against LPS-induced barrier disruption compared with control mice. These studies underscore the potential therapeutic effects of highly selective S1PR1 receptor agonists in reducing inflammatory lung injury, and highlight the critical role of the S1P delivery route, S1PR1 agonist concentration, and S1PR1 expression in target tissues.
SEW-2871; LPS; SB-649146; S1P; lung edema
Rationale: We previously demonstrated pre–B-cell colony enhancing factor (PBEF) as a biomarker in sepsis and sepsis-induced acute lung injury (ALI) with genetic variants conferring ALI susceptibility.
Objectives: To explore mechanistic participation of PBEF in ALI and ventilator-induced lung injury (VILI).
Methods: Two models of VILI were utilized to explore the role of PBEF using either recombinant PBEF or PBEF+/− mice.
Measurements and Main Results: Initial in vitro studies demonstrated recombinant human PBEF (rhPBEF) as a direct rat neutrophil chemotactic factor with in vivo studies demonstrating marked increases in bronchoalveolar lavage (BAL) leukocytes (PMNs) after intratracheal injection in C57BL/6J mice. These changes were accompanied by increased BAL levels of PMN chemoattractants (KC and MIP-2) and modest increases in lung vascular and alveolar permeability. We next explored the potential synergism between rhPBEF challenge (intratracheal) and a model of limited VILI (4 h, 30 ml/kg tidal volume) and observed dramatic increases in BAL PMNs, BAL protein, and cytokine levels (IL-6, TNF-α, KC) compared with either challenge alone. Gene expression profiling identified induction of ALI- and VILI-associated gene modules (nuclear factor-κB, leukocyte extravasation, apoptosis, Toll receptor pathways). Heterozygous PBEF+/− mice were significantly protected (reduced BAL protein, BAL IL-6 levels, peak inspiratory pressures) when exposed to a model of severe VILI (4 h, 40 ml/kg tidal volume) and exhibited significantly reduced expression of VILI-associated gene expression modules. Finally, strategies to reduce PBEF availability (neutralizing antibody) resulted in significant protection from VILI.
Conclusions: These studies implicate PBEF as a key inflammatory mediator intimately involved in both the development and severity of ventilator-induced ALI.
visfatin; acute lung injury; chemotaxis; apoptosis; mechanical ventilation
We have generated genetically engineered mice that are uniquely susceptible to lipopolysaccharide (LPS)-induced and mechanical ventilation-induced lung injury in a sex-specific and age-specific manner. These mice express a nonmuscle isoform of the myosin light chain kinase gene (nmMLCK2) targeted to the endothelium. Homozygous mice have significantly reduced fecundity and litter survival until weaning, and they are initially growth delayed but eventually exceed the size of wild-type littermates. Mice at all ages show increased protein transport across the lung barrier; however, the phenotype is most discernible in 8-12-week-old male mice. When subjected to a clinically relevant LPS-induced lung injury model, 8-12-week-old young females and 30-36-week-old males seem to be the most significantly injured group. In contrast, 30-36-week-old males remain the most significantly injured group when mechanically ventilated at high tidal volumes, which is a clinically relevant model of mechanical stress lung injury. These data reveal that nmMLCK2 overexpression in the endothelium exacerbates lung injury in vivo in a sexually dimorphic and age-dependent manner.
Rationale: Inducible nitric oxide synthase (iNOS) has been implicated in the development of acute lung injury. Recent studies indicate a role for mechanical stress in iNOS and endothelial NOS (eNOS) regulation. Objectives: This study investigated changes in lung NOS expression and activity in a mouse model of ventilator-induced lung injury. Methods: C57BL/6J (wild-type [WT]) and iNOS-deficient (iNOS−/−) mice received spontaneous ventilation (control) or mechanical ventilation (MV; VT of 7 and 20 ml/kg) for 2 hours, after which NOS gene expression and activity were determined and pulmonary capillary leakage assessed by the Evans blue albumin assay. Results: iNOS mRNA and protein expression was absent in iNOS−/− mice, minimal in WT control mice, but significantly upregulated in response to 2 hours of MV. In contrast, eNOS protein was decreased in WT mice, and nonsignificantly increased in iNOS−/− mice, as compared with control animals. iNOS and eNOS activities followed similar patterns in WT and iNOS−/− mice. MV caused acute lung injury as suggested by cell infiltration and nitrotyrosine accumulation in the lung, and a significant increase in bronchoalveolar lavage cell count in WT mice, findings that were reduced in iNOS−/− mice. Finally, Evans blue albumin accumulation in lungs of WT mice was significant (50 vs. 15% increase in iNOS−/− mice compared with control animals) in response to MV and was prevented by treatment of the animals with the iNOS inhibitor aminoguanidine. Conclusion: Taken together, our results indicate that iNOS gene expression and activity are significantly upregulated and contribute to lung edema in ventilator-induced lung injury.
inducible nitric oxide synthase; lung permeability; mechanical ventilation