Autotaxin production of lysophosphatidic acid mediates allergic asthmatic inflammation

The Structural Binding Mode of the Four Autotaxin Inhibitor Types that Differentially Affect Catalytic and Non-Catalytic Functions

Autotaxin (ATX) is a secreted lysophospholipase D, catalysing the conversion of lysophosphatidylcholine (LPC) to bioactive lysophosphatidic acid (LPA). LPA acts through two families of G protein-coupled receptors (GPCRs) controlling key cellular responses, and it is implicated in many physiological processes and pathologies. ATX, therefore, has been established as an important drug target in the pharmaceutical industry. Structural and biochemical studies of ATX have shown that it has a bimetallic nucleophilic catalytic site, a substrate-binding (orthosteric) hydrophobic pocket that accommodates the lipid alkyl chain, and an allosteric tunnel that can accommodate various steroids and LPA. In this review, first, we revisit what is known about ATX-mediated catalysis, crucially in light of allosteric regulation. Then, we present the known ATX catalysis-independent functions, including binding to cell surface integrins and proteoglycans. Next, we analyse all crystal structures of ATX bound to inhibitors and present them based on the four inhibitor types that are established based on the binding to the orthosteric and/or the allosteric site. Finally, in light of these data we discuss how mechanistic differences might differentially modulate the activity of the ATX-LPA signalling axis, and clinical applications including cancer.

Pleotropic Roles of Autotaxin in the Nervous System Present Opportunities for the Development of Novel Therapeutics for Neurological Diseases

Autotaxin (ATX) is a soluble extracellular enzyme that is abundant in mammalian plasma and cerebrospinal fluid (CSF). It has two known enzymatic activities, acting as both a phosphodiesterase and a phospholipase. The majority of its biological effects have been associated with its ability to liberate lysophosphatidic acid (LPA) from its substrate, lysophosphatidylcholine (LPC). LPA has diverse pleiotropic effects in the central nervous system (CNS) and other tissues via the activation of a family of six cognate G protein-coupled receptors. These LPA receptors (LPARs) are expressed in some combination in all known cell types in the CNS where they mediate such fundamental cellular processes as proliferation, differentiation, migration, chronic inflammation, and cytoskeletal organization. As a result, dysregulation of LPA content may contribute to many CNS and PNS disorders such as chronic inflammatory or neuropathic pain, glioblastoma multiforme (GBM), hemorrhagic hydrocephalus, schizophrenia, multiple sclerosis, Alzheimer's disease, metabolic syndrome-induced brain damage, traumatic brain injury, hepatic encephalopathy-induced cerebral edema, macular edema, major depressive disorder, stress-induced psychiatric disorder, alcohol-induced brain damage, HIV-induced brain injury, pruritus, and peripheral nerve injury. ATX activity is now known to be the primary biological source of this bioactive signaling lipid, and as such, represents a potentially high-value drug target. There is currently one ATX inhibitor entering phase III clinical trials, with several additional preclinical compounds under investigation. This review discusses the physiological and pathological significance of the ATX-LPA-LPA receptor signaling axis and summarizes the evidence for targeting this pathway for the treatment of CNS diseases.

Lysophosphatidic acids and their substrate lysophospholipids in cerebrospinal fluid as objective biomarkers for evaluating the severity of lumbar spinal stenosis

Lysophospholipids (LPLs) are known to have potentially important roles in the initiation and maintenance of neuropathic pain in animal models. This study investigated the association between the clinical severity of lumbar spinal stenosis (LSS) and the cerebrospinal fluid (CSF) levels of LPLs, using human samples. We prospectively identified twenty-eight patients with LSS and fifteen controls with idiopathic scoliosis or bladder cancer without neurological symptoms. We quantified LPLs from CSF using liquid chromatography-tandem mass spectrometry. We assessed clinical outcome measures of LSS (Neuropathic Pain Symptom Inventory (NPSI) and Zurich Claudication Questionnaire (ZCQ)) and categorized patients into two groups according to their severity. Five species of lysophosphatidic acid (LPA), nine species of lysophosphatidylcholine (LPC), and one species of lysophosphatidylinositol (LPI) were detected. The CSF levels of all species of LPLs were significantly higher in LSS patients than controls. Patients in the severe NPSI group had significantly higher LPL levels (three species of LPA and nine species of LPC) than the mild group. Patients in the severe ZCQ group also had significantly higher LPL levels (four species of LPA and nine species of LPC). This investigation demonstrates a positive correlation between the CSF levels of LPLs and the clinical severity of LSS. LPLs are potential biomarkers for evaluating the severity of LSS.

Population Pharmacokinetic and Pharmacodynamic Analysis of GLPG1690, an Autotaxin Inhibitor, in Healthy Volunteers and Patients with Idiopathic Pulmonary Fibrosis

BACKGROUND AND OBJECTIVES

GLPG1690 is an autotaxin inhibitor in development for the treatment of idiopathic pulmonary fibrosis. Several publications suggested a role of autotaxin in the control of disease-affected lung function and of lysophosphatidic acid in lung remodeling processes. The aim of the current article was to describe the exposure-response relationship of GLPG1690 and further develop a rational basis to support dose selection for clinical trials in patients with idiopathic pulmonary fibrosis.

METHODS

Two trials were conducted in healthy volunteers: in the first trial, GLPG1690 was administered as single doses from 20 mg up to 1500 mg, and subsequently in multiple daily doses of 300-1000 mg. In a second trial, the interaction of rifampin with 600 mg of GLPG1690 was evaluated. A third trial was conducted in patients with idiopathic pulmonary fibrosis administered 600 mg of GLPG1690 once daily for 12 weeks. The exposure-response (lysophosphatidic acid C18:2 reduction) relationship of GLPG1690 was first described using non-linear mixed-effects modeling and the model was subsequently deployed to simulate a lysophosphatidic acid C18:2 reduction as a biomarker of autotaxin inhibition in the dose range from 50 to 1000 mg once or twice daily.

RESULTS

The population pharmacokinetics and lysophosphatidic acid C18:2 response of GLPG1690 were adequately described by a combined population pharmacokinetic and pharmacokinetic/pharmacodynamic model. Dose, formulation, rifampin co-administration, health status (healthy volunteer vs. patient with idiopathic pulmonary fibrosis), and baseline lysophosphatidic acid C18:2 were identified as covariates in the model. The effect of dose on systemic clearance indicated that GLPG1690 followed a more than dose-proportional increase in exposure over the simulated dose range of 50-1000 mg once daily. Model-based simulations showed reductions in lysophosphatidic acid C18:2 of at least 80% with doses greater or equal to 200 mg once daily.

CONCLUSION

Based on these results, 200 and 600 mg once-daily doses were selected for future clinical trials in patients with idiopathic pulmonary fibrosis.

Evaluation of lipid markers in surfactant obtained from asthmatic horses exposed to hay

OBJECTIVE To evaluate the lipidomic profile of surfactant obtained from horses with asthma at various clinical stages and to compare results with findings for healthy horses exposed to the same conditions. SAMPLE Surfactant samples obtained from 6 horses with severe asthma and 7 healthy horses. PROCEDURES Clinical evaluation of horses and surfactant analysis were performed. Samples obtained from horses with severe asthma and healthy horses before (baseline), during, and after exposure to hay were analyzed. Crude surfactant pellets were dried prior to dissolution in a solution of isopropanol:methanol:chloroform (4:2:1) containing 7.5mM ammonium acetate. Shotgun lipidomics were performed by use of high-resolution data acquisition on an ion-trap mass spectrometer. Findings were analyzed by use of an ANOVA with a Tukey-Kramer post hoc test. RESULTS Results of lipidomic analysis were evaluated to detect significant differences between groups of horses and among exposure statuses within groups of horses. Significantly increased amounts of cyclic phosphatidic acid (cPA) and diacylglycerol (DAG) were detected in surfactant from severely asthmatic horses during exposure to hay, compared with baseline and postexposure concentrations. Concentrations of cPA and DAG did not change significantly in healthy horses regardless of exposure status. CONCLUSIONS AND CLINICAL RELEVANCE cPA 16:0 and DAG 36:2 were 2 novel lipid mediators identified in surfactant obtained from asthmatic horses with clinical disease. These molecules were likely biomarkers of sustained inflammation. Further studies are needed to evaluate a possible correlation with disease severity and potential alterations in the plasma lipidomic profile of horses with asthma.

Autotaxin is a novel target of microRNA-101-3p

Autotaxin (ATX), a vital enzyme that generates lysophosphatidic acid (LPA), affects many biological processes, including tumorigenesis, via the ATX–LPA axis. In this study, we demonstrate that microRNA‐101‐3p (miR‐101‐3p), a well‐known tumor suppressor, downregulates ATX expression at the posttranscriptional level. We found that miR‐101‐3p inhibits ATX regulation by directly targeting a conserved sequence in the ATX mRNA 3′UTR. Moreover, we observed an inverse correlation between ATX and miR‐101‐3p levels in various types of cancer cells. ATX is highly expressed in several human cancers. Here, we verified that ATX expression is significantly inhibited by miR‐101‐3p in U87 and HCT116 cells. ATX downregulation contributed to the suppression of migration, invasion, and proliferation mediated by miR‐101‐3p; furthermore, the tumor‐suppressing activity of miR‐101‐3p was partially reduced by the addition of LPA in U87 cells. Our data suggest that ATX is a novel target of miR‐101‐3p.

FoxO1 is a critical regulator of M2-like macrophage activation in allergic asthma

BACKGROUND

The pathogenesis of asthma and airway obstruction is the result of an abnormal response to different environmental exposures. The scientific premise of our study was based on the finding that FoxO1 expression is increased in lung macrophages of mice after allergen exposure and human asthmatic patients. Macrophages are capable of switching from one functional phenotype to another, and it is important to understand the mechanisms involved in the transformation of macrophages and how their cellular function affects the peribronchial stromal microenvironment.

METHODS

We employed a murine asthma model, in which mice were treated by intranasal insufflation with allergens for 2-8 weeks. We used both a pharmacologic approach using a highly specific FoxO1 inhibitor and genetic approaches using FoxO1 knockout mice (FoxO1fl/fl LysMcre). Cytokine level in biological fluids was measured by ELISA and the expression of encoding molecules by NanoString assay and qRT-PCR.

RESULTS

We show that the levels of FoxO1 gene are significantly elevated in the airway macrophages of patients with mild asthma in response to subsegmental bronchial allergen challenge. Transcription factor FoxO1 regulates a pro-asthmatic phenotype of lung macrophages that is involved in the development and progression of chronic allergic airway disease. We have shown that inhibition of FoxO1 induced phenotypic conversion of lung macrophages and downregulates pro-asthmatic and pro-fibrotic gene expression by macrophages, which contribute to airway inflammation and airway remodeling in allergic asthma.

CONCLUSION

Targeting FoxO1 with its downstream regulator IRF4 is a novel therapeutic target for controlling allergic inflammation and potentially reversing fibrotic airway remodeling.

Sirtuin 2 enhances allergic asthmatic inflammation

Allergic eosinophilic asthma is a chronic condition causing airway remodeling resulting in lung dysfunction. We observed that expression of sirtuin 2 (Sirt2), a histone deacetylase, regulates the recruitment of eosinophils after sensitization and challenge with a triple antigen: dust mite, ragweed, and Aspergillus fumigatus (DRA). Our data demonstrate that IL-4 regulates the expression of Sirt2 isoform 3/5. Pharmacological inhibition of Sirt2 by AGK2 resulted in diminished cellular recruitment, decreased CCL17/TARC, and reduced goblet cell hyperplasia. YM1 and Fizz1 expression was reduced in AGK2-treated, IL-4-stimulated lung macrophages in vitro as well as in lung macrophages from AGK2-DRA-challenged mice. Conversely, overexpression of Sirt2 resulted in increased cellular recruitment, CCL17 production, and goblet cell hyperplasia following DRA challenge. Sirt2 isoform 3/5 was upregulated in primary human alveolar macrophages following IL-4 and AGK2 treatment, which resulted in reduced CCL17 and markers of alternative activation. These gain-of-function and loss-of-function studies indicate that Sirt2 could be developed as a treatment for eosinophilic asthma.

Adipose-derived autotaxin regulates inflammation and steatosis associated with diet-induced obesity

Autotaxin (ATX) is a secreted enzyme that generates the bioactive lipid lysophosphatidic acid (LPA). We generated mice with global inducible post-natal inactivation or adipose-specific loss of the Enpp2 gene encoding ATX. The animals are phenotypically unremarkable and exhibit differences in adipocyte size and adipose tissue expression of inflammatory genes after high fat feeding without gross differences in fat distribution or body mass. Surprisingly, both models of Enpp2- deficiency exhibited marked protection from high fat diet-induced hepatic steatosis. This phenotype was not associated with differences in dietary fat absorption but may be accounted for by differences in hepatic expression of genes involved in de novo synthesis of triglycerides. These findings suggest that pharmacological inhibition of ATX might be protective against hepatic steatosis.

Function of secreted phospholipase A2 group-X in asthma and allergic disease

Elevated secreted phospholipase A₂ (sPLA₂) activity in the airways has been implicated in the pathogenesis of asthma and allergic disease for some time. The identity and function of these enzymes in asthma is becoming clear from work in our lab and others. We focused on sPLA₂ group X (sPLA₂-X) after identifying increased levels of this enzyme in asthma, and that it is responsible for a large portion of sPLA₂ activity in the airways and that the levels are strongly associated with features of airway hyperresponsiveness (AHR). In this review, we discuss studies that implicated sPLA₂-X in human asthma, and murine models that demonstrate a critical role of this enzyme as a regulator of type-2 inflammation, AHR and production of eicosanoids. We discuss the mechanism by which sPLA₂-X acts to regulate eicosanoids in leukocytes, as well as effects that are mediated through the generation of lysophospholipids and through receptor-mediated functions. This article is part of a Special Issue entitled Novel functions of phospholipase A2 Guest Editors: Makoto Murakami and Gerard Lambeau.

Autotaxin/lysophosphatidic acid signaling mediates obesity-related cardiomyopathy in mice and human subjects

Obesity is associated with increased cardiovascular morbidity and mortality, but the direct signals to initiate or exaggerate cardiomyopathy remain largely unknown. Present study aims to explore the pathophysiological role of autotaxin/lysophosphatidic acid (LPA) in the process of cardiomyopathy during obesity. Through utilizing mouse model and clinical samples, present study investigates the therapeutic benefits of autotaxin inhibitor and clinical correlation to obesity‐related cardiomyopathy. The elevated circulating levels of autotaxin are closely associated with cardiac parameters in mice. Administration with autotaxin inhibitor, PF‐8380 effectively attenuates high fat diet‐induced cardiac hypertrophy, dysfunction and inflammatory response. Consistently, autotaxin inhibition also decreases circulating LPA levels in obese mice. In in vitro study, LPA directly initiates cell size enlargement and inflammation in neonatal cardiomyocytes. More importantly, circulating levels of autotaxin are positively correlated with cardiac dysfunction and hypertrophy in 55 patients. In conclusion, present study uncovers the correlation between circulating autotaxin and cardiac parameters in mice and human patient, and provided solid evidence of the therapeutic application of autotaxin inhibitor in combating obesity‐related cardiomyopathy.

Transcriptional and functional diversity of human macrophage repolarization

BACKGROUND

Macrophage plasticity allows cells to adopt different phenotypes, a property with important implications in disorders such as cystic fibrosis (CF) and asthma.

OBJECTIVE

We sought to examine the transcriptional and functional significance of macrophage repolarization from an M1 to an M2 phenotype and assess the role of a common human genetic disorder (CF) and a prototypical allergic disease (asthma) in this transformation.

METHODS

Monocyte-derived macrophages were collected from healthy subjects and patients with CF and polarized to an M2 state by using IL-4, IL-10, glucocorticoids, apoptotic PMNs, or azithromycin. We performed transcriptional profiling and pathway analysis for each stimulus. We assessed the ability of M2-repolarized macrophages to respond to LPS rechallenge and clear apoptotic neutrophils and used murine models to determine conserved functional responses to IL-4 and IL-10. We investigated whether M2 signatures were associated with alveolar macrophage phenotypes in asthmatic patients.

RESULTS

We found that macrophages exhibit highly diverse responses to distinct M2-polarizing stimuli. Specifically, IL-10 activated proinflammatory pathways and abrogated LPS tolerance, allowing rapid restoration of LPS responsiveness. In contrast, IL-4 enhanced LPS tolerance, dampening proinflammatory responses after repeat LPS challenge. A common theme observed across all M2 stimuli was suppression of interferon-associated pathways. We found that CF macrophages had intact reparative and transcriptional responses, suggesting that macrophage contributions to CF-related lung disease are primarily shaped by their environment. Finally, we leveraged in vitro-derived signatures to show that allergen provocation induces distinct M2 state transcriptional patterns in alveolar macrophages.

CONCLUSION

Our findings highlight the diversity of macrophage polarization, attribute functional consequences to different M2 stimuli, and provide a framework to phenotype macrophages in disease states.

Preventing acute asthmatic symptoms by targeting a neuronal mechanism involving carotid body lysophosphatidic acid receptors

Asthma accounts for 380,000 deaths a year. Carotid body denervation has been shown to have a profound effect on airway hyper-responsiveness in animal models but a mechanistic explanation is lacking. Here we demonstrate, using a rat model of asthma (OVA-sensitized), that carotid body activation during airborne allergic provocation is caused by systemic release of lysophosphatidic acid (LPA). Carotid body activation by LPA involves TRPV1 and LPA-specific receptors, and induces parasympathetic (vagal) activity. We demonstrate that this activation is sufficient to cause acute bronchoconstriction. Moreover, we show that prophylactic administration of TRPV1 (AMG9810) and LPA (BrP-LPA) receptor antagonists prevents bradykinin-induced asthmatic bronchoconstriction and, if administered following allergen exposure, reduces the associated respiratory distress. Our discovery provides mechanistic insight into the critical roles of carotid body LPA receptors in allergen-induced respiratory distress and suggests alternate treatment options for asthma.

Acute bronchoconstriction is the leading cause of asthmatic sudden death following allergen exposure. The authors show that the systemic increase of LPA following inhaled allergen or bradykinin challenge activates the carotid bodies through TRPV1 and LPA-specific receptors and that systemic TRPV1 and LPA-specific receptor antagonists ameliorate acute bronchoconstriction.

Platelets, autotaxin and lysophosphatidic acid signalling: win-win factors for cancer metastasis

Platelets play a crucial role in the survival of metastatic cells in the blood circulation. The interaction of tumour cells with platelets leads to the production of plethoric factors among which our review will focus on lysophosphatidic acid (LPA), because platelets are the highest producers of this bioactive lysophospholipid in the organism. LPA promotes platelet aggregation, and blocking platelet function decreases LPA signalling and leads to inhibition of breast cancer cell metastasis. Autotaxin (ATX), a lysophospholipase D responsible for the basal concentration of LPA in blood, was detected in platelet α-granules. Functionally, active ATX is eventually released following tumour cell-induced platelet aggregation, thereby promoting metastasis. Megakaryocytes do not express ATX but respond to LPA stimulation. Whether LPA-primed megakaryocytes contribute to the recently reported negative action of megakaryocytes on cancer metastasis is not yet known. However, an understanding of the ATX/LPA signalling pathways in platelets, cancer cells and megakaryocytes opens up new approaches for fighting cancer metastasis.

Airway Epithelial Cell-Derived Colony Stimulating Factor-1 Promotes Allergen Sensitization

Airway epithelial cells (AECs) secrete innate immune cytokines that regulate adaptive immune effector cells. In allergen-sensitized humans and mice, the airway and alveolar microenvironment is enriched with colony stimulating factor-1 (CSF1) in response to allergen exposure. In this study we found that AEC-derived CSF1 had a critical role in the production of allergen reactive-IgE production. Furthermore, spatiotemporally secreted CSF1 regulated the recruitment of alveolar dendritic cells (DCs) and enhanced the migration of conventional DC2s (cDC2s) to the draining lymph node in an interferon regulatory factor 4 (IRF4)-dependent manner. CSF1 selectively upregulated the expression of the chemokine receptor CCR7 on the CSF1R⁺ cDC2, but not the cDC1, population in response to allergen stimuli. Our data describe the functional specification of CSF1-dependent DC subsets that link the innate and adaptive immune responses in T helper 2 (Th2) cell-mediated allergic lung inflammation.

Autotaxin in Pathophysiology and Pulmonary Fibrosis

Lysophospholipid signaling is emerging as a druggable regulator of pathophysiological responses, and especially fibrosis, exemplified by the relative ongoing clinical trials in idiopathic pulmonary fibrosis (IPF) patients. In this review, we focus on ectonucleotide pyrophosphatase-phosphodiesterase 2 (ENPP2), or as more widely known Autotaxin (ATX), a secreted lysophospholipase D (lysoPLD) largely responsible for extracellular lysophosphatidic acid (LPA) production. In turn, LPA is a bioactive phospholipid autacoid, forming locally upon increased ATX levels and acting also locally through its receptors, likely guided by ATX's structural conformation and cell surface associations. Increased ATX activity levels have been detected in many inflammatory and fibroproliferative conditions, while genetic and pharmacologic studies have confirmed a pleiotropic participation of ATX/LPA in different processes and disorders. In pulmonary fibrosis, ATX levels rise in the broncheoalveolar fluid (BALF) and stimulate LPA production. LPA engagement of its receptors activate multiple G-protein mediated signal transduction pathways leading to different responses from pulmonary cells including the production of pro-inflammatory signals from stressed epithelial cells, the modulation of endothelial physiology, the activation of TGF signaling and the stimulation of fibroblast accumulation. Genetic or pharmacologic targeting of the ATX/LPA axis attenuated disease development in animal models, thus providing the proof of principle for therapeutic interventions.

Mast cells regulate CD4+ T-cell differentiation in the absence of antigen presentation

BACKGROUND

Given their unique capacity for antigen uptake, processing, and presentation, antigen-presenting cells (APCs) are critical for initiating and regulating innate and adaptive immune responses. We have previously shown the role of nicotinamide adenine dinucleotide (NAD⁺) in T-cell differentiation independently of the cytokine milieu, whereas the precise mechanisms remained unknown.

OBJECTIVE

The objective of this study is to further dissect the mechanism of actions of NAD⁺ and determine the effect of APCs on NAD⁺-mediated T-cell activation.

METHODS

Isolated dendritic cells and bone marrow-derived mast cells (MCs) were used to characterize the mechanisms of action of NAD⁺ on CD4⁺ T-cell fate in vitro. Furthermore, NAD⁺-mediated CD4⁺ T-cell differentiation was investigated in vivo by using wild-type C57BL/6, MC^-/-, MHC class II^-/-, Wiskott-Aldrich syndrome protein (WASP)^-/-, 5C.C7 recombination-activating gene 2 (Rag2)^-/-, and CD11b-DTR transgenic mice. Finally, we tested the physiologic effect of NAD⁺ on the systemic immune response in the context of Listeria monocytogenes infection.

RESULTS

Our in vivo and in vitro findings indicate that after NAD⁺ administration, MCs exclusively promote CD4⁺ T-cell differentiation, both in the absence of antigen and independently of major APCs. Moreover, we found that MCs mediated CD4⁺ T-cell differentiation independently of MHC II and T-cell receptor signaling machinery. More importantly, although treatment with NAD⁺ resulted in decreased MHC II expression on CD11c⁺ cells, MC-mediated CD4⁺ T-cell differentiation rendered mice resistant to administration of lethal doses of L monocytogenes.

CONCLUSIONS

Collectively, our study unravels a novel cellular and molecular pathway that regulates innate and adaptive immunity through MCs exclusively and underscores the therapeutic potential of NAD⁺ in the context of primary immunodeficiencies and antimicrobial resistance.

Serum metabolic profiling identified a distinct metabolic signature in patients with idiopathic pulmonary fibrosis - a potential biomarker role for LysoPC

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a lethal lung disease of unknown etiology. Patients present loss of lung function, dyspnea and dry cough. Diagnosis requires compatible radiologic imaging and, in undetermined cases, invasive procedures such as bronchoscopy and surgical lung biopsy. The pathophysiological mechanisms of IPF are not completely understood. Lung injury with abnormal alveolar epithelial repair is thought to be a major cause for activation of profibrotic pathways in IPF. Metabolic signatures might indicate pathological pathways involved in disease development and progression. Reliable serum biomarker would help to improve both diagnostic approach and monitoring of drug effects.

METHOD

The global metabolic profiles measured by ultra high-performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS) of ten stable IPF patients were compared to the ones of ten healthy participants. The results were validated in an additional study of eleven IPF patients and ten healthy controls.

RESULTS

We discovered 10 discriminative metabolic features using multivariate and univariate statistical analysis. Among them, we identified one metabolite at a retention time of 9.59 min that was two times more abundant in the serum of IPF patients compared to healthy participants. Based on its ion pattern, a lysophosphatidylcholine (LysoPC) was proposed. LysoPC is a precursor of lysophosphatidic acid (LPA) - a known mediator for lung fibrosis with its pathway currently being evaluated as new therapeutic drug target for IPF and other fibrotic diseases.

CONCLUSIONS

We identified a LysoPC by UHPLC-HRMS as potential biomarker in serum of patients with IPF. Further validation studies in a larger cohort are necessary to determine its role in IPF.

TRIAL REGISTRATION

Serum samples from IPF patients have been obtained within the clinical trial NCT02173145 at baseline and from the idiopathic interstitial pneumonia (IIP) cohort study. The study was approved by the Swiss Ethics Committee, Bern (KEK 002/14 and 246/15 or PB_2016-01524).

Synaptic phospholipids as a new target for cortical hyperexcitability and E/I balance in psychiatric disorders

Lysophosphatidic acid (LPA) is a synaptic phospholipid, which regulates cortical excitation/inhibition (E/I) balance and controls sensory information processing in mice and man. Altered synaptic LPA signaling was shown to be associated with psychiatric disorders. Here, we show that the LPA-synthesizing enzyme autotaxin (ATX) is expressed in the astrocytic compartment of excitatory synapses and modulates glutamatergic transmission. In astrocytes, ATX is sorted toward fine astrocytic processes and transported to excitatory but not inhibitory synapses. This ATX sorting, as well as the enzymatic activity of astrocyte-derived ATX are dynamically regulated by neuronal activity via astrocytic glutamate receptors. Pharmacological and genetic ATX inhibition both rescued schizophrenia-related hyperexcitability syndromes caused by altered bioactive lipid signaling in two genetic mouse models for psychiatric disorders. Interestingly, ATX inhibition did not affect naive animals. However, as our data suggested that pharmacological ATX inhibition is a general method to reverse cortical excitability, we applied ATX inhibition in a ketamine model of schizophrenia and rescued thereby the electrophysiological and behavioral schizophrenia-like phenotype. Our data show that astrocytic ATX is a novel modulator of glutamatergic transmission and that targeting ATX might be a versatile strategy for a novel drug therapy to treat cortical hyperexcitability in psychiatric disorders.

Metabolomics analysis identifies sex-associated metabotypes of oxidative stress and the autotaxin-lysoPA axis in COPD

Chronic obstructive pulmonary disease (COPD) is a heterogeneous disease and a leading cause of mortality and morbidity worldwide. The aim of this study was to investigate the sex dependency of circulating metabolic profiles in COPD.

Serum from healthy never-smokers (healthy), smokers with normal lung function (smokers), and smokers with COPD (COPD; Global Initiative for Chronic Obstructive Lung Disease stages I–II/A–B) from the Karolinska COSMIC cohort (n=116) was analysed using our nontargeted liquid chromatography–high resolution mass spectrometry metabolomics platform.

Pathway analyses revealed that several altered metabolites are involved in oxidative stress. Supervised multivariate modelling showed significant classification of smokers from COPD (p=2.8×10⁻⁷). Sex stratification indicated that the separation was driven by females (p=2.4×10⁻⁷) relative to males (p=4.0×10⁻⁴). Significantly altered metabolites were confirmed quantitatively using targeted metabolomics. Multivariate modelling of targeted metabolomics data confirmed enhanced metabolic dysregulation in females with COPD (p=3.0×10⁻³) relative to males (p=0.10). The autotaxin products lysoPA (16:0) and lysoPA (18:2) correlated with lung function (forced expiratory volume in 1 s) in males with COPD (r=0.86; p<0.0001), but not females (r=0.44; p=0.15), potentially related to observed dysregulation of the miR-29 family in the lung.

These findings highlight the role of oxidative stress in COPD, and suggest that sex-enhanced dysregulation in oxidative stress, and potentially the autotaxin–lysoPA axis, are associated with disease mechanisms and/or prevalence.

Oxidative stress and the autotaxin–lysoPA axis evidence sex-associated metabotypes in the serum of COPD patientshttp://ow.ly/kAeE309MpdI

Discovery of 2-[[2-Ethyl-6-[4-[2-(3-hydroxyazetidin-1-yl)-2-oxoethyl]piperazin-1-yl]-8-methylimidazo[1,2-a]pyridin-3-yl]methylamino]-4-(4-fluorophenyl)thiazole-5-carbonitrile (GLPG1690), a First-in-Class Autotaxin Inhibitor Undergoing Clinical Evaluation for the Treatment of Idiopathic Pulmonary Fibrosis

Autotaxin is a circulating enzyme with a major role in the production of lysophosphatic acid (LPA) species in blood. A role for the autotaxin/LPA axis has been suggested in many disease areas including pulmonary fibrosis. Structural modifications of the known autotaxin inhibitor lead compound 1, to attenuate hERG inhibition, remove CYP3A4 time-dependent inhibition, and improve pharmacokinetic properties, led to the identification of clinical candidate GLPG1690 (11). Compound 11 was able to cause a sustained reduction of LPA levels in plasma in vivo and was shown to be efficacious in a bleomycin-induced pulmonary fibrosis model in mice and in reducing extracellular matrix deposition in the lung while also reducing LPA 18:2 content in bronchoalveolar lavage fluid. Compound 11 is currently being evaluated in an exploratory phase 2a study in idiopathic pulmonary fibrosis patients.

Adult Lysophosphatidic Acid Receptor 1-Deficient Rats with Hyperoxia-Induced Neonatal Chronic Lung Disease Are Protected against Lipopolysaccharide-Induced Acute Lung Injury

Aim: Survivors of neonatal chronic lung disease or bronchopulmonary dysplasia (BPD) suffer from compromised lung function and are at high risk for developing lung injury by multiple insults later in life. Because neonatal lysophosphatidic acid receptor-1 (LPAR1)-deficient rats are protected against hyperoxia-induced lung injury, we hypothesize that LPAR1-deficiency may protect adult survivors of BPD from a second hit response against lipopolysaccharides (LPS)-induced lung injury.

Methods: Directly after birth, Wistar control and LPAR1-deficient rat pups were exposed to hyperoxia (90%) for 8 days followed by recovery in room air. After 7 weeks, male rats received either LPS (2 mg kg⁻¹) or 0.9% NaCl by intraperitoneal injection. Alveolar development and lung inflammation were investigated by morphometric analysis, IL-6 production, and mRNA expression of cytokines, chemokines, coagulation factors, and an indicator of oxidative stress.

Results: LPAR1-deficient and control rats developed hyperoxia-induced neonatal emphysema, which persisted into adulthood, as demonstrated by alveolar enlargement and decreased vessel density. LPAR1-deficiency protected against LPS-induced lung injury. Adult controls with BPD exhibited an exacerbated response toward LPS with an increased expression of pro-inflammatory mRNAs, whereas LPAR1-deficient rats with BPD were less sensitive to this “second hit” with a decreased pulmonary influx of macrophages and neutrophils, interleukin-6 (IL-6) production, and mRNA expression of IL-6, monocyte chemoattractant protein-1, cytokine-induced neutrophil chemoattractant 1, plasminogen activator inhibitor-1, and tissue factor.

Conclusion: LPAR1-deficient rats have increased hyperoxia-induced BPD survival rates and, despite the presence of neonatal emphysema, are less sensitive to an aggravated “second hit” than Wistar controls with BPD. Intervening in LPA-LPAR1-dependent signaling may not only have therapeutic potential for neonatal chronic lung disease, but may also protect adult survivors of BPD from sequelae later in life.

FoxO1 regulates allergic asthmatic inflammation through regulating polarization of the macrophage inflammatory phenotype

Inflammatory monocyte and tissue macrophages influence the initiation, progression, and resolution of type 2 immune responses, and alveolar macrophages are the most prevalent immune-effector cells in the lung. While we were characterizing the M1- or M2-like macrophages in type 2 allergic inflammation, we discovered that FoxO1 is highly expressed in alternatively activated macrophages. Although several studies have been focused on the fundamental role of FoxOs in hematopoietic and immune cells, the exact role that FoxO1 plays in allergic asthmatic inflammation in activated macrophages has not been investigated. Growing evidences indicate that FoxO1 acts as an upstream regulator of IRF4 and could have a role in a specific inflammatory phenotype of macrophages. Therefore, we hypothesized that IRF4 expression regulated by FoxO1 in alveolar macrophages is required for established type 2 immune mediates allergic lung inflammation. Our data indicate that targeted deletion of FoxO1 using FoxO1-selective inhibitor AS1842856 and genetic ablation of FoxO1 in macrophages significantly decreases IRF4 and various M2 macrophage-associated genes, suggesting a mechanism that involves FoxO1-IRF4 signaling in alveolar macrophages that works to polarize macrophages toward established type 2 immune responses. In response to the challenge of DRA (dust mite, ragweed, and Aspergillus) allergens, macrophage specific FoxO1 overexpression is associated with an accentuation of asthmatic lung inflammation, whereas pharmacologic inhibition of FoxO1 by AS1842856 attenuates the development of asthmatic lung inflammation. Thus, our study identifies a role for FoxO1-IRF4 signaling in the development of alternatively activated alveolar macrophages that contribute to type 2 allergic airway inflammation.

Endogenous lysophosphatidic acid (LPA1 ) receptor agonists demonstrate ligand bias between calcium and ERK signalling pathways in human lung fibroblasts

BACKGROUND AND PURPOSE

Human lung fibroblasts (HLF) express high levels of the LPA₁ receptor, a GPCR that responds to the endogenous lipid mediator, lysophosphatidic acid (LPA). Several molecular species or analogues of LPA exist and have been detected in biological fluids such as serum and plasma. The most widely expressed of the LPA receptor family is the LPA₁ receptor, which predominantly couples to G_q/11 , G_i/o and G_12/13 proteins. This promiscuity of coupling raises the possibility that some of the LPA analogues may bias the LPA₁ receptor towards one signalling pathway over another.

EXPERIMENTAL APPROACH

Here, we have explored the signalling profiles of a range of LPA analogues in HLF that endogenously express the LPA₁ receptor. HLF were treated with LPA analogues and receptor activation monitored via calcium mobilization and ERK phosphorylation.

KEY RESULTS

These analyses demonstrated that the 16:0, 17:0, 18:2 and C18:1 LPA analogues appear to exhibit ligand bias between ERK phosphorylation and calcium mobilization when compared with 18:1 LPA, one of the most abundant forms of LPA that has been found in human plasma.

CONCLUSION AND IMPLICATIONS

The importance of LPA as a key signalling molecule is shown by its widespread occurrence in biological fluids and its association with disease conditions such as fibrosis and cancer. These findings have important, as yet unexplored, implications for the (patho-) physiological signalling of the LPA₁ receptor, as it may be influenced not only by the concentration of endogenous ligand but the isoform as well.

Autotaxin Expression Is Regulated at the Post-transcriptional Level by the RNA-binding Proteins HuR and AUF1

Autotaxin (ATX) is a key enzyme that converts lysophosphatidylcholine (LPC) into lysophosphatidic acid (LPA), a lysophospholipid mediator that regulates cellular activities through its specific G protein-coupled receptors. The ATX-LPA axis plays an important role in various physiological and pathological processes, especially in inflammation and cancer development. Although the transcriptional regulation of ATX has been widely studied, the post-transcriptional regulation of ATX is largely unknown. In this study, we identified conserved adenylate-uridylate (AU)-rich elements in the ATX mRNA 3'-untranslated region (3'UTR). The RNA-binding proteins HuR and AUF1 directly bound to the ATX mRNA 3'UTR and had antagonistic functions in ATX expression. HuR enhanced ATX expression by increasing ATX mRNA stability, whereas AUF1 suppressed ATX expression by promoting ATX mRNA decay. HuR and AUF1 were involved in ATX regulation in Colo320 human colon cancer cells and the LPS-stimulated human monocytic THP-1 cells. HuR knockdown suppressed ATX expression in B16 mouse melanoma cells, leading to inhibition of cell migration. This effect was reversed by AUF1 knockdown to recover ATX expression or by the addition of LPA. These results suggest that the post-transcriptional regulation of ATX expression by HuR and AUF1 modulates cancer cell migration. In summary, we identified HuR and AUF1 as novel post-transcriptional regulators of ATX expression, thereby elucidating a novel mechanism regulating the ATX-LPA axis.

Novel Inhibitory Effect of a Lysophosphatidic Acid 2 Agonist on Allergen-Driven Airway Inflammation

Lysophosphatidic acid (LPA) is a pleiotropic lipid signaling molecule associated with asthma pathobiology. LPA elicits its effects by binding to at least six known cell surface G protein-coupled receptors (LPA1-6) that are expressed in the lung in a cell type-specific manner. LPA2 in particular has emerged as an attractive therapeutic target in asthma because it appears to transduce inhibitory or cell-protective signals. We studied a novel and specific small molecule LPA2 agonist (2-[4-(1,3-dioxo-1H,3H-benzoisoquinolin-2-yl)butylsulfamoyl] benzoic acid [DBIBB]) in a mouse model of house dust mite-induced allergic airway inflammation. Mice injected with DBIBB developed significantly less airway and lung inflammation compared with vehicle-treated controls. Levels of lung Th2 cytokines were also significantly attenuated by DBIBB. We conclude that pharmacologic activation of LPA2 attenuates Th2-driven allergic airway inflammation in a mouse model of asthma. Targeting LPA receptor signaling holds therapeutic promise in allergic asthma.

Autotaxin activity increases locally following lung injury, but is not required for pulmonary lysophosphatidic acid production or fibrosis

Lysophosphatidic acid (LPA) is an important mediator of pulmonary fibrosis. In blood and multiple tumor types, autotaxin produces LPA from lysophosphatidylcholine (LPC) via lysophospholipase D activity, but alternative enzymatic pathways also exist for LPA production. We examined the role of autotaxin (ATX) in pulmonary LPA production during fibrogenesis in a bleomycin mouse model. We found that bleomycin injury increases the bronchoalveolar lavage (BAL) fluid levels of ATX protein 17-fold. However, the LPA and LPC species that increase in BAL of bleomycin-injured mice were discordant, inconsistent with a substrate-product relationship between LPC and LPA in pulmonary fibrosis. LPA species with longer chain polyunsaturated acyl groups predominated in BAL fluid after bleomycin injury, with 22:5 and 22:6 species accounting for 55 and 16% of the total, whereas the predominant BAL LPC species contained shorter chain, saturated acyl groups, with 16:0 and 18:0 species accounting for 56 and 14% of the total. Further, administration of the potent ATX inhibitor PAT-048 to bleomycin-challenged mice markedly decreased ATX activity systemically and in the lung, without effect on pulmonary LPA or fibrosis. Therefore, alternative ATX-independent pathways are likely responsible for local generation of LPA in the injured lung. These pathways will require identification to therapeutically target LPA production in pulmonary fibrosis.-Black, K. E., Berdyshev, E., Bain, G., Castelino, F. V., Shea, B. S., Probst, C. K., Fontaine, B. A., Bronova, I., Goulet, L., Lagares, D., Ahluwalia, N., Knipe, R. S., Natarajan, V., Tager, A. M. Autotaxin activity increases locally following lung injury, but is not required for pulmonary lysophosphatidic acid production or fibrosis.

Deficiency or inhibition of lysophosphatidic acid receptor 1 protects against hyperoxia-induced lung injury in neonatal rats

AIM

Blocking of lysophosphatidic acid (LPA) receptor (LPAR) 1 may be a novel therapeutic option for bronchopulmonary dysplasia (BPD) by preventing the LPAR1-mediated adverse effects of its ligand (LPA), consisting of lung inflammation, pulmonary arterial hypertension (PAH) and fibrosis.

METHODS

In Wistar rats with experimental BPD, induced by continuous exposure to 100% oxygen for 10 days, we determined the beneficial effects of LPAR1 deficiency in neonatal rats with a missense mutation in cytoplasmic helix 8 of LPAR1 and of LPAR1 and -3 blocking with Ki16425. Parameters investigated included survival, lung and heart histopathology, fibrin and collagen deposition, vascular leakage and differential mRNA expression in the lungs of key genes involved in LPA signalling and BPD pathogenesis.

RESULTS

LPAR1-mutant rats were protected against experimental BPD and mortality with reduced alveolar septal thickness, lung inflammation (reduced influx of macrophages and neutrophils, and CINC1 expression) and collagen III deposition. However, LPAR1-mutant rats were not protected against alveolar enlargement, increased medial wall thickness of small arterioles, fibrin deposition and vascular alveolar leakage. Treatment of experimental BPD with Ki16425 confirmed the data observed in LPAR1-mutant rats, but did not reduce the pulmonary influx of neutrophils, CINC1 expression and mortality in rats with experimental BPD. In addition, Ki16425 treatment protected against PAH and right ventricular hypertrophy.

CONCLUSION

LPAR1 deficiency attenuates pulmonary injury by reducing pulmonary inflammation and fibrosis, thereby reducing mortality, but does not affect alveolar and vascular development and, unlike Ki16425 treatment, does not prevent PAH in neonatal rats with experimental BPD.

Polyunsaturated lysophosphatidic acid as a potential asthma biomarker

Lysophosphatidic acid (LPA), a lipid mediator in biological fluids and tissues, is generated mainly by autotaxin that hydrolyzes lysophosphatidylcholine to LPA and choline. Total LPA levels are increased in bronchoalveolar lavage fluid from asthmatic lung, and are strongly induced following subsegmental bronchoprovocation with allergen in subjects with allergic asthma. Polyunsaturated molecular species of LPA (C22:5 and C22:6) are selectively synthesized in the airways of asthma subjects following allergen challenge and in mouse models of allergic airway inflammation, having been identified and quantified by LC/MS/MS lipidomics. This review discusses current knowledge of LPA production in asthmatic lung and the potential utility of polyunsaturated LPA molecular species as novel biomarkers in bronchoalveolar lavage fluid and exhaled breath condensate of asthma subjects.

Dual Action of Lysophosphatidate-Functionalised Titanium: Interactions with Human (MG63) Osteoblasts and Methicillin Resistant Staphylococcus aureus

Titanium (Ti) is a widely used material for surgical implants; total joint replacements (TJRs), screws and plates for fixing bones and dental implants are forged from Ti. Whilst Ti integrates well into host tissue approximately 10% of TJRs will fail in the lifetime of the patient through a process known as aseptic loosening. These failures necessitate revision arthroplasties which are more complicated and costly than the initial procedure. Finding ways of enhancing early (osseo)integration of TJRs is therefore highly desirable and continues to represent a research priority in current biomaterial design. One way of realising improvements in implant quality is to coat the Ti surface with small biological agents known to support human osteoblast formation and maturation at Ti surfaces. Lysophosphatidic acid (LPA) and certain LPA analogues offer potential solutions as Ti coatings in reducing aseptic loosening. Herein we present evidence for the successful bio-functionalisation of Ti using LPA. This modified Ti surface heightened the maturation of human osteoblasts, as supported by increased expression of alkaline phosphatase. These functionalised surfaces also deterred the attachment and growth of Staphylococcus aureus, a bacterium often associated with implant failures through sepsis. Collectively we provide evidence for the fabrication of a dual-action Ti surface finish, a highly desirable feature towards the development of next-generation implantable devices.

The Bulk of Autotaxin Activity Is Dispensable for Adult Mouse Life

Autotaxin (ATX, Enpp2) is a secreted lysophospholipase D catalysing the production of lysophosphatidic acid, a pleiotropic growth factor-like lysophospholipid. Increased ATX expression has been detected in a number of chronic inflammatory diseases and different types of cancer, while genetic interventions have proven a role for ATX in disease pathogenesis. Therefore, ATX has emerged as a potential drug target and a large number of ATX inhibitors have been developed exhibiting promising therapeutic potential. However, the embryonic lethality of ATX null mice and the ubiquitous expression of ATX and LPA receptors in adult life question the suitability of ATX as a drug target. Here we show that inducible, ubiquitous genetic deletion of ATX in adult mice, as well as long-term potent pharmacologic inhibition, are well tolerated, alleviating potential toxicity concerns of ATX therapeutic targeting.

Autotaxin-LPA receptor axis in the pathogenesis of lung diseases

Lysophosphatidic acid (LPA) is a small lipid which mediates a variety of cellular functions via the activation of LPA receptors. LPA is generated from lysophosphatidylcholine by the extracellular enzyme, autotaxin (ATX). Elevated ATX expression, LPA production and their signaling pathways have been reported in multiple pathological conditions of lung tissue, including inflammation, fibrosis and cancer. Emerging evidence has highlighted the importance of ATX and LPA receptors in the pathogenesis of lung diseases. Here, we briefly review the current knowledge of different roles of the ATX-LPA receptor axis in lung diseases focusing on inflammation, fibrosis and cancer.

Type I Interferons Function as Autocrine and Paracrine Factors to Induce Autotaxin in Response to TLR Activation

Lysophosphatidic acid (LPA) is an important phospholipid mediator in inflammation and immunity. However, the mechanism of LPA regulation during inflammatory response is largely unknown. Autotaxin (ATX) is the key enzyme to produce extracellular LPA from lysophosphatidylcholine (LPC). In this study, we found that ATX was induced in monocytic THP-1 cells by TLR4 ligand lipopolysaccharide (LPS), TLR9 ligand CpG oligonucleotide, and TLR3 ligand poly(I:C), respectively. The ATX induction by TLR ligand was abolished by the neutralizing antibody against IFN-β or the knockdown of IFNAR1, indicating that type I IFN autocrine loop is responsible for the ATX induction upon TLR activation. Both IFN-β and IFN-α were able to induce ATX expression via the JAK-STAT and PI3K-AKT pathways but with different time-dependent manners. The ATX induction by IFN-β was dramatically enhanced by IFN-γ, which had no significant effect on ATX expression alone, suggesting a synergy effect between type I and type II IFNs in ATX induction. Extracellular LPA levels were significantly increased when THP-1 cells were treated with IFN-α/β or TLR ligands. In addition, the type I IFN-mediated ATX induction was identified in human monocyte-derived dendritic cells (moDCs) stimulated with LPS or poly(I:C), and IFN-α/β could induce ATX expression in human peripheral blood mononuclear cells (PBMCs) and monocytes isolated form blood samples. These results suggest that, in response to TLR activation, ATX is induced through a type I INF autocrine-paracrine loop to enhance LPA generation.

Recruited alveolar macrophages, in response to airway epithelial-derived monocyte chemoattractant protein 1/CCl2, regulate airway inflammation and remodeling in allergic asthma

Although alveolar macrophages (AMs) from patients with asthma are known to be functionally different from those of healthy individuals, the mechanism by which this transformation occurs has not been fully elucidated in asthma. The goal of this study was to define the mechanisms that control AM phenotypic and functional transformation in response to acute allergic airway inflammation. The phenotype and functional characteristics of AMs obtained from human subjects with asthma after subsegmental bronchoprovocation with allergen was studied. Using macrophage-depleted mice, the role and trafficking of AM populations was determined using an acute allergic lung inflammation model. We observed that depletion of AMs in a mouse allergic asthma model attenuates Th2-type allergic lung inflammation and its consequent airway remodeling. In both human and mouse, endobronchial challenge with allergen induced a marked increase in monocyte chemotactic proteins (MCPs) in bronchoalveolar fluid, concomitant with the rapid appearance of a monocyte-derived population of AMs. Furthermore, airway allergen challenge of allergic subjects with mild asthma skewed the pattern of AM gene expression toward high levels of the receptor for MCP1 (CCR2/MCP1R) and expression of M2 phenotypic proteins, whereas most proinflammatory genes were highly suppressed. CCL2/MCP-1 gene expression was prominent in bronchial epithelial cells in a mouse allergic asthma model, and in vitro studies indicate that bronchial epithelial cells produced abundant MCP-1 in response to house dust mite allergen. Thus, our study indicates that bronchial allergen challenge induces the recruitment of blood monocytes along a chemotactic gradient generated by allergen-exposed bronchial epithelial cells.

Autotaxin and Endotoxin-Induced Acute Lung Injury

Acute Lung Injury (ALI) is a life-threatening, diffuse heterogeneous lung injury characterized by acute onset, pulmonary edema and respiratory failure. Lipopolysaccharide (LPS) is a common cause of both direct and indirect lung injury and when administered to a mouse induces a lung phenotype exhibiting some of the clinical characteristics of human ALI. Here, we report that LPS inhalation in mice results in increased bronchoalveolar lavage fluid (BALF) levels of Autotaxin (ATX, Enpp2), a lysophospholipase D largely responsible for the conversion of lysophosphatidylcholine (LPC) to lysophosphatidic acid (LPA) in biological fluids and chronically inflamed sites. In agreement, gradual increases were also detected in BALF LPA levels, following inflammation and pulmonary edema. However, genetic or pharmacologic targeting of ATX had minor effects in ALI severity, suggesting no major involvement of the ATX/LPA axis in acute inflammation. Moreover, systemic, chronic exposure to increased ATX/LPA levels was shown to predispose to and/or to promote acute inflammation and ALI unlike chronic inflammatory pathophysiological situations, further suggesting a differential involvement of the ATX/LPA axis in acute versus chronic pulmonary inflammation.

Definition of a Novel Pathway Centered on Lysophosphatidic Acid To Recruit Monocytes during the Resolution Phase of Tissue Inflammation

Blood-derived monocytes remove apoptotic cells and terminate inflammation in settings as diverse as atherosclerosis and Alzheimer’s disease. They express high levels of the proresolving receptor ALX/FPR2, which is activated by the protein annexin A1 (ANXA1), found in high abundance in inflammatory exudates. Using primary human blood monocytes from healthy donors, we identified ANXA1 as a potent CD14⁺CD16⁻ monocyte chemoattractant, acting via ALX/FPR2. Downstream signaling pathway analysis revealed the p38 MAPK-mediated activation of a calcium independent phospholipase A₂ with resultant synthesis of lysophosphatidic acid (LPA) driving chemotaxis through LPA receptor 2 and actin cytoskeletal mobilization. In vivo experiments confirmed ANXA1 as an independent phospholipase A₂–dependent monocyte recruiter; congruently, monocyte recruitment was significantly impaired during ongoing zymosan-induced inflammation in AnxA1^−/− or alx/fpr2/3^−/− mice. Using a dorsal air-pouch model, passive transfer of apoptotic neutrophils between AnxA1^−/− and wild-type mice identified effete neutrophils as the primary source of soluble ANXA1 in inflammatory resolution. Together, these data elucidate a novel proresolving network centered on ANXA1 and LPA generation and identify previously unappreciated determinants of ANXA1 and ALX/FPR2 signaling in monocytes.

The transcription factor PU.1 promotes alternative macrophage polarization and asthmatic airway inflammation

The transcription factor PU.1 is involved in regulation of macrophage differentiation and maturation. However, the role of PU.1 in alternatively activated macrophage (AAM) and asthmatic inflammation has yet been investigated. Here we report that PU.1 serves as a critical regulator of AAM polarization and promotes the pathological progress of asthmatic airway inflammation. In response to the challenge of DRA (dust mite, ragweed, and Aspergillus) allergens, conditional PU.1-deficient (PU/ER(T)(+/-)) mice displayed attenuated allergic airway inflammation, including decreased alveolar eosinophil infiltration and reduced production of IgE, which were associated with decreased mucous glands and goblet cell hyperplasia. The reduced asthmatic inflammation in PU/ER(T)(+/-) mice was restored by adoptive transfer of IL-4-induced wild-type (WT) macrophages. Moreover, after treating PU/ER(T)(+/-) mice with tamoxifen to rescue PU.1 function, the allergic asthmatic inflammation was significantly restored. In vitro studies demonstrate that treatment of PU.1-deficient macrophages with IL-4 attenuated the expression of chitinase 3-like 3 (Ym-1) and resistin-like molecule alpha 1 (Fizz-1), two specific markers of AAM polarization. In addition, PU.1 expression in macrophages was inducible in response to IL-4 challenge, which was associated with phosphorylation of signal transducer and activator of transcription 6 (STAT6). Furthermore, DRA challenge in sensitized mice almost abrogated gene expression of Ym-1 and Fizz-1 in lung tissues of PU/ER(T)(+/-) mice compared with WT mice. These data, all together, indicate that PU.1 plays a critical role in AAM polarization and asthmatic inflammation.

Toluene diisocyanate: Induction of the autotaxin-lysophosphatidic acid axis and its association with airways symptoms

Diisocyanates are industrial chemicals which have a wide range of applications in developed and developing countries. They are notorious lung toxicants and respiratory sensitizers. However, the mechanisms behind their adverse effects are not adequately characterized. Autotaxin (ATX) is an enzyme producing lysophosphatidic acid (LPA), and the ATX-LPA axis has been implicated in lung related inflammatory conditions and diseases, including allergic asthma, but not to toxicity of environmental low-molecular-weight chemicals. We investigated effects of toluene diisocyanate (TDI) on ATX induction in human lung epithelial cell models, and we correlated LPA-levels in plasma to biomarkers of TDI exposure in urine collected from workers exposed to <5ppb (parts per billion). Information on workers' symptoms was collected through interviews. One nanomolar TDI robustly induced ATX release within 10min in vitro. A P2X7- and P2X4-dependent microvesicle formation was implicated in a rapid ATX release and a subsequent protein synthesis. Co-localization between purinergic receptors and ATX was documented by immunofluorescence and confocal microscopy. The release was modulated by monocyte chemoattractant protein-1 (MCP-1) and by extracellular ATP. In workers, we found a dose-response relationship between TDI exposure biomarkers in urine and LPA levels in plasma. Among symptomatic workers reporting "sneezing", the LPA levels were higher than among non-symptomatic workers. This is the first report indicating induction of the ATX-LPA axis by an environmental low-molecular-weight chemical, and our data suggest a role for the ATX-LPA axis in TDI toxicity.

CARMA3 Is Critical for the Initiation of Allergic Airway Inflammation

Innate immune responses to allergens by airway epithelial cells (AECs) help initiate and propagate the adaptive immune response associated with allergic airway inflammation in asthma. Activation of the transcription factor NF-κB in AECs by allergens or secondary mediators via G protein-coupled receptors (GPCRs) is an important component of this multifaceted inflammatory cascade. Members of the caspase recruitment domain family of proteins display tissue-specific expression and help mediate NF-κB activity in response to numerous stimuli. We have previously shown that caspase recruitment domain-containing membrane-associated guanylate kinase protein (CARMA)3 is specifically expressed in AECs and mediates NF-κB activation in these cells in response to stimulation with the GPCR agonist lysophosphatidic acid. In this study, we demonstrate that reduced levels of CARMA3 in normal human bronchial epithelial cells decreases the production of proasthmatic mediators in response to a panel of asthma-relevant GPCR ligands such as lysophosphatidic acid, adenosine triphosphate, and allergens that activate GPCRs such as Alternaria alternata and house dust mite. We then show that genetically modified mice with CARMA3-deficient AECs have reduced airway eosinophilia and proinflammatory cytokine production in a murine model of allergic airway inflammation. Additionally, we demonstrate that these mice have impaired dendritic cell maturation in the lung and that dendritic cells from mice with CARMA3-deficient AECs have impaired Ag processing. In conclusion, we show that AEC CARMA3 helps mediate allergic airway inflammation, and that CARMA3 is a critical signaling molecule bridging the innate and adaptive immune responses in the lung.

Therapeutic exercise attenuates neutrophilic lung injury and skeletal muscle wasting

Early mobilization of critically ill patients with the acute respiratory distress syndrome (ARDS) has emerged as a therapeutic strategy that improves patient outcomes, such as the duration of mechanical ventilation and muscle strength. Despite the apparent efficacy of early mobility programs, their use in clinical practice is limited outside of specialized centers and clinical trials. To evaluate the mechanisms underlying mobility therapy, we exercised acute lung injury (ALI) mice for 2 days after the instillation of lipopolysaccharides into their lungs. We found that a short duration of moderate intensity exercise in ALI mice attenuated muscle ring finger 1 (MuRF1)-mediated atrophy of the limb and respiratory muscles and improved limb muscle force generation. Exercise also limited the influx of neutrophils into the alveolar space through modulation of a coordinated systemic neutrophil chemokine response. Granulocyte colony-stimulating factor (G-CSF) concentrations were systemically reduced by exercise in ALI mice, and in vivo blockade of the G-CSF receptor recapitulated the lung exercise phenotype in ALI mice. Additionally, plasma G-CSF concentrations in humans with acute respiratory failure (ARF) undergoing early mobility therapy showed greater decrements over time compared to control ARF patients. Together, these data provide a mechanism whereby early mobility therapy attenuates muscle wasting and limits ongoing alveolar neutrophilia through modulation of systemic neutrophil chemokines in lung-injured mice and humans.

Promising pharmacological directions in the world of lysophosphatidic Acid signaling

Lysophosphatidic acid (LPA) is a signaling lipid that binds to six known lysophosphatidic acid receptors (LPARs), named LPA₁-LPA₆. These receptors initiate signaling cascades relevant to development, maintenance, and healing processes throughout the body. The diversity and specificity of LPA signaling, especially in relation to cancer and autoimmune disorders, makes LPA receptor modulation an attractive target for drug development. Several LPAR-specific analogues and small molecules have been synthesized and are efficacious in attenuating pathology in disease models. To date, at least three compounds have passed phase I and phase II clinical trials for idiopathic pulmonary fibrosis and systemic sclerosis. This review focuses on the promising therapeutic directions emerging in LPA signaling toward ameliorating several diseases, including cancer, fibrosis, arthritis, hydrocephalus, and traumatic injury.

DNAH5 is associated with total lung capacity in chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is characterized by expiratory flow limitation, causing air trapping and lung hyperinflation. Hyperinflation leads to reduced exercise tolerance and poor quality of life in COPD patients. Total lung capacity (TLC) is an indicator of hyperinflation particularly in subjects with moderate-to-severe airflow obstruction. The aim of our study was to identify genetic variants associated with TLC in COPD.

METHODS

We performed genome-wide association studies (GWASs) in white subjects from three cohorts: the COPDGene Study; the Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints (ECLIPSE); and GenKOLS (Bergen, Norway). All subjects were current or ex-smokers with at least moderate airflow obstruction, defined by a ratio of forced expiratory volume in 1 second to forced vital capacity (FEV1/FVC) <0.7 and FEV1 < 80% predicted on post-bronchodilator spirometry. TLC was calculated by using volumetric computed tomography scans at full inspiration (TLCCT). Genotyping in each cohort was completed, with statistical imputation of additional markers. To find genetic variants associated with TLCCT, linear regression models were used, with adjustment for age, sex, pack-years of smoking, height, and principal components for genetic ancestry. Results were summarized using fixed-effect meta-analysis.

RESULTS

Analysis of a total of 4,543 COPD subjects identified one genome-wide significant locus on chromosome 5p15.2 (rs114929486, β = 0.42L, P = 4.66 × 10-8).

CONCLUSIONS

In COPD, TLCCT was associated with a SNP in dynein, axonemal, heavy chain 5 (DNAH5), a gene in which genetic variants can cause primary ciliary dyskinesia. DNAH5 could have an effect on hyperinflation in COPD.

Regulation of T cell motility in vitro and in vivo by LPA and LPA2

Lysophosphatidic acid (LPA) and the LPA-generating enzyme autotaxin (ATX) have been implicated in lymphocyte trafficking and the regulation of lymphocyte entry into lymph nodes. High local concentrations of LPA are thought to be present in lymph node high endothelial venules, suggesting a direct influence of LPA on cell migration. However, little is known about the mechanism of action of LPA, and more work is needed to define the expression and function of the six known G protein-coupled receptors (LPA 1-6) in T cells. We studied the effects of 18∶1 and 16∶0 LPA on naïve CD4+ T cell migration and show that LPA induces CD4+ T cell chemorepulsion in a Transwell system, and also improves the quality of non-directed migration on ICAM-1 and CCL21 coated plates. Using intravital two-photon microscopy, lpa2-/- CD4+ T cells display a striking defect in early migratory behavior at HEVs and in lymph nodes. However, later homeostatic recirculation and LPA-directed migration in vitro were unaffected by loss of lpa2. Taken together, these data highlight a previously unsuspected and non-redundant role for LPA2 in intranodal T cell motility, and suggest that specific functions of LPA may be manipulated by targeting T cell LPA receptors.

Challenges in accurate quantitation of lysophosphatidic acids in human biofluids

Lysophosphatidic acids (LPAs) are biologically active signaling molecules involved in the regulation of many cellular processes and have been implicated as potential mediators of fibroblast recruitment to the pulmonary airspace, pointing to possible involvement of LPA in the pathology of pulmonary fibrosis. LPAs have been measured in various biological matrices and many challenges involved with their analyses have been documented. However, little published information is available describing LPA levels in human bronchoalveolar lavage fluid (BALF). We therefore conducted detailed investigations into the effects of extensive sample handling and sample preparation conditions on LPA levels in human BALF. Further, targeted lipid profiling of human BALF and plasma identified the most abundant lysophospholipids likely to interfere with LPA measurements. We present the findings from these investigations, highlighting the importance of well-controlled sample handling for the accurate quantitation of LPA. Further, we show that chromatographic separation of individual LPA species from their corresponding lysophospholipid species is critical to avoid reporting artificially elevated levels. The optimized sample preparation and LC/MS/MS method was qualified using a stable isotope-labeled LPA as a surrogate calibrant and used to determine LPA levels in human BALF and plasma from a Phase 0 clinical study comparing idiopathic pulmonary fibrosis patients to healthy controls.