ABSTRACT
Although acute lung injury (ALI) contributes significantly to critical illness, resolution often occurs spontaneously through endogenous pathways. We recently found that mechanical ventilation increases levels of pulmonary adenosine, a signaling molecule known to attenuate lung inflammation. In this study, we hypothesized a contribution of transcriptionally controlled pathways to pulmonary adenosine receptor (ADOR) signaling during ALI. We gained initial insight from microarray analysis of pulmonary epithelia exposed to conditions of cyclic mechanical stretch, a mimic for ventilation-induced lung disease. Surprisingly, these studies revealed a selective induction of the ADORA2B. Using real-time RT-PCR and Western blotting, we confirmed an up to 9-fold induction of the ADORA2B following cyclic mechanical stretch (A549, Calu-3, or human primary alveolar epithelial cells). Studies using ADORA2B promoter constructs identified a prominent region within the ADORA2B promoter conveying stretch responsiveness. This region of the promoter contained a binding site for the transcription factor hypoxia-inducible factor (HIF)-1. Additional studies using site-directed mutagenesis or transcription factor binding assays demonstrated a functional role for HIF-1 in stretch-induced increases of ADORA2B expression. Moreover, studies of ventilator-induced lung injury revealed induction of the ADORA2B during ALI in vivo that was abolished following HIF inhibition or genetic deletion of Hif1a. Together, these studies implicate HIF in the transcriptional control of pulmonary adenosine signaling during ALI.
Subject(s)
Acute Lung Injury/physiopathology , Hypoxia-Inducible Factor 1, alpha Subunit/physiology , Receptor, Adenosine A2B/genetics , Stress, Mechanical , Ventilator-Induced Lung Injury/physiopathology , Acute Lung Injury/metabolism , Adenosine/physiology , Animals , Binding Sites , Cells, Cultured , Epithelial Cells/physiology , Female , Genes, Reporter , Humans , Hypoxia-Inducible Factor 1, alpha Subunit/deficiency , Lung/metabolism , Lung/physiopathology , Male , Mice , Mice, Knockout , Mice, Transgenic , Promoter Regions, Genetic/genetics , Receptor, Adenosine A2B/biosynthesis , Receptor, Adenosine A2B/physiology , Transcription, GeneticABSTRACT
Acute lung injury (ALI) is characterized by alveolar injury and uncontrolled inflammation. Since most cases of ALI resolve spontaneously, understanding the endogenous mechanisms that promote ALI resolution is important to developing effective therapies. Previous studies have implicated extracellular adenosine signaling in tissue adaptation and wound healing. Therefore, we hypothesized a functional contribution for the endogenous production of adenosine during ALI resolution. As a model, we administered intratracheal LPS and observed peak lung injury at 3 d, with resolution by d 14. Treatment with pegylated adenosine-deaminase to enhance extracellular adenosine breakdown revealed impaired ALI resolution. Similarly, genetic deletion of cd73, the pacemaker for extracellular adenosine generation, was associated with increased mortality (0% wild-type and 40% in cd73(-/-) mice; P<0.05) and failure to resolve ALI adequately. Studies of inflammatory cell trafficking into the lungs during ALI resolution revealed that regulatory T cells (Tregs) express the highest levels of CD73. While Treg numbers in cd73(-/-) mice were similar to controls, cd73-deficient Tregs had attenuated immunosuppressive functions. Moreover, adoptive transfer of cd73-deficient Tregs into Rag(-/-) mice emulated the observed phenotype in cd73(-/-) mice, while transfer of wild-type Tregs was associated with normal ALI resolution. Together, these studies implicate CD73-dependent adenosine generation in Tregs in promoting ALI resolution.
Subject(s)
5'-Nucleotidase/physiology , Acute Lung Injury/immunology , Acute Lung Injury/metabolism , Adenosine/physiology , T-Lymphocytes, Regulatory/enzymology , T-Lymphocytes, Regulatory/immunology , 5'-Nucleotidase/deficiency , Acute Lung Injury/pathology , Adenosine/deficiency , Adenosine Deaminase/administration & dosage , Adoptive Transfer , Animals , Homeodomain Proteins/genetics , Homeodomain Proteins/metabolism , Lipopolysaccharides/toxicity , Male , Mice , Mice, 129 Strain , Mice, Inbred C57BL , Mice, Knockout , Signal Transduction , T-Lymphocytes, Regulatory/pathologyABSTRACT
OBJECTIVE: Acute mitral stenosis (MS) following mitral valve (MV) repair is a rare but severe complication. We hypothesize that intraoperative echocardiography can be utilized to diagnose iatrogenic MS immediately after MV repair. METHODS: The medical records of 552 consecutive patients undergoing MV repair at a single institution were reviewed. Post-cardiopulmonary bypass peak and mean transmitral pressure gradients (TMPG), and pressure half time (PHT) were obtained from intraoperative transesophageal echocardiographic (TEE) examinations in each patient. RESULTS: Nine patients (9/552â=â1.6%) received a reoperation for primary MS, prior to hospital discharge. Interestingly, all of these patients already showed intraoperative post-CPB mean and peak TMPGs that were significantly higher compared to values for those who did not: 10.7±4.8 mmHg vs 2.9±1.6 mmHg; p<0.0001 and 22.9±7.9 mmHg vs 7.6±3.7 mmHg; p<0.0001, respectively. However, PHT varied considerably (87±37 ms; range: 20-439 ms) within the entire population, and only weakly predicted the requirement for reoperation (113±56 vs. 87±37 ms, pâ=â0.034). Receiver operating characteristic curves showed strong discriminating ability for mean gradients (AUCâ=â0.993) and peak gradients (area under the curve, AUCâ=â0.996), but poor performance for PHT (AUCâ=â0.640). A value of ≥7 mmHg for mean, and ≥17 mmHg for peak TMPG, best separated patients who required reoperation for MS from those who did not. CONCLUSIONS: Intraoperative TEE diagnosis of a peak TMPG ≥17 mmHg or mean TMPG ≥7 mmHg immediately following CPB are suggestive of clinically relevant MS after MV repair.
