AbstractsBiology & Animal Science

The acute respiratory distress syndrome (ARDS), due to mechanical ventilation, lung infection, aspiration, sepsis or prematurity, is the major cause of morbidity and mortality in Intensive Care Units of adults, children and neonates. Pulmonary hypertension, primary or secondary to existing condition, promotes similarly severe morbidity that may also lead to respiratory and cardiac failure. Limited therapies are effective nowadays in the management of both conditions. Since the molecular and cellular mechanisms of acute lung injury (the pathologic picture of ARDS) and pulmonary hypertension have not been clearly elucidated, their understanding is crucial to develop targeted and effective therapies. Lung inflammation and specifically innate immunity and macrophage accumulation appears to be a common denominator that contributes to pathology in both diseases.By utilizing wild-type (WT) mice and mice genetically modified in key – genes for inflammation and vascular function (Akt2 knock-out, lung specific inducible HO-1 transgenic), in the current study we investigate the nature of inflammatory response and the phenotype of macrophage activation in animal models of acute lung injury and pulmonary hypertension and we aim to elucidate its potential causative role in the pathogenesis of disease. To investigate the role of macrophage activation in aseptic lung injury and identify molecular mediators with therapeutic potential, lung injury was induced in WT and Akt2-/- mice by hydrochloric acid aspiration. Acid-induced lung injury in WT mice was characterized by decreased lung compliance and increased protein and cytokine concentration in bronchoalveolar lavage fluid. Alveolar macrophages acquired a classical activation (M1) phenotype. Acid-induced lung injury was less severe in Akt2-/- mice compared with WT mice. Alveolar macrophages from acid-injured Akt2-/- mice demonstrated the alternative activation phenotype (M2). Although M2 polarization suppressed aseptic lung injury, it resulted in increased lung bacterial load when Akt2-/- mice were infected with Pseudomonas aeruginosa. To understand macrophage activation in our model and the role of Akt2, we studied the TLR pathway. We found that mRNA levels of TRAF6, IRF5, STAT1 but not IRAK1 were increased in alveolar macrophages in WT mice exposed to acid. On the other hand, macrophages from Akt2-/- mice exposed to acid had lower levels of TRAF6, IRF5, STAT1 and IRAK1 compared to WT mice. Τhe mRNA levels of IRAK1, TRAF6, STAT1 and IRF5 are known to be targeted by the anti-inflammatory microRNA miR-146a. Indeed, miR-146a was found to be induced during the late phase of lung injury in WT mice, whereas it was increased early in Akt2-/- mice. MiR-146a overexpression in WT macrophages suppressed LPS induced inducible NO synthase (iNOS) and promoted M2 polarization, whereas miR-146a inhibition in Akt2-/- macrophages restored iNOS expression. Furthermore, miR-146a delivery or Akt2 silencing in WT mice exposed to acid resulted in suppression of iNOS in alveolar macrophages. In…