RNA expression in ex vivo ventilated human lungs
Rationale: Overstretching of lung parenchyma may lead to tissue injury, especially during mechanical ventilation. There are no specific biomarkers of lung stretch.    Objectives: To identify transcriptomic signatures of micro-RNAs and genes specifically related to lung stretch and validate them in preclinical models.  Methods: Data on micro-RNA expression in response to stretch in experimental models were systematically pooled. Signatures were identified as those micro-RNAs or genes with differential expression in samples from stretched cells, and optimized using a greedy algorithm. Transcriptomic scores were calculated as the difference of geometric means in expression of up- and down-regulated features, and compared among different magnitudes of stretch. The accuracy of these scores was validated in animal models of lung injury, ex vivo mechanically ventilated human lungs and in bronchoalveolar lavage fluid (BALF) from patients under different ventilatory conditions.  Measurements and main results: Eight micro-RNAs were differentially expressed in stretched cell cultures (n=24). Amongst the genes regulated by these micro-RNAs, a 180-gene signature was identified in ex vivo models (n=106) and refined using data from animal models (n=143) to obtain a 4-gene signature. The corresponding scores were significantly higher in samples submitted to stretch or injurious mechanical ventilation. The microRNA signatures were validated in human tissue and BALF, with areas under the ROC curve between 0.89 and 1 respectively to identify lung overdistention.  Conclusions: Lung cell stretch induces the expression of specific micro-RNA and genes. These signatures may be used to obtain an index of lung overstretching that can be measured at the bedside. Overall design: Human lungs not suitable for transplantation were exvivo perfused and maintained on continous positive airway pressure (CPAP, n=3) of 10 cmH2O or ventilated with a tidal volume of 12 ml/Kg of predicted body weight and zero end-expiratory pressure to induce ventilator-induced lung injury (VILI, n=3). After 4 hours of CPAP/ventilation, lungs were deflated and a portion of tissue homogenized in trizol.