Hyunwook Lee

Mammalian lung development requires coordinated gene regulation to drive lung bud formation, branching morphogenesis, proximal-distal patterning, and epithelial specification. While key transcriptional and signaling regulators are known, the epigenetic regulators are less well studied. Here, we identify the canonical BAF complex as essential for lung epithelial development. Complete loss of BAF complex function causes failure of lung formation, and selective deletion of ARID1A leads to loss of distal patterning and reduced alveolar type 1 (AT1) cell differentiation, with emergence of a highly proliferative cell state defined by joint activation of YAP and WNT signaling and loss of BMP response. Epigenomic analyses demonstrate broad failure of cell type-specific enhancer activation. Notably, exogenous BMP4 rescues distal differentiation in embryonic murine lung organoids, while YAP and WNT signaling require functional BAF complex. These data demonstrate a requirement for BAF complex activity during lung epithelial development and reveal a surprising differential specificity between signaling pathways.

The acute respiratory distress syndrome (ARDS) is a highly lethal condition that impairs lung function and causes respiratory failure. Mechanical ventilation (MV) maintains gas exchange in patients with ARDS but exposes lung cells to physical forces that exacerbate injury. Our data demonstrate that mTOR complex 1 (mTORC1) is a mechanosensor in lung epithelial cells and that activation of this pathway during MV impairs lung function. We found that mTORC1 is activated in lung epithelial cells following volutrauma and atelectrauma in mice and humanized in vitro models of the lung microenvironment. mTORC1 is also activated in lung tissue of mechanically ventilated patients with ARDS. Deletion of Tsc2 , a negative regulator of mTORC1, in epithelial cells impairs lung compliance during MV. Conversely, treatment with rapamycin at the time MV is initiated improves lung compliance without altering lung inflammation or barrier permeability. mTORC1 inhibition mitigates physiologic lung injury by preventing surfactant dysfunction during MV. Our data demonstrate that, in contrast to canonical mTORC1 activation under favorable growth conditions, activation of mTORC1 during MV exacerbates lung injury and inhibition of this pathway may be a novel therapeutic target to mitigate ventilator-induced lung injury during ARDS.

Mechanical ventilation generates injurious forces that exacerbate lung injury. These forces disrupt lung barrier integrity, trigger proinflammatory mediator release, and differentially regulate genes and non-coding oligonucleotides including microRNAs. In this study, we identify miR-146a as a mechanosensitive microRNA in alveolar macrophages that has therapeutic potential to mitigate lung injury during mechanical ventilation. We use humanized in-vitro systems, mouse models, and biospecimens from patients to elucidate the expression dynamics of miR-146a needed to decrease lung injury during mechanical ventilation. We find that the endogenous increase in miR-146a following injurious ventilation is not sufficient to prevent lung injury. However, when miR-146a is highly overexpressed using a nanoparticle delivery platform it is sufficient to prevent injury. These data indicate that the endogenous increase in microRNA-146a during mechanical ventilation is a compensatory response that partially limits injury and that nanoparticle delivery of miR-146a is an effective strategy for mitigating lung injury during mechanical ventilation.

Acute respiratory distress syndrome (ARDS) is a highly lethal condition that impairs lung function and causes respiratory failure. Mechanical ventilation maintains gas exchange in patients with ARDS, but exposes lung cells to physical forces that exacerbate lung injury. Our data demonstrate that mTOR complex 1 (mTORC1) is a mechanosensor in lung epithelial cells and that activation of this pathway during mechanical ventilation exacerbates lung injury. We found that mTORC1 is activated in lung epithelial cells following volutrauma and atelectrauma in mice and humanized in vitro models of the lung microenvironment. mTORC1 is also activated in lung tissue of mechanically ventilated patients with ARDS. Deletion of Tsc2 , a negative regulator of mTORC1, in epithelial cells exacerbates physiologic lung dysfunction during mechanical ventilation. Conversely, treatment with rapamycin at the time mechanical ventilation is initiated prevents physiologic lung injury (i.e. decreased compliance) without altering lung inflammation or barrier permeability. mTORC1 inhibition mitigates physiologic lung injury by preventing surfactant dysfunction during mechanical ventilation. Our data demonstrate that in contrast to canonical mTORC1 activation under favorable growth conditions, activation of mTORC1 during mechanical ventilation exacerbates lung injury and inhibition of this pathway may be a novel therapeutic target to mitigate ventilator induced lung injury during ARDS.

During mechanical ventilation, injurious biophysical forces exacerbate lung injury. These forces disrupt alveolar capillary barrier integrity, trigger proinflammatory mediator release, and differentially regulate genes and non-coding oligonucleotides such as microRNAs. In this study, we identify miR-146a as a mechanosensitive microRNA in alveolar macrophages that has therapeutic potential to mitigate lung injury during mechanical ventilation. We used humanized in-vitro systems, mouse models, and biospecimens from mechanically ventilated patients to elucidate the expression dynamics of miR-146a that might be required to decrease lung injury during mechanical ventilation. We found that the endogenous increase in miR-146a following injurious was relatively modest and not sufficient to prevent lung injury. However, when miR-146a was highly overexpressed using a nanoparticle-based delivery platform in vivo, it was sufficient to prevent lung injury. These data indicate that the endogenous increase in microRNA-146a during MV is a compensatory response that only partially limits VILI and that nanoparticle delivery approaches that significantly over-express microRNA-146a in AMs is an effective strategy for mitigating VILI.