The severity of ventilator-induced lung injury is regulated by the clock gene Bmal1 in myeloid cells

Abstract

Mechanical ventilation (MV) is life-saving, but may also exacerbate lung injury, a process termed ventilator-induced lung injury (VILI). We previously discovered that the circadian rhythm (CR) modulates the severity of VILI. In this study, we are exploring the role of the core clock component BMAL1 in myeloid cells for VILI. Mice with a myeloid specific knock down of Bmal1 (LyzMCre-Bmal1-/-) and LyzMCre mice as controls were subjected to high tidal volume MV for 4 hours at circadian time (CT) 0 or CT12 to induce VILI. Lung injury was quantified measuring compliance, pulmonary permeability, neutrophil recruitment, and markers of pulmonary inflammation. Neutrophil inflammatory response was analyzed in vitro in myeloid cells from bone marrow of WT and Bmal1-deficient animals, isolated at dawn ZT0 (Zeitgeber time 0) and dusk (ZT12). After stimulation with PMA or PBS, ROS production and neutrophil activation were quantified. Control mice ventilated at CT0 showed decrease of pulmonary compliance, worsening of oxygenation and increased mortality compared to CT12. LyzMCre-Bmal1-/- mice did not exhibit significant differences after MV at CT0 or CT12 and mortality at CT0 was reduced compared to controls. Neutrophils isolated at ZT0 showed a significantly higher level of activation and increased ROS production after PMA-stimulation at ZT0. ROS production of LyzMCre-Bmal1-/- neutrophils did not differ from ZT0 to ZT12. The deletion of the clock gene Bmal1 in myeloid cells leads to the loss of circadian variations in neutrophil ROS production and increased survival after injurious ventilation. This suggests that the internal clock in myeloid cells is an important modulator for VILI.