Mechanical Ventilation induced P21 in an Acute Aging Model of Lung Injury
Acute respiratory distress syndrome (ARDS) is a form of acute lung injury which leads to a paucity of oxygen. To remedy ARDS, patients are put on mechanical ventilators; however, the stretch resulting from the mechanical ventilator can lead to ventilator-induced lung injury or VILI. VILI is exacerbated by age. The combined effects of ARDS and mechanical ventilation can result in a hostile environment which may lead to senescence (stable cell cycle arrest). The role of senescence in VILI is poorly understood. Senescence is characterized by increased cyclin-dependent kinase inhibitors P16 and P21; however, P21 has been shown to occur in early senescence. We hypothesized that mechanical ventilation would lead to DNA damage and senescence-like phenotype. Both in vivo and in vitro models of VILI were used to investigate senescence and its mechanism in VILI. Mechanical ventilation increased senescence-associated markers such as DNA damage marker characterized by {gamma}H2AX, P21, senescence-associated secretory phenotype IL6, and decreased proliferation. Moreover, mechanical ventilation led to increased apoptosis. Lung sections were stained for KRT8 proteins, markers of transiently differentiated alveolar type 2 (AT2) cells which were reported to be more prone to DNA damage. Age and mechanical ventilation increased KRT8 positive cells. Finally, we probed a potential mediator of the stretch induced senescence in vitro by inhibiting P38-MAPK, which can be activated by DNA damage response, leading to increased P21. Inhibiting P38 decreased in P21 but did not decrease {gamma}H2AXThese findings suggest that mechanical ventilation may lead to a senescence-like phenotype involving the P38-MAPK pathway.