Acute lung injury is disease that affect all populations with the aging population being the most affected. The most severe form of ALI is ARDS or acute respiratory distress syndrome. Indeed, this disease is deadlier to the elderly population, and to remedy to the disease patients must be put on mechanical ventilators (MV). Despite the benefits that MV can provide, it can also lead to ventilator induced lung injury (VILI). VILI is characterized by biotrauma, increased in the severity of inflammation, volutrauma, over expansion of the alveoli and atelectrauma, the collapse of the air way. Moreover, some researches have shown that VILI is exacerbated with age. We believe that this hostile environment created by VILI leads to cellular senescence. Senescence is a process by which cell cycle comes to a complete stop, and it is characterized by increased cyclin dependent kinase inhibitors such as P16, P21 and P53. Senescent cells have a distinguishable morphology, they are enlarged and flatten. In addition, senescent cells produce secretomes called senescence associated secretory phenotype (SASP). SASP includes growth factors, cytokines and chemokines and matrix metalloproteinases. The mechanisms that lead to cellular senescence in VILI is not well understood. Moreover, senolytic drugs which selectively target senescent cells, have never been used to clear out senescent cells in VILI nor in aging models of lung injury. We hypothesize that during mechanical ventilation alveolar epithelial cells become senescent due to ventilator-induced cell stretch contributing to the loss of barrier integrity and SASP inflammatory response causing VILI. We further hypothesize that senolytic drugs may be a possible therapeutic target for VILI by attenuating the stretch-induced SASP. We will test these hypotheses through 3 aims: (1) Quantify senescence and SASP in an in vitro model of VILI with senolytic drugs treatments. To accomplish this aim, we will isolate alveolar type 1 and 2 (AT1 and AT2) cells from young, middle age and old mice and stretch them with LPS (to simulate acute lung injury) and add senolytic drugs. We predict that senolytic drugs will clear out senescent cells and decrease inflammatory cytokines in cells from old mice compared to young. (2) Assess the mechanism by why stretch induces senescence or SASP in an in vitro model of VILI. The same methods as in aim 1 will be used but with TGF?1 receptor and P38 inhibition. We expect to show that stretch induced senescence in VILI happens through TGF?1, P38, P53 and P21 pathway. (3) Assess the effect of age and senolytic drugs in an in vivo mouse model of VILI. Old, middle age, and young mice will be ventilated at protective and injurious settings and given LPS 24 hour prior to mechanical ventilation. We predict the old ventilated mice with LPS to have the worst outcome compared to other groups and senolytic drugs to improve those outcomes. This novel proposal will help us understand the role of senescence in VILI and benefits of senolytic drugs as treatment for age-related lung injury.
The proposed study examines the effect and the mechanism of cellular senescence in ventilator induced lung injury in the aging lung. This study combines in vivo and in vitro methods to identify if the cells lining the alveolar barrier become senescent, understand the mechanism by which senescence happens, and to use senolytic drugs to selectively target those senescent cells to improve lung function.
