Critical Roles of Inflammation and Apoptosis in Improved Survival in a Model of Hyperoxia-Induced Acute Lung Injury inPneumocystis murina-Infected Mice

Abstract

Pneumocystis infections increase host susceptibility to additional insults that would be tolerated in the absence of infection, such as hyperoxia. In an in vivo model using CD4-depleted mice, we previously demonstrated that Pneumocystis murina pneumonia causes significant mortality following an otherwise nonlethal hyperoxic insult. Infected mice demonstrated increased pulmonary inflammation and alveolar epithelial cell apoptosis compared to controls. To test the mechanisms underlying these observations, we examined expression of components of the Fas-Fas ligand pathway in P. murina-infected mice exposed to hyperoxia. Hyperoxia alone increased expression of Fas on the surface of type II alveolar epithelial cells; conversely, infection with P. murina led to increased lung expression of Fas ligand. We hypothesized that inhibition of inflammatory responses or direct inhibition of alveolar epithelial cell apoptosis would improve survival in P. murina-infected mice exposed to hyperoxia. Mice were depleted of CD4 ؉ T cells and infected with P. murina and then were exposed to >95% oxygen for 4 days, followed by return to normoxia. Experimental groups received vehicle, dexamethasone, or granulocyte-macrophage colony-stimulating factor (GM-CSF). Compared with the vehicletreated group, treatment with dexamethasone reduced Fas ligand expression and significantly improved survival. Similarly, treatment with GM-CSF, an agent we have shown protects alveolar epithelial cells against apoptosis, decreased Fas ligand expression and also improved survival. Our results suggest that the dual stresses of P. murina infection and hyperoxia induce lung injury via activation of the Fas-Fas ligand pathway and that corticosteroids and GM-CSF reduce mortality in P. murina-infected mice exposed to hyperoxic stress by inhibition of inflammation and apoptosis.

Differential Role of the Fas/Fas Ligand Apoptotic Pathway in Inflammation and Lung Fibrosis Associated with Reovirus 1/L-Induced Bronchiolitis Obliterans Organizing Pneumonia and Acute Respiratory Distress Syndrome

“…These authors demonstrated that synthetic double-stranded small interfering RNA (siRNA) targeting FADD introduced into the tissues of the whole animal suppressed apoptosis induction in septic lungs, prevented acute lung injury development, and dramatically improved the survival of CLP mice (65). A similar critical role of epithelial cell apoptosis via activation of the Fas/FasL pathway has been also described in a model of hyperoxia-induced acute lung injury in Pneumocystis murina -infected mice (66). These observations support the hypothesis that apoptosis of alveolar epithelial cells potentially through the Fas/FasL pathway is involved in the pathophysiology of acute lung injury and pulmonary fibrosis.…”

Suppression of inflammation and acute lung injury by Miz1 via repression of C/EBP-δ

“…ATII cells were isolated as described 21,45 . Briefly, perfused and lavaged lungs were digested with dispase (1 ml, BD Bioscience) and purified by negative immunoselection using a mixture of antibodies, including anti-CD16/32 (2.4G2, BD Biosciences), anti-TER-119 (TER-119, BD Biosciences), anti-CD45 (30-F11, BD Biosciences), and anti-CD90 (OX-7, BD Biosciences), followed by differential adherence to dishes.…”

GM-CSF provides autocrine protection for murine alveolar epithelial cells from oxidant-induced mitochondrial injury

“…In addition to this role in host defense, GM-CSF is a mitogen for AEC in vivo and in vitro (22,32). Using exposure to increased concentrations of oxygen to induce lung injury, we have found that GM-CSF is protective against lethal lung injury both in normal mice (32) and in mice rendered more susceptible to lung injury by infection with Pneumocystis murina (4). In these experiments, treatment with GM-CSF or overexpression of GM-CSF in the lung was associated with decreased apoptosis of AEC following exposure to hyperoxia.…”