Epithelial HO-1/STAT3 affords the protection of subanesthetic isoflurane against zymosan-induced lung injury in mice

Epithelial dysfunction is a key characteristic of acute lung injury (ALI). Isoflurane (ISO) confers lung protection via anti-inflammatory and anti-apoptotic properties. However, the specific role and potential mechanisms of subanesthetic ISO in lung epithelium protection during zymosan-induced ALI remain unclear. In this study, zymosan increased the expression and activity of beneficial heme oxygenase-1 (HO-1) and signal transducers and activators of transcription 3 (STAT3) in the lung and isolated type II alveolar epithelial cells (AECs-II) from wild-type (WT) mice, which was further enhanced by ISO treatment. ISO reduced the mortality, lung edema, histological changes and pulmonary cell apoptosis, and simultaneously decreased total cells, tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) levels in bronchoalveolar lavage fluid in the zymosan-stimulated WT mice but not in HO-1-deficient mice. Moreover, ISO abated zymosan-augmented lactate dehydrogenase activity, TNF-α and IL-1β production, and apoptosis in WT AECs-II but not in HO-1- or STAT3-silenced cells. Mechanisticly, the epithelial protective effects of ISO on zymosan insult in vivo and in vitro were mediated by a positive feedback loop comprising STAT3 and HO-1. Pro-survival and anti-apoptosis by ISO was highly reliant on activated STAT3, involving in downstream Akt activation and reduced ratio of pro-apoptotic/anti-apoptotic molecules. Overall, HO-1/STAT3 signaling is in favor of lung epithelial protection of ISO in zymosan-challenged mice, suggesting ISO as a valuable therapeutic agent for ALI.