LPS elevates ceramide levels through regulating ORMDL3 expression in macrophages and acute respiratory distress syndrome model

Abstract

Abstract Acute respiratory distress syndrome (ARDS) is a respiratory system failure defined by the acute onset of noncardiogenic pulmonary edema and hypoxemia. After triggered by diverse pulmonary toxicants, macrophages accumulate in lung and generate cytotoxic and proinflammatory mediators that induce pathogenic responses, including cytokines, chemokines, proteases and bioactive lipids. Ceramide is a lipid lies within cell membrane bilayer and functions as a signaling molecule, causing production of inflammatory cytokines and cell apoptosis. The generation of ceramide is controlled by serine palmitoyltransferase (SPT), which forms complex with orosomucoid-like protein 3 (ORMDL3) to regulate ceramide levels. Since the level of ceramide is highly associated with lung injury, we aim to investigate how LPS induces ceramide level. PMA-differentiated THP-1 cells were activated by LPS and the ceramide levels were analyzed by using UPLC-TOF-MS system. Proteins regulating ceramide synthesis and relative transcription factors were further determined. We found that ORMDL expressions were down-regulated and ceramides were increased in THP-1 cells upon LPS activation. ORMDL3 transcription factors, p300 and STAT6, were down-regulated but not Ets-1, CREB nor ubiquitin ligase Cbl-b. We established a LPS-induced B6 model for ARDS and analyzed BALF cells, cytokine and chemokine levels, and ceramide composition. ORMDL3 is also down-regulated in ARDS model, which may result in the increase of ceramide levels. Taken together, LPS may increase ceramide levels by regulating ORMDL3 expression through p300-STAT6 axis. These results may provide new therapeutic strategies for ARDS patients by targeting ORMDL3 to control ceramide levels.