Haem oxygenase‐1 up‐regulation by rosiglitazone via ROS‐dependent Nrf2‐antioxidant response elements axis or PPARγ attenuates LPS‐mediated lung inflammation

BACKGROUND AND PURPOSE: Haem oxygenase‐1 (HO‐1) is induced by thiazolidinediones including rosiglitazone and exerts anti‐inflammatory effects in various models. However, the molecular mechanisms underlying rosiglitazone‐induced HO‐1 expression remain largely unknown in human pulmonary alveolar epithelial cells (HPAEpiCs). EXPERIMENTAL APPROACH: HO‐1 expression was determined by real time‐PCR, Western blotting and promoter reporter analyses. Signalling pathways were investigated using pharmacological inhibitors or specific siRNAs. Interactions between nuclear factor erythroid‐2‐related factor (Nrf2) and antioxidant response elements (ARE) binding site of the HO‐1 promoter were investigated with chromatin immunoprecipitation assays. KEY RESULTS: Up‐regulation of HO‐1 in HPAEpiCs or in mice by rosiglitazone blunted ICAM‐1 expression and monocyte adhesion to HPAEpiCs challenged with LPS. Rosiglitazone‐induced HO‐1 expression was significantly attenuated by NADPH oxidase (NOX) inhibitors (apocynin and diphenyleneiodonium) or ROS scavenger (N‐acetyl cysteine). The involvement of NOX activity and ROS generation in rosiglitazone‐induced HO‐1 expression was confirmed by transfection with p47(phox) or NOX2 siRNA. Moreover, pretreatment with the inhibitors of c‐Src (c‐Srci II), proline‐rich tyrosine kinase 2 (Pyk2) (PF431396), Akt (Akti VIII) or PPARγ (GW9662) and transfection with siRNA of c‐Src, Pyk2, Akt or PPARγ abolished the rosiglitazone‐induced HO‐1 expression in HPAEpiCs. Subsequently, Nrf2 was activated by phosphorylation of c‐Src, Pyk2 and Akt, which turned on transcription of HO‐1 gene by binding to AREs binding site and enhancing ARE promoter activity. CONCLUSIONS AND IMPLICATIONS: Rosiglitazone induces HO‐1 expression via either NOX/ROS/c‐Src/Pyk2/Akt‐dependent Nrf2 activation or PPARγ in HPAEpiCs and suppresses LPS‐mediated inflammatory responses, suggesting that PPARγ agonists may be useful for protection against pulmonary inflammation.