SIRT 1 ‐ mediated regulation of oxidative stress induced by Pseudomonas aeruginosa lipopolysaccharides in human alveolar epithelial cells

Sirtuin1 (SIRT1) is an NAD+-dependent deacetylase that exhibits multiple biological functions, including cell differentiation inhibition, transcription regulation, cell cycle regulation and anti-apoptosis. Lipopolysaccharides (LPS) are crucial virulence factors produced by Pseudomonas aeruginosa and serve an important role in adjusting the interactions between the host and the pathogen. However, the effect of SIRT1 in the regulation of LPS-induced A459 human alveolar epithelial cells (AECs) oxidative stress remains unclear. The cellular reactive oxygen species (ROS) production was examined in A549 cells that were supplemented with LPS. Relative cell signaling pathway proteins were further investigated by western blot analysis. It was identified that LPS downregulated SIRT1 expression, however, upregulated ROS generation, which was associated with the increase of nuclear factor (NF)-κB and acetyl-NF-κB. Activation of SIRT1 by resveratrol significantly reversed the effects of LPS on A549 cells. By contrast, inhibition of SIRT1 by nicotinamide had the opposite effects that enhance cell ROS production. Thus, the results indicated that SIRT1 serves an important role in the regulation of oxidative stress induced by LPS in human AECs. Introduction Pseudomonas aeruginosa is one of the most prevalent opportunistic gram-negative bacteria that lead to pneumonia in immunocompromised patients through the production of numerous virulence factors, including enzymes and exotoxin, such as lipopolysaccharides (LPS) (1-5). P. aeruginosa accounts for 10-20% of all hospital-acquired infection (6), 18.1% of nosocomial pneumonia (7), 9.3% of ventilator-associated pneumonia (8) and 0.9-1.9% of community-acquired pneumonia requiring hospitalization (9-11). LPS are the most important pathogenic factors produced by P. aeruginosa and serve a major role in the interplay between the host and the pathogen. Type II alveolar epithelial cells (AECs) are major target cells of LPS locating in the alveolar corners, exhibiting various important functions including initiation of immune responses, fluid balance, mucus and surfactant production, and progenitor action to maintain the normal function of the alveoli (12-14). Sirtuin1 (SIRT1), an NAD+-dependent class III protein deacetylase, belongs to the silent information regulator (Sir) family (15) and is suggested to serve diverse roles in gene silencing, stress resistance, apoptosis, senescence, aging and inflammation (16-19). Previous studies have demonstrated that SIRT1 can regulate cellular oxidative stress and its toxicity (20-23). Modulation of the acetylation of the p65 subunit of nuclear factor kB (NF-κB) in cells or tissues is the major means via which SIRT1 regulates cellular oxidative status (24). At present, to the best of our knowledge, no reports have focused on the potential roles of SIRT1 in the regulation of oxidative stress induced by P. aeruginosa LPS in human AECs. In the current study, the effects of SIRT1 on the regulation of reactive oxidative stress, which is indicated by reactive oxygen species (ROS) generation, was examined in LPS-stimulated A549 cells. Materials and methods Cell culture and drug treatment. A549 cells were maintained as previously described (25). Briefly cells were maintained in SIRT1‐mediated regulation of oxidative stress induced by Pseudomonas aeruginosa lipopolysaccharides in human alveolar epithelial cells XIAOLI LIU1, TUO YANG2, TIEYING SUN3 and KUIQING SHAO4 1Department of Respiratory Medicine, Beijing Shijitan Hospital, Capital Medical University, Beijing 100038, P.R. China; 2Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15260, USA; 3Department of Respiratory and Critical Care Medicine, Beijing Hospital Ministry of Health, Beijing 100730; 4Department of Urinary Surgery, Xiyuan Hospital of China Academy of Chinese Medical Sciences, Beijing 100091, P.R. China Received January 10, 2016; Accepted October 19, 2016 DOI: 10.3892/mmr.2016. 6045 Correspondence to: Dr Tieying Sun, Department of Respiratory and Critical Care Medicine, Beijing Hospital Ministry of Health, 1 Dahua Street, Dongcheng, Beijing 100730, P.R. China E-mail: suntieying3@hotmail.com Dr Kuiqing Shao, Department of Urinary Surgery, Xiyuan Hospital of China Academy of Chinese Medical Sciences, 1 Xiyuancaochang, Hadian, Beijing 100091, P.R. China E-mail: shaokuiqing@163.com