Pseudomonas aeruginosa promotes autophagy to suppress macrophage-mediated bacterial eradication.
OBJECTIVE
To explore the role of autophagy on macrophage-mediated phagocytosis and intracellular killing of Pseudomonas aeruginosa (PA), a common extracellular bacterium which often causes various opportunistic infections.


METHODS
Macrophages were infected with PA or stimulated with zymosan bioparticles. Autophagy was tested by fluorescent microscopy and Western blot for LC3. Phagocytosis and killing efficiency were assessed by plate count assay, flow cytometry or immunofluorescent staining. Phagocytic receptor expression, ROS generation and NO production were examined by PCR, flow cytometry and Griess reaction, respectively.


RESULTS
PA infection induced autophagy activation in both mouse and human macrophages. Induction of autophagy by rapamycin or starvation significantly inhibited PA internalization by downregulating phagocytosis receptor expression, and suppressed intracellular killing of PA via reducing ROS and NO production in macrophages. While knockdown of autophagy molecules ATG7 or Beclin1 enhanced macrophage-mediated phagocytosis and intracellular killing of PA. Additionally, confocal microscopy data showed that induction of autophagy reduced the number of phagosomes and phagolysosomes in macrophages after stimulation with zymosan bioparticles.


CONCLUSIONS
Our study suggested that PA promotes autophagy to suppress macrophage-mediated bacterial phagocytosis and intracellular killing. These insights demonstrated a novel immune evasion mechanism employed by PA, which may provide potential therapeutic strategies of PA infectious diseases.
Department of Immunology, Institute of Tuberculosis Control, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou 510080, China; Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou 510080, China.
Yongjian
Y
Wu
Department of Clinical Laboratory, Jinling Hospital, School of Medicine, Nanjing University, Nanjing 243000, China.
Dandan
D
Li
Department of Immunology, Institute of Tuberculosis Control, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou 510080, China; Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou 510080, China.
Yi
Y
Wang
Department of Immunology, Institute of Tuberculosis Control, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou 510080, China; Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou 510080, China; Division of Clinical Laboratory, Zhongshan Hospital of Sun Yat-sen University, Zhongshan 528403, China.
Kang
K
Chen
Department of Immunology, Institute of Tuberculosis Control, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou 510080, China; Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou 510080, China.
Kun
K
Yang
Department of Immunology, Institute of Tuberculosis Control, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou 510080, China; Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou 510080, China.
Xi
X
Huang
School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China. Electronic address: zyqsinap@gmail.com.
Yuanqing
Y
Zhang
Department of Immunology, Institute of Tuberculosis Control, Institute of Human Virology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou 510080, China; Key Laboratory of Tropical Diseases Control (Sun Yat-sen University), Ministry of Education, Guangzhou 510080, China. Electronic address: wuminhao@mail.sysu.edu.cn.
Minhao
M
Wu
D000818:Animals; D001343:Autophagy / Q000235:genetics; D000071193:Autophagy-Related Protein 7 / Q000235:genetics / Q000378:metabolism*; D000071186:Beclin-1 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D057131:Immune Evasion / Q000235:genetics; D007113:Immunity, Innate / Q000235:genetics; D008264:Macrophages / Q000382:microbiology* / Q000502:physiology; D051379:Mice; D009569:Nitric Oxide / Q000378:metabolism; D011552:Pseudomonas Infections / Q000276:immunology*; D011550:Pseudomonas aeruginosa / Q000276:immunology*; D000067996:RAW 264.7 Cells; D034741:RNA, Small Interfering / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism
D000071186:Beclin-1; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; D009569:Nitric Oxide; D000071193:Autophagy-Related Protein 7
Autophagy; Bacterial killing; Macrophages; Phagocytosis; Pseudomonas aeruginosa