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Published on: July 26, 2017
TLR4 regulates ROS and autophagy to control neutrophil extracellular traps formation against Streptococcus pneumoniae
Yilin Dong1, Chunfang Jin1,2, Zhiqiang Ding3
1Department of Laboratory Medicine, Key Laboratory of Diagnostic Medicine (Ministry of Education), Chongqing Medical University, Chongqing, People's Republic of China.
Background:
Otitis media (OM), a prevalent pediatric infectious disease, is mainly caused by Streptococcus pneumoniae (S.pn). Neutrophil extracellular traps (NETs), a novel antimicrobial strategy, were reported in 2004. We found that NETs formed in the middle ear with acute otitis media (AOM) induced by S.pn. However, the mechanisms of NETs formation are not entirely clear.
Methods:
We stimulated neutrophils isolated from mouse bone marrow with S.pn clinical stain 19F in vitro, and established mouse model of AOM via transbullar injection with S.pn. NETs formation, reactive oxygen species (ROS) production, autophagy activation and bacterial load were analyzed in TLR4-/- and wild-type neutrophils stimulated in vitro with S.pn and in vivo during AOM.
Results:
We found that autophagy and ROS were required for S.pn-induced NETs formation. Moreover, TLR4 partly mediated NETs formation in response to S.pn in vitro and in vivo during AOM. We also showed that attenuated NETs formation in TLR4-/- neutrophils correlated with an impaired ROS production and autophagy activation in vitro and in vivo. In addition, both the in vivo and in vitro-produced NETs were able to engulf and kill S.pn.
Conclusions:
TLR4 regulates ROS and autophagy to control NETs formation against S.pn in the course of AOM.
Impact:
S.pn can induce NETs formation in vitro and in vivo; TLR4 regulates NETs formation by ROS and autophagy; NETs contribute to the clearance of bacteria in acute otitis media. In this study, we firstly found that autophagy and ROS were required for S.pn-induced NETs formation in the model of acute otitis media (AOM). And to some extent, TLR4 mediated NETs formation during AOM. Our research might provide a potential strategy for the treatment of otitis media.
Insights
Neutrophil extracellular traps (NETs) are crucial for fighting Streptococcus pneumoniae (S.pn) in acute otitis media (AOM). Toll-like receptor 4 (TLR4) regulates NETs formation via reactive oxygen species (ROS) and autophagy, aiding bacterial clearance.
Area of Science:
- Immunology
- Microbiology
- Pediatrics
Background:
- Otitis media (OM), a common pediatric infection, is primarily caused by Streptococcus pneumoniae (S.pn).
- Neutrophil extracellular traps (NETs) are an emerging antimicrobial mechanism.
- NETs formation in S.pn-induced acute otitis media (AOM) was observed, but the underlying mechanisms remained unclear.
Purpose of the Study:
- To investigate the mechanisms of S.pn-induced NETs formation in AOM.
- To elucidate the roles of reactive oxygen species (ROS), autophagy, and Toll-like receptor 4 (TLR4) in this process.
Main Methods:
- Neutrophils from mouse bone marrow were stimulated with S.pn in vitro.
- A mouse model of AOM was established via transbullar injection of S.pn.
- NETs formation, ROS production, autophagy activation, and bacterial load were analyzed in wild-type and TLR4-deficient neutrophils, both in vitro and in vivo.
Main Results:
- Autophagy and ROS were essential for S.pn-induced NETs formation.
- TLR4 partially mediated NETs formation in response to S.pn.
- Impaired NETs formation in TLR4-deficient neutrophils was linked to reduced ROS production and autophagy activation.
- NETs effectively engulfed and eliminated S.pn in vitro and in vivo.
Conclusions:
- TLR4 plays a role in regulating ROS and autophagy to control NETs formation against S.pn during AOM.
- NETs contribute to bacterial clearance in AOM.
- This study highlights the importance of autophagy, ROS, and TLR4 in S.pn-induced NETs formation, suggesting potential therapeutic strategies for otitis media.
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