Toll-like Receptor 4 Deficiency Aggravates Airway Hyperresponsiveness and Inflammation by Impairing Neutrophil Apoptosis in a Toluene Diisocyanate-Induced Murine Asthma Model

Shuyu Chen; Yao Deng; Qiaoling He; Yanbo Chen; De Wang; Weimin Sun; Ying He; Zehong Zou; Zhenyu Liang; Rongchang Chen; Lihong Yao; Ailin Tao

doi:10.4168/aair.2020.12.4.608

Toll-like Receptor 4 Deficiency Aggravates Airway Hyperresponsiveness and Inflammation by Impairing Neutrophil Apoptosis in a Toluene Diisocyanate-Induced Murine Asthma Model

Allergy Asthma Immunol Res. 2020 Jul;12(4):608-625. doi: 10.4168/aair.2020.12.4.608.

Authors

Shuyu Chen^#^{1

2}, Yao Deng^#^{1

2}, Qiaoling He^#^{1

2}, Yanbo Chen³, De Wang^{1

2}, Weimin Sun^{1

2}, Ying He^{1

2}, Zehong Zou^{1

2}, Zhenyu Liang⁴, Rongchang Chen⁴, Lihong Yao⁵, Ailin Tao^{1

6}

Affiliations

¹ The Second Affiliated Hospital, Guangdong Provincial Key Laboratory of Allergy & Clinical Immunology, State Key Laboratory of Respiratory Disease, Guangzhou Medical University, Guangzhou, China.
² Center for Immunology, Inflammation & Immune-Mediated Disease, Guangzhou Medical University, Guangzhou, China.
³ Guangzhou First People's Hospital, School of Medicine, South China University of Technology, Guangzhou, China.
⁴ State Key Laboratory of Respiratory Diseases, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital, Guangzhou Medical University, Guangzhou, China.
⁵ State Key Laboratory of Respiratory Diseases, Guangzhou Institute of Respiratory Health, The First Affiliated Hospital, Guangzhou Medical University, Guangzhou, China. yaolh4321@126.com.
⁶ Center for Immunology, Inflammation & Immune-Mediated Disease, Guangzhou Medical University, Guangzhou, China. allergyailintao@126.com, taoailin@gzhmu.edu.cn.

^# Contributed equally.

Abstract

Purpose: Accumulating evidence has suggested that toll-like receptor 4 (TLR4) is critically involved in the pathogenesis of asthma. The aim of this study was to investigate the role of TLR4 in toluene diisocyanate (TDI)-induced allergic airway inflammation.

Methods: TLR4^-/- and wild-type (WT) C57BL/10J mice were sensitized and challenged with TDI to generate a TDI-induced asthma model. B-cell lymphoma 2 (Bcl-2) inhibitors, ABT-199 (4 mg/kg) and ABT-737 (4 mg/kg), were intranasally given to TDI-exposed TLR4^-/- mice after each challenge.

Results: TDI exposure led to increased airway hyperresponsiveness (AHR), granulocyte flux, bronchial epithelial shedding and extensive submucosal collagen deposition, which were unexpectedly aggravated by TLR4 deficiency. Following TDI challenge, TLR4^-/- mice exhibited down-regulated interleukin-17A and increased colony-stimulating factor 3 in bronchoalveolar lavage fluid (BALF), while WT mice did not. In addition, TLR4 deficiency robustly suppressed the expression of NOD-like receptor family pyrin domain containing 3 and NLR family CARD domain containing 4, decreased caspase-1 activity in TDI-exposed mice, but had no effect on the level of high mobility group box 1 in BALF. Flow cytometry revealed that TDI hampered both neutrophil and eosinophil apoptosis, of which neutrophil apoptosis was further inhibited in TDI-exposed TLR4^-/- mice, with marked up-regulation of Bcl-2. Moreover, inhibition of Bcl-2 with either ABT-199 or ABT-737 significantly alleviated neutrophil recruitment by promoting apoptosis.

Conclusions: These data indicated that TLR4 deficiency promoted neutrophil infiltration by impairing its apoptosis via up-regulation of Bcl-2, thereby resulting in deteriorated AHR and airway inflammation, which suggests that TLR4 could be a negative regulator of TDI-induced neutrophilic inflammation.

Keywords: Toll-like receptor 4; apoptosis; asthma; neutrophlic inflammation; toluene diisocyanate.

Abstract

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