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

Abstract

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

TLR4 and CD14 trafficking and its influence on LPS-induced pro-inflammatory signaling

“…Therefore, these cells stimulated with LPS produce TNF-α but not IFN-β [131,132]. Activation of TLR4 in neutrophils leads to ROS generation, cytokine production and other responses which are cell specific, like autophagy and modulation of cell survival [30,[133][134][135][136]. In addition, in murine neutrophils, LPS induces production and secretion of histamine in a PI3K-dependent manner [137].…”

Platelets, Not an Insignificant Player in Development of Allergic Asthma

“…The onset of allergic asthma is influenced by both genetic backgrounds and environmental factors, and is closely related to allergic rhinitis [1,14]. Allergens that trigger allergic asthma include house dust mites, pollens, dander from cats and dogs, mold spores, cockroaches [15], and even small molecules such as toluene diisocyanate (TDI) [16].…”

Carbenoxolone Ameliorates Allergic Airway Inflammation through NF-κB/NLRP3 Pathway in Mice

“…The H&E-stained sections were semi-quantified; a scoring standard was created for stain assessment as previously described. 18) Finally, a suitable CBX dose was chosen for follow-up experiments based on the pathological staining results of H&E. The percentage of PAS-positive cells and collagen fibril deposition were analyzed using the ImageJ 1.8.0 software (National Institutes of Health). 18,19) Histopathological analysis was done in six mice from each group.…”