Effect of TLR7 gene expression mediating NF-κB signaling pathway on the pathogenesis of bronchial asthma in mice and the intervention role of IFN-γ.

OBJECTIVE

To explore the mechanism of TLR7 mediating NF-κB signaling pathway on the pathogenesis of bronchial asthma in mice and the intervention effect of IFN-γ in the process.

MATERIALS AND METHODS

The experimental animals were 70 C57BL/6J female mice of clean grade, which were divided into 7 groups according to different treatment protocols, including Normal group, Asthma group, Model+1-MT group, Model+IFN-γ group, Model+TLR7 agonist group, TLR7 deficient group, and Model+TLR7 deficient group. Hematoxylin-eosin (HE) staining was used to observe the pathological changes of lung tissues. The positive expression rates of TLR7, p-IKKα and NF-κBp65 were detected by immunohistochemistry. bronchoalveolar lavage fluid (BALF) cells were classified and counted. The contents of interleukin (IL)-4, IL-10, IL-12 and interferon (IFN)-γ in BALF supernatant were detected by enzyme-linked immunosorbent assay (ELISA). Following isolation, culture and plasmid construction of airway smooth muscle cells (ASMCS) from normal mice and asthmatic mice, cells were transfected and divided into the Control group, pcDNA-TLR7 NC group, siRNA-TLR7 NC group, pcDNA-TLR7 group, siRNA-TLR7 group, Asatone group, Triptolide group, and pcDNA-TLR7 +Asatone group. The expression of TLR7, IDO, p-IKKα and NF-κBp65 was detected by real-time polymerase chain reaction (RT-PCR) and Western blot, respectively. 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) was used to detect the proliferation of ASMCS. The cell cycle and apoptosis of ASMCS were detected by flow cytometry.

RESULTS

HE staining showed successful modeling of asthma. Immunohistochemical test showed that the positive expression rate of TLR7 in the Asthma group was significantly decreased, and that of IKKα and NF-κBp65 was significantly increased, with significantly increased IL-4, IL-10, IL-12 and IFN-γ levels (all p<0.05). Model+1-MT group and Model+TLR7 deficient group had a large number of inflammatory cell infiltration, increased IL-4, IL-10, IL-12 and IFN-γ levels, decreased expression levels of TLR7 and IDO, and increased expression of p-IKKα and NF-κBp65 (all p<0.05); while the opposites results were detected in Model+IFN-γ group and Model+TLR7 agonist group (all p<0.05). Cell transfection experiments revealed that pcDNA-TLR7 group and Triptolide group had increased TLR7 expression while decreased p-IKKα and NF-κBp65, decreased proliferation level, and increased cell apoptosis (all p<0.05); while the contrary results were found in siRNA-TLR7 group and Asatone group (all p<0.05); yet without significant difference in pcDNA-TLR7+Asatone group (all p>0.05).

CONCLUSIONS

Upregulation of TLR7 can inhibit the activation of NF-κB signaling pathway, reduces airway inflammation, inhibits ASMCS proliferation and thus promotes cell apoptosis in asthmatic mice. Besides, IFN-γ can exert a protective role in suppressing the progression of inflammation in asthma.