Animals
Female BALB/c mice aged 6-7 weeks were used in the experiments. The mice were housed with a separate ventilation system and given sterile food and water. Experiments were carried out after all of the mice were acclimatized for at least one week.
Virus and challenge
The H1N1 influenza virus (A/WSN/33) used in the experiment was described in our previous publication [15]. The half lethal dose (LD50) in mice was determined previously [16]. The mice were anesthetized with 50 μL of Zoletil (Virbac, Carros, France) by intramuscular injection and infected intranasally with a dose of 3 LD50 of H1N1 virus [16].
Reagents
SP600125 (Selleck Chemicals, USA) was dissolved at a concentration of 3 mg/mL at 37℃ in a solvent composed of 10% ethanol, 15% polyoxyethylene castor oil, 30% polyethylene glycol, 20% propylene glycol, and 25% physiological saline and stored at -20℃.
Treatment trial
Mice were randomly assigned to the H1N1 virus challenge group (H1N1-virus-infected mice treated with solvent), the SP600125 treatment group (H1N1-virus-infected mice treated with SP600125), or the control group (mice without virus infection or treatment). SP600125 was administered intraperitoneally to anaesthetized mice at a dose of 30 mg/kg body weight [13, 17], starting two days before viral challenge, five days in all. In the H1N1 virus challenge group, SP60025 was replaced by solvent, and there was no viral challenge or treatment in the control group. Survival, body weight, and clinical symptoms were observed daily for at least 14 continuous days. On day 3 and day 6 postinfection, lung tissues of three randomly selected mice from each group were collected in sterile tubes and stored in liquid nitrogen or in 4% formalin until required. The details of the experimental procedure are shown in Figure 1.
Histology and Immunochemistry
Lung tissues were collected from euthanized mice, rapidly transferred to 4% formalin, and stored for at least 48 h. Preparation of paraffin sections, staining with hematoxylin and eosin (H&E), immunohistochemistry (IHC), and evaluation of pathological changes were carried out by previously published methods [18].
Real-time quantitative PCR analysis
TRIzol Reagent (Invitrogen, UT, USA) was used to extract total RNA from lung tissue (approximately 10 mg) according to the manufacturer’s introductions. The procedures for analysis of gene expression were described previously [18]. The expression level of the NS1 gene of IAV was calculated using the relative quantification method. The constitutively expressed housekeeping gene β-actin was used as an internal control to determine the fold change in the NS1 gene. Expression of interferon (IFN)-γ, IFN-β, interleukin (IL)-6, IL-1β, and tumor necrosis factor (TNF)-α was measured by the relative quantification method. Changes in gene expression were normalized to the control using the 2-ΔΔct method with β-actin as an internal standard. The primers used are listed in Supplementary Table 1.
Western blot analysis
Lung tissues were collected and lysed in RIPA buffer with 10 mM phenylmethylsulfonyl fluoride (PMSF) on ice for 20 min. The procedures for determination of protein concentration and analysis of proteins were the same as in our previous publication [19]. Anti-phosphorylated-JNK (p-JNK) antibody (cat. no. 612540) was purchased from BD Biosciences, and anti-total-JNK (t-JNK) antibody (cat. no. 9252) was purchased from Cell Signaling Technology. β-actin served as an internal standard to determine the amount of protein loaded.
Statistical analysis
Data were expressed as the mean ± standard deviation (SD). Differential expression was determined using one-way or two-way ANOVA with GraphPad Prism 8. P < 0.05 was considered statistically significant, P < 0.01 was considered highly significant, and P < 0.001 was considered extremely significant.