Animals and treatment
Male Balb/c mice (6–8 weeks old, 23 ± 2 g) were purchased from Vital River Laboratory Animal Technology (Beijing Vital River Laboratory Animal Technology, China). Mice were randomly assigned to three groups: control group (n = 10); ConA group (n = 10); intravenous injections with 20 mg/kg ConA (20 mg/kg weight, Sigma, USA); SHED+ConA group (n = 10); intravenous injections with SHED cell (1x106) 7d prior to ConA challenge. After injection of ConA for 24 h, the mice were scarified for further analysis (Fig.1a). The protocols were approved by the Animal Care and Use Committee of the Health Science Center, Peking University (# 2015‐186).
Biochemical assay
Mice serum was collected for the inflammatory cytokine, ALT and AST analysis. The levels of ALT and AST were evaluated by the transaminase kit according to the manufacturer's instructions (Nanjing Jiancheng Bioengineering Institute, Nanjing, China). TNF-α and IFN-γ levels were measured using ELISA kits according to the manufacturer's instructions(ebioscience, USA)[19].
Immunohistochemistry
For immunohistochemistry, the sections were dewaxed with xylene, treated with gradient concentration of ethanol, washed with deionized water, followed by heated with a microwave in 10mmol / L sodium citrate (PH 6), added with 0.05% Tween 20, then blocked for 1 hour with 5% BSA and 0.1% Triton X-100 in PBS. Anti-CD3 (1:100), anti-CD4(1:100), anti-total caspase3 (1:100), anti TNF-α (1:100), anti IFN-γ (1:100) and anti NF-κB (1:400) were incubated overnight at 4 ℃. After washed three times, The sections were incubated with secondary antibody at room temperature for 1h, and observed under microscope (Leica, Wetzlar, Germany). The positive area was measured with Image-Pro Plus software 6.0 (Media Cybernetics, Silver Spring, MD, USA).
Immunofluorescence
After washed in PBS for 5 min, the frozen sections of tissues were treated with 0.1% Triton to rupture the membranes at room temperature for 30 min, and non-specific antigen binding site was blocked by 5% BSA. Rabbit anti-total caspase3 (1:100), anti-pNF-κB (1:400) and anti-NF-κB (1:400) were incubated overnight at 4 ℃. Nuclear staining was performed by DAPI (Vector Lab, Burlingame, CA)mounting medium after incubated with secondary antibody for 1h. All sections were observed with Zeiss fluorescence microscope (Zeiss, Thornwood, NY).
Cell culture and treatment
Murine liver cell line NCTC-1469 cells were purchased from the Institute of Biochemistry and Cell Biology, Chinese Academy of Science (Shanghai, China). Stem cells from human exfoliated deciduous teeth (SHED) cells were provided by Oral stem cell bank (Beijing, China) and isolated as previously reported[10]. NCTC-1469 cells were cultured in DMEM supplemented with 10% fetal bovine serum (FBS), 100 U/mL penicillin, and 100 U/mL streptomycin. SHED cells were cultured in α-MEM supplemented with 15% fetal bovine serum (FBS), 100 U/mL penicillin, and 100 U/mL streptomycin. NCTC cells (2 × 105 cells/well, 2 mL/well) were cultivated in 6-well plates and incubated with ConA of different concentrations(10、20、50、80、100μg/ml), which were studied in cell proliferation by cell counting. Then we selected the appropriate treatment concentration (50μg/ml). In order to study whether SHED cells can inhibit the death of NCTC cells caused by ConA in vitro. PKH26 labeled NCTC-1469 cells were inoculated into 6-well plates with density of 2 × 105cells/mL for 12 h. Then the cells were cultured with 50μg/ml Con A and SHED cells (1 × 105 cells/well) for 24h. The cells on the slide were fixed and observed with Zeiss fluorescence microscope (Zeiss, Thornwood, NY).
Determination of apoptosis and DNA damage
Apoptosis in liver tissues was detected by Terminal dUTP nick-end labeling (TUNEL) staining. The paraffin-embedded sections were deparaffinized and digested with 20 μg/mL proteinase K for 30 min at room temperature. After washed with PBS, the slices were incubated with the TUNEL reaction overnight at 4°C, followed by incubation with rabbit anti-mouse fluorescein isothiocyanate, and DAPI for nuclear labeling. The TUNEL+ cells were observed and counted in at least three different fields per section.
For the in vitro study,NCTC1469 cells were inoculated in 6-well plates at a density of 2 × 105cells/well, followed by the addition of ConA (50 μg/ml) and SHED cell (1 × 105 cells/well). After 24 hours of culture, the cells were collected, washed with PBS, and stained with Annexin V apoptosis detection kit. Flow cytometry was used to observe the fluorescence of cell. The cells on the slide were fixed and then immunofluorescence staining was used to determine the expression of apoptosis. After incubation in blocking buffer, cells were incubated with anti–caspase3 (1:400) overnight at 4°C, followed by incubation with goat anti-rabbit fluorescein isothiocyanate. Nuclear staining was performed by DAPI. The sections were observed with Zeiss fluorescence microscope (Zeiss, Thornwood, NY).