Chemicals and Reagents
Bleomycin A5 (BLMA5) (J1716055) was purchased from Aladdin (Shanghai, China). Recombinant Trx (MB1039) was purchased from Meilunbio (Dalian, China). Aminoguanidine (A111133), a peroxynitrite scavenger was purchased from Aladdin (Shanghai, China). Hydroxyproline assay kit was provided by Wanleibio (Shenyang, China). Antibody against Trx (ab26320) was purchased from Abcam (Cambridge, United Kingdom). Nitrotyrosine antibody (06-284) was purchased from Millipore (Danvers, MA, United States). Antibody against ASK1 (SC-390275) was purchased from Santa Cruz Biotechnology(United States). Antibodies against p38, iNOS and second antibodies were all obtained from Wanleibio (Shenyang, China). p38 activity kit (9790) was purchased from Cell Signal Technology Inc. (Danvers, MA, United States). Classic IP Kit (26146) was purchased form Thermo (NewYork, United States). SIN-1 was purchased from Cayman Chemical (Michigan, United States). MnTBAP chloride (CAS:55266-18-7) was purchased from Santa Cruz(United States). Tunnel (WL029a) kit and caspase3 (WLA047) kit were provided by Wanleibio (Shenyang, China).
Animal model of BLM-induced pulmonary fibrosis
All experimental procedures were reviewed and approved by The Animal Research Committee of Zheng Zhou University, Zheng Zhou, China. C57/BL6 mice (SPF grade, 8 weeks old and weight 20-25g) were purchased from Vital River Laboratories (Beijing, China). Mice housed in a room with controlled temperature (22±2℃) and humanity (65±5%) had free access to standard mice chow and water. All mice were acclimated to laboratory conditions for 7 days prior to the experiment. The mice were administered BLMA5 by intracheal injection (5.0 mg/kg body mass in phosphate-buffered saline) as described previously [14]. At 7 or 28 days after administration of BLMA5, the mice were euthanized using an overdose of chloral hydrate (10%). Before BLM administration, mice were randomized to receive either vehicle (0.9%NaCl), aminoguanidine (AG, a peroxynitrite scavenger, 40 mg/kg, continuously for 14 days), recombinant human Trx-1 (40ug/20g, continuously every 2 day for 14 days), or nitrated Trx-1 (please see details, continuously every 2 day for 14 days) by intraperitoneal injection. Pulmonary fibrosis was assessed from the lung histology. Lung histology was performed as described [15].
Histopathological examination of lung
Part of the upper lungs were inflated with 1 ml of 10% paraformaldehyde / PBS solution and embedded in paraffin. Sections (5µm thick) were treated for sample preparation. The lung tissues were stained with hematoxylin-eosin (H&E) and Masson’s trichrome, then evaluated under a light microscopy conducted by experienced pathologists. The lung fibrosis score, based on the severity and extent of lung fibrosis present in the peribronchial and interstitial tissues was assessed by a pulmonary pathologist blinded to the experimental protocol. Lungs were assigned a severity score from 0 to 4 (0=absence of fibrosis, 1=1% to 25%, 2= 26% to 50%, 3=51% to75%, 4=76% to 100% fibrosis) [16].
Determination of pulmonary cells apoptosis
Pulmonary cells apoptosis was determined by terminal deoxynucleotidyltransferase-mediated dUTP nick and labeling (TUNEL) staining and caspase-3 activity assay. Sections were stained as the manufacturer's protocol. Briefly, the sections were deparaffinized and treated by ethylenediaminetetraacetic acid solution while being heated in a microwave. The sections were then reacted in a solution of terminal deoxynucleotidyl transferase enzyme mixed with biotinylated nucleotide. Horseradish peroxidase-labeled streptavidin was bound to these biotinylated nucleotides, which were detected using the peroxidase substrate, hydrogen peroxide, and diaminobenzidine (DAB). The index of apoptosis (number of TUNEL positive nuclei / total number of nuclei×100) was automatically calculated for further analysis. The caspase-3 activity was determined as the instruction provided by the manufacturer.
Quantification of tissue nitrotyrosine content
Paraformaldehyde-fixed lung tissues were cut into semi-thin sections 4 to 5 µm thick and stained with a primary antibody against nitrotyrosine. Immunostaining was determined as described in our previous study [14]. Quantification of lung tissue nitrotyrosine content was performed by ELISA assay. Results are presented as micrograms per milligram(µg/mg) protein.
Western blotting analysis
Lung tissues were cut into small pieces and homogenized in lysis buffer on ice. The protein concentration was determined according to a protein assay kit, where 40 µg protein was loaded and separated by electrophoresis (sodium dodecyl sulfate-polyacrylamide gel electrophoresis), and transferred to 0.22 µm polyvinylidene difluoride (PVDF) membranes. Membranes were blocked using 5% nonfat milk in TRIS-buffered saline with Tween-20 (TBST) for 1 h and then were incubated with Trx antibody or iNOS antibody overnight. After washing with TBST, protein bands were detected with secondary antibody conjugated with horseradish peroxidase. The membranes were washed 3 times in TBST for 10 min each. The blot was developed with a super-signal chemiluminescent detection kit (Pierce) and visualized with a Kodak Image Station 400. The blot density was analyzed with Vision Works LS Acquisition and Analysis software.
Determination of Trx enzyme activity
Trx activity was determined by the insulin disulfide reduction assay [17]. In brief, 40 mg of tissue homogenates were pre-incubated at 37℃ for 15 min with 2 mL activation buffer (100 mmol/L HEPES, 2 mmol/L EDTA, 1 mg/mL bovine serum albumin, and 2 mmol/L dithiothreitol) for Trx reduction. Samples were then mixed with 20 uL reaction buffer (100 mmol/L HEPES, 2.0 mmol/L EDTA, 0.2 mmol/L NADPH, and 140 mmol/L insulin), the reaction was initiated by the addition of mammalian Trx reductase (1 mL, 15 mU, Sigma) or water to the controls, and the samples were incubated for 30 min at 37℃. Finally, the reaction was stopped by adding 125uL of stopping solution (0.2 mmol/L Tris-HCL, 10 mmol/L guanidine-HCl, and 1.7 mmol/L3-carboxy-4-nitrophenyl disulfide; DTNB) followed by absorption measurement at 412 nm.
Immunoprecipitation and immunoblotting
Trx-1 nitration and Trx-1/ASK1 interaction detection were performed as described [18]. In brief, Trx-1 in homogenized lung tissues was immunoprecipitated with a monoclonal antibody against Trx-1. Trx-1 nitration and Trx-1/ASK1 interaction were examined, respectively, by immunoblotting using a primary antibody against nitrotyrosine or against ASK1 after sample separation. After incubation with horseradish peroxidase conjugated secondary antibody, the blot was developed with an ECL-Plus chemiluminescence reagent kit and visualized with UVP Bio-Imaging Systems. Blot densities were analyzed with Vision Works LS Acquisition and Analysis software.
p38 MAPK activity assay
p38 MAPK activity assay was performed by p38 MAPK assay kit according to the manufacturer's instructions.
In vitro nitration of Trx-1
Human Trx-1 was subjected to in vitro nitration with a provided procedure described by Guo et al [19]. In brief, purified human Trx-1(dissolved in 0.1 µM phosphate buffer, pH 7.4, final concentration of 50 µM) was incubated at 37℃for 30 min with SIN-1 (final concentration of 100 µM). Unreacted SIN-1 was removed by ultrafiltration over membranes with a 3-kDa cutoff.
Statistical analysis
All values in the text and figures were presented as mean±SD of independent experiments. All data (except immunoblotting density) were subjected to two-way ANOVA followed by Bonferroni correction for post hoc t test. Immunoblotting densities were analyzed with the Kruskal-Wallis test followed by Dunn post hoc test. Probabilities of 0.05 or less were considered to be statistically significant.