Tissue samples and cell culture
From 2020-2021, patients with pancreatic cancer and patients with pancreatic trauma were included in each. All patients had no prior radiation or chemotherapy and were confirmed by pathological examination. Fibroblasts were extracted from patients with pancreatic cancer and pancreatic trauma, respectively. The cells were processed with trypsin to separate them into individual cells and passaged according to 1:1. Non-fibroblasts such as pancreatic cancer cells and endothelial cells with late apposition were removed utilizing the differential apposition principle, and cell morphology tended to be uniform and absent of apparent senescence phenotypes by the 3rd-4th generation in passaged culture. Human pancreatic adenocarcinoma cells (Panc-1) were obtained from the Chinese Academy of Sciences (Shanghai, China). The above cells were cultured in DMEM/F12 supplemented with 15% FBS. The CAFs were seeded in 15 cm dishes and cells were extracted when 75% confluence was reached. Hubei Cancer Hospital Ethics Committees approved this study.
Isolation and characterization of exosomes
CAFs were grown for 24 hours in a low-glucose basal medium. Cells were grown in exosome-depleted serum, which was generated by centrifuging FBS at 100,000×g for 4 hours at 4 °C. After 72 hours of incubation, we collected the culture liquid and centrifuged it. Following a 5 minute centrifugation at 400×g for 5 minutes at 4 °C, floating cells were collected from the medium. Following that, the supernatants were centrifuged at 3000×g for 20 minutes at 4 °C to remove any remaining cell debris. CAFs-derived exosomes were then added to the culture medium for continuous culture of pancreatic cancer cells Panc-1.
For our research, we utilized a transmission electron microscope to examine the morphology of the isolated exosomes (Hitachi HT7700, Japan). Size distribution of the separated exosomes was determined using qNano (Izon Science, New Zealand). The percentage of CAFs cells expressing for the molecular marker fibroblast activating protein (FAP) was determined using flow cytometry, and the fluorescence localization of α-SMA was determined using cellular immunofluorescence to further elucidate the cell phenotype. Anti-CD9 and anti-CD63 antibodies were utilized for the study of exosome markers in protein-based Western blotting.
RNA extraction and quantitative real-time PCR (qRT-PCR) analysis
Researchers used TRIzol reagent (Invitrogen) to extract RNA from cells and exosomes, and then they reverse transcribed the cDNA to duplicate the RNA. NNT-AS1 siRNAs were created by Ribobio (Guangzhou, China). We bought miR-889-3p mimics and NC mimics from Ribobio. The primer sequences for NNT-AS1 were: 5’- CTG GAA TCC CTG CTA CTC AGG A -3’ (the forward primer) and 5’- GCC ATG TGA TAT GCC TGC TC -3’ (the reverse primer). The primer sequences for β-actin were: 5′- CAG AGC AAG AGA GGC ATC C -3′ (the forward primer) and 5′- CTG GGG TGT TGA AGG TCT C -3′ (the reverse primer). The RNA primers were designed and synthesized by Ribobio. For quantitative real-time PCR, green SYBR qPCR was utilized (Takara Biotechnology, China). Normalizing miR-889-3p was done using U6, whereas normalizing NNT-AS1 was accomplished with β-actin. The relative change in RNA expression was determined using the 2-△△C method.
Luciferase reporter assay
After amplifying the section of NNT-AS1 sequences including the target-miR-889-3p binding sites, the products were inserted into the pmirGLO vectors (pmirGLO-NNT-AS1-WT). This plasmid was called NNT-AS1 WT. NNT-AS1 MUT was generated utilizing the target-miR-889-3p binding sites of NNT-AS1 as a template for PCR mutagenesis. Using the same approach, two HIF-1a constructs (one having the GAUAUUA binding sites, and the other carrying the CUAUAAU mutant binding sites) were created. Using Lipofectamine 2000, the Panc-1 cells were co-transfected mimics of miR-889-3p or NC mimics, along with either NNT-AS1 WT or NNT-AS1 MUT. We used pmirGLO-HIF-1a WT or pmirGLO-HIF-1a MUT together with miR-889-3p mimics or NC mimics in the same protocol. Luciferase activities were evaluated using a dual luciferase assay kit 48 hours after cells were lysed (Promega).
Vector constructs and transfections
The shRNA directed against NNT-AS1 was synthesized, reconstituted using pLVX-Puro vector, lentivirally packed, and transfected using lipofectamine 2000 (Invitrogen). Harvested logarithmic phase cells were plated onto 6-well plates. When cells reached about 80% confluence, they were transfected for 48 hours with miR-889-3p mimics, miR-889-3p-inh, pc-HIF-1α (pc-DNA3.1-HIF-1α), or their equivalent controls.
Western blot analysis
The BCA Protein Assay Kit was used to determine the protein content (Thermo, USA). For western blots, we used the HIF-1 antibody from Santa Cruz Biotechnology and the LDHA, PKM2, SDH, FH, and β-actin antibodies from Cell Signaling. The immune complexes were identified using enhanced chemiluminescence after a further 1h incubation with an anti-immunoglobin horseradish peroxidase-linked antibody (Cell Signaling Technology).
Glucose uptake, lactate secretion, and mitochondrial immunofluorescence staining
Cells were grown for 16 h in glucose-free DMEM and then incubated for an additional 24 hours in high-glucose DMEM. The glucose uptake and lactate secretion were performed using the Glucose Assay Kit (JianCheng, NanJing, China) and the Lactate Assay Kit (JianCheng, NanJing, China), respectively. Three times were repeated per experiment. Inverted fluorescence microscopy was used to detect mitochondrial activity in Panc-1 cells after 24 hours of incubation and immediately after 30 minutes of incubation with DMEM containing mitochondrial fluorescent probes.
CCK-8 assay
Cells were seeded at a density of 3×103/well in 96-well plates. The CCK-8 test was used to determine cell viability by measuring the absorbance OD at 450 nm with a microplate spectrophotometer (Molecular device, USA).
Wound healing assay
Six-well plates were prepared, with 1×106 cells planted, and cultured until they achieved a 90% confluence. Cell monolayers were scratched using a 200 ml plastic pipette tip, which produced wounds, and then cultured in new media for 24 hours. Measuring the average number of moving cells per field was done using photographs.
Cell migration assay
Invasion assays were conducted using 8.0μm pores in a Trans-well insert. A cell suspension of 1×105 cells was introduced to the top chamber of a trans-well, and the mixture was incubated overnight. 1/6 diluted matrigel filter media was used in the invasion test. The bottom chamber was mixed with DMEM containing 10% fetal bovine serum and left to incubate for 24 h. Paraformaldehyde was used to fix the migratory cells, after which they were stained with crystal violet at a concentration of 0.1 percent. Each of the five target fields was scrutinized using a 20×objective.
Bioinformatics analysis
DIANA (http://diana.imis.athena-innovation.gr/DianaTools/index.php) database for NNT-AS1 and miR-889-3p binding prediction. STARBASE (http://starbase.sysu.edu.cn/index.php) database for predicting HIF-1 and miR-889-3p binding.
Statistical analysis
The mean and standard deviation (SD) of at least three separate experiments are presented. We used the Student's t-test to analyze the data. A P<0.05 value was deemed significant. SPSS 20.0 was used to conduct all statistical analyses.