2.1 CCl4-induced hepatic fibrosis in mice
Male C57BL/6 mice (7–8 weeks old) were provided by the experimental animal center of Guangxi Medical University, which we used to develop the liver fibrosis model. To induce liver fibrosis, the mice were intraperitoneally injected with 20% CCl4, 0.4mL/100g twice a week. Simultaneously, the control group was administered with the same dose of olive oil. Liver tissue and peripheral blood were collected at 2,4,6, and 8 weeks. The perfused liver tissues were fixed with 4% formalin or preserved at − 80 ℃. We subjected the fixed liver tissues to HE staining, and then detected collagen via Masson staining. The expression of α-SMA was detected through immunohistochemistry analysis. Serum was separated from peripheral blood for further exosome extraction.Animal ethics review follows the Guiding Opinions on the Treatment of Laboratory Animals issued by the Ministry of Science and Technology of the People's Republic of China and the Laboratory Animal-Guideline for Ethical Review of Animal Welfare issued by the National Standard GB/T35892-2018 of the People's Republic of China.
2.2 Collection of human serum
Human serum samples were collected from 12 patients diagnosed with hepatitis B virus F3/4 fibrosis and 10 healthy volunteers aged between 45 and 65 years. We excluded the effects of taking drugs and drinking within 24 hours. No other potential diseases were found in all participants. The isolated serum samples were kept at − 80℃ for further analyses. The study was approved by the ethics committee of the First Affiliated Hospital of Guangxi Medical University. All subjects signed informed consent.
2.3 Collection of mouse serum
We collected the peripheral blood from C57BL/6 mice in the control group and liver fibrosis group via a retro-orbital bleed. Blood samples were centrifuged at 3,000 rpm for 10 min at 4℃ to remove blood cells. The supernatant was then centrifuged at 16,000 g for 10min at 4℃ to completely remove the larger vesicles. The serum samples were stored at − 80℃。
2.4 Serum EV purification
Human serum samples were centrifuged at low speed (300g×15min 4℃; 2,000g×10min 4℃) and 10,000g for 30min to remove large vesicles. A W41Ti rotor (Beckman Coulter, Brea, CA, USA) was applied to centrifuge the supernatant at 100,000×g for 90 min The pellets were washed in phosphate-buffered saline (PBS) to remove protein contaminants and centrifuged again at 100,000×g for 90 min. The exosomes were resuspended in PBS. 8㎍/ml of serum exosomes from normal adults and cirrhotic patients were co-cultured with LX-2 for 24h respectively, Total RNA from serum exosomes and LX-2 were extracted by miRNeasy Kits (Qiagen) and nuclearol (GeneBank). We applied the exoEeasy Midi Kit (Qiagen) to isolate exosomes of mouse serum according to the manufacturer's instructions. Briefly, 1 volume of buffer was added to 1 volume of the sample. The sample/Buffer XBP was mixed onto the exoEasy spin column and the device spun at 500g for 1min. We did another spin at 5,000g for 1min to eliminate all the liquid. This was followed by the addition of 3.5ml Buffer XWP and centrifugation at 3,000g for 5min to remove residual buffer. Exactly 400ul buffer XE was added to elute the exosomes for electron microscopic examination. To extract serum exosomal RNA, 700ul Qiazol was added. The serum exosomes were examined via transmission electron microscopy (TEM). Nanoparticle tracking analysis (NTA) of exosomes was performed using zetaview PMX 110.
2.5 HSC cultures and transfection
LX-2 cells were cultured in DMEM/10% FBS, seeded in 6-well plates, and then cultured in a serum-free medium for the next 24 h. LX-2 cells were treated with serum exosomes of healthy adults and cirrhotic patients for 24h, respectively. Expressions of collagen α1(I), α-SMA mRNA, and miR-574-5p were determined via qRT-PCR. miRNA mimic and miRNA inhibitor were transfected using Lipofectamine™ RNAiMAX Transfecti-
on Reagent (Invitrogen). To detect the expression of collagen α1(I) and α-SMA, we extracted RNA and protein at 24h and 48h, respectively. The miRNA-574-5p mimic, nc mimic, miRNA-574-5p inhibitor, and nc inhibitor were purchased from Jima.
2.6 EV binding assays
The serum exosomes labeled with PKH-67 (20㎍/ml) were added to LX-2 and incubated at 37℃ for 12–24 hours in the dark. The cells were washed with PBS and then fixed. We stained the nucleus with DAPI and examined it for fluorescence using a confocal microscope.
2.7 RNA extraction and RT-qPCR
Total RNA from cultured HSC and liver tissue were extracted by nuclearol (GeneBank) and reverse-transcribed using PrimeScript™ RT Master Mix(TAKARA) following the manufacturer's protocols. Quantitative real-time RT-PCR was performed using TB Green Premix Ex TaqTM II (TAKARA) with primers for α-SMA, collagen α1(I). Total RNA from serum exosomes and liver tissues were extracted by miRNeasy Micro Kit(Qiagen) and nuclearol (GeneBank) respectively, and then reverse-transcribed using miRcute Plus miRNA First-Strand cDNA Kit (TIANGEN). Quantitative real-time RT-PCR was performed using miRcute Plus miRNA qPCR Kit (TIANGEN). GAPDH (for mRNA) and U6 (for miRNA) acted as the reference gene.
2.8 Western Blotting
Protein was isolated through lysis with radioimmunoprecipitation assay (RIPA) buffer supplemented with 1:100 protease inhibitor (Solarbio). The BCA protein assay kit (BOSTER) was used for protein quantification. Samples were separated by SDS-PAGE gels and transferred onto a PVDF membrane (Millipore). The membranes were blocked for 1h with 5% skimmed milk and incubated overnight at 4 ℃ with primary antibodies: 1:1000 diluted anti-CD9 (ab92726, System Biosciences), 1:2000 anti-TSG101 (ab125011, System Biosciences), 1:2000 anti-COL1A1 (ab260043, abcam), 1:5000 anti-α-SMA (ab124964, abcam), 1:1000 GAPDH (41549, CST). Then, after 3 times wash, the membranes were incubated with the HRP-conjugated secondary anti-Rabbit antibody for 1h at room temperature. Immunoreactive bands were visualized using Immobilon Western HRP (GeneBank; USA) and analyzed in Image J software.
2.9 Statistical analysis
Masson staining, immunohistochemical staining, and Western-blot results were analyzed by Image J software. The expression levels of miRNAs in exosomes and liver tissues were determined by 2−△△CT. Data processing and statistical analyses were conducted using SPSS 20.0 software. Data were expressed as mean ± standard deviation. The software GraphPad 8.0 was used for plotting. Comparison of means between the multiple groups was achieved using One-way ANOVA, whereas an independent sample t-test was used for the comparison between the two groups. Spearman correlation coefficient was used for correlation analysis. P < 0.05 denoted statistically significant difference. Each experiment was conducted in three independent replicates.