Patients and grouping
The cartilage tissue of OA patients came from the knee joints of 30 patients who had undergone total knee arthroplasty. Meanwhile, the healthy cartilage tissue came from 20 patients who had not undergone OA or RA (rheumatoid arthritis). All patients voluntarily signed the informed notice. The current study obtained the approval of Ethics Committee of the hospital (ethic vote 198/203).
Cell culture
The femoral articular cartilage of the femur was obtained and cut. Then, it was digested by 0.2% type II collagenase, oscillation resolving for 40min at 37℃, washed by D-Hanks, and diluted in DMEM/F12 (Gibco, USA) combined with 10% FBS, 100 u/ml penicillin (Gibco, USA) as well as 100 mg/ml streptomycin (Gibco, USA). Then cells were culture in a saturated humidity incubator (37°C, 5% CO2). The solution was changed every two days until the chondrocytes grew into sheets and covered more than 85% of the wall of the bottle [21]. The cells of 2 or 3 generations were enrolled for the further investigation.
Cell transfection
PcDNA3.1-MEG3 overexpression vector, si-MEG3 (Sangon Biotech, Shanghai, China), miR-361-5p mimics and miR-361-5p mimics NC (Guangzhou Reeber) were prepared, followed by cells transfection according to the instructions of the transfection reagent. Based on different transfection, osteoarthritic chondrocytes were divided into Blank group, pcDNA3.1-NC group, pcDNA3.1-MEG3 group, si-NC group, si-MEG3 group, pcDNA3.1-NC + mimics NC group, pcDNA3.1-MEG3 + mimics NC group, pcDNA3.1-NC + miR-361-5p mimics group and pcDNA3.1-MEG3 + miR-361-5p mimics group. All transfection was carried out by Lipfectamine 2000 transfection kit (Invirtrogn,USA) according to the instructions. Then, the samples were treated with pcDNA3.1-NC and pcDNA3.1-MEG3 were cultured for 48 h by adding 10 μmol/l of Wnt/β-catenin signaling pathway inhibitor XAV939 (Tocris Bioscience), which was named as pcDNA3.1-NC +XAV939 group and pcDNA3.1-MEG3+ XAV939 group respectively. After 48 hours, the samples were treated with IL-1β (10 ng / ml) for 24 hours. Finally, cells of each group were collected for following experiments.
Real-time fluorescent quantitative PCR
Total RNA (500 ng) from sample of each group was obtained as well as quantified using TRIzol reagent, and cDNA template was synthesized by reagent kit (invitrogen, San Diego, USA). GAPDH was used as reference (Table 1). The associated conditions were: 95°C for 3 min, 39 cycles at 95 °C for 10 s, 55 °C. Fluorescence signals were collected at the end points of each cycle extension, followed by the amplification curve investigation. Relative expression of candidate genes were calculated by 2-∆∆CT method [22].
Luciferase reporter assay
The regulatory relation between MEG3 and miR-361-5p was revealed by using StarBase. A wild type (MEG3-WT) or mutant (MEG3-MUT) fragment of the MEG3 3'UTR containing miR-361-5p was synthesized. Then, the wild type or mutant were cloned into the pmirGLO reporter vector (Promega, USA). After inoculation of human chondrocytes in 24-well plates (5 × 105/well) for 24 hours, miR-361-5p mimic or miR-361-5p NC, MEG3-WT or MEG3-MUT were co-transfected into human chondrocytes by Lipofectamine 3000 (Thermo Fisher Scientific), followed by Kit (Promega, E1910, USA) detection 48 hours after transfection.
RIP assay
RIP was determined by using a Magna RIPTM RNA kit (Millipore, USA). Briefly, the cultured chondrocytes were further suspended in RIP lysis buffer (Solarbio). Then, cell extract was incubated overnight with RIP buffer containing human anti-Ago2 antibody beads (Millipore) (Input and normal IgG served as controls). Finally, RNA samples was extract using TRIzol reagent, followed by relative enrichment of MEG3 and miR-361-5p detection.
Western blotting
Cultured cells were treated with 100 μl/50mL protein lysate RIPA. Briefly, the extracted protein was quantified by bicinchoninic acid (BCA) method. A total of 50 g samples was investigated by 10% polyacrylamide gels, and transferred to polyvinylidenefluoride membranes (5% Skim milk/BSA). Samples was treated with primary antibodies including β-catenin (#8480), Non-phospho (Active) β-Catenin (#19807), MMP-1 (#54376), MMP-13 (#94808), cyclinD1(#2922), c-Myc (#9402), PCNA (#13110), Bax (#5023) and Bcl-2 (#4223) antibody (1:1000, Cell Signaling, Boston, USA), as well as Ki67 (ab92742), ADAMTS-5 (ab41037) and Aggrecan (ab36861) (Abcam, Cambridge, MA, USA) [20]. Then, samples were treated with the secondary antibody (1:5000, Biyuntian). Finally, the protein was stained with diaminobenzidine (DAB) kit. All experiments were repeated for 3 times.
CCK-8 assay
All cells were placed in 24-well plates (2 × 103 cells/well, 37 °C and 5% CO2). After being incubated for 0, 24, 48, 72 h, a total of 10 μL CCK-8 (Sigma-Aldrich) were mixed in samples for further incubation. OD490 value was measured by enzyme-linked immunosorbent assay [23].
Flow cytometry assay
Simply, the cells were treated by trypsin combining with 200 μL Annexin V-FITC, incubated for 10 min in dark, and then washed with 200 μL PBS and 10 μL PI. Cell cycle was then detected by using flow cytometry (Beckman Coulter), followed by the data analysis.
OA rat model construction
Male SD rats (200-250 g) were obtained from the Experimental Animal Center of Taishan Medical College. All rats were anesthetized with intramuscular injection of sodium pentobarbital (0.05 mg/g, Chuangdong Co., Chongqing, China). Then, SD rats was traversed by the medial collateral ligament and destabilized by the medial meniscus (DMM). One week after the operation, si-NC, si-MEG3 (1×109 PFU, 20 μl) was injected into the knee joint of the recipient rat (n = 6 for each group, 20 μL per joint) twice a week for 4 weeks. Eight weeks after the operation, the rats were sacrificed with cervical dislocation method (external force dislocated the cervical vertebra of rat and disconnects the spinal cord from the cerebrospinal cord), and then the knee joints were harvested. All experiment was performed in Experimental Center of Taishan Medical College. This study was approved by the Laboratory Animal Ethics Committee of Taishan Medical College (No. 2019146), and all experiments were in accordance with the guide for the care and use of laboratory animal.
Histological and immunostaining investigation
Cartilage samples was placed in paraformaldehyde (4%), embedded in paraffin and cut into sample slice (5μm/slice). The cartilage destruction was evaluated by using the Safranin ‘O’ staining. Histological scores were performed according to the International Osteoarthritis Research Association (OARSI) grading system, which ranging from 0 (normal) to 6 (>80% represented the cartilage loss). Scores were determined from multiple serial sections of the knee joint of each mouse.
Statistical Analysis
The SPSS 18.0 (Chicago, IL, USA) was selected as the software for data analysis. Meanwhile, all the data in current investigation were represented as the mean ± standard deviation (SD). Significant differences between two groups were assessed using Student’s t-test, while least significant difference between means (LSD)-t multiple comparison test was processed for more than two groups. P < 0.05 was considered as statistically significant [24].