To investigate the effect of tumor necrosis factor alpha (TNF-α) on the proliferation of fibroblast-like synoviocytes (FLS) and the expression of programmed cell death factor 5 (PDCD5) in an inflammatory microenvironment, for the further understanding of the mechanism of action of TNF-α in promoting the proliferation of synovial cells and the apoptosis of the chondrocytes.
Articular carriage specimens were obtained from 21 cases with osteoarthritis and 12 cases with femoral neck fractures as healthy controls during arthroplasties. The expression of PDCD5 was evaluated by immunofluorescence analyzed by mean option density (MOD) detected using the software ImagePro Plus. Real-time PCR was performed to evaluate the transcriptions of PDCD5 and TNF-α in synovium. FLS cells derived from rheumatoid arthritis patients were cultured in vitro and incubated with different concentrations of TNF-α. The effects of TNF-α at different concentrations on the proliferation of FLS cells were detected by Cell Counting Kit-8 (CCK-8) assay to evaluate the cell proliferation rate. After incubation with the absence or presence of recombinant human TNF-α at different concentrations, the FLS cells were isolated for detection of PDCD5 protein and PDCD5 gene. The expression of PDCD5 protein was detected by western-blot and the transcription of PDCD5 gene from the cells was detected by real-time quantitative PCR.
The MOD of PDCD5 as well as TNF-α of osteoarthritis cartilage sections were significantly increased compared with those of the controls, and in synovium there was a positive correlation between transcriptions of their mRNA. When the concentration of TNF-α was 1 ng/mL, the cell proliferation rate was not significantly different from that of the control group (P = 0.592), while the proliferation of FLS cells was significantly promoted when the concentration of TNF-α was 5, 10, 15, or 20 ng/mL, and the proliferation-promoting rates were 35.64% ± 6.96%, 48.72% ± 7.69%, 45.60% ± 8.85%, and 39.32% ± 6.18%, respectively (P < 0.01). The transcription of PDCD5 gene was significantly downregulated, which was 80.44% ± 4.07% and 84.30% ± 5.48%, respectively (P < 0.05), in the FLS cells incubated with TNF-α at the concentration of 10 and 15 ng/mL for 24 h. When the concentration of TNF-α was 1, 5, or 20 ng/mL, the transcription of PDCD5 mRNA in FLS cells was not significantly different from that in the control group (P > 0.05). The expression of PDCD5 protein was only significantly downregulated when the concentration of TNF-α was 10 ng/mL (P < 0.01), while the expression of PDCD5 protein in FLS cells was not significantly different from that in the control group (P > 0.05).
The expression of PDCD5 as well as TNF-α in osteoarthritis cartilage and synovium was significantly higher than in healthy tissues, and TNF-α can promote the proliferation of FLS cells in patients with rheumatoid arthritis, and inhibit the expression of PDCD5. PDCD5 may be involved in the abnormal proliferation of synoviocytes and the degeneration of chondrocytes stimulated by TNF-α.