Abstract
IntroductionOur previous work has revealed that expression of follistatin-like protein 1 (FSTL1) is elevated in the synovial tissues from osteoarthritis (OA) patients. The aim of this study was to elucidate the underlying molecular mechanisms by which FSTL1 plays a role in the pathogenesis of OA.MethodsCultured fibroblast-like synoviocytes (FLSs) from synovial tissues of OA patients were stimulated with human recombinant FSTL1, and then the expression of inflammatory cytokines in FLS and their concentrations in the cell supernatants were measured by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Nuclear factor kappa B (NF-κB) activation was examined by western blot and chromatin immunoprecipitation (ChIP) assay at the p65 binding site. Finally, the proliferation of FLSs and the expression level of the proliferation-related tumor suppressors (p53 and p21) were determined by MTS assay kit and western blot in the presence or absence of FSTL1, respectively.ResultsFSTL1 remarkably promoted expression levels of several inflammatory cytokines (tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6)) in vitro. Western blot analysis showed that FSTL1 activated the inflammatory-related NF-κB signaling pathway, as validated by ChIP assay detecting p65-binding level on the cytokine promoter region. Moreover, FSTL1 promoted the proliferation of OA FLS by downregulating the expression of p53 and p21. Interestingly, the concentration of synovial fluid IL-6 was remarkably elevated in OA patients, and was correlated with synovial fluid and serum FSTL1 levels.ConclusionsThese findings show that FSTL1 functions as an important proinflammatory factor in the pathogenesis of OA by activating the canonical NF-κB pathway and enhancing synoviocytes proliferation, suggesting that FSTL1 may be a promising target for the treatment of OA.
Highlights
Our previous work has revealed that expression of follistatin-like protein 1 (FSTL1) is elevated in the synovial tissues from osteoarthritis (OA) patients
These findings show that FSTL1 functions as an important proinflammatory factor in the pathogenesis of OA by activating the canonical nuclear factor kappa B (NF-κB) pathway and enhancing synoviocytes proliferation, suggesting that FSTL1 may be a promising target for the treatment of OA
We incubated fibroblast-like synoviocyte (FLS) with the two different FSTL1 concentrations (1 μg/ml and 5 μg/ml) for 24 hrs, we observed that FSTL1 remarkably increased the level of tumor necrosis factor alpha (TNF-α), interleukin 1β (IL-1β) and interleukin 6 (IL-6) mRNA in the FLSs in a dose-dependent way (Figure 1A)
Summary
Our previous work has revealed that expression of follistatin-like protein 1 (FSTL1) is elevated in the synovial tissues from osteoarthritis (OA) patients. The aim of this study was to elucidate the underlying molecular mechanisms by which FSTL1 plays a role in the pathogenesis of OA. Among multiple pathways and mediators influencing the development and persistence of OA, nuclear factorkappa B (NF-κB) transcription factor plays a prominent role [10,11]. The NF-κB family consists of P50 (NF-κB1), P52 (NF-κB2), P65 (RelA), RelB and C-Rel. NF-κB protein, a heterodimer of p50 and p65/RelA, is usually sequestered by inhibitor of kappa B alpha (IκBα) in the cytosol in the inactive state [12,13], NF-κB can be activated by proinflammatory cytokines, excessive mechanical stress and ECM degradation enzymes. NF-κB-activating kinases are one of the potential therapeutic OA targets [10]
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