TNF‑α increases the expression of inflammatory factors in synovial fibroblasts by inhibiting the PI3K/AKT pathway in a rat model of monosodium iodoacetate‑induced osteoarthritis

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Abstract

Osteoarthritis is a degenerative disease that often causes patients to experience joint pain and deformity. It has been demonstrated that tumor necrosis factor (TNF)-α is associated with the progression of osteoarthritis; however, to the best of our knowledge, the mechanisms by which TNF-α simulates the progression of osteoarthritis and the signaling pathway(s) it influences remain unknown. Therefore, the aim of the present study was to investigate the therapeutic effects of TNF-α inhibitor in an iodoacetate-induced rat model of osteoarthritis and identify its potential mechanisms of action. Western blotting, ELISA and histological analyses were performed to assess the effects of the TNF-α inhibitor on osteoarthritis. The effects of TNF-α and phosphoinositide 3-kinase (PI3K) inhibition on synovial fibroblasts isolated from rats with osteoarthritis were tested in vitro. Furthermore, the expression of various inflammatory cytokines and the PI3K/protein kinase B (AKT) signaling pathway were assessed in vitro. The results indicated that the inflammatory factors TNF-α, interleukin (IL)-1β, IL-17a and IL-8 were upregulated in synovial fibroblasts taken from rats with osteoarthritis compared with normal rats. By contrast, TNF-α inhibition downregulated IL-1β, IL-17a and IL-8 expression in synovial fibroblasts in vitro. The PI3K/AKT pathway was also upregulated in synovial fibroblasts harvested from rats with osteoarthritis compared with that in normal rats. It was demonstrated that treatment with the TNF-α inhibitor downregulated the serum and protein levels of IL-1β, IL-17a and IL-8 in rats with osteoarthritis. Furthermore, treatment with the TNF-α inhibitor also decreased matrix metalloproteinase (MMP)-3, MMP-9, vascular endothelial growth factor and ADAMTS4 expression in synovial fibroblasts isolated from rats with osteoarthritis. Treatment with the TNF-α inhibitor also inhibited the PI3K/AKT pathway in synovial fibroblasts isolated from rats with osteoarthritis. Treatment with the PI3K inhibitor ameliorated TNF-α-induced increases in IL-1β, IL-17a and IL-8 expression in synovial fibroblasts isolated from rats with osteoarthritis. Furthermore, treatment with the TNF-α inhibitor decreased inflammation, as well as joint and cartilage destruction in vivo. Taken together, the results of the present study indicate that TNF-α inhibition may downregulate the expression of inflammatory factors in synovial fibroblasts, suggesting that TNF-α inhibition may be a novel method for treating osteoarthritis by downregulating the PI3K/AKT signaling pathway.

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Inflammation in joint injury and post-traumatic osteoarthritis.

Jason Lieberthal, Nisha Sambamurthy, Carla R Scanzello (2015)

Inflammation is a variable feature of osteoarthritis (OA), associated with joint symptoms and progression of disease. Signs of inflammation can be observed in joint fluids and tissues from patients with joint injuries at risk for development of post-traumatic osteoarthritis (PTOA). Furthermore, inflammatory mechanisms are hypothesized to contribute to the risk of OA development and progression after injury. Animal models of PTOA have been instrumental in understanding factors and mechanisms involved in chronic progressive cartilage degradation observed after a predisposing injury. Specific aspects of inflammation observed in humans, including cytokine and chemokine production, synovial reaction, cellular infiltration and inflammatory pathway activation, are also observed in models of PTOA. Many of these models are now being utilized to understand the impact of post-injury inflammatory response on PTOA development and progression, including risk of progressive cartilage degeneration and development of chronic symptoms post-injury. As evidenced from these models, a vigorous inflammatory response occurs very early after joint injury but is then sustained at a lower level at the later phases. This early inflammatory response contributes to the development of PTOA features including cartilage erosion and is potentially modifiable, but specific mediators may also play a role in tissue repair. Although the optimal approach and timing of anti-inflammatory interventions after joint injury are yet to be determined, this body of work should provide hope for the future of disease modification tin PTOA.

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Circulating levels of IL-6 and TNF-α are associated with knee radiographic osteoarthritis and knee cartilage loss in older adults.

O Stannus, F Cicuttini, Diane J. Burgess … (2010)

The role of inflammation in osteoarthritis (OA) pathogenesis is unclear, and the associations between inflammatory cytokines and cartilage loss have not been reported. We determined the associations between serum levels of interleukin (IL)-6 and tumor necrosis factor-α (TNF-α), knee radiographic OA (ROA) and cartilage loss over 2.9 years in older adults. A total of 172 randomly selected subjects (mean 63 years, range 52-78, 47% female) were studied at baseline and approximately 3 (range 2.6-3.3) years later. IL-6 and TNF-α were assessed by radioimmunoassay. T1-weighted fat-suppressed magnetic resonance imaging of the right knee was performed at baseline and follow-up to determine knee cartilage volume. Knee ROA of both knees was assessed at baseline. At baseline, quartiles of IL-6 and TNF-α were associated with increased prevalence of medial tibiofemoral joint space narrowing (OARSI grade ≥ 1) in multivariate analyses [odds ratio (OR): 1.42 and 1.47 per quartile, respectively, both P<0.05]. Longitudinally, baseline IL-6 predicted loss of both medial and lateral tibial cartilage volume (β: -1.19% and -1.35% per annum per quartile, P<0.05 and P<0.01, respectively), independently of TNF-α. Change in IL-6 was associated with increased loss of medial and lateral tibial cartilage volume (β: -1.18% and -1.06% per annum per quartile, both P<0.05) and change in TNF-α was also negatively associated with change in medial cartilage volume (β: -1.27% per annum per quartile, P<0.05). Serum levels of IL-6 and TNF-α are associated with knee cartilage loss in older people suggesting low level inflammation plays a role in the pathogenesis of knee OA. Copyright © 2010 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

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Western blotting.

R. Paul Scofield, Biji Kurien (2006)

Western blotting (protein blotting or immunoblotting) is a powerful and important procedure for the immunodetection of proteins post-electrophoresis, particularly proteins that are of low abundance. Since the inception of the protocol for protein transfer from an electrophoresed gel to a membrane in 1979, protein blotting has evolved greatly. The scientific community is now confronted with a variety of ways and means to carry out this transfer. This review describes the various procedures that have been used to transfer proteins from a gel to a membrane based on the principles of simple diffusion, vacuum-assisted solvent flow and electrophoretic elution. Finally, a brief description of methods generally used to detect antigens on blots is also described.