n-3 polyunsaturated fatty acids alleviate the progression of obesity-related osteoarthritis and protect cartilage through inhibiting the HMGB1-RAGE/TLR4 signaling pathway.

Osteoarthritis (OA) is a common joint degenerative disease. There is currently no cure for OA. Dietary fatty acids have potential value in the prevention and treatment of OA. n-3 polyunsaturated fatty acids (PUFAs) have anti-inflammatory effects, but their anti-OA mechanism remains unclear. High-mobility group box 1 (HMGB1) promotes inflammation and participates the pathogenesis of OA. The purpose of this study was to investigate the protective effect of n-3 PUFAs on cartilage and whether n-3 PUFAs could exert an anti-OA effect through inhibiting HMGB1-RAGE/TLR4 signaling pathway. We established an obesity-related post-traumatic OA mice model and an in vitro study was conducted to explore the regulatory mechanism of n-3 PUFAs on HMGB1 and its signal pathway against OA. We found that diet rich in n-3 PUFAs alleviated OA-like lesions of articular cartilage with the decrease of HMGB1-RAGE/TLR4 signaling protein in mice. In SW1353 cells, DHA significantly reduced the expression of HMGB1-RAGE/TLR4 signaling protein which was up-regulated by IL-1ß stimulation. HMGB1 overexpression reversed the inhibitory effect of DHA on HMGB1-RAGE/TLR4 signaling pathway. The activation of SIRT1 may participate the inhibitory effect of DHA on HMGB1-RAGE/TLR4 signaling pathway. In conclusion, n-3 PUFAs could attenuate the progression of obesity-related OA and exert protective effect on cartilage by inhibiting HMGB1-RAGE/TLR4 signaling pathway, which may be associated with the activation of SIRT1. Dietary n-3 PUFAs supplements can be considered as a potential therapeutic substance for OA.

Leptin Induced TLR4 Expression via the JAK2-STAT3 Pathway in Obesity-Related Osteoarthritis.

Obesity is considered as a risk factor of osteoarthritis (OA), but the precise relationship is still poorly understood. Leptin, one of the most relevant factors secreted by adipose tissues, plays an important role in the pathogenesis of OA. Our aim was to investigate the regulation and molecular mechanism of the leptin signaling pathway in obesity-related OA. SD rats were fed with a high-fat diet (HFD) for 5, 15, and 27 weeks. The levels of leptin in serum increased from W5, while in the synovial fluid increased from W15. The histological evaluation showed that the pathological changes of OA occurred at 27 weeks rather than 5 or 15 weeks. We also found that leptin induced CD14/TLR4 activation by the JAK2-STAT3 signaling pathway to promote OA. Moreover, silencing SOCS3 enhanced leptin-induced JAK2-STAT3-CD14/TLR4 activation in rat primary chondrocytes. Our findings indicated that leptin may be one of the initiating factors of obesity-related OA. TLR4 is at least partially regulated by leptin through the JAK2-STAT3-CD14 pathway. Meanwhile, SOCS3 acting as a negative feedback inhibitor of leptin signaling presented a potential therapeutic prospect for obesity-related OA. Our study provided new evidence suggesting the key role of leptin in mediating obesity-related OA process and its underlying mechanisms.

Resveratrol Exerts Anti-Osteoarthritic Effect by Inhibiting TLR4/NF-κB Signaling Pathway via the TLR4/Akt/FoxO1 Axis in IL-1ß-Stimulated SW1353 Cells.

PURPOSE: Osteoarthritis (OA) is associated with chronic low-grade inflammation. Resveratrol exerts protective effects on OA through its anti-inflammatory property; however, the mechanism of resveratrol on anti-inflammatory signaling pathways has not been fully elucidated yet. The aim of the present study was to investigate whether resveratrol-mediated PI3K/Akt expression is linked to TLR4/NF-κB pathway and the role of TLR4/Akt/FoxO1 axis in the anti-osteoarthritic effect of resveratrol. METHODS: SW1353 cells stimulated by IL-1ß (10 ng/mL) were cultured in the presence or absence of resveratrol (50 µM) and then treated with TLR4 siRNA, PI3K inhibitor LY294002 or FoxO1 siRNA, respectively. The associated proteins of TLR4 signaling pathways and TLR4/Akt/FoxO1 axis were evaluated by Western blot. The level of IL-6 in the supernatant was detected by ELISA. RESULTS: IL-1ß treatment increased the expression of TLR4/NF-κB and phosphorylation of PI3K/Akt and FoxO1, while additional resveratrol further upregulated the expression of PI3K/Akt and FoxO1 phosphorylation but downregulated TLR4 signals in SW1353 cells. Further analyses by the inhibition of TLR4, PI3K/Akt and FoxO1 signaling pathways, respectively, showed that the activation of TLR4 can induce PI3K/Akt phosphorylation, which increases the phosphorylation of FoxO1 and inactivates it. Next, inactivated-FoxO1 can reduce the expression of TLR4, which forms a self-limiting mechanism of inflammation. Resveratrol treatment can upregulate PI3K/Akt phosphorylation and inactivate FoxO1, thereby reducing TLR4 and inflammation. CONCLUSION: This study reveals that TLR4/Akt/FoxO1 inflammatory self-limiting mechanism may exist in IL-1ß-stimulated SW1353 cells. This study reveals a novel cross-talk mechanism which is between integrated PI3K/Akt/FoxO1 signaling network and TLR4-driven innate responses in IL-1ß-stimulated SW1353 cells. Resveratrol may exert anti-OA effect by enhancing the self-limiting mechanism of inflammation through TLR4/Akt/FoxO1 axis.

Protective effect of resveratrol on obesity-related osteoarthritis via alleviating JAK2/STAT3 signaling pathway is independent of SOCS3.

Resveratrol (RES) has a protective effect on osteoarthritis (OA), nevertheless, the underlying mechanisms of RES towards obesity-related OA are still unclear. This study is aimed to determine whether leptin resistant mechanism presents in articular cartilage of obesity-related OA and whether the protective effect of RES is involved in the regulation of leptin signal by affecting suppressor of cytokine signaling 3 (SOCS3). Male C57BL/6 J mice were fed with standard chow diet, high fat diet (HFD) or high fat diet with RES (45 mg/kg.bw) for 22 weeks. Knee joints of mice were evaluated by histological and immunohistochemistry analysis. Serum level of leptin was measured by ELISA. The leptin, leptin receptor (OB-Rb), SOCS3 mRNA expression and JAK2, STAT3, OB-Rb and SOCS3 protein expression in cartilage were determined by real-time RT-PCR and western blot. In addition, SW1353 cells were pretreated with or without AG490, and stimulated with leptin in the presence or absence of RES to detect JAK2, STAT3, matrix metalloproteinase-13 (MMP-13) and SOCS3 expression. We found that HFD could induce obesity-related OA and RES prevented its progression. Serum leptin and mRNA expression in cartilage was up-regulated by HFD, while RES ameliorated the elevation. Besides, RES significantly inhibited the JAK2/STAT3 signaling pathway in cartilage, as well as SOCS3. In in vitro study, RES exhibited the same effect in SW1353 cells which stimulated with leptin. In conclusion, no significant leptin resistance existed in cartilage of obesity-related OA and the inhibitory effect of RES on obesity-related OA via alleviating JAK2/STAT3 signaling pathway is independent of SOCS3.

Resveratrol inhibits the development of obesity-related osteoarthritis via the TLR4 and PI3K/Akt signaling pathways.

Aim of the study: Obesity leads to mild, chronic inflammation which is a primary risk factor for osteoarthritis (OA). Resveratrol exerts a protective effect on OA through its anti-inflammatory properties, but the precise mechanism remains unknown. The present study aimed to investigate the mechanism by which resveratrol alleviates obesity-related OA, and whether it is linked to the TLR4 and PI3K/Akt signaling pathways. Materials and methods: C57BL/6J male mice were fed a high-fat diet (HFD) with or without resveratrol treatment and knee joints were collected for analysis. In addition, IL-1ß-induced SW1353 cells were used to study in vitro the reciprocal effects of TLR4 and PI3K/Akt pathways. Results: Resveratrol inhibited the development of OA in mice fed a HFD. TLR4 and PI3K/Akt signaling pathways were both activated in the articular cartilage; resveratrol treatment down-regulated TLR4 but up-regulated PI3K/Akt signaling. Further in vitro results showed that the effect of resveratrol alone on activation of PI3K/Akt was attenuated but not abolished by the TLR4 inhibitor CLI-095, and resveratrol failed to reduce TLR4 protein expression in IL-1ß stimulated cells pretreated with the PI3K inhibitor LY294002. Conclusions: Resveratrol may exert an anti-osteoarthritic effect by inhibiting TLR4 via the activation of PI3K/Akt signaling pathways. Resveratrol has potential as a drug for OA prevention.

Oral Administration of Resveratrol Alleviates Osteoarthritis Pathology in C57BL/6J Mice Model Induced by a High-Fat Diet.

Obesity has been associated with osteoarthritis (OA) due to increased mass and metabolic factors which are independent of the biomechanical contribution to joint load. Resveratrol, a natural polyphenolic compound, exerts protective effects on OA through its anti-inflammatory property. However, the mechanism of resveratrol on obesity-related OA is unclear. To investigate the effect and possible mechanism of oral resveratrol on obesity-related OA, we fed C57BL/6J mice with a high-fat diet (HFD) for 16 weeks to establish obesity-related OA model; then two doses (22.5 mg/kg and 45 mg/kg) of resveratrol were given by gavage for additional 12 weeks. Mice with HFD significantly increased body weights compared to the control mice, while resveratrol treatment did not cause obvious weight loss. Histological assessments showed that resveratrol at 45 mg/kg significantly improved OA symptoms. Levels of serum IL-1ß and leptin were decreased by resveratrol treatment and positively correlated with Mankin scores. Moreover, resveratrol significantly inhibited the expression of TLR4 and TRAF6 in cartilage. These results suggest that HFD induced obesity can lead to the occurrence of OA, and resveratrol may alleviate OA pathology by decreasing the levels of systematic inflammation and/or inhibiting TLR4 signaling pathway in cartilage. Thus, resveratrol might be a promising therapeutic treatment for obesity-related OA.