NF-κB Signaling Pathways in Osteoarthritic Cartilage Destruction

The PI3K/AKT/mTOR signaling pathway in osteoarthritis: a narrative review

Osteoarthritis (OA) is a complicated degenerative disease that affects whole joint tissue. Currently, apart from surgical approaches to treat late stage OA, effective treatments to reverse OA are not available. Thus, the mechanisms leading to OA, and more effective approaches to treat OA should be investigated. According to available evidence, the PI3K/AKT/mTOR signaling pathway is essential for normal metabolism of joint tissues, but is also involved in development of OA. To provide a wide viewpoint to roles of PI3K/AKT/mTOR signaling pathway in osteoarthritis, a comprehensive literature search was performed using PubMed terms 'PI3K OR AKT OR mTOR' and 'osteoarthritis'. This review highlights the role of PI3K/AKT/mTOR signaling in cartilage degradation, subchondral bone dysfunction, and synovial inflammation, and discusses how this signaling pathway affects development of the disease. We also summarize recent evidences of therapeutic approaches to treat OA by targeting the PI3K/AKT/mTOR pathway, and discuss potential challenges in developing these strategies for clinical treatment of OA.

Laquinimod Mitigated IL-1β-Induced Impairment of the Cartilage Extracellular Matrix in Human ATDC5 Chondrocytes

To date, a safe and reliable treatment of osteoarthritis (OA) has not yet been announced. Inflammatory response and degradation of the articular extracellular matrix (ECM) induced by IL-1β are important pathological characteristics of OA. Laquinimod is a quinoline-3-carboxamide and a novel oral immunomodulatory compound in clinical use. However, whether laquinimod has a beneficial effect in OA is not known. In our research, we found that laquinimod could ameliorate IL-1β-induced generation of ROS and improve mitochondrial function by increasing mitochondrial membrane potential (ΔΨm). Furthermore, treatment with laquinimod suppressed IL-1β-induced production of TNF-α and IL-6. Notably, laquinimod prevented the degradation of type II collagen by inhibiting MMP-3 and MMP-13. Meanwhile, the presence of laquinimod attenuated the reduction in aggrecan by mediating ADAMTS-4 and ADAMTS-5. Mechanistically, laquinimod ameliorated IL-1β-induced inflammation and degeneration of ECM by suppressing the activation of NF-κB. Taken together, our findings reveal that laquinimod possesses a beneficial effect against IL-1β insults in human chondrocytes, implying an important role of laquinimod in OA.

GRK5 Inhibition Attenuates Cartilage Degradation via Decreased NF-κB Signaling

OBJECTIVE

NF-κB-dependent signaling is an important modulator in osteoarthritis (OA), and G protein-coupled receptor kinase 5 (GRK5) regulates the NF-κB pathway. This study was undertaken to investigate the functional involvement of GRK5 in OA pathogenesis.

METHODS

GRK5 expression in normal and OA human knee joints was analyzed immunohistochemically. Gain- or loss-of-function experiments were performed using human and mouse chondrocytes. OA was induced in GRK5-knockout mice by destabilization of the medial meniscus, and histologic examination was performed. OA was also induced in wild-type mice, which were then treated with an intraarticular injection of amlexanox, a selective GRK5 inhibitor, every 5 days for 8 weeks.

RESULTS

GRK5 protein expression was increased in human OA cartilage. In vitro, expression levels of OA-related factors and NF-κB transcriptional activation were down-regulated by suppression of the GRK5 gene in human OA chondrocytes (3.49-fold decrease in IL6 [P < 0.01], 2.43-fold decrease in MMP13 [P < 0.01], and 2.66-fold decrease in ADAMTS4 [P < 0.01]). Conversely, GRK5 overexpression significantly increased the expression of OA-related catabolic mediators and NF-κB transcriptional activation. On Western blot analysis, GRK5 deletion reduced IκBα phosphorylation (up to 4.4-fold decrease [P < 0.05]) and decreased p65 nuclear translocation (up to 6.4-fold decrease [P < 0.01]) in mouse chondrocytes. In vivo, both GRK5 deletion and intraarticular amlexanox protected mouse cartilage against OA.

CONCLUSION

Our results suggest that GRK5 regulates cartilage degradation through a catabolic response mediated by NF-κB signaling, and is a potential target for OA treatment. Furthermore, amlexanox may be a major compound in relevant drugs.

UFL1 attenuates IL-1β-induced inflammatory response in human osteoarthritis chondrocytes

Osteoarthritis (OA) is a chronic inflammatory joint disease characterized by degradation of articular cartilage. Ubiquitin-fold modifier 1 (UFM1)-specific ligase 1 (UFL1) is an UFM1 E3 ligase that has been identified as a regulator of inflammatory response. However, the role of UFL1 in OA remains unknown. The aim of the present study was to explore the function of UFL1 in an in vitro OA system in chondrocytes. Our results showed that UFL1 was lowly expressed in both OA articular tissues and chondrocytes with IL-1β induction. Ectopic expression of UFL1 improved cell viability of IL-1β-induced chondrocytes. UFL1 suppressed the production of NO and PGE2, as well the expression levels of iNOS and COX-2 in IL-1β-induced chondrocytes. The IL-1β-induced increases in TNF-α and IL-6 levels were attenuated by UFL1. Ectopic expression of UFL1 inhibited the production of extracellular matrix (ECM) degrading enzymes including matrix metalloproteinase 3 (MMP-3), MMP-13, ADAMTS-4 and ADAMTS-5 in chondrocytes with IL-1β induction. Additionally, UFL1 suppressed IL-1β-induced activation of NF-κB signaling pathway in chondrocytes. In conclusion, these findings indicated that UFL1 exerted protective effect on IL-1β-induced chondrocytes. Thus, UFL1 might be a potential target for the treatment of OA.

Inhibitory Effects of Myrtucommuacetalone 1 (MCA-1) from Myrtus communis on Inflammatory Response in Mouse Macrophages

(1) Introduction: Reactive oxygen species (ROS) and nitric oxide (NO) are key signaling molecules that play important roles in the progression of inflammatory disorders. The objective of this study was to explore the use of myrtucommuacetalone-1 (MCA-1), as a novel compound of natural origin and a potential anti-inflammatory agent. (2) Methodology: The anti-inflammatory potential of MCA-1, which was isolated from Myrthus communis Linn, was determined by assaying superoxide, hydrogen peroxide, and nitric oxide production in macrophages. Furthermore, the effects of the compound were analyzed via phosphorylation and translocation of the transcription factor NF kappa B, which is a key regulator of iNOS activation. The effect of MCA-1 on the inducible nitric oxide synthase (iNOS) enzyme was also examined using in silico docking studies. The anticancer potential for MCA-1 was evaluated with an MTT cytotoxic assay. (3) Results: In stimulated macrophages, MCA-1 inhibited superoxide production by 48%, hydrogen peroxide by 53%, and nitric oxide (NO) with an IC₅₀ of <1 µg/mL. MCA-1 also showed a very strong binding pattern within the active site of the inducible nitric oxide synthase enzyme. Furthermore, 25 µg/mL of MCA-1 inhibited inducible nitric oxide synthase expression and abolished transcription factor (NFκB) phosphorylation and translocation to the nucleus. Cytotoxicity analyses of MCA-1 on 3T3 mouse fibroblasts, CC1 liver cell line, J774.2, macrophages and MDBK bovine kidney epithelial cell, yielded IC₅₀ values of 6.53 ± 1.2, 4.6 ± 0.7, 5 ± 0.8, and 4.6 ± 0.7, µg/mL, respectively. (4) Conclusion: Our results suggest that MCA-1, a major phloroglucinol-type compound, shows strong anti-inflammatory activity and has a potential to be a leading therapeutic agent in the future.

Protease-activated receptor 2 (PAR-2) antagonist AZ3451 as a novel therapeutic agent for osteoarthritis

Osteoarthritis (OA) is a highly prevalent joint disorder blamed for pain and disability in older individuals. It's commonly accepted that inflammation, apoptosis, autophagy and cellular senescence participate in the progress of OA. Protease activated receptor 2 (PAR2), a member of the G-protein coupled receptors, is involved in the regulation of various inflammation diseases. Previous studies have identified PAR2 as a potential therapeutic target for the treatment of OA. Here, we investigated the role of PAR2 antagonist AZ3451 in inflammation response, apoptosis, autophagy and cellular senescence during OA. We confirmed that PAR2 expression was significantly up-regulated in OA articular cartilage tissues as well as in interleukin 1β (IL-1β) stimulated chondrocytes. We demonstrated AZ3451 could prevent the IL-1β-induced inflammation response, cartilage degradation and premature senescence in chondrocytes. Further study showed that AZ3451 attenuated chondrocytes apoptosis by activating autophagy in vitro. The P38/MAPK, NF-κB and PI3K/AKT/mTOR pathways were involved in the protective effect of AZ3451. In vivo, we found that intra-articular injection of AZ3451 could ameliorate the surgery induced cartilage degradation in rat OA model. Our work provided a better understanding of the mechanism of PAR2 in OA, and indicated that PAR2 antagonist AZ3451 might serve as a promising strategy for OA treatment.

Regulatory Effects and Interactions of the Wnt and OPG-RANKL-RANK Signaling at the Bone-Cartilage Interface in Osteoarthritis

Cartilage and the bordering subchondral bone form a functionally active regulatory interface with a prominent role in osteoarthritis pathways. The Wnt and the OPG-RANKL-RANK signaling systems, as key mediators, interact in subchondral bone remodeling. Osteoarthritic osteoblasts polarize into two distinct phenotypes: a low secretory and an activated, pro-inflammatory and anti-resorptive subclass producing high quantities of IL-6, PGE2, and osteoprotegerin, but low levels of RANKL, thus acting as putative effectors of subchondral bone sclerosis. Wnt agonists, Wnt5a, Wisp-1 initiate excessive bone remodeling, while Wnt3a and 5a simultaneously cause loss of proteoglycans and phenotype shift in chondrocytes, with decreased expression of COL2A, aggrecan, and Sox-9. Sclerostin, a Wnt antagonist possesses a protective effect for the cartilage, while DKK-1 inhibits VEGF, suspending neoangiogenesis in the subchondral bone. Experimental conditions mimicking abnormal mechanical load, the pro-inflammatory milieu, but also a decreased OPG/RANKL ratio in the cartilage, trigger chondrocyte apoptosis and loss of the matrix via degradative matrix metalloproteinases, like MMP-13 or MMP-9. Hypoxia, an important cofactor exerts a dual role, promoting matrix synthesis via HIF-1α, a Wnt silencer, but turning on HIF-2α that enhances VEGF and MMP-13, along with aberrant collagen expression and extracellular matrix deterioration in the presence of pro-inflammatory cytokines.

Liraglutide suppresses TNF-α-induced degradation of extracellular matrix in human chondrocytes: a therapeutic implication in osteoarthritis

Osteoarthritis (OA) is a major global health problem; however, the etiology of the disease remains unknown and a reliable treatment strategy has yet to be discovered. Modulation of the receptor for glucagon-like peptide 1 (GLP-1) has emerged as a potential treatment strategy for various diseases including OA. In the present study, we investigated the effects of the specific GLP-1 receptor agonist liraglutide on factors of the pathogenesis of OA induced by tumor necrosis factor-α (TNF-α), including oxidative stress, expression of proinflammatory cytokines, degradation of articular cartilage extracellular matrix, and activation of the nuclear factor-κB (NF-κB) pathway. Our findings demonstrate that liraglutide exerted a potent beneficial effect in human primary chondrocytes by downregulating generation of reactive oxygen species and NADPH oxidase 4, suppressing expression of interleukin-6 and monocyte chemoattractant protein 1, rescuing type II collagen and aggrecan from degradation my matrix metalloproteinases and a disintegrin and metalloproteinase with type I thrombospondin motif, and inhibiting activation of the proinflammatory NF-κB signaling pathway. These findings demonstrate a potential role of GLP-1 receptor in the pathogenesis of OA and lay a foundation for further research on the mechanisms behind the potential therapeutic application of liraglutide in the treatment and prevention of OA.