NF-kappaB signaling: multiple angles to target OA

Artesunate alleviates interleukin‑1β‑induced inflammatory response and apoptosis by inhibiting the NF‑κB signaling pathway in chondrocyte‑like ATDC5 cells, and delays the progression of osteoarthritis in a mouse model

Osteoarthritis (OA) is a progressive and degenerative joint disorder that is highly prevalent worldwide and for which there is currently no effective medical therapy. Artesunate (ART), a natural compound used to treat malaria, possesses diverse biological properties, including the regulation of inflammation and apoptosis in various cells; however, its role in OA remains unclear. The aim of the present study was to investigate the effects of ART on interleukin (IL)‑1β‑induced chondrocyte‑like ATDC5 cells and in an OA mouse model. The results revealed that ART dose‑dependently relieved the inhibitory effect of IL‑1β on cell viability. Moreover, ART significantly reduced the overexpression of matrix metalloproteinase (MMP)‑3, MMP‑13, a disintegrin and metalloproteinase with thrombospondin motifs‑5 and cyclooxygenase‑2 at both the gene and protein levels in chondrocyte‑like ATDC5 cells stimulated by IL‑1β. Furthermore, ART decreased the expression of pro‑apoptotic Bax, cleaved caspase‑3 and cleaved caspase‑7 in a dose‑dependent manner, and increased the expression of the anti‑apoptotic factor Bcl‑2. These changes were mediated by the inhibitory effect of ART on the nuclear factor‑κB signaling pathway, defined as repression of the phosphorylation of IκBα and p65, and improved redistribution of p65. Additionally, ART blocked the advancement of the calcified cartilage zone and the loss of proteoglycan, and lowered histological scoring of OA in a mouse model. Taken together, these results indicate that ART may be of value as a therapeutic agent for OA.

NF-κB Signaling Pathways in Osteoarthritic Cartilage Destruction

Osteoarthritis (OA) is a type of joint disease associated with wear and tear, inflammation, and aging. Mechanical stress along with synovial inflammation promotes the degradation of the extracellular matrix in the cartilage, leading to the breakdown of joint cartilage. The nuclear factor-kappaB (NF-κB) transcription factor has long been recognized as a disease-contributing factor and, thus, has become a therapeutic target for OA. Because NF-κB is a versatile and multi-functional transcription factor involved in various biological processes, a comprehensive understanding of the functions or regulation of NF-κB in the OA pathology will aid in the development of targeted therapeutic strategies to protect the cartilage from OA damage and reduce the risk of potential side-effects. In this review, we discuss the roles of NF-κB in OA chondrocytes and related signaling pathways, including recent findings, to better understand pathological cartilage remodeling and provide potential therapeutic targets that can interfere with NF-κB signaling for OA treatment.

Sinomenine contributes to the inhibition of the inflammatory response and the improvement of osteoarthritis in mouse-cartilage cells by acting on the Nrf2/HO-1 and NF-κB signaling pathways

Pathological changes, such as articular cartilage degeneration, destruction, and hyperosteogeny, are regarded as the main features of osteoarthritis (OA). Sinomenine (SIN) is a monomeric component purified from the plant Sinomenium acutum which has been found to have anti-inflammatory effects, however, the mechanism of action of SIN on OA is not clear. In this study, we evaluated whether SIN could regulate the inflammatory response induced by interleukin (IL)-1β and improve outcomes in the instability model of OA (medial meniscus mice (DMM)) by acting on the Nrf2/HO-1 and NF-κ B signaling pathways in chondrocytes. From our experiments, which include Griess reaction, ELISA, Western blot, and immunofluorescence, we found that SIN not only down-regulated the expression of pro-inflammatory factors induced by IL-1β, including; inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), nitricoxide (NO), prostaglandin E2 (PGE2), tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6), but also decreased the production of IL-1β-induced cartilage matrix catabolic enzymes including; ADAMTS-5 and MMPs, in mouse chondrocytes. In addition, the degradation of aggrecan and type II collagen protein in the extracellular matrix (ECM) stimulated by IL-1β was reversed. Most importantly, we have revealed for the first time that in OA, SIN inhibited the inflammatory response and ECM degradation by activating the Nrf2/HO-1 signaling pathways and inhibiting NF-κB activity in mouse-cartilage cells. In in vivo experiments, SIN treatment helped to improve the cartilage destruction in OA model mice. In conclusion, this study has demonstrated that SIN inhibits the IL-1β-induced inflammatory response and cartilage destruction by activating the Nrf2/HO-1 signaling pathway and inhibiting the NF-κB signaling pathway in mouse chondrocytes, suggesting a new use for SIN in the treatment of OA.

Inducible knockout of CHUK/IKKα in adult chondrocytes reduces progression of cartilage degradation in a surgical model of osteoarthritis

CHUK/IKKα contributes to collagenase-driven extracellular matrix remodeling and chondrocyte hypertrophic differentiation in vitro, in a kinase-independent manner. These processes contribute to osteoarthritis (OA), where chondrocytes experience a phenotypic shift towards hypertrophy concomitant with abnormal matrix remodeling. Here we investigated the contribution of IKKα to OA in vivo. To this end, we induced specific IKKα knockout in adult chondrocytes in AcanCreER^T2/+; IKKα^f/f mice treated with tamoxifen (cKO). Vehicle-treated littermates were used as wild type controls (WT). At 12 weeks of age, WT and cKO mice were subjected to the destabilization of medial meniscus (DMM) model of post-traumatic OA. The cKO mice showed reduced cartilage degradation and collagenase activity and fewer hypertrophy-like features at 12 weeks after DMM. Interestingly, in spite of the protection from structural articular cartilage damage, the postnatal growth plates of IKKα cKO mice after DMM displayed abnormal architecture and composition associated with increased chondrocyte apoptosis, which were not as evident in the articular chondrocytes of the same animals. Together, our results provide evidence of a novel in vivo functional role for IKKα in cartilage degradation in post-traumatic OA, and also suggest intrinsic, cell-autonomous effects of IKKα in chondrocytes that control chondrocyte phenotype and impact on cell survival, matrix homeostasis, and remodeling.

Dihydroartemisinin derivative DC32 inhibits inflammatory response in osteoarthritic synovium through regulating Nrf2/NF-κB pathway

Synovitis is an aseptic inflammation that leads to joint effusion, pain and swelling. As one of the main drivers of pathogenesis in osteoarthritis (OA), the presence of synovitis contributes to pain, incidence and progression of OA. In our previous study, DC32 [(9α,12α-dihydroartemisinyl) bis(2'-chlorocinnmate)], a dihydroartemisinin derivative, was found to have an antirheumatic ability via immunosuppression, but the effect of DC32 on synovitis has not been fully illuminated. In this study, we chose to evaluate the effect and mechanism of DC32 on attenuating synovial inflammation. Fibroblast-like synoviocytes (FLSs) of papain-induced OA rats were isolated and cultured. And DC32 significantly inhibited the invasion and migration of cultured OA-FLSs, as well as the transcription of IL-6, IL-1β, CXCL12 and CX3CL1 in cultured OA-FLSs measured by qPCR. DC32 remarkably inhibited the activation of ERK and NF-κB pathway, increased the expression of Nrf2 and HO-1 in cultured OA-FLSs detected by western blot. DC32 inhibited the degradation and phosphorylation of IκBα which further prevented the phosphorylation of NF-κB p65 and the effect of DC32 could be relieved by siRNA for Nrf2. In papain-induced OA mice, DC32 significantly alleviated papain-induced mechanical allodynia, knee joint swelling and infiltration of inflammatory cell in synovium. DC32 upregulated the mRNA expression of Type II collagen and aggrecan, and downregulated the mRNA expression of MMP2, MMP3, MMP13 and ADAMTS-5 in the knee joints of papain-induced OA mice measured by qPCR. The level of TNF-α in the serum and secretion of TNF-α in the knee joints were also reduced by DC32 in papain-induced OA mice. In conclusion, DC32 inhibited the inflammatory response in osteoarthritic synovium through regulating Nrf2/NF-κB pathway and attenuated OA. In this way, DC32 may be a potential agent in the treatment of OA.

Liquiritigenin inhibits IL-1β-induced inflammation and cartilage matrix degradation in rat chondrocytes

Osteoarthritis (OA) is an age-related arthropathy which has been considered to be associated with inflammatory damage and cartilage degradation. Liquiritigenin (LG), the main bioactive component of the rhizomes of Glycyrrhiza uralensis, has exhibited promising anti-inflammatory and anti-oxidative potential in numerous inflammatory diseases. However, the effects of LG on OA remain unclear. In this study, the therapeutic effects as well as the underlying mechanisms of LG on interleukin-1β (IL-1β)-treated rat chondrocytes had been investigated. Our results showed that LG could inhibit the IL-1β-induced expression of nitic oxide (NO) and prostaglandin E₂ (PGE₂). In consist with these findings, the IL-1β-induced production of inducible nitic oxide synthase (iNOS) and cyclooxygenase-2 (COX2) could also be decreased by LG. Meanwhile, LG could suppress the IL-1β-induced upregulation of cartilage matrix catabolic enzymes including aggrecanase-2 (ADAMTS5) and matrix metalloproteinases (MMPs). Besides, the IL-1β-induced degradation of collagen II and aggrecan could be alleviated by LG. Moreover, LG prevented cartilage damage in IL-1β-treated rat cartilage explants. Mechanistically, LG functioned by inhibiting mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) pathways activation. In general, this study reveals the anti-inflammatory properties of LG on IL-1β-treated rat chondrocytes and the possible mechanisms behind it, which may provide new ideas for OA therapy.

Adipose-derived Stem Cells Attenuates Diabetic Osteoarthritis via Inhibition of Glycation-mediated Inflammatory Cascade

Diabetes mellitus (DM) is well-known to exert complications such as retinopathy, cardiomyopathy and neuropathy. However, in recent years, an elevated osteoarthritis (OA) complaints among diabetics have been observed, portending the risk of diabetic OA. Since formation of advanced glycation end products (AGE) is believed to be the etiology of various diseases under hyperglycemic conditions, we firstly established that streptozotocin-induced DM could potentiate the development of OA in C57BL/6J mouse model, and further explored the intra-articularly administered adipose-derived stem cell (ADSC) therapy focusing on underlying AGE-associated mechanism. Our results demonstrated that hyperglycemic mice exhibited OA-like structural impairments including a proteoglycan loss and articular cartilage fibrillations in knee joint. Highly expressed levels of carboxymethyl lysine (CML), an AGE and their receptors (RAGE), which are hallmarks of hyperglycemic microenvironment were manifested. The elevated oxidative stress in diabetic OA knee-joint was revealed through increased levels of malondialdehyde (MDA). Further, oxidative stress-activated nuclear factor kappa B (NF-κB), the marker of proinflammatory signalling pathway was also accrued; and levels of matrix metalloproteinase-1 and 13 were upregulated. However, ADSC treatment attenuated all OA-like changes by 4 weeks, and dampened levels of CML, RAGE, MDA, NF-κB, MMP-1 and 13. These results suggest that during repair and regeneration, ADSCs inhibited glycation-mediated inflammatory cascade and rejuvenated cartilaginous tissue, thereby promoting knee-joint integrity in diabetic milieu.

Nobiletin Inhibits IL-1β-Induced Inflammation in Chondrocytes via Suppression of NF-κB Signaling and Attenuates Osteoarthritis in Mice

Osteoarthritis (OA), a common degenerative joint disease, is principally characterized by inflammation and destruction of cartilage. Nobiletin, an extract of the peel of citrus fruits, is known to have anti-inflammatory properties. However, the mechanisms by which nobiletin plays a protective role in osteoarthritis (OA) are not completely understood. In the present study, we investigated the anti-inflammatory effects of nobiletin in the progression of OA in both in vitro and in vivo experiments. Mouse chondrocytes were pretreated with nobiletin (0, 10, 20, 40 μM) for 24 h and then incubated with IL-1β (10 ng/ml, 24 h) in vitro. The generation of PGE2 and NO was evaluated by the Griess reaction and ELISAs. The protein expression of inducible nitric oxide synthase, matrix metalloproteinase-3, matrix metalloproteinase-13, A disintegrin and metalloproteinase with thrombospondin motifs-5 (ADAMTS5), cyclooxygenase-2, collagen II, and aggrecan was analyzed by Western blotting. Immunofluorescence and Western blot analysis were used to detect nuclear factor-κB (NF-κB) signaling molecules. Induction of proinflammatory and catabolic mediators by IL-1β stimulation of mouse chondrocytes could be partially blocked by treatment with nobiletin or ammonium pyrrolidine dithiocarbamate (an NF-κB inhibitor). Furthermore, our results indicated that nobiletin exhibited a therapeutic effect through active inhibition of the NF-κB signaling pathway. In a mouse model of OA, injection of nobiletin (20 mg/kg) every 2 days for 8 weeks after surgery inhibited cartilage destruction and synovitis. Taken together, our findings suggest that nobiletin may be a potential therapeutic agent for the treatment of OA.

Evaluation of the effect of experimentally induced cartilage defect and intra-articular hyaluronan on synovial fluid biomarkers in intercarpal joints of horses

BACKGROUND

Inflammatory and degenerative activity inside the joint can be studied in vivo by analysis of synovial fluid biomarkers. In addition to pro-inflammatory mediators, several anabolic and anti-inflammatory substances are produced during the disease process. They counteract the catabolic effects of the pro-inflammatory cytokines and thus diminish the cartilage damage. The response of synovial fluid biomarkers after intra-articular hyaluronan injection, alone or in combination with other substances, has been examined only in a few equine studies. The effects of hyaluronan on some pro-inflammatory mediators, such as prostaglandin E2, have been documented but especially the effects on synovial fluid anti-inflammatory mediators are less studied. In animal models hyaluronan has been demonstrated to reduce pain via protecting nociceptive nerve endings and by blocking pain receptor channels. However, the results obtained for pain-relief of human osteoarthritis are contradictory. The aim of the study was to measure the synovial fluid IL-1ra, PDGF-BB, TGF-β1 and TNF-α concentrations before and after surgically induced cartilage defect, and following intra-articular hyaluronan injection in horses. Eight Standardbred horses underwent bilateral arthroscopic surgeries of their intercarpal joints under general anaesthesia, and cartilage defect was created on the dorsal edge of the third carpal bone of one randomly selected intercarpal joint of each horse. Five days post-surgery, one randomly selected intercarpal joint was injected intra-articular with 3 mL HA (20 mg/mL).

RESULTS

Operation type had no significant effect on the synovial fluid IL-1ra, PDGF-BB, TGF-β1 and TNF-α concentrations but compared with baseline, synovial fluid IL-1ra and TNF-α concentrations increased. Intra-articular hyaluronan had no significant effect on the biomarker concentrations but a trend of mild improvement in the clinical signs of intra-articular inflammation was seen.

CONCLUSIONS

Creation of the cartilage defect and sham-operation lead to an increase of synovial fluid IL-1ra and TNF-α concentrations but changes in concentrations of anabolic growth factors TGF-β1 and PDGF-BB could not be documented 5 days after the arthroscopy. Intra-articular hyaluronan was well tolerated. Further research is needed to document possible treatment effects of intra-articular hyaluronan on the synovial fluid biomarkers of inflammation and cartilage metabolism.

Chondroprotective Effects of Genistein against Osteoarthritis Induced Joint Inflammation

Genistein is an isoflavone extracted from soybean (Glycine max). This compound has anti-inflammatory, anti-oxidative, and anti-cancer effects; however, the mechanism underlying the effects of genistein on IL-1β-stimulated human osteoarthritis (OA) chondrocytes remains unknown. Our objectives in this study were to explore the anti-inflammatory effects of genistein on IL-1β-stimulated human OA chondrocytes and to investigate the potential mechanisms which underlie them. Our results from an in-vitro model of osteoarthritis indicate that genistein inhibits the IL-1β-induced expression of the catabolic factors nitric oxide synthase 2 (NOS2), cyclooxygenase 2 (COX-2), and matrix metalloproteinases (MMPs). Genistein was shown to stimulate Ho-1 expression, which has been associated with Nrf-2 pathway activation in human chondrocytes. In a rat model, genistein was also shown to attenuate the progression of traumatic osteoarthritis. Taken together, these results demonstrate the effectiveness of genistein in mediating the inflammation associated with joint disorders. Our results also indicate that genistein could potentially serve as an alternative therapeutic treatment for OA.

Trans-Cinnamaldehyde Inhibits IL-1β-Stimulated Inflammation in Chondrocytes by Suppressing NF-κB and p38-JNK Pathways and Exerts Chondrocyte Protective Effects in a Rat Model of Osteoarthritis

Objective

Trans-cinnamaldehyde (TCA), a compound from Cinnamomum cassia Presl, has been reported to have anti-inflammatory effect. However, its effect on cartilage degradation in osteoarthritis is unclear. This study is designed to examine the effects of TCA on cartilage in vitro and in vivo.

Material and Methods

SW1353 cells and human primary chondrocytes were treated with varying concentrations of TCA (2-20 μg/ml) for 2 h followed by IL-1β stimulation. Cell viability was examined by the MTT assay. Expression of MMP-1, MMP-3, MMP-13, ADAMTS-4, and ADAMTS-5 was examined by Western blot and RT-qPCR. Monosodium iodoacetate (MIA)-induced OA was established in rats to assess the chondrocyte protective effects of intraperitoneal injection of TCA (50 mg/kg).

Results

TCA at a concentration of 10 μg/ml had no significant effect on cell viability. MMP-1, MMP-3, MMP-13, ADAMTS-4, and ADAMTS-5 were decreased by TCA 2-10 μg/ml in a dose-dependent manner (all P<0.05). Pretreatment with TCA decreased the degradation of IκBα and increased the expression of p-IκBα, indicating that NF-κB inactivation was induced by TCA in IL-1β-stimulated SW1353 cells. Pretreatment with TCA decreased the levels of p-p38 and p-JNK, while the levels of p-ERK were not significantly affected. TCA 10 μg/ml significantly decreased expression levels of MMP-1, MMP-3, MMP-13, ADAMTS-4, and ADAMTS-5. In vivo results showed that TCA alleviated cartilage destruction and the OARSI scores.

Conclusion

TCA possesses anti-inflammatory effect in vitro and exerts chondrocyte protective effects in vivo, in which NF-κB and p38-JNK were involved.

Continuous low-intensity ultrasound attenuates IL-6 and TNFα-induced catabolic effects and repairs chondral fissures in bovine osteochondral explants

BACKGROUND

Cartilage repair outcomes are compromised in a pro-inflammatory environment; therefore, the mitigation of pro-inflammatory responses is beneficial. Treatment with continuous low-intensity ultrasound (cLIUS) at the resonant frequency of 5 MHz is proposed for the repair of chondral fissures under pro-inflammatory conditions.

METHODS

Bovine osteochondral explants, concentrically incised to create chondral fissures, were maintained under cLIUS (14 kPa (5 MHz, 2.5 Vpp), 20 min, 4 times/day) for a period of 28 days in the presence or absence of cytokines, interleukin-6 (IL-6) or tumor necrosis factor (TNF)α. Outcome assessments included histological and immunohistochemical staining of the explants; and the expression of catabolic and anabolic genes by qRT-PCR in bovine chondrocytes. Cell migration was assessed by scratch assays, and by visualizing migrating cells into the hydrogel core of cartilage-hydrogel constructs.

RESULTS

Both in the presence and absence of cytokines, higher percent apposition along with closure of fissures were noted in cLIUS-stimulated explants as compared to non-cLIUS-stimulated explants on day 14. On day 28, the percent apposition was not significantly different between unstimulated and cLIUS-stimulated explants exposed to cytokines. As compared to non-cLIUS-stimulated controls, on day 28, cLIUS preserved the distribution of proteoglycans and collagen II in explants despite exposure to cytokines. cLIUS enhanced the cell migration irrespective of cytokine treatment. IL-6 or TNFα-induced increases in MMP13 and ADAMTS4 gene expression was rescued by cLIUS stimulation in chondrocytes. Under cLIUS, TNFα-induced increase in NF-κB expression was suppressed, and the expression of collagen II and TIMP1 genes were upregulated.

CONCLUSION

cLIUS repaired chondral fissures, and elicited pro-anabolic and anti-catabolic effects, thus demonstrating the potential of cLIUS in improving cartilage repair outcomes.

Endothelial PPARγ Is Crucial for Averting Age-Related Vascular Dysfunction by Stalling Oxidative Stress and ROCK

Aging plays a significant role in the progression of vascular diseases and vascular dysfunction. Activation of the ADP-ribosylation factor 6 and small GTPases by inflammatory signals may cause vascular permeability and endothelial leakage. Pro-inflammatory molecules have a significant effect on smooth muscle cells (SMC). The migration and proliferation of SMC can be promoted by tumor necrosis factor alpha (TNF-α). TNF-α can also increase oxidative stress in SMCs, which has been identified to persuade DNA damage resulting in apoptosis and cellular senescence. Peroxisome proliferator-activated receptor (PPAR) acts as a ligand-dependent transcription factor and a member of the nuclear receptor superfamily. They play key roles in a wide range of biological processes, including cell differentiation and proliferation, bone formation, cell metabolism, tissue remodeling, insulin sensitivity, and eicosanoid signaling. The PPARγ activation regulates inflammatory responses, which can exert protective effects in the vasculature. In addition, loss of function of PPARγ enhances cardiovascular events and atherosclerosis in the vascular endothelium. This appraisal, therefore, discusses the critical linkage of PPARγ in the inflammatory process and highlights a crucial defensive role for endothelial PPARγ in vascular dysfunction and disease, as well as therapy for vascular aging.

N-Acylethanolamine acid amidase (NAAA) inhibitor F215 as a novel therapeutic agent for osteoarthritis

Osteoarthritis (OA), characterized by cartilage damage, synovitis inflammation and chronic pain, is a common degenerative joint disease that may lead to physical disability. In the present study, we first explored the association between N-Acylethanolamine acid amidase (NAAA) and OA progression, and then examined the capability of the NAAA inhibitor F215 to attenuate osteoarthritis. Increased NAAA expressions and decreased PEA levels in synovial membrane and lumbar spinal cord were observed in MIA induced osteoarthritic rats. F215 (i.a., and i.p.) significantly protected against cartilage damage and synovial inflammation by directly increasing PEA levels in joints, or normalization of PEA levels and resolution of inflammation in spinal cord. Moreover, F215 also markedly alleviated osteoarthritic pain in rats, and the therapeutic effects of F215 were blocked by the PPAR-α antagonist MK886. The results revealed that NAAA may has been implicated in OA progression, and treatment with NAAA inhibitor F215 alleviated OA development by preventing cartilage damage, reducing inflammation, and alleviating pain. Our study suggested that NAAA inhibitor might be a novel therapeutic agent for OA treatment.

Long noncoding RNA CHRF exacerbates IL-6-induced inflammatory damages by downregulating microRNA-146a in ATDC5 cells

Osteoarthritis (OA) is a frequent chronic musculoskeletal disorder which lacks applicably effective therapeutic strategy. In this study, we attempted to investigate whether long noncoding RNA (lncRNA) cardiac hypertrophy-related factor (CHRF) participated in mediating interleukin-6 (IL-6)-induced in vitro inflammatory damages as well as the regulatory mechanisms. ATDC5 cells were stimulated with IL-6, and then cellular damages were evaluated on the basis of cell viability by CCK-8, apoptotic cells by observation with flow cytometry, apoptosis-associated proteins by western blot analysis, and accumulation of inflammatory factors by quantitative reverse transcription polymerase chain reaction (RT-qPCR), enzyme-linked immunosorbent assay (ELISA), and western blot analysis. Then, effects of lncRNA CHRF on IL-6-treated cells were evaluated. We further explored the downstream factor of lncRNA CHRF and demonstrated whether lncRNA CHRF functioned through the downstream factor. Afterwards, crucial signaling cascades were anatomized. We found that IL-6 reduced cell viability, elevated apoptosis, induced upregulation of inflammatory factors, as well as upregulated lncRNA CHRF and down-regulated miR-146a expression. Then, we found lncRNA CHRF overexpression aggravated IL-6-induced alterations, and lncRNA CHRF knockdown showed the opposite effects. Furthermore, miR-146a was identified to be negatively regulated by lncRNA CHRF, and its overexpression abrogated the roles of lncRNA CHRF in IL-6-treated cells. IL-6-induced the accumulation of IκBα, p65, JAK1, and STAT3 at phosphorylated level was further facilitated by lncRNA CHRF whereas repressed by miR-146a. In conclusion, lncRNA CHRF aggravated the IL-6-induced inflammatory damages in ATDC5 cells. We further outlined a possible mechanism that through downregulating miR-146a, lncRNA CHRF evoked the activation of NF-κB and JAK1/STAT3 signaling cascades.

The protective effects of exenatide against AGEs-induced articular matrix degradation in human primary chondrocytes

Osteoarthritis (OA) presents a major global health burden and is projected to become even more prevalent in coming decades. Therefore, it is of utmost importance to uncover novel therapies for the treatment and prevention of this disease. In the present study, we investigated the effects of exenatide, a specific glucagon-like peptide (GLP) agonist, on degradation of type II collagen and aggrecan, the two main components of the articular extracellular matrix, in human primary chondrocytes. Our results reveal that exenatide could ameliorate degradation of type II collagen and aggrecan by inhibiting expression of metalloproteinases (MMPs) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) induced by advanced glycation end-products. We also found that exenatide reduces oxidative stress and inhibits activation of nuclear factor-κB through the p38 cellular signaling pathway. Taken together, the findings of this study indicate that exenatide may have potential as a novel treatment for osteoarthritis.

Excessive mechanical loading promotes osteoarthritis through the gremlin-1-NF-κB pathway

Exposure of articular cartilage to excessive mechanical loading is deeply involved in the pathogenesis of osteoarthritis. Here, we identify gremlin-1 as a mechanical loading-inducible factor in chondrocytes, detected at high levels in middle and deep layers of cartilage after cyclic strain or hydrostatic pressure loading. Gremlin-1 activates nuclear factor-κB signalling, leading to subsequent induction of catabolic enzymes. In mice intra-articular administration of gremlin-1 antibody or chondrocyte-specific deletion of Gremlin-1 decelerates osteoarthritis development, while intra-articular administration of recombinant gremlin-1 exacerbates this process. Furthermore, ras-related C3 botulinum toxin substrate 1 activation induced by mechanical loading enhances reactive oxygen species (ROS) production. Amongst ROS-activating transcription factors, RelA/p65 induces Gremlin-1 transcription, which antagonizes induction of anabolic genes such as Sox9, Col2a1, and Acan by bone morphogenetic proteins. Thus, gremlin-1 plays essential roles in cartilage degeneration by excessive mechanical loading.

Excessive mechanical stress promotes the development of osteoarthritis. Here Chang et al. identify gremlin-1 as a factor expressed in chondrocytes in response to mechanical stress, and contributing to osteoarthritis via activation of the NF-κB pathway.

Lipopolysaccharide-induced expression of astrocyte elevated gene-1 promotes degeneration and inflammation of chondrocytes via activation of nuclear factor-κB signaling

Osteoarthritis is an inflammatory disease characterized by joint degeneration and inflammation. Astrocyte elevated gene-1 (AEG-1) has been suggested as a novel inflammation-related factor in the pathological processes of various inflammatory diseases. To date, little is known about the role of AEG-1 in osteoarthritis. The aim of the present study was to explore the potential role of AEG-1 in the regulation of lipopolysaccharide-induced apoptosis and inflammation of chondrocytes. The results showed that AEG-1 expression was significantly upregulated in chondrocytes following exposure to lipopolysaccharide. Knockdown of AEG-1 increased the survival and decreased the expression of matrix metalloproteinases in chondrocytes treated with lipopolysaccharide. Moreover, silencing of AEG-1 restricted the lipopolysaccharide-induced production of proinflammatory cytokines. In contrast, AEG-1 overexpression caused opposite effects. Notably, we found that AEG-1 inhibition blocked the lipopolysaccharide-induced activation of nuclear factor-κB signaling through impeding the nuclear translocation of nuclear factor-κB p65 subunit. Additionally, inhibition of nuclear factor-κB partially reversed the AEG-1-mediated promotion of lipopolysaccharide-induced inflammatory injury in chondrocytes. In conclusion, our results demonstrate that inhibition of AEG-1 expression attenuates lipopolysaccharide-induced degeneration and inflammation of chondrocytes through suppressing the activation of nuclear factor-κB signaling. This work therefore highlights a potential role of AEG-1 in the pathogenesis of osteoarthritis, and indicates its potential as a therapeutic target.

NLRX1 alleviates lipopolysaccharide-induced apoptosis and inflammation in chondrocytes by suppressing the activation of NF-κB signaling

Osteoarthritis (OA) is a chronic debilitating disease characterized by joint degeneration. Excessive chondrocyte apoptosis and inflammation contributes to articular cartilage destruction in OA pathology. Nucleotide-binding oligomerization domain (NOD)-like receptor X1 (NLRX1) has emerged as a critical regulator of inflammation that participates in the pathology of diverse diseases. To date, little is known about the role of NLRX1 in OA. In the present study, we aimed to explore the function of NLRX1 in lipopolysaccharide (LPS)-induced injury in chondrocytes, an in vitro model of OA. NLRX1 mRNA was detected by quantitative polymerase chain reaction (qPCR) analysis. Protein expression of NLRX1, phosphorylated IκB kinase β (IKKβ), and phosphorylated nuclear factor-κB (NF-κB) p65 were examined by western blot. Cell viability was assessed by the MTT assay. Cell apoptosis was evaluated by measuring caspase-3 activity. Cytokine release was assessed by enzyme-linked immunosorbent assay (ELISA). NF-κB signaling activation was analyzed with a luciferase reporter assay. Herein, our results revealed that NLRX1 expression was markedly decreased in LPS-treated chondrocytes. Functional experiments demonstrated that NLRX1 overexpression significantly improved cell viability and attenuated LPS-treated chondrocyte apoptosis and inflammation, while NLRX1 silencing caused the opposite effects. Moreover, our results showed that NLRX1 regulated LPS-induced NF-κB signaling activation. Notably, NF-κB signaling inhibition significantly reversed the NLRX1-knockdown-mediated enhanced effects on LPS-induced apoptosis and inflammation. Overall, these results demonstrate that NLRX1 alleviates LPS-induced apoptosis and inflammation in chondrocytes by negatively regulating NF-κB signaling, results that indicate an anti-inflammatory role for NLRX1 in OA. Our findings suggest that NLRX1 may serve as a potential therapeutic target for OA.

The protective effect of sinapic acid in osteoarthritis: In vitro and in vivo studies

The anti-inflammatory effect of sinapic acid (SA) has been reported in several studies. However, whether SA has the same effect on osteoarthritis (OA) has yet to be clearly elucidated. We designed a series of in vitro and in vivo procedures to verify the above conjecture. Compared with controls, SA-pretreated human chondrocytes showed lower levels of interleukin (IL)-1β-induced IL-6, prostaglandin E2 (PGE2), nitric oxide (NO) and tumour necrosis factor-α (TNF-α) in vitro. Meanwhile, SA could also reverse the degradation of type II collage and aggrecan, as well as the overproduction of matrix metalloproteinase-9 (MMP-9) and matrix metalloproteinase-13 (MMP-13), inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2 and a disintegrin and metalloproteinase thrombospondin motifs (ADAMTS)-5. Furthermore, activation of nuclear factor κB (NF-κB), which was induced by IL-1β, was also inhibited by SA through the pathway of nuclear factor-erythroid 2-related factor-2 (Nrf2)/heme oxygenase 1. In vivo, SA could delay the progress of mice OA models. We propose that SA may be applied as a potential therapeutic drug in OA treatment.

Conditioned media from human osteoarthritic synovium induces inflammation in a synoviocyte cell line

AIM

Osteoarthritis (OA) is a whole joint pathology involving cartilage, synovial membrane, meniscus, subchondral bone, and infrapatellar fat pad (IFP). Synovitis has been widely documented in OA suggesting its important role in pathogenesis. The aim of this study was to investigate the role of different joint tissues in promoting synovitis.

MATERIALS AND METHODS

Conditioned media (CM) from cartilage, synovial membrane, meniscus, and IFP were generated from tissues of five patients undergoing total knee replacement and used to stimulate a human fibroblast-like synoviocytes cell line (K4IM). Cytokines, chemokines, and metalloproteases release was analyzed in all CM by Bio-Plex Assay and sulfated glycosaminoglycan (GAG) content by dimethylmethylene blue assay. Gene expression of several markers was evaluated by real-time PCR in K4IM cells stimulated with the CM obtained from joint tissues.

RESULTS

CM from all tissues produced high levels of IL-6, IL-8, and CCL2. CCL21, MMP-3, and -13 levels were detected in all CM except IFP. MMP-10 was present only in CM of cartilage and synovial tissues. IL-1β, IL-15, TNF-α, CCL5, and CCL19 were undetectable. However, only K4IM cells stimulated by the CM from OA synovium showed an increase of IL-6, CXCL-8, CCL21, MMP10, and IL-1β expression.

CONCLUSION

Our study showed that K4IM might be a suitable in vitro model for evaluating different cellular pathways in OA studies. Importantly, we demonstrated that in OA, all joint tissues might be involved in the progression of synovitis with a predominant role of synovial membrane itself compared to the other joint tissues.

Redox and NF-κB signaling in osteoarthritis

Human cells have to deal with the constant production of reactive oxygen species (ROS). Although ROS overproduction might be harmful to cell biology, there are plenty of data showing that moderate levels of ROS control gene expression by maintaining redox signaling. Osteoarthritis (OA) is the most common joint disorder with a multi-factorial etiology including overproduction of ROS. ROS overproduction in OA modifies intracellular signaling, chondrocyte life cycle, metabolism of cartilage matrix and contributes to synovial inflammation and dysfunction of the subchondral bone. In arthritic tissues, the NF-κB signaling pathway can be activated by pro-inflammatory cytokines, mechanical stress, and extracellular matrix degradation products. This activation results in regulation of expression of many cytokines, inflammatory mediators, transcription factors, and several matrix-degrading enzymes. Overall, NF-κB signaling affects cartilage matrix remodeling, chondrocyte apoptosis, synovial inflammation, and has indirect stimulatory effects on downstream regulators of terminal chondrocyte differentiation. Interaction between redox signaling and NF-κB transcription factors seems to play a distinctive role in OA pathogenesis.

Regional gene expression analysis of multiple tissues in an experimental animal model of post-traumatic osteoarthritis

OBJECTIVE

To characterize local disease progression of the medial meniscus transection (MMT) model of post-traumatic osteoarthritis (OA) at the molecular level, in order to establish a baseline for therapeutic testing at the preclinical stage.

DESIGN

Weight-matched male Lewis rats underwent MMT or sham surgery on the left limb with the right leg as contralateral control. At 1 and 3 weeks post-surgery, tissues were harvested from different areas of the articular cartilage (medial and lateral tibial plateaus, and medial osteophyte region) and synovium (medial and lateral), and analyzed separately. RNA was extracted and used for microarray (RT-PCR) analysis.

RESULTS

Gene expression changes due to surgery were isolated to the medial side of the joint. Gene changes in chondrocyte phenotype of the medial tibial plateau cartilage preceded changes in tissue composition genes. Differences in inflammatory markers were only observed at the osteophyte region at 3 weeks post-surgery. There was surgical noise in the synovium at week 1, which dissipated at week 3. At this later timepoint, meniscal instability resulted in elevated expression of matrix degradation proteins and osteogenic markers in the synovium and cartilage.

CONCLUSION

These results suggest feedback interactions between joint tissues during disease progression. Regional tissue expression differences found in MMT joints indicated similar pathophysiology to human OA, and provided novel insights about this degeneration model. The examination of gene expression at a localized level in multiple tissues provides a well-characterized baseline to evaluate mechanistic effects of potential therapeutic agents on OA disease progression in the MMT model.

Development of a peptide-siRNA nanocomplex targeting NF- κB for efficient cartilage delivery

Delivery of therapeutic small interfering RNAs (siRNAs) in an effective dose to articular cartilage is very challenging as the cartilage dense extracellular matrix renders the chondrocytes inaccessible, even to intra-articular injections. Herein, we used a self-assembling peptidic nanoparticle (NP) platform featuring a cell penetrating peptide complexed to NF-κB p65 siRNA. We show that it efficiently and deeply penetrated human cartilage to deliver its siRNA cargo up to a depth of at least 700 μm. To simulate osteoarthritis in vitro, human articular cartilage explants were placed in culture and treated with IL-1β, a cytokine with known cartilage catabolic and pro-inflammatory effects. Exposure of peptide-siRNA NP to cartilage explants markedly suppressed p65 activation, an effect that persisted up to 3 weeks after an initial 48 h exposure to NP and in the presence of continuous IL-1β stimulation. Suppression of IL-1β-induced p65 activity attenuated chondrocyte apoptosis and maintained cartilage homeostasis. These findings confirm our previous in vivo studies in a murine model of post-traumatic osteoarthritis and suggest that the ability of peptide-siRNA NP to specifically modulate NF-κB pathway, a central regulator of the inflammatory responses in chondrocytes, may potentially mitigate the progression of cartilage degeneration.

Electroacupuncture Delays Cartilage Degeneration by Modulating Nuclear Factor-κB Signaling Pathway

OBJECTIVE

To illustrate the molecular mechanisms underlying the therapeutic effects of electroacupuncture (EA) on knee osteoarthritis (OA).

METHODS

Twenty-seven six-month-old New Zealand white rabbits were allocated into three groups in accordance with a random number table: normal group (no surgery-induced OA; without treatment), model group (surgery-induced OA; without treatment) and EA group [surgery-induced OA; received treatment with EA at acupoints Dubi (ST 35) and Neixiyan (EX-LE 5), 30 min twice a day]. After eight consecutive weeks of treatment, the histopathological alterations in cartilage were observed using optical microscopy and transmission electron microscopy, cartilage degeneration was evaluated by modified Mankin's score principles, the synovial fluid concentration of interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and matrix metalloproteinase-3 (MMP-3) were evaluated by enzyme-linked immunosorbent assay, and the protein expression levels of IL-1β, IL-6, TNF-α, MMP-3, IκB kinase-β (IKK-β), nuclear factor of α light polypeptide gene enhancer in B-cells inhibitor α (IκB-α) and nuclear factor-κB (NF-κB) p65 were quantified by Western blot analysis.

RESULTS

EA treatment significantly improved cartilage structure arrangement and reduced cellular degeneration. The IL-1β, IL-6, TNF-α and MMP-3 of synovial fluid in the EA-treated group were significantly decreased compared with the model group (all P<0.01). Compared with the model group, the IL-1β, IL-6, TNF-α, MMP-3, IKK-β and NF-κB p65 protein expressions in cartilage of EA-treated group were significantly decreased (all P<0.01), whereas IκB-α expression was significantly up-regulated (P<0.01).

CONCLUSION

EA treatment may delay cartilage degeneration by down-regulating inflammatory factors through NF-κB signaling pathway, which may, in part, explain its clinical efficacy in the treatment of knee OA.

Effect of inositol -stabilized arginine silicate on arthritis in a rat model

The purpose of this study was to test the effects of arginine-silicate-inositol complex (ASI), compared to a combination of the individual ingredients (A+S+I) of the ASI, on inflammatory markers and joint health in a collagen-induced arthritis (CIA) rat model. A total of 28 Wistar rats were divided into four groups: (i) Control; (ii) Arthritic group, rats subjected to CIA induction by injection of bovine collagen type II (A); (iii) Arthritic group treated with equivalent doses of the separate components of the ASI complex (arginine hydrochloride, silicon, and inositol) (A+S+I); (iv) Arthritic group treated with the ASI complex. The ASI complex treatment showed improved inflammation scores and markers over the arthritic control and the A+S+I group. ASI group had also greater levels of serum and joint-tissue arginine and silicon than the A+S+I group. Joint tissue IL-6, NF-κB, COX-2, TNF-α, p38 MAPK, WISP-1, and β-Catenin levels were lower in the ASI group compared to the other groups (P < 0.05 for all). In conclusion, these results demonstrate that the ASI complex may be effective in reducing markers of inflammation associated with joint health and that the ASI complex is more effective than a combination of the individual ingredients.

Current concepts in intraosseous Platelet-Rich Plasma injections for knee osteoarthritis

Knee osteoarthritis (OA) is a degenerative process that slowly destroys the joints producing pain and loss of function, and diminishes the quality of life. Current treatments alleviate this symptomatology but do not stop the disease, being total knee arthroplasty the only definitive solution. Among the emerging treatments, Platelet-Rich Plasma (PRP) has shown promising results in the treatment of OA. However, to improve its effectiveness, it is necessary to approach this pathology targeting the whole joint, not only the cartilage, but including other tissues such as subchondral bone. The pathological processes that occur in the subchondral bone have influence of the cartilage loss, aggravating the disease. The combination of intraarticular infiltrations with intraosseous infiltrations regulates the biological processes of the tissues, reducing the inflammatory environment and modulating the overexpression of biomolecules that generate an aberrant cellular behavior. Although the first clinical results using this technique are promising, further research and developing adequate protocols are necessary to achieve good clinical results.

Targeting anti-chondrogenic factors for the stimulation of chondrogenesis: A new paradigm in cartilage repair

Trauma and age-related cartilage disorders represent a major global cause of morbidity, resulting in chronic pain and disability in patients. A lack of effective therapies, together with a rapidly aging population, creates an impressive clinical and economic burden on healthcare systems. In this scenario, experimental therapies based on transplantation or in situ stimulation of skeletal Mesenchymal Stem/progenitor Cells (MSCs) have raised great interest for cartilage repair. Nevertheless, the challenge of guiding MSC differentiation and preventing cartilage hypertrophy and calcification still needs to be overcome. While research has mostly focused on the stimulation of cartilage anabolism using growth factors, several issues remain unresolved prompting the field to search for novel solutions. Recently, inhibition of anti-chondrogenic regulators has emerged as an intriguing opportunity. Anti-chondrogenic regulators include extracellular proteins as well as intracellular transcription factors and microRNAs that act as potent inhibitors of pro-chondrogenic signals. Suppression of these inhibitors can enhance MSC chondrogenesis and production of cartilage matrix. We here review the current knowledge concerning different types of anti-chondrogenic regulators. We aim to highlight novel therapeutic targets for cartilage repair and discuss suitable tools for suppressing their anti-chondrogenic functions. Further effort is needed to unveil the therapeutic perspectives of this approach and pave the way for effective treatment of cartilage injuries in patients. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Urolithin A targets the PI3K/Akt/NF-κB pathways and prevents IL-1β-induced inflammatory response in human osteoarthritis: in vitro and in vivo studies

Osteoarthritis (OA) is a degenerative joint disease, whose progression is closely related to the inflammatory environment.

Methamphetamine and its immune-modulating effects

The recreational use of methamphetamine (METH, or ice) is a global burden. It pervades and plagues contemporary society; it has been estimated that there are up to 35 million users worldwide. METH is a highly addictive psychotropic compound which acts on the central nervous system, and chronic use can induce psychotic behavior. METH has the capacity to modulate immune cells, giving the drug long-term effects which may manifest as neuropsychiatric disorders, and that increase susceptibility to communicable diseases, such as HIV. In addition, changes to the cytokine balance have been associated with compromise of the blood-brain barrier, resulting to alterations to brain plasticity, creating lasting neurotoxicity. Immune-related signaling pathways are key to further evaluating how METH impacts host immunity through these neurological and peripheral modifications. Combining this knowledge with current data on inflammatory responses will improve understanding of how the adaptive and innate immunity responds to METH, how this can activate premature-ageing processes and how METH exacerbates disturbances that lead to non-communicable age-related diseases, including cardiovascular disease, stroke, depression and dementia.

ACY-1215 exhibits anti-inflammatory and chondroprotective effects in human osteoarthritis chondrocytes via inhibition of STAT3 and NF-κB signaling pathways

Cartilage degeneration is a basic pathological feature of osteoarthritis (OA), and there is growing evidence that it is associated with inflammation. ACY-1215, a selective HDAC6 inhibitor, has been reported to have anti-inflammatory effects. Here, we investigated the anti-inflammatory and chondroprotective effects of ACY-1215 in IL-1β-stimulated human primary chondrocytes and C28/I2 cells. The results suggested that ACY-1215 can markedly suppress the expression of inflammatory factors, including IL-1β and IL-6 in human primary chondrocytes and C28/I2 cells. Furthermore, ACY-1215 exerts potent chondroprotection through the amelioration of cartilage degradation by inhibiting the expression of matrix-degrading proteases, including MMP-1 and MMP-13 in chondrocytes. These effects may be related to ACY-1215 induced down-regulation of NF-κB and STAT3 pathways in OA chondrocytes. Taken together, our results show that ACY-1215 may be a potential and promising therapeutic drug for the management of OA.

Reciprocal inhibition of YAP/TAZ and NF-κB regulates osteoarthritic cartilage degradation

Osteoarthritis is one of the leading causes of pain and disability in the aged population due to articular cartilage damage. This warrants investigation of signaling mechanisms that could protect cartilage from degeneration and degradation. Here we show in a murine model of experimental osteoarthritis that YAP activation by transgenic overexpression or by deletion of its upstream inhibitory kinases Mst1/2 preserves articular cartilage integrity, whereas deletion of YAP in chondrocytes promotes cartilage disruption. Our work shows that YAP is both necessary and sufficient for the maintenance of cartilage homeostasis in osteoarthritis. Mechanistically, inflammatory cytokines, such as TNFα or IL-1β, trigger YAP/TAZ degradation through TAK1-mediated phosphorylation. Furthermore, YAP directly interacts with TAK1 and attenuates NF-κB signaling by inhibiting substrate accessibility of TAK1. Our study establishes a reciprocal antagonism between Hippo-YAP/TAZ and NF-κB signaling in regulating the induction of matrix-degrading enzyme expression and cartilage degradation during osteoarthritis pathogenesis.

Platelet-Rich Plasma and Cartilage Repair

PURPOSE OF REVIEW

To assess the utilization and efficacy of platelet-rich plasma (PRP), for the treatment of articular cartilage injury, most commonly characterized by progressive pain and loss of joint function in the setting of osteoarthritis (OA).

RECENT FINDINGS

PRP modulates the inflammatory and catabolic environment through a locally applied concentrate of platelets, leukocytes, and growth factors. Clinically, PRP has been shown to be possibly a viable treatment adjuvant for a variety of inflammatory and degenerative conditions. Recent efforts have focused on optimizing delivery methods that enable platelets to slowly degranulate their biological constituents, which may promote healing and improve OA symptoms for a longer duration. There are various factors that affect the progression of OA within joints, including inhibition of inflammatory cytokines and altering the level of enzymatic expression. PRP therapy aims to mediate inflammatory and catabolic factors in a degenerative environment through the secretion of anti-inflammatory factors and chemotaxic effects. There are a growing number of studies that have demonstrated the clinical benefit of PRP for non-operative management of OA. Additional randomized controlled trials with long-term follow-up are needed in order to validate PRP's therapeutic efficacy in this setting. Additionally, continued basic research along with well-designed pre-clinical studies and reporting standards are necessary in order to clarify the effectiveness of PRP for cartilage repair and regeneration for future clinical applications.

Brazilin blocks catabolic processes in human osteoarthritic chondrocytes via inhibition of NFKB1/p50

This study aimed to evaluate the chondroprotective and anti-inflammatory activity of brazilin in human osteoarthritic (OA) cartilage and chondrocytes with particular focus on the nuclear factor-kappa B (NF-κB) pathway. Therefore, brazilin was isolated from Caesalpinia sappan and identified using high performance liquid chromatography (HPLC). The effect of brazilin was assessed in cartilage explants treated with 10 ng/ml interleukin (IL)-1β and 10 ng/ml tumor necrosis factor (TNF)-α using histological and biochemical glycosaminoglycan (GAG) analyses and in primary chondrocytes treated with 10 ng/ml IL-1β using RT-qPCR, ELISA, and Western blot. The involvement of NF-κB signaling was examined using a human NF-κB signaling array and in silico pathway analysis. Brazilin was found to reduce the GAG loss from cartilage explants stimulated with IL-1β and TNF-α. NF-κB pathway analysis in chondrocytes revealed NFKB1/p50 as a central player regulating the anti-inflammatory activities of brazilin. Brazilin suppressed the IL-1β-mediated up-regulation of OA markers and the induction of NFKB1/p50 in chondrocytes. In conclusion, brazilin effectively attenuates catabolic processes in human OA cartilage and chondrocytes-at least in part due to the inhibition of NFKB1/p50-which indicates a chondroprotective potential of brazilin in OA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2431-2438, 2018.

Alleviation of Murine Osteoarthritis by Cartilage-Specific Deletion of IκBζ

OBJECTIVE

IκBζ, an atypical IκB family member, regulates gene expression in the nucleus as a transcriptional cofactor. Although IκBζ has been extensively studied in the immune system, its specific roles in osteoarthritis (OA) are currently unknown. The objective of this study was to investigate the potential role of IκBζ in chondrocyte catabolism and OA pathogenesis. We also determined the molecular mechanism underlying its relationship to the transcription factor NF-κB.

METHODS

We determined expression levels of IκBζ in mouse chondrocytes treated with interleukin-1β (IL-1β), in human OA cartilage, and in mouse experimental OA cartilage. Adenovirus-mediated overexpression and small interfering RNA knockdown of IκBζ were performed to determine the impact of IκBζ on catabolic gene expression in vitro. Cartilage-specific IκBζ-transgenic and -knockout mice were generated and used for in vivo studies. Experimental and spontaneous OA were induced by surgical destabilization of the medial meniscus and by aging, respectively. Coimmunoprecipitation assay was used to examine the association between IκBζ and NF-κB subunits.

RESULTS

IκBζ was highly up-regulated in chondrocytes in response to IL-1β and in OA cartilage of human and mouse knee joints. Overexpression of IκBζ in chondrocytes promoted spontaneous OA development by activating chondrocyte catabolism. Genetic ablation of IκBζ in chondrocytes abolished catabolic gene induction by IL-1β and protected against the development of experimental OA. IκBζ formed complexes with NF-κB members to regulate catabolic factor expression.

CONCLUSION

These findings demonstrate a critical role for IκBζ in OA pathogenesis. Inhibition of IκBζ function might be an effective therapeutic approach for OA treatment.

Phenotypic instability of chondrocytes in osteoarthritis: on a path to hypertrophy

Articular chondrocytes are quiescent, fully differentiated cells responsible for the homeostasis of adult articular cartilage by maintaining cellular survival functions and the fine-tuned balance between anabolic and catabolic functions. This balance requires phenotypic stability that is lost in osteoarthritis (OA), a disease that affects and involves all joint tissues and especially impacts articular cartilage structural integrity. In OA, articular chondrocytes respond to the accumulation of injurious biochemical and biomechanical insults by shifting toward a degradative and hypertrophy-like state, involving abnormal matrix production and increased aggrecanase and collagenase activities. Hypertrophy is a necessary, transient developmental stage in growth plate chondrocytes that culminates in bone formation; in OA, however, chondrocyte hypertrophy is catastrophic and it is believed to initiate and perpetuate a cascade of events that ultimately result in permanent cartilage damage. Emphasizing changes in DNA methylation status and alterations in NF-κB signaling in OA, this review summarizes the data from the literature highlighting the loss of phenotypic stability and the hypertrophic differentiation of OA chondrocytes as central contributing factors to OA pathogenesis.

Cartilage repair in degenerative osteoarthritis mediated by squid type II collagen via immunomodulating activation of M2 macrophages, inhibiting apoptosis and hypertrophy of chondrocytes

Cartilage lesions in degenerative osteoarthritis (OA) are involved with pathological microenvironmental alterations induced by inflammatory macrophages, and apoptotic and/or hypertrophic chondrocytes. However, current non-operative therapies for cartilage repair in OA can rarely achieve long-term and satisfactory outcomes. This study aims to evaluate a newly developed squid type II collagen (SCII) for repairing OA-induced cartilage lesions. Our in vitro data show that SCII induces M2 polarization of macrophages, and activates macrophages to express pro-chondrogenic genes (TGF-β and IGF), which greatly improves the microenvironment around chondrocytes to produce type II collagen and glycosaminoglycan. In addition, glycine in SCII activates glycine receptors on inflammatory chondrocytes to decrease intracellular calcium concentration, leading to effective inhibition of chondrocyte apoptosis and hypertrophy. The in vitro effects of SCII are further confirmed in vivo. In a rat model of OA, SCII increases the ratio of M2 macrophages, elevates the levels of pro-chondrogenic cytokines (TGF-β1 and TGF-β3) in synovial fluid, and inhibits chondrocyte apoptosis and MMP13 production. Our findings show that SCII immunomodulates M2 activation of macrophages to skew the local OA microenvironment towards a pro-chondrogenic atmosphere, and promotes cartilage repair under inflammatory condition. It shows great potential for SCII to be a novel biomaterial for cartilage repair in OA.

The protective effect of phloretin in osteoarthritis: an in vitro and in vivo study

Osteoarthritis (OA) is a degenerative joint disease characterized by the degradation and inflammation of cartilage. Phloretin, a type of dihydrochalcone mainly found in apples and apple-derived products, has been reported to possess various potent biological effects such as antioxidant, anticancer, anti-inflammatory, and immunomodulatory. However, the anti-inflammatory effects of phloretin on OA have not been reported. This study was aimed at assessing the effects of phloretin on human OA chondrocytes. Human OA chondrocytes were pretreated with phloretin (10, 30, and 100 μM) for 2 h and subsequently stimulated with IL-1β for 24 h. The production of NO, PGE2, TNF-α, and IL-6 was determined using the Griess reagent and ELISAs. The mRNA expression of COX-2, iNOS, MMP-3, MMP-13, and ADAMTS-5 was measured by real-time PCR. Changes in the protein expression of COX-2, iNOS, MMPs, ADAMTS, aggrecan, collagen-II, NF-κB, and the PI3K/Akt signaling pathway were detected by western blotting. In this study, we found that phloretin significantly inhibited the IL-1β-induced production of NO, PGE2, TNF-α, and IL-6, the expression of COX-2, iNOS, MMP-3, MMP-13, and ADAMTS-5, and the degradation of aggrecan and collagen-II in human OA chondrocytes. Furthermore, phloretin dramatically suppressed the IL-1β-stimulated phosphorylation of PI3K/Akt and activation of NF-κB in human OA chondrocytes. In addition, treatment with phloretin not only prevented the destruction of cartilage and the thickening of subchondral bone but also relieved synovitis in a mouse model of OA. Moreover, immunohistochemical results showed that phloretin significantly decreased the expression of MMP-13 and increased the expression of collagen-II in OA in mice. In conclusion, these results suggest that phloretin may be a potential agent for the treatment of OA.

Specnuezhenide Decreases Interleukin-1β-Induced Inflammation in Rat Chondrocytes and Reduces Joint Destruction in Osteoarthritic Rats

As a chronic disease, osteoarthritis (OA) leads to the degradation of both cartilage and subchondral bone, its development being mediated by proinflammatory cytokines like interleukin-1β. In the present study, the anti-inflammatory effect of specnuezhenide (SPN) in OA and its underlying mechanism were studied in vitro and in vivo. The results showed that SPN decreases the expression of cartilage matrix-degrading enzymes and the activation of NF-κB and wnt/β-catenin signaling, and increases chondrocyte-specific gene expression in IL-1β-induced inflammation in chondrocytes. Furthermore, SPN treatment prevents the degeneration of both cartilage and subchondral bone in a rat model of OA. To the best of our knowledge, this study is the first to report that SPN decreases interleukin-1β-induced inflammation in rat chondrocytes by inhibiting the activation of the NF-κB and wnt/β-catenin pathways, and, thus, has therapeutic potential in the treatment of OA.

Emodin ameliorates cartilage degradation in osteoarthritis by inhibiting NF-κB and Wnt/β-catenin signaling in-vitro and in-vivo

The overproduction of MMPs (matrix metalloproteinases) and members of the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) protein family plays an important role in the pathogenesis of osteoarthritis (OA). The potential of selective MMPs or ADAMTS inhibitors as chemopreventive agents for OA has been demonstrated in several studies. In this study, we investigated the protective effects of emodin (1,3,8-trihydroxy-6-methylanthaquinone), isolated from the root of Rheum palmatum L., in the inhibition of MMP and ADAMTS expression in both rat chondrocytes and an animal model of OA. The expression of MMP-3, MMP-13, ADAMTS-4, ADAMTS-5, aggrecan, and collagen II mRNA and protein in interleukin-1beta (IL-1β)-induced rat chondrocytes was followed by quantitative real-time PCR and western blot. The activation of the NF-κB and Wnt/β-catenin pathways by IL-1β was assessed by western blot. The in vivo effects of emodin were evaluated by intra-articular injection in rats in an experimental model of OA induced by anterior cruciate ligament transection. Emodin dose-dependently down-regulated the expression of MMP-3, MMP-13, ADAMTS-4 and ADAMTS-5 at both the mRNA and protein level in IL-1β-stimulated rat chondrocytes. In addition, the IL-1β-induced activation of NF-κB and Wnt signals was attenuated by emodin, as determined by western blotting. The intra-articular injection of emodin in a rat OA model ameliorated OA progression, as determined in morphological and histological analyses in vivo. Taken together, our findings demonstrate that emodin is a promising therapeutic agent for the prevention and treatment of OA.

Effects of TLR-2/NF-κB signaling pathway on the occurrence of degenerative knee osteoarthritis: an in vivo and in vitro study

The study aims to explore the effects of TLR-2/NF-κB signaling pathway on the occurrence of degenerative knee osteoarthritis (OA). Degenerative knee OA and normal cartilage samples were collected from patients with degenerative knee OA receiving total knee arthroplasty and amputation. Expressions of TLR-2, NF-κB and MMP-13 were determined by qRT-PCR and immunochemistry. The chondrocytes were divided into control, IL-1β, IL-1β + anti-TLR-2 and IL-1β + PDTC groups. MTT assay and flow cytometry were performed to determine proliferation and apoptosis of the chondrocytes. Expressions of TLR-2, NF-κB and MMP-13 were measured by Western blotting. ELISA was conducted to detect the expressions of related inflammatory factors. The positive expressions of TLR, NF-κB and MMP13 were associated with body mass index (BMI), family history, exercise, and WOMAC scores of OA patients. Logistic regression analysis showed that OA influencing factors were TLR, NF-κB, MMP13, BMI, family history and exercise. Compared with normal chondrocytes, the expressions of TLR-2, NF-κB, MMP-13 and related inflammatory factors increased in degenerative knee OA. The chondrocytes in the IL-1β + anti-TLR-2 and IL-1β + PDTC groups showed lower apoptosis rates than those in the IL-1β group. Compared with the control group, increased expressions of TLR-2, NF-κB, phosphorylated-NF-κB (p-NF-κB), MMP-13, IL-1, IL-6 and TNF-α were found in the IL-1β group. In the IL-1β + anti-TLR-2 and IL-1β + PDTC groups, decreased expressions of NF-κB, p-NF-κB, MMP-13, IL-1, IL-6 and TNF-α were found compared with those in the IL-1β group. TLR-2/NF-κB signaling pathway contributes to the occurrence of degenerative knee OA.

Evidence that miR-146a attenuates aging- and trauma-induced osteoarthritis by inhibiting Notch1, IL-6, and IL-1 mediated catabolism

Primary osteoarthritis (OA) is associated with aging, while post-traumatic OA (PTOA) is associated with mechanical injury and inflammation. It is not clear whether the two types of osteoarthritis share common mechanisms. We found that miR-146a, a microRNA-associated with inflammation, is activated by cyclic load in the physiological range but suppressed by mechanical overload in human articular chondrocytes. Furthermore, miR-146a expression is decreased in the OA lesions of human articular cartilage. To understand the role of miR-146a in osteoarthritis, we systemically characterized mice in which miR-146a is either deficient in whole body or overexpressed in chondrogenic cells specifically. miR-146a-deficient mice develop early onset of OA characterized by cartilage degeneration, synovitis, and osteophytes. Conversely, miR-146a chondrogenic overexpressing mice are resistant to aging-associated OA. Loss of miR-146a exacerbates articular cartilage degeneration during PTOA, while chondrogenic overexpression of miR-146a inhibits PTOA. Thus, miR-146a inhibits both OA and PTOA in mice, suggesting a common protective mechanism initiated by miR-146a. miR-146a suppresses IL-1β of catabolic factors, and we provide evidence that miR-146a directly inhibits Notch1 expression. Therefore, such inhibition of Notch1 may explain suppression of inflammatory mediators by miR-146a. Chondrogenic overexpression of miR-146a or intra-articular administration of a Notch1 inhibitor alleviates IL-1β-induced catabolism and rescues joint degeneration in miR-146a-deficient mice, suggesting that miR-146a is sufficient to protect OA pathogenesis by inhibiting Notch signaling in the joint. Thus, miR-146a may be used to counter both aging-associated OA and mechanical injury-/inflammation-induced PTOA.