Interplay Between Iron Overload and Osteoarthritis: Clinical Significance and Cellular Mechanisms

There are multiple diseases or conditions such as hereditary hemochromatosis, hemophilia, thalassemia, sickle cell disease, aging, and estrogen deficiency that can cause iron overload in the human body. These diseases or conditions are frequently associated with osteoarthritic phenotypes, such as progressive cartilage degradation, alterations in the microarchitecture and biomechanics of the subchondral bone, persistent joint inflammation, proliferative synovitis, and synovial pannus. Growing evidences suggest that the conditions of pathological iron overload are associated with these osteoarthritic phenotypes. Osteoarthritis (OA) is an important complication in patients suffering from iron overload-related diseases and conditions. This review aims to summarize the findings and observations made in the field of iron overload-related OA while conducting clinical and basic research works. OA is a whole-joint disease that affects the articular cartilage lining surfaces of bones, subchondral bones, and synovial tissues in the joint cavity. Chondrocytes, osteoclasts, osteoblasts, and synovial-derived cells are involved in the disease. In this review, we will elucidate the cellular and molecular mechanisms associated with iron overload and the negative influence that iron overload has on joint homeostasis. The promising value of interrupting the pathologic effects of iron overload is also well discussed for the development of improved therapeutics that can be used in the field of OA.

The Protective Effect of Kirenol in Osteoarthritis: an in Vitro and in Vivo Study

Background: Osteoarthritis (OA) is a chronic degenerative disease, its main characteristic involves articular cartilage destruction and inflammation response, absent of effective medical treatment. Our current research aimed to explore anti-inflammatory effect of kirenol, a diterpenoid natural product compound, in the development of OA and its potential molecular mechanism through in vitro and in vivo study.Methods: In vitro, chondrocytes were pretreated with kirenol for 2 h before IL-1β stimulation. Production of NO, PGE2, TNF-α, IL-6, aggrecan, collagen-II, MMP13and ADAMTS5 were evaluated by the Griess reaction and ELISAs. The mRNA (aggrecan and collagen-II) and protein expression (COX-2, iNOS, P65, IκB, PI3K, AKT) were measured by qRT-PCR and Western blot respectively. Immunofluorescence was used to assess the expression of collagen-II and P65. The in vivo effect of kirenol was evaluated in mice OA models induced by destabilization of the medial meniscus (DMM).Results: We found that kirenol inhibited IL-1β-induced expression of NO, PGE2, TNF-α, IL-6, COX-2, iNOS, ADAMTS-5. Besides, kirenol remarkably decreased IL-1β-induced degradation of aggrecan and collagen-II. Furthermore, kirenol significantly inhibited IL-1β-induced phosphorylation of PI3K/Akt and NF-κB signaling. In vivo, the cartilage in kirenol-treated mice exhibited less cartilage degradation and lower OARSI scores.Conclusions: Taken together, the results of this study provide potent evidence that kirenol could be utilized as a potentially therapeutic agent in prevention and treatment of OA.

PPARα−ACOT12 axis is responsible for maintaining cartilage homeostasis through modulating de novo lipogenesis

Here, in Ppara−/− mice, we found that an increased DNL stimulated the cartilage degradation and identified ACOT12 as a key regulatory factor. Suppressed level of ACOT12 was observed in cartilages of OA patient and OA-induced animal. To determine the role and association of ACOT12 in the OA pathogenesis, we generated Acot12 knockout (KO) (Acot12−/−) mice using RNA-guided endonuclease. Acot12−/− mice displayed the severe cartilage degradation with the stimulation of matrix MMPs and chondrocyte apoptosis through the accumulation of acetyl CoA. Delivery of acetyl CoA-conjugated chitosan complex into cartilage stimulated DNL and cartilage degradation. Moreover, restoration of ACOT12 into human OA chondrocytes and OA-induced mouse cartilage effectively rescued the pathophysiological features of OA by regulating DNL. Taken together, our study suggested ACOT12 as a novel regulatory factor in maintaining cartilage homeostasis and targeting ACOT12 could contribute to developing a new therapeutic strategy for OA.

Polymorphism of MMP-3 gene and imbalance expression of MMP-3 / TIMP-1 in articular cartilage are associated with an endemic osteochondropathy, Kashin- Beck disease

Background The etiology of Kashin-Beck disease (KBD), an endemic osteochondropathy, is largely unknown. Matrix metalloproteinase-3 (MMP-3) plays a central role in the initiation and progression of cartilage destruction, however, no study has reported on the relationship between KBD and MMP-3. The objective of this study was to explore the polymorphism of MMP-3 gene and expression of MMP-3 / TIMP-1(Tissue inhibitors of matrixmetalloproteinases-1) in the pathogenesis of KBD. Methods Single nucleotide polymorphism (SNP) genotyping was conducted in 274 KBD cases and 248 healthy controls for eight SNPs in MMP-3 using the Sequenom MassARRAY system. Additionally, the expression of MMP-3、TIMP-1 in different layers of the articular cartilage was analyzed by immunohistochemistry for 22 KBD patients, 15 osteoarthritis (OA) patients and 21 controls. Results The results showed that six SNPs (rs520540、rs591058、rs679620、rs602128、rs639752 and rs678815) in MMP-3 were associated with the increased risk of KBD, however, after Bonferroni correction, only the SNP rs679620 in the recessive model remained significant difference (OR = 2.31, 95%CI = 1.29–4.14, P = 0.0039), homozygous for “T” allele have a risk for KBD than “C” allele carriers. Moreover, the percentages of cells expressing MMP-3 in articular cartilage were significantly higher in the KBD and OA groups than in the controls (t = 5.37 and 4.19, P<0.01). While the KBD and OA groups had lower levels of TIMP-1 positive staining compared with the controls (t = 5.23and 5.06, P<0.01). And there was no significant different between KBD and OA for the levels of MMP-3 and TIMP-1 positive staining (t = 0.05and 0.28, P>0.05). Conclusions MMP-3 is associated with the susceptibility of KBD, and the imbalance expression of MMPs / TIMPs leading to cartilage degradation may play an important role in cartilage degradation and osteoarthritis formation in OA and KBD.

14-3-3η Promotes Invadosome Formation via the FOXO3–Snail Axis in Rheumatoid Arthritis Fibroblast-like Synoviocytes

Erosive destruction of joint structures is a critical event in the progression of rheumatoid arthritis (RA), in which fibroblast-like synoviocytes (FLS) are the primary effectors. We previously reported that the ability of RA FLS to degrade extracellular matrix (ECM) components depends on the formation of actin-rich membrane protrusions, called invadosomes, through processes that remain elusive. 14-3-3η belongs to a family of scaffolding proteins involved in a wide range of cellular functions, and its expression is closely related to joint damage and disease activity in RA patients. In this study, we sought to assess the role of 14-3-3η in joint damage by examining its contribution to the invadosome formation phenotype of FLS. Using human primary FLS, we show that 14-3-3η expression is closely associated with their ability to form invadosomes. Furthermore, knockdown of 14-3-3η using shRNAs decreases the level of invadosome formation in RA FLS, whereas addition of the recombinant protein to FLS from healthy individuals promotes their formation. Mechanistic studies suggest that 14-3-3η regulates invadosome formation by increasing Snail expression, a mechanism that involves nuclear exclusion of the transcription repressor FOXO3. Our results implicate the 14-3-3η–FOXO3–Snail axis in promoting the aggressive ECM-degrading phenotype of RA FLS, and suggest a role for this scaffolding protein in cartilage degradation.

The Impact of Trace Elements on Osteoarthritis

Osteoarthritis (OA) is a progressive degenerative disease characterized by cartilage degradation, synovial inflammation, subchondral sclerosis and osteophyte formation. It has a multifactorial etiology with potential contributions from heredity, endocrine function, abnormal mechanical load and nutrition. Of particular considerations are trace element status. Several trace elements, such as boron and magnesium are essential for normal development of the bone and joint in human. While cadmium correlates with the severity of OA. The present review focuses on the roles of trace elements (boron, cadmium, copper, iron, magnesium, manganese, selenium, zinc) in OA and explores the mechanisms by which they act.

Encapsulated Allogeneic Synovial Membrane Mesenchymal Stem Cells Provide Better Outcomes of Chondral Lesions in Horses

Osteoarthritis is the main cause of equine lameness, and its treatment remains ineffective. Synovial membrane mesenchymal stem cells (SMMSCs) provide satisfactory outcomes in joint injuries, mainly due to their immunomodulatory and reparative properties. This study aimed to evaluate the effect of SMMSCs, either encapsulated in alginate hydrogel or free, in chondral lesions of horses.Methods: Chondral lesions were surgically induced in the medial trochlea of the talus of fifteen horses. Animals were treated with PBS free SMMSCs or encapsulated SMMSCs. Physical evaluations, assignment of lameness scores and synovial fluid analysis were performed (cytological analysis and dosage of IL-1, IL-10, IL-6, INF-Ɣ, TNF 𝛼, P substance, serum amyloid A, TGF-β, IGF and PGE2) for two weeks. Cartilage biopsies were performed 150 days after induction for histological analysis and immunohistochemistry staining.Results: All groups initially presented inflammation. Although free SMMSCs showed moderate tissue repair, encapsulated SMMSCs had a lower grade of inflammation with superior tissue macro- and microscopic aspects at the end, while the control group showed fibrosis and poor cartilage aspect. This study suggests better effectiveness of stem cells in chondral defects when encapsulated MSCs are used.Conclusion: While the absence of treatment perpetuates cartilage degradation, encapsulated SMMSCs respond better to initial inflammation, interacting and modulating the environment through the release of anti-inflammatory cytokines. Better outcomes observed in encapsulated MSCs were related to the immuno- and physical barriers provided by the alginate hydrogel, allowing a longer period of permanence and interaction between MSCs and the environment.

Mechanical Cues: Bidirectional Reciprocity in the Extracellular Matrix Drives Mechano-Signalling in Articular Cartilage

The composition and organisation of the extracellular matrix (ECM), particularly the pericellular matrix (PCM), in articular cartilage is critical to its biomechanical functionality; the presence of proteoglycans such as aggrecan, entrapped within a type II collagen fibrillar network, confers mechanical resilience underweight-bearing. Furthermore, components of the PCM including type VI collagen, perlecan, small leucine-rich proteoglycans—decorin and biglycan—and fibronectin facilitate the transduction of both biomechanical and biochemical signals to the residing chondrocytes, thereby regulating the process of mechanotransduction in cartilage. In this review, we summarise the literature reporting on the bidirectional reciprocity of the ECM in chondrocyte mechano-signalling and articular cartilage homeostasis. Specifically, we discuss studies that have characterised the response of articular cartilage to mechanical perturbations in the local tissue environment and how the magnitude or type of loading applied elicits cellular behaviours to effect change. In vivo, including transgenic approaches, and in vitro studies have illustrated how physiological loading maintains a homeostatic balance of anabolic and catabolic activities, involving the direct engagement of many PCM molecules in orchestrating this slow but consistent turnover of the cartilage matrix. Furthermore, we document studies characterising how abnormal, non-physiological loading including excessive loading or joint trauma negatively impacts matrix molecule biosynthesis and/or organisation, affecting PCM mechanical properties and reducing the tissue’s ability to withstand load. We present compelling evidence showing that reciprocal engagement of the cells with this altered ECM environment can thus impact tissue homeostasis and, if sustained, can result in cartilage degradation and onset of osteoarthritis pathology. Enhanced dysregulation of PCM/ECM turnover is partially driven by mechanically mediated proteolytic degradation of cartilage ECM components. This generates bioactive breakdown fragments such as fibronectin, biglycan and lumican fragments, which can subsequently activate or inhibit additional signalling pathways including those involved in inflammation. Finally, we discuss how bidirectionality within the ECM is critically important in enabling the chondrocytes to synthesise and release PCM/ECM molecules, growth factors, pro-inflammatory cytokines and proteolytic enzymes, under a specified load, to influence PCM/ECM composition and mechanical properties in cartilage health and disease.

Antcin K Inhibits TNF-α, IL-1β and IL-8 Expression in Synovial Fibroblasts and Ameliorates Cartilage Degradation: Implications for the Treatment of Rheumatoid Arthritis

Extracts from Taiwan’s traditional medicinal mushroom, Antrodia cinnamomea, exhibit anti-inflammatory activities in cellular and preclinical studies. However, this paper is the first to report that Antcin K, a triterpenoid isolated from A. cinnamomea, inhibits proinflammatory cytokine production in human rheumatoid synovial fibroblasts (RASFs), which are major players in rheumatoid arthritis (RA) disease. In our analysis of the mechanism of action, Antcin K inhibited the expression of three cytokines (tumor necrosis factor alpha [TNF-α], interleukin 1 beta [IL-1β] and IL-8) in human RASFs; cytokines that are crucial to RA synovial inflammation. Notably, incubation of RASFs with Antcin K reduced the phosphorylation of the focal adhesion kinase (FAK), phosphoinositide 3-kinase (PI3K), protein kinase B (AKT) and nuclear factor-κB (NF-κB) signaling cascades, all of which promote cytokine production in RA. Intraperitoneal injections of Antcin K (10 mg/kg or 30 mg/kg) attenuated paw swelling, cartilage degradation and bone erosion, and decreased serum levels of TNF-α, IL-1β, IL-8 in collagen-induced arthritis (CIA) mice; in further experiments, IL-6 levels were similarly reduced. The inhibitory effects of Antcin K upon TNF-α, IL-1β and IL-8 expression in human RASFs was achieved through the downregulation of the FAK, PI3K, AKT and NF-κB signaling cascades. Our data support clinical investigations using Antcin K in RA disease.