Nitric Oxide Mediates Crosstalk between Interleukin 1β and WNT Signaling in Primary Human Chondrocytes by Reducing DKK1 and FRZB Expression

Pulsed electromagnetic fields potentiate bone marrow mesenchymal stem cell chondrogenesis by regulating the Wnt/β-catenin signaling pathway

BACKGROUND

Pulsed electromagnetic fields (PEMFs) show promise as a treatment for knee osteoarthritis (KOA) by reducing inflammation and promoting chondrogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs).

PURPOSE

To identify the efficacy window of PEMFs to induce BMSCs chondrogenic differentiation and explore the cellular mechanism under chondrogenesis of BMSCs in regular and inflammatory microenvironments.

METHODS

BMSCs were exposed to PEMFs (75 Hz, 1.6/2/3/3.8 mT) for 7 and 14 days. The histology, proliferation, migration and chondrogenesis of BMSCs were assessed to identify the optimal parameters. Using these optimal parameters, transcriptome analysis was performed to identify target genes and signaling pathways, validated through immunohistochemical assays, western blotting, and qRT-PCR, with or without the presence of IL-1β. The therapeutic effects of PEMFs and the effective cellular signaling pathways were evaluated in vivo.

RESULTS

BMSCs treated with 3 mT PEMFs showed the optimal chondrogenesis on day 7, indicated by increased expression of ACAN, COL2A, and SOX9, and decreased levels of MMP3 and MMP13 at both transcriptional and protein levels. The advantages of 3 mT PEMFs diminished in the 14-day culture groups. Transcriptome analysis identified sFRP3 as a key molecule targeted by PEMF treatment, which competitively inhibited Wnt/β-catenin signaling, regardless of IL-1β presence or duration of exposure. This inhibition of the Wnt/β-catenin pathway was also confirmed in a KOA mouse model following PEMF exposure.

CONCLUSIONS

PEMFs at 75 Hz and 3 mT are optimal in inducing early-stage chondrogenic differentiation of BMSCs. The induction and chondroprotective effects of PEMFs are mediated by sFRP3 and Wnt/β-catenin signaling, irrespective of inflammatory conditions.

WTAP-mediated m6A modification of FRZB triggers the inflammatory response via the Wnt signaling pathway in osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis. However, the exact pathogenesis remains unclear. Emerging evidence shows that N6-methyladenosine (m6A) modification may have an important role in OA pathogenesis. This study aimed to investigate the role of m6A writers and the underlying mechanisms in osteoarthritic cartilage. Among m6A methyltransferases, Wilms tumor 1-associated protein (WTAP) expression most significantly differed in clinical osteoarthritic cartilage. WTAP regulated extracellular matrix (ECM) degradation, inflammation and antioxidation in human chondrocytes. Mechanistically, the m6A modification and relative downstream targets in osteoarthritic cartilage were assessed by methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA sequencing, which indicated that the expression of frizzled-related protein (FRZB), a secreted Wnt antagonist, was abnormally decreased and accompanied by high m6A modification in osteoarthritic cartilage. In vitro dysregulated WTAP had positive effects on β-catenin expression by targeting FRZB, which finally contributed to the cartilage injury phenotype in chondrocytes. Intra-articular injection of adeno-associated virus-WTAP alleviated OA progression in a mouse model, while this protective effect could be reversed by the application of a Wnt/β-catenin activator. In summary, this study revealed that WTAP-dependent RNA m6A modification contributed to Wnt/β-catenin pathway activation and OA progression through post-transcriptional regulation of FRZB mRNA, thus providing a potentially effective therapeutic strategy for OA treatment.

Connection between Osteoarthritis and Nitric Oxide: From Pathophysiology to Therapeutic Target

Osteoarthritis (OA), a disabling joint inflammatory disease, is characterized by the progressive destruction of cartilage, subchondral bone remodeling, and chronic synovitis. Due to the prolongation of the human lifespan, OA has become a serious public health problem that deserves wide attention. The development of OA is related to numerous factors. Among the factors, nitric oxide (NO) plays a key role in mediating this process. NO is a small gaseous molecule that is widely distributed in the human body, and its synthesis is dependent on NO synthase (NOS). NO plays an important role in various physiological processes such as the regulation of blood volume and nerve conduction. Notably, NO acts as a double-edged sword in inflammatory diseases. Recent studies have shown that NO and its redox derivatives might be closely related to both normal and pathophysiological joint conditions. They can play vital roles as normal bone cell-conditioning agents for osteoclasts, osteoblasts, and chondrocytes. Moreover, they can also induce cartilage catabolism and cell apoptosis. Based on different conditions, the NO/NOS system can act as an anti-inflammatory or pro-inflammatory agent for OA. This review summarizes the studies related to the effects of NO on all normal and OA joints as well as the possible new treatment strategies targeting the NO/NOS system.

Implementing computational modeling in tissue engineering: where disciplines meet

In recent years, the mathematical and computational sciences have developed novel methodologies and insights that can aid in designing advanced bioreactors, microfluidic set-ups or organ-on-chip devices, in optimizing culture conditions, or predicting long-term behavior of engineered tissues in vivo. In this review, we introduce the concept of computational models and how they can be integrated in an interdisciplinary workflow for Tissue Engineering and Regenerative Medicine (TERM). We specifically aim this review of general concepts and examples at experimental scientists with little or no computational modeling experience. We also describe the contribution of computational models in understanding TERM processes and in advancing the TERM field by providing novel insights.

An ECHO of Cartilage: In Silico Prediction of Combinatorial Treatments to Switch Between Transient and Permanent Cartilage Phenotypes With Ex Vivo Validation

A fundamental question in cartilage biology is: what determines the switch between permanent cartilage found in the articular joints and transient hypertrophic cartilage that functions as a template for bone? This switch is observed both in a subset of OA patients that develop osteophytes, as well as in cell-based tissue engineering strategies for joint repair. A thorough understanding of the mechanisms regulating cell fate provides opportunities for treatment of cartilage disease and tissue engineering strategies. The objective of this study was to understand the mechanisms that regulate the switch between permanent and transient cartilage using a computational model of chondrocytes, ECHO. To investigate large signaling networks that regulate cell fate decisions, we developed the software tool ANIMO, Analysis of Networks with interactive Modeling. In ANIMO, we generated an activity network integrating 7 signal transduction pathways resulting in a network containing over 50 proteins with 200 interactions. We called this model ECHO, for executable chondrocyte. Previously, we showed that ECHO could be used to characterize mechanisms of cell fate decisions. ECHO was first developed based on a Boolean model of growth plate. Here, we show how the growth plate Boolean model was translated to ANIMO and how we adapted the topology and parameters to generate an articular cartilage model. In ANIMO, many combinations of overactivation/knockout were tested that result in a switch between permanent cartilage (SOX9+) and transient, hypertrophic cartilage (RUNX2+). We used model checking to prioritize combination treatments for wet-lab validation. Three combinatorial treatments were chosen and tested on metatarsals from 1-day old rat pups that were treated for 6 days. We found that a combination of IGF1 with inhibition of ERK1/2 had a positive effect on cartilage formation and growth, whereas activation of DLX5 combined with inhibition of PKA had a negative effect on cartilage formation and growth and resulted in increased cartilage hypertrophy. We show that our model describes cartilage formation, and that model checking can aid in choosing and prioritizing combinatorial treatments that interfere with normal cartilage development. Here we show that combinatorial treatments induce changes in the zonal distribution of cartilage, indication possible switches in cell fate. This indicates that simulations in ECHO aid in describing pathologies in which switches between cell fates are observed, such as OA.

Age-dependent changes in protein incorporation into collagen-rich tissues of mice by in vivo pulsed SILAC labelling

Collagen-rich tissues have poor reparative capacity that predisposes to common age-related disorders such as osteoporosis and osteoarthritis. We used in vivo pulsed SILAC labelling to quantify new protein incorporation into cartilage, bone, and skin of mice across the healthy life course. We report dynamic turnover of the matrisome, the proteins of the extracellular matrix, in bone and cartilage during skeletal maturation, which was markedly reduced after skeletal maturity. Comparing young adult with older adult mice, new protein incorporation was reduced in all tissues. STRING clustering revealed changes in epigenetic modulators across all tissues, a decline in chondroprotective growth factors such as FGF2 and TGFβ in cartilage, and clusters indicating mitochondrial dysregulation and reduced collagen synthesis in bone. Several pathways were implicated in age-related disease. Fewer changes were observed for skin. This methodology provides dynamic protein data at a tissue level, uncovering age-related molecular changes that may predispose to disease.

Adipose-Derived Mesenchymal Stromal Cells Treated with Interleukin 1 Beta Produced Chondro-Protective Vesicles Able to Fast Penetrate in Cartilage

The study of the miRNA cargo embedded in extracellular vesicles (EVs) released from adipose-derived mesenchymal stromal cells (ASC) preconditioned with IL-1β, an inflammatory stimulus driving osteoarthritis (OA), along with EVs-cartilage dynamic interaction represent poorly explored fields and are the purpose of the present research. ASCs were isolated from subcutaneous adipose tissue and EVs collected by ultracentrifugation. Shuttled miRNAs were scored by high-throughput screening and analyzed through bioinformatics approach that predicted the potentially modulated OA-related pathways. Fluorescently labeled EVs incorporation into OA cartilage explants was followed in vitro by time-lapse coherent anti-Stokes Raman scattering; second harmonic generation and two-photon excited fluorescence. After IL-1β preconditioning, 7 miRNA were up-regulated, 4 down-regulated, 37 activated and 17 silenced. Bioinformatics allowed to identify miRNAs and target genes mainly involved in Wnt, Notch, TGFβ and Indian hedgehog (IHH) pathways, cartilage homeostasis, immune/inflammatory responses, cell senescence and autophagy. As well, ASC-EVs steadily diffuse in cartilage cells and matrix, reaching a plateau 16 h after administration. Overall, ASCs preconditioned with IL-1β allows secretion of EVs embedded with a chondro-protective miRNA cargo, able to fast penetrate in collagen-rich areas of cartilage with tissue saturation in a day. Further functional studies exploring the EVs dose-effects are needed to achieve clinical relevance.

Effects of HDAC4 on IL-1β-induced matrix metalloproteinase expression regulated partially through the WNT3A/β-catenin pathway

Background:

Histone deacetylase 4 (HDAC4) regulates chondrocyte hypertrophy and bone formation. The aim of the present study was to explore the effects of HDAC4 on Interleukin 1 beta (IL-1β)-induced chondrocyte extracellular matrix degradation and whether it is regulated through the WNT family member 3A (WNT3A)/β-catenin signaling pathway.

Methods:

Primary chondrocytes (CC) and human chondrosarcoma cells (SW1353 cells) were treated with IL-1β and the level of HDAC4 was assayed using Western blotting. Then, HDAC4 expression in the SW1353 cells was silenced using small interfering RNA to detect the effect of HDAC4 knockdown on the levels of matrix metalloproteinase 3 (MMP3) and MMP13 induced by IL-1β. After transfection with HDAC4 plasmids, the overexpression efficiency was examined using Real-time quantitative polymerase chain reaction (qRT-PCR) and the levels of MMP3 and MMP13 were assayed using Western blotting. After incubation with IL-1β, the translocation of β-catenin into the nucleus was observed using immunofluorescence staining in SW1353 cells to investigate the activation of the WNT3A/β-catenin signaling pathway. Finally, treatment with WNT3A and transfection with glycogen synthase kinase 3 beta (GSK3β) plasmids were assessed for their effects on HDAC4 levels using Western blotting.

Results:

IL-1β downregulated HDAC4 levels in chondrocytes and SW1353 cells. Furthermore, HDAC4 knockdown increased the levels of MMP3 and MMP13, which contributed to the degradation of the extracellular matrix. Overexpression of HDAC4 inhibited IL-1β-induced increases in MMP3 and MMP13. IL-1β upregulated the levels of WNT3A, and WNT3A reduced HDAC4 levels in SW1353 cells. GSK-3β rescued IL-1β-induced downregulation of HDAC4 in SW1353 cells.

Conclusion:

HDAC4 exerted an inhibitory effect on IL-1β-induced extracellular matrix degradation and was regulated partially by the WNT3A/β-catenin signaling pathway.

Biomarkers of Joint Damage in Osteoarthritis: Current Status and Future Directions

Osteoarthritis (OA) is a disease of the whole joint organ, characterized by the loss of cartilage, and structural changes in bone including the formation of osteophytes, causing disability and loss of function. It is also associated with systemic mediators and low-grade inflammation. Currently, there is negligible/no availability of specific biomarkers that can be used to facilitate the diagnosis and treatment of OA. The most unmet clinical need is, however, related to the monitoring of disease progression over a short period that can be used in clinical trials. In this review, the value of biomarkers identified over the past decade has been highlighted. These biomarkers are associated with the synthesis and breakdown of cartilage, including collagenous and noncollagenous biomarkers, inflammatory and anti-inflammatory biomarkers, expressed in the biological fluid such as serum, synovial fluid, and urine. Broad validation of novel and clinically applicable biomarkers and their involvement in the pathways are particularly needed for early-stage diagnosis, monitoring disease progression, and severity and examining new drugs to mitigate the effects of this highly prevalent and debilitating condition.

The relationship between abnormal Core binding factor-β expression in human cartilage and osteoarthritis

Background

This study aimed to investigate the effect of abnormal Core binding factor-β expression on proliferation, differentiation and apoptosis of chondrocytes, and elucidate the relationship between Core binding factor-β and osteoarthritis-related markers and degenerative joint disease.

Methods

Cartilage tissues, from healthy subjects and patients with osteoarthritis, were collected for histology and expression of Core binding factor-β, MMP-13, IL-1β, COMP, and YKL-40. Human articular chondrocytes were cultured in vitro, and a viral vector was constructed to regulate cellular Core binding factor-β expression. Cellular proliferation and apoptosis were observed, and osteoarthritis-related inflammatory factor expression and cartilage metabolite synthesis assayed.

Results

Human osteoarthritis lesions had disordered cartilage structure and cellular arrangement, and increased emptying of cartilage lacunae. Normal cell counts were significantly reduced, cartilage extracellular matrix was obviously damaged, and type II collagen expression was significantly decreased. Core binding factor-β was highly expressed in the osteoarthritis cartilage (p < 0.001), and MMP-13, IL-1β, COMP and YKL-40 expression were greater than found in normal cartilage (p < 0.001). Cellular proliferation in the Core binding factor-β high-expression group was reduced and the total apoptosis rate was increased (p < 0.05), while the opposite was found in the Core binding factor-β inhibition group (p < 0.01). Compared with normal chondrocytes, high Core binding factor-β expression (Osteoarthritis and CBFB/pCDH groups) was associated with significantly increased MMP13, IL-1β, COMP and YKL-40 protein expression (p < 0.01), while Core binding factor-β inhibition (CBFB/pLKO.1 group) was associated with significantly decreased COMP, MMP13, IL-1β and YKL-40 expression in osteoarthritis cells (p < 0.001).

Conclusions

Abnormal Core binding factor-β expression might play an upstream regulatory role in mediating abnormal chondrocyte apoptosis and the inflammatory response. On inhibiting Core binding factor-β expression, a delay in cartilage degeneration was expected.

Trial registration

The study was registered for clinical trials in ChiCTR: ChiCTR1800017066 (Reg. Date-2018/7/10).

Preparation and characterization of amnion hydrogel and its synergistic effect with adipose derived stem cells towards IL1β activated chondrocytes

Inflammation leads to chondrocyte senescence and cartilage degeneration, resulting in osteoarthritis (OA). Adipose‐derived stem cells (ADSCs) exert paracrine effects protecting chondrocytes from degenerative changes. However, the lack of optimum delivery systems for ADSCs limits its use in the clinic. The use of extracellular matrix based injectable hydrogels has gained increased attention due to their unique properties. In the present study, we developed hydrogels from amnion tissue as a delivery system for ADSCs. We investigated the potential of amnion hydrogel to maintain ADSC functions, the synergistic effect of AM with ADSC in preventing the catabolic responses of inflammation in stimulated chondrocytes. We also investigated the role of Wnt/β-catenin signaling pathway in IL-1β induced inflammation in chondrocytes and the ability of AM-ADSC to inhibit Wnt/β-catenin signaling. Our results showed that AM hydrogels supported cell viability, proliferation, and stemness. ADSCs, AM hydrogels and AM-ADSCs inhibited the catabolic responses of IL-1β and inhibited the Wnt/β-catenin signaling pathway, indicating possible involvement of Wnt/β-catenin signaling pathways in IL-1β induced inflammation. The results also showed that the synergistic effect of AM-ADSCs was more pronounced in preventing catabolic responses in activated chondrocytes. In conclusion, we showed that AM hydrogels can be used as a potential carrier for ADSCs, and can be developed as a potential therapeutic agent for treating OA.

Sclerostin inhibits interleukin-1β-induced late stage chondrogenic differentiation through downregulation of Wnt/β-catenin signaling pathway

It is known that Wnt/β-catenin signaling induces endochondral ossification and plays a significant role in the pathophysiology of osteoarthritis (OA). Sclerostin is a potent inhibitor of the Wnt/β-catenin signaling pathway. This study investigated the role of sclerostin in the endochondral differentiation under an OA-like condition induced by proinflammatory cytokines. ATDC5 cells were used to investigate chondrogenic differentiation and terminal calcification, and 10 ng/ml IL-1β and/or 200 ng/ml sclerostin were added to the culture medium. IL-1β impaired early chondrogenesis from undifferentiated state into proliferative chondrocytes, and it was not altered by sclerostin. IL-1β induced progression of chondrogenic differentiation in the late stage and promoted terminal calcification. These processes were inhibited by sclerostin and chondrogenic phenotype was restored. In addition, sclerostin restored IL-1β-induced upregulation of Wnt/β-catenin signaling in the late stage. This study provides insights into the possible role of sclerostin in the chondrogenic differentiation under the IL-1β-induced OA-like environment. Suppression of Wnt signaling by an antagonist may play a key role in the maintenance of articular homeostasis and has a potential to prevent the progression of OA. Thus, sclerostin is a candidate treatment option for OA.

Tomatidine suppresses inflammation in primary articular chondrocytes and attenuates cartilage degradation in osteoarthritic rats

In this study, we investigated whether the anti-inflammatory effects of tomatidine alleviate osteoarthritis (OA)-related pathology in primary articular chondrocytes and a rat OA model. STITCH database analysis identified 22 tomatidine-target genes that were enriched in 78 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Moreover,39 of the 105 OA-related KEGG pathways were related to tomatidine-target genes. The top two OA-related KEGG pathways with tomatidine-target genes were the MAPK and neutrophin signaling pathways. Pretreating primary chondrocytes with tomatidine suppressed interleukin-1β (IL-1β)-induced expression of iNOS, COX-2, MMP1, MMP3, MMP13, and ADAMTS-5. Tomatidine also suppressed IL-1β-induced degradation of collagen-II and aggrecan proteins by inhibiting NF-κB and MAPK signaling. In a rat OA model, histological and immunohistochemical analyses showed significantly less cartilage degeneration in thetibiofemoral joints of rats treated for 12 weeks with tomatidine after OA induction (experimental group) than in untreated OA group rats. However, micro-computed tomography (μ-CT) showed that tomatidine did not affect remodeling of the subchondral bone at the tibial plateau. These data shows that tomatidine suppresses IL-1β-induced inflammation in primary chondrocytes by inhibiting the NF-κB and MAPK signaling pathways, and protects against cartilage destruction in a rat OA model.

The CRD of Frizzled 7 exhibits chondroprotective effects in osteoarthritis via inhibition of the canonical Wnt3a/β-catenin signaling pathway

Osteoarthritis (OA) is a chronic inflammatory joint disease without effective drugs. Frizzled 7 (FzD7) binds its ligand Wnt3a through an extracellular cysteine-rich domain (CRD) to transduce the canonical Wnt/β-catenin signaling pathway, which has been strongly implicated in OA pathogenesis. Effects of recombinant protein of FzD7 CRD on Wnt/β-catenin signaling and chondral destruction was evaluated in this study. Firstly, increased protein levels of FzD7, Wnt3a and β-catenin were detected in human OA cartilage implying that the canonical Wnt/β-catenin signaling mediated by Wnt3a and FzD7 executes an essential role in OA. Then we showed that FzD7 CRD antagonized the Wnt3a/β-catenin signaling pathway in a dose-dependent manner by binding Wnt3a. In addition, FzD7 CRD increased the expression of glycosaminoglycans (GAGs), Collagen II, aggrecan and reduced the expression of matrix metalloproteinase (MMP)-1, MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs 5 (ADAMTS-5) in Wnt3a-stimulated human chondrocytes. Furthermore, a single intra-articular injection of the FzD7 CRD was efficacious in destabilization of the medial meniscus (DMM) mouse OA model, significantly improving Osteoarthritis Research Society International (OARSI) histology scores compared to mice treated with PBS. The results indicate that the FzD7 CRD exhibits chondroprotective effects by binding Wnt3a to suppress the Wnt3a/β-catenin signaling. Targeting the FzD7 CRD may be a novel therapy for the treatment of OA.

Secreted Frizzled-related proteins (sFRPs) in osteo-articular diseases: much more than simple antagonists of Wnt signaling?

Osteo-articular diseases are characterized by a dysregulation of joint and/or bone homeostasis. These include diseases affecting the joints originally, such as osteoarthritis and rheumatoid arthritis, or the bone, such as osteoporosis. Inflammation and the involvement of Wingless-related integration site (Wnt) signaling pathways are key pathophysiological features of these diseases resulting in tissue degradation by matrix-degrading enzymes, namely matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinases with thrombospondin motifs (ADAMTs), secreted by the joint resident cells and/or by infiltrating immune cells. Activation of Wnt signaling pathways is modulated by different families of proteins, including Dickkopfs and the secreted Frizzled-related proteins (sFRPs). The sFRP family is composed of five secreted glycoproteins in mammals that regulate Wnt signaling in the extracellular compartment. Indeed, sFRPs are able to bind both to the soluble Wnt ligands and to their cell membrane receptors, the Frizzled proteins. Their expression profile is altered in osteo-articular diseases, suggesting that they could account for the abnormal activation of Wnt pathways. In the present article, we review how sFRPs are more than simple antagonists of the Wnt signaling pathways and discuss their pathophysiological relevance in the context of osteo-articular diseases. We detail their Wnt-dependent and their Wnt-independent roles, with a particular emphasis on their ability to modulate the inflammatory response and extracellular matrix (ECM) remodeling. We also discuss their potential therapeutic use with a focus on bone remodeling, osteo-articular cancers, and tissue engineering.

Rosa canina - Rose hip pharmacological ingredients and molecular mechanics counteracting osteoarthritis - A systematic review

BACKGROUND

The successful use of rose hip for the treatment of osteoarthritis is well documented. Several randomized placebo controlled double-blind studies, as mono or combination therapy, have demonstrated treatment efficacy as well as excellent tolerability.

PURPOSE

This review focuses on the molecular mechanism underlying the clinical effects of rose hip in osteoarthritis (OA).

METHODS

The database Medline was screened - using the search term "Rosa canina" or "rose hip" - for publications on pharmacological or mechanistic studies with relevance to OA; in addition for findings on pharmacologically active constituents as well as clinical studies. The screening results were complemented by following-up on cited literature.

RESULTS

In particular, 24 pharmacological studies on Rosa canina or preparations thereof were considered relevant. Potent antioxidant radical scavenging effects are well documented for numerous rose hip constituents besides Vitamin C. Furthermore, anti-inflammatory activities include the reduction of pro-inflammatory cytokines and chemokines, reduction of NF-kB signaling, inhibition of pro-inflammatory enzymes, including COX1/2, 5-LOX and iNOS, reduction of C-reactive protein levels, reduction of chemotaxis and chemoluminescence of PMNs, and an inhibition of pro-inflammatory metalloproteases.

CONCLUSION

The antioxidant and anti-inflammatory effects of Rosa canina match its clinical action - especially considering new findings on the pharmacological disease pattern of OA. The entirety of several compounds including phenolics, terpenoids, galactolipids, carotenoids, fruit acids and fatty oils can be considered responsible for the observed pharmacological and clinical effects. Further research is needed to eludicate how and in which manner single rose hip compounds interact with their molecular pharmacological targets.

Dopamine-melanin nanoparticles scavenge reactive oxygen and nitrogen species and activate autophagy for osteoarthritis therapy

Anti-oxidative agents hold great potential in osteoarthritis (OA) therapy. However, most radical scavengers have poor biocompatibility and potential cytotoxicity, which limit their applications. Herein we explore dopamine melanin (DM) nanoparticles as a novel scavenger of reactive oxygen species (ROS) and reactive nitrogen species (RNS). DM nanoparticles show low cytotoxicity and a strong ability to sequester a broad range of ROS and RNS, including superoxides, hydroxyl radicals, and peroxynitrite. This translates to excellent anti-inflammatory and chondro-protective effects by inhibiting intracellular ROS and RNS and promoting antioxidant enzyme activities. With an average diameter of 112.5 nm, DM nanoparticles can be intra-articularly (i.a.) injected into an affected joint and retained at the injection site. When tested in vivo in rodent OA models, DM nanoparticles showed diminished inflammatory cytokine release and reduced proteoglycan loss, which in turn slowed down cartilage degradation. Mechanistic studies suggest that DM nanoparticles also enhance autophagy that benefits OA control. In summary, our study suggests DM nanoparticles as a safe and promising therapeutic for OA.

Hyperphysiological compression of articular cartilage induces an osteoarthritic phenotype in a cartilage-on-a-chip model

Owing to population aging, the social impact of osteoarthritis (OA)-the most common musculoskeletal disease-is expected to increase dramatically. Yet, therapy is still limited to palliative treatments or surgical intervention, and disease-modifying OA (DMOA) drugs are scarce, mainly because of the absence of relevant preclinical OA models. Therefore, in vitro models that can reliably predict the efficacy of DMOA drugs are needed. Here, we show, using a newly developed microphysiological cartilage-on-a-chip model that enables the application of strain-controlled compression to three-dimensional articular cartilage microtissue, that a 30% confined compression recapitulates the mechanical factors involved in OA pathogenesis and is sufficient to induce OA traits. Such hyperphysiological compression triggers a shift in cartilage homeostasis towards catabolism and inflammation, hypertrophy, and the acquisition of a gene expression profile akin to those seen in clinical osteoarthritic tissue. The cartilage on-a-chip model may enable the screening of DMOA candidates.

Wnt and RUNX2 mediate cartilage breakdown by osteoarthritis synovial fibroblast-derived ADAMTS-7 and -12

Failure of therapeutic approaches for the treatment of osteoarthritis (OA) based on the inhibition of metalloproteinases, might be because of their constitutive expression in homeostasis, together with their network complexity. The knowledge of this network would contribute to selective target pathological conditions. In this sense, blockade of mediators produced by neighbouring joint cells, such as synovial fibroblasts (SF), would prevent cartilage damage. Thus, we studied the contribution of ADAMTS-7 and -12 from SF to cartilage oligomeric matrix protein (COMP) degradation, and the signalling pathways involved in their expression. We report for the first time in SF, the involvement of ERK-Runx2 axis and Wnt/β-catenin signalling in ADAMTS-12 and ADAMTS-7 expressions, respectively, with the subsequent consequences in COMP degradation from cartilage extracellular matrix. After stimulation with IL-1β or fibronectin fragments, we showed that ERK inhibition decreased Runx2 activation and ADAMTS-12 expression in OA-SF, also reducing Fn-fs-induced COMP degradation. Blockage of Wnt signalling by DKK1 reduced ADAMTS-7 and COMP degradation in OA-SF as well. In addition, Wnt7B expression was induced by IL-1β and by itself, also increasing ADAMTS-7. Our results could contribute to the development of disease-modifying OA drugs targeting ADAMTS-7 and -12 for the prevention of extracellular matrix components degradation like COMP.

Research of Pathogenesis and Novel Therapeutics in Arthritis

Arthritis has a high prevalence globally and includes over 100 types, the most common of which are rheumatoid arthritis, osteoarthritis, psoriatic arthritis and inflammatory arthritis. The exact etiology of arthritis remains unclear and no cure exists. Anti-inflammatory drugs are commonly used in the treatment of arthritis, but are associated with significant side effects. Novel modes of therapy and additional prognostic biomarkers are urgently needed for these patients. In this editorial, the twenty articles published in the Special Issue Research of Pathogenesis and Novel Therapeutics in Arthritis 2019 are summarized and discussed as part of the global picture of the current understanding of arthritis.

Glucocorticoid signaling and osteoarthritis

Glucocorticoids are steroid hormones synthesized and released by the adrenal cortex. Their main function is to maintain cell homeostasis through a variety of signaling pathways, responding to changes in an organism's environment or developmental status. Mimicking the actions of natural glucocorticoids, synthetic glucocorticoids have been recruited to treat many diseases that implicate glucocorticoid receptor signaling such as osteoarthritis. In osteoarthritis, synthetic glucocorticoids aim to alleviate inflammation and pain. The variation of patients' response and the possibility of complications associated with their long-term use have led to a need for a better understanding of glucocorticoid receptor signaling in osteoarthritis. In this review, we performed a literature search in the molecular pathways that link the osteoarthritic joint to the glucocorticoid receptor signaling. We hope that this information will advance research in the field and propose new molecular targets for the development of more optimized therapies for osteoarthritis.

Systematic Analysis of Transcriptomic Profile of Chondrocytes in Osteoarthritic Knee Using Next-Generation Sequencing and Bioinformatics

The phenotypic change of chondrocytes and the interplay between cartilage and subchondral bone in osteoarthritis (OA) has received much attention. Structural changes with nerve ingrowth and vascular penetration within OA cartilage may contribute to arthritic joint pain. The aim of this study was to identify differentially expressed genes and potential miRNA regulations in OA knee chondrocytes through next-generation sequencing and bioinformatics analysis. Results suggested the involvement of SMAD family member 3 (SMAD3) and Wnt family member 5A (WNT5A) in the growth of blood vessels and cell aggregation, representing features of cartilage damage in OA. Additionally, 26 dysregulated genes with potential miRNA⁻mRNA interactions were identified in OA knee chondrocytes. Myristoylated alanine rich protein kinase C substrate (MARCKS), epiregulin (EREG), leucine rich repeat containing 15 (LRRC15), and phosphodiesterase 3A (PDE3A) expression patterns were similar among related OA cartilage, subchondral bone and synovial tissue arrays in Gene Expression Omnibus database. The Ingenuity Pathway Analysis identified MARCKS to be associated with the outgrowth of neurite, and novel miRNA regulations were proposed to play critical roles in the pathogenesis of the altered OA knee joint microenvironment. The current findings suggest new perspectives in studying novel genes potentially contributing to arthritic joint pain in knee OA, which may assist in finding new targets for OA treatment.

The Role of Wnt Pathway in the Pathogenesis of OA and Its Potential Therapeutic Implications in the Field of Regenerative Medicine

Introduction

Osteoarthritis (OA) is a degenerative joint disease characterized by articular cartilage degradation, subchondral damage, and bone remodelling, affecting most commonly weight-bearing joints, such as the knee and hip. The loss of cartilage leads to joint space narrowing, pain, and loss of function which could ultimately require total joint replacement. The Wnt/β catenin pathway is involved in the pathophysiology of OA and has been proposed as a therapeutic target. Endogenous and pharmacological inhibitors of this pathway were recently investigated within innovative therapies including the use of platelet-rich plasma (PRP) and mesenchymal stem cells (MSCs).

Methods

A review of the literature was performed on the PubMed database based on the following inclusion criteria: article written in English language in the last 20 years and dealing with (1) the role of Wnt-β catenin pathway in the pathogenesis of osteoarthritis and (2) pharmacologic or biologic strategies modulating the Wnt-β catenin pathway in the OA setting.

Results

Evidences support that Wnt signalling pathway is likely linked to OA progression and severity. Its inhibition through natural antagonists and new synthetic or biological drugs shares the potential to improve the clinical condition of the patients by affecting the pathological activity of Wnt/β-catenin signalling.

Conclusions

While further research is needed to better understand the mechanisms regulating the molecular interaction between OA regenerative therapies and Wnt, it seems that biologic therapies for OA exert modulation on Wnt/β catenin pathway that might be relevant in achieving the beneficial clinical effect of those therapeutic strategies.

Interleukin-1β signaling in osteoarthritis - chondrocytes in focus

Osteoarthritis (OA) can be regarded as a chronic, painful and degenerative disease that affects all tissues of a joint and one of the major endpoints being loss of articular cartilage. In most cases, OA is associated with a variable degree of synovial inflammation. A variety of different cell types including chondrocytes, synovial fibroblasts, adipocytes, osteoblasts and osteoclasts as well as stem and immune cells are involved in catabolic and inflammatory processes but also in attempts to counteract the cartilage loss. At the molecular level, these changes are regulated by a complex network of proteolytic enzymes, chemokines and cytokines (for review: [1]). Here, interleukin-1 signaling (IL-1) plays a central role and its effects on the different cell types involved in OA are discussed in this review with a special focus on the chondrocyte.

Therapeutics in Osteoarthritis Based on an Understanding of Its Molecular Pathogenesis

Osteoarthritis (OA) is the most prevalent joint disease in older people and is characterized by the progressive destruction of articular cartilage, synovial inflammation, changes in subchondral bone and peri-articular muscle, and pain. Because our understanding of the aetiopathogenesis of OA remains incomplete, we haven’t discovered a cure for OA yet. This review appraises novel therapeutics based on recent progress in our understanding of the molecular pathogenesis of OA, including pro-inflammatory and pro-catabolic mediators and the relevant signalling mechanisms. The changes in subchondral bone and peri-articular muscle accompanying cartilage damage are also reviewed.

The Effects of the WNT-Signaling Modulators BIO and PKF118-310 on the Chondrogenic Differentiation of Human Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are multipotent cells, mainly from bone marrow, and an ideal source of cells in bone and cartilage tissue engineering. A study of the chondrogenic differentiation of MSCs is of particular interest for MSCs-based cartilage regeneration. In this study, we aimed to optimize the conditions for the chrondogenic differentiation of MSCs by regulating WNT signaling using the small molecule WNT inhibitor PKF118-310 and activator BIO. Human mesenchymal stem cells (hMSCs) were isolated from bone marrow aspirates and cultured in hMSCs proliferation medium. Pellet culture was subsequently established for three-dimensional chondrogenic differentiation of 5 weeks. WNT signaling was increased by the small molecule glycogen synthase kinase-3 inhibitor 6-bromoindirubin-3-oxim (BIO) and decreased by the WNT inhibitor PKF118-310 (PKF). The effects of BIO and PKF on the chondrogenesis of hMSCs was examined by real-time PCR, histological methods, and ELISA. We found that activation of canonical WNT-signaling by BIO significantly downregulated the expression of cartilage-specific genes SOX9, COL2A1, and ACAN, and matrix metalloproteinase genes MMP1/3/9/13, but increased ADAMTS 4/5. Inhibition of WNT signaling by PKF increased the expression of SOX9, COL2A1, ACAN, and MMP9, but decreased MMP13 and ADAMTS4/5. In addition, a high level of WNT signaling induced the expression of hypertrophic markers COL10A1, ALPL, and RUNX2, the dedifferentiation marker COL1A1, and glycolysis genes GULT1 and PGK1. Deposition of glycosaminoglycan (GAG) and collagen type II in the pellet matrix was significantly lost in the BIO-treated group and increased in the PKF-treated group. The protein level of COL10A1 was also highly induced in the BIO group. Interestingly, BIO decreased the number of apoptotic cells while PKF significantly induced apoptosis during chondrogenesis. The natural WNT antagonist DKK1 and the protein level of MMP1 in the pellet culture medium were decreased after PKF treatment. All of these chondrogenic effects appeared to be mediated through the canonical WNT signaling pathway, since the target gene Axin2 and other WNT members, such as TCF4 and β-catenin, were upregulated by BIO and downregulated by PKF, respectively, and BIO induced nuclear translocation of β-catenin while PKF inhibited β-catenin translocation into the nucleus. We concluded that addition of BIO to a chondrogenic medium of hMSCs resulted in a loss of cartilage formation, while PKF induced chondrogenic differentiation and cartilage matrix deposition and inhibited hypertrophic differentiation. However, BIO promoted cell survival by inhibiting apoptosis while PKF induced cell apoptosis. This result indicates that either an overexpression or overinhibition of WNT signaling to some extent causes harmful effects on chondrogenic differentiation. Cartilage tissue engineering could benefit from the adjustment of the critical level of WNT signaling during chondrogenesis of hMSC.