Inhibition of TAK1 and/or JAK can rescue impaired chondrogenic differentiation of human mesenchymal stem cells in osteoarthritis-like conditions

Notopterol mitigates IL-1β-triggered pyroptosis by blocking NLRP3 inflammasome via the JAK2/NF-kB/hsa-miR-4282 route in osteoarthritis

Objective

Osteoarthritis (OA), the most prevalent form of arthritis, impacts approximately 10% of men and 18% of women aged above 60 years. Currently, a complete cure for OA remains elusive, making clinical management challenging. The traditional Chinese herb Notopterygium incisum, integral to the Juanbi pill for rheumatism, shows promise in safeguarding chondrocytes through its strong anti-inflammatory effects.

Methods

To explore the protective effect of notopterol and miRNA (has-miR-4248) against inflammation, we simulated an inflammatory environment in chondrocytes cell lines C20A4 and C28/12, focusing on inflammasome formation and pyroptosis.

Results

Our finding indicates notopterol significantly reduced interleukin (IL)-18 and tumor necrosis factor (TNF)-alpha levels in inflamed cells, curtailed reactive oxygen species (ROS) production post-inflammation, and inhibited the JAK2/STAT3 signaling pathway, thus offering chondrocytes protection from inflammation. Importantly, notopterol also hindered inflammasome assembly and pyroptosis by blocking the NF-κB/NLRP3 pathway through hsa-miR-4282 modulation. In vivo experiments showed that notopterol treatment markedly decreased Osteoarthritis Research Society International (OARSI) scores in OA mice and boosted hsa-miR-4282 expression compared to control groups.

Conclusions

This study underscores notopterol's potential as a therapeutic agent in OA treatment, highlighting its capacity to shield cartilage from inflammation-induced damage, particularly by preventing pyroptosis.

Mechanical stress and inflammation have opposite effects on Wnt signaling in human chondrocytes

Dysregulation of Wingless and Int-1 (Wnt) signaling has been strongly associated with development and progression of osteoarthritis (OA). Here, we set out to investigate the independent effects of either mechanical stress (MS) or inflammation on Wnt signaling in human neocartilage pellets, and to relate this Wnt signaling to OA pathophysiology. OA synovium-conditioned media (OAS-CM) was collected after incubating synovium from human end-stage OA joints for 24 h in medium. Cytokine levels in the OAS-CM were determined with a multiplex immunoassay (Luminex). Human neocartilage pellets were exposed to 20% MS, 2% OAS-CM or 1 ng/mL Interleukin-1β (IL-1β). Effects on expression levels of Wnt signaling members were determined by reverse transcription-quantitative polymerase chain reaction. Additionally, the expression of these members in articular cartilage from human OA joints was analyzed in association with joint space narrowing (JSN) and osteophyte scores. Protein levels of IL-1β, IL-6, IL-8, IL-10, tumor necrosis factor α, and granulocyte-macrophage colony-stimulating factor positively correlated with each other. MS increased noncanonical WNT5A and FOS expression. In contrast, these genes were downregulated upon stimulation with OAS-CM or IL-1β. Furthermore, Wnt inhibitors DKK1 and FRZB decreased in response to OAS-CM or IL-1β exposure. Finally, expression of WNT5A in OA articular cartilage was associated with increased JSN scores, but not osteophyte scores. Our results demonstrate that MS and inflammatory stimuli have opposite effects on canonical and noncanonical Wnt signaling in human neocartilage. Considering the extent to which MS and inflammation contribute to OA in individual patients, we hypothesize that targeting specific Wnt pathways offers a more effective, individualized approach.

METTL3 promotes SMSCs chondrogenic differentiation by targeting the MMP3, MMP13, and GATA3

Objective

Synovium-derived mesenchymal stem cells (SMSCs) are multipotential non-hematopoietic progenitor cells that can differentiate into various mesenchymal lineages in adipose and bone tissue, especially in chondrogenesis. Post-transcriptional methylation modifications are relative to the various biological development procedures. N⁶-methyladenosine (m⁶A) methylation has been identified as one of the abundant widespread post-transcriptional modifications. However, the connection between the SMSCs differentiation and m⁶A methylation remains unknown and needs further exploration.

Methods

SMSCs were derived from synovial tissues of the knee joint of male Sprague-Dawley (SD) rats. In the chondrogenesis of SMSCs, m⁶A regulators were detected by quantitative real-time PCR (RT-PCR) and Western blot (WB). We observed the situation that the knockdown of m⁶A "writer" protein methyltransferase-like (METTL)3 in the chondrogenesis of SMSCs. We also mapped the transcript-wide m⁶A landscape in chondrogenic differentiation of SMSCs and combined RNA-seq and MeRIP-seq in SMSCs by the interference of METTL3.

Results

The expression of m⁶A regulators were regulated in the chondrogenesis of SMSCs, only METTL3 is the most significant factor. In addition, after the knockdown of METTL3, MeRIP-seq and RNA-seq technology were applied to analyze the transcriptome level in SMSCs. 832 DEGs displayed significant changes, consisting of 438 upregulated genes and 394 downregulated genes. DEGs were enriched in signaling pathways regulating the glycosaminoglycan biosynthesis-chondroitin sulfate/dermatan sulfate and ECM-receptor interaction via Kyoto Encyclopedia of genes and genomes (KEGG) pathway enrichment analysis. The findings of this study indicate a difference in transcripts of MMP3, MMP13, and GATA3 containing consensus m⁶A motifs required for methylation by METTL3. Further, the reduction of METTL3 decreased the expression of MMP3, MMP13, and GATA3.

Conclusion

These findings confirm the molecular mechanisms of METTL3-mediated m⁶A post-transcriptional change in the modulation of SMSCs differentiating into chondrocytes, thus highlighting the potential therapeutic effect of SMSCs for cartilage regeneration.

Intra-articular Administration of Triamcinolone Acetonide in a Murine Cartilage Defect Model Reduces Inflammation but Inhibits Endogenous Cartilage Repair

BACKGROUND

Cartilage defects result in joint inflammation. The presence of proinflammatory factors has been described to negatively affect cartilage formation.

PURPOSE

To evaluate the effect and timing of administration of triamcinolone acetonide (TAA), an anti-inflammatory drug, on cartilage repair using a mouse model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A full-thickness cartilage defect was created in the trochlear groove of 10-week-old male DBA/1 mice (N = 80). Mice received an intra-articular injection of TAA or saline on day 1 or 7 after induction of the defect. Mice were euthanized on days 10 and 28 for histological evaluation of cartilage defect repair, synovial inflammation, and synovial membrane thickness.

RESULTS

Mice injected with TAA had significantly less synovial inflammation at day 10 than saline-injected mice independent of the time of administration. At day 28, the levels of synovitis dropped toward healthy levels; nevertheless, the synovial membrane was thinner in TAA- than in saline-injected mice, reaching statistical significance in animals injected on day 1 (70.1 ± 31.9 µm vs 111.9 ± 30.9 µm, respectively; P = .01) but not in animals injected on day 7 (68.2 ± 21.86 µm vs 90.2 ± 21.29 µm, respectively; P = .26). A thinner synovial membrane was moderately associated with less filling of the defect after 10 and 28 days (r = 0.42, P = .02; r = 0.47, P = .01, respectively). Whereas 10 days after surgery there was no difference in the area of the defect filled and the cell density in the defect area between saline- and TAA-injected knees, filling of the defect at day 28 was lower in TAA- than in saline-injected knees for both injection time points (day 1 injection, P = .04; day 7 injection, P = .01). Moreover, there was less collagen type 2 staining in the filled defect area in TAA- than in saline-injected knees after 28 days, reaching statistical significance in day 1-injected knees (2.6% vs 18.5%, respectively; P = .01) but not in day 7-injected knees (7.4% vs 15.8%, respectively; P = .27).

CONCLUSION

Intra-articular injection of TAA reduced synovial inflammation but negatively affected cartilage repair. This implies that inhibition of inflammation may inhibit cartilage repair or that TAA has a direct negative effect on cartilage formation.

CLINICAL RELEVANCE

Our findings show that TAA can inhibit cartilage defect repair. Therefore, we suggest not using TAA to reduce inflammation in a cartilage repair setting.

Targeting Janus Kinase (JAK) for Fighting Diseases: The Research of JAK Inhibitor Drugs

Janus Kinase (JAK), a nonreceptor protein tyrosine kinase, has emerged as an excellent target through research and development since its discovery in the 1990s. As novel small-molecule targeted drugs, JAK inhibitor drugs have been successfully used in the treatment of rheumatoid arthritis (RA), myofibrosis (MF) and ulcerative colitis (UC). With the gradual development of JAK targets in the market, JAK inhibitors have also received very considerable feedback in the treatment of autoimmune diseases such as atopic dermatitis (AD), Crohn's disease (CD) and graft-versus host disease (GVHD). This article reviews the research progress of JAK inhibitor drugs: introducing the existing JAK inhibitors on the market and some JAK inhibitors in clinical trials currently. In addition, the synthesis of various types of JAK inhibitors were summarized, and the effects of different drug structures on drug inhibition and selectivity.

The potential roles of JAK/STAT signaling in the progression of osteoarthritis

Osteoarthritis (OA) is an age-related chronic progressive degenerative disease that induces persistent pain and disabilities. The development of OA is a complex process, and the risk factors are various, including aging, genetics, trauma and altered biomechanics. Inflammation and immunity play an important role in the pathogenesis of OA. JAK/STAT pathway is one of the most prominent intracellular signaling pathways, regulating cell proliferation, differentiation, and apoptosis. Inflammatory factors can act as the initiators of JAK/STAT pathway, which is implicated in the pathophysiological activity of chondrocyte. In this article, we provide a review on the importance of JAK/STAT pathway in the pathological development of OA. Potentially, JAK/STAT pathway becomes a therapeutic target for managing OA.

Tofacitinib Blocks Entheseal Lymphocyte Activation and Modulates MSC Adipogenesis, but Does Not Directly Affect Chondro- and Osteogenesis

Entheseal spinal inflammation and new bone formation with progressive ankylosis may occur in ankylosing spondylitis (AS) and psoriatic arthritis (PsA). This study evaluated whether JAK inhibition with tofacitinib modulated the key disease associated cytokines, TNF and IL-17A, and whether tofacitinib also modulated bone marrow stromal cell-derived mesenchymal stem cell (MSCs) function, including osteogenesis, since post inflammation new bone formation occurs under these conditions. Methods: Conventional entheseal derived αβ CD4+ and CD8+ T-cells were investigated following anti-CD3/CD28 bead stimulation to determine IL-17A and TNF levels in tofacitinib treated (1000 nM) peri-entheseal bone (PEB) and peripheral blood mononuclear cells (PBMC) using ELISA. Bone marrow stromal cell-derived mesenchymal stem cell (MSC) colony forming units (CFU-F) and multi-lineage potential were evaluated using tofacitinib (dosages ranging between 100, 500, 1000 and 10,000 nM). Results: Induced IL-17A and TNF cytokine production from both entheseal CD4+ T-cells and CD8+ T-cells was effectively inhibited by tofacitinib. Tofacitinib treatment did not impact on CFU-F potential or in vitro chondro- and osteogenesis. However, tofacitinib stimulation increased MSC adipogenic potential with greater Oil Red O stained areas. Conclusion: Inducible IL-17A and TNF production by healthy human entheseal CD4+ and CD8+ T-cells was robustly inhibited in vitro by tofacitinib. However, tofacitinib did not impact MSC osteogenesis, but stimulated in vitro MSC adipogenesis, the relevance of which needs further evaluation given that the adipocytes are associated with new bone formation in SpA.

Osteoarthritis-Related Inflammation Blocks TGF-β's Protective Effect on Chondrocyte Hypertrophy via (de)Phosphorylation of the SMAD2/3 Linker Region

Osteoarthritis (OA) is a degenerative joint disease characterized by irreversible cartilage damage, inflammation and altered chondrocyte phenotype. Transforming growth factor-β (TGF-β) signaling via SMAD2/3 is crucial for blocking hypertrophy. The post-translational modifications of these SMAD proteins in the linker domain regulate their function and these can be triggered by inflammation through the activation of kinases or phosphatases. Therefore, we investigated if OA-related inflammation affects TGF-β signaling via SMAD2/3 linker-modifications in chondrocytes. We found that both Interleukin (IL)-1β and OA-synovium conditioned medium negated SMAD2/3 transcriptional activity in chondrocytes. This inhibition of TGF-β signaling was enhanced if SMAD3 could not be phosphorylated on Ser213 in the linker region and the inhibition by IL-1β was less if the SMAD3 linker could not be phosphorylated at Ser204. Our study shows evidence that inflammation inhibits SMAD2/3 signaling in chondrocytes via SMAD linker (de)-phosphorylation. The involvement of linker region modifications may represent a new therapeutic target for OA.

Regeneration of Damaged Tendon-Bone Junctions (Entheses)-TAK1 as a Potential Node Factor

Musculoskeletal dysfunctions are highly prevalent due to increasing life expectancy. Consequently, novel solutions to optimize treatment of patients are required. The current major research focus is to develop innovative concepts for single tissues. However, interest is also emerging to generate applications for tissue transitions where highly divergent properties need to work together, as in bone-cartilage or bone-tendon transitions. Finding medical solutions for dysfunctions of such tissue transitions presents an added challenge, both in research and in clinics. This review aims to provide an overview of the anatomical structure of healthy adult entheses and their development during embryogenesis. Subsequently, important scientific progress in restoration of damaged entheses is presented. With respect to enthesis dysfunction, the review further focuses on inflammation. Although molecular, cellular and tissue mechanisms during inflammation are well understood, tissue regeneration in context of inflammation still presents an unmet clinical need and goes along with unresolved biological questions. Furthermore, this review gives particular attention to the potential role of a signaling mediator protein, transforming growth factor beta-activated kinase-1 (TAK1), which is at the node of regenerative and inflammatory signaling and is one example for a less regarded aspect and potential important link between tissue regeneration and inflammation.

Improving Cell Therapy Survival and Anabolism in Harsh Musculoskeletal Disease Environments

Cell therapies are an up and coming technology in orthopedic medicine that has the potential to provide regenerative treatments for musculoskeletal disease. Despite numerous cell therapies showing preclinical success for common musculoskeletal indications of disc degeneration and osteoarthritis, there have been mixed results when testing these therapies in humans during clinical trials. A theory behind the mixed success of these cell therapies is that the harsh microenvironments of the disc and knee they are entering inhibit their anabolism and survival. Therefore, there is much ongoing research looking into how to improve the survival and anabolism of cell therapies within these musculoskeletal disease environments. This includes research into improving cell function under specific microenvironmental conditions known to exist in the intervertebral disc (IVD) and knee environment such as hypoxia, low-nutrient conditions, hyperosmolarity, acidity, and inflammation. This research also includes improving differentiation of cells into desired native cell phenotypes to better enhance their survival and anabolism in the knee and IVD. This review highlights the effects of specific musculoskeletal microenvironmental challenges on cell therapies and what research is being done to overcome these challenges. Impact statement While there has been significant clinical interest in using cell therapies for musculoskeletal pathologies in the knee and intervertebral disc, cell therapy clinical trials have had mixed outcomes. The information presented in this review includes the environmental challenges (i.e., acidic pH, inflammation, hyperosmolarity, hypoxia, and low nutrition) that cell therapies experience in these pathological musculoskeletal environments. This review summarizes studies that describe various approaches to improving the therapeutic capability of cell therapies in these harsh environments. The result is an overview of what approaches can be targeted and/or combined to develop a more consistent cell therapy for musculoskeletal pathologies.

Transforming Growth Factor β-Activated Kinase 1 Regulates Mesenchymal Stem Cell Proliferation Through Stabilization of Yap1/Taz Proteins

Bone marrow-derived mesenchymal stem cells (BMMSCs) are multipotent stem cells capable of differentiation into a variety of cell types, proliferation, and production of clinically useful secretory factors. These advantages make BMMSCs highly useful for cell transplantation therapy. However, the molecular network underlying BMMSC proliferation remains poorly understood. Here, we showed that TGFβ-activated kinase 1 (Tak1) is a critical molecule that regulates the activation of cell cycling and that Tak1 inhibition leads to quiescence in BMMSCs both in vivo and in vitro. Mechanistically, Tak1 was phosphorylated by growth factor stimulations, allowing it to bind and stabilize Yap1/Taz, which could then be localized to the nucleus. We also demonstrated that the quiescence induction by inhibiting Tak1 increased oxidized stress tolerance and improved BMMSC engraftment in intramuscular and intrabone marrow cell transplantation models. This study reveals a novel pathway controlling BMMSC proliferation and suggests a useful method to improve the therapeutic effect of BMMSC transplantation. Stem Cells 2019;37:1595-1605.

The Interaction between Joint Inflammation and Cartilage Repair

Background

Articular cartilage lesions occur frequently but unfortunately damaged cartilage has a very limited intrinsic repair capacity. Therefore, there is a high need to develop technology that makes cartilage repair possible. Since joint damage will lead to (sterile) inflammation, development of this technology has to take into account the effects of inflammation on cartilage repair.

Methods

A literature search has been performed including combinations of the following keywords; cartilage repair, fracture repair, chondrogenesis, (sterile) inflammation, inflammatory factors, macrophage, innate immunity, and a number of individual cytokines. Papers were selected that described how inflammation or inflammatory factors affect chondrogenesis and tissue repair. A narrative review is written based on these papers focusing on the role of inflammation in cartilage repair and what we can learn from findings in other organs, especially fracture repair.

Results

The relationship between inflammation and tissue repair is not straightforward. Acute, local inflammation stimulates fracture repair but appears to be deleterious for chondrogenesis and cartilage repair. Systemic inflammation has a negative effect on all sorts of tissue repair.

Conclusion

Findings on the role of inflammation in fracture repair and cartilage repair are not in line. The currently widely used models of chondrogenesis, using high differentiation factor concentrations and corticosteroid levels, are not optimal. To make it possible to draw more valid conclusions about the role of inflammation and inflammatory factors on cartilage repair, model systems must be developed that better mimic the real conditions in a joint with damaged cartilage.

The role of BMP6 in the proliferation and differentiation of chicken cartilage cells

Previous studies have indicated that bone morphogenetic protein (BMP) 6 may play an important role in skeletal system development and progression. However, the mechanism underlying the effects of BMP6 in cartilage cell proliferation and differentiation remains unknown. In this study, cartilage cells were isolated from shanks of chicken embryos and treated with different concentrations of Growth Hormone. Cell proliferation potential was assessed using real-time polymerase chain reaction (RT-PCR), western blotting and CCK-8 assays in vitro. The results showed that at 48 h, the Collagen II and BMP6 expression levels in 50 ng/μl GH-treated cartilage cells were significantly higher than in groups treated with 100 ng/μl or 200 ng/μl GH. We further observed that knockdown of BMP6 in cartilage cells led to significantly decreased expression mRNAs and proteins of Collagen II and Collagen X. Moreover, the suppression of BMP6 expression by a specific siRNA led to significantly decreased expression mRNA levels of IGF1R, JAK2, PKC, PTH, IHH and PTHrP and decreased protein levels of PKC, IHH and PTHrP. Taken together, our data suggest that BMP6 may play a critical role in chicken cartilage cell proliferation and differentiation through the regulation of IGF1, JAK2, PKC, PTH, and IHH-PTHrP signaling pathways.

The antiviral protein viperin regulates chondrogenic differentiation via CXCL10 protein secretion

Viperin (also known as radical SAM domain–containing 2 (RSAD2)) is an interferon-inducible and evolutionary conserved protein that participates in the cell's innate immune response against a number of viruses. Viperin mRNA is a substrate for endoribonucleolytic cleavage by RNase mitochondrial RNA processing (MRP) and mutations in the RNase MRP small nucleolar RNA (snoRNA) subunit of the RNase MRP complex cause cartilage-hair hypoplasia (CHH), a human developmental condition characterized by metaphyseal chondrodysplasia and severe dwarfism. It is unknown how CHH-pathogenic mutations in RNase MRP snoRNA interfere with skeletal development, and aberrant processing of RNase MRP substrate RNAs is thought to be involved. We hypothesized that viperin plays a role in chondrogenic differentiation. Using immunohistochemistry, real-time quantitative PCR, immunoblotting, ELISA, siRNA-mediated gene silencing, plasmid-mediated gene overexpression, label-free MS proteomics, and promoter reporter bioluminescence assays, we discovered here that viperin is expressed in differentiating chondrocytic cells and regulates their protein secretion and the outcome of chondrogenic differentiation by influencing transforming growth factor β (TGF-β)/SMAD family 2/3 (SMAD2/3) activity via C-X-C motif chemokine ligand 10 (CXCL10). Of note, we observed disturbances in this viperin–CXCL10–TGF-β/SMAD2/3 axis in CHH chondrocytic cells. Our results indicate that the antiviral protein viperin controls chondrogenic differentiation by influencing secretion of soluble proteins and identify a molecular route that may explain impaired chondrogenic differentiation of cells from individuals with CHH.

Interleukin 1 β-induced SMAD2/3 linker modifications are TAK1 dependent and delay TGFβ signaling in primary human mesenchymal stem cells

BACKGROUND

Chondrogenic differentiation of mesenchymal stem cells (MSC) requires transforming growth factor beta (TGFβ) signaling. TGFβ binds to the type I receptor activin-like kinase (ALK)5 and results in C-terminal SMAD2/3 phosphorylation (pSMAD2/3C). In turn pSMAD2/3C translocates to the nucleus and regulates target gene expression. Inflammatory mediators are known to exert an inhibitory effect on MSC differentiation. In this study we investigated the effect of interleukin 1 β (IL1β) on SMAD2/3 signaling dynamics and post-translational modifications.

RESULTS

Co-stimulation of MSC with TGFβ and IL1β did not affect peak pSMAD2C levels at 1h post-stimulation. Surprisingly, SMAD3 transcriptional activity, as determined by the CAGA₁₂-luciferase reporter construct, was enhanced by co-stimulation of TGFβ and IL1β compared to TGFβ alone. Furthermore, IL1β stimulation induced CAGA₁₂-luciferase activity in a SMAD dependent way. As SMAD function can be modulated independent of canonical TGFβ signaling through the SMAD linker domain, we studied SMAD2 linker phosphorylation at specific threonine and serine residues. SMAD2 linker threonine and serine modifications were observed within 1h following TGFβ, IL1β or TGFβ and IL1β stimulation. Upon co-stimulation linker modified SMAD2 accumulated in the cytoplasm and SMAD2/3 target gene transcription (ID1, JUNB) at 2-4h was inhibited. A detailed time course analysis of IL1β-induced SMAD2 linker modifications revealed a distinct temperospatial pattern compared to TGFβ. Co-stimulation with both factors resulted in a similar kinetic profile as TGFβ alone. Nevertheless, IL1β did subtly alter TGFβ-induced pSMAD2C levels between 8 and 24h post-stimulation, which was reflected by TGFβ target gene expression (PAI1, JUNB). Direct evidence for the importance of SMAD3 linker modifications for the effect of IL1β on TGFβ signaling was obtained by over-expression of SMAD3 or a SMAD3 linker phospho-mutant. Finally, an inhibitor screening was performed to identify kinases involved in SMAD2/3 linker modifications. We identified TAK1 kinase activity as crucial for IL1β-induced SMAD2 linker modifications and CAGA₁₂-luciferase activity.

CONCLUSIONS

TGFβ and IL1β signaling interact at the SMAD2/3 level in human primary MSC. Down-stream TGFβ target genes were repressed by IL1β independent of C-terminal SMAD2 phosphorylation. We demonstrate that SMAD2/3 linker modifications are required for this interplay and identified TAK1 as a crucial mediator of IL1β-induced TGFβ signal modulation.

IL37 dampens the IL1β-induced catabolic status of human OA chondrocytes

Objective

A crucial feature of OA is cartilage degradation. This process is mediated by pro-inflammatory cytokines, among other factors, via induction of matrix-degrading enzymes. Interleukin 37 (IL37) is an anti-inflammatory cytokine and is efficient in blocking the production of pro-inflammatory cytokines during innate immune responses. We hypothesize that IL37 is therapeutic in treating the inflammatory cytokine cascade in human OA chondrocytes and can act as a counter-regulatory cytokine to reduce cartilage degradation in OA.

Methods

Human OA cartilage was obtained from patients undergoing total knee or hip arthroplasty. Immunohistochemistry was applied to study IL37 protein expression in cartilage biopsies from OA patients. Induction of IL37 expression by IL1β, OA synovium-conditioned medium and TNFα was investigated in human OA chondrocytes. Adenoviral overexpression of IL37 followed by IL1β stimulation was performed to investigate the anti-inflammatory potential of IL37.

Results

IL37 expression was detected in cartilage biopsies of OA patients and induced by IL1β. After IL1β stimulation, increased IL1β, IL6 and IL8 expression was observed in OA chondrocytes. Elevated IL37 levels diminished the IL1β-induced IL1β , IL6 and IL8 gene levels and IL1β and IL8 protein levels. In addition to the reduction in pro-inflammatory cytokine expression, IL37 reduced MMP1 , MMP3 , MMP13 and disintegrin and metalloproteinase with thrombospondin motifs 5 gene levels and MMP3 and MMP13 protein levels.

Conclusion

IL37 is induced by IL1β, and IL37 itself reduced IL1β, IL6 and IL8 production, indicating that IL37 is able to induce a counter-regulatory anti-inflammatory feedback loop in chondrocytes. In addition, IL37 dampens catabolic enzyme expression. This supports IL37 as a potential therapeutic target in OA.

Transcriptional profiling distinguishes inner and outer annulus fibrosus from nucleus pulposus in the bovine intervertebral disc

BACKGROUND

Cells in the intervertebral disc have unique phenotypes and marker genes that separate the nucleus pulposus (NP), annulus fibrosus (AF) and articular cartilage (AC) have been identified. Recently, it was shown that phenotypic marker genes exhibit variable expression in humans. In this study, the bovine tail was used to determine the ability of marker genes to distinguish the outer and inner AF from NP tissue and isolated cells.

METHODS

Bovine tail intervertebral discs from 13 donors were dissected and correct isolation of tissue was confirmed. mRNA was isolated directly from tissue or passage 0 monolayer cells and used for gene expression measurements (qPCR). Conventional marker genes (bAcan, bCol1a1, bCol2a1) and novel marker genes (bAdamts17, bBrachyury/T, bCD24, bCol5a1, bCol12a1, bFoxf1, bKrt19, bPax1, bSfrp2) were evaluated.

RESULTS

As expected bAcan, bCol2a1 and bCol1a1 distinguished outer AF from NP tissue, while inner AF and NP could not be discriminated. The NP markers bT, bCd24 and bKrt19 were significantly higher expressed in NP than inner and outer AF tissue. bFoxF1 and bPax1 only distinguished IVD tissues from AC. The AF markers bAdamts17, bCol5a1, bCol12a1 and bSfrp2 were higher expressed in the outer AF compared with inner AF and NP tissue. Monolayer culturing strongly decreased bAcan, bCol2a1, bCD24 and bCol5a1 expression, while bCol1a1, bT, bKrt19 and bSfrp2 were not affected.

CONCLUSION

The IVD phenotypic marker genes bT, bKrt19, bSfrp2 and bCol12a1 convincingly distinguished NP from outer AF in situ and in vitro.

Inflammatory conditions partly impair the mechanically mediated activation of Smad2/3 signaling in articular cartilage

Background

Joint trauma, which is frequently related with mechanical overloading of articular cartilage, is a well-established risk for osteoarthritis (OA) development. Additionally, reports show that trauma leads to synovial joint inflammation. In consequence, after joint trauma, cartilage is influenced by deleterious excessive loading combined with the catabolic activity of proinflammatory mediators. Since the activation of TGF-β signaling by loading is considered to be a key regulatory pathway for maintaining cartilage homeostasis, we tested the effect of proinflammatory conditions on mechanically mediated activation of TGF-β/Smad2/3P signaling in cartilage.

Methods

Cartilage explants were subjected to dynamic mechanical compression in the presence of interleukin-1 beta (IL-1β) or osteoarthritic synovium-conditioned medium (OAS-CM). Subsequently, the activation of the Smad2/3P pathway was monitored with QPCR analysis of reporter genes and additionally the expression of receptors activating the Smad2/3P pathway was analyzed. Finally, the ability for mechanically mediated activation of Smad2/3P was tested in human OA cartilage.

Results

IL-1β presence during compression did not impair the upregulation of Smad2/3P reporter genes, however the results were affected by IL-1β-mediated upregulations in unloaded controls. OAS-CM significantly impaired the compression-mediated upregulation of bSmad7 and Tgbfb1. IL-1β suppressed the compression-mediated bAlk5 upregulation where 12 MPa compression applied in the presence of OAS-CM downregulated the bTgfbr2. Mechanically driven upregulation of Smad2/3P reporter genes was present in OA cartilage.

Conclusions

Proinflammatory conditions partly impair the mechanically mediated activation of the protective TGF-β/Smad2/3P pathway. Additionally, the excessive mechanical compression, applied in the presence of proinflammatory conditions diminishes the expression of the type II TGF-β receptor, a receptor critical for maintenance of articular cartilage.

TAK1 is involved in the autophagy process in retinal pigment epithelial cells

Autophagy is an evolutionarily conserved mechanism for degrading long-lived or malfunctioning proteins and organelles, such as those resulting from oxidative stress. Several publications have demonstrated the importance of the autophagy process in the pathophysiology of dry age-related macular degeneration (AMD). Still, the mechanism underlying this process and its involvement in dry AMD are not fully characterized. Investigating the autophagy process in retinal pigment epithelial (RPE) cells, we identified transforming growth factor β activated kinase 1 (TAK1) as a key player in the process. We found increased TAK1 phosphorylation in ARPE-19 and D407 cells treated with different inducers of autophagy, such as oxidative stress and rapamycin. Moreover, utilizing TAK1 specific inhibitor prior to oxidative stress or rapamycin treatment, we found significant reduction in LC3A/B-II expression. These results point at the involvement of TAK1 in the regulation of autophagy in RPE cells. This study suggests that aberrant activity of this kinase impairs autophagy and subsequently leads to alterations in the vitality of RPE cells. Proper activity of TAK1 may be essential for efficient autophagy, and crucial for the ability of RPE cells to respond to stress and dispose of damaged organelles, thus preventing or delaying retinal pathologies.

Emerging targets in osteoarthritis therapy

Osteoarthritis (OA) is a destructive joint disease in which the initiation may be attributed to direct injury and mechanical disruption of joint tissues, but the progressive changes are dependent on active cell-mediated processes that can be observed or inferred during the generally long time-course of the disease. Based on clinical observations and experimental studies, it is now recognized a that it is possible for individual patients to exhibit common sets of symptoms and structural abnormalities due to distinct pathophysiological pathways that act independently or in combination. Recent research that has focused on the underlying mechanisms involving biochemical cross talk among the cartilage, synovium, bone, and other joint tissues within a background of poorly characterized genetic factors will be addressed in this review.

Human osteoarthritic synovium impacts chondrogenic differentiation of mesenchymal stem cells via macrophage polarisation state

OBJECTIVE

Mesenchymal stem cells (MSCs) are a promising cell type for the repair of damaged cartilage in osteoarthritis (OA). However, OA synovial fluid and factors secreted by synovium impede chondrogenic differentiation of MSCs, and the mechanism responsible for this effect remains unclear. In this study, we sought to investigate whether M1 and M2 synovial macrophages can contribute to the inhibition of MSC chondrogenesis.

DESIGN

The constitution of synovial macrophage subsets was analysed by immunohistochemical staining of human OA synovium sections for CD86 (M1 marker) and CD206 (M2 marker). To assess the effect of synovial macrophages on chondrogenesis, collagen type II (COL2) and aggrecan (ACAN) gene expression were compared between MSCs undergoing chondrogenic differentiation in medium conditioned (CM) by human OA synovial explants, human synovial macrophages and fibroblasts, or peripheral blood derived primary human monocytes differentiated towards an M1 or M2 phenotype.

RESULTS

OA synovium contained both M1 and M2 macrophages. Medium conditioned by synovial macrophages (CD45 + plastic adherent cells) down-regulated chondrogenic gene expression by MSCs. Additionally, CM of M1 polarised monocytes significantly decreased COL2 and ACAN gene expression by MSCs; this effect was not observed for treatment with CM of M2 polarised monocytes.

CONCLUSION

MSC chondrogenesis is inhibited by OA synovium CM through factors secreted by synovial macrophages and our findings suggest that M1 polarised subsets are potential mediators of this anti-chondrogenic effect. Modulation of macrophage phenotype may serve as a beneficial strategy to maximise the potential of MSCs for efficient cartilage repair.