Biomechanical modulation of collagen fragment-induced anabolic and catabolic activities in chondrocyte/agarose constructs

Recombinant protein drugs-based intra articular drug delivery systems for osteoarthritis therapy

Osteoarthritis (OA) is the most prevalent chronic degenerative joint disease. It weakens the motor function of patients and imposes a significant economic burden on society. The current medications commonly used in clinical practice do not meet the need for the treatment of OA. Recombinant protein drugs (RPDs) can treat OA by inhibiting inflammatory pathways, regulating catabolism/anabolism, and promoting cartilage repair, thereby showing promise as disease-modifying OA drugs (DMOADs). However, the rapid clearance and short half-life of them in the articular cavity limit their clinical translation. Therefore, the reliable drug delivery systems for extending drug treatment are necessary for the further development. This review introduces RPDs with therapeutic potential for OA, and summarizes their research progress on related drug delivery systems, and make proper discussion on the certain keys for optimal development of this area.

Attenuative Effects of Platelet-Rich Plasma on 30 kDa Fibronectin Fragment-Induced MMP-13 Expression Associated with TLR2 Signaling in Osteoarthritic Chondrocytes and Synovial Fibroblasts

Proteolytic fragments of fibronectin can have catabolic effects on cartilage, menisci, and synovium. Previous studies have reported that Toll-like receptor (TLR) signaling pathways might be associated with joint inflammation and joint destruction. Platelet-rich plasma (PRP) is increasingly being used to treat a range of joint conditions; however, it has yet to be determined whether PRP influences fibronectin fragment (FN-f) procatabolic activity and TLRs. In this study, human primary culture cells were treated with 30 kDa FN-f with/without PRP co-incubation, and then analyzed using real-time PCR to determine gene expression levels in articular chondrocytes, meniscal fibrochondrocytes, and synovial fibroblasts. Protein levels were evaluated by Western immunoblotting. This study observed an increase in the protein expression of matrix metalloproteinases (MMPs), Toll-like receptor 2 (TLR2), nitric oxide synthase 2 (NOS2), prostaglandin-endoperoxide synthase (PTGS2), and cyclooxygenase 2 (COX2) in articular chondrocytes, meniscal fibrochondrocytes, and synovial fibroblasts following insult with 30 kDa FN-f. Upregulation of these genes was significantly attenuated by PRP treatment. TLR2 and matrix metalloproteinase 13 (MMP-13) were also significantly attenuated by cotreatment with 30 kDa FN-f + PRP + TLR2 inhibitor. PRP treatment was shown to attenuate the 30 kDa FN-f-induced MMP-13 expression associated with the decreased expression of TLR2 in osteoarthritic chondrocytes and synovial fibroblasts. PRP treatment was also shown to attenuate procatabolic activity associated with MMP-13 expression via the TLR2 signaling pathway.

Vorinostat ameliorates IL-1α-induced reduction of type II collagen by inhibiting the expression of ELF3 in chondrocytes

Osteoarthritis (OA) is a common joint disease that ultimately causes physical disability and imposes an economic burden on society. Cartilage destruction plays a key role in the development of OA. Vorinostat is an oral histone deacetylase (HDAC) inhibitor and has been used for the treatment of T-cell lymphoma. Previous studies have reported the anti-inflammatory effect of HDAC inhibitors in both in vivo and in vitro models. However, it is unknown whether vorinostat exerts a protective effect in OA. In this study, our results demonstrate that treatment with vorinostat prevents interleukin 1α (IL-1α)-induced reduction of type II collagen at both gene and protein levels. Treatment with vorinostat reduced the IL-1α-induced production of mitochondrial reactive oxygen species (ROS) in T/C-28a2 cells. Additionally, vorinostat rescued the IL-1α-induced decrease in the expression of the collagen type II a1 (Col2a1) gene and the expression of Sry-related HMG box 9 (SOX-9). Importantly, we found that vorinostat inhibited the expression of matrix metalloproteinase-13 (MMP-13), which is responsible for the degradation of type II collagen. Furthermore, vorinostat suppressed the expression of E74-like factor 3 (ELF3), which is a key transcription factor that plays a pivotal role in the IL-1α-induced reduction of type II collagen. Also, the overexpression of ELF3 abolished the protective effects of vorinostat against IL-1α-induced loss of type 2 collagen by inhibiting the expression of SOX-9 whilst increasing the expression of MMP-13. In conclusion, our findings suggest that vorinostat might prevent cartilage destruction by rescuing the reduction of type II collagen, mediated by the suppression of ELF3.

Intervertebral Disc Regeneration Injection of a Cell-Loaded Collagen Hydrogel in a Sheep Model

Degenerated intervertebral discs (IVDs) were treated with autologous adipose-derived stem cells (ASC) loaded into an injectable collagen scaffold in a sheep model to investigate the implant's therapeutic potential regarding the progression of degeneration of previously damaged discs. In this study, 18 merino sheep were subjected to a 3-step minimally invasive injury and treatment model, which consisted of surgically induced disc degeneration, treatment of IVDs with an ASC-loaded collagen hydrogel 6 weeks post-operatively, and assessment of the implant's influence on degenerative tissue changes after 6 and 12 months of grazing. Autologous ASCs were extracted from subcutaneous adipose tissue and cultivated in vitro. At the end of the experiment, disc heights were determined by µ-CT measurements and morphological tissue changes were histologically examined.Histological investigations show that, after treatment with the ASC-loaded collagen hydrogel implant, degeneration-specific features were observed less frequently. Quantitative studies of the degree of degeneration did not demonstrate a significant influence on potential tissue regeneration with treatment. Regarding disc height analysis, at both 6 and 12 months after treatment with the ASC-loaded collagen hydrogel implant a stabilization of the disc height can be seen. A complete restoration of the intervertebral disc heights however could not be achieved.The reported injection procedure describes in a preclinical model a translational therapeutic approach for degenerative disc diseases based on adipose-derived stem cells in a collagen hydrogel scaffold. Further investigations are planned with the use of a different injectable scaffold material using the same test model.

Articular Chondrocyte Phenotype Regulation through the Cytoskeleton and the Signaling Processes That Originate from or Converge on the Cytoskeleton: Towards a Novel Understanding of the Intersection between Actin Dynamics and Chondrogenic Function

Numerous studies have assembled a complex picture, in which extracellular stimuli and intracellular signaling pathways modulate the chondrocyte phenotype. Because many diseases are mechanobiology-related, this review asked to what extent phenotype regulators control chondrocyte function through the cytoskeleton and cytoskeleton-regulating signaling processes. Such information would generate leverage for advanced articular cartilage repair. Serial passaging, pro-inflammatory cytokine signaling (TNF-α, IL-1α, IL-1β, IL-6, and IL-8), growth factors (TGF-α), and osteoarthritis not only induce dedifferentiation but also converge on RhoA/ROCK/Rac1/mDia1/mDia2/Cdc42 to promote actin polymerization/crosslinking for stress fiber (SF) formation. SF formation takes center stage in phenotype control, as both SF formation and SOX9 phosphorylation for COL2 expression are ROCK activity-dependent. Explaining how it is molecularly possible that dedifferentiation induces low COL2 expression but high SF formation, this review theorized that, in chondrocyte SOX9, phosphorylation by ROCK might effectively be sidelined in favor of other SF-promoting ROCK substrates, based on a differential ROCK affinity. In turn, actin depolymerization for redifferentiation would “free-up” ROCK to increase COL2 expression. Moreover, the actin cytoskeleton regulates COL1 expression, modulates COL2/aggrecan fragment generation, and mediates a fibrogenic/catabolic expression profile, highlighting that actin dynamics-regulating processes decisively control the chondrocyte phenotype. This suggests modulating the balance between actin polymerization/depolymerization for therapeutically controlling the chondrocyte phenotype.

Molecular docking and molecular dynamics to identify collagenase inhibitors as lead compounds to address osteoarthritis

Osteoarthritis (OA) is a degenerative disease which affects a large number of individuals. Collagenases, which belong to a class of metalloproteases (MMPs), are responsible for the degradation of cartilage manifested in OA. Inhibition of the catalytic domains of these MMPs is one of the important therapeutic strategies proposed for the prevention of OA. The main objective of this work is to evaluate the binding of curcumin and its metabolites with the active sites of collagenases in comparison to standard inhibitors on the basis of our hypothesis that curcumin/metabolites could exhibit an inhibitory effect on MMPs. Here, we report the molecular docking analysis of curcumin and its metabolites with collagenases (MMP-1, MMP-8, MMP-13). Among the molecules tested, curcumin monoglucuronide (CMG) demonstrated the best binding affinity with MMP-13, which is specifically implicated in OA. The CMG-MMP-complexes were further subjected to molecular dynamic simulations to explore the stability of the complexes and to estimate the free binding energies. The results indicated that CMG preferentially bind to MMP-13 in comparison to that of MMP-1 and MMP-8 with binding free energies (ΔG_bind) of (-60.55), (-27.02) and (-46.91) kcal/mol, respectively. This is the first study which suggests that curcumin monoglucuronide can be considered as an effective lead compound to prevent the progression of OA.Communicated by Ramaswamy H. Sarma.

Osteoarthritis: Prognosis and emerging therapeutic approach for disease management

Osteoarthritis (OA), a disorder of joints, is prevalent in older age. The contemporary cure for OA is aimed to confer symptomatic relief, consisting of temporary pain and swelling relief. In this paper, we discuss various modalities responsible for the onset of OA and associated with its severity. Inhibition of chondrocytes receptors such as DDR2, SDF-1, Asporin, and CXCR4 by specific pharmacological inhibitors attenuates OA, a critical step for finding potential disease modifying drugs. We critically analyzed recent OA studies with an emphasis on intermediate target molecules for OA intervention. We also explored some novel and safe treatments for OA by considering disease prognosis crosstalk with cellular signaling pathways.

Mechanotransduction and Stiffness-Sensing: Mechanisms and Opportunities to Control Multiple Molecular Aspects of Cell Phenotype as a Design Cornerstone of Cell-Instructive Biomaterials for Articular Cartilage Repair

Since material stiffness controls many cell functions, we reviewed the currently available knowledge on stiffness sensing and elucidated what is known in the context of clinical and experimental articular cartilage (AC) repair. Remarkably, no stiffness information on the various biomaterials for clinical AC repair was accessible. Using mRNA expression profiles and morphology as surrogate markers of stiffness-related effects, we deduced that the various clinically available biomaterials control chondrocyte (CH) phenotype well, but not to equal extents, and only in non-degenerative settings. Ample evidence demonstrates that multiple molecular aspects of CH and mesenchymal stromal cell (MSC) phenotype are susceptible to material stiffness, because proliferation, migration, lineage determination, shape, cytoskeletal properties, expression profiles, cell surface receptor composition, integrin subunit expression, and nuclear shape and composition of CHs and/or MSCs are stiffness-regulated. Moreover, material stiffness modulates MSC immuno-modulatory and angiogenic properties, transforming growth factor beta 1 (TGF-β1)-induced lineage determination, and CH re-differentiation/de-differentiation, collagen type II fragment production, and TGF-β1- and interleukin 1 beta (IL-1β)-induced changes in cell stiffness and traction force. We then integrated the available molecular signaling data into a stiffness-regulated CH phenotype model. Overall, we recommend using material stiffness for controlling cell phenotype, as this would be a promising design cornerstone for novel future-oriented, cell-instructive biomaterials for clinical high-quality AC repair tissue.

Long non-coding RNA XIST promotes extracellular matrix degradation by functioning as a competing endogenous RNA of miR-1277-5p in osteoarthritis

Osteoarthritis (OA) is a common and troublesome disease among the elderly, and is characterized by extracellular matrix (ECM) degradation. The function of the long non‑coding RNA X‑inactive‑specific transcript (XIST) and its working mechanism in ECM degradation remains unclear. In the present study, XIST was revealed to be upregulated in OA specimens and in articular chondrocytes (ACs) derived from OA tissue (AC/OA) and interleukin‑1β (IL‑1β)‑treated ACs. Loss‑of‑function experiments demonstrated that downregulation of XIST suppressed the degradation of the ECM in AC/OA and AC/IL‑1β‑5.0 cells. Furthermore, XIST, matrix metalloproteinase 13 (MMP‑13) and ADAM metallopeptidase with thrombospondin type 1 motif 5 (ADAMTS5) were identified as targets of microRNA (miR)‑1277‑5p, and the reciprocal inhibitive effect between XIST and miR‑1277‑5p was elucidated. Furthermore, the role of XIST in ECM degradation was confirmed to be functioning as a competing endogenous RNA (ceRNA) of miR‑1277‑5p. Finally, the protective effect of the downregulation of XIST on ECM degradation was verified in an OA rat model. In conclusion, the present study suggests that XIST promotes MMP‑13 and ADAMTS5 expression, indicating ECM degradation, by functioning as a ceRNA of miR‑1277‑5p in OA. The present study proposed a novel potential target with a new working mechanism in molecular treating of OA.

New insights on the MMP-13 regulatory network in the pathogenesis of early osteoarthritis

Osteoarthritis (OA) is the most common joint disorder and affects approximately half of the aged population. Current treatments for OA are largely palliative until the articular cartilage has been deeply damaged and irreversible morphological changes appear. Thus, effective methods are needed for diagnosing and monitoring the progression of OA during its early stages when therapeutic drugs or biological agents are most likely to be effective. Various proteinases involved in articular cartilage degeneration in pre-OA conditions, which may represent the earliest reversible measurable changes, are considered diagnostic and therapeutic targets for early OA. Of these proteinases, matrix metalloproteinase 13 (MMP-13) has received the most attention, because it is a central node in the cartilage degradation network. In this review, we highlight the main MMP-13-related changes in OA chondrocytes, including alterations in the activity and expression level of MMP-13 by upstream regulatory factors, DNA methylation, various non-coding RNAs (ncRNAs), and autophagy. Because MMP-13 and its regulatory networks are suitable targets for the development of effective early treatment strategies for OA, we discuss the specific targets of MMP-13, including upstream regulatory proteins, DNA methylation, non-coding RNAs, and autophagy-related proteins of MMP-13, and their therapeutic potential to inhibit the development of OA. Moreover, the various entities mentioned in this review might be useful as early biomarkers and for personalized approaches to disease prevention and treatment by improving the phenotyping of early OA patients.

Elevation of IGFBP2 contributes to mycotoxin T-2-induced chondrocyte injury and metabolism

Kashin-Beck disease (KBD) is an endemic degenerative osteoarthropathy. The mycotoxin of T-2 toxin is extensively accepted as a major etiological contributor to KBD. However, its function and mechanism in KBD remains unclearly elucidated. Here, T-2 toxin treatment induced chondrocyte injury in a time- and dose-dependent manner by repressing cell viability and promoting cell necrosis and apoptosis. Importantly, T-2 suppressed the transcription of type II collagen and aggrecan, as well as the release of sulphated glycosaminoglycan (sGAG). Furthermore, exposure to T-2 enhanced the transcription of matrix metalloproteinases (MMPs), including MMP-1, -2, -3 and -9. In contrast to control groups, higher expression of insulin-like growth factor binding protein 2 (IGFBP2) was observed in chondrocytes from KBD patients. Interestingly, T-2 toxin caused a dramatical elevation of IGFBP2 expression in chondrocytes. Mechanism analysis corroborated that cessation of IGFBP2 expression alleviated T-2-induced damage to chondrocytes. Simultaneously, transfection with IGFBP2 siRNA also attenuated matrix synthesis and catabolism-related gene expressions of MMPs. Together, this study validated that T-2 toxin exposure might promote the progression of KBD by inducing chondrocyte injury, suppressing matrix synthesis and accelerating cellular catabolism through IGFBP2. Therefore, this research will elucidate a new insight about how T-2 toxin participate in the pathogenesis of KBD.

Unilateral anterior crossbite induces aberrant mineral deposition in degenerative temporomandibular cartilage in rats

OBJECTIVE

To investigate whether mechanical stress induces mineral deposits that contribute to matrix degradation at the onset of osteoarthritis (OA) in temporomandibular joint (TMJ) cartilage.

DESIGN

Female Spraguee-Dawley rats were subjected to an unilateral anterior crossbite (UAC) procedure. Histology, electron microscopy, and energy dispersive spectrometer (EDS) were used to examine cartilage matrix structures and composition of mineral deposit in the affected TMJ cartilage. Protein and/or RNA expression of phenotypic markers and mineralization modulators and matrix degradation was analyzed by immunohistochemistry and/or real-time PCR. Synthetic basic calcium phosphate (BCP) and calcium pyrophosphate dehydrate (CPPD) crystals were used to stimulate ATDC5 cells for their impact on cell differentiation and gene expression.

RESULTS

Fragmented and disorganized collagen fibers, expanded fibrous spaces, and enhancement of matrix vesicle production and mineral deposition were observed in matrices surrounding hypertrophic chondrocytes in cartilage as early as 2-weeks post-UAC and exacerbated with time. The mineral deposits in TMJ cartilage at 12- and 20-weeks post-UAC had Ca/P ratios of 1.42 and 1.44, which are similar to the ratios for BCP. The expression of mineralization inhibitors, NPP1, ANK, CD73, and Matrix gla protein (MGP) was decreased from 2 to 8 weeks post-UAC, so were the chondrogenic markers, Col-2, Col-X and aggrecan. In contrast, the expression of tissue-nonspecific alkaline phosphatase (TNAP) and MMP13 was increased 4-weeks post-UAC. Treating ADTC5 cells with BCP crystals increased MMPs and ADAMTS5 expression, but reduced matrix production in a time-dependent manner.

CONCLUSION

UAC induces deposition of BCP-like minerals in osteoarthritic cartilage, which can stimulate matrix degradation by promoting the expression of cartilage-degrading enzymes to facilitate OA progression.

Fibronectin fragment-induced expression of matrix metalloproteinases is mediated by MyD88-dependent TLR-2 signaling pathway in human chondrocytes

Introduction

Fibronectin fragments (FN-fs) are increased in the cartilage of patients with osteoarthritis (OA) and have a potent chondrolytic effect. However, little is known about the cellular receptors and signaling mechanisms that are mediated by FN-fs. We investigated whether the 29-kDa amino-terminal fibronectin fragment (29-kDa FN-f) regulates cartilage catabolism via the Toll-like receptor (TLR)-2 signaling pathway in human chondrocytes.

Methods

Small interfering RNA was used to knock down TLR-2 and myeloid differentiation factor 88 (MyD88). TLR-2 was overexpressed in chondrocytes transfected with a TLR-2 expression plasmid. The expression levels of matrix metalloproteinase (MMP)-1, MMP-3, and MMP-13 were analyzed using quantitative real-time reverse transcription polymerase chain reactions, immunoblotting, or enzyme-linked immunosorbent assay. The effect of TLR-2 on 29-kDa FN-f-mediated signaling pathways was investigated by immunoblotting.

Results

TLR-2, TLR-3, TLR-4, and TLR-5 mRNA were significantly overexpressed in OA cartilage compared with normal cartilage, whereas no significant difference of TLR-1 mRNA expression was found. 29-kDa FN-f significantly increased TLR-2 expression in human chondrocytes in a dose- and time-dependent manner. Knockdown of TLR-2 or MyD88, the latter a downstream adaptor of TLR-2, significantly inhibited 29-kDa FN-f-induced MMP production at the mRNA and protein levels. Conversely, TLR-2 overexpression led to enhanced MMP production by 29-kDa FN-f. In addition, TLR-2 knockdown apparently inhibited 29-kDa FN-f-mediated activation of phosphorylated nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha, and p38, but not of c-Jun N-terminal kinase or extracellular signal-regulated kinase. Exposure to synovial fluid (SF) from affected joints of patients with OA elevated MMP-1, MMP-3, and MMP-13 expression markedly in primary chondrocytes without reducing cell viability. However, TLR-2 knockdown in chondrocytes significantly suppressed SF-induced MMP induction.

Conclusions

Our data demonstrate that the MyD88-dependent TLR-2 signaling pathway may be responsible for 29-kDa FN-f-mediated cartilage catabolic responses. Our results will enhance understanding of cartilage catabolic mechanisms driven by cartilage degradation products, including FN-f. The modulation of TLR-2 signaling activated by damage-associated molecular patterns, including 29-kDa FN-f, is a potential therapeutic strategy for the prevention of cartilage degradation in OA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0833-9) contains supplementary material, which is available to authorized users.

Insights into osteoarthritis progression revealed by analyses of both knee tibiofemoral compartments

OBJECTIVE

To identify disease relevant genes and pathways associated with knee Osteoarthritis (OA) progression in human subjects using medial and lateral compartment dominant OA knee tissue.

DESIGN

Gene expression of knee cartilage was comprehensively assessed for three regions of interest from human medial dominant OA (n = 10) and non-OA (n = 6) specimens. Histology and gene expression were compared for the regions with minimal degeneration, moderate degeneration and significant degeneration. Agilent whole-genome microarray was performed and data were analyzed using Agilent GeneSpring GX11.5. Significant differentially regulated genes were further investigated by Ingenuity Pathway Analysis (IPA) to identify functional categories. To confirm their association with disease severity as opposed to site within the knee, 30 differentially expressed genes, identified by microarray, were analyzed by quantitative reverse-transcription polymerase chain reaction on additional medial (n = 16) and lateral (n = 10) compartment dominant knee OA samples.

RESULTS

A total of 767 genes were differentially expressed ≥ two-fold (P ≤ 0.05) in lesion compared to relatively intact regions. Analysis of these data by IPA predicted biological functions related to an imbalance of anabolism and catabolism of cartilage matrix components. Up-regulated expression of IL11, POSTN, TNFAIP6, and down-regulated expression of CHRDL2, MATN4, SPOCK3, VIT, PDE3B were significantly associated with OA progression and validated in both medial and lateral compartment dominant OA samples.

CONCLUSIONS

Our study provides a strategy for identifying targets whose modification may have the potential to ameliorate pathological alternations and progression of disease in cartilage and to serve as biomarkers for identifying individuals susceptible to progression.

Infrared LED light therapy influences the expression of fibronectin and tenascin in skin wounds of malnourished rats--a preliminary study

The aim of this investigation was to evaluate the effect of infrared (λ 846±20nm) LED irradiation on the expression profile of the extracellular matrix protein components, tenascin and fibronectin on skin wounds induced in well nourished and malnourished rats. Eighteen albino rats (21 days old) were randomly divided into a well-nourished group (standard diet) and a malnourished group (regional basic diet). After receiving the diet for 70 days, skin wounds were created and the animals were subdivided into three groups: well-nourished control (n=6), malnourished control (n=6), and malnourished+LED irradiated (λ 846±20nm, 100mW, 4J/cm(2)) (n=6). The animals were sacrificed 3 and 7 days after injury and histological sections were immunostained for both proteins. They were examined for the presence, intensity, distribution and pattern of immunolabeling. At 3 days, the distribution of tenascin was shown to be greater in the wound bed of malnourished animals compared to the well-nourished group. The intensity and distribution of tenascin was shown to be lower in the malnourished LED irradiated group compared to the malnourished control. There was a significant difference regarding the presence of fibronectin in the malnourished and well-nourished groups after 7 days (p=0.03). The intensity of fibronectin was slight (100%) in the irradiated group and moderate to intense in the malnourished control group. The results of the present study indicate that infrared LED irradiation modulates positively the expression of tenascin and particularly fibronectin.

Fibronectin in tissue regeneration: timely disassembly of the scaffold is necessary to complete the build

Tissue injury initiates extracellular matrix molecule expression, including fibronectin production by local cells and fibronectin leakage from plasma. To benefit tissue regeneration, fibronectin promotes opsonization of tissue debris, migration, proliferation, and contraction of cells involved in the healing process, as well as angiogenesis. When regeneration proceeds, the fibronectin matrix is fully degraded. However, in a diseased environment, fibronectin clearance is often disturbed, allowing structural variants to persist and contribute to disease progression and failure of regeneration. Here, we discuss first how fibronectin helps tissue regeneration, with a focus on normal cutaneous wound healing as an example of complete tissue recovery. Then, we continue to argue that, although the fibronectin matrix generated following cartilage and central nervous system white matter (myelin) injury initially benefits regeneration, fibronectin clearance is incomplete in chronic wounds (skin), osteoarthritis (cartilage), and multiple sclerosis (myelin). Fibronectin fragments or aggregates persist, which impair tissue regeneration. The similarities in fibronectin-mediated mechanisms of frustrated regeneration indicate that complete fibronectin clearance is a prerequisite for recovery in any tissue. Also, they provide common targets for developing therapeutic strategies in regenerative medicine.

Low oxygen tension increased fibronectin fragment induced catabolic activities--response prevented with biomechanical signals

Introduction

The inherent low oxygen tension in normal cartilage has implications on inflammatory conditions associated with osteoarthritis (OA). Biomechanical signals will additionally contribute to changes in tissue remodelling and influence the inflammatory response. In this study, we investigated the combined effects of oxygen tension and fibronectin fragment (FN-f) on the inflammatory response of chondrocytes subjected to biomechanical signals.

Methods

Chondrocytes were cultured under free-swelling conditions at 1%, 5% and 21% oxygen tension or subjected to dynamic compression in an ex vivo 3D/bioreactor model with 29 kDa FN-f, interleukin-1beta (IL-1β) and/or the nitric oxide synthase (NOS) inhibitor for 6 and 48 hours. Markers for catabolic activity (NO, PGE₂), tissue remodelling (GAG, MMPs) and cytokines (IL-1β, IL-6 and TNFα) were quantified by biochemical assay. Aggrecan, collagen type II, iNOS and COX-2 gene expression were examined by real-time quantitative PCR. Two-way ANOVA and a post hoc Bonferroni-corrected t-test were used to analyse data.

Results

Both FN-fs and IL-1β increased NO, PGE₂ and MMP production (all P < 0.001). FN-f was more active than IL-1β with greater levels of NO observed at 5% than 1% or 21% oxygen tension (P < 0.001). Whilst FN-f reduced GAG synthesis at all oxygen tension, the effect of IL-1β was significant at 1% oxygen tension. In unstrained constructs, treatment with FN-f or IL-1β increased iNOS and COX-2 expression and reduced aggrecan and collagen type II (all P < 0.001). In unstrained constructs, FN-f was more effective than IL-1β at 5% oxygen tension and increased production of NO, PGE₂, MMP, IL-1β, IL-6 and TNFα. At 5% and 21% oxygen tension, co-stimulation with compression and the NOS inhibitor abolished fragment or cytokine-induced catabolic activities and restored anabolic response.

Conclusions

The present findings revealed that FN-fs are more potent than IL-1β in exerting catabolic effects dependent on oxygen tension via iNOS and COX-2 upregulation. Stimulation with biomechanical signals abolished catabolic activities in an oxygen-independent manner and NOS inhibitors supported loading-induced recovery resulting in reparative activities. Future investigations will utilize the ex vivo model as a tool to identify key targets and therapeutics for OA treatments.

Time-series transcriptional profiling yields new perspectives on susceptibility to murine osteoarthritis

OBJECTIVE

Chronological age is a powerful epidemiologic risk factor for osteoarthritis (OA), a multifactorial disease that is characterized by articular cartilage (AC) degradation. It is unclear from a molecular perspective how aging interacts with OA to produce this risk to AC integrity. To address this key question, we used in vivo time-course analysis of OA development and murine interstrain variability in natural susceptibility to OA to examine changes in non-OA-prone CBA mice versus OA-prone STR/Ort mice, which develop disease that bears significant histologic resemblance to human OA. Through global transcriptome profiling, we attempted to discover the molecular signature linked with both OA vulnerability and progression.

METHODS

Affymetrix Mouse Gene 1.0 ST Array profiles were generated from AC samples derived from CBA and STR/Ort mice at 3 different ages, corresponding to the stages prior to, at, and late after the natural onset of OA in the STR/Ort mice.

RESULTS

We found that the OA in STR/Ort mice exhibited a molecular phenotype resembling human OA, and we pinpointed a central role of NF-κB signaling and the emergence of an immune-related signature in OA cartilage over time. We discovered that, strikingly, young healthy AC has a highly expressed skeletal muscle gene expression program, which is switched off during maturation, but is intriguingly retained in AC during OA development in STR/Ort mice.

CONCLUSION

This study is the first to show that AC chondrocytes share a high-abundance gene-expression program with skeletal muscle. We show that failure to switch this program off, as well as the restoration of this program, is associated with inappropriate expression of NF-κB signaling pathways, skeletal muscle-related genes, and induction and/or progression of OA.

Hydromechanical stimulator for chondrocyte-seeded constructs in articular cartilage tissue engineering applications

Mechanical stimulation is a key technique used for controlling the mechanical properties of tissue engineered articular cartilage constructs proposed for defect repair. The present study introduces a new technical method and device for ‘hydromechanical’ stimulation of tissue engineered articular cartilage constructs. The stimulation consists of simultaneous cyclic compression, frictional shear from a sliding indenter contact and direct pressurized fluid perfusion. Each of these modes of mechanical loading has been shown by other research groups to effectively stimulate tissue engineered constructs. A device for applying these conditions was designed, developed and tested. Two sets (high and low perfusion flow rates) of three experiments were performed, each with two samples subjected to hydromechanical stimulation conditions (compression and friction forces along with perfusion). Two other samples from each set were subjected to just compression and dynamic frictional shear forces, and two more were used as controls (not stimulated). The average amount of glycosaminoglycan retained in the constructs after 3 weeks ranked from low to high as follows: controls, hydromechanical conditions with the low-flow rate, hydromechanical conditions with the high-flow rate and just compression plus dynamic frictional shear. Statistically significant differences were not detected. However, future studies would focus on glycosaminoglycan production in the superficial zone, measuring the glycosaminoglycan released to the nutrient media, and address altering the hydromechanical stimulation parameters using the results of the present study as guidance, in attempts to achieve statistically significant increases in glycosaminoglycan production compared with the controls.

Modulation of the proliferation and matrix synthesis of chondrocytes by dynamic compression on genipin-crosslinked chitosan/collagen scaffolds

Dynamic compression is an important physical stimulus for the physiology of chondrocyte and articular cartilage tissue engineering. In this study, modulation of chondrocyte behaviors in chitosan/collagen scaffolds with different mechanical properties under free-swelling or dynamic compression conditions was investigated. Rabbit chondrocytes were seeded in chitosan/collagen scaffolds crosslinked by genipin (GP) with different concentrations, and then cultured for 3 days prior to cyclic compression of 40% strain, 0.1 Hz, and 30 min/day for 2 weeks. The results showed that the cell proliferation was increased with increasing genipin concentrations and dynamic compression. On the other hand, although total glycosaminoglycans (GAGs) deposition was enhanced by dynamic compression under certain conditions, e.g. the GP0.5 chitosan/collagen scaffolds for 1 week of compression culture, normalized GAGs deposition per cell was decreased by dynamic compression. Our results suggest that while several studies suggest that dynamic compression benefits articular cartilage tissue engineering, many factors including scaffold types and compression conditions determine the outcome of dynamic compression culture.

Osteoarthritis, a disease bridging development and regeneration

The osteoarthritic diseases are common disorders characterized by progressive destruction of the articular cartilage in the joints, and associated with remodeling of the subchondral bone, synovitis and the formation of bone outgrowths at the joint margins, osteophytes. From the clinical perspective, osteoarthritis leads to joint pain and loss of function. Osteoarthritis is the leading cause of progressive disability. New data from genetic, translational and basic research have demonstrated that pathways with essential roles in joint and bone development also contribute to the postnatal homeostasis of the articular cartilage and are involved in osteoarthritis, making these potential therapeutic targets. Other systems of interest are the tissue-destructive enzymes that break down the extracellular matrix of the cartilage as well as mediators of inflammation that contribute to synovitis. However, the perspective of a durable treatment over years to decades highlights the need for a personalized medicine approach encompassing a global view on the disease and its management, thereby including nonpharmaceutical approaches such as physiotherapy and advanced surgical methods. Integration of novel strategies based on their efficacy and safety with the identification of individuals at risk and optimal individual rehabilitation management remains a major challenge for the medical community in particular, as the incidence of osteoarthritis is likely to further increase with the overall aging of the population.

Role of NF-κB in the skeleton

Since the discovery that deletion of the NF-κB subunits p50 and p52 causes osteopetrosis in mice, there has been considerable interest in the role of NF-κB signaling in bone. NF-κB controls the differentiation or activity of the major skeletal cell types - osteoclasts, osteoblasts, osteocytes and chondrocytes. However, with five NF-κB subunits and two distinct activation pathways, not all NF-κB signals lead to the same physiologic responses. In this review, we will describe the roles of various NF-κB proteins in basal bone homeostasis and disease states, and explore how NF-κB inhibition might be utilized therapeutically.