Tumor necrosis factor α activation of the apoptotic cascade in murine articular chondrocytes is associated with the induction of metalloproteinases and specific pro-resorptive factors

Follistatin-like protein 1 (FSTL1) promotes chondrocyte expression of matrix metalloproteinase and inflammatory factors via the NF-κB pathway

Background

The expression of follistatin‐like protein 1 (FSTL1) is closely associated with diseases of the musculoskeletal system. However, despite being a well characterized inflammatory mediator, the effects of FSTL1 on chondrocytes are not completely understood. In this study, we investigated the effects of FSTL1 on the expression of inflammatory and catabolic factors in rat chondrocytes.

Methods

Rat chondrocytes were treated directly with various concentrations of FSTL1 in vitro. The levels of matrix metalloproteinases (MMPs), inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)‐2, interleukin (IL)‐1β, tumour necrosis factor (TNF)‐α and IL‐6 were measured by polymerase chain reaction, ELISA and Western blotting. In addition, activation of the nuclear factor kappa B (NF‐κB) pathway was explored to identify potential regulatory mechanisms.

Results

Follistatin‐like protein 1 directly increased the expression of MMP‐1, MMP‐13, iNOS, COX‐2, IL‐1β, TNF‐α and IL‐6 at both gene and protein level in a dose‐dependent manner. Activation of NF‐ κB and phosphorylation of p65 were also promoted by FSTL1 stimulation.

Conclusions

Follistatin‐like protein 1 exerts pro‐inflammatory and catabolic effects on cultured chondrocytes via activation of the NF‐κB signalling pathway. FSTL1 may therefore be a target in the treatment of OA.

Anabolic role of lysyl oxidase like-2 in cartilage of knee and temporomandibular joints with osteoarthritis

Background

Lysyl oxidase like-2 (LOXL2) is a copper-dependent amine oxidase. Our previous studies showed that LOXL2 is elevated during mouse fracture healing. The goal of this study was to evaluate the potential of LOXL2 to act as an anabolic agent in cartilage affected by osteoarthritis (OA).

Methods

LOXL2 was visualized in tissues from human knee and hip joints and temporomandibular joints (TMJ) by immunofluorescence. The activity of LOXL2 in human articular and TMJ chondrocytes was assessed by cell-based assays, microarray analysis, and RT-qPCR, and LOXL2-mediated activation of NF-κB and extracellular signal-related kinase (ERK) signaling pathways was measured by western blotting. To examine LOXL2-induced effect in vivo, we implanted Matrigel-imbedded human chondrocytes into nude mice and exposed them to exogenous LOXL2 for 6 weeks. Finally, LOXL2-induced effects on collagen type 2 α1 (COL2A1) and phospho-SMAD2/3 were evaluated by immunofluorescence analysis.

Results

LOXL2 staining was detected in damaged regions of human TMJ, hip and knee joints affected by OA. Stimulation with transforming growth factor (TGF)-β1 upregulated LOXL2 expression, while pro-inflammatory cytokines IL-1β and TNF-α downregulated LOXL2, in human chondrocytes. Viral transduction of LOXL2 in OA chondrocytes increased the mRNA levels of chondroitin sulfate proteoglycan (CSPG4), aggrecan (ACAN), sex determining region Y-box containing gene 9 (SOX9), and COL2A1 but reduced the levels of extracellular matrix (ECM)-degrading enzymes matrix metalloproteinase (MMP)1, MMP3, and MMP13. Further, forced expression of LOXL2 promoted chondrogenic lineage-specific gene expression, increased the expression of COL2A1 in the presence of TNF-α, and inhibited chondrocyte apoptosis. LOXL2 expression also inhibited IL-1β-induced phospho-NF-κB/p65 and TGF-β1-induced ERK1/2 phosphorylation. Matrigel constructs of human chondrocytes from the knee joint and TMJ implanted in nude mice showed anabolic responses after LOXL2 transduction, including increased expression of SOX9, ACAN, and COL2A1. Finally, immunofluorescence staining revealed co-localization of LOXL2 with SOX9 in the nuclei of cells in the implants, decreased phospho-SMAD2/3, and increased COL2A1 staining.

Conclusion

Our results suggest that although LOXL2 is upregulated in cartilage affected by OA, this may be a protective response that promotes anabolism while inhibiting specific catabolic responses in the pathophysiology of OA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1388-8) contains supplementary material, which is available to authorized users.

Catabolic cytokines disrupt the circadian clock and the expression of clock-controlled genes in cartilage via an NFкB-dependent pathway

OBJECTIVE

To define how the catabolic cytokines (Interleukin 1 (IL-1) and tumor necrosis factor alpha (TNFα)) affect the circadian clock mechanism and the expression of clock-controlled catabolic genes within cartilage, and to identify the downstream pathways linking the cytokines to the molecular clock within chondrocytes.

METHODS

Ex vivo cartilage explants were isolated from the Cry1-luc or PER2::LUC clock reporter mice. Clock gene dynamics were monitored in real-time by bioluminescence photon counting. Gene expression changes were studied by qRT-PCR. Functional luc assays were used to study the function of the core Clock/BMAL1 complex in SW-1353 cells. NFкB pathway inhibitor and fluorescence live-imaging of cartilage were performed to study the underlying mechanisms.

RESULTS

Exposure to IL-1β severely disrupted circadian gene expression rhythms in cartilage. This effect was reversed by an anti-inflammatory drug dexamethasone, but not by other clock synchronizing agents. Circadian disruption mediated by IL-1β was accompanied by disregulated expression of endogenous clock genes and clock-controlled catabolic pathways. Mechanistically, NFкB signalling was involved in the effect of IL-1β on the cartilage clock in part through functional interference with the core Clock/BMAL1 complex. In contrast, TNFα had little impact on the circadian rhythm and clock gene expression in cartilage.

CONCLUSION

In our experimental system (young healthy mouse cartilage), we demonstrate that IL-1β (but not TNFα) abolishes circadian rhythms in Cry1-luc and PER2::LUC gene expression. These data implicate disruption of the chondrocyte clock as a novel aspect of the catabolic responses of cartilage to pro-inflammatory cytokines, and provide an additional mechanism for how chronic joint inflammation may contribute to osteoarthritis (OA).

Role of Fas and Treg cells in fracture healing as characterized in the fas-deficient (lpr) mouse model of lupus

Previous studies showed that loss of tumor necrosis factor α (TNFα) signaling delayed fracture healing by delaying chondrocyte apoptosis and cartilage resorption. Mechanistic studies showed that TNFα induced Fas expression within chondrocytes; however, the degree to which chondrocyte apoptosis is mediated by TNFα alone or dependent on the induction of Fas is unclear. This question was addressed by assessing fracture healing in Fas-deficient B6.MRL/Fas(lpr) /J mice. Loss of Fas delayed cartilage resorption but also lowered bone fraction in the calluses. The reduced bone fraction was related to elevated rates of coupled bone turnover in the B6.MRL/Fas(lpr) /J calluses, as evidenced by higher osteoclast numbers and increased osteogenesis. Analysis of the apoptotic marker caspase 3 showed fewer positive chondrocytes and osteoclasts in calluses of B6.MRL/Fas(lpr) /J mice. To determine if an active autoimmune state contributed to increased bone turnover, the levels of activated T cells and Treg cells were assessed. B6.MRL/Fas(lpr) /J mice had elevated Treg cells in both spleens and bones of B6.MRL/Fas(lpr) /J but decreased percentage of activated T cells in bone tissues. Fracture led to ∼30% to 60% systemic increase in Treg cells in both wild-type and B6.MRL/Fas(lpr) /J bone tissues during the period of cartilage formation and resorption but either decreased (wild type) or left unchanged (B6.MRL/Fas(lpr) /J) the numbers of activated T cells in bone. These results show that an active autoimmune state is inhibited during the period of cartilage resorption and suggest that iTreg cells play a functional role in this process. These data show that loss of Fas activity specifically in chondrocytes prolonged the life span of chondrocytes and that Fas synergized with TNFα signaling to mediate chondrocyte apoptosis. Conversely, loss of Fas systemically led to increased osteoclast numbers during later periods of fracture healing and increased osteogenesis. These findings suggest that retention of viable chondrocytes locally inhibits osteoclast activity or matrix proteolysis during cartilage resorption.

Prolactin promotes cartilage survival and attenuates inflammation in inflammatory arthritis

Chondrocytes are the only cells in cartilage, and their death by apoptosis contributes to cartilage loss in inflammatory joint diseases, such as rheumatoid arthritis (RA). A putative therapeutic intervention for RA is the inhibition of apoptosis-mediated cartilage degradation. The hormone prolactin (PRL) frequently increases in the circulation of patients with RA, but the role of hyperprolactinemia in disease activity is unclear. Here, we demonstrate that PRL inhibits the apoptosis of cultured chondrocytes in response to a mixture of proinflammatory cytokines (TNF-α, IL-1β, and IFN-γ) by preventing the induction of p53 and decreasing the BAX/BCL-2 ratio through a NO-independent, JAK2/STAT3-dependent pathway. Local treatment with PRL or increasing PRL circulating levels also prevented chondrocyte apoptosis evoked by injecting cytokines into the knee joints of rats, whereas the proapoptotic effect of cytokines was enhanced in PRL receptor-null (Prlr(-/-)) mice. Moreover, eliciting hyperprolactinemia in rats before or after inducing the adjuvant model of inflammatory arthritis reduced chondrocyte apoptosis, proinflammatory cytokine expression, pannus formation, bone erosion, joint swelling, and pain. These results reveal the protective effect of PRL against inflammation-induced chondrocyte apoptosis and the therapeutic potential of hyperprolactinemia to reduce permanent joint damage and inflammation in RA.

The identification of CD163 expressing phagocytic chondrocytes in joint cartilage and its novel scavenger role in cartilage degradation

Background

Cartilage degradation is a typical characteristic of arthritis. This study examined whether there was a subset of phagocytic chondrocytes that expressed the specific macrophage marker, CD163, and investigated their role in cartilage degradation.

Methods

Cartilage from the knee and temporomandibular joints of Sprague-Dawley rats was harvested. Cartilage degradation was experimentally-induced in rat temporomandibular joints, using published biomechanical dental methods. The expression levels of CD163 and inflammatory factors within cartilage, and the ability of CD163⁺ chondrocytes to conduct phagocytosis were investigated. Cartilage from the knees of patients with osteoarthritis and normal cartilage from knee amputations was also investigated.

Results

In the experimentally-induced degrading cartilage from temporomandibular joints, phagocytes were capable of engulfing neighboring apoptotic and necrotic cells, and the levels of CD163, TNF-α and MMPs were all increased (P<0.05). However, the levels of ACP-1, NO and ROS, which relate to cellular digestion capability were unchanged (P>0.05). CD163⁺ chondrocytes were found in the cartilage mid-zone of temporomandibular joints and knee from healthy, three-week old rats. Furthermore, an increased number of CD163⁺ chondrocytes with enhanced phagocytic activity were present in Col-II⁺ chondrocytes isolated from the degraded cartilage of temporomandibular joints in the eight-week experimental group compared with their age-matched controls. Increased number with enhanced phagocytic activity of CD163⁺ chondrocytes were also found in isolated Col-II⁺ chondrocytes stimulated with TNF-α (P<0.05). Mid-zone distribution of CD163⁺ cells accompanied with increased expression of CD163 and TNF-α were further confirmed in the isolated Col-II⁺ chondrocytes from the knee cartilage of human patients with osteoarthritis, in contrast to the controls (both P<0.05).

Conclusions

An increased number of CD163⁺ chondrocytes with enhanced phagocytic activity were discovered within degraded joint cartilage, indicating a role in eliminating degraded tissues. Targeting these cells provides a new strategy for the treatment of arthritis.

Urine matrix metalloproteinases (MMPs) as biomarkers for the progression of fracture healing

Whilst the majority of fractures heal normally, it is estimated that ∼10% of fractures exhibit some level of delayed or impaired healing. Although radiography is the primary diagnostic tool to assess the progression of fracture healing, radiographic features only qualitatively correlate with tissue level increases in mineral content and do not quantitatively measure underlying biological processes that are associated with the progression of healing. Specific metaloproteinases have been shown to be essential to processes of both angiogenesis and mineralised cartilage resorption and bone remodelling at different phases of fracture healing. The aim of this study was to determine the potential of using a simple urine based assay of the activity of two MMPs as a means of assessing the biological progression of fracture healing through the endochondral phase of healing. Using a standard mid-diaphyseal murine model of femoral fracture, MMP9 and MMP13 proteins and enzymatic activity levels were quantified in the urine of mice across the time-course of fracture healing and compared to the mRNA and protein expression profiles in the calluses. Both urinary MMP9 and MMP13 protein and enzymatic activity levels, assessed by Western blot, zymogram and specific MMP fluorometric substrate assays, corresponded to mRNA expression and immunohistologic assays of the proteins within callus tissues. These studies suggest that urinary levels of MMP9 and MMP13 may have potential as metabolic markers to monitor the progression of fracture healing.

Biomarker analysis of Morquio syndrome: identification of disease state and drug responsive markers

Background

This study was conducted to identify potential biomarkers that could be used to evaluate disease progression and monitor responses to enzyme replacement therapy (ERT) in patients with mucopolysaccharidosis (MPS) IVA.

Methods

Levels of 88 candidate biomarkers were compared in plasma samples from 50 healthy controls and 78 MPSIVA patients not receiving ERT to test for significant correlations to the presence of MPSIVA. MPSIVA samples were also tested for correlations between candidate biomarkers and age, endurance, or urinary keratin sulfate (KS) levels. Then, levels of the same 88 analytes were followed over 36 weeks in 20 MPSIVA patients receiving ERT to test for significant correlations related to ERT, age, or endurance.

Results

Nineteen candidate biomarkers were significantly different between MPSIVA and unaffected individuals. Of these, five also changed significantly in response to ERT: alpha-1-antitrypsin, eotaxin, lipoprotein(a), matrix metalloprotein (MMP)-2, and serum amyloid P. Three of these were significantly lower in MPSIVA individuals versus unaffected controls and were increased during ERT: alpha-1-antitrypsin, lipoprotein(a), and serum amyloid P.

Conclusions

Candidate biomarkers alpha-1-antitrypsin, lipoprotein(a), and serum amyloid P may be suitable markers, in addition to urinary KS, to follow the response to ERT in MPSIVA patients.

Downregulation of protein kinase CK2 activity facilitates tumor necrosis factor-α-mediated chondrocyte death through apoptosis and autophagy

Despite the numerous studies of protein kinase CK2, little progress has been made in understanding its function in chondrocyte death. Our previous study first demonstrated that CK2 is involved in apoptosis of rat articular chondrocytes. Recent studies have suggested that CK2 downregulation is associated with aging. Thus examining the involvement of CK2 downregulation in chondrocyte death is an urgently required task. We undertook this study to examine whether CK2 downregulation modulates chondrocyte death. We first measured CK2 activity in articular chondrocytes of 6-, 21- and 30-month-old rats. Noticeably, CK2 activity was downregulated in chondrocytes with advancing age. To build an in vitro experimental system for simulating tumor necrosis factor (TNF)-α-induced cell death in aged chondrocytes with decreased CK2 activity, chondrocytes were co-treated with CK2 inhibitors and TNF-α. Viability assay demonstrated that CK2 inhibitors facilitated TNF-α-mediated chondrocyte death. Pulsed-field gel electrophoresis, nuclear staining, flow cytometry, TUNEL staining, confocal microscopy, western blot and transmission electron microscopy were conducted to assess cell death modes. The results of multiple assays showed that this cell death was mediated by apoptosis. Importantly, autophagy was also involved in this process, as supported by the appearance of a punctuate LC3 pattern and autophagic vacuoles. The inhibition of autophagy by silencing of autophage-related genes 5 and 7 as well as by 3-methyladenine treatment protected chondrocytes against cell death and caspase activation, indicating that autophagy led to the induction of apoptosis. Autophagic cells were observed in cartilage obtained from osteoarthritis (OA) model rats and human OA patients. Our findings indicate that CK2 down regulation facilitates TNF-α-mediated chondrocyte death through apoptosis and autophagy. It should be clarified in the future if autophagy observed is a consequence versus a cause of the degeneration in vivo.

Smoking and impaired bone healing: will activation of cholinergic anti-inflammatory pathway be the bridge?

PURPOSE

This review was written to analyse the potential role of the cholinergic anti-inflammatory pathway in smoking-induced impairment of the bone healing process.

METHODS

Literature in PubMed was reviewed by entering the following keywords "smoking AND bone healing", "cholinergic anti-inflammatory pathway AND tumour necrosis factor", "tumour necrosis factor AND bone healing". All the related papers were recruited and carefully selected according to the content of this paper.

RESULTS

Literature review indicated that tumour necrosis factor alpha (TNF-α) plays a pivotal role in the fracture healing process. In brief, TNF-α may accelerate the endochondral ossification process by increasing matrix metalloproteinases (MMPs) level, chondrocyte apoptosis, as well as osteoclast formation, therefore reducing the cartilaginous stage leading to the acceleration of fracture healing. Nicotine is the main effective ingredient of tobacco, which has been found to inhibit the secretion of TNF-α through activation of the cholinergic anti-inflammatory pathway.

CONCLUSIONS

It is reasonable to believe that the nicotine in tobacco at least partly contributes to the delayed fracture healing by inhibiting TNF-α secretion through the activation of the cholinergic anti-inflammatory pathway. An in-depth study of this issue will contribute to the clinical treatment of nonunion, as well as the development of new therapies to accelerate bone healing.

TNF-alpha mediates diabetes-enhanced chondrocyte apoptosis during fracture healing and stimulates chondrocyte apoptosis through FOXO1

To gain insight into the effect of diabetes on fracture healing, experiments were carried out focusing on chondrocyte apoptosis during the transition from cartilage to bone. Type 1 diabetes was induced in mice by multiple low-dose streptozotocin injections, and simple transverse fractures of the tibia or femur was carried out. Large-scale transcriptional profiling and gene set enrichment analysis were performed to examine apoptotic pathways on total RNA isolated from fracture calluses on days 12, 16, and 22, a period of endochondral bone formation when cartilage is resorbed and chondrocyte numbers decrease. Tumor necrosis factor alpha (TNF-alpha) protein levels were assessed by ELISA and caspase-3 by bioactivity assay. The role of TNF was examined by treating mice with the TNF-specific inhibitor pegsunercept. In vitro studies investigated the proapoptotic transcription factor FOXO1 in regulating TNF-induced apoptosis of chondrogenic ATDC5 and C3H10T1/2 cells as representative of differentiated chondrocytes, which are important during endochondral ossification. mRNA profiling revealed an upregulation of gene sets related to apoptosis in the diabetic group on day 16 when cartilage resorption is active but not day 12 or day 22. This coincided with elevated TNF-alpha protein levels, chondrocyte apoptosis, enhanced caspase-3 activity, and increased FOXO1 nuclear translocation (p < .05). Inhibition of TNF significantly reduced these parameters in the diabetic mice but not in normoglycemic control mice (p < .05). Silencing FOXO1 using siRNA in vitro significantly reduced TNF-induced apoptosis and caspase activity in differentiated chondrocytes. The mRNA levels of the proapoptotic genes caspase-3, caspase-8, caspase-9, and TRAIL were significantly reduced with silencing of FOXO1 in chondrocytic cells. Inhibiting caspase-8 and caspase-9 significantly reduced TNF-induced apoptosis in chondrogenic cells. These results suggest that diabetes causes an upregulation of proapoptotic genes during the transition from cartilage to bone in fracture healing. Diabetes increased chondrocyte apoptosis through a mechanism that involved enhanced production of TNF-alpha, which stimulates chondrocyte apoptosis and upregulates mRNA levels of apoptotic genes through FOXO1 activation.

Suppressive effect of secretory phospholipase A2 inhibitory peptide on interleukin-1beta-induced matrix metalloproteinase production in rheumatoid synovial fibroblasts, and its antiarthritic activity in hTNFtg mice

INTRODUCTION

Secretory phospholipase A2 (sPLA2) and matrix metalloproteinase (MMP) inhibitors are potent modulators of inflammation with therapeutic potential, but have limited efficacy in rheumatoid arthritis (RA). The objective of this study was to understand the inhibitory mechanism of phospholipase inhibitor from python (PIP)-18 peptide in cultured synovial fibroblasts (SF), and to evaluate its therapeutic potential in a human tumor necrosis factor (hTNF)-driven transgenic mouse (Tg197) model of arthritis.

METHODS

Gene and protein expression of sPLA2-IIA, MMP-1, MMP-2, MMP-3, MMP-9, tissue inhibitor of metalloproteinase (TIMP)-1, and TIMP-2 were analyzed by real time PCR and ELISA respectively, in interleukin (IL)-1beta stimulated rheumatoid arthritis (RA) and osteoarthritis (OA) synovial fibroblasts cells treated with or without inhibitors of sPLA2 (PIP-18, LY315920) or MMPs (MMP Inhibitor II). Phosphorylation status of mitogen-activated protein kinase (MAPK) proteins was examined by cell-based ELISA. The effect of PIP-18 was compared with that of celecoxib, methotrexate, infliximab and antiflamin-2 in Tg197 mice after ip administration (thrice weekly for 5 weeks) at two doses (10, 30 mg/kg), and histologic analysis of ankle joints. Serum sPLA2 and cytokines (tumor necrosis factor (TNF)alpha, IL-6) were measured by Escherichia coli (E coli) assay and ELISA, respectively.

RESULTS

PIP-18 inhibited sPLA2-IIA production and enzymatic activity, and suppressed production of MMPs in IL-1beta-induced RA and OA SF cells. Treatment with PIP-18 blocked IL-1beta-induced p38 MAPK phosphorylation and resulted in attenuation of sPLA2-IIA and MMP mRNA transcription in RA SF cells. The disease modifying effect of PIP-18 was evidenced by significant abrogation of synovitis, cartilage degradation and bone erosion in hTNF Tg197 mice.

CONCLUSIONS

Our results demonstrate the benefit that can be gained from using sPLA2 inhibitory peptide for RA treatment, and validate PIP-18 as a potential therapeutic in a clinically relevant animal model of human arthritis.

High levels of tumor necrosis factor-alpha contribute to accelerated loss of cartilage in diabetic fracture healing

Diabetes interferes with fracture repair; therefore, we investigated mechanisms of impaired fracture healing in a model of multiple low-dose streptozotocin-induced diabetes. Microarray and gene set enrichment analysis revealed an up-regulation of gene sets related to inflammation, including tumor necrosis factor (TNF) signaling in the diabetic group, when cartilage is being replaced by bone on day 16, but not on days 12 or 22. This change coincided with elevated osteoclast numbers and accelerated removal of cartilage in the diabetic group (P < 0.05), which was reflected by smaller callus size. When diabetic mice were treated with the TNF-specific inhibitor, pegsunercept, the number of osteoclasts, cartilage loss, and number of TNF-alpha and receptor activator for nuclear factor kB ligand positive chondrocytes were significantly reduced (P < 0.05). The transcription factor forkhead box 01 (FOXO1) was tested for mediating TNF stimulation of osteoclastogenic and inflammatory factors in bone morphogenetic protein 2 pretreated ATDC5 and C3H10T1/2 chondrogenic cells. FOXO1 knockdown by small-interfering RNA significantly reduced TNF-alpha, receptor activator for nuclear factor kB ligand, macrophage colony-stimulating factor, interleukin-1alpha, and interleukin-6 mRNA compared with scrambled small-interfering RNA. An association between FOXO1 and the TNF-alpha promoter was demonstrated by chromatin immunoprecipitation assay. Moreover, diabetes increased FOXO1 nuclear translocation in chondrocytes in vivo and increased FOXO1 DNA binding activity in diabetic fracture calluses (P < 0.05). These results suggest that diabetes-enhanced TNF-alpha increases the expression of resorptive factors in chondrocytes through a process that involves activation of FOXO1 and that TNF-alpha dysregulation leads to enhanced osteoclast formation and accelerated loss of cartilage.

Differentially regulated expression of growth differentiation factor 5 and bone morphogenetic protein 7 in articular cartilage and synovium in murine chronic arthritis: potential importance for cartilage breakdown and synovial hypertrophy

OBJECTIVE

To examine whether the endogenous expression of growth differentiation factor 5 (GDF-5) and bone morphogenetic protein 7 (BMP-7) is altered in the cartilage and synovium of human tumor necrosis factor alpha (TNFalpha)-transgenic (hTNFtg) mice with chronic arthritis, and to investigate the response of hTNFtg chondrocytes as well as fibroblast-like synoviocytes (FLS) to these morphogens in vitro.

METHODS

Analyses were performed in hTNFtg mice with chronic destructive arthritis and in wild-type (WT) mice as controls. Expression of GDF-5 and BMP-7 in the articular cartilage and synovium was examined by real-time polymerase chain reaction and immunohistochemistry. Human TNFtg cartilage explants, chondrocytes, and FLS monolayer cultures were assessed for basal matrix biosynthesis as well as growth factor responsiveness, using (35)S-sulfate incorporation assays. In addition, the DNA content/cell proliferation rate was measured.

RESULTS

The expression of GDF-5 and BMP-7 was decreased in articular cartilage from hTNFtg mice, whereas expression of both morphogens was increased in arthritic synovium from hTNFtg mice, as compared with the levels in WT controls. Isotope incorporation revealed a marked reduction of matrix synthesis in hTNFtg cartilage as well as a decrease in responsiveness to GDF-5 and BMP-7. The DNA content did not change in arthritic cartilage as compared with WT cartilage. In hTNFtg FLS, growth factor stimulation increased the rate of cell proliferation and the production of extracellular matrix.

CONCLUSION

In this murine model of TNFalpha-mediated arthritis, the expression of GDF-5 and BMP-7 is regulated differentially in articular cartilage and synovium. In articular cartilage, the down-regulation of GDF-5 and BMP-7, which function to maintain matrix integrity, could potentially compromise tissue repair, whereas in synovium, the increased expression of GDF-5 and BMP-7 might contribute to synovial hypertrophy.

The lonely death: chondrocyte apoptosis in TNF-induced arthritis

Inflammatory joint disease typically provokes progressive cartilage damage. The proliferative synovial inflammatory tissue directly invades the cartilage and induces the expression and activation of degrading enzymes such as matrix metalloproteases (MMPs) and aggrecanases. However, also chondrocyte apoptosis has been observed in cartilage samples of inflamed joints. It remains unclear whether this is a secondary phenomenon due to cartilage damage or a primary event initiated by the synovial inflammation. To determine the presence or absence of chondrocyte death in experimental arthritis, we longitudinally assessed proteoglycan depletion and chondrocyte apoptosis in paw sections from human tumor necrosis factor transgenic (hTNFtg) mice and wild-type littermates. Whereas, wild-type mice showed no signs of cartilage damage, hTNFtg mice exhibited progressive proteoglycan loss starting at clinical onset of arthritis. However, we already found the first apoptotic chondrocytes well before cartilage matrix breakdown occurred indicating that chondrocyte death can be induced before matrix resorption. Chondrocyte death could constantly be observed until late stages of arthritis causing a continuous increase in the number of empty cartilage lacunae. As apoptotic cells in cartilage cannot be cleared by phagocytes due to their spatial isolation in the avascular lacunae of cartilage, having no contact to professional or amateur phagocytes. The dying cells are compelled to undergo a "lonely death" inevitable ending up in secondary necrosis giving rise to perpetuation of a pro-inflammatory cascade. These data indicate that chondrocyte death may play a primary role in inflammatory arthritis fueling cartilage inflammation and damage due to secondary necrosis.

Tumor necrosis factor-alpha: alternative role as an inhibitor of osteoclast formation in vitro

TNFalpha is known to stimulate the development and activity of osteoclasts and of bone resorption. The cytokine was found to mediate bone loss in conjunction with inflammatory diseases such as rheumatoid arthritis or chronic aseptic inflammation induced by wear particles from implants and was suggested to be a prerequisite for the loss of bone mass under estrogen deficiency. In the present study, the regulation of osteoclastogenesis by TNFalpha was investigated in co-cultures of osteoblasts and bone marrow or spleen cells and in cultures of bone marrow and spleen cells grown with CSF-1 and RANKL. Low concentrations of TNFalpha (1 ng/ml) caused a >90% decrease in the number of osteoclasts in co-cultures, but did not affect the development of osteoclasts from bone marrow cells. In cultures with p55TNFR(-/-) osteoblasts and wt BMC, the inhibitory effect was abrogated and TNFalpha induced an increase in the number of osteoclasts in a dose-dependent manner. Osteoblasts were found to release the inhibitory factor(s) into the culture supernatant after simultaneous treatment with 1,25(OH)(2)D(3) and TNFalpha, this activity, but not its release, being resistant to treatment with anti-TNFalpha antibodies. Dexamethasone blocked the secretion of the TNFalpha-dependent inhibitor by osteoblasts, while stimulating the development of osteoclasts. The data suggest that the effects of TNFalpha on the differentiation of osteoclast lineage cells and on bone metabolism may be more complex than hitherto assumed and that these effects may play a role in vivo during therapies for inflammatory diseases.

Cytokines, tumor necrosis factor-alpha and interleukin-1beta, differentially regulate apoptosis in osteoarthritis cultured human chondrocytes

OBJECTIVE

This study addresses the effects of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) on cell death in human chondrocytes.

METHODS

Osteoarthritis (OA) human chondrocytes stimulated with Actinomycin-D (ActD) were used as a cellular apoptotic model. Caspase family mRNA expression and protein synthesis were analyzed by the ribonuclease protection assay and Western-blot, respectively. Cell viability and apoptosis were evaluated using the 3-[4,5-dimethylthiazol-2yl] 2,5-diphenyl tetrazolium bromide (MTT) assay and flow cytometry, respectively. Prostaglandin E2 (PGE2) and nitric oxide (NO) were evaluated by enzyme-linked immunosorbent assay (ELISA) and the Griess method, respectively.

RESULTS

TNF-alpha and IL-1beta differentially affected the pattern of caspase mRNA expression by human chondrocytes. TNF-alpha induced a gradual increase in caspase-1 and -8 mRNA levels that was not seen with IL-1beta. The time sequence of caspase-3 and -7 inductions by TNF-alpha differs from that induced by IL-1beta. Cell viability was not modified by TNF-alpha or IL-1beta in cultured chondrocytes. Then, we employed ActD as a model to facilitate cell death. Treatment with TNF-alpha and ActD (TNF-alpha/ActD) increased cell death induced by ActD (23%). Treatment with IL-1beta and ActD (IL-1beta/ActD) did not modulate ActD-induced cell death. Similarly, IL-1beta/ActD did not induce an increase in the activation of caspase-3 and -7 and poly (ADP-ribose) polymerase (PARP) cleavage observed by the incubation with TNF-alpha/ActD. These different effects were not due to bcl-2 or mcl-1 levels. Inhibition of PGE2 synthesis by indomethacin increased the cell death induced by IL-1beta/Act-D (59%). An inhibitor of caspase-8 significantly reduced only the TNF-alpha/ActD-induced cell death (58%).

CONCLUSION

TNF-alpha and IL-1beta differentially regulate the apoptotic pathway in human chondrocytes. This difference is dependent on PGE2 and caspase-8 levels.

Transcriptomics and proteomics: advancing the understanding of genetic basis of fracture healing

Fracture healing is a complex physiological post-natal process, which involves the coordination of several different cell types. Exploring the orchestration of events and the simultaneous activation of osteogenesis and chondrogenesis that recapitulates mammalian embryological skeletal development seems to be not only sophisticated but also challenging. A large number of genes involved in the above process are known, but many more remain to be discovered. The functional characterisation of these genes promises to elucidate the repair process as well as skeletal abnormalities and aging. We here review the current knowledge on early and late gene expression during fracture healing, the genes so far associated with osteoblast and osteoclast differentiation, the BMP antagonists, and the Wnts signalling pathway.

Analysis of fracture healing by large-scale transcriptional profile identified temporal relationships between metalloproteinase and ADAMTS mRNA expression

The aim of this study was to validate the use of transcriptional profiling as a means of characterizing the complex interactions of the thousands of genes that are expressed during fracture healing. Standard mid-diaphyseal tibia fractures were generated in C57/B6 murine tibiae and the transcriptional expression of approximately 13,000 genes was assessed. Three time points after fracture were assessed: day 3, representative of the inflammatory phase; day 10, representative of the peak of cartilage formation; and day 21, representative of the period of primary bone formation and coupled remodeling. A self-organizing mapping approach of the data revealed the temporal relationships between the expression of mRNAs for extracellular matrix proteins and the proteases that degrade the proteoglycan and collagenous matrices. A broad group of extracellular matrix protein mRNAs representative of basement membranes, blood vessels and cartilage all showed elevated expression over the first 21 days of fracture healing. The sorting of the data identified an orderly temporal expression of the metalloproteinases and ADAMTS during the progression of fracture healing with (MMP2/MMP14/TIMP2) and ADAMTS4 and 15 preceding the expression of (MMP9/MMP13). Based on their patterns of expression, relative to the known activities of the encoded proteolytic enzymes, our results suggest that the dissolution of cartilage protoeglycans proceeds before the underlying collagenous components of the matrix are removed. The exclusion of several mRNAs that are normally expressed by osteoclasts in the profiles of mRNAs from days 3 and 10 suggests that osteoclastic activity was largely absent during the early periods of cartilage tissue formation and that proteoglycan and specific collagenase activities, precedes or is prerequisite to later osteoclast infiltration into the remodeling tissues.

In vitro evaluation of low-intensity pulsed ultrasound in herniated disc resorption

Herniated disc (HD) is often resolved spontaneously without surgical intervention. HD resorption (HDR) is associated with abundant vascularization and infiltration of macrophages (Mphi) into the intervertebral disc (ID), as well as with high levels of matrix metalloproteinases (MMPs). Low-intensity pulsed ultrasound (LIPUS) accelerates bone fracture healing in clinical studies, and angiogenic factors are involved in the mechanism of action. In the present study, we examined the effects of LIPUS on HDR in a rat in vitro HD model. HDR was enhanced by LIPUS as measured by the change in the wet weight of the cultured ID. The secretion of tumor necrosis factor-alpha (TNF-alpha) and macrophage chemoattractant protein-1 (MCP-1) from Mphi into the culture medium was stimulated by LIPUS. LIPUS also enhanced matrix metalloproteinase-3 (MMP-3) maturation. Moreover, many apoptotic cell death were observed in the HDR groups with LIPUS exposure. These results suggest that LIPUS enhanced the HDR via MMP-3 activation through TNF-alpha and MCP-1 pathways. Although animal studies and clinical trial are needed to understand the LIPUS effects on HDR, LIPUS treatment might be an effective treatment for accelerating HDR.

Retinoic acid blocks pro-inflammatory cytokine-induced matrix metalloproteinase production by down-regulating JNK-AP-1 signaling in human chondrocytes

The development of osteoarthritis (OA) has recently been implicated as a result of immune-mediated damage of chondrocytes and their supporting matrixes. Pro-inflammatory cytokines like interleukin (IL)-1 and tumor necrosis factor alpha (TNF-alpha) play pivotal roles in immunopathogenesis of OA. Because vitamins preserving anti-oxidative effects are suggested to provide protection in OA patients from joint damage, in the present study, we examined the effects and mechanisms of all-trans retinoic acid (t-RA) in suppressing pro-inflammatory cytokine-induced matrix metalloproteinases (MMPs) production in human chondrocytes. Chondrocytes were prepared from cartilage specimens of OA patients receiving total hip or total knee replacement. The protein concentration was measured by ELISA, the mRNA expression by reverse transcriptase-polymerase chain reaction, the protein expression by Western blotting, the transcription factor DNA-binding activity by electrophoretic mobility shift assay and the protein kinase activity by kinase assay. We showed that both MMP-1 and MMP-13 mRNA expression, protein production and enzyme activity induced by either IL-1 or TNF-alpha were suppressed by t-RA or different retinoid derivatives. The molecular investigation revealed that the t-RA-mediated suppression was likely through blocking p38 kinase and c-Jun N-terminal kinase-activator protein-1 signaling pathways. In contrast, t-RA had no effect on extracellular signal-regulated kinase activity, nuclear factor (kappa)B (NF-(kappa)B) DNA-binding activity and I(kappa)B(alpha) degradation. Furthermore, we showed that t-RA could reduce IL-1-induced TNF-alpha production in chondrocytes. Our results suggest that vitamin A may protect OA patients from pro-inflammatory cytokine-mediated damage of chondrocytes and their supporting matrixes.

Collaborative action of M-CSF and CTGF/CCN2 in articular chondrocytes: possible regenerative roles in articular cartilage metabolism

It is known that expression of the macrophage colony-stimulating factor (M-CSF) gene is induced in articular chondrocytes upon inflammation. However, the functional role of M-CSF in cartilage has been unclear. In this study, we describe possible roles of M-CSF in the protection and maintenance of the articular cartilage based on the results of experiments using human chondrocytic cells and rat primary chondrocytes. Connective tissue growth factor (CTGF/CCN2) is known to be a potent molecule to regenerate damaged cartilage by promoting the growth and differentiation of articular chondrocytes. Here, we uncovered the fact that M-CSF induced the mRNA expression of the ctgf/ccn2 gene in those cells. Enhanced production of CTGF/CCN2 protein by M-CSF was also confirmed. Furthermore, M-CSF could autoactivate the m-csf gene, forming a positive feed-back network to amplify and prolong the observed effects. Finally, promotion of proteoglycan synthesis was observed by the addition of M-CSF. These findings taken together indicate novel roles of M-CSF in articular cartilage metabolism in collaboration with CTGF/CCN2, particularly during an inflammatory response. Such roles of M-CSF were further supported by the distribution of M-CSF producing chondrocytes in experimentally induced rat osteoarthritis cartilage in vivo.

Tumor necrosis factor alpha (TNF-alpha) coordinately regulates the expression of specific matrix metalloproteinases (MMPS) and angiogenic factors during fracture healing

Recent studies from our laboratory demonstrate that TNF-alpha signaling contributes to the regulation of chondrocyte apoptosis and a lack of TNF-alpha signaling leads to a persistence of cartilaginous callus and delayed resorption of mineralized cartilage. This study examines how delays in the endochondral repair process affect the expression of specific mediators of proteolytic cartilage turnover and vascularization. Simple closed fractures were produced in wild type and TNF-alpha receptor (p55-/-/p75-/-)-deficient mice. Using ribonuclease protection assay (RPA) and microarray analysis, the expression of multiple mRNAs for various angiogenic factors and the metalloproteinase gene family were measured in fracture calluses. The direct actions of TNFalpha on the expression of specific angiogenic factors and metalloproteinases (MMPs) was examined in both cultured callus cells and articular chondrocytes to compare the effects of TNF-alpha in growth cartilage versus articular cartilage. MMPs 2, 9, 13, and 14 were quantitatively the most prevalent metalloproteases and all showed peaks in expression during the chondrogenic period. In the absence of TNF-alpha signaling, the expression of all of these mRNAs was reduced. The angiopoietin families of vascular regulators and their receptors were expressed at much higher levels than the VEGFs and their receptors and while the angiopoietins showed diminished or delayed expression in the absence of TNF-alpha signaling, VEGF and its receptors remained unaltered. The expression of vascular endothelial growth inhibitor (VEGI or TNFSF15) showed a near absence in its expression in the TNF-alpha receptor-deficient mice. In vitro assessment of cultured fracture callus cells in comparison to primary articular chondrocytes showed that TNF-alpha treatment specifically induced the expression of MMP9, MMP14, VEGI, and Angiopoietin 2. These results suggest that TNF-alpha signaling in chondrocytes controls vascularization of cartilage through the regulation of angiopoietin and VEGI factors which play counterbalancing roles in the induction of growth arrest, or apoptosis in endothelial cells. Furthermore, TNF-alpha appears to regulate, in part, the expression of two key proteolytic enzymes, MMP 9 and MMP14 that are known to be crucial to the progression of vascularization and turnover of mineralized cartilage. Thus, TNF-alpha signaling in healing fractures appears to coordinate the expression of specific regulators of endothelial cell survival and metalloproteolytic enzymes and is essential in the transition and progression of the endochondral phase of fracture repair.