Developments in the synovial biology field 2006

A device for high-throughput monitoring of degradation in soft tissue samples

This work describes the design and validation of a novel device, the High-Throughput Degradation Monitoring Device (HDD), for monitoring the degradation of 24 soft tissue samples over incubation periods of several days inside a cell culture incubator. The device quantifies sample degradation by monitoring its deformation induced by a static gravity load. Initial instrument design and experimental protocol development focused on quantifying cartilage degeneration. Characterization of measurement errors, caused mainly by thermal transients and by translating the instrument sensor, demonstrated that HDD can quantify sample degradation with <6 μm precision and <10 μm temperature-induced errors. HDD capabilities were evaluated in a pilot study that monitored the degradation of fresh ex vivo human cartilage samples by collagenase solutions over three days. HDD could robustly resolve the effects of collagenase concentration as small as 0.5 mg/ml. Careful sample preparation resulted in measurements that did not suffer from donor-to-donor variation (coefficient of variance <70%). Due to its unique combination of sample throughput, measurement precision, temporal sampling and experimental versality, HDD provides a novel biomechanics-based experimental platform for quantifying the effects of proteins (cytokines, growth factors, enzymes, antibodies) or small molecules on the degradation of soft tissues or tissue engineering constructs. Thereby, HDD can complement established tools and in vitro models in important applications including drug screening and biomaterial development.

Radiolabeled Selective Matrix Metalloproteinase 13 (MMP-13) Inhibitors: (Radio)Syntheses and in Vitro and First in Vivo Evaluation

The noninvasive imaging of MMP activity in vivo could have a high impact in basic research as well as in clinical applications. This approach can be established using radiolabeled MMP inhibitors (MMPIs) as tracers for the detection of activated MMPs by means of PET. However, the complexity of diseases associated with dysregulated MMP expression necessitates the imaging of distinct MMPs or MMP subgroups to distinguish their individual role in specific diseases. To this end, selective and potent MMP-13 inhibitors based on a N,N'-bis(benzyl)pyrimidine-4,6-dicarboxamide core have been synthesized and successfully radiolabeled with carbon-11, fluorine-18, and gallium-68. Selected radiolabeled candidates were evaluated in vitro and in vivo regarding their pharmacokinetic properties and metabolic stability.

Human cathelicidin LL-37 and its derivative IG-19 regulate interleukin-32-induced inflammation

Human cathelicidin LL-37 protects against infections and endotoxin-induced inflammation. In a recent study we have shown that IG-19, an LL-37-derived peptide, protects in a murine model of arthritis. Cytokine interleukin-32 (IL-32) is elevated and directly associated with the disease severity of inflammatory arthritis. Therefore, in this study we examined the effects of LL-37 and IG-19 on IL-32-induced responses in human peripheral blood-derived mononuclear cells (PBMC) and macrophages. We showed that CD14(+) monocytes are the primary cells that produce pro-inflammatory tumour necrosis factor-α (TNF-α) following stimulation of PBMC with IL-32. We demonstrated that LL-37 and IG-19 significantly suppress IL-32-induced production of pro-inflammatory cytokines, e.g. TNF-α and IL-1β, without altering chemokine production. In contrast, LL-37 and IG-19 enhance the production of the anti-inflammatory cytokine IL-1RA. Further mechanistic studies revealed that LL-37 and IG-19 suppress IL-32-mediated phosphorylation of Fyn (Y420) Src kinase. In contrast, IL-32-mediated phosphorylation of AKT-1 (T308) and MKP-1 (S359) is not suppressed by the peptides. LL-37 and IG-19 alone induce the phosphorylation of MKP-1 (S359), which is a known negative regulator of inflammation. Furthermore, the peptides induce the activity of p44/42 mitogen-activated protein kinase, which is known to phosphorylate MKP-1 (S359). This is the first study to demonstrate the regulation of IL-32-induced inflammation by LL-37 and its derivative peptide IG-19. The mechanistic results from this study suggest that regulation of immune-mediated inflammation by these peptides may be controlled by the dual phosphatase MKP-1. We speculate that LL-37 and its derivatives may contribute to the control of immune-mediated inflammatory diseases.

RING-finger type E3 ubiquitin ligase inhibitors as novel candidates for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) significantly affects quality of life. We recently cloned synoviolin, a RING-type E3 ubiquitin ligase implicated in the endoplasmic reticulum-associated degradation (ERAD) pathway. Synoviolin is highly expressed in rheumatoid synovial cells and may be involved in the pathogenesis of RA. Inhibition of synoviolin activity is a potentially useful therapeutic approach for the treatment of RA. We conducted a high-throughput screen of small molecules to find inhibitors of synoviolin autoubiquitination activity. We identified two classes of small molecules, named LS-101 and LS-102, which inhibited synoviolin activity. LS-102 selectively inhibited synoviolin enzymatic activity, while LS-101 inhibited a broad array of RING-type E3 ligases. Moreover, these inhibitors suppressed the proliferation of rheumatoid synovial cells, and significantly reduced the severity of disease in a mouse model of RA. Our results suggest that inhibition of synoviolin is a potentially useful approach in the treatment of RA.

Visfatin/pre-B-cell colony-enhancing factor (PBEF), a proinflammatory and cell motility-changing factor in rheumatoid arthritis

Adipokines such as adiponectin and visfatin/pre-B-cell colony-enhancing factor (PBEF) have been recently shown to contribute to synovial inflammation in rheumatoid arthritis (RA). In this study, we evaluated the pathophysiological implication of visfatin/PBEF in the molecular patterns of RA synovial tissue, focusing on RA synovial fibroblasts (RASFs), key players in RA synovium. Expression of visfatin/PBEF in synovial fluid and tissue of RA patients was detected by immunoassays and immunohistochemistry. RASFs were stimulated with different concentrations of visfatin/PBEF over varying time intervals, and changes in gene expression were evaluated at the RNA and protein levels using Affymetrix array, real-time PCR, and immunoassays. The signaling pathways involved were identified. The influence of visfatin/PBEF on fibroblast motility and migration was analyzed. In RA synovium, visfatin/PBEF was predominantly expressed in the lining layer, lymphoid aggregates, and interstitial vessels. In RASFs, visfatin/PBEF induced high amounts of chemokines such as IL-8 and MCP-1, proinflammatory cytokines such as IL-6, and matrix metalloproteinases such as MMP-3. Phosphorylation of p38 MAPK was observed after visfatin/PBEF stimulation, and inhibition of p38 MAPK showed strong reduction of visfatin-induced effects. Directed as well as general fibroblast motility was increased by visfatin/PBEF-induced factors. The results of this study indicate that visfatin/PBEF is involved in synovial fibroblast activation by triggering fibroblast motility and promoting cytokine synthesis at central sites in RA synovium.

Insulin-like growth factor binding protein-related protein 1 is expressed in rheumatoid synovium and regulates synovial fibroblast proliferation

Insulin-like growth factor binding protein-related protein 1 (IGFBP-rP1) is a secretory protein that shares a structural similarity with IGFBP. Studies have shown that IGFBP-rP1 synergistically increases fibroblast growth with insulin and stimulates angiogenesis in tumor tissues. In this report, we examined the expression and function of IGFBP-rP1 in rheumatoid arthritis (RA). IGFBP-rP1 expression in synovial tissues was examined by reverse transcription-polymerase chain reaction (RT-PCR), real-time PCR, and immunohistochemical analysis. In vitro, IGFBP-rP1 expression was examined in synovial fibroblasts established from rheumatoid synovium (RASFs) by RT-PCR, Western blot, and immunostaining. The effect of IGFBP-rP1 small interfering RNA (siRNA) on RASF proliferation was assessed by alamarBlue assay. IGFBP-rP1 mRNA was detected by RT-PCR in all synovial tissues from RA and OA patients. In immunohistochemical analysis, IGFBP-rP1 was mainly expressed in synovial cells in the lining layers and endothelial cells in the sublining layers of RA synovium. In vitro, constitutive expression of IGFBP-rP1 in RASFs was detected by RT-PCR, Western blot, and immunostaining. Treatment with IGFBP-rP1 siRNA induced a 26% decrease in RASF growth compared to control siRNA. A similar extent of growth-suppressive effect by IGFBP-rP1 siRNA was also observed when RASF proliferation was induced by TNF-α. Collectively, these data suggest that IGFBP-rP1 may regulate synovial fibroblast proliferation in RA.

Suppression of Autoimmune Arthritis by Small Molecule Inhibitors of the JAK/STAT Pathway

A skewed ratio of pro-inflammatory to anti-inflammatory cytokines, elevated growth factor synthesis and T- and B-lymphocyte activation are 3 hallmarks of rheumatoid arthritis (RA) pathology. Interleukin-6 (IL-6), IL-7, IL-17, IL-12/IL-23 and growth factors, granulocyte macrophage-colony stimulating factor, IL-3, and erythropoietin activate the Janus Kinase/Signal Transducers and Activators of Transcription (JAK/STAT) pathway. Evidence showed that STAT protein phosphorylation (p-STAT) by activated JAKs is permissive for p-STAT to act as transcription factors by binding to STAT-responsive gene promoter sequences. This event is critical for perpetuating RA, in part, by up-regulating pro-inflammatory cytokine gene transcription. Activation of JAK/STAT by cytokines and growth factors can induce ‘cross-talk’ with other signaling pathways by which Stress-Activated Protein/Mitogen-Activated Protein Kinase (SAP/MAPK) and Phosphatidylinositide-3-Kinase (PI3K)-mediated signaling are also activated. JAK-specific small molecule inhibitors (SMIs) were developed to test whether JAK/STAT pathway blockade would regulate autoimmune-mediated inflammation. JAK-specific SMI blockade inhibited p-STAT induced by pro-inflammatory cytokines in vitro. Systemically administered JAK-specific SMI blockade also ameliorated biomarkers of inflammation in well-validated arthritis animal models. A few JAK-specific SMIs have made their way into RA clinical trials. In fact, the JAK3-specific SMI, CP-690,500 is the first JAK/STAT SMI to be assessed for clinical efficacy in a Phase III RA trial.

Differential mechanism of NF-kappaB inhibition by two glucocorticoid receptor modulators in rheumatoid arthritis synovial fibroblasts

OBJECTIVE

To investigate and compare the molecular mechanisms by which 2 glucocorticoid receptor (GR)-activating compounds, dexamethasone (DEX) and Compound A (CpdA), interfere with the NF-kappaB activation pathway in rheumatoid arthritis (RA) synovial cells.

METHODS

Quantitative polymerase chain reaction was performed to detect the tumor necrosis factor alpha (TNFalpha)-induced cytokine gene expression of interleukin-1beta (IL-1beta) and to investigate the effects of DEX and CpdA in RA fibroblast-like synoviocytes (FLS) transfected with small interfering RNA (siRNA) against GR (siGR) compared with nontransfected cells. Immunofluorescence analysis was used to detect the subcellular distribution of NF-kappaB (p65) under the various treatment conditions, and active DNA-bound p65 was measured using a TransAM assay and by chromatin immunoprecipitation analysis of IL-1beta. Signaling pathways were studied via Western blotting of siGR-transfected cells, compared with nontransfected and nontargeting siRNA-transfected control cells, to detect the regulation of phospho-IKK, IkappaBalpha, phospho-p38, phospho-ERK, and phospho-JNK.

RESULTS

Both DEX and CpdA efficiently inhibited IL-1beta gene expression in a GR-dependent manner. In addition, CpdA attenuated the TNFalpha-induced nuclear translocation and DNA binding of p65 in RA FLS, via the attenuation of IKK phosphorylation and subsequent IkappaBalpha degradation. CpdA also displayed profound effects on TNFalpha-induced MAPK activation. The effects of CpdA on TNFalpha-induced kinase activities occurred independently of the presence of GR. In sharp contrast, DEX did not affect TNFalpha-induced IKK phosphorylation, IkappaBalpha degradation, p65 nuclear translocation, or MAPK activation in RA FLS.

CONCLUSION

DEX and CpdA display a dissimilar molecular mechanism of interaction with the NF-kappaB activation pathway ex vivo. A dual pathway, partially dependent and partially independent of GR (nongenomic), may explain the gene-inhibitory effects of CpdA in RA FLS.

Treating autoimmune disease by targeting CD8(+) T suppressor cells

Current treatments for autoimmune disease are hampered by the non-specificity of immunomodulatory interventions, having to accept broad suppression of immunoresponsiveness with potentially serious side effects, such as infection or malignancy. The development of antigen-specific approaches, downregulating pathogenic immune responses while maintaining protective immunity, would be a major step forward. One possible approach involves the targeting of physiological regulatory mechanisms, such as inhibitory CD8 T cells that are now recognized to fine-tune many aspects of immune responses. CD8 T suppressor (Ts) cells may directly inhibit other T cells or condition antigen-presenting cells in such a way that immune amplification steps are dampened. The promise of CD8 Ts cells lies in their potential to disrupt host-injurious immune responses in a targeted fashion. For therapeutic purposes, such CD8 Ts cells could either be generated in vitro and transferred into the host or their numbers and activity could be modulated by treating the patient with established or novel immunomodulators. Emerging evidence shows that several subsets of CD8 Ts cells exist. While there is still considerable uncertainty about the molecular mechanisms through which CD8 Ts cells can reset immune responses to protect the host, their potential diagnostic and therapeutic use is intriguing and has generated renewed interest.

The role of antioxidant supplement in immune system, neoplastic, and neurodegenerative disorders: a point of view for an assessment of the risk/benefit profile

This review will discuss some issues related to the risk/benefit profile of the use of dietary antioxidants. Thus, recent progress regarding the potential benefit of dietary antioxidants in the treatment of chronic diseases with a special focus on immune system and neurodegenerative disorders will be discussed here. It is well established that reactive oxygen species (ROS) play an important role in the etiology of numerous diseases, such as atherosclerosis, diabetes and cancer. Among the physiological defense system of the cell, the relevance of antioxidant molecules, such as glutathione and vitamins is quite well established. Recently, the interest of researchers has, for example, been conveyed on antioxidant enzyme systems, such as the heme oxygenase/biliverdin reductase system, which appears modulated by dietary antioxidant molecules, including polyphenols and beta-carotene. These systems possibly counteract oxidative damage very efficiently and finally modulate the activity of oxidative phenomena occurring, for instance, during pathophysiological processes. Although evidence shows that antioxidant treatment results in cytoprotection, the potential clinical benefit deriving from both nutritional and supplemental antioxidants is still under wide debate. In this line, the inappropriate assumption of some lipophylic vitamins has been associated with increased incidence of cancer rather than with beneficial effects.

IgG1 and IgG4 are the predominant subclasses among auto-antibodies against two citrullinated antigens in RA

OBJECTIVE

Antibody subclasses reflect specific immunological processes and may be indicative of the underlying pathological pattern in an autoimmune disease like RA. We therefore quantified anti-cyclic citrullinated peptides (CCP) and anti- citrullinated vimentin (MCV) IgG subclass titres in RA patients and compared them with the respective titres of antibodies directed against the varicella zoster virus (VZV) and to total serum titres.

METHODS

Sera of 77 patients fulfilling the ACR criteria for RA were collected. An IgG subclass-specific ELISA system was then established and combined with commercially available MCV, CCP and VZV pre-coated microtitre plates.

RESULTS

Even though IgG1 is the predominant subclass among antibodies against CCP and MCV in RA patients, IgG4 is second with respect to titres and frequencies. This increase in IgG4 among RA-specific antibodies is independent of disease duration and does not reflect a general skewing of the immune response in these patients as overall serum titres and antibodies directed against VZV show a normal distribution of IgG1, IgG2, IgG3 and IgG4.

CONCLUSION

Elevated IgG4 titres are specific for auto-antibodies against citrullinated antigens in RA and are indicative of a Th2-biased environment during the generation of auto-reactive plasma cells. We discuss here an indirect role for IgG4 auto-antibodies in hindering the elimination of auto-reactive B and plasma cells and thus driving the autoimmune process.

The study of angiogenesis in early rheumatoid arthritis--clinical, immunohistochemical and immunological correlations

OBJECTIVE

The objective of the study was to analyze several immunohistochemical, histological, and morphometrical aspects of angiogenesis in early rheumatoid arthritis synovium. We aimed to identify possible correlations between the histological and immunohistochemical patterns and the serum levels of VEGF, as well as with clinical and biological markers of disease activity.

METHODS

35 patients with early rheumatoid arthritis below 12 months from the onset, naive for DMARDs, underwent clinical standard examination as well as serum determinations for CRP, RF. anti-CCP2 antibodies and VEGF. DAS28 value has been determined for each patient in order to assess the disease activity. We performed biopsy sampling through arthroscopy, the synovium fragments beeing histopathologically processed, in order to elaborate a total histological score. Immunohistochemical analysis has been performed with quantification of synovial VEGF, VEGF-R1 and CD34 expression. Standard and activated microvascular density (sMVD and aMVD) have been evaluated through double immunostaining (CD34/ VEGF-R1).

RESULTS

VEGF and VEGF-R1 have been identified with high prevalence in endothelial cells, in lining and sublining synovial cells, as well as in inflammatory cells. The study focuses on the analysis of aMVD, a valuable parameter, representative for active angiogenesis, which proved to correlate significantly with the serum levels of VEGF, the composite histological score as well as with VEGF-R1 and DAS28.

CONCLUSION

The statistic analysis of the data support VEGF-R1 and aMVD as markers with predictive value regarding activity and progression in early stages of rheumatoid arthritis. The validation of preliminary conclusions oblige to continuous research through extending the study group and inclusion of several others biomarkers involved in synovial angiogenesis.

Cells of the synovium in rheumatoid arthritis. Chondrocytes

Rheumatoid arthritis (RA) is one of the inflammatory joint diseases in a heterogeneous group of disorders that share features of destruction of the extracellular matrices of articular cartilage and bone. The underlying disturbance in immune regulation that is responsible for the localized joint pathology results in the release of inflammatory mediators in the synovial fluid and synovium that directly and indirectly influence cartilage homeostasis. Analysis of the breakdown products of the matrix components of joint cartilage in body fluids and quantitative imaging techniques have been used to assess the effects of the inflammatory joint disease on the local remodeling of joint structures. The role of the chondrocyte itself in cartilage destruction in the human rheumatoid joint has been difficult to address but has been inferred from studies in vitro and in animal models. This review covers current knowledge about the specific cellular and biochemical mechanisms that account for the disruption of the integrity of the cartilage matrix in RA.

Pro-inflammatory cytokine-induced SAPK/MAPK and JAK/STAT in rheumatoid arthritis and the new anti-depression drugs

BACKGROUND

Adult rheumatoid arthritis (RA) patients are frequently clinically depressed. Peripheral inflammation in RA may influence neurotransmitter metabolism, neuroendocrine function, synaptic plasticity, as well as growth factor production, which can modify neural circuitry and contribute to depression.

OBJECTIVE

A convergence between pro-inflammatory cytokine-induced synovial joint inflammation in RA and the effects of pro-inflammatory cytokines on the brain may occur through activation of the stress-activated/mitogen-activated protein kinases (SAPK/MAPK) and/or Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathways.

METHODS

The PubMed and Medlines databases were critically evaluated for evidence of SAPK/MAPK and/or JAK/STAT pathway activation in RA and depression.

RESULTS/CONCLUSION

Some novel anti-depression drugs that were employed in animal models of 'sickness behavior' and in human depression clinical trials suppressed clinical markers of inflammation, as well as SAPK/MAPK and/or JAK/STAT signaling in vitro. Modifying pro-inflammatory cytokine signaling pathways in the brain with antidepressants may also be useful in ameliorating peripheral inflammation in RA.

Synoviolin, protein folding and the maintenance of joint homeostasis

Rheumatoid arthritis is a disease associated with painful joints that affects approximately 1% of the population worldwide, and for which no specific cure is available. Among other functions, the endoplasmic reticulum (ER) has an important role in protein folding. When the level of unfolded proteins in the ER exceeds the folding capacity of this organelle, defective proteins are eliminated by ER-associated degradation (ERAD), an ATP-dependent ubiquitin-proteasome degradation process, to reduce the burden on the ER. Synoviolin is an E3 ubiquitin ligase that is involved in ERAD. This protein is a pathogenic factor for arthropathy; it is overexpressed in the synovial cells of patients with rheumatoid arthritis. This overexpression results in a 'hyper-ERAD' state, in which the cell deals with accumulated unfolded proteins excessively. Rheumatoid synovial cells produce large amounts of various proteins such as cytokines and proteases, which consequently might confer an autonomous proliferation property on the cells. At least 30% of all newly synthesized, ER-sorted proteins are unfolded. Although degradation of unfolded proteins consumes large amounts of ATP and would seem an unconventional process, it is essential for joint homeostasis.