Julie Coudenys

Growth differentiation factor 15, a marker of lung involvement in systemic sclerosis, is involved in fibrosis development but is not indispensable for fibrosis development.

Transforming growth factor β superfamily members are involved in the pathogenesis of systemic sclerosis (SSc). Growth differentiation factor 15 (GDF‐15) is a distant member of this family. We undertook this study to evaluate the role of GDF‐15 in SSc pathogenesis.

A20 inhibition of STAT1 expression in myeloid cells: a novel endogenous regulatory mechanism preventing development of enthesitis.

Objectives A20 is an important endogenous regulator of inflammation. Single nucleotide polymorphisms in A20 have been associated with various immune-mediated inflammatory diseases, and cell-specific deletion of A20 results in diverse inflammatory phenotypes. Our goal was to delineate the underlying mechanisms of joint inflammation in myeloid-specific A20-deficient mice (A20myelKO mice). Methods Inflammation in A20myelKO mice was assessed in a time-dependent manner. Western blot analysis and quantitative PCR analysis were performed on bone marrow-derived macrophages from A20myelKO and littermate control mice to study the effect of A20 on STAT1/STAT3 expression and STAT1/STAT3-dependent gene transcription in myeloid cells. The in vivo role of Janus kinase-Signal Transducer and Activator of Transcription (JAK-STAT) signalling in the development of enthesitis in A20myelKO mice was assessed following administration of a JAK inhibitor versus placebo control. Results Enthesitis was found to be an early inflammatory lesion in A20myelKO mice. A20 negatively modulated STAT1-dependent, but generally not STAT3-dependent gene transcription in myeloid cells by suppressing STAT1 but not STAT3 expression, both in unstimulated conditions and after interferon-γ or interleukin-6 stimulation. The increase in STAT1 gene transcription in the absence of A20 was shown to be JAK-STAT-dependent. Moreover, JAK inhibition in vivo resulted in significant reduction of enthesitis, both clinically and histopathologically. Conclusions Our data reveal an important and novel interplay between myeloid cells and tissue resident cells at entheseal sites that is regulated by A20. In the absence of A20, STAT1 but not STAT3 expression is enhanced leading to STAT1-dependent inflammation. Therefore, A20 acts as a novel endogenous regulator of STAT1 that prevents onset of enthesitis.

A bidirectional crosstalk between iNKT cells and adipocytes mediated by leptin modulates susceptibility for T cell mediated hepatitis

BACKGROUND & AIMS Immunometabolism is an emerging field of clinical investigation due to the obesity epidemic worldwide. A reciprocal involvement of immune mediators in the body energy metabolism has been recognized for years, but is only partially understood. We hypothesized that the adipokine leptin could provide an important modulator of iNKT cells. METHODS The expression of leptin receptor (LR) on resting and activated iNKT cells was measured by flow cytometry. FACS-sorted hepatic iNKT cells were stimulated with anti-CD3/CD28Ab coated beads in the absence or presence of a neutralizing anti-leptin Ab. Furthermore, we evaluated the outcome of LR blocking nanobody treatment in ConA induced hepatitis and towards metabolic parameters in WT and iNKT cell deficient mice. RESULTS The LR is expressed on iNKT cells and leptin suppresses iNKT cell proliferation and cytokine production in vitro. LR deficient iNKT cells are hyper-responsive further enforcing the role of leptin as an important inhibitor of iNKT cell function. Consistently, in vivo blockade of LR signaling exacerbated ConA hepatitis in wild-type but not in iNKT cell deficient mice, through both Janus kinase (JAK)2 and mitogen-activated protein kinase (MAPK) dependent mechanisms. Moreover, LR inhibition altered fat pad features and was accompanied by insulin resistance, only in wild-type mice. Curiously, this interaction was strictly dependent on MAPK mediated LR signaling in iNKT cells and uncoupled from the more central effects of leptin. CONCLUSIONS Our data support a new concept of immune regulation by which leptin protects towards T cell mediated hepatitis via modulation of iNKT cells.

Distinct dysregulation of the small leucine-rich repeat protein family in osteoarthritic acetabular labrum compared to articular cartilage.

Articular cartilage is well studied in osteoarthritis (OA). However, the role of supporting structures, such as the acetabular labrum, a sealing structure surrounding the hip joint, has been investigated much less. We recently showed that fibrochondrocytic labrum cells are metabolically active. This study was undertaken to investigate hip OA–associated changes in human acetabular labrum cells.

Dysregulation of NF-kB in glandular epithelial cells results in Sjögren’s-like features

The autoimmune disease primary Sjögren’s syndrome (pSS) is characterized by hypofunction of the salivary glands (SGs), the cause of which is not correlated to lymphocytic SG infiltration, as prevailing dogma often states. We knocked out the NF-κB proinflammatory pathway inhibitor A20 in keratin14+ epithelial cells, to investigate if immune activated epithelial cells are capable of initiating pSS SG hallmarks. We show that immune activated epithelial cells can cause T cell dominated leukocytic infiltration and immune foci development of the SGs, reflecting the early clinical picture. Infiltrating leukocytes invaded striated ducts, similar to early stage lymphoepithelial lesions observed clinically. Expression of proinflammatory cyto-/chemokines IFNɣ, TNFα, IL-6, CXCL10 and CXCL13 increased in A20-/- SGs, and functionally both volume and mucin 10 content of whole stimulated saliva from A20-/- mice was significantly reduced. Epithelial cells may therefore represent the initial trigger for pSS SG pathologies, as opposed to simple reactionaries to pre-existing stimuli.

A3.4 Distinct dysregulation of the small leucine-rich repeat protein (SLRP) family in osteoarthritic labrum compared to articular cartilage

Background and objectives Osteoarthritis, characterised by a gradual progression of extracellular matrix (ECM) degradation, has been traditionally classified as a cartilage disease. However the new paradigm is that in OA the whole joint is involved, the cartilage but also synovium, subchondral bone and supporting structures, such as meniscus and the acetabular labrum. These supporting structures however remain largely unstudied. The acetabular labrum, is a fibrocartilageous horseshoe-shaped structure sealing the hip joint. We had previously proven that labrum cells are active in ECM synthesis and are able the react to pro-inflammatory cytokines. In this study our goal was to investigate hip OA specific gene expression changes in these cells in comparison with chondrocytes. Furthermore we aimed to investigate the functional importance of these gene expression differences. Material and methods Labrum cells from 5 OA patients en 3 healthy control patients were isolated and cultured in the 3-Dimensional alginate culture system. A genome wide gene expression analysis was performed using the Affymetrix microarray technology. Differential gene expression levels were confirmed on additional patient samples by quantitative PCR (qPCR), western blot and immunohistochemistry. Functional studies were performed by addition of recombinant protein the 3D-alginate labrum cultures. Results Pathway analysis performed on the microarray data indicate a distinct OA gene expression pattern in labrum cells, characterised by an increased cytokine and chemokine signalling as well as a reduced ECM receptor interaction and TGFβ signalling. Several genes were differentially regulated in OA compared to healthy labrum cells. We specifically focused on three proteins members of the short leucine rich repeat protein (SLRP) family: osteomodulin (OMD), osteoglycin (OGN) and asporin (ASPN). These proteins were found to be significantly downregulated in OA labrum but upregulated in OA cartilage. Moreover in vitro stimulation with OMD was able to induce proteoglycan synthesis in labrum cells. Conclusion Several features of OA chondrocytes are shared by OA labrum fibrochondrocytes, however SLRP expression seems to be differentially influenced in labrum compared to cartilage by OA degeneration. This suggest a distinct role for this supporting structure in hip OA, in which SLRP may play an important part.

Reduced levels of the TGFB family member GDF15 in spondyloarthritis versus other rheumatic diseases

Introduction The transforming growth factor (TGF)-β superfamily consists of a number of molecules that regulate a variety of cellular processes such as growth, differentiation and oncogenesis. Growth differentiation factor 15 is a distant member of this TGF-β family. GDF15 was previously shown to be elevated in serum of rheumatoid arthritis (RA)-patients compared to healthy controls. This study aims to compare GDF15 serum and synovial fluid levels in several inflammatory rheumatic diseases. Methods GDF15 levels were determined by ELISA in two different cohorts. A first group included serum samples from patients with an indication for an arthroscopic procedure for diagnostic purposes. A total of 37 RA patients, 63 spondyloarthritis (SpA) patients and 17 osteoarthritis patients was analysed. Synovial fluid levels in RA and SpA patients from this cohort were determined as well. A second confirmatory cohort constituted of a consecutive cohort of 555 patients visiting the outpatient clinic of the department of Rheumatology at Ghent University Hospital. Results SpA samples show a significant lower serum concentration of GDF15 compared to RA patients. When SpA patients were stratified according to the subdiagnosis (USpA, AS or PsA) no statistically significant differences could be observed between the groups. Interestingly, SpA patients, but not RA-patients, show a significant higher concentration of GDF15 in the synovial fluid compared to serum (serum=516.38 pg/ml ± 71.09 vs syn fluid 803.2167 pg/ml ± 99.14; paired sample t-test, p<0.001), pointing to a local production of GDF15 in the synovial joint. No significant correlations were observed between GDF15 concentration and routine biochemical (C-reactive protein, erythrocyte sedimentation rate) or clinical markers (number of swollen joints, DAS28), indicating that GDF15 serum levels might be indicative for a distinct underlying disease process. Analysis the second group consisting of a consecutive cohort of 555 patients confirmed the lower concentration of GDF15 in serum samples of SpA patients compared to RA patients. To estimate the diagnostic potential to discriminate SpA from RA patients, a ROC curve analysis was performed, characterised by a AUC of 0.76. In addition, it was demonstrated that GDF15 levels might have an added value to anti-CCP and rheumatoid factor to discriminate RA and SpA patients. Conclusion GDF15 serum concentrations are significantly lower in SpA patients compared to other inflammatory joint diseases. The serum levels are not directly correlated to inflammatory or known diagnostic parameters and thus may serve as an additional marker for diagnostic purposes in inflammatory joint diseases.

A multiparameter approach to monitor disease activity in collagen-induced arthritis

Introduction Disease severity in collagen-induced arthritis (CIA) is commonly assessed by clinical scoring of paw swelling and histological examination of joints. Although this is an accurate approach, it is also labour-intensive and the application of less invasive and less time-consuming methods is of great interest. However, it is still unclear which of these methods represents the most discriminating measure of disease activity.