An in vitro Model for Studying Mechanisms Underlying Synoviocyte-Mediated Cartilage Invasion in Rheumatoid Arthritis

Notch signalling pathways mediate synovial angiogenesis in response to vascular endothelial growth factor and angiopoietin 2

Objective

Notch signalling pathways are critical for angiogenesis and endothelial cell (EC) fate; however the mechanisms regulating these processes in the inflamed joint remain to be elucidated. Here, we examine whether Notch signalling mediates vascular endothelial growth factor (VEGF) and angiopoietin 2 (Ang2)-induced vascular function.

Methods

Notch-1 intracellular domain (Notch-1 IC), Notch-4 IC, Delta-like-ligand 4, Hes-related transcriptional repressors-1 and 2 (Hrt-1, Hrt-2) mRNA and/or protein expression was measured by Real-time PCR and/or western blot. VEGF/Ang2 induced EC function was assessed using transwell invasion chambers, matrigel tube formation assays and wound repair scratch assays ± Notch-1 siRNA or an γ-secretase inhibitor N-(N-(3,5-Difluorophenacetyl-L-alanly))-S-phenylglycine-t-Butyl Ester (DAPT) in RA synovial explants or human microvascular EC. Interleukin (IL)-6 and IL-8 were measured by ELISA and MMP2 and 9 by gelatine zymography.

Results

Notch-1 IC and Notch-4 IC protein expressions were demonstrated in RA and psoriatic arthritis synovial biopsies, with minimal expression observed in Osteoarthritis (OA). VEGF and Ang2 induced Notch-1 IC/ Notch-4 IC protein expression in synovial explant cultures and human microvascular EC levels were further potentiated by VEGF/Ang2 stimulation in combination. Notch-1, Delta-like-ligand 4, and Hrt-2 mRNA expression were significantly induced by VEGF and Ang2 alone and in combination. Furthermore VEGF/Ang2-induced EC invasion, angiogenesis and migration were inhibited by Notch-1 siRNA or DAPT. Conditioned media from VEGF/Ang2 stimulated RA synovial explants induced EC tube formation, an effect that was inhibited by DAPT. Finally, DAPT significantly decreased VEGF/Ang2 induced IL-6, IL-8, MMP2 and 9 expressions in RA synovial explants.

Conclusions

Notch-1 mediates VEGF/Ang2-induced angiogenesis and EC invasion in inflammatory arthritis.

Modulation of matrix metalloproteinase production by rheumatoid arthritis synovial fibroblasts after cadherin 11 engagement

OBJECTIVE

Cadherin 11 is a homophilic cell-to-cell adhesion molecule expressed on joint synovial fibroblasts. Absence of cadherin 11 in a mouse rheumatoid arthritis (RA) model led to striking reductions in cartilage erosion. Matrix metalloproteinases (MMPs) are enzymes expressed by synovial fibroblasts important for cartilage erosion. The objective of this study was to determine if synovial fibroblast MMP production is regulated by cadherin 11.

METHODS

To mimic cadherin 11 engagement, human RA synovial fibroblasts were stimulated with a chimeric construct consisting of the cadherin 11 extracellular domain linked to the human IgG1 Fc domain (Cad-11-Fc). Effects on MMP production were measured by enzyme-linked immunosorbent assay, quantitative reverse transcription-polymerase chain reaction analysis, and immunoblotting.

RESULTS

Human Cad-11-Fc up-regulated MMP-1 and MMP-3 protein production by RA synovial fibroblasts, both alone and in synergy with tumor necrosis factor α. This up-regulation required cell cadherin 11 engagement, since a mutant Cad-11-Fc with reduced binding affinity stimulated significantly less MMP production. Also, short hairpin RNA (shRNA) cadherin 11 silencing almost completely inhibited Cad-11-Fc-induced MMP expression. Cad-11-Fc stimulation increased RA synovial fibroblast MMP messenger RNA levels. It also increased the phosphorylation of the MAPKs JNK, ERK, and p38 kinase, the phosphorylation of NF-κB p65, and the nuclear translocation of activator protein 1 transcription factor. MAPK and NF-κB inhibitors partially blocked RA synovial fibroblast MMP expression.

CONCLUSION

Cadherin 11 engagement stimulates increased synthesis of several MMPs by RA synovial fibroblasts in a MAPK- and NF-κB-dependent manner. These results underscore the existence of a pathway by which cadherin 11 regulates MMP production and has important implications for joint destruction in RA.

Development of a high-throughput screening assay based on the 3-dimensional pannus model for rheumatoid arthritis

The 3-dimensional (3-D) pannus model for rheumatoid arthritis (RA) is based on the interactive co-culture of cartilage and synovial fibroblasts (SFs). Besides the investigation of the pathogenesis of RA, it can be used to analyze the active profiles of antirheumatic pharmaceuticals and other bioactive substances under in vitro conditions. For a potential application in the industrial drug-screening process as a transitional step between 2-dimensional (2-D) cell-based assays and in vivo animal studies, the pannus model was developed into an in vitro high-throughput screening (HTS) assay. Using the CyBitrade mark-Disk workstation for parallel liquid handling, the main cell culture steps of cell seeding and cultivation were automated. Chondrocytes were isolated from articular cartilage and seeded directly into 96-well microplates in high-density pellets to ensure formation of cartilage-specific extracellular matrix (ECM). Cell seeding was performed automatically and manually to compare both processes regarding accuracy, reproducibility, consistency, and handling time. For automated cultivation of the chondrocyte pellet cultures, a sequential program was developed using the CyBio Control software to minimize shear forces and handling time. After 14 days of cultivation, the pannus model was completed by coating the cartilage pellets with a layer of human SFs. The effects due to automation in comparison to manual handling were analyzed by optical analysis of the pellets, histological and immunohistochemical staining, and real-time PCR. Automation of this in vitro model was successfully achieved and resulted in an improved quality of the generated pannus cultures by enhancing the formation of cartilage-specific ECM. In addition, automated cell seeding and media exchange increased the efficiency due to a reduction of labor intensity and handling time.

Induction of an invasive phenotype by human parvovirus B19 in normal human synovial fibroblasts

OBJECTIVE

To investigate the possible role of human parvovirus B19 as an etiologic agent in rheumatoid arthritis (RA), with particular emphasis on its ability to induce invasiveness in human synovial fibroblasts.

METHODS

We established an experimental in vitro system in which normal primary human synovial fibroblasts were treated with or without parvovirus B19-containing human sera for 7 days. The fibroblasts were then tested for their ability to degrade reconstituted cartilage matrix using a well-characterized cartilage invasion assay system.

RESULTS

Incubation with parvovirus B19-containing serum induced an invasive phenotype in normal human synovial fibroblasts. B19 serum-treated synovial fibroblasts exhibited an increase in invasion of up to 248% compared with the activity of fibroblasts in media alone, in contrast to B19-negative sera-treated synovial fibroblasts, which exhibited no significant change compared with that in media alone. In addition, preincubation of viremic serum with a neutralizing antibody to B19 abrogated the observed effect.

CONCLUSION

These results provide direct evidence regarding the ability of parvovirus B19 to induce invasive properties in normal human synovial fibroblasts. Parvovirus B19 has been proposed as an etiologic agent of RA, and our data provide the first biologic link between exposure to B19 and phenotypic changes in normal human synovial fibroblasts.