Objectives Tumour necrosis factor α (TNF-α) and interferons (IFNs), which are abundantly present in the rheumatoid synovium, are thought to exert two opposing effects on RA pathology. We studied the opposing effects of IFNs and TNF on the proliferative capacity of rheumatoid fibroblast-like synoviocytes (FLS).

Methods IFN and/or TNF induced changes in FLS gene expression were measured by DNA-microarray analysis and data was analysed using Significance Analysis of Microarrays (SAM) and pathway analysis using PANTHER. Activation of STAT-1 was determined by immunofluorescence and real-time PCR. FLS proliferation was monitored by ³H-thymidine incorporation. Apoptosis was determined by staining with Annexin V and propidium iodide (PI). Staining with PI was also used to analyse cell cycle distribution. Expression of GADD45β mRNA was measured by real-time PCR.

Results Gene expression profiling of IFN-stimulated rheumatoid FLS provided evidence for inhibition of cell cycle regulation. Accordingly, IFN stimulation resulted in a >50% decrease in DNA synthesis. The inhibitory effect was not due to induction of apoptosis but was shown to be the consequence of limited cell cycle progression due to accumulation of cells in G0/1 phase. The inhibitory effect overruled TNFα-induced cell cycle progression to G2/M phase and proliferation. This effect correlated with expression of the Growth-Arrest and DNA Damage-Inducible gene GADD45β.

Conclusion These results indicate that IFN-induced inhibition of cell cycle progression in rheumatoid FLS overrules TNFα-induced proliferative effects.

Funding This work has been supported by the EU Marie Curie Training Network (EURO-RA), the EU integrated program AUTOCURE, and CMSB (Netherlands Centre of Excellenc on Genomics Research)