Background Gene expression profiling studies indicate that IL6-related T cell activation, and TNFα-dependent cell proliferation are major targets of therapy in the RA synovium1. We investigated whether expression of these pathways in early RA synovial biopsies is associated with clinically relevant information.
Methods We performed global transcriptomic studies (HGU133 Plus2.0) on early RA synovial biopsies, (GSE45867) and in TNFα-stimulated synovial fibroblasts (GSE15615). Immunostaining experiments (GADD45B, PDE4D) were performed on independent sets of early untreated RA samples, obtained by needle-arthroscopy (n=46), or by US-guided biopsies (n=35), next quantitated digitally.
Results In an initial set of 20 untreated early RA patients, 1,431 transcripts displayed at least a moderate correlation (r >0.4) and 77 of them displayed a good correlation (r >0.6) with DAS28-CRP. T cell associated genes were enriched in the 0.4 – 0.6 correlation range, while 38 out of the 77 transcripts with a correlation >0.6, were found to be induced by TNFα in cultured synovial fibroblasts (GADD45B, PDE4D, and CXCL14 were represented several times, by different probe sets). Immunostaining experiments on 46 independent synovial biopsy samples confirmed a higher PDE4D (median score 3.23 vs. 0.57, p =0.04) and GADD45B (median 0.60 vs. 0.31, p =0.09) staining in patients with DAS28-CRP >5.1.
Higher synovial expression of TNFα-induced genes predicts absence of response to TNF blockade in MTX-resistant RA patients2. We therefore wondered whether higher expression of these genes at baseline also predicts absence of response to first line therapy in early RA. In the microarray data, expression of 6 (GADD45B (x2), PDE4D, ADAMTS1, WWP2, MPPED1) out of 38 TNFα-dependent probe sets was significantly higher in patients who did not reach SDAI remission at month 6 in response to MTX therapy (all patients were DAS responders). In an independent group of patients, immunostaining of GADD45B (median score 2.39 vs. 0.29, p =0.002) and PDE4D (median score 5.47 vs. 0.48, p =0.002) produced a higher signal in baseline synovial biopsies of 14 EULAR non-responders (at 3 months) out of 46 early RA patients who received first line therapy, and in 8 non-responders out of the 16 who received methotrexate as a first line agent (GADD45B: 2.87 vs. 0.25, p =0.01; PDE4D: 7.74 vs. 0.48, p =0.07). Similarly, GADD45B immunostaining in US-guided biopsies was significantly higher at baseline in another set of 15 non-responders out of 35 early RA patients treated with MTX (median 0.76 vs. 0.22, p =0.03); no significant difference in PDE4D staining was observed in this set of samples. Disease activity at baseline itself did not predict response to therapy.
Conclusions Higher expression of TNFα-induced transcripts in early RA synovitis drives disease activity, and predicts poor response to first-line therapy. These results are important for patients' stratification in clinical trials, and open perspectives in terms of personalized medicine approaches in clinical practice.
Ducreux J, et al. Arthritis Rheum 66: 15-23.
Badot V, et al. Arthritis Res Ther 11: R57
Disclosure of Interest A. De Groof: None declared, F. Humby: None declared, J. Ducreux: None declared, S. Kelly: None declared, A. Nzeusseu Toukap: None declared, C. Pitzalis: None declared, P. Durez: None declared, B. Lauwerys Shareholder of: DNAlytics