RNA was isolated from four biological replicates for each patient and condition (control and TNFRSF11B-overexpressing chondrocytes) while pooling two pellets together to generate two independent samples for downstream analyses. Isolations were performed as described previously [12 (link)]. Total mRNA (150 ng) was processed with the first strand cDNA kit according to the manufacturer’s protocol (Roche Applied Science, Almere, The Netherlands). CDNA was further diluted five times, and preamplification with TaqMan preamp master mix (Thermo Fisher, Landsmeer, The Netherlands) was performed. Gene expression was measured (Supplementary Table S1, available at Rheumatology online) with RT-qPCR, and average of the two biological replicates was determined as relative levels (−ΔCt values) using expression levels of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and Acidic ribosomal phosphoprotein P0 (ARP) as housekeeping genes. Quality control of the results was performed as described before [12 (link)].