MMP9 and rheumatoid arthritis: MMP-3 expression increased significantly by 157-fold and 26-fold in p21 knockdown RA FLS and OA FLS, respectively, by IL-β stimulation (Fig. 5e), whereas MMP-9 expression increased significantly by 3.7-fold and 3.2-fold in p21 knockdown RA FLS and OA FLS, respectively (Fig. 5f).