MMP9 and rheumatoid arthritis: Meanwhile, studies have designed loaded PEI-SS-IND-MTX-MMP-9 siRNA nanoparticles for RA cartilage damage for the delivery of indindexin (IND), MTX, and MMP-9 siRNA, which significantly downregulated the expression of MMP-9 and various inflammatory factors in Raw-264.7 cells and showed anti-inflammatory activity and reversal of bone destruction in RA mice (291).