MMP9 and rheumatoid arthritis: MMP9, a protein from the calcium-dependent zinc-containing endopeptidase family, is engaged in the degradation of extracellular matrix, especially type-IV collagen, resulting in multiple physiological and pathological processes, including tissue remodeling, angiogenesis, cell migration, rheumatoid arthritis, and tumor invasion (Dufour et al., 2010; Xue et al., 2014; Li et al., 2021).