The first paper shows that MMP-8 deficiency increases joint inflammation and bone erosion suggesting the protective role of MMP-8, while the second one demonstrates that the lack of MMP-13 decreases both clinical and histological severity of arthritis indicating the promoting function of MMP-13 in the disease (Garcia et al., 2010;Singh et al., 2013). Here, MMP13 is linked to arthritic joint disease.