Osteoporosis is a common disorder of bone remodeling, caused by the imbalance between bone resorption by osteoclasts and bone formation by osteoblasts. Recently, we reported that matrix metalloproteinase-9 (MMP-9)-dependent histone H3 proteolysis is a key event for proficient osteoclast formation. Although it has been reported that several MMP-9 inhibitors, such as tetracycline and its derivatives, show an inhibitory effect on osteoclastogenesis, the molecular mechanisms for this are not fully understood. Here we show that tetracycline analogs, especially tigecycline and minocycline, inhibit osteoclast formation by blocking MMP-9-mediated histone H3 tail cleavage. Our molecular docking approach found that tigecycline and minocycline are the most potent inhibitors of MMP-9. We also observed that both inhibitors significantly inhibited H3 tail cleavage by MMP-9 in vitro. These compounds inhibited receptor activator of nuclear factor kappaB ligand (RANKL)-induced osteoclast formation by blocking the NFATc1 signaling pathway. Furthermore, MMP-9-mediated H3 tail cleavage during osteoclast differentiation was selectively blocked by these compounds. Treatment with both tigecycline and minocycline rescued the osteoporotic phenotype induced by prednisolone in a zebrafish osteoporosis model. Our findings demonstrate that the tetracycline analogs suppress osteoclastogenesis via MMP-9-mediated H3 tail cleavage, and suggest that MMP-9 inhibition could offer a new strategy for the treatment of glucocorticoid-induced osteoporosis.
Keywords: MMP-9; histone cleavage; minocycline; osteoclast; osteoporosis; tigecycline.