Differential regulation of MMP-13 (collagenase-3) and MMP-3 (stromelysin-1) in mouse calvariae

Bone resorption in mice involves the degradation of extracellular matrix. Whereas several proteases seem to be implicated in this process, it becomes increasingly clear that matrix metalloproteinases (MMPs), amongst them especially MMP-13 and MMP-3, play an essential role. We have purified MMP-13 and MMP-3 from mouse calvariae-conditioned media by differential fractionation and analyzed their collagenolytic, caseinolytic, gelatinolytic and proteoglycanolytic activities. It could be shown that in mouse calvariae-conditioned media most of the measured enzyme activities were due to MMP-13, although zymographies revealed that MMP-3, MMP-2, MMP-9 as well as TIMPs were present too. MMP-13 and MMP-3 proteins were detected and their enzyme activities were neutralized by specific polyclonal antisera. Furthermore, it was demonstrated that in cultures of mouse calvariae the production of MMP-13 was induced by the potent MMP-stimulator heparin and by parathyroid hormone (PTH), whereas the levels of MMP-3 remained unchanged. Although PTH-induced bone resorption was inhibited by calcitonin treatment, MMP-13 mRNA and protein expression were not significantly altered by this hormone. Together with previous observations, these results indicate that PTH regulates bone resorption through MMP-13, but not by MMP-3, and that its reversion by calcitonin involves neither of the two enzymes.