The participation of
collagenase in
bone resorption has been investigated by assaying the
procollagenase extracted from fetal mouse calvaria cultured under a variety of conditions, and by evaluating its ability to degrade bone
collagen.
Procollagenase was found in two separate pools, one requiring demineralization for its extraction, the other not. Culturing the bones with PTH,
1,25-dihydroxyvitamin D3,
prostaglandin E2,
interleukin-1,
tumor necrosis factor-alpha,
catabolin,
retinoic acid, or
endotoxin (but not with
heparin) induced resorption, enhanced lysosomal
enzyme release, and markedly increased the
procollagenase content of the second pool. The PTH-induced increase in
procollagenase was dose dependent and paralleled the extent of
calcium loss and lysosomal
enzyme release. The increase in
procollagenase was found in bone, periosteum, and
sutures, where its distribution was similar to that of nonmineralized
collagen. The increase in
procollagenase was abolished by
cycloheximide, but not by
indomethacin,
hydroxyurea,
glucocorticoids,
acetazolamide,
bisphosphonates, or
calcitonin.
Calcitonin and
bisphosphonates almost completely inhibited the PTH-induced Ca loss and lysosomal
enzyme release, but only partially inhibited the PTH-induced loss of
collagen. The latter was, however, completely prevented by the
collagenase inhibitor, CI-1. CI-1 also partially inhibited the PTH-induced Ca loss. Moreover,
collagen degradation occurred in PTH-precultured calvaria (but not in noncultured controls) when incubated in a
buffer under nonviable and nondemineralizing conditions. This degradation was inhibited by
collagenase inhibitors, either CI-1 or the natural
tissue inhibitor of metalloproteinases. This work thus indicates that the resorption of fetal bone explants proceeds along with an accumulation of
procollagenase, primarily within their nonmineralized matrix. Moreover the results suggest that
collagenase is likely to participate in the degradation of the nonmineralized
collagen of the bone explants. Whether it also participates in the degradation of the
collagen of the mineralized matrix remains to be elucidated.