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Abstract
Interleukin‐1β (IL‐1β) and tumor necrosis factor‐α (TNF‐α) greatly induces osteoclast formation and stimulates bone resorption of mouse calvaria in culture. We examined the effects of the two cytokines on the collagenolysis and bone resorption by induction of matrix metalloproteinases (MMPs). The cells were analyzed using zymographic analysis. It was shown that the mouse calvarial osteoblasts constitutively synthesize progelatinase‐A (MMP‐2). Interleukin‐1β markedly enhanced the messenger RNAs (mRNAs) expression of MMP‐2 (gelatinase A), but slightly MMP‐9 (gelatinase B), which associated with increases in bone matrix degradation. Both pro‐ and active‐forms of MMP‐2 were detected in the conditioned medium collected from calvarial cultures, and IL‐1β markedly stimulated both pro‐ and active‐forms of the MMP‐2. The expression of MMP‐2 mRNAs could be detected, and they were markedly enhanced by IL‐1β on days 1 and 2. These results demonstrate that the potency of induction of MMP‐2 by IL‐1β and TNF‐α is closely linked to the respective bone‐resorbing activity, suggesting that MMP‐2‐dependent degradation of bone matrix plays a key role in bone resorption induced by these cytokines. On the other hand, when the mouse osteoblasts were stimulated with parathyroid hormone, 1,25(OH)2D3, mononuclear cell conditioned medium (MCM) and IL‐1 as bone resorption agents, collagenolysis was increased by producing the active gelatinase. Interleukin‐1 in stimulating bone resorption was examined using fetal mouse long bone organ culture. Interleukin‐1 stimulated bone resorption and produced marked resorption when present simultaneously. Furthermore, treatment of indomethacin and dexamethasone clearly abolished the responses of IL‐1α and IL‐1β.