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The effects of recombinant human interleukin-1 alpha (IL-1 alpha) and murine epidermal growth factor (EGF) on the release of collagenase were studied in an in vitro model system using periosteal explants from rabbit calvariae. Following an incubation period of 72 h it was shown that IL-1 alpha in combination with EGF (IL-1 alpha + EGF) induced a synergistic increase in the amount of collagenase released by periosteal explants. This increase appeared to be at least 10-fold. Most of the enzyme was present in a latent form since the increase in enzyme activity was only detectable after activation by APMA and the molecular weight as determined in immunoblots corresponded to the latent form of this enzyme. Incubations carried out with IL-1 alpha alone resulted in a 2- to 4-fold increase of total enzyme activity, whereas the amount of collagenase in media of EGF-treated periosteal did not surpass control values. A neutralizing anti-IL-1 alpha antibody completely blocked the enhanced release of collagenase as induced both by IL-1 alpha and by IL-1 alpha + EGF. Indomethacin partially prevented the IL-1 alpha + EGF-induced increase in enzyme release, suggesting the involvement of prostaglandins. The amount of tissue inhibitor of metalloproteinases (TIMP) as determined by ELISA was slightly elevated in culture media obtained from all cytokine-treated explants. Comparable results were obtained by Western blot analysis as well as by a functional bioassay. It is suggested that the concomitant presence of the cytokines IL-1 alpha and EGF may play an important role in collagenase-mediated degradation of collagen.

It is now apparent that multiple proteinases cooperate in the degradation of the collagenous matrix. Among these proteinases are two biochemically related proteinases which were originally identified by their ability to degrade denatured collagens. The higher molecular weight proteinase (M(r) = 92,000) is predominantly expressed by inflammatory cells while the lower molecular weight proteinase (M(r) = 72,000) is secreted constitutively by fibroblasts. To explore the expression of the 92 kDa proteinase, the gelatinase from human neutrophils was purified and characterized and specific immunologic probes developed for its study in other cell types. Studies of leukemic cell lines (U937s and HL60s) which can be differentiated to a monocyte/macrophage phenotype revealed that after differentiation with phorbol myristic acetate the 92 kDa proteinase was the major proteinase produced. Additional studies of human alveolar macrophages and monocytes differentiated in vitro suggest that these cells secrete a proteinase immunologically and biochemically similar to human neutrophil gelatinase. Although the major gelatinase secreted by the fibroblasts is the 72 kDa proteinase, they also produce the 92 kDa proteinase in a regulated manner. These studies suggest that the regulation of these similar gelatinolytic proteinases varies dependent on cell type. Further studies of their regulation will be important to define the roles of these proteinases in physiologic and pathological processes.