title: The effect of tissue type plasminogen activator (tPA) on osteoclastic resorption in embryonic mouse long bone explants: a possible role for the growth factor domain of tPA.
abstract: Osteoblasts produce proteolytic enzymes and their production is regulated by osteotropic agents. It has been suggested that these proteases play a role in bone resorption by removing the superficial collagenous layer from the bone matrix and indirectly inducing migration of osteoclast precursors towards the bone matrix. We examined the effect of the plasminogen activator tPA on osteoclastic resorption using 17-day-old mouse embryonic long bone explants representing different stages of osteoclast development, that is, radii containing already mature osteoclasts and metacarpals containing no mature osteoclasts but only osteoclast precursors/progenitors which are still confined to the periosteum. Tissue type PA stimulated osteoclastic resorption (measured as 45Ca-release) in 17-day-old fetal metacarpals but not in radii of the same animal. Blocking the enzymatic activity of tPA did not inhibit its effect on osteoclastic resorption. Plasmin, the direct product of PA enzymatic activity, did not induce osteoclastic resorption. However, a tPA-mutant missing the growth-factor-like domain of the molecule, failed to stimulate 45Ca-release from the metacarpals. In addition, in both systems tPA and transforming growth factor alpha had similar effects on osteoclastic resorption. The finding that tPA stimulated 45Ca-release only in the metacarpals suggests that tPA has an effect on osteoclast formation rather than on the activity of already mature osteoclasts. Under the experimental conditions used this effect seems to be mediated by the growth factor domain of tPA rather than by the enzymatic activity of the molecule.
authors.affiliation: Department of Endocrinology and Metabolism, University Hospital Leiden, The Netherlands.
authors.forename: K
authors.initials: K
authors.lastname: Hoekman
authors.forename: C W
authors.initials: CW
authors.lastname: Löwik
authors.forename: M
authors.initials: M
authors.lastname: van de Ruit
authors.forename: O L
authors.initials: OL
authors.lastname: Bijvoet
authors.forename: J H
authors.initials: JH
authors.lastname: Verheijen
authors.forename: S E
authors.initials: SE
authors.lastname: Papapoulos
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D001862:Bone Resorption / Q000209:etiology* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D046508:Culture Techniques; D005260:Female; D005341:Fibrinolysin / Q000494:pharmacology; D051379:Mice; D009154:Mutation; D010010:Osteoclasts / Q000187:drug effects* / Q000378:metabolism; D011247:Pregnancy; D011994:Recombinant Proteins / Q000494:pharmacology; D010959:Tissue Plasminogen Activator / Q000235:genetics / Q000494:pharmacology*; D016211:Transforming Growth Factor alpha / Q000494:pharmacology
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D011994:Recombinant Proteins; D016211:Transforming Growth Factor alpha; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin; C040308:phenylalanyl-prolyl-arginine-chloromethyl ketone; D002118:Calcium