title: Role of plasminogen activator in degradation of extracellular matrix protein by live human alveolar macrophages.
abstract: Recent evidence indicates that human alveolar macrophages can degrade purified elastin in vitro by a cell contact-dependent process involving acidic proteinases of the cysteine proteinase class. It is unclear to what extent these cells can degrade elastin within a natural extracellular matrix. To address this question, we cultured live human alveolar macrophages on elastin-rich, 3H-lysine-labeled, extracellular matrices deposited by rat smooth muscle cells in vitro. Under various culture conditions, we then measured release of total radioactivity from the matrices during co-culture with cells as well as net loss of desmosine/isodesmosine as a specific marker of elastin degradation. Live macrophages adhered to and progressively solubilized matrix protein at a slow rate (approximately 5 micrograms/10(6) cells/24 h) but the rate of solubilization increased more than 15-fold in the presence of plasminogen. The elastin component of the complicated matrix was not measurably degraded in the absence of plasminogen, but in medium containing plasminogen, 3.5 X 10(6) macrophages degraded 25 +/- 8 micrograms of elastin in 72 h. After pretreatment of matrices with trypsin to remove glycoprotein elements, live cells degraded 16 +/- 4 micrograms of elastin under plasminogen-free conditions. The addition of serum to the medium (1 to 5%) inhibited degradation of elastin within whole matrices (approximately 50% compared to serum-free medium containing plasminogen) but had no effect on degradation of elastin in trypsin-pretreated matrices. An active site inhibitor of cysteine proteinases, Z-phenylalanine-phenylalanine-diazomethylketone, blocked approximately 50% of the elastin degradation.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115.
authors.forename: H A
authors.initials: HA
authors.lastname: Chapman
authors.forename: J J
authors.initials: JJ
authors.lastname: Reilly
authors.forename: L
authors.initials: L
authors.lastname: Kobzik
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology; D002478:Cells, Cultured; D004549:Elastin / Q000378:metabolism; D005109:Extracellular Matrix / Q000032:analysis / Q000378:metabolism*; D006801:Humans; D008264:Macrophages / Q000201:enzymology*; D009130:Muscle, Smooth / Q000378:metabolism; D010960:Plasminogen Activators / Q000378:metabolism*; D011506:Proteins / Q000032:analysis / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000201:enzymology*; D051381:Rats
chemical_list: D000596:Amino Acids; D011506:Proteins; D004549:Elastin; D010960:Plasminogen Activators