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)