Induction of human airway smooth muscle apoptosis by neutrophils and neutrophil elastase.

Neutrophils are an important component of airway inflammation and may interact with human airway smooth muscle cells (HASMC). We investigated the effect of neutrophils and of neutrophil-derived proteases on HASMC survival. When co-incubated with neutrophils (0.1–1 × 106 cells/ml), attachment of human ASMC was reduced to 12.3 ± 4.3% compared with untreated controls after 72 h. HASMC showed nuclear condensation and fragmentation (41.6 ± 8.1% compared with baseline of 3.1 ± 0.4%), and the biochemical markers of apoptosis, annexin V binding (9.7 ± 0.7%; baseline 1.1 ± 0.3%) and cleaved caspase-3 expression, were observed. The proteolytic activity released by neutrophils was essential for the proapoptotic effect because inhibition of elastase activity by α1-antitrypsin and MeOSuc-Ala-Ala-Pro-Ala-CMK (MSACK) reduced HASMC apoptosis. Human neutrophil elastase (0.1–3 μg/ml) induced apoptosis of HASMC, as well as other neutrophil serine proteases, cathepsin G, and proteinase 3. Fibronectin degradation products wer...