Extracellular matrix regulates apoptosis in human neutrophils

Background. During inflammation, polymorphonuclear neutrophils (PMNs) migra te into the affected tissue interacting with extracellular matrix (ECM) pro teins. We tested the hypothesis that PMN-matrix interaction affects PMN apo ptosis. Methods Apoptosis of human PMNs was detected by DNA-fragmentation assay and was quantitated by flow cytometry, ultraviolet and light microscopy. Cell adhesion was assessed by a toluidine blue assay, and cell spreading was det ected by phase contrast microscopy. Protein tyrosine phosphorylation was st udied using Western blotting and confocal microscopy. Results. PMN apoptosis was not different in unstimulated cultures on either surface-adherent fibronectin or on Poly-Hema, a surface that prevents cell adherence. However, tumor necrosis factor-alpha (TNF alpha) treatment sign ificantly increased apoptosis on fibronectin (37 +/- 4%) compared with Poly Hema (20 +/- 3%). Tests on other matrix substances revealed that the percen tage of apoptotic PMNs in the presence of TNF alpha was 8 +/- 1% on PolyHem a, 26 +/- 4% on fibronectin, 17 +/- 2% on collagen I, 16 +/- 2% on collagen TV, and 16 +/- 3% on laminin (P < 0.05 for all matrices compared with Poly Hema). Preincubation with genistein (50 mu M) significantly inhibited TNF a lpha-mediated apoptosis on fibronectin (39 +/- 4% to 21 +/- 4%) but not on PolyHema (21 +/- 4% to 16 +/- 4%). Genistein also reduced PMN spreading on fibronectin. In contrast, inhibitors of mitogen-activated protein kinase an d protein kinase C showed no effect on PMN apoptosis. Fibronectin strongly increased tyrosine phosphorylation of three 102, 63, and 54 kDa proteins. F ive newly tyrosine-phosphorylated 185, 85, 66, 56, and 42 kDa bands were al so visible. Using confocal microscopy, highest tyrosine phosphorylation was localized to sites of cell-matrix interaction. Conclusions. ECM influences apoptosis in TNF alpha-activated, adherent, spr eading PMNs. The process is regulated by tyrosine phosphorylation. Accelera tion of apoptosis may shorten the PMN lifespan and thereby locally regulate inflammation.