Leukocyte elastase induces epithelial apoptosis: role of mitochondial permeability changes and Akt.
During acute inflammation, neutrophil-mediated injury to epithelium may lead to disruption of epithelial function, including the induction of epithelial apoptosis. Herein, we report the effects of neutrophil transmigration and of purified leukocyte elastase on epithelial cell survival. Neutrophil transmigration induced apoptosis of epithelial cells [control monolayers: 5 +/- 1 cells/25 high-power fields (HPF) vs. neutrophil-treated monolayers: 29 +/- 10 cells/HPF, P < 0.05, n = 3 as determined by terminal deoxynucleotidyl transferase dUTP nick-end labeling assay] as did low concentrations (0.1 U/ml) of purified leukocyte elastase (control monolayers: 6.4 +/- 2.5% apoptotic vs. elastase: 26.2 +/- 2.9% apoptotic, P < 0.05, as determined by cytokeratin 18 cleavage). Treatment with elastase resulted in decreased mitochondrial membrane potential, release of cytochrome c to the cytosol, and cleavage of caspases-9 and -3 as determined by Western blot analysis, implicating altered mitochondrial membrane permeability as a primary mechanism for elastase-induced apoptosis. Additionally, incubation of epithelial cells with leukocyte elastase resulted in an early increase followed by a decrease in the phosphorylation of epithelial Akt, a serine/threonine kinase important in cell survival. Inhibition of epithelial Akt before elastase treatment potentiated epithelial cell apoptosis, suggesting that the initial activation of Akt represents a protective response by the epithelial cells to the proapoptotic effects of leukocyte elastase. Taken together, these observations suggest that epithelial cells exhibit a dual response to cellular stress imposed by leukocyte elastase with a proapoptotic response mediated via early alterations in mitochondrial membrane permeability countered by activation of the survival pathway involving Akt.
Ginzberg
Hedy H
HH
Division of respirology, Department of Medicine, University of Toronto, 1 Kings College Circle, Toronto, Ontario, Canada M5S 1A8.
Shannon
Patrick T
PT
Suzuki
Tomoko
T
Hong
Ouyang
O
Vachon
Eric
E
Moraes
Theo
T
Abreu
Maria Teresa Herrera
MT
Cherepanov
Vera
V
Wang
Xiaomin
X
Chow
Chung-Wai
CW
Downey
Gregory P
GP
D017209:Apoptosis / Q000502:physiology*; D020169:Caspases / Q000378:metabolism; D002465:Cell Movement; D002478:Cells, Cultured; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D007413:Intestinal Mucosa / Q000502:physiology*; D019272:Leukocyte Elastase / Q000378:metabolism*; D008931:Mitochondria, Muscle / Q000378:metabolism*; D009130:Muscle, Smooth / Q000378:metabolism; D009504:Neutrophils / Q000378:metabolism; D010539:Permeability; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D019061:src-Family Kinases / Q000378:metabolism
D020169:Caspases; D038362:Glycogen Synthase Kinase 3; D000071679:Glycogen Synthase Kinase 3 beta; D019272:Leukocyte Elastase; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019061:src-Family Kinases; C494918:AKT1 protein, human