C5a delays apoptosis of human neutrophils by a phosphatidylinositol 3-kinase-signaling pathway.
BACKGROUND
Studies have shown that survival factors including cytokines and growth factors delay apoptosis of human neutrophils via induction of the phosphatidylinositol-3 kinase (PI 3-K)/Akt pathway. In the present study, we explored whether complement fragment C5a has a modulatory effect on neutrophil apoptosis through this signaling pathway.


METHODS
Human neutrophils were isolated and treated with C5a for up to 24 hours, with or without wortmannin, a PI 3-K inhibitor, and staurosporine, a caspase-9 activator. Apoptosis was quantified by flow cytometry, using propidium iodide nuclear staining, and confirmed by the detection of DNA fragmentation on gel electrophoresis. PI 3-K downstream signaling events were evaluated by measuring the expression of cytosolic total and phosphorylated Akt and Bad proteins by Western blot analyses, and caspase-9 activity.


RESULTS
C5a inhibited neutrophil apoptosis in a dose- and time-dependent manner. The anti-apoptotic effects of C5a were markedly abrogated in the presence of wortmannin. Brief stimulation of neutrophils with C5a induced phosphorylation of Akt and Bad proteins through a PI 3-K-dependent pathway. Caspase-9 activity was minimal in C5a-treated cells, but markedly increased following PI 3-K inhibition by wortmannin. Finally, C5a reduced caspase-9 activity in staurosporine-treated cells.


CONCLUSIONS
This study demonstrates that C5a inhibits neutrophil apoptosis via a PI 3-K signaling pathway. This effect may be an important mechanism that improves cell survival and function in the inflammatory milieu.
Perianayagam
Mary C
MC
Division of Nephrology, Department of Medicine, Tupper Research Institute, New England Medical Center, Tufts University School of Medicine, Boston, Massachusetts, USA.
Balakrishnan
V S
VS
King
Andrew J
AJ
Pereira
Brian J G
BJ
Jaber
Bertrand L
BL
D000730:Androstadienes / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D015936:Complement C5a / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D009504:Neutrophils / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D019311:Staurosporine / Q000494:pharmacology; D000077191:Wortmannin; D051025:bcl-Associated Death Protein
D000730:Androstadienes; D002352:Carrier Proteins; D053453:Caspase 9; D020169:Caspases; D015936:Complement C5a; D004791:Enzyme Inhibitors; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019311:Staurosporine; D000077191:Wortmannin; D051025:bcl-Associated Death Protein; C494819:BAD protein, human; C494918:AKT1 protein, human; C506433:CASP9 protein, human