PI 3-kinase pathway is responsible for antiapoptotic effects of atrial natriuretic peptide in rat liver transplantation.
OBJECTIVE
To investigate the in vivo effect of atrial natriuretic peptide (ANP) and its signaling pathway during orthotopic rat liver transplantation.


METHODS
Rats were infused with NaCl, ANP (5 microg/kg), wortmannin (WM, 16 microg/kg), or a combination of both for 20 min. Livers were stored in UW solution (4 degrees C) for 24 h, transplanted and reperfused. Apoptosis was examined by caspase-3 activity and TUNEL staining. Phosphorylation of Akt and Bad was visualized by Western blotting and phospho-Akt-localization by confocal microscopy.


RESULTS
ANP-pretreatment decreased caspase-3 activity and TUNEL-positive cells after cold ischemia, indicating antiapoptotic effects of ANP in vivo. The antiapoptotic signaling of ANP was most likely caused by phosphorylation of Akt and Bad, since pretreatment with PI 3-kinase inhibitor WM abrogated the ANP-induced reduction of caspase-3 activity. Interestingly, analysis of liver tissue by confocal microscopy showed translocation of phosphorylated Akt to the plasma membrane of hepatocytes evoked by ANP.


CONCLUSIONS
ANP activates the PI-3-kinase pathway in the liver in vivo leading to phosphorylation of Bad, an event triggering antiapoptotic signaling cascade in ischemic liver.
Institute for Surgical Research, Klinikum Grosshadern, University of Munich, Germany.
Uwe
U
Grutzner
Melanie
M
Keller
Michael
M
Bach
Alexandra K
AK
Kiemer
Herbert
H
Meissner
Manfred
M
Bilzer
Stefan
S
Zahler
Alexander L
AL
Gerbes
Angelika M
AM
Vollmar
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D009320:Atrial Natriuretic Factor / Q000378:metabolism / Q000494:pharmacology*; D015153:Blotting, Western; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004789:Enzyme Activation; D006651:Histocytochemistry; D020287:In Situ Nick-End Labeling; D008099:Liver / Q000098:blood supply / Q000378:metabolism* / Q000502:physiology; D016031:Liver Transplantation; D008297:Male; D018613:Microscopy, Confocal; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D011917:Rats, Inbred Lew; D015427:Reperfusion Injury / Q000378:metabolism / Q000517:prevention & control; D015398:Signal Transduction; D051025:bcl-Associated Death Protein / Q000378:metabolism
C494821:Bad protein, rat; C472610:atrial natriuretic peptide, rat; D051025:bcl-Associated Death Protein; D009320:Atrial Natriuretic Factor; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases