Inhibition of nuclear factor kappaB and phosphatidylinositol 3-kinase/Akt is essential for massive hepatocyte apoptosis induced by tumor necrosis factor alpha in mice.
OBJECTIVE
Tumor necrosis factor (TNF)-alpha itself does not induce liver injury in normal mice or hepatocytes. Rather, this event, especially in vitro, is explained by the fact that the TNF-alpha/TNF receptor system not only triggers downstream signals leading to apoptosis but also induces an antiapoptotic pathway through the activation of nuclear factor (NF)-kappaB. The aim of this study was to determine whether inhibition of antiapoptotic pathways influences the susceptibility of mice to TNF-alpha. Here, we focused on the roles of NF-kappaB and phosphatidylinositol 3-kinase (PI3K)-regulated serine/threonine kinase Akt.


METHODS
TNF-alpha was administered to BALB/c mice after treatment with an adenovirus expressing a mutant form IkappaBalpha (Ad5IkappaB), the PI3K inhibitor wortmannin, or both. Liver injury was assessed biochemically and histologically. The expression of Bcl-2 family members and caspase activity were examined.


RESULTS
In the mice livers, treatment with Ad5IkappaB or the wortmannin suppressed the activation of NF-kappaB or Akt, respectively. Suppression of either NF-kappaB or Akt showed a slight increase in transaminase levels and focal liver cell death after TNF-alpha administration. However, in mice treated with both Ad5IkappaB and wortmannin, TNF-alpha administration resulted in massive hepatocyte apoptosis and hemorrhagic liver destruction in mice. The combination of Ad5IkappaB, wortmannin, and TNF-alpha markedly increased the activation of caspase-3 and -9, and activated caspase-8 to a lesser degree, suggesting that TNF-alpha-induced hepatocyte apoptosis is dependent on type II cell death signaling pathway, probably through the mitochondria. Inhibition of the NF-kappaB and PI3K/Akt pathways had no effect on expression of Bcl-2 families.


CONCLUSIONS
The inducible activation of NF-kappaB and constitutive activation of Akt regulate hepatocyte survival against TNF-alpha, which occurs independent of Bcl-2 families.
Imose
Motoaki
M
First Department of Internal Medicine, Gifu University School of Medicine, Gifu, Japan.
Nagaki
Masahito
M
Naiki
Takafumi
T
Osawa
Yosuke
Y
Brenner
David A
DA
Asano
Takahiko
T
Hayashi
Hideki
H
Kato
Tomohiro
T
Moriwaki
Hisataka
H
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000235:genetics; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D022781:Hepatocytes / Q000166:cytology* / Q000201:enzymology; D020672:I-kappa B Proteins / Q000235:genetics / Q000494:pharmacology; D066298:In Vitro Techniques; D017093:Liver Failure / Q000139:chemically induced / Q000188:drug therapy* / Q000378:metabolism; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D015778:Minor Histocompatibility Antigens; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009363:Neoplasm Proteins / Q000235:genetics; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D013047:Specific Pathogen-Free Organisms; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D000077191:Wortmannin; D051028:bcl-2-Associated X Protein; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein
D000730:Androstadienes; D000970:Antineoplastic Agents; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins; D061945:Caspase Inhibitors; D020169:Caspases; D004791:Enzyme Inhibitors; D020672:I-kappa B Proteins; D015778:Minor Histocompatibility Antigens; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B; D009363:Neoplasm Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D014409:Tumor Necrosis Factor-alpha; D000077191:Wortmannin; D051028:bcl-2-Associated X Protein; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein; C096816:BCL2-related protein A1; C494820:Bad protein, mouse; C494812:Bcl2l1 protein, mouse; C494815:Bid protein, mouse; C000606205:Nfkbia protein, mouse