Na+/H+ exchanger mediates TNF-alpha-induced hepatocyte apoptosis via the calpain-dependent degradation of Bcl-xL.
OBJECTIVE
It is well known that tumor necrosis factor-alpha (TNF-alpha) induces hepatocyte apoptosis and contributes to liver diseases. However, the exact mechanisms are not well understood.


METHODS
In the present study, we reported that Na(+)/H(+) exchanger (NHE) is involved in TNF-alpha-induced hepatocyte apoptosis.


RESULTS
TNF-alpha time dependently induced an increase in NHE activity in hepatocytes, but cariporide, an NHE inhibitor, blocked the TNF-alpha-induced increase of NHE activity in a dose-dependent manner. Increased NHE activity induced by TNF-alpha was associated with increased intracellular calcium (Ca(2+)(i)) concentration and calpain activity. Cariporide reversed these effects induced by TNF-alpha. In addition, TNF-alpha downregulated Bcl-xL, an anti-apoptotic protein, but not mRNA levels. The inhibition of either calpain or NHE blocked the TNF-alpha-induced decrease of the Bcl-xL protein. TNF-alpha did not change the pro-apoptotic Bax and Bak protein levels. Cariporide, calcium remover 1,2-bis (2-aminophenoxy) ethane-N,N,N0,N0-tetraacetic acid, or calpain inhibitor benzyloxycarbonyl-leucyl-leucinal attenuated TNF-alpha-induced hepatocyte apoptosis.


CONCLUSIONS
TNF-alpha via NHE results in hepatocyte apoptosis through the calcium/calpain/Bcl-xL pathway.
Liu
Zhan
Z
Department of Gastroenterology, The First Affiliated Hospital of Hunan Normal University (People's Hospital of Hunan Province), Changsha City, China. liuzhan2004@126.com
Wang
Shuangxi
S
Zhou
Huixin
H
Yang
Yuming
Y
Zhang
Mingliang
M
D017209:Apoptosis / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006146:Guanidines / Q000494:pharmacology; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D006801:Humans; D015398:Signal Transduction / Q000187:drug effects; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism*
C494826:BAX protein, human; C494811:BCL2L1 protein, human; D002614:Chelating Agents; D015853:Cysteine Proteinase Inhibitors; D004151:Dipeptides; D006146:Guanidines; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; D014409:Tumor Necrosis Factor-alpha; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; C400241:benzyloxycarbonylleucyl-leucine aldehyde; D004533:Egtazic Acid; C093373:cariporide; D002154:Calpain; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium