Bile acid-induced apoptosis in hepatocytes is caspase-6-dependent.
Apoptosis induced by hydrophobic bile acids is thought to contribute to liver injury during cholestasis. Caspase-6 is an executioner caspase that also appears to have regulatory functions in hematopoetic cell lines. We aimed to elucidate the role of caspase-6 in bile acid-induced apoptosis. The major human hydrophobic bile acid, glycochenodeoxycholic acid (GCDCA, 75 micromol/liter), rapidly induced caspase-6 cleavage in HepG2-Ntcp human hepatoma cells. GCDCA-induced, but not tumor necrosis factor alpha- or etoposide-induced activation of effector caspases-3 and -7 was significantly reduced by 50% in caspase-6-deficient HepG2-Ntcp cells as well as in primary rat hepatocytes pretreated with a caspase-6 inhibitor. Inhibition of caspase-9 reduced GCDCA-induced activation of caspase-6, whereas inhibition of caspase-6 reduced activation of caspase-8 placing caspase-6 between caspase-9 and caspase-8. GCDCA also induced apoptosis in Fas-deficient Hep3B-Ntcp and HuH7-Ntcp hepatoma cells. In addition, GCDCA-induced apoptosis was reduced by 50% in FADD-deficient HepG2-Ntcp cells, whereas apoptosis induced by tumor necrosis factor alpha was reduced by 90%. Collectively, these observations suggest that GCDCA can induce hepatocyte apoptosis in the absence of death receptor signaling, presumably by a compensatory mitochondrial pathway. In conclusion, caspase-6 appears to play an important regulatory role in the promotion of bile acid-induced apoptosis as part of a feedback loop.
Rust
Christian
C
Department of Medicine 2, Grosshadern, University of Munich, 81377 Munich, Germany. Electronic address: christian.rust@med.uni-muenchen.de.
Wild
Nadine
N
Department of Medicine 2, Grosshadern, University of Munich, 81377 Munich, Germany.
Bernt
Carina
C
Department of Medicine 2, Grosshadern, University of Munich, 81377 Munich, Germany; Eugenex Biotechnologies, 8274 Traegerwilen, Switzerland.
Vennegeerts
Timo
T
Department of Medicine 2, Grosshadern, University of Munich, 81377 Munich, Germany.
Wimmer
Ralf
R
Department of Medicine 2, Grosshadern, University of Munich, 81377 Munich, Germany.
Beuers
Ulrich
U
Department of Gastroenterology and Hepatology, Academic Medical Center, University of Amsterdam, 1105 Amsterdam, The Netherlands.
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001483:Base Sequence; D053178:Caspase 6 / Q000378:metabolism*; D002460:Cell Line; D017931:DNA Primers; D004789:Enzyme Activation; D020868:Gene Silencing; D005999:Glycochenodeoxycholic Acid / Q000494:pharmacology*; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D034741:RNA, Small Interfering; D051381:Rats
D017931:DNA Primers; D034741:RNA, Small Interfering; D005999:Glycochenodeoxycholic Acid; D053178:Caspase 6