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The bile acid glycochenodeoxycholate induces trail-receptor 2/DR5 expression and apoptosis
H Higuchi1, S F Bronk, Y Takikawa
1Division of Gastroenterology and Hepatology, Mayo Medical School, Clinic, and Foundation, Rochester, Minnesota 55905, USA.
Abstract:
Toxic bile salts induce hepatocyte apoptosis by both Fas-dependent and -independent mechanisms. In this study, we examined the cellular mechanisms responsible for Fas-independent, bile acid-mediated apoptosis. HuH-7 cells, which are known to be Fas deficient, were stably transfected with the sodium-dependent bile acid transporting polypeptide. The toxic bile acid glycochenodeoxycholate (GCDC)-induced apoptosis in these cells in a time- and concentration-dependent manner. Apoptosis and mitochondrial cytochrome c release were inhibited by transfection with dominant negative FADD, CrmA transfection, or treatment with the selective caspase 8 inhibitor IETD-CHO. These observations suggested the Fas-independent apoptosis was also death receptor mediated. Reverse transcriptase-polymerase chain reaction demonstrated tumor necrosis factor-R1, tumor necrosis factor-related apoptosis inducing ligand (TRAIL)-R1/DR4, -R2/DR5, and TRAIL, but not tumor necrosis factor-alpha expression by these cells. GCDC treatment increased expression of TRAIL-R2/DR5 mRNA and protein 10-fold while expression of TRAIL-R1 was unchanged. Furthermore, aggregation of TRAIL-R2/DR5, but not TRAIL-R1/DR4 was observed following GCDC treatment of the cells. Induction of TRAIL-R2/DR5 expression and apoptosis by bile acids provides new insights into the mechanisms of hepatocyte apoptosis and the regulation of TRAIL-R2/DR5 expression.
Insights
Toxic bile salts trigger hepatocyte apoptosis via Fas-independent pathways. Glycochenodeoxycholate (GCDC) upregulates TRAIL-R2/DR5, inducing cell death, offering new insights into liver injury mechanisms.
Area of Science:
- Hepatology
- Cell Biology
- Molecular Toxicology
Background:
- Toxic bile acids induce hepatocyte apoptosis through both Fas-dependent and -independent pathways.
- Understanding the precise mechanisms of Fas-independent apoptosis is crucial for liver disease research.
Purpose of the Study:
- To investigate the cellular mechanisms underlying Fas-independent, bile acid-mediated hepatocyte apoptosis.
- To elucidate the role of death receptors in bile acid-induced liver cell death.
Main Methods:
- HuH-7 cells, deficient in Fas, were transfected with a bile acid transporter.
- Cells were treated with glycochenodeoxycholate (GCDC) and analyzed for apoptosis, cytochrome c release, and death receptor expression.
- Techniques included dominant-negative FADD transfection, CrmA transfection, caspase 8 inhibition, and RT-PCR.
Main Results:
- GCDC induced time- and concentration-dependent apoptosis and mitochondrial cytochrome c release in HuH-7 cells.
- Apoptosis was inhibited by blocking FADD, CrmA, or caspase 8, indicating death receptor involvement.
- GCDC treatment significantly increased TRAIL-R2/DR5 mRNA and protein expression, leading to receptor aggregation.
Conclusions:
- Fas-independent hepatocyte apoptosis induced by bile acids is mediated through death receptors, specifically TRAIL-R2/DR5.
- Bile acids regulate TRAIL-R2/DR5 expression, providing novel insights into mechanisms of hepatocyte apoptosis and liver injury.