Bile acids regulate cysteine catabolism and glutathione regeneration to modulate hepatic sensitivity to oxidative injury
Yifeng Wang, Jibiao Li, David Matye, Yuxia Zhang, Katie Dennis, Wen-Xing Ding, Tiangang Li
Yifeng Wang, Jibiao Li, David Matye, Yuxia Zhang, Katie Dennis, Wen-Xing Ding, Tiangang Li
View: Text | PDF
Research Article Hepatology Metabolism

Bile acids regulate cysteine catabolism and glutathione regeneration to modulate hepatic sensitivity to oxidative injury

Abstract

Bile acids are signaling molecules that critically control hepatocellular function. Disrupted bile acid homeostasis may be implicated in the pathogenesis of chronic liver diseases. Glutathione is an important antioxidant that protects the liver against oxidative injury. Various forms of liver disease share the common characteristics of reduced cellular glutathione and elevated oxidative stress. This study reports a potentially novel physiological function of bile acids in regulating hepatic sulfur amino acid and glutathione metabolism. We found that bile acids strongly inhibited the cysteine dioxygenase type-1–mediated (CDO1-mediated) cysteine catabolic pathway via a farnesoid X receptor–dependent mechanism. Attenuating this bile acid repressive effect depleted the free cysteine pool and reduced the glutathione concentration in mouse liver. Upon acetaminophen challenge, cholestyramine-fed mice showed impaired hepatic glutathione regeneration capacity and markedly worsened liver injury, which was fully prevented by N-acetylcysteine administration. These effects were recapitulated in CDO1-overexpressing hepatocytes. Findings from this study support the importance of maintaining bile acid homeostasis under physiological and pathophysiological conditions, as altered hepatic bile acid signaling may negatively impact the antioxidant defense mechanism and sensitivity to oxidative injury. Furthermore, this finding provides a possible explanation for the reported mild hepatotoxicity associated with the clinical use of bile acid sequestrants in human patients.

Authors

Yifeng Wang, Jibiao Li, David Matye, Yuxia Zhang, Katie Dennis, Wen-Xing Ding, Tiangang Li

×

Figure 4

SHP repressed HNF4α transactivation of CDO1 reporter activity.

Options: View larger image (or click on image) Download as PowerPoint
SHP repressed HNF4α transactivation of CDO1 reporter activity. (A and B)...
(A and B) C57BL/6J male mice at 12 weeks of age (n = 5) were injected with empty adenovirus (Ad-Null) or Ad-shHNF4α. After 7 days, mice were fasted for 6 hours and sacrificed. The mRNA results are expressed as mean ± SD. *P < 0.05 versus Ad-Null. (C) WT and HNF4α-mutant CDO1-Intron 3-Luc constructs and pGL3-basic construct (0.2 μg), β-gal construct (0.05 μg), and 0.1 μg pcDNA3.0 or HNF4α plasmid were cotransfected into AML12 cells. Luciferase and β-gal activities were measured 48 hours later. The putative HNF4α binding site and mutant sequences are shown below the bar graph. *P < 0.05 versus pcDNA3.0; #P < 0.05 versus corresponding WT-Luc. NS, not significant. (D) ChIP assay detection of HNF4α occupancy to the intron 3 of the Cdo1 chromatin in mouse livers. *P < 0.05 versus IgG. (E) EMSA detection of HNF4α binding to the WT but not the mutant HNF4α binding site in the CDO1 intron 3 DNA probe. Mut, CDO1 probe with mutations introduced into the HNF4α binding site as shown in C. (F) CDO1-Intron 3-Luc plasmids (0.2 μg), β-gal expression construct (0.05 μg), and 0.2 μg pcDNA3.0 or 0.1 μg FXR and 0.1 μg RXR were cotransfected into AML12 cells. After 24 hours, cells were treated with vehicle (DMSA) or GW4064 (1 μM) for 24 hours. *P < 0.05 versus vehicle; #P < 0.05 versus corresponding pcDNA3.0. (G) Luciferase reporter constructs (0.2 μg), β-gal expression construct (0.05 μg), and 0.1 μg (+) or 0.2 μg (++) HNF4α and/or SHP expression plasmids were cotransfected into AML12 cells. Luciferase and β-gal activities were measured 48 hours later. *P < 0.05 versus control (first bar); #P < 0.05 versus HNF4α (third bar). (H) WT and mutant CDO1-Intron 3-Luc plasmids (0.2 μg), β-gal expression construct (0.05 μg), and 0.1 μg pcDNA3.0 or HNF4α were cotransfected into AML12 cells. Luciferase and β-gal activities were measured 48 hours later. *P < 0.05 versus pcDNA3.0; #P < 0.05 versus corresponding WT-Luc. All reporter assay results are shown as mean of triplicates ± SD (technical repeats). Statistical significance determined by 2-tailed Student’s t test (A and D) or 2-way ANOVA with Tukey’s post hoc test (C, F–H). CDO1, cysteine dioxygenase 1; SHP, small heterodimer partner; FXR, farnesoid X receptor; RXR, retinoic X receptor; HNF4α, hepatocyte nuclear factor 4α.