Sex differences in bile acid homeostasis and excretion underlie the disparity in liver cancer incidence between males and females
Department of Molecular and Integrative Physiology, University of Illinois, Urbana-Champaign, United States
Division of Nutritional Sciences, University of Illinois, Urbana-Champaign, United States
Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, United States
Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska, United States
Department of Systems Biology, The University of Texas MD Anderson Cancer Center, United States
CHA Bundang Medical Center, CHA University School of Medicine, Republic of Korea
Collaborative Mass Spectrometry Innovation Center, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, United States
Cancer center at Illinois, University of Illinois, Urbana-Champaign, United States
Department of Pathology, Baylor College of Medicine, United States
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Sex differences in bile acid homeostasis and excretion underlie the disparity in liver cancer incidence between males and females
insights into the influence of sex on bile acid metabolism and the risk of hepatocellular carcinoma (HCC). The data to support that there are inter-relationships between sex, bile acids, and HCC in mice are
, although this is a largely descriptive study. Future studies are needed to understand the interaction of sex hormones, bile acids, and chronic liver diseases and cancer at a mechanistic level. Also, there is not enough evidence to determine the clinical significance of the findings given the differences in bile acid composition between mice and men.
https://doi.org/10.7554/eLife.96783.4.sa0
: Findings that have theoretical or practical implications for a subfield
: Appropriate and validated methodology in line with current state-of-the-art
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Hepatocellular carcinoma (HCC), the common liver cancer, exhibits higher incidence in males. Here, we report that mice lacking bile acid (BA) regulators, Farnesoid X Receptor (FXR also termed NR1H4) and Small Heterodimer Partner (SHP also termed NR0B2), recapitulate the sex difference in liver cancer risk. Since few therapeutic options are available, we focused on understanding the intrinsic protection afforded to female livers. Transcriptomic analysis in control and NR1H4 and NR0B2 double knockout livers identified female-specific changes in metabolism, including amino acids, lipids, and steroids. To assess translational relevance, we examined if transcriptomic signatures obtained from this murine HCC model correlate with survival outcomes for HCC patients. Gene signatures unique to the knockout females correspond with low-grade tumors and better survival. Ovariectomy blunts the metabolic changes and promotes liver tumorigenesis in females that, intriguingly, coincides with increased serum bile acid (BA) levels. Despite similar genetics, knockout male mice displayed higher serum BA concentrations, while female knockouts excreted more BAs. Decreasing enterohepatic BA recirculation using cholestyramine, an FDA-approved resin, dramatically reduced the liver cancer burden in male mice. Overall, we reveal that sex-specific BA metabolism leading to lower circulating BA concentration protects female livers from developing cancer. Thus, targeting BA excretion may be a promising therapeutic strategy against HCC.
Liver cancer, a leading cause of cancer-related death, has diverse etiologies and displays sex-difference with reduced risk in females compared to males (
GBD 2013 Mortality and Causes of Death Collaborators, 2015
). Since current therapies for liver cancer fall short, we posit that understanding molecular mechanisms functioning in the female livers will reveal new therapeutic targets. Earlier studies have reported the role of sex hormones (
) in regulating the sex difference in hepatocellular carcinoma (HCC), but the role of metabolic pathways remains poorly understood.
Rewiring of cellular metabolism enables the tumor cells to maintain viability and grow disproportionately (
). We previously showed that the combined deletion of nuclear receptors, Farnesoid X Receptor (FXR, NR1H4), and Small Heterodimer Partner (SHP, NR0B2) resulted in spontaneous liver cancer in the year-old male mice (
). In this study, we report that, unlike the males, female
) double knockout (DKO) mice exhibit protection against tumorigenesis and thus mimic the sexual dimorphism in liver cancer incidence observed in clinics. Although 15-month-old individual
knockout mice were previously shown to develop liver cancer, unlike the DKO mice, their incidence does not show 100% penetrance nor sex differences (
transcript levels have been noted in cholestasis (reduced bile flow and subsequent increase in hepatic and serum bile acids [(BA])), fatty liver disease, and liver cancer (
). Moreover, individuals with chronic cholestasis exhibit an increased risk for HCC (
). Typically, BA levels are tightly controlled via receptor signaling, including NR1H4 and NR0B2 (
in mice results in juvenile onset cholestasis that progresses to HCC (
). We and others have shown that excessive accumulation and dysregulation of BA homeostasis are directly linked with liver cancer risk (
). However, whether BAs are contributing factors to the sex differences seen in HCC prevalence has not been evaluated.
Therefore, we performed transcriptomic analysis to identify distinct gene profiles from both sexes of control and DKO mice. Then, using five separate human clinical HCC cohorts, we tested the clinical utility of the identified gene signatures from our mouse model. Next, we investigated the role of endogenous estrogen signaling in the DKO mice by performing ovariectomy. We measured hepatic, serum, urine, and fecal BAs from male and female mice to understand their homeostasis. Finally, we manipulated the circulating BA levels in the DKO mice either with a chemical challenge or BA binding resins and examined its consequence on hepatic tumorigenesis. Overall, our data uncover that the differential BA homeostasis between the two sexes can orchestrate the observed gender differences in HCC burden in clinics.
DKO mice phenocopy clinical features of HCC
Here, we report that DKO mice exhibit the sexually dimorphic incidence of HCC observed in the clinic. Despite the loss of BA homeostatic machinery, one-year-old DKO female mice did not develop liver tumors. On the contrary, DKO male livers revealed HCC and well-defined adenomas. But both sexes of a year -old DKO mice displayed fat accumulation, and fibrotic sirius red staining (
). At six months of age, DKO female livers were smaller and displayed reduced sirius red staining, indicative of lower hepatic fibrosis compared to males (
). The difference in tumor burden was reflected in the gross liver to body weight ratio, which was significantly higher in DKO males than in DKO females (
). Serum ALT and AST were elevated in the DKO animals compared to WT, consistent with the cholestatic phenotype of these mice. However, these markers were higher in DKO males, corroborating with advanced disease (
transcript expression was reduced in liver cancer patients (
), underscoring the clinical relevance of this DKO mouse model.
double knockout (DKO) mouse model recapitulates sex difference observed in HCC incidence.
) One-year-old DKO male mice developed hepatocellular carcinoma, which was not observed in age-matched wild type (WT) and DKO female mice (
) Representative H&E stained liver secti