Alteration of hepatic nuclear receptor-mediated signaling pathways in hepatitis C virus patients with and without a history of alcohol drinking

Abstract

The current study tests a hypothesis that nuclear receptor signaling is altered in chronic hepatitis C patients and that the altered pattern is specific to alcohol drinking history. The expression of a panel of more than 100 genes encoding nuclear receptors, coregulators, and their direct/indirect targets was studied in human livers. Gene expression pattern was compared between 15 normal donor livers and 23 hepatitis C virus (HCV) genotype 1-positive livers from patients without a drinking history (matched for age, sex, and body mass index). HCV infection increased the expression of nuclear receptors small heterodimer partner and constitutive androstane receptor (CAR) as well as genes involved in fatty acid trafficking, bile acid synthesis and uptake, and inflammatory response. However, the expression of retinoid X receptor (RXR) α, peroxisomal proliferator-activated receptor (PPAR) α and β as well as steroid regulatory element-binding protein (SREBP)-1c was decreased in HCV-infected livers. Gene expression pattern was compared in chronic hepatitis C patients with and without a drinking history. Alcohol drinking increased the expression of genes involved in fatty acid uptake, trafficking, and oxidation, but decreased the expression of genes responsible for gluconeogenesis. These changes were consistent with reduced fasting plasma glucose levels and altered expression of upstream regulators that include RXRα, PPARα, and CAR. The messenger RNA levels of fibroblast growth factor 21, interleukin-10, and fatty acid synthase, which are all regulated by nuclear receptors, showed independent correlation with hepatic HCV RNA levels.

Conclusion: Our findings suggest that those genes and pathways that showed altered expression could potentially be therapeutic targets for HCV infection and/or alcohol drinking-induced liver injury.

Figure 1

The expressions of nuclear receptors and their downstream target genes were studied in 23 hepatitis C patients' livers and 15 donor livers. (A) Nuclear receptor and co-regulator genes. (B) Genes that regulate lipid homeostasis. (C) Genes that regulate bile acid synthesis and uptake. (D) Gene expression in inflammatory pathways. Mean ± SEM are shown. *: p<0.05 in comparisons between two groups. NL: normal livers; HC: hepatitis C.

Figure 2

The expression level of nuclear receptors and their downstream target genes were studied in the livers of male hepatitis C patients with (n=21) and without (n=13) an alcohol drinking history. (A) Nuclear receptor genes. (B) Genes in fatty acid oxidation pathway. (C) Genes in fatty acid uptake and intracellular trafficking pathways. (D) Genes in glucose uptake and gluconeogenesis pathways. HC: chronic hepatitis C patients without a history of drinking. HC+AL: chronic hepatitis C patients with a drinking history. Mean ± SEM are shown.*: p<0.05 in comparisons between HC and HC+AL.

Figure 3

Observed hepatic HCV RNA values versus predicted HCV RNA values based on hepatic FGF21, IL10, and FAS mRNA levels (standardized to have mean 0 and standard deviation 1). The adjusted R2 of this model was 0.63.

Figure 4

Nuclear receptor-mediated pathways in chronic hepatitis C patients. (1) Fat influx and efflux. FATP and CD36 are involved in fatty acid uptake and MTP is important to VLDL secretion. The expression levels of FATP5, FATP2, and MTP are up-regulated in livers with chronic hepatitis C infection compared with controls. (2) Fatty acid synthesis and oxidation. SREBP-1c and PPARα are the key regulators of fatty acid synthesis and oxidation. Their expression is down-regulated in livers with chronic hepatitis C infection compared with controls. (3) Glucose uptake. GLUT2 mediates facilitated glucose uptake. Its expression was up-regulated in livers with chronic hepatitis C infection compared with controls, but de novo fatty acid synthesis was not up-regulated. (4) Bile acid synthesis and uptake. CYP7A1 catalyzes the rate-limiting step in cholesterol catabolism and bile acid biosynthesis and NTCP is involved in hepatic sodium/bile acid uptake. Expression of both genes was up-regulated in livers with chronic hepatitis C infection compared with controls. Bile acids enhance genotype 1 HCV replication in an HCV-replication cell model (38, 39). (5) SHP plays a key role in the regulation of hepatic lipid metabolism (37, 55). SHP was up-regulated in livers with chronic hepatitis C infection compared with controls, but it was accompanied by up-regulated expression of CYP7A1, NTCP, and MTP. Gene names in yellow indicate expression increase in hepatitis C patients compared with controls. Gene names in white indicate expression decrease in hepatitis C patients compared with controls. Small arrows indicate the direction of the regulatory pathways. Big arrows suggest pathways are stimulated in hepatitis C patients compared with controls. X: The inhibitory function is compromised in hepatitis C patients.