Investigation of the role of SREBP-1c in the pathogenesis of HCV-related steatosis

doi:10.1016/j.jhep.2008.06.022

Journal of Hepatology

Volume 49, Issue 6, December 2008, Pages 1046-1054

https://doi.org/10.1016/j.jhep.2008.06.022 Get rights and content

Background/Aims

Increased expression of sterol regulatory element binding protein (SREBP)-1c, a transcription factor regulating lipogenesis, has been reported in HCV core protein-transfected hepatocytes. Our aim was to investigate the role of SREBP-1c in the pathogenesis of HCV-related steatosis.

Methods

One hundred and twenty-four patients with HCV and 13 subjects with histologically normal liver (NDL) were studied. The mRNA expression of SREBP-1c, fatty acid synthase (FAS), glycerol-3-phosphate acyltransferase (GPAT) and microsomal triglyceride transfer protein (MTP) was measured by qPCR, and SREBP-1 protein quantitated by immunohistochemistry.

Results

There was no significant difference in the hepatic expression of SREBP-1c mRNA between subjects with HCV and NDL. In patients with HCV, a significant negative relationship was seen between hepatic SREBP-1c mRNA expression and grade of steatosis (r_s = −0.28, p = 0.002), stage of fibrosis (r_s = −0.375, p < 0.001) and severity of inflammation (r_s = −0.313, p < 0.001). These relationships were observed for patients infected with either viral genotype 1 or 3. Following multivariate logistic regression analysis, hepatic SREBP-1c expression remained independently associated with fibrosis (p = 0.008) and hepatic inflammation (p = 0.005). HCV-infected patients with HOMA > 2 had significantly higher expression of FAS mRNA than HCV-infected subjects with HOMA ⩽ 2 (p = 0.006) and NDL (p = 0.016).

Conclusions

SREBP-1c may not play a prominent role in the pathogenesis of HCV-related steatosis.

Introduction

Chronic infection with hepatitis C virus (HCV) is a significant global health problem with 170 million people infected worldwide [1]. Approximately 51% of patients infected with HCV have hepatic steatosis [2], which is higher than the reported prevalence of steatosis in the general population [3]. Although steatosis may be seen in association with all HCV genotypes, there is clear evidence that steatosis is more prevalent and severe in subjects infected with viral genotype 3 [4], [5], [6]. The importance of hepatic steatosis in patients with chronic HCV lies in its relationship with enhanced progression of disease [7], [8].

The pathogenesis of hepatic steatosis is multifactorial involving host metabolic factors (obesity and insulin resistance) as well as viral factors (Reviewed in [8], [9]). Evidence for a direct viral steatogenic effect derives from studies showing that over-expression of HCV proteins in transgenic mice and cell culture models leads to accumulation of intracellular lipids [10], [11], and infection with HCV genotype 3 may induce steatosis more efficiently than infection with genotype 1 [12]. The molecular mechanisms leading to HCV-induced steatosis have not been completely defined. Microsomal triglyceride transfer protein (MTP), a key enzyme for the assembly of very-low density lipoproteins (VLDL), may play a role in HCV-related steatosis. A recent study found a significant negative relationship between hepatic MTP expression and steatosis in patients with chronic HCV [13].

In addition to reducing lipid export from hepatocytes, expression of HCV proteins may lead to altered regulation of lipid synthesis. Sterol regulatory element binding protein (SREBP)-1 is a key insulin-regulated transcription factor that controls fatty acid and triglyceride synthesis (reviewed in [14], [15], [16]). There are two SREBP-1 isoforms, SREBP-1a and SREBP-1c, however SREBP-1c is the predominant isoform expressed in human liver [17], [18]. SREBP-1c regulates the expression of genes encoding enzymes responsible for de novo lipogenesis, such as fatty acid synthase (FAS) and glycerol-3-phosphate acyltransferase (GPAT) [14], [15], [16].

Previous experimental studies found increased SREBP-1 expression in HCV-infected hepatocytes. Chimpanzees acutely infected with HCV had increased hepatic expression of SREBP-1 and genes associated with fatty acid biosynthesis [19]. Transfection of HCV core protein into hepatoma cells was associated with lipid accumulation, increased expression of SREBP-1 mRNA and protein [20] and activation of FAS [21], [22]. In addition, increased expression of SREBP-1c mRNA and proteolytic cleavage of SREBP-1 protein was observed in Huh-7 cells transfected with cell culture-derived infectious HCV virions (JHF-1 genomic RNA) [23]. These studies suggest that HCV infection may upregulate SREBP-1c, leading to increased de novo lipogenesis. The aim of the current study was to investigate the role of SREBP-1c in the pathogenesis of HCV-related steatosis in a cohort of patients with chronic HCV.

Section snippets

Study population

The study included 124 consecutive patients with chronic HCV who underwent a liver biopsy as part of their evaluation for treatment. Informed consent was obtained from each patient and the protocol was approved by both the Princess Alexandra Hospital and the University of Queensland Research Ethics Committees. All patients with HCV were positive for HCV antibody by a third generation enzyme linked immunosorbent assay (Abbott Laboratories, North Chicago, IL, USA), and infection was confirmed by

Clinical, histological and laboratory data for patients with HCV

The demographic and clinical characteristics of the 124 subjects with HCV are summarized in Table 2. The grade of steatosis was 0 in 62 patients (50%), 1 in 41 patients (33%) and 2 or 3 in 21 patients (17%). The stage of fibrosis (Scheuer score) was 0 in 12 patients (9.7%), 1 in 57 patients (46%), 2 in 33 patients (26.6%) and 3 or 4 in 22 patients (17.7%). Forty-four patients (35%) had mild hepatic inflammation and 80 patients (65%) had moderate or severe inflammation. Sixty-four patients (52%)

Discussion

Chronic HCV is frequently associated with hepatic steatosis, although the molecular mechanisms have not yet been completely defined. We sought to investigate the role of SREBP-1c in the pathogenesis of HCV-related steatosis. Overall we found no difference in the hepatic expression of SREBP-1c, FAS and GPAT mRNA in patients with HCV compared with subjects with NDL. Somewhat unexpectedly, we found a significant negative association between hepatic SREBP-1c mRNA levels and steatosis, and a trend

References (43)

G. Leandro et al.
Relationship between steatosis, inflammation, and fibrosis in chronic hepatitis C: a meta-analysis of individual patient data
Gastroenterology
(2006)
A. Lonardo et al.
Steatosis and hepatitis C virus: mechanisms and significance for hepatic and extrahepatic disease
Gastroenterology
(2004)
L. Rubbia-Brandt et al.
Hepatocyte steatosis is a cytopathic effect of hepatitis C virus genotype 3
J Hepatol
(2000)
L. Adinolfi et al.
Steatosis accelerates the progression of liver damage of chronic hepatitis C patients and correlates with specific HCV genotype and visceral obesity
Hepatology
(2001)
K. Abid et al.
An in vitro model of hepatitis C virus genotype 3a-associated triglycerides accumulation
J Hepatol
(2005)
S. Mirandola et al.
Liver microsomal triglyceride transfer protein is involved in hepatitis C liver steatosis
Gastroenterology
(2006)
D. Eberle et al.
SREBP transcription factors: master regulators of lipid homeostasis
Biochimie
(2004)
X. Hua et al.
Structure of the human gene encoding sterol regulatory element binding protein-1 (SREBF1) and localization of SREBF1 and SREBF2 to chromosomes 17p11.2 and 22q13
Genomics
(1995)
K.H. Kim et al.
HCV core protein induces hepatic lipid accumulation by activating SREBP1 and PPARgamma
Biochem Biophys Res Commun
(2007)
C. Jackel-Cram et al.
Up-regulation of fatty acid synthase promoter by hepatitis C virus core protein: genotype-3a core has a stronger effect than genotype-1b core
J Hepatol
(2007)

K. Ishak et al.

Histological grading and staging of chronic hepatitis

J Hepatol

(1995)

P.J. Scheuer

Classification of chronic viral hepatitis: a need for reassessment

J Hepatol

(1991)

S. Fleige et al.

RNA integrity and the effect on the real-time qRT-PCR performance

Mol Aspects Med

(2006)

T. Poynard et al.

Effect of treatment with peginterferon or interferon alfa-2b and ribavirin on steatosis in patients infected with hepatitis C

Hepatology

(2003)

I. Shimomura et al.

Increased levels of nuclear SREBP-1c associated with fatty livers in two mouse models of diabetes mellitus

J Biol Chem

(1999)

N. Yahagi et al.

Absence of sterol regulatory element-binding protein-1 (SREBP-1) ameliorates fatty livers but not obesity or insulin resistance in Lep(ob)/Lep(ob) mice

J Biol Chem

(2002)

J. Xu et al.

Sterol regulatory element binding protein-1 expression is suppressed by dietary polyunsaturated fatty acids. A mechanism for the coordinate suppression of lipogenic genes by polyunsaturated fats

J Biol Chem

(1999)

P.D. Denechaud et al.

Role of ChREBP in hepatic steatosis and insulin resistance

FEBS Lett

(2008)

K. Dheda et al.

The implications of using an inappropriate reference gene for real-time reverse transcription PCR data normalization

Anal Biochem

(2005)

WHO. Global surveillance and control of hepatitis C. Report of a WHO Consultation organized in collaboration with the...

S. Mihm et al.

Analysis of histopathological manifestations of chronic hepatitis C virus infection with respect to virus genotype

Hepatology

(1997)

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^☆: The authors declare that they received funding from The National Health and Medical Research Council of Australia, The Queensland Government’s Smart State Health and Medical Research Fund, The Princess Alexandra Hospital Research and Development Foundation and the Sasakawa Foundation, (Royal Children’s Hospital Brisbane). E.P. was the recipient of an unrestricted grant from Schering Plough. The other authors state that they did not receive funding from the manufacturers of the drugs involved.

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Investigation of the role of SREBP-1c in the pathogenesis of HCV-related steatosis☆

Background/Aims

Methods

Results

Conclusions

Introduction

Section snippets

Study population

Clinical, histological and laboratory data for patients with HCV

Discussion

Gastroenterology

Gastroenterology

J Hepatol

Hepatology

J Hepatol

Gastroenterology

Biochimie

Genomics

Biochem Biophys Res Commun

J Hepatol

J Hepatol

J Hepatol

Mol Aspects Med

Hepatology

J Biol Chem

J Biol Chem

J Biol Chem

FEBS Lett

Anal Biochem

Analysis of histopathological manifestations of chronic hepatitis C virus infection with respect to virus genotype

Hepatology