The S protein of hepatitis B virus promotes collagen type I expression in hepatic stellate cells by virtue of hepatocytes

Abstract

Abstract. This study was conducted in order to investigate whether hepatitis B surface S protein (HBs) was able to directly or indirectly promote the proliferation and expression of collagen type I (Col I) and α-smooth muscle actin (α-SMA) in hepatic stellate cells (HSCs). The LX-2 human cell line and the HepG2 human hepatocellular carcinoma cell line were employed as HSCs and as hepatocytes, respectively. Recombinant HBs was added to the LX-2 cells for 48 h and the cell proliferation was assessed by the MTT assay. Col I and α-SMA were measured in the supernatant by ELISA, following treatment of the LX-2 and̸or HepG2 cells with recombinant HBs. Transforming growth factor-β1 (TGF-β1) was also determined by ELISA in the HepG2 cell supernatants. The data demonstrated that high concentrations of recombinant HBs (10-50 ng/ml) inhibited the proliferation of LX-2 cells, whereas low concentrations (0.5-5 ng/ml) did not affect LX-2 cell proliferation. After treating LX-2 cells alone with recombinant HBs for 48 h, there was no significant increase in the Col I and α-SMA levels. However, Col I was increased ~1.7-fold in co-cultured (LX-2 and HepG2) cell supernatants following treatment with HBs for 24 h (HBs vs. control group: 48.51±3.51 vs. 28.23±2.55 ng̸ml, respectively). Furthermore, TGF-β1 was significantly increased in the HepG2 cell supernatants following treatment with recombinant HBs. Therefore, we concluded that HBs directly affected the proliferation of HSCs, but promoted the Col I expression in HSCs possibly by virtue of hepatocytes secreting TGF-β1. This may provide a novel explanation of the fibrogenetic mechanism induced by hepatitis B virus-related proteins. IntroductionThe infection with hepatitis B virus (HBV) is a major health concern worldwide. It is estimated that ~350 million individuals are carriers of the hepatitis B surface S protein (HBs) and over one million patients eventually succumb to HBV-related chronic liver diseases annually (1-2). Persistent HBV infection confers a high risk of chronic hepatitis, liver cirrhosis and hepatocellular carcinoma (HCC) (3). Three forms of viral particles may be detected in the serum of HBV-infected patients: 42-nm diameter mature virion particles, 22-nm diameter spherical particles and 22-nm diameter filamentous particles (4-5). Subviral particles (22 nm), composed of HBs, are unique in that do not contain viral DNA and usually exceed the numbers of virions by ≥1,000-fold in the patient serum (5). A number of individuals reportedly reached a state of non-replicative infection following persistent anti-virus therapy; however, numerous HBs particles were still detected in their serum and the prolonged immunological response to infection may result in the development of fibrosis in the majority of the patients and eventually lead to the development of cirrhosis, liver failure, or HCC in ~40% of the patients (6). During this process, HBs may play an important role. However, the mechanism underlying the hepatic fibrogenesis induced by HBs has not yet been fully eluci...

Possible Involvement of Hepatitis B Virus Infection of Hepatocytes in the Attenuation of Apoptosis in Hepatic Stellate Cells

“…HBV directly promotes collagen type I expression in LX-2 cells [ 40 ]. The HBV S antigen (HBsAg) also directly affects the proliferation of HSCs and promotes collagen type I expression in LX-2 cells [ 41 , 42 ]. It was also reported that HBeAg directly activated HSCs [ 43 ].…”

Insights into the impact of hepatitis B virus on hepatic stellate cell activation

“…Hepatic stellate cell (HSC) activation is a central event in liver fibrosis [ 9 , 10 ]. Although recent investigations have suggested that direct activation of HSCs mediated by HBV is associated with liver fibrosis [ 11 ], whether HBV can directly infect HSCs has not been fully confirmed. After HBV-induced liver injury, hepatocytes release a variety of soluble inflammation-related molecules, such as TGF-β and CTGF [ 12 , 13 ], to accelerate HSC activation.…”

“…It has been reported that HBV particles from HepG2.2.15 cells can transiently infect HSCs, specifically LX-2 cells, leading to HBsAg and HBcAg production in the cytoplasm of virus-infected HSCs and affecting their proliferation and expression of COL1A1 [ 11 ]. The viral particles derived from HepG2.2.15 cells also upregulate the expression of α-SMA, PDGF-B, and PDGFR-β, as well as enhance the phosphorylation of PDGFR-β, in HSCs [ 17 ].…”

“…Nevertheless, Wu et al found that purified HBV particles from chronic hepatitis B (CHB) patients could not infect LX-2 cells but could directly increase COL1A1 expression in HSCs outside the cells. Wu et al concluded that HBsAg might be implicated in the expression of COL1A1 in HSCs stimulated by extracellular HBV particles [ 19 ], whereas Liu et al showed that HBsAg has no direct effect on HSC activation [ 20 ]. To date, the reasons for these discrepancies remain unaddressed, and studies are required to investigate whether HBV can directly infect and replicate in HSCs to facilitate their activation and/or whether extracellular HBV particles are capable of stimulating HSC activation.…”

“…HSC activation stimulated by HBX-positive hepatocytes can be prevented by neutralizing monoclonal antibodies targeting TGF-β [ 13 ]. In addition to HBX, preS2-Ag and HBsAg have also been found to stimulate TGF-β secretion from hepatocytes to activate HSCs [ 20 , 39 ], however, potential regulatory mechanisms have not been reported. The results of whole-genome expression arrays showed that ITGBL1 expression was upregulated in liver biopsy samples from CHB patients having liver fibrosis.…”