Min Cong

Expression of extracellular matrix genes in cultured hepatic oval cells: an origin of hepatic stellate cells through transforming growth factor beta?

Background: Hepatic oval cells, progenitor cells in the liver, can differentiate into hepatocytes and bile duct cells both in vitro and in vivo. Although hepatic stellate cells are another important cell component in the liver, less attention has been focused on the relationship between hepatic oval cells and hepatic stellate cells.

Hepatitis B virus particles preferably induce Kupffer cells to produce TGF-β1 over pro-inflammatory cytokines

BACKGROUND Kupffer cells and related cytokines are thought to play a critical role in liver fibrosis; however, the role played by Kupffer cells in hepatitis B virus-related fibrogenesis is unknown. METHODS Primary rat Kupffer cells were cultured with different titres of hepatitis B virus particles and the concentrations of transforming growth factor (TGF)-β1, interleukin (IL)-1, IL-6 and tumour necrosis factor (TNF)-α in the culture supernatant were measured every 24h for 7 days. The mRNA and protein levels of these cytokines in Kupffer cells were also analysed using quantitative real-time polymerase chain reaction and western blotting, respectively. RESULTS Kupffer cells maintained normal morphology and function throughout the 7-day exposure to hepatitis B virus. The concentration of TGF-β1 secreted by hepatitis B virus-stimulated Kupffer cells (6 log IU/ml hepatitis B virus) increased 5.38- and 7.75-fold by Days 3 and 7, respectively (p<0.01). Western blotting showed that TGF-β1 expression in Kupffer cells exposed to high titres of hepatitis B virus increased 1.80- and 2.42-fold by Days 3 and 7, respectively (p<0.01). In contrast, Kupffer cell expression and secretion of pro-inflammatory cytokines (IL-6, IL-1 and TNF-α) was unchanged throughout the experiment. CONCLUSION Hepatitis B virus preferentially stimulates Kupffer cells to produce the pro-fibrogenic/anti-inflammatory cytokine TGF-β1 rather than the pro-inflammatory cytokines IL-6, IL-1 and TNF-α. This may partly explain why overt liver fibrosis still presents in cases of chronic hepatitis B virus infection with minimal (or no) necro-inflammation.

Antifibrotic Effects of a Recombinant Adeno-Associated Virus Carrying Small Interfering RNA Targeting TIMP-1 in Rat Liver Fibrosis

Elevated tissue inhibitor of metalloproteinase 1 (TIMP-1) expression contributes to excess production of extracellular matrix in liver fibrosis. Herein, we constructed a recombinant adeno-associated virus (rAAV) carrying siRNA of the TIMP-1 gene (rAAV/siRNA-TIMP-1) and investigated its effects on liver fibrosis in rats. Two models of rat liver fibrosis, the carbon tetrachloride and bile duct ligation models, were treated with rAAV/siRNA-TIMP-1. In the carbon tetrachloride model, rAAV/siRNA-TIMP-1 administration attenuated fibrosis severity, as determined by histologic analysis of hepatic collagen accumulation, hydroxyproline content, and concentrations of types I and III collagen in livers and sera. Levels of mRNA and active matrix metalloproteinase (MMP) 13 were elevated, whereas levels of mRNA and active MMP-2 were decreased. Moreover, a marked decrease was noted in the expression of α-smooth muscle actin, a biomarker of activated hepatic stellate cells (HSCs), and transforming growth factor-β1, critical for the development of liver fibrosis. Similarly, rAAV/siRNA-TIMP-1 treatment significantly alleviated bile duct ligation-induced liver fibrosis. Furthermore, this treatment dramatically suppressed TIMP-1 expression in HSCs from both model rats. These data indicate that the administration of rAAV/siRNA-TIMP-1 attenuated liver fibrosis by directly elevating the function of MMP-13 and diminishing activated HSCs. It also resulted in indirect decreased expression of type I collagen, MMP-2, and transforming growth factor-β1. In conclusion, rAAV/siRNA-TIMP-1 may be an effective antifibrotic gene therapy agent.

Primary isolated hepatic oval cells maintain progenitor cell phenotypes after two-year prolonged cultivation

BACKGROUND & AIMS Although expandable hepatic progenitors provide renewable cell sources for treatment of hepatic disorders, long-term cultivation of hepatic progenitors may affect proliferation and differentiation abilities, and even initiate the formation of malignant cancer stem cells. This study aims to determine characteristics of primary cultured hepatic oval cells after prolonged cultivation in vitro. METHODS Hepatic oval cells isolated from rats fed with a choline-deficient, ethionine-supplemented diet were continuously propagated every 5-7 days, to 100 passages over two years. Hepatocytic differentiation was induced by sodium butyrate and characterized using western blot, periodic acid Schiff assays, albumin secretion and urea production. Proliferation capacity was evaluated using growth-curve and cell-cycle analysis; anchorage-independent growth and tumorigenicity were determined using soft agar and xenograft assay. RESULTS After 2 years of serial passages, hepatic oval cells with typical epithelial morphology continuously expressed OV-6, BD-1, BD-2, and Dlk as markers for hepatic progenitors, cytokeratin 19 as a cholangiocyte marker, and alpha-fetoprotein and albumin as hepatocyte markers. Furthermore, sodium butyrate could induce these cells to become glycogen-storage cells with the functions of albumin secretion and ureagenesis from ammonia clearance, indicating hepatocytic differentiation. Although proliferation slightly accelerated after the 50th passage, hepatic oval cells stayed diploid cells with features of chromosomal stability, which did not acquire anchorage-independent growth capacity and caused no tumor in immunodeficient mice, suggesting no spontaneous malignant transformation. CONCLUSIONS Hepatic oval cells retain the progenitor cell features without spontaneous malignant transformation after prolonged cultivation, and thus may serve as an expandable cell source for future exploitation of stem cell technology.

HBV genes induce cytotoxic T-lymphocyte response upon adeno-associated virus (AAV) vector delivery into dendritic cells

Summary.  Hepatitis B virus (HBV) has been an increasing problem throughout the world and remains difficult to treat. But immunotherapeutic approaches offer new, effective treatments. Three recombinant adeno‐associated virus (AAV) type 2 vectors, carrying one of the HBV S, C or X gene, were used to load (transduce) professional antigen‐presenting dendritic cells (DC) for the purpose of stimulating cytotoxic T lymphocytes (CTL) in vitro. It was found that all three recombinant AAV/HBV antigen virus loaded DC at approximately 90% transduction efficiency. Most importantly, all three AAV‐loaded DC stimulated rapid, antigen‐specific and major histocompatibility complex (MHC)‐restricted CTL. In vitro, these CTL killed (30–50%) synthetic antigen‐positive autologous targets as well as HepG2 liver cell targets. In comparing the three antigens, it was found that AAV/HBV‐C‐derived CTL consistently had the highest killing efficiency. CTL derived from AAV/HBV‐C‐loaded DC also showed significantly higher killing of targets than that from bacterially generated C‐protein‐loaded DC. Further studies showed that AAV/HBV‐C‐derived CTL had higher interferon (IFN)‐gamma. These data suggest that AAV/HBV antigen gene‐loading of DC may be useful for immunotherapeutic protocols against HBV infection and that the HBV C antigen may be the most useful for this purpose.

EGF Suppresses the Initiation and Drives the Reversion of TGF‐β1‐induced Transition in Hepatic Oval Cells Showing the Plasticity of Progenitor Cells

Transforming growth factor‐β1 (TGF‐β1) induces hepatic progenitors to tumor initiating cells through epithelial‐mesenchymal transition (EMT), thus raising an important drawback for stem cell–based therapy. How to block and reverse TGF‐β1‐induced transition is crucial for progenitors’ clinical application and carcinogenic prevention. Rat adult hepatic progenitors, hepatic oval cells, experienced E‐cadherin to N‐cadherin switch and changed to α‐smooth muscle actin (α‐SMA) positive cells after TGF‐β1 incubation, indicating EMT. When TGF‐β1 plus EGF were co‐administrated to these cells, EGF dose‐dependently suppressed the cadherin switch and α‐SMA expression. Interestingly, if EGF was applied to TGF‐β1‐pretreated cells, the cells that have experienced EMT could return to their epithelial phenotype. Abruption of EGF receptor revealed that EGF exerted its blockage and reversal effects through phosphorylation of ERK1/2 and Akt. These findings suggest an important attribute of EGF on opposing and reversing TGF‐β1 effects, indicating the plasticity of hepatic progenitors. J. Cell. Physiol. 230: 2362–2370, 2015.

The CYP2E1 inhibitor DDC up-regulates MMP-1 expression in hepatic stellate cells via an ERK1/2- and Akt-dependent mechanism

DDC (diethyldithiocarbamate) could block collagen synthesis in HSC (hepatic stellate cells) through the inhibition of ROS (reactive oxygen species) derived from hepatocyte CYP2E1 (cytochrome P450 2E1). However, the effect of DDC on MMP-1 (matrix metalloproteinase-1), which is the main collagen degrading matrix metalloproteinase, has not been reported. In co-culture experiments, we found that DDC significantly enhanced MMP-1 expression in human HSC (LX-2) that were cultured with hepatocyte C3A cells either expressing or not expressing CYP2E1. The levels of both proenzyme and active MMP-1 enzyme were up-regulated in LX-2 cells, accompanied by elevated enzyme activity of MMP-1 and decreased collagen I, in both LX-2 cells and the culture medium. H2O2 treatment abrogated DDC-induced MMP-1 up-regulation and collagen I decrease, while catalase treatment slightly up-regulated MMP-1 expression. These data suggested that the decrease in ROS by DDC was partially responsible for the MMP-1 up-regulation. ERK1/2 (extracellular signal-regulated kinase 1/2), Akt (protein kinase B) and p38 were significantly activated by DDC. The ERK1/2 inhibitor (U0126) and Akt inhibitor (T3830) abrogated the DDC-induced MMP-1 up-regulation. In addition, a p38 inhibitor (SB203580) improved MMP-1 up-regulation through the stimulation of ERK1/2. Our data indicate that DDC significantly up-regulates the expression of MMP-1 in LX-2 cells which results in greater MMP-1 enzyme activity and decreased collagen I. The enhancement of MMP-1 expression by DDC was associated with H2O2 inhibition and coordinated regulation by the ERK1/2 and Akt pathways. These data provide some new insights into treatment strategies for hepatic fibrosis.

Connective tissue growth factor induces hepatic progenitor cells to differentiate into hepatocytes

Connective tissue growth factor (CTGF) plays an important role in the proliferation of hepatic progenitors, however, little is known concerning the mechanism(s) through which it influences their differentiation. The differentiation of hepatic progenitors (WB-F344), either stimulated with recombinant CTGF or stably transfected with a CTGF overexpression plasmid, was investigated. Expression of the differentiation markers α-fetoprotein (AFP), albumin (ALB) and cytokeratin-19 (CK-19) was assessed. To confirm the effects of CTGF on progenitor differentiation, cells were treated with an inhibitor (WP631) of CTGF. Treatment of WB-F344 cells with recombinant CTGF for 24 h did not change the survival rate significantly, but the progenitors were enlarged with a decreased nuclear/cytoplasmic ratio. CTGF downregulated the expression of the fetal hepatocyte marker, AFP, while it upregulated the mature hepatocyte cell marker, ALB. The effect of CTGF overexpression plasmid on WB-F344 cell differentiation was consistent with a pattern of direct CTGF stimulation, including decreased AFP and increased ALB expression. Furthermore, the suppression of CTGF induction by an inhibitor was associated with significant inhibition of hepatic progenitor cell differentiation into hepatocytes. Importantly, we showed that differentiated WB-F344 cells by CTGF had in vitro functions characteristic of hepatocytes, including ALB production, glycogen storage and cytochrome P450 activity. Both recombinant CTGF and the CTGF overexpression plasmid induced hepatic progenitor differentiation into hepatocytes. This was suppressed by the CTGF inhibitor.

TGF-β1 Induces the Dual Regulation of Hepatic Progenitor Cells with Both Anti- and Proliver Fibrosis

Transforming growth factor-beta 1 (TGF-β1) plays a central role in hepatic progenitor cells- (HPCs-) mediated liver repair and fibrosis. However, different effects of TGF-β1 on progenitor cells have not been described. In this study, both in vitro (HPCs cocultured with hepatic stellate cells (HSCs) in transwells) and in vivo (CCl4-injured liver fibrosis rat) systems were used to evaluate the impacts. We found that HPCs pretreated with TGF-β1 for 12 hours inhibited the activation of HSCs, while sensitization for 48 hours increased the activation of HSCs. Consistent with these in vitro results, the in vivo fibrosis rat model showed the same time-dependent dual effect of TGF-β1. Regression of liver fibrosis as well as normalization of serum aminotransferase and albumin levels was detected in the rats transplanted with HPCs pretreated with TGF-β1 for 12 hours. In contrast, severe liver fibrosis and elevated collagen-1 levels were detected in the rats transplanted with HPCs pretreated with TGF-β1 for 48 hours. Furthermore, the TGF-β1-pretreated HPCs were shown to deactivate HSCs via enhancing SERPINE1 expression. Inhibition of SERPINE1 reversed the deactivation response in a dose-dependent manner.

The Characteristics Variation of Hepatic Progenitors after TGF-β1-Induced Transition and EGF-Induced Reversion

Profibrogenesis cytokine, transforming growth factor- (TGF-) β1, induces hepatic progenitors experiencing epithelial to mesenchymal transition (EMT) to matrix synthesis cells, even tumor initiating cells. Our previous data found that epidermal growth factor (EGF) blocks and reverses TGF-β1-induced transition. The aim of this study is to determine the characteristic changes of hepatic progenitors after TGF-β1-induced transition and EGF-induced reversion. Hepatic oval cells, rat hepatic progenitors, were isolated from rats fed a choline-deficient diet supplemented with ethionine. TGF-β1-containing medium was used for inducing EMT, while EGF-containing medium was used for reversing EMT. During TGF-β1-induced transition and EGF-induced reversion, hepatic oval cells sustained their progenitor cell marker expression, including α-fetoprotein, albumin, and cytokeratin-19. The proliferation ability and differentiation potential of these cells were suppressed by TGF-β1, while EGF resumed these capacities to the level similar to the control cells. RNA microarray analysis showed that most of the genes with significant changes after TGF-β1 incubation were recovered by EGF. Signal pathway analysis revealed that TGF-β1 impaired the pathways of cell cycle and cytochrome P450 detoxification, and EGF reverted TGF-β1 effects through activating MAPK and PI3K-Akt pathway. EGF reverses the characteristics impaired by TGF-β1 in hepatic oval cells, serving as a protective cytokine to hepatic progenitors.