Alessandra Caligiuri

Heterogeneity of the proliferative capacity of rat cholangiocytes after bile duct ligation

We previously introduced the concept that intrahepatic bile duct epithelial cells, or cholangiocytes, are functionally heterogeneous. This concept is based on the observation that secretin receptor (SR) gene expression and secretin-induced cAMP synthesis are present in cholangiocytes derived from large (> 15 microns in diameter) but not small (< 15 microns in diameter) bile ducts. In work reported here, we tested the hypothesis that cholangiocytes are heterogeneous with regard to proliferative capacity. We assessed cholangiocyte proliferation in vivo by measurement of [3H]thymidine incorporation and in vitro by both [3H]thymidine incorporation and H3 histone gene expression in small (fraction 1) and large (fraction 2) cholangiocytes isolated from rats after bile duct ligation (BDL). In the two cholangiocyte subpopulations, we also studied basal somatostatin receptor (SSTR2) gene expression as well as the effects of somatostatin on 1) SR gene expression and secretin-induced cAMP synthesis and 2) [3H]thymidine incorporation and H3 histone gene expression. In normal rat liver, cholangiocytes, unlike hepatocytes, were mitotically dormant; after BDL, incorporation of [3H]thymidine markedly increased in cholangiocytes but not hepatocytes. When subpopulations of cholangiocytes were isolated after BDL, DNA synthesis assessed by both techniques was limited to large cholangiocytes, as was SSTR2 steady-state gene expression. In vitro, somatostatin inhibited SR gene expression and secretin-induced cAMP synthesis only in large cholangiocytes. Moreover, compared with no hormone, somatostatin inhibited DNA synthesis solely in large cholangiocytes. These results support the concept of the heterogeneity of cholangiocytes along the biliary tree, extend this concept to cholangiocyte proliferative activity, and imply that the proliferative compartment of cholangiocytes after BDL is located principally in the cholangiocytes lining large (> 15 microns) bile ducts.We previously introduced the concept that intrahepatic bile duct epithelial cells, or cholangiocytes, are functionally heterogeneous. This concept is based on the observation that secretin receptor (SR) gene expression and secretin-induced cAMP synthesis are present in cholangiocytes derived from large (>15 μm in diameter) but not small (<15 μm in diameter) bile ducts. In work reported here, we tested the hypothesis that cholangiocytes are heterogeneous with regard to proliferative capacity. We assessed cholangiocyte proliferation in vivo by measurement of [3H]thymidine incorporation and in vitro by both [3H]thymidine incorporation and H3 histone gene expression in small ( fraction 1) and large ( fraction 2) cholangiocytes isolated from rats after bile duct ligation (BDL). In the two cholangiocyte subpopulations, we also studied basal somatostatin receptor (SSTR2) gene expression as well as the effects of somatostatin on 1) SR gene expression and secretin-induced cAMP synthesis and 2) [3H]thymidine incorporation and H3 histone gene expression. In normal rat liver, cholangiocytes, unlike hepatocytes, were mitotically dormant; after BDL, incorporation of [3H]thymidine markedly increased in cholangiocytes but not hepatocytes. When subpopulations of cholangiocytes were isolated after BDL, DNA synthesis assessed by both techniques was limited to large cholangiocytes, as was SSTR2 steady-state gene expression. In vitro, somatostatin inhibited SR gene expression and secretin-induced cAMP synthesis only in large cholangiocytes. Moreover, compared with no hormone, somatostatin inhibited DNA synthesis solely in large cholangiocytes. These results support the concept of the heterogeneity of cholangiocytes along the biliary tree, extend this concept to cholangiocyte proliferative activity, and imply that the proliferative compartment of cholangiocytes after BDL is located principally in the cholangiocytes lining large (>15 μm) bile ducts.

Silybin, a component of sylimarin, exerts anti-inflammatory and anti-fibrogenic effects on human hepatic stellate cells

BACKGROUND/AIMS Hepatic fibrogenesis, a consequence of chronic liver tissue damage, is characterized by activation of the hepatic stellate cells (HSC). Silybin has been shown to exert anti-fibrogenic effects in animal models. However, scant information is available on the fine cellular and molecular events responsible for this effect. The aim of this study was to assess the mechanisms regulating the anti-fibrogenic and anti-inflammatory activity of Silybin. METHODS Experiments were performed on HSC isolated from human liver and activated by culture on plastic. RESULTS Silybin was able to inhibit dose-dependently (25-50 microM) growth factor-induced pro-fibrogenic actions of activated human HSC, including cell proliferation (P < 0.001), cell motility (P < 0.001), and de novo synthesis of extracellular matrix components (P < 0.05). Silybin (25-50 microM), inhibited the IL-1-induced synthesis of MCP-1 (P < 0.01) and IL-8 (P < 0.01) showing a potent anti-inflammatory activity. Silybin exerts its effects by directly inhibiting the ERK, MEK and Raf phosphorylation, reducing the activation of NHE1 (Na+/H+ exchanger, P < 0.05) and the IkBalpha phosphorylation. In addition, Silybin was confirmed to act as a potent anti-oxidant agent. CONCLUSION The results of the study provide molecular insights into the potential therapeutic action of Silybin in chronic liver disease. This action seems to be mostly related to a marked inhibition of the production of pro-inflammatory cytokines, a clear anti-oxidant effect and a reduction of the direct and indirect pro-fibrogenic potential of HSC.

Expression of platelet-derived growth factor in newly formed cholangiocytes during experimental biliary fibrosis in rats.

BACKGROUND/AIMS Chronic cholestasis stimulates a fibroductular reaction which may progress to secondary biliary fibrosis and cirrhosis. Since platelet-derived growth factor has been indicated as a major fibrogenic factor in chronic liver disease, we analyzed its expression and that of its receptor beta subunit in a rat model of chronic cholestasis. METHODS Liver tissue samples collected at 7, 10, 21, and 28 days after induction of cholestasis obtained by bile duct ligation, were analyzed by immunohistochemistry, in situ hybridization and RNase protection assay for the expression of platelet-derived growth factor (PDGF)-B chain and receptor beta subunit. Furthermore, the expression of PDGF-B chain mRNA was analyzed in highly purified cholangiocytes from normal and cholestatic rat liver. RESULTS In cholestatic liver, platelet-derived growth factor-BB and B chain mRNA expression increased up to 4 weeks in epithelial cells of proliferating bile ducts, and periductular mesenchymal cells. The increased expression of PDGF-B chain mRNA was confirmed in highly purified cholangiocytes obtained from normal and cholestatic rat liver. The expression of the receptor beta subunit progressively increased after induction of cholestasis and was mainly localized to desmin-positive periductular hepatic stellate cells. CONCLUSIONS These data suggest that platelet-derived growth factor-B chain can be synthesized by cholangiocytes during chronic cholestasis. The presence of its receptor on periductular hepatic stellate cells raises the possibility that, in this experimental setting, this cytokine might contribute to fibrogenesis in vivo.

Acute carbon tetrachloride feeding induces damage of large but not small cholangiocytes from BDL rat liver

Bile duct damage and/or loss is limited to a range of duct sizes in cholangiopathies. We tested the hypothesis that CCl4damages only large ducts. CCl4 or mineral oil was given to bile duct-ligated (BDL) rats, and 1, 2, and 7 days later small and large cholangiocytes were purified and evaluated for apoptosis, proliferation, and secretion. In situ, we measured apoptosis by morphometric and TUNEL analysis and the number of small and large ducts by morphometry. Two days after CCl4 administration, we found an increased number of small ducts and reduced number of large ducts. In vitro apoptosis was observed only in large cholangiocytes, and this was accompanied by loss of proliferation and secretion in large cholangiocytes and loss of choleretic effect of secretin. Small cholangiocytes de novo express the secretin receptor gene and secretin-induced cAMP response. Consistent with damage of large ducts, we detected cytochrome P-4502E1 (which CCl4 converts to its radicals) only in large cholangiocytes. CCl4induces selective apoptosis of large ducts associated with loss of large cholangiocyte proliferation and secretion.

gp120 modulates the biology of human hepatic stellate cells: a link between HIV infection and liver fibrogenesis

Objective In patients with hepatitis C virus (HCV)/HIV co-infection, a faster progression of liver fibrosis to cirrhosis has been reported. In this study, an investigation was carried out to determine whether gp120, an HIV envelope protein, modulates the biology of human hepatic stellate cells (HSCs), key cell types in the pathogenesis of fibrosis. Methods Myofibroblastic HSCs were isolated from normal human liver tissue. Gene expression was measured by real-time PCR. Cell migration was assessed in Boyden chambers. Intracellular signalling pathways were evaluated using phosphorylation-specific antibodies or by transfection of a reporter plasmid. Results Transcripts for the chemokine receptors CCR5 and CXCR4, which bind gp120, were detectable in human HSCs. Upon exposure to M-tropic recombinant gp120, which binds CCR5, a significant increase in HSC chemotaxis was observed (1.6±0.3-fold, p=0.03). The effects of gp120 were prevented by protein inactivation. gp120 also resulted in a significant increase in secretion (1.5±0.3-fold, p=0.03) and gene expression (1.47±0.13-fold, p=0.02) of the proinflammatory chemokine monocyte chemoattractant protein-1, and in increased gene expression of tissue inhibitor of metalloprotease-1 and interleukin-6 (2.03±0.57-fold, p=0.02). gp120-induced migration required Akt activation. gp120 also induced activation of nuclear factor-κB (NF-κB) and p38MAPK. Preincubation of HSCs with TAK779, a CCR5 receptor antagonist, prevented gp120-mediated chemotaxis and monocyte chemoattractant protein-1 secretion. Expression of CCR5 was detectable in areas of inflammation and fibrogenesis in liver biopsies of patients with HCV/HIV co-infection. Conclusions This study shows that HIV gp120 modulates different aspects of HSC biology, including directional cell movement and expression of proinflammatory cytokines. These results identify a direct pathway possibly linking HIV infection with liver fibrogenesis via envelope proteins.

Farnesoid X Receptor Critically Determines the Fibrotic Response in Mice but Is Expressed to a Low Extent in Human Hepatic Stellate Cells and Periductal Myofibroblasts

The nuclear bile acid receptor, farnesoid X receptor (FXR), may play a pivotal role in liver fibrosis. We tested the impact of genetic FXR ablation in four different mouse models. Hepatic fibrosis was induced in wild-type and FXR knock-out mice (FXR(-/-)) by CCl(4) intoxication, 3,5-diethoxycarbonyl-1,4-dihydrocollidine feeding, common bile duct ligation, or Schistosoma mansoni (S.m.)-infection. In addition, we determined nuclear receptor expression levels (FXR, pregnane X receptor (PXR), vitamin D receptor, constitutive androstane receptor (CAR), small heterodimer partner (SHP)) in mouse hepatic stellate cells (HSCs), portal myofibroblasts (MFBs), and human HSCs. Cell type-specific FXR protein expression was determined by immunohistochemistry in five mouse models and prototypic human fibrotic liver diseases. Expression of nuclear receptors was much lower in mouse and human HSCs/MFBs compared with total liver expression with the exception of vitamin D receptor. FXR protein was undetectable in mouse and human HSCs and MFBs. FXR loss had no effect in CCl(4)-intoxicated and S.m.-infected mice, but significantly decreased liver fibrosis of the biliary type (common bile duct ligation, 3,5-diethoxycarbonyl-1,4-dihydrocollidine). These data suggest that FXR loss significantly reduces fibrosis of the biliary type, but has no impact on non-cholestatic liver fibrosis. Since there is no FXR expression in HSCs and MFBs in liver fibrosis, our data indicate that these cells may not represent direct therapeutic targets for FXR ligands.

Adenosine monophosphate–activated protein kinase modulates the activated phenotype of hepatic stellate cells

Adiponectin limits the development of liver fibrosis and activates adenosine monophosphate–activated protein kinase (AMPK). AMPK is a sensor of the cellular energy status, but its possible modulation of the fibrogenic properties of hepatic stellate cells (HSCs) has not been established. In this study, we investigated the role of AMPK activation in the biology of activated human HSCs. A time‐dependent activation of AMPK was observed in response to a number of stimuli, including globular adiponectin, 5‐aminoimidazole‐4‐carboxamide‐1‐beta‐4‐ribofuranoside (AICAR), or metformin. All these compounds significantly inhibited platelet‐derived growth factor (PDGF)‐stimulated proliferation and migration of human HSCs and reduced the secretion of monocyte chemoattractant protein‐1. In addition, AICAR limited the secretion of type I procollagen. Knockdown of AMPK by gene silencing increased the mitogenic effects of PDGF, confirming the negative modulation exerted by this pathway on HSCs. AMPK activation did not reduce PDGF‐dependent activation of extracellular signal‐regulated kinase (ERK) or Akt at early time points, whereas a marked inhibition was observed 24 hours after addition of PDGF, reflecting a block in cell cycle progression. In contrast, AICAR blocked short‐term phosphorylation of ribosomal S6 kinase (p70S6K) and 4E binding protein‐1 (4EBP1), 2 downstream effectors of the mammalian target of rapamycin (mTOR) pathway, by PDGF. The ability of interleukin‐a (IL‐1) to activate nuclear factor kappa B (NF‐κB) was also reduced by AICAR. Conclusion: Activation of AMPK negatively modulates the activated phenotype of HSCs. (HEPATOLOGY 2007.)

Up-regulated expression of fractalkine and its receptor CX3CR1 during liver injury in humans

BACKGROUND/AIMS Little is known about the role of fractalkine (CX3CL1) in the liver. The aim of this study was to investigate the expression patterns of fractalkine and its receptor CX3CR1 in normal human liver and in conditions of injury. METHODS Distribution and expression of fractalkine and its receptor were investigated using immunohistochemistry, in situ hybridization, flow cytometry and reverse transcriptase-polymerase chain reaction. In vitro experiments were conducted in HepG2 cells. RESULTS Both fractalkine and CX3CR1 were up-regulated during chronic injury, in areas of portal and lobular inflammation. In severe acute hepatitis, fractalkine and CX3CR1 were expressed at high levels not only in areas of inflammation but also in regenerating epithelial cells within bile duct-like structures, which showed co-expression of fractalkine and cytokeratin-7 or CX3CR1. The human hepatocarcinoma cell line HepG2 expressed fractalkine at the gene and protein level, and HepG2-conditioned medium was chemotactic for cells overexpressing CX3CR1. Transcripts for CX3CR1 were detected in HepG2, and exposure of these cells to recombinant fractalkine induced cell migration. CONCLUSIONS This study shows that the fractalkine system is up-regulated during liver damage, and suggests that fractalkine may play a role in the recruitment and adhesion of inflammatory cells and in the biology of liver epithelial cells.

Intracellular reactive oxygen species are required for directional migration of resident and bone marrow-derived hepatic pro-fibrogenic cells

BACKGROUND & AIMS Liver fibrogenesis is sustained by myofibroblast-like cells originating from hepatic stellate cells (HSC/MFs), portal fibroblasts or bone marrow-derived cells, including mesenchymal stem cells (MSCs). Herein, we investigated the mechanistic role of intracellular generation of reactive oxygen species (ROS) and redox-sensitive signal transduction pathways in mediating chemotaxis, a critical profibrogenic response for human HSC/MFs and for MSC potentially engrafting chronically injured liver. METHODS Intracellular generation of ROS and signal transduction pathways were evaluated by integrating morphological and molecular biology techniques. Chemokinesis and chemotaxis were evaluated by wound healing assay and modified Boydens chamber assay, respectively. Additional in vivo evidence was obtained in human specimens from HCV-related cirrhosis. RESULTS Human MSCs and HSC/MFs migrate in response to a panel of polypeptide chemoattractants and extracellularly generated superoxide anion. All polypeptides induced a NADPH-oxidase-dependent intracellular rise in ROS, resulting in activation of ERK1/2 and JNK1/2. Moreover, menadione or 2,3-dimethoxy-1,4-naphthoquinone, which generate intracellular superoxide anion or hydrogen peroxide, respectively, induced ERK1/2 and JNK1/2 activation and migration. JNK1 activation was predominant for migration as shown by specific silencing. Finally, activation of ERK1/2 and JNK1/2 was found in extracts obtained from HSC/MFs during the course of an oxidative stress-mediated model of liver injury and phosphorylated JNK1/2 isoforms were detected in α-smooth muscle actin-positive myofibroblasts lining fibrotic septa in human cirrhotic livers. CONCLUSIONS Intracellular generation of ROS, through activation of specific signaling pathways, is a critical event for directional migration of HSC/MFs and MSCs.

Dose-dependent and divergent effects of superoxide anion on cell death, proliferation and migration of activated human hepatic stellate cells

Background and aim: Activated myofibroblast-like cells, originating from hepatic stellate cells (HSC/MFs) or other cellular sources, play a key profibrogenic role in chronic liver diseases (CLDs) that, as suggested by studies in animal models or rat HSC/MFs, may be modulated by reactive oxygen intermediates (ROI). In this study, human HSC/MFs, exposed to different levels of superoxide anion (O2•−) and, for comparison, hydrogen peroxide (H2O2), were analysed in terms of cytotoxicity, proliferative response, and migration. Methods: Cultured human HSC/MFs were exposed to controlled O2•− generation by hypoxanthine/xanthine oxidase systems or to a range of H2O2 concentrations. Induction of cell death, proliferation, and migration were investigated using morphology, molecular biology, and biochemical techniques. Results: Human HSC/MFs were shown to be extremely resistant to induction of cell death by O2•− and only high rates of O2•− generation induced either necrotic or apoptotic cell death. Non-cytotoxic low levels of O2•−, able to upregulate procollagen type I expression (but not tissue inhibitor of metalloproteinase 1 and 2), stimulated migration of human HSC/MFs in a Ras/extracellular regulated kinase (ERK) dependent, antioxidant sensitive way, without affecting basal or platelet derived growth factor (PDGF) stimulated cell proliferation. Non-cytotoxic levels of H2O2 did not affect Ras/ERK or proliferative response. A high rate of O2•− generation or elevated levels of H2O2 induced cytoskeletal alterations, block in motility, and inhibition of PDGF dependent DNA synthesis. Conclusions: Low non-cytotoxic levels of extracellularly generated O2•− may stimulate selected profibrogenic responses in human HSC/MFs without affecting proliferation.