Hypoxic stimulation of vascular endothelial growth factor expression in activated rat hepatic stellate cells

Bevacizumab attenuates hepatic fibrosis in rats by inhibiting activation of hepatic stellate cells

Angiogenesis is a fundamental part of the response to tissue injury, which is involved in the development of hepatic fibrosis. Vascular endothelial growth factor plays an important role in angiogenesis. The expression of VEGF is increased during hepatic fibrogenesis and correlates with the micro-vessel density. In this study, we investigated the effects of bevacizumab, an anti-angiogenetic drug, on the formation of hepatic fibrosis. We found that bevacizumab could attenuate the development of hepatic fibrosis and contribute to the protection of liver function. Bevacizumab was also found to downregulate the expression α-SMA and TGF-β1, which have been reported to be profibrogenic genes in vivo. We also observed that the expression of VEGF increased significantly during the development of hepatic fibrosis and CCl₄ was found to induce hepatocytes to secrete VEGF, which led to the activation and proliferation of HSCs. Bevacizumab was also found to block the effects of the hepatocytes on the activation and proliferation of HSCs. Our results suggest that bevacizumab might alleviate liver fibrosis by blocking the effect of VEGF on HSCs. Bevacizumab might be suitable as a potential agent for hepatic fibrosis therapy.

Curcumin ameliorates intrahepatic angiogenesis and capillarization of the sinusoids in carbon tetrachloride-induced rat liver fibrosis

Neoangiogenesis and the development of an abnormal angio-architecture in the liver are strongly linked with progressive fibrogenesis. This study aimed to evaluate the ability of curcumin to protect liver fibrosis-associated angiogenesis and capillarization of the sinusoids in experimental rats. Liver fibrosis was induced by intraperitoneal injection of carbon tetrachloride (CCl₄) with or without curcumin for 6 weeks. The results suggest that curcumin treatment markedly attenuated CCl₄-induced liver fibrosis, as assessed by histology and hydroxyproline content, and inhibited hepatic stellate cell activation. Curcumin ameliorated hepatic angiogenesis, as assessed by measuring microvessel density using Von Willebrand factor staining and by examining the expression of the endothelial cell markers CD31 and vascular endothelial growth factor receptor (VEGFR)-2 in the livers. Pathologic remodeling of liver sinusoidal capillarization, as assessed by electron-microscopic analysis of Disse's space and by evaluation of the levels of basement membrane protein expression, was also attenuated by curcumin administration. The intrahepatic gene or protein expression of hypoxia-inducible factor-1α, VEGFR-1, placental growth factor, and cyclooxygenase-2 decreased with treatment with curcumin in fibrotic rats. In conclusion, curcumin ameliorates hepatic angiogenesis and sinusoidal capillarization in CCl₄-induced rat liver fibrosis through suppressing multiple proangiogenic factors.

Origins and functions of liver myofibroblasts

Myofibroblasts combine the matrix-producing functions of fibroblasts and the contractile properties of smooth muscle cells. They are the main effectors of fibrosis in all tissues and make a major contribution to other aspects of the wound healing response, including regeneration and angiogenesis. They display the de novo expression of α-smooth muscle actin. Myofibroblasts, which are absent from the normal liver, are derived from two major sources: hepatic stellate cells (HSCs) and portal mesenchymal cells in the injured liver. Reliable markers for distinguishing between the two subpopulations at the myofibroblast stage are currently lacking, but there is evidence to suggest that both myofibroblast cell types, each exposed to a particular microenvironment (e.g. hypoxia for HSC-MFs, ductular reaction for portal mesenchymal cell-derived myofibroblasts (PMFs)), expand and exert specialist functions, in scarring and inflammation for PMFs, and in vasoregulation and hepatocellular healing for HSC-MFs. Angiogenesis is a major mechanism by which myofibroblasts contribute to the progression of fibrosis in liver disease. It has been clearly demonstrated that liver fibrosis can regress, and this process involves a deactivation of myofibroblasts, although probably not to a fully quiescent phenotype. This article is part of a Special Issue entitled: Fibrosis: Translation of basic research to human disease.

Transient repetitive exposure to low level light therapy enhances collateral blood vessel growth in the ischemic hindlimb of the tight skin mouse

The tight skin mouse (Tsk(-/+)) is a model of scleroderma characterized by impaired vasoreactivity, increased oxidative stress, attenuated angiogenic response to VEGF and production of the angiogenesis inhibitor angiostatin. Low-level light therapy (LLLT) stimulates angiogenesis in myocardial infarction and chemotherapy-induced mucositis. We hypothesize that repetitive LLLT restores vessel growth in the ischemic hindlimb of Tsk(-/+) mice by attenuating angiostatin and enhancing angiomotin effects in vivo. C57Bl/6J and Tsk(-/+) mice underwent ligation of the femoral artery. Relative blood flow to the foot was measured using a laser Doppler imager. Tsk(-/+) mice received LLLT (670 nm, 50 mW cm(-2), 30 J cm(-2)) for 10 min per day for 14 days. Vascular density was determined using lycopersicom lectin staining. Immunofluorescent labeling, Western blot analysis and immunoprecipitation were used to determine angiostatin and angiomotin expression. Recovery of blood flow to the ischemic limb was reduced in Tsk(-/+) compared with C57Bl/6 mice 2 weeks after surgery. LLLT treatment of Tsk(-/+) mice restored blood flow to levels observed in C57Bl/6 mice. Vascular density was decreased, angiostatin expression was enhanced and angiomotin depressed in the ischemic hindlimb of Tsk(-/+) mice. LLLT treatment reversed these abnormalities. LLLT stimulates angiogenesis by increasing angiomotin and decreasing angiostatin expression in the ischemic hindlimb of Tsk(-/+) mice.

Increased number and function of endothelial progenitor cells stimulate angiogenesis by resident liver sinusoidal endothelial cells (SECs) in cirrhosis through paracrine factors

BACKGROUND & AIMS

Recent studies have shown a pathological role of angiogenesis in the progression of chronic liver diseases (CLDs). The present study focused on numbers and angiogenic functions of circulating endothelial progenitor cells (EPCs) in patients with cirrhosis.

METHODS

Circulating EPCs were counted by flow-cytometry, and correlated with different parameters of liver disease. They were cultured in patients and controls to compare colony-formation, proliferation and tube formation. Interactions of EPCs with hepatic stellate cells (HSCs) and sinusoidal endothelial cells (SECs) were examined by indirect and direct co-cultures in presence of EPCs and EPC-conditioned medium, respectively. ELISA and inhibition assays were performed to assess the role of EPC-derived angiogenic factors.

RESULTS

The number of circulating EPCs was substantially higher in cirrhotic patients compared to controls (p<0.05), and showed good correlation with hepatic disease severity. Functional assays revealed that colonies and proliferation of EPCs were significantly increased in patients compared to controls (p<0.05). Direct and indirect co-cultures of patients' EPCs showed an increase in tube formation by SECs as compared to that observed with control EPCs (p<0.05). There was, however, no tube formation in HSC-EPC co-cultures. Levels of PDGF-BB and VEGF were substantially increased in patients' EPC media and inhibition of these factors by neutralizing antibodies led to a significant reduction in SECs proliferation.

CONCLUSIONS

Mobilization and proliferation of EPCs are significantly enhanced in cirrhotic patients in comparison to controls. EPCs may play an important paracrine role in liver angiogenesis by stimulating resident SECs in cirrhosis.

Mechanisms of disease progression in NASH: new paradigms

The incidence of nonalcoholic fatty liver disease is increasing at an astonishing rate in the US population. Although only a small proportion of these patients develop steatohepatitis (NASH), those who do have a greater likelihood of developing end-stage liver disease and complications. Research on liver fibrosis and NASH progression shows that hedgehog (Hh) is reactivated after liver injury to assist in liver repair and regeneration. When the process of tissue repair and regeneration is prolonged or when Hh ligand and related genes are aberrantly regulated and excessive, tissue repair goes awry and NASH progresses to cirrhosis and hepatocellular carcinoma.

Angiogenesis: a phenomenon which aggravates chronic liver disease progression

It has become increasingly clear that angiogenesis occurring during chronic wound healing and fibrogenesis provides a key contribution to disease progression and complications. The association of fibrogenesis and angiogenesis should be regarded as crucial in the modern evaluation of liver disease progression and in the search for therapeutic targets. Physiological hepatic angiogenesis occurs during liver regeneration, contributing to the formation of new functional sinusoids. Pathological angiogenesis in liver is characterized by intrahepatic vascular remodeling with capillarization of the sinusoids and development of intrahepatic shunts, which lead to increased hepatic resistance and decreased effective hepatocyte perfusion. The problem of angiogenesis in chronic hepatitis C and nonalcoholic fatty liver disease has not been fully resolved. This manuscript briefly describes pathogenesis of new blood vessel formation in chronic hepatitis and potential role of angiogenesis in disease progression.

Adipose derived mesenchymal stem cells transplantation via portal vein improves microcirculation and ameliorates liver fibrosis induced by CCl4 in rats

Introduction

Adipose derived mesenchymal stem cells (ADMSCs), carrying the similar characteristics to bone marrow mesenchymal stem cells, only much more abundant and easier to obtain, may be a promising treatment for liver fibrosis. We aim to investigate the therapeutic potential of ADMSCs transplantation in liver fibrosis caused by carbon tetrachloride (CCl₄) in rats as well as its underlying mechanism, and to further explore the appropriate infusion pathway.

Methods

ADMSCs were isolated, cultured and identified. Placebo and ADMSCs were transplanted via portal vein and tail vein respectively into carbon tetrachloride (CCl₄)-induced liver fibrosis rats. Computed tomography (CT) perfusion scan and microvessel counts were performed to measure the alteration of liver microcirculation after therapy. Liver function tests and histological findings were estimated.

Results

CT perfusion scan shown significant decrease of hepatic arterial perfusion index, significant increased portal vein perfusion, total liver perfusion in rats receiving ADMSCs from portal vein, and Factor VIII (FVIII) immunohistochemical staining shown significant decrease of microvessels in rats receiving ADMSCs from portal vein, indicating microcirculation improvement in portal vein group. Vascular endothelial growth Factor (VEGF) was significantly up-regulated in fibrosis models, and decreased after ADMSCs intraportal transplantation. A significant improvement of liver functional test and histological findings in portal vein group were observed. No significance was found in rats receiving ADMSCs from tail vein.

Conclusions

ADMSCs have a therapeutic effect against CCl₄-mediated liver fibrosis. ADMSCs may benefit the fibrotic liver through alteration of microcirculation, evidenced by CT perfusion scan and down-regulation of VEGF. Intraportal transplantation is a better pathway than tail vein transplantation.

Rho inhibitor prevents ischemia-reperfusion injury in rat steatotic liver

BACKGROUND & AIMS

Hepatic stellate cells are thought to play a role in modulating intrahepatic vascular resistance based on their capacity to contract via Rho signaling. We investigated the effect of a Rho-kinase inhibitor on ischemia-reperfusion injury in the steatotic liver.

METHODS

Steatotic livers, induced by a choline-deficient diet in rats, were subjected to ischemia-reperfusion injury. Hepatic stellate cells isolated from steatotic livers were analyzed for contractility and Rho signaling activity. The portal pressure of the perfused rat liver and the survival rate after ischemia-reperfusion were also investigated.

RESULTS

Hepatic stellate cells from steatotic livers showed increased contractility and upregulation of Rho-kinase 2 compared with those from normal livers. Furthermore, endothelin-1 significantly enhanced the contractility and phosphorylation level of myosin light chain and cofilin in hepatic stellate cells isolated from steatotic livers. A specific Rho-kinase inhibitor, fasudil, significantly suppressed the contractility and decreased the phosphorylation levels of myosin light chain and cofilin. Serum levels of endothelin-1 were markedly increased after IR in rats with steatotic livers, whereas fasudil significantly decreased endothelin-1 serum levels. Rats with steatotic livers showed a significant increase in portal perfusion pressure after ischemia-reperfusion and a significant decrease in survival rate; fasudil treatment significantly reduced these effects.

CONCLUSIONS

Activation of Rho/Rho-kinase signaling in hepatic stellate cells isolated from steatotic livers is associated with an increased susceptibility to ischemia-reperfusion injury. A Rho-kinase inhibitor attenuated the activation of hepatic stellate cells isolated from steatotic livers and improved ischemia-reperfusion injury in steatotic rats.

Hedgehog signaling antagonist promotes regression of both liver fibrosis and hepatocellular carcinoma in a murine model of primary liver cancer

OBJECTIVE

Chronic fibrosing liver injury is a major risk factor for hepatocarcinogenesis in humans. Mice with targeted deletion of Mdr2 (the murine ortholog of MDR3) develop chronic fibrosing liver injury. Hepatocellular carcinoma (HCC) emerges spontaneously in such mice by 50-60 weeks of age, providing a model of fibrosis-associated hepatocarcinogenesis. We used Mdr2(-/-) mice to investigate the hypothesis that activation of the hedgehog (Hh) signaling pathway promotes development of both liver fibrosis and HCC.

METHODS

Hepatic injury and fibrosis, Hh pathway activation, and liver progenitor populations were compared in Mdr2(-/-) mice and age-matched wild type controls. A dose finding experiment with the Hh signaling antagonist GDC-0449 was performed to optimize Hh pathway inhibition. Mice were then treated with GDC-0449 or vehicle for 9 days, and effects on liver fibrosis and tumor burden were assessed by immunohistochemistry, qRT-PCR, Western blot, and magnetic resonance imaging.

RESULTS

Unlike controls, Mdr2(-/-) mice consistently expressed Hh ligands and progressively accumulated Hh-responsive liver myofibroblasts and progenitors with age. Treatment of aged Mdr2-deficient mice with GDC-0449 significantly inhibited hepatic Hh activity, decreased liver myofibroblasts and progenitors, reduced liver fibrosis, promoted regression of intra-hepatic HCCs, and decreased the number of metastatic HCC without increasing mortality.

CONCLUSIONS

Hh pathway activation promotes liver fibrosis and hepatocarcinogenesis, and inhibiting Hh signaling safely reverses both processes even when fibrosis and HCC are advanced.

Hepatic stellate cells produce vascular endothelial growth factor via phospho-p44/42 mitogen-activated protein kinase/cyclooxygenase-2 pathway

Vascular endothelial growth factor (VEGF) is one of the major cytokines secreted by activated hepatic stellate cells (HSCs). VEGF is involved in hepatic angiogenesis and plays an important role in the development of liver fibrosis. TNP-470, an angiogenic inhibitor, attenuates the development of rat liver fibrosis with reduced angiogenesis, as demonstrated in our previous study. HSCs were prepared from specific pathogen-free Wister rat livers. The isolated HSCs were activated and stimulated with platelet-derived growth factor BB (PDGF-BB) or prostaglandin E2 with or without pretreatment with MAPK cascade inhibitors (PD98059, which inhibits MEK activation), SB203580 (a selective pharmacologic inhibitor of p38 MAPK), and SP600125 (a selective inhibitor of the c-Jun N-terminal kinase, JNK). VEGF production and those of related molecules were assayed at the protein and mRNA levels by immunostaining, western blot analysis, and real-time quantitative PCR. The activated HSCs produced more VEGF than the quiescent ones. Those that received PDGF-BB stimulation showed enhanced cyclooxygenase-2 (COX-2) expression and activation of phosphor-mitogen-activated protein kinase (MAPK) p44/p42. Pretreatment with PD98059 significantly inhibited COX-2 expression and VEGF production within the PDGF-activated HSCs, but the effect was nullified by exogenous prostaglandin E2. pJNK and p38 inhibitors do not show similar inhibitory effects on VEGF and COX-2 expression, and pJNK and p38 MAPK signals are not involved in the COX-2/MAPK signaling cascade. VEGF production in PDGF-stimulated HSCs is dependent on the overexpression of COX-2 protein via the phospho-p42/44 MAP kinase activation, based on PD98059 inhibition.

Three-dimensional co-culture of hepatocytes and stellate cells

Hepatocytes self-assemble in culture to form compacted spherical aggregates, or spheroids, that mimic the structure of the liver by forming tight junctions and bile canalicular channels. Hepatocyte spheroids thus resemble the liver to a great extent. However, liver tissue contains other cell types and has bile ducts and sinusoids formed by endothelial cells. Reproducing 3-D co-culture in vitro could provide a means to develop a more complex tissue-like structure. Stellate cells participate in revascularization after liver injury by excreting between hepatocytes a laminin trail that endothelial cells follow to form sinusoids. In this study we investigated co-culture of rat hepatocytes and a rat hepatic stellate cell line, HSC-T6. HSC-T6, which does not grow in serum-free spheroid medium, was able to grow under co-culture conditions. Using a three-dimensional cell tracking technique, the interactions of HSC-T6 and hepatocyte spheroids were visualized. The two cell types formed heterospheroids in culture, and HSC-T6 cell invasion into hepatocyte spheroids and subsequent retraction was observed. RT-PCR revealed that albumin and cytochrome P450 2B1/2 expression were better maintained in co-culture conditions. These three-dimensional heterospheroids provide an attractive system for in vitro studies of hepatocyte-stellate cell interactions.

Loss of expression of miR-335 is implicated in hepatic stellate cell migration and activation

Activation and migration of resident stellate cells (HSCs) within the hepatic space of Disse play an important role in hepatic fibrosis, which accounts for the increased numbers of activated HSCs in areas of inflammation during hepatic fibrosis. Currently, microRNAs have been found to play essential roles in HSC differentiation, proliferation, apoptosis, fat accumulation and collagen production. However, little is known about microRNA mediated HSC activation and migration. In this study, the miRNA expression profiles of quiescent HSCs, partially activated HSCs and fully activated HSCs were compared in pairs. Gene ontology (GO) and GO-Map network analysis indicated that the activation of HSCs was regulated by microRNAs. Among them miR-335 was confirmed to be significantly reduced during HSC activation by qRT-PCR, and restoring expression of miR-335 inhibited HSC migration and reduced α-SMA and collagen type I. Previous study revealed that tenascin-C (TNC), an extracellular matrix glycoprotein involved in cell migration, might be a target of miR-335. Therefore, we further studied the TNC expression in miR-335 over-expressed HSCs. Our data showed that exogenous TNC could enhance HSC migration in vitro and miR-335 restoration resulted in a significant inhibition of TNC expression. These results demonstrated that miR-335 restoration inhibited HSC migration, at least in part, via downregulating the TNC expression.

Development of an experimental model of cholestasis induced by hypoxic/ischemic damage to the bile duct and liver tissues in infantile rats

BACKGROUND

We aimed to develop experimental models of hypoxia/ischemia-induced cholestasis using neonatal and infantile rats.

METHODS

Hypoxia/ischemia was induced in the bile duct (BD) by injecting prostaglandin (PG) at birth and/or by coagulation of the hepatic artery (CHA) at about 3 weeks after birth. The rats were divided into 6 groups: control; PG-injected; sham-operated with or without PG; CHA; and CHA + PG. CHA was also performed in adult rats. Liver specimens and blood samples were obtained at 5 weeks after birth, and immunohistochemical and biochemical examinations were performed.

RESULTS

(1) BD proliferation with fibrosis (BDPF) was found in the intrahepatic portal tract in the CHA and CHA + PG groups. Low-grade BDPF was observed in the PG group. (2) Cyst formation in the extrahepatic BD (EBD) was observed in the porta hepatis of some rats in the CHA and CHA + PG groups. In these groups, the number of peribiliary vascular plexuses (PVPs) decreased. BD proliferation and infiltration of inflammatory cells were observed in the EBD wall in the CHA + PG group. (3) Ki-67 was expressed in BD and EBD cells in the CHA + PG group. (4) BDPF was not detected in adult rats with CHA. (5) Serum liver function tests indicated obstructive changes in the EBD in the CHA and CHA + PG groups.

CONCLUSION

Reduced blood flow in the EBD during infancy induced BDPF and obstructive changes in the EBD, which may, along with immature PVP and inflammatory changes in the EBD, contribute to hypoxia/ischemia of the EBD.

Ductal plates in hepatic ductular reactions. Hypothesis and implications. II. Ontogenic liver growth in childhood

This article discusses the processes of bile duct growth and new lobule formation in the liver during childhood in the light of the ductal plate (DP) hypothesis. Unlike in other organs in which tubular elongation and branching ends with the creation of the organ-specific terminal differentiation products, in the liver a steadily enlarging parenchymal mass needs to establish continuity of its canalicular network with the existing bile duct system. The hypothesis suggests that this occurs by DP formation, like in the embryonic liver, and further assumes that pathological ductular reactions (DRs) induced by cholestasis or hypoxia are amplified equivalents of similar mechanisms operating at low level during liver growth. The concept is confronted with data on porcine liver growth, since swine and non-swine liver growth is thought to be comparable. Relative bile acid load may be the driving force for establishment of new canaliculo-ductular connections, supported in zones of relative hypoxia by hypoxia-inducible factor 1 alpha secreted by hepatocytes. The latter mechanism is at the base for induction of appropriate vascular changes in selected sinusoids, resulting in the development of portal inlet venules and additional draining central veins. The process gives rise to the formation of new single lobules by formation of new portal tracts or to the transformation of single lobules in compound lobules by development of new vascular septa. The concept of postnatal DP formation is important in the elucidation of several unexplained findings in adult liver diseases.

Angiogenesis in chronic liver disease and its complications

Nowadays, liver cancer, cirrhosis and other liver-related diseases are the fifth most common cause of mortality in the UK. Furthermore, chronic liver diseases (CLDs) are one of the major causes of death, which are still increasing year-on-year. Therefore, knowledge about the pathophysiology of CLDs and its complications is of uttermost importance. The goal of this review is to clarify the role of angiogenesis in the disease progression of various liver diseases. Looking closer at the pathophysiology of portal hypertension (PH), fibrosis, cirrhosis, non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC), we find that angiogenesis is a recurring factor in the disease progression. In PH, several factors involved in its pathogenesis, such as hypoxia, oxidative stress, inflammation and shear stress are potential mediators for the angiogenic response. The progression from fibrosis to cirrhosis, the end-point of CLDs, is distinguished by a prolonged inflammatory and fibrogenic process that leads to an abnormal angioarchitecture distinctive for cirrhosis. In several stages of NASH, a link might be made between the disease progression and hepatic microvasculature changes. HCC is one of the most vascular solid tumours in which angiogenesis plays an important role in its development, progression and metastasis. The close relationship between the progression of CLDs and angiogenesis emphasises the need for anti-angiogenic therapy as a tool for blocking or slowing down the disease progression. The fact that angiogenesis plays a pivotal role in CLDs gives rise to new opportunities for treating CLDs and its complications.

Hypoxia-inducible factor-1α regulates the expression of genes in hypoxic hepatic stellate cells important for collagen deposition and angiogenesis

BACKGROUND/AIMS

Several studies have shown that regions of hypoxia develop in the liver during chronic injury. Furthermore, it has been demonstrated that hypoxia stimulates the release of mediators from hepatic stellate cells (HSCs) that may affect the progression of fibrosis. The mechanism by which hypoxia modulates gene expression in HSCs is not known. Recent studies demonstrated that the hypoxia-activated transcription factor, hypoxia-inducible factor (HIF)-1α, is critical for the development of fibrosis. Accordingly, the hypothesis was tested that HIF-1α is activated in HSCs and regulates the expression of genes important for HSC activation and liver fibrosis.

METHODS

Hepatic stellate cells were isolated from mice and exposed to hypoxia. HIF-1α and HIF-2α activation were measured, and gene expression was analysed by gene array analysis. To identify the genes regulated by HIF-1α, HSCs were isolated from control and HIF-1α-deficient mice.

RESULTS

Exposure of primary mouse HSCs to 0.5% oxygen activated HIF-1α and HIF-2α. mRNA levels of numerous genes were increased in HSCs exposed to 0.5% oxygen, many of which are important for HSC function, angiogenesis and collagen synthesis. Of the mRNAs increased, chemokine receptor (Ccr) 1, Ccr5, macrophage migration inhibitory factor, interleukin-13 receptor α1 and prolyl-4-hydroxylase α2 (P4h α2) were completely HIF-1α dependent. Upregulation of the vascular endothelial growth factor and the placental growth factor was partially HIF-1α dependent and upregulation of angiopoietin-like 4 and P4h α1 was HIF-1α independent.

CONCLUSIONS

Results from these studies demonstrate that hypoxia, through activation of HIF-1α, regulates the expression of genes that may alter the sensitivity of HSCs to certain activators and chemotaxins, and regulates the expression of genes important for angiogenesis and collagen synthesis.

Epithelial-mesenchymal interactions in biliary diseases

In most cholangiopathies, liver diseases of different etiologies in which the biliary epithelium is the primary target in the pathogenic sequence, the central mechanism involves inflammation. Inflammation, characterized by pleomorphic peribiliary infiltrate containing fibroblasts, macrophages, lymphocytes, as well as endothelial cells and pericytes, is associated to the emergence of "reactive cholangiocytes." These biliary cells do not possess bile secretory functions, are in contiguity with terminal cholangioles, and are of a less-differentiated phenotype. They have acquired several mesenchymal properties, including motility and ability to secrete a vast number of proinflammatory chemo/cytokines and growth factors along with de novo expression of a rich receptor machinery. These functional properties enable reactive cholangiocytes to establish intimate contacts and to mutually exchange a variety of paracrine signals with the different mesenchymal cell types populating the portal infiltrate. The extensive crosstalk between the epithelial and mesenchymal compartments is the driver of liver repair mechanisms in cholangiopathies, ultimately evolving toward portal fibrosis. Herein, the authors first review the properties of the different cell types involved in their interaction, and then analyze the underlying molecular mechanisms as they relate to liver repair in cholangiopathies.

The use of low molecular weight heparin-pluronic nanogels to impede liver fibrosis by inhibition the TGF-β/Smad signaling pathway

Low molecular weight heparin (LH) has been reported to have anti-fibrotic and anti-cancer effects. To enhance the efficacy and minimize adverse effects of LH, a low molecular weight heparin-pluronic nanogel (LHP) was synthesized by conjugating carboxylated pluronic F127 to LH. The LHP reduced anti-coagulant activity by about 33% of the innate activity. Liver fibrosis was induced by the injection of 1% dimethylnitrosamine (DMN) in rats, and LH or LHP (1000 IU/kg body weight) was treated once daily for 4 weeks. LHP administration prevented DMN-mediated liver weight loss and decreased the values of aspartate transaminase, alanine transaminase, total bilirubin, and direct bilirubin. LHP markedly reduced the fibrotic area compared to LH. Also, LHP potently inhibited mRNA or protein expression of alpha-smooth muscle actin, collagen type I, matrix metalloproteinase-2, and tissue inhibitor of metalloproteinase-1 compared to LH, in DMN-induced liver fibrosis. In addition, LHP decreased the expression of transforming growth factor-β(1) (TGF-β(1)), p-Smad 2, and p-Smad 3, which are all important molecules of the TGF-β/Smad signaling pathway. The results support an LHP shows anti-fibrotic effect in the liver via inhibition of the TGF-β/Smad pathway as well as by the elimination of the extracellular matrix.

Angiogenesis: multiple masks in hepatocellular carcinoma and liver regeneration

Hepatocellular carcinoma (HCC) is naturally resistant to radiotherapy and cytotoxic chemotherapy, leaving surgery as the mainstream therapeutic approach. However, the 5-year recurrence rate after curative resection is as high as 61.5%. The background hepatitis B- or C-induced cirrhosis and the presence of micrometastases at the time of surgery have been regarded as two main causes of recurrence. Recently, accumulating evidence suggests that growth factors and cytokines released during the physiological process of post-surgical liver regeneration could induce the activation of dormant micrometastatic lesions. The establishment of neovasculature to support either liver regeneration or HCC growth involves multiple cell types including liver sinusoidal endothelial cells, Kupffer cells, hepatic stellate cells, and circulating endothelial progenitors. The crosstalks among these cells are driven by multiple molecules and signaling pathways, including vascular endothelial growth factors and their receptors, platelet-derived growth factor, the angiopoietin/Tie family, hepatocyte growth factor/c-Met signaling, and others. Anti-angiogenic agent targeting liver cancer vasculature has been reported to be able to generate limited survival benefit of the patients. In this review, discussions are focused on various angiogenic mechanisms of HCC and liver regeneration, as well as the prevailing anti-angiogenic strategies.

Ephrin B2/EphB4 pathway in hepatic stellate cells stimulates Erk-dependent VEGF production and sinusoidal endothelial cell recruitment

Chemotaxis signals between hepatic stellate cells (HSC) and sinusoidal endothelial cells (SEC) maintain hepatic vascular homeostasis and integrity and also regulate changes in sinusoidal structure in response to liver injury. Our prior studies have demonstrated that the bidirectional chemotactic signaling molecules EphrinB2 and EphB4 are expressed in HSC. The aim of our present study was to explore whether and how the EphrinB2/EphB4 system in HSC could promote SEC recruitment, which is essential for sinusoidal structure and remodeling. Stimulation of human HSC (hHSC) with chimeric agonists (2 microg/ml) of either EphrinB2 or EphB4 (EphrinB2 Fc or EphB4 Fc, respectively) significantly increased VEGF mRNA levels in hHSC as assessed by quantitative PCR, with respective small interfering RNAs for EphrinB2 and EphB4 inhibiting this increase (P < 0.05, n = 3). EphrinB2 agonist-induced increase in VEGF mRNA levels in hHSC was associated with increased phosphorylation of Erk and was significantly blocked by U0126 (20 microM), an inhibitor of MEK, which is a kinase upstream from Erk (P < 0.05, n = 3). The EphB4 agonist also significantly increased human VEGF promoter activity (P < 0.05, n = 3) as assessed by promoter reporter luciferase assay in transfected LX2-HSC. This was associated with upregulation of the vasculoprotective transcription factor, Kruppel-like factor 2 (KLF2). In Boyden chamber assays, conditioned media from hHSC stimulated with agonists of EphrinB2 or EphB4 increased SEC chemotaxis in a VEGF-dependent manner, compared with control groups that included basal media with agonists of EphrinB2, EphB4, or HSC-conditioned media from HSC in absence of agonist stimulation (P < 0.05, n = 3). EphB4 expression was detected in situ within liver sinusoidal vessels of rats after carbon tetrachloride-induced liver injury. In summary, activation of the EphrinB2/EphB4 signaling pathway in HSC promotes chemotaxis of SEC through a pathway that involves Erk, KLF2, and VEGF. These studies identify EphrinB2 or EphB4 as a key intermediary that links HSC signal transduction pathways with angiogenesis and sinusoidal remodeling.

Serum vascular endothelial growth factor per platelet count in patients with biliary atresia

Background: Biliary atresia (BA) is a progressive, sclerosing, inflammatory process resulting in complete obliteration of the extrahepatic bile ducts. The obstruction of bile flow engenders worsening cholestasis, hepatic fibrosis, and cirrhosis, which lead to portal hypertension and a decline in hepatic synthetic function. Hepatic stellate cells, which play roles in hepatic fibrogenesis, are an important source of various inflammatory mediators including vascular endothelial growth factor (VEGF) in the injured liver. Objectives: Investigate the level of serum VEGF and serum VEGF per platelet count in patients with BA and its relation to clinical characteristics. Methods: Peripheral blood samples were taken from 70 BA patients and 15 healthy control children. Serum VEGF was measured by enzyme-linked immunosorbent assay. We compared serum VEGF and serum VEGF per platelet count in BA patients with the respective results obtained in healthy control children. The relation of serum VEGF per platelet count with clinical variables of BA patients was investigated. Results: Serum VEGF levels and serum VEGF per platelet count in BA patients were not significantly different from those in normal controls (289.64±230.01 pg/mL vs. 312.36±189.05 pg/mL; p=0.72 and 1.72±1.21x106 vs. 1.57±0.97x106; p=0.66). Significant differences were observed among BA patients when VEGF per platelet count was categorized by the presence of esophageal varice (p=0.03). Only in BA patients was the serum level of VEGF correlated with the number of platelets (r=0.53, p<0.001). Conclusion: A high serum VEGF per platelet count is a useful marker for the development of portal hypertension in BA patients, especially for esophageal varice. Serum VEGF per platelet count may be useful for monitoring disease course in BA after hepatic portoenterostomy.

Soluble angiogenesis factors in sera of Egyptian patients with hepatitis C virus infection: correlation with disease severity

Hepatitis C virus (HCV) infection causes chronic hepatitis, which gradually progresses to liver cirrhosis and subsequently to hepatocellular carcinoma (HCC). Angiogenesis plays a major role in chronic inflammation and may have prognostic value in disease progression. This study was designed to evaluate vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), and tumor necrosis factor-alpha (TNF-alpha) as prognostic factors of disease progression in Egyptian patients with different stages of HCV-related cirrhosis and HCC. VEGF, PDGF, and TNF-alpha were measured using enzyme-linked immunosorbent assay (ELISA) in 82 HCV-infected patients (20 mild, 20 moderate, and 20 severe cirrhosis patients, and 22 HCC patients), and 20 healthy controls. Our results showed comparable increases in VEGF and PDGF levels in those with increasing clinical stages of disease, with maximal production seen in HCC patients. A gradual elevation of TNF-alpha levels was seen also in HCV-infected patients at different stages of disease and HCC. A statistically significantly positive correlation between serum levels of VEGF, PDGF, and TNF-alpha, and grade of disease was recorded. Thus assessment of these parameters in those with different stages of disease may be helpful in choosing the best treatment strategy, and indicate that anti-angiogenic therapy may be useful.

Mechanisms of acetaminophen-induced liver necrosis

Although considered safe at therapeutic doses, at higher doses, acetaminophen produces a centrilobular hepatic necrosis that can be fatal. Acetaminophen poisoning accounts for approximately one-half of all cases of acute liver failure in the United States and Great Britain today. The mechanism occurs by a complex sequence of events. These events include: (1) CYP metabolism to a reactive metabolite which depletes glutathione and covalently binds to proteins; (2) loss of glutathione with an increased formation of reactive oxygen and nitrogen species in hepatocytes undergoing necrotic changes; (3) increased oxidative stress, associated with alterations in calcium homeostasis and initiation of signal transduction responses, causing mitochondrial permeability transition; (4) mitochondrial permeability transition occurring with additional oxidative stress, loss of mitochondrial membrane potential, and loss of the ability of the mitochondria to synthesize ATP; and (5) loss of ATP which leads to necrosis. Associated with these essential events there appear to be a number of inflammatory mediators such as certain cytokines and chemokines that can modify the toxicity. Some have been shown to alter oxidative stress, but the relationship of these modulators to other critical mechanistic events has not been well delineated. In addition, existing data support the involvement of cytokines, chemokines, and growth factors in the initiation of regenerative processes leading to the reestablishment of hepatic structure and function.

Hypoxia, angiogenesis and liver fibrogenesis in the progression of chronic liver diseases

Angiogenesis is a dynamic, hypoxia-stimulated and growth factor-dependent process, and is currently referred to as the formation of new vessels from pre-existing blood vessels. Experimental and clinical studies have unequivocally reported that hepatic angiogenesis, irrespective of aetiology, occurs in conditions of chronic liver diseases (CLDs) characterized by perpetuation of cell injury and death, inflammatory response and progressive fibrogenesis. Angiogenesis and related changes in liver vascular architecture, that in turn concur to increase vascular resistance and portal hypertension and to decrease parenchymal perfusion, have been proposed to favour fibrogenic progression of the disease towards the end-point of cirrhosis. Moreover, hepatic angiogenesis has also been proposed to modulate the genesis of portal-systemic shunts and increase splanchnic blood flow, thus potentially affecting complications of cirrhosis. Hepatic angiogenesis is also crucial for the growth and progression of hepatocellular carcinoma. Recent literature has identified a number of cellular and molecular mechanisms governing the cross-talk between angiogenesis and fibrogenesis, with a specific emphasis on the crucial role of hypoxic conditions and hepatic stellate cells, particularly when activated to the myofibroblast-like pro-fibrogenic phenotype. Experimental anti-angiogenic therapy has been proven to be effective in limiting the progression of CLDs in animal models. From a clinical point of view, anti-angiogenic therapy is currently emerging as a new pharmacologic intervention in patients with advanced fibrosis and cirrhosis.

The coagulation factor Xa/protease activated receptor-2 axis in the progression of liver fibrosis: a multifaceted paradigm

Hepatic fibrosis is a common response to virtually all forms of chronic liver injury independent of the etiologic agent. Despite the relatively large population of patients suffering from hepatic fibrosis and cirrhosis, no efficient and well-tolerated drugs are available for the treatment of this disorder. The lack of efficient treatment options is at least partly because the underlying cellular mechanisms leading to hepatic fibrosis are only partly understood. It is thus of pivotal importance to better understand the cellular processes contributing to the progression of hepatic fibrosis. Interestingly in this perspective, a common feature of fibrotic disease of various organs is the activation of the coagulation cascade and hepatic fibrosis is also accompanied by a local hypercoagulable state. Activated blood coagulation factors directly target liver cells by activating protease-activated receptors (PAR) thereby inducing a plethora of cellular responses like (among others) proliferation, migration and extracellular matrix production. Coagulation factor driven PAR activation thus establishes a potential link between activation of the coagulation cascade and the progression of fibrosis. The current review focuses on blood coagulation factor Xa and summarizes the variety of cellular functions induced by factor Xa-driven PAR-2 activation and the subsequent consequences for tissue repair and hepatic fibrosis.

Changes in microRNAs associated with hepatic stellate cell activation status identify signaling pathways

Activation of hepatic stellate cells (HSCs), which is regulated by multiple signal transduction pathways, is the key event in liver fibrosis. Moreover, members of these pathways are important targets for microRNAs (miRNAs). To better understand the critical pathways of HSC activation, we performed comprehensive comparative bioinformatics analysis of microarrays of quiescent and activated HSCs. Changes in miRNAs associated with HSC activation status revealed that 13 pathways were upregulated and 22 pathways were downregulated by miRNA. Furthermore, mitochondrial integrity, based on highly upregulated Bcl-2 and downregulated caspase-9, was confirmed in HSCs and fibrotic livers by immnofluorescence assay, quantitative RT-PCR, and western blot analysis. These findings provide in vitro and in vivo evidence that the mitochondrial pathway of apoptosis plays a significant role in the progression of liver fibrogenesis via HSC activation.

PTK787/ZK22258 attenuates stellate cell activation and hepatic fibrosis in vivo by inhibiting VEGF signaling

Liver fibrosis due to hepatic stellate cell (HSC) activation represents a common response to chronic liver injury. PTK787/ZK222584 (PTK/ZK) is a pan-VEGFR tyrosine kinase inhibitor. The aim of this study was to examine the effect of PTK/ZK in liver fibrosis. In primary HSCs, PTK/ZK inhibited the expression of alpha-smooth muscle actin (alpha-SMA), collagen, tissue inhibitor of metalloproteinase-1 (TIMP-1), as well as cell proliferation, migration and actin filament formation. PTK/ZK-induced apoptosis of HSCs, which was correlated with increased caspase-3 activation and suppressed Bcl-2 expression. PTK/ZK also induced cell cycle arrest, accompanied by increasing the expression of p27(Kip1) and downregulation of cyclin D1 and cyclin E. PTK/ZK significantly inhibited vascular endothelial growth factor (VEGF) expression, as well as VEGF-simulated cell proliferation and phosphorylation of Akt in activated HSCs. In a murine fibrotic liver, PTK/ZK attenuated collagen deposition and alpha-SMA expression in carbon tetrachloride-induced fibrosis in both a 'prevention' and 'treatment' dosing scheme. These beneficial effects were associated with reduced phosphorylation of Akt and suppressed mRNA expression of procollagen-(I), TIMP-1, matrix metalloproteinase-9 and CD31. These findings provide novel insights into the potential value of blocking VEGF signaling by a small molecule tyrosine kinase inhibitor in treating hepatic fibrosis.

Over-expression of C/EBP-alpha induces apoptosis in cultured rat hepatic stellate cells depending on p53 and peroxisome proliferator-activated receptor-gamma

Hepatic stellate cells (HSCs) play a key role in the pathogenesis of hepatic fibrosis. In our previous studies, CCAAT enhancer binding protein-alpha (C/EBP-alpha) has been shown to be involved in the activation of HSCs and to have a repression effect on hepatic fibrosis in vivo. However, the mechanisms are largely unknown. In this study, we show that the infection of adenovirus vector expressing C/EBP-alpha gene (Ad-C/EBP-alpha) could induce HSCs apoptosis in a dose- and time-dependent manner by Annexin V/PI staining, caspase-3 activation assay, and flow cytometry. Also, over-expression of C/EBP-alpha resulted in the up-regulation of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and P53, while P53 expression was regulated by PPAR-gamma. In addition, Fas, FasL, DR4, DR5, and TRAIL were studied. The results indicated that the death receptor pathway was mainly involved and regulated by PPAR-gamma and p53 in the process of apoptosis triggered by C/EBP-alpha in HSCs.

The gep oncogenes, Galpha(12) and Galpha(13), upregulate the transforming growth factor-beta1 gene

Transforming growth factor-beta1 (TGFbeta1) plays a role in neoplastic transformation and transdifferentiation. Galpha(12) and Galpha(13), referred to as the gep oncogenes, stimulate mitogenic pathways. Nonetheless, no information is available regarding their roles in the regulation of the TGFbeta1 gene and the molecules linking them to gene transcription. Knockdown or knockout experiments using murine embryonic fibroblasts and hepatic stellate cells indicated that a Galpha(12) and Galpha(13) deficiency reduced constitutive, auto-stimulatory or thrombin-inducible TGFbeta1 gene expression. In contrast, transfection of activated mutants of Galpha(12) and Galpha(13) enabled the knockout cells to promote TGFbeta1 induction. A promoter deletion analysis suggested that activating protein 1 (AP-1) plays a role in TGFbeta1 gene transactivation, which was corroborated by the observation that a deficiency of the G-proteins decreased the AP-1 activity, whereas their activation enhanced it. Moreover, mutation of the AP-1-binding site abrogated the ability of Galpha(12) and Galpha(13) to induce the TGFbeta1 gene. Transfection of a dominant-negative mutant of Rho or Rac, but not Cdc42, prevented gene transactivation and decreased AP-1 activity downstream of Galpha(12) and Galpha(13). In summary, Galpha(12) and Galpha(13) regulate the expression of the TGFbeta1 gene through an increase in Rho/Rac-dependent AP-1 activity, implying that the G-protein-coupled receptor (GPCR)-Galpha(12) pathway is involved in the TGFbeta1-mediated transdifferentiation process.

Advances in antifibrotic therapy

Sustained progress in defining the molecular pathophysiology of hepatic fibrosis has led to a comprehensive framework for developing antifibrotic therapies. Indeed, the single greatest limitation in bringing new drugs to the clinical setting is a lack of clarity regarding clinical trial and treatment end points, not a lack of promising agents. A range of treatments, including those developed for other indications, as well as those specifically developed for hepatic fibrosis, are nearing or in clinical trials. Most are focused on attacking features of either hepatic injury and/or activated stellate cells and myofibroblasts, which are the primary sources of extracellular matrix (scar) proteins. Thus, features of injury and stellate cell activation provide a useful template for classifying these emerging agents and point to a new class of therapies for patients with fibrosing liver disease.

[The role of activated hepatic stellate cells in liver fibrosis, portal hypertension and cancer angiogenesis]

Although hepatic stellate cells, which are liver specific pericytes, have been recognized within the vasculature of the sinusoid for more than one hundred years, the biology and function of these cells is unclear. Recent studies have highlighted the key role of stellate cells in a number of fundamental processes that include wound healing/fibrosis, vasoregulation, and vascular remodeling/angiogenesis. In the liver, these processes are particularly important in the development of cirrhosis, portal hypertension and cancer. This article highlights the recent advances in our understanding of the biology of hepatic stellate cells and discusses some of the recently-ascribed functions that are relevant to liver fibrosis, portal hypertension and cancer angiogenesis.

Genesis of hepatic fibrosis and its biochemical markers

Liver fibrosis is characterized by an abnormal hepatic accumulation of extracellular matrix (ECM) that results from both increased deposition and reduced degradation of collagen fibres. Fibrotic liver injury results in activation of the hepatic stellate cell (HSC). Surrogate markers are gradually being substituted for biomarkers that reflect the complex balance between synthesis and degradation of the extracellular matrix. Once the hepatic stellate cell is activated, the preceding matrix changes and recurrent injurious stimuli will perpetuate the activated state. The ECM directs cellular differentiation, migration, proliferation and fibrogenic activation or deactivation. The metabolism of the extracellular matrix is closely regulated by matrix metalloproteinases (MMP) and their specific tissue inhibitors (TIMP). Although liver biopsy combined with connective tissue stains has been a mainstay of diagnosis, there is a need for less invasive methods. These diagnostic markers should be considered in combination with liver function tests, ultrasonography and clinical manifestations.

Vascular changes in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most vascular solid tumors, in which angiogenesis plays an important role. The status of angiogenesis in HCC correlates with the disease progression and prognosis, and thus provides a potential therapeutic target. This review summarizes the vascular changes and molecular and cellular basis of angiogenesis in HCC. Development of HCC is characterized by arterialization of its blood supply and sinusoidal capillarization. Vascular endothelial growth factor (VEGF) is a potent angiogenic factor that plays a critical role in mediating angiogenesis in HCC. The VEGF can function on various types of cells, such as endothelial cells, hepatic stellate cells, endothelial progenitor cells and hemangiocytes, to induce vascular changes in HCC. Therefore, blockade of VEGF-mediated pathways, either by anti-VEGF neutralizing antibody or tyrosine kinase inhibitors that target VEGF receptors, suppresses carcinogenesis and angiogenesis in HCC. In addition to VEGF, several other angiogenic factors in HCC have recently been identified. These factors can also regulate angiogenic processes through interaction with VEGF or VEGF-independent pathways. Despite the fact that treatment of HCC remains a tough task due to lack of effective systemic therapy, antiangiogenic therapy has already entered clinical trials in HCC patients and sheds light on a promising novel treatment for this disease.

In search of the in vivo identity of mesenchymal stem cells

In spite of the advances in the knowledge of adult stem cells (ASCs) during the past few years, their natural activities in vivo are still poorly understood. Mesenchymal stem cells (MSCs), one of the most promising types of ASCs for cell-based therapies, are defined mainly by functional assays using cultured cells. Defining MSCs in vitro adds complexity to their study because the artificial conditions may introduce experimental artifacts. Inserting these results in the context of the organism is difficult because the exact location and functions of MSCs in vivo remain elusive; the identification of the MSC niche is necessary to validate results obtained in vitro and to further the knowledge of the physiological functions of this ASC. Here we show an analysis of the evidence suggesting a perivascular location for MSCs, correlating these cells with pericytes, and present a model in which the perivascular zone is the MSC niche in vivo, where local cues coordinate the transition to progenitor and mature cell phenotypes. This model proposes that MSCs stabilize blood vessels and contribute to tissue and immune system homeostasis under physiological conditions and assume a more active role in the repair of focal tissue injury. The establishment of the perivascular compartment as the MSC niche provides a basis for the rational design of additional in vivo therapeutic approaches. This view connects the MSC to the immune and vascular systems, emphasizing its role as a physiological integrator and its importance in tissue repair/regeneration.

Acute ethanol exposure disrupts VEGF receptor cell signaling in endothelial cells

Physiological angiogenesis is regulated by various factors, including signaling through vascular endothelial growth factor (VEGF) receptors. We previously reported that a single dose of ethanol (1.4 g/kg), yielding a blood alcohol concentration of 100 mg/dl, significantly impairs angiogenesis in murine wounds, despite adequate levels of VEGF, suggesting direct effects of ethanol on endothelial cell signaling (40). To examine the mechanism by which ethanol influences angiogenesis in wounds, we employed two different in vitro angiogenesis assays to determine whether acute ethanol exposure (100 mg/dl) would have long-lasting effects on VEGF-induced capillary network formation. Ethanol exposure resulted in reduced VEGF-induced cord formation on collagen and reduced capillary network structure on Matrigel in vitro. In addition, ethanol exposure decreased expression of endothelial VEGF receptor-2, as well as VEGF receptor-2 phosphorylation in vitro. Inhibition of ethanol metabolism by 4-methylpyrazole partially abrogated the effect of ethanol on endothelial cell cord formation. However, mice treated with t-butanol, an alcohol not metabolized by alcohol dehydrogenase, exhibited no change in wound vascularity. These results suggest that products of ethanol metabolism are important factors in the development of ethanol-induced changes in endothelial cell responsiveness to VEGF. In vivo, ethanol exposure caused both decreased angiogenesis and increased hypoxia in wounds. Moreover, in vitro experiments demonstrated a direct effect of ethanol on the response to hypoxia in endothelial cells, as ethanol diminished nuclear hypoxia-inducible factor-1alpha protein levels. Together, the data establish that acute ethanol exposure significantly impairs angiogenesis and suggest that this effect is mediated by changes in endothelial cell responsiveness to both VEGF and hypoxia.

Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver

The hepatic stellate cell has surprised and engaged physiologists, pathologists, and hepatologists for over 130 years, yet clear evidence of its role in hepatic injury and fibrosis only emerged following the refinement of methods for its isolation and characterization. The paradigm in liver injury of activation of quiescent vitamin A-rich stellate cells into proliferative, contractile, and fibrogenic myofibroblasts has launched an era of astonishing progress in understanding the mechanistic basis of hepatic fibrosis progression and regression. But this simple paradigm has now yielded to a remarkably broad appreciation of the cell's functions not only in liver injury, but also in hepatic development, regeneration, xenobiotic responses, intermediary metabolism, and immunoregulation. Among the most exciting prospects is that stellate cells are essential for hepatic progenitor cell amplification and differentiation. Equally intriguing is the remarkable plasticity of stellate cells, not only in their variable intermediate filament phenotype, but also in their functions. Stellate cells can be viewed as the nexus in a complex sinusoidal milieu that requires tightly regulated autocrine and paracrine cross-talk, rapid responses to evolving extracellular matrix content, and exquisite responsiveness to the metabolic needs imposed by liver growth and repair. Moreover, roles vital to systemic homeostasis include their storage and mobilization of retinoids, their emerging capacity for antigen presentation and induction of tolerance, as well as their emerging relationship to bone marrow-derived cells. As interest in this cell type intensifies, more surprises and mysteries are sure to unfold that will ultimately benefit our understanding of liver physiology and the diagnosis and treatment of liver disease.

Protease-activated receptor 1 knockout reduces experimentally induced liver fibrosis

Thrombin inhibition protects against liver fibrosis. However, it is not known whether the thrombin profibrogenic effect is due to effects on blood coagulation or to signaling via protease-activated receptors (PARs). We took advantage of the lack of blood coagulation defects in PAR-1-knockout mice. Acute carbon tetrachloride (CCl(4)) toxicity was similar in wild-type (WT), PAR-1(-/-), and PAR-1(+/-) mice as judged by aminotransferase levels, area of liver necrosis, and liver peroxidation measured by Fourier-transformed infrared spectroscopy. Fifteen mice/group received CCl(4) or its solvent for 6 wk (300 microl/kg, 3 times a week). Fibrosis area was increased 10-fold by CCl(4) treatment in WT mice. PAR-1 deficiency protected against fibrosis, with 36% and 56% decrease in PAR-1(+/-) and PAR-1(-/-) mice, respectively (P < 0.001). Similar results were obtained for area of activated fibrogenic cells (64% and 79% decrease in PAR-1(+/-) and PAR-1(-/-) mice, respectively, P < 0.001). These findings were corroborated by measurements of type I collagen, matrix metalloproteinase-2, and PDGF-beta receptor mRNA levels. There was also a significant decrease in T lymphocyte infiltration in PAR-1-deficient mice. Altogether, these results suggest that thrombin profibrogenic effects are independent of effects on blood coagulation and are instead due to direct effects on fibrogenic cells and possibly on T lymphocytes.

The effect of old age on liver oxygenation and the hepatic expression of VEGF and VEGFR2

In old age, the liver contains less ATP and hypoxia-responsive genes are upregulated. Age-related changes in hepatic perfusion and the liver sinusoidal endothelial cell (LSEC) could contribute to this altered hepatic oxygen-dependent metabolism by causing intrahepatocytic hypoxia. Furthermore, age-related changes in the LSEC ('pseudocapillarization') have been partially induced by ATP depletion. To investigate whether there is intracellular hypoxia in the old rat liver, pimonidazole immunohistochemistry in intact livers and ATP levels in isolated LSECs were studied from young and old rats. There were no age-related changes. To determine whether defenestration of the LSEC could impair oxygen diffusion, pimonidazole immunohistochemistry was performed in rats treated with poloxamer 407. Despite defenestration, there was no change in pimonidazole staining. Immunohistochemistry was then performed to determine whether there are age-related changes in VEGF and VEGFR2. VEGF staining was not associated with age. However, there was an increase in perisinusoidal VEGFR2 expression with increasing age. In conclusion, liver hypoxia does not occur in old age and LSEC pseudocapillarization does not constitute an oxygen-diffusion barrier. There are no age-related changes in VEGF expression but an increase in perisinusoidal VEGFR2 expression, which has implications for the effects of aging on the hepatic sinusoid.

Proangiogenic cytokines as hypoxia-dependent factors stimulating migration of human hepatic stellate cells

Pathological angiogenesis is associated with the fibrogenic progression of chronic liver diseases. Experimental data suggest that hypoxia and vascular endothelial growth factor (VEGF) may stimulate proliferation and synthesis of type I collagen in activated, myofibroblast-like rat hepatic stellate cells (HSC/MFs). In this study, we investigated whether hypoxia, recombinant VEGF, or angiopoietin 1 (Ang-1) may affect other crucial profibrogenic features. In human HSC/MFs, which constitutively express VEGF receptor-1 and -2 (VEGFR-1, VEGFR-2) and the Ang-1 receptor Tie-2, exposure to hypoxia, VEGF, or Ang-1 resulted in a Ras/Erk-dependent stimulation of chemokinesis and chemotaxis. Migration of human HSC/MFs under hypoxic conditions involved up-regulation of VEGF-A, Ang-1, and related receptors and was mainly dependent on VEGFR-2 (Flk-1). In specimens from either cirrhotic rat livers or from patients with hepatitis C virus-related cirrhosis, HSC/MFs expressed proangiogenic factors and related receptors in areas of active fibrogenesis (ie, at the leading or lateral edge of developing incomplete fibrotic septa). Data presented herein suggest that VEGF and Ang-1 may contribute to fibrogenesis by acting as hypoxia-inducible, autocrine, and paracrine factors able to recruit myofibroblast-like cells. Moreover, HSC/MFs, in addition to their established profibrogenic role, may also contribute to neoangiogenesis during chronic hepatic wound healing.

VEGF isoforms and receptors expression throughout acute acetaminophen-induced liver injury and regeneration

Acetaminophen (APAP) is a widely-used analgesic and a known hepatotoxic agent. Vascular endothelial growth factor (VEGF) is a growth factor with multiple functional roles. VEGF plays an important role in angiogenesis and hepatic regeneration. The aim of this study was to determine the expression of VEGF isoforms and its receptors throughout liver regeneration after the administration of a toxic dose of APAP in rats. Ten groups of adult male rats received a dose of 3.5 g/kg b.w. of APAP per os. The rats were killed post administration at 0-288 h. Blood and liver tissue were extracted. Determination of serum transaminases and alkaline phosphatase activities was performed. Liver injury and regeneration were assessed with hematoxylin-eosin specimens, morphometric analysis, hepatic thymidine kinase assay and Ki-67 expression. Reverse transcription-polymerase chain reaction and immunohistochemical methods were used for assessment of VEGF isoforms and receptors differential expression. High activities of aspartate aminotransferase were observed at 24 and 36 h with another peak of activity at 192 h post administration. Alanine aminotransferase was highest at 36 h. Alkaline phosphatase was increased post 24 h being higher at 72,192 and 240 h. Centrilobular necrosis was observed at 48-72 h and thorough restoration of the liver microarchitecture was observed at 288 h. Liver regeneration lasted from 24-192 h according to the results from thymidine kinase activity and Ki-67 expression. VEGF and VEGF receptor-2 m-RNA levels presented with a three-peak pattern of expression at 12-24, 72-96 and 192-240 h post administration. Significant difference was noted between periportal and centrilobular immunohistochemical expression. VEGF proves to play a critical role during APAP-induced liver regeneration as it presents with three points of higher expression. The first two time points are associated with the initial inflammatory reaction to the noxious stimulus and the hepatocyte regenerative process where as the third one is indicative of the potential involvement of VEGF in processes of remodeling.

Anti-fibrotic effects of tetrandrine on bile-duct ligated rats

Tetrandrine (Tet) (C38H42O8N2; molecular weight, 622), an alkaloid isolated from the Chinese medicinal herb Stephania tetrandra, has been shown to elicit anti-inflammatory and anti-fibrotic effects in pulmonary diseases, but the mechanism of action has yet to be investigated. In this study, we tested whether Tet exerts anti-fibrotic effects on rat hepatic fibrosis through anti-NFkappaB pathways. After bile-duct ligation, rats were given Tet (1 or 5 mg/kg) or silymarin (50 mg/kg, as a positive control) by gavage twice daily for 3 weeks. Liver sections were taken for Sirius red quantitative scoring, immunofluorescence double staining of alpha-smooth muscle actin (alpha-SMA) and NFkappaB, and for quantitative determinations of the mRNA expression levels of TGF-beta1, alpha-SMA, collagen 1alpha2, inducible nitric oxide synthase (iNOS), intercellular adhesion molecule 1 (ICAM-1), metallothionein, vascular endothelial growth factor (VEGF), and VEGF type II receptor (VEGFR2) genes. The results showed that both Tet and silymarin treatment significantly reduced the fibrosis scores and hepatic collagen content of BDL rats, compared with no treatment. Both Tet and silymarin treatments decreased the number of alpha-SMA- and NFkappaB-positive cells in fibrotic livers. Moreover, Tet and silymarin treatments attenuated the mRNA expression levels of TGF-beta1,alpha-SMA, collagen 1alpha2, iNOS, ICAM-1, VEGF, and VEGFR2 genes, and induced the mRNA expression of the metallothionein gene. This study suggests that the anti-fibrotic effects of Tet were related to the reduction of fibrosis-related gene transcription, the attenuation of NFkappaB-activated pathways, and the induction of metallothionein gene transcription in the livers of BDL rats.

Hypoxia induces the activation of human hepatic stellate cells LX-2 through TGF-beta signaling pathway

Hypoxia is a common environmental stress factor and is also associated with various physiological and pathological conditions such as fibrogenesis. The activation of hepatic stellate cells (HSCs) is the key event in the liver fibrogenesis. In this study, the behavior of human HSCs LX-2 in low oxygen tension (1% O2) was analyzed. Upon hypoxia, the expression of HIF-1alpha and VEGF gene was induced. The result of Western blotting showed that the expression of alpha-SMA was increased by hypoxic stimulation. Furthermore, the expression of MMP-2 and TIMP-1 genes was increased. Hypoxia also elevated the protein expression of the collagen type I in LX-2 cells. The analysis of TGF-beta/Smad signaling pathway showed that hypoxia potentiated the expression of TGF-beta1 and the phosphorylation status of Smad2. Gene expression profiles of LX-2 cells induced by hypoxia were obtained by using cDNA microarray technique.