Mechanisms of hepatic fibrogenesis

Daily genetic profiling indicates JAK/STAT signaling promotes early hepatic stellate cell transdifferentiation

AIM: To identify signaling pathways and genes that initiate and commit hepatic stellate cells (HSCs) to transdifferentiation.

METHODS: Primary HSCs were isolated from male Sprague-Dawley rats and cultured on plastic for 0-10 d. Gene expression was assessed daily (quiescent to day 10 culture-activation) by real time polymerase chain reaction and data clustered using AMADA software. The significance of JAK/STAT signaling to HSC transdifferentiation was determined by treating cells with a JAK2 inhibitor.

RESULTS: Genetic cluster analyses, based on expression of these 21 genes, showed similar expression profiles on days 1-3, days 5 and 6, and days 7-10, while freshly isolated cells (day Q) and day 4 cells were genotypically distinct from any of the other days. Additionally, gene expression clustering revealed strong upregulation of interleukin-6, JAK2 and STAT3 mRNA in the early stages of activation. Inhibition of the JAK/STAT signaling pathway impeded the morphological transdifferentiation of HSCs which correlated with decreased mRNA expression of several profibrotic genes including collagens, α-SMA, PDGFR and TGFβR.

CONCLUSION: These data demonstrate unique clustered genetic profiles during the daily progression of HSC transdifferentiation and that JAK/STAT signaling may be critical in the early stages of transdifferentiation.

Effect of dietary supplementation of grape skin and seeds on liver fibrosis induced by dimethylnitrosamine in rats

Grape is one of the most popular and widely cultivated fruits in the world. Although grape skin and seeds are waste product of the winery and grape juice industry, these wastes contain large amounts of phytochemicals such as flavonoids, phenolic acids, and anthocyanidins, which play an important role as chemopreventive and anticancer agents. We evaluated efficacies of grape skin and seeds on hepatic injury induced by dimethylnitrosamine (DMN) in rats. Treatment with DMN significantly increased levels of serum alanine transaminase, aspartate transaminase, alkaline phosphatase, and bilirubin. Diet supplementation with grape skin or seeds (10% daily for 4 weeks) prevented these elevations. The grape skin and seeds also restored serum albumin and total protein levels, and reduced the hepatic level of hydroxyproline and malondialdehyde. Furthermore, grape skin and seeds reduced DMN-induced collagen accumulation, as estimated by histological analysis of liver tissue stained with Sirius red. Grape skin and seeds also reduced hepatic stellate cell activation, as assessed by α-smooth muscle actin staining. In conclusion, grape skin and seeds exhibited in vivo hepatoprotective and antifibrogenic effects against DMN-induced liver injury, suggesting that grape skin and seeds may be useful in preventing the development of hepatic fibrosis.

E3 ubiquitin ligase synoviolin is involved in liver fibrogenesis

BACKGROUND AND AIM

Chronic hepatic damage leads to liver fibrosis, which is characterized by the accumulation of collagen-rich extracellular matrix. However, the mechanism by which E3 ubiquitin ligase is involved in collagen synthesis in liver fibrosis is incompletely understood. This study aimed to explore the involvement of the E3 ubiquitin ligase synoviolin (Syno) in liver fibrosis.

METHODS

The expression and localization of synoviolin in the liver were analyzed in CCl(4)-induced hepatic injury models and human cirrhosis tissues. The degree of liver fibrosis and the number of activated hepatic stellate cells (HSCs) was compared between wild type (wt) and Syno(+/-) mice in the chronic hepatic injury model. We compared the ratio of apoptosis in activated HSCs between wt and Syno(+/-) mice. We also analyzed the effect of synoviolin on collagen synthesis in the cell line from HSCs (LX-2) using siRNA-synoviolin and a mutant synoviolin in which E3 ligase activity was abolished. Furthermore, we compared collagen synthesis between wt and Syno(-/-) mice embryonic fibroblasts (MEF) using quantitative RT-PCR, western blotting, and collagen assay; then, we immunohistochemically analyzed the localization of collagen in Syno(-/-) MEF cells.

RESULTS

In the hepatic injury model as well as in cirrhosis, synoviolin was upregulated in the activated HSCs, while Syno(+/-) mice developed significantly less liver fibrosis than in wt mice. The number of activated HSCs was decreased in Syno(+/-) mice, and some of these cells showed apoptosis. Furthermore, collagen expression in LX-2 cells was upregulated by synoviolin overexpression, while synoviolin knockdown led to reduced collagen expression. Moreover, in Syno(-/-) MEF cells, the amounts of intracellular and secreted mature collagen were significantly decreased, and procollagen was abnormally accumulated in the endoplasmic reticulum.

CONCLUSION

Our findings demonstrate the importance of the E3 ubiquitin ligase synoviolin in liver fibrosis.

Non-invasive assessment of liver fibrosis: it is time for laboratory medicine

Chronic liver diseases (CLDs) represent a major cause of morbidity and mortality worldwide. In all etiologies of CLDs, staging of liver fibrosis is essential for both prognosis and management. Until a few years ago, liver biopsy was the only tool for the diagnosis of liver fibrosis in patients with CLDs. However, liver biopsy is an invasive and costly procedure. More recently, various serum biomarkers and laboratory tests have been proposed as surrogates of liver histology. Due to inadequate diagnostic accuracy or to lack of sufficient validation, guidelines still do not recommend them as a substitute for liver biopsy that is still considered the gold standard for the diagnosis of liver fibrosis. Notably, non-invasive serum biomarkers, when combined, may reduce by 50%-80% the number of liver biopsies needed for correctly classifying hepatic fibrosis. However, liver biopsy cannot be avoided completely, but should be used in those cases in which non-invasive methods show poor accuracy. In this view, serum biomarkers and liver biopsy represent a union between laboratory medicine and hepatology.

Antagonism of the chemokine Ccl5 ameliorates experimental liver fibrosis in mice

Activation of hepatic stellate cells in response to chronic inflammation represents a crucial step in the development of liver fibrosis. However, the molecules involved in the interaction between immune cells and stellate cells remain obscure. Herein, we identify the chemokine CCL5 (also known as RANTES), which is induced in murine and human liver after injury, as a central mediator of this interaction. First, we showed in patients with liver fibrosis that CCL5 haplotypes and intrahepatic CCL5 mRNA expression were associated with severe liver fibrosis. Consistent with this, we detected Ccl5 mRNA and CCL5 protein in 2 mouse models of liver fibrosis, induced by either injection of carbon tetrachloride (CCl4) or feeding on a methionine and choline-deficient (MCD) diet. In these models, Ccl5-/- mice exhibited decreased hepatic fibrosis, with reduced stellate cell activation and immune cell infiltration. Transplantation of Ccl5-deficient bone marrow into WT recipients attenuated liver fibrosis, identifying infiltrating hematopoietic cells as the main source of Ccl5. We then showed that treatment with the CCL5 receptor antagonist Met-CCL5 inhibited cultured stellate cell migration, proliferation, and chemokine and collagen secretion. Importantly, in vivo administration of Met-CCL5 greatly ameliorated liver fibrosis in mice and was able to accelerate fibrosis regression. Our results define a successful therapeutic approach to reduce experimental liver fibrosis by antagonizing Ccl5 receptors.

Gender-related distribution of the interleukin-1 beta and interleukin-1 receptor antagonist gene polymorphisms in patients with end-stage liver disease

Interleukin-1 beta (IL-1 beta) genetic polymorphisms and IL-1 receptor antagonist (IL1RN) variable number tandem repeat (VNTR) seem to be related with the occurrence of chronic diseases. This study aimed to verify whether IL-1 beta -511>C/T, -31>T/C, +3953>C/T and IL1RN VNTR were associated to the development of liver cirrhosis. Two hundred forty cirrhotic patients were involved in the study. A significant trend was detected, for increasing cirrhosis frequencies, grouping the patients as follows: females and males carrying neither the IL-1 beta (-511 -31) T-C/T-C or T-C/(T-T or C-C) diplotypes nor any IL1RN A2 allele (138/292), males carrying either the IL-1 beta T-C/T-C or T-C/(T-T or C-C) diplotypes or at least one IL1RN A2 allele (74/147) and males carrying either the IL-1 beta T-C/T-C or T-C/(T-T or C-C) diplotypes and at least one IL1RN A2 allele (28/37) (p < 0.01). IL-1 beta polymorphisms are associated with the occurrence of end stage liver disease. IL-1 beta inflammatory activity appears more pronounced in males.

CX3CL1-CX3CR1 interaction prevents carbon tetrachloride-induced liver inflammation and fibrosis in mice

Chronic liver disease is associated with hepatocyte injury, inflammation, and fibrosis. Chemokines and chemokine receptors are key factors for the migration of inflammatory cells such as macrophages and noninflammatory cells such as hepatic stellate cells (HSCs). The expression of CX3CR1 and its ligand, CX3CL1, is up-regulated in chronic liver diseases such as chronic hepatitis C. However, the precise role of CX3CR1 in the liver is still unclear. Here we investigated the role of the CX3CL1-CX3CR1 interaction in a carbon tetrachloride (CCl(4))-induced liver inflammation and fibrosis model. CX3CR1 was dominantly expressed in Kupffer cells in the liver. In contrast, the main source of CX3CL1 was HSCs. Mice deficient in CX3CR1 showed significant increases in inflammatory cell recruitment and cytokine production [including tumor necrosis factor α (TNF-α); monocyte chemoattractant protein 1; macrophage inflammatory protein 1β; and regulated upon activation, normal T cell expressed, and secreted (RANTES)] after CCl(4) treatment versus wild-type (WT) mice. This suggested that CX3CR1 signaling prevented liver inflammation. Kupffer cells in CX3CR1-deficient mice after CCl(4) treatment showed increased expression of TNF-α and transforming growth factor β and reduced expression of the anti-inflammatory markers interleukin-10 (IL-10) and arginase-1. Coculture experiments showed that HSCs experienced significantly greater activation by Kupffer cells from CCl(4)-treated CX3CR1-deficient mice versus WT mice. Indeed, augmented fibrosis was observed in CX3CR1-deficient mice versus WT mice after CCl(4) treatment. Finally, CX3CL1 treatment induced the expression of IL-10 and arginase-1 in WT cultured Kupffer cells through CX3CR1, which in turn suppressed HSC activation.

CONCLUSION

The CX3CL1-CX3CR1 interaction inhibits inflammatory properties in Kupffer cells/macrophages and results in decreased liver inflammation and fibrosis.

Liver fibrosis: from animal models to mapping of human risk variants

Liver fibrosis is the sequel of chronic liver diseases and the main reason for increased mortality in affected patients. The extent of liver fibrosis displays great interindividual variation, even after controlling for exogenous factors. Thus, host genetic factors are considered to play an important role in the process of liver scarring. From a genetic perspective, liver fibrosis is a complex trait with many genes contributing to the expression of the phenotype. In genetically manipulated and inbred animals several risk loci for liver fibrosis have been identified. Some of these loci have been replicated in case-control studies of patients with hepatitis C infection. In humans, genetic risk loci were identified by single marker studies, haplotype studies or the combination of single markers. Recently, the first genome-wide association studies have also been performed in patients with liver diseases. Some of the identified gene variants have been functionally characterized in vitro, thereby opening the potential for novel therapeutic approaches and risk stratification.

Role and cellular source of nicotinamide adenine dinucleotide phosphate oxidase in hepatic fibrosis

Reactive oxygen species (ROS) generated by nicotinamide adenine dinucleotide phosphate oxidase (NOX) is required for liver fibrosis. This study investigates the role of NOX in ROS production and the differential contribution of NOX from bone marrow (BM)-derived and non-BM-derived liver cells. Hepatic fibrosis was induced by bile duct ligation (BDL) for 21 days or by methionine-choline-deficient (MCD) diet for 10 weeks in wild-type (WT) mice and mice deficient in p47phox (p47phox knockout [KO]), a component of NOX. The p47phox KO chimeric mice were generated by the combination of liposomal clodronate injection, irradiation, and BM transplantation of p47phox KO BM into WT recipients and vice versa. Upon BDL, chimeric mice with p47phox KO BM-derived cells, including Kupffer cells, and WT endogenous liver cells showed a ∼25% reduction of fibrosis, whereas chimeric mice with WT BM-derived cells and p47phox KO endogenous liver cells, including hepatic stellate cells, showed a ∼60% reduction of fibrosis. In addition, p47phox KO compared to WT mice treated with an MCD diet showed no significant changes in steatosis and hepatocellular injury, but a ∼50% reduction in fibrosis. Cultured WT and p47phox KO hepatocytes treated with free fatty acids had a similar increase in lipid accumulation. Free fatty acids promoted a 1.5-fold increase in ROS production both in p47phox KO and in WT hepatocytes.

CONCLUSION

NOX in both BM-derived and non-BM-derived cells contributes to liver fibrosis. NOX does not play a role in experimental steatosis and the generation of ROS in hepatocytes, but exerts a key role in fibrosis.

Reduced nicotinamide adenine dinucleotide phosphate oxidase 2 plays a key role in stellate cell activation and liver fibrogenesis in vivo

BACKGROUND & AIMS

Hepatocyte apoptosis and activation of hepatic stellate cells (HSC) are critical events in fibrogenesis. We previously demonstrated that phagocytosis of apoptotic hepatocytes by HSC is profibrogenic. Based on this, as well as the observation that reduced nicotinamide adenine dinucleotide phosphate oxidase (NADPH) oxidase induction is central to fibrogenesis, our aim was to study the phagocytic NADPH oxidase NOX2.

METHODS

An in vivo phagocytosis model was developed by injecting wild type (wt) or NOX2(-/-) mice with lentiviral-green fluorescence protein (GFP) containing a hepatocyte-specific promoter, and adeno-tumor necrosis factor-related apoptosis-inducing ligand (ad-TRAIL). Fibrosis was evaluated in bile duct ligated (BDL) wt and NOX2(-/-) mice with or without gadolinium treatment. NOX2 expression was studied in human liver samples and in HSC isolated from fibrotic livers. The fibrogenic activity of NOX2 was assessed by collagen reporter assays.

RESULTS

In the phagocytosis model, engulfment of GFP-labeled apoptotic bodies was seen, and the expression of α-smooth muscle actin (α-SMA) and collagen I increased significantly in the wt but not in the NOX2(-/-) mice. Inhibiting apoptosis decreased the profibrogenic response. NOX2(-/-) animals exhibited significantly less fibrosis following BDL. Inactivating macrophages in wt BDL mice did not lower collagen production to the level observed in NOX2(-/-) mice, suggesting that NOX2-expressing HSC are important in fibrogenesis. NOX2 was up-regulated in HSC from fibrotic livers, and phagocytosis-induced NOX2 expression and activity were demonstrated. Based on reporter assays, production of NOX2-mediated reactive oxygen species directly induced collagen promoter activity in HSC.

CONCLUSIONS

Apoptosis and phagocytosis of hepatocytes directly induce HSC activation and initiation of fibrosis. NOX2, the phagocytic NADPH oxidase, plays a key role in this process and in liver fibrogenesis in vivo.

Atorvastatin attenuates hepatic fibrosis in rats after bile duct ligation via decreased turnover of hepatic stellate cells

BACKGROUND & AIMS

Activation of hepatic stellate cells (HSC) and transdifferentiation to myofibroblasts following liver injury is the main culprit for hepatic fibrosis. Myofibroblasts show increased proliferation, migration, contraction, and production of extracellular matrix (ECM). In vitro, HMG-CoA reductase inhibitors (statins) inhibit proliferation and induce apoptosis of myofibroblastic HSC. To investigate the antifibrotic effects of atorvastatin in vivo we used bile duct ligated rats (BDL).

METHODS

BDL rats were treated with atorvastatin (15 mg/kg/d) immediately after ligation (prophylactically) or in on-going fibrosis (therapeutically). Fibrosis was assessed by hydroxyproline content and Sirius-red staining. The activation of HSC was investigated by analysis of alphaSMA expression. mRNA levels of cytokines and procollagen were analyzed by RT-PCR, and MMP-2 activity by zymography. Proliferation was assessed by expression of cathepsins (B and D), proliferating cell nuclear antigen (PCNA), and Ki67-staining. Apoptosis was characterized by caspase-3 activity, cleavage of PARP-1, and TUNEL assay. Hepatic inflammation was investigated by serum parameters and liver histology.

RESULTS

Prophylactic and early therapy with atorvastatin significantly attenuated fibrosis and HSC activation. Later therapy lacked significant effects on fibrosis but reduced profibrotic cytokine expression and led to a more quiescent state of HSC with less proliferation and apoptosis, while hepatic inflammation did not change.

CONCLUSIONS

This study shows that very early atorvastatin treatment inhibits HSC activation and fibrosis in the BDL model in vivo, while late treatment reduces HSC turnover and activity. Our findings underline that long-term studies in humans are warranted.

Prevention of liver fibrosis by triple helix-forming oligodeoxyribonucleotides targeted to the promoter region of type I collagen gene

Hepatic fibrosis leading to cirrhosis remains a global health problem. The most common etiologies are alcoholism and viral infections. Liver fibrosis is associated with major changes in both quantity and composition of extracellular matix and leads to disorganization of the liver architecture and irreversible damage to the liver function. As of now there is no effective therapy to control fibrosis. The end product of fibrosis is abnormal synthesis and accumulation of type I collagen in the extracellular matrix, which is produced by activated stellate or Ito cells in the damaged liver. Therefore, inhibition of transcription of type I collagen should in principle inhibit its production and accumulation in liver. Normally, DNA exists in a duplex form. However, under some circumstances, DNA can assume triple helical (triplex) structures. Intermolecular triplexes, formed by the addition of a sequence-specific third strand to the major groove of the duplex DNA, have the potential to serve as selective gene regulators. Earlier, we demonstrated efficient triplex formation between the exogenously added triplex-forming oligodeoxyribonucleotides (TFOs) and a specific sequence in the promoter region of the COL1A1 gene. In this study we used a rat model of liver fibrosis, induced by dimethylnitrosamine, to test whether these TFOs prevent liver fibrosis. Our results indicate that both the 25-mer and 18-mer TFOs, specific for the upstream nucleotide sequence from -141 to -165 (relative to the transcription start site) in the 5' end of collagen gene promoter, effectively prevented accumulation of liver collagen and fibrosis. We also observed improvement in liver function tests. However, mutations in the TFO that eliminated formation of triplexes are ineffective in preventing fibrosis. We believe that these TFOs can be used as potential antifibrotic therapeutic molecules.

Ultrasound-based hepatic elastography: origins, limitations, and applications

A reliable, noninvasive marker to help clinicians evaluate hepatic fibrosis is urgently needed. The liver biopsy, an imperfect gold standard, has recognized limitations including sampling error and interobserver variability. Hepatic elastography (HE) is a novel sonographic method for assessing liver stiffness and has excellent accuracy in making the diagnosis of minimal fibrosis and cirrhosis. Several conditions intrinsic to the pathology of the liver compromise the positive predictive value of HE for fibrosis alone including acute hepatitis, obstructive cholestasis, and passive congestion. Technical considerations that hinder the performance of elastography include an advanced body mass index, the presence of ascites and narrow intercostal spaces. Despite these limitations, elastography has a role in staging fibrosis, prognosis of disease outcome, surveillance, and treatment decisions. HE is now being used in lieu of liver biopsy to investigate the natural history of chronic liver diseases. Additional studies are required to better define the appropriate role of HE in clinical practice.

Hepatic stellate cells in inflammation-fibrosis-carcinoma axis

Almost 80% of hepatocellular carcinoma (HCC) cases are associated with chronic hepatitis and cirrhosis resulting from inflammation and fibrosis. A three-step process of "inflammation-fibrosis-carcinoma" is believed to be involved in hepatocarcinogenesis. The activation of hepatic stellate cells (HSCs) may serve as an important mediator in the process of inflammation-fibrosis-carcinoma axis, even in tumor metastasis. A remarkable knowledge of activated HSCs in the pathology of HCC development is mostly focused on the liver fibrosis. The molecular links that connects inflammation and cancer in the activation of HSC are not completely known. This highlights urgent need to increase our understanding of the cellular and molecular mechanisms, by which activation of HSCs is involved in the hepatic inflammation, carcinogenesis, and metastasis.

A Chinese Herbal Decoction, Modified Yi Guan Jian, Induces Apoptosis in Hepatic Stellate Cells through an ROS-Mediated Mitochondrial/Caspase Pathway

The Chinese herb modified Yi Guan Jian (mYGJ) is an effective regimen that is usually used in outpatients with chronic liver diseases such as fibrosis and cirrhosis. However, the mechanism for the action of mYGJ on liver fibrosis is not yet clear. In this study, we found that mYGJ induced hepatic stellate cells (HSCs) apoptosis concomitant with the downregulation of Bcl-2 expression and slight elevation of Bax level. Moreover, the reactive oxygen species (ROS) were generated in the early stages of mYGJ-induced HSCs apoptosis to facilitate calcium and cytochrome c release from the mitochondria to cytosol. Subsequently, caspase 9 and caspase 3 were activated. Furthermore, the activation of ER stress-associated caspase 12 in HSCs was also evaluated. Together, we report the first evidence-based study to demonstrate that mYGJ decoction induces HSCs apoptosis through ROS accumulation and the intrinsic apoptosis pathway. These findings provide rationale for further clinical investigation of traditional Chinese medicine recipes against liver fibrosis.

Toll-like receptor 3 in liver diseases

Toll-like receptor 3 (TLR3) is a member of the TLR family that can recognize double-stranded RNA (dsRNA), playing an important role in antiviral immunity. Recent studies have shown that TLR3 is also expressed on parenchymal and nonparenchymal cells in the liver as well as on several types of immune cells. In this review, we summarize the role of TLR3 in liver injury, inflammation, regeneration, and liver fibrosis, and discuss the implication of TLR3 in the pathogenesis of human liver diseases including viral hepatitis and autoimmune liver disease.

New advances on critical implications of tumor- and metastasis-initiating cells in cancer progression, treatment resistance and disease recurrence

Accumulating lines of experimental evidence have revealed that the malignant transformation of multipotent tissue-resident adult stem/progenitor cells into cancer stem/progenitor cells endowed with a high self-renewal capacity and aberrant multilineage differentiation potential may be at origin of the most types of human aggressive and recurrent cancers. Based on new cancer stem/progenitor cell concepts of carcinogenesis, it is suggested that a small subpopulation of highly tumorigenic and migrating cancer stem/progenitor cells, also designated as cancer- and metastasis-initiating cells, can provide critical roles for primary tumor growth, metastases at distant tissues and organs, treatment resistance and disease relapse. Particularly, cancer initiation and progression to locally invasive and metastatic stages is often associated with a persistent activation of distinct developmental signaling pathways in these immature cells during epithelial-mesenchymal transition program. The signaling cascades that are often deregulated in cancer stem/progenitor cells include hedgehog, epidermal growth factor receptor (EGFR), Wnt/beta-catenin, NOTCH, polycomb gene product BMI-1 and/or stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4). Importantly, the results from recent investigations have also indicated that different cancer subtypes may harbor distinct subsets and/or number of cancer-initiating cells during cancer progression as well as before or after therapy initiation and disease recurrence. Therefore, the identification of the molecular transforming events that frequently occur in cancer- and metastasis-initiating cells versus their differentiated progenies is of immense interest to develop new targeting approach for improving current therapies against aggressive, metastatic, recurrent and lethal cancers.

Antifibrotic therapies: will we ever get there?

Progressive hepatic fibrosis is the final common pathway for most chronic liver injuries, leading to cirrhosis with risk of liver failure and hepatocellular carcinoma. It is now recognized that fibrosis is a dynamic process, and may be reversible prior to the establishment of advanced architectural changes to the liver. The most effective antifibrotic strategy is to cure the underlying disease process before advanced fibrosis has developed. Unfortunately, this is often not possible, and specific antifibrotic therapies are needed. Advances in the understanding of the pathogenesis of liver fibrosis have identified several potential novel therapeutic targets, but unfortunately clinical development has been disappointing. One major limitation has been the often prolonged natural history of fibrosis compared to experimental models, and difficulties in accurate noninvasive fibrosis assessment, thus making clinical trial design difficult. In this review, we highlight the most promising current antifibrotic strategies.

Leptin promotes the myofibroblastic phenotype in hepatic stellate cells by activating the hedgehog pathway

Trans-differentiation of quiescent hepatic stellate cells (Q-HSCs), which exhibit epithelial and adipocytic features, into myofibroblastic-HSC (MF-HSCs) is a key event in liver fibrosis. Culture models demonstrated that Hedgehog (Hh) pathway activation is required for transition of epithelioid/adipocytic Q-HSCs into MF-HSCs. Hh signaling inhibits adiposity and promotes epithelial-to-mesenchymal transitions (EMTs). Leptin (anti-adipogenic, pro-EMT factor) promotes HSC trans-differentiation and liver fibrosis, suggesting that the pathways may interact to modulate cell fate. This study aimed to determine whether leptin activates Hh signaling and whether this is required for the fibrogenic effects of leptin. Cultures of primary HSCs from lean and fa/fa rats with an inherited ObRb defect were examined. Inhibitors of PI3K/Akt, JAK/STAT, and Hh signaling were used to delineate how ObRb activation influenced Hh signaling and HSC trans-differentiation. Fibrogenesis was compared in wild type and db/db mice (impaired ObRb function) to assess the profibrotic role of leptin. The results demonstrate that leptin-ObR interactions activate Hh signaling with the latter necessary to promote trans-differentiation. Leptin-related increases in Hh signaling required ObR induction of PI3K/Akt, which was sufficient for leptin to repress the epithelioid/adipocytic program. Leptin-mediated induction of JAK/STAT was required for mesenchymal gene expression. Leptin-ObRb interactions were not necessary for HSC trans-differentiation to occur in vitro or in vivo but are important because liver fibrogenesis was attenuated in db/db mice. These findings reveal that leptin activates Hh signaling to alter gene expression programs that control cell fate and have important implications for liver fibrosis and other leptin-regulated processes involving EMTs, including development, obesity, and cancer metastasis.

Morphological and molecular pathology of CCL4-induced hepatic fibrosis in connexin43-deficient mice

Gap junction channels, formed by connexins (Cx), are involved in the maintenance of tissue homeostasis, cell growth, differentiation, and development. Several studies have shown that Cx43 is involved in the control of wound healing in dermal tissue. However, it remains unknown whether Cx43 plays a role in the control of liver fibrogenesis. Our study investigated the roles of Cx43 heterologous deletion on carbon tetrachloride (CCl(4))-induced hepatic fibrosis in mice. We administered CCl(4) to both Cx43-deficient (Cx43(+/-)) and wild-type mice and examined hepatocellular injury and collagen deposition by histological and ultrastructural analyses. Serum biochemical analysis was performed to quantify liver injury. Hepatocyte proliferation was analyzed immunohistochemically. Protein and messenger RNA (mRNA) expression of liver connexins were evaluated using immunohistochemistry as well as immunoblotting analysis and quantitative real-time PCR. We demonstrated that Cx43(+/-) mice developed excessive liver fibrosis compared with wild-type mice after CCl(4) -induced chronic hepatic injury, with thick and irregular collagen fibers. Histopathological evaluation showed that Cx43(+/-) mice present less necroinflammatory lesions in liver parenchyma and consequent reduction of serum aminotransferase activity. Hepatocyte cell proliferation was reduced in Cx43(+/-) mice. There was no difference in Cx32 and Cx26 protein or mRNA expression in fibrotic mice. Protein expression of Cx43 increased in CCl(4)-treated mice, although with aberrant protein location on cytoplasm of perisinusoidal cells. Our results demonstrate that Cx43 plays an important role in the control and regulation of hepatic fibrogenesis.

Long-term entecavir therapy results in the reversal of fibrosis/cirrhosis and continued histological improvement in patients with chronic hepatitis B

One year of treatment with entecavir (0.5 mg daily) in nucleoside-naive patients with hepatitis B e antigen (HBeAg)-positive or HBeAg-negative chronic hepatitis B (CHB) resulted in significantly improved liver histology and virological and biochemical endpoints in comparison with lamivudine. Patients who received at least 3 years of cumulative entecavir therapy in phase 3 studies and a long-term rollover study and underwent long-term liver biopsy were evaluated for improvements in histological appearance. Sixty-nine patients [50 HBeAg-positive and 19 HBeAg-negative] receiving entecavir therapy underwent long-term liver biopsy (median time of biopsy = 6 years, range = 3-7 years). Histological improvement was analyzed for 57 patients who had adequate baseline biopsy samples, baseline Knodell necroinflammatory scores > or =2, and adequate long-term biopsy samples. At the time of long-term biopsy, all patients in the cohort had a hepatitis B virus DNA level <300 copies/mL, and 86% had a normalized alanine aminotransferase level. Histological improvement (> or =2-point decrease in the Knodell necroinflammatory score and no worsening of the Knodell fibrosis score) was observed in 96% of patients, and a > or =1-point improvement in the Ishak fibrosis score was found in 88% of patients, including all 10 patients with advanced fibrosis or cirrhosis at the phase 3 baseline.

CONCLUSION

The majority of nucleoside-naive patients with CHB who were treated with entecavir in this long-term cohort achieved substantial histological improvement and regression of fibrosis or cirrhosis.

Curcumin protects hepatic stellate cells against leptin-induced activation in vitro by accumulating intracellular lipids

Obesity and type II diabetes mellitus are often associated with hyperleptinemia and commonly accompanied by nonalcoholic steatohepatitis, which could cause hepatic fibrosis. During hepatic fibrogenesis, the major effectors hepatic stellate cells (HSCs) become active, coupling with depletion of cellular lipid droplets and downexpression of genes relevant to lipid accumulation. Accumulating evidence supports the proposal that recovering the accumulation of lipids would inhibit HSC activation. We recently reported that leptin stimulated HSC activation, which was eliminated by curcumin, a phytochemical from turmeric. The current study was designed to explore the underlying mechanisms, focusing on their effects on the level of intracellular lipids. We hypothesized that one of the mechanisms by which leptin stimulated HSC activation was to stimulate the depletion of intracellular lipids, which could be abrogated by curcumin by inducing expression of genes relevant to lipid accumulation. In this report, we observed that leptin dose dependently reduced levels of intracellular fatty acids and triglycerides in passaged HSCs, which were eliminated by curcumin. The phytochemical abrogated the impact of leptin on inhibiting the activity of AMP-activated protein kinase (AMPK) in HSCs in vitro. The activation of AMPK resulted in inducing expression of genes relevant to lipid accumulation and increasing intracellular lipids in HSCs in vitro. In summary, curcumin eliminated stimulatory effects of leptin on HSC activation and increased AMPK activity, leading to inducing expression of genes relevant to lipid accumulation and elevating the level of intracellular lipids. These results provide novel insights into mechanisms of curcumin in inhibiting leptin-induced HSC activation.

Histone deacetylase inhibition suppresses the transforming growth factor beta1-induced epithelial-to-mesenchymal transition in hepatocytes

Transforming growth factor beta1 (TGFbeta1) plays a crucial role in the induction of the epithelial-to-mesenchymal transition (EMT) in hepatocytes, which contributes to the pathogenesis of liver fibrosis. The inhibition of the TGFbeta1 cascade suppresses EMT and the resultant fibrosis. In this study, we focus on EMT-induced fibrosis in hepatocytes and the epigenetic regulation of the type I collagen gene. Histone acetylation is an important, major epigenetic mechanism that modulates gene transcription. We evaluated the epigenetic regulation of type I collagen in alpha mouse liver 12 hepatocytes (an untransformed mouse cell line) that had undergone EMT after treatment with TGFbeta1. The histone deacetylase inhibitor trichostatin A (TSA) inhibited EMT; this was reflected by the preservation of epithelial markers and function (E-cadherin and albumin). Fibrosis, the ultimate outcome of EMT, was abolished by TSA; this was indicated by the inhibition of type I collagen deposition. TSA exerted its anti-EMT effects by deactivating the mothers against decapentaplegic homolog 3 (Smad3)/Smad4 transcription complex and by interfering with p300, a coactivator of the type I collagen promoter, and preventing its binding to Smad3. TSA also restored Friend leukemia virus integration 1, an inhibitor of the type I collagen gene. TGFbeta1-induced EMT and its inhibition by TSA were replicated in human primary hepatocytes.

CONCLUSION

Histone deacetylase inhibition abrogates TGFbeta1-induced EMT in hepatocytes and reverses EMT-induced fibrosis by epigenetic modulation of type I collagen.

Rat strain differences in susceptibility to alcohol-induced chronic liver injury and hepatic insulin resistance

The finding of more severe steatohepatitis in alcohol fed Long Evans (LE) compared with Sprague Dawley (SD) and Fisher 344 (FS) rats prompted us to determine whether host factors related to alcohol metabolism, inflammation, and insulin/IGF signaling predict proneness to alcohol-mediated liver injury. Adult FS, SD, and LE rats were fed liquid diets containing 0% or 37% (calories) ethanol for 8 weeks. Among controls, LE rats had significantly higher ALT and reduced GAPDH relative to SD and FS rats. Among ethanol-fed rats, despite similar blood alcohol levels, LE rats had more pronounced steatohepatitis and fibrosis, higher levels of ALT, DNA damage, pro-inflammatory cytokines, ADH, ALDH, catalase, GFAP, desmin, and collagen expression, and reduced insulin receptor binding relative to FS rats. Ethanol-exposed SD rats had intermediate degrees of steatohepatitis, increased ALT, ADH and profibrogenesis gene expression, and suppressed insulin receptor binding and GAPDH expression, while pro-inflammatory cytokines were similarly increased as in LE rats. Ethanol feeding in FS rats only reduced IL-6, ALDH1-3, CYP2E1, and GAPDH expression in liver. In conclusion, susceptibility to chronic steatohepatitis may be driven by factors related to efficiency of ethanol metabolism and degree to which ethanol exposure causes hepatic insulin resistance and cytokine activation.

Interferon-gamma-mediated inhibition of serum response factor-dependent smooth muscle-specific gene expression

IFNγ exerts multiple biological effects on effector cells by regulating many downstream genes, including smooth muscle-specific genes. However, the molecular mechanisms underlying IFNγ-induced inhibition of smooth muscle-specific gene expression remain unclear. In this study, we have shown that serum response factor (SRF), a common transcriptional factor important in cell proliferation, migration, and differentiation, is targeted by IFNγ in a STAT1-dependent manner. We show that the molecular mechanism by which IFNγ regulates SRF is via activation of the 2-5A-RNase L system, which triggers SRF mRNA decay and reduced SRF expression. As a result, decreased SRF expression reduces expression of SRF target genes such as smooth muscle α-actin and smooth muscle myosin heavy chain. Additionally, IFNγ reduced p300 and acetylated histone-3 binding in both smooth muscle α-actin and SRF promoters, epigenetically decreasing smooth muscle α-actin and SRF transcriptional activation. Our data reveal that SRF is a novel IFNγ-regulated gene and further elucidate the molecular pathway between IFNγ, IFNγ-regulated genes, and SRF and its target genes.

Withagulatin A inhibits hepatic stellate cell viability and procollagen I production through Akt and Smad signaling pathways

AIM

To investigate the effects of the natural product Withagulatin A on hepatic stellate cell (HSC) viability and type I procollagen production. The potential mechanism underlying the pharmacological actions was also explored.

METHODS

The effect of Withagulatin A on cell viability was evaluated in HSC and LX-2 cells using a sulforhodamine B (SRB) assay. Cell cycle distribution was analyzed using flow cytometry. Type I procollagen gene expression was determined using real-time PCR. Regulation of signaling molecules by Withagulatin A was detected using Western blotting.

RESULTS

Primary rat HSCs and the human hepatic stellate cell line LX-2 treated with Withagulatin A (0.625-20 micromol/L) underwent a dose-dependent decrease in cell viability, which was associated with S phase arrest and the induction of cell apoptosis. In addition, the natural product decreased phosphorylation of the Akt/mTOR/p70S6K pathway that controls cell proliferation and survival. Furthermore, Withagulatin A (1, 2 mumol/L) inhibited transforming growth factor-beta (TGF-beta) stimulated type I procollagen gene expression, which was attributable to the suppression of TGF-beta stimulated Smad2 and Smad3 phosphorylation.

CONCLUSION

Our results demonstrated that Withagulatin A potently inhibited HSC viability and type I procollagen production, thereby implying that this natural product has potential use in the development of anti-fibrogenic reagents for the treatment of hepatic fibrosis.

Macrophages: master regulators of inflammation and fibrosis

Macrophages are found in close proximity with collagen-producing myofibroblasts and indisputably play a key role in fibrosis. They produce profibrotic mediators that directly activate fibroblasts, including transforming growth factor-beta1 and platelet-derived growth factor, and control extracellular matrix turnover by regulating the balance of various matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases. Macrophages also regulate fibrogenesis by secreting chemokines that recruit fibroblasts and other inflammatory cells. With their potential to act in both a pro- and antifibrotic capacity, as well as their ability to regulate the activation of resident and recruited myofibroblasts, macrophages and the factors they express are integrated into all stages of the fibrotic process. These various, and sometimes opposing, functions may be performed by distinct macrophage subpopulations, the identification of which is a growing focus of fibrosis research. Although collagen-secreting myofibroblasts once were thought of as the master "producers" of fibrosis, this review will illustrate how macrophages function as the master "regulators" of fibrosis.

Cell death and fibrogenesis

Fibrosis is a common feature of chronic liver injury and is initiated by cell death inside the liver. Hepatocyte death results in apoptotic bodies and other cellular debris, which are phagocytosed by hepatic stellate cells (HSCs), resulting in their activation, proliferation, differentiation, and matrix deposition. This profibrotic effect of cellular death is balanced by an antifibrotic effect of HSC death. Many HSC survival signals are obtained from the extracellular matrix, and active proapoptotic signals are provided by immune cells, particularly natural killer (NK) cells. Quiescent HSCs are relatively resistant to apoptotic signals but become sensitive after activation. The important role of NK cells in inducing HSC apoptosis may explain the increased fibrosis associated with immune suppression (e.g., in the transplant recipient) and HIV infection. HSCs also undergo senescence, which limits their function and sensitizes them to apoptosis.

Update on the pathophysiology of liver fibrosis

Fibrogenesis represents the main pathophysiological consequence of chronic liver disease and leads to life-threatening clinical consequences. The knowledge in this field has grown exponentially in the past 20 years and, currently, evaluation and treatment of liver fibrosis are central issues in hepatology. Classic mechanisms of liver fibrogenesis have been expanded and consolidated over the past few years. Concomitantly, novel mechanisms have been suggested and demonstrated. The aim of this article is to provide an update on these mechanisms with an attempt to integrate classic and novel pathways responsible for the evolution of the fibrogenic process and, potentially, for its regression.

Evolving challenges in hepatic fibrosis

Continued elucidation of the mechanisms of hepatic fibrosis has yielded a comprehensive and nuanced portrait of fibrosis progression and regression. The paradigm of hepatic stellate cell (HSC) activation remains the foundation for defining events in hepatic fibrosis and has been complemented by progress in a number of new areas. Cellular sources of extracellular matrix beyond HSCs have been identified. In addition, the role of chemokine, adipokine, neuroendocrine, angiogenic and NAPDH oxidase signaling in the pathogenesis of hepatic fibrosis has been uncovered, as has the contribution of extracellular matrix stiffness to fibrogenesis. There is also increased awareness of the contribution of innate immunity and greater understanding of the complexity of gene regulation in HSCs and myofibroblasts. Finally, both apoptosis and senescence have been recognized as orchestrated programs that eliminate fibrogenic cells during resolution of liver fibrosis. Ironically, the progress that has been made has highlighted the growing disparity between advances in the experimental setting and their translation into new diagnostic tools and treatments. As a result, focus is shifting towards overcoming key translational challenges in order to accelerate the development of new therapies for patients with chronic liver disease.

Toll-like receptor signaling and liver fibrosis

Liver fibrosis occurs as a wound-healing scar response following acute and chronic liver inflammation including alcoholic liver disease, non-alcoholic steatohepatitis, hepatitis B and C, and autoimmune hepatitis. Myofibroblasts, mainly transdifferentiated from hepatic stellate cells, are pivotal cell types that produce fibrillar collagen. The activation of inflammatory cells, including Kupffer cells, is a crucial step for activating hepatic stellate cells. Toll-like receptors (TLRs) are pattern recognition receptors that sense pathogen-associated molecular patterns (PAMPs), which discriminate the products of microorganisms from the host. TLRs are expressed on Kupffer cells, endothelial cells, dendritic cells, biliary epithelial cells, hepatic stellate cells, and hepatocytes in the liver. TLR signaling induces potent innate immune responses in these cell types. The liver is constantly exposed to PAMPs, such as LPS and bacterial DNA through bacterial translocation because there is a unique anatomical link, the portal vein system between liver and intestine. Recent evidence demonstrates the role of TLRs in the activation of hepatic immune cells and stellate cells during liver fibrosis. Moreover, crosstalk between TLR4 signaling and TGF-β signaling in hepatic stellate cells has been reported. This paper highlights the role of TLR signaling in stellate cell activation and the progression of liver fibrosis.

Hepatic stellate cells and parasite-induced liver fibrosis

Fibrogenesis is a common feature of many diseases where there is severe insult to the liver. The hepatic stellate cell trans-differentiation into a myofibroblast has been identified as an important event in liver fibrogenesis and has been well investigated over the last few years in a number of liver diseases. The trans-differentiation process can be monitored in vitro by evaluation of biomarkers that are characteristic of normal quiescent hepatic stellate cells or activated myofibroblasts. Two major parasitic diseases associated with liver injury and fibrosis are schistosomiasis and echinococcosis. Recent studies have highlighted a role for activated hepatic stellate cells in both murine and human schistosomiasis as well as demonstrating that schistosome antigens are able to regulate this trans-differentiation process. Study of the hepatic stellate cell and its interaction with parasite-derived antigens may be pivotal in our understanding of the pathology associated with schistosomiasis and other parasitic diseases, including echinococcosis, as well as revealing new information on the trans-differentiation process in this cell type.

Inhibition of RhoA expression reduces the secretion of extracellular matrix components in hepatic stellate cells

AIM: To investigate the effects of antisense oligodeoxynucleotide- and small-interfering RNA (siRNA)-mediated inhibition of RhoA expression on the secretion of extracellular matrix components in hepatic stellate cells (HSC-T6) to seek new approaches for the treatment of liver fibrosis.

METHODS: An antisense oligodeoxynucleotide and a siRNA targeting the RhoA gene were designed and transfected into HSC-T6 cells. The expression of RhoA and type I collagen (Col I) mRNAs in HSC-T6 cells was detected by RT-PCR. The expression of RhoA protein in HSC-T6 cells was detected by Western blot. The contents of hyaluronic acid, laminin and PIIIP in cell supernatants were measured by ELISA.

RESULTS: After antisense oligodeoxynucleotide or siRNA transfection, the relative expression levels of RhoA mRNA were changed from 0.892 ± 0.051 and 0.937 ± 0.044 to 0.113 ± 0.024 and 0.212 ± 0.042, respectively; the expression of RhoA protein and the contents of extracellular matrix components decreased markedly; and the relative expression levels of Col I mRNA decreased from 0.709 ± 0.067 and 0.695 ± 0.087 to 0.436 ± 0.037 and 0.201 ± 0.044, respectively.

CONCLUSION: Specific blockade of RhoA expression decreases the secretion of extracellular matrix components in HSC-T6 cells. RhoA-specific siRNA is superior to antisense oligodeoxynucleotide in down-regulating RhoA expression and therefore represents a better strategy for gene therapy of liver fibrosis.

Resveratrol inhibits dimethylnitrosamine-induced hepatic fibrosis in rats

Resveratrol, a phytoalexin found in grapes and red wines, has been reported to exhibit a wide range of pharmacological properties. In this study, we investigated the protective effect of resveratrol on hepatic injury induced by dimethylnitrosamine (DMN) in rats. Oral administration of resveratrol (20 mg/kg daily for 4 weeks) remarkably prevented the DMN-induced loss in body and liver weight, and inhibited the elevation of serum alanine transaminase, aspartate transaminase, alkaline phosphatase and bilirubin levels. Resveratrol also increased serum albumin and hepatic glutathione levels and reduced the hepatic level of malondialdehyde due to its antioxidant effect. Furthermore, DMN-induced elevation of hydroxyproline content was reduced in the resveratrol treated rats, the result of which was consistent with the reduction in type I collagen mRNA expression and the histological analysis of liver tissue stained with Sirius red. The reduction in hepatic stellate cell activation, as assessed by alpha-smooth muscle actin staining, and the reduction in transforming growth factor-beta1 mRNA expression were associated with resveratrol treatment. In conclusion, resveratrol exhibited in vivo hepatoprotective and antifibrogenic effects against DMN-induced liver injury, suggesting that resveratrol may be useful in the prevention of the development of hepatic fibrosis.

The challenge of developing novel pharmacological therapies for non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is an umbrella term for a series of hepatic pathologies that begin with relatively benign steatosis and can, with appropriate triggers, lead to the serious entity of non-alcoholic steatohepatitis (NASH). This sets the stage for liver fibrosis and finally the development of cirrhosis in up to 20% of patients with NASH. NAFLD, already among the most common diseases in industrialized countries, is increasing in prevalence and roughly affects 30% of US adults and 10% of US children alone. NAFLD is strongly associated with insulin resistance (IR) and represents the hepatic manifestation of the metabolic syndrome. Indeed, treatments aimed at reducing IR are the current mainstay of therapeutic approaches to NAFLD. While lifestyle interventions may produce limited degrees of success, there remains an urgent need for improved pharmacological therapies. Emerging diagnostic and therapeutic opportunities as well as future developments in NAFLD, NASH and liver fibrosis were discussed by a panel of experts and are presented herein. Promising novel therapeutic targets include inhibitors of dipeptidyl peptidase 4 and the renin-angiotensin system. However, improved non-invasive technologies to diagnose and stage NAFLD are needed. Combined with a better understanding of the pathophysiological processes that underlie the mechanisms of hepatic fibrogenesis in NASH, rapid clinical validation of novel therapies is expected.

Leukamenin F suppresses liver fibrogenesis by inhibiting both hepatic stellate cell proliferation and extracellular matrix production

AIM

To investigate the inhibitory effect of the natural product Leukamenin F on liver fibrosis and explore its potential underlying mechanisms.

METHODS

Carbon tetrachloride (CCl(4))-treated mouse model in vivo and in hepatic stellate cells (HSC) in vitro were used. The effect on CCl(4)-induced liver fibrosis was studied using histochemical and biochemical analysis, while the inhibition on HSC was assessed using cell proliferation/apoptosis assay and collagen I production using real-time PCR. The inhibitory effects of Leukamenin F on Akt/mTOR/p70S6K and TGFbeta/Smad pathways was studied using Western blot and cell image analysis.

RESULTS

Leukamenin F (0.1-1 mg/kg, ip, q.d.x28) significantly reduced alpha-SMA and collagen specific Sirius red staining areas in CCl(4) -treated mouse livers. This compound at 1-2 micromol/L dose-dependently inhibited alpha-SMA expression, cell proliferation and type I procollagen mRNA expression in activated HSC. Furthermore it inhibited the Akt/mTOR/p70S6K pathway and suppressed TGFbeta -induced Smad2/Smad3 phosphorylation and nuclear translocation in HSC.

CONCLUSION

Our results demonstrated that Leukamenin F could attenuate CCl(4)-induced liver fibrogenesis in mice as an efficient inhibitor against both HSC proliferation and ECM production. This natural product provides a valuable structural hint for the development of anti-liver fibrosis reagents.

Toll-like receptor 9 promotes steatohepatitis by induction of interleukin-1beta in mice

BACKGROUND & AIMS

Development of nonalcoholic steatohepatitis (NASH) involves the innate immune system and is mediated by Kupffer cells and hepatic stellate cells (HSCs). Toll-like receptor 9 (TLR9) is a pattern recognition receptor that recognizes bacteria-derived cytosine phosphate guanine (CpG)-containing DNA and activates innate immunity. We investigated the role of TLR9 signaling and the inflammatory cytokine interleukin-1beta (IL-1beta) in steatohepatitis, fibrosis, and insulin resistance.

METHODS

Wild-type (WT), TLR9(-/-), IL-1 receptor (IL-1R)(-/-), and MyD88(-/-) mice were fed a choline-deficient amino acid-defined (CDAA) diet for 22 weeks and then assessed for steatohepatitis, fibrosis, and insulin resistance. Lipid accumulation and cell death were assessed in isolated hepatocytes. Kupffer cells and HSCs were isolated to assess inflammatory and fibrogenic responses, respectively.

RESULTS

The CDAA diet induced NASH in WT mice, characterized by steatosis, inflammation, fibrosis, and insulin resistance. TLR9(-/-) mice showed less steatohepatitis and liver fibrosis than WT mice. Among inflammatory cytokines, IL-1beta production was suppressed in TLR9(-/-) mice. Kupffer cells produced IL-1beta in response to CpG oligodeoxynucleotide. IL-1beta but not CpG-oligodeoxynucleotides, increased lipid accumulation in hepatocytes. Lipid accumulation in hepatocytes led to nuclear factor-kappaB inactivation, resulting in cell death in response to IL-1beta. IL-1beta induced fibrogenic responses in HSCs, including secretion of tissue inhibitor of metalloproteinase-1. IL-1R(-/-) mice had reduced steatohepatitis and fibrosis, compared with WT mice. Mice deficient in MyD88, an adaptor molecule for TLR9 and IL-1R signaling, also had reduced steatohepatitis and fibrosis. TLR9(-/-), IL-1R(-/-), and MyD88(-/-) mice had less insulin resistance than WT mice on the CDAA diet.

CONCLUSIONS

In a mouse model of NASH, TLR9 signaling induces production of IL-1beta by Kupffer cells, leading to steatosis, inflammation, and fibrosis.

New insights into the antifibrotic effects of sorafenib on hepatic stellate cells and liver fibrosis

BACKGROUND & AIMS

During the process of liver fibrosis, hepatic stellate cells (HSCs) play a critical role in the excessive production of extracellular matrix (ECM). We evaluated the therapeutic effects of sorafenib, a multiple receptor tyrosine kinase inhibitor, targeting platelet-derived growth factor (PDGF) receptor and the Raf/extracellular-signal-regulated kinase (ERK) signaling pathway, on liver fibrosis and HSC proliferation.

METHODS

The in vivo effects of sorafenib were monitored in the livers of rats with liver fibrosis, and simultaneously proliferation assays, apoptosis induction studies, and collagen synthesis measurement were conducted in vitro in rat and human HSCs and primary HSCs.

RESULTS

Sorafenib treatment attenuated liver fibrosis and was associated with a significant decrease in intrahepatic fibrogenesis, hydroxyproline accumulation and collagen deposition. Sorafenib reduced HSC proliferation and resulted in significantly higher levels of apoptosis. Moreover, sorafenib downregulated Cyclin D1 and Cyclin-dependent kinase 4 (Cdk-4), simultaneously increased expression of Fas, Fas-L, and Caspase-3, and decreased the ratio of Bcl-2 to Bax. Sorafenib treatment increased the ratio of matrix metalloproteinases (MMPs) to tissue inhibitor of matrix metalloproteinases (TIMPs) and reduced collagen synthesis in HSCs. Sorafenib inhibited the phosphorylation of ERK, Akt and 70-kDa ribosomal S6 kinase (p70S6K), both in vitro and in vivo.

CONCLUSIONS

Sorafenib induces the suppression of collagen accumulation and HSC growth warranting the use of sorafenib as a potential therapeutic agent in the treatment of liver fibrosis.

Activation of Rac1 promotes hedgehog-mediated acquisition of the myofibroblastic phenotype in rat and human hepatic stellate cells

Hepatic accumulation of myofibroblastic hepatic stellate cells (MF-HSCs) is pivotal in the pathogenesis of cirrhosis. Two events are necessary for MF-HSCs to accumulate in damaged livers: transition of resident, quiescent hepatic stellate cells (Q-HSCs) to MF-HSCs and expansion of MF-HSC numbers through increased proliferation and/or reduced apoptosis. In this study, we identified two novel mediators of MF-HSC accumulation: Ras-related C3 botulinum toxin substrate 1 (Rac1) and Hedgehog (Hh). It is unclear whether Rac1 and Hh interact to regulate the accumulation of MF-HSCs. We evaluated the hypothesis that Rac1 promotes activation of the Hh pathway, thereby stimulating signals that promote transition of Q-HSCs into MF-HSCs and enhance the viability of MF-HSCs. Using both in vitro and in vivo model systems, Rac1 activity was manipulated through adenoviral vector-mediated delivery of constitutively active or dominant-negative rac1. Rac1-transgenic mice with targeted myofibroblast expression of a mutated human rac1 transgene that produces constitutively active Rac1 were also examined. Results in all models demonstrated that activating Rac1 in HSC enhanced Hh signaling, promoted acquisition/maintenance of the MF-HSC phenotype, increased MF-HSC viability, and exacerbated fibrogenesis. Conversely, inhibiting Rac1 with dominant-negative rac1 reversed these effects in all systems examined. Pharmacologic manipulation of Hh signaling demonstrated that profibrogenic actions of Rac1 were mediated by its ability to activate Hh pathway-dependent mechanisms that stimulated myofibroblastic transition of HSCs and enhanced MF-HSC viability.

CONCLUSION

These findings demonstrate that interactions between Rac1 and the Hh pathway control the size of MF-HSC populations and have important implications for the pathogenesis of cirrhosis.

Broad-spectrum matrix metalloproteinase inhibition curbs inflammation and liver injury but aggravates experimental liver fibrosis in mice

Background

Liver fibrosis is characterized by excessive synthesis of extracellular matrix proteins, which prevails over their enzymatic degradation, primarily by matrix metalloproteinases (MMPs). The effect of pharmacological MMP inhibition on fibrogenesis, however, is largely unexplored. Inflammation is considered a prerequisite and important co-contributor to fibrosis and is, in part, mediated by tumor necrosis factor (TNF)-α-converting enzyme (TACE). We hypothesized that treatment with a broad-spectrum MMP and TACE-inhibitor (Marimastat) would ameliorate injury and inflammation, leading to decreased fibrogenesis during repeated hepatotoxin-induced liver injury.

Methodology/Principal Findings

Liver fibrosis was induced in mice by repeated carbon tetrachloride (CCl4) administration, during which the mice received either Marimastat or vehicle twice daily. A single dose of CCl₄ was administered to investigate acute liver injury in mice pretreated with Marimastat, mice deficient in Mmp9, or mice deficient in both TNF-α receptors. Liver injury was quantified by alanine aminotransferase (ALT) levels and confirmed by histology. Hepatic collagen was determined as hydroxyproline, and expression of fibrogenesis and fibrolysis-related transcripts was determined by quantitative reverse-transcription polymerase chain reaction. Marimastat-treated animals demonstrated significantly attenuated liver injury and inflammation but a 25% increase in collagen deposition. Transcripts related to fibrogenesis were significantly less upregulated compared to vehicle-treated animals, while MMP expression and activity analysis revealed efficient pharmacologic MMP-inhibition and decreased fibrolysis following Marimastat treatment. Marimastat pre-treatment significantly attenuated liver injury following acute CCl₄-administration, whereas Mmp9 deficient animals demonstrated no protection. Mice deficient in both TNF-α receptors exhibited an 80% reduction of serum ALT, confirming the hepatoprotective effects of Marimastat via the TNF-signaling pathway.

Conclusions/Significance

Inhibition of MMP and TACE activity with Marimastat during chronic CCl₄ administration counterbalanced any beneficial anti-inflammatory effect, resulting in a positive balance of collagen deposition. Since effective inhibition of MMPs accelerates fibrosis progression, MMP inhibitors should be used with caution in patients with chronic liver diseases.

Neuropilin-1 promotes cirrhosis of the rodent and human liver by enhancing PDGF/TGF-beta signaling in hepatic stellate cells

PDGF-dependent hepatic stellate cell (HSC) recruitment is an essential step in liver fibrosis and the sinusoidal vascular changes that accompany this process. However, the mechanisms that regulate PDGF signaling remain incompletely defined. Here, we found that in two rat models of liver fibrosis, the axonal guidance molecule neuropilin-1 (NRP-1) was upregulated in activated HSCs, which exhibit the highly motile myofibroblast phenotype. Additionally, NRP-1 colocalized with PDGF-receptor beta (PDGFRbeta) in HSCs both in the injury models and in human and rat HSC cell lines. In human HSCs, siRNA-mediated knockdown of NRP-1 attenuated PDGF-induced chemotaxis, while NRP-1 overexpression increased cell motility and TGF-beta-dependent collagen production. Similarly, mouse HSCs genetically modified to lack NRP-1 displayed reduced motility in response to PDGF treatment. Immunoprecipitation and biochemical binding studies revealed that NRP-1 increased PDGF binding affinity for PDGFRbeta-expressing cells and promoted downstream signaling. An NRP-1 neutralizing Ab ameliorated recruitment of HSCs, blocked liver fibrosis in a rat model of liver injury, and also attenuated VEGF responses in cultured liver endothelial cells. In addition, NRP-1 overexpression was observed in human specimens of liver cirrhosis caused by both hepatitis C and steatohepatitis. These studies reveal a role for NRP-1 as a modulator of multiple growth factor targets that regulate liver fibrosis and the vascular changes that accompany it and may have broad implications for liver cirrhosis and myofibroblast biology in a variety of other organ systems and disease conditions.

Epithelial-mesenchymal transition: from molecular mechanisms, redox regulation to implications in human health and disease

Epithelial to mesenchymal transition (EMT) is a fundamental process, paradigmatic of the concept of cell plasticity, that leads epithelial cells to lose their polarization and specialized junctional structures, to undergo cytoskeleton reorganization, and to acquire morphological and functional features of mesenchymal-like cells. Although EMT has been originally described in embryonic development, where cell migration and tissue remodeling have a primary role in regulating morphogenesis in multicellular organisms, recent literature has provided evidence suggesting that the EMT process is a more general biological process that is also involved in several pathophysiological conditions, including cancer progression and organ fibrosis. This review offers first a comprehensive introduction to describe major relevant features of EMT, followed by sections dedicated on those signaling mechanisms that are known to regulate or affect the process, including the recently proposed role for oxidative stress and reactive oxygen species (ROS). Current literature data involving EMT in both physiological conditions (i.e., embryogenesis) and major human diseases are then critically analyzed, with a special final focus on the emerging role of hypoxia as a relevant independent condition able to trigger EMT.

Targeting orphan nuclear receptor SHP in the treatment of metabolic diseases

IMPORTANCE OF THE FIELD

The orphan nuclear receptor small heterodimer partner (SHP; NR0B2) is an atypical nuclear receptor that contains a ligand-binding domain, but lacks the conserved DNA-binding domain. Since its discovery, SHP has been identified as a key transcriptional regulatory factor of genes involved in diverse metabolic pathways.

AREAS COVERED IN THIS REVIEW

We performed a Medline/Pubmed search to find published studies on the role of SHP in the regulation of metabolism in the liver, pancreatic islets, blood vessel, and kidney and on the feasibility of using SHP as a therapeutic target in metabolic disease.

WHAT THE READER WILL GAIN

In this review, we discuss the function of SHP as regulator of cholesterol, lipid and glucose metabolism, and the role of SHP in metabolic and fibrotic diseases.

TAKE HOME MESSAGE

The reviewed studies suggested that SHP could be a major target for therapeutic intervention in metabolic and fibrotic diseases, including metabolic syndrome and its complications. However, for SHP-targeted therapy, there are some outstanding issues, including the small number of known inducers of SHP and the lack of sufficient data in humans.

Novel therapies against aggressive and recurrent epithelial cancers by molecular targeting tumor- and metastasis-initiating cells and their progenies

A growing body of experimental evidence has revealed that the highly tumorigenic cancer stem/progenitor cells endowed with stem cell-like properties might be responsible for initiation and progression of numerous aggressive epithelial cancers into locally invasive, metastatic and incurable disease states. The malignant transformation of tissue-resident adult stem/progenitor cells or their progenies into tumorigenic and migrating cancer stem/progenitor cells and their resistance to current cancer therapies have been associated with their high expression levels of specific oncogenic products and drug resistance-associated molecules. In this regard, we describe the tumorigenic cascades that are frequently activated in cancer stem/progenitor cells versus their differentiated progenies during the early and late stages of the epithelial cancer progression. The emphasis is on the growth factor signaling pathways involved in the malignant behavior of prostate and pancreatic cancer stem/progenitor cells and their progenies. Of clinical interest, the potential molecular therapeutic targets to eradicate the tumor- and metastasis-initiating cells and their progenies and develop new effective combination therapies against locally advanced and metastatic epithelial cancers are also described.

Comparative effects of telmisartan, sitagliptin and metformin alone or in combination on obesity, insulin resistance, and liver and pancreas remodelling in C57BL/6 mice fed on a very high-fat diet

The aim of the present study was to evaluate the effects of monotherapies and combinations of drugs on insulin sensitivity, adipose tissue morphology, and pancreatic and hepatic remodelling in C57BL/6 mice fed on a very HF (high-fat) diet. Male C57BL/6 mice were fed on an HF (60% lipids) diet or SC (standard chow; 10% lipids) diet for 10 weeks, after which time the following drug treatments began: HF-T (HF diet treated with telmisartan; 5.2 mg x kg-1 of body weight x day-1), HF-S (HF diet treated with sitagliptin; 1.08 g x kg-1 of body weight.day-1), HF-M (HF diet treated with metformin; 310.0 mg x kg-1 of body weight x day-1), HF-TM (HF diet treated with telmisartan+metformin), HF-TS (HF diet treated with telmisartan+sitagliptin) and HF-SM (HF diet treated with sitagliptin+metformin). Treated groups also had free access to the HF diet, and treatments lasted for 6 weeks. Morphometry, stereological tools, immunostaining, ELISA, Western blot analysis and electron microscopy were used. The HF diet yielded an overweight phenotype, an increase in oral glucose intolerance, hyperinsulinaemia, hypertrophied islets and adipocytes, stage 2 steatosis (>33%), and reduced liver PPAR-alpha (peroxisome-proliferator-activated receptor-alpha) and GLUT-2 (glucose transporter-2) levels, concomitant with enhanced SREBP-1 (sterol-regulatory-element-binding protein-1) expression (P<0.0001). Conversely, all drug treatments resulted in significant weight loss, a reversal of insulin resistance, islet and adipocyte hypertrophy, and alleviated hepatic steatosis. Only the HF-T and HF-TS groups had body weights similar to the SC group at the end of the experiment, and the latter treatment reversed hepatic steatosis. Increased PPAR-alpha immunostaining in parallel with higher GLUT-2 and reduced SREBP-1 expression may explain the favourable hepatic outcomes. Restoration of adipocyte size was consistent with higher adiponectin levels and lower TNF-alpha (tumour necrosis factor-alpha) levels (P<0.0001) in the drug-treated groups. In conclusion, all of the drug treatments were effective in controlling the metabolic syndrome. The best results were achieved using telmisartan and sitagliptin as monotherapies or as a dual treatment, combining partial PPAR-gamma agonism and PPAR-alpha activation in the liver with extended incretin action.

Investigational approaches to therapies for idiopathic pulmonary fibrosis

IMPORTANCE OF THE FIELD

In fibrosing diseases, scar tissue begins to replace normal tissue, causing tissue dysfunction. For instance, in lung fibrosis, foci of what resembles scar tissue form in the lungs, impeding the ability of patients to breathe. These conditions represent a significant source of morbidity and mortality. More than 150,000 people in the USA have some form of fibrotic lung disease, and the 5-year mortality rate for these diseases can be as high as 80%. Despite this large unmet medical need, there are no FDA-approved therapies. Although our understanding of the causes and the biology of fibrosing diseases remains relatively poor, we have made impressive advances in identifying the major cell populations and many biochemical mediators that can drive this process. As a result, novel therapeutics are being developed based upon these discoveries.

AREAS COVERED IN THIS REVIEW

This review examines the experimental therapies currently under investigation as of late 2009 for a major class of lung fibrosis called idiopathic pulmonary fibrosis (IPF).

WHAT THE READER WILL GAIN

The reader will gain an overview of current experimental therapies for IPF.

TAKE HOME MESSAGE

With the recent approval of Pirfenidone in Japan for use in IPF, and a rich pipeline of experimental therapies in various stages of clinical development, the future looks bright for new treatment options.

Thrombocytopenia exacerbates cholestasis-induced liver fibrosis in mice

BACKGROUND & AIMS

Circulating platelet counts gradually decrease in parallel with progression of chronic liver disease. Thrombocytopenia is a common complication of advanced liver fibrosis and is thought to be a consequence of the destruction of circulating platelets that occurs during secondary portal hypertension or hypersplenism. It is not clear whether thrombocytopenia itself affects liver fibrosis.

METHODS

Thrombocytopenic mice were generated by disruption of Bcl-xL, which regulates platelet life span, specifically in thrombocytes. Liver fibrosis was examined in thrombocytopenic mice upon bile duct ligation. Effect of platelets on hepatic stellate cells (HSCs) was investigated in vitro.

RESULTS

Thrombocytopenic mice developed exacerbated liver fibrosis, with increased expression of type I collagen alpha1 and alpha2, during cholestasis. In vitro experiments revealed that, upon exposure to HSCs, platelets became activated, released hepatocyte growth factor (HGF), and then inhibited HSC expression of the type I collagen genes in a Met signal-dependent manner. In contrast to the wild-type mice, the thrombocytopenic mice did not accumulate hepatic platelets or phosphorylate Met in the liver following bile duct ligation. Administration of recombinant HGF to thrombocytopenic mice reduced liver fibrosis to the levels observed in wild-type mice and attenuated hepatic expression of the type I collagen genes.

CONCLUSIONS

Thrombocytopenia exacerbates liver fibrosis; platelets have a previously unrecognized, antifibrotic role in suppressing type I collagen expression via the HGF-Met signaling pathway.