Transforming growth factor beta (TGF-beta) expression in isolated and cultured rat hepatocytes

Transforming Growth Factor Beta-Induced Foxo3a Acts as a Profibrotic Mediator in Hepatic Stellate Cells

Hepatic stellate cells (HSCs) are major contributors to hepatic fibrogenesis facilitating liver fibrosis. Forkhead box O 3a (FoxO3a) is a member of the forkhead transcription factor family, which mediates cell proliferation and differentiation. However, the expression and function of FoxO3a during HSC activation remain largely unknown. FoxO3a overexpression was related to fibrosis in patients, and its expression was colocalized with desmin or α-smooth muscle actin, representative HSC markers. We also observed upregulated FoxO3a levels in two animal hepatic fibrosis models, a carbon tetrachloride-injected model and a bile duct ligation model. In addition, transforming growth factor beta (TGF-β) treatment in mouse primary HSCs or LX-2 cells elevated FoxO3a expression. When FoxO3a was upregulated by TGF-β in LX-2 cells, both the cytosolic and nuclear levels of FoxO3a increased. In addition, we found that the induction of FoxO3a by TGF-β was due to both transcriptional and proteasome-dependent mechanisms. Moreover, FoxO3a overexpression promoted TGF-β-mediated Smad activation. Furthermore, FoxO3a increased fibrogenic gene expression, which was reversed by FoxO3a knockdown. TGF-β-mediated FoxO3a overexpression in HSCs facilitated hepatic fibrogenesis, suggesting that FoxO3a may be a novel target for liver fibrosis prevention and treatment.

The Role of Signal Transducer and Activator of Transcription 5 and Transforming Growth Factor-β1 in Hepatic Fibrosis Induced by Chronic Hepatitis C Virus Infection in Egyptian Patients

OBJECTIVE

To investigate the possible role of signal transducer and activator of transcription 5 (STAT5) in the pathogenesis of liver fibrosis in Egyptian patients with chronic hepatitis C (CHC) virus infection and its relation to hepatic stellate cells (HSC).

SUBJECTS AND METHODS

Sixty-five patients (46 males and 19 females) were divided into 4 groups based on the severity of fibrosis as detected by Fibroscan as follows: F1, n = 15; F2, n = 21; F3, n = 13; and F4, n = 16. Twenty age- and gender-matched healthy persons volunteered as controls. The serum levels of STAT5, TGF-β1, α-smooth muscle actin (α-SMA), fasting blood sugar, and fasting insulin, as well as homeostasis model assessment of insulin resistance (HOMA-IR), were determined and compared for all groups. The usefulness of the studied serum biomarkers for predicting liver fibrosis was evaluated using a receiver operating characteristic curve.

RESULTS

Serum levels of STAT5 were significantly lower in patients compared to controls (9.69 ± 5.62 vs. 14.73 ± 6.52, p ≤ 0.001); on the contrary, TGF-β1, α-SMA, and HOMA-IR were significantly higher in patients compared to controls (mean: 1,796.04 vs. 1,636.94; 14.94 vs. 8.1; and 7.91 vs. 4.18; p ≤ 0.01 and 0.001, respectively). TGF-β1 and α-SMA showed a progressive increase with advancing severity of hepatic fibrosis (mean TGF-β1: 2,058.4 in F1-F2 and 1,583.8 in F3-F4, p ≤ 0.04; mean α-SMA: 13.59 in F1-F2 and 16.62 in F3-F4, p ≤ 0.05). STAT5 had a significant negative correlation with TGF-β1 (p ≤ 0.001), while no correlation was detected with α-SMA (p ≤ 0.8).

CONCLUSIONS

STAT5 may play a significant role in hepatic fibrogenesis through the induction of TGF-β1 but not through the activation of hepatic stellate cells.

Cloning and primary immunological study of TGF-β1 and its receptors TβR I /TβR II in tilapia(Oreochromis niloticus)

The transforming growth factor β (TGF-β) superfamily plays critical roles in tumor suppression, cell proliferation and differentiation, tissue morphogenesis, lineage determination, cell migration and apoptosis. Recently, TGF-β1, one important member of TGF-β superfamily, is suggested as an immune regulator in the teleost. In this study, we cloned the cDNAs of TGF-β1 and its receptors, TβR I and TβR II (including three isoforms) from tilapia (Genbank accession numbers: KP754231- KP754235). A tissue distribution profile analysis indicated that TGF-β1 was highly expressed in the head kidney, gill, spleen, kidney and PBLs (peripheral blood leukocytes); TβR I only showed considerable expression in the liver; and TβR II-2 was highly expressed in the kidney, gill, liver, head kidney and heart. We determined that the mRNA expressions of TGF-β and TβR I /TβR II-2 were significantly increased in tilapia head kidney and spleen leukocytes by the stimulation of Lipopolysaccharide (LPS) or Poly I: C. We also examined their expressions in the spleen and head kidney of tilapia after IP injection of streptococcus agalactiae. The results showed that the mRNA expressions of these three genes all increased in the head kidney as early as 6 h post infection, and in the spleen 3 d post infection. In addition, the protein level of TGF-β1 was also up-regulated in the head kidney and the spleen after infection. Taken together, our data indicate that the TGF-β1-TβR I /TβR II-2 system functions potentially in tilapia immune system.

Activation of TGF-β1 promoter by hepatitis C virus-induced AP-1 and Sp1: role of TGF-β1 in hepatic stellate cell activation and invasion

Our previous studies have shown the induction and maturation of transforming growth factor-beta 1 (TGF-β1) in HCV-infected human hepatoma cells. In this study, we have investigated the molecular mechanism of TGF-β1 gene expression in response to HCV infection. We demonstrate that HCV-induced transcription factors AP-1, Sp1, NF-κB and STAT-3 are involved in TGF-β1 gene expression. Using chromatin immunoprecipitation (ChIP) assay, we further show that AP-1 and Sp1 interact with TGF-b1 promoter in vivo in HCV-infected cells. In addition, we demonstrate that HCV-induced TGF-β1 gene expression is mediated by the activation of cellular kinases such as p38 MAPK, Src, JNK, and MEK1/2. Next, we determined the role of secreted bioactive TGF-β1 in human hepatic stellate cells (HSCs) activation and invasion. Using siRNA approach, we show that HCV-induced bioactive TGF-β1 is critical for the induction of alpha smooth muscle actin (α-SMA) and type 1 collagen, the markers of HSCs activation and proliferation. We further demonstrate the potential role of HCV-induced bioactive TGF-β1 in HSCs invasion/cell migration using a transwell Boyden chamber. Our results also suggest the role of HCV-induced TGF-β1 in HCV replication and release. Collectively, these observations provide insight into the mechanism of TGF-β1 promoter activation, as well as HSCs activation and invasion, which likely manifests in liver fibrosis associated with HCV infection.

Hepatitis C virus-induced furin and thrombospondin-1 activate TGF-β1: role of TGF-β1 in HCV replication

In this study, we demonstrated the molecular mechanisms of TGF-β1 induction as well as proteolytic activation in HCV (JFH-1)-infected cells. Our studies showed the synthesis and secretion of TGF-β1 in HCV-infected cells which was reduced in the presence of Ca(2+) chelators, an inhibitor of mitochondrial Ca(2+) uptake, and antioxidants. We also showed that the expression of HCV NS proteins NS3/4A, and NS5A can induce TGF-β1 by cell-based luciferase assay. Furthermore, mutational analysis revealed that the functionally active protease domain of NS3 and N-terminus domain of NS5A are required for TGF-β1 activity. Using siRNA approach we demonstrated that HCV-induced furin and thrombospondin-1 (TSP-1) are involved in the proteolytic activation of TGF-β1. Our results also suggest that TGF-β1 positively regulates HCV RNA replication. Collectively, these observations provide insight into the mechanism of TGF-β1 activation, which likely manifest in liver fibrosis associated with hepatitis C infection.

Loss of STAT5 causes liver fibrosis and cancer development through increased TGF-{beta} and STAT3 activation

The molecular mechanisms underlying the development of hepatocellular carcinoma are not fully understood. Liver-specific signal transducer and activator of transcription (STAT) 5A/B–null mice (STAT5-LKO) were treated with carbon tetrachloride (CCl₄), and histological analyses revealed liver fibrosis and tumors. Transforming growth factor (TGF)–β levels and STAT3 activity were elevated in liver tissue from STAT5-LKO mice upon CCl₄ treatment. To define the molecular link between STAT5 silencing and TGF-β up-regulation, as well as STAT3 activation, we examined STAT5-null mouse embryonic fibroblasts and primary hepatocytes. These cells displayed elevated TGF-β protein levels, whereas messenger RNA levels remained almost unchanged. Protease inhibitor studies revealed that STAT5 deficiency enhanced the stability of mature TGF-β. Immunoprecipitation and immunohistochemistry analyses demonstrated that STAT5, through its N-terminal sequences, could bind to TGF-β and that retroviral-mediated overexpression of STAT5 decreased TGF-β levels. To confirm the in vivo significance of the N-terminal domain of STAT5, we treated mice that expressed STAT5 lacking the N terminus (STAT5-ΔN) with CCl₄. STAT5-ΔN mice developed CCl₄-induced liver fibrosis but no tumors. In conclusion, loss of STAT5 results in elevated TGF-β levels and enhanced growth hormone–induced STAT3 activity. We propose that a deregulated STAT5–TGF-β–STAT3 network contributes to the development of chronic liver disease.

Activation of TGF-beta within cultured hepatocytes and in liver injury leads to intracrine signaling with expression of connective tissue growth factor

Recently, synthesis and secretion of connective tissue growth factor (CTGF)/CYR61/CTGF/NOV-family member 2 (CCN2) in cultures of hepatocytes were shown, which are sensitively up-regulated by exogenous TGF-beta. In this study TGF-beta-dependent CTGF/CCN2 expression in hepatocytes cultured under completely TGF-beta-free conditions was analysed by Western-blots, metabolic labelling, and CTGF-reporter gene assays. In alkaline phosphatase monoclonal anti-alkaline phosphatase complex (APAAP)-staining of cultured hepatocytes it was demonstrated that latent TGF-beta within the hepatocytes becomes rapidly detectable during culture indicating an intracellular demasking of the mature TGF-beta antigen. Subsequent signaling to theCTGF/CCN2 promoter occurs via p-Smad2, whereas p-Smad3 does not seem to be involved. Cycloheximide did not abolish the rapid immunocytochemical appearance of mature TGF-beta, but calpain inhibitors partially suppressed intracellular TGF-beta activation and subsequently CTGF up-regulation. Calpain treatment had the reverse effect. None of the inhibitors of extracellular TGF-beta signalling was effective in the reduction of spontaneous CTGF synthesis, but intracellularly acting Alk 4-/Alk 5-specific inhibitor SB-431542 was able to diminish CTGF expression. The assumption that latent intracellular TGF-beta is activated by calpains during culture-induced stress or injurious conditions in the liver in vivo was further validated by a direct effect of calpains on the activation of recombinant latent TGF-beta. In conclusion, these data are the first to suggest the possibility of intracrine TGF-beta signalling due to calpain-dependent intracellular proteolytic activation leading to transcriptional activation of CTGF/CCN2 as a TGF-beta-sensitive reporter gene. This mechanism might be deleterious for keeping long-term hepatocyte cultures due to TGF-beta-induced apoptosis and, further, might be of relevance for induction of apoptosis or epithelial-mesenchymal transition of hepatocytes in injured liver.

Intracrine signalling of activin A in hepatocytes upregulates connective tissue growth factor (CTGF/CCN2) expression

BACKGROUND/AIMS

Up to now, the effect of activin A on the expression of the important transforming growth factor (TGF)-beta downstream modulator connective tissue growth factor (CTGF) is not known, but might be of relevance for the functional effects of this cytokine on several liver cell types.

METHODS

In this study, activin A-dependent CTGF expression in hepatocytes (PC) primed by exogenous activin A and in PC maintained under complete activin-free culture conditions was analysed by Western blots, metabolic labelling, gene silencing, reverse transcriptase-polymerase chain reaction (RT-PCR) and CTGF reporter gene assays. This study was supplemented by immunocytochemical staining of activin A and CTGF in PC of injured liver.

RESULTS

Using alkaline phosphatase alpha-alkaline phosphatase staining, it is demonstrated that activin A becomes increasingly detectable during the course of CCl(4)-liver damage. Addition of activin A to cultured PC induced CTGF protein expression via phosphorylation of Smad2 and Smad3. This induction can be inhibited by the antagonist follistatin and alpha-activin A antibody respectively. When PC were cultured under serum(i.e. activin A)-free culture conditions, a time-dependent increase of activin expression during the course of the culture was proven by RT-PCR. Silencing of inhibin beta(A) gene expression under serum-free conditions by small interfering RNAs greatly suppressed CTGF synthesis and the phosphorylations of Smad2 and Smad3. However, both the extracellularly acting follistatin and the alpha-activin A antibody could not inhibit spontaneous CTGF expression, which, however, was achieved by the cell-permeable TGF-beta Alk4/Alk5 receptor-kinase-inhibitor SB431542.

CONCLUSIONS

In conclusion, the results point to activin A as an inducer of CTGF synthesis in PC. Intracellular activin A contributes to spontaneous CTGF expression in PC independent of exogenous activin A, which is proposed to occur via Alk4/Alk5-receptors. The findings might be important for many actions of activin A on the liver.

Role of metal-responsive transcription factor-1 (MTF-1) in EGF-dependent DNA synthesis in primary hepatocytes

Metal-responsive transcription factor-1 (MTF-1), which is involved in sensing heavy metal load, induces the transcription of several protective genes. The mouse Mtf-1 gene is essential, and Mtf-1(-/-) embryos die from liver degeneration. We showed that DNA synthesis induced in hepatocytes by epidermal growth factor (EGF) was delayed by inhibition of MTF-1. To inhibit MTF-1 activity, MTFDeltaC, a C-terminal deletion mutant of MTF-1, was expressed by infection with the virus Ad5MTFDeltaC. Lactate dehydrogenase (LDH) release and/or caspase-3/7 activation was not observed under our experimental conditions. The inhibitory effect of MTFDeltaC on EGF-dependent DNA synthesis in hepatocytes was not eliminated by zinc addition. EGF-dependent extracellular signal-related kinase (ERK) phosphorylation, an essential reaction for EGF-dependent DNA synthesis, was decreased in MTF-1-inhibited hepatocytes. Moreover, decrease of ERK phosphorylation was observed by using siRNA in MTF-1-downregulated hepatocytes. These results indicate that MTF-1 is particularly important for proper hepatocyte proliferation. This is the first report to suggest the function of MTF-1 in the ERK pathway.

Dysfunctional Smad Signaling Contributes to Abnormal Smooth Muscle Cell Proliferation in Familial Pulmonary Arterial Hypertension

Mutations in the bone morphogenetic protein type II receptor gene (BMPR2) are the major genetic cause of familial pulmonary arterial hypertension (FPAH). Although smooth muscle cell proliferation contributes to the vascular remodeling observed in PAH, the role of BMPs in this process and the impact of BMPR2 mutation remains unclear. Studies involving normal human pulmonary artery smooth muscle cells (PASMCs) suggest site-specific responses to BMPs. Thus, BMP-4 inhibited proliferation of PASMCs isolated from proximal pulmonary arteries, but stimulated proliferation of PASMCs from peripheral arteries, and conferred protection from apoptosis. These differences were not caused by differential activation of BMP signaling pathways because exogenous BMP-4 led to phosphorylation of Smad1, p38(MAPK), and ERK1/2 in both cell types. However, the proproliferative effect of BMP-4 on peripheral PASMCs was found to be p38MAPK/ERK-dependent. Conversely, overexpression of dominant-negative Smad1 converted the response to BMP-4 in proximal PASMCs from inhibitory to proliferative. Furthermore, we confirmed that proximal PASMCs harboring kinase domain mutations in BMPR2 are deficient in Smad signaling and are unresponsive to the growth suppressive effect of BMP-4. Moreover, we show that the pulmonary vasculature of patients with familial and idiopathic PAH are deficient in the activated form of Smad1. We conclude that defective Smad signaling and unopposed p38(MAPK)/ERK signaling, as a consequence of mutation in BMPR2, underlie the abnormal vascular cell proliferation observed in familial PAH.

Hypoxia potentiates transforming growth factor-beta expression of hepatocyte during the cirrhotic condition in rat liver

BACKGROUND/AIMS

Many studies have reported that hypoxia might be associated with angiogenesis and fibrogenesis, and the level of transforming growth factor-beta1 (TGF-beta1) was increased in fibrotic liver and maximal at cirrhosis. Therefore, we examined the expression of TGF-beta1, phosphorylated-Smad2/3 (p-Smad2/3) of the TGF-beta immediate down stream signaling system and hypoxic status during hepatic fibrogenesis.

METHODS

Fibrosis of rats was induced by carbon tetrachloride. Collagens were detected with Azan stain. Immunohistochemistry and immunoblotting was used.

RESULTS

TGF-beta1 was mainly produced by hypoxic hepatocytes at cirrhosis although myofibroblasts (MFBs) and macrophages producing TGF-beta1 were decreased. Moreover, distribution of p-Smad2/3 in hepatocytes was consistent with those of hypoxic hepatocytes regardless of MFBs. Furthermore, in recovery, most MFBs disappeared, whereas positive reactions of p-Smad2/3 still existed in the hepatocytes of hypoxic areas. Therefore, TGF-beta1 expression in hepatocytes might have been associated with hypoxia.

CONCLUSIONS

We put forward the hypothesis that TGF-beta1 is mainly produced by MFBs and macrophages at early and middle stages of fibrotic processes, but it is predominantly released by hypoxic hepatocytes in the last fibrotic stage or cirrhosis.

Interferon alpha-induced apoptosis on rat preneoplastic liver is mediated by hepatocytic transforming growth factor beta(1)

In previous work we showed that interferon alfa-2b (IFN-alpha2b) increases apoptosis on rat hepatic preneoplastic foci. The aim of this study was to determine if transforming growth factor beta1 (TGF-beta1) was involved in the programmed cell death on the foci. Animals were divided into 6 groups: subjected to a 2-phase model (diethylnitrosamine plus 2-acetylaminofluorene) of preneoplasia development (group 1); treated with IFN-alpha2b during the 2 phases (group 2); treated with IFN-alpha2b during initiation with diethylnitrosamine (group 3); treated with IFN-alpha2b during 2-acetylaminofluorene administration (group 4); subjected only to an initiation stage (group 5); and treated with IFN-alpha2b during the initiation period (group 6). Serum TGF-beta1 levels were increased in IFN-alpha2b-treated rats. Immunohistochemical studies showed that IFN-alpha2b significantly increased the quantity of TGF-beta1-positive hepatocytes in groups 2 to 4. Phosphorylated-Smads-2/3 (p-Smads-2/3) proteins in liver nuclear extracts were significantly elevated. To determine the source of TGF-beta1, isolated hepatocytes, Kupffer cells, and peritoneal macrophages from animals in groups 1 and 5 were cultured with or without IFN-alpha2b. IFN-alpha2b stimulus induced several-fold increases of TGF-beta1 secretion from hepatocytes. Neither Kupffer cells nor peritoneal macrophages secreted detectable TGF-beta1 levels when they were treated with IFN-alpha2b. IFN-alpha2b-stimulated cultured hepatocytes from preneoplastic livers showed enhanced apoptosis, measured by fluorescence microscopy and caspase-3 activity. They presented higher nuclear accumulation of p-Smads-2/3, indicating increased TGF-beta1 signaling. When anti-TGF-beta1 was added to the culture media, TGF-beta1 activation and apoptosis induced by IFN-alpha2b were blocked. In conclusion, IFN-alpha2b-induced production of TGF-beta1 by hepatocytes from preneoplastic liver is involved in the apoptotic elimination of altered hepatic foci.

Quantitative monitoring of the mRNA expression pattern of the TGF-beta-isoforms (beta 1, beta 2, beta 3) during transdifferentiation of hepatic stellate cells using a newly developed real-time SYBR Green PCR

Current methods to determine the mRNA of the TGF-beta-isoforms, beta 1, beta 2, and beta 3, are not sensitive enough to detect small alterations in the expression levels. Therefore, we established a SYBR Green I-based real-time quantitative PCR procedure with fragment-specific standards. The advantage of gene-specific quantification is the possibility to be abstain from the need to compare results with a house-keeping gene having a different sequence and PCR efficiency. Reproducibility of the results and analytical variances of the real-time PCR assays were tested. In transdifferentiating rat hepatic stellate cells (HSC) the TGF-beta 1-mRNA was found to be the predominant isoform expressed followed by TGF-beta 3 and low amounts of TGF-beta 2-mRNA. An alteration of the TGF-beta 1,-beta 2, and -beta 3 ratio during HSC transdifferentiation could not be detected. Furthermore, the GAPDH mRNA expression varied during HSC activation, and thus is not recommended as a standard in real-time PCR quantifications.

Hepatocytes convert to a fibroblastoid phenotype through the cooperation of TGF-β1 and Ha-Ras: steps towards invasiveness

In hepatocarcinogenesis, it is an open question whether transforming growth factor (TGF)-β1 provides a tumor-suppressive or a tumor-promoting role. To address this question, we employed immortalized murine hepatocytes, which display a high degree of differentiation and, expectedly, arrest in the G1 phase under exposure to TGF-β1. These hepatocytes maintain epithelial polarization upon expression of oncogenic Ha-Ras. However, Ras-transformed hepatocytes rapidly convert to a spindle-shaped, fibroblastoid morphology upon treatment with TGF-β1, which no longer inhibits proliferation. This epithelial to fibroblastoid conversion (EFC) is accompanied by disruption of intercellular contacts and remodeling of the cytoskeletal framework. Fibroblastoid derivatives form elongated branching cords in collagen gels and grow to severely vascularized tumors in vivo, indicating their increased malignancy and even invasive phenotype. Additionally, fibroblastoid cells secrete strongly enhanced levels of TGF-β1, suggesting an autocrine regulation of TGF-β signaling. Expression profiling further revealed that the loss of the adhesion component E-cadherin correlates with the upregulation of its transcriptional repressor Snail in fibroblastoid cells. Moreover, the phosphoinositide 3-OH (PI3) kinase pathway was required for the maintenance of EFC, as inhibition of PI3 kinase reverted fibroblastoid cells to an epithelial-like phenotype. Taken together, these data indicate a dual role of TGF-β1 in hepatocytes: it induces proliferation arrest but provides a crucial function in promoting late malignant events in collaboration with activated Ha-Ras.

Apoptosis in diseases of the liver

Apoptosis, or programmed cell death, and the elimination of apoptotic cells are crucial factors in the maintenance of liver health Apoptosis allows hepatocytes to die without provoking a potentially harmful inflammatory response In contrast to necrosis, apoptosis is tightly controlled and regulated via several mechanisms, including Fas/Fas ligand interactions, the effects of cytokines such as tumor necrosis factor alpha (TNF-alpha) and transforming growth factor beta (TGF-beta), and the influence of pro- and antiapoptotic mitochondria-associated proteins of the B-cell lymphoma-2 (Bcl-2) family. Efficient elimination of apoptotic cells in the liver relies on Kupffer cells and endothelial cells and is thought to be regulated by the expression of certain cell surface receptors. Liver disease is often associated with enhanced hepatocyte apoptosis, which is the case in viral and autoimmune hepatitis, cholestatic diseases, and metabolic disorders. Disruption of apoptosis is responsible for other diseases, for example, hepatocellular carcinoma. Use and abuse of certain drugs, especially alcohol, chemotherapeutic agents, and acetaminophen, have been associated with increased apoptosis and liver damage. Apoptosis also plays a role in transplantation-associated liver damage, both in ischemia/reperfusion injury and graft rejection. The role of apoptosis in various liver diseases and the mechanisms by which apoptosis occurs in the liver may provide insight into these diseases and suggest possible treatments.

Altered growth responses of pulmonary artery smooth muscle cells from patients with primary pulmonary hypertension to transforming growth factor-beta(1) and bone morphogenetic proteins

BACKGROUND

Mutations in the type II receptor for bone morphogenetic protein (BMPR-II), a receptor member of the transforming growth factor-beta (TGF-beta) superfamily, underlie many cases of familial and sporadic primary pulmonary hypertension (PPH). We postulated that pulmonary artery smooth muscle cells (PASMCs) from patients with PPH might demonstrate abnormal growth responses to TGF-beta superfamily members.

METHODS AND RESULTS

For studies of (3)H-thymidine incorporation or cell proliferation, PASMCs (passages 4 to 8) were derived from main pulmonary arteries. In control cells, 24-hour incubation with TGF-beta(1) (10 ng/mL) or bone morphogenetic protein (BMP)-2, -4, and -7 (100 ng/mL) inhibited basal and serum-stimulated (3)H-thymidine incorporation, and TGF-beta(1) and BMPs inhibited the proliferation of serum-stimulated PASMCs. In contrast, TGF-beta(1) stimulated (3)H-thymidine incorporation (200%; P<0.001) and cell proliferation in PASMCs from PPH but not from patients with secondary pulmonary hypertension. In addition, BMPs failed to suppress DNA synthesis and proliferation in PASMCs from PPH patients. Reverse transcription-polymerase chain reaction of PASMC mRNA detected transcripts for type I (TGF-betaRI, Alk-1, ActRI, and BMPRIB) and type II (TGF-betaRII, BMPR-II, ActRII, ActRIIB) receptors. Receptor binding and cross-linking studies with (125)I-TGF-beta(1) confirmed that the abnormal responses in PPH cells were not due to differences in TGF-beta receptor binding. Mutation analysis of PASMC DNA failed to detect mutations in TGF-betaRII and Alk-1 but confirmed the presence of a mutation in BMPR-II in 1 of 5 PPH isolates.

CONCLUSIONS

We conclude that PASMCs from patients with PPH exhibit abnormal growth responses to TGF-beta(1) and BMPs and that altered integration of TGF-beta superfamily growth signals may contribute to the pathogenesis of PPH.

Regulation of c-met expression in rats with acute hepatic failure

BACKGROUND

Earlier we described a model of fulminant hepatic failure (FHF) in the rat where partial hepatectomy is combined with induction of right liver lobe necrosis. In FHF rats, lack of hepatocyte proliferation was associated with delayed expression of HGF and HGF receptor c-met. Since the c-met promoter region has Sp1 binding sites, we decided to examine whether in FHF rats down-regulation of c-met is associated with decreased Sp1 function and whether changes in blood HGF, IL-6, and TGFbeta1 levels might be responsible for these effects.

MATERIALS AND METHODS

Induction of FHF, partial (2/3) hepatectomy (PH), and sham hepatectomy (SH) was performed in adult Sprague-Dawley rats. The levels of c-met mRNA and Sp1 DNA binding activity were studied in rat liver remnants at different time points after surgery. Blood levels of HGF, IL-6, and TGFbeta1 were also measured in these rats. Additionally, the effects of treatment with TGF-beta1, IL-6, or a combination of both on c-met expression and Sp1 DNA binding were studied in HGF-induced rat hepatocyte cultures.

RESULTS

Compared to SH rats, in PH rat livers c-met was up-regulated after 6 h and Sp1 DNA binding was at or only slightly lower than levels at all time points studied. In FHF rat livers, c-met expression was markedly reduced after 2 and 6 h, moderate after 12 h, and undetectable after 24 h. At the same time, Sp1 DNA binding was detected at 2 h postinduction only. In FHF rats, blood levels of all three cytokines showed early and sustained elevation. In vitro, IL-6 had no effect on c-met expression, whereas TGFbeta1 up-regulated c-met. When used alone, none of the cytokines affected Sp1 DNA binding activity. In contrast, a combination of IL-6 and TGFbeta1 down-regulated c-met expression as well as Sp1 DNA binding activity. These effects were dependent on the IL-6 concentration used. This study suggests that following massive loss of hepatocyte mass in rats, early increase in blood IL-6 and TGFbeta1 levels may weaken the expression of HGF receptor c-met in surviving hepatocytes through suppression of Sp1 DNA binding.

Transforming growth factor beta signal transduction in hepatic stellate cells via Smad2/3 phosphorylation, a pathway that is abrogated during in vitro progression to myofibroblasts. TGFbeta signal transduction during transdifferentiation of hepatic stellate cells

To current knowledge, transforming growth factor beta (TGFbeta) signaling is mandatory to establish liver fibrosis and various molecular interventions designed to affect the TGFbeta system were successfully used to inhibit fibrogenesis. Activated hepatic stellate cells (HSC), which are one important source of TGFbeta, are the major producers of extracellular matrix proteins in liver injury. We have previously shown that the TGFbeta response of this cell type is modulated during the transdifferentiation process. This work delineates the activation of TGFbeta downstream mediators, the Smads, in quiescent HSC and transdifferentiated myofibroblasts (MFB). The expression level of all Smads remained largely unchanged during this process. The response of HSC to TGFbeta, leading to, e.g., induction of alpha2 (I) collagen expression, is mediated by phosphorylation of Smad2 and Smad3 and subsequent nuclear translocation of a Smad containing complex. Neither TGFbeta-dependent nor endogenously phosphorylated Smad2/3 was detectable in comparable amounts in transdifferentiated MFB, indicating loss of TGFbeta sensitivity. Ectopic expression of Smad7 in HSC led to inhibition of Smad2 phosphorylation and abrogated TGFbeta response. In transdifferentiated MFB, expression of a constitutively active TGFbeta receptor I, but not treatment with TGFbeta1, resulted in transcriptional activation of a TGFbeta responsive promoter, thereby demonstrating completely restored TGFbeta signal transduction. Our data indicate that in contrast to a postulated mechanism of enduring autocrine TGFbeta signal transduction, early and late stages of HSC activation have to be distinguished, which is of importance for antifibrotic therapies.

Biology of transforming growth factor beta in hepatocarcinogenesis

TGF-beta is an important factor in the regulation of liver growth. It is an inhibitor of hepatocyte DNA synthesis and may induce active cell death, e.g., to remove excessive tissue mass. Studies using transgenic mice suggest that expression in the resting liver has to be well balanced; either under- or overexpression appear to cause an increased turnover of hepatocytes and to predispose to hepatocarcinogenesis. TGF-beta overexpression is frequently observed in human hepatocellular carcinomas, probably as a late event in tumor development. In men and mice, TGF-beta overexpression appears to be associated with loss of TGF-beta responsiveness often by disruption of TGF-beta signaling. However, mechanisms as mutations in TGF-beta receptor II or Smad2 and 4 genes, frequently observed in other human cancers, have only rarely been observed in hepatocellular carcinomas. Further studies may clarify the mechanisms by which hepatocellular tumors escape TGF-beta growth control, as well as analyze possible roles of TGF-beta overexpression in immunosuppression and angiogenesis.

Expression of Smads during in vitro transdifferentiation of hepatic stellate cells to myofibroblasts

TGFbeta is of crucial importance during transdifferentiation of resting retinoid-storing hepatic stellate cells (HSC) to extracellular matrix producing myofibroblasts (MFB) and consequently, inhibition of TGFbeta signal transduction is an effective means for preventing experimental fibrosis. We have shown that isolated HSC lose TGFbeta-dependent growth control during in vitro activation and that alpha2 (I) collagen production in transdifferentiated MFB is TGFbeta-independent. Furthermore, Smad complexes with SBE binding activity were only detected in early cultures of HSC, although TGFbeta receptor types I and II were significantly expressed in HSC and MFB. In the present report, we compared the expression pattern of TGFbeta downstream mediators, i.e., the Smads, in TGFbeta responsive HSC versus nonresponding MFB. The transdifferentiation process was monitored by morphology and increasing expression of TGFbeta and alpha-smooth muscle actin, and TGFbeta signaling was investigated by (CAGA)(9)-MLP-Luc. The expression level of all Smads remained essentially unchanged both during the activation process and after TGFbeta-treatment. Smad7 was transiently upregulated upon TGFbeta stimulation in quiescent HSC, indicating a negative feed back loop in responsive cells. In contrast, MFB neither displayed TGFbeta-inducible nor constitutively upregulated Smad7 expression. Instead, Smad3 mRNA was increased in MFB. Our data indicate that abrogation of the TGFbeta response in MFB versus HSC is not based on different regulation of Smad expression.

Temporary treatment of prepubescent rats with angiotensin inhibitors suppresses the development of hypertensive nephrosclerosis

Hypertensive nephrosclerosis is a leading cause of end-stage renal disease; therefore, strategies to prevent the development of renal disease require close study. Here it is demonstrated that transient treatment of prepubescent rats with angiotensin inhibitors attenuated their susceptibility to the development of hypertensive nephrosclerosis after maturation. Stroke-prone spontaneously hypertensive Izumo strain rats were divided into four groups, treated with vehicle, the angiotensin-converting enzyme inhibitor (ACEI) delapril (40 mg/kg per d), the angiotensin receptor antagonist (AT1R-Ant) candesartan cilexetil (1 mg/kg per d), or the vasodilator hydralazine (25 mg/kg per d) from weaning to puberty (3 to 10 wk of age), and then monitored without treatment for 6 mo. BP in the ACEI- and AT1R-Ant-treated groups remained significantly decreased, compared with the untreated and hydralazine-treated groups. Moreover, marked proteinuria and nephrosclerosis developed in the untreated and hydralazine-treated groups at 30 wk but were suppressed in the ACEI- and AT1R-Ant-treated groups. Of interest, plasma renin activity, plasma angiotensin II concentrations, and renal renin mRNA levels were reduced by >50% in the ACEI- and AT1R-Ant-treated rats, suggesting that the treatments may have attenuated the development of nephrosclerosis by overcoming the susceptibility of stroke-prone spontaneously hypertensive rats to overactivation of the renin-angiotensin system.

Biology of transforming growth factor beta in hepatocarcinogenesis

TGF-beta is an important factor in the regulation of liver growth. It is an inhibitor of hepatocyte DNA synthesis and may induce active cell death, e.g., to remove excessive tissue mass. Studies using transgenic mice suggest that expression in the resting liver has to be well balanced; either under- or overexpression appear to cause an increased turnover of hepatocytes and to predispose to hepatocarcinogenesis. TGF-beta overexpression is frequently observed in human hepatocellular carcinomas, probably as a late event in tumor development. In men and mice, TGF-beta overexpression appears to be associated with loss of TGF-beta responsiveness often by disruption of TGF-beta signaling. However, mechanisms as mutations in TGF-beta receptor II or Smad2 and 4 genes, frequently observed in other human cancers, have only rarely been observed in hepatocellular carcinomas. Further studies may clarify the mechanisms by which hepatocellular tumors escape TGF-beta growth control, as well as analyze possible roles of TGF-beta overexpression in immunosuppression and angiogenesis.

Autocrine expression of activated transforming growth factor-beta(1) induces apoptosis in normal rat liver

The aim of this study was to determine the differential effects of latent and activated transforming growth factor (TGF)-beta(1) in growth control of normal and proliferating hepatocytes in vivo. Rats were injected with adenoviruses expressing control transgenes (Ctrl), latent TGF-beta(1) [TGF-beta(L)], or activated TGF-beta(1) [TGF-beta(A)]. Additional animals underwent two-thirds partial hepatectomy (PH) 24 h after injection. Increased hepatocyte apoptosis was observed in TGF-beta(A)-injected but not TGF-beta(L)-injected animals 24 h postinjection (10.5%) compared with Ctrl animals (0.37%). The percent of apoptotic cells increased to 32.1% in TGF-beta(A)-injected animals 48 h after injection. Furthermore, TGF-beta(A)-injected rats did not survive 24 h after PH. Four hours after PH, 0.25 and 14.1% apoptotic hepatocytes were seen in Ctrl- and TGF-beta(A)-injected rats, respectively. TGF-beta(A)-induced apoptosis in primary rat hepatocytes was blocked with a pancaspase inhibitor. Thus autocrine expression of TGF-beta(A) but not TGF-beta(L) induces hepatocyte apoptosis in the normal rat liver. Rats overexpressing TGF-beta(A) do not survive two-thirds PH due to hepatic apoptosis. Thus activation of TGF-beta(1) may be a critical step in the growth control of normal and proliferating rat hepatocytes.

Interruption of activin A autocrine regulation by antisense oligodeoxynucleotides accelerates liver tumor cell proliferation

Administration of activin A, a member of the transforming growth factor-beta superfamily inhibits hepatocyte proliferation in vitro and reduces liver mass in vivo. However, a role of endogenous activin A in local growth modulation has not been established in any system. The aim of this study was to examine the production of activin A in the human hepatoma cell line HLF and to explore a possible autocrine role of activin as a cell growth inhibitor by blocking production of endogenous activin using antisense oligodeoxynucleotides. Administration of exogenous activin A suppressed HLF cell growth, and immunoreactive activin A was shown to be produced in the cells at confluency by Western blotting analysis. Cells were exposed to phosphorothioate-modified oligodeoxynucleotides, synthesized with antisense or randomly shuffled base sequences of activin betaA subunit messenger RNA, under serum-free conditions. Uptake of the oligodeoxynucleotides into the cells was confirmed by use of fluorescein isothiocyanate-labeled oligodeoxynucleotides. Administration of antisense oligodeoxynucleotides reduced activin A production as confirmed by both competitive PCR and Western blotting. Activin betaA antisense oligodeoxynucleotides significantly increased cell proliferation compared with controls. These findings are consistent with the existence of an autocrine role of activin A as an inhibitor of hepatocyte proliferation.

Cytokines, growth factors, and oxidative stress in HepG2 cells treated with ethanol, acetaldehyde, and LPS

Inflammatory mediators, including cytokines, growth factors, and reactive oxygen species, are associated with the pathology of chronic liver disease. In the liver, cytokine and growth factor secretion are usually associated with nonparenchymal cells, particularly Kupffer cells. In the present studies, the effect of 24 and 72 h administration of ethanol (50 mM). acetaldehyde (175 microM), and LPS (1 microg/ml) were studied on the expression and secretion of TNF-alpha, IL-1beta, IL-6, and TGF-beta3, lipid peroxidation damage and glutathion content in HepG2 cell cultures. A 24 h exposure to ethanol induced the expression of TNF-alpha and TGF-beta1, and the secretion of IL-1beta and TGF-beta1. With the same period of treatment, acetaldehyde markedly increased TNF-alpha expression, and stimulated IL-1beta secretion, while LPS exposure induced the expression of TNF-alpha, IL-6, and TGF-beta1, and the secretion of IL-1beta, IL-6, and TGF-beta1. A reduced in TNF-alpha response and TGF-beta1 expression were observed after 72 h exposure to ethanol. A 72 h acetaldehyde exposure decreased markedly TNF-alpha expression and stimulated a previously absent TGF-beta1 response. With the same time of exposure, LPS reduced slightly TGF-beta1 expression, and decreased its secretion. IL-1beta and IL-6 were not detected under 72 h exposure conditions. Lipid peroxidation damage was increased in all treatments, but higher values were found in 72 h treatments. Glutathion content diminished in all treatments. These findings suggest that HepG2 cells, independent of other cells such as Kupffer or macrophages, participate in a differential cytokine, growth factor and oxidative stress response, which differs according to the toxic agent and the time of exposure.

Transformation-dependent calcium influx by voltage-operated calcium channels in stellate cells of rat liver

BACKGROUND/AIMS

The transformation of hepatic stellate cells into myofibroblasts is a key step in the pathogenesis of fibrotic liver diseases. The intracellular signaling associated with hepatic stellate cell transformation becomes a point of interest, especially the role of cytosolic free calcium concentration ([Ca2+]i). The aim of the study was to investigate possible differences between various transformation phenotypes of hepatic stellate cells with regard to the calcium influx mediated by L-type voltage-operated calcium channels (L-type VOC).

METHODS

Hepatic stellate cells were isolated from rat liver by pronase-collagenase reperfusion and cultured under standard conditions. The transformation of hepatic stellate cells was stimulated by treatment with transforming growth factor-beta (TGF-beta) or inhibited with interferon-gamma (IFN-gamma) and characterized by immunocytochemistry for smooth muscle alpha-actin and determination of hyaluronan in the culture media with a ligand binding assay. [Ca2+]i was measured in individual cells with fluorescence microscopy using fura-2. VOCs were activated by the standard procedure of extracellular potassium elevation, to achieve depolarization, and identified by various controls.

RESULTS

In transformed myofibroblasts the activation of VOCs by potassium elevation from 5.4 mmol/l to 50.4 mmol/l led to a 19% increase in [Ca2+]i in contrast to 0.2% in hepatic stellate cells cultured for 3 days. In 7-day old hepatic stellate cells, after stimulation of cell transformation with TGF-beta-1, an enhanced [Ca2+]i response to potassium elevation was detected, while inhibition of transformation with IFN-gamma for the same time caused a decreased calcium signal compared with untreated control cultures. Short-term treatment with the cytokines (1 day) did not influence depolarization-dependent calcium signals.

CONCLUSION

The results show the [Ca2+]i increase via L-type VOCs to be dependent on the transformation level of hepatic stellate cells into myofibroblasts which can be influenced by the long-term treatment of hepatic stellate cells with TGF-beta or IFN-gamma. In contrast, there is no evidence for direct regulation of VOC activity by TGF-beta or IFN-gamma after short-term exposure.

Expression of different isoforms of TGF-beta and the latent TGF-beta binding protein (LTBP) by rat Kupffer cells

BACKGROUND/AIMS

Kupffer cells (liver resident macrophages) make an important contribution to the perpetuation of liver diseases by synthesis and secretion of TGF-beta. In some cell types TGF-beta, is expressed as a large latent complex containing the latent TGF-beta binding protein (LTBP) in addition to the N-terminal TGF-beta precursor (latency associated peptide). This study aimed to identify LTBP expression in rat Kupffer cells.

METHODS

Cells were isolated from rat liver by collagenase-pronase reperfusion, purified and cultured under standard conditions. TGF-beta and LTBP expression were characterized using alkaline phosphatase-anti-alkaline phosphatase immunostainings, reverse transcription-polymerase chain reaction and immunoprecipitation of metabolically labeled proteins.

RESULTS

Immunostainings of Kupffer cells with anti-sera against LTBP-1 (ab 39) and LTBP-2 indicated the expression of both LTBP isoforms in addition to the expression of latency associated peptide and TGF-beta. Transcripts of three LTBP isoforms (LTBP-1,-2,-3) and TGF-beta isoforms (TGF-beta-1,-2,-3) were detectable by reverse transcription-polymerase chain reaction. The LTBP-1D splice variant missing a part of the proteinase sensitive hinge region which has recently been described in hepatic stellate cells is expressed in Kupffer cells, too. Metabolic labeling of Kupffer cells with [35S]-Met/Cys followed by immunoprecipitation of the conditioned media using antisera against LTBP-1 and LTBP-2 indicated the secretion of high molecular mass TGF-beta complexes containing LTBP proteins of 230 and 170 kDa (LTBP-1) or 230 kDa (LTBP-2).

CONCLUSION

The results show that Kupffer cells partly synthesize and release TGF-beta as large latent complexes. This requires the extracellular activation of TGF-beta as a prerequisite for receptor binding and cellular signaling.

Levels of transforming growth factor beta and transforming growth factor beta receptors in rat liver during growth, regression by apoptosis and neoplasia

Transforming growth factor beta1 (TGF-beta1) has been implicated as inhibitor of cell proliferation and a potent inducer of apoptosis in vitro and in vivo after the administration of high doses. To assess the role of endogenous TGF-beta1, we quantitated the cytokine and its receptors in rat liver during regenerative and hyperplastic growth, regression by apoptosis, and in hepatocellular carcinoma (HCC). This was accomplished by Northern blot analysis and by RNase protection assay of the messenger RNA (mRNA) of TGF-beta1 and TGF-beta receptors (TbetaR) types I to III and by an activity bioassay of the TGF-beta proteins. Untreated rat livers were found to contain 15.6 +/- 4.8 ng TGF-beta1 protein/g tissue; TGF-beta2 protein was not detected. To induce toxic cell death and subsequent regenerative DNA synthesis in the liver, rats were treated with a necrogenic dose of carbon tetrachloride (CCl4). After 24 and 48 hours, there was an upregulation of TGF-beta1 (mRNA, up to tenfold; protein, about twofold) and of TbetaRs (mRNA: two- to fourfold); that indicates an overall enhanced production of and sensitivity to TGF-beta1, which may serve to confine the regenerative response. Hyperplastic liver growth and regression of the hyperplasia were induced by treatment with cyproterone acetate (CPA) or nafenopin (NAF) followed by withdrawal; neither mRNAs of TGF-beta1 and TbetaR types I to III nor TGF-beta1 protein exhibited significant changes during the growth phase or during regression by apoptosis. We also studied neoplastic growth. HCC, obtained after long-term treatment with NAF, exhibited high rates of cell replication and apoptosis. The majority of lesions contained mRNA and protein of TGF-beta1 and mRNA of TbetaR types I to III at concentrations similar to those of the surrounding tissue. In conclusion, during liver regeneration there is a pronounced upregulation of expression of both TGF-beta1 and TbetaRs I to III, but not during mitogen-induced liver growth or regression. It appears that apoptosis is induced via altered local concentration of TGF-beta1, in a paracrine and/or autocrine way. By this mechanism the lethal effects of TGF-beta1 may be locally confined, and overshoots of apoptosis in the liver may be prevented.

Transformation-dependent susceptibility of rat hepatic stellate cells to apoptosis induced by soluble Fas ligand

Cytokine-driven activation of hepatic stellate cells (HSC) in tissue injury and inflammation is a key pathogenetic event in liver fibrogenesis leading to an expanded pool of matrix producing myofibroblasts (MFB) which represent the transformed counterpart of HSC. We hypothesize that expansion of the pool of MFB might also be accomplished by modulation of apoptosis, which plays an opposite and complementary role to mitosis in the cellular homeostasis. We characterized the susceptibility of HSC in primary culture and of MFB in secondary culture to apoptosis induced by the soluble Fas ligand (sFasL) and related the effects to the expression levels of Fas (APO-1/CD95) and some major proapoptotic and contra-apoptotic protooncogenes. MFB showed a dose-dependent apoptotic reaction upon exposure to sFasL as evidenced by a strong increase of nucleosomal DNA fragments, loss of cellular DNA, positive TUNEL reaction, and annexin staining. The effect was found only if protein synthesis (cycloheximide) or RNA synthesis (actinomycin D) were arrested. HSC maintained for various times in primary culture were completely resistant to sFasL in combination with cycloheximide, but in late primary cultures (day 7 onward) an increasing susceptibility to sFasL-mediated apoptosis was developed. By semiquantitative reverse-transcriptase polymerase chain reaction (RT-PCR) analysis and alkaline phosphatase-anti-alkaline phosphatase staining Fas receptor was identified both in HSC and MFB at comparable expression levels. The expression of the contra-apoptotic protooncogenes bcl-2 and bcl-xl was found to be much stronger in early HSC than in late HSC and MFB as shown by ribonuclease protection assay. The expression of bcl-2 was additionally confirmed by semiquantitative RT-PCR and immunoblotting. Proapoptotic bax was found in comparable quantities at the RNA level in HSC and MFB but at the protein level MFB showed increased bax expression. It is concluded that transformation of HSC to MFB is paralleled by an increasing sensitivity to sFasL-mediated apoptosis, which might be related to a strong decrease of bcl-2 and bcl-xl expression, leading to a preponderance of proapoptotic gene expression in MFB. Modulation of apoptotic susceptibility of transforming HSC could be an important complementary pathway in the pathogenesis of fibrosis.

Analysis of the expression pattern of the latent transforming growth factor beta binding protein isoforms in normal and diseased human liver reveals a new splice variant missing the proteinase-sensitive hinge region

Latent transforming growth factor beta binding protein (LTBP), a component of the extracellular matrix (ECM) of various tissues, is important for the secretion of TGF-beta and, furthermore, for the storage of TGF-beta in ECM. The proteolytic cleavage of LTBP is assumed to be the prerequisite for the activation of TGF-beta. We investigated the mRNA expression pattern of the three LTBP isoforms (LTBP-1, -2, -3) and the protein distribution of the components of the large latent TGF-beta complex, namely LTBP-1 and -2, latency-associated protein (LAP), and TGF-beta, in human liver using reverse-transcription polymerase chain reaction (RT-PCR) and immunohistochemical alkaline phosphatase anti-alkaline phosphatase (APAAP) staining. Parts of explanted livers diagnosed as hepatitis B, hepatitis C, primary biliary cirrhosis (PBC), and primary sclerosing cholangitis (PSC) and normal liver tissue were examined. LTBP transcripts were detected in the same manner in all liver specimens. Interestingly, we found a new splice variant of LTBP-1 (LTBP-1D), in which the sequence coding for the proteinase-sensitive hinge region is deleted. The corresponding parts of the human LTBP-2 and LTBP-3 cDNA coding for the hinge region were sequenced and show neither similar proteinase cleavage sites nor deleted cDNA sequences. The proposed proteinase cleavage site of mouse LTBP-3 seems not to be conserved in the human LTBP-3 gene. By immunohistochemistry, LTBP-1, -2, and LAP were detectable in normal and diseased livers and showed a different staining pattern for both LTBP isoforms. By contrast, TGF-beta showed a spotted staining pattern in diseased livers only, predominantly in the area of parenchymal cells that are close to fibrotic tissue. This strongly suggests the release of active TGF-beta from preexisting latent complexes. The LTBP-1D splice variant, which is probably less sensitive against proteolytic degradation and therefore may protect TGF-beta from activation, may have importance for modulating the biological activity of TGF-beta in normal and diseased liver.

(Latent) transforming growth factor beta in liver parenchymal cells, its injury-dependent release, and paracrine effects on rat hepatic stellate cells

Cultured parenchymal liver cells (PC) were recently recognized to contain (latent) transforming growth factor beta (TGF-beta) while the expression of TGF-beta mRNA remains controversial. This study was designed to analyze PC in different microenvironments (liver in situ, highly purified, isolated, and cultured PC) regarding the qualitative and quantitative content of mature and latent TGF-beta protein (immunostainings, enzyme-linked immunosorbent assay [ELISA], and enzyme-labeled fluorescence [ELF] technique). The results were compared with its gene expression (reverse-transcription polymerase chain reaction [RT-PCR]). In all microenvironments, PC contained latent TGF-beta, which was partially activated after cell isolation and culture. The amount of total TGF-beta (mature plus latent) of latency-associated peptide (LAP) and of latent TGF-beta binding protein (LTBP) were shown to decrease during culture. In contrast, TGF-beta2 and TGF-beta3 mRNA and LTBP-1 and -3 mRNA expression were first detectable after culture. Permeabilization of cell membranes in whole liver and of isolated PC with streptolysin O or carbon tetrachloride, respectively, released TGF-beta, a part of which was integrated in the large latent complex as estimated by analytical gel filtration chromatography. The TGF-beta released by damaged PC induces paracrine effects on hepatic stellate cell cultures. It stimulates hyaluronan synthesis and antagonizes the effect of mitogenic factor(s) of PC on [3H]thymidine incorporation. The results strongly suggest that the main part of hepatocellular TGF-beta is not generated by de novo synthesis but from uptake into the liver in vivo. The immunodetection of preexisting mature TGF-beta after isolation of the cells is probably caused by intracellular activation of latent TGF-beta. The injury-dependent discharge of TGF-beta from PC might be an important mechanism for initiation and perpetuation of various forms of chronic human liver diseases.

Isoforms and splice variant of transforming growth factor beta-binding protein in rat hepatic stellate cells

BACKGROUND & AIMS

Hepatic stellate cells (HSCs) are one important source for transforming growth factor beta (TGF-beta). They produce TGF-beta in a latent form associated with latency-associated peptide and latent TGF-beta-binding protein (LTBP). This study was designed to investigate, on RNA and protein levels, which isoforms of LTBP and TGF-beta are expressed in HSCs and myofibroblasts.

METHODS

HSCs isolated from rat liver were analyzed for LTBP and TGF-beta at various times of culture during transdifferentiation into myofibroblasts using immunocytochemical staining, metabolic labeling and immunoprecipitation, reverse-transcription polymerase chain reaction (RT-PCR), and sequencing.

RESULTS

Alkaline phosphatase-anti-alkaline phosphatase staining and fluorescence immunostainings indicated the expression of all three components of the large latent TGF-beta complex in HSCs and myofibroblasts. Transcripts of three TGF-beta and LTBP isoforms were detected by RT-PCR and confirmed by sequence analyses. A new LTBP-1 splice form was found lacking part of the hinge region with a potential proteinase cleavage site. Metabolic labeling followed by immunoprecipitation with LTBP antiserum confirmed the synthesis and secretion of various LTBP-related proteins.

CONCLUSIONS

The existence of different LTBP isoforms and splice variants in HSCs and myofibroblasts suggests multiple functions of the LTBP family in rat liver, which might not be restricted to the maintenance of TGF-beta latency.

Production of B cell differentiation factors by mouse parenchymal liver cells

Previously we reported that most antibody secreting cells secreted IgA in the liver. Here we assessed the possibility that parenchymal liver cells (PLC) produced factors, transforming growth factor (TGF)-beta and IL-5, which participate in the differentiation of B cells to IgA-secreting cells. We showed that TGF-beta activity was present in the culture supernatant of PLC, and IL-5 activity was in the lysate of PLC. Moreover, it was confirmed that IL-5 protein produced by PLC was mainly localized in the cell membrane by histochemical staining. The findings that both TGF-beta and IL-5 were produced by PLC should provide useful information concerning the fact that IgA-secreting cells were dominant in the liver.

Pharmacological aspects of pentoxifylline with emphasis on its inhibitory actions on hepatic fibrogenesis

1. Pentoxifylline (PTX), a derivative of the methylxanthine theobromine, has been used for many years in the treatment of peripheral vascular diseases. Increased red blood cell flexibility, reduction of blood viscosity, and decreased potential of platelet aggregation are the basic actions of PTX, resulting in therapeutic benefits due to improved microcirculation and tissue oxygenation. 2. PTX's generally accepted mechanism of action is the inhibition of phosphodiesterases, leading to increased intracellular levels of cyclic adenosine monophosphate (cAMP). 3. A number of studies have shown PTX's effects on the cytokine network. The most relevant clinical results are the therapeutic benefits of PTX in attenuating the effects of tumor necrosis factor-alpha (TNF-alpha) in conditions such as septic shock. 4. PTX also has been found to exert antifibrogenic actions, using cultured fibroblasts or animal models of fibrosis, including liver fibrosis. 5. In hepatic stellate cell culture PTX has been shown to inhibit the basic reactions of liver fibrogenesis, being effective on cytokines and growth factors relevant in fibrogenesis of the liver, too. 6. Therefore, PTX might be an effective drug with few side effects in the treatment of liver fibrosis. Further clinical studies have to be done to establish the real therapeutic benefits of PTX in liver fibrosis and cirrhosis.

TGF-beta-mediated hepatocellular apoptosis by rat and human hepatoma cells and primary rat hepatocytes

BACKGROUND/AIMS

Primary cultures of rat hepatocytes, rat (FAO) and human (HepG2) hepatoma cells were studied by immunocytochemistry for expression of transforming growth factor (TGF)-beta, for the release of TGF-beta into the medium, and generation of hepatocellular apoptosis by the respective cell-conditioned media.

METHODS/RESULTS

Using the alkaline-phosphatase anti-alkaline-phosphatase technique, intense TGF-beta immunostaining was shown in all cell types. The cytokine is released almost entirely in the latent form into the culture medium; only the FAO-cells had a substantial fraction of bioactive TGF-beta in the native (unacidified) culture fluid. Exposure of hepatocytes with the respective cell-conditioned media in the activated, but not in the native form (except for FAO-cell media), induced severe detrimental effects as evidenced by: (i) gross morphological alterations, (ii) functional impairment (reduction of WST-1 test, detachment of cells, lactate dehydrogenase increase in the medium), and (iii) generation of apoptosis. The latter phenomenon was confirmed by an increase of internucleosomal DNA fragments, positive TUNEL reaction, and intense binding of the fluorochrome Hoechst 33342 to fragmented nuclei. All these effects, which were mimicked by addition of recombinant human TGF-beta 1, were almost entirely antagonized by pre-incubation of the conditioned media with latency associated peptide. In contrast to hepatocytes, both types of hepatoma cells were completely resistant to the multiple actions of TGF-beta and activated conditioned media.

CONCLUSIONS

It is concluded that hepatocytes might have the ability to induce autocrine, TGF-beta-mediated apoptosis, whereas hepatoma cells, because of their TGF-beta resistance, might generate TGF-beta-mediated peritumorous apoptosis of hepatocytes in a paracrine way, which could facilitate their expansion in situ. Both mechanisms, however, are critically dependent on extracellular TGF-beta activation.

Attenuation of TGF-beta-induced apoptosis in primary cultures of hepatocytes by calpain inhibitors

Apoptosis induced in primary cultures of rat hepatocytes by transforming growth factor beta 1 (TGF-beta 1) was greatly attenuated by inhibitors (5 microM) of calpain I and calpain II, respectively. Both inhibitors prevented the TGF-beta-elicited increase of nucleosomal DNA fragments and the occurrence of DNA-breaks in the TUNEL reaction. The detrimental effect of TGF-beta on cell viability measured by the WST-1 test was strongly reduced by calpain inhibitors. Calpain II > I inhibitors suppressed spontaneous DNA cleavage in hepatocytes during culture and prevented the appearance of immunocytochemically visible TGF-beta (APAAP staining), which occurs in untreated parenchymal cell cultures. The data show that inactivation of calpains attenuates both the TGF-beta-elicited and the spontaneous apoptosis of cultured hepatocytes; the latter effect is likely due to the suppression of endogenous TGF-beta activation. It is suggested that calpains participate in these processes.