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

Involvement of Fas system and active caspases in apoptotic signalling in testicular germ cells of ethanol-treated rats

The Fas system is involved in the regulation of germ cell apoptosis associated with testicular injury in experimental animals exposed to various insults. We tested the hypothesis that enhanced germ cell apoptosis mediated by the up-regulation of the Fas system and the activation of caspases may be involved in ethanol-induced testicular injury. Adult Wistar rats were fed either ethanol in Lieber-DeCarli liquid diet or an isocaloric control diet for 12 weeks. Marked Sertoli cell vacuolization and germ cell degeneration were observed in the testes of ethanol-treated rats (ETR) by both light and electron microscopy. Enhanced apoptosis of germ cells in ETR was detected by the terminal deoxynucleotidyl transferase-mediated deoxy-UTP nick end labelling (TUNEL) method, transmission electron microscopy, and was associated with elevated activity of caspase-3, -8 and -9. The expression levels of the Fas ligand (FasL) in Sertoli cells and of both Fas and caspase-3 in germ cells of ETR detected immunohistochemically were higher than those of the control testes. Furthermore, reverse transcriptase-polymerase chain reaction analysis demonstrated an increase in both Fas and FasL mRNA levels in ETR. Fas system up-regulation and the elevated activity of caspases in the testes of ETR may be a reflection of ethanol-induced testicular injury resulting in enhanced germ cells apoptosis, which may be involved in infertility associated with alcohol abuse.

Inhibition of apoptosis of activated hepatic stellate cells by tissue inhibitor of metalloproteinase-1 is mediated via effects on matrix metalloproteinase inhibition: implications for reversibility of liver fibrosis

The activated hepatic stellate cell (HSC) is central to liver fibrosis as the major source of collagens I and III and the tissue inhibitors of metalloproteinase-1 (TIMP-1). During spontaneous recovery from liver fibrosis, there is a decrease of TIMP expression, an increase in collagenase activity, and increased apoptosis of HSC, highlighting a potential role for TIMP-1 in HSC survival. In this report, we use tissue culture and in vivo models to demonstrate that TIMP-1 directly inhibits HSC apoptosis. TIMP-1 demonstrated a consistent, significant, and dose-dependent antiapoptotic effect for HSC activated in tissue culture and stimulated to undergo apoptosis by serum deprivation, cycloheximide exposure, and nerve growth factor stimulation. A nonfunctional mutated TIMP-1 (T2G mutant) in which all other domains are conserved did not inhibit apoptosis, indicating that inhibition of apoptosis was mediated through MMP inhibition. Synthetic MMP inhibitors also inhibited HSC apoptosis. Studies of experimental liver cirrhosis demonstrated that persistent expression of TIMP-1 mRNA determined by PCR correlated with persistence of activated HSC quantified by alpha smooth muscle actin staining, while in fibrosis, loss of activated HSC correlated with a reduction in TIMP-1 mRNA. We conclude that TIMP-1 inhibits apoptosis of activated HSC via MMP inhibition.

Plasminogen deficiency results in poor clearance of non-fibrin matrix and persistent activation of hepatic stellate cells after an acute injury

BACKGROUND/AIMS

Plasminogen directs matrix proteolysis during liver repair. Based on the role of hepatic stellate cells (HSCs) on matrix production, we investigated whether plasminogen-driven matrix proteolysis modulates the phenotype of HSCs.

METHODS

Carbon tetrachloride was injected intraperitoneally into mice deficient in plasminogen, fibrinogen, or both, and to normal littermates, followed by determination of the phenotype of HSCs, matrix deposition, and apoptosis.

RESULTS

Activation of HSCs was restricted to the zone of injury and increased >ten-fold above baseline regardless of the plasminogen status 2 days after toxin. Thereafter, the number of activated HSCs decreased to baseline levels between 7 and 14 days in normal mice, but remained elevated in plasminogen-deficient livers approximately ten-fold above non-targeted littermates. Despite the zonal increase in activated HSCs, the total number of desmin-stained HSCs was similar along the lobule in both genotypes. No appreciable difference in apoptosis of perisinusoidal cells was found between genotypes; however, fibrillary material was present in the subsinusoidal space of Plg(0) livers. This fibrillary material was not fibrin, as demonstrated by similar findings in Plg(0)/Fib(0) mice, which accumulated fibronectin in injured areas.

CONCLUSIONS

Proteolytic clearance of non-fibrin matrix components by plasminogen must occur for HSCs to restore the quiescent phenotype during liver repair.

15-deoxy-Delta 12,14-prostaglandin J2 induces apoptosis of human hepatic myofibroblasts. A pathway involving oxidative stress independently of peroxisome-proliferator-activated receptors

Hepatic myofibroblasts (hMFs) play a key role in the development of liver fibrosis associated with chronic liver diseases. Apoptosis of these cells is emerging as a key process in the resolution of liver fibrosis. Here, we examined the effects of cyclopentenone prostaglandins on apoptosis of human hMFs. Cyclopentenone prostaglandins of the J series markedly reduced hMF viability, with 15-deoxy-Delta(12,14)-prostaglandin J2 (15-d-PGJ2) being the most potent. This effect was independent of peroxisome-proliferator-activated receptors (PPARs), because PPARgamma and PPARalpha agonists did not affect hMF cell viability, and PPARgamma, the nuclear receptor for 15-d-PGJ2, was not expressed in hMFs. Moreover, 15-d-PGJ2 did not act via a cell surface G protein-coupled receptor, as shown in guanosine-5'-O-(3-thiotriphosphate) binding assays. Cell death resulted from an apoptotic process, because 15-d-PGJ2-treated hMFs exhibited condensed nuclei, fragmented DNA, and elevated caspase-3 activity. Moreover, the caspase inhibitor Z-Val-Ala-Asp(OCH3)-fluoromethyl ketone blocked the cytotoxic effect of 15-d-PGJ2. The apoptotic effects of 15-d-PGJ2 were reproduced by H2O2 and blocked by the antioxidants N-acetylcysteine (NAC), N-(2-mercapto-propionyl)-glycine (NMPG) and pyrrolidine dithiocarbamate (PDTC). Accordingly, 15-d-PGJ2 generated rapid production of reactive oxygen species in hMFs, via a NAC/NMPG/PDTC-sensitive pathway. In conclusion, 15-d-PGJ2 induces apoptosis of human hMFs via a novel mechanism involving oxidative stress and unrelated to activation of its nuclear receptor PPARgamma. These data underline the antifibrogenic potential of 15-d-PGJ2.

Hepatic stellate cells contain the functional estrogen receptor beta but not the estrogen receptor alpha in male and female rats

In an earlier study, we showed that estradiol (E2) inhibits proliferation and transformation in cultured rat hepatic stellate cells (HSCs) and that the actions of E2 are mediated through estrogen receptors (ERs). This study reports on an investigation of the cellular localization of ER subtypes ERalpha and ERbeta using immunohistochemistry in experimental fibrotic liver rats and of each ER subtype expression in cultured rat HSCs by evaluating the produced mRNA and protein. The results indicate that high levels of ERbeta expression and low or no levels of ERalpha expression were observed in normal and fibrotic livers and in quiescent and activated HSCs from both males and females. The specificity of E2-mediated antiapoptotic induction through the ERbeta was shown by dose-dependent inhibition by the pure ER antagonist ICI 182,780 in HSCs which were undergoing early apoptosis. These findings demonstrate for the first time that rat HSCs possess functional Erbeta, but not Eralpha, to respond directly to E2 exposure.

Decreased susceptibility to Fas-induced apoptosis of systemic sclerosis dermal fibroblasts

OBJECTIVE

To determine whether dysregulated apoptosis of systemic sclerosis (SSc) fibroblasts contributes to progressive fibrosis by promoting fibroblast longevity.

METHODS

We examined the pattern of fibroblast proliferation and apoptosis in SSc skin lesions and the susceptibility of cultured SSc dermal fibroblasts to apoptosis. Skin biopsy samples from SSc patients and control subjects were used to establish fibroblast cultures and were examined histologically. In skin sections, apoptosis was examined by TUNEL, and proliferation by immunostaining for proliferating cell nuclear antigen. Susceptibility of fibroblasts to apoptosis induced in vitro by different stimuli was studied by TUNEL. Expression of Bcl-2, Bcl-x, and Bax proteins in cultured fibroblasts was studied by Western blotting.

RESULTS

Proliferation of dermal fibroblasts was not observed in normal skin but was present in skin from patients with SSc and other inflammatory skin diseases. Apoptosis of fibroblasts in SSc fibrotic skin lesions was not observed. In vitro, SSc fibroblasts were specifically resistant to apoptosis induced by Fas receptor stimulation but had normal susceptibility to apoptosis induced by nonspecific stimuli (protein kinase inhibition or serum withdrawal). Decreased susceptibility to Fas stimulation was not caused by decreased levels of surface Fas receptor. In SSc fibroblasts, quiescence induced by confluence and serum starvation was followed by an abnormal down-regulation of proapoptotic Bax protein. Up-regulation of the Bax:Bcl-2 ratio in SSc fibroblasts by Bcl-2 antisense oligonucleotides restored their susceptibility to Fas-mediated apoptosis.

CONCLUSION

Our findings suggest that abnormal apoptotic regulation in fibroblasts can contribute to the pathogenesis of progressive fibrosis in SSc. Modulation of Bcl-2-related proteins appears to be a potential target for the development of apoptosis-based antifibrotic strategies.

Expression of the peripheral-type benzodiazepine receptor and apoptosis induction in hepatic stellate cells

BACKGROUND AND AIMS

Hepatic stellate cell (HSC) transformation and proliferation play an important role in liver fibrogenesis, and HSC apoptosis may be involved in the termination of this response.

METHODS

Expression of the peripheral benzodiazepine receptor (PBR) and PBR-ligand-induced apoptosis were studied in cultured rat liver HSC.

RESULTS

Transformation of HSC led to a transient expression of PBR at the messenger RNA and protein level, which was maximal after about 3 and 7 days of culture, respectively, and declined thereafter. Immunoreactive PBR showed a punctate staining and colocalized with mitochondrial manganese-dependent superoxide dismutase and adenine nucleotide translocator 1. The selective PBR ligands 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide (PK11195) and 4' chlorodiazepam (Ro5-4864), but not the centrally acting benzodiazepine ligand clonazepam, induced dose-dependent apoptosis in HSC. The apoptotic potency of PK11195 paralleled the level of PBR expression. PK11195 induced dephosphorylation of protein kinase B/Akt and Bad and a downregulation of Bcl-2. Collapse of the mitochondrial membrane potential preceeded PBR-ligand-induced apoptosis. No apoptosis was induced by PK11195 in parenchymal cells, despite the presence of PBR, and PK11195 had no effect in these cells on Bad phosphorylation and Bcl-2 expression.

CONCLUSIONS

Transformation of HSC leads to a transient expression of PBR and renders the cells sensitive to PBR-ligand-induced apoptosis, involving protein kinase B/Akt and Bad-dependent mechanisms.

Apoptosis in dissociation between DNA synthesis and cellular functions of activated hepatic stellate cells--a study with carbon tetrachloride-induced rat liver injury

It is widely believed that DNA synthesis and expressions of smooth muscle alpha actin and TGF-beta are all together increased in activated hepatic stellate cells both in vitro and in vivo. Our previous reports disclosed that these increases did not always coexist under experimental conditions. Liver necrosis was induced in rats by oral administration of carbon tetrachloride. Hepatic stellate cells were isolated from these rats 2 days later. When these cells were cultured on plastic dishes for 3 days, they showed marked DNA synthesis and smooth muscle alpha actin and TGF-beta mRNA expressions assessed by (3)H-thymidine incorporation and Northern blotting, respectively. In the cells further cultured for 7 days, the DNA synthesis was decreased, whereas both smooth muscle alpha actin and TGF-beta mRNA expressions were increased, compared to the cells cultured for 3 days. The cells cultured for 10 days showed apoptotic nuclei positive for nick-end labeling, and DNA extracted from the cells revealed laddering patterns on agarose gels by electrophoresis. Apoptotic nuclei were also immunohistochemically found in stellate cells in the liver of rats 4 days after the intoxication. We conclude that apoptosis developed in activated hepatic stellate cells both in vitro and in vivo, and this may contribute to the discrepancy between DNA synthesis and cellular functions of the cells.

Myofibroblasts defined by electron microscopy suggest the dedifferentiation of smooth muscle within the sac walls associated with congenital inguinal hernia

OBJECTIVE

To ascertain the presence of myofibroblasts in sacs associated with inguinal hernia in children, through an ultrastructural evaluation using electron microscopy.

MATERIALS AND METHODS

Sacs were obtained from 10 boys and 10 girls (of similar age, approximately 45 months) with inguinal hernia and processed for electron microscopy. Thin sections were examined specifically for the presence of myofibroblasts.

RESULTS

The ultrastructural evaluation showed myofibroblasts with classical electron microscopic features within all of the sacs, regardless of the gender of origin.

CONCLUSION

The persistence of smooth muscle hinders the obliteration of the processus vaginalis; myofibroblasts are found in association with smooth muscle and thus such cells within the sac walls seem to originate from the smooth muscle, reflecting the dedifferentiation of smooth muscle. This dedifferentiated state may represent attempted apoptosis, which usually causes the disappearance of the smooth muscle and obliteration of the processus vaginalis after the descent of the testis into the scrotum.

Nitric oxide diminishes apoptosis and p53 gene expression after renal ischemia and reperfusion injury

BACKGROUND

The role of nitric oxide in the ischemic injury of the kidney is still controversial. The aim of this study was to reevaluate the beneficial effect of exogenous nitric oxide and define its effects as regulator of gene p53 expression and apoptosis in the ischemic renal injury.

METHODS

Sprague-Dawley rats were subjected to 75 min of renal warm ischemia and contralateral nephrectomy. The animals were divided into six groups (n=6 per group): Two sham groups at 4 and 24 hr, two ischemic control (IC) at same times and two treated groups (Na-NP), studied at same intervals, where sodium nitroprusside (5 mg/kg) was given 15 min before reperfusion. The parameters evaluated included: serum creatinine, blood urea nitrogen, neutrophil infiltration determined by myeloperoxidase, gene p53 expression determined by reverse transcriptase polymerase chain reaction, apoptosis determined by peroxidase in situ technique and light histology.

RESULTS

There were significant improvements in serum creatinine and blood urea nitrogen at 24 hr in the NA-NP group when compared with the IC group (P<0.05). Myeloperoxidase levels were higher in the IC when evaluated against the Na-NP groups. Na-NP exhibited a downregulating effect in the expression of gene p53 when compared to the IC group. Apoptosis was more evident in the IC group and had moderately increased histological damage when compared to the Na-NP group.

CONCLUSIONS

Nitric oxide demonstrated a protective effect in the ischemic injury of the kidney and exerted an antiapoptotic action dowregulating the expression of gene p53.

Liver fibrosis

Knowledge on the development and progression of liver fibrosis has grown exponentially in the past decade. At present, liver fibrogenesis is referred to as a dynamic process involving complex cellular and molecular mechanisms, resulting from the chronic activation of the tissue repair mechanisms that follows reiterated liver tissue injury. The identification and characterization of the cell types and of the different mediators involved in this process has allowed a "re-visitation" of several issues related to liver cirrhosis and its immediate consequences. Among these, evaluation of the relationships occurring between fibrogenesis and portal hypertension, cholestasis and the development of hepatocellular carcinoma, represent some of the hottest areas of research in this field of hepatology. The elucidation of many of the cellular and molecular mechanisms responsible for the progression of liver fibrosis has provided a sound basis for the development of pharmacological strategies able to modulate this important pathophysiological process.

Nuclear factor kappaB in proliferation, activation, and apoptosis in rat hepatic stellate cells

BACKGROUND/AIMS

Activation of the transcription factor NFkappaB has been demonstrated in activated hepatic stellate cells (HSCs). We investigated the role of NFkappaB in proliferation, in activation, and in TNFalpha-induced apoptosis of HSCs.

METHODS

NFkappaB activation was inhibited using an adenovirus expressing an IkappaB dominant negative protein (Ad5IkappaB) in both quiescent and activated HSCs. Quiescent HSCs were infected with Ad5IkappaB or an adenovirus expressing beta-galactosidase (Ad5LacZ). The cells were cultured for 7 days. HSCs activation was determined by cell morphology, smooth muscle alpha-actin (alpha-sma) expression, and steady-state mRNA levels of alpha1(I) collagen as assessed by Western blot and RNase protection assay, respectively. Proliferation was determined in culture-activated HSCs by 3H-thymidine incorporation and direct cell counting. Apoptosis was analyzed by infecting quiescent or activated HSCs with Ad5IkappaB or Ad5LacZ, and then treating with TNFalpha. Apoptosis was demonstrated by determining cell number, assessing nuclear morphology, TUNEL assay and caspase 3 activity.

RESULTS

After 7 days in culture no differences were noted between the Ad5IkappaB- and the Ad5LacZ-infected cells in the morphology, alpha-sma expression or in alpha1(I) collagen mRNA levels. Ad5IkappaB infection did not modify proliferation in activated HSCs. TNFalpha induced apoptosis only in Ad5IkappaB-infected activated, but not quiescent HSCs. Apoptosis was initially demonstrated 12 h after exposure to TNFalpha. Twenty-four h after the TNFalpha treatment, 60% of the activated HSCs were apoptotic.

CONCLUSION

NFkappaB activity is not required for proliferation or activation of HSCs; however, NFkappaB protects activated HSCs against TNFalpha-induced apoptosis.

Apoptosis in hepatic pathophysiology

Apoptosis is a fundamental biologic process that is important in many physiologic and pathophysiologic processes in the liver. Although dysregulation of apoptosis may contribute to a wide range of diseases, the role of this process in liver disease and pathophysiology has only recently begun to be recognized and remains to be fully defined. Several important questions remain unanswered: How does excessive apoptosis in response to injury contribute to inflammation and fibrogenesis in the liver? How does control of apoptosis contribute to the regulation of hepatic structure following injury? What is the role of death receptors in hepatic disease? Can an understanding of apoptosis be helpful in therapeutic modulation of specific liver diseases or liver cancer? The identification of target molecules involved in apoptosis raises the prospect of pharmacologic modulation that may result in better treatment options for patients with liver diseases. Inhibition of apoptosis is likely to be useful in treating fulminant hepatic failure or in organ preservation before transplantation. In these situations, treatment is for a limited period, and the potential hazards of nonselective long-term inhibition of apoptosis are minimized. Safe and organ-specific inhibitors of apoptosis would be required for prolonged treatment of chronic liver diseases. For treatment of liver tumors, the goal is to induce apoptosis selectively in cancer cells. Drugs that decrease the apoptotic threshold by modulating the intracellular regulatory mechanisms and drugs that enhance the susceptibility of cancer cells to undergo immune-mediated apoptosis will be useful in the treatment of liver cancers. The rapid advances in the understanding of the intracellular mechanisms and the regulation of apoptosis will ultimately result in a better understanding of the role of apoptosis in the pathophysiology of liver diseases and may allow therapeutic modulation of this process.

Liver dysfunction due to apoptosis in a patient with systemic lupus erythematosus

We report on a 23-year-old Japanese female with a 13-year history of systemic lupus erythematosus (SLE), and two episodes of deterioration followed by treatment with high dose prednisolone. Although she had been recently treated with prednisolone (12.5 mg daily), her liver function became worse in July 1998. Results of a liver biopsy revealed multi-focal hepatic cell death in a severe fatty liver, without any inflammatory cell invasion. The biopsy also showed a positive TUNEL (Tdt-catalysed DNA nick end labelling) reaction indicating apoptosis. Her liver function recovered rapidly following steroid pulse therapy. Serum soluble Fas ligand (sFasL) was found to be elevated to a concentration of 0.395 ng/ml at the time of liver damage, but was less than 0.03 ng/ml before liver damage and after prednisolone treatment. The liver damage in this case appeared to be involved with apoptosis induced by sFasL. Although hepatitis associated with SLE is rare, apoptosis directly related to elevated sFasL levels might cause this complication.

Hepatic stellate cells express the low affinity nerve growth factor receptor p75 and undergo apoptosis in response to nerve growth factor stimulation

We have examined the expression of p75, a member of the TNF receptor superfamily in hepatic stellate cells (HSC) and pancreatic stellate cells (PSC). Activated HSC and PSC were demonstrated by Western blot analysis to express p75. p75 was immunolocalized to cells with a myofibroblast-like morphology in the fibrotic bands of six fibrotic and cirrhotic liver biopsies and three biopsies of fibrotic human pancreas. Immunostaining of parallel sections indicated that these cells were alpha-smooth muscle actin-positive, identifying them as activated HSC and PSC, respectively. HSC apoptosis in tissue culture in the presence of serum was quantified after addition of 0.1 to 100 ng/ml of nerve growth factor (NGF) a ligand for p75, by in situ counting of apoptotic bodies after addition of acridine orange. HSC demonstrated a significant increase in apoptosis in response to 100 ng/ml NGF (0.05 > P by Wilcoxon's rank; n = 7) after 24 hours. NGF 100 ng/ml had no effect on HSC proliferation, but reduced total HSC DNA by 19% relative to control after 24 hours (n = 3). These data demonstrate that activated HSC express p75 and respond to NGF stimulation by undergoing apoptosis. We therefore report p75 as a novel marker of activated HSC and suggest that signaling via ligand binding to p75 may provide a mechanism for selective apoptosis of HSC.

In vitro evaluation of hepatitis B virus polymerase mutations associated with famciclovir resistance

Several mutations (V521L, P525L, L528M, T532S, and V555I) in the gene for hepatitis B virus (HBV) polymerase have been identified in HBV isolated from patients that displayed break-through viremia during famciclovir treatment. To determine whether these mutations cause phenotypic resistance to famciclovir, we compared the inhibition constants (K(i)) of penciclovir triphosphate (PCVTP, the active metabolite of famciclovir) for recombinant wild-type and mutant HBV polymerases containing these mutations. In in vitro enzymatic assays, the V555I mutation displayed the most resistance (with K(i) increased by 6.2-fold) to PCVTP. The V521L and L528M mutations showed moderately decreased sensitivity to PCVTP (K(i) increased by >3-fold). We also analyzed the cross-resistance profiles of these variants for adefovir and lamivudine, two other antiviral agents that also inhibit DNA replication by HBV polymerase. All 5 famciclovir-associated mutations were sensitive to adefovir diphosphate (ADVDP) in in vitro enzymatic assays (<2.3-fold decreased sensitivity). The V521L, L528M, and T532S mutations were also sensitive to lamivudine triphosphate (LAMTP); however, the P525L and V555I mutations displayed moderately decreased sensitivity to LAMTP in enzymatic assays (3.6-fold decreased sensitivity). The lamivudine-resistant mutations M552I, M552V, and L528M+M552V, which were previously shown to display 8- to 25-fold resistance to LAMTP, were less resistant (< or = 3.1-fold) to PCVTP.

The metalloproteinase matrilysin proteolytically generates active soluble Fas ligand and potentiates epithelial cell apoptosis

BACKGROUND

The Fas ligand/Fas receptor (FasL/Fas) system is an important mediator of apoptosis in the immune system where the juxtaposition of cells expressing the cell-surface ligand induces the apoptotic pathway in Fas-expressing lymphocytes. The FasL/Fas system has also been shown to be involved in apoptosis in epithelial tissues, including the involuting rodent prostate. FasL can be shed through the action of an hitherto unidentified metalloproteinase to yield soluble FasL (sFasL), although the biological activity of sFasL has been disputed.

RESULTS

Here we report that the matrix metalloproteinase matrilysin can process recombinant and cell-associated FasL to sFasL, and that matrilysin-generated sFasL was effective at inducing apoptosis in a target epithelial cell population. In the involuting mouse prostate, FasL and matrilysin colocalized to the cell surface in a restricted population of epithelial cells. Mice deficient in matrilysin demonstrated a 67% reduction in the apoptotic index in the involuting prostate compared with wild-type animals, implicating matrilysin in this FasL-mediated process.

CONCLUSIONS

The results show that a functional form of sFasL was generated by the action of the metalloproteinase matrilysin, and suggest that matrilysin cleavage of FasL is an important mediator of epithelial cell apoptosis.

Persistent activation of nuclear factor-kappaB in cultured rat hepatic stellate cells involves the induction of potentially novel Rel-like factors and prolonged changes in the expression of IkappaB family proteins

Rat hepatic stellate cells (HSC) cultured in serum-containing medium underwent a rapid (3-hour) classical induction of p50:p65 and p65:p65 nuclear factor-kappaB (NF-kappaB) dimers. Subsequent culturing was associated with prolonged expression of active p50:p65 and persistent induction of a high-mobility NF-kappaB DNA binding complex consisting of potentially novel Rel-like protein(s). Formation of the latter complex was competed for by specific double-stranded oligonucleotides, was up-regulated by treatment of HSCs with tumor necrosis factor alpha (TNF-alpha), and was maintained at basal levels of expression by a soluble HSC-derived factor. An NF-kappaB-responsive CAT reporter gene was highly active in early cultured HSCs but was also trans-activated at a lower but significant level in longer-term cultured cells and could be completely suppressed by expression of dominant negative IkappaB-alpha. Physiological significance of the lower persistent NF-kappaB activities was also demonstrated by the ability of long-term cultured HSCs to support the activity of the NF-kappaB-dependent human intercellular adhesion molecule-1 (ICAM-1) promoter. Freshly isolated HSCs expressed high levels of IkappaB-alpha and IkappaB-beta. Culture activation was accompanied by a long-term reduction in levels of IkappaB-alpha with no detectable expression in the nuclear fraction of cells, under these conditions p50:p65 was detected in the nucleus. IkappaB-beta expression was transiently reduced and, upon replenishment, was associated with appearance of a lower-mobility IkappaB-beta antibody-reactive species. Bcl3 expression was absent in freshly isolated HSC but was induced during culturing and became a persistent feature of the activated HSC. Inhibition of NF-kappaB DNA binding activity by gliotoxin was associated with increased numbers of apoptotic cells. We suggest that activation of NF-kappaB in cultured HSC is required for expression of specific genes associated with the activated phenotype such as ICAM-1 and may be antiapoptotic for rat HSCs.

Liver fibrogenesis and the role of hepatic stellate cells: new insights and prospects for therapy

Hepatic fibrosis is a wound-healing response to chronic liver injury, which if persistent leads to cirrhosis and liver failure. Exciting progress has been made in understanding the mechanisms of hepatic fibrosis. Major advances include: (i) characterization of the components of extracellular matrix (ECM) in normal and fibrotic liver; (ii) identification of hepatic stellate cells as the primary source of ECM in liver fibrosis; (iii) elucidation of key cytokines, their cellular sources, modes of regulation, and signalling pathways involved in liver fibrogenesis; (iv) characterization of key matrix proteases and their inhibitors; (v) identification of apoptotic mediators in stellate cells and exploration of their roles during the resolution of liver injury. These advances have helped delineate a more comprehensive picture of liver fibrosis in which the central event is the activation of stellate cells, a transformation from quiescent vitamin A-rich cells to proliferative, fibrogenic and contractile myofibroblasts. The progress in understanding fibrogenic mechanisms brings the development of effective therapies closer to reality. In the future, targeting of stellate cells and fibrogenic mediators will be a mainstay of antifibrotic therapy. Points of therapeutic intervention may include: (i) removing the injurious stimuli; (ii) suppressing hepatic inflammation; (iii) down-regulating stellate cell activation; and (iv) promoting matrix degradation. The future prospects for effective antifibrotic treatment are more promising than ever for the millions of patients with chronic liver disease worldwide.

Transforming growth factor beta and tumor necrosis factor alpha inhibit both apoptosis and proliferation of activated rat hepatic stellate cells

Transforming growth factor beta (TGF-beta) as well as tumor necrosis factor alpha (TNF-alpha) gene expression are up-regulated in chronically inflamed liver. These cytokines were investigated for their influence on apoptosis and proliferation of activated hepatic stellate cells (HSCs). Spontaneous apoptosis in activated HSC was significantly down-regulated by 53% +/- 8% (P <.01) under the influence of TGF-beta and by 28% +/- 2% (P <.05) under the influence of TNF-alpha. TGF-beta and TNF-alpha significantly reduced expression of CD95L in activated HSCs, whereas CD95 expression remained unchanged. Furthermore, HSC apoptosis induced by CD95-agonistic antibodies was reduced from 96% +/- 2% to 51 +/- 7% (P <.01) by TGF-beta, and from 96% +/- 2% to 58 +/- 2% (P <.01) by TNF-alpha, suggesting that intracellular antiapoptotic mechanisms may also be activated by both cytokines. During activation, HSC cultures showed a reduced portion of cells in the G0/G1 phase and a strong increment of G2-phase cells. This increment was significantly inhibited (G1 arrest) by administration of TGF-beta and/or TNF-alpha to activated cells. In liver sections of chronically damaged rat liver (CCl4 model), using desmin and CD95L as markers for activated HSC, most of these cells did not show apoptotic signs (TUNEL-negative). Taken together, these findings indicate that TGF-beta and/or TNF-alpha both inhibit proliferation and also apoptosis in activated HSC in vitro. Both processes seem to be linked to each other, and their inhibition could represent the mechanism responsible for prolonged survival of activated HSC in chronic liver damage in vivo.

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.

Liver fibrosis

Knowledge on the development and progression of liver fibrosis has grown exponentially in the past decade. At present, liver fibrogenesis is referred to as a dynamic process involving complex cellular and molecular mechanisms, resulting from the chronic activation of the tissue repair mechanisms that follows reiterated liver tissue injury. The identification and characterization of the cell types and of the different mediators involved in this process has allowed a "re-visitation" of several issues related to liver cirrhosis and its immediate consequences. Among these, evaluation of the relationships occurring between fibrogenesis and portal hypertension, cholestasis and the development of hepatocellular carcinoma, represent some of the hottest areas of research in this field of hepatology. The elucidation of many of the cellular and molecular mechanisms responsible for the progression of liver fibrosis has provided a sound basis for the development of pharmacological strategies able to modulate this important pathophysiological process.