Synergism between hepatocytes and Kupffer cells in the activation of fat storing cells (perisinusoidal lipocytes)

Age-dependent development of liver fibrosis in Glmp (gt/gt) mice

Background

Mice lacking glycosylated lysosomal membrane protein (Glmp^gt/gt mice) have liver fibrosis as the predominant phenotype due to chronic liver injury. The Glmp^gt/gt mice grow and reproduce at the same rate as their wild-type siblings. Life expectancy is around 18 months.

Methods

Wild-type and Glmp^gt/gt mice were studied between 1 week and 18 months of age. Livers were analyzed using histological, immunohistochemical, biochemical, and qPCR analyses.

Results

It was shown that Glmp^gt/gt mice were not born with liver injury; however, it appeared shortly after birth as indicated by excess collagen expression, deposition of fibrous collagen in the periportal areas, and increased levels of hydroxyproline in Glmp^gt/gt liver. Liver functional tests indicated a chronic, mild liver injury. Markers of inflammation, fibrosis, apoptosis, and modulation of extracellular matrix increased from an early age, peaking around 4 months of age and followed by attenuation of these signals. To compensate for loss of hepatocytes, the oval cell compartment was activated, with the highest activity of the oval cells detected at 3 months of age, suggesting insufficient hepatocyte proliferation in Glmp^gt/gt mice around this age. Although constant proliferation of hepatocytes and oval cells maintained adequate hepatic function in Glmp^gt/gt mice, it also resulted in a higher frequency of liver tumors in older animals.

Conclusions

The Glmp^gt/gt mouse is proposed as a model for slowly progressing liver fibrosis and possibly as a model for a yet undescribed human lysosomal disorder.

Electronic supplementary material

The online version of this article (doi:10.1186/s13069-016-0042-4) contains supplementary material, which is available to authorized users.

MiR-29b inhibits collagen maturation in hepatic stellate cells through down-regulating the expression of HSP47 and lysyl oxidase

Altered expression of miR-29b is implicated in the pathogenesis and progression of liver fibrosis. We and others previously demonstrated that miR-29b down-regulates the expression of several extracellular-matrix (ECM) genes including Col 1A1, Col 3A1 and Elastin via directly targeting their 3'-UTRs. However, whether or not miR-29b plays a role in the post-translational regulation of ECM biosynthesis has not been reported. Heat shock protein 47 (HSP47) and lysyl oxidase (LOX) are known to be essential for ECM maturation. In this study we have demonstrated that expression of HSP47 and LOX was significantly up-regulated in culture-activated primary rat hepatic stellate cells (HSCs), TGF-β stimulated LX-2 cells and liver tissue of CCl4-treated mice, which was accompanied by a decrease of miR-29b level. In addition, over-expression of miR-29b in LX-2 cells resulted in significant inhibition on HSP47 and LOX expression. Mechanistically, miR-29b inhibited the expression of a reporter gene that contains the respective full-length 3'-UTR from HSP47 and LOX gene, and this inhibitory effect was abolished by the deletion of a putative miR-29b targeting sequence from the 3'-UTRs. Transfection of LX-2 cells with miR-29b led to abnormal collagen structure as shown by electron-microscopy, presumably through down-regulation of the expression of molecules involved in ECM maturation including HSP47 and LOX. These results demonstrated that miR-29b is involved in regulating the post-translational processing of ECM and fibril formation.

Monitoring fibrogenic progression in the liver

The clinical course of chronic liver diseases is significantly dependent on the progression rate of fibrosis which is the unstructured replacement of injured parenchyma by extracellular matrix. Despite intensive studies, the clinical opportunities for patients with fibrosing liver diseases have not improved. This will be changed by increasing knowledge of new pathogenetic mechanisms, which complement the "canonical principle" of fibrogenesis. The latter is based on the activation of hepatic stellate cells and their transdifferentiation to myofibroblasts induced by hepatocellular injury and consecutive inflammatory mediators such as TGF-β. Stellate cells express a broad spectrum of matrix components. New mechanisms indicate that the heterogeneous pool of (myo-)fibroblasts can be supplemented by epithelial-mesenchymal transition (EMT) from cholangiocytes and potentially also from hepatocytes to fibroblasts, by influx of bone marrow-derived fibrocytes in the damaged liver tissue and by differentiation of a subgroup of monocytes to fibroblasts after homing in the damaged tissue. These processes are regulated by the cytokines TGF-β and BMP-7, chemokines, colony-stimulating factors, metalloproteinases and numerous trapping proteins. They offer innovative diagnostic and therapeutic options. As an example, modulation of TGF-β/BMP-7 ratio changes the rate of EMT, and so the simultaneous determination of these parameters and of the connective tissue growth factor (CTGF) in serum might provide information on fibrogenic activity. Also, proteomic and glycomic approaches of serum are under investigation to set up specific protein profiles in patients with liver fibrosis. The aim of this article is to present the current pathogenetic concepts of liver fibrosis and to discuss established and novel diagnostic approaches to reflect the process of hepatic fibrogenesis in the medical laboratory.

Interleukin-10 gene modification attenuates hepatocyte activation of rat hepatic stellate cells in vitro

Activation of hepatic stellate cells (HSCs) plays a key role in the progression of liver fibrosis. Interleukin-10 (IL-10), a potential anti-fibrosis cytokine, has an unfavorable pharmacokinetic profile, which limits its clinical applications. A liver-targeting gene delivery system may maintain a longer-lasting concentration in hepatic tissue with fewer side‑effects in non-target tissues. In the present study, when delivered by asialoglycoprotein receptor-mediated liposomes, the IL-10 gene was highly expressed in BRL cells (a rat hepatocyte line) and attenuated the apoptosis of BRL cells induced by plasmid transfection. In a co-culture system, BRL cells demonstrated a marked ability to stimulate the proliferation of primary HSCs and their expression of α-SMA and procollagen type I. Following modification of the BRL cells with the IL-10 gene, this stimulation was attenuated and an accelerated apoptosis of the HSCs was induced. These results suggest that hepatocyte‑targeting gene delivery may be an ideal technique for the IL-10 gene therapy of liver fibrosis, which requires further confirmation by in vivo studies.

Combination therapy with andrographolide and d-penicillamine enhanced therapeutic advantage over monotherapy with d-penicillamine in attenuating fibrogenic response and cell death in the periportal zone of liver in rats during copper toxicosis

Long treatment regime with d-penicillamine is needed before it can exert clinically meaningful benefits in the treatment of copper toxicosis. The consequence of long-term d-penicillamine treatment is associated with numerous side effects. The limitations of d-penicillamine monotherapy prompted us to search for more effective treatment strategies that could decrease the duration of d-penicillamine therapy. The present study was designed to evaluate the therapeutic potential of d-penicillamine in combination with another hepatoprotective drug, andrographolide in treatment of copper toxicosis in rats. d-penicillamine treatment led to the excretion of copper through urine. Addition of andrographolide to d-penicillamine regime appeared to increase protection of liver by increasing the biliary excretion of copper and reduction in cholestatic injury. The early removal of the causative agent copper during combination treatment was the most effective therapeutic intervention that contributed to the early rectification of fibrosis in liver. Combination treatment reduced Kupffer cells accumulation and TNFα production in liver of copper exposed rats. In particular, andrographolide mediated the anti-inflammatory effect by inhibiting the cytokine production. However, another possible mechanism of cytoprotection of andrographolide was decreasing mitochondrial production of superoxide anions that resulted in better restoration of mitochondrial dysfunction during combination therapy than monotherapy. Furthermore, ROS inhibition by combination regimen resulted in significant decline in activation of caspase cascade. Inhibition of caspases attenuated apoptosis of hepatocytes, induced by chronic copper exposure. In summary, this study suggested that added benefit of combination treatment over use of either agent alone in alleviating the hepatotoxicity and fibrosis associated with copper toxicosis.

Darbepoetin-α inhibits the perpetuation of necro-inflammation and delays the progression of cholestatic fibrosis in mice

Biliary obstruction and cholestasis result in hepatocellular necro-inflammation and lead to the development of liver fibrosis. The objective of this study was to analyze whether the multiple tissue-protective properties of erythropoietin are salutary in an experimental model of liver fibrosis. For this purpose, C57BL/6J mice underwent common bile duct ligation (BDL) and were treated with either darbepoetin-α (10 μg/kg i.p.) or physiological saline every third day, beginning 24 h after BDL. Mice were killed at 2, 5, 14, and 28 days after BDL. Beside hematological parameters, markers of inflammation and fibrosis were assessed histomorphometrically and immunohistochemically as well as by quantitative real-time PCR. In addition, a 7-week survival study was performed. BDL provoked cholestatic hepatitis characterized by biliary infarcts with accumulation of macrophages followed by marked collagen deposition and increased expression of profibrotic gene transcripts. Darbepoetin-α treatment significantly diminished the area of focal necrosis, reduced the infiltration of macrophages, decreased levels of profibrotic genes, and lowered collagen deposition. Moreover, darbepoetin-α significantly reduced systemic anemia caused by BDL. Finally, darbepoetin-α treatment significantly prolonged the survival time after BDL. This study suggests that darbepoetin-α, which is a clinically well-established substance, might be used as an efficient therapeutic option for patients with chronic cholestatic liver disease.

Molecular mechanism of hepatic stellate cell activation and antifibrotic therapeutic strategies

Activation of hepatic stellate cells (HSCs) is the dominant event in liver fibrosis. The early events in the organization of HSC activation have been termed initiation. Initiation encompasses rapid changes in gene expression and phenotype that render the cells responsive to cytokines and other local stimuli. Cellular responses following initiation are termed perpetuation, which encompasses those cellular events that amplify the activated phenotype through enhanced growth factor expression and responsiveness. Multiple cells and cytokines play a part in the regulation of HSC activation. HSC activation consists of discrete phenotype responses, mainly proliferation, contractility, fibrogenesis, matrix degradation, chemotaxis and retinoid loss. Currently, antifibrotic therapeutic strategies include inhibition of HSC proliferation or stimulation of HSC apoptosis, downregulation of collagen production or promotion of its degradation, administration of cytokines, and infusion of mesenchymal stem cells. In this review, we summarize the latest advances in our understanding of the mechanisms of HSC activation and possible antifibrotic therapeutic strategies.

Inhibition of hepatic stellate cell activation following Yinchenhao decoction administration to dimethylnitrosamine-treated rats

AIM

In an effort to investigate the mechanism by which Yinchenhao decoction (YCHD) acts on liver injury, we investigated the potential antifibrogenic effects of YCHD in an experimental liver fibrosis rat model, with special focus on the mechanisms inhibiting the activation and promoting apoptosis of hepatic stellate cells (HSC).

METHODS

The rats were initially randomized into two groups: the control (n = 10) and dimethylnitrosamine-treated (DMN; n = 30) groups. DMN (10 mg/kg body weight) was administered intraperitoneally to the DMN-treated rats for three consecutive days each week. At the end of the second week, three rats from the control and six rats from the DMN-treated groups were killed for the fibrosis development assessment. The remaining DMN rats were further randomized into two groups: the DMN-water group (n = 12) and the DMN-YCHD group (n = 12). Both groups continued to receive weekly DMN treatment for another 2 weeks in addition to daily administration of either water or YCHD, which were given intragastrically at a dose of 0.418 g/100 g body weight.

RESULTS

Hepatic hydroxyproline content decreased and had improved histopathology in the DMN-YCHD rats. Compared to the DMN group, alpha-smooth muscle actin (SMA) and CD68 expression in the DMN-YCHD group was reduced significantly; however, alpha-SMA-positive HSC apoptosis was not observed by confocal microscopy; Fibrogenic proteins (tissue inhibitor matrix proteinases-1 and 2 and matrix metalloproteinase [MMP]-2/14) and cytokines (tumor necrosis factor-alpha and transforming growth factor-beta(1)) were decreased; MMP-9 was significantly upregulated.

CONCLUSION

Yinchenhao administration attenuates liver fibrosis at least in part by inhibiting HSC activation directly, rather than promoting cell apoptosis of activated HSC, and the suppressive activation of Kupffer cells.

Changing the pathogenetic roadmap of liver fibrosis? Where did it start; where will it go?

The pathophysiology of liver injury has attracted the interest of experimentalists and clinicians over many centuries. With the discovery of liver-specific pericytes - formerly called fat-storing cells, Ito-cells, lipocytes, and currently designated as hepatic stellate cells (HSC) - the insight into the cellular and molecular pathobiology of liver fibrosis has evolved and the pivotal role of HSC as a precursor cell-type for extracellular matrix-producing myofibroblasts has been established. Although activation and transdifferentiation of HSC to myofibroblasts is still regarded as the pathogenetic key mechanism of fibrogenesis, recent studies point to a prominent heterogeneity of the origin of myofibroblasts. Currently, the generation of matrix-synthesizing fibroblasts by epithelial-mesenchymal transition, by influx of bone marrow-derived fibrocytes into damaged liver tissue, and by differentiation of circulating monocytes to fibroblasts after homing in the injured liver are discussed as important complementary mechanisms to enlarge the pool of (myo-)fibroblasts in the fibrosing liver. Among the molecular mediators, transforming growth factor-beta (TGF-beta) plays a central role, which is controlled by the bone-morphogenetic protein (BMP)-7, an important antagonist of TGF-beta action. The newly discovered pathways supplement the linear concept of HSC activation to myofibroblasts, point to fibrosis as a systemic response involving extrahepatic organs and reactions, add further evidence to a more or less uniform concept of organ fibrosis in general (e.g. liver, lung, kidney), and offer innovative approaches for the development of non-invasive biomarkers and antifibrotic trials.

Protection by and anti-oxidant mechanism of berberine against rat liver fibrosis induced by multiple hepatotoxic factors

1. The aim of the present study was to investigate the effect and mechanism of berberine, an alkaloid extracted from the traditional Chinese medicine coptis, on rat liver fibrosis induced by multiple hepatotoxic factors. 2. Male Wistar rats were separated into five groups, a normal control group, a fibrotic control group and fibrotic groups treated with three different doses of berberine. The fibrotic models were established by introduction of multiple hepatotoxic factors, including CCl(4), ethanol and high cholesterol. Rats in the treatment groups were administered 50, 100 or 200 mg/kg berberine, intragastrically, daily for 4 weeks. Serum levels of alanine aminotransferase (ALT) and serum aspartate aminotransferase (AST), hepatic activity of superoxide dismutase (SOD) and hepatic malondialdehyde (MDA) and hepatic hydroxyproline (Hyp) content were determined. Liver biopsies were obtained for histological and immunohistochemical studies to detect the expressions of alpha-smooth muscle actin (SMA) and transforming growth factor (TGF)-beta1. 3. The results showed that, compared with the fibrotic control group, serum levels of ALT and AST and hepatic content of MDA and Hyp were markedly decreased, but the activity of hepatic SOD was significantly increased in berberine-treated groups in a dose-dependent manner. In addition, histopathological changes, such as steatosis, necrosis and myofibroblast proliferation, were reduced and the expression of a-SMA and TGF-b1 was significantly downregulated in the berberine-treated groups (P < 0.01). 4. These results suggest that berberine could be used to prevent experimental liver fibrosis through regulation of the anti-oxidant system and lipid peroxidation.

Evolving concepts of liver fibrogenesis provide new diagnostic and therapeutic options

Despite intensive studies, the clinical opportunities for patients with fibrosing liver diseases have not improved. This will be changed by increasing knowledge of new pathogenetic mechanisms, which complement the "canonical principle" of fibrogenesis. The latter is based on the activation of hepatic stellate cells and their transdifferentiation to myofibroblasts induced by hepatocellular injury and consecutive inflammatory mediators such as TGF-beta. Stellate cells express a broad spectrum of matrix components. New mechanisms indicate that the heterogeneous pool of (myo-)fibroblasts can be supplemented by epithelial-mesenchymal transition (EMT) from cholangiocytes and potentially also from hepatocytes to fibroblasts, by influx of bone marrow-derived fibrocytes in the damaged liver tissue and by differentiation of a subgroup of monocytes to fibroblasts after homing in the damaged tissue. These processes are regulated by the cytokines TGF-beta and BMP-7, chemokines, colony-stimulating factors, metalloproteinases and numerous trapping proteins. They offer innovative diagnostic and therapeutic options. As an example, modulation of TGF-beta/BMP-7 ratio changes the rate of EMT, and so the simultaneous determination of these parameters and of connective tissue growth factor (CTGF) in serum might provide information on fibrogenic activity. The extension of pathogenetic concepts of fibrosis will provide new therapeutic possibilities of interference with the fibrogenic mechanism in liver and other organs.

Variable expression of cystatin C in cultured trans-differentiating rat hepatic stellate cells

AIM: To study the expression of cystatin C (CysC), its regulation by transforming growth factor-β1 (TGF-β1) and platelet-derived growth factor (PDGF) and the potential interference of CysC with TGF-β1 signaling in this special cell type.

METHODS: We evaluated the CysC expression in cultured, profibrogenic hepatic stellate cells and trans-differentiated myofibroblasts by Northern and Western blotting and confocal laser scanning microscopy.

RESULTS: CysC was increased significantly in the course of trans-differentiation. Both TGF-β1 and PDGF-BB suppressed CysC expression. Furthermore, CysC secretion was induced by the treatment with TGF-β1. Although CysC induced an increased binding affinity of TGF-β receptor type III (beta-glycan) as assessed by chemical cross-linking with [¹²⁵I]-TGF-β1, it did not modulate TGF-β1 signal transduction as shown by evaluating the Smad2/3 phosphorylation status and [CAGA]-MLP-luciferase reporter gene assay. Interestingly, the shedding of type III TGF-β receptor beta-glycan was reduced in CysC-treated cells. Our data indicated that CysC expression was upregulated during trans-differentiation.

CONCLUSION: Increased CysC levels in the serum of patients suffering from liver diseases are at least partially due to a higher expression in activated hepatic stellate cells. Furthermore, TGF-β1 influences the secretion of CysC, highlighting a potentially important role of cysteine proteases in the progression of hepatic fibrogenesis.

Exposure to bacterial cell wall products triggers an inflammatory phenotype in hepatic stellate cells

Activated hepatic stellate cells (HSCs) secrete extracellular matrix components during hepatic fibrosis, but recent studies have shown that HSCs can also release a variety of proinflammatory cytokines. Moreover, bacterial endotoxemia is not only associated with systemic complications in the late stages of liver failure but is also a direct cause of liver damage, activating resident inflammatory cells. In this study, we investigated whether HSCs can respond directly to bacterial cell wall products acquiring a new phenotype. RT-PCR and immunocytochemistry assays were used to show that murine HSCs expressed specific mRNA transcripts and proteins for LPS and lipoteichoic acid (LTA) receptor systems and peptidoglycan recognition proteins. Exposing HSCs to bacterial endotoxins led to phosphorylation of mitogen-activated protein kinase ERK1 and the development of a proinflammatory phenotype. After exposure to LPS, LTA, or N-acetyl muramyl peptide, transforming growth factor-beta1, IL-6, and monocyte chemoattractant protein-1 (MCP-1) mRNA specific transcripts and proteins increased significantly in HSCs, as assayed by quantitative real-time RT-PCR and ELISA. These LPS-mediated effects in HSCs were receptor dependent, because LPS-induced ERK1 phosphorylation, IL-6, and MCP-1 mRNA and protein level upregulation were significantly less pronounced in HSCs isolated from C3H/HeJ mice lacking Toll-like receptor 4. In conclusion, our results show that murine HSCs express functional receptors for bacterial endotoxins, and HSCs exposed to bacterial products develop a strong proinflammatory phenotype. We speculate that high levels of bacterial endotoxins in the portal vein may directly induce a proinflammatory phenotype in HSCs that contributes to liver damage.

The role of non-parenchymal cells in liver growth

The main non-parenchymal cells of the liver, Kupffer cells, sinusoidal endothelial cells and stellate cells, participate in liver growth with respect to both their own proliferation, and effects on hepatocyte proliferation. In the well-characterised paradigm of 70% partial hepatectomy, they undergo DNA synthesis and cell division 20-24h later than the hepatocyte population. They exert both positive and negative influences on hepatocyte proliferation, including provision of an extracellular matrix-bound reservoir of hepatocyte growth factor that is activated after damage; priming of hepatocytes for DNA synthesis through rapid generation of TNF-alpha and IL-6; and generation of factors at later time points that curb hepatocyte DNA synthesis (IL-1, TGF-beta) and initiate reconstruction and reformation of matrix proteins.

LIM-domain protein cysteine- and glycine-rich protein 2 (CRP2) is a novel marker of hepatic stellate cells and binding partner of the protein inhibitor of activated STAT1

Activation of hepatic stellate cells is considered to be the main step in the development of liver fibrosis, which is characterized by the transition of quiescent vitamin-A-rich cells to proliferative, fibrogenic and contractile myofibroblasts. The identification of regulatory genes during early cell activation and transdifferentiation is essential to extend our knowledge of hepatic fibrogenesis. In liver, the gene CSRP2 is exclusively expressed by stellate cells, whereas no transcripts are detectable in hepatocytes, sinusoidal endothelial cells or Kupffer cells. The early activation of stellate cells induced by platelet-derived growth factor is accompanied by an enhanced expression of CSRP2. During later stages of transdifferentiation, the expression of CSRP2 in these cells is suppressed in vitro and in vivo. The CSRP2-encoded cysteine- and glycine-rich double-LIM-domain protein (CRP)2 is proposed to function as a molecular adapter, arranging two or more as yet unidentified protein constituents into a macromolecular complex. To identify these proteins and assign a cellular function to CRP2, a human cDNA library was screened with full-length CRP2 as bait in a yeast two-hybrid screen. The protein inhibitor of activated STAT1 ('PIAS1') was shown to associate selectively with the C-terminal LIM domain of CRP2. Physical interaction of both proteins in the cellular environment was confirmed by co-localization experiments with confocal laser scanning microscopy and co-immunoprecipitation analysis. These results establish CRP2 as a potential new factor in the JAK/STAT-signalling pathway and suggest that the suppression of CSRP2 might be a prerequisite for the myofibroblastic transition of hepatic stellate cells.

Organic osmolyte transport in quiescent and activated rat hepatic stellate cells (Ito cells)

Activation of hepatic stellate cells (HSCs) results in multiple alterations of cell function, but nothing is known about organic osmolytes in these cells. Organic osmolyte transport and transporter messenger RNA (mRNA) expression was studied in quiescent rat HSCs and after their transformation into alpha1-smooth muscle actin-positive myofibroblastlike cells. Quiescent stellate cells expressed in an osmosensitive manner the mRNA levels of the transporters for taurine (TAUT) and myoinositol (SMIT), whereas that for betaine was not detectable. However, these cells showed osmosensitive uptake not only of taurine and myoinositol but also of betaine. Osmosensitive betaine uptake was mediated by amino acid transport system A. After transformation into myofibroblasts, taurine and myoinositol uptake increased 5.5-fold and 4.5-fold, respectively, together with the respective transporter mRNA levels. Betaine uptake increased twofold because of osmosensitive induction of BGT1 expression. In both quiescent and activated HSCs, hypoosmotic cell swelling induced a rapid and 4, 4'-diisothiocyanatostilbene-2,2'-disulphonic acid-sensitive osmolyte efflux. In quiescent HSCs, hyperosmotic exposure increased the messenger RNA (mRNA) level of cyclooxygenase-2, which was counteracted by taurine but not by betaine or myoinositol. The study identifies taurine, myoinositol, and betaine as osmolytes in HSCs. Transformation of HSCs is accompanied by enhanced osmolyte transport activity and induction of the BGT1 transporter, which may be another activation marker of HSCs.

Differential expression of monocyte chemotactic protein-1 (MCP-1) in transforming rat hepatic stellate cells

BACKGROUNDS/AIMS

Hepatic stellate cells and infiltrating leukocytes play a key role in the pathogenesis of liver fibrosis. The chronic phase of liver inflammation is characterized by immigrating mononuclear cells. To understand the underlying mechanisms responsible for the attraction of mononuclear cells in the pathogenesis of liver fibrosis, we investigated the inducible production of chemotactic activities in hepatic stellate cells.

METHODS

Cultured hepatic stellate cells of different transformation grades and after in vitro transformation to myofibroblast-like cells were stimulated with tumor necrosis factor-a or bacterial lipopolysaccharide. Mononuclear cell attracting chemotactic activities were evaluated by chemotaxis assays, ELISA, and Northern blot analysis.

RESULTS

We observed a transformation grade-dependent differential responsiveness of hepatic stellate cells and myofibroblast-like cells. Monocyte chemotactic protein-1 was inducible by tumor necrosis factor-alpha in non-transformed hepatic stellate cells. In contrast, monocyte chemotactic protein-1 was not inducible by bacterial lipopolysaccharide until the cells were fully transformed into myofibroblast-like cells. Despite a delayed onset, the bacterial lipopolysaccharide-inducible monocyte chemotactic protein-1 expression did not depend on an endogenous production of tumor necrosis factor-alpha.

CONCLUSIONS

Our results indicate that the tumor necrosis factor-alpha and bacterial lipopolysaccharide-inducible production of chemokines plays a central role in the pathogenesis of liver fibrosis. These data suggest that when hepatic stellate cells have been transformed to a myofibroblast-like cells phenotype, e.g. by chronic injury, the cells become more sensitive to bacterial lipopolysaccharide, which may potentiate the production of chemotactic and fibrogenic mediators. A strong secretion of monocyte chemotactic protein-1 may contribute to the maintenance of an inflammatory infiltrate dominated by mononuclear cells.

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.

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

It is still a subject of debate whether hepatocytes have the ability to express TGF-beta. Therefore, we investigated in freshly isolated and in monolayer cultures of rat hepatocytes the expression of TGF-beta isoform s at the RNA and protein level applying RT-PCR, immunocytochemistry, immunoblotting, and functional assays of TGF-beta. TFG-beta 1, -beta 2, and -beta 3 transcripts were detected in cultured cells, and the level of m RNA increased up to 48/72 h, but TGF-beta 1 transcripts were absent in freshly isolated cells. Using APAAP stainings the proteins of all three TGF-beta isoforms were observed in hepatocyte cultures from 5-96 h, but in hepatocytes in the liver in situ and in freshly isolated cell suspensions TGF-beta staining was negative. SDS-PAGE under reducing conditions followed by Western blotting detected in cell lysates the subunit of mature TGF-beta at about 13 kd. Analysis of TGF-beta bioactivity with the mink cell (Mv1Lu) proliferation inhibition assay and competitive radioligand assay confirmed in activated (i.e., acidified and subsequently neutralized) hepatocyte-conditioned media the presence of TGF-beta, which, however, is almost entirely in the latent form. It is concluded that TGF-beta can be expressed in cultured hepatocytes and that the level of expression is quickly upregulated under abnormal, not yet known, microenvironmental conditions.

Kupffer cell iron overload induces intercellular adhesion molecule-1 expression on hepatocytes in genetic hemochromatosis

The mechanisms underlying iron-induced liver fibrogenesis in patients with genetic hemochromatosis are poorly understood. We studied signs of Kupffer cell activation and inflammatory responses in liver biopsy specimens obtained from 15 patients with untreated and six patients with treated hemochromatosis. Immunohistochemistry was performed on 11 of the untreated and all treated patients. Three of the untreated patients (20%) had cirrhosis and eight (53%) had fibrosis. None had chronic active hepatitis (CAH). Immunohistochemistry indicated that 55% of the untreated patients had sparse intercellular adhesion molecule-1 (ICAM-1) expression by hepatocytes, and all of these had Kupffer cell iron overload. No ICAM-1 expression was seen by hepatocytes in treated patients or healthy controls. ICAM-1 was strongly expressed by hepatocytes from control patients with inflammatory liver disease. HLA-DR reactivity was seen on sinusoidal cells in all groups, but not on hepatocytes except for two of the control patients with CAH. Twenty-seven percent of the untreated hemochromatosis patients displayed moderate infiltration by CD3-positive lymphocytes. Electron microscopy of samples from untreated hemochromatosis patients showed hypertrophic Kupffer cells containing iron-rich remnants of phagocytosed hepatocytes. Fat-storing cells close to iron-laden hepatocytes contained multiple lipid droplets and adjacent collagen fibril bundles. Thus, in patients with untreated genetic hemochromatosis and Kupffer cell iron overload, hepatocytes occasionally express ICAM-1. In regions with heavy iron overload, Kupffer cell hypertrophy and transition of fat-storing cells are seen. Our findings indicate that release of factors from iron-loaded, activated Kupffer cells is of importance for the transformation of fat-storing cells and increased collagen deposition seen in genetic hemochromatosis.