Cultured Ito cells of rat liver express the alpha 2-macroglobulin gene

Unraveling new players in helminth pathology: extracellular vesicles from Fasciola hepatica and Dicrocoelium dendriticum exert different effects on hepatic stellate cells and hepatocytes

Fasciola hepatica and Dicrocoelium dendriticum are parasitic trematodes residing in the bile ducts of mammalian hosts, causing, in some cases, impairment of liver function and hepatic fibrosis. Previous studies have shown that extracellular vesicles released by F. hepatica (FhEVs) and D. dendriticum (DdEVs) induce a distinct phenotype in human macrophages, but there is limited information on the effect of parasitic EVs on liver cells, which interact directly with the worms in natural infections. In this study, we isolated FhEVs and DdEVs by size exclusion chromatography and labeled them with a lipophilic fluorescent dye to analyze their uptake by human hepatic stellate cells (HSC) and hepatocytes, important cell types in liver pathology, using synthetic liposomes as internal labeling and uptake control. We analyzed EV uptake and the proteome profiles after the treatment with EVs for both cell types. Our results reveal that EVs establish unique and specific interactions with stellate cells and hepatocytes, suggesting a different role of EVs derived from each parasite, depending on the migration route to reach their final niche. FhEVs have a cytostatic effect on HSCs, but induce the extracellular matrix secretion and elicit anti-inflammatory responses in hepatocytes. DdEVs have a more potent anti-proliferative effect than FhEVs and trigger a global inflammatory response, increasing the levels of NF-κB and other inflammatory mediators in both cell types. These interactions may have a major influence on the progression of the disease, serving to generate conditions that may favor the establishment of the helminths in the host.

Hepatic stellate cells - from past till present: morphology, human markers, human cell lines, behavior in normal and liver pathology

Hepatic stellate cell (HSC), initially analyzed by von Kupffer, in 1876, revealed to be an extraordinary mesenchymal cell, essential for both hepatocellular function and lesions, being the hallmark of hepatic fibrogenesis and carcinogenesis. Apart from their implications in hepatic injury, HSCs play a vital role in liver development and regeneration, xenobiotic response, intermediate metabolism, and regulation of immune response. In this review, we discuss the current state of knowledge regarding HSCs morphology, human HSCs markers and human HSC cell lines. We also summarize the latest findings concerning their roles in normal and liver pathology, focusing on their impact in fibrogenesis, chronic viral hepatitis and liver tumors.

Tracking acute phase protein response during acute and chronic Toxoplasma gondii infection

Toxoplasmosis is a disease caused by the protozoan Toxoplasma gondii, which occurs worldwide in mammals and birds. Brain is the primary target organ because Toxoplasma gondii is a ubiquitous intracellular parasite that causes most frequently life-threatening encephalitis in immunocompromised patients. Relation of tissue cysts number, histopathology score and acute phase proteins were investigated. In this study, 36 mice are infected with Me49 strain of Toxoplasma gondii. The control group has 6 healthy mice. After inoculation of Toxoplasma gondii, at 10., 15., 20., 30., 45., 60. days, 6 each mice euthanized after collection of blood samples. Hemopexin, haptoglobulin, macroglobulin, serum amyloid A and clusterin levels are determined by ELISA. Then, brain tissues were investigated histopathologically and lesions were scored. The average cyst numbers were determined by counting three samples (25 μl each) of each brain homogenate under light microscopy. Inflammatory reaction was observed on day 10 days after inoculation (d.a.i.) The lesions were characterized by perivascular mononuclear cell infiltration, focal mononuclear cell infiltration in the meninges, and glial proliferation. Tissue cysts were observed in all Toxoplasma gondii-infected groups. The highest lesion score was observed at 60 d.a.i. And the most tissue cyst number were on day 30. d.a.i. Serum levels of hemopexin, haptoglobulin, macroglobulin, serum amyloid A and clusterin were significantly higher than the control group on day 10-20., 10., 10-30., 10.,10-45 d.a.i., respectively. High level of acute phase proteins in mice on certain days infected with Toxoplasma gondii was exhibited a relationship between brain lesions and tissue cysts.

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

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

Mesenchymal cells in the liver--one cell type or two?

The wall of the liver sinusoid is made of highly specialized cells, the hepatic stellate cells (HSC) which together with the sinusoidal endothelial cells represent a loose barrier to the corpusculate part of the blood flowing through the liver. Quiescent stellate cells (quiescent HSC) store Vitamin A; "activated" stellate cells become involved in the reaction to acute or chronic noxae damaging the liver parenchyma. Activated HSC show increased protein synthesis capacity, increased DNA-synthesis and acquire a myofibroblast-like phenotype. Under similar conditions liver myofibroblasts (MF) of the portal field and of the pericentral area may also become "activated" by increasing protein synthesis, DNA synthesis and cell division. They express the fibulin-2 gene and produce large amounts of IL-6. In contrast to "activated" HSC they do not undergo spontaneous apoptosis in vitro and do not express the CD95-ligand gene. So far no definite prove has been found for a "transdifferentiation" of HSC to myofibroblasts. On the contrary an increasing amount of data support the conviction that HSC and MF represent two similar but not identical cell populations the latter being comparable to those of other organs.

Expression of isoforms and splice variants of the latent transforming growth factor beta binding protein (LTBP) in cultured human liver myofibroblasts

BACKGROUND/AIMS

The activation of hepatic stellate cells (HSC) to extracellular matrix (ECM) producing myofibroblasts (MFB) is the key pathogenetic event in human liver fibrogenesis. Latent transforming growth factor beta binding protein (LTBP), a component of the profibrogenic large latent transforming growth factor (TGF)-beta complex, is suggested to be important for secretion, latency, storage and activation of TGF-beta in the ECM. This study was performed to identify the expression profile of all hitherto known LTBP isoforms and LTBP splice variants in conjunction with that of TGF-beta isoforms in cultured human liver MFB.

METHODS

Cultured human MFB were analyzed for TGF-beta and LTBP using reverse-transcription polymerase chain reaction (RT-PCR), sequence analysis, immunofluorescence staining, metabolic labeling, immunoprecipitation, and enzyme-linked immunosorbent assay (ELISA).

RESULTS

Transcripts of all three TGF-beta isoforms, of all four LTBP isoforms and of nearly all splice variants of LTBP-1 and LTBP-4 so far known were detected. Metabolic labeling followed by immunoprecipitation with anti-LTBP-1 antibody revealed the synthesis of LTBP proteins. Secretion of free LTBP and LTBP integrated into the large latent TGF-beta complex was demonstrated by size-exclusion chromatography. Co-localization of LTBP-1 and -2 with fibronectin and collagen type I was observed by double immunofluorescence staining.

CONCLUSION

The expression of a complete profile of hitherto known LTBP proteins by cultured human MFB suggests a role in modulating the bioactivity of TGF-beta in the diseased liver.

Rat liver myofibroblasts and hepatic stellate cells: different cell populations of the fibroblast lineage with fibrogenic potential

BACKGROUND & AIMS

Hepatic stellate cells (HSCs) are considered the principal matrix-producing cells of the damaged liver. However, other cell types of the fibroblast lineage that have not yet been characterized are also involved in liver tissue repair and fibrogenesis.

METHODS

We established cultures of cells of the fibroblast lineage, termed rat liver myofibroblasts, and analyzed their phenotypical and functional properties in comparison with HSCs.

RESULTS

HSCs and rat liver myofibroblasts were discernible by morphological criteria and growth behavior. Prolonged subcultivation of rat liver myofibroblasts was achieved, but HSCs were maintained in culture at maximum until second passage. HSCs were characterized by expression of glial fibrillary acidic protein, desmin, and vascular cell adhesion molecule 1, which were almost completely absent in rat liver myofibroblasts. For synthetic properties, HSCs and rat liver myofibroblasts displayed mostly overlapping properties with 4 striking differences. The complement-activating protease P100 and the protease inhibitor alpha(2)-macroglobulin were preferentially expressed by HSCs, whereas interleukin 6-coding messenger RNAs and the extracellular matrix protein fibulin 2 were almost exclusively detectable in rat liver myofibroblasts.

CONCLUSIONS

The data show that morphologically and functionally different fibroblastic populations, HSCs and rat liver myofibroblasts, can be derived from liver tissue. HSCs may not represent the single matrix-producing cell type of the fibroblast lineage in the liver.

Alpha2-macroglobulin reduces paracrine- and autocrine-stimulated matrix synthesis of cultured rat hepatic stellate cells

BACKGROUND

Transforming growth factor beta1 (TGF-beta1) is considered to represent a major fibrogenic mediator in the liver. The aim of the present study was to investigate whether alpha2-macroglobulin (alpha2M) might reduce paracrine- and autocrine-stimulated matrix synthesis of cultured rat hepatic stellate cells (HSCs) by scavenging TGF-beta.

METHODS AND RESULTS

Using native agarose electrophoresis, we demonstrated that alpha2M binds [125I]-TGF-beta1 within minutes. Preincubation of transiently acidified supernatants of cultured Kupffer cells, secondary cultured (activated) HSC and platelet lysate with, respectively, 500 and 2000 microg mL-1 alpha2M significantly reduced the concentration of active TGF-beta1 in these media. As a consequence of TGF-beta scavenging by alpha2M, paracrine-stimulated proteoglycan synthesis of primary cultured HSCs was reduced significantly. Furthermore, addition of 200 microg mL-1 alpha2M to passaged (activated) HSCs resulted in (a) a reduction in autocrine-stimulated extracellular matrix synthesis (proteoglycan -52%, fibronectin -55%) and (b) increased cell proliferation. A similar reduction in matrix synthesis was observed after the addition of 5 micromol L-1 TGF-beta1 antisense oligonucleotide to activated HSCs.

CONCLUSION

We conclude that alpha2M reduces paracrine-and autocrine-stimulated extracellular matrix synthesis of cultured HSCs by scavenging TGF-beta. These mechanisms might restrict liver fibrogenesis.

Effect of tumour necrosis factor-alpha on proliferation, activation and protein synthesis of rat hepatic stellate cells

BACKGROUND/AIMS

Hepatic stellate cells represent the principal matrix-synthesising cells of damaged liver and are targets of a number of cytokines currently under investigation. The study analyses the effects of tumour necrosis factor-alpha and interferon-gamma on proliferation, "activation" and protein synthesis of hepatic stellate cells.

METHODS

Primary cultures of hepatic stellate cells were exposed to tumour necrosis factor-alpha and interferon-gamma. Cell proliferation was studied by 3H-thymidine and bromo-deoxy-uridine incorporation. Protein synthesis was analysed using immunoprecipitation, Western- and Northern blotting techniques.

RESULTS

Proliferation of hepatic stellate cells was reduced by tumor necrosis factor-alpha and interferon-gamma, while "activation" of hepatic stellate cells as assessed by expression of smooth muscle alpha-actin and of TGF-beta/activin type I receptor was induced by tumour necrosis factor-alpha but downregulated by interferon-gamma. Tumour necrosis factor-alpha increased the synthesis of distinct extracellular matrix proteins, particularly of fibronectin and tenascin, but decreased collagen type III expression. In contrast, interferon-gamma reduced the synthesis of all connective tissue proteins tested. Among the protease inhibitors, interferon-gamma induced C1-esterase inhibitor synthesis, while tumour necrosis factor-alpha stimulated plasminogen activator inhibitor type 1 production.

CONCLUSIONS

Tumour necrosis factor-alpha and interferon-gamma decrease proliferation of hepatic stellate cells, while "activation" of hepatic stellate cells and synthesis of proteins involved in matrix metabolism are regulated in a differential, cytokine-specific manner, suggesting that both cytokines play an important role in liver repair.

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.

Transforming growth factor-beta-induced collagen synthesis by human liver myofibroblasts is inhibited by alpha2-macroglobulin

BACKGROUND

Transforming growth factor-beta (TGFbeta) plays a central role in the stimulation of matrix production during liver fibrosis. The action of TGFbeta in different systems has been shown to be influenced by alpha2-macroglobulin (alpha2M), a serum protein with strong protease-scavenging and cytokine-binding properties.

AIMS

In the present study, alpha2M derived from normal human plasma has been tested for its ability to modulate the TGFbeta-induced collagen production by human liver fat-storing cells (FSC), which had transformed into alpha-smooth muscle actin-expressing myofibroblasts in culture.

METHODS

Alpha2M has been tested after activation with methylamine (alpha2M-Me), an in vitro equivalent of protease activated alpha2M. The binding of 125I-TGFbeta1 to activated forms of alpha2M was demonstrated by rate electrophoresis. Collagen synthesis was examined in human liver myofibroblast cultures obtained from three different human livers by incorporation of 3H-proline into TCA-precipitable, specific collagenase degradable proteins. Uptake of alpha2M was studied by means of immunofluorescence.

RESULTS

TGFbeta (1 ng/ml) significantly stimulated collagen synthesis of controls in the absence of TGFbeta. Alpha2M-Me reduced this TGFbeta-induced collagen synthesis dose-dependently, reaching significant inhibition from 10 microg/ml alpha2M-Me onward. Upon addition of 100 microg/ml alpha2M-Me the effect of TGFbeta was reduced by 60% to 128+/-31% (mean+/-SD) of control values in the absence of TGFbeta. Human liver myofibroblasts endocytosed alpha2M-Me added to the cultures as detected by immunofluorescence. Accordingly, reduction of TGFbeta-activity by alpha2M-Me may be explained by receptor-mediated clearance of alpha2M-TGFbeta complexes by the cells.

CONCLUSIONS

TGFbeta-induced collagen formation by human liver myofibroblasts obtained from three different livers is reduced in vitro by activated alpha2M. From these results, we hypothesize that alpha2M may have an antifibrogenic effect in vivo by interference with TGFbeta-induced matrix synthesis during liver fibrosis.

Alpha-2-macroglobulin and hepatic fibrosis. Diagnostic interest

Alpha-2-macroglobulin (A2M) is a proteinase inhibitor. Cells synthesizing A2M are in first-order hepatocytes and in second-order activated Ito cells (in culture starting at day 4-5 after seeding). This study was undertaken in 525 alcoholic patients with different histological stages of alcoholic liver disease to assess if the A2M could improve the diagnostic value of PGA index for detection of cirrhosis or fibrosis among drinkers, particularly in patients without clinical symptoms of liver failure and portal hypertension, and to assess the specific correlation of serum A2M with the score of liver fibrosis adjusted for steatosis and alcoholic hepatitis and thereafter adjusted for GGT, PT, and ApoA1, the three components of the PGA index. In 525 alcoholic patients, we have demonstrated the independent diagnostic value of A2M. The predictive values of the weighted score, using linear discriminant function combining PT, GGT, ApoA1 and A2M of the PGAA score and of the PGA score were assessed in a training step and validated in a second step. Then, 316 alcoholic clinically asymptomatic patients were studied. In these patients, the discriminant function permitted correct classification of 72% of patients. The PGAA index had comparable diagnostic value with 70% of patients correctly classified. On the other hand, the PGA index including only PT, GGT, and ApoA1 had classified correctly less patients (65%) than the discriminant function and the PGAA index (P < 0.01). For a value of 7, PGAA had 79% specificity and 89% sensitivity for the diagnosis of cirrhosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Degradation of matrix proteins in liver fibrosis

Hepatic fibrosis occurs as a consequence of net accumulation of matrix proteins (particularly collagen types I and III) in liver. Current concepts of the pathogenesis of liver fibrosis place major emphasis on the activation of hepatic lipocytes (fat-storing or Ito cells) to a myofibroblast-like phenotype with a consequent increase in their synthesis of matrix proteins. While this is an important factor, there is increasing evidence to indicate that liver fibrosis is a dynamic pathologic process in which altered matrix degradation may also play a significant role. Extracellular degradation of matrix proteins is regulated by a family of enzymes called the matrix metalloproteinases, which is subdivided into three groups; collagenases which degrade interstitial collagens (types I, II and III), type IV collagenases/gelatinases which degrade basement membrane (type IV) collagen and gelatins and stromelysins which degrade a broad range of substrates including proteoglycans, laminin, gelatins and fibronectin. The extracellular activity of these enzymes is regulated by several mechanisms which include alterations in gene transcription and proenzyme synthesis, cleavage of secreted proenzymes to active forms, and specific inhibition of activated forms by tissue inhibitor(s) of metalloproteinases (TIMPs). In liver, current evidence indicates that activated hepatic lipocytes and Kupffer cells play a central role in synthesis of matrix metalloproteinases. Under defined conditions they synthesize interstitial collagenase, 72 kDa and 95 kDa type IV collagenase/gelatinase and possibly stromelysin. Moreover, lipocytes also contribute to regulation of the extracellular activity of these enzymes by secretion of TIMP-1 and alpha 2-macroglobulin.(ABSTRACT TRUNCATED AT 250 WORDS)

"Lipomatous" lesions of unknown cellular origin in the liver of B6C3F1 mice

The gross, microscopic, and ultrastructural features of lipomatous lesions in the liver of B6C3F1 mice are described. The cases were selected from a database of 45,406 male and 45,674 female mice used as treated, control, or vehicle-control animals in the National Cancer Institute's Bioassays or the National Toxicology Program's 2-year carcinogenicity studies. Thirteen hepatic lesions identified from cases within the database were re-evaluated microscopically and selected for further study. These lesions were present in ten males and three females that were between 85 and 113 weeks of age at the time of death. Grossly, the liver lesions were described as white to yellow or red to brown nodules/masses or foci that ranged from 2.0 to 25 mm in diameter. The lesions commonly involved the median and left lateral hepatic lobes. Microscopically, many of the lesions closely resembled lipomas described in the liver of human beings, and they consisted of nonencapsulated mature adipose-like tissue with irregular margins. The majority of the cells that comprised the lipomatous lesions were signet-ring shaped. These cells were positive for lipid as evidenced with oil red-O. The lipid droplets were also present within the hepatocytes that comprised the hepatic plates trapped within or surrounding many of the lipomatous lesions. At the margins of many of the lesions there were spindle-shaped cells that contained small intracytoplasmic lipid vacuoles. These cells were often within a stromal matrix that had focal areas of collagen and mucopolysaccharides, as evidenced by weak staining with Masson's trichrome and periodic acid-Schiff's stains, respectively. There was also disruption of the reticulum fibers in many of the lesions, as noted with a Gomori's reticulum stain. Ultrastructurally, cytoplasmic organelles, such as rough endoplasmic reticulum, free ribosomes and small lipid vacuoles, were present in the spindle-shaped cells, whereas signet-ring-shaped cells had few discernible organelles due to peripheral compression of the cytoplasm by single large vacuoles occupying the cytoplasmic space. The spindle-shaped cells were free of lysosomes. Thin collagen fibers were seen in contact with some of the spindle-shaped cells and were located between these cells and adjacent hepatocytes, or endothelial cells lining sinusoidal capillaries. A distinct basal lamina was not associated with spindle- or signet-ring-shaped cells. Similar lipomatous lesions were not found in other visceral organs. The exact cellular origin of the hepatic lesions described here is not known.

Contribution of sinusoidal endothelial liver cells to liver fibrosis: expression of transforming growth factor-beta 1 receptors and modulation of plasmin-generating enzymes by transforming growth factor-beta 1

Transforming growth factor-beta 1 is an important cytokine in the pathophysiology of liver fibrosis, stimulating the production of extracellular matrix. Whether this cytokine can also control the degradation of matrix proteins in liver cells has not been investigated. Because plasmin is an important protease for the degradation of matrix glycoproteins, we investigated whether sinusoidal endothelial liver cells could contribute to fibrosing liver disease through the modulation of plasmin-generating enzymes in response to transforming growth factor-beta 1. Sinusoidal endothelial cells from guinea pig liver were investigated in pure monolayer culture. Using 125I-labelled transforming growth factor-beta, we demonstrated high-affinity binding sites on sinusoidal endothelial cells at a density of 9.3 x 10(2) per cell, and a dissociation constant of about 5.5 x 10(-11) mol/L. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the known three classes of membrane receptors for transforming growth factor-beta. Using biosynthetic labeling of proteins with 35S-methionine, immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, we showed that sinusoidal endothelial cells produce and secrete plasminogen activator inhibitor type 1 from the beginning of culture. Treatment of confluent cell cultures for 24 hr with transforming growth factor-beta 1 increased synthesis and release of plasminogen activator inhibitor type 1. The response was almost maximal at a concentration of 1 ng transforming growth factor-beta/ml and paralleled the increased synthesis of fibronectin. On reverse fibrin autography we proved that transforming growth factor-beta 1 stimulated the release of functionally active plasminogen activator inhibitor type 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydrocortisone induces the synthesis of alpha 2-macroglobulin by rat mammary myoepithelial cells

The effects of lactogenic hormones on protein secretion by 25.5-G4.2.3 cells, a rat mammary myoepithelial cell line immortalised with a temperature-sensitive T-antigen, were investigated. Insulin, prolactin, estradiol and progesterone had no effect but hydrocortisone induced the secretion of two proteins with molecular masses of 175 kDa (p175) and 146 kDa (p146), 10-30-fold and 5-fold respectively. The induction of p175 and p146 synthesis by hydrocortisone was greater at 39.5 degrees C than at 33 degrees C reflecting the increased differentiation of 25.5-G4.2.3 cells at the higher temperature. Rat mammary epithelial cells did not synthesise p175. After addition of hydrocortisone to 25.5-G4.2.3 cells, there was a lag phase of 10 h before the synthesis of p175 was induced. Half-maximal induction of p175 synthesis required a hydrocortisone concentration of 0.5 microM. p175 was identified as alpha 2-macroglobulin by N-terminal amino-acid sequence determination and immunoprecipitation with a specific antibody. Hydrocortisone induced a 5-kb alpha 2-macroglobulin-specific mRNA transcript in 25.5-G4.2.3 cells. Myoepithelial cells are responsible for synthesising the basement membrane around the rapidly expanding mammary alveoli during pregnancy. Myoepithelial cells also secrete metalloproteinases which are probably involved in turnover of the basement membrane. We suggest that increased levels of hydrocortisone during pregnancy induce the synthesis of alpha 2-macroglobulin, which is believed to be a potent inhibitor of metalloproteinases, by rat mammary myoepithelial cells to reduce proteolytic degradation of the basement membrane.

C. L. Oakley Lecture (1993). Cellular and molecular aspects of hepatic fibrosis

Hepatic fibrosis, a consequence of most forms of chronic liver disease, is a dynamic process involving complex interactions between several cell types, the net result of which is accumulation of several distinct extracellular matrix (ECM) proteins. The resultant disruption of intrahepatic blood flow contributes to the development of portal hypertension. The effects, however, are not merely a space-occupying phenomenon; by changing the composition of the ECM, fibrosis may also alter hepatocyte function via cellular integrins. The principal source of ECM proteins in normal and fibrotic liver is the perisinusoidal cells which lie in the space of Disse. The response of this cell population to acute and chronic liver injury has been studied in detail. Perisinusoidal cells proliferate and become activated following hepatocyte necrosis. This phenomenon is transient in acute injuries, but in chronic liver disease, continued activation is associated with phenotypic modulation of perisinusoidal cells to myofibroblasts. This process is mediated by various cytokines including TGF-beta and PDGF. Some of the growth factors involved are derived from activated Kupffer cells and there is evidence of a complex interplay between mediators; injured sinusoidal endothelial cells and platelets are possible additional sources. Accumulation of ECM proteins in fibrosis can be explained not only by increased synthesis, but also by decreased degradation. There is growing evidence that in fibrotic liver there is decreased interstitial collagenase activity. This is, at least in part, due to expression of a tissue inhibitor of metalloproteinase, TIMP-1, by activated perisinusoidal cells.

Liver cytoprotection by prostaglandins

During the last decade intensive work on the relationships between the liver and the arachidonic acid cascade has greatly expanded our knowledge of this area of research. The liver has emerged as the major organ participating in the degradation and elimination of arachidonate products of systemic origin. The synthesis in the liver of arachidonate products derived from the cyclooxygenase, lipoxygenase and cytochrome P450 system pathways has been demonstrated. The participation of leukotriene B4 and cysteinyl-leukotrienes as mediators of liver damage and the possible therapeutic usefulness of prostaglandins (PGs) in acute liver injury has attracted the interest of clinicians. This article reviews the essential features regarding the role of arachidonate metabolites in liver disease and specially focuses on the cytoprotective effects on the liver displayed by PGE2, PGE1, PGI2 and synthetic PG analogs in experimental models of liver damage induced by ischemia-reperfusion injury, carbon tetrachloride, bacterial lipopolysaccharide and viral hepatitis and on the possible mechanisms underlying liver cytoprotection in these experimental models. The therapeutic usefulness of PGs in clinical practice is critically analyzed on the basis of available evidence in patients with fulminant hepatic failure and primary graft nonfunction following liver transplantation.

Fat-storing cells of the rat liver synthesize and secrete C1-esterase inhibitor; modulation by cytokines

During liver fibrogenesis, fat-storing cells transform into myofibroblast-like cells and produce increasing amounts of extracellular matrix proteins. Because fat-storing cells produce alpha 2-macroglobulin, an important serine protease inhibitor (serpin), we investigated whether fat-storing cells also synthesize C1-esterase inhibitor, another important serpin. C1-esterase inhibitor synthesis was studied in rat fat-storing cells at day 0, 3 and 7 after isolation by biosynthetic labeling, immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Messenger RNA was examined by Northern-blot analysis. C1-esterase inhibitor gene expression and synthesis were detectable in freshly isolated fat-storing cells and increased distinctly during the time in culture. The cellular source of C1-esterase inhibitor in fat-storing cell cultures was also identified by in situ hybridization of cells at different times after isolation. By inhibition of the N-glycosylation using tunicamycin, rat C1-esterase inhibitor was identified as a glycoprotein. The time course of C1-esterase inhibitor secretion was determined by pulse-chase experiments. C1-esterase inhibitor synthesis was increased 6-fold to 10-fold by interferon-gamma. Specific messenger RNA levels were also raised distinctly by this cytokine. In contrast, interferon-alpha and dexamethasone did not alter C1-esterase inhibitor gene expression. Because C1-esterase inhibitor synthesis is increased by advancing culture time and by the inflammatory mediator interferon-gamma, we suggest that fat-storing cells may enhance the deposition of extracellular matrix proteins by inhibiting their degradation.

Activation of rat liver perisinusoidal lipocytes by transforming growth factors derived from myofibroblastlike cells. A potential mechanism of self perpetuation in liver fibrogenesis

Rat liver perisinusoidal lipocytes (PL) cultured on uncoated plastic transform spontaneously within 6-10 d to myofibroblastlike cells (MFBlC). Parallel to the transformation the TGF alpha- and TGF beta 1-mRNA expression increased and was highest in MFBlC. Competitive radioligand binding assays demonstrated that in contrast to untransformed PL the MFBlC synthesize and secrete transforming growth factor (TGF)-alpha (15 fmol/cell per 24 h) and predominantly the latent form of TGF beta 1 (0.2 fmol/cell per 24 h). Medium conditioned by MFBlC (MFBcM) significantly stimulated PL proliferation with little effect on PL proteoglycan synthesis. By transient acidification of the MFBcM, known to activate the latent form of TGF beta 1, the stimulatory effect on PL proteoglycan synthesis was enhanced and furthermore PL transformation (measured by expression of iso-alpha smooth muscle actin and loss of retinylpalmitate) was accelerated. Preincubation of this medium with neutralizing antibodies to TGF beta resulted in (a) the growth inhibitory effect was converted to a growth stimulation and (b) the stimulatory effect on proteoglycan synthesis was abolished. In summary our data indicate that progressive activation of PL on plastic (transformation to MFBlC) leads to an enhanced expression of the TGF alpha- and TGF beta 1-mRNAs and secretion of the corresponding proteins. Medium conditioned by MFBIC stimulates proliferation, transformation, and PG synthesis of untransformed PL. These mechanisms are suggested to be relevant in self perpetuation of liver fibrogenesis.

Dexamethasone modulates alpha 2-macroglobulin and apolipoprotein E gene expression in cultured rat liver fat-storing (Ito) cells

Fat-storing (Ito) cells are perisinusoidal liver cells thought to play a central role in vitamin A metabolism and fibrongenesis. Glucocorticoids have been shown to be beneficial in the treatment of certain types of liver diseases by delaying the development of cirrhosis. To study the regulatory effects of dexamethasone on Ito cell gene expression, Ito cells were isolated from normal rat liver and primary cultures were established. The effect of dexamethasone on the synthesis of alpha 2-macroglobulin, apolipoprotein E, fibronectin and actin was examined. Protein synthesis was studied both at the protein level and at the RNA level by means of biosynthetic labeling, immunoprecipitation followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by Northern blot analysis of total RNA. After exposure to dexamethasone for 20 hr, alpha 2-macroglobulin protein synthesis was increased threefold, whereas apolipoprotein E expression was decreased 80%. Biosynthesis of fibronectin remained unaffected by hormone treatment. The dexamethasone effect became detectable 5 hr after beginning the exposure. Deinduction kinetic experiments showed that the glucocorticoid effect was detectable more than 12 hr after the replacement of the dexamethasone-containing culture medium by medium without the hormone. Corresponding to the data obtained at the protein level, dexamethasone increased the steady-state levels of alpha 2-macroglobulin-specific messenger RNA and reduced apolipoprotein E-specific transcripts, whereas fibronectin and actin messenger mRNA remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the gene of the alpha-smooth muscle-actin isoform in rat liver and in rat fat-storing (ITO) cells

Fat storing cells (FSCs) in the liver represent the main site of vitamin A deposition in the body. These cells are considered to play an important role during scar formation and fibrogenesis in the liver. The putative descent of FSCs from the fibroblastic or from the myofibroblastic system have not been determined yet by morphological or immunohistochemical studies. To further define the origin of these liver cells, we analysed the pattern of expression of three structural proteins: vimentin, desmin and the alpha-smooth muscle (SM)-actin isoform in FSCs of the rat liver, in smooth muscle cells (SMCs) from the aorta and in rat skin fibroblasts. FSCs were studied by immunohistochemical methods immediately after isolation, at days 3 and 7 after plating. FSC-gene-expression was also analysed by Northern blot analysis of total RNA extracted from cells in culture at days 3 and 7 after isolation. Arterial SMCs and skin fibroblasts were studied in a similar way. For comparison, isolated rat hepatocytes and Küpffer cells (Kc) were studied. Of freshly isolated FSCs, 100% were vimentin-positive, 50% were desmin-positive, but all were alpha-SM-actin negative. Three days after isolation, FSCs were clearly positive for vimentin and desmin and weakly alpha-SM-actin-positive, as demonstrated by indirect immunofluorescence as well as by the immunoperoxidase technique. Desmin, alpha-SM-actin and vimentin staining was further increased at day 7 after isolation, and alpha-actin specific transcripts in FSC-RNA were clearly detectable at day 7 after isolation. Passaged arterial SMCs were vimentin- and alpha-SM-actin-positive, but desmin-negative and fibroblasts were only vimentin-positive.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation of the perisinusoidal vitamin A-storing cells from rat liver on Ca2(+)-immobilized glass surfaces

Calcium was immobilized on glass slides employing covalently coupled iminodiacetic acid. The calcium-coated glass surfaces were then used for purification and culturing of perisinusoidal vitamin A-storing cells from rat liver. The cells were isolated in a yield of 0.9 x 10(6) cells/g rat liver without cross-contamination by other hepatic cell types. The cells were characterized by morphology, vitamin A fluorescence, and immunohistochemistry to detect expression of cellular retinol-binding protein.

Connective tissue biology and hepatic fibrosis: report of a conference

The past 15 years have seen major advances in the characterization of extracellular matrix proteins and structure of matrix. As a by-product of this work, investigators now have an array of molecular and immunological reagents for monitoring matrix metabolism. Progress in the isolation and culture of individual cell types from liver has made possible direct measurement of matrix protein production and also has opened the way to studies of matrix degradation. The expanding knowledge of soluble mediators of inflammation is being applied to the regulation of matrix protein synthesis and degradation. Finally, experimental models of fibrosis in vivo are available for defining the complexity of matrix metabolism in the intact tissue and for validating the findings from cell culture and in vitro systems.

Fat-storing (Ito) cells of rat liver synthesize and secrete apolipoproteins: comparison with hepatocytes

Fat-storing cells of the liver store most of the vitamin A of the body. Vitamin A is present in a few large fat droplets within the cell. The aim of our study was to investigate apolipoprotein biosynthesis in isolated fat-storing cells from rat liver during the time in culture. Isolated rat hepatocytes were studied for comparison. Proteins were biosynthetically labeled and further identified by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Apoproteins in culture supernatants were identified by density gradient ultracentrifugation and by one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of aliquots of the gradient. Rat plasma was processed in the same way and used for comparison. Fat-storing cells synthesized and secreted apoprotein E, apoprotein A-I, apoprotein A-IV, and low amounts of apoprotein C. The synthesis of these proteins increased during the culture time, reaching a maximum at the fifth day after isolation. The proteins were identified mostly as apoproteins of high-density lipoprotein. Hepatocytes synthesized and secreted apoproteins of all classes of lipoproteins. The distribution of high-density lipoprotein apoproteins was similar to that of fat-storing cells but hepatocytes produced larger amounts of the apoproteins.

The release of tumor necrosis factor from endotoxin-stimulated rat Kupffer cells is regulated by prostaglandin E2 and dexamethasone

Evidence is presented that upon stimulation with endotoxin (lipopolysaccharide, LPS), Kupffer cells, the body's largest pool of sessile macrophages, synthesize and liberate a factor whose immunological, cytotoxic and chemical properties are those described for tumor necrosis factor (TNF)-alpha. Hepatocytes and sinusoidal endothelial cells do not produce detectable amounts of this protein. Ten nanograms of LPS per ml medium are sufficient to stimulate a substantial release of this mediator. Recombinant interferon-gamma (rIFN gamma) per se is a poor inducer of TNF release. Costimulation with endotoxin and rIFN gamma shows only a slight increment in the release of this cytotoxic factor, relative to LPS alone. Exposure of Kupffer cells to the Ca2+ ionophore A23187 or to elicitors of the oxidative burst and superoxide production, e.g. zymosan or phorbol 12-myristate 13-acetate, stimulates only a fraction (20%) of the TNF release seen after endotoxin challenge. Prostaglandin E2, the synthesis of which is strongly enhanced after challenge of rat Kupffer cells with LPS, suppresses the release of TNF by these cells. This autoregulatory mechanism may explain the kinetics of TNF production by stimulated Kupffer cells. Dexamethasone is another important mediator capable of reducing the LPS-elicited TNF formation. An effect of the glucocorticoid hormone can still be provoked if it is added simultaneously with or shortly after LPS. This rapid action requires a mechanism that is different from the time-consuming one leading to the inhibition of prostaglandin synthesis in Kupffer cells.