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Biomedical subjects

A Geerts

Publications and source records attributed to A Geerts.

At least 19 recordsLinked to original sources
PubMed1992

Hepatocyte growth factor/hepatopoietin A is expressed in fat-storing cells from rat liver but not myofibroblast-like cells derived from fat-storing cells.

Hepatocyte growth factor/hepatopoietin A is a complete mitogen for parenchymal liver cells, and its expression is increased as an early response to acute liver injury. To identify the liver cell population responsible for hepatocyte growth factor gene expression, we investigated tissue sections and isolated and purified cell fractions from normal rat liver by in situ and Northern blot hybridization. Hepatocyte growth factor transcripts were present in sinusoidal liver cells, which were preferentially located in the periportal parenchyma. Northern hybridization analysis of RNA isolated from purified liver cell fractions demonstrated that HGF messenger RNA is present only in fat-storing cells. No specific hepatocyte growth factor gene expression was detected in parenchymal cells, endothelial cells and Kupffer cells. Myofibroblast-like transition of fat-storing cells, which is linked to fibrogenesis in chronic liver disease, results in the loss of hepatocyte growth factor expression. Hepatocyte growth factor gene expression in the normal liver, a new function of fat-storing cells, suggests that this growth factor may play a role in the physiological balance between cell death and replacement in the liver and that hepatocyte growth factor may also act in a paracrine manner. Furthermore, loss of hepatocyte growth factor expression in myofibroblast-like cells derived from fat-storing cells may be responsible for reduced parenchymal cell regeneration in chronic liver disease.

Animals↗
PubMed1992

Ito cell expression of a nuclear retinoic acid receptor.

Although it has been suggested that retinoids regulate Ito cell proliferation and collagen synthesis, little is known about the ability of Ito cells to respond to retinoids in vivo. Because retinoids may mediate their molecular effects through nuclear receptors, Ito cells were examined for the presence of one of these receptors, nuclear retinoic acid receptor-beta. The modulation of nuclear retinoic acid receptor-beta expression was also studied during cell culture and hepatic fibrogenesis. Northern hybridization analysis revealed that Ito cells freshly isolated from normal rat liver contained nuclear retinoic acid receptor-beta messenger RNA at levels significantly higher than those found in other hepatic cell types. Ito cells also contained messenger RNA for two other nuclear retinoic acid receptors, nuclear retinoic acid receptor-alpha and nuclear retinoic acid receptor-gamma. Using an antibody to human nuclear retinoic acid receptor-beta, the nuclear presence of this receptor was demonstrated in normal Ito cells. In contrast, Ito cells cultured for at least 7 days had no detectable messenger RNA or nuclear staining for nuclear retinoic acid receptor-beta despite a 20 +/- 5-fold increase in the messenger RNA level of another retinoid binding protein, cellular retinol binding protein. Analysis of Ito cells isolated from rats with carbon tetrachloride-induced hepatic fibrosis revealed an 81% +/- 3% decrease in nuclear retinoic acid receptor-beta messenger RNA levels in these cells when compared with normal Ito cells. No difference in the messenger RNA levels of cellular retinol binding protein was found in Ito cells isolated from either normal or fibrotic liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Localization and cellular source of the extracellular matrix protein tenascin in normal and fibrotic rat liver.

The distribution and the cellular source of the novel extracellular matrix glycoprotein tenascin were studied in normal and fibrotic rat liver. Cryostat sections of normal rat livers, livers of rats treated with intraperitoneal injections of CCl4 and 4-day-old and 8-day-old primary fat-storing cell cultures were stained for tenascin and desmin using an immunoperoxidase procedure or a double-label immunofluorescence technique. Fat-storing cell cultures were metabolically labeled with 3H-proline. Radiolabeled proteins were immunoprecipitated from the supernatant with antitenascin antiserum and subjected to polyacrylamide gel electrophoresis. In normal rat livers, tenascin was detected discontinuously along the sinusoids, whereas portal tracts were devoid of staining. In fibrotic rat livers, tenascin was preferentially expressed in areas of cell damage, in slender septa or at connective tissue-parenchymal interfaces. The middle region of broad septa was negative. Desmin-positive fat-storing cells accumulated in areas strongly immunoreactive for tenascin, and double-label immunofluorescence showed cells positive for both tenascin and desmin. In fat-storing cell cultures, both intracellular positivity for tenascin and staining of extracellular fibers were seen. Gel electrophoresis of immunoprecipitated proteins revealed two major and three minor bands with molecular weights consistent with tenascin. We conclude that tenascin is a component of the extracellular matrix of both normal and fibrotic rat livers. The strong expression of tenascin in areas of cell damage, in "early" septa or at septal-parenchymal interfaces, in contrast to its absence from the middle region of mature septa, suggests a role in early matrix organization. Fat-storing cells synthesize and secrete tenascin.

Animals↗
PubMed1992

Internalization of intact poliovirus by HeLa cells as shown by subcellular fractionation in isoosmotic Nycodenz gradients.

HeLa cells were infected with radiolabelled poliovirus at different temperatures, and the intracellular distribution of input radioactivity was studied. To this end, homogenates were fractionated by rate zonal centrifugation in linear isoosmotic (2 to 30%) Nycodenz gradients. Further purification of subcellular fractions was achieved by recentrifugation to equilibrium in 10 to 30% Nycodenz. Temperatures were kept below 30 degrees C to prevent virus capsid modification. Under these conditions, the cell-associated virions remained fully infectious. Below 18 degrees C, most of the viral label was recovered from a bottom region (BR) of the rate zonal gradients. Marker enzyme analysis and antibody accessibility showed that the BR consisted of virions bound to the plasma membrane. Between 18 degrees C and 26 degrees C, viral label also accumulated in a top region (TR) of the rate zonal gradients. According to the criterion of antibody accessibility, the virions associated with the TR were present within intracellular structures, probably lipid membranes. Electron microscopy confirmed the presence of vesicles and tubules in this region of the gradient. No correlation was found between the TR and endosomal, lysosomal or plasma membrane markers. The TR equilibrated at low density (1.10 g/ml) in Nycodenz (free virus, 1.31 g/ml). The results confirm that intact poliovirions can enter the cell and do so via lipid-bound vesicles.

Biomarkers↗
PubMed1992

Tenascin expression in human chronic liver disease and in hepatocellular carcinoma.

Tenascin is an oligomeric glycoprotein of the extracellular matrix synthesized during embryonic development. It is prominently expressed in a variety of tumors. The role of tenascin in liver tissue is, however, unknown. We used immunocytochemistry to define the localization of tenascin and compare this with the localization of non-collagenous proteins, such as laminin and fibronectin, in normal human liver and pathological liver from patients with chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. In normal liver, tenascin expression was localized along the sinusoidal and vascular wall. In fibrotic liver, tenascin was also observed in the region between the hepatic parenchyma and the fibrosing portal tracts, especially in areas of piecemeal necrosis in chronic hepatitis. Immuno-EM study of liver tissue in chronic hepatitis strongly suggested the synthesis and secretion of tenascin by fat-storing cells into the space of Disse. In hepatocellular carcinoma, tenascin was expressed in both the capsule and lobular septa, but not in the sinusoidal walls of the tumors. These results led us to postulate a close relationship between the occurrence of this protein and disease processes such as fibrosis and cancer invasion.

Carcinoma, Hepatocellular↗
PubMed1991

Role of fat-storing cells in hepatic fibrogenesis. Retinoids as possible therapeutic agents.

In normal liver, fat-storing cells are the main storage site of vitamin A derivatives, mainly of retinyl palmitate and oleate. During liver injury, the phenotype of fat-storing cells alters dramatically. The cells gradually lose their fat-droplets, proliferate and synthesize large amounts of connective tissue molecules. In the present paper, we summarize the characteristics of fat-storing cells, review the role of fat-storing cells in development of hepatic fibrosis, and describe how retinoids affect the protein synthesis and proliferation of these cells.

Animals↗
PubMed1991

Tissue distribution, quantitation and proliferation kinetics of fat-storing cells in carbon tetrachloride-injured rat liver.

In this study, we have investigated the cell population kinetics of fat-storing cells in livers of rats intoxicated with CCl4. Fat-storing cells were identified in cryostat sections by immunoperoxidase staining of desmin. The peroxidase label was visualized using diaminobenzidine/hydrogen peroxide containing Ni2+ and Co(2+)-ions (Nico/diaminobenzidine method). In normal rats, we found 12.8 fat-storing cells/0.1 mm2 in periportal areas vs. 9.4 in pericentral fields. After one injection of CCl4, the number of pericentral cells increased gradually to reach a maximum of 39.4 cells/0.1 mm2 96 hr after injection. The desmin staining intensity of the pericentral fat-storing cells increased from 48 hr onward. At 72 to 120 hr, strongly stained cells were observed in pericentral areas and in bands of tissue between adjacent central veins, reminiscent of the connective tissue septa in fibrotic livers. In the periportal areas the number of fat-storing cells was not altered. After a second and third injection of CCl4, the number of cells increased further in the pericentral areas. When more than three injections were given, the pericentral fat-storing cell population reached a new steady state with the cell number being seven times higher than in control animals. Proliferation of fat-storing cells at different stages of CCl4 intoxication was studied by intravenous administration of 3H-thymidine, followed by combined desmin staining and autoradiography. Autoradiographical labeling of fat-storing cells was nearly absent in control animals and at 24 hr after a single CCl4 injection. At 48 to 96 hr, labeling indices of pericentral fat-storing cells were significantly higher than in control animals, with a maximum at 72 hr when 22.9% of the cells were labeled. After multiple injections of CCl4, labeling indices between 4.9% and 8.4% were found. We conclude that fibrogenesis is preceded by a strong expansion of the fat-storing cell population in the pericentral areas of the liver lobules and in bands of tissue between adjacent central veins. Local proliferation is an important mechanism underlying the expansion of this cell population.

Animals↗
PubMed1990

Collagen type I and III occur together in hybrid fibrils in the space of Disse of normal rat liver.

Collagen type I and procollagen type III were localized at the ultrastructural level on ultrathin frozen sections of rat liver by the protein A-gold technique using affinity-purified primary antibodies. Both collagen type I and procollagen type III were localized on nearly all solitary and bundled fibrils in the space of Disse. Simultaneous localization of collagen type I and procollagen type III by a double-labeling procedure using protein A-gold probes of different sizes unequivocally demonstrated the presence of both collagens in the same fibrils. Measurement of the diameter of large numbers of collagen fibrils in the space of Disse of the rat liver showed a unimodal distribution of the fibril diameters around an average value of 62.4 nm (S.D. = 12.8 nm), and 91% of the collagen bundles contained less than 30 fibrils. Additional measurements on epoxy resin-embedded material of five biopsy specimens of normal human liver showed a comparable unimodal distribution of the fibril diameters around an average value of 57.2 nm (S.D. = 9.6 nm), and 74% of the bundles contained less than 60 fibrils. The latter observation demonstrates that human liver contains broader interstitial collagen bundles than rat liver. From these results, we conclude that the space of Disse of normal rat and human liver contains a uniform population of striated interstitial collagen fibrils. In the rat liver, these fibrils contain both collagen type I and procollagen type III. Therefore the concept that procollagen type III is predominantly localized in small diameter fibrils or bundles, whereas collagen type I is preferentially localized in thick ones, does not hold.

Animals↗
PubMed1990

Ultrastructure and function of hepatic fat-storing and pit cells.

The present paper reviews the literature on the ultrastructure and function of sinusoidal fat-storing cells and pit cells in the mammalian liver. Ultrastructurally, fat-storing cells are characterized by the presence of cytoplasmic fat droplets, well developed rough endoplasmic reticulum; a Golgi complex; multivesicular bodies; one or two centrioles; and few, rather small, lysosomes. These lysosomes are sometimes associated with fat droplets. Fat-storing cells may bear a cilium and project characteristic cytoplasmic processes into the space of Disse. These processes contain microtubules and filaments. Fat-storing cells are the main storage site of retinol esters in the mammalian body. Moreover, these cells have the potential of synthesizing several connective tissue components including the collagens type I, III, and IV; fibronectin; laminin; heparan sulfate; chondroitin sulfate; and dermatan sulfate. Pit cells are polarized cells, with most organelles localized at one site of the nucleus near the cytocentre. They are characterized electron microscopically by the presence of dense cytoplasmic granules with a specific ultrastructure, by rod-cored vesicles, and by multivesicular bodies. It has recently been shown that pit cells have natural killer activity to certain tumor cells and have many features in common with large granular lymphocytes. They therefore may act in the liver as a first line of defense against neoplasia, metastasis, and viral infections.

Animals↗
PubMed1989

In vitro differentiation of fat-storing cells parallels marked increase of collagen synthesis and secretion.

Fat-storing cells were isolated and purified from livers of normal adult rats and maintained in primary culture. By light and electron microscopy it was established that they underwent phenotypic changes into cells with the ultrastructural characteristics of myofibroblasts, between the third and sixth day in culture. These morphological changes were accompanied by a 2-fold increase of L-[3H]proline incorporation into secretory proteins and an 11-fold increase into secreted collagenase-sensitive proteins. In contrast, incorporation into cell layer-associated proteins and into cell layer-associated collagenase-sensitive proteins was not significantly elevated. Sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in combination with fluorography, demonstrated that the main collagen type secreted by the myofibroblast-like cells was collagen type I. Collagen types III and IV, and fibronectin were present in lesser amounts. The similarity between the well known in vivo alterations of fat-storing cells under pathological conditions and the spontaneous in vitro differentiation described in this study, makes primary cultures of fat-storing cells a valuable tool for studying their role in chronic liver disease.

Adipose Tissue↗
PubMed1988

Localization of four phosphatases in rat liver sinusoidal cells. An enzyme cytochemical study.

In the present study we have localized neutral phosphatase, acid phosphatase, alkaline phosphatase and 5' nucleotidase in the sinusoidal cells of rat liver using enzyme cytochemistry at light and electron microscopical level. Neutral phosphatase was present in the endoplasmic reticulum and nuclear envelope of parenchymal cells and of sinusoidal endothelial, Kupffer and fat-storing cells. The intensity of the neutral phosphatase reaction was stronger in sinusoidal than in parenchymal cells. Sinusoidal cells were devoid of cytochemically demonstrable alkaline phosphatase. Abundant acid phosphatase was present in the many lysosomes of endothelial and Kupffer cells. Substantially less acid phosphatase-positive lysosomes were found in fat-storing cells. 5' nucleotidase was present on the cell membrane of fat-storing cells, on 90% of all Kupffer cells and on the microvilli of parenchymal cells. We have further shown that combined staining for 5' nucleotidase and for endogenous peroxidase, offers a histochemical tool to discriminate between the three main sinusoidal cell types in normal rat liver.

5'-Nucleotidase↗
PubMed1988

Cell population kinetics of Kupffer cells during the onset of fibrosis in rat liver by chronic carbon tetrachloride administration.

The cell population kinetics of Kupffer cells (KCs) were investigated during the induction of fibrosis in rat liver by carbon tetrachloride. KCs, characterized microscopically by their specific peroxidase pattern, increased in number during the first 24 h after CCl4 injection. After repeated injections of the toxin the number of KCs increased logarithmically. After 9 weeks of CCl4 treatment, the KC population reached a new steady state with a 2.6-times-higher cell number than in control animals. Local KC proliferation was demonstrated by the metaphase arrest technique using vinblastine. It was calculated that at 24 h and at 72 h after one injection of CCl4, local proliferation did not account for the entire growth of the population. This means that, in addition to local proliferation of KCs, an influx of mononuclear phagocytes into the liver sinusoids occurred.

Animals↗
PubMed1987

Modulation of collagen synthesis by fat-storing cells, isolated from CCl4- or vitamin A-treated rats.

In an attempt to elucidate the role of fat-storing cells (FSCs) in liver fibrosis, we investigated the collagen synthesis by FSCs freshly isolated from rats treated with CCl4, with vitamin A, and from untreated rats. FSCs from CCl4-treated rats contained a small number of lipid droplets and an abundant rough endoplasmic reticulum (RER), while those from vitamin A-treated rats showed numerous large lipid droplets and scanty RER. The population doubling times of FSCs isolated from normal, CCl4-treated, and vitamin A-treated rats were 38 +/- 4.3, 24 +/- 2.5, and 48 +/- 6.3 hr, respectively. The rate of collagen synthesis by FSCs from CCl4-treated rats was four- to sixfold enhanced, while collagen synthesis by FSCs from vitamin A-treated rats was suppressed. The ratio of collagen type I to type III produced by FSCs from CCl4 rats was enhanced as compared with control rats (94.7:5.3 vs 87.6:12.4). Therefore, FSCs can be considered to play an important role in the pathogenesis of liver fibrosis.

Animals↗
PubMed1986

Immunogold localization of procollagen III, fibronectin and heparan sulfate proteoglycan on ultrathin frozen sections of the normal rat liver.

In the present study, we have localized by immunocytochemistry at the LM and EM level, procollagen type III (PIIIP), fibronectin (FN) and heparan sulfate proteoglycan (HSPG). Intracellularly, PIIIP was observed in both parenchymal and endothelial cells. In parenchymal cells, PIIIP was found in Golgi derived vesicles. This observation suggests that PIIIP synthesis is a normal function of liver parenchymal cells. In endothelial cells, vesicles, which could not be identified, were seen to contain PIIIP. This result does not allow to conclude, whether sinusoidal endothelial cells secrete or take up PIIIP. Extracellularly, PIIIP was present around portal and central veins, in the space of Disse and between adjacent parenchymal cells. In the space of Disse, almost all interstitial collagen fibrils reacted with the anti PIIIP antibodies. This observation leads to the conclusion that most fibrils of the space of Disse contain type III in addition to type I collagen molecules. By immunofluorescence, FN was seen mainly along the sinusoids in discrete dots. By EM, FN was found to be present in diffuse material closely associated with the sinusoidal membrane of the parenchymal cells and in strands connecting adjacent parenchymal cells, parenchymal and endothelial cells or parenchymal cells and collagen fibrils. FN was also present in vascular and ductular basal laminae. Strong HSPG reaction was observed around bile ducts. Moderate reaction was seen around blood vessels and in the space of Disse. In the latter location, the ultrastructural distribution of HSPG resembles that of FN, i.e. HSPG is present in diffuse material and in strands.

Animals↗
PubMed1986

Kupffer cells from CCl4-induced fibrotic livers stimulate proliferation of fat-storing cells.

The interaction between fat-storing cells (FSCs) and Kupffer cells (KCs) in vitro has been studied in an attempt to clarify certain aspects of the pathogenesis of fibrotic process in the liver. FSCs and KCs were isolated from the livers of rats either treated with CCl4 for 6 weeks, or with vitamin A for 6 weeks or from untreated rats by the pronase-collagenase digestion method. FSCs were further purified by centrifugation over a double layered metrizamide gradient, and KCs were separated from other sinusoidal cells by the dish adherence technique. FSCs from CCl4-treated rats divided rapidly, while those from vitamin A-treated rats divided slowly, as compared with untreated rats. Furthermore, the proliferation of FSCs was enhanced in the presence of KCs from CCl4-treated rats, but was slightly suppressed by KCs from normal and vitamin A-treated rats. This enhancement was mediated by a non-dialyzable, soluble factor present in the conditioned medium of KCs from CCl4-treated rats, but was not detected in the conditioned medium of KCs from normal or vitamin A-treated rats. From the present study, a growth factor secreted by KCs from CCl4-treated rats may play an important role in controlling the proliferation of FSCs during the pathogenesis of liver fibrosis.

Animals↗
PubMed1986

Serum and synovial fluid antibodies to collagen in rheumatic diseases: a review.

The literature on the occurrence and significance of antibodies to native or denatured collagen in rheumatic diseases is reviewed. Mainly type I and type II collagen have been investigated, both in serum and synovial fluid, with special reference to their possible role in rheumatoid arthritis. Brief results of the analysis of 40 synovial fluid samples, using an ELISA technique are included.

Arthritis, Rheumatoid↗