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T Knittel

Publications and source records attributed to T Knittel.

At least 37 records · Page 2Linked to original sources
PubMed1997

CD95/CD95L-mediated apoptosis of the hepatic stellate cell. A mechanism terminating uncontrolled hepatic stellate cell proliferation during hepatic tissue repair.

During liver tissue repair, hepatic stellate cells (HSC), a pericyte-like mesenchymal liver cell population, transform from a "quiescent" status ("resting" HSC) into myofibroblast-like cells ("activated" HSC) with the latter representing the principle matrix synthesizing cell of the liver. Presently, the mechanisms that terminate HSC cell proliferation when tissue repair is concluded are poorly understood. Controlled cell death known as apoptosis could be a mechanism underlying this phenomenon. Therefore, apoptosis and its regulation were studied in HSC using an in vitro and in vivo approach. Spontaneous apoptosis became detectable in parallel with HSC activation because resting cells (2 days after isolation) displayed no sign of apoptosis, whereas apoptosis was present in 8% (+/- 5%) of "transitional" cells (day 4) and in 18% (+/- 8%) of fully activated cells (day 7). Both CD95 (APO-1/Fas) and CD95L (APO-1-/Fas-ligand) became increasingly expressed during the course of activation. Apoptosis could be fully blocked by CD95-blocking antibodies in normal cells and HSC already entering the apoptotic cycle. Using CD95-activating antibodies, transition of more than 95% cells into apoptosis was evident at each activation step. The apoptosis-regulating proteins Bcl-2 and p53 could not be detected in resting cells but were found in increasing amounts at days 4 and 7 of cultivation. Whereas p53 expression was induced by the CD95-activating antibody, no change was inducible in Bcl-2 expression. The Bcl-2-related protein bax could be found at days 2 and 4 in similar expression, was considerably up-regulated at day 7, but was not regulated by CD95-agonistic antibodies. In vivo, acute tissue damage was first accompanied by activation and proliferation of HSC displaying no sign of apoptosis. In the recovery phase, apoptotic HSC were detectable in parallel to a reduction in the total number of HSC present in the liver tissue. The data demonstrate that apoptosis becomes detectable in parallel with HSC activation, which suggests that apoptosis might represent an important mechanism terminating proliferation of activated HSC.

Animals↗
PubMed1996

Glial fibrillary acidic protein--a cell type specific marker for Ito cells in vivo and in vitro.

BACKGROUND/AIMS: Glial fibrillary acidic protein is an intermediate filament first identified in the brain in astrocytes. This study examines glial fibrillary acidic protein immunoreactivity in normal and damaged rat livers. Glial fibrillary acidic protein-gene-expression in Ito cells, endothelial cells, Kupffer cells, and hepatocytes is also analyzed. METHODS: Sequential cryostat sections from normal, as well as acutely or chronically CC14 damaged rat livers were analyzed by immunostaining for the presence of glial fibrillary acidic protein and desmin. Glial fibrillary acidic protein-expression in isolated liver cells was studied by immunocytology, Western blot, Northern blot analysis, and reverse-transcription polymerase chain reaction. The specificity of polymerase chain reaction products was tested by Southern blot hybridization and partial sequencing. RESULTS: In the normal liver, glial fibrillary acidic protein-positive cells were detected in the perisinusoidal area. These cells were also desmin-immunoreactive as determined by immunostaining. In contrast, cells of the vessel walls were desmin-positive, but glial fibrillary acidic protein-negative. In the acutely damaged livers glial fibrillary acidic protein-positivity was detectable along the non-damaged sinusoids as well as in the necrotic areas. In chronically damaged livers glial fibrillary acidic protein was more detectable at the margins of the fibrotic septa, less inside the septa. All glial fibrillary acidic protein-positive cells were desmin-positive, but several desmin-positive cells were glial fibrillary acidic protein-negative (especially inside the septa). Among the different liver cell subpopulations tested in vitro, glial fibrillary acidic protein-gene expression was only detectable in Ito cells. During primary culture, glial fibrillary acidic protein-expression decreased in parallel to Ito cell activation. CONCLUSIONS: Glial fibrillary acidic protein is a new cell type specific marker for Ito cells, which might allow distinction between Ito cells and other fibroblastic liver cells (cells of the vessel walls). Cells located at the margins of fibrotic septa definitely represent Ito cells.

Animals↗
PubMed1996

Gene expression and regulation of plasminogen activator inhibitor type I in hepatic stellate cells of rat liver.

BACKGROUND & AIMS: Plasminogen activator inhibitor type 1 (PAI-1) plays a crucial role in the regulation of extracellular matrix-degrading enzymes and in the production of fibrogenic mediators such as transforming growth factor beta through inhibition of plasminogen activation. Because hepatic stellate cells (HSCs), the principal matrix-producing cell of the liver, might also affect extracellular matrix degradation and growth factor activation, the aim of this study was to analyze PAI-1 expression and its regulation in HSCs compared with other liver cells. METHODS: PAI-1 synthesis of liver cells at different time points of primary culture was studied by immunoprecipitation of endogenously labeled proteins followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by Northern blotting. RESULTS: Among the various types of liver cells, PAI-1 protein and specific transcripts were present in HSCs and endothelial cells, and no major PAI-1 synthesis was detected in Kupffer cells and hepatocytes. Transforming growth factor beta 1, tissue plasminogen activator, and dexamethasone increased PAI-1 production in HSCs. CONCLUSIONS: Apart from their role as the principal connective tissue-producing cell of the liver, HSCs might regulate extracellular matrix accumulation by modulating the activities of matrix-degrading enzymes and fibrogenic mediators through the production of PAI-1.

Animals↗
PubMed1996

Transforming growth factor beta 1-regulated gene expression of Ito cells.

During liver fibrogenesis, Ito cells are regarded as the principal matrix synthesizing cells and transforming growth factor beta 1 (TGF-beta 1) appears to be the main fibrogenic mediator. This study analyzed the effects of TGF-beta 1 on Ito cell activation, proliferation, and on the expression of a set of matrix proteins, antiproteases, and TGF-beta receptors both in "early cultured" and "culture-activated" Ito cells. Rat liver Ito cells at day 2 of primary culture ("early cultured" cells) were mainly smooth muscle alpha actin (SMA)-negative, whereas cells at day 6 were judged as "activated" cells (SMA-positive). Following 24-hour exposure to 1 ng/mL TGF-beta 1, total protein synthesis, cell proliferation, and expression of the "activation" marker SMA were not significantly changed. In addition to previously described stimulatory effects on collagen types I and III, fibronectin, undulin, and proteoglycan-gene expression, TGF-beta also dose-dependently increased synthesis and secretion of tenascin, laminin, entactin, collagen type IV, and alpha 2-macroglobulin, but decreased C1-esterase inhibitor production by Ito cells, as revealed by immunoprecipitation of endogenously labeled proteins and by Northern blot analysis. The stimulatory effect of TGF-beta was evident both in "early cultured" as well as "culture-activated" Ito cells. By reverse-transcription polymerase chain reaction (RT-PCR) analysis, TGF-beta type II, III, and TGF-beta/activin type I receptors were present in Ito cells, and their expression pattern was not changed upon TGF-beta exposure. Northern blot analysis demonstrated that type I TGF-beta/activin receptor was induced during in vitro activation and that TGF-beta exposure resulted in a slight increase of type I and III receptor messenger RNAs. In summary, the data illustrate that TGF-beta is an important fibrogenic mediator acting both on "early cultured" as well as "culture-activated" Ito cells, rather than a mitogenic or morphogenic mediator. The differential regulation of TGF-beta/activin receptors during in vitro activation and their up-regulation by TGF-beta 1 might represent a mechanism by which the receptor complex regulates TGF-beta signalling in Ito cells.

Adipocytes↗
PubMed1996

Expression of extracellular matrix proteoglycans perlecan and decorin in carbon-tetrachloride-injured rat liver and in isolated liver cells.

Proteoglycans are important components of the extracellular matrix. They are involved in liver regeneration as well as in liver fibrosis. The distribution and cellular source of proteoglycans under normal as well as pathological conditions is still under debate. Localization of decorin and perlecan was studied in normal, acutely damaged, and cirrhotic liver by histochemistry. Furthermore, their synthesis was analyzed in different liver cell populations isolated from normal rat liver. In normal liver, decorin positivity was observed in the perisinusoidal space and in the portal area. Perlecan was clearly detectable in the portal area (blood vessels and bile ducts); a moderate reaction was also seen along the sinusoids. Strong positivity for both proteoglycans was detectable in the necrotic areas of acutely damaged liver. Chronic liver damage was characterized by the deposition of decorin and perlecan in the fibrotic septa. Immunocytochemical reactions were positive for perlecan and decorin in cultured Ito and endothelial cells but not in hepatocytes and Kupffer cells. Northern hybridization confirmed the capacity of Ito cells and endothelial cells to express the two genes. Interestingly, although rat skin fibroblasts expressed strong messages for both proteoglycans, rat aortic smooth muscle cells did not synthesize decorin.

Animals↗
PubMed1996

Cell-type-specific expression of neural cell adhesion molecule (N-CAM) in Ito cells of rat liver. Up-regulation during in vitro activation and in hepatic tissue repair.

Ito cells (lipocytes, stellate cells) are regarded as the principle matrix-producing cell of the liver and have been shown recently to express glial fibrillary acidic protein, an intermediate filament typically found in glia cells of the nervous system. The present study examines 1) whether Ito cells of rat liver express central nervous system typical adhesion molecules, namely, neural cell adhesion molecule (N-CAM), in a cell-type-specific manner and 2) whether N-CAM expression is affected by activation of Ito cells in vitro and during rat liver injury in vivo. As assessed by reverse transcriptase polymerase chain reaction, Northern blotting, Western blotting, and immunocytochemistry of freshly isolated and cultivated hepatic cells, N-CAM expression was restricted to Ito cells and was absent in hepatocytes, Kupffer cells, and sinusoidal endothelial cells. Ito cells expressed predominantly N-CAM-coding transcripts of 6.1 and 4.8 kb in size and 140-kd isoforms of the N-CAM protein, which was localized on the cell surface membrane of Ito cells. In parallel to glial fibrillary acidic protein down-regulation and smooth muscle alpha-actin up-regulation, N-CAM expression was increased during in vitro transformation of Ito cells from resting to activated (myofibroblast-like) cells and by the fibrogenic mediator transforming growth factor-beta 1. By immunohistochemistry, N-CAM was detected in normal rat liver in the portal field as densely packed material and in a spot as well as fiber-like pattern probably representing nerve structures. However, after liver injury, N-CAM expression became detectable in mesenchymal cells within and around the necrotic area and within fibrotic septae. In serially cut tissue sections, N-CAM-positive cells were predominantly co-distributed with smooth muscle alpha-actin-positive cells rather than glial fibrillary acidic protein-positive cells, especially in fibrotic livers. The experimental results illustrate that N-CAM positivity in the liver cannot be solely ascribed to nerve endings as, among the different types of resident liver cells, Ito cells specifically express N-CAM in vitro and presumably in vivo. In addition to its role as potential cell-type-specific marker protein for activated Ito cells, the induction of N-CAM expression might illustrate a mechanism by which mesenchymal cell proliferation might be inhibited when tissue repair is concluded.

Actins↗
PubMed1995

Accumulation and cellular localization of fibrinogen/fibrin during short-term and long-term rat liver injury.

BACKGROUND/AIMS: During liver fibrosis, there is a putative pacemaker role of fibronectin. Fibrinogen is closely linked to fibronectin during clotting processes. The aim of this study was to show fibrinogen gene expression during liver damage. METHODS: Fibrinogen/fibrin deposition in damaged livers was studied by immunohistology. Fibrinogen gene expression was analyzed in vivo in a model of CCl4-induced rat liver damage and in vitro in isolated liver cells by means of Northern blot analysis and in situ hybridization. RESULTS: Immunohistology showed striking amounts of fibrinogen and fibrin deposits in pericentral necrotic areas (short-term damage) and within fibrotic septa (long-term damage). Total RNA extracted from short-term-damaged livers contained an increased fibrinogen messenger RNA level. By in situ hybridization, fibrinogen transcripts were localized in cells of the nonnecrotic areas (short-term damage) and outside fibrotic septa (long-term damage). In vitro studies showed fibrinogen de novo synthesis restricted to hepatocytes. CONCLUSIONS: The results show fibrinogen/fibrin deposition during short-term liver injury and liver fibrogenesis, which may suggest the involvement of a "clotting-like process" in short-term liver damage and liver fibrosis. The data might indicate that fibrin/fibronectin constitute a "provisional matrix," which affects the attraction and proliferation of inflammatory and matrix-producing cells.

Animals↗
PubMed1995

A conserved enhancer of the human and murine Hoxa-7 gene specifies the anterior boundary of expression during embryonal development.

The murine homeobox-containing gene Hoxa-7 is expressed in restricted patterns during embryogenesis and plays an important role in the control of region-specific differentiation. Previous studies have shown that separate elements specify lineage restriction and expression boundaries of Hoxa-7. In particular 3.6 kb of 5' flanking sequences were sufficient to establish an anterior boundary of Hoxa-7 gene expression. To identify the minimal regulatory element specifying the anterior boundary of expression, transgenic mice were generated carrying chimeric constructs with deletions of 5' flanking sequences fused to a thymidine kinase minimal promoter/E. coli lacZ reporter construct. By deletion analysis, a 470 bp long control element (AX 470) located 1.6 kb upstream of the transcription start site was identified that directed expression of the beta-galactosidase protein in a pattern reflecting the anterior boundary of expression of the endogenous Hoxa-7 gene. This element was active in either orientation and conferred region-specific expression to unrelated promoters, thereby behaving like an enhancer element. In contrast, transgenic mice carrying further 5' and 3' deletions of the 470 bp long element did not exhibit an anterior boundary of Hoxa-7 expression. Based on these results the minimal control element (AX 470) specifying the anterior boundary of Hox expression was designated as Hoxa-7 enhancer. Furthermore, 3 kb of the human HOXA7 upstream region were sequenced and compared to its mouse homologue in order to identify conserved regions. Sequence comparison revealed motifs that were strongly conserved between both species. The human homologue of the mouse Hoxa-7 enhancer was 70% identical at the nucleotide level and was also capable of directing an anterior boundary in transgenic mice. Using transgenic lines a detailed analysis of the Hoxa-7 enhancer-directed expression during embryogenesis was performed. lacZ expression was first detected in the allantois at day 7.5 p.c. and in mesoderm and ectoderm at day 8.5 of gestation. Between gestational ages E8.5 to E12.5 beta-gal expression was observed in the somites, spinal cord, spinal ganglia and paraxial mesoderm as well as in mesenchymal layers of the kidney. A distinct anterior limit of expression was noted in transgenic lines at level C4 (neural tube) and C5 (spinal ganglia). Our deletion experiments defined a minimal enhancer element specifying the anterior boundary of Hox gene expression in early and late phases of development. Further studies aim at characterizing the trans-acting factors that mediate the spatial and temporal expression of Hox genes in the developing embryo.

Animals↗
PubMed1995

Expression of von Willebrand factor in normal and diseased rat livers and in cultivated liver cells.

Von Willebrand factor (vWf) is an adhesive glycoprotein known to play an important role in hemostasis and in tissue injury. Because the latter process resembles hepatic fibrogenesis, we studied the tissue distribution of vWf in diseased livers. In normal rat liver vWf was strongly expressed in the vascular endothelium and as small spots or fiber-like structures in the hepatic parenchyma. During acute liver injury, pronounced staining was observed within the area of necrosis. In fibrotic livers vWf deposits were distributed predominantly at the scar-parenchyma interface but also within the septum and in sinusoidal lining cells. Testing different liver cell populations in vitro demonstrated that vWf gene expression was limited to endothelial cells (ECs) and, therefore, the latter cell population might represent the vWf-positive cells detected in vivo. The distribution of vWf within fibrotic septa suggests that vWf becomes a component of the extracellular matrix (ECM) in fibrotic livers.

Animals↗
PubMed1994

Entactin gene expression in normal and fibrotic rat liver and in rat liver cells.

BACKGROUND: Entactin, a constituent of basement membranes, is a sulfated glycoprotein with binding sites for laminin, collagen type IV, fibronectin, and cell surfaces. As it is known that excess matrix deposition and sinusoidal basement membrane formation is a central characteristic of liver fibrogenesis, we investigated whether the entactin gene is expressed in normal and in damaged rat liver and which cell types are able to express this gene. In addition, we were interested in the cellular origin and time course of laminin synthesis, a matrix protein closely associated with entactin. EXPERIMENTAL DESIGN: Entactin gene expression was analyzed in normal, acutely and chronically damaged rat livers (CCl4-model) by immunohistochemistry and in situ detection of specific transcripts. Rat fat-storing cells (FSC) (Ito), hepatocytes, Kupffer cells, liver endothelial cells, arterial smooth muscle cells (SMC), and skin fibroblasts (SF) were isolated according to standard techniques. Entactin gene expression in cultured cells was examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of immunoprecipitates, Northern blot analysis, and immunocytochemistry. RESULTS: In normal liver, entactin was detected in the vessel walls as continuous deposits and in a spot-like fashion along the sinusoids. Entactin was detectable among the cells of the inflammatory infiltrates of acutely damaged liver and in connective tissue septa, in the walls of newly formed vessels and bile ducts of fibrotic liver. Laminin distribution in the vessels was similar, but it was additionally present in the space of Dissé of damaged liver. By in situ hybridization, few entactin-positive cells were found in normal liver sections. Strongly positive cells were scattered over the injured parenchyma of acutely and chronically damaged livers. Northern blot analysis of total RNA extracted from normal and damaged liver tissue showed a distinct increase of entactin specific transcripts during development of fibrosis. Hybridization of total RNA from cultured FSC, hepatocytes, Kupffer cells, endothelial cells, SMC, and SF revealed entactin specific mRNA in FSC, SMC, SF, and endothelial cells; laminin mRNA was found in FSC and SF. Synthesis and secretion of both proteins were found in FSC, SMC and SF. Entactin and laminin gene expression increased in parallel to FSC during time in culture. CONCLUSIONS: Among the main liver cells, FSC show the highest entactin gene expression and might therefore play the dominant role in the synthesis of this protein in normal and fibrotic liver. However, endothelial cells and liver myofibroblasts could also contribute to entactin production.

Animals↗
PubMed1993

Coexpression of extracellular matrix glycoproteins undulin and tenascin in human autosomal dominant polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) is the most common entity of cystic diseases of the kidney leading to end-stage renal insufficiency. Changes in extracellular matrix (ECM) are regarded to be an important pathogenic factor connected with the genes assumed to be responsible for human ADPKD. In order to assess the biological significance of altered expression and deposition of ECM glycoproteins for human ADPKD at molecular levels fresh-frozen tissue from ADPKD kidneys, fetal kidneys and normal adult kidneys were comparatively tested by immunohistochemistry for the presence of multifunctional ECM glycoproteins undulin, tenascin and fibronectin, interstitial collagen types I, III and VI and intrinsic basement membrane components laminin and collagen type IV using monoclonal antibodies and polyclonal antisera. Studies were especially focused on ECM glycoproteins undulin and tenascin which in connection with interstitial collagens and fibronectin have specific structural and functional roles in tissue development and differentiation. Cultures of cyst-lining epithelial cells from two polycystic kidneys and autologous fibroblasts were investigated in vitro. By Northern blot analysis mRNA levels of undulin, tenascin and the ECM-regulating growth factor transforming growth factor-beta 1 (TGF-beta 1) were investigated. A strong increase of fibrogenesis was demonstrated in tissue architecture of polycystic kidneys. Immunohistochemically subepithelial fibrous tissue of cyst walls in ADPKD kidneys showed strong coexpression of both undulin and tenascin with marked intensity adjacent to cyst-lining epithelium. In contrast the normal adult human kidney and developmental stages of the fetal kidney showed expression patterns of undulin and tenascin which were significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Adhesion Molecules, Neuronal↗
PubMed1992

[Decompression sickness as differential diagnosis in internal medicine emergency admissions].

Two men (aged 37 years--patient 1, and 26 years--patient 2), both in good health, had dived as a sport to a depth of 40 and 45 m, respectively, reportedly keeping to the prescribed decompression times on their ascent. Patient 1 immediately developed shortness of breath and pain in the chest, later neurological deficits in both legs, as well as faecal and urinary incontinence. Examination 60 h later revealed paraparesis, increased leg proprioceptor reflexes and paraesthesia below the 10th thoracic vertebra, with abnormal posterior column function. After recompression (hyperbaric oxygenation, 6 treatment sessions of 4 h each over 8 days, as prescribed in US Navy Table No. 6) the signs improved and two months later there were no deficits. Patient 2 developed 30 min after a similar dive painful, doughy swellings and redness over the upper ventral half of the thorax and both upper arms. All signs and symptoms disappeared after recompression treatment (hyperbaric oxygenation for 3 h), begun 28 h after the dive. Previously elevated levels for haemoglobin (18.5 g/dl), haematocrit (0.56) and red blood corpuscles (5.98 x 10(6)/microliters) returned to normal. The described neurological abnormalities are typical for type II, redness and joint pains for type I decompression sickness.

Adult↗
PubMed1992

The gene of hepatocyte growth factor is expressed in fat-storing cells of rat liver and is downregulated during cell growth and by transforming growth factor-beta.

Hepatocyte growth factor (HGF) has been detected in non-parenchymal cells but not in hepatocytes. We performed Northern blot analysis of total RNA extracted from rat hepatocytes, Kupffer cells, endothelial cells and fat-storing (Ito-) cells. Total RNA was extracted from fat-storing cells at different times after isolation and from cells treated with different amounts of transforming growth factor beta. The RNA was hybridized with HGF, fibronectin-, and alpha-actin-specific cDNA probes, consecutively. We found an abundant amount of HGF mRNA in freshly isolated fat-storing cells, but not in other liver cells. The amount of the HGF transcripts decreases significantly in FSC during the time of culture, while fibronectin gene expression increases and alpha-actin gene expression as well. TGF-beta dramatically inhibits HGF gene expression, but causes an enhanced fibronectin mRNA level. Northern blot hybridisation of total RNA from CCl4-chronically damaged liver with HGF cDNA shows a significant increase of HGF mRNA during development of liver fibrosis. We suggest that in damaged liver either non-parenchymal cells, others than FSC, became able to express the HGF in vivo, or other mediators overcome the inhibitory effect of TGF-beta.

Actins↗
PubMed1992

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.

Animals↗
PubMed1992

Synthesis of undulin by rat liver fat-storing cells: comparison with fibronectin and tenascin.

Fat-storing cells (FSCs) are known to synthesize various components of the hepatic extracellular matrix and thereby play an important role during liver fibrogenesis. The aim of our study was to investigate the synthesis of undulin, a recently described connective tissue protein belonging to the fibronectin-tenascin superfamily of glycoproteins, by fat-storing cells in primary culture. SDS-PAGE analysis of immunoprecipitates from cell layer lysates or media pulse-labeled with radioactive methionine revealed undulin-specific bands A (270 kDa), B1 (190 kDa), and B2 (180 kDa) after reduction. A single undulin-specific transcript was detected at about 7 kb. Undulin synthesized by cell-free translation revealed two polypeptides migrating about 5000 Da below the B1 and B2 subunits. Treatment of FSCs with tunicamycin created two novel bands slightly below the B2 chain. Since the electrophoretic patterns of undulin chains recovered by cell-free translation and tunicamycin treatment of cells were very similar we suggest that N-glycosylation is the major post-translational processing event. Newly synthesized undulin was detected after 30 min of pulse labeling in the cell layer fraction and was secreted into the medium at a slower rate than fibronectin. In contrast to fibronectin and tenascin, undulin was already synthesized by freshly isolated FSCs and during the early stage of primary FSC culture ("resting" cells), supporting the hypothesis that undulin is associated with a differentiated mesenchyma. However, in analogy to fibronectin and tenascin, undulin was also synthesized by "activated" FSCs, indicating that undulin might also be of importance in dedifferentiated tissues.

Animals↗
PubMed1992

Synthesis of cellular fibronectin by rat liver fat-storing (Ito) cells: regulation by cytokines.

Fibronectins are multifunctional extracellular matrix glycoproteins that seem to play a pacemaker role in liver fibrogenesis. The expression of cellular fibronectin by rat liver fat-storing cells in primary culture and their modulation by cytokines was studied. Cellular fibronectin was localized in the cytoplasm and on the surface of cultured fat-storing cells as well as in extracellular matrix fibrils by indirect immunofluorescence. Immunoprecipitation of endogenously labeled fibronectin using type specific antibodies showed the synthesis and secretion of cellular fibronectin by fat-storing cells in vitro. ED1 positive sequences specific for cellular fibronectin and absent in plasma fibronectin were detected within the total RNA of fat-storing cells. Cellular fibronectin synthesis was severalfold enhanced in "activated" vs. "resting" fat-storing cells. Treatment of fat-storing cells with transforming growth factor beta 1 resulted in a dose dependent increase of fibronectin synthesis. In contrast, interferon gamma inhibited the synthesis of fibronectin. The stimulation of fibronectin synthesis by transforming growth factor beta 1 and the inhibition by interferon gamma might be of importance for pathophysiology and therapy of liver fibrogenesis.

Animals↗
PubMed1992

Differential expression of collagen types I, III, and IV by fat-storing (Ito) cells in vitro.

It has been observed that Ito cells in vitro undergo phenotypical changes ("activation") similar to those noted in vivo during the development of liver fibrosis. Because conflicting data have been published on the amount and different types of collagens synthesized by Ito cells in vitro, collagen biosynthesis was studied at different "activation" stages on both the protein and RNA levels. Immunoprecipitation of endogenously labeled collagen showed that freshly isolated ("resting") Ito cells synthesize mainly collagen type IV. Collagen type I was hardly detectable in the earlier stage of primary culture, but it clearly increased starting 5 days after isolation. Compared with the basal rates measured at day 3 after isolation, collagen types I, III, and IV increased 7.5-, 3.5-, and 1.9-fold, respectively, until day 7 of culture. The relative ratios of newly synthesized collagen types I, III, and IV on day 3 after isolation were approximately 10%, 45%, and 45%, and they changed to 45%, 40%, and 15% on day 7 of primary culture. On the RNA level, freshly isolated Ito cells contained predominantly collagen type IV- and III-specific transcripts. By densitometric analysis, collagen type I, III, and IV messenger RNAs increased 6.2-, 2.5-, and 3.5-fold from day 3 to day 7 of primary culture. These results indicate that "resting" Ito cells synthesize primarily collagen type IV and could be a major cellular source of this basement membrane component in normal liver. "Activated" Ito cells switch to the synthesis of the interstitial collagen types I and III and might be mainly responsible for the accumulation of collagen types I and III in fibrotic liver diseases.

Adipose Tissue↗