Desmin distinguishes cultured fat-storing cells from myofibroblasts, smooth muscle cells and fibroblasts in the rat

HEARTSVG: a fast and accurate method for identifying spatially variable genes in large-scale spatial transcriptomics

Identifying spatially variable genes (SVGs) is crucial for understanding the spatiotemporal characteristics of diseases and tissue structures, posing a distinctive challenge in spatial transcriptomics research. We propose HEARTSVG, a distribution-free, test-based method for fast and accurately identifying spatially variable genes in large-scale spatial transcriptomic data. Extensive simulations demonstrate that HEARTSVG outperforms state-of-the-art methods with higherF 1 scores (averageF 1 Score=0.948), improved computational efficiency, scalability, and reduced false positives (FPs). Through analysis of twelve real datasets from various spatial transcriptomic technologies, HEARTSVG identifies a greater number of biologically significant SVGs (average AUC = 0.792) than other comparative methods without prespecifying spatial patterns. Furthermore, by clustering SVGs, we uncover two distinct tumor spatial domains characterized by unique spatial expression patterns, spatial-temporal locations, and biological functions in human colorectal cancer data, unraveling the complexity of tumors.

Insight into the Characteristics of Novel Desmin-Immunopositive Perivascular Cells of the Anterior Pituitary Gland Using Transmission and Focused Ion Beam Scanning Electron Microscopy

Recently, another new cell type was found in the perivascular space called a novel desmin-immunopositive perivascular (DIP) cell. However, the differences between this novel cell type and other nonhormone-producing cells have not been clarified. Therefore, we introduced several microscopic techniques to gain insight into the morphological characteristics of this novel DIP cell. We succeeded in identifying novel DIP cells under light microscopy using desmin immunocryosection, combining resin embedding blocks and immunoelectron microscopy. In conventional transmission electron microscopy, folliculostellate cells, capsular fibroblasts, macrophages, and pericytes presented a flat cisternae of rough endoplasmic reticulum, whereas those of novel DIP cells had a dilated pattern. The number of novel DIP cells was greatest in the intact rats, though nearly disappeared under prolactinoma conditions. Additionally, focused ion beam scanning electron microscopy showed that these novel DIP cells had multidirectional processes and some processes reached the capillary, but these processes did not tightly wrap the vessel, as is the case with pericytes. Interestingly, we found that the rough endoplasmic reticulum was globular and dispersed throughout the cytoplasmic processes after three-dimensional reconstruction. This study clearly confirms that novel DIP cells are a new cell type in the rat anterior pituitary gland, with unique characteristics.

Antifibrotic Effects of Amyloid-Beta and Its Loss in Cirrhotic Liver

The function and regulation of amyloid-beta (Aβ) in healthy and diseased liver remains unexplored. Because Aβ reduces the integrity of the blood-brain barrier we have examined its potential role in regulating the sinusoidal permeability of normal and cirrhotic liver. Aβ and key proteins that generate (beta-secretase 1 and presenilin-1) and degrade it (neprilysin and myelin basic protein) were decreased in human cirrhotic liver. In culture, activated hepatic stellate cells (HSC) internalized Aβ more efficiently than astrocytes and HSC degraded Aβ leading to suppressed expression of α-smooth muscle actin (α-SMA), collagen 1 and transforming growth factor β (TGFβ). Aβ also upregulated sinusoidal permeability marker endothelial NO synthase (eNOS) and decreased TGFβ in cultured human liver sinusoidal endothelial cells (hLSEC). Liver Aβ levels also correlate with the expression of eNOS in transgenic Alzheimer’s disease mice and in human and rodent cirrhosis/fibrosis. These findings suggest a previously unexplored role of Aβ in the maintenance of liver sinusoidal permeability and in protection against cirrhosis/fibrosis via attenuation of HSC activation.

Fibroblasts in Pancreatic Ductal Adenocarcinoma: Biological Mechanisms and Therapeutic Targets

The desmoplastic reaction of pancreas cancer may begin as a wound healing response to the nascent neoplasm, but it soon creates an insidious shelter that can sustain the growing tumor and rebuff therapy. Among the many cell types subverted by transformed epithelial cells, fibroblasts are recruited and activated to lay a foundation of extracellular matrix proteins and glycosaminoglycans that alter tumor biophysics and signaling. Their near-universal presence in pancreas cancer and ostensible support of disease progression make fibroblasts attractive therapeutic targets. More recently, however, it has also become apparent that diverse subpopulations of fibroblasts with distinct phenotypes and secretomes inhabit the stroma, and that targeted depletion of particular fibroblast subsets could either provide substantial therapeutic benefit or accelerate disease progression. An improved characterization of these fibroblast subtypes, along with their potential relationships to tumor subtypes and mutational repertoires, is needed in order to make anti-fibroblast therapies clinically viable.

Identification of markers for quiescent pancreatic stellate cells in the normal human pancreas

Pancreatic stellate cells (PSCs) play a central role as source of fibrogenic cells in pancreatic cancer and chronic pancreatitis. In contrast to quiescent hepatic stellate cells (qHSCs), a specific marker for quiescent PSCs (qPSCs) that can be used in formalin-fixed and paraffin embedded (FFPE) normal human pancreatic tissue has not been identified. The aim of this study was to identify a marker enabling the identification of qPSCs in normal human FFPE pancreatic tissue. Immunohistochemical (IHC), double-IHC, immunofluorescence (IF) and double-IF analyses were carried out using a tissue microarray consisting of cores with normal human pancreatic tissue. Cores with normal human liver served as control. Antibodies directed against adipophilin, α-SMA, CD146, CRBP-1, cytoglobin, desmin, GFAP, nestin, S100A4 and vinculin were examined, with special emphasis on their expression in periacinar cells in the normal human pancreas and perisinusoidal cells in the normal human liver. The immunolabelling capacity was evaluated according to a semiquantitative scoring system. Double-IF of the markers of interest together with markers for other periacinar cells was performed. Moreover, the utility of histochemical stains for the identification of human qPSCs was examined, and their ultrastructure was revisited by electron microscopy. Adipophilin, CRBP-1, cytoglobin and vinculin were expressed in qHSCs in the liver, whereas cytoglobin and adipophilin were expressed in qPSCs in the pancreas. Adipophilin immunohistochemistry was highly dependent on the preanalytical time interval (PATI) from removal of the tissue to formalin fixation. Cytoglobin, S100A4 and vinculin were expressed in periacinar fibroblasts (FBs). The other examined markers were negative in human qPSCs. Our data indicate that cytoglobin and adipophilin are markers of qPSCs in the normal human pancreas. However, the use of adipophilin as a qPSC marker may be limited due to its high dependence on optimal PATI. Cytoglobin, on the other hand, is a sensitive marker for qPSCs but is expressed in FBs as well.

The stellate cell system (vitamin A-storing cell system)

Past, present, and future research into hepatic stellate cells (HSCs, also called vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells, or Ito cells) are summarized and discussed in this review. Kupffer discovered black-stained cells in the liver using the gold chloride method and named them stellate cells (Sternzellen in German) in 1876. Wake rediscovered the cells in 1971 using the same gold chloride method and various modern histological techniques including electron microscopy. Between their discovery and rediscovery, HSCs disappeared from the research history. Their identification, the establishment of cell isolation and culture methods, and the development of cellular and molecular biological techniques promoted HSC research after their rediscovery. In mammals, HSCs exist in the space between liver parenchymal cells (PCs) or hepatocytes and liver sinusoidal endothelial cells (LSECs) of the hepatic lobule, and store 50-80% of all vitamin A in the body as retinyl ester in lipid droplets in the cytoplasm. SCs also exist in extrahepatic organs such as pancreas, lung, and kidney. Hepatic (HSCs) and extrahepatic stellate cells (EHSCs) form the stellate cell (SC) system or SC family; the main storage site of vitamin A in the body is HSCs in the liver. In pathological conditions such as liver fibrosis, HSCs lose vitamin A, and synthesize a large amount of extracellular matrix (ECM) components including collagen, proteoglycan, glycosaminoglycan, and adhesive glycoproteins. The morphology of these cells also changes from the star-shaped HSCs to that of fibroblasts or myofibroblasts.

Bile duct ligation in mice: induction of inflammatory liver injury and fibrosis by obstructive cholestasis

In most vertebrates, the liver produces bile that is necessary to emulsify absorbed fats and enable the digestion of lipids in the small intestine as well as to excrete bilirubin and other metabolic products. In the liver, the experimental obstruction of the extrahepatic biliary system initiates a complex cascade of pathological events that leads to cholestasis and inflammation resulting in a strong fibrotic reaction originating from the periportal fields. Therefore, surgical ligation of the common bile duct has become the most commonly used model to induce obstructive cholestatic injury in rodents and to study the molecular and cellular events that underlie these pathophysiological mechanisms induced by inappropriate bile flow. In recent years, different surgical techniques have been described that either allow reconnection or reanastomosis after bile duct ligation (BDL), e.g., partial BDL, or other microsurgical methods for specific research questions. However, the most frequently used model is the complete obstruction of the common bile duct that induces a strong fibrotic response after 21 to 28 days. The mortality rate can be high due to infectious complications or technical inaccuracies. Here we provide a detailed surgical procedure for the BDL model in mice that induce a highly reproducible fibrotic response in accordance to the 3R rule for animal welfare postulated by Russel and Burch in 1959.

Dynamic expression of desmin, α-SMA and TGF-β1 during hepatic fibrogenesis induced by selective bile duct ligation in young rats

We previously described a selective bile duct ligation model to elucidate the process of hepatic fibrogenesis in children with biliary atresia or intrahepatic biliary stenosis. Using this model, we identified changes in the expression of alpha smooth muscle actin (α-SMA) both in the obstructed parenchyma and in the hepatic parenchyma adjacent to the obstruction. However, the expression profiles of desmin and TGF-β1, molecules known to be involved in hepatic fibrogenesis, were unchanged when analyzed by semiquantitative polymerase chain reaction (RT-PCR). Thus, the molecular mechanisms involved in the modulation of liver fibrosis in this experimental model are not fully understood. This study aimed to evaluate the molecular changes in an experimental model of selective bile duct ligation and to compare the gene expression changes observed in RT-PCR and in real-time quantitative PCR (qRT‐PCR). Twenty-eight Wistar rats of both sexes and weaning age (21-23 days old) were used. The rats were separated into groups that were assessed 7 or 60 days after selective biliary duct ligation. The expression of desmin, α-SMA and TGF-β1 was examined in tissue from hepatic parenchyma with biliary obstruction (BO) and in hepatic parenchyma without biliary obstruction (WBO), using RT-PCR and qRT‐PCR. The results obtained in this study using these two methods were significantly different. The BO parenchyma had a more severe fibrogenic reaction, with increased α-SMA and TGF-β1 expression after 7 days. The WBO parenchyma presented a later, fibrotic response, with increased desmin expression 7 days after surgery and increased α-SMA 60 days after surgery. The qRT‐PCR technique was more sensitive to expression changes than the semiquantitative method.

TEMPORARY REMOVAL: CD271 identifies functional human hepatic stellate cells, which localize in peri-sinusoidal and portal areas in liver after partial hepatectomy

BACKGROUND AIMS

Hepatic stellate cells (HSCs) are liver-resident mesenchymal cells involved in essential processes in the liver. However, knowledge concerning these cells in human livers is limited because of the lack of a simple isolation method.

METHODS

We isolated fetal and adult human liver cells by immunomagnetic beads coated with antibodies to a mesenchymal stromal cell marker (CD271) to enrich a population of HSCs. The cells were characterized by cell cultivation, immunocytochemistry, flow cytometry, reverse-transcription polymerase chain reaction and immunohistochemistry. Cells were injected into nude mice after partial hepatectomy to study in vivo localization of the cells.

RESULTS

In vitro, CD271(+) cells were lipid-containing cells expressing several HSC markers: the glial fibrillary acidic protein, desmin, vimentin and α-smooth muscle actin but negative for CK8, albumin and hepatocyte antigen. The cells produced several inflammatory cytokines such as interleukin (IL)-6, IL-1A, IL-1B and IL-8 and matrix metalloproteinases MMP-1 and MMP-3 and inhibitors TIMP-1 and TIMP-2. In vivo, fetal CD271(+) cells were found in the peri-sinusoidal space and around portal vessels, whereas adult CD271(+) cells were found mainly in the portal connective tissue and in the walls of the portal vessels, which co-localized with α-smooth muscle actin or desmin. CD271(-) cells did not show this pattern of distribution in the liver parenchyma.

CONCLUSIONS

The described protocol establishes a method for isolation of mesenchymal cell precursors for hepatic stellate cells, portal fibroblasts and vascular smooth muscle cells. These cells provide a novel culture system to study human hepatic fibrogenesis, gene expression and transcription factors controlling HSC regulation.

Hepatic stellate cell (vitamin A-storing cell) and its relative--past, present and future

HSCs (hepatic stellate cells) (also called vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells or Ito cells) exist in the space between parenchymal cells and liver sinusoidal endothelial cells of the hepatic lobule and store 50-80% of vitamin A in the whole body as retinyl palmitate in lipid droplets in the cytoplasm. In physiological conditions, these cells play pivotal roles in the regulation of vitamin A homoeostasis. In pathological conditions, such as hepatic fibrosis or liver cirrhosis, HSCs lose vitamin A and synthesize a large amount of extracellular matrix components including collagen, proteoglycan, glycosaminoglycan and adhesive glycoproteins. Morphology of these cells also changes from the star-shaped SCs (stellate cells) to that of fibroblasts or myofibroblasts. The hepatic SCs are now considered to be targets of therapy of hepatic fibrosis or liver cirrhosis. HSCs are activated by adhering to the parenchymal cells and lose stored vitamin A during hepatic regeneration. Vitamin A-storing cells exist in extrahepatic organs such as the pancreas, lungs, kidneys and intestines. Vitamin A-storing cells in the liver and extrahepatic organs form a cellular system. The research of the vitamin A-storing cells has developed and expanded vigorously. The past, present and future of the research of the vitamin A-storing cells (SCs) will be summarized and discussed in this review.

Vinculin and cellular retinol-binding protein-1 are markers for quiescent and activated hepatic stellate cells in formalin-fixed paraffin embedded human liver

Hepatic stellate cells (HSCs) have important roles in the pathogenesis of liver fibrosis and cirrhosis. As response to chronic injury HSCs are activated and change from quiescent into myofibroblast-like cells. Several HSC-specific markers have been described in rat or mouse models. The aim of our work was to identify the best marker(s) for human HSCs. To this end we used the automated high throughput NexES IHC staining device (Ventana Medical Systems) to incubate sections under standardized conditions. Formalin fixed paraffin embedded (FFPE) normal and diseased human livers were studied. With immunohistochemistry we examined the expression of synemin, desmin, vimentin, vinculin, neurotrophin-3 (NT-3), alpha-smooth muscle actin (alpha-SMA), cellular retinol-binding protein-1 (CRBP-1), glial fibrillary acidic protein (GFAP), cysteine- and glycine-rich protein 2 (CRP2), and cytoglobin/stellate cell activation-associated protein (cygb/STAP). This is the first study in which a series of HSC markers is compared on serial FFPE human tissues. CRBP-1 clearly stains lobular HSCs without reacting with smooth muscle cells (SMCs) and shows variable cholangiocyte positivity. Vinculin has a similar staining pattern as CRBP-1 but additionally stains SMCs, and (myo)fibroblasts. In conclusion, we therefore propose to use CRBP-1 and/or vinculin to stain HSCs in human liver tissues.

Disordered pancreatic inflammatory responses and inhibition of fibrosis in CD39-null mice

BACKGROUND & AIMS

Extracellular nucleotides are released from injured cells and bind purinergic-type 2 receptors (P2-Rs) that modulate inflammatory responses. Ectonucleotidases, such as CD39/nucleoside triphosphate diphosphohydrolase-1, hydrolyze extracellular nucleotides to integrate purinergic signaling responses. Because the role of extracellular nucleotides and CD39 in mediating inflammation and fibrosis are understood poorly, we studied the impact of CD39 gene deletion in a model of pancreatic disease.

METHODS

Pancreatitis was induced by cyclosporine pretreatment, followed by cerulein injections (50 mug/kg, 6 intraperitoneal injections/day, 3 times/wk); mice were killed at day 2, week 3, and week 6. Experimental parameters were correlated with cytokine levels in blood, RNA, and protein expression of purinergic and fibrosis markers in tissues. Immunohistochemistry and pancreatic morphometry of fibrosis were performed in wild-type and CD39-null mice. Effects of CD39 deletion on proliferation of primary pancreatic stellate cells (PSCs) were investigated in vitro.

RESULTS

Wild-type mice developed morphologic features of pancreatitis with the anticipated development of parenchymal atrophy and fibrosis. CD39 and P2-R became overexpressed in vascular and adventitious wild-type tissues. In contrast, CD39-null mice had inflammatory reactions but developed only minor pancreatic atrophy and limited fibrosis. Interferon-gamma became significantly increased in tissues and plasma of CD39-null mice. Wild-type PSCs expressed high levels of CD39 and P2-R. CD39-null PSCs showed decreased rates of proliferation and the expression of procollagen-alpha1 was inhibited significantly in vitro (P < .03).

CONCLUSIONS

CD39 deletion decreases fibrogenesis in experimental pancreatitis. Our data implicate extracellular nucleotides as modulators of PSC proliferation and collagen production in pancreatitis.

Hepatic stellate cells and liver fibrosis

Substantial evidence now exists to recognize hepatic stellate cells (HSCs) as the main matrix-producing cells in the process of liver fibrosis. Liver injury of any etiology will ultimately lead to activation of HSCs, which undergo transdifferentiation to fibrogenic myofibroblast-like cells. Quantitative analysis of HSC activation by immunohistochemistry has been shown to be useful in predicting the rate of progression of liver fibrosis in some clinical situations. In the activation process, transforming growth factor beta is thought to be the main mediator of fibrogenesis and platelet-derived growth factor is the major inducer of HSC proliferation. Different platelet-derived growth factor and transforming growth factor beta inhibitors have been shown to effectively prevent liver fibrosis in animal models and represent promising therapeutic agents for humans.

Thy1-positive mesenchymal cells promote the maturation of CD49f-positive hepatic progenitor cells in the mouse fetal liver

Previously, we reported a system to enrich mouse fetal hepatic progenitor cells (HPCs) by forming cell aggregates. In this study, we sorted two cell populations, CD49f(+)Thy1(-)CD45(-) cells (CD49f-positive cells) and CD49f(+/-)Thy1(+)CD45(-) cells (Thy1-positive cells), from the cell aggregates using a flow cytometer. CD49f-positive cells stained positive for endodermal specific markers such as alpha-fetoprotein (AFP), albumin (ALB), and cytokeratin 19 (CK19), and are thus thought to be HPCs. However, Thy1-positive cells were a morphologically heterogeneous population; reverse-transcription polymerase chain reaction (RT-PCR) and immunocytochemical analyses revealed the expression of mesenchymal cell markers such as alpha-smooth muscle actin, desmin, and vimentin, but not of AFP, ALB, or CK19. Therefore, Thy1-positive cells were thought to be of a mesenchymal lineage. When these two cell populations were co-cultured, the CD49f-positive colonies matured morphologically and stored a significant amount of glycogen. Furthermore, real-time RT-PCR demonstrated an increased expression of tyrosine amino transferase and tryptophan oxygenase mRNA, and transmission electron microscopy confirmed that co-cultured cells produced mature hepatocytes. However, when CD49f-positive cells were cultured alone or when the two populations were cultured separately, the CD49f-positive cells did not mature. These results indicate that CD49f-positive cells are primitive hepatic endodermal cells with the capacity to differentiate into hepatocytes, and that Thy1-positive cells promote the maturation of CD49f-positive cells by direct cell-to-cell contact. In conclusion, we were able to isolate CD49f-positive primitive hepatic endodermal cells and Thy1-positive mesenchymal cells and to demonstrate the requirement of cell-to-cell contact between these cell types for the maturation of the hepatic precursors.

Cellular retinol-binding protein-1 expression in normal and fibrotic/cirrhotic human liver: different patterns of expression in hepatic stellate cells and (myo)fibroblast subpopulations

BACKGROUND/AIMS

Cellular retinol-binding protein-1 (CRBP-1) which is involved in vitamin A metabolism is highly expressed in liver cells, particularly in hepatic stellate cells (HSCs). In this work, the CRBP-1 expression was studied by immunohistochemistry in the different liver cell populations, including HSCs and portal fibroblasts, of normal liver and of fibrotic and cirrhotic liver.

METHODS

Normal liver, fibrotic liver in different stages and cirrhotic liver sections were studied. Immunohistochemistry was performed using antibodies against CRBP-1, alpha-smooth muscle actin (SMA), CD 68 and CD 34.

RESULTS

In normal liver, quiescent HSCs expressed CRBP-1, while portal fibroblasts did not. In fibrotic or cirrhotic liver, activated HSCs co-expressed CRBP-1 and alpha-SMA; a variable proportion of portal and septal (myo)fibroblasts, more important in cirrhosis, neo-expressed both CRBP-1 and alpha-SMA. Biliary epithelial cells both in normal and pathological situations expressed CRBP-1. Neither Kupffer cells, nor endothelial cells showed CRBP-1 expression.

CONCLUSIONS

Our study demonstrates that CRBP-1 is a good marker to identify HSC in normal human liver. Furthermore, in fibrotic or cirrhotic liver, the different patterns of expression for CRBP-1 and alpha-SMA allow the distinction of different subsets of fibroblastic cells involved in fibrogenesis and septa formation.

Effects of lipopolysaccharides stimulated Kupffer cells on activation of rat hepatic stellate cells

AIM: To study the effects of Kupffer cell-conditioned medium (KCCM) derived from lipopolysaccharide (LPS) treatment on proliferation of rat hepatic stellate cells (HSC).

METHODS: HSC and Kupffer cells were isolated from the liver of Wistar rats by in situ perfusion with pronase and collagenase and density gradient centrifugation with Nycodenz and cultured. KCCM was prepared and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay was used to detect HSC proliferation. The content of type IV collagen and laminin secreted by HSC in the HSC-conditioned medium was determined by radioimmunoassay. TGF-β₁ production in the KCCM was detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS: HSC and Kupffer cells isolated had high purity. One microgram per mililiter LPS-activated KCCM and unstimulated KCCM could significantly promote HSC proliferation [0.132 ± 0.005 and 0.123 ± 0.008 vs control group (0.100 ± 0.003), P < 0.01], and there was a difference between them (P < 0.05). Ten microgram per mililiter LPS-activated KCCM (0.106 ± 0.010) was unable to promote HSC proliferation (P > 0.05). Adding anti-TGF-β₁ antibodies could suppress the proliferation promoted by unstimulated KCCM and LPS (1 μg/ml)-activated KCCM (0.109 ± 0.009 vs 0.123 ± 0.008, 0.115 ± 0.008 vs 0.132 ± 0.005, P < 0.01). LPS (1 μg/ml or 10 μg/ml) could not promote HSC proliferation immediately (0.096 ± 0.003 and 0.101 ± 0.004 vs 0.100 ± 0.003, P > 0.05). There was a parallel behavior between HSC proliferation and increased ECM level. One microgram per mililiter LPS-activated KCCM contained a larger amount of TGF-β₁ than unstimulated KCCM.

CONCLUSION: The technique for isolation of HSC and Kupffer cells described here is simple and reliable. KCCM stimulated by LPS may promote HSC proliferation and collagen accumulation, which are associated with hepatic fibrogenesis.

Neuroregulation of the neuroendocrine compartment of the liver

Liver progenitor cells as well as hepatic stellate cells have neuroendocrine features. Progenitor cells express chromogranin-A and neural cell adhesion molecule, parathyroid hormone-related peptide, S-100 protein, neurotrophins, and neurotrophin receptors, while hepatic stellate cells express synaptophysin, glial fibrillary acidic protein, neural cell adhesion molecule, nestin, neurotrophins, and their receptors. This phenotype suggests that these cell types form a neuroendocrine compartment of the liver, which could be under the control of the central nervous system. We recently showed that the parasympathetic nervous system promotes progenitor cell expansion after liver injury, since selective vagotomy reduces the number of progenitor cells after chemical injury in the rat. Similarly, after transplantation, which surgically denervates the liver, human livers that develop hepatitis have fewer progenitor cells than native, fully innervated livers with similar degrees of liver injury. There is also accumulating experimental evidence linking the autonomic system, in particular the sympathetic nervous system (SNS), with the pathogenesis of cirrhosis and its complications. Recently, it has been shown that hepatic stellate cells themselves respond to neurotransmitters. Moreover, inhibition of the SNS reduced fibrosis in carbon tetrachloride-induced liver injury. In view of the denervated state of transplanted livers, it is very important to unravel the neural control mechanisms of regeneration and fibrogenesis. Moreover, since there is a shortage of donor organs, a better understanding of the mechanisms of regeneration could have therapeutic possibilities, which could even obviate the need for orthotopic liver transplantation.

Vinculin: a novel marker for quiescent and activated hepatic stellate cells in human and rat livers

In liver injuries, the quiescent hepatic stellate cells (HSCs) promptly change to activated HSCs, which are easily identified by the intense immunoreactivity for alpha-smooth muscle actin. However, reproducible markers for quiescent HSCs in formalin-fixed, paraffin-embedded liver tissue sections have not yet been reported. We immunohistochemically examined the expression of vinculin, one major protein of dense plaques, on cultured LI90 cells and on HSCs in normal and diseased human and rat livers. In cultured LI90 cells, vinculin appeared as small linear patches. Although vinculin was consistently negative in the routine liver tissue sections, an antigen retrieval technique using microwave oven heating yielded excellent effects. Using this technique, the formalin-fixed, paraffin-embedded human and rat normal liver tissue sections showed the vinculin immunoreactivity along the sinusoidal wall. Immunoelectron microscopic observation of hepatic parenchyma demonstrated that the vinculin was exclusively expressed in quiescent HSCs. In fetal rat livers, vinculin-positive quiescent HSCs gradually increased in number with gestation. In diseased livers the activated HSCs showed more intense immunoreaction for vinculin. These results indicate that, using microwave pretreatment, vinculin is expressed in quiescent and activated HSCs in routinely processed liver tissue sections. It could allow us to evaluate the development and distribution of quiescent HSCs and to examine the relationship between quiescent and activated HSCs.

The myofibroblastic conversion of peribiliary fibrogenic cells distinct from hepatic stellate cells is stimulated by platelet-derived growth factor during liver fibrogenesis

The origin of myofibroblasts and the factors promoting their differentiation during liver fibrogenesis remain uncertain. During biliary-type fibrogenesis, the proliferation and chemoattraction of hepatic stellate cells (HSC) toward bile ducts is mediated by platelet-derived growth factor (PDGF), while myofibroblastic conversion of peribiliary cells distinct from HSC also occurs. We herein examined the phenotype of these peribiliary myofibroblasts as compared with myofibroblastic HSC and tested whether their differentiation was affected by PDGF. Biliary-type liver fibrogenesis was induced by common bile duct ligation in rats. After 48 hours, periductular fibrosis in portal tracts colocalized with smooth muscle alpha-actin-immunoreactive myofibroblasts, the majority of which were desmin negative. Simultaneously, in sinusoids, desmin immunoreactivity was induced in a large number of HSC, which were smooth muscle alpha-actin negative. Cultures of peribiliary myofibroblasts were expanded from isolated bile duct segments and compared with myofibroblastic HSC. Peribiliary myofibroblasts outgrowing from bile duct segments expressed smooth muscle alpha-actin, alpha1 (I) collagen mRNA, and PDGF receptor-beta subunit. Desmin immunoreactivity gradually decreased in cultured peribiliary myofibroblasts, contrasting with constant labeling of all myofibroblastic HSC. In addition, IL-6 expression in peribiliary myofibroblasts was up to 100-fold lower than in myofibroblastic HSC, whereas the expression of the complement-activating protease P100 in both cell types showed little difference and that of the extracellular matrix component fibulin 2 was similar. The expression of smooth muscle alpha-actin protein in cultured peribiliary myofibroblasts was stimulated by PDGF-BB and inhibited by STI571, a PDGF receptor tyrosine kinase inhibitor, whereas in bile duct-ligated rats, the administration of STI571 caused a significant decrease in peribiliary smooth muscle alpha-actin immunoreactivity, and to a lesser extent, a decrease in peribiliary fibrosis. These results indicate that peribiliary cells distinct from HSC undergo a PDGF-mediated conversion into myofibroblasts expressing IL-6 at lower levels than myofibroblastic HSC and contribute to the initial formation of biliary-type liver fibrosis.

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.

Dilinoleoylphosphatidylcholine prevents transforming growth factor-beta1-mediated collagen accumulation in cultured rat hepatic stellate cells

Polyenylphosphatidylcholine (PPC), a mixture of polyunsaturated phosphatidylcholines, protects against alcoholic and nonalcoholic liver fibrosis in baboons and rats, respectively. In this study, we assessed the antifibrogenic action of dilinoleoylphosphatidylcholine (DLPC), the main phosphatidylcholine species of PPC, against transforming growth factor-beta1-mediated expression of alpha1(I) procollagen, tissue inhibitor of metallopreoteinase-1 (TIMP-1) and matrix metalloproteinase-13 (MMP-13) in cultured rat hepatic stellate cells (HSCs). In primary culture-activated HSCs, TGF-beta1 up-regulated the alpha1(I) procollagen mRNA level with a concomitant increase in type I collagen accumulation in culture media. Whereas TIMP-1 mRNA levels and TIMP-1 accumulation in media were also increased by TGF-beta1, MMP-13 mRNA expression and MMP-13 concentration in media were not altered. DLPC fully blocked TGF-beta1-induced increase in alpha1(I) procollagen mRNA expression and decreased collagen accumulation in media. Whereas TIMP-1 mRNA level and TIMP-1 accumulation in media were decreased by DLPC, MMP-13 mRNA expression and MMP-13 concentration in media were not changed by this treatment. Palmitoyl-linoleoylphosphatidylcholine (PLPC), the second most abundant component of PPC, had no effect on the concentrations of collagen, TIMP-1, and MMP-13 in HSC culture. We conclude that DLPC prevents TGF-beta1-mediated HSC fibrogenesis through down-regulation of alpha1(I) procollagen and TIMP-1 mRNA expression. The latter effect leads to a decreased accumulation of TIMP-1 that, in the presence of unchanged MMP-13 mRNA expression and MMP-13 concentration, results in a larger ratio of MMP-13/TIMP-1 concentrations in the culture media, favoring collagen degradation and lesser collagen accumulation. This effect of DLPC may explain, at least in part, the antifibrogenic action of PPC against alcoholic and other fibrotic disorders of the liver.

Cystic degeneration/Spongiosis hepatis in rats

Cystic degeneration/spongiosis hepatis in rats has been proposed to be a preneoplastic and/or neoplastic lesion by some authors, because of its proliferative properties and persistent increased cell turnover rate in stop experiments using hepatocarcinogens, and the assumption that it can develop into a sarcoma. The neoplastic potential of cystic degeneration is questioned in this review article. Cystic degeneration, which appears to derive from altered Ito cells, does not have neoplastic histomorphologic characteristics, although it may be composed of cells with an increased mitotic index. In this regard, persistent proliferation is also seen with other nonneoplastic lesions. Arguments are presented to show that the induced, probably extremely rare sarcoma that was associated with cystic degeneration most likely derives from the very rare induced spherical Ito-cell aggregate with an unusually high cellular turnover rate in rats treated with hepatocarcinogens, and not from cystic degeneration. Also, in none of 12 referenced standard oncogenicity studies with chemically induced cystic degeneration was the lesion associated with mesenchymal (Ito-cell) tumors. Consequently, evidence is lacking that cystic degeneration in rats should be classified as a preneoplastic or neoplastic lesion. The 12 oncogenicity studies in rats with induced cystic degeneration showed a marked sex predilection, with males more likely to develop either spontaneous or chemically induced lesions. In these 12 studies, cystic degeneration was more often associated with hepatocellular hypertrophy or hepatotoxicity. rather than hepatocarcinogenicity. Thus, it is concluded that hepatocarcinogens induce cystic degeneration, not because they are carcinogenic. but because they have other effects on the liver, and that cystic degeneration may be a secondary/reparative change. Cystic degeneration in fish parallels the situation in rats in many respects, yet the existence of the lesion in other species, including man, is not as well supported. Based on the data presented in this review, spontaneous and induced cystic degeneration in rats and fish is not a preneoplastic or neoplastic lesion and risk assessment for man can be based on no-effect levels and safety margins, as for other nonneoplastic adverse effects that have no counterpart in man.

Hepatic stellate cell/myofibroblast subpopulations in fibrotic human and rat livers

BACKGROUND/AIMS

Hepatic stellate cells (HSC) are commonly considered the precursor population of septal myofibroblasts (MF) in cirrhosis. We studied the distribution and expression profile of mesenchymal (myo)fibroblast-like populations in fibrotic and cirrhotic liver, in an attempt to elucidate their possible interrelationships.

METHODS

Fibrotic/cirrhotic livers (from 22 human explants and from two rat models: carbon tetrachloride intoxication, bile duct-ligation) were studied by means of immunohistochemistry (single and double immunostaining) with antibodies raised against desmin, alpha-smooth muscle actin (alpha SMA), glial fibrillary acidic protein (GFAP), neural-cell adhesion molecule (N-CAM), synaptophysin, neurotrophins, neurotrophin receptors and alpha B-crystallin (ABCRYS).

RESULTS

Septal MF showed the same expression profile as portal MF, in human and rat, being alpha SMA/ABCRYS/brain-derived nerve growth factor/GFAP-expression, with additional N-CAM- and desmin-expression in rat portal/septal MF. Perisinusoidally located HSC stained with all tested markers, MF at the septal/parenchymal interface showed an expression profile, intermediate between the profiles of HSC and portal/septal MF.

CONCLUSIONS

In advanced fibrosis and in cirrhosis, regardless of cause or species, three distinct mesenchymal (myo)fibroblast-like liver cell subpopulations can be discerned: portal/septal MF, interface MF and perisinusoidally located HSC. The fact that septal MF share more characteristics with portal MF than with HSC might suggest descent.

Synaptophysin: A novel marker for human and rat hepatic stellate cells

Synaptophysin is a protein involved in neurotransmitter exocytosis and is a neuroendocrine marker. We studied synaptophysin immunohistochemical expression in 35 human liver specimens (normal and different pathological conditions), in rat models of galactosamine hepatitis and carbon tetrachloride-induced cirrhosis, and in freshly isolated rat stellate cells. Synaptophysin reactivity was present in perisinusoidal stellate cells in both human and rat normal liver biopsies. The number of synaptophysin-reactive perisinusoidal cells increased in pathological conditions. Double staining for alpha-smooth muscle actin and synaptophysin, detected by confocal laser scanning microscopy, unequivocally demonstrated colocalization of both markers in lobular stellate cells. In addition, freshly isolated rat stellate cells expressed synaptophysin mRNA (detected by polymerase chain reaction) and protein. Finally, electron microscopy showed the presence of small electron translucent vesicles, comparable to the synaptophysin-reactive synaptic vesicles in neurons, in stellate cell projections. We conclude that synaptophysin is a novel marker for quiescent as well as activated hepatic stellate cells. Together with the stellate cell's expression of neural cell adhesion molecule, glial fibrillary acidic protein, and nestin, this finding raises questions about its embryonic origin and its differentiation. In addition, the presence of synaptic vesicles in stellate cell processes suggests a hitherto unknown mechanism of interaction with neighboring cells.

Progelatinase A is produced and activated by rat hepatic stellate cells and promotes their proliferation

Activated hepatic stellate cells (HSCs) are a potential source of gelatinase A, which accumulates in fibrotic livers. Progelatinase A activation requires its binding to a complex of membrane-type matrix metalloproteinase (MT-MMP) and tissue inhibitor of metalloproteinases (TIMP)-2. These studies examine gelatinase A, MT1-MMP, and TIMP-2 synthesis by HSCs during activation in vitro and the potential role of gelatinase A in promoting HSC proliferation. Gelatinase A, MT1-MMP, and TIMP-2 messenger RNA (mRNA) were all upregulated in HSCs activated on plastic over 5 to 14 days. Gelatinase A expression was maximal at 7 days of culture, coinciding with the peak of HSC proliferation and the onset of procollagen I and alpha-smooth muscle actin (alpha-SMA) mRNA expression. Active forms of gelatinase A of 62 kd and 66 kd were secreted by activated HSCs and reached a maximum of 12.1% of total enzyme in 14-day culture supernatants. Treatment of HSCs with concanavalin A (con A) induced activation of MT1-MMP and enhanced secretion of activated gelatinase A, which reached a maximum of 44.4% of the total enzyme secreted into culture supernatants using 30 microgram/mL con A. [(14)C]-gelatin degradation assays confirmed the presence of gelatinolytic activity in activated HSC supernatants, which reached a maximum level at 7 days of culture. Antisense oligonucleotide inhibition of endogenous progelatinase A production, or the MMP inhibitor 1,10-phenanthroline inhibited (3)H-thymidine incorporation into HSC DNA by greater than 50%. We conclude that HSCs produce progelatinase A during activation in vitro and activate this enzyme coincident with MT1-MMP and TIMP-2 synthesis. Gelatinase A activity is required for maximal proliferation of HSCs in vitro suggesting this metalloproteinase is an autocrine proliferation factor for HSCs.

Ito cell tumor: immunohistochemical investigations of a rare lesion in the liver of mice

In 2 lifespan transgeneration experiments using a total of 4,682 CBA/J mice, we observed uncommon lipomatous lesions in the livers of 8 mice independent of the treatment. Macroscopically, the lesions were described as pale white areas (2) or nodules (6) during necropsy. The lesions ranged from 1 to 15 mm in diameter. Microscopically, the lesions consisted of nodular aggregations of round to spindle-shaped cells that partly caused distinct compression of the adjacent hepatic parenchyma. The tumor cells were smaller than hepatocytes and had dark oval nuclei. Many of the more spherical cells contained clear vacuoles of various sizes, which were shown to be lipid droplets by oil red O staining. In addition to Gomori's silver and Masson's trichrome staining, several immunohistochemical stains were used to characterize the origin of the proliferating cells. Tumor cells were labeled by vimentin, actin, desmin, and proliferating cell nuclear antigen. The 2 cell phenotypes showed similar staining characteristics. Increased amounts of laminin and tenascin, 2 extracellular matrix proteins of the liver, were detected within these neoplasms. Summarizing, we suggest that these tumors are of Ito cell origin.

The hepatic stellate (Ito) cell: its role in human liver disease

The hepatic stellate (Ito) cell lies within the space of Disse and has a variety of functions. Stellate cells store vitamin A in characteristic lipid droplets. In the normal human liver, the cells can be identified by the presence of these lipid droplets; in addition, many stellate cells in the normal liver express alpha-smooth muscle actin. In acute liver injury, there is an expansion of the stellate cell population with increased alpha-smooth muscle actin expression; stellate cells appear to play a role in extracellular matrix remodelling after recovery from injury. In chronic liver injury, the stellate cell differentiates into a myofibroblast-like cell with marked expression of alpha-smooth muscle actin and occasional expression of desmin. Myofibroblast-like cells have a high fibrogenic capacity in the chronically diseased liver and are also involved in matrix degradation. In vitamin A intoxication, hypertrophy and proliferation of the stellate and myofibroblast-like cells may lead to non-cirrhotic portal hypertension, fibrosis and cirrhosis. In liver tumours, myofibroblast-like cells are involved in the capsule formation around the tumour and in the production of extracellular matrix within it. The transition of stellate cells into myofibroblast-like cells is regulated by an intricate network of intercellular communication between stellate cells and activated Kupffer cells, damaged hepatocytes, platelets, endothelial and inflammatory cells, involving cytokines and nonpeptide mediators such as reactive oxygen species, eicosanoids and acetaldehyde. The findings suggest that the stellate cell plays an active role in a number of human liver diseases, with a particular reactivity pattern in fibrotic liver disorders.

Adventitial myofibroblasts contribute to neointimal formation in injured porcine coronary arteries

BACKGROUND

The adventitia undergoes remodeling changes after a deep medial coronary injury. Because this process is associated with the formation of adventitial myofibroblasts, which resemble medial smooth muscle (SM) cells, we have examined myofibroblast involvement in the development of neointima.

METHODS AND RESULTS

In a porcine model, severe endoluminal coronary injury resulted in fibroblast proliferation and adventitial remodeling. Significant adventitial responses were associated with increased neointimal formation (P < .01). To examine the contribution of adventitial cells to the development of neointima, proliferating cells were labeled with bromodeoxyuridine (BrdU) at 12 and 24 hours after injury, and their subsequent localization was determined by immunohistochemistry (n = 24). At 2 to 3 days after severe injury, the adventitia contained numerous BrdU-labeled cells (37 +/- 4%), whereas the media demonstrated infrequent labeled cells (4 +/- 1%). Adventitial cells lacked alpha-SM actin and desmin, which distinguished them from medial SM cells. At 7 to 8 days, some labeled cells acquired characteristics of myofibroblasts expressing alpha-SM actin. They were found to translocate to the gap between dissected media and contributed to the formation of neointima (76 +/- 19%). At 18 to 35 days, labeled cells were abundant in the neointima (86 +/- 5%). They showed uniform immunostaining for alpha-SM actin but not for desmin, thereby differing from medial SM cells and blood-borne cells.

CONCLUSIONS

This study demonstrates translocation of adventitial fibroblasts to neointima, their phenotypic modulation to myofibroblasts, and distinct characteristics of myofibroblasts within neointima after severe endoluminal coronary injury. These findings suggest the significance of vascular fibroblasts in the process of arterial repair.

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.

Rat hepatic lipocytes synthesize and secrete transin (stromelysin) in early primary culture

BACKGROUND & AIMS

Hepatic lipocyte proliferation and activation are pivotal in liver fibrosis. Disruption of normal lipocyte-matrix interactions may contribute to this process. The synthesis of transin, which degrades normal liver matrix, by culture-activated hepatic lipocytes was investigated.

METHODS

Lipocytes were isolated by pronase/collagenase perfusion, density gradient centrifugation, and centrifugal elutriation. Transin messenger RNA in lipocytes was analyzed by Northern blotting. Transin activity was analyzed by zymography, Western blotting, immunocytochemistry, and quantitative [14C]beta-casein degradation assay.

RESULTS

Transin messenger RNA was detected in early primary culture (3-5 days) but not in freshly isolated lipocytes or late primary culture. Zymography of lipocyte medium showed caseinolytic activity (relative molecular weight, 57 kilodaltons and 60 kilodaltons) inhibited by ethyl-enediaminetetraacetic acid but not thiol or serine protease inhibitors. Immunoblotting and immunocytochemistry confirmed the presence of transin in media and cells. Quantitative transin activity decreased progressively with increasing duration of primary lipocyte culture and myofibroblastic transformation.

CONCLUSION

Rat hepatic lipocytes express the transin gene and secrete its product during the early phase of lipocyte activation in primary culture. Because this enzyme degrades a wide spectrum of normal basement membrane proteins and activates progelatinase B and interstitial collagenase, it may have an important role in liver injury and fibrosis.

Novel insights into the biology and physiology of the Ito cell

Ito cells, perisinusoidal mesenchymal elements with possible pericytic functions within the liver, recently have been shown to play multiple physiological and pathophysiological roles. In particular, several in vivo and in vitro studies have clearly indicated that Ito cells play a relevant role in the progression of liver fibrogenesis. More recently, attention has been focussed on the mechanisms leading to Ito cell activation, proliferation and synthesis of extracellular matrix components. Among other soluble factors potentially involved in these processes, transforming growth factor-beta 1 and platelet-derived growth factor have been shown to act in a paracrine, and possibly autocrine, fashion on Ito cells, thus perpetuating their activated state. Finally, other studies have shown that Ito cells could play an active role in chronic liver tissue inflammation by promoting chemotaxis of infiltrating inflammatory cells.

Recent advances in the isolation of liver cells

The development of new and refined separation techniques--including FACS, FFE, CFE and isopyknic gradients--has had a profound impact on the ability of investigators to isolate specific cell types from the liver. Although some of these techniques, such as FFE, may be of limited preparative value, they are nonetheless important analytical tools that detect subtle differences among cell subpopulations. The isolation of highly purified preparations of liver cells in large yields requires the use of more conventional purification methods such as CFE and isopyknic centrifugation. Immunological approaches represent a key development for the isolation of specific liver cell types, especially when they are used in combination with other techniques. Excellent, reliable and relatively simple techniques now exist to isolate highly purified preparations of hepatocytes, cholangiocytes, KCs, SCs, FSC, myofibroblasts and pit cells. Additional work is necessary to refine techniques for the isolation of dendritic cells and lymphocytes.

Ito cell heterogeneity: desmin-negative Ito cells in normal rat liver

The presence of desmin is used to identify Ito cells in rat liver and to evaluate the purity of separated and cultured Ito cells. Heterogeneity of the normal Ito cell population has been suggested; this could include variations in the content of cytoskeletal components. For these reasons we decided to reevaluate the use of desmin staining as a phenotypical marker of Ito cells in normal rat liver. Our approach was to combine desmin staining with identification of vitamin A (autofluorescence), lipid droplets (Sudan III), vimentin, laminin and tenascin, using cryostat sections: Immunofluorescence, double-immunofluorescence or immunoperoxidase techniques were used. All the techniques described corroborate the existence of desmin-negative Ito cells, mainly located in pericentral areas. In fact, lobular desmin-positive cells showed uneven distribution because they were more frequent in periportal than in pericentral areas. On the contrary, Ito cells identified on the basis of morphological criteria or positivity for laminin were evenly distributed. Double immunofluorescence confirmed this observation, showing nearly complete codistribution of laminin and desmin in periportal areas. Outside this area, positivity for desmin was observed only in about 50% of laminin-positive cells. Our observations suggest that desmin cannot be viewed as a phenotypical marker but rather is a differentiation marker of Ito cells, possibly indicating a specific functional state.

Phosphatidylcholine protects against fibrosis and cirrhosis in the baboon

BACKGROUND/AIMS

Polyunsaturated soybean lecithin (55%-60% phosphatidylcholine [PC]) protects against fibrosis in alcohol-fed baboons. The present study was undertaken to determine whether PC is the active agent.

METHODS

Virtually pure PC (equivalent to that contained in the lecithin) was administered for up to 6.5 years with or without alcohol, and the results were compared with those of unsupplemented groups.

RESULTS

Control livers remained normal, whereas 10 of 12 baboons fed alcohol without PC developed septal fibrosis or cirrhosis with transformation of 81% +/- 3% of the hepatic lipocytes to collagen-producing transitional cells. By contrast, none of the eight animals fed alcohol with PC developed septal fibrosis or cirrhosis, and only 48% +/- 9% of their lipocytes were transformed, indicating that PC was indeed the protective compound. Ethanol feeding also resulted in decreased liver phospholipids and PC, and both were corrected by the supplementation. Furthermore, PC stimulated collagenase activity in cultured lipocytes. This PC consisted of several species, mainly dilinoleoylphosphatidylcholine (40%-52%) and palmitoyl-linoleoylphosphatidylcholine (23%-24%). Only dilinoleoylphosphatidylcholine duplicated the effect of the PC on collagenase. Other species of PC, phosphatidylethanolamine, free fatty acids, or choline were without effect.

CONCLUSIONS

PC prevents alcohol-induced fibrosis and cirrhosis in nonhuman primates, and dilinoleoylphosphatidylcholine appears to be the active species, possibly by promoting collagen breakdown.

Acetaldehyde-protein adducts, but not lactate and pyruvate, stimulate gene transcription of collagen and fibronectin in hepatic fat-storing cells

Hepatic fibrosis is an important morphological feature of alcohol-induced liver injury. We previously reported that acetaldehyde, but not ethanol can stimulate type I collagen and fibronectin synthesis in cultures of rat fat-storing cells (FSC) by increasing transcription of the specific genes. The effect of lactate and pyruvate was studied on collagen I, III, fibronectin accumulation by cultured rat FSCs and it was investigated whether acetaldehyde could increase procollagen I and fibronectin gene transcription through the formation of protein adducts. Lactate and pyruvate (5, 15 and 25 mmol/l) did not significantly affect collagen I, III and fibronectin production by cultured FSCs. Pyridoxal-phosphate and p-hydroxymecuribenzoate (inhibitors of acetaldehyde-protein adduct formation) blocked the stimulatory effect of acetaldehyde on procollagen I and fibronectin gene transcription. These data suggest that ethanol may act as a liver fibrogenic factor through acetaldehyde, its immediate metabolite, whereas lactate does not seem to play a role. Acetaldehyde might stimulate gene transcription of extracellular matrix components by liver FSCs through the formation of adducts with proteins.

Mitogenic effect of transforming growth factor-beta 1 on human Ito cells in culture: evidence for mediation by endogenous platelet-derived growth factor

We assessed the effect of transforming growth factor-beta 1 on the proliferation of human Ito cells. Ito cells in their myofibroblastlike phenotype were grown from explants of human liver and were characterized with electron microscopy and positive immunostaining for desmin and smooth muscle alpha-actin. Transforming growth factor-beta 1 was mitogenic for human Ito cells whatever the culture conditions, although it was, as previously described, inhibitory of growth for rat Ito cells. The mitogenic effect of transforming growth factor-beta 1 was likely due to induction of autocrine platelet-derived growth factor chain secretion by Ito cells themselves because (a) the mitogenic effect of transforming growth factor-beta 1 was blocked by specific platelet-derived growth factor antibodies, (b) transforming growth factor-beta 1 increased platelet-derived growth factor-A chain messenger RNA expression and platelet-derived growth factor-AA secretion by human Ito cells and (c) human Ito cells expressed the alpha-type platelet-derived growth factor-A receptor messenger RNA. Exogenous platelet-derived growth factor-AA was also mitogenic for human Ito cells, mimicking the effect of transforming growth factor-beta 1. Our data suggest that results obtained with rat Ito cells must be extrapolated with caution to human ones. The mitogenic effect of transforming growth factor-beta 1 on human Ito cells probably has pathophysiological relevance because transforming growth factor-beta 1 has been demonstrated in vivo at sites of active liver fibrogenesis.

Modulation of perisinusoidal cell cytoskeletal features during experimental hepatic fibrosis

Hepatic perisinusoidal cells (PSCs) proliferate and are thought to be the principal source of extracellular matrix proteins during the development of liver fibrosis. We have studied the classical model of carbon tetrachloride induced liver fibrosis in order to evaluate the possible modulation of PSCs into a synthetically active and contractile cell: the myofibroblast (MF). At the ultrastructural level, this modulation was characterized by reduction of lipid vacuoles and appearance of a developed rough endoplasmic reticulum as well as of microfilament bundles. On investigating the cytoskeletal equipment of PSCs and MFs using light and electron microscopic immunohistochemistry, we found a heterogeneity of phenotypic features. While typical PSCs in normal and fibrotic livers always contained desmin, MFs expressed alpha-smooth muscle (SM) actin in areas of tissue injury and active fibrogenesis. Cells co-expressing alpha-SM actin and desmin were most prominent in the prevenular zone of the lobule (known to be vulnerable to carbon tetrachloride toxicity) and in developing fibrous septa. As demonstrated by immunogold electron microscopy, labelling of microfilament bundles by alpha-SM actin antibody was noted in PSCs containing lipid droplets in early stages of fibrosis; here MFs gradually accumulated and showed alpha-SM actin containing microfilament bundles. In scar tissue, alpha-SM actin expression decreased in both PSCs and myofibroblasts. Our observations support the concept of phenotypic plasticity of PSCs and confirm, at the ultrastructural level, previous suggestions of modulation of these cells into MFs in the course of liver fibrosis.

Role of mesenchymal cell populations in porcine serum-induced rat liver fibrosis

The role of liver mesenchymal cell populations in porcine serum-induced rat liver fibrosis were studied morphologically and immunohistochemically. Five-week-old rats were intraperitoneally injected with porcine serum twice a week and examined at various intervals between 3 and 24 wk after the initial injection. At an early phase, numbers of fibroblasts and extracellular matrix increased in the walls of central veins and in portal and capsular connective tissues. In the walls of central veins, the number of "second-layer cells" (i.e., the fibroblasts located at the second layer of the wall) increased. Connective tissue septa, accompanying some fibroblasts, extended from these interstitial tissues into the hepatic parenchyma, and their foremost edges came into direct contact with the perisinusoidal stellate cells. The sinusoids adjacent to the newly formed septa collapsed and later disappeared; this process resulted in the formation of hepatic limiting plates along the septa. At a more advanced stage, the interstitial fibroblasts and septal cells-which were derived from interstitial fibroblasts and the stellate cells-increased and became multilayered, constructing three-dimensional cell networks. These networks, together with increased collagen fibrils and elastic fibers, constitute the fibrotic dense connective tissue. In the control rat, smooth muscle cells were positive on vimentin, desmin and smooth muscle-alpha-actin staining. The stellate cells, second-layer cells, capsular and portal fibroblasts were shown to be vimentin and desmin positive and smooth muscle-alpha-actin negative. In the fibrotic liver, septal(fibroblastic) cells were vimentin and desmin positive and smooth muscle-alpha-actin negative. We conclude that not only the perisinusoidal stellate cells but also the interstitial fibroblasts, including the second-layer cells, play substantial role in the development of porcine serum-induced septal fibrosis in rat liver.

Polyunsaturated lecithin prevents acetaldehyde-mediated hepatic collagen accumulation by stimulating collagenase activity in cultured lipocytes

We recently found that polyunsaturated lecithin prevents ethanol from causing cirrhosis in the baboon. Because transformation of lipocytes to transitional cells plays a key role in hepatic fibrogenesis in vivo, and because this process in alcohol-fed baboons was found to be attenuated by polyunsaturated lecithin, we focused on lipocytes to study the mechanism of the protective effect. Rat lipocytes cultured on plastic undergo spontaneous activation, accompanied by expression of alpha-smooth muscle actin isoform and production of substantial amounts of type I collagen. The latter was further increased on incubation with acetaldehyde. This in vitro model was used here to study how acetaldehyde-mediated collagen production and accumulation can be turned off. Addition of polyunsaturated lecithin (10 mumols/L) was found to prevent the acetaldehyde-induced increase in collagen accumulation by 83% (p less than 0.001). By contrast, a saturated phospholipid (10 mumols/L dilauroyl phosphatidylcholine), a monounsaturated one (10 mumols/L linoleoyl-palmitoyl phosphatidylcholine) or linoleic acid (20 mumols/L bound to albumin) had no such effect. Incorporation of [3H]proline into collagen and the expression of alpha-1 (I) procollagen mRNA were increased by acetaldehyde; the latter was not significantly affected by polyunsaturated lecithin. Polyunsaturated lecithin increased lipocyte collagenase activity by 100% (p less than 0.001), whereas dilauroyl phosphatidylcholine, linoleoyl-palmitoyl phosphatidylcholine and linoleic acid had no such action. We concluded that (a) polyunsaturated lecithin selectively prevents the acetaldehyde-induced increase in collagen accumulation in lipocyte cultures, whereas other phospholipids or linoleate have no such effect; and (b) polyunsaturated lecithin does not modify the acetaldehyde-mediated increase in alpha-1 (I) procollagen mRNA, but it increases collagenase activity, suggesting that the protective effect exerted by polyunsaturated lecithin against alcohol induced fibrosis in vivo is due at least in part to stimulation of collagenase activity, which may prevent excess collagen accumulation by offsetting increased collagen production.

The effects of hepatic fibrosis on Ito cell gene expression

While Ito cells appear to be a major source of increased matrix synthesis during hepatic fibrogenesis, the cellular changes that occur in these cells during liver fibrosis have not been well delineated. In this study we examined Ito cell gene expression in isolated cells from normal rats, and rats with carbon tetrachloride-induced fibrosis, in order to better define the changes occurring in these cells during this pathologic process. Specifically, we addressed three questions: (1) which matrix genes are over expressed in Ito cells in fibrotic liver; (2) do these cells increase their expression of the fibrogenic cytokine transforming growth factor-beta 1 (TGF-beta 1); and (3) do Ito cells change their phenotype during hepatic fibrogenesis as reflected by alterations in the expression of their intermediate filament genes? Northern hybridization analysis revealed that Ito cells isolated from fibrotic livers had significant increases in mRNA levels of types I, III and IV procollagen compared to normal cells, while no increases were found in hepatocytes, and Kupffer/endothelial cells had only an increase in type I procollagen mRNA. Analysis of other matrix proteins which increase during hepatic fibrogenesis revealed elevations in laminin B and fibronectin mRNA levels only in Ito cells. Increased Ito cell matrix gene expression was also associated with a 4-fold increase in TGF-beta 1 levels in these cells. No increase in TGF-beta 1 mRNA was found in hepatocytes, and less than a 2-fold increase was found in Kupffer/endothelial cells isolated from fibrotic livers.(ABSTRACT TRUNCATED AT 250 WORDS)

Desmin expression in fibroblasts of murine periovular granuloma during liver Schistosoma mansoni infection

We have studied the expression of the desmin gene, a muscle-specific intermediate filament protein in the granuloma cells of mouse liver infected with Schistosoma mansoni. In situ hybridization using a desmin DNA probe showed that fibroblastic cells in the granuloma strongly expressed desmin mRNAs, while in normal liver these cells did not express this mRNA to a detectable degree. The quantitative analysis of total RNAs demonstrated that the proportion of specific desmin mRNA increased from 14 to 18 weeks after infection and decreased at 20 weeks. The analysis of collagen gene expression indicated that the amount of type III collagen mRNAs was still increasing after 18 weeks from infection; in contrast, the amount of type I collagen mRNAs remained unchanged at that stage. A good correlation was observed between the detection of the specific mRNAs and the detection of both desmin and collagen molecules. Therefore, these data point to a coordinate induction of desmin and collagen gene expression during Schistosomal granuloma formation. They also suggest that the expression of the myofibroblast phenotype involves the induction of both genes.

von Willebrand factor antigen is not an accurate marker of rat and guinea pig liver endothelial cells

To determine whether von Willebrand Factor (vWF) is a valid marker of liver endothelial cells, we determined vWF immunoreactivity in rat and guinea pig liver sections and in smears of elutriated nonparenchymal cells isolated from these two species. In frozen sections, positive staining for vWF was seen only in the endothelium lining large hepatic vessels in both species, and no immunoactivity was detected in the sinusoids. On the other hand, immunohistochemical staining for vimentin (a marker of mesenchymal cells) showed positive reaction throughout the vascular and sinusoidal endothelial cells in both the rat and guinea pig liver. In fractions of elutriated rat and guinea pig nonparenchymal liver cells, which included almost exclusively liver endothelial cells, only 25-40% of the cells displayed a positive reaction for vWF. However, when these same fractions were stained for vimentin, 70-95% of the cells exhibited immunoreactivity. Most of the vWF-negative cells were not red and white blood cells, biliary epithelial and Kupffer cells, and hepatocytes, and had ultrastructural features of sinusoidal endothelial cells. We conclude that in both the rat and guinea pig, liver sinusoidal endothelial cells do not exhibit vWF immunoreactivity. Thus, in routine immunohistochemical assays, vWF is not an accurate marker of rat and guinea pig liver endothelial cells. Vimentin is more appropriate for this purpose, provided that other mesenchymal cells are separated or independently identified.

Acetaldehyde selectively stimulates collagen production in cultured rat liver fat-storing cells but not in hepatocytes

Hepatocytes and fat-storing cells have been implicated in the production of collagen, under both normal and pathological conditions. In this study, short-term primary cultures of rat hepatocytes, maintained in a serum-free, hormonally defined medium without dexamethasone and cultured on a fibronectin-collagen type IV substratum, were used. Primary and passage 1 and 2 cultures of fat-storing cells maintained on tissue culture plastic were also studied. Hepatocytes produced significant amounts of collagen type III, but formation of collagen type I was not detectable. Laminin and collagen type IV production were very low. Hepatocytes maintained their ability to metabolize ethanol (at levels comparable to those observed at 2 hr) for at least 48 hr after plating and this metabolism was inhibited 86% to 95% by 4-methylpyrazole (1 mmol/L). Neither ethanol (50 mmol/L) nor acetaldehyde (175 mumol/L, initial concentration) had any effect on the production of collagen type III or laminin. Fat-storing cells (95% to 100% desmin-positive) produced significant amounts of both type I and type III collagen. Production of collagen type IV and laminin was very low. Metabolism of ethanol by these cultures was not detected. Addition of ethanol had no effect on collagen or laminin production in fat-storing cells. In contrast, acetaldehyde significantly increased the production of collagen type I, but did not alter the production of collagen type III, IV or laminin. Incorporation of 3H-proline into total protein was not affected by addition of ethanol or acetaldehyde to fat-storing cells or hepatocytes. Exposure of fat-storing cells to ethanol or acetaldehyde did not change 3H-collagen degrading activity in the media.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of endothelial cells from bovine cerebral arteries

For our laboratory's investigation into the role of the endothelial cells in vasospasm following subarachnoid hemorrhage and in inflammatory diseases, we found it necessary to devise a modified method of cell culture, which would be appropriate for studying human endothelial cells from lobectomized brain. We report our techniques to increase cell harvest and ensure reproducibility, our method of culturing endothelial cells from bovine major cerebral arteries, and our morphologic and immunocytochemical characterization of these cells. To increase the harvest of endothelial cells, the blood cells were washed from the lumen of the major cerebral arteries at the slaughterhouse and a modified reversed vessel technique was employed. The monolayer of cultured endothelial cells displayed a cobblestone appearance when it reached confluency and transmission electron microscopy revealed junctional complexes and interdigitation of cytoplasm at Passages 10 and 17. The cells stained positively for Factor VIII-related antigen at Passages 3, 5, 7, 10, and 15. Also the cells metabolized acetylated low-density lipoprotein at Passage 8. To determine the purify of the cultured endothelial cells, an immunocytochemical study of the cytoskeleton was performed on Passage 5 cells using either rhodamine-phalloidin or antibodies against smooth muscle myosin, desmin, and vimentin.

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.

Effects of platelet-derived growth factor and other polypeptide mitogens on DNA synthesis and growth of cultured rat liver fat-storing cells

In vitro and in vivo studies suggest that liver fat-storing cells (FSC) may play an important role in the development of liver fibrosis. We explored the effects of platelet-derived growth factor (PDGF), epidermal growth factor (EGF), transforming growth factor (TGF)-alpha and TGF-beta, and basic fibroblast growth factor (bFGF) on DNA synthesis and growth of rat liver FSC. PDGF, EGF, TGF-alpha, and bFGF induced a dose-dependent increase in DNA synthesis with a peak effect at 24 h. PDGF produced the most striking effect with a maximum 18-fold increase over control. EGF, TGF-alpha, and bFGF elicited a maximum three- to fourfold increase in DNA synthesis. Analysis of growth curves revealed a similar pattern of potency of the growth factors. TGF-beta did not affect DNA synthesis of FSC; however, TGF-beta markedly potentiated the stimulatory effects of both EGF and PDGF. FSC showed high specific binding of 125I-PDGF and Scatchard analysis revealed high affinity receptors with an apparent Kd of 2.3 x 10(-10) M. Our data suggest that PDGF is a key mitogen for FSC and that the coordinate release of other growth factors together with PDGF by inflammatory cells represents a potent potential stimulus for FSC proliferation in conditions of chronic self-perpetuating liver inflammation.

Activation of cultured rat hepatic lipocytes by Kupffer cell conditioned medium. Direct enhancement of matrix synthesis and stimulation of cell proliferation via induction of platelet-derived growth factor receptors

Hepatic lipocytes appear to be central to the pathogenesis of hepatic fibrosis, undergoing activation during inflammation to a matrix-producing, proliferative cell type. We have studied the activation process in culture by examining the response of lipocytes to conditioned medium from hepatic macrophages (Kupffer cells). Lipocytes exposed to Kupffer cell medium (KCM) exhibited cellular and nuclear enlargement associated with up to a threefold increase in collagen and total protein synthesis per cell. Cell proliferation was also stimulated as measured by [3H]thymidine incorporation and direct cell counting. The latter effect was serum dependent and inhibited by antibodies to platelet-derived growth factor (PDGF). Proliferation could be stimulated by recombinant PDGF, but only after preincubation of cells with KCM. These findings suggested that KCM was eliciting expression of the PDGF receptor in lipocytes, and this was confirmed by immunoblot analysis with antibodies to the PDGF receptor. DNA synthesis in lipocytes exposed to KCM occurred at 48 h, which reflected the time required for PDGF receptor expression (24 h) plus initiation of [3H]thymidine incorporation (24 h). These results indicate that KCM has multiple stimulatory effects on cultured lipocytes similar to activation of these cells observed in vivo.

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.