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

Dissecting pulmonary fibroblasts heterogeneity in lung development, health and diseases

Lung fibroblasts are the major components in the connective tissue of the pulmonary interstitium and play essential roles in the developing of postnatal lung, synthesizing the extracellular matrix and maintaining the integrity of the lung architecture. Fibroblasts are activated in various disease conditions and exhibit functional heterogeneities according to their origin, spatial location, activated state and microenvironment. In recent years, advances in technology have enabled researchers to identify fibroblast subpopulations in both mouse and human. Here, we discuss pulmonary fibroblast heterogeneity, focusing on the developing, healthy and pathological lung conditions. We firstly review the expression profiles of fibroblasts during lung development, and then consider fibroblast diversity according to different anatomical sites of lung architecture. Subsequently, we discuss fibroblast heterogeneity in genetic lineage. Finally, we focus on how fibroblast heterogeneity may shed light on different pathological lung conditions such as fibrotic diseases, infectious diseases including COVID-19, and lung cancers. We emphasize the importance of comparative studies to illuminate the overlapping characteristics, expression profiles and signaling pathways of the fibroblast subpopulations across disease conditions, a better characterization of the functional complexity rather than the expression of a particular gene may have important therapeutic applications.

Hepatic stellate cells in physiology and pathology

Hepatic stellate cells (HSCs) comprise a minor cell population in the liver but serve numerous critical functions in the normal liver and in response to injury. HSCs are primarily known for their activation upon liver injury and for producing the collagen-rich extracellular matrix in liver fibrosis. In the absence of liver injury, HSCs reside in a quiescent state, in which their main function appears to be the storage of retinoids or vitamin A-containing metabolites. Less appreciated functions of HSCs include amplifying the hepatic inflammatory response and expressing growth factors that are critical for liver development and both the initiation and termination of liver regeneration. Recent single-cell RNA sequencing studies have corroborated earlier studies indictaing that HSC activation involves a diverse array of phenotypic alterations and identified unique HSC populations. This review serves to highlight these many functions of HSCs, and to briefly describe the recent genetic tools that will help to thoroughly investigate the role of HSCs in hepatic physiology and pathology.

The Liver and the Hepatic Immune Response in Trypanosoma cruzi Infection, a Historical and Updated View

Chagas disease was described more than a century ago and, despite great efforts to understand the underlying mechanisms that lead to cardiac and digestive manifestations in chronic patients, much remains to be clarified. The disease is found beyond Latin America, including Japan, the USA, France, Spain, and Australia, and is caused by the protozoan Trypanosoma cruzi. Dr. Carlos Chagas described Chagas disease in 1909 in Brazil, and hepatomegaly was among the clinical signs observed. Currently, hepatomegaly is cited in most papers published which either study acutely infected patients or experimental models, and we know that the parasite can infect multiple cell types in the liver, especially Kupffer cells and dendritic cells. Moreover, liver damage is more pronounced in cases of oral infection, which is mainly found in the Amazon region. However, the importance of liver involvement, including the hepatic immune response, in disease progression does not receive much attention. In this review, we present the very first paper published approaching the liver's participation in the infection, as well as subsequent papers published in the last century, up to and including our recently published results. We propose that, after infection, activated peripheral T lymphocytes reach the liver and induce a shift to a pro-inflammatory ambient environment. Thus, there is an immunological integration and cooperation between peripheral and hepatic immunity, contributing to disease control.

Dissecting Fibroblast Heterogeneity in Health and Fibrotic Disease

PURPOSE OF REVIEW

Fibroblasts, the major cell population in all connective tissues, are best known for their role in depositing and maintaining the extracellular matrix. Recently, numerous specialised functions have been discovered revealing unpredicted fibroblast heterogeneity. We will discuss this heterogeneity, from its origins in development to alterations in fibrotic disease conditions.

RECENT FINDINGS

Advances in lineage tracing and single-cell transcriptional profiling techniques have revealed impressive diversity amongst fibroblasts in a range of organ systems including the skin, lung, kidney and heart. However, there are major challenges in assimilating the findings and understanding their functional significance. Certain fibroblast subsets can make specific contributions to healthy tissue functioning and to fibrotic disease processes; thus, therapeutic manipulation of particular subsets could be clinically beneficial. Here we propose that four key variables determine a fibroblast's phenotype underpinning their enormous heterogeneity: tissue status, regional features, microenvironment and cell state. We review these in different organ systems, highlighting the importance of understanding the divergent fibroblast properties and underlying mechanisms in tissue fibrosis.

Conditioned Medium from Human Amnion-Derived Mesenchymal Stem Cells Regulates Activation of Primary Hepatic Stellate Cells

Mesenchymal stem cells (MSCs), or multipotent mesenchymal stromal cells, are present in almost all organs and tissues, including the amnion. Human amnion-derived mesenchymal stem cell (hAMSC) transplantation has been reported to ameliorate liver fibrosis in animal models. However, the mechanism for the prevention of liver fibrosis is poorly understood. In this study, we investigated the effects, and underlying mechanisms, of a conditioned medium obtained from hAMSC cultures (hAMSC-CM) on a primary culture of rat hepatic stellate cells (HSCs). We observed that in routine culture, hAMSC-CM in HSCs significantly inhibited the expression of alpha-smooth muscle actin (α-SMA), an activation marker of HSCs, and the production of collagen type 1 (COL1), a dominant component of the extracellular matrix (ECM) in the culture medium. In addition, hAMSC-CM upregulated the expression of ECM degradation-related genes, such as metalloproteinase- (Mmp-) 2, Mmp-9, Mmp-13, and tissue inhibitor of metalloproteinase- (Timp-) 1; however, it did not affect the expression of collagen type 1α1 (Col1a1). These regulatory effects on HSCs were concentration-dependent. A cell proliferation assay indicated that hAMSC-CM significantly suppressed HSC proliferation and downregulated the expression of cyclin B (Ccnb), a proliferation-related gene. Transforming growth factor-beta (TGF-β) treatment further activated HSCs and hAMSC-CM significantly inhibited the upregulation of α-Sma and Col1a1 induced by TGF-β. These findings demonstrated that hAMSC-CM can modulate HSC function via secretory factors and provide a plausible explanation for the protective role of hAMSCs in liver fibrosis.

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.

Hepatic stellate cells and liver fibrosis

Hepatic stellate cells are resident perisinusoidal cells distributed throughout the liver, with a remarkable range of functions in normal and injured liver. Derived embryologically from septum transversum mesenchyme, their precursors include submesothelial cells that invade the liver parenchyma from the hepatic capsule. In normal adult liver, their most characteristic feature is the presence of cytoplasmic perinuclear droplets that are laden with retinyl (vitamin A) esters. Normal stellate cells display several patterns of intermediate filaments expression (e.g., desmin, vimentin, and/or glial fibrillary acidic protein) suggesting that there are subpopulations within this parental cell type. In the normal liver, stellate cells participate in retinoid storage, vasoregulation through endothelial cell interactions, extracellular matrix homeostasis, drug detoxification, immunotolerance, and possibly the preservation of hepatocyte mass through secretion of mitogens including hepatocyte growth factor. During liver injury, stellate cells activate into alpha smooth muscle actin-expressing contractile myofibroblasts, which contribute to vascular distortion and increased vascular resistance, thereby promoting portal hypertension. Other features of stellate cell activation include mitogen-mediated proliferation, increased fibrogenesis driven by connective tissue growth factor, and transforming growth factor beta 1, amplified inflammation and immunoregulation, and altered matrix degradation. Evolving areas of interest in stellate cell biology seek to understand mechanisms of their clearance during fibrosis resolution by either apoptosis, senescence, or reversion, and their contribution to hepatic stem cell amplification, regeneration, and hepatocellular cancer.

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.

Monitoring fibrogenic progression in the liver

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

Differential increases in the expression of intermediate filament proteins and concomitant morphological changes of transdifferentiating rat hepatic stellate cells observed in vitro

The primary function of hepatic stellate cells (HSCs) is the storage of vitamin A. However, they are also responsible for liver fibrosis and are therapeutic targets for treatment of liver cirrhosis. Among the many molecular markers that define quiescent or activated states of HSCs, the characteristics of type III intermediate filaments are of particular interest. Whereas vimentin and desmin are upregulated in activated HSCs, glial fibrillary acidic protein is downregulated in activated HSCs. The functional differences between vimentin and desmin are poorly understood. By time-course quantifications of several molecular markers for HSC activation, we observed that the expression of vimentin preceded that of desmin during the transdifferentiation of HSCs. The immunoreactivity of vimentin in transdifferentiated HSCs was more intense in perinuclear regions compared to that of desmin. We propose that the delayed expression of desmin following the expression of vimentin and the peripheral localization of desmin compared to vimentin are both related to the more extended phenotype of transdifferentiating HSCs observed in vitro.

The role of retinoic acid receptors in activated hepatic stellate cells

Hepatic stellate cells (HSCs), also known as Ito cells, fat-storing cells, vitamin A-storing cells or lipocytes, reside in the spaces between hepatocytes and liver sinusoids. Vitamin A storage within the HSCs is achieved through the cooperative action of two proteins, cellular retinol-binding protein (CRBP) I and lecithin:retinol acyltransferase (LRAT). After the discovery that HSCs are responsible not only for the storage of vitamin A, but also for the development of liver fibrosis and subsequent liver cirrhosis, HSCs have been considered a therapeutic target for prevention or reversal of liver fibrogenesis. We have reported that HSCs acquire retinoid responsiveness after in vitro activation by post-transcriptional upregulation of retinoic acid receptor α gene expression. Here we extend this observation in relation to the functions of CRBP I and LRAT, and propose a hypothesis that increased retinoid signaling in activated HSCs forms a feedback loop toward vitamin A restoration in the liver.

Update on hepatic stellate cells: pathogenic role in liver fibrosis and novel isolation techniques

Hepatic stellate cells (HSCs), also called Ito cells or lipocytes, are vitamin A-storing cells located in the Dissé space between hepatocytes and sinusoidal endothelial cells. Upon liver injury, these cells transdifferentiate into extracellular matrix-producing, highly proliferative myofibroblasts that promote hepatic fibrogenesis. Other possible collagen-producing cells in liver fibrosis include portal fibroblasts, bone marrow-derived cells (mesenchymal stem cells, fibrocytes and hematopoietic cells) and parenchymal cells undergoing epithelial-to-mesenchymal transition. Important factors and signaling pathways for HSC activation, as well as different functions of HSC during homeostasis and fibrosis, such as collagen production, secretion of cytokines and chemokines, immune modulation and changes in contractile features, as well as vitamin A storage capacity, have been identified in vitro and in vivo. Novel isolation techniques, specifically HSC sorting by FACS via autofluorescence and antibodies, will provide us with further opportunities to advance our understanding of HSC biology in health and disease.

Distinct populations of hepatic stellate cells in the mouse liver have different capacities for retinoid and lipid storage

Hepatic stellate cell (HSC) lipid droplets are specialized organelles for the storage of retinoid, accounting for 50–60% of all retinoid present in the body. When HSCs activate, retinyl ester levels progressively decrease and the lipid droplets are lost. The objective of this study was to determine if the HSC population in a healthy, uninjured liver demonstrates heterogeneity in its capacity for retinoid and lipid storage in lipid droplets. To this end, we utilized two methods of HSC isolation, which leverage distinct properties of these cells, including their vitamin A content and collagen expression. HSCs were isolated either from wild type (WT) mice in the C57BL/6 genetic background by flotation in a Nycodenz density gradient, followed by fluorescence activated cell sorting (FACS) based on vitamin A autofluorescence, or from collagen-green fluorescent protein (GFP) mice by FACS based on GFP expression from a GFP transgene driven by the collagen I promoter. We show that GFP-HSCs have: (i) increased expression of typical markers of HSC activation; (ii) decreased retinyl ester levels, accompanied by reduced expression of the enzyme needed for hepatic retinyl ester synthesis (LRAT); (iii) decreased triglyceride levels; (iv) increased expression of genes associated with lipid catabolism; and (v) an increase in expression of the retinoid-catabolizing cytochrome, CYP2S1. Conclusion: Our observations suggest that the HSC population in a healthy, uninjured liver is heterogeneous. One subset of the total HSC population, which expresses early markers of HSC activation, may be “primed” and ready for rapid response to acute liver injury.

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.

Immunohistochemical studies of stellate cells in experimental cholestasis in newborn and adult rats

BACKGROUND AND AIMS

Although there is much known about liver diseases, some aspects remain unclear, such as the nature of the differences between the diseases observed in newborn infants and those in adults. For example, how do newborns respond to duct epithelial cell injury? Do the stellate cells in newborns respond similarly to those in adults during biliary obstruction?

METHODS

Ninety newborn Wistar rats aged six days, weighing 8.0 - 13.9 g each, and 90 adult rats weighing 199.7 - 357.0 g each, were submitted to bile duct ligation. After surgery, they were randomly divided and sacrificed on the 3rd, 5th, 7th, 14th, 21st or 28th day post-bile duct ligation. Hepatic biopsies were obtained and immunohistochemical semi-quantification of desmin and alpha-SMA expression was performed in hepatic stellate cells and in myofibroblasts in the portal space, and between the portal space and the liver lobule.

RESULTS

Desmin expression in the myofibroblast cells post-bile duct ligation was higher in young rats, reaching its peak level in a shorter time when compared to the adult animals. The differences between the groups for alpha-SMA expression were less significant than for desmin.

CONCLUSIONS

These findings indicate that there is an increase in the number of collagen-producing myofibroblast cells in young animals, suggesting that there is more intense fibrosis in this population. This finding may explain why young animals with bile duct obstruction experience more intense portal fibrosis that is similar to the pathology observed in the livers of newborns with biliary atresia.

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

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

Changes in inward rectifier K+ channels in hepatic stellate cells during primary culture

PURPOSE

This study examined the expression and function of inward rectifier K(+) channels in cultured rat hepatic stellate cells (HSC).

MATERIALS AND METHODS

The expression of inward rectifier K(+) channels was measured using real-time RT-PCR, and electrophysiological properties were determined using the gramicidin-perforated patch-clamp technique.

RESULTS

The dominant inward rectifier K(+) channel subtypes were K(ir)2.1 and K(ir)6.1. These dominant K(+) channel subtypes decreased significantly during the primary culture throughout activation process. HSC can be classified into two subgroups: one with an inward-rectifying K(+) current (type 1) and the other without (type 2). The inward current was blocked by Ba(2+) (100 microM) and enhanced by high K(+) (140 mM), more prominently in type 1 HSC. There was a correlation between the amplitude of the Ba(2+)-sensitive current and the membrane potential. In addition, Ba(2+) (300 microM) depolarized the membrane potential. After the culture period, the amplitude of the inward current decreased and the membrane potential became depolarized.

CONCLUSION

HSC express inward rectifier K(+) channels, which physiologically regulate membrane potential and decrease during the activation process. These results will potentially help determine properties of the inward rectifier K(+) channels in HSC as well as their roles in the activation process.

The equine endometrosis: new insights into the pathogenesis

This paper describes the histomorphological and immunohistochemical characterisation of phenotypic variations of endometrosis as well as potential etiological factors which may influence disease progression. In total, 779 endometrial biopsies were examined. These biopsies were taken in the breeding and non-breeding season (n=509), on defined days during the estrous cycle (n=70) and before and after experimentally induced bacterial endometritis (n=200). In addition to conventional histopathology, selected biopsies were investigated using alcianblue staining as well as immunohistochemical methods for the detection of steroid hormone receptors, Ki-67-antigen, vimentin, desmin, fibronectin, smooth-muscle-alpha-actin and laminin. The equine endometrosis can be divided into a destructive and a non-destructive form. Based on the morphology of the stromal cells involved, an active or inactive state can be distinguished in fibrotic foci. In all types of endometrosis, fibrotic stromal cells show a distinctly reduced expression of steroid hormone receptors in comparison to the intact stroma, indicating their dedifferentiation. However, the steroid hormone receptor expression of involved glandular epithelia seems to depend on the activity of the fibrosis. These results suggest an independency of all fibrotic foci from the hormonal control mechanism of the uterus. The characteristical features of destructive endometrosis are a large number of smooth-muscle-alpha-actin containing myofibroblasts, a pronounced epithelial vimentin expression, excessive extracellular matrix accumulation and a progressive alteration of the basal lamina. Furthermore, the frequently seen cystic glandular dilatation and mechanical destruction of the uterine glands may occur due to the contractibility of the myofibroblasts involved. As shown in this study, a simultaneous endometritis can cause a temporary activation of fibrotic stromal cells. However, cyclic and seasonal endocrine changes seem to have no effects on progression of the disease. It can be concluded that the various types of endometrosis represent different stages in the fibrotic process, possibly leading to the destruction of the glands and subsequently resulting in the development of a stromal fibrosis.

Effect of Jiazhu on α-SMA and TGF-β1 expression in rats with hepatic fibrosis

AIM: To investigate the effect of Jiazhu on α-SMA and TGF-β1 expression in the liver of rats with hepatic fibrosis and its anti-fibrosis mechanism.

METHODS: A model of rat hepatic fibrosis was induced by injecting 40% CCl4, which was interfered with high [2.0 g/(kg·d)], medium [1.0 g/(kg·d)] and low doses [0.5 g/(kg·d)] of Jiazhu. Hepatic function and serum TGF-β1 were examined. Expression of α-SMA and TGF-β1 was detected by immunohistochemistry and RT-PCR.

RESULTS: Compared with the model group, the levels of aspartate transaminase and alanine transaminase were significantly decreased in the high, medium and low Jiazhu dose groups. Total protein and albumin increased while serum bilirub and TGF-β1 were significantly reduced. The expression of α-SMA and TGF-β1 in liver tissue was decreased. The mRNA expression, stained area and gray scale of α-SMA and TGF-β1 in the high, medium and low Jiazhu dose groups were significantly different compared with the model group(α-SMA: 9.21 ± 1.12、12.63 ± 2.42、14.23 ± 1.57 vs 16.32 ± 2.14, P < 0.01、P < 0.01、P < 0.05; TGF-β1 mRNA: 5.58 ± 0.80、8.62 ± 1.16、11.92 ± 1.35 vs 14.57±1.59, P < 0.01、P < 0.01、P < 0.01), (dyeing area of α-SMA: 9.21% ± 1.29%、12.63% ± 1.44%、14.23% ± 1.41% vs 16.32% ± 1.75%, P < 0.01、P < 0.01、P < 0.05; dyeing area of TGF-β1: 5.31% ± 0.70%、8.37% ± 1.09%、11.92% ± 1.42% vs 14.47% ± 1.48%, P < 0.01、P < 0.01、P < 0.01), (gray scale of α-SMA: 91.29 ± 9.53、99.55 ± 11.83、107.18 ± 12.06 vs 116.44 ± 12.97, P < 0.01、P < 0.01、P < 0.05; gray scale of TGF-β1: 89.96 ± 9.64、106.92 ± 13.90、110.50 ± 12.91 vs 127.13 ± 14.88, P < 0.01、P < 0.01、P < 0.05).

CONCLUSION: Jiazhu can inhibit rat hepatic fibrosis induced by CCL₄.

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

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

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.

Role of alphavbeta6 integrin in acute biliary fibrosis

Acute biliary obstruction leads to periductal myofibroblasts and fibrosis, the origin of which is uncertain. Our study provides new information on this question in mice and humans. We show that bile duct obstruction induces a striking increase in cholangiocyte alphavbeta6 integrin and that expression of this integrin is directly linked to fibrogenesis through activation of transforming growth factor beta (TGF-beta). Administration of blocking antibody to alphavbeta6 significantly reduces the extent of acute fibrosis after bile duct ligation. Moreover, in beta6-null mice subjected to the injury, fibrosis is reduced by 50% relative to that seen in wild-type mice, whereas inflammation occurs to the same extent. The data indicate that alphavbeta6, rather than inflammation, is linked to fibrogenesis. It is known that alphavbeta6 binds latent TGF-beta and that binding results in release of active TGFbeta. Consistent with this, intracellular signaling from the TGFbeta receptor is increased after bile duct ligation in wild-type mice but not in beta6(-/-) mice, and a competitive inhibitor of the TGFbeta receptor type II blocks fibrosis to the same extent as antibody to alphavbeta6. In a survey of human liver disease, expression of alphavbeta6 is increased in acute, but not chronic, biliary injury and is localized to cholangiocyte-like cells.

CONCLUSION

Cholangiocytes respond to acute bile duct obstruction with markedly increased expression of alphavbeta6 integrin, which is closely linked to periductal fibrogenesis. The findings provide a rationale for the use of inhibitors of alphavbeta6 integrin or TGFbeta for down-regulating fibrosis in the setting of acute or ongoing biliary injury.

Immunohistochemical analyses of cell–cell interactions during hepatic organoid formation from fetal mouse liver cells cultured in vitro

Cell-cell interactions among cell types constituting the fetal liver such as hepatoblasts, stellate cells and endothelial cells lead to functional lobule development. The present study was undertaken to investigate hepatic histogenesis in the primary culture of E12.5 mouse livers, including cell-cell and cell-matrix interactions. Fetal livers were dispersed with protease treatment and cultured for 5 days. Cellular adhesion of each hepatic cell type, gene expression and extracellular matrix deposition were analyzed by immunohistochemistry and immunoblotting. Immunohistochemical analysis demonstrated that the primary culture of fetal liver cells contained at least hepatoblasts, mesenchymal cells, endothelial cells, hemopoietic cells and Kupffer cells. Although hepatoblasts, mesenchymal cells, and endothelial cells aggregated separately in the initial step, they then formed a spheroid together, adhering to the glass slide, which led to the formation of flattened hepatic organoids. Hepatoblasts more preferentially adhered to mesenchymal cells than endothelial cells. Several extracellular matrix depositions were seen in aggregates consisting of at least hepatoblasts and mesenchymal cells within 12 h, but were poor in those lacking hepatoblasts. These data show that the primary culture of fetal liver cells contains most cell types constituting fetal livers, and may be useful for studying cell-cell interactions during liver development.

Heterogeneous composition of voltage-dependent K(+) currents in hepatic stellate cells

PURPOSE

Hepatic stellate cells (HSC) are a type of pericyte with varying characteristics according to their location. However, the electrophysiological properties of HSC are not completely understood. Therefore, this study investigated the difference in the voltage-dependent K(+) currents in HSC.

MATERIALS AND METHODS

The voltage-dependent K(+) currents in rat HSC were evaluated using the whole cell configuration of the patch-clamp technique.

RESULTS

Four different types of voltage-dependent K(+) currents in HSC were identified based on the outward and inward K(+) currents. Type D had the dominant delayed rectifier K(+) current, and type A had the dominant transient outward K(+) current. Type I had an inwardly rectifying K(+) current, whereas the non-type I did not. TEA (5 mM) and 4-AP (2 mM) suppressed the outward K(+) currents differentially in type D and A. Changing the holding potential from -80 to -40 mV reduced the amplitude of the transient outward K(+) currents in type A. The inwardly rectifying K(+) currents either declined markedly or were sustained in type I during the hyperpolarizing step pulses from -120 to -150 mV.

CONCLUSION

There are four different configurations of voltage-dependent K(+) currents expressed in cultured HSC. These results are expected to provide information that will help determine the properties of the K(+) currents in HSC as well as the different type HSC populations.

Evolving concepts of liver fibrogenesis provide new diagnostic and therapeutic options

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

Identification of vitamin A-free cells in a stellate cell-enriched fraction of normal rat liver as myofibroblasts

Myofibroblasts (MFs) as well as hepatic stellate cells (HSCs) are known to be involved in liver fibrogenesis. Quiescent HSCs (qHSCs) in culture have been thought to differentiate to replicative activated HSCs (aHSCs). In this study a qHSC-enriched fraction isolated by Nycodenz-isodensity centrifugation was separated with a fluorescence-activated cell sorter, which revealed the presence of a small fraction (occupancy rate=0.4%) of cells that did not show vitamin A-autofluorescence under ultraviolet (UV)-irradiation (UV- cells). The remaining vitamin A-containing cells were autofluorescent (UV+) and originally expressed markers of qHSCs, and, in culture, did not grow, lost vitamin A, and expressed markers of aHSCs. UV- cells showed morphology of MFs, and, in culture, grew to form colonies and expressed markers of MFs. These results indicated that UV+ and UV- cells represent qHSCs and MFs, respectively, and that aHSCs have no growth potential and are a cell-type distinct from proliferative MFs. Gene expression profiles of UV- cells (MFs) newly identified gremlin as one of MF-preferential genes and its proteins were localized around fibrotic septa in rat and human livers. In addition, we suggested that the qHSC-enriched fraction included approximately 6% of liver MFs.

Hepatic stellate cells: Three-dimensional structure, localization, heterogeneity and development

Hepatic stellate cells (HSCs) are vitamin-A storing collagen-producing cells in hepatic lobules. The three-dimensional structure of HSCs has been demonstrated with the Golgi method, the maceration method for scanning electron microscopy, and confocal laser scanning microscopy. Many thorn-like microprojections or spines extend from the subendothelial processes and make contacts with hepatocytes. One HSC entwines two or more sinusoids and about 20-40 hepatocytes to create a cellular unit, 'the stellate cell unit' or 'stellon'. The Space of Disse is defined as the space between stellate cell-endothelial cell complex and hepatocytes. Intralobular heterogeneity of HSCs is assessed. HSCs develop from mesenchymal cells in the septum transversum. The developmental process of HSCs is reproduced partly in culture. In the lamprey abundant vitamin A is stored not only in HSCs, but in the fibroblast-like cells in the various other splanchnic organs. In vertebrates, the existence of both conventional fibroblast system in somatic tissues and vitamin A-storing cell system in splanchnic organs is suggested.

The effect of vitamin A on CCl4-induced hepatic injuries in rats: a histochemical, immunohistochemical and ultrastructural study

In this study, we aimed to investigate the effect of vitamin A on the transformation of the Ito cells to fibrogenic form and suppression of the development of fibrosis. Carbon tetrachloride intoxication was performed on rats for 2, 8, 12 or 20 weeks and 5x10(4) IU vitamin A (as retinol palmitate) was injected subcutaneously once every 4 weeks. Ito cells were detected by gold chloride impregnation, as well as desmin and alpha-smooth muscle actin (alpha-SMA) immunohistochemistry. Additionally, all groups were examined ultrastructurally. The number of Ito cells that were labelled positively with gold impregnation decreased in the fibrotic groups; however, alpha-SMA and desmin immunopositive Ito cells increased. The samples from animals that were treated with vitamin A showed an increase in labelling with gold impregnation but a decrease in alpha-SMA immunopositivity. The data showed that vitamin A can prevent hepatic injury, by suppressing the transformation of Ito cells to fibrogenic form. We conclude that vitamin A has potential for the treatment of hepatic fibrotic diseases. Alpha-SMA immunohistochemistry was found to be more informative than desmin immunohistochemistry for monitoring liver fibrosis.

Persistence of liver cirrhosis in association with proliferation of nonparenchymal cells and altered location of alpha-smooth muscle actin-positive cells

This study was carried out to achieve pathological understanding for the persistence of cirrhosis induced by thioacetamide (TAA). Forty-five, male,21-day-old, F344 rats were randomly allocated to group I and received drinking water as a control, and groups 2 and 3 given 0.015% or 0.03%TAA, respectively for 12 weeks. Two-third of animals per group were sacrificed, and remainder were maintained for a further 4 weeks without TAA treatment. Liver cirrhosis was induced in all animals in group 3 at week 12, with obvious increase of collagen content, and this persisted after cessation of TAA. Proliferating cell nuclear antigen (PCNA) positive labeling indices of nonparenchymal cells were increased significantly after cessation in groups 2 and 3 (p < 0.01). RT-RCR analysis of a-smooth muscle actin (alpha-SMA) showed significant increase in group 3 compared to that of control at both time points (p < 0.05). Immunohistochemical staining of it demonstrated positive cells to mainly be located around regenerating hepatic nodules at week 12, however, they were focused into enlarged portal areas consisting of fibrous tissues and pseudo-bile ductular cells after the cessation. Taken together, we conclude persistence of liver cirrhosis could be associated with the proliferation of nonparenchymal cells and altered location of alpha-SMA positive cells.

On the presence of hepatic stellate cells in portal spaces

Previous studies in mice with hypervitaminosis A have demonstrated that fat-storing cells (hepatic stellate cells-HSCs) participate in schistosomal granuloma fibrogenesis. The origin of such cells in portal areas, away from the Disse spaces, was herein investigated. HSCs were identified in frozen sections of the liver by means of Sudan III staining. They appeared as red-stained cells disposed along the sinusoids of normal mice, but were never found within portal spaces. However, in the chronically inflamed portal spaces of Capillaria hepatica-infected mice, Sudan III-positive cells were frequently present among leukocytes and fibroblast-like cells. Thus, there are no resident HSCs in portal spaces, but their presence there in chronic inflammatory processes indicates that they are able to migrate from peri-sinusoidal areas in order to reach the portal areas.

Sinusoidal endothelial COX-1-derived prostanoids modulate the hepatic vascular tone of cirrhotic rat livers

CCl(4) cirrhotic rat liver exhibits a hyperresponse to the alpha(1)-adrenergic agonist methoxamine (Mtx) that is associated with enhanced thromboxane A(2) (TXA(2)) production and is abrogated by indomethacin. To further elucidate the molecular mechanisms involved in the hyperresponse to vasoconstrictors, portal perfusion pressure dose-response curves to Mtx were performed in CCl(4) cirrhotic rats livers after preincubation with vehicle, the cyclooxygenase (COX)-1 selective inhibitor SC-560, and the COX-2 selective inhibitor SC-236. TXA(2) production was determined in samples of the perfusate. COX-1 expression was analyzed and quantified in hepatocytes, Kupffer cells, sinusoidal endothelial cells (SEC), and hepatic stellate cells (HSC) isolated from control and cirrhotic rat livers by double-immunofluorescence staining, with specific markers for each population using flow cytometry or Western blot analysis. COX-1 protein levels were not significantly increased in cirrhotic livers, but COX-2 protein expression was increased. COX-1 inhibition, but not COX-2, significantly attenuated the response to Mtx and prevented the increased production of TXA(2). Cirrhotic livers showed an increased expression of COX-1 in SEC and reduced expression in HSC compared with control livers, whereas COX-1 was similarly distributed in Kupffer cells. Despite abundant hepatic COX-2 expression, the increased response to Mtx of cirrhotic livers is mainly dependent of COX-1. Upregulation of COX-1 in cirrhotic SEC may be responsible for the hyperesponse to Mtx.

The plasticity of p19 ARF null hepatic stellate cells and the dynamics of activation

In the healthy adult liver, quiescent hepatic stellate cells (HSCs) present the major site for vitamin A storage in cytoplasmic lipid droplets. During liver injury due to viral infection or alcohol intoxication, HSCs get activated and produce high amounts of extracellular matrix components for tissue repair and fibrogenesis. Employing p19 ARF deficiency, we established a non-transformed murine HSC model to investigate their plasticity and the dynamics of HSC activation. Primary HSCs isolated from livers of adult p19 ARF null mice underwent spontaneous activation through long-term passaging without an obvious replicative limit. The immortalized cell line, referred to as M1-4HSC, showed stellate cell characteristics including the expression of desmin, glial fibrillary acidic protein, alpha-smooth muscle actin and pro-collagen I. Treatment of these non-tumorigenic M1-4HSC with pro-fibrogenic TGF-beta1 provoked a morphological transition to a myofibroblastoid cell type which was accompanied by enhanced cellular turnover and impaired migration. In addition, M1-4HSCs expressed constituents of cell adhesion complexes such as p120(ctn) and beta-catenin at cell borders, which dislocalized in the cytoplasm during stimulation to myofibroblasts, pointing to the epitheloid characteristics of HSCs. By virtue of its non-transformed phenotype and unlimited availability of cells, the p19(ARF) deficient model of activated HSCs and corresponding myofibroblasts render this system a highly valuable tool for studying the cellular and molecular basis of hepatic fibrogenesis.

A dual reporter gene transgenic mouse demonstrates heterogeneity in hepatic fibrogenic cell populations

Activation of hepatic stellate cells (HSCs) and other resident mesenchymal cells into myofibroblasts expressing alpha smooth muscle actin (alphaSMA) and collagen I is a key event in liver fibrogenesis. However, the temporal expression profiles of alphaSMA and collagen I genes in these cells is unknown. To address this question, we studied alphaSMA and collagen alpha1(I) transcriptional patterns in primary cultures of HSCs, and additionally, in an in vivo model of secondary biliary fibrosis using transgenic mice that express the Discomsoma sp. red fluorescent protein (RFP) and the enhanced green fluorescent protein (EGFP) reporter genes under direction of the mouse alphaSMA and collagen alpha1(I) promoter/enhancers, respectively. The alphaSMA-RFP mice were crossed with collagen-EGFP mice to generate double transgenic mice. Reporter gene expression in cultured HSCs demonstrated that both transgenes were induced at day 3 with continued expression through day 14. Interestingly, alphaSMA and collagen alpha1(I) transgenes were not coexpressed in all cells. Flow cytometry analysis showed three different patterns of gene expression: alphaSMA-RFP positive cells, collagen-EGFP positive cells, and cells expressing both transgenes. AlphaSMA-only and alphaSMA/collagen expressing cells showed higher expression levels of synaptophysin, reelin, MMP13, TIMP1, and ICAM-1 compared to collagen-only expressing cells, as assessed by real-time PCR. Following bile duct ligation, alphaSMA and collagen alpha1(I) transgenes were differentially expressed by peribiliary, parenchymal and vascular fibrogenic cells. Peribiliary cells preferentially expressed collagen alpha1(I), while parenchymal myofibroblasts expressed both alphaSMA and collagen alpha1(I). In conclusion, these data demonstrate heterogeneity of gene expression in myofibroblastic cells during active fibrogenesis. These reporter mice provide a useful tool to further characterize fibrogenic cell types and to evaluate antifibrotic drugs.

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.

Effect of antihypertensive agents on stellate cells during liver regeneration in rats

BACKGROUND: Although most studies have focused on the hepatocytes, all the hepatic cells participate in the regenerative process, among them the stellate cells. The stellate cells are mesenchymal cells involved in local neurotransmission and paracrine regulation of several liver functions. Acute hepatic tissue loss promotes the proliferation and activation of stellate cells from a quiescent state to myofibroblast-like cells. AIM: Investigate the effects of antihypertensive agents on the stellate cell population during the liver regenerative phenomenon in rats. METHODS: Adult male Wistar rats received lisinopril, losartan, bradykinin, or saline solution in a proportional volume, intraperitoneally, before and after 70% partial hepatectomy. Animals from the experimental and saline groups were sacrificed at 36 hours after partial hepatectomy. The alpha-smooth muscle actin labelled stellate cells population was counted in the periportal and pericentral zones of the liver specimen. RESULTS: The labelled stellate cells were more numerous in the control group both in the periportal and pericentral zones at 36 hours after partial hepatectomy than at the other times. The population of stellate cells was significantly lower in the losartan group and higher in the bradykinin and lisinopril groups than in the control group. CONCLUSIONS: These results suggest that losartan can inhibit and bradykinin and lisinopril can stimulate the stellate cell population during liver regeneration in rats. These cells synthesize several substances to stimulate liver regeneration.

Idiopathic hepatic fibrosis with cholestasis in broiler chickens: immunohistochemistry of hepatic stellate cells

Immunohistochemical examinations of hepatic stellate cells (HSCs) were performed on six enlarged livers from broiler chickens with malformation of the extrahepatic biliary tract (group 1) and on eight broiler livers affected with naturally occurring cholangiohepatitis without biliary malformation (group 2). The livers from both groups were grossly enlarged, firm and tan-coloured, and histologically revealed severe diffuse fibrosis with proliferation of bile ductules. HSCs positive for muscle actin and desmin actively proliferated in the perisinusoidal space and around newly formed bile ductules. There was no difference in the immunohistochemical reactivities and location of HSCs between the two groups. The findings suggest that the diffuse hepatic fibrosis found in group 2 as well as group 1 results from reactive proliferation of HSCs.

Rat liver myofibroblasts and hepatic stellate cells differ in CD95-mediated apoptosis and response to TNF-alpha

Hepatic stellate cells (HSC), particularly activated HSC, are thought to be the principle matrix-producing cell of the diseased liver. However, other cell types of the fibroblast lineage, especially the rat liver myofibroblasts (rMF), also have fibrogenic potential. A major difference between the two cell types is the different life span under culture conditions. Although nearly no spontaneous apoptosis could be shown in rMF cultures, 18 +/- 2% of the activated HSC (day 7) were apoptotic. Compared with activated HSC, CD95R was expressed in 70% higher amounts in rMF. CD95L could only be detected in activated HSC. Stimulation of the CD95 system by agonistic antibodies (1 ng/ml) led to apoptosis of all rMF within 2 h, whereas activated HSC were more resistant (5.3 h/ 40% of total cells). Although transforming growth factor-beta downregulated apoptosis in both activated HSC and rMF, tumor necrosis factor-alpha (TNF-alpha) upregulated apoptosis in rMF. Lack of spontaneous apoptosis and CD95L expression in rMF and the different reaction on TNF-alpha stimulation reveal that activated HSC and rMF belong to different cell populations.

Transforming growth factor-beta isoforms differently stimulate proalpha2 (I) collagen gene expression during wound healing process in transgenic mice

The role of many growth factors and cytokines in the process of wound healing has been intensively investigated in recent two decades. Among them, transforming growth factor-betas (TGF-betas) are well known to have a potent stimulatory effect on collagen synthesis as shown in various in vivo experimental systems. In the present study, we examined the effects of various growth factors on the promoter activity of the proalpha2 (I) collagen gene (COL1A2) during the wound healing process. For this purpose, we utilized transgenic mice harboring the -17 kb promoter sequence of the mouse COL1A2 linked to either a firefly luciferase or a bacterial beta-galactosidase gene. These mice exhibited normal phenotypic expression and the wound healing process was not impaired. Full thickness wounds were made by punch biopsy. We examined the effects of TGF-beta1, -beta2, -beta3, basic fibroblast growth factor, platelet-derived growth factor, and connective tissue growth factor by applying them locally to the open wound every 2 days. Among the growth factors examined, all of the three isoforms of TGF- exhibited a more potent stimulatory effect on COL1A2 promoter activity than did other factors. In addition, while TGF-beta1 and -beta2 significantly increased the number of fibroblasts which were positive for X-Gal staining, TGF-beta3 treatment did not change the number of beta-galactosidase expressing cells. Accumulation of collagen fibers was observed to the same extent in the mice treated with TGF-beta1 and those with TGF-beta3. These findings suggest that TGF-beta1 and -beta3 have similar but not identical regulatory mechanisms of COL1A2 expression, and that their pathophysiological roles in wound healing might be different from each other.

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.

Clinicopathological characterization of prion: a novel marker of activated human hepatic stellate cells

BACKGROUND/AIMS

We recently demonstrated prion as a new marker for hepatic stellate cell activation in rats. Here, we have examined prion expression in normal and diseased human livers.

METHODS

Prion expression was examined at protein level by immunohistochemistry and at mRNA level by in situ hybridization.

RESULTS

While normal livers were negative for prion, all liver specimens but one from patients with chronic liver disease were positively stained. In chronic hepatitis, prion protein expression was found not only in the sinusoidal lining cells within the lobules but also in mesenchymal cells in expanded portal tracts. In alcoholic liver disease, prion-positive cells were found mainly in the areas of alcoholic hepatitis. Immunoelectronmicroscopy revealed that prion-positive cells were activated stellate cells. In situ hybridization demonstrated that the distribution of prion mRNA is similar to that of prion protein. In chronic hepatitis, the number of prion-positive cells correlated with the grade of activity but not with the stage of fibrosis. In alcoholic liver disease, levels of prion protein expression were significantly increased in the presence of alcoholic hepatitis.

CONCLUSION

Prion as a novel marker of activated stellate cells correlates well with disease activity in human chronic liver diseases.

Characterization of 4-hydroxy-2-nonenal metabolism in stellate cell lines derived from normal and cirrhotic rat liver

During oxidative stress, reactive aldehydes, including trans-4-hydroxy-2-nonenal (4-HNE), are generated by peroxidation of membrane lipids and purportedly stimulate hepatic stellate cells to produce excessive extracellular matrix, including type I collagen. An important question concerning the ability of 4-HNE to modulate collagen production by stellate cells is the potential of these specialized cells to detoxify 4-HNE. The objective of the present study was to characterize the ability of stellate cell lines, derived from normal (NFSC) and cirrhotic (CFSC) rat livers, to metabolize 4-HNE by oxidative, reductive and conjugative pathways. These two stellate cell lines were noted to have differing susceptibilities to the cytotoxic effect of 4-HNE. Treatment of both stellate cell lines with a range of 4-HNE doses demonstrated that the concentration which was cytotoxic to 50% of CFSC (TD(50)) was 25% greater than that for NFSC (967.57+/-9.26 nmol/10(6) cells vs. 769.90+/-5.32 nmol/10(6) cells respectively). The capacity of these cell lines to metabolizes 4-HNE was determined by incubating them in suspension with 50 microM 4-HNE (10 nmol/10(6) cell); 4-HNE elimination and metabolite formation were quantified over a 20 min time course. Both stellate cell lines rapidly metabolized 4-HNE, with the CFSC line eliminating 4-HNE at a rate that was approx. 2-fold greater than the NFSC line. The rate of 4-HNE metabolism attributable to glutathione S-transferase (GST) was similar in both cell lines, though differential cell specific expressions of GST isoforms GSTP1-1 and GSTA4-4 were observed. The greater rate of 4-HNE elimination by CFSC was attributable to its aldehyde dehydrogenase (ALDH) activity which accounted for approx. 50% of 4-HNE metabolism in CFSC but was insignificant in NFSC. Neither cell line had detectable alcohol dehydrogenase activity or protein levels. Measurement of cellular GSH concentrations revealed that NFSC contain approx. 2-fold greater concentrations of GSH when compared to CFSC and that following 4-HNE treatment, GSH levels were rapidly depleted from both cell lines. Concomitant with 4-HNE mediated GSH depletion, a corresponding increase in the 4-HNE-glutathione adduct formation was observed with the NFSC line forming greater amounts of the glutathione adduct than did the CFSC line. Taken together, these data demonstrate that both stellate cell lines have the capacity to metabolize 4-HNE but that CFSC have a greater rate of metabolism which is attributable to their greater ALDH activity, suggesting that the stellate cells isolated from cirrhotic liver may be differentially responsive to the biologic effects of 4-HNE.

Uptake and killing of Leptospira interrogans and Borrelia burgdorferi, spirochetes pathogenic to humans, by reticuloendothelial cells in perfused rat liver

In situ-perfused rat livers were infused with a single dose of 1.5 x 10(7) radiolabeled cells of Leptospira interrogans serovar icterohaemorrhagiae, the agent of leptospirosis, or with Borrelia burgdorferi IRS, the agent of Lyme disease. Significant (P<0.0001) differences in the liver uptake of L. interrogans and of B. burgdorferi were observed, the uptakes being 37.4%+/-2.3% for L. interrogans and 60.5%+/-3.1% for B. burgdorferi. Leptospires, in contrast to borreliae, were recovered from the livers when liver samples were cultured in growth medium. Leptospires but not borreliae were recovered in bile within 30 min of infusion. The association of leptospires and borreliae with reticuloendothelial cells of the liver was demonstrated by immunohistochemistry. Leptospires and borreliae were found to be associated with vimentin-positive cells and not with desmin-positive cells. Few leptospires but no borreliae were also seen associated with vimentin- and desmin-negative cells, suggesting the presence of leptospires outside the sinusoidal spaces, in the liver parenchyma.

Pathogenesis of liver fibrosis: role of oxidative stress

In the liver, the progressive accumulation of connective tissue, a complex and dynamic process termed fibrosis, represents a very frequent event following a repeated or chronic insult of sufficient intensity to trigger a "wound healing"-like reaction. The fibrotic process recognises the involvement of various cells and different factors in bringing about an excessive fibrogenesis with disruption of intercellular contacts and interactions and of extracellular matrix composition. However, Kupffer cells, together with recruited mononuclear cells, and hepatic stellate cells are by far the key-players in liver fibrosis. Their cross-talk is triggered and favoured by a series of chemical mediators, with a prominent role played by the transforming growth factor beta. Both expression and synthesis of this inflammatory and pro-fibrogenic cytokine are mainly modulated through redox-sensitive reactions. Further, involvement of reactive oxygen species and lipid peroxidation products can be clearly demonstrated in other fundamental events of hepatic fibrogenesis, like activation and effects of stellate cells, expression of metalloproteinases and of their specific inhibitors. The important outcome of such findings as regards the pathogenesis of liver fibrosis derives from the observation of a consistent and marked oxidative stress condition in many if not all chronic disease processes affecting hepatic tissue. Hence, reactive oxidant species likely contribute to both onset and progression of fibrosis as induced by alcohol, viruses, iron or copper overload, cholestasis, hepatic blood congestion.