Perisinusoidal stellate cells (fat-storing cells, interstitial cells, lipocytes), their related structure in and around the liver sinusoids, and vitamin A-storing cells in extrahepatic organs

RESOLUTION OF CALVARIAL HYPEROSTOSIS IN AFRICAN LION CUBS (PANTHERA LEO LEO) AFTER VITAMIN A SUPPLEMENTATION

Two female (FL 1, FL 2) and one male (ML) 11-wk-old, intact, captive African lion cubs (Panthera leo leo) were presented with a history of mild vestibular signs. Initial serum vitamin A concentrations were low (140 nmol/L) for ML. Calvarial hyperostosis was confirmed using computed tomography (CT) of the head and cervical vertebrae in each cub. CT measurements were adapted in relation to the skull width. ML showed the most pronounced thickening of the tentorium cerebelli and occipital bone, represented by a tentorium cerebelli to skull width ratio (TCR) of 0.08 (FL 1: 0.06, FL 2: 0.05) and a basisphenoid to skull width ratio (BBR) of 0.07 (FL 1: 0.06, FL 2: 0.04). Magnetic resonance imaging (MRI) revealed cerebellar herniation and cervical intramedullary T2-weighted hyperintensity from C1, extending caudally for at least two cervical vertebrae in all cubs. Treatment was initiated with subcutaneous vitamin A supplementation and feeding of whole carcasses. Improvement in ataxia was noticed 3 wk later. Follow-up CT and MRI examinations were performed in ML after 3 and 8 mon. The affected bones appeared slightly less thickened and TCR and BBR had decreased to 0.05 after 3 mon. The cerebellum remained mildly herniated, accompanied by amelioration of cervical T2w hyperintensities. After 8 mon, evaluation and diagnostic imaging revealed further improvement regarding the neurologic status and measurements (TCR 0.05, BBR 0.04) despite persistence of a subtle cerebellar herniation. In conclusion, bone remodeling and improvement in clinical signs may be achievable in young lion cubs presented with calvarial hyperostosis and may be attributable to high-dose vitamin A supplementation.

Isolation of primary human liver cells from normal and nonalcoholic steatohepatitis livers

Here, we present a protocol for isolating human hepatocytes and neural progenitor cells from normal and nonalcoholic steatohepatitis livers. We describe steps for perfusion for scaled-up liver cell isolation and optimization of chemical digestion to achieve maximal yield and cell viability. We then detail a liver cell cryopreservation and potential applications, such as the use of human liver cells as a tool to link experimental and translational research.

The role of Ca2+ signalling in the pathology of exocrine pancreas

Exocrine pancreas has been the field of many successful studies in pancreatic physiology and pathology. However, related disease - acute pancreatitis (AP) is still takes it toll with more than 100,000 related deaths worldwide per year. In spite of significant scientific progress and several human trials currently running for AP, there is still no specific treatment in the clinic. Studies of the mechanism of initiation of AP have identified two crucial conditions: sustained elevations of cytoplasmic calcium concentration (Ca2+ plateau) and significantly reduced intracellular energy (ATP depletion). These hallmarks are interdependent, i.e., Ca2+ plateau increase energy demand for its clearance while energy production is greatly affected by the pathology. Result of long standing Ca2+ plateau is destabilisation of the secretory granules and premature activation of the digestive enzymes leading to necrotic cell death. Main attempts so far to break the vicious circle of cell death have been concentrated on reduction of Ca2+ overload or reduction of ATP depletion. This review will summarise these approaches, including recent developments of potential therapies for AP.

Retinoids stored locally in the lung are required to attenuate the severity of acute lung injury in male mice

Retinoids are potent transcriptional regulators that act in regulating cell proliferation, differentiation, and other cellular processes. We carried out studies in male mice to establish the importance of local cellular retinoid stores within the lung alveolus for maintaining its health in the face of an acute inflammatory challenge induced by intranasal instillation of lipopolysaccharide. We also undertook single cell RNA sequencing and bioinformatic analyses to identify roles for different alveolar cell populations involved in mediating these retinoid-dependent responses. Here we show that local retinoid stores and uncompromised metabolism and signaling within the lung are required to lessen the severity of an acute inflammatory challenge. Unexpectedly, our data also establish that alveolar cells other than lipofibroblasts, specifically microvascular endothelial and alveolar epithelial cells, are able to take up lipoprotein-transported retinoid and to accumulate cellular retinoid stores that are directly used to respond to an acute inflammatory challenge.

Recent advances in liver-on-chips: Design, fabrication, and applications

The liver is a multifunctional organ and the metabolic center of the human body. Most drugs and toxins are metabolized in the liver, resulting in varying degrees of hepatotoxicity. The damage of liver will seriously affect human health, so it is very important to study the prevention and treatment of liver diseases. At present, there are many research studies in this field. However, most of them are based on animal models, which are limited by the time-consuming processes and species difference between human and animals. In recent years, liver-on-chips have emerged and developed rapidly and are expected to replace animal models. Liver-on-chips refer to the use of a small number of liver cells on the chips to simulate the liver microenvironment and ultrastructure in vivo. They hold extensive applications in multiple fields by reproducing the unique physiological functions of the liver in vitro. In this review, we first introduced the physiology and pathology of liver and then described the cell system of liver-on-chips, the chip-based liver models, and the applications of liver-on-chips in liver transplantation, drug screening, and metabolic evaluation. Finally, we discussed the currently encountered challenges and future trends in liver-on-chips.

Lipid droplets, the Holy Grail of hepatic stellate cells: In health and hepatic fibrosis

Lipid droplets (LDs) are distinct morphological markers of hepatic stellate cells (HSCs). They are composed of a core of predominantly retinyl esters and triacylglycerols surrounded by a phospholipid layer; the latter harbors perilipins 2, 3, and 5, which help control LD lipolysis. Electron microscopy distinguishes between Types I and II LDs. Type I LDs are surrounded by acid phosphatase-positive lysosomes, which likely digest LDs. LD count and retinoid concentration are modulated by vitamin A intake. Alcohol consumption depletes hepatic retinoids and HSC LDs, with concomitant transformation of HSCs to fibrogenic myofibroblast-like cells. LD loss and accompanying HSC activation occur in HSC cell culture models. Loss of LDs is a consequence of and not a prerequisite for HSC activation. LDs are endowed with enzymes for synthesizing retinyl esters and triacylglycerols as well as neutral lipases and lysosomal acid lipase for breaking down LDs. HSCs have two distinct metabolic LD pools: an "original" pool in quiescent HSCs and a "new" pool emerging in HSC activation; this two-pool model provides a platform for analyzing LD dynamics in HSC activation. Besides lipolysis, LDs are degraded by lipophagy; however, the coordination between and relative contributions of these two pathways to LD removal are unclear. While induction of autophagy accelerates LD loss in quiescent HSCs and promotes HSC activation, blocking autophagy impairs LD degradation and inhibits HSC activation and fibrosis. This article is a critique of five decades of investigations into the morphology, molecular structure, synthesis, and degradation of LDs associated with HSC activation and fibrosis.

miR-345-5p curbs hepatic stellate cell activation and liver fibrosis progression by suppressing hypoxia-inducible factor-1alpha expression

Hepatic fibrosis, as a common stage of multiple liver diseases, currently has no effective drug treatment. Emerging evidence shows that miRNAs participate in the progression of liver fibrosis. However, the potential role of miRNAs in hepatic fibrosis is not yet fully understood. Herein, we first confirmed that miR-345-5p expression was significantly decreased in activated hepatic stellate cells (HSCs) and fibrotic livers. Functional analysis showed that overexpression of miR-345-5p in human LX-2 cells suppressed the expression of profibrotic markers and cellular proliferation in vitro. Using a dual-luciferase assay, we demonstrated that miR-345-5p regulates HSC activation by targeting the 3'UTR of HIF-1α mRNA. In addition, overexpression of miR-345-5p in vivo alleviated murine liver fibrosis induced by carbon tetrachloride (CCl4) injection, high-fat diet (HFD) feeding and bile duct ligation (BDL). Furthermore, overexpression of miR-345-5p downregulated the expression of HIF-1α and fibrosis markers in livers from different fibrosis models. Collectively, we conclude that miR-345-5p mediates the activation of HSCs by targeting HIF-1α, which subsequently modulates TGFβ/Smad2/Smad3 signaling. Thus, miR-345-5p may become a novel therapeutic target for the treatment of liver fibrosis.

Perivascular Mesenchymal Stem/Stromal Cells, an Immune Privileged Niche for Viruses?

Mesenchymal stem cells (MSCs) play a critical role in response to stress such as infection. They initiate the removal of cell debris, exert major immunoregulatory activities, control pathogens, and lead to a remodeling/scarring phase. Thus, host-derived ‘danger’ factors released from damaged/infected cells (called alarmins, e.g., HMGB1, ATP, DNA) as well as pathogen-associated molecular patterns (LPS, single strand RNA) can activate MSCs located in the parenchyma and around vessels to upregulate the expression of growth factors and chemoattractant molecules that influence immune cell recruitment and stem cell mobilization. MSC, in an ultimate contribution to tissue repair, may also directly trans- or de-differentiate into specific cellular phenotypes such as osteoblasts, chondrocytes, lipofibroblasts, myofibroblasts, Schwann cells, and they may somehow recapitulate their neural crest embryonic origin. Failure to terminate such repair processes induces pathological scarring, termed fibrosis, or vascular calcification. Interestingly, many viruses and particularly those associated to chronic infection and inflammation may hijack and polarize MSC’s immune regulatory activities. Several reports argue that MSC may constitute immune privileged sanctuaries for viruses and contributing to long-lasting effects posing infectious challenges, such as viruses rebounding in immunocompromised patients or following regenerative medicine therapies using MSC. We will herein review the capacity of several viruses not only to infect but also to polarize directly or indirectly the functions of MSC (immunoregulation, differentiation potential, and tissue repair) in clinical settings.

A Cytological Atlas of the Human Liver Proteome from PROTEOMESKY-LIVERHu 2.0, a Publicly Available Database

The liver plays a unique role as a metabolic center of the body, and also performs other important functions such as detoxification and immune response. Here, we establish a cell type-resolved healthy human liver proteome including hepatocytes (HCs), hepatic stellate cells (HSCs), Kupffer cells (KCs), and liver sinusoidal endothelial cells (LSECs) by high-resolution mass spectrometry. Overall, we quantify total 8354 proteins for four cell types and over 6000 proteins for each cell type. Analysis of this data set and regulatory pathway reveals the cellular labor division in the human liver follows the pattern that parenchymal cells make the main components of pathways, but nonparenchymal cells trigger these pathways. Human liver cells show some novel molecular features: HCs maintain KCs and LSECs homeostasis by producing cholesterol and ketone bodies; HSCs participate in xenobiotics metabolism as an agent deliverer; KCs and LSECs mediate immune response through MHC class II-TLRs and MHC class I-TGFβ cascade, respectively; and KCs play a central role in diurnal rhythms regulation through sensing diurnal IGF and temperature flux. Together, this work expands our understandings of liver physiology and provides a useful resource for future analyses of normal and diseased livers.

The suppression of pancreatic lipase-related protein 2 ameliorates experimental hepatic fibrosis in mice

Quiescent hepatic stellate cells (HSCs) store vitamin A as lipid droplets in the cytoplasm. When activated, these cells lose vitamin A and exhibit an increased capacity for proliferation, mobility, contractility, and the synthesis of collagen and other components of the extracellular matrix. Our previous work demonstrated that the lipid hydrolytic gene pancreatic lipase-related protein 2 (mPlrp2) is involved in the hydrolysis of retinyl esters (REs) in the liver. Here, we showed that bile duct ligation (BDL)-induced liver injury triggered the conditional expression of mPlrp2 in livers and describe evidence of a strong relationship between the expression of mPlrp2 and Acta-2, a marker for activated HSCs. RNA interference targeting mPlrp2 inhibited HSC activation and ameliorated hepatic fibrosis induced by BDL in mice. Liver BDL markedly reduced the adenosine level and increased the ratio between S-adenosyl-L-methionine (SAM) and S-adenosyl-L-homocysteine (SAH). Chromatin immunoprecipitation (ChIP) analysis demonstrated an increase in trimethylated histone H3K4 at the mPlrp2 promoter in BDL mice, which was associated with the conditional expression of mPlrp2 in the liver. SAM, a well-known hepatoprotective substance, inhibited mPlrp2 expression and reduced RE hydrolysis in mice with hepatic fibrosis induced by chronic CCl4 treatment. Liver fibrosis induced by CCl4 or BDL was improved in Plrp2-/- mice. Our results reveal that mPlrp2 suppression is a potential approach for treating hepatic fibrosis.

Fat causes necrosis and inflammation in parenchymal cells in human steatotic liver

Adapted fixation methods for electron microscopy allowed us to study liver cell fine structure in 217 biopsies of intact human livers over the course of 10 years. The following novel observations and concepts arose: single fat droplets in parenchymal cells can grow to a volume four times larger than the original cell, thereby extremely marginalizing the cytoplasm with all organelles. Necrosis of single parenchymal cells, still containing one huge fat droplet, suggests death by fat in a process of single-cell steatonecrosis. In a later stage of single-cell steatonecrosis, neutrophils and erythrocytes surround the single fat droplet, forming an inflammatory fat follicle indicating the apparent onset of inflammation. Also, fat droplets frequently incorporate masses of filamentous fragments and other material, most probably representing Mallory substance. No other structure or material was found that could possibly represent Mallory bodies. We regularly observe the extrusion of huge fat droplets, traversing the peripheral cytoplasm of parenchymal cells, the Disse space and the endothelium. These fat droplets fill the sinusoid as a sinusoidal lipid embolus. In conclusion, adapted methods of fixation applied to human liver tissue revealed that single, huge fat droplets cause necrosis and inflammation in single parenchymal cells. Fat droplets also collect Mallory substance and give rise to sinusoidal fat emboli. Therefore, degreasing of the liver seems to be an essential therapeutic first step in the self-repairing of non-alcoholic fatty liver disease. This might directly reduce single-cell steatotic necrosis and inflammation as elements in non-alcoholic steatohepatitis progression.

Hepatic stellate cells: current state and open questions

This review article summarizes 20 years of our research on hepatic stellate cells within the framework of two collaborative research centers CRC575 and CRC974 at the Heinrich Heine University. Over this period, stellate cells were identified for the first time as mesenchymal stem cells of the liver, and important functions of these cells in the context of liver regeneration were discovered. Furthermore, it was determined that the space of Disse - bounded by the sinusoidal endothelium and hepatocytes - functions as a stem cell niche for stellate cells. Essential elements of this niche that control the maintenance of hepatic stellate cells have been identified alongside their impairment with age. This article aims to highlight previous studies on stellate cells and critically examine and identify open questions and future research directions.

Improved Recovery from Liver Fibrosis by Crenolanib

Chronic liver diseases are associated with excessive deposition of extracellular matrix proteins. This so-called fibrosis can progress to cirrhosis and impair vital functions of the liver. We examined whether the receptor tyrosine kinase (RTK) class III inhibitor Crenolanib affects the behavior of hepatic stellate cells (HSC) involved in fibrogenesis. Rats were treated with thioacetamide (TAA) for 18 weeks to trigger fibrosis. After TAA treatment, the animals received Crenolanib for two weeks, which significantly improved recovery from liver fibrosis. Because Crenolanib predominantly inhibits the RTK platelet-derived growth factor receptor-β, impaired HSC proliferation might be responsible for this beneficial effect. Interestingly, blocking of RTK signaling by Crenolanib not only hindered HSC proliferation but also triggered their specification into hepatic endoderm. Endodermal specification was mediated by p38 mitogen-activated kinase (p38 MAPK) and c-Jun-activated kinase (JNK) signaling; however, this process remained incomplete, and the HSC accumulated lipids. JNK activation was induced by stress response-associated inositol-requiring enzyme-1α (IRE1α) in response to Crenolanib treatment, whereas β-catenin-dependent WNT signaling was able to counteract this process. In conclusion, the Crenolanib-mediated inhibition of RTK impeded HSC proliferation and triggered stress responses, initiating developmental processes in HSC that might have contributed to improved recovery from liver fibrosis in TAA-treated rats.

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

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

Liver Injury Impaired 25-Hydroxylation of Vitamin D Suppresses Intestinal Paneth Cell defensins, leading to Gut Dysbiosis and Liver Fibrogenesis

Vitamin D deficiency is co-prevalent with various liver diseases including cirrhosis, while the underlying mechanism remains elusive. Vitamin D receptor (VDR) is abundantly expressed in the distal region of small intestine, where the Paneth cells are enriched, suggesting that vitamin D signaling may modulates the intestinal Paneth cells and their production of defensins to restrain microbiome growth in the small intestine. In this study we found that in carbon tetrachloride-induced liver injury, hepatic 25-hydroxylation of vitamin D was impaired, leading to down regulated expression of Paneth cell fensins in the small intestine, gut dysbiosis, and endotoxinemia. While intraperitoneal injection of endotoxin (lipopolysaccharides) alone did not elicit liver fibrosis, it exacerbated the carbon tetrachloride initiated liver fibrogenesis. Oral gavage of synthetic Paneth cell alpha-defensin 5 (DEFA5) restored the homeostasis of gut microbiota, reduced endotoxemia, relieved liver inflammation, and ameliorated liver fibrosis. Likewise, Cholestyramine, cationic resin that can sequestrate endotoxin in the intestine, attenuated the liver fibrosis as well. Fecal transplant of the microbes derived from the DEFA5-treated donors improved liver fibrosis in the recipient mice. The intestinal Vdrconditional knockout mice exhibited reduction of Paneth cell defensins and lysozyme production, and worsened liver injury and fibrogenesis. Thus, liver injury impairs synthesis of 25(OH)VD3, which consequently impedes the Paneth cells functions in the small intestine, leading to gut dysbiosis for liver fibrogenesis.

Space of Disse: a stem cell niche in the liver

Recent evidence indicates that the plasticity of preexisting hepatocytes and bile duct cells is responsible for the appearance of intermediate progenitor cells capable of restoring liver mass after injury without the need of a stem cell compartment. However, mesenchymal stem cells (MSCs) exist in all organs and are associated with blood vessels which represent their perivascular stem cell niche. MSCs are multipotent and can differentiate into several cell types and are known to support regenerative processes by the release of immunomodulatory and trophic factors. In the liver, the space of Disse constitutes a stem cell niche that harbors stellate cells as liver resident MSCs. This perivascular niche is created by extracellular matrix proteins, sinusoidal endothelial cells, liver parenchymal cells and sympathetic nerve endings and establishes a microenvironment that is suitable to maintain stellate cells and to control their fate. The stem cell niche integrity is important for the behavior of stellate cells in the normal, regenerative, aged and diseased liver. The niche character of the space of Disse may further explain why the liver can become an organ of extra-medullar hematopoiesis and why this organ is frequently prone to tumor metastasis.

Pro- and Anti-fibrogenic Functions of Gram-Negative Bacterial Lipopolysaccharide in the Liver

Extensive research performed over several decades has identified cells participating in the initiation and progression of fibrosis, and the numerous underlying inter- and intra-cellular signaling pathways. However, liver fibrosis continues to be a major clinical challenge as the precise targets of treatment are still elusive. Activation of physiologically quiescent perisinusoidal hepatic stellate cells (HSCs) to a myofibroblastic proliferating, contractile and fibrogenic phenotype is a critical event in the pathogenesis of chronic liver disease. Thus, elucidation of the mechanisms of the reversal to quiescence or inhibition of activated HSCs, and/or their elimination via apoptosis has been the focus of intense investigation. Lipopolysaccharide (LPS), a gut-resident Gram-negative bacterial endotoxin, is a powerful pro-inflammatory molecule implicated in hepatic injury, inflammation and fibrosis. In both acute and chronic liver injury, portal venous levels of LPS are elevated due to increased intestinal permeability. LPS, via CD14 and Toll-like receptor 4 (TLR4) and its adapter molecules, stimulates macrophages, neutrophils and several other cell types to produce inflammatory mediators as well as factors that can activate HSCs and stimulate their fibrogenic activity. LPS also stimulates synthesis of pro- and anti-inflammatory cytokines/chemokines, growth mediators and molecules of immune regulation by HSCs. However, LPS was found to arrest proliferation of activated HSCs and to convert them into non-fibrogenic phenotype. Interestingly, LPS can elicit responses in HSCs independent of CD14 and TLR4. Identifying and/or developing non-inflammatory but anti-fibrogenic mimetics of LPS could be relevant for treating liver fibrosis.

Autophagic-CTSB-inflammasome axis modulates hepatic stellate cells activation in arsenic-induced liver fibrosis

Long-term exposure to arsenic can cause liver injury and fibrosis. The activation of hepatic stellate cells (HSCs) plays an essential role in the process of liver fibrosis. We found that NaAsO₂ caused liver damage and fibrosis in vivo, accompanied by excessive collagen deposition and HSCs activation. In addition, NaAsO₂ upregulated autophagy flux, elevated the level of cytoplasmic cathepsin B (CTSB), and activated the NOD-like receptors containing pyrin domain 3 (NLRP3) inflammasome in a subtle way. Consistent with these findings in vivo, we demonstrated that NaAsO₂-induced activation of HSCs depended on CTSB-mediated NLRP3 inflammasome activation in HSC-t6 cells and rats primary HSCs. Moreover, inhibition of autophagy decreased the cytoplasmic CTSB and alleviated the activation of the NLRP3 inflammasome, thereby attenuating the NaAsO₂-induced HSCs activation. In summary, these results indicated that NaAsO₂ induced HSCs activation via autophagic-CTSB-NLRP3 inflammasome pathway. These findings may provide a novel insight into the potential mechanism of NaAsO₂-induced liver fibrosis.

Quiescent hepatic stellate cells induce toxicity and sensitivity to doxorubicin in cancer cells through a caspase-independent cell death pathway: Central role of apoptosis-inducing factor

Hepatocellular carcinoma (HCC) is a major health problem worldwide and in the United States as its incidence has increased substantially within the past two decades. HCC therapy remains a challenge, primarily due to underlying liver disorders such as cirrhosis that determines treatment approach and efficacy. Activated hepatic stellate cells (A-HSCs) are the key cell types involved in hepatic fibrosis/cirrhosis. A-HSCs are important constituents of HCC tumor microenvironment (TME) and support tumor growth, chemotherapy resistance, cancer cell migration, and escaping immune surveillance. This makes A-HSCs an important therapeutic target in hepatic fibrosis/cirrhosis as well as in HCC. Although many studies have reported the role of A-HSCs in cancer generation and investigated the therapeutic potential of A-HSCs reversion in cancer arrest, not much is known about inactivated or quiescent HSCs (Q-HSCs) in cancer growth or arrest. Here we report that Q-HSCs resist cancer cell growth by inducing cytotoxicity and enhancing chemotherapy sensitivity. We observed that the conditioned media from Q-HSCs (Q-HSCCM) induces cancer cell death through a caspase-independent mechanism that involves an increase in apoptosis-inducing factor expression, nuclear localization, DNA fragmentation, and cell death. We further observed that Q-HSCCM enhanced the efficiency of doxorubicin, as measured by cell viability assay. Exosomes present in the conditioned media were not involved in the mechanism, which suggests the role of other factors (proteins, metabolites, or microRNA) secreted by the cells. Identification and characterization of these factors are important in the development of effective HCC therapy.

Function of Nr4a Orphan Nuclear Receptors in Proliferation, Apoptosis and Fuel Utilization Across Tissues

The Nr4a family of nuclear hormone receptors is composed of three members-Nr4a1/Nur77, Nr4a2/Nurr1 and Nr4a3/Nor1. While currently defined as ligandless, these transcription factors have been shown to regulate varied processes across a host of tissues. Of particular interest, the Nr4a family impinge, in a tissue dependent fashion, on cellular proliferation, apoptosis and fuel utilization. The regulation of these processes occurs through both nuclear and non-genomic pathways. The purpose of this review is to provide a balanced perspective of the tissue specific and Nr4a family member specific, effects on cellular proliferation, apoptosis and fuel utilization.

A novel technique to prepare a single cell suspension of isolated quiescent human hepatic stellate cells

To explore a simple and easy-to-learn procedure for the isolation of human quiescent hepatic stellate cells (HSCs) that requires no advanced training. Thus reducing costs and increasing efficiency. This protocol will provide sufficient primary cells with minimal contaminants for future basic research on diseases associated with human HSCs. Normal liver tissues were isolated from patients undergoing hepatic hemangioma resection, and a single cell suspension of these tissues was prepared using the Gentle MACS tissue processor. By using this method, the difficulty of the procedure was reduced, fewer cells were lost during the preparation treatments, and the maximal activity of single cells was maintained. Following preparation of the cell suspension, the HSCs were further isolated using a Nycodenz density gradient. Cell viability was examined by trypan blue staining, and the purity of the quiescent human HSCs was determined by autofluorescence and oil red O staining. Activated and quiescent human HSCs were identified using immunofluorescence and Western blotting. The cell cycle distribution in activated and quiescent human HSCs was analyzed by flow cytometry.The recovery rate of the HSCs was approximately (2.1 ± 0.23) × 10⁶ of tissue, with 94.43 ± 1.89% cell viability and 93.8 ± 1.52% purity. The technique used in this study is a simple, high-yield, and repeatable method for HSC isolation that is worthy of recommendation.

Vitamin A signaling and homeostasis in obesity, diabetes, and metabolic disorders

Much evidence has accumulated in the literature over the last fifteen years that indicates vitamin A has a role in metabolic disease prevention and causation. This literature proposes that vitamin A can affect obesity development and the development of obesity-related diseases including insulin resistance, type 2 diabetes, hepatic steatosis and steatohepatitis, and cardiovascular disease. Retinoic acid, the transcriptionally active form of vitamin A, accounts for many of the reported associations. However, a number of proteins involved in vitamin A metabolism, including retinol-binding protein 4 (RBP4) and aldehyde dehydrogenase 1A1 (ALDH1A1, alternatively known as retinaldehyde dehydrogenase 1 or RALDH1), have also been identified as being associated with metabolic disease. Some of the reported effects of these vitamin A-related proteins are proposed to be independent of their roles in assuring normal retinoic acid homeostasis. This review will consider both human observational data as well as published data from molecular studies undertaken in rodent models and in cells in culture. The primary focus of the review will be on the effects that vitamin A per se and proteins involved in vitamin A metabolism have on adipocytes, adipose tissue biology, and adipose-related disease, as well as on early stage liver disease, including non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH).

β-Carotene in the human body: metabolic bioactivation pathways - from digestion to tissue distribution and excretion

β-Carotene intake and tissue/blood concentrations have been associated with reduced incidence of several chronic diseases. Further bioactive carotenoid-metabolites can modulate the expression of specific genes mainly via the nuclear hormone receptors: retinoic acid receptor- and retinoid X receptor-mediated signalling. To better understand the metabolic conversion of β-carotene, inter-individual differences regarding β-carotene bioavailability and bioactivity are key steps that determine its further metabolism and bioactivation and mediated signalling. Major carotenoid metabolites, the retinoids, can be stored as esters or further oxidised and excreted via phase 2 metabolism pathways. In this review, we aim to highlight the major critical control points that determine the fate of β-carotene in the human body, with a special emphasis on β-carotene oxygenase 1. The hypothesis that higher dietary β-carotene intake and serum level results in higher β-carotene-mediated signalling is partly questioned. Alternative autoregulatory mechanisms in β-carotene / retinoid-mediated signalling are highlighted to better predict and optimise nutritional strategies involving β-carotene-related health beneficial mediated effects.

ARHGEF4-mediates the actin cytoskeleton reorganization of hepatic stellate cells in 3-dimensional collagen matrices

The actin cytoskeleton of hepatic stellate cells (HSCs) is reorganized when they are cultured in 3D collagen matrices. Here, we investigated the molecular mechanism of actin cytoskeleton reorganization in HSCs cultured in 3D floating collagen matrices (FCM) compared to those on 2D polystyrene surfaces (PS). First, we found that the generation of dendritic cellular processes was controlled by Rac1. Next, we examined the differential gene expression of HSCs cultured on 2D PS and in 3D FCM by RNA-Seq and focused on the changes of actin cytoskeleton reorganization-related molecular components and guanine nucleotide exchange factors (GEFs). The results showed that the expression of genes associated with actin cytoskeleton reorganization-related cellular components, filopodia and lamellipodia, were significantly decreased, but podosome-related genes was significantly increased in 3D FCM. Furthermore, we found that a Rac1-specific GEF, ARHGEF4, played roles in morphological changes, migration and podosome-related gene expression in HSCs cultured in 3D FCM.

Abbreviations: 2D PS: 2-dimensional polystyrene surface; 3D FCM: 3-dimensional floating collagen matrices; ARHGEF4: Rho guanine nucleotide exchange factor 4; ARHGEF6: Rho guanine nucleotide exchange factor 6; GEF: guanine nucleotide exchange factor; HSC: hepatic stellate cell

Role of the Gut-Liver Axis in Liver Inflammation, Fibrosis, and Cancer: A Special Focus on the Gut Microbiota Relationship

The gut and the liver are anatomically and physiologically connected, and this “gut–liver axis” exerts various influences on liver pathology. The gut microbiota consists of various microorganisms that normally coexist in the human gut and have a role of maintaining the homeostasis of the host. However, once homeostasis is disturbed, metabolites and components derived from the gut microbiota translocate to the liver and induce pathologic effects in the liver. In this review, we introduce and discuss the mechanisms of liver inflammation, fibrosis, and cancer that are influenced by gut microbial components and metabolites; we include recent advances in molecular‐based therapeutics and novel mechanistic findings associated with the gut–liver axis and gut microbiota.

Caveolin-1 is related to lipid droplet formation in hepatic stellate cells in human liver

Caveolins (CAVs) regulate intracellular cholesterol transport by a complex process involving caveolae, endoplasmic reticulum (ER), and the Golgi network. Hepatic stellate cells (HSCs) are the central site for retinoid storage in the liver and indeed the entire body. Herein, we attempted to elucidate the ultrastructural localization and expression of caveolin-1 (CAV-1) in human HSCs during the progression of liver cirrhosis (LC). Normal and hepatitis C-related cirrhotic liver samples were prepared using a modified perfusion-fixation method to fix organelle structures and molecules in their in vivo positions, and examined using immunoelectron microscopy. In control liver specimens, CAV-1 was minimally associated with low electron density lipid droplets (LDs) segregated around zones 1-2, and specifically associated with membranes surrounding LDs. CAV-1 was segregated in high-density LDs, consistent with the formation of membrane-enclosed lipid-rich vesicular structures, as well as caveolae on plasma membranes around zones 2-3. In cirrhotic liver specimens, CAV-1 molecules were inserted into the cytoplasmic leaflets of ER membranes for transportation to LDs. Thus, CAV-1 transport to LDs might represent an intracellular pathway from the ER in cirrhotic liver tissue.

Loureirin B inhibits the proliferation of hepatic stellate cells and the Wnt/β-catenin signaling pathway by regulating miR-148-3p

BACKGROUND

We investigated the activity of loureirin B against liver fibrosis and the underlying molecular mechanisms.

METHODS

Hepatic stellate cells (HSCs) from Sprague-Dawley rats were treated with different concentrations of loureirin B. We used the MTT assay to determine HSC proliferation, flow cytometry to analyze apoptosis, and western blot to determine the expressions of Bax, Bcl-2, Wnt1 and β-catenin. Real-time PCR was used to determine the expressions of Wnt1 and miR-148-3p.

RESULTS

The MTT assay showed that loureirin B treatment significantly inhibited the proliferation of HSCs in time- and dose-dependent manners. Loureirin B significantly promoted the apoptosis of HSCs, increased the expression of Bax and decreased the Bcl-2 level. Western blot analysis showed that the expressions of Wnt1 and β-catenin were obviously lower in the loureirin B treatment group than in the control group. We also found that loureirin B could decrease the Wnt1 mRNA level and increase miR-148-3p expression. Knockdown of miR-148-3p using inhibitor could reverse the effects of loureirin B on the proliferation and apoptosis of HSCs and the expressions of Bax, Bcl-2, Wnt1 and β-catenin.

CONCLUSION

Our results suggest that loureirin B inhibited the proliferation and promoted the apoptosis of HSCs, and suppressed the Wnt/β-catenin signaling pathway via regulation of miR-148-3p.

Stellate Cells in Tissue Repair, Inflammation, and Cancer

Stellate cells are resident lipid-storing cells of the pancreas and liver that transdifferentiate to a myofibroblastic state in the context of tissue injury. Beyond having roles in tissue homeostasis, stellate cells are increasingly implicated in pathological fibrogenic and inflammatory programs that contribute to tissue fibrosis and that constitute a growth-permissive tumor microenvironment. Although the capacity of stellate cells for extracellular matrix production and remodeling has long been appreciated, recent research efforts have demonstrated diverse roles for stellate cells in regulation of epithelial cell fate, immune modulation, and tissue health. Our present understanding of stellate cell biology in health and disease is discussed here, as are emerging means to target these multifaceted cells for therapeutic benefit.

Stellate cells and mesenchymal stem cells in benign mammary stroma are associated with risk factors for breast cancer - an observational study

Background

It is not known whether stromal cells in benign breast tissue can mediate risk of breast cancer. We recently described aldehyde dehydrogenase 1 A1 (ALDH1) positive (+) cells in morphologically normal breast stroma of premenopausal women, and the data indicated that their distribution is associated with clinical risk factors for breast cancer. The aim of the present study was to define the identities of these cells using histologic and immunohistologic methods, and to investigate associations between those cells and hormonal and genetic risk factors in pre- and postmenopausal women.

Methods

Stroma of morphologically normal tissue was analyzed in samples from 101 well-characterized women whose breasts had been operated. Morphology and immunolabeling were applied to determine cell identities based on the putative stem cell markers ALDH1 and stage-specific embryonic antigen-3 (SSEA3), and immunophenotypes indicating mast cells or stellate cells. The results were compared with the patients’ risk factors using regression analysis (two-tailed).

Results

ALDH1+ round/oval cells were associated with low parity in BRCA1/2 carriers (p = 0.022), while in non-BRCA1/2-carriers they were negatively associated with nulliparity (p = 0.057). In premenopausal women ALDH1+ round/oval cells were associated with family history (p = 0.058). SSEA3+ round/oval cells were morphologically and immunohistologically consistent with multilineage stress-enduring (Muse) cells, and these cells were independently associated with the breast cancer risk factors low parity (p = 0.015), family history (p = 0.021), and hormone use after menopause (p = 0.032). ALDH1+ spindle-shaped/polygonal cells were immunohistologically consistent with stellate cells, and were negatively associated with family history of breast cancer (p = 0.001).

Conclusion

This study identified novel stromal cell types in benign breast tissue that have a potential for stratifying women for breast cancer risk.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4151-x) contains supplementary material, which is available to authorized users.

Therapeutic pro-fibrogenic signaling pathways in fibroblasts

Myofibroblasts (MFs) play a critical role in the progression of chronic inflammatory and fibroproliferative diseases in different tissues/organs, whatever the etiology. Fibrosis is preceded and sustained by persistent injury and inflammatory response in a profibrogenic scenario involving mutual interactions, operated by several mediators and pathways, of MFs and related precursor cells with innate immunity cells and virtually any cell type in a defined tissue. These interactions, mediators and related signaling pathways are critical in initiating and perpetuating the differentiation of precursor cells into MFs that in different tissues share peculiar traits and phenotypic responses, including the ability to proliferate, produce ECM components, migrate and contribute to the modulation of inflammatory response and tissue angiogenesis. Literature studies related to liver, lung and kidney fibrosis have outlined a number of MF-related core regulatory fibrogenic signaling pathways conserved across these different organs and potentially targetable in order to develop effective antifibrotic therapeutic strategies.

Components of the Hepatocellular Carcinoma Microenvironment and Their Role in Tumor Progression

This review summarizes recently published data on the mechanisms of tumor cell interaction with the tumor microenvironment. Tumor stroma influences the processes of hepatocarcinogenesis, epithelial-to-mesenchymal transition, invasion, and metastasis. The tumor microenvironment includes both cellular and noncellular components. Main cellular components of hepatocellular carcinoma (HCC) stroma are tumor-associated fibroblasts, hepatic stellate cells, immune cells, and endothelial cells that produce extracellular components of tumor microenvironment such as extracellular matrix, various proteins, proteolytic enzymes, growth factors, and cytokines. The noncellular components of the stroma modulate signaling pathways in tumor cells and stimulate invasion and metastasis. The tumor microenvironment composition and organization can serve as prognostic factors in HCC pathogenesis. Current approaches in HCC targeted therapy are aimed at creating efficient strategies for interrupting tumor interactions with the stroma. Recent data on the composition and role of the microenvironment in HCC pathogenesis, as well as new developments in antitumor drug design are discussed.

Fibroblast growth factor 2 (FGF2) regulates cytoglobin expression and activation of human hepatic stellate cells via JNK signaling

Cytoglobin (CYGB) belongs to the mammalian globin family and is exclusively expressed in hepatic stellate cells (HSCs) in the liver. In addition to its gas-binding ability, CYGB is relevant to hepatic inflammation, fibrosis, and cancer because of its anti-oxidative properties; however, the regulation of CYGB gene expression remains unknown. Here, we sought to identify factors that induce CYGB expression in HSCs and to clarify the molecular mechanism involved. We used the human HSC cell line HHSteC and primary human HSCs isolated from intact human liver tissues. In HHSteC cells, treatment with a culture supplement solution that included fibroblast growth factor 2 (FGF2) increased CYGB expression with concomitant and time-dependent α-smooth muscle actin (αSMA) down-regulation. We found that FGF2 is a key factor in inducing the alteration in both CYGB and αSMA expression in HHSteCs and primary HSCs and that FGF2 triggered the rapid phosphorylation of both c-Jun N-terminal kinase (JNK) and c-JUN. Both the JNK inhibitor PS600125 and transfection of c-JUN-targeting siRNA abrogated FGF2-mediated CYGB induction, and conversely, c-JUN overexpression induced CYGB and reduced αSMA expression. Chromatin immunoprecipitation analyses revealed that upon FGF2 stimulation, phospho-c-JUN bound to its consensus motif (5'-TGA(C/G)TCA), located -218 to -222 bases from the transcription initiation site in the CYGB promoter. Of note, in bile duct-ligated mice, FGF2 administration ameliorated liver fibrosis and significantly reduced HSC activation. In conclusion, FGF2 triggers CYGB gene expression and deactivation of myofibroblastic human HSCs, indicating that FGF2 has therapeutic potential for managing liver fibrosis.

Molecular and functional characterization of CD133+ stem/progenitor cells infused in patients with end-stage liver disease reveals their interplay with stromal liver cells

BACKGROUND AIMS

Growing evidence supports the therapeutic potential of bone marrow (BM)-derived stem/progenitor cells for end-stage liver disease (ESLD). We recently demonstrated that CD133⁺ stem/progenitor cell (SPC) reinfusion in patients with ESLD is feasible and safe and improve, albeit transiently, liver function. However, the mechanism(s) through which BM-derived SPCs may improve liver function are not fully elucidated.

METHODS

Here, we characterized the circulating SPCs compartment of patients with ESLD undergoing CD133⁺ cell therapy. Next, we set up an in vitro model mimicking SPCs/liver microenvironment interaction by culturing granulocyte colony-stimulating factor (G-CSF)-mobilized CD133⁺and LX-2 hepatic stellate cells.

RESULTS

We found that patients with ESLD show normal basal levels of circulating hematopoietic and endothelial progenitors with impaired clonogenic ability. After G-CSF treatment, patients with ESLD were capable to mobilize significant numbers of functional multipotent SPCs, and interestingly, this was associated with increased levels of selected cytokines potentially facilitating SPC function. Co-culture experiments showed, at the molecular and functional levels, the bi-directional cross-talk between CD133⁺ SPCs and human hepatic stellate cells LX-2. Human hepatic stellate cells LX-2 showed reduced activation and fibrotic potential. In turn, hepatic stellate cells enhanced the proliferation and survival of CD133⁺ SPCs as well as their endothelial and hematopoietic function while promoting an anti-inflammatory profile.

DISCUSSION

We demonstrated that the interaction between CD133⁺ SPCs from patients with ESLD and hepatic stellate cells induces significant functional changes in both cellular types that may be instrumental for the improvement of liver function in cirrhotic patients undergoing cell therapy.

Endoplasmic reticulum oxidase 1α is critical for collagen secretion from and membrane type 1-matrix metalloproteinase levels in hepatic stellate cells

Upon liver injury, excessive deposition of collagen from activated hepatic stellate cells (HSCs) is a leading cause of liver fibrosis. An understanding of the mechanism by which collagen biosynthesis is regulated in HSCs will provide important clues for practical anti-fibrotic therapy. Endoplasmic reticulum oxidase 1α (ERO1α) functions as an oxidative enzyme of protein disulfide isomerase, which forms intramolecular disulfide bonds of membrane and secreted proteins. However, the role of ERO1α in HSCs remains unclear. Here, we show that ERO1α is expressed and mainly localized in the endoplasmic reticulum in human HSCs. When HSCs were transfected with ERO1α siRNA or an ERO1α shRNA-expressing plasmid, expression of ERO1α was completely silenced. Silencing of ERO1α expression in HSCs markedly suppressed their proliferation but did not induce apoptosis, which was accompanied by impaired secretion of collagen type 1. Silencing of ERO1α expression induced impaired disulfide bond formation and inhibited autophagy via activation of the Akt/mammalian target of rapamycin signaling pathway, resulting in intracellular accumulation of collagen type 1 in HSCs. Furthermore, silencing of ERO1α expression also promoted proteasome-dependent degradation of membrane type 1-matrix metalloproteinase (MT1-MMP), which stimulates cell proliferation through cleavage of secreted collagens. The inhibition of HSC proliferation was reversed by treatment with MT1-MMP-cleaved collagen type 1. The results suggest that ERO1α plays a crucial role in HSC proliferation via posttranslational modification of collagen and MT1-MMP and, therefore, may be a suitable therapeutic target for managing liver fibrosis.

Pancreatic stellate cells in pancreatic cancer: In focus

Pancreatic stellate cells are stromal cells that have multiple physiological functions such as the production of extracellular matrix, stimulation of amylase secretion, phagocytosis and immunity. In pancreatic cancer, stellate cells exhibit a different myofibroblastic-like morphology with the expression of alpha-smooth muscle actin, the activated form is engaged in several mechanisms that support tumorigenesis and cancer invasion and progression. In contrast to the aforementioned observations, eliminating the stromal cells that are positive for alpha-smooth muscle actin resulted in immune-evasion of the cancer cells and resulted in worse prognosis in animal models. Understanding the cancer-stromal signaling in pancreatic adenocarcinoma will provide novel strategies for therapy. Here we provide an updated review of studies that handle the topic "pancreatic stellate cells in cancer" and recent experimental approaches that can be the base for future directions in therapy.

Cellular retinoic acid bioavailability in various pathologies and its therapeutic implication

Retinoic acid (RA), an active metabolite of vitamin A, is a critical signaling molecule in various cell types. We found that RA depletion caused by expression of the RA-metabolizing enzyme CYP26A1 promotes carcinogenesis, implicating CYP26A1 as a candidate oncogene. Several studies of CYP26s have suggested that the biological effect of RA on target cells is primarily determined by "cellular RA bioavailability", which is defined as the RA level in an individual cell, rather than by the serum concentration of RA. Consistently, stellate cells store approximately 80% of vitamin A in the body, and the state of cellular RA bioavailability regulates their function. Based on the similarities between stellate cells and astrocytes, we demonstrated that retinal astrocytes regulate tight junction-based endothelial integrity in a paracrine manner. Since diabetic retinopathy is characterized by increased vascular permeability in its early pathogenesis, RA normalized retinal astrocytes that are compromised in diabetes, resulting in suppression of vascular leakiness. RA also attenuated the loss of the epithelial barrier in murine experimental colitis. The concept of "cellular RA bioavailability" in various diseases will be directed at understanding various pathologies caused by RA insufficiency, implying the potential feasibility of a therapeutic strategy targeting the stellate cell system.

Reversal of liver fibrosis: From fiction to reality

In chronic liver diseases, an ongoing hepatocellular injury together with inflammatory reaction results in activation of hepatic stellate cells (HSCs) and increased deposition of extracellular matrix (ECM) termed as liver fibrosis. It can progress to cirrhosis that is characterized by parenchymal and vascular architectural changes together with the presence of regenerative nodules. Even at late stage, liver fibrosis is reversible and the underlying mechanisms include a switch in the inflammatory environment, elimination or regression of activated HSCs and degradation of ECM. While animal models have been indispensable for our understanding of liver fibrosis, they possess several important limitations and need to be further refined. A better insight into the liver fibrogenesis resulted in a large number of clinical trials aiming at reversing liver fibrosis, particularly in patients with non-alcoholic steatohepatitis. Collectively, the current developments demonstrate that reversal of liver fibrosis is turning from fiction to reality.

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.

Genetic Variations Associated with Vitamin A Status and Vitamin A Bioavailability

Blood concentration of vitamin A (VA), which is present as different molecules, i.e., mainly retinol and provitamin A carotenoids, plus retinyl esters in the postprandial period after a VA-containing meal, is affected by numerous factors: dietary VA intake, VA absorption efficiency, efficiency of provitamin A carotenoid conversion to VA, VA tissue uptake, etc. Most of these factors are in turn modulated by genetic variations in genes encoding proteins involved in VA metabolism. Genome-wide association studies (GWAS) and candidate gene association studies have identified single nucleotide polymorphisms (SNPs) associated with blood concentrations of retinol and β-carotene, as well as with β-carotene bioavailability. These genetic variations likely explain, at least in part, interindividual variability in VA status and in VA bioavailability. However, much work remains to be done to identify all of the SNPs involved in VA status and bioavailability and to assess the possible involvement of other kinds of genetic variations, e.g., copy number variants and insertions/deletions, in these phenotypes. Yet, the potential usefulness of this area of research is exciting regarding the proposition of more personalized dietary recommendations in VA, particularly in populations at risk of VA deficiency.

Senescence in hepatic stellate cells as a mechanism of liver fibrosis reversal: a putative synergy between retinoic acid and PPAR-gamma signalings

Hepatic stellate cells (HSCs), also known as perisinusoidal cells, are pericytes found in the perisinusoidal space of the liver. HSCs are the major cell type involved in liver fibrosis, which is the formation of scar tissue in response to liver damage. When the liver is damaged, stellate cells can shift into an activated state, characterized by proliferation, contractility and chemotaxis. The activated HSCs secrete collagen scar tissue, which can lead to cirrhosis. Recent studies have shown that in vivo activation of HSCs by fibrogenic agents can eventually lead to senescence of these cells, which would contribute to reversal of fibrosis although it may also favor the insurgence of liver cancer. HSCs in their non-active form store huge amounts of retinoic acid derivatives in lipid droplets, which are progressively depleted upon cell activation in injured liver. Retinoic acid is a metabolite of vitamin A (retinol) that mediates the functions of vitamin A, generally required for growth and development. The precise function of retinoic acid and its alterations in HSCs has yet to be elucidated, and nonetheless in various cell types retinoic acid and its receptors (RAR and RXR) are known to act synergistically with peroxisome proliferator-activated receptor gamma (PPAR-gamma) signaling through the activity of transcriptional heterodimers. Here, we review the recent advancements in the understanding of how retinoic acid signaling modulates the fibrogenic potential of HSCs and proposes a synergistic combined action with PPAR-gamma in the reversal of liver fibrosis.

Adenovirus-mediated expression of orphan nuclear receptor NR4A2 targeting hepatic stellate cell attenuates liver fibrosis in rats

Liver fibrosis is a wound-healing response characterized with the accumulation of extracellular matrix (ECM). And hepatic stellate cells (HSCs) are the principal cell source of ECM. NR4A2 (Nurr1) is a member of orphan nuclear receptor NR4A family and acts as transcription factor. It participates in regulating cell differentiation, proliferation and apoptosis. We previously demonstrated that NR4A2 expression in fibrotic liver reduced significantly compared with normal liver and NR4A2 knockout in HSCs promoted ECM production. In the present study we explored the role of NR4A2 on liver fibrosis. Studies in cultured HSCs demonstrated that NR4A2 over-expression suppressed the activation of HSCs, such as ECM production and invasion ability. Moreover cell cycle was arrested, cell apoptosis was promoted and cell signaling pathway was influenced. Adenovirus-mediated delivery of NR4A2 in rats ameliorated significantly dimethylnitrosamine (DMN) induced liver fibrosis. The In vivo experiments produced results consistent with in vitro experiments. Taken together these results demonstrate NR4A2 enhancement attenuates liver fibrosis via suppressing the activation of HSCs and NR4A2 may be an ideal target for anti-fibrotic therapy.

New Concepts on Pathogenesis and Diagnosis of Liver Fibrosis; A Review Article

Liver fibrosis is a potentially reversible response to hepatic insults, triggered by different chronic diseases most importantly viral hepatitis, alcoholic, and nonalcoholic fatty liver disease. In the course of the chronic liver disease, hepatic fibrogenesis may develop, which is attributed to various types of cells, molecules, and pathways. Activated hepatic stellate cell (HSC), the primary source of extracellular matrix (ECM), is fundamental in pathophysiology of fibrogenesis, and thus is the most attractable target for reversing liver fibrosis. Although, liver biopsy has long been considered as the gold standard for diagnosis and staging of hepatic fibrosis, assessing progression and regression by biopsy is hampered by its limitations. We provide recent views on noninvasive approaches including serum biomarkers and radiologic techniques.

The Role of Lipin-1 in the Regulation of Fibrogenesis and TGF-β Signaling in Hepatic Stellate Cells

The adipogenic transcriptional regulation was reported to inhibit transdifferentiation of hepatic stellate cells (HSCs), which constitute the main fibrogenic cell type in the liver. Lipin-1 exhibits a dual function: an enzyme that catalyzes the conversion of phosphatidate to diacylglycerol and a transcriptional regulator. However, the involvement of Lipin-1 in the regulation of transforming growth factor-β (TGF-β) signaling and fibrogenesis in HSCs is not fully understood. Here, we showed that Lipin-1 was downregulated in activated primary HSCs and TGF-β-treated LX-2 cells, immortalized human HSC cell lines. The downregulation of Lipin-1 by TGF-β was not dependent on altered mRNA stability but rather on protein stability. Treatment of LX-2 cells with the proteasome inhibitor led to the accumulation of Lipin-1. Moreover, we observed a significant increase in Lipin-1 polyubiquitination. Overexpression of Lipin-1 attenuated TGF-β-induced fibrogenic gene expression. In addition, Lipin-1 inhibited TGF-β-mediated activation of Sma and Mad-related family (SMAD), a major transcription factor that transduces intracellular signals from TGF-β. Resveratrol, a well-known natural polyphenolic antioxidant, is known to inhibit liver fibrosis, although its mechanism of action remains unknown. Our data showed that resveratrol significantly increased the levels of Lipin-1 protein and mRNA in HSCs. Further investigation revealed that resveratrol blocked the polyubiquitination of Lipin-1. Resveratrol inhibited TGF-β-induced fibrogenic gene expression. TGF-β-induced SMAD binding element-luciferase reporter activity was significantly diminished by resveratrol with a simultaneous decrease in SMAD3 phosphorylation. Consistently, knockdown of the Lipin-1 gene using siRNA abolished the inhibitory effect of resveratrol. We conclude that Lipin-1 can antagonize HSC activation through the inhibition of TGF-β/SMAD signaling and that resveratrol may affect Lipin-1 gene induction and contribute to the inhibition of TGF-β-mediated hepatic fibrogenesis.

Stereological assessment of sexual dimorphism in the rat liver reveals differences in hepatocytes and Kupffer cells but not hepatic stellate cells

There is long-standing evidence that male and female rat livers differ in enzyme activity. More recently, differences in gene expression profiling have also been found to exist; however, it is still unclear whether there is morphological expression of male/female differences in the normal liver. Such differences could help to explain features seen at the pathological level, such as the greater regenerative potential generally attributed to the female liver. In this paper, hepatocytes (HEP), Kupffer cells (KC) and hepatic stellate cells (HSC) of male and female rats were examined to investigate hypothesised differences in number, volume and spatial co-localisation of these cell types. Immunohistochemistry and design-based stereology were used to estimate total numbers, numbers per gram and mean cell volumes. The position of HSC within lobules (periportal vs. centrilobular) and their spatial proximity to KC was also assessed. In addition, flow cytometry was used to investigate the liver ploidy. In the case of HEP and KC, differences in the measured cell parameters were observed between male and female specimens; however, no such differences were detected for HSC. Female samples contained a higher number of HEP per gram, with more binucleate cells. The HEP nuclei were smaller in females, which was coincident with more abundant diploid particles in these animals. The female liver also had a greater number of KC per gram, with a lower percentage of KC in the vicinity of HSC compared with males. In this study, we document hitherto unknown morphological sexual dimorphism in the rat liver, namely in HEP and KC. These differences may account for the higher regenerative potential of the female liver and lend weight to the argument for considering the rat liver as a sexually dimorphic organ.

Vitamin A and insulin are required for the maintenance of hepatic stellate cell quiescence

Transdifferentiation of vitamin A-storing hepatic stellate cells (HSCs) to vitamin A-depleted myofibroblastic cells leads to liver fibrosis. Vitamin A regulates lipid accumulation and gene transcription, suggesting that vitamin A is involved in the maintenance of HSC quiescence under a physiological condition. However, the precise mechanism remains elusive because there is no appropriate in vitro culture system for quiescent HSCs. Here, we show that treatment of quiescent HSCs with vitamin A partially maintained the accumulation of lipid droplets and expression of quiescent HSC markers (glial fibrillary acidic protein, peroxisome proliferator-activator receptor-γ and CCAAT/enhancer-binding protein-α) and also the expression of myofibroblastic markers (α-smooth muscle actin, heat shock protein 47 and collagen type I). On the other hand, combined treatment with vitamin A and insulin sustained the characteristic of HSC quiescence and completely suppressed the expression of myofibroblastic markers through activation of the JAK2/STAT5 signaling pathway and increased expression of sterol regulatory element binding protein-1. These treated HSCs transdifferentiated to myofibroblastic cells under a culture condition with fetal bovine serum. The results suggest an important role of vitamin A and insulin in the maintenance of HSC quiescence under a physiological condition.