p75 Neurotrophin receptor is a marker for precursors of stellate cells and portal fibroblasts in mouse fetal liver

Liver portal fibroblasts induce the functions of primary human hepatocytes in vitro

In vitro human liver models are critical to mitigate species-specific differences observed for toxicology, disease modeling, and regenerative medicine. Interactions with mesenchyme (i.e., fibroblasts) can promote phenotypic functions of primary human hepatocytes (PHHs) in culture; however, using liver-derived fibroblasts remains elusive. Portal fibroblasts (PFs) around the portal triad influence bile duct formation during development, but their role in regulating homeostatic hepatic functions remains unknown. Here, we show that human liver PFs induce long-term phenotypic functions in PHHs at higher levels than activated hepatic stellate cells across 2-dimensional and 3-dimensional culture formats. While PF-conditioned media induces some hepatic functions, partly via insulin-like growth factor binding protein-5 signaling, direct contact is necessary to induce optimal functional levels. Inhibiting Notch signaling reduces progenitor-like characteristics of PHHs and further enhances functionality. Overall, this work demonstrates a unique role for PFs in modulating hepatic functions and provides all-human and all-liver coculture strategies for downstream applications.

Establishment of human induced pluripotent stem cell-derived hepatobiliary organoid with bile duct for pharmaceutical research use

In vitro models of the human liver are promising alternatives to animal tests for drug development. Currently, primary human hepatocytes (PHHs) are preferred for pharmacokinetic and cytotoxicity tests. However, they are unable to recapitulate the flow of bile in hepatobiliary clearance owing to the lack of bile ducts, leading to the limitation of bile analysis. To address the issue, a liver organoid culture system that has a functional bile duct network is desired. In this study, we aimed to generate human iPSC-derived hepatobiliary organoids (hHBOs) consisting of hepatocytes and bile ducts. The two-step differentiation process under 2D and semi-3D culture conditions promoted the maturation of hHBOs on culture plates, in which hepatocyte clusters were covered with monolayered biliary tubes. We demonstrated that the hHBOs reproduced the flow of bile containing a fluorescent bile acid analog or medicinal drugs from hepatocytes into bile ducts via bile canaliculi. Furthermore, the hHBOs exhibited pathophysiological responses to troglitazone, such as cholestasis and cytotoxicity. Because the hHBOs can recapitulate the function of bile ducts in hepatobiliary clearance, they are suitable as a liver disease model and would be a novel in vitro platform system for pharmaceutical research use.

Plasticity, heterogeneity, and multifunctionality of hepatic stellate cells in liver pathophysiology

HSCs, the resident pericytes of the liver, have consistently been at the forefront of liver research due to their crucial roles in various hepatic pathological processes. Prior literature often depicted HSCs in a binary framework, categorizing them as either quiescent or activated. However, recent advances in HSC research, particularly the advent of single-cell RNA-sequencing, have revolutionized our understanding of these cells. This sophisticated technique offers an unparalleled, high-resolution insight into HSC populations, uncovering a spectrum of diversity and functional heterogeneity across various physiological states of the liver, ranging from liver development to the liver aging process. The single-cell RNA-sequencing revelations have also highlighted the intrinsic plasticity of HSCs and underscored their complex roles in a myriad of pathophysiological processes, including liver injury, repair, and carcinogenesis. This review aims to integrate and clarify these recent discoveries, focusing on how the inherent plasticity of HSCs is central to their dynamic roles both in maintaining liver homeostasis and orchestrating responses to liver injury. Future research will clarify whether findings from rodent models can be translated to human livers and guide how these insights are harnessed to develop targeted therapeutic interventions.

An idiosyncratic zonated stroma encapsulates desmoplastic liver metastases and originates from injured liver

A perimetastatic capsule is a strong positive prognostic factor in liver metastases, but its origin remains unclear. Here, we systematically quantify the capsule's extent and cellular composition in 263 patients with colorectal cancer liver metastases to investigate its clinical significance and origin. We show that survival improves proportionally with increasing encapsulation and decreasing tumor-hepatocyte contact. Immunostaining reveals the gradual zonation of the capsule, transitioning from benign-like NGFRhigh stroma at the liver edge to FAPhigh stroma towards the tumor. Encapsulation correlates with decreased tumor viability and preoperative chemotherapy. In mice, chemotherapy and tumor cell ablation induce capsule formation. Our results suggest that encapsulation develops where tumor invasion into the liver plates stalls, representing a reparative process rather than tumor-induced desmoplasia. We propose a model of metastases growth, where the efficient tumor colonization of the liver parenchyma and a reparative liver injury reaction are opposing determinants of metastasis aggressiveness.

Efficient Muscle Regeneration by Human PSC-Derived CD82+ ERBB3+ NGFR+ Skeletal Myogenic Progenitors

Differentiation of pluripotent stem cells (PSCs) is a promising approach to obtaining large quantities of skeletal myogenic progenitors for disease modeling and cell-based therapy. However, generating skeletal myogenic cells with high regenerative potential is still challenging. We recently reported that skeletal myogenic progenitors generated from mouse PSC-derived teratomas possess robust regenerative potency. We have also found that teratomas derived from human PSCs contain a skeletal myogenic population. Here, we showed that these human PSC-derived skeletal myogenic progenitors had exceptional engraftability. A combination of cell surface markers, CD82, ERBB3, and NGFR enabled efficient purification of skeletal myogenic progenitors. These cells expressed PAX7 and were able to differentiate into MHC+ multinucleated myotubes. We further discovered that these cells are expandable in vitro. Upon transplantation, the expanded cells formed new dystrophin⁺ fibers that reconstituted almost ¾ of the total muscle volume, and repopulated the muscle stem cell pool. Our study, therefore, demonstrates the possibility of producing large quantities of engraftable skeletal myogenic cells from human PSCs.

An autocrine signaling circuit in hepatic stellate cells underlies advanced fibrosis in nonalcoholic steatohepatitis

Advanced hepatic fibrosis, driven by the activation of hepatic stellate cells (HSCs), affects millions worldwide and is the strongest predictor of mortality in nonalcoholic steatohepatitis (NASH); however, there are no approved antifibrotic therapies. To identify antifibrotic drug targets, we integrated progressive transcriptomic and morphological responses that accompany HSC activation in advanced disease using single-nucleus RNA sequencing and tissue clearing in a robust murine NASH model. In advanced fibrosis, we found that an autocrine HSC signaling circuit emerged that was composed of 68 receptor-ligand interactions conserved between murine and human NASH. These predicted interactions were supported by the parallel appearance of markedly increased direct stellate cell-cell contacts in murine NASH. As proof of principle, pharmacological inhibition of one such autocrine interaction, neurotrophic receptor tyrosine kinase 3-neurotrophin 3, inhibited human HSC activation in culture and reversed advanced murine NASH fibrosis. In summary, we uncovered a repertoire of antifibrotic drug targets underlying advanced fibrosis in vivo. The findings suggest a therapeutic paradigm in which stage-specific therapies could yield enhanced antifibrotic efficacy in patients with advanced hepatic fibrosis.

Histopathological growth patterns of liver metastasis: updated consensus guidelines for pattern scoring, perspectives and recent mechanistic insights

The first consensus guidelines for scoring the histopathological growth patterns (HGPs) of liver metastases were established in 2017. Since then, numerous studies have applied these guidelines, have further substantiated the potential clinical value of the HGPs in patients with liver metastases from various tumour types and are starting to shed light on the biology of the distinct HGPs. In the present guidelines, we give an overview of these studies, discuss novel strategies for predicting the HGPs of liver metastases, such as deep-learning algorithms for whole-slide histopathology images and medical imaging, and highlight liver metastasis animal models that exhibit features of the different HGPs. Based on a pooled analysis of large cohorts of patients with liver-metastatic colorectal cancer, we propose a new cut-off to categorise patients according to the HGPs. An up-to-date standard method for HGP assessment within liver metastases is also presented with the aim of incorporating HGPs into the decision-making processes surrounding the treatment of patients with liver-metastatic cancer. Finally, we propose hypotheses on the cellular and molecular mechanisms that drive the biology of the different HGPs, opening some exciting preclinical and clinical research perspectives.

TNFAIP6 defines the MSC subpopulation with enhanced immune suppression activities

Background

Mesenchymal stromal/stem cells (MSCs) have been intensively investigated in both pre-clinical and clinical studies. However, the therapeutic efficacy varies resulting from the heterogenicity of MSCs. Therefore, purifying the specific MSC subpopulation with specialized function is necessary for their therapeutic applications.

Methods

The large-scale RNA sequencing analysis was performed to identify potential cell markers for the mouse MSCs. Then, the immune suppression activities of the purified MSC subpopulation were assessed in vitro and in vivo.

Results

The TNFAIP6 (tumor necrosis factor alpha-induced protein 6) has been identified as a potential cell marker for mouse MSCs, irrespective of tissue origin and laboratory origin. The TNFAIP6⁺ mouse MSCs showed enhanced immune suppression activities and improved therapeutic effects on the mouse model of acute inflammation, resulting from faster response to immune stimulation.

Conclusions

Therefore, we have demonstrated that the TNFAIP6⁺ MSC subpopulation has enhanced immune suppression capabilities.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03176-5.

Neurotrophic factors stimulate the activation of hepatic stellate cells in liver fibrosis

BACKGROUND AND AIMS

Patients with liver fibrosis who have pain in the liver region may have changed nerve factors. The expression of neurokines and hepatic nerves in liver fibrosis, however, was little understood. In order to better understand how liver fibrosis develops, we plan to look into the hepatic nerve and neurokine changes and how they relate to hepatic stellate cells (HSCs).

METHODS

The expression of neurokines in liver samples from 55 chronic hepatitis B patients and the carbon tetrachloride (CCl₄) animal model were studied. The co-staining of Nissl and α-SMA allowed us to investigate the neurons and their interaction with α-SMA in fibrotic livers, as well as the expression of the glial cell marker glial fibrillary acidic protein (GFAP) and its relationship with α-SMA, a marker of HSCs. SH-SY5Y cells were treated with a fibrotic serum to imitate the hepatic microenvironment on neuronal cells. We also used brain-derived neurotrophic factor (BDNF) to stimulate mouse primary HSCs and LX2.

RESULTS

The levels of mRNA for neurokines such as BDNF, GFAP, and growth-associated protein (GAP43) are significantly increased in both human and animal liver fibrosis. As liver fibrosis advances, we found that Nissl bodies and α-SMA may co-localize, suggesting a connection between hepatic nerves and HSCs. Human fibrotic serum may increase neurkines, notably BDNF, in SH-SY5Y cells. We also found that BDNF increased pro-inflammatory cytokines and fibrogenic markers in hHSCs.

CONCLUSIONS

Patients with hepatic fibrosis had significantly higher levels of BDNF, GFAP, GAP43, and nerve fibers. HSC and nerve fibers interact, and nerves also create neurogenic substances that promote liver fibrosis and HSC activation.

Cellular Mechanisms of Liver Fibrosis

The liver is a central organ in the human body, coordinating several key metabolic roles. The structure of the liver which consists of the distinctive arrangement of hepatocytes, hepatic sinusoids, the hepatic artery, portal vein and the central vein, is critical for its function. Due to its unique position in the human body, the liver interacts with components of circulation targeted for the rest of the body and in the process, it is exposed to a vast array of external agents such as dietary metabolites and compounds absorbed through the intestine, including alcohol and drugs, as well as pathogens. Some of these agents may result in injury to the cellular components of liver leading to the activation of the natural wound healing response of the body or fibrogenesis. Long-term injury to liver cells and consistent activation of the fibrogenic response can lead to liver fibrosis such as that seen in chronic alcoholics or clinically obese individuals. Unidentified fibrosis can evolve into more severe consequences over a period of time such as cirrhosis and hepatocellular carcinoma. It is well recognized now that in addition to external agents, genetic predisposition also plays a role in the development of liver fibrosis. An improved understanding of the cellular pathways of fibrosis can illuminate our understanding of this process, and uncover potential therapeutic targets. Here we summarized recent aspects in the understanding of relevant pathways, cellular and molecular drivers of hepatic fibrosis and discuss how this knowledge impact the therapy of respective disease.

Fibrotic Events in the Progression of Cholestatic Liver Disease

Cholestatic liver diseases including primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) are associated with active hepatic fibrogenesis, which can ultimately lead to the development of cirrhosis. However, the exact relationship between the development of liver fibrosis and the progression of cholestatic liver disease remains elusive. Periductular fibroblasts located around the bile ducts seem biologically different from hepatic stellate cells (HSCs). The fibrotic events in these clinical conditions appear to be related to complex crosstalk between immune/inflammatory mechanisms, cytokine signalling, and perturbed homeostasis between cholangiocytes and mesenchymal cells. Several animal models including bile duct ligation (BDL) and the Mdr2-knockout mice have improved our understanding of mechanisms underlying chronic cholestasis. In the present review, we aim to elucidate the mechanisms of fibrosis in order to help to identify potential diagnostic and therapeutic targets.

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.

A Deactivation Factor of Fibrogenic Hepatic Stellate Cells Induces Regression of Liver Fibrosis in Mice

BACKGROUND AND AIMS

Hepatic stellate cells (HSCs), a key player in the progression of liver fibrosis, are activated by various inflammatory stimuli and converted to myofibroblast-like cells with excessive collagen production. Despite many attempts to suppress activation of HSCs or inhibit collagen production in activated HSCs, their clinical applications have not been established yet. Recently, the deactivation of HSCs has been reported as a mechanism underlying the reversibility of experimental liver fibrosis. In the present study, we sought for deactivation factors of HSCs that induce regression of established liver fibrosis.

APPROACH AND RESULTS

We identified transcription factor 21 (Tcf21) as one of the transcription factors whose expression was up-regulated in parallel to the differentiation of fetal HSCs. Expression of Tcf21 in HSCs remarkably decreased during culture-induced activation in vitro and in murine and human fibrotic liver tissue in vivo. This reduced Tcf21 expression was recovered during the spontaneous regression of murine liver fibrosis. Tcf21 was also examined for its effects by adeno-associated virus serotype 6-mediated Tcf21 gene transfer into cultured activated HSCs and mice with carbon tetrachloride- or methionine-choline deficient diet-induced liver fibrosis. Overexpression of Tcf21 in activated HSCs not only suppressed fibrogenic gene expression but also restored cells, at least in part, to a quiescent phenotype both in vitro and in vivo. These phenotypic changes of HSCs were accompanied by the regression of steatohepatitis and fibrosis and improved hepatic architecture and function.

CONCLUSIONS

Tcf21 has been identified as a deactivation factor of fibrogenic HSCs, providing insight into a treatment strategy for the otherwise intractable liver fibrosis.

Vasoactive Intestinal Peptide Derived From Liver Mesenchymal Cells Mediates Tight Junction Assembly in Mouse Intrahepatic Bile Ducts

Formation of intrahepatic bile ducts (IHBDs) proceeds in accordance with their microenvironment. Particularly, mesenchymal cells around portal veins regulate the differentiation and ductular morphogenesis of cholangiocytes in the developing liver; however, further studies are needed to fully understand the arrangement of IHBDs into a continuous hierarchical network. This study aims to clarify the interaction between biliary and liver mesenchymal cells during IHBD formation. To identify candidate factors contributing to this cell–cell interaction, mesenchymal cells were isolated from embryonic day 16.5 matrix metalloproteinase 14 (MMP14)‐deficient (knockout [KO]) mice livers, in which IHBD formation is retarded, and compared with those of the wild type (WT). WT mesenchymal cells significantly facilitated the formation of luminal structures comprised of hepatoblast‐derived cholangiocytes (cholangiocytic cysts), whereas MMP14‐KO mesenchymal cells failed to promote cyst formation. Comprehensive analysis revealed that expression of vasoactive intestinal peptide (VIP) was significantly suppressed in MMP14‐KO mesenchymal cells. VIP and VIP receptor 1 (VIPR1) were mainly expressed in periportal mesenchymal cells and cholangiocytic progenitors during IHBD development, respectively, in vivo. VIP/VIPR1 signaling significantly encouraged cholangiocytic cyst formation and up‐regulated tight junction protein 1, cystic fibrosis transmembrane conductance regulator, and aquaporin 1, in vitro. VIP antagonist significantly suppressed the tight junction assembly and the up‐regulation of ion/water transporters during IHBD development in vivo. In a cholestatic injury model of adult mice, exogenous VIP administration promoted the restoration of damaged tight junctions in bile ducts and improved hyperbilirubinemia. Conclusion: VIP is produced by periportal mesenchymal cells during the perinatal stage. It supports bile duct development by establishing tight junctions and up‐regulating ion/water transporters in cholangiocytes. VIP contributes to prompt recovery from cholestatic damage through the establishment of tight junctions in the bile ducts.

Myofibroblasts control the proliferation of fetal hepatoblasts and their differentiated cholangiocytes during the hepatoblast-to-cholangiocyte transition

Mesenchymal cells in the liver provide the microenvironment for hepatoblasts expansion and differentiation. We have previously demonstrated that myofibroblasts (MFs) promoted hepatoblasts differentiation into cholangiocytes, whereas its role in controlling the proliferation of hepatoblasts and their differentiated cholangiocytes remains elusive. Here, we investigated the role of MFs in regulating the proliferation of hepatoblasts and their differentiated cholangiocytes using an indirect coculture system. When cocultured with hepatoblasts, MFs promoted hepatoblasts differentiation into cholangiocytes and inhibited the proliferation and stemness of hepatoblasts. However, when hepatoblasts already differentiated into cholangiocytes, MFs promoted the differentiated cholangiocytes proliferation. In addition, hepatoblast proliferation genes such as hepatocyte growth factor (HGF), insulin-like growth factor-1 and 2 (IGF-1 and 2), midkine 1 (Mdk1), and pleiotrophin (Ptn) expression in MFs were down-regulated compared with their levels in fibroblasts. Our findings uncover the role of MFs in controlling the proliferation of hepatoblasts and their differentiated cholangiocytes, potentially providing a novel therapeutic strategy for cholangiocyte regeneration.

Direct and indirect coculture of mouse hepatic progenitor cells with mouse embryonic fibroblasts for the generation of hepatocytes and cholangiocytes

The widespread use of hepatocytes and cholangiocytes for regenerative medicine and tissue engineering is restricted by the limited number of hepatocytes and cholangiocytes; a simple and effective method for the expansion and differentiation of the hepatic progenitor cells (HPCs) is required. Recent studies demonstrated that mouse embryonic fibroblasts (MEFs) play an important role in supporting the proliferation of the mouse hepatic progenitor cells (mHPCs). However, the effect of direct and indirect coculture of MEFs with mHPCs on the differentiation of mHPCs is poorly studied. Herein, we show that mHPCs rapidly proliferate and form colonies in direct or indirect contact coculture with MEFs in the serum-free medium. Importantly, after direct contact coculture of the mHPCs with MEFs for 6 days, mHPCs expressed the hepatic marker albumin (ALB) and did not express the cholangiocyte marker CK19, indicating their differentiation into hepatocytes. In contrast, after indirect contact coculture of the mHPCs with MEFs for 6 days, mHPCs expressed the cholangiocyte marker CK19 and did not express the hepatic marker ALB, indicating their differentiation into cholangiocytes. These results indicate that direct and indirect contact cocultures of the mHPCs with MEFs are useful for rapidly producing hepatocytes and cholangiocytes.

Hepatic stellate cells regulate hepatic progenitor cells differentiation via the TGF-β1/Jagged1 signaling axis

Hepatic stellate cells (HSCs) play an important microenvironmental role in hepatic progenitor cells (HPCs) differentiation fate. To reveal the specific mechanism of HSCs induced by transforming growth factor β1 (TGF-β1) signaling in HPCs differentiation process, we used Knockin and knockdown technologies induced by lentivirus to upregulate or downregulate TGF-β1 level in mouse HSCs (mHSCs) (mHSCs-TGF-β1 or mHSCs-TGF-βR1sih3). Primary mouse HPCs (mHPCs) were isolated and were cocultured with mHSCs-TGF-β1 and mHSCs-TGF-βR1sih3 for 7 days. Differentiation of mHPCs was detected by quantitative reverse transcriptase polymerase chain reaction analysis and immunofluorence in vitro. mHPCs-E_14.5 cell lines and differently treated mHSCs were cotransplanted into mice spleens immediately after establishment of acute liver injury model for animal studies. Engraftment and differentiation of transplanted cells as well as liver function recovery were measured at the seventh day via different methods. mHSCs-TGF-β1 were transformed into myofibroblasts and highly expressed Jagged1, but that expression was reduced after blockage of TGF-β1 signaling. mHPCs highly expressed downstream markers of Jagged1/Notch signaling and cholangiocyte markers (CK19, SOX9, and Hes1) after coculture with mHSCs-TGF-β1 in vitro. In contrast, mature hepatocyte marker (ALB) was upregulated in mHPCs in coculture conditions with mHSCs-TGF-βR1sih3. At the seventh day of cell transplantation assay, mHPCs-E _14.5 engrafted and differentiated into cholangiocytes after cotransplanting with TGF-β1-knockin mHSCs, but the cells had a tendency to differentiate into hepatocytes when transplanted with TGF-βR1-knockdown mHSCs, which corresponded to in vitro studies. HSCs play an important role in regulating HPCs differentiation into cholangiocytes via the TGF-β1/Jagged1 signaling axis. However, HPCs have a tendency to differentiate into hepatocytes after blockage of TGF-β1 signaling in HSCs.

Differential expression of Lutheran/BCAM regulates biliary tissue remodeling in ductular reaction during liver regeneration

Under chronic or severe liver injury, liver progenitor cells (LPCs) of biliary origin are known to expand and contribute to the regeneration of hepatocytes and cholangiocytes. This regeneration process is called ductular reaction (DR), which is accompanied by dynamic remodeling of biliary tissue. Although the DR shows apparently distinct mode of biliary extension depending on the type of liver injury, the key regulatory mechanism remains poorly understood. Here, we show that Lutheran (Lu)/Basal cell adhesion molecule (BCAM) regulates the morphogenesis of DR depending on liver disease models. Lu⁺ and Lu^- biliary cells isolated from injured liver exhibit opposite phenotypes in cell motility and duct formation capacities in vitro. By overexpression of Lu, Lu^- biliary cells acquire the phenotype of Lu⁺ biliary cells. Lu-deficient mice showed severe defects in DR. Our findings reveal a critical role of Lu in the control of phenotypic heterogeneity of DR in distinct liver disease models.

Bile is a green to yellow liquid that the body uses to break down and digest fatty molecules. The substance is produced by the liver, and then it is collected and transported to the small bowel by a series of tubes known as the bile duct.

When the liver is damaged, the ‘biliary’ cells that line the duct orchestrate the repair of the organ. In fact, the duct often reorganizes itself differently depending on the type of disease the liver is experiencing. For example, the biliary cells can form thin tube-like structures that deeply invade liver tissues, or they can grow into several robust pipes near the existing bile duct. However, it remains largely unknown which protein – or proteins – drive these different types of remodeling.

Miura et al. find that, in mice, the biliary cells which invade an injured liver have a large amount of a protein called Lutheran at their surface, but that the cells that form robust ducts do not. This protein helps a cell attach to its surroundings. In addition, the biliary cells can adopt different types of repairing behaviors depending on the amount of Lutheran in their environment.

Further experiments show that it is difficult for genetically modified mice without the protein to reshape their bile duct after liver injury. Finally, Miura et al. also detect Lutheran in the remodeling livers of patients with liver disease. Taken together, these results suggest that Lutheran plays an important role in tailoring the repairing roles of the biliary cells to a particular disease. The next step would be to clarify how different liver conditions coordinate the amount of Lutheran in biliary cells to create the right type of remodeling.

Generation of Hepatic Stellate Cells from Human Pluripotent Stem Cells Enables In Vitro Modeling of Liver Fibrosis

The development of complex in vitro hepatic systems and artificial liver devices has been hampered by the lack of reliable sources for relevant cell types, such as hepatic stellate cells (HSCs). Here we report efficient differentiation of human pluripotent stem cells into HSC-like cells (iPSC-HSCs). iPSC-HSCs closely resemble primary human HSCs at the transcriptional, cellular, and functional levels and possess a gene expression profile intermediate between that of quiescent and activated HSCs. Functional analyses revealed that iPSC-HSCs accumulate retinyl esters in lipid droplets and are activated in response to mediators of wound healing, similar to their in vivo counterparts. When maintained as 3D spheroids with HepaRG hepatocytes, iPSC-HSCs exhibit a quiescent phenotype but mount a fibrogenic response and secrete pro-collagen in response to known stimuli and hepatocyte toxicity. Thus, this protocol provides a robust in vitro system for studying HSC development, modeling liver fibrosis, and drug toxicity screening.

Isolation of a unique hepatic stellate cell population expressing integrin α8 from embryonic mouse livers

BACKGROUND

Hepatic stellate cells (HSCs) play an important role in liver fibrogenesis. However, little is known about their phenotype and role in liver development. The aim of this study is to identify specific markers for embryonic HSCs.

RESULTS

Using antibodies against ALCAM and PDPN, we separated mesothelial cells (MCs) and HSCs from developing livers and identified integrin α8 (ITGA8) as a marker for embryonic desmin+ HSCs that are preferentially localized near the developing liver surface and α-smooth muscle actin+ perivascular mesenchymal cells around the vein. A cell lineage-tracing study revealed that upon differentiation, MC-derived HSCs or perivascular mesenchymal cells express ITGA8 during liver development. Using anti-ITGA8 antibodies, we succeeded in isolating MC-derived HSCs and perivascular mesenchymal cells from embryonic livers. In direct co-culture, ITGA8+ mesenchymal cells promoted the expression of hepatocyte and cholangiocyte markers in hepatoblasts. In the normal adult liver, expression of ITGA8 was restricted to portal fibroblasts in the portal triad. Upon liver injury, myofibroblasts increased the expression of ITGA8.

CONCLUSIONS

ITGA8 is a specific cell surface marker of MC-derived HSCs and perivascular mesenchymal cells in the developing liver. Our data suggest that ITGA8+ mesenchymal cells maintain the phenotype of hepatoblast in liver development. Developmental Dynamics 247:867-881, 2018. © 2018 Wiley Periodicals, Inc.

Nerve growth factor upregulates sirtuin 1 expression in cholestasis: a potential therapeutic target

This study investigated the regulatory role of nerve growth factor (NGF) in sirtuin 1 (SIRT1) expression in cholestatic livers. We evaluated the expression of NGF and its cognate receptors in human livers with hepatolithiasis and the effects of NGF therapy on liver injury and hepatic SIRT1 expression in a bile duct ligation (BDL) mouse model. Histopathological and molecular analyses showed that the hepatocytes of human diseased livers expressed NGF, proNGF (a precursor of NGF), TrkA and p75NTR, whereas only p75NTR was upregulated in hepatolithiasis, compared with non-hepatolithiasis livers. In the BDL model without NGF therapy, p75NTR, but not TrkA antagonism, significantly deteriorated BDL-induced liver injury. By contrast, the hepatoprotective effect of NGF was abrogated only by TrkA and not by p75NTR antagonism in animals receiving NGF therapy. Intriguingly, a positive correlation between hepatic SIRT1 and NGF expression was found in human livers. In vitro studies demonstrated that NGF upregulated SIRT1 expression in mouse livers and human Huh-7 and rodent hepatocytes. Both NGF and proNGF induced protective effects against hydrogen peroxide-induced cytotoxicity in Huh-7 cells, whereas inhibition of TrkA and p75NTR activity prevented oxidative cell death. Mechanistically, NGF, but not proNGF, upregulated SIRT1 expression in human Huh-7 and rodent hepatocytes via nuclear factor (NF)-κB activity, whereas NGF-induced phosphoinositide-3 kinase/Akt, extracellular signal–regulated kinase and NF-κB signaling and SIRT1 activity were involved in its hepatoprotective effects against oxidative injury. These findings suggest that pharmacological manipulation of the NGF/SIRT1 axis might serve as a novel approach for the treatment of cholestatic disease.

Oncostatin M causes liver fibrosis by regulating cooperation between hepatic stellate cells and macrophages in mice

Fibrosis is an important wound-healing process in injured tissues, but excessive fibrosis is often observed in patients with chronic inflammation. Although oncostatin M (OSM) has been reported to play crucial roles for recovery from acute liver injury by inducing tissue inhibitor of metalloproteinase 1 (Timp1) expression, the role of OSM in chronic liver injury (CLI) is yet to be elucidated. Here, we show that OSM exerts powerful fibrogenic activity by regulating macrophage activation during CLI. Genetic ablation of the OSM gene alleviated fibrosis in a mouse model of chronic hepatitis. Conversely, continuous expression of OSM in a normal mouse liver by hydrodynamic tail vein injection (HTVi) induced severe fibrosis without necrotic damage of hepatocytes, indicating that OSM is involved in the fundamental process of liver fibrosis (LF) after hepatitis. In a primary coculture of hepatic stellate cells (HSCs) and hepatic macrophages (HMs), OSM up-regulated the expression of fibrogenic factors, such as transforming growth factor-β and platelet-derived growth factor in HMs, while inducing Timp1 expression in HSCs, suggesting the synergistic roles of OSM for collagen deposition in the liver. Fluorescence-activated cell sorting analyses using OSM-HTVi and OSM knockout mice have revealed that bone-marrow-derived monocyte/macrophage are responsive to OSM for profibrotic activation. Furthermore, depletion or blocking of HMs by administration of clodronate liposome or chemokine inhibitor prevented OSM-induced fibrosis.

CONCLUSION

OSM plays a crucial role in LF by coordinating the phenotypic change of HMs and HSCs. Our data suggest that OSM is a promising therapeutic target for LF. (Hepatology 2018;67:296-312).

Relationship between hepatic progenitor cell-mediated liver regeneration and non-parenchymal cells

Hepatic progenitor cells (HPCs) are thought to reside in the canals of Hering and can be activated and contribute to liver regeneration in response to liver injury by proliferating and differentiating towards both hepatocytes and biliary epithelial cells. In this setting, several cytokines, chemokines, and growth factors related to liver inflammation and other liver cells comprising the HPC niche, namely hepatic stellate cells (HSCs), play crucial roles in HPC activation and differentiation. In response to several types of liver injury, tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is secreted by several inflammatory cells, including monocytes, T lymphocytes, and macrophages, and acts as an initiator of the HPC niche and HSC activation. Following TWEAK-induced activation of the HPC niche, fibroblast growth factor 7 and hepatocyte growth factor released from activated HSC play central roles in maintaining HPC proliferation. In contrast, HGF-MET and Wnt3a-β-catenin signals are the predominant mediators of the hepatocyte differentiation of HPC, whereas epidermal growth factor receptor-NOTCH signaling controls HPC differentiation towards biliary epithelial cells. These signals are maintained exclusively by activated HSC and inflammatory cells surrounding HPC. Together, HSC and inflammatory cells surrounding HPC are responsible for the precise control of HPC proliferation and differentiation fate. In this review, we discuss recent progress in understanding of interactions between HPC and other liver cells in HPC-mediated liver regeneration in the setting of liver inflammation.

Proper BMP Signaling Levels Are Essential for 3D Assembly of Hepatic Cords from Hepatoblasts and Mesenchymal Cells

BACKGROUND

Because the molecular mechanisms of morphogenesis of the hepatic cord and sinus are unclear, we investigated the involvement of bone morphogenetic protein (BMP4) in hepatic sinusoid morphogenesis.

METHODS

We used embryonic chicken livers, which develop rapidly, as our model, and investigated expression of BMP-related genes. BMP4 activity was manipulated by overexpressing BMP4 and its antagonist, noggin.

RESULTS

During hepatic cord morphogenesis, BMP4 and its receptors are expressed in both peri-sinusoidal cells and hepatoblasts as the sinusoids form, whereas noggin is expressed transiently in peri-sinusoidal cells at early stages. Suppression of BMP activity with noggin overexpression disrupted normal hepatic sinusoid structure, leading to liver congestion, failure of fibronectin deposition, and markedly reduced numbers of peri-sinusoidal cells. However, overexpression of BMP did not change sinusoidal morphology but increased endothelial cell number. Noggin overexpression resulted in disrupted cord organization, and dilated sinusoidal space, eventually leading to increased apoptosis and failed hepatocyte differentiation.

CONCLUSIONS

Our results show that proper BMP signaling mediates peri-sinusoidal cell-hepatoblast interactions during development; this is essential for hepatic cord organization among hepatoblasts, endothelium, and presumptive hepatic stellate cells.

CPM Is a Useful Cell Surface Marker to Isolate Expandable Bi-Potential Liver Progenitor Cells Derived from Human iPS Cells

To develop a culture system for large-scale production of mature hepatocytes, liver progenitor cells (LPCs) with a high proliferation potential would be advantageous. We have found that carboxypeptidase M (CPM) is highly expressed in embryonic LPCs, hepatoblasts, while its expression is decreased along with hepatic maturation. Consistently, CPM expression was transiently induced during hepatic specification from human-induced pluripotent stem cells (hiPSCs). CPM⁺ cells isolated from differentiated hiPSCs at the immature hepatocyte stage proliferated extensively in vitro and expressed a set of genes that were typical of hepatoblasts. Moreover, the CPM⁺ cells exhibited a mature hepatocyte phenotype after induction of hepatic maturation and also underwent cholangiocytic differentiation in a three-dimensional culture system. These results indicated that hiPSC-derived CPM⁺ cells share the characteristics of LPCs, with the potential to proliferate and differentiate bi-directionally. Thus, CPM is a useful marker for isolating hiPSC-derived LPCs, which allows development of a large-scale culture system for producing hepatocytes and cholangiocytes.

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CPM is a novel marker for hepatoblasts during liver development

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Self-renewing hiPSC-derived CPM⁺ LPCs exhibit bi-potency in vitro

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An efficient and convenient protocol for the generation of hiPSC-derived LPCs

The development of hepatic stellate cells in normal and abnormal human fetuses - an immunohistochemical study

The precise embryological origin and development of hepatic stellate cells is not established. Animal studies and observations on human fetuses suggest that they derive from posterior mesodermal cells that migrate via the septum transversum and developing diaphragm to form submesothelial cells beneath the liver capsule, which give rise to mesenchymal cells including hepatic stellate cells. However, it is unclear if these are similar to hepatic stellate cells in adults or if this is the only source of stellate cells. We have studied hepatic stellate cells by immunohistochemistry, in developing human liver from autopsies of fetuses with and without malformations and growth restriction, using cellular Retinol Binding Protein-1 (cRBP-1), Glial Fibrillary Acidic Protein (GFAP), and α-Smooth Muscle Actin (αSMA) antibodies, to identify factors that influence their development. We found that hepatic stellate cells expressing cRBP-1 are present from the end of the first trimester of gestation and reduce in density throughout gestation. They appear abnormally formed and variably reduced in number in fetuses with abnormal mesothelial Wilms Tumor 1 (WT1) function, diaphragmatic hernia and in ectopic liver nodules without mesothelium. Stellate cells showed similarities to intravascular cells and their presence in a fetus with diaphragm agenesis suggests they may be derived from circulating stem cells. Our observations suggest circulating stem cells as well as mesothelium can give rise to hepatic stellate cells, and that they require normal mesothelial function for their development.

Bile acids and stellate cells

Hepatic stellate cells are mainly known for their contribution to fibrogenesis in chronic liver diseases, but their identity and function in normal liver remain unclear. They were recently identified as liver-resident mesenchymal stem cells (MSCs), which can differentiate not only into adipocytes and osteocytes, but also into liver epithelial cells such as hepatocytes and bile duct cells as investigated in vitro and in vivo. During hepatic differentiation, stellate cells and other MSCs transiently develop into liver progenitor cells with epithelial characteristics before hepatocytes are established. Transplanted stellate cells from the liver and pancreas are able to contribute to liver regeneration in stem cell-based liver injury models and can also home into the bone marrow, which is in line with their classification as MSCs. There is experimental evidence that bile acids support liver regeneration and are able to activate signaling pathways in hepatic stellate cells. For this reason, it is important to analyze the influence of bile acids on developmental fate decisions of hepatic stellate cells and other MSC populations.

Up-regulation of nerve growth factor in cholestatic livers and its hepatoprotective role against oxidative stress

The role of nerve growth factor (NGF) in liver injury induced by bile duct ligation (BDL) remains elusive. This study aimed to investigate the relationship between inflammation and hepatic NGF expression, to explore the possible upstream molecules up-regulating NGF, and to determine whether NGF could protect hepatocytes from oxidative liver injury. Biochemical and molecular detection showed that NGF was up-regulated in cholestatic livers and plasma, and well correlated with systemic and hepatic inflammation. Conversely, systemic immunosuppression reduced serum NGF levels and resulted in higher mortality in BDL-treated mice. Immunohistochemistry showed that the up-regulated NGF was mainly localized in parenchymal hepatocytes. In vitro mechanistic study further demonstrated that TGF-β1 up-regulated NGF expression in clone-9 and primary rat hepatocytes. Exogenous NGF supplementation and endogenous NGF overexpression effectively protected hepatocytes against TGF-β1- and oxidative stress-induced cell death in vitro, along with reduced formation of oxidative adducted proteins modified by 4-HNE and 8-OHdG. TUNEL staining confirmed the involvement of anti-apoptosis in the NGF-exhibited hepatoprotection. Moreover, NGF potently induced Akt phosphorylation and increased Bcl-2 to Bax ratios, whereas these molecular alterations by NGF were only seen in the H₂O₂-, but not TGF-β1-treated hepatocytes. In conclusion, NGF exhibits anti-oxidative and hepatoprotective effects and is suggested to be therapeutically applicable in treating cholestatic liver diseases.

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.

The neural crest: a versatile organ system

The neural crest is the name given to the strip of cells at the junction between neural and epidermal ectoderm in neurula-stage vertebrate embryos, which is later brought to the dorsal neural tube as the neural folds elevate. The neural crest is a heterogeneous and multipotent progenitor cell population whose cells undergo EMT then extensively and accurately migrate throughout the embryo. Neural crest cells contribute to nearly every organ system in the body, with derivatives of neuronal, glial, neuroendocrine, pigment, and also mesodermal lineages. This breadth of developmental capacity has led to the neural crest being termed the fourth germ layer. The neural crest has occupied a prominent place in developmental biology, due to its exaggerated migratory morphogenesis and its remarkably wide developmental potential. As such, neural crest cells have become an attractive model for developmental biologists for studying these processes. Problems in neural crest development cause a number of human syndromes and birth defects known collectively as neurocristopathies; these include Treacher Collins syndrome, Hirschsprung disease, and 22q11.2 deletion syndromes. Tumors in the neural crest lineage are also of clinical importance, including the aggressive melanoma and neuroblastoma types. These clinical aspects have drawn attention to the selection or creation of neural crest progenitor cells, particularly of human origin, for studying pathologies of the neural crest at the cellular level, and also for possible cell therapeutics. The versatility of the neural crest lends itself to interlinked research, spanning basic developmental biology, birth defect research, oncology, and stem/progenitor cell biology and therapy.

The types of hepatic myofibroblasts contributing to liver fibrosis of different etiologies

Liver fibrosis results from dysregulation of normal wound healing, inflammation, activation of myofibroblasts, and deposition of extracellular matrix (ECM). Chronic liver injury causes death of hepatocytes and formation of apoptotic bodies, which in turn, release factors that recruit inflammatory cells (neutrophils, monocytes, macrophages, and lymphocytes) to the injured liver. Hepatic macrophages (Kupffer cells) produce TGFβ1 and other inflammatory cytokines that activate Collagen Type I producing myofibroblasts, which are not present in the normal liver. Secretion of TGFβ1 and activation of myofibroblasts play a critical role in the pathogenesis of liver fibrosis of different etiologies. Although the composition of fibrogenic myofibroblasts varies dependent on etiology of liver injury, liver resident hepatic stellate cells and portal fibroblasts are the major source of myofibroblasts in fibrotic liver in both experimental models of liver fibrosis and in patients with liver disease. Several studies have demonstrated that hepatic fibrosis can reverse upon cessation of liver injury. Regression of liver fibrosis is accompanied by the disappearance of fibrogenic myofibroblasts followed by resorption of the fibrous scar. Myofibroblasts either apoptose or inactivate into a quiescent-like state (e.g., stop collagen production and partially restore expression of lipogenic genes). Resolution of liver fibrosis is associated with recruitment of macrophages that secrete matrix-degrading enzymes (matrix metalloproteinase, collagenases) and are responsible for fibrosis resolution. However, prolonged/repeated liver injury may cause irreversible crosslinking of ECM and formation of uncleavable collagen fibers. Advanced fibrosis progresses to cirrhosis and hepatocellular carcinoma. The current review will summarize the role and contribution of different cell types to populations of fibrogenic myofibroblasts in fibrotic liver.

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

BACKGROUND AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The portal fibroblast: not just a poor man's stellate cell

Portal fibroblasts, the resident fibroblasts of the portal tract, are found in the mesenchyme surrounding the bile ducts. Their roles in liver homeostasis and response to injury are undefined and controversial. Although portal fibroblasts almost certainly give rise to myofibroblasts during the development of biliary fibrosis, recent lineage tracing studies suggest that their contribution to fibrogenesis is limited compared with that of hepatic stellate cells. Other functions of portal fibroblasts include participation in the peribiliary stem cell niche, regulation of cholangiocyte proliferation, and deposition of specific matrix proteins. Portal fibroblasts synthesize elastin and other components of microfibrils; these may serve structural roles, providing stability to ducts and the vasculature under conditions of increased ductal pressure, or could regulate the bioavailability of the fibrogenic transforming growth factor β in response to injury. Viewing portal fibroblasts in the context of fibroblast populations throughout the body and studying their niche-specific roles in matrix deposition and epithelial regulation could yield new insights into their contributions in the normal and injured liver. Understanding the functions of portal fibroblasts will require us to view them as more than just an alternative to hepatic stellate cells in fibrosis.

Semaphorin 3E secreted by damaged hepatocytes regulates the sinusoidal regeneration and liver fibrosis during liver regeneration

The liver has a remarkable capacity to regenerate after injury. Although the regulatory mechanisms of hepatocytic regeneration have been a subject of intense study, the dynamism of the sinusoids, specialized blood vessels in the liver, remains largely unknown. Transient activation of hepatic stellate cells and hepatic sinusoidal endothelial cells, which constitute the sinusoids, contributes to liver regeneration during acute injury, whereas their sustained activation causes liver fibrosis during chronic injury. We focused on understanding the association between damaged hepatocytes and sinusoidal regeneration or liver fibrogenesis using a carbon tetrachloride-induced liver injury mouse model. Damaged hepatocytes rapidly expressed semaphorin 3E (Sema3e), which induced contraction of sinusoidal endothelial cells and thereby contributed to activating hepatic stellate cells for wound healing. In addition, ectopic and consecutive expression of Sema3e in hepatocytes by the hydrodynamic tail-vein injection method resulted in disorganized regeneration of sinusoids and sustained activation of hepatic stellate cells. In contrast, liver fibrosis ameliorated in Sema3e-knockout mice compared with wild-type mice in a chronic liver injury model. Our results indicate that Sema3e, secreted by damaged hepatocytes, affects sinusoidal regeneration in a paracrine manner during liver regeneration, suggesting that Sema3e is a novel therapeutic target in liver fibrogenesis.

Semaphorin 7A contributes to TGF-β-mediated liver fibrogenesis

Semaphorin7A (SEMA7A) is a membrane-anchored protein involved in immune and inflammatory responses, exerting an effect on pulmonary fibrosis. Thus, we aimed to investigate the role of SEMA7A in hepatic fibrosis. Liver injury was induced in vivo by carbon tetrachloride i.p. injection or bile duct ligation in wild-type and SEMA7A knockout (KO) mice. Human and mouse liver samples and primary mouse hepatic cell populations were used for Western blot analysis, quantitative real-time RT-PCR, and immunohistochemistry. SEMA7A is highly expressed in hepatic stellate cells (HSCs). The expression of SEMA7A and its receptor β1-integrin subunit increase during liver injury and in activated HSCs. Transforming growth factor β-stimulated HSCs showed increased expression of SEMA7A in a SMAD2/3-independent manner, leading to increased expression of fibrogenic and inflammation markers. This pattern was significantly blunted in SEMA7A KO HSCs. Overexpression of SEMA7A in HSCs showed increased fibrogenic and inflammation markers expression. In vivo, SEMA7A KO mice treated with carbon tetrachloride and bile duct ligation developed reduced fibrosis versus wild-type mice. Moreover, SEMA7A expression increased in liver samples of patients with fibrosis versus healthy controls. SEMA7A was expressed in the liver and was increased in the course of liver fibrosis, both in mice and in humans. SEMA7A was mainly expressed in HSCs with respect to other cell types in the liver and plays a critical role in regulating fibrosis.

Roles of myofibroblasts and notch and hedgehog signaling pathways in the formation of intrahepatic bile duct lesions in polycystic kidney rats

Polycystic kidney (PCK) rats, an animal model of Caroli's disease, show a dilatation of intrahepatic bile ducts (IHBD) called "ductal plate malformation." Mesenchymal cells and the Notch and Hedgehog signaling pathways in portal tracts are reportedly involved in the normal development of IHBD, although there have been no studies on the roles of these signaling pathways in PCK rats. We immunohistochemically examined the expression of the molecules related to these signaling pathways in portal tracts. All molecules related to these signaling pathways expressed in portal tracts in Sprague Dawley (SD) rats (control) were also expressed in PCK rats. Mesenchymal cells (myofibroblasts) were frequently found in the connective tissue of portal tracts of 20 embryonic-day-old (E20D), 1-day-old (1D), and 1-week-old (1W) SD and PCK rats and were abundant in PCK rats. Interestingly, myofibroblasts almost disappeared at in both strains of 3W rats. Jagged1 was expressed in mesenchymal cells in portal tracts and was abundant in PCK rats. Double immunostaining showed that Jagged1-positive cells were myofibroblasts. Notch2 and HES1 were expressed in cholangiocytes of the bile ducts of both rats. Sonic Hedgehog was similarly expressed in the bile ducts of both rats. A well-balanced and time-sequential expression of the Notch and Hedgehog family in portal tracts might be essential for the normal development of IHBD in E20D to 1W SD rats, and an imbalanced interaction of these molecules, particularly increased Jagged1 expression in periductal and periportal myofibroblasts and Notch2 expressed in cholangiocytes, may be involved in the formation of bile duct lesions in PCK rats.

Hepatic stellate cells in liver development, regeneration, and cancer

Hepatic stellate cells are liver-specific mesenchymal cells that play vital roles in liver physiology and fibrogenesis. They are located in the space of Disse and maintain close interactions with sinusoidal endothelial cells and hepatic epithelial cells. It is becoming increasingly clear that hepatic stellate cells have a profound impact on the differentiation, proliferation, and morphogenesis of other hepatic cell types during liver development and regeneration. In this Review, we summarize and evaluate the recent advances in our understanding of the formation and characteristics of hepatic stellate cells, as well as their function in liver development, regeneration, and cancer. We also discuss how improved knowledge of these processes offers new perspectives for the treatment of patients with liver diseases.

α1- and α5-containing laminins regulate the development of bile ducts via β1 integrin signals

Signals derived from basal lamina components are important for developing three-dimensional architecture of epithelial tissues. Laminins consisting of α, β, and γ subunits in basal lamina play pivotal roles in the formation and maintenance of epithelial tissue structures. However, it remains unclear which laminin isoforms transmit signals and how epithelial cells receive them to regulate multiple developmental processes. In three-dimensional culture of a liver progenitor cell line, Hepatic Progenitor Cells Proliferating on Laminin (HPPL), the cells establish apicobasal polarity and form cysts with a central lumen. Neutralizing antibody against β1 integrin blocked the formation and maintenance of the cyst structure, indicating that β1 integrin signaling was necessary throughout the morphogenesis. Although the addition of α1-containing laminin, a ligand of β1 integrin, induced cyst formation, it was dispensable for the maintenance of the cyst, suggesting that HPPL produces another ligand for β1 integrin to maintain the structure. Indeed, we found that HPPL produced α5-containing laminin, and siRNA against laminin α5 partially inhibited the lumen formation. In fetal liver, p75NTR(+) periportal fibroblasts and bile duct epithelial cells, known as cholangiocytes, expressed α1- and α5-containing laminins, respectively. In laminin α5 KO liver, cholangiocytes normally emerged, but the number of bile ducts was decreased. These results suggest that α1-containing laminin is sufficient as a component of the basal lamina for the commitment of bipotential liver progenitors to cholangiocytes and the apicobasal polarization, whereas α5-containing laminin is necessary for the formation of mature duct structures. Thus, α1- and α5-containing laminins differentially regulate the sequential events to form epithelial tissues via β1 integrin signals.

Anti-fibrotic activity and enhanced interleukin-6 production by hepatic stellate cells in response to imatinib mesylate

OBJECTIVE

To examine imatinib mesylate's effects on stellate cell responses in vivo and in vitro. The hepatic stellate cell (HSC) is a key target of anti-fibrotic therapies. Imatinib mesylate is a small molecule receptor tyrosine kinase inhibitor indicated for treatment of chronic myelogenous leukaemia and GI stromal tumours.

DESIGN

Because imatinib inhibits β-PDGFR signalling, which stimulates HSC proliferation, we assessed its activity in culture and in vivo, and examined downstream targets in a human stellate cell line (LX-2) using cDNA microarray.

METHODS AND RESULTS

Imatinib inhibited proliferation of LX-2 cells (0.5-10 mM) but not primary human stellate cells, with no effect on viability, associated with attenuated β-PDGFR phosphorylation. Mitochondrial activity and superoxide anion production were decreased in response to imatinib. cDNA microarray uncovered up-regulation of 29 genes in response to imatinib, including interleukin-6 (IL-6) mRNA, which was correlated with progressive IL-6 secretion. Imatinib also decreased gene expression of collagen α(1) (I), alpha smooth muscle actin, β-PDGFR, transforming growth factor β receptor type 1, matrix metalloproteinase 2 and tissue inhibitor of metalloproteinase 2. In vivo, imatinib administered to rats beginning 4 weeks after starting thioacetamide (TAA) led to reduced collagen content, with significant reductions in portal pressure and down-regulation of fibrogenic genes in whole liver. Importantly, hepatic IL-6 mRNA levels were significantly increased in TAA-treated animals receiving imatinib.

CONCLUSIONS

These findings reinforce the anti-fibrotic activity of imatinib and uncover an unexpected link between inhibition of HSC activation by imatinib and enhanced secretion of IL-6, a regenerative cytokine.

Hepatic stellate cell progenitor cells

Hepatic stellate cells (HSCs) are recognized as a major player in liver fibrogenesis. Upon liver injury, HSCs differentiate into myofibroblasts and participate in progression of fibrosis and cirrhosis. Additional cell types such as resident liver fibroblasts/myofibroblasts or bone marrow cells are also known to generate myofibroblasts. One of the major obstacles to understanding the mechanism of liver fibrogenesis is the lack of knowledge regarding the developmental origin of HSCs and other liver mesenchymal cells. Recent cell lineage analyses demonstrate that HSCs are derived from mesoderm during liver development. MesP1-expressing mesoderm gives rise to the septum transversum mesenchyme before liver formation and then to the liver mesothelium and mesenchymal cells, including HSCs and perivascular mesenchymal cells around the veins during liver development. During the growth of embryonic liver, the mesothelium, consisting of mesothelial cells and submesothelial cells, migrates inward from the liver surface and gives rise to HSCs and perivascular mesenchymal cells, including portal fibroblasts, smooth muscle cells around the portal vein, and fibroblasts around the central vein. Cell lineage analyses indicate that mesothelial cells are HSC progenitor cells capable of differentiating into HSCs and other liver mesenchymal cells during liver development.

Oxygen-dependent cleavage of the p75 neurotrophin receptor triggers stabilization of HIF-1α

Homeostatic control of oxygen availability allows cells to survive oxygen deprivation. Although the transcription factor hypoxia-inducible factor 1α (HIF-1α) is the main regulator of the hypoxic response, the upstream mechanisms required for its stabilization remain elusive. Here, we show that p75 neurotrophin receptor (p75(NTR)) undergoes hypoxia-induced γ-secretase-dependent cleavage to provide a positive feed-forward mechanism required for oxygen-dependent HIF-1α stabilization. The intracellular domain of p75(NTR) directly interacts with the evolutionarily conserved zinc finger domains of the E3 RING ubiquitin ligase Siah2 (seven in absentia homolog 2), which regulates HIF-1α degradation. p75(NTR) stabilizes Siah2 by decreasing its auto-ubiquitination. Genetic loss of p75(NTR) dramatically decreases Siah2 abundance, HIF-1α stabilization, and induction of HIF-1α target genes in hypoxia. p75(NTR-/-) mice show reduced HIF-1α stabilization, vascular endothelial growth factor (VEGF) expression, and neoangiogenesis after retinal hypoxia. Thus, hypoxia-induced intramembrane proteolysis of p75(NTR) constitutes an apical oxygen-dependent mechanism to control the magnitude of the hypoxic response.

The dual origin of the peripheral olfactory system: placode and neural crest

BACKGROUND

The olfactory epithelium (OE) has a unique capacity for continuous neurogenesis, extending axons to the olfactory bulb with the assistance of olfactory ensheathing cells (OECs). The OE and OECs have been believed to develop solely from the olfactory placode, while the neural crest (NC) cells have been believed to contribute only the underlying structural elements of the olfactory system. In order to further elucidate the role of NC cells in olfactory development, we examined the olfactory system in the transgenic mice Wnt1-Cre/Floxed-EGFP and P0-Cre/Floxed-EGFP, in which migrating NC cells and its descendents permanently express GFP, and conducted transposon-mediated cell lineage tracing studies in chick embryos.

RESULTS

Examination of these transgenic mice revealed GFP-positive cells in the OE, demonstrating that NC-derived cells give rise to OE cells with morphologic and antigenic properties identical to placode-derived cells. OECs were also positive for GFP, confirming their NC origin. Cell lineage tracing studies performed in chick embryos confirmed the migration of NC cells into the OE. Furthermore, spheres cultured from the dissociated cells of the olfactory mucosa demonstrated self-renewal and trilineage differentiation capacities (neurons, glial cells, and myofibroblasts), demonstrating the presence of NC progenitors in the olfactory mucosa.

CONCLUSION

Our data demonstrates that the NC plays a larger role in the development of the olfactory system than previously believed, and suggests that NC-derived cells may in part be responsible for the remarkable capacity of the OE for neurogenesis and regeneration.

Human anti-microbial cathelicidin peptide LL-37 suppresses the LPS-induced apoptosis of endothelial cells

Sepsis is a systemic disease resulting from harmful host response to bacterial infections. During the exacerbation of severe sepsis or septic shock, apoptosis of endothelial cells is induced in susceptible organs such as the lung and liver and triggers microcirculatory disorder and organ dysfunction. LPS, an outer membrane component of Gram-negative bacteria, is one of the major virulence factors for the pathogenesis. We previously reported that LL-37, a human anti-microbial cathelicidin peptide, potently neutralizes the biological activity of LPS and protects mice from lethal endotoxin shock. However, the effect of LL-37 on the LPS-induced endothelial cell apoptosis remains to be clarified. In this study, to further elucidate the action of LL-37 on severe sepsis/endotoxin shock, we investigated the effects of LL-37 on the LPS-induced endothelial cell apoptosis in vitro and in vivo using lung-derived normal human microvascular blood vessel endothelial cells (HMVEC-LBls) and D-galactosamine hydrochloride (D-GalN)-sensitized murine endotoxin shock model. LL-37 suppressed the LPS-induced apoptosis of HMVEC-LBls. In addition, LL-37 inhibited the binding of LPS possibly to the LPS receptors (CD14 and toll-like receptor 4) expressed on the cells. Thus, LL-37 can suppress the LPS-induced apoptosis of HMVEC-LBls via the inhibition of LPS binding to the cells. Furthermore, LL-37 drastically suppressed the apoptosis of hepatic endothelial cells as well as hepatocytes in the liver of murine endotoxin shock model. Together, these observations suggest that LL-37 could suppress the LPS-induced apoptosis of endothelial cells, thereby attenuating lethal sepsis/endotoxin shock.

Epigenetic cell fate regulation of hepatic stellate cells

Research in the past three decades has identified key mediators and signaling mechanisms responsible for myofibroblastic transdifferentiation (MTD) of hepatic stellate cells (HSC), the pivotal event in liver fibrogenesis. Yet, fundamental understanding of the MTD from the viewpoint of cell fate or lineage regulation has been elusive. Recent studies using genetic cell fate mapping techniques demonstrate HSC are derived from mesoderm and at least in part via septum transversum and mesothelium. HSC express markers for different cell types derived from multipotent mesenchymal progenitors. A regulatory commonality between differentiation of adipocytes and that of HSC is shown, and a shift from adipogenic to myogenic or neuronal phenotype characterizes HSC MTD. Central to this shift is a loss of expression of the master adipogenic regulator peroxisome proliferator activated receptor-γ (PPAR-γ). Restored expression of PPAR-γ and/or other adipogenic transcription factors reverses myofibroblastic HSC to differentiated cells. In MTD, Pparγ is epigenetically repressed by induction of methyl-CpG binding protein 2 and its enrichment to the promoter and polycomb repressive complex-facilitated histone H3 lysine 27 di/tri-methylation at the 3' exons. Blocking canonical wingless-related MMTV integration site (Wnt) signaling in myofibroblastic HSC with the co-receptor antagonist Dickkopf-1, abrogates these epigenetic mechanisms, restores PPAR-γ expression and HSC differentiation. Necdin, a melanoma antigen family protein, is identified as an upstream mediator for induction of the canonical Wnt10b and consequent Pparγ repression and HSC MTD. The identified morphogen-induced epigenetic regulation of Pparγ and HSC fate may serve as a novel target for manipulation of liver fibrosis and mesenchymal-epithelial interactions in liver regeneration.

Hepatic stellate cells and astrocytes: Stars of scar formation and tissue repair

Scar formation inhibits tissue repair and regeneration in the liver and central nervous system. Activation of hepatic stellate cells (HSCs) after liver injury or of astrocytes after nervous system damage is considered to drive scar formation. HSCs are the fibrotic cells of the liver, as they undergo activation and acquire fibrogenic properties after liver injury. HSC activation has been compared to reactive gliosis of astrocytes, which acquire a reactive phenotype and contribute to scar formation after nervous system injury, much like HSCs after liver injury. It is intriguing that a wide range of neuroglia-related molecules are expressed by HSCs. We identified an unexpected role for the p75 neurotrophin receptor in regulating HSC activation and liver repair. Here we discuss the molecular mechanisms that regulate HSC activation and reactive gliosis and their contributions to scar formation and tissue repair. Juxtaposing key mechanistic and functional similarities in HSC and astrocyte activation might provide novel insight into liver regeneration and nervous system repair.

Functional mesenchymal stem cell niches in adult mouse knee joint synovium in vivo

OBJECTIVE

We previously reported that human synovium contains cells that, after culture expansion, display properties of mesenchymal stem cells (MSCs). The objective of this study was to identify MSCs in native synovium in vivo.

METHODS

To identify stem cells in the synovium in vivo, a double nucleoside analog cell-labeling scheme was used in a mouse model of joint-surface injury. For labeling of slow-cycling cells, mice received iododeoxyuridine (IdU) for 30 days, followed by a 40-day washout period. For labeling of cells that proliferate after injury, mice underwent knee surgery to produce an articular cartilage defect and received chlorodeoxyuridine (CIdU) for 4 days, starting at multiple time points after surgery. Unoperated and sham-operated joints served as controls. Knee joint paraffin sections were analyzed by double and triple immunostaining to detect nucleoside analogs, conventional MSC markers, and chondrocyte-lineage markers.

RESULTS

Long-term-retaining, slow-cycling IdU-positive cells were detected in the synovium. At 4 days and 8 days after injury, there was marked proliferation of IdU-positive cells, which costained for CIdU. IdU-positive cells were nonhematopoietic, nonendothelial stromal cells, were distinct from pericytes, and stained positive for MSC markers. MSCs were phenotypically heterogeneous and located in topographically distinct niches in the lining layer and the subsynovial tissue. Twelve days after injury, double nucleoside-labeled cells within synovium were embedded in cartilage-specific metachromatic extracellular matrix and costained positive for the chondrocyte-lineage markers Sox9 and type II collagen.

CONCLUSION

Our findings provide the first evidence of the existence of resident MSCs in the knee joint synovium that undergo proliferation and chondrogenic differentiation following injury in vivo.

Fibrosis in autoimmune and cholestatic liver disease

Autoimmune and cholestatic liver disease account for a significant part of end-stage liver disease and are leading indications for liver transplantation. Especially cholestatic liver diseases (primary biliary cirrhosis and primary sclerosing cholangitis) appear to be different from other chronic liver diseases with regards to pathogenesis. Portal fibroblasts located in the connective tissue surrounding bile ducts appear to be different from hepatic stellate cells with regards to expression of marker proteins and response the profibrogenic and mitogenic stimuli. In addition there is increasing evidence for a cross talk between activated cholangiocytes and portal myofibroblasts. Several animal models have improved our understanding of the mechanisms underlying these chronic liver diseases. In the present review, we discuss the current concepts and ideas with regards to myofibroblastic cell populations, mechanisms of fibrosis, summarize characteristic histological findings and currently employed animal models of autoimmune and cholestatic liver disease.