TWEAK induces liver progenitor cell proliferation

Fn14 hepatic progenitor cells are associated with liver fibrosis in biliary atresia

PURPOSE

The liver in biliary atresia (BA) is characterized by progressing fibrosis which is promoted by unclear reasons. We aimed to understand the factors influencing liver fibrosis. This study hypothesized that HPCs (hepatic progenitor cells) are activated and associated with liver fibrosis in biliary atresia.

METHODS

Liver samples from biliary atresia patients are as BA group, and the normal liver derived from hepatoblastoma infants during operation are control group. The extent of fibrosis in liver samples was blindly evaluated by two experienced pathologists depending on Ishak system. The BA liver samples were divided into mild liver fibrosis group (grade I-IV, BA_a) and severe liver fibrosis group (grade V-VI, BA_b) to detect Fn14 protein expression.

RESULTS

In mRNA level, Fn14 expression was 21.23 ± 8.3 vs. 1.00 ± 0.17, p = 0.023 < 0.05 and CD133 expression was 6.02 ± 2.16 vs. 1.14 ± 0.75, p = 0.008 < 0.01 between BA group and control group. Fn14 cells co-expressed the progenitor marker CD133 in liver, and activated in BA. Fn14 andα-SMA were co-location in fibrous area in liver. Compared to the control group, Fn14, CD133, and α-SMA protein expression were 2.10 ± 0.53 vs. 0.97 ± 0.2, p = 0.001, 2.23 ± 0.57 vs. 1.00 ± 0.03, p = 0.000, 4.96 ± 2.4 vs. 1.00 ± 0.22, p = 0.001. The Fn14 protein expression was 2.60 ± 0.35 vs. 1.86 ± 0.42, p = 0.012, between BA_b and BA_a group.

CONCLUSION

Fn14 cells, which co-express the progenitor marker CD133 in liver, are HPCs and activated in BA. Fn14 + HPCs are associated with liver fibrosis in BA.

The progenitor cell dilemma: Cellular and functional heterogeneity in assistance or escalation of liver injury

Liver progenitor cells (LPCs) are quiescent cells that are activated during liver injury and thought to give rise to hepatocytes and cholangiocytes in order to support liver regeneration and tissue restitution. While hepatocytes are capable of self-renewal, during most chronic injuries the proliferative capacity of hepatocytes is inhibited, thus LPCs provide main source for regeneration. Despite extensive lineage tracing studies, their role and involvement in these processes are often controversial. Additionally, increasing evidence suggests that the LPC compartment consists of heterogeneous cell populations that are actively involved in cellular interactions with myeloid and lymphoid cells during regeneration. On the other hand, LPC expansion has been associated with an increased fibrogenic response, raising concerns about the therapeutic use of these cells. This review aims to summarize the current understanding of the identity, the cellular interactions and the key pathways affecting the biology of LPCs. Understanding the regulatory circuits and the specific role of LPCs is especially important as it could provide novel therapeutic platforms for the treatment of liver inflammation, fibrosis and regeneration.

Cellular Mechanisms of Liver Regeneration and Cell-Based Therapies of Liver Diseases

The emerging field of regenerative medicine offers innovative methods of cell therapy and tissue/organ engineering as a novel approach to liver disease treatment. The ultimate scientific foundation of both cell therapy of liver diseases and liver tissue and organ engineering is delivered by the in-depth studies of the cellular and molecular mechanisms of liver regeneration. The cellular mechanisms of the homeostatic and injury-induced liver regeneration are unique. Restoration of the mass of liver parenchyma is achieved by compensatory hypertrophy and hyperplasia of the differentiated parenchymal cells, hepatocytes, while expansion and differentiation of the resident stem/progenitor cells play a minor or negligible role. Participation of blood-borne cells of the bone marrow origin in liver parenchyma regeneration has been proven but does not exceed 1-2% of newly formed hepatocytes. Liver regeneration is activated spontaneously after injury and can be further stimulated by cell therapy with hepatocytes, hematopoietic stem cells, or mesenchymal stem cells. Further studies aimed at improving the outcomes of cell therapy of liver diseases are underway. In case of liver failure, transplantation of engineered liver can become the best option in the foreseeable future. Engineering of a transplantable liver or its major part is an enormous challenge, but rapid progress in induced pluripotency, tissue engineering, and bioprinting research shows that it may be doable.

Involvement of prolyl isomerase PIN1 in the cell cycle progression and proliferation of hepatic oval cells

Liver regenerates remarkably after toxic injury or surgical resection. In the case of failure of resident hepatocytes to restore loss, repopulation is carried out by induction, proliferation, and differentiation of the progenitor cell. Although, some signaling pathways have been verified to contribute oval cell-mediated liver regeneration, role of Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1(Pin1) in the oval cells proliferation is unknown. In the present study, we evaluate the role of Pin1 in oval cells proliferation. In our study, the expression of Pin1 in the mice liver increased after three weeks feeding of 3, 5-diethoxycarbonyl-1, 4-dihydrocollidine (DDC) diet along with the proliferation of oval cells. The expression of Pin1 was higher in oval cells compared to the hepatocytes.Pin1 inhibition by Juglone reduced oval cell proliferation, which was restored to normal when oval cells were treated with IGF-1. Consistent with increased cell growth, expression of Pin1, β-catenin and PCNA were increased in IGF-1 treated cells in a time dependent manner. In FACS analysis, siRNA-mediated knockdown of the Pin1 protein in the oval cells significantly increased the numbers of cells in G0/G1 phase. Furthermore, hepatocyte when treated with TGF-β showed marked reduction in cell proliferation and expression of Pin1 whereas this effect was not seen in the oval cells treated with TGF-β. In conclusion, Pin1 plays important role in the cell cycle progression and increase oval cells proliferation which may be crucial in chronic liver injury.

Injection of embryonic stem cell derived macrophages ameliorates fibrosis in a murine model of liver injury

Chronic liver injury can be caused by viral hepatitis, alcohol, obesity, and metabolic disorders resulting in fibrosis, hepatic scarring, and cirrhosis. Novel therapies are urgently required and previous work has demonstrated that treatment with bone marrow derived macrophages can improve liver regeneration and reduce fibrosis in a murine model of hepatic injury and fibrosis. Here, we describe a protocol whereby pure populations of therapeutic macrophages can be produced in vitro from murine embryonic stem cells on a large scale. Embryonic stem cell derived macrophages display comparable morphology and cell surface markers to bone marrow derived macrophages but our novel imaging technique revealed that their phagocytic index was significantly lower. Differences were also observed in their response to classical induction protocols with embryonic stem cell derived macrophages having a reduced response to lipopolysaccharide and interferon gamma and an enhanced response to IL4 compared to bone marrow derived macrophages. When their therapeutic potential was assessed in a murine, carbon tetrachloride-induced injury and fibrosis model, embryonic stem cell derived macrophages significantly reduced the amount of hepatic fibrosis to 50% of controls, down-regulated the number of fibrogenic myofibroblasts and activated liver progenitor cells. To our knowledge, this is the first study that demonstrates a therapeutic effect of macrophages derived in vitro from pluripotent stem cells in a model of liver injury. We also found that embryonic stem cell derived macrophages repopulated the Kupffer cell compartment of clodronate-treated mice more efficiently than bone marrow derived macrophages, and expressed comparatively lower levels of Myb and Ccr2, indicating that their phenotype is more comparable to tissue-resident rather than monocyte-derived macrophages.

TWEAK increases SIRT1 expression and promotes p53 deacetylation affecting human hepatic stellate cell senescence

To detect the effects of tumor necrosis factor-like weak inducer of apoptosis (TWEAK) on SIRT1 expression and p53 deacetylation, involving cell senescence, in activated human hepatic stellate cell (HSC) in vitro, human HSC LX-2 was cultured with TWEAK for 24 h. The result showed that the expression of membrane receptor Fn14 was remarkably increased by TWEAK, which upregulated SIRT1 in LX-2 cells, detected by Western blotting and real-time PCR. The expression of p53 was not significantly altered; however, the ac-p53 was decreased. Furthermore, the viability of LX-2 cells was significantly enhanced by TWEAK. The activity of SA-β-Gal was notably inhibited, showing a suppressing effect of TWEAK on the senescence of activated HSC. Primary cultured HSC on days 7 and 11 was used to examine the expression of TWEAK, Fn14, SIRT1, and the activity of SA-β-Gal. The result indicated that the mRNA of TWEAK, SIRT1, and Fn14 was all decreased on day 11 compared to that on day 7, and the activity of SA-β-Gal was higher on day 11 than that on day 7. The present study suggested that TWEAK enhanced the expression of SIRT1 and decreased the acetylation of p53, probably inhibiting the senescence of activated HSC in vitro, which provides a molecular basis for TWEAK as a potential target in the therapy of liver fibrosis.

Management of Neuropsychiatric Systemic Lupus Erythematosus: Current Approaches and Future Perspectives

Neuropsychiatric systemic lupus erythematosus (NPSLE) is a generic definition referring to a series of neurological and psychiatric symptoms directly related to systemic lupus erythematosus (SLE). NPSLE includes heterogeneous and rare neuropsychiatric (NP) manifestations involving both the central and peripheral nervous system. Due to the lack of a gold standard, the attribution of NP symptoms to SLE represents a clinical challenge that obligates the strict exclusion of any other potential cause. In the acute setting, management of these patients does not differ from other non-SLE subjects presenting with the same NP manifestation. Afterwards, an individualized therapeutic strategy, depending on the presenting manifestation and severity of symptoms, must be started. Clinical trials in NPSLE are scarce and most of the data are extracted from case series and case reports. High-dose glucocorticoids and intravenous cyclophosphamide remain the cornerstone for patients with severe symptoms that are thought to reflect inflammation or an underlying autoimmune process. Rituximab, intravenous immunoglobulins, or plasmapheresis may be used if response is not achieved. When patients present with mild to moderate NP manifestations, or when maintenance therapy is warranted, azathioprine and mycophenolate may be considered. When symptoms are thought to reflect a thrombotic underlying process, anticoagulation and antiplatelet agents are the mainstay of therapy, especially if antiphospholipid antibodies or antiphospholipid syndrome are present. Recent trials on SLE using new biologicals, based on newly understood SLE mechanisms, have shown promising results. Based on what we currently know about its pathogenesis, it is tempting to speculate how these new therapies may affect the management of NPSLE patients. This article provides a comprehensive and critical review of the literature on the epidemiology, pathophysiology, diagnosis, and management of NPSLE. We describe the most common pharmacological treatments used in NPSLE, based on both a literature search and our expert opinion. The extent to which new drugs in the advanced development of SLE, or the blockade of new targets, may impact future treatment of NPSLE will also be discussed.

Infliximab and Dexamethasone Attenuate the Ductular Reaction in Mice

Chronic hepatic injury is accompanied by a ductular response that is strongly correlated with disease severity and progression of fibrosis. To investigate whether anti-inflammatory drugs can modulate the ductular response, we treated mice suffering from a steatotic or cholestatic injury with anti-TNF-α antibodies (Infliximab) or glucocorticoids (Dexamethasone). We discovered that Dexamethasone and Infliximab can both modulate the adaptive remodeling of the biliary architecture that occurs upon liver injury and limit extracellular matrix deposition. Infliximab treatment, at least in these steatotic and cholestatic mouse models, is the safer approach since it does not increase liver injury, allows inflammation to take place but inhibits efficiently the ductular response and extracellular matrix deposition. Infliximab-based therapy could, thus, still be of importance in multiple chronic liver disorders that display a ductular response such as alcoholic liver disease or sclerosing cholangitis.

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.

Ductular reactions in the liver regeneration process with local inflammation after physical partial hepatectomy

Partial hepatectomy models in mice have been widely used for liver regeneration studies. A typical procedure removes ~2/3 of the liver by lobular ligation without tissue dissection. However, hepatectomy in humans involves physical damage (ie, physical partial hepatectomy, PPHx). Therefore, the liver regeneration process after PPHx should involve reactions to acute local injury followed by systematic remodeling. To clarify the liver regeneration process after PPHx, we used a murine liver injury model that mimics the actual human surgical procedure. A 20-30% PPHx was performed by transection of the left lobe of the liver using an ultrasonically activated scalpel in mice. Gene expression and morphological characteristics were analyzed during the liver regeneration process. Liver weight continuously increased by hypertrophic reaction of hepatocytes, whereas Ki67 staining showed hepatocyte proliferation. At the transected border, emergence of ductular reactions, a representative process of hepatic tissue remodeling that contain liver stem/progenitor cells, were observed. Gene expression of the transected border and non-damaged lobes revealed that inflammatory cytokine- and extracellular matrix-associated genes were significantly upregulated at the transected border. Our PPHx model triggered local extracellular matrix remodeling that resulted in ductular reactions. These processes occurred during the tissue repair process in local inflammatory responses as well as compensatory hepatocyte hypertrophy of the entire liver. These findings may provide insight for elucidating the mechanism of tissue repair and regeneration of the liver after PPHx.

Liver regeneration and fibrosis after inflammation

The liver is a unique organ with an extraordinary capacity to regenerate upon various injuries. In acute and transient liver injury by insults such as chemical hepatotoxins, the liver in rodents returns to the original architecture by proliferation and remodeling of the remaining cells within a week. In contrast, chronic liver inflammation due to various etiologies, e.g., virus infection and metabolic and immune disorders, results in liver fibrosis, often leading to cirrhosis and carcinogenesis. In both acute and chronic inflammation, a variety of immune and non-immune cells in the liver is involved in the processes resulting in either regeneration or fibrosis. In addition, chronic hepatitis often accompanies proliferation of atypical biliary cells, also known as liver progenitor cells or oval cells. Although the origin of liver progenitor cells and its contribution to hepatic repair is still under intense debate, recent studies have revealed a regulatory role for immune cells in progenitor proliferation and differentiation. In this review, we summarize recent studies on liver regeneration and fibrosis in the viewpoint of inflammation.

Macrophage Depletion Attenuates Extracellular Matrix Deposition and Ductular Reaction in a Mouse Model of Chronic Cholangiopathies

Chronic cholangiopathies, such as primary and secondary sclerosing cholangitis, are progressive disease entities, associated with periportal accumulation of inflammatory cells, encompassing monocytes and macrophages, peribiliary extracellular matrix (ECM) deposition and ductular reaction (DR). This study aimed to elucidate the relevance of macrophages in the progression of chronic cholangiopathies through macrophage depletion in a 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) mouse model. One group of mice received a single i.p. injection of Clodronate encapsulated liposomes (CLOLipo) at day 7 of a 14 day DDC treatment, while control animals were co-treated with PBSLipo instead. Mice were sacrificed after 7 or respectively 14 days of treatment for immunohistochemical assessment of macrophage recruitment (F4/80), ECM deposition (Sirius Red, Laminin) and DR (CK19). Macrophage depletion during a 14 day DDC treatment resulted in a significant inhibition of ECM deposition. Porto-lobular migration patterns of laminin-rich ECM and ductular structures were significantly attenuated and a progression of DR was effectively inhibited by macrophage depletion. CLOLipo co-treatment resulted in a confined DR to portal regions without amorphous cell clusters. This study suggests that therapeutic options selectively directed towards macrophages might represent a feasible treatment for chronic cholestatic liver diseases.

Serum soluble TWEAK levels are decreased in treatment naive noncirrhotic chronic hepatitis B patients

The mechanisms underlying hepatic inflammation and fibrogenesis in chronic hepatitis B (CHB) are complex and several cytokines are involved. Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor superfamily which also acts as a cytokine. This study was conducted to evaluate serum soluble TWEAK (sTWEAK) levels in noncirrhotic CHB patients.Fifty-two treatment naive CHB patients and 30 healthy controls were included in the study and serum sTWEAK concentrations were measured using commercially available ELISA kits.Mean serum sTWEAK concentration was significantly lower in CHB group than healthy controls (189.6 ± 63.3 pg/mL in CHB group and 297.6 ± 61.5 pg/mL in control group, P < 0.001). According to the degree of necroinflammation in liver biopsies mean sTWEAK concentrations were found to be 168.14 ± 51.51, 206.96 ± 58.51, and 223.62 ± 78.88 pg/mL in patients with mild, moderate, and severe inflammation, respectively, and the difference between groups was statistically significant (P = 0.022). sTWEAK concentration was also found to be significantly higher in patients with advanced fibrosis in liver biopsy samples (169.59 ± 52.02 and 211.17 ± 68.22 pg/mL in patients with mild and advanced fibrosis, respectively, P = 0.016). Receiver operating characteristic (ROC) curves were obtained in CHB group to differentiate patients with advanced fibrosis from patients with mild fibrosis. Area under curve (AUC) was 0.676 (95% Cl; 0.526-0.825) for sTWEAK and for the specified cut-off value of 213.67 pg/mL sensitivity and specificity were 60% and 81.4%, respectively. ROC curve for sTWEAK to differentiate patients with severe inflammation revealed an AUC of 0.664 (95% Cl; 0.450-0.878). A cut-off value of 243.27 pg/mL yielded 54.5% sensitivity and 82.9% specificity.Serum sTWEAK concentration is decreased in treatment naive CHB patients. Further studies with simultaneous determination of circulating sTWEAK concentrations and TWEAK and factor-inducible 14 (Fn14) expressions in the liver biopsy samples would clarify the exact association of TWEAK/Fn14 pathway in the pathogenesis of CHB.

Keratin 23 is a stress-inducible marker of mouse and human ductular reaction in liver disease

BACKGROUND & AIMS

Keratins (K) constitute the epithelial intermediate filaments. Among them, K7/K19 are widely used markers of the regenerative liver response termed ductular reaction (DR) that consists of activated biliary epithelial cells (BECs) and hepatic progenitor cells (HPCs) and correlates with liver disease severity. In the present study we aimed to characterize K23 in the liver.

METHODS

We analyzed the expression and localization of K23 in the digestive system under basal conditions as well as in various human and mouse liver diseases/stress models. Cell culture studies were used to study factors regulating K23 expression.

RESULTS

In untreated mice, K23 was restricted to biliary epithelia. It was (together with K7/K19) markedly upregulated in three different DR/cholestatic injury models, i.e., multidrug resistance protein 2 (Mdr2) knockouts, animals treated with 3,5-diethoxycarbonyl-1,4-dihydrocollidine or subjected to bile duct ligation. K23 levels correlated with the DR marker Fn14 and immunofluorescence staining showed a distinct co-localization with K7/K19. In chronic human liver disease, K23 expression increased in patients with a more prominent inflammation/fibrosis. A dramatic upregulation (>200times) was observed in patients with acute liver failure (ALF) and end-stage primary biliary cholangitis (PBC). Patients with alcoholic liver cirrhosis displayed increased K23 serum levels. In primary hepatocytes as well as hepatobiliary cell lines, treatment with TNF-related weak inducer of apoptosis (TWEAK), and the type I acute phase inducer interleukin (IL)-1β but not the type II inducer IL-6 elevated K23 expression.

CONCLUSIONS

K23 represents a specific, stress-inducible DR marker, whose levels correlate with liver disease severity. K23 may represent a useful non-invasive DR marker.

LAY SUMMARY

Ductular reaction represents a basic response to liver injury and correlates with liver disease severity. Our study identifies K23 as a novel ductular reaction marker in mice and humans.

Hepatic stellate cells: fibrogenic, regenerative or both? Heterogeneity and context are key

Since their original identification, our understanding of the role of hepatic stellate cells in both health and disease continues to grow. Numerous studies have delineated the role of stellate cell activation in contributing to the pool of myofibroblasts responsible for liver fibrosis, and these have resulted in the development of a number of anti-fibrotic strategies targeting this cell. However, their potential role in liver regeneration, both initiation and termination, is also emerging and needs to be contemplated when considering targeted therapy. Perhaps what is most striking is the increasing recognition that this is not just one cell, but rather, a heterogenous population made up of a number of different subsets of cells, each with differentiated and specific functions. The tools are emerging for this dissection and are greatly needed to truly develop targeted therapies that will inhibit fibrosis while promoting liver regeneration and repair.

Tenascin-C in Chronic Canine Hepatitis: Immunohistochemical Localization and Correlation with Necro-Inflammatory Activity, Fibrotic Stage, and Expression of Alpha-Smooth Muscle Actin, Cytokeratin 7, and CD3+ Cells

During fibrosis, the extracellular matrix (ECM) is continuously remodeled and increases in volume due to the production of various proteins. We studied the distribution of tenascin-C (TN-C) and the correlation of TN-C with the necro-inflammatory activity and expression of alpha–smooth muscle actin (α-SMA), cytokeratin 7 (CK7), and CD3+ T-lymphocytes in canine chronic hepatitis. This was analyzed using immunohistochemistry and semiquantitative scoring. We used 3 groups ( n = 19) of dogs: group 1 ( n = 5) with neonatal hepatitis/lobular dissecting hepatitis (NH/LDH), group 2 ( n = 8) with chronic hepatitis/cirrhosis (CH/CIRR), and group 3 ( n = 6) consisting of healthy animals. In normal livers, TN-C was localized in Disse's space and around bile ducts and blood vessels. In CH/CIRR livers, TN-C was localized at the periphery of the regenerating nodules and was conspicuous in the bridging fibrous bands. In NH/LDH, TN-C was diffusely distributed along the reticular fibers that dissected between single cells or groups of hepatocytes. α-SMA in the normal hepatic parenchyma showed an irregular distribution along the perisinusoidal linings. In other groups, α-SMA was increased in fibrotic septa and perisinusoidal linings. In normal livers, CK7 was positive in bile ducts. In other groups, CK7-expressing cells were conspicuous in the portal-parenchymal interface, the periphery of the regenerative nodules, and the degenerated parenchyma. The pattern of CD3+ lymphocytes was inversely proportional to that of TN-C. These results also showed that TN-C is strongly correlated with increased fibrotic stage, inflammatory activity, and expression of CK7 and α-SMA. TN-C, CK7, and CD3 expression did not differ between diagnostic groups.

Brief Report: The Deletion of the Phosphatase Regulator NIPP1 Causes Progenitor Cell Expansion in the Adult Liver

The Ppp1r8 gene encodes NIPP1, a nuclear interactor of protein phosphatase PP1. The deletion of NIPP1 is embryonic lethal at the gastrulation stage, which has hampered its functional characterization in adult tissues. Here, we describe the effects of a conditional deletion of NIPP1 in mouse liver epithelial cells. Ppp1r8(-/-) livers developed a ductular reaction, that is, bile-duct hyperplasia with associated fibrosis. The increased proliferation of biliary epithelial cells was at least partially due to an expansion of the progenitor cell compartment that was independent of liver injury. Gene-expression analysis confirmed an upregulation of progenitor cell markers in the liver knockout livers but showed no effect on the expression of liver-injury associated regulators of cholangiocyte differentiation markers. Consistent with an inhibitory effect of NIPP1 on progenitor cell proliferation, Ppp1r8(-/-) livers displayed an increased sensitivity to diet-supplemented 3,5-diethoxycarbonyl-1,4-dihydrocollidine, which also causes bile-duct hyperplasia through progenitor cell expansion. In contrast, the liver knockouts responded normally to injuries (partial hepatectomy, single CCl4 administration) that are restored through proliferation of differentiated parenchymal cells. Our data indicate that NIPP1 does not regulate the proliferation of hepatocytes but is a suppressor of biliary epithelial cell proliferation, including progenitor cells, in the adult liver. Stem Cells 2016;34:2256-2262.

The Involving Roles of Intrahepatic and Extrahepatic Stem/Progenitor Cells (SPCs) to Liver Regeneration

Liver regeneration is usually attributed to mature hepatocytes, which possess a remarkable potential to proliferate under mild to moderate injury. However, when the liver is severely damaged or hepatocyte proliferation is greatly inhibited, liver stem/progenitor cells (LSPCs) will contribute to the liver regeneration process. LSPCs in the developing liver have been extensively characterized, however, their contributing role to liver regeneration has not been completely understood. In addition to the restoration of the liver parenchymal tissue by hepatocytes or/and LSPCs, or in some cases bone marrow (BM) derived cells, such as hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs), the wound healing after injury in terms of angiopoiesis by liver sinusoidal endothelial cells (LSECs) or/and sinusoidal endothelial progenitor cells (SEPCs) is another important aspect taking place during regeneration. To conclude, liver regeneration can be mainly divided into three distinct restoring levels according to the cause and severity of injury: hepatocyte dominant regeneration, LSPCs mediated regeneration, extrahepatic stem cells participative regeneration. In this review, we focus on the recent findings of liver regeneration, especially on those related to stem/progenitor cells (SPCs)-mediated regeneration and their potential clinical applications and challenges.

DJ-1 deficiency attenuates expansion of liver progenitor cells through modulating the inflammatory and fibrogenic niches

Our previous study suggested that DJ-1 has a critical role in initiating an inflammatory response, but its role in the liver progenitor cell (LPC) expansion, a process highly dependent on the inflammatory niche, remains elusive. The objective of this study is to determine the role of DJ-1 in LPC expansion. The correlation of DJ-1 expression with LPC markers was examined in the liver of patients with hepatitis B or hepatitis C virus (HBV and HCV, respectively) infection, primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC), nonalcoholic fatty liver disease (NAFLD), cirrhosis or hepatocellular carcinoma (HCC), respectively. The role of DJ-1 in LPC expansion and the formation of LPC-associated fibrosis and inflammation was examined in a 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet-induced liver injury murine model. We also determined the ability of hepatic stellate cells (HSCs) in recruiting macrophages in DJ-1 knockout (KO) mice. The expression levels of DJ-1 were upregulated in the liver of HBV, HCV, PBC and PSC patients and DDC-fed mice. Additionally, DJ-1 expression was positively correlated with LPC proliferation in patients with liver injury and mice with DDC exposure. DJ-1 has no direct effect on LPC proliferation. Reduced activation of HSCs and collagen deposition were observed in DJ-1 KO mice. Furthermore, infiltrated CD11b⁺Gr-1^low macrophages and pro-inflammatory factors (IL-6, TNF-α) were attenuated in DJ-1 KO mice. Mechanistically, we found that HSCs isolated from DJ-1 KO mice had decreased secretion of macrophage-mobilizing chemokines, such as CCL2 and CX3CL1, resulting in impaired macrophage infiltration. DJ-1 positively correlates with LPC expansion during liver injury. DJ-1 deficiency negatively regulates LPC proliferation by impairing the formation of LPC-associated fibrosis and inflammatory niches.

Interaction of TWEAK with Fn14 leads to the progression of fibrotic liver disease by directly modulating hepatic stellate cell proliferation

Tumour necrosis factor‐like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor‐inducible 14 (Fn14) have been associated with liver regeneration in vivo. To further investigate the role of this pathway we examined their expression in human fibrotic liver disease and the effect of pathway deficiency in a murine model of liver fibrosis. The expression of Fn14 and TWEAK in normal and diseased human and mouse liver tissue and primary human hepatic stellate cells (HSCs) were investigated by qPCR, western blotting and immunohistochemistry. In addition, the levels of Fn14 in HSCs following pro‐fibrogenic and pro‐inflammatory stimuli were assessed and the effects of exogenous TWEAK on HSCs proliferation and activation were studied in vitro. Carbon tetrachloride (CCl₄) was used to induce acute and chronic liver injury in TWEAK KO mice. Elevated expression of both Fn14 and TWEAK were detected in acute and chronic human liver injury, and co‐localized with markers of activated HSCs. Fn14 levels were low in quiescent HSCs but were significantly induced in activated HSCs, which could be further enhanced with the profibrogenic cytokine TGFβin vitro. Stimulation with recombinant TWEAK induced proliferation but not further HSCs activation. Fn14 gene expression was also significantly up‐regulated in CCl₄ models of hepatic injury whereas TWEAK KO mice showed reduced levels of liver fibrosis following chronic CCl₄ injury. In conclusion, TWEAK/Fn14 interaction leads to the progression of fibrotic liver disease via direct modulation of HSCs proliferation, making it a potential therapeutic target for liver fibrosis. © 2016 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

TGR5 is essential for bile acid-dependent cholangiocyte proliferation in vivo and in vitro

OBJECTIVE

Cholestatic liver diseases in humans as well as bile acid (BA)-feeding and common bile duct ligation (CBDL) in rodents trigger hyperplasia of cholangiocytes within the portal fields. Furthermore, elevation of BA levels enhances proliferation and invasiveness of cholangiocarcinoma (CCA) cells in animal models, thus promoting tumour progression. TGR5 is a G-protein coupled BA receptor, which is highly expressed in cholangiocytes and postulated to mediate the proliferative effects of BA.

DESIGN

BA-dependent cholangiocyte proliferation was examined in TGR5-knockout and wild type mice following cholic acid (CA)-feeding and CBDL. TGR5-dependent proliferation and protection from apoptosis was studied in isolated cholangiocytes and CCA cell lines following stimulation with TGR5 ligands and kinase inhibitors. TGR5 expression was analysed in human CCA tissue.

RESULTS

Cholangiocyte proliferation was significantly reduced in TGR5-knockout mice in response to CA-feeding and CBDL. Taurolithocholic acid and TGR5-selective agonists induced cholangiocyte proliferation through elevation of reactive oxygen species and cSrc mediated epidermal growth factor receptor transactivation and subsequent Erk1/2 phosphorylation only in wild type but not in TGR5-knockout-derived cells. In human CCA tissue TGR5 was overexpressed and the pathway of TGR5-dependent proliferation via epidermal growth factor receptor and extracellular signal-regulated kinase (ERK)1/2 activation also translated to CCA cell lines. Furthermore, apoptosis was inhibited by TGR5-dependent CD95 receptor serine phosphorylation.

CONCLUSIONS

TGR5 is an important mediator of BA-induced cholangiocyte proliferation in vivo and in vitro. Furthermore, TGR5 protects cholangiocytes from death receptor-mediated apoptosis. These mechanisms may protect cholangiocytes from BA toxicity under cholestatic conditions, however, they may trigger proliferation and apoptosis resistance in malignantly transformed cholangiocytes, thus promoting CCA progression.

Soluble TNF-Like Weak Inducer of Apoptosis as a New Marker in Preeclampsia: A Pilot Clinical Study

Introduction. All findings of preeclampsia appear as the clinical consequences of diffuse endothelial dysfunction. Soluble tumor necrosis factor-like weak inducer of apoptosis (sTWEAK) was recently introduced as a TNF related cytokine in various inflammatory and noninflammatory disorders. sTWEAK was found to be related to endothelial dysfunction in patients with chronic kidney disease. In our study we aimed to compare sTWEAK levels in women with preeclampsia to corresponding levels in a healthy pregnant control group. Materials and Methods. The study was undertaken with 33 patients with preeclampsia and 33 normal pregnant women. The concentration of sTWEAK in serum was calculated with an enzyme linked immunosorbent assay (ELISA) kit. Results. Serum creatinine, uric acid, LDH levels, and uPCR were significantly higher in the patient group compared to the control group. sTWEAK levels were significantly lower in preeclamptic patients (332 ± 144 pg/mL) than in control subjects (412 ± 166 pg/mL) (p = 0.04). Discussion. Our study demonstrates that sTWEAK is decreased in patients with preeclampsia compared to healthy pregnant women. There is a need for further studies to identify the role of sTWEAK in the pathogenesis of preeclampsia and to determine whether it can be regarded as a predictor of the development of preeclampsia.

Management of Neuropsychiatric Systemic Lupus Erythematosus: Current Approaches and Future Perspectives

Neuropsychiatric systemic lupus erythematosus (NPSLE) is a generic definition referring to a series of neurological and psychiatric symptoms directly related to systemic lupus erythematosus (SLE). NPSLE includes heterogeneous and rare neuropsychiatric (NP) manifestations involving both the central and peripheral nervous system. Due to the lack of a gold standard, the attribution of NP symptoms to SLE represents a clinical challenge that obligates the strict exclusion of any other potential cause. In the acute setting, management of these patients does not differ from other non-SLE subjects presenting with the same NP manifestation. Afterwards, an individualized therapeutic strategy, depending on the presenting manifestation and severity of symptoms, must be started. Clinical trials in NPSLE are scarce and most of the data are extracted from case series and case reports. High-dose glucocorticoids and intravenous cyclophosphamide remain the cornerstone for patients with severe symptoms that are thought to reflect inflammation or an underlying autoimmune process. Rituximab, intravenous immunoglobulins, or plasmapheresis may be used if response is not achieved. When patients present with mild to moderate NP manifestations, or when maintenance therapy is warranted, azathioprine and mycophenolate may be considered. When symptoms are thought to reflect a thrombotic underlying process, anticoagulation and antiplatelet agents are the mainstay of therapy, especially if antiphospholipid antibodies or antiphospholipid syndrome are present. Recent trials on SLE using new biologicals, based on newly understood SLE mechanisms, have shown promising results. Based on what we currently know about its pathogenesis, it is tempting to speculate how these new therapies may affect the management of NPSLE patients. This article provides a comprehensive and critical review of the literature on the epidemiology, pathophysiology, diagnosis, and management of NPSLE. We describe the most common pharmacological treatments used in NPSLE, based on both a literature search and our expert opinion. The extent to which new drugs in the advanced development of SLE, or the blockade of new targets, may impact future treatment of NPSLE will also be discussed.

The role of TWEAK/Fn14 signaling in the MPTP-model of Parkinson's disease

The tumor necrosis factor like weak inducer of apoptosis (TWEAK) and its receptor, fibroblast growth factor-inducible 14 (Fn14), mediate inflammation and neuronal apoptosis in cerebral edema, ischemic stroke and multiple sclerosis. The downstream effectors and pathways linked to TWEAK-Fn14 signaling are strongly implicated in the pathology of Parkinson's disease (PD), thus indicating a putative role for TWEAK/Fn14 signaling in PD neurodegeneration. Using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model, we aimed to determine whether genetic ablation or pharmacologic mitigation of the TWEAK protein and its Fn14 receptor affected substantia nigra and striatum Parkinsonian pathology. Changes in endogenous TWEAK protein expression were also quantified in tissue from both MPTP-treated mice and PD human samples. TWEAK protein expression was transiently increased in the striatal tissue but remained unaltered in substantia nigra tissue of MPTP-treated mice. There was also no change of TWEAK protein levels in the substantia nigra or the striatum of human PD patients as compared to matched control subjects. Mitigating the effects of endogenous TWEAK protein using neutralizing antibody did affect MPTP-mediated neurotoxicity in the substantia nigra using the sub-acute model of MPTP (30mg/kg i.p. over five consecutive days). Neither TWEAK nor Fn14 genetic ablation led to attenuation of MPTP-toxicity in the acute model. These findings suggest that TWEAK signaling might be an aspect of MPTP-mediated neuropathology and be involved in the overall neurodegenerative pathology of PD.

Rat liver regeneration following ablation with irreversible electroporation

During the past decade, irreversible electroporation (IRE) ablation has emerged as a promising tool for the treatment of multiple diseases including hepatic cancer. However, the mechanisms behind the tissue regeneration following IRE ablation have not been investigated. Our results indicate that IRE treatment immediately kills the cells at the treatment site preserving the extracellular architecture, in effect causing in vivo decellularization. Over the course of 4 weeks, progenitor cell differentiation, through YAP and notch pathways, together with hepatocyte expansion led to almost complete regeneration of the ablated liver leading to the formation of hepatocyte like cells at the ablated zone. We did not observe significant scarring or tumor formation at the regenerated areas 6 months post IRE. Our study suggests a new model to study the regeneration of liver when the naïve extracellular matrix is decellularized in vivo with completely preserved extracellular architecture.

Taurine drinking ameliorates hepatic granuloma and fibrosis in mice infected with Schistosoma japonicum

In schistosomiasis, egg-induced hepatic granuloma formation is a cytokine-mediated, predominantly CD4⁺ Th2 immune response that can give rise to hepatic fibrosis. Hepatic fibrosis is the main cause of increased morbidity and mortality in humans with schistosome infection. Taurine has various physiological functions and hepatoprotective properties as well as anti-inflammatory and immunomodulatory activity. However, little is known about the role of taurine in schistosome egg-induced granuloma formation and fibrosis. We aimed to evaluate the therapeutic potential of taurine as preventative treatment for Schistosoma japonicum infection. Mice infected with S. japonicum cercariae were supplied with taurine drinking water (1% w/v) for 4 weeks starting at 4 weeks post-infection. Taurine supplementation significantly improved the liver pathologic findings, reduced the serum levels of aminotransferases and area of hepatic granuloma, and prevented fibrosis progression. In addition, taurine decreased the expression of the granulomatous and fibrogenic mediators transforming growth factor β1, tumor necrosis factor α, monocyte chemotactic protein 1α and macrophage inflammatory protein 1α as well as the endoplasmic reticulum stress marker glucose-regulated protein 78. Thus, taurine can significantly attenuate S. japonicum egg-induced hepatic granuloma and fibrosis, which may depend in part on the downregulation of some relevant cytokine/chemokines and reducing the endoplasmic reticulum stress response.

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Taurine has potential as preventative & therapeutic treatment for schistosomiasis.

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Taurine reduced the development of liver pathology caused by S. japonicum infection.

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Taurine attenuated S. japonicum egg-induced hepatic granuloma and fibrosis.

Stem/Progenitor Cell Niches Involved in Hepatic and Biliary Regeneration

Niches containing stem/progenitor cells are present in different anatomical locations along the human biliary tree and within liver acini. The most primitive stem/progenitors, biliary tree stem/progenitor cells (BTSCs), reside within peribiliary glands located throughout large extrahepatic and intrahepatic bile ducts. BTSCs are multipotent and can differentiate towards hepatic and pancreatic cell fates. These niches' matrix chemistry and other characteristics are undefined. Canals of Hering (bile ductules) are found periportally and contain hepatic stem/progenitor cells (HpSCs), participating in the renewal of small intrahepatic bile ducts and being precursors to hepatocytes and cholangiocytes. The niches also contain precursors to hepatic stellate cells and endothelia, macrophages, and have a matrix chemistry rich in hyaluronans, minimally sulfated proteoglycans, fetal collagens, and laminin. The microenvironment furnishes key signals driving HpSC activation and differentiation. Newly discovered third niches are pericentral within hepatic acini, contain Axin2+ unipotent hepatocytic progenitors linked on their lateral borders to endothelia forming the central vein, and contribute to normal turnover of mature hepatocytes. Their relationship to the other stem/progenitors is undefined. Stem/progenitor niches have important implications in regenerative medicine for the liver and biliary tree and in pathogenic processes leading to diseases of these tissues.

Liver progenitor cells-mediated liver regeneration in liver cirrhosis

Cirrhosis is defined as the histological development of regenerative nodules surrounded by fibrous bands in response to chronic liver injury. In cirrhotic liver where hepatocytes proliferation is compromised, liver progenitor cells (LPCs) are activated and then differentiated into hepatocytes and cholangiocytes, leading to the generation of regenerative nodules and functional restoration. Here, we summarize and discuss recent findings on the mechanisms underlying LPCs-mediated regeneration in liver cirrhosis. Firstly, we provide recent research on the mechanism underlying LPCs activation in severe or chronic liver injury. Secondly, we present new and exciting data on exploring the origin of LPCs, which reveal that the hepatocytes give rise to duct-like progenitors that then differentiate back into hepatocytes in chronic liver injury or liver cirrhosis. Finally, we highlight recent findings from the literature exploring the role of LPCs niche in directing the behavior and fate of LPCs. This remarkable insight into the cellular and molecular mechanisms of LPCs-mediated regeneration in liver cirrhosis will provide a basis for translating this knowledge into clinical application.

Integrin αvβ6 critically regulates hepatic progenitor cell function and promotes ductular reaction, fibrosis, and tumorigenesis

Integrin αvβ6 is rapidly up-regulated on cells of epithelial lineage during tissue injury, where one of its primary functions is activation of latent transforming growth factor beta 1 (TGFβ1). In human liver cirrhosis, αvβ6 is overexpressed by cells comprising the ductular reaction, and its inhibition suppresses experimental biliary fibrosis in rodents. Here, we show that αvβ6 is expressed on the actively proliferating subset of hepatic progenitor cells and is required for their progenitor function in vivo and in vitro through integrin αvβ6-dependent TGFβ1 activation. Freshly isolated αvβ6(+) liver cells demonstrate clonogenic potential and differentiate into cholangiocytes and functional hepatocytes in vitro, whereas colony formation by epithelial cell adhesion molecule-positive progenitor cells is blocked by αvβ6-neutralizing antibody and in integrin beta 6-deficient cells. Inhibition of progenitors by anti-αvβ6 antibody is recapitulated by TGFβ1 neutralization and rescued by addition of bioactive TGFβ1. Genetic disruption or selective targeting of αvβ6 with 3G9 antibody potently inhibits progenitor cell responses in mouse models of chronic biliary injury and protects from liver fibrosis and tumorigenesis, two conditions clinically associated with exacerbated ductular reaction.

CONCLUSION

These results suggest that αvβ6 is a promising target for chronic fibrotic liver diseases and associated cancers.

Molecular Survey of Cell Source Usage during Subtotal Hepatectomy-Induced Liver Regeneration in Rats

Proliferation of hepatocytes is known to be the main process in the hepatectomy-induced liver regrowth; however, in cases of extensive loss it may be insufficient for complete recovery unless supported by some additional sources e.g. mobilization of undifferentiated progenitors. The study was conducted on rat model of 80% subtotal hepatectomy; the objective was to evaluate contributions of hepatocytes and resident progenitor cells to the hepatic tissue recovery via monitoring specific mRNA and/or protein expression levels for a panel of genes implicated in growth, cell differentiation, angiogenesis, and inflammation. Some of the genes showed distinctive temporal expression patterns, which were loosely associated with two waves of hepatocyte proliferation observed at 2 and 7 days after the surgery. Focusing on genes implicated in regulation of the progenitor cell activity, we came across slight increases in expression levels for Sox9 and two genes encoding tumor necrosis factor-like cytokine TWEAK (Tnfsf12) and its receptor Fn14 (Tnfrsf12a). At the same time, no increase in numbers of cytokeratin 19-positive (CK19+) cells was observed in periportal areas, and no CK19+ cells were found in hepatic plates. Since CK19 is thought to be a specific marker of both cholangiocytes and the hepatic progenitor cells, the data indicate a lack of activation of the resident progenitor cells during recovery of hepatic tissue after 80% subtotal hepatectomy. Thus, proliferation of hepatocytes invariably makes the major contribution to the hepatic tissue recovery, although in the cases of subtotal loss this contribution is distinctively modulated. In particular, induction of Sox9 and TWEAK/Fn14 regulatory pathways, conventionally attributed to progenitor cell activation, may incidentally stimulate mitotic activity of hepatocytes.

Immunohistochemical analyses of cell cycle progression and gene expression of biliary epithelial cells during liver regeneration after partial hepatectomy of the mouse

The liver has a remarkable regeneration capacity, and, after surgical removal of its mass, the remaining tissue undergoes rapid regeneration through compensatory growth of its constituent cells. Although hepatocytes synchronously proliferate under the control of various signaling molecules from neighboring cells, there have been few detailed analyses on how biliary cells regenerate for their cell population after liver resection. The present study was undertaken to clarify how biliary cells regenerate after partial hepatectomy of mice through extensive analyses of their cell cycle progression and gene expression using immunohistochemical and RT-PCR techniques. When expression of PCNA, Ki67 antigen, topoisomerase IIα and phosphorylated histone H3, which are cell cycle markers, was immunohistochemically examined during liver regeneration, hepatocytes had a peak of the S phase and M phase at 48–72 h after resection. By contrast, biliary epithelial cells had much lower proliferative activity than that of hepatocytes, and their peak of the S phase was delayed. Mitotic figures were rarely detectable in biliary cells. RT-PCR analyses of gene expression of biliary markers such as Spp1 (osteopontin), Epcam and Hnf1b demonstrated that they were upregulated during liver regeneration. Periportal hepatocytes expressed some of biliary markers, including Spp1 mRNA and protein. Some periportal hepatocytes had downregulated expression of HNF4α and HNF1α. Gene expression of Notch signaling molecules responsible for cell fate decision of hepatoblasts to biliary cells during development was upregulated during liver regeneration. Notch signaling may be involved in biliary regeneration.

Progenitor cell expansion and impaired hepatocyte regeneration in explanted livers from alcoholic hepatitis

OBJECTIVE

In alcoholic hepatitis (AH), development of targeted therapies is crucial and requires improved knowledge of cellular and molecular drivers in liver dysfunction. The unique opportunity of using explanted livers from patients with AH having undergone salvage liver transplantation allowed to perform more in-depth molecular translational studies.

DESIGN

We studied liver explants from patients with AH submitted to salvage transplantation (n=16), from patients with alcoholic cirrhosis without AH (n=12) and fragments of normal livers (n=16). Hepatic cytokine content was quantified. Hepatocyte function and proliferation and the presence of hepatic progenitor cells (HPCs) were evaluated by immunohistochemistry, western blot or quantitative PCR. Mitochondrial morphology was evaluated by electron microscopy.

RESULTS

Livers from patients with AH showed decreased cytokine levels involved in liver regeneration (tumour necrosis factor α and interleukin-6), as well as a virtual absence of markers of hepatocyte proliferation compared with alcoholic cirrhosis and normal livers. Electron microscopy revealed obvious mitochondrial abnormalities in AH hepatocytes. Importantly, livers from patients with AH showed substantial accumulation of HPCs that, unexpectedly, differentiate only into biliary cells. AH livers predominantly express laminin (extracellular matrix protein favouring cholangiocyte differentiation); consequently, HPC expansion is inefficient at yielding mature hepatocytes.

CONCLUSIONS

AH not responding to medical therapy is associated with lack of expression of cytokines involved in liver regeneration and profound mitochondrial damage along with lack of proliferative hepatocytes. Expansion of HPCs is inefficient to yield mature hepatocytes. Manoeuvres aimed at promoting differentiation of HPCs into mature hepatocytes should be tested in AH.

Functional and genetic deconstruction of the cellular origin in liver cancer

During the past decade, research on primary liver cancers has particularly highlighted the uncommon plasticity of differentiated parenchymal liver cells (that is, hepatocytes and cholangiocytes (also known as biliary epithelial cells)), the role of liver progenitor cells in malignant transformation, the importance of the tumour microenvironment and the molecular complexity of liver tumours. Whereas other reviews have focused on the landscape of genetic alterations that promote development and progression of primary liver cancers and the role of the tumour microenvironment, the crucial importance of the cellular origin of liver cancer has been much less explored. Therefore, in this Review, we emphasize the importance and complexity of the cellular origin in tumour initiation and progression, and attempt to integrate this aspect with recent discoveries in tumour genomics and the contribution of the disrupted hepatic microenvironment to liver carcinogenesis.

Liver Stem Cells: Experimental Findings and Implications for Human Liver Disease

Evidence from human histopathology and experimental studies with rodents and zebrafish has shown that hepatocytes and cholangiocytes may function as facultative stem cells for each other in conditions of impaired regeneration. The interpretation of the findings derived from these studies has generated considerable discussion and some controversies. This review examines the evidence obtained from the different experimental models and considers implications that these studies may have for human liver disease.

Hepatic oval cells and liver diseases

In recent years, hepatic oval cells (HOC) have gradually become a research hotspot, and their participation in the reconstruction of liver structure and function has been preliminarily confirmed. This provides a new direction for the study of the pathogenesis and treatment of liver injury, hepatitis, liver fibrosis, cirrhosis, liver neoplasms and other liver diseases. This paper will discuss the relationship between hepatic oval cells and liver diseases.

Angiogenesis and proliferation of bile duct enhances ischemic tolerance in rats with cirrhosis

BACKGROUND/AIMS

Primary biliary cirrhosis (PBC), an autoimmune disease of the liver, is marked by slow progressive destruction of bile ducts. These patients with PBC often undergo orthotopic liver transplantation (OLT). Ischemic bile duct lesion (IBDL) is a major source of morbidity and even mortality after OLT. Cirrhosis of the liver has a higher tolerance to ischemia than a normal liver, but the mechanism remains unknown. Angiogenesis and proliferation of bile duct often responses in bile duct ischemia, which may enhance ischemic tolerance in patients with cirrhosis.

METHODOLOGY

To test the hypothesis, a rat model with cirrhosis was established. Biochemical indexes of ischemic severity were measured including total bilirubin (TBIL) and direct bilirubin (DBIL). Immunohistochemical assay was performed for Ki67 (a biomarker for the proliferation of bile duct) and CD34 (a biomarker of angiogenesis).

RESULTS

The levels were lower for TBIL and DBIL in the bile duct from rat model with cirrhosis than that from a normal rat after ischemic surgery (P < 0.05). The levels were higher for Ki67 and CD34 from a rat model with cirrhosis than that from a normal rat after ischemic surgery (P < 0.05).

CONCLUSIONS

The results suggest that a liver with cirrhosis has a better ischemic tolerance than a normal liver. Angiogenesis and proliferation of bile duct enhances ischemic tolerance in rats with cirrhosis. More research on the pathogenesis of IBDLs is needed for developing more specific preventive or therapeutic strategies.

Hepatic progenitor cells of biliary origin with liver repopulation capacity

Hepatocytes and cholangiocytes self-renew following liver injury. Following severe injury hepatocytes are increasingly senescent, but whether hepatic progenitor cells (HPCs) then contribute to liver regeneration is unclear. Here, we describe a mouse model where the E3 ubiquitin ligase Mdm2 is inducibly deleted in more than 98% of hepatocytes, causing apoptosis, necrosis and senescence with nearly all hepatocytes expressing p21. This results in florid HPC activation, which is necessary for survival, followed by complete, functional liver reconstitution. HPCs isolated from genetically normal mice, using cell surface markers, were highly expandable and phenotypically stable in vitro. These HPCs were transplanted into adult mouse livers where hepatocyte Mdm2 was repeatedly deleted, creating a non-competitive repopulation assay. Transplanted HPCs contributed significantly to restoration of liver parenchyma, regenerating hepatocytes and biliary epithelia, highlighting their in vivo lineage potency. HPCs are therefore a potential future alternative to hepatocyte or liver transplantation for liver disease.

Portal inflammation during NAFLD is frequent and associated with the early phases of putative hepatic progenitor cell activation

AIMS

We investigated whether portal tract inflammation observed in non-alcoholic fatty liver disease (NAFLD) is associated with hepatic progenitor cell compartment activation, as thoroughly evaluated with different markers of the staminal lineage.

METHODS

Fifty-two patients with NAFLD were studied. NAFLD activity score, fibrosis and portal inflammation were histologically evaluated. Putative hepatic progenitor cells, intermediate hepatobiliary cells and bile ductules/interlobular bile ducts were evaluated by immunohistochemistry for cytokeratin (CK)-7, CK-19 and epithelial cell adhesion molecule (EpCAM), and a hepatic progenitor cell compartment score was derived. Hepatic stellate cell and myofibroblast activity was determined by immunohistochemistry for α-smooth muscle actin.

RESULTS

Portal inflammation was absent in a minority of patients, mild in 40% of cases and more than mild in about half of patients, showing a strong correlation with fibrosis (r=0.76, p<0.001). Portal inflammation correlated with CK-7-counted putative hepatic progenitor cells (r=0.48, p<0.001), intermediate hepatobiliary cells (r=0.6, p<0.001) and bile ductules/interlobular bile ducts (r=0.6, p<0.001), and with the activity of myofibroblasts (r=0.5, p<0.001). Correlations were confirmed when elements were counted by immunostaining for CK-19 and EpCAM. Lobular inflammation, ballooning, myofibroblast activity and hepatic progenitor cell compartment activation were associated with portal inflammation by univariate analysis. In the multivariate model, the only variable independently associated with portal inflammation was hepatic progenitor cell compartment activation (OR 3.7, 95% CI 1.1 to 12.6).

CONCLUSIONS

Portal inflammation is frequent during NAFLD and strongly associated with activation of putative hepatic progenitor cells since the first steps of their differentiation, portal myofibroblast activity and fibrosis.

Osteopontin Promotes Hepatic Progenitor Cell Expansion and Tumorigenicity via Activation of β-Catenin in Mice

Upregulation of osteopontin (OPN) has been found in hepatic progenitor cells (HPCs) in several liver diseases with portal biliary proliferation. Here, we investigated the role of HPC-derived autocrine OPN in regulating HPC expansion, migration, and hepatocarcinogenesis in mice. Five-week-old, weighing between 18 and 20 g of either wild type (WT) or OPN gene knockout (OPN-KO) male mice were treated with modified choline-deficient, ethionine-supplemented diet (modified choline-deficient [MCDE]) for 2 weeks to induce HPC production, or 6-12 months to induce tumorigenesis. Epithelial cell adhesion molecule EpCAM(+) CD45(-) cells isolated from mouse liver and liver epithelial progenitor cells were used for in vitro study. OPN was blocked by specific antibody or RNAi-mediated silence to investigate the role of OPN. To evaluate correlation between OPN expression and β-catenin activity, expressions of OPN and β-catenin were assessed in human liver cancer specimens. We found autocrine OPN promotes HPC expansion and migration by decreasing membranous E-cadherin and increasing free cytoplasmic β-catenin via binding to αv integrin and activating Src activity. Depletion of OPN significantly attenuated MCDE-induced hepatocarcinogenesis. Clinical evidence revealed a strong correlation of high OPN expression with cytoplasmic/nuclear expression of β-catenin in 43 cases of human combined hepatocellular carcinoma and cholangiocarcinoma and mixed intrahepatic cholangiocarcinoma and 80 cases of hepatocellular carcinoma. Our results indicate that autocrine OPN plays a crucial role in HPC expansion, migration, and subsequent oncogenic transformation of HPCs, which may provide a new insight into hepatocarcinogenesis.

Two sides of one coin: massive hepatic necrosis and progenitor cell-mediated regeneration in acute liver failure

Massive hepatic necrosis is a key event underlying acute liver failure, a serious clinical syndrome with high mortality. Massive hepatic necrosis in acute liver failure has unique pathophysiological characteristics including extremely rapid parenchymal cell death and removal. On the other hand, massive necrosis rapidly induces the activation of liver progenitor cells, the so-called "second pathway of liver regeneration." The final clinical outcome of acute liver failure depends on whether liver progenitor cell-mediated regeneration can efficiently restore parenchymal mass and function within a short time. This review summarizes the current knowledge regarding massive hepatic necrosis and liver progenitor cell-mediated regeneration in patients with acute liver failure, the two sides of one coin.

Adaptive remodeling of the biliary architecture underlies liver homeostasis

Serving as the center for metabolism and detoxification, the liver is inherently susceptible to a wide variety of damage imposed by toxins or chemicals. Induction of cell populations with biliary epithelial phenotypes, which include progenitor-like cells and are referred to as liver progenitor cells, is often observed in histopathological examination of various liver diseases in both human patients and animal models and has been implicated in regeneration. However, the tissue dynamics underlying this phenomenon remains largely unclear. We have developed a simple imaging technique to reveal the global and fine-scale architecture of the biliary tract spreading in the mouse liver. Using this novel method, we show that the emergence and expansion of liver progenitor cells actually reflect structural transformation of the intrahepatic biliary tree in mouse liver injury models. The biliary branches expanded their area gradually and contiguously along with the course of chronic injury. Relevant regulatory signals known to be involved in liver progenitor cell regulation, including fibroblast growth factor 7 and tumor necrosis factor-like weak inducer of apoptosis, can modulate the dynamics of the biliary epithelium in different ways. Importantly, the structural transformations of the biliary tree were diverse and corresponded well with the parenchymal injury patterns. That is, when chronic hepatocyte damage was induced in the pericentral area, the biliary branches exhibited an extended structure from the periportal area with apparent tropism toward the distant injured area.

CONCLUSION

The hepatobiliary system possesses a unique and unprecedented structural flexibility and can remodel dynamically and adaptively in response to various injury conditions; this type of tissue plasticity should constitute an essential component to maintain liver homeostasis.

Novel insights into the function and dynamics of extracellular matrix in liver fibrosis

Emerging evidence suggests that altered components and posttranslational modifications of proteins in the extracellular matrix (ECM) may both initiate and drive disease progression. The ECM is a complex grid consisting of multiple proteins, most of which play a vital role in containing the essential information needed for maintenance of a sophisticated structure anchoring the cells and sustaining normal function of tissues. Therefore, the matrix itself may be considered as a paracrine/endocrine entity, with more complex functions than previously appreciated. The aims of this review are to 1) explore key structural and functional components of the ECM as exemplified by monogenetic disorders leading to severe pathologies, 2) discuss selected pathological posttranslational modifications of ECM proteins resulting in altered functional (signaling) properties from the original structural proteins, and 3) discuss how these findings support the novel concept that an increasing number of components of the ECM harbor signaling functions that can modulate fibrotic liver disease. The ECM entails functions in addition to anchoring cells and modulating their migratory behavior. Key ECM components and their posttranslational modifications often harbor multiple domains with different signaling potential, in particular when modified during inflammation or wound healing. This signaling by the ECM should be considered a paracrine/endocrine function, as it affects cell phenotype, function, fate, and finally tissue homeostasis. These properties should be exploited to establish novel biochemical markers and antifibrotic treatment strategies for liver fibrosis as well as other fibrotic diseases.

Pathogenesis and prognosis of hepatocellular carcinoma at the cellular and molecular levels

Different approaches predict the outcome for patients with hepatocellular carcinoma (HCC). The expression of biliary-hepatic progenitor cell markers generally correlates with poor prognosis. This article focuses on the pathogenesis of HCC, how differentiation or dedifferentiation leads to a phenotype switch, and heterogeneity in the same tumor. A tumor cell decides its fate based on a complex interplay of signaling pathways. Interaction with the microenvironment decides whether it will invade, proliferate, or enter survival mode. Several signaling pathways contribute to stemness features, reflecting a small chemoresistant subpopulation of the tumor that expresses biliary-hepatic progenitor cell markers.

A Paracrine Mechanism Accelerating Expansion of Human Induced Pluripotent Stem Cell-Derived Hepatic Progenitor-Like Cells

Hepatic stem/progenitor cells in liver development have a high proliferative potential and the ability to differentiate into both hepatocytes and cholangiocytes. In this study, we focused on the cell surface molecules of human induced pluripotent stem (iPS) cell-derived hepatic progenitor-like cells (HPCs) and analyzed how these molecules modulate expansion of these cells. Human iPS cells were differentiated into immature hepatic lineage cells by cytokines. In addition to hepatic progenitor markers (CD13 and CD133), the cells were coimmunostained for various cell surface markers (116 types). The cells were analyzed by flow cytometry and in vitro colony formation culture with feeder cells. Twenty types of cell surface molecules were highly expressed in CD13(+)CD133(+) cells derived from human iPS cells. Of these molecules, CD221 (insulin-like growth factor receptor), which was expressed in CD13(+)CD133(+) cells, was quickly downregulated after in vitro expansion. The proliferative ability was suppressed by a neutralizing antibody and specific inhibitor of CD221. Overexpression of CD221 increased colony-forming ability. We also found that inhibition of CD340 (erbB2) and CD266 (fibroblast growth factor-inducible 14) signals suppressed proliferation. In addition, both insulin-like growth factor (a ligand of CD221) and tumor necrosis factor-like weak inducer of apoptosis (a ligand of CD266) were provided by feeder cells in our culture system. This study revealed the expression profiles of cell surface molecules in human iPS cell-derived HPCs and that the paracrine interactions between HPCs and other cells through specific receptors are important for proliferation.

A disintegrin and metalloprotease with thrombospondin type I motif 7: a new protease for connective tissue growth factor in hepatic progenitor/oval cell niche

Hepatic progenitor/oval cell (OC) activation occurs when hepatocyte proliferation is inhibited and is tightly associated with the fibrogenic response during severe liver damage. Connective tissue growth factor (CTGF) is important for OC activation and contributes to the pathogenesis of liver fibrosis. By using the Yeast Two-Hybrid approach, we identified a disintegrin and metalloproteinase with thrombospondin repeat 7 (ADAMTS7) as a CTGF binding protein. In vitro characterization demonstrated CTGF binding and processing by ADAMTS7. Moreover, Adamts7 mRNA was induced during OC activation, after the implantation of 2-acetylaminofluorene with partial hepatectomy in rats or on feeding a 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet in mice. X-Gal staining showed Adamts7 expression in hepatocyte nuclear factor 4α(+) hepatocytes and desmin(+) myofibroblasts surrounding reactive ducts in DDC-treated Adamts7(-/-) mice carrying a knocked-in LacZ gene. Adamts7 deficiency was associated with higher transcriptional levels of Ctgf and OC markers and enhanced OC proliferation compared to Adamts7(+/+) controls during DDC-induced liver injury. We also observed increased α-smooth muscle actin and procollagen type I mRNAs, large fibrotic areas in α-smooth muscle actin and Sirius red staining, and increased production of hepatic collagen by hydroxyproline measurement. These results suggest that ADAMTS7 is a new protease for CTGF protein and a novel regulator in the OC compartment, where its absence causes CTGF accumulation, leading to increased OC activation and biliary fibrosis.

TWEAK/Fn14 Signaling Involvement in the Pathogenesis of Cutaneous Disease in the MRL/lpr Model of Spontaneous Lupus

Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK, TNFSF12) and its sole receptor Fn14, belonging to the TNF ligand and receptor superfamilies respectively, are involved in cell survival and cytokine production. The role of TWEAK/Fn14 interactions in the pathogenesis of cutaneous lupus has not been explored. TWEAK treatment of murine PAM212 keratinocytes stimulated the secretion of RANTES via Fn14 and promoted apoptosis. Parthenolide, but not wortmanin or the MAPK inhibitor PD98059, significantly decreased production of RANTES, indicating that this effect of TWEAK is mediated via NF-κB signaling. UVB irradiation significantly upregulated the expression of Fn14 on keratinocytes in vitro and in vivo and increased RANTES production. MRL/lpr Fn14 knockout (KO) lupus mice were compared with MRL/lpr Fn14 wild-type (WT) mice to evaluate for any possible differences in the severity of cutaneous lesions and the presence of infiltrating immune cells. MRL/lpr Fn14 KO mice had markedly attenuated cutaneous disease as compared with their Fn14 WT littermates, as evidenced by the well-maintained architecture of the skin and significantly decreased skin infiltration of T cells and macrophages. Our data strongly implicate TWEAK/Fn14 signaling in the pathogenesis of the cutaneous manifestations in the MRL/lpr model of spontaneous lupus and suggest a possible target for therapeutic intervention.

Chronic activation of FXR in transgenic mice caused perinatal toxicity and sensitized mice to cholesterol toxicity

The nuclear receptor farnesoid X receptor (FXR) (nuclear receptor subfamily 1, group H, member 4, or NR1H4) is highly expressed in the liver and intestine. Previous reports have suggested beneficial functions of FXR in the homeostasis of bile acids, lipids, and glucose, as well as in promoting liver regeneration and inhibiting carcinogenesis. To investigate the effect of chronic FXR activation in vivo, we generated transgenic mice that conditionally and tissue specifically express the activated form of FXR in the liver and intestine. Unexpectedly, the transgenic mice showed several intriguing phenotypes, including partial neonatal lethality, growth retardation, and spontaneous liver toxicity. The transgenic mice also displayed heightened sensitivity to a high-cholesterol diet-induced hepatotoxicity but resistance to the gallstone formation. The phenotypes were transgene specific, because they were abolished upon treatment with doxycycline to silence the transgene expression. The perinatal toxicity, which can be rescued by a maternal vitamin supplement, may have resulted from vitamin deficiency due to low biliary bile acid output as a consequence of inhibition of bile acid formation. Our results also suggested that the fibroblast growth factor-inducible immediate-early response protein 14 (Fn14), a member of the proinflammatory TNF family, is a FXR-responsive gene. However, the contribution of Fn14 induction in the perinatal toxic phenotype of the transgenic mice remains to be defined. Because FXR is being explored as a therapeutic target, our results suggested that a chronic activation of this nuclear receptor may have an unintended side effect especially during the perinatal stage.

Role of liver progenitors in liver regeneration

During massive liver injury and hepatocyte loss, the intrinsic regenerative capacity of the liver by replication of resident hepatocytes is overwhelmed. Treatment of this condition depends on the cause of liver injury, though in many cases liver transplantation (LT) remains the only curative option. LT for end stage chronic and acute liver diseases is hampered by shortage of donor organs and requires immunosuppression. Hepatocyte transplantation is limited by yet unresolved technical difficulties. Since currently no treatment is available to facilitate liver regeneration directly, therapies involving the use of resident liver stem or progenitor cells (LPCs) or non-liver stem cells are coming to fore. LPCs are quiescent in the healthy liver, but may be activated under conditions where the regenerative capacity of mature hepatocytes is severely impaired. Non-liver stem cells include embryonic stem cells (ES cells) and mesenchymal stem cells (MSCs). In the first section, we aim to provide an overview of the role of putative cytokines, growth factors, mitogens and hormones in regulating LPC response and briefly discuss the prognostic value of the LPC response in clinical practice. In the latter section, we will highlight the role of other (non-liver) stem cells in transplantation and discuss advantages and disadvantages of ES cells, induced pluripotent stem cells (iPS), as well as MSCs.

Role of Fn14 in acute alcoholic steatohepatitis in mice

TNF-like weak inducer of apoptosis (TWEAK) is a growth factor for bipotent liver progenitors that express its receptor, fibroblast growth factor-inducible 14 (Fn14), a TNF receptor superfamily member. Accumulation of Fn14(+) progenitors occurs in severe acute alcoholic steatohepatitis (ASH) and correlates with acute mortality. In patients with severe ASH, inhibition of TNF-α increases acute mortality. The aim of this study was to determine whether deletion of Fn14 improves the outcome of liver injury in alcohol-consuming mice. Wild-type (WT) and Fn14 knockout (KO) mice were fed control high-fat Lieber deCarli diet or high-fat Lieber deCarli diet with 2% alcohol (ETOH) and injected intraperitoneally with CCl₄ for 2 wk to induce liver injury. Mice were euthanized 3 or 10 days after CCl₄ treatment. Survival was assessed. Liver tissues were analyzed for cell death, inflammation, proliferation, progenitor accumulation, and fibrosis by quantitative RT-PCR, immunoblot, hydroxyproline content, and quantitative immunohistochemistry. During liver injury, Fn14 expression, apoptosis, inflammation, hepatocyte replication, progenitor and myofibroblast accumulation, and fibrosis increased in WT mice fed either diet. Mice fed either diet expressed similar TWEAK/Fn14 levels, but ETOH-fed mice had higher TNF-α expression. The ETOH-fed group developed more apoptosis, inflammation, fibrosis, and regenerative responses. Fn14 deletion did not reduce hepatic TNF-α expression but improved all injury parameters in mice fed the control diet. In ETOH-fed mice, Fn14 deletion inhibited TNF-α induction and increased acute mortality, despite improvement in liver injury. Fn14 mediates wound-healing responses that are necessary to survive acute liver injury during alcohol exposure.