Defective hepatic regeneration after partial hepatectomy in leptin-deficient mice is not rescued by exogenous leptin

Liver regeneration after partial hepatectomy (PH) is impaired in leptin-deficient ob/ob mice. Here, we tested whether exogenous leptin and/or correction of the obese phenotype (by food restriction or long-term leptin administration) would rescue hepatocyte proliferation and whether the hepatic progenitor cell compartment was activated in leptin-deficient ob/ob livers after PH. Because of the high mortality following 70% PH to ob/ob mice, we performed a less extensive (55%) resection. Compared to lean mice, liver regeneration after 55% PH was deeply impaired and delayed in ob/ob mice. Administration of exogenous leptin to ob/ob mice at doses that restored circulating leptin levels during the surgery and postsurgery period or for 3 weeks prior to the surgical procedure did not rescue defective liver regeneration. Moreover, correction of obesity, metabolic syndrome and hepatic steatosis by prolonged administration of leptin or food restriction (with or without leptin replacement at the time of PH) did not improve liver regeneration in ob/ob mice. The hepatic progenitor cell compartment was increased in ob/ob mice. However, after PH, the number of progenitor cells decreased and signs of proliferation were absent from this cell compartment. In this study, we have conclusively shown that neither leptin replacement nor amelioration of the metabolic syndrome, obese phenotype and hepatic steatosis, with or without restitution of normal circulating levels of leptin, was able to restore replicative competence to ob/ob livers after PH. Thus, leptin does not directly signal to liver cells to promote hepatocyte proliferation, and the obese phenotype is not solely responsible for impaired regeneration.     

Liver damage using suicide genes. A model for oval cell activation

Liver regeneration from the facultative hepatic stem cells, the oval cells, takes place in situations in which liver regeneration from pre-existing hepatocytes is prevented. Different models have been used to stimulate oval cell response. Many of them involve the use of carcinogenic agents with or without partial hepatectomy. In this study we show that adenovirus-mediated gene transfer of the suicide gene thymidine kinase followed by ganciclovir administration caused hepatotoxicity of variable intensity. Rats with moderate elevation in serum transaminases recovered normal liver architecture few weeks after adenovirus injection. In contrast, rats with severe liver damage exhibited a marked and persisting activation of oval cells accompanied by ductular hyperplasia. In some rats, such lesion eventually evolved to cholangiofibrosis and in one rat to cholangiocarcinoma. Deposition of fibronectin and increased number of hepatic stellate cells were found in association with oval cells and cholangiofibrotic lesions. Hepatocyte growth factor was hyperexpressed in the livers with intense oval cell response or ductular proliferation, suggesting a participation of this factor in those lesions. In summary, our data demonstrate activation of oval cell response after gene transfer of thymidine kinase followed by ganciclovir administration. These findings indicate that high doses of this therapy causes liver damage together with an impairment in hepatocellular regeneration.     

STAT-3 overexpression and p21 up-regulation accompany impaired regeneration of fatty livers

Fatty liver is an important cause of morbidity in humans and is linked to impaired liver regeneration after liver injury, but the mechanisms for impaired liver regeneration remain unknown. In the normal liver, the interleukin (IL)-6/STAT-3 pathway is thought to play a central role in regeneration because this pathway is disrupted in IL-6-deficient mice that exhibit impaired liver regeneration after 70% partial hepatectomy (PH). To determine whether inhibition of STAT-3 is involved in fatty liver-related mitoinhibition, regenerative induction of STAT-3 was compared in normal mice and leptin-deficient ob/ob mice that have fatty livers and markedly impaired liver regeneration after PH. In both groups, two waves of STAT-3 activation were observed, the first in endothelia and the second in hepatocytes. Before PH, a significantly higher percentage of ob/ob endothelial and hepatocyte nuclei expressed phosphorylated (activated) STAT-3. After PH, phospho-STAT-3 accumulated in liver nuclei of lean mice and this response was markedly exaggerated in ob/ob mice. Moreover, a striking inverse correlation was noted between hepatocyte nuclear accumulation of phospho-STAT-3 and DNA synthesis (as assessed by bromodeoxyuridine labeling), as well as cyclin D1 mRNA induction and protein expression. In contrast, STAT-3 activation was positively correlated with p21 protein expression in both groups of mice. Because these results link exaggerated STAT-3 activation with impaired hepatocyte proliferation, STAT-3 inhibition cannot be a growth-arrest mechanism in ob/ob fatty livers. Rather, hyperinduction of this factor may promote mitoinhibition by up-regulating mechanisms that impede cell cycle progression.     

Secreted factors of human liver-derived mesenchymal stem cells promote liver regeneration early after partial hepatectomy

Rapid liver regeneration is required after living-donor liver transplantation and oncologic liver resections to warrant sufficient liver function and prevent small-for-size syndrome. Recent evidence highlights the therapeutic potential of mesenchymal stem cells (MSC) for treatment of toxic liver injury, but whether MSC and their secreted factors stimulate liver regeneration after surgical injury remains unknown. Therefore, the aim of this study is to investigate the effect of human liver-derived MSC-secreted factors in an experimental liver resection model. C57BL/6 mice were subjected to a 70% partial hepatectomy and treated with either concentrated MSC-conditioned culture medium (MSC-CM) or vehicle control. Animals were analyzed for liver and body weight, hepatocyte proliferation, and hepatic gene expression. Effects of MSC-CM on gene expression in a human hepatocyte-like cell line (Huh7 cells) were analyzed using genome-wide gene expression arrays. Liver regeneration was significantly stimulated by MSC-CM as shown by an increase in liver to body weight ratio and hepatocyte proliferation. MSC-CM upregulated hepatic gene expression of cytokines and growth factors relevant for cell proliferation, angiogenesis, and anti-inflammatory responses. In vitro, treatment of Huh7 cells with MSC-CM significantly altered expression levels of ～3,000 genes. Functional analysis revealed strong effects on networks associated with protein synthesis, cell survival, and cell proliferation. This study shows that treatment with MSC-derived factors can promote hepatocyte proliferation and regenerative responses in the early phase after surgical resection. MSC-CM may represent a feasible new strategy to promote liver regeneration in patients undergoing extensive liver resection or after transplantation of small liver grafts.     

Fate-mapping evidence that hepatic stellate cells are epithelial progenitors in adult mouse livers

Liver injury activates quiescent hepatic stellate cells (Q-HSC) to proliferative myofibroblasts. Accumulation of myofibroblastic hepatic stellate cells (MF-HSC) sometimes causes cirrhosis and liver failure. However, MF-HSC also promote liver regeneration by producing growth factors for oval cells, bipotent progenitors of hepatocytes and cholangiocytes. Genes that are expressed by primary hepatic stellate cell (HSC) isolates overlap those expressed by oval cells, and hepatocytic and ductular cells emerge when HSC are cultured under certain conditions. We evaluated the hypothesis that HSC are a type of oval cell and, thus, capable of generating hepatocytes to regenerate injured livers. Because Q-HSC express glial fibrillary acidic protein (GFAP), we crossed mice in which GFAP promoter elements regulated Cre-recombinase with ROSA-loxP-stop-loxP-green fluorescent protein (GFP) mice to generate GFAP-Cre/GFP double-transgenic mice. These mice were fed methionine choline-deficient, ethionine-supplemented diets to activate and expand HSC and oval cell populations. GFP(+) progeny of GFAP-expressing precursors were characterized by immunohistochemistry. Basal expression of mesenchymal markers was negligible in GFAP(+)Q-HSC. When activated by liver injury or culture, HSC downregulated expression of GFAP but remained GFP(+); they became highly proliferative and began to coexpress markers of mesenchyme and oval cells. These transitional cells disappeared as GFP-expressing hepatocytes emerged, began to express albumin, and eventually repopulated large areas of the hepatic parenchyma. Ductular cells also expressed GFAP and GFP, but their proliferative activity did not increase in this model. These findings suggest that HSC are a type of oval cell that transitions through a mesenchymal phase before differentiating into hepatocytes during liver regeneration. Disclosure of potential conflicts of interest is found at the end of this article.     

Hepatic microenvironment affects oval cell localization in albumin-urokinase-type plasminogen activator transgenic mice

Mice carrying an albumin-urokinase type plasminogen activator transgene (AL-uPA) develop liver disease secondary to uPA expression in hepatocytes. Transgene-expressing parenchyma is replaced gradually by clones of cells that have deleted transgene DNA and therefore are not subject to uPA-mediated damage. Diseased liver displays several abnormalities, including hepatocyte vacuolation and changes in nonparenchymal tissue. The latter includes increases in laminin protein within parenchyma and the appearance of cytokeratin 19-positive bile ductule-like cells (oval cells) both in portal regions and extending into the hepatic parenchyma. In this study, we subjected AL-uPA mice to two-thirds partial hepatectomy to identify the response of these livers to additional growth stimulation. We observed several changes in hepatic morphology. First, the oval cells increased in number and often formed ductules in the parenchyma. Second, this cellular change was accompanied by a further increase in laminin associated with single or clusters of oval cells. Third, desmin-positive Ito cells increased in number and maintained close association with oval cells. Fourth, these changes were localized precisely to uPA-expressing areas of liver. Regenerating clones of uPA-deficient cells appeared to be unaffected both by stromal and cellular alterations. Thus, additional growth stimulation of diseased uPA-expressing liver induces an oval cell-like response, as observed in other models of severe hepatic injury, but the localization of this response seems to be highly regulated by the hepatic microenvironment.     

Tumour growth stimulation following partial hepatectomy in mice is associated with increased upregulation of c-Met

Hepatic resection is the preferred option for curative treatment of colorectal liver metastasis (CLM). However, this is associated with significant recurrence rates in both hepatic and extrahepatic sites. The upregulation of growth factors required for liver regeneration after resection is thought to stimulate the growth of micrometastases. The current study describes temporal changes in the expression of hepatocyte growth factor receptor (c-Met), epidermal growth factor receptor (EGFR) and insulin growth factor I receptor (IGF-IR) in an orthotopic mouse model of liver resection and tumour induction. Mice underwent 70 % hepatectomy and induction of liver metastases through intrasplenic injection of colorectal cancer cells. Control groups included sham-operated mice and 70 % hepatectomy alone. The expression levels of liver and tumour c-Met, EGFR and IGF-IR were quantified by quantitative RT-PCR at different time points. 70 % liver resection stimulates tumour growth; increases the expression of c-Met within established tumours and surrounding liver parenchyma; downregulates EGFR expression and increases IGF-IR expression within the liver parenchyma. In conclusion, we demonstrate in our mouse model that major hepatectomy stimulates engraftment and growth of CLM and that this effect is probably due to the upregulation of c-Met as a result of the liver regeneration process. Liver IGF-IR may also contribute to this phenomenon through a paracrine effect on tumour growth. This study provides support for the role of c-Met in the stimulation of tumour growth after resection possibly through the promotion of tumour cell proliferation.     

Oxidative stress and oval cell accumulation in mice and humans with alcoholic and nonalcoholic fatty liver disease

In animals, the combination of oxidative liver damage and inhibited hepatocyte proliferation increases the numbers of hepatic progenitors (oval cells). We studied different murine models of fatty liver disease and patients with nonalcoholic fatty liver disease or alcoholic liver disease to determine whether oval cells increase in fatty livers and to clarify the mechanisms for this response. To varying degrees, all mouse models exhibit excessive hepatic mitochondrial production of H(2)O(2), a known inducer of cell-cycle inhibitors. In mice with the greatest H(2)O(2) production, mature hepatocyte proliferation is inhibited most, and the greatest number of oval cells accumulates. These cells differentiate into intermediate hepatocyte-like cells after a regenerative challenge. Hepatic oval cells are also increased significantly in patients with nonalcoholic fatty liver disease and alcoholic liver disease. In humans, fibrosis stage and oval cell numbers, as well as the number of intermediate hepatocyte-like cells, are strongly correlated. However, cirrhosis is not required for oval cell accumulation in either species. Rather, as in mice, progenitor cell activation in human fatty liver diseases is associated with inhibited replication of mature hepatocytes. The activation of progenitor cells during fatty liver disease may increase the risk for hepatocellular cancer, similar to that observed in the Solt-Farber model of hepatocarcinogenesis in rats.     

Evidence for non-traditional activation of complement factor C3 during murine liver regeneration

Complement signaling has been implicated as important for normal hepatic regeneration. However, the specific mechanism by which complement is activated during liver regeneration remains undefined. To address this question, we investigated the hepatic regenerative response to partial hepatectomy in wildtype mice, C3-, C4-, and factor B-null mice, and C4-null mice treated with a factor B neutralizing antibody (mAb 1379). The results showed that following partial hepatectomy, C3-null mice exhibit reduced hepatic regeneration compared to wildtype mice as assessed by quantification of hepatic cyclin D1 expression and hepatocellular DNA synthesis and mitosis. In contrast, C4-null mice and factor B-null mice demonstrated normal liver regeneration. Moreover, animals in which all of the traditional upstream C3 activation pathways were disrupted, i.e. C4-null mice treated with mAb 1379, exhibited normal C3 activation and hepatocellular proliferation following partial hepatectomy. In order to define candidate non-traditional mechanisms of C3 activation during liver regeneration, plasmin and thrombin were investigated for their abilities to activate C3 in mouse plasma in vitro. The results showed that both proteases are capable of initiating C3 activation, and that plasmin can do so independent of the classical and alternative pathways. Conclusions: These results show that C3 is required for a normal hepatic regenerative response, but that disruption of the classical- or lectin-dependent pathways (C4-dependent), the alternative pathway (factor B-dependent), or all of these pathways does not impair the hepatic regenerative response, and indicate that non-traditional mechanisms by which C3 is activated during hepatic regeneration must exist. In vitro analysis raises the possibility that plasmin may contribute to non-traditional complement activation during liver regeneration in vivo.     

Bone marrow progenitors are not the source of expanding oval cells in injured liver

Liver progenitor/oval cells differentiate into hepatocytes and biliary epithelial cells, repopulating the liver when the regenerative capacity of hepatocytes is impaired. Recent studies have shown that hematopoietic bone marrow (BM) stem/progenitor cells can give rise to hepatocytes in diseased/damaged liver. One study has reported that BM cells can transdifferentiate into liver progenitor/oval cells, but it has not been proven that the latter can repopulate the liver. To answer this question, we have lethally irradiated female DPP4(-) mutant F344 rats and transplanted them with 50 million wild-type male F344 BM cells. One month after transplantation, the recipient BM was reconstituted with male hematopoietic cells, determined by quantitative polymerase chain reaction using primers for Y chromosome-specific sry gene. In addition, DPP4(+) cells, single or in clusters and predominantly in the periportal region, were detected in all liver sections of recipient rats. Animals were subjected to the following three different liver injury protocols for activation and expansion of oval cells: D-galactosamine, retrorsine/partial hepatectomy (Rs/PH), and 2-acetylaminofluorene/partial hepatectomy (2-AAF/PH). In all three models, prominent expansion and accumulation of cytokeratin 19-positive (CK-19(+)) oval cells was observed. However, most of the DPP4(+) clusters dispersed over time, and their total number decreased. Very few oval cells (less than 1%) showed double DPP4/CK-19 labeling. None of the small hepatocytic clusters in the Rs/PH or 2-AAF/PH model were comprised of DPP4(+) cells. These data demonstrate that the sources of oval cells and small hepatocytes in the injured liver are endogenous liver progenitors and that they do not arise through transdifferentiation from BM cells.     

Transforming growth factor-beta1 protein, proliferation and apoptosis of oval cells in acetylaminofluorene-induced rat liver regeneration

Administering of 2-acetylaminofluorene (2-AAF) before a two-thirds partial hepatectomy (PHx) results in suppression of hepatocyte proliferation and stimulation of oval cell proliferation. The objectives of this study was to examine the oval cell behaviour and associated transforming growth factor-beta1 (TGF-beta1) protein expression by combining 2-AAF with selective hepatic damage caused by PHx. We also studied the temporal relationship between TGF-beta1 expression, and proliferation and apoptosis of oval cells. Oval cells emerged from the portal areas and became more numerous with time fanning out into the periportal and midzonal hepatic parenchyma. Both smooth muscle actin (SMA) and TGF-beta1 immunostain revealed that TGF-beta1-positive cells were SMA-positive hepatic stellate cells (HSCs). Coinciding with the proliferation of oval cells, an increase expression of TGF-beta1 produced by SMA-positive HSCs was observed, thereafter apoptosis of oval cells reached its peak. This result implicated that TGF-beta1 produced by HSCs is intimately associated with proliferation and apoptosis of oval cells, and plays a role in the cessation of oval cell activation and remodeling of liver parenchyma in 2-AAF induced liver regeneration.     

肝再生过程中肝星状细胞及基质金属蛋白酶的动态变化

目的研究大鼠肝大部切除(PH)后再生过程中肝星状细胞(HSCs)的动态变化及肝MMP-2、MMP-9的活性变化,探讨肝星状细胞在肝再生中的作用。方法按Higgins等方法制备肝大部切除动物模型,于术后恢复不同时程取材,免疫组织化学法检测肝HSCs的动态变化,明胶酶谱电泳法检测肝中MMP-2、MMP-9的变化。结果(1)正常肝小叶内HSCs呈网架状分布,PH后Desmin阳性HSCs的数量递减;胶质纤维酸性蛋白(GFAP)阳性HSCs的数量也呈递减趋势。(2)PH后再生过程中,肝脏MMP-2、MMP-9的表达逐渐增多。结论肝再生过程中HSCs的增殖反应较慢且维持的时间短,这不同于肝纤维化等肝病过程中HSCs维持较长时间的激活状态。肝再生过程中基质金属蛋白酶-2,-9的表达发生显著改变,提示基质金属蛋白酶-2,-9参与了肝再生过程。     

Enhanced liver regeneration in IL-10-deficient mice after partial hepatectomy via stimulating inflammatory response and activating hepatocyte STAT3

Emerging evidence suggests that proinflammatory cytokines, including tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), play a critical role in the initiation and progression of liver regeneration; however, relatively little is known about the role of anti-inflammatory cytokine IL-10 in liver regeneration after partial hepatectomy (PHx). Here, we examined the role of IL-10 in liver regeneration using a model of PHx in several strains of genetically modified mice. After PHx, expression of IL-10 mRNA in the liver and spleen was significantly elevated. Such elevation was diminished in TLR4 mutant mice. Compared with wild-type mice, IL-10(-/-) mice had higher levels of expression of proinflammatory cytokines (IL-6, TNF-α, and IFN-γ) and inflammatory markers (CCR2 and F4/80) in the liver, as well as higher serum levels of proinflammatory cytokines after PHx. The number of neutrophils and macrophages was also higher in the livers of IL-10(-/-) mice than in wild-type mice after PHx. Liver regeneration as determined by BrdU incorporation after PHx was higher in IL-10(-/-) mice than in wild-type mice, which was associated with higher levels of activation of IL-6 downstream signal STAT3 in the liver. An additional deletion of STAT3 in hepatocytes significantly reduced liver regeneration in IL-10(-/-) mice after PHx. Collectively, IL-10 plays an important role in negatively regulating liver regeneration via limiting inflammatory response and subsequently tempering hepatic STAT3 activation.     

Cellular origin of regenerating parenchyma in a mouse model of severe hepatic injury

Several treatments in rodents, including administration of the alkylating agent dipin, followed by two-thirds partial hepatectomy in mice combine destruction of liver parenchyma with hepatocyte mitoinhibition. These treatments induce proliferation of bile epithelial-like cells (termed oval cells), development of foci composed of small hepatocytes, and eventual replacement of damaged parenchyma by healthy hepatocytes. It has been proposed that these oval cells represent transitional cells in a nonhepatocytic liver facultative stem cell lineage that can give rise to the small hepatocyte foci, and that these foci eventually become confluent and replace liver parenchyma. In this study, we used in vivo cell lineage marking in genetically chimeric livers to test the hypothesis that hepatocytes can serve as the precursor cell type to the small hepatocyte foci that develop in mouse liver after treatment with dipin plus partial hepatectomy. Although we do not exclude the possibility that some small hepatocyte foci may be stem cell-derived, we demonstrate that hepatocyte-derived foci are present after dipin-induced liver damage in mice.     

Amelioration of non-alcoholic steatohepatitis and glucose intolerance in ob/ob mice by oral immune regulation towards liver-extracted proteins is associated with elevated intrahepatic NKT lymphocytes and serum IL-10 levels

Non-alcoholic steatohepatitis (NASH) is a common cause of cryptogenic cirrhosis in the Western world. In an animal model of NASH, leptin-deficient ob/ob mice present with alterations in number and function of hepatic NKT and peripheral CD4 lymphocytes. Oral immune regulation is a method to alter the immune response towards orally administered antigens. To determine the effect of oral immune regulation towards liver-extracted proteins on the metabolic disorders in ob/ob mice, ob/ob mice and their lean littermates were orally administered liver extracts from wild-type or ob/ob mice or bovine serum albumin for 1 month. The effect of treatment on hepatic fat content was measured by magnetic resonance imaging (MRI) and using a histological steatohepatitis grading scale. Glucose tolerance was measured by an oral glucose tolerance test (GTT). T lymphocyte subpopulations were assessed by flow cytometry analysis. Induction of immune regulation by oral presentation of liver-extracted proteins resulted in a significant 18% reduction of the hepatic fat content in ob/ob mice fed with either wild-type or ob/ob liver extracts for 1 month. The MRI signal intensity index in treated mice decreased to 0.48 and 0.51, respectively, compared with 0.62 in BSA-fed controls (p = 0.037 and p = 0.019, respectively), while the histological steatohepatitis score decreased in both treated groups to 2.0, compared with 2.4 in BSA-fed controls (p = 0.05). A significant improvement in GTT was noted in treated ob/ob mice. These changes were accompanied by a marked increase in the intrahepatic NKT lymphocyte population in mice fed with proteins extracted from both wild-type and ob/ob mice (46.96% and 56.72%, respectively, compared with 26.21% in BSA-fed controls; p < 0.05) and a significant elevation in serum IL-10 levels. Oral immune regulation towards liver extracted proteins in leptin-deficient mice resulted in a marked reduction in hepatic fat content and improved glucose tolerance. This effect was associated with a significant increase in the intrahepatic NKT lymphocyte population and serum IL-10 levels, suggesting a Th1 to Th2 immune shift. Immune regulation towards disease-associated antigens holds promise as a new mode of therapy for NASH.     

Which stem cells for adult liver?

While hepatocytes can be considered conceptually as unipotent stem cells, the presence of true stem or progenitor cells within adult livers has been largely debated. It is now accepted that the atypical ductular reaction observed in livers with sub-massive hepatitis represents the proliferation of hepatic progenitor cells similar to rat oval cells and able to differentiate towards the biliary and the hepatocytic lineage through intermediate progeny. In the normal liver, the identification of progenitor cells with a panel of markers including c-kit, CD34, Ov6, CK7, CK19, chromogranine A, CD56 remains difficult because these cells are very few and most of the markers are not specific. These progenitor cells could be located either within the canals of Hering or in periductular situation or both. Mechanisms leading to the activation and the proliferation of hepatic progenitor cells are still largely unknown: they involve growth factors as the stem cell factor, ligand of c-kit, cytokines, chemokines as SDF1 a and vagal or sympathetic innervatio?. Other potential stem cells for liver could be hematopoietic stem cells from bone marrow. First publications have showed that hematopoietic stem cells were able to differentiate into hepatocytes and cholangiocytes and to yield high level engraftment of injured livers. However it appears now that this phenomenon is minimal or even absent in physiological and usual pathological conditions. It does occur in extreme experimental conditions either by true transdifferentiation or cell fusion. The shared property of stem cells and tumor cells to proliferate endlessly, rises the question of the potential role of progenitor cells in liver carcinogenesis. In a number of animal models of hepatocarcinogenesis, tumors originate from oval cells. The identification of progenitor cells close to murine oval cells in the human liver raises the hypothesis of a potential role of these cells in the development of human liver tumors. Liver progenitor cells have been identified morphologically and phenotypically in dysplastic foci of cirrhotic livers and hepatocellular adenomas. More generally speaking, typical hepatocellular carcinomas and cholangiocarcinomas are at the two ends of a spectrum which includes transitional-type tumors intermediate between hepatocellular carcinoma and cholangiocarcinoma and combined hepato-cellular cholangiocarcinoma; these intermediate and combined types can be more easily explained as deriving from progenitor cells. Despite the difficulties, the doubts and the potential dangers, new experimental modalities to obtain efficient repopulation of the liver from bone marrow stem cells are currently under study: exogenous administration of cytokines and chemokines involved in cell homing and differentiation or development of selective pressure strategies. Other cell types as intra-hepatic progenitor cells, bone marrow multipotent adult progenitor cells (MAPCs) or fetal hepatocytes could be alternative sources for liver cell therapy. Thus, progressing knowledge about stem cells in adult liver would allow to better understand mechanisms of hepatic homeostasia and regeneration and would open the way to cell-based therapy for liver diseases.     

Atypical ductular proliferation and its inhibition by transforming growth factor beta1 in the 3,5-diethoxycarbonyl-1,4-dihydrocollidine mouse model for chronic alcoholic liver disease

Many acute and chronic liver diseases are often associated with atypical ductular proliferation (ADP). These ADPs have gained increasing interest since a number of recent observations suggest that ADPs may represent progenies of the putative liver stem cell compartment. In this study, we show that feeding mice with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) results in persistent proliferation of primitive ductules with poorly defined lumens. Similar to oval cell proliferation in other rodent models as well as in various human liver diseases, DDC-induced ADP originated from the portal tract, spread into the hepatic lobule, and was associated closely with appearance of hepatocytes harboring an antigen (A6), which normally is expressed in biliary epithelium. Furthermore, DDC treatment severely inhibited the regenerative capacity of mice after partial hepatectomy. The development of ADP was selectively blocked in DDC-fed TGF-beta1 transgenic mice producing active TGF-beta1 in the liver and no accumulation of new hepatocytes expressing the A6 antigen was observed. Moreover, the transforming growth factor beta1 (TGF-beta1) transgenic mice did not survive beyond 3 weeks from starting the DDC-containing diet. The results suggest that persistent activation of the hepatic stem cell compartment is essential for liver regeneration in the DDC model and that active TGF-beta1 may negatively control activation of stem cells in the liver. These data further emphasize the relevance of the DDC model as an experimental tool for studying chronic liver diseases.