Hepatic progenitor cells, stem cells, and AFP expression in models of liver injury

HGF and SDF-1-mediated mobilization of CD133+ BMSC for hepatic regeneration following extensive liver resection

BACKGROUND

The molecular mechanisms of haematopoietic stem cells (HSC) mobilization and homing to the liver after partial hepatectomy (PH) remain largely unexplored.

METHODS

Functional liver volume loss and regain was determined by computerized tomography (CT) volumetry in 30 patients following PH. Peripheral HSC mobilization was investigated by fluorescence-activated cell sorting (FACS) analyses and cytokine enzyme-linked immunosorbent assay assays. Migration of purified HSC towards hepatic growth factor (HGF) and stroma-derived factor-1 (SDF-1) gradients was tested in vitro. Mice after 70% PH were examined for HSC mobilization by FACS and cytokine mRNA expression in the liver. FACS-sorted HSC were administered after PH and hepatocyte proliferation was evaluated by immunohistochemical staining for Ki67.

RESULTS

Impaired liver function was noted after extended hepatic resection when compared to smaller resections. Patients with large liver resections were characterized by significantly higher levels of peripheral HSC which were positively correlated with the extent of resected liver volume and its regain after 3 weeks. Increased plasma levels of HGF, SDF-1 and insulin like growth factor (IGF-1) were evident within the first 6 hours post resection. Migration assays of human HSC in vitro showed a specific target-demonstrated migration towards recombinant HGF and SDF-1 gradients in a concentration and specific receptor (c-Met and CXCR4) dependent manner. The evaluation of peripheral human alpha foetoprotein expression demonstrated pronounced stemness following increased CD133(+) HSC in the course of liver regeneration following PH. Our human data were further validated in a murine model of PH and furthermore demonstrated increased hepatocyte proliferation subsequent to CD133(+) HSC treatment.

CONCLUSION

HGF and SDF-1 are required for effective HSC mobilization and homing to the liver after hepatic resection. These findings have significant implications for potential therapeutic strategies targeting chemotactant modulation and stem cell mobilization for liver protection and regeneration.

Duck hepatitis B virus covalently closed circular DNA appears to survive hepatocyte mitosis in the growing liver

Nucleos(t)ide analogues that inhibit hepatitis B virus (HBV) DNA replication are typically used as monotherapy for chronically infected patients. Treatment with a nucleos(t)ide analogue eliminates most HBV DNA replication intermediates and produces a gradual decline in levels of covalently closed circular DNA (cccDNA), the template for viral RNA synthesis. It remains uncertain if levels of cccDNA decline primarily through hepatocyte death, or if loss also occurs during hepatocyte mitosis. To determine if cccDNA survives mitosis, growing ducklings infected with duck hepatitis B virus (DHBV) were treated with the nucleoside analogue, Entecavir. Viremia was suppressed at least 10(5)-fold, during a period when average liver mass increased 23-fold. Analysis of the data suggested that if cccDNA synthesis was completely inhibited, at least 49% of cccDNA survived hepatocyte mitosis. However, there was a large duck-to-duck variation in cccDNA levels, suggesting that low level cccDNA synthesis may contribute to this apparent survival through mitosis.

Awakened by cellular stress: isolation and characterization of a novel population of pluripotent stem cells derived from human adipose tissue

Advances in stem cell therapy face major clinical limitations, particularly challenged by low rates of post-transplant cell survival. Hostile host factors of the engraftment microenvironment such as hypoxia, nutrition deprivation, pro-inflammatory cytokines, and reactive oxygen species can each contribute to unwanted differentiation or apoptosis. In this report, we describe the isolation and characterization of a new population of adipose tissue (AT) derived pluripotent stem cells, termed Multilineage Differentiating Stress-Enduring (Muse) Cells, which are isolated using severe cellular stress conditions, including long-term exposure to the proteolytic enzyme collagenase, serum deprivation, low temperatures and hypoxia. Under these conditions, a highly purified population of Muse-AT cells is isolated without the utilization of cell sorting methods. Muse-AT cells grow in suspension as cell spheres reminiscent of embryonic stem cell clusters. Muse-AT cells are positive for the pluripotency markers SSEA3, TR-1-60, Oct3/4, Nanog and Sox2, and can spontaneously differentiate into mesenchymal, endodermal and ectodermal cell lineages with an efficiency of 23%, 20% and 22%, respectively. When using specific differentiation media, differentiation efficiency is greatly enhanced in Muse-AT cells (82% for mesenchymal, 75% for endodermal and 78% for ectodermal). When compared to adipose stem cells (ASCs), microarray data indicate a substantial up-regulation of Sox2, Oct3/4, and Rex1. Muse-ATs also exhibit gene expression patterns associated with the down-regulation of genes involved in cell death and survival, embryonic development, DNA replication and repair, cell cycle and potential factors related to oncogenecity. Gene expression analysis indicates that Muse-ATs and ASCs are mesenchymal in origin; however, Muse-ATs also express numerous lymphocytic and hematopoietic genes, such as CCR1 and CXCL2, encoding chemokine receptors and ligands involved in stem cell homing. Being highly resistant to severe cellular stress, Muse-AT cells have the potential to make a critical impact on the field of regenerative medicine and cell-based therapy.

Up-regulation of thy-1 promotes invasion and metastasis of hepatocarcinomas

Increasing evidence has revealed that thy-1 was a potential stem cell marker of liver cancer, but no data have been shown on how thy-1 regulates the pathophysiology of liver cancer, such as proliferation, apoptosis, invasion and migration. We previously demonstrated that thy-1 was expressed in about 1% of hepg2 cells, thy-1+ hepg2 cells, but not thy-1-, demonstrating high tumorigenesis on inoculation 0.5x10⁵ cells per BACA/LA mouse after 2 months. In the present study, our results showed that higher expression of thy-1 occurs in 72% (36/50 cases) of neoplastic hepatic tissues as compared to 40% (20/50 cases) of control tissues, and the expression of thy-1 is higher in poorly differentiated liver tumors than in the well-differentiated ones. In addition, thy-1 expression was detected in 85% of blood samples from liver cancer patients, but none in normal subjects or patients with cirrhosis or hepatitis. There was a significant negative correlation between thy-1 expression and E-cadherin expression (a marker of invasion and migraton), but not between thy-1 expression and AFP expression in all the liver cancer and blood samples. We further investigated the relationship between thy-1 and E- cadherin in liver cancer hepg2 cell line which was transfected with pReceiver-M29/thy-1 eukaryotic expression vector followed by aspirin treatment. Lower expression of E- cadherin but higher expressions of thy-1 were detected in hepg2 cells transfected with pReceiver-M29/thy-1. Taken together, our study suggested that thy-1 probably regulates liver cancer invasion and migration.

Effect of Yiguanjian decoction on cell differentiation and proliferation in CCl4-treated mice

AIM: To investigate the cellular mechanisms of action of Yiguanjian (YGJ) decoction in treatment of chronic hepatic injury.

METHODS: One group of mice was irradiated, and received enhanced green fluorescent protein (EGFP)-positive bone marrow transplants followed by 13 wk of CCl₄ injection and 6 wk of oral YGJ administration. A second group of Institute for Cancer Research mice was treated with 13 wk of CCl₄ injection and 6 wk of oral YGJ administration. Liver function, histological changes in the liver, and Hyp content were analyzed. The expression of α-smooth muscle actin (α-SMA), F4/80, albumin (Alb), EGFP, mitogen-activated protein kinase-2 (PKM2), Ki-67, α fetoprotein (AFP), monocyte chemotaxis protein-1 and CC chemokine receptor 2 were assayed.

RESULTS: As hepatic damage progressed, EGFP-positive marrow cells migrated into the liver and were mainly distributed along the fibrous septa. They showed a conspicuous coexpression of EGFP with α-SMA and F4/80 but no coexpression with Alb. Moreover, the expression of PKM2, AFP and Ki-67 was enhanced dynamically and steadily over the course of liver injury. YGJ abrogated the increases in the number of bone marrow-derived fibrogenic cells in the liver, inhibited expression of both progenitor and mature hepatocyte markers, and reduced fibrogenesis.

CONCLUSION: YGJ decoction improves liver fibrosis by inhibiting the migration of bone marrow cells into the liver as well as inhibiting their differentiation and suppressing the proliferation of both progenitors and hepatocytes in the injured liver.

Oval cell response is attenuated by depletion of liver resident macrophages in the 2-AAF/partial hepatectomy rat

BACKGROUND/AIMS

Macrophages are known to play an important role in hepatocyte mediated liver regeneration by secreting inflammatory mediators. However, there is little information available on the role of resident macrophages in oval cell mediated liver regeneration. In the present study we aimed to investigate the role of macrophages in oval cell expansion induced by 2-acetylaminofluorene/partial hepatectomy (2-AAF/PH) in rats.

METHODOLOGY/PRINCIPAL FINDINGS

We depleted macrophages in the liver of 2-AAF/PH treated rats by injecting liposome encapsulated clodronate 48 hours before PH. Regeneration of remnant liver mass, as well as proliferation and differentiation of oval cells were measured. We found that macrophage-depleted rats suffered higher mortality and liver transaminase levels. We also showed that depletion of macrophages yielded a significant decrease of EPCAM and PCK positive oval cells in immunohistochemical stained liver sections 9 days after PH. Meanwhile, oval cell differentiation was also attenuated as a result of macrophage depletion, as large foci of small basophilic hepatocytes were observed by day 9 following hepatectomy in control rats whereas they were almost absent in macrophage depleted rats. Accordingly, real-time polymerase chain reaction analysis showed lower expression of albumin mRNA in macrophage depleted livers. Then we assessed whether macrophage depletion may affect hepatic production of stimulating cytokines for liver regeneration. We showed that macrophage-depletion significantly inhibited hepatic expression of tumor necrosis factor-α and interleukin-6, along with a lack of signal transducer and activator of transcription 3 phosphorylation during the early period following hepatectomy.

CONCLUSIONS

These data indicate that macrophages play an important role in oval cell mediated liver regeneration in the 2-AAF/PH model.

Analysis of biodistribution and engraftment into the liver of genetically modified mesenchymal stromal cells derived from adipose tissue

Presently, orthotopic liver transplant is the major therapeutic option for patients affected by primary liver diseases. This procedure is characterized by major invasive surgery, scarcity of donor organs, high costs, and lifelong immunosuppressive treatment. Transplant of hepatic precursor cells represents an attractive alternative. These cells could be used either for allogeneic transplantation or for autologous transplant after ex vivo genetic modification. We used stromal cells isolated from adipose tissue (AT-SCs) as platforms for autologous cell-mediated gene therapy. AT-SCs were transduced with lentiviral vectors expressing firefly luciferase, allowing for transplanted cell tracking by bioluminescent imaging (BLI). As a complementary approach, we followed circulating human α1-antitrypsin (hAAT) levels after infusion of AT-SCs overexpressing hAAT. Cells were transplanted into syngeneic mice after CCl(4)-induced hepatic injury. Luciferase bioluminescence signals and serum hAAT levels were measured at different time points after transplantation and demonstrate persistence of transplanted cells for up to 2 months after administration. These data, along with immunohistochemical analysis, suggest engraftment and repopulation of injured livers by transplanted AT-SCs. Moreover, by transcriptional targeting using cellular tissue-specific regulatory sequences, we confirmed that AT-SCs differentiate towards a hepatogenic-like phenotype in vitro and in vivo. Additionally, in transplanted cells reisolated from recipient animals' livers, we detected activation of the α-fetoprotein (AFP) promoter. This promoter is normally transcriptionally silenced in adult tissues but can be reactivated during liver regeneration, suggesting commitment towards hepatogenic-like differentiation of engrafted cells in vivo. Our data support AT-SC-mediated gene therapy as an innovative therapeutic option for disorders of liver metabolism.

Klotho-beta overexpression as a novel target for suppressing proliferation and fibroblast growth factor receptor-4 signaling in hepatocellular carcinoma

Background

We had previously demonstrated overexpression of fibroblast growth factor receptor-4 (FGFR4) in hepatocellular carcinoma (HCC). However, additional molecular mechanisms resulting in amplified FGFR4 signaling in HCC remain under-studied. Here, we studied the mechanistic role of its co-receptor klotho-beta (KLB) in driving elevated FGFR4 activity in HCC progression.

Results

Quantitative real-time PCR analysis identified frequent elevation of KLB gene expression in HCC tumors relative to matched non-tumor tissue, with a more than two-fold increase correlating with development of multiple tumors in patients. KLB-silencing in Huh7 cells decreased cell proliferation and suppressed FGFR4 downstream signaling. While transient repression of KLB-FGFR4 signaling decreased protein expression of alpha-fetoprotein (AFP), a HCC diagnostic marker, prolonged inhibition enriched for resistant HCC cells exhibiting increased liver stemness.

Conclusions

Elevated KLB expression in HCC tissues provides further credence to the oncogenic role of increased FGFR4 signaling in HCC progression and represents a novel biomarker to identify additional patients amenable to anti-FGFR4 therapy. The restricted tissue expression profile of KLB, together with the anti-proliferative effect observed with KLB-silencing, also qualifies it as a specific and potent therapeutic target for HCC patients. The enrichment of a liver stem cell-like population in response to extended KLB-FGFR4 repression necessitates further investigation to target the development of drug resistance.

The power and the promise of liver cancer stem cell markers

Recently, there has been growing support for the cancer stem cell (CSC) hypothesis, which states that primary tumors are initiated and maintained by a small subpopulation of cancer cells that possess "stem-like" characteristics. CSCs have been identified in many tumor types, including hepatocellular carcinoma (HCC). The dye, Hoechst 33342, has been used to enrich CSCs into a side population. Alternatively, liver CSCs (LCSCs) can be identified by several cell surface antigens, including CD133, CD90, CD44, EpCAM, and CD13. In this review, we summarized the recent evidence regarding LCSC markers and discussed the origin and function of these markers. LCSC markers are essential to identify and isolate these cells, to develop future therapies targeting CSCs, and to predict prognosis and efficacy of these therapies. However, definite LCSC markers are still controversial, because none of these markers is exclusively expressed by LCSCs in HCC. By combining several positive or negative markers, it may be possible to isolate and identify CSC fractions beyond the ability of each individual assay. By grouping LCSC markers according to their cellular origin, the properties of LCSC markers may be better studied and new markers may be found. Lastly, markers could be used to estimate the number of LCSCs and therefore predict outcomes. From our point of view, selecting HCC tissue samples from patients with different prognoses and detecting expression patterns of marker combinations may be a new method to identify new and unique markers.

Long-term ethanol consumption promotes hepatic tumorigenesis but impairs normal hepatocyte proliferation in rats

Chronic and excessive alcohol consumption has been related to an increased risk of several cancers, including that of the liver; however, studies in animal models have yet to conclusively determine whether ethanol acts as a tumor promoter in hepatic tumorigenesis. We examined whether prolonged alcohol consumption could act as a hepatic tumor promoter after initiation by diethylnitrosamine (DEN) in a rat model. Male Sprague-Dawley rats were injected with 20 mg DEN/kg body weight 1 wk before introduction of either an ethanol liquid diet or an isoenergic control liquid diet. Hepatic pathological lesions, hepatocyte proliferation, apoptosis, PPARα and PPARγ, and plasma insulin-like growth factor 1 (IGF-1) levels were assessed after 6 and 10 mo. Mean body and liver weights, plasma IGF-1 concentration, hepatic expressions of proliferating cellular nuclear antigen and Ki-67, and cyclin D1 in ethanol-fed rats were all significantly lower after 10 mo of treatment compared with control rats. In addition, levels of hepatic PPARγ protein, not PPARα, were significantly higher in the ethanol-fed rats after prolonged treatment. Although ethanol feeding also resulted in significantly fewer altered hepatic foci, hepatocellular adenoma was detected in ethanol-fed rats at 10 mo, but not in control rats given the same dose of DEN. Together, these results indicate that chronic, excessive ethanol consumption impairs normal hepatocyte proliferation, which is associated with reduced IGF-1 levels, but promotes hepatic carcinogenesis.

Cellular senescence in livers from children with end stage liver disease

BACKGROUND

Senescent cells occur in adults with cirrhotic livers independent of the etiology.

AIM

Investigate the presence rate of cellular senescence and expression of cell cycle check points in livers from children with end stage disease.

METHODOLOGY/PRINCIPAL FINDINGS

Livers of five children aged three years or less undergoing liver transplantation due to tyrosinemia (n = 1), biliary atresia (n = 2), or fulminant hepatitis (n = 2) were analyzed for senescence associated beta-galactosidase (SA-betagal) activity and p16INK4a, p21cip1 and p53. All livers displayed positive cellular staining for SA-betagal in the canals of Hering and interlobular biliary ducts. In the presence of cirrhosis (3/5 cases) SA-betagal was found at the cholangioles and hepatocytes surrounding the regenerative nodules. Children with fulminant hepatic failure without cirrhosis had significant ductular transformation with intense SA-betagal activity. No SA-betagal activity was evident in the fibrous septa. Staining for p53 had a similar distribution to that observed for SA-betagal. Staining for p16(INK4a) and p21(cip1) was positive in the explanted liver of the patient with tyrosinemia, in the hepatocytes, the canals of Hering, cholangioles and interlobular bile ducts. In the livers with fulminant hepatitis, p21(cip1) staining occurred in the areas of ductular transformation and in the interlobular bile ducts.

CONCLUSIONS/SIGNIFICANCE

Cellular senescence in livers of children with end stage disease is associated with damage rather than corresponding to an age dependent phenomenon. Further studies are needed to support the hypothesis that these senescence markers correlate with disease progression.

Hepatic fibrosis is enhanced and accompanied by robust oval cell activation after chronic carbon tetrachloride administration to Egr-1-deficient mice

The transcription factor early growth response (Egr)-1 regulates the expression of genes required for execution of the wound healing response. Multiple cycles of injury, coupled to incomplete wound healing, lead to fibrosis. Therefore, we hypothesized that Egr-1 is required for the development of hepatic fibrosis. To test this hypothesis, we exposed wild-type and egr-1(-/-) mice to acute or chronic carbon tetrachloride (CCl(4)). Acute CCl(4) exposure established a profibrotic milieu in the liver, including activation of hepatic stellate cells as well as expression of type 1 collagen genes and tissue inhibitor of matrix metalloproteinase 1 in both wild-type and egr-1(-/-) mice. This response was exacerbated in egr-1(-/-) mice. After chronic CCl(4) exposure, hepatic fibrosis was established in both genotypes; however, the fibrotic response was profoundly worsened in Egr-1-deficient mice. Importantly, enhanced fibrosis in egr-1(-/-) mice was accompanied by a robust activation of the oval cell response, suggesting more severe liver injury and/or reduced hepatocyte proliferation when compared with wild-type mice. Hepatic expression of genes indicative of oval cell activation, as well as the number of cells expressing A6, a mouse oval cell marker, was greater in egr-1(-/-) mice. Taken together, these data reveal novel roles for Egr-1 as a negative regulator of both CCl(4)-induced hepatic fibrosis and the oval cell response.

Bone morphogenetic protein-4 induced rat hepatic progenitor cell (WB-F344 cell) differentiation toward hepatocyte lineage

Hepatic progenitor cells are local stem cells in the liver and they can be differentiated into either hepatocytes or cholangiocytes depending on different stimulations. These stimulations include extracellular growth factors and intracellular transcription factors. Bone morphogenetic protein 4 (BMP4) is a member of transforming growth factor beta (TGF-beta) superfamily and was first identified as growth factor to induce ectopic bone formation from skeletal muscle. Role of BMP4 in the liver is still unclear especially its role in hepatic progenitor cells (HPCs) differentiation. BMP4 was used to stimulate rat HPCs (WB-F344 cells) and differentiation of WB-F344 cells was investigated by reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot analysis. Both adenovirus delivered BMP4 and recombinant BMP4 were able to induce expression of hepatocyte markers such as albumin, TAT-1, and G6Pase but not cholangiocyte markers such as beta4-integrin and CK19. BMP4 induced differentiation of WB-F344 cells toward hepatocytes was mediated by increase in phosphorylation of Smad1 and ERK1/2. Moreover, BMP4 also stimulated expression of transcription factor--C/EBP-alpha, which involved in differentiation of WB-F344 cells toward hepatocytes. BMP4 is able to stimulate WB-F344 cells differentiation toward hepatocyte lineage.

Omentum facilitates liver regeneration

AIM: To investigate the mechanism of liver regeneration induced by fusing the omentum to a small traumatic injury created in the liver. We studied three groups of rats. In one group the rats were omentectomized; in another group the omentum was left in situ and was not activated, and in the third group the omentum was activated by polydextran particles.

METHODS: We pre-activated the omentum by injecting polydextran particles and then made a small wedge wound in the rat liver to allow the omentum to fuse to the wound. We monitored the regeneration of the liver by determining the ratio of liver weight/body weight, by histological evaluation (including immune staining for cytokeratin-19, an oval cell marker), and by testing for developmental gene activation using reverse transcription polymerase chain reaction (RT-PCR).

RESULTS: There was no liver regeneration in the omentectomized rats, nor was there significant regeneration when the omentum was not activated, even though in this instance the omentum had fused with the liver. In contrast, the liver in the rats with the activated omentum expanded to a size 50% greater than the original, and there was histologically an interlying tissue between the wounded liver and the activated omentum in which bile ducts, containing cytokeratin-19 positive oval cells, extended from the wound edge. In this interlying tissue, oval cells were abundant and appeared to proliferate to form new liver tissue. In rats pre-treated with drugs that inhibited hepatocyte growth, liver proliferation was ongoing, indicating that regeneration of the liver was the result of oval cell expansion.

CONCLUSION: Activated omentum facilitates liver regeneration following injury by a mechanism that depends largely on oval cell proliferation.

Fibroblast growth factor receptor 4 regulates proliferation, anti-apoptosis and alpha-fetoprotein secretion during hepatocellular carcinoma progression and represents a potential target for therapeutic intervention

BACKGROUND/AIMS

FGFR4, a member of the fibroblast growth factor receptor family, has been recently associated with progression of melanoma, breast and head and neck carcinoma. Given its uniquely high expression in the liver, we investigated its contributory role to hepatocellular carcinoma (HCC).

METHODS

We performed a comprehensive sequencing of full-length FGFR4 transcript in 57 tumor/normal HCC tissue pairs, and quantified their mRNA expressions. Notable mutations and expression patterns were correlated with patient data. Clinically significant trends were examined in in vitro models.

RESULTS

We found eight genetic alterations including two highly frequent polymorphisms (V10I and G338R). Secretion of alpha-fetoprotein (AFP), a HCC biomarker, was increased among patients bearing homozygous Arg388 alleles. One-third of these patients exhibited increased FGFR4 mRNA expression in the matched tumor/normal tissue. Subsequent in vitro perturbation of FGFR4 signaling through both FGF19-stimulation and FGFR4 silencing confirmed a mechanistic link between FGFR4 activities and tumor aggressiveness. More importantly, inhibition of FGFR activity with PD173074 exquisitely blocked HuH7 (high FGFR4 expression) proliferation as compared to control cell lines.

CONCLUSIONS

FGFR4 contributes significantly to HCC progression by modulating AFP secretion, proliferation and anti-apoptosis. Its frequent overexpression in patients renders its inhibition a novel and much needed pharmacological approach against HCC.

Wnt signaling in liver cancer

Hepatocellular carcinoma (HCC) is a major cause of cancer death worldwide. As in many other types of cancer, aberrant activation of the canonical Wnt/beta-catenin signaling pathway is an important contributor to tumorigenesis. In HCC this frequently occurs through mutations in the N-terminal region of beta-catenin that stabilize the protein and permit an elevated level of constitutive transcriptional activation by beta-catenin/TCF complexes. In this article we review the abundant evidence that Wnt/beta-catenin signaling contributes to liver carcinogenesis. We also discuss what is known about the roles of Wnt signaling in liver development, regeneration, and stem cell behavior, in an effort to understand the mechanisms by which activation of the canonical Wnt pathway promotes tumor formation in this organ. The Wnt/beta-catenin pathway presents itself as an attractive target for developing novel rational therapies for HCC, a disease for which few successful treatment strategies are currently available.

Hepatic progenitor cell surface markers and biological function

Hepatic progenitor cells have the bipotential capable of differentiation into mature hepatocytes and biliary epithelial cells when hepatocyte proliferation is inhibited and liver regeneration compromised. This review focuses on the surface markers and biological function of hepatic progenitor cells and the existed questions in this field are also discussed.

Advance in hepatic stem cells and liver injury

The liver diseases remain major causes of death all over the world. Although orthotopic liver transplantation is an effective treatment for end-stage liver diseases. However, shortage of healthy livers for transplantation worldwide have urgently limited the use of liver transplantation for acute and chronic liver diseases. Stem cells play an important role in the concert of liver regeneration. Hepatic stem cells have been shown experimentally to participate in liver proliferation. Furthermore, it has been postulated that hepatic stem cells are able to transdifferentiate into both hepatocytes and bole duct cells. These data indicate a possible role and therapeutic potential of hepatic stem cells in liver diseases. In this paper, we reviewed the application of stem cells in liver diseases.

Accumulation of hedgehog-responsive progenitors parallels alcoholic liver disease severity in mice and humans

BACKGROUND & AIMS

Improving outcomes in alcoholic liver disease (ALD) necessitates better understanding of how habitual ethanol (EtOH) consumption alters normal regenerative mechanisms within the liver. Hedgehog (Hh) pathway activation promotes expansion of progenitor populations in other tissues. We evaluated the hypothesis that chronic EtOH exposure activates Hh signaling in liver.

METHODS

Hh signaling, liver progenitors, transforming growth factor (TGF)-beta induction, and liver damage were compared in mice fed chow, high-fat diets (HF), or HF + EtOH for 4 weeks. Susceptibility to TGF-beta-mediated apoptosis was compared in Hh-responsive liver cells (eg, immature cholangiocytes and oval cells) and mature hepatocytes (which are unresponsive to Hh). Hepatic accumulation of Hh-responsive cells were compared in controls and ALD patients and correlated with a discriminant function (DF) that predicts subacute mortality.

RESULTS

Hh signaling and numbers of Hh-responsive cells were increased in HF mice and greatest in HF+EtOH mice. In both, progenitor and stromal cell populations harbored Hh-responsive cells. More ductular-type progenitors and fibrosis markers were noted in HF+EtOH mice than in HF mice. The former also expressed more TGF-beta-1. TGF-beta-1 treatment selectively promoted the viability of Hh-responsive immature liver cells and caused mature hepatocytes that survived to produce Hh ligands. Hh-responsive cells were increased in ALD patients. Lobular accumulation of Hh-responsive immature ductular cells was greater in those with a DF >32 than those with a DF <32.

CONCLUSIONS

Hh signaling is increased in ALD and may influence ALD outcomes by promoting hepatic accumulation of immature ductular cells.

Hepatic accumulation of Hedgehog-reactive progenitors increases with severity of fatty liver damage in mice

Progenitors regenerate fatty livers but the mechanisms involved are uncertain. The Hedgehog pathway regulates mesendodermal progenitors and modulates mesenchymal-epithelial interactions during tissue remodeling. To determine if Hedgehog signaling increases in liver progenitors during fatty liver injury, we compared expression of Hedgehog ligands and target genes across a spectrum of injury. Leptin-deficient ob/ob mice with fatty livers and their healthy lean littermates were studied before and after exposure to the hepatotoxin, ethionine. At baseline, ob/ob mice had greater liver damage than controls. Ethionine induced liver injury in both ob/ob and lean mice, with greater injury occurring in ob/ob mice. After ethionine, the ob/ob mice developed liver atrophy and fibrosis. Liver injury increased hepatic accumulation of progenitors, including ductular cells that produced and responded to Hedgehog ligands. A dose-response relationship was demonstrated between liver injury and expansion of Hedgehog-responsive progenitors. In severely damaged, atrophic livers, nuclei in mature-appearing hepatocytes accumulated the Hedgehog-regulated mesenchymal transcription factor, Gli2 and lost expression of the liver epithelial transcription factor, hepatocyte nuclear factor 6 (HNF-6). Hepatic levels of collagen mRNA and pericellular collagen fibrils increased concomitantly. Hence, fatty liver injury increases Hedgehog activity in liver progenitors, and this might promote epithelial-mesenchymal transitions that result in liver fibrosis.

Effects of granulocyte colony stimulating-factor in a rat model of acute liver injury

BACKGROUND/AIM

Controversial experimental observations suggest that granulocyte colony stimulating-factor may promote hepatic regeneration after hepatectomy and chemical injury either by directly stimulating adult liver cells or facilitating the mobilization of bone marrow cells and their homing to the liver. We investigated whether different schedules of granulocyte colony stimulating-factor administration protect against experimental acute liver injury.

METHODS

Acute liver injury was induced in Sprague-Dawley fed rats by injecting a single intraperitoneal dose of carbon tetrachloride. Recombinant human granulocyte colony stimulating-factor or vehicle was given daily after intoxication (4 days) or before (7 days) and after carbon tetrachloride administration. Liver injury and regeneration were assessed 2 and 4 days after damage. Bone marrow cells mobilization was evaluated by the white blood cell count and the assessment of circulating clonogenic haematopoietic progenitors (colony forming unit-cells).

RESULTS

In this experimental model, although granulocyte colony stimulating-factor induced the significant mobilization of colony forming unit-cells, the study cytokine had no effect on liver injury (serum alanine amino transaminase level and necrotic index) and liver regeneration (mitotic index and bromodeoxyuridine incorporation), regardless of the administration schedule.

CONCLUSIONS

This study does not support the conclusion that: (1) granulocyte colony stimulating-factor exerts a protective effect against toxic-induced, non-lethal acute liver injury and (2) promotes hepatocyte regeneration.