Hepatic oval cell activation in response to injury following chemically induced periportal or pericentral damage in rats

Gypenosides ameliorate ductular reaction and liver fibrosis via inhibition of hedgehog signaling

Backgroud and aims: Ductular reaction (DR) is a common pathological change and thought to have a key role in the pathogenesis and progression of liver fibrosis. Our previous study reported Gypenosides (GPs) ameliorated liver fibrosis, however, the anti-fibrotic mechanisms of GPs are still unclear. Methods: Liver fibrosis was induced in rats by carbon tetrachloride combining with 2-acerylaminofluorene (CCl4/2-AAF), and Mdr2 knockout (Mdr2 -/-) mice to evaluate the anti-fibrotic role of GPs. In vitro, WB-F344 cells, a hepatic progenitor cells (HPCs) line, with or without Gli1 overexpressing lentiviral vectors, were induced by sodium butyrate (SB) to validate the mechanism of GPs and NPLC0393, the main ingredient of GPs. Results: Both in CCl4/2-AAF-treated rats and Mdr2 -/- mice, GPs obviously reduced the deposition of collagen and hydroxyproline content, inhibited the activation of hepatic stellate cells and inflammatory cell infiltration. Notably, GPs reduced the expressions of Epcam, CK19, CK7, Dhh, Smo, Ptch2, Gli1 and Gli2. Furthermore, CK19+ cells co-expressed Gli1, while the number of CK19+/Gli1+ cells was decreased by GPs. In vitro, GPs and NPLC0393 inhibited the differentiation of WB-F344 cells toward a biliary phenotype. Mechanistically, GPs and NPLC0393 protected against DR by inhibiting hedgehog signaling, which was supported by the results that DR, triggered directly by Gli1 overexpressing lentiviral vector was blocked by administration with GPs or NPLC0393. Conclusion: GPs attenuated DR and liver fibrosis by inhibiting hedgehog signaling, which provided more evidences and a novel mechanism of anti-fibrotic effect of GPs.

Liver regeneration: biological and pathological mechanisms and implications

The liver is the only solid organ that uses regenerative mechanisms to ensure that the liver-to-bodyweight ratio is always at 100% of what is required for body homeostasis. Other solid organs (such as the lungs, kidneys and pancreas) adjust to tissue loss but do not return to 100% of normal. The current state of knowledge of the regenerative pathways that underlie this 'hepatostat' will be presented in this Review. Liver regeneration from acute injury is always beneficial and has been extensively studied. Experimental models that involve partial hepatectomy or chemical injury have revealed extracellular and intracellular signalling pathways that are used to return the liver to equivalent size and weight to those prior to injury. On the other hand, chronic loss of hepatocytes, which can occur in chronic liver disease of any aetiology, often has adverse consequences, including fibrosis, cirrhosis and liver neoplasia. The regenerative activities of hepatocytes and cholangiocytes are typically characterized by phenotypic fidelity. However, when regeneration of one of the two cell types fails, hepatocytes and cholangiocytes function as facultative stem cells and transdifferentiate into each other to restore normal liver structure. Liver recolonization models have demonstrated that hepatocytes have an unlimited regenerative capacity. However, in normal liver, cell turnover is very slow. All zones of the resting liver lobules have been equally implicated in the maintenance of hepatocyte and cholangiocyte populations in normal liver.

La plasticidad del hepatocito y su relevancia en la fisiología y la patología hepática

El hígado es uno de los principales órganos encargados de mantener la homeostasis en vertebrados,  además de poseer una gran capacidad regenerativa. El hígado está constituido por diversos tipos celulares que de forma coordinada contribuyen para que el órgano funcione eficientemente. Los hepatocitos representan el tipo celular principal de este órgano y llevan a cabo la mayoría de sus actividades; además, constituyen una población heterogénea de células epiteliales con funciones especializadas en el metabolismo. El fenotipo de los hepatocitos está controlado por diferentes vías de señalización, como la vía del TGFβ/Smads, la ruta Hippo/YAP-TAZ y la vía Wnt/β-catenina, entre otras. Los hepatocitos son células que se encuentran normalmente en un estado quiescente, aunque cuentan con una plasticidad intrínseca que se manifiesta en respuesta a diversos daños en el hígado; así, estas células reactivan su capacidad proliferativa o cambian su fenotipo a través de procesos celulares como la transdiferenciación o la transformación, para contribuir a mantener la homeostasis del órgano en condiciones saludables o desarrollar diversas  patologías.

Assessment of animal experimental models of toxic liver injury in the context of their potential application as preclinical models for cell therapy

Preclinical animal models allow to study development and progression of several diseases, including liver disorders. These studies, for ethical reasons and medical limits, are impossible to carry out in human patients. At the same time, such experimental models constitute an important source of knowledge on pathomechanisms for drug- and virus-induced hepatotoxicity, both acute and chronic. Carbon tetrachloride, D-Galactosamine, and retrorsine are xenobiotics that can be used in immunocompetent animal models of hepatotoxicity, where chemical-intoxicated livers present histological features representative of human viruses-related infection. A prolonged derangement into liver architecture and functions commonly lead to cirrhosis, eventually resulting in hepatocellular carcinoma. In human, orthotopic liver transplantation commonly resolve most the problems related to cirrhosis. However, the shortage of donors does not allow all the patients in the waiting list to receive an organ on time. A promising alternative treatment for acute and chronic liver disease has been advised in liver cell transplantation, but the limited availability of hepatocytes for clinical approaches, in addition to the immunosuppressant regiment required to sustain cellular long-term engraftment have been encouraging the use of alternative cell sources. A recent effective source of stem cells have been recently identified in the human amnion membrane. Human amnion epithelial cells (hAEC) have been preclinically tested and proven sufficient to rescue immunocompetent rodents lethally intoxicated with drugs. The adoption of therapeutic procedures based on hAEC transplant in immunocompetent recipients affected by liver diseases, as well as patients with immune-related disorders, may constitute a successful new alternative therapy in regenerative medicine.

Hepatic progenitor cell activation is induced by the depletion of the gut microbiome in mice

The homeostasis of the gut microbiome is crucial for human health and for liver function. However, it has not been established whether the gut microbiome influence hepatic progenitor cells (HPCs). HPCs are capable of self‐renewal and differentiate into hepatocytes and cholangiocytes; however, HPCs are normally quiescent and are rare in adults. After sustained liver damage, a ductular reaction occurs, and the number of HPCs is substantially increased. Here, we administered five broad‐spectrum antibiotics for 14 days to deplete the gut microbiomes of male C57BL/6 mice, and we measured the plasma aminotransferases and other biochemical indices. The expression levels of two HPC markers, SRY‐related high mobility group‐box gene 9 (Sox9) and cytokeratin (CK), were also measured. The plasma aminotransferase activities were not affected, but the triglyceride, lactate dehydrogenase, low‐density lipoprotein, and high‐density lipoprotein concentrations were significantly altered; this suggests that liver function is affected by the composition of the gut microbiome. The mRNA expression of Sox9 was significantly higher in the treated mice than it was in the control mice (p < 0.0001), and a substantial expression of Sox9 and CK was observed around the bile ducts. The mRNA expression levels of proinflammatory factors (interleukin [IL]‐1β, IL‐6, tumor necrosis factor [TNF]‐α, and TNF‐like weak inducer of apoptosis [Tweak]) were also significantly higher in the antibiotic‐treated mice than the levels in the control mice. These data imply that the depletion of the gut microbiome leads to liver damage, negatively impacts the hepatic metabolism and function, and activates HPCs. However, the underlying mechanisms remain to be determined.

Understanding the marvels behind liver regeneration

Tissue regeneration is a process by which the remaining cells of an injured organ regrow to offset the missed cells. This field is relatively a new discipline that has been a focus of intense research by clinicians, surgeons, and scientists for decades. It constitutes the cornerstone of tissue engineering, creation of artificial organs, and generation and utilization of therapeutic stem cells to undergo transformation to different types of mature cells. Many medical experts, scientists, biologists, and bioengineers have dedicated their efforts to deeply comprehend the process of liver regeneration, striving for harnessing it to invent new therapies for liver failure. Liver regeneration after partial hepatectomy in rodents has been extensively studied by researchers for many years. It is divided into three important distinctive phases including (a) Initiation or priming phase which includes an overexpression of specific genes to prepare the liver cells for replication, (b) Proliferation phase in which the liver cells undergo a series of cycles of cell division and expansion and finally, (c) termination phase which acts as brake to stop the regenerative process and prevent the liver tissue overgrowth. These events are well controlled by cytokines, growth factors, and signaling pathways. In this review, we describe the function, embryology, and anatomy of human liver, discuss the molecular basis of liver regeneration, elucidate the hepatocyte and cholangiocyte lineages mediating this process, explain the role of hepatic progenitor cells and elaborate the developmental signaling pathways and regulatory molecules required to procure a complete restoration of hepatic lobule. This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Signaling Pathways > Global Signaling Mechanisms Gene Expression and Transcriptional Hierarchies > Cellular Differentiation.

Liver stem cells: Plasticity of the liver epithelium

The liver has a high regenerative capacity after acute liver injury, but this is often impaired during chronic liver injury. The existence of a dedicated liver stem cell population that acts as a source of regeneration during chronic liver injury has been controversial. Recent advances in transgenic models and cellular reprogramming have provided new insights into the plasticity of the liver epithelium and directions for the development of future therapies. This article will highlight recent findings about the cellular source of regeneration during liver injury and the advances in promoting liver regeneration.

Necrosis-inducing peptide has the beneficial effect on killing tumor cells through neuropilin (NRP-1) targeting

The therapeutic efficacy of most anti-cancer drugs depends on their apoptosis-inducing abilities. Previously, we showed that a peptide containing the mitochondrial targeting domain (MTD) found in Noxa, a BH-3 only protein of Bcl-2 family, induces necrosis. Here, a fusion peptide of neuropilin-1 (NRP-1) targeting peptide and MTD peptide, designated tumor homing motif 17:MTD (TU17:MTD), was found to induce necrosis in cancer cells in vitro and to cause the regression of tumors when intravenously injected into mice bearing subcutaneous CT26 colorectal carcinoma tumors. The necrosis within tumor tissues was evident upon administering TU17:MTD. TU17:MTD penetrated into tumor cells by targeting to Neuropilin-1, which could be blocked by anti-NRP-1 antibody. The efficacy of TU17:MTD on tumor regression was higher than that of TU17:_D(KLAKLAK)₂, a fusion peptide of NRP-1 targeting peptide and a pro-apoptotic peptide. The necrotic cell death within tumor tissues was evident at day 1 after administering TU17:MTD systemically. Transplanted subcutaneous substantially reduced in size within two weeks and 5 days, respectively, with no apparent side effects. Together, these results propose that the pro-necrotic peptide MTD may present an alternative approach for development of targeted anti-cancer agents.

Hepatic progenitor cell activation in liver repair

The liver possesses an extraordinary ability to regenerate after injury. Hepatocyte-driven liver regeneration is the default pathway in response to mild-to-moderate acute liver damage. When replication of mature hepatocytes is blocked, facultative hepatic progenitor cells (HPCs), also referred to as oval cells (OCs) in rodents, are activated. HPC/OCs have the ability to proliferate clonogenically and differentiate into several lineages including hepatocytes and bile ductal epithelia. This is a conserved liver injury response that has been studied in many species ranging from mammals (rat, mouse, and human) to fish. In addition, improper HPC/OC activation is closely associated with fibrotic responses, characterized by myofibroblast activation and extracellular matrix production, in many chronic liver diseases. Matrix remodeling and metalloprotease activities play an important role in the regulation of HPC/OC proliferation and fibrosis progression. Thus, understanding molecular mechanisms underlying HPC/OC activation has therapeutic implications for rational design of anti-fibrotic therapies.

The diversity and plasticity of adult hepatic progenitor cells and their niche

The liver is a unique organ for homoeostasis with regenerative capacities. Hepatocytes possess a remarkable capacity to proliferate upon injury; however, in more severe scenarios liver regeneration is believed to arise from at least one, if not several facultative hepatic progenitor cell compartments. Newly identified pericentral stem/progenitor cells residing around the central vein is responsible for maintaining hepatocyte homoeostasis in the uninjured liver. In addition, hepatic progenitor cells have been reported to contribute to liver fibrosis and cancers. What drives liver homoeostasis, regeneration and diseases is determined by the physiological and pathological conditions, and especially the hepatic progenitor cell niches which influence the fate of hepatic progenitor cells. The hepatic progenitor cell niches are special microenvironments consisting of different cell types, releasing growth factors and cytokines and receiving signals, as well as the extracellular matrix (ECM) scaffold. The hepatic progenitor cell niches maintain and regulate stem cells to ensure organ homoeostasis and regeneration. In recent studies, more evidence has been shown that hepatic cells such as hepatocytes, cholangiocytes or myofibroblasts can be induced to be oval cell-like state through transitions under some circumstance, those transitional cell types as potential liver-resident progenitor cells play important roles in liver pathophysiology. In this review, we describe and update recent advances in the diversity and plasticity of hepatic progenitor cell and their niches and discuss evidence supporting their roles in liver homoeostasis, regeneration, fibrosis and cancers.

Transdifferentiation of human male germline stem cells to hepatocytes in vivo via the transplantation under renal capsules

Here we proposed a new concept that human spermatogonial stem cells (SSCs) can transdifferentiate into hepatocytes in vivo. We first established liver injury model of mice by carbon tetrachloride to provide proper environment for human SSC transplantation. Liver mesenchymal cells were isolated from mice and identified phenotypically. Human SSC line was recombined with liver mesenchymal cells, and they were transplanted under renal capsules of nude mice with liver injury. The grafts expressed hepatocyte hallmarks, including ALB, AAT, CK18, and CYP1A2, whereas germ cell and SSC markers VASA and GPR125 were undetected in these cells, implicating that human SSCs were converted to hepatocytes. Furthermore, Western blots revealed high levels of PCNA, AFP, and ALB, indicating that human SSCs-derived hepatocytes had strong proliferation potential and features of hepatocytes. In addition, ALB–, CK8–, and CYP1A2– positive cells were detected in liver tissues of recipient mice. Significantly, no obvious lesion or teratomas was observed in several important organs and tissues of recipient mice, reflecting that transplantation of human SSCs was safe and feasible. Collectively, we have for the first time demonstrated that human SSCs can be transdifferentiated to hepatocyte in vivo. This study provides a novel approach for curing liver diseases using human SSC transplantation.

Cholangiocytes act as facultative liver stem cells during impaired hepatocyte regeneration

Following liver injury, regeneration occurs through self-replication of hepatocytes. In severe liver injury, hepatocyte proliferation is impaired, a feature of human chronic liver disease1,2. It is contested whether other liver cell types can regenerate hepatocytes3–5. Here, we use two independent systems to impair hepatocyte proliferation during liver injury to evaluate the contribution of non-hepatocytes to parenchymal regeneration. Firstly, loss of β1-Integrin in hepatocytes with liver injury triggered a ductular reaction of cholangiocyte origin, and ~25% of hepatocytes being derived from a non-hepatocyte origin. Secondly cholangiocytes were lineage traced with concurrent inhibition of hepatocyte proliferation by β1-Integrin knockdown or p21 over-expression, resulting in the significant emergence of cholangiocyte derived hepatocytes. We describe a model of combined liver injury and inhibition of hepatocyte proliferation that causes physiologically significant levels of regeneration of functional hepatocytes from biliary cells.

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.

In vitro differentiated hepatic oval-like cells enhance hepatic regeneration in CCl4 -induced hepatic injury

Hepatic oval cells are likely to be activated during advanced stage of liver fibrosis to reconstruct damaged hepatic tissue. However, their scarcity, difficulties in isolation, and in vitro expansion hampered their transplantation in fibrotic liver. This study was aimed to investigate the repair potential of in vitro differentiated hepatic oval-like cells in CCl₄ -induced liver fibrosis. BMSCs and oval cells were isolated and characterized from C57BL/6 GFP⁺ mice. BMSCs were differentiated into oval cells by preconditioning with HGF, EGF, SCF, and LIF and analyzed for the oval cells-specific genes. Efficiency of oval cells to reduce hepatocyte injury was studied by determining cell viability, release of LDH, and biochemical tests in a co-culture system. Further, in vivo repair potential of differentiated oval cells was determined in CCl₄ -induced fibrotic model by gene expression analysis, biochemical tests, mason trichrome, and Sirius red staining. Differentiated oval cells expressed hepatic oval cells-specific markers AFP, ALB, CK8, CK18, CK19. These differentiated cells when co-cultured with injured hepatocytes showed significant hepato-protection as measured by reduction in apoptosis, LDH release, and improvement in liver functions. Transplantation of differentiated oval cells like cells in fibrotic livers exhibited enhanced homing, reduced liver fibrosis, and improved liver functions by augmenting hepatic microenvironment by improved liver functions. This preconditioning strategy to differentiate BMSCs into oval cell leads to improved survival and homing of transplanted cells. In addition, reduction in fibrosis and functional improvement in mice with CCl₄ -induced liver fibrosis was achieved.

miR-133b Regulation of Connective Tissue Growth Factor: A Novel Mechanism in Liver Pathology

miRNAs are involved in liver regeneration, and their expression is dysregulated in hepatocellular carcinoma (HCC). Connective tissue growth factor (CTGF), a direct target of miR-133b, is crucial in the ductular reaction (DR)/oval cell (OC) response for generating new hepatocyte lineages during liver injury in the context of hepatotoxin-inhibited hepatocyte proliferation. Herein, we investigate whether miR-133b regulation of CTGF influences HCC cell proliferation and migration, and DR/OC response. We analyzed miR-133b expression and found it to be down-regulated in HCC patient samples and induced in the rat DR/OC activation model of 2-acetylaminofluorene with partial hepatectomy. Furthermore, overexpression of miR-133b via adenoviral system in vitro led to decreased CTGF expression and reduced proliferation and Transwell migration of both HepG2 HCC cells and WBF-344 rat OCs. In vivo, overexpression of miR-133b in DR/OC activation models of 2-acetylaminofluorene with partial hepatectomy in rats, and 3,5-diethoxycarbonyl-1,4-dihydrocollidine in mice, led to down-regulation of CTGF expression and OC proliferation. Collectively, these results show that miR-133b regulation of CTGF is a novel mechanism critical for the proliferation and migration of HCC cells and OC response.

In Vivo Zonal Variation and Liver Cell-Type Specific NF-κB Localization after Chronic Adaptation to Ethanol and following Partial Hepatectomy

NF-κB is a major inflammatory response mediator in the liver, playing a key role in the pathogenesis of alcoholic liver injury. We investigated zonal as well as liver cell type-specific distribution of NF-κB activation across the liver acinus following adaptation to chronic ethanol intake and 70% partial hepatectomy (PHx). We employed immunofluorescence staining, digital image analysis and statistical distributional analysis to quantify subcellular localization of NF-κB in hepatocytes and hepatic stellate cells (HSCs). We detected significant spatial heterogeneity of NF-κB expression and cellular localization between cytoplasm and nucleus across liver tissue. Our main aims involved investigating the zonal bias in NF-κB localization and determining to what extent chronic ethanol intake affects this zonal bias with in hepatocytes at baseline and post-PHx. Hepatocytes in the periportal area showed higher NF-κB expression than in the pericentral region in the carbohydrate-fed controls, but not in the ethanol group. However, the distribution of NF-κB nuclear localization in hepatocytes was shifted towards higher levels in pericentral region than in periportal area, across all treatment conditions. Chronic ethanol intake shifted the NF-κB distribution towards higher nuclear fraction in hepatocytes as compared to the pair-fed control group. Ethanol also stimulated higher NF-κB expression in a subpopulation of HSCs. In the control group, PHx elicited a shift towards higher NF-κB nuclear fraction in hepatocytes. However, this distribution remained unchanged in the ethanol group post-PHx. HSCs showed a lower NF-κB expression following PHx in both ethanol and control groups. We conclude that adaptation to chronic ethanol intake attenuates the liver zonal variation in NF-κB expression and limits the PHx-induced NF-κB activation in hepatocytes, but does not alter the NF-κB expression changes in HSCs in response to PHx. Our findings provide new insights as to how ethanol treatment may affect cell-type specific processes regulated by NF-κB activation in liver cells.

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 Progenitor Cells Contribute to the Progression of 2-Acetylaminofluorene/Carbon Tetrachloride-Induced Cirrhosis via the Non-Canonical Wnt Pathway

Hepatic progenitor cells (HPCs) appear to play an important role in chronic liver injury. In this study, cirrhosis was induced in F-344 rats (n = 32) via subcutaneous injection of 50% carbon tetrachloride (CCl4) twice a week for 8 weeks. Then, 30% CCl4 was administered in conjunction with intragastric 2-acetylaminofluorine (2-AAF) for 4 weeks to induce activation of HPCs. WB-F344 cells were used to provide direct evidence for differentiation of HPCs to myofibroblasts. The results showed that after administration of 2-AAF, the hydroxyproline content and the expressions of α-SMA, Col I, Col IV, TGF-β1, CD68, TNF-α, CK19 and OV6 were significantly increased. OV6 and α-SMA were largely co-expressed in fibrous septum and the expressions of Wnt5b, frizzled2, frizzled3 and frizzled6 were markedly increased, while β-catenin expression was not statistically different among the different groups. Consistent with the above results, WB-F344 cells, treated with TGF-β1 in vitro, differentiated into myofibroblasts and α-SMA, Col I, Col IV, Wnt5b and frizzled2 expressions were significantly increased, while β-catenin expression was decreased. After blocking the non-canonical Wnt pathway via WIF-1, the Wnt5b level was down regulated, and α-SMA and F-actin expressions were significantly decreased in the WIF-1-treated cells. In conclusion, these results indicate that HPCs appear to differentiate into myofibroblasts and exhibit a profibrotic effect in progressive cirrhosis via activation of the non-canonical Wnt pathway. Blocking the non-canonical Wnt pathway can inhibit the differentiation of HPCs into myofibroblasts, suggesting that blocking this pathway and changing the fate of differentiated HPCs may be a potential treatment for cirrhosis.

PPARα-Deficient ob/ob Obese Mice Become More Obese and Manifest Severe Hepatic Steatosis Due to Decreased Fatty Acid Oxidation

Obesity poses an increased risk of developing metabolic syndrome and closely associated nonalcoholic fatty liver disease, including liver cancer. Satiety hormone leptin-deficient (ob/ob) mice, considered paradigmatic of nutritional obesity, develop hepatic steatosis but are less prone to developing liver tumors. Sustained activation of peroxisome proliferator-activated receptor α (PPARα) in ob/ob mouse liver increases fatty acid oxidation (FAO), which contributes to attenuation of obesity but enhances liver cancer risk. To further evaluate the role of PPARα-regulated hepatic FAO and energy burning in the progression of fatty liver disease, we generated PPARα-deficient ob/ob (PPARα(Δ)ob/ob) mice. These mice become strikingly more obese compared to ob/ob littermates, with increased white and brown adipose tissue content and severe hepatic steatosis. Hepatic steatosis becomes more severe in fasted PPARα(Δ)ob/ob mice as they fail to up-regulate FAO systems. PPARα(Δ)ob/ob mice also do not respond to peroxisome proliferative and mitogenic effects of PPARα agonist Wy-14,643. Although PPARα(Δ)ob/ob mice are severely obese, there was no significant increase in liver tumor incidence, even when maintained on a diet containing Wy-14,643. We conclude that sustained PPARα activation-related increase in FAO in fatty livers of obese ob/ob mice increases liver cancer risk, whereas deletion of PPARα in ob/ob mice aggravates obesity and hepatic steatosis. However, it does not lead to liver tumor development because of reduction in FAO and energy burning.

Osteopontin induces ductular reaction contributing to liver fibrosis

OBJECTIVE

In human chronic liver disease, there is association between ductular reaction (DR) and fibrosis; yet, the mechanism triggering its onset and its role in scar formation remains unknown. Since we previously showed that osteopontin (OPN) is highly induced during drug-induced liver fibrosis, we hypothesised that OPN could drive oval cells (OC) expansion and DR and signal to hepatic stellate cells (HSC) to promote scarring.

RESULTS

In vivo studies demonstrated increased OPN expression in biliary epithelial cells (BEC) and in OC in thioacetamide (TAA)-treated mice. OPN ablation protected mice from TAA and bile duct ligation-induced liver injury, DR and scarring. This was associated with greater hepatocyte proliferation, lower OC expansion and DR along with less fibrosis, suggesting that OPN could activate the OC compartment to differentiate into BEC, which could then signal to HSC to enhance scarring. Since TAA-treated wild-type mice and cirrhotic patients showed TGF-β(+) BEC, which were lacking in TAA-treated Opn(-/-) mice and in healthy human explants, this suggested that OPN could regulate TGF-β, a profibrogenic factor. In vitro experiments confirmed that recombinant OPN (rOPN) decreases hepatocyte proliferation and increases OC and BEC proliferation. To evaluate how BEC regulate collagen-I production in HSC, co-cultures were established. Co-cultured BEC upregulated OPN and TGF-β expression and enhanced collagen-I synthesis by HSC. Lastly, recombinant TGF-β (rTGFβ) and rOPN promoted BEC proliferation and neutralisation of OPN and TGF-β reduced collagen-I expression in co-cultured HSC.

CONCLUSIONS

OPN emerges as a key matricellular protein driving DR and contributing to scarring and liver fibrosis via TGF-β.

Re-evaluation of liver stem/progenitor cells

Liver stem/progenitor cells (LPCs) are defined as cells that supply two types of liver epithelial cells, hepatocytes and cholangiocytes, during development, cellular turnover, and regeneration. Hepatoblasts, which are fetal LPCs derived from endoderm stem cells, robustly proliferate and differentiate into hepatocytes and cholangiocytes during fetal life. Between mid-gestation and the neonatal period, some cholangiocytes function as LPCs. Although LPCs in adult livers can be enriched in cells positive for cholangiocyte markers, their tissue localization and functions in cellular turnover remain obscure. On the other hand, it is well known that liver regeneration under conditions suppressing hepatocyte proliferation is supported by LPCs, though their origin has not been clearly identified. Recently many groups took advantage of new techniques including prospective isolation of LPCs by fluorescence-activated cell sorting and genetic lineage tracing to facilitate our understanding of epithelial supply in normal and injured livers. Those works suggest that, in normal livers, the turnover of hepatocytes mostly depends on duplication of hepatocytes. It is also demonstrated that liver epithelial cells as well as LPCs have great plasticity and flexible differentiation capability to respond to various types of injuries by protecting or repairing liver tissues.

Bone marrow cell-based regenerative therapy for liver cirrhosis

Bone marrow cells are capable of differentiation into liver cells. Therefore, transplantation of bone marrow cells has considerable potential as a future therapy for regeneration of damaged liver tissue. Autologous bone marrow infusion therapy has been applied to patients with liver cirrhosis, and improvement of liver function parameters has been demonstrated. In this review, we summarize clinical trials of regenerative therapy using bone marrow cells for advanced liver diseases including cirrhosis, as well as topics pertaining to basic in vitro or in vivo approaches in order to outline the essentials of this novel treatment modality.

Proteins related to early changes in carcinogenesis of hepatic oval cells after treatment with methylnitronitrosoguanidine

Hepatic oval cells are considered as facultative progenitor/stem cells of liver and able to differentiate into either hepatocytes or biliary epithelial cells. The transformed oval cells by carcinogen possess potential to develop carcinomas in animal models. In order to better understand the molecular mechanism in carcinogenetic process, we used a proteomic approach to assess the early changes in protein expression of oval cells (OC3W3-15) initiated by methylnitronitrosoguanidine (MNNG). Meanwhile, we compared cell biologic characteristics of the MNNG treated OC3W3-15 cells and control oval cells by electron microscopy, flow cytometry, karyotype and soft agar assay. The mRNA levels of GGT and GSTP1 determined by real-time PCR were also detected in both cell lines. Our results showed that MNNG-treated OC3W3-15 cells exhibited characteristics of malignant transformation, including growth rate, chromosomal aberrations, abnormal DNA content, and the ability to form colonies. The cells expressed higher levels of the tumor marker AFP, GGT and GSTP1 mRNA than that of control cells. Significant changes of several proteins involved in the malignant transformation process, including cell cycle related proteins, proteins involved in organism development and cell differentiation, are found in OC3W3-15 cells. The proteins may provide early affection in malignant transformation of hepatic oval cells, and yield further insight into mechanism of carcinogenesis of hepatocellular carcinoma.

Hepatocyte polarity

Hepatocytes, like other epithelia, are situated at the interface between the organism's exterior and the underlying internal milieu and organize the vectorial exchange of macromolecules between these two spaces. To mediate this function, epithelial cells, including hepatocytes, are polarized with distinct luminal domains that are separated by tight junctions from lateral domains engaged in cell-cell adhesion and from basal domains that interact with the underlying extracellular matrix. Despite these universal principles, hepatocytes distinguish themselves from other nonstriated epithelia by their multipolar organization. Each hepatocyte participates in multiple, narrow lumina, the bile canaliculi, and has multiple basal surfaces that face the endothelial lining. Hepatocytes also differ in the mechanism of luminal protein trafficking from other epithelia studied. They lack polarized protein secretion to the luminal domain and target single-spanning and glycosylphosphatidylinositol-anchored bile canalicular membrane proteins via transcytosis from the basolateral domain. We compare this unique hepatic polarity phenotype with that of the more common columnar epithelial organization and review our current knowledge of the signaling mechanisms and the organization of polarized protein trafficking that govern the establishment and maintenance of hepatic polarity. The serine/threonine kinase LKB1, which is activated by the bile acid taurocholate and, in turn, activates adenosine monophosphate kinase-related kinases including AMPK1/2 and Par1 paralogues has emerged as a key determinant of hepatic polarity. We propose that the absence of a hepatocyte basal lamina and differences in cell-cell adhesion signaling that determine the positioning of tight junctions are two crucial determinants for the distinct hepatic and columnar polarity phenotypes.

Human adipose tissue derived stem cells promote liver regeneration in a rat model of toxic injury

In the light of the persisting lack of donor organs and the risks of allotransplantations, the possibility of liver regeneration with autologous stem cells from adipose tissue (ADSC) is an intriguing alternative. Using a model of a toxic liver damage in Sprague Dawley rats, generated by repetitive intraperitoneal application of retrorsine and allyl alcohol, the ability of human ADSC to support the restoration of liver function was investigated. A two-thirds hepatectomy was performed, and human ADSC were injected into one remaining liver lobe in group 1 (n = 20). Injection of cell culture medium performed in group 2 (n = 20) served as control. Cyclosporine was applied to achieve immunotolerance. Blood samples were drawn weekly after surgery to determine liver-correlated blood values. Six and twelve weeks after surgery, animals were sacrificed and histological sections were analyzed. ADSC significantly raised postoperative albumin (P < 0.017), total protein (P < 0.031), glutamic oxaloacetic transaminase (P < 0.001), and lactate dehydrogenase (P < 0.04) levels compared to injection of cell culture medium alone. Transplanted cells could be found up to twelve weeks after surgery in histological sections. This study points towards ADSC being a promising alternative to hepatocyte or liver organ transplantation in patients with severe liver failure.

G protein-coupled receptor 87 (GPR87) promotes the growth and metastasis of CD133⁺ cancer stem-like cells in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a prevalent disease worldwide, and the majority of HCC-related deaths occur due to local invasion and distant metastasis. Cancer stem cells (CSCs) are a small subpopulation of cancer cells that have been hypothesized to be responsible for metastatic disease. Recently, we and others have identified a CSC population from human HCC cell lines and xenograft tumors characterized by their expression of CD133. However, the precise molecular mechanisms by which CD133⁺ cancer stem-like cells mediate HCC metastasis have not been sufficiently analyzed. Here, we have sorted HCC cells using CD133 as a cancer stem cell (CSC) marker by magnetic-activated cell sorting (MACS) and demonstrated that the CD133⁺ HCC cells not only possess greater migratory and invasive capacity in vitro but are also endowed with enhanced metastatic capacity in vivo and in human HCC specimens when compared to CD133⁻ HCC cells. Gene expression analysis of the CD133⁺ and CD133⁻ cells of the HCC line SMMC-7721 revealed that G protein-coupled receptor 87 (GPR87) is highly expressed in CD133⁺ HCC cells. In this study, we explored the role of GPR87 in the regulation of CD133 expression. We demonstrated that the overexpression of GPR87 up-regulated CD133 expression, promoted CSC-associated migratory and invasive properties in vitro, and increased tumor initiation in vivo. Conversely, silencing of GPR87 expression reduced the levels of CD133 expression. Conclusion: GPR87 promotes the growth and metastasis of CD133⁺ cancer stem-like cells, and our findings may reveal new targets for HCC prevention or therapy.

Hematopoietic stem cells are pluripotent and not just "hematopoietic"

Over a decade ago, several preclinical transplantation studies suggested the striking concept of the tissue-reconstituting ability (often referred to as HSC plasticity) of hematopoietic stem cells (HSCs). While this heralded an exciting time of radically new therapies for disorders of many organs and tissues, the concept was soon mired in controversy and remained dormant for almost a decade. This commentary provides a concise review of evidence for HSC plasticity, including more recent findings based on single HSC transplantation in mouse and clinical transplantation studies. There is strong evidence for the concept that HSCs are pluripotent and are the source for the majority, if not all, of the cell types in our body. Also discussed are some biological and experimental issues that need to be considered in the future investigation of HSC plasticity.

Principles of liver regeneration and growth homeostasis

Liver regeneration is perhaps the most studied example of compensatory growth aimed to replace loss of tissue in an organ. Hepatocytes, the main functional cells of the liver, manage to proliferate to restore mass and to simultaneously deliver all functions hepatic functions necessary to maintain body homeostasis. They are the first cells to respond to regenerative stimuli triggered by mitogenic growth factor receptors MET (the hepatocyte growth factor receptor] and epidermal growth factor receptor and complemented by auxiliary mitogenic signals induced by other cytokines. Termination of liver regeneration is a complex process affected by integrin mediated signaling and it restores the organ to its original mass as determined by the needs of the body (hepatostat function). When hepatocytes cannot proliferate, progenitor cells derived from the biliary epithelium transdifferentiate to restore the hepatocyte compartment. In a reverse situation, hepatocytes can also transdifferentiate to restore the biliary compartment. Several hormones and xenobiotics alter the hepatostat directly and induce an increase in liver to body weight ratio (augmentative hepatomegaly). The complex challenges of the liver toward body homeostasis are thus always preserved by complex but unfailing responses involving orchestrated signaling and affecting growth and differentiation of all hepatic cell types.

Liver progenitor cell interactions with the extracellular matrix

Liver progenitor cells (LPCs) are a promising source of cells to treat liver disease by cell therapy, due to their capability for self-replication and bipotentiality. In order to establish useful culture systems of LPCs and apply them to future clinical therapies, it is necessary to understand their interactions with their microenvironment and especially with the extracellular matrix (ECM). There is considerable evidence from in vivo studies that matrix proteins affect the activation, expansion, migration and differentiation of LPCs, but the information on the role that specific ECMs play in regulating LPCs in vitro is more limited. Nevertheless, current studies suggest that laminin, collagen type III, collagen type IV and hyaluronic acid help to maintain the undifferentiated phenotype of LPCs and promote their proliferation when cultured in media supplemented with growth factors chosen for LPC expansion, whereas collagen type I and fibronectin are generally associated with a differentiated phenotype under the same conditions. Experimental evidence suggests that α6β1 and α5β1 integrins as well as CD44 on the surface of LPCs, and their related downstream signals, are important mediators of interactions between LPCs and the ECM. The interactions of LPCs with the ECM form the focus of this review and the contribution of ECM molecules to strategies for optimizing in vitro LPC cultures for therapeutic applications is discussed.

Ex vivo-expanded bone marrow stem cells home to the liver and ameliorate functional recovery in a mouse model of acute hepatic injury

BACKGROUND

Stem cell transplantation provides a theoretical approach for liver regeneration medicine; it may promote liver regeneration and self-repair. However, the transplantation of bone marrow-mesenchymal stem cells expanded ex vivo as a therapy for liver disease has rarely been investigated. This study aimed to explore whether bone marrow stem cells expanded ex vivo home to the liver and foster hepatic recovery after CCl4 injury.

METHODS

Bone marrow cells from BALB/c mice were expanded ex vivo by multiple-passage cultivation, characterized by cytoflow immunofluorescence, and pre-labeled with PKH26 before intravenous infusion into animals treated with CCl4. The integration of bone marrow cells into the liver was examined microscopically, and plasma hepatic enzymes were determined biochemically.

RESULTS

Cultured bone marrow cells exhibited antigenic profiles comparable to those of primary medullary stem cells. Double immunofluorescence showed colocalization of these cells with proliferative activity and albumin expression in the liver of CCl4-treated mice. Densitometry showed increased in situ cell proliferation (50+/-14 vs 20+/-3 cells/high-power field, P<0.05) and albumin expression (149+/-25 vs 20+/-5 cells/high-power field, P<0.05) in the liver, as well as reduced serum aminotransferase levels (P<0.05) and better survival rates (P<0.05) in animals receiving cultured bone marrow cells relative to controls.

CONCLUSIONS

Ex vivo-expanded bone marrow cells are capable of relocating to and proliferating in the chemically-injured liver. Transplantation of these pluripotent stem cells appears to improve serum indices of liver function and survival rate in mice after CCl4-induced hepatic damage.

Liver precursor cells increase hepatic fibrosis induced by chronic carbon tetrachloride intoxication in rats

Hepatic fibrosis, the major complication of virtually all types of chronic liver damage, usually begins in portal areas, and its severity has been correlated to liver progenitor cells (LPC) expansion from periportal areas, even if the primary targets of injury are intralobular hepatocytes. The aim of this study was to determine the potential fibrogenic role of LPC, using a new experimental model in which rat liver fibrosis was induced by chronic carbon tetrachloride (CCl(4)) administration for 6 weeks, in combination with chronic acetylaminofluorene treatment (AAF), which promotes activation of LPC compartment. Treatment with CCl(4) alone caused a significant increase in serum transaminase activity as well as liver fibrosis initiating around central veins and leading to formation of incomplete centro-central septa with sparse fibrogenic cells expressing α-smooth muscle actin (αSMA). In AAF/CCl(4)-treated animals, the fibrogenic response was profoundly worsened, with formation of multiple porto-central bridging septa leading to cirrhosis, whereas hepatocellular necrosis and inflammation were similar to those observed in CCl(4)-treated animals. Enhanced fibrosis in AAF/CCl(4) group was accompanied by ductule forming LPC expanding from portal areas, αSMA-positive cells accumulation in the fibrotic areas and increased expression of hepatic collagen type 1, 3 and 4 mRNA. Moreover, CK19-positive LPC expressed the most potent fibrogenic cytokine transforming growth factor-β (TGFβ) without any expression of αSMA, desmin or fibroblast-specific protein-1, demonstrating that LPC did not undergo an epithelial-mesenchymal transition. In this new experimental model, LPC, by expressing TGFβ, contributed to the accumulation of αSMA-positive myofibroblasts in the ductular reaction leading to enhanced fibrosis but also to disease progression and to a fibrotic pattern similar to that observed in humans.

Stimulation of oval cell and hepatocyte proliferation by exogenous bombesin and neurotensin in partially hepatectomized rats

AIM: To investigate the effect of the neuropeptides bombesin (BBS) and neurotensin (NT) on oval cell proliferation in partially hepatectomized rats not pretreated with a known hepatocyte inhibitor.

METHODS: Seventy male Wistar rats were randomly divided into five groups: I = controls, II = sham operated, III = partial hepatectomy 70% (PHx), IV = PHx + BBS (30 μg/kg per day), V = PHx + NT (300 μg/kg per day). Forty eight hours after liver resection, portal endotoxin levels and hepatic glutathione redox state were determined. α-fetoprotein (AFP) mRNA (in situ hybridisation), cytokeratin-19 and Ki67 antigen expression (immunohistochemistry) and apoptosis (TUNEL) were evaluated on liver tissue samples. Cells with morphological features of oval cells that were cytokeratin-19 (+) and AFP mRNA (+) were scored in morphometric analysis and their proliferation was recorded. In addition, the proliferation and apoptotic rates of hepatocytes were determined.

RESULTS: In the control and sham operated groups, oval cells were significantly less compared to groups III, IV and V (P < 0.001). The neuropeptides BBS and NT significantly increased the proliferation of oval cells compared to group III (P < 0.001). In addition, BBS and NT induced a significant increase of hepatocyte proliferation (P < 0.001), whereas it decreased their apoptotic activity (P < 0.001) compared to group III. BBS and NT significantly decreased portal endotoxemia (P < 0.001) and increased the hepatic GSH: GSSG ratio (P < 0.05 and P < 0.001, respectively) compared to group III.

CONCLUSION: BBS and NT stimulated oval cell proliferation in a model of liver regeneration, without use of concomitant suppression of hepatocyte proliferation as oval cell activation stimuli, and improved the hepatocyte regenerative response. This peptides-induced combined stimulation of oval cell and hepatocyte proliferation might serve as a possible treatment modality for several liver diseases.

CD24-positive cells from normal adult mouse liver are hepatocyte progenitor cells

The identification of specific cell surface markers that can be used to isolate liver progenitor cells will greatly facilitate experimentation to determine the role of these cells in liver regeneration and their potential for therapeutic transplantation. Previously, the cell surface marker, CD24, was observed to be expressed on undifferentiated bipotential mouse embryonic liver stem cells and 3,5-diethoxycarbonyl-1,4-dihydrocollidine-induced oval cells. Here, we describe the isolation and characterization of a rare, primary, nonhematopoietic, CD24+ progenitor cell population from normal, untreated mouse liver. By immunohistochemistry, CD24-expressing cells in normal adult mouse liver were colocalized with CK19-positive cholangiocytes. This nonhematopoietic (CD45-, Ter119-) CD24+ cell population isolated by flow cytometry represented 0.04% of liver cells and expressed several markers of liver progenitor/oval cells. The immunophenotype of nonhematopoietic CD24+ cells was CD133, Dlk, and Sca-1 high, but c-Kit, Thy-1, and CD34 low. The CD24+ cells had increased expression of CK19, epithelial cell adhesion molecule, Sox 9, and FN14 compared with the unsorted cells. Upon transplantation of nonhematopoietic CD24+ cells under the sub-capsule of the livers of Fah knockout mice, cells differentiated into mature functional hepatocytes. Analysis of X and Y chromosome complements were used to determine whether or not fusion of the engrafted cells with the recipient hepatocytes occurred. No cells were found that contained XXXY or any other combination of donor and host sex chromosomes as would be expected if cell fusion had occurred. These results suggested that CD24 can be used as a cell surface marker for isolation of hepatocyte progenitor cells from normal adult liver that are able to differentiate into hepatocytes.

Proliferation of Hepatic Oval Cells via Cyclooxygenase-2 and Extracellular Matrix Protein Signaling during Liver Regeneration Following 2-AAF/Partial Hepatectomy in Rats

BACKGROUND/AIMS

In the 2-acetylaminofluorene (2-AAF)/70% partial hepatectomy (PHx) model, the mechanism underlying the differentiation of activated hepatic oval cells (HOCs) into hepatocytes and bile ductile cells is unclear. We investigated the role of cyclooxygenase-2 (COX-2) in HOCs and the relationship between COX-2 and extracellular matrix proteins in cellular proliferation.

METHODS

Reverse transcription-polymerase chain reaction, immunohistochemical staining, and Western blotting were used to assess COX-2 expression. The co-localization of COX-2 with Thy1, c-Met, epithelial cell adhesion molecule, and α-smooth muscle actin was also examined. Additionally, we investigated whether connective tissue growth factor (CTGF), fibronectin (FN), extracellular signal-regulated kinase 1/2 (P-ERK1/2), and AKT were expressed in HOCs.

RESULTS

The expression of COX-2, prostaglandin E2 receptors, and c-Met was upregulated in HOCs. However, HOCs treated with the COX-2 inhibitor NS398 showed decreased COX-2, CTGF, FN, and AKT expression, whereas P-ERK1/2 was unaffected. Additionally, NS398 inhibited HOC proliferation, but not the proliferation of HOCs cultured on FN-coated dishes. Furthermore, the proliferative response of HOCs treated with NS398 was reversed by hepatic growth factor treatment.

CONCLUSIONS

These results suggest that HOC proliferation is mediated through COX-2, extracellular FN expression, and AKT activation. Thus, COX-2 plays an important role in HOC proliferation following acute injury.

Management of Liver Failure: From Transplantation to Cell-Based Therapy

The severe shortage of deceased donor organs has driven a search for alternative methods of treating liver failure. In this context, cell-based regenerative medicine is emerging as a promising interdisciplinary field of tissue repair and restoration, able to contribute to improving health in a minimally invasive fashion. Several cell types have allowed long-term survival in experimental models of liver injury, but their therapeutic potential in humans should be regarded with deep caution, because few clinical trials are currently available and the number of patients enrolled so far is too small to assess benefits versus risks. This review summarizes the current literature on the physiological role of endogenous stem cells in liver regeneration and on the therapeutic benefits of exogenous stem cell administration with specific emphasis on the potential clinical uses of mesenchymal stem cells. Moreover, critical points that still need clarification, such as the exact identity of the stem-like cell population exerting the beneficial effects, as well as the limitations of stem cell-based therapies, are discussed.

Liver regeneration: alternative epithelial pathways

Loss of hepatic tissue triggers a regenerative response in the whole organ. Under typical normal conditions, all hepatic cells (epithelial: hepatocytes and biliary epithelial cells; non-epithelial: stellate cells, macrophages and endothelial cells) undergo one to three rounds of replication to establish the original number of cells and restore organ size. The review summarizes the literature of regenerative patterns in situations in which proliferation of either hepatocytes or biliary epithelial cells is inhibited. The evidence strongly suggests that under these circumstances, hepatocytes or biliary epithelial cells can function as facultative stem cells for each other and replenish the inhibited cellular compartment by a process of transdifferentiation, involving complex signaling pathways. These pathways are activated under experimental conditions in rodents and in fulminant hepatitis associated with liver failure in humans. Mechanistic analysis of these pathways has implications for liver biology and for potential therapeutic modalities in human liver disease.

Liver regeneration: alternative epithelial pathways

Loss of hepatic tissue triggers a regenerative response in the whole organ. Under typical normal conditions, all hepatic cells (epithelial: hepatocytes and biliary epithelial cells; non-epithelial: stellate cells, macrophages and endothelial cells) undergo one to three rounds of replication to establish the original number of cells and restore organ size. The review summarizes the literature of regenerative patterns in situations in which proliferation of either hepatocytes or biliary epithelial cells is inhibited. The evidence strongly suggests that under these circumstances, hepatocytes or biliary epithelial cells can function as facultative stem cells for each other and replenish the inhibited cellular compartment by a process of transdifferentiation, involving complex signaling pathways. These pathways are activated under experimental conditions in rodents and in fulminant hepatitis associated with liver failure in humans. Mechanistic analysis of these pathways has implications for liver biology and for potential therapeutic modalities in human liver disease.

Bombesin and neurotensin exert antiproliferative effects on oval cells and augment the regenerative response of the cholestatic rat liver

The regenerative capacity of the cholestatic liver is significantly attenuated. Oval cells are hepatic stem cells involved in liver's regeneration following diverse types of injury. The present study investigated the effect of the neuropeptides bombesin (BBS) and neurotensin (NT) on oval cell proliferation as well as on hepatocyte and cholangiocyte proliferation and apoptosis in the cholestatic rat liver. Seventy male Wistar rats were randomly divided into five groups: controls, sham operated, bile duct ligated (BDL), BDL+BBS (30 μg/kg/d), BDL+NT (300 μg/kg/d). Ten days later, alpha-fetoprotein (AFP) mRNA (in situ hybridization), cytokeratin-19 and Ki67 antigen expression (immunohistochemistry) and apoptosis (TUNEL) were evaluated on liver tissue samples. Cells with morphologic features of oval cells that were cytokeratin-19(+) and AFP mRNA(+) were scored in morphometric analysis and their proliferation was recorded. In addition, the proliferation and apoptotic rates of hepatocytes and cholangiocytes were determined. Alanine aminotransferase (ALT) levels and hepatic oxidative stress (lipid peroxidation and glutathione redox state) were also estimated. The neuropeptides BBS and NT significantly reduced ALT levels and hepatic oxidative stress. Both agents exerted similar and cell type-specific effects on oval cells, hepatocytes and cholangiocytes: (a) oval cell proliferation and accumulation in the cholestatic liver was attenuated, (b) hepatocyte proliferation was increased along with a decreased rate of their apoptosis and (c) cholangiocyte proliferation was attenuated and their apoptosis was increased. These observations might be of potential value in patients with extrahepatic cholestasis.

Granulocyte colony-stimulating factor enhances bone marrow mononuclear cell homing to the liver in a mouse model of acute hepatic injury

BACKGROUND

Experiments have reported that granulocyte colony stimulating factor (G-CSF) can mobilize stem cells. However, few studies have examined the effect of G-CSF on bone marrow mononuclear cell (BMMC) mobilization, in particular regarding their capability to home to acutely injured liver.

AIMS

The aim of this study was to evaluate the effort of G-CSF on BMMC homing to the liver following chemically-induced hepatic failure.

METHODS

BMMC were isolated from mice, pre-labeled with PKH26 and infused into the mice in which hepatic injury had been induced followed by administration of G-CSF or vehicle. Livers were studied by fluorescent microscopy after transplantation of pre-labeled BMMC.

RESULTS

PKH26 labeled cells were found in liver tissue at 102 ± 10 cells/high power field in the BMMC+G-CSF group and 30 ± 5 cells/high power field in the BMMC group, but none in the G-CSF group and the control group (P < 0.05). In the former two groups the majority of PKH26 labeled cells colocalized with proliferative cell nuclear antigen (PCNA). The number of PCNA positive cells in the BMMC+G-CSF group was 20 ± 4 cells/high power field, while in the BMMC group it was 14 ± 2 cells/high power field, in the G-CSF group 12 ± 2 cells/high power field, and 8 ± 1 cells/high power field in the control group. Moreover, albumin expression was increased in the BMMC+G-CSF treated group (149 ± 7/high power field) relative to the BMMC group (48 ± 6/high power field), the G-CSF group (44 ± 5/high power field) and the vehicle group (30 ± 6/high power field), with the former three groups showing elevated levels as compared to vehicle control (30 ± 6) (P < 0.05).

CONCLUSION

Transplanted BMMC may home to injured liver, which appears to be enhanced by G-CSF administration.

Liver regeneration by small hepatocyte-like progenitor cells after necrotic injury by carbon tetrachloride in retrorsine-exposed rats

Liver regeneration after partial hepatectomy (PH) in rats exposed to the pyrrolizidine alkaloid retrorsine is accomplished through the proliferation and differentiation of a population of small hepatocyte-like progenitor cells (SHPCs). The activation, emergence, and outgrowth of SHPCs in response to the liver deficit generated through surgical PH have been well characterized. However, the participation of these cells in the restoration of hepatocyte numbers and regeneration of liver tissue mass following necrotic injury has not been investigated. To investigate the capacity of SHPCs to respond to necrotizing liver injury, we combined retrorsine treatment with the centrilobular-specific toxin carbon tetrachloride (CCl(4)). Male Fischer 344 rats were treated with retrorsine (30 mg/kg ip) at 6 and 8 weeks of age, followed by CCl(4) treatment (1500 mg/kg ip) 5 weeks later. Liver tissues were harvested at 3, 7, 14, 21, and 30-days post-injection. The dose of CCl(4) employed resulted in the necrotic destruction of 59±2% of liver mass and elicited a regenerative response equivalent to that of surgical PH. Livers from retrorsine-exposed CCl(4)-treated rats exhibit SHPC proliferation similar to retrorsine-exposed rats subjected to PH (RP). SHPCs appear at 3-days post-injection, continue to expand at 7-days and 14-days post-injection, and completely regenerate/restore the liver mass and structure in these animals by 30-days post-injection. The magnitude of SHPC response observed in the undamaged periportal zone of the liver in these animals is unaffected (versus RP rats) by the loss of the centrilobular region. The results of this study show that SHPCs are capable of regenerating liver after exposure to necrotizing agents and suggest that the progenitor cell of origin of the SHPCs is not restricted to the centrilobular zone of the liver parenchyma.

Comparative proteome profile during the early period of small-for-size liver transplantation in rats revealed the protective role of Prdx5

BACKGROUND & AIMS

In living-donor liver transplantation (LDLT), "small-for-size graft (SFSG) syndrome" is a complex process resulting primarily from ischemia-reperfusion injury (IRI) and portal hypertension associated with size mismatch between graft and recipient. In the early period of LDLT, molecular events related to subsequent apoptosis, necrosis, proliferation and regeneration appeared in specific protein expression patterns.

METHODS

We used 2D-PAGE and MALDI-TOF/TOF technology to construct a comparative proteome profile for small-for-size liver grafts (SFSGs) during the early period of LDLT in rats (ischemia 1h, and 2, 6, 24, 48 h post-reperfusion); sham-operated liver was the control. Western blotting was used to confirm the proteomics results and immunohistochemistry was carried out to explore the cellular localization of selected proteins. We further performed cluster and bioinformatics analyses of differential proteins. Lastly, we overexpressed Prdx5 in liver grafts using an adenoviral vector to evaluate its protective role.

RESULTS

We identified 314 differential protein spots corresponding to 259 different proteins. Cluster analyses revealed six expression patterns, and bioinformatics analyses revealed that each pattern was related to many specific cell processes. We also showed that Prdx5 overexpression could attenuate injury to SFSGs and increase survival in recipients.

CONCLUSIONS

Taken together, these results reveal an important proteome profile that is functional in SFSGs during early period of LDLT, and provide a strong basis for further research.