Stem cell factor restores hepatocyte proliferation in IL-6 knockout mice following 70% hepatectomy

The Crosstalk between Mesenchymal Stromal/Stem Cells and Hepatocytes in Homeostasis and under Stress

Liver diseases, characterized by high morbidity and mortality, represent a substantial medical problem globally. The current therapeutic approaches are mainly aimed at reducing symptoms and slowing down the progression of the diseases. Organ transplantation remains the only effective treatment method in cases of severe liver pathology. In this regard, the development of new effective approaches aimed at stimulating liver regeneration, both by activation of the organ's own resources or by different therapeutic agents that trigger regeneration, does not cease to be relevant. To date, many systematic reviews and meta-analyses have been published confirming the effectiveness of mesenchymal stromal cell (MSC) transplantation in the treatment of liver diseases of various severities and etiologies. However, despite the successful use of MSCs in clinical practice and the promising therapeutic results in animal models of liver diseases, the mechanisms of their protective and regenerative action remain poorly understood. Specifically, data about the molecular agents produced by these cells and mediating their therapeutic action are fragmentary and often contradictory. Since MSCs or MSC-like cells are found in all tissues and organs, it is likely that many key intercellular interactions within the tissue niches are dependent on MSCs. In this context, it is essential to understand the mechanisms underlying communication between MSCs and differentiated parenchymal cells of each particular tissue. This is important both from the perspective of basic science and for the development of therapeutic approaches involving the modulation of the activity of resident MSCs. With regard to the liver, the research is concentrated on the intercommunication between MSCs and hepatocytes under normal conditions and during the development of the pathological process. The goals of this review were to identify the key factors mediating the crosstalk between MSCs and hepatocytes and determine the possible mechanisms of interaction of the two cell types under normal and stressful conditions. The analysis of the hepatocyte-MSC interaction showed that MSCs carry out chaperone-like functions, including the synthesis of the supportive extracellular matrix proteins; prevention of apoptosis, pyroptosis, and ferroptosis; support of regeneration; elimination of lipotoxicity and ER stress; promotion of antioxidant effects; and donation of mitochondria. The underlying mechanisms suggest very close interdependence, including even direct cytoplasm and organelle exchange.

Association between Immunologic Markers and Cirrhosis in Individuals from a Prospective Chronic Hepatitis C Cohort

Background: Chronic hepatitis C virus (HCV) infection can affect immune response and inflammatory pathways, leading to severe liver diseases such as cirrhosis and hepatocellular carcinoma (HCC). Methods: In a prospective cohort of chronically HCV-infected individuals, we sampled 68 individuals who developed cirrhosis, 91 controls who did not develop cirrhosis, and 94 individuals who developed HCC. Unconditional odds ratios (ORs) from polytomous logistic regression models and canonical discriminant analyses (CDAs) were used to compare categorical (C) baseline plasma levels for 102 markers in individuals who developed cirrhosis vs. controls and those who developed HCC vs. cirrhosis. Leave-one-out cross validation was used to produce receiver operating characteristic curves to assess predictive ability of markers. Lastly, biological pathways were assessed in association with cirrhotic development compared to controls. Results: After multivariable adjustment, DEFA-1 (OR: C2v.C1 = 7.73; p < 0.0001), ITGAM (OR: C2v.C1 = 4.03; p = 0.0002), SCF (OR: C4v.C1 = 0.19; p-trend = 0.0001), and CCL11 (OR: C4v.C1 = 0.31; p-trend= 0.002) were all associated with development of cirrhosis compared to controls; these markers, together with clinical/demographics variables, improved prediction of cirrhosis from 55.7% (in clinical/demographic-only model) to 74.9% accuracy. A twelve-marker model based on CDA results further increased prediction of cirrhosis to 88.0%. While six biological pathways were found to be associated with cirrhosis, cell adhesion was the only pathway associated with cirrhosis after Bonferroni correction. In contrast to cirrhosis, DEFA-1 and ITGAM levels were inversely associated with HCC risk. Conclusions: Pending validation, these findings highlight the important role of immunological markers in predicting HCV-related cirrhosis even 11 years post-enrollment.

Senescent hepatic stellate cells promote liver regeneration through IL-6 and ligands of CXCR2

Senescent cells have long been associated with deleterious effects in aging-related pathologies, although recent studies have uncovered their beneficial roles in certain contexts, such as wound healing. We have found that hepatic stellate cells (HSCs) underwent senescence within 2 days after 2/3 partial hepatectomy (PHx) in young (2–3 months old) mice, and the elimination of these senescent cells by using the senolytic drug ABT263 or by using a genetic mouse model impaired liver regeneration. Senescent HSCs secrete IL-6 and CXCR2 ligands as part of the senescence-associated secretory phenotype, which induces multiple signaling pathways to stimulate liver regeneration. IL-6 activates STAT3, induces Yes-associated protein (YAP) activation through SRC family kinases, and synergizes with CXCL2 to activate ERK1/2 to stimulate hepatocyte proliferation. The administration of either IL-6 or CXCL2 partially restored liver regeneration in mice with senescent cell elimination, and the combination of both fully restored liver weight recovery. Furthermore, the matricellular protein central communication network factor 1 (CCN1, previously called CYR61) was rapidly elevated in response to PHx and induced HSC senescence. Knockin mice expressing a mutant CCN1 unable to bind integrin α₆β₁ were deficient in senescent cells and liver regeneration after PHx. Thus, HSC senescence, largely induced by CCN1, is a programmed response to PHx and plays a critical role in liver regeneration through signaling pathways activated by IL-6 and ligands of CXCR2.

Liver regeneration biology: Implications for liver tumour therapies

The liver has remarkable regenerative potential, with the capacity to regenerate after 75% hepatectomy in humans and up to 90% hepatectomy in some rodent models, enabling it to meet the challenge of diverse injury types, including physical trauma, infection, inflammatory processes, direct toxicity, and immunological insults. Current understanding of liver regeneration is based largely on animal research, historically in large animals, and more recently in rodents and zebrafish, which provide powerful genetic manipulation experimental tools. Whilst immensely valuable, these models have limitations in extrapolation to the human situation. In vitro models have evolved from 2-dimensional culture to complex 3 dimensional organoids, but also have shortcomings in replicating the complex hepatic micro-anatomical and physiological milieu. The process of liver regeneration is only partially understood and characterized by layers of complexity. Liver regeneration is triggered and controlled by a multitude of mitogens acting in autocrine, paracrine, and endocrine ways, with much redundancy and cross-talk between biochemical pathways. The regenerative response is variable, involving both hypertrophy and true proliferative hyperplasia, which is itself variable, including both cellular phenotypic fidelity and cellular trans-differentiation, according to the type of injury. Complex interactions occur between parenchymal and non-parenchymal cells, and regeneration is affected by the status of the liver parenchyma, with differences between healthy and diseased liver. Finally, the process of termination of liver regeneration is even less well understood than its triggers. The complexity of liver regeneration biology combined with limited understanding has restricted specific clinical interventions to enhance liver regeneration. Moreover, manipulating the fundamental biochemical pathways involved would require cautious assessment, for fear of unintended consequences. Nevertheless, current knowledge provides guiding principles for strategies to optimise liver regeneration potential.

Extracellular vesicles containing miR-146a-5p secreted by bone marrow mesenchymal cells activate hepatocytic progenitors in regenerating rat livers

Background

Small hepatocyte-like progenitor cells (SHPCs) appear to form transient clusters in rat livers treated with retrorsine (Ret) and 70% partial hepatectomy (PH). We previously reported that the expansion of SHPCs was amplified in Ret/PH-treated rat livers transplanted with Thy1⁺ cells derived from d-galactosamine-treated injured livers. Extracellular vesicles (EVs) produced by hepatic Thy1⁺ donor cells activated SHPCs via interleukin (IL)-17 receptor B signaling. As bone marrow-derived mesenchymal cells (BM-MCs) also express Thy1, we aimed to determine whether BM-MCs could also promote the growth of SHPCs.

Methods

BM-MCs were isolated from dipeptidyl-peptidase IV (DPPIV)-positive rats. BM-MCs or BM-MC-derived EVs were administered to DPPIV-negative Ret/PH rat livers, and the growth and the characteristics of SHPC clusters were evaluated 14 days post-treatment. miRNA microarrays and cytokine arrays examined soluble factors within EVs. Small hepatocytes (SHs) isolated from an adult rat liver were used to identify factors enhancing hepatocytic progenitor cells growth.

Results

The recipient’s livers were enlarged at 2 weeks post-BM-MC transplantation. The number and the size of SHPCs increased remarkably in livers transplanted with BM-MCs. BM-MC-derived EVs also stimulated SHPC growth. Comprehensive analyses revealed that BM-MC-derived EVs contained miR-146a-5p, interleukin-6, and stem cell factor, which could enhance SHs’ proliferation. Administration of EVs derived from the miR-146a-5p-transfected BM-MCs to Ret/PH rat livers remarkably enhanced the expansion of SHPCs.

Conclusions

miR-146a-5p involved in EVs produced by BM-MCs may play a major role in accelerating liver regeneration by activating the intrinsic hepatocytic progenitor cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02387-6.

Biomaterial-based cell delivery strategies to promote liver regeneration

Chronic liver disease and cirrhosis is a widespread and untreatable condition that leads to lifelong impairment and eventual death. The scarcity of liver transplantation options requires the development of new strategies to attenuate disease progression and reestablish liver function by promoting regeneration. Biomaterials are becoming an increasingly promising option to both culture and deliver cells to support in vivo viability and long-term function. There is a wide variety of both natural and synthetic biomaterials that are becoming established as delivery vehicles with their own unique advantages and disadvantages for liver regeneration. We review the latest developments in cell transplantation strategies to promote liver regeneration, with a focus on the use of both natural and synthetic biomaterials for cell culture and delivery. We conclude that future work will need to refine the use of these biomaterials and combine them with novel strategies that recapitulate liver organization and function in order to translate this strategy to clinical use.

C-Kit, a Double-Edged Sword in Liver Regeneration and Diseases

Previous studies have reported an important role of c-kit in embryogenesis and adulthood. Activation of the SCF/KIT signal transduction pathway is customarily linked to cell proliferation, migration and survival thus influence hematopoiesis, pigmentation, and spermatogenesis. The role of c-kit in the liver is controversial, it is however argued that it is a double-edged sword in liver regeneration and diseases. First, liver c-kit⁺ cells, including oval cells, bile epithelial cells, and part of hepatocytes, participate in liver tissue repair by regenerating target cells according to the type of liver injury. At the same time, c-kit⁺ mast cells, act as immature progenitors in circulation, playing a critical role in liver fibrosis. Furthermore, c-kit is also a proto-oncogene. Notably, c-kit overexpression regulates gastrointestinal stromal tumors. Various studies have explored on c-kit and hepatocellular carcinoma, nevertheless, the intricate roles of c-kit in the liver are largely understudied. Herein, we extensively summarize previous studies geared toward providing hints for future clinical and basic research.

IL6R is a target of miR-197 in human keratinocytes

Psoriasis is a chronic inflammatory disorder with cutaneous and systemic manifestations and substantial negative effects on patients' quality of life. MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression that play a role in the pathogenesis of psoriasis. Previously studies, from others and by us, highlighted specific miRNAs that are dysregulated in psoriatic lesions. MicroRNA-197-3p (miR-197) expression is downregulated in psoriatic lesions compared to normal or uninvolved skin in patients with psoriasis. We have previously reported that miR-197 could modulate IL-22 and IL-17 signalling in psoriasis. Herein, we identify additional biochemical targets of miR-197 in psoriasis. We applied a transcriptome-wide biochemical approach, Protein argonaute-2 photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation (Ago2 PAR-CLIP), to search for new targets of miR-197 in live keratinocytes, and validated its results using reporter assay and analysing by Western blot protein levels in cells overexpressing miR-197. Ago2 PAR-CLIP identified biochemical targets of miR-197, including the alpha subunit of the IL-6 receptor (IL6R). This work provides evidence that IL6R in bona-fide biochemical target of miR-197. IL6R is known to be up-regulated in psoriasis and even was considered as a possible therapeutic target. From the present data and our previous studies, it appears that miR-197 is a major regulator of the interaction between immune system cells and keratinocytes.

Induction of synthesis of matrix metalloproteinases by interleukin-6; evidence for hepatic regeneration following hemi-hepatectomy

Aim of the study

Interleukin-6 (IL-6) can play a role in hepatic regeneration through many mechanisms, one of which is the induction of synthesis of matrix metalloproteinases (MMPs). The aim of the study is to focus on the significance and role of MMPs in the regenerative process to reveal the correlation between IL-6 and MMPs in rats following partial hepatectomy.

Material and methods

Following hemi-hepatectomy, eighty male rats were divided into a control group and a group treated with IL-6 35 µg/100 gm body weight according to a lethality study. The blood samples were drawn from all animal groups for MMP-9 serum level assessment. For the quantitative determination of MMP-9 an enzyme-linked immunosorbent assay (ELISA) was used (Cytoimmune Science Inc., MD) through the quantitative sandwich immunosorbent assay technique. A monoclonal antibody for MMP-9 was pre-coated onto microplate standards. After washing away the unbound substances, an enzyme-linked polyclonal antibody specific for cytokine was added to the wells and color developed in proportion to the amount of total cytokine (pro and/or active) bound in the initial step. The color development was stopped and the intensity of the color was measured.

Results

The liver regeneration rate (%) was significantly higher in the group of rats treated with IL-6 (median value was 49.55% vs. 33.20%), p < 0.001. The MMPs’ serum level was significantly higher in the group of rats with resection and treatment (median value was 8.01).

Conclusions

These results give evidence for the vital role of MMPs in the process of hepatic regeneration, the level of which, in turn, has a close relationship with the level of IL-6. MMPs have diverse effects in promoting angiogenesis, remodeling of extracellular matrix and endothelial cell proliferation.

Role of interleukin 6 in liver cell regeneration after hemi-hepatectomy, correlation with liver enzymes and flow cytometric study

Aim of the study

Liver regeneration after hemi-hepatectomy may be affected by several growth factors and cytokines. The aim is to evaluate the importance of interleukin 6 (IL-6) in the induction of liver cell regeneration and find correlations with other parameters such as liver enzymes, and DNA analysis by flow cytometric studies.

Material and methods

80 adult male Sprague-Dawley rats were obtained and divided into two equal groups (n = 40 rats) to undergo 70% partial hepatectomy: group 1 - untreated (control) group; 40 rats not treated; and group 2 - treated group, 40 rats treated with IL-6 35 μg/100 gm body weight according to a lethality study for a period of 4 days, then hepatic resection was carried out according to the steps of Higgins and Anderson. Assessment of liver enzymes and bilirubin level was done. Flow cytometric study was done using a flow cytometer (FACSCalibur; Becton Dickinson) and DNA content was estimated with CellQuest software (Becton Dickinson).

Results

The levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) were significantly higher in the untreated group of rats with liver resection. A higher value of bilirubin was observed in the treated group. Rat weight at sacrification was significantly lower in the group of rats treated with IL-6 than those without treatment, p < 0.001. Liver weight at sacrification was significantly higher in the group of rats treated with IL-6 (p < 0.001). The percentage of apoptotic cells with hypodiploid DNA content was determined from DNA histograms. Untreated rat resected liver showed a peak pattern that represented liver damage with high damage of 73.4%.

Conclusions

Interleukin 6 is of value in induction of liver cell regeneration after seventy percent hemi-hepatectomy as evident by increased liver cell mass, liver enzymes and flow cytometric analysis.

Effect of Stem Cell Treatment on Acute Liver Failure Model Using Scaffold

BACKGROUND

Injecting MSCs via blood vessel is most commonly used method, which has a major drawback of safety. The aim of our study was to evaluate efficacy using scaffold-loaded MSCs in acute liver failure model.

METHOD

Acute liver failure was induced in mice using thioacetamide (TAA) (200 mg/kg, i.p) once a day for two consecutive days. The animals were divided in four acute liver failure groups: (1) TAA; (2) empty scaffold; (3) MSCs injected through tail vein; (4) MSC + Scaffold, scaffold loaded with MSCs, to evaluate the mortality and changes in liver function. Polylactic-co-glycolic acid scaffold alone and loaded with human MSCs was implanted on mice dorsum.

RESULTS

TAA dose was titrated until one-third mortality rate was achieved. TAA (200 mg/kg) once daily for two consecutive days was injected to establish the acute liver failure model. The mortality of TAA and scaffold groups was 55.9% and 63.2%, respectively. Although, mortality of MSC-TV group decreased 14.7% as compared to TAA group (p = 0.200), MSC + Scaffold group had the lowest mortality (31.4%) (p = 0.013). Cells implanted in PLGA biomaterial were survived until 3 weeks, and their function was increased. Area of hepatic inflammation and necrosis was significantly reduced in MSC-TV and MSC + Scaffold groups; but there was no difference between the two groups. Gene expressions related to inflammation were significantly decreased in MSC-TV and MSC + Scaffold groups compared to TAA group. In MSC + Scaffold group, no migration of stem cells to liver tissue was observed. Although, not all cells in scaffold were stained, some of them were differentiated into hepatocyte-like cells which stained positive for PAS and CYP2E1 antibody.

CONCLUSION

Scaffold loaded with MSCs showed protective effects via paracrine signaling on acute liver failure model.

Current Understanding of Stem Cell and Secretome Therapies in Liver Diseases

Liver failure is one of the main risks of death worldwide, and it originates from repetitive injuries and inflammations of liver tissues, which finally leads to the liver cirrhosis or cancer. Currently, liver transplantation is the only effective treatment for the liver diseases although it has a limitation due to donor scarcity. Alternatively, cell therapy to regenerate and reconstruct the damaged liver has been suggested to overcome the current limitation of liver disease cures. Several transplantable cell types could be utilized for recovering liver functions in injured liver, including bone marrow cells, mesenchymal stem cells, hematopoietic stem cells, macrophages, and stem cell-derived hepatocytes. Furthermore, paracrine effects of transplanted cells have been suggested as a new paradigm for liver disease cures, and this application would be a new strategy to cure liver failures. Therefore, here we reviewed the current status and challenges of therapy using stem cells for liver disease treatments.

Bioactivity of CD34+ cells in patients with acute-on-chronic liver failure

Liver failure is a life-threatened serious disease with many complications and high mortality rate. Stem cells have been applied to replacement therapy, gene therapy and tissue engineering for its capacity of self-renewal and multi-lineage differentiation. To investigate the bioactivity of the peripheral blood hematopoietic stem cells (PBHSC) in patients with acute-on-chronic liver failure, we isolated CD34+ cells from peripheral blood of patients with acute-on-chronic liver failure and healthy controls. After cultured it in serum-free medium (SFEM), we studied the bioactivity of CD34+ cells by observing the morphology, recording growth curve, detecting cell cycle and cell apoptosis. CD34+ cells and culture solution were collected at the time points of 3, 5, 7, 10, 12 and 14 days, and the levels of hepatocyte growth factor (HGF), matrix metalloproteinase-9 (MMP-9), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in culture solution were detected by ELISA. Also, the expressions of pyruvate kinase muscle isoenzyme 2 (PKM2), integrin-β1 and liver-type pyruvate kinase (LPK) were detected by RT-PCR and immunofluorescence. Our results showed the bioactivity of CD34+ cells from patients with acute-on-chronic liver failure was identified to be similar with that from healthy controls. HGF, MMP-9, TNF-α and IL-6 were found in cell culture medium. RT-PCR and immunofluorescence results indicated that PKM2, Integrin-β1 expressed on CD34+ cells from patients with acute-on-chronic liver failure. In conclusion, bioactivity of CD34+ cells of patients with acute-on-chronic liver failure was demonstrated to be normal, which could secrete HGF, MMP-9, TNF-α and IL-6, promote the growth of hepatocytes, and differentiate along a direction to hepatocyte lineage.

Deficiency of periostin impairs liver regeneration in mice after partial hepatectomy

Periostin (Postn) is a crucial extracellular remodeling factor that has been implicated in the pathogenesis of hepatic inflammation, fibrosis, non-alcoholic fatty liver disease and liver cancer. However, the role of Postn in liver regeneration remains unclear. Here, we demonstrate that Postn mRNA and protein levels are significantly upregulated in the mice after 2/3 partial hepatectomy (PHx). Compared with wild-type mice, Postn-deficient mice exhibit lower liver/body weight ratio and less Ki67-positive cells at days 2, 8 and 14 after PHx. Macrophage infiltration and the levels of TNF-α, IL-6 and HGF in the livers of Postn-deficient mice are significantly decreased compared with wild-type mice one day after PHx. In addition, overexpression of Postn leads to higher liver/body weight ratio and more Ki67-positive cells in the livers of mice and promotes hepatocyte proliferation in vitro. Moreover, liver sinusoidal endothelial cells, biliary epithelial cells and hepatocytes can express Postn after PHx, and Postn deficiency impairs angiogenesis during liver regeneration. Our findings indicate that Postn deficiency impairs liver regeneration in mice after PHx and Postn might be a novel promoter for liver regeneration.

The Inhibition of Indoleamine 2,3-Dioxygenase Accelerates Early Liver Regeneration in Mice After Partial Hepatectomy

BACKGROUND AND AIM

The inflammatory response accelerates early liver regeneration after liver injury and resection. Recent studies have demonstrated that indoleamine 2,3-dioxygenase-1 (IDO1) suppresses the activation of inflammatory cells and induces immune tolerance. In this study, we examined the role of IDO1 in liver regeneration after partial hepatectomy (PHx).

METHODS

WT or IDO1-knockout (IDO1-KO) mice received 70% PHx. The liver-body weight ratio after PHx was measured and hepatocyte growth was assessed by immunostaining. The expression of cell cycle genes and pro-inflammatory cytokines in the liver was analyzed by quantitative RT-PCR. In addition, 1-methyl-DL-tryptophan (1-MT), which is an IDO1 inhibitory agent, was given to WT mice and the liver-body weight ratio was measured after PHx.

RESULTS

The liver-body weight ratio was significantly increased in IDO1-KO mice compared with that in WT mice after PHx. More Ki-67-positive cells were present in IDO1-KO mice than in WT mice after PHx. The expression of cell cycle genes (cyclin D1, cyclin E) and pro-inflammatory cytokines (IL-1β, TNF-α and IL-6) was up-regulated in the remnant liver of IDO1-KO mice compared with WT mice. Moreover, treatment with 1-MT promoted liver regeneration.

CONCLUSION

IDO1 deficiency promoted early liver regeneration after PHx, indicating that IDO1 suppresses the production of inflammatory cytokines and subsequently inhibits hepatocyte proliferation during liver regeneration.

A Positive TGF-β/c-KIT Feedback Loop Drives Tumor Progression in Advanced Primary Liver Cancer

Hepatocellular carcinoma (HCC) is globally the second most common cause of cancer mortality. The majority of HCC patients are diagnosed at advanced stage disease for which no curative treatments exist. TGF-β has been identified as a potential therapeutic target. However, the molecular mechanisms mediating its functional switch from a tumor suppressor to tumor promoter in HCC and its interactions with other signaling pathways are poorly understood. Here, we demonstrate an aberrant molecular network between the TGF-β and c-KIT pathway that mediates the functional switch of TGF-β to a driver of tumor progression in HCC. TGF-β/SMAD2 signaling transcriptionally regulates expression of the c-KIT receptor ligand (stem cell factor [SCF]) with subsequent auto- and paracrine activation of c-KIT/JAK1/STAT3 signaling. SCF induces TGF-β1 ligand expression via STAT3, thereby forming a positive feedback loop between TGF-β/SMAD and SCF/c-KIT signaling. This network neutralizes TGF-β–mediated cell cycle inhibition and induces tumor cell proliferation, epithelial-to-mesenchymal-transition, migration, and invasion. Disruption of this feedback loop inhibits TGF-β tumor-promoting effects and restores its antiproliferative functions. Consistent with our in vitro data, we demonstrate SCF overexpression and its correlation to SMAD2 and STAT3 activation in human HCC tumors, advanced tumor-node-metastasis stages, and shorter survival. CONCLUSIONS: Canonical TGF-β and c-KIT signaling forms a positive, tumor-promoting feedback loop. Disruption of this loop restores TGF-β tumor suppressor function and provides the rationale for targeting the TGF-β/SCF axis as a novel therapeutic strategy for HCC.

Serum translationally controlled tumor protein is involved in rat liver regeneration after hepatectomy

AIM

The translationally controlled tumor protein (TCTP) has been reported to promote progression of many physiological processes. However, whether TCTP is involved in liver regeneration has been rarely studied. This study aimed to investigate the potential role of serum TCTP in liver regeneration after two-thirds partial hepatectomy.

METHODS

The synthesis rate and accumulated expression of TCTP was assessed by phosphor imaging and Western blot analysis, respectively. The mRNA expression of tctp was analyzed by quantitative real-time PCR. The effect of serum TCTP on hepatocyte proliferation was investigated by bromodeoxyuridine incorporation, liver/body weight ratio, albumin concentration, and histological examination of liver following treatment of rat with anti-TCTP antibody or prokaryotic TCTP protein before hepatectomy. The MTT assay was used to examine effect of TCTP on hepatocyte proliferation in vitro.

RESULTS

The results showed that the expression of intracellular and serum TCTP protein was significantly increased in rats after two-thirds partial hepatectomy. In vivo bromodeoxyuridine labeling assay suggested that treatment with anti-TCTP antibody before hepatectomy significantly decreased hepatocyte proliferation and liver/body weight ratio. The prokaryotic TCTP had a potential promoting effect on hepatocyte proliferation both in vivo and in vitro, although prokaryotic TCTP given to rats prior to hepatectomy did not increase the proliferation ratio or liver/body weight ratio. Furthermore, anti-TCTP antibody pretreatment decreased the expression of cyclin E, cdk2, and interleukin-6 in rat liver.

CONCLUSION

These findings suggest serum TCTP is involved in rat liver regeneration through promoting hepatocyte proliferation.

Cellularized biosynthetic microhydrogel polymers for intravascular liver tissue regeneration therapy

INTRODUCTION

The liver is the natural microenvironment for hepatocytes transplantation but unfortunately engraftment efficiency is low. Cell-laden microhydrogels made of fibrinogen attached to poly(ethylene glycol) (PEG)-diacrylate side chains, were used as a cell carrier, for intravascular transplantation. This approach may reduce shear stress and immediate immunological pressure after intravascular transplantation and provide biomatrix for environmental support.

AIMS

In vitro assessment of HuH-7 viability and function after polymerization within PEGylated fibrinogen-hydrogel. In vivo assessment of intraportal transplantation of cell-laden microhydrogels with rat adult parenchymal cells.

METHODS

(1) In vitro assessment of HuH-7 cell viability and function, after cell-laden hydrogel (hydrogel volume 30 μL) fabrication, by propidium iodide (PI)/fluorescein diacetate (FDA), and MTT assays, albumin concentration and CYP1A activity. (2) Fabrication of cell-laden microhydrogels and their intraportal transplantion. Engraftment efficiency in vivo was evaluated by real-time qPCR of Y chromosome (SRY gene) and histology.

RESULTS

The viability of cells in hydrogels in culture was comparable to viability of not embedded cells during the first 48 h. However, the viability of cells in hydrogels was reduced after 72 h compared with not embedded cells. Activity of CYP1A in hydrogel was comparable to that of not embedded cells (4.33±1 pmole/μg DNA/4 h vs. 5.13±1 pmole/μg DNA/4 h, respectively). Albumin concentration increased at day 3 in hydrogels to 1.4±0.6 μg/10(4)/24 h and was greater to that of free cells, 0.3±0.1 μg/10(4)/24 h. Cell-laden microhydrogels at a size of 150-150-600 μm (6×10(6) cells/rat) showed better engraftment efficiency at 21 days post-transplantation, compared with isolated cell transplantation (54.6%±5% vs. 1.8%±1.2%, p<0.001).

CONCLUSIONS

The in vitro HuH-7 viability and function after polymerization in PEGylated fibrinogen hydrogel was comparable to cells without the hydrogel. Long-term survival and engraftment efficiency of intravascular transplanted adult hepatocytes is much better in within cell-laden microhydrogels compared with isolated cells. The overall efficiency of the procedure needs to be improved.

The adult livers of immunodeficient mice support human hematopoiesis: evidence for a hepatic mast cell population that develops early in human ontogeny

The liver plays a vital role in hematopoiesis during mammalian prenatal development but its hematopoietic output declines during the perinatal period. Nonetheless, hepatic hematopoiesis is believed to persist into adulthood. We sought to model human adult-liver hematopoiesis by transplantation of fetal and neonatal hematopoietic stem cells (HSCs) into adult immunodeficient mice. Livers were found to be engrafted with human cells consisting primarily of monocytes and B-cells with lesser contributions by erythrocytes, T-cells, NK-cells and mast-cells. A resident population of CD117(++)CD203c(+) mast cells was also documented in human midgestation liver, indicating that these cells comprise part of the liver's resident immune cell repertoire throughout human ontogeny. The murine liver was shown to support human multilineage hematopoiesis up to 321 days after transplant. Evidence of murine hepatic hematopoiesis was also found in common mouse strains as old as 2 years. Human HSC engraftment of the murine liver was demonstrated by detection of high proliferative-potential colony-forming cells in clonal cultures, observation of CD38-CD34(++) and CD133(+)CD34(++) cells by flow cytometry, and hematopoietic reconstitution of secondary transplant recipients of chimeric liver cells. Additionally, chimeric mice with both hematopoietic and endothelial reconstitution were generated by intrasplenic injection of immunodeficient mice with liver specific expression of the urokinase-type plasminogen activator (uPA) transgene. In conclusion, the murine liver is shown to be a hematopoietic organ throughout adult life that can also support human hematopoiesis in severely immunodeficient strains. Further humanization of the murine liver can be achieved in mice harboring an uPA transgene, which support engraftment of non-hematopoietic cells types. Thus, offering a model system to study the interaction of diverse human liver cell types that regulate hematopoiesis and immune function in the liver.

Liver regeneration

The liver is unique in its ability to regenerate in response to injury. A number of evolutionary safeguards have allowed the liver to continue to perform its complex functions despite significant injury. Increased understanding of the regenerative process has significant benefit in the treatment of liver failure. Furthermore, understanding of liver regeneration may shed light on the development of cancer within the cirrhotic liver. This review provides an overview of the models of study currently used in liver regeneration, the molecular basis of liver regeneration, and the role of liver progenitor cells in regeneration of the liver. Specific focus is placed on clinical applications of current knowledge in liver regeneration, including small-for-size liver transplant. Furthermore, cutting-edge topics in liver regeneration, including in vivo animal models for xenogeneic human hepatocyte expansion and the use of decellularized liver matrices as a 3-dimensional scaffold for liver repopulation, are proposed. Unfortunately, despite 50 years of intense study, many gaps remain in the scientific understanding of liver regeneration.

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.

A20 promotes liver regeneration by decreasing SOCS3 expression to enhance IL-6/STAT3 proliferative signals

Liver regeneration is of major clinical importance in the setting of liver injury, resection, and transplantation. A20, a potent antiinflammatory and nuclear factor kappa B (NF-κB) inhibitory protein, has established pro-proliferative properties in hepatocytes, in part through decreasing expression of the cyclin dependent kinase inhibitor, p21. Both C-terminal (7-zinc fingers; 7Zn) and N-terminal (Nter) domains of A20 were required to decrease p21 and inhibit NF-κB. However, both independently increased hepatocyte proliferation, suggesting that additional mechanisms contributed to the pro-proliferative function of A20 in hepatocytes. We ascribed one of A20's pro-proliferative mechanisms to increased and sustained interleukin (IL)-6-induced signal transducer and activator of transcription 3 (STAT3) phosphorylation, as a result of decreased hepatocyte expression of the negative regulator of IL-6 signaling, suppressor of cytokine signaling 3 (SOCS3). This novel A20 function segregates with its 7Zn not Nter domain. Conversely, total and partial loss of A20 in hepatocytes increased SOCS3 expression, hampering IL-6-induced STAT3 phosphorylation. Following liver resection in mice pro-proliferative targets downstream of IL-6/STAT3 signaling were increased by A20 overexpression and decreased by A20 knockdown. In contrast, IL-6/STAT3 proinflammatory targets were increased in A20-deficient livers, and decreased or unchanged in A20 overexpressing livers. Upstream of SOCS3, levels of its microRNA regulator miR203 were significantly decreased in A20-deficient livers.

CONCLUSION

A20 enhances IL-6/STAT3 pro-proliferative signals in hepatocytes by down-regulating SOCS3, likely through a miR203-dependent manner. This finding together with A20 reducing the levels of the potent cell cycle brake p21 establishes its pro-proliferative properties in hepatocytes and prompts the pursuit of A20-based therapies to promote liver regeneration and repair.

Serum from hepatectomized rats induces the differentiation of adipose tissue mesenchymal stem cells into hepatocyte-like cells and upregulates the expression of hepatocyte growth factor and interleukin-6 in vitro

Adipose tissue-derived mesenchymal stem cells (AT-MSCs) are an attractive alternative for clinical application due to their minimally invasive accessibility and availability in the body. However, the hepatic differentiation efficiency of AT-MSCs is insufficient for therapeutic application and the role of extrahepatic stem cells in liver regeneration remains poorly understood. This study was designed to investigate the effects of serum from rats subjected to 70% partial hepatectomy (PH) on the differentiation ability of rat AT-MSCs in vitro, and to explore the potential role of AT-MSCs in vivo following PH injury. Results showed that AT-MSCs treated with serum collected from rats 24 h after 70% PH differen-tiated into hepatocyte-like cells, resembled hepatocyte-like cells with round or polygonal shape, expressed α-fetoprotein, secreted albumin, synthesized urea and acquired cytochrome P450 type 3A4 enzyme activity, and upregulated the expression of interleukin (IL)-6 and hepatocyte growth factor (HGF) transiently in vitro, although the hepatic differentiation efficiency was extremely low. AT-MSC transplantation after 70% PH ameliorated liver injury and promoted liver regeneration, but did not increase the serum levels of IL-6 and HGF in vivo. This result suggests that the therapeutic effect of AT-MSCs in vivo after 24 h of 70% PH does not increase IL-6 and HGF expression.

Loss of intracellular lipid binding proteins differentially impacts saturated fatty acid uptake and nuclear targeting in mouse hepatocytes

The liver expresses high levels of two proteins with high affinity for long-chain fatty acids (LCFAs): liver fatty acid binding protein (L-FABP) and sterol carrier protein-2 (SCP-2). Real-time confocal microscopy of cultured primary hepatocytes from gene-ablated (L-FABP, SCP-2/SCP-x, and L-FABP/SCP-2/SCP-x null) mice showed that the loss of L-FABP reduced cellular uptake of 12-N-methyl-(7-nitrobenz-2-oxa-1,3-diazo)-aminostearic acid (a fluorescent-saturated LCFA analog) by ∼50%. Importantly, nuclear targeting of the LCFA was enhanced when L-FABP was upregulated (SCP-2/SCP-x null) but was significantly reduced when L-FABP was ablated (L-FABP null), thus impacting LCFA nuclear targeting. These effects were not associated with a net decrease in expression of key membrane proteins involved in LCFA or glucose transport. Since hepatic LCFA uptake and metabolism are closely linked to glucose uptake, the effect of glucose on L-FABP-mediated LCFA uptake and nuclear targeting was examined. Increasing concentrations of glucose decreased cellular LCFA uptake and even more extensively decreased LCFA nuclear targeting. Loss of L-FABP exacerbated the decrease in LCFA nuclear targeting, while loss of SCP-2 reduced the glucose effect, resulting in enhanced LCFA nuclear targeting compared with control. Simply, ablation of L-FABP decreases LCFA uptake and even more extensively decreases its nuclear targeting.

Amphiregulin stimulates liver regeneration after small-for-size mouse liver transplantation

This study investigated whether amphiregulin (AR), a ligand of the epidermal growth factor receptor (EGFR), improves liver regeneration after small-for-size liver transplantation. Livers of male C57BL/6 mice were reduced to ~50% and ~30% of original sizes and transplanted. After transplantation, AR and AR mRNA increased in 50% but not in 30% grafts. 5-Bromodeoxyuridine (BrdU) labeling, proliferating cell nuclear antigen (PCNA) expression and mitotic index increased substantially in 50% but not 30% grafts. Hyperbilirubinemia and hypoalbuminemia occurred and survival decreased after transplantation of 30% but not 50% grafts. AR neutralizing antibody blunted regeneration in 50% grafts whereas AR injection (5 μg/mouse, iv) stimulated liver regeneration, improved liver function and increased survival after transplantation of 30% grafts. Phosphorylation of EGFR and its downstream signaling molecules Akt, mTOR, p70S6K, ERK and JNK increased markedly in 50% but not 30% grafts. AR stimulated EGFR phosphorylation and its downstream signaling pathways. EGFR inhibitor PD153035 suppressed regeneration of 50% grafts and largely abrogated stimulation of regeneration of 30% grafts by AR. AR also increased cyclin D1 and cyclin E expression in 30% grafts. Together, liver regeneration is suppressed in small-for-size grafts, as least in part, due to decreased AR formation. AR supplementation could be a promising therapy to stimulate regeneration of partial liver grafts.

Immunological and regenerative aspects of hepatic mast cells in liver allograft rejection and tolerance

The precise roles of mast cells in liver allograft rejection and tolerance are still unknown. This study aimed to explore the roles of mast cells in immune regulation and liver regeneration for tolerance induction by using rat models of orthotopic liver transplantation (OLT). Stem cell factor (SCF) and its receptor c-Kit, which are critical to the migration and development of not only stem cells but also mast cells, significantly increased in the tolerogenic livers as compared with rejected livers. The significant elevation of mast cell tryptase, high-affinity IgE receptor, and histamine suggested the activation of mast cells in liver allografts at the tolerogenic phase after OLT. Immunohistochemical analysis using confocal microscope clearly showed colocalization of mast cells, Foxp3+ Tregs, γδ T cells, and recipient-derived hepatic progenitor cells with higher expression of SCF, IL-9, IL-10, TGF-β1, and IL-17 related to immunoregulation and liver regeneration in the donor grafts of a tolerogenic OLT model. Cross-talk among mast cells and other cells was evaluated by in vitro studies demonstrating that syngeneic bone marrow-derived mast cells (BMMCs) co-cultured with naïve splenocytes or primary hepatocytes significantly increased the population of splenic γδ T cells by mitogen stimulation or by mast cell degranulation, and also significantly induced the hepatocyte proliferation, respectively. Our results suggested that mast cells in the donor grafts may play important roles in the induction/maintenance of immune tolerance and liver regeneration resulting in the replacement of hepatic cells from donor to recipient.

Role of angiotensin-1 receptor blockade in cirrhotic liver resection

BACKGROUND

The regeneration capacity of cirrhotic livers might be affected by angiotensin-1 (AT1) receptors located on hepatic stellate cells (HSC). The effect of AT1 receptor blockade on microcirculation, fibrosis and liver regeneration was investigated.

MATERIALS AND METHODS

In 112 Lewis rats, cirrhosis was induced by repetitive intraperitoneal injections of CCl(4) . Six hours, 3, 7 and 14 days after partial hepatectomy or sham operation, rats were sacrificed for analysis. Animals were treated with either vehicle or 5 mg/kg body weight losartan pre-operatively and once daily after surgery by gavage. Microcirculation and portal vein flow were investigated at 6 h. The degree of cirrhosis was assessed by Azan Heidenhein staining, activation of HSC by desmin staining, apoptosis by ssDNA detection and liver regeneration by Ki-67 staining. Changes in expression of various genes important for liver regeneration and fibrosis were analysed at 6 h and 3 days. Haemodynamic parameters and liver enzymes were monitored.

RESULTS

Losartan treatment increased sinusoidal diameter, sinusoidal blood flow and portal vein flow after partial hepatectomy (P<0.05), but not after sham operation. AT1 receptor blockade resulted in increased apoptosis early after resection. HSC activation was reduced and after 7 days, a significantly lower degree of cirrhosis in resected animals was observed. Losartan increased the proliferation of hepatocytes at late time-points and of non-parenchymal cells early after partial hepatectomy (P<0.05). Tumour necrosis factor (TNF)-α was significantly upregulated at 6 h and stem cell growth factor (SCF) was downregulated at 3 days (P<0.05).

CONCLUSION

Losartan increased hepatic blood flow, reduced HSC activation and liver fibrosis, but interfered with hepatocyte proliferation after partial hepatectomy in cirrhotic livers.

Regulation of liver regeneration by growth factors and cytokines

The capability of the liver to fully regenerate after injury is a unique phenomenon essential for the maintenance of its important functions in the control of metabolism and xenobiotic detoxification. The regeneration process is histologically well described, but the genes that orchestrate liver regeneration have been only partially characterized. Of particular interest are cytokines and growth factors, which control different phases of liver regeneration. Historically, their potential functions in this process were addressed by analyzing their expression in the regenerating liver of rodents. Some of the predicted roles were confirmed using functional studies, including systemic delivery of recombinant growth factors, neutralizing antibodies or siRNAs prior to liver injury or during liver regeneration. In particular, the availability of genetically modified mice and their use in liver regeneration studies has unraveled novel and often unexpected functions of growth factors, cytokines and their downstream signalling targets in liver regeneration. This review summarizes the results obtained by functional studies that have addressed the roles and mechanisms of action of growth factors and cytokines in liver regeneration after acute injury to this organ.

c-Kit and stem cell factor regulate PANC-1 cell differentiation into insulin- and glucagon-producing cells

Recent evidence has shown that stem cell factor (SCF) and its receptor, c-Kit, have an important role in pancreatic islet development by promoting islet cell differentiation and proliferation. In this study, we examined the role of c-Kit and SCF in the differentiation and proliferation of insulin- and glucagon-producing cells using a human pancreatic duct cell line (PANC-1). Our study showed that increased expression of endocrine cell markers (such as insulin and glucagon) and transcription factors (such as PDX-1 and PAX-6) coincided with a decrease in CK19(+) and c-Kit(+) cells (P<0.001) during PANC-1 cell differentiation, determined by immunofluorescence and qRT-PCR. Cells cultured with exogenous SCF showed an increase in insulin(+) (26%) and glucagon(+) (35%) cell differentiation (P<0.01), an increase in cell proliferation (P<0.05) and a decrease in cell apoptosis (P<0.01). siRNA knockdown of c-Kit resulted in a decrease in endocrine cell differentiation with a reduction in PDX-1 and insulin mRNA, as well as the number of cells immunostaining for PDX-1 and insulin. Taken together, these results show that c-Kit/SCF interactions are involved in mediating islet-like cluster formation and islet-like cell differentiation in a human pancreatic duct cell line.

Apobec-1 complementation factor modulates liver regeneration by post-transcriptional regulation of interleukin-6 mRNA stability

Apobec-1 complementation factor (ACF) is the RNA binding subunit of a core complex that mediates C to U RNA editing of apolipoprotein B (apoB) mRNA. Targeted deletion of the murine Acf gene is early embryonic lethal and Acf(-/-) blastocysts fail to implant and proliferate, suggesting that ACF plays a key role in cell growth and differentiation. Here we demonstrate that heterozygous Acf(+/-) mice exhibit decreased proliferation and impaired liver mass restitution following partial hepatectomy (PH). To pursue the mechanism of impaired liver regeneration we examined activation of interleukin-6 (IL-6) a key cytokine required for induction of hepatocyte proliferation following PH. Peak induction of hepatic IL-6 mRNA abundance post PH was attenuated >80% in heterozygous Acf(+/-) mice, along with decreased serum IL-6 levels. IL-6 secretion from isolated Kupffer cells (KC) was 2-fold greater in wild-type compared with heterozygous Acf(+/-) mice. Recombinant ACF bound an AU-rich region in the IL-6 3'-untranslated region with high affinity and IL-6 mRNA half-life was significantly shorter in KC isolated from Acf(+/-) mice compared with wild-type controls. These findings suggest that ACF regulates liver regeneration following PH at least in part by controlling the stability of IL-6 mRNA. The results further suggest a new RNA target and an unanticipated physiological function for ACF beyond apoB RNA editing.

The impact of the intra-abdominal space on liver regeneration after a partial hepatectomy in rats

BACKGROUND

Little is known about the relationship between intra-abdominal space and liver regeneration. The present study was experimentally designed to investigate the influence of the "occupied space" or the "loss of occupied space" on a regenerating liver.

METHODS

Experiment 1: Rats were randomly assigned to two groups: SO (space occupied) rats (n = 40); occupancy of intra-abdominal space followed by a two-thirds partial hepatectomy (PH) and control rats (n = 40); A PH alone. The rats in both groups were euthanized at 24, 48, 96, and 168 h after the operation. Computed tomography (CT) images were analyzed to evaluate the regenerating-direction and the shape of the regenerated remnant liver. The liver to body weight ratio and the proliferating cell nuclear antigen (PCNA) labeling index were measured at each time point. Experiment 2: A second laparotomy was performed at 168 h after the PH in both groups; occupier-removal for the SO rats and a sham operation for the control rats. The rats in both groups were euthanized at 24 and 168 h after the second operation. The liver to body weight ratio and PCNA labeling index were measured at each time point.

RESULTS

Experiment 1: The remnant liver of the SO rats enlarged toward the dorsal and caudal side because liver regeneration toward the ventral side in the SO rats was inhibited with the occupier in the abdominal space at 96 h, and later, after the PH. CT images showed a statistically significant difference in the shape of the regenerated remnant liver between the control group and the SO group. The liver/body weight ratio was significantly decreased in the SO rats at 96 and 168 h after PH (P < 0.05). There was no significant difference between the groups in the PCNA labeling index. The SO rats showed a significant increase of the PCNA labeling of the inferior right lobe (10.6%) in comparison with the index of the superior right lobe (7.8%), which came in direct contact with the occupier, at 96 h after the operation (P < 0.05). The cell density of superior right lobe of the SO rats group was significantly higher than that of the control group at 168 h after operation (P < 0.05). Experiment 2: There was no statistically significant difference in the liver/body weight ratio at 168 hrs after the second operation between the groups. However, there was a statistically significant increase of the PCNA labeling index 24 h after the second operation in the occupier-removal rats in comparison with the control rats (P < 0.05).

CONCLUSION

The occupied intra-abdominal space was therefore found to suppress liver regeneration after a partial hepatectomy, while the removal of such an occupied space stimulated the regeneration of the liver.

Roles of stem cell factor on the depletion of interstitial cells of Cajal in the colon of diabetic mice

The aim of this study was to investigate the effects of stem cell factor (SCF) on interstitial cell of Cajal (ICC) depletion in the colon of diabetic mice. Male C57/BL6 mice were treated by a single intraperitoneally injected dose of streptozotocin, and those displaying sustained high blood glucose were selected as diabetes mellitus models. Six groups of mice were used: three groups of normal nondiabetic mice (untreated and treated with IgG or SCF antibody), and three groups of diabetic mice (untreated and treated with vehicle or SCF). Changes of the ICC quantities were analyzed by immunohistochemistry. ICC morphologies were observed with transmission electron microscopy. The SCF levels in sera and colon tissues were detected by ELISA and Western blot, respectively. The nondiabetic mice treated with SCF antibody and the untreated diabetic mice showed decreased SCF levels in the sera and colonic tissues, reduced numbers of ICC, and pathological changes of the ICC ultrastructures, whereas the nondiabetic mice treated with mouse IgG showed no significant changes compared with the nondiabetic mice. The diabetic mice treated with exogenous SCF showed restored SCF levels in both sera and colon tissues and improvement in the numbers of ICC and the damages of ICC ultrastructures, whereas the vehicle control of diabetic mice showed no significant changes compared with the diabetic mice. The blood glucose remained high and unchanged with the treatment of SCF or vehicle in the diabetic mice. These results indicate that diabetic mice show a decline in the number of ICC and impairment in the ultrastructures of ICC, and these abnormalities are attributed to a deficiency in the endogenous SCF but are not related to hyperglycemia. Exogenous SCF partially reverses the pathological changes of ICC in diabetic mice.

IL-22 is involved in liver regeneration after hepatectomy

Hepatocyte proliferation following partial hepatectomy is an important component of liver regeneration, and recent in vitro studies have shown that IL-22 is involved in cellular proliferation in a variety of cell types, including hepatocytes. IL-22 functions through IL-10Rbeta and IL-22Ralpha. The goal of this study was to investigate the potential role of IL-22 in liver regeneration after 70% hepatectomy. Following 70% hepatectomy, done under general anesthesia in mice, serum IL-22 and hepatic IL-22Ralpha mRNA were significantly increased. Although administration of exogenous IL-22 prior to hepatectomy did not increase hepatocyte proliferation, administration of anti-IL-22 antibody before hepatectomy did significantly decrease hepatocyte proliferation. Furthermore, IL-22 treatment prior to 70% hepatectomy induced stat-3 activation; no significant changes were seen in ERK1/2 activation, stat-1 activation, or stat-5 activation. IL-22 pretreatment also significantly increased hepatic and serum IL-6 levels. In addition, animals treated with anti-IL-22 antibody also expressed less TGF-alpha. In conclusion, these data suggest that IL-22 is involved in liver regeneration and this may be due to interaction with IL-6 and TGF-alpha cascades.

Expression of stem cell factor receptor c-kit in human nontumoral and tumoral hepatic cells

INTRODUCTION

The aim of this study was to examine and compare the stem cell factor receptor c-kit expression in hepatocellular carcinoma (HCC) with the corresponding peritumoral tissue. To confirm the immunohistochemical results in the investigated HCC tissues, HCC cell lines were analyzed for c-kit expression.

METHODS

Expression of c-kit (SCF receptor) has been evaluated in 72 HCC and in the corresponding surrounding nontumorous tissue. Additionally, immunohistochemical analysis reverse transcription-polymerase chain reaction was also used to examine the mRNA expression of c-kit protooncogene in tumor homogenates. Furthermore, three HCC cell lines (HUH-7, HepG2, and SK-Hep1) were used for gene-expression analysis of c-kit mRNA.

RESULTS

C-kit expression was detected immunohistochemically in 70% of HCC with different degrees of intensity. Moreover, c-kit expression could also be found in about 90% of the corresponding peritumoral noncirrhotic as well as in cirrhotic liver tissues. C-kit mRNA was detectable in 83% of HCC and in 75% of the corresponding peritumoral noncirrhotic as well as in 100% of corresponding peritumoral cirrhotic samples. In addition, two of the three HCC cell lines (HUH-7 and SK-Hep1) showed a well detectable PCR-product for c-kit.

CONCLUSION

Hepatocytes express the c-kit receptor at different grade of intensity under normal and altered pathological conditions. The presence of c-kit on HCC cell lines supports the assumption that SCF might play a role in the regulation of proliferative activity of tumorous and nontumorous hepatic cells.

Mesenchymal stromal cells as supportive cells for hepatocytes

Hepatocytes and hematopoietic stem cells (HSCs) appear to share many of the same requirements for their survival, functionality, and proliferation. This may be due to a shared location during fetal development. Moreover, hepatocytes and HSCs are unable to function, or even survive, without stromal cell support. Bone marrow-derived mesenchymal stromal cells (MSCs) support the proliferation and functionality, not only of HSCs, but also of hepatocytes. Although knowledge of the mechanisms underlying HSCs' support is far more advanced than for hepatocytes, data suggest that many agents important for HSCs also maintain the normal hepatocyte phenotype in vitro. Thus, it is possible that new techniques for the maintenance and expansion of HSCs may also be useful for hepatocytes. Bone marrow-derived MSCs are easily cultured and expanded in vitro, and some data suggest that they are immunoregulatory as well as relatively nonimmunogenic. These observations suggest that allogeneic MSCs may be useful not only in supporting hepatocyte growth and proliferation but also in modulating immune responses such as stellate cell activation.

Expression of stem cell factor and its receptor c-Kit during the development of intrahepatic cholangiocarcinoma

Stem cell factor (SCF) and its receptor, c-Kit, constitute an important signal transduction system with proliferative and anti-apoptotic functions. Besides regulating hemopoietic stem cell proliferation and liver regeneration, it has been implicated in the regulation of human malignancies. However, the cellular expression of the SCF-c-Kit gene system in the liver during cholangiocarcinogenesis has not been studied to date. The protein- and mRNA-expression levels of SCF and c-Kit genes were examined in normal rat liver, in isolated normal rat liver cells and in a thioacetamide-induced rat model of intrahepatic cholangiocarcinoma (CC). Immunohistochemical analysis of the normal liver showed that SCF is expressed in the wall of the hepatic artery and in some cells, which were located along the sinusoids, although it was absent from hepatocytes and biliary epithelial cells. The mRNA analysis of isolated normal liver cell populations revealed a co-expression of SCF- and c-Kit-mRNA in sinusoidal endothelial cells and in Kupffer cells, whereas passaged and cultured liver myofibroblasts (MFs) expressed only SCF. Low levels of the SCF- and c-Kit-mRNA expression could be detected in isolated hepatocytes of the normal liver. Immunohistochemical analysis of the CC tissue showed SCF positivity in proliferating biliary cells (CK-19(+)), in macrophages (ED-1(+)) and in MFs (alpha-smooth-muscle-actin, alpha-SMA(+)) of the tumoral microenvironment. c-Kit-positivity could be detected on hepatocytes of the regenerating nodules and on the proliferating bile ducts of CC. Compared with the normal liver tissue, SCF-mRNA from the CC tissue was upregulated up to 20-fold, whereas c-Kit-mRNA was upregulated up to fivefold. These data indicate that several cell populations may become able to express SCF and/or c-Kit during cholangiocarcinogenesis. Therefore, the SCF-c-Kit system may contribute to tumor development, for instance, by inducing proliferation of hepatocytes and of biliary cells and by acting as a surviving factor for CC cells.

Stem cell factor and c-kit are involved in hepatic recovery after acetaminophen-induced liver injury in mice

Stem cell factor (SCF) and its receptor c-kit are important in hematopoiesis and cellular proliferation. c-kit has also been identified as a cell surface marker for progenitor cells. We have previously shown that there is a large reservoir of hepatic SCF, and this molecule plays a significant role in liver regeneration after 70% hepatectomy. In the current study, we further examined the expression of SCF and c-kit in acetaminophen (APAP)-induced liver injury in C57BL/6J mice or SCF-deficient sl-sld mice and their appropriate wild-type controls. Following APAP-induced liver injury, c-kit mRNA expression increased, with peak levels detected 48 h postinjury. Hepatic SCF mRNA levels after APAP injury were also increased, with peak levels seen 16 h post-APAP. The mortality rate in SCF-deficient mice treated with APAP was significantly higher than that of wild-type mice; furthermore, administration of exogenous SCF significantly reduced the mortality of APAP-treated wild-type mice. Bromodeoxyuridine incorporation experiments showed that SCF significantly increased hepatocyte proliferation at 48 and 72 h in APAP-treated mice. SCF inhibited APAP-induced hepatocyte apoptosis and increased Bcl-2 and Bcl-xL expression, suggesting that this decrease in hepatocyte apoptosis is mediated through Bcl-2 and Bcl-xL. In summary, SCF and c-kit expression was increased after APAP-induced liver injury. Administration of exogenous SCF reduces mortality in APAP-treated mice, increases hepatocyte proliferation, and prevents hepatocyte apoptosis induced by APAP, suggesting that these molecules are important in the liver's recovery from these injuries.

Stem cell factor and c-kit are involved in hepatic recovery after acetaminophen-induced liver injury in mice

Stem cell factor (SCF) and its receptor c-kit are important in hematopoiesis and cellular proliferation. c-kit has also been identified as a cell surface marker for progenitor cells. We have previously shown that there is a large reservoir of hepatic SCF, and this molecule plays a significant role in liver regeneration after 70% hepatectomy. In the current study, we further examined the expression of SCF and c-kit in acetaminophen (APAP)-induced liver injury in C57BL/6J mice or SCF-deficient sl-sld mice and their appropriate wild-type controls. Following APAP-induced liver injury, c-kit mRNA expression increased, with peak levels detected 48 h postinjury. Hepatic SCF mRNA levels after APAP injury were also increased, with peak levels seen 16 h post-APAP. The mortality rate in SCF-deficient mice treated with APAP was significantly higher than that of wild-type mice; furthermore, administration of exogenous SCF significantly reduced the mortality of APAP-treated wild-type mice. Bromodeoxyuridine incorporation experiments showed that SCF significantly increased hepatocyte proliferation at 48 and 72 h in APAP-treated mice. SCF inhibited APAP-induced hepatocyte apoptosis and increased Bcl-2 and Bcl-xL expression, suggesting that this decrease in hepatocyte apoptosis is mediated through Bcl-2 and Bcl-xL. In summary, SCF and c-kit expression was increased after APAP-induced liver injury. Administration of exogenous SCF reduces mortality in APAP-treated mice, increases hepatocyte proliferation, and prevents hepatocyte apoptosis induced by APAP, suggesting that these molecules are important in the liver's recovery from these injuries.

Stem cell factor and its receptor, c-kit, are important for hepatocyte proliferation in wild-type and tumor necrosis factor receptor-1 knockout mice after 70% hepatectomy

BACKGROUND

Stem cell factor (SCF) has well-known proliferative effects on hematopoietic cells. SCF also has effects on differentiation and proliferation in other cell types. Interleukin-6 (IL-6) and tumor necrosis factor (TNF)-alpha have proliferative effects in the liver. Recent studies in our laboratory have linked SCF's hepatoproliferative actions to those of IL-6, demonstrating that IL-6-induced hepatocyte proliferation depends, at least in part, on SCF. We now hypothesize that TNF-alpha's hepatoproliferative effects are also dependent on SCF.

METHODS AND RESULTS

In vitro studies using primary mouse hepatocytes show that SCF is induced by TNF-alpha; anti-SCF antibody treatment in this system inhibits TNF-alpha-induced hepatocyte proliferation, suggesting that TNF-alpha-induced hepatocyte proliferation is also SCF dependent. Additional in vivo experiments were performed in which wild type and/or TNF-alpha receptor-1 knockout mice (TNFR1(-/-)) were subjected to 70% hepatectomy or sham laparotomy. TNFR1(-/-) mice are known to have delayed hepatic regeneration after partial hepatectomy. Initial experiments demonstrated that the SCF receptor, c-kit, is upregulated after partial hepatectomy in wild-type mice, further emphasizing the importance of this system in the restoration of hepatic mass. SCF administration to TNFR1(-/-) mice in the context of partial hepatectomy restores hepatocyte proliferation to normal. Further, SCF administration to TNFR1(-/-) mice before hepatectomy increases phosphotyrosine signal transducer and activator (p-stat-3) levels, suggesting that SCF-induced increases in hepatocyte proliferation may also be stat-3 mediated.

CONCLUSIONS

These data suggest that TNF-alpha-induced hepatocyte proliferation depends, at least in part, on SCF and that SCF and its receptor, c-kit, are important for the liver's regenerative processes.

Physiological variations of stem cell factor and stromal-derived factor-1 in murine models of liver injury and regeneration

BACKGROUND/AIMS

Stem cell factor (SCF) and stromal-derived factor-1 (SDF-1) regulate the regenerative response to liver injury, possibly through activation of liver progenitor 'oval' cells and recruitment of circulating, marrow-derived progenitors.

METHODS

We performed a detailed analysis of SCF, SDF-1 and oval cell proliferation induced by tyrosinaemia, 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) or liver irradiation in mice by ELISA and immunofluorescence.

RESULTS

Liver injury in the tyrosinaemia mouse is characterized by a dramatic decline in plasma SCF and absence of oval cell proliferation. In contrast, DDC induces bile duct (BD) and oval cell proliferation, and a modest decline in plasma SCF. Focal liver irradiation increases plasma SCF, but not oval cell density. In normal mouse liver, SCF is localized primarily to Kupffer cells, cholangiocytes and arterial smooth muscle, with little or no expression in hepatocytes. However, SCF appears in hepatocyte nuclei after injury, where its function is unknown. In all three models, SDF-1 is expressed exclusively in BD epithelium, indicating that tissue SDF-1 levels are proportional to the total mass of oval cells and cholangiocytes. However, increased plasma levels of SDF-1 in fumaryl acetoacetate hydroxylase-null mice were not accompanied by oval cell proliferation.

CONCLUSION

Changes in SCF and SDF-1 varied with the nature of liver injury and were not directly related to oval cell proliferation.

Gene expression during liver regeneration after partial hepatectomy in mice lacking type 1 tumor necrosis factor receptor

BACKGROUND

To investigate the function of tumor necrosis factor-alpha (TNF-alpha) during hepatocyte proliferation, we studied liver regeneration following partial hepatectomy in mice lacking type 1 TNF receptor (TNFR-1).

MATERIALS AND METHODS

TNFR-1 knockout (KO) and wild-type mice were subjected to partial (two-thirds) hepatectomy. Liver regeneration was evaluated by assessing liver weights and Ki67 immunohistochemistry. Riken complementary DNA microarray analysis was performed for liver samples from mice undergoing partial hepatectomy to better compare different mouse partial hepatectomy models (TNFR-1 KO mice, KO group; and wild-type mice, W group).

RESULTS

Liver weight was regained after 14 days in the KO group, and after 7 days in the W group. Genes including lipopolysaccharide, toll-like receptor 4 precursor, mitogen-activated protein kinase kinase kinase 4, mitogen-activated protein kinase kinase kinase kinase 4, and mitogen-activated protein kinase 8-interacting protein were up-regulated in the KO group. As for the cell-cycle-regulated genes, the levels of cyclin D1, nuclear factor-kappa B light chain, and TNF receptor super family membrane 1a were down-regulated in the KO group. Microarray analysis showed decreased activities of the hexokinase- and phospho-fructokinase-related glycolytic pathways in the KO group.

CONCLUSIONS

These results contribute to the better understanding of the mechanisms of liver regeneration after partial hepatectomy in TNFR-1 KO mice.

Regulation of liver regeneration and hepatocarcinogenesis by suppressor of cytokine signaling 3

Suppressor of cytokine signaling 3 (SOCS3) down-regulates several signaling pathways in multiple cell types, and previous data suggest that SOCS3 may shut off cytokine activation at the early stages of liver regeneration (Campbell, J.S., L. Prichard, F. Schaper, J. Schmitz, A. Stephenson-Famy, M.E. Rosenfeld, G.M. Argast, P.C. Heinrich, and N. Fausto. 2001.J. Clin. Invest. 107:1285–1292). We developed Socs3 hepatocyte-specific knockout (Socs3 h-KO) mice to directly study the role of SOCS3 during liver regeneration after a two-thirds partial hepatectomy (PH). Socs3 h-KO mice demonstrate marked enhancement of DNA replication and liver weight restoration after PH in comparison with littermate controls. Without SOCS3, signal transducer and activator of transcription 3 (STAT3) phosphorylation is prolonged, and activation of the mitogenic extracellular signal-regulated kinase 1/2 (ERK1/2) is enhanced after PH. In vitro, we show that SOCS3 deficiency enhances hepatocyte proliferation in association with enhanced STAT3 and ERK activation after epidermal growth factor or interleukin 6 stimulation. Microarray analyses show that SOCS3 modulates a distinct set of genes, which fall into diverse physiological categories, after PH. Using a model of chemical-induced carcinogenesis, we found that Socs3 h-KO mice develop hepatocellular carcinoma at an accelerated rate. By acting on cytokines and multiple proliferative pathways, SOCS3 modulates both physiological and neoplastic proliferative processes in the liver and may act as a tumor suppressor.

KIT is required for hepatic function during mouse post-natal development

Background

The Kit gene encodes a receptor tyrosine kinase involved in various biological processes including melanogenesis, hematopoiesis and gametogenesis in mice and human. A large number of Kit mutants has been described so far showing the pleiotropic phenotypes associated with partial loss-of-function of the gene. Hypomorphic mutations can induce a light coat color phenotype while complete lack of KIT function interferes with embryogenesis. Interestingly several intermediate hypomorphic mutations induced in addition growth retardation and post-natal mortality.

Results

In this report we investigated the post-natal role of Kit by using a panel of chemically-induced hypomorphic mutations recently isolated in the mouse. We found that, in addition to the classical phenotypes, mutations of Kit induced juvenile steatosis, associated with the downregulation of the three genes, VldlR, Lpin1 and Lpl, controlling lipid metabolism in the post-natal liver. Hence, Kit loss-of-functions mimicked the inactivation of genes controlling the hepatic metabolism of triglycerides, the major source of energy from maternal milk, leading to growth and viability defects during neonatal development.

Conclusion

This is a first report involving KIT in the control of lipid metabolism in neonates and opening new perspectives for understanding juvenile steatosis. Moreover, it reinforces the role of Kit during development of the liver and underscores the caution that should be exerted in using KIT inhibitors during anti-cancer treatment.

Role of ischaemic preconditioning in liver regeneration following major liver resection and transplantation

Liver ischaemic preconditioning (IPC) is known to protect the liver from the detrimental effects of ischaemic-reperfusion injury (IRI), which contributes significantly to the morbidity and mortality following major liver surgery. Recent studies have focused on the role of IPC in liver regeneration, the precise mechanism of which are not completely understood. This review discusses the current understanding of the mechanism of liver regeneration and the role of IPC in this setting. Relevant articles were reviewed from the published literature using the Medline database. The search was performed using the keywords “liver”, “ischaemic reperfusion”, “ischaemic preconditioning”, “regeneration”, “hepatectomy” and “transplantation”. The underlying mechanism of liver regeneration is a complex process involving the interaction of cytokines, growth factors and the metabolic demand of the liver. IPC, through various mediators, promotes liver regeneration by up-regulating growth-promoting factors and suppresses growth-inhibiting factors as well as damaging stresses. The increased understanding of the cellular mechanisms involved in IPC will enable the development of alternative treatment modalities aimed at promoting liver regeneration following major liver resection and transplantation.

Implication of stem cell factor in human liver regeneration after transplantation and resection

The stem cell factor (SCF), besides regulating hemopoietic stem cells homing and proliferation, has proliferative effects on hepatocytes and may be involved in liver regeneration. We investigate if liver transplantation (LT) and hepatic resection (HR) modify the concentration of soluble SCF (s-SCF) in peripheral blood of 15 LT and 7 HR. s-SCF was measured by ELISA as ng/ml. s-SCF basal levels were higher in LT that in HR (818 +/- 349 vs. 479 +/- 79, p = 0.005). A significant increase of s-SCF, peaking at postoperative day +3, was seen after LT (from 818 +/- 349 to 1212 +/- 461, p = 0.01) and HR (from 479 +/- 79 to 698 +/- 122, p = 0.004). s-SCF peak levels were higher after LT than HR (p = 0.0008). At day +7 s-SCF concentration returned to baseline values. LT have a higher basal s-SCF level than HR. These data show for the first time that liver injury affects s-SCF level and suggest that SCF may be involved also in clinical liver regeneration.