Hepatic stem cells

Stem Cell-Based Strategies: The Future Direction of Bioartificial Liver Development

Acute liver failure (ALF) results from severe liver damage or end-stage liver disease. It is extremely fatal and causes serious health and economic burdens worldwide. Once ALF occurs, liver transplantation (LT) is the only definitive and recommended treatment; however, LT is limited by the scarcity of liver grafts. Consequently, the clinical use of bioartificial liver (BAL) has been proposed as a treatment strategy for ALF. Human primary hepatocytes are an ideal cell source for these methods. However, their high demand and superior viability prevent their widespread use. Hence, finding alternatives that meet the seed cell quality and quantity requirements is imperative. Stem cells with self-renewing, immunogenic, and differentiative capacities are potential cell sources. MSCs and its secretomes encompass a spectrum of beneficial properties, such as anti-inflammatory, immunomodulatory, anti-ROS (reactive oxygen species), anti-apoptotic, pro-metabolomic, anti-fibrogenesis, and pro-regenerative attributes. This review focused on the recent status and future directions of stem cell-based strategies in BAL for ALF. Additionally, we discussed the opportunities and challenges associated with promoting such strategies for clinical applications.

"Small Hepatocytes" in the Liver

Mature hepatocytes (MHs) in an adult rodent liver are categorized into the following three subpopulations based on their proliferative capability: type I cells (MH-I), which are committed progenitor cells that possess a high growth capability and basal hepatocytic functions; type II cells (MH-II), which possess a limited proliferative capability; and type III cells (MH-III), which lose the ability to divide (replicative senescence) and reach the final differentiated state. These subpopulations may explain the liver's development and growth after birth. Generally, small-sized hepatocytes emerge in mammal livers. The cells are characterized by being morphologically identical to hepatocytes except for their size, which is substantially smaller than that of ordinary MHs. We initially discovered small hepatocytes (SHs) in the primary culture of rat hepatocytes. We believe that SHs are derived from MH-I and play a role as hepatocytic progenitors to supply MHs. The population of MH-I (SHs) is distributed in the whole lobules, a part of which possesses a self-renewal capability, and decreases with age. Conversely, injured livers of experimental models and clinical cases showed the emergence of SHs. Studies demonstrate the involvement of SHs in liver regeneration. SHs that appeared in the injured livers are not a pure population but a mixture of two distinct origins, MH-derived and hepatic-stem-cell-derived cells. The predominant cell-derived SHs depend on the proliferative capability of the remaining MHs after the injury. This review will focus on the SHs that appeared in the liver and discuss the significance of SHs in liver regeneration.

CINC-2 and miR-199a-5p in EVs secreted by transplanted Thy1+ cells activate hepatocytic progenitor cell growth in rat liver regeneration

BACKGROUND

Small hepatocyte-like progenitor cells (SHPCs) are hepatocytic progenitor cells that transiently form clusters in rat livers treated with retrorsine (Ret) that underwent 70% partial hepatectomy (PH). We previously reported that transplantation of Thy1⁺ cells obtained from D-galactosamine-treated livers promotes SHPC expansion, thereby accelerating liver regeneration. Extracellular vesicles (EVs) secreted by Thy1⁺ cells induce sinusoidal endothelial cells (SECs) and Kupffer cells (KCs) to secrete IL17B and IL25, respectively, thereby activating SHPCs through IL17 receptor B (RB) signaling. This study aimed to identify the inducers of IL17RB signaling and growth factors for SHPC proliferation in EVs secreted by Thy1⁺ cells (Thy1-EVs).

METHODS

Thy1⁺ cells isolated from the livers of rats treated with D-galactosamine were cultured. Although some liver stem/progenitor cells (LSPCs) proliferated to form colonies, others remained as mesenchymal cells (MCs). Thy1-MCs or Thy1-LSPCs were transplanted into Ret/PH-treated livers to examine their effects on SHPCs. EVs were isolated from the conditioned medium (CM) of Thy1-MCs and Thy1-LSPCs. Small hepatocytes (SHs) isolated from adult rat livers were used to identify factors regulating cell growth in Thy1-EVs.

RESULTS

The size of SHPC clusters transplanted with Thy1-MCs was significantly larger than that of SHPC clusters transplanted with Thy1-LSPCs (p = 0.02). A comprehensive analysis of Thy1-MC-EVs revealed that miR-199a-5p, cytokine-induced neutrophil chemoattractant-2 (CINC-2), and monocyte chemotactic protein 1 (MCP-1) were candidates for promoting SHPC growth. Additionally, miR-199a-5p mimics promoted the growth of SHs (p = 0.02), whereas CINC-2 and MCP-1 did not. SECs treated with CINC-2 induced Il17b expression. KCs treated with Thy1-EVs induced the expression of CINC-2, Il25, and miR-199a-5p. CM derived from SECs treated with CINC-2 accelerated the growth of SHs (p = 0.03). Similarly, CM derived from KCs treated with Thy1-EVs and miR-199a-5p mimics accelerated the growth of SHs (p = 0.007). In addition, although miR-199a-overexpressing EVs could not enhance SHPC proliferation, transplantation of miR-199a-overexpressing Thy1-MCs could promote the expansion of SHPC clusters.

CONCLUSION

Thy1-MC transplantation may accelerate liver regeneration owing to SHPC expansion, which is induced by CINC-2/IL17RB signaling and miR-199a-5p via SEC and KC activation.

Isolation of Small Hepatocyte-Like Progenitor Cells from Retrorsine/Partial Hepatectomy Rat Livers by Laser Microdissection

Small hepatocyte-like progenitor cells (SHPCs) are known as liver stem/progenitor cells (LSPCs). SHPCs transiently appear and form clusters in rat livers treated with retrorsine (Ret) and a 70% partial hepatectomy (PH). The Ret/PH model has been used widely to analyze the effectiveness of cell transplantation and the mechanisms of LSPC proliferation. Laser microdissection (LMD) is a powerful tool that can excise and collect specific areas of cells from a tissue slice with a laser under a microscope. These cells exhibiting morphological alterations different from the surrounding cells may be analyzed by gene expression profiling. Specific markers of SHPCs have not yet been identified, in part, because it is difficult to isolate SHPCs from the liver using fluorescence or magnetic-activated cell sorting. To examine the underlying mechanism for SHPC growth, we established comprehensive gene expression profiles for SHPCs captured from liver sections using LMD. In this chapter, we introduce a method to isolate SHPCs from liver tissue sections using LMD for gene expression analysis.

Amniotic fluid stem cells as a novel strategy for the treatment of fetal and neonatal neurological diseases

Even in the context of modern medicine, infants with fetal and neonatal neurological diseases such as cerebral palsy and myelomeningocele suffer serious long-lasting impairment due to the irreversible neuronal damage. The promotion of neurologically intact survival in patients with perinatal intractable neurological diseases requires the development of novel strategies. One promising strategy involves the use of human amniotic fluid stem cells (hAFSCs), which have attracted much attention in recent years and are known to exert anti-inflammatory and neuroprotective effects. In recent years, the therapeutic effects of hAFSCs on fetal-neonatal neurological diseases have become evident as per intense research efforts by our group and others. Specifically, hAFSCs administered into the nasal cavity migrated to the brain and controlled local inflammation in a rodent model of neonatal hypoxic-ischemic encephalopathy. In contrast, hAFSCs administered intraperitoneally did not migrate to the brain; they rather formed spheroids in the abdominal cavity, resulting in the suppression of systemic inflammation (including in the brain) via the secretion of anti-inflammatory cytokines in concert with peritoneal macrophages in a rodent model of periventricular leukomalacia. Moreover, studies in a rat model of myelomeningocele suggested that hAFSCs administered in utero secreted hepatocyte growth factor and protected the exposed spinal cord during pregnancy. Importantly, autologous hAFSCs, whose use for fetal-neonatal treatment does not raise ethical issues, can be collected during pregnancy and prepared in sufficient numbers for therapeutic use. This article outlines the results of preclinical research on fetal stem cell therapy, mainly involving hAFSCs, in the context of perinatal neurological diseases.

Non-alcoholic fatty liver disease: molecular and cellular interplays of the lipid metabolism in a steatotic liver

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) affects ~25% of world population and cases have increased in recent decades. These anomalies have several etiologies; however, obesity and metabolic dysfunctions are the most relevant causes. Despite being considered a public health problem, no effective therapeutic approach to treat NAFLD is available. For that, a deep understanding of metabolic routes that support hepatic diseases is needed.

AREAS COVERED

This review covers aspects of the onset of NAFLD. Thereby, biochemistry routes as well as cellular and metabolic effects of the gut microbiota in body's homeostasis and epigenetics are contextualized.

EXPERT OPINION

Recently, the development of biological sciences has generated innovative knowledge, bringing new insights and perspectives to clarify the systems biology of liver diseases. A detailed comprehension of epigenetics mechanisms will offer possibilities to develop new therapeutic and diagnostic strategies for NAFLD. Different epigenetic processes have been reported that are modulated by the environment such as gut microbiota, suggesting strong interplays between cellular behavior and pathology. Thus, a more complete description of such mechanisms in hepatic diseases will help to clarify how to control the establishment of fatty liver, and precisely describe molecular interplays that potentially control NAFLD.

Transplantation of Thy1+ Cells Accelerates Liver Regeneration by Enhancing the Growth of Small Hepatocyte-Like Progenitor Cells via IL17RB Signaling

Small hepatocyte-like progenitor cells (SHPCs) transiently form clusters in rat livers treated with retrorsine (Ret)/70% partial hepatectomy (PH). When Thy1⁺ cells isolated from d-galactosamine-treated rat livers were transplanted into the livers of Ret/PH-treated rats, the mass of the recipient liver transiently increased during the first 30 days after transplantation, suggesting that liver regeneration was enhanced. Here we addressed how Thy1⁺ cell transplantation stimulates liver regeneration. We found that the number and size of SHPC clusters increased in the liver at 14 days after transplantation. GeneChip analysis revealed that interleukin 17 receptor b (IL17rb) expression significantly increased in SHPCs from livers transplanted with Thy1⁺ cells. We subsequently searched for ligand-expressing cells and found that sinusoidal endothelial cells (SECs) and Kupffer cells expressed Il17b and Il25, respectively. Moreover, extracellular vesicles (EVs) separated from the conditioned medium of Thy1⁺ cell culture induced IL17b and IL25 expression in SECs and Kupffer cells, respectively. Furthermore, EVs enhanced IL17rb expression in small hepatocytes (SHs), which are hepatocytic progenitor cells; in culture, IL17B stimulated the growth of SHs. These results suggest that Thy1-EVs coordinate IL17RB signaling to enhance liver regeneration by targeting SECs, Kupffer cells, and SHPCs. Indeed, the administration of Thy1-EVs increased the number and size of SHPC clusters in Ret/PH-treated rat livers. Sixty days post-transplantation, most expanded SHPCs entered cellular senescence, and the enlarged liver returned to its normal size. In conclusion, Thy1⁺ cell transplantation enhanced liver regeneration by promoting the proliferation of intrinsic hepatic progenitor cells via IL17RB signaling. Stem Cells 2017;35:920-931.

Global dynamics of a viral infection model with full logistic terms and antivirus treatments

In this paper, mathematical analysis of the global dynamics of a viral infection model in vivo is carried out. Though the model is originally to study hepatitis C virus (HCV) dynamics in patients with high baseline viral loads or advanced liver disease, similar models still hold significance for other viral infection, such as hepatitis B virus (HBV) or human immunodeficiency virus (HIV) infection. By means of Volterra-type Lyapunov functions, we know that the basic reproduction number [Formula: see text] is a sharp threshold para-meter for the outcomes of viral infections. If [Formula: see text], the virus-free equilibrium is globally asymptotically stable. If [Formula: see text], the system is uniformly persistent, the unique endemic equilibrium appears and is globally asymptotically stable under a sufficient condition. Other than that, for the global stability of the unique endemic equilibrium, another sufficient condition is obtained by Li–Muldowney global-stability criterion. Using numerical simulation techniques, we further find that sustained oscillations can exist and different maximum de novo hepatocyte influx rate can induce different global dynamics along with the change of overall drug effectiveness. Finally, some biological implications of our findings are given.

An efficient and simple co-culture method for isolating primary human hepatic cells: Potential application for tumor microenvironment research

Co-cultivation of non-parenchymal cells (NPCs) and tumor cells from the same donor is important for metastatic cancer research. This study aimed to optimize a protocol for liver NPC isolation. Two novel 3D organotypic co‑culture models for hepatocyte, endothelial cell (EC) and Kupffer cell (KC) isolation were used. Long‑term cell co‑culture, density gradient centrifugation and magnetic‑activated cell sorting (MACS) were established. ECs were isolated from the co‑culture system; the purity of the ECs was 92±1.2%. The island‑like shape of hepatocytes was noted in the 3D co‑culture system, and spindle cells were found in the rest space. Immunofluorescence analysis showed a net structure; the connective tissue was positively stained with VE‑cadherin or CD68, which were ECs and KCs/macrophages. KCs were enriched in this system and separated by using selective adherence to plastic. Clec4f+ KCs consisted of 87±6.3% of these cells. Heterogeneous endothelium populations were detected, including sinusoid ECs, microvascular ECs and hepatic lymphatic vessel epithelial cells. In addition, hepatic progenitor cells were isolated and differentiated into hepatoblasts. Dendritic cells (DCs), invariant natural killer T (iNKT) cells were further separated by density gradient centrifugation and magnetic bead sorting. In the present study, high protein expression levels of desmin and GFAP were observed in the hepatic stellate cells (HSCs). Most of the HSCs were α‑SMA‑positive cells, which underlined the identity of activated HSCs. Intrahepatic human biliary epithelial cells (hBECs) were semi‑purified by centrifugation on a Percoll gradient and were further immunopurified. In conclusion, we provide an efficient long‑term culture method to obtain liver NPCs in sufficient number and purity.

Taohong Qizhu Ruangan Jian reverses epithelial-mesenchymal transition via transforming growth factor beta/Smad signaling pathway

AIM: To explore whether Taohong Qizhu Ruangan Jian (TQRJ) reverses epithelial-mesenchymal transition (EMT) and the underlying mechanism.

METHODS: HepG2 cells were divided into seven groups: a blank group, an EMT group, low-, medium- and high-dose TQRJ groups, a Fuzheng Huayu recipe group (FZHY group), and a colchicine group (QSXJ group). Immunofluorescence and Western blot were used to detect the expression of E-cadherin, Vimentin, Smad2, and transforming growth factor beta (TGF-β) R1. The levels of alanine aminotransferase (ALT), aspartate transaminase (AST), and alpha fetoprotein (AFP) in cell supernatants were also determined.

RESULTS: AFP concentration significantly decreased after 3 d in the EMT group (P < 0.05). After drug intervention, ALT and AST levels decreased significantly compared with the EMT group (P < 0.05). ALT levels were significantly lower in the low- and medium-dose TQRJ groups than in the FZHY and QSXJ groups (P < 0.05), and AST levels were significantly lower in the medium- and high-dose TQRJ groups than in the FZHY and QSXJ groups (P < 0.05). TQRJ could improve EMT, especially in the medium- and high-dose TQRJ groups. TQRJ could increase E-cadherin expression and reduce the expression of Smad2, TGF-β R1 and Vimentin.

CONCLUSION: TQRJ can reverse EMT possibly via the TGF-β/Smad signaling pathway and thus may has anti-liver fibrotic effects.

Mouse models of liver fibrosis mimic human liver fibrosis of different etiologies

The liver has the amazing capacity to repair itself after injury; however, the same processes that are involved in liver regeneration after acute injury can cause serious consequences during chronic liver injury. In an effort to repair damage, activated hepatic stellate cells trigger a cascade of events that lead to deposition and accumulation of extracellular matrix components causing the progressive replacement of the liver parenchyma by scar tissue, thus resulting in fibrosis. Although fibrosis occurs as a result of many chronic liver diseases, the molecular mechanisms involved depend on the underlying etiology. Since studying liver fibrosis in human subjects is complicated by many factors, mouse models of liver fibrosis that mimic the human conditions fill this void. This review summarizes the general mouse models of liver fibrosis and mouse models that mimic specific human disease conditions that result in liver fibrosis. Additionally, recent progress that has been made in understanding the molecular mechanisms involved in the fibrogenic processes of each of the human disease conditions is highlighted.

Current understanding of somatic stem cells in leiomyoma formation

OBJECTIVE

To provide a detailed summary of current scientific knowledge of somatic stem cells (SSCs) in murine and human myometrium and their putative implication in leiomyoma formation, as well as to establish new therapeutic options.

DESIGN

Pubmed and Scholar One manuscripts were used to identify the most relevant studies on SSCs and their implications in human myometrium and leiomyomas.

SETTING

University research laboratory-affiliated infertility clinic.

PATIENT(S)

Not applicable.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

Not applicable.

RESULT(S)

Despite numerous publications on SSCs, it was not until 2007 that scientific evidence based on the use of 5-bromo-2'-deoxyuridine (BrdU) and side population (SP) methods in murine and human myometrium were first published. Recently, it has been reported that SP cells are present in human leiomyomas; however, to date the pathogenesis of this benign tumor remains unclear. Besides many genetic/epigenetic alterations, changes to steroid hormones and growth factors may also be associated with the impaired function, proliferation, and differentiation of a subset of putative SSCs in human myometrium.

CONCLUSION(S)

These findings open up new possibilities for understanding the origin of this benign tumor and help to develop new nonsurgical approaches for their management.

Molecular mechanisms of stem cell therapy in alcoholic liver disease

Alcoholic liver disease affects a great number of people worldwide. With limited therapeutic options, stem cell therapy offers significant potential for these patients. To date, a limited number of clinical trials have produced transient clinical responses to cell therapy in patients with alcoholic liver disease. Stem cell therapy to reorganize the postnatal liver is an important theme and mission for patients with chronic liver disorders including alcoholic liver injury. We therefore should redevelop the evidence of cell-based liver regeneration therapy, focusing on targets (disease, patient's status and hepatic function), materials (cells, cytokines and genes), and methodology (stem cell types and their derived microparticles, transplantation route, implantation technology and tissue engineering). In this review, we summarize the recent findings regarding the experimental and clinical use of mesenchymal and liver stem cells, focusing mainly on the treatment of alcoholic liver disorders and their relevance in the field of regenerative medicine, and advances on the role of microvesicles and exosomes in this process. We discuss new advances in stem cell therapy from liver regeneration to liver re-organization, which is involved in the recent progress of on-going clinical trials, basic research in stem cell therapy and liver regeneration, and updated exosomes/microvesicles recovery/repairing technology.

Two-tier regenerative response in liver failure in humans

Acute and chronic liver failure is associated with high mortality. The enormous regenerative potential of the liver has generated a lot of attention. We undertook this work to assess the two-tier regenerative response in liver failure by immunohistochemistry and to correlate such response with liver histology in acute liver failure (ALF), acute-on-chronic liver failure (ACLF), and decompensated cirrhosis (CHD). Histological examination and immunohistochemical analysis of proliferating hepatocytes and activated hepatic progenitor cells (HPCs) were performed on the liver tissue of patients with ALF (25), ACLF (70), and CHD (70). Comparative analysis of regenerative markers and correlation with histological parameters were done in ALF, ACLF, and CHD. Hepatocytes proliferated significantly more in ALF in comparison to ACLF (p < 0.001) and CHD (p < 0.001). HPC proliferation was significantly higher in ACLF (p < 0.001) and CHD (p < 0.001) than in ALF. ACLF patients showed the highest HPC proliferation and differentiation. Significantly more intermediate hepatocytes were found in ACLF than in ALF and CHD (p < 0.001). Marked parenchymal replacement by fibrosis and/or necrosis correlated significantly with activation of HPC in ACLF (p = 0.01, odds ratio (OR) 4.95) and in CHD (p = 0.05, OR 4.19). The study of liver regeneration in human acute and chronic liver failure suggests that hepatocyte proliferation, providing the first line of regeneration response, is most active in ALF whereas HPC activation, the second line of defense, is more prominent in ACLF. More HPC differentiate to hepatocytes in ACLF than in CHD, reflecting better regenerative potential in ACLF.

The roles of transforming growth factor-β, Wnt, Notch and hypoxia on liver progenitor cells in primary liver tumours (Review)

Primary liver tumours have a high incidence and mortality. The most important forms are hepatocellular carcinoma and intrahepatic cholangiocarcinoma, both can occur together in the mixed phenotype hepatocellular-cholangiocarcinoma. Liver progenitor cells (LPCs) are bipotential stem cells activated in case of severe liver damage and are capable of forming both cholangiocytes and hepatocytes. Possibly, alterations in Wnt, transforming growth factor-β, Notch and hypoxia pathways in these LPCs can cause them to give rise to cancer stem cells, capable of driving tumourigenesis. In this review, we summarize and discuss current knowledge on the role of these pathways in LPC activation and differentiation during hepatocarcinogenesis.

Links between hepatic fibrosis, ductular reaction, and progenitor cell expansion

Interactions between cells and their extracellular matrix have been shown to be crucial in a wide range of biological processes, including the proliferation and differentiation of stem cells. Ductular reactions containing both hepatic progenitor cells and extracellular matrix are seen in response to acute severe and chronic liver injury. Understanding the molecular mechanisms whereby cell-matrix interactions regulate liver regeneration may allow novel strategies to enhance this process. Both the ductular reaction in humans and hepatic progenitor cells in rodent models are closely associated with collagen and laminin, although there is still debate about cause and effect. Recent studies have shown a requirement for matrix remodeling by matrix metalloproteinases for the proliferation of hepatic progenitor cells and suggested defined roles for specific matrix components. Understanding the interactions between progenitor cells and matrix is critical for the development of novel regenerative and antifibrotic therapies.

Human hepatic progenitor cells express hematopoietic cell markers CD45 and CD109

OBJECTIVE

To clarify the precise characteristics of human hepatic progenitor cells (HPCs) for future cytotherapy in liver diseases.

METHODS

Hepatic progenitor-like cells were isolated and cultured from the livers of patients who had undergone partial hepatectomy for various pathologies but displayed no sign of hepatic dysfunction. These cells were characterized by transcriptomic profiling, quantitative real-time PCR and immunocyto/histochemistry.

RESULTS

Cultured HPCs contained polygonal, high nucleus/cytoplasm ratio and exhibited a global gene expression profile similar (67.8%) to that of primary hepatocytes. Among the genes with more than 20-fold higher expression in HPCs were a progenitor marker (CD90), a pentraxin-related gene (PTX3), collagen proteins (COL5A2, COL1A1 and COL4A2), cytokines (EGF and PDGFD), metabolic enzymes (CYBRD1, BCAT1, TIMP2 and PAM), a secreted protein (SPARC) and an endothelial protein C receptor (PROCR). Moreover, eight markers (ALB, AFP, CK8, CK18, CK19, CD90, CD117 and Oval-6) previously described as HPC markers were validated by qRT-PCR and/or immunocyto/histochemistry. Interestingly, human HPCs were also positive for the hematopoietic cell markers CD45 and CD109. Finally, we characterized the localization of HPCs in the canals of Hering and periportal areas with six previously described markers (Oval-6, CK8, CK18, CK19, CD90 and CD117) and two potential markers (CD45 and CD109).

CONCLUSION

The human HPCs are highly similar to primary hepatocytes in their transcriptional profiles. The CD45 and CD109 markers could potentially be utilized to identify and isolate HPCs for further cytotherapy of liver diseases.

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.

Trefoil factor 3 as an endocrine neuroprotective factor from the liver in experimental cerebral ischemia/reperfusion injury

Cerebral ischemia, while causing neuronal injury, can activate innate neuroprotective mechanisms, minimizing neuronal death. In this report, we demonstrate that experimental cerebral ischemia/reperfusion injury in the mouse causes upregulation of the secretory protein trefoil factor 3 (TFF3) in the hepatocyte in association with an increase in serum TFF3. Partial hepatectomy (~60% liver resection) immediately following cerebral injury significantly lowered the serum level of TFF3, suggesting a contribution of the liver to the elevation of serum TFF3. Compared to wild-type mice, TFF3^-/- mice exhibited a significantly higher activity of caspase 3 and level of cell death in the ischemic cerebral lesion, a larger fraction of cerebral infarcts, and a smaller fraction of the injured cerebral hemisphere, accompanied by severer forelimb motor deficits. Intravenous administration of recombinant TFF3 reversed changes in cerebral injury and forelimb motor function due to TFF3 deficiency. These observations suggest an endocrine neuroprotective mechanism involving TFF3 from the liver in experimental cerebral ischemia/reperfusion injury.

Endothelial progenitor cells in regeneration after acute lung injury: do they play a role?

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are common disorders in patients requiring critical care. The clinical management of these disorders is difficult and unrewarding, and thus they are among the most common causes of death in intensive care units. The activation and damage of pulmonary endothelium comprise the hallmark of ALI/ARDS. Therefore, the recruitment of circulating endothelial progenitor cells (EPCs) to these lesions may exert a beneficial effect on the clinical course of ALI/ARDS. Consequently, cell-based therapies using stem cells to regenerate lung tissue have emerged as potential novel treatment strategies. Although initial studies suggested implantations of exogenously administered bone marrow-derived progenitor cells into damaged vessel walls, recent evidence indicates that this is rather a rare occurrence with uncertain physiologic significance. In the past few years, different populations of progenitor cells were identified, with different functional capacities. This review (1) highlights the different populations of EPCs identified or administered in different models of ALI/ARDS, (2) reports on whether beneficial effects of EPCs could be demonstrated, and (3) puts the conflicting results of different studies into perspective.

Maintaining hepatic stem cell gene expression on biological and synthetic substrata

The liver is a highly resilient organ that possesses enormous regenerative capacity. This is mediated mainly through the most abundant cell type found in the liver, the hepatocyte. When the regenerative capacity of the hepatocyte is compromised, during chronic or acute liver injury, hepatic progenitor cells (HPCs) are activated to replace the damaged tissue. The HPC resides in a laminin-rich environment; as HPCs differentiate toward a hepatic or biliary fate, the extracellular matrix (ECM) composition changes, influencing cell behavior. To assess the impact that the biological ECM and the synthetic ECM have on the maintenance of hepatic stem cell gene expression, a murine hepatic stem cell line was employed. We demonstrate that hepatic stem cell gene expression could be maintained using a biological or synthetic substratum, but not on plastic alone.

Integrative toxicopathological evaluation of aflatoxin B₁ exposure in F344 rats

In this study, male F344 rats were orally exposed to a single dose of aflatoxin B₁ (AFB₁) at 0, 50, 250, or 1,000 µg/kg body weight (BW) or repeated dose of 0, 5, 10, 25, or 75 µg/kg BW for up to 5 weeks. Biochemical and histological changes were assessed together with the formation of AFB1-lysine adduct (AFB-Lys) and liver foci positive for placental form glutathione S transferase (GST-P⁺). In single-dose protocol, serum aspartate transaminase (AST), alanine transaminase (ALT), and alkaline phosphatase (ALP) showed dose-related elevation, with maximal changes observed (>100-fold) at day 3 after treatment. Animals that received 250 µg/kg AFB₁ showed concurrent bile duct proliferation, necrosis, and GST-P⁺ hepatocytes at 3 day, followed by liver GST-P⁺ foci appearance at 1 week. In repeated-dose protocol, bile duct proliferation and liver GST-P⁺ foci co-occurred after 3-week exposure to 75 µg/kg AFB₁, followed by proliferation foci formation after 4 week and dramatic ALT, AST, and CK elevations after 5 weeks. Liver GST-P⁺ foci were induced temporally and in a dose-related manner. Serum AFB-Lys increased temporally at low doses (5-25 µg/kg), and reached the maximum after 2-week exposure at 75 µg/kg. This integrative study demonstrated that liver GST-P⁺ cells and foci are sensitive biomarkers for AFB₁ toxic effect and correlated with bile duct proliferation and biochemical alterations in F344 rats.

Cardioprotective proteins upregulated in the liver in response to experimental myocardial ischemia

Myocardial ischemia (MI) activates innate cardioprotective mechanisms, enhancing cardiomyocyte tolerance to ischemia. Here, we report a MI-activated liver-dependent mechanism for myocardial protection. In response to MI in the mouse, hepatocytes exhibited 6- to 19-fold upregulation of genes encoding secretory proteins, including α-1-acid glycoprotein (AGP)2, bone morphogenetic protein-binding endothelial regulator (BMPER), chemokine (C-X-C motif) ligand 13, fibroblast growth factor (FGF)21, neuregulin (NRG)4, proteoglycan 4, and trefoil factor (TFF)3. Five of these proteins, including AGP2, BMPER, FGF21, NRG4, and TFF3, were identified as cardioprotective proteins since administration of each protein significantly reduced the fraction of myocardial infarcts (37 ± 9%, 34 ± 7%, 32 ± 8%, 39 ± 6%, and 31 ± 7%, respectively, vs. 48 ± 7% for PBS at 24 h post-MI). The serum level of the five proteins elevated significantly in association with protein upregulation in hepatocytes post-MI. Suppression of a cardioprotective protein by small interfering (si)RNA-mediated gene silencing resulted in a significant increase in the fraction of myocardial infarcts, and suppression of all five cardioprotective proteins with siRNAs further intensified myocardial infarction. While administration of a single cardioprotective protein mitigated myocardial infarction, administration of all five proteins furthered the beneficial effect, reducing myocardial infarct fractions from PBS control values from 46 ± 6% (5 days), 41 ± 5% (10 days), and 34 ± 4% (30 days) to 35 ± 5%, 28 ± 5%, and 24 ± 4%, respectively. These observations suggest that the liver contributes to cardioprotection in MI by upregulating and releasing protective secretory proteins. These proteins may be used for the development of cardioprotective agents.

Implication of hepatic stem cells in functional liver repopulation

The liver has an enormous potential to restore the parenchymal tissue loss due to injury. This is accomplished by the proliferation of either the hepatocytes or liver progenitor cells in cases where massive damage prohibits hepatocytes from entering the proliferative response. Under debate is still whether hepatic stem cells are involved in liver tissue maintenance and regeneration or even whether they exist at all. The definition of an adult tissue-resident stem cell comprises basic functional stem cell criteria like the potential of self-renewal, multipotent, i.e. at least bipotent differentiation capacity and serial transplantability featuring the ability of functional tissue repopulation. The relationship between a progenitor and its progeny should exemplify the lineage commitment from the putative stem cell to the differentiated cell. This is mainly assessed by lineage tracing and immunohistochemical identification of markers specific to progenitors and their descendants. Flow cytometry approaches revealed that the liver stem cell population in animals is likely to be heterogeneous giving rise to progeny with different molecular signatures, depending on the stimulus to activate the putative stem cell compartment. The stem cell criteria are met by a variety of cells identified in the fetal and adult liver both under normal and injury conditions. It is the purpose of this review to verify hepatic stem cell candidates in the light of the stem cell definition criteria mentioned. Also from this point of view adult stem cells from non-hepatic tissues such as bone marrow, umbilical cord blood or adipose tissue, have the potential to differentiate into cells featuring functional hepatocyte characteristics. This has great impact because it opens the possibility of generating hepatocyte-like cells from adult stem cells in a sufficient amount and quality for their therapeutical application to treat end-stage liver diseases by stem cell-based hepatocytes in place of whole organ transplantation.

Increased susceptibility to severe chronic liver damage in CXCR4 conditional knock-out mice

BACKGROUND

The chemokine SDF-1 and its receptor CXCR4 are essential for the proper functioning of multiple organs. In the liver, cholangiocytes and hepatic progenitor cells (HPCs) are the main cells that produce SDF-1, and SDF-1 is thought to be essential for HPC-stimulated liver regeneration.

AIMS

In this study, CXCR4 conditionally targeted mice were used to analyze the role of SDF-1 in chronically damaged liver.

METHODS

Chronic liver damage was induced in MxCre CXCR4(f/null) mice and the control MxCre CXCR4(f/wt) mice by CCl(4). Serum markers were analyzed to assess liver function and damage, the number of cytokeratin-positive cells as a measure of HPCs, and the extent of liver fibrosis. Additional parameters relating to liver damage, such as markers of HPCs, liver function, MMPs, and TIMPs were measured by real-time PCR.

RESULTS

Serum ALT was significantly higher in MxCre CXCR4(f/null) mice than MxCre CXCR4(f/wt) mice. The number of cytokeratin-positive cells and the area of fibrosis were also increased in the MxCre CXCR4(f/null) mice. The expression of mRNAs for several markers related to hepatic damage and regeneration was also increased in the liver of MxCre CXCR4(f/null) mice, including primitive HPC marker prominin-1, MMP9, TNF-α, and α-SMA.

CONCLUSIONS

MxCre CXCR4(f/null) mice were susceptible to severe chronic liver damage, suggesting that SDF-1-CXCR4 signals are important for liver regeneration and preventing the progression of liver disease. Modulation of SDF-1 may therefore be a promising treatment strategy for patients with chronic liver disease.

Organotypic liver culture models: meeting current challenges in toxicity testing

Prediction of chemical-induced hepatotoxicity in humans from in vitro data continues to be a significant challenge for the pharmaceutical and chemical industries. Generally, conventional in vitro hepatic model systems (i.e. 2-D static monocultures of primary or immortalized hepatocytes) are limited by their inability to maintain histotypic and phenotypic characteristics over time in culture, including stable expression of clearance and bioactivation pathways, as well as complex adaptive responses to chemical exposure. These systems are less than ideal for longer-term toxicity evaluations and elucidation of key cellular and molecular events involved in primary and secondary adaptation to chemical exposure, or for identification of important mediators of inflammation, proliferation and apoptosis. Progress in implementing a more effective strategy for in vitro-in vivo extrapolation and human risk assessment depends on significant advances in tissue culture technology and increasing their level of biological complexity. This article describes the current and ongoing need for more relevant, organotypic in vitro surrogate systems of human liver and recent efforts to recreate the multicellular architecture and hemodynamic properties of the liver using novel culture platforms. As these systems become more widely used for chemical and drug toxicity testing, there will be a corresponding need to establish standardized testing conditions, endpoint analyses and acceptance criteria. In the future, a balanced approach between sample throughput and biological relevance should provide better in vitro tools that are complementary with animal testing and assist in conducting more predictive human risk assessment.

Tissue engineering and regenerative medicine: history, progress, and challenges

The past three decades have seen the emergence of an endeavor called tissue engineering and regenerative medicine in which scientists, engineers, and physicians apply tools from a variety of fields to construct biological substitutes that can mimic tissues for diagnostic and research purposes and can replace (or help regenerate) diseased and injured tissues. A significant portion of this effort has been translated to actual therapies, especially in the areas of skin replacement and, to a lesser extent, cartilage repair. A good amount of thoughtful work has also yielded prototypes of other tissue substitutes such as nerve conduits, blood vessels, liver, and even heart. Forward movement to clinical product, however, has been slow. Another offshoot of these efforts has been the incorporation of some new exciting technologies (e.g., microfabrication, 3D printing) that may enable future breakthroughs. In this review we highlight the modest beginnings of the field and then describe three application examples that are in various stages of development, ranging from relatively mature (skin) to ongoing proof-of-concept (cartilage) to early stage (liver). We then discuss some of the major issues that limit the development of complex tissues, some of which are fundamentals-based, whereas others stem from the needs of the end users.

Hypothesis

Circannual rhythms are innately timed long-term (tau ≈ 12 months) cycles of physiology and behavior, crucial for life in habitats ranging from the equator to the Poles. Here the authors propose that circannual rhythm generation depends on tissue-autonomous, reiterated cycles of cell division, functional differentiation, and cell death. They see the feedback control influencing localized stem cell niches as crucial to this cyclical histogenesis hypothesis. Analogous to multi-oscillator circadian organization, circannual rhythm generation occurs in multiple tissues with hypothalamic and pituitary sites serving as central pacemakers. Signals including day length, nutrition, and social factors can synchronize circannual rhythms through hormonal influences, notably via the thyroid and glucocorticoid axes, which have profound effects on histogenesis. The authors offer 4 arguments in support of this hypothesis: (1) Cyclical histogenesis is a prevalent process in seasonal remodeling of physiology. It operates over long time domains and exhibits tissue autonomy in its regulation. (2) Experiments in which selected peripheral endocrine signals are held constant indicate that circannual rhythms are not primarily the product of interacting hormonal feedback loops. (3) Hormones known to control cell proliferation, differentiation, and organogenesis profoundly affect circannual rhythm expression. (4) The convergence point between photoperiodic input pathways and circannual rhythm expression occurs in histogenic regions of the hypothalamus and pituitary. In this review, the authors discuss how testing this hypothesis will depend on the use of cellular/molecular tools and animal models borrowed from developmental biology and neural stem cell research.

Developmental definition of MSCs: new insights into pending questions

Mesenchymal stem cells (MSCs) are a rare heterogeneous population of multipotent cells that can be isolated from many different adult and fetal tissues. They exhibit the capacity to give rise to cells of multiple lineages and are defined by their phenotype and functional properties, such as spindle-shaped morphology, adherence to plastic, immune response modulation capacity, and multilineage differentiation potential. Accordingly, MSCs have a wide range of promising applications in the treatment of autoimmune diseases, tissue repair, and regeneration. Recent studies have shed some light on the exact identity and native distribution of MSCs, whereas controversial results are still being reported, indicating the need for further review on their definition and origin. In this article, we summarize the important progress and describe some of our own relevant work on the developmental definition of MSCs.

A review on the therapeutic potential of embryonic and induced pluripotent stem cells in hepatic repair

Despite the liver being proliferatively quiescent, it maintains balance between cell gain and cell loss, invokes a rapid regenerative response following hepatocyte loss, and restores liver mass. Human liver has immense regenerative capacity. Liver comprises many cell types with specialized functions. Of these cell types, hepatocytes play several key roles, but are most vulnerable to damage. Recent studies suggest that the extrahepatic stem cell pool contributes to liver regeneration. Stem cell therapies have the potential to enhance hepatic regeneration. Both embryonic and induced pluripotent stem cells could be a suitable source to regenerate hepatocytes. In the present review, we discuss the therapeutic potential of stem cells in hepatic repair and focus on the clinical applications of stem cells.

Growth ability and repopulation efficiency of transplanted hepatic stem cells, progenitor cells, and mature hepatocytes in retrorsine-treated rat livers

Cell-based therapies as an alternative to liver transplantation have been anticipated for the treatment of potentially fatal liver diseases. Not only mature hepatocytes (MHs) but also hepatic stem/progenitor cells are considered as candidate cell sources. However, whether the stem/progenitor cells have an advantage to engraft and repopulate the recipient liver compared with MHs has not been comprehensively assessed. Therefore, we used Thy1(+) (oval) and CD44(+) (small hepatocytes) cells isolated from GalN-treated rat livers as hepatic stem and progenitor cells, respectively. Cells from dipeptidylpeptidase IV (DPPIV)(+) rat livers were transplanted into DPPIV(-) livers treated with retrorsine following partial hepatectomy. Both stem and progenitor cells could differentiate into hepatocytes in host livers. In addition, the growth of the progenitor cells was faster than that of MHs until days 14. However, their repopulation efficiency in the long term was very low, since the survival period of the progenitor cells was much shorter than that of MHs. Most foci derived from Thy1(+) cells disappeared within 2 months. Many cells expressed senescence-associated β-galactosidase in 33% of CD44-derived foci at day 60, whereas the expression was observed in 13% of MH-derived ones. The short life of the cells may be due to their cellular senescence. On the other hand, the incorporation of sinusoidal endothelial cells into foci and sinusoid formation, which might be correlated to hepatic maturation, was completed faster in MH-derived foci than in CD44-derived ones. The survival of donor cells may have a close relation to not only early integration into hepatic plates but also the differentiated state of the cells at the time of transplantation.

In vitro trans-differentiation of human umbilical cord derived hematopoietic stem cells into hepatocyte like cells using combination of growth factors for cell based therapy

The aim of the study was to develop a new strategy for the differentiation of hematopoietic stem cell (HSC) derived from UCB into hepatocyte like cells and also to estimate the effects of combination of fibroblast growth factor 4 (FGF 4) and hepatocyte growth factor (HGF) on hematopoietic stem cell differentiation. HSCs were isolated and purified by magnetic activated cell sorting. HSCs were induced to hepatocyte like cells under a 2-step protocol with combination of growth factors. Reverse transcription polymerase chain reaction was performed to detect multiple genes related to hepatocyte like cells development and function. Hepatocyte like morphology was illustrated by inverted repeat microscope and the secretion of albumin and α- fetoprotein by these cells was confirmed by enzyme linked immunosorbent assay. Hepatocyte like cells was observed at the end of the protocol (days 14). These differentiated cells were observed to show high expression of genes related to hepatocytes (tryptophan 2, 3-dioxygenase [TO], glucose 6-phosphate [G6P], cytokeratin 18 [CK 18], albumin and α- fetoprotein [AFP]). The quantities of albumin and AFP at day 0 were low and upon differentiation the cells were able to produce albumin and AFP at high levels. Our results show a new strategy for differentiation in a short duration, using a combination of growth factors for the differentiation of umbilical cord blood derived HSC into hepatocyte like cells under certain in vitro conditions. After further studies this approach has the potency, for widespread cell replacement therapy for liver diseases.

Mobilization of hepatic mesenchymal stem cells from human liver grafts

Extensive studies have demonstrated the potential applications of bone marrow-derived mesenchymal stem cells (BM-MSCs) as regenerative or immunosuppressive treatments in the setting of organ transplantation. The aims of the present study were to explore the presence and mobilization of mesenchymal stem cells (MSCs) in adult human liver grafts and to compare their functional capacities to those of BM-MSCs. The culturing of liver graft preservation fluids (perfusates) or end-stage liver disease tissues resulted in the expansion of MSCs. Liver-derived mesenchymal stem cells (L-MSCs) were equivalent to BM-MSCs in adipogenic and osteogenic differentiation and in wingless-type-stimulated proliferative responses. Moreover, the genome-wide gene expression was very similar, with a 2-fold or greater difference found in only 82 of the 32,321 genes (0.25%). L-MSC differentiation into a hepatocyte lineage was demonstrated in immunodeficient mice and in vitro by the ability to support a hepatitis C virus infection. Furthermore, a subset of engrafted MSCs survived over the long term in vivo and maintained stem cell characteristics. Like BM-MSCs, L-MSCs were found to be immunosuppressive; this was shown by significant inhibition of T cell proliferation. In conclusion, the adult human liver contains an MSC population with a regenerative and immunoregulatory capacity that can potentially contribute to tissue repair and immunomodulation after liver transplantation.

Critical appraisal of ex vivo expansion of human limbal epithelial stem cells

The stem cells (SCs) of the corneal epithelium located in the limbal basal layer are the ultimate source to maintain corneal epithelial homeostasis. Like other adult tissue-specific SCs, self renewal and fate decision of limbal SCs are regulated by a specialized in vivo microenvironment, termed "niche". Loss of limbal SCs or dysfunction of the limbal niche renders corneas with a unique clinical disease labeled limbal stem cell deficiency (LSCD). Besides transplantation of autologous or allogeneic limbal SCs or amniotic membrane, a new strategy of treating LSCD is to transplant a bio-engineered graft by expanding limbal SCs ex vivo. Herein, we conduct a critical appraisal of six protocols that have successfully been practiced in treating human patients with LSCD, and identify issues whether niche regulation has been disrupted or maintained during isolation and expansion. Consequently, we propose a future direction that may circumvent the potential pitfalls existing in these conventional protocols by preserving the interaction between limbal SCs and their native niche cells during isolation and expansion. Such an approach may one day help realize considerable promise held by adult SCs in treating a number of diseases.

Stem cells and their implications for colorectal cancer

The colonic crypt is home to several multipotent stem cells. These stem cells reside in a niche at the base of the crypt, which controls their behavior and maintains the stem cell's homeostasis through a variety of signaling pathways and interactions. Several attempts have been made to define markers that can identify colonic stem cells, the most useful of which is Lgr5, a Wnt target gene. Although the crypt base contains several stem cells, each colonic crypt comprises a single clone of cells. Investigators have attempted to reconcile these apparently contradictory observations by conducting research into stem cell division. The propagation of stem-cell-acquired mutations through a crypt results in a monocryptal adenoma that, through crypt fission, develops into a microadenoma. Some early adenomas become polyclonal through an as yet unknown mechanism. The discovery of subpopulations of cancer cells that can initiate tumors when implanted into mice has renewed interest in the existence of cancer stem cells, especially with regard to their implications for the use of chemotherapy. Various potential markers of cancer stem cells have been investigated, particularly CD133, but the cancer stem cell theory still has some limitations.

Autologous bone marrow infusion activates the progenitor cell compartment in patients with advanced liver cirrhosis

Several clinical trials of bone marrow cell infusion in patients with liver cirrhosis (LC) have shown clinical improvement, despite conflicting results from animal models. We investigated serial pathological features and the clinical impact after autologous bone marrow infusion (ABMI) in patients with advanced LC. Ten patients with advanced LC due to chronic hepatitis B virus infection underwent ABMI. Serological tests, MRI, and liver biopsies were performed, and quality of life was assessed by a questionnaire. Median serum albumin and hemoglobin levels increased significantly after ABMI. All patients showed an improvement in quality of life, with no serious adverse events. Liver volume, measured by MRI, increased in 80% of the patients, and ascites decreased after ABMI. Child-Pugh scores were also significantly improved at 6 months after ABMI. In the serially biopsied livers, a gradually increasing activation of the hepatic progenitor cell (HPC) compartment, including HPC activation (ductular reaction) and HPC differentiation (intermediate hepatocyte), reached a peak after 3 months, with continued proliferation of hepatocytes, and returned to baseline levels after 6 months. There was no significant change in grade or stage of liver fibrosis or stellate cell activation after ABMI. ABMI is suggested to improve liver function and to activate the progenitor cell compartment. Although clinical improvement was sustained for more than 6 months, histological changes in the liver returned to baseline 6 months after ABMI. Further comparative studies are warranted.

Human Fetal Liver-Derived Stem Cell Transplantation as Supportive Modality in the Management of End-Stage Decompensated Liver Cirrhosis

Liver transplantation is the only existing modality for treating decompensated liver cirrhosis. Several factors, such as nonavailability of donors, combined with operative risks, complications associated with rejection, usage of immunosuppressive agents, and cost intensiveness, make this strategy available to only a few people. With a tremendous upsurge in the mortality rate of patients with liver disorders worldwide, there is a need to search for an alternative therapeutic tool that can combat the above limitations and serve as a supportive therapy in the management of liver diseases. Cell therapy using human fetal liver-derived stem cells can provide great potential to conservatively manage end-stage liver diseases. Therefore, the present investigation aimed to study and prove the safety and efficacy of human fetal liver-derived stem cell transplantation in patients with end-stage liver cirrhosis. Twenty-five patients with liver cirrhosis of different etiologies were infused with human fetal liver-derived stem cells (EpCAM+ve) labeled with Tc-HMPAO through hepatic artery. Our high throughput analysis using flow cytometry, RT-PCR, and cellular characterization exemplifies fetal liver cells with their high proliferation rate could be the best source for rejuvenating the diseased liver. Further, no episodes related to hepatic encephalopathy recurred in any of the subjects following hepatic stem cell transplantation. There was marked clinical improvement observed in terms of all clinical and biochemical parameters. Further, there was decrease in mean MELD score ( p < 0.01) observed in 6 months follow-up in all patients. Therapy using human fetal liver stem/progenitor cells offers a potentially supportive modality to organ transplantation in the management of liver diseases.

Scopolamine treatment and muscarinic receptor subtype-3 gene ablation augment azoxymethane-induced murine liver injury

Previous work suggests that vagus nerve disruption reduces hepatocyte and oval cell expansion after liver injury. The role of postneuronal receptor activation in response to liver injury has not been ascertained. We investigated the actions of scopolamine, a nonselective muscarinic receptor antagonist, and specific genetic ablation of a key cholinergic receptor, muscarinic subtype-3 (Chrm3), on azoxymethane (AOM)-induced liver injury in mice. Animal weights and survival were measured as was liver injury using both gross and microscopic examination. To assess hepatocyte proliferation and apoptosis, ductular hyperplasia, and oval cell expansion, we used morphometric analysis of 5-bromo-2'-deoxyuridine-, activated caspase-3-, hematoxylin and eosin-, cytokeratin-19-, and epithelial cell adhesion molecule-stained liver sections. Sirius red staining was used as a measure of collagen deposition and its association with oval cell reaction. In AOM-treated mice, both muscarinic receptor blockade with scopolamine and Chrm3 ablation attenuated hepatocyte proliferation and augmented gross liver nodularity, apoptosis, and fibrosis. Compared with control, scopolamine-treated and Chrm3(-/-) AOM-treated mice had augmented oval cell reaction with increased ductular hyperplasia and oval cell expansion. Oval cell reaction correlated robustly with liver fibrosis. No liver injury was observed in scopolamine-treated and Chrm3(-/-) mice that were not treated with AOM. Only AOM-treated Chrm3(-/-) mice developed ascites and had reduced survival compared with AOM-treated wild-type controls. In AOM-induced liver injury, inhibiting postneuronal cholinergic muscarinic receptor activation with either scopolamine treatment or Chrm3 gene ablation results in prominent oval cell reaction. We conclude that Chrm3 plays a critical role in the liver injury response by modulating hepatocyte proliferation and apoptosis.

Involvement of extracellular matrix protein matrilin-2 in oval cell-mediated rat liver regeneration

AIM: To investigate possible involvement of extracellular matrix (ECM) protein matrilin-2 in oval cell-mediated liver regeneration in rats.

METHODS: A rat model of hepatic oval cell proliferation was established using the modified Soft-Farber protocol. The control group was fed normal saline. On days 2, 4, 6, 9, 12 and 15 after partial hepatectomy (PH), rat liver tissue samples were collected. The dynamic relationship between matrilin-2 protein expression and oval cell distribution during the proliferation and differentiation of oval cells was analyzed using immunohistochemistry and Western blot.

RESULTS: On day 2 after PH, oval cells began to proliferate around the portal area, and matrilin-2 deposition was observed in the hepatic sinusoids in the periportal area. On day 9, proliferating oval cells were present in the hepatic acini, and matrilin-2 upregulation was noted. On day 12, as oval cells differentiated to form hepatocellular nodules, matrilin-2 was distributed mainly in the periphery of the nodules, and little protein was present in the nodules. The expression level of matrilin-2 protein began to be upregulated on day 2 after PH, and reached the peak on day 9. After day 12, the protein level returned to physiological level.

CONCLUSION: The close relationship between matrilin-2 expression and oval cell distribution suggests a role for the protein in stem cell-fed liver regeneration.

The quest for liver progenitor cells: a practical point of view

Many chronic liver diseases can lead to hepatic dysfunction with organ failure. At present, orthotopic liver transplantation represents the benchmark therapy of terminal liver disease. However this practice is limited by shortage of donor grafts, the need for lifelong immunosuppression and very demanding state-of-the-art surgery. For this reason, new therapies have been developed to restore liver function, primarily in the form of hepatocyte transplantation and artificial liver support devices. While already offered in very specialized centers, both of these modalities still remain experimental. Recently, liver progenitor cells have shown great promise for cell therapy, and consequently they have attracted a lot of attention as an alternative or supportive tool for liver transplantation. These liver progenitor cells are quiescent in the healthy liver and become activated in certain liver diseases in which the regenerative capacity of mature hepatocytes and/or cholangiocytes is impaired. Although reports describing liver progenitor cells are numerous, they have not led to a consensus on the identity of the liver progenitor cell. In this review, we will discuss some of the characteristics of these cells and the different ways that have been used to obtain these from rodents. We will also highlight the challenges that researchers are facing in their quest to identify and use liver progenitor cells.

Thy1-positive cells have bipotential ability to differentiate into hepatocytes and biliary epithelial cells in galactosamine-induced rat liver regeneration

In galactosamine (GalN)-induced rat liver injury, hepatic stem/progenitor cells, small hepatocytes (SHs) and oval cells, transiently appear in the initial period of liver regeneration. To clarify the relationship between SHs and oval cells, CD44(+) and Thy1(+) cells were sorted from GalN-treated livers and used as candidates for SHs and oval cells, respectively. Some Thy1(+) cells isolated 3 days after GalN-treatment (GalN-D3) formed CD44(+) cell colonies, but those from GalN-D2 could form few. GeneChip (Affymetrix, Inc, Santa Clara, CA) analysis of the sorted cells and cultured Thy1(+) cells suggested that hepatocytic differentiation progressed in the order Thy1(+) (GalN-D3), Thy1(+) cell colony (Thy1-C), and CD44(+) (GalN-D4) cells. When Thy1(+), Thy1-C, and CD44(+) cells were transplanted into retrorsine/PH rat livers, they could proliferate to form hepatocytic foci. At 30 days after transplantation most cells forming the foci derived from CD44(+) cells possessed C/EBPalpha(+) nuclei, whereas only a few cells derived from Thy1-C showed this positivity. When Thy1(+) (GalN-D3) cells were cultured between collagen gels in medium with hepatocyte growth factor(+)/dexamethasone(-)/dimethyl sulfoxide(-), ducts/cysts consisting of biliary epithelial cells appeared, whereas with CD44(+) and Thy1(+) (GalN-D2) cells they did not. Taken together, these results indicate that the commitment of Thy1(+) cells to differentiate into hepatocytes or biliary epithelial cells may occur between Day 2 and Day 3. Furthermore, some Thy1(+) cells may differentiate into hepatocytes via CD44(+) SHs.

Cross-species immunohistochemical investigation of the activation of the liver progenitor cell niche in different types of liver disease

BACKGROUND

When hepatocyte replication during liver disease is insufficient for regeneration, liver progenitor cells (LPCs) are activated. The cells and stroma in the immediate environment of LPCs, together termed the LPC niche, are thought to play an important role in this activation. Among these cells are the hepatic stellate cells (HSCs)/myofibroblasts (MFs).

AIMS/METHODS

We assessed the activation of HSC/MFs and LPCs in relation to the histological location and extent of liver disease in immunohistochemically (double) stained serial sections. Markers of HSC/MFs [alpha-smooth muscle actin, glial fibrillary acidic protein (GFAP), neurotrophin 3 and neural-cell adhesion molecule], markers of LPCs (keratin 7 and keratin 19) and a proliferation marker (Ki67) were used. A very relevant spontaneous model to evaluate LPC niche activation in a translational approach seems to be the dog. Therefore, both human and canine liver diseases with different degree of fibrosis and disease activity were included.

RESULTS

In human and canine liver disease, type and extent of LPC niche activation depended on type and severity of disease (P<0.05) and corresponded to the main location of disease. Activated HSCs surrounded the activated LPCs. In chronic hepatitis and non-alcoholic steatohepatitis lobular-type HSCs were activated, while during biliary disease portal/septal MFs were mainly activated. In canine liver, GFAP further presented as an early marker of HSC activation. Activation of the LPCs correlated with disease location and severity (P<0.01), and was inversely related to hepatocyte proliferation, as was previously shown in man.

CONCLUSION

A shared involvement of HSC/MFs, LPCs and disease severity during hepatic disease processes is shown, which is highly similar in man and dog.

Stem cells and solid cancers

Recently, there have been significant advances in our knowledge of stem cells found in tissues that can develop solid tumours. In particular, novel stem cell markers have been identified for the first time identifying multipotential cells: a required characteristic of a stem cell. The scarcity of cancer stem cells has been questioned. Current dogma states that they are rare, but novel research has suggested that this may not be the case. Here, we review the latest literature on stem cells, particularly cancer stem cells within solid tumours. We discuss current thinking on how stem cells develop into cancer stem cells and how they protect themselves from doing so and do they express unique markers that can be used to detect stem cells. We attempt to put into perspective these latest advances in stem cell biology and their potential for cancer therapy.

The dog liver contains a "side population" of cells with hepatic progenitor-like characteristics

The aim of this study was to isolate and characterize potential progenitor cells from healthy dog livers. Stem/progenitor cells can be prospectively isolated from a diversity of tissues using their ability to efficiently pump out the dye Hoechst33342, thereby portraying a side population (SP) in dual-wavelength flow cytometry. We here describe the detection of a SP in dog liver, constituting approximately 3 % of the nonparenchymal-enriched cell fractions. A subpopulation of the SP (approximately 30 %) was immunonegative for the panhematopoietic marker CD45, and consisted predominantly of small, mononuclear, keratin 7-immunoreactive cells; characteristics suggestive of a liver progenitor cell phenotype. Both the CD45- and CD45+ SP showed upregulated expression of progenitor/cholangiocyte marker genes, but also low-level expression of hepatocyte markers, suggesting the presence of progenitor cells committed to the hepatic lineage in both SP fractions. Our findings demonstrate that healthy canine liver contains a small population of cells with progenitor-like characteristics that can be isolated on the basis of efficient Hoechst33342 expulsion.

Intrahepatic transplantation of hepatic oval cells for fulminant hepatic failure in rats

AIM: To evaluate the effect of intrahepatic trans-plantation of hepatic oval cells (HOC) on fulminant hepatic failure (FHF) in rats.

METHODS: HOC obtained from rats were labeled with green fluocescent protein (GFP) or 5, 6-carboxyfluorescein diacetate succinmidyl ester (CFDA-SE). Cell fluorescence was observed under fluorescent microscope at 6, 24, 48 and 72 h after labeling. CFDA-SE labeled HOC (5 × 10⁶ cells each rat) were injected into livers of rats with FHF induced by D-galactosamine. Serum albumin (ALB), alanine aminotransferase (ALT), aspartate aminotransferase (AST) and total bilirubin (TBil) levels were measured at different time points. Liver function of rats was examined on days 3, 7, 14 and 21 after HOC transplantation.

RESULTS: The positive rate of GFP and CFDA-SE labeled HOC was 10% and 90%, respectively, with no significant change in cell viabilities. The survival rate was higher in HOC transplantation group than in control group, especially 48 (9/15 vs 6/15) and 72 h (9/15 vs 4/15) after HOC transplantation. The serum ALT, AST and TBil levels were decreased while the serum Alb level was increased after HOC transplantation. Fluorescence became faded and diffused in liver tissues, suggesting that proliferation and differentiation occur in transplanted HOC.

CONCLUSION: CFDA-SE is superior to GFP in labeling HOC, although fluorescence intensity is decreased progressively with cell division. HOC transplantation can improve the liver function and increase the survival rate of recipients.

From embryonic stem cells to blastema and MRL mice

New scientific knowledge offers fresh opportunities for regenerative medicine and tissue repair. Among various clinical options, multipotent embryonic stem cells (ESC) prepared from inner cell masses of rabbit blastocysts have been tested over many years. More recently, stem cells have been isolated from individual tissues and from umbilical cord blood. These methods seemingly offer similar rates of repair and avoid ethical complexities arising from the need for human embryos to prepare ESC. Different methods of regenerating tissues have now emerged, based on the well-known forms of organ regeneration in urodeles such as salamanders. These methods depend on the formation of a blastema, and recent studies on MRL mice have revealed that they possess similar methods of repair as in salamanders. There is also some evidence showing that this form of repair is also active in human fetuses but not in adults. Detailed knowledge of these various forms of tissue repair is now urgently needed in order to assess the benefits of each form of treatment. These matters are discussed at the end of this review where various investigations clarify the benefits and drawbacks of these varied approaches to tissue repair.