Hepatic stellate cells promote hepatocyte engraftment in rat liver after prostaglandin-endoperoxide synthase inhibition

Kupffer cells abrogate homing and repopulation of allogeneic hepatic progenitors in injured liver site

BACKGROUND

Allogeneic hepatocyte transplantation is an emerging approach to treat acute liver defects. However, durable engraftment of the transplanted cells remains a daunting task, as they are actively cleared by the recipient's immune system. Therefore, a detailed understanding of the innate or adaptive immune cells-derived responses against allogeneic transplanted hepatic cells is the key to rationalize cell-based therapies.

METHODS

Here, we induced an acute inflammatory regenerative niche (3-96 h) on the surface of the liver by the application of cryo-injury (CI) to systematically evaluate the innate immune response against transplanted allogeneic hepatic progenitors in a sustained micro-inflammatory environment.

RESULTS

The resulting data highlighted that the injured site was significantly repopulated by alternating numbers of innate immune cells, including neutrophils, monocytes and Kupffer cells (KCs), from 3 to 96 h. The transplanted allo-HPs, engrafted 6 h post-injury, were collectively eliminated by the innate immune response within 24 h of transplantation. Selective depletion of the KCs demonstrated a delayed recruitment of monocytes from day 2 to day 6. In addition, the intrasplenic engraftment of the hepatic progenitors 54 h post-transplantation was dismantled by KCs, while a time-dependent better survival and translocation of the transplanted cells into the injured site could be observed in samples devoid of KCs.

CONCLUSION

Overall, this study provides evidence that KCs ablation enables a better survival and integration of allo-HPs in a sustained liver inflammatory environment, having implications for rationalizing the cell-based therapeutic interventions against liver defects.

Cell therapy in end-stage liver disease: replace and remodel

Liver disease is prevalent worldwide. When it reaches the end stage, mortality rises to 50% or more. Although liver transplantation has emerged as the most efficient treatment for end-stage liver disease, its application has been limited by the scarcity of donor livers. The lack of acceptable donor organs implies that patients are at high risk while waiting for suitable livers. In this scenario, cell therapy has emerged as a promising treatment approach. Most of the time, transplanted cells can replace host hepatocytes and remodel the hepatic microenvironment. For instance, hepatocytes derived from donor livers or stem cells colonize and proliferate in the liver, can replace host hepatocytes, and restore liver function. Other cellular therapy candidates, such as macrophages and mesenchymal stem cells, can remodel the hepatic microenvironment, thereby repairing the damaged liver. In recent years, cell therapy has transitioned from animal research to early human studies. In this review, we will discuss cell therapy in end-stage liver disease treatment, especially focusing on various cell types utilized for cell transplantation, and elucidate the processes involved. Furthermore, we will also summarize the practical obstacles of cell therapy and offer potential solutions.

Cellular crosstalk during liver regeneration: unity in diversity

The liver is unique in its ability to regenerate from a wide range of injuries and diseases. Liver regeneration centers around hepatocyte proliferation and requires the coordinated actions of nonparenchymal cells, including biliary epithelial cells, liver sinusoidal endothelial cells, hepatic stellate cells and kupffer cells. Interactions among various hepatocyte and nonparenchymal cells populations constitute a sophisticated regulatory network that restores liver mass and function. In addition, there are two different ways of liver regeneration, self-replication of liver epithelial cells and transdifferentiation between liver epithelial cells. The interactions among cell populations and regenerative microenvironment in the two modes are distinct. Herein, we first review recent advances in the interactions between hepatocytes and surrounding cells and among nonparenchymal cells in the context of liver epithelial cell self-replication. Next, we discuss the crosstalk of several cell types in the context of liver epithelial transdifferentiation, which is also crucial for liver regeneration.

Transplanted hepatocytes rescue mice in acetaminophen-induced acute liver failure through paracrine signals for hepatic ATM and STAT3 pathways

Acute liver failure constitutes a devastating condition that needs novel cell and molecular therapies. To elicit synergisms in cell types of therapeutic interest, we studied hepatocytes and liver sinusoidal endothelial in mice with acetaminophen-induced acute liver failure. The context of regenerative signals was examined by transplants in peritoneal cavity because it possesses considerable capacity and allows soluble signals to enter the systemic circulation. Whereas transplanted hepatocytes and liver sinusoidal endothelial cells engrafted in peritoneal cavity, only the former could rescue mice in liver failure by improving injury outcomes, activating hepatic DNA damage repair, and inducing liver regeneration. The cytokines secreted by donor hepatocytes or liver sinusoidal endothelial cells differed and in hepatocytes from mice undergoing acetaminophen toxicity major cytokines were even rendered deficient (eg, G-CSF, VEGF, and others). Significantly, recapitulating hepatotoxicity-related DNA damage response in cultured cells identified impairments in ATM and JAK/STAT3 intersections since replacing cytokines produced less from injured hepatocytes restored these pathways to avoid acetaminophen hepatotoxicity. Similarly, hepatocyte transplantation in acute liver failure restored ATM and JAK/STAT3 pathways to advance DNA damage/repair and liver regeneration. The unexpected identification of novel hepatic G-CSF receptor expression following injury allowed paradigmatic studies of G-CSF supplementation to confirm the centrality of this paracrine ATM and STAT3 intersection. Remarkably, DNA damage/repair and hepatic regeneration directed by G-CSF concerned rebalancing of regulatory gene networks overseeing inflammation, metabolism, and cell viability. We conclude that healthy donor hepatocytes offer templates for generating specialized cell types to replace metabolic functions and regenerative factors in liver failure.

Hepatic Stellate Cell Regulation of Liver Regeneration and Repair

The hepatic mesenchyme has been studied extensively in the context of liver fibrosis; however, much less is known regarding the role of mesenchymal cells during liver regeneration. As our knowledge of the cellular and molecular mechanisms driving hepatic regeneration deepens, the key role of the mesenchymal compartment during the regenerative response has been increasingly appreciated. Single-cell genomics approaches have recently uncovered both spatial and functional zonation of the hepatic mesenchyme in homeostasis and following liver injury. Here we discuss how the use of preclinical models, from in vivo mouse models to organoid-based systems, are helping to shape our understanding of the role of the mesenchyme during liver regeneration, and how these approaches should facilitate the precise identification of highly targeted, pro-regenerative therapies for patients with liver disease.

Tumor Necrosis Factor Directs Allograft-Related Innate Responses and Its Neutralization Improves Hepatocyte Engraftment in Rats

The innate immune system plays a critical role in allograft rejection. Alloresponses involve numerous cytokines, chemokines, and receptors that cause tissue injury during rejection. To dissect these inflammatory mechanisms, we developed cell transplantation models in dipeptidylpeptidase-deficient F344 rats using mycophenolate mofetil and tacrolimus for partial lymphocyte-directed immunosuppression. Syngeneic hepatocytes engrafted in liver, whereas allogeneic hepatocytes were rejected but engrafted after immunosuppression. These transplants induced mRNAs for >40 to 50 cytokines, chemokines, and receptors. In allografts, innate cell type-related regulatory networks extended to granulocytes, monocytes, and macrophages. Activation of Tnfa and its receptors or major chemokine receptor-ligand subsets persisted in the long term. An examination of the contribution of Tnfa in allograft response revealed that it was prospectively antagonized by etanercept or thalidomide, which resolved cytokine, chemokine, and receptor cascades. In bioinformatics analysis of upstream regulator networks, the Cxcl8 pathway exhibited dominance despite immunosuppression. Significantly, Tnfa antagonism silenced the Cxcl8 pathway and decreased neutrophil and Kupffer cell recruitment, resulting in multifold greater engraftment of allogeneic hepatocytes and substantially increased liver repopulation in retrorsine/partial hepatectomy model. We conclude that Tnfa is a major driver for persistent innate immune responses after allogeneic cells. Neutralizing Tnfa should help in avoiding rejection and associated tissue injury in the allograft setting.

Alternative Cell Sources for Liver Parenchyma Repopulation: Where Do We Stand?

Acute and chronic liver failure is a highly prevalent medical condition with high morbidity and mortality. Currently, the therapy is orthotopic liver transplantation. However, in some instances, chiefly in the setting of metabolic diseases, transplantation of individual cells, specifically functional hepatocytes, can be an acceptable alternative. The gold standard for this therapy is the use of primary human hepatocytes, isolated from livers that are not suitable for whole organ transplantations. Unfortunately, primary human hepatocytes are scarcely available, which has led to the evaluation of alternative sources of functional hepatocytes. In this review, we will compare the ability of most of these candidate alternative cell sources to engraft and repopulate the liver of preclinical animal models with the repopulation ability found with primary human hepatocytes. We will discuss the current shortcomings of the different cell types, and some of the next steps that we believe need to be taken to create alternative hepatocyte progeny capable of regenerating the failing liver.

Cellular cytokine receptor signaling and ATM pathway intersections affect hepatic DNA repair

Pathways involving ataxia telangiectasia mutated (ATM) gene and its downstream partners and effectors are critical for the DNA damage response. Cell survival, proliferation and tissue homeostasis are dependent upon preservation of DNA integrity but additional intracellular mechanisms contribute in these processes. As receptor-mediated signaling with beneficial intersections in ATM pathways could have therapeutic significance, we interrogated such intersections with assays using HuH-7 cells (hepatocytes). These cells were subjected to acetaminophen toxicity, which is a leading cause of hepatic injury and acute liver failure in people. The ATM pathway was examined in HuH-7-ATM-Prom-tdT cells containing fluorescent td-Tomato transgene reporter for ATM promoter activity. Titrated doses of specific growth factors were used as ligands for receptor-mediated signaling. The contribution of JAK/STAT3 signaling was defined by the loss-of-function approach with the JAK antagonist, ruxolitinib. In these assays, impairment in ATM-related DNA damage response following acetaminophen toxicity was ameliorated by selected growth factors, including fibroblast growth factors, granulocyte colony stimulating factor and vascular endothelial growth factor. The JAK/STAT3 signaling was exclusive to granulocyte colony stimulating factor but concerned additional pathways in cases of other growth factors. Antagonism of JAK/STAT3 by ruxolitinib abrogated benefits in ATM pathway-mediated DNA repair; and identification of the ruxolitinib-sensitive component of cytoprotection allowed separations of these pathway intersections. Therefore, this subtractive approach for ATM and other regulators in pathways will be informative for DNA damage response. These mechanisms will benefit therapeutic development for ATM-related tissue and organ injuries.

Hepatic differentiation of human pluripotent stem cells by developmental stage-related metabolomics products

Endogenous cell signals regulate tissue homeostasis and are significant for directing the fate of stem cells. During liver development, cytokines released from various cell types are critical for stem/progenitor cell differentiation and lineage expansions. To determine mechanisms in these stage-specific lineage interactions, we modeled potential effects of soluble signals derived from immortalized human fetal liver parenchymal cells on stem cells, including embryonic and induced pluripotent stem cells. For identifying lineage conversion and maturation, we utilized conventional assays of cell morphology, gene expression analysis and lineage markers. Molecular pathway analysis used functional genomics approaches. Metabolic properties were analyzed to determine the extent of hepatic differentiation. Cell transplantation studies were performed in mice with drug-induced acute liver failure to elicit benefits in hepatic support and tissue regeneration. These studies showed signals emanating from fetal liver cells induced hepatic differentiation in stem cells. Gene expression profiling and comparison of regulatory networks in immature and mature hepatocytes revealed stem cell-derived hepatocytes represented early fetal-like stage. Unexpectedly, differentiation-inducing soluble signals constituted metabolomics products and not proteins. In stem cells exposed to signals from fetal cells, mechanistic gene networks of upstream regulators decreased pluripotency, while simultaneously inducing mesenchymal and epithelial properties. The extent of metabolic and synthetic functions in stem cell-derived hepatocytes was sufficient for providing hepatic support along with promotion of tissue repair to rescue mice in acute liver failure. During this rescue, paracrine factors from transplanted cells contributed in stimulating liver regeneration. We concluded that hepatic differentiation of pluripotent stem cells with metabolomics products will be significant for developing therapies. The differentiation mechanisms involving metabolomics products could have an impact on advancing recruitment of stem/progenitor cells during tissue homeostasis.

Efficient Reconstitution of Hepatic Microvasculature by Endothelin Receptor Antagonism in Liver Sinusoidal Endothelial Cells

Reconstitution of healthy endothelial cells in vascular beds offers opportunities for mechanisms in tissue homeostasis, organ regeneration, and correction of deficient functions. Liver sinusoidal endothelial cells express unique functions, and their transplantation is relevant for disease models and for cell therapy. As molecular targets for improving transplanted cell engraftment and proliferation will be highly significant, this study determined whether ET_A/B receptor antagonism by the drug bosentan could overcome cell losses due to cell transplantation-induced cytotoxicity. Cell engraftment and proliferation assays were performed with healthy wild-type liver sinusoidal endothelial cells transplanted into the liver of dipeptidylpeptidase IV knockout mice. Transplanted cells were identified in tissues by enzyme histochemistry. Cells with prospective ET_A/B antagonism engrafted significantly better in hepatic sinusoids. Moreover, these cells underwent multiple rounds of division under liver repopulation conditions. The gains of ET_A/B antagonism resulted from benefits in cell viability and membrane integrity. Also, in bosentan-treated cells, mitochondrial homeostasis was better maintained with less oxidative stress and DNA damage after injuries. Intracellular effects of ET_A/B antagonism were transduced by conservation of ataxia telangiectasia mutated protein, which directs DNA damage response. Therefore, ET_A/B antagonism in donor cells will advance vascular reconstitution. Extensive experience with ET_A/B antagonists will facilitate translation in people.

Cox-2 inhibition potentiates mouse bone marrow stem cell engraftment and differentiation-mediated wound repair

BACKGROUND

Engraftment of transplanted stem cells is often limited by cytokine and noncytokine proinflammatory mediators at the injury site. We examined the role of Cyclooxygenase-2 (Cox-2)-induced cytokine-mediated inflammation on engraftment of transplanted bone marrow stem cells (BMSCs) at the wound site.

METHODS

BMSCs isolated from male C57/BL6J mice were transplanted onto excisional splinting wounds in syngenic females in presence or absence of celecoxib, Cox-2 specific inhibitor (50 mg/kg, body weight [b wt]), to evaluate engraftment and wound closure. Inflammatory cell infiltration and temporal expression of inflammatory cytokines at the wound bed were determined using immunohistochemical and quantitative-real time polymerase chain reaction (qPCR) analysis, respectively. Mechanistic studies were performed on a murine macrophage cell line (J774.2) to evaluate the effect of interleukin (IL)-17A.

RESULTS

Celecoxib administration led to a significantly high percent of wound closure, cellular proliferation, collagen deposition, BMSCs engraftment and re-epithelialization at the wound site. Interestingly, recruitment of CD4⁺T cells and F4/80⁺ macrophages as well as BMSC transplantation induced up-regulation of Cox-2 and IL-17A gene expression levels were reverted by celecoxib administration. Exogenous supplementation of recombinant interleukin (rIL)-17 to J774.2 cells significantly increased proliferation and gene expression of cytokines -IL-1β, IL-6, IL-8, IL-18 and tumor necrosis factor (TNF)-α via nuclear translocation of nuclear factor kappa B (NFκB)p65/50 subunit. Conditioned media of rIL-17 treated J774.2 cells when supplemented to BMSCs depicted a dose-dependent increase in the number of apoptotic cells and proapoptotic protein expression that was perturbed by celecoxib or IL-17 neutralizing antibody. Finally, celecoxib led to a dose-dependent increase in BMSC differentiation into keratinocyte-like cells in vitro.

CONCLUSION

Celecoxib protects transplanted BMSCs from Cox-2/IL-17-induced inflammation and increases their engraftment, differentiation into keratinocytes and re-epithelialization thereby potentiating wound tissue repair.

Early activated hepatic stellate cell-derived paracrine molecules modulate acute liver injury and regeneration

The effects of paracrine action from early activated hepatic stellate cells (HSCs) on resident liver epithelium cells are not clear. Here, we investigated whether a systemic infusion of early activated HSC-derived paracrine factors (HSC-CM) would evoke an enhanced liver protective response in acetaminophen (APAP)-induced acute liver injury (ALI) in mice and explored the possible underlying mechanisms. The survival rate, liver injury, and liver regeneration were analyzed in mice with or without HSC-CM treatment in vivo. A systemic infusion of HSC-CM provided a significant survival benefit in APAP-induced ALI. HSC-CM therapy resulted in a reduction of hepatocellular death and increased numbers of both proliferating hepatocytes and adult hepatic progenitor cells (AHPCs) with up-regulation of liver regeneration relevant genes. The HSC-CM treatment reduced leukocyte infiltration and down-regulated systemic inflammation with decreases in IFN-γ, IL-1ra, IL-1β, TNF-α, and increases in IL-10. The direct anti-death and pro-regeneration effects of HSC-CM on AHPCs were demonstrated using in vitro assays. Treatment with HSC-CM promoted AHPCs proliferation and resulted in increased pAkt expression in vitro, and this effect was abolished by the PI3K/Akt inhibitor LY294002. These data provide evidence that early activated HSC-CM therapy offered trophic support to the acutely injured liver by inhibiting liver cell death and stimulating regeneration, potentially creating a new method for the treatment of ALI.

Thalidomide promotes transplanted cell engraftment in the rat liver by modulating inflammation and endothelial integrity

BACKGROUND & AIMS

For liver-directed cell therapy, efficient engraftment of transplanted cells is critical. This study delineated whether anti-inflammatory and endothelial disrupting properties of thalidomide could promote transplanted cell engraftment and proliferation in liver.

METHODS

We used dipeptidyl peptidase IV-deficient rats for cell transplantation studies, including gene expression analysis, morphological tissue analysis, serological assays, cell culture assays, and assays of transplanted cell engraftment and proliferation.

RESULTS

Thalidomide-pretreatment increased engraftment and proliferation of transplanted hepatocytes due to decreased inflammation. Moreover, thalidomide exacerbated cell transplantation-induced endothelial injury. This combined anti-inflammatory and endothelial injury effect of thalidomide was superior to the anti-inflammatory effect alone of repertaxin or etanercept, which block cytokines/chemokines/receptor-dependent inflammation. In thalidomide-pretreated animals, liver repopulation accelerated, including when cells were primed with bosentan to block endothelin-1 receptors.

CONCLUSIONS

Thalidomide improved transplanted cell engraftment and liver repopulation. Therefore, this class of drugs will advance applications of liver cell therapy in people.

LAY SUMMARY

This work aimed to develop effective drug treatments for improving engraftment of transplanted cells because that constitutes a critical step in rebuilding liver with healthy cells. Studies in animal models of cell transplantation led to identification of an old drug, thalidomide, which blocked inflammation and altered the liver microenvironment to yield superior engraftment and proliferation of transplanted cells. This will be appropriate for liver cell therapy in people.

Immunological aspects of liver cell transplantation

Within the field of regenerative medicine, the liver is of major interest for adoption of regenerative strategies due to its well-known and unique regenerative capacity. Whereas therapeutic strategies such as liver resection and orthotopic liver transplantation (OLT) can be considered standards of care for the treatment of a variety of liver diseases, the concept of liver cell transplantation (LCTx) still awaits clinical breakthrough. Success of LCTx is hampered by insufficient engraftment/long-term acceptance of cellular allografts mainly due to rejection of transplanted cells. This is in contrast to the results achieved for OLT where long-term graft survival is observed on a regular basis and, hence, the liver has been deemed an immune-privileged organ. Immune responses induced by isolated hepatocytes apparently differ considerably from those observed following transplantation of solid organs and, thus, LCTx requires refined immunological strategies to improve its clinical outcome. In addition, clinical usage of LCTx but also related basic research efforts are hindered by the limited availability of high quality liver cells, strongly emphasizing the need for alternative cell sources. This review focuses on the various immunological aspects of LCTx summarizing data available not only for hepatocyte transplantation but also for transplantation of non-parenchymal liver cells and liver stem cells.

Effects of small interfering RNA-mediated downregulation of the Krüppel-like factor 4 gene on collagen metabolism in human hepatic stellate cells

The nuclear transcription factor Krüppel-like factor 4 (KLF4) has an important role in cellular biological processes. However, the influence of KLF4 on collagen metabolism remains to be elucidated. In the present study, the effects and underlying mechanism of action of KLF4 on collagen metabolism was investigated in human hepatic stellate cells (HSC), by downregulating KLF4 expression using small interfering RNA (siRNA). The effects of KLF4 silencing by three predesigned siRNAs (siRNA1‑3) were evaluated using both reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blotting in the human LX2 HSC line. The mRNA expression levels of KLF4 were decreased by ~34, 40, and 69% in the siRNA1, siRNA2, and siRNA3 groups, respectively, as compared with the control group. These results were concordant with the protein expression levels of KLF4, as determined by western blot analysis. In the siRNA3 group, the quantity of type Ⅰ and type III collagen, and the expression levels of collagen metabolism proteins including matrix metalloproteinase‑1 (MMP‑1) and tissue inhibitors of metalloproteinases‑1 (TIMP‑1), were determined using both RT‑qPCR and western blotting. Both the mRNA and protein expression levels of type I and type III collagen were significantly decreased in the siRNA3 group, as compared with the control group. The mRNA and protein expression levels of TIMP‑1 were also significantly reduced in the siRNA3‑treated cells, whereas the mRNA and protein expression levels of MMP‑1 were significantly upregulated. Furthermore, KLF4 gene silencing significantly decreased the expression levels of numerous cytokines, including transforming grow factor‑β1, tumor necrosis factor‑α, and interleukin‑1β. The results of the present study provide evidence of siRNA‑mediated silencing of KLF4 expression, which may promote extracellular matrix (ECM) degradation, and inhibition of ECM synthesis. Therefore, KLF4 may be a promising target for the development of novel antifibrotic therapies.

Cell therapy for liver disease: From liver transplantation to cell factory

Work over several decades has laid solid foundations for the advancement of liver cell therapy. To date liver cell therapy in people has taken the form of hepatocyte transplantation for metabolic disorders with a hepatic basis, and for acute or chronic liver failure. Although clinical trials using various types of autologous cells have been implemented to promote liver regeneration or reduce liver fibrosis, clear evidence of therapeutic benefits have so far been lacking. Cell types that have shown efficacy in preclinical models include hepatocytes, liver sinusoidal endothelial cells, mesenchymal stem cells, endothelial progenitor cells, and macrophages. However, positive results in animal models have not always translated through to successful clinical therapies and more realistic preclinical models need to be developed. Studies defining the optimal repopulation by transplanted cells, including routes of cell transplantation, superior engraftment and proliferation of transplanted cells, as well as optimal immunosuppression regimens are required. Tissue engineering approaches to transplant cells in extrahepatic locations have also been proposed. The derivation of hepatocytes from pluripotent or reprogrammed cells raises hope that donor organ and cell shortages could be overcome in the future. Critical hurdles to be overcome include the production of hepatocytes from pluripotent cells with equal functional capacity to primary hepatocytes and long-term phenotypic stability in vivo.

Etanercept blocks inflammatory responses orchestrated by TNF-α to promote transplanted cell engraftment and proliferation in rat liver

Engraftment of transplanted cells is critical for liver-directed cell therapy, but most transplanted cells are rapidly cleared from liver sinusoids by proinflammatory cytokines/chemokines/receptors after activation of neutrophils or Kupffer cells (KCs). To define whether tumor necrosis factor alpha (TNF-α) served roles in cell-transplantation-induced hepatic inflammation, we used the TNF-α antagonist, etanercept (ETN), for studies in syngeneic rat hepatocyte transplantation systems. After cell transplantation, multiple cytokines/chemokines/receptors were overexpressed, whereas ETN before cell transplantation essentially normalized these responses. Moreover, ETN down-regulated cell-transplantation-induced intrahepatic release of secretory cytokines, such as high-mobility group box 1. These effects of ETN decreased cell-transplantation-induced activation of neutrophils, but not of KCs. Transplanted cell engraftment improved by several-fold in ETN-treated animals. These gains in cell engraftment were repeatedly realized after pretreatment of animals with ETN before multiple cell transplantation sessions. Transplanted cell numbers did not change over time, indicating absence of cell proliferation after ETN alone. By contrast, in animals preconditioned with retrorsine and partial hepatectomy, cell transplantation after ETN pretreatment significantly accelerated liver repopulation, compared to control rats.

CONCLUSION

TNF-α plays a major role in orchestrating cell-transplantation-induced inflammation through regulation of multiple cytokines/chemokines/receptor expression. Because TNF-α antagonism by ETN decreased transplanted cell clearance, improved cell engraftment, and accelerated liver repopulation, this pharmacological approach to control hepatic inflammation will help optimize clinical strategies for liver cell therapy.

Cell therapy to remove excess copper in Wilson's disease

To achieve permanent correction of Wilson's disease by a cell therapy approach, replacement of diseased hepatocytes with healthy hepatocytes is desirable. There is a physiological requirement for hepatic ATP7B-dependent copper (Cu) transport in bile, which is deficient in Wilson's disease, producing progressive Cu accumulation in the liver or brain with organ damage. The ability to repopulate the liver with healthy hepatocytes raises the possibility of cell therapy in Wilson's disease. Therapeutic principles included reconstitution of bile canalicular network as well as proliferation in transplanted hepatocytes, despite toxic amounts of Cu in the liver. Nonetheless, cell therapy studies in animal models elicited major differences in the mechanisms driving liver repopulation with transplanted hepatocytes in Wilson's disease versus nondiseased settings. Recently, noninvasive imaging was developed to demonstrate Cu removal from the liver, including after cell therapy in Wilson's disease. Such developments will help advance cell/gene therapy approaches, particularly by offering roadmaps for clinical trials in people with Wilson's disease.

Endothelin-1 receptor A blocker darusentan decreases hepatic changes and improves liver repopulation after cell transplantation in rats

Cell transplantation-induced hepatic ischemia and recruitment of vasoconstrictors (e.g., endothelin-1; Edn1) leads to clearance of transplanted cells and poses problems for liver repopulation. Therefore, we determined whether darusentan (DAR), which potently blocks Edn1 receptor type A, could benefit cell engraftment. We transplanted primary F344 rat hepatocytes with or without DAR in dipeptidyl peptidase IV-deficient rats. Analysis of microcirculatory events included hepatic ischemia, endothelial injury, including with gene expression arrays, and activations of Kupffer cells (KCs), neutrophils, or hepatic stellate cells (HSCs). The retrorsine-partial hepatectomy model was used for liver repopulation studies. Whether DAR was directly cytoprotective was examined in cultured rat hepatocytes or CFSC-8B rat HSCs. We found that DAR induced hepatic sinusoidal vasodilation, caused more transplanted cells to be deposited in liver parenchyma, and decreased hepatic ischemia and endothelial injury. This lessened perturbations in expression of endothelial biology genes, including regulators of vessel tone, inflammation, cell adhesion, or cell damage, versus drug-untreated controls. Moreover, in DAR-treated animals, cell transplantation-induced activation of KCs, albeit not of neutrophils, decreased, and fewer HSCs expressed desmin. In DAR-treated rats, improvements in cell engraftment led to greater extent of liver repopulation, compared to drug-untreated controls. In cell-culture assays, DAR did not stimulate release of cytoprotective factors, such as vascular endothelial growth factor, from HSCs. Moreover, DAR did not protect hepatocytes from tumor necrosis factor alpha- or oxidative stress-induced toxicity. Endothelin receptor A blockade in vitro did not improve engraftment of subsequently transplanted hepatocytes.

CONCLUSION

Systemic administration of DAR decreases hepatic ischemia-related events and thus indirectly improves cell engraftment and liver repopulation. This vascular mechanism may permit the development of combinatorial drug-based regimens to help optimize cell therapy.

Nonselective inhibition of prostaglandin-endoperoxide synthases by naproxen ameliorates acute or chronic liver injury in animals

The rising prevalence of hepatic injury due to toxins, metabolites, viruses, etc., necessitates development of further mechanisms for protecting the liver and for treating acute or chronic liver diseases. To examine whether inhibition of inflammation is directed by cyclo-oxygenase pathways, we performed animal studies with naproxen, which inhibits prostaglandin-endoperoxide synthases 1 and 2 and is in extensive clinical use. We administered carbon tetrachloride to induce acute liver injury and ligated the common bile duct to induce chronic liver injury in adult rats. These experimental manipulations produced abnormalities in liver tests, tissue necrosis, compensatory hepatocyte or biliary proliferation, and onset of fibrosis, particularly after bile duct ligation. After carbon tetrachloride-induced acute injury, naproxen decreased liver test abnormalities, tissue necrosis and compensatory hepatocellular proliferation. After bile duct ligation-induced chronic injury, naproxen decreased liver test abnormalities, tissue injury and compensatory biliary hyperplasia. Moreover, after bile duct ligation, naproxen-treated rats showed more periductular oval liver cells, which have been classified as hepatic progenitor cells. In naproxen-treated rats, we found greater expression in hepatic stellate cells and mononuclear cells of cytoprotective factors, such as vascular endothelial growth factor. The ability of naproxen to induce expression of vascular endothelial growth factor was verified in cell culture studies with CFSC-8B clone of rat hepatic stellate cells. Whereas assays for carbon tetrachloride toxicity using cultured primary hepatocytes established that naproxen was not directly cytoprotective, we found conditioned medium containing vascular endothelial growth factor from naproxen-treated CFSC-8B cells protected hepatocytes from carbon tetrachloride toxicity. Therefore, naproxen was capable of ameliorating toxic liver injury, which involved naproxen-induced release of physiological cytoprotective factors in nonparenchymal liver cells. Such drug-induced release of endogenous cytoprotectants will advance therapeutic development for hepatic injury.

Human Liver Progenitor Cells for Liver Repair

Because of their high proliferative capacity, resistance to cryopreservation, and ability to differentiate into hepatocyte-like cells, stem and progenitor cells have recently emerged as attractive cell sources for liver cell therapy, a technique used as an alternative to orthotopic liver transplantation in the treatment of various hepatic ailments ranging from metabolic disorders to end-stage liver disease. Although stem and progenitor cells have been isolated from various tissues, obtaining them from the liver could be an advantage for the treatment of hepatic disorders. However, the techniques available to isolate these stem/progenitor cells are numerous and give rise to cell populations with different morphological and functional characteristics. In addition, there is currently no established consensus on the tests that need to be performed to ensure the quality and safety of these cells when used clinically. The purpose of this review is to describe the different types of liver stem/progenitor cells currently reported in the literature, discuss their suitability and limitations in terms of clinical applications, and examine how the culture and transplantation techniques can potentially be improved to achieve a better clinical outcome.

Therapeutic liver repopulation for metabolic liver diseases: Advances from bench to bedside

Metabolic liver diseases are characterized by inherited defects in hepatic enzymes or other proteins with metabolic functions. Therapeutic liver repopulation (TLR), an approach of massive liver replacement by transplanted normal hepatocytes, could be used to provide the missing metabolic function elegantly. However, partial and transient correction of the underlying metabolic defects due to very few integrated donor cell mass remains the major obstacle for the effective and widespread use of this approach. Little engraftment and proliferation insufficiency lead to the poor outcome. This article reviews the advances in the mechanisms of initial engraftment and selective proliferation and suggests some effective treatment strategies, from pharmacological preconditioning to stem cell transplantation, to optimize liver repopulation with liver cell transplantation. Enhancing cell viability and plating efficiency, increasing sinusoidal spaces, regulation of sinusoidal endothelial cell barrier and controlling inflammatory reaction may promote initial cell engraftment. Liver-directed irradiation, reversible portal vein embolization and fetal liver stem/progenitor cell transplantation induce preferential proliferation of donor cells substantially without severe side-effects. Furthermore, it seems better to use combined approaches to achieve a high level of liver repopulation for the management of metabolic liver diseases.

Augmenter of liver regeneration improves therapeutic effect of hepatocyte homotransplantation in acute liver failure rats

Hepatocyte transplantation (HCT) is an available option on treatment for acute liver failure (ALF). However, short-term survival of engraftment and immunological rejections of recipient are major obstacles. Augmenter of liver regeneration (ALR) has cytoprotective and immunoregulatory effects in liver injury, and has been used in many experimental applications. In the present study, we investigated the potential effect and mechanism of recombinant human ALR (rhALR) on ALF rats treated with intraperitoneal HCT. ALF rats induced by d-galactosamine (GalN) were studied in vivo, and were intraperitoneal injected with or without hepatocytes and rhALR 24h after the induction. Animal survival, serum and ascites liver enzymes, tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were assessed. Histological examination was performed, and liver regeneration, apoptosis and immunological responses were identified by immunohistochemistry assay. Our results showed that rhALR promoted hepatocytes regeneration, attenuated liver injury and suppressed immunological responses. The ascites liver enzyme, serum and ascites pro-inflammatory cytokines (TNF-α, IL-1β), liver histological injury, apoptotic hepatocytes and activated immunocytes were significantly reduced in ALF rats treated with rhALR and HCT compared with those without rhALR. The proliferative and mitotic hepatocytes were markedly increased, and overall survival improved with rhALR. The administration of rhALR improved survival and promoted liver recovery in HCT treatment for ALF, which was associated with the role of proliferative promoter and immunosuppressor. This study suggests that co-treated with rhALR and HCT can provide a promising strategy for the treatment of ALF.

Directly acting drugs prostacyclin or nitroglycerine and endothelin receptor blocker bosentan improve cell engraftment in rodent liver

To optimize strategies for liver-directed cell therapy, prevention of initial transplanted cell losses is particularly important for subsequent liver repopulation. After cell transplantation in hepatic sinusoids, perturbations in hepatic microcirculation along with changes in various liver cell types are among the earliest changes. Therefore, for advancing further concepts in cell engraftment we studied vascular and related events in the liver after transplanting syngeneic hepatocytes into dipeptidyl peptidase IV-deficient rats. We treated rats with vascular drugs to define whether deleterious cell transplantation-induced events could be controlled followed by improvements in transplanted cell engraftment and proliferation. We found cell transplantation altered liver gene expression related to vessel tone, inflammation, cell adhesion, thrombosis, or tissue damage/remodeling. This was due to hepatic ischemia, endothelial injury, and activation of neutrophils, Kupffer cells, and hepatic stellate cells. Treatment of rats before cell transplantation with the angiotensin converting enzyme blocker, lisinopril, or angiotensin II receptor blocker, losartan, did not improve cell engraftment. By contrast, direct-acting nitroglycerine or prostacyclin improved cell engraftment and also kinetics of liver repopulation. These drugs lowered hepatic ischemia and inflammation, whereas pretreatment of rats with the dual endothelin-1 receptor blocker, bosentan, improved cell engraftment independently of hepatic ischemia or inflammation, without improving liver repopulation. However, incubation of hepatocytes with bosentan protected cells from cytokine toxicity in vitro and produced superior cell engraftment and proliferation in vivo.

CONCLUSION

Cell transplantation-induced changes in hepatic microcirculation contributed to transplanted cell clearances from liver. Vascular drugs, such as nitroglycerine, prostacyclin, and bosentan, offer opportunities for improving cell therapy results through superior cell engraftment and liver repopulation. Ongoing clinical use of these drugs will permit rapid translation of the findings in people.

Molecular perturbations restrict potential for liver repopulation of hepatocytes isolated from non-heart-beating donor rats

Organs from non-heart-beating donors are attractive for use in cell therapy. Understanding the nature of molecular perturbations following reperfusion/reoxygenation will be highly significant for non-heart-beating donor cells. We studied non-heart-beating donor rats for global gene expression with Affymetrix microarrays, hepatic tissue integrity, viability of isolated hepatocytes, and engraftment and proliferation of transplanted cells in dipeptidyl peptidase IV-deficient rats. In non-heart-beating donors, liver tissue was morphologically intact for >24 hours with differential expression of 1, 95, or 372 genes, 4, 16, or 34 hours after death, respectively, compared with heart-beating donors. These differentially expressed genes constituted prominent groupings in ontological pathways of oxidative phosphorylation, adherence junctions, glycolysis/gluconeogenesis, and other discrete pathways. We successfully isolated viable hepatocytes from non-heart-beating donors, especially up to 4 hours after death, although the hepatocyte yield and viability were inferior to those of hepatocytes from heart-beating donors (P < 0.05). Similarly, although hepatocytes from non-heart-beating donors engrafted and proliferated after transplantation in recipient animals, this was inferior to hepatocytes from heart-beating donors (P < 0.05). Gene expression profiling in hepatocytes isolated from non-heart-beating donors showed far greater perturbations compared with corresponding liver tissue, including representation of pathways in focal adhesion, actin cytoskeleton, extracellular matrix-receptor interactions, multiple ligand-receptor interactions, and signaling in insulin, calcium, wnt, Jak-Stat, or other cascades.

CONCLUSION

Liver tissue remained intact over prolonged periods after death in non-heart-beating donors, but extensive molecular perturbations following reperfusion/reoxygenation impaired the viability of isolated hepatocytes from these donors. Insights into molecular changes in hepatocytes from non-heart-beating donors offer opportunities for improving donor cell viability, which will advance the utility of non-heart-beating donor organs for cell therapy or other applications.

Improving the techniques for human hepatocyte transplantation: report from a consensus meeting in London

On September 6 and 7, 2009 a meeting was held in London to identify and discuss what are perceived to be current roadblocks to effective hepatocyte transplantation as it is currently practiced in the clinics and, where possible, to offer suggestions to overcome the blocks and improve the outcomes for this cellular therapy. Present were representatives of most of the active clinical hepatocyte transplant programs along with other scientists who have contributed substantial basic research to this field. Over the 2-day sessions based on the experience of the participants, numerous roadblocks or challenges were identified, including the source of cells for the transplants and problems with tracking cells following transplantation. Much of the discussion was focused on methods to improve engraftment and proliferation of donor cells posttransplantation. The group concluded that, for now, parenchymal hepatocytes isolated from donor livers remain the best cell source for transplantation. It was reported that investigations with other cell sources, including stem cells, were at the preclinical and early clinical stages. Numerous methods to modulate the immune reaction and vascular changes that accompany hepatocyte transplantation were proposed. It was agreed that, to obtain sufficient levels of repopulation of liver with donor cells in patients with metabolic liver disease, some form of liver preconditioning would likely be required to enhance the engraftment and/or proliferation of donor cells. It was reported that clinical protocols for preconditioning by hepatic irradiation, portal vein embolization, and surgical resection had been developed and that clinical studies using these protocols would be initiated in the near future. Participants concluded that sharing information between the groups, including standard information concerning the quality and function of the transplanted cells prior to transplantation, clinical information on outcomes, and standard preconditioning protocols, would help move the field forward and was encouraged.

Control of HBV replication by antiviral microRNAs transferred by lentiviral vectors for potential cell and gene therapy approaches

BACKGROUND

Because molecular mechanisms regulating host cell and virus interactions are not fully understood, we further defined roles of antiviral microRNAs (miRNAs) in HBV replication.

METHODS

We studied small interfering RNA sequences inserted into the miR-30 backbone in cell systems. Antiviral sequences were cloned into lentiviral vectors upstream of a green fluorescent protein reporter. Transduced cells included HepG2 or HepG2 2.2.15 cell lines and hTERT-FH-B fetal human liver cells. HBV replication was analysed by several assays.

RESULTS

In 2.2.15 cells treated with constructs primarily targeting HBV polymerase and surface antigen or HBV polymerase and X open reading frames, HBV core protein, HBV DNA and HBV RNA expression decreased. This antiviral effect was more pronounced when the two constructs were expressed together. Similarly, antiviral constructs decreased HBV replication in HepG2 cells transduced with adenoviral vector to express HBV. Although antiviral sequences were expressed in hTERT-FH-B cells, these cells were non-permissive for HBV, possibly owing to expression of miRNAs reported to inhibit HBV replication, whereas these miRNAs were absent in HepG2 cells. Expression of antiviral miRNAs did not affect cell viability or proliferation and no deleterious changes were observed in expression of native cellular miRNAs. Moreover, expression of antiviral miRNA did not affect engraftment and survival of transplanted cells in mice.

CONCLUSIONS

Identification of effective antiviral miRNAs and transfer of suitable constructs by lentiviral vectors will be helpful for pathophysiological studies of host cell-virus interactions. Simultaneously, this will advance potential mechanisms for cell/gene therapy in those afflicted with chronic hepatitis and refractory liver disease.