Direct and indirect contribution of human embryonic stem cell-derived hepatocyte-like cells to liver repair in mice

MicroRNA signatures associated with thioacetamide-induced liver fibrosis in mice

Multiple etiologies of liver injury are associated with fibrosis in which the key event is the activation of hepatic stellate cells (HSCs). Although microRNAs (miRNAs) are reportedly involved in fibrogenesis, the complete array of miRNA signatures associated with the disease has yet to be elucidated. Here, deep sequencing analysis revealed that compared to controls, 80 miRNAs were upregulated and 21 miRNAs were downregulated significantly in the thioacetamide (TAA)-induced mouse fibrotic liver. Interestingly, 58 of the upregulated miRNAs were localized to an oncogenic miRNA megacluster upregulated in liver cancer. Differential expression of some of the TAA-responsive miRNAs was confirmed, and their human orthologs were similarly deregulated in TGF-β1-activated HSCs. Moreover, a functional analysis of the experimentally validated high-confidence miRNA targets revealed significant enrichment for the GO terms and KEGG pathways involved in HSC activation and liver fibrogenesis. This is the first comprehensive report of miRNAs profiles during TAA-induced mouse liver fibrosis.

Human Kidney-Derived Cells Ameliorate Acute Kidney Injury Without Engrafting into Renal Tissue

Previous studies have suggested that CD133⁺ cells isolated from human kidney biopsies have the potential to ameliorate injury following intravenous (IV) administration in rodent models of kidney disease by integrating into damaged renal tissue and generating specialized renal cells. However, whether renal engraftment of CD133⁺ cells is a prerequisite for ameliorating injury has not yet been unequivocally resolved. Here, we have established a cisplatin‐induced nephropathy model in immunodeficient rats to assess the efficacy of CD133⁺ human kidney cells in restoring renal health, and to determine the fate of these cells after systemic administration. Specifically, following IV administration, we evaluated the impact of the CD133⁺ cells on renal function by undertaking longitudinal measurements of the glomerular filtration rate using a novel transcutaneous device. Using histological assays, we assessed whether the human kidney cells could promote renal regeneration, and if this was related to their ability to integrate into the damaged kidneys. Our results show that both CD133⁺ and CD133⁻ cells improve renal function and promote renal regeneration to a similar degree. However, this was not associated with engraftment of the cells into the kidneys. Instead, after IV administration, both cell types were exclusively located in the lungs, and had disappeared by 24 hours. Our data therefore indicate that renal repair is not mediated by CD133⁺ cells homing to the kidneys and generating specialized renal cells. Instead, renal repair is likely to be mediated by paracrine or endocrine factors. Stem Cells Translational Medicine2017;6:1373–1384

Milk Fat Globule-EGF Factor 8, Secreted by Mesenchymal Stem Cells, Protects Against Liver Fibrosis in Mice

BACKGROUND & AIMS

Mesenchymal stem cells (MSCs) mediate tissue repair and might be used to prevent or reduce liver fibrosis. However, little is known about the anti-fibrotic factors secreted from MSCs or their mechanisms.

METHODS

Umbilical cord-derived MSCs (UCMSCs) were differentiated into hepatocyte-like cells (hpUCMSCs), medium was collected, and secretome proteins were identified and quantified using nanochip-liquid chromatography/quadrupole time-of-flight mass spectrometry. Liver fibrosis was induced in mice by intraperitoneal injection of thioacetamide or CCl4; some mice were then given injections of secretomes or proteins. Liver tissues were collected and analyzed by histology or polymerase chain reaction array to analyze changes in gene expression patterns. We analyzed the effects of MSC secretomes and potential anti-fibrotic proteins on transforming growth factor β 1 (TGFβ1)-mediated activation of human hepatic stellate cell (HSC) lines (hTert-HSC and LX2) and human primary HSCs. Liver tissues were collected from 16 patients with liver cirrhosis and 16 individuals without cirrhosis (controls) in Korea and analyzed by immunohistochemistry and immunoblots.

RESULTS

In mice with fibrosis, accumulation of extracellular matrix proteins was significantly reduced 3 days after injecting secretomes from UCMSCs, and to a greater extent from hpUCMSCs; numbers of activated HSCs that expressed the myogenic marker α-smooth muscle actin (α-SMA, encoded by ACTA2 [actin, alpha 2, smooth muscle]) were also reduced. Secretomes from UCMSCs, and to a greater extent from hpUCMSCs, reduced liver expression of multiple fibrotic factors, collagens, metalloproteinases, TGFβ, and Smad proteins in the TGFβ signaling pathways. In HSC cell lines and primary HSCs, TGFβ1-stimulated upregulation of α-SMA was significantly inhibited (and SMAD2 phosphorylation reduced) by secretomes from UCMSCs, and to a greater extent from hpUCMSCs. We identified 32 proteins in secretomes of UCMSCs that were more highly concentrated in secretomes from hpUCMSCs and inhibited TGFβ-mediated activation of HSCs. One of these, milk fat globule-EGF factor 8 (MFGE8), was a strong inhibitor of activation of human primary HSCs. We found MFGE8 to down-regulate expression of TGFβ type I receptor by binding to αvβ3 integrin on HSCs and to be secreted by MSCs from umbilical cord, teeth, and bone marrow. In mice, injection of recombinant human MFGE8 had anti-fibrotic effects comparable to those of the hpUCMSC secretome, reducing extracellular matrix deposition and HSC activation. Co-injection of an antibody against MFGE8 reduced the anti-fibrotic effects of the hpUCMSC secretome in mice. Levels of MFGE8 were reduced in cirrhotic liver tissue from patients compared with controls.

CONCLUSIONS

MFGE8 is an anti-fibrotic protein in MSC secretomes that strongly inhibits TGFβ signaling and reduces extracellular matrix deposition and liver fibrosis in mice.

Platelets prime hematopoietic and vascular niche to drive angiocrine-mediated liver regeneration

In mammals, the livers regenerate after chemical injury or resection of hepatic lobe by hepatectomy. How liver regeneration is initiated after mass loss remains to be defined. Here, we report that following liver injury, activated platelets deploy SDF-1 and VEGF-A to stimulate CXCR7⁺ liver sinusoidal endothelial cell (LSEC) and VEGFR1⁺ myeloid cell, orchestrating hepatic regeneration. After carbon tetrachloride (CCl₄) injection or hepatectomy, platelets and CD11b⁺VEGFR1⁺ myeloid cells were recruited LSEC, and liver regeneration in both models was impaired in thrombopoietin-deficient (Thpo^-/-) mice lacking circulating platelets. This impeded regeneration phenotype was recapitulated in mice with either conditional ablation of Cxcr7 in LSEC (Cxcr7^iΔ/iΔ) or Vegfr1 in myeloid cell (Vegfr1^lysM/lysM). Both Vegfr1^lysM/lysM and Cxcr7^iΔ/iΔ mice exhibited suppressed expression of hepatocyte growth factor and Wnt2, two crucial trophogenic angiocrine factors instigating hepatocyte propagation. Of note, administration of recombinant thrombopoietin restored the prohibited liver regeneration in the tested genetic models. As such, our data suggest that platelets and myeloid cells jointly activate the vascular niche to produce pro-regenerative endothelial paracrine/angiocrine factors. Modulating this "hematopoietic-vascular niche" might help to develop regenerative therapy strategy for hepatic disorders.

Collection of Serum- and Feeder-free Mouse Embryonic Stem Cell-conditioned Medium for a Cell-free Approach

The capacity of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) to generate various cell types has opened new avenues in the field of regenerative medicine. However, despite their benefits, the tumorigenic potential of ESCs and iPSCs has long been a barrier for clinical applications. Interestingly, it has been shown that ESCs produce several soluble factors that can promote tissue regeneration and delay cellular aging, suggesting that ESCs and iPSCs can also be utilized as a cell-free intervention method. Therefore, the method for harvesting mouse embryonic stem cell (mESC)-conditioned medium (mESC-CM) with minimal contamination of serum components (fetal bovine serum, FBS) and feeder cells (mouse embryonic fibroblasts, MEFs) has been highly demanded. Here, the present study demonstrates an optimized method for the collection of mESC-CM under serum- and feeder-free conditions and for the characterization of mESC-CM using senescence-associated multiple readouts. This protocol will provide a method to collect pure mESC-specific secretory factors without serum and feeder contamination.

Induction of hepatocyte-like cells from human umbilical cord-derived mesenchymal stem cells by defined microRNAs

Generating functional hepatocyte‐like cells (HLCs) from mesenchymal stem cells (MSCs) is of great urgency for bio‐artificial liver support system (BALSS). Previously, we obtained HLCs from human umbilical cord‐derived MSCs by overexpressing seven microRNAs (HLC‐7) and characterized their liver functions in vitro and in vivo. Here, we aimed to screen out the optimal miRNA candidates for hepatic differentiation. We sequentially removed individual miRNAs from the pool and examined the effect of transfection with remainder using RT‐PCR, periodic acid—Schiff (PAS) staining and low‐density lipoprotein (LDL) uptake assays and by assessing their function in liver injury models. Surprisingly, miR‐30a and miR‐1290 were dispensable for hepatic differentiation. The remaining five miRNAs (miR‐122, miR‐148a, miR‐424, miR‐542‐5p and miR‐1246) are essential for this process, because omitting any one from the five‐miRNA combination prevented hepatic trans‐differentiation. We found that HLCs trans‐differentiated from five microRNAs (HLC‐5) expressed high level of hepatic markers and functioned similar to hepatocytes. Intravenous transplantation of HLC‐5 into nude mice with CCl₄‐induced fulminant liver failure and acute liver injury not only improved serum parameters and their liver histology, but also improved survival rate of mice in severe hepatic failure. These data indicated that HLC‐5 functioned similar to HLC‐7 in vitro and in vivo, which have been shown to resemble hepatocytes. Instead of using seven‐miRNA combination, a simplified five‐miRNA combination can be used to obtain functional HLCs in only 7 days. Our study demonstrated an optimized and efficient method for generating functional MSC‐derived HLCs that may serve as an attractive cell alternative for BALSS.

Differentiation of Human Embryonic Stem Cells to Endothelial Progenitor Cells on Laminins in Defined and Xeno-free Systems

A major hurdle for in vitro culturing of primary endothelial cells (ECs) is that they readily dedifferentiate, hampering their use for therapeutic applications. Human embryonic stem cells (hESCs) may provide an unlimited cell source; however, most current protocols deriving endothelial progenitor cells (EPCs) from hESCs use direct differentiation approaches albeit on undefined matrices, yet final yields are insufficient. We developed a method to culture monolayer hESCs on stem cell niche laminin (LN) LN511 or LN521 matrix. Here, we report a chemically defined, xeno-free protocol for differentiation of hESCs to EPCs using LN521 as the main culture substrate. We were able to generate ∼95% functional EPCs defined as VEGFR2⁺CD34⁺CD31⁺VE-Cadherin⁺. RNA-sequencing analyses of hESCs, EPCs, and primary human umbilical vein endothelial cells showed differentiation-related EC expression signatures, regarding basement membrane composition, cell-matrix interactions, and changes in endothelial lineage markers. Our results may facilitate production of stable ECs for the treatment of vascular diseases and in vitro cell modeling.

Self-assembled 3D spheroids and hollow-fibre bioreactors improve MSC-derived hepatocyte-like cell maturation in vitro

3D cultures of human stem cell-derived hepatocyte-like cells (HLCs) have emerged as promising models for short- and long-term maintenance of hepatocyte phenotype in vitro cultures by better resembling the in vivo environment of the liver and consequently increase the translational value of the resulting data. In this study, the first stage of hepatic differentiation of human neonatal mesenchymal stem cells (hnMSCs) was performed in 2D monolayer cultures for 17 days. The second stage was performed by either maintaining cells in 2D cultures for an extra 10 days, as control, or alternatively cultured in 3D as self-assembled spheroids or in multicompartment membrane bioreactor system. All systems enabled hnMSC differentiation into HLCs as shown by positive immune staining of hepatic markers CK-18, HNF-4α, albumin, the hepatic transporters OATP-C and MRP-2 as well as drug-metabolizing enzymes like CYP1A2 and CYP3A4. Similarly, all models also displayed relevant glucose, phase I and phase II metabolism, the ability to produce albumin and to convert ammonia into urea. However, EROD activity and urea production were increased in both 3D systems. Moreover, the spheroids revealed higher bupropion conversion, whereas bioreactor showed increased albumin production and capacity to biotransform diclofenac. Additionally, diclofenac resulted in an IC₅₀ value of 1.51 ± 0.05 and 0.98 ± 0.03 in 2D and spheroid cultures, respectively. These data suggest that the 3D models tested improved HLC maturation showing a relevant biotransformation capacity and thus provide more appropriate reliable models for mechanistic studies and more predictive systems for in vitro toxicology applications.

Hepatocyte-like cells derived from induced pluripotent stem cells

The discovery that coordinated expression of a limited number of genes can reprogram differentiated somatic cells to induced pluripotent stem cells (iPSC) has opened novel possibilities for developing cell-based models of diseases and regenerative medicine utilizing cell reprogramming or cell transplantation. Directed differentiation of iPSCs can potentially generate differentiated cells belonging to any germ layer, including cells with hepatocyte-like morphology and function. Such cells, termed iHeps, can be derived by sequential cell signaling using available information on embryological development or by forced expression of hepatocyte-enriched transcription factors. In addition to the translational aspects of iHeps, the experimental findings have provided insights into the mechanisms of cell plasticity that permit one cell type to transition to another. However, iHeps generated by current methods do not fully exhibit all characteristics of mature hepatocytes, highlighting the need for additional research in this area. Here we summarize the current approaches and achievements in this field and discuss some existing hurdles and emerging approaches for improving iPSC differentiation, as well as maintaining such cells in culture for increasing their utility in disease modeling and drug development.

Sustained Delivery Growth Factors with Polyethyleneimine-Modified Nanoparticles Promote Embryonic Stem Cells Differentiation and Liver Regeneration

Stem-cell-derived hepatocyte transplantation is considered as a potential method for the therapy of acute and chronic liver failure. However, the low efficiency of differentiation into mature and functional hepatocytes remains a major challenge for clinical applications. By using polyethyleneimine-modified silica nanoparticles, this study develops a system for sustained delivery of growth factors, leading to induce hepatocyte-like cells (iHeps) from mouse embryonic stem cells (mESCs) and improve the expression of endoderm and hepatocyte-specific genes and proteins significantly, thus producing a higher population of functional hepatocytes in vitro. When transplanted into liver-injured mice after four weeks, mESC-derived definitive endoderm cells treated with this delivery system show higher integration efficiency into the host liver, differentiated into iHeps in vivo and significantly restored the injured liver. Therefore, these findings reveal the multiple advantages of functionalized nanoparticles to serve as efficient delivery platforms to promote stem cell differentiation in the regenerative medicine.

Transplantation of a human iPSC-derived hepatocyte sheet increases survival in mice with acute liver failure

BACKGROUND & AIMS

Hepatocyte transplantation is one of the most attractive approaches for the treatment of patients with liver failure. Because human induced pluripotent stem cell-derived hepatocyte-like cells (iPS-HLCs) can be produced on a large scale and generated from a patient with liver failure, they are expected to be used for hepatocyte transplantation. However, when using conventional transplantation methods, i.e., intrasplenic or portal venous infusion, it is difficult to control the engraftment efficiency and avoid unexpected engraftment in other organs because the transplanted cells are delivered into blood circulation before their liver engraftment.

METHODS

In this study, to resolve these issues, we attempted to employ a cell sheet engineering technology for experimental hepatocyte transplantation. The human iPS-HLC sheets were attached onto the liver surfaces of mice with liver injury.

RESULTS

This method reduced unexpected engraftment in organs other than the liver compared to that by intrasplenic transplantation. Human albumin levels in the mice with human iPS-HLC sheets were significantly higher than those in the intrasplenically-transplanted mice, suggesting the high potential for cell engraftment of the sheet transplantation procedure. In addition, human iPS-HLC sheet transplantation successfully ameliorated lethal acute liver injury induced by the infusion of carbon tetrachloride (CCl4). Moreover, we found that the hepatocyte growth factor secreted from the human iPS-HLC sheet played an important role in rescuing of mice from acute hepatic failure.

CONCLUSIONS

Human iPS-HLC sheet transplantation would be a useful and reliable therapeutic approach for a patient with severe liver diseases.

Small Molecules Facilitate Single Factor-Mediated Hepatic Reprogramming

Recent studies have shown that defined factors could lead to the direct conversion of fibroblasts into induced hepatocyte-like cells (iHeps). However, reported conversion efficiencies are very low, and the underlying mechanism of the direct hepatic reprogramming is largely unknown. Here, we report that direct conversion into iHeps is a stepwise transition involving the erasure of somatic memory, mesenchymal-to-epithelial transition, and induction of hepatic cell fate in a sequential manner. Through screening for additional factors that could potentially enhance the conversion kinetics, we have found that c-Myc and Klf4 (CK) dramatically accelerate conversion kinetics, resulting in remarkably improved iHep generation. Furthermore, we identified small molecules that could lead to the robust generation of iHeps without CK. Finally, we show that Hnf1α supported by small molecules is sufficient to efficiently induce direct hepatic reprogramming. This approach might help to fully elucidate the direct conversion process and also facilitate the translation of iHep into the clinic.

Nanotopography Promotes Pancreatic Differentiation of Human Embryonic Stem Cells and Induced Pluripotent Stem Cells

Although previous studies suggest that nanotopographical features influence properties and behaviors of stem cells, only a few studies have attempted to derive clinically useful somatic cells from human pluripotent stem cells using nanopatterned surfaces. In the present study, we report that polystyrene nanopore-patterned surfaces significantly promote the pancreatic differentiation of human embryonic and induced pluripotent stem cells. We compared different diameters of nanopores and showed that 200 nm nanopore-patterned surfaces highly upregulated the expression of PDX1, a critical transcription factor for pancreatic development, leading to an approximately 3-fold increase in the percentage of differentiating PDX1(+) pancreatic progenitors compared with control flat surfaces. Furthermore, in the presence of biochemical factors, 200 nm nanopore-patterned surfaces profoundly enhanced the derivation of pancreatic endocrine cells producing insulin, glucagon, or somatostatin. We also demonstrate that nanopore-patterned surface-induced upregulation of PDX1 is associated with downregulation of TAZ, suggesting the potential role of TAZ in nanopore-patterned surface-mediated mechanotransduction. Our study suggests that appropriate cytokine treatments combined with nanotopographical stimulation could be a powerful tool for deriving a high purity of desired cells from human pluripotent stem cells.

Mitochondrial Molecular Pathophysiology of Nonalcoholic Fatty Liver Disease: A Proteomics Approach

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver condition that can progress to nonalcoholic steatohepatitis, cirrhosis and cancer. It is considered an emerging health problem due to malnourishment or a high-fat diet (HFD) intake, which is observed worldwide. It is well known that the hepatocytes’ apoptosis phenomenon is one of the most important features of NAFLD. Thus, this review focuses on revealing, through a proteomics approach, the complex network of protein interactions that promote fibrosis, liver cell stress, and apoptosis. According to different types of in vitro and murine models, it has been found that oxidative/nitrative protein stress leads to mitochondrial dysfunction, which plays a major role in stimulating NAFLD damage. Human studies have revealed the importance of novel biomarkers, such as retinol-binding protein 4, lumican, transgelin 2 and hemoglobin, which have a significant role in the disease. The post-genome era has brought proteomics technology, which allows the determination of molecular pathogenesis in NAFLD. This has led to the search for biomarkers which improve early diagnosis and optimal treatment and which may effectively prevent fatal consequences such as cirrhosis or cancer.

Concise review: cell therapies for hereditary metabolic liver diseases-concepts, clinical results, and future developments

The concept of cell-based therapies for inherited metabolic liver diseases has been introduced for now more than 40 years in animal experiments, but controlled clinical data in humans are still not available. In the era of dynamic developments in stem cell science, the "right" cell for transplantation is considered as an important key for successful treatment. Do we aim to transplant mature hepatocytes or do we consider the liver as a stem/progenitor-driven organ and replenish the diseased liver with genetically normal stem/progenitor cells? Although conflicting results from cell tracing and transplantation experiments have recently emerged about the existence and role of stem/progenitor cells in the liver, their overall contribution to parenchymal cell homeostasis and tissue repair is limited. Accordingly, engraftment and repopulation efficacies of extrahepatic and liver-derived stem/progenitor cell types are considered to be lower compared to mature hepatocytes. On the basis of these results, we will discuss the current clinical cell transplantation programs for inherited metabolic liver diseases and future developments in liver cell therapy.

Antisenescence effect of mouse embryonic stem cell conditioned medium through a PDGF/FGF pathway

Cellular senescence, an irreversible state of growth arrest, underlies organismal aging and age-related diseases. Recent evidence suggests that aging intervention based on inhibition of cellular senescence might be a promising strategy for treatment of aging and age-related diseases. Embryonic stem cells (ESCs) and ESC conditioned medium (CM) have been suggested as a desirable source for regenerative medicine. However, effects of ESC-CM on cellular senescence remain to be determined. We found that treatment of senescent human dermal fibroblasts with CM from mouse ESCs (mESCs) decreases senescence phenotypes. We found that platelet-derived growth factor BB in mESC-CM plays a critical role in antisenescence effect of mESC-CM through up-regulation of fibroblast growth factor 2. We confirmed that mESC-CM treatment accelerates the wound-healing process by down-regulating senescence-associated p53 expression in in vivo models. Taken together, our results suggest that mESC-CM has the ability to suppress cellular senescence and maintain proliferative capacity. Therefore, this strategy might emerge as a novel therapeutic strategy for aging and age-related diseases.

Transplantation of hESC-derived hepatocytes protects mice from liver injury

Background

Hepatic cell therapy has become a viable alternative to liver transplantation for life-threatening liver diseases. However, the supply of human hepatocytes is limited due to the shortage of suitable donor organs required to isolate high-quality cells. Human pluripotent stem cells reflect a potential renewable source for generating functional hepatocytes. However, most differentiation protocols use undefined matrices or factors of animal origin; as such, the resulting hepatocytes are not Good Manufacturing Practice compliant. Moreover, the preclinical studies employed to assess safety and function of human embryonic stem cell (hESC)-derived hepatocytes are generally limited to immunodeficient mice. In the present study, we evaluate the generation of hepatocytes under defined conditions using a European hESC line (VAL9) which was derived under animal-free conditions. The function capacity of VAL9-derived hepatocytes was assessed by transplantation into mice with acetaminophen-induced acute liver failure, a clinically relevant model.

Methods

We developed a protocol that successfully differentiates hESCs into bipotent hepatic progenitors under defined conditions, without the use of chromatin modifiers such as dimethyl sulphoxide. These progenitors can be cryopreserved and are able to generate both committed precursors of cholangiocytes and neonate-like hepatocytes.

Results

Thirty days post-differentiation, hESCs expressed hepatocyte-specific markers such as asialoglycoprotein receptor and hepatic nuclear factors including HNF4α. The cells exhibited properties of mature hepatocytes such as urea secretion and UGT1A1 and cytochrome P450 activities. When transplanted into mice with acetaminophen-induced acute liver failure, a model of liver damage, the VAL9-derived hepatocytes efficiently engrafted and proliferated, repopulating up to 10 % of the liver. In these transplanted livers, we observed a significant decrease of liver transaminases and found no evidence of tumourigenicity. Thus, VAL9-derived hepatocytes were able to rescue hepatic function in acetaminophen-treated animals.

Conclusions

Our study reveals an efficient protocol for differentiating VAL9 hESCs to neonatal hepatocytes which are then able to repopulate livers in vivo without tumour induction. The human hepatocytes are able to rescue liver function in mice with acetaminophen-induced acute toxicity. These results provide proof-of-concept that replacement therapies using hESC-derived hepatocytes are effective for treating liver diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0227-6) contains supplementary material, which is available to authorized users.

Stem cell-based regenerative opportunities for the liver: State of the art and beyond

The existing mismatch between the great demand for liver transplants and the number of available donor organs highlights the urgent need for alternative therapeutic strategies in patients with acute or chronic liver failure. The rapidly growing knowledge on stem cell biology and the intrinsic repair processes of the liver has opened new avenues for using stem cells as a cell therapy platform in regenerative medicine for hepatic diseases. An impressive number of cell types have been investigated as sources of liver regeneration: adult and fetal liver hepatocytes, intrahepatic stem cell populations, annex stem cells, adult bone marrow-derived hematopoietic stem cells, endothelial progenitor cells, mesenchymal stromal cells, embryonic stem cells, and induced pluripotent stem cells. All these highly different cell types, used either as cell suspensions or, in combination with biomaterials as implantable liver tissue constructs, have generated great promise for liver regeneration. However, fundamental questions still need to be addressed and critical hurdles to be overcome before liver cell therapy emerges. In this review, we summarize the state-of-the-art in the field of stem cell-based therapies for the liver along with existing challenges and future perspectives towards a successful liver cell therapy that will ultimately deliver its demanding goals.

Regenerative medicine: Hepatic progenitor cells up their game in the therapeutic stakes

Bipotential hepatic progenitor cells (HPCs) are recognized as making modest contributions to hepatocyte regeneration, though never credited with major liver repopulation. A new study in mice demonstrates HPCs can make a massive contribution to hepatocyte replacement, suggesting HPCs have the potential to be an effective cell therapy for liver failure.

Epigenetic Alterations of IL-6/STAT3 Signaling by Placental Stem Cells Promote Hepatic Regeneration in a Rat Model with CCl4-induced Liver Injury

BACKGROUND

Human chorionic plate-derived mesenchymal stem cells (CP-MSCs) isolated from the placenta have been reported to demonstrate therapeutic effects in animal models of liver injury; however, the underlying epigenetic mechanism of this effect has not been elucidated. Thus, we investigated whether CP-MSCs influence epigenetic processes during regeneration of the injured liver.

METHODS

CP-MSCs were engrafted into a carbon tetrachloride (CCl4)-injured rat model through direct transplantation into the liver (DTX), intrasplenic transplantation (STX), and intravenous transplantation via the tail vein (TTX). Non-transplanted (NTX) rats were maintained as sham controls. Liver tissues were analyzed after transplantation using immunohistochemistry, western blot analysis, and quantitative methylation-specific polymerase chain reaction. Proliferation and human interleukin-6 (hIL-6) enzyme-linked immunosorbent assays were performed using CCl4-treated hepatic cells that were co-cultured with CP-MSCs.

RESULTS

The Ki67 labeling index, cell cyclins, albumin, IL-6, and gp130 levels were elevated in the CP-MSC transplantation groups. The concentration of hIL-6 in supernatants and the proliferation of CCl4-treated rat hepatic cells were enhanced by co-culturing with CP-MSCs (p<0.05), while the methylation of IL-6/IL-6R and STAT3 by CP-MSC transplantation decreased.

CONCLUSION

These results suggest that administration of CP-MSCs promotes IL-6/STAT3 signaling by decreasing the methylation of the IL-6/SATA3 promoters and thus inducing the proliferation of hepatic cells in a CCl4-injured liver rat model. These data advance our understanding of the therapeutic mechanisms in injured livers, and can facilitate the development of cell-based therapies using placenta-derived stem cells.

Osteogenic embryoid body-derived material induces bone formation in vivo

The progressive loss of endogenous regenerative capacity that accompanies mammalian aging has been attributed at least in part to alterations in the extracellular matrix (ECM) composition of adult tissues. Thus, creation of a more regenerative microenvironment, analogous to embryonic morphogenesis, may be achieved via pluripotent embryonic stem cell (ESC) differentiation and derivation of devitalized materials as an alternative to decellularized adult tissues, such as demineralized bone matrix (DBM). Transplantation of devitalized ESC materials represents a novel approach to promote functional tissue regeneration and reduce the inherent batch-to-batch variability of allograft-derived materials. In this study, the osteoinductivity of embryoid body-derived material (EBM) was compared to DBM in a standard in vivo ectopic osteoinduction assay in nude mice. EBM derived from EBs differentiated for 10 days with osteogenic media (+β-glycerophosphate) exhibited similar osteoinductivity to active DBM (osteoinduction score = 2.50 ± 0.27 vs. 2.75 ± 0.16) based on histological scoring, and exceeded inactive DBM (1.13 ± 0.13, p < 0.005). Moreover, EBM stimulated formation of new bone, ossicles, and marrow spaces, similar to active DBM. The potent osteoinductivity of EBM demonstrates that morphogenic factors expressed by ESCs undergoing osteogenic differentiation yield a novel devitalized material capable of stimulating de novo bone formation in vivo.

Inflammatory models drastically alter tumor growth and the immune microenvironment in hepatocellular carcinoma

Initiation and progression of hepatocellular carcinoma (HCC) is intimately associated with a chronically diseased liver tissue. This diseased liver tissue background is a drastically different microenvironment from the healthy liver, especially with regard to immune cell prevalence and presence of mediators of immune function. To better understand the consequences of liver disease on tumor growth and the interplay with its microenvironment, we utilized two standard methods of fibrosis induction and orthotopic implantation of tumors into the inflamed and fibrotic liver to mimic the liver condition in human HCC patients. Compared to non-diseased controls, tumor growth was significantly enhanced under fibrotic conditions. The immune cells that infiltrated the tumors were also drastically different, with decreased numbers of natural killer cells but greatly increased numbers of immune-suppressive CD11b⁺ Gr1^hi myeloid cells in both models of fibrosis. In addition, there were model-specific differences: Increased numbers of CD11b⁺ myeloid cells and CD4⁺ CD25⁺ T cells were found in tumors in the bile duct ligation model but not in the carbon tetrachloride model. Induction of fibrosis altered the cytokine production of implanted tumor cells, which could have farreaching consequences on the immune infiltrate and its functionality. Taken together, this work demonstrates that the combination of fibrosis induction with orthotopic tumor implantation results in a markedly different tumor microenvironment and tumor growth kinetics, emphasizing the necessity for more accurate modeling of HCC progression in mice, which takes into account the drastic changes in the tissue caused by chronic liver disease.

Phenotypic and functional analyses show stem cell-derived hepatocyte-like cells better mimic fetal rather than adult hepatocytes

BACKGROUND & AIMS

Hepatocyte-like cells (HLCs), differentiated from pluripotent stem cells by the use of soluble factors, can model human liver function and toxicity. However, at present HLC maturity and whether any deficit represents a true fetal state or aberrant differentiation is unclear and compounded by comparison to potentially deteriorated adult hepatocytes. Therefore, we generated HLCs from multiple lineages, using two different protocols, for direct comparison with fresh fetal and adult hepatocytes.

METHODS

Protocols were developed for robust differentiation. Multiple transcript, protein and functional analyses compared HLCs to fresh human fetal and adult hepatocytes.

RESULTS

HLCs were comparable to those of other laboratories by multiple parameters. Transcriptional changes during differentiation mimicked human embryogenesis and showed more similarity to pericentral than periportal hepatocytes. Unbiased proteomics demonstrated greater proximity to liver than 30 other human organs or tissues. However, by comparison to fresh material, HLC maturity was proven by transcript, protein and function to be fetal-like and short of the adult phenotype. The expression of 81% phase 1 enzymes in HLCs was significantly upregulated and half were statistically not different from fetal hepatocytes. HLCs secreted albumin and metabolized testosterone (CYP3A) and dextrorphan (CYP2D6) like fetal hepatocytes. In seven bespoke tests, devised by principal components analysis to distinguish fetal from adult hepatocytes, HLCs from two different source laboratories consistently demonstrated fetal characteristics.

CONCLUSIONS

HLCs from different sources are broadly comparable with unbiased proteomic evidence for faithful differentiation down the liver lineage. This current phenotype mimics human fetal rather than adult hepatocytes.

Advances in hepatic stem/progenitor cell biology

The liver is famous for its strong regenerative capacity, employing different modes of regeneration according to type and extent of injury. Mature liver cells are able to proliferate in order to replace the damaged tissue allowing the recovery of the parenchymal function. In more severe scenarios hepatocytes are believed to arise also from a facultative liver progenitor cell compartment. In human, severe acute liver failure and liver cirrhosis are also both important clinical targets in which regeneration is impaired, where the role of this stem cell compartment seems more convincing. In animal models, the current state of ambiguity regarding the identity and role of liver progenitor cells in liver physiology dampens the enthusiasm for the potential use of these cells in regenerative medicine. The aim of this review is to give the basics of liver progenitor cell biology and discuss recent results vis-à-vis their identity and contribution to liver regeneration.

Pancreatic Islet-Like Three-Dimensional Aggregates Derived From Human Embryonic Stem Cells Ameliorate Hyperglycemia in Streptozotocin-Induced Diabetic Mice

We previously reported the in vitro differentiation of human embryonic stem cells (hESCs) into pancreatic endoderm. Here we demonstrate that islet-like three-dimensional (3D) aggregates can be derived from the pancreatic endoderm by optimizing our previous protocol. Sequential treatment with Wnt3a, activin A, and noggin induced a transient upregulation of T and MixL1, followed by increased expression of endodermal genes, including FOXA2, SOX17, and CXCR4. Subsequent treatment with retinoic acid highly upregulated PDX1 expression. We also show that inhibition of sonic hedgehog signaling by bFGF/activin βB and cotreatment with VEGF and FGF7 produced many 3D cellular clusters that express both SOX17 and PDX1. We found for the first time that proteoglycans and vimentin(+) mesenchymal cells were mainly localized in hESC-derived PDX1(+) clusters. Importantly, treatment with chlorate, an inhibitor of proteoglycan sulfation, together with inhibition of Notch signaling significantly increased the expression of Neurog3 and NeuroD1, promoting a transition from PDX1(+) progenitor cells toward mature pancreatic endocrine cells. Purified dithizone(+) 3D aggregates generated by our refined protocol produced pancreatic hormones and released insulin in response to both glucose and pharmacological drugs in vitro. Furthermore, the islet-like 3D aggregates decreased blood glucose levels and continued to exhibit pancreatic features after transplantation into diabetic mice. Generation of islet-like 3D cell aggregates from human pluripotent stem cells may overcome the shortage of cadaveric donor islets for future cases of clinical islet transplantation.

The fetal liver as cell source for the regenerative medicine of liver and pancreas

Patients affected by liver diseases and diabetes mellitus are in need for sources of new cells to enable a better transition into clinic programs of cell therapy and regenerative medicine. In this setting, fetal liver is becoming the most promising and available source of cells. Fetal liver displays unique characteristics given the possibility to isolate cell populations with a wide spectrum of endodermal differentiation and, the co-existence of endodermal and mesenchymal-derived cells. Thus, the fetal liver is a unique and highly available cell source contemporarily candidate for the regenerative medicine of both liver and pancreas. The purpose of this review is to revise the recent literature on the different stem cells populations isolable from fetal liver and candidate to cell therapy of liver diseases and diabetes and to discuss advantages and limitation with respect to other cell sources.

Engrafted human stem cell-derived hepatocytes establish an infectious HCV murine model

The demonstrated ability to differentiate both human embryonic stem cells (hESCs) and patient-derived induced pluripotent stem cells (hiPSCs) into hepatocyte-like cells (HLCs) holds great promise for both regenerative medicine and liver disease research. Here, we determined that, despite an immature phenotype, differentiated HLCs are permissive to hepatitis C virus (HCV) infection and mount an interferon response to HCV infection in vitro. HLCs differentiated from hESCs and hiPSCs could be engrafted in the liver parenchyma of immune-deficient transgenic mice carrying the urokinase-type plasminogen activator gene driven by the major urinary protein promoter. The HLCs were maintained for more than 3 months in the livers of chimeric mice, in which they underwent further maturation and proliferation. These engrafted and expanded human HLCs were permissive to in vivo infection with HCV-positive sera and supported long-term infection of multiple HCV genotypes. Our study demonstrates efficient engraftment and in vivo HCV infection of human stem cell-derived hepatocytes and provides a model to study chronic HCV infection in patient-derived hepatocytes, action of antiviral therapies, and the biology of HCV infection.

Evidence for multipotent endodermal stem/progenitor cell populations in human gallbladder

BACKGROUND & AIMS

Multipotent stem/progenitor cells are found in peribiliary glands throughout human biliary trees and are able to generate mature cells of hepato-biliary and pancreatic endocrine lineages. The presence of endodermal stem/progenitors in human gallbladder was explored.

METHODS

Gallbladders were obtained from organ donors and laparoscopic surgery for symptomatic cholelithiasis. Tissues or isolated cells were characterized by immunohistochemistry and flow cytometry. EpCAM+ (Epithelial Cell Adhesion Molecule) cells were immunoselected by magnetic microbeads, plated onto plastic in self-replication conditions and subsequently transferred to distinct serum-free, hormonally defined media tailored for differentiation to specific adult fates. In vivo studies were conducted in an experimental model of liver cirrhosis.

RESULTS

The gallbladder does not have peribiliary glands, but it has stem/progenitors organized instead in mucosal crypts. Most of these can be isolated by immune-selection for EpCAM. Approximately 10% of EpCAM+ cells in situ and of immunoselected EpCAM+ cells co-expressed multiple pluripotency genes and various stem cell markers; other EpCAM+ cells qualified as progenitors. Single EpCAM+ cells demonstrated clonogenic expansion ex vivo with maintenance of stemness in self-replication conditions. Freshly isolated or cultured EpCAM+ cells could be differentiated to multiple, distinct adult fates: cords of albumin-secreting hepatocytes, branching ducts of secretin receptor+ cholangiocytes, or glucose-responsive, insulin/glucagon-secreting neoislets. EpCAM+ cells transplanted in vivo in immune-compromised hosts gave rise to human albumin-producing hepatocytes and to human Cytokeratin7+ cholangiocytes occurring in higher numbers when transplanted in cirrhotic mice.

CONCLUSIONS

Human gallbladders contain easily isolatable cells with phenotypic and biological properties of multipotent, endodermal stem cells.

Efficient Engraftment of Human Induced Pluripotent Stem Cell-Derived Hepatocyte-Like Cells in uPA/SCID Mice by Overexpression of FNK, a Bcl-xL Mutant Gene

Human liver chimeric mice are expected to be applied for drug toxicity tests and human hepatitis virus research. Human induced pluripotent stem cell-derived hepatocyte-like cells (iPSC-HLCs) are a highly attractive donor source for the generation of human liver chimeric mice because they can be produced on a large scale and established from an individual. Although these cells have been successfully used to generate human liver chimeric mice, there is still room for improvement in the repopulation efficiency. To enhance the repopulation efficacy, the human iPSC-HLCs were transduced with an adenovirus vector (Ad-FNK) expressing FNK, a hyperactive mutant gene from Bcl-xL, which was expected to inhibit apoptosis in the process of integration into liver parenchyma. We then transplanted Ad-FNK-transduced human iPSC-HLCs into urokinase-type plasminogen activator-transgenic severe combined immunodeficiency (uPA/SCID) mice (FNK mice) and evaluated the repopulation efficacy. The antiapoptotic effects of the human iPSC-HLCs were enhanced by FNK overexpression in vitro. Human albumin levels in the transplanted mice were significantly increased by transplantation of Ad-FNK-transduced human iPSC-HLCs (about 24,000 ng/ml). Immunohistochemical analysis with an anti-human αAT antibody revealed greater repopulation efficacy in the livers of FNK mice than control mice. Interestingly, the expression levels of human hepatocyte-related genes in the human iPSC-HLCs of FNK mice were much higher than those in the human iPSC-HLCs before transplantation. We succeeded in improving the repopulation efficacy of human liver chimeric mice generated by transplanting the Ad-FNK-transduced human iPSC-HLCs into uPA/SCID mice. Our method using ectopic expression of FNK was useful for generating human chimeric mice with high chimerism.

Stem cells in liver regeneration and their potential clinical applications

Stem cells constitute a population of "primitive cells" with the ability to divide indefinitely and give rise to specialized cells under special conditions. Because of these two characteristics they have received particular attention in recent decades. These cells are the primarily responsible factors for the regeneration of tissues and organs and for the healing of lesions, a feature that makes them a central key in the development of cell-based medicine, called Regenerative Medicine. The idea of wound and organ repair and body regeneration is as old as the mankind, reflecting the human desire for inhibiting aging and immortality and it is first described in the ancient Greek myth of Prometheus. It is of interest that the myth refers to liver, an organ with remarkable regenerative ability after loss of mass and function caused by liver injury or surgical resection. Over the last decade there has been an important progress in understanding liver physiology and the mechanisms underlying hepatic development and regeneration. As liver transplantation, despite its difficulties, remains the only effective therapy for advanced liver disease so far, scientific interest has nowadays been orientated towards Regenerative Medicine and the use of stem cells to repair damaged liver. This review is focused on the available literature concerning the role of stem cells in liver regeneration. It summarizes the results of studies concerning endogenous liver regeneration and stem cell experimental protocols. Moreover, this review discusses the clinical studies that have been conducted in humans so far.

Regenerative medicine. Knocking on the door to successful hepatocyte transplantation

With the ongoing shortage of livers available for transplantation, attention has turned to cell-based approaches to support liver function and enable liver regeneration. However, hepatocyte transplantation is beset with problems and a clinically adoptable strategy is lacking. How can a plentiful supply of hepatocyte-like cells with long-term proliferation be generated?

Cellular therapy for liver disease

Regenerative medicine is energizing and empowering basic science and has the potential to dramatically transform health care in the future. Given the remarkable intrinsic regenerative properties of the liver, as well as widespread adoption of regenerative strategies for liver disease (eg, liver transplant, partial hepatectomy, living donor transplant), hepatology has always been at the forefront of clinical regenerative medicine. However, an expanding pool of patients awaiting liver transplant, a limited pool of donor organs, and finite applicability of the current surgical approaches have created a need for more refined and widely available regenerative medicine strategies. Although cell-based therapies have been used extensively for hematologic malignant diseases and other conditions, the potential application of cellular therapy for acute and chronic liver diseases has only more recently been explored. New understanding of the mechanisms of liver regeneration and repair, including activation of local stem/progenitor cells and contributions from circulating bone marrow-derived stem cells, provide the theoretical underpinnings for the rational use of cell-based therapies in clinical trials. In this review, we dissect the scientific rationale for various modalities of cell therapy for liver diseases being explored in animal models and review those tested in human clinical trials. We also attempt to clarify some of the important ongoing questions that need to be addressed in order to bring these powerful therapies to clinical translation. Discussions will cover transplant of hepatocytes and liver stem/progenitor cells as well as infusion or stimulation of bone marrow-derived stem cells. We also highlight tremendous scientific advances on the horizon, including the potential use of induced pluripotent stem cells and their derivatives as individualized regenerative therapy for liver disease.

Human hepatocytes with drug metabolic function induced from fibroblasts by lineage reprogramming

Obtaining fully functional cell types is a major challenge for drug discovery and regenerative medicine. Currently, a fundamental solution to this key problem is still lacking. Here, we show that functional human induced hepatocytes (hiHeps) can be generated from fibroblasts by overexpressing the hepatic fate conversion factors HNF1A, HNF4A, and HNF6 along with the maturation factors ATF5, PROX1, and CEBPA. hiHeps express a spectrum of phase I and II drug-metabolizing enzymes and phase III drug transporters. Importantly, the metabolic activities of CYP3A4, CYP1A2, CYP2B6, CYP2C9, and CYP2C19 are comparable between hiHeps and freshly isolated primary human hepatocytes. Transplanted hiHeps repopulate up to 30% of the livers of Tet-uPA/Rag2(-/-)/γc(-/-) mice and secrete more than 300 μg/ml human ALBUMIN in vivo. Our data demonstrate that human hepatocytes with drug metabolic function can be generated by lineage reprogramming, thus providing a cell resource for pharmaceutical applications.

Mouse liver repopulation with hepatocytes generated from human fibroblasts

Human induced pluripotent stem cells (iPSCs) have the capability of revolutionizing research and therapy of liver diseases by providing a source of hepatocytes for autologous cell therapy and disease modelling. However, despite progress in advancing the differentiation of iPSCs into hepatocytes (iPSC-Heps) in vitro, cells that replicate the ability of human primary adult hepatocytes (aHeps) to proliferate extensively in vivo have not been reported. This deficiency has hampered efforts to recreate human liver diseases in mice, and has cast doubt on the potential of iPSC-Heps for liver cell therapy. The reason is that extensive post-transplant expansion is needed to establish and sustain a therapeutically effective liver cell mass in patients, a lesson learned from clinical trials of aHep transplantation. Here, as a solution to this problem, we report the generation of human fibroblast-derived hepatocytes that can repopulate mouse livers. Unlike current protocols for deriving hepatocytes from human fibroblasts, ours did not generate iPSCs but cut short reprogramming to pluripotency to generate an induced multipotent progenitor cell (iMPC) state from which endoderm progenitor cells and subsequently hepatocytes (iMPC-Heps) could be efficiently differentiated. For this purpose we identified small molecules that aided endoderm and hepatocyte differentiation without compromising proliferation. After transplantation into an immune-deficient mouse model of human liver failure, iMPC-Heps proliferated extensively and acquired levels of hepatocyte function similar to those of aHeps. Unfractionated iMPC-Heps did not form tumours, most probably because they never entered a pluripotent state. Our results establish the feasibility of significant liver repopulation of mice with human hepatocytes generated in vitro, which removes a long-standing roadblock on the path to autologous liver cell therapy.

Contribution of human adipose tissue-derived stem cells and the secretome to the skin allograft survival in mice

BACKGROUND

Despite considerable evidence showing the immunosuppressive properties of mesenchymal stem cells (MSCs) in vitro, such properties have not been fully demonstrated in vivo. The aim of this study was to evaluate the effect of MSCs and/or MSC secretome in inducing tolerance in a mouse skin transplantation model.

METHODS

After receiving full-thickness skin allotransplantation on the back of the mouse, the recipient mice were infused with phosphate-buffered saline, adipose tissue-derived stem cells (ASCs), conditioned media (CM), and control media. Specifically, ASCs (1.0 × 10(6)/0.1 mL) were transplanted to ASC-infused mice and 25-fold concentrated CM, which had been obtained from ASC culture were infused to CM-infused mice. Graft survival rates and the parameters reflecting immunologic consequences were assessed.

RESULTS

The serum level of proinflammatory cytokine interleukin 6 decreased in mice treated with ASCs or CM compared with the control groups after infusion (P < 0.05). Interferon gamma, interleukin 10, and tumor necrosis factor alpha messenger RNA levels in the skin graft seemed to be decreased in the ASC-infused mice and CM-infused mice. Hyporesponsiveness was identified in mixed lymphocyte reaction assay at 30-d posttransplantation in ASC- or CM-infused mice. And, administering ASCs and CM markedly increased skin allograft survival compared with control animals (P < 0.001).

CONCLUSIONS

These findings suggest that ASCs and their secretome have the potential to induce immunologic tolerance. Moreover, our results demonstrate that the immunosuppressive properties of ASCs are mediated by the ASC secretome. Our approach could provide insights into a promising strategy to avoid toxicities of chemical immunosuppressive regimen in solid organ transplantation.

Differentiation of nonhuman primate embryonic stem cells into hepatocyte-like cells

OBJECTIVE

To investigate whether cells derived from rhesus monkey embryonic stem cells (ESC) had hepatocyte characteristics after the differentiation.

METHODS

Rhesus monkey ESC were induced towards hepatocyte-like cells via a four-step differentiation process: the formation of embryoid bodies (EB), EB in activin A and insulin-transferrin-selenium medium for 4 days, in fibroblast growth factor (FGF)-4 and bone morphogenetic protein-2 (BMP2) medium for 8 days, in hepatocyte culture medium containing hepatocyte growth factor for 3 days and then with oncostatin M and dexamethasone for another 5 days. Expression of albumin (ALB), glucose-6-phosphatase, α-fetoprotein (AFP) and α-1 antitrypsin (α1-AT) at the mRNA level in differentiated cells were detected by reverse transcription-polymerase chain reaction. The expression of hepatocyte markers AFP, ALB, hepatocyte nuclear factor 4 (HNF4), cytokeratin 8 (CK8), CK19 and cell proliferation marker, Ki67, in the differentiated cells were determined by immunocytochemistry. The ultrastructure of the differentiated cells was examined by electron microscopy. Indocyanine green (ICG) uptake was also explored.

RESULTS

After induction, some differentiated cells were binucleate, which is typical of hepatocytes. Hepatocyte-specific genes ALB, glucose-6-phosphatase, AFP and α1-AT were expressed in the differentiated cells. The differentiated cells expressed hepatocyte markers AFP, ALB, HNF4, CK8 and CK19 at the protein level. The cells also expressed cell proliferation marker Ki67. Under electron microscopy, the ultrastructures of hepatocyte-like cells, such as mitochondrion and catalase-containing peroxisomes, were observed in the differentiated cells. ICG uptake test was positive in differentiated cells.

CONCLUSIONS

With cytokine induction, rhesus monkey ESC differentiated into cells displaying morphological features, gene expression patterns and metabolic activities characteristic of hepatocytes.

Valproic acid promotes differentiation of hepatocyte-like cells from whole human umbilical cord-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are mesoderm-derived cells that are considered a good source of somatic cells for treatment of many degenerative diseases. Previous studies have reported the differentiation of mesodermal MSCs into endodermal and ectodermal cell types beyond their embryonic lineages, including hepatocytes and neurons. However, the molecular pathways responsible for the direct or indirect cell type conversion and the functional ability of the differentiated cells remain unclear and need further research. In the present study, we demonstrated that valproic acid (VPA), which is a histone deacetylase inhibitor, induced an increase in the expression of endodermal genes including CXCR4, SOX17, FOXA1, FOXA2, GSC, c-MET, EOMES, and HNF-1β in human umbilical cord derived MSCs (hUCMSCs). In addition, we found that VPA is able to increase these endodermal genes in hUCMSCs by activating signal transduction of AKT and ERK. VPA pretreatment increased hepatic differentiation at the expense of adipogenic differentiation. The effects of VPA on modulating hUCMSCs fate were diminished by blocking AKT and ERK activation using specific signaling inhibitors. Together, our results suggest that VPA contributes to the lineage conversion of hUCMSCs to hepatic cell fate by upregulating the expression of endodermal genes through AKT and ERK activation.

Human induced pluripotent stem cells in hepatology: beyond the proof of concept

The discovery of the wide plasticity of most cell types means that it is now possible to produce virtually any cell type in vitro. This concept, developed because of the possibility of reprogramming somatic cells toward induced pluripotent stem cells, provides the opportunity to produce specialized cells that harbor multiple phenotypical traits, thus integrating genetic interindividual variability. The field of hepatology has exploited this concept, and hepatocyte-like cells can now be differentiated from induced pluripotent stem cells. This review discusses the choice of somatic cells to be reprogrammed by emergent new and nonintegrative strategies, as well as the application of differentiated human induced pluripotent stem cells in hepatology, including liver development, disease modeling, host-pathogen interactions, and drug metabolism and toxicity. The actual consensus is that hepatocyte-like cells generated in vitro present an immature phenotype. Currently, developed strategies used to resolve this problem, such as overexpression of transcription factors, mimicking liver neonatal and postnatal modifications, and re-creating the three-dimensional hepatocyte environment in vitro and in vivo, are also discussed.

Divergent angiocrine signals from vascular niche balance liver regeneration and fibrosis

Chemical or traumatic damage to the liver is frequently associated with aberrant healing(fibrosis) that overrides liver regeneration^1–5. The mechanism by which hepatic niche cells differentially modulate regeneration and fibrosis during liver repair remains to be defined^6–8. Hepatic vascular niche predominantly represented by liver sinusoidal endothelial cells (LSECs), deploys paracrine trophogens, known as angiocrine factors, to stimulate regeneration^9–15. Nevertheless, it remains unknown how pro-regenerative angiocrine signals from LSECs is subverted to promote fibrosis^16,17. Here, by combining inducible endothelial cell (EC)-specific mouse gene deletion strategy and complementary models of acute and chronic liver injury, we revealed that divergent angiocrine signals from LSECs elicit regeneration after immediateinjury and provoke fibrosis post chronic insult. The pro-fibrotic transition of vascular niche results from differential expression of stromal derived factor-1 (SDF-1) receptors, CXCR7 and CXCR4^18–21in LSECs. After acute injury, CXCR7 upregulation in LSECs acts in conjunction with CXCR4 to induce transcription factor Id1, deploying pro-regenerative angiocrine factors and triggering regeneration. Inducible deletion of Cxcr7 in adult mouse LSECs (Cxcr7^iΔEC/iΔEC) impaired liver regeneration by diminishing Id1-mediated production of angiocrine factors^9–11. By contrast, after chronic injury inflicted by iterative hepatotoxin (carbon tetrachloride) injection and bile duct ligation, constitutive FGFR1 signaling in LSECs counterbalanced CXCR7-dependent pro-regenerative response and augmented CXCR4 expression. This predominance of CXCR4 over CXCR7 expression shifted angiocrine response of LSECs, stimulating proliferation of desmin⁺hepatic stellate-like cells^22,23 and enforcing a pro-fibrotic vascular niche. EC-specific ablation of either Fgfr1 (Fgfr1^iΔEC/iΔEC) or Cxcr4 (Cxcr4^iΔEC/iΔEC) in mice restored pro-regenerative pathway and prevented FGFR1-mediated maladaptive subversion of angiocrine factors. Similarly, selective CXCR7 activation in LSECs abrogated fibrogenesis. Thus, we have demonstrated that in response to liver injury, differential recruitment of pro-regenerative CXCR7/Id1 versus pro-fibrotic FGFR1/CXCR4 angiocrine pathways in vascular niche balances regeneration and fibrosis. These results provide a therapeutic roadmap to achieve hepatic regeneration without provoking fibrosis^1,2,4.

Generation of functional hepatocyte-like cells from human pluripotent stem cells in a scalable suspension culture

Recent advances in human embryonic and induced pluripotent stem cell-based therapies in animal models of hepatic failure have led to an increased appreciation of the need to translate the proof-of-principle concepts into more practical and feasible protocols for scale up and manufacturing of functional hepatocytes. In this study, we describe a scalable stirred-suspension bioreactor culture of functional hepatocyte-like cells (HLCs) from the human pluripotent stem cells (hPSCs). To promote the initial differentiation of hPSCs in a carrier-free suspension stirred bioreactor into definitive endoderm, we used rapamycin for "priming" phase and activin A for induction. The cells were further differentiated into HLCs in the same system. HLCs were characterized and then purified based on their physiological function, the uptake of DiI-acetylated low-density lipoprotein (LDL) by flow cytometry without genetic manipulation or antibody labeling. The sorted cells were transplanted into the spleens of mice with acute liver injury from carbon tetrachloride. The differentiated HLCs had multiple features of primary hepatocytes, for example, the expression patterns of liver-specific marker genes, albumin secretion, urea production, collagen synthesis, indocyanin green and LDL uptake, glycogen storage, and inducible cytochrome P450 activity. They increased the survival rate, engrafted successfully into the liver, and continued to present hepatic function (i.e., albumin secretion after implantation). This amenable scaling up and outlined enrichment strategy provides a new platform for generating functional HLCs. This integrated approach may facilitate biomedical applications of the hPSC-derived hepatocytes.

Differentiation of hepatocytes from pluripotent stem cells

Differentiation of human embryonic stem (ES) and induced pluripotent stem (iPS) cells into hepatocyte-like cells provides a platform to study the molecular basis of human hepatocyte differentiation, to develop cell culture models of liver disease, and to potentially provide hepatocytes for treatment of end-stage liver disease. Additionally, hepatocyte-like cells generated from human pluripotent stem cells could serve as platforms for drug discovery, determination of pharmaceutical-induced hepatotoxicity, and evaluation of idiosyncratic drug-drug interactions. Here, we describe a step-wise protocol previously developed in our laboratory that facilitates the highly efficient and reproducible differentiation of human pluripotent stem cells into hepatocyte-like cells. Our protocol uses defined culture conditions and closely recapitulates key developmental events that are found to occur during hepatogenesis.

Whole-organ re-engineering: a regenerative medicine approach to digestive organ replacement

Recovery from end-stage organ failure presents a challenge for the medical community, considering the limitations of extracorporeal assist devices and the shortage of donors when organ replacement is needed. There is a need for new methods to promote recovery from organ failure and regenerative medicine is an option that should be considered. Recent progress in the field of tissue engineering has opened avenues for potential clinical applications, including the use of microfluidic devices for diagnostic purposes, and bioreactors or cell/tissue-based therapies for transplantation. Early attempts to engineer tissues produced thin, planar constructs; however, recent approaches using synthetic scaffolds and decellularized tissue have achieved a more complex level of tissue organization in organs such as the urinary bladder and trachea, with some success in clinical trials. In this context, the concept of decellularization technology has been applied to produce whole organ-derived scaffolds by removing cellular content while retaining all the necessary vascular and structural cues of the native organ. In this review, we focus on organ decellularization as a new regenerative medicine approach for whole organs, which may be applied in the field of digestive surgery.