Jolien Vanhove

Human pluripotent stem cell-derived hepatocytes support complete replication of hepatitis C virus

BACKGROUND & AIMS Worldwide, about 180 million people are chronically infected with the hepatitis C virus (HCV). Current in vitro culture systems for HCV depend chiefly on human hepatoma cell lines. Although primary human hepatocytes support HCV infection in vitro, and immunodeficient mice repopulated with human hepatocytes support HCV infection in vivo, these models are limited because of shortage of human livers to isolate hepatocytes. Therefore, there is significant interest in the establishment from of a HCV culture system in human stem cell-derived hepatocyte-like cells. METHODS Human embryonic stem cell (hESC)-derived hepatocytes were infected with HCV in the presence or absence of direct acting antivirals. After inoculation, replication of HCV was analyzed extensively. RESULTS We demonstrate that hESC-derived hepatocytes can be infected with the HCV JFH1 genotype 2a, resulting in the production of viral RNA in the stem cell progeny. Viral replication is inhibited by a non-nucleoside HCV polymerase-inhibitor (HCV-796), a cyclophilin binding molecule (Debio 025-Alisporivir) and the protease inhibitor VX-950 (Telaprevir). Stem cell-derived hepatocytes produced, for more than 10 days, the HCV core protein as well as virions that were capable of re-infecting hepatoma cells. CONCLUSIONS Hepatocytes derived from hESC support the complete HCV replication cycle (including the production of infectious virus), and viral replication in these cells is efficiently inhibited by selective inhibitors of HCV replication.

Efficient Recombinase-Mediated Cassette Exchange in hPSCs to Study the Hepatocyte Lineage Reveals AAVS1 Locus-Mediated Transgene Inhibition

Summary Tools for rapid and efficient transgenesis in “safe harbor” loci in an isogenic context remain important to exploit the possibilities of human pluripotent stem cells (hPSCs). We created hPSC master cell lines suitable for FLPe recombinase-mediated cassette exchange (RMCE) in the AAVS1 locus that allow generation of transgenic lines within 15 days with 100% efficiency and without random integrations. Using RMCE, we successfully incorporated several transgenes useful for lineage identification, cell toxicity studies, and gene overexpression to study the hepatocyte lineage. However, we observed unexpected and variable transgene expression inhibition in vitro, due to DNA methylation and other unknown mechanisms, both in undifferentiated hESC and differentiating hepatocytes. Therefore, the AAVS1 locus cannot be considered a universally safe harbor locus for reliable transgene expression in vitro, and using it for transgenesis in hPSC will require careful assessment of the function of individual transgenes.

Prospectively Isolated NGN3‐Expressing Progenitors From Human Embryonic Stem Cells Give Rise to Pancreatic Endocrine Cells

Pancreatic endocrine progenitors obtained from human embryonic stem cells (hESCs) represent a promising source to develop cell‐based therapies for diabetes. Although endocrine pancreas progenitor cells have been isolated from mouse pancreata on the basis of Ngn3 expression, human endocrine progenitors have not been isolated yet. As substantial differences exist between human and murine pancreas biology, we investigated whether it is possible to isolate pancreatic endocrine progenitors from differentiating hESC cultures by lineage tracing of NGN3. We targeted the 3′ end of NGN3 using zinc finger nuclease‐mediated homologous recombination to allow selection of NGN3eGFP+ cells without disrupting the coding sequence of the gene. Isolated NGN3eGFP+ cells express PDX1, NKX6.1, and chromogranin A and differentiate in vivo toward insulin, glucagon, and somatostatin single hormone‐expressing cells but not to ductal or exocrine pancreatic cells or other endodermal, mesodermal, or ectodermal lineages. This confirms that NGN3+ cells represent pancreatic endocrine progenitors in humans. In addition, this hESC reporter line constitutes a unique tool that may aid in gaining insight into the developmental mechanisms underlying fate choices in human pancreas and in developing cell‐based therapies.

Directed Differentiation of Pluripotent Stem Cells to Functional Hepatocytes

Differentiation of human stem cells to hepatocytes is crucial for industrial applications as well as to develop new therapeutic strategies for liver disease. The protocol described here, using sequentially growth factors known to play a role in liver embryonic development, efficiently differentiates human embryonic stem cells (hESC) as well as human-induced pluripotent stem cells (hiPSC) to hepatocytes by directing them through defined embryonic intermediates, namely, mesendoderm/definitive endoderm and hepatoblast and hepatocyte phenotype. After 28 days, the final differentiated progeny is a mixture of cells, comprising cells with characteristics of hepatoblasts and a smaller cell fraction with morphological and phenotypical features of mature hepatocytes. An extensive functional characterization of the stem cell progeny should be used to confirm that differentiated cells display functional characteristics of mature hepatocytes including albumin secretion, glycogen storage, and several detoxifying functions such as urea production, bilirubin conjugation, glutathione S-transferase activity, cytochrome activity and drug transporter activity.

H3K27me3 Does Not Orchestrate the Expression of Lineage-Specific Markers in hESC-Derived Hepatocytes In Vitro

Summary Although pluripotent stem cells can be differentiated into the hepatocyte lineages, such cells retain an immature phenotype. As the chromatin state of regulatory regions controls spatiotemporal gene expression during development, we evaluated changes in epigenetic histone marks in lineage-specific genes throughout in vitro hepatocyte differentiation from human embryonic stem cells (hESCs). Active acetylation and methylation marks at promoters and enhancers correlated with progressive changes in gene expression. However, repression-associated H3K27me3 marks at these control regions showed an inverse correlation with gene repression during transition from hepatic endoderm to a hepatocyte-like state. Inhibitor of Enhancer of Zeste Homolog 2 (EZH2) reduced H3K27me3 decoration but did not improve hepatocyte maturation. Thus, H3K27me3 at regulatory regions does not regulate transcription and appears dispensable for hepatocyte lineage differentiation of hESCs in vitro.

Rapid and Efficient Generation of Recombinant Human Pluripotent Stem Cells by Recombinase-mediated Cassette Exchange in the AAVS1 Locus

Even with the revolution of gene-targeting technologies led by CRISPR-Cas9, genetic modification of human pluripotent stem cells (hPSCs) is still time consuming. Comparative studies that use recombinant lines with transgenes integrated into safe harbor loci could benefit from approaches that use site-specific targeted recombinases, like Cre or FLPe, which are more rapid and less prone to off-target effects. Such methods have been described, although they do not significantly outperform gene targeting in most aspects. Using Zinc-finger nucleases, we previously created a master cell line in the AAVS1 locus of hPSCs that contains a GFP-Hygromycin-tk expressing cassette, flanked by heterotypic FRT sequences. Here, we describe the procedures to perform FLPe recombinase-mediated cassette exchange (RMCE) using this line. The master cell line is transfected with a RMCE donor vector, which contains a promoterless Puromycin resistance, and with FLPe recombinase. Application of both a positive (Puromycin) and negative (FIAU) selection program leads to the selection of RMCE without random integrations. RMCE generates fully characterized pluripotent polyclonal transgenic lines in 15 d with 100% efficiency. Despite the recently described limitations of the AAVS1 locus, the ease of the system paves the way for hPSC transgenesis in isogenic settings, is necessary for comparative studies, and enables semi-high-throughput genetic screens for gain/loss of function analysis that would otherwise be highly time consuming.

Dynamic regulation of EZH2 from HPSc to hepatocyte-like cell fate

Currently, drug metabolization and toxicity studies rely on the use of primary human hepatocytes and hepatoma cell lines, which both have conceivable limitations. Human pluripotent stem cell (hPSC)—derived hepatocyte-like cells (HLCs) are an alternative and valuable source of hepatocytes that can overcome these limitations. EZH2 (enhancer of zeste homolog 2), a transcriptional repressor of the polycomb repressive complex 2 (PRC2), may play an important role in hepatocyte development, but its role during in vitro hPSC-HLC differentiation has not yet been assessed. We here demonstrate dynamic regulation of EZH2 during hepatic differentiation of hPSC. To enhance EZH2 expression, we inducibly overexpressed EZH2 between d0 and d8, demonstrating a significant improvement in definitive endoderm formation, and improved generation of HLCs. Despite induction of EZH2 overexpression until d8, EZH2 transcript and protein levels decreased from d4 onwards, which might be caused by expression of microRNAs predicted to inhibit EZH2 expression. In conclusion, our studies demonstrate that EZH2 plays a role in endoderm formation and hepatocyte differentiation, but its expression is tightly post-transcriptionally regulated during this process.

P110 GENE EXPRESSION DURING HEPATOCYTE DIFFERENTIATION DRIVEN BY EPIGENETIC CHANGES: VIA PROMOTERS OR ENHANCERS?

non-tubular structures surrounded by hepatocellular parenchyma. COH length was measured as distance from limiting plates. Local context was recorded (budding ducts and cholestatic feathery degeneration of buds). Results: COH number was higher in non-biliary vs biliary disease (p < 0.0001) and vs controls (p < 0.0001). COH were longer in nonbiliary vs biliary disease (p < 0.0001) and controls (p < 0.0001). Budding correlates with COH number (p = 0.0026). Biliary disease was associated with feathery degeneration of bud structures (p < 0.0001). Conclusions: COH are increased in chronic liver disease. During regeneration, buds of hepatocytes arise from distal ducts, leaving remnants of these ducts that are dragged into nascent parenchyma as buds mature. These remnants have a morphology identical to COH. Low COH number and length in biliary disease may reflect bile duct loss and lack of bud maturation because of destruction by cholestatic feathery degeneration.