Zhiying He

Induction of functional hepatocyte-like cells from mouse fibroblasts by defined factors

The generation of functional hepatocytes independent of donor liver organs is of great therapeutic interest with regard to regenerative medicine and possible cures for liver disease. Induced hepatic differentiation has been achieved previously using embryonic stem cells or induced pluripotent stem cells. Particularly, hepatocytes generated from a patient’s own induced pluripotent stem cells could theoretically avoid immunological rejection. However, the induction of hepatocytes from induced pluripotent stem cells is a complicated process that would probably be replaced with the arrival of improved technology. Overexpression of lineage-specific transcription factors directly converts terminally differentiated cells into some other lineages, including neurons, cardiomyocytes and blood progenitors; however, it remains unclear whether these lineage-converted cells could repair damaged tissues in vivo. Here we demonstrate the direct induction of functional hepatocyte-like (iHep) cells from mouse tail-tip fibroblasts by transduction of Gata4, Hnf1α and Foxa3, and inactivation of p19Arf. iHep cells show typical epithelial morphology, express hepatic genes and acquire hepatocyte functions. Notably, transplanted iHep cells repopulate the livers of fumarylacetoacetate-hydrolase-deficient (Fah−/−) mice and rescue almost half of recipients from death by restoring liver functions. Our study provides a novel strategy to generate functional hepatocyte-like cells for the purpose of liver engineering and regenerative medicine.

Hepatoblast-Like Progenitor Cells Derived From Embryonic Stem Cells Can Repopulate Livers of Mice

BACKGROUND & AIMS Hepatocyte-like cells can be derived from pluripotent stem cells such as embryonic stem (ES) cells, but ES cell-derived hepatic cells with extensive capacity to repopulate liver have not been identified. We aimed to identify and purify ES cell-derived hepatoblast-like progenitor cells and to explore their capacity for liver repopulation in mice after in vitro expansion. METHODS Unmanipulated mouse ES cells were cultured under defined conditions and allowed to undergo stepwise hepatic differentiation. The derived hepatic cells were examined by morphologic, fluorescence-activated cell sorting, gene expression, and clonal expansion analyses. The capacities of ES cell-derived hepatic progenitor cells to repopulate liver were investigated in mice that were deficient in fumarylacetoacetate hydrolase (Fah) (a model of liver injury). RESULTS Mouse ES cells were induced to differentiate into a population that contained hepatic progenitor cells; this population included cells that expressed epithelial cell adhesion molecule (EpCAM) but did not express c-Kit. Clonal hepatic progenitors that arose from single c-Kit(-)EpCAM(+) cells could undergo long-term expansion and maintain hepatoblast-like characteristics. Enriched c-Kit(-)EpCAM(+) cells and clonally expanded hepatic progenitor cells repopulated the livers of Fah-deficient mice without inducing tumorigenesis. CONCLUSIONS ES cell-derived c-Kit(-)EpCAM(+) cells contain a population of hepatoblast-like progenitor cells that can repopulate livers of mice.

Combined activin A/LiCl/Noggin treatment improves production of mouse embryonic stem cell‐derived definitive endoderm cells

Induction of definitive endoderm (DE) cells is a prerequisite for the whole process of embryonic stem (ES) cells differentiating into hepatic or pancreatic progenitor cells. We have established an efficient method to induce mouse ES cell‐derived DE cells in suspension embryonic body (EB) culture. Similar to previous studies, mouse ES cell‐derived DE cells, which were defined as Cxcr4+c‐Kit+, Cxcr4+E‐cadherin+ cells or Cxcr4+PDGFRa− cells, could be induced in the serum‐free EBs at Day 4 of induction. The activations of Wnt, Nodal, and FGF signaling pathways in differentiating EBs promoted DE cell differentiation, while activation of BMP4 signaling inhibited the process. In the present study, we found that chemical activation of canonical Wnt signaling pathway by LiCl could synergize with Activin A‐mediated Nodal signaling pathway to promote induction of DE cells, and inhibition of Bmp4 signaling by Noggin along with Activin A/LiCl further improved the efficiency of DE cell differentiation. The derived DE cells were proved for their capacities to become hepatic progenitor cells or pancreatic progenitor cells. In conclusion, we significantly improved the efficiency of generating mouse ES cell‐derived DE cells by combined Activin A/LiCl/Noggin treatment. Our work will be greatly helpful to generate ES cell‐derived hepatic cells and ES cell‐derived pancreatic cells for future regenerative medicine. J. Cell. Biochem. 112: 1022–1034, 2011.

H3K27 Trimethylation is an Early Epigenetic Event of p16INK4a Silencing for Regaining Tumorigenesis in Fusion Reprogrammed Hepatoma Cells

Stable epigenetic silencing of p16INK4a is a common event in hepatocellular carcinoma (HCC) cells, which is associated with abnormal cell proliferation and liberation from cell cycle arrest. Understanding the early epigenetic events in silencing p16INK4a expression may illuminate a prognostic strategy to block HCC development. Toward this end, we created a reprogram cell model by the fusion mouse HCC cells with mouse embryonic stem cells, in which the ES-Hepa hybrids forfeited HCC cell characteristics along with reactivation of the silenced p16INK4a. HCC characteristics, in terms of gene expression pattern and tumorigenic potential, was restored upon induced differentiation of these reprogrammed ES-Hepa hybrids. The histone methylation pattern relative to p16INK4a silencing during differentiation of the ES-Hepa hybrids was analyzed. H3K27 trimethylation at the p16INK4a promoter region, occurring in the early onset of p16INK4a silencing, was followed by H3K9 dimethylation at later stages. During the induced differentiation of the ES-Hepa hybrids, H3K4 di- and trimethylations were maintained at high levels during the silencing of p16INK4a, strongly suggesting that H3K4 methylation events did not cause the silencing of p16INK4a. Our results suggested that the enrichment of H3K27 trimethylation, independent of H3K9 dimethylation, trimethylation, and DNA methylation, was an early event in the silencing of p16INK4a during the tumor development. This unique chromatin pattern may be a heritable marker of epigenetic regulation for p16INK4a silencing during the developmental process of hepatocellular carcinogenesis.

Reversal of hepatocyte senescence after continuous in vivo cell proliferation

A better understanding of hepatocyte senescence could be used to treat age‐dependent disease processes of the liver. Whether continuously proliferating hepatocytes could avoid or reverse senescence has not yet been fully elucidated. We confirmed that the livers of aged mice accumulated senescent and polyploid hepatocytes, which is associated with accumulation of DNA damage and activation of p53‐p21 and p16ink4a‐pRB pathways. Induction of multiple rounds continuous cell division is hard to apply in any animal model. Taking advantage of serial hepatocyte transplantation assays in the fumarylacetoacetate hydrolase‐deficient (Fah−/−) mouse, we studied the senescence of hepatocytes that had undergone continuous cell proliferation over a long time period, up to 12 rounds of serial transplantations. We demonstrated that the continuously proliferating hepatocytes avoided senescence and always maintained a youthful state. The reactivation of telomerase in hepatocytes after serial transplantation correlated with reversal of senescence. Moreover, senescent hepatocytes harvested from aged mice became rejuvenated upon serial transplantation, with full restoration of proliferative capacity. The same findings were also true for human hepatocytes. After serial transplantation, the high initial proportion of octoploid hepatocytes decreased to match the low level of youthful liver. Conclusion: These findings suggest that the hepatocyte “ploidy conveyer” is regulated differently during aging and regeneration. The findings of reversal of hepatocyte senescence could enable future studies on liver aging and cell therapy. (Hepatology 2014;60:349–361)

Oncoprotein BMI-1 induces the malignant transformation of HaCaT cells

BMI‐1 (B‐cell‐specific Moloney murine leukemia virus integration site 1), a novel oncogene, has attracted much attention in recent years for its involvement in the initiation of a variety of tumors. Recent evidence showed that BMI‐1 was highly expressed in neoplastic skin lesions. However, whether dysregulated BMI‐1 expression is causal for the transformation of skin cells remains unknown. In this study, we stably expressed BMI‐1 in a human keratinocyte cell line, HaCaT. The expression of wild‐type BMI‐1 induced the malignant transformation of HaCaT cells in vitro. More importantly, we found that expression of BMI‐1 promoted formation of squamous cell carcinomas in vivo. Furthermore, we showed that BMI‐1 expression led to the downregulation of tumore suppressors, such as p16INK4a and p14ARF, cell adhesion molecules, such as E‐Cadherin, and differentiation related factor, such as KRT6. Therefore, our findings demonstrated that dysregulated BMI‐1 could indeed lead to keratinocytes transformation and tumorigenesis, potentially through promoting cell cycle progression and increasing cell mobility. J. Cell. Biochem. 106: 16–24, 2009.

Conversion of immortal liver progenitor cells into pancreatic endocrine progenitor cells by persistent expression of Pdx-1.

The conversion of expandable liver progenitor cells into pancreatic beta cells would provide a renewable cell source for diabetes cell therapy. Previously, we reported the establishment of liver epithelial progenitor cells (LEPCs). In this work, LEPCs were modified into EGFP/Pdx‐1 LEPCs, cells with stable expression of both Pdx‐1 and EGFP. Unlike previous work, with persistent expression of Pdx‐1, EGFP/Pdx‐1 LEPCs acquired the phenotype of pancreatic endocrine progenitor cells rather than giving rise to insulin‐producing cells directly. EGFP/Pdx‐1 LEPCs proliferated vigorously and expressed the crucial transcription factors involved in beta cell development, including Ngn3, NeuroD, Nkx2.2, Nkx6.1, Pax4, Pax6, Isl1, MafA and endogenous Pdx‐1, but did not secrete insulin. When cultured in high glucose/low serum medium supplemented with cytokines, EGFP/Pdx‐1 LEPCs stopped proliferating and gave rise to functional beta cells without any evidence of exocrine or other islet cell lineage differentiation. When transplanted into diabetic SCID mice, EGFP/Pdx‐1 LEPCs ameliorated hyperglycemia by secreting insulin in a glucose regulated manner. Considering the limited availability of beta cells, we propose that our experiments will provide a framework for utilizing the immortal liver progenitor cells as a renewable cell source for the generation of functional pancreatic beta cells. J. Cell. Biochem. 104: 224–236, 2008.

Xeno-repopulation of Fah−/−Nod/Scid mice livers by human hepatocytes

Functional human hepatocytes xenografted into the liver of mice can be used as a model system to study pharmacokinetics, infection of hepatitis viruses, and the efficacy of hepatitis vaccines. Significant levels of liver xeno-repopulation have been reported in Fah−/−Rag2−/−Il2rg−/− mice. However, the high mortality and low breeding rate of this model may hinder its application. A new model, termed Fah−/−Nod/Scid mice, which combines the advantages of liver repopulation in Fah−/− mice with the ease of xenotransplantation in Nod/Scid mice was obtained by gradual cross-breeding. Fah−/−Nod/Scid mice were easily maintained in breeding colonies and in adult animal care facilities. FK506 treatment combined with gradual withdrawal of NTBC before cell transplantation ensured that Fah−/−Nod/Scid mice were susceptible to liver xeno-repopulation by human hepatocytes; the proportion of engrafted human hepatocytes reached 33.6%. The function of the expanded human hepatocytes within the chimeric liver was confirmed by weight curve analysis, the expression of characteristic proteins, and the biochemical analysis of liver function. These results show that Fah−/−Nod/Scid mice are an ideal humanized liver mouse model with many useful applications.

DUSP16 ablation arrests the cell cycle and induces cellular senescence

Dual‐specificity phosphatases (DUSPs) are a family of protein phosphatases that dephosphorylate both phosphotyrosine and phosphoserine/phosphothreonine residues. DUSPs are de‐regulated in many human diseases, including cancers. However, the function of DUSPs in tumorigenesis remains largely unknown. Here, using short hairpin RNA‐based gene knockdown, we found that several members of the DUSP family play critical roles in regulating cell proliferation. In particular, we showed that DUSP16 ablation leads to a G1/S transition arrest, reduced incorporation of 5‐bromodeoxyuridine, enhanced senescence‐associated β‐galactosidase activity, and formation of senescence‐associated heterochromatic foci. Mechanistically, DUSP16 silencing causes cellular senescence by activating the tumor suppressors p53 and Rb. The phosphatase activity of DUSP16 is necessary for antagonizing cellular senescence. Importantly, the expression levels of DUSP16 are up‐regulated in human liver cancers, and are positively correlated with tumor cell proliferation. Taken together, our findings indicate that DUSP16 plays a role in tumorigenesis by protecting cancer cells from senescence.

Murine fertilized ovum, blastomere and morula cells lacking SP phenotype

In the field of stem cell research, SP (side population) phenotype is used to define the property that cells maintain a high efflux capability for some fluorescent dye, such as Hoechst 33342. Recently, many researches proposed that SP phenotype is a phenotype shared by some stem cells and some progenitor cells, and that SP phenotype is regarded as a candidate purification marker for stem cells. In this research, murine fertilized ova (including conjugate and single nucleus fertilized ova), 2-cell stage and 8-cell stage blastomeres, morulas and blastocysts were isolated and directly stained by Hoechst 33342 dye. The results show that fertilized ovum, blastomere and morula cells do not demonstrate any ability to efflux the dye. However, the inner cell mass (ICM) cells of blastocyst exhibit SP phenotype, which is consistent with the result of embryonic stem cells (ESCs) in vitro. These results indicate that the SP phenotype of ICM-derived ESCs is an intrinsic property and independent of the culture condition in vitro, and that SP phenotype is one of the characteristics of at least some pluripotent stem cells, but is not shared by totipotent stem cells. In addition, the result that the SP phenotype of ICM cells disappeared when the inhibitor verapamil was added into medium implies that the SP phenotype is directly associated with ABCG2. These results suggest that not all the stem cells demonstrate SP phenotype, and that SP phenotype might act as a purification marker for partial stem cells such as some pluripotent embryonic stem cells and multipotent adult stem cells, but not for all stem cells exampled by the totipotent stem cells in the very early stage of mouse embryos.