Generation of Scaffold-free, Three-dimensional Insulin Expressing Pancreatoids from Mouse Pancreatic Progenitors <em>In Vitro</em>

The pancreas is a complex organ composed of many different cell types that work together to regulate blood glucose homeostasis and digestion. These cell ...

Baylor College of Medicine

Efficient gene editing is essential to fully utilize human pluripotent stem cells (hPSCs) in regenerative medicine. Custom endonuclease-based gene targeting involves two mechanisms of DNA repair: homology directed repair (HDR) and non-homologous end joining (NHEJ). HDR is the preferred mechanism for common applications such knock-in, knock-out or precise mutagenesis, but remains inefficient in hPSCs. Here, we demonstrate that synchronizing synchronizing hPSCs in G2/M with ABT phase increases on-target gene editing, defined as correct targeting cassette integration, 3 to 6 fold. We observed improved efficiency using ZFNs, TALENs, two CRISPR/Cas9, and CRISPR/Cas9 nickase to target five genes in three hPSC lines: three human embryonic stem cell lines, neural progenitors and diabetic iPSCs. neural progenitors and diabetic iPSCs. Reversible synchronization has no effect on pluripotency or differentiation. The increase in on-target gene editing is locus-independent and specific to the cell cycle phase as G2/M phase enriched cells show a 6-fold increase in targeting efficiency compared to cells in G1 phase. Concurrently inhibiting NHEJ with SCR7 does not increase HDR or improve gene targeting efficiency further, indicating that HR is the major DNA repair mechanism after G2/M phase arrest. The approach outlined here makes gene editing in hPSCs a more viable tool for disease modeling, regenerative medicine and cell-based therapies. 

Enrichment of G2/M cell cycle phase in human pluripotent stem cells enhances HDR-mediated gene repair with customizable endonucleases.

Pediatric liver cancer is a rare but serious disease whose incidence is rising, and for which the therapeutic options are limited. Development of more targeted, less toxic therapies is hindered by the lack of an experimental animal model that captures the heterogeneity and metastatic capability of these tumors.

Novel patient-derived xenograft and cell line models for therapeutic testing of pediatric liver cancer.

Many metabolic liver disorders are refractory to drug therapy and require orthotopic liver transplantation. Here we demonstrate a new strategy, which we call metabolic pathway reprogramming, to treat hereditary tyrosinaemia type I in mice; rather than edit the disease-causing gene, we delete a gene in a disease-associated pathway to render the phenotype benign. Using CRISPR/Cas9 in vivo, we convert hepatocytes from tyrosinaemia type I into the benign tyrosinaemia type III by deleting Hpd (hydroxyphenylpyruvate dioxigenase). Edited hepatocytes (Fah(-/-)/Hpd(-/-)) display a growth advantage over non-edited hepatocytes (Fah(-/-)/Hpd(+/+)) and, in some mice, almost completely replace them within 8 weeks. Hpd excision successfully reroutes tyrosine catabolism, leaving treated mice healthy and asymptomatic. Metabolic pathway reprogramming sidesteps potential difficulties associated with editing a critical disease-causing gene and can be explored as an option for treating other diseases. 

Reprogramming metabolic pathways in vivo with CRISPR/Cas9 genome editing to treat hereditary tyrosinaemia.

The transcription factor  is an embryonic stem cell signature gene that is upregulated in multiple aggressive cancer types, but its role in skin tumorigenesis has not yet been defined. Here we document TCF7L1 upregulation in skin squamous cell carcinoma (SCC) and demonstrate that TCF7L1 overexpression increases tumor incidence, tumor multiplicity, and malignant progression in the chemically induced mouse model of skin SCC. Additionally, we show that downregulation of TCF7L1 and its paralogue TCF7L2 reduces tumor growth in a xenograft model of human skin SCC. Using separation-of-function mutants, we show that TCF7L1 promotes tumor growth, enhances cell migration, and overrides oncogenic RAS-induced senescence independently of its interaction with β-catenin. Through transcriptome profiling and combined gain- and loss-of-function studies, we identified LCN2 as a major downstream effector of TCF7L1 that drives tumor growth. Our findings establish a tumor-promoting role for TCF7L1 in skin and elucidate the mechanisms underlying its tumorigenic capacity.

TCF7L1 promotes skin tumorigenesis independently of β-catenin through induction of LCN2.

Only one out of 10 drugs in development passes clinical trials. Many fail because experimental animal models poorly predict human xenobiotic metabolism. Human liver chimeric mice are a step forward in this regard, as the human hepatocytes in chimeric livers generate human metabolites, but the remaining murine hepatocytes contain an expanded set of P450 cytochromes that form the major class of drug-metabolizing enzymes. We therefore generated a conditional knock-out of the NADPH-P450 oxidoreductase (Por) gene combined with Il2rg  /Rag2  /Fah  (PIRF) mice. Here we show that homozygous PIRF mouse livers are readily repopulated with human hepatocytes, and when the murine Por gene is deleted (<5%), they predominantly use human cytochrome metabolism. When given the anticancer drug gefitinib or the retroviral drug atazanavir, the Por-deleted humanized PIRF mice develop higher levels of the major human metabolites than current models. Humanized, murine Por-deficient PIRF mice can thus predict human drug metabolism and should be useful for preclinical drug development.Human liver chimeric mice are increasingly used for drug testing in preclinical development, but express residual murine p450 cytochromes. Here the authors generate mice lacking the Por gene in the liver, and show that human cytochrome metabolism is used following repopulation with human hepatocytes.

A novel humanized mouse lacking murine P450 oxidoreductase for studying human drug metabolism.

Replacement of lost beta cells in patients with diabetes has the potential to alleviate them of their disease, yet current protocols to make beta cells are inadequate for therapy. In vitro screens can reveal the signals necessary for endocrine maturation to improve beta cell production, however the complexities of in vivo development that lead to beta cell formation are lost in two-dimensional systems. Here, we create three-dimensional organotypic pancreatic cultures, named pancreatoids, composed of embryonic day 10.5 murine epithelial progenitors and native mesenchyme. These progenitors assemble in scaffold-free, floating conditions and, with the inclusion of native mesenchyme, develop into pancreatoids expressing markers of different pancreatic lineages including endocrine-like cells. Treatment of pancreatoids with (-)-Indolactam-V or phorbol 12-myristate 13-acetate, two protein kinase C activators, leads to altered morphology which otherwise would be overlooked in two-dimensional systems. Protein kinase C activation also led to fewer Insulin+ cells, decreased Ins1 and Ins2 mRNA levels, and increased Pdx1 and Hes1 mRNA levels with a high number of DBA+ cells. Thus, organotypic pancreatoids provide a useful tool for developmental studies, and can further be used for disease modeling, small molecules and genetic screens, or applied to human pluripotent stem cell differentiation for beta-like cell formation.

Organotypic pancreatoids with native mesenchyme develop Insulin producing endocrine cells.

An incorrect version of the Supplementary Information was inadvertently published with this Article where the wrong file was included. The HTML has been updated to include the correct version of the Supplementary Information.

Diane Yang

Center for Cell and Gene Therapy,
Texas Children's Hospital,
and Houston Methodist Hospital,
Molecular and Cellular Biology Department,
Stem Cell and Regenerative Medicine Center,
Center for Cell and Gene Therapy, Texas Children's Hospital, and Houston Methodist Hospital

Baylor College of Medicine

Generation of Scaffold-free, Three-dimensional Insulin Expressing Pancreatoids from Mouse Pancreatic Progenitors In Vitro